Introduction to WR140 = HD 193793
Links Colliding-wind binaries WR140 radio variation X-MEGA Campaign Episodic dust-makers WR140 orbital motion Massive Stars Web site WR140 configurations Co-ordinates J2000 R.A. 20 20 27.98 Dec. +43 51 16.3	WR 140 (= HD 193793 = BD +43° 3571) is a binary system comprising a WC7 type Wolf-Rayet star and an O5 star. The classification of the latter has been revised from using new measurements of the He I 4472 and HeII 4542 lines. It is the more massive and luminous component. Both stars have fast (3000 km/s), radiatively driven stellar winds which carry significant kinetic energy. Between the two stars, the winds collide, releasing some of this energy and producing shocks, resulting in particle acceleration and heating and compression of the plasma. The consequences of these colliding-wind processes are observed at X-ray and radio wavelengths, making WR140 one of the brightest non-compact stellar X-ray sources [1] and a non-thermal radio source [2]. Variations of the X-ray and radio emission are observed as the stars move in their eccentric binary orbit [3]. WR140 was also the first Wolf-Rayet star to show a sudden brightening in its infrared flux, attributed to an episode of dust formation [4]. This dust (a form of carbon) condensed in the stellar wind, absorbing a small fraction of the stars' UV-optical radiation. This radiation heats the dust to a temperature of about 1000K, causing the brightening at infrared wavelengths. The newly formed dust is dispersed by the stellar wind and cools, causing its infrared emission to fade. Another episode of dust formation by WR140 was observed in 1985, and it was argued that these were periodic and also linked to the binary orbit, occurring near the time of periastron passage [3]. WR140 is the prototype episodic dust-maker. The most recent (2001) dust cloud formation has been imaged at high resolution in the infrared: in mid-2001 with aperture-masking on the Keck telescope by Monnier et al. [5], then with near-IR cameras and adaptive optics systems on the Hale and William Herschel telescopes, and then at wavelengths between 3.6 and 10 µm with UKIRT [6] and Gemini (N) as the cloud expanded and cooled. This work is described in [7]
Periastron passage occurred in 2009 and configurations of the system around that time are given here.
Above: Infrared L' (3.8 µm) magnitudes of WR140 observed since 1973 showing regular episodes of ten-fold brightening at intervals of 2900 days (7.94 years), followed by fading over about 5 years.
Right: Infrared "light curves", at three wavelengths phased to the 2900-day period, showing variations in emission by heated dust [3]. Zero phase corresponds to periastron passage in the orbit. The sudden rises, caused by episodes of dust formation, occur every 2900 days, most recently in March 2001. The emission fades more slowly at the longer wavelengths (8.75 µm) because the dust is cooling.
Right: Spectral energy distributions of WR140 over six decades of wavelength, from the visible to radio. Black: WR140 in "quiescence". Red squares: fluxes measured at infrared maximum. Blue: fluxes measured at radio maximum. Green: the O5 star, which is brightest in the optical.
rev: 30 Sep 2009 Peredur Williams [Home page]	[1] A.M.T. Pollock ApJ 320, 283, 1987 [2] R.H. Becker & R.L. White ApJ 297, 649, 1985 [3] P.M. Williams et al. MNRAS 243, 662, 1990 [4] P.M. Williams et al. MNRAS 185, 467, 1978 [5] J.D. Monnier, P.G. Tuthill & W.C. Danchi ApJ 567, L137, 2002 [6] P.M. Williams, W.P. Varricatt, A.P. Marston & N.M. Ashok ASPC 367, 285, 2007 [7] P.M. Williams et al. MNRAS 395, 1749, 2009