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Register a new userResolving Decades of Periodic Spirals from the Wolf-Rayet Dust Factory WR 112
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WR 112 is a dust-forming carbon-rich Wolf-Rayet (WC) binary with a dusty circumstellar nebula that exhibits a complex asymmetric morphology, which traces the orbital motion and dust formation in the colliding winds of the central binary. Unraveling the complicated circumstellar dust emission around WR 112 therefore provides an opportunity to understand the dust formation process in colliding-wind WC binaries. In this work, we present a multi-epoch analysis of the circumstellar dust around WR 112 using seven high spatial resolution (FWHM $sim0.3-0.4$) N-band ($lambda sim12$ $mu$m) imaging observations spanning almost 20 years and includes newly obtained images from Subaru/COMICS in Oct 2019. In contrast to previous interpretations of a face-on spiral morphology, we observe clear evidence of proper motion of the circumstellar dust around WR 112 consistent with a nearly edge-on spiral with a $theta_s=55^circ$ half-opening angle and a $sim20$-yr period. The revised near edge-on geometry of WR 112 reconciles previous observations of highly variable non-thermal radio emission that was inconsistent with a face-on geometry. We estimate a revised distance to WR 112 of $d = 3.39^{+0.89}_{-0.84}$ kpc based on the observed dust expansion rate and a spectroscopically derived WC terminal wind velocity of $v_infty= 1230pm260$ km s$^{-1}$. With the newly derived WR 112 parameters we fit optically-thin dust spectral energy distribution models and determine a dust production rate of $dot{M}_d=2.7^{+1.0}_{-1.3}times10^{-6}$ M$_odot$ yr$^{-1}$, which demonstrates that WR 112 is one of the most prolific dust-making WC systems known.
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We present high spatial resolution mid-infrared images of the nebula around the late-type carbon-rich Wolf-Rayet (WC)-OB binary system WR~112 taken by the recently upgraded VLT spectrometer and imager for the mid-infrared (VISIR) with the PAH1, NeII_2, and Q3 filters. The observations reveal a morphology resembling a series of arc-like filaments and broken shells. Dust temperatures and masses are derived for each of the identified filamentary structures, which exhibit temperatures ranging from $179_{-6}^{+8}$ K at the exterior W2 filament to $355_{-25}^{+37}$ K in the central 3. The total dust mass summed over the features is $2.6pm0.4times10^{-5}$ $mathrm{M}_odot$. A multi-epoch analysis of mid-IR photometry of WR~112 over the past $sim20$ yr reveals no significant variability in the observed dust temperature and mass. The morphology of the mid-IR dust emission from WR~112 also exhibits no significant expansion from imaging data taken in 2001, 2007, and 2016, which disputes the current interpretation of the nebula as a high expansion velocity ($sim1200$ km s$^{-1}$) pinwheel-shaped outflow driven by the central WC-OB colliding-wind binary. An upper limit of $lesssim120$ km s$^{-1}$ is derived for the expansion velocity assuming a distance of $4.15$ kpc. The upper limit on the average total mass-loss rate from the central 3 of WR~112 is estimated to be $lesssim8times10^{-6}$ $mathrm{M}_odot$ yr$^{-1}$. We leave its true nature as an open question, but propose that the WR~112 nebula may have formed in the outflow during a previous red or yellow supergiant phase of the central Wolf-Rayet star.
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.
We present a dust spectral energy distribution (SED) and binary stellar population analysis revisiting the dust production rates (DPRs) in the winds of carbon-rich Wolf-Rayet (WC) binaries and their impact on galactic dust budgets. DustEM SED models of 19 Galactic WC ``dustars reveal DPRs of $dot{M}_dsim10^{-10}-10^{-6}$ M$_odot$ yr$^{-1}$ and carbon dust condensation fractions, $chi_C$, between $0.002 - 40%$. A large ($0.1 - 1.0$ $mu$m) dust grain size composition is favored for efficient dustars where $chi_Cgtrsim1%$. Results for dustars with known orbital periods verify a power-law relation between $chi_C$, orbital period, WC mass-loss rate, and wind velocity consistent with predictions from theoretical models of dust formation in colliding-wind binaries. We incorporated dust production into Binary Population and Spectral Synthesis (BPASS) models to analyze dust production rates from WC dustars, asymptotic giant branch stars (AGBs), red supergiants (RSGs), and core-collapse supernovae (SNe). BPASS models assuming constant star formation (SF) and a co-eval $10^6$ M$_odot$ stellar population were performed at low, Large Magellanic Cloud (LMC)-like, and solar metallicities (Z = 0.001, 0.008, and 0.020). Both constant SF and co-eval models show that SNe are net dust destroyers at all metallicities. Constant SF models at LMC-like metallicities show that AGB stars slightly outproduce WC binaries and RSGs by factors of $2-3$, whereas at solar metallicites WC binaries are the dominant source of dust for $sim60$ Myr until the onset of AGBs, which match the dust input of WC binaries. Co-eval population models show that for bursty SF, AGB stars dominate dust production at late times ($tgtrsim 70$ Myr).
The Wolf-Rayet (WR) phenomenon is widespread in astronomy. It involves classical WRs, very massive stars (VMS), WR central stars of planetary nebula CSPN [WRs], and supernovae (SNe). But what is the root cause for a certain type of object to turn into an emission-line star? In this contribution, I discuss the basic aspects of radiation-driven winds that might reveal the ultimate difference between WR stars and canonical O-type stars. I discuss the aspects of (i) self-enrichment via CNO elements, (ii) high effective temperatures Teff, (iii) an increase in the helium abundance Y, and finally (iv) the Eddington factor Gamma. Over the last couple of years, we have made a breakthrough in our understanding of Gamma-dependent mass loss, which will have far-reaching consequences for the evolution and fate of the most massive stars in the Universe. Finally, I discuss the prospects for studies of the WR phenomenon in the highest redshift Ly-alpha and He II emitting galaxies.
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.
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