14,625 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 Auger-hole method : a field measurement of the hydraulic conductivity of soil below the water table
The stellar content of the Hamburg/ESO survey. IV. Selection of candidate metal-poor stars
We present the quantitative methods used for selecting candidate metal-poor
stars in the Hamburg/ESO objective-prism survey (HES). The selection is based
on the strength of the Ca II K line, B-V colors (both measured directly from
the digital HES spectra), as well as J-K colors from the 2 Micron All Sky
Survey. The KP index for Ca II K can be measured from the HES spectra with an
accuracy of 1.0 Angstrom, and a calibration of the HES B-V colors, using CCD
photometry, yields a 1-sigma uncertainty of 0.07 mag for stars in the color
range 0.3 < B-V < 1.4. These accuracies make it possible to reliably reject
stars with [Fe/H] > -2.0 without sacrificing completeness at the lowest
metallicities. A test of the selection using 1121 stars of the HK survey of
Beers, Preston, and Shectman present on HES plates suggests that the
completeness at [Fe/H] < -3.5 is close to 100% and that, at the same time, the
contamination of the candidate sample with false positives is low: 50% of all
stars with [Fe/H] > -2.5 and 97% of all stars with [Fe/H] > -2.0 are rejected.
The selection was applied to 379 HES fields, covering a nominal area of 8853
square degrees of the southern high Galactic latitude sky. The candidate sample
consists of 20,271 stars in the magnitude range 10 < B < 18. A comparison of
the magnitude distribution with that of the HK survey shows that the magnitude
limit of the HES sample is about 2 mag fainter. Taking the overlap of the sky
areas covered by both surveys into account, it follows that the survey volume
for metal-poor stars has been increased by the HES by about a factor of 10 with
respect to the HK survey. We have already identified several very rare objects
with the HES, including, e.g., the three most heavy-element deficient stars
currently known.Comment: 11 pages, 10 figures, accepted for publication in A&
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