Aug 09, 2014 UT: ASAS-SN14cv

Michael Richmond
Aug 09, 2014

On the night of Aug 08/09, 2014, I observed the cataclysmic variable star ASAS-SN14cv. It declined slowly from about V = 15.3 to V = 15.6 over the observations, with no obvious dips or rises. You can read more about ASAS-SN14cv, which was discovered only recently, at

• ASASSN Transients Page

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

• The sky was not as hazy as last night, but the Sun and Moon were both tinged with red, so the smoke from Canada must still be present at some level. There were indications of light cirrus now and then.
• Bright nearly full Moon to the south, made the sky bright. Hard to see all the stars in the Big Dipper.
• 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. Note a few bumps caused by cirrus.

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 brief peaks due to clouds, plus some gradual changes due to haze.

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 target is the outlier around instrumental mag 5.6. Other outliers are due to instrumental problems.

The target, shown in green, shows a slight, gradual decrease in brightness in the second half of the run.

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 9, 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
Aug09.05787     2456878.55787  2456878.55869  15.279  0.050 
Aug09.05858     2456878.55858  2456878.55940  15.285  0.049 
Aug09.05931     2456878.55931  2456878.56013  15.293  0.048 

• Download ASCII data file 'asas14cv_aug09ut.dat'

Last modified 8/08/2014 by MWR.