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Dumusque X.,Harvard - Smithsonian Center for Astrophysics | Dumusque X.,National Science Foundation | Boisse I.,Laboratoire Dastrophysique Of Marseille Umr 6110 | Santos N.C.,University of Porto
Astrophysical Journal | Year: 2014

This paper presents SOAP 2.0, a new version of the Spot Oscillation And Planet (SOAP) code that estimates in a simple way the photometric and radial velocity (RV) variations induced by active regions. The inhibition of the convective blueshift (CB) inside active regions is considered, as well as the limb brightening effect of plages, a quadratic limb darkening law, and a realistic spot and plage contrast ratio. SOAP 2.0 shows that the activity-induced variation of plages is dominated by the inhibition of the CB effect. For spots, this effect becomes significant only for slow rotators. In addition, in the case of a major active region dominating the activity-induced signal, the ratio between the FWHM and the RV peak-to-peak amplitudes of the cross correlation function can be used to infer the type of active region responsible for the signal for stars with v sin i ≤8 km s-1. A ratio smaller than three implies a spot, while a larger ratio implies a plage. Using the observation of HD 189733, we show that SOAP 2.0 manages to reproduce the activity variation as well as previous simulations when a spot is dominating the activity-induced variation. In addition, SOAP 2.0 also reproduces the activity variation induced by a plage on the slowly rotating star α Cen B, which is not possible using previous simulations. Following these results, SOAP 2.0 can be used to estimate the signal induced by spots and plages, but also to correct for it when a major active region is dominating the RV variation. © 2014. The American Astronomical Society. All rights reserved. Source

Kallinger T.,University of Vienna | Kallinger T.,University of British Columbia | Weiss W.W.,University of Vienna | Barban C.,CNRS Laboratory for Space Studies and Astrophysical Instrumentation | And 12 more authors.
Astronomy and Astrophysics | Year: 2010

Context: Observations and analysis of solar-type oscillations in red-giant stars is an emerging aspect of asteroseismic analysis with a number of open questions yet to be explored. Although stochastic oscillations have previously been detected in red giants from both radial velocity and photometric measurements, those data were either too short or had sampling that was not complete enough to perform a detailed data analysis of the variability. The quality and quantity of photometric data as provided by the CoRoT satellite is necessary to provide a breakthrough in observing p-mode oscillations in red giants. We have analyzed continuous photometric time-series of about 11 400 relatively faint stars obtained in the exofield of CoRoT during the first 150 days long-run campaign from May to October 2007. We find several hundred stars showing a clear power excess in a frequency and amplitude range expected for red-giant pulsators. In this paper we present first results on a sub-sample of these stars. Aims: Knowing reliable fundamental parameters like mass and radius is essential for detailed asteroseismic studies of red-giant stars. As the CoRoT exofield targets are relatively faint (11-16 mag) there are no (or only weak) constraints on the stars' location in the H-R diagram. We therefore aim to extract information about such fundamental parameters solely from the available time series. Methods: We model the convective background noise and the power excess hump due to pulsation with a global model fit and deduce reliable estimates for the stellar mass and radius from scaling relations for the frequency of maximum oscillation power and the characteristic frequency separation. Results: We provide a simple method to estimate stellar masses and radii for stars exhibiting solar-type oscillations. Our method is tested on a number of known solar-type pulsators. © 2010 ESO. Source

Lanza A.F.,National institute for astrophysics | Bonomo A.S.,National institute for astrophysics | Bonomo A.S.,Laboratoire Dastrophysique Of Marseille Umr 6110 | Pagano I.,National institute for astrophysics | And 13 more authors.
Astronomy and Astrophysics | Year: 2010

Context. The CoRoT satellite has recently discovered a hot Jupiter that transits across the disc of a F9 main-sequence star called CoRoT-6 with a period of 8.886 days. Aims. We model the photospheric activity of the star and use the maps of the active regions to study stellar differential rotation and the star-planet interaction. Methods. We apply a maximum entropy spot model to fit the optical modulation as observed by CoRoT during a uninterrupted interval of ~ 140 days. Photospheric active regions are assumed to consist of spots and faculae in a fixed proportion with solar-like contrasts. Results. Individual active regions have lifetimes up to 30-40 days. Most of them form and decay within five active longitudes whose different migration rates are attributed to the stellar differential rotation for which a lower limit of ΔΩ/Ω = 0.12 ± 0.02 is obtained. Several active regions show a maximum of activity at a longitude lagging the subplanetary point by ~ 200° with the probability of a chance occurrence being smaller than 1 percent. Conclusions. Our spot modelling indicates that the photospheric activity of CoRoT-6 could be partially modulated by some kind of star-planet magnetic interaction, while an interaction related to tides is highly unlikely because of the weakness of the tidal force. © 2010 ESO. Source

Deleuil M.,Laboratoire Dastrophysique Of Marseille Umr 6110 | Moutou C.,Laboratoire Dastrophysique Of Marseille Umr 6110
EAS Publications Series | Year: 2010

CoRoT is the first instrument aiming at detecting exoplanets from space, using the transit method. It has been built in order to explore the domain of planets with orbital period less than three months, and size down to about two Earth radii. Successfully launched on the 27th of December 2006, the instrument started its science observations by the beginning of February 2007. The first detections show the capability of the instrument to enlarge the parameter space and to explore the transition regime between gaseous giant and terrestrial planets. Five new transiting giant planets discovered by CoRoT are fully characterized at the time of writing. © EAS, EDP Sciences, 2010. Source

Deleuil M.,Laboratoire Dastrophysique Of Marseille Umr 6110 | Bouret J.C.,Laboratoire Dastrophysique Of Marseille Umr 6110 | Feldman P.,JHU | Lecavelier Des Etangs A.,CNRS Paris Institute of Astrophysics | And 3 more authors.
EAS Publications Series | Year: 2010

Circumstellar disks surrounding young forming stars, are likely the location where planets form. While the gaseous phase represents up to ∼!99% of the disk mass and control the dynamics, most of disk properties relies on dust analyses. The main constituent of the gaseous component, molecular hydrogen (H}{2}), remains nearly out of reach and the gas disk is probed through emission lines of minor tracers, such as CO. In this lecture, we will first recall how {H}{2} symmetric molecular structure makes its detection difficult. We will then review the most significant results achieved so far, thanks to new generation of ground and space-based telescopes, with a special emphasize given to Herbig Ae/be, which are pre-main sequence stars of intermediate mass. Though the first direct estimates of circumstellar disk mass have been reported, observation of {H} {2} is still challenging detection. © EAS, EDP Sciences, 2010. Source

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