2025ApJ...982...79B

Query : 2025ApJ...982...79B

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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Number of rows : 106
N Identifier Otype ICRS (J2000)
RA 		ICRS (J2000)
DEC 		Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2026 		#notes
1 2MASS J00043065-2603596 BD* 00 04 30.65544 -26 03 59.6268           T2 8 0
2 WISE J000458.45-133654.9 BD* 00 04 58.47 -13 36 55.1           T2 3 0
3 WISE J001354.39+063448.1 BD* 00 13 54.922753 +06 34 44.87848           T8 11 0
4 UNCOVER DR1 29466 BD* 00 14 03.33 -30 21 21.7           T8-T9 12 0
5 HD 1154 * 00 15 48.9301782360 -11 59 24.663250716   8.97 8.88     A0V 24 0
6 ULAS J002136.01+155227.4 BD* 00 21 36.01200 +15 52 27.4152           T4p 3 0
7 * 54 Psc B BD* 00 39 18.9174 +21 15 16.309           T7.5 86 1
8 WISE J004555.05+795848.7 BD* 00 45 55.13 +79 58 48.7           d/sdL9 2 0
9 LSPM J0055+5948 WD* 00 55 58.2997210526 +59 48 02.534995690   15.2   16.0   DC: 22 0
10 CWISE J005559.92+594744.3 BD* 00 55 59.923925 +59 47 44.39813           T8 5 0
11 2MASS J00575687+2013075 BD* 00 57 56.87160 +20 13 07.5396           sdL7? 8 0
12 HD 9612 Be* 01 37 22.2214008672 +74 18 03.436741908 6.27 6.589 6.573     B8IV 38 0
13 ULAS J014016.91+015054.7 BD* 01 40 16.91064 +01 50 54.7620           T4.5 3 0
14 HD 18571 * 02 59 16.7596506264 +01 14 40.474198968   8.66 8.63     A0V 44 0
15 2MASS J03011916-2319195 BD* 03 01 19.16688 -23 19 19.5168           T1 7 0
16 WISE J030919.67-501614.3 BD* 03 09 19.12199 -50 16 16.4146           T7 8 0
17 2MASS J03485853-5620201 BD* 03 48 58.53504 -56 20 20.1408           T3 3 0
18 WISEA J041102.17+471423.6 BD* 04 11 02.417294 +47 14 22.59409           d/sdT7.5 3 0
19 WISE J041451.64-585457.0 BD* 04 14 51.67 -58 54 56.7           esdT6: 10 0
20 WISE J042941.10+320127.9 BD* 04 29 41.116297 +32 01 25.51698           T1 1 0
21 WISE J043309.27+100903.9 BD* 04 33 09.153706 +10 09 08.23508           T8 5 0
22 BD+43 1021 * 04 37 18.7237673208 +44 08 31.509877164   9.60 9.33     A0V 9 0
23 BD+45 981 * 04 45 47.8333137624 +45 44 13.478679276   9.98 9.53     A0V 8 0
24 WISE J044853.28-193548.6 BD* 04 48 52.64780 -19 35 56.3753           T5pec 11 0
25 CWISE J052306.42-015355.4 BD? 05 23 06.4212 -01 53 55.443           ~ 5 0
26 2MASS J05325346+8246465 BD* 05 32 54.4345118405 +82 46 45.161005926           esdL7 65 0
27 HD 37887 * 05 41 36.0354571656 -03 43 52.274509320   7.69 7.67     B9.5IV/V 50 0
28 2MASS J06164006-6407194 BD* 06 16 40.06 -64 07 19.5           sdL5 19 0
29 WISE J062316.17+071511.4 BD* 06 23 16.199372 +07 15 05.62591           sdT3 1 0
30 HD 47540 SB* 06 36 27.4720239648 -50 19 21.934801596   8.14 7.22     G8IV 17 0
31 2MASS J06453153-6646120 BD* 06 45 31.53216 -66 46 12.0432           sdL8 12 0
32 V* AW Cam SB* 06 47 28.8078949632 +69 37 44.773517568   8.28 8.26     A0V 81 0
33 WISE J065919.44+161554.4 BD* 06 59 19.424138 +16 15 51.92158           T1 1 0
34 HD 65486B BD* 07 58 01.32768 -25 38 58.7544           T4.5V 10 0
35 WISE J075831.22+571155.7 BD* 07 58 31.22016 +57 11 55.7556           T6.5 2 0
36 HD 71906 * 08 31 19.9662429960 +37 15 53.796537612   6.127 6.174     A0V 62 0
37 WISE J083337.82+005214.1 BD* 08 33 37.30144 +00 52 30.8685           T9 15 0
38 WISE J083641.10-185947.0 BD* 08 36 41.20406 -18 59 45.1583           T8pec 12 0
39 ULAS J084325.51+290438.4 BD* 08 43 25.351890 +29 04 35.68323           L6: 2 0
40 CWISE J084506.51-330532.7 BD* 08 45 06.511114 -33 05 32.67577           T7 2 0
41 HD 74721 HB* 08 45 59.2614567408 +13 15 48.591616392 8.88 8.75 8.72     A0V 166 0
42 2MASS J08503941-0221528 BD* 08 50 39.3941974964 -02 21 52.901805659           sdL7 4 0
43 WISE J091105.05+214648.9 BD* 09 11 05.12949 +21 46 55.5380           T9 3 0
44 2MASSI J0937347+293142 BD* 09 37 34.87968 +29 31 40.9908           T6 99 1
45 2MASS J09393548-2448279 BD* 09 39 35.48976 -24 48 27.9432           T8 69 0
46 G 48-43B BD* 09 50 47.33040 +01 17 33.0068           T8p 20 1
47 WISE J095316.40-094317.5 BD* 09 53 16.40784 -09 43 17.5980           T5.5 2 0
48 2MASS J10194509-3911542 BD* 10 19 45.09408 -39 11 54.2220           T3 6 0
49 2MASS J10353492-0711479 BD* 10 35 34.92408 -07 11 47.9292           sdL7 3 0
50 CWISE J105512.11+544328.3 BD* 10 55 14.78785 +54 43 31.9751           sdT8 8 0
51 WISE J111055.11-174735.6 BD* 11 10 55.080571 -17 47 32.76090           T8 2 0
52 HD 98884 * 11 22 42.5671419720 -16 09 58.370145732   8.28 8.10     A0V 13 0
53 HD 98989 * 11 23 46.4661158280 +34 14 33.808215984   9.25 9.24     A0V 29 0
54 WISEA J113010.66+313954.0 BD* 11 30 11.647236 +31 40 09.73285           d/sdT5.5 3 0
55 WISE J113019.39-115813.8 BD* 11 30 19.78214 -11 58 17.8647           sdT5? 2 0
56 WISE J113833.99+721206.9 BD* 11 38 35.10751 +72 12 04.9201           d/sdT7 3 0
57 V* Z Dra SB* 11 45 29.2091494248 +72 14 58.328231100   11.11 10.67     A5V 153 0
58 2MASS J11582077+0435014 BD* 11 58 20.7331430107 +04 35 02.400141131           sdL7 26 0
59 WISE J120444.38-235924.8 BD* 12 04 44.620935 -23 59 20.10799           d/sdT7 2 0
60 HD 109055 * 12 31 41.2764865080 +22 07 24.416279400   8.86 8.82     A0V 51 0
61 HD 110649 * 12 43 47.1041226624 -23 51 04.986429696   9.81 9.78     A0V 9 0
62 BD+13 2618C BD* 13 00 42.0799 +12 21 14.800         23.28 T8.5p 153 0
63 WISE J130440.58+281927.5 BD* 13 04 40.450067 +28 19 27.69014           d/sdL9: 1 0
64 ULAS J130710.22+151103.4 BD* 13 07 10.22040 +15 11 03.4908           sdL8 3 0
65 WISE J130841.47-032159.7 BD* 13 08 41.313109 -03 21 57.79209           d/sdT8 2 0
66 HD 114381 * 13 10 04.7190695304 +12 19 13.227127824   9.55 9.49     A0V 22 0
67 ULAS J131610.28+075553.0 BD* 13 16 10.28 +07 55 53.0           sdT6.5 13 0
68 ULAS J133836.97-022910.7 BD* 13 38 37.01088 -02 29 08.4480           sdL7 8 0
69 WISE J140118.37+432556.8 BD* 14 01 18.543457 +43 26 03.55767           d/sdT5.5 2 0
70 * alf Dra SB* 14 04 23.3575968507 +64 22 33.130623243 3.520 3.640 3.680     A0III 290 0
71 HD 123233 PM* 14 06 09.5676700560 +09 53 43.249342812   8.71 8.63     A0V 31 0
72 HD 124773 * 14 15 11.0993307552 +17 31 03.272784780   8.97 8.96     A0V 13 0
73 ULAS J141623.94+134836.3 BD* 14 16 23.94216 +13 48 36.3204           T7.5p 64 0
74 HD 126053B BD* 14 23 20.79 +01 16 38.2           T8 32 0
75 HD 128039 * 14 33 23.4612849192 +44 19 53.862105648   9.44 9.27     A0V 28 0
76 GJ 570 D BD* 14 57 14.96256 -21 21 47.7504           T8 242 1
77 WISE J145838.11+173447.7 BD* 14 58 38.41205 +17 34 47.3830           T8 4 0
78 BD+06 2986B BD* 15 04 57.390096 +05 37 57.41508         23.85 sdT5.5 26 0
79 WISE J151521.21-215734.8 BD* 15 15 20.997449 -21 57 30.46172           d/sdT6 3 0
80 WISE J152443.27-262001.0 BD* 15 24 43.145067 -26 20 01.87785           sdT0 1 0
81 WISEA J153429.75-104303.3 BD? 15 34 30.76516 -10 42 37.5166           ~ 14 0
82 HD 139273 * 15 38 45.9328833648 -39 58 40.470734676   10.24 10.13     A0V 8 0
83 WISE J155349.98+693355.2 BD* 15 53 49.98864 +69 33 55.2240           sdT4 8 0
84 HD 147384 * 16 22 36.7286031696 -24 22 58.684301292 9.24 9.03 8.62 3.47 3.33 A0V 67 0
85 WISE J171003.23+453756.1 BD* 17 10 02.999185 +45 37 56.41723           T6 1 0
86 NAME Galactic Center reg 17 45 39.60213 -29 00 22.0000           ~ 16269 0
87 G 204-39B BD* 17 58 05.45496 +46 33 09.9108           T7 51 1
88 WISE J180122.57+471738.8 BD* 18 01 22.594269 +47 17 41.47254           d/sdT5 1 0
89 HD 164899 * 18 01 29.3407777959 +40 19 25.401245837   7.93 7.92     A0Vs 13 0
90 WISE J181006.21-101000.3 BD* 18 10 06.18 -10 10 00.5           esdT3: 17 0
91 HD 333145 * 19 57 20.7027017928 +29 21 18.609290244   9.41 9.34     A0 12 0
92 Wolf 1130 B BD* 20 05 21.77853 +54 24 43.2739           T8p 45 0
93 WISE J201342.58-032639.7 BD* 20 13 42.275285 -03 26 43.81536           d/sdT6 2 0
94 HD 192230 * 20 14 09.8463202176 -12 13 40.520517348   9.68 9.59     A0V 6 0
95 CWISE J202130.08+152418.0 BD* 20 21 30.084829 +15 24 18.02732           d/sdL9 1 0
96 2MASS J21052823-6235461 BD* 21 05 28.23792 -62 35 46.1652           T1.5 10 0
97 WISE J211250.37-052920.8 BD* 21 12 50.117086 -05 29 25.36767           sdT1 1 0
98 WISEA J211255.76+303036.8 BD* 21 12 55.576107 +30 30 37.63455           d/sdT2.5 1 0
99 HD 203769 * 21 24 40.8800036880 -11 46 44.626780056   8.37 8.28     A0V 8 0
100 V* HN Peg B BD* 21 44 28.47168 +14 46 07.7988           T2.5 143 0
101 Wolf 940 B BD* 21 46 38.4345 -00 10 34.714           T8.5 62 0
102 WISE J221859.33+114644.7 BD* 22 18 59.412787 +11 46 42.74540           T7pec 4 0
103 WISE J225109.33-074038.7 BD* 22 51 08.831494 -07 40 40.03972           d/sdT7 3 0
104 NAME Thamnos Stream St* ~ ~           ~ 63 0
105 NAME Gaia Enceladus-Sausage St* ~ ~           ~ 860 0
106 NAME Helmi Stream St* ~ ~           ~ 144 0

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