Dynamical ejections of massive stars from young star clusters under diverse initial conditions

AbstractThe young star clusters we observe today are the building blocks of a new generation of stars and planets in our Galaxy and beyond. Despite their fundamental role we still lack knowledge about the initial conditions under which star clusters form and the impact of these often harsh environments on the formation and evolution of their stellar and substellar members.We present recent results showing that mass segregation in realistic models of young star clusters occurs very quickly for subvirial spherical systems without substructure. This finding is a critical step to resolve the controversial debate on mass segregation in young star clusters and provides strong constraints on their initial conditions. The rapid concentration of massive stars is usually associated with strong gravitational interactions early on during cluster evolution and the subsequent formation of multiple systems and ejection of stars.

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Ionizing the intergalactic medium by star clusters: the first empirical evidence

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2286 ◽

2019 ◽

Vol 491 (1) ◽

pp. 1093-1103 ◽

Cited By ~ 22

Author(s):

E Vanzella ◽

G B Caminha ◽

F Calura ◽

G Cupani ◽

M Meneghetti ◽

...

Keyword(s):

Massive Stars ◽

Star Clusters ◽

Young Star ◽

Ultraviolet Emission ◽

Stellar Feedback ◽

Stellar Component ◽

High Ionization ◽

Exceptional Object ◽

Young Star Clusters ◽

Work Supports

ABSTRACT We present a VLT/X-Shooter spectroscopy of the Lyman continuum (LyC) emitting galaxy Ion2 at z = 3.2121 and compare it to that of the recently discovered strongly lensed LyC emitter at z = 2.37, known as the Sunburst arc. Three main results emerge from the X-Shooter spectrum: (a) the Ly α has three distinct peaks with the central one at the systemic redshift, indicating a ionized tunnel through which both Ly α and LyC radiation escape; (b) the large O32 oxygen index ([O iii] λλ4959, 5007/[O ii] λλ3727, 3729) of $9.18_{-1.32}^{+1.82}$ is compatible to those measured in local (z ∼0.4) LyC leakers; (c) there are narrow nebular high-ionization metal lines with σv < 20 km s−1, which confirms the presence of young hot, massive stars. The He iiλ1640 appears broad, consistent with a young stellar component including Wolf–Rayet stars. Similarly, the Sunburst LyC emitter shows a triple-peaked Ly α profile and from VLT/MUSE spectroscopy the presence of spectral features arising from young hot and massive stars. The strong lensing magnification, (μ > 20), suggests that this exceptional object is a gravitationally bound star cluster observed at a cosmological distance, with a stellar mass M ≲ 107 M⊙ and an effective radius smaller than 20 pc. Intriguingly, sources like Sunburst but without lensing magnification might appear as Ion2-like galaxies, in which unresolved massive star clusters dominate the ultraviolet emission. This work supports the idea that dense young star clusters can contribute to the ionization of the IGM through holes created by stellar feedback.

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Metallicity and X-ray luminosity variations in NGC 922

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3290 ◽

2020 ◽

Vol 500 (1) ◽

pp. 962-975

Author(s):

K Kouroumpatzakis ◽

A Zezas ◽

A Wolter ◽

A Fruscione ◽

K Anastasopoulou ◽

...

Keyword(s):

Star Formation ◽

Stellar Population ◽

Massive Stars ◽

Star Clusters ◽

Young Star ◽

X Ray ◽

Star Forming ◽

Star Forming Regions ◽

Main Driver ◽

Young Star Clusters

ABSTRACT We present a systematic study of the metallicity variations within the collisional ring galaxy NGC 922 based on long-slit optical spectroscopic observations. We find a metallicity difference between star-forming regions in the bulge and the ring, with metallicities ranging from almost solar to significantly sub-solar ($\rm {[12+\log (O/H)]\sim 8.2}$). We detect $\rm{He\,{\small I}}$ emission in all the studied regions of the bulge and the ring, indicating ionization from massive stars associated with recent (<10 Myr) star formation, in agreement with the presence of very young star clusters. We find an anticorrelation between the X-ray luminosity and metallicity of the sub-galactic regions of NGC 922. The different regions have similar stellar population ages, leaving metallicity as the main driver of the anticorrelation. The dependence of the X-ray emission of the different regions in NGC 922 on metallicity is in agreement with similar studies of the integrated X-ray output of galaxies and predictions from X-ray binary population models.

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Gamma-rays from massive stars in Cygnus and Orion

Symposium - International Astronomical Union ◽

10.1017/s0074180900213144 ◽

2003 ◽

Vol 212 ◽

pp. 706-709 ◽

Cited By ~ 5

Author(s):

Roland Diehl ◽

Karsten Kretschmer ◽

Stefan Plüschke ◽

Miguel Cerviño ◽

Dieter H. Hartmann

Keyword(s):

Gamma Rays ◽

Massive Stars ◽

Line Emission ◽

Star Clusters ◽

Young Star ◽

Synthesis Methods ◽

Population Synthesis ◽

Supernova Explosions ◽

Γ Ray ◽

Young Star Clusters

Radioactive 26Al, ejected by massive stars through winds and supernova explosions, leads to γ-ray line emission that can serve as a probe of the interstellar environment in and near young star clusters. The ~ 1 Myr decay time of 26Al is long enough to allow transport over significant distances, which can cause substantial angular offsets between γ-ray emission and cluster stars. Details of such offsets are determined by the morphology of the ISM. We discuss observations in Cygnus and Orion, and models based on population synthesis methods.

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Formation of massive binaries

Symposium - International Astronomical Union ◽

10.1017/s0074180900211674 ◽

2003 ◽

Vol 212 ◽

pp. 80-90 ◽

Cited By ~ 12

Author(s):

Hans Zinnecker

Keyword(s):

Stellar Evolution ◽

Massive Stars ◽

Star Clusters ◽

Young Star ◽

Spectroscopic Binaries ◽

Stellar Clusters ◽

Multiple Systems ◽

Short Period ◽

Young Star Clusters ◽

Runaway Stars

The formation of massive stars is one of the major unsolved problems in stellar astrophysics. However, only few if any of these are found as single stars, on average massive stars have more than one companion. Many of them are born in dense stellar clusters and several clusters have an excess of massive short-period spectroscopic binaries, with severe implication for binary-related stellar evolution including mergers, and also for the origin of massive runaway stars. The multiplicity of massive stars seems to increase with increasing primary mass and with increasing density of young star clusters. These observations suggest that massive binary and multiple systems originate mainly from dynamical gravitational interactions and accretion-induced protostellar collisions in dense clusters. If true, the binary properties of massive stars in less dense OB associations should be less extreme. This prediction should be tested by future observations. The paper reviews both the latest observations and theoretical ideas related to the origin of massive binaries. It concludes with a speculation on how the binary properties might change with metallicity (e.g., LMC/SMC).

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From hydrodynamics to N-body simulations of star clusters: mergers and rotation

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3763 ◽

2020 ◽

Author(s):

Alessandro Ballone ◽

Stefano Torniamenti ◽

Michela Mapelli ◽

Ugo N Di Carlo ◽

Mario Spera ◽

...

Keyword(s):

Initial Conditions ◽

Star Clusters ◽

Mass Function ◽

Young Star ◽

Initial Mass Function ◽

Early Evolution ◽

Stellar Feedback ◽

Gas Removal ◽

Hydrodynamical Simulations ◽

Young Star Clusters

Abstract We present a new method to obtain more realistic initial conditions for N-body simulations of young star clusters. We start from the outputs of hydrodynamical simulations of molecular cloud collapse, in which star formation is modelled with sink particles. In our approach, we instantaneously remove gas from these hydrodynamical simulation outputs to mock the end of the gas-embedded phase, induced by stellar feedback. We then enforce a realistic initial mass function by splitting or joining the sink particles based on their mass and position. Such initial conditions contain more consistent information on the spatial distribution and the kinematical and dynamical states of young star clusters, which are fundamental to properly study these systems. For example, by applying our method to a set of previously run hydrodynamical simulations, we found that the early evolution of young star clusters is affected by gas removal and by the early dry merging of sub-structures. This early evolution can either quickly erase the rotation acquired by our (sub-)clusters in their embedded phase or “fuel” it by feeding of angular momentum by sub-structure mergers, before two-body relaxation acts on longer timescales.

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The Wolf-Rayet Stars in 30 Doradus

Symposium - International Astronomical Union ◽

10.1017/s007418090002934x ◽

1982 ◽

Vol 99 ◽

pp. 545-549 ◽

Cited By ~ 1

Author(s):

Jorge Melnick

Keyword(s):

Star Formation ◽

Chemical Composition ◽

Massive Star ◽

Massive Stars ◽

Star Clusters ◽

Hii Regions ◽

Young Star ◽

Hii Region ◽

Formation And Evolution ◽

Young Star Clusters

Giant HII regions as sites of massive star formation.Giant HII regions are the brightest extragalactic emission line objects that can be studied in detail. With diameters of several hundreds of parsecs, these nebulae can be easily resolved out to distances of a few Mpc. Typically 100 or more 0 stars are required to account for the observed ionization of the nebular gas and this implies that the cores of giant HII regions contain populous young star clusters. The stars in these clusters have essentially the same age and chemical composition. Thus, giant HII region cores provide excellent sites where theories of the formation and evolution of massive stars and, in particular, of Wolf-Rayet (WR) stars can be tested.

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The origin of very wide binary systems

Proceedings of the International Astronomical Union ◽

10.1017/s1743921309991633 ◽

2009 ◽

Vol 5 (S266) ◽

pp. 438-441

Author(s):

M. B. N. Kouwenhoven ◽

S. P. Goodwin ◽

Richard J. Parker ◽

M. B. Davies ◽

D. Malmberg ◽

...

Keyword(s):

Binary Systems ◽

Galactic Halo ◽

Initial Conditions ◽

Large Fraction ◽

Star Clusters ◽

Young Star ◽

Wide Binary ◽

Multiple Systems ◽

Galactic Field ◽

Young Star Clusters

AbstractThe majority of stars in the Galactic field and halo are part of binary or multiple systems. A significant fraction of these systems have orbital separations in excess of thousands of astronomical units, and systems wider than a parsec have been identified in the Galactic halo. These binary systems cannot have formed through the ‘normal’ star-formation process, nor by capture processes in the Galactic field. We propose that these wide systems were formed during the dissolution phase of young star clusters. We test this hypothesis using N-body simulations of evolving star clusters and find wide binary fractions of 1–30%, depending on initial conditions. Moreover, given that most stars form as part of a binary system, our theory predicts that a large fraction of the known wide ‘binaries’ are, in fact, multiple systems.

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