Interview with James Lequeux

Sullivan: 00:02

November 7th, 1972. And at Groningen, we're interviewing James Lequeux about early days of French radio astronomy. Well, now, you said that French radio astronomy began in 1947, actually.

Lequeux: 00:16

About '47, '48, but I became only aware of radio astronomy (I had contacts with people there) in '53. Actually, I did some research as a student in '54. And after that, I had to finish my studies and do my military service, and I came back to the group in January, '59.

Sullivan: 00:42

This is a group at Meudon?

Lequeux: 00:43

The group at Meudon. In fact, initially, the group wasn't at Meudon It was connected with physics laboratory in the École Normale Supérieure. And the origin of the group comes from the interest of Professor Rocard, who is still the head of the lab. He was the head of the lab at this time, and he is still the head of the lab. And Professor Rocard has put his hand on some German Würzburg radars. There are some in the Netherlands too. And he had, as far as I remember, three or four of these.

Sullivan: 01:16

What was his background?

Lequeux: 01:18

He came from Germany.

Sullivan: 01:19

No, no, his background. Was he a--

Lequeux: 01:21

Okay. He's a physicist. He's a physicist, a [unclear]. He has nothing to-- he has never been directly connected with research in radio astronomy. But he has a strong interest in that. And he wanted to use his radars, and an obvious way was to use them for radio astronomy. And he had a few people who became interested. I think the three founders of the group. Denisse has a physics background. He was mostly interested in plasma physics. So he wasn't an electronic engineer. And the two others, Jacques-Émile Blum and Jean-Louis Steinberg. Those two people were radio engineers at the beginning. Blum, I think, has worked for the French Navy for some time. They set up a very small group, all three together. And after that tour, two other people joined them; Boischot, who is still active in radio astronomy in Meudon. And Leroux.  Leroux was a very funny man. He is one of the most strange persons I have met. He was a complete autodidact. He had been at the university, but he had no contact with research before he came by chance to visit Paris. He is from Brittany. And he is in quite a remote place of Brittany, and his parents were selling art in some very remote place. So he came to visit the lab by chance, and he became very interested in what was done there. And Steinberg or Blum (I don't remember, I wasn't there at the time) asked him to join them for some research as a student, and even told him that he could be paid a bit. "Oh, I would do that and I would be paid!" He was very fascinated. [laughter]

Sullivan: 03:22

The idea of being paid.

Lequeux: 03:23

The idea of being paid for doing something interesting [laughter] had never crossed him. And he has been extremely good, both as a theoretician, and as, he was one of the first to work seriously on synchrotron radiation. He was actually the first to give the formulae for synchrotron absorption. He has been also very active in building receivers. But his largest activity was a theory of the electron as an elementary particle, but he never succeeded in this direction. All the people who have taken lot of time for doing that have never succeeded. He has disappeared now: he's teaching physics in the University of Rennes. But he's no more connected with radio astronomy.

Sullivan: 04:16

And his name is Leroux?

Lequeux: 04:17

Leroux. Leroux. L-E-R-O-U-X. So he's one of the founders who have disappeared. The other people are still active in radio astronomy.

Sullivan: 04:27

Now, this first group, where did they get their inspiration to get interested in radio astronomy? Was it from [crosstalk]?

Lequeux: 04:33

Well, I think that there have been at the very beginning contacts with other people doing radio astronomy abroad. I think mostly of Christiansen. Christiansen is a personal friend of Steinberg.

Sullivan: 04:47

I see.

Lequeux: 04:48

And I think they had received some help. Of course, at the time there was nearly no question to do anything but solar radio astronomy. And they started with a very small instrument on the roof of the laboratory, and after that they added -

Sullivan: 05:04

At Meudon?

Lequeux: 05:05

No, this was in Paris at École Normale Supérieure is in Paris, very close to the Pantheon.

Sullivan: 05:10

Oh, I see.

Lequeux: 05:12

And there was no connection with astronomy at the time, as with conventional astronomers at this time.

Sullivan: 05:19

Was this with the Würzburg dish?

Lequeux: 05:21

No, there was a small dish and after that two Würzburg were set up with alt-azimuth mount. And they started to do solar radio astronomy with that. I found this sort of situation with about five or six people when I came in '53, when I was a student. And in '54, I made with Denisse and Leroux the first non-solar observation of the staff. This was mapping the galaxy at 33 centimeters in the continuum. This was quite an experience, because observations were not as easy in those times as they are now. We have alt-azimuth mount, and we had to draw, we had no computer, so we had to draw and calculate the equatorial coordinates to look at the sources-- we have no computer. So we had to draw by hand an abacus for this and every half minute--

Sullivan: 06:10

Correct them.

Lequeux: 06:11

--we have to set up the telescope to the right position and so on. So that was rather painful. I remember also being measuring refraction by observing the sun setting and rising and it was terribly cold. We had to be outside in very uncomfortable position, looking at the sun with an optical telescope. And when the sun crossed the wires, then you pressed a button and you had a mark on the chart. So we measured the refraction that way. That was rather funny.

Sullivan: 06:45

But this was around '54?

Lequeux: 06:48

This was around '54.

Sullivan: 06:49

And where was this published, this survey?

Lequeux: 06:51

This was published in the Comptes Rendus of the Académie des Sciences. This was the only scientific journal in front at the time. So was also some [crosstalk]--

Sullivan: 07:02

Annales d’Astrophysique?

Lequeux: 07:04

No, Annales d’Astrophysique, it did not exist, I think, at the time.

Sullivan: 07:08

I see.

Lequeux: 07:08

I think not. I know it's better to check, better to check. I'm not sure. But you know, we were not connected with astronomy at the time. Not at all.

Sullivan: 07:17

I see. More physicists--

Lequeux: 07:19

More physicists. But at this time the lab grew, the physics lab grew. And we thought that it would be time to join true astronomers. And in fact, that was about the time when we moved to Meudon Observatory. And there the director of the Paris-Meudon Observatory at the time was Professor Danjon. He was a fundamental astronomer, but he was very clever and he understood at once the future of radio astronomy so he really helped us quite a lot. And so we moved because there was not enough room in Paris, so we moved to Meudon because there were new buildings available there.

Sullivan: 08:17

Right. And the optical people were already at Meudon.

Lequeux: 08:19

Yes. There were people at Meudon doing mostly solar astronomy since 1880 or so. So this was a long-standing observatory.

Sullivan: 08:28

You just joined them out there.

Lequeux: 08:29

So we joined those. And as far as I remember, we had very good contact with those optical people. This has not always been the case in the history of radio astronomy. Sometimes there was some misunderstanding between optical and radio astronomy, but that was not the case. Thanks to Danjon who was a very, very clever man.

Sullivan: 08:50

Well, let me ask about the two Würzburg dishes. They were used as an interferometer?

Lequeux: 08:54

No, no, no, no. We had two. They were working at different frequencies. The first was used for solar observation at relatively low frequency - I don't remember - meter wavelength or so. And the second one was used for first solar and then galactic radio astronomy at 33 centimeters. We had mixers which were quite good at the time where the noise temperature was about seven hundred degrees, which was quite nice for the time. And at about this time, we-- actually, it was a bit earlier. The radio astronomers decided that the site near Paris-- the two were no more in Paris, it was about 20 kilometers south of Paris in a strawberry field. That's an interesting place to observe [laughter]. Well at about this time, actually, I think the first step was taken in '52. We decided that-- I wasn't yet connected with the group, but the people who were there decided that they would better have an observing station far from Paris because they were already frightened by the problem of interference. The interferences were becoming already serious at this time. And so Ecole Normale Supérieure, to which the physics lab belonged, decided to purchase a piece of land at Nançay, 200 kilometers south of Paris. Now this was purchased in '52 and a major activity of the group was to build new instruments for Nançay.  And the first instrument, the first important instrument which was built was a solar interferometer. This was a 32-element east-west interferometer working at 169 MHz. And this instrument has been very successful. It was put into operation in '56, as far as I remember. This has been very successful. They discovered the type IV solar burst with this instrument.

Sullivan: 11:07

Who worked with that instrument primarily?

Lequeux: 11:09

Blum and Boischot . And the group was now much bigger, I think with about 25 or 30 people at the time. And so they were very active in solar astronomy. And about this time they have also set up a three centimeter multi element array with 16 antennas. And those two instrument still exist and they're still working now in Nançay. And there were a number of improvements, but most of the activity was purely solar. The first exception was this work I did with Denisse and Leroux, this mapping of the galactic plane, mapping the galaxy at thirty centimeters. And after Mohan Joshi, who is now in Bombay at the Tata Institute, observed the position of fluxes of radio sources using the solar interferometer, which was sensitive enough to detect those sources. And in the meantime another instrument was set up at Nançay for non-solar astronomy. This is an instrument which used two of the Würzburgs which were previously used for [crosstalk].

Sullivan: 12:34

The same two?

Lequeux: 12:35

No, they were not the same two. Oh, it's a complicated story. I think from the two Würzburgs that we use initially, one stays on the spot and another one moved to Nançay. There were two other Würzburgs available and one has been moved to Meudon for another group of radio astronomy, a very small group headed by Marius Laffineur and the fourth one was moved to Nançay so we used one of the original Würzburg plus another one. And with that we built an interferometer. These Würzburgs were mounted on an equatorial mount, home-made, and with that I started to observe at the time I came back. Most of the electronics was done by Leroux and I did my thesis with that.

Sullivan: 13:26

[inaudible].

Lequeux: 13:27

This was the observation of structure of radio sources.

Sullivan: 13:29

You say when you came back--

Lequeux: 13:31

When I came back, after my military service.

Sullivan: 13:33

Oh, after your military service.

Lequeux: 13:34

I told you before that there was a gap.

Sullivan: 13:36

[crosstalk].

Lequeux: 13:36

There was a gap in my work between '54, '55, and '59, mostly due to military service. So I started to work [inaudible] and now it's sort of modern history so you would find what happens in all the books [crosstalk].

Sullivan: 13:52

I mean, why were the Würzburgs so popular, even at that late date?

Lequeux: 13:57

Well, I think they were very good antennas, very good construction, and they could easily be dismantled into reasonably sized panels of a few meters. They were very good antennas--

Sullivan: 14:14

Very portable, right.

Lequeux: 14:14

They were 7 meter in diameter and the surface was quite good as 30 centimeters. And the mesh was good for 21 centimeter too. I think it could have been used down to, say, 15 centimeter, with some work. They were rather light as made mostly of aluminum.

Sullivan: 14:34

It's just interesting how many different groups use these Würzburgs--

Lequeux: 14:36

Yes, they were quite a lot.

Sullivan: 14:38

--after the war.

Lequeux: 14:39

Yes. The Germans built an enormous number, probably 100 or so, and they were scattered all around Europe. There was many in France, mainly on the Atlantic coast. There were some in the Netherlands too, some in Belgium, and a number in Germany also. They were the long-range radars used, I think, at decimeter wavelengths

Sullivan: 15:03

And the English took a couple back with them, I think, and the Americans.

Lequeux: 15:05

Yes. Most of the people took--

Sullivan: 15:07

Americans took several over.

Lequeux: 15:08

Actually, we also took from Germany some pieces of electronics which were very useful in the beginning, pieces of electronics which were part of the radars. This was very advanced.

Sullivan: 15:19

Insulators and things like that?

Lequeux: 15:21

Yes. This was a very advanced system for the time.

Sullivan: 15:25

Well, I suppose this was especially important for a country like France or Holland that was occupied. I mean, the English and the Americans were developing their own radar systems but--

Lequeux: 15:34

Yes, but we couldn't, so actually, no one was involved in radio studies in France because it was impossible. In Great Britain the situation was quite different because a number of people who are now doing radio astronomy like Hey for example, were radar people. And most of the Australians like John Bolton and Gordon Stanley and all these people were first radar engineers.

Sullivan: 15:59

Right. So I thought of another question. You mentioned these solar interferometers at Nancay with many elements. I was just wondering where the development of that came from. Was that--?

Lequeux: 16:10

I think it's partly-- I think it's that the prototype of all interferometers were Christiansen's instrument in Fleurs.

Sullivan: 16:17

That's what it sounded like to me. I just wanted to verify that.

Lequeux: 16:19

Yes, these instruments still exist. It has been improved simply by adding a number of antennas. Christiansen’s instrument was completed before the Nançay one. I haven't been very much involved in the building of this instrument but I guess there has been a constant exchange of information between Fleurs and France. We had permanent contact with Australia at this time.

Lequeux: 16:46

And the French made several new developments. For example, we had the first, I think, the first multi-beam system for the north-south arm. Because after the east-west arm, which was completed in '56, we had the north-south arm completed, I think, in '58. And this one has a multi-beam system about 15 simultaneous beams in declination.

Sullivan: 17:16

You think that was the first time?

Lequeux: 17:16

That was the first time. And this was mostly Blum's work. And Blum has always been developing new instrumentation and he was also the inventor of the correlation receiver. Not the autocorrelation receiver but the correlation receiver, which came much before.

Sullivan: 17:36

For an interferometer.

Lequeux: 17:38

For an interferometer. And he was the first to, I think he was the first to develop correlators for interferometry. He has the idea of having a correlation receiver in which you divide the signal input in a magic T and then you have two independent receivers and then you correlate the outputs. So this eliminates the DC component. And all the receivers at Nançay are made in this way.

Sullivan: 17:59

That was Blum.

Lequeux: 18:00

Yeah, that was Blum.

Sullivan: 18:01

So I should definitely talk to him about that sort of thing.

Lequeux: 18:02

Yeah, because he has a lot of-- it would be very important to contact him for the history of early instrumentation in radio astronomy. And actually, he was the first who has the idea of the autocorrelation receiver. The sort of thing that Sandy Weinreb developed later. But this was published but unfortunately, we have never done practical.

Sullivan: 18:22

Never got involved in it.

Lequeux: 18:23

Yeah. We haven't done any radio line observation before the large Nançay radio telescope was completed.

Sullivan: 18:33

That was the first time?

Lequeux: 18:33

That was the first time. Most of previous observations were in the continuum.

Sullivan: 18:37

And the Nançay dish, when was that completed?

Lequeux: 18:39

Well, the first part was completed in '54. No, I'm sorry, '64. '64. And it was only entirely completed and working in '68. So four years from now only. It's relatively late. Most people imagine that it was completed much before but that wasn't true.

Sullivan: 18:58

And, well, if I can just take the history a little bit later up till the Nançay dish. That seems like a good breakout point. Now, you say you did your thesis on structure of radio sources using this two-element interferometer. Was that movable? One element movable?

Lequeux: 19:13

Yes, yes. Actually, it was the largest movable interferometer at this time. At this time, there were three groups working on interferometry, and we were actually more of the pioneers in the field. I think the first one to do interferometry successfully was Jennison, Jennison in Jodrell Bank. He had a small interferometer working at 10 cm. And he published the first visibility curve of signals [Cas and Cygnus A?]. This was in 1957 or something like that. And after that, there were three interferometers, which were completed at about the same time. One in Caltech, which exists till now, and another one telescope [used Mark I?] in Jodrell Bank, plus a remote antenna. And this was used by Palmer and collaborators.

Sullivan: 20:08

In Malvern?

Lequeux: 20:09

No, no. This was purely Jodrell. There was no--

Sullivan: 20:12

No, no. [?] was a [crosstalk]--

Lequeux: 20:14

No, the interferometer was [inaudible] much later.

Sullivan: 20:17

--microwave link, right? That's like--

Lequeux: 20:18

Yeah, it was much later. But they had a microwave link between Mark I Jodrell Bank plus another telescope in a remote station. They had a pretty good resolving power, but not terribly good sensitivity. Our instrument had a baseline of 1.5-kilometers east-west and about 400 meters north-south. It wasn't very powerful in sensitivity because the dishes were very small. So we have an integrating device. We are able to integrate the fringes for about one hour in total. So this was a very elaborate, very sophisticated device for the time for integrating-- for phase integration. But we have never succeeded in phase measurements because phase stability wasn't very good. But Moffet, at Caltech, he had much bigger antennas and he had phase stability, but the resolution was much smaller, about a factor of two smaller than ours. So all three groups competed together. It was a lot of fun.

Sullivan: 21:36

Spurred each other on and-- well, it sounds like you were getting complementary information also.

Lequeux: 21:40

Yes, this was very complementary, yes. For example, we--

Sullivan: 21:45

You had to resort models, I suppose, for your sources?

Lequeux: 21:48

We had rather detailed results on bright sources. I think we were the first one to see the radio jet at the center of Virgo A, for example. We had also information about its halo and we saw that it was elongated; we had a way of comparing them with Caltech’s results for example. But that was other thing we are doing.

Sullivan: 22:16

Now precisely, which years was this that you're talking about now? Which years?

Lequeux: 22:23

This was between '59 and '62. I had my PhD degree at the end of '62 and then I kept doing interferometric observations up to the end of '63. I think M82 was the last object. But this was really the limit of sensitivity of the telescope. I had observed about 40 sources in total but after that we were killed by the lack of sensitivity of instrument and this instrument has been abandoned.

Sullivan: 22:53

Still, where were Wurzburg dishes-- and probably the latest observations that were done with them, the Sirius observations.

Lequeux: 22:59

No, I think Kootwijk has observed much later, no?

Sullivan: 23:03

Than '63?

Lequeux: 23:04

'63-- was still in use, no?

Sullivan: 23:07

I don't think so.

Lequeux: 23:08

Dwingeloo was up at this time. [crosstalk]--

Sullivan: 23:10

Yeah, the big telescope in Dwingeloo was up in '58 or so.

Lequeux: 23:15

Yeah, but I think we kept doing some [crosstalk]--

Sullivan: 23:18

I have to ask about that.

Lequeux: 23:18

But I am not sure. You better ask.

Sullivan: 23:20

Anyway, it was used at Meudon, no, at Nançay --

Lequeux: 23:22

Yeah, we used them up to--

Sullivan: 23:24

Till '63.

Lequeux: 23:24

--'63. And now they are no more used.

Sullivan: 23:27

Now, were there any other instruments there before the big telescope?

Lequeux: 23:32

No, we had all solar instruments and that was all. We were thinking of an interferometer with two 25-meter dishes at the same time than Caltech, but we had no money. We were obliged to confine only on two 7-meters. I think that was a big shame for the French radio astronomy. We could--

Sullivan: 23:55

You could have done a lot.

Lequeux: 23:56

We could have done a lot of things with it. Well, actually, there has been a sort of gap in in the observing work between the end of my observation in '63 and the beginning of operation of the big radio telescope. Most people were involved in building it. And this time, there was a sort of crisis in the lab because people were tired to build and build equipment and not doing observations. After that, in fact, I was sort of disgusted by radio astronomy, I turned to infrared for a few years.

Sullivan: 24:30

To what? [crosstalk]

Lequeux: 24:31

To infrared. Steinberg left the group and is now heading a space radio astronomy group, very successfully. He is still in Meudon.  He is no more connected with ground-based radio astronomy now. So these [unclear] happens in

Sullivan: 24:49

Well, I'd like to ask, the building of the big telescope in 64 to 68. It seems like several large telescopes that were built in that era had various difficulties in the building. Did this one goes smoothly or -

Lequeux: 25:03

Sullivan:

Lequeux: 25:21

No, we had only one engineer, only one mechanical engineer, all the rest we had to do by ourselves. Several people spent a number of hours designing equipment.

It wasn’t done by an outside contractor?

No, we had an outside contractor, it was very good for mechanical building. But for the rest, we have to do everything by ourselves, for example, the pointing of the plane mirrors, and the tracking of the focus was entirely conceived by ourselves, by [unclear] and myself. It was built by Ferranti in Edinburgh, but we had to spend one or two years thinking, making measurements of the [surface?] and so on to have the radiotelescope working.

Sullivan: 25:53

And all this took longer than you thought it would do I suppose.

Lequeux: 25:59

It took a very long time. And we were somewhat tired to do the job. That is something that a scientist must do, of course, but we were not prepared to do that sort of thing. That's one of the reasons of the sort of craziness [unclear]. Well, now I think everything over, the results are coming and our situation is good, is good again, and I turned back to radio astronomy.

Sullivan: 26:23

So one last question. Is there any other radio astronomy in France beside the Meudon group?

Lequeux: 26:29

There actually is a small group small group in the Institut d’Astrophysique in Paris headed by Marius Laffineur. They built an instrument in the grounds of Haute Provence Observatory. This was the interferometer with two simple cylindrical [parabola?] cylinders. On the way, the survey of -

Sullivan: 26:56

What era, what time was this?

Lequeux: 26:58

A long time ago. I think that he started in 1957 or so or perhaps even earlier. But they haven't done very many things with that, you know, they were only two or three people and now their radio telescope is abandoned.

Sullivan: 27:13

I see. So was there anything published on it at all?

Lequeux: 27:16

I don't think they have published many results. It didn't make any noise.

Sullivan: 27:25

And was there any other -

Lequeux: 27:26

Now there is another group in Bordeaux Observatory building a millimeter interferometer. It is an emanation of the Meudon group.

Sullivan: 27:38

But that's a very modern development.

Lequeux: 27:41

Yes. It's very recent. Three years old only.

Sullivan: 27:44

Okay. Well, thank you very much.

Sullivan: 27:47

That finishes the interview with James Lequeux on 7 November 1972. Today that undoubtedly tricky Dicky is going to get a second term over McGovern. Well, it's now 4pm here and that's 9am on the east coast of the US, the polls are only been open a couple hours. Obviously, I should visit Meudon and talk to Boischot, Blum, and Steinberg. But that ends it for now. It’s the end of the tape, this side of the tape.