On Sep 20, 2003, EDT, I used the 12-inch Meade LX-200 to measure the cataclysmic variable star V585 Lyrae.
Notes from the night
Here's a chart of the field of V585 Lyr, taken with our equipment: the field is about 16 arcminutes wide.
I measured the instrumental magnitude of each star with aperture photometry, using a radius of 5 pixels = 9.3 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. The zero-point is set by star B, at (19 13 52.35, +40 45 28.0); the USNO A2.0 says this has mags B=12.6, R=11.4.
One of the many outliers at differential mag = 3.5 is V585 Lyr.
It is clear that most of the stars in the field are not varying appreciably, but V585 Lyr is, as the green light curve shows The other data belong to stars A, B, C, D, E, F.
After making the ensemble solution, I looked at the values for star "D". If its magnitude in one particular image lay more than 3 standard deviations from its mean magnitude, I declared the image BAD and discarded it from all subsequent analysis. There were 3 "BAD" out of 248 images.
Here's a closeup of the variation in V585 Lyr itself:
I've made a table of the measurements themselves, with three different flavors of time. Here's the start of the table:
# Measurements of V585 Lyr made at RIT Observatory, Sep_ 21, 2003 UT, # taken by Michael Richmond. # All data taken with 12-inch Meade LX-200 + no filter + SBIG ST-8 CCD # Each exposure 30 seconds long; the tabulated times are midexposure # and accurate only to +/- 1 second. # 'mag' is the difference between V585 Lyr and star B (19 13 52.35, +40 45 28.0 # # UT day JD-2,450,000 HJD-2,450,000 mag Sep_21.01522 2903.51522 2903.51671 3.215 Sep_21.01576 2903.51576 2903.51725 3.163 Sep_21.01633 2903.51633 2903.51782 3.182
Last modified 9/21/2003 by MWR