Astrophys. J., 596, 1295-1304 (2003/October-3)
The unusual 2001 periastron passage in the ``Clockwork'' colliding-wind binary WR 140.
MARCHENKO S.V., MOFFAT A.F.J., BALLEREAU D., CHAUVILLE J., ZOREC J., HILL G.M., ANNUK K., CORRAL L.J., DEMERS H., EENENS P.R.J., PANOV K.P., SEGGEWISS W., THOMSON J.R. and VILLAR-SBAFFI A.
Abstract (from CDS):
We follow, using both optical spectroscopy and photometry, the ``textbook'' colliding-wind WR+O binary WR 140 through and between the periastron passages of 1993 and 2001. An extensive collection of high-quality spectra allows us to derive precise orbital elements for both components simultaneously. We confirm the extremely high eccentricity of the system, e=0.881±0.005, find an excellent match of the newly derived period to the previous estimates, P=2899.0±1.3 days, and improve the accuracy of the time of periastron passage, T0=HJD2,446,147.4±3.7. Around periastron, at orbital phases φ∼0.995-1.015, additional emission components appear on the tops of the broad Wolf-Rayet emission lines of relatively low ionization potential. The phase-dependent behavior of these excess line emissions points to their origin in the wind-wind collision zone, which allows us to place some limits on the orbital inclination of the system, i=50°±15°, and half-opening angle of the bow shock cone, θ=40°±15°. The relatively sudden appearance and disappearance of the extra emission components probably signify a rapid switch from an adiabatically to a radiatively dominated regime and back again. Multiyear UBV photometry provides one more surprise: in 2001 at φ=0.02-0.06, the system went through a series of rapid, eclipse-like events. Assuming these events to be related to an episode of enhanced dust formation at periastron, we estimate the characteristic size of the dust grains to be a∼0.07 µm.
Stars: Binaries: Spectroscopic - Stars: Early-Type - Stars: Individual: Alphanumeric: WR 140 - Stars: Wolf-Rayet
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