This is the README file for the final pass photometry. 

The stars x,y positions in the *.XYVIQ file are converted to RA and Dec using
the F606W fits image available from the Twiki page. The result is pasted to the
*.XYVIQ file to create a *.RDVIQ file. 

The *.RDVIQ is then input into fortran code that applies the CTE correction to
the long and short exposure magnitudes and refines the magnitude offsets between
the long and short magnitudes. The code also calculates the photometric error
for stars with only 1 measurement using the root(n) noise in the star. The
results are output into a file called *.RDVIQ.cal. Note that any star with
wV or wI equal to 3 comes from the satphot algorithm applied to saturated stars.

The *.RDVIQ.cal files are then adjusted to the astrometric zeropoint derived from
the 2MASS catalog and named *.RDVIQ.cal.adj.

The *.RDVIQ.cal.*.zpt files include the new photometric zeropoints for ACS/WFC
from ACS-ISR-2007-02 (Mack et al. 2007).

The columns in the *.RDVIQ.cal.* files are:

id = star number from the original files
x  = star x position on the master frame
y  = star y position on the master frame
Vvega = F606W VEGA mag from Sirianni et al. (2005) (Table 10)
err   = error in F606W mag from column 7 in .XYVIQ file
VIvega  = V-I VEGAmag
err    = error in V-I VEGAmag
Ivega  = F814W VEGA mag from Sirianni (2005) (Table 10)
err    = error in F814W mag from column 8 in .XYVIQ file
Vground = ground-based V mag from Sirianni et al. (2005) (Table 18)
Iground = ground-based I mag from Sirianni et al. (2005) (Table 18)
Nv      = number of measurements in the V mag
Ni      = number of measurements in the I mag
wV      = where did the V mag come from (1=deep unsat, 2=short unsat)
wI      = where did the I mag come from (3=short sat, 4=deep sat)
xsig    = RMS of x positions
ysig    = RMS of y positions
othv    = fraction of F606W light from other stars
othi    = fraction of F814W light from other stars
qfitV   = quality of the V fit (smaller is better)
qfitI   = quality of the I fit
RA      = RA from the COMB.fits file header
Dec     = Dec from the COMB.fits file header

A value of 9.900 for any quantity means that it has no measurement.

There are also two other files - Vcte_check.dat and Icte_check.dat. These list
information for stars in the magnitude overlap between the long and short exposure
images. These have the following columns (same for the V and I files):

id       = star number from the original files
Yraw     = raw y-position (on the original image)
Vsky     = sky value in e-
V_short  = mag from the short exposures adjusted to the long exp frames
V_short_cte_adj = short exp mag corrected for CTE and adjusted to the scale of the long exp
V_long_cte_adj  = long exp mag corrected for CTE

The idea is to plot the difference between the long and short exp mags to look for
trends with Y-position or anything else that might signal a problem.