Constraint on ion–neutral drift velocity in the Class 0 protostar B335 from ALMA observations

Aims. Ambipolar diffusion can cause a velocity drift between ions and neutrals. This is one of the non-ideal magnetohydrodynamics (MHD) effects proposed to enable the formation of large-scale Keplerian disks with sizes of tens of au. To observationally study ambipolar diffusion in collapsing protostellar envelopes, we compare here gas kinematics traced by ionized and neutral molecular lines and discuss the implication on ambipolar diffusion. Methods. We analyzed the data of the H13CO+ (3–2) and C18O (2–1) emission in the Class 0 protostar B335 obtained with our ALMA observations. We constructed kinematical models to fit the velocity structures observed in the H13CO+ and C18O emission and to measure the infalling velocities of the ionized and neutral gas on a 100 au scale in B335. Results. A central compact (~1′′–2′′) component that is elongated perpendicular to the outflow direction and exhibits a clear velocity gradient along the outflow direction is observed in both lines and most likely traces the infalling flattened envelope. With our kinematical models, the infalling velocities in the H13CO+ and C18O emission are both measured to be 0.85 ± 0.2 km s−1 at a radius of 100 au, suggesting that the velocity drift between the ionized and neutral gas is at most 0.3 km s−1 at a radius of 100 au in B335. Conclusions. The Hall parameter for H13CO+ is estimated to be ≫1 on a 100 au scale in B335, so that H13CO+ is expected to be attached to the magnetic field. Our non-detection or upper limit of the velocity drift between the ionized and neutral gas could suggest that the magnetic field remains rather well coupled to the bulk neutral material on a 100 au scale in this source, and that any significant field-matter decoupling, if present, likely occurs only on a smaller scale, leading to an accumulation of magnetic flux and thus efficient magnetic braking in the inner envelope. This result is consistent with the expectation from the MHD simulations with a typical ambipolar diffusivity and those without ambipolar diffusion. On the other hand, the high ambipolar drift velocity of 0.5–1.0 km s−1 on a 100 au scale predicted in the MHD simulations with an enhanced ambipolar diffusivity by removing small dust grains, where the minimum grain size is 0.1 μm, is not detected in our observations. However, because of our limited angular resolution, we cannot rule out a significant ambipolar drift only in the midplane of the infalling envelope. Future observations with higher angular resolutions (~0. ′′1) are needed to examine this possibility and ambipolar diffusion on a smaller scale.

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Kinematics of neutral and ionzied gas in the candidate protostar with efficient magnetic braking B335

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319003739 ◽

2018 ◽

Vol 14 (A30) ◽

pp. 120-120

Author(s):

Hsi-Wei Yen ◽

Bo Zhao ◽

Patrick M. Koch

Keyword(s):

Magnetic Field ◽

Ambipolar Diffusion ◽

Neutral Gas ◽

Upper Limit ◽

Hall Parameter ◽

Neutral Material ◽

Magnetic Braking ◽

Velocity Drift ◽

The Magnetic Field ◽

Inner Envelope

AbstractAmbipolar diffusion can cause a velocity drift between ions and neutrals. This is one of the non-ideal MHD effects proposed to enable the formation of large Keplerian disks with sizes of tens of au (Zhao et al. 2018). To observationally study ambipolar diffusion in collapsing protostellar envelopes, we analyzed the ALMA H13CO+ (3–2) and C18O (2–1) data of the protostar B335, which is a candidate source with efficient magnetic braking (Yen et al. 2015). We constructed kinematical models to fit the velocity structures observed in H13CO+ and C18O. With our kinematical models, the infalling velocities in H13CO+ and C18O are both measured to be 0.85 ± 0.2 km s−1 at a radius of 100 au, suggesting that the velocity drift between the ionized and neutral gas is at most 0.3 km s−1 at a radius of 100 au in B335. The Hall parameter for H13CO+ is estimated to be ≫1 on a 100 au scale in B335, so that H13CO+ is expected to be attached to the magnetic field. Our non-detection or upper limit of the velocity drift between the ionized and neutral gas could suggest that the magnetic field remains rather well coupled to the bulk neutral material on a 100 au scale in B335, and that any significant field-matter decoupling, if present, likely occurs only on a smaller scale, leading to an accumulation of magnetic flux and thus efficient magnetic braking in the inner envelope in B335.

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Untersuchung des Druckaufbaus einer stationären, magnetfeldstabilisierten Helium-Entladung mit Hilfe magnetischer Messungen

Zeitschrift für Naturforschung A ◽

10.1515/zna-1967-1023 ◽

1967 ◽

Vol 22 (10) ◽

pp. 1599-1612 ◽

Cited By ~ 2

Author(s):

Otto Klüber

Keyword(s):

Magnetic Field ◽

Magnetic Flux ◽

Plasma Column ◽

Ambipolar Diffusion ◽

Nernst Effect ◽

Thermomagnetic Effect ◽

Field Coil ◽

Neutral Gas ◽

Ring Currents ◽

The Magnetic Field

A stationary discharge is produced bya current flowing parallel to the magnetic field ofa cylindrical coil. In the region where the field is homogeneous the pressure in the plasma column is much higher than that in the surrounding neutral gas. This is mainly caused by diamagnetic ring currents, as is shown by measuring the magnetic flux due to these currents. Two effects are primarily responsible for the ring currents in this region: The already known effect of the ambipolar diffusion across the magnetic field anda thermomagnetic effect, called NERNST effect, whose influence on the pressure build-up ofa plasma has not been investigated hitherto. Other phenomena causing ring currents occur in the plasma near the coil ends and outside the field coil.

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The impact of non-ideal effects on the circumstellar disk evolution and their observational signatures

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319003697 ◽

2018 ◽

Vol 14 (A30) ◽

pp. 116-116

Author(s):

Y. Tsukamoto ◽

S. Okuzumi ◽

K. Iwasaki ◽

M. N. Machida ◽

S. Inutsuka

Keyword(s):

Magnetic Field ◽

Hall Effect ◽

Recent Observation ◽

Ambipolar Diffusion ◽

Circumstellar Disk ◽

Neutral Drift ◽

Disk Formation ◽

Evolutionary Phase ◽

The Impact ◽

The Magnetic Field

AbstractIt has been recognized that non-ideal MHD effects (Ohmic diffusion, Hall effect, ambipolar diffusion) play crucial roles for the circumstellar disk formation and evolution. Ohmic and ambipolar diffusion decouple the gas and the magnetic field, and significantly reduces the magnetic torque in the disk, which enables the formation of the circumstellar disk (e.g., Tsukamoto et al. 2015b). They set an upper limit to the magnetic field strength of ∼ 0.1 G around the disk (Masson et al. 2016). The Hall effect notably changes the magnetic torques in the envelope around the disk, and strengthens or weakens the magnetic braking depending on the relative orientation of magnetic field and angular momentum. This suggests that the bimodal evolution of the disk size possibly occurs in the early disk evolutionary phase (Tsukamoto et al. 2015a, Tsukamoto et al. 2017). Hall effect and ambipolar diffusion imprint the possibly observable characteristic velocity structures in the envelope of Class 0/I YSOs. Hall effect forms a counter-rotating envelope around the disk. Our simulations show that counter rotating envelope has the size of 100–1000 au and a recent observation actually infers such a structure (Takakuwaet al. 2018). Ambipolar diffusion causes the significant ion-neutral drift in the envelopes. Our simulations show that the drift velocity of ion could become 100-1000 ms–1.

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Magnetically-Driven Winds from Protostellar Disks

International Astronomical Union Colloquium ◽

10.1017/s0252921100043190 ◽

1997 ◽

Vol 163 ◽

pp. 561-565 ◽

Cited By ~ 1

Author(s):

Mark Wardle

Keyword(s):

Magnetic Field ◽

Angular Momentum ◽

Large Scale ◽

Disk Surface ◽

Mhd Equations ◽

Protostellar Disks ◽

Neutral Gas ◽

Disk Material ◽

Large Scale Magnetic Field ◽

The Magnetic Field

AbstractAngular momentum transport in protostellar disks can be achieved by the action of a large scale magnetic field that runs vertically through the disk. The magnetic field centrifugally drives material from the disk surfaces into a wind, initiating a bipolar outflow. One apparent difficulty for this model is that the conductivity of the disk is extremely low in the inner 0.1–10 AU of the disk, where grains are the dominant charge carriers. Near the midplane, charged grains are unable to drift through the neutral gas and there is negligible coupling between the magnetic field and the disk material.However, the removal of angular momentum and acceleration of a wind by a magnetic field can still take place in the surface layers of the disk where the gas conductivity increases dramatically. Solutions to the multifluid MHD equations for the vertical structure of a disk at a particular radius are presented. Most of the disk material sits in hydrostatic equilibrium and does not interact with the magnetic field running vertically through it. Near the disk surfaces, the coupling between the magnetic field and disk material is sufficient to initiate an outflow from the disk surface.

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Collisional polarization of molecular ions: a signpost of ambipolar diffusion

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038196 ◽

2020 ◽

Vol 638 ◽

pp. L7

Author(s):

Boy Lankhaar ◽

Wouter Vlemmings

Keyword(s):

Magnetic Field ◽

Classical Model ◽

Critical Density ◽

Molecular Ions ◽

Ambipolar Diffusion ◽

Neutral Medium ◽

Magnetic Field Direction ◽

Collision Partner ◽

Velocity Drift ◽

The Magnetic Field

Magnetic fields play a role in the dynamics of many astrophysical processes, but they are hard to detect. In a partially ionized plasma, a magnetic field works directly on the ionized medium but not on the neutral medium, which gives rise to a velocity drift between them: ambipolar diffusion. This process is suggested to be important in the process of star formation, but has never been directly observed. We introduce a method that could be used to detect ambipolar diffusion and the magnetic field that gives rise to it, where we exploit the velocity drift between the charged and neutral medium. By using a representative classical model of the collision dynamics, we show that molecular ions partially align themselves when a velocity drift is present between the molecular ion and its main collision partner H2. We demonstrate that ambipolar diffusion potently aligns molecular ions in regions denser than their critical density. We include a model for HCO+ and show that collisional polarization could be detectable for the ambipolar drifts predicted by numerical simulations of the inner protostellar disk regions. The polarization vectors are aligned perpendicular to the magnetic field direction projected on the plane of the sky.

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Evolution of Large-Scale Coronal Structures

International Astronomical Union Colloquium ◽

10.1017/s0252921100024945 ◽

1994 ◽

Vol 144 ◽

pp. 29-33

Author(s):

P. Ambrož

Keyword(s):

Magnetic Field ◽

Field Line ◽

Large Scale ◽

Coronal Magnetic Field ◽

Source Surface ◽

Solar Cycles ◽

Characteristic Relationship ◽

The Magnetic Field ◽

Coronal Structures

AbstractThe large-scale coronal structures observed during the sporadically visible solar eclipses were compared with the numerically extrapolated field-line structures of coronal magnetic field. A characteristic relationship between the observed structures of coronal plasma and the magnetic field line configurations was determined. The long-term evolution of large scale coronal structures inferred from photospheric magnetic observations in the course of 11- and 22-year solar cycles is described.Some known parameters, such as the source surface radius, or coronal rotation rate are discussed and actually interpreted. A relation between the large-scale photospheric magnetic field evolution and the coronal structure rearrangement is demonstrated.

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An 84-μG Magnetic Field in a Galaxy at Z=0.692?

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308027439 ◽

2008 ◽

Vol 4 (S254) ◽

pp. 95-96

Author(s):

Arthur M. Wolfe ◽

Regina A. Jorgenson ◽

Timothy Robishaw ◽

Carl Heiles ◽

Jason X. Prochaska

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Faraday Rotation ◽

Large Scale ◽

Dynamo Model ◽

Magnetic Field Generation ◽

Interstellar Gas ◽

Splitting Technique ◽

Average Value ◽

The Magnetic Field

AbstractThe magnetic field pervading our Galaxy is a crucial constituent of the interstellar medium: it mediates the dynamics of interstellar clouds, the energy density of cosmic rays, and the formation of stars (Beck 2005). The field associated with ionized interstellar gas has been determined through observations of pulsars in our Galaxy. Radio-frequency measurements of pulse dispersion and the rotation of the plane of linear polarization, i.e., Faraday rotation, yield an average value B ≈ 3 μG (Han et al. 2006). The possible detection of Faraday rotation of linearly polarized photons emitted by high-redshift quasars (Kronberg et al. 2008) suggests similar magnetic fields are present in foreground galaxies with redshifts z > 1. As Faraday rotation alone, however, determines neither the magnitude nor the redshift of the magnetic field, the strength of galactic magnetic fields at redshifts z > 0 remains uncertain.Here we report a measurement of a magnetic field of B ≈ 84 μG in a galaxy at z =0.692, using the same Zeeman-splitting technique that revealed an average value of B = 6 μG in the neutral interstellar gas of our Galaxy (Heiles et al. 2004). This is unexpected, as the leading theory of magnetic field generation, the mean-field dynamo model, predicts large-scale magnetic fields to be weaker in the past, rather than stronger (Parker 1970).The full text of this paper was published in Nature (Wolfe et al. 2008).

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No-z Model for Magnetic Fields of Different Astrophysical Objects and Stability of the Solutions

Data ◽

10.3390/data6010004 ◽

2021 ◽

Vol 6 (1) ◽

pp. 4

Author(s):

Evgeny Mikhailov ◽

Daniela Boneva ◽

Maria Pashentseva

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Large Scale ◽

Point Of View ◽

Accretion Discs ◽

Wide Range ◽

Astrophysical Objects ◽

Alpha Effect ◽

The Stability ◽

The Magnetic Field

A wide range of astrophysical objects, such as the Sun, galaxies, stars, planets, accretion discs etc., have large-scale magnetic fields. Their generation is often based on the dynamo mechanism, which is connected with joint action of the alpha-effect and differential rotation. They compete with the turbulent diffusion. If the dynamo is intensive enough, the magnetic field grows, else it decays. The magnetic field evolution is described by Steenbeck—Krause—Raedler equations, which are quite difficult to be solved. So, for different objects, specific two-dimensional models are used. As for thin discs (this shape corresponds to galaxies and accretion discs), usually, no-z approximation is used. Some of the partial derivatives are changed by the algebraic expressions, and the solenoidality condition is taken into account as well. The field generation is restricted by the equipartition value and saturates if the field becomes comparable with it. From the point of view of mathematical physics, they can be characterized as stable points of the equations. The field can come to these values monotonously or have oscillations. It depends on the type of the stability of these points, whether it is a node or focus. Here, we study the stability of such points and give examples for astrophysical applications.

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Circumstellar environment of 55 Cancri

Astronomy and Astrophysics ◽

10.1051/0004-6361/201937186 ◽

2020 ◽

Vol 633 ◽

pp. A48 ◽

Cited By ~ 6

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.

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Large scale magnetic anomalies over western Canada and the Arctic: a discussion

Canadian Journal of Earth Sciences ◽

10.1139/e76-082 ◽

1976 ◽

Vol 13 (6) ◽

pp. 790-802 ◽

Cited By ~ 37

Author(s):

R. L. Coles ◽

G. V. Haines ◽

W. Hannaford

Keyword(s):

Magnetic Field ◽

Large Scale ◽

Elevated Temperatures ◽

Magnetic Anomalies ◽

The Arctic ◽

Evolutionary Development ◽

Magnetic Feature ◽

Western Canada ◽

Arctic Regions ◽

The Magnetic Field

A contoured map of vertical magnetic field residuals (relative to the IGRF) over western Canada and adjacent Arctic regions has been produced by amalgamating new data with those from previous surveys. The measurements were made at altitudes between 3.5 and 5.5 km above sea level. The map shows the form of the magnetic field within the waveband 30 to 5000 km. A magnetic feature of several thousand kilometres wavelength dominates the map, and is probably due in major part to sources in the earth's core. Superimposed on this are several groups of anomalies which contain wavelengths of the order of a thousand kilometres. The patterns of the short wavelength anomalies provide a broad view of major structures and indicate several regimes of distinctive evolutionary development. Enhancement of viscous magnetization at elevated temperatures may account for the concentration of intense anomalies observed near the western edge of the craton.

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