V603 Aql: Jul 18, 2003 EDT

On Jul 18, 2003, EDT, I used the 12-inch Meade LX-200 to measure the variable star V603 Aql.

The plan:

• the Meade 12-inch telescope + SBIG ST-8E CCD
• V-band filter
• 30 second exposure times
• flatfielding

Notes from the night

• Clouds nearly covered the sky from around midnight to about 1 AM; the data taken during that interval was poor, and I discarded it.
• A nearly full moon rose around midnight, but wasn't much of a problem
• Air temperature was cool: start at 21 C in dome, dropped to 18 C by 10:30 PM, then to 13 C at 3:40 AM. I refocused at 10:17 PM and 11:40 PM, but should have done so again around 1:30 or 2:00 AM.

Here's a chart of the field of V603 Aql, taken with our equipment: the field is about 16 arcminutes wide.

Note that

• star A = HD 174066 = BD+00 4023, V mag = 8.5
• star B = BD+00 4022 = GSC 00448-00731, V mag = 9.9
• star E = GSC 00448-00243 = USNO-A2.0 0900-13636967
• the variable, V603 Aql, is roughly V mag = 11.

I measured the instrumental magnitude of each star with aperture photometry, using a radius of 6 pixels = 11.2 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. Note that star "A" is saturated. I did not include it in the solution as a reference. I also removed star "B" from the ensemble reference set, since I suspect it is close enough to saturated to be unreliable as a comparison.

The outlier at differential mag = 3.3 is V603 Aql.

It is clear that most of the stars in the field are not varying appreciably, but V603 Aql is, as the green light curve shows The other data belong to stars B, C, E and F, and P.

After making the ensemble solution, I looked at the values for star "C". 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 was 1 "BAD" out of 419 images.

Here's a closeup of the variation in V603 Aql itself:

I've modified the way I report the differential magnitudes. I now use the star marked "E" in the chart above

      star E  =  USNO-A2.0 0900-13636967 
              =  GSC 00448-00243
              =  RA 18:49:01.91  Dec +00:33:46.2  (J2000)

I've made a table of the measurements themselves, with three different flavors of time. Here's the start of the table:

# Measurements of V603 Aql made at RIT Observatory, Jul_ 19, 2003 UT, 
#   taken by Michael Richmond. 
# All data taken with 12-inch Meade LX-200 + V 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 V603 Aql and star E = GSC00448-00243 
# 
# UT day      JD-2,450,000  HJD-2,450,000   mag 
Jul_19.06634     2839.56634   2839.57159  -1.107 
Jul_19.06689     2839.56689   2839.57214  -1.094 
Jul_19.06744     2839.56744   2839.57269  -1.034 

• download the entire table (plain ASCII)

Last modified 7/19/2003 by MWR.