UT Nov 25, 2021: photometry of V1004 Cyg

Michael Richmond
Nov 26, 2021

On the night of Nov 24/25, 2021, I observed the eclipsing binary star V1004 Cyg for one of our capstone projects. Finally, the weather and star cooperated, and I was able to measure almost all of the portion of the light curve that was missing.

V1004 Cyg

We acquired images of the eclipsing binary system V1004 Cyg as part of a capstone project.

The main setup was:

• Meade 12-inch telescope
• no focal reducer, so working at f/10
• ATIK 11000 CCD camera
• B, V filters, exptime 30 seconds
• images binned 2x2
• no guiding
• focus values:
  • V: 0.491 yielding FWHM 2.8 at T = 46/7
  I set the focus to a mid-point, 0.020 higher than the V-band value, so that both V and B would be out of focus by a similar amount.
• camera ran at T = -20 C

Notes from the night:

• mostly clear for the entire run, strangely enough, as cirrus was present at sunset
• third quarter Moon was 10 degrees above NE horizon when I left
• no skunks
• quit at 9:35 PM, at a temperature of 35 C/2 F

The object is located at

  RA = 19:50:29.44  Dec = +33:08:32.2    (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. You can find reference magnitudes for these stars at the AAVSO:

• AAVSO chart for the field
• table of magnitudes from the AAVSO: sequence X27032O

I used to use the star marked as "C" in the picture above, or "118" in the AAVSO charts, to shift the instrumental magnitudes to the standard scale. However, since it lies relatively far from the target in the field, I discovered that on a few nights, it suffered from a slightly variable amount of vignetting; that caused the relative magnitudes of the target and star "C" to vary by up to 0.1 mag from one night to the next. Star "E" is a better choice. If the three stars just to the East of V1004 had good calibrated magnitudes, they would be even better.

Label	B	V
C	12.717	11.803
E	12.840	12.182

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 sharp drop at first, as I started observing while the Sun was only 9 degrees below the horizon. Clear after that.

The FWHM graph below shows changes due to the temperature drop, and adjustments I made to bring the V-band images into better focus.

Using aperture photometry with a radius of 10 pixels in B and V filters (binned 2x2, each pixel is 1.24 arcsec, so a radius of 12.4 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 was about 0.009 mag in B.

The change in zeropoint shows little evidence for clouds; the brief rise is due to lowering and raising the dome slit.

Last modified 11/26/2021 by MWR.