Las Campanas Observatory

One of the most interesting experiences I had in graduate school was accompanying Jeremy Mould on an observing run at Las Campanas Observatory in the Andes foothills of Chile. Jeremy is a good guy and was very popular with the graduate students at Caltech. He was also one of the handful of Caltech astronomers who did some stellar astronomy. Unfortunately, his popularity meant that it was impossible to get him as my advisor, but I did get to do some work with him on asymptotic giant branch stars.

Asymptotic giant branch stars are similar in mass to the sun, but have reached a point in their evolution in which they have converted all the hydrogen and helium in their cores into carbon and oxygen. They are not massive enough to generate temperatures at which the carbon and oxygen begin to burn into still heavier elements, so the core becomes inert and shrinks. This is mirrored by the outer layers of the star, which expand and cool. The star becomes a luminous red star, similar to ordinary red giants (which have exhausted their hydrogen and have not yet begun to burn helium.) One reason Jeremy was interested in asymptotic giant stars was because he believed they could serve as "standard candles" at infrared wavelengths, allowing astronomers to refine the cosmic distance scale.

Our trip to Chile was an asymptotic giant hunt. These stars are numerous in globular clusters, but theoretically they should also be present (in much smaller numbers) in open clusters. We had picked out a few candidates that we were going to observe photometrically and spectroscopically. The photometry was to look for an infrared excess (AGB stars are anomalously bright at infrared wavelengths, compared to visible wavelengths) and the spectroscopy was to measure the radial velocity and confirm that the star was actually a member of the open cluster rather than a foreground or background object.

Las Campanas is run by the Carnegie Institute of Washington, but the Caltech astronomers were allocated some time on the telescopes in return for an allocation of time at Palomar to Carnegie astronomers. In 1987, if I recall correctly, the du Pont 100" telescope was the largest telescope on the mountain, and it was one of the telescopes we were scheduled to use.

Flying into Chile is an interesting experience. We had flown out of Los Angeles International; my initial reaction to the Santiago airport was that it was squalid in a quaint, rustic kind of way, in contrast with the grand, cosmopolitan squalor that characterizes LAX. There were no terminals per se at Santiago. You disembarked well out on the runway into buses, which took you to customs. Jeremy had a Commonwealth passport (he was born in Britain and raised in Australia) and received less attention than I did, with my American passport. Apparently the Chilean government was unhappy with the American government at the time.

I've been told Chile has the healthiest economy in South American. I wouldn't have guessed. On the way from the airport to the bus station, I was struck by the symptoms of poverty everywhere. It seemed pretty bad. I guess I haven't seen really bad.

La Serena is about a hundred miles north of Santiago, which would be a two-hour trip on the U.S. interstate system. It takes eight hours by bus. Not long before I went to Chile, the local airline that ran a flight between Santiago and La Serena had its airplane crash with no survivors, so the bus was the only choice. Charles Steidel, who was a graduate student then but has since achieved some prominence, was supposed to be on the flight that crashed. He almost got religion from the experience.

The bus was very comfortable. The seats were spaced about as far apart as first-class airline seats, so there was plenty of legroom. There was even a stewardess to provide soft drinks (Jeremy recommended I take them without ice), cheese sandwiches, or a blanket and pillow. The roads were in better shape than some roads I have seen in New Mexico, perhaps for lack of traffic, but it seemed like there was a checkpoint and uniformed men with Uzzis every fifteen miles. That helped account for some of the length of the trip.

We arrived in La Serena early in the evening and settled into the observatory headquarters complex in town. This was quite pleasant, with good sleeping quarters, safe water, and food. However, a bunch of us decided to head into town for dinner - one of the other astronomers claimed he knew a good place. He was right. None of us was fluent in Spanish, and none of the restaurant staff were fluent in English, but somehow we communicated our wishes and in a surprisingly short time we had salads, fries, and enormous steaks in front of us. The staff were most attentive and I thoroughly enjoyed myself. Cost of the evening: $6 U.S. And I mean U.S.; it seemed to be the de facto currency.

The next morning, we drove up to the observatory itself. The site is superb, with the right terrain for minimal air turbulence and with the extremely dry air coveted by IR astronomers. (La Serena is at the southern edge of the Atacama Desert.) The observatory is at about 7000 feet, so I experienced no altitude sickness. There is, as Jeremy might have said, miles and miles of miles and miles in every direction; I have never seen a site so isolated. At night, you didn't see more than five or six lights in the distance in any direction.

Curiously, the observatory is just high enough to peek over the coastal range to the ocean. However, the surface haze was thick enough that I never saw water. What I did see one evening was the famous green flash. I refer, not to a comic book character, but a rare optical phenomenon seen in conjuction with a setting sun. We were finishing dinner when the sun went down, and for about three seconds as the disk disappeared, there was a intensely green pinpoint of light on the horizon. My reflexes weren't quite fast enough to bring up my camera in time, which is really too bad. It was breathtaking.

Food is cheap in Chile if you are paying for it with U.S. dollars. The cuisine at the observatory was the best at any observatory I have visited. Lunch was typically an enormous serving of meat in some kind of broth with noodles. Dinner likewise. Meals were accompanied by excellent bread and various soups, all of which were good, though the cream of chicken soup did get old. I don't know about breakfast because I never bothered - I was too tired after a long night at the telescope. There was, however, one exception to the superb cooking: a local delicacy that Jeremy called locos.

I don't know if that's its correct name. I thought locos was the Spanish word for crazy. Actually, that may be about right. Locos is apparently a species of abalone that lives off the Chilean coast, and a prize catch for Chilean divers who peel it off the rocks and let it ripen in the sun for a few hours before preparation and consumption. My impression of it was that it had the taste of spoiled calimari and the texture of raw liver. I found a big chunk of it sitting in broth on the lunch table one day, took a couple of nibbles, and decided that it wasn't my kind of delicacy.

But it wouldn't go away. That night it was diced up and served on a bed of lettuce. I sent it back. The next day it was served again, swimming in my cream of chicken fat soup. I sent it back. The next day we had empanadas.

Jeremy warned me about these. The cook prepared these stuffed pastries every Sunday in quantity, and they were a prized midnight snack. Most were stuffed with meat, onion, and olives and were superb. (Though you were well advised to look out for stray olive pits.) Some contained a cheese mixture that was not bad at all.

The remainder contained leftover locos.

I managed to dodge the bullet; though it was impossible to guess the contents from external appearance, all the empanadas I ate were either beef or cheese.

Another wonderful thing about Las Campanas was the wildlife. There was a colony of feral burros wandering around the mountaintop; they left you alone if you left them alone. I also spent about twenty minutes standing and watching an eagle hovering overhead. I was walking along the road from the monastery to the du Pont telescope, which follows the crest of a narrow ridge. There was a steady breeze across the ridge, and this eagle was hovering on the breeze, holding a more or less fixed position relative to the ground while he watched for rodents. He sort of looked me over and decided I was harmless, and did not react much even when I pulled my camera out and took a picture. He could not have been more than thirty feet above my head.

It was my first time in the Southern Hemisphere, so I eagerly looked for southern constellations I had never seen before. Achernar was prominent overhead, and I was able to find Alpha and Beta Centauri and the Southern Cross. But the special treat was that this was 1987, and Supernova 1987A in the Large Magellanic Cloud, the first naked-eye supernova in over four hundred years, was still visible. I was thrilled to catch a glimpse of it. The astronomer who discovered it, Ian Shelton, was still on the mountain completing his photographic atlas of the LMC, and a photographer from National Geographic showed up for a couple of days to work on a story about the supernova. She had worked in a couple of war zones and seemed an unlikely choice for a science story, but there it is.

One interesting sensation that I did not expect was the strong feeling that I really was in the Southern Hemisphere. I have been a close observer of the heavens since I was young, and it was eerie to see the Sun pass through the northern sky instead of the southern sky. I don't know if I would have had this sensation if I was not so attuned to the heavens.

The first couple of days of our run were devoted to photometry. Infrared photometry is challenging because of the strong background from the atmosphere. We were using a rotating beam splitter (plated with gold, which is highly reflective in the infrared) to substitute blank sky for the star every tenth of a second. This allowed the background to be efficiently subtracted out. We used a smaller telescope (40", if memory serves) for these observations.

The second half of our run was performed at the du Pont 100" telescope. This telescope had an echelle spectrograph that I fell in love with. It used photomultipliers to count photons and was quite sensitive across the visible spectrum, and it had excellent wavelength resolution. The control software allowed you to see the counts build up on a video screen, so you could see the image of the spectrum slowly emerge, ghostly at first and then clearer as the counts climbed. Photomultipliers require enormous voltage and expend tremendous power; bringing up the spectrograph was about a 45-minute procedure. I felt like I was bringing a nuclear reactor on line. The guide camera was extremely sensitive, and at highest gain you could pick out stars that Jeremy estimated at about 19th magnitude. I found it eerie to peer deep into the heart of a cluster and see a star, just at the limit of detection, that was probably a white dwarf several hundred light-years away.

One evening, Jeremy went back to do some more photometry on the 40" and left me running the spectrograph on the 100". One of the stars on the list had a most startling spectrum: as the counts accumulated, it took on a peculiar pebbled appearance. I got quite excited and called Jeremy to report the unusual spectrum. Jeremy is utterly unflappable and refused to get worked up, but he found a reason to wander over later and look at what I had. The mystery was resolved when we looked at a second star that was known to be a carbon star: The spectrum showed the same pebbled appearance. A carbon star has a high percentage of carbon in its atmosphere, and this produces vast numbers of bands and lines from various high-temperature molecules, accounting for the appearance. Jeremy's laconic comment was "So that's what a carbon star looks like at high resolution," and he wandered back over to the 40".

We were in Chile in October, which meant that there was danger of spring storms. One hit midway through our run and shut us down for two nights. Fortunately, like most large telescopes, the du Pont had a small library, and I spent the time reading Run Silent, Run Deep and watching the rain blowing past the front door. Large telescope time is extremely expensive; you do not go to bed merely because it is raining cats and dogs, because you cannot risk wasting a break in the weather. There were no breaks in this particular storm.

I also took time to write postcards to a couple of girls back home. It's not what you think; I wasn't going steady with either, though I think I would have liked to. The postcards arrived the day after I got home. I also had an Asia tape that I played much of the time, and I still cannot hear Heat of the Moment without thinking about Chile.

We brought several large data tapes back with us. I concentrated on reducing the spectral data. This involved using an iron-arc comparison spectrum to calibrate the wavelength scale, then using a correlation algorithm to determine the wavelength shift of each star relative to a standard star with a similar spectrum. I'm forgotten some of the details. However, it was possible to determine the radial velocity to within a couple of hundred meters per second. I then had to subtract out the Earth's orbital velocity around the Sun and the rotational velocity of the observatory around the axis of the Earth to get the true heliocentric radial velocity.

I don't believe we actually found any asymptotic giant stars. The sample was too small and the stars were rarer than we had hoped. But we had lots of fun looking.