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229 results on '"Lignières, F."'

104. Long-term magnetic field monitoring of the Sun-like starξBootis A

Author

Morgenthaler, A., primary, Petit, P., additional, Saar, S., additional, Solanki, S. K., additional, Morin, J., additional, Marsden, S. C., additional, Aurière, M., additional, Dintrans, B., additional, Fares, R., additional, Gastine, T., additional, Lanoux, J., additional, Lignières, F., additional, Paletou, F., additional, Ramírez Vélez, J. C., additional, Théado, S., additional, and Van Grootel, V., additional

Published
2012
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105. Long-term magnetic field stability of Vega

Author

Alina, D., primary, Petit, P., additional, Lignières, F., additional, Wade, G. A., additional, Fares, R., additional, Aurière, M., additional, Böhm, T., additional, and Carfantan, H., additional

Published
2012
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110. The rapid rotation and complex magnetic field geometry of Vega

Author

Petit, P., primary, Lignières, F., additional, Wade, G. A., additional, Aurière, M., additional, Böhm, T., additional, Bagnulo, S., additional, Dintrans, B., additional, Fumel, A., additional, Grunhut, J., additional, Lanoux, J., additional, Morgenthaler, A., additional, and Van Grootel, V., additional

Published
2010
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116. Magnetic geometries of Sun-like stars: exploring the mass-rotation plane

Author

Petit, Pascal, primary, Dintrans, B., additional, Aurière, M., additional, Catala, C., additional, Donati, J.-F., additional, Fares, R., additional, Gastine, T., additional, Lignières, F., additional, Morgenthaler, A., additional, Morin, J., additional, Paletou, F., additional, Ramirez, J., additional, Solanki, S. K., additional, and Théado, S., additional

Published
2008
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117. Large-scale magnetic topologies of mid M dwarfs★

Author

Morin, J., primary, Donati, J.-F., additional, Petit, P., additional, Delfosse, X., additional, Forveille, T., additional, Albert, L., additional, Aurière, M., additional, Cabanac, R., additional, Dintrans, B., additional, Fares, R., additional, Gastine, T., additional, Jardine, M. M., additional, Lignières, F., additional, Paletou, F., additional, Ramirez Velez, J. C., additional, and Théado, S., additional

Published
2008
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118. Large-scale magnetic topologies of early M dwarfs★

Author

Donati, J.-F., primary, Morin, J., additional, Petit, P., additional, Delfosse, X., additional, Forveille, T., additional, Aurière, M., additional, Cabanac, R., additional, Dintrans, B., additional, Fares, R., additional, Gastine, T., additional, Jardine, M. M., additional, Lignières, F., additional, Paletou, F., additional, Velez, J. C. Ramirez, additional, and Théado, S., additional

Published
2008
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121. Weak magnetic fields in Ap/Bp stars

Author

Aurière, M., primary, Wade, G. A., additional, Silvester, J., additional, Lignières, F., additional, Bagnulo, S., additional, Bale, K., additional, Dintrans, B., additional, Donati, J. F., additional, Folsom, C. P., additional, Gruberbauer, M., additional, Hui Bon Hoa, A., additional, Jeffers, S., additional, Johnson, N., additional, Landstreet, J. D., additional, Lèbre, A., additional, Lueftinger, T., additional, Marsden, S., additional, Mouillet, D., additional, Naseri, S., additional, Paletou, F., additional, Petit, P., additional, Power, J., additional, Rincon, F., additional, Strasser, S., additional, and Toqué, N., additional

Published
2007
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122. A BCool magnetic snapshot survey of solar-type stars.

Author

Marsden, S. C., Petit, P., Jeffers, S. V., Morin, J., Fares, R., Reiners, A., do Nascimento, J.-D., Aurière, M., Bouvier, J., Carter, B. D., Catala, C., Dintrans, B., Donati, J.-F., Gastine, T., Jardine, M., Konstantinova-Antova, R., Lanoux, J., Lignières, F., Morgenthaler, A., and Ramìrez-Vèlez, J. C.

Subjects
MAGNETIC fields, SOLAR system, HIGH resolution imaging, SPECTROPOLARIMETERS, ROTATIONAL motion, SOLAR chromosphere
Abstract

We present the results of a major high-resolution spectropolarimetric BCool project magnetic survey of 170 solar-type stars. Surface magnetic fields were detected on 67 stars, with 21 classified as mature solar-type stars, a result that increases by a factor of 4 the number of mature solar-type stars on which magnetic fields have been observed. In addition, a magnetic field was detected for 3 out of 18 of the subgiant stars surveyed. For the population of K-dwarfs, the mean value of |Bl| (|Bl|mean) was also found to be higher (5.7 G) than |Bl|mean measured for the G-dwarfs (3.2 G) and the F-dwarfs (3.3 G). For the sample as a whole, |Bl|mean increases with rotation rate and decreases with age, and the upper envelope for |Bl| correlates well with the observed chromospheric emission. Stars with a chromospheric S-index greater than about 0.2 show a high magnetic field detection rate and so offer optimal targets for future studies. This survey constitutes the most extensive spectropolarimetric survey of cool stars undertaken to date, and suggests that it is feasible to pursue magnetic mapping of a wide range of moderately active solar-type stars to improve our understanding of their surface fields and dynamos. [ABSTRACT FROM AUTHOR]

Published
2014

123. A search for weak or complex magnetic fields in the B3V star ι Herculis★.

Author

Wade, G. A., Folsom, C. P., Petit, P., Petit, V., Lignières, F., Aurière, M., and Böhm, T.

Subjects
STELLAR magnetic fields, SIGNAL-to-noise ratio, STELLAR mass, STELLAR rotation, STOKES shift
Abstract

We obtained 128 high signal-to-noise ratio Stokes V spectra of the B3V star ι Her on five consecutive nights in 2012 with the ESPaDOnS spectropolarimeter at the Canada–France–Hawaii Telescope, with the aim of searching for the presence of weak and/or complex magnetic fields. Least-squares deconvolution (LSD) mean profiles were computed from individual spectra, averaged over individual nights and over the entire run. No Zeeman signatures are detected in any of the profiles. The longitudinal magnetic field in the grand average profile was measured to be −0.24 ± 0.32 G, as compared to −0.22 ± 0.32 G in the null profile. Our observations therefore provide no evidence for the presence of Zeeman signatures analogous to those observed in the A0V star Vega by Lignières et al. We interpret these observations in three ways. First, we compare the LSD profiles with synthetic Stokes V profiles corresponding to organized (dipolar) magnetic fields, for which we find an upper limit of about 8 G on the polar strength of any surface dipole present. Secondly, we compare the grand average profile with calculations corresponding to the random magnetic spot topologies of Kochukhov & Sudnik, inferring that spots, if present, of 2° radius with strengths of 2–4 G and a filling factor of 50 per cent should have been detected in our data. Finally, we compare the observations with synthetic V profiles corresponding to the surface magnetic maps of Vega (Petit et al.) computed for the spectral characteristics of ι Her. We conclude that while it is unlikely we would have detected a magnetic field identical to Vega's, we would have likely detected one with a peak strength of about 30 G, i.e. approximately four times as strong as that of Vega. [ABSTRACT FROM AUTHOR]

Published
2014
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126. A search for magnetic fields in the variable HgMn starαAndromedae

Author

Wade, G. A., primary, Aurière, M., additional, Bagnulo, S., additional, Donati, J.-F., additional, Johnson, N., additional, Landstreet, J. D., additional, Lignières, F., additional, Marsden, S., additional, Monin, D., additional, Mouillet, D., additional, Paletou, F., additional, Petit, P., additional, Toqué, N., additional, Alecian, E., additional, and Folsom, C., additional

Published
2006
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127. Large-scale magnetic field of the G8 dwarf ξ Bootis A

Author

Petit, P., primary, Donati, J.-F., additional, Aurière, M., additional, Landstreet, J. D., additional, Lignières, F., additional, Marsden, S., additional, Mouillet, D., additional, Paletou, F., additional, Toqué, N., additional, and Wade, G. A., additional

Published
2005
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129. GAUDI: A Preparatory Archive for theCOROTMission

Author

Solano, E., primary, Catala, C., additional, Garrido, R., additional, Poretti, E., additional, Janot-Pacheco, E., additional, Gutiérrez, R., additional, González, R., additional, Mantegazza, L., additional, Neiner, C., additional, Fremat, Y., additional, Charpinet, S., additional, Weiss, W., additional, Amado, P. J., additional, Rainer, M., additional, Tsymbal, V., additional, Lyashko, D., additional, Ballereau, D., additional, Bouret, J. C., additional, Hua, T., additional, Katz, D., additional, Lignières, F., additional, Lüftinger, T., additional, Mittermayer, P., additional, Nesvacil, N., additional, Soubiran, C., additional, van 't Veer-Menneret, C., additional, Goupil, M. J., additional, Costa, V., additional, Rolland, A., additional, Antonello, E., additional, Bossi, M., additional, Buzzoni, A., additional, Rodrigo, C., additional, Aerts, C., additional, Butler, C. J., additional, Guenther, E., additional, and Hatzes, A., additional

Published
2005
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130. Rotational periods of four roAp stars

Author

Ryabchikova, T., primary, Wade, G. A., additional, Aurière, M., additional, Bagnulo, S., additional, Donati, J.-F., additional, Jeffers, S. V., additional, Johnson, N., additional, Landstreet, J. D., additional, Lignières, F., additional, Lueftinger, T., additional, Marsden, S., additional, Mouillet, D., additional, Paletou, F., additional, Petit, P., additional, Reegen, P., additional, Silvester, J., additional, Strasser, S., additional, and Toque, N., additional

Published
2005
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131. Abundance analysis of targets for the COROT/MONS asteroseismology missions

Author

Bruntt, H., primary, Bikmaev, I. F., additional, Catala, C., additional, Solano, E., additional, Gillon, M., additional, Magain, P., additional, Van't Veer-Menneret, C., additional, Stütz, C., additional, Weiss, W. W., additional, Ballereau, D., additional, Bouret, J. C., additional, Charpinet, S., additional, Hua, T., additional, Katz, D., additional, Lignières, F., additional, and Lueftinger, T., additional

Published
2004
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133. Photospheric magnetic field and surface differential rotation of the FK Com star HD 199178

Author

Petit, P., primary, Donati, J.-F., additional, Oliveira, J. M., additional, Aurière, M., additional, Bagnulo, S., additional, Landstreet, J. D., additional, Lignières, F., additional, Lüftinger, T., additional, Marsden, S., additional, Mouillet, D., additional, Paletou, F., additional, Strasser, S., additional, Toqué, N., additional, and Wade, G. A., additional

Published
2004
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136. Surface Differential Rotation of Evolved Fast Rotators

Author

Petit, P., primary, Donati, J.-F., additional, Wade, G. A., additional, Landstreet, J. D., additional, Sigut, T.A.A., additional, Shorlin, S.L.S., additional, Bagnulo, S., additional, Lüftinger, T., additional, Strasser, S., additional, Oliveira, J. M., additional, Aurière, M., additional, Lignières, F., additional, Mouillet, D., additional, and Paletou, F., additional

Published
2004
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137. Long-term magnetic field stability of Vega.

Author

Alina, D., Petit, P., Lignières, F., Wade, G. A., Fares, R., Aurière, M., Böhm, T., and Carfantan, H.

Subjects
COSMIC magnetic fields, BRIGHTEST stars, ASTROPHYSICAL spectropolarimetry, ASTRONOMICAL observations, TIME series analysis, SPECTRUM analysis, LEAST squares
Abstract

We present new spectropolarimetric observations of the normal A-type star Vega, obtained during the summer of 2010 with NARVAL at Télescope Bernard Lyot (Pic du Midi Observatory). This new time-series is constituted of 615 spectra collected over 6 different nights. We use the Least-Square-Deconvolution technique to compute, from each spectrum, a mean line profile with a signal-to-noise ratio close to 20,000. After averaging all 615 polarized observations, we detect a circularly polarized Zeeman signature consistent in shape and amplitude with the signatures previously reported from our observations of 2008 and 2009. The surface magnetic geometry of the star, reconstructed using the technique of Zeeman-Doppler Imaging, agrees with the maps obtained in 2008 and 2009, showing that most recognizable features of the photospheric field of Vega are only weakly distorted by large-scale surface flows (differential rotation or meridional circulation). [ABSTRACT FROM AUTHOR]

Published
2012
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140. Abundance analysis of targets for the COROT/MONS asteroseismology missions

Author

Bruntt, H., primary, Catala, C., additional, Garrido, R., additional, Rodríguez, E., additional, Stütz, C., additional, Knoglinger, P., additional, Mittermayer, P., additional, Bouret, J. C., additional, Hua, T., additional, Lignières, F., additional, Charpinet, S., additional, Van't Veer-Menneret, C., additional, and Ballereau, D., additional

Published
2002
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142. Exploration of the BaSeL stellar library for 9 F-type stars COROT potential targets ***

Author

Lastennet, E., Lignières, F., Buser, R., Lejeune, Th., Lüftinger, Th., Cuisinier, F., Veer-Menneret, C. van't, Lastennet, E., Lignières, F., Buser, R., Lejeune, Th., Lüftinger, Th., Cuisinier, F., and Veer-Menneret, C. van't

Abstract

The Basel Stellar Library (BaSeL models) is constituted of the merging of various synthetic stellar spectra libraries, with the purpose of giving the most comprehensive coverage of stellar parameters. It has been corrected for systematic deviations detected in respect to UBVRIJHKLMphotometry at solar metallicity, and can then be considered as the state-of-the-art knowledge of the broad band content of stellar spectra. In this paper, we consider a sample of 9 F-type stars with detailed spectroscopic analysis to investigate the Basel Stellar Library in two photometric systems simultaneously, Johnson ($B-V$, $U-B$) and Strömgren ($b-y$, m1, and c1). The sample corresponds to potential targets of the central seismology programme of the COROT space experiment, which have been recently observed at OHP. The atmospheric parameters Teff, [Fe/H], and log gobtained from the BaSeL models are compared with spectroscopic determinations as well as with results of other photometric calibrations. For a careful interpretation of the BaSeL solutions, we computed confidence regions around the best χ2-estimates and projected them on Teff-[Fe/H], Teff-log g, and log g-[Fe/H] diagrams. We first derive the 3 atmospheric parameters from the full photometric information available (Johnson and Strömgren data). The BaSeL library has only been calibrated for broad band UBVRIJHKLMphotometry, and it presents therefore intrinsic limitations in respect to other photometric systems, especially with different bandwidth. Thus, using this combination (Johnson and Strömgren), BaSeL temperatures are systematically lower (∼130 K), and the discrepancy for the gravity and the metallicity can be quite large in comparison to the other methods. To disentangle these unexpected discrepancies, we fixed the temperatures at their spectroscopic values and studied the relative influence of each colour index in the log g-[Fe/H] diagrams. We find inconsistent results between Strömgren and Johnson synthetic colours. While the Johnson colours give impressively good log g-[Fe/H] solutions, the combination of the m1and c1Strömgren synthetic indices does not provide reliable results. This is not, of course, due to any intrinsic superiority of the UBVover the Strömgren system, but to the properties of the BaSeL models. Finally, in order to simultaneously and accurately determine the stellar parameters Teff, [Fe/H] and log g, we suggest to use the combination of the synthetic BaSeL indices $B-V$, $U-B$and $b-y$rather than $B-V$, $U-B$, $b-y$, m1and c1.

Published
2001
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143. Study of KIC 8561221 observed by Kepler: an early red giant showing depressed dipolar modes?

Author

García, R. A., Hernández, F. Pérez, Benomar, O., Aguirre, V. Silva, Ballot, J., Davies, G. R., Doğan, G., Stello, D., Christensen-Dalsgaard, J., Houdek, G., Lignières, F., Mathur, S., Takata, M., Ceillier, T., Chaplin, W. J., Mathis, S., Mosser, B., Ouazzani, R. M., Pinsonneault, M. H., and Reese, D. R.

Subjects
RED giants, STELLAR structure, STELLAR magnetic fields, AMPLITUDE estimation
Abstract

Context. The continuous high-precision photometric observations provided by the CoRoT and Kepler space missions have allowed us to understand the structure and dynamics of red giants better using asteroseismic techniques. A small fraction of these stars show dipole modes with unexpectedly low amplitudes. The reduction in amplitude is more pronounced for stars with a higher frequency of maximum power, Vmax. Aims. In this work we want to characterise KIC 8561221 in order to confirm that it is currently the least evolved star among this peculiar subset and to discuss several hypotheses that could help explain the reduction of the dipole mode amplitudes. Methods. We used Kepler short- and long-cadence data combined with spectroscopic observations to infer the stellar structure and dynamics of KIC 8561221. We then discussed different scenarios that could contribute to reducing the dipole amplitudes, such as a fast-rotating interior or the effect of a magnetic field on the properties of the modes. We also performed a detailed study of the inertia and damping of the modes. Results. We have been able to characterise 36 oscillations modes, in particular, a few dipole modes above Vmax that exhibit nearly normal amplitudes. The frequencies of all the measured modes were used to determine the overall properties and the internal structure of the star.We have inferred a surface rotation period of ~91 days and uncovered a variation in the surface magnetic activity during the last 4 years. The analysis of the convective background did not reveal any difference compared to "normal" red giants. As expected, the internal regions of the star probed by the ⨏ = 2 and 3 modes spin 4 to 8 times faster than the surface. Conclusions. With our grid of standard models we are able to properly fit the observed frequencies. Our model calculation of mode inertia and damping give no explanation for the depressed dipole modes. A fast-rotating core is also ruled out as a possible explanation. Finally, we do not have any observational evidence of a strong deep magnetic field inside the star. [ABSTRACT FROM AUTHOR]

Published
2014
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144. Large-scale magnetic topologies of early M dwarfs.

Author

Morin, J., Donati, J. -F., Petit, P., Delfosse, X., Forveille, T., Albert, L., Aurière, M., Cabanac, R., Dintrans, B., Fares, R., Gastine, T., Jardine, M. M., Lignières, F., Paletou, F., Ramirez Velez, J. C., and Théado, S.

Subjects
DWARF stars, TOPOLOGY, MAGNETIC fields, ELECTROMAGNETIC induction, MAGNETIC flux, STARS
Abstract

We present here additional results of a spectropolarimetric survey of a small sample of stars ranging from spectral type M0 to M8 aimed at investigating observationally how dynamo processes operate in stars on both sides of the full convection threshold (spectral type M4). The present paper focuses on early M stars (M0–M3), that is above the full convection threshold. Applying tomographic imaging techniques to time series of rotationally modulated circularly polarized profiles collected with the NARVAL spectropolarimeter, we determine the rotation period and reconstruct the large-scale magnetic topologies of six early M dwarfs. We find that early-M stars preferentially host large-scale fields with dominantly toroidal and non-axisymmetric poloidal configurations, along with significant differential rotation (and long-term variability); only the lowest-mass star of our subsample is found to host an almost fully poloidal, mainly axisymmetric large-scale field resembling those found in mid-M dwarfs. This abrupt change in the large-scale magnetic topologies of M dwarfs (occurring at spectral type M3) has no related signature on X-ray luminosities (measuring the total amount of magnetic flux); it thus suggests that underlying dynamo processes become more efficient at producing large-scale fields (despite producing the same flux) at spectral types later than M3. We suspect that this change relates to the rapid decrease in the radiative cores of low-mass stars and to the simultaneous sharp increase of the convective turnover times (with decreasing stellar mass) that models predict to occur at M3; it may also be (at least partly) responsible for the reduced magnetic braking reported for fully convective stars. [ABSTRACT FROM AUTHOR]

Published
2008
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145. Diffusion of a trace element in anisotropic radiative hydrodynamic turbulence

Author

Vincent, A. and Lignières, F.

Abstract

We consider the problem of trace elements diffusion in parts of radiative envelopes where radiative transfer is not negligible, i.e.viscosity is mainly due to an exchange of momentum between photons and ions and when one has local thermodynamical equilibrium. The flow is made anisotropic by an external shear that mimics the effect of meridional circulation. Although the photons are nearly thermalized, the radiation field is not isotropic because there is an external flux of radiation in the radial (here vertical) direction The tracer is then released into the flow and we study how the anisotropy of turbulence breaks the diffusion of a trace element.

Published
2005
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146. Turbulent transport in stellar radiative zones

Author

Lignières, F., Toqué, N., and Vincent, A.

Abstract

Abundances anomalies and helioseismology provide constraints on the turbulent transport of chemical species in stellar radiative zone. We use these constraints to derive upper bounds on the velocity and lengthscale of the vertical turbulent motions. We also present numerical simulations showing that a strong anisotropy between horizontal and vertical motions could help understand the observed transport.

Published
2005
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147. Surface Differential Rotation of Evolved Fast Rotators

Author

Petit, P., Donati, J. -F, Musicos, Collaboration, Wade, G. A., Landstreet, J. D., Sigut, T. A. A., Shorlin, S. L. S., Bagnulo, S., Lüftinger, T., Strasser, S., Oliveira, J. M., Aurière, M., Lignières, F., Mouillet, D., and Frédéric Paletou

148. Weak magnetic fields in CP stars

Author

Aurière, M., Wade, G. A., Lignières, F., Landstreet, J. D., Donati, J. -F, Hui Bon Hoa, A., Ilian Iliev, Petit, P., Roudier, T., Silvester, J., Theado, S., Laboratoire Astrophysique de Toulouse-Tarbes (LATT), Centre National de la Recherche Scientifique (CNRS)-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées, and University of Western Ontario (UWO)

Subjects
[PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], stars: magnetic fields, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Earth and Planetary Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics::Galaxy Astrophysics, stars: chemically peculiar
Abstract

International audience; We present the first results of a magnetic survey of main sequence A and late B stars with NARVAL, the new generation spectropolarimeter available at Telescope Bernard Lyot at Pic du Midi Observatory. We observed 3 HgMn stars, 12 Am stars and the only Ap star for which no Zeeman detection was obtained with MuSiCoS. If we combine our results with those of our previous survey of weak magnetic fields in spectroscopically selected Ap/Bp stars we get the following situation: - Ap/Bp stars: all these stars appear to host a detectable magnetic field. A threshold dipolar magnetic field of 300 G appears to exist, below which fields are very rare and perhaps altogether absent. - Am and HgMn stars: no magnetic field is detected up to now for the 15 observed stars. An accuracy down to 0.3 G (respectively 1 G) is reached on longitudinal magnetic field measurements for Am (respectively HgMn) stars. We propose a possible interpretation of the observed threshold field which naturally explains the magnetic dichotomy: there exists a critical field strength above which stable magnetic configurations exist and below which any large scale field configuration is destroyed by some instability.

150. Toroidal versus poloidal magnetic fields in Sun-like stars: a rotation threshold.

Author

Petit, P., Dintrans, B., Solanki, S. K., Donati, J.-F., Aurière, M., Lignières, F., Morin, J., Paletou, F., Ramirez, J., Catala, C., and Fares, R.

Subjects
*TOROIDAL magnetic circuits, *STELLAR rotation, *MAGNETIC fields, *SOLAR magnetic fields, *POLARIMETRY, *MAGNETIC energy storage
Abstract

From a set of stellar spectropolarimetric observations, we report the detection of surface magnetic fields in a sample of four solar-type stars, namely HD 73350, HD 76151, HD 146233 (18 Sco) and HD 190771. Assuming that the observed variability of polarimetric signal is controlled by stellar rotation, we establish the rotation periods of our targets, with values ranging from 8.8 d (for HD 190771) to 22.7 d (for HD 146233). Apart from rotation, fundamental parameters of the selected objects are very close to the Sun's, making this sample a practical basis to investigate the specific impact of rotation on magnetic properties of Sun-like stars. We reconstruct the large-scale magnetic geometry of the targets as a low-order spherical harmonic expansion of the surface magnetic field. From the set of magnetic maps, we draw two main conclusions. (i) The magnetic energy of the large-scale field increases with rotation rate. The increase in chromospheric emission with the mean magnetic field is flatter than observed in the Sun. Since the chromospheric flux is also sensitive to magnetic elements smaller than those contributing to the polarimetric signal, this observation suggests that a larger fraction of the surface magnetic energy is stored in large scales as rotation increases. (ii) Whereas the magnetic field is mostly poloidal for low rotation rates, more rapid rotators host a large-scale toroidal component in their surface field. From our observations, we infer that a rotation period lower than ≈12 d is necessary for the toroidal magnetic energy to dominate over the poloidal component. [ABSTRACT FROM AUTHOR]

Published
2008
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