6 The short-period orbit

Lines of the component B1 of the eclipsing pair (which is the brighter, but less massive and cooler component) can always be recognized, however reliable velocities can only be obtained in phase ranges during which the lines are clearly separated from the A line and not affected by the CCD defect. These cases are compiled in Table 3. The resulting values of the semi-amplitude $K_{\rm B1}$ and systemic velocity $\gamma _{\rm B1}$could be rather accurately determined as:

$$K_{\rm B1} = 259.7 \pm 2.0\, {\rm km\,s}^{-1}, \ \gamma_{\rm B1} = +1.7\, {\rm km\,s}^{-1}.$$

In two cases (spectra ECH 12 and ECH 19) also tentative radial velocities of the secondary component were derived. Unfortunately, the positions of the fainter B2 lines, which are certainly present as deformations of the A line, are very difficult to measure. Note that in some cases, the integral profiles can even hardly be interpreted under our general assumptions: it happens that the depth of the 4922 line blend differs much from the expected values for certain phases, and also the O II 4925 line contribution must occasionally have changed its depth. From its general appearance one might expect that spectrum CAT 3 may yield a good value of the B2 velocity, but it turned out that the line component was too weak at this epoch to provide a reliable velocity value.

 

 

Table 3: Radial velocities of B components

Spectrum	Phase	$V_{\rm B1}$(kms-1)	$V_{\rm B2}$(kms-1)
ECH 2	0.2304	262
ECH 3	0.2402	251
ECH 4	0.2502	261
ECH 12	0.2453	263	-219
CAT 3	0.2419	269
ECH 14	0.6064	-195
ECH 15	0.7441	-258
ECH 16	0.7516	-257
ECH 17	0.7763	-248
ECH 19	0.7293	-271	83
CAT 6	0.7549	-251

Figure 6: Examples of profiles of the He II 4686 line. The dotted curves indicate the expected photospheric profiles, see text. The line at bottom center corresponds to the $\gamma _{\rm B1}$ velocity

As already noted above, the line He II 4686 is strongly variable. For instance in one spectrum the line is clearly in emission (ECH 15), in another spectrum taken only one hour later (ECH 16) the profile does not rise above continuum at all, see Fig. 6. The photospheric profiles of He II 4686 are expected to be similar in shape (albeit of different depth) to those of He I 4922. As illustration, Fig. 6 depicts a few of such profiles; their depth has been decreased such that they fit that part of the line wing, which is not affected by emission. The width of the emission profiles is quite large. It is therefore suggested that the emission is not originating within a possible disk around the B1 component, but comes from a region closer to the B system mass center - e.g. from the L₁point. Accordingly, it can be anticipated that no emission is present in spectra taken at phases near eclipse minima.