A LAMOST BHB Catalog and Kinematics Therein I: Catalog and Halo Properties

Abstract

We collect a sample of stars observed both in LAMOST and Gaia which have colors implying a temperature hotter than 7000 K. We train a machine learning algorithm on LAMOST spectroscopic data which has been tagged with stellar classifications and metallicities, and use this machine to construct a catalog of Blue Horizontal Branch stars (BHBs) with metallicity information. Another machine is trained using Gaia parallaxes to predict absolute magnitudes for these stars. The final catalog of 13,693 BHBs is thought to be about 86\% pure, with ${\sigma }_{[Fe/H]}\sim$0.35 dex and ${\sigma }_G\sim$0.31 mag. These values are confirmed via comparison to globular clusters, although a covariance error seems to affect our magnitude and abundance estimates. We analyze a subset of this catalog in the Galactic Halo. We find that BHB populations in the outer halo appear redder, which could imply a younger population, and that the metallicity gradient is relatively flat around [Fe/H] = -1.9 dex over our sample footprint. We find that our metal rich BHB stars are on more radial velocity dispersion dominated orbits ($\beta \sim 0.70$) at all radii than our metal poor BHB stars ($\beta \sim 0.62$).

arXiv comment13 Pages, 7 Figures, accepted to apj

References in corpus (64)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• Astropy: A Community Python Package for Astronomy
• The NumPy array: a structure for efficient numerical computation
• The Sloan Digital Sky Survey: Technical Summary
• Gaia Data Release 2. Summary of the contents and survey properties
• A 3D Dust Map Based on Gaia, Pan-STARRS 1 and 2MASS
• The merger that led to the formation of the Milky Way's inner stellar halo and thick disk
• Tracing Galaxy Formation with Stellar Halos I: Methods
• Co-formation of the Galactic disc and the stellar halo
• Differential Galaxy Evolution in Cluster and Field Galaxies at z=0.3
• The First Data Release (DR1) of the LAMOST general survey
• The Ghost of Sagittarius and Lumps in the Halo of the Milky Way
• The Milky Way's Circular Velocity Curve to 60 kpc and an Estimate of the Dark Matter Halo Mass from Kinematics of ~2400 SDSS Blue Horizontal Branch Stars
• Modelling the Galactic Interstellar Extinction Distribution in Three Dimensions
• Two Stellar Components in the Halo of the Milky Way
• Debris streams in the solar neighbourhood as relicts from the formation of the Milky Way
• Galactic stellar haloes in the CDM model
• The SEGUE Stellar Parameter Pipeline. I. Description and Initial Validation Tests
• Evidence for Two Early Accretion Events That Built the Milky Way Stellar Halo
• The ACS Survey of Galactic Globular Clusters. IX. Horizontal Branch Morphology and the Second Parameter Phenomenon
• A three-dimensional Galactic extinction model
• The Cannon: A data-driven approach to stellar label determination
• Identification of A-colored Stars and Structure in the Halo of the Milky Way from SDSS Commissioning Data
• Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy
• Galactic Rotation and Solar Motion from Stellar Kinematics
• The Milky Way stellar halo out to 40 kpc : Squashed, broken but smooth
• The Biggest Splash
• On the use of Gaia magnitudes and new tables of bolometric corrections
• Automatic Determination of Stellar Atmospheric Parameters and Construction of Stellar Spectral Templates of the Guoshoujing Telescope (LAMOST)
• Chemical Evolution in Hierarchical Models of Cosmic Structure II: The Formation of the Milky Way Stellar Halo and the Distribution of the Oldest Stars
• Two distinct halo populations in the solar neighborhood. II. Evidence from stellar abundances of Mn, Cu, Zn, Y, and Ba
• The Shape and Profile of the Milky Way Halo as Seen by the CFHT Legacy Survey
• Confirmation of the $Gaia$ DR2 parallax zero-point offset using asteroseismology and spectroscopy in the $Kepler$ field
• Reverse engineering the Milky Way
• Extreme deconvolution: Inferring complete distribution functions from noisy, heterogeneous and incomplete observations
• Distances and parallax bias in Gaia DR2
• Blue horizontal branch stars in the Sloan Digital Sky Survey: I. Sample selection and structure in the Galactic halo
• Carbon-Enhanced Metal-Poor Stars in the Inner and Outer Halo Components of the Milky Way
• Apocenter Pile-Up: Origin of the Stellar Halo Density Break
• Deriving the stellar labels of LAMOST spectra with Stellar LAbel Machine (SLAM)
• The Gravitational Force Field of the Galaxy Measured From the Kinematics of RR Lyrae in Gaia
• A 3D extinction map of the Northern Galactic Plane based on IPHAS photometry
• The Outer Stellar Halos of Galaxies: how Radial Merger Mass Deposition, Shells and Streams depend on Infall-Orbit Configurations
• Stellar streams around the Magellanic Clouds
• Distant field BHB stars and the mass of the Galaxy I: Classification of halo A-type stars
• Stellar Population Variations in the Milky Way's Stellar Halo
• Anisotropy of the Milky Way's stellar halo using K giants from LAMOST and $Gaia$
• The Century Survey Galactic Halo Project III: A Complete 4300 deg^2 Survey of Blue Horizontal Branch Stars in the Metal-Weak Thick Disk and Inner Halo
• The Structure of the Sagittarius Stellar Stream as Traced by Blue Horizontal Branch Stars
• Assessing distances and consistency of kinematics in Gaia/TGAS
• 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
• The tale of the tail -- disentangling the high transverse velocity stars in Gaia DR2
• The age structure of the Milky Way's halo
• Identifying Blue Horizontal Branch Stars Using the z Filter
• Chronography of the Milky Way's Halo System with Field Blue Horizontal-Branch Stars
• The stellar halo of the Milky Way traced by blue horizontal-branch stars in the Subaru Hyper Suprime-Cam Survey
• Beta Dips in the Gaia Era: Simulation Predictions of the Galactic Velocity Anisotropy Parameter for Stellar Halos
• The Pristine survey -- VII. A cleaner view of the Galactic outer halo using blue horizontal branch stars
• To the Galactic Virial Radius with Hyper Suprime-Cam
• Structure of the Milky Way stellar halo out to its outer boundary with blue horizontal-branch stars
• LAMOST DR1: Stellar parameters and chemical abundances with SP_Ace
• Constraints on the Galactic Inner Halo Assembly History from the Age Gradient of Blue Horizontal-branch Stars
• An extended view of the Pisces Overdensity from the SCUSS survey

Cited by in corpus (4)

• Constraints on the assembly history of the Milky Way's smooth, diffuse stellar halo from the metallicity-dependent, radially-dominated velocity anisotropy profiles probed with K giants and BHB stars using LAMOST, SDSS/SEGUE, and Gaia
• Transferring spectroscopic stellar labels to 217 million Gaia DR3 XP stars with SHBoost
• A Pristine-UNIONS view on the Galaxy: Kinematics of the distant spur feature of the Sagittarius stream traced by Blue Horizontal Branch stars
• The origin of B-type runaway stars based on kinematics