Recent Talks
List of all the talks in the archive, sorted by date.
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.
Friday November 6, 2009
Prof. Kazunari Shibata
Hida Observatories, Kyoto University, Japan
Abstract
The 3.8m optical and infrared telescope, which is Japan's first segmented mirror telescope, is now being constructed using the world's first super high precision, high speed grinding technology and the world's first truss structure drive system. This is the joint project between Kyoto University, Nagoya University, National Astronomical Observatory, and Nano-Optonics Energy (private company) with the budget of the Nnao-Optonics Energy and Dr Hiroshi Fujiwara (CEO of the Nano-Optonics Energy). The telescope will be completed in 2012 and installed in Okayama, and will become the biggest optical and infrared telescope in east Asia. The technologies for making this telescope such as (1) grinding technology, (2) segmented mirror, and (3) truss structure drive system are also basic technologies for the future extremely large telescope such as the 30m telescope. The scientific objective of the telescope is the search for the transient objects (gamma ray bursts, black hole binaries, stellar flares) and the extra solar planets. How this project has emerged and developed will be discussed in detail, including also the discussion about the possible future international collaboration.
Thursday November 5, 2009
Prof. Rony Keppens
Centre for Plasma-Astrophysics, K. U. Leuven, Belgium
Abstract
I will present grid-adaptive computational studies of both magnetized and unmagnetized jet flows, with significantly relativistic bulk speeds, as appropriate for AGN jets. Our relativistic jet studies shed light on the observationally established classification of Fanaroff-Riley galaxies, where the appearance in radio maps distinguishes two types of jet morphologies. We investigate how density changes in the external medium can induce one-sided jet decelerations, explaining the existence of hybrid morphology radio sources. Our simulations explore under which conditions highly energetic FR II jets may suddenly decelerate and continue with FR I characteristics. In a related investigation, we explore the role of dynamically important, organized magnetic fields in the collimation of the relativistic jet flows. In that study, we concentrate on morphological features of the bow shock and the jet beam, for various jet Lorentz factors and magnetic field helicities. We show that the helicity of the magnetic field is effectively transported down the beam, with compression zones in between diagonal internal cross-shocks showing stronger toroidal field regions. For the high speed jets considered, significant jet deceleration only occurs beyond distances exceeding hundred jet radii, as the axial flow can reaccelerate downstream to internal cross-shocks. This reacceleration is magnetically aided, due to field compression across the internal shocks which pinch the flow.
Saturday October 24, 2009
Dr. Johan Knapen
Instituto de Astrofísica de Canarias, Spain
Abstract
Galaxies are the basic building blocks of the Universe, and understanding their formation and evolution is crucial to many areas of current astrophysical research. Nearby galaxies, being the 'fossil record' of the evolution of galaxies, provide a wealth of detail to test extensively the current models of galaxy formation and evolution. A galaxy's structure is linked to both its mass and evolutionary history. Probing galactic structure requires understanding the distribution of stars among galaxies of all types and luminosities across the full range of environments. We are performing a complete volume-limited (d < 40 Mpc) survey of over 2200 nearby spiral, elliptical and dwarf galaxies at 3.6 and 4.5 μ in the Spitzer Warm Mission to address fundamental questions of galactic structure that are united by the common need for deep, uniform, unbiased maps of the stellar mass in galaxies. I will introduce the survey, give examples of images and of the science that can be done, and explain how other researchers at the IAC can become involved in analysing these exciting data.Upcoming talks
- Properties and origin of thick disks in external galaxiesDr. Francesca PinnaThursday January 16, 2025 - 10:30 GMT (Aula)
- Seminar by Luigi TibaldoLuigi TibaldoTuesday January 21, 2025 - 12:30 GMT (Aula)
Recent Colloquia
Recent Talks
