338 research outputs found
Internal rapid rotation and its implications for stellar structure and pulsations
Massive and intermediate mass stars play a crucial role in astrophysics.
Indeed, massive stars are the main producers of heavy elements, explode in
supernovae at the end of their short lifetimes, and may be the progenitors of
gamma ray bursts. Intermediate mass stars, although not destined to explode in
supernovae, display similar phenomena, are much more numerous, and have some of
the richest pulsation spectra. A key to understanding these stars is
understanding the effects of rapid rotation on their structure and evolution.
These effects include centrifugal deformation and gravity darkening which can
be observed immediately, and long terms effects such as rotational mixing due
to shear turbulence, which prolong stellar lifetime, modify chemical yields,
and impact the stellar remnant at the end of their lifetime. In order to
understand these effects, a number of models have been and are being developed
over the past few years. These models lead to increasingly sophisticated
predictions which need to be tested through observations. A particularly
promising source of constraints is seismic observations as these may
potentially lead to detailed information on their internal structure. However,
before extracting such information, a number of theoretical and observational
hurdles need to be overcome, not least of which is mode identification. The
present proceedings describe recent progress in modelling these stars and show
how an improved understanding of their pulsations, namely frequency patterns,
mode visibilities, line profile variations, and mode excitation, may help with
deciphering seismic observations.Comment: Proceedings for the CoRoT 3/KASC 7 meeting in Toulous
Mode identification in rapidly rotating stars from BRITE data
Apart from recent progress in Gamma Dor stars, identifying modes in rapidly
rotating stars is a formidable challenge due to the lack of simple, easily
identifiable frequency patterns. As a result, it is necessary to look to
observational methods for identifying modes. Two popular techniques are
spectroscopic mode identification based on line profile variations (LPVs) and
photometric mode identification based on amplitude ratios and phase differences
between multiple photometric bands. In this respect, the BRITE constellation is
particularly interesting as it provides space-based multi-colour photometry.
The present contribution describes the latest developments in obtaining
theoretical predictions for amplitude ratios and phase differences for
pulsation modes in rapidly rotating stars. These developments are based on full
2D non-adiabatic pulsation calculations, using models from the ESTER code, the
only code to treat in a self-consistent way the thermal equilibrium of rapidly
rotating stars. These predictions are then specifically applied to the BRITE
photometric bands to explore the prospects of identifying modes based on BRITE
observations.Comment: 8 pages, 3 figures, proceedings of the 3rd BRITE Science Worksho
Non-adiabatic oscillations of fast-rotating stars: the example of Rasalhague
Early-type stars generally tend to be fast rotators. In these stars, mode
identification is very challenging as the effects of rotation are not well
known. We consider here the example of Ophiuchi, for which dozens of
oscillation frequencies have been measured. We model the star using the
two-dimensional structure code ESTER, and we compute both adiabatic and
non-adiabatic oscillations using the TOP code. Both calculations yield very
complex spectra, and we used various diagnostic tools to try and identify the
observed pulsations. While we have not reached a satisfactory mode-to-mode
identification, this paper presents promising early results.Comment: 4 pages, 3 figures. SF2A 2017 proceeding
RUBIS: a simple tool for calculating the centrifugal deformation of stars and planets
In this article we present RUBIS (Rotation code Using Barotropy conservation
over Isopotential Surfaces), a fully Python-based centrifugal deformation
program available at https://github.com/pierrehoudayer/RUBIS. The code has been
designed to calculate the centrifugal deformation of a star or planet resulting
from a given cylindrical rotation profile, starting from a spherically
symmetric non-rotating model. Furthermore, it can handle models with
discontinuities in the density profile.
The underlying assumption in RUBIS is that the relationship between density
and pressure is preserved during the deformation process. This leads to many
procedural simplifications. For instance, RUBIS only needs to solve Poisson'
equation, either in spheroidal or spherical coordinates depending on whether
the 1D model has discontinuities or not.
In this paper, we present the benefits of using RUBIS to deform polytropic
models and more complex barotropic structures, thus providing, to a certain
extent, insights into baroclinic models. The resulting structures can be used
for a wide range of applications, including the seismic study of models.
Finally, we illustrate how RUBIS is beneficial specifically in the analysis of
Jupiter's gravitational moments, thanks to its ability to handle discontinuous
models while retaining a high accuracy compared to current methods
Asteroseismology, standard candles and the Hubble Constant: what is the role of asteroseismology in the era of precision cosmology?
Classical Cepheids form one of the foundations of modern cosmology and the
extragalactic distance scale, however, cosmic microwave background observations
measure cosmological parameters and indirectly the Hubble Constant, H0, to
unparalleled precision. The coming decade will provide opportunities to measure
H0 to 2% uncertainty thanks to the GAIA satellite, JWST, ELTs and other
telescopes using Cepheids and other standard candles. In this work, we discuss
the upcoming role for variable stars and asteroseismology in calibrating the
distance scale and measuring H0 and what problems exist in understanding these
stars that will feedback on these measurements.Comment: 8 pages, summary of splinter session at IAU Symposium 301, Precision
Asteroseismology, August 2013, Wroclaw, Polan
Asteroseismic modelling strategies in the PLATO era. II. Automation of seismic inversions and quality assessment procedure
*Context*. In the framework of the PLATO mission, to be launched in late
2026, seismic inversion techniques will play a key role in the mission
precision requirements of the stellar mass, radius, and age. It is therefore
relevant to discuss the challenges of the automation of seismic inversions,
which were originally developed for individual modelling.\\ *Aims*. We tested
the performance of our newly developed quality assessment procedure of seismic
inversions, which was designed in the perspective of a pipeline
implementation.\\ *Methods*. We applied our assessment procedure on a testing
set composed of 26 reference models. We divided our testing set into two
categories, calibrator targets whose inversion behaviour is well known from the
literature and targets for which we assessed manually the quality of the
inversion. We then compared the results of our assessment procedure with our
expectations as a human modeller for three types of inversions, the mean
density inversion, the acoustic radius inversion, and the central entropy
inversion.\\ *Results*. We found that our quality assessment procedure performs
as well as a human modeller. The mean density inversion and the acoustic radius
inversion are suited for a large-scale application, but not the central entropy
inversion, at least in its current form.\\ *Conclusions*. Our assessment
procedure showed promising results for a pipeline implementation. It is based
on by-products of the inversion and therefore requires few numerical resources
to assess quickly the quality of an inversion result.Comment: Accepted for publication in Astronomy & Astrophysic
Observational - relation for Sct stars using eclipsing binaries and space photometry
Delta Scuti ( Sct) stars are intermediate-mass pulsators, whose
intrinsic oscillations have been studied for decades. However, modelling their
pulsations remains a real theoretical challenge, thereby even hampering the
precise determination of global stellar parameters. In this work, we used space
photometry observations of eclipsing binaries with a Sct component to
obtain reliable physical parameters and oscillation frequencies. Using that
information, we derived an observational scaling relation between the stellar
mean density and a frequency pattern in the oscillation spectrum. This pattern
is analogous to the solar-like large separation but in the low order regime. We
also show that this relation is independent of the rotation rate. These
findings open the possibility of accurately characterizing this type of
pulsator and validate the frequency pattern as a new observable for
Sct stars.Comment: 11 pages, including 2 pages of appendix, 2 figures, 2 tables,
accepted for publication in ApJ
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