Univerza v Ljubljani, Fakulteta za matematiko in fiziko

torek, 2. 6. 2009, ob 15h v F6

I will present the first results of Ice Cube, the neutrino detector located on Antarctic station Amundsen-Scott. Since 2007 it has detected more than 5000 neutrinos and determined their sources on the sky with one degree accuracy. Their distribution agrees well with expected background except one point source which might be the ”first light” of this telescope. When Ice Cube is finished in 2011 it will be a completely new tool to observe our universe.

Univerza v Ljubljani, Fakulteta za matematiko in fiziko

torek, 2. 6. 2009, ob 15h v F6

I will review the current state of the RAdial Velocity Experiment (RAVE), an ambitious ongoing spectroscopic survey which already secured over a third million stellar spectra. For many of these spectra not only the radial velocity but also stellar parameters have been determined from spectral analysis. This requires automated reduction, analysis and classification techniques which have to be checked against other spectroscopic and photometric datasets. The adopted solutions are important for any RAVE user who wants to take full advantage of the claimed rather impressive typical errors: less than 2 km/s error in radial velocity, 200 K in temperature, 0.3 dex in gravity and 0.2 dex in metallicity. The talk will also outline the improvements planned for the next approximately yearly data releases. Possibilities for RAVE’s extension using a modern multiple-object spectrograph will be discussed.

Univerza v Ljubljani, Fakulteta za matematiko in fiziko

torek, 26. 5. 2009, ob 15h v F6

In the past few years cosmological simulations had rapidly advanced to a point where they became useful and powerful tool to constraint cosmological models. They can be used to study physics on variety of scales, from galaxy collisions to clusters and large-scale structure formation. In this talk I would like to present basic steps to run your own cosmological simulation and what physics can be constrained from the results.

Univerza v Ljubljani, Fakulteta za matematiko in fiziko

torek, 26. 5. 2009, ob 15h v F6

IHerschel space observatory has been successfully launched on 14 May 2009. It will observe in the 55-672 \mu m wavelength spectral range. Hershel is the only space facility dedicated to this part of the far infrared and submilimetre spectral range. The choice of an operational orbit around L2 provides a stable thermal environment which together with a very low telesope emissivity offers a stable background enabling very sensitive photometric range. I will describe some basic telescope charateristics and scientific objectives of this mission.

Univerza v Ljubljani, Fakulteta za matematiko in fiziko

torek, 19. 5. 2009, ob 15h v F6

Gamma Ray Bursts (GRBs) are violent explosions releasing of energy in a very short time (a fraction of a second to 1 hour). These brief flashes of gamma rays are followed at longer wavelengths by rapidly fading “afterglows”. In the last 4 years many new insights into GRBs physics have been brought by the Swift satellite. Rapid and accurate localization of GRBs by the Swift enables rapid response ground-based telescopes to routinely commence with observations of optical afterglows within minutes after the burst. The combination of gamma-ray, X-ray, optical and ultraviolet data from Swift instruments with deep, early-time optical imaging from ground-based telescopes is providing unprecedented multiwavelength datasets. I will present the observational strategy and some results of rapid, automatic, optical follow-up observations of a sample of GRBs using the 2-m robotic Liverpool and Faulkes Telescopes. I will review and discuss possible interpretation of the large variety in early afterglow behavior.

INAF – Padova Astronomical Observatory

torek, 12. 5. 2009, ob 15h v F6

Low Mass X-ray binaries with either a black hole or a neutron star show power spectra characterized by several enhanced fractions of power at given frequencies, such as Quasi Periodic Oscillations (QPOs). Twin peak high frequency QPOs are typical of Keplerian time-scales a few gravitational radii away from the compact object, hence QPOs may carry fingerprints of General Relativity in the strong field limit.

Most of the proposed models in the past ten years deal with matter or biting the compact object. However the modelling still suffers in explaining many features such as coherence and rms values of the peaks, their frequencies, the observed power law in the power spectra and the emission mechanism which should account for hard X-ray photons.

Recent studies about tidal interaction of small satellites with a compact object have been proposed to explain the NIR-X rayflaring activity observed in the super massive black hole at galactic center. Simulations have shown that small satellites (e.g. asteroids or comets) on highly eccentric orbits can be brought down to the black hole by tidal evolution. Once close to thehole, say within 10 r_g , tides are so strong that small satellites are highly disrupted and can release an energy as high as a few percent of their rest mass.

I will give a general reviewof the QPOs phenomenon in Low Mass X-ray binaries and I will also discuss both preliminary results in modelling this phenomenon with tidal interaction and still open issues.

Observatorij Hvar Geodetske fakultete v Zagrebu

torek, 5. 5. 2009, ob 15h v F6

Atmosfera Sonca, posebno pa Sončeva korona, je zelo dinamičen magneto-plazemski sistem, ki ga poganjajo konvekcijska gibanja pod površjem in Sončeva diferencialna rotacija v sodelovanju s Sončevim magnetnim poljem. V atmosfero prinešena energija se delno porabi za segrevanje korone (T > 10^6 K) in poganjanje Sončevega vetra (v = 300 – 800 km/s), delno pa se shranjuje v nepotencialnih magnetnih strukturah v aktivnih področjih. Po nastopu nestabilnosti se ta vskladiščena energija lahko eksplozivno sprosti v dveh fizikalno različnih (čeprav povezanih) procesih, ki jih imenujemo Sončev izbruh (solar flare) in koronalni izbruh (coronal mass ejection). Sončevi izbruhi so posledica rezistivnih plazemskih nestabilnosti, ki omogočajo magnetno rekonekcijo. V procesu rekonekcije se plazma segreje do nekaj 10^7 K, netermalni delci pa dosežejo relativistične energije ter provzročijo močno radijsko in rentgentsko sevanje. Po drugi strani so koronalni izbruhi rezultat idealnih magnetohidrodinamičnih nestabilnosti na večjih skalah, ki lahko izstrelijo v medplanetarni prostor več kot 10^13 kg koronalne plazme s hitrostmi večjimi od 1000 km/s. Oba procesa, ki lahko sprostita več kot 10^25 J energije, močno vplivata na naš planet, predvsem v obliki geomagnetnih neviht ter ionosferskih motenj. V predavanju bodo prikazani tudi prispevki Observatorija Hvar na tem področju fizike Sonca.

Univerza v Ljubljani, Fakultet za matematiko in fiziko

torek, 21. 4. 2009, ob 15h v F3

In the age of large automated spectroscopic surveys such as RAVE and GAIA, synthetic spectra are an essential tool for the task of determining stellar parameters –such as effective temperature, gravity, chemical composition, and rotation velocity– for a very large sample of objects. It is therefore crucial to have as good spectrum synthesis methods as possible, and to understand the many quirks and pitfalls researchers face when working with them.

Although the future of the field clearly lies in full 3D hydrodynamic atmosphere models –which start from very basic principles to use as few free parameter as possible– it seems that long computation times will make their generalized use for research impractical in the next 5-10 years. Currently, the emphasis is on classical 1D stationary models with varying degrees of sophistication.

I will briefly describe some of the current most important spectrum synthesis methods, describing their relative advantages in terms of physical complexity of the underlying models, computation time, and public availability of the code –an essential, but often overlooked consideration in scientific research. I will also describe in some detail one of the de facto standards in the field, the Kurucz family of spectrum synthesis programs, to give an idea of a typical spectrum synthesis procedure.

Univerza v Ljubljani, Fakulteta za matematiko in fiziko

torek, 7. 4. 2009, ob 15h v F3

Overview of current state of night sky light pollution in Slovenia and neighbour countries. Instrumentation, observing methods and results of night sky monitoring during the past 3 years period will be presented. Also some examples of good practice, energy saving and reduction of light pollution after the adoption of Light Pollution legislation by Government of RS on Aug. 30, 2007. Most recent record dark sky measurements at Črni Vrh observatory will be commented and compared with other darkest places in Europe.

INAF – Trieste Astronomical Observatory

torek, 31. 3. 2009, ob 15h v F3

Hydrodynamical simulations of galaxy clusters – IntraCluster Medium and AGN feed back. Cosmological hydrodynamical simulations are widely used to investigate the effects of physical processes during the formation of large scale cosmic structures. I will present the study of AGN feedback effect on IntraCluster Medium (ICM) and galaxy population properties in hydrodynamical simulations of galaxy clusters. Our simulations are performed with the GADGET2 code, where the energy release from black hole accretion (Springel et al. 2005) and a detailed model of chemical enrichment (Tornatore et al. 2007) are included. Simulations are carried out for a set of 16 clusters spanning the range of mass 1e14-1e15 Msun/h. I will show the effect of different AGN schemes of the thermo- and chemo-dynamical properties of ICM, e.g. the temperature and metallicity profiles, on galaxy groups and galaxy clusters scale. I will critically assess the reliability of our models through a comparison with observational data in the X-ray band.