scholarly journals Unraveling the variability of σ Ori E

2014 ◽  
Vol 9 (S307) ◽  
pp. 348-352
Author(s):  
M. E. Oksala ◽  
O. Kochukhov ◽  
J. Krtička ◽  
M. Prvák ◽  
Z. Mikulášek
Keyword(s):  
Magnetic Field ◽  
Light Curve ◽  
Elemental Abundance ◽  
Doppler Imaging ◽  
Thermodynamical Equilibrium ◽  
Circumstellar Material ◽  
Magnetic Field Topology ◽  
Non Local ◽  
Optical Brightness ◽  
Physical Phenomena

Abstractσ Ori E (HD 37479) is the prototypical helium-strong star shown to harbor a strong magnetic field, as well as a magnetosphere consisting of two clouds of plasma. The observed optical (ubvy) light curve of σ Ori E is dominated by eclipse features due to circumstellar material, however, there remain additional features unexplained by the Rigidly Rotating Magnetosphere (RRM) model of Townsend & Owocki (2005). Using the technique of magnetic Doppler imaging (MDI), spectropolarimetric observations of σ Ori E are used to produce maps of both the magnetic field topology and various elemental abundance distributions. We also present an analysis utilizing these computed MDI maps in conjunction with non-local thermodynamical equilibrium TLUSTY models to study the optical brightness variability of this star arising from surface inhomogeneities. It has been suggested that this physical phenomena may be responsible for the light curve inconsistencies between the model and observations.

scholarly journals Searching for a link between the presence of chemical spots on the surface of HgMn stars and their weak magnetic fields

2008 ◽  
Vol 4 (S259) ◽  
pp. 401-402 ◽  
Author(s):  
Igor S. Savanov ◽  
S. Hubrig ◽  
J. F. González ◽  
M. Schöller
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Imaging Technique ◽  
Doppler Imaging ◽  
Magnetic Field Topology ◽  
Weak Magnetic Fields

AbstractWe present the results of mapping the HgMn star AR Aur using the Doppler Imaging technique for several elements and discuss the obtained distributions in the framework of a magnetic field topology.

scholarly journals Modeling the magnetosphere of the B2Vp star σ Ori E

2010 ◽  
Vol 6 (S272) ◽  
pp. 124-129
Author(s):  
Mary E. Oksala ◽  
Gregg A. Wade ◽  
Rich H. D. Townsend ◽  
Oleg Kochukhov ◽  
Stan P. Owocki
Keyword(s):  
Magnetic Field ◽  
Longitudinal Magnetic Field ◽  
Doppler Imaging ◽  
Centrifugal Forces ◽  
Chemical Abundances ◽  
Period Analysis ◽  
Circumstellar Material ◽  
Hα Emission ◽  
Future Work ◽  
Photometric Variation

AbstractThis paper presents results obtained from Stokes I and V spectra of the B2Vp star sigma Ori E, observed by both the Narval and ESPaDOnS spectropolarimeters. Using Least-Squares Deconvolution, we investigate the longitudinal magnetic field at the current epoch, including period analysis exploiting current and historical data. σ Ori E is the prototypical helium-strong star that has been shown to harbor a strong magnetic field, as well as a magnetosphere, consisting of two clouds of plasma forced by magnetic and centrifugal forces to co-rotate with the star on its 1.19 day period. The Rigidly Rotating Magnetosphere (RRM) model of Townsend & Owocki (2005) approximately reproduces the observed variations in longitudinal field strength, photometric brightness, Hα emission, and various other observables. There are, however, small discrepancies between the observations and model in the photometric light curve, which we propose arise from inhomogeneous chemical abundances on the star's surface. Using Magnetic Doppler Imaging (MDI), future work will attempt to identify the contributions to the photometric variation due to abundance spots and due to circumstellar material.

scholarly journals Magnetic field topology of the cool, active, short-period binary system σ2 Coronae Borealis

2018 ◽  
Vol 613 ◽  
pp. A60 ◽  
Author(s):  
L. Rosén ◽  
O. Kochukhov ◽  
E. Alecian ◽  
C. Neiner ◽  
J. Morin ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Energy ◽  
Binary Star ◽  
Brightness Distribution ◽  
Opposite Polarity ◽  
Doppler Imaging ◽  
Primary Star ◽  
Magnetic Field Topology ◽  
Short Period ◽  
The Magnetic Field

Aims. The goal of this work is to study the cool, active binary star σ2 CrB, focussing on its magnetic field. The two F9–G0 components of this system are tidally locked and in a close orbit, increasing the chance of interaction between their magnetospheres. Methods. We used Stokes IV data from the twin spectropolarimeters Narval at the TBL and ESPaDOnS at the CFHT. The least-squares deconvolution multi-line technique was used to increase the signal-to-noise ratio of the data. We then applied a new binary Zeeman–Doppler imaging code to reconstruct simultaneously the magnetic topology and brightness distribution of both components of σ2 CrB. This analysis was carried out for two observational epochs in 2014 and 2017. Results. A previously unconfirmed magnetic field of the primary star has been securely detected. At the same time, the polarisation signatures of the secondary appear to have a systematically larger amplitude than that of the primary. This corresponds to a stronger magnetic field, for which the magnetic energy of the secondary exceeds that of the primary by a factor of 3.3–5.7. While the magnetic energy is similar for the secondary star in the two epochs, the magnetic energy is about twice as high in 2017 for the primary. The magnetic field topology of the two stars in the earlier epoch (2014) is very different. The fractions of energy in the dipole and quadrupole components of the secondary are similar and thereafter decrease with increasing harmonic angular degree ℓ. At the same time, for the primary the fraction of energy in the dipole component is low and the maximum energy contribution comes from ℓ = 4. However, in the 2017 epoch both stars have similar field topologies and a systematically decreasing energy with increasing ℓ. In the earlier epoch, the magnetic field at the visible pole appears to be of opposite polarity for the primary and secondary, suggesting linked magnetospheres. The apparent rotational periods of both σ2 CrB components are longer than the orbital period, which we interpret as an evidence of a solar-like differential rotation. Conclusions. Despite their nearly identical fundamental parameters, the components of σ2 CrB system exhibit different magnetic field properties. This indicates that the magnetic dynamo process is a very sensitive function of stellar parameters.

scholarly journals Magnetic Doppler Imaging of He-strong star HD 184927

2013 ◽  
Vol 9 (S302) ◽  
pp. 306-308
Author(s):  
I. Yakunin ◽  
G. Wade ◽  
D. Bohlender ◽  
O. Kochukhov ◽  
V. Tsymbal ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Measurements ◽  
Rotation Period ◽  
Doppler Imaging ◽  
Physical Parameters ◽  
Imaging Analysis ◽  
Chemical Abundance ◽  
Magnetic Field Topology

AbstractWe have employed an extensive new timeseries of Stokes I and V spectra obtained with the ESPaDOnS spectropolarimeter at the 3.6-m Canada-France-Hawaii Telescope to investigate the physical parameters, chemical abundance distributions and magnetic field topology of the slowly-rotating He-strong star HD 184927. We infer a rotation period of 9d .53071 ± 0.00120 from Hα, Hβ, LSD magnetic measurements and EWs of helium lines. We used an extensive NLTE TLUSTY grid along with the SYNSPEC code to model the observed spectra and find a new value of luminosity. In this poster we present the derived physical parameters of the star and the results of Magnetic Doppler Imaging analysis of the Stokes I and V profiles. Wide wings of helium lines can be described only under the assumption of the presence of a large, very helium-rich spot.

scholarly journals Do young Suns undergo magnetic reversals?

2009 ◽  
Vol 5 (S264) ◽  
pp. 130-135
Author(s):  
Stephen C. Marsden ◽  
Sandra V. Jeffers ◽  
Jean-Francois Donati ◽  
Matthew W. Mengel ◽  
Ian A. Waite ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Theoretical Models ◽  
Small Sample ◽  
Doppler Imaging ◽  
Field Reversal ◽  
Magnetic Field Topology ◽  
Global Magnetic Field ◽  
Tentative Evidence ◽  
The Magnetic Field ◽  
Magnetic Field Reversal

AbstractA key part of the modern-day regenerative solar magnetic dynamo is the reversal of the Sun's global magnetic field every eleven years. However, recent theoretical models indicate that young-rapidly rotating Sun-like stars may not always undergo full magnetic reversals, but instead may sometimes undergo “attempted” reversals where the magnetic field declines in strength only to return with the same polarity. Using the technique of Zeeman Doppler imaging we have mapped the magnetic field topology of a small sample of young Sun-like stars at multiple epochs, and present tentative evidence of an “attempted” magnetic field reversal on one of our stars.

scholarly journals The role of complex magnetic topologies on stellar spin-down

2015 ◽  
Vol 11 (S320) ◽  
pp. 297-302
Author(s):  
Victor Réville ◽  
Allan Sacha Brun ◽  
Antoine Strugarek ◽  
Sean P. Matt ◽  
Jérôme Bouvier ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Coronal Magnetic Field ◽  
Doppler Imaging ◽  
Source Surface ◽  
Surface Magnetic Field ◽  
Magnetic Field Topology ◽  
Magnetic Stars ◽  
Field Lines ◽  
Open Flux

AbstractThe rotational braking of magnetic stars through the extraction of angular momentum by stellar winds has been studied for decades, leading to several formulations. We recently demonstrated that the dependency of the braking law on the coronal magnetic field topology can be taken into account through a simple scalar parameter: the open magnetic flux. The Zeeman-Doppler Imaging technique has brought the community a reliable and precise description of the surface magnetic field of distant stars. The coronal structure can then be reconstructed using a potential field extrapolation, a technique that relies on a source surface radius beyond which all field lines are open, thus avoiding a computationally expensive MHD simulations. We developed a methodology to choose the best source surface radius in order to estimate open flux and magnetic torques. We apply this methodology to five K-type stars from 25 to 584 Myr and the Sun, and compare the resulting torque to values expected from spin evolution models.

Magnetic field topology by MDI data: Active region

2012 ◽  
Vol 38 (8) ◽  
pp. 531-542 ◽  
Author(s):  
N. G. Makarenko ◽  
I. S. Knyazeva ◽  
L. M. Karimova
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Magnetic Field Topology

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.

scholarly journals The influence of magnetic field topology and orientation on the 1 distribution of thermal electrons in the Martian magnetotail 2

2020 ◽  
Author(s):  
Murti Nauth ◽  
Christopher M Fowler ◽  
Laila Andersson ◽  
Gina A Dibraccio ◽  
Shaosui Xu ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Field Topology
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