J/ApJ/934/178 L/T transition BDs from NIR SpeX spectra (Ashraf+, 2022)
Disentangling the signatures of blended-light atmospheres in L/T transition
brown dwarfs.
Ashraf A., Bardalez Gagliuffi D.C., Manjavacas E., Vos J.M., Mechmann C.,
Faherty J.K.
<Astrophys. J., 934, 178 (2022)>
=2022ApJ...934..178A 2022ApJ...934..178A
ADC_Keywords: Stars, brown dwarf; Spectral types; Spectra, infrared;
Stars, L-type; Stars, T-type; Photometry, infrared;
Stars, variable
Keywords: Brown dwarfs ; L dwarfs ; T dwarfs ; Atmospheric variability ;
Astronomical techniques ; Spectroscopy ; Near infrared astronomy
Abstract:
We present a technique to identify spectrophotometrically variable
L7-T3 brown dwarfs with single-epoch, low-resolution, near-infrared
SpeX spectra. We calculated spectral indices on known variable brown
dwarfs and used them to select 11 index-index parameter spaces where
known variables can be distinguished from the rest of the general
population of brown dwarfs. We find 62 candidate variables, 12 of
which show significant variability amplitude in independent
photometric monitoring surveys. This technique constitutes the first
formal method to identify a time-dependent effect such as variability
from peculiarities in their integrated light spectra. This technique
will be a useful tool to prioritize targets for future photometric and
spectroscopic monitoring in the era of the James Webb Space Telescope
and 30m-class telescopes.
Description:
Our spectral sample was retrieved from the SpeX Prism Library (SPL;
Burgasser 2014ASInC..11....7B 2014ASInC..11....7B) and is composed of 325 spectra from
270 unique objects within the L7-T3 range of dwarf spectral type
(1150K≲Teff≲1350K). The SPL contains over 2000 NIR spectra of
ultracool and brown dwarfs collaboratively collected since the year
2000 with SpeX, a spectrograph mounted on the 3m NASA Infrared
Telescope Facility in Maunakea, HI.
We used spectra in wavelength range between 0.75 and 2.5um at a
dispersion of 20-30Å/pixel. See Section 2.
From our sample of L/T transition objects, we select as "benchmarks"
21 spectra from 15 objects that have confirmed light-curve amplitudes
>1% in J, [3.6], or [4.5] bands from previous time-resolved,
photometric monitoring across several variability studies that vary in
sensitivity and/or wavelength coverage. See Section 3.1.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 72 15 Confirmed variability sources used as benchmarks
in our study
table4.dat 119 62 Variability candidates with spectral types
between L7-T3
tablea1.dat 58 325 Complete spectral sample run through each
index-index correlation
tablea2.dat 80 73 L7-T3 dwarf spectral binary candidates from our
index-selection technique
refs.dat 70 81 References
--------------------------------------------------------------------------------
See also:
J/ApJ/564/421 : Spectra of T dwarfs. I. (Burgasser+, 2002)
J/AJ/123/3409 : SDSS M, L, and T dwarfs (Hawley+, 2002)
J/AJ/126/1526 : IR photometry of ultracool dwarfs (Bouy+, 2003)
J/AJ/127/2856 : Brown dwarfs in the 2MASS Survey (Burgasser+, 2004)
J/AJ/127/3553 : JHK phot. and spectroscopy for L and T dwarfs (Knapp+, 2004)
J/ApJ/637/1067 : Near-IR spectral classif. of T dwarfs (Burgasser+, 2006)
J/AJ/131/2722 : New L and T dwarfs from the SDSS (Chiu+, 2006)
J/AJ/132/891 : Binaries among nearby L dwarfs (Reid+, 2006)
J/AJ/133/439 : Luminosity function of M7-L8 ultracool dwarfs (Cruz+, 2007)
J/AJ/134/1162 : 11 new T dwarfs in 2MASS (Looper+, 2007)
J/AJ/133/2258 : Activity and kinematics of ultracool dwarfs (Schmidt+, 2007)
J/ApJ/689/1295 : Lithium test implications for BDs (Kirkpatrick+, 2008)
J/ApJ/676/1281 : L and T dwarfs in 2MASS/SDSS (Metchev+, 2008)
J/AJ/136/1290 : Ultracool dwarfs from the 2MASS (Reid+, 2008)
J/AJ/137/1 : PMs and astrometry of late-type dwarfs (Faherty+, 2009)
J/ApJ/710/1142 : SpeX spectrosc. of low mass binaries. I. (Burgasser+, 2010)
J/MNRAS/402/1380 : Rot. velocities in Pleiades and αPer (Jackson+, 2010)
J/ApJS/190/100 : NIR proper motion survey using 2MASS (Kirkpatrick+, 2010)
J/AJ/142/77 : New T dwarfs identified in Pan-STARRS 1 (Deacon+, 2011)
J/ApJS/197/19 : First brown dwarfs discovered by WISE (Kirkpatrick+, 2011)
J/ApJS/201/19 : Hawaii Infrared Parallax Program. I. (Dupuy+, 2012)
J/AJ/144/8 : Sp. of ∼100 G/K/M-type Sco-Cen complex members (Song+, 2012)
J/MNRAS/430/1171 : Sub-stellar birth rate from UKIDSS (Day-Jones+, 2013)
J/ApJS/205/6 : T dwarf population revealed by WISE (Mace+, 2013)
J/PASP/125/809 : New nearby M, L, and T dwarfs (Thompson+, 2013)
J/ApJ/794/143 : New SpeX Observations of M7-L6 Dwarfs (Bardalez+, 2014)
J/ApJ/783/121 : BANYAN II. Nearby young assoc. cand. members (Gagne+, 2014)
J/ApJ/787/126 : WISE reduced PMs and spectral types (Luhman+, 2014)
J/AJ/147/34 : SpeX library of L-type dwarfs (Schneider+, 2014)
J/ApJ/814/118 : L/T dwarfs search with PS1 & WISE. II. (Best+, 2015)
J/ApJ/810/158 : M,L,T dwarfs fundamental param. and SEDs (Filippazzo+, 2015)
J/ApJ/798/73 : BANYAN All-Sky Survey cat. V. Nearby YMGs (Gagne+, 2015)
J/ApJS/219/33 : BANYAN. VII. Candidate YMG members from BASS (Gagne+, 2015)
J/ApJS/225/10 : Kinematic analysis of M7-L8 dwarfs (Faherty+, 2016)
J/ApJ/833/96 : Hawaii IR parallax prog. II. Ultracool dwarfs (Liu+, 2016)
J/ApJ/817/112 : NEOWISE/AllWISE high PM objects (Schneider+, 2016)
J/AJ/154/112 : NIR spectroscopy of new L & T dwarf cand. (Kellogg+, 2017)
J/ApJ/856/23 : BANYAN. XI. The BANYAN Σ algorithm (Gagne+, 2018)
J/AJ/155/265 : Solar neighborhood. XLIV. RECONS discoveries (Henry+, 2018)
J/ApJ/883/205 : Ultracool SpeXtroscopic survey. I. M7-L5 (Bardalez+, 2019)
J/A+A/629/A145 : L9-T3.5 brown dwarfs light curves (Eriksson+, 2019)
J/AJ/157/101 : Cloud Atlas: HST/WFC3 NIR sp. library (Manjavacas+, 2019)
J/AJ/159/257 : Hawaii IR parallax prog. IV. L0-T8 BDs (Best+, 2020)
J/AJ/160/38 : Spitzer variability detections of brown dwarfs (Vos+, 2020)
J/AJ/161/42 : Volume-limited sample of cool dwarfs. I. L0-T8 (Best+, 2021)
J/ApJS/253/7 : A full-sky census of BDs within 20pc (Kirkpatrick+, 2021)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 25 A25 --- Name Source Name
27- 47 A21 --- OName Other Name
49- 53 A5 --- SpT-Opt Spectral type, Optical
55- 58 A4 --- SpT-NIR Spectral type, SpeX/NIR
60- 60 A1 --- Young? [YN] Youth indicator
62- 63 I2 --- Ref1 ? Reference, Optical SpT (see refs.dat file)
65- 66 I2 --- Ref2 [3/23]? Reference, Youth (see refs.dat file)
68- 72 A5 --- Ref3 Reference(s), Variability (see refs.dat file)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 1 I1 --- Subset [1/2] Subset: 1) strong; 2) weak
3- 3 A1 --- f_Name Flag on Name (1)
5- 29 A25 --- Name Source Name
31- 34 A4 --- SpT SpeX-based spectral classification
36- 40 F5.1 % Prob1 [49/100]? BANYAN Σ probability of belonging
to the young moving group 1
42- 46 A5 --- YMG1 Young moving group 1 (2)
48- 49 I2 % Prob2 ? BANYAN Σ probability of belonging
to the young moving group 2
51- 55 A5 --- YMG2 Young moving group 2 (2)
57 A1 --- n_Prob1 [*] *=no measurement of parallax
59- 69 A11 --- Filter Variability filters
71-107 A37 % Amp Variability Amplitude(s)
109-110 I2 --- Ref1 ? Reference, Youth (see refs.dat file)
112-113 I2 --- Ref2 [43/60]? Reference, Variability (see refs.dat file)
115-119 A5 --- Ref3 Reference(s), Spectral binary (see refs.dat file)
--------------------------------------------------------------------------------
Note (1): Flag as follows:
d = These objects are young based on our classifications that come
from both moving group association and spectral indicators of youth in
the literature.
Note (2): Codes as follows:
FLD = field
CARN = Carina Near
ABDMG = AB Doradus
ARG = Argus
UMA = Ursa Major
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 28 A28 --- Name Source Name
30- 31 A2 --- SpT SpeX-based Spectral Type
33- 33 I1 --- Youth [0/1] Index, Youth
35- 35 I1 --- I1 [0/1] Index, H2O-J vs. CH4-H (1)
37- 37 I1 --- I2 [0/1] Index, H2O-J vs H-bump (1)
39- 39 I1 --- I3 [0/1] Index, CH4-J vs. CH4 -H (1)
41- 41 I1 --- I4 [0/1] Index, CH4-J vs. H-bump (1)
43- 43 I1 --- I5 [0/1] Index, CH4-H vs. H2 O-K (1)
45- 45 I1 --- I6 [0/1] Index, CH4-H vs. CH4-K (1)
47- 47 I1 --- I7 [0/1] Index, CH4-H vs. H-dip (1)
49- 49 I1 --- I8 [0/1] Index, CH4-H vs. J-curve (1)
51- 51 I1 --- I9 [0/1] Index, H2O-K vs. H-bump (1)
53- 53 I1 --- I10 [0/1] Index, H-dip vs. K-slope (1)
55- 55 I1 --- I11 [0/1] Index, H-dip vs. H-bump (1)
57- 58 I2 --- Total [0/11] Total Index
--------------------------------------------------------------------------------
Note (1): Wavelength ranges of spectral indices (Table 2):
-----------------------------------------------------------------------------
Sp Index Numerator Denominator Feature Ref
Range (um) range (um)
-----------------------------------------------------------------------------
H2O-J 1.14-1.165 1.26-1.285 1.15um H2O 1
CH4-J 1.315-1.335 1.26-1.286 1.32um CH4 1
J-curve 1.04-1.07+ 1.14-1.17 Curvature across J-band 4
1.26-1.29
CH4-H 1.635-1.675 1.56-1.60 1.65um CH4 1
H-bump 1.54-1.57 1.66-1.69 Slope across H-band peak 4
H-dip 1.61-1.64 1.56-1.59+ 1.63um FeH/CH_4 2
1.66-1.69
H2O-K 1.975-1.995 2.08-2.10 1.90um H2O 1
CH4-K 2.215-2.255 2.08-2.12 2.20um CH4 1
K-slope 2.06-2.10 2.10-2.14 K-band shape/collision-induced 3
absorption (CIA) H2
-----------------------------------------------------------------------------
Note. Numerical values of the wavelength regions of the spectral indices
shown in Figure 2. For the indices where the range has a plus sign,
the range is the average of the two wavelength ranges listed.
References.
1 = Burgasser et al. (2006, J/ApJ/637/1067);
2 = Burgasser et al. (2010, J/ApJ/710/1142);
3 = Burgasser et al. (2002, J/ApJ/564/421);
4 = Bardalez Gagliuffi et al. (2014, J/ApJ/794/143).
See Section 3.2.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tablea2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 1 I1 --- Subset [1/3] Subset (1)
3- 29 A27 --- Name Source name
31- 34 A4 --- SpT SpeX-based Spectral Type
36- 36 A1 --- l_Jmag Limit flag on Jmag
38- 43 F6.3 --- Jmag [11.5/18] J-band magnitude
45- 48 F4.2 --- e_Jmag [0/0.3]? Uncertainty in Jmag
50- 50 A1 --- l_Kmag Limit flag on Kmag
52- 57 F6.3 --- Kmag [9.5/17.1]? K-band magnitude
59- 62 F4.2 --- e_Kmag [0/0.31]? Uncertainty in Kmag
64- 64 I1 --- Total [2/6] Total
66- 71 F6.2 --- SNR [4/133] Signal-to-noise ratio
73- 74 I2 --- Ref1 [62/98] Reference, spectrum (see refs.dat file)
76- 77 I2 --- Ref2 Reference, Spectral binary candidate
(see refs.dat file)
79- 80 I2 --- Ref3 ? Reference, Confirmed binarity/variability
(see refs.dat file)
--------------------------------------------------------------------------------
Note (1): Subset as follows:
1 = Confirmed Spectral Binaries;
2 = Confirmed Variable Sources;
3 = Candidate Spectral Binaries.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: refs.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Ref Reference code
4- 28 A25 --- Auth First author's name(s)
30- 48 A19 --- BibCode Bibcode of the reference
50- 70 A21 --- Comm Comment
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 30-Jul-2024