UT Jul 26, 2021: Photometry of V627 Peg

Michael Richmond
Jul 26, 2021

On the night of Jul 25/26, 2021, under mediocre conditions, I acquired images of the cataclysmic variable star V627 Peg. One can find information about it at

• AAVSO Alert Notice 747.

Smoke and haze, plus bright moonlight, made this dataset pretty noisy. Also, moisture started to condense on the dewar window near the end of the run, which ruined measurements of the target over the final hour or so.

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 15 seconds
• images binned 2x2
• no guiding
• focus in V
  • 1.181 yields FWHM = 2.6 at T = 76/24
• camera ran at T = -16 C

Notes from the night:

• smoke and haze all night, becoming more intense in the second half. Stupid forest fires.
• full Moon made sky bright, and the haze scattered it strongly. Shadows cast by the full Moon were very weak at times.
• no guiding
• no problems with MaximDL -- phew.
• Moisture condensed on the dewar window near the end of the run, but only in the area of the target. That caused the target to APPEAR to fade by 0.7 mag. I have removed that data from all reported measurements. Must refresh the dessicant in the camera box.
• The skunk was active all night in the back yard and in the fenced area near the dome -- at one point I surprised it and was afraid I was going to be sprayed. At one point around 3 AM, I saw a SECOND skunk, smaller and blacker than the other, investigating the back yard near the house. Oh, dear.

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.

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 a high background, which grows 1.5 times as bright in the second half before returning to its original value.

The FWHM graph below shows only small changes. I didn't re-focus.

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 0.005 mag after I removed a few images with large outliers.

The change in zeropoint shows the same arrival of heavy haze as the sky graph.

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. I have deleted from the reported measurements those values inside the pink-shaded region, which suffer from errors due to condensation on the dewar window.

Here's a closeup.

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 Jul 26, 
#    in mediocre conditions (moonlit haze), 
#    by Michael Richmond, 
#    using Meade 12-inch LX200 and ATIK 11000. 
# Exposures 15 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
Jul26.09187     2459421.59187  2459421.59568  10.708  0.014 
Jul26.09247     2459421.59247  2459421.59628  10.710  0.014 

• download ASCII text file, UT 2021 Jul 26, V627 Peg from RIT Obs

Last modified 7/26/2021 by MWR.