scholarly journals The Galactic Bulge

2016 ◽  
Vol 33 ◽  
Author(s):  
B. Barbuy
Keyword(s):  
Globular Clusters ◽  
Stellar Population ◽  
Thick Disk ◽  
Galactic Bulge ◽  
Multiple Populations ◽  
Secular Evolution ◽  
Rr Lyrae ◽  
The Galaxy ◽  
Formation And Evolution

AbstractThe Galactic bulge is the least studied component of our Galaxy. Yet, its formation and evolution are key to understand the formation of the Galaxy itself. Studies on the Galactic bulge have increased significantly in the last years, but still there are many points of controversy. This volume contains several contributions from experts in different aspects of the bulge. Issues discussed include the following: the presence of an old spheroidal bulge, or identification of its old stellar population with the thick disk or halo; fraction of stars younger than 10 Gyr is estimated to be of < 5 to 22% depending on method and authors; multiple populations or only a metal-poor and a metal-rich ones; spheroidal or ellipsoidal distribution of RR Lyrae; formation of the bulge from early mergers or from secular evolution of the bar; different methods of mapping extinction; selection and identification of bulge globular clusters.

scholarly journals Globular Clusters in the Galactic Bulge

2016 ◽  
Vol 33 ◽  
Author(s):  
E. Bica ◽  
S. Ortolani ◽  
B. Barbuy
Keyword(s):  
Globular Clusters ◽  
Deep Understanding ◽  
Selective Absorption ◽  
Galactic Bulge ◽  
Chemical Abundances ◽  
Elemental Abundances ◽  
The Galaxy ◽  
Formation And Evolution ◽  
Future Work ◽  
Shed Light

AbstractA view of the Galactic bulge by means of their globular clusters is fundamental for a deep understanding of its formation and evolution. Connections between the globular cluster and field star properties in terms of kinematics, orbits, chemical abundances, and ages should shed light on different stellar population components. Based on spatial distribution and metallicity, we define a probable best list of bulge clusters, containing 43 entries. Future work on newly discovered objects, mostly from the VVV survey, is suggested. These candidates might alleviate the issue of missing clusters on the far side of the bulge. We discuss the reddening law affecting the cluster distances towards the centre of the Galaxy, and conclude that the most suitable total-to-selective absorption value appears to be RV=3.2, in agreement with recent analyses. An update of elemental abundances for bulge clusters is provided.

How many thick disk subsystems are there in the Milky Way Galaxy?

2021 ◽  
pp. 117-122
Author(s):  
V. A. MARSAKOV ◽  
M. L. GOZHA ◽  
V. V. KOVAL
Keyword(s):  
Globular Clusters ◽  
Thin Disk ◽  
Thick Disk ◽  
Chemical Compositions ◽  
Milky Way Galaxy ◽  
Rr Lyrae ◽  
Satellite Galaxy ◽  
The Galaxy ◽  
Type Ia ◽  
Disk Subsystem

It was shown that stellar populations of the Galaxy with the thick disk kinematics, namely globular clusters, field RR Lyrae variables (lyrids), and nearby field F - G stars, have different chemical compositions. Based on the analysis of the nature of the dependencies of [alpha/Fe] on [Fe/H] for these objects, it was concluded that the thick disk subsystem in the Galaxy is composite, and at least three components independently exist inside it. The oldest subsystem consists of the metal-rich globular clusters which were formed from a single protogalactic cloud shortly after onset of the explosions of type Ia supernova in it. Then a subsystem of the field thick disk stars was formed as a result of the "heating" of the stars of the primary thin disk already formed in the Galaxy by a rather massive dwarf satellite galaxy which fell onto the Galaxy. And, finally, the subsystem of field stars (including the lyrids) with the kinematics of not only the thick, but even the thin disk that fell onto the Galaxy from this captured satellite galaxy.

scholarly journals The Age of Old Galactic Populations

1998 ◽  
Vol 11 (1) ◽  
pp. 560-561
Author(s):  
M. Grenon
Keyword(s):  
High Velocity ◽  
Radial Velocities ◽  
Thick Disk ◽  
Early Evolution ◽  
Galactic Bulge ◽  
Colour Class ◽  
The Galaxy ◽  
Nearby Stars

As a preparation to the HIPPARCOS mission, a large observing programme on NLTT stars (propermotion > 0.18 ″/yr) was started in Genevaphotometry. The original programme consists of 10047 stars brighter than mR = 11.5, or mR = 12.5 if of colour class m. Among them, 7813 targets could be included in the HIPPARCOS programme, selected according to their observability and internal priorities in favour of large parallaxe stars (photometric distances < 100 pc) and high-velocity stars. The bulk of new nearby, halo, mild-metal poor and SMR stars in the HIP Catalogue originates from this proposal (N° 139). No less than 208 new nearby stars with π ≥ 40 mas were discovered south of δ +10°, the closest has π(HIP)= 182 mas. Radial velocities were obtained with CORAVEL at OHP and ESO. Most aspects of the early evolution of the Galaxy may be addressed with this sample. Here we discuss, as examples, the ages of the thick disk and of the galactic bulge.

scholarly journals A New Sample of Thick Disk and Halo Stars

1995 ◽  
Vol 164 ◽  
pp. 386-386
Author(s):  
C. Soubiran ◽  
M.N. Perrin ◽  
R. Cayrel ◽  
E. Chereul
Keyword(s):  
Stellar Population ◽  
Thin Disk ◽  
Thick Disk ◽  
The Other ◽  
Chemical Characteristics ◽  
Fundamental Parameters ◽  
Halo Stars ◽  
Synthetic Spectra ◽  
The Galaxy ◽  
Comparison Stars

The aim of our stellar population study is to investigate the kinematical and chemical characteristics of the thin disk, thick disk and halo of the Galaxy. We have selected 51 stars in 2 astrometric and photometric surveys at l = 42°, b = +79° (Soubiran 1992) and l = 167°, b = +47° (Ojha et al. 1994), on the basis of the Reduced Proper Motion Diagram. They were observed with the 193cm telescope at Observatoire de Haute-Provence, with the CARELEC spectrograph (dispersion of 66Å/mm, FWHM of 3.0Å, range λλ4600 – 5500Å), together with 43 comparison stars with known fundamental parameters. The derivation of Teff, logg and [Fe/H] was done differentially using a grid of synthetic spectra and the comparison stars, as described in Cayrel et al. (1991). Twenty of the target stars were found to be more deficient than −0.5. In the (V, [Fe/H]) distribution, the halo stars are clearly separated from the other stars with a mean of (V, [Fe/H]) ≃ (−210km/s, – 1.4dex). Because of the small size of the sample, it was not possible to discriminate the thick disk from the thin disk. We have taken 200 more spectra, and with these new observations, we hope to be able to deconvolve the 3 populations in the (U, V, W, [Fe/H]) space as we did previously with the (U, V) velocity (Soubiran 1993).

scholarly journals The age of the Milky Way inner stellar spheroid from RR Lyrae population synthesis

2020 ◽  
Vol 641 ◽  
pp. A96 ◽  
Author(s):  
A. Savino ◽  
A. Koch ◽  
Z. Prudil ◽  
A. Kunder ◽  
R. Smolec
Keyword(s):  
Stellar Population ◽  
Milky Way ◽  
Population Synthesis ◽  
Milky Way Galaxy ◽  
First Stars ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
The Galaxy ◽  
Stellar Halo ◽  
Lyrae Stars

The central kiloparsecs of the Milky Way are known to host an old, spheroidal stellar population, whose spatial and kinematical properties set it apart from the boxy-peanut structure that constitutes most of the central stellar mass. The nature of this spheroidal population, whether it is a small classical bulge, the innermost stellar halo, or a population of disk stars with large initial velocity dispersion, remains unclear. This structure is also a promising candidate to play host to some of the oldest stars in the Galaxy. Here we address the topic of the inner stellar spheroid age, using spectroscopic and photometric metallicities for a sample of 935 RR Lyrae stars that are constituents of this component. By means of stellar population synthesis, we derive an age-metallicity relation for RR Lyrae populations. We infer, for the RR Lyrae stars in the bulge spheroid, an extremely ancient age of 13.41 ± 0.54 Gyr and conclude they were among the first stars to form in what is now the Milky Way galaxy. Our age estimate for the central spheroid shows a remarkable agreement with the age profile that has been inferred for the Milky Way stellar halo, suggesting a connection between the two structures. However, we find mild evidence for a transition in the halo properties at rGC ∼ 5 kpc. We also investigate formation scenarios for metal-rich RR Lyrae stars, such as binarity and helium variations, and consider whether they can provide alternative explanations for the properties of our sample. We conclude that within our framework, the only viable alternative is to have younger, slightly helium-rich, RR Lyrae stars. This is a hypothesis that would open intriguing questions for the formation of the inner stellar spheroid.

scholarly journals Spectroscopic study of formation, evolution and interaction of M31 and M33 with star clusters

2014 ◽  
Vol 10 (S312) ◽  
pp. 201-202 ◽  
Author(s):  
Zhou Fan ◽  
Yanbin Yang
Keyword(s):  
Globular Clusters ◽  
Stellar Population ◽  
Local Group ◽  
Spiral Galaxies ◽  
Star Clusters ◽  
Star Cluster ◽  
Physical Parameters ◽  
Cluster Systems ◽  
Nearby Galaxies ◽  
Formation And Evolution

AbstractThe recent studies show that the formation and evolution process of the nearby galaxies are still unclear. By using the Canada France Hawaii Telescope (CFHT) 3.6m telescope, the PanDAS shows complicated substructures (dwarf satellite galaxies, halo globular clusters, extended clusters, star streams, etc.) in the halo of M31 to ~150 kpc from the center of galaxy and M31-M33 interaction has been studied. In our work, we would like to investigate formation, evolution and interaction of M31 and M33, which are the nearest two spiral galaxies in Local Group. The star cluster systems of the two galaxies are good tracers to study the dynamics of the substructures and the interaction. Since 2010, the Xinglong 2.16m, Lijiang 2.4m and MMT 6.5m telescopes have been used for our spectroscopic observations. The radial velocities and Lick absorption-line indices can thus be measured with the spectroscopy and then ages, metallicities and masses of the star clusters can be fitted with the simple stellar population models. These parameters could be used as the input physical parameters for numerical simulations of M31-M33 interaction.

scholarly journals Multiple Populations in Globular Clusters – The Spectroscopic View

2012 ◽  
Vol 10 (H16) ◽  
pp. 232-233
Author(s):  
Judith G. Cohen
Keyword(s):  
Recent Work ◽  
Globular Clusters ◽  
Stellar Population ◽  
Multiple Populations

AbstractI review the evidence supporting and characterizing multiple populations within globular clusters (GCs) based on spectroscopy, i.e. on abundance variations within the stellar population of an individual GC, which dates back to almost 40 years ago. I discuss some of my recent work in this area.

scholarly journals RR Lyrae stars as probes of the Milky Way structure and formation

2015 ◽  
Vol 11 (S317) ◽  
pp. 116-119
Author(s):  
Pawel Pietrukowicz ◽  
Keyword(s):  
Galactic Center ◽  
Variable Stars ◽  
Wide Field ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
The Galaxy ◽  
First Results ◽  
Formation And Evolution ◽  
Lyrae Stars ◽  
Distance Indicators

AbstractRR Lyrae stars being distance indicators and tracers of old population serve as excellent probes of the structure, formation, and evolution of our Galaxy. Thousands of them are being discovered in ongoing wide-field surveys. The OGLE project conducts the Galaxy Variability Survey with the aim to detect and analyze variable stars, in particular of RRab type, toward the Galactic bulge and disk, covering a total area of 3000 deg2. Observations in these directions also allow detecting background halo variables and unique studies of their properties and distribution at distances from the Galactic Center to even 40 kpc. In this contribution, we present the first results on the spatial distribution of the observed RRab stars, their metallicity distribution, the presence of multiple populations, and relations with the old bulge. We also show the most recent results from the analysis of RR Lyrae stars of the Sgr dwarf spheroidal galaxy, including its center, the globular cluster M54.

scholarly journals Iron-peak elements Sc, V, Mn, Cu, and Zn in Galactic bulge globular clusters

2018 ◽  
Vol 616 ◽  
pp. A18 ◽  
Author(s):  
H. Ernandes ◽  
B. Barbuy ◽  
A. Alves-Brito ◽  
A. Friaça ◽  
C. Siqueira-Mello ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Massive Stars ◽  
Theoretical Models ◽  
Thick Disk ◽  
Galactic Bulge ◽  
Abundance Pattern ◽  
Chemical Enrichment ◽  
Very Large Telescope ◽  
Type Ia ◽  
Cu And Zn

Aims. Globular clusters are tracers of the history of star formation and chemical enrichment in the early Galaxy. Their abundance pattern can help understanding their chemical enrichment processes. In particular, the iron-peak elements have been relatively little studied so far in the Galactic bulge. Methods. The main aim of this work is to verify the strength of abundances of iron-peak elements for chemical tagging in view of identifying different stellar populations. Besides, the nucleosynthesis processes that build these elements are complex, therefore observational data can help constraining theoretical models, as well as give suggestions as to the kinds of supernovae that enriched the gas before these stars formed. Results. The abundances of iron-peak elements are derived for the sample clusters, and compared with bulge field, and thick disk stars. We derived abundances of the iron-peak elements Sc, V, Mn, Cu, and Zn in individual stars of five bulge globular clusters (NGC 6528, NGC 6553, NGC 6522, NGC 6558, HP 1), and of the reference thick disk/or inner halo cluster 47 Tucanae (NGC 104). High resolution spectra were obtained with the UVES spectrograph at the Very Large Telescope over the years. Conclusions. The sample globular clusters studied span metallicities in the range –1.2 ≲ [Fe/H] ≲ 0.0. V and Sc appear to vary in lockstep with Fe, indicating that they are produced in the same supernovae as Fe. We find that Mn is deficient in metal-poor stars, confirming that it is underproduced in massive stars; Mn-over-Fe steadily increases at the higher metallicities due to a metallicity-dependent enrichment by supernovae of type Ia. Cu behaves as a secondary element, indicating its production in a weak-s process in massive stars. Zn has an alpha-like behaviour at low metallicities, which can be explained in terms of nucleosynthesis in hypernovae. At the metal-rich end, Zn decreases with increasing metallicity, similarly to the alpha-elements.

scholarly journals Globular clusters in the Sagittarius stream

2020 ◽  
Vol 636 ◽  
pp. A107 ◽  
Author(s):  
M. Bellazzini ◽  
R. Ibata ◽  
K. Malhan ◽  
N. Martin ◽  
B. Famaey ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Main Body ◽  
Rr Lyrae ◽  
The Galaxy ◽  
Tidal Stream ◽  
Galactic Globular Clusters

We reconsider the case for the association of Galactic globular clusters to the tidal stream of the Sagittarius dwarf spheroidal galaxy (Sgr dSph) using Gaia DR2 data. We used RR Lyrae variables to trace the stream in 6D and we selected clusters matching the observed stream in position and velocity. In addition to the clusters residing in the main body of the galaxy (M 54, Ter 8, Ter 7, Arp 2) we confirm the membership of Pal 12 and Whiting 1 to the portion of the trailing arm populated by stars lost during recent perigalactic passages. NGC 2419, NGC 5634, and NGC 4147 are very interesting candidates, possibly associated with more ancient wraps of the Sagittarius stream. With the exception of M 54, which lies within the stellar nucleus of the galaxy, we note that all these clusters are found in the trailing arm of the stream. The selected clusters are fully consistent with the [Fe/H] versus [Mg/Fe], [Ca/Fe] patterns and the age-metallicity relation displayed by field stars in the main body of Sgr dSph.

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