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

Abstract

We report on photometry and high-resolution spectroscopy for IRAS 19285+0517. The spectral energy distribution based on visible and near-IR photometry and far-IR fluxes shows that the star is surrounded by dust at a temperature of $T_{\mathrm{d}}$ $\sim$ 250 K. Spectral line analysis shows that the star is a K giant with a projected rotational velocity $vsini$ = 9 $\pm$ 2 km s${}^{-1}$. We determined the atmospheric parameters: $T_{\mathrm{eff}}$ = 4500 K, log $g$ = 2.5, ${\xi }_t$ = 1.5 km s${}^{-1}$, and [Fe/H] = 0.14 dex. The LTE abundance analysis shows that the star is Li-rich (log $\epsilon$(Li) = 2.5$\pm$0.15), but with essentially normal C, N, and O, and metal abundances. Spectral synthesis of molecular CN lines yields the carbon isotopic ratio ${}^{12}$C/${}^{13}$C = 9 $\pm$3, a signature of post-main sequence evolution and dredge-up on the RGB. Analysis of the Li resonance line at 6707 Åfor different ratios ${}^6$Li/${}^7$Li shows that the Li profile can be fitted best with a predicted profile for pure ${}^7$Li. Far-IR excess, large 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.

To appear in AJ; 40 pages, 9 figures

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