The discovery of the very hot exoplanet HD
189733b was announced
by the team of F. Bouchy of the Observatoire de Haute
Provence (France) on October 5th, 2005. His team, founded by Michel Mayor of Geneva
Observatory (Switzerland), had started an
exoplanet search programme biased towards
high-metallicity stars, named ELODIE, in
March 2004, using high-precision radial velocity
measurements. HD 189733b is the 9th transiting
exoplanet found to date. It is located in Vulpecula,
just 0.3 degress from the Dumbell Nebula (M27).
HD 189733b was reported to be a transiting hot
Jupiter, with a period of 2.219d, and with a
photometric depth of about 3%. Considering that HD
189733, a type K-star, has the same visual magnitude
as the well known exoplanet host star HD 209458, of
which I succeeded to observe an exoplanet transit
in September 2003, I decided to start
photometric observations of HD 189733 at the first
possible transit opportunity.
2005, October 16/17
The night of October 16/17, 2005 presented such a
possibility. Observing conditions were far from ideal
: full moon, low altitude of the
star at the moment of the ingress (approx 40d),
cirrus near the start of the transit and clouds
towards the end of the session. I started V-filtered CCD observations
at 20h48m UT (Oct 16.867 UT), about 1 hour in
advance of the predicted time of ingress.
Mid-transit of HD 189733b was expected at 22h55m UT.
The session was stopped after 2h and 140 useful CCD
images. At that moment, HD 189733 was less than 30 degrees above my local horizon, hence too low for
As comparison star, I used SAO 88041, a G0-type
star of mag 8.94, about 8'40" (P.A. 267°) from
HD 189733. Exposure times varied from 15 to 30 sec, and
initially slight defocusing was applied when necessary to
Analysis of the observations
Data analysis was done using the aperture
photometry function of MIRA AP, on non-stacked
images. I used the S/N values produced by MIRA to
eliminate poor quality images. I then used Peranso
to create a 'binned' lightcurve, grouping
observations in 9-min bins and indicating the
standard deviation per bin. The final result is presented below.
Note : amateur astronomer Ron Bissinger
(California) also succeeded in capturing a transit
of HD 189733b at his private observatory, on Oct
10th, 2005. His observations are depicted below.