Astronomical Applications Department, U.S. Naval Observatory thesis Page 34
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summarizes these observations.
Galaxy Telescope Filter Exposure Time s Date
HoII
MLO
U
1200
Nov
2, 1995
MLO
B
300
Feb 24, 1995
MLO
R
120
Feb 24, 1995
MLO
H
600
Feb 24, 1995
IC2574 MLO
U
1200
May 25, 1995
MLO
B
300
May 25, 1995
MLO
V
120
May 25, 1995
MLO
R
120
Nov 23, 1995
MLO
H
1200
Nov 11, 1995
Sex-A LCO
U
1200
Apr 25, 1996
LCO
B
600
Apr 25, 1996
LCO
V
120
May 28, 1995
LCO
R
500
Apr 24, 1996
LCO
H
1200
Apr 24, 1996
Table 2.2. Optical Observations
The optical images are median combined with at least two other images having
the same exposure time to remove cosmic rays and other defects. Astrometry and
photometry are implemented using standard IDL procedures for data reduction.
Background values are determined for each image by taking the mean of pixels in
20, 10
10 pixel boxes.
HoII broad-band images are calibrated using unpublished photoelectric pho-
tometry Corwin 1997 of three bright stars in the galaxy. The IC2574 broad-band
images are calibrated using published photometry of seven stars in the galaxy eld
Sandage & Tammann 1974. The Sextans A broad-band images are calibrated
using published photometry of six stars in the galaxy eld from Van Dyk
et
al.
1998. Total magnitudes of the galaxies given in the RC3 agree with our measured
values within reasonable limits providing a check of the calibration constants.
The H lter at Mt. Laguna has a centroid wavelength 6573 A and width
