The Spectra of T Dwarfs I: Near-Infrared Data and Spectral Classification

Adam J. Burgasser, J. Davy Kirkpatrick, Michael E. Brown, I. Neill Reid, Adam Burrows, James Liebert, Keith Matthews, John E. Gizis, Conard C. Dahn, David G. Monet, Roc M. Cutri, and Michael F. Skrutskie

[abstract] [the paper] [new T dwarfs] [spectra] [links]

Abstract

We present near-infrared spectra for a sample of T dwarfs, including eleven new discoveries made using the Two Micron All Sky Survey. These objects are distinguished from warmer (L-type) brown dwarfs by the presence of methane absorption bands in the 1--2.5 um spectral region. A first attempt at a near-infrared classification scheme for T dwarfs is made, based on the strengths of CH4 and H2O bands and the shapes of the 1.25, 1.6, and 2.1 um flux peaks. Subtypes T1 V through T8 V are defined, and spectral indices useful for classification are presented. The subclasses appear to follow a decreasing Teff scale, based on the evolution of CH4 and H2O bands and the properties of L and T dwarfs with known distances. However, we speculate that this scale is not linear with spectral type for cool dwarfs, due to the settling of dust layers below the photosphere and subsequent rapid evolution of spectral morphology around Teff ~ 1300--1500 K. Similarities in near-infrared colors and continuity of spectral features suggest that the gap between the latest L dwarfs and earliest T dwarfs has been nearly bridged. This argument is strengthened by the possible role of CH4 as a minor absorber shaping the K-band spectra of the latest L dwarfs. Finally, we discuss one peculiar T dwarf, 2MASS 0937+2931, which has very blue near-infrared colors (J-Ks = -0.89+/-0.24) due to suppression of the 2.1 um peak. The feature is likely caused by enhanced collision-induced H2 absorption in a high pressure or low metallicity photosphere.
Accepted by ApJ, v563, December 2001

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New 2MASS T dwarf discoveries

The following table lists coordinates, spectral types, and 2MASS JHKs mags for new T dwarfs identified in the paper. For a list of all the known T dwarfs, please see the table on the T dwarf page. Photometric errors are listed in parentheses. Finder charts for these objects are given at the bottom of the page.

Object J2000 Coord Subtype 2MASS J 2MASS H 2MASS Ks
2MASS 0243-2453 02 43 13.7
-24 53 29
T6 V 15.40(0.05) 15.15(0.10) 15.21(0.17)
2MASS 0415-0935 04 15 19.5
-09 35 06
T8 V 15.71(0.06) 15.57(0.12) 15.45(0.20)
2MASS 0727+1710 07 27 18.2
+17 10 01
T7 V 15.55(0.07) 15.82(0.18) 15.56(0.21)
2MASS 0755+2212 07 55 48.0
+22 12 18
T5 V: 15.72(0.07) 15.66(0.14) 15.77(0.21)
2MASS 0937+2931 09 37 34.7
+29 31 42
T6 Vp 14.65(0.04) 14.68(0.07) 15.54(0.24)
2MASS 1534-2952 15 34 49.8
-29 52 27
T5.5 V 14.90(0.04) 14.89(0.09) 14.86(0.11)
2MASS 1546-3325 15 46 27.1
-33 25 11
T5.5 V 15.60(0.05) 15.44(0.09) 15.42(0.17)
2MASS 1553+1532 15 53 02.2
+15 32 36
T7 V 15.81(0.08) 15.92(0.17) 15.51(0.19)
2MASS 2254+3123 22 54 18.8
+31 23 49
T5 V 15.28(0.05) 15.04(0.09) 14.83(0.14)
2MASS 2339+1352 23 39 10.1
+13 52 30
T5.5 V 15.88(0.08) 16.04(0.17) 15.70(0.28)
2MASS 2356-1553 23 56 54.7
-15 53 10
T6 V 15.80(0.06) 15.64(0.10) 15.83(0.19)

Finder Charts [1] [2] [3] [4]

Spectral Data

This table lists the available spectra for confirmed T dwarfs from the classification paper. Also check out the spectra on the T dwarf page. I also encourage interested parties to also visit Sandy Legget's vast repository of spectral and photometric data at ftp://ftp.jach.hawaii.edu/pub/ukirt/skl/. You can also download all of the NIRC and OSIRIS data in one shot if you are so inclined. You may need to massage the headers for these files in order to read them in to your favorite software. Please remember to cite the paper if you are going to use these data, it's the only way some of us keep our jobs :)

Object
(finder chart)
Type NIRC
1-2.5um
R~60-120
OSIRIS
1.2-2.35um
R~1200
2MASS 0243-2453 T6 V [000124] [991221]
2MASS 0415-0935 T8 V [991118]
[000124]
.
2MASS 0559-1404 T5 V [000123]
[000124
[991220]
2MASS 0727+1710 T7 V [000123] [991220]
2MASS 0937+2931 T6 Vp [000123]
[000124]
[991221]
2MASS 1047+2124 T6.5 V [000123]
[000124]
.
2MASS 1217-0311 T7.5 V [000123] .
2MASS 1225-2739 T6 V
(T6 V)
. [000718]
2MASS 1237+6526 T6.5 Ve [000124] .
SDSS 1254-0122 T2 V . [000716]
SDSS 1346-0031 T6 V [000123] .
Gliese 570D T8 V [000124] [000716]
2MASS 1534-2952 T5.5 V . [000718]
2MASS 1546-3325 T5.5 V . [000719]
2MASS 1553+1532 T7 V [000722] [000717]
[000718]
SDSS 1624+0029 T6 V . [000715]
2MASS 2254+3123 T5 V [000722] [000716]
2MASS 2339+1352 T5.5 V [000722] [000716]
2MASS 2356-1553 T6 V [991118] [000717]
Subtypes are from Burgasser et al. 2001, ApJ, 563, in press.
6-digit identifiers are UT observation dates YYMMDD.

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since 2001 August 29
This page created by Adam Burgasser
http://www.gps.caltech.edu/~pa/adam/classification/index.html