Circumstellar CO J = 3→2 detected around the evolving metal-poor ([Fe/H] ≈ -1.15 dex) AGB star RU Vulpeculae
Abstract
We report the first detection of CO J = 3→2 around a truly metal-poor evolved star. RU Vulpeculae is modelled to have Teff ≈ 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) Al2O3 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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- January 2020
- DOI:
- 10.1093/mnras/stz3009
- arXiv:
- arXiv:1910.10464
- Bibcode:
- 2020MNRAS.491.1174M
- Keywords:
-
- stars: AGB and post-AGB;
- circumstellar matter;
- stars: mass-loss;
- stars: winds;
- outflows;
- infrared: stars;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- Accepted MNRAS, 16 pages, 7 figures