scholarly journals Using Chandra/LETG Spectra to Probe Stellar Coronae

2004 ◽  
Vol 219 ◽  
pp. 301-305
Author(s):  
Gaitee A. J. Hussain ◽  
Nancy Brickhouse ◽  
A. K. Dupree ◽  
Adriaan A. van Ballegooijen ◽  
Andrew Collier Cameron ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Light Curves ◽  
High Latitudes ◽  
Intrinsic Variability ◽  
Period Analysis ◽  
X Ray ◽  
Rotational Modulation ◽  
Rotating Star ◽  
The Relationship ◽  
Coronal Field

We probe the relationship between surface magnetic fields and the X-ray emitting corona in the rapidly rotating star, AB Dor. Circularly polarised spectra have been inverted to produce a surface (photospheric) magnetic field map. This surface map has been extrapolated to model AB Dor's coronal field topology and X-ray light curve. Chandra/LETG light curves of AB Dor from the same epoch show intrinsic variability at the 30% level. Period analysis indicates a fraction of this is due to rotational modulation. We measure velocity shifts in emission line centroids as a function of Prot and find evidence of rotational modulation (max. vel. ∼ 40 ± 13km s—1). This modulation may indicate the presence of a localised X-ray emitting region at mid-to-high latitudes.

scholarly journals Superflares on AB Doradus observed with TESS

2019 ◽  
Vol 628 ◽  
pp. A79 ◽  
Author(s):  
J. H. M. M. Schmitt ◽  
P. Ioannidis ◽  
J. Robrade ◽  
S. Czesla ◽  
P. C. Schneider
Keyword(s):  
Solar Flare ◽  
Total Solar Irradiance ◽  
Time Variable ◽  
Solar Neighborhood ◽  
Light Curves ◽  
Active Star ◽  
X Ray ◽  
Rotational Modulation ◽  
Order Of Magnitude ◽  
Optical Wavelengths

We present short-cadence data of the ultra-active star AB Dor measured by the Transiting Exoplanet Survey Satellite (TESS). In the TESS light curves of AB Dor, we found numerous flare events in addition to time-variable rotational modulation with an amplitude of up to 7%. We identified eight superflares (releasing more than 1034 erg) and studied their morphologies and energetics. We compared these flares to both the most energetic solar flare seen in total solar irradiance measurements as well as to a very energetic flare on AB Dor observed by XMM-Newton, the superflare nature of which we also demonstrate. The total energy of both the solar flare and the event on AB Dor emitted in the optical exceed their respective X-ray outputs possibly by an order of magnitude, suggesting that the dominant energy loss of such flares actually occurs at optical wavelengths. Superflares are found to take place on AB Dor at a rate of about one per week, and due to the star’s proximity and brightness can be studied in excruciating detail. Thus the TESS data offer a superb possibility to study the frequency and energetics of superflare events for stars in the solar neighborhood and at large.

scholarly journals Modeling the Radio and X-ray Emission of SN 1993J and SN 2002ap

2005 ◽  
Vol 192 ◽  
pp. 59-69
Author(s):  
Claes Fransson ◽  
Claes-Ingvar Björnsson
Keyword(s):  
Magnetic Field ◽  
Particle Acceleration ◽  
Loss Rate ◽  
Relativistic Particle ◽  
Mass Loss Rate ◽  
Light Curves ◽  
Magnetic Field Generation ◽  
Absorption Mechanism ◽  
X Ray ◽  
Physical Mechanisms

SummaryModeling of radio and X-ray observations of supernovae interacting with their circumstellar media are discussed, with special application to SN 1993J and SN 2002ap. We emphasize the importance of including all relevant physical mechanisms, especially for the modeling of the radio light curves. The different conclusions for the absorption mechanism (free-free or synchrotron self-absorption), as well as departures from an ρ ∝ r−2 CSM, as inferred by some authors, are discussed in detail. We conclude that the evidence for a variation in the mass loss rate with time is very weak. The results regarding the efficiencies of magnetic field generation and relativistic particle acceleration are summarized.

Synthesis and X-Ray Analysis of Complex Ferrites

2017 ◽  
Vol 744 ◽  
pp. 393-398 ◽  
Author(s):  
Mukhametkali Musagalievich Mataev ◽  
M.R. Abdraimova ◽  
S.M. Saxena ◽  
D.Zh. Nuketaeva ◽  
B.T. Zheksembieva
Keyword(s):  
Magnetic Field ◽  
Comparative Analysis ◽  
Crystal Lattice ◽  
Complex Oxides ◽  
Mixed Complex ◽  
X Ray ◽  
Unit Cells ◽  
First Time ◽  
The Relationship ◽  
Crystal Lattice Parameters

Ferrite with mixed complex oxides BiNaFe2O5, BiKFe2O5 was synthesized by high temperature solid state reaction. The structure of the ferrites, type of syngony, parameters of the unit cells, radiographic and pycnometric densities were determined by X-ray phase analysis for a first time: BiNaFe2O5 – а=5,577, с=13,86 Å, γ=120º, Vun.cell. = 373,9 Å3, Z=4, ρrad.= 7,5262 г/см3, ρpicn.=7,5271 г/см3, BiKFe2O5 –а=5,545, с=13,65 Å, γ=120º, Vun.cell.= 363,45Å3, Z=6, ρrad.= 8,0367, ρpicn.=8,0375 г/см3. A comparative analysis of the relationship between crystal lattice parameters with parameters of the crystal lattice of initial oxides and complex ferrites has been performed. Research dependence of the magnetic moment of the complex ferrite BiNaFe2O5 of the applied magnetic field at a constant temperature T = 6.1405 K showed a paramagnetic shift in the structure.

scholarly journals Modelling multiwavelength emissions from PSR B1259–63/LS 2883: Effects of the stellar disc on shock radiations

2019 ◽  
Vol 627 ◽  
pp. A87 ◽  
Author(s):  
A. M. Chen ◽  
J. Takata ◽  
S. X. Yi ◽  
Y. W. Yu ◽  
K. S. Cheng
Keyword(s):  
Magnetic Field ◽  
Gamma Ray ◽  
Thermal Emission ◽  
Orbital Plane ◽  
Light Curves ◽  
Double Peak ◽  
Stellar Disc ◽  
X Ray ◽  
Pulsar Wind ◽  
Star Binary

PSR B1259–63/LS 2883 is an elliptical pulsar/Be star binary that emits broadband emissions from radio to TeV γ-rays. The massive star possesses an equatorial disc that is inclined with the orbital plane of the pulsar. Non-thermal emission from the system is believed to be produced by pulsar wind shock and double-peak profiles in the X-ray, and TeV γ-ray light curves are related to the phases of the pulsar passing through the disc region of the star. In this paper, we investigate the interactions between the pulsar wind and stellar outflows, especially with the presence of the disc, and present a multiwavelength modelling of the emission from this system. We show that the double-peak profiles of X-ray and TeV γ-ray light curves are caused by the enhancements of the magnetic field and soft photons at the shock during the disc passages. As the pulsar is passing through the equatorial disc, the additional pressure of the disc pushes the shock surface closer to the pulsar, which causes the enhancement of magnetic field in the shock, and thus increases the synchrotron luminosity. The TeV γ-rays due to the inverse-Compton (IC) scattering of shocked electrons with seed photons from the star are expected to peak around periastron, which is inconsistent with observations. However, the shock heating of the stellar disc could provide additional seed photons for IC scattering during the disc passages, and thus produces the double-peak profiles as observed in the TeV γ-ray light curve. Our model can possibly be examined and applied to other similar gamma-ray binaries, such as PSR J2032+4127/MT91 213, HESS J0632+057, and LS I+61°303.

scholarly journals Study of the relationship between magnetic field and dielectric properties in two ferromagnetic complexes

RSC Advances ◽  
2017 ◽  
Vol 7 (76) ◽  
pp. 47913-47919 ◽  
Author(s):  
Li Yang ◽  
Jing Li ◽  
Tian-Cheng Pu ◽  
Ming Kong ◽  
Jing Zhang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Susceptibility ◽  
Dielectric Properties ◽  
Single Crystal ◽  
Magnetic Susceptibility Measurement ◽  
X Ray Diffraction ◽  
X Ray ◽  
The Relationship

Two heterometallic niccolite structure frameworks [NH2(CH3)2][CrIIIMII(HCOO)6] (M = Fe, Ni) were reported and characterized by single crystal X-ray diffraction, dielectric and magnetic susceptibility measurement.

scholarly journals The Relationship between CMEs and Prominence Eruptions

2001 ◽  
Vol 203 ◽  
pp. 310-313
Author(s):  
B. Schmieder ◽  
L. van Driel-Gesztelyi ◽  
C. Delannée ◽  
G. M. Simnett ◽  
J. E. Wiik
Keyword(s):  
Magnetic Field ◽  
Coronal Mass Ejections ◽  
Temporal Relationship ◽  
Time History ◽  
Coronal Magnetic Field ◽  
Poloidal Field ◽  
Shear Forces ◽  
The Relationship ◽  
Coronal Field ◽  
Fast Increase

We have studied the temporal relationship between three selected prominence eruptions and their associated coronal mass ejections (CME). For these three events it is not possible to predict from the CME time history when the prominence would erupt. However, both are signatures of destabilisation of the global coronal magnetic field. The lack of a precise temporal relationship reflects the fact that several coronal stuctures are destabilised, and in general one will predominate in the CME structure. If this structure happens to be the same as that constraining the prominence, then the latter will erupt following the launch of the CME. If the prominence is constrained by a separate magnetic structure, then it may erupt before or after the main CME. Reconfiguration of the global coronal field probably drives a fast increase of the poloidal field in the prominence flux tube or introduces destabilising shear forces. Events on May 1, 1996, September 25-27, 1996, and May 31 1997 are discussed.

scholarly journals Magnetic wind-driven accretion in dwarf novae

2019 ◽  
Vol 626 ◽  
pp. A116 ◽  
Author(s):  
Nicolas Scepi ◽  
Guillaume Dubus ◽  
Geoffroy Lesur
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Turbulent Transport ◽  
Momentum Equation ◽  
Light Curves ◽  
Rotational Instability ◽  
Dwarf Novae ◽  
X Ray ◽  
The Impact ◽  
X Ray Binaries

Context. Dwarf novae (DNe) and X-ray binaries exhibit outbursts thought to be due to a thermal-viscous instability in the accretion disk. The disk instability model (DIM) assumes that accretion is driven by turbulent transport, customarily attributed to the magneto-rotational instability (MRI). However, recent results point out that MRI turbulence alone fails to reproduce the light curves of DNe. Aims. Our aim is to study the impact of wind-driven accretion on the light curves of DNe. Local and global simulations show that magneto-hydrodynamic winds are present when a magnetic field threads the disk, even for relatively high ratios of thermal pressure to magnetic pressure (β ≈ 105). These winds are very efficient in removing angular momentum but do not heat the disk, thus they do not behave as MRI-driven turbulence. Methods. We add the effect of wind-driven magnetic braking in the angular momentum equation of the DIM but neglect the mass loss due to the wind. We assume a fixed magnetic configuration: dipolar or constant with radius. We use prescriptions for the wind torque and the turbulent torque derived from shearing box simulations. Results. The wind torque enhances the accretion of matter, resulting in light curves that look like DNe outbursts when assuming a dipolar field with a moment μ ≈ 1030 G cm3. In the region where the wind torque dominates the disk is cold and optically thin, and the accretion speed is super-sonic. The inner disk behaves as if truncated, leading to higher quiescent X-ray luminosities from the white dwarf boundary layer than expected with the standard DIM. The disk is stabilized if the wind-dominated region is large enough, potentially leading to “dark” disks that emitting little radiation. Conclusion. Wind-driven accretion can play a key role in shaping the light curves of DNe and X-ray binaries. Future studies will need to include the time evolution of the magnetic field threading the disk to fully assess its impact on the dynamics of the accretion flow.

scholarly journals The Magnetic Field of the Intermediate Polar RE 0751+14

1996 ◽  
Vol 158 ◽  
pp. 183-183
Author(s):  
H. Väth
Keyword(s):  
Magnetic Field ◽  
White Dwarf ◽  
Accretion Rate ◽  
Shock Structure ◽  
Light Curves ◽  
X Rays ◽  
Strong Magnetic Fields ◽  
X Ray ◽  
Spin Period ◽  
The Magnetic Field

Piirola, Hakala & Coyne (1993) modeled the optical/IR light curve of RE 0751+14 assuming a uniform shock structure and neglecting the hard X-ray emission. In this paper, we model the light curves at optical/IR and hard X-ray wavelengths and include the effects of the shock structure.We base our model on accretion onto a white dwarf with a displaced magnetic dipole for a range of likely white dwarf masses. We find that the observed intensity variations of X-rays and in the I band over one spin period largely determine the position of the emission regions. Furthermore, the observed maximum X-ray flux constrains the specific accretion rate. We deduce that the magnetic field at the pole is likely to be in the range 9 .. .21 MG, which is consistent with the estimates of Piirola et al. (1993). It had been proposed previously that there must exist asynchronous rotators with sufficiently strong magnetic fields such that the binaries will evolve into AM Her binaries (Chanmugam & Ray 1984; King, Frank & Ritter 1985). With this deduced high magnetic field RE 0751+14 is the most likely example of such a system known to date.

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