J/AJ/154/112 NIR spectroscopy of new L and T dwarf candidates (Kellogg+, 2017)
A statistical survey of peculiar L and T dwarfs in SDSS, 2MASS, and WISE.
Kellogg K., Metchev S., Miles-Paez P.A., Tannock M.E.
<Astron. J., 154, 112-112 (2017)>
=2017AJ....154..112K 2017AJ....154..112K (SIMBAD/NED BibCode)
ADC_Keywords: Stars, L-type ; Stars, T-type ; Stars, dwarfs ; Spectral types ;
Spectra, infrared ; Spectroscopy
Keywords: binaries: close - brown dwarfs - infrared: stars -
stars: individual: 2MASS J03530419+0418193 - stars: late-type -
stars: peculiar
Abstract:
We present the final results from a targeted search for brown dwarfs
with unusual near-infrared colors. From a positional cross-match of
the Sloan Digital Sky Survey (SDSS), 2-Micron All-Sky Survey (2MASS),
and Wide-Field Infrared Survey Explorer (WISE) catalogs, we have
identified 144 candidate peculiar L and T dwarfs. Spectroscopy
confirms that 20 of the objects are peculiar or are candidate
binaries. Of the 420 objects in our full sample 9 are young (≲200Myr;
2.1%) and another 8 (1.9%) are unusually red, with no signatures of
youth. With a spectroscopic J-Ks color of 2.58±0.11mag, one of the
new objects, the L6 dwarf 2MASS J03530419+0418193, is among the
reddest field dwarfs currently known and is one of the reddest objects
with no signatures of youth known to date. We have also discovered
another potentially very-low-gravity object, the L1 dwarf 2MASS
J00133470+1109403, and independently identified the young L7 dwarf
2MASS J00440332+0228112, which was first reported by Schneider and
collaborators. Our results confirm that signatures of low gravity are
no longer discernible in low to moderate resolution spectra of objects
older than ∼200Myr. The 1.9% of unusually red L dwarfs that do not
show other signatures of youth could be slightly older, up to ∼400Myr.
In this case a red J-Ks color may be more diagnostic of moderate
youth than individual spectral features. However, its is also possible
that these objects are relatively metal-rich, and thus have enhanced
atmospheric dust content.
Description:
We implemented a photometric search for peculiar L and T dwarfs using
combined optical (SDSS), near-infrared (2MASS) and mid-infrared (WISE)
fluxes. In Paper I (Kellogg et al. 2015AJ....150..182K 2015AJ....150..182K), we reported a
sample of 314 objects that passed all of our selection criteria and
visual verification. After refining our visual verification, our total
candidate L and T dwarf list was cut to 156 objects including 104 new
candidates.
We obtained near-infrared spectroscopic observations of the remaining
104 objects in our survey (66 peculiarly red, 13 candidate binary, and
25 general ultra-cool dwarf candidates) using the SpeX instrument on
the NASA Infrared Telescope Facility (IRTF) and the Gemini
Near-Infrared Spectrograph (GNIRS) instrument on the Gemini North
telescope.
We obtained the majority of our follow-up observations (91 of 104)
with the SpeX spectrograph on the IRTF in prism mode (0.75-2.5µm;
R∼75-150), between 2014 October and 2016 April. The observing
sequences and instrument settings were the same as those in Paper I
(Kellogg et al. 2015AJ....150..182K 2015AJ....150..182K). Table1 gives observation epochs
and SpeX instrument settings for each science target.
We followed-up the remaining 13 objects in our candidate list using
the Gemini Near-Infrared Spectrograph (GNIRS) on Gemini North
(0.9-2.5µm). We observed these objects in queue mode between 2015
October and 2017 May. We took the observations in cross-dispersed mode
with the short-blue camera with 32l/mm grating and a 1.0''*7.0'' slit,
resulting in a resolution of R∼500. We used a standard A-B-B-A nodding
sequence along the slit to record object and sky spectra. Individual
exposure times were 120s per pointing. Table2 gives Gemini/GNIRS
observation epochs for each science target.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 61 91 Infrared Telescope Facility/SpeX (IRTF/SpeX)
observations
table2.dat 57 13 Gemini/Gemini Near-Infrared Spectrograph
(Gemini/GNIRS) observations
table3.dat 78 116 Results from spectroscopic classification and
synthetic photometry
table4.dat 106 12 Unknown object properties
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See also:
V/147 : The SDSS Photometric Catalogue, Release 12 (Alam+, 2015)
II/328 : AllWISE Data Release (Cutri+ 2013)
V/139 : SDSS Photometric Catalog, Release 9 (Adelman-McCarthy+, 2012)
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
J/ApJ/810/158 : M,L,T dwarfs parameters and SEDs (Filippazzo+, 2015)
J/ApJ/794/143 : New SpeX Observations of M7-L6 Dwarfs (Bardalez+, 2014)
J/AJ/147/34 : SpeX library of L-type dwarfs (Schneider+, 2014)
J/PASP/125/809 : New nearby M, L, and T dwarfs (Thompson+, 2013)
J/ApJS/205/6 : T dwarf population revealed by WISE (Mace+, 2013)
J/ApJ/710/1142 : SpeX spectroscopy of low mass binaries. I. (Burgasser+, 2010)
J/AJ/137/1 : PMs and astrometry of late-type dwarfs (Faherty+, 2009)
J/ApJ/637/1067 : Near-IR spectral classification of T dwarfs (Burgasser+, 2006)
J/AJ/131/2722 : New L and T dwarfs from the SDSS (Chiu+, 2006)
J/other/ARA+A/43.195 : L and T dwarf stars (Kirkpatrick, 2005)
J/AJ/127/3553 : Photometry and spectroscopy for L and T dwarfs (Knapp+, 2004)
J/AJ/127/2856 : Brown dwarfs in the 2MASS Survey (Burgasser+, 2004)
J/ApJ/564/421 : Spectra of T dwarfs. I. (Burgasser+, 2002)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- --- [2MASS]
7- 23 A17 --- 2MASS 2MASS identifier (JHHMMSS.ss+DDMMSS.s)
25 A1 --- f_2MASS [ab] Flag for independent reports (a or b) (G1)
27- 37 A11 "Y:M:D" Date UT observation date
39- 43 F5.2 mag Jmag [14.51/17.56] 2MASS J band magnitude
45- 47 F3.1 arcsec Slit [0.8/1.6] Slit width
49- 50 I2 min Exp [10/76] Exposure time
52- 61 A10 --- A0 Name of A0 type calibrator
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Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- --- [2MASS]
7- 23 A17 --- 2MASS 2MASS identifier (JHHMMSS.ss+DDMMSS.s)
25 A1 --- f_2MASS [a] Flag for independent reports (a) (G1)
27- 37 A11 "Y:M:D" Date UT observation date
39- 43 F5.2 mag Jmag [15.9/17.4] 2MASS J band magnitude
45- 47 I3 min Exp [40/124] Exposure time
49- 57 A9 --- A0 Name of A0 type Calibrator
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Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- --- [2MASS]
7- 23 A17 --- 2MASS 2MASS identifier (JHHMMSS.ss+DDMMSS.s)
25 I1 --- Type [1/5] Candidate type (1)
27- 31 A5 --- SpT Infrared Spectral type
33- 42 A10 --- n_SpT Note on SpT (interpretation of spectrum)
44 A1 --- f_z-J [ab] Flag on z-J when synthetic color calculations
are limited by spectrum (2)
46- 49 F4.2 mag z-J [0.9/4.4]? Synthetic z-J color index computed from
spectrum
51- 54 F4.2 mag e_z-J [0.03/0.16]? Uncertainty in z-J
56- 59 F4.2 mag J-H [0.3/2.7] Synthetic J-H color index computed from
spectrum
61- 64 F4.2 mag e_J-H [0.03/0.3] Uncertainty in J-H
66- 69 F4.2 mag J-Ks [0.3/3.7] Synthetic J-Ks color index computed from
spectrum
71- 74 F4.2 mag e_J-Ks [0.02/0.26] Uncertainty in J-Ks
76 A1 --- 1sig Object greater than 1σ outlier in
color (3)
78 A1 --- 2sig Object greater than 2σ outlier in
color (3)
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Note (1):
The objects were divided into the different categories based on their
photometric colors. The objects in the "Peculiarly Red and Candidate
Binary" category passed both the peculiarly red and candidate L+T binary
selection criteria:
1 = Peculiarly Red;
2 = Candidate Binary;
3 = Peculiarly Red and Candidate Binary;
4 = General Ultra-cool Dwarf Candidates;
5 = False positive.
Note (2): Synthetic color calculations are defined as follows:
a = The spectra of these objects are from the Gemini Near-InfraRed
Spectrograph (GNIRS), and do not cover the entire SDSS z-band, so we
are unable to calculate synthetic z-J colors;
b = The spectra of these objects are from Magellan/FIRE. The FIRE prism
spectra do not cover the entire SDSS z-band so we are unable to
calculate the z-J colors.
Note (3): We identify color outliers by comparing the synthetic J-Ks color
of each object to the median J-Ks colors of M7--M9 and T0--T8 dwarfs
from Faherty et al. 2009 (Cat. J/AJ/137/1) and for L0--L9 dwarfs from
Faherty et al. (2013ApJ..888..33F). The + and - signs indicate whether
the object is above or below the average, respectively.
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Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- --- [2MASS]
7- 23 A17 --- 2MASS 2MASS identifier (JHHMMSS.ss+DDMMSS.s)
25- 37 A13 --- Tel Telescope+Instrument setup
39- 40 A2 --- Survey Survey in which identified (P1=Kellogg et al.
2015AJ....150..182K 2015AJ....150..182K or P2=this work)
42- 46 F5.2 mag zmag [18.8/20.5] SDSS z band magnitude
48- 51 F4.2 mag e_zmag [0.04/0.16] Uncertainty in zmag
53- 57 F5.2 mag Jmag [15.8/17.5] 2MASS J band magnitude
59- 62 F4.2 mag e_Jmag [0.07/0.3] Uncertainty in Jmag
64- 68 F5.2 mag Hmag [13.9/16.5] 2MASS H band magnitude
70- 73 F4.2 mag e_Hmag [0.03/0.3] Uncertainty in Hmag
75- 79 F5.2 mag Ksmag [13/15.6] 2MASS Ks band magnitude
81- 84 F4.2 mag e_Ksmag [0.02/0.2] Uncertainty in Ksmag
86- 90 F5.2 mag W1mag [12/15.4] WISE W1 band magnitude
92- 95 F4.2 mag e_W1mag [0.02/0.04] Uncertainty in W1mag
97-101 F5.2 mag W2mag [11.1/15] WISE W2 band magnitude
103-106 F4.2 mag e_W2mag [0.02/0.07] Uncertainty in W2mag
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Global Notes:
Note (G1): Independent reports are defined as follows:
a = Independently reported by Schneider et al. (2017AJ....153..196S 2017AJ....153..196S);
b = Independently reported by Best et al. (2017arXiv170100490B 2017arXiv170100490B).
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References:
Kellogg et al., Paper I 2015AJ....150..182K 2015AJ....150..182K
History:
From electronic version of the journal
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 05-Feb-2018