Jul 14, 2014 UT: ASAS-SN14cv

Michael Richmond
Jul 14, 2014

On the night of Jul 13/14, 2014, I observed the cataclysmic variable star ASAS-SN14cv. You can read more about this star, which was discovered only recently, at

ASAS14cv shows some variation, though hard to describe in this brief run, shortened due to clouds. The star continues to fade slowly, now V = 13.4 or so.

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 clouds arriving near 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 that clouds passed through twice before they halted things.

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 some variation, but only about one-half a period due to the short observing run. Rats.

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 14, 2014 UT, 
#    in mediocre conditions (cut short by clouds), 
#    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
Jul14.08021     2456852.58021  2456852.58148  13.441  0.009 
Jul14.08094     2456852.58094  2456852.58221  13.465  0.008 
Jul14.08166     2456852.58166  2456852.58293  13.445  0.009 

Last modified 7/14/2014 by MWR.