Episodic dust formation by HD 192641 (WR 137) – II |
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| Authors: | P M Williams M R Kidger K A van der Hucht P W Morris M Tapia M Perinotto L Morbidelli A Fitzsimmons D M Anthony J J Caldwell A Alonso V Wild |
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| Institution: | Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ; Instituto Astrofísica de Canarias, La Laguna, E-38200 Santa Cruz de Tenerife, Spain; Space Research Organization Netherlands, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands; SSC, IPAC, California Institute of Technology, Pasadena, CA 91125, USA; Universidad Nacional Autónoma de México, Instituto de Astronomía, Apartado Postal 877, Ensenada BC, Mexico; Dípartimento di Astronomia e Scienza dello Spazio, Universitádi Firenze, Largo E. Fermi 5, I-50125 Firenze, Italy; CAISMI/CNR, Largo E. Fermi 5, I-50125 Firenze, Italy; APS Division, Physics Department, Queen's University, Belfast BT7 1NN; Department of Physics and Astronomy, York University, 4700 Keele Street, Toronto, Ontario, M3J 1P3, Canada |
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| Abstract: | We present new infrared photometry of the WC7-type Wolf–Rayet star HD 192641 (WR 137) from 1985 to 1999. These data track the cooling of the dust cloud formed in the 1982–84 dust-formation episode from 1985 to 1991, the increase of the infrared flux from 1994.5 to a new dust-formation maximum in 1997 and its subsequent fading. From these and earlier data we derive a period of 4765±50 d (13.05±0.15 yr) for the dust-formation episodes. Between dust-emission episodes, the infrared spectral energy distribution has the form of a power law, λF λ ∝ λ ?1.86. The rising branch of the infrared light curve (1994–97) differs in form from that of the episodic dust-maker WR 125. Time-dependent modelling shows that this difference can be attributed to a different time dependence of dust formation in WR 137, which occurred approximately ∝ t 2 until maximum, whereas that of WR 125 could be described by a step function, akin to a threshold effect. For an adopted distance of 1.6 kpc, the rate of dust formation was found to be 5.0×10?8 M⊙ yr?1 at maximum, accounting for a fraction f C≈1.5×10?3 of the carbon flowing in the stellar wind. The fading branches of the light curves show evidence for secondary 'mini-eruptions' in 1987, 1988 and 1990, behaviour very different from that of the prototypical episodic dust-maker HD 193793 (WR 140), and suggesting the presence in the WR 137 stellar wind of large-scale structures that are crossed by the wind–wind collision region. |
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| Keywords: | circumstellar matter stars: individual: WR 137 stars: Wolf–Rayet infrared: stars |
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