Photometric Follow-up Observations of the Transiting Neptune-Mass Planet GJ 436b

TL;DR

This study provides detailed multi-band photometric observations of GJ 436b, refining its orbital and physical parameters, and investigates potential additional planets through transit timing variations.

Contribution

It presents new ground-based transit light curves of GJ 436b and refines its orbital and physical parameters, including the possibility of additional planets.

Findings

Refined orbital period to 2.64386 days.

Determined planet mass as 23.1 Earth masses.

Detected potential small TTVs and impact parameter variations.

Abstract

This paper presents multi-band photometric follow-up observations of the Neptune-mass transiting planet GJ 436b, consisting of 5 new ground-based transit light curves obtained in May 2007. Together with one already published light curve we have at hand a total of 6 light curves, spanning 29 days. The analysis of the data yields an orbital period P = 2.64386+-0.00003 days, mid-transit time T_c [HJD] =2454235.8355+-0.0001, planet mass M_p = 23.1+-0.9 M_{\earth} = 0.073+-0.003 M_{Jup}, planet radius R_p = 4.2+-0.2 R_{\earth} = 0.37+-0.01 R_{Jup} and stellar radius R_s = 0.45+-0.02 R_{\sun}. Our typical precision for the mid transit timing for each transit is about 30 seconds. We searched the data for a possible signature of a second planet in the system through transit timing variations (TTV) and variation of the impact parameter. The analysis could not rule out a small, of the order of a minute, TTV and a long-term modulation of the impact parameter, of the order of +0.2 year^{-1}.