599 research outputs found
Abundance ratios of red giants in low mass ultra faint dwarf spheroidal galaxies
Low mass dwarf spheroidal galaxies are key objects for our understanding of
the chemical evolution of the pristine Universe and the Local Group of
galaxies. Abundance ratios in stars of these objects can be used to better
understand their star formation and chemical evolution. We report on the
analysis of a sample of 11 stars belonging to 5 different ultra faint dwarf
spheroidal galaxies (UfDSph) based on X-Shooter spectra obtained at the VLT.
Medium resolution spectra have been used to determine the detailed chemical
composition of their atmosphere. We performed a standard 1D LTE analysis to
compute the abundances.
Considering all the stars as representative of the same population of low
mass galaxies, we found that the [alpha/Fe] ratios vs [Fe/H] decreases as the
metallicity of the star increases in a way similar to what is found for the
population of stars belonging to dwarf spheroidal galaxies. The main difference
is that the solar [alpha/Fe] is reached at a much lower metallicity for the
UfDSph than the dwarf spheroidal galaxies.
We report for the first time the abundance of strontium in CVnI. The star we
analyzed in this galaxy has a very high [Sr/Fe] and a very low upper limit of
barium which makes it a star with an exceptionally high [Sr/Ba] ratio.
Our results seem to indicate that the galaxies which have produced the bulk
of their stars before the reionization (fossil galaxies) have lower [X/Fe]
ratios at a given metallicity than the galaxies that have experienced a
discontinuity in their star formation rate (quenching).Comment: 22 pages, 12 figures, submitted to A&
Duality and o-O structure in non reflexive banach spaces
Let E be a Banach space with a supremum type norm induced by a collection of functionals L ⊂ X∗where X is a reflexive Banach space. Familiar spaces of this type are BMO, BV, C0,α(0 < α < 1), Lq,∞, for q > 1. For most of these spaces E, the predual E∗ exists and can be defined by atomic decomposition of its elements. Another typical result, when it is possible to define a rich vanishing subspace E0⊂ E is the "two star theorem ", namely (E0)∗ = E∗. This fails for E = BV and E =C0,1= Lip
Chemical Abundances from the Continuum
The calculation of solar absolute fluxes in the near-UV is revisited,
discussing in some detail recent updates in theoretical calculations of
bound-free opacity from metals. Modest changes in the abundances of elements
such as Mg and the iron-peak elements have a significant impact on the
atmospheric structure, and therefore self-consistent calculations are
necessary. With small adjustments to the solar photospheric composition, we are
able to reproduce fairly well the observed solar fluxes between 200 and 270 nm,
and between 300 and 420 nm, but find too much absorption in the 270-290 nm
window. A comparison between our reference 1D model and a 3D time-dependent
hydrodynamical simulation indicates that the continuum flux is only weakly
sensitive to 3D effects, with corrections reaching <10% in the near-UV, and <2%
in the optical.Comment: 10 pages, 5 figures, to appear in the proceedings of the conference A
Stellar Journey, a symposium in celebration of Bengt Gustafsson's 65th
birthday, June 23-27, 2008, Uppsal
A wide angle view of the Sagittarius dwarf Spheroidal Galaxy. I: VIMOS photometry and radial velocities across Sgr dSph major and minor axis
The Sagittarius dwarf Spheroidal Galaxy (Sgr dSph) provides us with a unique
possibility of studying a dwarf galaxy merging event while still in progress.
Due to its low distance (25 kpc), the main body of Sgr dSph covers a vast area
in the sky (roughly 15 x 7 degrees). Available photometric and spectroscopic
studies have concentrated either on the central part of the galaxy or on the
stellar stream, but the overwhelming majority of the galaxy body has never been
probed. The aim of the present study is twofold. On the one hand, to produce
color magnitude diagrams across the extension of Sgr dSph to study its stellar
populations, searching for age and/or composition gradients (or lack thereof).
On the other hand, to derive spectroscopic low-resolution radial velocities for
a subsample of stars to determine membership to Sgr dSph for the purpose of
high resolution spectroscopic follow-up. We used VIMOS-VLT to produce V and I
photometry and spectroscopy on 7 fields across the Sgr dSph minor and major
axis, plus 3 more centered on the associated globular clusters Terzan 7, Terzan
8 and Arp 2. A last field has been centered on M 54, lying in the center of Sgr
dSph. We present photometry for 320,000 stars across the main body of Sgr dSph,
one of the richest, and safely the most wide-angle sampling ever produced for
this fundamental object. We also provide robust memberships for more than one
hundred stars, whose high resolution spectroscopic analysis will be the object
of forthcoming papers. Sgr dSph appears remarkably uniform among the observed
fields. We confirm the presence of a main Sgr dSph population characterized
roughly by the same metallicity of 47 Tuc, but we also found the presence of
multiple populations on the peripheral fields of the galaxy, with a metallicity
spanning from [Fe/H]=-2.3 to a nearly solar value.Comment: 10 pages, 12 figures, accepted for publication in A&
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