The multiplicity of massive stars

Sana, H.; Evans, C. J.

doi:10.1017/s1743921311011124

Cited by 89 publications

(80 citation statements)

References 37 publications

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“…Mason et al (1998) derived a binary fraction of ∼70% in massive field stars, although the exact numbers depend on the stellar spectral type considered (Raghavan et al 2010). In a clustered context, Sana & Evans (2011) and Sana et al ( , 2012a found a binary fraction of around 50% in young open clusters, including in the 30 Doradus region, which ties in very well with the ∼55% binary fraction quoted by Kobulnicky et al (2014) for the Cygnus OB2 association. Kouwenhoven et al (2005) studied the Scorpius OB2 association in detail and provided similar binary fractions, notably separated as a function of stellar spectral type.…”

Section: Introductionsupporting

confidence: 58%

The dynamical importance of binary systems in young massive star clusters

Grijs

Geller³

2015

Proc. IAU

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Abstract. Characterization of the binary fractions in star clusters is of fundamental importance for many fields in astrophysics. Observations indicate that the majority of stars are found in binary systems, while most stars with masses greater than 0.5M⊙ are formed in star clusters. In addition, since binaries are on average more massive than single stars, in resolved star clusters these systems are thought to be good tracers of (dynamical) mass segregation. Over time, dynamical evolution through two-body relaxation will cause the most massive objects to migrate to the cluster center, while the relatively lower-mass objects remain in or migrate to orbits at greater radii. This process will globally dominate a cluster's stellar distribution. However, close encounters involving binary systems may disrupt 'soft' binaries. This process will occur more frequently in a cluster's central, dense region than in its periphery, which may mask the effects of mass segregation. Using high resolution Hubble Space Telescope observations, combined with sophisticated N -body simulations, we investigate the radial distributions of the main-sequence binary fractions in massive young Large Magellanic Cloud star clusters. We show that binary disruption may play an important role on very short timescales, depending on the environmental conditions in the cluster cores. This may lead to radial binary fractions that initially decline in the cluster centers, which is contrary to the effects expected from dynamical mass segregation.

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Section: Introductionsupporting

confidence: 58%

The dynamical importance of binary systems in young massive star clusters

Grijs

Geller³

2015

Proc. IAU

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“…Many of the most massive stars exist in tight (orbital periods of a few days) binaries (Zinnecker & Yorke 2007). For a recent update on massive binary properties, see Sana & Evans (2011).…”

Section: Formation Of Clusters and High-mass Starsmentioning

confidence: 99%

Star Formation in the Milky Way and Nearby Galaxies

Kennicutt

Evans

2012

Annu. Rev. Astron. Astrophys.

2,684

139

2,728

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We review progress over the past decade in observations of large-scale star formation, with a focus on the interface between extragalactic and Galactic studies. Methods of measuring gas contents and star formation rates are discussed, and updated prescriptions for calculating star formation rates are provided. We review relations between star formation and gas on scales ranging from entire galaxies to individual molecular clouds. Subject headings: star formation, galaxies, Milky Way 1. OVERVIEW 1.1. Introduction Star formation encompasses the origins of stars and planetary systems, but it is also a principal agent of galaxy formation and evolution, and hence a subject at the roots of astrophysics on its largest scales.The past decade has witnessed an unprecedented stream of new observational information on star formation on all scales, thanks in no small part to new facilities such as the Galaxy Evolution Explorer (GALEX), the Spitzer Space Telescope, the Herschel Space Observatory, the introduction of powerful new instruments on the Hubble Space Telescope (HST), and a host of groundbased optical, infrared, submillimeter, and radio telescopes. These new observations are providing a detailed reconstruction of the key evolutionary phases and physical processes that lead to the formation of individual stars in interstellar clouds, while at the same time extending the reach of integrated measurements of star formation rates (SFRs) to the most distant galaxies known. The new data have also stimulated a parallel renaissance in theoretical investigation and numerical modelling of the star formation process, on scales ranging from individual protostellar and protoplanetary systems to the scales of molecular clouds and star clusters, entire galaxies and ensembles of galaxies, even to the first objects, which are thought to have reionized the Universe and seeded today's stellar populations and Hubble sequence of galaxies.This immense expansion of the subject, both in terms of the volume of results and the range of physical scales explored, may help to explain one of its idiosyncracies, namely the relative isolation between the community studying individual star-forming regions and stars in the Milky Way (usually abbreviated hereafter as MW, but sometimes referred to as "the Galaxy"), and the largely extragalactic community that attempts to characterise the star formation process on galactic and cosmologiElectronic address: robk@ast.cam.as.uk Electronic address: nje@astro.as.utexas.edu cal scales. Some aspects of this separation have been understandable. The key physical processes that determine how molecular clouds contract and fragment into clumps and cores and finally clusters and individual stars can be probed up close only in the Galaxy, and much of the progress in this subject has come from in-depth case studies of individual star-forming regions. Such detailed observations have been impossible to obtain for even relatively nearby galaxies. Instead the extragalactic branch of the subject has focused on the co...

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“…The presence of a nearby companion can strip the envelope from a star before it reaches giant dimensions, effectively reducing the number of red supergiants by up to 40% (assuming the distribution functions of Sana & Evans 2010). In addition, the accreting star or merger resulting from binary interaction may under certain circumstances produce blue supergiants as suggested for the progenitor of SN1987A and the companion of SN1993J (Hillebrandt et al 1987;Walborn et al 1989;Maund et al 2004).…”

Section: Interacting Binariesmentioning

confidence: 99%

“…Data from nearby open clusters suggest about 4 out of 10 O stars have companions that are nearby enough to interact (Sana & Evans 2010). Even though the fraction of stars whose properties have been altered by binary interaction may not be that large, the consequences of such interactions for the stellar luminosity are potentially severe due to the steep dependence of the luminosity on mass.…”

Section: Interacting Binariesmentioning

confidence: 99%

Resolved photometry of extragalactic young massive star clusters

Larsen

Mink

Eldridge

et al. 2011

A&A

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Aims. We present colour-magnitude diagrams (CMDs) of young massive star clusters in several galaxies located well beyond the Local Group. The richness of these clusters allows us to obtain large samples of post-main sequence stars and test how well the observed CMDs are reproduced by canonical stellar isochrones. Methods. We use imaging of seven clusters in the galaxies NGC 1313, NGC 1569, NGC 1705, NGC 5236 and NGC 7793 obtained with the Advanced Camera for Surveys on board the Hubble Space Telescope and carry out PSF-fitting photometry of individual stars in the clusters. The clusters have ages in the range ∼(5−50) × 10 6 years and masses of ∼10 5 M -10 6 M . Although crowding prevents us from obtaining photometry in the inner regions of the clusters, we are still able to measure up to 30-100 supergiant stars in each of the richest clusters. The resulting CMDs and luminosity functions are compared with photometry of artificially generated clusters, designed to reproduce the photometric errors and completeness as realistically as possible.Results. In agreement with previous studies, our CMDs show no clear gap between the H-burning main sequence and the Heburning supergiant stars, contrary to predictions by common stellar isochrones. In general, the isochrones also fail to match the observed number ratios of red-to-blue supergiant stars, although the difficulty of separating blue supergiants from the main sequence complicates this comparison. In several cases we observe a large spread (1-2 mag) in the luminosities of the supergiant stars that cannot be accounted for by observational errors. We find that this spread can be reproduced by including an age spread of ∼(10−30) × 10 6 years in the models. However, age spreads cannot fully account for the observed morphology of the CMDs and other processes, such as the evolution of interacting binary stars, may also play a role. Conclusions. Colour-magnitude diagrams can be successfully obtained for massive star clusters out to distances of at least 4-5 Mpc. Comparing such CMDs with models based on canonical isochrones we find several areas of disagreement. One interesting possibility is that an age spread of up to ∼30 Myr may be present in some clusters. The data presented here may provide useful constraints on models for single and/or binary stellar evolution.

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The multiplicity of massive stars

Cited by 89 publications

References 37 publications

The dynamical importance of binary systems in young massive star clusters

The dynamical importance of binary systems in young massive star clusters

Star Formation in the Milky Way and Nearby Galaxies

Resolved photometry of extragalactic young massive star clusters

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