3 Results

In order to reinforce the assignments of peculiarity in Renson's catalogue, additional parameters for the intrinsic (chemically) peculiarity such as $\Delta a$ (Maitzen 1976) and $\Delta p$ (Masana et al. 1998) are presented. Unfortunately, $\Delta p$ is not as specific (for CP2 stars) as the $\Delta a$ index especially for stars later than A0. We have not included the Geneva peculiarity index $\Delta$(V1-G) because of its dependence on the interstellar reddening.

Six stars (HD 40312, HD 148112, HD 151965, HD 175362, HD 193722 and HD 219749) from Catalano & Renson (1997) have a period agreeing with HVA but the period quoted there from the literature does not agree with that of Catalano & Renson.

Furthermore we have identified eight possible members (HD 4058, HD 75202, HD 79781, HD 95321, HD 111709, HD 125081, HD 149420 and HD 167858) of the $\gamma$ Doradus stars (Breger & Beichbuchner 1996). The given spectral types and found periods are typical for this group of pulsating stars. But further observational efforts are needed to establish their true nature.

The following stars deserve further attention:
HD 4058: Budaj (1996) reported a period which is one day longer than that of the HVA.
HD 23848: The period extracted from literature in the HVA is not correct, Martin & Hube (1988) reported P=1.765346d.
HD 30466: according to the Photometric Notes and References of HVA the published period 1.3900 days taken from Rakosch & Fiedler (1978) does not fit the Hipparcos data. Vice versa the Rakosch & Fiedler data yield a nearly perfect scatter diagram when reduced with the Hipparcos period of 4.0779 days. This fact is supported by the data basis of Maitzen (1977) leading to a period (2.7795 d) not in accord with the HVA period. On the other hand Maitzen's period reveals a double wave light variation in agreement with the light curve of HVA. A possible cause for deriving a discordant period is the low degree of variability in the Hipparcos photometric band whereas the variability for hot CP2 stars is more pronounced in bluer bands where Rakosch & Fiedler, as well as Maitzen obtained their observations.
HD 74067: There seems to be a misclassification of the variability type (BCEP) in the HVA. Since this star is classified as A0CrSr in Renson (1991) we tend to believe that the variations are due to rotation.
HD 85037: Renson (1983) derived a period which is half the value from HVA.
HD 126515: There is practically unanimous agreement on a 130 days period of this outstanding magnetic star, based on published photometric, spectroscopic and magnetic field variations (see e.g. North & Adelman 1995). The HVA period of 3.16414 days yields a light curve with rather enhanced scatter and should be considered as artifact of the intrinsically long period together with a rather low level of variability in the photometric band of Hipparcos.
HD 145792: Cernicharo et al. (1985) used this star as (an a priori constant) comparison star for HD 145102 and HD 147010. They found periods of 1.69253 and 3.99827d, respectively. These results are probably influenced by the variability of HD 145792 and have to be reanalyzed.
HD 182255: This star is a single-lined spectroscopic binary system with a period of 367d. Hube & Aikman (1991) reported additional variations with an interval of 1.09d. This results is confirmed by HVA although the period is slightly longer.

The newly found rotation periods of stars with known vsini values (taken from Uesugi & Fukuda 1982, Abt & Morrell 1995 and Levato et al. 1996), were used (34 objects in total) to test the oblique rotator model. An implication of this model is that the relationship between the observed period and the apparent rotation can be estimated as (Preston 1971):

$$v = \frac{50.6\,R}{P}$$

where v is the equatorial rotational velocity, R is the stellar radius in solar units and P is the observed period in days. Since only the projected rotational velocity can be determined, all stars should fall below the given relation assuming a certain stellar radius. Figure 1 shows this relation for the selected 34 objects assuming R=3.2$R_{\hbox{$\odot$}}$.Only three stars (HD 88158, B8Si; HD 104810, B8Si and HD 151363, B9Si) seem to lie above the chosen upper limit. Taking into account that in reality there should be a certain spread in stellar radii we feel justified to state that this result fits nicely into the constraints of the oblique rotator model and therefore also supports the peculiar nature of these stars.

  

Figure 1: P vs. vsini for 34 CP stars. The open circle indicate stars with only upper values for vsini found in the literature

It is interesting to note that all 26 bona fide CP1 stars (beside the eight possible $\gamma$ Doradus candidates) are members of eclipsing binary systems and no other kind of variability was detected.

Acknowledgements

This research was carried out within the working group Asteroseismology-AMS with funding from the Fond zur Förderung der wissenschaftlichen Forschung (project S7303-AST). Use was made of the Simbad database, operated at CDS, Strasbourg, France.