Jun 25, 2009 UT: Photometry of cataclysmic variable RXJ1643+34 = V1084 Her

Michael Richmond
Jun 25, 2009

On the night of June 24/25, 2009, I observed the cataclysmic variable star RXJ1643+34 = V1084 Her. Joe Patterson of the Center for Backyard Astrophysics suggested that members of the CBA observe this star during the summer. The object is at RA = 16:43:45.70 Dec = +34:02:40, so it is placed near the meridian at sunset.

The setup was:

Notes from the night

This is a chart of the field taken from the DSS.

The chart has several of the brighter stars in the field labelled with letters, just to keep me straight as I perform the reductions. Star A is photometry provided by Mickaelian et al., A&A 381, 894 (2002):

label                           RA        Dec            B        V
  A  USNOB1.0 1240-0246555   16:43:40.59 +34:03:02     13.51    12.97
  B  TYC 2585-1631-1         16:43:27.81 +34:02:07     13.20    12.16

I measured the instrumental magnitude of each star with aperture photometry, using a radius of 4 pixels = 5.6 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.

One output of the ensemble solution is the value of the zero-point of each frame relative to the others. In the graph below, I plot this zero-point as a function of time. Note the bumps -- they are due to clouds passing overhead. I removed one stretch of images due to the clouds.

Note how well the times of high zero-point, in the graph above, match the times when fewer objects were detected, in the graph below.

Below is a graph of the scatter in differential magnitude versus magnitude in the ensemble solution.

The floor of this diagram corresponds to a scatter of about 0.008 mag. RXJ1643 appears at differential magnitude 0.4; its scatter of 0.050 mag is much larger than that of other bright stars. showing that it is a variable.

Light curves for selected stars (RXJ1643 and stars A - D) in the field are shown below. The target is shown by light green crosses. I've shifted star "C" (pink squares) a bit to separate it from star "A" (red plus signs).

Here's a closeup of the variation in RXJ1643 and a few comparison stars.

I've made a table of the measurements themselves, with three different flavors of time. The differential magnitudes from the ensemble solution have been shifted so that star "A" in my chart, USNOB1.0 1240-0246555, has value 12.97.

Here's the start of the table.

# Measurements of RXJ1643+34 made at RIT Obs, Jun 25, 2009 UT, 
#    by Michael Richmond, using 12-inch Meade LX-200 and SBIG ST-8E CCD. 
# Each exposure 15 seconds long with no filter. 
# Tabulated times are midexposure (FITS header time - half exposure length) 
#    and accurate only to +/- 1 second (??). 
# 'mag' is a differential magnitude based on ensemble photometry 
#    using a circular aperture of radius 5.6 arcseconds. 
#    which has been shifted so USNOB1.0 1240-0246555 has V=12.97 
#    to match value from Mickaelian et al., A&A 381, 894 (2002) 
# UT_day             JD            HJD        mag    uncert
Jun25.08410     2455007.58410  2455007.58691  12.434  0.011 
Jun25.08438     2455007.58438  2455007.58719  12.458  0.010 
Jun25.08465     2455007.58465  2455007.58746  12.470  0.010 

Last modified 6/25/2009 by MWR.