Non-radial oscillations in rotating intermediate mass stars

ii [i.e. xii], 118 leaves : ill. ; 29 cm.Includes bibliographical references (leaves 111-118).Includes abstract.In this work I investigate the influence of rotation on pulsation frequencies in upper main sequence stars. I use 2D stellar structure models and a 2D linear adiabatic pulsation code to calculate pulsation frequencies for both uniformly and differentially rotating 10 [Special characters omitted.] ZAMS models. Current techniques for these calculations often assume that the pulsation mode can be modelled using a single spherical harmonic and that the rotation rate is slow enough for second order perturbation theory approaches to be valid. These techniques require the rotation rate to be small enough to be considered a small linear perturbation. Using my 2D models, I am able to determine independent limits on the rotation rates for which these techniques are valid. These limits depend strongly on the mode and property in question, and range from 50-400 km sˉ¹. In general, uniform rotation decreases both the frequencies and the large separations, but produces increases in the small separations. In differentially rotating models, the frequencies may either increase or decrease, depending on the mode. Since these variations move in opposite directions, it may be possible to constrain the interior angular momentum distribution from stellar pulsations. Unfortunately, the differences are small, and the observational challenges may be insurmountable. Finally, I investigate how the distortion in the shape of the eigenfunction influences photometric mode identification techniques. Increasing rotation increases the variation in photometric mode identification as a function of inclination, with the result that it may be impossible to rule out certain modes

Models of Achernar : evolution and atmospheres of a rapidly rotating B star

[ix], 70 leaves : ill. ; 28 cm.Includes abstract.Includes bibliographical references (leaves 66-70).I investigate the effects of varying internal angular momentum distributions on the SEDs of massive stars. Rapidly rotating stars are deformed by rotation, and the degree of deformation can give us a further constraint on stellar evolution models, possibly allowing us to constrain the internal angular momentum distribution of these stars. I have modelled three different internal angular momentum distributions: uniform rotation and two different power law distributions. I use a fully implicit 2D stellar evolution code to determine the variation in surface properties exactly. The variation in surface properties of these evolutionary models are then used as the input for atmospheric modelling. I have made a grid of atmospheric intensities at values of T eff and log g , which I then use to interpolate the intensities in the direction of the observer over the surface of the star to produce a synthetic spectral energy distribution. I have used Achernar as a test case for this modelling

Faint variable stars observed with

We present preliminary analysis of approximately 10 variable stars observed with Kepler. The sample stars are faint, and have temperatures greater than 8000 K. The stars were observed for up to three quarters (Q14-Q16) in long cadence mode. Frequencies were extracted with Period04, and 1-21 frequencies were detected in each quarter, with an average of 8 frequencies per quarter. Some variability is detected from quarter to quarter, while the dominant frequencies remain unchanged. We fit the frequencies using MESA models between 1.5 and 3 solar masses, and varied the core overshoot. Best fitting properties of each of these stars will be discussed

Core overshoot and convection in δ Scuti and γ Doradus stars

The effects of rotation on pulsation in δ Scuti and γ Doradus stars are poorly understood. Stars in this mass range span the transition from convective envelopes to convective cores, and realistic models of convection are thus a key part of understanding these stars. In this work, we use 2D asteroseismic modelling of 5 stars observed with the Kepler spacecraft to provide constraints on the age, mass, rotation rate, and convective core overshoot. We use Period04 to calculate the frequencies based on short cadence Kepler observations of five γ Doradus and δ Scuti stars. We fit these stars with rotating models calculated using MESA and adiabatic pulsation frequencies calculated with GYRE. Comparison of these models with the pulsation frequencies of three stars observed with Kepler allowed us to place constraints on the age, mass, and rotation rate of these stars. All frequencies not identified as possible combinations were compared to theoretical frequencies calculated using models including the effects of rotation and overshoot. The best fitting models for all five stars are slowly rotating at the best fitting age and have moderate convective core overshoot. In this work, we will discuss the results of the frequency extraction and fitting process

Core overshoot and convection in δ Scuti and γ Doradus stars

The effects of rotation on pulsation in δ Scuti and γ Doradus stars are poorly understood. Stars in this mass range span the transition from convective envelopes to convective cores, and realistic models of convection are thus a key part of understanding these stars. In this work, we use 2D asteroseismic modelling of 5 stars observed with the Kepler spacecraft to provide constraints on the age, mass, rotation rate, and convective core overshoot. We use Period04 to calculate the frequencies based on short cadence Kepler observations of five γ Doradus and δ Scuti stars. We fit these stars with rotating models calculated using MESA and adiabatic pulsation frequencies calculated with GYRE. Comparison of these models with the pulsation frequencies of three stars observed with Kepler allowed us to place constraints on the age, mass, and rotation rate of these stars. All frequencies not identified as possible combinations were compared to theoretical frequencies calculated using models including the effects of rotation and overshoot. The best fitting models for all five stars are slowly rotating at the best fitting age and have moderate convective core overshoot. In this work, we will discuss the results of the frequency extraction and fitting process

Mass loss in 2D Rotating Stellar Models

International audienceRadiatively driven mass loss is an important factor in the evolution of massive stars. The mass-loss rates depend on a number of stellar parameters, including the effective temperature and luminosity. Massive stars are also often rapidly rotating, which affects their structure and evolution. In sufficiently rapidly rotating stars, both the effective temperature and radius vary significantly as a function of latitude, and hence mass loss rates can vary appreciably between the poles and the equator. In this work, we discuss the addition of mass loss to a 2D stellar evolution code (ROTORC) and compare evolution sequences with and without mass loss

Mass loss in 2D rotating stellar models

International audienceRadiatively driven mass loss is an important factor in the evolution of massive stars. The mass loss rates depend on a number of stellar parameters, including the effective temperature and luminosity. Massive stars are also often rapidly rotating, which affects their structure and evolution. In sufficiently rapidly rotating stars, both the effective temperature and surface flux vary significantly as a function of latitude, and hence mass loss rates can vary appreciably between the poles and the equator. In this work, we discuss the addition of mass loss to a 2D stellar evolution code (ROTORC) and compare evolution sequences with and without mass loss