scholarly journals 3D MHD simulations and synthetic radio emission from an oblique rotating magnetic massive star

2019 ◽  
Vol 489 (3) ◽  
pp. 3251-3268
Author(s):  
S Daley-Yates ◽  
I R Stevens ◽  
A ud-Doula
Keyword(s):  
Mass Loss ◽  
Massive Star ◽  
Thermal Emission ◽  
Mass Loss Rate ◽  
Cylindrical Symmetry ◽  
Phase Dependence ◽  
Spectral Flux ◽  
Oblique Rotator ◽  
Spherical And Cylindrical Symmetry

ABSTRACT We have performed 3D isothermal MHD simulation of a magnetic rotating massive star with a non-zero dipole obliquity and predicted the radio/sub-mm observable light curves and continuum spectra for a frequency range compatible with ALMA. From these results we also compare the model input mass-loss to that calculated from the synthetic thermal emission. Spherical and cylindrical symmetry is broken due to the obliquity of the stellar magnetic dipole resulting in an inclination and phase dependence of both the spectral flux and inferred mass-loss rate, providing testable predictions of variability for oblique rotator. Both quantities vary by factors between 2 and 3 over a full rotational period of the star, demonstrating that the role of rotation as critical in understanding the emission. This illustrates the divergence from a symmetric wind, resulting in a two-armed spiral structure indicative of an oblique magnetic rotator. We show that a constant spectral index, α, model agrees well with our numerical prediction for a spherical wind for ν < 103 GHz; however it is unable to capture the behaviour of emission at ν > 103 GHz. As such we caution the use of such constant α models for predicting emission from non-spherical winds such as those which form around magnetic massive stars.

scholarly journals Line-driven ablation of circumstellar discs – IV. The role of disc ablation in massive star formation and its contribution to the stellar upper mass limit

2018 ◽  
Vol 483 (4) ◽  
pp. 4893-4900 ◽  
Author(s):  
Nathaniel Dylan Kee ◽  
Rolf Kuiper
Keyword(s):  
Star Formation ◽  
Massive Star ◽  
Loss Rate ◽  
Massive Stars ◽  
Mass Loss Rate ◽  
Ablation Rate ◽  
Massive Star Formation ◽  
Future Studies ◽  
Accretion Rates

Abstract Radiative feedback from luminous, massive stars during their formation is a key process in moderating accretion on to the stellar object. In the prior papers in this series, we showed that one form such feedback takes is UV line-driven disc ablation. Extending on this study, we now constrain the strength of this effect in the parameter range of star and disc properties appropriate to forming massive stars. Simulations show that ablation rate depends strongly on stellar parameters, but that this dependence can be parameterized as a nearly constant, fixed enhancement over the wind mass-loss rate, allowing us to predict the rate of disc ablation for massive (proto)stars as a function of stellar mass and metallicity. By comparing this to predicted accretion rates, we conclude that ablation is a strong feedback effect for very massive (proto)stars which should be considered in future studies of massive star formation.

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 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.

scholarly journals CONSTRAINING THE PULSAR POWER IN GAMMA-RAY BINARIES THROUGH THERMAL X-RAY EMISSION

2012 ◽  
Vol 08 ◽  
pp. 132-137
Author(s):  
VÍCTOR ZABALZA ◽  
VALENTÍ BOSCH-RAMON ◽  
JOSEP MARIA PAREDES
Keyword(s):  
Stellar Wind ◽  
Binary Systems ◽  
Massive Star ◽  
Gamma Ray ◽  
Thermal Emission ◽  
Mass Loss Rate ◽  
X Rays ◽  
Orbital Inclination ◽  
X Ray ◽  
Pulsar Wind

Gamma-ray binaries are binary systems that show non-thermal broadband emission from radio to gamma rays. If the system comprises a massive star and a young non-accreting pulsar, their winds collide producing non-thermal emission, most likely from the shocked pulsar wind. Thermal X-rays are expected from the shocked stellar wind, with a spectrum akin to the one observed in massive star binaries. The goal of this work is, through the study of the thermal X-ray emission from the shocked stellar wind in pulsar gamma-ray binaries, constrain the pulsar spin-down luminosity and the stellar wind properties. A semi-analytic model is developed to compute the thermal X-ray emission from the shocked stellar wind in pulsar gamma-ray binaries. The model results are compared with XMM-Newton observations of LS 5039, a candidate pulsar gamma-ray binary with a strong stellar wind. Exploring the range of possible values for the stellar mass-loss rate and orbital inclination, we obtain an upper limit on the pulsar spin-down luminosity of 6 × 1036 erg s-1. We conclude that, to explain the non-thermal luminosity of LS 5039 in the pulsar wind scenario, a non-thermal to spin-down luminosity ratio very close to unity may be required.

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 The enigmatic binary system HD 5980

2019 ◽  
Vol 486 (1) ◽  
pp. 725-742 ◽  
Author(s):  
D John Hillier ◽  
Gloria Koenigsberger ◽  
Yaël Nazé ◽  
Nidia Morrell ◽  
Rodolfo H Barbá ◽  
...  
Keyword(s):  
Mass Loss ◽  
Emission Line ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Phase Dependence ◽  
Wind Speeds ◽  
Line Intensities ◽  
Orbital Phase ◽  
Emission Line Spectrum ◽  
Luminous Blue Variable

Abstract The Small Magellanic Cloud multiple system HD 5980 contains a luminous blue variable (LBV) that underwent a major eruption in 1994, and whose current spectrum is that of a hydrogen-rich Wolf–Rayet (WR) star. Since the eruption, the wind mass-loss rate has been declining while wind speeds have been steadily increasing. Observations obtained in 2014 when Star A (the LBV) eclipses Star B indicate that the fitted mass-loss rate and luminosity have reached the lowest values ever determined for such spectra: $\dot{M}$  = 4.5 × 10−5$\mathrm{M}_\odot \, \hbox{yr}^{-1}$, L  = 1.7 × 106 L⊙. In addition, the radius of the LBV’s continuum-emitting region is similar to that derived from the eclipse light curves of the late 1970s. Hence, it appears to have attained a similar ‘low’ state to that of the late 1970s. While a good fit to the emission spectrum is obtained using a cmfgen model, there are discrepancies in the UV. In particular, the extent of the observed absorption profiles is ∼1000 km s−1 greater than predicted by the emission-line intensities. Further, HST UV observations obtained in 2016, when Star A is eclipsed by Star B, show unusual P Cygni profiles that are not easily explained. Surprisingly the 2016 emission-line spectrum is similar to that at the opposite eclipse obtained in 2014. The complex UV profiles are likely to arise as a consequence of the dynamics of the wind–wind collision and radiative braking, both of which will cause significant departures from spherical symmetry, and have a strong orbital phase dependence. However, other scenarios, such as intrinsically aspherical winds, cannot be ruled out.

scholarly journals The metallicity dependence of WR winds

2016 ◽  
Vol 12 (S329) ◽  
pp. 171-175 ◽  
Author(s):  
R. Hainich ◽  
T. Shenar ◽  
A. Sander ◽  
W.-R. Hamann ◽  
H. Todt
Keyword(s):  
Mass Loss ◽  
Metal Content ◽  
Loss Rate ◽  
Massive Stars ◽  
Mass Loss Rate ◽  
Host Galaxy ◽  
Empirical Relations ◽  
Iron Abundance ◽  
Low Metallicity

AbstractWolf-Rayet (WR) stars are the most advanced stage in the evolution of the most massive stars. The strong feedback provided by these objects and their subsequent supernova (SN) explosions are decisive for a variety of astrophysical topics such as the cosmic matter cycle. Consequently, understanding the properties of WR stars and their evolution is indispensable. A crucial but still not well known quantity determining the evolution of WR stars is their mass-loss rate. Since the mass loss is predicted to increase with metallicity, the feedback provided by these objects and their spectral appearance are expected to be a function of the metal content of their host galaxy. This has severe implications for the role of massive stars in general and the exploration of low metallicity environments in particular. Hitherto, the metallicity dependence of WR star winds was not well studied. In this contribution, we review the results from our comprehensive spectral analyses of WR stars in environments of different metallicities, ranging from slightly super-solar to SMC-like metallicities. Based on these studies, we derived empirical relations for the dependence of the WN mass-loss rates on the metallicity and iron abundance, respectively.

scholarly journals Winds from Cataclysmic Variables

1997 ◽  
Vol 163 ◽  
pp. 465-474
Author(s):  
J. E. Drew
Keyword(s):  
Boundary Layer ◽  
Mass Loss ◽  
Radiation Pressure ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Cataclysmic Variables ◽  
Recent Developments ◽  
Orbital Phase ◽  
The Impact

AbstractThe winds associated with high states of non-magnetic (diskaccreting) cataclysmic variables are described and discussed. A quick summary of the basic phenomenology is given, and followed by a presentation of some of the more important recent developments in our understanding. The near-ubiquity of orbital-phase linked variability of the UV resonance lines (generally thought of as mainly wind-produced) is noted and its implications are considered. The impact of the much lower-thanexpected boundary layer luminosity upon mass loss rate determinations is also discussed. Current work on the role of radiation pressure (mediated by line opacity) is placed in context.

scholarly journals The Evolutionary State of Zeta Aurigae

1982 ◽  
Vol 69 ◽  
pp. 153-156
Author(s):  
Robert D. Chapman
Keyword(s):  
Mass Loss ◽  
Flow Velocity ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
The State ◽  
Wind Flow ◽  
Qualitative Model ◽  
Phase Dependence ◽  
Evolutionary State

Ultraviolet studies, originally undertaken to ascertain the state of the atmosphere of the K-supergiant component of the zeta Aurigae system, have been sidetracked by the discovery of significant accretion effects. An analysis of the phase dependence of the profiles of resonance lines in Mg II and C IV has led to a qualitative model of the wind flow from the K star. At the position of the B star, the flow velocity is about 100 km/sec and the density is 3 x 10-6 cm-3 , leading to a mass loss rate of 2 x 10-8 solar masses per year. This wind interacts with the B star in a shock, which will be described, leading to accretion on the B star at a rate of 4 x 10-10 solar masses per year.

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