Apr 10, 2006 UT: Photometry of AM CVn

Michael Richmond
Apr 10, 2006

On the night of Apr 09/10, 2006 EST, I used the RIT Observatory's 12-inch Meade telescope and SBIG ST8E CCD camera to take pictures of the cataclysmic variable AM CVn, a CBA target

The plan:

Notes from the night


For background information on this cataclysmic variable, read

This is a chart of the field based on images taken last night. The bright star (with the upside-down numeral 2) just west of star "B" was slightly saturated in some images, so I discarded it from the solution.

J. Smak's article Light variability of AM CVn /= HZ 29/ , measures a magnitude V = 12.41 for the star marked "A" in the charts above. My instrumental photometry falls somewhere between V and R passbands. I will shift the instrumental magnitudes so that cause Smak's star "A" = USNOB1.0 1275-0248811 to have V = 12.410.

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.

AM CVn is the star at differential mag 1.9, with a scatter of about 0.022 mag. It has just barely more variability that other stars of similar brightness. Star "A" is the second-brightest object in the graph, at differential magnitude 0.09.

Light curves for selected stars in the field are shown below. AM CVn, shown by light green crosses near the middle, varies only slightly more than randomly.

Here's a closeup of the variation in AM CVn itself, again marked by the light green crosses.

I've made a table of the measurements themselves, with three different flavors of time. The differential unfiltered magnitudes from the ensemble solution have been shifted so that the value of star "A" matches the Smak hotometry.

Here's the start of the table.

# Measurements of AM CVn made at RIT Obs, Apr 10, 2006 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 30 seconds long; tabulated times are midexposure 
#    and accurate only to +/- 1 second. 
# 'mag' is a differential magnitude based on ensemble photometry 
#    which has been shifted to match Smak's V-band magnitude 
#    of star A = USNOB1.0 1275-0248811 so V=12.410. 
# UT day      JD-2,450,000  HJD-2,450,000   mag    uncert
Apr10.09642      3835.59642   3835.60041  14.223  0.021 
Apr10.09697      3835.59697   3835.60096  14.222  0.021 
Apr10.09750      3835.59750   3835.60149  14.224  0.022 

Last modified 4/10/2006 by MWR.