THE HAWAII INFRARED PARALLAX PROGRAM. II. YOUNG ULTRACOOL FIELD DWARFS

By Michael C. Liu, T. Dupuy, K. Allers. 2016

200 citations recorded by the source corpus.

We present a large, uniform analysis of young (≈10–150 Myr) ultracool dwarfs, based on new high-precision infrared (IR) parallaxes for 68 objects. We find that low-gravity (vl-g) late-M and L dwarfs form a continuous sequence in IR color–magnitude diagrams, separate from the field population and from current theoretical models. These vl-g objects also appear distinct from young substellar (brown dwarf and exoplanet) companions, suggesting that the two populations may have a different range of physical properties. In contrast, at the L/T transition, young, old, and spectrally peculiar objects all span a relatively narrow range in near-IR absolute magnitudes. At a given spectral type, the IR absolute magnitudes of young objects can be offset from ordinary field dwarfs, with the largest offsets occurring in the Y and J bands for late-M dwarfs (brighter than the field) and mid-/late-L dwarfs (fainter than the field). Overall, low-gravity (vl-g) objects have the most uniform photometric behavior, while intermediate gravity (int-g) objects are more diverse, suggesting a third governing parameter beyond spectral type and gravity class. We examine the moving group membership for all young ultracool dwarfs with parallaxes, changing the status of 23 objects (including 8 previously identified planetary-mass candidates) and fortifying the status of another 28 objects. We use our resulting age-calibrated sample to establish empirical young isochrones and show a declining frequency of vl-g objects relative to int-g objects with increasing age. Notable individual objects in our sample include high-velocity (≳100 km s−1) int-g objects, very red late-L dwarfs with high surface gravities, candidate disk-bearing members of the MBM20 cloud and β Pic moving group, and very young distant interlopers. Finally, we provide a comprehensive summary of the absolute magnitudes and spectral classifications of young ultracool dwarfs, using a combined sample of 102 objects found in the field and as substellar companions to young stars.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/6c1b0b413c99eb05631046799ce46361e0665fd0

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In Astronomy and Astrophysics

1. Michael C. Liu
2. T. Dupuy
3. D. Lafrèniere
4. L. Malo
5. J. Gagné
6. R. Doyon
7. B. Bowler
8. Eric Mamajek

In Instrumentation

1. Michael C. Liu
2. T. Dupuy
3. L. Malo
4. J. Gagné
5. Eric Mamajek
6. R. Doyon
7. D. Lafrèniere
8. Jacqueline K. Faherty

Citations in the corpus

• The Field Substellar Mass Function Based on the Full-sky 20 pc Census of 525 L, T, and Y Dwarfs (2020, unknown): “33+121949.2 (Gaia Collaboration et al. 2018), 2MASS J21580457-1550098 (Smart et al. 2018), and 2MASS J23512200+3010540 (Liu et al. 2016).”
• BANYAN. XI. The BANYAN Σ Multivariate Bayesian Algorithm to Identify Members of Young Associations with 150 pc (2018, background): “They correspond to predictions for the radial velocity and distance of a star, assuming that the star is a true member of H (e.g., Liu et al. 2016 obtain BANYAN II distance predictions with accuracies as low as ∼ 20% by ignoring this fact).”
• Individual Dynamical Masses of Ultracool Dwarfs (2017, background): “…association of NLTT 20346 to the 2MASS J0850+1057 system is questionable (see Section 6.4 of Dupuy & Liu 2012), and the discovery and characterization of young late-L dwarfs indicates that they tend to be fainter at J-band, not brighter (Faherty et al. 2012; Liu et al. 2013a; Liu et al. 2016).”