Telescope: ESO 2.2m
Instrument: Wide Field Imager
Dates: 15-18/5/2000
Observer: G. Szokoly
Comments:

  The following fields were observed with close to photometric sky but
horrible seeing (1.2-2.0"), in bright time:

Q1246 (I)
RXJ 1347 (Z)
Cen-X-4 (Z)
Gal Ridge 2 (I)
G21 (I, with some ZRVB)
NGC 4666 (I)
RXJ 1354 (I)
Cent. B (I)
A 1983 (Z)
MKW9 (Z)
W49B (I)

  Most of the fields were integrated on for 10x600s (i.e. 6 ksec total) in
either I or Z. For most of the fields a dithering pattern was used with
small offsets to elliminate gaps and bad pixels (this still gives a field
of view larger than needed for follow-up).
  One exception is the G21 field, where the 10 I-band exposures were taken with
much larger separation to cover all 5 X-Ray pointings. In this area, additional
bands were also used with fewer exposures (3-5 exposures per band, 600s each,
in bands Z, R, V and B).
  The I-band data for this field is also reduced to some exctent. Estimate
for depth is (for a single, 600s exposure):
Zeropoint: 30.05
Sky sigma: 56
Seeing: 1.3"
  This gives a S/N  for an I  point source (a factor of 2 worse than
the book value). At this stage photometry is probably 5% accurate (need
more work and testing) and astrometry is better than 1" (needs to be tested).
The astrometry reference frame is the USNO-2 catalog. A preliminary 'I' image
for the field is available (750 MBytes, 14kx14k pixels). I'm working on the
catalog. Just by looking at the image I estimate that the typical separation
between objects is a few arc seconds (less than 5) so a very accurate
X-Ray astrometry will be needed (this is a galactic field at 21.5, -1
galactic coordinates).

Gyula