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$).

13 Pages, 7 Figures, accepted to apj

References in corpus (15)

• The NumPy array: a structure for efficient numerical computation
• 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
• Two Stellar Components in the Halo of the Milky Way
• The SEGUE Stellar Parameter Pipeline. I. Description and Initial Validation Tests
• Evidence for Two Early Accretion Events That Built the Milky Way Stellar Halo
• Reverse engineering the Milky Way
• Distances and parallax bias in Gaia DR2
• A 3D extinction map of the Northern Galactic Plane based on IPHAS photometry
• 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 tale of the tail -- disentangling the high transverse velocity stars in Gaia DR2
• The age structure of the Milky Way's halo
• The stellar halo of the Milky Way traced by blue horizontal-branch stars in the Subaru Hyper Suprime-Cam Survey
• To the Galactic Virial Radius with Hyper Suprime-Cam
• The Pristine survey -- VII. A cleaner view of the Galactic outer halo using blue horizontal branch stars
• Constraints on the Galactic Inner Halo Assembly History from the Age Gradient of Blue Horizontal-branch Stars

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