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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
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:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 180 155 Observed M dwarfs table2.dat 161 155 Measured quantities and stellar ages
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
Bytes Format Units Label Explanations
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)
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, 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, 2007, Cat. J/AJ/133/2825) unless otherwise noted. Daemgen et al. (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). 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): 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.
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
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)
Note (10): CaH (wide; Kirkpatrick et al. 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) (EW←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.
History: From electronic version of the journal
(End) Emmanuelle Perret [CDS] 30-Jun-2011
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