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HALO7D. III. Chemical Abundances of Milky Way Halo Stars from Medium-resolution Spectra

McKinnon, Kevin A.; Cunningham, Emily C.; Rockosi, Constance M.; Guhathakurta, Puragra; Escala, Ivanna; Kirby, Evan N.; Deason, Alis J.

HALO7D. III. Chemical Abundances of Milky Way Halo Stars from Medium-resolution Spectra Thumbnail


Kevin A. McKinnon

Emily C. Cunningham

Constance M. Rockosi

Puragra Guhathakurta

Ivanna Escala

Evan N. Kirby


The Halo Assembly in Lambda Cold Dark Matter: Observations in 7 Dimensions (HALO7D) survey measures the kinematics and chemical properties of stars in the Milky Way (MW) stellar halo to learn about the formation of our Galaxy. HALO7D consists of Keck II/DEIMOS spectroscopy and Hubble Space Telescope–measured proper motions of MW halo main-sequence turnoff stars in the four Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey fields. HALO7D consists of deep pencil beams, making it complementary to other contemporary wide-field surveys. We present the [Fe/H] and [α/Fe] abundances for 113 HALO7D stars in the Galactocentric radial range of ∼10–40 kpc along four separate pointings. Using the full 7D chemodynamical data (3D positions, 3D velocities, and abundances) of HALO7D, we measure the velocity anisotropy, β, of the halo velocity ellipsoid for each field and for different metallicity-binned subsamples. We find that two of the four fields have stars on very radial orbits, while the remaining two have stars on more isotropic orbits. Separating the stars into high-, mid-, and low-[Fe/H] bins at −2.2 and −1.1 dex for each field separately, we find differences in the anisotropies between the fields and between the bins; some fields appear dominated by radial orbits in all bins, while other fields show variation between the [Fe/H] bins. These chemodynamical differences are evidence that the HALO7D fields have different fractional contributions from the progenitors that built up the MW stellar halo. Our results highlight the additional information available on smaller spatial scales compared to results from a spherical average of the stellar halo.


McKinnon, K. A., Cunningham, E. C., Rockosi, C. M., Guhathakurta, P., Escala, I., Kirby, E. N., & Deason, A. J. (2023). HALO7D. III. Chemical Abundances of Milky Way Halo Stars from Medium-resolution Spectra. Astrophysical Journal, 951(1), Article 43.

Journal Article Type Article
Acceptance Date Mar 13, 2023
Online Publication Date Jul 3, 2023
Publication Date Jul 1, 2023
Deposit Date Oct 25, 2023
Publicly Available Date Oct 25, 2023
Journal The Astrophysical Journal
Print ISSN 0004-637X
Electronic ISSN 1538-4357
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 951
Issue 1
Article Number 43
Keywords Space and Planetary Science; Astronomy and Astrophysics
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Copyright Statement
© 2023. The Author(s). Published by the American Astronomical Society.
Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

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