[Aavso-photometry] Final reduction of TrES-1 transit observations

[Tonny Vanmunster]

Dear colleagues,

I herewith include updated information on my transit observations of
exoplanet TrES-1, dd September 1st, 2004. The article featured on the
Sky&Telescope website shows a picture of my raw (unprocessed) transit light
curve, that was based on a single comparison star.

Meanwhile, I have used the technique of ensemble photometry (using 7
comparison stars) to increase the accuracy of my observations. This has
resulted in a better photometric light curve, which is reproduced on my web
site (www.cbabelgium.com). Each data point or bin is the average value of 5
subsequent CCD measurements. Also shown is the standard deviation per bin.
Overall, I obtained a photometric accuracy of 0.003 mag.

Based on the improved data, I furthermore derive :

- magnitude drop : 0.025 mag
- time of ingress (heliocentric) : 2004, Sep 1 at 21h23m UT +/- 2 min (about
10 min later than the transitsearch ephemeris)
- time of egress (heliocentric) : 2004, Sep 1 at 23h50m UT +/- 3 min (about
4 min later than predicted)
- duration central transit : 147 min (published value : 152 min)

Tomorrow brings another opportunity over Europe to observe a transit of
TrES-1. It would be interesting to learn about follow-up observations, and
to see if the above statements regarding ingress/egress time differences are
confirmed.

Best regards,
Tonny

Tonny Vanmunster
CBA Belgium Observatory
http://www.cbabelgium.com
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PERANSO : The Final Frontier of Period Analysis Software
http://www.peranso.com
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