STELLAR SCIENCE

STELLAR SCIENCE

STELLAR SCIENCE

The main goal of the Stellar Science (STESCI) activities is to provide to the PDC specifications, methods and tools to determine stellar parameters such as mass, radius, age, chemical composition, information on stellar activity and rotation, in order to achieve the PLATO scientific objectives.

During the definition phase, STESCI will demonstrate the feasibility of the full characterization of the stars at the required level of precision.

STESCI ensures the development of methods and algorithms related to the stellar physics programme, such as oscillation mode inversion techniques, production of grids of stellar evolution models involving new physical ingredients (rotation, internal waves, magnetic fields), etc...

The STESCI activities are divided into six major topics addressing areas of expertise that require input from the scientific community to the PLATO mission and an interface between STESSI and the other work packages. Each work package is divided into several topics corresponding to specific studies to carry out. Valuable models and numerical tools already exist that will provide a first generation of outputs and will serve as a starting basis for building an improved, second generation of relevant models and tools. Activities will continue after launch, based on PLATO data exploitation.

Detailed organisation

PSPM WP 120000

Title: Stellar Science coordination

Leader: M.J. Goupil

Objectives: Coordination of the work packages WP121000 to WP127000.

PSPM WP 121000

Title: Stellar modeling

Leader: M.A. Dupret

Objectives: Coordination of works from work packages WP 121 100 to WP 121 500.

1. Provide grids of state-of-the-art stellar models produced by selected, accurate and tested stellar

evolution codes along with their pulsation frequencies (WP 121 100);

2. Establish a set of stellar objects (clusters, binaries) as test cases for the grid code(s) (WP 121 100)

3. Develop improved descriptions for the constitutional physics of stars from multi-dimensional simulations

of rotation and convection (WP 121 400) and the influence of binarity (WP 121 500) with

specific emphasis on mixing processes inside stars and the effect on pulsational properties;

4. Implement these improved descriptions in a 1-D stellar evolution including rotation (WP 121 200 and WP 121 300);

5. Provide a second generation of updated stellar models (WP 121 100, WP 121 200, WP 121 300) with such an

improved code including these new descriptions;

6. Test these improvements with available (CoRoT and Kepler) data

7.Finally provide a third and final grid of models including all of the above

PSPM WP 121100

Title: 1D Stellar models

Leader: Y. Lebreton

Objectives: To provide grids of high quality 1D stellar models and an automated evolutionary code specifically adapted to low mass, main sequence stars

PSPM WP 121110

Title: Very low mass stars

Leader: S. Cassisi

Objectives: To provide an extended and updated grid of state-of-the-art evolutionary models for stellar structures in the Very Low Mass Stars regime (M<0.5 solar mass) for any specified chemical composition. These models will be computed from the Pre-Main Sequence to the Main Sequence.

PSPM WP 121120

Title: Low mass stellar models

Leader: J. Montalban

Objectives: Provide grids of high quality 1D stellar models for low mass, main sequence stars

PSPM WP 121130

Title: Theoretical oscillation frequencies

Leader: J. C. Suarez

Objectives: Provide grids of high quality 1D stellar models for low mass, main sequence stars

PSPM WP 121200

Title: Transport processes

Leader: A. Palacios

Objectives: To model several transport processes, beyond classical convective heat transport, that are known or expected to play an important role in determining stellar structure and influence stellar evolution. Formulations for transport of heat, chemical elements and angular momentum induced by motions such as convection, rotation, turbulence or waves will be improved or developed with the objective of implementation in a 1D stellar evolutionary code.

PSPM WP 121300

Title: PMS evolution

Leader: J. P. Marques

Objectives: To build a computation tool that provides PMS stellar models with rotation profiles and initial conditions as realistic as possible.

PSPM WP 121400

Title: 2D/3D Stellar evolution models

Leader: M. Rieutord

Objectives: The objective of the WP is to deliver very precise 2D stellar models. Indeed, the determination of the bulk parameter of a star (Age, Mass, etc.) from seismic data needs a very good preliminary model of the star. Such good models require at least two spatial dimensions to properly include the effects of rotation. We therefore propose to deliver models at the state-of-the-art level, which can be combined to the best oscillations codes out of which the most precise stellar parameters can be drawn.

PSPM WP 121500

Title: Binarity

Leader: S. Mathis

Objectives: The first objective of this WP is to deliver advanced models of tidal, MHD, and accretion torques applied to stars hosting planetary or/and stellar companions. Second, the modification of their rotational and chemical evolution because of the presence of a companion will be studied using ab-initio models for internal transport mechanisms and applied torques. The corresponding new generation of stellar evolution models will be delivered as well as the corresponding seismic diagnosis.

PSPM WP 122000

Title: Non seismic diagnostics and model atmospheres

Leader: T. Morel

Objectives: Define general objectives of WG and assess means to achieve them. Define tasks of the four working subgroups (3D NLTE model atmospheres and stellar chemical composition, determination of Te, L and BC, determination of limb darkening, atmospheres of M dwarfs).

PSPM WP 122100

Title: 3D hydrodynamical stellar atmospheres and non-LTE stellar spectra

Leader: M. Asplund

Objectives: Assess reliability of 1D LTE model atmospheres (e.g., temperature-optical depth relation) for FGK dwarfs and the impact that the neglect of granulation may have on the stellar parameters derived for the host stars. Derive chemical compositions of very and low mass stars.

PSPM WP 122200

Title: HR diagram and chemical abundances

Leader: C. Allende Prieto

Objectives: Assess limitations and accuracy of current methods for the determination of Te and BC in FGK dwarfs. Based on the expectations for the GAIA data, estimate the accuracy on the radius of the stellar host that is presently achievable. Provide these quantities and their uncertainties as input to the others SPM WP.

PSPM WP 122300

Title: Determination of limb-darkening

Leader: A. Claret

Objectives: to determine with precision the limb-darkening distribution of the host stars. Identify and quantify the sources of uncertainties in masses, radii and effective temperatures of the host stars.

PSPM WP 122400

Title: Model atmospheres of M dwarfs

Leader: B. Plez

Objectives: M dwarfs are particularly suited to detect planets. It is therefore mandatory to understand properly the physics of the atmospheres of these cool stars and their relation to planetary transits and to provide high quality model atmospheres.

PSPM WP 123000

Title: Stellar activity and rotation

Leader: A.F. Lanza

Objectives: a) To measure the level of stellar magnetic activity, the rotation period, and the latitudinal differential rotation. They will be input to modeling of stellar structure and evolution, stellar atmospheres, and hydromagnetic dynamo action; b) to predict magnetic field effects on stellar eigenfrequencies; c) to predict the radial velocity perturbations arising from magnetic perturbations of surface convection and photospheric brightness inhomogeneities this is of fundamental importance to confirm telluric planets and measure their mass. The measure of the rotation period, in combination with models of stellar angular momentum evolution, can be used to estimate the age of planet-hosting stars in the field through the methods of gyro-chronology. A knowledge of stellar rotation is fundamental also to study tidal effects in planetary systems with close-in planets. The level of stellar magnetic activity controls the photo-evaporation of the atmosphere of close-in planets and the space weather in planetary systems having late-type stars with winds coming from magnetically controlled coronae.

PSPM WP 123100

Title: Spot models

Leader: B. Mosser

Objectives: To provide methods and algorithms for the measurement of spot distributions, in close relation with the stellar activity (WP123000)

PSPM WP 123200

Title: Surface convection (1D-3D)

Leader: F. Kupka

Objectives: This WG must provide information on the properties of surface activity of the host stars. In particular, it is dedicated to determine the properties of surface convection (granulation,) in function of the spectral type using both 3D numerical simulations and 1D models of convection.

PSPM WP 123300

Title: Model of rotational evolution and gyrochronology

Leader: M. Pinsonneault

Objectives: Testing of theoretical models of stellar angular momentum loss, internal angular momentum transport, and the associated mixing. There are two distinct applications: understanding of stellar physics and applications to stellar population studies. Examples of the former would include asteroseismic tests of dynamo models and distinguishing between magnetic, wave-driven, and hydrodynamic transport processes in stellar interiors. Examples of the latter would include exploring rotation as an age indicator for low mass stars and synthesizing connections between stellar activity (chromospheric and coronal), rotation, age, and mass for habitability studies.

PSPM WP 123400

Title: Dynamos and differential rotation

Leader: A.S. Brun

Objectives: Most stars rotate and exhibit a large diversity of magnetic fields. It is believed that dynamo action, i.e the complex, nonlinear interplay between, convection, large scale flows (differential rotation and meridional circulation) and magnetic fields, is the source of the magnetism of solar like stars and M dwarfs, the main stellar targets of PLATO. Being able to constrain all these MHD processes is crucial to our understanding of stars and their impact on their environment. Seismic inversions of the extent of convective envelope, the surface and internal profiles of large scale flows and of proxies of the magnetic activity will help reaching this goal.

PSPM WP 123500

Title: Tools to measure rotational modulation

Leader: S. Messina

Objectives: To derive the stellar rotation period from the stellar flux rotational modulation. The latter is induced either by surface temperature inhomogeneities that are carried in and out of view by the stellar rotation or eclipses in close binary systems. Different algorithms (e.g., Fourier-based methods, phase dispersion minimization, amplitude of variance) will be used to analyze the photometric time series, to assign a quality flag to each inferred rotation period, and to estimate their confidence level. Possible rotation period variations related to surface differential rotation will be also investigated.

PSPM WP 123600

Title: Stellar rotation from transits

Leader: A. Silva-Valio

Objectives: Modelling of starspots occulted by the planet during its transits and estimate of the rotation rate at the occulted latitude using starspots as tracers. In combination with the out-of-transit light curve modelling, this allows us to estimate stellar differential rotation.

PSPM WP 124000

Title: Seismic diagnostics

Leader: M. Cunha

Objectives: To deliver inverse and forward procedures to the PDC and associated validated numerical codes which are able to provide precise mass, age radius and other information on the host stars.

PSPM WP 124100

Title: Forward approaches

Leader: I. Roxburgh

Objectives: To test and compare forward procedures that can deliver total mass, radius, age, and other information on the host stars. The adopted procedures will focus on low mass, main sequence stars from F to M spectral types.

PSPM WP 124200

Title: Inverse techniques

Leader: D. Reese

Objectives: To develop inverse methods that can provide total mass, internal density profile and other information on the host stars, The adopted procedures will focus on low mass, main sequence stars from F to M spectral types.

PSPM WP 125000

Title: Determination of stellar parameters

Leader: J. Christensen-Dalsgaard

Objectives: Coordinate the definition of the work in WP 125100, 125200, 125300 and 125400, such that it will result in the establishment of procedures to determine masses, radii, composition and other relevant properties with a precision required by the exoplanet WPs. Maintain close coordination with the activities under WP 121000 (Stellar models) to ensure that reliable modelling tools will be available for use in the analysis of the data. Maintain close coordination with WP122000 to ensure that optimal modelling tools will be available for use for determination of 'classical' parameters under WP125200.

PSPM WP 125100

Title: Scaling laws

Leader: A. Miglio

Objectives: Provide procedures to compute mass, radius, and other relevant quantities from asteroseismic and non-asteroseismic data, through the application of scaling laws and other relevant relations between the observed quantities, in particular frequencies and power distribution, and the stellar properties. This must include procedures for full statistical analysis,allowing determination of error properties of the inferred quantities.

PSPM WP 125200

Title: Classical parameters

Leader: S. Feltzing

Objectives: Prepare procedures to incorporate reliable information about classical stellar properties in the analysis to determine stellar parameters. These properties include effective temperature, luminosity, radius, composition from ground-based photometry and spectroscopy and, in particular, from the Gaia observations, expected to be available when PLATO is launched. The analysis must include use of optimal stellar atmosphere modelling for the interpretation of the observations. Procedures must be included for full statistical analysis, allowing determination of error properties of the inferred quantities.

PSPM WP 125300

Title: Seismic Parameters

Leader: C. Karoff

Objectives: Based on procedures from 125100 and 125200, combine the results in procedures to determine the desired properties of the stars (mass, radius, age, composition, ...) in an optimal fashion, including also a study of the benefit of including individual frequencies in the analysis. Procedures must be included for full statistical analysis, allowing determination of error properties of the inferred quantities. As a side benefit, information should be extracted which documents, in a statistically solid fashion, errors in the underlying stellar models, to be used in updating the modelling and hence reducing the systematic errors in the inferred stellar parameters.

PSPM WP 125400

Title: Open Clusters

Leader: S. Basu

Objectives: Based on procedures from WP125100 and WP125200, and using input from WP125300, identify and develop the procedures that make use of the specific information provided from the fact that stars are members of open clusters. This includes specific requirements on the 'classical' information under WP125200. Procedures must be included for full statistical analysis, allowing determination of error properties of the inferred quantities. As a side benefit, information should be extracted which documents, in a statistically solid fashion, errors in the underlying stellar models, to be used in updating the modelling and hence reducing the systematic errors in the inferred stellar parameters, noting that internal consistency amongst cluster stars may be particularly relevant for this.

PSPM WP 126000

Title: Mode Physics

Leader: K. Belkacem

Objectives: The mode physics WP126000 to WP126400 are designed to provide realistic determinations of mode amplitudes and line-widths, in relation with WP123000. The objectives are to provide realistic stellar lightcurves including oscillations as well as an estimation and modeling of sub-surface effects (e.g. turbulent pressure, granulation, magnetic effects) on mode parameters. These developments will benefi t from the CoRoT and KEPLER legacy.

PSPM WP 126100

Title: Mode amplitude and surface effects on mode parameters

Leader: R. Samadi

Objectives: The first objective is to prepare and provide effcient tools that give us access to a realistic determination of mode amplitudes across the HR-diagram by using semi-analytical modeling as well as 3D hydrodynamic simulations. Using CoRoT and Kepler observations will test the results. The second objective is to investigate one specific contribution to what is commonly called surface e effects, e.g. the effect of turbulent pressure.

PSPM WP 126200

Title: Mode line-width

Leader: M.A. Dupret

Objectives: This WP aims to improve the theoretical determination of mode line-width. A quantitative estimation of mode line-widths of solar-like stars across the HR diagram will be provided. It is an important objective since the line-width determines the mode detectability.

PSPM WP 126300

Title: Relation Intensity-Velocity

Leader: G. Houdek

Objectives: Relation between mode Intensity and velocity: the CoRoT mission taught us that a correct modeling of mode amplitude and line-width is not sufficient to reproduce the observations. Indeed, the ratio between mode intensity (luminosity) and velocity amplitudes is also needed. To progress on the knowledge of this ratio, dominated by non-adiabatic effects, ground-based spectroscopic as well as photometric observations are needed on the same targets. In addition, this work package aims to investigate the effect of adopting various stellar atmospheres on the superadiabatic outer stellar layers and consequently mode amplitude ratios.

PSPM WP 126400

Title: Seismology of magnetic activity

Leader: L. Gizon

Objectives: The main objective is to characterize and parameterize the influence of magnetic field on mode parameters.

PSPM WP127 000

Title: Seismic constraints from ageing stars

Leader: B. Mosser

Objectives: This WP aims at coordinating the activities of stellar modelling and seismic tools specific for the case of evolved stars. This concerns first exoplanets orbiting red giants stars, but also procedures that constraints stellar evolution for strengthening the properties of stars hosting planets at all evolutionary stages.

PSPM WP127 100

Title: Stellar models of evolved stars

Leader: P. Ventura

Objectives: Provide grids of high quality 1D stellar models for low and intermediate mass in the phases of red giant branch (RGB) and core He-burning (He-B). These grids are an extension of those delivered by WP 121 100 for a reduced set of stellar parameters and lower precision than that required for main sequence models. The domain of mass and age will be determined by the constraints provided by the age of the universe and the maximum luminosity for exo-planet transit detection in the framework of PLATO.

PSPM WP127 200

Title: Seismic diagnostics for evolved stars

Leader: A. Miglio

Objectives: To develop seismic diagnostics specific to evolved stars that can provide precise stellar mass, age, radius and properties of the stellar interior. This objective has three applications: providing accurate stellar parameters for planetary host stars, understanding of stellar physics, and characterising stellar populations monitored by PLATO. These developments build upon the CoRoT, Kepler, and K2 legacy.

PSPM WP127 300

Title: Constraints on main-sequence stars

Leader: J. Montalban

Objectives: Deriving constraints on main-sequence stars hosting planets from the comprehensive study of the observations of stellar populations including all evolutionary stages

PSPM WP128 000

Title: Power spectrum fitting tools

Leader: W.J. Chaplin

Objectives: Coordination of the workpackages WP128100 through WP128250, which deal with the application of data analysis techniques -- in particular "peak bagging" -- to the frequency-power spectra of the lightcurves, in order to extract estimates of the seismic parameters.

PSPM WP128 100

Title: Average seismic parameters

Leader: R. Garcia

Objectives: To specify requirements and procedures for the estimation of average seismic parameters for solar-type stars. These data will be used to provide asteroseismic stellar properties estimates which will be final estimates where no further detailed "peak bagging" analysis for individual modes is possible (low SNR targets); or serve as preliminary estimates if further detailed modelling, using individual frequencies, is performed. These average parameters will also be crucial as prior inputs for the peak-bagging analyses.

PSPM WP128 200

Title: Mode fitting tools

Leader: W.J. Chaplin

Objectives: Coordination of the workpackages WP128210 through WP128240 which are devoted to peak-bagging, i.e., estimation of the seismic parameters on individual modes.

PSPM WP128 210

Title: Solar-like stars

Leader: Chaplin (UoB)

Objectives: Specify optimal requirements, techniques and procedures for peak-bagging solar-type stars.

PSPM WP128 220

Title: Solar-like stars with planets

Leader: T. Campante

Objectives: Specify additional requirements and procedures when peak-bagging planet hosts (e.g., requirements on preparation of the data so that signatures of the transits do not interfere with the fitting of the modes, including estimation of intrinsic stellar sources of broad-band background power).

PSPM WP128 230

Title: Multiple Stars

Leader: G.R. Davies

Objectives: Specify additional techniques and procedures for fitting stars in known binaries, i.e., to leverage the additional prior constraints available in such systems, in particular "seismic binaries" where the power spectra of two physically associated stars are detected in the frequency-power spectrum of the same lightcurve.

PSPM WP128 240

Title: Ensemble Fit

Leader: J. Ballot

Objectives: Specify additional techniques and procedures for fitting stars in clusters, i.e., to leverage the additional prior constraints available on such stars.

PSPM WP128 250

Title: Red Giants

Leader: S. Hekker

Objectives: Specify special techniques and procedures needed to extract seismic parameters on the oscillations of red giant stars.

PSPM WP 129000

Title: Interfaces

Leader: F. Baudin

Objectives: Interface between Stellar Science and other WPs, specifically PDC and Exoplanet WPs.

Chair: Marie-Jo Goupil Observatoire de Paris

MarieJo.Goupil at obspm.fr