Sep 21, 2005 UT: Photometry of LS Peg

Michael Richmond
George Privon
Sep 22, 2005

On the night of Sep 20/21, 2005 EDT, George Privon used the RIT Observatory's 12-inch Meade telescope and SBIG ST8E CCD camera to take pictures of the cataclysmic variable LS Peg, a CBA target

The plan:

• the Meade 12-inch telescope with SBIG ST-8E CCD (no focal reducer); the plate scale is about 1.85 arcsec per pixel
• no filter
• exposure time 30 seconds

Notes from the night

• the night was pretty good
• the nearly full moon was only a minor annoyance
• we re-discovered the hard way that when one interrupts the guiding process using an ancient version of MaximDL, the main chip's sequence is ALSO stopped. We lost two hours of good conditions while the camera software simply didn't take any pictures ....

LS Peg

For background information on this cataclysmic variable, read

• The Unusual Cataclysmic Variable S193 by Garnavich and Szokody, JAAVSO 21, 81 (1992).
• Taylor, Thorstensen and Patterson (PASP 756, 184, 1999)

This is a chart of the field based on images taken last night. Click on the chart for a larger version.

The best photometry I could find for the stars in this field comes from Arne Henden. He has very kindly made available a datafile containing UBVRI measurements of a number of stars around LS Peg.

• Arne's photometry around LS Peg (plain ASCII)

The stars marked "A" through "G" in the chart above all have measurements in Arne's sequence: they are, in fact, the third-brightest through ninth-brightest in V-band (the brightest, the star just north of LS, is saturated in my images; the second-brightest is LS Peg itself). My instrumental photometry seems somewhere between V and R passbands. I will shift the instrumental magnitudes so that they match Henden's measurement of star "A" = USNOB1.0 1040-0618266, of V = 12.066.

I measured the instrumental magnitude of each star with aperture photometry, using a radius of 4 pixels = 7.4 arcseconds and sky defined by an annulus around each star. 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.

Below is a graph of the scatter in differential magnitude versus magnitude.

LS Peg is the bright star with large scatter.

Light curves for selected stars in the field are shown below. LS Peg, shown by light green crosses near the top, is clearly variable. Note the big gap caused by the issue with the camera control software (sigh).

Here's a closeup of the variation in LS Peg itself.

I've made a table of the measurements themselves, with three different flavors of time. The differential unfiltered magnitudes from the ensemble solution have been shifted so that the value of star "A" matches the Henden V photometry.

Here's the start of the table.

# Measurements of LS Peg made at RIT Obs, Sep 21, 2005 UT, 
#   made by George Privon. 
# All data taken with 12-inch LX-200 + no filter + SBIG ST-8 CCD 
#    no focal reducer, so at native f/10 
# Each exposure 30 seconds long; tabulated times are midexposure 
#    and accurate only to +/- 1 second. 
# 'mag' is a differential magnitude based on ensemble photometry 
#    which has been shifted to match Henden's V-band magnitudes 
#    (example: star A = USNOB1.0 1040-0618266 has V=12.066). 
# 
# UT day      JD-2,450,000  HJD-2,450,000   mag    uncert
Sep21.12868      3634.62868   3634.63351  11.882  0.053 
Sep21.12925      3634.62925   3634.63408  11.892  0.050 
Sep21.12980      3634.62980   3634.63463  11.892  0.050 

• download the entire table (plain ASCII)

Last modified 9/22/2005 by MWR.