\documentstyle[twoside, epsf]{article}

\input ibvs2.sty

\begin{document}
\IBVShead{5412}{14 May 2003}

\IBVStitle{The start of the 2003 eclipse of EE~Cephei}


\IBVSauth{Miko{\l}ajewski, M.$^1$; Tomov, T.$^{1}$; Graczyk, D.$^1$; Kolev, D.$ ^{2}$; Ga{\l}an, C.$^{1}$; \\ Galazutdinov, G.$^{1,3} $}

\IBVSinst{Centrum Astronomii, Uniwersytet Miko{\l}aja Kopernika, Pl-87100
Toru\'n, Poland, \\ e-mail(MM): mamiko@astri.uni.torun.pl}
\IBVSinst{NAO Rozhen, PO Box 136, BG-4700 Smolyan, Bulgaria}
\IBVSinst{Special Astrophysical Observatory, Nizhnij Arkhyz, 369167, Russia}


\SIMBADobjAlias{EE Cep}{BD+55 2693}
\IBVStyp{ E }
\IBVSkey{photometry, spectra}
\IBVSabs{EE~Cep is an eclipsing binary whose nature still remains unclear. The}
\IBVSabs{various features observed during the different eclipses and the lack}
\IBVSabs{of any evidence for a star-like secondary are in favour with the}
\IBVSabs{hypothesis that the secondary contains a dark, opaque disc covering}
\IBVSabs{a central low-luminosity star or binary system.}


\begintext

The variable nature of 11th magnitude star EE~Cep ( $=$BD$+55\deg2693$) was
discovered by Romano (1956), and confirmed by Weber (1956), who observed two
independent deep ($\Delta B \geq 1\fmm5$) minima in 1947 and 1952. The eclipsing
nature of these minima was first suggested by Romano \& Perissinotto (1966) who
noticed a third minimum in 1958 July. Meinunger (1973) then observed two more
minima in 1964 and 1969, and confirmed this suggestion. He published the first
ephemeris for EE~Cep eclipses with orbital period of 2049 days (5.6 years).
So far there have been no traces of secondary eclipse in the light curve of
EE~Cep.

The most striking characteristics of EE~Cep are the extremely large changes of
shape and depth of the minima. Recently, Graczyk et al. (2003) compiled
light curves of all available past eclipses. The observed depths range from
about $2\mm$ in 1958 and 1964 to about $0\fmm6-0\fmm8$ in 1969 and 1992. The
depths of the eclipses correlate roughly inversely to their total durations. As
an example, two different shape minima are presented in Fig.~1. The extremely
shallow minimum ($\Delta B \approx 0\fmm6$) in 1969 was simultaneously the
longest one ($D \approx 60\day$). Additionally, this eclipse showed a flat
bottom phase with duration $d  \approx 20\day$. Most typical eclipses are
similar to that of 1975.  They have depth at least $1\fmm5$ and show asymmetry
of the ascending branch produced by a kind of slope-bottom phase in the minimum.
A sketch view of such a typical minimum is presented in Fig.~2.

\IBVSfig{5.5cm}{5412-f1.ps}{Examples of shallow, flat-bottom
(\textit{left}) and deep, slope-bottom (\textit{right}) eclipses of EE~Cep
(Graczyk et al. 2003, and references therein).}
%\IBVSfigKey{5412-f1.ps}{EE Cep}{light curve}

Multicolour $UBVRI$ observations of a 1997 eclipse (Miko{\l}ajewski \& Graczyk
1999) showed that the amplitude of the minimum changes very weakly with the
wavelength, from about $1\fmm75$ in $ U $, to about $1\fmm45$ in $ I $ light.
This is probably caused by selective extinction in semitransparent parts of a
dark eclipsing body. The contribution of the secondary light in the red $RI$
bands is negligible. The characteristic slope-bottom phase (C-D part in Fig.~2)
during the eclipse is easy to understand if the obscuring body is very
elongated and tilted with respect to the direction of motion (Graczyk et al.
2003). Changes of tilt angle produce variations in the duration and slope of
this transit phase. In particular, when the tilt angle is very small, a
flat-bottom phase would be observed during the minimum. Simultaneously, the
effective thickness of the eclipsing body also changes during the different
eclipses, causing variations of the minima depths. The most promising model
remains that of a dark, precessing disk around a low luminosity central object
(Miko{\l}ajewski \& Graczyk 1999, Graczyk et al. 2003). The precession changes
both the inclination of the disc to the line of sight, and the tilt of its
cross-section to the transit direction. The unique shape of the eclipse observed
in 1969 can be explained by a practically edge-on and non-tilted projection of
the disc. Two hypotheses can be considered for such a disc: (i) it has a
proto-planetary origin; (ii) it is a post-planetary object (a result of
planetary disintegration). An important question is the nature of the central
body embedded in the disk. It can be a low massive single star or a close binary
system. The only similar object previously known with a dark circumstellar disc
is $\epsilon$ Aur -- the longest period ($\sim 27$ years) eclipsing binary.

Surprisingly, low resolution spectroscopic observations during past eclipses
(Br$\ddot{\rm u}$kner 1976, Baldinelli, Ferri \& Ghedini 1981) did not detect
any trace of secondary spectrum. Moreover, there were no changes in the spectrum
(especially in H$\alpha$, H$\beta$ emissions) despite the large depth of the
minima (about $1\fmm5)$. Our recent observations at Asiago Observatory ($R =
\lambda/\Delta\lambda \approx 4000$) show that the profiles of the H$\alpha$ and
H$\beta$ lines in the spectrum of EE~Cep are very similar to those observed in
Be stars. However, we cannot be sure that they indeed belong to the visible,
eclipsed  B5III component. The observed H$\alpha$ and H$\beta$ profiles are
rather characteristic for Be stars located nearly pole-on (\textit{e.g.}
Hanuschik et al. 1996). Already far outside eclipse we found spectacular
variations in the H$\alpha$ emission (Graczyk et al.2003), which seem to be more
naturally connected with the complex around the secondary. Additionally, in
the same paper we pointed out variations in the radial velocities of the NaI
absorption doublet. This finding can be considered an indication of its
possible circumstellar origin. Moreover, last month we found these lines as
pure P-Cyg type profiles (Fig.~3). This dramatic change can already be connected
with the beginning of the eclipse.

\IBVS2fig{7.5cm}{5412-f2.ps}{Schematic view of the EE~Cep eclipse: A--B - descending atmospheric phase; B--C eclipse ingress; C--D transit phase; D--E eclipse egress; E--F ascending atmospheric phase.}{5412-f3.ps}{Profiles ($R = \lambda/\Delta\lambda \approx 15000$) of NaI~D$_{1,2}$ doublet obtained with the coud{\'e} spectrograph of the 2m telescope at Rozhen Observatory.}
%\IBVSfigKey{5412-f2.ps}{EE Cep}{light curve}
%\IBVSfigKey{5412-f3.ps}{EE Cep}{spectrum}

The incoming event, according to the ephemeris of Miko{\l}ajewski \& Graczyk
(1999), has number $ E=9 $. The mid-eclipse should occur on June 3, 2003. The
external first contact of the semitransparent part of the disc (A in Fig.~2) can
start at least three weeks earlier ($\sim$~May~13). The central part of the
minimum (B-C-D-E in Fig. 2) should occur between $\sim$~May~23 and
$\sim$~June~13 corresponding to the occultation of the primary by the inner,
opaque part of the disc. The end of the minimum should take place
$\sim$~June~24. We would like to remember that the eclipse duration $D$ can last
even $2-3$ weeks. In Graczyk et al. (2003) we speculate that the possible
precession period may be about 50 years and the shape of the eclipse can be
similar to the one observed in 1952. That one was very deep (at least $1\fmm9$)
and no longer than $40$ days. A slope-bottom with inverse inclination, placed on
the ascending branch of the present eclipse, would not be a surprise.

Photometric observations of EE~Cep (with CCDs or photomultipliers) from widely
spaced longitudes will help to obtain a detailed light curve of this minimum
and to determine precisely all six contacts A-F (Fig.~2). These observations
will be useful for numerical modelling of the disc. We recommend as comparison
and check stars the brightest objects from the Meinunger's (1975) sequence
(Fig.~4). Their Johnson magnitudes, obtained using a diaphragm cooled photometer
attached to the 60cm reflector at Toru\'n observatory, are:

\vskip 3mm

%\centerline{Table 1. .........}
%\vskip 3mm
\begin{center}
\begin{tabular}{ccccccc}
%\hline
Star   &  $U$  &  $B$ & $V$   &  $R$  & $I$  &  n  \\
\hline
${\rm a} = {\rm BD}+55\deg2690$ & 10.86 & 10.68 & 10.38 & 10.09 & 9.87 & 40 \\
${\rm b} = {\rm GSC}\ 3973\ 2150$ & 11.31 & 11.47 & 11.23 & 10.99 & 10.81 & 5 \\
${\rm c} = {\rm BD}+55\deg2691$ & 11.59 & 11.47 & 11.22 & 10.96 & 10.75 & 2 \\
%\hline
\end{tabular}
\end{center}

\vskip 2mm

Our data are in good agreement with earlier $UBV$ measurements for star ``a''
(Meinunger 1976), $V$ brightness for ``b'' and ``c'' stars (Skiff 2003) and
$BRI$ estimations for all these objects from USNO-B1 catalogue (Monet et al.
2003). Star ``c'' was suspected variable (Baldinelli \& Ghedini 1976), and its
contemporary magnitudes differ about $0\fmm1$ from the data of Barbieri et al.
(1973). Nevertheless, our own observations and the observations of Skiff (2003)
do not confirm its variability.

Very important will be high resolution spectroscopic observations during
the eclipse. We expect the appearance of strong shell spectrum from the gaseous
component of the disc, as in $\epsilon$~Aur (Ferluga \& Mangiacapra 1991), and
possible strengthening of the diffuse interstellar bands (DIBs) caused by the
dust component of the disc. Several strong DIBs (\textit{e.g.}
$\lambda\lambda\,6619$\,\AA, $5780$\,\AA, $5797$\,\AA, $5850$\,\AA) are visible
already in the spectrum outside the eclipse. Possible changes in the Balmer line
profiles should determine where their emissions arise, i.e. whether the primary
is a Be star. Of course, systematic radial velocity measurements are necessary
for the spectroscopic orbit solution and the estimation of the masses of the
EE~Cep system components.

\IBVSfig{7.5cm}{5412-f4.ps}{$10^\prime \times 10^\prime$ DSS-2-red finding
chart for EE~Cep.}
%\IBVSfigKey{5412-f4.ps}{EE Cep}{finding chart}

Also very important should be infrared photometric (at least $JHK$)
observations during and outside the eclipse. These could be helpful in finding
the flux originating  in the disc and its central object, as well as in
estimating their temperatures.

We started our $UBVR_{C}I_{C}$ and optical spectroscopic observations of EE~Cep
at Toru\'n, Rozhen and Asiago observatories. Of course, it is not realistic to
expect that we will be able to secure enough data for a good photometric and
spectral coverage of the eclipse. Because of this we welcome future
collaboration with interested observers.

\textit{Acknowledgements:} This work was supported by KBN Grant No.
5~P03D~003~20. We are grateful to Fred E.J. Linton for the improvement of 
English.


\vskip 1cm

\references

Baldinelli, L. \& Ghedini, S., 1976, {\it IBVS}, No. 1225

Baldinelli, L., Ferri, A. \& Ghedini, S., 1981, {\it IBVS}, No. 1939

Barbier, M., Bernard, A., Bigay, J.H., \& Garnier, R., 1973, {\it A\&A}
{\bf 27}, 421

Br$\ddot{\rm u}$kner, V., 1976,  {\it Mitt. Ver\"an. Sterne}
{\bf 7}, 114

Ferluga, S. \& Mangiacapra, D., 1991, {\it A\&A} {\bf 243}, 230

Graczyk, D., Miko{\l}ajewski, M., Tomov, T., Kolev  D., \& Iliev , I., 2003,
{\it A\&A}, in press (\textit{astro-ph/0303547})

Meinunger, L., 1973, {\it Mitt. Ver\"an. Sterne} {\bf 6}, 89

Meinunger, L., 1975, {\it IBVS}, No. 965

Meinunger, L., 1976, {\it Mitt. Ver\"an. Sterne} {\bf 7}, 97

Miko{\l}ajewski, M. \& Graczyk, D., 1999, {\it MNRAS} {\bf 303}, 521

Monet, D. G., Levine, S. E., Cauzian, L. B., et al., 2003, {\it AJ} {\bf 125},
984

Romano, G., 1956,  {\it Coelum} {\bf 24}, 135

Romano, G. \& Perissinotto, M., 1966,  {\it Mem. Soc. Astr. Ital.} {\bf 37}, 255

Skiff, B., 2003,  \\
{\tt http://mailman.mcmaster.ca/mailman/private/aavso-discussion/0302.gz/msg00161.html}

Weber, R., 1956, {\it Documentation des Observateurs Circulaire}, {\bf 9}


\endreferences


\end{document}
