UT Nov 07, 2020: Photometry of RT And

Michael Richmond
Nov 7, 2020

On the night of Nov 06/07, 2020, under good conditions, I acquired B-band and R-band images of the eclipsing variable star RT And, which one of my capstone students will analyze. I caught one eclipse near the end of the run.

The other star in the field which I suspect to be an eclipsing binary showed no variations ...

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 and R-filter alternating, at 10 sec, 564 images each
• images binned 2x2
• no guiding
• focus in B at 1.374, focus in R at 1.424; decided to put focus closer to B at 1.393, later 1.434 as temperature dropped.
• camera ran at T = -20 C

Notes from the night:

• bright Moon rose after the start of the run, was pretty far from the field
• maybe a brief time with light cloud early, then clear.
• temperature was very warm (nice!) -- around 68 F / 10 C at start (5:46 PM), and 52 F / 11 F at end (1:20 AM).
• the FWHM was around 4.5 pix in B early, then 5.0 pix after I modified the focus. In R-band, it was 5.2 pix early, then about 4.5 pix after shifting focus. My goal was to prevent saturation with the same exposure time (10 sec) in each passband, and this appeared to work fine. In the future, though, I'll try to use pairs of filters which are closer to parfocal.

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. It also has magnitude r = 10.127 according to the APASS catalog.

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 suffered a short period of light cloud early, 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 9 pixels for photometry.

Using aperture photometry with a radius of 9 pixels (binned 2x2, each pixel is 1.25 arcsec, so a radius of 11.25 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 0.006 mag in B with 10-second exposures. I marked all the bright stars as possible variable.

The outliers in the photometric solution are due to my adjustments of the dome slit.

Last modified 11/7/2020 by MWR.