Another look at the UBV variability of T Tauri stars

Details Another look at the UBV variability of T Tauri stars Another look at the UBV variability of T Tauri stars

May 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...444..818s&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 444, no. 2, p. 818-830

Astronomy and Astrophysics

Astronomy

9

Infrared Astronomy, Periodic Variations, Stellar Color, Stellar Models, Stellar Rotation, T Tauri Stars, Balmer Series, Emission Spectra, Light Curve, Spectral Signatures, Stellar Spectrophotometry, Time Dependence

Scientific paper

The UBV variability of classical T Tauri stars is investigated using a large data set compiled by Herbst et al. (1994). The analysis is based on the covariance of the UBV colors, which is independent of the obscuration and the temporal sampling, and is a powerful tool for finding trends that otherwise would be hidden in the complex time-dependence of the data. I find that there are two types of UBV variability and introduce the nomenclature 'ortho-' and 'para-UBV' variations, or in short 'type-O' and 'type-P' variations. Objects with a predominance of ortho-UBV variability show strong variability in both the Balmer and Paschen continua, whereas objects dominated by para-UBV changes vary mostly in the Paschen continuum. I show that type-O variations can be explained in terms of rotating spots, variable obscuration, or changes intrinsic to the source that obey the law Delta TS/TS varies as Delta nH/nH, where TS and nH are, respectively, the gas temperature and the number density of hydrogen nuclei. Type-P variations can be explained only by changes intrinsic to the source with Delta TS/TS varies as - Delta nH/nH, and I speculate on a possible origin for these changes. The covariance ellipse of the UBV colors is a versatile tool for studying the connection between variability and other spectral signatures of classical T Tauri stars; its use for this purpose is illustrated by studying the correlation between the presence of CO first-overtone bands in emission and the type of variability. I find that objects with CO band emission are also those with type-P variability and propose an observational test to validate this conclusion.

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