Vesolje-SI

Space exploration

The Astrophysics working group at the center of excellence Space-SI is involved in a number of space programs and missions, performing research activities and successfully cooperating with the international scientific community.

Observing the universe with ground based telescopes

• The RAdial Velocity Experiment (RAVE) is one of the key projects focused on measuring radial velocities of nearby stars that are part of the Milky Way galaxy. The project is a collaboration bringing together 60 scientists from nine countries: Germany, Great Britain, France, Italy, Netherlands, Australia, USA, Canada and Slovenia. The RAVE project is carried out at the 1.2 meter telescope of the Anglo-australian Observatory, using a multi-object multi-fiber spectrograph to simultaneously obtain stellar spectra. Since the beginning of the project in 2003 researchers succeed in measuring stellar radial velocities and were able from their spectra to determine relevant physical parameters for more than half a million stars belonging to our Galaxy, ten times more than ever measured before! Prof. T. Zwitter from the Astrophysics group of the center Space-SI is the project scientist at RAVE. Among the most important scientific achievements we should mention the discovery of a new stellar stream in Milky way , whose stars were part of an uknown, now distrupted, dwarf galaxy; the discovery of metal-poor stars, whose properties disfavor direct accretion of stars from dwarf galaxies into the thick disk as a major contributor to the thick-­disk population; the most precise determination so far of stellar distances with a new technique that accounts for stellar evolution models; and the second release of RAVE data – the biggest catalogue of stellar physical parameters.

• The GALAH survey (GALactic Archaeology with HERMES) is devoted to astroarchaeology of our Galaxy: the main goal is to reconstruct stellar substructures in the protogalaxy to obtain detailed information about formation and evolution of the Galaxy. The survey will make use of the new high-resolution spectrograph HERMES (High Efficiency and Resolution Multi-Element Spectrograph) under construction at the 3.9 meter Angloaustralian telescope. Final results will be stellar spectra in four spectral bands, from which researchers will be able to obtain results about 15 different chemical elements inside each star. The Astrophysics group is leading the binary star working group.

• Gaia-ESO is an international project that will observe more than 10.000 stars in different galaxy components, from the galactic halo to the star forming regions, by using the FLAMES specrograph at Very Large Telescope in Chile. The public spectroscopic survey will be the first to obtain a homogeneous distribution of chinematical and chemical stellar properties and will combine simultaneously the results with the Gaia astrometry. Members of the group will perform spectroscopical observations of stars in our Galaxy with the Very Large Telescope at the European Southern Observatory.

• The space mission Gaia is a leading project of the European space agency and is scheduled for launch in 2013. The main goal is to perform extremely precise astrometry, photometry and spectroscopy of 1000 millions stars. Beside it will also observe asteroids, Kuiper belt objects, quasars, supernovae, binary stars. Project member prof. Zwitter leads a group of researchers at Faculty of mathematics and physics that is involved in studies on the radial velocity spectrometer. The group is collaborating with astronomers from Padua in the optimization of instrumetal properties and extracting astrophysical informations from Gaia spectra. We are involved also in the Gaia Science Alerts Working Group.

• Kepler is a NASA mission dedicated to discover new planets around nearby stars in the habitable zone of the Galaxy. The Astrophysics group at Space-SI collaborates in the working group of eclipse binary stars, that prepares a catalogue of 2000 stars that will Kepler observe. Binaries in the catalogue are particularly interesting because of a very accurately defined properties. Modelling lightcurves of eclipse binary stars in crucial in order not to confuse them with planetary transits, that are the main targets of the Kepler mission.

• Swift is the space multiwavelength telescope devoted to gamma ray burst (GRB) observations and afterglows in X-ray, ultraviolet and optical light. The main goal of the mission is to determine the origine of GRBs, their classification and evolution and to understand the interaction of GRBs with the surrounding medium. Dr. Gomboc from the Astrophysics group is actively involved in robotic observations of optical afterglows and their polarization with telescopes on Canary islands, Australia and Hawaii. She collaborates in spectroscopic observations of GRB afterglows and host galaxies wit the Very Large Telescope (VLT) that will enable the study of low density medium in GRB circum­burst environment, of properties of interstellar gas in host galaxies as well as the study of intergalactic gas between us and GRBs.

The space missions, from the space telescopes as Gaia and Kepler to the ground-based telescopes as Hermes and Gaia-ESO, will be able to recover with high accuracy important properties of a large number of galactic stars. With this observational effort the international researchers community will obtain informations on the formation and evolution of different parts of the Galaxy. By combining information from ground-based and space observations about high-energy phenomena also distant galaxies and intergalactic gas properties will be studied.

Research projects in 2011

Astrophysics working group at Space-SI is currently involved in three main research topics that span a wide range of astrophysical objects, from massive structures in the universe to single stars and explosive events. In 2011 our research was focused on:

• Galaxy groups and clusters are the most massive structures in the universe. Highly ionized gas in clusters forms a so called cluster atmosphere. Physical processes in such plasma gas allow us to observe very distant clusters. These kind of observations can be made only beyond Earth’s atmosphere. High energy photons are collected by particular telescopes orbiting on distances from 10.000 to 100.000 km. Galaxy clusters can be also studied by means of simulations.

Using cosmological simulations we were able to study the behaviour of the highly ionized gas in approximately 140 simulated galaxy clusters. The aim was to understand the accuracy of scaling relations in describing the total cluster mass. A precise determination of galaxy clusters’ masses is becoming very important in cosmological studies.

• The second main research topic is our Milky Way galaxy. For stars in our Galaxy we can measure radial velocities and distances as well as other interesting properties, from temperature to their content of chemical elements. In this kind of research it is important to carefully measure stellar properties for a large number of nearby stars.

As part of the RAVE collaboration we observed properties for half a million of stars, among which we found also some belonging to an old stellar stream, probably a small galaxy stripped by ours. These information are important to understand how our Milky Way galaxy formed and evolved in time.

• Gamma-ray bursts are are caused by individual stars and are in fact the most powerful known explosions in the universe. They can either happen when a massive star collapses or when two neutron stars or black holes merge (the released energy is more than the total energy that our Sun will produce during 10 billion years of its life). These bursts are unpredictable and last for a short time, from 10 milliseconds to 1000 seconds, and cannot be predicted. Gamma-ray bursts can be observed only with space satellites, since gamma rays cannot penetrate Earth’s atmosphere.

We are currently studying an interesting burst observed on 1st September 2010. This event happened when our universe was only one third of its current age (light travelled to us for 9 billion years). For these studies it is important to observe the gamma-ray burst afterglow in optical wavelengths with ground-based robotized telescopes. The connection between satellite and ground-based observations is crucial to understand these phenomena, that are one of the hottest topics in modern astrophysics.