Photometric observations of Grid Giant Star Survey candidates

We compare variability of radial velocity (RV) and brightness for a sample of red giants which were selected as candidates for the Grid Giant Star Survey (GGSS). The purpose of the survey is to select astrometrically stable stars as a reference frame for the future Space Interferometry Mission. We incorporate photometric data taken by ROTSE-I and being taken by ROTSE-III robotic telescopes. Typically 2/3 of all GGSS stars to the north of DEC=-35 were observed 76 and 8 times by ROTSE-I and III respectively in white-light filters. It is shown that photometric stability at the 0.02 mag level cannot be used for a pre-selection of RV-stable stars, and the most important tool remains high-resolution spectroscopy. We deeply thank the ROTSE collaboration providing us observing time at the ROTSE-IIIb telescope. We gratefully acknowledge NASA grant NRA-99-04-OSS-058.