High cadence near infrared timing observations of extrasolar planets^*,**

I. GJ 436b and XO-1b

¹ P. Universidad Católica de Chile, Departamento de Astronomía y Astrofísica, Casilla 306, Santiago 22, Chile e-mail: cccacere@astro.puc.cl
² European Southern Observatory, Av. Alonso de Cordova 3107, Santiago 19001, Chile
³ Specola Vaticana, V00120 Vatican City State, Italy
⁴ Departamento of Astronomía, Universidad de Concepción, Casilla 160-C, Concepción, Chile

Received: 3 September 2008
Accepted: 5 May 2009

Abstract

Currently the only technique sensitive to Earth mass planets around nearby stars (that are too close for microlensing) is the monitoring of the transit time variations. We search for additional planets in the systems of the hot Neptune GJ 436b, and the hot-Jupiter XO-1b, using high cadence observations in the J and K_S bands. New high-precision transit timing measurements are reported: GJ 436b T_C = 2 454 238.47898 ± 0.00046 HJD; XO-1b T_C(A) = 2 454 218.83331 ± 0.00114 HJD, T_C(B) = 2 454 222.77539 ± 0.00036 HJD, T_C(C) = 2 454 222.77597 ± 0.00039 HJD, T_C(D) = 2 454 226.71769 ± 0.00034 HJD, and they were used to derive new ephemeris values. We also determined depths for these transits. No statistically significant timing deviations were detected. We demonstrate that the high cadence, ground based near-infrared observations are successful in constraining the mean transit time to ~30 s, and are a viable alternative to space missions.