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In footnotes or endnotes please cite AIP interviews like this:
Interview of Pierre Demarque by David DeVorkin on 1977 February 21,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
For multiple citations, "AIP" is the preferred abbreviation for the location.
In this interview Pierre Demarque discusses topics such as: his early interest in astronomy; listening to radio lectures by Fred Hoyle; study at the University of Toronto; interest in cosmology; work with Leonard Searle; master's thesis on stellar structure; influence of Searle and J. Beverly Oke; move to the United States and Louisiana State University; University of Illinois and the influence of Ivan King; Ludwig Biermann; George McVittie; going to the University of Chicago and contact with Chandrasekhar; stellar evolution; Yerkes Observatory; leaving Chicago for Yale University; Walter Baade philosophy of studying cosmology; globular clusters; John Eddy's work on solar variability; stellar populations and galaxy evolution.
To begin with, I know you were born in Morocco. But I’d like to have more information about your early life, and this would be your life as it pertains primarily to your education, influences upon you and how you came to Canada, anything in the early period that you think is important.
Well, I guess mostly important from the scientific point of view.
I was 14 when I came to Canada, because my parents moved to Canada, and so I finished my secondary school education in Montreal, in a French school actually. And I didn’t start to learn English until I went to college. I went to McGill University. I was already interested in astronomy. Actually I began to get interested in astronomy just about at the time when I came to Canada. Since there was no astronomy offered at McGill, and most people seemed to think at least my family seemed to think — that astronomy was a rather strange thing to do, I studied math and physics of course and went through the course there. In fact, when I went to the University of Toronto for graduate work, I went with the intention of taking graduate degree in applied mathematics, thinking that perhaps in the future I might do some astronomy, but that was more or less a safer thing to do, and I was interested in applied math too.
Going back, what do you feel was the influence that got you interested in astronomy when you came to Canada?
I guess it was the reading of books in the library. I think perhaps the one thing that I consider most important that really convinced I to eventually go into astronomy were the radio lectures by Fred Hoyle on the nature of the universe. These lectures were transcribed from the BBC series and given on the CEC in Montreal, the CBC English network actually. And there was very exciting series of lectures on astro-physics, the formation of stars and their evolution and what people knew at that time — the expanding universe, the steady state universe.
This was when you were 14 approximately?
Well, I was older l6 I think when I heard those, and that really convinced me that that was really a great thing to do. I really wanted to be an astronomer from then on.
This was pretty much in the early years of the war, World War II?
No. I was born in ‘32, so that was right after the war. We came to Canada right at the end of the war. I lived in France during the war. Although I was born in North Africa, my parents moved to France just before the war. I remember a little bit about North Africa, and we spent the war in France, and then after the war my father wanted to emigrate, which turned out to be a good thing, I think. So I was still quite young. I don’t think the years of war in France were particularly important so far as astronomy is concerned. But they had a very very deep effect on me personally. I remember the war very vividly. But on the other hand, I was young enough coming to Canada; so I think I’ve been very much influenced by things British. I don’t think French Canada affected me that much, although I’m familiar with the place. I do very much like British things actually. That’s probably why I went to McGill and the University of Toronto.
You mentioned you didn’t really study English until you were at the college level. Were the Hoyle radio talks translated into French?
No. They were in English.
And you did understand English well enough?
Yes, I could understand some English. Actually, you know, when I think about the Hoyle talks, it may have been after my first year in college. I think it was actually. I was already a student at McGill when they were given.
You didn’t take any formal astronomy at McGill?
No, there was none, offered.
But then when you graduated from McGill, you worked for Canadair for a year.
Yes, I worked for a while at Canadair. It was applied math work, and I never intended to continue. I wanted to save money for graduate school. So after doing one year of work at Canadair, I had saved a little bit and decided that maybe that was the time to make the jump and go to Toronto.
Was there anyone at McGill that you would feel was a continuing influence on you or should we move right on to Toronto?
Let’s move on to Toronto. I did not enjoy my time at McGill very much. I had a lot of personal problems. The University was not very hospitable to French-speaking people. So generally I did not enjoy my years at McGill, although I learned a good deal of physics I’m sure.
Then on what did you base your choice of Toronto?
Toronto and McGill, at the time, at least in my eyes, were the major graduate schools in Canada and still are actually, and Toronto had a good department of mathematics and applied mathematics. So that’s why I just applied there and was accepted. And actually the fact that there was an observatory and the only graduate department of astronomy there was not really relevant. Although I was thinking of astronomy, it was to me very much something that was not practical for me to do. So I had this feeling that I should get a graduate degree in math or physics, theoretical physics, and get a job and maybe I can get my interest in astronomy continued in this way. I didn’t really see astronomy as something separate from physics.
Is this part of your upbringing, your parents?
Yes, it was essentially my home influence. The secondary school I went to in Montreal was a school which had probably never seen any of its graduates go into science. They went into medicine or law and things like that.
What was the background of your father and your parents?
My father was a civil engineer, and he thought that anybody who can do math should be an engineer essentially. To him that was a natural thing to do. He regarded things in a rather practical way.
And this was very much an influence on you.
Well, I did fight it but I was afraid. I was really concerned about this problem of making a living, and I knew that I had to make a living, and since. I knew math and physics, I thought in the back of my mind: “Well, I can always find a job at Chalk River,” you know, where the atomic energy establishment in Canada was, or something like that. I never thought at the time in terms of an academic career. That was not something that was quite my background. In fact, it [astronomy] was more resisted in my family. It was considered as a bit of a weird inclination, you know.
Did you get some of this feeling after you went to Toronto? Or was this before that?
I think it was before that. I think when I got to the point where I was financially independent, and I was a man and I could do more or less what I wanted and it was accepted that I was free to do whatever I wanted really.
This was when you went to Canadair.
When I went to Canadair and I went on to Toronto for graduate studies. I went on my own. That was my business so far as my parents were concerned. If I wanted to do something unusual, that was up to me.
Let’s move on to the Toronto years then. You said that you had, gone there with the idea still of astronomy in the future but presently you’re going into mathematics. So how did you end up in astronomy?
Well, I was interviewed by the math department as soon as I got there, and they asked me what I wanted to do. I mentioned astronomy as one of the things that I had in mind. And the faculty member told me: “Well, you know, there is an astronomy department here. Why don’t you go and talk to them?”
Do you remember the name of the person who interviewed you?
I think it was Professor Pounder. He was an old gentleman who probably retired soon after.
But no astronomical background.
No, he was a pure mathematician. I don’t know what he did really. So I went to the astronomy department there and met Bev Oke, who was a young assistant professor then, and who spent quite a bit of time talking to me about what they were doing. And it turned out that Bev Oke was interested in stellar structure among other things and convinced me, “Why don’t I give it a try.” They had only one other student in astronomy at that time at Toronto actually, and so the department was just beginning really as far as graduate studies were concerned. They had been giving a master’s, for a long time, but I was actually the third Ph.D. at Toronto. They had given two Ph.D.’s before I went there. He convinced me and I just transferred to the astronomy department. That’s how it started really.
When you did transfer, were you interested in one particular aspect of astronomical research or generally astronomy?
I was interested in astronomy, but I think I was interested in the sort of things that Hoyle had been discussing in his lectures and in particular cosmology, and to a lesser extent subjects like stellar structure. Cosmology was the key, an almost magical word. I was much more inclined to the more mathematical things in those days. But very soon I realized there was much more to astronomy than that. In fact, at the time when I was a graduate student, cosmology was not a good field to go into for the theoretician because I think most of the basic work had been done a long time before, and the new developments that led to the expansion of cosmology that we have just seen have been in the last few years did not exist. There was no new observational data. There was no three degree black body background. That was a major thing. There were no quasars.
But at the time you went to Toronto, this was ‘56, ‘57 approximately?
Baada just revised the distance scale, among other things, and there were many changes. How did you come about choosing a specialty? Did you work with Leonard Searle there?
Yes. Leonard Searle was also on the faculty there, and I guess Leonard Searle and Bev Oke were both assistant professors; they were more or less on the modern side of the department. The Toronto department was very traditional in its approach to astronomy. They were mostly at the time working on a large program of radial velocities. Donald McCrea, who’s now the director, was beginning to get interested in radio astronomy, and that was the exciting new thing in those days. The 21 centimeter work was just beginning and expanding very rapidly.
Did they appreciate the cosmological value?
They thought more in terms of galactic structure. That was the thing the possibility of unraveling spiral structure, that sort of thing. So there was a small program in radio astronomy done jointly with the electrical engineering department. For some reason this did not particularly attract me. I think the emphasis was very much on the observational and technical aspects. I was more interested in theory. Right from the beginning I did have to do quite a bit of observing at Toronto — that was part of the responsibility that everyone at the observatory had to observe. You were scheduled once or several times a week, and you took spectra for the observatory program essentially. I did a lot of that. And I was partly supported this way. But otherwise Oke and Searle were the modern astrophysicists there. They were both pretty fresh out of Princeton, and they were coming with all these exciting things that people were doing at Princeton — astrophysics — and that really turned me on. So very quickly I did some work with Oke on stellar structure. In those days they required people to write a master’s thesis, and I wrote a master’s thesis on stellar structure. In fact, my thesis I’m quite proud to say, because it was never published, came about simultaneously a few months earlier — with a paper by Schwarzschild and Harm on the internal structure of early type stars, including radiation pressure. Now, when I saw the Schwarzschild and Harm paper appear in the Aps, I realized that I had done it in a much more complicated way than was necessary. I did it in a very awkward way. But I got my models done and devised a very intricate fitting procedure. It was done with a UV plane and so forth.
Right. This is R. H. Fowler’s UV plane that you’re referring to?
It was Milne’s really. The first integration that I made was done by hand.
This is an important question.
Right. But anyway I was very very pleased with these models because they were the first early type sequence models that are more or less realistic, I think.
By hand, of course, you mean you had some kind of mechanical aid, mechanical desk calculator?
Yes. The very first calculator I used at Toronto was entirely manual and mechanical. You had to crank for the multiplication and shift manually. It was a very slow process. But electric calculators existed, and I think because the observatory was poor, they weren’t available at the time, but I think they existed in commercial establishments.
How long did the calculations take for your fitting procedure?
Well, with the electric calculator it wou1d take me about two good days per integration, and that was working long days. You needed 10, 15 integrations or something of the sort. That was a bare minimum per model. So there were a number of days of just hand computation.
Did labor like that cause you to rethink your work in stellar structure to any degree, or did you know that computers were on the horizon?
That was partly so, yes. I knew computers were on the horizon. But that aspect didn’t bother me.
The idea of computing for several days simply for fitting one model, then realizing that if you were going to do an evolutionary sequence?
No, numerical work has never bothered me. I like numerical work.
I don’t find it as much of a drudge as I think a lot of people do. It’s not very intelligent work — it’s a routine sort of thing — but it requires a lot of concentration.
At the time you were learning fitting techniques, was this a fitting technique that you’d actually derived yourself, or did it have anything to do with Henyeys early work?
No. It was really derived from Schwarzschild’s early work. Now, Schwarzschild’s book did not exist, of course, so you had to learn from the literature essentially the techniques in the UV plane. And the techniques had to be developed because of the extra complication of radiation pressure. So my technique was very cumbersome. Schwarzschild made a clever transformation and things were a lot simpler, but I hadn’t thought of it.
These are the starred co-efficients that he uses in his textbook?
With the radiation pressure it’s related to that, yes, but there is an extra transformation which I can’t think of.
That’s all right. It’s the basic idea that I’m getting at, of course, in the labor of the computation and how this caused you possibly to rethink numerical techniques as opposed to analytic techniques.
Yes, right. That was very new to me, and perhaps that’s why I didn’t mind doing it. As an undergraduate most of us do mostly analytical work? Certainly at McGill we went through quite a bit of applied math that was very elegant. Most of this turned out to be good grounding but rather useless in a direct way to integrating stellar models. And the numerical techniques were all new to me, and I really was quite impressed by that. Now, I think it’s perhaps not fair to say it was entirely new because when I worked at Canadair I worked on the computer, and actually I did work on the numerical solution of differential equations and similar problems. So I really started to get interested in that there. But the application to actual physical problems that were of interest to me — that was new, and I really liked that for some reason. I really was very excited about that.
If you were somewhat scooped by Schwarzschild and Harm on your master’s, how about the Ph.D. dissertation?
Well, the Ph.D. dissertation was started and computers had become available then, and even though we were still doing fitting by hand, the numerical integration was done with computers. I started with Oke and then Oke left for Caltech before I was finished, and then Searle who was also interested in the problem was the obvious person to take over, did take over. Searle actually has had about as much influence on me, perhaps more than Oke, because he also taught me several courses, and I also worked on a research project with him as his assistant.
What was the project?
The project was on the Balmer decrement in hydrogen recombination in nebulae. You’d find the paper in the ApJ somewhere. He was very kind to me personally, and. I learned an enormous amount from him. But then for my thesis I was pretty much on my own because he went away to California also.
They both went to Caltech?
Yes. I more or less did my thesis by myself, although we did correspond and so forth. That was pretty much my own effort. The thesis was on the internal structure of the sub-dwarfs. Now, the sub-dwarfs were hot things because they were. Main Sequence and in the halo, and people wanted to know where they were really in the H. R. diagram, the theoretical H.R. diagram. It’s a little hard for us now to think of the internal structure of main sequence stars as a hot subject, but Hoyle was working on the subject at the same time, and you’ll find the Monthly Notices about the same time in a paper by Hazelgrove and Hoyle on the internal structure of metal-poor main sequence star.
This is approximately 1960 when I recall vaguely that there was a big reversal in the ideas of the relative importance of radiation and convection in the interior of the sun at least and other stars. Did this come into your work at all?
Well, actually, you know, that came out of the work of Oke. Stellar structure started at Toronto before Oke. Actually stellar structure started at Toronto through R. E. Williamson, who taught at the University of Toronto for several years. Williamson was a student of S. Chandrasekhar, and he was an expert on stellar dynamics and on stellar structure. Williamson left Toronto in the mid ‘50s and went to Los Alamos and never did any more astronomy after that. So that’s why you may not have heard of him. Well, Williamson was Oke’s teacher, and Oke took a master’s degree at Toronto (Oke was at Toronto also) on the internal structure of the sun, and one of the things he discovered in his very important master’s thesis that the proton-proton chain was running the sun rather than the CNO cycle. So on the basis of this very fine thesis, he went to Princeton for his Ph.D. and came back later to Toronto.
When was that exactly? That must have been quite a bit earlier than we’re talking about.
That was ‘52, ‘53.
Schwarzschild had been there just a few years himself, at Princeton.
Yes. That’s right, five years. Schwarzschild must have been quite a young man then. I guess he was in his thirties maybe. Anyway Oke’s paper you will find, if you’re interested in that because it’s a very important paper, in the Journal of the Royal Astronornical Society of Canada, 1952. That’s his master’s thesis.
That is a very important historical question because when students do look back at the work of Bethe, they’re always surprised to see that it’s the CNO cycle when they always think in terms of the proton-proton cycle for the sun, and it’s an initial source of confusion, which is only clarified by more reading, and most students don’t read that far.
Yes, the sun is marginal. It’s right at the boundary between the two processes, and that’s why there’s a problem.
You knew all this, of course, while you were working with Oke, of the history of his work?
Yes, I was familiar with his work, yes. He was much less in stellar structure, of course, at that time. Williamson had another student who did some nice work in stellar structure at Toronto and who was around, whose name was G. Duff. You’ll find papers by Williamson and Duff. Well, Duff is a mathematician now, a professor of math at Toronto, and has not done astronomy for a long, long time. But he was around and I knew him, so I just mention that.
Certainly. Well, let’s get back to the thesis and pretty much 1960 and move on from then.
Okay. So the thesis was on the sub-dwarfs and really I have worked pretty much in a continuation of this since then. Do you want to know where I went?
I have that down in a profile.
My next job was at Louisiana State in the United States.
I’m interested in knowing how you would come to the new positions, how you found the new positions, and how the conditions for research were there, how you chose your problems.
We’re talking about Louisiana State now.
Okay, so I went to Louisiana State. And actually when I got my Ph.D., which was in ‘60 really officially but I finished in ‘59, it was very hard to find a job.
This was post-Sputnik and everything?
It was post, but the expansion had not started yet. At least I was not aware of jobs. In fact, I got only two offers. One was Wisconsin State College in Oshkosh, which was not much of a center for astronomy, and I was very philosophical about this thing — it didn’t worry me at all. I was very happy about any jobs. I think it’s hard for me to understand how I felt seeing some of the students we have now who have much higher expectations than I always had. When I was an undergraduate, I didn’t think about an academic position until I went to graduate school and I realized I could do that, and it was the normal thing that everybody was doing. And then when I got my degree, I was not in a’ major astronomy department where everybody went to other major universities and got teaching jobs in universities. So I did not know what to expect, and so when I got a job I was happy. It didn’t bother me.
Was this a place where you were the only person teaching astronomy?
Right, right. When I went to Louisiana, I was very pleased to go to Louisiana, because Louisiana had much better facilities than Wisconsin State.
They had a. good computer, and that was the thing that made the difference to me. And they had a good library; it turned out — at least much better than Wisconsin, an adequate library and quite well actually. So I went down and visited the place and was quite attracted. So I went there and made extensive use of their IBM 650 that they had. And I continued much along the line of my thesis, extended that.
So you certainly had research capabilities.
Oh, yes. The only problem was that the teaching loads were very much higher. Of course, I had to teach all the courses.
How many courses did you teach?
Were these all astronomy courses?
They were introductory astronomy courses. You know the kind, with very large classes. Essentially I taught the same course to various sections several times.
Getting back to one item that I missed, you mentioned that at least for your master’s thesis you did not have Schwarzschild’s book, but by the time you did your Ph.D. it was certainly out.
Yes, by the, time I got my Ph.D. When I started to work on the Ph.D. and so forth, the book was not out yet.
And so it would be difficult to assess, let’s say, the effect of the book on your own work.
No, it really didn’t affect me very much.
You could possibly assess, though, its effect on graduate students you met later on.
You had no reason to use it in Louisiana.
No, because I didn’t teach that level of students. I’m sure I bought a copy as soon as it came out. I don’t think I have a copy here, but my copy is very very worn. And of course, I used it as a text as soon as I started to teach that level of student.
So you were there at Louisiana State for one year or two?
I was there for one year, and I went for the next two years to the University of Illinois, and that was a good experience — ‘60 to ’62 — and then I went back to Toronto and stayed there for four years.
It seems from your profile that you did not actually receive your degree until after you went to Louisiana?
Yes, officially I got it in 1960 but I finished the work earlier.
That explains it. The University of Illinois — which campus was that?
It was Urbana-Champaign, and that turned out to be a good experience because there were some good people there.
Who was there?
The director was McVittie, and I shared an office — that was a most important experience — with Ivan King and got to know him very well during those two years. As you know, Ivan is an encyclopedic person and he in some way took me under his wing, anyway he taught me a tremendous amount. That turned out to be a very valuable experience. We were in an extremely small office, the two of us. It was really too small for one person even. Occasionally some of Ivan’s students would come and measure. There was a measuring engine in the room, so you could actually barely move. So the conditions weren’t very good, but that was very valuable. Now, it’s during the time I was at Illinois that L. Biermann came to visit Illinois. At that time I was interested in models for red giants. I became interested in evolving my star. Of course, very quickly my thesis essentially opened up the whole of stellar astronomy to me. There was particular emphasis on the halo and the old stars really. And at the time one of the major problems was the ages of the globular clusters. So I became interested in that and spent a lot of time at that time on convection; although I didn’t really publish any work on the theory of convection, I did spend a lot of time on that and did a lot of reading on convection. I worked on programs for giants on “Illiac,” which was quite a job because there was no compiler. You had to write your programs in machine language. That was Illiac II, which was one of the early computers.
They had one at Urbana?
I imagine there weren’t very many of them around so that was good to be there.
No. I think that may have been the only one for that matter here.
What was Biermann’s reaction to some of the numerical techniques that were possible in computing at this point?
We didn’t discuss the numerical techniques I remember when he came, but he asked me very many questions. I showed him some of my results and models of red giants. That was not too long after a paper he had written jointly with Kippenhahn and Temas which was a very important paper, on the construction of red giant. So things were still reasonably fresh in his mind, and of course he had been interested in outer convection zones. So, he asked me a lot of questions and he made a number of very interesting comments mostly about the physics of convection. He was concerned about the structure of the super-adiabatic region and the fact that you have a density inversion and problems of that kind. He was very kind, really very kind, and helpful. I remember he gave a lecture on comets at the time.
I know you were working on models of red giants, but had anyone actually evolved a red giant from the main sequence by that time?
Yes, there was the famous paper by Hoyle and Schwarzschild in 1955, which is really the great classic, I think, in the field.
That was step-wise continuous integration?
Yes. These models were not evolved in the sense we understand it now.
That’s what I meant.
No. There had been a very early attempt to evolve by Hoyle, and I think this is not often recognized. Hazelgrove and Hoyle actually pioneered in this actual automatic evolution. I think perhaps they don’t get as much credit as they should. Maybe historians like you are aware of this.
Not yet. This is what we want to become aware of, partly through the oral history.
These papers were published in the Monthly Notices. I think Hoyle’s paper is ‘56 or something like that. Because their techniques were very crude — I guess the computers were small then and so on — they could use only a very few integration steps and very few time steps in following the stars, their results were really quite wrong. But they got the right qualitative features for the evolution, the giant branch and so forth.
Through your talks with Biermann did you ever discuss the growth of his work in evolution stellar models? Anything that would come to mind?
No, I have to admit I discussed his paper that I mentioned, but it was a fairly narrow technical discussion of the physics of those giants and nothing of a broad scope.
Let’s concentrate on Urbana and the possibilities, you had. Did you have contact with McVittie, and did this increase your interest in cosmology? Because there’s a big reversal also in 1960 in cosmology on the part of Hoyle.
Well, yes. It did maintain my interest — let’s put it this way — and actually Ivan King was interested in these problems, too. As a matter of fact, he even wrote a little note I think it was in The Observatory — on the tests of comparison between steady state and big bang cosmology. It was very elegant. It’s about the distribution of ages you would expect in defining galaxies. I was impressed by that, too, I remember. And I remember sitting in some of McVittie’s classes on cosmology, and in fact Bill Bonner, who is now at the. University of London visited at the time and also gave a course, part of which I attended. Yes, “we received visits from cosmologists also on occasion, and it was mostly a case of listening and being interested and doing some general reading. I didn’t do any research on it.
Had you met Hoyle by this time? Was he one of the visitors?
No, he was not one of the visitors. I don’t think he was on such friendly terms with McVittie.
No, I wouldn’t think so. How deep did their differences go to your knowledge?
Oh, it was very deep. I don’t know on the part of Hoyle. I think Hoyle probably dismisses McVittie as not of that much importance. But in the case of McVittie I think it ran very deep. He felt very strongly about it. That’s about the time he wrote his little book Fact and theory in cosmology. I remember he talked a lot about such things. I think generally now I realize that most relativists do not have a very high regard for McVittie’s relativity and his physical understanding and sense when it comes to general relativity. He’s really a very classical applied mathematician, you know, of the British school. He was a good teacher of classical mechanics and all that sort of thing. It’s hard to say. In some ways, my position, if I have to take a position in this controversy and all that, is very ambiguous, because I admire Hoyle enormously, probably more of the two; and I owe him in a way being in the field and so forth. But I rarely, in a way, believe what Hoyle says, and in some ways I have a much more sober attitude toward astronomy. I might say that I’m not close to Hoyle, but I know Hoyle fairly well and we get along very well. He knows me quite well; he’s always very nice to me. And he understands my point of view, I think, even though we haven’t discussed it not such an important cog in the whole process. I don’t want to overemphasize my point of view, but I do discuss the things a little bit with him sometimes, and he understands the point of view and he’s very kind in the sense of understanding.
What are some of these points of view? I would be very interested to know them.
Well, for example, he came up a couple of years ago with a theory of the sun, trying to explain the lack of solar neutrinos.
This is a question I certainly wanted to direct to you later.
This involves, you know, a very dense inert core with early elements. But you don’t want nitrogen, only those early elements which are not going to modify the nuclear reaction; you don’t want a CNO cycle. It’s an involved theory. So in order to explain this really far-out structure for the sun, he hangs this on a very elaborate cosmological theory. This was connected with this new cosmology with Narlikar, a very elaborate theoretical background. The whole thing seems, in a way like such an artificial construction. While you wish you would be able to explain solar neutrinos without having to change the whole of cosmology, it makes the sun such a special case in the whole structure. He said, “Well, of course, you’re right. This is just an idea.” But sometimes his ideas are far out of the way, but some of it remains and has turned out to be very important, and I think he’s right. But I think he understands that some people may have a much more sober point of view.
Is this before or after Davis’s experiments?
Oh, that was after. That’s only a few years ago.
So this is the difficulty in explaining the lack of neutrinos.
The lack of solar neutrinos. People were coming up with the most extraordinary models.
You had models which involved more angular momentum in the core.
Right. These models unfortunately cannot work the way we had them. There were objections based on stability arguments, and I was aware of those, but was ready to disregard them. The model was very much idealized. There is so much we don’t really know. In fact, we know nearly nothing about the hydrodynamics of stellar interiors or of the solar interior particularly; so that even though it posed some problems, it explained so many other things that I was ready to say, “Well, perhaps there is something to the model.” The main problem really is that models are too oblate.
In the core.
In the core and the surface would be too oblate. And I think that’s probably more oblate than we would be willing to accept. So from that point of view I think we are ruled out. I still think it’s possible, though, that rotation plays an important role because no one really has constructed adequate models for the sun with a rotating interior, which takes into account all the motions. And it may very well be that there is a configuration with a rapidly rotating core which is not oblate at the surface. So I wouldn’t be surprised if it’s part of the solution. I still believe that it’s part of the solution. The models we presented, though, are really unacceptable.
Would you say that the reaction of the theoretical stellar interiors community to Davis’s work was appropriate, the flurry of restructuring models, or do you think there was enough criticism of Davis’s own observation of the possibility that more than one neutrino existed that could not be detected by his “cleaning fluid?”
I don’t know. My attitude about this whole solar neutrino experiment is a little different maybe than that of some other people. It’s a little different certainly from that of Bahcall, who is I guess the leader in this business. Bahcall has been presenting this discrepancy as sort of a major catastrophe, and I think partly because he wanted to make sure that Davis would get grants to continue his experiments. The truth of the matter is that this neutrino flux depends on an incredibly accurate knowledge of the solar temperature. You have to know the temperature of the sun to an accuracy which is much greater than the accuracy that I would attribute to most of our models, I think.
This is the internal core temperature.
Yes. And now it’s true that, Bahcall and his associates looked into the possible errors that were involved in the various physical processes, as we understand them ‘now, and they found that the discrepancy is larger, than the errors. I mean they’ve tried to analyze the problems very well. But it seems to me we are really looking for a very small effect. Now, if we can develop detectors that can detect much lower energy neutrinos and get some sort of a neutrino spectrum of the solar central region, then maybe we can talk about what’s going on in a way that would be much more useful. But at the present time you can only detect the high energy neutrinos, and there are so few of them that it’s just not a sensitive experiment at all. I think there are some people who want a problem; they want to maintain the problem, you know, to have something exciting. I think an awful lot of the more fashionable astronomy is partly very exciting but is also a bit of a P.R. bit. I’m afraid there is a lot of that going on. And perhaps it’s right. Perhaps this is the only way to keep peoples interest and get support. But I think it’s all right so long as the scientists are aware that that’s what’s going on; that it’s really not a major problem so that the foundations of physics are in danger or something like that.
The discussion of neutrinos is one of the most fascinating, as would be several others that I hope to talk about, but without taking your complete afternoon, maybe we should move on to other things. If we move back to the Urbana period — and I think you’ve discussed that to a degree — how did you come to leave there? You went to Chicago after that?
No, actually I went back to Toronto. [Page skipped by transcriber]
I guess more for a personal reason than for anything else. I think at that time I wanted very much to go back to Canada, and I got this offer at the University of Toronto, which was my old school, and I was glad to go back.
And that was between ‘62 and ‘66.
That’s right. And actually my first couple of years at Toronto were, very very good years, I think. It’s possible that they may have been the years when I did the best work that I did.
You continued on primarily with stellar structure.
Yes, but then the large computers were available — the new generation. And then we learned the Henyey method and completely retooled. The programs became not only much more sophisticated in terms of numerical methods, but it became possible to use much more detailed physics for a great part of the star. And it really became the era of automatic stellar evolution on a large scale. We really were off on a fairly large scale, and I had some very good graduate students there. I guess I was young and very active. At the time I was still young enough that I had very little distraction other than my job. I mean the more immediate research aspect and teaching aspect of the job. And it turned out there were some good students around at the time.
Who were they?
Well, Richard Larson was one of them.
I didn’t realize he was one of your students.
Larson was a fantastic student. John Percy and David Hartwick; Juliana Sackman were students there. She’s Mrs. Christie now, the wife of the Caltech provost, but she was a graduate student there. I have a feeling I missed some important ones.
That’s a good list.
Yes, there were several others. Anyway there were some very good students there. Actually Bob McClure was, but he was not in stellar interiors. And we did some good work, and the only reason we did not perhaps develop the great amount of stellar structure work that developed, that, for example; I. Iben turned out, was partly lack of facilities, computer time. I came in with the computer and it was new and there was a lot available, and the facility became saturated very quickly at the University, and it became very difficult. It was partly my incompetence in getting computer time, my inability to raise money and so forth. I didn’t know how to go about it.
What computer did you have at that time?
It was an IBM 7090. I guess the 709 was the big improvement, but the one we had was a 90 which became a 94 very quickly. Actually we had it when you were here at Yale.
Yes, they had two of them in the “Stretch” version. What caused you to leave Toronto?
I think there it’s mostly the fact that I was frustrated because I didn’t see any hope of getting the computer time I wanted. I think that was the main thing. There were some other problems, but that was perhaps the main scientific thing. And then I did get this very nice offer from Chicago.
Who made the offer?
The letter was from W.W. Morgan, I think. He must have been chairman at the time. It came from the astronomy department at…
Was this an unsolicited offer?
It came out of the blue as far as I’m concerned.
Who do you think was behind it?
I really don’t know. I’m sure Chandrasekhar had something to do with it or was in favor of it, let’s put it that way. I went to visit Chicago before the offer. I was first invited to give a colloquium, and at that time was taken around to Chandrasekhar’s office and he presented me with a book which is at home, I think. You know, Chandrasekhar can be very gracious when he wants to be. Actually he is very gracious most of the time. It was one of that series of the Chicago Compendium. Stars and Stellar Systems. The particular one he gave me is at home, I think. It was a nice dedication, and I was very young and very impressed, and that meant a lot to me.
Had you followed Chandrasekhar’s work?
Well, I’d read his books, sure. His book on stellar structure I’d really studied particularly and the radioactive transfer book and to a lesser extent the Stellar Dynamics. But I really had no acquaintance with the others.
When had you read those books?
As a graduate student.
What was the influence of books upon your work, the influence of other people, your opinions of the work of those people and their personalities and how that might have affected research? All of these are very important. We might have missed a few inches there with the leader on the first side. Your comments about Schwarzschild’s book and how you reacted to them. Would you mind repeating that quickly?
Actually there’s something interesting about Schwarzschild book. A good fraction of Schwarzschild’s book was familiar to me before it was published, because I was familiar with the notes that Bev Oke had taken while a graduate student at Princeton. So these notes on stellar structure had very much, of course, in common with the textbook that Schwarzschild wrote, because that course was given by Schwarzschild, of course. The book was the outgrowth of several years of teaching at Princeton. It’s not surprising. So the heart of it was actually sort of known to me. It was not that unfamiliar when I saw it.
Did you ever meet Harm?
It is of interest to know the relationship between Schwarzschild and Harm, and we hope to be able to derive that from Schwarzschild. But if there’s anything that comes to mind about their relationship that you feel we might be able to ask or shouldn’t ask, I’d appreciate any discussion now.
I really know nothing about their relationship, but if you’re interested, I had a little bit to do with Harm. But I really, don’t know much about Schwarzschild and Harm.
Okay. Certainly some information on Harm would be interesting.
I did get to know Harm when I went to Princeton. Soon after I went to Toronto from Illinois, I realized that I just had to learn the Henyey method. Actually the Henyey method had been around for quite a while. In fact Henyey did not invent it, and Henyey had been using his method at Berkeley for a while.
I recall that was in the ‘50s.
Yes, the paper in the American Physics Journal (APJ) is ‘59. But I couldn’t understand that paper. I just could not. But I knew I had to get to know that, and I knew Schwarzschild was gearing up for it. That might be of interest to you, how it all started to spread. It spread, of course, because computers became available. But the actual notes went that way: Henyey gave a lecture at the IAU in 1961, a series of lectures on this method, at which in particular. The Germans — the Munich group in stellar structure — took very good notes. These people went home and thought more about it and organized the notes very well.
Was this Biermann [???].
This was Kippenhahn and others. And these notes somehow made their way back to Princeton and I think were used and served as the basis for the techniques of the Henyey code that was used at Princeton. The Munich and the Princeton codes are different actually in many respects. They started from the same set of notes really. Okay, when I learned that Schwarzschild was working on it and knew and understood the Henyey method, I went down to Princeton. I missed Henyey’s talk — I didn’t know, about it — at the IAU. I was at the IAU in ’61, but I did not hear his lecture. So I really did not understand the article, so I went down to Princeton to get essentially what was a full day’s lecture by Schwarzschild as what the Henyey method was —which was very clarifying, but a very strenuous sort of experience.
It was one day. It was really a cram session in the Henyey method.
Was this the first time you’d met Schwarzschild?
No. The first time I met Schwarzschild I was a graduate student. I went to an AAS meeting at the University of Rochester.
Well, let’s get back to that interesting day.
Okay. And. Harm was there. I think I stayed overnight, and the next morning I went over to Harm. I think Schwarzschild was very busy, and so I went to Harm, and he gave me copies of his flow diagrams and an additional explanation on the Henyey code.
Now, a flow diagram would be what we think of today in the same sense in a computer code?
Yes it was actually a computer code flow diagram. And so what I did was go back home and first really try to understand. I essentially reconstructed their code in a way from the flow diagrams that Harm had given me, and then we developed somewhat different codes afterwards. But this is how I understood the principle of it. It’s very simple once you know but is very hard to understand at first. At least I found it very, difficult, and I’m told that even now students find it very difficult. One of them told me that a few days ago. It’s much more difficult to understand than the fitting techniques that Schwarzschild developed. Jas Smith — the fellow who just knocked at the door — who is very good in numerical analysis — told me that they still find it hard. Anyway that’s my acquaintance with Harm, and I’ve gone back to Princeton once or twice and discussed codes a little bit with him a few times.
I think the important thing I’m interested in getting at would be his position regarding Schwarzschild. Was he merely a computer or much more than that?
I have the impression he’s mostly a computer, yes. More so than the graduate student might be. He is not really an astronomer, I think, or that much of a physicist. He’s definitely a computer.
In terms of the evolution of the code and its application to computers, would he be a worthwhile person to interview, or would we get the historical information that would be in your opinion important from Schwarzschild alone?
I think you might find it worthwhile to talk to him. He’s definitely the one who writes the code and runs it.
He would have the best knowledge of the interaction of the computer and the needs of the code. He would know what the computer could do and could not do.
Oh, he’s very competent in that line.
The big problem of the amount of core you have to work with and the integrations.
Oh, that would be more his line than Schwarzschild’s. I don’t know how close to the code Schwarzschild really is. I understand he keeps very close track of what’s going on by meeting frequently with Harm, but I think they mostly discuss the physics. How much they discuss the numerical details, I don’t know.
The interest I have there is the ability to perceive what kind of integration steps are realistic and what are not realistic, how they are constrained by the computer, this sort of thing.
I see what you mean. I think the present computers enable you to gain all the numerical accuracy you need. I don’t think that’s a problem really.
But historically at least at that time?
At the beginning it wasn’t the case. No, that’s right.
So he would be a valuable person to examine for that?
The early helium flash calculations, for example, that he did with Schwarzschild would be a good example of something they did in a very crude way.
Yes. Do you find that we’re really at the point now where we can trace a continuous course easily through the helium flash to the processing or production of heavier elements?
Well, we can do it. We can do it in some ways to the first approximation, but there are many points that we don t really understand as we go along. It could well be that there are some real differences — I mean some fairly serious errors in the approximation. That is to say.
This is at present?
Mixing, yes. I think we still may be omitting some aspects of the problem. In fact, we know that, because there are some kinds of stars we can’t explain, like the CH stars.
The technetium problem still bothers people?
Yes, that sort of thing. But, on the other hand, it looks very much as if the gross features of evolution are pretty much understood.
One question I want to get to, which involves the fine features of star evolution, involves John Eddy’s recent findings but I don’t want to jump ahead to that just now. That’s on the variability of the sun, if you’ve had any thoughts on that.
No, I really don’t.
Okay, then maybe we wouldn’t deal with it. Let’s go back to Chicago then and place you in time moving to Chicago and your work there. How did you find the working conditions and what was the general atmosphere?
Well, actually Chicago was a great place but was also a bad place.
Well, I hope you give us both sides of it.
Right. The great aspect of it, at least for me, was that in some way, even though it seems a little strange to say this, I did get at Chicago the kind of maturing experience that a lot of people get in their post-doctoral years. Because of my background, I was to a great extent self-taught, particularly in theory. Even somebody like Searle, who is relatively quiet strong in theory, among observational astronomers is mainly an observationalist; and his point of view is not that of a theoretician, although he knows a lot of theory and understands a lot of theory. The same with Oke. His concern when he was at Toronto was the scanner and things of that kind.
Yet both of these people came partially from Princeton.
They came from Princeton, and they have a very good background in theory, but their concern at the time was not theoretical. Their research was more observational.
Could that possibly be because of Spitzer?
Possibly. Incidentally, they were both thesis students of Spitzer. So for me it was a chance to meet real theoreticians for the first time, you know, and, I really learned a lot in a very short time there, just talking to these people and listening to them. As you know, they like to talk at Chicago. Certainly Chendra and these types talk.
And the other names would be Vanderoort?
Well, there was Vanderoort, yes. It was mostly Chandra, but Vanderoort, Dick Miller, and Nelson Limber was there still, although he was not as easy to talk to, and of course he was at Yerkes at that time. But those were the major ones. And of course Morgan, but that’s not theory, but we talked a lot.
What was the environment, as you found it [???] — The scientific environment?
So from that point of view it was great, but the scientific environment was not favorable to me for two reasons. First, it was even worse than Toronto as far as computer time is concerned. I had a really hard time. And there was even a feeling in the administration that computer work was not the kind of research that they wanted to promote at the University.
This is just a wild guess, but could that have anything to do with Chandrasekhar?
I think it probably had something to do with Chandra, but it had a lot to do with the dean. That was Dean Albert, who was a mathematician, and who felt very strongly that the really important things came out of more purely theoretical things. And of course Chandra got along very well without a computer. So the situation was bad from that point of view, and also there was very little interaction with the observers. I mean the department was split into two, and even though one went back and forth, there was really I don’t think very fruitful interaction.
I saw you a few times at colloquia at Yerkes — possibly two or three times.
I went there a good many times though. I don’t think I went every week but quite a few times.
How about the working conditions with the other astronomers? Did you find differences of opinion between you and others, or did you find possibly the differences between others affected your ability to do work?
No. You know, people have the impression that at Yerkes people are fighting all the time.
It has a history of that. I’d like to have your impressions.
There were differences of opinion on things, but I never encountered any actual outward fights between people, or exchanges even, unpleasant exchanges. I’ve never seen that. Faculty meetings were always on a very very polite level, at least those that I have attended. Even when there were disagreements between Chandra and Morgan and people like that.
Scientific disagreements, or disagreements about choice of faculty and that sort of thing, they were very legitimate differences, and people were certainly very tolerant, outwardly very tolerant. So I did not encounter that kind of problem.
Then negative aspects were pretty much in availability of computer time and things like that.
Yes. I think Mihalis found that same problem later on, although to a lesser extent.
He went there after his graduate work at Caltech?
Yes, He went on the faculty there for a while, after I had left. And I think he did a lot of computing, quite a bit of which was done at Argonne. But I think this is perhaps the major reason why he went back to Colorado, where he is now.
That’s quite interesting.
So from that point of view, Chicago was a great period, but there was this problem. I don’t know. I had the feeling, although I was under great pressure to stay there, when I was there that somehow eventually I would go somewhere else.
Who was exerting this pressure?
Oh, Chandrasekhar in particular.
He thought a lot of you.
I guess he must have.
While you were there, at least the last year you were there, the famous pacer by Hodge and Wallerstein came out, which I’m interested in everyone’s reactions to. I know that you had discussed the implications of the change in the distance scale. What was the reaction of some of the other people around you, the general reaction?
I think it was a problem. But to the real theoreticians like Chandrasekhar or Vanderoort, it wasn’t a terribly, terribly important problem. I think it concerned observationalists and people who were interested in other aspects of stellar astronomy. And then, of course, the observationalists were often very opposed. I got some very unfriendly comments about it. The type of comments you would get was: “I never thought that anybody would ever suggest that one should measure parallaxes by doing stellar interiors.” That sort of thing. Which I think indicated that they misunderstood what I really meant. All I meant was that there was a discrepancy there and that therefore it was interesting, that people should look into it.
The implications you pointed out were really what, meant to say what?
I think one of the problems was that the mass/luminosity relation that one got was different for the Hyades. It was different from stars in the field. And Hodge and Wallerstein said, “Well, if we change the distance modulus, we can’t fix this problem.” But what I pointed out was that you can’t just change the distance modulus without changing other things, too; and that although it removed one inconsistency, at least with the mass/luminosity relation, it really did not remove the inconsistency with the mass/radius relation, and that it’s only when you adjust the two so that they are both compatible that you can actually get agreement. I think they saw that point quite quickly and in fact made an adjustment to their modification which satisfied everybody. Now were slowly going back to the old Hodge/ Wallerstein idea because the models have been improved on, and were still going back to something that’s nearly .4 magnitudes.
That’s not all the way, as far as they suggest in the revision — 20% somehow (?).
It’s not quite what they suggested, but it’s more than half. Their paper was really very important in this regard.
I know that people are still talking about. My interest there you pretty much mentioned, at least that the pure theoreticians were pretty much oblivious. Or if not oblivious, they just were not concerned with a paper like this. What are your general views on the efficacy of that kind of opinion?
Well, I think there is a case for the pure theoretician. I think that all theoreticians should not be pure. I think there is room for people that are concerned with the interface between theory and observation. Sometimes the work is done by the observationalist and sometimes by some kind of theorist. It doesn’t really matter that much. But I think in a way it’s a very much neglected part of astronomy. It’s one of the most difficult parts of astronomy, this question of the interface between observation and theory. I find it one of the most interesting myself. But I do think that theorists like me who were more interested in this question of interface in comparison with observations should know as much theory of the pure kind as we can. Otherwise I think you’re very limited.
Your role is very interesting in that you were one of the few theoreticians who did respond to the Hodge/Wallerstein paper and also as we’re learning in the interview here, your discussions with Hoyle seemed to put you in the same role, as one who is trying to constantly reconcile that interface. If we would think in terms of your models and the state of evolution today, of course bringing it up to your move to Yale, we might hopefully, continue this kind of a topic into cosmology, into presently what is happening today.
Yes. Well the kind of work I do, if it is important, and, of course, I think it is — I hope it is — is not important because I bring new theoretical ideas to the subject, but because of this: it stimulates both that aspect of theory that has to do with the comparison with observation, and stimulates the observers to go and look at things that can be compared with observation. Some people don’t call that theory. It doesn’t matter what you call it, but in physics a lot of that is done by the experimentalist, and the theoreticians tend to be very abstract. But as I say the kind of theoretical background that the experimentalist would do before he performs the experiment or after. But we don’t do that in astronomy.
I know what you mean when you say some people would call this not theory. Who would not call this theory? I’d be interested to know.
I’m not sure, but for example, that Chandrasekhar would call that theory. He never really said that to me.
But he wanted to keep you on, and so he — saw the value of your work?
Yes, but I think he thought he could convert me to real theory. He thought: “Well, this guy can probably learn some real good theory and maybe I can get him to do some good work someday.” I think he looked at me more or less that way.
What about Schwarzschild? What would his attitude be?
Schwarzschild is different. Schwarzschild is a physicist. Schwarzschild is perhaps not that interested in the qualitative feature of observation. If there is a new phenomenon he wants to provide a new theory to explain it. And Schwarzschild wants to be the first one to do it. He’s very competitive. It’s a rather interesting combination in Schwarzschild of generosity and at the same time fierce competitiveness, which is interesting. It’s not often so well balanced actually as you find in him. But Schwarzschild, for example, would not have been that interested in the Hyades probably. For some reason that’s not his style, because he doesn’t really require well, no new physics is there no new mechanism is involved there to challenge him I think. On the other hand, he was interested in what happened in shell flashes and new thermal instabilities. He was the first one to calculate the helium core flash. Now, what he did was very crude, but he was the first one to do it, and in a way, you know, he did it right. I think that’s the sort of thing that he likes to be remembered for.
Is there actually new physics in that?
Well, it’s not new fundamental physics, no. But it’s a new application. No, it’s not new fundamental physics. It’s a new physical phenomenon in a way which describes the star. He worked through the actual detailed calculations. On the main sequence, everybody knows what main sequence stars are like roughly.
Okay, that’s quite interesting. What did finally bring you to Yale?
Well, I think one of the problems at Chicago had to do with the divided department and the living conditions I think we’re a little difficult. Our children were just beginning to grow. It wasn’t so bad when they were small. The other attraction of Yale, I have to admit was something that had nothing to do with science. The idea of going to a new place where you could start something new and I thought the chance of success was rather good because Yale is a well-established institution and had a good tradition in astronomy, and it’s always easier to try to build something up in something that’s well established, I would think, than in a new place.
Yet you were coming to a department which had a long tradition of doing a very different kind of astronomy than what you were doing. Were there understandings when you came that there would be computer time and that there would be support?
There were some understandings, yes. I think I had very good support when I came, and I think we still have very good support considering the situation. Generally you hear scientists complaining at Yale about how they are treated, but I think the astronomy department has been well treated.
What I’m interested in mainly in these years is the change in the department after you came, primarily now when we see so much more interest in cosmology and how this interest developed.
Well, it was clear to me when I came here that they wanted to do astrophysics. That’s what they said.
Excuse me, was this Brewster directly, or was this the physics department?
[???] was director for the physical science I think the title was. He’s a physics professor. And the provost was Charles Taylor, who was very anxious to do something about the astronomy department. The physics department may have had something to do with it. I met some people in the physics department, and I met some people in engineering and applied science. But the initiative came from the central administration. Now, I don’t really know that much about what happened before. Perhaps I was not that interested in knowing because I knew there had been many difficulties of various kinds. Several people had turned the job down. I was too young normally for the job, and they obviously had gone down the list, and while here was this promising young man, it was a bit of a gamble: “we’ll give it a try” because really they were getting a bit desperate. They figured well, they can’t lose that much. If I don’t turn out that well as the chairman, they can keep me as a faculty member. I had done some good work and other things, you know. I think something like that must have gone through their minds, you know. It was obvious they wanted astrophysics, but I did not really do anything very adventurous in the sense that all I did was bring in people that had interests that were different but not too different from mine. You’re interested in the fact that things have been moving into cosmology now?
I think it’s certainly understood that you developed a very strong center for work on stellar interiors and stellar astronomy. There’s much of the flavor of David Dunlap Observatory here.
Well, they’re two former graduates. I’m not sure there is that much.
Well, both in observation and theory.
Oh, perhaps in the combination of the two.
That’s what I meant, yes.
Although I think if you went to David Dunlap you’d find it a very different place. David Dunlap is a very, very strongly observational place and was rather weak in theory and it still is, although it’s stronger than it was.
I think that when I said that, I meant both the observatory and Toronto. Are they two separate entities?
Well, they’re at two different locations, yes. But they’re the same people.
It’s the — same department of astronomy?
The same people. But they’re at two locations. In fact, some people, like Sydney van den Bush is at the observatory most the time and not downtown at the University. Yes, well, I’m afraid this is the way stellar astronomy is going, isn’t it? The problem of stellar populations and stellar systems, the application of what we know about stellar astronomy to the larger cosmological problem seems to be one of the most exciting things we can do now. In fact, it is the way to do cosmology. You know, that brings us to what we were saying about Baade before. This is the way Baade envisioned I think the study of cosmology, and I think he turned out to be right. Obviously you have to study the cosmology the other way, study it on a large scale and study the most distant objects.
That’s the Hubble way?
That’s the Hubble approach. But you have to, in order to really know enough about these, understand galaxies. So you have to know both. In other words, it has to be a coordinated effort. Now, some departments, like perhaps Caltech emphasize the distant objects, perhaps because they have the big telescope. We have so far been emphasizing mostly the stellar astronomy aspect. But, as you say, we have several galaxy people now, and I think that’s proper.
Well, at Caltech you also have Jesse Greenstein, who’s very much involved with chemical history of the galaxy. And this sort of question here is very, important. It seems like there are more and more people getting together in different aspects of galactic evolution. Have there been any policy statements in the department over the past few years, anybody sit down and make decisions that this is what you’re going to study? How do departments evolve like this?
There is no way for me to tell anybody what they should be doing.
Oh, no, not after they come, but before when people are thinking of hiring.
Yes, I suppose you decide when you pick people. But on the other hand, you know, sometimes you don’t know which way people are going to go. Let’s put it this way: many of the most active stellar astronomers are realizing that this is a normal extension of their research, and I’ve seen the new horizon in that direction. There are a few things in stellar astronomy that still are very exciting. There are strictly stellar astronomers. But more and more it seems to me the frontier tends to be to the stellar populations in other systems. Maybe this is a natural thing in an active department, to get more interested. I don’t know. There has been no policy.
The interest I think is to see the general awareness of stellar astronomers has become more cosmological. Are you moving in this direction?
Oh, yes. And I think this is the right way to go about it.
How do you think people are moving in this direction, with the advance of theory, technique, instrumentation?
I guess it’s the advance of instrumentation and, of course, theory. But now it’s possible to study the stellar populations in galaxies with large telescopes. You can even get spectra of individual stars that are much fainter than was possible before with high resolution with Eschol spectrographs. Now we have several very large telescopes in operation, and. the theory of the evolution of galaxies, the dynamic evolution of galaxies, has progressed enormously in the last few years.
I would imagine that Ivan King and Richard Larson are very important.
Ivan King is very important in that direction, Larson and Ostriker, Jim Gunn at Caltech. These people are just changing the subject.
Right. “Changing the subject” in the sense of realizing the cosmological significance of local study, of a local group of galaxies, the evolution of galaxies?
Yes, and they’re also studying galactic structure and the problems of the dynamics and the evolution of galaxies in considerably more detail. It started with perhaps with these theories of spiral structures — you know the C.C. Lin density wave theory.
Do you feel that really started things going?
Well, no, perhaps not. That came a little earlier. But then the dynamical theories like the problems of stability of discs, this problem of the massive halo, which is connected to it, that Ostriker brought into astronomy and that Bardeen studied in very beautiful work actually. All this was very recent. And then the problem of understanding the evolution of qalaxies as a complete system. Larson has contributed an awful lot to that. Gosh, people weren’t thinking that way at all a few years ago it seems to me.
What caused that change and does this have anything to do with the evolution of the symposium that you’re involved in later this spring?
Yes. Well, I think it’s partly, you know, that stellar evolution now has changed. I mean in 1962 or ‘3 so little about stellar evo1ution had been done. And now look: practically all the phases have been covered. I mean there are so many things, but it’s more or less filling in gaps here and there, some of which are important holes, but now that we really know all these things, we can integrate all this. For example, one of the things we’re doing now — and I’ve been thinking about this for years, but I didn’t take the time to do things — is to put together all the information about stellar evolution and make synthetic models of galaxies and so forth. Now, of course, this is the base of the reputation that Beatrice Tinsley made; and I think there are other people who work on this now. Peter Biermann, the son of L. Biermann, in Germany, and I guess some other Princeton people — Gott.
If you feel that you’re ready for this synthesis of let’s say the history of the galaxy by collective study of the populations found within it, is this part of the reason why the symposium is being called now?
Yes, Oh, I thought the time was just right. I mean I started to think about it in ‘75 when I was at Caltech. And I knew that Beatrice Tinsley was going to becoming to and I was myself more and more interested in that aspect of stellar evolution.
You’re certainly working in that direction.
So that’s what we’re doing now to a certain extent, although I don’t think I’m going to push too much farther than what I’m doing now. So I thought it might be nice to have a meeting here on the subject Yale, and that’s how it started. And so I mentioned that to Larson, who discussed it with Beatrice, and then it evolved into the present set-up.
What were the main questions that you want to ask? I mean can you pretty much get that from the schedule of speakers or is there a bit of capriciousness in the set-up depending on who will come and who won’t? I mean what kind of reactions to the meeting have you gotten?
The reactions have been good. Well, the only major figure that’s not really coming — probably because he doesn’t want to come — is Sandage.
Sandage was certainly invited?
Oh, yes. In fact, he was to be the main speaker. He accepted at first and then he turned it down.
Do you know why?
Oh, because he’s too busy, I guess, and he doesn’t really like meetings.
But this is an element of really great importance as opposed to the relative effectiveness of two different ways of studying the same problem, isn’t it?
There’s a personal question there. He doesn’t care too much for some of the people who are organizing the meeting.
Well, do you have anyone else representing the Hubble side you might say?
Actually when you look at it, at least it’s a bit biased. You know, the people who have been turning toward this problem of the evolution of galaxies and stellar population are the people who think it’s important. So it’s definitely the California axis. There are some people at Princeton who weren’t very happy because they didn’t figure it was big enough, but then Ostriker was given this time to make some opening remarks so that he has a chance to say anything he wants really there. I should tell you that I really had nothing to do with the organization of the meeting. I don’t mean by that that I didn’t approve of it. I think it’s a very good program. But I really was not asked.
It was Beatrice Tinsley and the general names on the list.
It was these people, the Scientific Organizing Committee, and actually most of the important decisions were made by Beatrice with the help of Richard Larson. And I think the Scientific Organizing Committee probably had a chance the rest had a chance to give their opinions about the meeting. But it evolved in such a way that I just essentially concentrated on the local arrangements, and that’s the way it goes.
You have de Vaucouleurs in the first session. This would be pretty much on the Hubble side of the study, the study of stability of c1usters classification, and that sort of thing. Is the controversy between de Vaucouleurs and Abell as to the reality of the super clustering — is that still an active question amongst cosmologists?
I don’t know. I wouldn’t he surprised, but I really don’t want to comment. I know that Abell is coming. Actually the participants are going to be a very varied group. There has been no exclusion in the sense of people who are actually working in that general area. There’s going to be a very fine distribution of people.
Has Schwarzschild made any comment about this?
Schwarzschild is not coming. I don’t know what Schwarzschild thinks really. Spitzer is coming, though. So that’s something very good. And a number of the younger Princeton people. I guess Ostriker will be there and Gott and some of the younger people like York. So for a while we thought we might not get much of a Princeton representation, which would have been a pity.
What about Harvard and George Field and that group up there? When they called a local group meeting on the question on the openness of the universe, was this a well thought out action on their part? Are they interested in the problem?
I don’t know. I really don’t know much about this meeting. Is it over now?
Yes this was a meeting that was late last year. James Gunn was there and Beatrice Tinsley and Peebles.
Yes, I think Beatrice was probably invited. I don’t know. Maybe it was a good meeting. I don’t know.
I’m thinking in terms of the interest in the problem.
I think this is a good idea. The local group is obviously the focus of all this. Most of the galaxies that we can study and that we are interested in are in the local group.
When I said local group, actually I meant the local group of the schools.
Oh, you don’t mean the local group of galaxies. Well, we have a neighborhood meeting coming up.
On the distance scale?
On the distance scale.
Will this address similar problems? It sounds like it.
I guess so, yes. It will. That’s the fifth neighborhood meeting, yes. Gary Steigman set it up because he wanted a field in which we would have enough Yale expertise, you know, and that would include the astrometry types like Bill van Altena and Bob Hanson, who have been working on the Hyades, as well. I think he wants to have some contributions, for example, for the ages of the clusters and or the people here in the department that has competencies in these other things. I don’t know if we will have anything new to talk about. This is a problem. But I think it’s just a good excuse for meeting with neighboring astronomers.
Right. As far as ages, I know that you dealt with ages in clusters, and I remember a talk that you gave once about calibrating ages against radioactive decay techniques, and recently there’s been quite a serious re-calibration of the decay rates of some basic substances — I’m not too sure exactly which decay rates it was. I was wondering if you had any thoughts on that. The implication was that the universe was twice as old as it was previously considered, something on the order of 20 billion years now.
Well, I don’t know what to say except that I really look only mostly at the traditional techniques of stellar evolution, and we have this new grid. We’ve had the new grid now for a few months, and one of the uses for it is to recalibrate the globular clusters. And I was hoping that we might have some of these results at least in a preliminary way ready for the meeting here. The tendency from just looking at things in a preliminary way seems to be for larger ages, also on the basis of our calculations. But it seems to me that the whole problem of determining observationally the turnoffs is to be particularly reconsidered. I think the data that we have is inadequate, and we’re going to have to use all the new techniques — Kron, cameras and other devices.
Is this a problem of narrowing the main sequence?
Yes, you really need to narrow the main sequence to get the position of the turnoff, the shape and position of the turnoff much more accurately than we have it. Otherwise, we can’t. You know, we don’t have the accuracy to talk about it.
To really follow an evolutionary track or the isochron.
This you see as one of the major problems today. It’s really an observational problem.
Yes and actually determining the age of the universe is really one very good way to get at the model of the universe. The Hubble parameter comes in. That’s probably a better way to determine it. For example, if you can determine the density of the universe and the Hubble parameter, you can determine, without looking out. And. I think perhaps it’s worthwhile now for people to concentrate on trying to do these things locally.
Well, the age and the basic two fundamental cosmological constants can also tell you pretty much how much time there was available to build up various elements from the hydrogen in the Original big bang, and. I imagine this has quite a bit of significance for your work on stellar models and globular clusters and that sort of thing.
What do you think is going to be done in this realm in the near future? What are the big problems now?
You mean the problem of the helium abundance?
Well, you know, it’s a very funny thing. The problem hasn’t changed for the last 20 years, and people have been kicking them around, and they’ve really not done that much about them. And the real way to solve these problems is to study sub dwarfs, binaries, and observationally try to get good masses, distances, so you can really get the mass/luminosity relation. That’s how you can get the helium abundance, or perhaps looking a bit into the infrared and see if you can see some helium lines.
Well, how well do you think the helium abundance is known?
Most people seem to think its high compared to the old values. Let’s say about 20%, maybe 25 by mass. But the position of the main sequence: we have to solve this whole problem of convection in late type stars. We really haven’t solved these problems. We just forgot about them for twenty years and now we’re back at them, and now we realize we have to solve them after all.
Which brings back the whole question of technetium, as you said, the mixing?
Yes, there are really some exciting/things there, what happens in intermixing processes in stars. We don’t understand. And they are related with the nucleus synthesis and so on. That’s really the major thing. And that maybe important because of the ages, too, because it would modify the ages.
Do you have any feeling at this point as to which side of the question you feel like taking?
Oh, I don’t take sides on such things. I really don’t care, to tell you the truth.
Do you have any sense of how the community is reacting?
Oh, I think the problem is important, but I don’t care which way, it goes. I don’t have any philosophical feeling or ideas as to how the universe should be. That is something that doesn’t affect me at all.
Well, we’ve covered everything I think I wanted to ask you at this point. You indicated that you have no particular ideas about John Eddy’s work, our variable sun. The one question I wanted to ask you in that regard was simply: do you think this is a question that can be examined with very accurate stellar models to be able to detect these very small variable outputs?
Yes, I imagine that solar physics is going ‘to become very important from the point of view of stellar structure again. People are going to study the sun in much more detail.
Do you think he’s found anything truly new? I mean the concept of the variable star has been with us for a long time.
Yes, why not? No, I think he probably has, and all these pulsation modes that are observed are very important things. They may not all be right, because in fact there are some discrepancies between various investigators and so on.
Yes, as there always are.
So there obviously are some things that are wrong.
The tie-in with the neutrino problem — and this may be completely off — but some people might think that the neutrino flux variable is a function of what is happening in the interior of the sun, which if it is known as a variable star might just not be putting out very much right, now. Do you have any thoughts on that?
Oh, it’s quite possible. I don’t know if you saw the last article I think by Bahcall and Davis — it was in Science — in which they give the curve of the neutrino flux as measured fight from the beginning of the experiments. And it looks like the beginning of a sine wave, and a lot of people noticed that I think. And apparently there are new points now which go down just in the right way. Now, the period is something like a year and a half, and John Bahcall gets very excited about his, very upset, because he said, “Well, look, the thermal time scale in the interior of the sun is much longer than that.” So nothing can happen at such a short time scale.
By the thermal time scale, does he mean mixing...?
Essentially it’s the same as the gravitational time scale, the sound time.
This is the reaction time.
Yes, the thermal response of this. But things may not be in equilibrium. You may have non-equilibrium phenomena in there. Yes, I think there are obviously mysterious things going on. I would like to think that the sun is variable, but this is just speculation. If you ask me, I would bet this is what’s happening, that there are some perhaps cyclical instabilities that are causing motions, perhaps some diffusion like processes inside the sun, which may be responsible for the problem we have. But this is all speculation. I don’t really know the answer, but I think more work should be done in that direction.
So he certainly has created a very real awareness.
I think it is a real interesting topic. All these things are going to be important, though, for the ages of the clusters. Anyway the tendencies are you mix the interior of the sun or a star, you’re going to make the ages longer. And so it’s possible we may see the ages of the clusters go up.
You also with mixing sort of spread out the concept of populations, which has been occurring in the last few years, hasn’t it? Population distinctions are nowhere as distinct as they used to be?
That’s right. This question of the population being tied to the chemical composition and metallicity is breaking down really. I don’t know if you’ve seen this paper that Bob McClure and I just finished — we have a preprint on this actually — where we find two clusters, actually 47 Tucanae and NGC 2420, which have the same metallicity. But one belongs to the halo population; one to the nuclear core population.
Well, the nuclear bulge you know: 47 Tucanae. They have the same metallicity and they belong to the two populations, so you can compare their color/magnitude diagrams, and you can show that the color/magnitude diagrams differ not only in their ages, as you might expect, but there is something else that differs.
You were talking about the recent paper by you and Bob McClure.
Right. What we find is that there are differences even though these two clusters — one which belongs to the old disk population, the other to the nuclear halo population has the same metallicity. They have differences which cannot be accounted for on the basis of age differences alone. So we looked for what other causes there might be for the possible parameter, and we find it with helium. You can explain it in terms of helium difference in the sense that the nuclear cluster — 47 Tuc has higher helium abundance. Or CNO element abundances, or say nitrogen. People seem to like nitrogen. It would mean that NGC 2420 has high nitrogen abundance. And essentially what we say is: “okay, these two clusters have roughly the same metallicity but they have gone through very different histories of enrichment. “Now, the collapsed model of the galaxy of Larsen, for example, predicts a gradient in composition, as discovered, in fact, by James on the plane of the galaxy.
Yes, this was his thesis.
It predicts that, and it also predicts that the stars with the same metallicity, belonging to different populations, have reached that level of metallicity by different processes; so if you lumped all the heavy elements in one bag, you can call them metals. They have the same metallicity. If you look at the relative abundances of the heavy elements, they might be different from system to system. For example, you would expect that the disk population objects, which have been enriched to a great extent by planetary nebular ejection, would be rich in nitrogen NGC 2420 then would be expected to have larger nitrogen abundance than a globular cluster which was formed presumably in the very early stages of the galaxy, and which probably formed all its heavy elements through supernova or some super massive object exploding or something like that, some objects of these kinds. So this is all consistent with that picture.
So you’re beginning to spread out the concept of population within the class of globular cluster itself.
That could well be the difference between the nuclear globular clusters and those of the outer halo and also it looks as if in the galaxy there is this composition gradient, which is a function of radio distance in the plane, but could also be a function of latitude. We know it’s a function of latitude since the far out things in the halo are more metal poor than those that are near the center. So you have a rather complex picture there. And the age composition correlation is not a one to one relationship. It’s one to one for each distance, each point away from the center, but not in the galaxy as a whole.
One final question on galaxy evolution. Astronomers are working, of course, on a collapsed model; and when they try to compare relative ages, they’re working from the standpoint that different positions in the galaxy indicate different ages. One different approach — slightly different, but not different enough I think too be significant — would be the, study of Minas of different orbits. And I know that this work has been done for quite some time by Preston and by others. How well do let’s say studies of ages of Minis of different high and low galactic orbits fit some of the composition differences that you’re finding, or is there any correlation yet found?
I’m driving at the possibility of a test for the initial assumption of collapse as opposed to Ambutsurmian’s idea that the centers of galaxies explode. This is the direction of the evolution of a galaxy, in other words.
Well, of course, there is the work of Eggen, Lynden — Bell and Sandage on the collapse on the basis of the orbits of stars of different ages and compositions. Now, the Minas I guess would be very useful because they’re particularly bright and you can spot them way out there. Can you detect differences in metallicity, though, between Minas?
This is what I didn’t know. I was asking you.
I don’t know either.
Okay. This might be a good question to ask Preston.
Don Fermi has a very special interest in Minas, and he might be able to tell you that.
Right now this isn’t a historical question, but it just came up that there might be a need beyond the Eggen/ Lyden-Bell/Sandage work for confirmation of the collapse process.
I think I see what you mean. Obviously their model has to be revised, but I’m not sure exactly how you would go about it. I know that Bob McClure is very interested in those intermediate age clusters like NGC 2420. There is another one that Terry Forrester and [???] are working on now — NGC 2506 — which was studied by Shapley, which appears also to be metal poor and seemed to be nearly a twin of NGC 2420. Apparently there’s a whole string of those, and those by their very presence actually pose a very serious problem for Eggen, Lynden-Bell and Sandage. In fact, they don’t follow in line with the theory.
That was the problem?
That was the problem, but I might mention something from the historical point of view that might interest you: when McClure became interested in studying that cluster he knew that these clusters aren’t very rich, so you have to worry quite a lot about membership and the problems. So the idea would be to have proper motion studies of these clusters. So when I was at Hale I looked into their file to find whether they had old plates of these clusters so that Bill van Altena could get proper motions and eliminate none — members, and I did find some plates. But the interesting thing about it is that those plates were taken by Shapley with a 60-inch around 1910 or something like that so they’re good for proper motion.
It couldn’t have been quite that early. He went there in 1913 or 1914. But that certainly is the range.
It was before the First World War.
Yes, It certainly was that.
Anyway I looked at the observing book, and Shapley was systematically observing these clusters one after the other NGC 2420 and NGC 2506 and all that. But did he know that they belonged to a special population of c1usters — these old galactic clusters? Did he realize the importance? He couldn’t possibly, I guess, but he would have later on. But it’s interesting that he was observing them the same night.
That might have been a little serendipity. He was a very creative fellow. He certainly was working on globules at that time. That’s, a fascinating piece of information.
I don’t know what his motivation was for observing this cluster.
Was he taking any crude photographic, photo visual pairs? Was he trying to work of let’s say color indices for the stars or straight magnitudes?
As far as I know, they were just plates in one color.
Because I do know that after Hertzspring in 1911 came out with his first extensive cluster diagram, by that time Shapley was at Mt. Wilson and they did become very interested — Shapley and Russell — in cluster work. Exactly how they would go about doing it, I’m not sure. Were these Cassegrain plates to your recollection or were they prime focus?
I don‘t know.
Well, that can be found out. The idea would be that he was simply taking large-scale plates to do photometric work.
Yes. I guess so.
Very long exposure?
Yes. I don’t know how faint he could go.
It’s an interesting piece of information. At least you’re going way back for first epoch plates. Have these membership studies been made?
Yes. Bill has done 2506, I think. He’s done the measuring and I think the reduction has been done, but you know it went through PDS at Berkeley and all sorts of processes. You might ask him. I think his young lady there was working on that.
Well, you’ve managed to bring in just about everybody involved in the department in one way or another in galaxy evolution. That’s very good.
Well, we’re all involved in different ways; Dennis Butler is really interested in very similar problems. He’s a Spectroscopist, so he sees things like Preston might, or Kraft. He’s been taking spectra of the background of the globular clusters. He’s been trying to find information about the very faint star population. He looks in between the stars instead of actually looking at the stars, and he’s been doing very interesting things.
That’s very interesting. Might get some idea of the blending effects? The spectra of stars of solar type?
Yes. He’s trying to look at the turnoff population and things like that, and I don’t know exactly what he’s doing, and he’s doing that with the 4-meter, you know, so it’s really faint. There are very interesting things going on here. You should talk to Gus Oemler, who’s working on clusters of galaxies. He’s interested in tidal interaction between galaxies.
Yes. Well, then that gets back to Ivan King’s work again, all of his dynamical work. Ivan King is one person that we certainly want to talk to.
And I’m hoping that during the time that he’s out here if we’re not able to get out there first, that we’ll have some time to talk to him. Actually we’ve gone over a tremendous amount of material, and I will say: all of it sounds find. I really thank you for the session. Again I’d like to repeat for our use only.
 M. Schwarzschild “Structure and Evolution of the Stars”, (Princeton, 1958)
 On the revision of the distance to the Hyades, 1966 PASP
 He didn’t attend
 He didn’t attend