The TEP network is a group of collaborators searching for Transits of Extrasolar Planets. Our major effort is the observation of the eclipsing binary star CM-Draconis for signs of the presence of planets using the transit method. For a quick introduction to the project, read the Poster from the JENAM-95 conference. A technical introduction is given in an article in Astronomy and Astrophysics (1998, Vol 338, p 479, preprint in postscript , pdf).
Note 30 Dec. 2002: Since the TEP project finished in 2001, this site
is not being updated any longer.
New: Animation of the transiting planet
around the star HD209458
Sep 2000 - Results from follow up observations
Observations undertaken during spring and summer 2000 rule out most candidates of transiting planets around CM Draconis (see entry for Dec 1999). Among them is the previously best candidate, which had a confidence of 73%. Currently, only 3 candidates remain, which we have been unable to observe at predicted transit times. The probability that one of these candidates turns out to be a real planet is however low. When verification of these remaining candidates is finished, the TEP project will be completed, with the exception of occasional follow ups of eclipse minimum times of CM Draconis for the next few years (see entry for May 2000).
May 2000 - Candidate for massive planet found through eclipse minimum timing
Small variations in the time of the eclipse minima indicate a massive planet candidate with 1.5-3 Jupiter masses and a period of 750 - 1050 days around CM Draconis. Verification of this candidate will need 3-4 eclipse minima timing observations per year, for several more years. More details are given in a paper in Astronomy and Astrophysics (Vol 358, L5-L8; preprint in postscript)
Dec 1999 - Several Planet candidates
In a paper in the Astrophysical Journal (Vol. 535, p. 338, preprint in html or postscript) describing the detection probabilities of terrestrial sized planets in the CM Dra system, the TEP group announces several planet candidates, one of them with a confidence of about 70%. This planet would have a diameter of 2.3-2.5 times the Earth's and a period of 22.6 days, positioning it in the habitable zone. Follow-up observations to verify this candidate are sceduled for spring 2000. If verified, this would be the smallest planet found to date.
Nov 1998 - An Earth sized planet is found?
That is what several newspaper articles suggested the TEP group had found. A scientific paper was published in October 1998 in Astronomy and Astrophysics (Vol 338, p. 479, preprint in postscript , pdf) which gives an overview of the observations of CM Dra from 1994-1996, and a preliminary analysis of the data. There were five events found, that are not incompatible with the transits of planets of sizes of 2 -2.5 Earth radii. However, the presence of a planet cannot be concluded from them yet. First, it must be excluded that the observed drops are false detections. They might result from some other cause, like rare atmospheric variations, or they might be instrumental effects.
An evaluation of the significance of these events is the subject of current intensive work. An announcement about the detection of a planet can be made only when such events have been observed with a regularity that can only result from the repeated transits of a planet across its central star. That means, we will have to predict from the current events when further transits should occur again. Only if such predicted transits can be observed, are we certain to have found a planet.
For planets significantly larger then 2.5 Earth radii and of periods of
less then 60 days, we are confident with over 90% that they are absent, since
no event found has amplitudes large enough.
This is exactly what Guinan and collaborators from Villanova University claimed
to have found (IAU Circular 6864) - a 70 day periodic
shift in minimum times with an amplitude of 18 seconds, indicative of a brown
dwarf with 0.06 solar or 60 Jupiter masses. An analysis of 32 minimum times
obtained by the TEP network (IAU Circular 6875)
showed neither the 70day periodicity, nor any other periodicity of more then
4 seconds. In fact, the standard deviation of our minimum times is about
7 seconds, and that excludes any sinusoidal signal with an amplitude of
more then 11 seconds. We are therefore certain that this claimed brown
dwarf does not exist. The group by Guinan has not published further results
(besides the IAU Circular). The presence of a brown dwarf or massive planet
in the CM Dra system is however not completely ruled out: our data since
1994 have only a coverage long enough to be sensitive to periodicities of
less then a few years. So, longer periodic massive planets may still be there
and could only be found through occasional minimum timing observations spanning
a long time line.
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Last update: 15/Mar/2005. For comments, send email to Hans-Jörg Deeg at hXdeeg@ll.iaXc.es (NOTE: remove the X from adress)