scholarly journals Collisions of Main-Sequence Stars and the Formation of Blue Stragglers in Globular Clusters

1996 ◽  
Vol 468 ◽  
pp. 797 ◽  
Author(s):  
James C., Jr. Lombardi ◽  
Frederic A. Rasio ◽  
Stuart L. Shapiro
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
Main Sequence Stars ◽  
Blue Stragglers

scholarly journals Observations of blue straggler stars in globular clusters

2006 ◽  
Vol 2 (14) ◽  
pp. 438-439
Author(s):  
Francesco R. Ferraro ◽  
Barbara Lanzoni
Keyword(s):  
Globular Clusters ◽  
Binary Systems ◽  
Stellar Population ◽  
Main Sequence ◽  
Formation Mechanisms ◽  
Main Sequence Stars ◽  
Blue Stragglers ◽  
Photometric And Spectroscopic Observations ◽  
Blue Straggler ◽  
Dynamical Simulations

AbstractBlue stragglers stars (BSS) define a sparsely populated sequence extending to higher luminosity than the turnoff point of normal main sequence stars in the color magnitude diagrams of stellar aggregates, thus mimicking a rejuvenated (more massive) stellar population. The nature of these stars has been a puzzle for many years and their formation mechanism is not completely understood, yet. Two mechanisms have been proposed to produce BSS: (i) the mass transfer in binary systems; and ((ii) the merger of two stars induced by stellar interactions. In this contribution we schematically report on the main properties of BSS in globular clusters (GCs) in the light of the most recent photometric and spectroscopic observations. These results, combined with dynamical simulations, indicate that both the proposed formation mechanisms play an important role in the production of BSS in GCs.

scholarly journals SPH Calculations of Collisions Between Main-Sequence Stars

1996 ◽  
Vol 174 ◽  
pp. 253-262
Author(s):  
Frederic A. Rasio
Keyword(s):  
Smoothed Particle Hydrodynamics ◽  
Globular Clusters ◽  
Main Sequence ◽  
Theoretical Models ◽  
Main Sequence Stars ◽  
Sph Method ◽  
Blue Stragglers ◽  
Particle Hydrodynamics ◽  
Smoothed Particle

The hydrodynamics of collisions and mergers of main-sequence stars is discussed in the light of recent 3-D calculations using the smoothed particle hydrodynamics (SPH) method. Theoretical models for the formation of blue stragglers are reviewed in the context of recent comparisons between the observed properties of blue stragglers in dense globular clusters and the predictions of those models.

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.

scholarly journals A high-spectral-resolution study of abundances and isotopic composition of BHB stars in NGC 6397 and NGC 6752

2009 ◽  
Vol 5 (S266) ◽  
pp. 421-421
Author(s):  
S. Hubrig ◽  
F. Castelli ◽  
G. De Silva ◽  
J. F. González ◽  
Y. Momany ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
High Spectral Resolution ◽  
Horizontal Branch ◽  
Main Sequence Stars ◽  
Chemical Abundances ◽  
Chemically Peculiar ◽  
Abundance Anomalies ◽  
Isotopic Anomalies ◽  
Resolution Study

AbstractLarge abundance anomalies have previously been detected in horizontal-branch B-type stars. We present the first high-resolution study of isotopic anomalies and chemical abundances in six horizontal-branch B-type stars in the globular clusters NGC 6397 and NGC 6752, carried out with UVES on the VLT and compare them to those observed in chemically peculiar main-sequence stars.

scholarly journals A Spectroscopic Study of Blue Stragglers in M67

2008 ◽  
Vol 4 (S252) ◽  
pp. 391-397
Author(s):  
G. Q. Liu ◽  
L. Deng ◽  
M. Chávez ◽  
E. Bertone
Keyword(s):  
Effective Temperature ◽  
Spectral Properties ◽  
Main Sequence ◽  
Open Cluster ◽  
Observational Constraints ◽  
Photometric System ◽  
Main Sequence Stars ◽  
Complete Sample ◽  
Blue Stragglers ◽  
Fitting Method

AbstractSpectrophotometric observations of the complete sample of twenty four blue stragglers (BSs) in the old galactic open cluster M67 (NGC2682) have been collected, using the Guillermo Haro Observatory in Cananea, Mexico. All the calibrated spectra were re-calibrated by the Beijing Arizona Taipei Connecticut (BATC) photometric system which includes fluxes in 11 photometric bands covering ~3600–10000 Å. The goal of the current work is to provide observational constraints on spectral properties of BSs by determining the effective temperature (Teff) and surface gravity (log g). The overall results, obtained by applying the flux fitting method, indicate that Teff and surface gravities of BSs in M67 are fully compatible with those expected for main sequence stars.

scholarly journals Color-Luminosity Relations for the Resolved Hot Stellar Populations in the Centers of M31 and M32

1999 ◽  
Vol 192 ◽  
pp. 195-202
Author(s):  
Thomas M. Brown ◽  
Henry C. Ferguson ◽  
S. A. Stanford ◽  
Jean-Michel Deharveng
Keyword(s):  
Stellar Population ◽  
Main Sequence ◽  
Uv Spectra ◽  
Agb Stars ◽  
Main Sequence Stars ◽  
Blue Stragglers ◽  
Faint Object ◽  
Luminosity Functions ◽  
Uv Upturn ◽  
Small Field Of View

We present Faint Object Camera (FOC) ultraviolet images of the central 14 x 14″ of Messier 31 and Messier 32. The hot stellar population detected in the composite UV spectra of these galaxies is partially resolved into stars, and we measure their colors and apparent magnitudes. We detect 433 stars in M31 and 138 stars in M32, down to limits of mF275W = 25.5 mag and mF175W = 24.5 mag. We investigate the luminosity functions of the sources, their spatial distribution, their color-magnitude diagrams, and their total integrated far-UV flux. Although M32 has a weaker UV upturn than M31, the luminosity functions and color-magnitude diagrams of M31 and M32 are surprisingly similar, and are inconsistent with a majority contribution from any of the following: post-AGB stars more massive than 0.56 M⊙, main sequence stars, or blue stragglers. The luminosity functions and color-magnitude diagrams are consistent with a dominant population of stars evolving from the extreme horizontal branch (EHB) along tracks of mass 0.47–0.53 M⊙. These stars are well below the detection limits of our images while on the zero-age EHB, but become detectable while in the more luminous (but shorter) post-HB phases. Our observations require that only a very small fraction of the main sequence population (2% in M31 and 0.5% in M32) in these two galaxies evolve though the EHB and post-EHB phases, with the remainder rapidly evolving through bright post-AGB evolution with few resolved stars expected in the small field of view covered by the FOC.

scholarly journals Building Blue Stragglers with Stellar Collisions

2007 ◽  
Vol 3 (S246) ◽  
pp. 363-364
Author(s):  
Evert Glebbeek ◽  
Onno R. Pols
Keyword(s):  
Main Sequence ◽  
Main Sequence Star ◽  
Main Sequence Stars ◽  
Blue Stragglers ◽  
Stellar Collisions ◽  
Hydrodynamical Simulations

AbstractThe evolution of stellar collision products in cluster simulations has usually been modelled using simplified prescriptions. Such prescriptions either replace the collision product with an (evolved) main sequence star, or assume that the collision product was completely mixed during the collision.It is known from hydrodynamical simulations of stellar collisions that collision products are not completely mixed, however. We have calculated the evolution of stellar collision products and find that they are brighter than normal main sequence stars of the same mass, but not as blue as models that assume that the collision product was fully mixed during the collision.

scholarly journals Observational signatures of lithium depletion in the metal-poor globular cluster NGC6397

2009 ◽  
Vol 5 (S268) ◽  
pp. 263-268 ◽  
Author(s):  
Karin Lind ◽  
Francesca Primas ◽  
Corinne Charbonnel ◽  
Frank Grundahl ◽  
Martin Asplund
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Main Sequence ◽  
Galactic Halo ◽  
Main Sequence Stars ◽  
Surface Evolution ◽  
Halo Stars ◽  
Systematic Uncertainties ◽  
Low Mass ◽  
Lithium Depletion

AbstractThe “stellar” solution to the cosmological lithium problem proposes that surface depletion of lithium in low-mass, metal-poor stars can reconcile the lower abundances found for Galactic halo stars with the primordial prediction. Globular clusters are ideal environments for studies of the surface evolution of lithium, with large number statistics possible to obtain for main sequence stars as well as giants. We discuss the Li abundances measured for >450 stars in the globular cluster NGC 6397, focusing on the evidence for lithium depletion and especially highlighting how the inferred abundances and interpretations are affected by early cluster self-enrichment and systematic uncertainties in the effective temperature determination.

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