Gamma-ray bursts as probes of galaxy evolution

Dr. Daniele Malesani

Dark Cosmology Centre (DARK), Niels Bohr Institute, University of Copenhagen

v ponedeljek, 12. maja 2014, ob 13. uri v predavalnici F-4

Gamma-ray bursts are powerful explosions at high redshift which probe star formation in a wide set of cosmic environments. I will present our program to extract information from GRB afterglow spectroscopy, to probe the content of gas, metals, dust, and molecules in star forming galaxies across the Universe.

LSST: an era of big data in astronomy

Dr. Emmanuel Gangler

Université de Lyon 1, France

CNRS/IN2P3, Institut de Physique Nucléaire de Lyon

v ponedeljek, 5. maja 2014, ob 13. uri v predavalnici F-4

With the advent of the Large Synoptic Survey Telescope which shall take its first light in 2020, the data flow in optical astronomy will be put to an unprecedented rate. The 3.2 Gpixel-enabled camera will scan all the visible sky in but 3 nights, repeating over the measurements during 10 years, opening up an extensive time domain view of the field. Before concentrating on the emerging new field of astroinformatics which will address the data-related issues both from archive access perspective and new data analysis prospects, I’ll present the LSST project as a whole, and I will briefly review some of the numerous astrophysical topics that will benefit from this massive data set.

The Galactic habitable zone of the Milky Way and M31 from chemical evolution models with gas radial flows

dr. Emanuele Spitoni

Department of Physics, University of Trieste

v četrtek, 24. aprila 2014, ob 10. uri v predavalnici F5

The galactic habitable zone is defined as the region with sufficient abundance of heavy elements to form planetary systems in which Earth-like planets could be born and might be capable of sustaining life, after surviving to close supernova explosion events. Galactic chemical evolution models can be useful for studying the galactic habitable zones in different systems.

We apply detailed chemical evolution models including radial gas flows to find the galactic habitable zones in our Galaxy and M31. We compare the results to the relative galactic habitable zones found with “classical” models, where no gas inflows were included. For both the Milky Way and Andromeda, the main effect of the gas radial inflows is to enhance the number of stars hosting a habitable planet with respect to the “classical” model results, in the region of maximum probability for this occurrence.

These results are obtained by taking into account the supernova destruction processes. In particular, we find that in the Milky Way the maximum number of stars hosting habitable planets lies at 8 kpc from the Galactic center, and the model with radial flows predicts a number which is 38% larger than that predicted by the classical model.

Vloga trojnih sistemov pri določanju osnovnih parametrov zvezd

Dr. Andrej Prša

Villanova University

v ponedeljek, 31. marca 2014, ob 13. uri v predavalnici F4

Prekrivalne dvojne zvezde že od nekdaj veljajo za temelj zvezdne astrofizike, saj z oprijemljivimi metodami lahko določimo mase, radije, izseve in temperature posameznih zvezd v dvojnih sistemih z natančnostjo do 1-3%. Odkar smo deležni podatkov Nasine vesoljske misije Kepler, pa se dvojnicam pridružujejo še večkratni sistemi. Pri predavanju bom predstavil nekaj trojnih sistemov in rezultatov, ki sledijo iz fotodinamične analize, kjer natančnost v posameznih parametrih presega 0.2%.

Hearbeat stars and the ringing of tidal pulsations

Kelly Hambleton

University of Central Lancashire

v četrtek, 27. marca 2014, ob 10. uri v predavalnici F5

With the advent of high precision photometry from satellites such as Kepler and CoRoT, a whole new layer of interesting and astounding astronomical objects has been revealed: heartbeat stars are a prime example of such objects. Heartbeat stars are eccentric ellipsoidal variables that undergo strong tidal interactions at the time of closest approach, when the stars are almost in contact. These interactions cause a significant variation in the surface area of the stars and are observed in the form of a tidal pulse. A subset of these objects ~20% show prominent tidally induced pulsations. We now have a fully functional code that models binary star features (using PHOEBE) and stellar pulsations simultaneously, enabling a complete and accurate heartbeat model to be determined. In this talk we show the results of our new code, which uses Markov chain Monte Carlo techniques, to generate a full set of stellar and orbital parameters. We further highlight some of the interesting features of selected heartbeat stars, including resonant pulsations, frequency modulation, solar like oscillations and apsidal motion.

Observations of Short Gamma-Ray Bursts and future prospects

Prof. Paul O’Brien

University of Leicester

v ponedeljek, 24. marca 2014, ob 13h v F4

Long duration GRBs are thought to arise from the core-collapse of a rapidly-rotating massive star while short-duration GRBs are thought to originate from the merger of compact binary systems. I will summarise recent multi-wavelength observations of short GRBs which have complex light curves which are hard to explain with black holes. An alternative central engine is a magnetar, a massive, rapidly-rotating, highly magnetised neutron star. While consistent with the data, the existence of magnetars and the large derived magnetic fields could pose a major problem for merger models. Future gravitational wave observations may allow us to distinguish between black hole and magnetar models. I will also discuss the current status of GRB finders and the options for future space-based, high-energy missions to monitor the transient universe.

Zgodnja optična emisija pri izbruhih sevanja gama

dr. Drejc Kopač

Fakulteta za matematiko in fiziko, Univerza v Ljubljani

v ponedeljek, 3. marca 2014, ob 13h v F4

Emisija v prvih ~1000 sekundah po izbruhu predstavlja pomembno orodje za razumevanje fizike izbruhov sevanja gama. Opazovanje tako zgodnje emisije preko širokega območja valovnih dolžin nam razkriva mehanizme, ki so odgovorni za nastanek in naravo izbruhov ter nam pomaga potrditi oziroma ovreči različne fizikalne modele izbruhov.

V astrodebati bom predstavil podrobno študijo vzorca izbruhov, pri katerih je bila optična emisija detektirana že med glavno gama emisijo. Z modeliranjem opazovanih svetlobnih krivulj in energijskih spektrov ter s primerjavo s preprostim fizikalnim modelom izbruhov smo pokazali, da lahko v nekaterih primerih zgodnjo optično in glavno gama emisijo povzročijo enaki fizikalni procesi.

Predstavil bom probleme pri modeliranju zgodnjih svetlobnih krivulj in določanju izvora zgodnje optične emisije, ki so pogosto povezani s slabo časovno resolucijo opazovanj ter s predolgim odzivnim časom robotskih teleskopov. Na koncu se bom na kratko posvetil še zgodnji optični polarimetriji, ki lahko predstavlja pomembno orodje za razumevanje zgodnje optične emisije.

Chemical evolution of galaxies: a problem of astroarchaeology

Prof. Francesca Matteucci

Department of Physics, University of Trieste

and INAF – National Institute for Astrophysics (INAF – OATs)

v ponedeljek, 24. februarja 2014, ob 13h v F4

During the Big Bang only light elements (H, D, He, L) were formed whereas all the other elements have been formed inside stars. Chemical evolution of galaxies studies how the majority of chemical elements evolved and distributed in galaxies. To compute chemical evolution we need to assume an history of star formation for each galaxy and take into account possible gas flows (in and out). Stars restore the new chemical elements formed in their interiors at their deaths, which can be quiet or violent (supernovae). Therefore, we need to know the stellar yields, namely the amount of mass in the form of various elements that stars restore into the interstellar medium (ISM) when they die.

I will show how to compute models of chemical evolution for galaxies of different morphological type and the results obtained from these models will be compared to observations. In particular, the comparison between the observed abundances and abundance ratios of the more common elements from carbon to iron and beyond (C, O, Ne, Mg, Si, S, Ca, Fe, s- and r-process elements) to the predicted ones, allows us to impose important constraints on the mechanisms of formation of galaxies as well as on stellar nucleosynthesis. I will show some examples involving galaxies of different type, including the Milky Way, to illustrate how astroarchaeology can shed light on the past history of galaxies and on their early evolutionary phases.

Searching for the dark matter in the Universe

Prof. Francesc Ferrer

Washington University in St. Louis, USA

v sredo, 18. decembra 2013, ob 12h v F3

Numerous experimental efforts to unveil the fundamental nature of the dark matter are underway, and several tantalizing observations have been linked to its effects in recent years. We will review the properties of several candidates that appear in extensions of the Standard Model of Particle Physics, and the different strategies to detect them. Eighty years after the existence of vast amounts of dark matter was first postulated, its non-gravitational interactions might be soon brought up to light.

Cosmological Lithium Problem: A Different Approach

Dr. Tijana Prodanović

University of Novi Sad, Serbia

v ponedeljek, 25. novembra 2013, ob 13h v F5

A discrepancy between primordial lithium abundance predicted by the Big Bang Nucleosynthesis theory, and measurements of pre-galactic lithium abundance in low metallicity systems, has been, for mode than a decade, known as the lithium problem. While measured abundances of other primordial elements are in agreement with their predicted values, lithium in low-metallicity halo stars has been observed to be a factor of 2-4 lower than its expected primordial abundance. No mechanism has been successful in destroying lithium to the observed level so far. Furthermore, the existing lithium problem can become even more severe if any additional pre-galactic source of lithium is present. Possible contaminants could be in the form of cosmic rays that arise during the process of large scale structure formation, or during tidal interactions between galaxies. Gamma-ray observations of the extragalactic gamma-ray background and of galaxy clusters can be used to constrain possible structure-formation cosmic rays and their additional lithium production. On the other hand, measurements of lithium abundance in systems that have recently experienced close fly-bys with neighboring galaxies, such as the Small Magellanic Cloud, can be used to constrain lithium production by tidal cosmic-ray population. Moreover, since lithium has recently been observed in the SMC as its first gas-phase measurement in a low-metallicity system, in order to test the origin of the lithium problem, the importance of determining if lithium was also tidally produced in such system is even greater.

ISON Comet & Iron Tail

Dr. Marco Fulle

INAF – OATs, Italy

v torek, 19. novembra 2013, ob 12h v F3

On November 28, 2013, Comet ISON C/2012S1 will pass its perihelion at a distance of about 10^6 km (less than the Sun’s diameter) from Sun’s surface. In the following week, it is expected to be one of the brightest comets of past decades, possibly brighter than Comet McNaught C/2006P1 or even Comet Ikeya-Seki C/1965S1, the brightest comets of the past century with a perihelion closer than Mercury’s Sun distance. After an introduction to comets, I will explain some of the peculiar phenomena that comets show at these close distances from our star, which allow us to glimpse the metal composition of comet nuclei and the chemistry occurring at high temperature on the surface of dust grains ejected by the comet nucleus.

What Can OPTICON Do for You?

Dr. John K. Davies

OPTICON Project Scientist, UK Astronomy Technology Centre, Edinburgh

v torek, 5. novembra 2013, ob 12h v F3

OPTICON (www.astro-opticon.org) is an integrating activity for optical astronomy which is funded by the EC to the tune of 8.5 million Euro over 4 years (2013-16). I will outline the exisiting OPTICON programme in technology research, community building and its contribution to planing for the next generation of large facilities (E-ELT and VLTI). I will also describe how new communities can gain access to state of the art 2-4m telescopes via the OPTICON Trans-National Access programme and the steps OPTICON is taking to make this process easier.

Spectroscopically Resolved Orbits of Supermassive Binary Black Holes

Dr. Edi Bon

Astronomical Observatory, Belgrade

v torek, 29. oktobra 2013, ob 12h v F3

Active galactic nuclei (AGN) are the most luminous objects in the Universe. There are many scenarios that can explain how AGN are triggered. One of the most intriguing involves the existence of a supermassive binary black hole system in their cores. AGN monitoring spectra can reveal such systems by analysing their emission line shapes and continuum flux variation.
Recently, we discovered the first orbit of sub-parsec supermassive black hole, using very long monitoring campaign spectra and a method typically used for spectroscopic binary stars. We obtained radial velocity curves from which we calculated orbital elements and made estimates about black hole masses. Given the large observational effort needed to reveal this spectroscopically resolved binary orbital motion, we suggest that many such systems may exist in similar objects even if they are hard to find. Detecting more of them will provide us with insight into the supermassive black hole mass growth process.

Solar and Stellar Flares: Observations, Modeling and Synergies

Prof. Petr Heinzel

Astronomical Institute, Academy of Sciences

Ondrejov, Czech Republic

v petek, 11. oktobra 2013, ob 12h v F4

I will briefly review the current status of observations of chromospheric flares on the Sun and other cool stars, with a focus on their spectral properties. Modeling the spectra and light curves represents a challenge for our understanding of the underlying physical processes of the energy transport and dissipation. I will discuss different scenarios of the chromospheric-type emission during flares and point to various synergies between solar and stellar cases. I will also show recent SDO/EVE spectra of the Sun-as-a-star, which can provide important links to stellar flare studies.

Trivialno paralelizabilno vzorčenje

Dr. Anže Slosar

Brookhaven National Laboratory, Upton, NY

v ponedeljek, 30. septembra 2013, ob 10h v F3

Monte Carlo markove verige (MCMC) so standardna metoda za vzorčenje kompleksnih več-dimenzionalnih (N=5-100) verjetnostih porazdelitev v kozmologiji. Kljub temu, da je metoda izredno uspešna, ni razširljiva na računalnike z nekaj tisoč jedri. Predstavil bom pregled problema, teorijo markovih verig in opisal novo metodo, ki obeta veliko boljšo razširljivost in hitrejšo konvergenco. To je delo v teku.