Jul 12, 2014 UT: ASAS-SN14cv

Michael Richmond
Jul 12, 2014

On the night of Jul 11/12, 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 variations of amplitude 0.05 mag at mag V = 13.3 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

• Nearly full Moon made the sky very bright.
• Light cirrus at dusk dissipated for a few hours, then returned with a vengeance, halting the measurements. Never really clear.
• Twilight sky flats.
• 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 that clouds were present frequently throughout the observations, particularly near the end.

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. You can see the effect of clouds early and late in the larger scatter at those times.

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 12, 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
Jul12.07762     2456850.57762  2456850.57891  13.259  0.010 
Jul12.07834     2456850.57834  2456850.57963  13.266  0.010 
Jul12.07978     2456850.57978  2456850.58107  13.264  0.010 

• Download ASCII data file 'asas14cv_jul12ut.dat'

Last modified 7/12/2014 by MWR.