Recent Talks
List of all the talks in the archive, sorted by date.
Thursday December 3, 2009
Dr. Fabrice Martins
University of Montpellier II, France
Abstract
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'.
Wednesday December 2, 2009
Dr. Elisa Delgado Mena
Instituto de Astrofísica de Canarias, Spain
Abstract
The surface abundance of lithium on the Sun is 140 times less than protosolar, yet the temperature at the base of the surface convective zone is not hot enough to burn Li. A large range of Li abundances in solar type stars of the same age, mass and metallicity is observed, but theoretically difficult to understand. An earlier suggestion that Li is more depleted in stars with planets was weakened by the lack of a proper comparison sample of stars without detected planets. Here we report Li abundances for an unbiased sample of solar-analogue stars with and without detected planets. We find that the planet-bearing stars have less than 1 per cent of the primordial Li abundance, while about 50 per cent of the solar analogues without detected planets have on average 10 times more Li. The presence of planets may increase the amount of mixing and deepen the convective zone to such an extent that the Li can be burned. We also present Be abundances for a sample of stars with and without known planets and discuss the possible relation of these light element with the presence of planetary systems.
Tuesday December 1, 2009
Prof. Rajesh Kochhar
Indian Institute of Science Education and Research Mohali, India
Abstract
Human beings are born astronomers. Ever since they learned to walk upright they have looked at the sky and wondered. The sky has remained the same but not its meaning. We can distinguish between three phases in the history of humankind’s relationship with its cosmic environment: (i) propitiatory phase; (ii) negotiatory phase; and the current (iii) sky-as-an-object phase. My concern today is to discuss the interplay between astronomy and culture in general in the Indian context. Much of the discussion belongs to the negotiatory phase. More specifically I would discuss how in the formative era, sacred texts influenced astronomy, how these texts themselves were modified under the influence of new scientific developments, and how mythology was upgraded to keep pace with science.
Friday November 20, 2009
Dr. Robert Williams
Space Telescope Science Institute, USA
Abstract
Spectroscopic observations of novae date back a century, and the fundamental nature of the outburst has been understood for 50 years. Yet, recent observations suggest possible major modifications to the standard nova paradigm. A high-resolution spectroscopic survey of novae has revealed short-lived heavy element absorption systems near maximum light consisting of Fe-peak and s-process elements. The absorbing gas is circumbinary and it must pre-exist the outburst. Its origin appears to be mass ejection from the secondary star, implying large episodic mass transfer events from the secondary that initiate the nova outburst. The spectroscopic evolution of novae is interpreted in terms of two distinct interacting gas systems in which the bright continuum is produced by the outburst ejecta but absorption and emission lines originate in gas ejected by the secondary star in a way that may explain dust formation and X-ray emission from novae.
Friday November 20, 2009
Dr. Pasi Hakala
Tuorla Observatory, University of Turku, Finland
Abstract
I present some recent results from our Optical and NIR studies of five short period low-mass X-ray binaries (LMXB's; X1822-371, X1957+115, UW CrB, X1916-05 and X0614+091). Optical photometry and spectroscopy reveal some surprising results on the geometry and evolution of accretions discs in LMXB's. Based on our data, it is increasingly clear that accretion discs in these systems are far from being stable and must undergo substantial precession and/or warping behaviour on timescales less than a day in case of the shortest period systems.
Thursday November 19, 2009
Prof. Alexander Burinskii
Theoretical Physics Laboratory, NSI, Russian Academy of Sciences, Moscow, Russia.
Abstract
Exact solutions of the Einstein-Maxwell equations in the Kerr-Schild formalism are discussed. We show that black hole horizon is unstable with respect to electromagnetic excitations. Contrary to smooth harmonic functions used in perturbative solutions, the exact solutions for electromagnetic excitations on the Kerr background have the form of singular twistor-beams which have very strong back reaction to metric and break the black-hole horizon, forming in it holes which allow radiation to escape interior of black-hole. As a result, under action of the external electromagnetic field the horizon may be covered by a set of fluctuating micro-holes, which corresponds to a semi-classical mechanism of Hawking radiation.
Monday November 16, 2009
Dr. Clementine Bechet
European Southern Observatory, Garching, Germany
Abstract
The ambitious astrophysical objectives of the Extremely Large Telescopes (ELTs) will be achievable only with innovative Adaptive Optics (AO) systems to correct for the wavefront distortions induced by the turbulence in the atmosphere. One of the key components of an AO system is the wavefront reconstruction, which is a real-time estimate of the wavefront distortions above the telescope aperture from data. This reconstruction can be described by an inverse problem approach (IPA),taking advantage of the modeling of second-order statistics of both turbulence and data noise.First, the benefits of the IPA to wavefront reconstruction is enhanced for two particularities of the ELTs: very high number of estimated parameters (~104) and elongated spots on the sensor for AO using Laser Guide Stars. Moreover, this IPA can be implemented with a fast algorithm for high number of degrees of freedom, which makes it a candidate for the implementation on a future AO system of the E-ELT. The correction performance in closed-loop AO has also been assessed thanks to end-to-end simulations of single-conjugate AO and Ground-Layer AO with Laser Guide Stars on the E-ELT.
Friday November 13, 2009
Prof. Hiroshi Karoji
SUBARU Telescope, National Astronomical Observatory of Japan
Abstract
In 2006, NAOJ proposed to construct the Hyper Suprime-Cam (HSC) as a second generation instrument for Subaru telescope. This is a very wide-field camera covering 1.5 degrees of sky at a time. The focal plane area to be covered will be around 530mm. A total of 110 2kx4k CCD detectors will be placed adjacent to each other in order to cover this large field of view. The HSC will be a prime focus camera, and will enlarge the current field of view (FOV) of Subaru, as provided by the first generation Suprime Cam, by a factor of 10. The HSC will be the largest CCD camera in the world, and will have a total performance, as measured by the product of the telescope aperture area and the field of view, which will exceed that of all other telescopes. Only the planned LSST will have a better performance, but that will be in a time frame of three or more years later than the HSC. The main scientific goal of the HSC will be weak lensing studies over large areas of the sky. Approximately 1000 square degrees will be surveyed every year. Weak lensing distortions of background galaxies due to the large scale structure, so called cosmic shear, will be examined. From statistical properties of cosmic shear, the properties of dark energy will be constrained. Along with the weak lensing study, a large survey project is planned to use more than 200 nights of HSC and Subaru to cover interesting science topics with the large dataset.
Thursday November 12, 2009
Dr. Aníbal García Hernández
Instituto de Astrofísica de Canarias, Spain
Abstract
Asymptotic 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.
Wednesday November 11, 2009
Dr. Jörg Büchner
Max-Planck Institut für Sonnensystemforschung, Germany
Abstract
The dynamics of the solar atmosphere is largely controlled by its magnetic coupling to the photosphere of the Sun. Since the solar magnetic field is complex, numerical simulation must be utilized to investigate the coupling processes. Results will be shown of treating this way the two unresolved issues - the heating of the corona and the acceleration of the solar wind.Upcoming talks
- Coloquio con Isabel Pérez Grande (AEE)Dr. Isabel Pérez GrandeTuesday November 26, 2024 - 10:30 GMT (Aula)
- Revisiting mass transfer and accretion in symbiotic binaries in the Gaia eraDr. Jaroslav MercThursday November 28, 2024 - 10:30 GMT (Aula)
Recent Colloquia
Recent Talks
