UT Mar 30, 2022: Photometry of PZ UMa

Michael Richmond
Mar 30, 2022

On the night of Mar 29/30, 2022, under good conditions, RIT undergrads Matthew Klein, Bill Kern, and I acquired images of the eclipsing binary PZ UMa as part of their class project for Observational Astronomy.

The night was mostly clear and dark, but some light clouds arrived at around 2-3 AM and thickened toward the morning. I tried taking some measurements of AI CVn after 3:30 AM, but didn't get much before the clouds rolled in.

PZ UMa

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
• I focused mid-way between the best positions for B and V filters
  • foc in B = 0.720, V = 0.701 yielding FWHM 2.2 at T = 27 / -3
  • foc in B = 0.708, V = 0.678 yielding FWHM 2.0 at T = 19 / -7
• camera ran at T = -20 C

Notes from the night:

• clear early and cold, with temperatures ranging from 30 / -1 to 16 / -9; clouds arrived around 4 AM and ruined the end of the night
• waning crescent Moon rose late, had no effect
• the camera rotated, as usual, so I had to de-rotate the measurements.
• the measurements of this object from ASASSN
may be of use.

The object is located at

  RA = 09:29:07.08  Dec = +49:51:23.0   (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	10.948	10.220
B	12.771	12.096

I'll use star "A" to shift my instrumental magnitudes to the B-band scale.

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 clear early, but clouds at the end of the measurements.

The FWHM graph below shows a small jump when I re-focused to get a better FWHM in V-band.

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 0.010 mag in B.

The change in zeropoint shows a steep climb near the end, due to increased airmass and clouds.

Last modified 3/30/2022 by MWR.