Thermosolutal-convective instability of a stellar atmosphere in the presence of suspended particles (original) (raw)

Thermosolutal-Convective Instability In Stern’s Type Configuration

WSEAS TRANSACTIONS ON SYSTEMS

The thermal-convective instability of a stellar atmosphere in the presence of stable solute gradient in Stern’s type configuration is studied in the presence of radiative transfer effect. A criterion for monotonic instability is obtained in terms of the source functions S. The criterion for monotonic instability is found to be unchanged in the presence of radiative transfer and rotation effects. The problem of thermosolutal-convective instability of a hydromagnetic composite medium is also studied to include the frictional effects with neutrals. The criterion derived for monotonic instability in terms of heat-loss function is found to be the same in the presence or absence of the collisional effects.

Thermal-convective-instability of a stellar atmosphere in the presence of a nonlinear magnetic field

Astrophysics and Space Science, 1992

Thermal-convective-instability of a stellar atmosphere is investigated in the presence of a nonlinear magnetic field. A model proposed by Roberts (1981) in the context of neutron stars is used. The simultaneous effect of both nonlinear magnetic field and rotation is also considered. The criteria obtained for monotonic instability generalize the criterion derived by in the absence of magnetic field and rotation.

Magnetic Instabilities in Stellar Atmospheres

International Astronomical Union Colloquium, 1983

ABSTRACT.The extensive theory for magnetohydrodynamic instability of a flux tube is briefly reviewed, together with its application to tokamaks and solar flares. In a star a single coronal loop whose footprints are anchored in the dense photosphere may become unstable to the kink instability when it is twisted too much. Magnetic arcades may also be subject to an eruptive instability when they are sheared too much. After the eruption the magnetic field closes back down by reconnection and continues to heat the plasma long after the impulsive phase. Global instability of a large part of the coronal magnetic field is also possible when the stored energy is too great.

A Thermodynamically Induced Finite-Amplitude Convective Instability in Stellar Envelopes

The Astrophysical Journal, 2001

Stellar envelopes are subject to a finite-amplitude convective instability that originates with the reduction in the adiabatic exponent accompanying partial ionization of the principle plasma constituents, G p (d ln P/d ln r) 1 a d notably hydrogen. The instability is one-sided; low-perturbations are unstable, while high-perturbations are G G 1 1 stable. Since a partially ionized fluid has a lower adiabatic exponent than either a fully recombined or fully ionized one, convective downflows are stabilized in the upper regions of a convective envelope where the nearly fully recombined fluid is embedded in a partially ionized background. They are significantly destabilized at a depth, however, where the partially ionized downflowing fluid has a lower than does the highly ionized mean G 1 state. Convective upflows, by contrast, are stabilized at a depth where their fully ionized state contrasts with the partially ionized background and are destabilized only in the very upper layers where the mean state of the fluid is nearly fully recombined and the upflows are partially ionized. This Letter illustrates the instability mechanism, its finite-amplitude character, and its possible significance to both idealized compressible convection simulations and the solar convective envelope.

Quiescent and Catastrophic Events in Stellar Atmospheres

Mathematical Physics - Proceedings of the 12th Regional Conference, 2007

Six different phases of the 11-year starspot cycles: 0.00 (top, cycle minimum), 0.16, 0.33, 0.49 (near cycle maximum), 0.65, and 0.82 (bottom). Sample magnetograms for these phases for the simulations of the Sun-like star and of the most active star are shown in Fig. above. • The field line density within each panel is statistically proportional to field strength. Dynamic finely structured stellar atmosphere Stellar Atmospheres Pakistan, March, 2006 3 Stellar magnetic activity => wealth of phenomena: starspots, nonradiatively heated outer atmospheres, activity cycles, deceleration of rotation rates, and even, in close binaries, stellar cannibalism. Key topics : radiative transfer, convective simulations, dynamo theory, outer-atmospheric heating, stellar winds and angular momentum loss. Magnetically active stars shed angular momentum-lose mass through their asterospheric magnetic fields. This process involves the interaction of a topologically complex, evolving coronal magnetic field with embedded plasma, which is heated throughout the corona + accelerated on its way to interstellar space. Stellar observations suggest: Sun was magnetically active even before it became a hydrogen-burning star. Activity smoothly declining over billions of years-angular momentum is lost through a magnetized solar wind (e.g., Schrijver et al. 2003). Evolution of corona cartoon: gravitationally stratified layers in the 1950s (left); vertical flux tubes with chromospheric canopies (1980s, middle); fully inhomogeneous mixing of photospheric, chromospheric, TR and coronal zones by such processes as heated upflows, cooling downflows, interminent heating (ε), nonthermal electron beams (e), field line motions and reconnections, emission from hot plasma, absorption and scattering in cool plasma, acoustic waves, shock waves (right) (Shrijver 2001). Associating the traditional layers with temperature rather than height is only a little better.

The Role of Magnetic Fields in the Heating of Stellar Atmospheres — Theory

Solar and Stellar Magnetic Fields: Origins and Coronal Effects, 1983

The last ten years of observations have shown beyond doubt the fundamental role played by the magnetic field in the heating of stellar atmospheres. After the recognition of the extreme inhomogeneity of the solar corona, two basic new trends have appeared in the theoretical literature on the coronal heating problem. One is the adoption of a glob al point of view that stresses the connection of the properties of the upper layers to those of the underlying ones. In this way a general framework is provided, capable of accomodating many possible heating mechanisms that need not to be specified at this stage. The second nov elty is the explicit inclusion in the theory of the inhomogeneous nature of the stellar envelopes, as a result of the presence of magnetic fields. The present status of knowledge on the subject as determined by the above evolution of the theoretical approach will be reviewed.

Suspended Particles and the Gravitational Instability of Rotating Magnetised Medium

Beiträge aus der Plasmaphysik, 1985

The effect of uniform rotation on the self gravitational instability of an infinite homogeneous magnetised gas particle medium in the presence of suspended particles is investigated. The equations of the problem are linearized and the general dispersion relation for such system is obtained. The rotation is assumed along two different directions and separate dispersion relation for each case is obtained. The dispersion relation for propagation parallel and perpendicular to the uniform magnetic field along with rotation is derived. The effect of suspended particles on the different modes of propagation is investigated. It is found that in presence of suspended particles, magnetic field, rotation and viscosity, Jeans' criterion determines the condition of gravitational instability of gas‐particle medium.

The Magnetoviscous-Thermal Instability

The Astrophysical Journal, 2012

Accretion flows onto underluminous black holes, such as Sagittarius A* at the center of our galaxy, are dilute (mildly collisional to highly collisionless), optically thin, and radiatively inefficient. Therefore, the accretion properties of such dilute flows are expected to be modified by their large viscosities and thermal conductivities. Second, turbulence within these systems needs to transport angular momentum as well as thermal energy generated through gravitational infall outwards in order to allow accretion to occur. This is in contrast to classical accretion flows, in which the energy generated through accretion down a gravitational well is locally radiated. In this paper, using an incompressible fluid treatment of an ionized gas, we expand on previous research by considering the stability properties of a magnetized rotating plasma wherein the thermal conductivity and viscosity are not negligible and may be dynamically important. We find a class of MHD instabilities that can transport angular momentum and thermal energy outwards. They are plausible candidates to describe accretion in radiatively inefficient accretion flows (RIAFs). We finish by discussing the implications for analytic models and numerical MHD simulations of mildly dilute or collisionless astrophysical plasmas, and immediate directions for further research.