The TEP network

What is TEP

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 

The Transit Method (link to intro)


News & Results

2002 - The TEP project has finished
Follow-up observations of the remaining 3 planet candidates (see below, in entry for Sep 2000) were taken during 2001. While two of these candidates were discarded when no transits showed up during follow-up observations, for one candidate a transit-like feature appared right on time. We got excited about this, while keeping in mind that the probability for random noise to create such a feature is about 3%  (this is described in more detail in Doyle et al, 2000, Astrophysical Journal, 535, 338). Indeed, during two further follow-up observations, the feature did not show up at predicted transit times  and that candidate had to be discarded as well. Consequently, the TEP project did not discover any planet, but it remains as the first observational project that probed the presence of terrestrial-sized planets around any star.

Jan 2001 - Article in Sunday Times

A news report in the Sunday Times from 7 Jan 2001 claimed that several planets were found around CM Draconis. This is incorrect and the article contains several statments that are grossly distorted. For a follow-up, see this article in

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.

April 1998 - A brown dwarf (~60 Jupiter masses)?

Massive planets , or brown dwarfs circling an eclipsing binary system will cause a periodic offset in the time of the eclipse minima. No transits are needed to detect a massive planet this way, but one needs to measure very precise times of the eclipse minima. This periodic offset is due to the motion of the eclipsing binary around the common barycenter of the planetary system (= eclipsing binary + planets). Hence, the eclipsing binary is closer or more distant from the Earth, depending on the position of the massive planet - and light from the binary will arrive a few seconds earlier or later, in rhythm with the orbital period of the massive planet.

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.

June 1996 - A Jupiter-sized planet?

An announcement (IAU Circular 6423) of a possible transit of a big Jupiter-sized planet, with a temporal faintening of CM Dra by 8%, was alos made by the group of Guinan, McCook, and Wright at Villanova University. The TEP group, with a much larger observational coverage of CM Dra -over 700 hours-, has never encountered any event of comparable magnitude (see IAU Circular 6425).  Also, meanwhile (Nov 1998) we are certain that such a Jupiter-sized planet is absent, as it should have left a clear periodicity in the eclipse minimum times of CM Dra. This claimed transit by Guinan et al. also has never been published.

References related to the work by the TEP group and to the Transit method

Links to other projects using the transit method

Links to other sites related to extrasolar planets and the search for life in the universe:

The Extrasolar Planets Encyclopedia
The Darwin - space infrared interferometer project's planets page
The Astrobiology Web
Eric Mamajek's Exoplanet Page

 'vaphot', the optimized aperture photmetry package (for IRAF) written for the TEP project is available by ftp from .

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Last update: 15/Mar/2005. For comments, send email to Hans-Jörg Deeg at (NOTE: remove the X from adress)