J/AJ/115/168 J/AJ/115/168 Kinematics of red giant and RR Lyrae stars M Chiba Y Yoshii Astron. J. 115 168 1998 1998AJ....115..168C I/196 : Hipparcos Input Catalogue, Version 2 (Turon+ 1993) I/239 : The Hipparcos and Tycho Catalogues (ESA 1997) Proper motions Stars, giant Stars, variable Galaxy: abundances Galaxy: evolution Galaxy: halo The kinematics of 122 red giant and 124 RR Lyrae stars in the solar neighborhood are studied using accurate measurements of their proper motions obtained by the Hipparcos astrometry satellite, combined with their published photometric distances, metal abundances, and radial velocities. A majority of these sample stars have metal abundances of [Fe/H]<=-1 and thus represent the old stellar populations in the Galaxy. The halo component, with [Fe/H]<=-1.6, is characterized by a lack of systemic rotation [(<U>, <V>, <W>)=(16+/-18, -217+/-21, -10+/-12)km/s] and a radially elongated velocity ellipsoid [(<U>, <V>, <W>)=(161+/-10, 115+/-7, 108+/-7)km/s]. About 16% of such metal-poor stars have low orbital eccentricities (e<0.4), and we see no evidence of a correlation between [Fe/H] and e. Based on the model for the e-distribution of orbits, we show that this fraction of low-e stars for [Fe/H]<=-1.6 is explained by the halo component alone, without introducing the extra disk component claimed by recent workers. This is also supported by the absence of a significant change in the e-distribution with height from the Galactic plane. In the intermediate-metallicity range (-1.6<[Fe/H]<=-1), we find that stars with disklike kinematics have only modest effects on the distributions of rotational velocities and e for the sample at |z|<1kpc. This disk component appears to constitute only 10% for -1.6<[Fe/H]<=-1 and 20% for -1.4<[Fe/H]<=-1. It is also verified that this metal-weak disk has a mean rotation of ~195km/s and a vertical extent of 1 kpc, which is consistent with the thick disk's dominating at [Fe/H]=-0.6 to -1. We find no metallicity gradient in the halo, whereas there is an indication of a metallicity gradient in the metal-weak tail of the thick disk. The implications of these results for the early evolution of the Galaxy are also presented.

Hipparcos

Type Type of the stars RG: Red giants; RR: RR Lyrae --- HIC(P) HIC or HIP (Cat. <I/239>) number --- Name Other name --- plx Trigonometric parallax mas e_plx rms uncertainty on plx mas pmRA* Proper motion in RA time cos{delta} mas/yr e_pmRA* rms uncertainty on pmRA mas/yr pmDE Proper motion in DE mas/yr e_pmDE rms uncertainty on pmDE mas/yr Dist Photometric distance kpc e_Dist rms uncertainty on Dist kpc [Fe/H] Metallicity [Sun] e_[Fe/H] rms uncertainty on [Fe/H] [Sun] RV Radial velocity km/s e_RV rms uncertainty on RV km/s pmRAold Old proper motion in RA arcsec/yr pmDEold Old proper motion in DE arcsec/yr r_Dist References for Dist and [Fe/H] number=1 1: Anthony-Twarog & Twarog, 1994AJ....107.1577A, Cat. <J/AJ/107/1577> 1s: Spectroscopic abundances compiled by Anthony-Twarog & Twarog, 1994 2: Bond, 1980ApJS...44..517B 2s: Spectroscopic abundances compiled by Anthony-Twarog & Twarog, 1994 3: Layden, 1994AJ....108.1016L, Cat. <J/AJ/108/1016> 4: Layden et al., 1996AJ....112.2110L --- --- --- r_RV References for RV number=2 1: Bond 1980ApJS...44..517B 2: Carney & Latham, 1986AJ.....92...60C 3: Norris, Bessell & Pickles, 1985 4: Barbier-Brossat, 1989A&AS...80...67B, Cat. <III/161> 5: Wilson, 1953, Cat. <III/21> 6: Evans, 1978BICDS..15..121J, Cat. <III/42> 7: Griffin et al., 1982MNRAS.198..637G 8: Papers quoted by Bond, 1980ApJS...44..517B 9: Layden, 1994AJ....108.1016L, Cat. <J/AJ/108/1016> --- --- --- r_pmRA* References for proper motions number=3 1: Lick Northern Proper Motion Catalogue, Cat. <I/199> 2: Hipparcos Input Catalogue, Cat. <I/196> 3: Wan, Mao & Ji, 1980, Ann. Shanghai Obs., 2, 1 --- Patricia Bauer CDS 1998Mar10 UNKNOWN UNKNOWN Copied from the electronic version of AJ J_AJ_115_168.xml