UT Nov 24, 2021: Photometry of V445 Cas

Michael Richmond
Nov 24, 2021

On the night of Nov 23/24, 2021, under good conditions, Michael Dussault and I acquired images of the eclipsing binary system V445 Cas as part of a capstone project. This fills the last bit of the phase curve!

No problems with the equipment.

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: 0.527 yields FWHM 3.0 at T = 32/0
  • later decreased focus to 0.507 as the telescope cooled off
  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 skies for the entire run (though we saw one or two small puffs of cloud as we closed)
• waning gibbous Moon rose near the end, didn't matter much
• the temperature dropped to 22/-6 at the end of the run (9:44 PM)
• No skunks. :-(

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

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 big drop after sunset -- we started very early tonight.

The FWHM graph below shows small jumps as I made adjustments.

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 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 0.003 mag -- excellent!

The change in zeropoint shows just one bad image.

Last modified 11/24/2021 by MWR.