scholarly journals Galactic mass and anisotropy profile with halo K-giant and blue horizontal branch stars from LAMOST/SDSS and Gaia

2019 ◽  
Vol 14 (S353) ◽  
pp. 91-95
Author(s):  
Sarah A. Bird ◽  
Xiang-Xiang Xue ◽  
Chao Liu ◽  
Juntai Shen ◽  
Chris Flynn ◽  
...  
Keyword(s):  
Velocity Dispersion ◽  
Galactic Halo ◽  
Anisotropy Parameter ◽  
Horizontal Branch ◽  
Stellar Kinematics ◽  
Horizontal Branch Stars ◽  
Wide Range ◽  
Stellar Halo ◽  
Mass Profile

AbstractA major uncertainty in the determination of the mass profile of the Milky Way using stellar kinematics in the halo is the poorly determined anisotropy parameter, , where σr is the Galactocentric radial velocity dispersion, and σθ and σφ are the tangential components of the velocity dispersion. We have used a sample of over 24,000 Galactic halo K giant and blue horizontal branch stars from the LAMOST stellar spectroscopic survey and SDSS/SEGUE, combined with proper motions from Gaia Data Release 2, to measure β(rgc) over a wide range of Galactocentric distances rgc from 5 to 80 kpc. Kinematic substructures have been carefully removed to reveal the underlying diffuse stellar halo prior to measuring β. We find that orbits are generally radial (β > 0) and β is constant out to distances of about 40 kpc, with a dependence on metallicity of the stars, such that β declines with lower metallicity. Similar behavior is seen in both the K giant and BHB samples.

scholarly journals Early-Type Stars

1995 ◽  
Vol 164 ◽  
pp. 119-127
Author(s):  
K.C. Freeman
Keyword(s):  
Main Sequence ◽  
Velocity Dispersion ◽  
Galactic Rotation ◽  
Horizontal Branch ◽  
Early Type ◽  
Horizontal Branch Stars ◽  
The Galaxy ◽  
Stellar Halo ◽  
Early Type Stars ◽  
Insight Into

Away from the young disk, several classes of early type stars are found. They include (i) the old, metal-poor blue horizontal branch stars of the halo and the metal-poor tail of the thick disk; (ii) metal-rich young A stars in a rapidly rotating subsystem but with a much higher velocity dispersion than the A stars of the young disk, and (iii) a newly discovered class of metal-poor young main sequence A stars in a subsystem of intermediate galactic rotation (Vrot ≈ 120 km s−1). The existence and kinematics of these various classes of early type stars provide insight into the formation of the metal-poor stellar halo of the Galaxy and into the continuing accretion events suffered by our Galaxy.

scholarly journals Stars in the Galactic Halo

1995 ◽  
Vol 164 ◽  
pp. 75-83
Author(s):  
T.D. Kinman
Keyword(s):  
Globular Clusters ◽  
Galactic Halo ◽  
Horizontal Branch ◽  
Field Star ◽  
Horizontal Branch Stars

The field star halo is comprised of those field stars that are like the stars found in the halo globular clusters. We discuss the halo properties — in particular whether Vrot is a function of z. An analysis of recent surveys for blue horizontal branch stars is described; the halo that is defined by these stars is composite and contains both a spherical and flat component.

scholarly journals Enhanced cluster lensing models with measured galaxy kinematics

2019 ◽  
Vol 631 ◽  
pp. A130 ◽  
Author(s):  
P. Bergamini ◽  
P. Rosati ◽  
A. Mercurio ◽  
C. Grillo ◽  
G. B. Caminha ◽  
...  
Keyword(s):  
Mass Distribution ◽  
Velocity Dispersion ◽  
Stellar Kinematics ◽  
Multiple Images ◽  
Effective Velocity ◽  
Strong Lensing ◽  
The Galaxy ◽  
Galaxy Kinematics ◽  
Halo Masses

We present an improved determination of the total mass distribution of three massive clusters from the Cluster Lensing and Supernova Survey with Hubble and Hubble Frontier Fields, MACS J1206.2−0847 (z = 0.44), MACS J0416.1−2403 (z = 0.40), Abell S1063 (z = 0.35). We specifically reconstructed the sub-halo mass component with robust stellar kinematics information of cluster galaxies, in combination with precise strong lensing models based on large samples of spectroscopically identified multiple images. We used integral-field spectroscopy in the cluster cores, from the Multi Unit Spectroscopic Explorer on the Very Large Telescope, to measure the stellar velocity dispersion, σ, of 40−60 member galaxies per cluster, covering four to five magnitudes to mF160W ≃ 21.5. We verified the robustness and quantified the accuracy of the velocity dispersion measurements with extensive spectral simulations. With these data, we determined the normalization and slope of the galaxy L–σ Faber–Jackson relation in each cluster and used these parameters as a prior for the scaling relations of the sub-halo population in the mass distribution modeling. When compared to our previous lens models, the inclusion of member galaxies’ kinematics provides a similar precision in reproducing the positions of the multiple images. However, the inherent degeneracy between the central effective velocity dispersion, σ0, and truncation radius, rcut, of sub-halos is strongly reduced, thus significantly alleviating possible systematics in the measurements of sub-halo masses. The three independent determinations of the σ0 − rcut scaling relation in each cluster are found to be fully consistent, enabling a statistical determination of sub-halo sizes as a function of σ0, or halo masses. Finally, we derived the galaxy central velocity dispersion functions of the three clusters projected within 16% of their virial radius, finding that they are well in agreement with each other. We argue that such a methodology, when applied to high-quality kinematics and strong lensing data, allows the sub-halo mass functions to be determined and compared with those obtained from cosmological simulations.

scholarly journals The Distribution of Field Horizontal–Branch Stars in the Galactic Halo

1977 ◽  
Vol 4 (2) ◽  
pp. 73-74
Author(s):  
A. G. Davis Philip
Keyword(s):  
Density Distribution ◽  
Galactic Halo ◽  
Galactic Plane ◽  
Horizontal Branch ◽  
Schmidt Telescope ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Horizontal Branch Stars ◽  
General Program ◽  
Objective Prism

Since the time allowed per paper at this joint discussion is short only one aspect of the stellar distribution at high galactic latitudes will be presented here, namely the distribution of field horizontal-branch stars (FHB) in the galactic halo. First, the method by which FHB stars are found will be described. Second, the density distribution of FHB stars will be compared with that of the RR Lyrae stars.As part of a general program to study the stellar density distribution perpendicular to the galactic plane a number of possible FHB stars has been discovered. In each survey area objective prism plates (at a dispersion of 280 Å/mm. to a limiting magnitude of V = 14) are taken with the Michigan Curtis Schmidt telescope at Cerro Tololo Inter-American Observatory or the Schmidt telescope at the Warner and Swasey Observatory. A set of direct plates are taken also to obtain photographic magnitudes for the stars with spectral classifications.

scholarly journals Spectral Characteristics of A-Type Stars in the Galactic Halo

1993 ◽  
Vol 138 ◽  
pp. 432-436
Author(s):  
C.J. Corbally ◽  
R.O. Gray
Keyword(s):  
Galactic Halo ◽  
Spectral Characteristics ◽  
Horizontal Branch ◽  
Dwarf Stars ◽  
Horizontal Branch Stars

AbstractAmong 67 early A-type stars at high galactic latitudes, selected to have both small m1 and large c1 Strömgren photometric indices, we find about one third to have quite normal dwarf or subgiant spectra at MK classification dispersion. Those stars with peculiarities included 10 new λ Bootis stars, though none of these appeared significantly evolved. We wonder whether some of the metal-weak dwarf stars in our set may be field horizontal-branch equivalents of the blue, downward-curving, low-luminosity end of the blue horizontal-branch stars.

scholarly journals Structure of the Milky Way stellar halo out to its outer boundary with blue horizontal-branch stars

2018 ◽  
Vol 70 (4) ◽  
Author(s):  
Tetsuya Fukushima ◽  
Masashi Chiba ◽  
Daisuke Homma ◽  
Sakurako Okamoto ◽  
Yutaka Komiyama ◽  
...  
Keyword(s):  
Milky Way ◽  
Outer Boundary ◽  
Horizontal Branch ◽  
Horizontal Branch Stars ◽  
Stellar Halo
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