May 04, 2015 UT: CSS 080505

Michael Richmond
May 04, 2015

On the night of May 03/04, 2015, I observed the cataclysmic variable star CSS 080505:163121+103134. You can read more about this star, which has been detected in only one earlier outburst, at

• Kato et al., PASJ 62, 1525 (2010)
• Drake et al., ApJ 696, 870 (2009)

It showed regular variation during my run, though the signal-to-noise ratio was low.

The main setup was:

• Meade 12-inch telescope
• no focal reducer, so working at f/10
• SBIG ST-9E CCD camera with clear filter
• 60-second guided exposures

Notes from the night

• Conditions were fair: clear for several hours, then patches of broken clouds. The Full Moon was bright all night, and not too far from the target.
• Twilight sky flats. There was quite a systematic leftover gradient after flatfielding; I blame the Moon.
• Divided all raw frames by 2 to avoid exceeding the 15-bit limit of XVista software.

Here's a chart of the field of CSS 080505, which is at

      RA = 16:31:21        Dec = +10:31:34     (J2000)

The chart is about 12x12 arcminutes.

Several of the reference stars marked above have photometry listed in the UCAC4. I used star "A" to convert the instrumental magnitudes to the V-band scale (though of course, they are unfiltered measurements)

     A   =    UCAC4 503-064345      V = 11.885

Below is a graph showing the sky brightness as a function of time during the observing run. Note the clouds in the second half of the run.

Below is a graph showing the FWHM as a function of time during the observing run. I refocused once, at 2:24 AM, frame 173.

I used 60-second exposures during this observing run. The target had about 800 peak counts/2 with this exposure time, and the bright stars A and B about 10,000.

Using aperture photometry with a radius of 4 pixels (radius of 5.7 arcsec), I measured the instrumental magnitudes of a number of reference stars and the target. 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 used the UCAC4 V-band magnitude of star "A" to convert the ensemble instrumental magnitudes to a reported "V"-band magnitude (but remember, it's a clear filter).

Sigma-vs-mag plot: The target is the outlier at mag 2.8.

The target, shown in green, shows sawtooth variations with an amplitude of about 0.10 mag, with an average magnitude around 14.7.

# Measurements of CSS080505 made at RIT Obs, May 4, 2015 UT, 
#    in fair conditions, 
#    by Michael Richmond, using 12-inch Meade and SBIG ST-9E CCD. 
# Exposures 60 seconds long, no filter. 
# Tabulated times are midexposure (FITS header time - half exposure length) 
#    and accurate only to +/- 1 second (??). 
# 'mag' is a differential magnitude based on ensemble photometry 
#    using a circular aperture of radius 5.7 arcseconds.  
#    which has been shifted so UCAC4 503-064345 has mag=11.885 
#    which is its V-band mag according to the UCAC4.  
# 
# UT_day             JD            HJD        mag    uncert
May04.11895     2457146.61895  2457146.62356  14.695  0.035 
May04.11976     2457146.61976  2457146.62437  14.693  0.035 
May04.12056     2457146.62056  2457146.62517  14.693  0.035 

• Download ASCII data file 'css080505_may04ut.dat'

Last modified 5/04/2015 by MWR.