Magnetic Rossby Waves in the Solar Tachocline and Rieger-Type Periodicities

Zaqarashvili, T. V.; Carbonell, M.; Oliver, R.; Ballester, J. L.

doi:10.1088/0004-637x/709/2/749

Cited by 98 publications

(131 citation statements)

References 66 publications

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“…The periodicity of the spotted area variations is close to 4 times the mean rotation period of the star, while in the Sun it is ≈6 times and in CoRoT-2 is ≈6.5 times the rotation period. Those oscillations of the spotted area may be associated with hydromagnetic Rossby-type waves propagating in the upper part of the convection zone or at the interface between the radiative interior and the convection zone where the dynamo is probably located (Lou 2000;Zaqarashvili et al 2010). Since only a few examples of stars displaying Rieger-type cycles are known (cf., Massi et al 2005;Lanza et al 2009a), the new results on Kepler-17 are particularly interesting for a better understanding of this phenomenon in the framework of the solar-stellar connection.…”

Section: Discussionmentioning

confidence: 99%

“…They were called Rieger cycles because they were first detected in the periodicity of occurrence of large solar flares by Rieger et al (1984). In the Sun, the periodicity is ≈160 d with small variations from one cycle to the other, although only some of the sunspot maxima show evidence of this short-term periodicity (Oliver et al 1998;Krivova & Solanki 2002;Zaqarashvili et al 2010). A behaviour similar to that of Kepler-17 was found in CoRoT-2, a G7V star that showed a Rieger-type cycle in the variation of its spotted area with a period of 28.9 ± 4.3 d (Lanza et al 2009a).…”

Section: Variation Of the Spotted Areamentioning

confidence: 99%

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Starspot activity and rotation of the planet-hosting star Kepler-17

Bonomo

Lanza

2012

A&A

101

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Context. Kepler-17 is a G2V sun-like star accompanied by a transiting planet with a mass of ≈2.5 Jupiter masses and an orbital period of 1.486 d, recently discovered by the Kepler space telescope. This star is highly interesting as a young solar analogue. It is also a good candidate for a test of the tidal theories for solar-like stars. Aims. We used about 500 days of high-precision, high-duty-cycle optical photometry collected by Kepler to study the rotation of the star and the evolution of its photospheric active regions.Methods. We applied a maximum-entropy light curve inversion technique to model the flux rotational modulation induced by active regions that consist of dark spots and bright solar-like faculae with a fixed area ratio. Their configuration was varied after a fixed time interval to take their evolution into account. Active regions were used as tracers to study stellar differential rotation, and planetary occultations were used to constrain the latitude of some spots. Results. Our modelling approach reproduces the light variations of Kepler-17 with a standard deviation of the residuals comparable with the precision of Kepler photometry. We find several active longitudes where individual active regions appear, evolve, and decay with lifetimes comparable to those observed in the Sun, although the star has a spotted area ≈10−15 times larger than the Sun at the maximum of the 11-yr cycle. Kepler-17 shows a solar-like latitudinal differential rotation, but the fast spot evolution prevents a precise determination of its amplitude. Moveover, the star shows a cyclic variation of the starspot area with a period of 47.1 ± 4.5 d, particularly evident during the last 200 days of the observations, similar to the solar Rieger cycles. Possible effects of the close-in massive planet on stellar photospheric activity cannot be excluded, but require a long-term monitoring to be unambiguously detected.

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Section: Discussionmentioning

confidence: 99%

Section: Variation Of the Spotted Areamentioning

confidence: 99%

Starspot activity and rotation of the planet-hosting star Kepler-17

Bonomo

Lanza

2012

A&A

101

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“…Moreover, if we attribute Rieger-type periods to Rossby waves according to Lou's model, then the question arises as to why observations favor waves with even m values, thus excluding other periodicities which are theoretically possible. Recently, Zaqarashvili et al (2010aZaqarashvili et al ( , 2010b have attempted to answer such questions considering the instability of magnetic Rossby waves in the tachocline and they concluded that ∼1.3 yr periodicity is possible when the magnetic field strength is greater than 10 5 G and Rieger-type periods correspond to the presence of a relatively weak magnetic field ( 10 4 G). However, the existence of such strong magnetic fields in the tachocline is a new area of research.…”

Section: Discussionmentioning

confidence: 99%

Periodicities in the X-Ray Emission From the Solar Corona

Chowdhury

Jain

Awasthi

2013

ApJ

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We have studied the time series of full disk integrated soft and hard X-ray emission from the solar corona during 2004 January to 2008 December, covering the entire descending phase of solar cycle 23 from a global point of view. We employ the daily X-ray index derived from 1 s cadence X-ray observations from the Si and CZT detectors of the "Solar X-ray Spectrometer" mission in seven different energy bands ranging between 6 and 56 keV. X-ray data in the energy bands 6-7, 7-10, 10-20, and 4-25 keV from the Si detector are considered, while 10-20, 20-30, and 30-56 keV high energy observations are taken from the CZT detector. The daily time series is subjected to power spectrum analysis after appropriate correction for noise. The Lomb-Scargle periodogram technique has shown prominent periods of ∼13.5 days, ∼27 days, and a near-Rieger period of ∼181 days and ∼1.24 yr in all energy bands. In addition to this, other periods like ∼31, ∼48, ∼57, ∼76, ∼96, ∼130, ∼227, and ∼303 days are also detected in different energy bands. We discuss our results in light of previous observations and existing numerical models.

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“…Klahr & Bodenheimer 2003;Petersen et al 2007a,b;Lesur & Papaloizou 2010;Lyra & Klahr 2011) and the Sun (Gilman & Fox 1997;Zaqarashvili et al 2010; to name only a few studies). In these analyses potential vorticity disturbances are effectively baroclinically torqued by some process that is either thermal or magnetic or, in some investigations, a combination of both.…”

Section: Summary and Discussionmentioning

confidence: 99%

“…In those studies of magnetic Rossby waves in the Sun (e.g. Gilman & Fox 1997;Zaqarashvili et al 2010), Rossby waves will propagate along those places where there are strong gradients in the solar differential rotation. Treated as a hydrodynamic problem, these Rossby waves are not necessarily unstable on their own, especially for the differential rotation profiles inferred to be characteristic of the Sun's tachochline (Spiegel & Zahn 1992).…”

Section: Summary and Discussionmentioning

confidence: 99%

Potential vorticity dynamics in the framework of disk shallow-water theory

Umurhan¹

2012

A&A

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Context. We consider potential vorticity dynamics for astrophysical disks. Aims. The aim of this work is to extend exploration of shear instabilities in cold astrophysical disks that are three-dimensional and whose mean states are baroclinic. In particular, we seek to demonstrate the potential existence of traditional baroclinic instabilities in meteorological studies. We show this in a simplified two-layer Philips disk model of a midplane symmetric disk. Methods. We analyze the dynamical normal-mode response of thin annular disks with two strongly localized potential vorticity gradients, one in each of two disk layers. Each disk layer is of constant but differing densities. The resulting mean azimuthal velocity profile shows a variation in the vertical direction, implying that the system is baroclinic in the mean state. The stability of the system is treated in the context of disk shallow-water theory, wherein azimuthal disturbances are much longer than the corresponding radial or vertical scales. The normal-mode problem is solved numerically using two different methods. Results. The results of a symmetric single-layer barotropic model is considered and it is found that instability persists for models in which the potential vorticity profiles are not symmetric, consistent with previous results. The instaiblity is interpreted in terms of interacting Rossby waves. For a two-layer system, in which the flow is fundamentally baroclinic, we report here that instability takes on the form of mixed barotropic-baroclinic type: instability occurs, but it qualitatively follows the pattern of instability found in the barotropic models. Instability arises because of the phase locking and interaction of the Rossby waves between the two layers. The strength of the instability weakens as the density contrast between layers increases. Conclusions. Baroclinic instability is feasible for astrophysical disks but has the character of mixed barotropic-baroclinic type. The instability as explored in this study could be present in protoplanetary disks with weak vertical density stratification.

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Magnetic Rossby Waves in the Solar Tachocline and Rieger-Type Periodicities

Cited by 98 publications

References 66 publications

Starspot activity and rotation of the planet-hosting star Kepler-17

Starspot activity and rotation of the planet-hosting star Kepler-17

Periodicities in the X-Ray Emission From the Solar Corona

Potential vorticity dynamics in the framework of disk shallow-water theory

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