A STELLAR CENSUS OF THE TUCANA-HOROLOGIUM MOVING GROUP

“2MASS The Two-Micron All-Sky Survey (2MASS; Skrutskie et al. 2006) observed the entire sky in the J, H, and Ks bands over the interval of 1998–2002.”

“Tuc-Hor is likely one of the largest young stellar populations within d 100 pc, making it a robust site for measuring population statistics (the IMF, multiplicity properties, disk frequencies, and activity rates).”

“SDSS The Sloan Digital Sky Survey (SDSS; York et al. 2000) is an ongoing deep optical imaging and spectroscopic survey of the northern galactic cap and selected regions of the southern cap.”

“Tuc-Hor is likely one of the largest young stellar populations within d 100 pc, making it a robust site for measuring population statistics (the IMF, multiplicity properties, disk frequencies, and activity rates).”

“5 (Larson 1981).”

“…the higher completeness of using UV wavelengths to search for young M dwarfs (Findeisen & Hillenbrand 2010; Shkolnik et al. 2011; Rodriguez et al. 2011, 2013), making the NASA Galaxy Evolution Explorer (GALEX; Martin et al. 2005) a useful resource with which to expand the young low-mass census.”

“The dwarf and young-star temperature scales of Pecaut & Mamajek (2013) both fall between these limits.”

“Given a short-period binary frequency of F ∼ 10% for a < 2 AU (e.g., Raghavan et al. 2010), then our 142 members should be matched by ∼14 SBs that could have been rejected by their discrepant RVs, much as the 34 objects confirmed by Li include 5 RVdiscrepant objects that likely are SB1s.”

“…these young moving groups makes them especially advantageous for the study of circumstellar processes that depend on angular resolution (such as multiple star formation; Brandeker et al. 2003, 2006; Evans et al. 2012) and searches for extrasolar planets (Marois et al. 2008; Lagrange et al. 2009).”

“The most recent data release (DR9; Ahn et al. 2012) reported imaging results in five filters (ugriz) for 14,555 deg2.”

“Given the strong evidence that the IMF is universal for most young populations in the solar neighborhood (e.g., Bastian et al. 2010 and references therein), then a comparison of Tuc-Hor to the standard IMF can demonstrate which mass ranges of members are still incomplete.”

“The typical absolute astrometric accuracy is ∼45 mas rms for sources brighter than r ∼ 20, declining to 100 mas at r ∼ 22 (Pier et al. 2003); absolute astrometry was calibrated with respect to stars from UCAC2, which is calibrated to the ICRS.”

“We reduced the raw spectra using the CarPy pipeline (Kelson 2003)7 but used observations of spectrophotometric standard stars to measure and flatten the blaze function due to the uncertain temperature of the flat lamp.”

“We also observed standard stars nightly from the list of Nidever et al. (2002), which serve as both RV and spectral type templates, as well as most of the known Tuc-Hor members with SpT≥K3, numerous members of the ScoCen OB association, and a selection of known members from other nearby young…”

“100 Myr) have been identified among the nearby field population (Kastner et al. 1997; Webb et al. 1999; Mamajek et al. 1999; Torres et al. 2000; Zuckerman & Webb 2000; Zuckerman & Song 2004).”

“If we use the young-star temperature sequence of Luhman et al. (2003) for ≥M1, the sequence is shifted ∼0.5 subclass later for a given mass or temperature.”

“This trend is consistent with the results of Pecaut et al. (2012), who use several other age diagnostics to determine that the Upper Scorpius subgroup of the Sco-Cen OB association might be a factor of ∼2 older (τ ∼ 11 Myr) than its traditionally accepted isochronal age for low-mass members (τ ∼ 5…”

“Selection of Young Stars with GALEX Stellar activity is known to be an indicator of youth (Preibisch et al. 2002, 2005), so X-ray and UV all-sky surveys are well-suited to finding active young stars.”

“We converted the model Teff values to spectral types using the dwarf temperature sequence of Schmidt-Kaler (1982) for ≤M0 stars and the dwarf sequence of Golimowski et al. (2004) for ≥M1 stars.”

“50 pc) have subsequently identified several additional populations, including the AB Dor, Carina-Near, HerculesLyra, and Tucana-Horologium associations (Zuckerman & Song 2004; Zuckerman et al. 2006; Torres et al. 2008; Eisenbeiss et al. 2013).”

“100 Myr) have been identified among the nearby field population (Kastner et al. 1997; Webb et al. 1999; Mamajek et al. 1999; Torres et al. 2000; Zuckerman & Webb 2000; Zuckerman & Song 2004).”

“100 Myr) have been identified among the nearby field population (Kastner et al. 1997; Webb et al. 1999; Mamajek et al. 1999; Torres et al. 2000; Zuckerman & Webb 2000; Zuckerman & Song 2004).”

“The full description of the instrumental performance is presented by Morrissey et al. (2005).”

“Selection of Young Stars with GALEX Stellar activity is known to be an indicator of youth (Preibisch et al. 2002, 2005), so X-ray and UV all-sky surveys are well-suited to finding active young stars.”

“These system velocities are more uncertain due to the significant systematic uncertainties in pre-main sequence evolutionary models (e.g., Hillenbrand & White 2004), but based on the members which can be independently confirmed from lithium or Hα (and hence should be comoving with Tuc-Hor), we…”

“We describe the motivation and details in Kraus & Hillenbrand (2007).”

“• Hα emission: Old main sequence stars exhibit a wide range of activity levels (e.g., Kafka & Honeycutt 2006; West et al. 2011), and hence the presence of strong Hα emission can not be used as a positive criterion for determining membership.”

“The SACY search of Tuc-Hor (Torres et al. 2006, 2008) found 17 members with spectral types of K3-M0, of which we recovered 15 as candidates.”

“Most programs have only identified a small number of candidates (Kiss et al. 2011) or have concentrated on higher-mass membership (Zuckerman & Song 2004; Torres et al. 2006, 2008; Zuckerman et al. 2011).”

“The low distances also result in additional sensitivity for flux-limited studies of disks (Low et al. 2005; Bouwman et al. 2006; Plavchan et al. 2009) and the (sub)stellar mass function (Gizis 2002; Lyo et al. 2006; Murphy et al. 2010; Shkolnik et al. 2011).”

“Based on the criteria suggested by Luhman & Mamajek (2012), all targets are Class III (diskless) sources with W1 − W3 1.”

“Barrado y Navascués et al. (2004) reported a boundary at Mbol = 10.24± 0.15 in IC 2391, as well as updating the results of Stauffer et al. (1998, 1999) for α Per (Mbol = 11.31 ± 0.15) and the Pleiades (Mbol = 12.14 ± 0.15).”

“• Radial velocities: By definition, young moving groups are comoving with a very small velocity dispersion (σ ∼1 km/s for TWA; Mamajek 2005), and hence the radial velocities of Tuc-Hor members should correlate very well with the projection of the group UVW velocity into the line of sight.”

“Most of our new members are not found in the active M dwarf census of Riaz et al. (2006), and indeed, the majority do not have ROSAT counterparts at all; only 53 of our 129 previously unidentified members have an X-ray counterpart in the ROSAT All-Sky Survey within <30′′.”

“The low distances also result in additional sensitivity for flux-limited studies of disks (Low et al. 2005; Bouwman et al. 2006; Plavchan et al. 2009) and the (sub)stellar mass function (Gizis 2002; Lyo et al. 2006; Murphy et al. 2010; Shkolnik et al. 2011).”

“This process is described in more detail in Kraus et al. (2011) and Law 8 http://www.astro.utoronto.ca/ rucinski/ 8 et al. (2012).”

“We ultimately trace this paucity of identified candidates to their choice of input samples, which were based on ROSAT or GALEX.”

“However, young stars exhibit a lower bound on their Hα emission as a function of spectral type, and this boundary has been well-determined for the similaraged clusters IC 2602 and IC 2391 (Stauffer et al. 1997).”

“100 Myr) have been identified among the nearby field population (Kastner et al. 1997; Webb et al. 1999; Mamajek et al. 1999; Torres et al. 2000; Zuckerman & Webb 2000; Zuckerman & Song 2004).”

“…be robustly calibrated for the age of Tuc-Hor, then their measurement for stars unaffiliated with any moving group can distinguish analogs to stars in star-forming regions (τ = 1–20 Myr) from the young (τ = 50–300 Myr) field population (Shkolnik et al. 2012) and old field stars (Reid et al. 2004).”

“We ultimately trace this paucity of identified candidates to their choice of input samples, which were based on ROSAT or GALEX.”

“However, our census only adds a modest number of stars with SpT earlier than K5, so we refer the reader to a comprehensive analysis of the known higher-mass members by Mentuch et al. (2008) and da Silva et al. (2009).”

“100 Myr) have been identified among the nearby field population (Kastner et al. 1997; Webb et al. 1999; Mamajek et al. 1999; Torres et al. 2000; Zuckerman & Webb 2000; Zuckerman & Song 2004).”

“100 Myr) have been identified among the nearby field population (Kastner et al. 1997; Webb et al. 1999; Mamajek et al. 1999; Torres et al. 2000; Zuckerman & Webb 2000; Zuckerman & Song 2004).”

“Many of the diagnostics of youth have only been firmly calibrated for higher-mass stars (e.g., Mentuch et al. 2008), so our measurements also yield the first robust calibration of isochronal parameter sequences for mid-K to midM dwarfs in Tuc-Hor.”

“Barrado y Navascués et al. (2004) reported a boundary at Mbol = 10.24± 0.15 in IC 2391, as well as updating the results of Stauffer et al. (1998, 1999) for α Per (Mbol = 11.31 ± 0.15) and the Pleiades (Mbol = 12.14 ± 0.15).”

“%) were observed and lie above the FNUV /FJ > 10 −4 threshold used by Shkolnik et al. (2011).”

“The low distances also result in additional sensitivity for flux-limited studies of disks (Low et al. 2005; Bouwman et al. 2006; Plavchan et al. 2009) and the (sub)stellar mass function (Gizis 2002; Lyo et al. 2006; Murphy et al. 2010; Shkolnik et al. 2011).”

“At an age of τ ∼ 30 Myr, lithium should be completely depleted for stars of SpT K7–M4, but not yet burned for earlier and later types (Randich et al. 2001; Dobbie et al. 2010).”

“The low distances also result in additional sensitivity for flux-limited studies of disks (Low et al. 2005; Bouwman et al. 2006; Plavchan et al. 2009) and the (sub)stellar mass function (Gizis 2002; Lyo et al. 2006; Murphy et al. 2010; Shkolnik et al. 2011).”

“50 pc) have subsequently identified several additional populations, including the AB Dor, Carina-Near, HerculesLyra, and Tucana-Horologium associations (Zuckerman & Song 2004; Zuckerman et al. 2006; Torres et al. 2008; Eisenbeiss et al. 2013).”

“DENIS The Deep Near Infrared Survey of the Southern Sky (DENIS; Epchtein et al. 1994) observed ∼84% of the 3 southern sky (with some gaps) in the optical (with a Gunn i filter) and the near-infrared (with J , and Ks filters) during 1995-2001.”

“If the former effect dominates, then it would indicate that geometric analyses are of limited use for determining trace-back ages, and more generally that these moving groups formed in a distributed manner (similar to Taurus-Auriga; Simon 1997; Kraus & Hillenbrand 2008) rather than as compact clusters that have since…”

“A similar spatial distribution can be seen in the activityselected candidates reported by Rodriguez et al. (2013).”

“This trend is consistent with the results of Pecaut et al. (2012), who use several other age diagnostics to determine that the Upper Scorpius subgroup of the Sco-Cen OB association might be a factor of ∼2 older (τ ∼ 11 Myr) than its traditionally accepted isochronal age for low-mass members (τ ∼ 5 Myr; Preibisch et al…”

“In Shkolnik et al. (2011) we used the NStars 25-pc census (≈1500 M dwarfs; Reid et al. 2007) to calibrate our GALEX selection criteria.”

“…use Previous searches for low-mass YMG members using GALEX used color and proper motion cuts coupled with NUV and/or FUV selection criteria (Shkolnik et al. 2011 and Rodriguez et al. 2011 for TWA and Rodriguez et al. 2013 for Tuc-Hor) before acquiring optical spectra for candidate confirmation.”

“…these young moving groups makes them especially advantageous for the study of circumstellar processes that depend on angular resolution (such as multiple star formation; Brandeker et al. 2003, 2006; Evans et al. 2012) and searches for extrasolar planets (Marois et al. 2008; Lagrange et al. 2009).”

“This method is similar to that used by Lépine & Simon (2009) and Schlieder et al. (2010).”

“…these young moving groups makes them especially advantageous for the study of circumstellar processes that depend on angular resolution (such as multiple star formation; Brandeker et al. 2003, 2006; Evans et al. 2012) and searches for extrasolar planets (Marois et al. 2008; Lagrange et al. 2009).”

“…these young moving groups makes them especially advantageous for the study of circumstellar processes that depend on angular resolution (such as multiple star formation; Brandeker et al. 2003, 2006; Evans et al. 2012) and searches for extrasolar planets (Marois et al. 2008; Lagrange et al. 2009).”

“Schlieder et al. (2012) have already shown that two of these stars are field interlopers, indicating that our more precise proper motions might be better at rejecting field stars that are only moderately discrepant from the proper motion of Tuc-Hor.9 Of the 58 late-type stars identified as…”

“At an age of τ ∼ 30 Myr, lithium should be completely depleted for stars of SpT K7–M4, but not yet burned for earlier and later types (Randich et al. 2001; Dobbie et al. 2010).”

“In the canonically ∼125 Myr Pleiades cluster, King et al. (2000) found the boundary to lie at Teff = 4420 K (SpT = K4.”

“The GALEX satellite has imaged most of the sky simultaneously in two bands: near-UV (NUV; 1750– 2750 Å) and far-UV (FUV; 1350–1750 Å), with angular resolutions of 5′′ and 6.5′′.”

“50 pc) have subsequently identified several additional populations, including the AB Dor, Carina-Near, HerculesLyra, and Tucana-Horologium associations (Zuckerman & Song 2004; Zuckerman et al. 2006; Torres et al. 2008; Eisenbeiss et al. 2013).”

“The low distances also result in additional sensitivity for flux-limited studies of disks (Low et al. 2005; Bouwman et al. 2006; Plavchan et al. 2009) and the (sub)stellar mass function (Gizis 2002; Lyo et al. 2006; Murphy et al. 2010; Shkolnik et al. 2011).”

“Cargile et al. (2010) reported a boundary for Blanco 1 at Mbol = 11.99± 0.30.”

“…have employed various combinations of all-sky surveys in order to systematically measure proper motions of both clusters and field stars; USNOB is itself a product of such analysis, Gould & Kollmeier (2004) combined SDSS and USNOB, and the PPMXL survey (Roeser et al. 2010) combined 2MASS and USNOB.”

“Also, activity signatures show wide variations in any single-aged population (Stelzer et al. 2012, Shkolnik & Barman, in preparation), though some show a lower bound that allows for dispositive rejection of nonmembers.”

“• Hα emission: Old main sequence stars exhibit a wide range of activity levels (e.g., Kafka & Honeycutt 2006; West et al. 2011), and hence the presence of strong Hα emission can not be used as a positive criterion for determining membership.”

“We have addressed this problem by adopting proper motions for bright stars as measured by the Third USNO CCD Astrograph Catalog (UCAC3; Zacharias 2010).”

“…et al. 2001; (35) Neuhäuser et al. 2003; (36) Zuckerman & Song 2004; (37) Gontcharov 2006; (38) Anderson & Francis 2012; (39) Bobylev et al. 2006; (40) Kraus et al. 2014; (41) Zuckerman & Webb 2000; (42) Grenier et al. 1999; (43) Pecaut & Mamajek 2013; (44) Elliott et al. 2014; (45) Webb et…”

“Not accounting for unresolved multiples, our sample includes a total of 89 members of the AB Dor moving group, 27 members of Argus, 97 members of the BPMG, 12 members of Carina, 50 members of Columba, 18 members of η Cha, 189 members of Tuc-Hor, 30 members of TWA, and 14 members of 32 Ori.”

“Several planetary-mass companions have been imaged around binary stars on wide circumbinary orbits: ROXs 42B b (Kraus et al. 2014a; Currie et al. 2014b), Ross 458 c (Goldman et al. 2010; Scholz 2010), SR 12 C (Kuzuhara et al. 2011), HD 106906 b (Bailey et al. 2014; Lagrange et al. 2016), and VHS…”

“0 (Monet et al. 2003), as described in Kraus & Hillenbrand (2007) and Kraus et al. (2014), to estimate both parameters.”