Benchmarking Substellar Evolutionary Models Using New Age Estimates for HD 4747 B and HD 19467 B

Abstract

Constraining substellar evolutionary models (SSEMs) is particularly difficult due to a degeneracy between the mass, age, and luminosity of a brown dwarf. In cases where a brown dwarf is found as a directly imaged companion to a star, as in HD 4747 and HD 19467, the mass, age, and luminosity of the brown dwarf are determined independently, making them ideal objects to use to benchmark SSEMs. Using the Center for High Angular Resolution Astronomy Array, we measured the angular diameters and calculated the radii of the host stars HD 4747 A and HD 19467 A. After fitting their parameters to the Dartmouth Stellar Evolution Database, MESA Isochrones and Stellar Tracks, and Yonsei-Yale isochronal models, we adopt age estimates of $10.74_{-6.87}^{+6.75}$ Gyr for HD 4747 A and $10.06_{-0.82}^{+1.16}$ Gyr for HD 19467 A. Assuming the brown dwarf companions HD 4747 B and HD 19467 B have the same ages as their host stars, we show that many of the SSEMs under-predict bolometric luminosities by $\sim$ 0.75 dex for HD 4747 B and $\sim 0.5$ dex for HD 19467 B. The discrepancies in luminosity correspond to over-predictions of the masses by $\sim$ 12\% for HD 4747 B and $\sim$ 30\% for HD 19467 B. We also show that SSEMs that take into account the effect of clouds reduce the under-prediction of luminosity to $\sim 0.6$ dex and the over-prediction of mass to $\sim 8\%$ for HD 4747 B, an L/T transition object that is cool enough to begin forming clouds. One possible explanation for the remaining discrepancies is missing physics in the models, such as the inclusion of metallicity effects.

12 pages, 6 figures, 5 tables, accepted to ApJ

References in corpus (15)

• Modules for Experiments in Stellar Astrophysics (MESA)
• The Dartmouth Stellar Evolution Database
• New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
• Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics
• The Evolution of L and T Dwarfs in Color-Magnitude Diagrams
• Techniques and Review of Absolute Flux Calibration from the Ultraviolet to the Mid-Infrared
• Asteroseismology for "à la carte" stellar age-dating and weighing: Age and mass of the CoRoT exoplanet host HD 52265
• The asteroseismic potential of TESS: exoplanet-host stars
• Keck Laser Guide Star Adaptive Optics Monitoring of 2MASS J1534-2952AB: First Dynamical Mass Determination of a Binary T Dwarf
• Revised Filter Profiles and Zero Points for Broadband Photometry
• A comparison of gyrochronological and isochronal age estimates for transiting exoplanet host stars
• Keck Laser Guide Star Adaptive Optics Monitoring of the M8+L7 Binary LHS 2397aAB: First Dynamical Mass Benchmark at the L/T Transition
• New Evidence for a Substellar Luminosity Problem: Dynamical Mass for the Brown Dwarf Binary Gl 417BC
• Accurate Gravities of F, G, and K stars from High Resolution Spectra Without External Constraints
• Discrepancies between isochrone fitting and gyrochronology for exoplanet host stars?