**Table 1:** Characteristics of the sample of T Tauri stars, sorted by H $\alpha$ emission, for which high resolution X-ray spectra have been analyzed. In the case of resolved multiple systems the stellar mass, spectral type, and bolometric luminosity refer to the component responsible for the X-ray emission.
Name	Mass	Spectral	EW(H $\alpha$ )^a	$L_{\rm X}^{b}$	$\log (L_{\rm X}^{b}/L_{\rm bol})$	$N_{\rm e}^{c}$	References^d
	( $M_{\odot}$ )	type	(Å)	${\rm (erg~s^{-1})}$		${\rm (cm^{-3})}$
TW Hya	$\sim$ 0.7	K7	-220.0	$1.3\times10^{30}$	-2.7	$\sim$ 10¹³	1, 2, 3, 4
TWA 5	$\sim$ 0.5	M1.5	-13.4	$6.7\times10^{29}$	-3.1	<10¹¹	2, 5, 6
HD 98800	$\sim$ 1.1	K5	0.0	$4.1\times10^{29}$	-3.8	$\la$ 10¹¹	2, 7, 8
PZ Tel	$\sim$ 1.1	K0	0.1	$2.2\times10^{30}$	-3.2	<10¹²	9, 10, 11
HD 283572	$\sim$ 1.8	G5	1.1	$7.8\times10^{30}$	-3.1	$\cdot\cdot\cdot$	12, 13, 14

^a Negative values of H $\alpha$ equivalent width mark an emission line. ^b X-ray luminosity evaluated in the 6-20 Å band, using the XMM/MOS or Chandra/HETGS best fit models presented in the relevant papers. ^c Densities estimated from the O VII and Ne IX triplets. ^d Data from: (1) Batalha et al. (2002); (2) Reid (2003); (3) Stelzer & Schmitt (2004); (4) Kastner et al. (2002); (5) this work; (6) Jensen et al. (1998); (7) Kastner et al. (2004); (8) Prato et al. (2001); (9) Cutispoto et al. (2002); (10) Thatcher & Robinson (1993); (11) Argiroffi et al. (2004); (12) Strassmeier & Rice (1998); (13) Fernandez & Miranda (1998); (14) Scelsi et al. (2005).

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