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Ultraviolet and Visual Flux and Line Variations of One of the Least Variable Bp Stars HD 64740
Astronomy & Astrophysics manuscript no. hd64740 c ESO 2018 August 28, 2018 Ultraviolet and visual flux and line variations of one of the least variable Bp stars HD 64740⋆ J. Krtiˇcka1, J. Jan´ık1, H. Markov´a1, Z. Mikul´aˇsek1,2, J. Zverko1, M. Prv´ak1, and M. Skarka1 1 Department of Theoretical Physics and Astrophysics, Masaryk University, Kotl´aˇrsk´a2, CZ-611 37 Brno, Czech Republic 2 Observatory and Planetarium of J. Palisa, VSBˇ – Technical University, Ostrava, Czech Republic Received ABSTRACT Context. The light variability of hot magnetic chemically peculiar stars is typically caused by the flux redistribution in spots with peculiar abundance. This raises the question why some stars with surface abundance spots show significant rotational light variability, while others do not. Aims. We study the Bp star HD 64740 to investigate how its remarkable inhomogeneities in the surface distribution of helium and silicon, and the corresponding strong variability of many spectral lines, can result in one of the faintest photometric variabilities among the Bp stars. Methods. We used model atmospheres and synthetic spectra calculated for the silicon and helium abundances from surface abundance maps to predict the ultraviolet and visual light and line variability of HD 64740. The predicted fluxes and line profiles were compared with the observed ones derived with the IUE, HST, and Hipparcos satellites and with spectra acquired using the FEROS spectrograph at the 2.2m MPG/ESO telescope in La Silla. Results. We are able to reproduce the observed visual light curve of HD 64740 assuming an inhomogeneous distribution of iron correlated with silicon distribution. -
POSTERS SESSION I: Atmospheres of Massive Stars
Abstracts of Posters 25 POSTERS (Grouped by sessions in alphabetical order by first author) SESSION I: Atmospheres of Massive Stars I-1. Pulsational Seeding of Structure in a Line-Driven Stellar Wind Nurdan Anilmis & Stan Owocki, University of Delaware Massive stars often exhibit signatures of radial or non-radial pulsation, and in principal these can play a key role in seeding structure in their radiatively driven stellar wind. We have been carrying out time-dependent hydrodynamical simulations of such winds with time-variable surface brightness and lower boundary condi- tions that are intended to mimic the forms expected from stellar pulsation. We present sample results for a strong radial pulsation, using also an SEI (Sobolev with Exact Integration) line-transfer code to derive characteristic line-profile signatures of the resulting wind structure. Future work will compare these with observed signatures in a variety of specific stars known to be radial and non-radial pulsators. I-2. Wind and Photospheric Variability in Late-B Supergiants Matt Austin, University College London (UCL); Nevyana Markova, National Astronomical Observatory, Bulgaria; Raman Prinja, UCL There is currently a growing realisation that the time-variable properties of massive stars can have a funda- mental influence in the determination of key parameters. Specifically, the fact that the winds may be highly clumped and structured can lead to significant downward revision in the mass-loss rates of OB stars. While wind clumping is generally well studied in O-type stars, it is by contrast poorly understood in B stars. In this study we present the analysis of optical data of the B8 Iae star HD 199478. -
Arxiv:1910.04776V2 [Astro-Ph.SR] 2 Dec 2019 Lion Years
Astronomy & Astrophysics manuscript no. smsmax c ESO 2019 December 3, 2019 Letter to the Editor Maximally accreting supermassive stars: a fundamental limit imposed by hydrostatic equilibrium L. Haemmerle´1, G. Meynet1, L. Mayer2, R. S. Klessen3;4, T. E. Woods5, A. Heger6;7 1 Departement´ d’Astronomie, Universite´ de Geneve,` chemin des Maillettes 51, CH-1290 Versoix, Switzerland 2 Center for Theoretical Astrophysics and Cosmology, Institute for Computational Science, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland 3 Universitat¨ Heidelberg, Zentrum fur¨ Astronomie, Institut fur¨ Theoretische Astrophysik, Albert-Ueberle-Str. 2, D-69120 Heidelberg, Germany 4 Universitat¨ Heidelberg, Interdisziplinares¨ Zentrum fur¨ Wissenschaftliches Rechnen, Im Neuenheimer Feld 205, D-69120 Heidelberg, Germany 5 National Research Council of Canada, Herzberg Astronomy & Astrophysics Research Centre, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada 6 School of Physics and Astronomy, Monash University, VIC 3800, Australia 7 Tsung-Dao Lee Institute, Shanghai 200240, China Received ; accepted ABSTRACT Context. Major mergers of gas-rich galaxies provide promising conditions for the formation of supermassive black holes (SMBHs; 5 4 5 −1 & 10 M ) by direct collapse because they can trigger mass inflows as high as 10 − 10 M yr on sub-parsec scales. However, the channel of SMBH formation in this case, either dark collapse (direct collapse without prior stellar phase) or supermassive star (SMS; 4 & 10 M ), remains unknown. Aims. Here, we investigate the limit in accretion rate up to which stars can maintain hydrostatic equilibrium. −1 Methods. We compute hydrostatic models of SMSs accreting at 1 – 1000 M yr , and estimate the departures from equilibrium a posteriori by taking into account the finite speed of sound. -