The Unusual 2001 Periastron Passage in the “Clockwork” Colliding‐Wind Binary WR 140

Abstract

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 ¼ 0:881 � 0:005, find an excellent match of the newly derived period to the previous estimates, P ¼ 2899:0 � 1:3 days, and improve the accuracy of the time of periastron passage, T0 ¼ HJD 2; 446; 147:4 � 3:7. Around periastron, at orbital phases � � 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 ¼ 50 � � 15 � , and half-opening angle of the bow shock cone, � ¼ 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 � ¼ 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 lm. Subject headings: binaries: spectroscopic — stars: early-type — stars: individual (WR 140) — stars: Wolf-Rayet On-line material: machine-readable tables