We present an abundance analysis of the heavy elements Zr, Ba, La, Ce, and Nd for Hyades cluster F-K dwarfs based on high resolution, high S/N ratio spectra from Keck/HIRES. The derived abundances show the stellar members to be highly uniform, although some elements show a small residual trend with temperature. The rms scatter for each element for the cluster members is as follows; Zr = 0.055 dex, Ba = 0.049 dex, Ce = 0.025 dex, La = 0.025 dex, Nd = 0.032 dex. This is consistent with the measurement errors, and implies that there is little or no intrinsic scatter among the Hyades members. Several stars thought to be non-members of the cluster based on their kinematics are found to deviate from the cluster mean abundances by about 2sigma. Establishing chemical homogeneity in open clusters is the primary requirement for the viability of chemically tagging Galactic disk stars to common formation sites, in order to unravel the dissipative history of early disk formation.Comment: Accepted for publication in A

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We present a differential abundance analysis of Hyades F-K dwarfs in search for evidence of stellar enrichment from accreted hydrogen-deficient disk material. Metallicities and relative abundance ratios of several species have been determined. We derive a cluster mean [Fe/H ¼ 0:13 AE 0:01. Two stars show abundances $0.2 dex larger than the cluster mean. In addition, one star, which was added by a recent study as a cluster member, shows significantly lower abundances than the cluster mean. These three stars have questionable membership characteristics. The remaining stars in the survey have an rms of 0.04 dex in the differential [Fe/H] values. The Hyades cluster members have apparently not been significantly chemically enriched. The abundance ratios of Si, Ti, Na, Mg, Ca, and Zn with respect to Fe are in their solar proportions.

Hubble Space Telescope (HST ) observations of the nearby (3.22 pc), K2 V star ǫ Eridani have been combined with ground-based astrometric and radial velocity data to determine the mass of its known companion. We model the astrometric and radial velocity measurements simultaneously to obtain the parallax, proper motion, perturbation period, perturbation inclination, and perturbation size. Because of the long period of the companion, ǫ Eri b, we extend our astrometric coverage to a total of 14.94 years (including the three year span of the HST data) by including lower-precision ground-based astrometry from the Allegheny Multichannel Astrometric Photometer. Radial velocities now span 1980.8 -2006.3. We obtain a perturbation period, P = 6.85 ± 0.03 yr, semi-major axis α = 1.88 ± 0.20 mas, and inclination i = 30. • 1 ± 3. • 8. This inclination is consistent with a previously measured dust disk inclination, suggesting coplanarity. Assuming a primary mass M * = 0.83M ⊙ , we obtain a companion mass M = 1.55 ± 0.24 M Jup . Given the relatively young age of ǫ Eri (∼800 Myr), this accurate exoplanet mass and orbit can usefully inform future direct imaging attempts. We predict the next periastron at 2007.3 with a total separation, ρ = 0. ′′ 3 at position angle, p.a. = -27 • . Orbit orientation and geometry dictate that ǫ Eri b will appear brightest in reflected light very nearly at periastron. Radial velocities spanning over 25 years indicate an acceleration consistent with a Jupiter-mass object with a period in excess of 50 years, possibly responsible for one feature of the dust morphology, the inner cavity.

Over the six years since the discovery of the gamma-ray burst GRB 980425, which was associated with the nearby (distance approximately 40 Mpc) supernova 1998bw, astronomers have debated fiercely the nature of this event. Relative to bursts located at cosmological distance (redshift z approximately 1), GRB 980425 was under-luminous in gamma-rays by three orders of magnitude. Radio calorimetry showed that the explosion was sub-energetic by a factor of 10. Here we report observations of the radio and X-ray afterglow of the recent GRB 031203 (refs 5-7), which has a redshift of z = 0.105. We demonstrate that it too is sub-energetic which, when taken together with the low gamma-ray luminosity, suggests that GRB 031203 is the first cosmic analogue to GRB 980425. We find no evidence that this event was a highly collimated explosion viewed off-axis. Like GRB 980425, GRB 031203 appears to be an intrinsically sub-energetic gamma-ray burst. Such sub-energetic events have faint afterglows. We expect intensive follow-up of faint bursts with smooth gamma-ray light curves (common to both GRB 031203 and 980425) to reveal a large population of such events.