We show that the errors in the Hipparcos parallaxes towards the Pleiades and the Hyades open clusters are spatially correlated over angular scales of 2 to 3 degrees, with an amplitude of up to 2 mas. We suggest that this correlation on small angular scales is a generic feature of the Hipparcos parallaxes all over the sky. We predict the parallaxes of individual cluster members, πpm, from their ...

We derive parameters and abundances of several elements in two cool Pleiades dwarfs, four cool NGC 2264 preÈmain-sequence stars, and a probable NGC 2264 nonmember from high-resolution, moderate signal-to-noise ratio, Keck/HIRES spectra. Our Pleiades Fe abundance agrees with previous spectroscopic and photometric values of hotter stars and does not resolve the 0.3 mag distance modulus discrepanc...

Hipparcos parallax measurements of stars in the Pleiades notoriously result in a cluster distance of 118 pc, which is approximately 10% shorter than the 'classical' result obtained from earlier main sequence (MS) fitting studies. In an earlier paper we developed a purely empirical MS-fitting method in an attempt to address this problem. This work produced conflicting results for the Pleiades be...

We report deep 3.6 cm radio observations of a small sample of the most rapidly{ rotating G{K dwarf stars in the Pleiades open cluster. Of the 4 ultra{fast rotators (UFRs) observed, 3 were detected. The G8 dwarf HII 1136, the fastest rotating G dwarf known in the Pleiades cluster, displayed a are that rose to a peak ux density of 1 mJy (peak radio luminosity of 210 16 erg Hz ?1 s ?1) in less tha...

We explore the sensitivity in open cluster ages obtained by the lithium depletion boundary (LDB) technique to the stellar model input physics. The LDB age technique is limited to open clusters with ages ranging from 20 to 200 Myr. Effective 1-σ errors in the LDB technique due to uncertain input physics are roughly 3% at the oldest age increasing to 8% at the youngest age. Bolometric correction ...

We present lithium abundances for ∼50 X-ray selected candidate members of the 30–50 Myr old open clusters IC 2602 and IC 2391. These data enlarge and extend to cooler temperatures previous Li surveys of these clusters by Stauffer et al. (1989) and Randich et al. (1997). We also give for the first time an estimate of the metallicity of the two clusters which turns out to be close to solar. Radia...

We present a reanalysis of the light curves of HD 23642, a detached eclipsing binary star in the Pleiades open cluster, with emphasis on a detailed error analysis. We compare the masses and radii of the two stars to predictions of stellar evolutionary models and find that the metal and helium abundances of the Pleiades are approximately solar. We present a new method for finding distances to ec...

We explore the sensitivity in open cluster ages obtained by the lithium depletion boundary (LDB) technique to the stellar model input physics. The LDB age technique is limited to open clusters with ages ranging from 20 to 200 Myr. Effective 1-σ errors in the LDB technique due to uncertain input physics are roughly 3% at the oldest age increasing to 7% at the youngest age. Bolometric correction ...

We find that a steady state bar induces transient features at low velocities in the solar neighborhood velocity distribution due to the initial response of the disk, following the growth of the bar. We associate these velocity streams with two quasi-periodic orbital families, librating around the stable x1(1) and x1(2) orbits near the bar’s outer Lindblad resonance (OLR). In a reference frame m...

The Pleiades mission is part of the French-Italian ORFEO system (Optical and Radar Federated Earth Observation) and has the aim to provide very-high resolution optical imagery from space for civilian and military needs. Within the Pleiades evaluation program, the 3DOM Unit at the Bruno Kessler Foundation in Trento (Italy) received a triplet by Pleiades-1A over Trento testfield for research purp...