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Spirals and Wobbles: A Complete Orbital Characterization of the Brown Dwarf LHS 1610 b using Astrometry and Precise Radial Velocities

Presentation #601.13 in the session Planet Detection - Radial Velocities.

Published onApr 03, 2024
Spirals and Wobbles: A Complete Orbital Characterization of the Brown Dwarf LHS 1610 b using Astrometry and Precise Radial Velocities

The combination of Gaia astrometric solutions and high precision radial velocities (RVs) is proving to be a fruitful method for the detection and characterization of massive companions to low mass stars. Using the available Gaia two-body astrometric solution, discovery RVs from TRES, and newly obtained precision RVs from the Habitable-zone Planet Finder, we characterize the nearby LHS 1610 system, an M5 dwarf hosting a brown dwarf on a 10.6 day, eccentric orbit. The Gaia+RV constraints yield a complete orbital solution, including an orbital inclination of 117.2±0.9° and a mass constraint of 50.9±0.9 Jupiter masses. A discrepancy between the RV eccentricity (e = 0.3702±0.0003) and the Gaia two-body solution eccentricity (e = 0.52±0.03) requires the full astrometric time series data (Gaia DR4) to diagnose. Assuming our Gaia+RV constraints are correct, LHS 1610 b would become the second most precisely known mass of brown dwarfs orbiting M stars within 25 parsecs. This same methodology is enabling the characterization of long period giant planet companions to low mass stars which have been previously undetectable. Using the software stella we determine a flare rate of 0.28±0.07 flares per day for the host star as observed in TESS Sectors 42-44. With this flare rate and a rotation period of 84±8 days from MEarth observations, LHS 1610 joins other mid M stars, including Proxima Centauri and YZ Ceti, as nearby mid M dwarfs with flare rates on the higher end for their long rotation periods. These stars are promising candidates for searching for sub-Alfvénic star-companion interactions, raising the question whether LHS 1610 b could be driving the flares on its host star. The available TESS photometry is insufficient to confirm or rule out the expected orbital phase-dependence of the flares, but we show that the LHS 1610 system, as a nearby mid M star with a large, short-period companion and complete orbital solution, is a promising target to look for evidence of star-companion interactions or auroral emission from the brown dwarf at radio wavelengths. LHS 1610 b may prove to be a worthwhile test ground for sub-Alfvénic interactions, pushing us towards detection of the same interactions induced by a giant planet companion and enabling the first measurement of an exoplanetary magnetic field.

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