4,186 research outputs found
Population III by Popular Demand - Progress and Previews
I discuss the ongoing search for stars of the Milky Way which have been
referred to as members of Population III. Following a discussion of possible
definitions for these stars, I consider the reasons why astronomers have
undertaken this search, and list some of the numerous astrophysical uses of the
extremely metal-poor stars found along the way. I then review survey techniques
which have been used in the past, and provide an update on plans for future
investigations. Finally, the question of when one might consider the search for
Population III Finished is addressed.Comment: 12 pages, 0 figures, to appear in proceedings of THE FIRST STARS
meeting, held in Garching, Germany, August 199
The Chemo-Dynamical History of the Milky Way as Revealed by SDSS/SEGUE
Although originally conceived as primarily an extragalactic survey, the Sloan
Digital Sky Survey (SDSS-I), and its extensions SDSS-II and SDSS-III, continue
to have a major impact on our understanding of the formation and evolution of
our host galaxy, the Milky Way. The sub-survey SEGUE: Sloan Extension for
Galactic Exploration and Understanding, executed as part of SDSS-II, obtained
some 3500 square degrees of additional ugriz imaging, mostly at lower Galactic
latitudes, in order to better sample the disk systems of the Galaxy. Most
importantly, it obtained over 240,000 medium-resolution spectra for stars
selected to sample Galactocentric distances from 0.5 to 100 kpc. In combination
with stellar targets from SDSS-I, and the recently completed SEGUE-2 program,
executed as part of SDSS-III, the total sample of SDSS spectroscopy for
Galactic stars comprises some 500,000 objects.
The development of the SEGUE Stellar Parameter Pipeline has enabled the
determination of accurate atmospheric parameter estimates for a large fraction
of these stars. Many of the stars in this data set within 5 kpc of the Sun have
sufficiently well-measured proper motions to determine their full space
motions, permitting examination of the nature of much more distant populations
represented by members that are presently passing through the solar
neighborhood. Ongoing analyses of these data are being used to draw a much
clearer picture of the nature of our galaxy, and to supply targets for detailed
high-resolution spectroscopic follow-up with the world's largest telescopes.
Here we discuss a few highlights of recently completed and ongoing
investigations with these data.Comment: 8 pages, 5 figures, to appear in IAU Symp. 26
Searches for the Most Metal-Poor Candidates from SDSS and SEGUE
We report on efforts to identify large samples of very and extremely
metal-poor stars based on medium-resolution spectroscopy and ugriz photometry
obtained during the course of the Sloan Digital Sky Survey (SDSS), and its
extension, SDSS-II, which includes the program SEGUE: Sloan Extension for
Galactic Understanding and Exploration. To date, over 8000 stars with [Fe/H] <=
-2.0 and effective temperatures in the range 4500K < T_eff < 7000K have been
found, with the expected numbers in this temperature range to be well over
10,000 once SEGUE is completed. The numbers roughly double when one includes
warmer blue stragglers and Blue Horizontal-Branch (BHB) stars in these counts.
We show the observed low-metallicity tails of the Metallicity Distribution
Functions for the cooler SDSS/SEGUE stars obtained thus far. We also comment on
the confirmation of an inner/outer halo dichotomy in the Milky Way, and on how
this realization may be used to direct searches for even more metal-poor stars
in the near future.Comment: 5 pages, 4 figures, from the conference "First Stars III", held in
July 200
The Innovation Performance of Foreign Affiliates: Evidence from Dutch Manufacturing Firms
innovation, performance, manufacturing, firms
New Results From Bright Metal-Poor Stars In The Hamburg/Eso Survey
We present an abundance analysis of BE 1327-2326, currently the most iron-poor star known, based on a newly acquired VLT spectrum. The ID abundance pattern is corrected for 3D effects. The 3D iron abundance is [Fe/H] = -5.9, while the CNO elements of the star are extremely overabundant [CNO[Fe] similar to 3 to 4). The cosmologically important element Li is still not detected; the new upper limit is A (Li) < 0.6. A new analysis of the medium-resolution data of the sample of bright metal-poor stars from the Hamburg/ESO Survey (HES) was carried out. We are using this sample to obtain clues to the chemical nature of the early Universe by investigating the kinematic properties of the sample. Based on estimated [Fe/H] and [C/Fe], we are also able to use the sample to test a formation mechanism for low-mass metal-poor stars.Astronom
Stellar haloes in Milky-Way mass galaxies: From the inner to the outer haloes
We present a comprehensive study of the chemical properties of the stellar
haloes of Milky-Way mass galaxies, analysing the transition between the inner
to the outer haloes. We find the transition radius between the relative
dominance of the inner-halo and outer-halo stellar populations to be ~15-20 kpc
for most of our haloes, similar to that inferred for the Milky Way from recent
observations. While the number density of stars in the simulated inner-halo
populations decreases rapidly with distance, the outer-halo populations
contribute about 20-40 per cent in the fiducial solar neighborhood, in
particular at the lowest metallicities. We have determined [Fe/H] profiles for
our simulated haloes; they exhibit flat or mild gradients, in the range
[-0.002, -0.01 ] dex/kpc. The metallicity distribution functions exhibit
different features, reflecting the different assembly history of the individual
stellar haloes. We find that stellar haloes formed with larger contributions
from massive subgalactic systems have steeper metallicity gradients. Very
metal-poor stars are mainly contributed to the halo systems by lower-mass
satellites. There is a clear trend among the predicted metallicity distribution
functions that a higher fraction of low-metallicity stars are found with
increasing radius. These properties are consistent with the range of behaviours
observed for stellar haloes of nearby galaxies.Comment: 11 pages, 6 figures. Accepted MNRAS. Revised version after referee's
comment
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