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For Classical T Tauri Stars (CTTSs), the resonance lines of N V, Si IV, and C IV, as well as the He II 1640 A line, act as diagnostics of the accretion process. Here we assemble a large high-resolution dataset of these lines in CTTSs and Weak T Tauri Stars (WTTSs). We present data for 35 stars: one Herbig Ae star, 28 CTTSs, and 6 WTTSs. We decompose the C IV and He II lines into broad and narrow Gaussian components (BC & NC). The most common (50 %) C IV line morphology in CTTSs is that of a low-velocity NC together with a redshifted BC. The velocity centroids of the BCs and NCs are such that V_BC > 4 * V_NC, consistent with the predictions of the accretion shock model, in at most 12 out of 22 CTTSs. We do not find evidence of the post-shock becoming buried in the stellar photosphere due to the pressure of the accretion flow. The He II CTTSs lines are generally symmetric and narrow, less redshifted than the CTTSs C IV lines, by ~10 km/sec. The flux in the BC of the He II line is small compared to that of the C IV line, consistent with models of the pre-shock column emission. The observations are consistent with the presence of multiple accretion columns with different densities or with accretion models that predict a slow-moving, low-density region in the periphery of the accretion column. For HN Tau A and RW Aur A, most of the C IV line is blueshifted suggesting that the C IV emission is produced by shocks within outflow jets. In our sample, the Herbig Ae star DX Cha is the only object for which we find a P-Cygni profile in the C IV line, which argues for the presence of a hot (10^5 K) wind. For the overall sample, the Si IV and N V line luminosities are correlated with the C IV line luminosities, although the relationship between Si IV and C IV shows large scatter about a linear relationship and suggests that TW Hya, V4046 Sgr, AA Tau, DF Tau, GM Aur, and V1190 Sco are silicon-poor., Accepted in the ApJSS. 52 pages, 9 tables, 20 figures

Ratios of emission probabilities of rotational lines of the Lyman and Werner band systems, B 1∑+u →X 1∑+g and C 1∏u →X1∑+g, respectively, are calculated by different methods. These theoretical ratios are compared to the experimental intensity ratios of about a hundred lines selected from a vacuum ultraviolet emission spectrum whose intensity is investigated for the first time at high resolution. The computation permits to compare two ways of solving a system of two coupled equations with discrete eigenvalues. In most cases the effect of the mutual rotational perturbation between B and C states is found significant on the ratio of P and R line intensities. Ambiguity in labeling a few B and C levels is discussed.

We calculate free‐bound two‐dimensional Franck‐Condon factors for a molecule HXD with constant angle HXD. We assume separability into normal modes, but the normal modes are different for the attractive and the repulsive potential surfaces. These Franck‐Condon factors can be related to the linewidth of a predissociated level and to the relative probability of dissociation into the channel H+XD or the channel D+XH. Classically, we can predict that the Franck‐Condon factor will be a maximum as a function of energy if one of the turning points (for vibration in the bound state) happens to be on the repulsive surface at that energy; furthermore, the location of this turning point on the repulsive surface determines the isotope effect, which can be favorable to either D+XH or H+XD. Our two‐dimensional study of the O‐ν and ν‐0 levels shows that these classical predictions are correct, in contrast to the results obtained using a one‐dimensional model; in the latter case, strong enhancement of the Franck‐Condon factors can occur through interference effects that cannot be predicted classically; interference effects do not show up in the two‐dimensional calculation. For the 3–3, 2–2, and 3–2 levels, classical predictions are in rough agreement with the calculations, but we observe strong enhancement of the Franck‐Condon factors for certain relative positions of the two surfaces. In conclusion, interference effects do exist for two‐dimensional Franck‐Condon factors, though they disappear for 0‐ν and ν‐0 levels.