The Zanstra Mechanism for Nebular Condensations.

Daub, C. T.

doi:10.1086/147495

Cited by 8 publications

(7 citation statements)

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“…The cutoff wave number for a condensation mode is again given by the condition (61), which is the same as the Field's criterion for condensation instability (Field 1965). It can be noted that this cutoff condition does not and remain same as in absence of collision (μ = 0).…”

Section: With Magnetic Fieldmentioning

confidence: 95%

“…The quantity μ denotes the collision frequency of the ions with the neutrals, and the generalized heat-loss function L(ρ, T ) represents the total energy loss (energy loss minus energy gain) per unit mass per unit time, exclusive of thermal conduction (Field 1965). Here, we have assumed that the thermal radiation from the neutrals is very negligible and the thermal conductivity is mainly due to the electrons (plasma).…”

Section: Physical Modelmentioning

confidence: 99%

“…In a photoionized nebula, viz., in planetary nebular regions (or in H II regions), the cooling appears mainly through the emission of forbidden lines (Sutherland and Dopita 1993 (Spitzer 1948;Daub 1963), we can approximate the cooling functions as…”

Section: Cooling By Forbidden Line Emissionmentioning

confidence: 99%

“…Thermal instability has been long thought to be a relevant astrophysical process which is responsible for the existence of smaller, nongravitational condensations such as those found in solar prominences, interstellar clouds, and planetary nebulae (PNe). Earlier works on thermal instability include those of Parker (1953), Weymann (1960), andField (1965), among which Field's seminal work on thermal instability is considered to be a comprehensive treatise on the subject until now. It was Parker (1953) who first gave the physical reasoning leading to thermal instability in reference to solar prominences.…”

mentioning

confidence: 99%

“…He argued that when the thermal balance of the medium is between the temperature-independent heating process and the temperature-dependent radiative losses, if by some mechanism in a certain area of the medium, the losses exceed the energy gain, the cooler-than-average area loses further energy and its temperature drops below the average ambient temperature of the medium. This process is known as thermal condensation (instability), which helps in understanding the existence of a cold and dense localized region in pressure equilibrium with its hot surroundings (Field 1965). Some recent works have addressed the process of thermal instability in a gravitating medium undergoing expansion with (Bora and Buzar Baruah 2008) and without dust (Gomez-Pelaez and Moreno-Insertis 2002).…”

mentioning

confidence: 99%

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Radiation condensation instability in a plasma with ionization and recombination

Baruah

Chatterjee

Bora

2009

Astrophys Space Sci

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In this work, we consider radiation (thermal) instability in a weakly ionized plasma with continuous ionization and recombination. The situation can be visualized in the case of envelopes of planetary nebulae, which are envelopes of ionized plasmas surrounding red giant stars. Various observations report continuous photoionization of these plasmas by the highly energetic streams of photons emanating from the parent star. Recently, it has been shown that thermal instability can be a probable candidate in such plasmas for the existence of small scale structures (viz., striations) whose kinematic age is much smaller than that of the parent nebula. We therefore report a systematic study of these plasmas with photoionization and determine the instability domain. We have shown that the continuous ionization and recombination may lead to modification of the underlying instability, which may limit the size of the small structures that are believed to form from these instabilities, and may thus provide an explanation of the physical processes responsible for the existence of these structures. We further show that in many cases the system bifurcates to an ovserstable (growing wave) state from a condensation instability (monotonic) and vice versa.

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Section: With Magnetic Fieldmentioning

confidence: 95%

Section: Physical Modelmentioning

confidence: 99%