Found 14 talks width keyword stellar evolution
We present the new stellar population synthesis models based on the empirical stellar spectral library MILES, which can be regarded nowadays as standard in the field of stellar population studies. The synthetic SEDs cover the whole optical range at resolution 2.3 Å (FWHM). The unprecedented stellar parameter coverage of MILES allowed us to extend our model predictions from intermediate- to very-old age regimes, and the metallicity coverage from super-solar to [M/H] = -2.3. Observed spectra can be studied by means of full spectrum fitting or line-strengths. For the latter we propose a new Line Index System (LIS) to avoid the intrinsic uncertainties associated with the popular Lick/IDS system and provide more appropriate, uniform, spectral resolution. We present a web-page with a suite of on-line tools to facilitate the handling and transformation of the spectra. Online examples with practical applications to work with stellar spectra for a variety of instrumental setups will be shown. Furthermore we will also show examples of how to compute spectra and colors with varying instrumental setup, redshift and velocity dispersion for a suite of Star Formation Histories.
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.
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.
AbstractRed Dwarf (dM) stars are the most numerous stars in our Galaxy. These faint, cool, long-lived, and low mass stars make up > 80% of all stars in the Universe. Determining the number of red dwarfs with planets and assessing planetary habitability (a planet’s potential to develop and sustain life) are critically important because such studies would indicate how common life is in the universe. Our program - "Living with a Red Dwarf" addresses these questions by investigating the long-term nuclear evolution and magnetic-dynamo coronal and chromospheric X-ray to Ultraviolet properties of red dwarf stars with widely different ages. The major focus of the program is to study the magnetic-dynamo generated X-ray-Ultraviolet emissions and flare properties of red dwarf stars from youth to old age. Emphasized are how the stellar X-UV emissions, flares & winds affect hosted planets and impact their habitability. We have developed age-rotation-activity relations and also are constructing irradiance tables (X-UV fluxes) that can be used to model the effects of X-UV radiation on planetary atmospheres and on possible life on nearby hosted planets. Despite the earlier pessimistic view that red dwarfs stars are not suitable for habitable planets - mainly because their low luminosities require a hosted planet to orbit quite close (r <0.3 AU) to be sufficiently warm to support life. Our initial results indicate that red dwarf stars (in particular the warmer dM stars) can indeed be suitable hosts for habitable planets capable of sustaining life for hundreds of billion years. Some examples of red dwarf stars currently known to host planets are discussed.
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