Stellar coronal magnetic fields and star-planet interaction

Lanza, A. F.

doi:10.1051/0004-6361/200912367

Cited by 123 publications

(160 citation statements)

References 53 publications

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“…It is also worthwhile to note that Lanza (2010) reported evidence that hot Jupiters orbiting close to their stars can affect their angular momentum evolution by interaction with their coronal fields (Lanza 2009). This would complicate our approach, because slightly different rotation rates would be expected for stars with giant planets, which would prevent us from predicting the stellar axis inclination from the same activity-v sin i distribution as for general stars.…”

Section: Stellar Inclination From Activity and Rotationmentioning

confidence: 99%

Optimizing exoplanet transit searches around low-mass stars with inclination constraints

Herrero

Ribas

Jordi

et al. 2012

A&A

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Aims. We investigate a method to increase the efficiency of a targeted exoplanet search with the transit technique by preselecting a subset of candidates from large catalogs of stars. Assuming spin-orbit alignment, this can be achieved by considering stars that have a higher probability to be oriented nearly equator-on (inclination close to 90 • ). Methods. We used activity-rotation velocity relations for low-mass stars with a convective envelope to study the dependence of the position in the activity-v sin i diagram on the stellar axis inclination. We composed a catalog of G-, K-, M-type main-sequence simulated stars using isochrones, an isotropic inclination distribution and empirical relations to obtain their rotation periods and activity indexes. Then the activity-v sin i diagram was completed and statistics were applied to trace the areas containing the higher ratio of stars with inclinations above 80 • . A similar statistics was applied to stars from real catalogs with log(R HK ) and v sin i data to find their probability of being oriented equator-on. Results. We present our method to generate the simulated star catalog and the subsequent statistics to find the highly inclined stars from real catalogs using the activity-v sin i diagram. Several catalogs from the literature are analyzed and a subsample of stars with the highest probability of being equator-on is presented. Conclusions. Assuming spin-orbit alignment, the efficiency of an exoplanet transit search in the resulting subsample of probably highly inclined stars is estimated to be two to three times higher than with a general search without preselection.

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Section: Stellar Inclination From Activity and Rotationmentioning

confidence: 99%

Optimizing exoplanet transit searches around low-mass stars with inclination constraints

Herrero

Ribas

Jordi

et al. 2012

A&A

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“…Fares et al 2010). Lanza (2008Lanza ( , 2009 argued that a flux rope between the host star's coronal magnetic field and the planet's magnetosphere experiences a decrease in relative helicity and reacts with an energy release from the flux rope's footpoint(s). His model predicts a greater prominence activity for stars with planets than without, caused by the accumulation of matter evaporated from the planet.…”

Section: Orbital-induced Magnetic Activity?mentioning

confidence: 99%

Binary-induced magnetic activity?

Strassmeier

Carroll

Weber

et al. 2011

A&A

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Context. Multi-wavelength time-series observations with high cadence and long duration are needed to resolve and understand the many variations of magnetically active late-type stars, which is an approach often used to observe the Sun. Aims. We present a first and detailed study of the bright and active K0IV-III star HD 123351. Methods. We acquired a total of 955 high-resolution STELLA echelle spectra during the years 2006-2010 and a total of 2260 photometric VI C data points during 1998-2010. These data are complemented by some spectra from CFHT and KPNO. Results. The star is found to be a single-lined spectroscopic binary with a period of 147.8919 ± 0.0003 days and a large eccentricity of e = 0.8086 ± 0.0001. The rms of the orbital solution is just 47 m s −1 , making it the most precise orbit ever obtained for an active binary system. The rotation period is constrained from long-term photometry to be 58.32 ± 0.01 days. It shows that HD 123351 is a very asynchronous rotator, rotating five times slower than the expected pseudo-synchronous value. Two spotted regions persisted throughout the 12 years of our observations. We interpret them as active longitudes on a differentially rotating surface with a ΔP/P of 0.076. Four years of Hα, Ca ii H&K and He i D3 monitoring identifies the same main periodicity as the photometry but dynamic spectra also indicate that there is an intermittent dependence on the orbital period, in particular for Ca ii H&K in 2008. Line-profile inversions of a pair of Zeeman sensitive/insensitive iron lines yield an average surface magnetic-flux density of 542 ± 72 G. The time series for 2008 is modulated by the stellar rotation as well as the orbital motion, such that the magnetic flux is generally weaker during times of periastron and that the chromospheric emissions vary in anti-phase with the magnetic flux. We also identify a broad and asymmetric lithium line profile and measure an abundance of log n(Li) = 1.70 ± 0.05. The star's position in the H-R diagram indicates a mass of 1.2 ± 0.1 M and an age of 6-7 Gyr. Conclusions. We interpret the anti-phase relation of the magnetic flux with the chromospheric emissions as evidence that there are two magnetic fields present at the same time, a localized surface magnetic field associated with spots and a global field that is oriented towards the (low-mass) secondary component. We suggest that the inter-binary field is responsible for the magnetic-flux dilution at periastron. It is also likely to be responsible for the unexpected slow and asynchronous rotation of the primary star.

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“…Kivelson & Russell 1995). However, for planets orbiting stars that are significantly more magnetised than the Sun or/and are located at close distances, the stellar magnetic pressure may play an important role in setting the magnetospheric limits (Ip et al 2004;Zieger et al 2006;Lovelace et al 2008;Lanza 2009;Vidotto et al 2009Vidotto et al , 2010bVidotto et al , 2012Vidotto et al , 2011bSterenborg et al 2011;Khodachenko et al 2012;Buzasi 2013). The extent of the magnetosphere of planets orbiting in the HZ of dM stars have been investigated by other authors (e.g.…”

Section: Introductionmentioning

confidence: 99%

Effects of M dwarf magnetic fields on potentially habitable planets

Vidotto

Jardine

Morin

et al. 2013

A&A

147

161

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We investigate the effect of the magnetic fields of M dwarf (dM) stars on potentially habitable Earth-like planets. These fields can reduce the size of planetary magnetospheres to such an extent that a significant fraction of the planet's atmosphere may be exposed to erosion by the stellar wind. We used a sample of 15 active dM stars, for which surface magnetic-field maps were reconstructed, to determine the magnetic pressure at the planet orbit and hence the largest size of its magnetosphere, which would only be decreased by considering the stellar wind. Our method provides a fast means to assess which planets are most affected by the stellar magnetic field, which can be used as a first study to be followed by more sophisticated models. We show that hypothetical Earth-like planets with similar terrestrial magnetisation (∼1 G) orbiting at the inner (outer) edge of the habitable zone of these stars would present magnetospheres that extend at most up to 6 (11.7) planetary radii. To be able to sustain an Earth-sized magnetosphere, with the exception of only a few cases, the terrestrial planet would either (1) need to orbit significantly farther out than the traditional limits of the habitable zone; or else, (2) if it were orbiting within the habitable zone, it would require at least a magnetic field ranging from a few G to up to a few thousand G. By assuming a magnetospheric size that is more appropriate for the young-Earth (3.4 Gyr ago), the required planetary magnetic fields are one order of magnitude weaker. However, in this case, the polar-cap area of the planet, which is unprotected from transport of particles to/from interplanetary space, is twice as large. At present, we do not know how small the smallest area of the planetary surface is that could be exposed and would still not affect the potential for formation and development of life in a planet. As the star becomes older and, therefore, its rotation rate and magnetic field reduce, the interplanetary magnetic pressure decreases and the magnetosphere of planets probably expands. Using an empirically derived rotation-activity/magnetism relation, we provide an analytical expression for estimating the shortest stellar rotation period for which an Earth-analogue in the habitable zone could sustain an Earth-sized magnetosphere. We find that the required rotation rate of the early-and mid-dM stars (with periods 37-202 days) is slower than the solar one, and even slower for the late-dM stars ( 63-263 days). Planets orbiting in the habitable zone of dM stars that rotate faster than this have smaller magnetospheric sizes than that of the Earth magnetosphere. Because many late-dM stars are fast rotators, conditions for terrestrial planets to harbour Earth-sized magnetospheres are more easily achieved for planets orbiting slowly rotating early-and mid-dM stars.

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Stellar coronal magnetic fields and star-planet interaction

Cited by 123 publications

References 53 publications

Optimizing exoplanet transit searches around low-mass stars with inclination constraints

Optimizing exoplanet transit searches around low-mass stars with inclination constraints

Binary-induced magnetic activity?

Effects of M dwarf magnetic fields on potentially habitable planets

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