UT Oct 02, 2021: Photometry of V445 Cas

Michael Richmond
Oct 03, 2021

On the night of Oct 01/02, 2021, under good conditions (at first), RIT undergrad Michael Dussault and I acquired images of the eclipsing binary system V445 Cas as part of his capstone project. We did catch one of the light curve's minima.

Clouds arrived around 2:30 AM and cut the run short. It was just before that time that I realized that I mis-typed the filter assignment in MaximDL, and all of our "V" images were actually R-band. Whoops.

See the end of this page for brief notes on using the 14-inch telescope with the SBIG ST-9 CCD camera.

V445 Cas

The main setup was:

• Meade 12-inch telescope
• no focal reducer, so working at f/10
• ATIK 11000 CCD camera
• B, R filters, exptime 30 seconds
• images binned 2x2
• no guiding
• focus in R: 1.249 yields FWHM 2.3 pix at T = 61/16. We set focus to 1.268 to be midway between B and "V" (really R)
• camera ran at T = -20 C

Notes from the night:

• clouds arrived around 2-2:30 PM, eventually ending the run
• thin crescent Moon rising when clouds arrived, no real effect
• the temperature dropped from 61/16 at start of run to 53/12 at 3:24 AM. As it did, the focus grew much worse in B-band, but better in R-band. Since the focus position of B-band is about +0.060 LARGER than R-band, this means that the effective focus position DECREASED as the temperature DECREASED. On second thought, we should have nudged the focuser to a slightly higher value as the temperature dropped, to keep both B-band and R-band images equally out of focus.
• reports that the skunk was active in the early evening. Hooray!

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 arriving late.

The FWHM graph below shows the effect of temperature dropping by about 8 Celsius.

Using aperture photometry with a radius of 7 pixels in B and R 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 0.06 mag.

The change in zeropoint was small until clouds arrived.

Notes on the 14-inch

Because we have four student projects this semester, I decided to open up the 14-inch as a test tonight. Could we use it and our old SBIG ST-9 CCD camera at the same time as the 12-inch?

The short answer is "probably yes."

• I turned on the 14-inch telescope control system and re-set the clock, which had drifted by about 20 minutes.
• I re-aligned the small finder telescope. Now, when a star is centered in its cross-hairs, the star appears in the main scope's field of view.
• I connected the ST-9 camera to the telescope and adjusted the main focus screw until stars were in focus.
• The ST-9 camera's dessicant plug had become ineffective after a very long rest -- no surprise. I've since recharged the plug at home.
• I updated the drivers for the ST-9
• MaximDL connects to the camera just fine. The filter names are currently all wrong:
  • "Red" is really B
  • "Green" is really R
  • "Blue" is really V
  • "Luminance" is really I (or U??)
  • "Filter 5" is really clear
  I'll re-set the names next time.
• The camera was oriented so that its flat side (with the connectors) faced the metal bar on the telescope back which is closer to the small finder. In that orientation, MaximDL displays images with North up, East to the left. Convenient.

Last modified 10/3/2021 by MWR.