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, a blanketing parameter and a parameter sensitive to luminosity and blanketing. Before using B2-V1 to determine , 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 vs. B2-V1 relation is not influenced by luminosity effect. was derived from a relation between and B2-V1 (Hauck 1994). The precision of such a is of order of . Hauck & Künzli (1996) have shown that the determined by the relation between and B2-V1 have an accurency of the same order as those determined by the code of Künzli et al. (1997), i.e. . Since many Bootis stars have a high value it should be recalled that B2-V1 is affected by such high values (Hauck & Slettebak 1989). Stars with high values have too red a B2-V1 value. For A1 stars for instance, the mean B2-V1 value for values between 0 and 100 is 0.134 while it is -0.100 for values between 200 and 400. Thus for the latter stars the value given in Table 1 (click here) is only an estimate of the real .
Since the 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. , the difference between , is a blanketing parameter, well-correlated to [Fe/H] (Hauck 1978). Stars with a negative value have a lower [Fe/H] than the Hyades stars. According to , the following stars are metal-deficient: HD 36496, HD 110377, HD 111604, HD 141851, a few others being only slightly metal-deficient ().
Some other stars possess interesting photometric properties:
HD 108283 has a positive value of (of the same order as an Am or Ap star) and we may assume that this star does not belong to the Bootis group. It is mentioned as Sr? by Renson (1992), classified as A9 IVnp Sr II by Gray & Garrison (1989) but A9 Vp ( 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 parameter.
HD 204965 has high d and values and thus in a d vs. diagram it is located in the region of luminosity class III stars. Iliev & Barzova (1995) have recently confirmed the assumption that Bootis stars are main-sequence stars. So we may wonder if HD 204965 belongs to the 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 parameters. This star is reddened, therefore we cannot derive a value.
Thus, on the basis of the photometric data, we can exclude these four stars from the Bootis group.