Large-scale magnetic topologies of mid M dwarfs<sup>★</sup>

Morin, J.; Donati, J.‐F.; Petit, P.; Delfosse, X.; Forveille, T.; Li, Albert; Aurière, M.; Cabanac, R.; Dintrans, B.; Farès, R.; Gastine, T.; Jardine, M.; Lignières, F.; Paletou, F.; Vélez, J. C. Ramírez; Théado, S.

doi:10.1111/j.1365-2966.2008.13809.x

Cited by 414 publications

(539 citation statements)

References 47 publications

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“…Using ZDI, one can reconstruct the large-scale magnetic field (intensity and orientation) at the surface of the star from a series of circular polarisation spectra. In this work, we concentrated on dM stars and used the maps that were published in Donati et al (2008) and Morin et al (2008bMorin et al ( , 2010. Our sample consists of 15 stars with masses ranging from 0.1 to 0.75 M , spanning spectral types M0−M6.…”

Section: Star Samplementioning

confidence: 99%

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Effects of M dwarf magnetic fields on potentially habitable planets

Vidotto

Jardine

Morin

et al. 2013

A&A

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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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Section: Star Samplementioning

confidence: 99%

“…Table 1 shows some properties of the entire sample of dM stars considered. Data from the first eight columns are taken from Donati et al (2008) and Morin et al (2008bMorin et al ( , 2010. Effective temperatures and bolometric luminosities are derived from NextGen models (Baraffe et al 1998).…”

Section: Star Samplementioning

confidence: 99%

Effects of M dwarf magnetic fields on potentially habitable planets

Vidotto

Jardine

Morin

et al. 2013

A&A

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141

160

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“…Assuming a given magnetic field strength and orientation for each pixel, local Stokes V profiles are calculated under the weak-field assumption (Morin et al 2008;Petit et al 2010;Morgenthaler et al 2012). The rotation period, inclination angle, and v sin i adopted for our model are discussed below.…”

Section: Zeeman Doppler Imagingmentioning

confidence: 99%

Magnetic field structure in single late-type giants:βCeti in 2010–2012

Tsvetkova

Petit

Aurière

et al. 2013

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Aims. We study the behavior of the magnetic field and the line activity indicators of the single late-type giant β Ceti. Using spectropolarimetric data, we aim to reconstruct the magnetic field structure on the star's surface and to present the first magnetic maps for β Ceti. Methods. The data were obtained using two spectropolarimeters -Narval at the Bernard Lyot Télescope, Pic du Midi, France, and ESPaDOnS at CFHT, Hawaii. Thirty-eight circularly-polarized spectra have been collected in the period June 2010-January 2012. The least square deconvolution method was applied for extracting high signal-to-noise ratio line profiles, from which we measured the surface-averaged longitudinal magnetic field B l . Chromospheric activity indicators CaII K, Hα, CaII IR (854.2 nm), and radial velocity were simultaneously measured, and their variability was analyzed along with the behavior of B l . The Zeeman Doppler imaging (ZDI) inversion technique was employed for reconstructing the large-scale magnetic field and two magnetic maps of β Ceti are presented for two periods (June 2010-December 2010 and June 2011-January 2012). Results. The B l stays with a same positive polarity for the whole observational period and shows significant variations in the interval 0.1-8.2 G. The behavior of the line activity indicators is in good agreement with the B l variations. Searching for periodic signals in the Stokes V time series, we found a possible rotation period of 215 days. The two ZDI maps show a mainly axisymmetric and poloidal magnetic topology and a simple surface magnetic field configuration dominated by a dipole. Little evolution is observed between the two maps, in spite of a 1 yr interval between both subsets. We also use state-of-the-art stellar evolution models to constrain the evolutionary status of β Ceti. We derive a mass of 3.5 M and propose that this star is already in the central helium-burning phase. Conclusions. Considering all our results and the evolutionary status of the star, we suggest that dynamo action alone may not be efficient enough to account for the high magnetic activity of β Ceti. As an alternate option, we propose that it is a descendant of an Ap star presently undergoing central helium-burning and still exhibiting a remnant of the Ap star magnetic field.

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“…However, these techniques are very challenging to apply for such faint objects. Nevertheless, it is still possible to observe the brightest objects and use a least square deconvolution (LSD) method (see Donati et al 1997) to construct an average line profile based on selected individual atomic lines for which Landé factors are accurately known, as was done in a series of papers by Donati et al (2006Donati et al ( , 2008 and Morin et al (2008). The authors found the presence of regions with strong magnetic fields that occupy large surface areas in selected M dwarfs, but the field geometry of the majority of them are dominated by the poloidal component, which indicates rather homogeneous magnetic fields.…”

Section: Introductionmentioning

confidence: 99%

Exploring the magnetic field complexity in M dwarfs at the boundary to full convection

Shulyak

Reiners

Seemann

et al. 2014

A&A

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Context. Magnetic fields play a pivotal role in the formation and evolution of low-mass stars, but the dynamo mechanisms generating these fields are poorly understood. Measuring cool star magnetism is a complicated task because of the complexity of cool star spectra and the subtle signatures of magnetic fields. Aims. Based on detailed spectral synthesis, we carry out quantitative measurements of the strength and complexity of surface magnetic fields in the four well-known M dwarfs GJ 388, GJ 729, GJ 285, and GJ 406 that populate the mass regime around the boundary between partially and fully convective stars. Very high-resolution (R = 100 000), high signal-to-noise (up to 400), near-infrared Stokes I spectra were obtained with CRIRES at ESO's Very Large Telescope covering regions of the FeH Wing-Ford transitions at 1 μm and Na i lines at 2.2 μm.Methods. A modified version of the Molecular Zeeman Library (MZL) was used to compute Landé g-factors for FeH lines. We determined the distribution of magnetic fields by magnetic spectral synthesis performed with the Synmast code. We tested two different magnetic geometries to probe the influence of field orientation effects. Results. Our analysis confirms that FeH lines are excellent indicators of surface magnetic fields in low-mass stars of type M, particularly in comparison to profiles of Na i lines that are heavily affected by water lines and that suffer problems with continuum normalization. The field distributions in all four stars are characterized by three distinct groups of field components, and the data are consistent neither with a smooth distribution of different field strengths nor with one average field strength covering the full star. We find evidence of a subtle difference in the field distribution of GJ 285 compared to the other three targets. GJ 285 also has the highest average field of 3.5 kG and the strongest maximum field component of 7-7.5 kG. The maximum local field strengths in our sample seem to be correlated with rotation rate. While the average field strength is saturated, the maximum local field strengths in our sample show no evidence of saturation. Conclusions. We find no difference between the field distributions of partially and fully convective stars. The one star with evidence of field distribution different from the other three is the most active star (i.e. with X-ray luminosity and mean surface magnetic field) rotating relatively fast. A possible explanation is that rotation determines the distribution of surface magnetic fields, and that local field strengths grow with rotation even in stars in which the average field is already saturated.

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Large-scale magnetic topologies of mid M dwarfs^★

Cited by 414 publications

References 47 publications

Effects of M dwarf magnetic fields on potentially habitable planets

Effects of M dwarf magnetic fields on potentially habitable planets

Magnetic field structure in single late-type giants:βCeti in 2010–2012

Exploring the magnetic field complexity in M dwarfs at the boundary to full convection

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Large-scale magnetic topologies of mid M dwarfs★

Cited by 414 publications

References 47 publications

Effects of M dwarf magnetic fields on potentially habitable planets

Effects of M dwarf magnetic fields on potentially habitable planets

Magnetic field structure in single late-type giants:βCeti in 2010–2012

Exploring the magnetic field complexity in M dwarfs at the boundary to full convection

Contact Info

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Large-scale magnetic topologies of mid M dwarfs^★