scholarly journals Why binary interaction does not necessarily dominate the formation of Wolf-Rayet stars at low metallicity

2020 ◽  
Vol 634 ◽  
pp. A79 ◽  
Author(s):  
T. Shenar ◽  
A. Gilkis ◽  
J. S. Vink ◽  
H. Sana ◽  
A. A. C. Sander
Keyword(s):  
Mass Range ◽  
Magellanic Clouds ◽  
Initial Mass ◽  
Binary Interaction ◽  
Additional Contribution ◽  
Apparent Contradiction ◽  
Single Star ◽  
Binary Channel ◽  
The Galaxy ◽  
Low Metallicity

Context. Classical Wolf-Rayet (WR) stars are massive, hydrogen-depleted, post main-sequence stars that exhibit emission-line dominated spectra. For a given metallicity Z, stars exceeding a certain initial mass MsingleWR(Z) can reach the WR phase through intrinsic mass-loss or eruptions (single-star channel). In principle, stars of lower masses can reach the WR phase via stripping through binary interactions (binary channel). Because winds become weaker at low Z, it is commonly assumed that the binary channel dominates the formation of WR stars in environments with low metallicity such as the Small and Large Magellanic Clouds (SMC, LMC). However, the reported WR binary fractions of 30−40% in the SMC (Z = 0.002) and LMC (Z = 0.006) are comparable to that of the Galaxy (Z = 0.014), and no evidence for the dominance of the binary channel at low Z could be identified observationally. Here, we explain this apparent contradiction by considering the minimum initial mass MspecWR(Z) needed for the stripped product to appear as a WR star. Aims. By constraining MspecWR(Z) and MsingleWR(Z), we estimate the importance of binaries in forming WR stars as a function of Z. Methods. We calibrated MspecWR using the lowest-luminosity WR stars in the Magellanic Clouds and the Galaxy. A range of MsingleWR values were explored using various evolution codes. We estimated the additional contribution of the binary channel by considering the interval [MspecWR(Z), MsingleWR(Z)], which characterizes the initial-mass range in which the binary channel can form additional WR stars. Results. The WR-phenomenon ceases below luminosities of log L ≈ 4.9, 5.25, and 5.6 [L⊙] in the Galaxy, the LMC, and the SMC, respectively, which translates to minimum He-star masses of 7.5, 11, 17 M⊙ and minimum initial masses of MspecWR = 18, 23, 37 M⊙. Stripped stars with lower initial masses in the respective galaxies would tend not to appear as WR stars. The minimum mass necessary for self-stripping, MsingleWR(Z), is strongly model-dependent, but it lies in the range 20−30, 30−60, and ≳40 M⊙ for the Galaxy, LMC, and SMC, respectively. We find that that the additional contribution of the binary channel is a non-trivial and model-dependent function of Z that cannot be conclusively claimed to be monotonically increasing with decreasing Z. Conclusions. The WR spectral appearance arises from the presence of strong winds. Therefore, both MspecWR and MsingleWR increase with decreasing metallicity. Considering this, we show that one should not a-priori expect that binary interactions become increasingly important in forming WR stars at low Z, or that the WR binary fraction grows with decreasing Z.

scholarly journals Spectroscopy of Overluminous Cepheids in the Magellanic Clouds

1984 ◽  
Vol 108 ◽  
pp. 223-224
Author(s):  
Horace A. Smith ◽  
Leo Connolly
Keyword(s):  
Globular Cluster ◽  
Large Magellanic Cloud ◽  
Variable Stars ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
Small Magellanic Cloud ◽  
Single Star ◽  
Rr Lyrae ◽  
Short Period ◽  
The Galaxy

The Small Magellanic Cloud is known to contain types of short period Cepheid variable stars not yet discovered in either the Large Magellanic Cloud or, with the exception of a single star, in the Galaxy. These variables can be divided into two categories: anomalous Cepheids and Wesselink-Shuttleworth (WS) stars. The former, which have also been found in dwarf spheroidal systems and in the globular cluster NGC 5466, have periods of 0.4–3 days, but average 0.7–1.0 mag. brighter than RR Lyrae and BL Her stars of equal period. The stars we call WS stars have periods less than about 1.1 day and, at MV = −1 to −2, are brighter than anomalous Cepheids of equal period.

The EROS2 Microlensing Study of the Galaxy

2004 ◽  
Vol 220 ◽  
pp. 131-132
Author(s):  
Clarisse Hamadache
Keyword(s):  
Optical Depth ◽  
Galactic Center ◽  
Mass Range ◽  
Magellanic Clouds ◽  
Strong Limit ◽  
Gravitational Microlensing ◽  
The Galaxy

The latest results of the Eros2 experiment are presented. the search for gravitational microlensing events toward the Galactic Center and toward the Magellanic Clouds yielded an optical depth τbulge = 0.94 ± 0.29 × 10–6, and a strong limit, combining all Eros analyses, on the composition of the halo. Less than 25% of a standard halo can be composed of MACHOs with a mass range [10–7, 1] M⊙ at the 95% C.L.

scholarly journals Massive stellar models: rotational evolution, metallicity effects

2010 ◽  
Vol 6 (S272) ◽  
pp. 62-72 ◽  
Author(s):  
Sylvia Ekström ◽  
Cyril Georgy ◽  
Georges Meynet ◽  
André Maeder ◽  
Anahí Granada
Keyword(s):  
Magellanic Clouds ◽  
Stellar Structure ◽  
Be Stars ◽  
Transport Mechanisms ◽  
Single Star ◽  
Fast Rotation ◽  
The Galaxy ◽  
Rotational Evolution ◽  
Be Star ◽  
Theoretical Results

AbstractThe Be star phenomenon is related to fast rotation, although the cause of this fast rotation is not yet clearly established. The basic effects of fast rotation on the stellar structure are reviewed: oblateness, mixing, anisotropic winds. The processes governing the evolution of the equatorial velocity of a single star (transport mechanisms and mass loss) are presented, as well as their metallicity dependence. The theoretical results are compared to observations of B and Be stars in the Galaxy and the Magellanic Clouds.

Spectroscopy of complete populations of Wolf-Rayet binaries in the Magellanic Clouds

2018 ◽  
Vol 14 (S346) ◽  
pp. 307-315
Author(s):  
Tomer Shenar ◽  
R. Hainich ◽  
W.-R. Hamann ◽  
A. F. J. Moffat ◽  
H. Todt ◽  
...  
Keyword(s):  
Spectral Analysis ◽  
Mass Loss ◽  
Massive Stars ◽  
Large Population ◽  
Magellanic Clouds ◽  
Binary Interaction ◽  
Stellar Winds ◽  
Single Star ◽  
Mass Removal ◽  
Star Evolution

AbstractClassical Wolf-Rayet stars are evolved, hydrogen depleted massive stars that exhibit strong mass-loss. In theory, these stars can form either by intrinsic mass loss (stellar winds or eruptions), or via mass-removal in binaries. The Wolf-Rayet stars in the Magellanic Clouds are often thought to have originated through binary interaction due to the low ambient metallicity and, correspondingly, reduced wind mass-loss. We performed a complete spectral analysis of all known WR binaries of the nitrogen sequence in the Small and Large Magellanic Clouds, as well as additional orbital analyses, and constrained the evolutionary histories of these stars. We find that the bulk of Wolf-Rayet stars are luminous enough to be explained by single-star evolution. In contrast to prediction, we do not find clear evidence for a large population of low-luminosity Wolf-Rayet stars that could only form via binary interaction, suggesting a discrepancy between predictions and observations.

scholarly journals The Evolution of Stars on the AGB: The Mass Loss Intensity and the Formation of Carbon Stars

1989 ◽  
Vol 106 ◽  
pp. 224-224
Author(s):  
Yu. L. Frantsman
Keyword(s):  
Mass Loss ◽  
Mass Distribution ◽  
White Dwarfs ◽  
Magellanic Clouds ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Element Abundance ◽  
Agb Stars ◽  
Carbon Stars ◽  
The Galaxy

Simulated populations of white dwarfs and N type carbon stars were generated for a Salpeter initial mass function and constant stellar birth rate history. The effect of very strong mass loss on the mass distribution of white dwarfs and the luminosity distribution of carbon stars is discussed and the results are compared with observations. A significant mass loss by stars on the TP-AGB occurs besides regular stellar wind and planetary nebulae ejection. Thus it is possible to explain the luminosity functions of carbon and M stars in the Magellanic Clouds (with very few stars brighter than Mbol = -6.0), the very narrow mass distribution of white dwarfs, and the very small number of white dwarfs with M > 1.0 MΘ. The luminosity of some AGB stars in the SMC is so high that they may be supernova of type 1 1/2 precursors. There are no such stars in the LMC. Comparison of the theoretical and observed luminosity distributions of high-luminosity AGB stars in the Magellanic Clouds shows that the mass-loss rate of these stars in the LMC is about an order of magnitude larger than in the SMC. In the Galaxy carbon stars may form only from stars with initial mass less than 1.5 MΘ due to the relatively small initial heavy element abundance in these stars; this is perhaps the main reason for the absence of carbon stars in open clusters in the Galaxy.

scholarly journals Binary interactions on the RGB: Dusty post-RGB stars

2016 ◽  
Vol 12 (S323) ◽  
pp. 223-226
Author(s):  
Devika Kamath ◽  
Hans Van Winckel ◽  
Peter Wood
Keyword(s):  
Radial Velocity ◽  
Planetary Nebula ◽  
Planetary Nebulae ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
Binary Interaction ◽  
Small Magellanic Cloud ◽  
Preliminary Results ◽  
Low Metallicity ◽  
Binary Evolution

AbstractIt is widely accepted that binary interactions are responsible for the shaping of planetary nebula. However, these binary interactions and evolutionary channels are poorly understood. Our recent study revealed a newly discovered population of low-luminosity, low-metallicity, likely binaries in the Magellanic Clouds: dusty post-RGB stars. They are likely to have evolved off the RGB via binary interaction. In this paper we present preliminary results of the first radial velocity monitoring of the post-RGB stars in the Small Magellanic Cloud (SMC) and the implications on stellar (binary) evolution. We also investigate their link, if any, to the planetary nebulae systems.

scholarly journals Herschel spectroscopy of massive young stellar objects in the Magellanic Clouds

2019 ◽  
Vol 490 (3) ◽  
pp. 3909-3935
Author(s):  
J M Oliveira ◽  
J Th van Loon ◽  
M Sewiło ◽  
M-Y Lee ◽  
V Lebouteiller ◽  
...  
Keyword(s):  
Line Emission ◽  
Far Infrared ◽  
Magellanic Clouds ◽  
Young Stellar Objects ◽  
Stellar Objects ◽  
Heating Efficiency ◽  
Photodetector Array ◽  
The Galaxy ◽  
Low Metallicity ◽  
Ir Emission

ABSTRACT We present Herschel Space Observatory Photodetector Array Camera and Spectrometer (PACS) and Spectral and Photometric Imaging Receiver Fourier Transform Spectrometer (SPIRE FTS) spectroscopy of a sample of 20 massive Young Stellar Objects (YSOs) in the Large and Small Magellanic Clouds (LMC and SMC). We analyse the brightest far-infrared (far-IR) emission lines, that diagnose the conditions of the heated gas in the YSO envelope and pinpoint their physical origin. We compare the properties of massive Magellanic and Galactic YSOs. We find that [O i] and [C ii] emission, that originates from the photo-dissociation region associated with the YSOs, is enhanced with respect to the dust continuum in the Magellanic sample. Furthermore the photoelectric heating efficiency is systematically higher for Magellanic YSOs, consistent with reduced grain charge in low metallicity environments. The observed CO emission is likely due to multiple shock components. The gas temperatures, derived from the analysis of CO rotational diagrams, are similar to Galactic estimates. This suggests a common origin to the observed CO excitation, from low-luminosity to massive YSOs, both in the Galaxy and the Magellanic Clouds. Bright far-IR line emission provides a mechanism to cool the YSO environment. We find that, even though [O i], CO, and [C ii] are the main line coolants, there is an indication that CO becomes less important at low metallicity, especially for the SMC sources. This is consistent with a reduction in CO abundance in environments where the dust is warmer due to reduced ultraviolet-shielding. Weak H2O and OH emission is detected, consistent with a modest role in the energy balance of wider massive YSO environments.

scholarly journals Origins of Type Ibn SNe 2006jc/2015G in interacting binaries and implications for pre-SN eruptions

2019 ◽  
Vol 491 (4) ◽  
pp. 6000-6019 ◽  
Author(s):  
Ning-Chen Sun ◽  
Jusytn R Maund ◽  
Ryosuke Hirai ◽  
Paul A Crowther ◽  
Philipp Podsiadlowski
Keyword(s):  
Main Sequence ◽  
Hubble Space Telescope ◽  
Optical Observations ◽  
Initial Mass ◽  
Binary Interaction ◽  
Lower Mass ◽  
Single Star ◽  
Circumstellar Material ◽  
Luminous Blue Variables ◽  
Star Evolution

ABSTRACT Type Ibn supernovae (SNe Ibn) are intriguing stellar explosions whose spectra exhibit narrow helium lines with little hydrogen. They trace the presence of circumstellar material (CSM) formed via pre-SN eruptions of their stripped-envelope progenitors. Early work has generally assumed that SNe Ibn come from massive Wolf–Rayet (WR) stars via single-star evolution. In this paper, we report ultraviolet (UV) and optical observations of two nearby Type Ibn SNe 2006jc and 2015G conducted with the Hubble Space Telescope (HST) at late times. A point source is detected at the position of SN 2006jc, and we confirm the conclusion of Maund et al. that it is the progenitor’s binary companion. Its position on the Hertzsprung–Russell (HR) diagram corresponds to a star that has evolved off the main sequence (MS); further analysis implies a low initial mass for the companion star (M2 ≤ 12.3$^{+2.3}_{-1.5}$ M⊙) and a secondary-to-primary initial mass ratio very close to unity (q = M2/M1 ∼ 1); the SN progenitor’s hydrogen envelope had been stripped through binary interaction. We do not detect the binary companion of SN 2015G. For both SNe, the surrounding stellar populations have relatively old ages and argue against any massive WR stars as their progenitors. These results suggest that SNe Ibn may have lower mass origins in interacting binaries. As a result, they also provide evidence that the giant eruptions commonly seen in massive luminous blue variables (LBVs) can also occur in much lower mass, stripped-envelope stars just before core collapse.

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