# Color-Color Analysis of GLIMPSE Point Sources

### 1. Introduction to GLIMPSE

For my project, I made use of new data from the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE), which uses the Spitzer space telescope. GLIMPSE covers the longitude range |l| = 10-65 and latitude b = -1 to 1 in four mid-infrared wavelength bands, 3.6, 4.5, 5.8, and 8.0 microns. For more information, please visit the GLIMPSE website, or take a look at Benjamin et al. 2003 (1).

### 2. Color Analysis

I spent a lot of time this summer learning how to create, and then analyze, what are called color-color diagrams. In astronomy, a color is defined as the difference between a magnitude at one wavelength and a magnitude at another wavelength. On a color-color diagram, we plot one color versus another color. Another useful plot is a color-magnitude diagram, which plots the magnitude at a certain wavelength versus some color. Sometimes, we will color select objects, meaning we isolate a group of objects that are located in a certain area on the color-color diagram. When I began my work here, I was provided with a list of point sources from the GLIMPSE survey that had a [K]-[8.0] color of at least 3. This means that all these objects were 3 magnitudes brighter at 8.0 microns than at 2.17 microns. Basically, these are very red objects; in fact, there are only 44,464 objects with this color selection out of the 30 million point sources in the GLIMPSE catalog. In addition, I had a list of OH/IR stars from a catalog by Sevenster. Laura Chomiuk, one of Prof Churchwell's graduate students, provided me with these two lists. A color-color diagram was then created by making a contour diagram of the [K]-[8.0]>3 sources, along with red symbols representing the OH/IR stars and green points representing regular field stars:

This diagram has [3.6]-[4.5] on the x-axis and [3.6]-[8.0] on the y-axis. As you can see from the contour diagram, there are two distinct peaks in the distribution of the [K]-[8.0]>3 objects. So, it became my job to try to figure out what kinds of objects are populating these two peaks, what I call my “mystery objects.”

In addition, I should note that the color-color plots, as well as any other plot I made, were created using IDL.

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