scholarly journals Past and Future Evolution of Sakurai's Object

2003 ◽  
Vol 209 ◽  
pp. 111-112 ◽  
Author(s):  
Falk Herwig
Keyword(s):  
Stellar Evolution ◽  
Convection Zone ◽  
Central Star ◽  
Evolutionary Time ◽  
Future Evolution ◽  
The Past ◽  
Envelope Material ◽  
Mixing Length Theory ◽  
Born Again ◽  
Model Sequence

We present a stellar evolution model sequence of the past and future evolution of the post-AGB born again star Sakurai's object (V 4334 Sgr). In order to match the short evolutionary time scale we have to assume that the convective ingestion of hydrogen-rich envelope material into the He-flash convection zone proceeds slower than predicted by the mixing length theory. For the future we predict a swift second evolution through the central star region before a second born-again evolution occurs.

scholarly journals New models for the rapid evolution of the central star of the Stingray Nebula

2021 ◽  
Author(s):  
T M Lawlor
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Planetary Nebula ◽  
Rapid Evolution ◽  
Central Star ◽  
Asymptotic Giant Branch ◽  
Initial Mass ◽  
Thermal Pulse ◽  
The Past ◽  
New Models

Abstract We present stellar evolution calculations from the Asymptotic Giant Branch (AGB) to the Planetary Nebula (PN) phase for models of initial mass 1.2 M⊙ and 2.0 M⊙ that experience a Late Thermal Pulse (LTP), a helium shell flash that occurs following the AGB and causes a rapid looping evolution between the AGB and PN phase. We use these models to make comparisons to the central star of the Stingray Nebula, V839 Ara (SAO 244567). The central star has been observed to be rapidly evolving (heating) over the last 50 to 60 years and rapidly dimming over the past 20–30 years. It has been reported to belong to the youngest known planetary nebula, now rapidly fading in brightness. In this paper we show that the observed timescales, sudden dimming, and increasing Log(g), can all be explained by LTP models of a specific variety. We provide a possible explanation for the nebular ionization, the 1980’s sudden mass loss episode, the sudden decline in mass loss, and the nebular recombination and fading.

scholarly journals New models for the convective flux in stellar atmospheres

1996 ◽  
Vol 176 ◽  
pp. 557-564 ◽  
Author(s):  
F. Kupka
Keyword(s):  
Stellar Evolution ◽  
Stellar Atmosphere ◽  
Stellar Atmospheres ◽  
Turbulence Theory ◽  
Mixing Length ◽  
Convective Flux ◽  
The Past ◽  
New Models ◽  
F Stars ◽  
Mixing Length Theory

Over the past decades various forms of the mixing length theory (MLT) have been used to describe convection in stellar atmospheres. Recent advances in turbulence theory now allow for major improvements in modelling thermal convection. We review several models for convection which have been derived from turbulence theory, and describe one of them, the “CM model”, in detail. The CM model has been used in several stellar evolution and helioseismology codes during the last four years and has now been applied to model atmospheres. An overwiew comparing stellar atmosphere models based on the CM formulation with its MLT predecessors indicates improvements on model atmospheres for A and F stars.

Fossil fields in early stellar evolution

2008 ◽  
Vol 4 (S259) ◽  
pp. 443-444
Author(s):  
Rainer Arlt
Keyword(s):  
Magnetic Fields ◽  
Stellar Evolution ◽  
Time Scale ◽  
Convection Zone ◽  
Evolutionary Time ◽  
Evolutionary Time Scale ◽  
Zone Depth

AbstractFavored explanations for the presence of magnetic fields on CP stars and the presence of the solar tachocline below the convection zone both imply fossil magnetic fields in the radiative zones. The initial, convective evolution of magnetic fields in a proto-star is studied by numerical, global simulations. The computations are to be extended by a change of the convection zone depth on an evolutionary time-scale.

Stellar Evolution

1962 ◽  
Vol 11 (02) ◽  
pp. 137-143
Author(s):  
M. Schwarzschild
Keyword(s):  
Solar System ◽  
Stellar Evolution ◽  
Space Craft ◽  
New Techniques ◽  
Substantial Body ◽  
Individual Stars ◽  
The Past ◽  
Evolution Of Galaxies ◽  
History Of ◽  
Fast Flow

It is perhaps one of the most important characteristics of the past decade in astronomy that the evolution of some major classes of astronomical objects has become accessible to detailed research. The theory of the evolution of individual stars has developed into a substantial body of quantitative investigations. The evolution of galaxies, particularly of our own, has clearly become a subject for serious research. Even the history of the solar system, this close-by intriguing puzzle, may soon make the transition from being a subject of speculation to being a subject of detailed study in view of the fast flow of new data obtained with new techniques, including space-craft.

scholarly journals Twenty years of observations of PM 1-188: Its chemical abundances and extraordinary kinematics

2021 ◽  
Author(s):  
Miriam Peña ◽  
Liliana Hernández-Martínez ◽  
Francisco Ruiz-Escobedo
Keyword(s):  
Chemical Composition ◽  
Planetary Nebula ◽  
Central Star ◽  
Emission Lines ◽  
Type I ◽  
Chemical Abundances ◽  
Line Intensities ◽  
Physical Conditions ◽  
The Past ◽  
Spectrophotometric Data

Abstract The analysis of 20 years of spectrophotometric data of the double shell planetary nebula PM 1-188 is presented, aiming to determine the time evolution of the emission lines and the physical conditions of the nebula, as a consequence of the systematic fading of its [WC 10] central star whose brightness has declined by about 10 mag in the past 40 years. Our main results include that the [O iii], [O ii], [N ii] line intensities are increasing with time in the inner nebula as a consequence of an increase in electron temperature from 11 000 K in 2005 to more than 14 000 K in 2018, due to shocks. The intensity of the same lines are decreasing in the outer nebula, due to a decrease in temperature, from 13 000 K to 7000 K, in the same period. The chemical composition of the inner and outer shells was derived and they are similar. Both nebulae present subsolar O, S and Ar abundances, while they are He, N and Ne rich. For the outer nebula the values are 12+log He/H = 11.13 ± 0.05, 12+log O/H = 8.04 ± 0.04, 12+log N/H = 7.87 ± 0.06, 12+log S/H = 7.18 ± 0.10 and 12+log Ar = 5.33 ± 0.16. The O, S and Ar abundances are several times lower than the average values found in disc non-Type I PNe, and are reminiscent of some halo PNe. From high resolution spectra, an outflow in the N-S direction was found in the inner zone. Position-velocity diagrams show that the outflow expands at velocities in the −150 to 100 km s−1 range, and both shells have expansion velocities of about 40 km s−1.

scholarly journals Dark Stars: Dark matter in the first stars leads to a new phase of stellar evolution

2008 ◽  
Vol 4 (S255) ◽  
pp. 56-60 ◽  
Author(s):  
Katherine Freese ◽  
Douglas Spolyar ◽  
Anthony Aguirre ◽  
Peter Bodenheimer ◽  
Paolo Gondolo ◽  
...  
Keyword(s):  
Black Holes ◽  
Dark Matter ◽  
Cross Section ◽  
Stellar Evolution ◽  
Weakly Interacting Massive Particles ◽  
First Stars ◽  
History Of ◽  
Born Again ◽  
The Universe ◽  
New Phase

AbstractThe first phase of stellar evolution in the history of the universe may be Dark Stars, powered by dark matter heating rather than by fusion. Weakly interacting massive particles, which are their own antiparticles, can annihilate and provide an important heat source for the first stars in the the universe. This talk presents the story of these Dark Stars. We make predictions that the first stars are very massive (~800M⊙), cool (6000 K), bright (~106L⊙), long-lived (~106years), and probable precursors to (otherwise unexplained) supermassive black holes. Later, once the initial DM fuel runs out and fusion sets in, DM annihilation can predominate again if the scattering cross section is strong enough, so that a Dark Star is born again.

The Second Century Papers: Looking Ahead in Aeronautics—2. The Future for Agricultural Aviation

1968 ◽  
Vol 72 (687) ◽  
pp. 191-197
Author(s):  
A. H. Wheeler
Keyword(s):  
Second Century ◽  
Agricultural Chemicals ◽  
Future Evolution ◽  
The Past ◽  
Look Back ◽  
The World ◽  
The Future

Predicting the future for Agricultural Aviation is rendered even more uncertain than predictions for most forms of aviation because in this case the future depends on two entirely separate sets of unknowns. These are the normal unknowns affecting aeronautical development but, more important, there are the unknowns affecting the development of agricultural chemicals. Also, in predicting the future evolution of any activity one must normally look back over the rate and the trend of developments in the activity, so far as they are relevant, from the past and then project this rate and trend into the future, bending and extending the line of projection in accordance with known or foreseeable influences. Here again we get a third set of unknowns related to future farming techniques, although these unknowns are perhaps less significant because the main expansion in agricultural aviation will probably lie in the vast undeveloped regions of the world where the farming techniques will merely be brought up to present standards, or just introduced where there was literally no agriculture before.

scholarly journals Analyses of the LMC Novae

1999 ◽  
Vol 190 ◽  
pp. 391-392
Author(s):  
Karen M. Vanlandingham ◽  
Greg J. Schwarz ◽  
Sumner Starrfield ◽  
Peter H. Hauschildt ◽  
Steven N. Shore ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Large Magellanic Cloud ◽  
Optical Spectra ◽  
Classical Novae ◽  
Preliminary Results ◽  
Elemental Abundances ◽  
Ultraviolet Spectra ◽  
The Past ◽  
Consistent Manner ◽  
Ism Abundances

In the past 10 years, 6 classical novae have been observed in the Large Magellanic Cloud (LMC). We have begun a study of these objects using ultraviolet spectra obtained by IUE and optical spectra from nova surveys. We are using the results of this study to further our understanding of novae and stellar evolution.Our study includes analysis of both the early, optically thick spectra using model atmospheres (Hauschildt et al. 1992), and the later nebular spectra using optimization of photoionization codes (Ferland 1996; James & Roos 1993). By analysing all the LMC novae in a consistent manner, we can compare their individual results and use their combined properties to calibrate Galactic novae. In addition, our studies can be used to determine the elemental abundances of the nova ejecta, the amount of mass ejected, and the contribution of novae to the ISM abundances. To date we have analysed Nova LMC 1988#1 (Schwarz et al. 1998) and Nova LMC 1990#1 (Vanlandingham et al. 1999), and have obtained preliminary results for Nova LMC 1991. The results of this work are presented in this poster.

Of 'Sour Grapes' and 'Children's Teeth': Inherited Guilt, Human Rights and Processes of Restoration in Ghanaian Pentecostalism

Exchange ◽  
2004 ◽  
Vol 33 (4) ◽  
pp. 334-353 ◽  
Author(s):  
J. Kwabena Asamoah-Gyadu
Keyword(s):  
Human Rights ◽  
Critical Area ◽  
African Countries ◽  
Charismatic Movement ◽  
The Past ◽  
Traditional Religions ◽  
Traditional Institutions ◽  
In Christ ◽  
Born Again ◽  
Ritual Context

AbstractThe rise of the Pentecostal/Charismatic movement in African countries like Ghana has inspired new ways of dealing with the challenges of life. A critical area of operation for the movement is the 'healing and deliverance' ministry. One of its main aims is to help people deal with inherited guilt through rituals for healing the past. The worldview of mystical causality that underlies a system of shrine slavery among the Ewe of Ghana called Trokosi, offer one example from traditional religions, of how such traditional institutions may stigmatise victims and generations after them, sometimes perpetually. Vestiges of such stigmatisation still remain even in places where shrine slavery has been abolished by law. In keeping with the prophetic declaration by Ezekiel that the sins of the fathers shall no more be visited on their children (Ezekiel 18), the Pentecostal/Charismatic ministry of 'healing and deliverance' provides a Christian ritual context in which the enslaving effects of generational curses resulting from the sins of one's ancestry may be broken. Pentecostals believe that it is through the 'deliverance' that the born again Christian may experience fullness of life in Christ.

Sign in / Sign up

Export Citation Format

Share Document