The Clumpy Environment of Pre-Main Sequence Stars

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Session 44 -- Young Stars, T Tauri Stars, Herbig Haro Objects
Display presentation, Wednesday, 1, 1994, 9:20-6:30

[44.07] The Clumpy Environment of Pre-Main Sequence Stars

J.A. Graham (CIW-DTM)

Spectra of the pre-main sequence stars R CrA and S CrA show signatures of circumstellar material which change on night-to-night time scales. Observations are reported which were made during week-long runs at Las Campanas Observatory over the years 1990$-$1993. Correlations between emission and absorption line intensities are examined. Features originating in (a) the photosphere and the chromosphere; (b) circumstellar disk-like shells; (c) outflowing winds; are identified. In the wavelength range studied between 4900 and 9000 angstroms, the underlying photospheric spectrum is only rarely glimpsed in R CrA but is seen more frequently (i.e. at least once a week) in S CrA. Although the photospheric spectral types are as late as A5 in R CrA and G8$-$K2 in S CrA, broad helium lines are enduring features of the spectra. It is proposed that they are excited by UV photons generated by material falling onto the inner circumstellar disks. The material infall is indicated by red-shifted circumstellar absorption lines, principally those of He I, Na I, Si II, and O I. Despite discomfort expressed by the theoretical community, there is strong evidence to support clumpiness in the circumstellar material on scales of the order of stellar diameters. As R CrA changes in brightness, the absolute intensities of the [O I] and [S II] lines remain much the same. If, as seems likely, some of the optical variability is caused by circumstellar obscuring clouds, the clouds probably lie inside the region where the forbidden lines are formed. However, the detailed profiles of the forbidden lines do vary with time and lend support to the inhomogeneous wind structures proposed by Grinin and Mitskevich (Astr.Sp.Sci. 185, 107, 1991).

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