scholarly journals A census of massive stars in NGC 346

2019 ◽  
Vol 626 ◽  
pp. A50 ◽  
Author(s):  
P. L. Dufton ◽  
C. J. Evans ◽  
I. Hunter ◽  
D. J. Lennon ◽  
F. R. N. Schneider
Keyword(s):  
Massive Stars ◽  
Rotational Velocity ◽  
Magellanic Cloud ◽  
Small Magellanic Cloud ◽  
Spectral Multiplicity ◽  
Transform Method ◽  
Galactic Clusters ◽  
Early Type Stars ◽  
Stellar Masses ◽  
Inner Region

Spectroscopy for 247 stars towards the young cluster NGC 346 in the Small Magellanic Cloud has been combined with that for 116 targets from the VLT-FLAMES Survey of Massive Stars. Spectral classification yields a sample of 47 O-type and 287 B-type spectra, while radial-velocity variations and/or spectral multiplicity have been used to identify 45 candidate single-lined (SB1) systems, 17 double-lined (SB2) systems, and one triple-lined (SB3) system. Atmospheric parameters (Teff and log g) and projected rotational velocities (ve sin i) have been estimated using TLUSTY model atmospheres; independent estimates of ve sin i were also obtained using a Fourier Transform method. Luminosities have been inferred from stellar apparent magnitudes and used in conjunction with the Teff and ve sin i estimates to constrain stellar masses and ages using the BONNSAI package. We find that targets towards the inner region of NGC 346 have higher median masses and projected rotational velocities, together with smaller median ages than the rest of the sample. There appears to be a population of very young targets with ages of less than 2 Myr, which have presumably all formed within the cluster. The more massive targets are found to have lower projected rotational velocities consistent with previous studies. No significant evidence is found for differences with metallicity in the stellar rotational velocities of early-type stars, although the targets in the Small Magellanic Cloud may rotate faster than those in young Galactic clusters. The rotational velocity distribution for single non-supergiant B-type stars is inferred and implies that a significant number have low rotational velocity (≃10% with ve <  40 km s−1), together with a peak in the probability distribution at ve≃ 300 km s−1. Larger projected rotational velocity estimates have been found for our Be-type sample and imply that most have rotational velocities between 200–450 km s−1.

scholarly journals Seven young star clusters in the inner region of the Small Magellanic Cloud

2008 ◽  
Vol 389 (1) ◽  
pp. 429-440 ◽  
Author(s):  
Andrés E. Piatti ◽  
Doug Geisler ◽  
Ata Sarajedini ◽  
Carme Gallart ◽  
Marina Wischnjewsky
Keyword(s):  
Star Clusters ◽  
Young Star ◽  
Magellanic Cloud ◽  
Small Magellanic Cloud ◽  
Inner Region ◽  
Young Star Clusters

scholarly journals SPITZERSAGE-SMC INFRARED PHOTOMETRY OF MASSIVE STARS IN THE SMALL MAGELLANIC CLOUD

2010 ◽  
Vol 140 (2) ◽  
pp. 416-429 ◽  
Author(s):  
A. Z. Bonanos ◽  
D. J. Lennon ◽  
F. Köhlinger ◽  
J. Th. van Loon ◽  
D. L. Massa ◽  
...  
Keyword(s):  
Massive Stars ◽  
Magellanic Cloud ◽  
Small Magellanic Cloud ◽  
Infrared Photometry

scholarly journals Variability of massive stars with known spectral types in the Small Magellanic Cloud using 8 years of OGLE-III data

2014 ◽  
Vol 562 ◽  
pp. A125 ◽  
Author(s):  
M. Kourniotis ◽  
A. Z. Bonanos ◽  
I. Soszyński ◽  
R. Poleski ◽  
G. Krikelis ◽  
...  
Keyword(s):  
Massive Stars ◽  
Magellanic Cloud ◽  
Small Magellanic Cloud

scholarly journals Massive Star Formation in the Sparsest Environments

2015 ◽  
Vol 11 (S315) ◽  
Author(s):  
Sally Oey ◽  
Joel B. Lamb
Keyword(s):  
Star Formation ◽  
Massive Star ◽  
Massive Stars ◽  
Hii Regions ◽  
Magellanic Cloud ◽  
Small Magellanic Cloud ◽  
Massive Star Formation ◽  
Ob Stars ◽  
Runaway Stars

AbstractThere is growing evidence that massive stars sometimes form in extremely sparse environments. The RIOTS4 survey presents a variety of evidence supporting this scenario, including a sample of 14 OB stars in the Small Magellanic Cloud (SMC) that appear to have formed in situ as field stars. This is based on the presence of dense, symmetric HII regions hosting apparent non-runaway stars. We also present a spatially complete IMF of SMC field OB stars for masses > 7 M⊙, showing that the slope is much steeper than the Salpeter value. The binary fraction among field OB stars is also the same as in clusters, based on a RIOTS4 subsample. These results suggest a relative, but incomplete, suppression of massive star formation in the sparsest regimes.

scholarly journals Mass-loss predictions and stellar masses of early-type stars

2003 ◽  
Vol 212 ◽  
pp. 164-165 ◽  
Author(s):  
Alex de Koter ◽  
Jorick S. Vink
Keyword(s):  
Mass Loss ◽  
Massive Stars ◽  
Spectroscopic Binaries ◽  
Evolution Theory ◽  
Early Type ◽  
Direct Measurements ◽  
Wind Theory ◽  
Early Type Stars ◽  
Stellar Masses

We show that the stellar masses implied by our predictions of the wind properties of massive stars are in agreement with masses derived from evolution theory and from direct measurements using spectroscopic binaries, contrary to previous attempts to derive masses from wind theory.

scholarly journals Origin of Structural and Kinematic Properties of the Small Magellanic Cloud

2009 ◽  
Vol 26 (1) ◽  
pp. 37-57 ◽  
Author(s):  
Kenji Bekki ◽  
Masashi Chiba
Keyword(s):  
Spatial Distribution ◽  
Rotational Velocity ◽  
Magellanic Cloud ◽  
Slow Rotation ◽  
Small Magellanic Cloud ◽  
Disk Model ◽  
Radial Profiles ◽  
Galaxy Interaction ◽  
Spheroidal Model ◽  
Kinematic Properties

AbstractWe investigate structural, kinematic and chemical properties of stars and gas in the Small Magellanic Cloud (SMC) interacting with the Large Magellanic Cloud (LMC) and the Galaxy based on a series of self-consistent chemodynamical simulations. We adopt a new ‘dwarf spheroidal model’ in which the SMC initially has both old stars with a spherical spatial distribution and an extended Hi gas disk. We mainly investigate the evolution of the SMC for the last ∼3 Gyr, during which the Magellanic Stream (MS) and the Magellanic Bridge (MB) could have formed as a result of the LMC–SMC–Galaxy interaction. Our principal results, which can be tested against observations, are as follows: The final spatial distribution of the old stars projected onto the sky is spherical, even after strong LMC–SMC–Galaxy interaction, whereas that of the new ones is significantly flattened and appears to form a bar structure. Old stars have a line-of-sight velocity dispersion σ ≃ 30 km s−1 and slow rotation, with a maximum rotational velocity, V < 20 km s−1 and show asymmetry in the radial profiles. New stars have a smaller Σ than old ones and a significant amount of rotation (V/σ > 1). Hi gas shows velocity dispersions of σ = 10–40 km s−1, a high maximum rotational velocity (V ∼ 50 km s−1) and a spatial distribution similar to that of new stars. New stars with ages younger than 3 Gyr show a negative metallicity gradient in the sense that more metal-rich stars are located in the inner regions of the SMC. The MB inevitably contains old stars with surface mass densities of 6−300 × 104 M⊙ deg−2 depending on initial stellar distributions of the modeled SMC. We find that the dwarf spheroidal model can explain more self-consistently the observed kinematic properties of stars and gas, compared with another type of the model (‘the disk model’) in which the SMC initially consists of stellar and gas disks. We suggest that, to better understand its evolution, the SMC needs to be modeled as having a spheroidal component, rather than being a pure disk.

scholarly journals The Relation Between Field Massive Stars and Clusters

2007 ◽  
Vol 3 (S246) ◽  
pp. 65-66
Author(s):  
M. S. Oey ◽  
N. L. King ◽  
J. Wm. Parker ◽  
J. B. Lamb
Keyword(s):  
Small Groups ◽  
Stellar Population ◽  
Massive Stars ◽  
Magellanic Cloud ◽  
Small Magellanic Cloud ◽  
Multiple Origins ◽  
External Galaxies ◽  
Runaway Stars ◽  
Massive Field

AbstractMassive “field” stars are those that appear in apparent isolation, in contrast to those in clusters. Whereas cluster stars are formed together in large aggregates, simultaneously, field stars have multiple origins. Some massive field stars may be the “tip of the iceberg” on small groups of physically associated stars, while others appear to be “runaway” stars that are dynamically ejected from clusters. What is the intrinsic relation between clusters and field stars, and what is the faction of runaway stars? Since massive stars are the most luminous stellar population, their demographics are accessible in the nearest external galaxies. We present our current efforts to understand these issues for the Small Magellanic Cloud.

scholarly journals A dearth of young and bright massive stars in the Small Magellanic Cloud

2020 ◽  
Author(s):  
A. Schootemeijer ◽  
N. Langer ◽  
D. Lennon ◽  
C. J. Evans ◽  
P. A. Crowther ◽  
...  
Keyword(s):  
Massive Stars ◽  
Magellanic Cloud ◽  
Small Magellanic Cloud

scholarly journals Wolf–Rayet stars in the Small Magellanic Cloud as testbed for massive star evolution

2018 ◽  
Vol 611 ◽  
pp. A75 ◽  
Author(s):  
A. Schootemeijer ◽  
N. Langer
Keyword(s):  
Main Sequence ◽  
Massive Stars ◽  
Magellanic Cloud ◽  
Compact Objects ◽  
Binary Interaction ◽  
Small Magellanic Cloud ◽  
Low Metallicity ◽  
Black Hole Binary ◽  
Stellar Models ◽  
Massive Star Evolution

Context. The majority of the Wolf–Rayet (WR) stars represent the stripped cores of evolved massive stars who lost most of their hydrogen envelope. Wind stripping in single stars is expected to be inefficient in producing WR stars in metal-poor environments such as the Small Magellanic Cloud (SMC). While binary interaction can also produce WR stars at low metallicity, it is puzzling that the fraction of WR binaries appears to be about 40%, independent of the metallicity.Aim. We aim to use the recently determined physical properties of the twelve known SMC WR stars to explore their possible formation channels through comparisons with stellar models.Methods. We used the MESA stellar evolution code to construct two grids of stellar models with SMC metallicity. One of these consists of models of rapidly rotating single stars, which evolve in part or completely chemically homogeneously. In a second grid, we analyzed core helium burning stellar models assuming constant hydrogen and helium gradients in their envelopes.Results. We find that chemically homogeneous evolution is not able to account for the majority of the WR stars in the SMC. However, in particular the apparently single WR star SMC AB12, and the double WR system SMC AB5 (HD 5980) appear consistent with this channel. We further find a dichotomy in the envelope hydrogen gradients required to explain the observed temperatures of the SMC WR stars. Shallow gradients are found for the WR stars with O star companions, while much steeper hydrogen gradients are required to understand the group of hot apparently single WR stars.Conclusions. The derived shallow hydrogen gradients in the WR component of the WR+O star binaries are consistent with predictions from binary models where mass transfer occurs early, in agreement with their binary properties. Since the hydrogen profiles in evolutionary models of massive stars become steeper with time after the main sequence, we conclude that most of the hot (Teff > 60 kK ) apparently single WR stars lost their envelope after a phase of strong expansion, e.g., as the result of common envelope evolution with a lower mass companion. The so far undetected companions, either main sequence stars or compact objects, are then expected to still be present. A corresponding search might identify the first immediate double black hole binary progenitor with masses as high as those detected in GW150914.

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