UT Oct 06, 2022: Photometry of XX And

Michael Richmond
Oct 9, 2022

On the night of Oct 05/06, 2022, I observed the RR Lyrae star XX And for a capstone project.

XX And

The star XX And is a variable star of the RR Lyr "AB" type. Its period may be changing slightly on long timescales -- that will be one focus of our study of it.

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 values:
  • V: 1.683 yielding FWHM 2.3 at T = 60/15
  • B: 1.723 yielding FWHM 2.4 at T = 60/15
  I set the focus to be about 1.693, about 0.030 units smaller than the B-band value, in order to lie between the best focus for B and V.
• camera ran at T = -20 C

Notes from the night:

• probably light cirrus over much of the sky for most of the night, with a few brief periods of thicker cloudiness. Decent data quality nonetheless
• nearly full Moon lit up the sky for the first half, set around 1:30 AM
• no skunks or other creatures
• pretty warm -- T = 50/10 at the end of the night. Nice.

The object is located at

  RA = 01:17:27.41  Dec = +38:57:02.0    (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. You can find reference magnitudes for these stars at the AAVSO:

• AAVSO chart for the field
• table of magnitudes from the AAVSO: sequence X27032O

I'm not sure yet which reference star(s) might be best to shift the instrumental magnitudes to the standard scale. These might be good choices:

Label	B	V
C = 111	11.575	11.101
E = 117	12.503	11.745

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 minor bumps, indicating light clouds now and then.

The FWHM graph below shows relatively steady value; I didn't make any adjustments to focus.

Using aperture photometry with a radius of 7 pixels (binned 2x2, each pixel is 1.24 arcsec, so a radii 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 0.007 mag in V, and 0.008 in B.

The change in zeropoint shows two episodes of mild clouds.

Photometry shows the star reaching minimum, rising quickly to its peak, and then declining. Note the "shoulder" in the rise.