UT Sep 09, 2022: Photometry of V1004 Cyg

Michael Richmond
Sep 09, 2022

On the night of Sep 08/09, 2022, I (with some help from Chris Bass) observed the eclipsing binary star V1004 Cyg for one of our capstone projects. This was the first time I'd measured this star since 2021, so it's only a short run with the R filter. But the small taste leaves me intrigued.


V1004 Cyg

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

The main setup was:

Notes from the night:

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:

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.

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 gradual rise, due mostly to the Moon, I think.

The FWHM graph below shows a pretty steady value, with outliers due to trailing.

Using aperture photometry with a radius of 5 pixels in R (binned 2x2, each pixel is 1.24 arcsec, so a radius of 6.1 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 in R.

The change in zeropoint shows little evidence for clouds.

Photometry shows only a modest change in brightness during this brief observing run. The peculiar thing, however, is that these measurements suggest that the star reaches a maximum brightness around JD 31.65, but this is far from the predicted time of maximum from the GCVS ephemeris.

Since one of our capstone students will be analyzing last year's measurements, I think it will be worthwhile to acquire some additional measurements this fall, too. Is the period changing significantly on relatively short timescales?