Proc. SPIE 6689, 66890C, 1−8, 2007
Solar Physics and Space Weather Instrumentation II
S. Fineschi and R.A. Viereck (eds)
© SPIE − The International Society for Optical Engineering

A Procedure for Fitting Point Sources in SMEI White-Light Full-Sky Maps

P.P. Hick, A. Buffington and B.V. Jackson
Center for Astrophysics and Space Sciences, University of California San Diego


The Solar Mass Ejection Imager (SMEI) instrument consists of three CCD cameras with individual fields of view of 60°x3° that combined sweep a 160° arc of sky. SMEI covers the entire sky in one spacecraft orbit of 102 minutes. Individual 4-s exposures from each orbit are assembled into full-sky maps. The primary objective in the SMEI data reduction is to isolate the Thomson-scattering signal across the sky from free electrons in the solar wind. One of the steps needed to achieve the required photometric precision is the individual fitting and removal of stars brighter than 6th magnitude from the full-sky maps. The point-spread function of the SMEI optics has several unusual properties. It has a full width of about one degree, is asymmetric, and varies in width depending on where in the field of view the image is formed. Moreover, the orientation of the PSF on the sidereal sky rotates over 360° over the course of a year. We describe the procedure used to fit and subtract individual stars from the SMEI full-sky maps. A by-product of this procedure are time series at the orbital time resolution for stars brighter than 6th magnitude. These results are used by Buffington et al. (2007) to calibrate the SMEI instrument against the LASCO C3 coronagraph.