UT Nov 06, 2021: Photometry of V445 Cas

Michael Richmond
Nov 05, 2021

On the night of Nov 05/06, 2021, under good conditions, I acquired images of the eclipsing binary system V445 Cas as part of a capstone project. This _almost_ completes the binary's phase coverage.

Conditions were good. The camera rotated slightly over the course of the run (which I'd seen in another night of V445 Cas data), so I wrote a script to de-rotate the positions of the stars and facilitate photometric reductions.

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
• guiding with 3-sec exptime, X aggr = 2.0
• focus:
  • V: 0.467 yields FWHM 2.4 at T = 34/1
  I set the focus position to 0.487 so that it would be between the V and B positions. After two hours, I decreased the focus to 0.476.
• camera ran at T = -20 C

Notes from the night:

• mostly clear, but one short period of light clouds from JD 524.72 - 524.76.
• no Moon at all
• the temperature dropped from 34/1 at start of run (9:47 PM) to a frigid 25/-4 at the end (4:38 AM).
• just after I mounted the CCD camera on the telescope, it slipped off the back of the telescope! Fortunately, the bungee cord caught it.
• the field rotated by a total of about 3 degrees from the start to the end of the run. This may be due to the position of the field -- far to the North. I had to write a little script to de-rotate the star positions in order to run the photometry pipeline properly.
• No skunks. I grow worried about them.

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 very little clouds, but see zeropoint graph below.

The FWHM graph below shows that my adjustments to the focus position didn't help.

Using aperture photometry with a radius of 7 pixels in B and V filters (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 0.003 mag -- very nice!

The change in zeropoint shows a brief period of light clouds.

Last modified 11/17/2021 by MWR.