318 research outputs found
The interior angular momentum of core hydrogen burning stars from gravity-mode oscillations
A major uncertainty in the theory of stellar evolution is the angular
momentum distribution inside stars and its change during stellar life. We
compose a sample of 67 stars in the core-hydrogen burning phase with a
value from high-resolution spectroscopy, as well as an asteroseismic
estimate of the near-core rotation rate derived from gravity-mode oscillations
detected in space photometry. This assembly includes 8 B-type stars and 59
AF-type stars, covering a mass range from 1.4 to 5\,M, i.e., it
concerns intermediate-mass stars born with a well-developed convective core.
The sample covers projected surface rotation velocities km\,s and core rotation rates up to Hz, which
corresponds to 50\% of the critical rotation frequency. We find deviations from
rigid rotation to be moderate in the single stars of this sample. We place the
near-core rotation rates in an evolutionary context and find that the core
rotation must drop drastically before or during the short phase between the end
of the core-hydrogen burning and the onset of core-helium burning. We compute
the spin parameter, which is the ratio of twice the rotation rate to the mode
frequency (also known as the inverse Rossby number), for 1682 gravity modes and
find the majority (95\%) to occur in the sub-inertial regime. The ten stars
with Rossby modes have spin parameters between 14 and 30, while the
gravito-inertial modes cover the range from 1 to 15.Comment: Manuscript of 5 pages, including 2 figures, accepted for publication
in The Astrophysical Journal Letter
The interior rotation of a sample of gamma Doradus stars from ensemble modelling of their gravity mode period spacings
CONTEXT. Gamma Doradus stars (hereafter gamma Dor stars) are known to exhibit
gravity- and/or gravito-intertial modes that probe the inner stellar region
near the convective core boundary. The non-equidistant spacing of the pulsation
periods is an observational signature of the stars' evolution and current
internal structure and is heavily influenced by rotation.
AIMS. We aim to constrain the near-core rotation rates for a sample of gamma
Dor stars, for which we have detected period spacing patterns.
METHODS. We combined the asymptotic period spacing with the traditional
approximation of stellar pulsation to fit the observed period spacing patterns
using chi-squared optimisation. The method was applied to the observed period
spacing patterns of a sample of stars and used for ensemble modelling.
RESULTS. For the majority of stars with an observed period spacing pattern we
successfully determined the rotation rates and the asymptotic period spacing
values, though the uncertainty margins on the latter were typically large. This
also resulted directly in the identification of the modes corresponding with
the detected pulsation frequencies, which for most stars were prograde dipole
gravity and gravito-inertial modes. The majority of the observed retrograde
modes were found to be Rossby modes. We further discuss the limitations of the
method due to the neglect of the centrifugal force and the incomplete treatment
of the Coriolis force.
CONCLUSION. Despite its current limitations, the proposed methodology was
successful to derive the rotation rates and to identify the modes from the
observed period spacing patterns. It forms the first step towards detailed
seismic modelling based on observed period spacing patterns of moderately to
rapidly rotating gamma Dor stars.Comment: 12 pages, 15 figures, 5 tables. Accepted for publication in Astronomy
& Astrophysic
Passive mechanical obstacles vs impairment of neurological command in infant vs adult-acquired spastic paresis
Obstacles mécaniques passifs vs déficit de commande neurologique dans la parésie spastique de l’adulte d’origine infantile et d’origine acquise
HD 41641: A classical Sct-type pulsator with chemical signatures of an Ap star
Among the known groups of pulsating stars, Sct stars are one of the
least understood. Theoretical models do not predict the oscillation frequencies
that observations reveal. Complete asteroseismic studies are necessary to
improve these models and better understand the internal structure of these
targets. We study the Sct star HD 41641 with the ultimate goal of
understanding its oscillation pattern. The target was simultaneously observed
by the CoRoT space telescope and the HARPS high-resolution spectrograph. The
photometric data set was analyzed with the software package PERIOD04, while
FAMIAS was used to analyze the line profile variations. The method of spectrum
synthesis was used for spectroscopically determining the fundamental
atmospheric parameters and individual chemical abundances. A total of 90
different frequencies was identified and analyzed. An unambiguous
identification of the azimuthal order of the surface geometry could only be
provided for the dominant p-mode, which was found to be a nonradial prograde
mode with m = +1. Using and , we estimated the mass,
radius, and evolutionary stage of HD 41641. We find HD 41641 to be a moderately
rotating, slightly evolved Sct star with subsolar overall atmospheric
metal content and unexpected chemical peculiarities. HD 41641 is a pure
Sct pulsator with p-mode frequencies in the range from 10 d to
20 d. This pulsating star presents chemical signatures of an Ap star and
rotational modulation due to surface inhomogeneities, which we consider
indirect evidence of the presence of a magnetic field.Comment: 11 pages, 11 figures, accepted for publication in A&
The HERMES Solar Atlas and the spectroscopic analysis of the seismic solar analogue KIC3241581
Solar-analog stars provide an excellent opportunity to study the Sun's
evolution, i.e. the changes with time in stellar structure, activity, or
rotation for solar-like stars. The unparalleled photometric data from the NASA
space telescope Kepler allows us to study and characterise solar-like stars
through asteroseismology. We aim to spectroscopically investigate the
fundamental parameter and chromospheric activity of solar analogues and twins,
based on observations obtained with the HERMES spectrograph and combine them
with asteroseismology. Therefore, we need to build a solar atlas for the
spectrograph, to provide accurate calibrations of the spectroscopically
determined abundances of solar and late type stars observed with this
instrument and thus perform differential spectral comparisons. We acquire
high-resolution and high signal-to-noise spectroscopy to construct three solar
reference spectra by observing the reflected light of Vesta and Victoria
asteroids and Europa (100<S/N<450) with the \Hermes spectrograph. We then
observe the Kepler solar analog KIC3241581 (S/N~170). We constructed three
solar spectrum atlases from 385 to 900 nm obtained with the Hermes spectrograph
from observations of two bright asteroids and Europa. A comparison between our
solar spectra atlas to the Kurucz and HARPS solar spectrum shows an excellent
agreement. KIC3241581 was found to be a long-periodic binary system. The
fundamental parameter for the stellar primary component are Teff=5689+/-11K,
logg=4.385+/-0.005, [Fe/H]=+0.22+/-0.01, being in agreement with the published
global seismic values confirming its status of solar analogue. KIC 3241581 is a
metal rich solar analogue with a solar-like activity level in a binary system
of unknown period. The chromospheric activity level is compatible to the solar
magnetic activity.Comment: 12 pages, 8 figures, accepted for publication in A&
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