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Distances, Ages, and Epoch of Formation of Globular Clusters
Fusi Pecci, Flavio; Carretta, Eugenio; Clementini, Gisella +1 more
We review the results on distances and absolute ages of Galactic globular clusters (GCs) obtained after the release of the Hipparcos catalog. Several methods aimed at the definition of the Population II local distance scale are discussed, and their results compared, exploiting new results for RR Lyraes in the Large Magellanic Cloud (LMC). We find …
Models for Old, Metal-poor Stars with Enhanced α-Element Abundances. I. Evolutionary Tracks and ZAHB Loci; Observational Constraints
VandenBerg, Don A.; Alexander, David R.; Swenson, Fritz J. +2 more
Stellar evolutionary tracks have been computed for 17 [Fe/H] values from -2.31 to -0.30 assuming, in each case, [α/Fe]=0.0, 0.3, and 0.6. The helium abundance was assumed to vary from Y=0.2352 at [Fe/H]=-2.31 to Y=0.2550 at [Fe/H]=-0.30 and held constant for the different choices of [α/Fe] at a fixed iron content. Masses in the range 0.5<=M
K-Band Calibration of the Red Clump Luminosity
Alves, David R.
The average near-infrared (K-band) luminosity of 238 Hipparcos red clump giants is derived and then used to measure the distance to the Galactic center. These Hipparcos red clump giants have been previously employed as I-band standard candles. The advantage of the K-band is a decreased sensitivity to reddening and perhaps a reduced systematic depe…
Identification of a Nearby Stellar Association in theHipparcos Catalog: Implications for Recent, Local Star Formation
Zuckerman, B.; Webb, R. A.
The TW Hydrae Association (~55 pc from Earth) is the nearest known region of recent star formation. Based primarily on the Hipparcos catalog, we have identified a group of nine or 10 comoving star systems at a common distance (~45 pc) from Earth that appear to comprise another, somewhat older association (``the Tucanae Association''). Together wit…
Magnetic AP Stars in the Hertzsprung-Russell Diagram
Hubrig, S.; North, P.; Mathys, G.
The evolutionary state of magnetic Ap stars is rediscussed using the recently released Hipparcos data. The distribution of the magnetic Ap stars of mass below 3 Msolar in the H-R diagram differs from that of the normal stars in the same temperature range at a high level of significance. Magnetic stars are concentrated toward the center …
The Origin of Runaway Stars
de Bruijne, J. H. J.; de Zeeuw, P. T.; Hoogerwerf, R.
Milliarcsecond astrometry provided by Hipparcos and by radio observations makes it possible to retrace the orbits of some of the nearest runaway stars and pulsars to determine their site of origin. The orbits of the runaways AE Aurigae and µ Columbae and of the eccentric binary ι Orionis intersected each other ~2.5 Myr ago in the nascent Tra…
The η Chamaeleontis Cluster: Origin in the Sco-Cen OB Association
Feigelson, Eric D.; Mamajek, Eric E.; Lawson, Warrick A.
A young, nearby compact aggregate of X-ray-emitting pre-main-sequence stars was recently discovered in the vicinity of η Chamaeleontis. In this paper, we further investigate this cluster: its membership, its environs, and its origins. ROSAT High Resolution Imager X-ray data for the cluster's T Tauri stars show high levels of magnetic activity and …
Mining the Metal-rich Stars for Planets
Laughlin, Gregory
We examine the correlation between stellar metallicity and the presence of short-period planets. It appears that approximately 1% of dwarf stars in the solar neighborhood harbor short-period planets characterized by near-circular orbits and orbital periods P<20 days. However, among the most metal-rich stars (defined as having [Fe/H]>0.2 dex)…
The Optical Gravitational Lensing Experiment: Red Clump Stars as a Distance Indicator
Udalski, A.
We present relation of the mean I-band brightness of red clump stars on metallicity. Red clump stars were proposed to be a very attractive standard candle for distance determination. The calibration is based on 284 nearby red giant stars whose high-quality spectra made it possible to determine accurate individual metal abundances. High-quality par…
Two K Giants with Supermeteoritic Lithium Abundances: HDE 233517 and HD 9746
Henry, Gregory W.; Fekel, Francis C.; Uitenbroek, Han +1 more
Two unusual Li-rich K giants, HDE 233517 and HD 9746, have been studied. Optical spectroscopy and photometry have been obtained to determine the fundamental parameters of HDE 233517, a single K2 III with an extremely large infrared excess. The spectra yield Teff=4475 K, logg=2.25, [Fe/H]=-0.37, vsini=17.6 km s-1, and a non-LT…