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J/AJ/115/168        Kinematics of red giant and RR Lyrae stars (Chiba+ 1998)

Early evolution of the Galactic halo revealed from Hipparcos observations of metal-poor stars Chiba M., Yoshii Y. <Astron. J. 115, 168 (1998)> =1998AJ....115..168C
ADC_Keywords: Stars, giant ; Stars, variable ; Proper motions Mission_Name: Hipparcos Keywords: Galaxy: abundances - Galaxy: evolution - Galaxy: halo Abstract: 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. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 127 298 Program stars
See also: I/196 : Hipparcos Input Catalogue, Version 2 (Turon+ 1993) I/239 : The Hipparcos and Tycho Catalogues (ESA 1997) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 2 A2 --- Type [RG] Type of the stars, as RG = Red giants; RR = RR Lyrae 4- 9 I6 --- HIC(P) HIC or HIP (Cat. I/239) number 11- 22 A12 --- Name Other name 24- 29 F6.2 mas plx Trigonometric parallax 31- 35 F5.2 mas e_plx rms uncertainty on plx 37- 43 F7.2 mas/yr pmRA* Proper motion in RA time cosδ 45- 49 F5.2 mas/yr e_pmRA* rms uncertainty on pmRA* 51- 57 F7.2 mas/yr pmDE Proper motion in DE 59- 63 F5.2 mas/yr e_pmDE rms uncertainty on pmDE 65- 69 F5.3 kpc Dist ? Photometric heliocentric distance 71- 75 F5.3 kpc e_Dist ? rms uncertainty on Dist 77- 81 F5.2 [Sun] [Fe/H] ? Metallicity 83- 86 F4.2 [Sun] e_[Fe/H] ? rms uncertainty on [Fe/H] 88- 94 F7.2 km/s RV ? Radial velocity 96-100 F5.2 km/s e_RV ? rms uncertainty on RV 102-107 F6.3 arcsec/yr pmRAo ? Old proper motion in RA 109-114 F6.3 arcsec/yr pmDEo ? Old proper motion in DE 116-117 A2 --- rf1 References for Dist and [Fe/H] (1) 118 A1 --- --- [/] 119-123 A5 --- rf2 References for RV (2) 124 A1 --- --- [/] 125 I1 --- rf3 ? References for proper motions (3)
Note (1): References for Dist and [Fe/H] as follows: 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 Note (2): References of radial velocity as follows: 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 Note (3): References of proper motion as follows: 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
History: Copied from the electronic version of AJ
(End) Patricia Bauer [CDS] 10-Mar-1998

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