The MOST Asteroseismology Mission: Ultraprecise Photometry from Space

Abstract

The Microvariablity and Oscillations of Stars ( MOST ) mission is a low‐cost microsatellite designed to detect low‐degree acoustic oscillations (periods of minutes) with micromagnitude precision in solar‐type stars and metal‐poor subdwarfs. There are also plans to detect light reflected from giant, short‐period, extrasolar planets and the oscillations of roAp stars and the turbulent variability in the dense winds of Wolf‐Rayet stars. This paper describes the experiment and how we met the challenge of ultraprecise photometry despite severe constraints on the mass, volume, and power available for the instrument. A side‐viewing, 150 mm aperture Rumak‐Maksutov telescope feeds two frame‐transfer CCDs, one for tracking and the other for science. There is a single 300 nm wide filter centered at 525 nm. Microlenses project Fabry images of the brighter (V≤10) target stars onto the science CCD. Fainter target stars will be focused directly elsewhere on the CCD. MOST was launched on 2003 June 30 into a low‐Earth, Sun‐synchronous, polar orbit allowing stars between −19° and +36° declination to be viewed continuously for up to 60 days. Attitude is controlled by reaction wheels and magnetotorquers. A solar safety shutter over the telescope diagonal is the only other moving part. Accumulated photometry will be used to calibrate response across the target field stop, and data will be compressed and downloaded to three dedicated ground stations.