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Register a new userConditions in the WR 140 wind-collision region revealed by the 1.083-micron He I line profile
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Peredur Williams Dr
Publication date
2021
fields
Physics
and research's language is
English
Authors
Peredur M. Williams
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We present spectroscopy of the P~Cygni profile of the 1.083-micron He I line in the WC7 + O5 colliding-wind binary (CWB) WR 140 (HD 193793), observed in 2008, before its periastron passage in 2009, and in 2016-17, spanning the subsequent periastron passage. Both absorption and emission components showed strong variations. The variation of the absorption component as the O5 star was occulted by the wind-collision region (WCR) sets a tight constraint on its geometry. While the sightline to the O5 star traversed the WCR, the strength and breadth of the absorption component varied significantly on time-scales of days. An emission sub-peak was observed on all our profiles. The variation of its radial velocity with orbital phase was shown to be consistent with formation in the WCR as it swung round the stars in their orbit. Modelling the profile gave a measure of the extent of the sub-peak forming region. In the phase range 0.93-0.99, the flux in the sub-peak increased steadily, approximately inversely proportionally to the stellar separation, indicating that the shocked gas in the WCR where the line was formed was adiabatic. After periastron, the sub-peak flux was anomalously strong and varied rapidly, suggesting formation in clumps down-stream in the WCR. For most of the time, its flux exceeded the 2-10-keV X-ray emission, showing it to be a significant coolant of the shocked wind.
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Wolf-Rayet stars represent one of the final stages of massive stellar evolution. Relatively little is known about this short-lived phase and we currently lack reliable mass, distance, and binarity determinations for a representative sample. Here we report the first visual orbit for WR 140(=HD193793), a WC7+O5 binary system known for its periodic dust production episodes triggered by intense colliding winds near periastron passage. The IOTA and CHARA interferometers resolved the pair of stars in each year from 2003--2009, covering most of the highly-eccentric, 7.9 year orbit. Combining our results with the recent improved double-line spectroscopic orbit of Fahed et al. (2011), we find the WR 140 system is located at a distance of 1.67 +/- 0.03 kpc, composed of a WR star with M_WR = 14.9 +/- 0.5 Msun and an O star with M_O = 35.9 +/- 1.3 Msun. Our precision orbit yields key parameters with uncertainties times 6 smaller than previous work and paves the way for detailed modeling of the system. Our newly measured flux ratios at the near-infrared H and Ks bands allow an SED decomposition and analysis of the component evolutionary states.
The periodic spectroscopic events in eta Carinae are now well established and occur near the periastron passage of two massive stars in a very eccentric orbit. Several mechanisms have been proposed to explain the variations of different spectral features, such as an eclipse by the wind-wind collision boundary, a shell ejection from the primary star or accretion of its wind onto the secondary. All of them have problems explaining all the observed phenomena. To better understand the nature of the cyclic events, we performed a dense monitoring of eta Carinae with 5 Southern telescopes during the 2009 low excitation event, resulting in a set of data of unprecedented quality and sampling. The intrinsic luminosity of the He II 4686 emission line (L~310 Lsun) just before periastron reveals the presence of a very luminous transient source of extreme UV radiation emitted in the wind-wind collision (WWC) region. Clumps in the primarys wind probably explain the flare-like behavior of both the X-ray and He II 4686 light-curves. After a short-lived minimum, He II 4686 emission rises again to a ne
We present updated orbital elements for the Wolf-Rayet (WR) binary WR,140 (HD,193793; WC7pd + O5.5fc). The new orbital elements were derived using previously published measurements along with {color{black}160} new radial velocity measurements across the 2016 periastron passage of WR 140. Additionally, four new measurements of the orbital astrometry were collected with the CHARA Array. With these measurements, we derive stellar masses of $M_{rm WR} = 10.31pm0.45 M_odot$ and $M_{rm O} = 29.27pm1.14 M_{odot}$. We also include a discussion of the evolutionary history of this system from the Binary Population and Spectral Synthesis (BPASS) model grid to show that this WR star likely formed primarily through mass loss in the stellar winds, with only a moderate amount of mass lost or transferred through binary interactions.
The eccentric WR+O binary system WR 140 produces dust for a few months at intervals of 7.94 yrs coincident with periastron passage. We present the first resolved images of this dust shell, at binary phases ~0.039 and ~0.055, using aperture masking techniques on the Keck-I telescope to achieve diffraction-limited resolution. Proper motions of approximately 1.1 milliarcsecond per day were detected, implying a distance ~1.5 kpc from the known wind speed. The dust plume observed is not as simple as the ``pinwheel nebulae seen around other WR colliding wind binaries, indicating the orbital plane is highly inclined to our line-of-sight and/or the dust formation is very clumpy. Follow-up imaging in the mid-infrared and with adaptive optics is urgently required to track the dust motion further, necessary for unambiguously determining the orbital geometry which we only partially constrain here. With full knowledge of the orbital elements, these infrared images can be used to reconstruct the dust distribution along the colliding wind interface, providing a unique tool for probing the post-shock physical conditions of violent astrophysical flows.
Observations of the WC9+OB system WR 65 in the infrared show variations of its dust emission consistent with a period near 4.8~yr, suggesting formation in a colliding-wind binary (CWB) having an elliptical orbit. If we adopt the IR maximum as zero phase, the times of X-ray maximum count and minimum extinction to the hard component measured by Oskinova & Hamann fall at phases 0.4--0.5, when the separation of the WC9 and OB stars is greatest. We consider WR 65 in the context of other WC8-9+OB stars showing dust emission.
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