scholarly journals Butterfly diagram of a Sun-like star observed using asteroseismology

2018 ◽  
Vol 619 ◽  
pp. L9 ◽  
Author(s):  
M. Bazot ◽  
M. B. Nielsen ◽  
D. Mary ◽  
J. Christensen-Dalsgaard ◽  
O. Benomar ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Stellar Evolution ◽  
Theoretical Models ◽  
Observational Constraint ◽  
Stellar Rotation ◽  
Magnetic Field Generation ◽  
Rotation Rates ◽  
Butterfly Diagram ◽  
Stellar Magnetic Fields ◽  
First Time

Stellar magnetic fields are poorly understood, but are known to be important for stellar evolution and exoplanet habitability. They drive stellar activity, which is the main observational constraint on theoretical models for magnetic field generation and evolution. Starspots are the main manifestation of the magnetic fields at the stellar surface. In this study we measured the variation in their latitude with time, called a butterfly diagram in the solar case, for the solar analogue HD 173701 (KIC 8006161). To this end, we used Kepler data to combine starspot rotation rates at different epochs and the asteroseismically determined latitudinal variation in the stellar rotation rates. We observe a clear variation in the latitude of the starspots. It is the first time such a diagram has been constructed using asteroseismic data.

scholarly journals Infrared Measurements of Stellar Magnetic Fields

1994 ◽  
Vol 154 ◽  
pp. 437-447 ◽  
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.

scholarly journals Magnetar birth: rotation rates and gravitational-wave emission

2020 ◽  
Vol 494 (4) ◽  
pp. 4838-4847 ◽  
Author(s):  
S K Lander ◽  
D I Jones
Keyword(s):  
Viscous Dissipation ◽  
Radio Burst ◽  
Stellar Rotation ◽  
Radio Pulsars ◽  
Rotation Rates ◽  
Buoyancy Forces ◽  
Wave Emission ◽  
Fast Radio Burst ◽  
Electromagnetic Signals ◽  
First Time

ABSTRACT Understanding the evolution of the angle χ between a magnetar’s rotation and magnetic axes sheds light on the star’s birth properties. This evolution is coupled with that of the stellar rotation Ω, and depends on the competing effects of internal viscous dissipation and external torques. We study this coupled evolution for a model magnetar with a strong internal toroidal field, extending previous work by modelling – for the first time in this context – the strong protomagnetar wind acting shortly after birth. We also account for the effect of buoyancy forces on viscous dissipation at late times. Typically, we find that χ → 90° shortly after birth, then decreases towards 0° over hundreds of years. From observational indications that magnetars typically have small χ, we infer that these stars are subject to a stronger average exterior torque than radio pulsars, and that they were born spinning faster than ∼100–300 Hz. Our results allow us to make quantitative predictions for the gravitational and electromagnetic signals from a newborn rotating magnetar. We also comment briefly on the possible connection with periodic fast radio burst sources.

scholarly journals On Magnetic Mixing and Rotation in Stellar Evolution

1978 ◽  
Vol 80 ◽  
pp. 323-331
Author(s):  
Peter G. Gross
Keyword(s):  
Magnetic Fields ◽  
Stellar Evolution ◽  
Evolutionary Status ◽  
Relevant Parameter ◽  
Stellar Rotation ◽  
Convective Turbulence ◽  
Stellar Interior ◽  
Magnetic Mixing ◽  
Ap Stars

In this paper some thoughts and problems are presented from the viewpoint that the evolution of stars may play a key role in generating magnetic fields which, in turn, may affect the mixing of nuclearly processed elements from the stellar interior to the surface. The relevant parameter is stellar rotation which, upon interaction with convective turbulence driven by thermal instabilities, leads to the generation of magnetic fields. A possible connection to Bidelman's hypothesis on the evolutionary status of Ap stars is also discussed in the context of a post-core-helium-flash hypothesis.

scholarly journals Dynamo-generated magnetic fields in fast rotating single giants

2008 ◽  
Vol 4 (S259) ◽  
pp. 433-434 ◽  
Author(s):  
Renada Konstantinova-Antova ◽  
Michel Aurière ◽  
Klaus-Peter Schröder ◽  
Pascal Petit
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Stellar Evolution ◽  
Red Giants ◽  
Good Opportunity ◽  
Early Results ◽  
First Time ◽  
Fast Rotating

AbstractRed giants offer a good opportunity to study the interplay of magnetic fields and stellar evolution. Using the spectro-polarimeter NARVAL of the Telescope Bernard Lyot (TBL), Pic du Midi, France and the LSD technique we began a survey of magnetic fields in single G-K-M giants. Early results include 6 MF-detections with fast rotating giants, and for the first time a magnetic field was detected directly in an evolved M-giant: EK Boo. Our results could be explained in the terms of α–ω dynamo operating in these giants.

scholarly journals Stellar magnetic activity and their influence on the habitability of exoplanets

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.

scholarly journals Measuring T Tauri star magnetic fields

2008 ◽  
Vol 4 (S259) ◽  
pp. 345-356 ◽  
Author(s):  
Christopher M. Johns–Krull
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Scaling Laws ◽  
Main Sequence ◽  
Critical Role ◽  
X Rays ◽  
Stellar Rotation ◽  
T Tauri ◽  
Dipole Component ◽  
Stellar Magnetic Fields

AbstractStellar magnetic fields including a strong dipole component are believed to play a critical role in the early evolution of newly formed stars and their circumstellar accretion disks. It is currently believed that the stellar magnetic field truncates the accretion disk several stellar radii above the star. This action forces accreting material to flow along the field lines and accrete onto the star preferentially at high stellar latitudes. It is also thought that the stellar rotation rate becomes locked to the Keplerian velocity near the radius where the disk is truncated. This paper reviews recent efforts to measure the magnetic field properties of low mass pre-main sequence stars, focussing on how the observations compare with the theoretical expectations. A picture is emerging indicating that quite strong fields do indeed cover the majority of the surface on these stars; however, the dipole component of the field appears to be alarmingly small. The current measurements also suggest that given their strong magnetic fields, T Tauri stars are somewhat faint in X-rays relative to what is expected from simple main sequence star scaling laws.

scholarly journals Extended main sequence turnoffs in open clusters as seen by Gaia – II. The enigma of NGC 2509

2019 ◽  
Vol 491 (2) ◽  
pp. 2129-2136 ◽  
Author(s):  
M de Juan Ovelar ◽  
S Gossage ◽  
S Kamann ◽  
N Bastian ◽  
C Usher ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Narrow Range ◽  
Open Cluster ◽  
Open Clusters ◽  
Stellar Rotation ◽  
Rotation Rates ◽  
Magnitude Diagram ◽  
Stellar Density

ABSTRACT We investigate the morphology of the colour–magnitude diagram (CMD) of the open cluster NGC 2509 in comparison with other Galactic open clusters of similar age using Gaia photometry. At ${\sim}900\,\rm {Myr}$ Galactic open clusters in our sample all show an extended main sequence turnoff (eMSTO) with the exception of NGC 2509, which presents an exceptionally narrow CMD. Our analysis of the Gaia data rules out differential extinction, stellar density, and binaries as a cause for the singular MSTO morphology in this cluster. We interpret this feature as a consequence of the stellar rotation distribution within the cluster and present the analysis with mesa Isochrones and Stellar Tracks (MIST) stellar evolution models that include the effect of stellar rotation on which we based our conclusion. In particular, these models point to an unusually narrow range of stellar rotation rates (Ω/Ωcrit, ZAMS = [0.4, 0.6]) within the cluster as the cause of this singular feature in the CMD of NGC 2509. Interestingly, models that do not include rotation are not as good at reproducing the morphology of the observed CMD in this cluster.

scholarly journals Modeling the solar cycle: what the future holds

2011 ◽  
Vol 7 (S286) ◽  
pp. 54-64
Author(s):  
Dibyendu Nandy
Keyword(s):  
Solar Cycle ◽  
Magnetic Fields ◽  
Solar Interior ◽  
Magnetic Field Generation ◽  
Kinematic Dynamo ◽  
The Future ◽  
Dynamo Mechanism ◽  
Stellar Magnetic Fields ◽  
Magnetohydrodynamic Models ◽  
Evolution With Time

AbstractStellar magnetic fields are produced by a magnetohydrodynamic dynamo mechanism working in their interior – which relies on the interaction between plasma flows and magnetic fields. The Sun, being a well-observed star, offers an unique opportunity to test theoretical ideas and models of stellar magnetic field generation. Solar magnetic fields produce sunspots, whose number increases and decreases with a 11 year periodicity – giving rise to what is known as the solar cycle. Dynamo models of the solar cycle seek to understand its origin, variation and evolution with time. In this review, I summarize observations of the solar cycle and describe theoretical ideas and kinematic dynamo modeling efforts to address its origin. I end with a discussion on the future of solar cycle modeling – emphasizing the importance of a close synergy between observational data assimilation, kinematic dynamo models and full magnetohydrodynamic models of the solar interior.

scholarly journals Stellar magnetic fields across the H-R diagram: observational evidence

2008 ◽  
Vol 4 (S259) ◽  
pp. 323-332 ◽  
Author(s):  
Svetlana V. Berdyugina
Keyword(s):  
Magnetic Fields ◽  
Stellar Evolution ◽  
Measurement Methods ◽  
Observational Evidence ◽  
Substellar Objects ◽  
Stellar Magnetic Fields

AbstractThis review presents most recent measurements of magnetic fields in various types of stars and substellar objects across the H-R diagram with the emphasis on measurement methods, observational and modeling biases, and the role of magnetic fields in stellar evolution.

scholarly journals Measurements of magnetic fields on T Tauri stars

2007 ◽  
Vol 3 (S243) ◽  
pp. 31-42 ◽  
Author(s):  
Christopher M. Johns–Krull
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Critical Role ◽  
Current Data ◽  
Stellar Rotation ◽  
T Tauri ◽  
Dipole Component ◽  
Field Lines ◽  
Stellar Magnetic Fields ◽  
The Magnetic Field

AbstractStellar magnetic fields including a strong dipole component are believed to play a critical role in the early evolution of newly formed stars and their circumstellar accretion disks. It is currently believed that the stellar magnetic field truncates the accretion disk several stellar radii above the star. This action forces accreting material to flow along the field lines and accrete onto the star preferentially at high stellar latitudes. It is also thought that the stellar rotation rate becomes locked to the Keplerian velocity near the radius where the disk is truncated. This paper reviews recent efforts to measure the magnetic field properties of low mass pre-main sequence stars, focussing on how the observations compare with the theoretical expectations. A picture is emerging indicating that quite strong fields do indeed cover the majority of the surface on these stars; however, the dipole component of the field appears to be alarmingly small. On the other hand, at least one accretion model which takes into account the non-dipole nature of the magnetic field provides predictions relating various stellar and accretion parameters which are present in the current data.

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