Interview with Nannielou H. Dieter

Sullivan: 00:01

Okay, this is interviewing Nan Dieter, 7th September 1971 at Green Bank.

Dieter: 00:09

When I was at NRL from 1951 to '55 a lot of exciting things went on that are pretty historical at this point. One of them was the discovery of the hydrogen ion spectrum in the spectrum of bright sources. This all sounds quite simple now, as I say it, but at the time we had found only a few bright sources, more or less by stumbling on them. There was no background to this at NRL. Those sources were discovered at around 21 cm, 20 cm actually. At about the same time that these sources were discovered in the continuum, they were doing a hydrogen line survey of the plane. Ed McClain had worked up a recording system, of course an analog recorder at that point, which he thought was very clever, and indeed it was, in which one could record the continuum and the line at the same time, practically looking at a window and a signal channel at the same time.

Sullivan: 01:07

Frequency switching really.

Dieter: 01:08

Yeah. So, he had two parallel pieces of paper, and they began doing a record that they were going to use quite separately, the continuum and hydrogen line. And when the continuum went up, the hydrogen line went down, and everybody was totally surprised. Perhaps one of the--

Sullivan: 01:29

You were looking for emission in other words.

Dieter: 01:30

Yes. They weren't related and it wasn't-- it was just that we could get two things at once, not that they would be related. And he, of course, thought something was wrong with his recording system. I think the impression one gets from reading literature is that these discoveries are all made by intent. My feeling is mostly by chance, the stumbling on them and being lucky.

Sullivan: 01:51

How soon after the Harvard discovery of emission, well at Harvard and then verified in Holland and Australia?

Dieter: 01:57

That was in early '51. I guess this must have been '52 or '53 perhaps. It was quite a long time. At the time the discovery was made of course, there wasn't a hydrogen line receiver at NRL. It was developed afterwards. But they had a great headstart in doing it because of all their electronics background.

Sullivan: 02:18

Do you have any idea why the delay in not finding absorption for a couple of years or was no hydrogen work done at all?

Dieter: 02:25

People didn't look in the direction of-- well, and of course, we didn't know about the sources.

Sullivan: 02:31

Okay, that's the reason.

Dieter: 02:31

Yes. The survey in the continuum was there and that's kind of fun too. I was out of college and not yet in graduate school. That's a long way in the future. And I was kind of a data reducer, but I've had some undergraduate training in astronomy. And we were kind of scanning the sky for sources to scan like a plane to see when the continuum around that region would go up.

Sullivan: 03:00

Using the NRL 50 ft.

Dieter: 03:01

Yes, right. And that was something of a problem with the analog drive. And the positions, of course, were very bad. We just come upon it, so someone tried to pin down as well as we could what the position was. Signals or noise is not what it is today of course. We just made a list of them and we came to-- actually we found a bright source which was called NRL number five. And then we discovered later on that underlying this very bright, sharp peak was a broader component which was called NRL number nine. And I was keeping the records for this, and so that I recorded from the output that we had the position. And it didn't mean anything to any of the people around there. But it was 17 hours, minus 27 degrees, realized it was the Galactic Center. But it just illustrates the point, nobody went at this with the intent of what is it in the Galactic Center. It was exciting to put the two things together afterwards.

Sullivan: 04:09

Just pretty random [inaudible].

Dieter: 04:10

Yeah, because we didn't know what we were looking for.

Sullivan: 04:13

You don't know if you're looking at radio galaxies or something like that.

Dieter: 04:15

The word wasn't invented. It was--

Sullivan: 04:18

That's right.

Sullivan: 04:19

Cygnus A was known. That was [inaudible].

Dieter: 04:21

Yes, I think so. Yes, at that time, yeah. But it was colliding galaxies at that point. It was a very strange object. It wasn't at all clear that there was a large population of these things.

Sullivan: 04:34

So, was this the first detection of Sagittarius A?

Dieter: 04:37

Yes, I guess some of the excitement of that time was also in the continuum work that Fred Haddock was doing at short wavelengths. Nobody had done anything other than the Sun as short as 10 cm, I guess that's what it was. In that case, and by the time he did that, he had a little better notion of what to do. And so, he set out looking at known optical H II regions. But, of course, signal to noise is not what it is today. And I remember the very great excitement that Fred had when he saw the Orion Nebula. Seeing the Orion Nebula now sounds like nothing and it isn't anything now, but at the time it was as exciting as any discovery is now.

Sullivan: 05:25

It's like finding a new molecule in the Orion Nebula.

Dieter: 05:26

Yeah, right. Right.

Sullivan: 05:29

More so than that even.

Dieter: 05:31

But you had less to guess about it.

Sullivan: 05:33

This was 10 cm.

Dieter: 05:35

Yeah, and that was his first detection.

Sullivan: 05:38

Okay, so you had the absorption. Did you find it in several sources?

Dieter: 05:41

Yes. Well, they began [inaudible]. I was somewhat out of it by the time that they haven't [inaudible] I contact with it, with seeing the two pens go in two different directions.

Sullivan: 05:56

Now I've heard, and maybe you can straighten me out on this, that NRL in the first hydrogen absorption paper didn't really understand what they were seeing. In other words, they didn't realize it was hydrogen in front of a background source. They didn't understand the nature of absorption relative to emission.  They thought it was a hydrogen source that was doing something.

Dieter: 06:22

No, I don't think that's right. I think the original William McClain paper talks about clouds in between to explain the circuit. The explanation isn't right, but it's not as wrong as that. That's my [inaudible].

Sullivan: 06:33

I haven't read.

Unidentified: 06:34

Some people are so hungry they can't wait. [laughter]

Sullivan: 06:37

Hungry for knowledge. I'll get to you. Well now there was in ‘55, I guess it was the Lilley and McClain paper which has the equation ready to transfer and all that. Yes, that's the reason why [crosstalk]--

Dieter: 06:50

Oh, oh, [crosstalk] it's the Hagen and Lilley--

Sullivan: 06:53

Before Lilley, I think.

Dieter: 06:54

Hagen and McClain [crosstalk]. That's right.

Sullivan: 06:56

Right, because they were not really trained in [crosstalk].

Dieter: 06:58

And I think that's correct. And now that you remind me, I think that the original Hagen and McClain thing was not correct. But it's not really surprising. The talent these people brought to it was electronics.

Sullivan: 07:09

Electronics, right.

Dieter: 07:10

And that's why they didn't know where the Galactic Center was. Obviously, Ed Lilley would have known if he had been there.

Sullivan: 07:16

I have to look back at those papers myself because someone mentioned that to me if you look at them, you can see that they really didn't know what they were seeing. They just knew it was opposite to the emission. But, I mean, that's easy in hindsight. [inaudible]. So then after NRL, you went to grad school at Harvard.

Dieter: 07:33

Yes, Harvard.

Sullivan: 07:35

And then to AFCRL again I guess, and then to Berkeley.

Dieter: 07:40

Right.

Sullivan: 07:41

You went to Berkeley just before the OH was discovered.

Dieter: 07:44

Not quite. OH was discovered in absorption in November 1953. I was still at AFCRL then, but I was able-- [inaudible] and I was able to confirm the observation, the detection of OH in absorption at the same time that it was confirmed in Australia and almost about the same time at Berkeley.

Sullivan: 08:04

After using an AFCRL dish?

Dieter: 08:06

Yes.

Sullivan: 08:07

And also, Sam Goldstein told me, just for your information, that they confirmed it at Harvard, also at Agassiz, using the Agassiz dish. This may have been a little bit later in time.

Dieter: 08:17

Yes, they were three papers were published at once [crosstalk]--

Sullivan: 08:20

I'm sorry, not a real confirmation. I'm saying they looked at it shortly afterward. They didn't publish anything.

Dieter: 08:26

The three papers [crosstalk]--

Sullivan: 08:28

--one of the published ones. I didn't realize that.

Dieter: 08:31

Nature had series of them all at once.

Sullivan: 08:34

Right.

Dieter: 08:34

We were all working at it. And of course, the marvelous story about that is what everybody missed, because they didn't believe in the baselines of their receivers, all of it, the detection, everything. Of course, they found it in Cas, and then they also looked at Sagittarius. And so, we tried to do both things also, looking avidly and hard for the zero-velocity component, which of course is the strongest thing. What we found eventually after a lot of trouble was very small little blips, something one would have used for confirmation, perhaps, but would have been pretty nervous about making detection on the basis. And everybody had very bad baselines. Receivers were thrown together more or less for this confirmation, especially ours. Just awful. And then it took a discovery at Harvard later on, to show that it wasn't based on [inaudible] and we just didn't have enough faith in it. We waited long enough, we scanned long enough, we would have gone back up again. And in fact, then I guess it was the Australians who discovered the second large feature because Harvard hadn't gone far enough. So, it's very much concentrating on what you expect. We were expecting a narrow feature, near zero and that's what we saw. Maybe that's a lesson we'll see [inaudible].

Sullivan: 09:50

That's true too. Another thing. Now on emissions, did you have ideas when you went to Berkeley about the same emissions [crosstalk]--?

Dieter: 09:57

Yeah. In fact I had [inaudible] but the program that led to it. When I was there to after this was a confirmation plan. I got a parametric amplifier on an entirely improved system with the idea of looking for OH in absorption in front of galactic H II regions. The reason for that was that at 18 cm they're reasonably strong and in addition, they are large and angular size, so that on a small antenna large beam wouldn't be so handicapped. So that's what I was planning to do and then quote all of this. But during the time of this, I was getting receiver together and everything to do it. There was a fire in the front end of the receiver due to [inaudible] burned up the whole, not the parametric amplifier, but all of the rest of it was melted. [crosstalk]--

Sullivan: 10:49

Another historic fire. You know the one about the Dutch fire?

Dieter: 10:52

Yeah.

Sullivan: 10:53

[inaudible] here we have another one.

Dieter: 10:55

But it never got back together, not before I left. But I left there in March of 1965 and I struggled, and struggled, and struggled all that time to try to get it done. There wasn't a thing they were primarily interested in. I had to scrounge things from everywhere.

Sullivan: 11:10

How big a dish was this?

Dieter: 11:12

The 85.  [inaudible] It was used primarily for one thing [inaudible].

Sullivan: 11:20

Let me just check one thing. So, when you went out to Berkeley, were you thinking of doing some follow-up OH work?

Dieter: 11:28

I was thinking of doing what I was unable to do there. And, of course, that was such an obvious thing to do with the small dish. They said they had the same idea also. Actually, David Williams and Harold Weaver began the survey. And I was really kind of peripherally connected with it at that point more or less in the background. And they saw emission in W49 and it was as surprising as you could imagine. Again, it shouldn't have gone and that direction. The immediate thing next was what do we look at second? And I said, "Orion Nebula." And that wasn't entirely as obvious as it seems now but it appeared to be the [guess?]. And then as I told you after we found some more such blips and they got to be stranger and stranger, I went to Rudolph Minkowski and said, "What would you suggest? What's really a neat place to look next?" And he said that he had, during the time of making the Palomar Survey, done some photographing that he wasn't really supposed to do in testing the instrument. He had done some work in the south of the Survey. And in that area that he photographed was this beautiful big H II region, NGC 6334. And it looked full of interest to him and he said, "Look there." And we did. And it was there that we found some of the most volatile type of OH. We certainly found OH emissions stronger at 1665 and 67. And it was there that I saw first the variation with time [crosstalk].

Sullivan: 13:11

All right. Okay. Before we get to time variation, I definitely want to go through that of course, but I want to make sure I have it straight that your program was definitely designed to look into HII regions right from the start.

Dieter: 13:23

Yes.

Sullivan: 13:23

And how many did you look into before you got to W49? That's one of the very first ones. Do you remember it?

Dieter: 13:29

Yes. There were probably not very many and I can't be certain. I suspect that what happened was that we had the [inaudible] catalog and just went down the bright ones and the ones that happened to be at the right bright extension. There was no sense to it at the beginning.

Sullivan: 13:46

Yeah. It's interesting because Goldstein said that they looked in all sorts of things and then just on a whim, he said, "Well, let's try HII regions." They saw a different approach.

Dieter: 13:56

Yeah. We had a really [crosstalk].

Sullivan: 13:57

Did you know that they were doing this at Harvard?

Dieter: 13:59

No.

Sullivan: 13:59

That they were looking at a similar program?

Dieter: 14:00

No.

Sullivan: 14:00

So, you didn't feel any competition there or pressure?

Dieter: 14:02

Well, somewhere toward the end, after we had found it, we heard rumors that they had found something exciting. And so, we thought that perhaps it was the same thing. I guess there was competition in that sense.

Sullivan: 14:14

Right.

Dieter: 14:15

It's hard to reconstruct that kind of thing.

Sullivan: 14:16

When did you find the emission? What month was that?

Dieter: 14:19

Let’s see. Late May or early June 1965.

Sullivan: 14:24

So, they did beat you by six months in terms of actually seeing it?

Dieter: 14:27

Did they?

Sullivan: 14:28

According to him anyway. In November, they saw W49.

Dieter: 14:33

Well, they certainly didn't say anything about--

Sullivan: 14:34

No, they didn't. I can tell you this. I have this tape recording-- at least his version of it. Okay. So, you picked up the sources that are reported in the first paper in Nature, I guess it is.

Dieter: 14:46

Right.

Sullivan: 14:47

And then when did you become aware of the time variations?

Dieter: 14:52

Well, very early, because the discovery was made in June and then there was something-- I've forgotten what it was now but there was a delay in doing some more observations and then we picked it up again in mid-July. And that was where the 6334 change was so very apparent. That, of course, is one of the largest changes that we've seen. And one wouldn't believe it on the basis of a single case like that. And in fact, of course, we argued and talked and fought for a long time before we said anything to anybody. But the fact that within the spectrum there were features which did not change meant that we could take care of any receiver problems with us that [crosstalk].

Sullivan: 15:31

No, exactly, of course, because now we know they're highly polarized, and perhaps the polarization characteristics of the receiver, you weren't worrying about that factor at all probably.

Dieter: 15:38

No. But we did, about the same time, begin to do polarization measurements. Somebody else had founded that they were polarized. I've forgotten now who it was but that wasn't discovered.

Sullivan: 15:50

I think that was MIT.

Dieter: 15:52

Yeah, yeah. We followed that up and included it in a primitive way, very primitive compared to what you're doing now. But yes, there lots of things that could have led us astray. Fortunately, they did vary in time.

Sullivan: 16:04

When did you become aware that there were two sources in 6334? I forget now, the ApJ Supplement has this map with [crosstalk]--

Dieter: 16:11

Yes, I can't remember exactly, but I know that I remember when we saw one of these sources and looked at the picture. It was in a very dark dusty region in it, and the notion had already come about that maybe that had something to do with the emissions. And so, we began looking around 6334 at other dark regions. And that's when it turned out-- that's where --

Sullivan: 16:37

Yeah, yeah. And so, the other thing that's of interest to me is the reaction to this time variation. I know it wasn't generally believed.

Dieter: 16:48

Absolutely not. For more than a year, I guess. I had different reactions. Some of them were aggressively against it, and others were very sweet. One of them was, "I'm really very sorry, Nan, but we don't see any changes." Which made me more angry, I suppose, than the other.

Sullivan: 17:09

Were they actually monitoring 6334?

Dieter: 17:11

No. No, they weren't. And we were. And also Orion. We, of course, thought variations in Orion too, of a smaller size. That's what I kept saying. Have you looked? When did you look? And if people began to look some, but never in a monitoring sense. It was always an occasional look and always been hard to actually compare observations because they weren't made it quite the same time. So, there was an honest skepticism, all right, which got me rather long drawn on. But the theoreticians were perfectly willing to accept that they were ready to start spinning theories on this basis and said, "Well, sure, it's an unstable situation," but the observer said, "Prove it." And, of course, they're right.

Sullivan: 17:51

Well, when did it come to be believed? Did someone confirm it, and then--

Dieter: 17:54

Yes. It was Litt Meeks, I think, at least he first told me that he had indeed seen the--

Sullivan: 18:00

I don’t think this ever thought-- or I guess it was, the [crosstalk].

Dieter: 18:04

Yeah, I know that he talked-- I don't remember then, but they talked about it.

Sullivan: 18:06

I'm sorry, they have time variations of 6334.

Dieter: 18:10

Yes, and he talked about it in a meeting. That's where I--

Sullivan: 18:12

Yeah, probably in [crosstalk].

Dieter: 18:13

Then I saw it in Australia, too, even after they had said it didn't occur. Well, it's amusing to hear the ease with which the water vapor variations are accepted. Nobody had any fight about that at all.

Sullivan: 18:26

There was a little bit of problems in the first few days, but it was pretty easy after that.

Dieter: 18:29

This was the first year or so.

Sullivan: 18:32

In terms of us believing it ourselves.

Dieter: 18:35

Oh, yeah. Well, at that time things didn't vary in astronomy. That was just not a thing anybody ever considered. It's just too large scale and all that.

Sullivan: 18:45

Pre-pulsars.

Dieter: 18:47

Well, yes, yeah. So, there was nothing that varied. And all of a sudden everything does, including quasars. I guess there weren't quasar variations known before.

Sullivan: 18:54

That was prior to the discovery of quasars in ’64, ‘65. So, there may have been no variable regular sources. Maybe Cas A was known to [crosstalk].

Dieter: 19:03

Or long, slow change, yeah, but not this rapid thing.

Sullivan: 19:07

Yeah, that's true. You didn't really undertake a monitoring program after that.

Dieter: 19:11

Oh, yes.

Sullivan: 19:12

Yeah, that's right. You did. The [inaudible] has two or three years. I'm sorry. I take that back.

Dieter: 19:16

[inaudible].

Sullivan: 19:19

You didn't look at that.

Dieter: 19:21

We also tried finding variations of a very short nature, and that was entirely unsuccessful. One could believe that we saw variations over a period of about a week but nothing any shorter. And in fact, more recently, we saw [inaudible] for example to see it in shorter--

Sullivan: 19:39

Is he taking tapes out of the [crosstalk]?

Dieter: 19:41

Yes, and he's about to publish this, I think. It's only just really finished, I think, the analysis and they don't see anything. I don't know exactly what minute the reminiscence in connection with ammonia has to do with here in Charlie Townes talk about the possibility of detection of the molecule and having people say to him there can't be any such [inaudible] ignored it. [inaudible] is not being indoctrinated in what the things ought to be in it. So, I mean, if he looked, of course, he has lots of knowledge back of that, but I guess it was shortly after the discovery of the 1-1 line, then they looked for the 2-2 line also as a confirmation and -- they didn't really expect to find very much, but they found some which suggested that the local temperature was higher than had been expected. So that made it plausible to look for the water, which is such a high-lying line. And Jack Welch did that. And I remember they had an HM [heterodyne-mixer?] receiver and I knew that he had just begun to try to look for it. And he was on a telephone and hung it up and came down the hall to me with a yellow piece of paper with eight numbers on it. And he said, "Look, it's there." It was it and there was a peak in the middle of it the that [crosstalk].

Sullivan: 21:18

And what source is this?

Dieter: 21:20

[inaudible] 49.

Sullivan: 21:23

So, Jack Welch primarily was doing the dirty work that led to water.  What about ammonia?  Was that mainly Townes?

Dieter: 21:30

Yes.

Sullivan: 21:31

[inaudible] behind all this. Townes had been working on it for two or three years [crosstalk]

Dieter: 21:36

Yes, he came.

Sullivan: 21:37

Fun fact, [inaudible] these were most of the first observations on the 20 ft.

Dieter: 21:41

The 20 ft, yes. It had just gotten into operation in the continuum. And Townes pushed this line work right away to everybody's joy. He supplied people to help build things to do it and money.

Sullivan: 21:56

Was he sort of instrumental in getting the antenna itself?

Dieter: 22:00

No, Jack Welch was the main driver.  And we had the antenna when he came. We just didn't have the line work going because it was--

Sullivan: 22:06

[crosstalk].

Dieter: 22:07

Yeah, that wasn't so vital at first. Jack was particularly interested in planets and in continuum things and he knew that the line development would be expensive and would take people. So that Townes was saying, "Let's look here. It's worth the effort," is what brought that about. So, it's a very neat way to begin observations with an antenna. Two discoveries.

Sullivan: 22:35

Okay. Tell me about the Bok years at Harvard.

Dieter: 22:38

That's a long story.

Sullivan: 22:38

You said [crosstalk].

Dieter: 22:39

No, he was head of the radio astronomy group there and was influential helping Ed Lilley and Dave Heeschen do the first observations of the 21 cm line there with the 24 ft antenna, and then he--

Sullivan: 22:54

At Agassiz?

Dieter: 22:55

Yes, at the Agassiz. And he got the money for the 60 ft antenna to go on with that and gathered around a group of students who were inspired by his saying, “You have the biggest instrument in the world,” which we did at that time. Dave Heeschen had graduated by that time, but he came back for a while. Kochu Menon was there. Tom Matthews, Mary Connelley Sandage, May Kassim, Bill Howard, Frank Drake, Carlos Varsavsky, and I. So, we spread abroad since then. So Bok had a big influence.

Sullivan: 23:29

I don't quite understand how Bok was head of a radio astronomy group. I mean, he's primarily an optical astronomer, is he not?

Dieter: 23:36

He was, but he saw the importance of radio astronomy and 21 cm in particular. He's a Galactic astronomer. And he looked at [inaudible] as an [outpost?].

Sullivan: 23:43

So, this is sort of unusual. He's really, and maybe still, the only head of an astronomy place that didn't know much about electronics in [inaudible] astronomer.

Dieter: 23:51

Yes, that's right. And that, I'm sure, made a difference, because then the problems at Harvard were directed not by the electronics that was feasible. But of course, a very important factor in that was Doc Ewen, who had discovered the hydrogen line. He supplied it with the electronics know-how par excellence.

Sullivan: 24:08

What was his position there?

Dieter: 24:10

I don’t know, it was some researching connection with the observatory. It wasn't a position there. He had his own company, and Ewen-Knight had made the receiver there. He saw the importance of frequency switching and that's what the receiver did for scanning back then.

Sullivan: 24:30

So, this was all 21 cm line work that they were concentrating on [crosstalk].

Dieter: 24:34

Yes.

Sullivan: 24:36

And the only other people doing-- well, there was [inaudible] doing things [inaudible].

Dieter: 24:45

[inaudible].  [Tape cuts off at end of interview.]