Beatrice Tinsley

DeVorkin:

Could you give us your impression of the outcome of the Conference on Cosmology and also give us some idea of the history of the developuent of the Conference. Who had the initial idea to have the Conference, and how was it originally organized?

Tinsley:

I understand that the original idea was Pierre Demarque's. I wasn't here at the time, and when I came to Yale, they invited me to be the chairman of the organizing committee. So we put together a list of people whom we would like to have on the organizing committee and in particular people who knew a lot of others and who were experts in the field. I should say it was not a conference on cosmology. It was specifically on the evolution of galaxies and stellar populations. It was very relevant to cosmology, but we were not discussing cosmology as such.

DeVorkin:

The idea, though, seems to be that it's becoming more and more relevant as time goes on, Is this one of the reasons for the Conference?

Tinsley:

We had in mind that a lot of particularly important questions were being asked at the time and that maybe some sense was being made towards generating answers. In particular, what is the origin of the Rubble sequence of galaxy types, That was one of the key questions we had in mind at the time we were thinking about the Conference; and what poduces galaxies- in the shapes they have; why are there observed correlations between morphological properties and colors; gas contents and other indicators of stellar populations? And I must say that as time went on, it became clear that the subject was a great deal more complicated than that.

And I'm glad that it worked out that way. It should be like this with conferences. We originally had in mind more or less the answers that we wanted to put in as the meeting went by, and then we found that by the time the meeting came, these were the old-hat ideas. They were the zero order approximations to the right answer, and that what people were going to say were complications and remarks that really made us think again that we were nowhere near a clear understanding of galaxies.

DeVorkin:

Do you recall any of the remarks that were of most interest to you as far as being new? Not necessarily new ideas, but things that woke you up to the present status of knowledge. What were some of the most poignant things that occurred?

Tinsley:

I think one of the clearest things is that a large number of galaxies do not evolve as closed and isolated systems; that interactions among galaxies merging with galaxies — cannibalism, that kind of process — is really very effective in a lot of cases.

DeVorkin:

How long has this idea of cannibalism been around? I know that in your article that you wrote that just came out in PHYSICS TODAY,* you certainly had H. Arp's two good examples of one galaxy eating another galaxy.

Tinsley:

I'm not sure that Arp would have interpreted them in that way.

DeVorkin:

He wouldn't have done it himself that way.

Tinsley:

I don't think so.

DeVorkin:

So this is a fortuitous thing from his catalogue?

Tinsley:

Yes. I couldn't be exact about the history of the subject, but a lot of people have discussed the effects of interaction among the galaxies, mass loss and mass exchange between galaxies.

DeVorkin:

Of course, more interested in your impressions now. Do you recall your own first impressions about this non-evolutionary mechanism, if you can call it that?

Tinsley:

I had not personally thought about it until it impinged on my own work of evolutionary corrections in cosmology. That was at the time that J. Ostriker and S. Treiuaine realized that galaxies merging with each other in large clusters could mean potentially a very large evolutionary correction for cosmology. Of course at the time when they wrote about it, it was evident that there was a past history of people working on the process of dynamical friction and the merging of galaxies.

But this is where, it hit my own thinking, as another correction in cosmology. Now, of course, it's evolved into a very interesting thing in its own right, particularly, as Ostriker shows, that this process can explain a large number of the observed properties of cD galaxies.

DeVorkin:

Do you think it's at the point now where you can account for variations in qo in terms of dynamical friction in galaxies eating other galaxies?

Tinsley:

It isn't a question of variations in qo. It's a question of not being able to determine qo. We do not have a quantitative value for this correction yet. Ostriker is trying to point out how it's closely related to what Sandage calls the Bautz-Morgan correction, a statistical correction for galaxy magnitudes based on the kind of cluster they are in. And in a sense this is an empirical correction for that effect. As yet we don't know if it's the exact correction done in the way it should be, but that's not impossible.

DeVorkin:

Is Sandage working on this, too, then?

Tinsley:

I'm not sure whether he is now. This is in his past work on the Hubble diagram. He has developed this quantity called the Bautz-Morgan correction, which is an empirical correction.

DeVorkin:

Ostriker is the one that is working primarily on this then.

Tinsley:

Yes.

DeVorkin:

This has some relationship to collision events, doesn't it?

Tinsley:

Certainly. Ostriker and M. Hausman, a student of his, are working on the published paper for the Ap. J. which is what Ostriker's paper for the Conference is about. That will be by Ostriker and Hausman.*

DeVorkin:

What about the types of collisions where you have two equal galaxies that somehow strip each other of their interstellar mediums?

Tinsley:

This is something else, something that Toomre is talking about and that Ken Freeman referred to on the origin of ring galaxies, for example.

DeVorkin:

Right. This is not a related situation where you're talking about a joint galaxy eating a small one.

Tinsley:

It's a process that happens on a rather different time scale. The dynamical friction time scale can be very short, as Simon White has shown. It can be as short as l0 years, but the other process is more on the time scale of 108 years, which is just the galaxy passage or the passage of two galaxies in a rather rapid orbit.

DeVorkin:

Do you really feel then, moving on in the direction of dynamical friction, that these problems will eventually give us an empirical handle that will give us a better understanding?

Tinsley:

It's too soon to say. The corrections that you need have to be so exact that if you want to know the value of qo, you have to remember that any systematic effect which is on the order of a few percent per billion years changes qo by one,. And likewise a similar effect, if you have a selection effect of a few percent in magnitude at a red shift on the order of 1, you change qo by 1. The sensitivity is enormous. And its not at all clear that these things can be done accurately enough to get a useful answer, I think the emphasis just has to change from trying to find qo to trying to learn about galaxies.

DeVorkin:

I think this is the essence of what I want to be able to better appreciate, and somehow it seems to be bound up with having this conference on galaxies, at least at this particular time. A year or so ago when you came here, you seem to be pretty decided that the universe was open, and therefore you had a handle on qo. But things have changed.

Tinsley:

It was based on different sorts of evidence. If you accept the simplest sort of cosmological models, finding qo is equivalent to finding the density of the universe, It has been clear to me anyway for years that

*J. P. Ostriker and M. A. Hausman, 1977 Ap. J.(Letters) 217, Ll25. M. A. Hausman and J. P. Ostriker, 1978 Ap. J. 224, 320.

 

qo has not been known as determined from the deceleration itself. Finding the density is something which is very much easier. It's based on essentially local data in a cosmological sense, and it's possible to get I think a fairly good handle on what the density is. And from nearly all indications, the density is less than the critical value that would be required to close the universe.

DeVorkin:

Well, it's been that for many many years.

Tinsley:

It's still true.

DeVorkin:

But people are constantly looking for hidden mass, that sort of thing. But what I'm really trying to get, at least in this particular session with you, is a feeling for your own impressions about the growing applicability of studying galaxies for cosmological answers, answers to cosmological questions.

Tinsley:

Let's call cosmology not just finding the value of qo, but understanding how things originate in the universe and how they evolve. And then I think there's another extremely important question that was discussed a lot at the meeting, although it was not specifically a subject for discussion, which is how stars form, at what rate and in what conditions. Some of the problems are, for example: how do you get stars in elliptical galaxies; why do some elliptical galaxies have very bright ultraviolet colors. And this seems to be showing up also in studies of clusters of fairly modest red shifts on the order of a half or so.

But some clusters have anomolously blue galaxies that must have very vigorous rates of star formation; much faster than one sees in morphologically similar clusters that are nearby* And the implication is that these galaxies were making stars very vigorously at that time, but the equivalent objects now are not; so something happened to quench the star formation that is not understood.

DeVorkin:

Even more vigorous than, let's say, the Magellanic Clouds?

Tinsley:

Possibly. I don't think it's known that accurately yet what the colors are and how they translate into a star formation rate.

DeVorkin:

I see. But we do think, do we not, that if there was an original population, it was a very energetic phase.

Tinsley:

Oh, yes. But one doesn't expect to see that at a red shift of a half but rather at red shifts of several. At red shifts of several they have not been seen. Presumably they're too faint, too far away. But at red shifts of around a half, a number of workers have. Independently, Richard Kron at Berkeley and Oemler and Butcher have discovered very blue clusters at modest red shifts.

DeVorkin:

This was sort of an unsung topic at the conference?

Tinsley:

It came up in Spinrad's talk and in the discussion afterwards, that one must understand what's going on in those galaxies. Star formation was also discussed by Larson and by Freeman. There were a number of problems there. One of the things which came up there which is new is that

*H. Butcher and A. Oemler, 1978 Ap. J. 219, 18.

there's very good evidence that the initial mass function for star formation is not a universal quantity. That's a disappointment. Had it been something universal or had there been no evidence to the contrary, then one very very important unknown parameter in galactic evolution is eliminated. But now there is good evidence for a variation in the mass function so it has to be determined.

DeVorkin:

Is this from galaxy to galaxy or within galaxies?

Tinsley:

At least within galaxies. Freeman and his collaborators have shown that certain globular clusters had very different mass functions from each other. But some of the bright clusters in the Magellanic Clouds have different initial mass functions from each other and from the solar neighborhood. Larson pointed out evidence that galaxies have different mass functions in different regions of star formation, which is also seen in our own galaxy.

DeVorkin:

Is this an enrichment problem, an angular momentum problem, or density waves?

Tinsley:

One doesn't know what it is. It's presumably something to do with the physics of the gas clouds that turn into stars and under what conditions that happens, I don't think that the physics is well enough understood, at least by me, to speculate on it.

DeVorkin:

Well, does this have something to do with some of Rees's suggestions about collapse, the nature of the galactic halo?

Tinsley:

In principle it would if one understood all that was going on there; If one understood exactly what drives different mass functions in djfferent star forming regions now, one could perhaps apply the same physics to the early stages of galaxy formation. But that's premature at the present time, it just says that we have no right to assume a constant mass function everywhere.

DeVorkin:

That makes the picture quite a bit more complicated.

Tinsley:

It certainly does.

DeVorkin:

How do you feel about that? How does that affect your particular work?

Tinsley:

It says that the things that I published beforehand on the models of galaxies are nothing but the first order of approximation, maybe a zero order of approximation. Because the hope was that one could assume that the mass function was constant everywhere, and then the main variable is just the rate of star formation — the time scale for galaxies to make stars. And that sort of idea provided a reasonably consistent explanation of the whole Hubble sequence, the major dominant properties of it; but now we realize that that's a very oversimplified picture.

DeVorkin:

How do you think you're going to derive the next approximation now that you have a handle on the more complete picture?

Tinsley:

It's probably time to wait around and concentrate on something else until studies of star formation itself have given some answers. It may be possible to get a few clues by computing the predicted colors of galaxies, the properties of galaxies, with different mass functions and different rates of star formation, comparing with the data. But on the whole I think detailed studies of stars in regions where they form have to be concentrated on now.

DeVorkin:

These feelings came up during the course of the Conference in talking with other people?

Tinsley:

Certainly I was aware of the problems beforehand partly because I'd been talking to the participants beforehand, But it seemed that something that would have been a rather radical suggestion and a surprise a little while ago, by the end of the Conference was accepted by everybody. Nobody raised any objections to the possibility of strongly variable initial mas functions. The general feeling was: "Oh, well, here's something else we've really got to consider."

DeVorkin:

It makes it very difficult I can see. I mean just from what I know of Salpeter's early work in the luminosity function where he had to assume some very very uniform things at the outset.

Tinsley:

That was just on the basis of the solar neighborhood, and of course the hope was that if you could determine by counting stars exactly what the mass function had been in the solar neighborhood, then you could use that everywhere. That may be a pretty good first approximation, but it's not the whole story.

DeVorkin:

Yes, so the picture has gotten very complicated.

Tinsley:

That's true.

DeVorkin:

And you wouldn't venture to guess in what direction one would have to go? You're talking about star formation rates. That's the most important direction?

Tinsley:

Rates and the mass distribution of stars when they form.

DeVorkin:

And once these are better understood, what will be the direction that you'll be working in then?

Tinsley:

It would certainly be interesting to know what these imply for the whole evolution of galaxies. As you change the mass function, you change the chemical evolution. Different masses of stars produce different kinds of chemical elements, and that ties into some other things that were discussed a lot at the Conference, which is that the relative abundances of chemical elements seem to vary throughout galaxies and within galaxies and among galaxies in different places. So one is not seeing completely mixed products of nucleosynthesis in the same proportions everywhere.

DeVorkin:

Is this ever thought to be an accretion phenomenon?

Tinsley:

Accretion would probably only dilute the chemical elements. It wouldn't change their relative abundance.

DeVorkin:

What about simply a metal to hydrogen ratio?

Tinsley:

It would change that, yes, but we're talking about metal to metal ratios, or things that are not really metals but carbon to nitrogen or oxygen. And then this is tied up then with what kinds of masses of stars do you form, what are their lifetimes, how well mixed are the products of nuc1eoynthesis?

DeVorkin:

In James Gunn's summation he said that many problems had been defined at this conference, at least, and this is the impression that you're giving me. That's a very exciting thing.

Tinsley:

Yes, that seems to me to be a more exciting thing than to give the answers.

DeVorkin:

Well, you're always suspicious of answers.

Tinsley:

Yes, exactly.

DeVorkin:

I do want to ask some mechanical kinds of questions dealing with the formation of the Conference itself. You were not in on the initial idea. You had not been here on the start, as you mentioned. But you had been here for quite some, ti'me, apd you were the, chairman of.

Tinsley:

The organizing committee, the scientific organizing committee.

DeVorkin:

And you did deal with the participants?

Tinsley:

Yes.

DeVorkin:

We would be very interested to know your experiences. Was this the first conference that you had been involved in like this?

Tinsley:

Yes.

DeVorkin:

What are your impressions in organizing conferences like this then from the mechanical standpoint?

Tinsley:

It's been a very great deal of work and a considerable amount of pressure, I think the main reason being that we decided we must limit the numbers. Otherwise it would have been impossible to have a fairly intensive conference in which people could just get up and talk and discuss without always having to come to the front and pick up the microphone and so on.

So we really had to limit the numbers. And then you run into the problem that there are far more people who want to be invited than you possibly can invite, and it's very difficult to make decisions to reject people, I think we had an excellent list of participants in the end. There were many excellent astronomers in the field whom we invited who were not able to come, and I was certainly very pleased with the quality of people we had in the end, most of the people that one would have wanted with some notable exceptions.

DeVorkin:

Well, would you mind talking about those exceptions? (pause) I'd be very interested to know this from the standpoint of the types of people who represented certain lines of research.

Tinsley:

Every speaker we invited accepted, and that was a very nice thing, with one exception.* We hoped Alan Sandage would come to give the introductory talk, but he doesn't like conferences. He very regretfully declined in a very friendly way, and I'm not at all surprised. I know he dislikes conferences.

DeVorkin:

You feel that was the reason; there wasn't the idea that here you do have definitely a conference on galactic evolution, on the evolution of galaxies, with very strong cosmological overtones.

Tinsley:

Oh, no, I don't think so, because originally he said he'd be delighted to come and tell about his new work with Visvanathan, which was reviewed anyway by Sandra Faber. And then he declined more or less on the basis of disliking conferences in general, He's a good friend of Pierre Demarque, and there's no ill feeling, But then we were very lucky that Ivan King accepted immediately to replace him as the introductory speaker, and Ivan gave a really superb talk.

DeVorkin:

Yes. Well, it's not so much a question of personal friendships. We're interested in the historical question of differences in philosophy of how to go about solving cosmological questions, either dealing at global distances and looking for global effects.

Tinsley:

Well, this was not a conference on cosmology, and I don't think that could possibly have been any sort of motivation. It was a conference on galactic evolution and what he was about to discuss was on galactic evolution.

DeVorkin:

Were we incorrect in assuming that there was an underlying theme as far as applying stellar evolution and galactic evolution now to cosmological questions, that this was a meeting that could have been formed partly to determine just how applicable stellar evolution studies and galactic evolution studies were to cosmological questions?

Tinsley:

No, I'd say that the emphasis of the meeting was that we were trying to understand galaxies, and it came up very much as just a byline that this would be relevant to determining the cosmological model. But it was by no means an underlying theme. I dont think it was uppermost in anybodyts mind.

DeVorkin:

We're looking for these kinds of undercurrents because there is constantly this kind of question.

Tinsley:

I wouldn't call it an undercurrent. It was obvious to anybody who knew about the subject that that would be applicable, but it was not discussed as such.

DeVorkin:

Okay. Well, let's get back then to the mechanics again. In choosing your original list of participants, what were your criteria?

Tinsley:

People who we felt had contributed very substantially to the study of galaxies and with a particular emphasis on stellar populations. It's such a very wide field that if you just say galaxies, you could include

*See p.9 & 15 for another regret.

 

almost anybody, all of the X-ray astronomers even, for instance, and most of the radio astronomers. We looked at the people who had particularly studied the evolution of stellar populations, the nature of stellar populations, and other things such as radio astronomy which would be relevant to this. A few experts of nucleosynthesis, which is relevant; a few people in stellar evolution which is relevant. That kind of person.

DeVorkin:

I had the feeling from talking to people during the Conference after people had started looking at the questionnaire that their reaction was that they wanted me to realize that I was polling a very biased sample of astronomers. And in talking to a number of them I didn't get a very clear impression of what they meant by biased, and I' was wondering if you would be able to clear that up.

Tinsley:

I wonder if they meant that they really had the conventional views on most things. We did not have people who are against or "hold unusual" the usual theories on cosmology here. We just didn't want to get into arguments about whether, for example, red shifts mean the universe was expanding. We wanted to discuss galaxies as such. So you probably didn't find anybody in there who answered your questions about relativistic models not being applicable, who would put strongly negative. Some of them might have had some doubts, but you wouldn't have had people who thought that quasars were ejected from the center of galaxies.

It was probably a fairly conventional group in that respect. I think that's probably what they meant. I should mention somebody else whom we invited who was very sorry not to come and who wrote a very nice personal, letter. That was J. H, Oort. He would have been a delightful person to have had and we could have asked him to have given a special address. But he sent back his sincere regrets and asked me to convey that to the organizing committee. His letter said that it looked like an exceptionally interesting meeting and he was very sorry not to attend, and would I please convey his regrets to the organizing committee.

DeVorkin:

Were there people who wanted to attend and participate who were not allowed to, that expressed any disappointment to you?

Tinsley:

Yes, there were a few, On the whole I made up, with the help of others, what I thought was a sort of polite and clear form letter essentially to the effect that almost everything anybody does in astronomy could be construed as relevant to the evolution of galaxies, Galaxies contain all of astronomy that there is in a way. And on the whole those people that I decided regretfully we had to send regrets to were people whose work was really marginally relevant to the subject, and I think that the couple or so who called back and said they wished they could be invited more had the motive that it looked like a good place to come and talk to other people, rather than that they were actually interested in the subject under discussion, So that was the main criterion.

Also, in discussing the criterion for selecting people, we realized when we first put together a list that it contained mostly the pundits the professors, the people we'd heard of who'd written a lot of papers. So then we went out of our way to invite their students and postdocs if they wrote and said, "Could we ask So-and-So?" So we did also have young people whom we wouldn't have heard of but who these people thought were coming into the field.

DeVorkin:

Right. I especially liked the format where you had the people who gave the introductory speeches for the session or the review papers you might call them, and then really the other people who participated either did it from their seats or as a relatively informal thing. It seemed to work very nicely, Did you like that format? Was that something that was decided upon by you?

Tinsley:

Yes, I was very glad it worked like that. We sort of gradually started out thinking we could have a few contributed papers and worked it down to "Let's have none," just on the grounds that if people really had something good to say they could give the abstract from the floor, and leave the time for substantive discussion of the issues. I'm very glad the way it worked out, It was a little risky. We could have had everybody feeling that they didn't get their bit in.

But, as it turned out, I think everybody felt that the discussions were thoroughly productive, that the issues were hashed out without pausing for somebody to get up and give their l0-minute paper, Lots of people showed slides — movies even and got to say what they had to say and there wasn't a sense of rushing, I think nobody felt disappointed that they didn't get to say things. Of course all the remarks are being published, almost all of them, and people are putting in their references and so on.

DeVorkin:

It was an awful lot of work. What was most of your time taken up by?

Tinsley:

Countless little things, each one of which wouldn't sound like a big thing. For one thing, a large number of participants didn't just write back yes or no, but they had other questions. So I was always writing off short little letters to people. That's what comes of knowing almost everybody personally. They asked: "Was there a cheaper hotel in town," or "would it be in order if I brought some slides?" and "Will you have room for my post-doc?" and "Can my spouse go swimming?"

DeVorkin:

What about questions as to what other people were going to be talking about? Did you get any questions like that?

Tinsley:

Well, we had asked them in the original letter of invitation to send any papers they wanted to be reviewed to the speaker, so almost everything got sent to the other speakers, who used them in their reviews, Occasionally things would be sent to me, and I would either parcel them out or talk to the person about them.

DeVorkin:

I see. So then each speaker in each review session was pretty much an editor for that session, too.

Tinsley:

Oh, yes. I had almost no requests beforehand from people who wanted to give short papers. I think we made the message very clear that they could bring their slides and show them from the floor. So it all sort of happened at the meeting.

DeVorkin:

Did you actually have any meetings of the organizing committee here that made any of these substantive decisions as to how it would be organized, or was it pretty much your own...?

Tinsley:

No, originally Pierre Demarque and Richard Larson asked me if I would be the chairman of the organizing committee. And then we put together a list of who we wanted on the organizing committee, all of whom accepted, and we decided more or less what the format would be and sent out a letter to all these people. There were two we couldn't get on the telephone — K. Freeman and M. Rees.

And they all agreed, and thought it was an excellent idea. So we sent out a sort of form letter soliciting further ideas. We were never all together, more than three or four of us. We met with everybody one way or another during the summer at the IAU meetings last year where we then agreed to a preliminary list of participants and then they mailed in their other suggestions. We put together the list of speakers and called them up first.

DeVorkin:

Why do you think you were asked to be the chairman? It certainly wasn't from the standpoint that you had nothing else to do?

Tinsley:

I seem to remember being asked because they said they wanted to have a meeting on galaxies and they needed somebody who knew a lot of people, which, as it turned out, I did.

DeVorkin:

Would you do it again?

Tinsley:

I think I want to rest for a while; it's been very very time-consuming and now there's editing the book and everything.

DeVorkin:

Well, in a conference like this, though, something much more than just publication comes out of it. You do gain a better awareness of the state of problems in the discipline. Do you feel that this really was accomplished, that this was successful?

Tinsley:

It's been my feeling and the people I've talked to since the Conference who were here thought that it was a successful conference. Problems were clarified. One person wrote, "That guy even changed my mind about some things."

DeVorkin:

Any idea as to what types of things would have been changed in most people's minds in addition to what you were talking about, about the nonuniform mass function?

Tinsley:

I'm afraid I would find it very hard to guess that because there were things at the meeting that I'd known about before because I'd talked to people — maybe others wouldn't. One of the other very surprising things, that had been surprising when I first learned about it a few months ago, was in the paper by R. D. McClure, which will be published by McClure and Demarque. They had assigned an age to NGC 188, which is only 5 billion years, and the fact that almost no stars in the disc of the galaxy are older than that. At the same time the globular clusters have ages between 12 and 15 billion years, which makes the disc very much younger than the halo.

DeVorkin:

Is the question what happened in between?

Tinsley:

Very few stars formed; that seems to be what happened.

DeVorkin:

Is this sort of an outline of the period of collapse of the galaxy?

Tinsley:

It seems to be something like this. I've been working subsequently on some of Richard Larson's models for the formation of disc galaxies — he and I have been working together — and those models, when they were published by Larson in 1976 predicted, that the disc stars would have a mean age very much less than the halo, and this is exactly in accord with McClure and Demarque's work on the ages of stars. And the reason essentially is that the disc forms over a very long period of time just from gas slowly dissipating and circling it. I think these ages were quite a surprise to all the people who hadn't seen them before.

DeVorkin:

It's quite remarkable.

Tinsley:

Leonard Searle also brought up some very interesting things which Sargent had additional data to complement from a paper by Ann Cowley. W. Sargent and Hartwick on the abundance of stars in the halo. It's been known for some time that the metal abundances of stars decreases as you go outwards in the galaxy. But their point was that from a distance of maybe 10 or out to at least 100 kiloparsecs, even though there's a wide range of rather low metalicties, it does not decline; in other words, that there is very little abundance gradient in the outer part of the halo. But I did sense at the meeting that there was much more general agreement about the existence of massive halos around galaxies than there had been in the past. I'm not sure, Certainly everybody didn't agree. At least I know this from private discussions. At least Larson and Faber and King (amongst the ones I can think of there must be more Freeman I think) are very skeptical about the existence of halos. That's just a selected group of people I remember hearing about. But Sargent came out with some very interesting evidence based on quaser absorption lines; and velocity dispersions in our own galaxy show that the mass of the galaxy extends out a long way beyond the sun.

DeVorkin:

I noticed that there were a number of definite centers of activity that were represented. Certainly Hale Observatories was represented; Yale certainly was, and Berkeley was. Were there some that I missed as far as centers for galaxy studies? George Field was not here, but were there others from Harvard here?

Tinsley:

Ed Turner was from Harvard. Harvard does not concentrate on galaxy study and certainly not in the optical.

DeVorkin:

Well, Morton Roberts was here. Is he still at Harvard?

Tinsley:

No, he's at NRAO. I'm sure a very active group under Ken Freeman in Australia. His students and he just produce marvelous things. It's difficult to answer that question. I hadn't thought about it in that way. There were several from Kitt Peak here and some others who couldn't come because the funds were limited.

DeVorkin:

Was George Field invited for his interstellar or intergalactic interests?

Tinsley:

He was invited, and I don't remember the form in which he decided not to come, whether he replied and sent back the form with the "no" checked off — I don't remember.

DeVorkin:

This was not exactly on the heels of the Texas Symposium — it deals with a different topic and all but is there any feeling of this being a meeting which is of that kind of spirit, the nature of the Texas Symposia?

Tinsley:

I always think that the Texas Symposia are very different. They tend to be so big that it's more like somebody getting up and giving a definitive lecture which there is hardly time to comment on afterwards and very difficult to comment in a hall of hundreds and hundreds of people. This was supposed to be much more intensive, more like a workshop meeting. It got a bit big for that. But the Texas Symposia are not working meetings except for the small sessions they had in the evening on special subjects. And I think we fairly deliberately tried to avoid that format. Incidentally, talking of centers, I think there were several people from the institute of Astronomy at Cambridge here, in England. They were certainly well represented in view of the difficulty of getting here. And also quite a group from Meudon. DeVokin: From Meudon. There were at least two from Texas There were more than that probably, Bash was here and de Vancouleurs.

Tinsley:

Yes, and Meiere.*

DeVorkin:

Do you find that different problems or different aspects of galaxy studies are being concentrated on from different centers?

Tinsley:

yes, its almost necessary.

DeVorkin:

How has that been changing and what kind of directions do you think will be in the future here at Yale and at other various centers? What can you look for?

Tinsley:

I find it hard to predict because I'm not up enough on what goes on in the observational world. It seems to depend mostly on what new gadget people have attached to their telescopes. If they get a grand new.

*Note: the affiliations of conference participants are listed in the book, which is a more reliable source than my memory here.

 

spectrograph, they can start studying abundances. If they get some grand new camera, they can start taking pictures. Kitt Peak has had a fantastic surge of activity with the IPPS. It's really hard to say how things are going to go.

DeVorkin:

Well, the PDS will be here.

Tinsley:

Yes, that will make a difference. Oemler would be the person to talk to about that. I would be unable to predict the effect. I don't anticipate myself doing things other than theory.

DeVorkin:

It won't get so excited as to try some observation?

Tinsley:

Oh, I don't know.

DeVorkin:

I know it's very important to interface observation and theory.

Tinsley:

Yes.

DeVorkin:

What are your feelings?

Tinsley:

That was one of the noticeable things about the Conference — that the best talks were the ones that must had the theory completely interwoven with the observations, so that they weren't talking about either one or the other but were tying them all together.

DeVorkin:

Do you ever have the feeling, as a theoretician, that observations make life a little more difficult for you?

Tinsley:

Life would be absolutely impossible without them. There would be nothing to theorize about.

DeVorkin:

Well, would there? You would go all the way back to the Friedman universe I guess and still play around with formalism.

Tinsley:

We just would have stayed with the static universe. The Einstein static universe would have been the only one. I left something out when we were discussing the mechanics of the Conference. I should say that members of the organizing committee did a very great deal of work. In particular, Richard Larson did a great deal of work because his office is next door, and whenever I needed the advice of someone, he was there; and I would like to record that, They did carry quite a bit of the responsibility when it came to choosing who not to invite, who to invite to speak and so on.

DeVorkin:

That is a very difficult matter. Did you find that it was a political problem, too, with some people?

Tinsley:

It's always difficult to say no to people. It was very much easier if I consulted at least one other member of the organizing committee so I could say, "We have decided," When it was really difficult decisions, I talked to everybody I could on the telephone. Also Pierre Demarque, of course, did an enormous amount, not only in just the things that he's credited for in the local organization, but sort of holding things together.

DeVorkin:

And this, of course, was absolutely necessary to keep you from going crazy in developing the Conference?

Tinsley:

Yes, I must have almost gone crazy anyway. Certainly with the support of a few friends around here, it was infinitely easier.

DeVorkin:

Well, that's good to hear. Did you resort to form letters at any point?

Tinsley:

I had been advised to do so as much as possible. Sidney Van den Bergh had organized a meeting in Paris last summer, and he said to me, "Take my advice and prepare form letters for every possible occasion." And it did save time. I had a form letter, and then if I wanted to say almost what was in the form letter, I could scribble a little personal note on the bottom.

DeVorkin:

Did you have any adverse reactions to it?

Tinsley:

I don't know. It might possibly have discouraged some people coming, that they got an invitation to "Dear Colleague," but that was hard to do better when we sent out several hundred.

DeVorkin:

Did you send one out to W. W. Morgan by any chance?

Tinsley:

Yes. Now, he's somebody who really regreted not being able to come. He talked to me on the telephone and explained that he was exceptionally busy preparing his major lectures for his week at the Atlanta meeting on the HR diagram. And he said that he would prefer to keep concentrating on stars and not get back off into galaxies. We invited him to be. one of the speakers, I'd forgotten that he was a speaker we'd asked to come who couldn't. He's made enormous contributions to the field of galaxies in understanding stellar populations.

DeVorkin:

Where do you think stellar populations are going? Are they becoming blurred now? Or would you still talk to an elementary class in astronomy in terms of the two Stellar Populations?

Tinsley:

Two is a better approximation than what came out of the Vatican Conference, which was five. If you're going to go beyond two, you might as well talk about a continuum and all the variations and the several dimensions, I think the mistake of that classification into five was that t was a single dimensional sequence.

Age, you might say, was the primary parameter, but then they were very tightly divided up by position in the galaxy and by metal abundance and of course the things that go with it — the kinematics and so on. That just isn't really the case, Things are much mre conused than that. There's old and young population 1; there's old and young population 2 — if you define them by metal abundance.

DeVorkin:

And what do you see in your mind as the cause for this confusion? Are you talking about again the different mass functions, the different effects due to accretion? You were talking about accretion as being more of a dilution more than anything else.

Tinsley:

It sounds confused because the world is complicated and the grand simplication that made the understanding possible was Walter Baade deciding that there were two populations. That was much more important, realizing that creating only two made sense of things. And somehow, working with the confusion is made easier by the fact that one learned about the two populations first. Certainly some of the confusion is due to the fact that stellar metalicities have a wide range of values if you look at stars of a given age in the neighborhood.

So you cannot order stars by age by measuring their metalicities. That's one of the sources of confusion. Another thing is that there are galaxies such as the Magellanic Clouds in particular — the Small Cloud, which has a young stellar population, is quite metal poor. The Magellanic Clouds contain things that look like globular clusters but they're very young, and by globular cluster standards they're metal rich. So there is a sort of sequence but not a one-dimensional sequence, but a whole array of possible things. Once you've basically got the idea about the aging of stellar populations and metal enrichment in the galaxy', the two populations put it in some order, Then it's relatively' easy to understand the confusions that come along. I'm not saying it is easy'. Things haven't been understood.

DeVorkin:

Well, considering the fact that it's not one-dimensional, it's a multi-dimensional problem, did you ask de Vaucouleurs directly to talk about his classification system with this in mind?

Tinsley:

Yes.

DeVorkin:

And how did you think his talk was received? At least how did you feel his work on classification is going at this point?

Tinsley:

His written paper is a monumental thing. He modestly calls it a progress report, but it was excellent, It has a great many useful facts. In fact, that was the reason we asked him to talk, that he would really set the stage for the meeting on a large number of useful things.

DeVorkin:

I can appreciate the need for a two-dimensional or a three- dimensional system in galaxies. But he seemed to be presenting diagrams which correlated various characteristics of galaxies with one another and coining up with interesting correlations on his classification sequence. But he was correlating means rather than simple points, and I was confused about that. Do you think that his correlations were significant?

Tinsley:

Well, they mean something in that if you've got the mean of a mean of a mean, you know what a peculiar galaxy is when you see it. There's soinething to have a perfectly normal galaxy, and then when you see one that disobeys that - like its elliptical in shape but very blue — then you know you're going to be surprised, So the correlations mean something. Also in terms of the simple models that you can do, it's useful to have as smooth correlations as one can get. Your very basic models have to explain them. And the extra complications have to explain the peculiar points that don't lie on the perfect sequence. You might ask what they mean in a strict statistcal sense, but there is something useful to that kind of very highly ordered correlations.

DeVorkin:

So he's not confusing the issue in any way. He's trying, from a purely empirical standpoint, to get these correlations out, to make them available.

Tinsley:

Yes, so then you know what they mean.

DeVorkin:

When do you think things will be formed in your mind to the point where you can look back in a little more perspective about cosmology in general?

Tinsley:

I think the review I wrote in PHYSICS TODAY sort of summarizes what I can say about cosmology probably for some time. If one has to do better by really understanding the dynamical evolution of galaxies, that's a several year observing project before it's worth trying to understand the theory any better.

DeVorkin:

What particular observations?

Tinsley:

Studying galaxies in all different kinds of clusters. Galaxies at different places in clusters and just to what extent the swallowing of galaxies by each other is going on and what effect it has on their luminosity; whether it can be understood statistically in terms of cluster properties. And until that's done, you certainly can't do cosmology in the sense of trying to get qo from the Hubble diagram. I think a lot of complicated, exciting work like Richard Kron's at Berkeley is being done that will take a lot of time to digest. There are new observations coming up with unexpected things like the very blue clusters with small red shifts.

DeVorkin:

What about the blue stars in globulars, the B-29 objects? Do these seem to be strange interlopers that might give us some clue?

Tinsley:

I think they're a clue to stellar evolution.

DeVorkin:

To stellar evolution itself.

Tinsley:

Yes.

DeVorkin:

Okay Well, is there anything we've left out dealing primarily with the Conference?

Tinsley:

Well, we certainly haven't talked about each of the papers, and I wouldn't like that to be construed as saying that any one was less important than the others. Each of the speakers gave really first rate papers; they gave really good review papers — exciting ideas. I think they're going to make a good book,

DeVorkin:

Well, I hope so. I certainly hope that we'll be able to spring for a copy.* Okay, well, thank you very much.

Tinsley:

Thanks very much.

*A copy is in NBL: B. Tinsley and R. Larson, eds. (Yale, 1977).