Photometry of WZ Sge at RIT Observatory: July 27, 2001 UT

On the night of July 27, 2001 UT, Michael Richmond used the RIT Observatory's 10-inch Meade LX200 telescope to monitor WZ Sge. He was assisted by a succession of kind people: Stacey Davis, Kevin Beaulieu, Dustin Crabtree. 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:

See note at the end of this document concerning the star marked U, which turns out to be an eclipsing binary!

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 nearly perfect: the clearest, darkest night I've experienced in four years in Rochester, New York. Around an hour after midnight, a small band of low fluffy clouds passed overhead; that was the only departure from perfection. We worked from sunset to sunrise, gathering 1088 images of the field. 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 star "A" = GSC 1612.1830 = HD 191083 at zero, and star "B" = HD 351517 at 1.048. The scatter for these bright stars is very small: star "A" has a standard deviation of 0.005 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 1079 measurements of WZ Sge over a span of seven and a half 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)

Eclipsing binary star "U"

The star marked U in the chart above is at
        RA  =  20:07:55.40
        Dec = +17:31:17.4

During the course of our run on WZ Sge, we found that this star also varied, with a period of about 9 hours and an amplitude in V-band of 0.6 mag peak-to-peak:

I have looked for this star in SIMBAD and in the GCVS, but find no mention of it. Perhaps this is a serendipitous discovery! I believe that may be a contact binary.

Last modified 8/22/2001 by MWR.