Thermal Infrared Imaging and Atmospheric Modeling of VHS J125601.92-125723.9 b: Evidence for Moderately Thick Clouds and Equilibrium Carbon Chemistry in a Hierarchical Triple System

Abstract

We present and analyze Subaru/IRCS L' and M' images of the nearby M dwarf VHS J125601.92-125723.9 (VHS 1256), which was recently claimed to have a ~11 M_Jup companion (VHS 1256 b) at ~102 au separation. Our AO images partially resolve the central star into a binary, whose components are nearly equal in brightness and separated by 0.106" +/- 0.001". VHS 1256 b occupies nearly the same near-IR color-magnitude diagram position as HR 8799 bcde and has a comparable L' brightness. However, it has a substantially redder H - M' color, implying a relatively brighter M' flux density than for the HR 8799 planets and suggesting that non-equilibrium carbon chemistry may be less significant in VHS 1256 b. We successfully match the entire SED (optical through thermal infrared) for VHS 1256 b to atmospheric models assuming chemical equilibrium, models which failed to reproduce HR 8799 b at 5 microns. Our modeling favors slightly thick clouds in the companion's atmosphere, although perhaps not quite as thick as those favored recently for HR 8799 bcde. We estimate that the system is at least older than 200 Myr and the masses of the stars comprising the central binary are at least 58 M_Jup each. Moreover, we find some of the properties of VHS 1256 are inconsistent with the recent suggestion that it is a member of the AB Dor moving group. Given the possible ranges in distance (12.7 pc vs. 17.1 pc), the lower mass limit for VHS 1256 b ranges from 10.5 - 26.2 M_Jup. Our detection limits rule out companions more massive than VHS 1256 b exterior to 6-8 au, placing significant limits on and providing some evidence against a second, more massive companion that may have scattered the wide-separation companion to its current location. VHS 1256 is most likely a very low mass hierarchical triple system, and could be the third such system in which all components reside in the brown dwarf mass regime.

12 pages, 7 figures; accepted in ApJ

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Cited by in corpus (10)

• The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems II: A 1 to 20 Micron Spectrum of the Planetary-Mass Companion VHS 1256-1257 b
• Spectral Variability of VHS J1256-1257 b from 1 to 5 $\mu$m
• Strong Near-Infrared Spectral Variability of the Young Cloudy L Dwarf Companion VHS J1256-1257 b
• The JWST Early Release Science Program for the Direct Imaging & Spectroscopy of Exoplanetary Systems
• On the Masses, Age, and Architecture of the VHS J1256-1257AB b System
• Roaring Storms in the Planetary-Mass Companion VHS 1256-1257 b: Hubble Space Telescope Multi-epoch Monitoring Reveals Vigorous Evolution in an Ultra-cool Atmosphere
• Moderate-Resolution $K$-Band Spectroscopy of the Substellar Companion VHS 1256 b
• Leaning Sideways: VHS 1256-1257 b is a Super-Jupiter with a Uranus-like Obliquity
• Radio emission in a nearby ultracool dwarf binary: a multi-frequency study
• Next-generation Exo-REM atmospheric models: application to VHS 1256 b to emulate patchy clouds