DIRECT IMAGING IN THE HABITABLE ZONE AND THE PROBLEM OF ORBITAL MOTION
1. Jared R. Males (a)
2. Andrew J. Skemer (a)
3. Laird M. Close (a)
a. Steward Observatory, University of Arizona, Tucson, AZ 85721, USA
High contrast imaging searches for exoplanets have been conducted on 2.4-10 m telescopes, typically at H band (1.6 μm) and used exposure times of ~1 hr to search for planets with semi-major axes of gsim 10 AU. We are beginning to plan for surveys using extreme-AO systems on the next generation of 30 m class telescopes, where we hope to begin probing the habitable zones (HZs) of nearby stars. Here we highlight a heretofore ignorable problem in direct imaging: planets orbit their stars. Under the parameters of current surveys, orbital motion is negligible over the duration of a typical observation. However, this motion is not negligible when using large diameter telescopes to observe at relatively close stellar distances (1-10 pc), over the long exposure times (10-20 hr) necessary for direct detection of older planets in the HZ. We show that this motion will limit our achievable signal-to-noise ratio and degrade observational completeness. Even on current 8 m class telescopes, orbital motion will need to be accounted for in an attempt to detect HZ planets around the nearest Sun-like stars α Cen A&B, a binary system now known to harbor at least one planet. Here we derive some basic tools for analyzing this problem, and ultimately show that the prospects are good for de-orbiting a series of shorter exposures to correct for orbital motion.