2,098 research outputs found
Detailed Chemical Analysis of Two Giants in the SGR DSPH
The 8m class telescopes allow for the first time to study stars of external
galaxies with the same resolution and S/N ratio which has been so far used for
Galactic stars. It is quite likely that this study will shake some of our
current beliefs. In this poster we highlight some of the results which have
been obtained for two giants in the Sgr dSph thanks to the UVES spectrograph on
the ESO 8.2m Kueyen telescope. Further details on the observations and data
analysis may be found in Bonifacio et al (2000).Comment: To appear in `Cosmic Evolution' Conference at IAp, Paris, honoring
Jean Audouze and Jim Truran, 13-17 Nov 200
On the lithium content of the globular cluster M92
I use literature data and a new temperature calibration to determine the Li
abundances in the globular cluster M 92. Based on the same data, Boesgaard et
al. have claimed that there is a dispersion in Li abundances in excess of
observational errors. This result has been brought as evidence for Li depletion
in metal-poor dwarfs. In the present note I argue that there is no strong
evidence for intrinsic dispersion in Li abundances, although a dispersion as
large as 0.18 dex is possible. The mean Li abundance, A(Li)=2.36, is in good
agreement with recent results for field stars and TO stars in the metal-poor
globular cluster NGC 6397. The simplest interpretation is that this constant
value represents the primordial Li abundance.Comment: A&A accepte
On the origin of HE0107-5240, the most iron deficient star presently known
We show that the "puzzling" chemical composition observed in the extremely
metal poor star HE0107-5240 may be naturally explained by the concurrent
pollution of at least two supernovae. In the simplest possible model a
supernova of quite low mass (~15 Msun), underwent a "normal" explosion and
ejected ~0.06 Msun of 56Ni while a second one was massive enough (~35 Msun) to
experience a strong fall back that locked in a compact remnant all the
carbon-oxygen core. In a more general scenario, the pristine gas clouds were
polluted by one or more supernovae of relatively low mass (less than ~25 Msun).
The successive explosion of a quite massive star experiencing an extended fall
back would have largely raised the abundances of the light elements in its
close neighborhood.Comment: 10 pages; 3 figures; accepted for publication in the The
Astrophysical Journal Letter
Galactic globular cluster 47 Tucanae: new ties between the chemical and dynamical evolution of globular clusters?
It is generally accepted today that Galactic globular clusters (GGCs) consist
of at least two generations of stars that are different in their chemical
composition and perhaps age. However, knowledge about the kinematical
properties of these stellar generations, which may provide important
information for constraining evolutionary scenarios of the GGCs, is still
limited. We therefore study the connections between chemical and kinematical
properties of different stellar generations in the Galactic globular cluster 47
Tuc. To achieve this goal, we used abundances of Li, O, and Na determined in
101 main sequence turn-off (TO) stars with the aid of 3D hydrodynamical model
atmospheres and NLTE abundance analysis methodology. We divided our sample TO
stars into three groups according to their position in the [Li/Na]-[Na/O] plane
to study their spatial distribution and kinematical properties. We find that
there are statistically significant radial dependencies of lithium and oxygen
abundances, A(Li) and A(O), as well as that of [Li/Na] abundance ratio. Our
results show that first-generation stars are less centrally concentrated and
dynamically hotter than stars belonging to subsequent generations. We also find
a significant correlation between the velocity dispersion and O and Na
abundance, and between the velocity dispersion and the [Na/O] abundance ratio.Comment: 4 pages, 6 figures, accepted for publication in A&
Optical bistability in sideband output modes induced by squeezed vacuum
We consider two-level atoms in a ring cavity interacting with a broadband
squeezed vacuum centered at frequency and an input monochromatic
driving field at frequency . We show that, besides the central mode
(at \o), many other {\em sideband modes} are produced at the output, with
frequencies shifted from by multiples of .
Here we analyze the optical bistability of the two nearest sideband modes, one
red-shifted and the other blue-shifted.Comment: Replaced with final published versio
Lithium abundances in extremely metal-poor turn-off stars
We discuss the current status of the sample of Lithium abundances in
extremely metal poor (EMP) turn-off (TO) stars collected by our group, and
compare it with the available literature results. In the last years, evidences
have accumulated of a progressive disruption of the Spite plateau in stars of
extremely low metallicity. What appears to be a flat, thin plateau above
[Fe/H]\sim-2.8 turns, at lower metallicities, into a broader distribution for
which the plateau level constitutes the upper limit, but more and more stars
show lower Li abundances. The sample we have collected currently counts
abundances or upper limits for 44 EMP TO stars between [Fe/H]=-2.5 and -3.5,
plus the ultra-metal poor star SDSS J102915+172927 at [Fe/H]=-4.9. The
"meltdown" of the Spite plateau is quite evident and, at the current status of
the sample, does not appear to be restricted to the cool end of the effective
temperature distribution. SDSS J102915+172927 displays an extreme Li depletion
that contrasts with its otherwise quite ordinary set of [X/Fe] ratios.Comment: 6 pages, 4 figures, proceedings of the "Lithium in the Cosmos"
conference, Paris, 27-29 February 201
The cosmic lithium problem: an observer's perspective
Using the cosmological constants derived from WMAP, the standard big bang
nucleosynthesis (SBBN) predicts the light elements primordial abundances for
4He, 3He, D, 6Li and 7Li. These predictions are in satisfactory agreement with
the observations, except for lithium which displays in old warm dwarfs an
abundance depleted by a factor of about 3. Depletions of this fragile element
may be produced by several physical processes, in different stellar
evolutionary phases, they will be briefly reviewed here, none of them seeming
yet to reproduce the observed depletion pattern in a fully convincing way.Comment: Invited review at the conference Lithium in the cosmos, Paris 27-29
Feb 2012, one reference adde
- âŠ