Found 105 talks archived in Stars

Video
Tuesday July 7, 2015
Dr. Nicholas C. Sterling
University of West-Georgia, USA

Abstract

The origins of neutron(n)-capture elements (atomic number Z > 30) have historically been discerned from the interpretation of stellar spectra. However, in the last decade nebular spectroscopy has been demonstrated to be a potentially powerful new tool to study the nucleosynthesis of n-capture elements. In this talk, I will discuss exciting new advances made in this field with near-infrared and optical observations of planetary nebulae, and atomic data investigations that enable the analysis of spectroscopic data.


Video
Thursday June 18, 2015
Prof. Pavel Kroupa
Univ. of Bonn

Abstract

The stellar initial mass function (IMF) is usually assumed to be a probability density distribution function. Recent data appear to question this interpretation though, and I will discuss alternative applications and results concerning the possibly true nature of the IMF. Empirical evidence has emerged that the IMF becomes top-heavy in intense star bursts and at low metallicity. Related to the IMF are binary star distribution functions, and these evolve through dynamical processes in embedded star clusters. The insights gained from these considerations lead to a mathematically computable method for calculating stellar populations in galaxies, with possibly important implications for the matter cycle in galaxies. It turns out that the galaxy-wide IMF, the IGIMF, becomes increasingly top-heavy with increasing galaxy-wide star formation rate, while at the same time the binary fraction in the galactic field decreases.


Video
Thursday June 11, 2015
Dr. Federico Marocco
University of Hertforshire

Abstract

 A comprehensive understanding of sub-stellar objects (brown dwarfs and extrasolar giant planets) and their population characteristics (e.g. IMF, formation history) is only possible through the robust interpretation of ultra-cool objects spectroscopy. However, the physics of ultra-cool atmospheres is complicated by a variety of challenging ingredients (dust properties, non-equilibrium chemistry, molecular opacities). Moreover, while hydrogen-burning stars stabilize on the stellar main-sequence, sub-stellar objects continuously cool down (since they lack an internal source of energy) and evolve towards later spectral types. Their atmospheric parameters are a strong function of age. In this talk I will present the spectroscopic analysis of a large sample of L and T dwarfs, complementing the spectroscopic data with astrometry from the PARSEC program, in order to constrain the sub-stellar initial mass function and formation history. I will then describe our new effort to identify and characterize a large sample of benchmark systems, combining Gaia capabilities with large area near-infrared surveys such as UKIDSS, SDSS, and VVV, in order to calibrate effectively the theoretical models.
    


Video
Wednesday June 10, 2015
Dr. Nikolay Kacharov
University of Heidelberg

Abstract

I will talk about our current understanding of globular cluster (GC) formation and what we have yet to learn about them. I will particularly focus on the chemical and dynamical properties of the neglected GC NGC4372, which I studied for the first time with  high-resolution spectroscopic observations.
Its chemical abundances revealed it as a typical representative of the old, metal-poor halo group. More interesting, however, are its structural and kinematic properties as the cluster has an unusually high intrinsic rotation for its metallicity and appears to be rotationally flattened. I will discuss what
rotating GCs tell us about their early evolution.


Video
Thursday May 14, 2015
Dr. Peter Pessev
GTC

Abstract

MASTER-Kislovodsk auto-detection system discovered a faint transient in the Andromeda galaxy on January 13th 2015. It was originally identified as a classical nova and received designation M31N 2015-01a. Further observations showed discrepancies with the spectra and lightcurves typical for the classical novae. The transient was re-identified as a likely stellar merger (aka Luminous Red Nova (LRN)), similar to V838Mon. In this presentation I will deliver a short overview of our current understanding of this class of objects and a summary of the current state of the ongoing observing campaign of the M31 LRN. Recent results will be discussed with a particular emphasis on the contributions made possible by GTC and other observing facilities at Observatorio Roque de los Muchachos. At the final part of the presentation I will touch on follow up observations once M31 is available for observations again.


Video
Thursday April 23, 2015
Dr. Matteo Miluzio
IAC

Abstract

With the aim of testing the relation between supernova (SN) rate and star formation rate, we conducted a SN search in a sample of local starburst galaxies (SBs) where both star formation rates and extinction are extremely high. The search was performed in the near-infrared, where the bias due to extinction is reduced using HAWK-I on the VLT. We discovered six SNe, in excellent agreement with expectations, when considering that, even in our search, about 60% of events remain hidden in the nuclear regions due to a combination of reduced search efficiency and very high extinction.
In addition I will present my plans for next months at IAC for the "Starbursts and EMIR project". I will participate in the commissioning of the instrument at La Palma, collaborating in the development of the ETC and I  will compile a catalog of starbursts for EMIR with the aim to study their imprint in the cosmic evolution of galaxies.


Video
Tuesday March 17, 2015
Mr. Bartek Gauza
IAC

Abstract

Direct imaging of wide planetary mass companions provide a unique opportunity to fully characterize their spectroscopic and photometric properties. They share similar physical properties to gas giant exoplanets found by radial velocity and transit techniques, with overlapping temperatures in the range of ~1000–1500K and masses from a few to a dozen Jupiter masses. We have recently identified a young L-type companion at ~100 AU of a previously unrecognized M dwarf. We determined the parallactic distance of the system of 12.7 ± 1.0 pc. By comparison with evolutionary models we derived a mass of 73 (+20, -15) MJup for the primary, at around the substellar mass limit and 11.2 (+9.7, -1.8) MJup for the secondary, near the deuterium burning mass limit. In this talk I will present the properties of the two components of this new pair and discuss the possibilities for future thorough characterization.


Video
Thursday February 12, 2015
Dr. David Jones
IAC

Abstract

I will report on the results of our paper published in Nature this week, outlining the discovery of a super-Chandrasekhar double-degenerate binary system at the heart of the planetary nebula Hen 2-428.  Planetary nebulae (PNe) represent the final stage in the evolution of low- and intermediate-mass stars, forming from the mass ejected by the star during its AGB evolution before being ionised by the star's, now exposed, core.  As binarity is expected to play a key role in the formation of aspherical PN morphologies, we have been intensively searching for new binary central stars in a push towards a statistical sample.  One of our newly-discovered binary systems, lying at the heart of Hen 2-428, had a further surprise to reveal, with observations and modelling showing the system to consist of twin evolved stars with a total mass greater than the Chandrasekhar limit.  The short period of the system, only 4.2 hours, means that the two stars will merge together in approximately 700 Myr, resulting in a Supernova Type Ia.  While the super-Chandrasekhar merger of two white dwarfs has long been considered a formation pathway for SN Ia, this is the first system found that is confirmed to be both massive enough and in a tight enough orbit to merge in less than a Hubble time.


Video
Thursday January 29, 2015
Dr. France Allard
Centre de Recherche Astronomique de Lyon

Abstract

Understanding the atmospheric and evolutive properties of very low mass stars, brown dwarfs, and gas giant exoplanets have been important challenges for modelers around the world since the discovery of the first brown dwarfs in the Pleiades cluster (Rebolo et al. 1995) and in the field (Nakajima et al. 1995). The early studies of brown dwarfs have provided rich insights into atmospheric physics, with discoveries ranging from cloud formation (Tsuji et al. 1996), methane bands (Oppenheimer et al. 1995) and ammonia bands (Delorme et al. 2008), to the formation of wasi-molecular KI-H2 absorption (Allard et al. 2007), and to disequilibrium chemistry (Yelle & Griffith 2001). New classical 1D models yield spectral energy distribution (SED) that match relatively well despite these complexities. These models have for instance explained the spectral transition from M to L, T and now Y brown dwarf spectral types (Allard et al. 2013). However, in presence of surface inhomogeneities revealed recently for a nearby (2 pc) brown dwarf (Crossfield et al. 2014), the SED may well fit even exactly, but the model parameters could be far from exact, e.g. with the effective temperature by several hundred kelvins too cool in the case of dusty brown dwarfs and young gas giant exoplanets! I will review the progress achieved in reproducing the spectral properties of very low mass stars, brown dwarfs and gas giant exoplanets, and review progress in modeling more accurately their atmospheres using Radiation HydroDynamical (RHD) simulations.


Video
Thursday November 27, 2014
Dr. Melanie Godart
IAC

Abstract

Massive stars shape and drive our Universe. Many issues such as their formation, their stability and the mass loss effects for example, are nowadays far for being completely understood. To improve our understanding, asteroseismology provides a powerful tool and excellent results have been obtained over the last years. Recent ground-based and space observations have shown the presence of pulsations in massive main sequence and post-main sequence stars, such as acoustic and gravity modes excited by the kappa-mechanism and even solar-like oscillations. Theoretical studies emphasized the presence of strange modes in massive models, excited by the strange mode instability mechanism. Moreover, recent theoretical analyses have shown that hot supergiants can also pulsate in oscillatory convective modes propagating in the superficial layers of these stars. I will expose here the instability domains of massive stars as well as their excitation mechanisms and present the latest results in the domain.



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