J/AJ/149/158 The BUD sample. I. L dwarf activity sample (Schmidt+, 2015)
BOSS ultracool dwarfs. I. Colors and magnetic activity of M and L dwarfs.
Schmidt S.J., Hawley S.L., West A.A., Bochanski J.J., Davenport J.R.A.,
Ge J., Schneider D.P.
<Astron. J., 149, 158 (2015)>
=2015AJ....149..158S 2015AJ....149..158S
ADC_Keywords: Stars, dwarfs ; Stars, late-type ; Equivalent widths ;
Spectral types
Keywords: astronomical databases: miscellaneous - brown dwarfs -
stars: chromospheres - stars: late-type - stars: low-mass
Abstract:
We present the colors and activity of ultracool (M7-L8) dwarfs from
the Tenth Data Release of the Sloan Digital Sky Survey (SDSS). We
combine previous samples of SDSS M and L dwarfs with new data obtained
from the Baryon Oscillation Sky Survey (BOSS) to produce the BOSS
Ultracool Dwarf (BUD) sample of 11820 M7-L8 dwarfs. By combining SDSS
data with photometry from 2MASS and the Wide-field Infrared Sky
Explorer (WISE) mission, we present ultracool dwarf colors from i-z to
W2-W3 as a function of spectral type, and extend the SDSS-2MASS-WISE
color locus to include ultracool dwarfs. The i-z, i-J, and z-J colors
provide the best indication of spectral type for M7-L3 dwarfs. We also
examine ultracool dwarf chromospheric activity through the presence
and strength of Hα emission. The fraction of active dwarfs rises
through the M spectral sequence until it reaches ∼90% at spectral type
L0. The fraction of active dwarfs then declines to 50% at spectral
type L5; no Hα emission is observed in the late-L dwarfs in the
BUD sample. The fraction of active L0-L5 dwarfs is much higher than
previously observed. The strength of activity declines with spectral
type from M7 through L3, after which the data do not show a clear
trend. Using one-dimensional chromosphere models, we explore the range
of filling factors and chromospheric temperature structures that are
consistent with Hα observations of M0-L7 dwarfs. M dwarf
chromospheres have a similar, smoothly varying range of temperature
and surface coverage, while L dwarf chromospheres are cooler and have
smaller filling factors.
Description:
As part of the Sloan Digital Sky Survey (SDSS)-III (Eisenstein et al.,
2011AJ....142...72E 2011AJ....142...72E), the Baryon Oscillation Sky Survey (BOSS; Dawson
et al., 2013AJ....145...10D 2013AJ....145...10D) continued to use the SDSS 2.5m telescope
with a similar fiber-fed spectrograph for additional optical
spectroscopy. We were awarded a BOSS ancillary program to target
candidate ultracool dwarfs and increase the number of M7 and later
dwarfs with optical spectra from SDSS. Over the course of the survey,
BOSS obtained spectra of ∼10000 ultracool dwarf candidates. In this
paper, we introduce the initial BOSS Ultracool Dwarfs (BUD) sample,
which includes data from the first two years of BOSS.
The BUD sample combines data from three different components of the
SDSS: 9614 M7-M9 dwarfs from the DR7 M dwarf sample described by West
et al. 2011 (cat. J/AJ/141/97), 484 L dwarfs from the DR7 L dwarf
sample discussed by Schmidt et al. 2010 (cat. J/AJ/139/1808), and
late-M and L dwarfs selected from the Baryon Oscillation Sky Survey
(BOSS) component of the Tenth Data Release (DR10; Ahn et al.,
2014ApJS..211...17A 2014ApJS..211...17A). The DR7 spectra were observed with the original
SDSS-I/-II spectrographs, with a wavelength range of 3800-9200Å and
an average resolution of R∼2000. The DR10 spectra were taken with the
updated BOSS spectrographs, with the same resolution but an increased
wavelength coverage of 3600-10400Å. While the spectra extend far
into blue wavelengths, for these faint red objects they are typically
too noisy to analyze at wavelengths bluer than 5000-6000Å.
Of the 551 L dwarfs in the BUD sample, 26 have sufficient
signal-to-noise ratio (S/N) to classify them as either active or
inactive (21 active, 3 inactive, and 2 maybe active). To supplement
the sample of L dwarfs with activity classifications, we include
Hα detections and non-detections for objects that have been
published as part of discovery papers (e.g., Kirkpatrick et al.,
1999ApJ...519..802K 1999ApJ...519..802K, 2000AJ....120..447K 2000AJ....120..447K), activity surveys (e.g.,
Schmidt et al. 2007, cat. J/AJ/133/2258; Reiners & Basri,
2008ApJ...684.1390R 2008ApJ...684.1390R), and serendipitous detections (e.g., Hall,
2002ApJ...564L..89H 2002ApJ...564L..89H; Liebert et al., 2003AJ....125..343L 2003AJ....125..343L; Burgasser et
al., 2011ApJ...739...49B 2011ApJ...739...49B). Data from these sources are listed in
Table6 (we refer to this sample as the "L dwarf activity sample"). The
L dwarf activity sample includes data for active and inactive (upper
limit of HαEW>0.75Å) BUD L dwarfs but excludes objects which
did not meet the S/N>3 criterion.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table6.dat 51 225 L dwarf Hα detections and emission strength
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See also:
V/139 : The SDSS Photometric Catalog, Release 9 (Adelman-McCarthy+, 2012)
II/294 : The SDSS Photometric Catalog, Release 7 (Adelman-McCarthy+, 2009)
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
J/AJ/141/97 : SDSS DR7 M dwarfs (West+, 2011)
J/AJ/139/1808 : Colors and kinematics of SDSS L dwarfs (Schmidt+, 2010)
J/A+A/497/619 : New ultra-cool dwarfs from SDSS and 2MASS (Zhang+, 2009)
J/AJ/133/2258 : Activity and kinematics of ultracool dwarfs (Schmidt+, 2007)
J/AJ/133/439 : Luminosity function of M7-L8 ultracool dwarfs (Cruz+, 2007)
Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 16 A16 --- 2MASS 2MASS designation (HHMMSSss+DDMMSSs, J2000)
18- 21 A4 --- SpT Spectral type
23 I1 --- r_EWHa [1/8] Reference for EWHa (1)
25 A1 --- l_EWHa [<] Upper limit flag on EWHa
26- 32 F7.2 0.1nm EWHa [-1.1/174] Hα equivalent width; in Å
34 A1 --- l_logLHa [<] Upper limit flag on logLHa
35- 40 F6.2 [-] logLHa [-7/-3.6] Log of Hα luminosity ratio to
bolometric luminosity, log(LHα/Lbol)
42- 44 F3.1 --- sigHa ? Normalized Hα standard deviation
σ(Hα)/<Hα>
46- 49 F4.1 --- Var [0/20]? Fractional variability (2)
51 A1 --- V Variable? (y=yes or n=no)
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Note (1): The reference codes are defined as follows:
1 = Reiners & Basri (2008ApJ...684.1390R 2008ApJ...684.1390R);
2 = Schmidt et al. 2007 (cat. J/AJ/133/2258);
3 = Kirkpatrick et al. (2000AJ....120..447K 2000AJ....120..447K);
4 = Kirkpatrick et al. (1999ApJ...519..802K 1999ApJ...519..802K);
5 = Liebert et al. (2003AJ....125..343L 2003AJ....125..343L);
6 = This paper;
7 = Hall (2002ApJ...564L..89H 2002ApJ...564L..89H);
8 = Burgasser et al. (2011ApJ...739...49B 2011ApJ...739...49B).
Note (2): Defined as the total range of EWHα divided by the minimum
EWHα.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Sylvain Guehenneux [CDS] 22-May-2015