Found 20 talks width keyword massive stars
Massive stars lose mass through powerful, radiatively driven stellar winds. Building on the original "CAK" model for steady, spherical winds driven by line-scattering, this talk will review recent research on the multi-faceted nature of such wind mass loss under varied conditions, for example due to rapid rotation, magnetic channeling, binary interaction, or a luminosity near the Eddington limit. An overall theme is that wind mass loss can in this way lead to a wide variety of astrophysical phenomena, including bipolar nebulae, massive star magnetospheres, colliding winds or compact companion accretion, and luminous blue variable eruption. The discussion here will summarize these with an emphasis on their varied observational signatures.
In this talk I consider two questions. First, I investigate the formation of molecular clouds from diffuse interstellar gas. It has been argued that the midplane pressure controls the fraction of molecular hydrogen present, and thus the star formation rate. Alternatively, I and others have suggested that the gravitational instability of the disk controls both. I present numerical results demonstrating that the observed correlations between midplane pressure, molecular hydrogen fraction, and star formation rate can be explained within the gravitational instability picture. Second, I discuss how ionization affects the formation of massive stars. Although most distinctive observables of massive stars can be traced back to their ionizing radiation, it does not appear to have a strong effect on their actual formation. Rather, I present simulations suggesting that stars only ionize large volumes after their accretion has already been throttled by gravitational fragmentation in the accretion flow. At the same time these models can explain many aspects of the observations of ultracompact H II regions.
Massive stars dominate the light output of entire galaxies, with luminosities in excess of 105 L⊙. This makes them powerful probes with which to study a range of astrophysical phenomena. In this talk I will review the recent results of our group, in which we have been able to shed new light on the recent star-forming history of our Galaxy, and the nature of supernova progenitors. I will also discuss our latest project, which is to use massive stars as tracers of extra-galactic star-forming histories out to distances of 10 Mpc and beyond.
The formation of massive stars is not fully understood. The high luminosity and temperature of massive protostars complicate the accretion mechanism at work in intermediate and low mass young stellar objects. Nonetheless, several scenarios exist to explain the formation of massive stars. In this talk, we will focus on the process of triggered star formation on the borders of H II regions. Due to the feedback effects of OB stars, a layer of molecular material is collected during the expansion of the H II region. Instabilities develop in this layer and give birth to new stars. We will present a detailed study of three Galactic H II regions (RCW79, RCW82 and RCW120). Near-infrared integral field observations have been carried out with SINFONI on the VLT. We will see how they reveal the nature of both the ionizing stars and of the YSOs in the collected layer and how they support the scenario of 'triggered star formation'.
AbstractAsymptotic Giant Branch (AGB) stars are a principal source of gas and dust input into the interstellar medium, being an important driver of chemical evolution in galaxies. Rubidium is a key element to distinguish between high mass (~4-8 M⊙) AGB stars and low mass (~1-4 M⊙) AGBs - high mass AGBs are predicted to produce a lot of rubidium as a consequence of the genuine nucleosynthetic processes (the s-process) that characterise these stars. The Magellanic Clouds (MCs) offer a unique opportunity to study the stellar evolution and nucleosynthesis of AGB stars in low metallicity environments where distances (and so the star's luminosity) are known. We present the discovery of extragalactic rubidium-rich AGB stars in the MCs confirming that the more massive AGB stars are generally brighter than the standard adopted luminosity limit (Mbol~-7.1) for AGB's. In addition, massive MC-AGBs are more enriched in Rb than their galactic counterparts, as it is qualitatively predicted by the present theoretical models; the Rb over-abundance increase with increasing stellar mass and with decreasing metallicity. However, present theoretical models are far from matching the extremely high Rb overabundances observed.
The last decade has brought the discovery of a large number of massive (M > 10000 M?) young open clusters in the Milky Way, which had previously not been thought to exist. I will present a brief review of these discoveries, with strong emphasis on the use of these clusters as astrophysical laboratories. I will also present the very recent discovery of a number of massive clusters concentrated towards a small region of the Scutum Arm, providing evidence for the existence of starburst activity on a much larger scale than previously assumed.
AbstractThe Orion star forming region is an ideal laboratory for many astrophysical studies. In this talk I will present a study of the chemical composition of early B-type stars in the Orion OB1 association. The main ideas I will talk about are: (1) The importance of self-consistent spectroscopic techniques for the abundance analysis in this type of stellar objects; (2) the study of the homogeneity of abundances in stars from the various stellar subgroups in OriOB1; (3) the comparison of O stellar abundances with recent Solar determinations; (4) the comparison of stellar abundances with those resulting from the analysis of the emission line spectra of the Orion nebula (M42); (5) the study of the oxygen depletion onto dust grains in the Orion nebula. La región de formación estelar de Orión es una laboratorio perfecto para muchos tipos de estudios en astrofísica. En esta charla me centraré en el estudio de abundancias de las estrellas de tipo B temprano presentes en la asociación OriOB1. Las principales ideas que presentaré son: (1) La importancia de los análisis espectroscópicos detallados en la determinación de abundancias en estrellas de tipo B temprano; (2) el estudio de la homogeneidad química de los distintos subgrupos estelares que componen OriOB1; (3) la comparación de la abundancias estelares de oxígeno con determinaciones recientes en el Sol; (4) La comparación de abundancias estelares con aquellas obtenidas a partir de análisis del espectro de M42, la nebulosa de Orion; (5) el estudio de la depleción de oxígeno en granos de polvo en la nebulosa de Orión.
AbstractRadiation-driven mass loss largely determines the life expectancy of massive stars. I will present our most recent mass-loss predictions for massive stars, which are obtained from Monte-Carlo multi-line radiative transfer calculations. I will show how these predictions are expected to change as a function of metallicity (and redshift!) and confront the results against data from the VLT FLAMES large programme of massive stars. Finally, I discuss some of the more intricate aspects of the physics of radiation-driven outflows, emphasizing the relevance for the rotational evolution of massive stars into the Luminous Blue Variable phase. This is shown to lead to some rather unexpected results... in particular for the progenitors of supernovae and gamma-ray bursts -- calling for some major paradigm shifts of even our most basic framework of massive star evolution.
AbstractIn the first (optical) part, we present our recent results on mass and luminosity function of Galactic open clusters, a new statistical study based on the ASCC-2.5 catalogue of bright stars, complete to about 1 kpc around the Sun. This includes a new determination of the fraction of field stars born in open clusters. It also briefly addresses the issue whether all massive stars are exclusively born in clusters. In the second (infrared) part, we discuss the prospects of a 42m European ELT to "see" the origin of massive stars in dense embedded protoclusters, by penetrating dense proto- cluster clouds up to 200 mag of visual extinction at 2-5 microns. High-angular resolution AO imaging as well as 3D integral field spectroscopy are required to study the stellar density, binary content, and dynamical properties of these highly obscured, massive, compact star clusters.
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- Beyond the gap; do galaxies care about group dynamics?Dr. Habib KhosroshahiThursday February 22, 2018 - 10:30
- Identifying nearby red nuggets : the unusual globular cluster system of a massive relic galaxyDr. Mike BeasleyTuesday February 27, 2018 - 12:30