Synthesis of C-rich dust in CO nova outbursts

¹ Departament de Física, EUETIB, Universitat Politècnica de Catalunya, c/Comte d’Urgell 187, 08036 Barcelona, Spain
e-mail: jordi.jose@upc.edu
² Institut d’Estudis Espacials de Catalunya, c/Gran Capità 2−4, Ed. Nexus-201, 08034 Barcelona, Spain
³ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁴ Department of Physics, American University of Beirut, Bliss St. 11-0236, 1107 2020 Beirut, Lebanon

Received: 11 May 2016
Accepted: 15 June 2016

Abstract

Context. Classical novae are thermonuclear explosions that take place in the envelopes of accreting white dwarfs in stellar binary systems. The material transferred onto the white dwarf piles up under degenerate conditions, driving a thermonuclear runaway. In these outbursts, about 10^-7−10^-3 M_⊙, enriched in CNO and sometimes other intermediate-mass elements (e.g., Ne, Na, Mg, or Al for ONe novae) are ejected into the interstellar medium. The large concentrations of metals spectroscopically inferred in the nova ejecta reveal that the solar-like material transferred from the secondary mixes with the outermost layers of the underlying white dwarf.

Aims. Most theoretical models of nova outbursts reported to date yield, on average, outflows characterized by O > C, from which, in principle, only oxidized condensates (e.g., O-rich grains) would be expected.

Methods. To specifically address whether CO novae can actually produce C-rich dust, six different hydrodynamic nova models have been evolved, from accretion to the expansion and ejection stages, with different choices for the composition of the substrate with which the solar-like accreted material mixes. Updated chemical profiles inside the H-exhausted core have been used, based on stellar evolution calculations for a progenitor of 8 M_⊙ through H- and He-burning phases.

Results. We show that these profiles lead to C-rich ejecta after the nova outburst. This extends the possible contribution of novae to the inventory of presolar grains identified in meteorites, particularly in a number of carbonaceous phases (i.e., nanodiamonds, silicon carbides, and graphites).