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Session 40 - The Environment of Stars: From Protostars to the Main Sequence.
Display session, Tuesday, June 11
The use of low resolution optical spectra in determining spectral and luminosity classes of T Tauri stars in the Orion Nebula Cluster is investigated. The most accurate means of locating stars on H-R diagrams typically uses multicolor photometry to determine apparent magnitudes (e.g. V mag) and colors (e.g. B-V). However, colors can be significantly affected by interstellar and circumstellar reddening. Hence, observed colors cannot be relied on to derive effective temperatures for T Tauri stars which are frequently embedded in circumstellar disks. In the case of unknown reddening effects, the more accurate, however less precise method for determining effective temperatures and luminosities of T Tauri stars is to classify their optical spectra, a method often used for stars subject to intrinsic reddening effects. We present low resolution spectra of a well-defined sample of T Tauri stars selected from the magnitude-limited CCD survey of variable stars in the Orion Nebula Cluster conducted by Attridge and Herbst (1992 ApJL 398, L61). The spectra were obtained at the Steward Observatory 2.3-m telescope during the 1993/1994 and 1995 observing seasons. Some stars were observed during both seasons and comparisons of their spectra are made. A comparison between the spectral types we determine for these T Tauri stars with those determined by Edwards et al. (1993 AJ 106, 372) shows a systematic difference of several spectral sub classes. An investigation of spectral types of pre-main sequence stars and the effects of spectral classification errors on statistical studies of T Tauri stars is presented.
Program listing for Tuesday