Are the Hosts of Gamma-Ray Bursts Sub-Luminous and Blue Galaxies?
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Fotosferas, Envelopes E Evoluç˜Ao Na Seqüência Principal Ronaldo
Estrelas Be: Fotosferas, Envelopes e Evolu¸c˜ao na Seq¨uˆencia Principal Ronaldo Savarino Levenhagen Orientador: Prof. Dr. Nelson Vani Leister Tese apresentada como requisito para a obten¸c˜ao do grau de Doutor em Ciˆencias Departamento de Astronomia Instituto de Astronomia, Geof´ısica e Ciˆencias Atmosf´ericas Universidade de S˜ao Paulo Brasil Outubro 2004 Dedicada `a minha querida Rose e meu pequeno Bruno Estrelas Be: Fotosferas, Envelopes e Evolu¸c˜ao na Seq¨uˆencia Principal Ronaldo Savarino Levenhagen Resumo As estrelas Be compreendem uma grande faixa de massas e temperaturas. Por defini¸c˜ao, s˜ao objetos de tipo B com classe de luminosidade entre V e III que apre- sentam, ou apresentaram alguma vez, linhas de Balmer em emiss˜ao (eventualmente metais uma vez ionizados) e/ou linhas com padr˜oes de absor¸c˜ao shell1, possivelmente formadas em um envelope circunstelar. Embora se saiba h´a muito tempo que esses objetos s˜ao rodadores r´apidos e que giram pelo menos 1,5 a 2 vezes mais r´apido do que as estrelas B normais, ainda ´e incerto se esses objetos s˜ao ou n˜ao em m´edia rodadores cr´ıticos, n˜ao obstante as re- centes observa¸c˜oes interferom´etricas de HD 10144 (Achernar)2 (uma estrela Be t´ıpica) indicarem se tratar de um rodador cr´ıtico. Devidoas ` suas altas taxas de rota¸c˜ao, as quais originam distor¸c˜oes geom´etricas e distribui¸c˜oes n˜ao uniformes de temperatura dependentes da latitude estelar, os valores de velocidade de rota¸c˜ao derivados por m´etodos cl´assicos s˜ao sistematicamente subes- timados. -
Spectroscopic Analysis of Southern B and Be Stars 3
Mon. Not. R. Astron. Soc. 000, 1–8 (2005) Printed 2 September 2018 (MN LATEX style file v2.2) Spectroscopic analysis of southern B and Be stars R. S. Levenhagen1⋆ and N. V. Leister1⋆† 1Instituto de Astronomia, Geof´ısica e Ciˆencias Atmosf´ericas da Universidade de S˜ao Paulo, CUASO 05508-900 S˜ao Paulo, Brazil Accepted 1988 December 15. Received 1988 December 14; in original form 1988 October 11 ABSTRACT Spectroscopic monitoring of 141 southern field B type stars, 114 of them known to exhibit the Be phenomenon, allowed the estimation of their projected rotational ve- locities, effective temperatures and superficial gravities from both line and equivalent width fitting procedures. Stellar ages, masses and bolometric luminosities were derived from internal structure models. Without taking into account for the effects of gravity darkening, we notice the occurrence of the Be phenomenon in later stages of main sequence phase. Key words: line: profile – stars: emission-line – stars: fundamental parameters – stars: rotation – techniques: spectroscopic. 1 INTRODUCTION the onset of new observational evidences indicate that these objects are in fact near critical rotators, with ω ≃ 0.88 Despite the large amount of works on the subject of B and Be (Zorec, Fr´emat & Cidale 2005, Fr´emat et al. 2005, Townsend, stars published in the past years, both theoretical and obser- Owocki & Howarth 2004). vational, there are still many remaining unsolved problems There are actually three main possibilities for that: (i) concerning their outstanding peculiarities. Among them the it would be a permanent innate property; (ii) it would be origin of their high rotation velocities, dependence of Be due to spin up by binary mass transfer; (iii) or it would frequency counts with evolutionary stages in the main se- be acquired somehow during the main sequence evolution quence, presence and origin of magnetic fields and mass loss phase (Crampin & Hoyle 1960, Schild & Romanishin 1976). -
Curriculum Vitae Krzysztof Z. Stanek
Curriculum Vitae Krzysztof Z. Stanek Work Address: Department of Astronomy The Ohio State University 140 W. 18th Avenue Columbus, OH 43210-1173 tel: (614) 292–1773 fax: (614) 292–7467 e-mail: [email protected] WWW: http://www.astronomy.ohio-state.edu/~kstanek/ EDUCATION: Princeton University, Princeton, NJ 1992 – 1996 Department of Astrophysical Sciences Ph.D. received November 1996 M.A. received November 1994 PhD Thesis Topic: Properties of the Inner Galaxy Thesis Advisor: Prof. Bohdan Paczy´nski Warsaw University, Warsaw, Poland 1987 – 1991 Department of Physics Magister of Astronomy (equiv. to M.Sc.), December 1991 EMPLOYMENT: The Ohio State University, Columbus, Ohio Department of Astronomy Professor October 2009 – present Associate Professor September 2005 – September 2009 Harvard University, Cambridge, Massachusetts Department of Astronomy Associate Professor January 2005 – August 2005 Assistant Professor January 2001 – December 2004 Harvard-Smithsonian CfA, Cambridge, Massachusetts Hubble Postdoctoral Fellow September 1999 – December 2000 CfA Postdoctoral Fellow September 1996 – August 1999 Princeton University, Princeton, New Jersey Department of Astrophysical Sciences Research Assistant September 1992 – August 1996 Copernicus Astronomical Center, Warsaw, Poland Research Assistant January – September 1992 RESEARCH INTERESTS Variable objects throughout the Universe, massive stars, gamma-ray bursts, supernovae and other stellar explosions, extragalactic distance scale, transit searches for planets and many other things. STUDENTS AND POSTDOCS SUPERVISED IN RESEARCH: I am a co-author of about 80 papers written with a graduate student as the first author and about 20 papers written with a postdoc at the first author. Rubab Khan, Ohio State, 2008-present, Ph.D. student, “Dusty stars in nearby galaxies”, “Cosmic explosions”, six joint papers published/submitted. -
Candidate Main-Sequence Stars with Debris Disks: a New Sample of Vega
THE ASTROPHYSICAL JOURNAL, 497:330È341, 1998 April 10 ( 1998. The American Astronomical Society. All rights reserved. Printed in U.S.A. CANDIDATE MAIN-SEQUENCE STARS WITH DEBRIS DISKS: A NEW SAMPLE OF VEGA-LIKE SOURCES VINCENT MANNINGS Division of Physics, Mathematics and Astronomy, California Institute of Technology, MS 105-24, Pasadena, CA 91125 AND MICHAEL J. BARLOW Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK Received 1996 July 24; accepted 1997 November 17 ABSTRACT Vega-like sources are main-sequence stars that exhibit IR Ñuxes in excess of expectations for stellar photospheres, most likely due to reradiation of stellar emission intercepted by orbiting dust grains. We have identiÐed a large sample of main-sequence stars with possible excess IR radiation by cross- correlating the Michigan Catalog of Two-dimensional Spectral Types for the HD Stars with the IRAS Faint Source Survey Catalog. Some 60 of these Vega-like sources were not found during previous surveys of the IRAS database, the majority of which employed the lower sensitivity Point Source Catalog. Here, we provide details of our search strategy, together with a preliminary examination of the full sample of Vega-like sources. Subject headings: circumstellar matter È infrared: stars 1. INTRODUCTION understand the Vega-like stars within the context of the end Vega-like sources are main-sequence stars with disks or products of the evolution of circumstellar disks associated rings of orbiting dust grains. These circumstellar structures with preÈmain-sequence stars, the possible formation of may be the evolved remnants of once massive disks, perhaps planetesimals and planets, and perhaps even the disruption augmented by debris products generated during the of infalling cometary bodies.