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\IBVShead{5177}{21 September 2001}

\IBVStitle{WR 140 in ``Eclipse'' Again}

\IBVSauth{Panov, Kiril P.; Dimitrov, Dinko}

\IBVSinsto{Institute of Astronomy, Bulgarian Academy of Sciences,
Zarigradsko Chosse 72, 1784 Sofia, Bulgaria \\ \indent email: kpanov@astro.bas.bg, dinko@astro.bas.bg}

\SIMBADobjAlias{HD 193793}{WR 140}
\IBVSkey{Wolf-Rayet, photometry}

\begintext

WR 140 = HD 193793 (WC7 + O4-5) attracted much attention during recent
years as a periodic dust maker. Brightenings in the IR in 1977, 1985,
and in 1993 were reported by Williams et al.\ (1978, 1987a, 1987b,
1990) and Williams (1997), and which were attributed to the building of
dust grains in the WR 140 wind. The re-occurrence of dust follows
exactly the 7.94-yr orbital period and coincides with the periastron
passage (PP), where the wind-wind interaction is strongest ($e =
0.84$). In 1993, several months after the PP, it was first observed a
dip in the $UBV$ with an amplitude of $\sim 0\fmm03$ (Panov et al.\ 2000).

The ``eclipse'' was probably caused by the carbon dust envelope,
triggered at the PP by the colliding winds. After 1993, the dust
envelope was gradually dispersed and light in $UBV$ gradually increased
to reach the ``pre-eclipse'' level in 1998. Here we present photometry
of WR 140 after the recent PP in 2001.14. The observations were taken
in June--August, 2001, with the 60-cm telescope and the
$UBV$-photoelectric photometer of the Rozhen National Astronomical
Observatory.

In Fig.~1 the differential light curve of WR 140 (comparison star = HD
193888, check star = HD193926) is shown in the sense HD 193888${}-{}$WR
140, for the 1991--2000 (squares, Panov et al.\ 2000) and the 2001
observations (crosses). The June 2001 observations show light minimum
with an amplitude of about 0\fmm13 in $V$, 0\fmm14 in $B$, and 0\fmm20
in $U$, much deeper than the ``eclipse'' at the previous PP in 1993.
However, in 1993 we observed WR 140 at orbital phases 0.052--0.06 while
in 2001 we were able to cover the phases 0.037--0.068. It is
interesting to note, that the June 2001 dust was rapidly dispersed, and
the $UBV$ light of WR 140 in July increased and almost reached the
``pre-eclipse'' level (Fig.~2). The observations in August are
consistent with the normal WR 140 light. Thus, the June ``dust
episode'' was very brief, compared to the respective dust grain
building in 1993. Fig.~2 shows clearly the difference in the light
behaviour in the phase interval 0.055--0.058. The reason for the
different photometric behaviour of the dust after the 2001.14 PP is not
yet clear.

From the present observations, the deepest light minimum of WR 140 so
far observed occurred at orbital phases 0.038--0.046, if we assume a
smooth trend of the light curves between these orbital phases. The
orbital phases are calculated with $T_0 = 2446160$ (periastron passage)
and $P_{\rm orb} = 2900$ d. Our observations confirm the build-up of
dust in the wind of WR 140, probably triggered by the interacting
winds of the two stars by the 2001.14 PP.

\IBVSfig{19cm}{5177-f1.ps}{WR 140 light curve for 1991--2001.
Squares: observations from 1991--2000. Crosses: 2001 observations}

\IBVSfig{19cm}{5177-f2.ps}{WR 140 light near periastron passages in
1993 (squares) and 2001 (crosses)}

\clearpage

This work was partly supported by the grant F--826 of the Bulgarian
National Science Foundation.

\references

Panov, K.P., Altmann, M., Seggewiss, W., 2000, {\it A\&A}, {\bf 355}, 607

Williams, P.M., Beattie, D.H., Lee, T.J., et al., 1978, {\it MNRAS}, {\bf 185}, 467

Williams, P.M., van der Hucht, K.A., The, P.S., 1987a, {\it A\&A}, {\bf 182}, 91 

Williams, P.M., van der Hucht, K.A., The, P.S., 1987b, {\it QJRAS}, {\bf 28}, 248

Williams, P.M., van der Hucht, K.A., Pollock, A.M.T., et al., 1990, {\it MNRAS},
{\bf 243}, 662

Williams, P.M., 1997, {\it Ap\&SS}, {\bf 251}, 321 


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