Spectroscopy of RY Sagittarii during the 1993 minimum

Abstract

The R Coronae Borealis (RCB) star RY Sgr underwent a deep minimum (Delta(V) approximately 7m5) in 1993. Here medium and low resolution observations from approximately 35 days into the decline are presented together with photometry from the early phases until some 100 days thereafter. The spectra show sharp chromospheric emission lines of Fe, Ti II, Sc II, Ba II and Y II, as well as broad emission from Na D, He I, K and Mg I. In general the braod lines are stationary or slightly blueshifted relative to the star. An absorption feature in Na D2 corresponds to a radial velocity of -200 km/s. The helium line at 587.6 nm is surprisingly weak, which suggests high optical depths and electron densities. Strong emission bands due to Swan bands of C2 are found and two extended emission `bumps' around 390 nm and 590 nm still lack definite identification. I also present the first identified forbidden lines in RY Sgr and the first published detection of (Ca II) in a RCB star. Other lines are tentatively ascribed to (N II0) and (C I). Comparison of calcium line ratios indicates an electron density of approximately 109/cu cm, but it seems like at least two different regions emit the broad lines: a high density chromospheric environment and a much less dense nebula-like region.