[Bolton, 1976]
Bolton, 1976 (Photo courtesy of NRAO/AUI/NSF)




NATIONAL RADIO ASTRONOMY OBSERVATORY ARCHIVES

Papers of Woodruff T. Sullivan III: Tapes Series

Interview with John G. Bolton
At Parkes Observatory
March 15, 1978
Interview time: 3 hours, 40 minutes
Transcribed for Sullivan by Pamela M. Jernegan

Note: The interview listed below was either transcribed as part of Sullivan's research for his book, Cosmic Noise: A History of Early Radio Astronomy (Cambridge University Press, 2009) or was transcribed in the NRAO Archives by Sierra Smith in 2012-2013. The transcription may have been read and edited for clarity by Sullivan, and may have also been read and edited by the interviewee. Any notes added in the reading/editing process by Sullivan, the interviewee, or others who read the transcript have been included in brackets. If the interview was transcribed for Sullivan, the original typescript of the interview is available in the NRAO Archives. Sullivan's notes about each interview are available on the individual interviewee's Web page. During processing, full names of institutions and people were added in brackets and if especially long the interview was split into parts reflecting the sides of the original audio cassette tapes. We are grateful for the 2011 Herbert C. Pollock Award from Dudley Observatory which funded digitization of the original cassette tapes, and for a 2012 grant from American Institute of Physics, Center for the History of Physics, which funded the work of posting these interviews to the Web.

Please bear in mind that: 1) This material is a transcript of the spoken word rather than a literary product; 2) An interview must be read with the awareness that different people's memories about an event will often differ, and that memories can change with time for many reasons including subsequent experiences, interactions with others, and one's feelings about an event.

Part 1 | Part 2 | Part 3 | Part 5

Sullivan

John Bolton on 15 March ’78. You said that someone at ONR had always wanted to put a radio dish up on Palomar?

Bolton

No. When I said put alongside, I meant figuratively.

Sullivan

I see. So you went to Caltech in 1955 and brought Gordon Stanley with you. And what was the situation you found there? Did you have a lump of money and had to decide...

Bolton

No, I didn't have any money. I found I had a grant of $90,000 for the first year from ONR, and there was no university support yet with it. In fact, the university was taking 33% of that in overhead. And I essentially had to think of what I was going to do. I had talked in letters to Dubridge about the possibility of using an interferometer, a variable spacing interferometer, consisting of two quite sizable steerable telescopes or perhaps a Mills Cross. At that time I hadn't made up my mind, it was only when Gordon and I started looking at the Mills Cross and all of its problems that we decided the dishes were the thing and the high frequencies. And then I had to write a proposal to try and get money. We tried approaching the Rockefeller Foundation for money and that approach was actually in competition with Taffy Bowen’s approach on the 210. But ONR were really staggered when I came up with my first estimate of what the Owens Valley was going to cost - something of the order of $760,000 was my first accounting for this, you see. But they really did back me very handsomely as it turned out, it was closer to a million four years later and three quarters of a million was estimated, it wasn't too bad.

Sullivan

But in fact, your proposal was for two 90 foot dishes?

Bolton

Yes.

Sullivan

It didn't have to get scaled down?

Bolton

No. 90 foot was a sort of larger size. I could see Dover Heights, I could look at my 80 foot hole in the ground and visualize that on a mounting, but then I looked 220 feet down to the sea and I couldn't see that on a mounting at that stage. At least not as far as I was concerned.

Sullivan

That was a whole new regime.

Bolton

That was a whole new regime.

Sullivan

Which, of course, was the Parkes dish and the Jodrell Bank dish demonstrated. But how long did it take to get this money, first of all? And then tell me about the construction and so forth.

Bolton

Well we just continued on around $100,000 budget a year. We had a small group, [Thomas A.] Matthews joined us. We built- first of all, we had to do a site survey and find out where the best place would be - this took maybe six months. In the meantime, Stanley was keen to get a small dish built - a) to experiment with the receivers, b) with the drives. So in the first year, we started working on the 32 foot dish, which we build at Palomar, which was a model of, I remember building out of different pieces of brass wire and so on. What I felt the restricted polar axis design with intersecting axes was the cheapest of all. It wouldn't give us, get us ±4 hours an hour angle, that was a restriction on it. And of course, Bruce Rule and C. W. Jones started pushing backwards and forwards the ideas on the actual 90 footers. In the meantime we were doing scaling on the 30 foot. We drove the telescope with server motors and magnetic amplifiers and we scaled this. A lot of the design work for the 90 footers on the drive and receiver system was done on the 32 foot as well. Then we picked on the Owens Valley.

Sullivan

What were the criteria that you had for a site?

Bolton

Protection principally. The Owens Valley appealed to me because the whole valley was owned by the Los Angeles Municipality and knowing that industrial development was not going to take place there.

Sullivan

Also because they had taken out all the water.

Bolton

Taken out the water and so on. I remember the meeting we had with the president of the Water Resources of Los Angeles County. Lee DuBridge and I and I think Art [Laffer?] from ONR had lunch with him, and we put our case and it looked very, very difficult. The man just had no reaction whatsoever. At the end of it he said, "Do you know I've seen thirteen solar eclipses?" So we got our site in the Owens Valley and we started to develop it. The ONR funds would only cover the operation and the personal property, and I think it was one of the directors of Bullock's who was talked into, that's a store in Pasadena, into giving us $100,000 for on-site development, the rail tracks, and the housing, and that kind of thing.

Sullivan

So you didn't get anything directly from Caltech? Except your salaries, I suppose.

Bolton

Caltech paid half my salary - that was all their contribution to radio astronomy. They charged overhead on the other half which paid for it.

Sullivan

Was there any push from the optical astronomers at this time, particularly Baade and Minkowski or were they just on the sidelines entirely?

Bolton

I got to Caltech and of course, I started this. I was given a room and a desk and a chair and at 9:00 on the first Monday morning, Rudolph came into my office and he said, "Well, I don't want to influence you, but...." And I think for the next four years Rudolph appeared at 9:00 on Monday mornings to find out how, he wanted his weekly report on how things were going.

Sullivan

So he was very interested?

Bolton

He was very interested.

Sullivan

But did he actually have any influence on, for instance, trying to get you...

Bolton

No. I mean, he was interested in the identification problem. What he wanted to make sure of was that I was doing the right thing to get what he wanted.

Sullivan

But what I'm trying to get at is that there was apparently no push from the optical astronomers at Caltech for this radio observatory. They didn't fight it, but they weren't really out there fighting with you either.

Bolton

Yes. I think Jesse Greenstein helped greatly. And some of the younger people like Guido Munch and so on. But I mean, to them it was obviously going to take us a number of years to get going, particularly on something as massive as what I was proposing. So there wasn't really the direct interest until things started to happen.

Sullivan

You say 'as massive as what you were proposing', the dishes were of somewhat different design, however, an 85 foot dish in that day was large, but not unheard of, right? There was going in at NRL and of course, the Dwingeloo dish and so forth.

Bolton

The Dwingeloo dish was the only one.

Sullivan

Well, the 84 foot at NRL, well, I guess that was a little bit later, wasn't it?

Bolton

90 footers were the first of that size to be operational.

Sullivan

Is that right? And of course they were on rail tracks, which was an entirely new aspect also. So in fact, I guess there were a lot of unknowns that you had to look into, which naturally spread out the construction time and so forth. Were there any particular troubles during construction or did it all go pretty smoothly if maybe a bit slowly?

Bolton

No, it all went very well. We had tremendous assistance from Bruce Rule and he and I worked very closely together for four years and...

Sullivan

What was his position?

Bolton

He was chief engineer at Caltech. He was essentially in charge of the synchrotron, the engineering for the 200 inch and that kind of thing. And he was, Bruce was a quite surprising person. He really wanted to understand what the scientist was doing. He wasn't the sort of person who would take 'make this for me' - he wanted to understand why it was being made and whether it was the best method of tackling the problem. And I worked quite closely with him. I used to go with him on his trips to Palomar; I helped scrub the mirror for the first successful coating that was put on the 200 inch; I worked with him on the gearing of the Lick telescope, the Lick 120 inch when it was in difficulties. So I learned as much about optical telescopes from him as he learned from our radio telescopes from me. It was one of those associations for which I'm very grateful at Caltech. Of course Bruce, when this telescope was getting to its bidding stage, when the design was almost complete, Taffy Bowen had Bruce and I go to London for a month to do a criticism of the Parkes telescope. Bruce came out here during its construction and that kind of thing.

Sullivan

So you're saying there were no particular cost overruns or lengthy delays?

Bolton

No. There weren't cost overruns, but I've always been a person who kept reasonably within his costs. For many years I used to do estimates for people. I remember one occasion I was involved in the setting up of Green Bank and that kind of thing. I was kicked off a committee which approved the 140 foot and Rule resigned from it. And I remember one occasion, I think it must have been about 1958 at Boulder, Dick [Richard] Emberson said, "John, what do you think the 140 foot is going to cost us," and I said, "Well, you won't have any change after $20 million, Dick." He said, "I've got a surprise for you - I've got bid for $4.8 million from..." and I said...

Sullivan

Your statement still stood?

Bolton

My statement still stood.

Sullivan

What was the final cost of the 140 foot?

Bolton

$19.5 million. That was after the contractors had been changed three times and the design had been changed four times.

Sullivan

When was the first, when were the first observations taken with a single 90 foot at least and then two?

Bolton

The day it was dedicated, I think, about November of 1958 or 1959. Was it ’58 or ’59?

Sullivan

I could probably check that.

Bolton

Probably November 1958. We had a working receiver on the single telescope.

Sullivan

What about as an interferometer?

Bolton

Roughly 12 months later. That was the first observations, we didn't really get working until, well, let's see, I took a few months off at that stage and we got the two dishes completed, and I came out here for Christmas and then went to Europe. It was in passing through ONR that Russell Sloanaker talked to me and showed me his...

Sullivan

You mean NRL?

Bolton

Yes, NRL. Showed me his records of Jupiter, you know, he got 400° in temperature.

Sullivan

At 10 centimeters?

Bolton

10 centimeters. And I was awfully convinced, and I rang up Gordon Stanley, I think this was in February and told him of Russell's results. By the time I got back to Caltech, which was only two or three days later, he and Roberts had found Jupiter at 960 and it wasn't 400°, it was 6,000°.

Sullivan

So Caltech got involved with the Jupiter radiation?

Bolton

Yes. And then, of course, later on when we got the interferometer, [Venkataraman] Radhakrishnan and I did the, showed that it was belt radiation.

Sullivan

Just out of curiosity, when you went to Caltech, when did you think that you would probably get something going? Did you think it was going to be four or five years?

Bolton

I thought two years.

Sullivan

But of course, you didn't know what you were going to build either at that stage.

Bolton

No, I initially had gone for two years.

Sullivan

Oh you mean you thought you'd come back after two years.

Bolton

I thought I'd get something off the ground in two years. And I had an initial two year appointment. It did spread out to, well it was very close to four, but then I expected to go with the go ahead and the money to build something. Essentially, it took over two years to overcome the inertia and I remember Jesse one day when I, Jesse Greenstein, one day when I was really infuriated at the delays that were being imposed, getting very fed up about it and Jesse said to me, "You don't have to worry, John, you're at Caltech, you've arrived." I said, "I didn’t come for that Jesse. I came to build you an observatory. I'd like to get on with it."

Sullivan

Having these visions...

Bolton

You know, things like the negotiations for the land in the Owens Valley was really protracted. The difficulties with the Navy as to whether they could own something which was not, they can have something on land. Owens Valley would not give us the land, you see...

Sullivan

The Los Angeles County.

Bolton

The Los Angeles County, the water supply wouldn't give us the land, so there were all sorts of difficulties. Three things I learned in Pasadena were union law, contract law and patent law.

Sullivan

Probably doesn't do you much good in Australia where they're all different.

Bolton

No. I mean the complications one gets into with federal funds with a nonprofit organization in the State of California with a contractor based in Arizona and so on.

Sullivan

On Municipal land.

Bolton

On land which is owned by the Los Angeles Water Supply.

Sullivan

It seems to me that from all the talking about sort of large projects that it’s not always the same set, but there's always a set of problems.

Bolton

Sure.

Sullivan

It always takes about one and a half or two times as long as anticipated.

Bolton

Yes. I had hoped to see the dishes going up in two years. Of course, when they did go up, they went up very fast because we chose a method of construction in which we specified everything. We designed it down to the last nut and bolt, instead of saying here is an outline, as a matter of fact, the scheme's got some problems that way because we had already spent a lot of money on the details of the design which many companies would have done themselves, but we still had to put up with the overhead which goes along with doing that. I mean the company the finally built 90 footers was, I can't remember the name of it, Phoenix, Arizona, built highway bridges and guardrails on the Arizona highways. But they only had one engineer on the staff and two draftsmen, but our job suited them because it was ready to go into the machine shop.

Sullivan

Well, let's talk about, before we get into the radio astronomy that came out of Caltech, let's talk about a couple of meetings and trips that you took, for instance I see here that the Manchester Symposium you presented a paper showing some variations in Hydra A which I guess in hindsight turned out to be probably not correct. Do you remember this?

Bolton

Oh yes. That was mainly Bruce Slee's work. We got certain days, I mean, undoubtedly the variations were there, and no doubt it's peculiar atmospheric phenomenon. But exactly why, I don't think it's ever been chased down.

Sullivan

But you were at Jodrell Bank, you presented that paper, but what I'm simply interested in is your reactions to what went on at this meeting. What do you think were the high points of that meeting? What are your recollections of it?

Bolton

Zero.

Sullivan

Zero. You don't remember at all the 2C results or...

Bolton

Oh yes, of course, and that was by Dublin.

Sullivan

That's right.

Bolton

Well, no, my reaction was that there was something horribly wrong, in fact, we had a special meeting one night of the IAU [International Astronomical Union] in Dublin. I mean it was just impossible to distinguish the old business, discernibility and detectability.

Sullivan

Right. So you had already been through all this.

Bolton

Right. And I just couldn't pin it down. And out of that of course, came a letter to the Observatory which I wrote, which said how it happened. This must have been the Observatory around the end of 1955. [Sullivan: April 1956]

Sullivan

Okay. I don't seem to find that one here, but...

Bolton

Maybe you can look it up in the library.

Sullivan

Well, in any case, so in this paper, you pointed this very fact out? That they were confusion limited essentially?

Bolton

The thing that I pointed out is whether you are noise limited or confusion limited. You will always get an answer which is steeper than the real slope. And the reason for this is the following: that if you say take an ideal universe, Euclidian universe with all the objects the same initial power and you get a slope of -3/2and it intersects the X-axis at some point which is based on what the average power is and what the average density is. Now then, if you then take a population of objects which has some dispersion around that absolute power, you get a line which intersects the axis further along. Now if you make experimental errors, and those errors increase as your flux density decreases, you are going to go from one line to another line to another line. And this is what raises the slope. I mean, a very crude object...

Sullivan

Right. This is closely related to the Malmquist effect, I believe, is another name for it. Namely one's sensitivity cuts this off that you get a systematic effect at the low signal noise points.

Bolton

But then back at Caltech, Westfold and me, had Westfold joined me? No he hadn't, he hadn't at that stage. I did an experiment with two graduate students. I took the 2C antenna and synthesized a strip of the sky and what we did was we had a sample of sources which would give us a log N - log S slope of 3/2, we wrote them on paper and threw them into a hat and then we took another 10,000 bits of paper and wrote source on 300 of them, approximately 300 and put them in another hat. Then the graduate students sat down and pulled pieces of paper out and when they came to a source. Oh, we had another hat, too, with some relative phases. So when they came to a source, you pick a flux out and you pick a relative phase out, and then we synthesized what you have seen with the interferometer. Now the first experiment we just took the first 50 sources out. I mean we had a listing where they come in the sky, what flux they were and what the phase relative to the adjoining sources would be, because this is important in interferometry see. And then we synthesized the interference pattern. First with the 50 sources, and the other graduate student analyzed this and he picked out, I think, 30 of the 50 sources pretty reasonably in flux and position. And then we did it again by adding it to 100 and presented him with this again, see.

Sullivan

With 100 sources now?

Bolton

Yes. 100 sources. And he picked 20 with reasonable results. And then we put the other 200 in. And I think he got 2. This was just to satisfy yourself that...

Sullivan

Didn't publish that result, huh?

Bolton

No, we didn't publish that.

Sullivan

That's too bad. It would have been known as the three hat experiment or something. Did those graduate students later go into radio astronomy, just out of curiosity?

Bolton

No, one was George Wallerstein, I think.

Sullivan

Really?

Bolton

I couldn't be sure of that. George did work with us to a certain extent. It might have been George.

Sullivan

So you said there was a special evening meeting at Dublin, what took place at this meeting?

Bolton

This was the IAU in 1955 at Dublin, in which Ryle gave his results and Minkowski and I got very hot under the collar. I mean, 2C produced a slope of -3.

Sullivan

Yes, right. But why did Minkowski get upset?

Bolton

I think Minkowski was very well aware of confusion. Minkowski worked with all the data that came out, trying to identify. He and I talked on the philosophy for the 90 foot dishes. You've really got to pull the source with a primary beam before you can disentangle it with the interferometer. I mean, he...

Sullivan

Right. But now, hold it, this is the summer of 1955, before you'd gone to Caltech.

Bolton

Yes.

Sullivan

So you...

Bolton

No, I was at Caltech then.

Sullivan

You'd been there for a few months before...

Bolton

Yes, I'd gone there in January of 1955.

Sullivan

Oh, I'm sorry. So you'd been discussing these issues?

Bolton

Yes. Yes.

Sullivan

That's interesting, because I see him as one who is very interested in radio astronomy, but not as one who might appreciate the subtleties, such as confusion and how it works.

Bolton

Yes. Minkowski was trying to identify things from the Mills survey, from the 3C survey and so on, and I was arguing all the time, you know, the inherent accuracy is just not there. This is what we're going to... this is where we, this is what we're building this for.

Sullivan

He wasn't finding anything?

Bolton

He wasn't finding anything. And I knew he wasn't finding anything because there was nothing to find.

Sullivan

Okay. That Green Bank Meeting was also the one where the Russians claimed the deuterium line.

Bolton

Yes. Well, that stimulated me to get Stanley and Price to publish their results.

Sullivan

To write that up? Yes. Let's see, during this chronological period, in terms of publications, the next thing I find is Bolton and Wild, I believe, where Paul Wild just told me about this last week, where he just happened to be passing through and... but nevertheless, I'd like to hear your side of the story. How did this idea come about with the Zeeman splitting?

Bolton

Well, Paul, I think was spending some time at Harvard and I'd invited him to come to Caltech and spend something like, six weeks he spent with us there. He was coming up to Palomar to do some observations or get some, help get the thirty foot running. Paul was there when we got the 30 foot running at Palomar and also when we opened the Owens Valley site. I don’t remember whether he spent six weeks or three months with us at the time, but Paul had, he visited Mt. Wilson the day before and seen Horace's solar magnetograph.

Sullivan

Babcock?

Bolton

Babcock, Horace Babcock's solar magnetograph, and we went, we drove, the idea came to us when we were driving up to Palomar and we began discussing, I think, the question as to whether one could see the hydrogen 21 cm line in our own atmosphere in absorption against the Sun. And we began to think of all the things which would blur it out, and the Zeeman effect one of them. Paul is sort of a little more theoretical than I am and has numbers in his head and we worked out that one Gauss the Zeeman...

Sullivan

2.8 megahertz per Gauss, I think.

Bolton

Per Gauss would wipe out any possibility of seeing hydrogen in the space between us and the Sun. And I forget which one of us said what about the Galaxy? And of course, Paul had seen Horace's system and the two things together made, the detection of intergalactic absorption and...

Sullivan

Interstellar you mean.

Bolton

Interstellar absorption possible, and I think at that time, Ed McClain had got the first 21 cm with narrowing off profiles.

Sullivan

Yes, that had been around for a year or two at that time, with quite a narrow profile.

Bolton

That's right. And so we decided it could be done and we wrote that paper.

Sullivan

And Paul had written that theoretical paper on the hydrogen spectrum, but also I was interested to learn earlier today that you had had an interest in the hydrogen line even though you never published anything on it, in fact, this may be your only publication on the hydrogen line, I'm not sure. I was always wondering how that came out of the blue. But it seems like mainly during these four years there wasn't time to do any research here. You were sort of totally preoccupied with getting the observatory going.

Bolton

Oh, we did quite a bit. We had low frequency array at Owens Valley.

Sullivan

Oh, you did?

Bolton

Barry Clark and I, I think, published the first observation of the Crab Nebula by the Sun.

Sullivan

Stanley and Clark? Bolton, Stanley, and Clark?

Bolton

That's right.

Sullivan

'58 PASP [Publications of the Astronomical Society of the Pacific] "Lunar Occultation of Taurus A at 12 Meters," I see.

Bolton

Solar occultation.

Sullivan

Oh, I had lunar written here, but you're right. No, that was not the first.

Bolton

No, it was not the first, but it was the first really good one.

Sullivan

Okay.

Bolton

I think Vitkevich had done some.

Sullivan

Right. And Cambridge, they'd also done a couple.

Bolton

Yes, but this was the first one at very low frequencies.

Sullivan

At Dwingeloo even before the antenna could be fully moved, they put one together.

Bolton

Ours showed something like a two week occultation, we saw the parameter out to about 15 million miles.

Sullivan

Because you were at such a low frequency. And what was this antenna? What did it consist of?

Bolton

Dipole arrays in the ground.

Sullivan

Did you do anything else with that?

Bolton

We did, what was your question?

Sullivan

Did you do anything else with that Dipole ray besides see occultation?

Bolton

Yes, we started, tried to determine how much of apparent scintillation an interferometer was phase and how much amplitude.

Sullivan

From the ionosphere?

Bolton

Yes.

Sullivan

And you were telling me that that in fact, never got published because you...

Bolton

No, we were interested in that because I had consulted on low frequency, low angle effects with the people who were interested in the direction of space vehicles which were to come. This was before the days of inertial guidance, and also, we wanted to devise fringe tracking equipment for later 90 foot interferometers.

Sullivan

So this was good training for someone like Barry Clark?

Bolton

Yes. Barry was with me for a very long time. He started work in his first year as an undergraduate.

Sullivan

Oh really?

Bolton

Yes.

Sullivan

I didn't realize that. So he was a freshman when you arrived, you both came to Caltech at the same time?

Bolton

Well, he got a summer job with me doing survey work and digging post holes.

Sullivan

What about the 30 foot dish which you've already said is primary purpose was as a model for the larger dishes, but it did do some hydrogen line work. Seems to me that it was just sort of filling in, I mean, it was just minor projects. Would you agree with that?

Bolton

Yes, with the 30 foot, we did a survey, I forget, what declination range it covered, but we did survey actually as far as we could get into the southern hemisphere.

Sullivan

I think you went to 294.

Bolton

Yes. We extended Dutch HI survey down to...

Sullivan

But you didn't do any analysis of this really, just...

Bolton

No, I mean...

Sullivan

Your heart wasn't in it is what I mean. You were just killing time in a sense.

Bolton

Yes. You've got to do some observing to find out how good or how bad the hardware is, and of course, as soon as things started to move on the construction of the 90 foot, the whole effort transferred to the Owens Valley.

Sullivan

Well, okay, let's talk about the first experiments that were done with the 90 foot. I think even before the interferometer was ready, there was the single dish worked on, is that right?

Bolton

Yes, one of the very first observations was the one I referred to on Jupiter. And we first of all started off to make a finding list of sources for work with the interferometer to find out what their fluxes were. We originally started off on, we had the idea of 400 megahertz, when we started. Now what changed our minds, I think, was the ability to make good switches at much higher frequencies when the RF diodes came in. And we had mechanical switches for 400 but these are [?] when we went to higher frequencies, so actually the first observation I think, we done at 700 megahertz, and within just a few months, we transferred to 960. The reason for 960 was that it a frequency reserved for satellite communication.

Sullivan

I see. That didn't lead to any problems later on when there were...

Bolton

No. No.

Sullivan

Many satellites.

Bolton

In fact the first receiver that was 960 which was the Vanguard and the Vanguard station was directly copied from from Caltech design.

Sullivan

And you say the Jupiter thing was one of the first. When you found out at NRL they had discovered a very high brightness. And I have here [Robert W.] Wilson and Bolton, I'm sorry, that's another paper. So you weren't on that paper because you were away, is that right?

Bolton

That was Stanley and [James A.] Roberts who wrote about Jupiter. I would say they did it.

Sullivan

Right. I talked to Jim Roberts about that.

Bolton

Yes. In general, one of the staff members at Caltech took one of the students and although we all worked together to a tremendous extent, for example, the work which [Alan T.] Moffet and Morris did on anglicized sources, for example, each time we moved a 90 footer to a longer base line, we had additional problems and Bob Wilson and Radhakrishnan and Jim Roberts and...

Sullivan

Ken [Kenneth I.] Kellermann?

Bolton

No, Ken was a bit later. Alan Moffet and I would go up and we would make the thing, solve all the problems for making it work on the next base line and we'd do some Jupiter work and then we'd leave it to Moffet and [David] Morris to continue with a couple of weeks observation and then they...

Sullivan

It was a real group effort?

Bolton

The [brains trust?] would come up later. In general, one staff member was associated with one student. I mean, there were student projects really, so you had Roberts and Harris who produced the CTA catalogue, which was mainly false findings, 3C sources, Bob Wilson and I did galactic plane survey, later on Radhakrishnan and Barry Clark did the hydrogen line detection work and so on. So it's generally one student and one staff member.

Sullivan

Well, besides from the Jupiter, what do you look upon as the main results that came out of the early years at Owens Valley?

Bolton

I think everybody did, all the projects did something useful. Moffet's thesis, the work Morris and Moffet did essentially said- you know, gave us the statistics of the radio source population in terms which they proved that it was no fluke that Centaurus was a double and Cygnus was a double. Many, many sources had multiple structure. That was one thing that came out of it. The Jupiter work, demonstrating in fact that Jupiter had a sort of super Van Allen belt system. The work by Radhakrishnan and Clark on the two temperature interstellar medium, I think this is a rather fundamental thing. And last but not least, the improvement in the source positions and the identifications which we got.

Sullivan

So the CTA survey was to check 3C positions?

Bolton

Well, we had to have a finding list for sources, and so Dan Harris and Jim Roberts started out to find out where the 3C sources were so that we could point the primary beam of one dish at them and then work at it with the interferometer. Actually, of course, Ken Kellermann always claimed that I set astronomy back ten years by following up 3C sources- what we should have done was an independent survey and discovered all the high frequency phenomena which later, of course, we exploited very much at Parkes.

Sullivan

But what you found is that these sources are reliable, but often shifted by a lobe or two?

Bolton

It would often take a whole night to find a 3C source, because your [?] lobe positions were not necessarily correct. The most likely thing is for a lobe shift, that is the source is completely isolated within the 3C antenna system and it's not isolated so fractional lobe shifts, all the fractional lobe shifts come in. So in fact, one really had to survey something like 5° square.

Sullivan

I see.

Bolton

Say 5° x 2° to find the 3C source and this is where the odd sources like CTA 26 and so on with the peculiar inverted spectra as they now know came from. I mean, they were the other things that were found along the way. So the CTA survey is mostly 3C sources, but also picked up quite a few high frequencies.

Sullivan

CTA 102, also?

Bolton

CTA 102, yes.

Sullivan

So you concluded, was it you then concluded about the reliability of the 3C survey?

Bolton

Well, we'd have saved ourselves a lot of time by doing the survey in the sky.

Sullivan

Right. And is this work, you think, what convinced the Cambridge people to have a 3CR, or how did that come about?

Bolton

I don't know how the 3CR came about, but they only had to look at the CTA catalogue to find out how bad they were.

Sullivan

There was no one else checking these positions?

Bolton

No.

Sullivan

No one else could really, I guess.

Bolton

No. Of course, when the objects were isolated the Cambridge positions were very, very good. At least in the right ascension. And we did lean on the Cambridge results and I suppose the two prize identifications that came out of Caltech in the days when I was there were 3C295, which Minkowski got the richest record which has stood...

Sullivan

Until a couple of years ago.

Bolton

Until a couple of years ago. And 3C48. Now we really depended upon the cooperation of two observatories for that. As I said earlier, even before I went to Caltech, intuitively I felt that one could describe, if you had a source which was so many minutes of arc in diameter it was a galactic source of that size, or an extra-galactic source much smaller. Now one of the things we wanted were fundamental calibration points in the sky for the interferometer, and high declination sources where we could measure declinations fairly accurately. Right ascension depended, of course, upon [?], a reason you can make a declination very accurately is because you observe a source near zero. Your error in your base line parameters is so small on the period method. But we were looking, you see, radio galaxies, for example, work we'd done on structure. It was quite clear from Moffet's work that the optical center and the radio center didn't necessarily coincide. Quite obviously, the further you put something away, the less error you make in the assumption that the radio center is the optical center.

Sullivan

Yes, that's right.

Bolton

And so we took sort of major effort, the four sources which the Manchester people had been unable to resolve out with their longest base line interferometer, one of them was C295 and the other was C48.

Sullivan

Right, I think they had less than 10 arc seconds sort of sizes.

Bolton

That's right. Now, in the case of 3C295, our right ascension and the Cambridge right ascension were almost identical, and this said to us that neither of these systems which have totally different primary beams is affected by confusion. And this was enough to talk Minkowski into going after the spectrum of 3C295. Now once we had 3C295 we had fundamental calibrator for a right ascension, and the next source we attempted, well, we attempted a detailed analysis of many observations and the mean and everything like that, was 3C48. And, of course, 3C48 came out in 16th magnitude star and if it wasn't that 16th magnitude star on the Schmidt plate that 16th, the image of that 16th magnitude star was indeed covering up something.

Sullivan

What sort of error box did you have for your position for 3C48?

Bolton

About five seconds, which you see, is the size, is less than the image size.

Sullivan

Which is highly unusual to find a 16th magnitude star...

Bolton

Yes. Now 295 I think we had something like five seconds of right ascension, that’s combining our position with the Cambridge position, and something like 15 seconds of arc declination. And this, in fact, included two galaxies. And Minkowski got a spectrum of them both.

Part 1 | Part 2 | Part 3 | Part 5


Modified on Tuesday, 23-Dec-2014 14:30:19 EST by Ellen Bouton, Archivist (Questions or feedback)