Found 105 talks archived in Stars

Video
Thursday November 20, 2014
Dr. Santi Cassisi
INAF-Osservatorio Astronomico di Teramo

Abstract

Since the early 50' of last century the study of Horizontal Branch stars in Galactic GCs has been of pivotal relevance since the core He-burning stage is an 'amplifier' of any evolutionary/physical process occurring during the early evolutionary stages. Thanks to the huge observational effort devoted to this issue many outstanding 'anomalies' have been discovered concerning the physical properties of GC HB stars. The situation is becoming more complex when accounting for the discovery of the Multiple Population phenomenon in Galactic GCs. We will review the main anomalies related to the HB evolutionary stage, their (when available) theoretical interpretations, and current shortcomings. We will also discuss how the discovery of the Multiple Population Phenomenon offers a new approach for interpreting many observational evidence.


Video
Wednesday November 19, 2014
Dr. Cyril Georgy
Keele University

Abstract

We will start by recalling the effects of rotation on stellar evolution and briefly explain its implementation in a stellar evolution code. We will present a set of various grids of massive stars models, and then show some recent results obtained by our new SYCLIST toolbox, which is able (among other things) to generate synthetic stellar clusters, including various physical ingredients, such as initial rotation and angle of view distributions, gravity and limb darkening, etc.


Video
Friday October 24, 2014
Dr. Pere Blay
IAC-NOT

Abstract

High Mas X-ray Binary Systems are important sources of information for many astrophysical fields of research. They are composed by a compact object (black hole or neutron star) and an early type star (usually known as the optical companion). Mass transfer from the later onto the compact companion ends up as very bright emission of high energy photons. The multi-wavelength approach becomes mandatory in order to understand these systems: a) Optical and IR bands are used to characterize the optical companion, b) Mass transfer and the local ambient matter in these systems can be traced in UV and IR bands, c) The behavior and properties of the compact companion can be inferred from X-rays/gamma-rays observations, etc. We will review how this approach helps to understand the behavior of several peculiar systems, including the discovery of optical counterparts, the estimation of compact object masses, the characterization of the ambient matter (local extinction), etc.


Video
Tuesday October 21, 2014
Dr. Michael Bode
Astrophysics Research Institute (Univ. John Moores Liverpoool)

Abstract

The Astrophysics Research Institute (ARI) was established at LJMU in 1992. Today the Institute comprises around 70 staff and research students working on topics ranging from stellar evolution to cosmology. In this talk I will give an overview and some highlights of the work undertaken in recent years on Classical and Recurrent novae by the nova group of the ARI. This involves multi-frequency observations of both Galactic novae and those in Local Group galaxies and includes topics such as the exploration of their potential links to the progenitors of Type Ia supernovae. Along the way, I will briefly describe the work of the Liverpool Telescope on La Palma, one of whose primary science drivers is the efficient and effective observation of transient objects such as these, and look forward to our plans for the development of an even larger and faster-reacting robotic telescope at ORM - currently codenamed 'LT2".


Video
Thursday October 2, 2014
Dr. Adam Burgasser
University of California San Diego

Abstract

Over the past two decades, advances in infrared instrumentation have allowed us to identify a vast and previously unseen population of low-temperature stars, brown dwarfs and free-floating extrasolar planets, collectively called ultracool dwarfs. These sources, with surface temperatures reaching below 0ºC, encompass three new spectral classes and include some of the nearest systems to the Sun. Research in this field is now concentrating on the physical characterization of the ultracool dwarf population and application to Galactic studies. In this talk, I will summarize the recent observational advances in ultracool dwarf research, including the recent discovery of the Y dwarf spectral class. I will then describe our ongoing IRTF/SpeX survey, which has measured the low-resolution, near-infrared spectra of over 1500 late M, L and T dwarfs and uncovered new subpopulations of young (5-30 Myr) brown dwarf, metal-poor halo brown dwarfs and short-period spectral binaries.


Video
Thursday July 10, 2014
Dr. Geroges Meynet
Univ. of Geneve

Abstract

In the early Universe, massive stars played a key role in the early chemical evolution of galaxies and in injecting important amount of ionising radiation in their environments. The first question that will be addressed in this seminar is the following one: can we infer some properties of the first stellar generations in the Universe by studying the surface composition of very metal poor stars in the halo of our Galaxy? The talk will focus on both the regular halo stars and the so-called Carbon Enhanced Metal Poor (CEMP) stars. The second topic that will be addressed in this talk deals with a much more recent event, the birth of the Solar System. Here the question will be: what do the presence of short lived radioactive elements in the proto-solar nebula tell us about the stellar environment of the Sun 4.56 billion years ago? The talk will focus on the discussion of the origin of 26Al and 60Fe in the proto-solar nebula.


Video
Tuesday April 29, 2014
Dr. Sergio Simon
IAC

Abstract

The application of the Fourier transform (FT) technique to high resolution spectra of OB-type stars has challenged our previous knowledge about stellar rotation in stars in the upper region of the HRD. The FT is an old and powerful tool that has being widely used in the case of cool stars, but only very recently applied to massive stars in a systematic way. In this talk I will present the results of the line-broadening characterization of ~250 Galactic OB-type stars (including dwarfs, giants and supergiants with spectral types O4-B9) from the IACOB spectroscopic database. I will show how these analyses have led to a downward revision of previously determined projected rotational velocities in these stars, and have definitely confirmed the presence of a non-negligible extra line-broadening contribution (commonly called macroturbulent broadening) in the whole OB star domain. I will also provide some notes about the importance of these findings on the evolution of massive stars and the detection of stellar oscillations along the lifetime of these important astrophysical objects.


Video
Wednesday April 9, 2014
Dr. Nicolas Fabas
IAC

Abstract

To study the extended atmosphere of evolved stars such as Mira-type variables, spectropolarimetry is an innovative tool. For many kinds of stars, it has been used to measure global magnetic fields through circular polarization and the Zeeman effect. However, linear polarization has seldom been used in the past years even though phenomena such as scattering and the Hanle effect can definitely be studied as well, as it is done in solar physics. In this presentation, I am going to describe original results coming from a spectropolarimetric survey of Mira stars with NARVAL@TBL. Such results concern spectral lines like the Balmer lines of hydrogen and calcium lines. More specifically, I will focus on linear polarization and link this polarization to the propagation of the hypersonic radiative shock wave which is typical of Miras' atmospheres. In general, these environements are very dynamical and scattering in an aspherical atmosphere and velocity gradients can induce a strong linear polarization, likely to be further affected by weak magnetic fields. This analysis is very inspired of what is already done with solar spectra. In addition to that, I am going to present exclusive results about the first detection of a surface magnetic field in a Mira star and explain how the shock wave can impact this field. This work is likely to lead to collaborations with other disciplines such as interferometry (geometry of the scattering environement and characterization of the shock) and radio-astronomy (study of the polarization of masers).


Video
Tuesday April 1, 2014
Dr. N. Kameswara Rao
Indian Institute of Astrophysics

Abstract

R Coronae Borealis (RCB) stars are the more prominent group  of high luminosity hydrogen deficient stars that are rich in carbon  and helium. They also show characteristic irregular light drops of  several magnitudes (between 3 and 8 magnitudes) at unpredictable  times, caused by expulsion of self-made clouds of dust. They range in 
surface temperatures from 4500 K to  20000 K. Some of them seem to  have made even such complex molecules like fullerenes (C60) in their  circumstellar regions. Neither their evolutionary history nor the dust 
formation mechanism are well understood. Two scenarios that have been  suggested are that the present stars are a result of merger of two  white dwarfs (CO+He) or a post born-again (AGB) giant that is  surviving after a final helium shell flash. The talk would describe  the RCB properties and highlight the problems and challenges they pose 
in understanding their origins and dust production.


Video
Tuesday March 25, 2014
Dr. Pieter Degroote
Institute for Astronomy- KU Leuven

Abstract

The theory of stellar evolution is well developed over the past decades, and in particular the predictions of one dimensional numerical models have passed basic observational tests. With the advent of high precision astronomical observations, these tests can now be improved to fine tune the physics of the models. In particular, the combination of exploiting binary properties with the information obtained from asteroseismology, proves to provide a promising test framework. However, both binarity and seismology increase the complexity of the observational models and their relation to the stellar evolutionary model, and therefore require as many independent tests as possible.



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