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The double dust envelopes of R Coronae Borealis stars

Montiel, E.J., Clayton, G.C., Sugerman, B. E. K., Evans, A., Garcia-Hernandez, D. A., Kameswara, R. N., Matsuura, Mikako and Tisserand, P. 2018. The double dust envelopes of R Coronae Borealis stars. Astronomical Journal 156 (4) 10.3847/1538-3881/aad772

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Abstract

The existence of extended, cold dust envelopes surrounding R Coronae Borealis (RCB) stars has been known about for over 30 years. RCB stars are an exotic group of extremely hydrogen-deficient, carbonrich supergiants that are known for their spectacular declines in brightness (up to 8 mags) at irregular intervals. There are three possible origins of these envelopes: (1) they are fossil planetary nebulae (PNe), indicating that RCB stars formed via a final Helium-shell flash; (2) they are the remnant material from the merger of a CO and a He white dwarf binary, (3) they have been constructed from dust ejection events during the current phase of the central stars. In the first scenario we expect to find the shell H–rich, while in the remaining two scenarios the shell is H–poor. We have examined new and archival Spitzer Space Telescope and Herschel Space Observatory images in the mid/far infrared and submillimeter of these envelopes to examine the morphology of these dusty shells. Herschel has, in particular, has revealed the first ever bow shock associated with an RCB star with its observations of SU Tauri. These new data have allowed the assembly of the most comprehensive spectral energy distributions (SEDs) of these stars with multi–wavelength data from the ultraviolet to the submillimeter. Radiative transfer modeling of the SEDs implies that the RCB stars in this sample are surrounded by an inner warm (up to 1,200 K) and an outer cold (up to 200 K) envelope. The outer shells are suggested to contain up to 10−3 M� of dust and have existed for up to 105 yr depending on the expansion rate of the dust. This age limit indicates that these structures have most likely been formed during the RCB phase.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Subjects: Q Science > QB Astronomy
Publisher: Institute of Physics
ISSN: 0004-6256
Date of First Compliant Deposit: 2 August 2018
Date of Acceptance: 30 July 2018
Last Modified: 20 Oct 2019 15:26
URI: http://orca.cf.ac.uk/id/eprint/113861

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