On the night of Jun 14/15, 2022, under medicore conditions, I acquired images of the outbursting cataclysmic variable star U Sco.
The target was low in the south, not far from the nearly full Moon. The second half of the brief run was plagued by light cloud. Still, I did measure the same pattern of variation seen by others.
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. The weather in Rochester was so poor that this was my first opportunity to try measuring the event.
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 30 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 clear early, but clouds in the second half (though they cleared at the end).
The FWHM graph below shows a steady value; the temperature didn't drop much at all.
Using aperture photometry with a radius of 7 pixels in V 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 0.013 mag in V.
The change in zeropoint shows a steep climb in the second half, due to increased clouds.
The measurements are noisy, but one can see that U Sco rose by about 0.25 mag, then started to fall back again. 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 15, # in medicore conditions, # by Michael Richmond, # using Meade 12-inch LX200 and ATIK 11000. # Exposures 30 seconds long, V 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 Jun15.11922 2459745.61922 2459745.62482 13.144 0.046 Jun15.11968 2459745.61968 2459745.62528 13.164 0.048 Jun15.12014 2459745.62014 2459745.62574 13.104 0.046
Last modified 3/30/2022 by MWR.