About science; About superhot atmospheres
Right. This is about science produced by the California Institute of Technology and originally broadcast by station KPCC in Pasadena California. The programs are made available to this station by a national educational radio. This program is about super hot atmospheres with host Dr. Albert Higgs and his guest Arthur Vaughan Jr.. Here now is Dr. Hitz. The phrase super hot atmospheres may bring to mind a typical day in Southern California in the middle of August. But really we're talking about something. Hotter than that up in the thousands of degrees. The atmosphere that surrounds stars such as our sun. It turns out that the atmosphere of the sun is really a rather quiet and uninteresting one compared to many other stars which in some ways are quite similar to our own private one the sun. One of the investigators of this particular branch of astronomy a very difficult
branch is our guest tonight Dr. Vaughn. He was with some new type of equipment and some new approaches looked into the atmospheres of stars. Surround us and there discovered the kind of activities that are going on in their atmosphere. Dr. Von I think to start out with I'd like to ask you something about the. Structure and the definition of the stars atmosphere. Afterall a star is a ball of gas from the inside all the way out how can you specify a boundary and say the atmosphere starts here and ends there. Well for a definition I think that that would be fair to say the atmosphere is the part of this star that we see. The photons that escape from the star and reach us come from. The definition of. The outer layers of the atmosphere of the star. Oh this is good. This is sort of an operational definition of what we see as atmosphere. Yes I'm with you. Now. I I think that. The atmosphere of the sun
is in fact not very simple. Some colleagues who specialize in it would would object to that. In fact I think it's an extremely complicated and messy place. Because there are for example sunspots in the atmosphere which are. On the Go. And there are magnetic fields associated with. Their terrible. Forms of magnetic. Forms of various kinds of. Players. In fact you need a glossary of terms to describe the. Effects that you can observe in the atmosphere of the sun. And in a way. You don't see these things in other stars because they're too far away. So in fact I don't suppose that the existence of such effects would ever have been postulated. You know their stories if we couldn't see them for ourselves in the sun.
Like studying the weather in a way when you study the surface of the sun one engineer I know who is concerned with non-linear problems that the less we have seen surf on the shore of an ocean nobody would have predicted. The same is probably true of life. Let us talk of a structure simply a Larry because you say that the atmosphere in the rest a star like the atmosphere of the. Earth the boundaries. You delineate different regimes different types of physical conditions are rather vague. But. There is one layer which is fairly well defined and that's the layer of the. Bald surface called. But a sphere which is the surface that we see in white light. If you look at the sun through. A glass it looks like it has a sharp bit. It's a pretty sharp edge. The density is falling very fast there.
But. Not that sort of portion of the atmosphere. Yet with you now if you look at the density gradient. In the report of this. Layer of the sun that we see. Find that it falls off to a third of its density. Then. 100 kilometers or so something of that order of magnitude. So as I despise a grain that is very steep if you consider to be sharp. Now what happens in the sun is that we find that. The temperature reaches a minimum. In this region at this distance from the center. In the surface of the called the photosphere. The minimum temperature of being about. Five thousand degrees forty five hundred degrees Kelvin. Then. The gas although it continues to decrease in density as we go further out doesn't decrease as fast. As I just said.
Practice it extends quite a bit further now and. Then another one is are dictated by the idea that in hydrostatic equilibrium. How about what so elaborate for it continues to decrease in density but the atmosphere goes. Appreciably further so say three to six thousand. Kilometers and are still something there. Whereas if it's. In hydrostatic equilibrium and continued to fall at the rate of one third factor third every hundred kilometers it would be virtually nothing left except the. Planet Earth. And as the density falls as you move out. The temperature rises for. 500 degrees up to. 20000 degrees or so. Then you come to this. View in this region. Of. Increasing temperature. We see most of these. Layered. And. Complicated effects that
are associated with the. Goetic fields and so on and this is in the end this is a lesson this three in this has to do with it takes place apparently outside the photosphere. Within three to six thousand kilometers. Of the photosphere as this region is called the chromosphere because it can be seen it can be. In fact it was a long ago. Given this name because you can. See it in an eclipse. At the moment of totality. As in the books that describe eclipses. Not everyone is lucky enough to see one. Not exactly the right kind. The. Atmosphere. Visible around the limb of the moon. Is a. Brilliant red. And very bright by comparison. With the sky around very bright. Colors. Sphere.
In spite of its a high temperature. It does not give us the normal visible light from the sun that comes from a colder region which lies below. While the photosphere of gases which are mostly hydrogen our. Sun is mostly hydrogen that. Are nearly transparent or almost perfectly transparent. That almost all. Wavelengths in the visible spectrum with the exception of. Special wavelengths where the light is absorbed or emitted. By. The atoms or times. Its red color that is seen visually. Is. The. Emission line of hydrogen. About. AS. A child. Is being stimulated by the life alone it wow it's big it's a recombination line in that this gas is ionized. It consists of protons and electrons which are colliding and occasionally they recombine and then the atom. Fall
down to a lower energy level and emits these lines. But this wouldn't happen if the gases weren't so hot in fact. Evidence that the gases have a temperature of 20000 degrees or so. I'm from a study of the. Emission spectrum. Talking about well you have to look at stars which were. Considerably further away from the sun and ways. Well first of all how did you choose a star you looked at. Well later tonight you're I think several million of it. People say that you don't know the chromosphere has been known in the sun for a long time. It has been studied by solar astronomers. In very much detail. But the. Amount of light which it. Produces. Is a very small fraction of the total energy generated by the sun not how much it's about one part in 10000. By comparison the corona produces about one part in one millionth. Of the total energy out is a sign you're still further off and if
you look at the. Picture of the sun with. Your graph. But it at some particular. Feature in the sun such as a flare or. An active region where things are hotter than they are on the average the chromosphere. Can be seen. If you look at the light of the whole sun such as a sunlit sky in the daytime. The chromosphere produces almost no. Their rule. The fact that all we watch how this the latter. Type of observation is similar to the observation. I make of other stars because you again don't resolve any specific features. In the. Disk of the star. You see it as a point of light. I think it would be. Obvious question would be. Whether
other stars have chromosphere. But Sun has a chromosphere expected. The reason there is has been since in fact since even 100. Or so evidence that. Leads you to presume that other stars do have chromosphere. We should. Mention. Some of the ways in which the chromosphere of the sun can be studied the light of hydrogen is one another. Is the light of calcium so-called agent K. lines of calcium which are in the violent part of the spectrum. These are strong. Mission lines. THE AGENT. In the chromosphere of. These also come from a combination. Yes and. Now the the H and K lines in the sun are a complicated they consists partly of a strong absorption lines which
originate in the photosphere. But. Imposed. On these lines or emission components which originate presumably. In the photosphere in the excuse me in the chromosphere line they just cancel each other. Well because that's a good question. There's an answer to it. Good they don't. Be. The reason they don't is because the. Sun was fierce so much hotter than the photosphere that. The chromosphere can be seen in the mission against the background of the photos for a quite. A while I have but I know I'm still trying to get to the stars get looked at unless. Son Is this what you are and how the returns we there is evidence from spectroscopy. That Chrome's fears exist in another star. And this evidence consist mainly or
consisted mainly of the observation that other stars showed. Their spectrum in their spectrum. Emission very similar in character to the to that of the sun. So we of course. Had to. Select the stars which showed such effects. How they came on rage and chaos are complicated. As I said because they originate partly in the photosphere. The only lines in the spectrum which. Originates. The chromosphere. My presumption then that they originate only at very high temperatures of the order of 20000 degrees or the line. Neutral. And there are in the sun there is a line of neutral helium in the infrared at about 1 micron wavelength 2030. Which is extremely weak. And we chose to. For this line of. Ours which.
But were of the same general type. That might be expected to have chromosphere. And they were successful. Did you find that we were successful. We started our work by looking at the. One star which. Would be the most likely to show this. And after perfecting our technique somewhat and it's difficult to observe in this part of the spectrum. The. Infirmed that there was the line in this star how white light he said I just said you know was the most likely what what we are about to start our eyes to. Start. Them to Andromeda. As enormously strong calcium emission. Proposed. In the center of the phosphoric absorption on. The back the mission. Is among the strongest of any that are now. And furthermore the star shows other helium lines in its spectrum and so it would be quite difficult
to explain why it should not show this at 10:30. And give Did you kill to look at this because at least the set of this was a better temperature indicator than callous Well I really would chose to look at it because we were undertaking a new type. Of duration we were trying to do. By resolution spectroscopy. In the region of the spectrum photographic emotions don't work very well at all and we were in fact using. Other techniques where they were. How did you find it then I could use. Well I might say that people have done spectroscopy in the infrared with film with the cost a very long exposure time. We started by using. But the 100 inch telescope will not will see. A. Photo electric. Detector. It was connected to the spectrograph. Then we would scan. Along the wavelength very slowly.
And count photons one to time. And this technique was less. Argumentative. By the use of the fabric bro interferometer. Location that perhaps we needn't go into it it simply is a tool of. Terror which. Allows you to achieve high spectral resolution while still using a fairly wide. Hole to let the star light. Conventionally most likely cuts fast. Yes now this is the way in which we found. Had a successful result on land and drama. But it had some disadvantages for our work and. Could look at only a little bit of the spectrum. Thanks to her too. Fact and we really wanted to have more information about the. About the neighborhood in the spectrum because it hadn't been observed before. The specter. Or. Very
poorly known in that. Region. We acquired. And into red sensitive image too. From the. Movie on the image to. Which tube manufactured by RCA. Similar to a television to. This island to. Some extent perhaps just in case of the tube consists of a photo electrically sensitive cathode in the front on which the spectrum is focus. Electrons are released when photons strike this earth. Their Excel aerated back. Focused on an electrostatic gland. And a phosphorus green in the back of the tube. In our case there were. Was a simple as that other tubes have an internal stages of amplification but this dude. In the back of the tube is photographed. This is followed by a lens and if you use ordinary specters got. The graphic.
And expose for a couple of hours. We installed this thing. At the 200 inch in the coup de spectrograph. And were able to obtain. The spectrum. Of stars in somewhat more time than it took using the scanner technique. Got to say time took more time somewhat more time two and a half times as much time. But we had all this extra information we could cover instead of two or three extra. Hundred extra zero hundred fifty. So. We could not only will look for the helium line but we could watch how the other lines in this vector behave the information rate per hour was considerably better. I suppose so. No I'm not. Yes I guess it was. Yes at least for the information you have on it. Yeah. But what you know what to show you what kind of activity did you see first if you find commas fears and the other stuff of a star as well as I said the evidence. As for the existence of Christmas there's another story already existed
they had at the chromosphere and other stars have been systematically stuck studied. For perhaps the last 10 years so you know at least already exist largely by all the Wilson Observatory. So we had a good basis for for what we were trying to do. But. We found that a considerable fraction of the stars that we looked at namely stars whose temperatures were. 3000 degrees to perhaps 10000 degrees where the sun being in the middle showed the helium line and the existence of this line automatically indicates the existence of a hot. Layer which we might as well call the chromosphere temperatures must be of the same order of magnitude as the growth of the sun. Temperatures you just said a moment ago were photosphere temperatures yes yes yes that's a that's right and now what
you're looking for and he mines of the atmosphere is about. Yes and could you make any determination of the temperatures of these all about all we can say is that when the line is present the temperature must be of the order of 20000 degrees because you can calculate the extension that would be required. It's a very sharp steep function of temperature so there's really very little you can say about the temperature other than that it's times that high in some stars. We found the helium line to be perhaps a hundred times stronger than it is in the sun. Does that imply higher Can I just sensor at it's hard to say. It's hard to say. It may not well in the sun. We know that when there is a flare or a substantial area of the surface of the sun is covered by active regions that the.
Well I should what I mean to say is that the helium line is enhanced in these in these cases. So we may presume that perhaps a very large fraction of the surface of some stars is covered. They this is a fraction of the surface of the sun which is covered by these affairs warts and pimples and so on. Are is of the order of 1 percent 1 or 2 percent generally. Now that does leave room for a name for a gain of a factor 104 you have to start talking about the whole higher temperatures and so on. Yes yes. Is it possible from any of this to deduce the nature of any activity and other stars could you make any statements about the likelihood of flares and other stars emerge in the sun. Of course that's one thing we were interested in trying to do very little right now as it is now understood about the physical conditions in the chromosphere of the sun so it's perhaps what we can do is to attempt to see whether other stars have in any way a sort of a similar appearance.
Our results showed for example that the helium line that we found was quite a bit broader than the other lines that are produced by the photosphere and the lines which are produced by the photosphere. Now this probably indicates that there are large velocities involved gases are really moving our finger with your eye now it's already rather well established. In the sun that the chromosphere is in not in in a sort of a static equilibrium but a dynamic equilibrium and that it consists of moving elements of gas called jets or spicules which are dense fairly dense but which cover a small fraction of the surface. This appears to be the case in other stars although the evidence isn't
anywhere near as overwhelming it is as it is in the sun. But at least you observe similar results. We observe a broad line which is shallow. This implies that there isn't very much that there is. It implies something like you get in the sun but not the whole surface of the stars covered by whatever is producing the line. But. That the elements producing the eally mix station are. Perhaps optically dense hot and moving. Was the one thing lines that you observe constantly in the other star. We were surprised I think to find out that when we repeated some of our spectra that year after we first took them the line strength had changed. In fact in one star the first time we observed it we saw
instead of an absorption line I should have pointed out that most of these are absorption lines. Had gone over and become an emission line. I would have it was the first time we saw it it was an emission line the second time we looked at it it was no longer there any mission but there was a little bit of absorption instead. So we presume. It implies I well I don't know. Something has changed. It may be that the star is covered by you know Ormus players similar to solar flares. Maybe I don't have any real strong evidence for this. And of course we know that solar flares come and go. We do know that in order to see the line emission as opposed to absorption the density must be rather high end of the 12 atoms per cubic centimeter compared to compared to a hundred times less ten times less for a normal.
Now how far apart are these two stories two observations you mention between them. I don't remember exactly but it was of the order of a year now we when we found out of course we began repeating other yes Specter. And we found a considerable number of changes with how do these changes compare with those are typical for the sun does it undergo anything when I was a man at the Kitt Peak Observatory. I looked at that question. They looked at the question of. He asked what if you looked at the sun from a distance. What kinds of changes might you expect to see the way he went about determining the answer to this was to examine. SPECTER Healey grams taken at the Mount Wilson solar observatory over a period of years in the calcium calcium K line I think it was. Perhaps it was an H alpha or both and he used he measured the area or fractional area covered by active
regions in each plate and he assumed that the strength of the chromosphere effect would be proportional to the this and he found changes in the overall effect of the order of 20 percent. Which is small and I might say I don't think we would see such a. Small change in our stars because of our relatively crude results. Dr. well-stocked Roland Wilson is currently engaged in a program of observing other stars with the Photoelectric technique somewhat like the one we started with only he's working in the K line instead of the Agent K lines. And he has developed a technique whereby he can measure the strength of the K line emission with an accuracy of about 2 percent. And the equipment should remain stable over quite a number of years and he plans to continue this work to look for
changes in stars that are like the sun and then have a very direct comparison with this conclusion about the way the sun would have. Yes. But now these are changes which that last types of changes we've been discussing. That they could peak astronomers looked into. Are those associated with the solar cycle the 22 year or 11 year sort sunspot cycle. It's a 22 year period if you consider the reversal of the magnetic field. It would be very interesting to see whether other stars show such cycles and so far there is no result on this. I haven't had a lot of time. That's right. I'm not working on that but I'm very interested in that. The result I think that what we observed were not changes associated with anything like the solar cycle but they were probably changes associated with flares or with perhaps. There perhaps there was
- About science
- About superhot atmospheres
- Producing Organization
- California Institute of Technology
- KPCC-FM (Radio station : Pasadena, Calif.)
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- University of Maryland (College Park, Maryland)
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- This program focuses on the scientific study of superhot atmospheres. The guest for this program is Dr. Arthur Vaughan, Jr.
- Interview series on variety of science-related subjects, produced by the California Institute of Technology. Features three Cal Tech faculty members: Dr. Peter Lissaman, Dr. Albert R. Hibbs, and Dr. Robert Meghreblian.
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Guest: Vaughan, Arthur, Jr.
Host: Hibbs, Albert R.
Producing Organization: California Institute of Technology
Producing Organization: KPCC-FM (Radio station : Pasadena, Calif.)
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