The Type IV R Line Profiles

Figures 5.14 and 5.15 show the Pa Beta and Br Gamma emission lines classified as Type IV R.

  
Figure 5.14: Pa Beta Type IV R line profiles. Emission lines are ordered by L/C at line peak, starting with the strongest emission line.

  
Figure 5.15: Br Gamma Type IV R line profiles. Emission lines are ordered by L/C at line peak, starting with the strongest emission line.

Type IV R line profiles correspond to inverse P Cygni (IPC) profiles. By the very nature of IPC profiles, the extent of the blue wing in these lines is obviously larger than the extent of the red wing. Like for the other profile types, the blue wing reaches a typical velocity of -300 km/s for Pa Beta and -350 km/s for Br Gamma (median of the distributions) whereas the corresponding velocities for the red wing are only +100 km/s for Pa Beta and +50 km/s for Br Gamma. This can be seen in figure 5.16, where the histograms of these quantities are shown.

  
Figure 5.16: Histogram of the maximum velocities seen in the Pa Beta and Br Gamma line wings for Type IV R line profiles. The top panel shows the Pa Beta and Br Gamma data for the blue wing while the lower panel shows the data for the red wing. Pa Beta data is represented by solid line and Br Gamma data by a dotted line.

Plotting the histograms for the velocity at which the line peak occurs (see Figure 5.17) one sees that while the Pa Beta Type IV R line profiles tend to peak near the rest velocity of the star or slightly to the blue, the Br Gamma Type IV R lines tend to peak slightly blueward of the zero velocity but also at higher blueshifted velocities (~ 80 km/s).

  
Figure 5.17: Histogram of velocity of the Pa Beta and Br Gamma emission peaks for Type IV R line profiles. The top panel shows the Pa Beta data and the bottom panel the Br Gamma data. The dotted line on the bottom panel represents the histogram of the velocity of the Pa Beta line peak considering only the same stars that display Type IV R at Br Gamma .

The number of Br Gamma profiles classified as Type IV R is only 6 (cf. to the 14 found at Pa Beta) and it could be that those stars show, independently of the type of profile displayed, lines with higher blueshifts. In order to check that, the histogram for the velocity of the peak of the Pa Beta emission lines for the same stars is over plotted on the lower panel of Figure 5.17. Note that at Pa Beta these stars show various types of line profiles, not necessarily Type IV R profiles. As can be seen from this graph, a systematic bias towards higher blueshifts does not seem to be present for this sample of stars. One therefore concludes that Br Gamma Type IV R line profiles indeed tend to peak at higher blueshifted velocities than Type IV R Pa Beta lines. This shift is discussed in Section 5.4.2 below.

The distribution of the FWHM of the Type IV R line profiles is slightly different from the distribution considering all line profiles. About 60% of the Type IV R have FWHM between 160 km/s and 220 km/s. Just a few profiles of Type IV R display widths larger than 220 km/s. This difference, when compared to the Type I line profiles, was expected and results from the fact that the red wing of Type IV R suffers strongly from absorption.

One expects the redshifted absorption in Type IV R profiles to imply the Assymmetry Factors in these lines to be, on average, larger than those of the more symmetric Type I line profiles. In fact, the median of the distribution of Af moves from near 1.2 for the Type I profiles to 1.8 for the Type IV R profiles. Af's as large as 4 are observed.