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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 (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), 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). 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:
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
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
Bytes Format Units Label Explanations
1- 5 A5 --- --- [2MASS] 7- 23 A17 --- 2MASS 2MASS identifier ( 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
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 5 A5 --- --- [2MASS] 7- 23 A17 --- 2MASS 2MASS identifier ( 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
Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 5 A5 --- --- [2MASS] 7- 23 A17 --- 2MASS 2MASS identifier ( 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)
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.
Byte-by-byte Description of file: table4.dat
Bytes Format Units Label Explanations
1- 5 A5 --- --- [2MASS] 7- 23 A17 --- 2MASS 2MASS identifier ( 25- 37 A13 --- Tel Telescope+Instrument setup 39- 40 A2 --- Survey Survey in which identified (P1=Kellogg et al. 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
Global Notes: Note (G1): Independent reports are defined as follows: a = Independently reported by Schneider et al. (2017AJ....153..196S); b = Independently reported by Best et al. (2017arXiv170100490B).
References: Kellogg et al., Paper I 2015AJ....150..182K History: From electronic version of the journal
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 05-Feb-2018
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