The Narrow Emission Lines of T Tauri Stars

Abstract

view Abstract Citations (58) References (36) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Narrow Emission Lines of T Tauri Stars Batalha, C. C. ; Stout-Batalha, N. M. ; Basri, G. ; Terra, M. A. O. Abstract We present the first comprehensive study of the narrow emission lines of T Tauri stars (TTS). These narrow lines have been reported in the literature as originating in the stellar atmosphere and having Gaussian-type profiles centered at the stellar rest velocity, with a base width not larger than 50 km s-1. Here, we concentrate on the Ca II lines λλ8498, 8542, and 8662 and the helium line λ5876. After applying veiling corrections, the average narrow component line emission is found to be larger than that found in active main-sequence stars: up to several times larger for classical T Tauri stars with strong rates of disk accretion. More striking is the finding that the resulting line emission strengths of these lines correlate with veiling. The correlation is confirmed on individual stars for which observations at several epochs exist and for which veiling varies widely on relatively short timescales. We also find a correlation between the narrow emission fluxes and the near-infrared excesses for stars with low levels of veiling, which includes the few weak-lined TTS of the sample. We discuss possible formation sites for the narrow emission lines in the classical TTS, and we present simple models to explain the observations. In these models, the excess line emission found for the stars with higher accretion rates is assumed to originate in localized regions near the magnetic footpoints of the accretion column. We refer to these hypothetical regions in the atmosphere collectively as the "hot chromosphere" since we assume they are additionally heated by the reprocessed energy of the colliding gas in the accretion process. Computing two chromospheric models, one representing the typical weak TTS chromosphere and the other representing the best guess at the "hot chromosphere," we find the following. The "hot chromosphere" is characterized by a steep temperature gradient beginning at low continuum optical depths in order to give simultaneously the large observed central flux and the relatively narrow baselines (50-60 km s-1). The chromosphere temperature rise is not similar to the earlier deep chromosphere models in which a sudden chromospheric temperature rise is appended to the photosphere at relatively large mass column. For the most extreme cases (i.e., largest line fluxes), 20%, at most, of the star's surface must be covered by "hot chromospheric" regions. Publication: The Astrophysical Journal Supplement Series Pub Date: March 1996 DOI: 10.1086/192275 Bibcode: 1996ApJS..103..211B Keywords: LINE: PROFILES; STARS: CHROMOSPHERES; STARS: EMISSION-LINE; BE; STARS: PRE-MAIN-SEQUENCE full text sources ADS | data products SIMBAD (28)