May 07, 2015 UT: CSS 080505

Michael Richmond
May 07, 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

It showed small variations, with a pattern of sharp rise, gradual fall, and then small eclipse before the next rise. The amplitude was only about 0.10 mag, and the signal-to-noise of my measurements was not high.

The object had an average "V" magnitude of about 15.3, which is 0.6 mag fainter than it was 3 days ago on May 04 UT.

The main setup was:

Notes from the night

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 brief period of light cloud early.

Below is a graph showing the FWHM as a function of time during the observing run. I tried refocusing at 12:19 local, but it didn't make much difference.

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 15,000.

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 very slight outlier at mag 3.3.

Image adjustment factor: note the clouds early.

The target, shown in green, shows sawtooth variations with an amplitude of about 0.10 mag, with an average magnitude around 15.3.

Here's a closeup. Are those real eclipses just before the rise?

# Measurements of CSS080505 made at RIT Obs, May 7, 2015 UT, 
#    in good 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
May07.11628     2457149.61628  2457149.62098  15.290  0.028 
May07.11708     2457149.61708  2457149.62178  15.285  0.028 
May07.11788     2457149.61788  2457149.62258  15.321  0.029 

Last modified 5/07/2015 by MWR.