For this group and the other peculiarity groups we decided to present
the results graphically in such a way that the original a-values
rather than the 
values were used. Since the slope of the normality
line is a constant as described above we had only to choose a zero point
for the a-values, which we set to 0 for b-y=0.
Figure 2: a vs. b-y for CP2 stars
Figure 3: a vs. b-y for CP1 stars
Figure 4: a vs. b-y for CP3, CP4 and unidentified stars
Figure 2 (click here) exhibits the diagram a vs. b-y for the 24 stars of our
sample which according to Renson (1991) are CP2 stars, thus
magnetic peculiar stars of the upper main sequence. In order to show the
effect of Renson's grouping in 4 probability classes we have chosen
different symbols for them. We notice that all stars with at least 3
standard deviations above the normality line are in his categories "well
established" or "very probable". Only one star with question mark
is obviously significantly above the line: HD 204411 with =19, very
similar to the result of Maitzen & Seggewiss (1980) with
=16. The erroneous attribution of CP2 character for HD 118214 is
reflected by its completely normal photometric behaviour (=3).
Comparison with Maitzen (1976) is possible for three cases.
In the sense this work minus Maitzen (1976) the difference in
is: for HD 71866 +9 mmags, for HD 115708 0 mmags and for HD 118022
+3 mmags. Lebedev (1986) has 5 CP2 stars in his catalogue in
common with our sample for which the differences in are:
HD 90044 +22 mmags, HD 118022 +10 mmags, HD 120198 +1 mmags,
HD 196178
-1 mmags and HD 204411 +5 mmags.
The tendency of slightly larger values is expected by the fact that
the central wavelength of the g2 filter in our system has been
slightly shifted to the blue, thereby moving into the deeper part of
the 5200 A depression feature.
Comparison with Geneva photometry: in all cases where our values
indicate photometric non-peculiarity, we also find non-peculiar values of
the Geneva indices, i.e. for HD 86274 (?), 92728, 94334 (?), 115708 (*)
118214 (
), 196133 (?) (the signs in parentheses mark the probability
of peculiarity as given by Renson 1991). The photometric
evidence obviously supports the assessment of the Renson-catalogue, taking
into account that HD 115708 is a very late type CP2-star (for this type
only in very rare cases shows peculiar values).
Note on an individual object:
HD 210432 and HD 210433 form a visual binary, for which Renson
(1991) because of similar brightness concludes the impossibility to
assign peculiarity to one of both. Looking at our uvby and values we
are in favour of HD 210432 to be the CP2 star and HD 210433 to have
spectral type B9.5 V, contrary to Abt (1985) and also to the
entry in Renson (1991). HD 210433 has served as normal star in
our study for the definition of the normality line.
Figure 3 (click here) shows the diagram a vs. b-y for this group.
HD 196655 is outstanding
with = 34 mmags. Such a high value has never been observed for a metallic
line star. The classification as CP1 star rests on Bidelman
(1985) using objective prism spectra. We propose this object for
reobserving both spectroscopically and photometrically in order to decide
whether this star is CP1 or CP2. The same applies also to those
five stars which are in such a distance above the normality line that they would
be individually considered to be moderate CP2 stars if no other information
should be available: HD 107168, 116235, 196425, 204541 and 209845 with
= 18, 16, 17, 17 and 15, resp.
Only one star deviates significantly below the normality line: the 
Del
star HD 79066 with =-16 mmags.
Discarding the 6 cases of significant deviations above the normality line and those cases with question mark in the Renson-catalogue we arrive at the conclusion that the average deviation of CP1 stars above the normality line is less than one standard deviation from the mean of the group.
A note is due to the following CP1 star:
HD 209711=RNS 58360 has a published value, cited in Renson
(1991) m1=137 mmags. Considering the other Strömgren
parameters this would mean that the star is metal deficient, not Am as
listed in the Renson catalogue (A3-). Since this star exhibits the largest
difference between observed and published m1 by far, we tend to
assume that the correct value would be clearly larger than 200 mmags
and that perhaps 137 should be replaced by 237.
Our 8 stars are very close to the normality line in Fig. 4 (click here) with
one exception:
HD 196821 which has = 14 mmags, and thus is just at the threshold of
peculiarity in this index. This means that at such low levels of
photometric peculiarity one has to be careful to assign the star to
the CP2 group as well as in the case of CP1 stars with similar values.
Spectroscopy has also to be improved in order to establish the final type.
The slightly trend towards positive values for the CP3 stars of
our sample is in good agreement with the results of North
(1984).
We should add a note here concerning values for three CP3 stars of
our sample common to the catalogue of Lebedev (1986): for
HD 77350, 78316 and 89822 he derived (from spectrophotometric scans) =
18, 15, 16, resp. while our photometry yields 1, 1, 6, resp. It would be
interesting to find out the reason for the peculiarity of Lebedev's
synthetic values.
Including one He strong star
HD 209339 in this grouping we notice that
only one of those 5 stars has a peculiar =31: HD 79158
(Fig. 4 (click here)) and therefore may be considered as magnetic peculiar star.
This group consists of 6 stars and is characterized by the fact that
from the spectral type in the Renson catalogue it is not possible
to derive any conclusion why those stars have received an entry
in the catalogue. Our values are neutral concerning this question,
since all stars are close to the normality line.