UT Nov 08, 2020: Photometry of RT And

Michael Richmond
Nov 8, 2020

On the night of Nov 07/08, 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 in the middle of the run.

The other star in the field which I suspect to be an eclipsing binary showed no variations, for the second night in a row.

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, 474 images each
• images binned 2x2
• no guiding
• focus in B at 1.395, focus in V at 1.455, focus in R at 1.455, focus in I at 1.475, focus in clear at 1.370. decided to put focus at 1.410, between best for B and R.
• camera ran at T = -20 C

Note the focus values are roughly:

    B:   V - 0.060
    V:   (reference)
    R:   V + 0
    I:   V + 0.020
clear:   V - 0.085

Notes from the night:

• bright Moon only rose near the end of the run, was pretty far from the field
• no clouds at all
• temperature was very warm (nice!) -- around 70 F / 21 C at start (6:03 PM), and 50 F / 10 F at end (12:50 AM).
• the FWHM was around 3.8 pix in B early, then rose to about 4.2 pix by the end.

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 no real evidence for clouds; good.

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 11/8/2020 by MWR.