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5. Discussion

5.1. Difference of tex2html_wrap_inline1731 between H8 and CaII-K lines

As noticed in Paper I, we may remark in some cases a difference between the radial velocity deduced from tex2html_wrap_inline2003 and that from CaII-K. Our sample is now sufficiently large to see clearly from the data of Table 3 (click here) that this is not a general property since nearly half of the sample does not exhibit such a gradient, including tex2html_wrap_inline1683 Boo itself. Moreover, no correlation has been found between the presence or absence of this gradient and one of the criteria, or suspected criteria, such as the IR excess or UV depression. However, as can be seen from Table 1 (click here), nearly all the stars studied are spectroscopic binaries or have a variable radial velocity. Thus we can assume that this difference is due to the binarity of these stars.

5.2. Variation of tex2html_wrap_inline1731 between two periods of observations

A variation of tex2html_wrap_inline1731 between two or more periods of observations could be an indication of binarity or of pulsation. There are too few measurements for a clear conclusion to be reached from our observations. We can only remark that of the six stars for which we have data in the same spectral regions at two or three epochs only one (HD 204965) exhibits a severe change of radial velocity in one year and one (HD 38545) a moderate change, while the other four (HD 31295, HD 34787, HD 210418 and HD 220061) are seen to undergo no, or only a small, change.

5.3. Difference of tex2html_wrap_inline1731 between the photospheric lines and the circumstellar lines

We can consider the difference of tex2html_wrap_inline1731 between the photospheric line and the circumstellar line for stars for which a circumstellar component has been detected on the CaII-K line. This difference may be interpreted as being the radial component of the circumstellar gas movement. This gradient is positive for the following stars, indicating a fall of the gas on the star: HD 2904, HD 16811. For the following stars the gradient is negative, indicating an expansion of the gas: HD 5789, HD 34787 (in 1994 and 1995), HD 141851, HD 161868, HD 217782. The gradient is slightly negative for HD 38545. Two stars of the 1993 mission that also show an onfall, HD 16955 and HD 204965, can be added to the first of the above-mentioned group.

5.4. Rotation velocities of tex2html_wrap_inline1683 Bootis stars with a CS component

Holweger & Rentzsch-Holm (1995) have shown that the tex2html_wrap_inline1683 Bootis stars with detectable CS gas are to be found preferably among rapid rotators. This is still true if we consider our results. With the exception of HD 204965 and HD 221756, all the stars of Table 4 (click here) possess tex2html_wrap_inline1789 values that are greater than 100 tex2html_wrap_inline2123. However, on the basis of their photometric data, these two stars cannot be considered to be tex2html_wrap_inline1683 Bootis stars. It may also be remarked that not all tex2html_wrap_inline1683 Bootis stars with a tex2html_wrap_inline1789 value in excess of 100 tex2html_wrap_inline2123 exhibit a CS component.

Holweger and Rentzsch-Holm thus conclude that tex2html_wrap_inline1789 is the prime factor responsible for the presence or absence of CS absorption in CaII-K. They also make the assumption that tex2html_wrap_inline1683 Bootis stars are pre- main-sequence objects that are still accreting material left over from the protostellar phase. Our discussion in 5.3 shows that it is difficult to confirm or rule out this assumption on the basis of the difference of tex2html_wrap_inline1727 between the photospheric lines and the circumstellar lines.

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