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\begin{document}

\IBVShead{5702}{15 May 2006}

\IBVStitle{Active Motion of Matter in the Envelope of DI Cephei}

\IBVSauth{Ismailov, N. Z.; Aliyeva, A. A.}

\IBVSinsto{Shamakha Astrophysical Observatory, National Academy
of Sciences of Azerbaijan, Shamakha, Azerbaijan;\\
e-mail: Box1955n@yahoo.com}

\SIMBADobj{DI Cep}

\IBVSkey{Young variable stars, spectral variability}


\begintext

Emission spectra of T~Tauri stars (TTSs) carry important
information from disk accretion areas that interact with the
star's magnetosphere. Balmer profiles of young stars suggest the
presence of magnetic funnel flows, created as the stellar
magnetosphere truncates the inner disk and redirects the
accretion flow along magnetic trajectories terminating in
accretion shocks on the stellar surface (K\"onigl 1991, Muzerolle
et al. 1998, Beristain et al. 1998). However, details of this
process are not clear yet. A detailed spectroscopic study of the
structure of a star's emission lines can give us information
important for understanding interaction of disk accretion with
the star's atmosphere.

We present new results of our study of the hydrogen emission
lines for the TTS DI~Cep. We used the echelle spectrometer in the
Cassegrain focus of the 2~m telescope (Shamakha Observatory,
Azerbaijan) with a $580\times 530$-pixel CCD (Mikailov et al.
2005). The spectral range was $\lambda\lambda4400 - 6800$~\AA,
the spectral resolution was $R=14000$. The whole range was
divided into 28 orders, each of them about 100~\AA\ wide. The
linear dispersion varied between 11 and 6~\AA/mm. The average
signal-to-noise ratio was 60 and 40, respectively in the
H$\alpha$ and H$\beta$ region. The mean exposure time for one
spectrum was about one hour. The spectral reductions made use of
software developed by Galazutdinov (1992). To undertake cleaning
for the telluric lines, we use a special technique (Alieva and
Ismailov, 2005) based on the following procedure: after precise
position identification of telluric lines, we derive a
pseudo-continuum, which ignores positions of the telluric lines.
After dividing by this pseudo-continuum, we obtain the so-called
``divisor" spectrum, which contains the telluric lines. We then
apply this spectrum as a spectrum of a standard star with a
smooth continuum (Galazutdinov, 1992). Two spectra were obtained
in 2004 and 18, in 2005. Ten of these spectra were obtained on
the night of JD~2453589, at 5-minute intervals, to check for
rapid variability of the H$\alpha$ emission. In these spectra,
the signal-to-noise ratio is $S/N=8$, thus the equivalent widths
of the H$\beta$ lines are not measurable; the data for
JD~2453589.486 in Table~1 (see description below) are mean
parameters for these 10~spectra. The mean uncertainty of our
radial velocity measurements for standard stars was within
2~km/s, that for equivalent widths was about 4-5\%.


The H$\alpha$ line profiles in different spectra are presented in
Fig.~1. The profile basically has two strong peaks (Nos.~3 and~4
in Fig.~1), with a depression between them. In turn, each of the
peaks~3 and~4 shows a complex structure. On some nights, weak
emission peaks displaced to the blue and to the red in the
spectrum by $\pm400$~km/s (peaks~1 and~5) were observed. The blue
wing of the emission peak~1 is very extended and smoothly merges
with the continuum at a displacement of $-600$~km/s. These peaks
are especially strong in the spectrum acquired on JD~2453588. The
absorption~2 has a blue shift about $-320$~km/s and forms a
typical P~Cyg structure. The peak~5 on the same night had a
displacement about $+491$~km/s. Thus we observe strong variations
of the H$\alpha$ structure from night to night as well as within
a night.

{\small
\begin{center}
{\normalsize Table 1. Parameters of the H$\alpha$ line in the
spectrum of DI~Cep}

\medskip

\begin{tabular}{cccccccc}
\hline
\noalign{\medskip}
JD 24... & $W_1$, & $W_2$, & $W_3$, & $W_4$, & $W_5$, & $W$, & FWHM,\\
         &\AA  &\AA  &\AA &\AA    &\AA   &\AA  &\AA \\
\noalign{\medskip}
\hline
\noalign{\medskip}
53240.298 &    &    & 12 & 15 & &27  & 6.96\\
53240.392 &0.34&0.14&13.1&17.7&0.09&30.8&7.13\\
53587.390 &    &    & 5.7&6.7 &    &12.5\\
53587.420 &0.12&0.22&16.7&19.2&0.21&35.8&7.35\\
53587.488 &0.20&0.10&17.7&25  &0.12&39.3&7.87\\
53588.428 &0.71&0.56&29.5&26.2&0.78&55.7&8.03\\
53588.476 &0.61&0.50&30.6&28.3&1.18&58.9&7.67\\
53589.486 &    &    & 24.7& 13.5&    & 38.3&7.69\\
53590.392 &0.24&0.12&25.9&12.9&    &38.8&7.06\\
\noalign{\medskip}
\hline
\noalign{\medskip}
 &$V_1$,& $V_2$,&$V_3$,&$V_4$, &$V_5$,& $V_6$,\\
 &km/s&km/s&km/s&km/s&km/s&km/s\\
\noalign{\medskip}
\hline
\noalign{\medskip}
53240.298&      &     &--103&  53 &     & --28\\
53240.392& --377&--356&--80 &  56 & 349 &--25\\
53587.390&      &     &--99 & 10  &     & --42\\
53587.420&--414 &--323&--119& 18  &395  & --33\\
53587.488&--495 &--318&--116& 23  &440  &--27\\
53588.428&--412 &--339&--74 & 13  &381  &--37\\
53588.476&--417 &--336&--74 & 18  &491  &--34\\
53589.486&      &     &--104& 42  &     &--32\\
53590.392&--406 &--337&--26 & 66  &     & 22\\
\noalign{\medskip}
\hline
\end{tabular}

\end{center}
}

\medskip

The results of our measurements of equivalent widths and radial
velocities of individual H$\alpha$ components are presented in
Table~1. To measure equivalent widths of individual components, we
used the following method from the DECH20 (Galazutdinov, 1992) 
software package: for 
each component, we limited the left and right sides of its peak
with vertical lines and determined the area between these lines
by integration. In our case, we could not apply Gaussian fitting
because, for our profiles, the wings of individual components
remained mainly unresolved.


The first part of Table~1 presents equivalent widths of the main
components marked in Fig.~1. $W$ is the full equivalent width of
the emission, FWHM is a line width at half intensity. In the
second part of Table~1, radial velocities of the same components
are presented.

Figure~2 shows the H$\beta$ line profiles for the same
spectrograms. It can be seen that this line exhibits structures
similar to those we observe for the H$\alpha$ line. The  H$\beta$
profile is quite similar to the H$\alpha$ line structure for
JD~2453588.476. Here we simultaneously observe the components
displaced into the blue and red parts of the spectrum,
respectively by about --408 and +328 km/s.  On JD~2453588, the
H$\beta$ profiles recorded one after another have the peaks~1
and~4 barely visible in the first spectrogram, these peaks were
observed stronger in the spectrogram acquired one hour later.
Note that, while the blue-displaced component~1 is observed
confidently enough, the component~4 is rarely observed and shows
active variations. The parameters of the H$\beta$ line are
collected in Table~2, which is similar in its contents to
Table~1, but the component numbers refer to Fig.~2. We find
direct correlation between equivalent widths of individual
emission components of the H$\alpha$ and H$\beta$ lines, with
correlation coefficients $\sim 80\%$. For example, we obtained a
direct correlation between the equivalent widths of the blue
peak~3 of H$\alpha$ and peak~2 of H$\beta$, with the correlation
coefficient $r = 84\%$. Signatures of simultaneous accretion on
T~Tauri stars and outflow from them were first observed by Walker
(1972) who had noticed an additional absorption component redward
of the redshifted emission peak, then the event was observed for
other classical TTSs (CTTSs) (Bertout, 1984; Batalha et al.,
2001). Our observations show that the H$\alpha$ and H$\beta$ line
profiles of the CTTS DI~Cep vary actively. Unstable accretion and
emission components of the two hydrogen lines have been observed
on the same spectrogram for the first time. This is a rare
phenomenon, it also demonstrates the discrete character of the
accretion process.

Periodic spectral and photometric variations of the star
($P=9\fday24$) were observed (Ismailov, 2003). If they are
related to the asymmetric and inhomogeneous envelope, one of the
possible causes of the inhomogeneity is the structure of the
magnetosphere, with accretion along the magnetic lines. In
principle, such activity of DI Cep can be easily explained in
modern magnetospheric-accretion models. High activity of the star
is provided by kinetic energy of matter accreted onto the star
surface across magnetic field lines (Muzerolle et al. 1998,
Lamzin 1998).

\IBVSfig{7cm}{5702-f1.eps}{The H$\alpha$ profiles in the
spectrum of DI~Cep}
\IBVSfigKey{5702-f1.eps}{DI Cep}{spectrum}

{\small
\begin{center}
{\normalsize Table 2. Parameters of the H$\beta$ line in the
spectrum of DI~Cep}
\begin{tabular}{cccccccccccc}
\hline \noalign{\medskip}
JD 24... & $W_1$, & $W_2$, & $W_3$, & $W_4$,& $W$, &FWHM,
&$V_1$,&$V_2$,&$V_3$, &$V_4$,& $V_5$,\\
         &\AA  &\AA  &\AA &\AA   &\AA  &\AA
&km/s&km/s&km/s&km/s&km/s\\
\noalign{\medskip}
\hline
\noalign{\medskip}
53240.298 &    &2.4  & 1.5 &     &3.9  &6.96 &    &--93.2    &--5.3&
&--27.2\\
53240.392 &0.07&3.2  & 1.8 &     &5.0  &4.29 &--398  &--97.2 & 28.3&
&--2.1\\
53587.390 &    &3.5  & 2.4 &     &6.0  &4.98 &       &--109  &--9.4&
&--34.1\\
53587.420 &0.09&3.9  & 3.2 &     &7.0  &5.44 &--344  &--111  &--7.6&
&--46\\
53587.488 &0.17&4.8  & 3.7 & 0.20&8.5  &5.35 &--420  &--93.9 & 73.5&
441   &--16.4\\
53588.428 &0.08&5.8  & 5.6 & 0.45&11.7 &5.20 &--410  &--85.1 &100.7&
325   &--19.7\\
53588.476 &0.83&6.5  & 4.5 & 1.68&10.9 &5.71 &--408  &--94.2 & 38.6&
323   &--3.8\\
53590.392 &    &4.2  & 2.9 &     & 7.1 &5.27 &       &--107.3& 15.5&
&--35.1\\
\noalign{\medskip}
\hline
\end{tabular}

\end{center}
}



\newpage

Thus, we can make the following conclusions:

1. Profile variations of the H$\alpha$ and H$\beta$ hydrogen
lines during a night and from night to night, on time scales from
an hour to a day, are observed.

2. For the first time, signatures of matter accretion and outflow
were simultaneously observed for the CTTS DI~Cep, providing evidence of
complex structure of its circumstellar disk.

\medskip

We thank Dr.~N.N.~Samus for discussions and assistance during the
preparation of the manuscript.


\IBVSfig{7cm}{5702-f2.eps}{The H$\beta$ profiles in the spectrum
of DI~Cep}
\IBVSfigKey{5702-f2.eps}{DI Cep}{spectrum}



\references


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Bertout, C., 1984, {\it Reports Progr. Phys.}, {\bf 47}, 111

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Ismailov, N.Z., 2003, {\it Inform. Bull. Var. Stars}, No. 5466

K\"onigl, A., 1991, {\it Astrophys. J.}, {\bf 370}, L39

Lamzin, S.A., 1998, {\it Astronomy Reports}, {\bf 42}, 322

Mikailov, Ch.M., Chalilov, V.M., Alekperov, I.A., 2005, {\it
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Muzerolle, J., Calvet, N., Hartmann, L., 1998, {\it Astrophys.
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Walker, M.F., 1972, {\it Astrophys. J.}, {\bf 175}, 89

\endreferences


\end{document}
