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.