The Orbit of the L Dwarf + T Dwarf Spectral Binary SDSS J080531.84+481233.0*

Abstract

SDSS J080531.84+481233.0 is a closely-separated, very-low-mass binary identified through combined-light spectroscopy and confirmed as an astrometric variable. Here we report four years of radial velocity monitoring observations of the system that reveal significant and periodic variability, confirming the binary nature of the source. We infer an orbital period of 2.02±0.03 yr, a semi-major axis of 0.76 +0.05 −0.06 AU, and an eccentricity of 0.46±0.05, consistent with the amplitude of astrometric variability and prior attempts to resolve the system. Folding in constraints based on the spectral types of the components (L4±0.7 and T5.5±1.1), corresponding effective temperatures, and brown dwarf evolutionary models, we further constrain the orbital inclination of this system to be nearly edge-on (90 • ± 19 • ), and deduce a large system mass ratio (M 2 /M 1 = 0.86 +0.10 −0.12 ), substellar components (M 1 = 0.057 +0.016 −0.014 M ⊙ , M 2 = 0.048 +0.008 −0.010 M ⊙ ), and a relatively old system age (minimum age = 4.0 +1.9 −1.2 Gyr). The measured projected rotational velocity of the primary (V rot sin i = 34.1±0.7 km s −1 ) implies that this inactive source is a rapid rotator (period 3 hr) and a viable system for testing spin-orbit alignment in very-low-mass multiples. Robust model-independent constraints on the component masses may be possible through measurement of the reflex motion of the secondary at wavelengths in which it contributes a greater proportion of the combined luminence, while the system may also be resolvable through sparse-aperature mask interferometry with adaptive optics. The combination of well-determined component atmospheric properties and masses near and/or below the hydrogen minimum mass make SDSS J0805+4812AB an important system for future tests of brown dwarf evolutionary models.

Individual Dynamical Masses of Ultracool Dwarfs* † ‡

“…After making the cuts described above, the final complete, de-biased sample comprises 22 ultracool visual binaries. In addition, we examine published orbits for various unresolved binaries: three astrometric orbits (Sahlmann et al 2015a,b;Koren et al 2016), three spectroscopic orbits Joergens et al 2010;Burgasser et al 2016), and one double-lined eclipsing orbit for a very young brown dwarf binary in Orion (Stassun et al 2006). Figure 18 shows all of these results, spanning more than three orders of magnitude in period.…”

An eclipsing substellar binary in a young triple system discovered by SPECULOOS

“…This analysis confirmed membership in the Argus Association with 89% probability, versus 11% probability of being a field star contaminant. The roughly 40 members of Argus have a mean distance of 72 pc from the Sun, and a consensus isochronal age of [40][41][42][43][44][45][46][47][48][49][50]71,58;19]. Hence, membership is consistent with the surface gravity classifications of the low-resolution spectra of 2M1510A and B, which are intermediate between VL-G (≈ 10 Myr) and INT-G (≈100 Myr; [41]); as well as the age inferred from the evolutionary models based on our mass and radius constraints (Figure 2).…”

SIMP J013656.5+093347 Is Likely a Planetary-mass Object in the Carina-Near Moving Group

“…Spectral data in order 33 (2.29-2.33 μm) were forwardmodeled using the Markov Chain Monte Carlo analysis described in detail in Burgasser et al (2016). We used the atmosphere models of Allard et al (2012) and the telluric transmission spectrum from the Solar atlas of Livingston & Wallace (1991).…”