489 research outputs found
Narrow absorption lines from intervening material in supernovae I: measurements and temporal evolution
No full textNarrow absorption features in nearby supernova (SN) spectra are a powerful diagnostic of the slow-moving material in the line of sight: they are extensively used to infer dust extinction from the host galaxies, and they can also serve in the detection of circumstellar material originating from the SN progenitor and present in the vicinity of the explosion. Despite their wide use, very few studies have examined the biases of the methods to characterize narrow lines, and not many statistical analyses exist. This is the first paper of a series in which we present a statistical analysis of narrow lines of SN spectra of various resolutions. We develop a robust automated methodology to measure the equivalent width (EW) and velocity of narrow absorption lines from intervening material in the line of sight of SNe, including Na I D , Ca II H&K, K i and diffuse interstellar bands (DIBs). We carefully study systematic biases in heterogeneous spectra from the literature by simulating different signal-to-noise, spectral resolution, slit size and orientation and present the real capabilities and limitations of using low- and mid-resolution spectra to study these lines. In particular, we find that the measurement of the equivalent width of the narrow lines in low-resolution spectra is highly affected by the evolving broad P-Cygni profiles of the SN ejecta, both for core-collapse and type Ia SNe, inducing a conspicuous apparent evolution. We present thus an easy way to detect and exclude those cases to obtain more robust and reliable measurements. Finally, after considering all possible effects, we analyse the temporal evolution of the narrow features in a large sample of nearby SNe to detect any possible variation in their EWs over time. We find no time evolution of the narrow line features in our large sample for all SN type
Geology of Olkiluoto
No full textOlkiluoto Island, which is located in SW Finland, has been selected as the deep geological repository for the high-level nuclear waste generated by the nuclear power plants operated by the Finnish power companies TVO and Fortum, and the repository is expected to become operational in the early 2020s. Posiva is an expert organisation responsible for the management and implementation of the nuclear waste repository at Olkiluoto and is owned by TVO and Fortum. Posiva submitted a construction licence application to the Finnish government in December 2012 and an integrated description of the Olkiluoto site, including its geology, was a part of the background material. After their review, in early 2015, the Radiation and Nuclear Safety Authority in Finland (STUK) gave a positive statement to the Ministry of Employment and the Economy: "the final disposal facility designed by Posiva can be built to be safe". In 2016, the Finnish Government granted a licence to Posiva for the construction of a final disposal facility for spent nuclear fuel.Posiva has continued updating the multidisciplinary site description, which is aiming at the last licencing stage of the repository - the application of the operating licence. Understanding the geology of Olkiluoto is a substantial part of the site description work. It is based on data from hundreds of outcrops, tens of kilometers of drill core, extensive tunnel mapping programme and a wide variety of geophysical investigations. The Palaeoproterozoic bedrock in Olkiluoto consists of variably migmatised supracrustal high-grade metamorphic rocks: migmatized meta-pelites, meta-arenites and intermediate, pyroclastic metavolcanites. They are intruded by Paleoproterozoic felsic, granitic–tonalitic plutonic rocks and granitic pegmatoids, and diabase dikes. The rocks were metamorphosed simultaneously with the different phases of ductile deformation. Hydrothermal alteration at Olkiluoto can be subdivided into two different modes on the basis how the fluids have proceeded in the rock mass: fracture- or veinlet-controlled alteration and pervasive or disseminated alteration. The brittle deformation history of Olkiluoto can be reconstructed through paleostress inversion of fault-slip data from outcrops and drill cores and from K-Ar ages if fault gouge illites: seven distinct paleostress states can be identified, spanning in time from ca. 1.7 Ga to 1.0 Ga
A Mesopotamian Omen in the Cycle of Cyrus the Great
No full textThe Author discusses the legends and stories concerning the ascent to the power by Cyrus the Great, with particular reference to Ctesias' account
Energetic nuclear transients in luminous infrared galaxies
No full textThere have been a number of observations of infrared (IR) echoes associated with tidal disruption events (TDEs). These arise as a result of re-radiation of the TDE’s UV/optical photons by dust in the nuclear environment. Furthermore, there have been multiple fortuitous discoveries of IR echoes in the nuclei of luminous infrared galaxies (LIRGs) over the last few years, which have been identified as TDE candidates. LIRGs are dusty systems often resulting from galaxy mergers and hosting both a powerful starburst and an active galactic nucleus (AGN). TDE candidates in the dusty nuclei of LIRGs are challenging to identify and can often be out of the reach of optical or X-ray observations due to the large column densities of gas and dust obscuring them. Therefore, IR observations are required to characterise them, and can provide important information on the population of TDEs and their rates in these dust obscured nuclear environments. Additionally, IR echoes can be used to probe the total radiated energies from TDEs in cases where a significant fraction of the radiated energy was re-processed by dust to IR wavelengths.
Here we present our search for nuclear transients within local LIRGs using mid-IR observations performed by the WISE satellite, which are almost unaffected by dust extinction. In this search we found multiple new TDE candidates through detection of luminous and slowly evolving mid-IR outbursts. We characterise the nature of these objects through modelling of the spectral energy distributions of their host galaxies and measurements of their luminosities and resulting energetics as well as by comparison of these properties with those of previously published TDEs and TDE candidates. Combining previous discoveries with the new transients detected as part of this search, we set a new lower limit for the rate of dust obscured TDEs occurring within LIRGs. We discuss the potential of ground-bases IR observations for such studies using the current and future facilities
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