LBT observations of the HR 8799 planetary system^⋆

First detection of HR 8799e in H band

¹ INAF – Osservatorio Astrofisico di Arcetri L.go E. Fermi 5, 50125 Firenze, Italy
e-mail: esposito@arcetri.astro.it
² INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
³ Steward Observatory, Department of Astronomy, University of Arizona, Tucson, AZ 85721, USA
⁴ INAF – Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
⁵ Dipartimento di Fisica e Astronomia – Universitá di Padova, via Marzolo 8, Padova, Italy
⁶ LBT Observatory, Univ. of Arizona, 933 North Cherry Ave., Tucson, AZ 85721, USA
⁷ INAF – Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio ( RM), Italy
⁸ Minnesota Institute of Astrophysics, University of Minnesota, Minneapolis, MN 5455, USA

Received: 12 March 2012
Accepted: 1 August 2012

Abstract

We have performed H and K_S band observations of the planetary system around HR 8799 using the new AO system at the Large Binocular Telescope and the PISCES Camera. The excellent instrument performance (Strehl ratios up to 80% in H band) enabled the detection of the innermost planet, HR 8799e, at H band for the first time. The H and K_S magnitudes of HR 8799e are similar to those of planets c and d, with planet e being slightly brighter. Therefore, HR 8799e is likely slightly more massive than c and d. We also explored possible orbital configurations and their orbital stability. We confirm that the orbits of planets b, c and e are consistent with being circular and coplanar; planet d should have either an orbital eccentricity of about 0.1 or be non-coplanar with respect to b and c. Planet e can not be in circular and coplanar orbit in a 4:2:1 mean motion resonances with c and d, while coplanar and circular orbits are allowed for a 5:2 resonance. The analysis of dynamical stability shows that the system is highly unstable or chaotic when planetary masses of about 5 M_J for b and 7 M_J for the other planets are adopted. Significant regions of dynamical stability for timescales of tens of Myr are found when adopting planetary masses of about 3.5, 5, 5, and 5 M_J for HR 8799b, c, d, and e respectively. These masses are below the current estimates based on the stellar age (30 Myr) and theoretical models of substellar objects.