scholarly journals Effect of a Dipole Magnetic Field on Stellar Mass-Loss

2016 ◽  
Vol 12 (S329) ◽  
pp. 242-245
Author(s):  
Chris Bard ◽  
Richard Townsend
Keyword(s):  
Magnetic Fields ◽  
Mass Loss ◽  
Large Scale ◽  
Massive Star ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Local Environment ◽  
Surface Mass ◽  
B Stars ◽  
Dipole Magnetic Field

AbstractMassive star winds greatly influence the evolution of both their host star and local environment though their mass-loss rates, but current radiative line-driven wind models do not incorporate any magnetic effects. Recent surveys of O and B stars have found that about ten percent have large-scale, organized magnetic fields. These massive-star magnetic fields, which are thousands of times stronger than the Sun’s, affect the inherent properties of their own winds by changing the mass-loss rate. To quantify this, we present a simple surface mass-flux scaling over the stellar surface which can be easily integrated to get an estimate of the mass-loss rate for a magnetic massive star. The overall mass-loss rate is found to decrease by factors of 2-5 relative to the non-magnetic CAK mass-loss rate.

scholarly journals On the significance of mass loss for the evolution of massive stars

1981 ◽  
Vol 59 ◽  
pp. 265-270
Author(s):  
L.R. Yungelson ◽  
A.G. Massevitch ◽  
A.V. Tutukov
Keyword(s):  
Mass Loss ◽  
Stellar Wind ◽  
Loss Rate ◽  
Massive Stars ◽  
Mass Loss Rate ◽  
Hydrogen Burning ◽  
B Stars ◽  
The Core ◽  
Input Parameters ◽  
Satisfactory Theory

It is shown that mass loss by stellar wind with rates observed in O, B-stars cannot change qualitatively their evolution in the core hydrogen-burning stage. The effects, that are usually attributed to the mass loss, can be explained by other causes: e.g., duplicity or enlarged chemically homogeneous stellar cores.The significance of mass loss by stellar wind for the evolution of massive stars was studied extensively by numerous authors (see e.g. Chiosi et al. (1979) and references therein). However, the problem is unclear as yet. There does not exist any satisfactory theory of mass loss by stars. Therefore one is usually forced to assume that mass loss rate depends on some input parameters.

scholarly journals The luminosity distribution of RSGs to test their mass-loss rate

2015 ◽  
Vol 11 (A29B) ◽  
pp. 454-454 ◽  
Author(s):  
Cyril Georgy ◽  
Sylvia Ekström
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Massive Star ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Red Supergiants ◽  
Loss Rates

AbstractThe red supergiant phase is an important phase of the evolution of massive star, as it mostly determines its final stages. One of the most important driver of the evolution during this phase is mass loss. However, the mass-loss rates prescription used for red supergiants in current stellar evolution models are still very inaccurate.Varying the mass-loss rate makes the star evolve for some time in yellow/blue regions of the HRD, modifying the number of RSGs in some luminosity ranges. Figure 1 shows how the luminosity distribution of RSGs is modified for various mass-loss prescriptions. This illustrates that it is theoretically possible to determine at least roughly what is the typical mass loss regime of RSGs in a stellar evolution perspective.

Applicability of FLASH-CAT Model to Cable Tray Fire Modeling in Zone Model BRI2002

2020 ◽  
Author(s):  
Koji Shirai ◽  
Koji Tasaka ◽  
Toshiko Udagawa
Keyword(s):  
Mass Loss ◽  
Large Scale ◽  
Fire Test ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Zone Model ◽  
Gas Temperature ◽  
Fire Source ◽  
Gas Burner ◽  
Tray Fire

Abstract To clarify the heat and smoke propagation in multi-compartments under the spread of cable fire, a large-scale multi-compartment fire test (hereinafter the CFS-2 test) was performed by the Institut de Radioprotection et de Sûreté Nucléaire (IRSN) in France within the framework promoted by the Nuclear Energy Agency (NEA) in Organization for Economic Co-operation and Development (OECD) program PRISME2 (OECD/NEA, 2017). In the CFS-2 test, two rooms of a large-scale facility were adopted and these rooms have an identical volume (120 m3) enclosed with fire walls and were connected by a doorway (0.8 m in width and 2.17 m in height). As a fire source, five-layer cable trays (tray length of 2.4m, tray width of 0.45m and separation distance between trays of 0.3 m) with a fire-retardant PVC cable (77 kg) were used and ignited by a propane gas burner. The power level of the propane gas burner was set to around 80 kW. Moreover, all rooms were mechanically ventilated, and the renewal rate was 15 times per hour (3600 m3/h). During the fire test, the mass loss rate of fuel, gas and soot mass concentration, gas temperature, and etc. were measured. The measured peak values of the HRR, the mass loss rate and gas temperature were about 800 kW, 58 g/s and greater than 600 °C, respectively (Zavaleta, 2017). As a fire model predicting fire characteristics in a compartment, a two-zone model, which divides the fire room into the hot smoke upper layer and lower layer consisting of cool fresh air, is widely used due to the advantages of the brevity of the calculation routine and the reliability of the calculation results. Among them, the BRI2 series, developed in Japan, is now reaching the current BRI2002 software (Wakamatsu, 2004) after several upgrades to improve the calculation precision. The Central Research Institute of Electric Power Industry (CRIEPI) introduced the cable tray fire source model based on the FLASH-CAT (Flame Spread over Horizontal Cable Trays) developed by National Institute of Standards and Technology (NIST) (McGrattan, 2012) into the zone code BRI2002. By comparing the numerical results with the experimental values measured during the CFS-2 test, the methodology for ignition time delay of each tray and horizontal flame propagation speed for each tray were discussed.

scholarly journals Ionization Structure and Mass Loss for Rapidly-Rotating Near Main-Sequence B Stars

2000 ◽  
Vol 175 ◽  
pp. 632-635
Author(s):  
J.E. Bjorkman ◽  
B.P. Abbott
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Main Sequence ◽  
Mass Loss Rate ◽  
Spherically Symmetric ◽  
Line Profiles ◽  
Disk Model ◽  
B Stars ◽  
Ionization Structure

AbstractUsing the wind-compressed disk model to determine the density and velocity of a rapidly rotating wind, we calculate the 2-D ionization structure and corresponding line profiles. We find that previous estimates of the mass-loss rate based on spherically symmetric models may be a factor of 5–10 too small.

scholarly journals Influence of Coronal Mass Ejections from the Red Dwarf Component on the Accretion Pattern in CVs and LMXBs

1995 ◽  
Vol 151 ◽  
pp. 195-196
Author(s):  
Roberto Minarini ◽  
Grigory Beskin
Keyword(s):  
Mass Loss ◽  
Coronal Mass Ejections ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Magnetic Activity ◽  
The Sun ◽  
Surface Mass ◽  
Red Dwarfs ◽  
Low Mass ◽  
Transient Events

Low-mass main sequence stars show a magnetic activity similar to the Sun and as a consequence they lose mass in the form of a variable stellar wind. In the latest spectral types (red dwarfs) the activity and the mass loss rate appear to increase by a large factor of ∼ 103 with respect to the solar case, reaching Ṁ ∼ 2 · 10−11 M⊙/yr (Badalyan & Livshits 1992, Katsova 1993). The same happens for coronal mass ejections (CMEs), which are the most relevant transient events of mass loss in these objects. In the Sun, these appear as bubbles of coronal material, with dimensions of some fraction of the solar surface, mass M ≃ 2 · 1014 - 2 · 1016 g and ejection velocity v ≃ 3 · 107 - 2 · 108 cm/s, with an instantaneous mass loss rate Ṁ ∽ 10−13 - 10−11 M⊙/yr (Wagner 1984). In red dwarfs, as recently observed, the ejection velocities are higher, up to v ≃ 3 · 108 cm/s and the mass loss rate can reach the value Ṁ ≃ 10−8 M⊙/yr (Mullan et al. 1989, Houdebine et al. 1990). In both cases, the observations suggest that a bubble expands, once ejected, with a velocity of several hundreds of km/s.

scholarly journals The WR/WRProgenitor Number Ratio: Theory and Observations

1991 ◽  
Vol 143 ◽  
pp. 553-553
Author(s):  
D. Vanbeveren
Keyword(s):  
Mass Loss ◽  
Massive Star ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Mass Range ◽  
Theoretical Explanation ◽  
The Sun ◽  
Evolutionary Computations ◽  
Number Ratio ◽  
Observational Uncertainty

A direct comparison between the observed WR/WRprogenitor number ratio within 2.5 kpc from the sun and the predicted value (using evolutionary computations of single stars of Maeder and Meynet, 1987, A.&A.182, 243) reveals a discrepancy of at least a factor of two. In a previous study (Vanbeveren, 1990, A.&A. in press) I proposed a solution based on the incompleteness of the observed OB type star sample within 2.5 kpc from the sun. In this summary, I propose a theoretical explanation for the discrepancy. The theoretically predicted WR/WRprogenitor number ratio critically depends on the adopted M formalism in evolutionary computations during the red supergiant phase (RSG) of a massive star, especially in the mass range 20-40 M⊙. Since any M formalism predicts the mass loss rate with an uncertainty of at least a factor of two, I have tried to look for solutions for the WR/WRprogenitor problem by using different values of M during the RSG (in the mass range 20-40 M⊙); the M values and formalism that were adopted were always choosen within the observational uncertainty (i.e. within a factor of two when compared to the formalism used by Maeder and Meynet, 1987).

scholarly journals Diffusion and He Overabundances: Hydrodynamical Implications

1985 ◽  
Vol 87 ◽  
pp. 453-469
Author(s):  
G. Michaud
Keyword(s):  
Magnetic Fields ◽  
Mass Loss ◽  
White Dwarfs ◽  
Loss Rate ◽  
Main Sequence ◽  
Mass Loss Rate ◽  
Horizontal Branch ◽  
Main Sequence Stars ◽  
Horizontal Branch Stars ◽  
Cno Abundances

AbstractIn the absence of mass loss, diffusion leads to underabundances of He in main sequence stars. Because of a very strong observational link with Ap and He weak stars, it has however been suggested that diffusion is the explanation for the He rich stars of the upper main sequence. This requires a mass loss rate of 10−12 Mo yr−1 or slightly lower. The mass loss rate must decrease as Teff increases. Magnetic fields must apparently be involved to reduce the mass loss rate. Since this model predicts that the CNO abundances should be normal in the cooler He rich stars, it leads to a clear observational test. Detailed calculations should be made to confirm the importance of this test. The effects of separation in the wind, the atmosphere and the envelope are discussed to conclude that separation in the atmosphere is likely to be most important. The importance of diffusion for He rich white dwarfs and horizontal branch stars are briefly discussed.

The solar proxy κ1 Cet and the planetary habitability around the young Sun

2016 ◽  
Vol 12 (S328) ◽  
pp. 338-349
Author(s):  
J.-D. do Nascimento ◽  
A. A. Vidotto ◽  
P. Petit ◽  
C. Folsom ◽  
G. F. Porto de Mello ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Mass Loss ◽  
Large Scale ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Field Measurements ◽  
Stellar Winds ◽  
Surface Magnetic Field ◽  
Magnetic Strength ◽  
Planetary Habitability

AbstractAmong the solar proxies, κ1 Cet, stands out as potentially having a mass very close to solar and a young age. We report magnetic field measurements and planetary habitability consequences around this star, a proxy of the young Sun when life arose on Earth. Magnetic strength was determined from spectropolarimetric observations and we reconstruct the large-scale surface magnetic field to derive the magnetic environment, stellar winds, and particle flux permeating the interplanetary medium around κ1 Cet. Our results show a closer magnetosphere and mass-loss rate 50 times larger than the current solar wind mass-loss rate when Life arose on Earth, resulting in a larger interaction via space weather disturbances between the stellar wind and a hypothetical young-Earth analogue, potentially affecting the habitability. Interaction of the wind from the young Sun with the planetary ancient magnetic field may have affected the young Earth and its life conditions.

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