Zachary Hartman: Examining the Multiplicity of the Galactic Halo through Lick A.O., Speckle Imaging and More!

Thursday, 07 December 2023 2 p.m. — 3 p.m. MST

Gemini North Hilo Base Facility | 670 N A’ohoku Place Hilo, Hawaii, 96720, USA

Gemini North Talks
Zachary Hartman (Gemini Observatory, NSF’s NOIRLab)
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Galactic halo stars represent some of the oldest and most metal-poor stars in our Galaxy. As such, they are critically important to our grasp of the dynamical history and chemical evolution of the Galaxy. And yet, our current understanding of the halo binary population within 100 pc of the Sun is still relatively uncertain. This uncertainty has a trickle-down effect on our knowledge of the local halo luminosity function, the mass-luminosity relation for local halo stars, and ultimately our insight into how these stars formed in an environment much different from today. In particular, studies over the past decade have estimated the multiplicity fraction of the Galactic Halo to be between 12%-40%. To better constrain this estimate, we present results of a multiplicity survey of local Galactic halo stars using Lick A.O., speckle imaging at Gemini, and HST imaging. Our sample is drawn from high proper motion stars from Gaia DR3 and extends to a Gaia G magnitude of 18 out to a distance of 100 pc. We then combine the results of our survey with the SUPERWIDE wide binary catalog to effectively search for equal magnitude companions down to the diffraction limits of the telescopes. Our results indicate a lower multiplicity fraction compared to similar studies of the Galactic halo population.

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