Apr 12, 2006 UT: Photometry of IY UMa

Michael Richmond
Apr 12, 2006

On the night of Apr 11/12, 2006 EST, I used the RIT Observatory's 12-inch Meade telescope and SBIG ST8E CCD camera to take pictures of the cataclysmic variable IY UMa, a CBA target

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
• exposure time 30 seconds

Notes from the night

• a poor night: bright gibbous moon and thick cirrus at start of run
• I only worked for about two hours due to the conditions

IY UMa

For background information on this cataclysmic variable, read

• Discovery of a New Deeply Eclipsing SU UMa-Type Dwarf Nova, IY UMa (= TmzV 85)
• Superhumps in Cataclysmic Binaries. XVIII. IY Ursae Majoris
• Late superhumps and the stream-disc impact in IY UMa
• High-speed energy-resolved STJ photometry of the eclipsing dwarf nova IY

Note added 4/12/2006: Patrick Schmeer provides the following measurements, which date the start of the outburst very well:

   UMAIY 20060406.333  170CR SPK
   UMAIY 20060407.308  169CR SPK
   UMAIY 20060408.211  133CR SPK
   UMAIY 20060409.202  130CR SPK
   Instrument: University of Iowa, Rigel Telescope (0.37-m Cassegrain)
   Sequence: Henden and Sumner (R magnitudes derived from V and B-V)

If we call the start of the outburst UT Apr 08, 2006, then my observations here, on UT Apr 12, occur on day 4.

This is a chart of the field based on images taken last night. The bright star "Q" was saturated in my images, so I discarded it from the solution. Click on the chart for a larger version.

Arne Henden has calibrated stars in this field. He finds that the star marked "B" = USNOB1.0 1481-0247104 in the chart above has V = 13.554. My instrumental photometry falls somewhere between V and R passbands. I will shift the instrumental magnitudes so that the star "B" has Henden's mag V = 13.554.

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.

IY UMa is the star with the enormous scatter of over 0.25 mag. Star "B" has differential magnitude about 3.0 and scatter of 0.012 mag.

Light curves for selected stars in the field are shown below. Star "A" is in red, star "B" in blue. IY UMa, shown by light green crosses, is clearly varying like crazy. My observing run corresponds roughly to one period of the orbit.

Here's a closeup of the variation in IY UMa 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 "B" matches the Henden photometry.

Here's the start of the table.

# Measurements of IY UMa made at RIT Obs, Apr 12, 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 Henden's V-band magnitude 
#    of star B = USNOB1.0 1481-0247104 so V=13.554. 
# 
# UT day      JD-2,450,000  HJD-2,450,000   mag    uncert
Apr12.05043      3837.55043   3837.55204  14.012  0.023 
Apr12.05095      3837.55095   3837.55256  13.966  0.020 
Apr12.05147      3837.55147   3837.55308  13.960  0.021 

• download the entire table (plain ASCII)

Last modified 4/12/2006 by MWR.