Spectral analysis of two directly imaged benchmark L dwarf companions at the stellar-substellar boundary

Abstract

We used multiple epochs of high-contrast imaging spectrophotometric observations to determine the atmospheric characteristics and thermal evolution of two previously detected benchmark L dwarf companions, HD 112863 B and HD 206505 B. We analyzed IRDIS and IFS data from VLT/SPHERE of each companion, both of which have dynamical masses near the stellar-substellar boundary. We compared each companion with empirical spectral standards, as well as constrained their physical properties through atmospheric model fits. From these analyses, we estimate that HD 112863 B is spectral type $\mathrm{L}3\pm 1$ and that HD 206505 B is spectral type $\mathrm{L}2\pm 1$. Using the BT-Settl atmospheric model grids, we find a bimodal solution for the atmospheric model fit of HD 112863 B, such that $T_{\mathrm{eff}}=1757_{-36}^{+37}$ K or $2002_{-24}^{+23}$ K and $\log g=4.973_{-0.063}^{+0.057}$ or $5.253_{-0.033}^{+0.037}$, while for HD 206505 B, $T_{\mathrm{eff}}=1754_{-13}^{+13}$ K and $\log g=4.919_{-0.029}^{+0.031}$. Comparing the bolometric luminosities of both companions with evolutionary models imply that both companions are likely above the hydrogen burning limit.

Accepted for publication in Astronomy & Astrophysics

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