Sep 06, 2007 UT: Photometry of HS 2331+3905

Michael Richmond
Sep 06, 2007

On the night of Sep 05/06, 2007 EDT, I used the RIT Observatory's 12-inch Meade telescope and SBIG ST8 CCD camera to monitor the cataclysmic variable star HS 2331+3905, which was in the early stages of an outburst. This star is a cataclysmic variable similar to WZ Sge. For more information about it, read

The plan:

Notes from the night

This is a chart of the field based on images taken on this night. Click on the chart for a larger version.

The chart has several of the brighter stars in the field labelled with letters, just to keep me straight as I perform the reductions. Some of these stars have good photometry, as mentioned in AAVSO Alert Notice 357 .

label     RA               Dec                 V               B       visual
      23:37:10.49     +39:27:09.7      8.366 (0.014)   9.430 (0.025)   84
      23:31:57.51     +39:19:43.4      9.248 (0.024)   9.969 (0.031)   93
      23:33:05.63     +39:23:11.8      9.572 (0.029)  10.693 (0.059)   96
      23:33:53.74     +38:57:22.6     10.007 (0.042)  11.115 (0.087)  100
      23:34:46.69     +39:16:44.0     10.310 (0.043)  10.961 (0.054)  103
 B    23:33:23.41     +39:17:58.8     10.481 (0.055)  11.167 (0.070)  105
 A    23:34:23.38     +39:15:34.9     10.900 (0.078)  11.393 (0.076)  109

I'll use the star marked "A" to set the zeropoint of my differential magnitudes back onto the standard system, at least roughly.

I measured the instrumental magnitude of each star with aperture photometry, using a radius of 3 pixels = 5.6 arcseconds (this was less noisy than apertures of 4 or 5 pixels). and sky defined by an annulus around each star. Following the procedures outlined by Kent Honeycutt's article on inhomogeneous ensemble photometry, I used all stars available in each image to define a reference frame, and measured each star against this frame.

I wasn't kidding when I said the night was cloudy. Here's an estimate of the zero-point of the instrumental magnitudes as a function of time during my run. Small values on this graph mean "clear skies".

Below is a graph of the scatter in differential magnitude versus magnitude in the ensemble solution.

HS 2331 is the brightest star in the ensemble, with a mean differential mag of 0.0 (by definition). The brightest two comparison stars, "A" and "B", have a scatter of about 0.02 or 0.03 mag from their mean values. On a really good night, the scatter would be less than 0.01 mag.

Light curves for selected stars (HS 2331 and stars A - G) in the field are shown below. HS 2331, shown by light green crosses near the top, is clearly variable.

Here's a closeup of the variation in HS 2331 itself. I've also plotted the measurments of star "A", shifting them by 1.7 magnitudes so that they would fit nicely on the graph. Star "A" has errorbars to show the estimated uncertainty in each measurement -- note how the uncertainty increases when clouds pass through and cause its differential magnitude to vary.

Whenever the comparison star "A" shows a lot of scatter, my measurements of HS 2331 aren't very good, either.

I've made a table of the measurements themselves, with three different flavors of time. The differential magnitudes from the ensemble solution have been shifted so that star "A" in my chart, TYC 3231-533-1, has value 10.900.

Here's the start of the table.

# Measurements of HS 2331+3905 made at RIT Obs, Sep 6, 2007 UT, 
#   made by Michael Richmond. 
# All data taken with 12-inch LX-200 + V filter + SBIG ST-8 CCD 
#    no focal reducer, so at native f/10 
# Each exposure 10 seconds long; tabulated times are midexposure 
#    and accurate only to +/- 1 second. 
# 'mag' is a differential magnitude based on ensemble photometry 
#    which has been shifted so TYC 3231-533-1 mag=10.900 
#    to match value from AAVSO Alert Notice 357. 
# UT day      JD-2,450,000  HJD-2,450,000   mag    
Sep06.02453      4349.52453   4349.52851   8.656  
Sep06.02476      4349.52476   4349.52874   8.716  
Sep06.02499      4349.52499   4349.52897   8.646  
Sep06.02521      4349.52521   4349.52919   8.681  

Last modified 9/6/2007 by MWR.