HD209458 Exoplanet transit

The first amateur observation of exoplanet transit from Nyrölä Observatory September 16, 2000

The winner of SBIG contest of January 2002!

Drawing of planet transiting HD209458.
Copyright: Lynette Cook. Used with permission.
As the night darkened at Nyrölä observatory on September 16, 2000 group of amateur astronomers of Jyväskylän Sirius prepared to observe a planet orbiting a star 153 light years away. The star was HD209458 in Pegeasus and its still unnamed jupiter-like planet was about to transit over the star face. The planet orbits very close of the star and transits every 3.5 days dimming the star just a bit. Before these transits had been observed by a few professional observatories.

Observers included some of the most active members of Sirius: Marko Moilanen, Jalo Ojanperä, Jouni Sorvari, Aki Id and Arto Oksanen. We started the observing run at 20.33 UT when there was about one hour to the beginning of transit by prdiction published on exoplaners.org web page. Even though the star is too dim to see on naked eye it was very bright object for CCD-imager and limited the exposure time to just 10 seconds. We logged about four images per minute and continued observing for next four and half hours to record full transit.

The first one of the 866 raw images recorded on September 16, 2000. HD209458 is the brightest star on the image.
From the individual images the dimming caused by the planet was not measurable. The measurement errors vere far larger than the magnitude drop. All 866 images were carefully calibrated and each star was measured with IRAF software. Still the transit was not visible even though the preliminary lightcurve showed some indications of it. Only after all measurements of each 10 minute timeslot were averaged to reduce errors the transit became very obvious on the lightcurve. The transit times agreed very well with the predictions and observed magnitude drop on V-band was 0.02 magnitudes. Still the errors are quite large, but less than the magnitude drop. One of the field stars was used to check the measurements and its magnitude remained constant (within errors) during the transit. We had succeeded in what we thought to be impossible, we had detected a exoplanet transit!

Final lightcurve of the September 16, 2000 transit. HD209458 is on the top and ja bellow is one of the check stars offsetted by 0.05 magnitudes.
Professor Geoffrey Marcy from University of California at Berkeley confirmed our observation and told that we were the first amateur group succeeded observing exoplanet transit. In the future we will try to find new transiting exoplanets using the predictions Marcy's research group has computed from spectroscopic observations.

The equipments used on the observation were a 16-inch Meade LX200 telescope and SBIG ST7E CCD-imager with photometric V-filter. Meade f6.3 focal reducer and JMI's NGF-S digital focuser were used as well. The CCD was controlled with MaxIm DL 2.0 software.

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