UT Nov 16, 2021: photometry of V1004 Cyg

Michael Richmond
Nov 05, 2021

On the night of Nov 15/16, 2021, I observed the eclipsing binary star V1004 Cyg for one of our capstone projects. In the early evening, the star would go through a section its light curve that we had not yet observed.

It was raining when I arrived at the Observatory, but cleared eventually .... for one hour. Then the snow started. And that one hour ... was a portion of the light curve that we'd already observed.

Sigh.

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: 0.473 yielding FWHM 2.7 at T = 35/1
  I set the focus to a mid-point, 0.030 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:

• rain at first, then clearing briefly, then snow. The snow started to fall before I closed the dome, so a few drops/flakes fell on the telescope's front lens. Oh, well.
• bright waxing gibbous Moon lit clouds up brightly
• no skunks
• quit at 9:00 PM, at a temperature of 33 C/0 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 the star marked as "C" in the picture above, or "118" in the AAVSO charts, to shift the instrumental magnitudes to the standard scale.

Label	B	V
C	12.717	11.803

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 the brief clear period before the clouds returned.

The FWHM graph below shows little change until the clouds hit.

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 0.007 mag in B.

The change in zeropoint shows clouds thickening at the end of the run.

Last modified 11/16/2021 by MWR.