scholarly journals Observations and Interpretation of Luminous Blue Variables

1995 ◽  
Vol 155 ◽  
pp. 176-191
Author(s):  
Henny J.G.L.M. Lamers
Keyword(s):  
Effective Temperature ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Variable Mass ◽  
Mode Interaction ◽  
Stellar Radius ◽  
Luminous Blue Variables ◽  
Different Types ◽  
Apparent Variation ◽  
Eddington Limit

AbstractThe different types of variations of LBVs are discussed. The “typical LBV variations” have amplitudes of ΔV ≃ 0.5 to 2.0 magnitudes and irregular time-scales of months to years. This is due to changes in the stellar radius and the effective temperature. Modelling of this variability for one star, S Dor, shows that the radius of the star varies between 100 and 380 R⊙, the effective temperature between 20,000 and 9,000 K, and the luminosity between log L* = 6.10 to 5.9. The variation of the radius is not an apparent variation of the effective radius of the wind due to a variable mass loss rate (which has often been assumed) but it is a true variation of the radius of the star itself. The changes in L* suggest that about 10−3 to 10−2M* takes part in the expansion of the star. The irregular microvariations with amplitudes of about ΔV ≃ 0.2m on timescales of weeks are probably due to non-adiabatic pulsations with mode-interaction. We argue that LBVs are close to their effective Eddington Limit and discuss a qualitative scenario to explain their location in the HR-diagram.

scholarly journals Ionisation fractions and mass-loss in O stars

1987 ◽  
Vol 122 ◽  
pp. 449-450
Author(s):  
Raman K. Prinja ◽  
Ian D. Howarth
Keyword(s):  
High Resolution ◽  
Mass Loss ◽  
Column Density ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Terminal Velocity ◽  
Stellar Radius ◽  
Left Part ◽  
Hr Diagram

The most sensitive indicators of mass-loss for stars in the upper left part of the HR diagram are the UV P Cygni profiles observed in the resonance lines of common ions such as N V, Si IV, and C IV. We present here some results from a study of these lines in the high resolution IUE spectra of 197 Ï stars. Profile fits were carried out in the manner described by Prinja & Howarth (1986) for all unsaturated P Cygni resonance doublets. The parameterisations adopted enable the product of mass-loss rate (Ṁ) and ion fraction (qi) to be determined at a given velocity, such that Ṁ qi°C Ni R* v∞, where Ni is the column density of the observed ion i, v∞ is the terminal velocity, and R⋆ is the stellar radius. The accompanying figures illustrate the behaviour of Ṁ qi (evaluated at 0.5 v∞) for N V and C IV.

scholarly journals On the evolutionary status and instability mechanism of the Luminous Blue Variables (LBV)

1989 ◽  
Vol 113 ◽  
pp. 15-26
Author(s):  
André Maeder
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Light Curves ◽  
Evolutionary Status ◽  
Average Mass ◽  
Luminous Blue Variables ◽  
Ir Sources ◽  
Order Of Magnitude ◽  
Lower Luminosity

AbstractVarious evolutionary sequences leading to LBV are examined. The sequence O-Of-LBV-WR-SN is well supported by the models; some LBV with relatively lower luminosity may turn into OH/IR sources. The overall duration of the LBV phase depends mainly on the average mass loss rate; for <Ṁ> = 10−3M⊙y−1, it lasts about 104y.Very massive stars undergo, when they reach logTeff= 3.9, strong departure from hydrostatic equilibrium due to supra-Eddington luminosities at some depth in the outer layers. This results in heavy mass loss, as the growth rate of the instability is very fast. We suggest that the amount of mass ejected in a shell episode is mainly determined by the mass of such a layer that its thermal adjustment timescale is within an order of magnitude of the stellar dynamical timescale. Simulations of B-light curves due to shell ejections by LBV are performed and some sensitive properties are identified.

scholarly journals Numerical Simulation Study of Variable-Mass Permeation of the Broken Rock Mass under Different Cementation Degrees

2018 ◽  
Vol 2018 ◽  
pp. 1-8
Author(s):  
Chong Li ◽  
Banghua Yao ◽  
Qingqing Ma
Keyword(s):  
Numerical Simulation ◽  
Rock Mass ◽  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Water Inrush ◽  
Variable Mass ◽  
Erosion Effect ◽  
Porosity And Permeability ◽  
Rock Specimens

In order to analyze variable-mass permeation characteristics of broken rock mass under different cementation conditions and reveal the water inrush mechanism of geological structures containing broken rock masses like karst collapse pillars (KCPs) in the coal mine, the EDEM-FLUENT coupling simulation system was used to implement a numerical simulation study of variable-mass permeation of broken rock mass under different cementation conditions and time-dependent change laws of parameters like porosity, permeability, and mass loss rate of broken rock specimens under the erosion effect were obtained. Study results show that (1) permeability change of broken rock specimens under the particle migration effect can be divided into three phases, namely, the slow-changing seepage phase, sudden-changing seepage phase, and steady seepage phase. (2) Specimen fillings continuously migrate and run off under the water erosion effect, porosity and permeability rapidly increase and then tend to be stable, and the mass loss rate firstly rapidly increases and then gradually decreases. (3) Cementation degree has an important effect on permeability of broken rock mass. As cementing force of the specimen is enhanced, its maximum mass loss rate, mass loss, porosity, and permeability all continuously decrease. The study approach and results not only help enhance coal mining operations safety by better understanding KCP water inrush risks. It can also be extended to other engineering applications such as backfill paste piping and tailing dam erosion.

scholarly journals Mass loss and fate of the most massive stars

2011 ◽  
Vol 7 (S279) ◽  
pp. 29-33
Author(s):  
Jorick S. Vink
Keyword(s):  
Mass Loss ◽  
Effective Temperature ◽  
Loss Rate ◽  
Massive Stars ◽  
Mass Loss Rate ◽  
Normal Type ◽  
Novel Method ◽  
Loss Rates

AbstractThe fate of massive stars up to 300M⊙ is highly uncertain. Do these objects produce pair-instability explosions, or normal Type Ic supernovae? In order to address these questions, we need to know their mass-loss rates during their lives. Here we present mass-loss predictions for very massive stars (VMS) in the range of 60-300M⊙. We use a novel method that simultaneously predicts the wind terminal velocities v∞ and mass-loss rate Ṁ as a function of the stellar parameters: (i) luminosity/mass Γ, (ii) metallicity Z, and (iii) effective temperature Teff. Using our results, we evaluate the likely outcomes for the most massive stars.

Observational Evidence for Atmospheric Physical Characteristics Relevant to Stellar Evolution

1977 ◽  
Vol 4 (2) ◽  
pp. 105-114
Author(s):  
R. and G. Cayrel
Keyword(s):  
Mass Loss ◽  
Nuclear Fuel ◽  
Stellar Evolution ◽  
Effective Temperature ◽  
Time Scale ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Observational Evidence ◽  
High Luminosity ◽  
Very High

As a star burns its nuclear fuel, its radius R and its luminosity L are modified. Its mass may as well be affected if the mass loss rate has a time scale comparable to the nuclear time scale; this is likely to occur for stars of very high luminosity. Currently, the change in radius R and luminosity L of an evolving star is described in the socalled theoretical Herzsprung-Russel diagramme with in abscissa the logarithm of the effective temperature defined by:

scholarly journals iPTF14hls as a variable hyper-wind from a very massive star

2019 ◽  
Author(s):  
Takashi J Moriya ◽  
Paolo A Mazzali ◽  
Elena Pian
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Variable Mass ◽  
Stellar Winds ◽  
Spectral Evolution ◽  
Extreme Wind ◽  
Sudden Outburst ◽  
Bright Phase

Abstract The origin of iPTF14hls, which had Type IIP supernova-like spectra but kept bright for almost two years with little spectral evolution, is still unclear. We here propose that iPTF14hls was not a sudden outburst like supernovae but rather a long-term outflow similar to stellar winds. The properties of iPTF14hls, which are at odds with a supernova scenario, become natural when interpreted as a stellar wind with variable mass-loss rate. Based on the wind hypothesis, we estimate the mass-loss rates of iPTF14hls in the bright phase. We find that the instantaneous mass-loss rate of iPTF14hls during the 2-year bright phase was more than a few M⊙ yr−1 (“hyper-wind”) and it reached as much as 10 M⊙ yr−1 . The total mass lost over two years was about 10 M⊙. Interestingly, we find that the light curve of iPTF14hls has a very similar shape to that of η Carinae during the Great Eruption, which also experienced a similar but less extreme brightening accompanied by extraordinary mass loss, shedding more than 10 M⊙ in 10 years. The progenitor of iPTF14hls is less than 150 M⊙ if it still exists, which is similar to η Carinae. The two phenomena may be related to a continuum-driven extreme wind from very massive stars.

scholarly journals Modelling the stellar winds of the [WC10] central stars CPD–56° 8032 and He 2–113

1997 ◽  
Vol 180 ◽  
pp. 102-102
Author(s):  
Orsola de Marco ◽  
P. A. Crowther ◽  
M. J. Barlow ◽  
P. J. Storey
Keyword(s):  
Loss Rate ◽  
Mass Loss Rate ◽  
Model Atmosphere ◽  
Moving Frame ◽  
Stellar Winds ◽  
Spherically Symmetric ◽  
Model Calculations ◽  
Stellar Radius ◽  
Stellar Temperature ◽  
Central Stars

[WC] stars are H–deficient central stars of PN which can mimic the spectra of massive (Min∼50M⊙) Wolf-Rayet stars of the carbon sequence and can be modelled using the same techniques. Our model calculations for the [WC10] CPD–56° 8032 and He 2–113 are based on the iterative technique of Hillier (A&A 231 111 1990) which solves the transfer equation in the co-moving frame subject to statistical and radiative equilibrium, assuming an expanding, spherically-symmetric, homogeneous and time-independent atmosphere. In extended atmospheres the stellar radius (R∗) is defined as the inner boundary of the model atmosphere at τRoss=20, with the stellar temperature (T∗) defined by the usual Stefan-Boltzmann (T∗ = (L∗/4 π σ R2∗)1/4) relation. For a given mass loss rate (M), the density and velocity field (v(r) = V∞ (1 - R∗/r)β for the supersonic part) are related via the equation of continuity M = 4 π r2 ρ(r) v(r).

scholarly journals On the variations of [OIII] lines intensities in the spectrum of PN IC 4997

1997 ◽  
Vol 180 ◽  
pp. 289-289
Author(s):  
A. G. Yeghikyan
Keyword(s):  
Mass Loss ◽  
Electron Temperature ◽  
Effective Temperature ◽  
Stellar Wind ◽  
Planetary Nebula ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Radiation Fields ◽  
Ionization Structure ◽  
Ionization Model

The causes of asynchronous variations of the intensities of OIII ions forbidden lines in the spectrum of compact planetary nebula IC 4997 are considered on the basis of the observational data of. It is shown that the rise of the intensity of line 4363 å and decrease of the intensities of N1 and N2 lines may be best explained by increase of mass-loss-rate from nucleous from 5 × 10–8 up to 2 × 10–7 M/yr within a few years (at constant nucleous effective temperature), with appropriate change of ionization structure of nebula. The arguments of existence of variable hot stellar wind are discussed. The theoretical intensities of lines are calculated by the ionization model of planetary nebulae [4], gyven the radiation fields of the nucleous and hot stellar wind with electron temperature Te= 500000 K.

scholarly journals Models for GRBs and diverse transients

2007 ◽  
Vol 365 (1854) ◽  
pp. 1129-1139 ◽  
Author(s):  
S.E Woosley ◽  
Weiqun Zhang
Keyword(s):  
Massive Star ◽  
Loss Rate ◽  
Gamma Ray ◽  
Mass Loss Rate ◽  
Variable Mass ◽  
Gamma Ray Bursts ◽  
Basic Model ◽  
Central Engine ◽  
Relativistic Jet ◽  
Natural Inclination

The observational diversity of gamma-ray bursts (GRBs) has been increasing, and the natural inclination is a proliferation of models. We explore the possibility that at least part of this diversity is a consequence of a single basic model for the central engine operating in a massive star of variable mass, differential rotation rate and mass loss rate. Whatever that central engine may be—and here the collapsar is used as a reference point—it must be capable of generating both a narrowly collimated, highly relativistic jet to make the GRB and a wide angle, sub-relativistic outflow responsible for exploding the star and making the supernova bright. To some extent, the two components may vary independently; therefore, it is possible to produce a variety of jet energies and supernova luminosities. We explore, in particular, the production of low-energy bursts and find a lower limit of approximately 10 48  erg s −1 to the power required for a jet to escape a massive star before that star either explodes or is accreted. Lower energy bursts and ‘suffocated’ bursts may be particularly prevalent when the metallicity is high, i.e. in the modern universe at low red shift.

scholarly journals The wind of P Cygni

1989 ◽  
Vol 113 ◽  
pp. 259-260
Author(s):  
J. Puls ◽  
A.W.A. Pauldrach ◽  
R.P. Kudritzki
Keyword(s):  
Energy Distribution ◽  
Mass Loss ◽  
Radiation Pressure ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Terminal Velocity ◽  
Scaling Relations ◽  
Self Consistent ◽  
Line Pressure ◽  
Eddington Limit

The stationary features of the wind of P Cygni are considerably different from those of ‘normal’ supergiant winds with comparable luminosity. In contrast to such winds, which are generally accepted to be driven by radiation pressure, P Cygni’s mass-loss rate is higher by a factor of 5, the terminal velocity is higher by a factor of 10, and the velocity law itself is much flatter than would be expected from a first glance at glance at typical scaling relations. However, these relations depend crucially and non-linearly on the star’s distance from the Eddington limit, which for P Cyg is very small (see below). Here we investigate whether the acceleration mechanism of P Cygni’s wind can also be explained by line pressure and to what extent self-consistent wind models represent the observed quantities (especially the IR energy distribution).

Sign in / Sign up

Export Citation Format

Share Document