1995 lia co-32-239-mass-acell

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This document summarizes a study examining the hypergiant star ρ Cassiopeiae. The researchers developed a model to explain ρ Cassiopeiae's variable mass loss rate, high microturbulent velocity, and Hα emission line profile using a stochastic field of shock waves in the star's atmosphere. Their model successfully reproduced the observed mass loss rate, microturbulent velocity, and aspects of the Hα profile using only one parameter - the maximum Mach number of shock waves in the atmosphere. The model indicates that thin, hot regions behind shock waves are responsible for the observed microturbulence and contribute to Hα emission.

2012 newsrelease-hypergiantKees De Jager

2001 mnras 32-452-instabregions

Kees De Jager

This document outlines and compares three instability regions for blueward evolving supergiants in the Hertzsprung-Russell (HR) diagram: 1. Areas where stars are dynamically unstable based on the criterion that the first generalized adiabatic exponent G1 is less than 4/3. 2. Areas where the effective acceleration in the upper part of the photospheres is negative, directed outward. 3. Areas where the sonic points of the stellar winds are situated inside the photospheres deeper than an optical depth of 0.01. The document compares the results to the positions of actual stars in the HR diagram and finds evidence that recent strong contraction of the yellow hypergiant

1995 a+a 302-811-atm-stability

Kees De Jager

1998 aspc 154-1601-rhocas

Kees De Jager

This document summarizes a study checking the reality of the "yellow evolutionary void" in the Hertzsprung-Russell diagram through an analysis of three stars - HD 33579, HR 8752, and IRC+10420. The study finds that HD 33579 has a large mass and stable behavior, suggesting it is a young, redward-evolving supergiant allowed in the void. HR 8752 and IRC+10420 have lower masses, placing them in a post-red blueward evolutionary loop, and they show evidence of "bouncing" as they approach the void. The photometric variations of HD 33579 and HR 8752 are attributed to pulsations.

1997 mnras 290l-50-obstacleevolKees De Jager

2012 hr8752-void-crossing

Kees De Jager

This study examines the evolution of the yellow hypergiant star HR 8752 over nearly a century based on spectroscopic observations and photometry. The star underwent successive gas ejections, seen as downward excursions in effective temperature. During each ejection, a pseudo-photosphere formed with lower gravity and higher turbulence. After the ejected shells dispersed, a hotter, more compact photosphere emerged. Analysis of observations shows variation over time in the star's effective temperature, luminosity, radius, and mass, suggesting it is evolving away from an unstable region in the HR diagram known as the "yellow evolutionary void."

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This document discusses the origin and evolution of galaxies, stars, and planets in the universe. It describes how the universe began in a hot dense state 13.8 billion years ago and has expanded and cooled since then. Within the first few hundred million years, the first proto-galaxies formed from dense clouds of hydrogen and helium gas. These proto-galaxies eventually hosted the earliest giant stars, some hundreds to thousands of times more massive than the Sun. These short-lived early stars played a key role in producing heavier elements through supernova explosions, seeding the universe for future star and planet formation.

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