UT Nov 04, 2020: Photometry of RT And

Michael Richmond
Nov 4, 2020

On the night of Nov 03/04, 2020, under fair conditions, I acquired B-band images of the eclipsing variable star RT And, which one of my capstone students will analyze. The star was just coming out of an eclipse at the start of the run.

I noticed that a different, fainter star in the field was _also_ coming out of an eclipse of its own. That star is, as far as I can tell, an un-noticed variable....

RT And

You can find some basic information on this star at the SIMBAD's page for it.

The main setup was:

• Meade 12-inch telescope
• no focal reducer, so working at f/10
• ATIK 11000 CCD camera
• B filter, at 10 sec, 699 images; 20 seconds yielded some saturated images of RT And
• images binned 2x2
• no guiding
• focus in B at 1.444, yielding FWHM = 2.7 pix
• camera ran at T = -20 C

Notes from the night:

• bright Moon, fortunately not very close to the field
• clouds delayed the start of the run until several hours after sunset. There are two brief intervals of clouds during the run.
• temperature was cold -- around 39 F / 4 C at start (7:07 PM), and 30 F / -2 F at end (1:17 AM).
• the FWHM of images increased briefly near the end of the run, from about 3.5 pix to almost 6 pix, and then decreased back to about 3.8 pixels by the end. The images look soft, but not trailed. Perhaps the wind shifted and blew into the dome; the slit was pointed nearly due west at the time.

The object is at

  RA = 23 11 17.9   Dec = +52 59 59.2    (J2000)

A chart of the field based on pictures tonight is shown below. The size of the chart is about 38 x 26 arcminutes.

The stars "A", "B", and "C" appear in the charts and tables for this field made by the AAVSO. see

• RT And chart from AAVSO
• RT And photometry from AAVSO

I used the star labelled A = "102" to shift my measurements to the "B" magnitude scale. It has B = 10.336.

Here's a picture of the TV with the finder's field of view when pointing at RT And:

The dark current was normal this evening:

The sky value shows that the sky was mostly clear, but there were two brief periods of clouds. The low point is when I closed the slit to move the panel to the top of the dome.

The number of objects detected.

I used an aperture of 5 arcsec for photometry. Note the brief rise and fall near the end.

Using aperture photometry with a radius of 5 pixels (binned 2x2, each pixel is 1.25 arcsec, so a radius of 6.25 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 with 10-second exposures. I marked all the bright stars as possible variable.

The jumps in the photometric solution are due to clouds.

Here are light curves of the variable and the field stars. Note that RT And is coming out of an eclipse at the start, and that star "X" is doing the same (with a longer egress).

Last modified 11/4/2020 by MWR.