Planetary Messages in the Doppler Residuals

The Doppler residuals to the Keplerian fits for extrasolar planets reveal important properties of the planets and host stars. Stellar magnetic fields modify the photospheric velocity fields, causing Doppler fluctuations with unknown time scales. This Doppler “jitter”, seen prominently in the magnetic stars Epsilon Eridani and ξ Boo A, compromises the detectability of planets. The Doppler residuals during the transit of HD209458 reveal that the planet orbits in the same direction as the star spins. Moreover, the transit path across the star is nearly parallel to the stellar equator. Most interestingly, the Doppler residuals of known planets often reveal additional coherent variations, probably caused by additional companions. Both 55 Cancri and HD168443 reveal such coherent Doppler residuals. Another five planet–bearing stars observed at Lick show trends in the Doppler residuals indicating the presence of additional companions. Remarkably, about half of the known extrasolar planets reveal such coherent variations. This suggests that stars with planets have a high occurrence rate of harboring more distant companions, planetary or otherwise.

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Stellar activity and winds shaping the atmospheres of Earth-like planets

Proceedings of the International Astronomical Union ◽

10.1017/s174392131900293x ◽

2018 ◽

Vol 14 (S345) ◽

pp. 181-184

Author(s):

Theresa Lueftinger ◽

Manuel Güdel ◽

Sudeshna Boro Saikia ◽

Colin Johnstone ◽

Beatrice Kulterer ◽

...

Keyword(s):

Magnetic Fields ◽

Extreme Environments ◽

Doppler Imaging ◽

Research Network ◽

Theoretical Understanding ◽

Stellar Activity ◽

Active Stars ◽

Earth Like Planets ◽

Stellar Magnetic Fields ◽

Host Stars

AbstractPlanets orbiting young, active stars are embedded in an environment that is far from being as calm as the present solar neighbourhood. They experience the extreme environments of their host stars, which cannot have been without consequences for young stellar systems and the evolution of Earth-like planets to habitable worlds. Stellar magnetism and the related stellar activity are crucial drivers of ionization, photodissociation, and chemistry. Stellar winds can compress planetary magnetospheres and even strip away the outer layers of their atmospheres, thus having an enormous impact on the atmospheres and the magnetospheres of surrounding exoplanets. Modelling of stellar magnetic fields and their winds is extremely challenging, both from the observational and the theoretical points of view, and only ground breaking advances in observational instrumentation and a deeper theoretical understanding of magnetohydrodynamic processes in stars enable us to model stellar magnetic fields and their winds – and the resulting influence on the atmospheres of surrounding exoplanets – in more and more detail. We have initiated a national and international research network (NFN): ‘Pathways to Habitability – From Disks to Active Stars, Planets to Life’, to address questions on the formation and habitability of environments in young, active stellar/planetary systems. We discuss the work we are carrying out within this project and focus on how stellar evolutionary aspects in relation to activity, magnetic fields and winds influence the erosion of planetary atmospheres in the habitable zone. We present recent results of our theoretical and observational studies based on Zeeman Doppler Imaging (ZDI), field extrapolation methods, wind simulations, and the modeling of planetary upper atmospheres.

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Period spacings of gravity modes in rapidly rotating magnetic stars

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935462 ◽

2019 ◽

Vol 627 ◽

pp. A64 ◽

Cited By ~ 6

Author(s):

V. Prat ◽

S. Mathis ◽

B. Buysschaert ◽

J. Van Beeck ◽

D. M. Bowman ◽

...

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Internal Magnetic Field ◽

Rotating Stars ◽

Frequency Shifts ◽

Perturbative Approach ◽

Magnetic Stars ◽

Stellar Magnetic Fields ◽

Rapidly Rotating Stars ◽

The Magnetic Field

Context. Stellar magnetic fields are often invoked to explain the missing transport of angular momentum observed in models of stellar interiors. However, the properties of an internal magnetic field and the consequences of its presence on stellar evolution are largely unknown. Aims. We study the effect of an axisymmetric internal magnetic field on the frequency of gravity modes in rapidly rotating stars to check whether gravity modes can be used to detect and probe such a field. Methods. Rotation is taken into account using the traditional approximation of rotation and the effect of the magnetic field is computed using a perturbative approach. As a proof of concept, we compute frequency shifts due to a mixed (i.e. with both poloidal and toroidal components) fossil magnetic field for a representative model of a known magnetic, rapidly rotating, slowly pulsating B-type star: HD 43317. Results. We find that frequency shifts induced by the magnetic field scale with the square of its amplitude. A magnetic field with a near-core strength of the order of 150 kG (which is consistent with the observed surface field strength of the order of 1 kG) leads to signatures that are detectable in period spacings for high-radial-order gravity modes. Conclusions. The predicted frequency shifts can be used to constrain internal magnetic fields and offer the potential for a significant step forward in our interpretation of the observed structure of gravity-mode period spacing patterns in rapidly rotating stars.

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The Interpretation of Line Profiles

International Astronomical Union Colloquium ◽

10.1017/s0252921100053318 ◽

1977 ◽

Vol 36 ◽

pp. 191-215

Author(s):

G.B. Rybicki

Keyword(s):

Magnetic Fields ◽

Atomic Physics ◽

Velocity Fields ◽

Spectral Lines ◽

Inhomogeneous Structure ◽

The Sun ◽

Line Profiles ◽

Physical Phenomena

Observations of the shapes and intensities of spectral lines provide a bounty of information about the outer layers of the sun. In order to utilize this information, however, one is faced with a seemingly monumental task. The sun’s chromosphere and corona are extremely complex, and the underlying physical phenomena are far from being understood. Velocity fields, magnetic fields, Inhomogeneous structure, hydromagnetic phenomena – these are some of the complications that must be faced. Other uncertainties involve the atomic physics upon which all of the deductions depend.

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Radio Wavelength Observations of Magnetic Fields on Active Dwarf-M, RS CVN and Magnetic Stars,

10.21236/ada171985 ◽

1986 ◽

Author(s):

Kenneth R. Lang

Keyword(s):

Magnetic Fields ◽

Magnetic Stars ◽

Radio Wavelength

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Infrared Measurements of Stellar Magnetic Fields

Symposium - International Astronomical Union ◽

10.1017/s0074180900124696 ◽

1994 ◽

Vol 154 ◽

pp. 437-447 ◽

Cited By ~ 1

Author(s):

Steven H. Saar

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Pressure Support ◽

Field Research ◽

Future Directions ◽

Rotation Rates ◽

Infrared Measurements ◽

Cool Stars ◽

Rs Cvn Variables ◽

Stellar Magnetic Fields

I review the advantages, techniques, and results of measurement of magnetic fields on cool stars in the infrared (IR). These measurements have generated several important results, including the following: the first data on the magnetic parameters of dMe and RS CVn variables; evidence for field strength confinement by photospheric gas pressure; support for the correlation between magnetic flux and rotation, with possible saturation at high rotation rates; indications of horizontal and/or vertical magnetic field structure; and evidence of spatial variations in B over a stellar surface. I discuss these results in detail, and suggest future directions for IR magnetic field research.

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Observing and Modelling Stellar Magnetic Fields

EAS Publications Series ◽

10.1051/eas/0939001 ◽

2009 ◽

Vol 39 ◽

pp. 1-20 ◽

Cited By ~ 7

Author(s):

J.D. Landstreet

Keyword(s):

Magnetic Fields ◽

Stellar Magnetic Fields

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Global MHD phenomena and their importance for stellar surfaces

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311015146 ◽

2010 ◽

Vol 6 (S273) ◽

pp. 141-147

Author(s):

Rainer Arlt

Keyword(s):

Magnetic Fields ◽

Mean Field ◽

Momentum Equation ◽

Small Scale ◽

Dynamo Action ◽

Complex Activity ◽

Mhd Instabilities ◽

Stellar Magnetic Fields ◽

Mean Field Dynamo

AbstractThis review is an attempt to elucidate MHD phenomena relevant for stellar magnetic fields. The full MHD treatment of a star is a problem which is numerically too demanding. Mean-field dynamo models use an approximation of the dynamo action from the small-scale motions and deliver global magnetic modes which can be cyclic, stationary, axisymmetric, and non-axisymmetric. Due to the lack of a momentum equation, MHD instabilities are not visible in this picture. However, magnetic instabilities must set in as a result of growing magnetic fields and/or buoyancy. Instabilities deliver new timescales, saturation limits and topologies to the system probably providing a key to the complex activity features observed on stars.

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The macrodynamics of α-effect dynamos in rotating fluids

Journal of Fluid Mechanics ◽

10.1017/s0022112075000390 ◽

1975 ◽

Vol 67 (3) ◽

pp. 417-443 ◽

Cited By ~ 140

Author(s):

W. V. R. Maekus ◽

M. R. E. Proctor

Keyword(s):

Magnetic Fields ◽

Large Scale ◽

Magnetic Energy ◽

Finite Amplitude ◽

Small Scale ◽

Past Study ◽

Ohmic Loss ◽

General Will ◽

Rotating Systems ◽

Stellar Magnetic Fields

Past study of the large-scale consequences of forced small-scale motions in electrically conducting fluids has led to the ‘α-effect’ dynamos. Various linear kinematic aspects of these dynamos have been explored, suggesting their value in the interpretation of observed planetary and stellar magnetic fields. However, large-scale magnetic fields with global boundary conditions can not be force free and in general will cause large-scale motions as they grow. I n this paper the finite amplitude behaviour of global magnetic fields and the large-scale flows induced by them in rotating systems is investigated. In general, viscous and ohmic dissipative mechanisms both play a role in determining the amplitude and structure of the flows and magnetic fields which evolve. In circumstances where ohmic loss is the principal dissipation, it is found that determination of a geo- strophic flow is an essential part of the solution of the basic stability problem. Nonlinear aspects of the theory include flow amplitudes which are independent of the rotation and a total magnetic energy which is directly proportional to the rotation. Constant a is the simplest example exhibiting the various dynamic balances of this stabilizing mechanism for planetary dynamos. A detailed analysis is made for this case to determine the initial equilibrium of fields and flows in a rotating sphere.

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