scholarly journals Massive star archeology in globular clusters

2014 ◽  
Vol 9 (S307) ◽  
pp. 96-97
Author(s):  
W. Chantereau ◽  
C. Charbonnel ◽  
G. Meynet
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Massive Star ◽  
Massive Stars ◽  
Hot Stars ◽  
Low Mass Stars ◽  
Multiple Populations ◽  
Long Time ◽  
Low Mass ◽  
The Universe

AbstractGlobular clusters are among the oldest structures in the Universe and they host today low-mass stars and no gas. However, there has been a time when they formed as gaseous objects hosting a large number of short-lived, massive stars. Many details on this early epoch have been depicted recently through unprecedented dissection of low-mass globular cluster stars via spectroscopy and photometry. In particular, multiple populations have been identified, which bear the nucleosynthetic fingerprints of the massive hot stars disappeared a long time ago. Here we discuss how massive star archeology can be done through the lense of these multiple populations.

scholarly journals The Circumstellar Environment of Embedded Massive Stars

2002 ◽  
Vol 12 ◽  
pp. 143-145 ◽  
Author(s):  
Lee G. Mundy ◽  
Friedrich Wyrowski ◽  
Sarah Watt
Keyword(s):  
Massive Star ◽  
Massive Stars ◽  
Low Mass Stars ◽  
Submillimeter Wavelength ◽  
Star Forming ◽  
Star Forming Regions ◽  
Low Mass ◽  
Circumstellar Environments ◽  
Near Future

Millimeter and submillimeter wavelength images of massive star-forming regions are uncovering the natal material distribution and revealing the complexities of their circumstellar environments on size scales from parsecs to 100’s of AU. Progress in these areas has been slower than for low-mass stars because massive stars are more distant, and because they are gregarious siblings with different evolutionary stages that can co-exist even within a core. Nevertheless, observational goals for the near future include the characterization of an early evolutionary sequence for massive stars, determination if the accretion process and formation sequence for massive stars is similar to that of low-mass stars, and understanding of the role of triggering events in massive star formation.

scholarly journals Core-hydrogen-burning RSGs in the early globular clusters

2015 ◽  
Vol 11 (A29B) ◽  
pp. 473-473
Author(s):  
Dorottya Szécsi ◽  
Jonathan Mackey ◽  
Norbert Langer
Keyword(s):  
Globular Clusters ◽  
Stellar Population ◽  
Massive Stars ◽  
Shell Formation ◽  
Low Mass Stars ◽  
Hydrogen Burning ◽  
The Core ◽  
Anomalous Surface ◽  
Low Metallicity ◽  
Low Mass

AbstractThe first stellar generation in galactic globular clusters contained massive low-metallicity stars (Charbonnel et al. 2014). We modelled the evolution of this massive stellar population and found that such stars with masses 100-600 M⊙ evolve into cool RSGs (Szécsi et al. 2015). These RSGs spend not only the core-He-burning phase but even the last few 105 years of the core-H-burning phase on the SG branch. Due to the presence of hot massive stars in the cluster at the same time, we show that the RSG wind is trapped into photoionization confined shells (Mackey et al. 2014). We simulated the shell formation around such RSGs and find them to become gravitationally unstable (Szécsi et al. 2016). We propose a scenario in which these shells are responsible for the formation of the second generation low-mass stars in globular clusters with anomalous surface abundances.

scholarly journals Supergiants and their shells in young globular clusters

2018 ◽  
Vol 612 ◽  
pp. A55 ◽  
Author(s):  
Dorottya Szécsi ◽  
Jonathan Mackey ◽  
Norbert Langer
Keyword(s):  
Star Formation ◽  
Globular Clusters ◽  
Second Generation ◽  
Massive Stars ◽  
Low Mass Stars ◽  
Hydrogen Burning ◽  
Mass Budget ◽  
Low Metallicity ◽  
Low Mass ◽  
Galactic Globular Clusters

Context. Anomalous surface abundances are observed in a fraction of the low-mass stars of Galactic globular clusters, that may originate from hot-hydrogen-burning products ejected by a previous generation of massive stars. Aims. We aim to present and investigate a scenario in which the second generation of polluted low-mass stars can form in shells around cool supergiant stars within a young globular cluster. Methods. Simulations of low-metallicity massive stars (Mi ~ 150−600 M⊙) show that both core-hydrogen-burning cool supergiants and hot ionizing stellar sources are expected to be present simulaneously in young globular clusters. Under these conditions, photoionization-confined shells form around the supergiants. We have simulated such a shell, investigated its stability and analysed its composition. Results. We find that the shell is gravitationally unstable on a timescale that is shorter than the lifetime of the supergiant, and the Bonnor-Ebert mass of the overdense regions is low enough to allow star formation. Since the low-mass stellar generation formed in this shell is made up of the material lost from the supergiant, its composition necessarily reflects the composition of the supergiant wind. We show that the wind contains hot-hydrogen-burning products, and that the shell-stars therefore have very similar abundance anomalies that are observed in the second generation stars of globular clusters. Considering the mass-budget required for the second generation star-formation, we offer two solutions. Either a top-heavy initial mass function is needed with an index of −1.71 to −2.07. Alternatively, we suggest the shell-stars to have a truncated mass distribution, and solve the mass budget problem by justifiably accounting for only a fraction of the first generation. Conclusions. Star-forming shells around cool supergiants could form the second generation of low-mass stars in Galactic globular clusters. Even without forming a photoionizaton-confined shell, the cool supergiant stars predicted at low-metallicity could contribute to the pollution of the interstellar medium of the cluster from which the second generation was born. Thus, the cool supergiant stars should be regarded as important contributors to the evolution of globular clusters.

scholarly journals Young and old massive star clusters and their stellar populations - Theoretical challenges for the next decade

2015 ◽  
Vol 12 (S316) ◽  
pp. 1-8
Author(s):  
Corinne Charbonnel
Keyword(s):  
Globular Clusters ◽  
Massive Star ◽  
Local Group ◽  
Stellar Populations ◽  
Low Mass Stars ◽  
Open Questions ◽  
Low Mass ◽  
Near Future ◽  
Massive Clusters ◽  
Two Populations

AbstractSeveral models presented in the literature compete to explain the origin of multiple stellar populations in globular clusters (GC), but they all fail to reproduce the large variety of present-day characteristics of these systems. In parallel, independent clues on GC early evolution may be derived from observations of young massive clusters (YMC) in the Local Group. But are these two populations of clusters related? And can we reconcile the informations and data concerning GCs and YMCs? Here we summarize some open questions on the nucleosynthetic origin of multiple stellar populations in GCs, on the actual evolution and characteristics of GC low-mass stars, and on early gas expulsion from massive clusters. We propose theoretical paths to be explored in the near future.

scholarly journals Pulsars in Globular Clusters

1996 ◽  
Vol 174 ◽  
pp. 181-182 ◽  
Author(s):  
S. R. Kulkarni ◽  
S. B. Anderson
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Massive Stars ◽  
Orbital Evolution ◽  
Precise Determination ◽  
Radio Pulsars ◽  
Dense Cores ◽  
Short Period ◽  
Low Mass ◽  
Low Magnetic Field

Since the discovery of the first globular cluster pulsar in M28 (Lyne et al. 1987) a total of 33 pulsars have been found to reside within 13 seperate clusters. Many (but not all) of the cluster pulsars have properties similar to the millisecond pulsars in the disk: short period, binarity and low magnetic field strength. The common understanding is that these pulsars are primordial neutron stars (i.e. the remnants of massive stars in clusters) which have been spun up by accretion of matter from a companion. Therefore, in this framework, the cluster pulsars are descendents of Low Mass X-ray Binaries (LMXBs) (Alpar et al. 1982). This hypothesis is by no means accepted by all workers (e.g. Michel 1987, Ray & Kluzniak 1990, Romani 1990, Bailyn & Grindlay 1993). These workers have argued that at least some (if not all) cluster pulsars could be formed by accretion induced collapse of massive white dwarfs. In either case, it is clear from the sensitivity limits of current cluster searches, and the luminosity of field pulsars, that there are currently O(103) extant radio pulsars in the Galactic globular cluster system.In this review, specifically targeted for astronomers working in the field of globular clusters, not pulsar astronomers, we argue that cluster pulsars have provided us with a new window into the population of long-dead massive stars and the physics of tidal capture. The precision with which pulsars can be timed has created new diagnostics: measurement of the mass distribution in the dense cores, measurement of orbital evolution on short timescales and precise determination of orbital characteristics. It is fair to say that all these diagnostics are unique, and not obtainable by other observations. Despite this, it is our assessment that the typical astronomer who works in the field of globular clusters is apparently unaware of these relevant contributions. Hopefully this review will bridge this gap. A complete copy of the review article may be found at http://astro.caltech.edu/~srk.

scholarly journals Possible Constituents of Halos

1987 ◽  
Vol 117 ◽  
pp. 395-409
Author(s):  
Martin J. Rees
Keyword(s):  
Galaxy Formation ◽  
Massive Stars ◽  
Critical Density ◽  
Big Bang ◽  
Galactic Halos ◽  
Low Mass Stars ◽  
Groups Of Galaxies ◽  
Low Mass ◽  
The Big Bang ◽  
The Universe

There still seem to be three serious contenders for the dark matter in galactic halos and groups of galaxies: (i) very low mass stars, (ii) black hole remnants of very massive stars or (iii) some species of particle (e.g. axions, photinos, etc.) surviving from the big bang. There are genuine prospects of detecting individual objects in all three of these categories, and thereby narrowing down the present range of options. If the Universe has the critical density (Ω = 1), rather than the lower value (Ω = 0.1–0.2) inferred from dynamical evidence, then the galaxies must be more clustered than the overall distribution even on scales 10–20 Mpc. “Biased” galaxy formation could account for this.

scholarly journals The Chemical Inhomogeneity within Globular Clusters

1988 ◽  
Vol 126 ◽  
pp. 93-106
Author(s):  
John Norris
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Binary Systems ◽  
Chemical Inhomogeneity ◽  
Low Mass Stars ◽  
Stellar Collisions ◽  
Low Mass ◽  
Abundance Anomalies ◽  
Insight Into ◽  
The Way

Twenty years ago it was believed by most astronomers that globular clusters were chemically homogeneous - where by homogeneous one means that the outer layers of all stars within a given cluster are the same to within a few tens of percent. Today it is possible to defend the case that no Galactic globular cluster has this characteristic. The reason that this phenomenon has exercised the minds of so many groups in the past 15 years is exciting and obvious: if one can ascertain which are the relevant physical processes in operation, one stands to gain significant insight into both the way in which globular clusters formed and/or the way in which individual low mass stars evolve and mix the products of their nucleosynthesis into their outer layers. A second important driver at the back of the minds of workers in this field is the possible ramifications of an understanding of the phenomenon; for example, if one concludes that the abundance anomalies are being driven today by some particular effect (angular momentum, magnetic fields, interactions within binary systems, stellar collisions - or whatever) this may lead to insight into other important globular cluster phenomena (eg bimodal horizontal branches, gaps at the base of the giant branch, horizontal branch rotation, etc.)

scholarly journals Did globular clusters contribute to the stellar population of the Galactic halo?

2015 ◽  
Vol 11 (S317) ◽  
pp. 104-109
Author(s):  
Corinne Charbonnel ◽  
Martin Krause
Keyword(s):  
Globular Clusters ◽  
Massive Star ◽  
Stellar Population ◽  
Local Group ◽  
Galactic Halo ◽  
Chemical Properties ◽  
Star Clusters ◽  
Alternative Interpretation ◽  
Low Mass Stars ◽  
Low Mass

AbstractThe origin of Galactic halo stars and the contribution of globular clusters (GC) to this stellar population have long been (and still are) debated. The discovery of multiple stellar populations with peculiar chemical properties in GCs both in the Milky Way and in Local Group galaxies recently brought a renewal on these questions. Indeed most of the scenarios that compete to reproduce the present-day GC characteristics call for fast expulsion of both gas and low-mass stars from these clusters in their early infancy. In this framework, the initial masses of GCs could have been 8 to 25 times higher than their present-day stellar mass, and they could have contributed to 5 to 20 % of the low-mass stars in the Galactic halo. Here we revisit these conclusions, which are in tension with observations of dwarf galaxies and of young massive star clusters in the Local Group. We come back in particular on the paradigm of gas expulsion from massive star clusters, and propose an alternative interpretation of the GC abundance properties. We conclude by proposing a major revision of the current concepts regarding the role massive star clusters play in the assembly of galactic haloes.

scholarly journals The systematically varying stellar IMF

2019 ◽  
Vol 14 (S351) ◽  
pp. 117-121 ◽  
Author(s):  
Pavel Kroupa
Keyword(s):  
Globular Clusters ◽  
Massive Star ◽  
Milky Way ◽  
Dwarf Galaxies ◽  
Star Formation Rate ◽  
High Redshift ◽  
Formation Rate ◽  
Low Mass Stars ◽  
Dynamical Mass ◽  
Low Mass

AbstractSome ultra-compact dwarf galaxies have large dynamical mass to light (M / L) ratios and also appear to contain an overabundance of LMXB sources, and some Milky Way globular clusters have a low concentration and appear to have a deficit of low-mass stars. These observations can be explained if the stellar IMF becomes increasingly top-heavy with decreasing metallicity and increasing gas density of the forming object. The thus constrained stellar IMF then accounts for the observed trend of metallicity and M / L ratio found amongst M31 globular star clusters. It also accounts for the overall shift of the observationally deduced galaxy-wide IMF from top-light to top-heavy with increasing star formation rate amongst galaxies. If the IMF varies similarly to deduced here, then extremely young very massive star-burst clusters observed at a high redshift would appear quasar-like (Jerabkova et al. 2017).

scholarly journals Theoretical evolutionary framework for low-mass stars in massive star clusters

2015 ◽  
Vol 12 (S316) ◽  
pp. 320-327
Author(s):  
Santi Cassisi
Keyword(s):  
Energy Distribution ◽  
Globular Clusters ◽  
Massive Star ◽  
Spectral Energy Distribution ◽  
Star Clusters ◽  
Spectral Energy ◽  
Stellar Systems ◽  
Low Mass Stars ◽  
Specific Chemical ◽  
Low Mass

AbstractRecent spectroscopic and photometric surveys of Galactic Globular Clusters have shown that these stellar systems host distinct sub-populations of stars characterised by peculiar chemical patterns. In the following we wish to address the issue of how these specific chemical patterns affect both the structural and evolutionary properties of stars as well as their spectral energy distribution. The implications of these effects on the photometric appearance of multiple stellar populations in different photometric planes are also briefly discussed.

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