scholarly journals The Age of Old Galactic Populations

1998 ◽  
Vol 11 (1) ◽  
pp. 560-561
Author(s):  
M. Grenon
Keyword(s):  
High Velocity ◽  
Radial Velocities ◽  
Thick Disk ◽  
Early Evolution ◽  
Galactic Bulge ◽  
Colour Class ◽  
The Galaxy ◽  
Nearby Stars

As a preparation to the HIPPARCOS mission, a large observing programme on NLTT stars (propermotion > 0.18 ″/yr) was started in Genevaphotometry. The original programme consists of 10047 stars brighter than mR = 11.5, or mR = 12.5 if of colour class m. Among them, 7813 targets could be included in the HIPPARCOS programme, selected according to their observability and internal priorities in favour of large parallaxe stars (photometric distances < 100 pc) and high-velocity stars. The bulk of new nearby, halo, mild-metal poor and SMR stars in the HIP Catalogue originates from this proposal (N° 139). No less than 208 new nearby stars with π ≥ 40 mas were discovered south of δ +10°, the closest has π(HIP)= 182 mas. Radial velocities were obtained with CORAVEL at OHP and ESO. Most aspects of the early evolution of the Galaxy may be addressed with this sample. Here we discuss, as examples, the ages of the thick disk and of the galactic bulge.

scholarly journals The RAVE harvest: from the relation between abundances and kinematic of the Milky Way stars to tools for the abundance analysis of the spectra

2013 ◽  
Vol 9 (S298) ◽  
pp. 292-297
Author(s):  
Corrado Boeche ◽  
Keyword(s):  
Milky Way ◽  
Radial Velocities ◽  
Proper Motions ◽  
Chemical Abundances ◽  
Stellar Spectra ◽  
Chemical Gradients ◽  
Single Process ◽  
The Galaxy ◽  
Nearby Stars ◽  
Kinematic Information

AbstractRAVE is a spectroscopic survey of the Milky Way which collected more than 500,000 stellar spectra of nearby stars in the Galaxy. The RAVE consortium analysed these spectra to obtain radial velocities, stellar parameters and chemical abundances. These data, together with spatial and kinematic information like positions, proper motions, and distance estimations, make the RAVE database a rich source for galactic archaeology. I present recent investigations on the chemo-kinematic relations and chemical gradients in the Milky Way disk using RAVE data and compare our results with the Besançon models. I also present the code SPACE, an evolution of the RAVE chemical pipeline, which integrates the measurements of stellar parameters and chemical abundances in one single process.

scholarly journals 1.5. SiO maser sources in the Galactic bulge and a kinematic signature of the bar structure

1998 ◽  
Vol 184 ◽  
pp. 25-26
Author(s):  
S. Deguchi
Keyword(s):  
Central Region ◽  
Radial Velocities ◽  
Kinematic Structure ◽  
Agb Stars ◽  
Galactic Bulge ◽  
The Galaxy ◽  
Forbidden Regions ◽  
Maser Sources

We are studying the kinematic structure of our Galaxy by detecting SiO maser lines around 43 GHz with the Nobeyama 45-m telescope. Till today, about 500 IRAS sources (AGB stars) in the central region of the Galaxy are observed and the radial velocities of about 300 detected sources are obtained. The longitude-velocity map of SiO sources clearly shows a presence of forbidden regions (holes) which are located at the same positions of HI and CO holes. The presence of holes is interpreted as a streaming motions of stars due to a bar structure of the Galactic bulge

scholarly journals 4.13. A high velocity molecular cloud near the center of the Galaxy

1998 ◽  
Vol 184 ◽  
pp. 193-194 ◽  
Author(s):  
Tomoharu Oka ◽  
Tetsuo Hasegawa ◽  
Glenn J. White ◽  
Fumio Sato ◽  
Masato Tsuboi ◽  
...  
Keyword(s):  
High Velocity ◽  
Molecular Cloud ◽  
Molecular Clouds ◽  
Galactic Center ◽  
Galactic Disk ◽  
External Pressure ◽  
Galactic Bulge ◽  
Physical Conditions ◽  
Large Velocity ◽  
The Galaxy

Molecular clouds in the Galactic center region are characterised by their large velocity widths and physical conditions which differ from clouds in the Galactic disk (e.g., Morris 1996). These clouds may not be gravitationally bound, but in equilibrium with the high external pressure in the Galactic bulge (Spergel & Blitz 1992, Oka et al. 1997a).

scholarly journals A systematic study of NLTE abundances of nearby stars

2013 ◽  
Vol 9 (S298) ◽  
pp. 400-400
Author(s):  
Y. Q. Chen ◽  
G. Zhao ◽  
L. Mashonkina ◽  
J. R. Shi ◽  
H. W. Zhang ◽  
...  
Keyword(s):  
Chemical Evolution ◽  
Systematic Study ◽  
Stellar Populations ◽  
Thin Disk ◽  
Thick Disk ◽  
Spectral Lines ◽  
Surface Gravity ◽  
Elemental Abundances ◽  
The Galaxy ◽  
Nearby Stars

AbstractApproximately 80 stars from the thin disk, the thick disk and the halo of the Galaxy, in the range of −3.0 < [Fe/H] < +0.5, surface gravity of 3.0 < logg < 4.7 and temperature of 4500 K < Teff < 6500 K, have been observed with the Shane/Hamilton and CFHT/Espadons spectrographs in order to carry out a systematic NLTE study of nearby stars in a consistent way. We will determine reliably stellar parameters and determine precise elemental abundances via a comprehensive NLTE analysis of the spectral lines of Li, Na, Mg, Al, Si, K, Ca, Sc, Mn, Fe, Sr, Zr, Ba, Nd, and Eu elements. Finally, we aim to investigate the chemical evolution of the Galaxy through different stellar populations based on the NLTE abundances for total 15 elements.

scholarly journals Element Abundance Analysis of the Metal-rich Stellar Halo and High-velocity Thick Disk in the Galaxy

2021 ◽  
Vol 915 (1) ◽  
pp. 9
Author(s):  
Haifan Zhu ◽  
Cuihua Du ◽  
Yepeng Yan ◽  
Jianrong Shi ◽  
Jun Ma ◽  
...  
Keyword(s):  
High Velocity ◽  
Thick Disk ◽  
Element Abundance ◽  
The Galaxy ◽  
Stellar Halo

scholarly journals Existence of the Metal-rich Stellar Halo and High-velocity Thick Disk in the Galaxy

2020 ◽  
Vol 903 (2) ◽  
pp. 131
Author(s):  
Yepeng Yan ◽  
Cuihua Du ◽  
Hefan Li ◽  
Jianrong Shi ◽  
Jun Ma ◽  
...  
Keyword(s):  
High Velocity ◽  
Thick Disk ◽  
The Galaxy ◽  
Stellar Halo

scholarly journals The Galactic Bulge

2016 ◽  
Vol 33 ◽  
Author(s):  
B. Barbuy
Keyword(s):  
Globular Clusters ◽  
Stellar Population ◽  
Thick Disk ◽  
Galactic Bulge ◽  
Multiple Populations ◽  
Secular Evolution ◽  
Rr Lyrae ◽  
The Galaxy ◽  
Formation And Evolution

AbstractThe Galactic bulge is the least studied component of our Galaxy. Yet, its formation and evolution are key to understand the formation of the Galaxy itself. Studies on the Galactic bulge have increased significantly in the last years, but still there are many points of controversy. This volume contains several contributions from experts in different aspects of the bulge. Issues discussed include the following: the presence of an old spheroidal bulge, or identification of its old stellar population with the thick disk or halo; fraction of stars younger than 10 Gyr is estimated to be of < 5 to 22% depending on method and authors; multiple populations or only a metal-poor and a metal-rich ones; spheroidal or ellipsoidal distribution of RR Lyrae; formation of the bulge from early mergers or from secular evolution of the bar; different methods of mapping extinction; selection and identification of bulge globular clusters.

Galactic orbits of stars

1966 ◽  
Vol 25 ◽  
pp. 93-97
Author(s):  
Richard Woolley
Keyword(s):  
Globular Cluster ◽  
Potential Field ◽  
High Velocity ◽  
Velocity Vector ◽  
Variable Stars ◽  
The Sun ◽  
Proper Motions ◽  
Rr Lyrae ◽  
The Galaxy

It is now possible to determine proper motions of high-velocity objects in such a way as to obtain with some accuracy the velocity vector relevant to the Sun. If a potential field of the Galaxy is assumed, one can compute an actual orbit. A determination of the velocity of the globular clusterωCentauri has recently been completed at Greenwich, and it is found that the orbit is strongly retrograde in the Galaxy. Similar calculations may be made, though with less certainty, in the case of RR Lyrae variable stars.

scholarly journals Abundances in the Gaseous Galactic Halo

1998 ◽  
Vol 11 (1) ◽  
pp. 86-89
Author(s):  
Ulysses J. Sofia
Keyword(s):  
Interstellar Medium ◽  
Gas Phase ◽  
High Velocity ◽  
Galactic Halo ◽  
Solar Neighborhood ◽  
Local Interstellar Medium ◽  
The Galaxy ◽  
Metal Abundances ◽  
High Velocity Clouds

Abstract The well measured gas-phase abundances in the low halo suggest that this region of the Galaxy has total (gas plus dust) metal abundances which are close to those in the solar neighborhood. The gas-phase abundances in the halo are generally higher than those seen in the disk, however, this affect is likely due to the destruction of dust in the halo clouds. Observations of high velocity clouds (HVCs) in the halo suggest that these clouds have metal abundances which are substantially lower than those measured for the local interstellar medium. These determinations, however, are often of lower quality than those for the low halo because of uncertainties in the hydrogen abundances along the sightlines, in the incorporation of elements into dust, and in the partial ionization of the clouds.

scholarly journals A quantitative spectral analysis of 14 hypervelocity stars from the MMT survey

2018 ◽  
Vol 615 ◽  
pp. L5 ◽  
Author(s):  
A. Irrgang ◽  
S. Kreuzer ◽  
U. Heber ◽  
W. Brown
Keyword(s):  
Main Sequence ◽  
Galactic Center ◽  
Radial Velocities ◽  
Stellar Ages ◽  
The Galaxy ◽  
Quantitative Spectral Analysis ◽  
Kinematic Studies ◽  
Ejection Mechanism ◽  
Photometric Measurements ◽  
Stellar Masses

Context. Hypervelocity stars (HVSs) travel so fast that they may leave the Galaxy. The tidal disruption of a binary system by the supermassive black hole in the Galactic center is widely assumed to be their ejection mechanism. Aims. To test the hypothesis of an origin in the Galactic center using kinematic investigations, the current space velocities of the HVSs need to be determined. With the advent of Gaia’s second data release, accurate radial velocities from spectroscopy are complemented by proper motion measurements of unprecedented quality. Based on a new spectroscopic analysis method, we provide revised distances and stellar ages, both of which are crucial to unravel the nature of the HVSs. Methods. We reanalyzed low-resolution optical spectra of 14 HVSs from the MMT HVS survey using a new grid of synthetic spectra, which account for deviations from local thermodynamic equilibrium, to derive effective temperatures, surface gravities, radial velocities, and projected rotational velocities. Stellar masses, radii, and ages were then determined by comparison with stellar evolutionary models that account for rotation. Finally, these results were combined with photometric measurements to obtain spectroscopic distances. Results. The resulting atmospheric parameters are consistent with those of main sequence stars with masses in the range 2.5–5.0 M⊙. The majority of the stars rotate at fast speeds, providing further evidence for their main sequence nature. Stellar ages range from 90 to 400 Myr and distances (with typical 1σ-uncertainties of about 10–15%) from 30 to 100 kpc. Except for one object (B 711), which we reclassify as A-type star, all stars are of spectral type B. Conclusions. The spectroscopic distances and stellar ages derived here are key ingredients for upcoming kinematic studies of HVSs based on Gaia proper motions.

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