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\IBVShead{5615}{18 March 2005}

\IBVStitletl{Optical observations of BQ C\lowercase{am} using}{ ROTSE3d observations}


\IBVSauth{Baykal, A.$^{1,3}$; Kizilo\u{g}lu, \"U.$^1$; Kizilo\u{g}lu, N.$^{1,2}$}

\IBVSinst{Physics Dept., Middle East Technical University, Ankara 06531, Turkey; e-mail: umk@astroa.physics.metu.edu.tr}
\IBVSinst{e-mail: nil@astroa.physics.metu.edu.tr}
\IBVSinst{e-mail: altan@astroa.physics.metu.edu.tr}

\SIMBADobj{BQ Cam}

\begintext

BQ Cam is the optical counterpart of the transient X-ray source V0332+53.
This system which consists of a Be star and a 4.4 s X-ray pulsator has an
orbital period of 34.25 days, eccentricity of 0.31 and  semi-major axis of 48
light seconds (Stella et al., 1985). The mass function of 0.1 M$_\odot$ indicates
 an inclination angle smaller than 11\deg\ for the Be star of mass between 16-20 M$_\odot$ and a neutron star mass of 1.4 M$_\odot$.

Two optical brightenings of BQ Cam were detected: one is in 1983 and the 
other is in 1989 (Goranskij, 2001). Both optical brightenings which were related to the ejection of circumstellar shells were accompanied by X-ray outbursts.
Bernacca et al. (1984) indicated that the H$_\alpha$ line showed
 a P-Cygni profile on their spectra which was
 obtained in about 20 days after the maximum
brightness of BQ Cam was reached. 
However, Kodaira et al. (1985) did not confirm this identification and
found that H$_\alpha$  emission line is the
most prominent feature in their spectra.
Iye and Kodaira (1985) and Corbet~et~al. (1986) reported 
the decline of the equivalent width of the H$_\alpha$  emission line
in their spectrum which was related to evolving circumstellar envelope that surrounds Be star.

At the beginning of the year 2004, Goranskij and Barsukova (2004) informed
that BQ Cam reached to its brightness maximum
predicting a new X-ray outburst within 1-2 years. About 300 days later, Swank et al. (2004) reported the first 
All Sky Monitor detection of the November 2004 X-ray outburst.

Optical observations of BQ Cam were obtained between JD 2453235 (August 2004)
 and JD 2453384 (January 2005)
 using  ROTSE3d robotic telescope located at Bak{\i}rl{\i}tepe, Turkey.
It operates without filters and has a wide passband which peaks at
550 nm (Akerlof et al., 2003).
ROTSE magnitudes were calculated by comparing all the field stars to
USNO 2.0 R-band catalog.
About 1600 CCD frames were analyzed following the procedure
 described in 
 K{\i}z{\i}lo\u{g}lu et al. (2005), 
Smith et al. (2002) and Smith et al. (2003).

All frames are dark-and-flat-field corrected automatically as soon as they are
exposed. A pipeline procedure feeds corrected frames to SExtractor package
(Bertin and Arnouts, 1996). 
5 pixel (17 arcsec) diameter aperture is used to determine all source 
candidates 
within the FOV. Gaussian centers and the instrumental magnitudes of the 
identified objects are compared against
USNO A2.0 catalog with a triangle-matching technique. An approximate 
R-band magnitude zero point offset of each frame is calculated  using
a relative photometry algorithm which results in a calibrated list of 
R-band magnitudes  of the objects.  Unfortunately 
ROTSE has no color information. Approximate V-band values can be obtained 
by applying a constant correction factor from the observations of 
the reference stars (Goranskij, 2001). We applied differential photometry 
in order to eliminate the atmospheric and other systematic effects 
over hundred days of observations. These include seeing variations 
in a specific night and  between observation days, and  also pointing  
variations of the order of $\sim0\fdeg3$ in large FOV ($1\fdeg8$).
Table 1 lists the reference stars used for the light curve. $m_{ROTSE}$
is the mean measured ROTSE magnitude and $\sigma$ is the estimated error of
the mean for all the frames.

 \vskip 1cm

\centerline{Table 1. Coordinates and photometric magnitudes of BQ Cam and
the reference stars.}
\vskip 3mm
\begin{center}
\begin{tabular}{ccccccccc}
\hline
Star & $\alpha(J2000)$ & $\delta(J2000)$ & USNO.A2.0 R  & $m_{ROTSE}$  &
$\sigma$ \\
\hline
BQ Cam & 03\hr 34\mm 59\fsec92 & +53\deg 10\arcm 23\farcs3 & 14.2 & &   \\
 1     & 03\hr 34\mm 52\fsec90 & +53\deg 11\arcm 53\farcs6 & 13.8 & 13.919 & 0.106 \\
 2     & 03\hr 35\mm 11\fsec46 & +53\deg 08\arcm 56\farcs3 & 13.3 & 13.255 & 0.103 \\
 3     & 03\hr 35\mm 03\fsec73 & +53\deg 12\arcm 09\farcs1 & 13.2 & 13.147 & 0.102 \\
\hline
\end{tabular}
\end{center}

\vskip 0.5cm


\IBVSfig{10cm}{5615-f1.eps}{ ROTSE3d light curve of  BQ Cam (upper panel) 
and X-ray light curve (lower panel) of
V0332+53 taken with RXTE/ASM (daily average of 5.0-15.0 KeV band light 
curve).  Error bars on ROTSE3d data points are not shown for clarity however 
estimated errors are of the order $\sim 0\fmm02$.
Dotted line shows mean differential magnitude calculated 
for the data  before the periastron passage time.
Arrow points the first ASM detection of
November  2004 outburst (MJD = JD $-$ 2400000.5). The region of periastron
passage is also indicated with its uncertainty in time. }
\IBVSfigKey{5615-f1.eps}{BQ Cam}{light curve}


In Figure 1 the difference in the  
ROTSE magnitudes of BQ Cam 
and the mean of the reference stars 
were plotted together with the X-Ray observations. RXTE-ASM/C-band daily 
averaged data of V0332+53 shows the Nov 23, 2004 X-ray outburst in counts/s. 
On the same figure the periastron passage time is also shown with its 
uncertainty in time. The X-ray outburst occurs close to the time of
periastron passage. 

The light curve of BQ Cam which is in Be star phase
remained almost the same during the observation  time interval of about 
150 days, however $\sim 0\fmm04$ decrease in
brightness before the X-ray outburst is notable. Observed rapid low-amplitude 
 variability on 
time scales of few days is typical to BQ Cam 
 (Goranskij, 2001). Figure 2a is an example of low-amplitude
irregular variability with an amplitude of about 
$\sim 0\fmm02$.
Figure 2b shows a near sinusoidal variation  of duration $\sim11$ days. 
The fading of the source can be expected after the X-ray 
outburst was completed if the cessation of X-ray outburst was accompanied by 
a decline of optical brightness. 


\vskip 0.5cm

\IBVSfig{9cm}{5615-f2.eps}{Examples of the daily averaged variations of 
ROTSE3d light curve of  BQ Cam before and after November  2004 outburst 
(MJD = JD $-$ 2400000.5). Error bars are the variance of variations within each 
 night of observations.   }
\IBVSfigKey{5615-f2.eps}{BQ Cam}{light curve}


 Further ROTSE3d observations 
 are being performed to see the long term variations.

\bigskip

\leftline{\bf Acknowledgements:} This study was supported by TUG (Turkish
National Observatory), TUBITAK ( Turkish Scientific and Research Council).

\newpage

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\endreferences


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