UT Nov 17, 2021: Photometry of V445 Cas

Michael Richmond
Nov 17, 2021

On the night of Nov 16/17, 2021, under fair conditions, I acquired images of the eclipsing binary system V445 Cas as part of a capstone project. This fills in a significant portion of the remaining gap in the light curve -- but leaves about 2 hours unmeasured.

No problems with the equipment. Clouds stopped the run a few hours before I would have liked.

V445 Cas

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:
  • V: 0.531 yields FWHM 3.4 at T = 39/4
  • V: 0.509 yields FWHM 2.4 at T = 33/0
  The focus appeared to change relatively quickly at the start of the night. I set the position 0.030 units above the V-band focus so that both B and V would be partially out of focus.
• camera ran at T = -20 C

Notes from the night:

• clear for the first few hours, but then thin clouds gradually thickening for the final half of the run.
• bright gibbous Moon made the clouds bright
• the temperature dropped to 30/-1 at the end of the run (12:09 AM)
• No skunks. Sigh.

The object is located at

  RA = 00:31:39.65   Dec = +53:13:00.3   (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. The bright star P is the ninth-magnitude HD 2826.

Label	B	V
A	10.094	9.378
B	10.353	10.202

I'll use star "A" to shift my instrumental magnitudes to the B and V-band scales (and pretend that tonight's R-band images have the same V-band calibation)

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 clouds slowly building up.

The FWHM graph below shows my adjustment of the focus after about an hour. It helped the V, but spread out the B a bit.

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 0.006 mag -- very nice!

The change in zeropoint shows a few bad images, as well as clouds.

Last modified 11/17/2021 by MWR.