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arxiv:astro-ph/9806371v1 29 jun 1998a&a manuscript no.(will be inserted by hand later)your thesaurus codes are:06(08.09.2 cm dra,08.16.2,08.02.2,08.12.2,08.06.1,03.20.4)astronomyandastrophysics1.2.2008near-term detectability of terrestrial extrasolar planets:tep network observations of cm draconish.j. deeg 1 , l.r. doyle 2 , v.p. kozhevnikov 3 , e.l. mart´ın 1,⋆ , b. oetiker 4 , e. palaiologou 5 , j. schneider 6 , c.afonso 6 , e.w. dunham 7 , j.m. jenkins 2 , z. ninkov 8 , r.p.s. stone 9 , p.e. zakharova 31instituto de astrof´ısica de canarias, e-38200 la laguna, tenerife, spain, hdeeg@bigfoot.com2seti institute, ms 245-3, nasa ames research center, mof f ett field, ca 94035, usa, doyle@gal.arc.nasa.gov3astronomical observatory, ural state university, lenin ave. 51, ekaterinburg, 620083, russia4university of new mexico, dept. of physics and astronomy, albuquerque, nm 87131, usa5university of crete, skinakas observatory, p.o. box 1527, heraklion 71110, crete, greece6cnrs-observatoire de paris, 92195 meudon, france7lowell observatory, flagstaf f , az 86001, usa8center for imaging science, rochester institute of technology, rochester, ny 14623-5604, usa9university of california, lick observatory, mount hamilton, ca 95040, usareceived 17 october 1997; accepted 9 june 1998abstract.results from a photometric search for extrasolar planetarytransits across the eclipsing binary cm dra are presented. thetep (transits of extrasolar planets) network has observedthis star since 1994, and a lightcurve with 617 hours of coveragehas been obtained. the data give a complete phase coverageof the cm dra system at each of the 3 years of observations,with a noise of less than 5 mmag. new epoch and period valuesfor cm dra are derived, and a low f l are rate of 0.025 hr −1 hasbeen conf i rmed. the absence of periodic variations in eclipseminimum times excludes the presence of very massive planetswith periods of less than a few years. the lightcurve was visu-ally scanned for the presence of unusual events which may beindicative of transits of extrasolar planets with ’massive earth’sizes. six suspicious events were found which are being followedup for future transits, by planets with sizes between 1.5 and2.5 r e (earth radii). however, none of these events has am-plitudes compatible with planets larger than 2.5 r e . coplanarplanets larger than 2.5 r e and with orbital periods of less than60 days can therefore be ruled out with a conf i dence of about80%. planets smaller than 1.5 r e cannot be detected in thedata without a sub-noise detection algorithm. a preliminarysignal detection analysis shows that there is a 50% detectionconf i dence for 2 r e planets with a period from 10 to 30 dayswith the current data. this data-set demonstrates that it ispossible to detect terrestrial sized planets with ground basedphotometry, and that strong constraints on the sizes of planetsorbiting in the plane of the cm dra system can be set.send of f print requests to: h.j. deeg⋆ present address: university of california at berkeley, 601campbell hall, ca 94720key words: stars:individual:cm dra - planetary systems -binaries: eclipsing - stars:low mass - stars: f l are - techniques:photometric1. introductionin this paper we describe the observations and analysis thathave been performed in a search for photometrically detectablesignals from the presence of extrasolar planets around theeclipsing binary cm draconis. this is the f i rst long-term ob-servational application of the transit method for the detec-tion of extrasolar planets. the transit method is based onobserving small drops in the brightness of a stellar system,resulting from the transit of a planet across the disk of itscentral star. such transits would cause characteristic changesin the central star’s brightness and, to a lesser extend, color.the depth of a transit is proportional to the surface area ofthe planet, and the duration of a transit is indicative of theplanet’s velocity. if the central star’s mass is known, the dis-tance and period of the planet can then be derived. once re-peated transits of the same planet are observed, the period canbe obtained with great precision. the transit method was f i rstproposed by struve (1952); later developments are describedin rosenblatt (1971), borucki & summers 1984, deeg (1997).previous observational tests have been prevented by the re-quired photometric precision (which is about 1 part in 10 5 inthe case of an earth-sized planet transiting a sun-like star),and by the generally low probability that a planetary planeis aligned correctly to produce transits. this probability oforbital alignment is about 1% for planetary systems similarto our solar system. an observationally appealing applica-tion is available with close binary systems, where the prob-ability is high that the planetary orbital plane is coplanarwith the binary orbital plane, and thus in the line sight.this makes the observational detection of planetary tran-sits feasible in systems with an inclination very close to 90 o