Related papers: An asteroseismic signature of helium ionization
The region of the second ionization of helium in the Sun is a narrow layer near the surface. Ionization induces a local change of the adiabatic exponent $\Gamma_1$, which produces a characteristic signature in the frequencies of p-modes. By…
Element diffusion is expected to occur in all kinds of stars : according to the relative effect of gravitation and radiative acceleration, they can fall or be pushed up in the atmospheres. Helium sinks in all cases, thereby creating a…
There are regions in stars, such as ionization zones and the interface between radiative and convective regions, that cause a localized sharp variation in the sound speed. These are known as "acoustic glitches". Acoustic glitches leave…
In the present paper, we aim to constrain the properties of the ionisation region in a star from the oscillation frequency variation (a so-called glitch) caused by rapid structural variations in this very region. In particular, we seek to…
Asteroseismology is found to be a excellent tool for detecting diffusion-induced helium gradients inside main-sequence A stars. Models have been computed for 1.6 and 2.0 M$_{\odot}$ stars with pure helium diffusion, at different ages, so…
Regions of rapid variation in the internal structure of a star are often referred to as acoustic glitches since they create a characteristic periodic signature in the frequencies of p modes. Here we examine the localized disturbance arising…
Asteroseismology of solar-type stars is an important tool for constraining stellar parameters and internal structure. Several frequency combinations are largely used for comparisons between models and observations. In particular, the…
We present a summary of an asteroseismic signature of helium ionization reported by Houdek & Gough (2007, 2008, 2009) for low-degree p modes in solar-type stars, and illustrate its applications for asteroseismic diagnoses.
Intermediate degree modes of the solar oscillations have previously been used to determine the solar helium abundance to a high degree of precision. However, we cannot expect to observe such modes in other stars. In this work we investigate…
Low amplitude is the defining characteristic of solar-like oscillations. The space projects $Kepler$ and $CoRoT$ give us a great opportunity to successfully detect such oscillations in numerous targets. Achievements of asteroseismology…
Determining the properties of solar-like oscillating stars can be subject to many biases. A particularly important example is the helium-mass degeneracy, where the uncertainties regarding the internal physics can cause a poor determination…
The large frequency separation between modes of the same degree and consecutive orders in a star is approximately proportional to the square root of its mean density. To determine the large frequency separation as accurately as possible a…
Acoustic glitches are regions inside a star where the sound speed or its derivatives change abruptly. These leave a small characteristic oscillatory signature in the stellar oscillation frequencies. With the precision achieved by {\it…
We present an improved model for an asteroseismic diagnostic contained in the frequency spacing of low-degree acoustic modes. By modelling in a realistic manner regions of rapid variation of dynamically relevant quantities, which we call…
High-precision frequencies of acoustic modes in red giant stars are now available thanks to the long observing length and high-quality of the light curves provided by the NASA Kepler mission, thus allowing to probe the interior of evolved…
The structural stratification of a solar-type main sequence star primarily depends on its mass and chemical composition. The surface heavy element abundances of the solar-type stars are reasonably well determined using conventional…
The large separations between the oscillation frequencies of solar-like stars are measures of stellar mean density. The separations have been thought to be mostly constant in the observed range of frequencies. However, detailed…
Current stellar model predictions of adiabatic oscillation frequencies differ significantly from the corresponding observed frequencies due to the non-adiabatic and poorly understood near-surface layers of stars. However, certain…
It has been established earlier that sharp features like the base of the convective zone or the second helium ionisation zone inside a star give rise to sinusoidal oscillations in the frequencies of pulsation. The acoustic depth of such…
Helioseismology is the study of the solar interior using observations of oscillations at the surface. It suffers from systematic errors, such as a center-to-limb error in travel-time measurements. Understanding these errors requires a good…