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A&A
Volume 487, Number 1, August III 2008
Page(s) L5 - L8
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:200810007
Published online 01 July 2008


A&A 487, L5-L8 (2008)
DOI: 10.1051/0004-6361:200810007

Letter

Limits to the planet candidate GJ 436c

R. Alonso1, M. Barbieri1, M. Rabus2, H. J. Deeg2, J. A. Belmonte2, and J. M. Almenara2

1  Laboratoire d'Astrophysique de Marseille, UMR 6110, CNRS/Université de Provence, Traverse du Siphon, 13376 Marseille, France
    e-mail: roi.alonso@oamp.fr
2  Instituto de Astrofísica de Canarias, 38205 La Laguna, Spain

Received 18 April 2008 / Accepted 6 June 2008

Abstract
We report on H-band, ground-based observations of a transit of the hot Neptune GJ 436b. Once combined to achieve sampling equivalent to archived observations taken with Spitzer, our measurements reach comparable precision levels. We analyze both sets of observations in a consistent way, and measure the rate of orbital inclination change to be of 0.02 $\pm$ 0.04° in the time span between the two observations (253.8 d, corresponding to 0.03 $\pm$ 0.05° yr-1 if extrapolated). This rate allows us to put limits on the relative inclination between the two planets by performing simulations of planetary systems, including a second planet, GJ 436c, whose presence has been recently suggested (Ribas et al. 2008). The allowed inclinations for a 5 $M_{\oplus}$ super-Earth GJ 436c in a 5.2 d orbit are within ~7° of the orbit of GJ 436b; for larger differences the observed inclination change can be reproduced only during short sections (<50%) of the orbital evolution of the system. The measured times of three transit centers of the system do not show any departure from linear ephemeris, a result that is only reproduced in <1% of the simulated orbits. Put together, these results argue against the proposed planet candidate GJ 436c.


Key words: stars: planetary systems -- techniques: photometric



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