2,930 research outputs found
Deep inside low-mass stars
Low-mass stars exhibit, at all stages of their evolution, the signatures of
complex physical processes that require challenging modeling beyond standard
stellar theory. In this review, we recall the most striking observational
evidences that probe the interaction and interdependence of various transport
processes of chemicals and angular momentum in these objects. We then focus on
the impact of atomic diffusion, large scale mixing due to rotation, and
internal gravity waves on stellar properties on the main sequence and slightly
beyond.Comment: Invited Review to be published in the proceedings of the IAU
Symposium 252 "The Art of Modelling stars in the 21st Century" - Sanya -
China - April 200
Angular momentum transport by internal gravity waves. IV - Wave generation by surface convection zone, from the pre-main sequence to the early-AGB in intermediate mass stars
This is the fourth in a series of papers that deal with angular momentum
transport by internal gravity waves in stellar interiors. Here, we want to
examine the potential role of waves in other evolutionary phases than the main
sequence. We study the evolution of a 3Msun Population I model from the
pre-main sequence to the early-AGB phase and examine whether waves can lead to
angular momentum redistribution and/or element diffusion at the external
convection zone boundary. We find that, although waves produced by the surface
convection zone can be ignored safely for such a star during the main sequence,
it is not the case for later evolutionary stages. In particular, angular
momentum transport by internal waves could be quite important at the end of the
sub-giant branch and during the early-AGB phase. Wave-induced mixing of
chemicals is expected during the early-AGB phase.Comment: A&A in press; 11 figure
Angular momentum transport by internal gravity waves III - Wave excitation by core convection and the Coriolis effect
This is the third in a series of papers that deal with angular momentum
transport by internal gravity waves. We concentrate on the waves excited by
core convection in a 3Msun, Pop I main sequence star. Here, we want to examine
the role of the Coriolis acceleration in the equations of motion that describe
the behavior of waves and to evaluate its impact on angular momentum transport.
We use the so-called traditional approximation of geophysics, which allows
variable separation in radial and horizontal components. In the presence of
rotation, the horizontal structure is described by Hough functions instead of
spherical harmonics. The Coriolis acceleration has two main effects on waves.
It transforms pure gravity waves into gravito-inertial waves that have a larger
amplitude closer to the equator, and it introduces new waves whose restoring
force is mainly the conservation of vorticity. Taking the Coriolis acceleration
into account changes the subtle balance between prograde and retrograde waves
in non-rotating stars. It also introduces new types of waves that are either
purely prograde or retrograde. We show in this paper where the local deposition
of angular momentum by such waves is important.Comment: 9 pages, 10 figures, accepted for publication by A&
Completion of the mixed unit interval graphs hierarchy
We describe the missing class of the hierarchy of mixed unit interval graphs,
generated by the intersection graphs of closed, open and one type of half-open
intervals of the real line. This class lies strictly between unit interval
graphs and mixed unit interval graphs. We give a complete characterization of
this new class, as well as quadratic-time algorithms that recognize graphs from
this class and produce a corresponding interval representation if one exists.
We also mention that the work in arXiv:1405.4247 directly extends to provide a
quadratic-time algorithm to recognize the class of mixed unit interval graphs.Comment: 17 pages, 36 figures (three not numbered). v1 Accepted in the TAMC
2015 conference. The recognition algorithm is faster in v2. One graph was not
listed in Theorem 7 of v1 of this paper v3 provides a proposition to
recognize the mixed unit interval graphs in quadratic time. v4 is a lot
cleare
Hydrodynamical stellar models including rotation, internal gravity waves and atomic diffusion. I. Formalism and tests on Pop I dwarfs
In this paper, we develop a formalism in order to incorporate the
contribution of internal gravity waves to the transport of angular momentum and
chemicals over long time-scales in stars. We show that the development of a
double peaked shear layer acts as a filter for waves, and how the asymmetry of
this filter produces momentum extraction from the core when it is rotating
faster than the surface. Using only this filtered flux, it is possible to
follow the contribution of internal waves over long (evolutionary) time-scales.
We then present the evolution of the internal rotation profile using this
formalism for stars which are spun down via magnetic torquing. We show that
waves tend to slow down the core, creating a "slow" front that may then
propagate from the core to the surface. Further spin down of the surface leads
to the formation of a new front. Finally we show how this momentum transport
reduces rotational mixing in a 1.2Msun, Z=0.02 model, leading to a surface
lithium abundance in agreement with observations in the Hyades.Comment: 14 pages, accepted for publication in A&
The quantum Neumann model: refined semiclassical results
We extend the semiclassical study of the Neumann model down to the deep
quantum regime. A detailed study of connection formulae at the turning points
allows to get good matching with the exact results for the whole range of
parameters.Comment: 10 pages, 5 figures Minor edit
Decomposing 8-regular graphs into paths of length 4
A -decomposition of a graph is a set of edge-disjoint copies of in
that cover the edge set of . Graham and H\"aggkvist (1989) conjectured
that any -regular graph admits a -decomposition if is a tree
with edges. Kouider and Lonc (1999) conjectured that, in the special
case where is the path with edges, admits a -decomposition
where every vertex of is the end-vertex of exactly two paths
of , and proved that this statement holds when has girth at
least . In this paper we verify Kouider and Lonc's Conjecture for
paths of length
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