Astronomy and Astrophysics, volume 608A, 79-79 (2017/12-1)
In-depth study of moderately young but extremely red, very dusty substellar companion HD 206893B.
DELORME P., SCHMIDT T., BONNEFOY M., DESIDERA S., GINSKI C., CHARNAY B., LAZZONI C., CHRISTIAENS V., MESSINA S., D'ORAZI V., MILLI J., SCHLIEDER J.E., GRATTON R., RODET L., LAGRANGE A.-M., ABSIL O., VIGAN A., GALICHER R., HAGELBERG J., BONAVITA M., LAVIE B., ZURLO A., OLOFSSON J., BOCCALETTI A., CANTALLOUBE F., MOUILLET D., CHAUVIN G., HAMBSCH F.-J., LANGLOIS M., UDRY S., HENNING T., BEUZIT J.-L., MORDASINI C., LUCAS P., MAROCCO F., BILLER B., CARSON J., CHEETHAM A., COVINO E., DE CAPRIO V., DELBOULBE A., FELDT M., GIRARD J., HUBIN N., MAIRE A.-L., PAVLOV A., PETIT C., ROUAN D., ROELFSEMA R. and WILDI F.
Abstract (from CDS):
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 1.64µm of the companion and additional photometry at 2.11 and 2.25µm. 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 6MJup (2MJup) at 0.5'' for an age of 300Myr (50Myr). 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 50Myr and a maximum of 700Myr, 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 (logg∼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 15-30MJup aged 100-300Myr, our analysis is also compatible with a range of masses and ages going from a 50Myr 12MJup planetary-mass object to a 50MJup 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.
© ESO, 2017
brown dwarfs - planets and satellites: atmospheres - techniques: high angular resolution - planet-disk interactions - planet-disk interactions
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