The Hercules-Lyra association revisited

Abstract

Context. The Hercules-Lyra association, a purported nearby young moving group, contains a few tens of zero age main sequence stars of spectral types F to M. The existence and the properties of the Her-Lyr association are controversial and have been discussed in the literature. Aims. The present work reassesses the properties and the member list of the Her-Lyr association based on kinematics and age indicators. Many objects form multiple systems or have low-mass companions and so we need to properly account for multiplicity. Methods. We use our own new imaging observations 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. Results. The candidates selected from the literature belong to 35 stellar systems, 42.9% of which are multiple. Four multiple systems (V538 Aur, DX Leo, V382 Ser, and HH Leo) are confirmed in this work by common proper motion. An orbital solution is presented for the binary system which forms a hierarchical triple with HH Leo. Indeed, a group of candidates displays signatures of youth. Seven canonical members are identified The distribution of Li equivalent widths 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 roughly 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, lithium equivalent width, chromospheric activity, and gyrochronological age. In total, eleven 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 low-mass members, which remain unidentified.

Activity and magnetic field structure of the Sun-like planet-hosting star HD 1237

“…Placing these measurements in the context of other stars, similar variations have been observed in the long-term monitoring of the active Sun-like star ξ Boo A (∼4-9 G, Age: ∼0.2 Gyr, Mamajek & Hillenbrand 2008;Morgenthaler et al 2012), the K-dwarf exoplanet host Eri (∼10-12 G, Age: ∼0.2-0.8 Gyr, Janson et al 2008;Jeffers et al 2014b), and more recently for the young solar analogue HN Peg (∼14 G, Age: ∼0.2 Gyr, Eisenbeiss et al 2013;Boro Saikia et al 2015). The chromospheric and X-ray activity levels of these stars are also very similar to HD 1237.…”

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

“…Again, we find that 2MASS J0213+3648 AB does not match any known young moving groups and lies outside the loosely defined young ( 125 Myr) Local Association (Zuckerman & Song 2004). We also found that 2MASS J0213+3648 AB did not match the kinematics of other groups not shown in our plot: Octans (Murphy & Lawson 2014), Hercules-Lyra (Eisenbeiss et al 2013), 32 Ori (Mamajek 2006), Carina Near (Zuckerman et al 2006) and Ursa Majoris (King et al 2003).…”

LACEwING: A New Moving Group Analysis Code

“…Where no uncertainty is quoted, the uncertainty is set at 50 mÅ. This matches the limits of several major papers reporting lithium, including Eisenbeiss et al (2013), Kraus et al (2014b), and Rodriguez et al (2013); the largest upper limits reported by Malo et al (2013) and Moór et al (2013) are 46 mÅ.…”

“…3. Eisenbeiss et al (2013) conducted an analysis of Her-Lyr using gyrochronology, isochrone fits, lithium abundances, and chromospheric activity, concluding with the identification of seven "canonical" members, which we adopt as bona fide members. 4.…”