RAS_WEB (Page 3,782)

Implications from Late-Time X-ray Detections of Optically Selected Tidal Disruption Events: State Changes, Unification, and Detection Rates. (arXiv:1906.12236v1 [astro-ph.HE]) <a href="http://arxiv.org/find/astro-ph/1/au:+Jonker_P/0/1/0/all/0/1">P.G. Jonker</a> (SRON, Netherlands Institute for Space Research &amp; Radboud University), <a href="http://arxiv.org/find/astro-ph/1/au:+Stone_N/0/1/0/all/0/1">N.C. Stone</a> (University of Maryland, The Hebrew University &amp; Columbia University), <a href="http://arxiv.org/find/astro-ph/1/au:+Generozov_A/0/1/0/all/0/1">A. Generozov</a> (University of Colorado &amp; Columbia University), <a href="http://arxiv.org/find/astro-ph/1/au:+Velzen_S/0/1/0/all/0/1">S. van Velzen</a> (NYU &amp; University of Maryland), <a href="http://arxiv.org/find/astro-ph/1/au:+Metzger_B/0/1/0/all/0/1">B. Metzger</a> (Columbia University) Using Chandra X-ray observations we detect three out of four optically-selected tidal disruption events (TDEs) 4-9 years after their discovery. The spectrum of PTF09axc is consistent with a power law with index of 2.5$pm$0.1, whereas the spectrum of PTF09geRead More →

Cosmic ray acceleration by shocks: spectral steepening due to turbulent magnetic field amplification. (arXiv:1906.12240v1 [astro-ph.HE]) <a href="http://arxiv.org/find/astro-ph/1/au:+Bell_A/0/1/0/all/0/1">Anthony Bell</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Matthews_J/0/1/0/all/0/1">James Matthews</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Blundell_K/0/1/0/all/0/1">Katherine Blundell</a> We show that the energy required to turbulently amplify magnetic field during cosmic ray (CR) acceleration by shocks extracts energy from the CR and steepens the CR energy spectrum. We show that the energy required to turbulently amplify magnetic field during cosmic ray (CR) acceleration by shocks extracts energy from the CR and steepens the CR energy spectrum. http://arxiv.org/icons/sfx.gifRead More →

The Hunt for Primordial Interactions in the Large Scale Structures of the Universe. (arXiv:1906.12244v1 [astro-ph.CO]) <a href="http://arxiv.org/find/astro-ph/1/au:+Biagetti_M/0/1/0/all/0/1">Matteo Biagetti</a> The understanding of the primordial mechanism that seeded the cosmic structures we observe today in the sky is one of the major goals in cosmology. The leading paradigm for such a mechanism is provided by the inflationary scenario, a period of violent accelerated expansion in the very early stages of evolution of the Universe. While our current knowledge of the physics of inflation is limited to phenomenological models which fit observations, an exquisite understanding of the particle content and interactions taking place during inflation would provide breakthroughsRead More →

The origin of spin in binary black holes: Predicting the distributions of the main observables of Advanced LIGO. (arXiv:1906.12257v1 [astro-ph.HE]) <a href="http://arxiv.org/find/astro-ph/1/au:+Bavera_S/0/1/0/all/0/1">Simone S. Bavera</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fragos_T/0/1/0/all/0/1">Tassos Fragos</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Qin_Y/0/1/0/all/0/1">Ying Qin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zapartas_E/0/1/0/all/0/1">Emmanouil Zapartas</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Neijssel_C/0/1/0/all/0/1">Coenraad J. Neijssel</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mandel_I/0/1/0/all/0/1">Ilya Mandel</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Batta_A/0/1/0/all/0/1">Aldo Batta</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gaebel_S/0/1/0/all/0/1">Sebastian M. Gaebel</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kimball_C/0/1/0/all/0/1">Chase Kimball</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Stevenson_S/0/1/0/all/0/1">Simon Stevenson</a> We study the formation of coalescing binary black holes via the evolution of isolated field binaries that go through the common envelope phase in order to obtain the combined distributions of the main observables of Advanced LIGO. We use a hybrid technique that combines the parametric binary population synthesis code COMPAS withRead More →

Astrophysical neutrinos: theory. (arXiv:1906.12258v1 [astro-ph.CO]) <a href="http://arxiv.org/find/astro-ph/1/au:+Pisanti_O/0/1/0/all/0/1">Ofelia Pisanti</a> In the era of multi-messenger astronomy, neutrinos are among the most important astronomical messengers, due to their interaction properties. In these lessons I briefly review the main issues concerning the theory on astrophysical neutrinos. In the era of multi-messenger astronomy, neutrinos are among the most important astronomical messengers, due to their interaction properties. In these lessons I briefly review the main issues concerning the theory on astrophysical neutrinos. http://arxiv.org/icons/sfx.gifRead More →

The warm Gaseous Disk and the Anisotropic Circumgalactic Medium of the Milky Way. (arXiv:1906.12259v1 [astro-ph.GA]) <a href="http://arxiv.org/find/astro-ph/1/au:+Qu_Z/0/1/0/all/0/1">Zhijie Qu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bregman_J/0/1/0/all/0/1">Joel N. Bregman</a> The warm ($log~Tapprox5$) gas is an important gaseous component in the galaxy baryonic cycle. We built a 2-dimension disk-CGM model to study the warm gas distribution of the Milky Way (MW) using the absorption line surveys of Si IV and O VI. In this model, the disk component of both ions has the same density profile ($n(r, z)=n_0exp(-|z|/z_0)exp(-r/r_0)$) with a scale height of $z_0=2.6pm0.4rm~kpc$ and a scale length of $r_0=6.1pm1.2rm~kpc$. For this disk component, we calculate the warm gas mass of $log(M/M_odot)=(7.6pm0.2)-logfrac{Z}{Z_odot}$. TheRead More →

Asteroseismology of solar-type stars. (arXiv:1906.12262v1 [astro-ph.SR]) <a href="http://arxiv.org/find/astro-ph/1/au:+Garcia_R/0/1/0/all/0/1">R. A. Garcia</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ballot_J/0/1/0/all/0/1">J. Ballot</a> Until the last few decades, investigations of stellar interiors had been restricted to theoretical studies only constrained by observations of their global properties and external characteristics. However, in the last thirty years the field has been revolutionized by the ability to perform seismic investigations of stellar interiors. This revolution begun with the Sun, where helioseismology has been yielding information competing with what can be inferred about the Earth’s interior from geoseismology. The last two decades have witnessed the advent of asteroseismology of solar-like stars, thanks to a dramatic development of new observingRead More →

Helium Variation Across Two Solar Cycles Reveals A Speed-Dependent Phase Lag. (arXiv:1906.12273v1 [physics.space-ph]) <a href="http://arxiv.org/find/physics/1/au:+Alterman_B/0/1/0/all/0/1">B. L. Alterman</a>, <a href="http://arxiv.org/find/physics/1/au:+Kasper_J/0/1/0/all/0/1">Justin C. Kasper</a> We study the relationship between solar wind helium to hydrogen abundance ratio ($A_mathrm{He}$), solar wind speed ($v_mathrm{SW}$), and sunspot number (SSN) over solar cycles 23 and 24. This is the first full 22-year Hale cycle measured with the Wind spacecraft covering a full cycle of the solar dynamo with two polarity reversals. While previous studies have established a strong correlation between $A_mathrm{He}$ and SSN, we show that the phase delay between $A_mathrm{He}$ and SSN is a monotonic increasing function of $v_mathrm{SW}$. Correcting for thisRead More →

Resolving numerical star formation: A cautionary tale. (arXiv:1906.12276v1 [astro-ph.SR]) <a href="http://arxiv.org/find/astro-ph/1/au:+Wurster_J/0/1/0/all/0/1">James Wurster</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bate_M/0/1/0/all/0/1">Matthew R. Bate</a> Resolution studies of test problems set baselines and help define minimum resolution requirements, however, resolution studies must also be performed on scientific simulations to determine the effect of resolution on the specific scientific results. We perform a resolution study on the formation of a protostar by modelling the collapse of gas through 14 orders of magnitude in density. This is done using compressible radiative non-ideal magnetohydrodynamics. Our suite consists of an ideal magnetohydrodynamics (MHD) model and two non-ideal MHD models, and we test three resolutions for each model. TheRead More →

A Mellin Space Approach to Cosmological Correlators. (arXiv:1906.12302v1 [hep-th]) <a href="http://arxiv.org/find/hep-th/1/au:+Sleight_C/0/1/0/all/0/1">Charlotte Sleight</a> We propose a Mellin space approach to the evaluation of late-time momentum-space correlation functions of quantum fields in $left(d+1right)$-dimensional de Sitter space. The Mellin-Barnes representation makes manifest the analytic structure of late-time correlators and, more generally, provides a convenient general $d$ framework for the study of conformal correlators in momentum space. In this work we focus on tree-level correlation functions of general scalars as a prototype, including $n$-point contact diagrams and $4$-point exchanges. For generic scalars, both the contact and exchange diagrams are given by (generalised) Hypergeometric functions, which reduce to existing expressionsRead More →

The partial ionisation zone of heavy elements in F-stars: a study on how it correlates with rotation. (arXiv:1906.12308v1 [astro-ph.SR]) <a href="http://arxiv.org/find/astro-ph/1/au:+Brito_A/0/1/0/all/0/1">Ana Brito</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lopes_I/0/1/0/all/0/1">Il&#xed;dio Lopes</a> We study the relation between the internal structures of 10 benchmark main-sequence F-stars and their rotational properties. Stellar rotation of main-sequence F-type stars can be characterised by two distinct rotational regimes. Early-type F-stars are usually rapid rotators with periods typically below 10 days, whereas later-type F-stars have longer rotation periods. Specifically, and since the two rotational regimes are tightly connected to the effective temperatures of the stars, we investigate in detail the characteristics of the partial ionisation zones in theRead More →

Coverage Area Determination for Conical Fields of View Considering an Oblate Earth. (arXiv:1906.12318v1 [physics.space-ph]) <a href="http://arxiv.org/find/physics/1/au:+Nugnes_M/0/1/0/all/0/1">Marco Nugnes</a>, <a href="http://arxiv.org/find/physics/1/au:+Colombo_C/0/1/0/all/0/1">Camilla Colombo</a>, <a href="http://arxiv.org/find/physics/1/au:+Tipaldi_M/0/1/0/all/0/1">Massimo Tipaldi</a> This paper introduces a new analytical method for the determination of the coverage area modeling the Earth as an oblate ellipsoid of rotation. Starting from the knowledge of the satellite’s position vector and the direction of the navigation antenna line of sight, the surface generated by the intersection of the oblate ellipsoid and the assumed conical field of view is decomposed in many ellipses, obtained by cutting the Earth’s surface with every plane containing the navigation antenna line of sight. The geometricalRead More →

Limitations on Standard Sirens tests of gravity from screening. (arXiv:1906.12333v1 [astro-ph.CO]) <a href="http://arxiv.org/find/astro-ph/1/au:+Dalang_C/0/1/0/all/0/1">Charles Dalang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lombriser_L/0/1/0/all/0/1">Lucas Lombriser</a> Modified gravity theories with an effective Newton constant that varies over cosmological timescales generally predict a different gravitational wave luminosity distance than General Relativity. While this holds for a uniform variation, we show that if locally screened at the source and at the observer as required to pass stringent astrophysical tests of gravity, the General Relativistic distance is restored. In the absence of such a screening, the same effect must modify electromagnetic luminosity distances inferred from supernovae Type Ia, to the extent that the effects can cancel inRead More →

Morpheus: A Deep Learning Framework For Pixel-Level Analysis of Astronomical Image Data. (arXiv:1906.11248v1 [astro-ph.GA]) <a href="http://arxiv.org/find/astro-ph/1/au:+Hausen_R/0/1/0/all/0/1">Ryan Hausen</a> (UCSC), <a href="http://arxiv.org/find/astro-ph/1/au:+Robertson_B/0/1/0/all/0/1">Brant Robertson</a> (UCSC, IAS) We present Morpheus, a new model for generating pixel level morphological classifications of astronomical sources. Morpheus leverages advances in deep learning to perform source detection, source segmentation, and morphological classification pixel-by-pixel via a semantic segmentation algorithm adopted from the field of computer vision. By utilizing morphological information about the flux of real astronomical sources during object detection, Morpheus shows resiliency to false positive identifications of sources. We evaluate Morpheus by performing source detection, source segmentation, morphological classification on the Hubble Space TelescopeRead More →

Convective Overshoot and Macroscopic Diffusion in Pure-Hydrogen Atmosphere White Dwarfs. (arXiv:1906.11252v1 [astro-ph.SR]) <a href="http://arxiv.org/find/astro-ph/1/au:+Cunningham_T/0/1/0/all/0/1">Tim Cunningham</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tremblay_P/0/1/0/all/0/1">Pier-Emmanuel Tremblay</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Freytag_B/0/1/0/all/0/1">Bernd Freytag</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ludwig_H/0/1/0/all/0/1">Hans-G&#xfc;nther Ludwig</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Koester_D/0/1/0/all/0/1">Detlev Koester</a> We present a theoretical description of macroscopic diffusion caused by convective overshoot in pure-hydrogen DA white dwarfs using three-dimensional (3D), closed-bottom, radiation hydrodynamics CO$^5$BOLD simulations. We rely on a new grid of deep 3D white dwarf models in the temperature range 11400 K $leq T_{mathrm{eff}} leq$ 18000 K where tracer particles and a tracer density are used to derive macroscopic diffusion coefficients driven by convective overshoot. These diffusion coefficients are compared to microscopic diffusion coefficients from one-dimensional structures.Read More →

Late time transitions in the quintessence field and the $H_0$ tension. (arXiv:1906.11255v1 [astro-ph.CO]) <a href="http://arxiv.org/find/astro-ph/1/au:+Valentino_E/0/1/0/all/0/1">Eleonora Di Valentino</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ferreira_R/0/1/0/all/0/1">Ricardo Z. Ferreira</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Visinelli_L/0/1/0/all/0/1">Luca Visinelli</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Danielsson_U/0/1/0/all/0/1">Ulf Danielsson</a> We consider a quintessence field which transitions from a matter-like to a cosmological constant behavior between recombination and the present time. We aim at easing the tension in the measurement of the present Hubble rate, and we assess the $Lambda$CDM model properly enlarged to include our quintessence field against cosmological observations. The model does not address the scope we proposed. This result allows us to exclude a class of quintessential models as a solution to the tension inRead More →

An empirically-derived formula for the shape of planet-induced gaps in protoplanetary disks. (arXiv:1906.11256v1 [astro-ph.EP]) <a href="http://arxiv.org/find/astro-ph/1/au:+Duffell_P/0/1/0/all/0/1">Paul C. Duffell</a> This study uses numerical hydrodynamics calculations and a novel method for densely sampling parameter space to measure the precise shape of a gap opened by a planet in a gaseous disk, as a function of planet-to-star mass ratio, disk Mach number, and disk viscosity. Formulas for gap depth and width are determined, which are combined to form a complete formula for surface density as a function of radius in the disk. This new analytical formula is compared with numerically-derived gaps opened by planets ranging from very lowRead More →

Dragonfly imaging of the galaxy NGC5907: a revised view of the iconic stellar stream. (arXiv:1906.11260v1 [astro-ph.GA]) <a href="http://arxiv.org/find/astro-ph/1/au:+Dokkum_P/0/1/0/all/0/1">Pieter van Dokkum</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gilhuly_C/0/1/0/all/0/1">Colleen Gilhuly</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bonaca_A/0/1/0/all/0/1">Ana Bonaca</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Merritt_A/0/1/0/all/0/1">Allison Merritt</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Danieli_S/0/1/0/all/0/1">Shany Danieli</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lokhorst_D/0/1/0/all/0/1">Deborah Lokhorst</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Abraham_R/0/1/0/all/0/1">Roberto Abraham</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Conroy_C/0/1/0/all/0/1">Charlie Conroy</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Greco_J/0/1/0/all/0/1">Johnny P. Greco</a> In 2008 it was reported that the stellar stream of the edge-on spiral NGC5907 loops twice around the galaxy, enveloping it in a giant corkscrew-like structure. Here we present imaging of this iconic object with the Dragonfly Telephoto Array, reaching $1sigma$ surface brightness levels of $mu_gapprox 30.5$ mag/arcsec$^2$ on arcminute scales. We find that the stream has a qualitatively differentRead More →