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\begin{document}

\IBVShead{5605}{25 February 2005}

\IBVStitle{Spectroscopic and Photometric Observations of SN~2004\lowercase{dj}}

\IBVSauth{Kor\v{c}\'{a}kov\'{a}, D.$^1$; Mikul\'a\v{s}ek, Z.$^2$; Kawka, A.$^1$; Kub\'{a}t, J.$^1$; Hornoch, K.$^3$; \v{S}a\-rou\-no\-v\'{a}, L.$^1$; Ku\v{s}nir\'ak, P.$^1$; Hadrava, P.$^1$; Wolf, M.$^4$; \v{S}lechta, M.$^1$; \v{S}koda, P.$^1$; Dov\v{c}iak, M.$^1$; Libich, J.$^{1,4}$}

\IBVSinst{Astronomick\'y \'ustav AV \v{C}R, Fri\v{c}ova 298,
CZ-251~65 Ond\v{r}ejov, Czech Republic;
\\email: kor@sunstel.asu.cas.cz}

\IBVSinst{\'Ustav teoretick\'e fyziky a astrofyziky, Masarykova
    univerzita,
           Kotl\'{a}\v{r}sk\'{a} 2, CZ-611\,37 Brno, Czech Republic;}

\IBVSinst{CZ-664 31 Lelekovice 393, Czech Republic;}

\IBVSinst{Astronomick\'y \'ustav UK, V Hole\v{s}ovi\v{c}k\'ach 2,
CZ-182~00 Praha 8, Czech Republic.}

\SIMBADobj{SN 2004DJ}
\NEDobj{SN 2004dj}
\IBVSkey{supernova - photometry, spectroscopy}

\IBVSabs{Photometric and spectroscopic observations of the supernova}
\IBVSabs{SN 2004dj are presented.}


\begintext

\vspace*{-1cm}

The supernova SN\,2004dj in NGC\,2403 was first reported by Nakano
et al. (2004). It has been classified as a normal type II-P
supernova (Patat et al. 2004). We present spectroscopic and
photometric observations of the supernova SN\,2004dj obtained at the
Ond\v{r}ejov observatory and Lelekovice private observatory during
August, September, and October 2004.

We obtained a total of 15 spectra of the supernova during 8 nights
between 3rd August and 1st September 2004 at the Ond\v{r}ejov 2m
reflector using the Coud\'e spectrograph 
(for a description see \v{S}koda et al. 2002)
with a spectral range 6330 to 6773 \AA. The resolution power of the
spectrograph in the H$\alpha$ region is about 13\,000. We used the
Coud\'e 700mm  camera with the SITe CCD 2030$\times$800 15$\mu$
pixels. Spectra were obtained as a series of exposures during the
same night were co-added. The development of the H$\alpha$ profile
is shown in Fig~\ref{fig:5605-f1.eps}. All spectra were
normalized to 1 using the continuum near 6330 \AA. All spectra were
analysed using principal component analysis (PCA) combined with our
own version of robust regression (Mikul\'a\v{s}ek et al. 2003),
where all 8 observed H$\alpha$ line profiles are expressed as a
linear combination of basic mutually orthonormal functions, i.e.,
principal components. After a careful analysis we concluded we could
confine ourselves to the first three terms of the PCA decomposition,
since the amplitude of higher order terms being negligible with
respect to the errors. Telluric lines were removed prior to the
analysis.

The H$\alpha$ line is described by the radial velocities of the
minimum and maximum of the broad P Cygni profile and by the ratio of
the maximum and minimum line intensity of the profile (see
Tab.~\ref{charakteristiky}, Fig.~\ref{5605-f2}). 
The radial velocities are calculated relative to the 
frame coupled with supernova.
Measured values of radial velocities were corrected for the radial
velocity of the host galaxy NGC 2403, which is $129$\,km/s (Ho et al.
1997). The positions of the line minimum and maximum were found 
to decrease from 6960$\pm$20 to 4890$\pm$40 km/s and 
1273$\pm$4 to 772$\pm$5 km/s, respectively. The initial
change in radial velocities is steep, however it flattens out with
time (see Fig.\,\ref{5605-f2}a). We found  only a small change in
the ratio of the maximum and minimum line intensities. Initially,
the ratio was 5.29$\pm$0.10, then it reached 6.3$\pm$0.2 at JD
24453234.6$\pm$0.5 before it dropped down to 4.9$\pm$0.2
(Fig.\,\ref{5605-f2}b). The blue edge of the absorption part of
the line profile remained more or less constant: 
10\,300~km/s.


\IBVSfig{9.5cm}{5605-f1.eps}{Spectra of SN\,2004dj obtained
at the Coud\'e spectrograph  of the Ond\v{r}ejov 2m telescope. The
$y$ axis denotes the relative flux, individual spectra are shifted
and labeled with the Julian date at the middle of the exposure of
co-added spectra (\emph{JD}$-$2453200).}
\IBVSfigKey{5605-f1.eps}{SN 2004dj}{spectrum}

\begin{table}[!hr]
\begin{center}
\caption{The H$\alpha$ line characteristics of SN\,2004dj. The JD
given is the mid-exposure time of co-added spectra, $N$ is the
number of co-added spectra, $RV_{\rm{max}}$ and $RV_{\rm{min}}$ are
the radial velocities of the maximum and minimum of the H$\alpha$
profile corrected for the radial velocity of the host galaxy
($RV_{\rm{g}}=129$\,km/s, Ho et al., 1997), respectively,
$I_{\rm{max}}/I_{\rm{min}}$ is the ratio of the maximum and minimum
intensities, $RV_{\rm{abs}}$ is the corrected radial velocity of the
blue absorption feature and $I_{\rm{cabs}}$ is its central depth.}
\label{charakteristiky}
\medskip
\normalsize
\begin{tabular}{|ccccccc|}
\hline \emph{JD}-2450000 & \emph{N} & $RV_{\rm{max}}$ [km/s] &
$RV_{\rm{min}}$ [km/s] & $I_{\rm{max}}/I_{\rm{min}}$
& $RV_{\rm{abs}}$ [km/s] & $I_{\rm{cabs}}$ \\
\hline
3\,221.48 & 2 & 6955$\pm$25  &1275$\pm$5  & 5.3$\pm$0.2 & 9090$\pm$70  & 0.030$\pm$0.011\\
3\,222.44 & 2 & 6840$\pm$30  &1206$\pm$5  & 5.5$\pm$0.2 & 9040$\pm$90  & 0.023$\pm$0.011\\
3\,224.41 & 2 & 6530$\pm$60  &1091$\pm$6  & 5.3$\pm$0.2 & 8750$\pm$60  & 0.040$\pm$0.013\\
3\,225.49 & 2 & 6340$\pm$110 &1028$\pm$9  & 5.9$\pm$0.3 & 8730$\pm$130 & 0.035$\pm$0.024\\
3\,226.45 & 1 & 6210$\pm$50  &970$\pm$6   & 6.0$\pm$0.2 & 8720$\pm$230 & 0.012$\pm$0.014\\
3\,236.50 & 2 & 5590$\pm$120 &707$\pm$9   & 5.8$\pm$0.6 & 8300$\pm$150 & 0.07$\pm$0.05\\
3\,240.50 & 2 & 5250$\pm$50  &687$\pm$5   & 6.1$\pm$0.2 & 8310$\pm$50  & 0.070$\pm$0.017\\
3\,249.59 & 2 & 4890$\pm$40  &672$\pm$5   & 4.9$\pm$0.2 & 8290$\pm$30  & 0.130$\pm$0.020\\
\hline
\end{tabular}
\end{center}
\vspace*{-1cm}
\end{table}

We want to draw attention to the absorption feature in the blue part
of the absorption wing of the H$\alpha$ P Cygni profile (see
Fig.\,\ref{fig:5605-f1.eps}). The center of the absorption
feature was to move towards the red, similarly to the maximum of the
main H$\alpha$ line profile (see
Fig.\,\ref{fig:5605-f1.eps}). The depth at the center of the
feature increases from $0.021\pm0.006$ to $0.112\pm0.015$
with respect to undisturbed H$\alpha$ profile. A~similar
feature was observed in SN 1999em (see Fig.\,13 in Leonard et al.
2001). However, it remains uncertain whether the absorption feature
belongs to the H$\alpha$ line profile or whether it can be
attributed to absorption of some other chemical element.

Ond\v{r}ejov photometric observations have been carried out with the
0.65-m f/3.6 telescope equipped with an AP7 CCD camera (SITe
512$\times$512 pixels) at the primary focus, in BVR Johnson-Cousins
standard photometric bands (Bessell 1990). Stars GSC\,4120:685 and
GSC\,4120:725 served as the comparison and check stars, respectively
(see Figure \ref{fig:5605-f3.eps}).


\IBVSfig{8cm}{5605-f2.eps}{\,\,(a)\,Time dependence of radial velocities of
H$\alpha$'s profile maximum ($\Delta$) and minimum ($\nabla$). Dots
($\bullet$) denote the radial velocity of the absorption 
feature center found in
the blue part of the wing. (b)\,Time dependence of the ratio of
maximum and minimum intensity of the H$\alpha$'s profile. \label{5605-f2}}
\IBVSfigKey{5605-f2.eps}{SN 2004dj}{}

\IBVS2fig{6.5cm}{5605-f3.eps}{ An image taken at Ond\v{r}ejov showing the position of SN\,2004dj, the check star (GSC\,4120:725, 13.085 R) and the comparison star (GSC\,4120:685, 11.48 R).}{5605-f4.eps}{ An image taken at Lelekovice showing the position of SN\,2004dj and the comparison stars, GSC\,4120:764 (A, 10.205 R), GSC\,4120:718 (B, 13.165 R) and GSC\,4120:725 (C, 13.085 R).}
\IBVSfigKey{5605-f3.eps}{SN 2004dj}{finding chart}
\IBVSfigKey{5605-f4.eps}{SN 2004dj}{finding chart}


In Lelekovice, we obtained photometry in the
 \emph{R} Johnson-Cousins standard photometric
band using the 0.35-m f/4.7 telescope equipped with the SBIG ST-6V
CCD. We co-added 6-10 individual images with exposure times of 60
seconds to improve the signal-to-noise ratio. We used the comparison
star GSC\,4120:764 and the two check stars, GSC\,4120:718 and
GSC\,4120:725 (see Fig.\,\ref{fig:5605-f4.eps}) to obtain the
Lelekovice \emph{R} light curve.

The comparison stars from both Ond\v{r}ejov and Lelekovice posts
were calibrated using the calibration fields near M31 and M13, which have
already been well calibrated using the standard fields measured by
Landolt (1992). The comparison stars and calibration fields near M31
and M13 were observed during two nights under average conditions
with an estimated accuracy of 0.05 mag in \emph{R}. 
All data except of the last one: JD=2453297.406, R=13.91 mag, have been
reported in Hornoch (2004a,b).
The results of photometric observations are shown in the
Fig.\,\ref{fig:5605-f5.eps}
and Table\,2 (only in electronic version).

\IBVSedata{5605-t2.txt}
\IBVSdataKey{5605-t2.txt}{SN 2004DJ}{photometry}

\IBVSfig{8cm}{5605-f5.eps}{The \emph{R} light curve from both 
Lelekovice (triangles) and Ond\v{r}ejov (circles) observatories.
Arrows indicate nights when the spectra in Fig.\,\ref{fig:5605-f1.eps}.
were obtained. All of them were taken during the phase of the very slow 
decrease after the brightness maximum.}
\IBVSfigKey{5605-f5.eps}{SN 2004dj}{light curve}


{\bf Acknowledgements:}

This research has made use of NASA's Astrophysics Data System. This
work was supported by grants GA \v{C}R 205/02/0445, 205/02/0735,
205/04/1267 and 205/04/P224. The Astronomical Institute Ond\v{r}ejov
is supported by project Z10030501.


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