Sep 29, 2004: a short run on ASAS 002511

Michael Richmond
Sep 30, 2004

On the night of Sept 27/28, 2004 EDT, I used the RIT Observatory's 12-inch Meade telescope and SBIG ST8 CCD camera to monitor the cataclysmic variable star ASAS 002511; it's under study by the Center for Backyard Astrophysics. I also tried using our PC-164C video camera on a small telescope attached to our 16-inch telescope, as a finder for the big telescope.

The plan:

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

Notes from the night

• the sky was clear at sunset, but clouds arrived just about two hours later
• the nearly full moon made the sky very bright, and was close to the target star. Our images have quite a bit of scattered light ...
• the target star, ASAS 002511, faded by over two magnitudes since our previous run. As a result, the short, 15-second exposures do not yield good signal-to-noise on the target

Here's a chart of the field of ASAS 002511 taken on Sep 18, 2004. The field is about 20 arcminutes wide. Click on the picture for a larger version.

Arne Henden's calibration of stars in the field indicates

• star A = GSC 599-255 has V=11.16
• star B = GSC 599-1272 has V=11.49
• star C = GSC 599-184 has V=12.06
• the variable, ASAS 002511, is roughly V = 12.3 on this night

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. 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.

ASAS 002511 is the star near differential mag 3.8, with a slightly elevated scatter. The brightest stars (of mag V=11.2 and 11.5) have a formal scatter of 0.006 and 0.009 mag, respectively.

Light curves for selected stars in the field are shown below. ASAS 002511, in green, has very low signal-to-noise.

Here's a closeup of the variation in ASAS 002511 itself:

It's hard to say anything about the light curve :-( I'll use longer exposure times next time.

I've made a table of the measurements themselves, with three different flavors of time. The differential unfiltered magnitudes from the ensemble solution has been shifted so that star "B" in my chart, GSC 559-1272, has value 11.485, matching its V-band magnitude as determined by Arne Henden.

Here's the start of the table:

# Measurements of ASAS002511 made at RIT Obs, Sep_ 30, 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 15 seconds long; the tabulated times are midexposure 
#    and accurate only to +/- 1 second. 
# 'mag' is a differential magnitude based on ensemble photometry 
#    which has been shifted to star GSC 599-1272 has mag=11.485  
#    (matching Henden's calibration of the star to V=11.485)  
# 
# UT day      JD-2,450,000  HJD-2,450,000   mag 
Sep_30.00909     3278.50909   3278.51479  14.799 
Sep_30.00947     3278.50947   3278.51517  14.777 
Sep_30.00984     3278.50984   3278.51554  14.888 

• download the entire table (plain ASCII)

Last modified 9/30/2004 by MWR.