scholarly journals 35. Stellar Constitution

1985 ◽  
Vol 19 (1) ◽  
pp. 479-502
Author(s):  
A. N. Cox ◽  
D. Sugimoto ◽  
P. H. Bodenheimer ◽  
C. S. Chiosi ◽  
D. J. Faulkner ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Planetary Nebula ◽  
Massive Stars ◽  
Structure Stability ◽  
Current Interest ◽  
Late Type ◽  
Dwarf Stars ◽  
Entire Field ◽  
Stellar Formation ◽  
Central Stars

This report of Commission 35, as in past reports, consists of some details of only a few selected topics. This is necessary because a survey of the entire field of stellar formation, structure, stability, evolution, pulsation, and explosions for the three year period from mid-1981 to mid-1984 would be excessively long. Our topics here, in order from the most massive stellar classes to the least are: Massive Stars (R.M. Humphreys), Rotation in Late Type Stars (W. Benz), Helioseismology (J. Christensen-Dalsgaard), Planetary Nebula Central Stars (E.M. Sion), Pulsations in Hot Degenerate Dwarf Stars (A.N. Cox and S.D. Kawaler), and White Dwarfs (V. Weidemann). There is some overlap in the reviewing of these last three reports because the topics are very closely related. Concentration in this dying stage of stellar evolution seems appropriate because of the great current interest in these matters.

35. Stellar Constitution (Constitution Des Étoiles)

1988 ◽  
Vol 20 (01) ◽  
pp. 473-492
Author(s):  
D. Sugimoto ◽  
A. Maeder ◽  
P.H. Bodenheimer ◽  
C.S. Chiosi ◽  
A.N. Cox ◽  
...  
Keyword(s):  
Neutron Stars ◽  
Mass Loss ◽  
Structure Stability ◽  
X Ray ◽  
Entire Field ◽  
Physical Mechanisms ◽  
Stellar Formation ◽  
Great Progress

This report of Commission 35, as in past reports, consists of some details of only a few selected topics. This is necessary because a survey of the entire field of stellar formation, structure, stability, evolution, explosion, and nucleosynthesis for the three year period from mid-1984 to mid-1987 would be excessively long. Our topics here, in order from early to late evolutionary pahses are: Convective Overshooting (N.H. Baker), Mass Loss (I. Appenzeller), Novae (M. Livio), Presupernova Models and SN1987A (K. Nomoto), and Structure of X-Ray Bursting Neutron Stars (M.Y. Fujimoto and D. Sugimoto). In addition, Asteroseismology (H. Shibahashi) is reported briefly as one of the new disciplines now being developed. About two decades ago, Professor Martin Schwarzschild suggested convection, mass loss, and calculation of models through supernova stage as ones of the most important problems to attack. Though great progress has been achieved in these topics, we still have some fundamental questions concerning physical mechanisms involved. This is the reason why these topics are selected for this report.

scholarly journals Structure of selected Planetary Nebulae surrounding WR-type central stars

1997 ◽  
Vol 180 ◽  
pp. 230-230
Author(s):  
S.K. Górny ◽  
K. Gȩsicki ◽  
A. Acker
Keyword(s):  
Velocity Field ◽  
Planetary Nebula ◽  
Radial Direction ◽  
Planetary Nebulae ◽  
Late Type ◽  
Computer Codes ◽  
Central Stars

The main aim of this work was to confirm that expansion of planetary nebulae surrounding Wolf-Rayet type central stars is characterized by turbulent motions or strong variations of velocity in the radial direction relative to the nucleus. Such properties have already been found in Ml-25, M3-15 and Pel-1 by Gesicki & Acker (1995). We have analyzed the photoionization structure and velocity field of the NGC 40 - a planetary nebula with late type ([WC 8]) Wolf-Rayet nucleus. The spectra of Hα and [NII] lines have been obtained with the 1.5m telescope at the Observatoire de Haute-Provence. The spectrograph Aurelie with dispersion of 5Å/mm and a 3″ circular entrance was used. The method and the details of the applied computer codes are published in Gesicki et al. (1996).

scholarly journals The EREBOS project: Investigating the effect of substellar and low-mass stellar companions on late stellar evolution

2019 ◽  
Vol 630 ◽  
pp. A80 ◽  
Author(s):  
V. Schaffenroth ◽  
B. N. Barlow ◽  
S. Geier ◽  
M. Vučković ◽  
D. Kilkenny ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Planetary Nebula ◽  
Eclipsing Binaries ◽  
Atmospheric Parameter ◽  
Reflection Effect ◽  
Common Envelope ◽  
Period Distribution ◽  
Hot Subdwarfs ◽  
Substellar Companions ◽  
Central Stars

Eclipsing post-common-envelope binaries are highly important for resolving the poorly understood, very short-lived common-envelope phase of stellar evolution. Most hot subdwarfs (sdO/Bs) are the bare helium-burning cores of red giants that have lost almost all of their hydrogen envelope. This mass loss is often triggered by common-envelope interactions with close stellar or even substellar companions. Cool companions to hot subdwarf stars such as late-type stars and brown dwarfs are detectable from characteristic light-curve variations – reflection effects and often eclipses. In the recently published catalog of eclipsing binaries in the Galactic Bulge and in the Asteroid Terrestrial-impact Last Alert System (ATLAS) survey, we discovered 125 new eclipsing systems showing a reflection effect seen by visual inspection of the light curves and using a machine-learning algorithm, in addition to the 36 systems previously discovered by the Optical Gravitational Lesing Experiment (OGLE) team. The Eclipsing Reflection Effect Binaries from Optical Surveys (EREBOS) project aims at analyzing all newly discovered eclipsing binaries of the HW Vir type (hot subdwarf + close, cool companion) based on a spectroscopic and photometric follow up to derive the mass distribution of the companions, constrain the fraction of substellar companions, and determine the minimum mass needed to strip off the red-giant envelope. To constrain the nature of the primary we derived the absolute magnitude and the reduced proper motion of all our targets with the help of the parallaxes and proper motions measured by the Gaia mission and compared those to the Gaia white-dwarf candidate catalog. It was possible to derive the nature of a subset of our targets, for which observed spectra are available, by measuring the atmospheric parameter of the primary, confirming that less than 10% of our systems are not sdO/Bs with cool companions but are white dwarfs or central stars of planetary nebula. This large sample of eclipsing hot subdwarfs with cool companions allowed us to derive a significant period distribution for hot subdwarfs with cool companions for the first time showing that the period distribution is much broader than previously thought and is ideally suited to finding the lowest-mass companions to hot subdwarf stars. The comparison with related binary populations shows that the period distribution of HW Vir systems is very similar to WD+dM systems and central stars of planetary nebula with cool companions. In the future, several new photometric surveys will be carried out, which will further increase the sample of this project, providing the potential to test many aspects of common-envelope theory and binary evolution.

scholarly journals Planetary nebulae with Wolf–Rayet-type central stars – I. The case of the high-excitation NGC 2371

2020 ◽  
Vol 496 (1) ◽  
pp. 959-973
Author(s):  
V M A Gómez-González ◽  
J A Toalá ◽  
M A Guerrero ◽  
H Todt ◽  
L Sabin ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Planetary Nebula ◽  
Symmetry Axis ◽  
High Excitation ◽  
Central Cavity ◽  
Isaac Newton ◽  
Double Structure ◽  
High Ionization ◽  
Isaac Newton Telescope ◽  
Central Stars

ABSTRACT We present the analysis of the planetary nebula (PN) NGC 2371 around the [Wolf–Rayet] (WR) star WD 0722+295. Our Isaac Newton Telescope intermediate dispersion spectrograph spectra, in conjunction with archival optical and ultraviolet images, unveil in unprecedented detail the high ionization of NGC 2371. The nebula has an apparent multipolar morphology, with two pairs of lobes protruding from a barrel-like central cavity, a pair of dense low ionization knots misaligned with the symmetry axis embedded within the central cavity, and a high-excitation halo mainly detected in He ii. The abundances from the barrel-like central cavity and dense knots agree with abundance determinations for other PNe with [WR]-type central stars of PNe. We suggest that the densest knots inside NGC 2371 are the oldest structures, remnant of a dense equatorial structure, while the main nebular shell and outer lobes resulted from a latter ejection that ended the stellar evolution. The analysis of position–velocity diagrams produced from our high-quality spectra suggests that NGC 2371 has a bipolar shape with each lobe presenting a double structure protruding from a barrel-like central region. The analysis of the spectra of WD 0722+295 results in similar stellar parameters as previously reported. We corroborate that the spectral subtype corresponds with a [WO1] type.

scholarly journals The Brightest Stars in the Magellanic Clouds and Other Late-Type Galaxies

1984 ◽  
Vol 108 ◽  
pp. 145-156
Author(s):  
Roberta M. Humphreys
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Stellar Population ◽  
Massive Stars ◽  
Magellanic Clouds ◽  
Stellar Winds ◽  
Stellar Content ◽  
Late Type ◽  
Observational Astronomy ◽  
Distant Galaxies

The brightest stars always receive considerable attention in observational astronomy, but why are we so interested in these most luminous, and therefore most massive stars? These stars are our first probes for exploring the stellar content of distant galaxies. Admittedly, they are only the tip of the iceberg for the whole stellar population and very interesting processes are occurring among the less massive, older stars, but the most massive stars are our first indicators for studies of stellar evolution in other galaxies. They provide the first hint that stellar evolution may have been different in a particular galaxy because they evolve so quickly. The most luminous stars also highly influence their environments via their strong stellar winds and mass loss and eventually as supernovae.

scholarly journals Ring Nebulae Around Massive Stars

1991 ◽  
Vol 143 ◽  
pp. 349-364
Author(s):  
You-Hua Chu
Keyword(s):  
Stellar Evolution ◽  
Spectral Properties ◽  
Massive Stars ◽  
Ambient Medium ◽  
Stellar Winds ◽  
Luminous Blue Variables ◽  
Stellar Properties ◽  
Ring Nebulae ◽  
Central Stars ◽  
Temperature Correlations

Ring nebulae have been found around WR stars, OB and Of stars, and luminous blue variables. Ring nebulae are formed by the interaction between the central stars and their ambient medium via different combinations of stellar winds, ejecta, and radiation. The spectral properties of the nebulae can be used to diagnose the stellar properties, such as luminosity and effective temperature. Correlations between ring nebulae and their central stars may be used to check scenarios of stellar evolution.

Excited OH Masers in Late-Type Stellar Objects

2017 ◽  
Vol 13 (S336) ◽  
pp. 385-386
Author(s):  
A. Strack ◽  
E. D. Araya ◽  
M. E. Lebrón ◽  
R. F. Minchin ◽  
H. G. Arce ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Ground State ◽  
Planetary Nebula ◽  
Late Type ◽  
Stellar Objects ◽  
Stellar Pulsations ◽  
Maser Line ◽  
Low Mass ◽  
Significant Mass Loss ◽  
Significant Mass

AbstractThe final stages of low-mass stellar evolution are characterized by significant mass loss due to stellar pulsations during the AGB phase, which lead to the development of planetary nebulae. Molecular masers of H2O, SiO, and ground state OH transitions are commonly detected in oxygen-rich late-type stars (OH/IR objects). In contrast, excited OH maser transitions are rare. We discuss our study of the carbon-rich pre-planetary nebula CRL618 (a prototypical post-AGB star). Observations conducted in May 2008 with the 305m Arecibo Telescope resulted in the first detection of a 4765MHz OH maser line in a late-type stellar object; the detection was confirmed a few months later also with Arecibo. Subsequent observations in 2015 and 2017 resulted in non-detection of the 4765MHz OH line. Our observations indicate that the 4765MHz OH maser in CRL 618 is highly variable, possibly tracing a short-lived phenomenon during the development of a pre-planetary nebula.

scholarly journals Proto-Planetary Nebulae

2003 ◽  
Vol 209 ◽  
pp. 113-120 ◽  
Author(s):  
Bruce J. Hrivnak
Keyword(s):  
Stellar Evolution ◽  
Planetary Nebula ◽  
Planetary Nebulae ◽  
Asymptotic Giant Branch ◽  
Central Stars

The study of proto-planetary nebulae (PPNs) leads to a better understanding of both the preceding asymptotic giant branch and the succeeding planetary nebula phases of stellar evolution. Recent results are reviewed, emphasizing the properties of the central stars and the shape and chemistry of the nebulae. The study of PPNs is seen to be important in its own right.

scholarly journals Oxygen Depletion Variations in Planetary Nebulae and Shells Ejected from Luminous Population I Stars

1989 ◽  
Vol 131 ◽  
pp. 216-216
Author(s):  
Reginald J. Dufour
Keyword(s):  
Stellar Evolution ◽  
Planetary Nebula ◽  
Massive Stars ◽  
Planetary Nebulae ◽  
Oxygen Depletion ◽  
Uv Spectrophotometry ◽  
Type I ◽  
Eta Carinae ◽  
Compositional Variations ◽  
Hr Diagram

Recent studies by the Peimberts have noted an anticorrelation between 0 and N abundances in the Type I He- and N-rich PN, such that N+) is approximately constant. We report observations of the spectra and composition of several “planetary nebula-like” shells surrounding more luminous population I O- and WR-stars, which indicate that this 0-N anticorrelation extends upwards in the HR diagram to among the most luminous stars known, with O/H values in the shells ranging down to −2 dex below Solar. We report optical and UV spectrophotometry of the shell nebulae NGC 2359, NGC 6164-5, NGC 6888, NGC 7635, AG Carinae, and the condensations around Eta Carinae, which generally support this anticorrelation trend. We also discuss variations in other elements such as He, C, S, and Ar in these shell nebulae, and compare the compositional variations to the expectations from stellar evolution and nucleosynthesis models of intermediate and massive stars.

scholarly journals 12. The Nuclei of Planetary Nebulae as Progenitors of White Dwarfs

1971 ◽  
Vol 42 ◽  
pp. 77-78
Author(s):  
C. R. O'Dell
Keyword(s):  
Stellar Evolution ◽  
Planetary Nebula ◽  
White Dwarfs ◽  
Rapid Change ◽  
Planetary Nebulae ◽  
Review Article ◽  
The Past ◽  
The Subject ◽  
Central Stars

Stellar evolution is characterized by fast and slow phases. Usually the periods of rapid change are difficult to follow observationally; but, this does not seem to be the case when passing through the planetary nebula stage. Because of their high intrinsic luminosities and easy identification, it is possible to identify and study these objects and their central stars rather completely. It is quite relevant to discuss these objects at a symposium on white dwarfs since the central stars may be in the immediate progenitor stage before white dwarfs. The actual picture of the evolution of the nuclei has changed rather little in the past few years and is the subject of an earlier review article (O'Dell, 1968) to which the reader is referred.

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