STELLAR SCIENCE
STELLAR SCIENCE
STELLAR SCIENCE
This package has the responsibility of organizing the development of theory and modeling in stellar physics in order to optimize the scientific impact of PLATO. The goal of Stellar Science work package is to develop and provide procedures (methods and algorithms) related to the stellar physics programme for implementation in the PDC. These procedures must allow the computation of very precise mass, age, radii and other needed information about the host stars. We indeed need to devise specific methods adapted to PLATO data in order to measure accurately radius, mass, age, chemical composition, rotation, and limb-darkening of the planet host stars and therefore match the PLATO scientific requirements. The WP will also have the important duty of providing estimates of the impact of stellar physics uncertainties and unknowns on our knowledge of the host stars on planet parameters. These developments will be grounded on our knowledge of stellar physics but will require a better understanding of stellar structure and evolution as well as a more detailed modeling of stellar activity. These developments will also benefit from CoRoT and KEPLER legacy and from results of the Gaia mission.
Developments will consist of:
Production of grids of validated stellar evolution models including the most recently modelled physical ingredients (rotation, internal waves, magnetic fields).
Production of grids of validated model atmospheres including the most recently modelled physical ingredients in order to determine stellar parameters such as the chemical composition of the star, produce detailed and accurate boundaries to stellar models, to carry out specific studies of surface effects on the oscillations.
Production of validated seismic forward and inversion techniques specifically adapted to PLATO data and developed in order to reach the level of accuracy necessary to achieve the main goals of PLATO
Production of validated models describing all aspects of stellar activity and interaction with the surrounding
During the definition phase, the Stellar Science will demonstrate the feasibility to characterize the host star with a very high precision level.
The leader of each WP will be charge of the organization of the work within their WP, i.e.
To define general objectives and expected science impact given the instrumental performances;
To determine detailed goals and means to be achieved (tasks, list of available tools and development of inexistent but necessary ones, definition of H&H exercises);
To make sure that deadlines are met, so that the methods are ready and the work is done on time.
Input from the PSPM to the PDC will include specifications of methods and tools to determine all needed characteristics of the host stars (mass, age, radii, chemical composition, rotation, activity, granulation, magnetic fields) by means of a combination of seismic and classical (non seismic) methods.
Specific Activities
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: adapted to low mass, main sequence stars.
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: A. Moya
Objectives: Provide grids of high quality 1D stellar models for low mass, main sequence stars
PSPM WP 121200
Title: Transport processes
Leader: S. Talon
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: F. Palla
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: considered star has a stellar companion (star or a compact object). Second, as it will be the case in PLATO, the studied star hosts a planetary system with one or several planets. In each case, if the companion (stellar or planetary) is closed enough, the system evolution is modified by tidal interactions. First, a large-scale torque due to the equilibrium tide is exerted on the convective envelope of solar-type stars. Then, low-frequency stellar oscillations (inertial in convection zones and gravito-inertial in radiation zones) are excited by the tidal potential: this is the dynamical tide. Each type of tide induces a supplementary transport of angular momentum in stellar interiors, which couples with those treated in the single star case (meridional circulation, turbulence, magnetic field, and internal gravity waves excited by the convection). This of course modifies the studied star internal evolution and mixing. Furthermore, this also induces the evolution of the companion orbit (Keplerian elements) and angular momentum (synchronism, obliquity), which in turn leads to a new tidal potential that modifies once again the system evolution. The orbital and spin state of the system then gives strong constraints on the age of the system. The study of binarity will thus be very important both for close binary stars and for star-planets studies in PLATO.
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: I. Hubeny
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: M. Cunha
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: Inversion methods
Leader: M. Thompson
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: Incorporating 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. Karo
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: Red giant stars
Leader: J. Montalban
PSPM WP127 100
Title: Red giant stellar models
Leader: P. Ventura
PSPM WP127 200
Title: Seismic tools for red giants
Leader: A. Miglio
PSPM WP 127000
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