Follow-up Photometry and Spectroscopy of Space Interferometry Mission Planet Quest Grid Giant Star Candidates
Abstract
We show our results on followup photometry and spectroscopy of the Grid Giant Star Survey (GGSS) candidates we are establishing in our Space Interferometry Mission (SIM) Preparatory Science program. The GGSS has established thousands of metal-poor giants as SIM Astrometric Grid candidates, based on single-epoch photometric and low resolution spectroscopic observations. Metal-poor G-K giant stars are excellent Grid Candidates because, for a given apparent magnitude, they are very distant and thus show less astrometric ``jitter'' and they are also very numerous and well distributed. Our project is to obtain Followup, multi-epoch photometric and high resolution spectroscopic observations of half of the GGSS candidates (∼ 1000 objects in each hemisphere) in order to monitor photometric and velocity stability. Our RV sample of G-K giants is larger than any previous study. We find that about 2/3 of our stars are variable at these low velocity errors (50-100 m/s), independent of metallicity. The cause of this variation (binarity, planets, star spots, atmospheric jitter, etc.) is not clear. For 3132 stars observed photometrically in the North with ROTSE, we find only a small fraction of observed GGSS candidates are photometrically variable. A lack of correlation between the photometric and RV variability is seen. Thus, it is shown that photometric stability at the 0.025 mag level cannot be used for a pre-selection of RV-stable stars, and the most important tool remains high-resolution spectroscopy.
- Publication:
-
Revista Mexicana de Astronomia y Astrofisica Conference Series
- Pub Date:
- June 2006
- Bibcode:
- 2006RMxAC..26R.180G