scholarly journals The possible role of stellar mergers for the formation of multiple stellar populations in globular clusters

2019 ◽  
Vol 491 (1) ◽  
pp. 440-454 ◽  
Author(s):  
Long Wang ◽  
Pavel Kroupa ◽  
Koh Takahashi ◽  
Tereza Jerabkova
Keyword(s):  
Stellar Evolution ◽  
Globular Clusters ◽  
Main Sequence ◽  
Stellar Populations ◽  
Initial Mass Function ◽  
Asymptotic Giant Branch ◽  
High Mass ◽  
Mass Star ◽  
Main Sequence Stars ◽  
Stellar Mergers

ABSTRACT Many possible scenarios for the formation of multiple stellar populations (MSPs) in globular clusters (GCs) have been discussed so far, including the involvement of asymptotic giant branch stars, fast-rotating main-sequence stars, very massive main-sequence stars and mass-transferring massive binaries based on stellar evolution modelling. But self-consistent, dynamical simulations of very young GCs are usually not considered. In this work, we perform direct N-body modelling of such systems with total masses up to 3.2 × 105 M⊙, taking into account the observationally constrained primordial binary properties, and discuss the stellar mergers driven both by binary stellar evolution and dynamical evolution of GCs. The occurrence of stellar mergers is enhanced significantly in binary-rich clusters such that stars forming from the gas polluted by merger-driven ejection/winds would appear as MSPs. We thus emphasize that stellar mergers can be an important process that connects MSP formation with star cluster dynamics, and that multiple MSP formation channels can naturally work together. The scenario studied here, also in view of a possible top-heavy initial mass function, may be particularly relevant for explaining the high mass fraction of MSPs (the mass budget problem) and the absence of MSPs in young and low-mass star clusters.

scholarly journals The Effects of Main-Sequence Mass Loss on Surface C/N Abundance Ratios During the Ascent of the First Giant Branch

1989 ◽  
Vol 106 ◽  
pp. 228-228
Author(s):  
J. A. Guzik ◽  
T. E. Beach
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Mass Fraction ◽  
Main Sequence ◽  
High Mass ◽  
Core Material ◽  
Main Sequence Stars ◽  
Rapid Rotation ◽  
Final Mass ◽  
Evolution Modeling

The surface C/N abundance ratios of many cluster and field G and K giants following the 1st dredge-up phase are much lower than predicted from standard stellar evolution modeling. The occurrence of substantial mass loss, either during or immediately after the main-sequence phase would both reduce the mass fraction of the unprocessed envelope necessary to contaminate with CN-cycle products, as well as allow CN-processing of a greater amount of core material during the earlier high-mass phase. Willson, Bowen and Struck-Marcell (1987) have proposed that a combination of pulsation and rapid rotation could drive substantial mass loss in main-sequence stars of initial mass 1-3 MΘ. We evolved a grid of 16 mass-losing models from the zero-age main sequence through 1st dredge-up. The models have initial masses of 1.25, 1.5, 1.75 and 2.0 MΘ, and exponentially decreasing mass-loss rates with e-folding times 0.2, 0.4, 1.0 and 2.0 Gyr; all models evolve toward a final mass of 1.0 M". Since the mass-loss epoch is short-lived, most of the models reach 1.0 M0 rapidly, and follow the evolutionary track of a standard 1 MΘ model redward away from the main sequence and up the 1st giant branch. The convecuve envelope deepens during 1st dredge-up to homogenize the outer 3/4 of the star's final mass.

scholarly journals Implications of a density dependent IMF for the statistics of progenitors of gravitational wave sources

2018 ◽  
Vol 14 (S346) ◽  
pp. 464-467
Author(s):  
Indulekha Kavila ◽  
Megha Viswambharan
Keyword(s):  
Globular Clusters ◽  
Formation Rate ◽  
Compact Object ◽  
Mass Function ◽  
Initial Distribution ◽  
Initial Mass Function ◽  
High Mass ◽  
Mass Star ◽  
Stellar Masses ◽  
The Impact

AbstractObservations of mergers of multi-compact object systems offer insights to the formation processes of massive stars in globular clusters. Simulations of stellar clusters, may be used to understand and interpret observations. Simulations generally adopt an Initial Mass Function (IMF) with a Salpeter slope at the high mass end, for the initial distribution of stellar masses. However, observations of the nearest high mass star forming regions point to the IMF at the high mass end being flatter than Salpeter, in regions where the stellar densities are high. We explore the impact of this on the formation rate of potential GW sources, estimated from standard considerations. Globular clusters being significant contributors to the ionization history of the universe, the results have implications for the same. It impacts our ability to explore the putative mass gap, between the upper limit for neutron star masses and the lower limit for black hole masses, also.

scholarly journals Spectroscopic evidence of multiple populations in globular clusters

2012 ◽  
Vol 10 (H16) ◽  
pp. 230-231
Author(s):  
R. Gratton ◽  
S. Lucatello ◽  
E. Carretta ◽  
A. Bragaglia
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
Stellar Populations ◽  
Basic Data ◽  
Red Giants ◽  
Main Sequence Stars ◽  
Multiple Populations ◽  
Spectroscopic Evidence ◽  
General Properties ◽  
Multiple Population

AbstractWe review spectroscopic evidence of multiple stellar populations in globular clusters. First, we lay down the basic data: the C-N, Na-O, Mg-Al anti-correlations among red giants and main sequence stars, and discuss how they appear to be general properties of globular clusters, in spite of cluster-to-cluster differences. We will then describe what is currently known about He from spectroscopy. We will then present the implications and current observations for the interpretation of the horizontal branches, showing that the multiple population phenomenon is strongly related to the distribution of stars along them. We will briefly mention the spectroscopic evidence related to some less understood cases, like the clusters with multiple subgiant branches. Finally, we summarize the relation between multiple populations and general properties for globular clusters, and their implications for the formation scenario.

scholarly journals The initial mass function in the extended ultraviolet disc of M83

2019 ◽  
Vol 491 (2) ◽  
pp. 2366-2390 ◽  
Author(s):  
S M Bruzzese ◽  
David A Thilker ◽  
G R Meurer ◽  
Luciana Bianchi ◽  
A B Watts ◽  
...  
Keyword(s):  
Main Sequence ◽  
Hubble Space Telescope ◽  
Formation Rate ◽  
Mass Function ◽  
Initial Mass Function ◽  
High Mass ◽  
Initial Mass ◽  
Main Sequence Stars ◽  
Red Giant ◽  
The Imf

ABSTRACT Using Hubble Space Telescope ACS/WFC data we present the photometry and spatial distribution of resolved stellar populations of four fields within the extended ultraviolet disc (XUV disc) of M83. These observations show a clumpy distribution of main-sequence stars and a mostly smooth distribution of red giant branch stars. We constrain the upper end of the initial mass function (IMF) in the outer disc using the detected population of main-sequence stars and an assumed constant star formation rate (SFR) over the last 300 Myr. By comparing the observed main-sequence luminosity function to simulations, we determine the best-fitting IMF to have a power-law slope α = −2.35 ± 0.3 and an upper mass limit $M_{\rm u}=25_{-3}^{+17} \, \mathrm{M}_\odot$. This IMF is consistent with the observed H $\rm \alpha$ emission, which we use to provide additional constraints on the IMF. We explore the influence of deviations from the constant SFR assumption, finding that our IMF conclusions are robust against all but strong recent variations in SFR, but these are excluded by causality arguments. These results, along with our similar studies of other nearby galaxies, indicate that some XUV discs are deficient in high-mass stars compared to a Kroupa IMF. There are over one hundred galaxies within 5 Mpc, many already observed with HST, thus allowing a more comprehensive investigation of the IMF, and how it varies, using the techniques developed here.

scholarly journals Evolution of Globular Clusters Including a Degenerate Component

1988 ◽  
Vol 126 ◽  
pp. 665-666
Author(s):  
Hyung Mok Lee
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
High Mass ◽  
Main Sequence Stars ◽  
Compact Binaries ◽  
The Core ◽  
Degenerate Component ◽  
Low Mass ◽  
Mass Segregation ◽  
Very High

Low mass X-ray sources observed in many globular clusters are usually interpreted as compact binaries with degenerate components (e.g., Hertz and Grindlay 1983). Degenerate stars can exist in globular clusters if the IMF contains a sufficiently large number of high mass stars. Since the main-sequence lifetime is a very steep function of stellar mass, most of degenerate stars can be regarded as primordial. If the typical mass of degenerate stars is higher than that of main-sequence stars, mass segregation makes the core crowded with degenerate stars. Tidally captured binaries between degenerates and main-sequence stars can abundantly form as the core density becomes very high.

scholarly journals New insights on the origin of multiple stellar populations in globular clusters

2017 ◽  
Vol 13 (S334) ◽  
pp. 316-317
Author(s):  
Jaeyeon Kim ◽  
Young-Wook Lee
Keyword(s):  
Star Formation ◽  
Globular Clusters ◽  
Ad Hoc ◽  
Stellar Populations ◽  
Mass Function ◽  
Blast Waves ◽  
Initial Mass Function ◽  
Asymptotic Giant Branch ◽  
Star Formation History ◽  
Asymptotic Giant Branch Stars

AbstractIn order to investigate the origin of multiple stellar populations in the halo and bulge of the Milky Way, we have constructed chemical evolution models for the low-mass proto-Galactic subsystems such as globular clusters (GCs). Unlike previous studies, we assume that supernova blast waves undergo blowout without expelling the pre-enriched gas, while relatively slow winds of massive stars (WMS), together with the winds and ejecta from low and intermediate mass asymptotic-giant-branch stars (AGBs), are all locally retained in these less massive systems. We find that the observed Na-O anti-correlations in metal-poor GCs can be reproduced, when multiple episodes of starbursts are allowed to continue in these subsystems. A specific form of star formation history (SFH) with decreasing time intervals between the stellar generations, however, is required to obtain this result, which is in good agreement with the parameters obtained from our stellar evolution models for the horizontal-branch. The “mass budget problem” is also much alleviated by our models without ad-hoc assumptions on star formation efficiency (SFE) and initial mass function (IMF). We also applied these models to investigate the origin of super-helium-rich red clump stars in the metal-rich bulge as recently suggested by Lee et al. (2015). We find that chemical enrichments by the WMS can naturally reproduce the required helium enhancement (ΔY/ΔZ = 6) for the second generation stars. Disruption of proto-GCs in a hierarchical merging paradigm would have provided helium enhanced stars to the bulge field.

scholarly journals Multiple Stellar Populations at Less-evolved Stages-II: No Evidence of Significant Helium Spread among NGC 1846 Dwarfs

2021 ◽  
Vol 921 (2) ◽  
pp. 171
Author(s):  
Chengyuan Li
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
Hubble Space Telescope ◽  
Star Clusters ◽  
Stellar Populations ◽  
Color Variation ◽  
Nitrogen Enrichment ◽  
Main Sequence Stars ◽  
Red Giant ◽  
Cluster Age

Abstract The detection of star-to-star chemical variations in star clusters older than 2 Gyr has changed the traditional view of star clusters as canonical examples of “simple stellar populations” into the so-called “multiple stellar populations” (MPs). Although the significance of MPs seems to correlate with cluster total mass, it seems that the presence of MPs is determined by cluster age. In this article, we use deep photometry from the Hubble Space Telescope to investigate whether the FG-type dwarfs in the ∼1.7 Gyr old cluster NGC 1846, have helium spread. By comparing the observation with the synthetic stellar populations, we estimate a helium spread of ΔY ∼ 0.01 ± 0.01 among the main-sequence stars in NGC 1846. The maximum helium spread would not exceed ΔY ∼ 0.02, depending on the adopted fraction of helium-enriched stars. To mask the color variation caused by such a helium enrichment, a nitrogen enrichment of at least Δ[N/Fe] = 0.8 dex is required, which is excluded by previous analyses of the red-giant branch in this cluster. We find that our result is consistent with the ΔY–mass relationship for Galactic globular clusters. To examine whether or not NGC 1846 harbors MPs, higher photometric accuracy is required. We conclude that under the adopted photometric quality, there is no extreme helium variation among NGC 1846 dwarfs.

scholarly journals Tracing early stellar evolution with asteroseismology: pre-main sequence stars in NGC 2264

2015 ◽  
Vol 101 ◽  
pp. 01010 ◽  
Author(s):  
Konstanze Zwintz ◽  
Luca Fossati ◽  
Tatiana Ryabchikova ◽  
David Guenther ◽  
Conny Aerts
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Main Sequence Stars

scholarly journals Globular clusters and the evolution of their multiple stellar populations

2015 ◽  
Vol 12 (S316) ◽  
pp. 328-333
Author(s):  
W. Chantereau ◽  
C. Charbonnel ◽  
G. Meynet
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
Chemical Properties ◽  
Stellar Populations ◽  
Chemical Compositions ◽  
Low Mass Stars ◽  
Sequence Band ◽  
Low Mass ◽  
Chemical Distribution ◽  
Host Stars

AbstractOur knowledge of the formation and early evolution of globular clusters (GCs) has been totally shaken with the discovery of the peculiar chemical properties of their long-lived host stars. Therefore, the interpretation of the observed Colour Magnitude Diagrams (CMD) and of the properties of the GC stellar populations requires the use of new stellar models computed with relevant chemical compositions. In this paper we use the grid of evolution models for low-mass stars computed by Chantereau et al. (2015) with the initial compositions of second-generation stars as predicted by the fast rotating massive stars scenario to build synthesis models of GCs. We discuss the implications of the assumed initial chemical distribution on 13 Gyr isochrones. We build population synthesis models to predict the fraction of stars born with various helium abundances in present day globular clusters (assuming an age of 13 Gyr). With the current assumptions, 61 % of stars on the main sequence are predicted to be born with a helium abundance in mass fraction, Yini, smaller than 0.3 and only 11 % have a Yini larger than 0.4. Along the horizontal branch, the fraction of stars with Yini inferior to 0.3 is similar to that obtained along the main sequence band (63 %), while the fraction of very He-enriched stars is significantly decreased (only 3 % with Yini larger than 0.38).

scholarly journals The importance of helium and metals diffusion in stars

1997 ◽  
Vol 189 ◽  
pp. 355-360
Author(s):  
Charles R. Proffitt
Keyword(s):  
Sound Speed ◽  
Globular Clusters ◽  
Main Sequence ◽  
Chemical Elements ◽  
Substantial Reduction ◽  
Solar Interior ◽  
Relative Importance ◽  
Main Sequence Stars ◽  
Gravitational Settling ◽  
Hydrodynamic Processes

Comparisons between models of the solar interior and sound speed profiles derived from inversions of helioseismic data have demonstrated that it is essential to include the effects of gravitational settling when calculating the structure and evolution of the Sun. Including settling should also be necessary for models of metal poor main-sequence stars and results in a substantial reduction in the ages derived for globular clusters.In many cases it is clear that competing hydrodynamic processes, such as mass loss or rotationally driven mixing, will limit the effectiveness of gravitational separation of chemical elements. However, the quantitative details and even the relative importance of the different processes in various types of stars remains poorly understood.

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