Sep 18, 2004: ASAS 002511

Michael Richmond
Sep 19, 2004

On the night of Sept 18/19, 2004 EDT, Tracy Davis and I used the RIT Observatory's 12-inch Meade telescope and SBIG ST8 CCD camera to monitor the newly-discovered cataclysmic variable star ASAS 002511; it's a hot new item 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
• 15 second exposure times

Notes from the night

• the sky was clear and reasonably still
• the air was cool throughout the run, so we could run the camera at T=-14 Celsius, the lowest temperature of the season so far (though with 15-second exposures, it doesn't matter much)
• we also took about 40 images of TrES-1, a star with a planet which occasionally transits; we're going to try detecting a transit soon.

Here's a chart of the field of ASAS 002511 taken on this night. 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 = 11.6 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 bright star with the larger-than-normal scatter in this diagram. The brightest stars have a formal scatter of 0.004 and 0.005 mag, respectively.

Light curves for selected stars in the field are shown below. ASAS 002511, in green, is clearly variable.

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

Michael Koppelman also observed ASAS 002511 on this night, and sends this message ...

I saw you had your data online. I combined your data and my data and did a Fourier analysis and got P=0.0573 +/- 0.0003, just slightly different than I got with only my data. Using your data alone I get P=0.0573 +/- 0.0002. Hmmm. Apparently longer runs of higher quality data are better! ;)

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_ 19, 2004 UT, 
#   made by Michael Richmond and Tracy Davis. 
# 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_19.05042     3267.55042   3267.55597  11.620 
Sep_19.05126     3267.55126   3267.55681  11.583 
Sep_19.05168     3267.55168   3267.55723  11.606 
Sep_19.05209     3267.55209   3267.55764  11.586 

• download the entire table (plain ASCII)

Last modified 9/19/2004 by MWR.