Recent Talks

I will describe the roles of jets in several quite different astrophysical systems. These include exploding core collapse supernovae, expelling common envelopes, and heating gas in clusters of galaxies. Hot bubbles inflated by jets seem to be a key ingredient in the interaction of jets with the ambient gas. The understanding that jets can efficiently interact with the ambient gas leads to new notions, such as the jittering jets model to explode massive stars, and the grazing envelope evolution(GEE) that can replace the common envelope evolution in some cases.

I will present results from The X-Shooter Lens Survey (XLENS). With XLENS we are unambiguously separate the stellar from the dark-matter content in the internal region of lens early-type galaxies (ETGs) to understand their interplay and to probe directly their formation and dynamical evolution. We combine precise strong gravitational lensing and dynamical constraints on the mass distribution with high signal-to-noise spectroscopy in the entire rest-frame visible to the NIR.In this talk I will present results obtained on a sample of very massive lens ETGs from the SLACS Survey, with velocity dispersions greater than 250 km/s and redshift>0.1.

First I will show how to constrain the low mass end of the Initial Mass Function (IMF)directly from galaxy optical spectra using a new set of non-degenerate optical spectroscopic indices which are strong in cool giants and dwarfs and almost absent in main sequence stars (Spiniello et al., 2014a). I will present unambiguous evidence that the low-mass end of the IMF is not universal. Then, I will demonstrate that the combination of this SSP modelling with a fully self-consistent joint lensing+dynamics analysis (Barnabè et al. 2012) allows us to disentangle IMF slope variations from internal dark-matter variations and, for the first time ever, to contemporary put constrains on the IMF cutoff mass (Barnabè et al., 2013, Spiniello et al., in prep).

All the elements from carbon to uranium present in the Solar System were produced by hundreds to thousands of stars belonging to different stellar generations that evolved and died during the presolar evolution of the Galaxy. Using the abundances of radioactive nuclei inferred from meteoritic analysis we can date the last of these stellar additions. We have found that the last contribution of elements such as carbon and slow neutron-capture elements to the Solar System from an asymptotic giant branch star occurred 15-30 Myr before the formation of the Sun. This provides us with an upper limit of the time when the precursor material of the Solar System became isolated from the bulk of the galactic material. Interestingly, it compares well to the lifetime of high-mass molecular clouds suggesting that the Sun was born in a very large family of stars.

In this talk we will present our most recent numerical and observational results on the formation, evolution, and X-ray emission from hot bubbles in nebulae around evolved stars. Our studies include hot bubbles around massive and low-mass stars, e.g., Wolf-Rayet nebulae and planetary nebulae. Our results show that the diffuse X-ray emission from these hot bubbles is a dynamic process that involves mixing of nebular material into the hot bubble due to hydrodynamical instabilities, photoevaporation, thermal conduction, and dust cooling. The formation of these hot bubbles is governed by the evolution of the stellar wind parameters, and its properties can be used to study stellar evolution.

We present correlation between quasar properties and large-scale density with the largest spectroscopic dataset of quasars and galaxies to date. We construct a galaxy (number) density field on large-scale (~15Mpc) using the Sloan Digital Sky Survey (SDSS) Data Release 12 (DR12) Constant MASS (CMASS) galaxies following the 20 nearest-neighbors approach over the redshift range 0.46<z<0.59. Quasar sample is prepared from the DR7 of SDSS I/II. We examine a correlation of incidence of quasars with large-scale density and dependences of quasar properties such as bolometric luminosity, black hole mass, and Eddington ratio on large-scale density. We find a monotonic correlation between the quasar density and large-scale density, which is fitted well with a linear function in log-log space and doesn't change much with redshift. The dependences of quasar properties on the large-scale density are detected, but these are very weak. Based on the results, we discuss the possibility of using quasars as a tracer of Large-Scale Structure (LSS), which will be crucial in the near future to go more deeply in the universe.

One of the most exciting possibilities enabled by transiting exoplanets is to measure their atmospheric properties through the technique of transmission spectroscopy: the variation of the transit depth as a function of wavelength due to starlight interacting with the atmosphere of the exoplanet. Motivated by the need of optical transmission spectra of exoplanets, we recently launched the Arizona-CfA-Católica Exoplanet Spectroscopy Survey (ACCESS), which aims at studying the atmospheres of ~20 exoplanets ranging from super-Earths to hot-Jupiters in the entire optical atmospheric window using ground-based facilities. In this talk, I will present the survey, the astrostatistical challenges it poses and first results.

The presence of Dark Matter (DM) is required in the universe regulated by the standard general relativistic theory of gravitation. The nature of DM is however still elusive to any experimental search. We discuss here the process of accumulation of evidence for the presence of DM in the universe, the astrophysical constraints for the leading DM scenarios that can be obtained through a multi-frequency analysis of cosmic structures on large scales, and a new strategy related to the search for the nature of the DM with the Square Kilometer Array (SKA).

The origins of neutron(n)-capture elements (atomic number Z > 30) have historically been discerned from the interpretation of stellar spectra. However, in the last decade nebular spectroscopy has been demonstrated to be a potentially powerful new tool to study the nucleosynthesis of n-capture elements. In this talk, I will discuss exciting new advances made in this field with near-infrared and optical observations of planetary nebulae, and atomic data investigations that enable the analysis of spectroscopic data.

More than 600 000 small objects of the Solar System (SoSS) are currently known. The physical characterization exists only for a small fraction of them. Their understanding is important both for scientific and practical point of view: SoSS can offer important clues regarding the origins and the evolution of the Solar System, and they are the key objects for the development of the Solar System exploration.

I will present the near-infrared spectrophotometric data of more than 35 000 SoSS imaged by VISTA-survey. First, the pipeline used for obtaining the observations from the survey catalogs will be described. Second, the statistics derived from the resulted measurements and their impact in the compositional map of SoSS is shown.

Additional techniques were employed over this large set of values, such as comparing color variation with the taxonomic classification and combining the near infrared spectrophotometric data with complementary measurements (albedo, spectral data). The results significantly improve the image of the physical properties of SoSS.

Almost all cosmologists accept nowadays that the redshift of the galaxies is due to the expansion of the Universe (cosmological redshift), plus some Doppler effect of peculiar motions, but can we be sure of this fact by means of some other independent cosmological test? Here I will review some recent tests: CMBR temperature versus redshift, time dilation, the Hubble diagram, the Tolman or surface brightness test, the angular size test, the UV surface brightness limit and the Alcock-Paczynski test. Some tests favour expansion and others favour a static Universe. Almost all the cosmological tests are susceptible to the evolution of galaxies and/or other effects. Tolman or angular size tests need to assume very strong evolution of galaxy sizes to fit the data with the standard cosmology, whereas the Alcock-Paczynski test, an evaluation of the ratio of observed angular size to radial/redshift size, is independent of it.