[Previous] | [Session 46] | [Next]
S. Urban, B. Mason (USNO), E. Horch (RIT), E. Holdenried, T. Rafferty, W. Hartkopf (USNO), W. van Altena (Yale)
The 6000 stars making up the SIM grid need to be astrometrically stable at the 4 microarcsecond level over the course of SIM's 5 year mission. As explained in the poster by Mason et al. at this meeting, the need to avoid doubles is imperative. To survey potential candidate stars for duplicity, one needs to cover spatial separation from a few milliarcseconds to several arcseconds and magnitude differences up to 8; no single observing system can handle this, therefore several techniques must be employed. The USNO is leading a project to survey 7200 stars using Fourier Transform Spectroscopy (FTS), optical interferometry, speckle interferometry, and wide-field imaging -- by both conventional CCD and CMOS technology -- to maximize the likelihood that final list contains few multiple systems.
The initial candidate list was selected not only to exclude known or suspected multiple systems and to be spatially uniform, but also to reflect the regimes where all techniques can be employed. Each of the techniques works best on brighter stars. One, the FTS, is primarily sensitive to detect companions around stars of later spectral types. The initial candidate list, therefore, includes only stars in the magnitude range of V=6.5 to V=8.5 and spectral types A5V through G5V.
Surveying of this initial list of 7200 stars has begun utilizing archival speckle interferometry observations as well as new speckle observations on the WIYN 3.5m and the McDonald 2.1m telescopes. Characteristics of the initial list and the observations made to date are presented.
This work has been supported by NASA and the SIM preparatory science program through NRA 98-OSS-007. We gratefully acknowledge this support.