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Biases in Orbital Fitting of Directly Imaged Exoplanets with Small Orbital Coverage

Ferrer-Chávez, Rodrigo and Wang, Jason J. and Blunt, Sarah (2021) Biases in Orbital Fitting of Directly Imaged Exoplanets with Small Orbital Coverage. Astronomical Journal, 161 (5). Art. No. 241. ISSN 0004-6256. doi:10.3847/1538-3881/abf0a8.

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The eccentricity of a planet's orbit and the inclination of its orbital plane encode important information about its formation and history. However, exoplanets detected via direct imaging are often only observed over a very small fraction of their period, making it challenging to perform reliable physical inferences given wide, unconstrained posteriors. The aim of this project is to investigate biases (deviation of the median and mode of the posterior from the true values of orbital parameters, and the width and coverage of their credible intervals) in the estimation of orbital parameters of directly imaged exoplanets, particularly their eccentricities, and to define general guidelines to perform better estimations of uncertainty. For this, we constructed various orbits and generated mock data for each spanning ~0.5% of the orbital period. We used the Orbits For The Impatient algorithm to compute orbit posteriors and compared those to the true values of the orbital parameters. We found that the inclination of the orbital plane is the parameter that most affects our estimations of eccentricity, with orbits that appear near edge on producing eccentricity distributions skewed away from the true values and often bimodal. We also identified a degeneracy between eccentricity and inclination that makes it difficult to distinguish posteriors of face-on, eccentric orbits and edge-on, circular orbits. For the exoplanet-imaging community, we propose practical recommendations, guidelines, and warnings relevant to orbit fitting.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Ferrer-Chávez, Rodrigo0000-0002-2683-2396
Wang, Jason J.0000-0003-0774-6502
Blunt, Sarah0000-0002-3199-2888
Additional Information:© 2021. The American Astronomical Society. Received 2020 October 30; revised 2021 March 17; accepted 2021 March 20; published 2021 April 26. This work was supported by the Heising-Simons Foundation through grant 2019-1698. We thank Kelly O'Neil, Rob De Rosa, and Isabel Angelo for their insights. We also thank the anonymous referee, whose comments greatly improved the quality of this work.
Funding AgencyGrant Number
Heising-Simons Foundation2019-1698
Subject Keywords:Exoplanet astronomy; Orbit determination; Bayesian statistics; Exoplanets
Issue or Number:5
Classification Code:Unified Astronomy Thesaurus concepts: Exoplanet astronomy (486); Orbit determination (1175); Bayesian statistics (1900); Exoplanets (498)
Record Number:CaltechAUTHORS:20210528-142057552
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Official Citation:Rodrigo Ferrer-Chávez et al 2021 AJ 161 241
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:109308
Deposited By: Tony Diaz
Deposited On:28 May 2021 22:10
Last Modified:28 May 2021 22:10

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