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COSMOS HST/ACS Data   (I-band)                                  Version 1.3
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The Cosmic Evolution Survey (COSMOS) is an HST Treasury Project to survey
a 2 square degree equatorial field, centered on RA=10:00:28.6 and
DEC=+02:12:21.0, using the ACS camera. The project also incorporates major
commitments from other observatories around the world, including the VLA
radio telescope, ESO's VLT in Chile, ESA's XMM X-ray satellite, and the
Japanese 8-meter Subaru telescope in Hawaii.

These data represent the third public release of the COSMOS observations
from the ACS instrument on HST. Included in this release are 81 image tiles
comprising the entire survey, observed using the F814W (I-band) filter.

The key characteristics of these data:

	Instrument:		HST Advanced Camera for Surveys (ACS)
	Dates of observations:	Cycle 12-13 (Jul 2003 - Jun 2005)
	Observing time:		4 exposures / 1 orbit / pointing
	Filter:			F814W (I-band)
	Area:			~2 sq deg
	Resolution:		0.05"/pixel (drizzled data)

These data were reduced by Anton Koekemoer (koekemoer@stsci.edu) using 
the MultiDrizzle software package (Koekemoer et all. 2002).  More information 
on MultiDrizzle can be found here:

Koekemoer, A. M., Fruchter, A. S., Hook, R. H., Hack, W. 2002, HST Calibration
Workshop, p. 337

http://www.stsci.edu/hst/acs/analysis/multidrizzle

The data products available here include:

	(1) drizzled, flux calibrated, astrometrically correct images,
	    rotated such that north is up, east to the left, and tiled
	    to match the COSMOS ground-based observations
	(2) corresponding weight images (exposure maps)

The image files follow a standard naming scheme where, for example:

	acs_I_092_sci_13.fits

refers to an HST/ACS I-band (F814W) mosaic image at tile position 92,
version 1.3. Both science images ("_sci_" in file name) and weighting
images ("_wht_" in file name) are provided.

New in this version of the data is a slight rotation adjustment to the
field, and delivery of the data in tiles, matching the 144 tile positions
of the COSMOS ground-based data. This produces larger files than in
previous versions of the ACS data, but allows for easier comparison with
other COSMOS data products. This release is essentially a "convenience"
release, and so science done using versions 1.2 and 1.3 of the ACS data
should produce identical results.

Please note: The COSMOS ACS FITS images contain floating point data but do
not use IEEE NaN values to denote blank pixels.  Rather each image has an
associated weight image mask (also a floating point FITS image) that should
be used to weight image operations.  In particular, mask values of zero
indicate areas of no data (including pixels masked off because of radiation
hits).

Further information may be obtained from the main COSMOS web page:

	http://cosmos.astro.caltech.edu/

and the COSMOS HST/ACS web page:

	http://www.stsci.edu/~koekemoe/cosmos/

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The COSMOS Team, Patrick Shopbell (Archive Lead), and Anton Koekemoer
pls@astro.caltech.edu, koekemoer@stsci.edu

January 11, 2007