scholarly journals Z Cha – Another Case of Gravitational Radiation?

1979 ◽  
Vol 53 ◽  
pp. 503-503
Author(s):  
H. Ritter
Keyword(s):  
Gravitational Radiation ◽  
White Dwarf ◽  
Loss Rate ◽  
Main Sequence ◽  
Hot Spot ◽  
Mass Loss Rate ◽  
Physical Parameters ◽  
Low Mass ◽  
The One ◽  
R Relation

By combining spectroscopic data obtained by Vogt (1979) and photometric data obtained by Bailey (1979) and Fabian et al. (1979) it is possible to determine the physical parameters of the southern dwarf nova Z Cha (Ritter, 1979). The resulting values are: mass of the white dwarf primary M1=(0.035±0.06)M⊙, radius of the white dwarf R1=(1.8 10-2)R⊙, mass of the secondary M2=(0.16±0.02)M⊙, radius of the secondary R2=(0.19±0.01)M⊙, inclination i = 748±0.8°. Accordingly the primary conforms to the theoretical M-R relation of white dwarfs and the secondary to the theoretical low mass main sequence. The mass exchange rate derived from the luminosity of the accretion disk and from the hot spot respectively turns out to be Ṁ ≈ 4.10-11 M⊙/year, about 102 times more than is expected from the nuclear evolution of the secondary. On the other hand, angular momentum losses due to gravitational radiation predicts a mass loss rate (Faulkner, 1971) which is almost identical to the one derived from observations. Therefore after the binary pulsar (Taylor et al., 1979), Z Cha seems to be another case presenting strong evidence for the action of gravitational waves.

scholarly journals Planets, Planetary Nebulae, and Intermediate Luminosity Optical Transients (ILOTs)

2018 ◽  
Author(s):  
Noam Soker
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Main Sequence ◽  
Mass Loss Rate ◽  
Planetary Nebulae ◽  
Gravitational Energy ◽  
Asymptotic Giant Branch ◽  
Main Sequence Star ◽  
Low Mass ◽  
Optical Transient

I review some aspects related to the influence of planets on the evolution of stars before and beyond the main sequence. Some processes include the tidal destruction of a planet on to a very young main sequence star, on to a low mass main sequence star, and on to a brown dwarf. This process releases gravitational energy that might be observed as a faint intermediate luminosity optical transient (ILOT) event. I then summarize the view that some elliptical planetary nebulae are shaped by planets. When the planet interacts with a low mass upper asymptotic giant branch (AGB) star it both enhances the mass loss rate and shapes the wind to form an elliptical planetary nebula, mainly by spinning up the envelope and by exciting waves in the envelope. If no interaction with a companion, stellar or sub-stellar, takes place beyond the main sequence, the star is termed a Jsolated star, and its mass loss rates on the giant branches are likely to be much lower than what is traditionally assumed.

scholarly journals Evolution of the Precursor of SN1987A

1988 ◽  
Vol 108 ◽  
pp. 410-411 ◽  
Author(s):  
P.R. Wood ◽  
D.J. Faulkner
Keyword(s):  
Mass Loss ◽  
Stellar Wind ◽  
Loss Rate ◽  
Main Sequence ◽  
Mass Loss Rate ◽  
Expansion Velocity ◽  
Continuous Line ◽  
The One ◽  
Hr Diagram

The evolution of a 17.5 M⊙ star, chosen to be similar to the precursor of SN1987A, has been studied using the input physics described in Wood and Faulkner (1987). The calculations: use opacities from the Astrophysical Opacity Library of Huebner et al (1977) with H, He, C, N, O and other metals in LMC ratios; treat semi-convection in the manner of Lamb, Iben and Howard (1976); and assume the mass loss rate to be the minimum of (a) α times the rate give in Waldron (1985) (this rate applied in the blue part of the HR diagram), and (b) L/(cv) (this rate applied in the red), where v is the stellar wind expansion velocity which was taken to be 12 km s−1.Typical evolutionary tracks resulting from these calculations are shown in Figure 1. The track shown as a continuous line is the one shown in Wood and Faulkner (1987) and corresponds to α = 2.5, while the track shown as a dotted line results from a slightly different treatment of semi-convection on the main-sequence and to α = 1.

scholarly journals Two-dimensional simulations of mixing in classical novae: The effect of white dwarf composition and mass

2018 ◽  
Vol 619 ◽  
pp. A121 ◽  
Author(s):  
Jordi Casanova ◽  
Jordi José ◽  
Steven N. Shore
Keyword(s):  
White Dwarf ◽  
Binary Systems ◽  
Main Sequence ◽  
Chemical Species ◽  
Two Dimensions ◽  
Classical Novae ◽  
Nova Shells ◽  
Solar Abundances ◽  
Low Mass ◽  
Thermonuclear Runaway

Context. Classical novae are explosive phenomena that take place in stellar binary systems. They are powered by mass transfer from a low-mass main sequence star onto either a CO or ONe white dwarf. The material accumulates for 104–105 yr until ignition under degenerate conditions, resulting in a thermonuclear runaway. The nuclear energy released produces peak temperatures of ∼0.1–0.4 GK. During these events, 10−7−10−3 M⊙ enriched in intermediate-mass elements, with respect to solar abundances, are ejected into the interstellar medium. However, the origin of the large metallicity enhancements and the inhomogeneous distribution of chemical species observed in high-resolution spectra of ejected nova shells is not fully understood. Aims. Recent multidimensional simulations have demonstrated that Kelvin-Helmholtz instabilities that operate at the core-envelope interface can naturally produce self-enrichment of the accreted envelope with material from the underlying white dwarf at levels that agree with observations. However, such multidimensional simulations have been performed for a small number of cases and much of the parameter space remains unexplored. Methods. We investigated the dredge-up, driven by Kelvin-Helmholtz instabilities, for white dwarf masses in the range 0.8–1.25 M⊙ and different core compositions, that is, CO-rich and ONe-rich substrates. We present a set of five numerical simulations performed in two dimensions aimed at analyzing the possible impact of the white dwarf mass, and composition, on the metallicity enhancement and explosion characteristics. Results. At the time we stop the simulations, we observe greater mixing (∼30% higher when measured in the same conditions) and more energetic outbursts for ONe-rich substrates than for CO-rich substrates and more massive white dwarfs.

scholarly journals Asteroseismological Probing of the Thermal Evolution of White Dwarf Stars

1992 ◽  
Vol 9 ◽  
pp. 643-645
Author(s):  
G. Fontaine ◽  
F. Wesemael
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Main Sequence ◽  
Thermal Evolution ◽  
Sequence Evolution ◽  
Helium Burning ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
The Galaxy ◽  
Low Mass

AbstractIt is generally believed that the immediate progenitors of most white dwarfs are nuclei of planetary nebulae, themselves the products of intermediate- and low-mass main sequence evolution. Stars that begin their lifes with masses less than about 7-8 M⊙ (i.e., the vast majority of them) are expected to become white dwarfs. Among those which have already had the time to become white dwarfs since the formation of the Galaxy, a majority have burnt hydrogen and helium in their interiors. Consequently, most of the mass of a typical white dwarf is contained in a core made of the products of helium burning, mostly carbon and oxygen. The exact proportions of C and 0 are unknown because of uncertainties in the nuclear rates of helium burning.

scholarly journals Classical Novae – Before and After Outburst

1988 ◽  
Vol 108 ◽  
pp. 226-231
Author(s):  
Mario Livio
Keyword(s):  
White Dwarf ◽  
Main Sequence ◽  
Orbital Parameters ◽  
Classical Novae ◽  
Classical Nova ◽  
Before And After ◽  
Low Mass ◽  
Orbital Periods ◽  
Thermonuclear Runaway ◽  
Nova Outburst

Classical nova (CN) and dwarf nova (DN) systems have the same binary components (a low-mass main sequence star and a white dwarf) and the same orbital periods. An important question that therefore arises is: are these systems really different ? (and if so, what is the fundamental difference ?) or, are these the same systems, metamorphosing from one class to the other ?The first thing to note in this respect is that the white dwarfs in DN systems are believed to accrete continuously (both at quiescence and during eruptions). At the same time, both analytic (e.g. Fujimoto 1982) and numerical calculations show, that when sufficient mass accumulates on the white dwarf, a thermonuclear runaway (TNR) is obtained and a nova outburst ensues (see e.g. reviews by Gallagher and Starrfield 1978, Truran 1982). It is thus only natural, to ask the question, is the fact that we have not seen a DN undergo a CN outburst (in about 50 years of almost complete coverage) consistent with observations of DN systems ? In an attempt to answer this question, we have calculated the probability for a nova outburst not to occur (in 50 years) in 86 DN systems (for which at least some of the orbital parameters are known).

scholarly journals Jsolated Stars of Low Metallicity

Galaxies ◽  
2018 ◽  
Vol 6 (3) ◽  
pp. 89
Author(s):  
Efrat Sabach
Keyword(s):  
Angular Momentum ◽  
Mass Loss ◽  
Stellar Evolution ◽  
Planetary Nebula ◽  
Luminosity Function ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Solar Metallicity ◽  
Low Metallicity ◽  
Low Mass

We study the effects of a reduced mass-loss rate on the evolution of low metallicity Jsolated stars, following our earlier classification for angular momentum (J) isolated stars. By using the stellar evolution code MESA we study the evolution with different mass-loss rate efficiencies for stars with low metallicities of Z = 0 . 001 and Z = 0 . 004 , and compare with the evolution with solar metallicity, Z = 0 . 02 . We further study the possibility for late asymptomatic giant branch (AGB)—planet interaction and its possible effects on the properties of the planetary nebula (PN). We find for all metallicities that only with a reduced mass-loss rate an interaction with a low mass companion might take place during the AGB phase of the star. The interaction will most likely shape an elliptical PN. The maximum post-AGB luminosities obtained, both for solar metallicity and low metallicities, reach high values corresponding to the enigmatic finding of the PN luminosity function.

scholarly journals Enhanced mass-loss rate evolution of stars with ≳18 M⊙ and missing optically observed type II core-collapse supernovae

2020 ◽  
Vol 494 (4) ◽  
pp. 5230-5238
Author(s):  
Roni Anna Gofman ◽  
Naomi Gluck ◽  
Noam Soker
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Main Sequence ◽  
Mass Loss Rate ◽  
Core Collapse ◽  
Type Ii ◽  
Instability Strip ◽  
Stellar Envelope ◽  
Explosion Mechanism ◽  
Hydrogen Mass

ABSTRACT We evolve stellar models with zero-age main-sequence (ZAMS) mass of MZAMS ≳ 18 M⊙ under the assumption that they experience an enhanced mass-loss rate when crossing the instability strip at high luminosities and conclude that most of them end as type Ibc supernovae (SNe Ibc) or dust-obscured SNe II. We explore what level of enhanced mass-loss rate during the instability strip would be necessary to explain the ‘red supergiant problem’. This problem refers to the dearth of observed core-collapse supernovae progenitors with MZAMS ≳ 18 M⊙. Namely, we examine what enhanced mass-loss rate could make it possible for all these stars actually to explode as core-collapse supernovae (CCSNe). We find that the mass-loss rate should increase by a factor of at least about 10. We reach this conclusion by analysing the hydrogen mass in the stellar envelope and the optical depth of the dusty wind at the explosion, and crudely estimate that under our assumptions only about a fifth of these stars explode as unobscured SNe II and SNe IIb. About 10–15 per cent end as obscured SNe II that are infrared-bright but visibly very faint, and the rest, about 65–70 per cent, end as SNe Ibc. However, the statistical uncertainties are still too significant to decide whether many stars with MZAMS ≳ 18 M⊙ do not explode as expected in the neutrino driven explosion mechanism, or whether all of them explode as CCSNe, as expected by the jittering jets explosion mechanism.

scholarly journals Stellar wind models of central stars of planetary nebulae

2020 ◽  
Vol 635 ◽  
pp. A173 ◽  
Author(s):  
J. Krtička ◽  
J. Kubát ◽  
I. Krtičková
Keyword(s):  
Mass Loss ◽  
White Dwarf ◽  
Planetary Nebula ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Planetary Nebulae ◽  
Terminal Velocity ◽  
Asymptotic Giant Branch ◽  
Central Stars ◽  
Loss Rates

Context. Fast line-driven stellar winds play an important role in the evolution of planetary nebulae, even though they are relatively weak. Aims. We provide global (unified) hot star wind models of central stars of planetary nebulae. The models predict wind structure including the mass-loss rates, terminal velocities, and emergent fluxes from basic stellar parameters. Methods. We applied our wind code for parameters corresponding to evolutionary stages between the asymptotic giant branch and white dwarf phases for a star with a final mass of 0.569 M⊙. We study the influence of metallicity and wind inhomogeneities (clumping) on the wind properties. Results. Line-driven winds appear very early after the star leaves the asymptotic giant branch (at the latest for Teff ≈ 10 kK) and fade away at the white dwarf cooling track (below Teff = 105 kK). Their mass-loss rate mostly scales with the stellar luminosity and, consequently, the mass-loss rate only varies slightly during the transition from the red to the blue part of the Hertzsprung–Russell diagram. There are the following two exceptions to the monotonic behavior: a bistability jump at around 20 kK, where the mass-loss rate decreases by a factor of a few (during evolution) due to a change in iron ionization, and an additional maximum at about Teff = 40−50 kK. On the other hand, the terminal velocity increases from about a few hundreds of km s−1 to a few thousands of km s−1 during the transition as a result of stellar radius decrease. The wind terminal velocity also significantly increases at the bistability jump. Derived wind parameters reasonably agree with observations. The effect of clumping is stronger at the hot side of the bistability jump than at the cool side. Conclusions. Derived fits to wind parameters can be used in evolutionary models and in studies of planetary nebula formation. A predicted bistability jump in mass-loss rates can cause the appearance of an additional shell of planetary nebula.

scholarly journals Mass-Losing Peculiar Red Giants: The Comparison Between Theory and Observations

1989 ◽  
Vol 106 ◽  
pp. 339-347
Author(s):  
M. Jura
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Main Sequence ◽  
Mass Loss Rate ◽  
Solar Neighborhood ◽  
Asymptotic Giant Branch ◽  
Red Giants ◽  
Main Sequence Stars ◽  
Dwarf Stars ◽  
White Dwarf Stars

AbstractThe mass loss from evolved red giants is considered. It seems that red giants on the Asymptotic Giant Branch (AGB) are losing between 3 and 6 10-4 MΘ kpc-2 yr-1 in the solar neighborhood. If all the main sequence stars between 1 and 5 MΘ ultimately evolve into white dwarfs with masses of 0.7 MΘ the predicted mass loss rate in the solar neighborhood from these stars is 8 10-4 MΘ kpc-2 yr-1. Although there are still uncertainties, it appears that there is no strong disagreement between theory and observation. However, it could also be that we have not yet identified much of the source of the mass-loss from pre-white dwarf stars.

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