scholarly journals Ultraviolet spectral libraries of massive stars at low metallicity

1999 ◽  
Vol 193 ◽  
pp. 616-617
Author(s):  
Carmelle Robert
Keyword(s):  
Stellar Population ◽  
Massive Stars ◽  
Magellanic Clouds ◽  
Solar Neighbourhood ◽  
Hot Stars ◽  
Star Forming ◽  
Distant Star ◽  
Medium Resolution ◽  
Low Metallicity ◽  
Spectral Libraries

Three new ultraviolet spectral libraries of massive, hot stars using high and medium resolution spectra of objects located in the solar neighbourhood and the Magellanic Clouds are presented. Massive stars display unique wind signatures which are relatively easy to study in the ultraviolet. These libraries are crucial tools when investigating the massive stellar population of distant star-forming galaxies.

scholarly journals Synthetic high-resolution line spectra of star-forming galaxies below 1200 Å, based on FUSE spectral libraries of hot stars

2003 ◽  
Vol 212 ◽  
pp. 744-746
Author(s):  
Carmelle Robert ◽  
Anne Pellerin ◽  
Alessandra Aloisi ◽  
Claus Leitherer ◽  
Charles G. Hoopes ◽  
...  
Keyword(s):  
Stellar Population ◽  
Magellanic Clouds ◽  
Population Synthesis ◽  
Hot Stars ◽  
Star Forming ◽  
Synthetic Spectra ◽  
Stellar Population Synthesis ◽  
The Galaxy ◽  
Wind Profiles ◽  
Spectral Libraries

We have generated far-UV stellar libraries using spectra of hot stars in the Galaxy and the Large and Small Magellanic Clouds. These libraries were implemented into the stellar population synthesis codes starburst99 and lavalsb and used to compute synthetic spectra of star-forming galaxies. Model spectra for galaxies are presented and variations of the hot star photospheric and wind profiles are discussed. This poster summarizes the work of Robert et al. (2002).

scholarly journals Populations of OB-type stars in galaxies

2010 ◽  
Vol 6 (S272) ◽  
pp. 233-241
Author(s):  
Christopher J. Evans
Keyword(s):  
Stellar Evolution ◽  
Massive Stars ◽  
Spectral Synthesis ◽  
High Redshift ◽  
Young Star ◽  
Magellanic Clouds ◽  
Star Forming ◽  
The Galaxy ◽  
External Galaxies

AbstractOne of the challenges for stellar astrophysics is to reach the point at which we can undertake reliable spectral synthesis of unresolved populations in young, star-forming galaxies at high redshift. Here I summarise recent studies of massive stars in the Galaxy and Magellanic Clouds, which span a range of metallicities commensurate with those in high-redshift systems, thus providing an excellent laboratory in which to study the role of environment on stellar evolution. I also give an overview of observations of luminous supergiants in external galaxies out to a remarkable 6.7 Mpc, in which we can exploit our understanding of stellar evolution to study the chemistry and dynamics of the host systems.

scholarly journals Mass loss and evolution of massive stars in the Magellanic Clouds

1991 ◽  
Vol 148 ◽  
pp. 480-482 ◽  
Author(s):  
Claus Leitherer ◽  
Norbert Langer
Keyword(s):  
Mass Loss ◽  
Iterative Procedure ◽  
Metal Content ◽  
Loss Rate ◽  
Massive Stars ◽  
Mass Loss Rate ◽  
Magellanic Clouds ◽  
Evolutionary Models ◽  
Low Metallicity ◽  
Self Consistency

The structure and evolution of massive stars is significantly influenced by effects of chemical composition in a low-metallicity environment (as compared to the solar neighbourhood, SN), such as the Magellanic Clouds. A fundamental ingredient in evolutionary models is the stellar mass-loss rate M. Lower metal content decreases the mass-loss rates derived theoretically, which in turn affects the stellar evolution models. On the other hand, different evolutionary models predict different stellar parameters (especially L), which again influence M so that an iterative procedure is required to achieve self-consistency.

scholarly journals Core-hydrogen-burning RSGs in the early globular clusters

2015 ◽  
Vol 11 (A29B) ◽  
pp. 473-473
Author(s):  
Dorottya Szécsi ◽  
Jonathan Mackey ◽  
Norbert Langer
Keyword(s):  
Globular Clusters ◽  
Stellar Population ◽  
Massive Stars ◽  
Shell Formation ◽  
Low Mass Stars ◽  
Hydrogen Burning ◽  
The Core ◽  
Anomalous Surface ◽  
Low Metallicity ◽  
Low Mass

AbstractThe first stellar generation in galactic globular clusters contained massive low-metallicity stars (Charbonnel et al. 2014). We modelled the evolution of this massive stellar population and found that such stars with masses 100-600 M⊙ evolve into cool RSGs (Szécsi et al. 2015). These RSGs spend not only the core-He-burning phase but even the last few 105 years of the core-H-burning phase on the SG branch. Due to the presence of hot massive stars in the cluster at the same time, we show that the RSG wind is trapped into photoionization confined shells (Mackey et al. 2014). We simulated the shell formation around such RSGs and find them to become gravitationally unstable (Szécsi et al. 2016). We propose a scenario in which these shells are responsible for the formation of the second generation low-mass stars in globular clusters with anomalous surface abundances.

scholarly journals Star cluster formation and cloud dispersal by radiative feedback: dependence on metallicity and compactness

2020 ◽  
Vol 497 (3) ◽  
pp. 3830-3845 ◽  
Author(s):  
Hajime Fukushima ◽  
Hidenobu Yajima ◽  
Kazuyuki Sugimura ◽  
Takashi Hosokawa ◽  
Kazuyuki Omukai ◽  
...  
Keyword(s):  
Star Formation ◽  
Massive Stars ◽  
Cluster Formation ◽  
Star Clusters ◽  
Star Cluster ◽  
Star Forming ◽  
Dynamical Time ◽  
Low Metallicity ◽  
Higher Temperature ◽  
Dust Attenuation

ABSTRACT We study star cluster formation in various environments with different metallicities and column densities by performing a suite of 3D radiation hydrodynamics simulations. We find that the photoionization feedback from massive stars controls the star formation efficiency (SFE) in a star-forming cloud, and its impact sensitively depends on the gas metallicity Z and initial cloud surface density Σ. At Z = 1 Z⊙, SFE increases as a power law from 0.03 at Σ = 10 M⊙ pc−2 to 0.3 at $\Sigma = 300\,\mathrm{M}_{\odot }\, {\rm pc^{-2}}$. In low-metallicity cases $10^{-2}\!-\!10^{-1}\, \mathrm{Z}_{\odot }$, star clusters form from atomic warm gases because the molecule formation time is not short enough with respect to the cooling or dynamical time. In addition, the whole cloud is disrupted more easily by expanding H ii bubbles that have higher temperature owing to less efficient cooling. With smaller dust attenuation, the ionizing radiation feedback from nearby massive stars is stronger and terminate star formation in dense clumps. These effects result in inefficient star formation in low-metallicity environments: the SFE drops by a factor of ∼3 at Z = 10−2 Z⊙ compared to the results for Z = 1 Z⊙, regardless of Σ. Newborn star clusters are also gravitationally less bound. We further develop a new semi-analytical model that can reproduce the simulation results well, particularly the observed dependencies of the SFEs on the cloud surface densities and metallicities.

scholarly journals The X-ray stellar population of the LMC

2008 ◽  
Vol 4 (S256) ◽  
pp. 20-29 ◽  
Author(s):  
Yaël Nazé
Keyword(s):  
Stellar Population ◽  
Main Sequence ◽  
Massive Stars ◽  
High Energy ◽  
Magellanic Clouds ◽  
X Rays ◽  
X Ray ◽  
Energy Domain ◽  
X Ray Binaries

AbstractIn the study of stars, the high energy domain occupies a place of choice, since it is the only one able to directly probe the most violent phenomena: indeed, young pre-main sequence objects, hot massive stars, or X-ray binaries are best revealed in X-rays. However, previously available X-ray observatories often provided only crude information on individual objects in the Magellanic Clouds. The advent of the highly efficient X-ray facilities XMM-Newton and Chandra has now dramatically increased the sensitivity and the spatial resolution available to X-ray astronomers, thus enabling a fairly easy determination of the properties of individual sources in the LMC.

scholarly journals The star formation process in the Magellanic Clouds

2008 ◽  
Vol 4 (S256) ◽  
pp. 191-202
Author(s):  
J. M. Oliveira
Keyword(s):  
Star Formation ◽  
High Redshift ◽  
Critical Density ◽  
Mass Function ◽  
Magellanic Clouds ◽  
Initial Mass Function ◽  
Star Forming ◽  
Bridge Span ◽  
Individual Star ◽  
Low Metallicity

AbstractThe Magellanic Clouds offer unique opportunities to study star formation both on the global scales of an interacting system of gas-rich galaxies, as well as on the scales of individual star-forming clouds. The interstellar media of the Small and Large Magellanic Clouds and their connecting bridge, span a range in (low) metallicities and gas density. This allows us to study star formation near the critical density and gain an understanding of how tidal dwarfs might form; the low metallicity of the SMC in particular is typical of galaxies during the early phases of their assembly, and studies of star formation in the SMC provide a stepping stone to understand star formation at high redshift where these processes can not be directly observed. In this review, I introduce the different environments encountered in the Magellanic System and compare these with the Schmidt-Kennicutt law and the predicted efficiencies of various chemo-physical processes. I then concentrate on three aspects that are of particular importance: the chemistry of the embedded stages of star formation, the Initial Mass Function, and feedback effects from massive stars and its ability to trigger further star formation.

scholarly journals Extremely metal-poor galaxies with HST/COS: laboratories for models of low-metallicity massive stars and high-redshift galaxies

2019 ◽  
Vol 488 (3) ◽  
pp. 3492-3506 ◽  
Author(s):  
Peter Senchyna ◽  
Daniel P Stark ◽  
Jacopo Chevallard ◽  
Stéphane Charlot ◽  
Tucker Jones ◽  
...  
Keyword(s):  
Massive Stars ◽  
High Redshift ◽  
Formation Rate ◽  
Uv Spectra ◽  
High Redshift Galaxies ◽  
Star Forming ◽  
High Ionization ◽  
Moderate Resolution ◽  
Low Metallicity ◽  
Nearby Galaxies

Abstract Ultraviolet (UV) observations of local star-forming galaxies have begun to establish an empirical baseline for interpreting the rest-UV spectra of reionization-era galaxies. However, existing high-ionization emission line measurements at z > 6 ($\rm W_{C\, {\scriptscriptstyle IV},0}{} \gtrsim 20$ Å) are uniformly stronger than observed locally ($\rm W_{C\, {\scriptscriptstyle IV},0}{} \lesssim 2$ Å), likely due to the relatively high metallicities (Z/Z$\odot$ > 0.1) typically probed by UV surveys of nearby galaxies. We present new HST/COS spectra of six nearby (z < 0.01) extremely metal-poor galaxies (XMPs, Z/Z$\odot$ ≲ 0.1) targeted to address this limitation and provide constraints on the highly uncertain ionizing spectra powered by low-metallicity massive stars. Our data reveal a range of spectral features, including one of the most prominent nebular C iv doublets yet observed in local star-forming systems and strong He ii emission. Using all published UV observations of local XMPs to date, we find that nebular C iv emission is ubiquitous in very high specific star formation rate systems at low metallicity, but still find equivalent widths smaller than those measured in individual lensed systems at z > 6. Our moderate-resolution HST/COS data allow us to conduct an analysis of the stellar winds in a local nebular C iv emitter, which suggests that some of the tension with z > 6 data may be due to existing local samples not yet probing sufficiently high α/Fe abundance ratios. Our results indicate that C iv emission can play a crucial role in the JWST and ELT era by acting as an accessible signpost of very low metallicity (Z/Z$\odot$ < 0.1) massive stars in assembling reionization-era systems.

scholarly journals Massive Stars at High Redshifts

2007 ◽  
Vol 3 (S250) ◽  
pp. 415-428
Author(s):  
Max Pettini
Keyword(s):  
Massive Stars ◽  
High Redshift ◽  
Mass Function ◽  
Initial Mass Function ◽  
Stellar Spectra ◽  
Star Forming ◽  
Star Forming Regions ◽  
Look Ahead ◽  
Low Metallicity ◽  
High Redshift Universe

AbstractThe five years that have passed since the last IAU Symposium devoted to massive stars have seen a veritable explosion of data on the high redshift universe. The tools developed to study massive stars in nearby galaxies are finding increasing application to the analysis of the spectra of star-forming regions at redshifts as high as z = 7. In this brief review, I consider three topics of relevance to this symposium: the determination of the metallicities of galaxies at high redshifts from consideration of their ultraviolet stellar spectra; constraints on the initial mass function of massive stars in galaxies at z = 2 − 3; and new clues to the nucleosynthesis of carbon and nitrogen in massive stars of low metallicity. The review concludes with a look ahead at some of the questions that may occupy us for the next five years (at least!).

scholarly journals Homogeneity in the early chemical evolution of the Sextans dwarf spheroidal galaxy

2020 ◽  
Vol 644 ◽  
pp. A75 ◽  
Author(s):  
R. Lucchesi ◽  
C. Lardo ◽  
F. Primas ◽  
P. Jablonka ◽  
P. North ◽  
...  
Keyword(s):  
Stellar Population ◽  
Near Infrared ◽  
Milky Way ◽  
Spectroscopic Analysis ◽  
Large Scatter ◽  
Full Sample ◽  
Medium Resolution ◽  
Low Metallicity ◽  
Unambiguous Detection ◽  
Metal Poor Star

We present the high-resolution spectroscopic analysis of two new extremely metal-poor star (EMPS) candidates in the dwarf spheroidal galaxy Sextans. These targets were preselected from medium-resolution spectra centered around the Ca II triplet in the near-infrared and were followed-up at higher resolution with VLT/UVES. We confirm their low metallicities with [Fe/H] = −2.95 and [Fe/H] = −3.01, which place them among the most metal-poor stars known in Sextans. The abundances of 18 elements, including C, Na, the α, Fe-peak, and neutron-capture elements, are determined. In particular, we present the first unambiguous detection of Zn in a classical dwarf at extremely low metallicity. Previous indications were made of a large scatter in the abundance ratios of the Sextans stellar population around [Fe/H] ∼ − 3 when compared to other galaxies, particularly with very low observed [α/Fe] ratios. We took the opportunity of reanalyzing the full sample of EMPS in Sextans and find a [α/Fe] Milky Way-like plateau and a ∼0.2 dex dispersion at fixed metallicity.

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