Photometric Zeropoints for the KPNO IRIM Observations
of the Hubble Deep Field
Most of the time spent observing the HDF with IRIM was photometric.
However, a few intervals were not perfectly clear, although usable data
was obtained nevertheless. For the version 1 release, we have set the
zeropoints for the "grand sum" images by bootstrapping from subsets
of the data taken at low airmass and during photometric conditions
as established by standard star observations. For version 2, we plan
more extensive checks of the photometric calibration, but we believe
that the version 1 calibration should be good to 5%.
The zeropoints below are given in the sense that
mag = zeropoint - 2.5 log N
where N is the number of counts measured for the object of interest
in the HDF/IRIM v1 release images. Airmass corrections have already
been incorporated.
Note that the zeropoints are in the standard system where Vega has
m=0 in all bandpasses; these are not AB magnitude
zeropoints. The photometric calibration was done using the faint
UKIRT standard stars of Casali and Hawarden (1992, JCMT-UKIRT Newsletter,
No. 3, p. 33). The K-band observations were made through a "short K" (Ks)
filter, but calibrated under the assumption that K=Ks for the standard
stars.
The zeropoints are:
| Bandpass
| Zeropoint
|
| J |
25.25 |
| H |
25.16 |
| K |
24.57 |
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Copyright © 1997 The Association of Universities for
Research in Astronomy, Inc. All Rights Reserved.
Mark Dickinson: med@stsci.edu 10/24/96