Jul 23, 2014 UT: ASAS-SN14cv rebrightens!

Michael Richmond
Jul 23, 2014

On the night of Jul 22/23, 2014, I observed the cataclysmic variable star ASAS-SN14cv -- which has started to increase in brightness! It went from approx V = 16.1 to V = 15.5 in a period of four hours. 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. Conditions worsened near the end of the run.

Below is a graph showing the FWHM as a function of time during the observing run. Conditions worsened near the end of the 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 bumps near the end due to clouds, as well as a rise due to increasing airmass.

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 giant outlier at instrumental mag 6.0 is ASAS-14cv. The two brightest stars were both saturated, and so I gave them zero weight in the ensemble calculations.

The target, shown in green, increases in brightness by about 0.5 magnitudes during the roughly 4 hours of observation.

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 23, 2014 UT, 
#    in fair conditions. 
#    by Michael Richmond, using 12-inch Meade and SBIG ST-8E CCD. 
# Exposures 30 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
Jul23.06984     2456861.56984  2456861.57098  16.128  0.107 
Jul23.07038     2456861.57038  2456861.57152  16.023  0.101 
Jul23.07093     2456861.57093  2456861.57207  15.976  0.102 

Last modified 7/23/2014 by MWR.