The Multichannel Astrometric Photometer with Spectrograph: An Instrument for Characterizing Planetary Systems.

A. Snyder Hale, G.D. Gatewood (University of Pittsburgh), R.S. McMillan (University of Arizona), D.D.S. Hale, W.T. Persinger (University of Pittsburgh)

With few exceptions, the recently detected extrasolar planetary systems are of a totally unexpected nature, and hence give rise to questions about current theories of planetary evolution and formation. To better address these questions, and to eventually better understand our own solar system, more detailed study of these systems is needed. One instrument with the ability to detect planets of Uranian mass, and hence the ability to better characterize known extrasolar planetary systems, has already been awarded observing time on the Keck II telescope. That instrument, the Multichannel Astrometric Photometer with Spectrograph (MAPS), is unique in many ways, and has attributes that give it distinct advantages in a long term observing program. It is the only instrument to simultaneously use two detection techniques (radial velocity and astrometric methods are used). It also makes use of very small field relative astrometry, and the simultaneous measurement of its objects in two colors to substantially improve the astrometric precision attained. The MAPS spectrograph also has resolving power sufficient to discern the shapes of stellar absorption lines, which is important in avoiding false planet detections due to stellar magnetic activity cycles. The instrument, its capabilities, and preliminary results are discussed.