Why study one brown dwarf when you can study two... or three? The Cool Star lab investigates low-mass multiples as laboratories for measuring the their fundamental physical properties (mass and radius) and to test atmosphere and evolutionary models. We deploy a wide range of techniques, including high-resolution imaging with adaptive optics, radial velocity and astrometric monitoring, and the "spectral blend" method developed by our group. Our work has uncovered the shortest period low-mass binary and a rare substellar eclipsing system, and has demonstrated how multiplicity influences the L/T transition. 

Recent Research Results

Blended brown dwarf binaries from Backyard Worlds

(Oct 2023) Undergraduate researcher Alexia Bravo worked with collaborator Adam Schneider to analyze three peculiar brown dwarf spectra obtained as part of the Backyward Worlds project. She identified two spectral blend binaries and one potentially variable brown dwarf. The binaries may prove to be closely-separated systems for which mass measurements can be made, while the variable brown dwarf allows study of cloud formation and dynamics in low temperature atmospheres (see the preprint by Bravo et al. and the AAS Nova highlight)

A Wide Pair of L dwarfs Found by Citizen Scientists

(Aug 2023): The Cool Star Lab obtained Keck/NIRES and Keck/NIRSPEC data for a newly-resolved L dwarf binary pair identified by citizen scientists in the Backyard Worlds: Planet 9 program. CWISE J0617+1945AB is an L2 + L4 pair at 28 pc separated by 1.3 arcseconds. Its wide separation makes it an important benchmark for comparative L dwarf studies (read the Research Note by Humphries et al.). 

Planet host star has a dim companion

(Jun 2023): Adam Burgasser and Carl Melis obtained Lick/Kast optical spectra for one of two new low-mass planet host stars identified in TESS + SPECULOOS. The star, TOI-2084, has a previously unrecognized co-moving, low-mass stellar companion 1400 AU away, giving the 6.7 Earth-mass planet a second "dim red bulb" to illuminate it (read the preprint by Barkaoui et al.). 

The first Y dwarf binary

(Mar 2023): Cool Star Lab researchers contributed to the discovery of the first Y dwarf binary, WISE J0336-0143AB, identified with JWST/NIRCam. The close pair is separated by less than 1 AU, and the secondary has a mass near or below the deuterium fusion limit, often consider the boundary between brown dwarf and planetary masses. The article has been accepted for publication in ApJ Letters (read the paper by Calissendorff et al. at ApJ Letters).

Shortest-period ultracool dwarf binary 

(Jan 2023) Dino Hsu, a PhD graduate of the Cool Star Lab and now postdoctoral scholar at Northwestern University, reported the discovery of the shortest-period ultracool dwarf binary, LP 413-53AB, based on multiple epochs of Keck/NIRSPEC measurements. This remarkable binary has an orbit of only 17 hours, and its components appear to straddle the hydrogen fusion mass limit. The discovery was reported at a press conference at the AAS 241 meeting in Seattle, WA (read the press release and the paper by Hsu et al. at ApJ Letters).