Notes to accompany the file XO-1.surveydata.txt.  

The first column, as indicated, is the Heliocentric Julian Date (HJD).
The second column (deltamag1) and the third column (deltamag2) are
differential magnitudes with respect to the star in its out-of-transit
state; deltamag1 and deltamag2 are identical except one is flagged
appropriately, based upon weather conditions, sky brightness
(moon), etc. Flagged values are indicated with NaN. 

We do not use deltamag2 values in our analysis unless a trained human
examines those data with due diligence. Sorry, we do not have the
resources to provide the training and auxillary data so that others
may perform that due diligence. ("Do not use deltamag2" is good advice.)

You will note that often the HJD values come in pairs, with each pair
separated by <~ 0.0003 days.  To facilitate our analysis, a 0.25-minute
offset is added arbitrarily to the times of one of the cameras.  Because
the two XO camera's data are not differentiated in this table, there's
no way to know which values have been shifted. It may be best for you
to imagine that the error in the timing is 0.25 minute.  (Some nights
only one camera is operational.)

If you read these into IDL, you might use this command:

IDL> rdfloat,'XO-1.surveydata.txt',t,m1,m2,/double,skip=1
% RDFLOAT: 4327 lines of data read
IDL> help,t,m1,m2
T               DOUBLE    = Array[4327]
M1              DOUBLE    = Array[4327]
M2              DOUBLE    = Array[4327]
IDL>

The double precision is required to retain the precision of the HJD.

You should be able to re-create Figure 2 of McCullough et al (2006, astroph/0605414)
from {t,m1} using the ephemeris given in that paper. 

Peter McCullough, Jun 1, 2006