Abstract. EK Dra (HD 129333) is a young, active, nearby star that is orbited by a low mass companion. By combining new speckle observations with old and new radial velocity measurements we find that the orbit is highly eccentric with e = 0.82 ± 0.03, and we derive the true masses of both components. The masses are 0.9 ± 0.1 M and 0.5 ± 0.1 M , for the primary and secondary, respectively. From high resolution spectra we derive a new T eff of 5700 ± 70 K and a log g of 4.37 ± 0.10, which is different to previous estimates. However, the new spectroscopic distance differs by only 5.8% to the distance derived by parallax measurement by the Hipparcos satellite and thus the stellar parameters are presumably more realistic than older determinations. We derive a somewhat higher value for the metallicity of [Fe/H] = −0.16 ± 0.07. EK Dra turns out to be one of the few nearby young stars that will evolve similarly to the Sun. The precise radial velocity measurements taken in the course of this program also allow us to shed more light on the activity of this star. In 2001 and 2002 we find radial velocity variation with a period of 2.767 ± 0.005 days which we interpret as the rotation period. This signal vanishes in 2003. However the signal can be recovered if only the spectra in which the photospheric lines are asymmetric are used. On the other hand, we do not find a close correlation between the asymmetry of photospheric lines and the radial velocity.

We report HST/STIS spectroscopy and Gemini/GMOS-N imaging of the Damped Lyman Alpha (DLA) system toward HS 1543+5921 caused by the host star-forming galaxy (SFG) SBS 1543+593. The Gemini image shows new morphological details of this well resolved DLA galaxy. In combination with previous optical spectra, the new UV spectra enable us to compare for the first time, ionized and neutral gas-phase alpha-element abundances derived from emission-and absorption-line spectroscopy, in a bona fide DLA galaxy. The abundances we determine using emission-line diagnostics agree with those from absorption-line diagnostics. We present our results on a metallicity versus redshift diagram that combines local HII regions and SFGs with high-redshift DLAs, and discuss implications for the chemical evolution of galaxies.

We report the discovery of the nearby (d= 24 pc) HD 75767 as an eight billion year old quadruple system consisting of a distant M dwarf pair, HD 75767 C–D, in orbit around the known short‐period P= 10.25 d single‐lined binary HD 75767 A–B, the primary of which is a solar‐like G star. On the reasonable assumption of synchronous orbital rotation as well as rotational and orbital coplanarity for the inner pair, we get MB= 0.96 M⊙ for the unseen HD 75767 B, that is, the case of a massive white dwarf. Upon future evolution, mass transfer towards HD 75767 B will render the MA= 0.96 M⊙ G‐type primary, now a turnoff star, to become a helium white dwarf of MA∼ 0.33 M⊙. Depending on the mass accretion rate, accretion efficiency and composition of the massive white dwarf, this in turn may result in a collapse of HD 75767 B with the formation of a millisecond pulsar, i.e. the creation of a low‐mass binary pulsar (LMBP), or, instead, a Type Ia supernova explosion and the complete disruption of HD 75767 B. Irrespective of which scenario applies, we point to the importance of the distant M dwarfs as the likely agents for the formation of the inner, short‐period HD 75767 A–B pair, and hence a path that particularly avoids preceding phases of common envelope evolution.

Abstract.We present an H-band image of the companion of χ 1 Orionis taken with the Keck adaptive optic system and NIRC 2 camera equipped with a 300 mas-diameter coronographic mask. The direct detection of this companion star enables us to calculate dynamical masses using only Kepler's laws (M A = 1.01 ± 0.13 M , M B = 0.15 ± 0.02 M ), and to study stellar evolutionary models at a wide spread of masses. The application of Baraffe et al. (1998) pre-main-sequence models implies an age of 70-130 Myrs. This is in conflict to the age of the primary, a confirmed member of the Ursa Major Cluster with a canonical age of 300 Myrs. As a consequence, either the models at low masses underestimate the age or the Ursa Major Cluster is considerably younger than assumed.