J/ApJ/699/649 Young M dwarfs within 25pc. I. (Shkolnik+, 2009)
Identifying the young low-mass stars within 25 pc.
I. Spectroscopic observations.
Shkolnik E., Liu M.C., Reid I.N.
<Astrophys. J., 699, 649-666 (2009)>
=2009ApJ...699..649S 2009ApJ...699..649S
ADC_Keywords: Equivalent widths ; Spectral types ; Stars, M-type ;
Stars, ages ; Stars, distances ; Stars, nearby
Keywords: solar neighborhood - stars: activity - stars: chromospheres -
stars: low-mass - brown dwarfs - X-rays: stars
Abstract:
We have completed a high-resolution (R∼60000) optical spectroscopic
survey of 185 nearby M dwarfs identified using ROSAT data to select
active, young objects with fractional X-ray luminosities comparable to
or greater than Pleiades members. Our targets are drawn from the
"NStars" 20pc census and the "Moving-M" sample with distances
determined from parallaxes or spectrophotometric relations. We limited
our sample to 25pc from the Sun, prior to correcting for
pre-main-sequence overluminosity or binarity. Nearly half of the
resulting M dwarfs are not present in the Gliese catalog and have no
previously published spectral types. We identified 30 spectroscopic
binaries (SBs) from the sample, which have strong X-ray emission due
to tidal spin-up rather than youth.
Description:
We drew ∼800 targets from the "NStars" 20pc census (Reid et al. 2003,
Cat. J/AJ/126/3007 2004, Cat. J/AJ/128/463). In addition to these, we
included ∼300 newly cataloged M dwarfs that exhibit significant proper
motion between the POSSI and 2MASS surveys (i.e., the "Moving-M"
sample; Reid et al. 2007, Cat. J/AJ/133/2825).
We acquired high-resolution echelle spectra of 185 low-mass stars over
four nights with the High Resolution Echelle Spectrometer (HIRES) on
the Keck I 10m telescope and over six nights with the Echelle
SpectroPolarimetric Device for the Observation of Stars (ESPaDOnS) on
the Canada-France-Hawaii 3.6m Telescope (CFHT), both located on the
summit of Mauna Kea. We identified 30 spectroscopic binaries (SBs)
from the sample and 155 M dwarfs.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 180 155 Observed M dwarfs
table2.dat 161 155 Measured quantities and stellar ages
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See also:
III/123 : Dwarf K and M stars of small proper motion (Stephenson 1986)
III/259 : Stephenson's dwarf K and M stars (StKM) (Stephenson, 1986)
J/A+A/325/159 : Companions to M dwarfs within 5pc (Leinert+ 1997)
J/A+A/326/249 : Chromospheric models of dwarf M stars (Mauas+ 1997)
J/A+A/348/897 : Ages of main-sequence stars (Lachaume+, 1999)
J/AJ/126/3007 : Spectroscopy of faint red NLTT dwarfs (Reid+, 2003)
J/AJ/128/463 : A preliminary 20pc census from the NLTT catalogue (Reid+, 2004)
J/AJ/132/866 : New M dwarfs in solar neighborhood (Riaz+, 2006)
J/AJ/133/2825 : Star beyond the NLTT catalog (Reid+, 2007)
J/A+A/467/785 : SuperWASP/ROSAT periodic variable stars (Norton+, 2007)
J/AJ/135/785 : SDSS-DR5 low-mass star spectroscopic sample (West+, 2008)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 27 A27 --- Name Name (1)
29- 30 I2 h RAh 2MASS hour of right ascension (J2000)
32- 33 I2 min RAm 2MASS minute of right ascension (J2000)
35- 39 F5.2 s RAs 2MASS second of right ascension (J2000)
41 A1 --- DE- 2MASS declination sign (J2000)
42- 43 I2 deg DEd 2MASS degree of declination (J2000)
45- 46 I2 arcmin DEm 2MASS arcminute of declination (J2000)
48- 51 F4.1 arcsec DEs 2MASS arcsecond of declination (J2000)
52 A1 --- f_Name [j] low-resolution spectrum (2)
54- 57 A4 --- Tel Telescope (CFHT or Keck) (3)
59- 61 F3.1 --- SpT Spectral type (±0.5) (3)
62 A1 --- f_SpT [eh] poor S/N or seeing (4)
64 A1 --- l_Dist [∼ ] Limit flag on Dist
65- 69 F5.1 pc Dist ? Distance (5)
71- 73 F3.1 pc e_Dist ? Distance uncertainty
74 A1 --- n_Dist [gkl] oeigin of the distance (6)
76- 80 F5.2 mag Imag ? USNO I-band magnitude
82- 87 F6.3 mag Jmag 2MASS Johnson J-band magnitude
89- 94 F6.3 [-] [Fx/Fj] ? ROSAT fractional X-ray flux (log scale) (7)
96-178 A83 --- Bin Remarks about binarity (8)
180 A1 --- f_Bin [f] questionable binarity (9)
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Note (1): Those target names with directions in parentheses were resolved
as visual binaries (VB) and when possible, both components were
observed. If a target was resolved as a VB by another group (see the
last column) but not resolved at the telescope, resulting spectrum is
a composite of the both components. Likewise, the published photometry
is of the combined system. In tables 1 and 2, 2MASS J1442809-0424078
is a misprint for 2MASS J14442809-0424078; corrected at CDS.
Note (2):
j = Low-resolution spectra were obtained of these targets by Riaz et al.
(2006, Cat. J/AJ/132/866).
Note (3): Each of the two spectrographs used, Keck+HIRES and CFHT+ESPaDOnS,
produces a different measurement error for the TiO index and thus,
errors of the of the calculated SpTs are δ(SpT)=0.33, 0.11,
respectively. However, the calibration is based on a sample binned to
0.5 subclasses, limiting the true uncertainty to this value.
Note (4): Flag as follows:
e = Due to either poor S/N or bad seeing, we were unable to measure reliable
TiO indices for these targets and defer to the published SpT (±0.5
subclasses) based on low-resolution data (Reid et al. 2002AJ....124..519R 2002AJ....124..519R,
2007, Cat. J/AJ/133/2825).
h = These targets were plagued with poor seeing and/or low S/N and no
previously published SpT. Therefore, we did a by-eye comparison of the
TiO bands with spectra of known SpT. The error for these is ±1 subclass.
Note (5): Photometric distances from Reid et al. (2002AJ....124..519R 2002AJ....124..519R,
2007, Cat. J/AJ/133/2825) unless otherwise noted. Daemgen et al.
(2007ApJ...654..558D 2007ApJ...654..558D) revised the distances to those VBs resolved by
them (see the last column). Distances of those VBs resolved by us
during acquisition have been corrected for their binarity assuming
equal flux for each component.
Note (6): Flag as follows:
g = Distances from the Hipparcos and Tycho Catalogs (Perryman & ESA 1997,
Cat. I/239) using trigonometric parallaxes.
k = The photometric distances have been corrected here for over luminosity due
to the very young stellar ages listed in Table 2 using evolutionary models
of Baraffe et al. (1998, Cat. J/A+A/337/403). The binarity of
2MASS J15534211-2049282 has also been taken into account.
l = Distance from Allers et al. (2009ApJ...697..824A 2009ApJ...697..824A).
Note (7): Fractional X-ray flux from the ROSAT All-Sky Survey. Three
Targets were not detected by ROSAT but have been included in the
sample due to previously published indications of youth (see Column 7
of Table 2).
Note (8): Visual binaries are marked as "VB." Stars observed during two
epochs with no RV variation are marked as "SB1"
Note (9):
f = Norton et al. (2007, Cat. J/A+A/467/785) attribute the photometric period
to an eclipsing binary of BY Dra-type; however, we see no evidence that
this target is an SB.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 27 A27 --- Name Name
29- 31 F3.1 --- SpT M spectral sub-type (±0.5)
33- 36 F4.2 --- CaHw ? Surface gravity-sensitive indice CaH wide (10)
38- 41 F4.2 --- CaHn ? Surface gravity-sensitive indice CaH narrow (10)
43- 46 F4.2 0.1nm W(K) KI equivalent width (11)
48- 53 F6.2 0.1nm W(Ha) Hα equivalent width (11)
55- 59 A5 --- Youth Youth index (12)
61-149 A89 --- Notes Youth indicator from literature
151-152 A2 --- l_Age [d>≲ ] Limit flag on Age (14)
153-156 I4 Myr Age Estimated age (13)
157 A1 --- --- [-]
158-161 I4 Myr Age.u ? Estimated age, upper limit (13)
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Note (10): CaH (wide; Kirkpatrick et al. 1991ApJS...77..417K 1991ApJS...77..417K) and CaH
(narrow; this work) as given in figure 7 are :
CaHwide=-0.0067SpT2+0.0986SpT+1.0633 and
CaHnarr=-0.00891SpT2+0.13364SpT+1.1053.
See section 5.1 for further explanations
Note (11): Each of the two spectrographs used, Keck+HIRES and CFHT+ESPaDOnS,
produces different error bars for measured values. As discussed in
Section 4, the smaller errors for the CFHT data are due to the more
stable fiber-fed instrumental setup of ESPaDOnS (see Table 1). The
measurement errors for Keck and CFHT, respectively, are:
δ(CaH-wide)=0.035, 0.008, δ(CaH-narr)=0.051, 0.013,
δ(KIEW)=0.24, 0.16, δ(HαEW)=0.45, 0.21. Negative
Hα EWs indicate the line is in emission.
Note (12): Youth index in binary format in order of least to most
restrictive age indicator: low-g from CaH (1), low-g from KI (2),
HeI emission (3), Li detection (4), strong Hα emission (5)
(EWHα←10Å). Note that determining low-g targets of SpT≳M6
from the CaH and KI indicators is difficult unless extremely young.
See Section 5.1 for more details. Also, due to either poor S/N or bad
seeing, we were unable to measure reliable CaH indices from those
spectra (denoted by a "?").
Note (13): Age limits are based on youth diagnostics discussed in Section 5,
unless a target has been previously published to be a member of known
YMG, in which case the age of the group is adopted. For stars with no
additional indications of youth, the lower limit is based on the lack
of lithium in the spectra and the upper limit is the statistical age
determined from their SpT and X-ray emission, i.e., A star of SpT
earlier than M2.5 has an upper age limit of 150Myr and one of later
SpT 300Myr. For the 11 stars with no significant Hα emission
(i.e., >-1Å), we list their activity lifetimes (≥400Myr) as
determined by West et al. (2008, Cat. J/AJ/135/785). These ages have
large error bars on the order of 500Myr.
Note (14):
d = LP 348-40, GJ 1041A (SW) and G 108-36 appear to have low surface gravity
using both the CaH and KI diagnostics but do not have any Hα
emission. According to West et al. (2008, Cat. J/AJ/135/785), the lack of
Hα implies an age >2000, 400, and 1200 (±400)Myr, respectively.
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History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 30-Jun-2011