Friday, July 14, 2006

Astronomy Internship - Day 35


After finally going through all of the tedious photometry, my advisor has sent me some of the preliminary results. One of the things that we're looking to do, is create a color-magnitude diagram (CMD), essentially an HR Diagram, for NGC 7142. Last night, she put together one from the first round of subtraction (before I went back and with the second routine to get the remaining stars).

So here's an inside look at what's going on! First off, the CMD:

Sketched in here, is the main sequence (yellow) and the red giant branch (red). Keep in mind that this is still a very rough piece because there's still a good amount of calibration to be going through. The cluster will need to be dereddened (ie, the effects of the interstellar cloud accounted for and subtracted) which should help a lot of the scatter along the main sequence.

Additionally, this is instrumental magnitude, meaning how bright it appeared to our instruments. But since each instrument is different, it will eventually have to be brought to a standard system. That's another adventure to look forward to.

Both of these corrections (as well as possible others) will help make things look much prettier.

But that's not all I got today! I also got a plot of the error vs the instrumental magnitude in the V filter:

You'll notice there's a definate trend here in which the uncertainty goes up significantly the fainter the star is (fainter --> higher magnitude number --> further right).

But you'll notice there's a good number of stars on there in the bluish area I put in, that don't really fall on this trend. There's several reasons for this. One is that those stars could have been on the edge of the frame and cut off differently in different exposures, thus making them seem brighter when more was present, and dimmer when most was cut off. That variation between frames drives up the uncertainty.

Perhaps more excitingly, it's possible that those stars in the blue region aren't having a large variation due to problems with our instruments, but because they're actual variable stars. I've already mentioned that there was already one known variable star, but that study was rather incomplete in comparison to the one we're conducting, and it's quite possible that we'll uncover more variable stars.

So now that we've located potential variable stars, we'll have to go back, make sure that the variation isn't caused by something else, and if they do turn out to be true variables, produce as much of a light curve as we can with our limited date in hopes that we can identify the type.

That's my story for the day. Tomrrow I'll probably be spending some time producing more CMDs from the 2MASS data we've obtained.

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