Query : 1997A&A...321..492M

1997A&A...321..492M - Astronomy and Astrophysics, volume 321, 492-496 (1997/5-2)

Quantitative spectroscopic criteria for the classification of pre-main sequence low-mass stars.


Abstract (from CDS):

The discovery of hundreths of X-ray emitting stars possibly associated with pre-main sequence (PMS) low-mass stars far from molecular clouds, makes it necessary to adopt quantitative spectroscopic criteria for classifying them. T Tauri stars have young ages (<10Myr) and low masses (M<2M). As a consequence, it is shown that they must verify two spectroscopic conditions: (1) spectral type in the range K0-M6, and either (2a) strong emission lines and UV-optical-NIR continuum excesses, or (2b) weak-emission lines and a photospheric LiIλ670.8 absorption feature with a "minimum" equivalent width which depends on its spectral type. Classical T Tauris meet criteria (1) and (2a), while weak T Tauris (WTTS) meet criteria (1) and (2b). T Tauri stars occupy a different region in the Teff-WLiI diagramme than the low-mass members of young open clusters. Post T Tauri stars (PTTSs) later than about K2 can be clearly identified in the same diagramme because they fill an empty region (PTT-gap), intermediate between the T Tauris and the young cluster stars. The application of the spectroscopic criteria defined in this work to the PMS stars claimed to have been discovered in recent X-ray surveys of molecular clouds is hampered by the lack of high-resolution optical spectra for most of them. On the basis of the sparse and modest-resolution data that is available, the preliminary results indicate that the majority of these stars (∼60%) are not WTTSs. Only ∼25% of the non-WTTS X-ray discovered stars are clearly PTTSs according to this study. The PMS status of the remaining stars is dubious. It seems unlikely that the PTTSs indentified in X-ray surveys outnumber the T Tauri stars. Far away from molecular clouds, the number of WTTSs and PTTSs appear to decrease significantly.

Abstract Copyright:

Journal keyword(s): stars: pre-main sequence - fundamental parameters - X-rays: stars

Simbad objects: 3

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Number of rows : 3
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
1 IC 2391 OpC 08 41 10 -52 59.5           ~ 766 0
2 IC 2602 OpC 10 42 27 -64 25.6           ~ 611 0
3 IC 4665 OpC 17 46 13 +05 36.9           ~ 337 0

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