UT Aug 05, 2021: Photometry of V627 Peg (and a faint eclipsing binary)

Michael Richmond
Aug 05, 2021

On the night of Aug 05/06, 2021, under good conditions, I acquired images of the cataclysmic variable star V627 Peg. One can find information about it at

• AAVSO Alert Notice 747.

No moisture condensed tonight, thank goodness. Perhaps the adjustment I made to the camera's window heater helped.

V627 Peg

Christian Knigge is soliciting observations of this cataclysmic variable star at all wavelengths. The AAVSO has advertised for optical measurements, and I'm joining the effort.

The main setup was:

• Meade 12-inch telescope
• no focal reducer, so working at f/10
• ATIK 11000 CCD camera
• V filter, exptime 30 seconds
• images binned 2x2
• guiding with 3-sec exptime, worked well
• focus
  • 0.240 yields FWHM = 1.5 at T = 75 / 24
  I didn't see any significant drift in FWHM during the night, so I didn't change the focus. The final temperature was 62 / 17 at dawn.
• camera ran at T = -15 C for all images

Notes from the night:

• except for two brief periods of clouds, sky was clear
• tiny waning crescent Moon had no effect on sky brightness
• guiding with 3-second exposures worked well, put target at (1112, 458) to get the bright guide star
• in order to avoid moisture condensing on the dewar window, I used the Atik camera configuration program, at C:\Program Files(x86)\Config\Config.exe, to change the EEPROM's ""Aux power" value from 0 to 125. That should provide power to a small heater which is designed to keep the dewar window warm enough to avoid condensation. It seemed to work: the relative humidity was 93% at dawn, but there was no condensation to be seen. Hooray!
• I saw the skunk inside the fenced area only briefly

The object is located at

  RA =  21:38:06.63    Dec = +26:19:56.0     (J2000)

A chart of the field is shown below. The size of the chart is about 31 x 26 arcminutes.

I've marked the location of several comparison stars as well. See

• this chart from the AAVSO
• this list of stars and photometry from AAVSO

I'll use star "D" to shift my instrumental magnitudes to the V-band scale. It has a V-band magnitude (according to AAVSO chart X26768AQ) of 12.002, and (B-V) = 0.692.

The star marked "X" is an eclipsing binary of type EW, with a period of 0.36 days and amplitude of about +/- 0.3 mag in V-band.

• ASASSN-V J213808.68+261704.4 / VSX J213808.7+261704

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 two very brief periods of cloud.

The FWHM graph below shows no significant drift.

Using aperture photometry with a radius of 7 pixels in a 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 0.006 mag after I removed a few images with large outliers.

The change in zeropoint shows only a few outliers.

Here is the light curve of the object and several field stars in the V filter; I've shifted the instrumental magnitudes so that star "D" = 000-BJV-433 on AAVSO chart X26767AK has the value given by AAVSO as its V-band magnitude.

Here's a closeup, also showing the light curve of star "X", the EW variable just south of the target.

I have submitted these measurements to the AAVSO, CBA, and VSNet.

You can download my measurements below. A copy of the header of the file is shown to explain the format.

# Measurements of V627Peg made at RIT Obs, UT 2021 Aug 6, 
#    in good 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-BJV-433 has mag=12.002 
#    which is its V-band magnitude according to AAVSO chart X26767AK.  
# 
# UT_day             JD            HJD        mag    uncert
Aug06.08007     2459432.58007  2459432.58429  13.581  0.043 
Aug06.08058     2459432.58058  2459432.58480  13.525  0.042 
Aug06.08109     2459432.58109  2459432.58531  13.580  0.043 

• download ASCII text file, UT 2021 Aug 06, V627 Peg from RIT Obs

Last modified 8/06/2021 by MWR.