FG SAGITTAE - A NEWBORN R-CORONAE-BOREALIS STAR

We have monitored FG Sge's spectroscopic changes since the time just p rior to its dramatic fading in 1992 August. The most significant quali tative changes in the spectrum include large variations in the strengt h of the C-2 molecular bands and the gradual appearance of broad blues hifted high-velocity (similar to 200 km s(-1) relative to the photosph ere) absorption components of the Na I D lines. During the deep minima of 1994 May and 1996 June, an emission-line spectrum temporarily appe ared superimposed on a weak continuum; in addition to the previously r eported nebular emission lines, the spectra displayed the C-2 and rare earth element lines in emission. Much of the behavior exhibited by FG Sge since 1992 resembles that seen in R CrB stars, including the phot ometric behavior, the evolution of the Na I D line profiles, variation s of the C, band strengths, and the appearance of narrow emission line s. The results of our abundance analysis (using model atmospheres with a solar He/H ratio) indicate that the carbon abundance is currently g reater than that determined by Langer et al., who reported on the dram atic increase in the abundances of the rare earth elements in FG Sge. We derive higher relative abundances of the rare earths ([Me/Fe] simil ar to 3) than either Langer et al. or Kipper & Kipper, which we attrib ute to some enhancement of these elements since similar to 1970. We co nfirm previous claims that the relative scandium abundance is high ([S c/Fe] similar to 1) in FG Sge and suggest that it is the result of neu tron captures by the light elements leading up to Sc-45. The H alpha p rofile of FG Sge is very similar to that of V854 Cen, a R CrB star def icient in H by 2-3 dex. This is the first evidence pointing toward H-d eficiency in the atmosphere of FG Sge, which further strengthens its l ink with the R CrB class. Additional study is required before we can s ay definitively whether or not its atmosphere is H deficient.