Photometry of WZ Sge at RIT Observatory: August 30, 2001 UT

On the night of August 30, 2001 UT, Matt Aggleton, Stacey 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 15 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 (North is up, East to the left):

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: no clouds, but a bright waxing gibbous moon.

Due to a sharp drop in temperature at the start of the night, the images fell out of focus for a time; the effect is worst from JD *151.60 to *151.645. After *151.645, we refocused the telescope, and the images remained in good focus for the rest of the night. There is a small trend in the relative magnitudes of some stars during this span, with a sudden jump of up to 0.035 mag after re-focusing. The size of the effect varies with position in the field, and -- fortunately -- is nearly zero at the position of WZ Sge.

The exposure time of 15 seconds caused the primary comparison star, "A" = GSC 1612.1830 = HD 191083, to be at or near saturation in some images. We did not use "A" as a comparison in the reductions below, though we did track its measurements.

We gathered about 850 images of the field. We fed all raw instrumental magnitudes of 178 stars into a program which implemented Honeycutt's inhomogeneous ensemble photometry technique. The solution gave most weight to the stars marked "A" and "B" in the chart 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       0.010     
         B    0.965     0.017

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 832 measurements of WZ Sge, over a period of 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 8/31/2001 by MWR.