scholarly journals The large-scale magnetic field of Proxima Centauri near activity maximum

2020 ◽  
Vol 500 (2) ◽  
pp. 1844-1850
Author(s):  
Baptiste Klein ◽  
Jean-François Donati ◽  
Élodie M Hébrard ◽  
Bonnie Zaire ◽  
Colin P Folsom ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Circular Polarization ◽  
Large Scale ◽  
Doppler Imaging ◽  
Magnetic Star ◽  
Mass Star ◽  
Activity Maximum ◽  
Long Term Study ◽  
Large Scale Magnetic Field ◽  
Polarization Spectra

ABSTRACT We report the detection of a large-scale magnetic field at the surface of the slowly rotating fully convective (FC) M dwarf Proxima Centauri. 10 circular polarization spectra, collected from 2017 April to July with the HARPS-Pol spectropolarimeter, exhibit rotationally modulated Zeeman signatures suggesting a stellar rotation period of 89.8 ± 4.0 d. Using Zeeman–Doppler Imaging, we invert the circular polarization spectra into a surface distribution of the large-scale magnetic field. We find that Proxima Cen hosts a large-scale magnetic field of typical strength 200 G, whose topology is mainly poloidal, and moderately axisymmetric, featuring, in particular, a dipole component of 135 G tilted at 51° to the rotation axis. The large-scale magnetic flux is roughly 3× smaller than the flux measured from the Zeeman broadening of unpolarized lines, which suggests that the underlying dynamo is efficient at generating a magnetic field at the largest spatial scales. Our observations occur ∼1 yr after the maximum of the reported 7 yr-activity cycle of Proxima Cen, which opens the door for the first long-term study of how the large-scale field evolves with the magnetic cycle in an FC very low mass star. Finally, we find that Proxima Cen’s habitable zone planet, Proxima-b, is likely orbiting outside the Alfvèn surface, where no direct magnetic star–planet interactions occur.

scholarly journals Direct evidence of a full dipole flip during the magnetic cycle of a sun-like star

2018 ◽  
Vol 620 ◽  
pp. L11 ◽  
Author(s):  
S. Boro Saikia ◽  
T. Lueftinger ◽  
S. V. Jeffers ◽  
C. P. Folsom ◽  
V. See ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Activity Cycle ◽  
Doppler Imaging ◽  
Dipolar Field ◽  
Magnetic Cycle ◽  
Activity Maximum ◽  
Cycle Minimum ◽  
Chromospheric Activity ◽  
Cycle Maximum

Context.The behaviour of the large-scale dipolar field, during a star’s magnetic cycle, can provide valuable insight into the stellar dynamo and associated magnetic field manifestations such as stellar winds.Aims.We investigate the temporal evolution of the dipolar field of the K dwarf 61 Cyg A using spectropolarimetric observations covering nearly one magnetic cycle equivalent to two chromospheric activity cycles.Methods.The large-scale magnetic field geometry is reconstructed using Zeeman Doppler imaging, a tomographic inversion technique. Additionally, the chromospheric activity is also monitored.Results.The observations provide an unprecedented sampling of the large-scale field over a single magnetic cycle of a star other than the Sun. Our results show that 61 Cyg A has a dominant dipolar geometry except at chromospheric activity maximum. The dipole axis migrates from the southern to the northern hemisphere during the magnetic cycle. It is located at higher latitudes at chromospheric activity cycle minimum and at middle latitudes during cycle maximum. The dipole is strongest at activity cycle minimum and much weaker at activity cycle maximum.Conclusions.The behaviour of the large-scale dipolar field during the magnetic cycle resembles the solar magnetic cycle. Our results are further confirmation that 61 Cyg A indeed has a large-scale magnetic geometry that is comparable to the Sun’s, despite being a slightly older and cooler K dwarf.

scholarly journals Zeeman-Doppler imaging of II Peg

2008 ◽  
Vol 4 (S259) ◽  
pp. 437-438 ◽  
Author(s):  
Thorsten A. Carroll ◽  
Markus Kopf ◽  
Klaus G. Strassmeier ◽  
Ilya Ilyin ◽  
Ilkka Tuominen
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Field Structure ◽  
Doppler Imaging ◽  
High Latitudes ◽  
Magnetic Vector ◽  
Magnetic Field Structure ◽  
Surface Magnetic Field ◽  
Large Scale Magnetic Field ◽  
The Magnetic Field

AbstractWe present Zeeman-Doppler images of the active K2 star II Peg for the years 2004 and 2007. The surface magnetic field was reconstructed with our new ZDI code iMap which provides a full polarized radiative transfer driven inversion to simultaneously reconstruct the surface temperature and magnetic vector field distribution. II Peg shows a remarkable large scale magnetic field structure for both years. The magnetic field is predominantly located at high latitudes and is arranged in active longitudes. A dramatic evolution in the magnetic field structure is visible for the two years, where a dominant and largely unipolar field in 2004 has changed into two distinct and large scale bipolar structures in 2007.

scholarly journals The magnetic field of the evolved star W43A

2008 ◽  
Vol 4 (S259) ◽  
pp. 109-110
Author(s):  
Nikta Amiri ◽  
Wouter Vlemmings ◽  
Huib Jan van Langevelde
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Circular Polarization ◽  
Magnetic Field Strength ◽  
Large Scale ◽  
Zeeman Splitting ◽  
Density Region ◽  
Evolved Stars ◽  
Large Scale Magnetic Field ◽  
The Magnetic Field

AbstractPlanetary nebulae (PNe) often show large departures from spherical symmetry. The origin and development of these asymmetries is not clearly understood. The most striking structures are the highly collimated jets that are already observed in a number of evolved stars before they enter the PN phase. The aim of this project is to observe the Zeeman splitting of the OH maser of the W43A star and determine the magnetic field strength in the low density region. The 1612 MHz OH masers of W43A were observed with MERLIN to measure the circular polarization due to the Zeeman splitting of 1612 OH masers in the envelope of the evolved star W43A. We measured the circular polarization of the strongest 1612 OH masers of W43A and found a magnetic field strength of ~100μG. The magnetic field measured at the location of W43A OH masers confirms that a large scale magnetic field is present in W43A, which likely plays a role in collimating the jet.

scholarly journals The relation between stellar magnetic field geometry and chromospheric activity cycles – I. The highly variable field of ε Eridani at activity minimum

2017 ◽  
Vol 471 (1) ◽  
pp. L96-L100 ◽  
Author(s):  
S. V. Jeffers ◽  
S. Boro Saikia ◽  
J. R. Barnes ◽  
P. Petit ◽  
S. C. Marsden ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Activity Cycle ◽  
Doppler Imaging ◽  
The Sun ◽  
Chromospheric Activity ◽  
Large Scale Magnetic Field ◽  
Large Scale Field ◽  
Solar Type ◽  
Field Geometry

Abstract The young and magnetically active K dwarf ε Eridani exhibits a chromospheric activity cycle of about 3 yr. Previous reconstructions of its large-scale magnetic field show strong variations at yearly epochs. To understand how ε Eridani’s large-scale magnetic field geometry evolves over its activity cycle, we focus on high-cadence observations spanning 5 months at its activity minimum. Over this time-span, we reconstruct three maps of ε Eridani’s large-scale magnetic field using the tomographic technique of Zeeman–Doppler imaging. The results show that at the minimum of its cycle, ε Eridani’s large-scale field is more complex than the simple dipolar structure of the Sun and 61 Cyg A at minimum. Additionally, we observe a surprisingly rapid regeneration of a strong axisymmetric toroidal field as ε Eridani emerges from its S-index activity minimum. Our results show that all stars do not exhibit the same field geometry as the Sun, and this will be an important constraint for the dynamo models of active solar-type stars.

scholarly journals The magnetic helicity density patterns from non-axisymmetric solar dynamo

2021 ◽  
Vol 87 (1) ◽  
Author(s):  
Valery V. Pipin
Keyword(s):  
Magnetic Field ◽  
Differential Rotation ◽  
Conservation Law ◽  
Large Scale ◽  
Solar Dynamo ◽  
Magnetic Helicity ◽  
Dynamo Model ◽  
Density Distributions ◽  
Large Scale Magnetic Field ◽  
Helicity Conservation

We study the helicity density patterns which can result from the emerging bipolar regions. Using the relevant dynamo model and the magnetic helicity conservation law we find that the helicity density patterns around the bipolar regions depend on the configuration of the ambient large-scale magnetic field, and in general they show a quadrupole distribution. The position of this pattern relative to the equator can depend on the tilt of the bipolar region. We compute the time–latitude diagrams of the helicity density evolution. The longitudinally averaged effect of the bipolar regions shows two bands of sign for the density distributions in each hemisphere. Similar helicity density patterns are provided by the helicity density flux from the emerging bipolar regions subjected to surface differential rotation.

scholarly journals Propagation of an MHD Shock in the Vicinity of a Magnetic Neutral Sheet

1980 ◽  
Vol 91 ◽  
pp. 323-326
Author(s):  
D. J. Mullan ◽  
R. S. Steinolfson
Keyword(s):  
Magnetic Field ◽  
Cosmic Rays ◽  
Solar Corona ◽  
Large Scale ◽  
Field Structure ◽  
Neutral Sheet ◽  
Solar Cosmic Rays ◽  
Magnetic Field Structure ◽  
Large Scale Magnetic Field ◽  
Highly Correlated

The acceleration of solar cosmic rays in association with certain solar flares is known to be highly correlated with the propagation of an MHD shock through the solar corona (Svestka, 1976). The spatial structure of the sources of solar cosmic rays will be determined by those regions of the corona which are accessible to the flare-induced shock. The regions to which the flare shock is permitted to propagate are determined by the large scale magnetic field structure in the corona. McIntosh (1972, 1979) has demonstrated that quiescent filaments form a single continuous feature (a “baseball stitch”) around the surface of the sun. It is known that helmet streamers overlie quiescent filaments (Pneuman, 1975), and these helmet streamers contain large magnetic neutral sheets which are oriented essentially radially. Hence the magnetic field structure in the low solar corona is characterized by a large-scale radial neutral sheet which weaves around the entire sun following the “baseball stitch”. There is therefore a high probability that as a shock propagates away from a flare, it will eventually encounter this large neutral sheet.

scholarly journals Circumstellar environment of 55 Cancri

2020 ◽  
Vol 633 ◽  
pp. A48 ◽  
Author(s):  
C. P. Folsom ◽  
D. Ó Fionnagáin ◽  
L. Fossati ◽  
A. A. Vidotto ◽  
C. Moutou ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Stellar Wind ◽  
Large Scale ◽  
Rotation Axis ◽  
Doppler Imaging ◽  
Magnetic Pole ◽  
Average Strength ◽  
Detailed Understanding ◽  
The Magnetic Field ◽  
Circumstellar Environment

Context. 55 Cancri hosts five known exoplanets, most notably the hot super-Earth 55 Cnc e, which is one of the hottest known transiting super-Earths. Aims. Because of the short orbital separation and host star brightness, 55 Cnc e provides one of the best opportunities for studying star-planet interactions (SPIs). We aim to understand possible SPIs in this system, which requires a detailed understanding of the stellar magnetic field and wind impinging on the planet. Methods. Using spectropolarimetric observations and Zeeman Doppler Imaging, we derived a map of the large-scale stellar magnetic field. We then simulated the stellar wind starting from the magnetic field map, using a 3D magneto-hydrodynamic model. Results. The map of the large-scale stellar magnetic field we derive has an average strength of 3.4 G. The field has a mostly dipolar geometry; the dipole is tilted by 90° with respect to the rotation axis and the dipolar strength is 5.8 G at the magnetic pole. The wind simulations based on this magnetic geometry lead us to conclude that 55 Cnc e orbits inside the Alfvén surface of the stellar wind, implying that effects from the planet on the wind can propagate back to the stellar surface and result in SPI.

AGN torus threaded by large scale magnetic field

2018 ◽  
Vol 27 (10) ◽  
pp. 1844006
Author(s):  
A. Dorodnitsyn ◽  
T. Kallman
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Accretion Disk ◽  
Large Scale ◽  
Three Dimensional ◽  
X Ray ◽  
Radiative Feedback ◽  
Large Scale Magnetic Field ◽  
Three Dimensional Simulations

Large scale magnetic field can be easily dragged from galactic scales toward AGN along with accreting gas. There, it can contribute to both the formation of AGN “torus” and help to remove angular momentum from the gas which fuels AGN accretion disk. However the dynamics of such gas is also strongly influenced by the radiative feedback from the inner accretion disk. Here we present results from the three-dimensional simulations of pc-scale accretion which is exposed to intense X-ray heating.

scholarly journals The large scale magnetic field of the G0 dwarf HD 206860 (HN Peg)

2013 ◽  
Vol 9 (S302) ◽  
pp. 146-147
Author(s):  
Sudeshna Boro Saikia ◽  
Sandra V. Jeffers ◽  
Pascal Petit ◽  
Stephen Marsden ◽  
Julien Morin ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Spectral Type ◽  
Large Scale ◽  
Longitudinal Magnetic Field ◽  
Chromospheric Activity ◽  
Large Scale Magnetic Field ◽  
Debris Disk ◽  
Infrared Triplet

AbstractHD 206860 is a young planet (HN Peg b) hosting star of spectral type G0V and it has a potential debris disk around it. In this work we measure the longitudinal magnetic field of HD 206860 using spectropolarimetric data and we measure the chromospheric activity using Ca II H&K, H-alpha and Ca II infrared triplet lines.

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