Orbital and spectral characterization of the benchmark T-type brown dwarf HD19467B

Abstract

Context. Detecting and characterizing substellar companions for which the luminosity, mass, and age can be determined independently is of utter importance to test and calibrate the evolutionary models due to uncertainties in their formation mechanisms. HD 19467 is a bright and nearby star hosting a cool brown dwarf companion detected with radial velocities and imaging, making it a valuable object for such studies.

Aims. We aim to further characterize the orbital, spectral, and physical properties of the HD 19467 system.

Methods. We present new high-contrast imaging data with the SPHERE and NaCo instruments. We also analyze archival data from the instruments HARPS, NaCo, HIRES, UVES, and ASAS. Furthermore, we use proper motion data of the star from HIPPARCOS and Gaia.

Results. We refined the properties of the host star and derived an age of 8.0(-1.0)(+2.0) Gyr based on isochrones, gyrochronology, and chemical and kinematic arguments. This age estimate is slightly younger than previous age estimates of similar to 9-11 Gyr based on isochrones. No orbital curvature is seen in the current imaging, radial velocity, and astrometric data. From a joint fit of the data, we refined the orbital parameters for HD19467B, including: a period of 398(-93)(+95) yr, an inclination of 129.8(-5.1)(+8.1) deg, an eccentricity of 0.56 +/- 0.09, a longitude of the ascending node of 134.8 +/- 4.5 deg, and an argument of the periastron of 64.2(-6.3)(+5.5) deg. We assess a dynamical mass of 74(-9)(+12) M-J. The fit with atmospheric models of the spectrophotometric data of the companion indicates an atmosphere without clouds or with very thin clouds, an effective temperature of 1042(-71)(+77) K, and a high surface gravity of 5.34(-0.09)(+0.08) dex. The comparison to model predictions of the bolometric luminosity and dynamical mass of HD19467B, assuming our system age estimate, indicates a better agreement with the Burrows et al. (1997, ApJ, 491, 856) models; whereas, the other evolutionary models used tend to underestimate its cooling rate.