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\IBVShead{6022}{4 May 2012}

\IBVStitletl{Photometric behaviour of V1343~Aquilae (SS~433) in 2011}


\IBVSauth{Volkov, Igor$^{1,2}$}

\IBVSinsto{$^{1}$Sternberg Astronomical Institute, M.V. Lomonosov Moscow University,
Universitetsky Ave.,13, Moscow 119992, Russia}

\IBVSinsto{$^{2}$Astronomical Institute of the Slovak Academy of
Sciences, 059 60 Tatransk\'a Lomnica, Slovak Republic;\\
 e-mail: \tt volkov@ta3.sk}

\SIMBADobjAlias{V1343 Aql}{SS 433}
\IBVSkey{photometry}

\IBVSabs{Multicolour photometry of the microquasar SS 433}
\IBVSabs{revealed that it was in the active state in 2011.}
\IBVSabs{The colours of the object did not vary significantly}
\IBVSabs{with the precession phase and in the flare.}
\IBVSabs{The main eclipses became very shallow.}
\IBVSabs{The nutation period has shortened.}
\IBVSabs{Precise magnitudes of the comparison stars were derived.}

\begintext
The X-ray orbital satellite $INTEGRAL$  observed SS~433 in
October 2011. In order to synchronize these observations with the
optical light curve, I have observed the star during 34 nights at
the Crimean Astrophysical Observatory (Simeiz site), Ukraine, with the 
1-m telescope. Two CCD detectors: VersArray~512UV~(Peltier
cooling, --50$^{\circ}$C) and VersArray~1340$\times$1300~(liquid nitrogen cooling,
--110$^{\circ}$C) were used. The same filter set for both detectors provided
the instrumental systems close to the standard Johnson $UBVRI$.
The observations at JD=2\,455\,856~(last point in Fig.~1) were made at
Star\'a Lesn\'a Observatory of the Astronomical Institute of the
Slovak Academy of Sciences (VersArray~512UV camera and a 60-cm Zeiss
reflector). All the observations were corrected for atmospheric
extinction by the method described in Moshkalev and Khaliullin (1985)
 and reduced to the standard Johnson $UBVRI$~system. These
data are available in electronic table. The mean errors of the
individual observations in $U, B, V, R, I$ are 0.07, 0.03, 0.02,
0.015 and 0.018 magnitude, respectively.

During three nights with the most stable atmospheric transparency,
I obtained magnitudes of stars in the frame with respect of the
secondary photometric standard\\ \mbox{GSC~479.740 = 111.2009} from the
Moffett and Barnes (1979) list. The results are presented in
Table~1.

\begin{table}[!hb]
\centerline{{\bf Table 1.} Photoelectric magnitudes of neighboring
stars}
\begin{center}
\begin{tabular}{cccccc}
\hline
 Star & $V$ & ${U-B}$ & ${B-V}$ & ${V-R}$ & ${R-I}$  \\
\hline
1        & $11.422(5) $ & $1.112(25)$ & $1.483(9) $ & $1.347(6) $ & $1.056(9) $  \\
2        & $13.396(6) $ & $0.443(20)$ & $1.037(9) $ & $0.912(7) $ & $0.748(10)$  \\
3        & $13.005(6) $ & $0.237(23)$ & $0.770(9) $ & $0.709(7) $ & $0.543(9) $  \\
4        & $12.769(7) $ & $0.243(19)$ & $0.799(10)$ & $0.730(8) $ & $0.575(6) $  \\
5        & $15.488(24)$ & $0.575(83)$ & $0.995(27)$ & $0.958(25)$ & $0.655(28)$  \\
26       & $12.886(5) $ & $-0.031(10)$ & $0.750(9)$ & $0.732(6) $ & $0.548(16)$  \\
\hline
\end{tabular}
\end{center}
\end{table}

The numbers of the stars are those from Leibowitz and Mendelson
(1982; hereafter, LM). My standardization in the $V$ band coincides with
LM better than to 0\fmm02 for all stars in common except No.~1 and
No~2. Star No.~1 was supposed to be variable with an amplitude of 0\fmm1
by Kemp et al. (1986). It also shows irregular variations
of brightness in present observations, with the full amplitude of
0\fmm04 in $V$. Its spectral type derived from the photometry
is M2V if we assume $A_V~=~0$, see Fig.~2. The star's high
proper motion, $\mu~=~0.123 ^{\prime \prime} /{\mathrm year}$ in the Tycho-2 catalogue,
indicates the proximity of the star and agrees with such a
possibility. Thus, it could be a BY~Dra variable. Star No.~2 has a
red companion at 6$^{\prime \prime}$ distance that could influence measurements
on nights with bad seeing. Therefore, star No.~4 was used as
the main comparison star and star No.~3, as the check one. Their
magnitudes match LM data well, and these stars did not show any
significant variability in the present observations.

I have used all available $V$-band observations of SS~433 collected
by Goranskij (2011) and the ephemeris from the same publication to obtain
the mean curve of the star phased with the precession period:
HJD ${\rm Max} = 2 449 998.0 + 162.278\cdot E$.

\IBVSfig{10cm}{6022-f1.eps}{Nightly mean magnitudes of SS 433. The
points corresponding to the flare are encircled. The
solid curves in the upper panel denote the mean precession
curve.}
\IBVSfigKey{6022-f1.eps}{SS 433}{light curve}

The comparison of this mean curve with the present data reveals
that the object was in the active state during the autumn
observations, see Fig.~1. A flare observed on JD~2455835 supports
such an idea. It is interesting to note that the colours of the
object did not change significantly during the flare (Fig.~1).
Figure~2 displays the position of SS~433 in the two-colour $U-B,
B-V$ diagram. Assuming that almost all the visible light comes
from the thick disk (Leibowitz 1984, Antokhina and Cherepashchuk
1987, Hirai and Fukue 2001), one can find from this diagram that
the spectrum of the object is B3 and $E(B-V)~=~2.37\pm0.06$, so
the lower limit of the temperature of the disk should be
$T\approx19000$~K. The interstellar extinction for SS~433 is
$A_V~=~7.35\pm0.18$, somewhat lower than the commonly accepted
value from Perez and Blundell (2010): $A_V~=~7.8$.

\IBVSfig{8cm}{6022-f2.eps}{The position of SS~433 in the $U-B, B-V$
diagram - black points. Luminosity classes are plotted according
to Straizys (1977): the dotted line stays for the luminosity
class III and the solid line for $V$. The point in the
flare is encircled. Big circles correspond to all
measured stars in the sky region. The reddening vector is
indicated by the arrow.}
\IBVSfigKey{6022-f2.eps}{SS 433}{two colour diagram}

The analysis of the present data except for points in a flash for
periodicity reveals another interesting fact. It is not the
orbital period but the nutation period that dominates the
periodogram, see Fig.~3. We present the nightly mean data folded
with the best period found, $P_{nut}~=~6$\fday109, in Fig.~4 and the
data folded with the orbital period, \\
HJD ${\rm Min} = 2 450 023.746 + 13.08223\cdot E$ according to Goranskij
(2011), in Fig.~5.

\IBVSfig{8cm}{6022-f3.eps}{The periodogram of the $V$-band light
variations in SS~433 based on 333 data points during 2011. The
average precession curve was subtracted from the data. The double
nutation period is also presented. Extra peaks are mainly due to the
approximately three month gap between the observational sets.}
\IBVSfigKey{6022-f3.eps}{SS 433}{periodogram}

\IBVSfig{8cm}{6022-f4.eps}{The $V$-band light curve phased with the
nutation period, 6\fday109. The average precession curve was
subtracted from the data.}
\IBVSfigKey{6022-f4.eps}{SS 433}{light curve}

\IBVSfig{8cm}{6022-f5.eps}{The $V$-band light curve phased with the
orbital period, 13\fday08223. The average precession curve was
subtracted from the data. The primary minimum is almost
invisible.}
\IBVSfigKey{6022-f5.eps}{SS 433}{light curve}

One can see that the present value of the nutation period is
shorter than it follows from the equation: $1/P_{\rm nut} = 2/P_{\rm orb}
+ 1/P_{\rm prec}$, $P_{\rm nut}~=~6$\fday2877. This could be explained by
the precession period variations found by Davydov, Esipov and
Cherepashchuk (2008) spectroscopically. In this study, we may
associate this effect with the active state of the object. It
should be noted from Figs.~1 and 4 that the flare occurred at the
brightness maxima of the nutation and precession curves, when
the opening of the disk to the observer was maximal.


{\bf Acknowledgements}. This study was supported by the SAIA
(Slovakia) scholarship and the grant 11-02-01213a from the Russian
Foundation for Basic Research. I would like to thank Dr. N. Samus
for important discussions.

\newpage
\references

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Hirai, Y. and Fukue, J., 2001, {\it PASJ}, {\bf 53}, 679 %\BIBCODE{2001PASJ...53..679H}

Kemp, J.\ C., Henson, G.\ D., Kraus, D.\ J., Carroll, L.\ C., Beardsley, I.\ S., Takagishi, K., Jugaku, J., Matsuoka, M.,
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Moffett, T.\ J. and Barnes, T.\ G., 1979, {\it AJ}, {\bf 84}, 627 %\BIBCODE{1979AJ.....84..627M}

Moshkalev, V.\ G. and Khaliullin, K.\ F., 1985, {\it SvA}, {\bf 29}, 227 %\BIBCODE{1985SvA....29..227M}

Perez, S.\ M. and Blundell, K.\ M., 2010, {\it MNRAS}, {\bf 408}, 2 %\BIBCODE{2010MNRAS.408....2P}

Straizys, V.\ L., 1977, {\it Multicolor Stellar Photometry},
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