In which I return triumphant
Oh, world, did you think I had forgotten you? Never.
I’ve been on an observing run in Arizona, working with the very telescopes I use from Cambridge. The observatory is at the top of Mt. Hopkins, which is about halfway between Tucson and the AZ-Mexico border. It’s home to several scopes, including two siblings of 48″ and 60″ (i.e., they have primary mirrors of 48″ and 60″). The two scopes are housed in the same building, on the mountain’s shoulder. In a chamber next door is a 51″ telescope which does infrared imaging and is run entirely remotely — its observer can open and close its dome, uncover its mirrors, etc. from afar. Behind the 51″ is a big gamma-ray dish, which looks a bit like a satellite dish, except the dish is made of hundreds of hexagonal mirrors. A few steps up the road is a cluster of five little robotic scopes called the HATs (Hungarian Automated Telescope, I think), which are really just adorable. They’re refractors, instead of reflectors — they have lenses instead of mirrors — and have tiny 4-inch apertures. They look so earnest when they’re observing, little noses pointed skyward…
I realize I’m talking of telescopes the way other people talk of kittens. But really…aww, HATs!
Up on the summit of the mountain is the MMT, which stands for Multiple Mirror Telescope. The name is a little puzzling, because the MMT has, as far as I can tell, just the usual number of mirrors. I take it that there once were seven, arranged in a flower pattern to comprise the primary mirror, but they’ve recently swapped those for a single primary 6.5 meters wide. Which is pretty big.
The smaller telescopes live inside chambers with a domed roof; the dome opens a window and rotates around so that the scope can see out. At the MMT, the entire BUILDING rotates. I heard that someone once parked his car too close to the edge of the building, and when he went to rotate the scope…well, it was not pretty. Something like
Dear Insurance Company,
A telescope ran into my car. Please advise.
-Astronomer
When working from Cambridge, I observe with the 48″ and do direct imaging, a.k.a. pretty pictures. The 60″, on the other hand, is used for spectroscopy, which, oh man, spectroscopy. Taking a spectrum involves capturing light from an object, separating it into its component colors — think rainbow — and measuring the amount of each color. I love spectroscopy. I really do. I love it with an unbridled and possibly inappropriate passion. Spectra are just SO COOL. You can look at a spectrum and know immediately whether it’s a star or a planet or a supernovaor a galaxy; how hot it is; how fast it’s moving with respect to you; what it’s made out of; how intense its surface gravity is; and whether, somewhere far, far away, something has gone terribly wrong…
Anyway, I was working with the 60″ this time, which meant I got trained in the physical operation of the telescopes: the dewar-filling, drive-enabling, dome-opening, real day-to-day care and feeding of the beasts. And oh man it was awesome. But now I’m back, and there are p-sets to be completed and posts to be written and data to analyze. To work, world, to work!
Filed under: life, observing | 5 Comments
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An MIT undergrad lusts after physics. Meanwhile, life happens. Excitement and high drama ensue.
I’ve spent quite some time looking at one of the papers on stellar variability using the HAT telescopes … astro-ph/0405597 … it’s a good read, with lots of pretty light curves.
Awwwwwwwwww! I had to go look up HATs on Google, and the are cute. ^_^
p.s. How do you get surface gravity from spectra? Why isn’t the gravitational redshift inextricable from the cosmological and doppler redshifts?
Aaron: if you are trying to get surface gravity, then you looking at stars, and if you are looking at stars then they are in the Milky Way (or an extremely nearby galaxy), and the cosmological redshift is irrelevant.
Ahhhhhhhhh… right-o.
About that surface gravity: high surface gravity causes high stellar atmospheric pressure, which causes amazing pressure broadening in things like white dwarfs. At higher pressures, atoms collide more often, so the resulting radiation has a higher energy spread. It turns up in spectra as a widening of the absorption line. So lines in, say, a normal A star are usually pretty narrow all the way down, but in a white dwarf they are just hugely wide at the base, but narrow towards the peak (because pressure broadening results in a lorentzian profile).
Also collision directions are random, so although the effect is a kind of Doppler shift, it goes in both the red and the blue directions. Which is why it’s a broadening instead of a line shift.