Photometry of WZ Sge at RIT Observatory: July 25, 2001 UT

On the night of July 25, 2001 UT, Tracy Davis and Michael Richmond used the RIT Observatory's 10-inch Meade LX200 telescope to monitor WZ Sge. All exposures were taken without the focal reducer, through a V-band filter, onto an SBIG ST-8 CCD camera. Each exposure was 10 seconds long. Due to the design of the SBIG software, the time of each exposure is accurate only to +/- 1 second. The field of view was about 17 by 12 arcminutes; a typical example is shown below:

We subtracted dark current from the images and divided by a median twilight sky flatfield. We ran software to detect all stars more than 4 sigma above the sky, then measured the light from each star within a circular aperture of radius 13 arcseconds.

The night wasn't perfect: bands of cumulus clouds passed through every hour or so. Of the original 568 images of the field, we chose 512 good ones. We fed all raw instrumental magnitudes of 72 stars on those 512 images into a program which implemented Honeycutt's inhomogeneous ensemble photometry technique. The solution gave most weight to the bright stars "A" and "B" (marked above). The standard deviation from the mean magnitudes in the solution are shown below, as a function of differential magnitude.

The solution placed the mean magnitude of WZ Sge at zero; the mean magnitudes for star "A" = GSC 1612.1830 = HD 191083 was 0.401, and star "B" = HD 351517 was 1.389. The scatter for these bright stars is very small: star "A" has a standard deviation of 0.004 magnitudes.

We used star "B" as a check star to detect errors due to clouds or poor images (which clearly were present in the entire night's run). We discarded any image in which star "B" differed from its mean magnitude by more than +/- 3 times its standard deviation.

The final result is 483 measurements of WZ Sge over a span of five hours. Here is the light curve:

You can download an ASCII text file with the measurements:

The file has some comments at the top, followed by data lines with 4 numbers per line, like this:

       Jul_25.07053     2115.57053   2115.57519  -0.193 
The columns are:
  1. UT day
  2. Julian Date - 2,450,000
  3. Heliocentric Julian Date - 2,450,000
  4. differential V-band magnitude of WZ Sge (relative to star "A" = HD 191083)

Last modified 8/22/2001 by MWR.