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\IBVShead{4454}{6 March 1997}

\title{Photoelectric Observations of X PERSEI}

\begintext

X Persei (HD\,24534) is the optical counterpart of X-ray transient
source 4U 0352+30. The system consists of a neutron star secondary accreting
from an O9.5IIIe primary via stellar wind processes.
To investigate whether the last fading phase of X Persei beginning
in 1990 is going on, we observed the system. The present observations were
made in Johnson's UBV bands with the 30-cm Maksutov telescope  of Ankara
University Observatory. In the observations, BD+31\degr0655 was used as
comparison star while BD+29\degr0632 and BD+30\degr0582 were chosen
as the check stars. The magnitude differences between check stars and
comparison star were constant within probable errors of ${\pm}0.026$ in V
band. The individual differential observations were corrected for atmospheric
extinction and light time effect of Earth's motion, and the V band differential magnitude determinations were transformed to the standard system.

Since the end of 19th century X Persei has been known to be a variable on a
long time-scale. Roche et al. (1993) presented the most comprehensive
optical light curve over the period 1964-1992. During this period the Be
star has undergone two extended faint, non-variable phases, seen in
1974-1977 and 1990-1992. After this study, Zamanov and Zamanova (1995) have
observed X Persei in the period 1992-1994. Their data are shown as (+) in
the figures and are evaluated together with our data. Their observations showed the
optical low state that began in the mid-1990 finished in the spring of 1993.
After this, the star has entered the optical high state. Our observations
between 1994-1996 (see Table 1) indicate that the brightness of the system
decreased again in 1995 and the star was still in a low state
during our last observations in 1996 (Figure 1).


Figure 1 presents the V band light curve over the period 1991-1996.
Our observations shown as open circles have completed the missing data
in the vicinity of maximum after the 1990-1993 low state. The magnitude at
maximum obtained at the end of October 1994 is found of 6.23 close to the
values of the previous maxima. Also the current low state is similar to the
previous ones $(V\approx6.6-6.7)$, and only the minimum in 1990-1993 is
deeper than others $(V\approx6.8)$. If these minima are due to the loss of
the Be star circumstellar disk, the current low phase must be associated
with a $\rm{new}$ partial (or complete) disk-loss state.

The B$-$V and U$-$B colour changes are shown in Figures 2 and 3.
Although the observed B$-$V and U$-$B colour index values show a large
amount of scatter, it is seen that during the rapid brightening that
followed the 1990-1993 low state, the B$-$V colour became redder as expected. At
1990-1993 low state the observed U$-$B index is between $-$0.65 and $-$0.7.
This value is consistent with a B0 star which has a colour excess
E(B$-$V)=0.39 given by Fabregat et al. (1992). During the stage of
high luminosity the observed U$-$B increased to about $-$0.85  suggesting
that the disk radiation contributes to the observed Balmer excess.
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\centerline{2}
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\epsfysize=6.6cm
\centerline{\epsffile{4454-f1.ps}}
\centerline{Figure 1. The long term V band light curve of X Persei}
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\centerline{\epsffile{4454-f2.ps}}
\centerline{Figure 2. The B$-$V colour changes of X Persei over the past 4 years}
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\centerline{\epsffile{4454-f3.ps}}
\centerline{Figure 3. The U$-$B colour changes of X Persei over the past 4 years}
\vfill \eject

\centerline{3}

\vskip 1mm
\begin{center}
\begin{tabular}{cccc}
\hline
    HJD      &     V  & B$-$V & U$-$B\\
\hline
\\
2449655.4292 &   6.240 &  0.332 &  $-$0.801\\
2449662.3049 &   6.250 &  0.309 &  $-$0.802\\
2449683.3035 &   6.304 &  0.337 &  $-$0.805\\
2449686.2576 &   6.303 &  0.337 &  $-$0.852\\
2449725.2500 &   6.409 &  0.316 &  $-$0.872\\
2449732.1701 &   6.307 &  0.437 &  $-$0.867\\
2449739.1910 &   6.459 &  0.285 &  $-$0.842\\
2449795.2382 &   6.481 &  0.290 &  $-$0.841\\
2449943.5250 &   6.581 &  0.227 &  $-$0.826\\
2449956.4424 &   6.635 &  0.222 &  $-$0.824\\
2449970.4125 &   6.650 &  0.198 &  $-$0.805\\
2449977.4424 &   6.675 &  0.193 &  $-$0.800\\
2450005.5299 &   6.689 &  0.188 &  $-$0.784\\
2450033.3597 &   6.669 &  0.180 &  $-$0.808\\
2450096.3618 &   6.646 &  0.209 &  $-$0.783\\
2450117.2819 &   6.660 &  0.209 &  $-$0.786\\
2450390.3243 &   6.642  & 0.209 &  $-$0.770\\
2450397.4993 &   6.682 &  0.203 &  $-$0.775\\
2450404.5097 &   6.664 &  0.202 &  $-$0.754\\
2450411.5417 &   6.632 &  0.238 &  $-$0.759\\
\hline
\end{tabular}
\end{center}


\vskip 1cm

\beginauthors
\authorsrightcol
Semanur ENGIN 
Kutluay Y\"{U}CE
Ankara University Observatory
Science Faculty, Tando\u{g}an
06100, Ankara, TURKEY
\endauthors

\references

Fabregat, J., Reglero, V., Coe, M.J., et al., 1992, {\it A\&A}, {\bf 259}, 522

Roche, P., Coe, M.J., Fabregat, J., et al., 1993, {\it A\&A}, {\bf 270}, 122

Zamanov, R.K., Zamanova, V.I., 1995, {\it Inf. Bull. Var. Stars}, No.\,4189

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