Aug 31, 2004: V1101 Aql

Michael Richmond
Sep 01, 2004

On the night of August 31/Sep01, 2004 EDT, I used the RIT Observatory's 12-inch Meade telescope and SBIG ST8 CCD camera to monitor the star V1101 Aql, a cataclysmic variable under study by the Center for Backyard Astrophysics.

The plan:

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

Notes from the night

• not a good night! Clouds covered the sky completely twice, halting observations for a half hour each time, and on several other occasions they ruined a few images.
• the nearly full moon made the sky very bright, which lowered the precision of the stellar measurements

Here's a chart of the field of V1101 Aql taken Aug 21, 2004. The field is about 20 arcminutes wide. Click on the picture for a larger version.

Note that

• star A = USNO-A2.0 1050-16879362 shows gradual change relative to other stars at high airmass; I'm suspicious of it
• star B = USNO-A2.0 1050-16888785, B=13.9, R=12.8
• star E = USNO-A2.0 1050-16868448, B=14.2, R=12.5
• star F = USNO-A2.0 1050-16868261, B=15.1, R=14.6
• the variable, V1101 Aql, is roughly V mag = 14.

Stars P and Q are new variables, with R-band magnitudes roughly 15.7 and 13.6, respectively; see the Aug 21/22, 2004 EDT observations for their story.

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. Note that the brightest stars included in the solution may be slightly saturated. I made a series of preliminary solutions and discarded stars which had large scatter due to close companions, or due to their position near the edge of the frame, etc.

V1101 Aql does not appear outside the locus of "ordinary" stars in this plot for two reasons:

• the scatter overall is higher than usual, due to the poor conditions and bright sky
• V1101 Aql was relatively constant in brightness during the run

Light curves for selected stars in the field are shown below. The waviness of almost all the measurements shows the poor quality of the night. V1101 Aql, in green, is barely more variable than the others.

Here are light curves of the two new variable stars, P (faint) and Q (bright):

Here's a closeup of the variation in V1101 Aql itself:

The wierd bright/faint alternation after JD 249.70 really bothers me; star "E" doesn't show the same effect. I don't know what's causing it. It's certainly not real.

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

# Measurements of V1101Aql made at RIT Obs, Sep_ 1, 2004 UT, 
#   made by Michael Richmond. 
# All data taken with 12-inch LX-200 + no filter + SBIG ST-8 CCD 
#    no focal reducer, so at native f/10 
# Each exposure 60 seconds long; the tabulated times are midexposure 
#    and accurate only to +/- 1 second. 
# 'mag' is a differential magnitude based on ensemble photometry 
#    tabulated value is 'mag fainter than star E = USNOA2.0 1050-16868448' 
#    (not star A = USNOA2.0 1050-16879362 as on Aug 22 UT)' 
# 
# UT day      JD-2,450,000  HJD-2,450,000   mag 
Sep_01.02236     3249.52236   3249.52656   0.706 
Sep_01.02417     3249.52417   3249.52837   0.743 
Sep_01.02508     3249.52508   3249.52928   0.727 

• download the entire table (plain ASCII)

Last modified 9/01/2004 by MWR.