scholarly journals Observational connections between LBV’s and other stars, with emphasis on Wolf-Rayet stars

1989 ◽  
Vol 113 ◽  
pp. 229-240
Author(s):  
A. F. J. Moffat ◽  
L. Drissen ◽  
C. Robert
Keyword(s):  
Mass Loss ◽  
Massive Stars ◽  
Underlying Mechanism ◽  
High Mass ◽  
Strong Line ◽  
Essential Step ◽  
High Mass Loss ◽  
Loss Rates ◽  
R Domain

Abstract.We suggest that the LBV mechanism is an essential step to “force” massive stars (M(ZAMS) ≥ 40M⊙) to finally enter the Wolf-Rayet (W-R) domain in the Hertzsprung-Russel diagram (HRD). Just as massive supergiants showincreasingvariability as theyapproachthe Humphreys-Davidson (H-D)instability limit (horizontally in the HRD diagram), so the W-R stars showdecreasingvariability as theyrecede fromthe H-D limit (at first horizontally into the WNL domain, then, with their high mass loss rates, plunging irreversably downwards as ever hotter, smaller and fainter, strong-line W-R stars). Among the W-R stars, the luminous WNL subtypes (especially WN8) are the most variable, probably as a consequence of blob ejection in the wind. The underlying mechanism which triggers this ejection is possibly related to wind instabilities and may thus be quite different from the source of variability in luminous supergiants or LBV’s in quiescence, where photospheric effects dominate.

scholarly journals ISOCAM and DENIS Survey of 0.5 square degrees in the Bar of the LMC. Detection of the whole TP-AGB Star Population

1999 ◽  
Vol 191 ◽  
pp. 561-566
Author(s):  
C. Loup ◽  
E. Josselin ◽  
M.-R. Cioni ◽  
H.J. Habing ◽  
J.A.D.L. Blommaert ◽  
...  
Keyword(s):  
Mass Loss ◽  
High Mass ◽  
Evolutionary Models ◽  
Agb Stars ◽  
Complete Sample ◽  
High Mass Loss ◽  
Low Mass ◽  
The One ◽  
Good Agreement ◽  
Loss Rates

We surveyed 0.5 square degrees in the Bar of the LMC with ISOCAM at 4.5 and 12 μm, and with DENIS in the I, J, and Ks bands. Our goal was to build a complete sample of Thermally-Pulsing AGB stars. Here we present the first analysis of 0.14 square degrees. In total we find about 300 TP-AGB stars. Among these TP-AGB stars, 9% are obscured AGB stars (high mass-loss rates); 9 of them were detected by IRAS, and only 1 was previously identified. Their luminosities range from 2 500 to 14 000 L⊙, with a distribution very similar to the one of optical TP-AGB stars (i.e. those with low mass-loss rates). Such a luminosity distribution, as well as the percentage of obscured stars among TP-AGB stars, is in very good agreement with the evolutionary models of Vassiliadis & Wood (1993) if most of the TP-AGB stars that we find have initial masses smaller than 1.5 to 2 M⊙.

scholarly journals Progenitors of early-time interacting supernovae

2020 ◽  
Vol 496 (2) ◽  
pp. 1325-1342 ◽  
Author(s):  
Ioana Boian ◽  
Jose H Groh
Keyword(s):  
Mass Loss ◽  
Large Scale ◽  
Massive Stars ◽  
Early Time ◽  
High Mass ◽  
Single Star ◽  
Circumstellar Material ◽  
Wide Range ◽  
Wind Velocities ◽  
Loss Rates

ABSTRACT We compute an extensive set of early-time spectra of supernovae interacting with circumstellar material using the radiative transfer code cmfgen. Our models are applicable to events observed from 1 to a few days after explosion. Using these models, we constrain the progenitor and explosion properties of a sample of 17 observed interacting supernovae at early times. Because massive stars have strong mass-loss, these spectra provide valuable information about supernova progenitors, such as mass-loss rates, wind velocities, and surface abundances. We show that these events span a wide range of explosion and progenitor properties, exhibiting supernova luminosities in the 108 to 1012 L⊙ range, temperatures from 10 000 to 60 000 K, progenitor mass-loss rates from a few 10−4 up to 1 M⊙ yr−1, wind velocities from 100 to 800 km s−1, and surface abundances from solar-like to H-depleted. Our results suggest that many progenitors of supernovae interacting with circumstellar material have significantly increased mass-loss before explosion compared to what massive stars show during the rest of their lifetimes. We also infer a lack of correlation between surface abundances and mass-loss rates. This may point to the pre-explosion mass-loss mechanism being independent of stellar mass. We find that the majority of these events have CNO-processed surface abundances. In the single star scenario this points to a preference towards high-mass RSGs as progenitors of interacting SNe, while binary evolution could impact this conclusion. Our models are publicly available and readily applicable to analyse results from ongoing and future large-scale surveys such as the Zwicky Transient Factory.

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 Wolf-Rayet stars in starbursts: Effects of a change of mass loss rate

1995 ◽  
Vol 163 ◽  
pp. 318-319
Author(s):  
G. Meynet
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Main Sequence ◽  
Mass Loss Rate ◽  
High Mass ◽  
New Models ◽  
Theoretical Predictions ◽  
High Mass Loss ◽  
Low Metallicity ◽  
Loss Rates

We present here starburst models based on the most recent grids of stellar evolutionary tracks obtained by the Geneva group. These new models, computed with enhanced mass loss rates during the main sequence and the Wolf-Rayet WNL phases, very well reproduce the luminosities, surface abundances and statistics of WR stars (Maeder & Meynet 1994). This change of the mass loss rates considerably affects the way the WR stars, born in a starburst's episode, are distributed among the different WR subtypes. We compare the theoretical predictions with recent observations and conclude that: (1) to reproduce the high observed ratios of WNL to O-type stars, a flat IMF seems to be required; and (2) the models which reproduce the best the observed characteristics of WR stars, i.e., those computed with an enhanced mass loss rate, can also account for the observed properties of the WR populations observed in starbursts. Moreover, the possible presence of numerous WC stars found in the low metallicity He2-10 A starburst by Vacca and Conti (1992), can only be accounted for when the high mass loss rate stellar models are used.

scholarly journals Wolf-Rayet stars in I Zw 18

1999 ◽  
Vol 193 ◽  
pp. 606-607
Author(s):  
Francoid Legrand ◽  
Daniel Kunth ◽  
Jean-René Roy ◽  
J. Miguel Mas-Hesse ◽  
Jeremy R. Walsh
Keyword(s):  
Mass Loss ◽  
Emission Line ◽  
High Mass ◽  
Starburst Galaxy ◽  
Individual Stars ◽  
Binary Channel ◽  
High Mass Loss ◽  
Low Metallicity ◽  
Loss Rates ◽  
Integrated Luminosity

Wolf-Rayet stars have been detected in the NW region of the metal–poor starburst galaxy I Zw 18. The integrated luminosity and FWHM of the bumps at 4650 Å and 5808 Å are consistent with the presence of a few individual stars of WC4 or WC5 type. The unexpected presence of WC stars in such a low-metallicity galaxy could, however, be explained by high mass loss rates, or alternatively favor a binary channel for WR formation. WC stars could also account for the strong and narrow He II 4686Å emission line which peaks co-spatially with the WR bump emission (see Schaerer 1996).

scholarly journals Effects of a stochastic initial mass function on the upper main sequence band

1981 ◽  
Vol 59 ◽  
pp. 293-296
Author(s):  
C. Chiosi ◽  
L. Greggio
Keyword(s):  
Mass Loss ◽  
Effective Temperature ◽  
Main Sequence ◽  
Massive Stars ◽  
Mass Function ◽  
Initial Mass Function ◽  
High Mass ◽  
Initial Mass ◽  
Sequence Band ◽  
High Mass Loss

The theoretical (Mb versus Log Te) HR diagram for the brightest galactic OB stars shows an upper boundary for the luminosity, which is characterized by a decreasing luminosity with decreasing effective temperature (Humphreys and Davidson, 1979). The existence of this limit was interpreted by Chiosi et al. (1978) as due to the effect of mass loss by stellar wind on the evolution of most massive stars in core H-burning phase. In fact, evolutionary models calculated at constant mass cover a wider and wider range in effective temperature as the initial mass increases during the main sequence phase. On the contrary, sufficiently high mass-loss rates make the evolutionary sequences of most massive stars (M 60⩾Mʘ) shrink toward the zero age main sequence whenever, due to mass loss, CNO processed material is brought to the surface (Chiosi et al., 1978; de Loore et al., 1978; Maeder, 1980).

scholarly journals Helium-star Mass Loss and Its Implications for Black Hole Formation and Supernova Progenitors

2002 ◽  
Vol 19 (2) ◽  
pp. 233-237 ◽  
Author(s):  
Onno R. Pols ◽  
Jasinta D. M. Dewi
Keyword(s):  
Black Hole ◽  
Mass Loss ◽  
High Mass ◽  
Binary Interaction ◽  
Compact Binary ◽  
Helium Stars ◽  
High Mass Loss ◽  
Helium Star ◽  
Black Hole Masses ◽  
Loss Rates

AbstractRecently the observationally derived stellar-wind mass-loss rates for Wolf-Rayet stars, or massive naked helium stars, have been revised downwards by a substantial amount. We present evolutionary calculations of helium stars incorporating such revised mass-loss rates, as well as mass transfer to a close compact binary companion. Our models reach final masses well in excess of 10 M⊙, consistent with the observed masses of black holes in X-ray binaries. This resolves the discrepancy found with previously assumed high mass-loss rates between the final masses of stars which spend most of their helium-burning lifetime as Wolf-Rayet stars (˜3 M⊙) and the minimum observed black hole masses (6 M⊙). Our calculations also suggest that there are two distinct classes of progenitors for Type Ic supernovae: one with very large initial masses (35 M⊙), which are still massive when they explode and leave black hole remnants, and one with moderate initial masses (˜12–20 M⊙) undergoing binary interaction, which end up with small pre-explosion masses and leave neutron star remnants.

scholarly journals First detection of X-ray line emission from Type IIn supernova 1978K with XMM-Newton’s RGS

2020 ◽  
Vol 72 (2) ◽  
Author(s):  
Yuki Chiba ◽  
Satoru Katsuda ◽  
Takashi Yoshida ◽  
Koh Takahashi ◽  
Hideyuki Umeda
Keyword(s):  
Mass Loss ◽  
Surface Composition ◽  
Massive Stars ◽  
Line Emission ◽  
Asymptotic Giant Branch ◽  
High Mass ◽  
Expansion Velocity ◽  
X Ray ◽  
Elemental Abundances ◽  
High Mass Loss

Abstract We report on robust measurements of elemental abundances of the Type IIn supernova SN 1978K, based on the high-resolution X-ray spectrum obtained with the Reflection Grating Spectrometer (RGS) onboard XMM-Newton. The RGS clearly resolves a number of emission lines, including N Ly$\alpha$, O Ly$\alpha$, O Ly$\beta$, Fe xvii, Fe xviii, Ne He$\alpha$, and Ne Ly$\alpha$ for the first time from SN 1978K. The X-ray spectrum can be represented by an absorbed, two-temperature thermal emission model, with temperatures of $kT \sim 0.6$ keV and 2.7 keV. The elemental abundances are obtained to be N $=$$2.36_{{-0.80}}^{{+0.88}}$, O $=$$0.20 \pm {0.05}$, Ne $=$$0.47 \pm {0.12}$, Fe $=$$0.15_{{-0.02}}^{{+0.01}}$ times the solar values. The low metal abundances except for N show that the X-ray emitting plasma originates from the circumstellar medium blown by the progenitor star. The abundances of N and O are far from the CNO-equilibrium abundances expected for the surface composition of a luminous blue variable, and resemble the H-rich envelope of less massive stars with masses of 10–25$\, M_{\odot }$. Together with other peculiar properties of SN 1978K, i.e., a low expansion velocity of 500–1000 km s$^{-1}$ and SN IIn-like optical spectra, we propose that SN 1978K is a result of either an electron-capture SN from a super asymptotic giant branch star, or a weak Fe core-collapse explosion of a relatively low-mass ($\sim \! \! 10\, M_{\odot }$) or high-mass ($\sim$20–25$\, M_{\odot }$) red supergiant star. However, these scenarios cannot naturally explain the high mass-loss rate of the order of $\dot{M} \sim 10^{-3}\, M_{\odot }\:{\rm yr^{-1}}$ over $\gtrsim$1000 yr before the explosion, which is inferred by this work as well as many other earlier studies. Further theoretical studies are required to explain the high mass-loss rates at the final evolutionary stages of massive stars.

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