Prime Focus CCD Imaging May 29-30th, 1998.

These observations were carried out by K. Glazebrook, R. Abraham and C. Tinney at the Anglo-Australian Telescope on the nights of May 29-30th 1998.  All observations were carried out with a TEK 1024x1024 CCD (0.391 arcsec/pixel) with a FOV of 6.6 arcmin.

May 29th was a photometric night with seeing 0.8 arcsec all night. Most of the data was taken on this night.  See below for the photometric zeropoint information.

May 30th was a non-photometric night with seeing of 2-3 arcsec and variable extinction (up to 1 mag).

All images are stacked and cosmic-ray clipped and have RA/DEC World Coordinate System added by comparing with the USNO A2.0 star catalog (Monet et al., 1998). The average astrometric offset between overlapping images in the AAT-WFPC2 and AAT-STIS fields is 0.12 arcsec. This finding chart shows the locations of the WFPC2 and STIS fields.

Zeropoints given allow calculation of magnitudes via:

Mag. of an object = Z - 2.5 * log (total counts from object in combined frame)

Summary details of the photometry, astrometry and data reduction are given in Glazebrook et al., (2006) AJ in press and are described more fully in this Supplemental Appendix.


WFPC2 field


 
R-band image (FITS file 4Mb), taken in photometric conditions and 0.8 arcsec seeing. The HDF was offset from the field centre to minimise contaminating ghosting from the very bright star just off the FOV, and is approximately located at (x,y)=(807,503).  Zeropoint based on the mean airmass is  Z=31.21

B-band image (FITS file 4Mb) was taken in the same conditions and the same centre.   Z=31.23
 

STIS field

R-band image (FITS file 4Mb), taken in photometric conditions and 0.8 arcsec seeing. Again the HDF was offset from the field centre to minimise contaminating ghosting from the very bright star just off the FOV, and is approximately located at (x,y)=(804,585).   Z=31.24
 

B-band image (FITS file 4Mb), taken in non-photometric conditions and 2.2 arcsec seeing. Same field centre as the R image. Cross-matching with the AAT-WFPC2 B image allows robust determination of the zeropoint Z=30.97, see the AJ paper for full details.

Photometric Zeropoints Information.

The magnitudes of the Landolt (AJ 104, 340, 1992) standards are fit with the equation:

Zpt = Z0 - a * airmass -  b * (BLan -RLan)

Where Zpt is the Landolt magnitude - Instrumental magnitude (= -2.5 * log counts/sec).

For the night of 29 May I derive the following fits from 29 stars (7 Landolt fields):
 
 

Band Z0  a  b RMS residual 
(mags)
B (plot) 24.899 0.256 -0.094 0.058
R (plot) 24.742 0.112 -0.017 0.052
Notes:
  1. The colour term between the CCD and the Landolt system is small.
  2. The extinction values, a, agree very well with the values tabulated in the AAO CCD Imaging Manual, confirming the night was indeed photometric.
  3. The tabulated values are used, with the mean airmass and b=0, to derive the zeropoints given above for each combined frame in the CCD system.
  4. The plots have an arbitrary constant of 20 subtracted from Z0
 

And finally...

Many thanks to Bob Abraham for riding in the Prime Focus cage and making these observations possible!

All data was reduced using the Perl Data Language.

BobPF

Last Change: Karl Glazebrook, June 22nd 1998. (Updated Dec 2005).