Characterising brown dwarf companions with IRDIS long-slit spectroscopy: HD 1160 B and HD 19467 B

TL;DR

This study presents medium-resolution IRDIS long-slit spectroscopy of two brown dwarf companions, revealing their atmospheric properties, spectral types, and ages, thus providing insights into their formation and evolution.

Contribution

First medium-resolution spectroscopic observations of these brown dwarfs, enabling detailed atmospheric characterization beyond low-resolution data.

Findings

HD 1160 B has a peculiar spectrum not fitting current libraries.

HD 1160 B's spectral type is M5-M7, T_eff ~2800-2900 K, low gravity, young age (~10-20 Myr).

HD 19467 B is a T6+/-1 dwarf with T_eff ~1000 K, high gravity, and evolved status.

Abstract

The determination of the fundamental properties (mass, separation, age, gravity and atmospheric properties) of brown dwarf companions allows us to infer crucial informations on their formation and evolution mechanisms. Spectroscopy of substellar companions is available to date only for a limited number of objects (and mostly at very low resolution, R<50) because of technical limitations, i.e., contrast and angular resolution. We present medium resolution (R=350), coronagraphic long-slit spectroscopic observations with SPHERE of two substellar companions, HD 1160 B and HD 19467 B. We found that HD 1160 B has a peculiar spectrum that cannot be fitted by spectra in current spectral libraries. A good fit is possible only considering separately the Y+J and the H spectral band. The spectral type is between M5 and M7. We also estimated a T_eff of 2800-2900 K and a log(g) of 3.5-4.0 dex. The low surface gravity seems to favour young age (10-20 Myr) and low mass (~20 M Jup ) for this object. HD 19467 B is instead a fully evolved object with a T_eff of ~1000 K and log g of ~5.0 dex. Its spectral type is T6+/-1.