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VLT/SPHERE robust astrometry of the HR8799 planets at milliarcsecond-level accuracy Orbital architecture analysis with PyAstrOFit

Wertz, O. and Absil, O. and Gomez Gonzalez, C. A. and Milli, J. and Girard, J. H. and Mawet, D. and Pueyo, L. (2017) VLT/SPHERE robust astrometry of the HR8799 planets at milliarcsecond-level accuracy Orbital architecture analysis with PyAstrOFit. Astronomy & Astrophysics, 598 . Art. No. A83. ISSN 0004-6361. doi:10.1051/0004-6361/201628730.

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Context. HR8799 is orbited by at least four giant planets, making it a prime target for the recently commissioned Spectro-Polarimetric High-contrast Exoplanet REsearch (VLT/SPHERE). As such, it was observed on five consecutive nights during the SPHERE science verification in December 2014. Aims. We aim to take full advantage of the SPHERE capabilities to derive accurate astrometric measurements based on H-band images acquired with the Infra-Red Dual-band Imaging and Spectroscopy (IRDIS) subsystem, and to explore the ultimate astrometric performance of SPHERE in this observing mode. We also aim to present a detailed analysis of the orbital parameters for the four planets. Methods. We performed thorough post-processing of the IRDIS images with the Vortex Imaging Processing (VIP) package to derive a robust astrometric measurement for the four planets. This includes the identification and careful evaluation of the different contributions to the error budget, including systematic errors. Combining our astrometric measurements with the ones previously published in the literature, we constrain the orbital parameters of the four planets using PyAstrOFit, our new open-source python package dedicated to orbital fitting using Bayesian inference with Monte-Carlo Markov Chain sampling. Results. We report the astrometric positions for epoch 2014.93 with an accuracy down to 2.0 mas, mainly limited by the astrometric calibration of IRDIS. For each planet, we derive the posterior probability density functions for the six Keplerian elements and identify sets of highly probable orbits. For planet d, there is clear evidence for nonzero eccentricity (e ~ 0.35), without completely excluding solutions with smaller eccentricities. The three other planets are consistent with circular orbits, although their probability distributions spread beyond e = 0.2, and show a peak at e ≃ 0.1 for planet e. The four planets have consistent inclinations of approximately 30° with respect to the sky plane, but the confidence intervals for the longitude of the ascending node are disjointed for planets b and c, and we find tentative evidence for non-coplanarity between planets b and c at the 2σ level.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Wertz, O.0000-0003-3849-2285
Absil, O.0000-0002-4006-6237
Gomez Gonzalez, C. A.0000-0003-2050-1710
Milli, J.0000-0001-9325-2511
Girard, J. H.0000-0001-8627-0404
Mawet, D.0000-0002-8895-4735
Pueyo, L.0000-0003-3818-408X
Additional Information:© 2017 ESO. Received: 15 April 2016. Accepted: 7 October 2016. Published online: 06 February 2017. The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (ERC Grant Agreement No. 337569), and from the French Community of Belgium through an ARC grant for Concerted Research Action.
Group:Astronomy Department
Funding AgencyGrant Number
European Research Council (ERC)337569
Communauté française de Belgique – Actions de recherche concertéesUNSPECIFIED
Subject Keywords:planetary systems stars: individual: HR8799 methods: data analysis
Record Number:CaltechAUTHORS:20170418-110403489
Persistent URL:
Official Citation:VLT/SPHERE robust astrometry of the HR8799 planets at milliarcsecond-level accuracy - Orbital architecture analysis with PyAstrOFit O. Wertz, O. Absil, C. A. Gómez González, J. Milli, J. H. Girard, D. Mawet and L. Pueyo A&A, 598 (2017) A83 DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:76634
Deposited By: Ruth Sustaita
Deposited On:18 Apr 2017 18:54
Last Modified:15 Nov 2021 17:01

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