UT Aug 03, 2021: Photometry of V627 Peg

Michael Richmond
Aug 03, 2021

On the night of Aug 02/03, 2021, under very good conditions, I acquired images of the cataclysmic variable star V627 Peg. One can find information about it at

• AAVSO Alert Notice 747.

I replaced the focus controller unit, so focusing is back to normal. One issue during the night, when the computer reported that the ATIK camera driver had stopped working. Lost 10-20 minutes of data, no big deal.

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 20 seconds
• images binned 2x2
• no guiding
• focus
  • 0.216 yields FWHM = 2.0 at T = 71/21
  • 0.214 yields FWHM = 2.5 at T = 59/15
• camera ran at T = -20 C

Notes from the night:

• sky was clear all night
• waning crescent Moon had no real effect on sky brightness
• no guiding
• MaximDL reported late in the night that the ATIK camera driver had stopped working. I did the following to restore normal operations:
  • use Task Manager to kill Atik camera driver process
  • quit MaximDL
  • unplug-and-replug Atik camera power and USB cables
  • restart MaximDL
• I replaced the old focus controller unit with its twin from the 14-inch dome. No problems, it just worked. Will purchase another unit, try to fix the old one.
• the skunk spent most of the night outside the fenced area, with a brief visit to the interior

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 no clouds at all. The brief break is due to the ATIK driver issue, and a short period when the chip was cooling down again.

The FWHM graph below shows a pretty steady value.

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 0.010 mag after I removed a few images with large outliers. Conditions were good. In order to decrease the scatter, I will have to increase exposure time to 30 seconds, perhaps.

The change in zeropoint shows quite a few outliers, due to bad tracking, mostly.

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.

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 3, 
#    in good conditions, 
#    by Michael Richmond, 
#    using Meade 12-inch LX200 and ATIK 11000. 
# 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 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
Aug03.05985     2459429.55985  2459429.56397  11.393  0.010 
Aug03.06056     2459429.56056  2459429.56468  11.384  0.010 
Aug03.06091     2459429.56091  2459429.56503  11.401  0.010 

• download ASCII text file, UT 2021 Aug 03, V627 Peg from RIT Obs

Last modified 8/03/2021 by MWR.