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\IBVShead{4488}{6 June 1997}

\title{PHOTOELECTRIC OBSERVATIONS FOR TWO MISCLASSIFIED}
\vspace{-0.35in}
\title{VARIABLES: AF CRUCIS AND CG SAGITTARII ARE NOT CEPHEIDS}

\begintext

The present note addresses the status of two stars that are identified as Cepheid variables
in the fourth edition of the {\it General Catalogue of Variable Stars}: AF Crucis
and CG Sagittarii.

Grayzeck (1978a) found the star AF Cru to be a Cepheid variable with the elements:

\vskip 1mm
\centerline{Max JD$_{hel}$ = 2441786.576 + 9.297 $\times$ E.}
\vskip 1mm

\noindent
Its $V$ magnitude was found to vary in brightness between 9.75 and 10.10
(Grayzeck 1978b). However, the shape of its light curve is very asymmetric,
which is unusual for a classical Cepheid of that period.

Gerasimovic (1927) found CG Sgr, discovered previously by Bailey (1924), to be a
long-period Cepheid variable with the elements:

\vskip 1mm
\centerline{Max JD = 2414127 + 64.1 $\times$ E.}
\vskip 1mm
\noindent

In order to examine the light curves of both stars in greater detail, we observed them
photoelectrically at the South African Astronomical Observatory in April-May 1997
using the 50-cm telescope. A total of 29 $VR_c$ measurements were obtained for
AF Cru (Table 1), and a total of 43 $V(RI)_c$ measurements were obtained for
CG Sgr (Table 2), the accuracy of the individual data being near $\pm 0\fm01$ in all
filters.

It is readily seen that our observations for CF Cru do not satisfy the elements given by
Grayzeck and that the star appears not to be varying. A search of the literature
revealed that AF Cru was discovered by Uitterdijk (1936) as an eclipsing
variable with the elements:

\vskip 1mm
\centerline{Min JD$_{hel}$ = 2424988.959 + 1.895669 $\times$ E,}
\vskip 1mm

\noindent
and a short eclipse duration of $D=0\fp 06$. Figure 1 illustrates that our
observations do not conflict with Uitterdijk's elements. Our data suggest
that AF Cru is indeed an eclipsing variable, although we have no
measurements near the times of eclipses.

Regarding Grayzeck's (1978b) observations, they do not satisfy Uitterdijk's
elements. Our attempts to find a new period using both the present and Grayzeck's
observations were unsuccessful.

During the observing run for CG Sgr it was found that the star's brightness varied
on a time scale of hours not days, in direct conflict with the elements of
Gerasimovic. Although the light amplitude is comparable to that of certain RR Lyrae
and $\delta$ Scuti variables, the time scale of variability appears to be too small for
an object of the RR Lyrae class. It appears that CG Sgr may be a $\delta$ Sct star.
Our attempts to find new elements for it were unsuccessful.

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\centerline{2}
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\centerline{Figure 1}
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\centerline{Table 1. VR$_c$ observations of AF Cru}
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\begin{center}
\begin{tabular}{cccccc}
\hline
$JD_{hel}$&$V$&$(V-R)_c$&$JD_{hel}$&$V$&$(V-R)_c$\\
2450500+ & & &2450500+ & & \\
\hline
\\
41.5860& 9.771&  .530&  78.4412& 9.783&  .545\\
42.5988& 9.790&  .557&  79.4437& 9.772&  .546\\
68.4660& 9.786&  .550&  80.3507& 9.772&  .543\\
70.3868& 9.779&  .541&  80.4086& 9.769&  .529\\
72.3457& 9.785&  .549&  80.4347& 9.774&  .528\\
73.3404& 9.771&  .527&  82.3603& 9.769&  .538\\
73.4321& 9.759&  .542&  82.4283& 9.781&  .554\\
74.4629& 9.776&  .544&  82.4573& 9.770&  .534\\
75.3275& 9.777&  .538&  83.3326& 9.769&  .547\\
75.4246& 9.765&  .542&  83.3538& 9.785&  .564\\
76.3313& 9.790&  .539&  83.4255& 9.780&  .547\\
76.4218& 9.793&  .539&  84.3438& 9.784&  .529\\
76.4791& 9.786&  .537&  84.4066& 9.793&  .544\\
77.4913& 9.761&  .532&  84.4412& 9.806&  .548\\
78.3662& 9.778&  .538&         &      &      \\
\hline
\end{tabular}
\end{center}


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\centerline{3}
\vskip 1mm
\centerline{Table 2. VR$_c$ observations of CG Sgr}
\vskip 1mm
\begin{center}
\begin{tabular}{cccccccc}
\hline
$JD_{hel}$&$V$&$(V-R)_c$&$(V-I)_c$&$JD_{hel}$&$V$&$(V-R)_c$&$(V-I)_c$\\
2450500+ & & & &2450500+ & & & \\
\hline
\\
72.6293&13.269& 1.324& 3.046&  82.5683&13.459& 1.389& 3.184\\
73.6060&13.321& 1.353& 3.097&  82.5976&13.342& 1.315& 3.037\\
74.5403&13.262& 1.287& 3.042&  82.6161&13.392& 1.353& 3.107\\
74.5990&13.249& 1.262& 3.015&  82.6462&13.429& 1.354& 3.128\\
75.5009&13.439&    - & 3.171&  82.6632&13.536& 1.417& 3.224\\
75.5846&13.278& 1.314& 3.029&  83.4406&13.497& 1.383& 3.196\\
76.5477&13.408& 1.389& 3.155&  83.4440&13.509& 1.395& 3.192\\
76.6278&13.273& 1.313& 3.052&  83.4682&13.350& 1.342& 3.075\\
77.5546&13.394& 1.361& 3.136&  83.4944&13.543& 1.417& 3.226\\
77.6532&13.269& 1.310& 3.027&  83.5598&13.437& 1.343& 3.114\\
78.5327&13.488& 1.440& 3.226&  83.6174&13.512& 1.423& 3.186\\
78.5982&13.249& 1.306& 3.026&  84.4385&13.620& 1.461& 3.285\\
78.6539&13.318& 1.357& 3.093&  84.5003&13.498& 1.377& 3.189\\
79.4584&13.457& 1.398& 3.200&  84.5366&13.523& 1.417& 3.228\\
79.5264&13.454& 1.402& 3.184&  84.5503&13.446& 1.396& 3.161\\
79.5827&13.356& 1.374& 3.116&  84.5676&13.502& 1.408& 3.201\\
80.4432&13.490& 1.416& 3.217&  84.5897&13.475& 1.424& 3.180\\
80.4777&13.477& 1.415& 3.206&  84.6065&13.443& 1.354& 3.138\\
80.5876&13.404& 1.392& 3.142&  84.6243&13.373& 1.325& 3.102\\
80.6375&13.347& 1.333& 3.089&  84.6386&13.614& 1.457& 3.308\\
82.4762&13.547& 1.442& 3.238&  84.6541&13.369& 1.313& 3.080\\
82.5515&13.564& 1.443& 3.262&         &      &      &      \\
\hline
\end{tabular}
\end{center}
\vskip 5mm

The research described here was supported in part by the Russian Foundation
of Basic Research and the State Science and Technology Program ``Astronomy"
to LNB and through NSERC Canada to DGT. We would also like to express
our gratitude to the administration of the SAAO for their allocation of a large
block of observing time.

\vskip 1cm
\beginauthors
 L.N.~BERDNIKOV
 Sternberg Astronomical Institute
 13, Universitetskij prosp.
 Moscow 119899, Russia
\authorsrightcol
 D.G.~TURNER
 Saint Mary's University
 Halifax, Nova Scotia, B3H 3C3
 Canada
\vskip 2mm
\endauthors

\references

Bailey, S., 1924, {\it Harvard Bulletin}, No\,803

Gerasimovic, B., 1927, {\it Harvard Bulletin}, No.\,846

Grayzeck, E.J., 1978a, {\it Astron. J.}, {\bf 83}, 1390

Grayzeck, E.J., 1978b, {\it Astron. J.}, {\bf 83}, 1397

Uitterdijk,  J., 1936, {\it B.A.N.}, {\bf 7}, 338


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