Thursday, December 11, 2008


This is M52:

It's an Open Cluster of stars. This past quarter, my group for my Observational Astrophysics class set out to figure out how far away from us the cluster was and how old the cluster was. We found that the cluster was 894 Parsecs, or 2915 lightyears away and somewhere between 400 million and 3 billion years old. Accepted values say that the cluster is somewhere between 3000 and 7000 lightyears away and more like 30 million years old, so obviously we were off by a little bit. Still, it was an interesting experience. I can't get the pdf uploaded, but basically here's what we did:

First, we got lots of data. We used a CCD camera with multiple filters, which meant we gwere able to take pictures with different wavelengths of light. The picture above was taken with a red filter. Some of the data we got was of Landolt Standard stars, which are stars which have a known magnitude in a variety of wavelengths. From here we were able to get factors which allowed us to calculate the actual magnitudes of the stars in the cluster in various wavelengths. From there, we made a Color-Magnitude Diagram, with the magnitude in the Visual minus the magnitude in the Red on the x-axis and the magnitude in the Visual on the y-axis.

Ordinarily, a Color-Magnitude diagram looks a little like this:

See that nice pattern of stars in the middle? That's the main sequence. Here's our graph:
Notice the complete lack of any sort of pattern like the main sequence. However, we were able to calculate a theoretical main sequence based on Absolute Magnitudes, which is the magnitude of each star if it were located at a distance of 10 parsecs. That graph looked like this:
That line of pinkish dots is what our data should look like. The distance to the cluster should be the distance between the line of the blue data points and the pink theoretical main sequence. That's how we got our distance of 894 Parsecs.

To get the distance, we just found the theoretically youngest star in the cluster, based on its color, and therefore spectral type. That explains why our estimate was way off--the published estimates simply found another star as the youngest in the cluster--a star we didn't observe.

So yeah. That's what I spent a large amount of time this last quarter, and about 10 hours Monday night, doing. It was complicated and annoying, but that's what we got. Astro is fun.

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