scholarly journals The Dark Side of Globular Clusters

1996 ◽  
Vol 174 ◽  
pp. 377-378
Author(s):  
P.-Y. Longaretti ◽  
R. Taillet ◽  
P. Salati
Keyword(s):  
Globular Clusters ◽  
Mass Function ◽  
Dynamical Analysis ◽  
Dark Side ◽  
Low Mass Stars ◽  
First Results ◽  
Low Mass ◽  
Non Parametric

Searches of low-mass stars have become possible in globular clusters, and the first results suggest that the mass function turns up below ∼ 0.4 M⊙ (Fahlman et al. 1989; Richer et al., 1990; Richer et al. 1991; G. Piotto, these proceedings). This conclusion is independently supported by the non-parametric dynamical analysis of four clusters by Gebhardt and Fisher 1995.

scholarly journals Globular Clusters: Low Mass Stars, Still No Brown Dwarfs!

2003 ◽  
Vol 211 ◽  
pp. 215-222
Author(s):  
Guido De Marchi
Keyword(s):  
Globular Clusters ◽  
Functional Form ◽  
Dynamical Evolution ◽  
Mass Function ◽  
Brown Dwarf ◽  
Low Mass Stars ◽  
Homogeneous Sample ◽  
Original Mass ◽  
Low Mass ◽  
The Imf

In spite of all the attempts to find them, no one has yet detected any brown dwarf in a globular cluster. Although powerful instruments such as the VLT and Advanced Camera could further push the frontiers of this search, globular clusters will probably hold tight to their secrets for a while longer. Nonetheless, the search for very low mass stars in globular clusters has taught us a lot about their original mass distribution (IMF) and its evolution in time. I shall review the results of an investigation carried out over what is presently the largest, most homogeneous sample, and discuss the reasons suggesting that: 1. dynamical evolution (internal and external) has reshaped the cluster mass function over time, but the imprint of the IMF is still visible; 2. the IMF appears to vary very little from cluster to cluster; 3. the most likely functional form of the IMF is that of a power law that rises to a peak at ˜ 0.3 M⊙ and tapers off at smaller masses.

The Initial Mass Function of Low-Mass Stars in Globular Clusters

1997 ◽  
Vol 476 (1) ◽  
pp. L19-L22 ◽  
Author(s):  
Guido De Marchi ◽  
Francesco Paresce
Keyword(s):  
Globular Clusters ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Low Mass Stars ◽  
Low Mass

Dynamical Evolution of Globular Clusters with Mass Spectrum

1991 ◽  
Vol 9 (1) ◽  
pp. 41-44
Author(s):  
Hyung Mok Lee
Keyword(s):  
Mass Spectrum ◽  
Globular Clusters ◽  
Numerical Models ◽  
Relaxation Times ◽  
Dynamical Evolution ◽  
Planck Equation ◽  
Mass Function ◽  
Low Mass Stars ◽  
Wide Range ◽  
Three Body

AbstractWe present a series of numerical models describing the dynamical evolution of globular clusters with a mass spectrum, based on integration of the Fokker-Planck equation. We include three-body binary heating and a steady galactic tidal field. A wide range of initial mass functions is adopted and the evolution of the mass function is examined. The mass function begins to change appreciably during the post-collapse expansion phase due to the selective evaporation of low mass stars through the tidal boundary. One signature of highly evolved clusters is thus the significant flattening of the mass function. The age (in units of the half-mass relaxation time) increases very rapidly beyond about 100 signifying the final stage of cluster disruption. This appears to be consistent with the sharp cut-off of half-mass relaxation times at near 108 years for the Galactic globular clusters.

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 Multi-Wavelength High-Resolution Spectroscopy for Exoplanet Detection: Motivation, Instrumentation and First Results

Geosciences ◽  
2018 ◽  
Vol 8 (8) ◽  
pp. 289 ◽  
Author(s):  
Serena Benatti
Keyword(s):  
High Resolution ◽  
Near Infrared ◽  
Giant Planet ◽  
High Resolution Spectroscopy ◽  
M Dwarfs ◽  
Low Mass Stars ◽  
First Results ◽  
Multi Wavelength ◽  
Low Mass ◽  
Rocky Planets

Exoplanet research has shown an incessant growth since the first claim of a hot giant planet around a solar-like star in the mid-1990s. Today, the new facilities are working to spot the first habitable rocky planets around low-mass stars as a forerunner for the detection of the long-awaited Sun-Earth analog system. All the achievements in this field would not have been possible without the constant development of the technology and of new methods to detect more and more challenging planets. After the consolidation of a top-level instrumentation for high-resolution spectroscopy in the visible wavelength range, a huge effort is now dedicated to reaching the same precision and accuracy in the near-infrared. Actually, observations in this range present several advantages in the search for exoplanets around M dwarfs, known to be the most favorable targets to detect possible habitable planets. They are also characterized by intense stellar activity, which hampers planet detection, but its impact on the radial velocity modulation is mitigated in the infrared. Simultaneous observations in the visible and near-infrared ranges appear to be an even more powerful technique since they provide combined and complementary information, also useful for many other exoplanetary science cases.

scholarly journals Observations of low mass stars in clusters: Some constraints and puzzles for stellar evolution theory

1984 ◽  
Vol 105 ◽  
pp. 123-138
Author(s):  
R.D. Cannon
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
Star Clusters ◽  
Variable Stars ◽  
Open Clusters ◽  
Low Mass Stars ◽  
Theory Of Evolution ◽  
Theoretical Predictions ◽  
Low Mass ◽  
Red Giant

This review will attempt to do two things: (i) discuss some of the data which are available for testing the theory of evolution of low mass stars, and (ii) point out some problem areas where observations and theory do not seem to agree very well. This is of course too vast a field of research to be covered in one brief review, so I shall concentrate on one particular aspect, namely the study of star clusters and especially their colour-magnitude (CM) diagrams. Star clusters provide large samples of stars at the same distance and with the same age, and the CM diagram gives the easiest way of comparing theoretical predictions with observations, although crucial evidence is also provided by spectroscopic abundance analyses and studies of variable stars. Since this is primarily a review of observational data it is natural to divide it into two parts: (i) galactic globular clusters, and (ii) old and intermediate-age open clusters. Some additional evidence comes from Local Group galaxies, especially now that CM diagrams which reach the old main sequence are becoming available. For each class of cluster I shall consider successive stages of evolution from the main sequence, up the hydrogen-burning red giant branch, and through the helium-burning giant phase.

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 The Globular Cluster Population of X-ray Binaries

1987 ◽  
Vol 125 ◽  
pp. 187-197 ◽  
Author(s):  
Frank Verbunt ◽  
Piet Hut
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Mass Function ◽  
Initial Mass Function ◽  
Encounter Rate ◽  
Formation Mechanisms ◽  
Main Sequence Stars ◽  
X Ray ◽  
Low Mass ◽  
X Ray Binaries

We discuss formation mechanisms for low-mass X-ray binaries in globular clusters. We apply the most efficient mechanism, tidal capture in close two-body encounters between neutron and main-sequence stars, to the clusters of our galaxy. The observed number of X-ray sources in these can be explained if the birth velocities of neutron stars are higher than estimated from velocity measurements of radiopulsars, or if the initial mass function steepens at high masses. We perform a statistical test on the distribution of X-ray sources with respect to the number of close encounters in globular clusters, and find satisfactory agreement between the tidal capture theory and observation, apart from the presence of low-mass X-ray binaries in four clusters with a very low encounter rate: Ter 1, Ter 2, Gr 1 and NGC 6712.EXOSAT observations indicate that some dim globular cluster sources may be less luminous than hitherto assumed, and support the view that the brighter dim sources may be soft X-ray transients in quiescence.

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