arXiv subjects

Frederic Baudin

Publications and source records attributed to Frederic Baudin.

4 recordsLinked to original sources

arXiv2025

Activity of low mass stars in the light of spot signature in the Fourier domain

Context. Magnetic fields exhibit a wide variety of behaviours in low mass stars and further characterization is required to understand these observations. Stellar photometry from space missions such as MOST, CoRoT, Kepler, and, in future PLATO, provide thousands of highly precise light curves (LC) that can shed new light upon stellar activity, in particular through the signature of transiting spots. Aims. We study the impact of star spots on light curves in the Fourier domain, reducing the degeneracies encountered by direct spot modelling in the temporal domain, and use this new formulation to explore the spot properties from the available data. Methods. We propose a model of LC power spectra at low frequency based on a description of spot transits that allows us to retrieve information about the amplitude of their photometric impact $\mathcal{H}$, and about the spot mean lifetime over the observation $\tau_{\rm life}$ when the power spectrum exibits rotation peaks. We first validate this method with simulated LCs and then apply it to the Kepler data to extract global trends over a set of more than 37 755 stars. Results. This analysis leads to a classification of the sample into "peakless" or "with peaks" spectra, and enables the identification of different activity regimes based on $\mathcal{H}$ and $\tau_{\rm life}$ for different ranges of Rossby number. More specifically, we observe an intense regime of activity between Ro = 0.7 and Ro = 1, for stars with masses under 1$M_\odot$. Conclusions. This new systematic method can be used to provide new observational constraints on stellar activity (and possibly a link with stellar magnetism) when applied to large photometric datasets, such as those from the future PLATO mission.

astro-ph.SR↗

arXiv2024

The PLATO Mission

PLATO (PLAnetary Transits and Oscillations of stars) is ESA's M3 mission designed to detect and characterise extrasolar planets and perform asteroseismic monitoring of a large number of stars. PLATO will detect small planets (down to <2 R_(Earth)) around bright stars (<11 mag), including terrestrial planets in the habitable zone of solar-like stars. With the complement of radial velocity observations from the ground, planets will be characterised for their radius, mass, and age with high accuracy (5 %, 10 %, 10 % for an Earth-Sun combination respectively). PLATO will provide us with a large-scale catalogue of well-characterised small planets up to intermediate orbital periods, relevant for a meaningful comparison to planet formation theories and to better understand planet evolution. It will make possible comparative exoplanetology to place our Solar System planets in a broader context. In parallel, PLATO will study (host) stars using asteroseismology, allowing us to determine the stellar properties with high accuracy, substantially enhancing our knowledge of stellar structure and evolution. The payload instrument consists of 26 cameras with 12cm aperture each. For at least four years, the mission will perform high-precision photometric measurements. Here we review the science objectives, present PLATO's target samples and fields, provide an overview of expected core science performance as well as a description of the instrument and the mission profile at the beginning of the serial production of the flight cameras. PLATO is scheduled for a launch date end 2026. This overview therefore provides a summary of the mission to the community in preparation of the upcoming operational phases.

astro-ph.IM↗

arXiv2014

The red giants in NGC 6633 as seen with CoRoT, HARPS and SOPHIE

The open cluster NGC 6633 was observed with CoRoT in 2011 and simultaneous high-resolution spectroscopy was obtained with the SOPHIE and HARPS spectrographs. One of the four targets was not found to be a cluster member. For all stars we provide estimates of the seismic and spectroscopic parameters.

astro-ph.SR↗

arXiv2011

Monitoring a high--amplitude Delta Sct star for 152 days: discovery of 12 additional modes and modulation effects in the light curve of CoRoT 101155310

The detection of small-amplitude nonradial modes in high-amplitude Delta Sct (HADS) variables has been very elusive until at least five of them were detected in the light curve of V974 Oph obtained from ground-based observations. The combination of radial and nonradial modes has a high asteroseismic potential, thanks to the strong constraints we can put in the modelling. The continuous monitoring of ASAS 192647-0030.0=CoRoT 101155310 (P=0.1258 d, V=13.4) ensured from space by the CoRoT (Convection, Rotation and planetary Transits) mission constitutes a unique opportunity to exploit such potential. The 22270 CoRoT measurements were performed in the chromatic mode. They span 152 d and cover 1208 consecutive cycles. After the correction for one jump and the long-term drift, the level of the noise turned out to be 29 micromag. The phase shifts and amplitude ratios of the coloured CoRoT data, the HARPS spectra, and the period-luminosity relation were used to determine a self-consistent physical model. In turn, it allowed us to model the oscillation spectrum, also giving feedback on the internal structure of the star. In addition to the fundamental radial mode f1=7.949 c/d with harmonics up to 10f1, we detected 12 independent terms. Linear combinations were also found and the light curve was solved by means of 61 frequencies (smallest amplitude 0.10 mmag). The newest result is the detection of a periodic modulation of the f1 mode (triplets at +/-0.193 c/d centred on f1 and 2f1), discussed as a rotational effect or as an extension of the Blazhko effect to HADS stars. The physical model suggests that CoRoT 101155310 is an evolved star, with a slight subsolar metallic abundance, close to the terminal age main sequence. All the 12 additional terms are identified with mixed modes in the predicted overstable region.

astro-ph.SR↗