As I write this it is April 9 (though it will only be posted
much later after editing), and I am on the train home from Jamaica Station: the
last leg of a journey that began over twenty-seven hours ago when I departed from
Cerro Tololo Inter-American Observatory in Chile. Many interesting things happened to me in Chile
March 28, 2014: I woke up early in a peaceful dorm room within the
AURA (Associated Universities for Research in Astronomy) compound in the
seaside town of La Serena, Chile. I had
to hurry to catch the Carryall – a big white van – up to Cerro Tololo, where I
will be using the 4 meter Blanco Telescope.
The one and a half hour drive from La Serena to the observatory runs first
through pastures and vineyards and then up into desolate, beautiful mountains
where few have reason to be except the miners who exploit Chile
The 4m Blanco was built as a twin of the Mayall telescope at
Kitt Peak Kitt
Peak
I have come up to the observatory early: my observations do
not actually start until tomorrow night.
I plan to spend the intervening 24 hours getting some familiarity with
the telescope and instrument. I hope to
meet tonight’s observer at dinner and ask permission to be present in the
control room. It turns out that
tonight’s observations will be part of a long-term campaign monitoring and
searching for light-echoes from ancient supernovae and other huge stellar
outbursts. As this campaign requires many widely-spaced, single nights of
observations, it would be silly for the main astronomer in charge to fly from
the US to Chile
One of my favorite things about visiting observatories is
talking to other astronomers about the interesting research they are doing, and
tonight turns out to be especially good in that respect. In addition to tonight’s observer and the
telescope operator, another astronomer spends much of the night in the control
room. Both astronomers have fascinating things to say. We talk about light-echoes from Eta Carinae’s
Great Outburst, and from the supernova observed by Tycho Brahe. We talk about spectroscopy of extremely
metal-poor stars that were born in the early universe. Such stars are
metal-poor because they were born so early in cosmic history that few of the
massive stars whose explosions release metals into the galaxy had yet had time
to form and die. It turns out that some
of these metal-poor stars have unusual patterns of elemental abundances –
patterns that suggest the explosion of just one earlier massive star may be responsible
for all their heavy elements. Thus we
should imagine a wild, brand-new galaxy with stars just beginning to form, and
in a given region of the galaxy there has probably only yet been one supernova. The low-mass stars that form in that region,
some of which survive to this day, bear in their elemental abundances the
unique signature of that specific supernova.
As the exact elements produced by a supernova depend on the mass of the
star that exploded, studying these unusual low-mass stars allows us to do
something remarkable: estimate the masses of long-dead giant stars that
exploded when our galaxy itself was newly formed.
The actual operation of DECam, the instrument I have come to
use, turns out to be very simple, though different from most astronomical
instruments. In general, when I take an
astronomical image I give a computer command to move the telescope to the
precise location I want, and then another command (often on a separate computer
that runs the instrument) to take the image.
If I want to change something, such as the filter that defines the
colors of light being observed, or the image exposure time, or the telescope
focus, I execute another set of computer commands (or for the focus, sometimes
even analog commands using a hand paddle).
Not with DECam. With DECam I must
make a set of observing scripts ahead of time, specifying the coordinates,
filter, exposure time, and other parameters of each image. If I have set the script up properly, all I
have to do is command the computer to run it and then sit back, relax, and
watch the telescope work for me. In
principle, a whole night’s observations could be put into a single script. In practice, I will want perhaps a dozen
scripts each night, and will make some of them ‘on the fly’, only minutes
before they are needed – in order to give me flexibility to adapt to changing
conditions or implement new ideas I have thought of to optimize the final set
of images I will obtain. I like using
DECam, once I have got used to it. The discipline of having a new script fully
ready before the old one is finished takes some getting used to at first (and
this is very important, to avoid the wasteful and embarrassing situation of
having the huge, powerful telescope sit idle while I am finishing a script). However, the fact that I can write a script
and check it over in several different ways before running it undoubtedly makes
for fewer mistakes and a more organized set of final observations. It also makes some of the observing skills I
have carefully honed over years of practice – the skills that help prevent me
from making mistakes – unnecessary. I
can live with this, however.
