Modeling of cosmic ray 22Ne-enrichment in compact star clusters

Abstract 22Ne/20Ne isotopic ratio is found to be about 5 times higher in Galactic cosmic rays (GCRs) than in the solar wind. In this paper we develop the hypothesis that the 22Ne overabundance in CRs is generated in compact massive star clusters which contain populations of Wolf-Rayet stars. Winds of Wolf-Rayet stars are considered to have high content of 22Ne. We assume that particle acceleration occurs on the ensemble of strong shocks from the massive stars’ winds. We present a model of cosmic ray enrichment with 22Ne, adding isotopic yields from supernovae and taking into account the acceleration efficiency during the lifetime of the stars. The impact of the parameters (the initial mass function in the cluster, rotation velocity, black hole cut-off mass) is discussed. The energy balance for our model is calculated.

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Realistic modelling of wind and supernovae shocks in star clusters: addressing 22Ne/20Ne and other problems in Galactic cosmic rays

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa286 ◽

2020 ◽

Vol 493 (3) ◽

pp. 3159-3177 ◽

Cited By ~ 1

Author(s):

Siddhartha Gupta ◽

Biman B Nath ◽

Prateek Sharma ◽

David Eichler

Keyword(s):

Massive Star ◽

Star Clusters ◽

Cosmic Ray ◽

Mass Function ◽

Galactic Cosmic Rays ◽

Star Cluster ◽

Stellar Winds ◽

Isotopic Abundances ◽

Γ Ray ◽

Massive Clusters

ABSTRACT Cosmic ray (CR) sources leave signatures in the isotopic abundances of CRs. Current models of Galactic CRs that consider supernovae (SNe) shocks as the main sites of particle acceleration cannot satisfactorily explain the higher 22Ne/20Ne ratio in CRs compared to the interstellar medium. Although stellar winds from massive stars have been invoked, their contribution relative to SNe ejecta has been taken as a free parameter. Here, we present a theoretical calculation of the relative contributions of wind termination shocks (WTSs) and SNe shocks in superbubbles, based on the hydrodynamics of winds in clusters, the standard stellar mass function, and stellar evolution theory. We find that the contribution of WTSs towards the total CR production is at least $25{{\ \rm per\ cent}}$, which rises to $\gtrsim 50{{\ \rm per\ cent}}$ for young (≲10 Myr) clusters, and explains the observed 22Ne/20Ne ratio. We argue that since the progenitors of apparently isolated supernovae remnants (SNRs) are born in massive star clusters, both WTS and SNe shocks can be integrated into a combined scenario of CRs being accelerated in massive clusters. This scenario is consistent with the observed ratio of SNRs to γ-ray bright (Lγ ≳ 1035 erg s−1) star clusters, as predicted by star cluster mass function. Moreover, WTSs can accelerate CRs to PeV energies, and solve other long-standing problems of the standard SN paradigm of CR acceleration.

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Star formation at low rates - the impact of lacking massive stars on stellar feedback

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316011261 ◽

2016 ◽

Vol 11 (S321) ◽

pp. 99-101 ◽

Cited By ~ 2

Author(s):

Gerhard Hensler ◽

Patrick Steyrleithner ◽

Simone Recchi

Keyword(s):

Star Formation ◽

Massive Star ◽

Dwarf Galaxies ◽

Self Regulation ◽

Mass Function ◽

Initial Mass Function ◽

Stellar Cluster ◽

Stellar Feedback ◽

Intermediate Mass Stars ◽

The Impact

AbstractDue to their low masses dwarf galaxies experience low star-formation rates resulting in stellar cluster masses insufficient to fill the initial mass function (IMF) to the uppermost mass. Numerical simulations usually do not account for the completeness of the IMF, but treat a filed IMF by numbers, masses, and stellar feedback by fractions. To ensure that only entire stars are formed, we consider an IMF filled from the lower-mass regime and truncated where at least one entire massive star is formed.By 3D simulations we investigate the effects of two possible IMFs on the evolution of dwarf galaxies: filled vs. truncated IMF. For the truncated IMF the star-formation self-regulation is suppressed, while the energy release by typeII supernovae is larger, both compared to the filled IMF. Moreover, the abundance ratios of particular elements yielded from massive and intermediate-mass stars differ significantly between the two IMF distributions.

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The life and death of star clusters

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307001512 ◽

2006 ◽

Vol 2 (S237) ◽

pp. 222-229 ◽

Cited By ~ 1

Author(s):

B. C. Whitmore

Keyword(s):

Massive Star ◽

Cluster Formation ◽

Star Clusters ◽

Mass Function ◽

Initial Mass Function ◽

Merging Galaxies ◽

Life And Death ◽

Large Numbers ◽

Super Star Clusters ◽

Massive Clusters

AbstractIt is generally believed that most stars are born in groups and clusters, rather than in the field. It has also been demonstrated that merging galaxies produce large numbers of young massive star clusters, sometimes called super star clusters. Hence, understanding what triggers the formation of these young massive clusters may provide important information about what triggers the formation of stars in general. In recent years it has become apparent that most clusters do not survive more than ≈10 Myr (i.e., “infant mortality”). Hence, it is just as important to understand the disruption of star clusters as it is to understand their formation if we want to understand the demographics of both star clusters and field stars. This talk will first discuss what triggers star cluster formation in merging galaxies (primarily in the Antennae galaxies), will then demonstrate that most of the faint objects detected in the Antennae are clusters rather than individual stars (which shows that the initial mass function was a power law rather than a Gaussian), and will then outline a general framework designed to empirically fit observations of both star clusters and field stars in a wide variety of galaxies from mergers to quiescent spirals.

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The massive star Initial Mass function

Symposium - International Astronomical Union ◽

10.1017/s007418090021303x ◽

2003 ◽

Vol 212 ◽

pp. 642-651 ◽

Cited By ~ 3

Author(s):

Daniel Schaerer

Keyword(s):

Massive Star ◽

Current Knowledge ◽

Star Clusters ◽

Mass Function ◽

Initial Mass Function ◽

H Ii Regions ◽

Star Forming ◽

Star Forming Regions ◽

Super Star Clusters ◽

The Imf

We review our current knowledge on the IMF in nearby environments, massive star forming regions, super star clusters, starbursts and alike objects from studies of integrated light, and discuss the various techniques used to constrain the IMF. In most cases, including UV-optical studies of stellar features and optical-IR analysis of nebular emission, the data is found to be compatible with a ‘universal’ Salpeter-like IMF with a high upper mass cut-off over a large metallicity range. In contrast, near-IR observations of nuclear starbursts and LIRG show indications of a lowerMupand/or a steeper IMF slope, for which no alternate explanation has yet been found. Also, dynamical mass measurements of seven super star clusters provide so far no simple picture of the IMF. Finally, we present recent results of a direct stellar probe of the upper end of the IMF in metal-rich H ii regions, showing no deficiency of massive stars at high metallicity, and determining a lower limit ofMup≳ 60 – 90 M⊙.

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The influence of multiple stars on the high-mass stellar initial mass function and age dating of young massive star clusters

Monthly Notices of the Royal Astronomical Society ◽

10.1111/j.1365-2966.2008.14258.x ◽

2009 ◽

Vol 393 (2) ◽

pp. 663-680 ◽

Cited By ~ 41

Author(s):

C. Weidner ◽

P. Kroupa ◽

T. Maschberger

Keyword(s):

Massive Star ◽

Star Clusters ◽

Mass Function ◽

Initial Mass Function ◽

Age Dating ◽

High Mass ◽

Initial Mass ◽

Multiple Stars ◽

Stellar Initial Mass Function

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Young massive star clusters: achievements and challenges

Proceedings of the International Astronomical Union ◽

10.1017/s174392130999086x ◽

2009 ◽

Vol 5 (S266) ◽

pp. 49-57 ◽

Cited By ~ 1

Author(s):

Richard de Grijs

Keyword(s):

Massive Star ◽

Initial Conditions ◽

Cluster Formation ◽

Star Clusters ◽

Dynamical Evolution ◽

Mass Function ◽

Large Magellanic Cloud ◽

Initial Mass Function ◽

Ongoing Research ◽

Mass Segregation

AbstractIn spite of significant recent and ongoing research efforts, most of the early evolution and long-term fate of young massive star clusters remain clouded in uncertainties. Here, I discuss our understanding of the initial conditions of star cluster formation and the importance of initial substructure for the subsequent dynamical-evolution and mass-segregation timescales. I also assess our current understanding of the (initial) binary fraction in star clusters and the shape of the stellar initial mass function at the low-mass end in the low-metallicity environment of the Large Magellanic Cloud. Finally, I question the validity of our assumptions leading to dynamical cluster mass estimates. I conclude that it seems imperative that observers, modellers and theorists combine efforts and exchange ideas and data freely for the field to make a major leap forward.

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