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Register a new userThe interplay between chemistry and nucleation in the formation of carbonaceous dust in supernova ejecta
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Davide Lazzati
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Core-collapse supernovae are considered to be important contributors to the primitive dust enrichment of the interstellar medium in the high-redshift universe. Theoretical models of dust formation in stellar explosions have so far provided controversial results and a generally poor fit to the observations of dust formation in local supernovae. We present a new methodology for the calculation of carbonaceous dust formation in young supernova remnants. Our new technique uses both the nucleation theory and a chemical reaction network to allow us to compute the dust growth beyond the molecular level as well as to consider chemical erosion of the forming grains. We find that carbonaceous dust forms efficiently in the core of the ejecta, but takes several years to condensate, longer than previously estimated. It forms unevenly and remains concentrated in the inner part of the remnant. These results support the role of core-collapse supernovae as dust factories and provide new insight on the observations of SN 1987A, in which large amounts of dust have been detected to form on a timescale of years after core collapse.
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We study the formation and destruction of molecules in the ejecta of Population III supernovae (SNe) using a chemical kinetic approach to follow the evolution of molecular abundances from day 100 to day 1000 after explosion. The chemical species included range from simple di-atomic molecules to more complex dust precursor species. All relevant chemical processes that are unique to the SN environment are considered. Our work focuses on zero-metallicity progenitors with masses of 20, 170, and 270 Msun, and we study the effect of different levels of heavy element mixing and the inward diffusion of hydrogen on the ejecta chemistry. We show that the ejecta chemistry does not reach a steady state within the relevant time-span for molecule formation. The primary species formed are O2, CO, SiS, and SO. The SiO, formed as early as 200 days after explosion, is rapidly depleted by the formation of silica molecular precursors in the ejecta. The rapid conversion of CO to C2 and its thermal fractionation at temperatures above 5000 K allow for the formation of carbon chains in the oxygen-rich zone of the unmixed models, providing an important pathway for the formation of carbon dust in hot environments where the C/O ratio is less than 1. We show that the fully-mixed ejecta of a 170 Msun progenitor synthesizes 11.3 Mun of molecules whereas 20 Msun and 270 Msun progenitors produce 0.78, and 3.2 Msun of molecules, respectively. The admixing of 10 % of hydrogen into the fully-mixed ejecta of the 170 Msun progenitor increases its molecular yield to ~ 47Msun. The unmixed ejecta of a 170 Msun progenitor supernova without hydrogen penetration synthesizes ~37 Msun of molecules, whereas its 20 Msun counterpart produces ~ 1.2 Msun. Finally, we discuss the cosmological implication of molecule formation by Pop. III SNe in the early universe.
Massive stars in their late stages of evolution as Red Supergiants experience mass loss. The resulting winds show various degrees of dynamical and chemical complexity and produce molecules and dust grains. This review summarises our knowledge of the molecular and dust components of the wind of Red Supergiants, including VY CMa and Betelgeuse. We discuss the synthesis of dust as a non-equilibrium process in stellar winds, and present the current knowledge of the chemistry involved in the formation of oxygen-rich dust such as silicates and metal oxides.
We present new Herschel photometric and spectroscopic observations of Supernova 1987A, carried out in 2012. Our dedicated photometric measurements provide new 70 micron data and improved imaging quality at 100 and 160 micron compared to previous observations in 2010. Our Herschel spectra show only weak CO line emission, and provide an upper limit for the 63 micron [O I] line flux, eliminating the possibility that line contaminations distort the previously estimated dust mass. The far-infrared spectral energy distribution (SED) is well fitted by thermal emission from cold dust. The newly measured 70 micron flux constrains the dust temperature, limiting it to nearly a single temperature. The far-infrared emission can be fitted by 0.5+-0.1 Msun of amorphous carbon, about a factor of two larger than the current nucleosynthetic mass prediction for carbon. The observation of SiO molecules at early and late phases suggests that silicates may also have formed and we could fit the SED with a combination of 0.3 Msun of amorphous carbon and 0.5 Msun of silicates, totalling 0.8 Msun of dust. Our analysis thus supports the presence of a large dust reservoir in the ejecta of SN 1987A. The inferred dust mass suggests that supernovae can be an important source of dust in the interstellar medium, from local to high-redshift galaxies.
We study the formation of dust in the expanding gas ejected as a result of a common envelope binary interaction. In our novel approach, we apply the dust formation model of Nozawa et al. to the outputs of the 3D hydrodynamic SPH simulation performed by Iaconi et al., that involves a giant of 0.88~ms and 83~rs, with a companion of 0.6~ms placed on the surface of the giant in circular orbit. After simulating the dynamic in-spiral phase we follow the expansion of the ejecta for $simeq 18,000$~days. During this period the gas is able to cool down enough to reach dust formation temperatures. Our results show that dust forms efficiently in the window between $simeq 300$~days (the end of the dynamic in-spiral) and $simeq 5000$~days. The dust forms in two separate populations; an outer one in the material ejected during the first few orbits of the companion inside the primarys envelope and an inner one in the rest of the ejected material. We are able to fit the grain size distribution at the end of the simulation with a double power law. The slope of the power law for smaller grains is flatter than that for larger grains, creating a knee-shaped distribution. The power law indexes are however different from the classical values determined for the interstellar medium. We also estimate that the contribution to cosmic dust by common envelope events is not negligible and comparable to that of novae and supernovae.
In order to understand the contribution of core-collapse supernovae to the dust budget of the early universe, it is important to understand not only the mass of dust that can form in core-collapse supernovae but also the location and rate of dust formation. SN 2005ip is of particular interest since dust has been inferred to have formed in both the ejecta and the post-shock region behind the radiative reverse shock. We have collated eight optical archival spectra that span the lifetime of SN 2005ip and we additionally present a new X-shooter optical-near-IR spectrum of SN 2005ip at 4075d post-discovery. Using the Monte Carlo line transfer code DAMOCLES, we have modelled the blueshifted broad and intermediate width H$alpha$, H$beta$ and He I lines from 48d to 4075d post-discovery using an ejecta dust model. We find that dust in the ejecta can account for the asymmetries observed in the broad and intermediate width H$alpha$, H$beta$ and He I line profiles at all epochs and that it is not necessary to invoke post-shock dust formation to explain the blueshifting observed in the intermediate width post-shock lines. Using a Bayesian approach, we have determined the evolution of the ejecta dust mass in SN 2005ip over 10 years presuming an ejecta dust model, with an increasing dust mass from ~10$^{-8}$ M$_{odot}$ at 48d to a current dust mass of $sim$0.1 M$_{odot}$.
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