Photometry of WZ Sge at RIT Observatory: August 22, 2001 UT

On the night of August 22, 2001 UT, Michael Richmond and Stacey Davis 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 15 seconds long. This was probably a mistake: the telescope's drive has a periodic error which can cause a slight trailing, and the effect is much stronger in 15-second exposures than 10-second exposures. 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 6.6 arcseconds.

The night was good and bad: clear after sunset for a few hours, then covered by fluffy clouds, and again clear for the last few hours. The first clear period runs from JD *2143.53 to *2143.60, and the second from JD *2143.73 to *2143.87. The airmass was over 2.5 for the last observations, so their quality is poor.

We gathered about 900 images of the field, but discarded many due to the weather. We fed all raw instrumental magnitudes of 169 stars on 603 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 stars "A" = GSC 1612.1830 = HD 191083 and "B" = HD 351517 as follows:

       star   mean      stdev
         A    0.0       0.005
         B    0.967     0.012 

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 593 measurements of WZ Sge, in two segments. 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.