Astronomy: Observing at La Silla

La Silla Observatory

Astronomers, particularly those that deal with observations (like me), tend to go to remote places to observe the stars. These tend to be high up on mountain tops in isolated areas far from cities. This past week was the first time I visited La Silla Observatory. This post summarizes my experience from the last few days.

La Silla is one of the various observatories in Chile controlled by the European Southern Observatory (ESO). The other main one is Paranal, where the four Very Large Telescopes (VLTs) are. APEX, which I've visited previously, is also managed in part by ESO.

La Silla is located 160 km North of La Serena in Chile. I've been to La Serena on several occasions; it's the place to stop at if you go to Cerro Tololo, Cerro Pachon, Las Campanas, or La Silla. Thus far, I've only been to Cerro Tololo and (now) to La Silla, but next month I'll be heading to Las Campanas.

The main telescopes at La Silla. At the top is the 3.6-m, home of the HARPS spectrograph of planet-hunting fame. The more rectangular one is the NTT. The silver dome in the foreground is the MPG 2.2-m, the one I was using.

La Silla and Las Campanas are close to each other. Tololo and Pachon (where Gemini South is) are also fairly close to each other. However, the La Silla/Las Campanas combo is farther from La Serena and it took us about 2 hours for our van to reach the observatory from the La Serena airport.

Las Campanas Observatory, as seen from La Silla

Arriving at new places can always be a bit daunting, but fortunately I've been to several observatories and they are all fairly similar: quiet places with dormitories, a main dining room, the control room(s).
I had plenty of time before my run (I started two nights from then) and so I could rest up a bit and acclimatize. I have to say that I felt I needed it. I was super exhausted upon arrival and had a mild headache. Not sure if it was the altitude or the lack of sleep or the travel fatigue. After a night's rest, though, I was fine and ready to work on my OBs.

OBs are Observing Blocks and ESO telescopes require them to schedule your run. In most cases, these have to be prepared well in advance, but for a visiting run like mine I could do them the day before. I had already started them and had all my targets selected, so it was just a matter of copy pasting the target data into the OBs. Half-way through I realized it would be better to write a script, but too late. Maybe for next time.

I walked around a bit the observatory in my spare time. There's not much to do in places like these (you're here to work, after all), but the vistas can be quite impressive. Despite looking like a barren desert (in contrast to places like Lick or Palomar), there's actually quite a bit of wildlife. I saw quite a few foxes, birds, and donkeys.

Some of the wildlife at La Silla

The weather was excellent for my run: clear skies, little moisture in the air, low winds. One thing I had forgotten, though is that 15% of the time is allocated for Target of Opportunity observations and similar things. There was a gamma-ray burst astronomer here that used that fraction of the time. Fortunately, most of his observations were in twilight or otherwise early in the night when I had slightly less interesting targets to observe.

The main problems I had, though, were with my setup. I was using the FEROS spectrograph at the 2.2-meter, but it was my first time with the instrument. Despite reading the manual, I was surprised by my early results. In particular, the flats taken simultaneously with my objects were getting saturated and nothing we tried could fix this. This was probably happening since I was binning the data (my stars were faint) rather than using the full resolution, and I guess this is not something that's typically done. The pipeline wasn't working the first night due to some missing calibrations, but once I saw the quick-reduction results the next night it looks like the saturated flats were doing more damage than good. Needless to say, I changed my observing strategy to remedy this. I think this may just be a result of the quick-reduction nature of this pipeline and the full reduction will look better. It may also be possible to ignore or mask out those saturated flats if I run the pipeline myself.

One interesting curiosity at La Silla is that all telescopes are run from the same control room. The room is very large, though, and perhaps things were being run in service mode for the NTT and 3.6-m since I rarely heard conversation at that end of the room. It was all so very quiet, well, except for the radio. That was good, but they did have it on all night (maybe even all day?), which can get tiring after 8 hours.

An all-sky image of the night sky at La Silla. The band across the image is the Milky Way, our Galaxy. The letters indicate where the various telescopes were pointing.

Overall, it was a good experience. Despite my problems the first night, I know I have some good data to work with over the next few months. The quick-reduction already revealed some interesting things worthy of publication. So, wish me luck as I learn to reduce the data! I look forward to my next visit to La Silla.