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 $\alpha$ 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 Δν\Delta\nu-ρˉ\bar\rho relation for δ\delta Sct stars using eclipsing binaries and space photometry

Delta Scuti ($\delta$ 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 $\delta$ 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 $\delta$ Sct stars.Comment: 11 pages, including 2 pages of appendix, 2 figures, 2 tables, accepted for publication in ApJ