Abstract

The Her-Lyr assoc., a nearby young MG, contains a few tens of ZAMS stars of SpT F to M. The existence and the properties of the Her-Lyr assoc. are controversial and discussed in the literature. The present work reassesses properties and the member list of Her-Lyr assoc., based on kinematics and age. Many objects form multiple systems or have low-mass companions and so we need to account for multiplicity. We use our own new imaging obs. and archival data to identify multiple systems. The colors and magnitudes of kinematic candidates are compared to isochrones. We derive further information on the age based on Li depletion, rotation, and coronal and chromospheric activity. A set of canonical members is identified to infer mean properties. Membership criteria are derived from the mean properties and used to discard non-members. The candidates selected from the literature belong to 35 stellar systems, 42.9% of which are multiple. Four multiple systems are confirmed in this work by common proper motion. An orbital solution is presented for the binary system HH Leo B and C. Indeed, a group of candidates displays signatures of youth. 7 canonical members are identified. The distribution of EWLi of canonical Her-Lyr members is spread widely and is similar to that of the Pleiades and the UMa group. Gyrochronology gives an age of 257+-46 Myr which is in between the ages of the Pleiades and the Ursa Major group. The measures of chromospheric and coronal activity support the young age. Four membership criteria are presented based on kinematics, EWLi, chromospheric activity, and gyro. age. In total, 11 stars are identified as certain members including co-moving objects plus additional 23 possible members while 14 candidates are doubtful or can be rejected. A comparison to the mass function, however, indicates the presence of a large number of additional unidentified low-mass members.

Highlights

  • The Hercules-Lyra (Her-Lyr) association is one of the closest young moving groups (MGs)

  • The candidates selected from the literature belong to 35 stellar systems, 42.9% of which are multiple

  • Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the MaxPlanck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC). (Eggen 1994)

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Summary

Introduction

The Hercules-Lyra (Her-Lyr) association is one of the closest young moving groups (MGs). Based on observations made with ESO Telescopes at the Paranal Observatory under programs ID: 380.C-0248(A) (Service Mode, VLTYepun) and ID: 074.C-0084(B) (on 2005 Jan. 06, VLT-Yepun). Many nearby young moving groups have been identified with ages below 100 Myr (Zuckerman & Song 2004; Torres et al 2008). They are located at average distances of about 30 pc and beyond (Torres et al 2008)

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