Planetary eclipse mapping of CoRoT-2a

Huber, K. F.; Czesla, S.; Wolter, Uwe; Schmitt, J. H. M. M.

doi:10.1051/0004-6361/200913914

Cited by 56 publications

(72 citation statements)

References 18 publications

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“…Although its power is significantly below the level corresponding to a false-alarm probability of 1%, a component of the spot area modulation with that period cannot be excluded. The independent modelling by Huber et al (2010) confirms the variation of the total spotted area vs. time found by Lanza et al (2009), giving support to their results. …”

Section: Spot Temporal Evolutionsupporting

confidence: 78%

“…The same result has been obtained by Huber et al (2010) as they derived the rotation period by minimizing the drift of the active longitudes.…”

Section: Rotation Period At the Transit Latitudesupporting

confidence: 77%

“…Furthermore, both the rotation modulation and transits of the CoRoT-2 light-curve were modelled by Huber et al (2010) with a low angular resolution, reaching 15 • during transits. Their modelling yields a rotation period within the transit band of 4.55 days, while a longer period is suggested for the noneclipsed latitudes, giving a latitudinal differential rotation ΔΩ > ∼ 0.1 rad/d.…”

Section: Introductionmentioning

confidence: 99%

“…The authors also find two preferred longitudes on opposite hemispheres. Here we focus on the modelling of the photometric modulations produced by starspots during transits, aiming at a significantly higher longitude resolution than Huber et al (2010), thanks to the method introduced by Silva (2003). This approach allows a better characterization of the properties of the individual starspots along the occulted band, detecting spots as A&A 529, A36 (2011) small as ∼0.2 planetary radii, i.e., 2 • of longitude on the stellar surface (Silva-Valio et al 2010, see also Sect.…”

Section: Introductionmentioning

confidence: 99%

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Time evolution and rotation of starspots on CoRoT-2 from the modelling of transit photometry

Válio

Lanza

2011

A&A

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Context. CoRoT-2, the second planet-hosting star discovered by the CoRoT satellite, is a young and active star. A total of 77 transits were observed for this system over a period of 135 days. Aims. Small modulations detected in the optical light curve of the planetary transits are used to study the position, size, intensity, and temporal evolution of the photospheric spots on the surface of the star that are occulted by the planetary disk. Methods. We apply a spot model to these variations and create a spot map of the stellar surface of CoRoT-2 within the transit band for every transit. From these maps, we estimate the stellar rotation period and obtain the longitudes of the spots in a reference frame rotating with the star. Moreover, the spots temporal evolution is determined. This model achieves a spatial resolution of 2 • . Results. Mapping of 392 spots vs. longitude indicates the presence of a region free of spots, close to the equator, which is reminiscent of the coronal holes observed on the Sun during periods of maximum activity. With this interpretation, the stellar rotation period within the transit latitudes of −14.• 6 ± 10 • is obtained from the auto-correlation function of the time-integrated spot flux deficit, which yields a rotation period of 4.48 days. With this period, the temporal evolution of the spot surface coverage in individual 20 • longitude bins has periodicities ranging from 9 to 53 days with an average value of 31 ± 15 days. On the other hand, the longitude integrated spot flux, which is independent of the stellar rotation period, oscillates with a periodicity of 17.7 days, and its false-alarm probability is ∼3%. Conclusions. The rotation period of 4.48 days obtained here is shorter than the 4.54 days derived from the out-of-transit light modulation. Because the transit data sample a region close to the stellar equator while the period determined from out-of-transit data reflects the average rotation of the star, this is taken as an indication of a latitudinal differential rotation of about 3% or 0.042 rad/d.

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Section: Spot Temporal Evolutionsupporting

confidence: 78%

“…The same result has been obtained by Huber et al (2010) as they derived the rotation period by minimizing the drift of the active longitudes.…”

Section: Rotation Period At the Transit Latitudesupporting

confidence: 77%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Time evolution and rotation of starspots on CoRoT-2 from the modelling of transit photometry

Válio

Lanza

2011

A&A

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“…The visible photometric variations suggest rotational modulation due to starspots. It is reasonable to expect that some of the spots are occulted by the planet when crossing the disk, leading to deformations of the transit profile (see, e.g., Huber et al 2010). The detailed investigation of how starspots influence the determination of LDCs is beyond the scope of this work, however, the strong temperature dependence of LD suggests a non-negligible effect for substantially spotted stars.…”

Section: Outlier Objectsmentioning

confidence: 93%

High-precision stellar limb-darkening measurements

Müller

Huber

Czesla

et al. 2013

A&A

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Context. Planetary transit light curves are influenced by a variety of fundamental parameters, such as the orbital geometry and the surface brightness distribution of the host star. Stellar limb darkening (LD) is therefore among the key parameters of transit modeling. In many applications, LD is presumed to be known and modeled based on synthetic stellar atmospheres. Aims. We measure LD in a sample of 38 Kepler planetary candidate host stars covering effective temperatures between 3000 K and 8900 K with a range of surface gravities from 3.8 to 4.7. In our study we compare our measurements to widely used theoretically predicted quadratic limb-darkening coefficients (LDCs) to check their validity. Methods. We carried out a consistent analysis of a unique stellar sample provided by the Kepler satellite. We performed a Markov chain Monte Carlo (MCMC) modeling of low-noise, short-cadence Kepler transit light curves, which yields reliable error estimates for the LD measurements in spite of the highly correlated parameters encountered in transit modeling. Results. Our study demonstrates that it is impossible to measure accurate LDCs by transit modeling in systems with high impact parameters (b 0.8). For the majority of the remaining sample objects, our measurements agree with the theoretical predictions, considering measurement errors and mutual discrepancies between the theoretical predictions. Nonetheless, theory systematically overpredicts our measurements of the quadratic LDC u 2 by about 0.07. Systematic errors of this order for LDCs would lead to an uncertainty on the order of 1% for the derived planetary parameters. Conclusions. We find that it is adequate to set the commonly used theoretical LDCs as fixed parameters in transit modeling. Furthermore, it is even indispensable to use theoretical LDCs in the case of transiting systems with a high impact parameter, since the host star's LD cannot be determined from their transit light curves.

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Stellar differential rotation in theory and observation

et al. 2013

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Stellar differential rotation is intimately related to the stellar magnetic dynamo and, thus, to stellar activity. In recent years, significant progress in the measurement of differential rotation on the basis of Doppler imaging techniques and the availability of space-based long-term photometry has been achieved. Similarly, simulations incorporate ever more details of the complexity of convective zones. While some aspects of solar and stellar differential rotation can be explained now, several important questions remain open or controversial. In this splinter session, we discussed the latest observational and theoretical progress in the field of differential rotation.

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Planetary eclipse mapping of CoRoT-2a

Cited by 56 publications

References 18 publications

Time evolution and rotation of starspots on CoRoT-2 from the modelling of transit photometry

Time evolution and rotation of starspots on CoRoT-2 from the modelling of transit photometry

High-precision stellar limb-darkening measurements

Stellar differential rotation in theory and observation

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