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\centerline{\ft UBV OBSERVATIONS OF AB Dor, 1993}

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The peculiar, active, cool dwarf AB Dor (= HD\,36705, SAO\,249286)
has received considerable  international attention  in recent years
(cf.\ Vilhu {\em et al}., 1993),
being the target of several multi-site, multi-wavelength `campaigns',
most recently in 1994 when the HST, EUVE, ASCA and other major facilities
were brought into concerted action in its direction.

A good earlier photometric review is that of Innis {\em et al}.\ (1988),
who supplied the ephemeris Min = JD\,2444296.575 + 0\fd 51479$\times$E,
that has been generally favoured in subsequent studies.
AB Dor has been usually assigned a peculiar, early K
spectral type.

The star was observed using the automated photometer (`APT')
of the Kotipu Place Observatory (Hudson {\em et al.}, 1993)
on six nights between 29 Sep and 14 November, 1993,
using the $UBV$ filters provided with the SSP 5
photometer of Optec Inc.  The observation period overlaps
with the recently published data set of Anders (1994) and Bos (1994).
The (partial) light curves of these authors for the
time interval involved are essentially confirmed by the APT.

The main comparison star was HD 37297 ($V$ = 5.34, $B - V$ = 1.04,
$U - B$ = 0.85, sp.\ type K0III --- cf.\ SIMBAD) with occasional checks
being made on HD 35537, also a K0III star.  For this star we derive the
following: $V$ = 7.84, $B - V$ = 0.99, $U - B$ = 0.71.

The observations have been reduced on a PC
(cf.\ Budding, 1993), and  the resulting $V$ light curve is
presented in Figure 1. This light curve results from
binning some 683 individual data into 85 ``normal" points,
and correcting slightly the magnitudes due to the small
redness excess of the comparison star with respect to AB Dor
($\Delta (B - V)$ = 0.20, $\epsilon$ = 0.019).

The $B$ and $U$ light curves are essentially similar in shape
to the $V$ one.
The $B$ magnitude ranges from 7.68 at brightest  ($V$ = 6.82) to
7.82 at the phases 0.0 and 0.2, corresponding to
the lowest (6.94) on this $V$ data set.  Individual $B$
observations have a scatter of about 0.02 mag, i.e.\ comparable to
that of the raw data in $V$. The $U$ data, on the other hand, has
a noticeably larger dispersion --- up to 0.04 mag
around the phase region 0.4-0.5, where the raw data quality
appears to be at its poorest.  The $U$ light curve ranges from
about 8.03 to 8.19 mag.
The conformities in shape, though slightly greater ranges
in the $B$ and $U$, when set against the $V$ light curve, support maculation
as a likely explanation for the photometric behaviour. 
The slight reddening at the minimum was also noted by Bos (1994).

These light curves are almost complete,
though there is a small phase interval
close to the bottom of the minimum not covered by the present
dataset. Bos (private communication) observed this region
on Nov 13 1993, just before the last APT night presented here, and 
essentially confirmed
the phase, magnitude range and shape of this minimum.\hfill

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\centerline{Figure 1}
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There is a slight difference in phase of Bos' minimum ($\sim 0.06$)
and ours, however, which, from the shape of the descending
sides would be located somewhat closer to 0.1.
Anders' (1994) minimum, which derives from observations
a few weeks later, is still earlier in phase --- close to zero, in fact.
Hence, there is a suggestion, from these three data sets, which range
over the later months of 1993, of a tendency for the `spot(s)'
associated with the maculation, to have drifted slightly
 backwards in phase,
relative to the ephemeris of Innis {\em et al}.\ (1988), while
preserving the overall shape of the photometric effect.

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% Call for macros \authors - \authorsrightcol - \endauthors
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E. BUDDING, 
G. HUDSON and 
R. HUDSON
Carter and Kotipu Place 
Observatories, 
Wellington, New Zealand
\endauthors

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\references

Anders, G.J., 1994, {\em IBVS}, No.\,3985

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

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

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

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

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

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