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\IBVShead{4330}{24 April 1996}

\begin{center}
{\ft UBV OBSERVATIONS OF AB Dor, LATE 1995}
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\begintext

Monitoring of the rapidly rotating, cool (early K type) and relatively
bright dwarf
AB Dor (= HD\,36705, SAO\,249286) is needed for a  fuller account of
the properties of electrodynamically active stars
(cf.\ Vilhu {\em et al}., 1993; Collier Cameron, 1995;
and references cited therein).
The ephemeris of Innis {\em et al}.\ (1988),
 Min = 2444296.575 + 0.51479 $\times$ E, is usually used to calculate
phase values for reference purposes.

The star was observed in $B$ and $V$ ranges on 5 good nights in 1995:
Sep 9 and 12,  and Dec 18 and 27,
with the 20 cm F10 S-C telescope and DC photometer
of the Mt Molehill Observatory (cf.\ Bos, 1994);
and Oct 22 with the automated photometer (`APT')
at the Kotipu Place Observatory (KPO),
using the $UBV$ filters provided with the SSP 5 `Optec'
photometer (cf.\ Hudson {\em et al.}, 1993).


Standard reduction procedures have been followed
(cf.\ e.g.\ Budding, 1993).
The main comparison star was again HD\,37297 ($V$ = 5.34, $B - V$ = 1.04,
$U - B$ = 0.85, spectral type K0III --- cf.\ SIMBAD). This comparison was regularly
checked against HD\,36876 at Mt Molehill (Table 1). Measurements were
made every 15-20 minutes, depending on conditions.
  At KPO HD\,37297 was checked
against HD\,35537, also a K0III star (Budding {\em et al.}, 1994).
The vagaries of the check against comparison are typically $\sim$0.01 mag  in
the data sets presented, although sometimes reaching 0.02. The scatter of
individual points is somewhat greater for the KPO data, and also greater in $B$
than in $V$ data.

These data sets are shown in Figures 1 and 2. Figure 1 combines
the Mt Molehill (Bos) and KPO data, since there appears to be
a general continuity for the September-October period.
 Figure 2 shows the December data.  The $U$-data from KPO for Oct 22
follows the trend of the  other two ($B$, $V$) data sets, but it is not plotted
here. The $U$ magnitude ranges from about 7.98 at phase 0.5 to 8.07 at
phase 0.32, with a typical scatter of 0.02 mag.
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Table 1. Variability of AB Dor --- amplitude and minimum phase
\begin{tabular}{ccccc}
\hline
  & Max. & Min. & Amplitude & Phase \\
\hline
     Figure 1a &   6.77&    6.88&     0.11 &     0.08\\
     Figure 1b &   7.60&    7.71&     0.11 & $\sim$0.1\\
     Figure 2a &   $<$6.81&  6.88&    $>$0.07 & $\sim$0.0, 0.7 \\
     Figure 2b &   $<$7.62&  7.70&    $>$0.08 & $\sim$0.0, 0.7\\
\hline
\end{tabular}
\end{center}


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\centerline{2}
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\centerline{Figure 1. AB Dor: $B,V$ light curves for Sep-Oct, 1995}
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\centerline{3}
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\centerline{\epsffile{4330-f2.ps}}
\centerline{Figure 2. AB Dor: $B,V$ light curves for Dec, 1995}
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\centerline{4}
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        The observed minima may be related to
spot A of Innis {\em et al}.\ (1988), rather than spot B, but in view of
the apparent tendency of the minima to move downward in phase, reported
before (Bos {\em et al}., 1995), and evident in the trend for late 1995 indicated
in this article, the old scheme of Innis {\em et al}.\ is rather placed
in doubt. One possibility is that another value of the period will
give a better general representation of the variation
resulting from macul{\ae} which would be at fixed longitudes.
A shorter period of 0.5138d has been suggested by Bos (1994).  This period
produces a well repetitive light curve, with a steady minimum at phase
0.5 through 1995.

The maximum  brightness of AB Dor increased slightly
(up to 6.77 in $V$) since the 1993 and 1994 observations. The relatively longer
proportion of darkened time on the 1995 data sets cannot be reproduced
with just one large starspot, however. Spottedness must cover an
appreciable range of longitude in the September-October period,
though the relatively unspotted, cusp-like phase range has widened out somewhat
by December.

Observations have continued from late 1995 into 1996, 
and the more recent data retains a consistent phasing of
the minima with 1995, using the shorter period of Bos (1994).
These newer data will be reported separately later.

\vskip 1cm
\beginauthors
M. BOS, 
G. HUDSON, 
R. HUDSON
E. BUDDING
Mt Molehill Observatory, Auckland,
Kotipu Place Observatory, Pukerua Bay,
Carter Observatory, Wellington, and
Central Institute of Technology,
Heretaunga, New Zealand
\authorsrightcol
\endauthors

\references

Bos, M., 1994, {\it IBVS}, No.\,4111

Bos, M., Budding, E., Hudson, G. and Hudson, R., 1995,
{\it IBVS}, No.\,4203

Budding, E., 1993, {\it An Introduction to Astronomical Photometry},
 Cambridge Univ. Press, Cambridge

Budding, E., Hudson, G. and Hudson, R., 1994, {\it IBVS}, No.\,4139

Collier Cameron, A., 1995, Preprint, submitted to {\it Mon.
Not. Royal Astron. Soc.}

Hudson, G., Hudson, R. and Budding, E., 1993,
{\it Proc. IAU Coll. 136}, (Posters) eds. I.S. Elliott and C.J.
Butler, Dublin Institute for Advanced Studies, 107


Innis, J.L., Thompson, K., Coates, D.W. and Lloyd Evans, T.,
1988, {\it Mon. Not. Roy. Astron. Soc.}, {\bf 235}, 1411


Vilhu, O., Tsuru, T., Cameron, A.C., Budding, E., Banks, T.,
Slee, O.B., Ehrenfreund,
P. and Foing, B.H., 1993, {\it Astron. Astrophys.}, {\bf 278}, 467

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