From: "cosmicrock2001" <ursamajor_1@mac.com>

Date: August 29, 2010 9:18:26 AM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: My First (partial accidental) Variable Star

This is a really neat bit of work Milton.  Given your SN error is slightly greater than the expected dip, its no surprise it doesn't clearly show up in the data.  I presume you used an uncooled TIS or similar 'video cam'.  Do you think a cooled ccd camera with better signal, less noise would do better under the conditions you had?  And what source do you use to select your 'transit star' and others for comparison?   I haven't tried the diff photometry feature in AstroIIDC yet, but hope to in the future.  

Ron

--- In Astro_IIDC@yahoogroups.com, "milton_aupperle" <milton@...> wrote:

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