In-depth study of moderately young but extremely red, very dusty substellar companion HD 206893B

P. Delorme (1) , T. Schmidt (2) , M. Bonnefoy (1) , S. Desidera (3) , C. Ginski (4, 5) , B. Charnay (2) , C. Lazzoni (3) , V. Christiaens (6, 7, 8) , S. Messina (3, 9) , V. d'Orazi (3, 10) , J. Milli (11, 1) , J. E. Schlieder (12, 13) , R. Gratton (3) , L. Rodet (1) , A.-M. Lagrange (1) , O. Absil (14) , Arthur Vigan (15) , R. Galicher (2) , J. Hagelberg (1) , M. Bonavita (3, 16) , B. Lavie (17, 18) , A. Zurlo (3, 19) , J. Olofsson (12, 20) , A. Boccaletti (2) , F. Cantalloube (12, 1, 21) , D. Mouillet (1) , G. Chauvin (1) , F. -J. Hambsch (22) , M. Langlois (15) , S. Udry (18) , T. Henning (12) , J. -L. Beuzit (1) , C. Mordasini (12, 17) , Philippe Lucas (23) , F. Marocco (24) , B. Biller (12, 16) , J. Carson (12, 25) , A. Cheetham (18) , E. Covino (26) , V. de Caprio (27) , A. Delboulbe (1) , M. Feldt (12) , J. Girard (11) , N. Hubin (28) , A. -L. Maire (3) , A. Pavlov (12) , C. Petit (21) , D. Rouan (2) , R. Roelfsema (29) , F. Wildi (18)

1 IPAG - Institut de Planétologie et d'Astrophysique de Grenoble
2 LESIA (UMR_8109) - Laboratoire d'études spatiales et d'instrumentation en astrophysique
3 OAPD - INAF - Osservatorio Astronomico di Padova
4 Leiden Observatory [Leiden]
5 AI PANNEKOEK - Astronomical Institute Anton Pannekoek
6 Departamento de Astronomía
7 Millenium Nucleus Protoplanetary Disks in ALMA Early Science
8 STAR - Space Sciences, Technologies and Astrophysics Research Institute
9 OACT - INAF - Osservatorio Astrofisico di Catania
10 Monash University [Melbourne]
11 ESO - European Southern Observatory [Santiago]
12 MPIA - Max-Planck-Institut für Astronomie
13 NExScI - NASA ExoPlanet Science Institute
14 Université de Liège
15 LAM - Laboratoire d'Astrophysique de Marseille
16 SUPA, Institute for Astronomy
17 Physikalisches Institut [Bern]
18 ObsGE - Observatoire Astronomique de l'Université de Genève
19 UDP - Universidad Diego Portales [Santiago]
20 Instituto de Fisica y Astronomia [Valparaiso]
21 DAAA, ONERA, Université Paris-Saclay [Châtillon]
22 ROAD - Remote Observatory Atacama Desert
23 AML - Arizona Materials Laboratory
24 Centre for Astrophysics Research [Hatfield]
25 College of Charleston
26 INAF - Istituto Nazionale di Astrofisica
27 OAC - INAF - Osservatorio Astronomico di Capodimonte
28 ESO - European Southern Observatory
29 NOVA Optical Infrared Instrumentation Group

Context. The substellar companion HD 206893b has recently been discovered by direct imaging of its disc-bearing host star with the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument.Aims. We investigate the atypical properties of the companion, which has the reddest near-infrared colours among all known substellar objects, either orbiting a star or isolated, and we provide a comprehensive characterisation of the host star-disc-companion system.Methods. We conducted a follow-up of the companion with adaptive optics imaging and spectro-imaging with SPHERE, and a multi-instrument follow-up of its host star. We obtain a R = 30 spectrum from 0.95 to 1.64 μm of the companion and additional photometry at 2.11 and 2.25 μm. We carried out extensive atmosphere model fitting for the companions and the host star in order to derive their age, mass, and metallicity.Results. We found no additional companion in the system in spite of exquisite observing conditions resulting in sensitivity to 6 MJup (2 MJup) at 0.5′′ for an age of 300 Myr (50 Myr). We detect orbital motion over more than one year and characterise the possible Keplerian orbits. We constrain the age of the system to a minimum of 50 Myr and a maximum of 700 Myr, and determine that the host-star metallicity is nearly solar. The comparison of the companion spectrum and photometry to model atmospheres indicates that the companion is an extremely dusty late L dwarf, with an intermediate gravity (log g ~ 4.5–5.0) which is compatible with the independent age estimate of the system.Conclusions. Though our best fit corresponds to a brown dwarf of 15–30 MJup aged 100–300 Myr, our analysis is also compatible with a range of masses and ages going from a 50 Myr 12 MJup planetary-mass object to a 50 MJup Hyades-age brown dwarf. Even though this companion is extremely red, we note that it is more probable that it has an intermediate gravity rather than the very low gravity that is often associated with very red L dwarfs. We also find that the detected companion cannot shape the observed outer debris disc, hinting that one or several additional planetary mass objects in the system might be necessary to explain the position of the disc inner edge.

Keywords: brown dwarfs; planets and satellites: atmospheres; techniques: high angular resolution; planet-disk interactions; brown dwarfs; brown dwarfs; brown dwarfs

Domains: Physics [physics]; Astrophysics [astro-ph]

P. Delorme, T. Schmidt, M. Bonnefoy, S. Desidera, C. Ginski, et al.. In-depth study of moderately young but extremely red, very dusty substellar companion HD 206893B. Astronomy and Astrophysics - A&A, 2017, 608, pp.A79. ⟨10.1051/0004-6361/201731145⟩. ⟨hal-01764682⟩