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J/AJ/115/168 Kinematics of red giant and RR Lyrae stars (Chiba+ 1998)
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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 (SIMBAD/NED BibCode)
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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:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 127 298 Program stars
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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
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Bytes Format Units Label Explanations
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1- 2 A2 --- Type [RG] Type of the stars
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 cos{delta}
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 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 pmRAold ? Old proper motion in RA
109-114 F6.3 arcsec/yr pmDEold ? Old proper motion in DE
116-117 A2 --- r_Dist References for Dist and [Fe/H] (1)
118 A1 --- --- [/]
119-123 A5 --- r_RV References for RV (2)
124 A1 --- --- [/]
125 I1 --- r_pmRA* ? References for proper motions (3)
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Note (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
Note (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>
Note (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
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History: Copied from the electronic version of AJ
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(End) Patricia Bauer [CDS] 10-Mar-1998