Magnetic activity in the photosphere of CoRoT-Exo-2a

Lanza, A. F.; Pagano, I.; Leto, G.; Messina, S.; Aigrain, S.; Alonso, R.; Auvergne, M.; Baglin, A.; Barge, P.; Bonomo, A. S.; Boumier, P.; Cameron, A. Collier; Comparato, M.; Cutispoto, G.; Medeiros, J. R. De; Foing, B. H.; Kaiser, Andreas; Moutou, C.; Parihar, Padmakar; Silva-Válio, Adriana; Weiß, W. W.

doi:10.1051/0004-6361:200810591

Cited by 158 publications

(229 citation statements)

References 44 publications

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“…Even if the full characterization of such a complex pattern is currently beyond reach for other stars, precise photometric observations by COROT shows that solar-like stars can exhibit several short-lived spots at the same time (for example Mosser et al 2009) or show a complex pattern between spots and plages (e.g. Lanza et al 2009, for a young solar-like star). We obtain the main following results.…”

Section: Resultsmentioning

confidence: 99%

Using the Sun to estimate Earth-like planets detection capabilities

Meunier¹,

Desort²,

Lagrange³

2010

A&A

263

391

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Aims. Stellar activity produced by spots and plages affects the radial velocity (RV) signatures. Because even low activity stars would produce such a signal, it is crucial to determine how it influences our ability to detect small planetary signals such as those produced by Earth-mass planets in the habitable zone (HZ). In a recent paper, we investigated the impact of sunlike spots. We aim here to investigate the additional impact of plages. Methods. We used the spot and plage properties over a solar cycle to derive the RV that would be observed if the Sun was seen edgeon. The RV signal comes from the photometric contribution of spots and plages and from the attenuation of the convective blueshift in plages. We analyzed the properties of the RV signal at different activity levels and compared it with commonly used activity indicators such as photometry and the Ca index. We also compared it with the signal that would be produced by an Earth-mass planet in the HZ. Results. We find that the photometric contributions of spots and plages to the RV signal partially balance each other out, so that the residual signal is comparable to the spot signal. However, the plage contribution due to the convective blueshift attenuation dominates the total signal, with an amplitude over the solar cycle of about 8-10 m/s. Short-term variations are also significantly greater than the spot and plage photometric contribution. This contribution is very strongly correlated with the Ca index on the long term, which may be a way to distinguish between stellar activity and a planet. Conclusions. Providing a very good temporal sampling and signal-to-noise ratio, the photometric contribution of plages and spots should not prevent detection of Earth-mass planets in the HZ. However, the convection contribution makes such a direct detection impossible, unless its effect can be corrected for by methods that still need to be found. We show that it is possible to identify the convection contribution if the sensitivity is good enough, for example, by using activity indicators.

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Section: Resultsmentioning

confidence: 99%

Using the Sun to estimate Earth-like planets detection capabilities

Meunier¹,

Desort²,

Lagrange³

2010

A&A

263

391

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“…In the present study, we neglected their contribution since we are interested in the infrared bands where the facular effect may be considered less important. Moreover, the facular contribution to the optical flux variations is negligible in the case of stars significantly more active than the Sun (cf., e.g., Lanza et al 2009, and references therein).…”

Section: Modelling Stellar Activitymentioning

confidence: 99%

Multiwavelength flux variations induced by stellar magnetic activity: effects on planetary transits

Ballerini

Micela

Lanza

et al. 2012

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102

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Stellar magnetic activity is a source of noise in the study of the transits of extrasolar planets. It induces flux variations that significantly affect the transit depth determination and the derivations of planetary and stellar parameters. Furthermore, the colour dependence of stellar activity may significantly influence the characterization of planetary atmospheres. Here we present a systematic approach to quantify the corresponding stellar flux variations as a function of wavelength bands. We consider a star with spots covering a given fraction of its disc and model the variability in both the UBVRIJHK photometric system and the Spitzer/IRAC wavebands for dwarf stars from G to M spectral types. We compare activity-induced flux variations in different passbands with planetary transits and quantify how they affect the determination of the planetary radius and the analysis of the transmission spectroscopy in the study of planetary atmospheres. We suggest that the monitoring of the systems by using broad-band photometry, from visible to infrared, helps us to constrain activity effects. The ratio of the relative variations in the stellar fluxes at short wavelength optical bands (e.g., U or B) to near-infrared ones (e.g., J or K) can be used to distinguish starspot brightness dips from planetary transits in a stellar light curve. In addition to the perturbations in the measurement of the planetary radius, we find that starspots can affect the determinations of both the relative semimajor axis and the inclination of the planetary orbit, which have a significant impact on the derivation of the stellar density from the transit light curves.

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“…In the case of LHS 6343 A, the amplitude of the rotational modulation is ∼0.001, while the average error of the points is ∼5 × 10 −5 in relative flux units, giving a signal-to-noise ratio of ∼20. The significant impact of the noise on the light curve makes the regularization a critical process, and a different criterion than that applied for CoRoT-2 (see Lanza et al 2009a) or CoRoT-6 (see Lanza et al 2011) must be adopted, because in those cases the signal-to-noise ratio was >100. For the present case, we increase the regularization until we obtain |μ reg | = β 0 , where μ reg is the mean of the residuals of the regularized light curve, and 0 ≡ σ 0 / √ N is the standard error of the residuals of the unregularized light curve (i.e., obtained with λ = 0), defined as the ratio of their standard deviation σ 0 to the square root of the number of data points N in each individual segment A66, page 6 of 14 of duration Δt f fitted by our model (see below).…”

Section: Spot Modellingmentioning

confidence: 99%

Photospheric activity, rotation, and magnetic interaction in LHS 6343 A

Herrero

Lanza

Ribas

et al. 2013

A&A

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Context. The Kepler mission has recently discovered a brown dwarf companion transiting one member of the M4V+M5V visual binary system LHS 6343 AB with an orbital period of 12.71 days. Aims. The particular interest of this transiting system lies in the synchronicity between the transits of the brown dwarf C component and the main modulation observed in the light curve, which is assumed to be caused by rotating starspots on the A component. We model the activity of this star by deriving maps of the active regions that allow us to study stellar rotation and the possible interaction with the brown dwarf companion.Methods. An average transit profile was derived, and the photometric perturbations due to spots occulted during transits are removed to derive more precise transit parameters. We applied a maximum entropy spot model to fit the out-of-transit optical modulation as observed by Kepler during an uninterrupted interval of ∼500 days. It assumes that stellar active regions consist of cool spots and bright faculae whose visibility is modulated by stellar rotation. Results. Thanks to the extended photometric time series, we refine the determination of the transit parameters and find evidence of spots that are occulted by the brown dwarf during its transits. The modelling of the out-of-transit light curve of LHS 6343 A reveals several starspots rotating with a slightly longer period than the orbital period of the brown dwarf, i.e., 13.13 ± 0.02 days. No signature attributable to differential rotation is observed. We find evidence of a persistent active longitude on the M dwarf preceding the subcompanion point by ∼100 • and lasting for at least ∼500 days. This can be relevant for understanding how magnetic interaction works in low-mass binary and star-planet systems.

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Magnetic activity in the photosphere of CoRoT-Exo-2a

Cited by 158 publications

References 44 publications

Using the Sun to estimate Earth-like planets detection capabilities

Using the Sun to estimate Earth-like planets detection capabilities

Multiwavelength flux variations induced by stellar magnetic activity: effects on planetary transits

Photospheric activity, rotation, and magnetic interaction in LHS 6343 A

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