On the night of Aug 19/20, 2014, I observed the cataclysmic variable stars ASAS-SN14cv. It was roughly steady at V = 16.9, showing variations with a small amplitude.
You can read more about this star 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 bump, then sharp rise, near the end: clouds started to move in.
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, I use these stars to convert the instrumental magnitudes to the V-band scale (though of course, they are unfiltered measurements)
A UCAC44 711-058151 V = 11.518
B UCAC44 711-058147 V = 11.899
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.
I used 120 second exposures because the target has faded to around mag 16. With these long exposures, star "A" is slightly saturated, so I switched to using star "B" for photometric calibration.
The image adjustment factor graph shows a smooth curve for the first half, then a bump and rise in sync with the "sky" values: a sign of clouds.
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 "B" to convert the ensemble instrumental magnitudes to a reported "V"-band magnitude (but remember, it's a clear filter).
Sigma-vs-mag plot: The brightest 3 stars saturated (or nearly so), so I gave them zero weight in the ensemble calculations. The target has a slightly higher scatter than other stars at instrumental magnitude 6.4.
The target, shown in green, shows a pretty clear variation.
# Measurements of ASAS_SN14cv made at RIT Obs, Aug 20, 2014 UT, # in good conditions. # by Michael Richmond, using 12-inch Meade and SBIG ST-8E CCD. # Exposures 120 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 711-058147 has mag=11.899 # which is its V-band mag according to UCAC4. # # UT_day JD HJD mag uncert Aug20.06638 2456889.56638 2456889.56696 16.900 0.085 Aug20.06796 2456889.56796 2456889.56854 16.970 0.084 Aug20.06956 2456889.56956 2456889.57014 16.940 0.083
Last modified 8/22/2014 by MWR.