Rapidly rotating massive stars in the early universe solve the carbon enhancement problem observed in metal-poor stars by producing significantly more carbon through rotation-induced mixing and line-driven winds, while also enabling the S-process for heavy element production through neutron capture reactions involving carbon-13, helium, and protons at temperatures around 10^8 Kelvin.
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ASI 2026 | Plenary Session-IV追加:
Hi, good morning to everybody. So, we have come to the last day of this exciting ASA conference. So we have uh four plenary talks in the morning and poster session and later in the afternoon parallel sessions. No. So let's start with the first of these plenary talks by Projoual Banerjee. So he have the title there rapidly rotating massive stars as a source of high carbon and heavy elements in the early universe. Please go ahead.
>> Thanks. uh I would like to thank uh the SOC for giving me an opportunity to present my work. So first half of the talk is from the CC uh work by Gina and the second half is something I did earlier. So I'll be talking about uh as the title suggests massive stars in the early universe which can resolve some potential problems uh with respect to what we see in our own galaxy in the early galaxy.
So u what I'll uh use is what is called stellar archaeology with very metal pore stars. So these are stars which have very little iron in them about 100 times less iron. So you can find these stars in our galaxy today and by looking at them you can learn about what happened long time early back. So if you go all the way back to big bang the cartoon. So there would be uh the first stars that would have formed after a few hundred million years and the IMF of these stars are expected to be very different from the IMF that we see around us today. So these are mostly massive stars more than 10 solar masses. They undergo core collapse. Some of them can explode. When they explode they throw out the metals that allows the transition from top heavy IMF to salpeter like IMF where you find these low mass stars along with massive stars. And if their mass is less than8 solar mass, we know that the lifetime is more than the age of the universe. So that you can find them today. So these will have very little metals in them. And so again, it's a cartoon of a star. So most uh of the time you're looking at the surface of the star and if you look at the composition of the star, it will be essentially unchanged over time because all the nuclear reactions is happening in the core. The envelope ch remains unchanged. which means envelope is the same as looking back at the snapshot of the ISM from at which at the time they were formed. So within first giga years so you can get a host of important information in this is something times referred to as near field cosmology because you're looking at stars that are in the milky way to study things that happen at very high rate shifts. So because there contribute very few events contribute to this uh the formation of the star you can kind of study individual events and the individual events we're talking about is obviously the first generation of massive stars and maybe the earliest generation of massive stars as well and then by studying the composition you can compare with theoretical calculations to constrain the nature of the first stars and early massive stars. So that is what I'm going to kind of focus on today. You can also get a lot of information out by studying these stars about early galaxy formation, star formation, chemical evolution etc. Uh so these very metal pore stars, stars which have iron less than 100 times than the sun are hard to find but over the last 30 years due to hard work by observers several hundreds have been found maybe more than a thousand and uh what we find here is something called carbon enhancement. So we can define nominal carbon enhancement relative to iron relative to solar 7. So a factor of fiveish. Uh so what we see is if you look at the very metal poor stars stars that satisfy this criteria carbon over iron greater than 7 their frequency cumulative frequency which is on the y-axis one means all of them are carbon enhanced. So they kind of keep on increasing and you can see below a certain F of minus3 or minus4 majority of them are carbon enhanced and at the very low uh iron content they are essentially all carbon enhanced. So this means that as we expect that we go back in time means a lower metallicity the early first generation of mass stars must be doing something different to produce this carbon enhancement. Okay.
So that is about the relative abundance of carbon relative to iron. What about the absolute abundance? So absolute abundance is essentially log epsilon or whatever you're familiar with number of carbon atoms relative to hydrogen log of that + 12. So if you plot that this is called a unbe diagram. If you plot the absolute carbon of very metal pore stars. So these are stars which have normal carbon. These are all carbon enhanced meaning satisfying carbon over Fe greater than 7. you form three groups and these three groups have uh they're colored in red and green. So the green ones are what are called carbon enhanced metal poor est stars. It's a little confusing terminology. What it means is it has uh in addition to carbon high enhancement of heavy elements. So we will for now discount them. They're thought to be from binary revolution but I'll say something about them in the later second part of my talk. But I'll focus on these red circles. These are carbon enhanced metal poor no star. no means no enhancement of heavy elements.
Okay. Uh so these are thought to be bonafideed descendants of the first generation of stars or not polluted by binary evolution. So these would be like the snapshot of the ISM. So what you see here is uh carbon absolute carbon uh levels in these stars varying from around 2.5 orders of magnitude as you scan the various FP over. So 5 to 7.5.
Now the question is whatever the first stars make in addition to carbon over iron you have to also produce this level of carbon after you dilute with some hydrogen. So this becomes an important point as you'll see. So before u going on further here's a kind of a cartoon of a core collapse supernova. So this is an attempt my attempt to explain to you how people uh you know calculate models and then fit it to observations. So this is the structure of the star as it is about to collapse. You have the iron core which is not where the iron comes from.
It is going back to form neutron star or a black hole. But uh you'll have an explosion core collapse and an explosion. That explosion will create iron here right in around here. Okay.
What the important thing is that this has this concentric u layers of lighter and lighter elements. So the heavier elements are at the center lighter elements outside. So if you have depending on what kind of explosion you have normal, medium or weak explosion uh people have seen that a fraction of the innermost material will fall back onto the remnant and there will be a preferential uh ejection of the outer layers. So this apparently was more common in the first stars. So what people have done obviously the simulations in 3D are very expensive. uh so it is seen in 3D simulations but on a large scale what people do is in 1D calculation they say that a fraction of the material in the inner region will come out whereas most of the material in the outer region will be ejected so you can as you can see carbon is sitting here iron is sitting here you can control the carbon relative to iron by playing around playing with the fraction ejected so that is uh what people have done and what they find is so this is uh two works from two different groups one is a Japanese group and this is American/Australian group uh Alex Hegger Stanley's group. So what they plot is essentially these black circles on the left and the red circles on the right are the observations and the lines you see are the theoretical predictions. They are slightly different using slightly different quantities. This is X over FE which you are familiar with. This is production factor same as X over FE but not normalized to iron. Okay, it's relative to the sun. So what you see what you find what they find is that you can explain the carbon over iron quite well. So if you can control the iron relative to carbon ejection as I uh showed you in the last slide you can fit the uh carbon relative to iron quite well. So this is kind of resolved. So the only thing is that first stars were mostly having kind some kind of they had uh some kind of weaker explosion which led to this enhancement. So theoretically we are kind of fine with the carbon over Fe. So uh the problem comes with the absolute abundance of carbon. Okay. So uh as you know when a supernova explodes you cannot just say that my carbon that is ejected by the supernova uh will just form the next generation of stars uh without going undergoing any dilution. Dilution is a fundamental property of any supernova explosion. You will have dilution you'll have the next generation of star formation. And uh then you can show that there would be at least a minimum amount of dilution. That would be the amount of uh you know mass swept up by the blast wave supernova blast wave that's at a minimum that dilution has to under um a supernova ejector has to undergo which means whatever you eject will be mixed with at least uh around 10^ the 4 solar mass of material you cannot avoid that okay it has some scaling with explosion energies but um then you can ask the question what is how much carbon can you produce in a supernova right it turns out the carbon that you can produce produce in a regular supernova is around half a solar mass not that much actually from 10 to 40 solar mass massive stars you only produce.5 solar mass of carbon and that amounts to a maximum carbon enrichment even if you assume the minimum dilution of six 6.1 so if you go back to this original plot that I showed about the absolute carbon abundance you see that it falls way short of uh the the stars the red circles group two and group one it only can explain the lower end of this group one group two stars.
So none of these stars. Okay. So this cannot be explained. So this is a problem which means massive stars which are normal massive stars cannot produce the carbon that you need although they can match the carbon to hydrogen. Okay.
So uh this is a so we thought of looking at rotating stars. So these were this was the story that I told you was true for uh non-rotating stars. For rotating stars the story is different. So before I go there, here's a model uh structure of a non-rotating star. X-axis is the interior mass. It's a proxy for the radius. It's easier to plot. Y-axis is the mass fraction. Just gives you the abundance. This is a snapshot of when you just at the end of main sequence.
Okay. So hydrogen is depleted at the center helium. So you essentially have a helium core of about six solar mass for a massive star of 25 solar mass at the end of the hydrogen burning. So what happens if you take the same model and if it is rotating very fast, what happens is uh rotation induced mixing continuously uh keeps mixing hydrogen into the core and the core keeps on growing. So much so that by the end of hydrogen burning you have essentially a helium star. A helium star meaning the mass fraction of helium you can say is almost one except for the fact that there's some little hydrogen left in the outer region. So we refer to them as quasi chemically homogeneous. The word quasi means there is some hydrogen left in the outer regions but but essentially they are helium stars. Okay. Uh so you can see that the evolution is completely different. Okay. So what happens after these after helium main sequence. So this is a snapshot of progressively uh in uh later stages of the star of various stages of helium burning. So I can say that as you as you can see the helium burns into carbon. These are the dash black lines and this is oxygen. As helium is burning it will mix out due to rotation induced mixing. Then from nitrogen 14 after a while the car the carbon itself uh will reach the surface.
Once it reaches the surface it can drive sorry drive line driven winds. So although a zero metallicity star does not lose mass generally if metal can get to the surface it can lose mass. And you can see here the mass that it will lose is essentially carbon, helium and oxygen. Here you can see. So this mass that you lose in rotating stars is pure almost a third of it is carbon. Okay. So a lot of carbon uh is uh uh lost. And this is lost in terms of wind. It is not a supernova. It's a wind. So the energies are much less. The typical velocities are 1500 km/s. This is somewhat of a compact star. So velocities are slightly larger. Uh so what we find is I told you you produce half a solar mass of carbon in regular non-rotating supernova you can produce that much just from the wind of rotating stars just from the wind. Okay.
Uh what about the rest of the star? So if you discount if you uh keep the wind on u on one side you can look at the remaining part which is the core again the non-rotating star just at the time of collapse. I have just plotted some of the isotopes and the rotating star at the time of collapse. You can see the black solid line is the carbon here. You very little carbon is produced here in this 25 solar mass non-rotating model whereas huge amount of carbon is produced in this rotating model which is entirely 25 solar mass almost helium star. Okay. So what we find here is uh this because they have such a large core they produce loads of carbon and uh the carbon for example is about an order of magnitude higher from non-rotating models for a 25 solar mass these are the numbers 2.67 for rotating 27 for non-rotating as an example. So you have lots of carbon in the core. So now we can ask the question again what is the carbon uh enrichment in the early galaxy. So this was what we had for non-rotating star half a solar mass 6.1. If you just have the wind uh you produce the same amount of carbon almost but your ex energies in the wind is much much less about a 50 times less than a regular supernova. So because you have low energies your dilutions are less so you can produce a very high carbon enrichment. Okay. And if the star after ejecting the wind is about is able to explode which is not a guarantee.
Sometimes they may, sometimes they may not. They can do that. The dilution in this case will be larger. But on the other hand, as I told you, the core has enormous amount of carbon. So that can kind of counteract a little bit. So that you end up with still some a carbon which is an order of magnitude larger than non-rotating stars.
Okay. So this is what we get in the final. So we can explain essentially the entire range of carbon enhancement that we see in the CMP stars. And uh yeah so that essentially solves the problem. So we think that rotating stars is the way to go if you want to explain uh this carbon enrichment which tells you something about the first stars. So this is the summary of the first part of my talk. The two scenarios can explain the carbon enhancement and obviously this is telling you the first stars were rapidly rotating. So if the first stars were rapidly rotating the first second generation star pop two stars the earliest pop two stars would likely also be rapidly rotating. what happens in that in those stars. So they turn out to be doing the same thing that I showed you for pop three stars first generation stars but because they have some inherent metals in them iron they produce prolific amounts of what is called heavy elements by S process. So uh the origin of heavy elements I because of lack of time I don't have time to go into all the details. It's a very it's an important problem in astrophysics. We are still figuring out the details of it. But broadly speaking, this is the solar system abundance, number abundance. You may have seen this many times uh relative to silicon. This is mass number. You can see that beyond iron there is a huge drop. These are called heavy elements. These are very difficult to make. The only way to make it is by neutron capture which is very hard. It it is it comes by very hard in a in a very limited fashion in the universe. So that's why you have this limited heavy element production. So you can do the neutron capture in two ways.
You can start from iron, keep capturing neutrons to produce heavy elements.
That's the idea. You can do it in a slow fashion. This will take several hundred thousand years, which is the slowest process. And it happens, we think that it happens, at least people think that it happens in AGB stars. There are also observational evidences. So the important thing to note here is because they are low mass stars, uh they cannot operate in the early galaxy. So S process per se should not operate in the early galaxy because of the long lifetimes of low mass stars till they get to AGB phase. Right? The other way is rapid neutron capture process. So instead of 100,000 year time scale here you do this in 1 second 2 seconds maximum 10 seconds time scale. So you have lots of neutrons uh for a short amount of time. That happens in neutron star mergers or magneto rotational supernova. So this can happen in early galaxy and they're prolific but the thing is they're rare they're rare okay they produce a lot but they don't happen very often but they can operate in the early galaxy so we they expect that the early galaxy is mostly S pro R process and observationally speaking without going into the detail you can uh differentiate between the output the nucleiosynthesis output of the two processes by just plotting the abundance pattern this is the elemental abundance pattern in terms of atomic number and I've uh normalized it to berium. So you see the red curve, red dotted curve is R process. The blue dotted curve is S process. They're different of course uh you can see different peak positions.
But uh if you want to measure just two elements to see which process is this you can measure berium and europium.
Here is berium. Here is europium. You can see berium and europium is around 10. Number ratio is 10 for our process.
This is about a factor of 2,000 or more for S process. Okay. So um they are clearly different and now so people are people expect our process to operate in the early galaxy no S process and then there is some other process in between uh which is called intermediate neutron capture process. The site of this is still uncertain but the idea is this is some neither too rapid nor too slow somewhere in between and they lead to abundance pattern that lies between this red and blue curve. Okay. And they are sometimes referred to as R/S pattern.
Okay.
Uh, so there are some major unresolved problems. Unfortunately, I don't have time to go over them, but I'll just list. So, one of the thing is this S process should not exist in the early universe. But, uh, I told you the CMP SARS that I showed you earlier, they're thought to be in binaries, but there are some hints that some of these are single stars. So, if there are single stars, then you need to explain the S process in these. uh elements in these stars and now they have also found stars that look like R/S something in between R and S among the CMP stars. So then origin of I process as I told you is uncertain. We don't know the exact site. There are some suggestions. Uh and then uh as I told you you can measure berium and europium in many many stars and berium onopium gives you an idea whether it's R process or S process. So what we see is the berium of europium starts out as R process in the early galaxy but quickly tries to go away from that value closer to S process. So this early onset in the very early galaxy of S process is something which people don't understand.
And lastly what is interesting is that whenever you can measure heavy elements in any of these very metal poor stars you're it's above the threshold detection threshold you always end up measuring stronium and barerium in these very metal pore stars which means in the early galaxy this heavy element production must have been very very common. So you cannot explain that with rare process sites like neutron star mergers. Okay. So all this points towards some additional neutron capture mechanism in massive stars including the first massive stars. So the idea is that massive stars are by far the most common nucleosynthetic source and uh you should um u expect that if they can produce heavy elements then they can then you can explain the ubiquity of heavy elements and if they can produce srocess patterns they can also I process patterns. You can address these two as well as well as the fact that you see a deviation from S process values R process values very early in the galaxy.
Okay. So as I told you the rotating stars that I showed you for first generation stars if you just do the repeat the calculation for stars which have some inbuilt metals in them meaning from their birth material iron. So they have let's say they have iron 100 1,000 times less than the sun if you over minus 3 and they happen to be a massive rotating star uh they can produce uh u lots of neutrons. So how do you produce neutrons in stars? So the mechanism is very common very simple and commonly known. What you need is three resources hydrogen u sorry helium carbon 12 and hydrogen protons. And you need temperatures where it is at least hot enough which means 10 the 8 in this case. Okay. So uh the reaction chain involves the first two reactions in the CNO cycle. So which is known to everyone. You do proton capture on carbon 12 nitrogen 13. Nitrogen 13 will beta decay to carbon 13 in 10 minutes.
And then uh you can release this is the last step is the most important step.
This happens very commonly in nature.
The last step is very uncommon in nature which is you can get the neutrons from a carbon 13 back if you have helium and if it is hot enough 10 to the 8. So you need this condition which turns out to be extremely rare in the universe almost uh I mean it's only found in very very specific cases as I told you AGB star is one case okay so this is what it is uh you need helium burning products mixed with protons where the temperature is hot enough so it's this is exactly what happens in rotating stars so this is a plot again during hydrogen burning helium during helium burning the green line is helium what I've done here is I have this dashed line is carbon 13. So what I've done is I've enhanced the abundance of carbon 13 by a factor of 10 to the 3 so that you can see clearly. So you can see that here in this region where uh carbon is leaking out they produce carbon 13 by CNO cycle by reacting with the little bit of protons and what happens is this carbon 13 then can mix back into the core as the core goes conve convectively and then this carbon 13 alpha n will reduce produce neutrons. So this is the neutron abundance on the red solid line. As you can see it's highest at the center because it is hottest at the center.
Okay. So this it turns out gives you prolific S process uh in the in so you can produce lots of neutrons and what is happening here is you have iron sitting in the core that will see these neutrons keep absorbing these neutrons and how long do you have you'll have all the time when it burns helium. It's a long process 100,000 years you can easily do that. This is exactly the time scale for S process. And in the innermost region the neutron abundance can be even high as close approaching I process. That is what we found. Okay. So what happens? S process will happen here. Some of it will be mixed out lost in the wind. Some of it will be in the core which can be ejected if there are explosions.
So and due to lack of time I'll just show you the results. Uh so on the left uh what you have is a CMPS star which is a star which looks like S process okay and on the right is a star which is one of the well-known star which looks like a mixture of RS process. So what we found is if you just have the wind ejector going into the ISM you can exactly explain the S process very well.
So you can explain all the things from struium. So this is atomic number stium here is barerium here is lead. lead is where you sort of finish your neutron capture roughly. So you can explain everything very well and the pattern matches very well and if you are able to eject a part of the core which have this higher neutron densities you can actually also explain uh quite well the abundance of RS stars. So we did this for many CMPS stars and found that uh you can explain the abundances of u many of the CMPS stars and even some of the RS stars not all but some. Okay.
So that is a summary of the second part.
So the same thing that we did in pop three stars which gave us carbon gives us uh heavy elements plus carbon in pop two stars and u they obviously will be very common in the early galaxy if the first stars or early massive stars were rapidly rotating uh and they can give excellent match to observations and then can also as I told you solve the problem of heavy element in general in the early galaxy. Okay. So one of the thing I did not show explicitly due to lack of time is that if you repeat the calculation at different metalicities this automatically turns off which is a very nice feature at F over H of minus 1.5 metallicity of minus 1.5 it automatically turns off due to high mass loss the rotation mixing is not very efficient due to higher mass loss at higher metalicity so this is a feature that only comes in at the early galaxy and this is also consistent with the fact that most of CMP S and R stars are also found in the early galaxy at low metalicities. Okay. Yeah. So with that and the final thing is you can put the two together and see that you know this there's a common origin between the CMP no stars which and then some of the CMPS and RS stars and uh all both of them suggest that the first and the early massive stars were rapidly rotating and uh that will have a very important implications uh in our understanding of the nature of the first stars. Thanks.
Thank you Rajul for this interesting talk. So we have uh time for many questions. So please go ahead.
>> So Projal I I had a naive idea that the rotation of stars is directly related to its age. That is it slows down as it uh ages. is that uh I mean not a factor here.
>> Um uh so these are bond with very high angular momentum. So it may slow down if it loses it quote unquote slows down if it loses mass but uh as I told you by the time main sequence ends it's already the the helium core has already formed like chemically homogeneous and there is sufficient rotation after that to sustain rotation mixing where where you can mix carbon out a little bit. So all of that we don't see I mean there is slow slowing down we have magnetic braking in our calculation uh but it doesn't it's not enough to slow down completely it does slow down though yeah >> okay thank you >> yeah we were there next question >> so about the first part of the talk only so you said pop three and pop two both can have very high uh rotation to start with but the environment from the start is can be different right because one is out of cloud the pop two and then you have metallicity more and the other one is different so >> that is true yeah I mean uh that there are arguments but we I am talking about uh very early massive uh stars meaning a metalicity of minus4 minus 3 so that can happen literally even in relatively small halos where I mean the cloud star formation could be this transitioning from low high top heavy to uh salpater light. So yeah, I mean there is no strong argument that they must have rotation. But there are some suggestions that if you go to LMC and SMC, you do see more rapidly rotating stars than in our local galaxy. So that that idea you can extend to very early galaxy saying that in any case if you go to 100 times or thousand times less iron rotations would be rapid. Whether they'll be extremely rapid that we don't know.
Nice talk Prejour. So this um about this CMPS stars like uh we know that most of them are in binaries and u and so so do you think this one this channel whatever you are proposing does it operate in very specific metallicities compared to the other AGV binary mass transfer? Uh yeah essentially it operates at exactly the same metallicity as you see the CMPS stars minus2 minus3 minus yeah in that range minus 3 to -2 fu over h >> so so there is u no that's not different from the AGB star I mean AGB stars operate at all metalities correct this operates at minus 3 to minus 3 where you see the CMP >> so would you be able to say that this channel predominant dominates in certain metalities compared to AGBs or >> yeah I mean we think that it should be quite dominant but the only thing is the binary companion we have some constraint on the nature of binary sometimes you think we know that it is a white dwarf in this case if it's a binary then it has to be a massive star with a low mass star companion that I don't know how likely it is but it can happen because these are winds winds are slow so there can be mass transfer uh to binary companion in regardless if and if so there are some CMPS stars which are not in a binary at least we think may not be in a binary Right? So then this becomes the only way to kind of do this and also it can just do S process in the early galaxy anyway as like a chem chemical evolution rather than mass transfer.
>> Yeah. One more question there.
>> Hi um thanks for the nice talk. Um am I correct to assume that you are considering mixing and rotation in a spherically symmetric model?
>> Yes.
>> And then here's the blunt question. How trustworthy is it? Is the mixing and you know chemical instability, fluid instability is properly studied in such a system to assume it to be you know properly >> I mean yeah the short answer is it's not reliable in that sense that we have not studied it. The way it is done is yeah we approximate the mixing and put it in a 1D format the mixing due to let's say meridonial circulation and sheer mixing.
uh there are some uh so what has done is that we we can do this for LMC SMC rotations massive stars and match the nitrogen abundances so the way do we do this is there are mixing and there are some parameters that control the efficiency of mixing it's matched to match the nitrogen abundances of rotating stars and then we use the same parameters for low mass stars low metallicity stars and get this evolution so in that regard uh yeah >> I see >> that is some kind of calibration but No first principle calculation.
>> I see. Thank you.
>> We have a last question.
Very interesting talk. When you talk about this rotation and all you tell nitrogen is coming up uh S process elements are coming up. You also mentioned helium is also a very important ingredient. What about helium?
Does it also get enhanced in this process?
>> Yeah. I mean essentially you convert the entire star into a helium star.
>> Yes. Yes. So helium is the most enhanced in some sense but uh in the wind also you lose a chunk of helium. Um so in the wind one/3 is helium 1/3 is carbon and one third is oxygen. If you transfer that material to some low mass star >> then it could appear to be like a considerably helium enriched.
>> So has any studies done to look for helium in stars?
>> No I I don't think so. But it is an interesting thing because this mass this mass that will be transferred or could be transferred would be quite a helium ridge. Thank you.
>> Okay. Yeah, we we have to go on. So thank you again. So >> yeah the next talk you can go ahead.
The next talk is by Arab Saragi.
supernova and the origin of cosmic destiny.
This is good.
Okay.
So it is of uh great pride and pleasure to speak at this general assembly and I would uh like to believe uh that people at the very far far corners of this auditorium will remain interested in what I'm going to say.
So I want to connect cosmic dust and supernova with various aspect of astrophysics.
naively looking at any galaxy we find stars. They hold almost all the mass uh of of the of the bionic universe. While on the other hand, they are so compact that they only occupy a very little volume of of the galaxies. On the other hand, the rest of the galaxies we see are full of molecules and dust grains which are basically chemical compounds made up of few tens to hundreds to thousands of uh elements together clustering and that is what you see. So if any cross-section of the observable universe you go to you will find tons and tons of these clusters all around us. But that would mean that we would have at some point of the universe have gone through several phases of chemical reactions. So where we can have these chemical reactions to look for that we go to all the places in the universe and then we go to stars. We find that the stars are too hot and they do not provide us conditions where we can have neutral molecules to have formed inside the surface of the star or even inside it at all. If we go to the interstellar medium, interstellar medium is cold and diffused and if I give you a st of elements most of the elements to grow to molecules and clusters would need some coffee to go through these phases and they do not have that energy to go through. So what happens is that we do not reach conditions to go through chemical reactions in the interstellar medium starting from elements.
We are left with the environments of evolved stars. What are evolved stars?
Which are stars in the end of their lives which has gone past main sequence.
In this figure in HR diagram, you can see all these stars from the left end to the right end which has gone past its main sequence. They provide conditions which have accurate physical conditions such as high temperatures but not high enough to ionize everything. On the other hand also have very high densities.
On the other hand, these conditions only are say in in a galaxy there is 0.5% of the stars at a time which are evolved and also they are very very shortlived which means that whatever I will be talking about happens in a very rapidly like evolving phase and out of equilibrium unsteady conditions and all these galaxies around you what you see the molecules clusters have been produced at least the seeds of them have been produced in such conditions which are very very rapidly evolving and turbulent in many or many ways. In this talk, I will focus on the evolved stars from massive stars. I mean evolved massive stars which are above 10 in solar mass and I will talk particularly about the red super giants, the supernova and the ultright stars.
Now why do we want to talk about supernova? If we go to the very earliest galaxies which are less than 1 billion years old, we see a lot of dust present in those galaxies as well and only massive stars which live only a very few million only live a few million years.
They have that time to reach to that evolved condition to have produced those dust while low mass stars would not have reached conditions that could produce dust in those stars. So supernova gets a major push from the early universe that they should be one of the major drivers of forming molecules and dust in the early universe. This can be seen our in our local universe as well. If we look at supernova around us like supernova 87A has notoriously been very very dusty from the very origin and if you see the evolution of it from from its commencement to now and with the JWS taken one year back they find a lot of dust present in the inner core. This is the ejector and this is the ring. So in the ejector itself they find a lot of dust present inside. You can even find it on earth if you take a meteorite sample and if you make a cross-section like the one that I'm holding, you can see grains inside which have the elemental abundances which matches the nucleiosynthesis phases that Pul was just talking about. So they do prove that supernova has produced dust grains which have been transformed to us. I mean which has been carried to us and which we actually have on earth or in on on the surface of the moon.
Now massive stars become important because a lot of these elements that we see embedded in molecules and dust have actually formed in those ones. Like if you see the periodic table and their origin you see the oxygen, neon and magnesium and part of silicon and part of carbon they all come from exploding massive stars and the lot of these elements are actually found in in locked up in molecules and dust grains.
Now how do they actually form? I'm talking about we need a lot of chemical reactions, right? So because the environments that we see around us are so turbulent, we can only form them in in in a very non-equilibrium kind of way. To model that, what we try to do is we take into account all possible chemical reactions and then we grow them through phase by phase. Initially everything remains ionized and then they become larger and larger. I mean they form neutral molecules and molecules grow to clusters they grow to nanometer sizes and then they grow to even bigger close to.1 to 1 micron which we actually see in the intestinal medium and that goes through nucleation and coagulation and accretion and all these phases happen in a coupled together. So gas phase and dust phase gets coupled because some molecules molecular reactions while are already occurring in the gas phase. on the other hand you already start forming some dust currents in in in the gas and computationally you have to take into account all of them together because you don't know which interplays with each other now back to what I was so this is the mechanism of how you form now I will be talking about the the massive stars as I said so if we look at the red super giants this is a zoomed in HR diagram it is the same diagram that I showed if you look at the population of stars in the large melaninic cloud There are a lot of red super giants as you see in the far end. They are relatively cool stars which is temperatures between 2,000 to around 4,000 and their luminosities are attend between 10 to the 4 to 10 the 5.
Now observing them we have a lot of them in around us as well like Beetlejuice and antis you can actually see them va you can actually see them in our night sky. If we try to observe them, what we will find interesting is that a lot of these stars show evidence of high mass loss in the very end phase of their life. This figure on the left, what it is showing is that after those evolved star, I mean red super giant has exploded as a supernova. It has shown signs of very dense material present around it. Two interesting things to look at this figure. One is that they have found a mass loss rate of 10 theus4 tus3 per year looking at the x-ray luminosities and secondly the interaction I mean with the the x-rays I mean are found immediately after the explosion these are 10 days or even before 10 days which means that whatever mass loss has happened in that star is sitting right over the star which is unusual because stellar wind is common we all know stars are bright they can drive away wind But these are cool stars and also these winds are not been driven away. They are almost sitting on top of the star. So this mechanism remains unknown. We do not actually know what can drive such mass loss phases where mass loss is high but the velocities are low and they just sit around the star.
These mass loss winds or whatever these circumstar material they actually sit around the star and they are a place where you can form a lot of dust. Lately there has been lot of observations of supernova progenitors like you see 2025 PHT which has bright infrared emission detected by JWST and it so what I want to say is that the they have a dense circumstellular material and this circumstellular material is dusty in nature. So both are open questions. How do they form this circumstellular material? How is the mass loss rate so high? And also how do the dust form in that wind? To look at that we actually try to simulate these massive stars and lot of them these red super giants because they are so uh like l in size they tend to pulsate in the very end phase of their life which is very difficult to show in a PDF presentation but the way that they pulsate sometimes they reaches L by M conditions luminosity to mass conditions that creates phases of enhanced mass loss. This enhanced mass loss can be parameterized mathematically to have phases of mass loss which can reach 10 theus 3 -4 which is not normal for stars like this. And so we simulate conditions which would lead to super wind kind of heavy mass loss. And then another phase called dynamical ejection which is a kind of mass loss. When there is a buildup of shock on the surface then this mass gets ejected suddenly out of the star. These are motivated by observations because there are a lot of supernova progentors which has been measured for the column densities and we try to match what type of column densities we can have and also we could actually get a idea about the progenitor mass because different progenitors 12 13 14 16 as I am showing they all evolve differently. So based on the progenitor mass how these winds will be produced and how this dense CSM will be around the star and how much column density of gas you expect. These can be matched with the supernova progenitors to find out what type of mass the progenitor did have.
Now this is the gas we have produced some circumstellular material around it.
So this is a cartoon of showing how this mass loss happens. So this is the red super giant. It has driven some winds.
Winds can have different velocities. I will not go into the details of that. It can be a continuous wind. It can be accelerated after it is ejected. And then when suitable conditions appear, you start forming some molecules. Then those molecules grow into clusters. And those clusters grow into dust. And if they are produced very close to the star, it will significantly impact the spectra of the star because the light from the star will pass through all of that and the infrared emission will be completely dominated by the material around it. infrared and optical both and that is what is showing I am showing here based on just theoretical estimates of different mass loss rate what kind of spectra you get and we compared it to the circumstellar spectra of I mean spectra of the progenitor of 2023 IF which has HST and speedzer observations and we try to see what kind of temperature of the star would fit well with the and the mass loss rates would fit well with the observed spectra when we produce dust in those winds and also we found that there is a significant evidence of these winds being clumpy in nature which is both found when we are matching the column densities as well as when we were doing the spectral modeling after the dust has formed. So this is also observationally often proposed that these winds from the stars are not entirely smooth but in clumps and our models also have found evidence of that.
Now I will also talk about uh ultra stars because whatever I was talking about red super giants exactly get flipped when we look at the ultra stars.
If you see these very end ultra stars are extremely luminous and more importantly has a very very high temperature. So it can drive winds very fast and it it provides you conditions everything that could never be able to form dust because it has a very fast wind. mass loss rates are very low and the temperatures are very high. So how will you have chemical reactions over there? But there are there are evidence of lot of ultright stars around it which are dusty like ultright 140 which has been observed in several telescopes lately with JWST and what we have found that there is a special scenario where these binary ulright stars have a colliding wind between the two and then due to this collision for I'm just showing for ultright 140 which has a very eccentric orbit has a eccentricity of 0.89 and because of this eccentricity when they are very close by due to the collision you have high densities and that drives shocks and shock leads to radiative cooling I mean radiative shocks leads to radiative cooling and you form a very dense shell with all these history I'm not showing I'm just showing the result that when these stars are very close in the phase you have this small region where you actually form dust on the other side you cannot because then the winds are not as dense dense enough when the stars are far out and that leads to this ring like dusty shells and this is theoretical like how you these dusty cells propagate. We do not exactly match how this looks like but this is the idea of how these dusty rings will propagate when you have colliding winds in binaries. If it had been a single star, I have not known a theory which would be able to produce dust in the wind of a single star wolfright star single wolfright star because of this high temperature and low mass loss rates and high velocities.
Now I am supposed to talk about supernova 20 minutes gone. I have not yet reached there. So all these things happen just before the star explodes.
Now the s star has exploded and uh now there can be different phases because I was talking about mass loss rate right based on mass loss rate the star can lose a lot of its hydrogen shell the star can lose a part of it depend on that how the star will look at the time of explosion now the star explodes this is a complex picture but I would like to break it down it is complex in reality everything gets exploded in a very rapidly evolving manner. So whatever star was doing for millions of years in a blink of an eye, it gives all the material back now in the interstellar medium. I mean going towards the interstellar medium and we have a lot of radioactive species. Radioactive species control the temperature and these nickel 56 control the evolution of what is happening chemically in the gas. And all these expanding gas has this race against time that if you get suitable condition it will lead to dust formation. If it does not then the gas will just become too diffused and you cannot and this is clearly seen in supernova. Some supernova end up producing a lot of dust. Some do not just because of how you explode, how much nickel you produce, what is the explosion energy, how much fast the velocity it is and how fast it is expanding based on all these factors.
Now to simplify the picture back this onion shell like structure it had before the explosion it kind of retains the structure especially in 1D model you can assume that because it is not easy to assume mixing in there and we have found evidence in observation that there is no microscopic mixing between these layers means you cannot take one layer and mix totally with the other one. There can be some surface mixing all the time but those are microscopic in nature that does not affect the chemistry because chemistry happens in microscopic scales.
So if you look at these zones you see there are some carbonri zone there are some oxygenrich zone and the chemistry will be different in each zones and you will end up forming multiple type of dust grains in a supernova in this metalrich core of the star in the same chemistry that I was talking about I'll not repeat it but all these reactions happens in in those environment based on what elements you have in what regions and you end up forming different dust masses. So this is a summary of what kind of dust how much of it you expect from different progenitor masses. You see there is a large dependence on the progenitor mass on type of dust. You see carbon dust becomes important for smaller progenitors 10 12 and then it decreases. Oxygen rich dust keeps on increasing. There are some aluminum which rich dust and silicon carbide dust as well. But mostly silicates and carbon dominates the uh supernova dust that comes from it based on the progenitor.
Also you see there is a large amount of stoasticity in in the in the results.
And when we go deeper into the stellar revolution to compare that we actually see that there is a large amount of randomness also in the amount of nickel and silicon you produce actually sorry magnesium and silicon you produce in these in these massive stars. And it is a matter of research on what is the reason behind these large amount of randomness. There are some theories on mixing in the boundaries and uh and mixing in the boundaries and also several margers between the shells that increases the abundance of one species versus another. There are other species that also shows this randomness. But because silicon and magnesium goes directly to form silicate dust and silicate dust forms shows these large amount of stoasticity. I am showing how much random the abundances are. If you see this 18 and you see 18.5 you see there is two order of magnitude difference in how much silicon a star has produced. And this remains a matter of research both theoretically and observationally that how can we constrain the amount of heavy elements a star is producing.
All these were theory. Now we have to actually account for that in observations as well. So how much do we actually find in in the supernova around us? These are the summary of all supernova that we have observed over the few decades. And you see that there is a certain amount of gap. So there are two things here. One is that you see the masses over here is of the order of 10 the minus4 solar masses in the first thousand days. And then there are two supernova remnants observed in late times which has like observed very high masses like close to one solar masses and there is a large gap in observation in this period because the supernova remnant became too cold to actually keep tracking in the infrared. Now this leads to this supernova dust mass problem where theoretical models have predicted that supernova is a very suitable place to form dust. It will produce a lot of it within the first couple of years which observers have not been able to find. And there are debates on is it that we miss the dust or is it that the theoretical predictions are not accurate? Is it too optically thick? The is the light actually coming to us or we miss a large part of it because it becomes cold. All these theories are are present.
last two years the we have been able to shed a bit of infrared light onto this because we have JWST data now coming we have a lot of active programs going on and we are detecting supernova around us which is one minute I'll take that this is really amazing to think that these objects some of them are 20 30 year old it has does not have a star and it is just a cold expanding gas and yet it is bright enough that we can detect them after 20 30 years with a infrared telescope. The first detection happened of 2004. It was in all of lot of news and then we have been able to detect around 17 to 18 supernova until now. And I will just show snippets of two three interesting results. You see this is 2005 IP. This supernova was one of the brightest interacting supernova with a lot of circumstellar material around it and it was detected after 18 years. It was the first supernova which shows P showed PH features. You see these clear PH lines which has never been observed before in any other supernova. This is the infrared spectra and these PS you see this belongs to the silicate nature. The these two bumps one at 10 micron around 10 micron and one around 80 micron. If you go to the another object 2007 it which is the current one it is not yet published. We were we are finding that a very large mass close to 2 solar masses of dust dominated by carbonri components. No other supernova has been detected with with this level of dust warm dust in there. In supernova 87A people have found 4 to 6 but that is cold dust. So there can be some contamination here and there but in this case this is warm dust coming from the ejector itself and point 2 is not yet published but it should be the largest among the normal core collapse supernova that has been detected until now and then coming to the summary all these supernova we put together if you look at what I was pointing out 2007 OD and 2007 it are the current two supernova we are working on the JWST results you see there is three order of magnitude difference in the dust masses. So all these theoretical sorry all these idea that supernova explodes it has heavy metals it will condense it will produce dust. How does this randomness happen?
How is it possible that two supernova both 20 years old has three order of magnitude difference? All were massive stars. They were all between 10 to 20 solar masses of progenitor and they should not have these large difference unless there was something happening in the star how they evolved that have been captured in in this detection. The same thing happens in the luminosities as well. There is a large spread in lum infrared luminosities while type 2 ends the interacting supernova are found to be more luminous which is expected.
Another interesting aspect I'll end with is that the light curves of supernova remains bright for decades after decades which is still a mystery. We do not understand exactly how because you to have something in the infrared you need an optical source. These guys do not have an optical source. There is no star there. There is nothing there. And until now we thought that they would just become a cold expanding gas. But they are found to have bright infrared luminosity even after two three decades post explosion. And who is heating these guys up after 20? We have tried to find optical sources. We have put HST. We have put E to all these like objects.
But there is nothing in optical. There is no signal coming in other wavelengths. On the other hand, infrared is still bright. So it remains a mystery why they have such a bright infrared light curves after at a such a late time. So I like to finish here thanking all the people working with me at uh IA and they have contributed to lot of this work that I was presenting at the summary is that like as I said massive stars lose mass. It remains a open question how especially red super giants what is the mechanism for them to lose mass? these randomness of the elements.
We have to connect stars with the dust to actually find out the history of stellar evolution because it is only in dust that you able to see what was happening inside these stars for millions of years. So once you understand what is present in dust, you would be able to tell what happened in the star during its lifetime. And finally these massive stars produce a lot of dust and we are detecting them now. But are they enough to account for the early universe? What? How the large amount of dust there that remains still a question and we need to need more I mean better theoretical models and more data in observations to build this uh hypothesis strongly.
Lastly, there is an advertisement. I am happy to say that we will be organizing IAU symposium next year. The topic is dusty stellar environment shaped by winds, eruptions and explosions. It has been approved only last week. And uh I am the SOC chair. I mean there are several chairs but I am one of them and we will be organizing it proposed to organize it in Goa and I would like to see many of you present there. It will be a nice discussion on how stars evolve and how they form dust. Thank you.
>> Thank you. Thank you.
So we have uh time for questions. Please uh raise your hand. Yeah, there.
Hi. Uh very interesting talk. Uh I have one question regarding the uh environment of the uh super giant and the red super giant and the wulbrate stars.
>> So uh you are mentioning that uh there are dust grains. So uh are there any studies on the size of these dust grains around these massive stars?
>> So there is like when you are fitting a spectra you would need to assume some kind of size distribution but we have seen that it does not have a significant impact on the spectral result. So it would need whenever you have some data to match it you need to have some kind of size distriution of the grains.
Theoretically we do like when you are forming these dust grains we have to produce them by distribution of sizes.
So we have that theoretical estimate. It does not impact too much into the spectra that >> thank you.
>> Yeah. Um so this is regarding the plot that you showed uh that there is a three orders of magnitude difference in the dust masses uh at for similar supernova uh and you said this must be attributed to a difference in the uh properties of the originating star. So, but given that these supernova themselves are quite similar to each other, they're all coming from the same kind of massive stars, why is there such a large variation in the dust mass?
>> Yeah. So, their progenitors are all between 10 to 20 and only the progenitor mass would not be enough to explain this discrepancy that I agree. But there can be other aspects like the explosion energy and mass loss rates and all these things and the stoasticity in how much elements are produced those can impact largely but how much it's uh it's still open >> simulation are models and simulations able to predict this difference or >> yeah so see if I take say thermonucleus supernova which are very like very fast evolving we would see very easily that we would struggle to produce any dust there. So all these ranges are there but say we can have supernova with very high energy very little ejector mass which would end up forming no dust at all but what kind of condition was there that is still unknown. Yeah.
>> Yeah. Very nice talk. So I have just a knife question. You mentioned that uh dust can only form if you have a colliding wind binary scenario in WR stars but uh what about like there are studies where they have shown wind clumping and episodic mass loss right and that could also uh >> yeah so uh >> yeah so is it correct to say that you will have only if you have colliding wind scenario >> so theoretically speaking I think in those cases there has to be colliding ing wind of the own star that leads to formation of the dust in single ultra stars because the the mass loss rates are too low and the wind is too fast to actually form these in a just free flowing gas. So you need some kind of enhancement that happens when you have collision between the own wind as well as like binary stars hitting each other >> because there are some cases like I think WR7 or something it's a single star but you do see uh dust formation.
>> Yeah. So that can happen one of the scenarios I proposed that that can have like different phase mass loss which are building up against each other >> but yeah other theories are still unclear. I also don't know.
>> Okay. Thanks.
>> Yeah. Thank you again and we'll go to the next speaker.
>> Thank you.
>> I'm sure You can see the background.
And then there are three component radio.
The one from the background, the one from the And these are frequency and that respond care about.
Hold on to that.
And then here it all numbers are the signatures of this particular transient which happening in the sun in radio wavelengths. So basically one can see that each and every part or some emission can also come from here. Each and every part of this transient can give some signatures in radio wavelengths. For example, this is the shock which is moving ahead. So we have an a signature of of called type two radio burst in the in the solar ding spectra as well as the images. Then along the open magnetic field lines we see a type three radio burst. It tells us how the electrons are accelerated and how it is transported. And then from the footpoint and also in very rare cases uh from the core of this coronal mass ejection we can see a type four radio burst can come from postarchcade loop as well as the core of the CME and at present from observational evidence.
This is the only way to estimate the coronal magnetic field in the middle corona directly from the data or observations.
So one can say that each and every part of the transient has some signatures in radio wavelength and what are and what are these eruptions are basically the signatures of accelerated electrons in the solar atmosphere. So for example, if you see 300 MHz would correspond to slightly higher heights in the corona and 17 GHz would corresponds to lowest corona and uppermost uh chromosphere. So this means as one moves out in the solar atmosphere the plasma frequency decreases. Again magnetic field also mostly decreases depends upon the uh time of the observations and uh so if we are tracing this basically we are tracing layer bylayer information on the sun and that is what we try to do in radio observations.
Since these are the direct signatures of accelerated electrons, we can also because we are tracing the heights, we can also trace how it is moving in the in the solar atmosphere. So this is one of the only wavelength that can give us these kind of information.
Uh so coming to how do we do all these observations are there are four type of observation observational technique. The first one is single frequency observation. You some of you have heard about f 10.7 cm or 2.8 GHz observation which is the second most reliable method to predict the solar variability and cycle because it is the longest one of the longest available data uh after sunspot cycle. So this is the current scenario. This is a global picture how it looks like what kind of instruments we have for these kind of observations.
So x-axis is time and yaxis is frequency. It appears quite filled.
However, 2.7 cm uh 2.7 GHz we only have two instrument currently operational in the world and none of them are in Asian time domain. This is how this is how the uh uh observation sun this is sun as a star observation. So this is how the data looks like when we do the observations and then we calibrate and can also get polar uh information. Uh the second type of observation is a spectrometer and spectropolarimeter.
This is again sun as a star observations but we get more information because we have a continuous coverage in frequency that means we are continuously tracing the or tracking the solar layers solar atmosphere layers. So this appears that this is quite filled. We have a lot of instruments in the world dedicated for for solar radio spectrometer. However, note that there are none for a spectropolar meter. Uh this is how sun is a star observations would look like.
So the background is quite sun. Uh the bright features here are the emissions associated with different kind of solar transients. Uh then the third observation when the when we resolve the sun we can do solar imaging using interferometric observations and that's what uh we have done here. So again we have time and frequency. The this light brown color instrument is not operational here uh yet. It's just there. This is for all the instrument which were operational are currently operational and will be operational in future. So this scenario if we just remove this looks like almost at low frequencies we have IAS Gordiv radio observatories graph instrument and then at high frequencies uh we had this instrument in Japan which is not currently operational and that is why we have currently are going to develop this particular instrument Arun at Udipur solar observatory. So if you see here at different frequencies when in UV observations you could see some brightness and some waves moving and each and every part of wave has a counterpart in uh radio imaging observations and imaging is important to pinpoint the location of the accelerated electrons in term where the transient was happening.
The last kind of observation is called direction finding observation. This is done with space-based instrument because we cannot put a interferometry instrument in in the space. So we use multiple spacecrafts. So and then we can trace how this is the tracing of different layers on the sun is what I was talking about. So you could see electrons which are accelerated or how it is moving outwards from the sun. So it can this ispecially for great importance for space weather purposes.
uh so radio observations alone are not sufficient we always combine it with multi-wavelength observations in white light x-ray and EUV so in this plot here on x-axis we have frequency on y-axis we have height above the solar atmosphere in terms of r and kilometers so these three lines uh tells us three different kind of emission mechanism which are expected from the sun in radio wavelengths so plasma emission bremastral and gyo resonance and synchroton. So just by looking at your observational frequency we can tell what was the initial mechanism and in turn we can also estimate heights as it can be seen here. This is again model dependent but most of the time it works and we can also estimate coronal temperature as well as the plasma conditions.
uh when we compared this with multi-wavelength observations uh uh these two images are from Aditya's VLC and suit uh this lower portion is covered by uh X-ray EUV and slightly upper portion of the corona is covered by coronographs. This is just an example. We have multiple other spacecrafts dedicated for solar studies which can give us information in this region.
uh but these reasons also have counterparts in radio techniques. So lower frequency lower heights that means the higher frequencies we can do ground based radio interferometric observations. So this image is taken with GMRT and then for uh see higher heights in the heliosphere we use a technique called IPS for which UTI this image is taken from UTI. uh yesterday some of you have heard the talk by KK where these telescopes has started observing IPS regular observations again for the past one year and in between we have farad rotation uh methods though it is very well established how it has not been very well probed for solar studies but this can give us magnetic field variability especially in these high terrains. So it can also be done from a spacecraft signal and coming to the earth or from a say a pulsar signal coming to the earth with observe with some uh giant uh radio telescope. So if you see above 10 megahertz we can do groundbased observations. Uh we do have multiple instruments as we have been seeing below 10 mehz we cannot do because ionosphere is would not let radio waves come down.
So we have to go to this space.
India has a lot of instruments in not definitely not dedicated to solar radio case but we have radio instruments at G GMRT and at UTI to do uh we can do this solar studies or or heliospheric studies and we also have a dedicated imaging instrument at Goribnu radio uh observatory for the lower part this imaging part. However, India does not have any uh radio payload till now.
Adita has multiple wavelength observations instrument as shown here.
So to complement this uh we are building uh some radio instruments at Udipur solar observatory of a PRL. So this is the team uh most of them work in instrumentation and some of them work in simulation. So I will not be covering simulation part in this talk.
So this is how the radio environment at USO looks like. Uh so this is from a few uh megahertz to 2.5 GHz. So you could see a lot of bands. But if you just zoom in, we have a lot of usable band. Again, sun is noise for other people. It's RFI for other radio astronomers. It's the main source for us. So when the sun is active we can also see the signal going much above this in some of the cases usually we filter out the frequencies we do not need using notch filters. So this was uh maybe six years back uh USO had established a readym made uh system which is called ealister. This is a couple of are couple of these instruments are in India and a lot of are in abroad as well for 24 + 7 monitoring of the sun. So the front end is a log periodic dipole antenna and the back end is a is this uh system in a board which can work from 40 to 400 megahertz. So building on to this this is a spectrometer. However, as mentioned, we do not have a spectropolar meters at all. And it is important because any signal that comes from the sun when it passes through this different layer due to high parade uh rotation, we do expect it to be decomposing into E and O mode. And because of that, we expect uh some percent of circular polarization and because of if we have a handle on this circular polarization, we can in turn get estimate the coronal magnetic field.
And at present we only have a few a few methods to especially extrapolation method to estimate the coronal magnetic field. So for that the first instrument which we are developing is ARSO is a spectropolar meter. Ideally the antenna works from almost 40 to 40 MHz to 1 GHz but we are chopping it off around 50 to 500 with back backend restriction. uh so the sensitivity is around 0 SFU at the lowest frequency and around 80 SFU at the at 500 MHz. Ideally we we plan to have two mode of oper operation high resolution mode where we will be having 10 millisecond 10 kilohz but on a regular mode when the sun is relatively quieter we'll go for 100 millcond and 100 kilohz uh temporal and spectral resolution. So this is how the antenna looks like. It's a cross polarized lock periodic dipole antina. It has a moderate gain of around 7 dBi and has a broad beam as shown here. This is how the radiation pattern looks like. Uh we need a broad uh broad beam because we are not steering the antenna. So it's a transit instrument. The sun would come in field and then go away. So this is around 70 uh uh degrees. So sun would be in field of view for roughly around uh uh 6 to 7 hours. We have some side loopes as well. Sun is a bright source so it leaks in this as well. So we'll be able to observe it. Uh the back end is being implemented on a board called ADC plus FPG on a together board called radio frequency system on chip RFOC third gen. Uh for that initially we are using Simulink to do the firmware design and then we will beh translating it into Vivo. So we have to since we have two antennas because it's cross polarized.
So two ADCs and then we do PFBs and FFTs and then we uh do the crossorrelation and autocorrelation uh calculations on board and then we packetize the data and send it uh to the data acquisition PC using uh 10G Ethernet.
So the first slide from this is expected to come in November uh this year. uh uh recently we got some funding to deploy the same instrument but a mini version of that so 100 MHz to 500 MHz at India's Arctic research station Himadri so uh my postto Harsha will be going in in October November to set up the system and then it is expected to do automatic uh observations in summer next year uh so that was a spectropolar meter so it observed the sun as a star uh but sun is Star observation would only tell us the trans there is a transient that's happening within 8 and a half minutes.
But where is the transient happening?
For that we would need imaging observations. So for that uh we are building a uh 1 m roughly 1 m dish interferometer. So in the beginning we only have four dishes just to do the technology demonstration as phase one which would be around 20 m up. The longest baseline is around 20 m. The back end is since we are again limited by the bandwidth of the back end. So we are uh this this works from 1 to 12 GHz.
So we are dividing the RF signal into four bands and then kind of super hetrodining we are doing here. This is the analog cartridge and then uh we will be only doing these imaging observations at four frequencies for RFI free frequencies. Uh so we had tried a lot of antennas because our bandwidth is 1 is to 12. So it's it's more than an octave.
So for that we went finally after a lot of trial and error we uh set up on this antenna. It's a planner antenna. It's called a Valdi antenna. It's almost broadband from around 1 ghahertz to almost 11 GHz except this one band is not functional. However, it doesn't fall in our four uh observational band bands.
So, we are just as of now ignoring it.
We we also need to put this ground plane and putting the ground plane has made the VWR really bad. This has a beam width of around 70°. Uh we would need around 90° based on our dishes size.
However, for that we would need to do some modification. But this is version zero and it appears to be working. So we'll be fabricating it soon in order to um do characterization of it. So there is a poster by uh my student Samridi. So if you have some time please go ahead and check it out. There would be more details.
Uh so again when I was talking about single frequency observations I mentioned how important f 10.7 cm is and for that we are building RFM radio flux monitor. So the front end is being built by USO and then the back end is being built by uh in collaboration with RRI. So the front end again is planned to have we plan to have a 1.2 or so meter dish which will be commercially available. However, the tracking and controller as well as the feed is being designed by us. So this is the first version of the feed. This is a horn antina of around 10 cm uh meter size. So that looks like there would be a lot of okay shadow on it. However, uh we are this is again version zero of the feed. Uh the back end is being implemented on red pitia board. So the plan is to have a for longtime monitoring of the sun at this frequency because it is important for solar cycle variable variability study. uh we want to make it as a cartridge which can be installed at multiple places in India as well.
Uh so this is the last instrument which is uh which is we are planning to develop and demonstrate a modular instrument that can be uh that can be plugged into any satellite bus. So till now all the three instruments are groundbased instrument and this one is a space-based radio goarometric plus polarometric studies. This is in collaboration with IIT Kpur with uh Dr. Mundan. Some of you might have heard the detailed talk in on the first day of the workshop because we cannot observe less than say 10 or 15 MHz from the ground.
So we have to go to space. However, we are testing on the fragibility of this.
So we are developing a lab model for this. The digital back end is in quite advanced stage. It is again for test purpose. for the lab model we are developing it on a red pit board. We have a poster by our student Purva Singh. So if you have time please go ahead and check it out.
Uh so these these were the instruments we are currently developing at Dodu Solar Observatory of PRL. However, what kind of observations we can do and how we can complement uh multi-wavelength observations from radio uh side uh is what I will show you in next 5 minutes or so. So again there can be three kind of observations in radio wavelengths.
Quiet sun, active sun and eruptive sun.
And then each of these observations can very well complement multi wavelength observation in such a sense that uh for example all these plasma properties which we observe in other wavelength may have non non-therrmal components which can be very well probed using radio observations. Again uh we can uh we can understand or get a handle on the bulk uh plasma properties of these transient sites as well as the particles which are being accelerated, how they are accelerated and how they are transported in the in the solar atmosphere. And there has been recent studies uh where people have used very high fidelity high sensitivity sensitive radio imaging instrument to comment on the coronal heating budget. Uh so however this radio observations still remain quite underutilized when we do the solar as well as space weather studies. So where radio observations can fit into is uh it can complement very well to the thermal diagnostics of these non-thermal physics with the non-thermal physics as well as this large scale connectivities where we as I have shown one of the images where you we could trace how these accelerated particles are traveling say till.5 r or so. So again uh in this the type of observation there can be two observations one is long-term observation another one is event specific observations to coming to uh long-term observations as I have been emphasizing on the point that radio observations are quite underutilized probe so in order to emphasis on that we did a multiple uh almost two solar cycle radio metric radio observations to understand can we comment on or how effective they are when if they we have a signature close to the earth how effectively we can comment on the space weather events. So what we found that it could be very effective estimating the coronal magnetic field close to the sun.
However, this is not a very effective method to do uh to estimate or do things close to the sun. So we have to move lower and lower frequency that means higher and higher heights in radio observations.
uh very recently uh this we used a instrument which is not functional anymore in Japan it's called noama radio helioraph where we found we found signatures of differential rotation as well as polar word flows uh so this is how the differential rotation at this 3,000 plus minus uh uh 500 km above the solar surface would look like because we do not have height ambiguity as other wavelength observations because radio frequencies this correspond to plas uh to uh heights and temperature very nicely. We reaffirmed that how the chromosphere is rotating uh and this was done with some 28 years of data for pole float which are very important to understand the variability of next solar cycle. Uh this is how this butterfly diagram in the radio would look like.
One of the least seen images which recently got accepted. So we found the first evidence of upper chromosphere lowest corona uh this meridonal flow signatures. So which we are calling at magnetic tree connectivity.
Uh very recently we also uh studied how the polar coronal hole are related with the peak brightness in microwave because this noyama works at 17 g used to work at 17 GHz microwave observations. So this movie should be playing. Okay. So what we found that they are very very well correlated that means uh that and they are these polar coronal holes are very important to study because uh this higheed electron streams comes from them. uh here uh uh and then coming to standalone observations where we do not do long-term we just pick one peculiar events uh there has been theories that these radio wors cannot be generated without without uh uh coral mass ejections. However, we have been for the past few years, we have been uh trying to uh convince the community that it can anything that can generate a shock in the corona can give rise to these particular events. So, we have a couple of studies in the past two years and then DA has a poster based on this where we used Adita and uh solo data to understand why these what else can produce shop that can produce these radio events. uh and again uh what kind of instrument which should be what should be the limit of the interferometers which we are making. So we had a study where we put a limit on the size of the radio interferometer one has to make at lower frequencies uh because making a 80 kilometer baseline would be an overkill and making a 2 km baseline is not enough for us. So this study is was talking about that just brushing through some of the glimpse of the science results which we have been doing for the past one and a half years.
Uh DA has a poster feel free to go. So just to summarize everything we have a lot of interesting developments in the solar radio instrumentation at the solar observatory of PRL and some of the science questions which we try to answer using radio observations. So thank you.
>> Yeah. Thank you, Anu. So, we have time for questions.
>> Yeah.
>> Yeah. So several uh places you are saying that uh the measurement of magnetic field in the corner is difficult and and you mentioned one method that's the only method to measure the magnetic field >> or observational >> observation. Yeah. So there's a one way to measure the magnetic field is to get the phase velocity of the MHD wave and and also get the density and then you get the planer sky of the magnetic field. So how useful that uh uh magnetic field in terms of like the study that you are >> so what kind of so what kind of heights are you talking about >> it's mostly in the lower corner >> so this is for middle corner >> the middle corner right >> yeah so we have and then there is another method where we do the geometrical structure of the wave and cme as well however all these are for middle corona that is why explicitly mentioned in the middle corona direct observational evidence Any more questions?
So uh in the figure where you are trying to see if uh the magnetic field obtained from metric observations uh how can we use that to obtain uh if we can use that to see the magnetic field change in the near earth. So what observations were used to obtain the magnetic field for that particular figure?
>> Uh so we had all the split band observations. So it's symmetric burst.
So we had a list of all the past two solar cycle all the split band type two radio burst and then we compared it with whatever we get at 1 AU. However there is a big gap because still since 10 or 20 AU there are a lot of changes happening. So this study now we are trying to replicate using DH type two split bands. However there are none I mean like two we found.
>> Okay. So I would say you can look at overall WA there will many. So can I ask one more question?
>> Yeah >> just go ahead.
>> Yeah.
>> Yeah. So what sort of angular resolution are you getting are you targeting for uh >> for Arun?
>> Yeah. Uh so for phase one we will have six beams on the sun. So uh 6 by 30 at highest frequency 10 gahertz because this 20 m or around uh 20 m is my highest longest baseline and we have 1 m dishes. So we have to also integrate a lot in time but this is just a technology demonstration phase. So we want to show that it can be done and then we will be we are pl we have phase two and phase three planned where we will be increasing the baseline as well as the number of antennas.
>> Okay. Thank you. Thank you. I'll show next speaker.
Shashikan Ganesh will talk on comets in the solar system. Please go ahead.
Okay, thanks.
Will I go from that corner? Okay, thanks. Uh, yeah, before I start, I would like to thank the SOC of the ASI for this uh opportunity.
It's uh it marks the 30 years of my professional career in astronomy and I actually started observing comets on the in the first year of my work. U so I really thank uh ASI for this opportunity. I think it's the first time that comets have been given this plinary stage and it's really high time. Um okay so I will not take up a lot of time in introduction and things like that. I'll just summarize the recent results because one of the uh ideas was to review the state of the field at the moment particularly in the Indian context. Okay. U so these are just couple of images. I think you can just barely see the pointer but yeah u so there have been a lot of people who have worked with me over the years and uh we'll cover some details from the work that people have done.
Yeah. Uh this is kind of a oneshot overview or an introduc I mean summary of the entire work. We have it as a poster in our lobby outside and I thought it would be good to start with this and uh zoom in on different areas u but it's uh a little outdated so I'll just switch to the results and then we'll speak it for itself. So comets are pristine remnants from the time of formation of the solar system and most of the time they spend their time I mean most of them they are at far off distances and they become active and they move closer to the sun okay and as they come closer to perihelion the molecular emissions and other uh interesting features start up and these have been of course studied since several millennia because they for occasions when comets become bright enough to be seen even in the daytime and if you're interested in the history you should look at papers by professor Kapoor from IA he has a big story on that uh yeah so I said that cometry spec I mean comets are from the time of formation of the sun and what is the evidence for that the evidence comes from looking at uh the spectra of comets especially in the infrared and comparing them with the young stellar objects. Okay. So of course now we have much better uh much better spectra than these but these were the first ones where we had the infrared space observatory looking at uh the same object I mean the same kind of material one in comet Hailbop and the other one in cometry uh in the young star cluster or stellar dust cloud they called it. Uh this is again a more recent uh work where the uh hailbop and the HD star have been compared with the comet temple ejector when we had the deep impact mission. Go ahead.
Uh recently I came across this nice paper which mentioned to me a couple of days ago when I met him first during this ASI I think it'll be interesting to go through this. It's a lot of infrared work that he has compiled in this. Uh so what do we understand about comets?
Okay. It's uh especially interesting to note the number of comets that we know so far. 4,000 comets. Okay. It's much less than the number of exoplanet candidates that we have. Okay. So I think it gives an idea where we should be putting funds especially since comets are more dangerous compared to exoplanets. Right? But anyway, uh that's a different uh story. Uh so you have comet. If you look at the eccentricity versus the semi- major axis plot, you can see that they are distributed uh in reservoirs. And this is the kind of uh extrapolation that one can do. Uh in that you have the main asteroid belt here very close between Mars and Jupiter. There are active comets in this. uh so what we call active asteroids or main belt comets and then you have the quipper belted just beyond that and then the so-called wood cloud even further out okay uh the I think the observational challenge is to try and detect the wood cloud for stars in the other uh for other stars it's difficult to do that for the sun because it's too uh diffuse I mean too dispersed okay based on various parameters you can um classify comets and so far people had been talking about short and long period comets based on whether their period was below 200 years or more than that. And then uh we also talked about dynamically new or dynamically old in the sense that whether they are objects which are coming in for the first time into the inner solar system or whether they are uh old enough and they have come several times. Okay. Based on composition you can talk about whether comets are u carbon depleted or carbonri or basically carbon typical. So these are we'll come to that in a moment.
Based on the dustiness of the comet also one can talk about it as being carbon rich I mean dustri or dust poor. Each of these have uh are derived from observational aspects and we can basically use all kinds of techniques which uh is available to the astronomer to study comets. Okay. But there are some limitations in the sense that comets are usually when they're bright enough they are closer to the sun. So we have very limited time when you can actually observe them. They are at too low an elevation to go for observations.
in many of the cases.
Um so let's start looking at each of these results one by one. I mean how we can make use of these tools. If you'll take a polarization then the scattered light from the sun is actually polarized and this uh is a function of the phase angle at the time of observations the wavelength at which you observe the refractive index of the scattering particles and the size distribution of the particles. So these are things which uh every single observation helps in understanding this and if you once you do that uh okay so this is just to recap that uh it's been 30 years since we started observing I started observing the observatory and the instrument had been observing much before that in fact the first observations were uh by this group from Kawalur with the same instrument which we eventually put on our telescope later on uh yeah so once you do uh the phase observations over a long period of time you can make this kind of plots which is the phase angle versus the polarization and the black dots are for comet hailbop this was the one of the best studied uh comets available in the literature even till today and over 50 citations to this paper from 1998 which is quite a nice uh record for our uh instrument uh when you compare it with data from all other observations over uh compiled from the literature then you can come up with this kind of plot where you can try and understand what kind of material is going into the um in the dust. Okay. So we talk about elomerated debris or solids and hierarchical aggregates or rough practical aggregates things like that.
Okay. U so this uh can then be simulated using uh various codes. I think there might be a couple of slides at a later date. The second thing that we can do is of course spectroscopy at optical bands optical infrared I mean all the gamut of spectroscopy.
Uh mostly you see fluoresence emission from daughter molecules in the cometary coma. uh from the nucleus itself we have very less uh signal coming out by the time it is observable in the optical longchain organic material is supposed to be some of the parent material for V.
So when you look at the um spectrum most of these observations and results are from the work of Kumar Kumar Winkni and we'll talk about uh Kumar at a later point.
So the uh typical spectrum of a carbonri or carbon typical um comet has a lot of strong molecular bands from C2C3 and the strongest is the CN in just in the blue side of the spectrum. Most of the spectrographs that people design are for 400 nanometer and beyond. But Kumar showed that by careful calibration we could actually use the spectrograph even less shorter wavelengths and get this CN band uh calibrated.
Most comets have that kind of spectra this kind the one shown at the top. But there was one specific comet comet 2016 R2 which had spectra very very different from the rest of the comets. And in fact there's some uh discussion whether this could be a interstellar comet which has just seeped into the uh solar system.
But u our there are I mean simulations on the boundedness of the comet and they show that this is not exactly an interstellar comet. It is bound to the solar system.
Okay. U we have a strong collaboration with the Belgians now over the last couple of years and uh the first result from that uh was the compilation of material I mean um observations from uh from our telescope and the Trappist uh telescopes of the Belgians. And here we show the uh first work on comet 46P uh which had uh multiple epochs. All these uh squares the solid squares are uh uh the data from Mount Abu and uh Mount Abu data and the open squares are the phototric data from um Trappist.
Okay. Uh this comet is a short period comet. So there have been measurements for this comet earlier also in the literature which you can see in the U mark uh with the black blue and green asterisks. Okay. And typically what we would like to study are the CN and C2 production rates and then the rate ratios which is shown in the top panel.
This is the one which is uh uh important to understand because that tells you whether it's a carbon typical comet or a carbon depleted comet. Okay, basically the strength of the C2 line as a reference to the CN line.
Uh going for forward, I think many of you might recall this uh 2020 F3 comet which appeared in July uh of 2020. uh it brightened up at that time and uh luckily we were able to get 3 minutes of uh spectroscopy from there from the Himalayan Chundra telescope. It's I think one of the most productive 3minut exposures ever taken with that instrument hosk on the city. So using that 3minut data we were able to actually cover uh we had to organize the slit across the photo center and also going into the new uh tail. So looking at the spectra we were able to actually detect strong ionic emissions from the comet and these are insects showing various details.
One of the important points here is the detection of CO2 plus in this comet.
It's very rarely reported in the cometary literature. We have to really go back to very old data uh sets to show that it is really present. Okay.
Then uh uh the other more recent work is by Goldie and uh collaborators. U so this is based on I think almost 32 months of observations uh using the VRL as well as the IA telescopes and the trap telescopes from Belgium. Uh we were able to get I think some six five or six epochs of spectroscopy and 60 epochs of photometry.
And uh it shows that this particular comet is actually relatively less active in terms of molecular emission but uh there are signatures.
uh what is interesting about this comet is is that uh initially people thought it's a dynamically new comet and we in fact even had that in the title dynamically new comet and uh but then eventually it's from our own work later on we see that it seems to be a dynamically I mean it's returning uh comet not dynamically completely new so that brings me to the second part of my talk uh are Are these comics unique to our solar system or do we get objects from outside? So this is something which work has been going on in the literature for quite a while and some of the recent work I mean the last works which people did in Aayuka for example Sai and Rana Ashok s and nsana these people had proposed based on various simulations that one interstellar comet could be there in about two centuries. Okay. So this was various assuming various uh details and the level of uh detection capability and things like that. Uh what has happened is that in the last 10 years three interstellar objects have been discovered. Okay. One is an inter the first one was an interstellar asteroid which was detected as it was leaving after it had actually passed perihelion. Okay. The second one was comet 2i Boriso.
Let me just show you the details. It was detected discovered on 30th August by this guy Genned Boriso with his self-built 65 cm telescope at a perihelion distance of 2 AU and uh it had an orbital eccentricity of 3.36 really high and velocity at infinity of 32 km/s which could not be achieved by any solar system body so it had to be of interstellar origin and uh using our Hanlay telescope and in fact even the 1.2 meter we were actually able to get images and spectra of this comet which is quite spectacular. We didn't expect that we would be able to study an interstellar comet a faint one at that using the 2 m telescope. It was quite nice and this comet has this particular paper by Arvin has received a lot of citations in recent times because of the discovery of uh the third interstellar comet.
Let me just come back in a moment. Uh yeah, I can can go ahead. So um as the uh comet approached perihelion, the production rates went up. We were actually able to get uh data points before and after perihelion and these were among the best results around perihelion because there was no other observations uh from this uh for this comet. The earlier measurements were all by 8 mclass telescopes. Our numbers show that uh it probably formed in a protostellar system uh undergoing very inhomogeneous mixing of uh material in the uh in the star at that time. Okay. Uh the optical colors were redder than the solar and that also indicated that they were similar to the uh solar system comets in that sense. uh Sana Ahmed and Kinsuk uh at PRL had worked on the theoretical aspects of this one and uh she has uh she spoke about exoccommitics the other day and she has covered a lot of ground in uh starting with from first principles and building up a cometricoma chemistry model and these are results from that and if you're interested you should please talk to her about it.
uh Pritish Halder and collaborators have worked uh enormously on covering as I mentioned the polarization measurements and he considers so he has coded uh uh programs to work with GPUs as well and the scattering simulations and measurements allow him to compute this kind of polarization phase curves and also get various other details. uh he considers a very uh range of parameters because so that's the problem with uh uh this subject is that it's a multiparameter fit. So you need to do some kind of a uh simulation at various with various numbers to try and uh fit the observations. So the more observations that you have the better the result are. Um the third I think now I'll come to the third interstellar comet because this is the one which we have really received a lot of uh measurements for and a lot of interest was there in the press because of the famous Harvard astronomer so-called uh I will not go into that detail because it's a whole talk on its own u so the comet was discovered on first I mean it was reported on the 1st of July so that was just after the deadline for the proposal submissions and uh but we were able to get some measurements. Nevertheless, uh the onset of CN emissions was detected on 12th of August and Arvin who had been who did his PhD from PR is now in Belgium on a very competitive posttock and he was able to get uh spectra from the UVS on the VT. uh some of these observations were with one-hour long exposures on the VT. Okay. And I think they have covered the measurements over a month across using this more results are in expected to be in press and I think this is some kind of work that could be done and achieved with uh with the NLOT with suitable instruments.
So we should be looking at that kind of uh capabilities.
Going further, the same kind of same comet was also observed over a much longer period uh and also in detail using the uh studied in detail for nickel and iron uh emission. Okay. Uh nickel um is shown in all these red lines and the blue marks are for the uh no it's the other ways. Nickel is blue and the red ones are iron. Okay. you see them very prominently in the UV part of the spectrum and uh there's a lot of interest in looking at this spectrum once it becomes publicly available.
Okay. So comet with this specific comet uh it came with a velocity of over 50 kilometers per hour per second. So then uh if you look at the path uh you can see this purple line it's going almost uh without any kind of uh interaction with the sun. It just vises past okay you if you look at solar system comets if they're coming this close uh you would just see them just going back.
Okay but in this case uh what we realized early on was that it is going to come very close to Jupiter. So what we did was also to look at how this uh object would move under the influence of uh both Mars and Jupiter and uh we have looked at the parameters various orbital parameters and how that changes with uh with the close approach to these two planets and uh here we show the inclination and then the this is a different plot I'll show you come to it later. So with this inclination you can see that the inclination goes up a little bit after uh the close approach to Mars and then the second line vertical line is the perihelion date and then later on when it comes close to Jupiter you have different uh again a very big strong uh change. Now this strong change is a function of what kind of non-gravitational acceleration might be there in the coma in the uh comet based on how the u gas emissions happen. So we're considering that uh we also looked at how close it would approach Jupiter and that is shown in the third panel. So the uh the hill radius is supposed to be at this point for Jupiter. And we saw that for some specific uh very high probably non uh plausible kind of uh numbers you might expect that the comet would come much within the hill uh within the hill radius of Jupiter. Uh eventually it turns out that it might have been closer or just beyond the hill radius. Uh so this was again work done by Goldie and uh published almost very soon after the discovery of the comet.
We have also carried out a lot of postpilian observations of this and it was in fact the first observations from Mount Abu who were the first ones to publicize publicize that it's actually a comet and also public get the spectrum of this and over the couple of months we were able to cover using both HCT as well as the 1.2 2 meter we were able to cover a lot of spectra.
Uh it's definitely much more carbonri compared to uh compared to the uh 2i and a lot of other numbers are coming out.
It's uh this work is presently under circulation within the community. We'll be submitting it for uh publication soon.
One of the interesting things about this comet was it was bright enough to be even picked up by amateur telescopes.
Okay. With small setups. So in fact this is just a 130 mm refractor operated by Vikrant Agnihotri at his uh rooftop observatory in Kota and uh using that data we were actually able to constrain the phase. There are several options possible but then it's possible that it might be close to this 12.8 8 hour rotation period. Yeah. U so I suggest that this might be a good option. In fact once LSST comes online we will be requiring large number of telescope time to follow up on the u various objects that will keep coming up. So setting up a farm of telescopes with this kind of small lowcost instruments might be a good way to follow up on these objects.
Um there are several posters also at this ASI related to comets. Uh some of which I just want to highlight two of them. One is by uh Akshhatraat and Kinsukaria.
And they are again going forward from what Sana's work had been and trying to make a thermal model for the comet actually for the cometry nucleus by considering the shape that goes on the surface. Okay. uh they consider some different different facets to the and they started with 67P which had really very good observations available.
Uh the second poster is by Goldie and myself. Uh please visit the posters both of them are available still and uh discuss with the I think I'll stop with this summary.
Um but the main takeaway is this that comet spec science in India is really a very subcritical uh domain. We have hardly two groups working on this and most of the time we are involved in other details other works as well. So we should I think very strongly of hiring more people and especially the younger people who are coming in. I'll stop at this point, take some questions and then go back to one last slide with the chair's permission.
>> Yeah.
>> Yeah. Yeah. It's open for questions.
Thank you.
>> So, uh I would Yeah.
>> So, I'm Chari from Presidency University in Kolkata. Um I thought that since this is a talk and comment in the ASI plenary session, some of you may be interested to uh you know hear about this historical remark not exactly related to your work but very much with the history of it. So in 1910 when Hal's comet was arriving there's a lot of interest to observe it in India and and worldwide >> and not all of this interest was positive in the sense that some people thought the comet's tail will pass through the earth's atmosphere and the atmosphere may be poisoned and human civilization is in problem etc. All right.
>> So people set up telescopes including in Kolkata area there's a 7in telescope set up just to observe this >> and after the observation etc was done later in 1910 an astronomical society of India of that time was established in Kolkata. The president was a British person working in the treasury department named Ag Tomkins. Okay.
>> And CV Raman was an office bearer >> and it lasted for about 12 years. Then in 1922 due to lack of real scientific work that could be done etc. It was not continuing. They also had a journal called the journal of the astronomical society of India which is archived in the digital archives. Okay. and RC Kapoor of IIA has written in details about that and Rajinder Singh in >> also in science and culture. So I thought that it would be of interest that comets were the sort of the reason for which the forgotten but first astronomical society of India was formed in in India in Kolkata.
>> Thank you.
>> Thanks.
>> Thank you for the historical. Yeah the question. Yeah, I also read somewhere that you know after they detected CN in the in Ali's comet, there are a lot of sales of gas masks at that time because of this passing through the tail thing.
Yeah.
>> Uh so this three eye atlas spectra that you showed.
>> Yes.
>> So they show quite different uh peaks for and sometimes this at the same place you see absorption as well. Yeah.
>> So is this because uh you are looking at different phase of the phases of the comet or is it because the environment is changing and the temperature is changing and all.
>> So uh it's a function of it's arranged as a function of date uh from so it's basically as it went close to perihelion the blue spectra are from the Hanlay 2 m telescope and the black ones are from 1.2 2 m amount of telescope. Okay. And basically as you go further and further away the spectra become noisier.
So the blue spectra which uh and the black ones both of them when they are close and at the brightest then you have the strong emission lines prominent the continuum has been subtracted by the way. So uh you don't see any kind of absorption lines which are I mean the ones which are there are marked in the gray bands. These are from Teluric.
Okay. So, yeah.
>> Yeah. So, yeah, you mostly focus on spectral.
>> Yeah. Yeah. Yeah. Sure.
>> But on a lighter thing, >> you know, from solar observations.
>> Yes.
>> SOHO has discovered 5,000 comets, >> right?
>> And recently as you are walking on the Atlas, there's a new uh mission called Punch.
>> It's actually looking at several hundred solar radi. Atlas has been tracked for several weeks.
>> Mhm. There is a large community actually in US is working on this.
>> Okay.
>> I attended the punch science meeting and I found out that from the heliospheric images also you see beautiful commentary tail they get swayed by the solar wind.
Sometimes they are actually the CMEs are interacting with the tails they get splitted into multiple pieces. So there are other kind of diagnostics one can probably do from that domain as well. So I I agree with you. You know this >> this field is not really explored in a full strength from India but there are multiple avenues to work on.
>> On another note of historical perspective when comet Heli came back >> that was the first occasion when I was in college to get a chance to really get a handle of a telescope. So I don't know whether pure physics student eventually got into a bit of astronomy.
So that interest the commentary things are so much useful for outreach.
>> Exactly.
>> So I think we are not exploiting it in our fullest extent. So I think you have a point.
>> Yeah. In fact comet Hali when 1986 was the time when uh I also got interested because I made my telescope first one at that time based on a report in sky and telesc in science. I think there's a science report or some magazine like that. So my teacher had shown me that.
So that's where I made one. Uh yeah, in fact I've been talking to a week that we should use comets as test particles for the solar system dynamics.
These are a nice >> Yeah, there is a question there.
>> Yeah.
>> Yeah.
>> Hi. So uh very interesting talk and uh uh so in one of the plots in your I think it was in the first part of your talk you had shown uh where C2 and CN things you were showing. So you had shown a plot in which on Y-axis you had plotted Q. So is it the strokes parameter or it's something else?
>> Sorry. Okay. Yeah, this one.
>> Uh no, >> I think this is one of them. Anyway, >> ah this is one of them. Yeah. Yeah.
Yeah. So is it Stokes parameter or something else?
>> Yeah. Sorry about not explaining this in detail. I was running through many of the slides without going to detail. So this is actually the ratio of the production rates. It's not the strokes parameter. It's the production rates. So we can estimate them from the spectral uh information and then the so the Q is basically that and then what uh tells you whether the comet is typical or depleted. Okay. So it's just a measurement basis for defining whether a comet is I mean rich in carbon or depleted in carbon.
Basically the CN strength remains strong but then the C2 and C3 they decline.
Okay, just one follow-up question. So when you compare the dust properties in the solar system versus the uh interstellar medium >> then what sort of different abundances do you see? I mean >> wow. Okay.
Yeah. So u in the interstellar medium you expect much smaller grains to dominate and then uh probably long chains as well. Okay.
>> Whereas the cometary dust will be a bit more uh complicated to deal with. Okay.
Actually with Pripish and uh others we are trying to come up with a unified model and see if we can use the same dust grains to explain both in polarization as well as uh cometary polarization. It's not very easy to do that. It's too many parameters to fit.
>> Yeah. Thank you.
>> Yeah.
>> Yeah. You can now go with your last >> right. Yeah. Okay. So, thanks for that.
Yeah. Uh yeah. I just wanted to take a moment uh to uh remember Kumar Watni. It's been a year since he passed and uh I wouldn't have been able to give this talk last year. It was too shattering.
It's just a pick of him working with the very lowcost instrument that he started with. It's a instrument which just cost us around five lakhs for the spectrograph and then some 20 lakhs for the telescope and he spent a lot of time uh actually making it compatible for science and this something all of this last 10 years of spectroscopy in India has started with his work.
I just request a moment in silence.
Yeah. Thanks.
>> Yeah, please stand up for the one minute silence that is requested.
Thanks.
>> Okay. Thank you. Yeah. I note that comet has been named after him.
>> Yes, it's an asteroid.
>> Asteroid, sir.
>> Yes.
>> I was happy to hear that actually. So, >> yeah. Thank you, Shashik. And thank all the speakers this morning.
>> Thank you.
There are a couple of announcements.
Yeah. From the SOC side. Uh so the parallel session will start at 1:45 today. Not 2:15 as we had for the first 3 days. It is at 1:45 today. Please take note.
>> Uh poster session is on from uh the tea break and poster session is on. Yeah.
Okay.
>> Yeah. So uh there are a couple of I think queries. So there there was a query again about participation certificate from um few participants. So this will be available in your website in your registration portal hopefully early from early next week and uh ASI office will close in late evening. So those who are interested in membership thing please collect form if you are going to fill in. Okay. Thank you.
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