Her04: Jun 27, 2004 UT

On Jun 27, 2004, UT, I used the 12-inch Meade LX-200 to measure again the star Her04:

• Information on Her04 from the AAVSO
• CBA Belgium has been observing Her04, too

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

The plan:

• the Meade 12-inch telescope + SBIG ST-9E CCD (no focal reducer this time)
• no filter
• 30 second exposure times
• include flatfielding, since the images appear much cleaner without the focal reducer

Notes from the night

• the telescope misbehaved early
• not so cool, so no fog
• I ran the CCD at temp -20 C
• the autoguider worked reasonably well; I cut out several frames which featured double exposures and streaks
• clouds moved in around 3:00 AM local time, cutting the run short by about an hour

Here's a chart of the field of Her04 based on a stack of 20 images from this night:

Note that

• star A is again slowly variable
• star B = TYC 211-489-1, Vt = 12.3
• the variable is marked by a pair of lines

I measured the instrumental magnitude of each star with aperture photometry, using a radius of 5 pixels = 6.3 arcseconds (note the pixel scale is not the same as last night's, since I'm not using the focal reducer), 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. Most of the outliers among the bright stars as members of close doubles, which confuses my analysis programs.

Her04 is the point at differential mag 1.590 with scatter 0.05. Most of the other stars with large scatter are either close doubles.

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, H 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_ 27, 2004 UT, 
#   taken by Michael Richmond. 
# All data taken with 12-inch LX-200 + no filter + SBIG ST-9 CCD 
#    no focal reducer, so at native f/10 
# 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_27.09034     3183.59034   3183.59366   1.199 
Jun_27.09082     3183.59082   3183.59414   1.177 
Jun_27.09132     3183.59132   3183.59464   1.192 

• download the entire table (plain ASCII)

Last modified 6/27/2004 by MWR.