As mentioned in Sect. 2.3, we have found eight stars, in addition to HD
16955 and HD 204965 already discussed in Paper I, presenting a CS
component and we have used a relation proposed by Higurashi & Hirata
(1978) to derive the extension of the shell. This relation is:
where r/r* is the extension of the shell in stellar radius, the half-width at half-depth and j a parameter depending from the rotation law of the shell gas. In our case, keplerian rotation, j = 1/2.
We have applied it to the stars of our sample with a CS component, Table 4 (click here) showing the results of our calculations.
In addition to the stars of Table 4 (click here), we have found two stars for which the presence of a CS component is less marked: HD 39283 and HD 108283. On the basis of its photometric data HD 108283 is not a Bootis star but an Am or Ap star. No evidence has been found for a CS component in the case of HD 31295 and HD 110411, whereas Sturenburg (1993) finds a marginal CS component for both of these stars. For HD 110411, Holweger & Rentzsch-Holm (1995) find a very weak CS component.
The presence of a CS component in the stars of Table 4 (click here) is confirmed by some other studies. Andrillat et al. (1995) also find a CS component for HD 38545 and HD 217782. Furthermore, Sturenburg (1993) and Bohlender & Walker (1994) indicate the presence of a CS component for HD 38545. The fact that some authors find a CS component and others do not is perhaps due to a temporal variation of this CS component. In September 1993, we noticed such a CS component in the spectrum of HD 204965 and in October 1995 this component had disappeared.
Several of our programme stars display the sodium doublet. These stars are listed in Table 5 (click here), which includes some of their spectroscopic characteristics and the extension of the circumstellar shell, for which the relation of Higurashi & Hirata (1978) was used, as in the case of CaII-K. Five of the stars in Table 5 (click here) possess a CS component on the CaII-K line.
The 14 other stars observed in the NaID region do not display the NaID doublet, either because it is too weak or because it is completely masked by the telluric lines which overcrowd this spectral domain.
A comparison of the RVs of the CaII-K CS component (Table 4 (click here)) with the NaI doublet (Table 5 (click here)) reveals that they are always similar to each other. It may be assumed that these ions are associated in the expansion/contraction movement of the circumstellar shell. It is also noted that the absorption shell of NaI is inside that of CaII. Special mention is made of the sodium doublet of HD 225180, shown in Fig. 4 (click here). These lines are strong and all the lines of the optical spectrum possess a shell component. The NaI doublet presents a double structure in which a photospheric and a red-shift shell component may be identified. The shell component has an asymmetric background.
Figure 4: Spectrum of HD 225180 near the NaI doublet
The RVs of the points of inflexion on each blue edge are 1 (5890 Å) and (5896 Å) respectively. Close to the stellar continuum, at I = 0.96, the total width of each line is 83.2 and 77.7 and the RV line at this level is -21.0 and .
Finally, the velocity gradient along each line is +12.6 and +12.1 respectively, indicating a circumstellar movement towards the star (onfall).
|Na I 5890||Na I 5896|
|RV = radial velocity of the deepest point of the line|
|d = depth of the line, in unit of the continuum intensity (I = 1)|
|= width of the Na I D line at half-depth;|
|RV1/2 = radial velocity of the line at half-depth|
|W = equivalent width of the line (in mÅ)|
|r/r* = extension of the Na I circumstellar cloud, expressed in radii of the central star|
|The underlined stars are those which present a circumstellar absorption on the Ca II K photspheric|
|line (see Table 4 (click here)).|