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3. Photometric data

Data for Table 1 (click here) are taken from the Geneva Database maintained by G. Burki. B2-V1 is a temperature parameter, d a luminosity parameter, tex2html_wrap_inline1805 a blanketing parameter and tex2html_wrap_inline1807 a parameter sensitive to luminosity and blanketing. Before using B2-V1 to determine tex2html_wrap_inline1809, we have to consider if the stars are reddened. For this we can first of all use the Strömgren photometry and then the code developed by Künzli et al. (1997). Only HD 225180 was detected as being reddened.

As regards a luminosity effect on B2-V1, Hauck (1985) has shown that as far as classes V to III are concerned the tex2html_wrap_inline1809 vs. B2-V1 relation is not influenced by luminosity effect. tex2html_wrap_inline1809 was derived from a relation between tex2html_wrap_inline1809 and B2-V1 (Hauck 1994). The precision of such a tex2html_wrap_inline1809 is of order of tex2html_wrap_inline2703. Hauck & Künzli (1996) have shown that the tex2html_wrap_inline1809 determined by the relation between tex2html_wrap_inline1809 and B2-V1 have an accurency of the same order as those determined by the code of Künzli et al. (1997), i.e. tex2html_wrap_inline2709. Since many tex2html_wrap_inline1683 Bootis stars have a high tex2html_wrap_inline1789 value it should be recalled that B2-V1 is affected by such high values (Hauck & Slettebak 1989). Stars with high tex2html_wrap_inline1789 values have too red a B2-V1 value. For A1 stars for instance, the mean B2-V1 value for tex2html_wrap_inline1789 values between 0 and 100 is 0.134 while it is -0.100 for tex2html_wrap_inline1789 values between 200 and 400. Thus for the latter stars the tex2html_wrap_inline1809 value given in Table 1 (click here) is only an estimate of the real tex2html_wrap_inline1809.

Since the tex2html_wrap_inline1683 Bootis stars are metal-deficient, it is interesting to use the properties of the Geneva system to consider whether the stars of our sample meet this assumption. tex2html_wrap_inline1805, the difference between tex2html_wrap_inline2731, is a blanketing parameter, well-correlated to [Fe/H] (Hauck 1978). Stars with a negative tex2html_wrap_inline1805 value have a lower [Fe/H] than the Hyades stars. According to tex2html_wrap_inline1805, the following stars are metal-deficient: HD 36496, HD 110377, HD 111604, HD 141851, a few others being only slightly metal-deficient (tex2html_wrap_inline2737).

Some other stars possess interesting photometric properties:

HD 108283 has a positive value of tex2html_wrap_inline1805 (of the same order as an Am or Ap star) and we may assume that this star does not belong to the tex2html_wrap_inline1683 Bootis group. It is mentioned as Sr? by Renson (1992), classified as A9 IVnp Sr II by Gray & Garrison (1989) but A9 Vp (tex2html_wrap_inline1683 Boo) by Abt & Morrell (1995). Jaschek et al. (1991) found a moderate shell for this star. We have also found shell components for the same star.

HD 47152 is a well-known Hg star (Osawa 1965) and this is confirmed by its positive value of the tex2html_wrap_inline2745 parameter.

HD 204965 has high d and tex2html_wrap_inline1807 values and thus in a d vs. tex2html_wrap_inline1807 diagram it is located in the region of luminosity class III stars. Iliev & Barzova (1995) have recently confirmed the assumption that tex2html_wrap_inline1683 Bootis stars are main-sequence stars. So we may wonder if HD 204965 belongs to the tex2html_wrap_inline1683 Bootis group. We can also reach the same conclusion for HD 225180, which is classified by Gray & Garrison (1987) as A1 II-III and this is confirmed by our d and tex2html_wrap_inline1807 parameters. This star is reddened, therefore we cannot derive a tex2html_wrap_inline1805 value.

Thus, on the basis of the photometric data, we can exclude these four stars from the tex2html_wrap_inline1683 Bootis group.

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