From: "milton_aupperle" <milton@outcastsoft.com>

Date: August 28, 2010 3:59:20 PM MDT

To: Astro_IIDC@yahoogroups.com

Subject: My First (partial accidental) Variable Star

Hi Folks;

On July 24 (about the last time I used my scope due to the horrible weather here), I decided to try imaging CoRoT-2b (Mag 12.6 in Aquilla @ RA 19 27 06.52 DEC +01 23 01.7) which has an exoplanet and dips 0.035 magnitudes over a period of 137 minutes (1:23 am to 3:39 am MDT).  Because of timing constraints, I could not catch the end of it as it would disappears behind the edge of my Condo building about 15 minutes too soon. Conditions were less than ideal with a nearly full moon, thin haze and my usual +/- 6 arc seconds turbulence (measured FWHM 5.7 to 6.5 arc seconds). My S/N Error was around +/- 0.04 magnitudes for each magnitude measurement as the moon and city "light up" the slightest amount of haze in the air here. To test the stability / repeatability of my system, I started imaging an hour before first traversal of the exoplanet to get a baseline, which was a lucky coincidence.

In any case, I have been re-processing what I did record that night using Astro IIDC via the "Measure Differential Photometry.."

After the usual trial and error attempts, I selected two good constant stars and then was trying to find a good "check" variable star to compare with the CoRoT-2b stars. Ideally I wanted something within about 0.7 mags of CoRoT-2b and similar color.

In checking some candidate stars, I managed to find a variable star (U0900_15190277 Mag 12.8) which dimmed by 0.15 magnitudes over the course of 2 hours. Here are the light curves:

http://tech.groups.yahoo.com/group/Astro_IIDC/files/Other/CoRoT2b_U090015190277_MJA.png

for my seven candidate stars and you can clearly see the dip in the "Pink" (Apples' Magenta) U0900_1590277 curve. I've only found one reference to USNO-A2.0 0900-15190277 (or TYC465-787-1 or [KRE2007] V47) which indicates it has change of 0.07 mags every 1.439 days (34.536 hours) and it was reported in 2007 during an exoplanet search.

The light curve for CoRoT-2b (in Red) is also shown, along with the vertical lines marking the start and mid point of the Exoplanet transit. There might be a dip (?), but even with using a 9 point forward averaging to smooth the data out, it's far from certain.

The Graph your seeing was done completely in "Plot"

http://plot.micw.eu/

which is a fairly robust Mac app for plotting Light Curves and doing light duty annotation of it.

Have a great saturday..

Milton Aupperle