Sep 07, 2007 UT: Photometry of HS 2331+3905

Michael Richmond
Sep 07, 2007

On the night of Sep 06/07, 2007 EDT, Tracy Davis and 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 earlier nights. 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 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.

Look at the difference between the ensemble zero-point on a cloudy night (Sep 05/06, shown in green) and a clearish night (this night, Sep 06/07, shown in red).

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 0.01 mag from their mean values.

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. It has faded a bit since last night, however: It had V-band mag of about 8.7 last night, but was at V-band of about 9.2 tonight.

Here's a closeup of the variation in HS 2331 itself. I've also plotted the measurments of star "A", shifting them by 1.3 magnitudes so that they would fit nicely on the graph. Star "A" has errorbars to show the estimated uncertainty in each measurement.

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 7, 2007 UT, 
#   made by Michael Richmond and Tracy Davis. 
# 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    
Sep07.02148      4350.52148   4350.52550   9.167  
Sep07.02170      4350.52170   4350.52572   9.210  
Sep07.02192      4350.52192   4350.52594   9.182  
Sep07.02215      4350.52215   4350.52617   9.129  

Last modified 9/7/2007 by MWR.