Discovery of the Fomalhaut C debris disc

G. M. Kennedy , M. C. Wyatt , P. Kalas , G. Duchêne (1) , B. Sibthorpe , J. -F. Lestrade (2) , B. C. Matthews , J. Greaves

1 IPAG - Institut de Planétologie et d'Astrophysique de Grenoble
2 Observatoire de Paris

Fomalhaut is one of the most interesting and well-studied nearby stars, hosting at least one planet, a spectacular debris ring and two distant low-mass stellar companions (TW PsA and LP 876-10, a.k.a. Fomalhaut B and C). We observed both companions with Herschel, and while no disc was detected around the secondary, TW PsA, we have discovered the second debris disc in the Fomalhaut system, around LP 876-10. This detection is only the second case of two debris discs seen in a multiple system, both of which are relatively wide (≳3000 au for HD 223352/40 and 158 kau [0.77 pc] for Fomalhaut/LP 876-10). The disc is cool (24 K) and relatively bright, with a fractional luminosity L_disc/L_⋆ = 1.2 × 10^-4, and represents the rare observation of a debris disc around an M dwarf. Further work should attempt to find if the presence of two discs in the Fomalhaut system is coincidental, perhaps simply due to the relatively young system age of 440 Myr, or if the stellar components have dynamically interacted and the system is even more complex than it currently appears.

Keywords: binaries: general; circumstellar matter; stars: individual: AT Mic; stars: individual: Fomalhaut; stars: individual: LP 876-10; stars: individual: TW PsA

Domains: Sciences of the Universe [physics]; Astrophysics [astro-ph]

G. M. Kennedy, M. C. Wyatt, P. Kalas, G. Duchêne, B. Sibthorpe, et al.. Discovery of the Fomalhaut C debris disc. Monthly Notices of the Royal Astronomical Society: Letters, 2014, 438, pp.L96-L100. ⟨10.1093/mnrasl/slt168⟩. ⟨insu-03618602⟩