On the night of Jun 06/07, 2024, under good conditions (until clouds came, when I stopped) I acquired images of the cataclysmic variable star SS Cyg. This star has just (Jun 02) started its outburst (yay!), and the operators of the XRISM satellite would like to start observing it as soon as it brightens. The AAVSO has posted Alert 858 asking observers to monitor it frequently.
I acquired images in B and V passbands for about 1.7 hours. The star continues to dim -- at V = 9.45 tonight. This may be a "brief" outburst for SS Cyg.
This cataclysmic variable brightens by about 4 magnitudes every two months or so, from mag 12 to about mag 8.
These observations involved:
Notes from the night:
The picture below shows an image of the field of SS Cyg from May 30/31. The field of view is about 22 arcminutes across.
I've marked the location of several comparison stars, with magnitudes and names taken from the AAVSO's chart.
star name B V
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A 000-BCP-235 9.872 8.556
B 000-BCP-198 10.162 9.974
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When the target is centered, the finder TV shows this field:
Here's the sky background over the course of the run. I discarded measurements taken after the clouds arrived.
The FWHM was pretty steady.
The graph below shows changes in the photometric zeropoint of an ensemble solution of the instrumental magnitudes over the course of the run. The drop at the beginning shows that I changed exposure time from 12 to 20 seconds.
Using aperture photometry with a radius of 5 pixels in V filter (binned 4x4, each pixel is 1.052 arcsec, so a radius of 5.3 arcsec), and 7 pixels in B 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 in V-band was about 0.004 mag, which is good. It was 0.004 in B-band, too. The outlier is a star hit by a cosmic ray in one image.
The measurements show a nearly steady brightness, with very small rolling variations of timescale approximately one hour.
You can download my measurements below. A copy of the header of the file is shown to explain the format. First, the V-band data.
# Measurements of SS_Cyg made at RIT Obs, UT 2024 Jun 7, # in good conditions, # by Michael Richmond, # using Meade 12-inch LX200 and ASI 6200MM. # Exposures 20 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 5 pix = 5.2 arcseconds. # which has been shifted so AAVSO 000-BCP-198 has mag=9.794 # which is its V-band magnitude according to AAVSO chart X36666LX. # # UT_day JD HJD mag uncert Jun07.22847 2460468.72847 2460468.72823 9.245 0.004 Jun07.22876 2460468.72876 2460468.72852 9.241 0.004 Jun07.22905 2460468.72905 2460468.72881 9.241 0.004
Now, the B-band data.
# Measurements of SS_Cyg made at RIT Obs, UT 2024 Jun 7, # in good conditions, # by Michael Richmond, # using Meade 12-inch LX200 and ASI 6200MM. # Exposures 30 seconds long, B 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 = 7.2 arcseconds. # which has been shifted so AAVSO 000-BCP-198 has mag=10.162 # which is its B-band magnitude according to AAVSO chart X36666LX. # # UT_day JD HJD mag uncert Jun07.23097 2460468.73097 2460468.73073 9.337 0.004 Jun07.23190 2460468.73190 2460468.73166 9.354 0.004 Jun07.23284 2460468.73284 2460468.73260 9.356 0.004
I've submitted these measurements to the AAVSO and to VSNet.