V603 Aql: Jul 13, 2003 EDT

On Jul 13, 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 (for the first time during this summer's observations of V603 Aql)

Notes from the night

• The night was clear, but the full moon was only about 25 degrees from V603, so the sky was bright
• Air temperature dropped a lot, from 23 C at start to 15 C around 3 AM. I refocused at around 2 AM, but that was too late. I should refocus around midnight, I think.

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 were 2 "BAD" out of 438 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_ 14, 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_14.06937     2834.56937   2834.57470  -1.064 
Jul_14.06994     2834.56994   2834.57527  -1.115 
Jul_14.07050     2834.57050   2834.57583  -1.102 

• download the entire table (plain ASCII)

Last modified 7/14/2003 by MWR.