scholarly journals Blue Stragglers: Spectra of Globular Clusters

2009 ◽  
Vol 5 (S262) ◽  
pp. 23-26
Author(s):  
A. J. Cenarro ◽  
J. L. Cervantes ◽  
M. A. Beasley ◽  
A. Marin-Franch ◽  
A. Vazdekis
Keyword(s):  
Globular Clusters ◽  
Stellar Population ◽  
Main Sequence ◽  
Stellar Systems ◽  
Blue Stragglers ◽  
Horizontal Branch Stars ◽  
Blue Straggler ◽  
Balmer Lines ◽  
Specific Frequency ◽  
High Metallicity

AbstractThe integrated Balmer lines of unresolved stellar systems have been widely used as age indicators, since they are sensitive to the temperature of the main sequence turn-off. However, the existence of “non-canonical” stellar stages such as hot horizontal branch stars and blue straggler stars (BSSs) can lead to underestimations of the true stellar population ages. Using an optimized Hβ index in conjunction with HST/WFPC2 color-magnitude diagrams (CMDs), we find that Galactic globular clusters of similar metallicity exhibit a large scatter in their Hβ strengths, which does not correlate with their CMD-derived ages. Instead, we demonstrate that the specific frequency of BSSs is responsible for the observed Hβ scatter at intermediate-to-high metallicity, in the sense that, at fixed metallicity, higher BSS ratios lead to larger integrated Hβ strengths. Therefore, the specific frequency of BSSs sets a fundamental limit on the accuracy for which integrated spectroscopic ages can be determined for globular clusters and, probably, other stellar systems like galaxies. The observational implications of this result are discussed.

scholarly journals Exotic populations in globular clusters: blue stragglers as tracers of the internal dynamical evolution of stellar systems

2014 ◽  
Vol 10 (S312) ◽  
pp. 171-180
Author(s):  
Francesco R. Ferraro
Keyword(s):  
Radial Distribution ◽  
Globular Clusters ◽  
Stellar Population ◽  
Dynamical Evolution ◽  
Stellar Systems ◽  
Internal Dynamics ◽  
Blue Stragglers ◽  
Blue Straggler ◽  
Specific Frequency ◽  
Definition Of

AbstractIn this paper I present an overview of the main observational properties of a special class of exotic objects (the so-called Blue Straggler Stars, BSSs) in Galactic Globular Clusters (GCs). The BSS specific frequency and their radial distribution are discussed in the framework of using this stellar population as probe of GC internal dynamics. In particular, the shape of the BSS radial distribution has been found to be a powerful tracer of the dynamical evolution of stellar systems, thus allowing the definition of an empirical “clock”able to measure the dynamical age of stellar aggregates from pure observational properties.

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 Mid-UV Spectral Diagnostics

2009 ◽  
Vol 5 (S262) ◽  
pp. 351-352
Author(s):  
Sara R. Heap ◽  
Don Lindler
Keyword(s):  
Stellar Evolution ◽  
Stellar Population ◽  
Main Sequence ◽  
Horizontal Branch ◽  
Spectral Indices ◽  
Blue Stragglers ◽  
Horizontal Branch Stars ◽  
Spectral Diagnostics ◽  
Diagnostic Region

AbstractThe mid-ultraviolet is an important diagnostic region due to its sensitivity to the hottest stars of a stellar population. Sources of mid-UV flux include main sequence turn-off stars, the basic clocks of stellar evolution, and also blue horizontal branch stars and blue stragglers. We describe some observed trends in mid-UV colors and spectral indices.

An empirical clock to measure the dynamical age of star clusters

2019 ◽  
Vol 14 (S351) ◽  
pp. 377-383
Author(s):  
Francesco R. Ferraro
Keyword(s):  
Radial Distribution ◽  
Special Class ◽  
Globular Clusters ◽  
Stellar Population ◽  
Star Clusters ◽  
Dynamical Evolution ◽  
Stellar Systems ◽  
Central Segregation ◽  
Blue Straggler ◽  
Definition Of

AbstractThe observational properties of a special class of stars (the so-called Blue Straggler stars - BSSs) in Globular Clusters are discussed in the framework of using this stellar population as probe of the dynamical processes occurring in high-density stellar systems. In particular, the shape of the BSS radial distribution and their level of central segregation have been found to be powerful tracers of the level of the dynamical evolution of the hosting cluster, thus allowing the definition of an empirical chronometer able to measure the dynamical age of star clusters.

scholarly journals The WAGGS project-III. Discrepant mass-to-light ratios of Galactic globular clusters at high metallicity

2020 ◽  
Vol 492 (3) ◽  
pp. 3859-3871 ◽  
Author(s):  
H Dalgleish ◽  
S Kamann ◽  
C Usher ◽  
H Baumgardt ◽  
N Bastian ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Stellar Population ◽  
Milky Way ◽  
Population Models ◽  
Theoretical Predictions ◽  
Field Unit ◽  
Stellar Masses ◽  
Kinematic Information ◽  
High Metallicity ◽  
Integral Field

ABSTRACT Observed mass-to-light ratios (M/L) of metal-rich globular clusters (GCs) disagree with theoretical predictions. This discrepancy is of fundamental importance since stellar population models provide the stellar masses that underpin most of extragalactic astronomy, near and far. We have derived radial velocities for 1622 stars located in the centres of 59 Milky Way GCs – 12 of which have no previous kinematic information – using integral-field unit data from the WAGGS project. Using N-body models, we determine dynamical masses and M/LV for the studied clusters. Our sample includes NGC 6528 and NGC 6553, which extend the metallicity range of GCs with measured M/L up to [Fe/H] ∼ −0.1 dex. We find that metal-rich clusters have M/LV more than two times lower than what is predicted by simple stellar population models. This confirms that the discrepant M/L–[Fe/H] relation remains a serious concern. We explore how our findings relate to previous observations, and the potential causes for the divergence, which we conclude is most likely due to dynamical effects.

scholarly journals Spectroscopic Binaries in the Open Cluster M67

1992 ◽  
Vol 135 ◽  
pp. 155-157 ◽  
Author(s):  
David W. Latham ◽  
Robert D. Mathieu ◽  
Alejandra A.E. Milone ◽  
Robert J. Davis
Keyword(s):  
Circular Orbit ◽  
Main Sequence ◽  
Open Cluster ◽  
Radial Velocities ◽  
Spectroscopic Binaries ◽  
Eccentric Orbit ◽  
Circular Orbits ◽  
Blue Stragglers ◽  
Short Period ◽  
Blue Straggler

AbstractFor almost 400 members of M67 we have accumulated about 5,000 precise radial velocities. Already we have orbital solutions for more than 32 spectroscopic binaries in M67. Many of these orbits were derived by combining the Palomar and CfA observations, thus extending the time coverage to more than 20 years. The distribution of eccentricity versus period shows evidence for tidal circularization on the main sequence. The transition from circular orbits is fairly clean. Excluding the blue stragglers, the first eccentric orbit has a period of 11.0 days, while the last circular orbit has a period of 12.4 days. For longer periods the distribution of eccentricity is the same as for field stars. The blue straggler S1284 has an eccentric orbit despite its short period of 4.2 days.

scholarly journals The origin of the two populations of blue stragglers in M30

2019 ◽  
Vol 621 ◽  
pp. L10 ◽  
Author(s):  
S. Portegies Zwart
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
The Other ◽  
Core Collapse ◽  
Blue Stragglers ◽  
The Core ◽  
Constant Rate ◽  
Blue Straggler ◽  
Binary Evolution ◽  
Two Populations

We analyze the position of the two populations of blue stragglers in the globular cluster M30 in the Hertzsprung–Russell diagram. Both populations of blue stragglers are brighter than the cluster’s turn-off, but one population, the blue blue-stragglers, aligns along the zero-age main sequence whereas the other, red population is elevated in brightness (or color) by ∼0.75 mag. Based on stellar evolution and merger simulations we argue that the red population, which composes about 40% of the blue stragglers in M 30, has formed at a constant rate of ∼2.8 blue stragglers per gigayear over the last ∼10 Gyr. The blue population on the other hand formed in a burst that started ∼3.2 Gyr ago at a peak rate of 30 blue stragglers per gigayear with an e-folding time scale of 0.93 Gyr. We speculate that the burst resulted from the core collapse of the cluster at an age of about 9.8 Gyr, whereas the constantly formed population is the result of mass transfer and mergers through binary evolution. In this scenario, about half the binaries in the cluster effectively result in a blue straggler.

scholarly journals Measuring the GC luminosity function up to z ~ 0.2

2009 ◽  
Vol 5 (S266) ◽  
pp. 351-351
Author(s):  
K. A. Alamo-Martínez ◽  
R. A. González-Lópezlira ◽  
J. Blakeslee
Keyword(s):  
Galaxy Formation ◽  
Globular Clusters ◽  
Surface Brightness ◽  
Luminosity Function ◽  
Elliptical Galaxy ◽  
Angular Size ◽  
Spectroscopic Studies ◽  
Stellar Systems ◽  
Surface Brightness Fluctuations ◽  
Specific Frequency

AbstractGlobular clusters (GCs) are stellar systems (~106 M⊙) with very regular symmetry, single age, and single metallicity. Spectroscopic studies have revealed very old ages, suggesting that GCs were formed in the earliest stages of galaxy formation and assembly. The aim of this work is to find out how far we can measure the GC luminosity function, specific frequency, and radial distribution, applying the surface-brightness-fluctuations (SBF) technique to deep ACS images. To this end, we apply the effects caused by higher redshift to HST/ACS images (in two optical bands, F606W and F814W) of M87, an elliptical galaxy with a very well-studied GC system. The effects involved are: (i) evolution, (ii) inverse k correction, (iii) binning of the image to smaller angular size, (iv) cosmological dimming of surface brightness, and (v) noise addition to account for different exposure times. After processing the images we detect the brightest GCs through direct photometry (e.g., with SExtractor), whereas the unresolved clusters are measured through SBFs. The above treatment is repeated for z=0.05, 0.1, 0.14, and 0.18, and the results are compared to the measurements at z=0 to estimate biases and incompleteness.

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 An overview of the rotational behavior of metal-poor stars

2009 ◽  
Vol 5 (S266) ◽  
pp. 374-374
Author(s):  
C. Cortés ◽  
J. R. P. Silva ◽  
A. Recio–Blanco ◽  
M. Catelan ◽  
J. D. Do Nascimento ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Globular Clusters ◽  
Main Sequence ◽  
Rotational Velocity ◽  
Transport Mechanisms ◽  
Rotation Rates ◽  
Blue Straggler ◽  
Low Metallicity ◽  
Red Giant ◽  
Fast Rotating

AbstractWe describe the behavior of the rotational velocity in metal-poor stars ([Fe/H] ~ −0.5 dex) at different evolutionary stages, based on v sin i values from the literature. Our sample is composed of stars in the field and in some Galactic globular clusters, including stars on the main sequence (MS), red-giant branch (RGB), and horizontal branch (HB). The metal-poor stars are mainly slow rotators, and their v sin i distribution along the Hertzsprung–Russell diagram is quite homogeneous. Nevertheless, a few moderate to high values of v sin i are found for stars located on the MS and the HB. We show that the overall distribution of v sin i values is basically independent of metallicity for the stars in our sample. In particular, the fast-rotating MS stars in our sample exhibit similar rotation rates as their metal-rich counterparts, suggesting that some may actually be fairly young, in spite of their low metallicity, or else that at least some would be better classified as blue straggler stars. We do not find significant evidence of evolution in v sin i values as a function of position on the RGB. In particular, we do not confirm previous suggestions that stars close to the RGB tip rotate faster than their less-evolved counterparts. While the presence of fast rotators among moderately cool blue-HB stars has been suggested as due to angular-momentum transport from a stellar core that has retained significant angular momentum during its prior evolution, we find that any such transport mechanisms must likely operate very fast as the star arrives on the zero-age HB (ZAHB), since we do not find a link between evolution off the ZAHB and v sin i values.

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