EDP Sciences
Free access
Volume 480, Number 2, March III 2008
Page(s) 563 - 571
Section Planets and planetary systems
DOI http://dx.doi.org/10.1051/0004-6361:20079000

A&A 480, 563-571 (2008)
DOI: 10.1051/0004-6361:20079000

Extrasolar planet detection by binary stellar eclipse timing: evidence for a third body around CM Draconis

H. J. Deeg1, B. Ocaña1, 2, V. P. Kozhevnikov3, D. Charbonneau4, F. T. O'Donovan5, and L. R. Doyle6

1  Instituto de Astrofísica de Canarias, C. Via Lactea S/N, 38205 La Laguna, Tenerife, Spain
    e-mail: hdeeg@iac.es
2  Instituto de Radio Astronomía Milimétrica (IRAM), Av. Divina Pastora 7, Núcleo Central, 18012 Granada, Spain
3  Astronomical Observatory, Ural State University, Lenin ave. 51, Ekaterinburg, 620083, Russia
4  Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA
5  California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, USA
6  SETI Institute, 515 N. Whisman Road, Mountain View, CA 94043, USA

(Received 5 November 2007 / Accepted 28 December 2007)

Aims.Our objective is to elucidate the physical process that causes the observed observed-minus-calculated (O-C) behavior in the M4.5/M4.5 binary CM Dra and to test for any evidence of a third body around the CM Dra system.
Methods.New eclipse minimum timings of CM Dra were obtained between the years 2000 and 2007. The O-C times of the system are fitted against several functions, representing different physical origins of the timing variations.
Results.Using our observational data in conjunction with published timings going back to 1977, a clear non-linearity in O-C times is apparent. An analysis using model-selection statistics gives about equal weight to a parabolic and to a sinusoidal fitting function. Attraction from a third body, either at large distance in a quasi-constant constellation across the years of observations or from a body on a shorter orbit generating periodicities in O-C times is the most likely source of the observed O-C times. The white dwarf GJ 630.1B, a proper motion companion of CM Dra, can however be rejected as the responsible third body. Also, no further evidence of the short-periodic planet candidate described by Deeg et al. (2000, A&A, 358, L5) is found, whereas other mechanisms, such as period changes from stellar winds or Applegate's mechanism can be rejected.
Conclusions.A third body, being either a few-Jupiter-mass object with a period of 18.5 $\pm$ 4.5 years or an object in the mass range of 1.5 $M_{\rm jup}$ to 0.1 $M_{\odot}$ with periods of hundreds to thousands of years is the most likely origin of the observed minimum timing behavior.

Key words: stars: individual: CM Dra -- stars: binaries: eclipsing -- eclipses -- stars: planetary systems

© ESO 2008