A self-consistent, absolute isochronal age scale for young moving groups in the solar neighbourhood

Abstract

We present a self-consistent, absolute isochronal age scale for young ( 200 Myr), nearby ( 100 pc) moving groups in the solar neighbourhood based on homogeneous fitting of semi-empirical pre-main-sequence model isochrones using the τ 2 maximumlikelihood fitting statistic of Naylor & Jeffries in the M V , V − J colour-magnitude diagram. The final adopted ages for the groups are: 149 +51 −19 Myr for the AB Dor moving group, 24 ± 3 Myr for the β Pic moving group (BPMG), 45 +11 −7 Myr for the Carina association, 42 +6 −4 Myr for the Columba association, 11 ± 3 Myr for the η Cha cluster, 45±4 Myr for the Tucana-Horologium moving group (Tuc-Hor), 10±3 Myr for the TW Hya association, and 22 +4 −3 Myr for the 32 Ori group. At this stage we are uncomfortable assigning a final, unambiguous age to the Argus association as our membership listfor the association appears to suffer from a high level of contamination, and therefore it remains unclear whether these stars represent a single population of coeval stars.Our isochronal ages for both the BPMG and Tuc-Hor are consistent with recent lithium depletion boundary (LDB) ages, which unlike isochronal ages, are relatively insensitive to the choice of low-mass evolutionary models. This consistency between the isochronal and LDB ages instills confidence that our self-consistent, absolute age scale for young, nearby moving groups is robust, and hence we suggest that these ages be adopted for future studies of these groups. Software implementing the methods described in this study is available from http: //www.astro.ex.ac.uk/people/timn/tau-squared/.

A High-Precision Near-Infrared Survey for Radial Velocity Variable Low-Mass Stars Using Cshell and a Methane Gas Cell

“…15 Myr for the system, consistent with the age of the βPictoris moving group (24±3 Myr; Bell et al 2015a). They, however, obtain a dynamical mass for GJ3305B that is discrepant with that of evolutionary models, which they suggest could be explained by the presence of an unresolved companion.…”

“…The young sample was constructed by selecting K-to mid-M-type young stars in the solar neighborhood, mainly from known members of young moving groups, such as βPictoris (24±3 Myr; Zuckerman et al 2001;Bell et al 2015a), ABDoradus ( -+ 149 19 51 Myr; Zuckerman et al 2004;Bell et al 2015a), and the Octans-Near association (≈30-100 Myr; Zuckerman et al 2013), with Two Micron All Sky Survey (2MASS) K S -band magnitudes brighter than 7.1 (the brightest target, εEridani, has K S =1.8) so that an S/N of ∼80 could be achieved within approximately an hour. The young age of all stars in this sample is strongly constrained by kinematic membership in these young associations, typically in addition to lithium abundance measurements or comparison to isochrones (e.g., Torres et al 2008), except for the starεEridani, which is not a member of any known young moving group.…”

2MASS 0213+3648 C: A wide T3 benchmark companion to an an active, old M dwarf binary

“…While studies of younger (10-15 Myr) clusters show significant amounts of disc emission around many M dwarfs (e.g. Currie et al 2008), Simon et al (2012) found no disc excesses in the M dwarf population of Tucana Horologium (45 ± 4 Myr, Bell, Mamajek & Naylor 2015) and AB Dor (149 +51 −19 Bell et al 2015). Hence, the lack of disc excess indicates that 2MASS J0213+3648 AB is older than around 20 Myr.…”

Orbiting a binary

“…The availability of Gaia DR1 data sets (Gaia Collaboration et al 2016a) as well as the recent revision of the ages of several young moving groups used as reference (Bell et al 2015) calls for a reassessment of the stellar properties. We also exploit photometric time series to refine the Article number, page 4 of 15 Allard et al (2012) and assuming an age of 35 Myrs.…”