Photometry of WZ Sge at RIT Observatory: August 15, 2001 UT

On the night of August 15, 2001 UT, Michael Richmond, Stacey Davis, Dustin Crabtree and Kevin Beaulieu 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 8.8 arcseconds.

The night was clear and dark -- a very good one. We spent a short time after sunset taking pictures of asteroids for a group of high-school students, and so spent a bit less time than usual following WZ Sge: from JD *2136.57 UT to *2136.85 UT.

We gathered 1082 images of the field, but discarded a few due to problems of one sort or another. We fed all raw instrumental magnitudes of 203 stars on 1082 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.

In the graph above, the two points with large scatter at diff mag = 2.5 are spurious, due to confusion of one close double.

The solution placed the mean magnitude of stars "A" = GSC 1612.1830 = HD 191083 and "B" = HD 351517 as follows:

       star   mean      stdev
         A    0.0       0.004
         B    0.988     0.008 

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 907 measurements of WZ Sge over a span of about 6.7 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_27.06510     2117.56510   2117.56977   0.046 
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.