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

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.

Author(s):  
Sally Oey ◽  
Joel B. Lamb

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.


2010 ◽  
Vol 140 (2) ◽  
pp. 416-429 ◽  
Author(s):  
A. Z. Bonanos ◽  
D. J. Lennon ◽  
F. Köhlinger ◽  
J. Th. van Loon ◽  
D. L. Massa ◽  
...  

2014 ◽  
Vol 562 ◽  
pp. A125 ◽  
Author(s):  
M. Kourniotis ◽  
A. Z. Bonanos ◽  
I. Soszyński ◽  
R. Poleski ◽  
G. Krikelis ◽  
...  

Author(s):  
A. Schootemeijer ◽  
N. Langer ◽  
D. Lennon ◽  
C. J. Evans ◽  
P. A. Crowther ◽  
...  

2009 ◽  
Vol 5 (S262) ◽  
pp. 329-330
Author(s):  
Bruno Dias ◽  
Paula Coelho ◽  
Leandro Kerber ◽  
Beatriz Barbuy ◽  
Thais Idiart

AbstractAnalysis of integrated spectra of star clusters in the Magellanic Clouds can bring important information for studies on the chemical evolution of the Clouds. The aim of the present work is to derive ages and metallicities from integrated spectra of 15 star clusters in the Small Magellanic Cloud (SMC), some of them not studied so far. Making use of a full spectrum fitting technique, we compared the integrated spectra of the sample clusters to three different sets of single stellar population models available in the literature. We derived ages and metallicities for the sample clusters employing the codes STARLIGHT and ULySS. Out of the 15 clusters in our sample, 9 are old/intermediate age clusters and 6 are young clusters. We point out the results for the newly identified as old/intermediate age clusters HW1, NGC 152, Lindsay 3 and 11. We also confirm old ages for NGC 361, NGC 419 and Kron 3, and the oldest well-known SMC cluster NGC 121.


1999 ◽  
Vol 190 ◽  
pp. 217-221
Author(s):  
Deidre A. Hunter

The luminous, compact star cluster R136 in the Large Magellanic Cloud is 300 times more spatially concentrated than a typical OB association and contains at least 39 O3 stars, the most massive of which is ~150 M⊙. Yet, the stellar IMF for 2.8–120 M⊙ is normal. The massive stars are 1–2 Myrs old, and Wolf-Rayet stars are not evolved.


2018 ◽  
Vol 611 ◽  
pp. A75 ◽  
Author(s):  
A. Schootemeijer ◽  
N. Langer

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.


2019 ◽  
Vol 626 ◽  
pp. A50 ◽  
Author(s):  
P. L. Dufton ◽  
C. J. Evans ◽  
I. Hunter ◽  
D. J. Lennon ◽  
F. R. N. Schneider

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.


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