Spectroscopic Study of IRAS 19285+0517 (PDS 100): A Rapidly Rotating L[CLC]i[/CLC]-rich K Giant

We report on photometry and high-resolution spectroscopy for IRAS 19285+0517.The spectral energy distribution based on visible and near-IR photometry andfar-IR fluxes shows that the star is surrounded by dust at a temperature of$T_{\rm {d}}$ $\sim$ 250 K. Spectral line analysis shows that the star is a Kgiant with a projected rotational velocity $v sin i$ = 9 $\pm$ 2 km s$^{-1}$.We determined the atmospheric parameters: $T_{\rm {eff}}$ = 4500 K, log $g$ =2.5, $\xi_{t}$ = 1.5 km s$^{-1}$, and [Fe/H] = 0.14 dex. The LTE abundanceanalysis shows that the star is Li-rich (log $\epsilon$(Li) = 2.5$\pm$0.15),but with essentially normal C, N, and O, and metal abundances. Spectralsynthesis of molecular CN lines yields the carbon isotopic ratio$^{12}$C/$^{13}$C = 9 $\pm$3, a signature of post-main sequence evolution anddredge-up on the RGB. Analysis of the Li resonance line at 6707 \AA fordifferent ratios $^{6}$Li/$^{7}$Li shows that the Li profile can be fitted bestwith 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, thatan instability in the RGB outer layers triggered a sudden enrichment of Li andcaused mass-loss.Comment: To appear in AJ; 40 pages, 9 figure