THE UNUSUAL 2001 PERIASTRON PASSAGE IN THE 'CLOCKWORK' COLLIDING-WIND BINARY WR 140

摘要

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, T_0 = HJD 2, 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 adiabati-cally 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.