The origin of T tauri X-ray emission: New insights from the chandra orion ultradeep project

Thomas Preibisch, Yong Cheol Kim, Fabio Favata, Eric D. Feigelson, Ettore Flaccomio, Konstantin Getman, Giusi Micela, Salvatore Sciortino, Keivan Stassun, Beate Stelzer, Hans Zinnecker

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Abstract

The Chandra Orion Ultradeep Project (COUP) provides the most comprehensive data set ever acquired on the X-ray emission of pre-main-sequence stars. In this paper, we study the nearly 600 X-ray sources that can be reliably identified with optically well-characterized T Tauri stars (TTSs) in the Orion Nebula Cluster. With a detection limit of L X, min ∼ 10 27.3 ergs s -1 for lightly absorbed sources, we detect X-ray emission from more than 97% of the optically visible late-type (spectral types F-M) cluster stars. This proves that there is no "X-ray-quiet" population of late-type stars with suppressed magnetic activity. We use this exceptional optical, infrared, and X-ray data set to study the dependencies of the X-ray properties on other stellar parameters. All TTSs with known rotation periods lie in the saturated or supersaturated regime of the relation between activity and Rossby numbers seen for main-sequence (MS) stars, but the TTSs show a much larger scatter in X-ray activity than that seen for the MS stars. Strong near-linear relations between X-ray luminosities, bolometric luminosities, and mass are present. We also find that the fractional X-ray luminosity L X/L bol rises slowly with mass over the 0.1-2 M range. The plasma temperatures determined from the X-ray spectra of the TTSs are much hotter than in MS stars but seem to follow a general solar-stellar correlation between plasma temperature and activity level. The scatter about the relations between X-ray activity and stellar parameters is larger than the expected effects of X-ray variability, uncertainties in the variables, and unresolved binaries. This large scatter seems to be related to the influence of accretion on the X-ray emission. While the X-ray activity of the nonaccreting TTSs is consistent with that of rapidly rotating MS stars, the accreting stars are less X-ray active (by a factor of ∼2-3 on average) and produce much less well-defined correlations than the nonaccretors. We discuss possible reasons for the suppression of X-ray emission by accretion and the implications of our findings on long-standing questions related to the origin of the X-ray emission from young stars, considering in particular the location of the X-ray-emitting structures and inferences for pre-main-sequence magnetic dynamos.

Original languageEnglish (US)
Pages (from-to)401-422
Number of pages22
JournalAstrophysical Journal, Supplement Series
Volume160
Issue number2
DOIs
StatePublished - Oct 1 2005

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Preibisch, T., Kim, Y. C., Favata, F., Feigelson, E. D., Flaccomio, E., Getman, K., Micela, G., Sciortino, S., Stassun, K., Stelzer, B., & Zinnecker, H. (2005). The origin of T tauri X-ray emission: New insights from the chandra orion ultradeep project. Astrophysical Journal, Supplement Series, 160(2), 401-422. https://doi.org/10.1086/432891