Evaluation von Promotionsprogrammen an der Ludwig-Maximilians-Universität München

Braun, Manuela

doi:10.1007/978-3-642-41257-8_11

Cited by 9 publications

(14 citation statements)

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“…Because the maximum entropy and the minimum thermal energy principle apply, states with lower energy are necessarily occupied with larger probability than high energy states, which requires a unique positive temperature in the occupation functions (22) and (23). Nevertheless, several authors claimed the observation of negative temperatures [38][39][40][41][42]. In the present section, it is shown that such claims are not substantiated, which agrees with early remarks by Giauque [43].…”

Section: What Is Wrong With Negative Absolute Temperatures?supporting

confidence: 82%

From heat to entropy

Hoffmann

2020

Materialwissenschaft Werkst

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Milestones in the development of thermodynamics are the discovery of the absolute temperature scale and the recognition that differential “heat” is a form of energy given as the product of absolute temperature and differential entropy. Following a new path, the last statement results from a careful analysis of the heat transfer applying the first theorem without reference to the usual cycles in thermodynamics. This confirms also characteristic properties of entropy. In particular, the total entropy can never decrease in a process. In thermal equilibrium, the differential thermal energy is proportional to the differential entropy with the constant of proportionality being the temperature of the heat and entropy. Hence, thermal energy and entropy are transferred simultaneously into the same storage facilities, some of which are mentioned. However, the issue which one is the superior quantity is obsolete. The entropy is maximum for a given amount of exchanged thermal energy and, vice versa, for a given amount of exchanged entropy the concomitant energy is minimum. We calculate the thermal energy and entropy of phonons (as bosons) in oscillators and of electrons (as fermions) in their states of solids and melts as examples from statistical thermodynamics. The thermal energy or heat is the sum of the energies of all bosons and fermions in their elementary states or quantum states according to Bose Einstein and Fermi Dirac statistics in thermal equilibrium minus the total energy in the limit T→0 K. The entropy can be written as mixing entropy of all of these quantum states weighted with their occupancies, in agreement with an earlier publication. Thus, entropy is a logarithmic metrics of the number of all possible variants to distribute the respective total energy over all elementary states in thermal equilibrium.

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Section: What Is Wrong With Negative Absolute Temperatures?supporting

confidence: 82%

From heat to entropy

Hoffmann

2020

Materialwissenschaft Werkst

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“…Thermohaline mixing is included in KEPLER using the formalism of Braun (1997) and Kippenhahn et al (1980), but adapted to a general equation of state as done for the stability considerations described in Heger et al (2005) and using an efficiency coefficient, α Th , of unity. This formulation has also been used by Cantiello & Langer (2010).…”

Section: Physics Employedmentioning

confidence: 99%

The Remarkable Deaths of 9–11 Solar Mass Stars

Woosley

Heger

2015

ApJ

268

265

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The post-helium-burning evolution of stars from M 7  to M 11  is complicated by the lingering effects of degeneracy and off-center ignition. Here, stars in this mass range are studied using a standard set of stellar physics. Two important aspects of the study are the direct coupling of a reaction network of roughly 220 nuclei to the structure calculation at all stages and the use of a subgrid model to describe the convective bounded flame that develops during neon and oxygen burning. Below M 9.0  degenerate oxygen-neon cores form that may become either white dwarfs or electron-capture supernovae. Above M 10.3  the evolution proceeds "normally" to iron-core collapse, without composition inversions or degenerate flashes. Emphasis here is upon the stars in between, which typically ignite oxygen burning off-center. After oxygen burns in a convectively bounded flame, silicon burning ignites in a degenerate flash that commences closer to the stellar center and with increasing violence for stars of larger mass. In some cases the silicon flash is so violent that it could lead to the early ejection of the hydrogen envelope. This might have interesting observable consequences. For example, the death of a M 10.0  star could produce two supernova-like displays, a faint low-energy event due to the silicon flash, and an unusually bright supernova many months later as the low-energy ejecta from core collapse collides with the previously ejected envelope. The potential relation to the Crab supernova is discussed.

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“…The stellar models were computed with a state-of-theart, one-dimensional hydrodynamic implicit Lagrangian code (BEC), which incorporates latest input physics (for details, see Braun 1997;Yoon et al 2006;Brott et al 2011;Köhler et al 2015, and references therein). Convection was treated as in the standard non-adiabatic mixing length approach (Böhm-Vitense 1958;Kippenhahn & Weigert 1990) and a mixing length parameter of α = l/H p = 1.5 (Langer 1991) was adopted, with l and H p being the mixing length and the pressure scale height, respectively.…”

Section: Stellar Modelsmentioning

confidence: 99%

“…Massive stars are powerful engines and strongly affect the evolution of star-forming galaxies throughout cosmic time (Bresolin et al 2008). In particular the most massive stars produce copious amounts of ionising photons (Doran et al 2013), emit powerful stellar winds (e.g.…”

Section: Introductionmentioning

confidence: 99%

Massive main-sequence stars evolving at the Eddington limit

Sanyal

Grassitelli

Langer

et al. 2015

A&A

144

199

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Context. Massive stars play a vital role in the Universe. However, their evolution even on the main sequence is not yet well understood. Aims. Due to the steep mass-luminosity relation, massive main sequence stars become extremely luminous. This brings their envelopes very close to the Eddington limit. We are analysing stellar evolutionary models in which the Eddington limit is reached and exceeded, and explore the rich diversity of physical phenomena which take place in their envelopes, and we investigate their observational consequences. Methods. We use the published grids of detailed stellar models by Brott et al. (2011) andKöhler et al. (2015), computed with a state-of-the-art one-dimensional hydrodynamic stellar evolution code using LMC composition, to investigate the envelope properties of core hydrogen burning massive stars. Results. We find that at the stellar surface, the Eddington limit is almost never reached, even for stars up to 500 M ⊙ . When we define an appropriate Eddington limit locally in the stellar envelope, we can show that most stars more massive than ∼ 40 M ⊙ actually exceed this limit, in particular in the partial ionization zones of iron, helium or hydrogen. While most models adjust their structure such that the local Eddington limit is exceeded at most by a few per cent, our most extreme models do so by a factor of more than seven. We find that the local violation of the Eddington limit has severe consequences for the envelope structure, as it leads to envelope inflation, convection, density inversions and possibly to pulsations. We find that all models with luminosities higher than 4 × 10 5 L ⊙ , i.e. stars above ∼ 40 M ⊙ show inflation, with a radius increase of up to a factor of about 40. We find that the hot edge of the S Dor variability region coincides with a line beyond which our models are inflated by more than a factor of two, indicating a possible connection between S Dor variability and inflation. Furthermore, our coolest models show highly inflated envelopes with masses of up to several solar masses, and appear to be candidates to produce major LBV eruptions. Conclusions. Our models show that the Eddington limit is expected to be reached in all stars above ∼ 40 M ⊙ in the LMC, and by even lower mass stars in the Galaxy, or in close binaries or rapid rotators. While our results do not support the idea of a direct super-Eddington wind driven by continuum photons, the consequences of the Eddington limit in the form of inflation, pulsations and possibly eruptions may well give rise to a significant enhancement of the the time averaged mass loss rate.

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Evaluation von Promotionsprogrammen an der Ludwig-Maximilians-Universität München

Cited by 9 publications

References 0 publications

From heat to entropy

From heat to entropy

The Remarkable Deaths of 9–11 Solar Mass Stars

Massive main-sequence stars evolving at the Eddington limit

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