Damon Frezza and Katelyn Allers (Bucknell University)
How are stars born? One of the least understood stages in a star’s evolution is its formation. In order to study star formation we must look deep into dense clouds of dust and gas called nebulae. One such nebula is Rho Ophiuchus and, at a distance of 130 parsecs, it is the closest star-forming region to Earth. An integral part of studying the nebula is distinguishing between the objects which are a part of it and the distant stars which lie behind it. We use Spitzer Space Telescope images from 2004 and 2013 to make the distinction between background stars and Ophiuchus members. We establish the movement of objects across the sky (proper motion). Members of Ophiuchus will have motion consistent with the bulk motion of the nebula. Ophiuchus moves approximately 29 milliarcseconds per year across the sky (about 1/120,000th of a degree). This is a small motion in comparison with the size of the Spitzer image pixels but Spitzer/IRAC is very stable, allowing for very accurate astrometry. The limit on astrometric precision to date has been the default 3rd order IRAC distortion solution. We created a 5th order distortion solution which improves the theoretical astrometric noise floor from ~0.2 arcseconds to ~0.02 arcseconds at each epoch. Using this we are creating a source list for further study.