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THE MAGELLANIC CLOUDS NEWSLETTER an Electronic Publication Dedicated to the Magellanic Clouds, and Astrophysical Phenomena Therein
THE MAGELLANIC CLOUDS NEWSLETTER An electronic publication dedicated to the Magellanic Clouds, and astrophysical phenomena therein No. 135 — 1 June 2015 http://www.astro.keele.ac.uk/MCnews Editor: Jacco van Loon Editorial Dear Colleagues, It is my pleasure to present you the 135th issue of the Magellanic Clouds Newsletter. From magnetism and galactic structure and interaction, to variable, massive, (post-)AGB and exploding stars, and more on star cluster content – there’s something for everyone. Hope to see you at the IAU General Assembly in August, or in Baltimore in October! The next issue is planned to be distributed on the 1st of August. Editorially Yours, Jacco van Loon 1 Refereed Journal Papers Photometric identification of the periods of the first candidate extragalactic magnetic stars Ya¨el Naz´e1, Nolan R Walborn2, Nidia Morrell3, Gregg A Wade4 and MichaÃl K. Szyma´nski5 1University of LI`ege, Belgium 2STScI, USA 3Las Campanas Observatory, Chile 4Royal Military College, USA 5Warsaw University, Poland Galactic stars belonging to the Of?p category are all strongly magnetic objects exhibiting rotationally modulated spectral and photometric changes on timescales of weeks to years. Five candidate Of?p stars in the Magellanic Clouds have been discovered, notably in the context of ongoing surveys of their massive star populations. Here we describe an investigation of their photometric behaviour, revealing significant variability in all studied objects on timescales of one week to more than four years, including clearly periodic variations for three of them. Their spectral characteristics along with these photometric changes provide further support for the hypothesis that these are strongly magnetized O stars, analogous to the Of?p stars in the Galaxy. -
Infrared Flux Excesses from Hot Subdwarfs
ASTRONOMY & ASTROPHYSICS OCTOBER I 1998,PAGE1 SUPPLEMENT SERIES Astron. Astrophys. Suppl. Ser. 132, 1–12 (1998) Infrared flux excesses from hot subdwarfs? II. 72 more objects?? A. Ulla1,2 and P. Thejll3 1 Universidade de Vigo, Departamento de F´ısica Aplicada, Area de F´ısica da Terra, Astronom´ıa e Astrof´ısica, Facultade de Ciencias, Campus Marcosende-Lagoas, Apartado Postal 874, E-36200 Vigo, Spain 2 Instituto de Astrof´ısica de Canarias, E-38200 La Laguna, Spain 3 Danish Meteorological Institute, Lyngbyvej 100, DK-2100 Copenhagen, Denmark Received December 19, 1996; accepted March 20, 1998 Abstract. In our search, started in February, 1994, for 1. Introduction JHK excess fluxes among the hot subdwarf population as an indicator for the presence of binary companions, Thejll et al. (1995; hereafter Paper I) discussed the pos- results for 72 more hot objects (=63 hot subdwarfs + sible origin for excess infrared fluxes detected from the 1 Horizontal Branch B star + 7 white dwarfs + 1 non- direction of a hot subdwarf star (sd). They presented a subdwarf object) observed with the Carlos S´anchez CVF set of JHK measurements for 27 hot objects: 23 hot sds, IR photometer (in June and October, 1994), are presented. GD274 –which the authors reclassify as sd+K3-K8, and 3 The exact number of binary hot subdwarfs has gained re- white dwarfs (WDs). An analysis was also presented for newed importance after the recent discovery of pulsators the, then 24, hot subdwarfs. After considering a wind ex- with G-F companions. The total number of candidates we pelled from the hot atmosphere as the source of the excess propose may help to set some constraints; for example, IR radiation, the authors concluded that the most likely out of 41 objects with excesses, 13 may have G-type bi- explanation is the presence of a cool stellar companion nary companions. -
Discovery of a Close Substellar Companion to the Hot Subdwarf Star Hd 149382—The Decisive Influence of Substellar Objects on Late Stellar Evolution
The Astrophysical Journal, 702:L96–L99, 2009 September 1 doi:10.1088/0004-637X/702/1/L96 C 2009. The American Astronomical Society. All rights reserved. Printed in the U.S.A. DISCOVERY OF A CLOSE SUBSTELLAR COMPANION TO THE HOT SUBDWARF STAR HD 149382—THE DECISIVE INFLUENCE OF SUBSTELLAR OBJECTS ON LATE STELLAR EVOLUTION S. Geier1, H. Edelmann1,3, U. Heber1, and L. Morales-Rueda2 1 Dr. Remeis-Sternwarte, Institute for Astronomy, University Erlangen-Nurnberg,¨ Sternwartstr. 7, 96049 Bamberg, Germany; [email protected] 2 Department of Astrophysics, Faculty of Science, Radboud University Nijmegen, P.O. Box 9010, 6500 GL Nijmegen, The Netherlands 3 McDonald Observatory, University of Texas at Austin, 1 University Station, C1402, Austin, TX 78712-0259, USA Received 2009 April 29; accepted 2009 August 5; published 2009 August 17 ABSTRACT Substellar objects, like planets and brown dwarfs orbiting stars, are by-products of the star formation process. The evolution of their host stars may have an enormous impact on these small companions. Vice versa a planet might also influence stellar evolution as has recently been argued. Here, we report the discovery of an 8−23 Jupiter-mass substellar object orbiting the hot subdwarf HD 149382 in 2.391 d at a distance of only about five solar radii. Obviously, the companion must have survived engulfment in the red giant envelope. Moreover, the substellar companion has triggered envelope ejection and enabled the sdB star to form. Hot subdwarf stars have been identified as the sources of the unexpected ultraviolet (UV) emission in elliptical galaxies, but the formation of these stars is not fully understood. -