Evolution of Stellar Magnetic Fields

Algol-type binaries are basically known to undergo hydrodynamic processes related to mass exchange between components. Recent observations on radio, X-ray emission and flare-like events have raised the question of possible magnetic activity in the secondary component of these systems (Hall, 1989).From a microwave emission survey we have shown that the radio emission from Algol systems cannot be accounted for by thermal emission from an hot corona (T ≥ 107K) and that their radio luminosities compare very well with those of the magnetically active RS CVn systems (Umana et al., 1990).

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Stellar activity and coronal heating: an overview of recent results

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2014.0259 ◽

2015 ◽

Vol 373 (2042) ◽

pp. 20140259 ◽

Cited By ~ 33

Author(s):

Paola Testa ◽

Steven H. Saar ◽

Jeremy J. Drake

Keyword(s):

Magnetic Activity ◽

Coronal Heating ◽

Complementary Information ◽

Stellar Activity ◽

X Ray ◽

Solar Observations ◽

Term Evolution ◽

Wide Range ◽

Stellar Magnetic Fields

Observations of the coronae of the Sun and of solar-like stars provide complementary information to advance our understanding of stellar magnetic activity, and of the processes leading to the heating of their outer atmospheres. While solar observations allow us to study the corona at high spatial and temporal resolution, the study of stellar coronae allows us to probe stellar activity over a wide range of ages and stellar parameters. Stellar studies therefore provide us with additional tools for understanding coronal heating processes, as well as the long-term evolution of solar X-ray activity. We discuss how recent studies of stellar magnetic fields and coronae contribute to our understanding of the phenomenon of activity and coronal heating in late-type stars.

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Star-Planet Interaction: The Curious Case of the Planet Spoon-feeding Its Host Star (and Other Amenities)

Proceedings of the International Astronomical Union ◽

10.1017/s174392131500592x ◽

2015 ◽

Vol 10 (S314) ◽

pp. 262-263

Author(s):

Ignazio Pillitteri ◽

S. J. Wolk ◽

A. Maggio ◽

T. Matsakos

Keyword(s):

Magnetic Fields ◽

Magnetic Reconnection ◽

Hot Spot ◽

Planetary Motion ◽

Eccentric Orbit ◽

X Ray ◽

Hot Jupiters ◽

Mhd Simulations ◽

Stellar Magnetic Fields ◽

Parent Star

AbstractWe report two cases of Star-Planet Interaction (SPI) in two systems with hot Jupiters: HD 189733 and HD 17156. We used HST-COS to study the FUV variability of HD 189733 after the planetary eclipse. With the support of MHD simulations, we evince that material is likely evaporating from the planet and accreting onto the parent star. This produces a hot spot on the stellar surface, co-moving with the planetary motion and responsible of the X-ray and FUV variability at peculiar planetary phases. In HD 17156, which hosts a hot Jupiter in an eccentric orbit, we observed an enhancement of the X-ray activity at the passage of its planet at the periastron. The origin can be due to magnetic reconnection between the planetary and stellar magnetic fields, or due to material tidally stripped from the planet and accreting onto the star.

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X-rays from magnetic massive OB stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314002427 ◽

2013 ◽

Vol 9 (S302) ◽

pp. 330-333

Author(s):

V. Petit ◽

D. H. Cohen ◽

Y. Nazé ◽

M. Gagné ◽

R. H. D. Townsend ◽

...

Keyword(s):

Magnetic Fields ◽

Large Scale ◽

Massive Stars ◽

Magnetic Activity ◽

Magnetic Characteristics ◽

Driving Mechanism ◽

X Rays ◽

X Ray ◽

Ob Stars ◽

Strong Winds

AbstractThe magnetic activity of solar-type and low-mass stars is a well known source of coronal X-ray emission. At the other end of the main sequence, X-rays emission is instead associated with the powerful, radiatively driven winds of massive stars. Indeed, the intrinsically unstable line-driving mechanism of OB star winds gives rise to shock-heated, soft emission (~0.5 keV) distributed throughout the wind. Recently, the latest generation of spectropolarimetric instrumentation has uncovered a population of massive OB-stars hosting strong, organized magnetic fields. The magnetic characteristics of these stars are similar to the apparently fossil magnetic fields of the chemically peculiar ApBp stars. Magnetic channeling of these OB stars' strong winds leads to the formation of large-scale shock-heated magnetospheres, which can modify UV resonance lines, create complex distributions of cooled Halpha emitting material, and radiate hard (~2-5 keV) X-rays. This presentation summarizes our coordinated observational and modelling efforts to characterize the manifestation of these magnetospheres in the X-ray domain, providing an important contrast between the emission originating in shocks associated with the large-scale fossil fields of massive stars, and the X-rays associated with the activity of complex, dynamo-generated fields in lower-mass stars.

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Stellar magnetic activity and their influence on the habitability of exoplanets

Proceedings of the International Astronomical Union ◽

10.1017/s1743921315005001 ◽

2014 ◽

Vol 10 (S305) ◽

pp. 333-339

Author(s):

T. Lüftinger ◽

M. Güdel ◽

C. Johnstone

Keyword(s):

Magnetic Fields ◽

International Research ◽

Planetary Systems ◽

Magnetic Activity ◽

Doppler Imaging ◽

Research Network ◽

Stellar Rotation ◽

Theoretical Understanding ◽

Points Of View ◽

Stellar Magnetic Fields

AbstractStellar magnetism, explorable via polarimetry, is a crucial driver of activity, ionization, photodissociation, chemistry and winds in stellar environments. Thus it has an important impact on the atmospheres and magnetospheres of surrounding planets. Modeling of stellar magnetic fields and their winds is extremely challenging, both from the observational and the theoretical points of view, and only recent ground breaking advances in observational instrumentation - as were discussed during this Symposium - and a deeper theoretical understanding of magnetohydrodynamic processes in stars enable us to model stellar magnetic fields and winds and the resulting influence on surrounding planets 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. In this contribution we discuss the work we are carrying out within this project and focus on how stellar magnetic fields, their winds and the relation to stellar rotation can be assessed observationally with relevant techniques such as Zeeman Doppler Imaging (ZDI), field extrapolation and wind simulations.

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Some Developments of the Weak Stellar Magnetic Field Determination Method for the Example of Cygnus X-1

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311026962 ◽

2011 ◽

Vol 7 (S282) ◽

pp. 75-76

Author(s):

N. G. Bochkarev ◽

E. A. Karitskaya

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Least Square ◽

Determination Method ◽

Optical Counterpart ◽

X Ray ◽

Stellar Magnetic Fields

AbstractSome developments of measurements of the weak stellar magnetic fields by the least square technique applied to spectropolarimetric data are proposed and used for the X-ray binary Cyg X-1 = HDE 226868 (the optical counterpart is an O 9.7 supergiant).

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Coronal Magnetic Fields Deduced from Radio Methods

International Astronomical Union Colloquium ◽

10.1017/s0252921100029171 ◽

1993 ◽

Vol 141 ◽

pp. 249-257 ◽

Cited By ~ 1

Author(s):

A. Krüger ◽

J. Hildebrandt

Keyword(s):

Magnetic Fields ◽

Solar Atmosphere ◽

Active Regions ◽

Physical Processes ◽

Poor Knowledge ◽

X Ray ◽

The Poor ◽

Coronal Magnetic Fields ◽

Spectral Ranges ◽

Different Levels

AbstractMajor problems of the physics of the solar atmosphere and processes of solar activity are due to the poor knowledge of the magnetic fields outside the photosphere. Unique methods to determine magnetic fields in the corona and chromosphere make use of radio observations in close connection with information obtained in other spectral ranges e.g. the optical and X-ray regions. Based on relevant emission and propagation processes, the basic radio methods providing information on the parent magnetic fields are summarized. Signatures in the microwave and meter wave regions are used to derive magnetic field parameters at different levels in the solar atmosphere of active regions during quiet and flaring conditions. Implications on fine and gross structures are briefly discussed and consequences on acting physical processes mentioned.

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Surface Magnetic Fields in Early-Type Stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100056098 ◽

2000 ◽

Vol 175 ◽

pp. 334-336 ◽

Cited By ~ 1

Author(s):

V. S. Airapetian

Keyword(s):

Magnetic Fields ◽

Magnetic Activity ◽

Stellar Atmospheres ◽

Early Type ◽

Inertial Oscillations ◽

Early Type Stars ◽

Stressed Surface

AbstractRecent observations imply magnetic activity in atmospheres of early-type stars. We explore the possibility that stressed surface magnetic fields can be driven by inertial oscillations, such as r-modes which are vorticity waves. We show that vorticIAL MOTIOns are able to supply helicity to drive magnetic activity in stellar atmospheres.

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Investigating magnetic activity in very stable stellar magnetic fields

Astronomy and Astrophysics ◽

10.1051/0004-6361/201527925 ◽

2016 ◽

Vol 590 ◽

pp. A11 ◽

Cited By ~ 42

Author(s):

K. Vida ◽

L. Kriskovics ◽

K. Oláh ◽

M. Leitzinger ◽

P. Odert ◽

...

Keyword(s):

Magnetic Fields ◽

Magnetic Activity ◽

Stellar Magnetic Fields

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X-ray spectra and polarization from magnetar candidates

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa204 ◽

2020 ◽

Vol 492 (4) ◽

pp. 5057-5074 ◽

Cited By ~ 1

Author(s):

R Taverna ◽

R Turolla ◽

V Suleimanov ◽

A Y Potekhin ◽

S Zane

Keyword(s):

Magnetic Fields ◽

Physical Processes ◽

X Ray ◽

Surface Emission ◽

Present Universe ◽

Emission Models ◽

Qed Effects ◽

Vacuum Effects ◽

Insight Into ◽

Proper Account

ABSTRACT Magnetars are believed to host the strongest magnetic fields in the present universe ($B\gtrsim 10^{14}$ G) and the study of their persistent emission in the X-ray band offers an unprecedented opportunity to gain insight into physical processes in the presence of ultra-strong magnetic fields. Up to now, most of our knowledge about magnetar sources came from spectral analysis, which allowed to test the resonant Compton scattering scenario and to probe the structure of the star magnetosphere. On the other hand, radiation emitted from magnetar surface is expected to be strongly polarized and its observed polarization pattern bears the imprint of both scatterings on to magnetospheric charges and quantum electro-dynamics (QED) effects as it propagates in the magnetized vacuum around the star. X-ray polarimeters scheduled to fly in the next years will finally allow to exploit the wealth of information stored in the polarization observables. Here we revisit the problem of assessing the spectro-polarimetric properties of magnetar persistent emission. At variance with previous investigations, proper account for more physical surface emission models is made by considering either a condensed surface or a magnetized atmosphere. Results are used to simulate polarimetric observations with the forthcoming Imaging X-ray Polarimetry Explorer. We find that X-ray polarimetry will allow to detect QED vacuum effects for all the emission models we considered and to discriminate among them.

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