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\IBVShead{5634}{21 July 2005}

\IBVStitletl{Time-Resolved H{\large \boldmath $\alpha$} Monitoring}{ of the Herbig A\lowercase{e}/B\lowercase{e} Star HD~200775}

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

\IBVSinsto{Shamakha Astrophysical Observatory, Shamakha, Azerbaijan}


\SIMBADobj{V380 Cep}

\IBVSkey{Young variable stars, spectral variability}

\IBVSabs{Our time-resolved H_alpha monitoring of V380 Cep has revealed}
\IBVSabs{no significant rapid profile variations for the components of the}
\IBVSabs{H_alpha line. A slow shift to shorter wavelengths of individual}
\IBVSabs{line components was observed during 20 days. The results are}
\IBVSabs{difficult to interpret as resulting from the star's axial rotation.}


\begintext

\vspace*{-1cm}

Many Herbig Ae/Be stars demonstrate strong variability in the
structure of their spectral-line profiles that can be interpreted
as resulting from disk accretion and variable stellar wind.
According to different studies, these variations are caused by
longitudinal stratification of the star-wind zones, i.e. by the
presence of inhomogeneous dense fragments of clouds in the
circumstellar environment, interacting with the star's shell
(Beskrovnaya et al., 1994; Grinin and Rastopchina, 1996; Pogodin
et al., 2000). Thus, we can expect to observe rapid variations of
the spectrum and brightness for such stars. In this paper, we
present the results of our time-resolved spectral variability
monitoring of the Herbig Ae/Be star HD~200775 = V380~Cep.

Our observations used the echelle spectrometer in the Cassegrain
focus of the 2~m telescope with a $580\times530$-pixel CCD. In
1998--2003, this system was in use in the Coude focus (Aliyev and
Ismailov, 2000), and then it was adapted, on the base of a UAGS
spectrograph, for the Cassegrain focus (Mikailov et al., 2005). The
spectral range was $\lambda\lambda4400-6800$~\AA\AA, the spectral
resolution was $R=14000$. We selected 38 orders from orders
70--140, each of them about 100~\AA\ wide, with linear
dispersions between 11 and 6~\AA/mm. The readout and reductions
of the spectra were performed using software developed at the
Special Astrophysical Observatory of the Russian Academy of
Sciences (Galazutdinov, 1992). The observations we report on here
were acquired in June -- August, 2004. Each night, the variable
star was continuously observed for 1.5--2.5 hours, with short
intervals between exposures. For the signal-to-noise ratio
$S/N=150-200$, the average exposure time was $5-7$ minutes. The
observing nights are summarized in Table~1, where the Julian
dates correspond to the middles of each observing period. A total
of about 150~spectrograms were obtained for the variable and the
standard stars. The mean uncertainty of our radial-velocity
measurements for standard stars was within 2 km/s, that for the
equivalent widths was about 4-5\%, and that for the central
residual intensities, 0.6\%.

The H$_\alpha$ line in the spectrum of HD~200775 is known to have
a double-peaked emission structure with small absorption at the
centre of the line. We measured the line parameters using the
method described by us earlier (Ismailov, 2003). To remove the
influence of the terrestrial-atmosphere water lines, we used the
standard software option of dividing the observed spectrum by the
spectrum of an early-type standard star. After such a procedure,
we used the rectified spectra to derive equivalent widths and
relative intensities. The following parameters of the line have
been measured: $Va$, the radial velocity of the central
absorption; $V1$ and $V2$, respectively the radial velocities of
the blue and red emission components of the line; $W$(\AA), the
emission's full equivalent width; and $W1$ and $W2$, the
equivalent widths respectively of the blue and red components.
Besides, the line's profile variations were looked for during all
the series as well as for individual observing dates. Our
observations during 9 nights revealed no obvious changes of the
measured H$_\alpha$ parameters within any of the nightly series.
Significant differences of the line parameters were found from
night to night. These variations are summarized in Table~2.

{\small
\begin{center}
{\normalsize Table 1. The spectroscopic observations of HD 200775}
\vskip2mm
\begin{tabular}{ccccc}
\hline
Night& JD & Series & No. of & Mean exposure\\
No.&2453000+& duration (minutes)&spectrograms&(minutes)\\
\hline
1&202.348&70&12&5\\
2&203.342&90&22&5\\
3&216.325&20&4&5\\
4&217.342&81&12&5\\
5&220.315&25&5&5\\
6&233.279&72&7&8\\
7&236.367&126&15&7\\
8&238.307&105&18&5\\
9&239.297&65&8&7\\
\hline
\end{tabular}
\end{center}
}

{\small
\begin{center}
{\normalsize Table 2. Nightly-mean H$\alpha$ radial velocities and
equivalent widths} \vskip2mm
\begin{tabular}{ccccccc}
\hline
No.&$V1$, km/s&$Va$, km/s&$V2$, km/s&$W1$, \AA& $W2$, \AA&$W$, \AA\\
\hline
1&$-55.1$&$-2.8$&$59.7$&$31.9$&$27.7$&$58.4$\\
2&$-52.9$&$-2.6$&$57.8$&$30.0$&$26.8$&$56.8$\\
3&$-54.3$&$-16.6$&$48.2$&$26.5$&$22.1$&$48.6$\\
4&$-53.5$&$-19.0$&$45.7$&$31.7$&$26.2$&$58.0$\\
5&$-53.6$&$-19.4$&$41.7$&$30.5$&$24.8$&$55.3$\\
6&$-57.8$&$-18.3$&$44.6$&$48.5$&$44.6$&$93.1$\\
7&$-65.2$&$-23.8$&$35.5$&$32.5$&$28.8$&$61.1$\\
8&$-47.2$&$-4.3$&$55.0$&$34.3$&$30.3$&$64.5$\\
9&$-46.6$&$-4.5$&$53.6$&$34.7$&$31.1$&$65.7$\\
\hline
\end{tabular}
\end{center}
}


Figure~1 (top panel) displays radial velocities of the H$_\alpha$
components in the spectra for each observing series. Each data
point is for one of the series listed in Table~1. The relative
equivalent widths, $W1/W2$, for each series, are presented in the
bottom panel. This graph makes it possible to follow the
displacements of individual line components. It appears from
Fig.~1 that, beginning with series~3, a displacement of the line
components to the blue is observed on JD 2453216--JD2453236
(series 3--7). The largest displacement, almost 20 km/s for all
the components, was observed for series~7 on JD2453236. Besides,
there is an increase of the equivalent width of the H$_\alpha$
emission's violet component compared to that of the red one; as a
result, the relative equivalent widths of the line's emission
components also increase synchronously with the radial
velocities. Some of the emission components changed their
equivalent widths by more than 20\%. Figure~1 shows that the
radial velocities of the individual components vary from night to
night. While the velocities of the absorption component ($Va$)
and of the red emission component ($V2$) vary almost
synchronously, the velocity of the blue component ($V1$) changes
irregularly. The difference between displacements of the
components can be as high as 10~km/s for the series 3--6, in a
significant variance with the series 1 and 2, when all the
components showed nearly equal shifts. The displacements of the
red and blue emission components become practically the same in
the series~7 and then do not vary with respect of each other. The
series~7 also reveals an interesting abrupt increase of the full
and relative equivalent widths of the emission components, due to
the increased strength of the red component. In the series 8 and
9, the absorption is redshifted by +10~km/s, whereas both
emission components show identical, almost zero, relative
displacements. This figure clearly shows the presence of
considerable dynamic variations in the circumstellar environment
and in the star's atmosphere during approximately 20~days.

\newpage

\IBVSfig{10cm}{5634-f1.eps}{Variations of the H$_\alpha$-line
parameters for HD~200775. Top: Radial velocities of individual
line components. Triangles: $V1$; filled circles: $V2$; open
circles: $Va$. Each data point corresponds to one of the series
listed in Table~1. Bottom: Relative equivalent widths, $W1/W2$,
for each series.}
\IBVSfigKey{5634-f1.eps}{radial velocity curve}{HD 200775}

\vspace*{-1cm}

Figure~2 shows the $H_\alpha$ profiles from three different
nights. The general structure of the lines does not appear to
change from night to night.

Thus, our study is the first one to present time-resolved
monitoring of the structure and main details of the H$_\alpha$
emission profile. It allows to follow displacements of the
individual emission components and the central absorption,
continuously for times from one hour to several days. Our
observations span about 2 months. Within 1--2.5~hours, we find no
rapid changes in the structure or in the parameters of the
H$_\alpha$ line. However, there is significant variability from
night to night, especially on JD 2453216--2453236. During this
time interval, approximately for 20 days, systematic
displacements to the blue, up to 10--20~km/s, were observed for
individual components of the H$_\alpha$ line.

The star's rotational velocity is $v \sin i = 103$~km/s
(Ruusalepp, 1987) or 40~km/s (Bohm \& Catala, 1995). From Watt et
al. (1986), the star's orbital inclination is $i = 70\deg$. For
the spectral type B3IV (Altamore et al., 1980) and radius $R_* =
4.5$~$R_\odot$, the primary component's longest possible
axial-rotation period is 5\fday4. This period is nearly 4~times
shorter than the H$_\alpha$ activity time scale found by us.
Thus, the systematic change we have observed in the H$_\alpha$
line cannot be explained by the existence of relatively stable
local inhomogeneous clouds in the atmosphere, observable because
of modulation by the star's axial rotation. Ismailov (2003) found
the star to be a spectroscopic binary, with the orbital period $P
= 1180\day$. Later, Pogodin et al. (2004) confirmed the system's
binarity and derived the orbital period $P = 1341\day$. The
orbital phases for the dates of observations from our study
computed with the elements from Ismailov (2003) are
0\fper88--0\fper92, the phases with the elements from Pogodin et
al. (2004) are 0\fper02--0\fper03, so we observed the very
minimum of the binary's radial velocity curves. The two radial
velocity curves in the cited papers, based on independent data,
show that a radial-velocity change just of the size we have found
is possible at these phases. Thus, the observed variations of the
H$_\alpha$ line can be partially due to the system's orbital
motion.

\IBVSfig{13cm}{5634-f2.eps}{H$_\alpha$ profiles for three individual
nights.}
\IBVSfigKey{5634-f2.eps}{}{HD 200775}



\vspace*{-1.7cm}

\references

Aliyev, S.G., Ismailov, N.Z., 2000, {\it Astron. Reports}, {\bf 44}, 738

Altamore, A., Baratta, G.B., Casatella, A. et al., 1980, {\it
Astron. \& Astrophys.}, {\bf 90}, 290

Beskrovnaya, N.G., Pogodin, M.A., Shcherbakov, A.G., Tarasov,
A.E., 1994, {\it Astron. \& Astrophys.}, {\bf 287}, 564

Bohm, T., Catala, C., 1995, {\it Astron. \& Astrophys.}, {\bf
301}, 155

Galazutdinov, G.A., 1992, {\it SAO Preprint}, No.~92

Grinin, V.P., Rastopchina, A.N., 1996, {\it Astron. Reports},
{\bf 40}, 171

Ismailov, N.Z., 2003, {\it Astron. Reports}, {\bf 47}, 206

Mikailov, Ch. M., Khalilov, V.M., Alekberov, I.A. 2005, {\it ShAO
Circular}, No.~9

Pogodin, M.A., Miroshnichenko, A.S, Tarasov, A.E., et al., 2004,
{\it Astron. \& Astrophys.}, {\bf 417}, 715

Ruusalepp, M., 1987, {\it Publ. Tartu Astrophys. Observ.}, {\bf
52}, 302

Watt, G.D., Burton, W.B., Choe, S.U., List, H.S., 1986, {\it
Astron. \& Astrophys.}, {\bf 163}, 194

\endreferences


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