Spectroscopic Study of IRAS 19285+0517 (PDS 100): A Rapidly Rotating Li-rich K Giant

We report on photometry and high-resolution spectroscopy for IRAS 19285+0517. The spectral energy distribution based on visible and near-infrared photometry and far-infrared fluxes shows that the star is surrounded by dust at a temperature of Td ∼ 250 K. Spectral line analysis shows that the star is a K giant with a projected rotational velocity of v sin i = 9 ± 2 km s-1. We determined the atmospheric parameters: Teff = 4500 K, log g = 2.5, ξt = 1.5 km s-1, and [Fe/H] = 0.14 dex. The LTE abundance analysis shows that the star is Li-rich [log ϵ(Li) = 2.5 ± 0.15], but with essentially normal C, N, O, and metal abundances. Spectral synthesis of molecular CN lines yields the carbon isotopic ratio 12C/13C = 9 ± 3, a signature of post–main-sequence evolution and dredge-up on the red giant branch (RGB). Analysis of the Li resonance line at 6707 Å for different 6Li/7Li ratios shows that the Li profile can be best fitted with a predicted profile for pure 7Li. Far-infrared excess, high Li abundance, and rapid rotation suggest that a planet has been swallowed or, perhaps, that an instability in the RGB outer layers triggered a sudden enrichment of Li and caused mass loss.