UT Apr 18, 2022: Photometry of RR Lyr star BK UMa and test of Guest camera

Michael Richmond
Apr 18, 2022

On the night of Apr 17/18, 2022, under very good conditions, I acquired additional images of the RR Lyr star BK UMa as part of a class project for Observational Astronomy. In addition, AST grad student Lazar Buntic used the 14-inch telescope at the same time to acquire images of Betelgeuse and NGC 2158 in order to test a new low-noise camera his lab is examining.

• An example of one of his images

I was unable to use MaximDL this evening (for reasons that should not recur), so I used Atik's own Artemis Capture software to control the camera. It had some problems with the filterwheel, so I took images in V-band only.

BK UMa

The main setup was:

• Meade 12-inch telescope
• no focal reducer, so working at f/10
• ATIK 11000 CCD camera
• V filter, exptime 30 seconds
• images binned 2x2
• no guiding
• I focused only once, at start of run
  • foc in V = 0.499 yielding FWHM 2.3 at T = 43 / 6
  At the end of the run, the temperature was 32 / 0, but the focus did not degrade much.
• camera ran at T = -20 C

Notes from the night:

• clear all night
• bright nearly full Moon rose about one hour into the run, making the sky grow bright
• I had to use Atik's "Artemis" software to control the camera. The FITS headers are a bit different, and, most important, the images are flipped horizontally from their usual orientation.

The object is located at

  RA = 10:50:18.94  Dec = +42:34:08.5   (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.

Label	B	V
A	10.799	10.168
B	11.825	11.088

I'll use star "B" to shift my instrumental magnitudes to the V-band scale, as star "A" was saturated.

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 sharp increase when the Moon rises.

The FWHM graph below shows little change, despite a drop of 11 degrees Fahrenheit / 6 Celsius.

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 0.006 mag in V.

The change in zeropoint shows a small climb as the field began to set.

Last modified 4/18/2022 by MWR.