Direct Detection and Orbit Analysis of the Exoplanets HR 8799 bcd from Archival 2005 Keck/NIRC2 Data

TL;DR

This study analyzes archival Keck/NIRC2 data from 2005 to detect and refine the orbital parameters of HR 8799 exoplanets, revealing inclined orbits and constraining eccentricities, thus enhancing understanding of their dynamical configuration.

Contribution

First detection of HR 8799 planets in 2005 archival data and detailed orbital analysis revealing non-face-on, inclined orbits and eccentricity constraints.

Findings

HR 8799 d's orbit is inclined at least 25° from face-on.

Orbital eccentricities are constrained to less than 0.18--0.3.

Few orbital solutions with 4:2:1 resonance are face-on or coplanar.

Abstract

We present previously unpublished July 2005 $H$-band coronagraphic data of the young, planet-hosting star HR 8799 from the newly-released Keck/NIRC2 archive. Despite poor observing conditions, we detect three of the planetary companions (HR 8799 bcd), two of them (HR 8799 bc) without advanced image processing. Comparing these data with previously published 1998-2011 astrometry and that from re-reduced October 2010 Keck data constrains the orbits of the planets. Analyzing the planets' astrometry separately, HR 8799 d's orbit is likely inclined at least 25$^\circ$ from face-on and the others may be on in inclined orbits. For semimajor axis ratios consistent with a 4:2:1 mean-motion resonance, our analysis yields precise values for HR 8799 bcd's orbital parameters and strictly constrains the planets' eccentricities to be less than 0.18--0.3. However, we find no acceptable orbital solutions with this resonance that place the planets in face-on orbits; HR 8799 d shows the largest deviation from such orbits. Moreover, few orbits make HR 8799 d coplanar with b and c, whereas dynamical stability analyses used to constrain the planets' masses typically assume coplanar and/or face-on orbits. This paper illustrates the significant science gain enabled with the release of the NIRC2 archive.