Self-gravity in magnetized accretion discs as a result of a dynamo mechanism with outflows

2020 ◽  
Vol 493 (2) ◽  
pp. 2101-2110
Author(s):  
S Karimzadeh ◽  
A R Khesali ◽  
A Khosravi
Keyword(s):  
Magnetic Field ◽  
Vertical Direction ◽  
Galactic Nuclei ◽  
Young Stellar Objects ◽  
Stellar Objects ◽  
Magnetic Diffusivity ◽  
Dynamo Mechanism ◽  
Self Gravity ◽  
The Magnetic Field ◽  
Effective Contribution

ABSTRACT We investigate the stationary model of a geometrically thin, magnetized accretion disc, which has a dipole-symmetry magnetic field that is produced by an α−ω dynamo and can emanate winds from the disc’s surfaces. Although self-gravity has an important role in the evolution of astrophysical systems, it has been disregarded in many cases, because the equations become more complicated when the mass distribution of the disc is included in the total gravitational potential. In this paper, we consider the effects of self-gravity on the above-mentioned model. It is shown that in the presence of vertical self-gravity, while the magnetic diffusivity decreases, the magnetic field bends and the inflow speed increases. Also, in the inner parts of the disc, mass flux resulting from the wind has a positive value compared with the non-self-gravitating solution, in which all accreted materials are lost. These results can be used for the discs of active galactic nuclei, in which self-gravity is only important in the vertical direction. However, for other types, such as the discs surrounding young stellar objects, self-gravity can be considered in both vertical and radial directions. Here, our analysis of fully self-gravitating discs has revealed that, in this case, the inflow speed depends on the radius. In the model we study, it is also found that the outflows have no effective contribution to the removal of angular momentum for certain radii r ≥ 6R, as is > 60°. However, the system cannot be stabilized by viscous dissipation.

Magnetic Fields and Disks in Star-forming Regions

1993 ◽  
Vol 10 (3) ◽  
pp. 247-249 ◽  
Author(s):  
C.M. Wright ◽  
D.K. Aitken ◽  
C.H. Smith ◽  
P.F. Roche
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Transverse Component ◽  
Young Stellar Objects ◽  
Stellar Objects ◽  
Star Forming ◽  
Star Forming Regions ◽  
Molecular Outflow ◽  
The Magnetic Field

AbstractThe star-formation process is an outstanding and largely unsolved problem in astrophysics. The role of magnetic fields is unclear but is widely considered to be important at all stages of protostellar evolution, from cloud collapse to ZAMS. For example, in some hydromagnetic models, the field may assist in removing angular momentum, thereby driving accretion and perhaps bipolar outflows.Spectropolarimetry between 8 and 13μm provides information on the direction of the transverse component of a magnetic field through the alignment of dust grains. We present results of 8–13μm spectropolarimetric observations of a number of bipolar molecular outflow sources, and compare the field directions observed with the axes of the outflows and putative disk-like structures observed to be associated with some of the objects. There is a strong correlation, though so far with limited statistics, between the magnetic field and disk orientations. We compare our results with magnetic field configurations predicted by current models for hydromagnetically driven winds from the disks around Young Stellar Objects (YSOs). Our results appear to argue against the Pudritz and Norman model and instead seem to support the Uchida and Shibata model.

scholarly journals MAGNETIC FIELD EFFECTS NEAR THE LAUNCHING REGION OF ASTROPHYSICAL JETS

2010 ◽  
Vol 19 (06) ◽  
pp. 729-739 ◽  
Author(s):  
E. M. DE GOUVEIA DAL PINO ◽  
G. KOWAL ◽  
L. H. S. KADOWAKI ◽  
P. PIOVEZAN ◽  
A. LAZARIAN
Keyword(s):  
Magnetic Field ◽  
Active Galactic Nuclei ◽  
Magnetic Energy ◽  
Galactic Nuclei ◽  
Young Stellar Objects ◽  
Magnetic Field Effects ◽  
Astrophysical Jets ◽  
Stellar Objects ◽  
Fundamental Properties

One of the fundamental properties of astrophysical magnetic fields is their ability to change topology through reconnection and in doing so, to release magnetic energy, sometimes violently. In this work, we review recent results on the role of magnetic reconnection and associated heating and particle acceleration in jet/accretion disk systems, namely young stellar objects (YSOs), microquasars, and active galactic nuclei (AGNs).

scholarly journals Using Herschel and Planck observations to delineate the role of magnetic fields in molecular cloud structure

2019 ◽  
Vol 629 ◽  
pp. A96 ◽  
Author(s):  
Juan D. Soler
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Molecular Clouds ◽  
Thermal Emission ◽  
Relative Orientation ◽  
Young Stellar Objects ◽  
Circular Statistics ◽  
Stellar Objects ◽  
Submillimeter Wavelengths ◽  
The Magnetic Field

We present a study of the relative orientation between the magnetic field projected onto the plane of sky (B⊥) on scales down to 0.4 pc, inferred from the polarized thermal emission of Galactic dust observed by Planck at 353 GHz, and the distribution of gas column density (NH) structures on scales down to 0.026 pc, derived from the observations by Herschel in submillimeter wavelengths, toward ten nearby (d < 450 pc) molecular clouds. Using the histogram of relative orientation technique in combination with tools from circular statistics, we found that the mean relative orientation between NH and B⊥ toward these regions increases progressively from 0°, where the NH structures lie mostly parallel to B⊥, with increasing NH, in many cases reaching 90°, where the NH structures lie mostly perpendicular to B⊥. We also compared the relative orientation between NH and B⊥ and the distribution of NH, which is characterized by the slope of the tail of the NH probability density functions (PDFs). We found that the slopes of the NH PDF tail are steepest in regions where NH and B⊥ are close to perpendicular. This coupling between the NH distribution and the magnetic field suggests that the magnetic fields play a significant role in structuring the interstellar medium in and around molecular clouds. However, we found no evident correlation between the star formation rates, estimated from the counts of young stellar objects, and the relative orientation between NH and B⊥ in these regions.

scholarly journals Distance, magnetic field, and kinematics of the filamentary cloud LDN 1157

2020 ◽  
Vol 639 ◽  
pp. A133
Author(s):  
Ekta Sharma ◽  
Maheswar Gopinathan ◽  
Archana Soam ◽  
Chang Won Lee ◽  
Shinyoung Kim ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Galactic Plane ◽  
Young Stellar Objects ◽  
Kinematic Structure ◽  
Single Filament ◽  
Stellar Objects ◽  
Density Peaks ◽  
Field Geometry ◽  
Cloud Complex ◽  
The Magnetic Field

Context. LDN 1157 is one of several clouds that are situated in the cloud complex LDN 1147/1158. The cloud presents a coma-shaped morphology with a well-collimated bipolar outflow emanating from a Class 0 protostar, LDN 1157-mm, that resides deep inside the cloud. Aims. The main goals of this work are (a) mapping the intercloud magnetic field (ICMF) geometry of the region surrounding LDN 1157 to investigate its relationship with the cloud morphology, outflow direction, and core magnetic field (CMF) geometry inferred from the millimeter- and submillimeter polarization results from the literature, and (b) to investigate the kinematic structure of the cloud. Methods. We carried out optical (R-band) polarization observations of the stars projected on the cloud to map the parsec-scale magnetic field geometry. We made spectroscopic observations of the entire cloud in the 12CO, C18O, and N2H+ (J = 1–0) lines to investigate its kinematic structure. Results. We obtained a distance of 340 ± 3 pc to the LDN 1147/1158, complex based on the Gaia DR2 parallaxes and proper motion values of the three young stellar objects (YSOs) associated with the complex. A single filament of ~1.2 pc in length (traced by the Filfinder algorithm) and ~0.09 pc in width (estimated using the Radfil algorithm) is found to run throughout the coma-shaped cloud. Based on the relationships between the ICMF, CMF, filament orientations, outflow direction, and the hourglass morphology of the magnetic field, it is likely that the magnetic field played an important role in the star formation process in LDN 1157. LDN 1157-mm is embedded in one of the two high-density peaks detected using the Clumpfind algorithm. The two detected clumps lie on the filament and show a blue-red asymmetry in the 12CO line. The C18O emission is well correlated with the filament and presents a coherent structure in velocity space. Combining the proper motions of the YSOs and the radial velocity of LDN 1147/1158 and an another complex, LDN 1172/1174, that is situated ~2° east of it, we found that the two complexes are moving collectively toward the Galactic plane. The filamentary morphology of the east-west segment of LDN 1157 may have formed as a result of mass lost by ablation through interaction of the moving cloud with the ambient interstellar medium.

scholarly journals A universal relation for the propeller mechanisms in magnetic rotating stars at different scales

2018 ◽  
Vol 610 ◽  
pp. A46 ◽  
Author(s):  
Sergio Campana ◽  
Luigi Stella ◽  
Sandro Mereghetti ◽  
Domitilla de Martino
Keyword(s):  
Magnetic Field ◽  
General Relation ◽  
Young Stellar Objects ◽  
Universal Relation ◽  
Rotating Stars ◽  
Stellar Objects ◽  
Spin Period ◽  
Magnetic Poles ◽  
The Magnetic Field ◽  
Measured Magnetic Field

Accretion of matter onto a magnetic, rotating object can be strongly affected by the interaction with its magnetic field. This occurs in a variety of astrophysical settings involving young stellar objects, white dwarfs, and neutron stars. As matter is endowed with angular momentum, its inflow toward the star is often mediated by an accretion disc. The pressure of matter and that originating from the stellar magnetic field balance at the magnetospheric radius: at smaller distances the motion of matter is dominated by the magnetic field, and funnelling towards the magnetic poles ensues. However, if the star, and thus its magnetosphere, is fast spinning, most of the inflowing matter will be halted at the magnetospheric radius by centrifugal forces, resulting in a characteristic reduction of the accretion luminosity. The onset of this mechanism, called the propeller, has been widely adopted to interpret a distinctive knee in the decaying phase of the light curve of several transiently accreting X-ray pulsar systems. By comparing the observed luminosity at the knee for different classes of objects with the value predicted by accretion theory on the basis of the independently measured magnetic field, spin period, mass, and radius of the star, we disclose here a general relation for the onset of the propeller which spans about eight orders of magnitude in spin period and ten in magnetic moment. The parameter-dependence and normalisation constant that we determine are in agreement with basic accretion theory.

scholarly journals Magnetic field dispersion in the neighbourhood of Bok Globules

2013 ◽  
Vol 9 (S302) ◽  
pp. 21-24
Author(s):  
C. V. Rodrigues ◽  
V. de S. Magalhães ◽  
J. W. Vilas-Boas ◽  
G. Racca ◽  
A. Pereyra
Keyword(s):  
Magnetic Field ◽  
Statistical Tests ◽  
Spectral Energy Distribution ◽  
Field Direction ◽  
Young Stellar Objects ◽  
Spectral Energy ◽  
Magnetic Field Direction ◽  
Stellar Objects ◽  
Bok Globules ◽  
The Magnetic Field

AbstractWe performed an observational study of the relation between the interstellar magnetic field alignment and star formation in twenty (20) sky regions containing Bok Globules. The presence of young stellar objects in the globules is verified by a search of infrared sources with spectral energy distribution compatible with a pre main-sequence star. The interstellar magnetic field direction is mapped using optical polarimetry. These maps are used to estimate the dispersion of the interstellar magnetic field direction in each region from a Gaussian fit, σB. In addition to the Gaussian dispersion, we propose a new parameter, η, to measure the magnetic field alignment that does not rely on any function fitting. Statistical tests show that the dispersion of the magnetic field direction is different in star forming globules relative to quiescent globules. Specifically, the less organised magnetic fields occur in regions having young stellar objects.

scholarly journals Jet Interactions with Molecular Clouds: C–Shock Models

1990 ◽  
Vol 140 ◽  
pp. 332-332
Author(s):  
M.D. Smith ◽  
P.W.J.L. Brand
Keyword(s):  
Young Stellar Objects ◽  
Stellar Objects ◽  
Hydrogen Emission ◽  
Shock Models ◽  
Hydrogen Emission Lines ◽  
Bow Shocks ◽  
Hh Objects ◽  
Jet Interactions ◽  
Model Context ◽  
The Magnetic Field

Molecular hydrogen emission lines are associated with collimated outflows from young stellar objects. They have been measured near Herbig–Haro objects within jets as well as at the jet termination. Similarly to HH objects, the lines are produced from radiative shocks which may be in the form of oblique internal jet shocks or bow shocks. A J-shock can only be invoked in a dynamical model context since the H2 lines are often wide (> 30 km s−1). The alternative is the MHD C–shock in which the ionisation level is sufficiently low so that the magnetic field and ions interact weakly with the neutrals. We have investigated C-shock flows by employing approximate forms for the ion-neutral drag, cooling and other processes with the following results.

scholarly journals Water fountains: bipolar fast stellar jets traced by water vapor maser emission

2012 ◽  
Vol 8 (S290) ◽  
pp. 227-228
Author(s):  
Hiroshi Imai
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Asymptotic Giant Branch ◽  
Young Stellar Objects ◽  
Agb Stars ◽  
Stellar Objects ◽  
Stellar Jets ◽  
The Masses ◽  
Host Stars ◽  
Maser Sources

AbstractHighly collimated, bipolar fast jets are found in asymptotic giant branch (AGB) and post-AGB stars as well as in active galactic nuclei and young stellar objects. It is still unclear how to launch such jets from dying stars that were originally spherically symmetric. Exploration of the stellar jet evolution is also expected to probe its role in shaping a planetary nebula. Interestingly, some of stellar H2O maser sources — water fountains — exhibit stellar jets with spatially and kinematically high collimation in the earliest phase (<1000 years) of the jet evolution. Such water fountains have been identified in 14 sources to date. We have recently conducted interferometric (VLBA, EVN, VERA, VLA) maser and the single-dish (ASTE) CO J = 3 → 2 line observations of the water fountains. They have revealed a typical dynamical age (< 100 yr) and the detailed kinematical structures of the water fountains, possibility of the coexistence of “equatorial flows”, and their locations and kinematics in the Milky Way. Based on these results, the masses and evolutionary statuses of the host stars are also estimated.

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