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Dust formation by the colliding-wind WC5+O9 binary WR19 at periastron passage  [PDF]
P. M. Williams,G. Rauw,K. A. van der Hucht
Physics , 2009, DOI: 10.1111/j.1365-2966.2009.14681.x
Abstract: We present infrared photometry of the episodic dust-making Wolf-Rayet system WR19 (LS3), tracking its fading from a third observed dust-formation episode in 2007 and strengthening the view that these episodes are periodic (P = 10.1+/-0.1 y). Radial velocities of the O9 component observed between 2001 and 2008 show RV variations consistent with WC19 being a spectroscopic binary of high eccentricity (e=0.8), having periastron passage in 2007.14, shortly before the phase of dust formation. In this respect, WR19 resembles the archetypical episodic dust-making colliding-wind binary system WR140.
Orbitally modulated dust formation by the WC7+O5 colliding-wind binary WR140  [PDF]
P. M. Williams,S. V. Marchenko,A. P. Marston,A. F. J. Moffat,W. P. Varricatt,S. M. Dougherty,M. R. Kidger,L. Morbidelli,M. Tapia
Physics , 2009, DOI: 10.1111/j.1365-2966.2009.14664.x
Abstract: We present high-resolution infrared (2--18 micron) images of the archetypal periodic dust-making Wolf-Rayet binary system WR140 (HD 193793) taken between 2001 and 2005, and multi-colour (J -- [19.5]) photometry observed between 1989 and 2001. The images resolve the dust cloud formed by WR140 in 2001, allowing us to track its expansion and cooling, while the photometry allows tracking the average temperature and total mass of the dust. The combination of the two datasets constrains the optical properties of the dust. The most persistent dust features, two concentrations at the ends of a `bar' of emission to the south of the star, were observed to move with constant proper motions of 324+/-8 and 243+/-7 mas/y. Longer wavelength (4.68-micron and 12.5-micron) images shows dust emission from the corresponding features from the previous (1993) periastron passage and dust-formation episode. A third persistent dust concentration to the east of the binary (the `arm') was found to have a proper motion ~ 320 mas/y. Extrapolation of the motions of the concentrations back to the binary suggests that the eastern `arm' began expansion 4--5 months earlier than those in the southern `bar', consistent with the projected rotation of the binary axis and wind-collision region (WCR) on the sky. Comparison of model dust images and the observations constrain the intervals when the WCR was producing sufficiently compressed wind for dust nucleation in the WCR, and suggests that the distribution of this material was not uniform about the axis of the WCR, but more abundant in the following edge in the orbital plane.
A High Resolution H I Study of the ISM Local to Galactic Wolf-rayet Stars  [cached]
Marcelo Arnal
Revista mexicana de astronomía y astrofísica , 2001,
Abstract: The neutral matter distribution from the interstellar medium (ISM) located i n the vicinity of the Galactic Wolf-Rayet (WR) stars WR132 and WR140 has been examined by means of the H I 21-cm line observations obtained with high angular resolution observations. The most interesting discoveries are the presence of huge ovoidal H I minimum spanning the velocity range +13 to +21 km/s (WR132) and -18 to -7 km/s (WR140). These minima were created, very likely, by the join t action of the progenitor of both WR stars and the WR star itself. Inside each cavity, two minima are clearly discernible. The WR star is offset with respect to either the geometrical centre of the main H I void or the inner H I minima. The dual H I minimum geometry observed inside the main H I cavity, a feature also seen in the H I distribution od the ISM located close to other Galactic WR stars, may be a consequence of the interaction process itself.
Wolf-Rayet Stars in Starburst Galaxies  [PDF]
J. Miguel Mas-Hesse,Daniel Kunth,Miguel Cervino
Physics , 1999, DOI: 10.1016/S1387-6473(00)00052-X
Abstract: Wolf-Rayet stars have been detected in a large number of galaxies experiencing intense bursts of star formation. All stars initially more massive than a certain, metallicity-dependent, value are believed to experience the Wolf-Rayet phase at the end of their evolution, just before collapsing in supernova explosion. The detection of Wolf-Rayet stars puts therefore important constraints on the evolutionary status of starbursts, the properties of their Initial Mass Functions and their star formation regime. In this contribution we review the properties of galaxies hosting Wolf-Rayet stars, with special emphasis on the factors that determine their presence and evolution, as well as their impact on the surrounding medium.
The Interacting Wolf-Rayet Galaxy Haro 15  [cached]
Angel R. Lu00F3pez Su00E1nchez,Cu00E9sar Esteban
Revista mexicana de astronomía y astrofísica , 2003,
Abstract: Actualmente se conocen algo menos de 150 galaxias Wolf-Rayet. Muchas de ellas son enanas o irregulares, y algunas muestran objetos compa eros cercanos. En muchos casos aparecen morfologías peculiares como fusiones o colas de marea conectadas a peque os agregados estelares. De esta forma, pensamos que las interacciones podrían ser un mecanismo importante que dispare la formación estelar en las galaxias Wolf-Rayet, sobre todo en las enanas. Hemos usado imágenes profundas CCD en óptico e infrarrojo cercano para analizar algunas galaxias Wolf-Rayet y objetos circundantes con el objetivo de estudiar su interrelación. Presentamos algunas de nuestras conclusiones sobre la morfología, cinemática, colores y composición química del gas ionizado de Haro 15, así como el análisis de las edades de los brotes observados usando modelos teóricos de síntesis espectral.
A Morphological Diagnostic for Dynamical Evolution of Wolf-Rayet Bubbles  [PDF]
Robert A. Gruendl,You-Hua Chu,Bryan C. Dunne,Sean D. Points
Physics , 2000, DOI: 10.1086/316830
Abstract: We have observed H-alpha and [OIII] emission from eight of the most well defined Wolf-Rayet ring nebulae in the Galaxy. We find that in many cases the outermost edge of the [OIII] emission leads the H-alpha emission. We suggest that these offsets, when present, are due to the shock from the Wolf-Rayet bubble expanding into the circumstellar envelope. Thus, the details of the WR bubble morphology at H-alpha and [OIII] can then be used to better understand the physical condition and evolutionary stage of the nebulae around Wolf-Rayet stars, as well as place constraints on the nature of the stellar progenitor and its mass loss history.
Finding Wolf-Rayet Stars in the Local Group  [PDF]
Philip Massey,Kathryn F. Neugent,Nidia Morrell
Physics , 2015,
Abstract: We summarize past and current surveys for Wolf-Rayet stars among the Local Group galaxies, emphasizing both the how and the why. Such studies are invaluable for helping us learn about massive star evolution, and for providing sensitive tests of the stellar evolution models. But for such surveys to be useful, the completeness limits must be well understood. We illustrate that point in this review by following the "evolution" of the observed WC/WN ratio in nearby galaxies. We end by examining our new survey for WR stars in the Magellanic Clouds, which has revealed a new type of WN star, never before seen.
The impact of rotation on the line profiles of Wolf-Rayet stars  [PDF]
Tomer Shenar,Wolf-Rainer Hamann,Helge Todt
Physics , 2014, DOI: 10.1051/0004-6361/201322496
Abstract: Massive Wolf-Rayet stars are recognized today to be in a very common, but short, evolutionary phase of massive stars. While our understanding of Wolf-Rayet stars has increased dramatically over the past decades, it remains unclear whether rapid rotators are among them. There are various indications that rapidly rotating Wolf-Rayet stars should exist. Unfortunately, due to their expanding atmospheres, rotational velocities of Wolf-Rayet stars are very difficult to measure. However, recently observed spectra of several Wolf-Rayet stars reveal peculiarly broad and round emission lines. Could these spectra imply rapid rotation? In this work, we model the effects of rotation on the atmospheres of Wolf-Rayet stars. We further investigate whether the peculiar spectra of five Wolf-Rayet stars may be explained with the help of stellar rotation, infer appropriate rotation parameters, and discuss the implications of our results. We make use of the Potsdam Wolf-Rayet (PoWR) non-LTE model atmosphere code. Since the observed spectra of Wolf-Rayet stars are mainly formed in their expanding atmospheres, rotation must be accounted for with a 3D integration scheme of the formal integral. For this purpose, we assume a rotational velocity field consisting of an inner co-rotating domain and an outer domain, where the angular momentum is conserved. We find that rotation can reproduce the unique spectra analyzed here. However, the inferred rotational velocities at the stellar surface are large (~200 km/s), and the inferred co-rotation radii (~10 stellar radii) suggest the existence of very strong photospheric magnetic fields (~20 kG).
Wolf-Rayet Stars in Very Young Starburst Galaxies  [PDF]
Thierry Contini
Physics , 1996,
Abstract: Preliminary results from spectrophotometric observations of galaxies with very young starbursts are presented. Starburst galaxies with an age of the burst in the range between 3 and 6 Myr have been observed and new detections of Wolf-Rayet galaxies are reported. We discuss the origin of high excitation nebular lines observed in these galaxies and their possible link with the population of Wolf-Rayet stars.
Radio Proper Motions of Wolf-Rayet Stars
Dzib, S.;Rodríguez, L. F.;
Revista mexicana de astronomía y astrofísica , 2009,
Abstract: we present the analysis of observations taken from the very large array archive of six wolf-rayet stars with radio emission, with the purpose of determining their proper motions. typically, these observations cover periods of 10 to 20 years. to verify the method, we included wr 140 in the sample, and found that the proper motions determined by us are a few times more accurate than, and consistent within noise, with those of hipparcos. the other five wr stars were not studied by hipparcos and we report their proper motions for the first time. the proper motions for wr 145a = cyg x-3 are consistent with the source being stationary with respect to its local standard of rest and suggest that the black hole in this binary system formed by direct collapse of a massive star, without expulsion of a supernova remnant.
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