scholarly journals Results from HST Observations of Six LMC Globular Cluster Fields

1999 ◽  
Vol 190 ◽  
pp. 448-449 ◽  
Author(s):  
K. A. G. Olsen ◽  
P. W. Hodge ◽  
M. Mateo ◽  
E. W. Olszewski ◽  
R. A. Schommer ◽  
...  
Keyword(s):  
Star Formation ◽  
Globular Clusters ◽  
Milky Way ◽  
Evolutionary Models ◽  
First Stars ◽  
Field Star ◽  
Star Studies ◽  
Red Giant ◽  
Star Formation Histories ◽  
Best Fit

We present deep HST color-magnitude diagrams of fields centered on the six old LMC globular clusters NGC 1754, NGC 1835, NGC 1898, NGC 1916, NGC 2005, and NGC 2019. Separate cluster and field star CMDs are shown. The time of formation of the LMC is studied from an analysis of the cluster CMDs. Based on a comparison of the CMDs with sequences of the Milky Way clusters M3, M5, and M55, we suggest that the LMC formed its first stars at the same time as the Milky Way to within 1 Gyr. We find additional evidence that these LMC globular clusters are as old as the oldest Milky Way clusters through a comparison of our data with the horizontal branch evolutionary models of Lee, Demarque, & Zinn (1994).The evolution of the LMC following its formation is studied through an analysis of the field star CMDs. Through an automated comparison with stellar evolution models, we extract the star formation histories implied by the CMDs. Our best-fit star formation histories imply that the LMC has been actively forming stars over the last 4 Gyr, in agreement with previous field star studies. The four fields that lie in the Bar also contain significant numbers of stars with ages of 4–8 Gyr in the best-fit cases. The most notable disagreement between the best-fit models and observed CMDs is in the color of the red giant branch.

scholarly journals Light element abundance inhomogeneities in globular clusters: probing star formation and evolution in the early Milky Way

1994 ◽  
Vol 72 (11-12) ◽  
pp. 772-781 ◽  
Author(s):  
Michael M. Briley ◽  
Roger A. Bell ◽  
James E. Hesser ◽  
Graeme H. Smith
Keyword(s):  
Star Formation ◽  
Globular Clusters ◽  
Main Sequence ◽  
Light Element ◽  
Star Formation History ◽  
Element Abundance ◽  
Chemical Compositions ◽  
Original Material ◽  
Abundance Patterns ◽  
Red Giant

Abundance patterns of the elements C, N, and O are sensitive probes of stellar nucleosynthesis processes and, in addition, O abundances are an important input for stellar age determinations. Understanding the nature of the observed distribution of these elements is key to constraining protogalactic star formation history. Patterns deduced from low-resolution spectroscopy of the CN, CH, NH, and CO molecules for low-mass stars in their core-hydrogen or first shell-hydrogen burning phases in the oldest ensembles known, the Galactic globular star clusters, are reviewed. New results for faint stars in NGC 104 (47 Tuc, C0021-723) reveal that the bimodal, anticorrelated pattern of CN and CH strengths found among luminous evolved stars is also present in stars nearing the end of their main-sequence lifetimes. In the absence of known mechanisms to mix newly synthesized elements from the interior to the observable surface layers of such unevolved stars, those particular inhomogeneities imply that the original material from which the stars formed some 15 billion years ago was chemically inhomogeneous in the C and N elements. However, in other clusters, observations of abundance ratios and C isotope ratios suggest that alterations to surface chemical compositions are produced as stars evolve from the main sequence through the red giant branch. Thus, the current observed distributions of C, N, and O among the brightest stars (those also observed most often) may not reflect the true distribution from which the protocluster cloud formed. The picture that is emerging of the C, N, and O abundance patterns within globular clusters may be one which requires a complicated combination of stellar evolutionary and primordial effects for its explanation.

scholarly journals COMPARING M31 AND MILKY WAY SATELLITES: THE EXTENDED STAR FORMATION HISTORIES OF ANDROMEDA II AND ANDROMEDA XVI

2014 ◽  
Vol 789 (1) ◽  
pp. 24 ◽  
Author(s):  
Daniel R. Weisz ◽  
Evan D. Skillman ◽  
Sebastian L. Hidalgo ◽  
Matteo Monelli ◽  
Andrew E. Dolphin ◽  
...  
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Star Formation Histories

scholarly journals Substructure in Dwarf Galaxies

2004 ◽  
Vol 21 (4) ◽  
pp. 379-381
Author(s):  
Matthew Coleman
Keyword(s):  
Dark Matter ◽  
Star Formation ◽  
Large Scale ◽  
Stellar Population ◽  
Milky Way ◽  
Dwarf Galaxies ◽  
Tidal Interaction ◽  
Kinematic Evolution ◽  
Dark Material ◽  
Star Formation Histories

AbstractRecent years have seen a series of large-scale photometric surveys with the aim of detecting substructure in nearby dwarf galaxies. Some of these objects display a varying distribution of each stellar population, reflecting their star formation histories. Also, dwarf galaxies are dominated by dark matter, therefore luminous substructure may represent a perturbation in the underlying dark material. Substructure can also be the effect of tidal interaction, such as the disruption of the Sagittarius dSph by the Milky Way. Therefore, substructure in dwarf galaxies manifests the stellar, structural, and kinematic evolution of these objects.

scholarly journals IC 4499 revised: Spectro-photometric evidence of small light-element variations

2018 ◽  
Vol 618 ◽  
pp. A131 ◽  
Author(s):  
E. Dalessandro ◽  
C. Lardo ◽  
M. Cadelano ◽  
S. Saracino ◽  
N. Bastian ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
Light Element ◽  
High Resolution Spectroscopy ◽  
Multiple Populations ◽  
Number Ratio ◽  
Red Giant ◽  
Good Agreement

It has been suggested that IC 4499 is one of the very few old globulars to not host multiple populations with light-element variations. To follow-up on this very interesting result, here we have made use of accurate HST photometry and FLAMES at VLT high-resolution spectroscopy to investigate in more detail the stellar population properties of this system. We find that the red giant branch of the cluster is clearly bimodal in near-UV-optical colour-magnitude diagrams, thus suggesting that IC 4499 is actually composed by two sub-populations of stars with different nitrogen abundances. This represents the first detection of multiple populations in IC 4499. Consistently, we also find that one star out of six is Na-rich to some extent, while we do not detect any evidence of intrinsic spread in both Mg and O. The number ratio between stars with normal and enriched nitrogen is in good agreement with the number ratio – mass trend observed in Galactic globular clusters. Also, as typically found in other systems, nitrogen rich stars are more centrally concentrated than normal stars, although this result cannot be considered conclusive because of the limited field of view covered by our observations (∼1rh). On the contrary, we observe that both the RGB UV colour spread, which is a proxy of N variations, and Na abundance variations, are significantly smaller than those observed in Milky Way globular clusters with mass and metallicity comparable to IC 4499. The modest N and Na spreads observed in this system can be tentatively connected to the fact that IC 4499 likely formed in a disrupted dwarf galaxy orbiting the Milky Way, as previously proposed based on its orbit.

scholarly journals Complexity in small-scale dwarf spheroidal galaxies

2009 ◽  
Vol 5 (S265) ◽  
pp. 227-232
Author(s):  
Andreas Koch ◽  
Daniel Adén ◽  
Eva K. Grebel ◽  
Sofia Feltzing
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Galactic Halo ◽  
Photometric Data ◽  
Small Scale ◽  
Chemical Abundance ◽  
First Stars ◽  
Dwarf Spheroidal Galaxies ◽  
Chemical Enrichment ◽  
Large Numbers

AbstractOur knowledge about the chemical evolution of the more luminous dwarf spheroidal (dSph) galaxies is constantly growing. However, little is known about the enrichment of the ultrafaint systems recently discovered in large numbers in large Sky Surveys. Low-resolution spectroscopy and photometric data indicate that these galaxies are predominantly metal-poor. On the other hand, the most recent high-resolution abundance analyses indicate that some of these galaxies experienced highly inhomogenous chemical enrichment, where star formation proceeds locally on the smallest scales. Furthermore, these galaxy-contenders appear to contain very metal-poor stars with [Fe/H]< −3 dex and could be the sites of the first stars. Here, we consider the presently available chemical abundance information of the (ultra-) faint Milky Way satellite dSphs. In this context, some of the most peculiar element and inhomogeneous enrichment patterns will be discussed and related to the question of to what extent the faintest dSph candidates and outer halo globular clusters could have contributed to the metal-poor Galactic halo.

scholarly journals Properties of Wolf-Rayet Stars

2007 ◽  
Vol 3 (S250) ◽  
pp. 47-62 ◽  
Author(s):  
Paul A. Crowther
Keyword(s):  
Star Formation ◽  
Empirical Evidence ◽  
Recent Progress ◽  
Milky Way ◽  
Spectroscopic Analysis ◽  
Evolutionary Models ◽  
Chemical Abundances ◽  
Near Ir ◽  
Stellar Temperatures

AbstractA review of recent progress relating to Wolf-Rayet (WR) stars is presented. Topics include improved Milky Way statistics from near-IR surveys, different flavours of hydrogen-rich and hydrogen-poor WN stars, WR masses from binary orbits, plus spectroscopic analysis of WR stars resulting in stellar temperatures, luminosities, ionizing fluxes, plus wind properties accounting for clumping. Chemical abundances of WN and WC stars are presented, including a discussion of neon abundances in WC and WO stars fromSpitzerobservations. Empirical evidence supporting metallicity-dependent winds is also presented, including its effect on subtype distributions in different environments. Finally, difficulties in comparisons between evolutionary models and observations are highlighted, plus outstanding issues with predictions from continuous star formation and instantaneous bursts in the Milky Way,

scholarly journals Connections between MWG Star Clusters and Dwarf Galaxies

2012 ◽  
Vol 10 (H16) ◽  
pp. 275-277
Author(s):  
Kim A. Venn
Keyword(s):  
Star Formation ◽  
Globular Clusters ◽  
Dwarf Galaxies ◽  
Star Clusters ◽  
Theoretical Models ◽  
Stellar Populations ◽  
Observational Evidence ◽  
Paradigm Shifts ◽  
The Past ◽  
Star Formation Histories

It seems that in the past decade, there have been two paradigm shifts regarding star clusters. Firstly, the observational evidence for multiple stellar populations requires more extended and often complex star formation histories in star clusters. Secondly, theoretical models that form globular clusters in dwarf galaxies that are accreted at very early epochs (z > 5) are able to reproduce the age-metallicity relations observed. For the accretion scenario to be viable, globular clusters should also resemble the chemistry of at least some dwarf galaxies.

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