scholarly journals The Concept of Old Stellar Populations

1983 ◽  
Vol 6 ◽  
pp. 95-100
Author(s):  
Gösta Lyngå
Keyword(s):  
Globular Clusters ◽  
Stellar Population ◽  
Age Groups ◽  
Stellar Populations ◽  
Heavy Elements ◽  
The Galaxy ◽  
Star Formation In Galaxies ◽  
Solar Abundances ◽  
Central Bulge ◽  
Stellar Envelopes

Almost 25 years ago Walter Baade told the Vatican conference about the meaning of stellar populations:“We also understand now why the two stellar populations, either singly or combined, are such conspicuous features in most galaxies. They are age groups which represent two significant phases of the star formation in galaxies.”There appeared a straight-forward picture with an old, metal-poor halo containing stars in elongated galactic orbits and a younger disk population, where the stars have near solar abundances and near circular orbits. The central bulge of the galaxy was considered part of the older system.New observations have made the picture more complex and also more controversial, indicating that it still might not be fully understood. Stars in the bulge of our spiral galaxy have been shown to have rather high contents of heavy elements. The gas and perhaps also the stars of the disk show a metal content that is decreasing outwards in the disk. The abundances in globular clusters differ widely between individual clusters and even between individual stars of the same cluster. It has become clear that one must discuss separately the different heavy elements; that some abundances may be considered primordial and thus characteristic of the evolution of the stellar population, whereas other abundance differences may be caused by mixing into the stellar envelopes.

scholarly journals Peculiarities of the Stellar Population of Bars in the LMC and Other Barred Galaxies

1999 ◽  
Vol 190 ◽  
pp. 349-350
Author(s):  
A. S. Gusev
Keyword(s):  
Star Formation ◽  
Stellar Population ◽  
Age Groups ◽  
Stellar Populations ◽  
Large Magellanic Cloud ◽  
Star Formation History ◽  
Barred Galaxies ◽  
The Galaxy ◽  
Using Data ◽  
Color Sequence

The age distributions in the bar and disk of the Large Magellanic Cloud are studied using data for 262 clusters with known ages, of which 89 are located in the bar. The spatial distributions for clusters in different age groups are investigated. Epochs of active star formation are determined for the bar and disk of the LMC. The ages of the stellar populations in the bar differ from that for the galaxy as a whole: in the bar, there is a deficit of intermediate-age clusters (5 × 108–6 × 109 yr) and an excess of young clusters with ages 3 × 107–5 × 108 yr. This indicates that the star formation history in the bar differs from that in regions outside the bar at the same distances from the center of the galaxy. Data on the composition of the old stellar populations in the bar and the disk of the LMC and the spatial distribution of intermediate-age clusters in the galaxy suggest that the LMC bar formed (2–6) × 109 years ago. Deviation of colors of bars from the normal color sequence of galaxies on several two-color diagrams is found using multicolor surface photometry for eight barred galaxies. Using results of evolutionary synthesis modeling, I can model the abnormal colors of bars by an intermediate-age star (~ 109 yr) deficiency. I find that the deficiency of an intermediate-age stellar population is a general property of bars.

Stellar Population Models of Distant Radio Galaxies

1996 ◽  
Vol 175 ◽  
pp. 588-590
Author(s):  
D. Villani ◽  
S. Di Serego Alighieri
Keyword(s):  
Energy Distribution ◽  
Galaxy Formation ◽  
Stellar Population ◽  
Spectral Energy Distribution ◽  
Formation Rate ◽  
Stellar Populations ◽  
Radio Galaxies ◽  
Initial Mass Function ◽  
Spectral Energy ◽  
The Galaxy

Stellar populations of high redshift radio galaxies (HzRG) (z up to 4.2) are the oldest stellar systems known, that is the ones formed at the earliest cosmological epochs. Therefore they are the best objects for providing us with information about the epoch of galaxy formation. The information on the stellar populations in HzRG are obtained from the study of their Integrated Spectral Energy Distribution (ISED) which are gathered both from spectra and integrated magnitudes. The most common approach for the interpretation of colors and spectral features of the energy distribution of galaxies is the Evolutionary Population Synthesis (EPS), which has been introduced for the first time by Tinsley in 1972. EPS models have often been used in the past to interpret the ISED of HzRG (Chambers & Charlot 1990; Lilly & Longair 1984; di Serego Alighieri et al. 1994) in order to draw conclusions on the age of the stellar populations and therefore on the epoch of galaxy formation. The results are sometimes conflicting and a number of very recent EPS models have become available (Bressan et al. 1995; Bruzual & Charlot 1993; Buzzoni 1989; Guiderdoni & Rocca-Volmerange 1987): we are therefore analysing the differences between the various EPS models with the aim of assessing their suitability to study the stellar population at early epochs. The EPS models assume for stars a given Initial Mass Function(IMF) as well as a Star Formation Rate (SFR). Then one can compute the number of stars with given mass present in the galaxy as a function of time. The position of each star in the HR diagram is determined by means of the isochrones, which are calculated from stellar evolutionary models. The ISED of a galaxy is obtained from the superposition of the spectra of single stars obtained from a stellar spectral library. Thus these models describe the galaxy ISED as a function of the time, giving a complete evolutionary picture.

scholarly journals Deep Multi-Colour Starcounts

1994 ◽  
Vol 161 ◽  
pp. 423-424
Author(s):  
I.N. Reid ◽  
S.R. Majewski
Keyword(s):  
Standard Model ◽  
Stellar Population ◽  
Stellar Populations ◽  
The North ◽  
Halo Stars ◽  
The Standard Model ◽  
The Galaxy ◽  
Best Fitting ◽  
Galactic Stellar Populations ◽  
North Galactic

Starcounts remain one of the most effective methods of probing the structure of the Galactic stellar populations. However, studies of the distribution at large distances above the Plane demand accurate photometry extending to faint magnitudes (V > 20), and such datasets are still rare. We (Reid & Majewski 1993) have analyzed data from one field — Majewski's (1992) UJF observations of SA57, the North Galactic Pole field. Our results revealed significant discrepancies with the standard model of the Galaxy (see refs. in Reid & Majewski), notably a paucity in the number of halo stars by a factor of two and the presence of a factor of two more disk stars than predicted — sufficient stars that the disk is the majority stellar population, outnumbering halo stars 2:1 even at V = 21. Majewski et al. (1993) has obtained UJFN photographic data for several other fields, and Fig. 1 shows a preliminary comparison of these observations with the predictions of the best-fitting SA57 model. Given that none of the parameters have been modified, the agreement is surprisingly good.

scholarly journals Helium-rich stars in globular clusters: constraints for self-enrichment by massive stars

2009 ◽  
Vol 5 (S268) ◽  
pp. 135-140 ◽  
Author(s):  
Thibaut Decressin ◽  
G. Meynet ◽  
C. Charbonnel
Keyword(s):  
Globular Clusters ◽  
Massive Stars ◽  
Stellar Populations ◽  
The Self ◽  
Heavy Elements ◽  
Light Elements ◽  
Intracluster Gas ◽  
Fast Rotating

AbstractGlobular clusters exhibit peculiar chemical patterns where Fe and heavy elements are constant inside a given cluster while light elements (Li to Al) show strong star-to-star variations. This pattern can be explained by self-pollution of the intracluster gas by the slow winds of fast rotating massive stars. Besides, several main sequences have been observed in several globular clusters which can be understood only with different stellar populations with distinct He content. Here we explore how these He abundances can constrain the self-enrichment in globular clusters.

HR Diagrams of Galaxies: Ages and Stages of Evolution

1978 ◽  
Vol 80 ◽  
pp. 247-257
Author(s):  
Beatrice M. Tinsley
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Stellar Populations ◽  
Young Star ◽  
Red Giants ◽  
Type I ◽  
Type Ii ◽  
Hubble Sequence ◽  
The Galaxy ◽  
Bright Blue

Baade (1944) based his concept of stellar populations in galaxies on the HR diagrams that he inferred from the magnitude at which their brightest stars could be resolved. His type I population had bright blue supergiants like those in the disk of the Milky Way, while the brightest stars in type II were the red giants found in globular clusters. He postulated that the Hubble sequence of galaxy types from irregulars to ellipticals contained increasing proportions of Population II relative to Population I, and that similar differences characterized nuclear bulges of spirals relative to their disks. A very important revision of this picture came with the discovery by Morgan and Mayall (1957; Morgan, 1956, 1959) that the integrated blue light of the nuclear bulges of M31 and the Galaxy is dominated by strong-lined CN giants, not by the weak-lined type found in globular clusters. On the basis of integrated spectra of galaxies, Morgan developed a revised population scheme, in which the extreme types are a young-star rich population, like Baade's extreme Population I, and a young-star deficient population, analogous to Population II but generally metal-rich. Different proportions of these two types are still thought to represent the main differences among stellar populations in different regions of galaxies.

scholarly journals CCD Photometry in the Core of the Fornax Dwarf Galaxy

1988 ◽  
Vol 126 ◽  
pp. 583-584
Author(s):  
Robert M. Light ◽  
P. Seitzer
Keyword(s):  
Globular Clusters ◽  
Stellar Population ◽  
Dwarf Galaxy ◽  
Field Population ◽  
Ccd Photometry ◽  
The Core ◽  
The Galaxy ◽  
Good Determination ◽  
Giant Branch Stars

The present study is concerned with the examination of properties of stars in the core of the Fornax dwarf spheroidal galaxy. Previous studies have shown that Fornax has a very diverse stellar population. Four of the globular clusters associated with Fornax were found to have metallicities significantly lower than the mean metallicity of the field population of the galaxy (Buonanno et al. 1985); these clusters point out an older, metal-poor population. Also, there are a number of luminous carbon stars, which are indicative of a much younger population (see Mould and Aaronson 1986). Studies of the field population of Fornax (Demers, Kunkel, and Hardy, 1979; Buonanno et al., 1985) have shown a dispersion in metallicity. We have measured a large sample of giant branch stars, enabling a good determination of mean properties of the Fornax stellar population, as well as allowing a comparison of stars as a function of distance from the center of Fornax.

scholarly journals Stellar parameters in the bulge cluster NGC 6553

1997 ◽  
Vol 189 ◽  
pp. 203-206 ◽  
Author(s):  
B. Barbuy ◽  
S. Ortolani ◽  
E. Bica ◽  
A. Renzini ◽  
M.D. Guarnieri
Keyword(s):  
Globular Clusters ◽  
Stellar Population ◽  
Spectroscopic Analysis ◽  
Galactic Center ◽  
Stellar Populations ◽  
The Sun ◽  
Galactic Bulge ◽  
Complete Understanding ◽  
Luminosity Functions ◽  
Bulge Formation

Globular clusters in the Galactic bulge form a flattened system, extending from the Galactic center to about 4.5 kpc from the Sun (Barbuy et al. 1997). A study of abundance ratios in these clusters is very important for a more complete understanding of the bulge formation. In this work we present a spectroscopic analysis of individual stars in NGC 6553. This cluster is a key one because it is located at d⊙ ≍ 5.1 kpc, therefore relatively close to us, and at the same time it is representative of the Galactic bulge stellar population: (a) Ortolani et al. (1995) showed that NGC 6553 and NGC 6528 show very similar Colour-Magnitude Diagrams (CMDs), and NGC 6528 is located at d⊙ ≍ 7.83 kpc, very close to the Galactic center; (b) the stellar populations of the Baade Window is also very similar to that of NGC 6553 and NGC 6528 as Ortolani et al. (1995) have shown by comparing their luminosity functions.

scholarly journals Spectra of Type II Cepheids

1975 ◽  
Vol 67 ◽  
pp. 555-555
Author(s):  
T. Lloyd Evans
Keyword(s):  
Globular Clusters ◽  
Line Strength ◽  
Type Ii ◽  
Long Period ◽  
Molecular Features ◽  
Metallic Line ◽  
Short Period ◽  
The Galaxy ◽  
Metal Abundance ◽  
Central Bulge

Spectra of over 100 stars classed as type II Cepheids of short period (BL Her-type) or long period (W Vir-type) or RV Tauri stars have been obtained. A range of metallic line strength and hence presumably metal abundance is present at all periods, those having weak lines being found especially in the globular clusters and the central bulge of the Galaxy. Stars which have enhanced Carbon molecular features (CH, CN and sometimes C2) occur at all periods but are probably distributed differently in space from the other stars.

scholarly journals The building blocks of the Milky Way halo using APOGEE and Gaia or Is the Galaxy a typical galaxy?

2019 ◽  
Vol 14 (S351) ◽  
pp. 170-173 ◽  
Author(s):  
Ricardo P. Schiavon ◽  
J. Ted Mackereth ◽  
Joel Pfeffer ◽  
Rob A. Crain ◽  
Jo Bovy
Keyword(s):  
Numerical Simulations ◽  
Globular Clusters ◽  
Milky Way ◽  
Galactic Halo ◽  
Dwarf Galaxies ◽  
Stellar Populations ◽  
Building Blocks ◽  
Stellar Content ◽  
The Galaxy ◽  
Milky Way Halo

AbstractWe summarise recent results from analysis of APOGEE/Gaia data for stellar populations in the Galactic halo, disk, and bulge, leading to constraints on the contribution of dwarf galaxies and globular clusters to the stellar content of the Milky Way halo. Intepretation of the extant data in light of cosmological numerical simulations suggests that the Milky Way has been subject to an unusually intense accretion history at z ≳ 1.5.

scholarly journals Constraining nuclear star cluster formation using MUSE-AO observations of the early-type galaxy FCC 47

2019 ◽  
Vol 628 ◽  
pp. A92 ◽  
Author(s):  
Katja Fahrion ◽  
Mariya Lyubenova ◽  
Glenn van de Ven ◽  
Ryan Leaman ◽  
Michael Hilker ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Stellar Population ◽  
High Mass ◽  
Host Galaxy ◽  
Main Body ◽  
Early Type ◽  
Cluster Galaxy ◽  
The Galaxy ◽  
Poor Population

Context. Nuclear star clusters (NSCs) are found in at least 70% of all galaxies, but their formation path is still unclear. In the most common scenarios, NSCs form in-situ from the galaxy’s central gas reservoir, through the merging of globular clusters (GCs), or through a combination of both. Aims. As the scenarios pose different expectations for angular momentum and stellar population properties of the NSC in comparison to the host galaxy and the GC system, it is necessary to characterise the stellar light, NSC, and GCs simultaneously. The large NSC (reff = 66 pc) and rich GC system of the early-type Fornax cluster galaxy FCC 47 (NGC 1336) render this galaxy an ideal laboratory to constrain NSC formation. Methods. Using Multi Unit Spectroscopic Explorer science verification data assisted by adaptive optics, we obtained maps for the stellar kinematics and stellar-population properties of FCC 47. We extracted the spectra of the central NSC and determined line-of-sight velocities of 24 GCs and metallicities of five. Results. The galaxy shows the following kinematically decoupled components (KDCs): a disk and a NSC. Our orbit-based dynamical Schwarzschild model revealed that the NSC is a distinct kinematic feature and it constitutes the peak of metallicity and old ages in FCC 47. The main body consists of two counter-rotating populations and is dominated by a more metal-poor population. The GC system is bimodal with a dominant metal-poor population and the total GC system mass is ∼17% of the NSC mass (∼7 × 108 M⊙). Conclusions. The rotation, high metallicity, and high mass of the NSC cannot be explained by GC-inspiral alone. It most likely requires additional, quickly quenched, in-situ formation. The presence of two KDCs likely are evidence of a major merger that has significantly altered the structure of FCC 47, indicating the important role of galaxy mergers in forming the complex kinematics in the galaxy-NSC system.

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