Aug 01, 2014 UT: ASAS-SN14cv

Michael Richmond
Aug 01, 2014

On the night of Jul 31/Aug 01, 2014, I observed the cataclysmic variable star ASAS-SN14cv. It faded steadily from roughly V = 15.0 to 15.2 during tonight's run. You can read more about ASAS-SN14cv, which was discovered only recently, at

The main setup was:

Notes from the night

Below is a graph showing the sky brightness as a function of time during the observing run. Note the small bumps due to clouds in the middle of the run, and big rise at the end.

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


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

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 small bumps due to cirrus, then a big jump at 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 two brightest stars were both saturated, and so I gave them zero weight in the ensemble calculations. The outlier at instrumental mag = 5.1 mag is ASAS-14cv.

The target, shown in green, decreases slightly over the the roughly 3.7 hours of observation. The scatter increases near the end due to bad conditions.

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, Aug 1, 2014 UT, 
#    in fair 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
Aug01.06610     2456870.56610  2456870.56708  15.105  0.029 
Aug01.06682     2456870.56682  2456870.56780  15.061  0.029 
Aug01.06755     2456870.56755  2456870.56853  15.020  0.029 

Last modified 8/01/2014 by MWR.