On the night of Jun 19/20, 2022, under medicore conditions, Tracy Davis and I acquired images of the outbursting cataclysmic variable star U Sco.
The target was low in the south, but at least the Moon didn't interfere with the measurements. There were some light clouds, though. I switched to unfiltered measurements, and that did help quite a bit.
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 = 14.
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.
The sky value shows a few brief periods of cloud.
The FWHM graph below shows a steady value, despite a drop in temperature of about 6 degrees C.
Using aperture photometry with a radius of 7 pixels in clear filter (binned 2x2, each pixel is 1.24 arcsec, so a radius of 8.7 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 0.012 mag.
The change in zeropoint shows both clouds, and the effects of high airmass at start and end.
The measurements are noisy, but one can see that U Sco rose and then fell over the period of measurement. This behavior mirrors the measurements made by other observers on the same night in the AAVSO database.
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 2021 Jun 20, # in fair conditions, # by Michael Richmond, # using Meade 12-inch LX200 and ATIK 11000. # Exposures 30 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 = 8.8 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 Jun20.10565 2459750.60565 2459750.61109 13.849 0.032 Jun20.10611 2459750.60611 2459750.61155 13.778 0.032 Jun20.10656 2459750.60656 2459750.61200 13.802 0.032
Last modified 6/20/2022 by MWR.