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\IBVShead{4175}{23 March 1995}
 
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\ft PHOTOMETRIC EXAMINATION OF CP2-PECULIARITY FOR \\
 HD\,200405, HR\,44, HR\,7752  and HR\,9092 
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In the course of a programme aimed at checking spectroscopic peculiarity
assignments of chemically peculiar stars on the upper main sequence
belonging to group CP2 (in older terms: the $\alpha^{2}$ CVn variables)
we have chosen the above stars for 3 runs at the L. Figl Observatory
(Univ. of Vienna) on the summit of Sch\"opfl 
using its 60cm photometric telescope
equipped with a classical one-channel photoelectric photometer
(photomultiplier: EMI 9844A, Peltier-cooled). Observer was AS.

The filter system employed is that of $\Delta a$
(Maitzen, 1976) which has been shown to identify CP2 stars as effectively
as classification spectroscopy (Maitzen and Vogt, 1983).
Details on the filters $g1$ and $g2$ were given in
Maitzen and Floquet (1981), the third filter is a conventional
Str\"oemgren system filter $y$.

Measurements for this programme were obtained on August 5/6,
August 9/10 and October 15/16, 1994. 10 stars were chosen to
define the normality line of the index $a (=g2-(g1+y)/2)$ versus
the colour index $b-y$, the deviation of which has been defined
as $\Delta a$-value. A measurement series for a programme star
consisted of 8-12 repeats of the sequence $g1,g2,y$ each 
covering 15 seconds of integration. The resulting mean error for
the HR-stars was 2-3 millimags in $a$, and 3-4 millimags in $g1-y$.
Only for the relatively faint HD\,200405 the error was 3-4 millimags
in $a$ and 4-5 millimags in $g1-y$.

We have taken the $b-y$-values from Hauck and Mermilliod (1990),
but no such value seems to have been published for the peculiarity candidate
HD 200405. Since a very good correlation between $b-y$ and the colour difference
$g1-y$ had been found on previous occasions, we made use of it also in
the present case. Fig.~1 shows this correlation with  a slope of
0.51.
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Figure 1. Correlation between $g1-y$ and $b-y$ (both in mmags). Candidates for peculiarity are represented by open circles. 
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Figure 2. Peculiarity index $a$ vs. $b-y$ (both in mmags). Open circles are for 
measurements of CP2 candidates. Full line is the locus of normal stars. 
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From this correlation a value $b-y=0.013$ can be inferred
for HD\,200405. Even  considering an error of 0.020 mag of this
value, this will only very marginally influence the resulting $\Delta a$-value.
The relationship $a$ vs. $b-y$ is displayed in Fig.~2. A regression
curve yields \par
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\centerline{$a=-144+0.12(b-y)- 0.0002(b-y)^2$}
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\noindent with a scatter of only 2.28 millimags for the normal stars.
Table 1 gives the results of our $\Delta a$-system measurements
individually for the 3 nights, expressed in millimags.
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RESULTS AND DISCUSSION: 

{\bf 1. HD\,200405 = Renson (1991) Catalogue (=RE) 55830.}

North (1994) has shown that this binary has the shortest orbital 
period (1.63 days) known among those which host a CP2 star. Although
he reports a $\Delta(V1-G)=0.021$ indicating a CP2 star photometrically,
North (private communication) asked for an independent confirmation
of this result. Without any doubt
we can give this confirmation based on our photometry:

\noindent our $\Delta a$-values (36, 43, 34 millimags, obtained on
JD 2449/570.513,574.553,641.374, resp.) classify the pertaining component
as medium strong peculiar star with a slight indication that it may be
variable. Variability should not be very pronounced according to the
orbital analysis of North (1994) since the star seems to be seen nearly
pole-on. Future observations may help to get more insight into this
very special example of a binary containing a CP2-star whose characteristics
are obviously preserved despite the important tidal forces exerted by
the nearby companion (North, 1994).

{\bf 2. HR\,44 = RE\,150}

Cowley et al. (1969) have classified this star A1V Si:. This prompted
Floquet (1975) to reobserve this object and she derived A0III for this star.
Our $\Delta a$-result (obtained on JD 2449641.434)
is in agreement with a non-peculiar star.

{\bf 3. HR\,7752 = RE\,53850}
 
Osawa (1959) classified this star B9.5Vp with the remark that the K-line
is as strong as in A1 and that He I 4026 is visible. Floquet (1970),
however, classifies this object as normal A0V star which is in agreement
with our completely normal $\Delta a$-values (obtained on JD
 2449/570.398 and 574.395). 
 
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Table 1. $\Delta a$-photometry 
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    \begin{tabular}{|lr|rrr|rrr|rrr|}     \hline
    Object & $b-y$ & &$a$  & & &$\Delta a$  & && $g1-y$  &   \\
        \hline
        \hline
HD\,200405 &  13 & $-$107 &$-$100 &$-$110 & 36 & 43 & 34 & $-$3 & $-$5 &  0 \\
HR\,44     &  $-$3 &      &     &$-$148 &    &    &$-$4 &    &    &$-$12 \\
HR\,7752   &  $-$4 & $-$145 &$-$145 &     & $-$1 & $-$1 &    &$-$19 &$-$15 &   \\
HR\,9092   &  98 &      &     &$-$134 &    &    &  0 &    &    & 46 \\
\hline
HR\,68     &  26 &      &     &$-$141 &    &    &  0 &    &    &  0 \\
HR\,70     & $-$33 &      &     &$-$151 &    &    & $-$3 &    &    &$-$11 \\
HR\,114    & 169 &      &     &$-$129 &    &    &  0 &    &    & 82 \\
HR\,7253   & 176 &      &$-$130 &     &    & $-$1 &    &    & 89 &    \\
HR\,7453   & 146 & $-$133 &$-$132 &     & $-$2 & $-$1 &    & 70 & 65 &    \\
HR\,7756   & 281 & $-$127 &$-$129 &     & $-$1 & $-$3 &    &129 &138 &    \\
HR\,7769   &  13 & $-$144 &$-$143 &     & $-$2 & $-$1 &    & $-$6 & $-$5 &    \\
HR\,7792   & $-$17 & $-$142 &$-$147 &$-$144 & 4 & $-$1 &2 & $-$9 &$-$12 &$-$12 \\
HR\,7826   &  31 &      &$-$139 &     &    &  2 &    &    &  8 &    \\
HR\,8463   &  76 & $-$133 &$-$132 &$-$133 &  3 &  4 &  3 & 37 & 29 & 35 \\
 \hline
  \end{tabular}
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{\bf 4. HR\,9092 = HD\,224995}
 
Contrary to the preceding three stars this object is not contained in
the Renson catalogue of Ap and Am stars. It has been included in our
programme because $\Delta a$-photometry of Vogt et al. (1995) exhibited
a marginally peculiar value (0.015 mags). 

Except for the observation of Hauck (1986) that HR\,9092 is one of
22 stars classified as dwarfs in the Bright Star Catalogue, but which have
the same Geneva colours as giants, this star does not show a
peculiar behaviour, and lacks CP2 characteristics. Our photometric
value has been obtained on JD 2449641.418.       

As a summary we arrive at the conclusion that only HD\,200405 is
photometrically a CP2-star. Because of its special nature as member of a
close binary system  it deserves further observations. The other three
stars are normal in our photometry.

This research has made use of the Simbad database, operated
at CDS, Strasbourg, France.
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\beginauthors
\authorsrightcol
A. SCHNELL
H. M. MAITZEN
Institut f\"ur Astronomie
Universit\"at Wien
T\"urkenschanzstr. 17, A-1180 Wien
maitzen@astro.ast.univie.ac.at               %email

\endauthors


\references

Cowley, A.P., Cowley, C.R., Jaschek, M., Jaschek,C.: 1969, {\it AJ}, {\bf 74}, 375 

Floquet, M.: 1970, {\it A\&AS}, {\bf 1}, 1 

Floquet, M.: 1975, {\it A\&AS}, {\bf 21}, 25  

Hauck, B.: 1986, {\it A\&A}, {\bf 155}, 371 

Hauck, B., Mermilliod, J.C.: 1990, {\it A\&AS}, {\bf 86}, 107 

Maitzen, H.M.: 1976, {\it A\&A}, {\bf 52}, 223 

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Maitzen, H.M., Floquet, M.: 1981, {\it A\&A}, {\bf 100}, 3 

Maitzen, H.M., Vogt, N.: 1983, {\it A\&A}, {\bf 123}, 48 

North, P.: 1994, in: The 25th Workshop and Meeting of 
       European Working Group on CP Stars, eds.: I. Jankovics, I.J. Vincze,
       ELTE Gothard Astrophysical Observatory, Szombathely, p.~3 

Osawa, K.: 1959, {\it ApJ}, {\bf 130}, 159 

Renson, P.: 1991, Catalogue G\'en\'eral des Etoiles Ap et Am, Institut d'
       Astrophysique, Universit\'e de Li\`ege 

Vogt, N., Kerschbaum, F., Maitzen, H.M.: 1995, {\it A\&A} submitted

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