On the differential rotation of CoRoT-2a

Fröhlich, H.‐E.; Küker, M.; Hatzes, A. P.; Strassmeier, K. G.

doi:10.1051/0004-6361/200911895

Cited by 38 publications

(43 citation statements)

References 17 publications

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“…Afterward, this error-integrated likelihood was additionally integrated over all conceivable magnitude off-sets so that it was not necessary to specify any zero point. Both integrations were made analytically (Fröhlich et al 2009). It is important to note that each part has its own characteristic error variance and magnitude off-set.…”

Section: Some General Remarksmentioning

confidence: 99%

Magnetic activity, differential rotation, and dynamo action in the pulsating F9IV star KIC 5955122

Bonanno

Fröhlich

Karoff

et al. 2014

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We present photometric spot modeling of the nearly four-year long light-curve of the Kepler target KIC 5955122 in terms of persisting dark circular surface features. With a Bayesian technique, we produced a plausible surface map that shows dozens of small spots. After some artifacts are removed, the residuals are at ±0.16 mmag. The shortest rotational period found is P = 16.4 ± 0.2 days. The equator-to-pole extrapolated differential rotation is 0.25 ± 0.02 rad/d. The spots are roughly half as bright as the unperturbed stellar photosphere. Spot latitudes are restricted to the zone ±60 • latitude. There is no indication for any near-pole spots. In addition, the p-mode pulsations enabled us to determine the evolutionary status of the star, the extension of the convective zone, and its radius and mass. We discuss the possibility that the clear signature of active regions in the light curve of the F9IV star KIC 5955122 is produced by a flux-transport dynamo action at the base of the convection zone. In particular, we argue that this star has evolved from an active to a quiet status during the Q0-Q16 period of observation, and we predict, according to our dynamo model, that the characteristic activity cycle is of the order of the solar one.

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Section: Some General Remarksmentioning

confidence: 99%

Magnetic activity, differential rotation, and dynamo action in the pulsating F9IV star KIC 5955122

Bonanno

Fröhlich

Karoff

et al. 2014

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“…Lanza et al 2009;Fröhlich et al 2009;Silva-Valio et al 2010;Gondoin et al 2012). Photometric monitoring programs have produced a large number of measurements of this kind in young open clusters (e.g.…”

Section: Introductionmentioning

confidence: 99%

X-ray emission regimes and rotation sequences in M 35

Gondoin

2013

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Context. Late-type stars in young open clusters show two kinds of dependence of their X-ray emission on rotation. They also tend to group into two main sub-populations that lie on narrow sequences in diagrams where their rotation periods are plotted against their (B − V) colour indices. A correlation between these two regimes of X-ray emission and the rotation sequences has been recently observed in the M 34 open cluster. Sun-like M 34 stars also show a drop of their X-ray to bolometric luminosity ratio by about one order of magnitude at a Rossby number of about 0.3. Aims. The present study looks for similar connections between X-ray activity and rotation in an other open cluster. The aim is to consolidate a model of X-ray activity evolution on the main sequence and to provide observational constraints on dynamo processes in the interiors of late-type stars. Methods. The paper compares XMM-Newton measurements of X-ray stellar emission in M 35 with X-ray luminosity distributions derived from rotation period measurements assuming either an X-ray regime transition at a critical Rossby number or a correlation between X-ray emission regimes and rotation sequences. Results. This second hypothesis could account for the low number of M 35 stars detected in X-rays. A model of X-ray activity evolution is proposed based on the correlation. One major output is that the transition from saturated to non-saturated X-ray emission occurs at Rossby numbers between about 0.13 and 0.4 for each star depending on its mass and initial period of rotation on the ZAMS. This prediction agrees with observations of stellar X-ray emission in M 34. It explains the large range of X-ray luminosities observed among Sun-like stars in young open clusters. Conclusions. I conclude that the correlation between X-ray emission regimes and rotation sequences could be a fundamental property of the early evolution of stellar magnetic activity on the main sequence. I argue that the angular momentum redistribution mechanism(s) responsible for the transition between rotation sequences could result in a changing mixture of dynamo processes occurring side by side, possibly including a turbulent dynamo at high rotation rate and an interface-type dynamo whose efficiency decreases progressively at later stage of stellar evolution when rotation dies away.

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“…In CoRoT-2 the out-of-transit light modulation is dominated by the lack of spots within the coronal hole close to the equator, yielding almost no differential rotation. Lanza et al (2009) and Fröhlich et al (2009). Considering the results of Barnes et al (2005), the differential rotation of CoRoT-2 is approximately half the pole-equator angular velocity difference generally found in late-type stars of similar effective temperature and rotation period, suggesting that its spots are concentrated in an equatorial belt, as in the Sun.…”

Section: Discussionmentioning

confidence: 66%

“…5. If interpreted as the effect of moving spots, these bridges can be used to derive the differential rotation (cf., e.g., Fröhlich et al 2009). However, the transit maps suggest that they are not single migrating spots, but instead are locations where spots appear and disappear between the two active longitudes, like "hot spots" where activity is preferentially located between the active longitudes.…”

Section: Comparison With the Out-of-transit Spot Modellingmentioning

confidence: 99%

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

Válio

Lanza

2011

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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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On the differential rotation of CoRoT-2a

Cited by 38 publications

References 17 publications

Magnetic activity, differential rotation, and dynamo action in the pulsating F9IV star KIC 5955122

Magnetic activity, differential rotation, and dynamo action in the pulsating F9IV star KIC 5955122

X-ray emission regimes and rotation sequences in M 35

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

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