On the night of Jul 07/08, 2022, under fair conditions, I acquired images of the outbursting cataclysmic variable star U Sco.
Several times during the night, light broken clouds moved across the sky, and the waxing gibbous Moon wasn't too far away. As a result, the measurements of U Sco have a pretty large scatter tonight: about 0.06 mag.
U Sco is a cataclysmic variable which only rarely is caught in an outburst. This one was first noticed at UT 2022 June 6.720 by Masayuki Moriyama. The star reached a peak brightness of about V = 8, but faded quite a bit by this evening; it is currently about V = 15.2.
The main setup was:
Notes from the night:
The object is located at
RA = 16:22:30.78 Dec = -17:52:42.8 (J2000)
A chart of the field is shown below. The size of the chart is about 42 x 30 arcminutes.
I've marked the location of several comparison stars as well, which appear on the AAVSO chart of comparison stars.
I'll use star "A" to shift my instrumental magnitudes to the V-band scale.
I took a photo of the finder TV's screen when pointing to this target; this could be a useful reference for the future:
The sky value shows several episodes of clouds.
The FWHM graph below shows an increase near the end of the night; could be due to temperature change, or increased airmass.
Using aperture photometry with a radius of 7 pixels in clear filter (binned 4x4, each pixel is 1.052 arcsec, so a 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.
Sigma-vs-mag plots show that the floor was about 0.010 mag after discarding a dozen particularly bad images.
The change in zeropoint shows several episodes of clouds.
The measurements show a small decline in brightness.
You can download my measurements below. A copy of the header of the file is shown to explain the format.
# Measurements of U_Sco made at RIT Obs, UT 2022 Jul 8, # in fair conditions, # by Michael Richmond, # using Meade 12-inch LX200 and ASI 6200MM. # Exposures 45 seconds long, clear 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 pix = 7.4 arcseconds. # which has been shifted so AAVSO 000-BBX-431 has mag=10.707 # which is its V-band magnitude according to AAVSO. # # UT_day JD HJD mag uncert Jul08.08200 2459768.58200 2459768.58657 15.316 0.057 Jul08.08263 2459768.58263 2459768.58720 15.237 0.061 Jul08.08388 2459768.58388 2459768.58845 15.170 0.057
Last modified 7/08/2022 by MWR.