Search for associations containing young stars (SACY)

Abstract

Context. Our study is a follow-up of the SACY project, an extended high spectral resolution survey of more than two thousand optical counterparts to X-ray sources in the southern hemisphere targeted to search for young nearby association. Nine associations have either been newly identified, or have had their member list revised. Groups belonging to the Sco-Cen-Oph complex are not considered in the present study. Aims. These nine associations, with ages of between about 6 Myr and 70 Myr, form an excellent sample to study the Li depletion in the pre-main sequence (PMS) evolution. In the present paper, we investigate the use of Li abundances as an independent clock to constrain the PMS evolution. Methods. Using our measurements of the equivalent widths of the Li resonance line and assuming fixed metallicities and microturbulence, we calculated the LTE Li abundances for 376 members of various young associations. In addition, we considered the effects of their projected stellar rotation. Results. We present the Li depletion as a function of age in the first hundred million years for the first time for the most extended sample of Li abundances in young stellar associations. Conclusions. A clear Li depletion can be measured in the temperature range from 5000 K to 3500 K for the age span covered by the nine associations studied in this paper. The age sequence based on the Li-clock agrees well with the isochronal ages, the Cha association being the only possible exception. The lithium depletion patterns for the associations presented here resemble those of the young open clusters with similar ages, strengthening the notion that the members proposed for these loose young associations have indeed a common physical origin. The observed scatter in the Li abundances hampers the use of Li in determining reliable ages for individual stars. For velocities above 20 km s −1 , rotation seems to play an important role in inhibiting the Li depletion.

CARMENES input catalogue of M dwarfs

“…The spectra of stars brighter than J = 9.0 mag were published by Lépine et al (2013), while most of the remaining fainter ones are published here. -M dwarf candidates in nearby young moving groups (e.g., Montes et al 2001;Zuckermann & Song 2004;da Silva et al 2009;Shkolnik et al 2012;Gagné et al 2014;Klutsch et al 2014), in multiple systems containing FGK-type primaries that are subjects of metallicity studies (Gliese & Jahreiss 1991;Poveda et al 1994;Gould & Chanamé 2004;Rojas-Ayala et al 2012;Terrien et al 2012;Mann et al 2013;Montes et al 2013), in fragile binary systems at the point of disruption by the Galactic gravitational field (Caballero 2012, and references therein), and resulting from new massive virtual-observatory searches (Jiménez-Esteban et al 2012;Aberasturi et al 2014). Such a broad diversity of sources allowed us to widen the investigated intervals of age, activity, multiplicity, metallicity, and dynamical evolution.…”

Search for associations containing young stars (SACY)

“…The large number of RV values calculated in this work was used to revise and refine the member list (da Silva et al 2009). With this new data any targets that no longer had a high probability of membership were removed from the overall analysis and statistics of the associations (initial members and revised members are shown in Table D.1).…”

“…The mass distribution was constructed using effective temperatures from da Silva et al (2009). First, available effective temperature were used directly with age estimates, as given in Torres et al (2006), to obtain a model-based mass using isochrones (Baraffe et al 1998(Baraffe et al , 2003Siess et al 2000).…”

“…The median effective temperature for each spectral subclass within each association was used to estimate a value for those targets with a spectral type, ascalculated by the method described in Torres et al (2006), but without an effective temperature value. Linear interpolation was used for those spectral subclasses without any corresponding temperature values from da Silva et al (2009). In the case of Carina (CAR), effective temperature values for targets of spectral type K3 and later were taken from median values of Tucana-Horologium (THA), which are approximately the same age, and having a much larger population in this spectral type range.…”

Proper motions of young stars in Chamaeleon

“…To assess how clearly we can separate the different populations based on the available proper motions, and to check the possible presence of interlopers from the foreground clusters in our Chamaeleon I and II lists, we compiled two lists of members for the Cha and η Cha associations, merging the catalogues provided by and Fernández et al (2008) for both groups, and adding the objects from the lists by Luhman & Steeghs (2004) in η Cha and by da Silva et al (2009) in Cha. Membership of these objects in the corresponding cluster has been confirmed by several different means, including spectroscopy and proper motions.…”