The density distribution of the Galactic stellar halo as traced by blue horizontal branch stars

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.

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Early-Type Stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900108484 ◽

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.

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

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/psy060 ◽

2018 ◽

Vol 70 (4) ◽

Cited By ~ 8

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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Contribution of Gaia Sausage to the Galactic Stellar Halo Revealed by K Giants and Blue Horizontal Branch Stars from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, Sloan Digital Sky Survey, and Gaia

The Astrophysical Journal ◽

10.3847/1538-4357/ac31ac ◽

2022 ◽

Vol 924 (1) ◽

pp. 23

Author(s):

Wenbo Wu ◽

Gang Zhao ◽

Xiang-Xiang Xue ◽

Sarah A. Bird ◽

Chengqun Yang

Keyword(s):

Gaussian Mixture ◽

Sloan Digital Sky Survey ◽

Horizontal Branch ◽

Integrals Of Motion ◽

Eccentric Orbits ◽

Horizontal Branch Stars ◽

Sky Survey ◽

Stellar Halo ◽

The Mean ◽

K Giants

Abstract We explore the contribution of the Gaia Sausage to the stellar halo of the Milky Way by making use of a Gaussian mixture model (GMM) and applying it to halo star samples of Large Sky Area Multi-Object Fiber Spectroscopic Telescope K giants, Sloan Extension for Galactic Understanding and Exploration K giants, and Sloan Digital Sky Survey blue horizontal branch stars. The GMM divides the stellar halo into two parts, of which one represents a more metal-rich and highly radially biased component associated with an ancient, head-on collision referred to as the Gaia Sausage, and the other one is a more metal-poor and isotropic halo. A symmetric bimodal Gaussian is used to describe the distribution of spherical velocity of the Gaia Sausage, and we find that the mean absolute radial velocity of the two lobes decreases with the Galactocentric radius. We find that the Gaia Sausage contributes about 41%–74% of the inner (Galactocentric radius r gc < 30 kpc) stellar halo. The fraction of stars of the Gaia Sausage starts to decline beyond r gc ∼ 25–30 kpc, and the outer halo is found to be significantly less influenced by the Gaia Sausage than the inner halo. After the removal of halo substructures found by integrals of motion, the contribution of the Gaia Sausage falls slightly within r gc ∼ 25 kpc but is still as high as 30%–63%. Finally, we select several possible Sausage-related substructures consisting of stars on highly eccentric orbits. The GMM/Sausage component agrees well with the selected substructure stars in their chemodynamical properties, which increases our confidence in the reliability of the GMM fits.

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A-type stars in the Canada–France Imaging Survey I. The stellar halo of the Milky Way traced to large radius by blue horizontal branch stars

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/sty2604 ◽

2018 ◽

Vol 481 (4) ◽

pp. 5223-5235 ◽

Cited By ~ 11

Author(s):

Guillaume F Thomas ◽

Alan W McConnachie ◽

Rodrigo A Ibata ◽

Patrick Côté ◽

Nicolas Martin ◽

...

Keyword(s):

Milky Way ◽

Large Radius ◽

Horizontal Branch ◽

Horizontal Branch Stars ◽

Stellar Halo

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KINEMATICS OF THE STELLAR HALO AND THE MASS DISTRIBUTION OF THE MILKY WAY USING BLUE HORIZONTAL BRANCH STARS

The Astrophysical Journal ◽

10.1088/0004-637x/761/2/98 ◽

2012 ◽

Vol 761 (2) ◽

pp. 98 ◽

Cited By ~ 117

Author(s):

Prajwal R. Kafle ◽

Sanjib Sharma ◽

Geraint F. Lewis ◽

Joss Bland-Hawthorn

Keyword(s):

Mass Distribution ◽

Milky Way ◽

Horizontal Branch ◽

Horizontal Branch Stars ◽

Stellar Halo

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The stellar halo of the Milky Way traced by blue horizontal-branch stars in the Subaru Hyper Suprime-Cam Survey

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/psz052 ◽

2019 ◽

Vol 71 (4) ◽

Cited By ~ 6

Author(s):

Tetsuya Fukushima ◽

Masashi Chiba ◽

Mikito Tanaka ◽

Kohei Hayashi ◽

Daisuke Homma ◽

...

Keyword(s):

Power Law ◽

Milky Way ◽

Outer Boundary ◽

Axial Ratio ◽

Ex Situ ◽

Horizontal Branch ◽

Radial Density ◽

Horizontal Branch Stars ◽

Stellar Halo ◽

Hydrodynamical Simulations

Abstract We report on the global structure of the Milky Way (MW) stellar halo up to its outer boundary based on the analysis of blue horizontal-branch stars (BHBs). These halo tracers are extracted from the (g, r, i, z)-band multi-photometry in the internal data release of the ongoing Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) surveyed over a ∼550 deg2 area. In order to select the most likely BHBs by removing blue straggler stars (BSs) and other contamination in a statistically significant manner, we have developed and applied an extensive Bayesian method, instead of the simple color cuts adopted in our previous work, where each of the template BHBs and non-BHBs obtained from the available catalogs are represented as a mixture of multiple Gaussian distributions in the color–color diagrams. We found from the candidate BHBs in the range of 18.5 < g < 23.5 mag that the radial density distribution over a Galactocentric radius of r = 36–360 kpc can be approximated as a single power-law profile with an index of $\alpha =3.74^{+0.21}_{-0.22}$ or a broken power-law profile with an index of $\alpha _{\rm in}=2.92^{+0.33}_{-0.33}$ at r below a broken radius of $r_{\rm b}=160^{+18}_{-19}\:$kpc and a very steep slope of $\alpha _{\rm out}=15.0^{+3.7}_{-4.5}$ at r > rb. The latter profile with a prolate shape having an axial ratio of $q=1.72^{+0.44}_{-0.28}$ is most likely and this halo may hold a rather sharp boundary at r ≃ 160 kpc. The slopes of the halo density profiles are compared with those from the suite of hydrodynamical simulations for the formation of stellar halos. This comparison suggests that the MW stellar halo may consist of the two overlapping components: the in situ inner halo as probed by RR Lyrae stars showing a relatively steep radial density profile and the ex situ outer halo with a shallow profile probed by BHBs here, which is made by accretion of small stellar systems.

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

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319008299 ◽

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.

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