Circumstellar CO J = 3→2 detected around the evolving metal-poor ([Fe/H] ≈ −1.15 dex) AGB star RU Vulpeculae. Issue 1 (30th October 2019)

• Record Type: Journal Article
• Authors: McDonald, I; Uttenthaler, S; Zijlstra, A A; Richards, A M S; Lagadec, E
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 491:Issue 1(2020)
• Page Start: 1174
• Page End: 1189
• Publication Date: 2019-10-30
• Subjects: stars: AGB and post-AGB -- circumstellar matter -- stars: mass-loss -- stars: winds, outflows -- infrared: stars; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stz3009
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: We report the first detection of CO J = 3→2 around a truly metal-poor evolved star. RU Vulpeculae is modelled to have T eff ≈ 3620 K, L ≈ 3128 ± 516 L⊙, log( g ) = 0.0 ± 0.2 dex and [Fe/H] = −1.3 to −1.0 dex, and is modelled to have recently undergone a thermal pulse. Its infrared flux has approximately doubled over 35 yr. ALMA observations show the 3→2 line is narrow (half-width ∼1.8–3.5 km s −1 ). The 2→1 line is much weaker: it is not confidently detected. Spectral-energy-distribution fitting indicates very little circumstellar absorption, despite its substantial mid-infrared emission. A VISIR mid-infrared spectrum shows features typical of previously observed metal-poor stars, dominated by a substantial infrared excess but with weak silicate and (possibly) Al2 O3 emission. A lack of resolved emission, combined with weak 2→1 emission, indicates the dense circumstellar material is truncated at large radii. We suggest that rapid dust condensation is occurring, but with an aspherical geometry (e.g. a disc or clumps) that does not obscure the star. We compare with T UMi, a similar star which is currently losing its dust.