A Proper Motion Census of Ophiuchus
Abstract
The motivation for this survey is to discover new objects not detected by previous photometric surveys; objects such as disk-less (Class III) objects, brown dwarfs, and very low luminosity objects. We use proper motion to determine whether or not objects are members of Ophiuchus and therein complete a census of the region. We use Spitzer/IRAC images from two epochs (2004 and 2013) to establish which objects have moved and how far with respect to the background stars. The reported motion of Ophiuchus is ~29 milliarcseconds per year, which is difficult to detect because the IRAC plate scale is large (1,223 milliarcseconds/pixel). Since Spitzer/IRAC is very stable, we should be able to detect very small motions of objects. 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 astrometric noise floor from ~0.2 arcseconds to ~0.02 arcseconds at each epoch. With it we have been able to decrease errors in the positions of detections to under 75 milliarcseconds per image in both the 2004 data and 2013 data. This allows us to identify candidate Ophiuchus members with high statistical significance.
- Publication:
-
American Astronomical Society Meeting Abstracts #223
- Pub Date:
- January 2014
- Bibcode:
- 2014AAS...22344127F