scholarly journals Predictions of variable mass loss for Luminous Blue Variables

2002 ◽  
Vol 393 (2) ◽  
pp. 543-553 ◽  
Author(s):  
Jorick S. Vink ◽  
A. de Koter
Keyword(s):  
Mass Loss ◽  
Variable Mass ◽  
Luminous Blue Variables

scholarly journals The winds of Luminous Blue Variables and the mass of AG Carinae

2003 ◽  
Vol 212 ◽  
pp. 259-260
Author(s):  
Jorick S. Vink ◽  
Alex de Koter
Keyword(s):  
Mass Loss ◽  
Variable Mass ◽  
Luminous Blue Variables ◽  
Theoretical Results ◽  
Loss Rates

We present radiation-driven wind models for Luminous Blue Variables and predictions of their mass-loss rates. A comparison between our theoretical results and observations of AG Car shows that the variable mass loss behaviour of LBVs is due the recombination/ionisation of Fe iv/iii and Fe iii/ii. A present-day mass of 35 M⊙ for AG Car is derived.

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 Variability in X-ray line ratios in helium-like ions of massive stars: the wind-driven case

2019 ◽  
Vol 625 ◽  
pp. A86 ◽  
Author(s):  
R. Ignace ◽  
Z. Damrau ◽  
K. T. Hole
Keyword(s):  
Mass Loss ◽  
Massive Stars ◽  
Mass Loss Rate ◽  
Variable Mass ◽  
Line Ratio ◽  
High Spectral Resolution ◽  
X Rays ◽  
Wind Integration ◽  
X Ray ◽  
Wind Variability

Context. High spectral resolution and long exposure times are providing unprecedented levels of data quality of massive stars at X-ray wavelengths. Aims. A key diagnostic of the X-ray emitting plasma are the fir lines for He-like triplets. In particular, owing to radiative pumping effects, the forbidden-to-intercombination line luminosity ratio, R = f∕i, can be used to determine the proximity of the hot plasma to the UV-bright photospheres of massive stars. Moreover, the era of large observing programs additionally allows for investigation of line variability. Methods. This contribution is the second to explore how variability in the line ratio can provide new diagnostic information about distributed X-rays in a massive star wind. We focus on wind integration for total line luminosities, taking account of radiative pumping and stellar occultation. While the case of a variable stellar radiation field was explored in the first paper, the effects of wind variability are emphasized in this work. Results. We formulate an expression for the ratio of line luminosities f∕i that closely resembles the classic expression for the on-the-spot result. While there are many ways to drive variability in the line ratio, we use variable mass loss as an illustrative example for wind integration, particularly since this produces no variability for the on-the-spot case. The f∕i ratio can be significantly modulated owing to evolving wind properties. The extent of the variation depends on how the timescale for the wind flow compares to the timescale over which the line emissivities change. Conclusions. While a variety of factors can ellicit variable line ratios, a time-varying mass-loss rate serves to demonstrate the range of amplitude and phased-dependent behavior in f∕i line ratios. Importantly, we evaluate how variable mass loss might bias measures of f∕i. For observational exposures that are less than the timescale of variable mass loss, biased measures (relative to the time-averaged wind) can result; if exposures are long, the f∕i ratio is reflective of the time-averaged spherical wind.

scholarly journals Luminous Blue Variables, cool hypergiants and some impostors in the H-R diagram

2003 ◽  
Vol 212 ◽  
pp. 38-46
Author(s):  
Roberta M. Humphreys
Keyword(s):  
Magnetic Fields ◽  
Mass Loss ◽  
Surface Activity ◽  
Massive Star ◽  
Massive Stars ◽  
High Mass ◽  
Luminous Blue Variables ◽  
Star Evolution ◽  
High Mass Loss ◽  
Massive Star Evolution

Current observations of the S Dor/LBVs and candidates and the implications for their important role in massive star evolution are reviewed. Recent observations of the cool hypergiants are altering our ideas about their evolutionary state, their atmospheres and winds, and the possible mechanisms for their asymmetric high mass loss episodes which may involve surface activity and magnetic fields. Recent results for IRC+10420, ρ Cas and VY CMa are highlighted. S Dor/LBVs in eruption, and the cool hypergiants in their high mass loss phases with their optically thick winds are not what their apparent spectra and temperatures imply; they are then ‘impostors’ on the H-R diagram. The importance of the very most massive stars, like η Carinae and the ‘supernovae impostors’ are also discussed.

scholarly journals Mass loss and evolution of hot massive stars

2008 ◽  
Vol 4 (S252) ◽  
pp. 271-281 ◽  
Author(s):  
Jorick S. Vink
Keyword(s):  
Angular Momentum ◽  
Mass Loss ◽  
Main Sequence ◽  
Gamma Ray ◽  
Massive Stars ◽  
Gamma Ray Bursts ◽  
Absorption Profile ◽  
Luminous Blue Variables ◽  
Progenitor Stars

AbstractWe discuss the role of mass loss for the evolution of the most massive stars, highlighting the role of the predicted bi-stability jump that might be relevant for the evolution of rotational velocities during or just after the main sequence. This mechanism is also proposed as an explanation for the mass-loss variations seen in the winds from Luminous Blue Variables (LBVs). These might be relevant for the quasi-sinusoidal modulations seen in a number of recent transitional supernovae (SNe), as well as for the double-throughed absorption profile recently discovered in the Hα line of SN 2005gj. Finally, we discuss the role of metallicity via the Z-dependent character of their winds, during both the initial and final (Wolf-Rayet) phases of evolution, with implications for the angular momentum evolution of the progenitor stars of long gamma-ray bursts (GRBs).

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.

The ocean response to changes of the Greenland Ice sheet in a warming climate

2020 ◽  
Author(s):  
Marianne S. Madsen ◽  
Shuting Yang ◽  
Christian Rodehacke ◽  
Guðfinna Aðalgeirsdóttir ◽  
Synne H. Svendsen ◽  
...  
Keyword(s):  
Mass Loss ◽  
Ocean Circulation ◽  
Large Scale ◽  
Climate Model ◽  
Variable Mass ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Model System ◽  
Meridional Overturning Circulation ◽  
The Arctic

<p>During recent decades, increased and highly variable mass loss from the Greenland ice sheet has been observed, implying that the ice sheet can respond to changes in ocean and atmospheric conditions on annual to decadal time scales. Changes in ice sheet topography and increased mass loss into the ocean may impact large scale atmosphere and ocean circulation. Therefore, coupling of ice sheet and climate models, to explicitly include the processes and feedbacks of ice sheet changes, is needed to improve the understanding of ice sheet-climate interactions.</p><p>Here, we present results from the coupled ice sheet-climate model system, EC-Earth-PISM. The model consists of the atmosphere, ocean and sea-ice model system EC-Earth, two-way coupled to the Parallel Ice Sheet Model, PISM. The surface mass balance (SMB) is calculated within EC-Earth, from the precipitation, evaporation and surface melt of snow and ice, to ensure conservation of mass and energy. The ice sheet model, PISM, calculates ice dynamical changes in ice discharge and basal melt as well as changes in ice extent and thickness. Idealized climate change experiments have been performed starting from pre-industrial conditions for a) constant forcing (pre-industrial control); b) abruptly quadrupling the CO<sub>2</sub> concentration; and c) gradually increasing the CO<sub>2</sub> concentration by 1% per year until 4xCO<sub>2</sub> is reached.  All three experiments are run for 350 years.</p><p>Our results show a significant impact of the interactive ice sheet component on heat and fresh water fluxes into the Arctic and North Atlantic Oceans. The interactive ice sheet causes freshening of the Arctic Ocean and affects deep water formation, resulting in a significant delay of the recovery of the Atlantic Meridional Overturning Circulation (AMOC) in the coupled 4xCO<sub>2</sub> experiments, when compared with uncoupled experiments.</p>

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.

Determination of PVC in Presence of Reactive Fillers

1987 ◽  
Vol 60 (2) ◽  
pp. 310-318 ◽  
Author(s):  
S. E. Walter
Keyword(s):  
Mass Loss ◽  
Variable Mass ◽  
Bulk Polymerization ◽  
Chlorine Content ◽  
Thermogravimetric Data ◽  
Organic Chlorine ◽  
Halogenated Polymers ◽  
Rule Out ◽  
Co2 Elimination

Abstract PVC content in thermoplastic materials can be determined from the total chlorine or more specifically from organic chlorine content. Organic chlorine content can be determined by ASTM D 1551 using the described modifications. Presence of reactive fillers such as CaCO3 results in large negative errors. When reactive fillers are expected to be present, the quantity of PVC should be determined with methods measuring total chlorine or by TGA. TGA can be used successfully for the analysis of such samples. Plasticizers and PVC stabilizers are extracted before analysis to eliminate interfering or variable mass loss in PVC thermograms. This technique can also be used for the analysis of PVC/NBR mixtures. In unknown compounds, the technique should be used in conjunction with FTIR analysis to facilitate polymer identification and to rule out interference by other halogenated polymers. Excess of unreacted CaCO3 can be observed and the amount determined from thermograms. Remaining CaCO3 can be determined from mass loss due to elimination of CO2. If a cooling step is introduced before the atmosphere is switched from nitrogen to air, a clearer separation of residue oxidation and CO2 elimination are obtained. On reheating, residue oxidation then takes place between 450 and 500°C, well separated from CO2 elimination at about 700°C. Variation of thermograms using PVC obtained by different polymerization procedures needs to be further investigated. Structural differences and thermal stability of PVC samples made by emulsion, suspension, and bulk polymerization have been examined by various techniques, but no thermogravimetric data are given.

Attitude Behavior of a Variable Mass Cylinder

1995 ◽  
Vol 62 (4) ◽  
pp. 935-940 ◽  
Author(s):  
F. O. Eke ◽  
Song-Min Wang
Keyword(s):  
Mass Loss ◽  
Variable Mass ◽  
Cylindrical Body ◽  
Rigid Bodies ◽  
Transverse Motion ◽  
Attitude Motion ◽  
Key Factors ◽  
Great Contrast ◽  
Attitude Behavior

This paper examines the attitude motion of a cylindrical body with mass loss. It is found that mass variation can have a substantial influence on the behavior of such a system. Specifically, the initial dimensions as well as the manner in which mass loss affects system inertia are found to be key factors in the determination of the characteristics of the lateral motion of the system. In great contrast to the attitude behavior of spinning rigid bodies, oblate variable mass cylinders exhibit divergent transverse attitude motion, while the transverse motion of prolate variable mass cylinders is found to be bounded in general.

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