Abstract
Abstract 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 Ldisc/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.
Highlights
Fomalhaut is perhaps the most interesting nearby stellar and planetary system outside our own
The Herschel (Pilbratt et al 2010)1 DEBRIS Key Programme observed an unbiased sample of nearby stars with the goal of discovering and characterizing the extrasolar Kuiper belt analogues known as ‘debris discs’ around hundreds of nearby stars (e.g. Matthews et al 2010)
The sample comprises the nearest ∼90 each of A, F, G, K and M spectral types that are not confused by proximity to the Galactic plane (Phillips et al 2010), and includes TW PsA and LP 876−10
Summary
Fomalhaut is perhaps the most interesting nearby stellar and planetary system outside our own. At only a few dozen light years from Earth, this remarkable system provides a unique laboratory in which to observe one outcome of star and planet formation in detail (see Kalas et al 2013; Mamajek et al 2013, for reviews of the Fomalhaut planetary and stellar systems). 445 445 721 1345 a debris disc and at least one planet, this detection of yet another planetary system component is exciting. We describe the Herschel observations and describe some basic properties of the debris disc around LP 876−10 and quantify the non-detection of debris around TW PsA, noting some possible implications of this discovery for the overall system status and evolution
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