V585 Lyr: Sep 20, 2003 EDT

On Sep 20, 2003, EDT, I used the 12-inch Meade LX-200 to measure the cataclysmic variable star V585 Lyrae.

The plan:

• the Meade 12-inch telescope + SBIG ST-8E CCD
• no filter (this is a faint star)
• 30 second exposure times
• flatfielding

Notes from the night

• A good night: clear and dark
• Air temperature dropped a bit; I should have refocused after about an hour
• The field drops low in the sky by 1:00 AM or so, so we can't follow it all night

Here's a chart of the field of V585 Lyr, taken with our equipment: the field is about 16 arcminutes wide.

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Note that

• star A has coords (19 13 50.46, +40 41 25.93) and mags B=12.9, R=11.8 according to the USNO A2.0
• star B has mags B=12.6, R=11.4
• star F has mags B=16.6, R=15.7
• the variable, V585 Lyr, is roughly R mag = 15.

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 

• download the entire table (plain ASCII)

Last modified 9/21/2003 by MWR