WR140 orbit

Orbital motion of WR140

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The WC7 and O5 stars in WR 140 move in very eccentric orbits with a period of just under 2900 days. WR 140 (HD 193793) was long known to vary in radial velocity [1], but demonstration that it was a spectroscopic binary occurred [2] only when the periodicity of its infrared emission caused by dust formation was determined. Since then, radial velocity orbits of ever increasing accuracy (and increasing eccentricity!) have been derived from both optical and ultraviolet spectra. The most recent RV orbit, that by Fahed et al. [Ref 10] below, used observations taken in an intensive campaign to study WR 140 around the time of its 2009 periastron passage. The campaign was unusual in combining the efforts of both amateur and professional astronomers, reported at a workshop "Stellar Winds in Interaction" held at the Convento da Arrábida in May 2010.

Radial velocity orbital elements of WR 140

P (d)	2885 ± 73	(2900)*	2893	(2900)*	2899.0 ± 1.3	2896.5 ± 0.7
e	0.7 ± 0.05	0.84 ± 0.04	0.85 ± 0.01	0.87 ± 0.05	0.881 ± 0.007	0.8962 ± 0.0014
ω (°)	42 ± 10	32 ± 8 (abs)	40.8 ± 3.1	31 ± 9	46.7 ± 1.6	44.6 ± 1.1
T₀ (JD)	2423069±35	2446160±29	2449036±4	2448956±117	2446147.4±3.7	2446156.2±2.2
To (Y)	1922.04	1985.26	1993.13	1992.92	1985.22	1985.25
K_O5 km/s	22 ± 3	28 ± 3	33.8 ± 1.5	25 ± 15	30.5 ± 1.9	30.9 ± 0.6
K_WC7 km/s	-40 ± 17	-79 ± 50	-91.3 ± 4.8	--	-82.0 ± 2.3	-75.5 ± 0.7
data	optical, 1922-85	optical, 1922-85	optical, 1980-93	UV, 1985-95	1922-2002 + UV	Ref [5] + 2007-2009
ref	[3]	[4]	[5]	[6]	[7]	[10]

* The 2900-d period in these solutions was adopted from the infrared light curves

Fully defined orbit in three dimensions

From high-resolution imaging of the radio emission between phases 0.74 and 0.97, Dougherty et al. [8] demonstrated that the WR 140 system rotates clockwise on the sky, and derived an orbital inclination, i = 122±5°. The binary itself was resolved by Monnier et al. (2004) [9], who measured the stellar separation and position angle at phase 0.297. Using this and the inclination, Dougherty et al. determined the longitude of ascending node (Ω = 353±3°), completing the description of the orbit. Further high resolution observations by Monnier et al. (2011) [9] allowed derivation of an astrometric orbit which, combined with the RV observations, yield the definitive orbit below, together with a distance of 1.67±0.03 kpc and masses of 14.9±0.5 M_☉ and 35.9±1.3 M_☉ for the WC7 and O5 stars respectively.

P (days)	e	ω (°)	T₀ (JD)	Ω (°)	i (°)
2896.35 ± 0.20	0.8964 ^+0.0004_-0.0007	46.8 ± 0.4	2446155.3 ± 0.8	353.6 ± 0.4	119.6 ± 0.5

References:

rev: 2 October 2015
Peredur Williams

[1] J.K. McDonald Pub. DAO VII, 311, 1947
[2] P.M. Williams et al. in: H.J.G.L.M. Lamers & C.W.H. de Loore (Eds), Instabilities in luminous early type stars (Dordrecht, D. Reidel) 1987, p. 221-226.
[3] A.F.J. Moffat et al. ApJ 312, 807, 1987.
[4] P.M. Williams et al. MNRAS 243, 662, 1990
[5] K. Annuk in IAU Symposium No. 163, p. 231, 1994
[6] D.Y.A. Setia Gunawan et al. A&A 376, 460, 2001
[7] S.V Marchenko et al. ApJ 596, 1295,2003.
[8] S.M. Dougherty et al. ApJ 623, 447, 2005.
[9] J.D. Monnier et al. ApJ 602, 57L, 2004.
[10] R. Fahed et al. MNRAS 418, 2, 2011.
[11] J.D. Monnier et al. ApJ 742, 1L, 2011.