- [*] ACS Flat Field and Low-Order "L-flat" Corrections from
Observations of 47 Tucanae
- Mack J., Bohlin R., Gilliland R., van der Marel R.P.,
de Marchi G., Blakeslee J.
- in the 2002 HST Calibration Workshop, Arribas S., Koekemoer A.,
Whitmore B., eds., Space Telescope Science Institute, Baltimore,
p. 23-30, 2003
- © 2003. The Association of Universities for
Research in Astronomy, Inc. All Rights Reserved.
The uniformity of the WFC and HRC detector response has been assessed
using multiple dithered pointings of 47 Tucanae. By placing the same
stars over different portions of the detector and measuring relative
changes in brightness, low frequency spatial variations in the
response of each detector have been measured. The original WFC and HRC
laboratory flat fields produce photometric errors of 6 to 18 percent
from corner-to-corner. The required low-order correction (L-flat) has
been applied to the lab flats, and new flat fields have been delivered
for use in the calibration pipeline. Initial results indicate that the
photometric response for a given star is now the same to approximately
1 percent for any position in the field of view. A comparison of the
improved flat fields with high signal-to-noise observations of the
bright earth at 3300 Angstrom and with preliminary sky flats at 7700
Angstrom also shows agreement to within 1%
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Last modified March 30, 2003.
Roeland van der Marel,