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

Abstract

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. 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. 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 ($e\simeq 0.35$), 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 $e\simeq 0.1$ for planet e. The four planets have consistent inclinations of about $30°$ with respect to the sky plane, but the confidence intervals for the longitude of ascending node are disjoint for planets b and c, and we find tentative evidence for non-coplanarity between planets b and c at the $2\sigma$ level.

23 pages, 14 figures

References in corpus (10)

• Direct Imaging of Multiple Planets Orbiting the Star HR 8799
• Fundamental limitations of high contrast imaging set by small sample statistics
• HST/NICMOS detection of HR 8799 b in 1998
• Reconnaissance of the HR 8799 Exosolar System II: Astrometry and Orbital Motion
• SPHERE IRDIS and IFS astrometric strategy and calibration
• Deep Thermal Infrared Imaging of HR 8799 bcde: New Atmospheric Constraints and Limits on a Fifth Planet
• The LEECH Exoplanet Imaging Survey. Further constraints on the planet architecture of the HR 8799 system
• High precision astrometry with a diffractive pupil telescope
• Long-term stability of the HR 8799 planetary system without resonant lock
• A high precision technique to correct for residual atmospheric dispersion in high-contrast imaging systems

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• Two Directly Imaged, Wide-orbit Giant Planets around the Young, Solar Analog TYC 8998-760-1
• Radial Velocity Measurements of HR 8799 b and c with Medium Resolution Spectroscopy
• In-depth study of moderately young but extremely red, very dusty substellar companion HD206893B
• A survey of the linear polarization of directly imaged exoplanets and brown dwarf companions with SPHERE-IRDIS. First polarimetric detections revealing disks around DH Tau B and GSC 6214-210 B
• Separating extended disc features from the protoplanet in PDS 70 using VLT/SINFONI
• Discovery of a directly imaged planet to the young solar analog YSES 2
• On the Chemical Abundance of HR 8799 and the Planet c
• A New Standard for Assessing the Performance of High Contrast Imaging Systems
• Orbital and dynamical analysis of the system around HR 8799. New astrometric epochs from VLT/SPHERE and LBT/LUCI
• Multiple Populations of Extrasolar Gas Giants
• A faint companion around CrA-9: protoplanet or obscured binary?
• The SHARDDS survey: limits on planet occurrence rates based on point sources analysis via the Auto-RSM framework
• Detection of H$\alpha$ emission from PZ Tel B using SPHERE/ZIMPOL
• ISPY - the NaCo Imaging Survey for Planets around Young stars: A young companion candidate embedded in the R CrA cloud
• On-sky closed loop correction of atmospheric dispersion for high-contrast coronagraphy and astrometry
• PACOME: Optimal multi-epoch combination of direct imaging observations for joint exoplanet detection and orbit estimation
• Improving the RSM map exoplanet detection algorithm: PSF forward modelling and optimal selection of PSF subtraction techniques
• Low-mass stellar and substellar candidate companions around massive stars in Sco OB1 and M17