Flare stars in the TW Hydrae association: the HIP 57269 syste

Abstract

We discuss a new member candidate of the TW Hydrae association (TWA) among the stars of the Gershberg et al. ( te{gershberg}) flare star catalog. TWA is one of the closest known associations of young stars at about 60 pc. Three supposedly young flare stars are located in the same region of the sky as TWA. One of them (HIP 57269) shows strong lithium absorption with spectral type K1/K2V and a high level of chromospheric and coronal activity. It is located at a distance of 48.7±6.3 pc in common with the five TWA members observed with Hipparcos (46.7 to 103.9 pc). HIP 57268 A has a wide companion C which also shows lithium absorption at 6707 Å and which has common proper motion with HIP 57269, as well as a close companion resolved visually by Tycho. HIP 57269 A&C lie above the main sequence and are clearly pre-main-sequence stars. The UVW-space velocity is more consistent with the star system being a Pleiades super cluster member. The two other flare stars in the TWA sky region do not show lithium at all and are, hence, unrelated.

Data obtained at ESO La Silla and ESO Paranal with programs: 66.C-0138(B), 67.C-0073(A), 68.C-0009(A), 68.C-0018(A)