HDF version 2
For the time being, processed data are being stored on the staging
disk of the HST archive. They can can be retrieved by anonymous
ftp from stdatu.stsci.edu, in the directory /pub/hdf/v2, or via
the web links below.
The names of the data sets below reflect the directory structure on
stdatu. Other portions of the HDF web pages provide details on how these
images were constructed. The additional processing for version 2
has resulted in about 10% improvement in S/N
for the F450W, F606W, and F814W filters. 10 sigma limiting magnitudes are now
roughly as follows, within an aperture of area 0.2 square arcsec:
Filter AB Mag limit (10 sigma)
F300W 26.98
F450W 27.86
F606W 28.21
F814W 27.60
The table below lists the number of frames, total exposure time,
and summed sky levels in DN for the version 2 images.
Filter Nframes Texp Sky1 Sky2 Sky3 Sky4
F300W 77 153700 39.259 78.642 92.954 89.686
F450W 58 120600 65.055 310.133 319.222 309.483
F606W 103 109050 238.507 1146.402 1155.758 1131.676
F814W 58 123600 158.615 768.667 771.862 754.104
Note that the v2 drizzled images have had sky subtracted and
are normalized to 1 sec exposure time.
Photometric zeropoints are the
same as for version 1.
Much of the improvement in S/N came from the inclusion of data
that was rejected from version 1 due to either
scattered light or
small rotations of the field. The scattered light pattern was
carefully subtracted from the affected frames before combining
them into the version 2 drizzled images. A number of frames
were
not used in version2, either
because they had high background, or few enough exposures that
it was difficult to remove cosmic rays completely.
NOTE: 3/13/96
There is a problem in the World Coordinate System (WCS) in the version
2 images. The v2 image headers have had a lot of stuff stripped out of
them that was in the v1 edition. 99% of that information was useless,
but two keywords pertaining to the WCS were not. The parameters
CTYPE1 and CTYPE2 should be set to 'RA---TAN' and 'DEC--TAN',
respectively (note the number of dashes in each entry!). Currently,
they are incorrectly set to 'PIXEL'.
calibration.
Calibration frames used
in the HDF pipeline. This includes the superdark, the superbias,
and the flats. The calibration images for version 2 are identical
to those for version 1.
dither
Stacked images at each dither position.
drizzled
Images at the different dither positions registered to a small fraction
of an original pixel, corrected for geometric distortion, and
``drizzled''
onto a final image with a sampling of 0.04 arcsec/pixel. An image with a
rough estimate 1/variance at the sky level at each pixel is also available.
Catalogs of objects.
Harry Ferguson ferguson@stsci.edu 7/31/96
Andy Fruchter fruchter@stsci.edu 8/1/96