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Absorber model of the intergalactic medium

Absorber model of the intergalactic medium

Vid Iršič: Absorber model of the intergalactic medium

V četrtek, 21. decembra ob 12. uri bo imel Vid Iršič (University of Washington, ZDA) Astrodebato o absorpciji svetlobe v medgalaktičnem prostoru ter pripadajočem modelu, ki opisuje razporeditev snovi v zgodnjem vesolju. Predavanje bo v predavalnici F7 na Jadranski 19. Vljudno vabljeni!

Absorber model of the intergalactic medium

Vid Iršič
University of Washington, ZDA 

The last two decades have seen tremendous progress in cosmological hydro-dynamical simulations and their uses to simulate the gaseous environment of the intergalactic medium. Primarily through the Lyman-alpha forest as the statistical tool of choice, the state-of-the-art simulations have ushered the intergalactic medium to an era of precision cosmology to rival large galaxy surveys. 

While they have allowed us a much more precise estimation of cosmological parameters, deeper understanding of the interplay of physical processes involved in the intergalactic gas has been lagging behind. This can be attributed to lack of any successful analytic model that would in its final result preserve the inherent difference in the cosmological and astrophysical growth (or suppression) of structure.

I will present a new semi-analytic model of the Lyman-alpha forest clustering, where the transmitted flux is split into contributions from discrete absorbers, tracing the underlying matter fluctuations. The model conveys intuitive perspective into the building blocks of the absorption signal, offers a tool to construct new, optimally-weighted, statistics, and provides a unified framework in which many current systematic effects can be estimated (metal absorption, high-column density systems, etc.).

Considerations for Robust Modeling of Triple Stellar Systems

Considerations for Robust Modeling of Triple Stellar Systems

Kyle Conroy: Considerations for Robust Modeling of Triple Stellar Systems

V četrtek, 14. decembra ob 12. uri bo imel Kyle Conroy (Villanova University, ZDA) Astrodebato o trojnih zvezdah in izzivih pri njihovem modeliranju. Predavanje bo v predavalnici F7 na Jadranski 19. Vljudno vabljeni!

Considerations for Robust Modeling of Triple Stellar Systems

Eclipsing binary stars allow for the direct measurement of stellar parameters and distances and are therefore an important tool in the calibration of stellar relationships.  In several cases, astronomers have been able to achieve a precision of 2-3% in stellar parameters through modeling these systems.  By introducing an additional component, however, it is possible to achieve precisions as low as 0.5%.  In order to precisely and accurately model these complex systems, we must take into account several considerations, including: light time effects, perturbations to orbital elements, and distortion of the stellar surface (in the case of a close inner-binary).

Življenje v vesolju – debata

Življenje v vesolju – debata

Andrej Prša in Janez Kos bosta ta četrtek ob 18:00 v Mafija kafeju vodila debato na temo življenja v vesolju. S pomočjo radovednosti in domišljije publike bomo skupaj krmilili skozi teme kot so pogoji za življenje, izvenzemeljske civilizacije in iskanje življenja v vesolju.

Vljudno vabljeni!

Several interesting eclipsing systems

Several interesting eclipsing systems

dr. Petr Zasche

Astronomical Institute
Faculty of mathematics and physics
Charles University in Prague

v četrtek, 9. novembra 2017, ob 12. uri v predavalnici F7 (Jadranska 19, Ljubljana)

I will talk about our recent studies on several interesting multiple star systems in our Galaxy as well as in the Magellanic Clouds. Also the currently prepared publication of eccentric binaries is being discussed and a few extreme eccentric systems will be shown.

The nature of the First Stars: the point of view of the neutron capture elements

The nature of the First Stars: the point of view of the neutron capture elements

dr. Gabriele Cescutti

INAF – National Institute for Astrophysics
Astronomical Observatory of Trieste

v sredo, 31. maja 2017, ob 12. uri v predavalnici F4 (Jadranska 19, Ljubljana)

In the last years our group has found that many chemical anomalies observed in very metal-poor halo stars in the light elements suggest the first stellar generations to have been fast rotators (spinstars). Recently, theoretical computations have found that spinstars can also play a role in the chemical enrichment of neutron capture elements providing a early contribution of s-process. By means of a stochastic chemical evolution model, it is possible to identify the spinstars s-process contribution as the missing component responsible for the spread in the ratio between light (Sr) to heavy (Ba) neutron capture elements. A specific distribution is predicted for the isotopic ratio of Ba in halo stars and this imprint could be the smoking gun of the role played by spinstars in the spread of [Sr/Ba] ratio.  In this context, regarding the still unknown origin of the complementary r-process component, I present new constraints on the rate and time scales of r-process events, based on the recent discovery of the r-process rich stars in the ultra faint galaxy Reticulum 2.

Spektroskopija obrnjena na glavo

Spektroskopija obrnjena na glavo

dr. Janez Kos

Sydney Institute for Astronomy, Univerza v Sydneyu, Avstralija

v ponedeljek, 29. maja 2017, ob 12. uri v predavalnici F6 (Jadranska 19, Ljubljana)

Moderni spektroskopi lahko hkrati opazujejo stotine ali tisoče zvezdnih spektrov. S pomočjo optičnih vlaken pripeljejo svetlobo zvezd v spektroskop in tako izkoristijo celoten razpon optike in ccd detektorja. Ker navadno potreba po kvantiteti prevlada nad kvaliteto, je take spektre težko obdelati, ne da bi zavrgli kar nekaj informacije.

Če zelo dobro poznamo optiko spektroskopa in optičnih vlaken, lahko obdelavo v celoti izpustimo. Namesto da bi spektre obdelali in jih nato analizirali, lahko proces obrnemo: izdelamo sintetične spektre, modele, ki predstavljajo spektre v rangu nekih parametrov (temperatura, kovinskost zvezde, itd), ki jih iščemo, ter jih konvuliramo z dobro znano prenosno funkcijo optike spektroskopa in vlaken. Tako lahko iz modela spektra zgradimo ”surov” neobdelan spekter in ga primerjamo z izmerjenim, prav tako neobdelanim spektrom. Prednost te metode je, da izboljša resolucijo nad nominalno vrednost spektroskopa, pravilno uteži spektre, ki se na surovi sliki prekrivajo in omogoča manj konzervativen dizajn bodočih spektroskopov. Slabost je seveda ta, da je metoda računsko zelo zahtevna in terja dobro poznavanje optike inštrumenta.

Pokazal bom kako smo natančno parametrizirali optiko 4 meterskega teleskopa AAT in spektroskopa Hermes ter predstavil prve rezultate nove metode, ki sem jo razvil.

Hydrodynamical simulations: AGN feedback and its influence on the ICM of Galaxy Clusters

Hydrodynamical simulations: AGN feedback and its influence on the ICM of Galaxy Clusters

dr. Elena Rasia

INAF – National Institute for Astrophysics
Astronomical Observatory of Trieste

v sredo, 24. maja 2017, ob 12. uri v predavalnici F4 (Jadranska 19, Ljubljana)

Powerful phenomena determine the energy of Galaxy Clusters from sub-pc scales to Mpc distances. Via high-resolution, cosmological and hydrodynamical simulations we study how the main properties of the ICM (entropy, temperature, pressure, and metallicity) are influenced by the presence of the central AGN. We compare the results from runs with AGN feedback with those with “exclusively” stellar feedback to enhance the importance of the powerful AGN source. We found that the AGN are key to create the observed metal profile and to produce clusters which are cool cores. Observationally, cool-core clusters have precise physical characteristics: they are found in regular clusters with a symmetric and peaked surface brightness distribution and have a peaked metal profile. Our numerical models are able to reproduce most of the observed properties, thus can be used to derive some predictions on the evolution of these systems.

Supernovae seen through gravitational telescopes

Supernovae seen through gravitational telescopes

Tanja Petrushevska

Department of Physics, Faculty of Science, Stockholm
The Oskar Klein Centre for Cosmo Particle Physics, Sweden

v sredo, 26. aprila 2017, ob 12. uri v predavalnici F4 (Jadranska 19, Ljubljana)

Galaxies, and clusters of galaxies, can act as gravitational lenses and magnify the light of objects behind them. The effect enables observations of very distant supernovae, that otherwise would be too faint to be detected by existing telescopes, and allows studies of the frequency and properties of these rare phenomena when the universe was young. Under the right circumstances, multiple images of the lensed supernovae can be observed, and due to the variable nature of the objects, the difference between the arrival times of the images can be measured. Since the images have taken different paths through space before reaching us, the time-differences are sensitive to the expansion rate of the universe. One class of supernovae, Type Ia, are of particular interest to detect. Their well known brightness can be used to determine the magnification, which can be used to understand the lensing systems. I will also report our discovery of the first resolved multiply-imaged gravitationally lensed supernova Type Ia.

Na zgornji sliki je shema učinka, ki ga ima gravitacijsko lečenje zaradi bližnje galaksije na svetlobo, ki prihaja iz oddaljene galaksije. Bližnja galaksija deluje kot leča, ki popači sliko oddaljenih objektov ter jih naredi svetlejše, v primeru na sliki je prisoten prstan svetlobe, ki mu pravimo Einsteinov prstan. Analiza popačitve je pokazala, da nekatere izmed oddaljenih galaksij, v katerih nastajajo nove zvezde, svetijo kot 40 tisoč milijard Sonc ter da je povečava zaradi lečenja kar 22-kratna.

 

Eksoplanetna odkritja pokvarjenega Keplerja, misija K2

Eksoplanetna odkritja pokvarjenega Keplerja, misija K2

Teo Močnik

Astrophysics Group, Keele University, Staffordshire, UK

v sredo, 19. aprila 2017, ob 12. uri v predavalnici F4 (Jadranska 19, Ljubljana)

Vesoljski teleskop Kepler je zaslužen za največ potrjenih odkritij eksoplanetov doslej. To je bilo možno zaradi večletnega praktično neprekinjenega in zelo natančnega merjenja svetlosti več kot 100.000 zvezd v ozvezdju Laboda. Odkar se je maja 2013 pokvarilo še drugo od skupno štirih Keplerjevih reakcijskih koles, stabilna usmeritev v ozvezdje Laboda več ni bila mogoča, kar je pomenilo konec opazovalne misije Kepler. Po enem letu iskanja rešitev in testiranj je NASA leta 2014 potrdila načrt nadaljne uporabe teleskopa Kepler, poimenovan misija K2. Od takrat teleskop opazuje polja vzdolž ekliptike, kar omogoča zadostno natančnost usmeritve kjub zgolj dvema delujočima reakcijskima kolesoma.

Najprej bom predstavil postopek obdelave K2 opazovanj s katerim odpravimo napake v svetlobnih krivuljah kot posledice nepopolne stabilnosti usmeritve teleskopa. Nato se bomo sprehodili skozi galerijo zanimivih planetnih sistemov, ki so bili opazovani v okviru misije K2 v 1-min kadenčnem načinu. V sistemih WASP-85, Qatar-2 in WASP-107 smo zaznali okultacije zvezdnih peg, ki razkrijejo natančno rotacijsko periodo matične zvezde in dragocen podatek (ne)poravnanosti osi vrtenja zvezde z orbitalno osjo planeta. Vročemu Jupitru Qatar-2b je uspelo popačiti obliko zvezde gostiteljice v elipsoid, kar je edinstvena meritev v okviru misije K2. WASP-118b pa je prvi odkriti eksoplanet, ki kroži okoli pulzirajoče zvezde tipe Gamma Doradus. Omenil bom še WASP-75 z navideznim mimoletom svetlega asteroida in WASP-55.

Ali je temna snov zamegljena?

Ali je temna snov zamegljena?

dr. Vid Iršič

Institute for Advanced Studies, Princeton, University of Washington, Department of Astronomy

v četrtek, 22. decembra 2016, ob 15. uri v predavalnici F2 (Jadranska 19, Ljubljana)

Standardni kozmološki model, ki vsebuje hladno temno snov (CDM), neverjetno uspešno opiše razvoj vesolja na velikih razdaljah. Na razdaljih, ki so tipične za galaksije in jate galaksij (< 10 Mpc) pa model nima močne podpore meritev. Eden od načinov, kako razložiti razlike med napovedmi kozmološkega modela in meritvami, je v tem kaj temna snov pravzaprav je. Meritve porazdelitve gostote v Lyman-alpha gozdu najbolj omejujejo raznovrstne modele temne snovi. S pomočjo podatkov ESO raziskave X-Shooter XQ-100, lahko izmerimo Lyman-alfa gozd v spektrih 100 kvazarjev (QSO) v podobnem obsegu rdečih zamikov kot pregled neba SDSS (z=3 - 4.2), vendar z veliko večjo natančnostjo na majhnih razdaljah (k_max ~ 6 h/Mpc). V tej predstavitvi bom povzel najnovejše rezultate in komentiral analizo podatkov. Skupaj z meritvami posameznih kvazarjev pri višjih rdečih zamikih, lahko podamo nove rezultate o modelih tople temne snovi (WDM). V glavnem delu predstavitve bom komentiral kako ti rezultati vplivajo na rešitev nerešenih vprašanj standardnega kozmološkega modela.

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