Subject:	XO Project Data Release 1, XO-DR1
Date: 		January 29, 2007
From:		McCullough, P. R., XO Project Principal Investigator

The XO Project Data Release 1, XO-DR1, is hereby released into
the public domain. The main purpose of doing so is to stimulate
useful collaboration between qualified researchers.  Four potential
applications are immediately apparent: 1) collaborative data sharing
to improve detection of transiting exoplanets, especially by those with
complementary observations of the same stars, 2) collaborative improvement
of calibration and exoplanet-detection techniques, 3) discovery of
variable stars, and 4) wider appreciation of the potential of such data
sets to contribute to discovery and study of variable stars. There is no
support from the XO Project for other potential applications of XO-DR1
such as education and outreach.

The contents of the XO-DR1 are briefly summarized here.  See McCullough
et al. (2005, PASP 117, 783, especially Section 5) for additional
information. The nominal center of the 7 degree by 7 degree field of
view is RA=240 degrees, DEC=+31 degrees. Only stars approximately in the
range 9 < V < 12 are recorded.  There are two cameras with a (nearly)
common bore sight on the same German equatorial mount, so nominally there
are two observations at each epoch, artificially offset by 15 seconds in
the epoch.  Column 5 of the 240p31key.fits reports which camera (0 or 1)
made the observation.  Also, the mount scans northward when it is east
of the meridian and southward when it is west of the meridian, so the
CCD X value flips accordingly, approximately about the center of the
CCD (col=512). The mount repeats each scan with a 10-minute cadence, so
there are 12 observations per hour of each star, nominally.  The Julian
dates range from 2453080 to 2453566, or 2004.03.15 to 2005.07.14. All
observations were made on Haleakala, Maui, Hawaii, USA.

Except where noted below, each file is a 2-dimensional (NAXIS=2) floating
point (BITPIX=-32) FITS format image, arranged with 2503 stars (columns)
and 4502 epochs (rows), or 45077760 bytes uncompressed. One exception is
the 240p31key.fits, which stores 65 keywords per epoch instead of the 2503
stars. The keywords are described by the included file, bnkeys.pro, which
contains conditions at the moment of the observation, such as weather,
positions of the Sun and Moon, etc.

All FITS files have been losslessly gzip compressed, approximately by 2x.
The flat-fielded images exist from which the photometry was extracted but
are not part of the XO-DR1, primarily to make the data volume manageable:
a single CD can store the uncompressed XO-DR1 in its entirety.

You are welcome to re-distribute the XO-DR1 so long as you do so in its
entirety, including this description. Distribution of modified versions
of the XO-DR1 are encouraged so long as they are clearly labeled as such.

Citations to XO-DR1 may use the following or an equivalent:
McCullough, P. R., 2007 XO Data Release 1, XO-DR1, private communication.

..........................................................................

Files may be retrieved with the following command:
wget -r -nd -np http://www-int.stsci.edu/~pmcc/xo/XO-DR1/

........................Contents of XO-DR1................................

readme.html		This file.

240p31key.fits		Keywords.
240p31r.fits		Right Ascension.
240p31d.fits		Declination.
240p31mag.fits		Magnitudes, raw, instrumental. V = (Instrumental - 2.7)
240p31emag.fits		Error in Magnitude, lower limit, theoretical, unreliable.
240p31cal0.fits		Calibrated magnitudes, 0th order.
240p31cal.fits		Calibrated magnitudes, penultimate prior to flagging.
240p31calf.fits		Calibrated and flagged magnitudes, final.
240p31cc.fits		Correlation Coefficient of PSF with nominal Gaussian.
240p31air.fits		Airmass.
240p31sky.fits		Sky values.
240p31x.fits		CCD X values (columns).
240p31y.fits		CCD Y values (rows)

bnkeys.pro		Limited description of contents of 240p31key.fits.
xo_dr1.pro		Example of light curve extraction (for XO-1b).
			(cf. McCullough et al. 2006, ApJ, 648, 1228).
..........................................................................

Bibliography
McCullough et al. 2005
McCullough et al. 2006