Subaru Seminars



This Month






Site Map

The Subaru Seminar is usually held in Room 104 of the Hilo Base Facility, adjacent to the main lobby. Everyone is welcome to attend. If you are interested in giving a seminar, please contact Subaru seminar organizers (Tadayuki Kodama, Kumiko S. Usuda, Naoyuki Tamura, Tomonori Usuda) by email : (please change"_at_" to @).

June 28, Tuesday, at 11:00 am

" The formation of the Milky Way stellar halo as traced by chemicalabundances of metal-poor stars "

Miho Ishigaki

(NAOJ, Mitaka)

Chemical abundances in atmospheres of metal-poor stars are well-preserved quantities from the early Universe, which is one of the only observational signatures on the ancient stellar and supernovae nucleosynthesis in the Milky Way Galaxy. Together with phase-space coordinates (position, distance and 3-d velocity components), chemical abundances in old stars have provided tremendous implications on the chemodynamical evolution of the early stage of our Galaxy. In this talk, I will summarize how chemical compositions of nearby stars have been used to make constraints on the formation of each structural component of our Galaxy, namely, the thin disk, thick disk and stellar halo. Then, I will talk about the state of our ongoing Subaru HDS study on homogenous chemical abundance analyses of nearby halo stars. Our sample includes ~90 metal-poor (-4<[Fe/H]<-0.5) dwarf and giant stars located within a few kilo-persec from the Sun, that show a wide range in orbital characteristics (e.g. large eccentricity or highly retro-grade motion). In particular, the sample stars whose orbit reaches the outer part of the Galactic halo are quite suitable for examining the merging history of our Galaxy, since remnants of tidally disrupted stellar systems (e.g. dwarf galaxy), may largely persist in the outer halo. Chemical abundances of key-elements, including alpha, iron-peak and neutron-capture elements have been obtained with a LTE abundance analysis code. We show that the estimated alpha-elements-to-iron abundance ratios ([alpha/Fe]), one of the important diagnostic for star formation history in a stellar system, show a mild decreasing gradient with metallicity. This result is broadly consistent with a hypothesis that the halo stars are partly originated from a system with a lower star formation rate where delayed enrichments of Fe from Type Ia SNe are responsible for the decrease in the [alpha/Fe]. Implications on the building blocks of the Milky Way stellar halo will be discussed based on the estimated abundances of various key-elements will be presented.

Seminars are also held at JAC, CFHT, and IfA.

Copyright (c) 1999-2000 Subaru Telescope, NAOJ. All rights reserved.