SSI: Stellar Seismic Indices data base
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Stellar Seismic Indices

Thanks to CoRoT (CNES) and Kepler (NASA) seismic observations, it is now possible to detect many solar-like oscillations in a very high number of stars. The observed oscillation spectra can be quite complicate to analyse and interpret. Nevertheless, these spectra show characteristic pattern, which can be more simply characterized with that we call stellar seismic indices. More specifically, the stellar seismic indices correspond to characteristic global seismic numbers that are extracted from the oscillation spectra of solar-like pulsating stars. Among them we distinguish in particular:

  • the mean large separation (delta_nu)
  • the peak frequency (nu_max)

The first one corresponds to the mean frequency separation between two modes of same angular degree while the second one corresponds to the frequency at which the oscillation spectrum peaks. These seismic indices obey characteristic scaling relations that depend directly on the radius, mass and effective temperature of the star. From the knowledge of these quantities it is possible to estimate the mass and radius of a star, and subsequently the surface gravity of the star (log g).

Because they are relatively easy to measure thanks to CoRoT and Kepler, it has already been possible to measure seismic indices in about 10 000 red giants and sub-giants, and subsequently to derive their mass, radius and evolutionary status. Theses seismic indices are more and more used in the stellar physic but also for the study of Galactic population. These seismic indices have opened the way toward that we name now ensemble asteroseismology.

The light-curves of redgiants have also unveiled the presence of a signal characterizing the stellar granulation, which is a superficial signature of convection inside the star. As for the seismic indices, it is possible to extract in rather easy way the characteristic parameters of stellar granulation. These parameters also obey scaling relations, which in addition to seismic scaling relations, provide information about the surface layers of the star (see e.g. this short news).

About the SSI project

In this context, we have developed the present data base containing Stellar Seismic Indices (SSI) derived in a homogeneous way for a very large set of CoRoT and Kepler targets. In addition to these seismic indices, the data base also provides the characteristic parameters of the stellar granulation, namely the time-scale (tau_eff) and the mean-square brightness fluctuations (sigma²) associated with the granulation background.

All these stellar parameters were generated on the basis of the MLEUP method (de Assis Peralta, Samadi, Michel, 2016, submitted). This new method relies on the Universal Pattern (Mosser et al., 2011) and takes advantage of the Maximum Likelihood Estimator (MLE) algorithm. It provides simultaneously and in a consistent way both the seismic indices and the characteristic parameters of the stellar granulation.

The indices populating the current data base were extracted from all Kepler long-cadence light-curves and from all CoRoT light curves acquired in the faint field (exo channel) with a duration longer than 50 days.

A total of about 320,000 light-curves have been analysed, among which stellar indices (seismic and granulation parameters) were extracted for a total number of about 18,000 red giants.

Access to the data is possible through the Search interface as well as through the Seismic Plus portal

Note: Masses, radii and log g can typically be derived using seismic scaling relations from the provided seismic indices and given effective temperature measurements obtained from other data bases ; to derive the parameters of the stars (M,R, log g) from the seismic indices see e.g. this note. To learn more about the seismic scaling relations, please have a look to the list of articles and reviews given in the section Documents. Also, The Seismic Plus portal implements a tool to derive masses, radii, and log g from the various data bases that provide effective temperatures and seismic indices.

This project was developed in the framework of the SPACEInn project financed by the European Union under the Seventh Framework Programme (FP7).

It has been developed at the Laboratoire d’Etudes Spatiales et d’Instrumentation en Astrophysique (LESIA, Obervatoire de Paris). It has benefited from the support of the VO- Paris Data Center. We also acknowledge Programme National de Physique Stellaire (PNPS) for financial supports.

The CoRoT space mission has been developed and operated by CNES, with contributions from Austria, Belgium, Brazil, ESA (RSSD and Science Program), Germany, and Spain. Funding for the Kepler Discovery mission were provided by NASAs Science Mission Directorate.