Asteroseismology and Interferometry

Asteroseismology provides us with a unique opportunity to improve our understanding of stellar structure and evolution. Recent developments, including the first systematic studies of solar-like pulsators, have boosted the impact of this field of research within Astrophysics and have led to a significant increase in the size of the research community. In the present paper we start by reviewing the basic observational and theoretical properties of classical and solar-like pulsators and present results from some of the most recent and outstanding studies of these stars. We centre our review on those classes of pulsators for which interferometric studies are expected to provide a significant input. We discuss current limitations to asteroseismic studies, including difficulties in mode identification and in the accurate determination of global parameters of pulsating stars, and, after a brief review of those aspects of interferometry that are most relevant in this context, anticipate how interferometric observations may contribute to overcome these limitations. Moreover, we present results of recent pilot studies of pulsating stars involving both asteroseismic and interferometric constraints and look into the future, summarizing ongoing efforts concerning the development of future instruments and satellite missions which are expected to have an impact in this field of research.Comment: Version as published in The Astronomy and Astrophysics Review, Volume 14, Issue 3-4, pp. 217-36

The Gaia-ESO Public Spectroscopic Survey: Motivation, implementation, GIRAFFE data processing, analysis, and final data products

The Gaia-ESO Public Spectroscopic Survey is an ambitious project designed to obtain astrophysical parameters and elemental abundances for 100,000 stars, including large representative samples of the stellar populations in the Galaxy, and a well-defined sample of 60 (plus 20 archive) open clusters. We provide internally consistent results calibrated on benchmark stars and star clusters, extending across a very wide range of abundances and ages. This provides a legacy data set of intrinsic value, and equally a large wide-ranging dataset that is of value for homogenisation of other and future stellar surveys and Gaia's astrophysical parameters. This article provides an overview of the survey methodology, the scientific aims, and the implementation, including a description of the data processing for the GIRAFFE spectra. A companion paper (arXiv:2206.02901) introduces the survey results. Gaia-ESO aspires to quantify both random and systematic contributions to measurement uncertainties. Thus all available spectroscopic analysis techniques are utilised, each spectrum being analysed by up to several different analysis pipelines, with considerable effort being made to homogenise and calibrate the resulting parameters. We describe here the sequence of activities up to delivery of processed data products to the ESO Science Archive Facility for open use. The Gaia-ESO Survey obtained 202,000 spectra of 115,000 stars using 340 allocated VLT nights between December 2011 and January 2018 from GIRAFFE and UVES. The full consistently reduced final data set of spectra was released through the ESO Science Archive Facility in late 2020, with the full astrophysical parameters sets following in 2022

EELT-HIRES the high-resolution spectrograph for the E-ELT

The first generation of E-ELT instruments will include an optic-infrared High Resolution Spectrograph, conventionally indicated as EELT-HIRES, which will be capable of providing unique breakthroughs in the fields of exoplanets, star and planet formation, physics and evolution of stars and galaxies, cosmology and fundamental physics. A 2-year long phase A study for EELT-HIRES has just started and will be performed by a consortium composed of institutes and organisations from Brazil, Chile, Denmark, France, Germany, Italy, Poland, Portugal, Spain, Sweden, Switzerland and United Kingdom. In this paper we describe the science goals and the preliminary technical concept for EELT-HIRES which will be developed during the phase A, as well as its planned development and consortium organisation during the study.This work was supported from the Italian National Institute for Astrophysics (Istituto Nazionale Italiano di Astrofisica, INAF). RM , DB, CH, MF, XS, DQ and MGH acknowledge support from the UK Science and Technology Facilities Council (STFC). MGH is supported by the ERC Advanced grant Emergence-32056. This work was supported by Fundaçao para a Ciência e a Tecnologia (FCT, Portugal), project ref. PTDC/FIS-AST/1526/2014, through national funds and by FEDER through COMPETE2020 (ref. POCI-01-0145-FEDER-016886), as well as through grant UID/FIS/04434/2013 (POCI-01-0145-FEDER-007672). P.F. and N.C.S. also acknowledge the support from FCT through Investigador FCT contracts of reference IF/01037/2013, IF/00169/2012, and IF/00028/2014, respectively, and POPH/FSE (EC) by FEDER funding through the program “Programa Operacional de Factores de Competitividade - COMPETE”. P.F. further acknowledge support from FCT in the form of exploratory projects of reference IF/01037/2013CP1191/CT0001 and IF/00028/2014/CP1215/CT0002. PJA acknowledges financial support from AYA2011-30147-C03-01 and AYA2014-54348-C3-1-R by MINECO/Spain, partially supported by FEDER funds/EU. Research activities of the Board of Stellar Astronomy, at the Federal University of Rio Grande do Norte are supported by continuous grant of CNPq, FAPERN and CAPES brazilian agencies and by the INCT INEspaço. E.D.M and V.Zh.A. also acknowledge the support from the FCT (Portugal) in the form of the grants SFRH/BPD/76606/2011 and SFRH/BPD/70574/2010, respectively

Métodos Numéricos

Neste conjunto de notas pretende-se dar uma visão geral dos métodos numéricos, das suas condições de aplicabilidade e das suas limitações. O tratamento de cada tópico é feito a nível introdutório, incidindo no significado geométrico sempre que possível.Pretende-se transmitir conhecimentos que permitam a classificação e/ou a adequação de problemas numéricos a problemas tipo, a escolha do método numérico mais adequado e a compreensão dos diagnósticos de erro e diagnósticos de solução

Seismic properties of the Sun's superadiabatic layer .1. Theoretical modelling and parametrization of the uncertainties

Some alternatives to the traditional mixing-length theory (MLT) have recently been proposed for modelling convective heat transport inside stars. The ideal formulation is one that does not involve any free parameters. However, in our present state of ignorance we still need at least one free parameter in order to build solar models with the correct radius. Having adjusted this parameter (e.g. the mixing-length parameter α_c_) to obtain the observed radius, we cannot discriminate non-seismically between different convective theories, regardless of how low-efficiency convection is treated. In this paper we consider how the additional information provided by global p-mode frequencies can be used to investigate low-efficiency convection at the top of the solar convective envelope and discriminate between different theories. We consider a parametrization which in addition to the mixing length has two further parameters: one (β_c_) which regulates the relative degree of overadiabaticity (or inefficiency) of convection, and a second (m) that affects the transition between the regimes of efficient and inefficient convection. Our parametrization includes traditional MLT__ and the theory of Canuto & Mazzitelli as particular cases. We study the effect of varying these parameters by constructing a series of envelope models with the same depth of the convection zone and computing their oscillation frequencies. We discuss our results in terms of kernels relating frequency changes to changes in the structure of the superadiabatic region.Some alternatives to the traditional mixing-length theory (MLT) have recently been proposed for modelling convective heat transport inside stars. The ideal formulation is one that does not involve any free parameters. However, in our present state of ignorance we still need at least one free parameter in order to build solar models with the correct radius. Having adjusted this parameter (e.g. the mixing-length parameter alpha(c)) to obtain the observed radius, we cannot discriminate non-seismically between different convective theories, regardless of how low-efficiency convection is treated. In this paper we consider how the additional information provided by global p-mode frequencies can be used to investigate low-efficiency convection at the top of the solar convective envelope and discriminate between different theories. We consider a parametrization which in addition to the mixing length has two further parameters: one (beta(c)) which regulates the relative degree of overadiabaticity (or inefficiency) of convection, and a second (m) that affects the transition between the regimes of efficient and inefficient convection. Our parametrization includes traditional MLT and the theory of Canuto & Mazzitelli as particular cases. We study the effect of varying these parameters by constructing a series of envelope models with the same depth of the convection zone and computing their oscillation frequencies. We discuss our results in terms of kernels relating frequency changes to changes in the structure of the superadiabatic region

SEISMIC STUDY OF OVERSHOOT AT THE BASE OF THE SOLAR CONVECTIVE ENVELOPE

Sharp transitions in the internal stratification of a star give rise to a characteristic signature in normal-mode frequencies. In particular, if in the Sun such a feature were located well inside the acoustic cavity of many solar p modes, it would give rise to a signal that was a periodic function of the frequency of the modes. We use this signature to detect the base of the solar convection zone and to investigate the existence of convective overshoot into the radiative interior. Two methods are considered. The 'absolute' method obtains the residuals in the frequencies after making a smooth fit in mode order n, and then uses an asymptotic description of the eigenfunctions to make a fit to the residuals. The 'differential' method makes an asymptotic fit to the differences between solar frequencies and the frequencies of a theoretical model. Various theoretical models of overshoot at the base of the convection zone predict the existence of a rather abrupt transition to subadiabatic stratification at the base of the overshoot region. We find no strong evidence for the existence of an overshoot region of this kind. Indeed if the overshoot consists of an essentially adiabatic extension of the convection zone followed by an abrupt transition to radiative stratification then we may (at the 95% confidence level) put an upper limit of 0.07 local pressure scale heights on the extent of the overshoot layer.Sharp transitions in the internal stratification of a star give rise to a characteristic signature in normal-mode frequencies. In particular, if in the Sun such a feature were located well inside the acoustic cavity of many solar p modes, it would give rise to a signal that was a periodic function of the frequency of the modes. We use this signature to detect the base of the solar convection zone and to investigate the existence of convective overshoot into the radiative interior. Two methods are considered. The ''absolute'' method obtains the residuals in the frequencies after making a smooth fit in mode order n, and then uses an asymptotic description of the eigenfunctions to make a fit to the residuals. The ''differential'' method makes an asymptotic fit to the differences between solar frequencies and the frequencies of a theoretical model. Various theoretical models of overshoot at the base of the convection zone predict the existence of a rather abrupt transition to subadiabatic stratification at the base of the overshoot region. We find no strong evidence for the existence of an overshoot region of this kind. Indeed if the overshoot consists of an essentially adiabatic extension of the convection zone followed by an abrupt transition to radiative stratification then we may (at the 95% confidence level) put an upper limit of 0.07 local pressure scale heights on the extent of the overshoot layer

Possible solar cycle variations in the convection zone

Using data from the Global Oscillations Network Group (GONG) that covers the period from 1995 to 1998 we study the change in frequencies of solar oscillations with solar activity. From these frequencies we attempt to determine any possible variation in solar structure with solar activity. We do not find any evidence of a change in the convection zone depth or extent of overshoot below the convection zone during the solar cycle

Radius determination of solar-type stars using asteroseismology: what to expect from the Kepler mission

For distant stars, as observed by the NASA Kepler satellite, parallax information is currently of fairly low quality and is not complete. This limits the precision with which the absolute sizes of the stars and their potential transiting planets can be determined by traditional methods. Asteroseismology will be used to aid the radius determination of stars observed during NASA's Kepler mission. We report on the recent asteroFLAG hare-and-hounds Exercise#2, where a group of "hares" simulated data of F-K main-sequence stars that a group of "hounds" sought to analyze, aimed at determining the stellar radii. We investigated stars in the range 9 < V < 15, both with and without parallaxes. We further test different uncertainties in Teff, and compare results with and without using asteroseismic constraints. Based on the asteroseismic large frequency spacing, obtained from simulations of 4 yr time series data from the Kepler mission, we demonstrate that the stellar radii can be correctly and precisely determined, when combined with traditional stellar parameters from the Kepler Input Catalogue. The radii found by the various methods used by each independent hound generally agree with the true values of the artificial stars to within 3%, when the large frequency spacing is used. This is 5-10 times better than the results where seismology is not applied. These results give strong confidence that radius estimation can be performed to better than 3% for solar-like stars using automatic pipeline reduction. Even when the stellar distance and luminosity are unknown we can obtain the same level of agreement. Given the uncertainties used for this exercise we find that the input log g and parallax do not help to constrain the radius, and that Teff and metallicity are the only parameters we need in addition to the large frequency spacing. It is the uncertainty in the metallicity that dominates the uncertainty in the radius

CoRoT observations of the young open cluster Dolidze 25 RID B-4715-2008

We present some preliminary results based on the CoRoT observations of the young distant cluster Dolidze 25. The light curve for the 28 stars observed by the satellite have been analyzed and the relevant periodogram presented. As a result we have found two binary, three Pulsating Be, three SPB, two Spotted and one ellipsoidal variables. Noteworthy, we have also identified one PMS delta Scuti candidate