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Direct imaging photometry with the MOST satellite
Canada's first space telescope, MOST (Microvariablity and Oscillationsof Stars) was successfully launched on June 30, 2003 with a primarymission to perform ultra-high-precision photometry to detect acousticoscillations in solar-like stars. MOST has the ability to observe singlefields for uninterrupted periods of up to two months and targets can beobserved either through Fabry lens imaging or Direct imaging. Thisreport reviews the Direct imaging capabilities of the MOST satellite andthe extraction of accurate stellar photometry.MOST is a Canadian Space Agency mission, operated jointly by Dynacon, Inc., and the Universities of Toronto and British Columbia, with assistance from the University of Vienna.
| An Upper Limit on the Albedo of HD 209458b: Direct Imaging Photometry with the MOST Satellite
We present space-based photometry of the transiting exoplanetary systemHD 209458 obtained with the Microvariablity and Oscillations of Stars(MOST) satellite, spanning 14 days and covering 4 transits and 4secondary eclipses. The HD 209458 photometry was obtained in MOST'slower precision direct imaging mode, which is used for targets in thebrightness range 6.5>=V>=13. We describe the photometric reductiontechniques for this mode of observing, in particular the corrections forstray earthshine. We do not detect the secondary eclipse in the MOSTdata, to a limit in depth of 0.053 mmag (1 σ). We set a 1 σupper limit on the planet-star flux ratio of 4.88×10-5corresponding to a geometric albedo upper limit in the MOST bandpass(400-700 nm) of 0.25. The corresponding numbers at the 3 σ levelare 1.34×10-4 and 0.68, respectively. HD 209458b ishalf as bright as Jupiter in the MOST bandpass. This low geometricalbedo value is an important constraint for theoretical models of the HD209458b atmosphere, in particular ruling out the presence of reflectiveclouds. A second MOST campaign on HD 209458 is expected to be sensitiveto an exoplanet albedo as low as 0.13 (1 σ), if the star does notbecome more intrinsically variable in the meantime.MOST is a Canadian Space Agency mission, operated jointly by Dynacon,Inc., and the Universities of Toronto and British Columbia, withassistance from the University of Vienna.
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