V603 Aql: Jun 25, 2003 EST

On Jun 25, 2003, EST, I decided to put the 12-inch Meade LX-200 into some serious use: photometry of the variable star V603 Aql.

The plan:

• the Meade 12-inch telescope + f/6.3 focal reducer + SBIG ST-8E CCD
• V-band filter
• 10, 20, 30 second exposure times
• no flatfielding, since the main feature of images is an internal reflection off the focal reducer

What I discovered:

• at this time of year, the sky is the right brightness for twilight flats around 9:15 PM
• because the night was so warm (28 C at start, 22 C at finish), I ran the camera at -5 Celsius all night long.
• the sky starts to become seriously bright around 4:00 AM EST
• V603 Aql is very low in the bright eastern sky until midnight or so
• decent focus is 2.0-2.5 pixels FWHM with 3x3 binning, which means about 5 arcsec FWHM. It might be better without the binning, but for my purposes, this is fine.

Here's a chart of the field of V603 Aql, taken with our equipment: the field is about 20 arcminutes wide.

Note that

• star A = HD 174066 = BD+00 4023, V mag = 8.5
• star B = BD+00 4022 = GSC 00448-00731, V mag = 9.9
• the variable, V603 Aql, is roughly V mag = 11.

I discarded some 10-second and 20-second images taken early in the evening and kept only the 30-second data. I measured the instrumental magnitude of each star with aperture photometry, using a radius of 5 pixels = 11.5 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 star "A" is saturated. I did not include it in the solution as a reference.

The outlier at differential mag = 3.3 is V603 Aql. The other prominent outlier is a star with a nearby companion which was sometimes mixed into its aperture.

It is clear that most of the stars in the field are not varying appreciably, but V603 Aql is, as the green light curve shows. The other data belong to stars B, C, D, E and F.

Here's a closeup of the variation in V603 Aql itself:

I've made a table of the measurements themselves, with three different flavors of time. Here's the start of the table:

# Measurements of V603 Aql made at RIT Observatory, Jun_ 26, 2003 UT, 
#   taken by Michael Richmond. 
# All data taken with 12-inch Meade LX-200 + V filter + SBIG ST-8 CCD 
# Each exposure 30 seconds long; the tabulated times are midexposure 
#    and accurate only to +/- 1 second. 
# 'mag' is the difference between V603 Aql and BD+00 4022 = GSC 00448.00731 
# 
# UT day      JD-2,450,000  HJD-2,450,000   mag 
Jun_26.14100     2816.64100   2816.64632   3.350 
Jun_26.14154     2816.64154   2816.64686   3.324 
Jun_26.14208     2816.64208   2816.64740   3.300 
Jun_26.14263     2816.64263   2816.64795   3.314 

• download the entire table (plain ASCII)

After I had acquired the field of V603 Aql and found a good guide star (hint: place star "A" at pixel [356,226] on the main CCD), there wasn't a lot to do. About every 20 minutes, I had to move the dome to follow the telescope, but that was it. In the breaks, I worked on our 16-inch telescope. We placed it on a new Astrophysics German equatorial mount last fall, but hadn't used it much before the cold weather set it. I used both the "2-star" and "star drift" methods to improve the polar alignment of this telescope. However, since I was using an eyepiece without a reticle, it's likely that some additional work needs to be done.

I also believe that the mirror in the 16-inch can flop out of place if one points down low enough ... I should watch out not to do that next time.

Last modified 6/26/2003 by MWR.