Orbital Constraints on the beta Pic Inner Planet Candidate with Keck Adaptive Optics

TL;DR

This study uses adaptive optics imaging from Keck Observatory to constrain the orbit of the beta Pictoris planet candidate, ruling out certain orbital configurations and guiding future observations.

Contribution

It provides the first orbital constraints on the beta Pic candidate using multi-epoch adaptive optics data, refining possible orbital parameters.

Findings

No detection beyond 5.5 AU in 2008, indicating inward movement since 2003.

Allowed low-eccentricity orbits with semimajor axes ~8-9 AU.

Future non-detections will further restrict the candidate's orbital parameters.

Abstract

A point source observed 8 AU in projection from beta Pictoris in L' (3.8 micron) imaging in 2003 has been recently presented as a planet candidate. Here we show the results of L'-band adaptive optics imaging obtained at Keck Observatory in 2008. We do not detect beta Pic b beyond a limiting radius of 0.29 arcsec, or 5.5 AU in projection, from the star. If beta Pic b is an orbiting planet, then it has moved >=0.12 arcsec (2.4 AU in projection) closer to the star in the five years separating the two epochs of observation. We examine the range of orbital parameters consistent with the observations, including likely bounds from the locations of previously inferred planetesimal belts. We find a family of low-eccentricity orbits with semimajor axes ~8-9 AU that are completely allowed, as well as a broad region of orbits with e<~0.2, a>~10 AU that are allowed if the apparent motion of the planet was towards the star in 2003. We compare this allowed space with predictions of the planetary orbital elements from the literature. Additionally, we show how similar observations in the next several years can further constrain the space of allowed orbits. Non-detections of the source through 2013 will exclude the interpretation of the candidate as a planet orbiting between the 6.4 and 16 AU planetesimal belts.