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
Abstract
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.