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Register a new userMassive Binary WR112 and Properties of Wolf-Rayet Dust
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S.V. Marchenko
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Some hot, massive, population-I Wolf-Rayet (WR) stars of the carbon subclass are known to be prolific dust-producers. How dust can form in such a hostile environment remains a mystery. Here we report the discovery of a relatively cool, extended, multi-arc dust envelope around the star WR112, most likely formed by wind-wind collision in a long-period binary system. We derive the binary orbital parameters, the dust temperature and the dust mass distributions in the envelope. We find that amorphous carbon is a main constituent of the dust, in agreement with earlier estimates and theoretical predictions. However, the characteristic size of the dust grains is estimated to be ~1 micron, significantly larger than theoretical limits. The dust production rate is 6.1*10^[-7] M_Sun / yr and the total detectable dust mass is found to be about 2.8*10^[-5] M_Sun (for d=4.15 kpc). We also show that, despite the hostile environment, at least ~20% of the initially-formed dust may reach the interstellar medium.
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This paper discusses our ongoing efforts to characterize dust-enshrouded Wolf-Rayet (WR) stars in the radio and infrared. We have used the Very Large Array to measure the broadband radio spectrum of WR stars in suspected binary systems and discovered non-thermal emission, which is usually attributed to colliding winds. In addition, infrared imaging using aperture masking interferometry on the Keck-I telescope has resolved the dust shells around a number of WR stars with K-magnitudes brighter than ~6. Although this admittedly small study suffers from selection bias, we note that all the dust-enshrouded WR stars with radio detections show evidence for colliding winds, supporting the theory that wind compression in a binary system is necessary for efficient dust production. A consequence of this hypothesis is that virtually all WC8-10 stars must be in binaries, since most are dusty. Single-star and binary stellar evolution models will have to be modified to accommodate this observational result if confirmed.
Near infrared spectroscopy and photometry of the Wolf-Rayet Star WR 143 (HD 195177) were obtained in the $JHK$ photometric bands. High resolution spectra observed in the J and H bands exhibit narrow 1.083-micron He I line and the H I Pa Beta and the Brackett series lines in emission superposed on the broad emission line spectrum of the Wolf-Rayet star, giving strong indications of the presence of a companion. From the narrow emission lines observed, the companion is identified to be an early-type Be star. The photometric magnitudes exhibit variations in the JHK bands which are probably due to the variability of the companion star. The flux density distribution is too steep for a Wolf-Rayet atmosphere. This is identified to be mainly due to the increasing contribution from the early-type companion star towards shorter wavelengths.
The Wolf-Rayet nebula M1-67 around WR124 is located above the Galactic plane in a region mostly empty of interstellar medium, which makes it the perfect target to study the mass-loss episodes associated with the late stages of massive star evolution. Archive photometric observations from WISE, Spitzer (MIPS) and Herschel (PACS and SPIRE) are used to construct the spectral energy distribution (SED) of the nebula in the wavelength range of 12-500$mu$m. The infrared (photometric and spectroscopic) data and nebular optical data from the literature are modeled simultaneously using the spectral synthesis code Cloudy, where the free parameters are the gas density distribution and the dust grain size distribution. The infrared SED can be reproduced by dust grains with two size distributions: a MRN power-law distribution with grain sizes between 0.005 and 0.05$mu$m and a population of large grains with representative size 0.9$ mu$m. The latter points towards an eruptive origin for the formation of M1-67. The model predicts a nebular ionized gas mass of $M_mathrm{ion} = 9.2^{+1.6}_{-1.5}~mathrm{M}_odot$ and the estimated mass-loss rate during the dust-formation period is $dot{M} approx 6 times 10^{-4} mathrm{M}_odot$yr$^{-1}$. We discuss the implications of our results in the context of single and binary stellar evolution and propose that M1-67 represents the best candidate for a post-common envelope scenario in massive stars.
Wolf-Rayet ([WR]) and weak emission-line ($wels$) central stars of planetary nebulae (PNe) have hydrogen-deficient atmospheres, whose origins are not well understood. In the present study, we have conducted plasma diagnostics and abundance analyses of 18 Galactic PNe surrounding [WR] and $wels$ nuclei, using collisionally excited lines (CELs) and optical recombination lines (ORLs) measured with the Wide Field Spectrograph on the ANU 2.3-m telescope at the Siding Spring Observatory complemented with optical archival data. Our plasma diagnostics imply that the electron densities and temperatures derived from CELs are correlated with the intrinsic nebular H$beta$ surface brightness and excitation class, respectively. Self-consistent plasma diagnostics of heavy element ORLs of N${}^{2+}$ and O${}^{2+}$ suggest that a small fraction of cool ($lesssim 7000$ K), dense ($sim 10^4-10^5$ cm$^{-3}$) materials may be present in some objects, though with large uncertainties. Our abundance analyses indicate that the abundance discrepancy factors (ADF$equiv$ORLs/CELs) of O${}^{2+}$ are correlated with the dichotomies between forbidden-line and He I temperatures. Our results likely point to the presence of a tiny fraction of cool, oxygen-rich dense clumps within the diffuse warm ionized nebulae. Moreover, our elemental abundances derived from CELs are mostly consistent with AGB models in the range of initial masses from 1.5 to 5M$_{odot}$. Further studies are necessary to understand better the origins of abundance discrepancies in PNe around [WR] and $wels$ stars.
The majority of planetary nebulae (PNe) show axisymmetric morphologies, whose causes are not well understood. In this work, we present spatially resolved kinematic observations of 14 Galactic PNe surrounding Wolf-Rayet ([WR]) and weak emission-line stars ($wels$) based on the H$alpha$ and [N II] emission taken with the Wide Field Spectrograph on the ANU 2.3-m telescope. Velocity-resolved channel maps and position--velocity diagrams, together with archival Hubble Space Telescope ($HST$) and ground-based images, are employed to construct three-dimensional morpho-kinematic models of 12 objects using the program SHAPE. Our results indicate that these 12 PNe have elliptical morphologies with either open or closed outer ends. Kinematic maps also illustrate on-sky orientations of elliptically symmetric morphologies of the interior shells in NGC 6578 and NGC 6629, and the compact ($leq 6$ arcsec) PNe Pe1-1, M3-15, M1-25, Hen2-142, and NGC 6567, in agreement with the high-resolution $HST$ images containing morphological details. Point-symmetric knots in Hb4 exhibit deceleration with distance from the nebular center that could be due to shock collisions with the ambient medium. Velocity dispersion maps of Pe1-1 disclose point-symmetric knots similar to those in Hb4. Collimated outflows are also visible in the position--velocity diagrams of M3-30, M1-32, M3-15, and K2-16, which are reconstructed by tenuous prolate ellipsoids extending upwardly from thick toroidal shells in our models.
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