Her04: Jun 26, 2004 UT

On Jun 26, 2004, UT, I used the 12-inch Meade LX-200 to measure a variable star which had just recently been discovered. This new cataclysmic variable doesn't have an official name yet, so I called it Her04, one of the temporary names for it. You can read more about the variable star at this site from the AAVSO:

• Information on Her04 from the AAVSO

            RA = 18 39 26.16     Dec = +26 04 10    (J2000)

The plan:

• the Meade 12-inch telescope + f/6.3 focal reducer + SBIG ST-9E CCD
• no filter
• 30 second exposure times
• no flatfielding, since the main feature of images is an internal reflection off the focal reducer -- and since all we really care about is changes in the variable's brightness

Notes from the night

• thick clouds early, clearing only about 90 minutes after sunset
• cool all night (air in dome was 16 C at start, 11 C at end), with fog forming near dawn
• I ran the CCD at temp -20 C
• the autoguider worked reasonably well; I cut out several frames which featured double exposures and streaks
• I acquired a total of 428 images, but only about 387 were good

Here's a chart of the field of Her04 based on one of my images; the field is about 15 arcminutes wide.

Note that

• star P = TYC 2111-365-1, Vt = 8.9 (very satured in my images)
• star A appears to be slowly variable (see below)
• star B = TYC 211-489-1, Vt = 12.3
• the variable, marked by a pair of lines, is about V = 13.5

I measured the instrumental magnitude of each star with aperture photometry, using a radius of 4 pixels = 7.2 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 several of the brightest stars in the field must be saturated, since their scatter is slightly larger than those stars which are fainter. I did not include these brightest stars in the solution as references.

The two stars with differential magnitudes between 2 and 3 and large scatter are close doubles, which confuses my aperture photometry. Her04 is a point at differential mag 3.209 with scatter 0.046. Most of the other stars with large scatter are either close doubles or located near the edges of the frame.

I made a graph (below) showing differential magnitude in the ensemble solution versus time during the night. One can see that most of the stars in the field are not varying appreciably, but Her04 is, as the green light curve shows. Star B is the blue dots (nice and level -- good!). Note that star A, in red, shows a small decline and gradual rise in brightness during the night. I suggest it not be used as a comparison. The other data belong to stars marked C, D, E in the chart above.

Here's a closeup of the variation in Her04 itself:

I've made a table of the measurements themselves, with three different flavors of time. "HJD" is heliocentric Julian Date. I report the magnitude of the variable star relative to that of star B = TYC 2111-489-1, in the sense:

        mag  =  (Her04 - B)

Here's the start of the table:

# Measurements of Her04 made at RIT Obs, Jun_ 26, 2004 UT, 
#   taken by Michael Richmond. 
# All data taken with 12-inch LX-200 + no filter + SBIG ST-9 CCD 
#    with focal reducer yielding f/6.3 
# Each exposure 30 seconds long; the tabulated times are midexposure 
#    and accurate only to +/- 1 second. 
# 'mag' is a differential magnitude based on ensemble photometry 
#    tabulated value is 'mag fainter than star B = TYC 2111-489-1' 
# 
# UT day      JD-2,450,000  HJD-2,450,000   mag 
Jun_26.15060     3182.65060   3182.65395   1.239 
Jun_26.15110     3182.65110   3182.65445   1.242 
Jun_26.15159     3182.65159   3182.65494   1.239 

• download the entire table (plain ASCII)

Last modified 6/26/2004 by MWR.