Good morning! I apologize for not being able to write anything last week-- I had
2 midterms and 3 papers due, and I was barely able to come into work at all! But now
things have calmed down; Spring Break is next week, and I'm finished with all of my
classes.
Our observing run is coming up quickly! Since next week is Spring Break, I will
actually leave for Arizona on Wednesday (my parents live in Arizona, so I'll spend a
few days with them before going down to Kitt Peak) The run begins on the night of
March 25, and ends on the morning of March 29. I sure hope we'll have good weather!!
Yesterday, my boss sent me a list of all the objects which we should try to observe--I
believe we're going to have a meeting on Monday to plan everything out. I have never done
anything like this, so I'll be learning as much as you will!!
Since we're building a star catalog, it is very important for us to be certain that
the data we collect is completely accurate. I mentioned before that part of my job is to
remove the instrumental "signatures" left by the telescope itself. Another very important
part of building the catalog is having a separate set of stars whose photometric
information is already known to compare our stars to. We therefore call the stars we're
observing for our catalog "Program stars"; the stars for which the information is already
known are called "Standard stars." The standard stars come from a catalog which was
compiled by an astronomer named Arno Landolt. He spent several years observing around
the celestial equator (the celestial equator is just like the earth's equator-- stars
near the celestial equator would be almost directly overhead to a person standing on
earth's equator). Stars near the celestial equator are visible to people both in the
northern hemisphere and the southern hemisphere. His catalog is filled with literally
hundreds of stars from this region, and are often called the "Landolt standards."
Have you ever looked at what happens to sunlight when it passes through a prism? The
light separates into the colors of the rainbow, right? Well, this visible light is just
a small part of what scientists call the "electromagnetic spectrum." The electromagnetic
spectrum includes the entire range of waves, waves can teach us about the amount of
energy a star is producing. A picture of our sun in radio waves would look very different
from a picture in x-rays, and both would look very different from what the sun looks
like in the visible wavelengths -- wavelengths our eyes can see.
When collecting photometric information about the stars, astronomers typically use
five of what we call 'passbands': U (ultraviolet), B (blue), V (visible), R (red), and
I (near- infrared). A passband, as you might have guessed, is a narrow region of the
electromagnetic spectrum. In order to only study within a certain passband, astronomers
have to block out the rest of the spectrum with very sensitive filters. Of course, many
astronomers choose other filters, but these five are probably the most common. The first
GSPC catalog included data only from the B and V filters; the second GSPC (which I'm
working on) will contain B, V, and R data and will also include much fainter stars.
So what does all this have to do with our observing run? Well, when we go out to the
telescope, it's important not only for us to know which "program" stars to observe for
our catalog, but also which "standard" stars to use. The standard stars help us to
account for atmospheric distortions. When a star is directly overhead, its light will
pass through much less atmosphere than when the star is near the horizon. We therefore
observe these standard stars at many positions in the sky (overhead, at 30 degrees that
we can take into account the effects of the atmosphere when reducing the data from our
program stars. Does this make sense? We already know what the data from the standard
stars SHOULD be, so when we measure them at many positions in the sky, we can compare
the differences between what the standard star data SHOULD be and what it really is.
We can then take that information and apply it to our program stars.
Pretty neat, huh?
Well, I'll be sure to write more next week before I leave, and I promise to write from
Kitt Peak!!