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Register a new userDust in the Wolf-Rayet Nebula M1-67
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Added by
Palmira Jim\\'enez-Hern\\'andez
Publication date
2020
fields
Physics
and research's language is
English
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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.
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The Wolf-Rayet (WR) nebula NGC3199 has been suggested to be a bow shock around its central star WR18, presumably a runaway star, because optical images of the nebula show a dominating arc of emission south-west of the star. We present the XMM-Newton detection of extended X-ray emission from NGC3199, unveiling the powerful effect of the fast wind from WR18. The X-ray emission is brighter in the region south-east of the star and analysis of the spectral properties of the X-ray emission reveals abundance variations: i) regions close to the optical arc present nitrogen-rich gas enhanced by the stellar wind from WR18 and ii) gas at the eastern region exhibits abundances close to those reported for nebular abundances derived from optical studies, signature of an efficient mixing of the nebular material with the stellar wind. The dominant plasma temperature and electron density are estimated to be $Tapprox1.2times$10$^{6}$ K and $n_mathrm{e}$=0.3 cm$^{-3}$ with an X-ray luminosity in the 0.3-3.0 keV energy range of $L_mathrm{X}$=2.6$times$10$^{34}$ erg s$^{-1}$. Combined with information derived from Herschel and the recent Gaia first data release, we conclude that WR18 is not a runaway star and the formation, chemical variations, and shape of NGC3199 depend on the initial configuration of the interstellar medium.
We present a comprehensive infrared (IR) study of the iconic Wolf-Rayet (WR) wind-blown bubble NGC6888 around WR136. We use Wide-field Infrared Survey Explorer (WISE), Spitzer IRAC and MIPS and Herschel PACS IR images to produce a sharp view of the distribution of dust around WR136. We complement these IR photometric observations with Spitzer IRS spectra in the 5-38 $mu$m wavelength range. The unprecedented high-resolution IR images allowed us to produce a clean spectral energy distribution, free of contamination from material along the line of sight, to model the properties of the dust in NGC6888. We use the spectral synthesis code Cloudy to produce a model for NGC6888 that consistently reproduces its optical and IR properties. Our best model requires a double distribution with the inner shell composed only of gas, whilst the outer shell requires a mix of gas and dust. The dust consists of two populations of grain sizes, one with small sized grains $a_mathrm{small}$=[0.002-0.008] $mu$m and another one with large sized grains $a_mathrm{big}$=[0.05-0.5] $mu$m. The population of big grains is similar to that reported for other red supergiants stars and dominates the total dust mass, which leads us to suggest that the current mass of NGC6888 is purely due to material ejected from WR136, with a negligible contribution of swept up interstellar medium. The total mass of this model is 25.5$^{+4.7}_{-2.8}$ M$_{odot}$, a dust mass of $M_mathrm{dust}=$0.14$^{+0.03}_{-0.01}$ M$_{odot}$, for a dust-to-gas ratio of $5.6times10^{-3}$. Accordingly, we suggest that the initial stellar mass of WR136 was $lesssim$50 M$_{odot}$, consistent with current single stellar evolution models.
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).
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.
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.
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