T Class Brown Dwarf HD 19467B's Directly Observed Spectrum

Direct Spectrum of the Benchmark T dwarf HD 19467 B

Authors:

Crepp et al

Abstract:

HD 19467 B is presently the only directly imaged T dwarf companion known to induce a measurable Doppler acceleration around a solar type star. We present spectroscopy measurements of this important benchmark object taken with the Project 1640 integral field unit at Palomar Observatory. Our high-contrast R~30 observations obtained simultaneously across the JH bands confirm the cold nature of the companion as reported from the discovery article and determine its spectral type for the first time. Fitting the measured spectral energy distribution to SpeX/IRTF T dwarf standards and synthetic spectra from BT-Settl atmospheric models, we find that HD 19467 B is a T5.5+/-1 dwarf with effective temperature Teff=978+20−43 K. Our observations reveal significant methane absorption affirming its substellar nature. HD 19467 B shows promise to become the first T dwarf that simultaneously reveals its mass, age, and metallicity independent from the spectrum of light that it emits.

HD 19467B: Old and Cold T Class Brown Dwarf Around a G Class Star

THE TRENDS HIGH-CONTRAST IMAGING SURVEY. V. DISCOVERY OF AN OLD AND COLD BENCHMARK T-DWARF ORBITING THE NEARBY G-STAR HD 19467

Authors:

Crepp et al

Abstract:

The nearby Sun-like star HD 19467 shows a subtle radial velocity (RV) acceleration of −1.37  ±  0.09 m s−1 yr−1 over a 16.9 yr time baseline (an RV trend), hinting at the existence of a distant orbiting companion. We have obtained high-contrast images of the star using NIRC2 at Keck Observatory and report the direct detection of the body that causes the acceleration. The companion, HD 19467 B, is ΔKs = 12.57 ± 0.09 mag fainter than its parent star (contrast ratio of 9.4 × 10−6), has blue colors J − Ks = −0.36 ± 0.14 (J − H = −0.29 ± 0.15), and is separated by ρ = 1farcs653 ± 0farcs004 (51.1 ± 1.0 AU). Follow-up astrometric measurements obtained over a 1.1 yr time baseline demonstrate physical association through common parallactic and proper motion. We calculate a firm lower-limit of for the companion mass from orbital dynamics using a combination of Doppler observations and imaging. We estimate a model-dependent mass of from a gyrochronological age of Gyr. Isochronal analysis suggests a much older age of 9 ± 1 Gyr, which corresponds to a mass of . HD 19467 B's measured colors and absolute magnitude are consistent with a late T dwarf [≈T5-T7]. We may infer a low metallicity of [Fe/H] =−0.15 ± 0.04 for the companion from its G3V parent star. HD 19467 B is the first directly imaged benchmark T dwarf found orbiting a Sun-like star with a measured RV acceleration.