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\IBVShead{5779}{19 June 2007}

\IBVStitletl{V2467 Cyg --- A Nova with Extremely Strong}{  O\,I\,8446\,\AA\ Emission}

\IBVSauth{Tomov,~T.; Miko{\l}ajewski,~M.; Ragan,~E.; Cika{\l}a,~M.; {\'S}wierczy{\'n}ski,~E.; Bro{\.z}ek,~T.; Karska,~A.; Wychudzki,~P.; Wi\c{e}cek,~M.; Ga{\l}an,~C.; Koziatek,~P.; Lewandowski,~M.; Radomski,~T.; Czart,~K.; Zajczyk,~A.; Konorski,~P.; Niedzielski,~A.}

\IBVSinsto{Centrum Astronomii, Uniwersytet Miko{\l}aja Kopernika, ul.\
Gagarina 11, Pl-87100 Toru\'n, Poland}

\SIMBADobjAlias{V2467 Cyg}{Nova Cyg 2007}
\IBVSkey{novae, photometry, spectra}

\begintext

V2467~Cyg${}\equiv{}$Nova Cyg 2007 was discovered by Tago (see Nakano et al.,
2007) at 7\fmm4 on March 15.8 already declining from the maximum. The
brightness maximum occurred somewhere between this date and Tago's last
negative observation on March 12.8 (Nakano et al., 2007). The nova was
confirmed spectroscopically on March 16.8 with an expansion velocity of
$\sim 1200$~km\,s$^{-1}$, measured for the P~Cyg absorption component of
H$\alpha$ (Nakano et al., 2007). Kubat \& Niemczura (2007) reported a velocity
of 968~km\,s$^{-1}$ on March 17.1 and 900~km\,s$^{-1}$ on March 17.2.
Munari et al.\ (2007) presented a detailed quantitative description of the
optical spectrum on March 18.2 and concluded that V2467~Cyg belongs to
Williams's (1992) ``Fe\,II'' class. They reported the presence of two P~Cyg
absorption components in the H{$\alpha$} and H{$\beta$} profiles with
velocities 913~km\,s$^{-1}$ and 1900~km\,s$^{-1}$. Steeghs et al.\ (2007)
identified the progenitor as an early A spectral type object with IPHAS
magnitudes $r'=18\fmm46\pm0\fmm01$ and $i'=17\fmm49\pm0\fmm1$. They
estimated the distance to V2467~Cyg in the range 1.5--4~kpc and an outburst
amplitude $\sim12$\mm\ typical for ``Fe\,II'' type galactic novae.

Photometric and spectral observations of V2467~Cyg at the Toru{\'n}
Observatory began on March 24, about ten days after the maximum
brightness. Photometric data were recorded with the 60-cm Cassegrain and
60/90-cm Schmidt--Cassegrain telescopes and the SAVS equipment
(Niedzielski et al., 2003), all of them equipped with CCD cameras.  We used
the Henden \& Munari (2007) photometric sequence to reduce our
observational data. Additionally, we carried out rapid brightness
variation monitoring, mainly in $V$ and $R_{\rm C}$. The photometric data
are listed in Table~1, the monitoring data are available electronically.

Spectra with $R\sim3000$, $\sim1500$ and $\sim750$ covering different
regions in the spectral interval 4000~\AA--8800~\AA\ were recorded with the
Canadian Copernicus Spectrograph (CCS) attached to the 60/90-cm
Schmidt--Cassegrain telescope. Additionally, with the same telescope, we
obtained prismatic spectra in the range 4300~\AA--10500~\AA\ with a
resolution of about $\sim5$~\AA, $\sim20$~\AA\ and $\sim60$~\AA\ at
H$\gamma$, H$\alpha$ and 9000~\AA, respectively.

The nova light curve and the color indices after April 12, 2007 are shown
in Fig.~1. The star is already $\sim4\mm$ fainter than at maximum, one
month earlier. During the following month the V2467~Cyg brightness in $V$
decreased by about 0\fmm9. The most remarkable variation is a dip
between JD~2454206 and JD~2454214. The colors $U-B$ and $B-V$ vary around
0\fmm4 and 1\mm, respectively. Stronger variations are apparent in the
$V-R$ and $V-I$ colors. $V-R$ became bluer by about $0\fmm40$ and $V-I$
changed from $3\fmm6$ to $2\fmm7$.

\begin{table}
\begin{center}
\small
Table 1. Toru{\'n} $UBVR_{\rm C}I_{\rm C}$ photometric observations of V2467~Cyg
\vskip 1mm
\begin{tabular}{cccccccl}
\hline
HJD   &  $U$  &  $B$ & $V$   &  $R_{\rm C}$  & $I_{\rm C}$ & Telescope & Monitoring$^*$ \\
\hline
2454184.611 &           &           &  9.56 &         &         & SAVS & \\
2454185.615 &           &           &  9.70 &         &         & SAVS & \\
2454203.458 &          &  12.40 & 11.42 &         &         & 90-cm & $3\fhr6~(V)$ \\
2454203.595 & 12.87 & 12.45 & 11.37 & 8.92 & 7.84 & 60-cm & $0\fhr3~(B),~0\fhr9~(R_{\rm C})$ \\
2454204.508 & 12.95 & 12.47 & 11.42 & 8.93 & 7.87 & 60-cm & $2\fhr3~(B),~2\fhr2~(R_{\rm C})$ \\
2454206.483 & 13.09 & 12.64 & 11.60 & 9.10 & 8.07 & 60-cm & $2\fhr8~(B),~2\fhr7~(R_{\rm C})$ \\
2454207.481 & 13.43 & 12.82 & 11.84 & 9.34 & 8.37 & 60-cm & \\
2454207.549 &           &           & 11.79 &         &         & SAVS & \\
2454209.551 &           &           & 12.11 &         &         & SAVS & \\
2454211.598 & 13.23 & 12.80 & 11.81 & 9.39 & 8.46 & 60-cm & $3\fhr4~(V),~3\fhr3~(R_{\rm C})$ \\
2454212.544 &           &           & 11.71 &         &         & SAVS & \\
2454216.503 & 13.09 & 12.73 & 11.71 & 9.37 & 8.52 & 60-cm & $1\fhr6~(V), 1\fhr7~(R_{\rm C})$ \\
2454217.475 & 13.18 & 12.72 & 11.71 & 9.34 & 8.48 & 60-cm & $2\fhr6~(V, R_{\rm C})$ \\
2454218.588 & 13.12 & 12.79 & 11.76 & 9.41 & 8.57 & 60-cm & $2\fhr7~(V, R_{\rm C})$ \\
2454221.455 & 13.25 & 12.89 & 11.84 & 9.53 & 8.75 & 60-cm & $3\fhr0~(R_{\rm C})$ \\
2454222.430 & 13.29 & 12.75 & 11.76 & 9.49 & 8.73 & 60-cm & $2\fhr9~(V),~3\fhr5~(R_{\rm C})$ \\
2454224.433 & 13.37 & 12.80 & 11.77 & 9.52 & 8.75 & 60-cm & $3\fhr5~(V, R_{\rm C})$ \\
2454226.457 & 13.45 & 12.91 & 11.88 & 9.65 & 8.91 & 60-cm & $1\fhr0~(R_{\rm C})$ \\
2454230.501 &           & 12.99 & 12.04 & 9.82 & 9.17 & 60-cm & \\
2454240.560 &           &          & 12.13 & 9.98 & 9.42 & 60-cm & \\
2454241.419  & 13.17  & 13.01 & 12.12 & 9.96 & 9.37 & 60-cm & $3\fhr5~(V, R_{\rm C})$ \\
2454244.554 & 13.06 & 12.96 & 11.99 & 9.92 & 9.30 & 60-cm & \\
2454245.397 &          & 13.05 & 12.04 & 9.94 & 9.34 & 60-cm & \\
2454246.392 &          & 13.12 & 12.21 & 10.06 & 9.54 & 60-cm & \\
2454249.421 & 13.80 & 13.19 & 12.32 & 10.19 & 9.66 & 60-cm & \\
\hline
\end{tabular}

* Available at the IBVS website for $B,V,R_{\rm C}$ filters as files 5779-t1.txt, 5779-t2.txt, 5779-t3.txt, 
respectively
 \IBVSedata{5779-t1.txt}
 \IBVSedata{5779-t2.txt}
 \IBVSedata{5779-t3.txt}

\end{center}
\end{table}

\vspace{-12pt}

\IBVSfig{10.4cm}{5779-f1.eps}{The $V$ light curve and the color variations
of V2467~Cyg. In the two bottom panels, the flux ratio
O\,I~8446~\AA/H$\alpha$ and the H$\alpha$ flux from our objective prism
spectra are shown}
 \IBVSfigKey{5779-f1.eps}{V2467 Cyg}{light curve}

\IBVSfig{5.22cm}{5779-f2.eps}{Examples of the rapid brightness
variations of V2467~Cyg in $V$ and $R_{\rm C}$ filters}
 \IBVSfigKey{5779-f2.eps}{V2467 Cyg}{light curve}

\vspace{-36pt}

\IBVSfig{8.25cm}{5779-f3.eps}{The power spectra and the light curves
in $V$ and $R_{\rm C}$, phased with the corresponding periods marked by
arrows}
 \IBVSfigKey{5779-f3.eps}{V2467 Cyg}{periodogram ; light curve}

\IBVSfig{4.667cm}{5779-f4.eps}{The lower curve shows the objective prism
spectrum of V2467~Cyg obtained on April 13, 2007. The same spectrum
multiplied by 8 is also plotted}
 \IBVSfigKey{5779-f4.eps}{V2467 Cyg}{spectrum}

\vspace{-24pt}

In Fig.~2 examples of our $V$ and $R_{\rm C}$ monitoring are shown.
Similar short time variability is obvious in both filters with a
significantly larger amplitude in $V$. Fourier analysis cannot distinguish
a single coherent frequency in both $V$ and $R_{\rm C}$ bands. We have
analyzed residuals from each night's mean brightness for 18.4 hours and 1220
observational points in $V$, and 17.3 hours and 983 points in the $R_{\rm
C}$ band, obtained during the period April 12--May 5. The resulting power
spectra are shown in Fig.~3 and look like a superposition of two quasi
periodic oscillations (QPO) $P_1\geq3\hr$ and $P_2\leq2\hr$, just
above and below the period gap for cataclysmic variables. The most
probable period lies between the peaks at 6.24~d$^{\rm -1}$ for $R_{\rm
C}$ and at 6.72~d$^{\rm -1}$ for $V$, both marked in Fig.~3. The light
curves corresponding to these frequencies are presented in the right panels
of the same figure. The light curves for any other strong aliases look
similar.

Since the beginning of our observations, V2467~Cyg followed a normal
``Fe\,II'' nova spectral evolution. At the end of March, the spectrum was
dominated by Balmer and Fe\,II emission lines. Two P~Cyg absorption
components were obvious in the Balmer lines and the slowest one was easily
visible in the Fe\,II lines as well. Their velocities were about
2290~km\,s$^{-1}$ and 1300~km\,s$^{-1}$ on March 24 and increased to
$\sim 2590$~km\,s$^{-1}$ and $\sim 1405$~km\,s$^{-1}$ on April 1.

Between April 1 and 13 the nova spectrum changed significantly. The [OI]
lines 6300~\AA\ and 6364~\AA, visible as weak emissions since the
beginning of our observations, increased significantly during this period.
Many new emission lines appeared in the spectrum. The most intensive among
them were [OIII] 5007~\AA, [OI] 5577~\AA, [NII] 5755~\AA, He\,I 5876~\AA,
6678~\AA, 7065~\AA, C\,II 7234~\AA, [OII] 7325~\AA{}. However, the
strongest emission line was O\,I 8446~\AA\ (Fig.~4). We started our
objective prism observations covering this region on April 13 but the line
was probably present in the spectrum during all the time of our
observations. The reason why we think this relates to the other O\,I line
at 7774~\AA\ visible at the red edge of our CCS spectrum obtained on March
26. In the later spectra, both O\,I lines were visible together and the
8446~\AA\ one was much stronger. In Fig.~1 the changes in the H$\alpha$
flux as well as the flux ratio O\,I 8446~\AA/H$\alpha$ are shown. The
H$\alpha$ flux decreases from $\sim4.9\times10^{-10}$
erg\,cm$^{-2}$\,sec$^{-1}$ in mid April to $\sim2.0\times10^{-10}$
erg\,cm$^{\rm -2}$\,sec$^{\rm -1}$ in mid May. During the same time the
flux ratio O\,I~8446~\AA/H$\alpha$ changes from $\sim1.2$ to $\sim0.5$.
The O\,I~8446~\AA\ flux larger than H$\alpha$ is probably exceptional.
However, this O\,I line is produced in a fluorescent cascade as a result
of pumping by Ly$\beta$ H\,I photons (Kastner \& Bhatia, 1995), so such a
strong O\,I flux could indicate an extremely high oxygen overabundance.

{\bf Acknowledgements.} This work was supported by the Polish MNiSW
Grant N203 018 32/2338. We are grateful to Boud Roukema for the
improvement of English.

\vspace{-12pt}

\references

Henden, A., Munari, U., 2007, {\it IBVS}, No.\ 5769

Kastner, S.O., Bhatia, A.K., 1995, {\it ApJ}, {\bf 439}, 346

Kubat, J., Niemczura, E., 2007, {\it CBET}, No.\ 894

Munari, U., Dalla Via, G., Valisa, P., Dallaporta, S., Castellani, F.,
2007, {\it CBET}, No.\ 897

Nakano, S., Tago, A., Nishiyama, K., Sakamoto, T., 2007, {\it IAUC}, No.\ 8821

Niedzielski, A., Maciejewski, G., Czart, K., 2003, {\it AcA},
{\bf 53}, 281

Steeghs, D., Drew, J., Greimel, R., et al., 2007, {\it ATel}, No.\ 1031

Williams, R.E., 1992, {\it AJ}, {\bf 104}, 725

\endreferences


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