5 Line parameters

Having a set of reliable parameters characterizing a given spectral line is of importance for the understanding of the physical conditions in the region where the line is formed. The following parameters were computed for the emission lines presented in this work: line to continuum ratio at emission line peak and velocity at which it occurs ( $v_{\rm peak}$), full width at half maximum (FWHM), half width at zero intensity (HWZI), maximum velocities observed in the line wings ( $v_{\rm blue}$ and $v_{\rm red}$), equivalent width (EW) and Asymmetry Factor (Af). The HWZI was computed from $v_{\rm blue}$ and $v_{\rm red}$ which were calculated at the 2% level of the the peak intensity. The name "HWZI'' is therefore slightly misleading since, in reality, the width was not computed at zero intensity. However, "HWZI'' will be used throughout this work. The Af is defined as the ratio of the line equivalent width blueward of the zero velocity to the line equivalent width redward of the zero velocity.

  

 

Table 5: Br ${\rm\gamma }$ inverse P Cygni line profiles - Equivalent widths of the emission and of the absorption (measured below the continuum) component, central velocity of the absorption feature and line to continuum ratio (L/C) at the bottom of the absorption feature

Star	$EW_{\rm emission}$	$EW_{\rm absorption}$	$V_{\rm abs}$	L/C
	( ${\rm km\ s}^{-1}$)	( ${\rm km\ s}^{-1}$)	( ${\rm km\ s}^{-1}$)
BM And	$-9.3\pm0.4$	$8.4\pm0.2$	60	0.94
CW Tau	$-31.2\pm0.2$	$4.3\pm0.1$	160	0.96
DF Tau	$-18.2\pm0.2$	$3.3\pm0.1$	120	0.98
HP Tau	$-24.8\pm0.2$	$11.5\pm0.1$	185	0.92
RW Aur	$-109.0\pm0.3$	$5.6\pm0.1$	275	0.96

A method devised to measure these parameters and to estimate the associated uncertainties is described in Folha (1998).

5.1 Line parameters: Results

The results obtained for the T Tauri stars' Pa ${\rm\beta }$ and Br ${\rm\gamma }$ line parameters are presented in Tables 4 to 7. Tables 6 and 7 show results of parameters specific to type IV R line profiles, such as the EW of the emission and absorption components, the central velocity of the redshifted absorption feature and the line-to-continuum ratio at the bottom of the absorption. Before proceeding, a point should be made about the impact of the wavelength calibration uncertainties in some of the parameters presented in Tables 4 and 5. Those uncertainties, presented in column 3 of those tables, affect mostly the values of $v_{\rm peak}$ and Af. The uncertainties quoted in Tables 4 and 5 for $v_{\rm peak}$ are often similar to or smaller than the wavelength calibration uncertainty. The uncertainty quoted for Af in Tables 4 and 5 results only from the noise in the spectrum. There is, however, an uncertainty in the zero velocity that results from the wavelength calibration. Such an uncertainty is propagated into Af via $EW_{\rm blue}$ and $EW_{\rm red}$. The final relative uncertainty in Af can be of the order of a few tenths. These two points should be kept in mind in the remainder of this paper.