Sep 30, 2007 UT: Photometry of HS 2331+3905 (= V455 And)

Michael Richmond
Sep 30, 2007

On the night of Sep 29/30, 2007 EDT, Michael Richmond used the RIT Observatory's 12-inch Meade telescope and SBIG ST8 CCD camera to monitor the cataclysmic variable star HS 2331+3905 (also known as V455 And), 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 tonight:

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 4 pixels = 7.4 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.

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

HS 2331 is the star with large scatter at differential magnitude 3.6. The brightest comparison star, "B", is definitely saturated. Stars "A" and "C" have scatter of 0.006 and 0.008 mag, respectively, from their mean values.

Light curves for selected stars (HS 2331 and stars A - J) in the field are shown below. HS 2331, shown by light green crosses near the bottom, is clearly variable. You can see that the clouds which arrived near the end of the run ruined the last images. Don't pay attention to any measurements after JD 373.55

Here's a closeup of the variation in HS 2331 itself. I've also plotted the measurments of nearby star "J", shifting them by 1.0 magnitudes so that they would fit nicely on the graph

You can see that the star has faded considerably since the outburst was discovered on Sep 4 -- but the fading almost stopped between JD 368 and 373. The amplitude of variation increased in this most recent night.

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. Remember: this data is unfiltered, but I am shifting the zeropoint to make star "A" match its V-band value.

Here's the start of the table.

# Measurements of HS 2331+3905 made at RIT Obs, Sep 30, 2007 UT, 
#   made by Michael Richmond. 
# All data taken with 12-inch LX-200 + no filter + SBIG ST-8 CCD 
#    no focal reducer, so at native f/10 
# Each exposure 15 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    uncert
Sep29.99851      4373.49851   4373.50304  13.931  0.032 
Sep29.99881      4373.49881   4373.50334  13.869  0.029 
Sep29.99912      4373.49912   4373.50365  13.872  0.029 

Last modified 9/26/2007 by MWR.