Jul 10, 2014 UT: ASAS-SN14cv

Michael Richmond
Jul 10, 2014

On the night of Jul 09/10, 2014, I observed the cataclysmic variable star ASAS-SN14cv. You can read more about this star, which was discovered only recently, at

• ASASSN Transients Page

ASAS14cv shows smooth quick-rise-slow-fall variations of amplitude 0.05 mag at mag V = 13.1 or so.

The main setup was:

• Meade 12-inch telescope
• no focal reducer, so working at f/10
• SBIG ST-8E CCD camera with clear filter
• 45-second guided exposures

Notes from the night

• Waxing gibbous Moon made the sky bright.
• Heavy low clouds covered the sky at sunset and continued until about 11 PM. I was able to observe later than usual, with one short interruption for another set of clouds.
• Twilight sky flats -- taken of the bottom of clouds.
• Very nice guiding, all night long.
• Divided all raw frames by 2 to avoid exceeding the 15-bit limit of XVista software.

Below is a graph showing the sky brightness as a function of time during the observing run.

Below is a graph showing the FWHM as a function of time during the observing run.

ASAS-14cv

Here's a chart of the field of ASAS-SN14cv, which is at

      RA = 17:43:48.58     Dec = +52:03:46.8   (J2000)

Some of the reference stars marked above have magnitudes in the UCAC4. Specifically, star "A" above is

• star UCAC44 711-058151
• has V-band magnitude 11.518

The television camera on the finder scope shows the following when we're pointed at ASAS-14cv. North up, East left, field about 1 degree on a side.

The image adjustment factor graph shows a big rise surrounding the gap in observations, when a formation of clouds moved across the sky.

Using aperture photometry with a radius of 4 pixels (radius of 7.4 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 shows very clear periodic variations, with a larger amplitude than a few nights ago.

You can see my measurements of the star in the ASCII text file below. The first few lines are shown here:

# Measurements of ASAS_SN14cv made at RIT Obs, Jul 10, 2014 UT, 
#    in mediocre conditions, 
#    by Michael Richmond, using 12-inch Meade and SBIG ST-8E CCD. 
# Exposures 45 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 7.4 arcseconds.  
#    which has been shifted so UCAC4 711-058151 has mag=11.518 
#    which is its V-band mag according to UCAC4.  
# 
# UT_day             JD            HJD        mag    uncert
Jul10.16479     2456848.66479  2456848.66610  13.172  0.006 
Jul10.16551     2456848.66551  2456848.66682  13.174  0.006 
Jul10.16696     2456848.66696  2456848.66827  13.171  0.006 

• Download ASCII data file 'asas14cv_jul10ut.dat'

Last modified 7/10/2014 by MWR.