RAS_WEB (Page 4,637)

Gamma-ray burst localisation strategies for the SPHiNX hard X-ray polarimeter. (arXiv:1901.08948v1 [astro-ph.IM]) <a href="http://arxiv.org/find/astro-ph/1/au:+Heckmann_L/0/1/0/all/0/1">L. Heckmann</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Iyer_N/0/1/0/all/0/1">N. K. Iyer</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kiss_M/0/1/0/all/0/1">M. Kiss</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pearce_M/0/1/0/all/0/1">M. Pearce</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Xie_F/0/1/0/all/0/1">F. Xie</a> SPHiNX is a proposed gamma-ray burst (GRB) polarimeter mission operating in the energy range 50-600 keV with the aim of studying the prompt emission phase. The polarisation sensitivity of SPHiNX reduces as the uncertainty on the GRB sky position increases. The stand-alone ability of the SPHiNX design to localise GRB positions is explored via Geant4 simulations. Localisation at the level of a few degrees is possible using three different routines. This results in a large fraction (>Read More →

Enrichment of the Galactic disc with neutron capture elements: Sr. (arXiv:1901.08955v1 [astro-ph.GA]) <a href="http://arxiv.org/find/astro-ph/1/au:+Mishenina_T/0/1/0/all/0/1">T. Mishenina</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pignatari_M/0/1/0/all/0/1">M. Pignatari</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gorbaneva_T/0/1/0/all/0/1">T. Gorbaneva</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bisterzo_S/0/1/0/all/0/1">S. Bisterzo</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Travaglio_C/0/1/0/all/0/1">C. Travaglio</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Thielemann_F/0/1/0/all/0/1">F. K. Thielemann</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Soubiran_C/0/1/0/all/0/1">C.Soubiran</a> The enrichment history of heavy neutron-capture elements in the Milky Way disc provides fundamental information about the chemical evolution of our Galaxy and about the stellar sources that made those elements. In this work we give new observational data for Sr, the element at the first neutron-shell closure beyond iron, N=50, based on the analysis of the high resolution spectra of 276 Galactic disc stars. The Sr abundance was derived by comparingRead More →

Opacity calculations for stellar astrophysics. (arXiv:1901.08959v1 [astro-ph.SR]) <a href="http://arxiv.org/find/astro-ph/1/au:+Pain_J/0/1/0/all/0/1">Jean-Christophe Pain</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gilleron_F/0/1/0/all/0/1">Franck Gilleron</a> Opacity is a key ingredient of stellar structure and evolution. In the present work, we recall the role of opacity in asteroseismology, focusing mainly on two kinds of astrophysical objects: $beta$ Cephei-type stars, and the Sun. The detailed opacity code SCO-RCG for local-thermodynamic-equilibrium plasmas is described and interpretation of laser and Z-pinch experiments are presented and discussed. The possible role of multi-photon processes on radiative accelerations is outlined, and the main aspects of opacity modeling which should be improved are mentioned. Opacity is a key ingredient of stellar structure and evolution. InRead More →

ALMA photometry of extragalactic radio sources. (arXiv:1901.08976v1 [astro-ph.GA]) <a href="http://arxiv.org/find/astro-ph/1/au:+Bonato_M/0/1/0/all/0/1">M. Bonato</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Liuzzo_E/0/1/0/all/0/1">E. Liuzzo</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Herranz_D/0/1/0/all/0/1">D. Herranz</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gonzalez_Nuevo_J/0/1/0/all/0/1">J. Gonzalez-Nuevo</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bonavera_L/0/1/0/all/0/1">L. Bonavera</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tucci_M/0/1/0/all/0/1">M. Tucci</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Massardi_M/0/1/0/all/0/1">M. Massardi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zotti_G/0/1/0/all/0/1">G. De Zotti</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Negrello_M/0/1/0/all/0/1">M. Negrello</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zwaan_M/0/1/0/all/0/1">M. A. Zwaan</a> We present a new catalogue of ALMA observations of 3,364 bright, compact radio sources, mostly blazars, used as calibrators. These sources were observed between May 2011 and July 2018, for a total of 47,115 pointings in different bands and epochs. We have exploited the ALMA data to validate the photometry given in the new Planck Multi-frequency Catalogue of Non-thermal sources (PCNT), for which an externalRead More →

$N$-body chaos and the continuum limit in numerical simulations of self-gravitating systems, revisited. (arXiv:1901.08981v1 [astro-ph.GA]) <a href="http://arxiv.org/find/astro-ph/1/au:+Cintio_P/0/1/0/all/0/1">Pierfrancesco Di Cintio</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Casetti_L/0/1/0/all/0/1">Lapo Casetti</a> We revise the r^{o}le of discreteness and chaos in the dynamics of self-gravitating systems by means of $N$-body simulations with active and frozen potentials, starting from spherically symmetric stationary states and considering the orbits of single particles as well as the orbits of the system in the full $2N$-dimensional phase space. We investigate the dependence on $N$ of the largest Lyapunov exponent both of single particle orbits and of the full $N$-body system. We also show that the use of frozen $N$-body potentialsRead More →

Modelling Ion Populations in Astrophysical Plasmas: Carbon in the Solar Transition Region. (arXiv:1901.08992v1 [astro-ph.SR]) <a href="http://arxiv.org/find/astro-ph/1/au:+Dufresne_R/0/1/0/all/0/1">R.P. Dufresne</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zanna_G/0/1/0/all/0/1">G. Del Zanna</a> A collisional-radiative model for carbon has been developed to determine ion populations in lower-temperature, higher-density plasmas, such as the solar transition region. These conditions mean the often-used coronal approximation no longer holds for the modelling. The most up-to-date atomic rates have been employed for the processes which influence the populations in these regions. In the absence of level-resolved rates for electron-impact direct ionisation and excitation-autoionisation, new calculations have been made using atomic codes. Comparison with laboratory cross-sections and previous studies, where available, show satisfactoryRead More →

Global radiation signature from early structure formation. (arXiv:1901.08994v1 [astro-ph.GA]) <a href="http://arxiv.org/find/astro-ph/1/au:+Liu_B/0/1/0/all/0/1">Boyuan Liu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jaacks_J/0/1/0/all/0/1">Jason Jaacks</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Finkelstein_S/0/1/0/all/0/1">Steven L. Finkelstein</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bromm_V/0/1/0/all/0/1">Volker Bromm</a> We use cosmological hydrodynamic zoom-in simulations to study early structure formation in two dark matter (DM) cosmologies, a standard CDM model, and a warm DM (WDM) model with a particle mass of $m_{chi}c^{2}=3$ keV. We focus on DM haloes with virial masses $Msim 10^{10} M_{odot}$. We find that the first star formation activity is delayed by $sim 200$ Myr in the WDM model, with similar delays for metal enrichment and the formation of the second generation of stars. However, the differences between theRead More →

The puzzling high velocity G5 supergiant star HD 179821 : new insight from Gaia DR2 data. (arXiv:1901.08995v1 [astro-ph.SR]) <a href="http://arxiv.org/find/astro-ph/1/au:+Parthasarathy_M/0/1/0/all/0/1">M. Parthasarathy</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jasniewicz_G/0/1/0/all/0/1">G. Jasniewicz</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Thevenin_F/0/1/0/all/0/1">F. Th&#xe9;venin</a> HD 179821 is classified as G5 Ia star. From the IRAS colors and spectral energy distributions it was classified as a post-AGB star. But some studies classify it as a massive (30 to 19 Msun ) post-red supergiant evolving to become a Type II supernova. Its mass and evolutionary status remained a hotly debated question even after several detailed spectroscopic studies as the distance was not known. We use the parallax of HD 179821 from the second GaiaRead More →

Large Volcanic Event on Io Inferred from Jovian Sodium Nebula Brightening. (arXiv:1901.08996v1 [astro-ph.EP]) <a href="http://arxiv.org/find/astro-ph/1/au:+Morgenthaler_J/0/1/0/all/0/1">Jeffrey P. Morgenthaler</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rathbun_J/0/1/0/all/0/1">Julie A. Rathbun</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Schmidt_C/0/1/0/all/0/1">Carl A. Schmidt</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Baumgardner_J/0/1/0/all/0/1">Jeffrey Baumgardner</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Schneider_N/0/1/0/all/0/1">Nicholas M. Schneider</a> Using narrow-band images recorded on over 150 nights by the 35 cm coronagraph which comprises PSI’s Io Input/Output Facility (IoIO), we detected a 6-month long enhancement in the Jovian sodium nebula. The onset of the enhancement occurred in the mid December 2017 — early January 2018 timeframe. Sodium emission over the IoIO 0.4 degree field-of-view of was seen to increase through January 2018 and peak in early March 2018. By early June 2018,Read More →

Constraining the Rate of Protostellar Accretion Outbursts in the Orion Molecular Clouds. (arXiv:1901.08062v1 [astro-ph.SR]) <a href="http://arxiv.org/find/astro-ph/1/au:+Fischer_W/0/1/0/all/0/1">William J. Fischer</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Safron_E/0/1/0/all/0/1">Emily Safron</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Megeath_S/0/1/0/all/0/1">S. Thomas Megeath</a> Outbursts due to dramatic increases in the mass accretion rate are the most extreme type of variability in young stellar objects. We searched for outbursts among 319 protostars in the Orion molecular clouds by comparing 3.6, 4.5, and 24 micron photometry from the Spitzer Space Telescope to 3.4, 4.6, and 22 micron photometry from the Wide-field Infrared Survey Explorer (WISE) obtained ~ 6.5 yr apart. Sources that brightened by more than two standard deviations above the mean variability at allRead More →

The First Metallicity Study of M83 using the integrated UV light of Star Clusters. (arXiv:1901.08063v1 [astro-ph.GA]) <a href="http://arxiv.org/find/astro-ph/1/au:+Hernandez_S/0/1/0/all/0/1">Svea Hernandez</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Larsen_S/0/1/0/all/0/1">S&#xf8;ren Larsen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Aloisi_A/0/1/0/all/0/1">Alessandra Aloisi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Berg_D/0/1/0/all/0/1">Danielle A. Berg</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Blair_W/0/1/0/all/0/1">William P. Blair</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fox_A/0/1/0/all/0/1">Andrew J. Fox</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Heckman_T/0/1/0/all/0/1">Timothy M. Heckman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+James_B/0/1/0/all/0/1">Bethan L. James</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Long_K/0/1/0/all/0/1">Knox S. Long</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Skillman_E/0/1/0/all/0/1">Evan D. Skillman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Whitmore_B/0/1/0/all/0/1">Bradley C. Whitmore</a> Stellar populations are powerful tools for investigating the evolution of extragalactic environments. We present the first UV integrated-light spectroscopic observations for 15 young star clusters in the starburst M83 with a special focus on metallicity measurements. The data were obtained with the Cosmic Origins Spectrograph (COS) onboard theRead More →

General relativistic smoothed particle hydrodynamics. (arXiv:1901.08064v1 [astro-ph.IM]) <a href="http://arxiv.org/find/astro-ph/1/au:+Liptai_D/0/1/0/all/0/1">David Liptai</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Price_D/0/1/0/all/0/1">Daniel J. Price</a> We present a method for general relativistic smoothed particle hydrodynamics (GRSPH), based on an entropy-conservative form of the general relativistic hydrodynamic equations for a perfect fluid. We aim to replace approximate treatments of general relativity in current SPH simulations of tidal disruption events and accretion discs. We develop an improved shock capturing formulation that distinguishes between shock viscosity and conductivity in relativity. We also describe a new Hamiltonian time integration algorithm for relativistic orbital dynamics and GRSPH. Our method correctly captures both Einstein and spin-induced precession around black holes. We benchmarkRead More →

Blazar jet evolution revealed by multi-epoch broadband radio polarimetry. (arXiv:1901.08066v1 [astro-ph.GA]) <a href="http://arxiv.org/find/astro-ph/1/au:+Anderson_C/0/1/0/all/0/1">C. S. Anderson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+OSullivan_S/0/1/0/all/0/1">S. P. O&#x27;Sullivan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Heald_G/0/1/0/all/0/1">G. H. Heald</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hodgson_T/0/1/0/all/0/1">T. Hodgson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pasetto_A/0/1/0/all/0/1">A. Pasetto</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gaensler_B/0/1/0/all/0/1">B. M. Gaensler</a> We investigate the previously proposed possibility that multi-epoch broadband polarimetry could act as a complement or limited proxy for VLBI observations of blazars, in that the number of polarised emission components in the jet, and some of their properties and those of the foreground environment, might be inferred from the object’s time-varying 1D Faraday depth spectrum (FDS) alone. We report on a pilot-scale experiment designed to establish the basic plausibility and utilityRead More →

Extreme chemical abundance ratio suggesting an exotic origin for an ultra-diffuse galaxy. (arXiv:1901.08068v1 [astro-ph.GA]) <a href="http://arxiv.org/find/astro-ph/1/au:+Martin_Navarro_I/0/1/0/all/0/1">Ignacio Martin-Navarro</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Romanowsky_A/0/1/0/all/0/1">Aaron J. Romanowsky</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Brodie_J/0/1/0/all/0/1">Jean P. Brodie</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ferre_Mateu_A/0/1/0/all/0/1">Anna Ferre-Mateu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Alabi_A/0/1/0/all/0/1">Adebusola Alabi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Forbes_D/0/1/0/all/0/1">Duncan A. Forbes</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sharina_M/0/1/0/all/0/1">Margarita Sharina</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Villaume_A/0/1/0/all/0/1">Alexa Villaume</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pandya_V/0/1/0/all/0/1">Viraj Pandya</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Martinez_Delgado_D/0/1/0/all/0/1">David Martinez-Delgado</a> Ultra diffuse galaxies are a population of extended galaxies but with relatively low luminosities. The origin of these objects remains unclear, largely due to the observational challenges of the low surface brightness Universe. We present here a detailed stellar population analysis of a relatively isolated UDG, DGSAT I, based on spectroscopic data from the Keck Cosmic Web ImagerRead More →

Globular cluster number density profiles using Gaia DR2. (arXiv:1901.08072v1 [astro-ph.GA]) <a href="http://arxiv.org/find/astro-ph/1/au:+Boer_T/0/1/0/all/0/1">T.J.L. de Boer</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gieles_M/0/1/0/all/0/1">M. Gieles</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Balbinot_E/0/1/0/all/0/1">E. Balbinot</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Henault_Brunet_V/0/1/0/all/0/1">V. Henault-Brunet</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sollima_A/0/1/0/all/0/1">A. Sollima</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Watkins_L/0/1/0/all/0/1">L.L. Watkins</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Claydon_I/0/1/0/all/0/1">I. Claydon</a> Using data from Gaia DR2, we study the radial number density profiles of the Galactic globular cluster sample. Proper motions are used for accurate membership selection, especially crucial in the cluster outskirts. Due to the severe crowding in the centres, the Gaia data is supplemented by literature data from HST and surface brightness measurements, where available. This results in 81 clusters with a complete density profile covering the full tidal radius (and beyond)Read More →

High-resolution confirmation of an extended helium atmosphere around WASP-107b. (arXiv:1901.08073v1 [astro-ph.EP]) <a href="http://arxiv.org/find/astro-ph/1/au:+Allart_R/0/1/0/all/0/1">R. Allart</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bourrier_V/0/1/0/all/0/1">V. Bourrier</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lovis_C/0/1/0/all/0/1">C. Lovis</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ehrenreich_D/0/1/0/all/0/1">D. Ehrenreich</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Aceituno_J/0/1/0/all/0/1">J. Aceituno</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Guijarro_A/0/1/0/all/0/1">A. Guijarro</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pepe_F/0/1/0/all/0/1">F. Pepe</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sing_D/0/1/0/all/0/1">D. K. Sing</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Spake_J/0/1/0/all/0/1">J.J. Spake</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wyttenbach_A/0/1/0/all/0/1">A. Wyttenbach</a> Probing the evaporation of exoplanet atmospheres is key to understanding the formation and evolution of exoplanetary systems. The main tracer of evaporation in the UV is the Lyman-alpha transition, which can reveal extended exospheres. Recently, NIR metastable helium triplet (1.08 microns) revealed extended thermospheres in several exoplanets, opening a new window into evaporation. We aim at spectrally resolving the first helium absorption signatureRead More →

Spectro-photometric decomposition of galaxy structural components. (arXiv:1901.08075v1 [astro-ph.GA]) <a href="http://arxiv.org/find/astro-ph/1/au:+Mendez_Abreu_J/0/1/0/all/0/1">J. M&#xe9;ndez-Abreu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sanchez_S/0/1/0/all/0/1">S. F. S&#xe1;nchez</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lorenzo_Caceres_A/0/1/0/all/0/1">A. de Lorenzo-C&#xe1;ceres</a> Galaxies are complex systems made up of different structural components such as bulges, discs, and bars. Understanding galaxy evolution requires unveiling, independently, their history of stellar mass and metallicity assembly. We introduce C2D, a new algorithm to perform spectro-photometric multi-component decompositions of integral field spectroscopy (IFS) datacubes. The galaxy surface-brightness distribution at each wavelength (quasi-monochromatic image) is fitted using GASP2D, a 2D photometric decomposition code. As a result, C2D provides both a characteristic one-dimensional spectra and a full datacube with all the spatial and spectral informationRead More →