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We report on H-band, ground-based observations of a transit of the hotNeptune GJ 436b. Once combined to achieve sampling equivalent to archivedobservations taken with Spitzer, our measurements reach comparable precisionlevels. We analyze both sets of observations in a consistent way, and measurethe rate of orbital inclination change to be of 0.02+/-0.04 degrees in the timespan between the two observations (253.8 d, corresponding to 0.03+/-0.05degrees/yr if extrapolated). This rate allows us to put limits on the relativeinclination between the two planets by performing simulations of planetarysystems, including a second planet, GJ 436c, whose presence has been recentlysuggested (Ribas et al. 2008). The allowed inclinations for a 5 M_E super-EarthGJ 436c in a 5.2 d orbit are within ~7 degrees of the one of GJ 436b; forlarger differences the observed inclination change can be reproduced onlyduring short sections (<50%) of the orbital evolution of the system. Themeasured times of three transit centers of the system do not show any departurefrom linear ephemeris, a result that is only reproduced in <1% of the simulatedorbits. Put together, these results argue against the proposed planet candidateGJ 436c.

Limits to the planet candidate GJ 436c