The Relation Between Rotation and Magnetic Activity on Lower Main Sequence Stars as Derived from Chromospheric Indicators

It is now firmly established that lower main sequence (LMS) stars show a qualitative correlation between rotation rate and chromospheric and coronal emission. By analogy with the Sun, the emission is believed to be intimately associated with surface magnetic fields. This association is especially close on the Sun for the Ca II H and K lines, for which the spatial correlation between chromospheric emission and photospheric fields is essentially one-to-one down to scales at least as fine as a few arcseconds and for which the emission flux from an area on the Sun is approximately proportional to the total magnetic flux passing through the same area in the underlying photosphere (Leighton 1959; Skumanich, Smythe, and Frazier 1975; Frazier 1971). The extension of the association to other LMS stars, while based on appeal to analogy, has been strengthened by recent detections of strong magnetic fields covering large fraction of the surface area of chromospherically active stars (see review by Marcy in this symposium).

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Differential Rotation and Magnetic Activity of the Lower Main Sequence Stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100075539 ◽

1980 ◽

Vol 51 ◽

pp. 296-297

Author(s):

G. Belvedere ◽

L. Paterno ◽

M. Stix

Keyword(s):

Spherical Shell ◽

Differential Rotation ◽

Main Sequence ◽

Magnetic Activity ◽

The Sun ◽

Coupling Constant ◽

Main Sequence Stars ◽

Dynamo Theory ◽

Magnetic Cycles ◽

Surface Convection

AbstractWe extend to the lower main sequence stars the analysis of convection interacting with rotation in a compressible spherical shell, already applied to the solar case (Belvedere and Paterno, 1977; Belvedere et al. 1979a). We assume that the coupling constant ε between convection and rotation, does not depend on the spectral type. Therefore we take ε determined from the observed differential rotation of the Sun, and compute differential rotation and magnetic cycles for stars ranging from F5 to MO, namely for those stars which are supposed to possess surface convection zones (Belvedere et al. 1979b, c, d). The results show that the strength of differential rotation decreases from a maximum at F5 down to a minimum at G5 and then increases towards later spectral types. The computations of the magnetic cycles based on the αω-dynamo theory show that dynamo instability decreases from F5 to G5, and then increases towards the later spectral types reaching a maximum at MO. The period of the magnetic cycles increases from a few years at F5 to about 100 years at MO. Also the extension of the surface magnetic activity increases substantially towards the later spectral types. The results are discussed in the framework of Wilson’s (1978) observations.

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Global Evolution of Photospheric Magnetic Fields

Symposium - International Astronomical Union ◽

10.1017/s0074180900044247 ◽

1990 ◽

Vol 138 ◽

pp. 281-295

Author(s):

V. I. Makarov ◽

K. R. Sivaraman

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Large Scale ◽

Active Regions ◽

Magnetic Activity ◽

Field Pattern ◽

The Sun ◽

Coronal Emission ◽

Global Magnetic Field ◽

Global Modes

The main features concerning the evolution of the large scale photospheric magnetic fields derived from synoptic maps as well as from H-alpha synoptic charts are reviewed. The significance of a variety of observations that indicate the presence of a high latitude component as a counterpart to the sunspot phenomenon at lower latitudes is reviewed. It is argued that these two components describe the global magnetic field on the sun. It is demonstrated that this scenario is able to link many phenomena observed on the sun (coronal emission, ephemeral active regions, geomagnetic activity, torsional oscillations, polar faculae and global modes in the magnetic field pattern) with the global magnetic activity.

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The Age Evolution of Ca II Emission in Late Type Stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100080192 ◽

1991 ◽

Vol 130 ◽

pp. 480-482

Author(s):

C. Trigilio ◽

S. Catalano ◽

E. Marilli ◽

V. Reglero ◽

G. Umana

Keyword(s):

Main Sequence ◽

Magnetic Activity ◽

Late Type ◽

Main Sequence Stars ◽

Dynamo Action ◽

Solar Mass ◽

Surface Rotation ◽

Chromospheric Emission ◽

Moving Groups ◽

Insight Into

It has been widely demonstrated that chromospheric emission is dependent on rotation rate (Hartmann and Noyes, 1987, Catalano, 1990, for recent reviews). Since the rotation decays with time, the chromospheric activity of single main sequence stars is also dependent on age. Catalano and Marilli (1983) suggested that the chromospheric emission of solar mass stars decays exponentially with the square root of the time, as recently confirmed by Barry (1988). Magnetic activity depends also on the convection parameters, i.e. on the mass. Since the evolution of surface rotation is faster for lower mass stars (Catalano et al., 1988), the internal rotation distribution, and therefore the dynamo action, should change with time in a different way for different masses.In order to get insight into the evolution of dynamo action we have studied the CaII chromospheric emission as a function of mass and age. Here we present some preliminary results of observations of late type stars in young clusters and old moving groups.

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Magnetic Activity of Pre-main Sequence Stars near the Stellar-Substellar Boundary

Proceedings of the International Astronomical Union ◽

10.1017/s1743921315006146 ◽

2015 ◽

Vol 10 (S314) ◽

pp. 126-127

Author(s):

David Principe ◽

Joel. H. Kastner ◽

David Rodriguez

Keyword(s):

Spectral Type ◽

Main Sequence ◽

Brown Dwarfs ◽

Magnetic Activity ◽

Main Sequence Stars ◽

Coronal Emission ◽

Low Mass Stars ◽

X Ray ◽

Low Mass ◽

Age Range

AbstractX-ray observations of pre-main sequence (pre-MS) stars of M-type probe coronal emission and offer a means to investigate magnetic activity at the stellar-substellar boundary. Recent observations of main sequence (MS) stars at this boundary display a decrease in fractional X-ray luminosity (LX/Lbol) by almost two orders of magnitude for spectral types M7 and later. We investigate magnetic activity and search for a decrease in X-ray emission in the pre-MS progenitors of these MS stars. We present XMM-Newton X-ray observations and preliminary results for ~10 nearby (30-70 pc), very low mass pre-MS stars in the relatively unexplored age range of 10-30 Myr. We compare the fractional X-ray luminosities of these 10-30 Myr old stars to younger (1-3 Myr) pre-MS brown dwarfs and find no dependence on spectral type or age suggesting that X-ray activity declines at an age later than ~30 Myr in these very low-mass stars.

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3D Perspectives of Stellar Activity: Observation and Modelling

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314004761 ◽

2012 ◽

Vol 10 (H16) ◽

pp. 109-110

Author(s):

Moira Jardine

Keyword(s):

Magnetic Field ◽

Main Sequence ◽

Solar Magnetic Field ◽

3D Structure ◽

Magnetic Activity ◽

The Sun ◽

Main Sequence Stars ◽

Rotation Rates ◽

Low Activity ◽

Coronal Structures

AbstractAs the Sun emerges from a period of unprecedented low activity, the nature of the Sun's magnetic field compared to that of other stars is a particularly timely question. Just as observations of the full 3D structure of the solar magnetic field are becoming available through STEREO and SDO, advances in spectropolarimetric techniques now allow us to map the surface magnetic fields of other stars, revealing the great diversity of magnetic geometries that stars of different masses and rotation rates can display. This has now been possible for over 60 main sequence stars, with a smaller number of younger, pre-main sequence stars also mapped. Modelling of coronal structures based on these observations is revealing the full nature of stellar magnetic activity and its possible impact on orbiting planets.

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Magnetic fields in non-convective regions of stars

Royal Society Open Science ◽

10.1098/rsos.160271 ◽

2017 ◽

Vol 4 (2) ◽

pp. 160271 ◽

Cited By ~ 21

Author(s):

Jonathan Braithwaite ◽

Henk C. Spruit

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Main Sequence ◽

Field Model ◽

The Sun ◽

Early Type ◽

Main Sequence Stars ◽

Current State ◽

Recent Developments ◽

Early Type Stars

We review the current state of knowledge of magnetic fields inside stars, concentrating on recent developments concerning magnetic fields in stably stratified (zones of) stars, leaving out convective dynamo theories and observations of convective envelopes. We include the observational properties of A, B and O-type main-sequence stars, which have radiative envelopes, and the fossil field model which is normally invoked to explain the strong fields sometimes seen in these stars. Observations seem to show that Ap-type stable fields are excluded in stars with convective envelopes. Most stars contain both radiative and convective zones, and there are potentially important effects arising from the interaction of magnetic fields at the boundaries between them; the solar cycle being one of the better known examples. Related to this, we discuss whether the Sun could harbour a magnetic field in its core. Recent developments regarding the various convective and radiative layers near the surfaces of early-type stars and their observational effects are examined. We look at possible dynamo mechanisms that run on differential rotation rather than convection. Finally, we turn to neutron stars with a discussion of the possible origins for their magnetic fields.

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Chromospheric activity as a function of age in main-sequence stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900053146 ◽

1966 ◽

Vol 24 ◽

pp. 40-43

Author(s):

O. C. Wilson ◽

A. Skumanich

Keyword(s):

Main Sequence ◽

The Sun ◽

Main Sequence Stars ◽

Tentative Conclusion ◽

Chromospheric Activity ◽

General Field ◽

Large Clusters

Evidence previously presented by one of the authors (1) suggests strongly that chromospheric activity decreases with age in main sequence stars. This tentative conclusion rests principally upon a comparison of the members of large clusters (Hyades, Praesepe, Pleiades) with non-cluster objects in the general field, including the Sun. It is at least conceivable, however, that cluster and non-cluster stars might differ in some fundamental fashion which could influence the degree of chromospheric activity, and that the observed differences in chromospheric activity would then be attributable to the circumstances of stellar origin rather than to age.

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Stellar 5 min Oscillations

International Astronomical Union Colloquium ◽

10.1017/s0252921100095828 ◽

1983 ◽

Vol 66 ◽

pp. 469-486

Author(s):

Jørgen Christensen-Dalsgaard ◽

Søren Frandsen

Keyword(s):

Spectral Type ◽

Main Sequence ◽

Total Flux ◽

The Sun ◽

Major Fraction ◽

Main Sequence Stars ◽

Red Supergiants

AbstractEstimates are given for the amplitudes of stochastically excited oscillations in Main Sequence stars and cool giants; these were obtained using the equipartition between convective and pulsational energy which was originally proposed by Goldreich and Keeley. The amplitudes of both velocity and luminosity perturbation generally increase with increasing mass along the Main Sequence as long as convection transports a major fraction of the total flux, and the amplitudes also increase with the age of the model. The 1.5 Mʘ ZAMS model, of spectral type F0, has velocity amplitudes ten times larger than those found in the Sun. For very luminous red supergiants luminosity amplitudes of up to about 0ṃ.1 are predicted, in rough agreement with observations presented by Maeder.

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