SIMBAD references

2025ApJ...982...79B - Astrophys. J., 982, 79 (2025/April-1)

New Cold Subdwarf Discoveries from Backyard Worlds and a Metallicity Classification System for T Subdwarfs.

BURGASSER A.J., SCHNEIDER A.C., MEISNER A.M., CASELDEN D., HSU C.-C., GERASIMOV R., AGANZE C., SOFTICH E., KARPOOR P., THEISSEN C.A., BROOKS H., BICKLE T.P., GAGNE J., ARTIGAU E., MARSSET M., ROTHERMICH A., FAHERTY J.K., KIRKPATRICK J.D., KUCHNER M.J., ANDERSEN N.S., BEAULIEU P., COLIN G., GANTIER J.M., GRAMAIZE L., HAMLET L., HINCKLEY K., KABATNIK M., KIWY F., MARTIN D.W., MASSAT D.H., PENDRILL W., SAINIO A., SCHUMANN J., THEVENOT M., WALLA J., WEDRACKI Z. (The Backyard Worlds: Planet 9 Collaboration)

Abstract (from CDS):

We report the results of a spectroscopic survey of candidate T subdwarfs identified by the Backyard Worlds: Planet 9 program. Near-infrared spectra of 31 sources with red J - W2 colors and large J-band reduced proper motions show varying signatures of subsolar metallicity, including strong collision-induced H2 absorption, obscured methane and water features, and weak K I absorption. These metallicity signatures are supported by spectral model fits and 3D velocities, indicating thick disk and halo population membership for several sources. We identify three new metal-poor T subdwarfs ([M/H] ≲ -0.5), CWISE J062316.19+071505.6, WISEA J152443.14-262001.8, and CWISE J211250.11-052925.2; and 19 new “mild” subdwarfs with modest metal deficiency ([M/H] ≲ -0.25). We also identify three metal-rich brown dwarfs with thick disk kinematics. We provide kinematic evidence that the extreme L subdwarf 2MASS J053253.46+824646.5 and the mild T subdwarf CWISE J113010.07+313944.7 may be part of the Thamnos population, while the T subdwarf CWISE J155349.96+693355.2 may be part of the Helmi stream. We define a metallicity classification system for T dwarfs that adds mild subdwarfs (d/sdT), subdwarfs (sdT), and extreme subdwarfs (esdT) to the existing dwarf sequence. We also define a metallicity spectral index that correlates with metallicities inferred from spectral model fits and iron abundances from stellar primaries of benchmark T dwarf companions. This expansion of the T dwarf classification system supports investigations of ancient, metal-poor brown dwarfs now being uncovered in deep imaging and spectroscopic surveys.

Abstract Copyright: © 2025. The Author(s). Published by the American Astronomical Society.

Journal keyword(s): Brown dwarfs - L dwarfs - L subdwarfs - T subdwarfs - T dwarfs - Stellar classification

Status at CDS : Large table(s) will be appraised for possible ingestion in VizieR.

CDS comments: In tables 2 and 3 the authors wrote "All designations are from the CatWISE2020 catalog (F. Marocco et al. 2021) and are proper-motion corrected to epoch 2015 May 28 except for noted sources". This is a confusion between identifiers and coordinates. The CWISE designations must not be corrected for any epoch; they are unique identifiers defined and listed in the CatWISE catalogue (II/365/catwise). Of course coordinates may be given at any epoch, but not the identifiers. As a result about 80% of the CWISE designations in tables 2 and 3 are erroneous.

Simbad objects: 106

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