1,108 research outputs found
Abundance anomalies in pre-main-sequence stars: Stellar evolution models with mass loss
The effects of atomic diffusion on internal and surface abundances of A and F
pre-main-sequence stars with mass loss are studied in order to determine at
what age the effects materialize, as well as to further understand the
processes at play in HAeBe and young ApBp stars. Self-consistent stellar
evolution models of 1.5 to 2.8Msun with atomic diffusion (including radiative
accelerations) for all species within the OPAL opacity database were computed
and compared to observations of HAeBe stars. Atomic diffusion in the presence
of weak mass loss can explain the observed abundance anomalies of
pre-main-sequence stars, as well as the presence of binary systems with metal
rich primaries and chemically normal secondaries such as V380 Ori and HD72106.
This is in contrast to turbulence models which do not allow for abundance
anomalies to develop on the pre-main-sequence. The age at which anomalies can
appear depends on stellar mass. For A and F stars, the effects of atomic
diffusion can modify both the internal and surface abundances before the onset
of the MS. The appearance of important surface abundance anomalies on the
pre-main-sequence does not require mass loss, though the mass loss rate affects
their amplitude. Observational tests are suggested to decipher the effects of
mass loss from those of turbulent mixing. If abundance anomalies are confirmed
in pre-main-sequence stars they would severely limit the role of turbulence in
these stars.Comment: 9 pages, 6 figures, accepeted for publicatio
Ribbon homology cobordisms
We study 4-dimensional homology cobordisms without 3-handles, showing that
they interact nicely with Thurston geometries, character varieties, and
instanton and Heegaard Floer homologies. Using these, we derive obstructions to
such cobordisms, with topological applications.Comment: 50 pages, 6 figures. Major reorganization of sections for improved
exposition. Result on Dehn surgery extended from Seifert fibered homology
spheres to rational homology sphere
Whole-blood sorting, enrichment and in situ immunolabeling of cellular subsets using acoustic microstreaming
Analyzing undiluted whole human blood is a challenge due to its complex composition of hematopoietic cellular populations, nucleic acids, metabolites, and proteins. We present a novel multi-functional microfluidic acoustic streaming platform that enables sorting, enrichment and in situ identification of cellular subsets from whole blood. This single device platform, based on lateral cavity acoustic transducers (LCAT), enables (1) the sorting of undiluted donor whole blood into its cellular subsets (platelets, RBCs, and WBCs), (2) the enrichment and retrieval of breast cancer cells (MCF-7) spiked in donor whole blood at rare cell relevant concentrations (10 mL− 1), and (3) on-chip immunofluorescent labeling for the detection of specific target cellular populations by their known marker expression patterns. Our approach thus demonstrates a compact system that integrates upstream sample processing with downstream separation/enrichment, to carry out multi-parametric cell analysis for blood-based diagnosis and liquid biopsy blood sampling
Sirius A: turbulence or mass loss?
Context. Abundance anomalies observed in a fraction of A and B stars of both
Pop I and II are apparently related to internal particle transport. Aims. Using
available constraints from Sirius A, we wish to determine how well evolutionary
models including atomic diffusion can explain observed abundance anomalies when
either turbulence or mass loss is used as the main competitor to atomic
diffusion. Methods. Complete stellar evolution models, including the effects of
atomic diffusion and radiative accelerations, have been computed from the zero
age main-sequence of 2.1M\odot stars for metallicities of Z0 = 0.01 \pm 0.001
and shown to agree with the observed parameters of Sirius A. Surface abundances
were predicted for three values of the mass loss rate and for four values of
the mixed surface zone. Results. A mixed mass of ~ 10^-6 M\odot or a mass loss
rate of 10^-13 M\odot/yr were determined through comparison with observations.
Of the 17 abundances determined observationally which are included in our
calculations, up to 15 can be predicted within 2 sigmas and 3 of the 4
determined upper limits are compatible. Conclusions. While the abundance
anomalies can be reproduced slightly better using turbulence as the process
competing with atomic diffusion, mass loss probably ought to be preferred since
the mass loss rate required to fit abundance anomalies is compatible with the
observationally determined rate. A mass loss rate within a factor of 2 of
10^-13 M\odot/yr is preferred. This restricts the range of the directly
observed mass loss rate.Comment: Accepted by A&A, 25/07/201
Chemical composition of A and F dwarfs members of the Hyades open cluster
Aims: Abundances of 15 chemical elements have been derived for 28 F and 16 A stars members of the Hyades open cluster in order to set constraints on self-consistent evolutionary models that include radiative and turbulent diffusion.
Methods: A spectral synthesis, iterative procedure was applied to derive the abundances from selected high-quality lines in high-resolution, high-signal-to-noise spectra obtained with SOPHIE and AURELIE at the Observatoire de Haute Provence.
Results: The abundance patterns found for A and F stars in the Hyades resemble those observed in Coma Berenices and Pleiades clusters. In graphs representing the abundances versus the effective temperature, A stars often display much more scattered abundances around their mean values than the coolest F stars do. Large star-to-star variations are detected in the Hyades A dwarfs in their abundances of C, Na, Sc, Fe, Ni, Sr, Y, and Zr, which we interpret as evidence of transport processes competing with radiative diffusion. In A and Am stars, the abundances of Cr, Ni, Sr, Y, and Zr are found to be correlated with that of Fe as in the Pleiades and in Coma Berenices. The ratios C/Fe and O/Fe are found to be anticorrelated with Fe/H as in Coma Berenices. All Am stars in the Hyades are deficient in C and O and overabundant in elements heavier than Fe but not all are deficient in Ca and/or Sc. The F stars have solar abundances for almost all elements except for Si. The overall shape of the abundance pattern of the slow rotator HD 30210 cannot be entirely reproduced by models including radiative diffusion and different amounts of turbulent diffusion.
Conclusions: While part of the discrepancies between derived and predicted abundances could come from non-LTE effects, including competing processes such as rotational mixing and/or mass loss seems necessary in order to improve the agreement between the observed and predicted abundance patterns
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