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\IBVShead{5751}{22 January 2007}

\IBVStitletl{Spectroscopy of the Faint Old Novae}{ V P\lowercase{er} and V500 A\lowercase{ql}}

\IBVSauth{Haefner, R.; Fiedler, A.}

\IBVSinsto{Universit\"ats-Sternwarte M\"unchen, Scheinerstr.\ 1, D-81679
M\"unchen, Germany}

\SIMBADobj{V Per} 
\SIMBADobj{V500 Aql}

\IBVSabs{Results of time-resolved spectroscopy of the old novae V Per}  
\IBVSabs{and V500 Aql are reported for the first time.}

\begintext

Results of time-resolved spectroscopy of the faint old novae V Per and V500 Aql
are reported for the first time. The observations were performed using the Low
Resolution Spectrograph (LRS) at the 9.2-m Hobby-Eberly Telescope (HET) and the
FORS1 instrument at the ESO Very Large Telescope (VLT) Unit No.~1. Table 1 lists
the observing log for each object. All spectra were reduced with IRAF\IBVSfm\
standard tools. Radial velocities were measured applying the double-Gaussian
convolution method (see e.g.\ Shafter et al., 1986).  The corresponding code was
written using the yorick language.
 \IBVSfoot{IRAF is distributed by the National Optical Astronomy Observatories,
which are operated by the Association of Universities for Research in Astronomy,
Inc., under cooperative agreement with the National Science Foundation.}

\begin{table}[h]
\begin{center}
\caption{Journal of observations. UT times refer to the start of the
  first and last exposure, respectively}
\vskip3mm
\begin{tabular}{lcccccccr} 
\hline
Object & Date & First exp. & Last exp. & Indiv.\ exp.  & No.  &
Res. & Tel. \\ 
  &   & (UT) & (UT) &  time (s) & exp. & (\AA/pix) &    \\
\hline
V Per    & 2001 Oct.~14 & 04:21:34 & 05:48:42 & 500 & 8 &2 &HET \\
         & 2001 Oct.~14 & 09:13:47 & 10:01:15 & 500 & 5 &2 &HET \\
         & 2001 Nov.~25 & 06:30:38 & 07:38:39 & 500 & 8 &2 &HET \\
V500 Aql & 1999 June 11 & 06:47:12 & 10:24:54 & 420/720 & 20 &1.2 &VLT \\
\hline
\end{tabular}
\end{center}
\end{table}

V Per (Nova Persei 1887) is a faint ($V \approx 18$) eclipsing ($\Delta V
\approx 1.3$) classical nova. The orbital period of the system is 2.571~hr, thus
placing it near the middle of the period gap of cataclysmic variables (Shafter
\& Abbott, 1989).  In their recent eclipse analysis Shafter \& Misselt (2006)
investigated the structure of the accretion disk and estimated the masses of the
components to be most likely $M_{1} = 0.85~M_{\odot}$ and $M_{2} =
0.17~M_{\odot}$. The only spectrum of the postnova known so far is that
published by Shafter \& Abbott (1989). The exposure time was around 1~hr thus
covering nearly half an orbital cycle. Besides the Balmer emissions
(H$_{\alpha}$, H$_{\beta}$, H$_{\gamma}$) the spectrum shows the high excitation
lines He II $\lambda$4686 and $\lambda$5411 which are characteristic for old
novae. Moreover, the fact that He II $\lambda$4686 is stronger than H$_{\beta}$
led the authors to suggest that V Per might be a magnetic system. But the object
was not detected as an X-ray source in the ROSAT All Sky Survey (Verbunt et al.,
1997) and shows no circular polarization (Stockman et al., 1992) which would
have strengthened this interpretation.

\newpage

\IBVSfig{8.5cm}{5751-f1.eps}{Grey-scale representation of the He II
$\lambda$4686 and H$_{\beta}$ lines (left) and the H$_{\alpha}$ line (right) of
V~Per. The spectra are folded on the orbital period and averaged into 11 phase
bins. A velocity scale is given on top: the central large tick represents zero
velocity for each line and the smaller ticks to the left and right follow in
steps of $\pm1000$~km/s. The double-peaked structure of H$_{\alpha}$ and
H$_{\beta}$ around phase 0.5 is clearly recognisable whereas the He II line
remains single-peaked}
 \IBVSfigKey{5751-f1.eps}{V Per}{spectrum}

\IBVSfig{8.5cm}{5751-f2.eps}{Radial velocity curve of the H$_{\alpha}$ line in V
Per along with the best-fitting sinusoid. The velocities were measured using a
(full) Gaussian separation of 1400~km/s. Note the large phase lag of 75\deg. A
separation of e.g.\ 1960~km/s (He~II) would reduce the phase lag only marginally
by 3\deg\ but would increase the scatter of the radial velocity curve}
 \IBVSfigKey{5751-f2.eps}{V Per}{radial velocity curve}

\IBVSfig{8.5cm}{5751-f3.eps}{Orbital emission line variations of V500 Aql. The
spectra are normalised to continuum level and separated vertically by constant
offsets. Phase zero is arbitrarily assigned to the first spectrum of the series.
The spectrum for phase 0.97 (actually an average of three) shows larger scatter
since the data suffer from large air mass and a possible partial coverage of the
shallow eclipse}
 \IBVSfigKey{5751-f3.eps}{V500 Aql}{spectrum}

\IBVSfig{8.5cm}{5751-f4.eps}{Radial velocity curve of the H$_{\beta}$ line in
V500 Aql along with the best-fitting sinusoid ($K_{1}= 65\pm13$~km/s,
$\gamma = -72\pm10$~km/s). The velocities were measured using a (full)
Gaussian separation of 1890~km/s and folded on the orbital period (3.485 hr).
Note that phase zero is arbitrary}
\IBVSfigKey{5751-f4.eps}{V500 Aql}{radial velocity curve}

\vspace{-36pt}

V500 Aql (Nova Aquilae 1943) is a faint ($\sim 18$ mag) old nova which shows
eclipses ($\sim 0.4$ mag) repeating with a period of 3.485 hr (Haefner, 1999).
No spectroscopic information on the postnova is known in the literature.
 
The phases for our 21 time-resolved spectra of V Per (wavelength range
$\lambda\lambda$4500--7000~\AA) were computed using the new ephemeris given by
Shafter \& Misselt (2006). The spectra cover the phase interval $\varphi =
0.31$--0.97 with respect to the eclipse time. Bet\-ween $\varphi = 0.39$ and
$\varphi = 0.60$ the H$_{\alpha}$ and H$_{\beta}$ emissions exhibit a moderate
double-peaked structure whereas the strong He II $\lambda$4686 line remains
single-peaked at all times, a phenomenon shared with the SW~Sex stars. Since the
spectra are unevenly distributed over the phase, they were averaged into 11
almost evenly spaced phase bins for better presentation of the effect
(\mbox{Fig.~1}). Because the high-velocity wings of all lines seemed to be
undisturbed an attempt was made to determine radial velocities. The resulting
radial velocity curve for H$_{\alpha}$ ($K_{1} = 308\pm21$~km/s, $\gamma =
56\pm18$~km/s)  is convincing (\mbox{Fig.~2}). However, the pronounced phase lag
of $75\deg\pm4\deg$ relative to the photometric ephemeris shows that
H$_{\alpha}$ does not follow the motion of the white dwarf. The same holds true
for the H$_{\beta}$ and He II $\lambda$4686 lines.  But, whereas a (full)
Gaussian separation of 1400~km/s was essential to obtain the H$_{\alpha}$
radial velocity curve showing the least scatter, separations of 1800~km/s and
1960~km/s were required for an optimal solution in the case of H$_{\beta}$ and
He II, respectively. The corresponding radial velocity curves though being of
suboptimal quality show lower semi-amplitudes ($K_{1}\sim235$~km/s) and
phase lags on the order of some 60\deg.  Therefore, there must be severe
departures from symmetric line emission across the whole accretion disk or the
system really harbours a magnetic white dwarf. Though the incomplete phase
coverage might have some influence on the resulting radial velocity curves,
their amplitudes constitute in any case no reliable quantity to derive e.g.\ the
mass of the primary. In view of this it rather becomes redundant to mention that
the measured large values of $K_{1}$ would result in an unrealistically small
mass for the white dwarf ($M_{1}\ll M_{2}$).

Our 20 time-resolved spectra of V500 Aql (wavelength range  
$\lambda\lambda$4000--5000 \AA) cover one orbital revolution 
and show the typical emission line features of old novae. The Balmer 
lines, as compared with V Per, are quite weak with He II $\lambda$4686 
being less prominent than H$_{\beta}$. The C~III/N~III $\lambda$4640--4650 
complex, however, exhibits the same intensity as the He~II line. Since 
the individual spectra are rather noisy (in particular the first three 
and last four of the series with individual exposure times of 420 s) 
the data were averaged resulting in nine spectra which are nearly
equally spaced in phase. Complex changes especially in the Balmer line 
profiles can be recognized (\mbox{Fig.~3}). Nevertheless, at least the 
H$_{\beta}$ line seemed to be suitable for radial velocity measurements. 
The resulting radial velocity curve (\mbox{Fig.~4}) exhibits a moderate 
amplitude, but disallows any reliability check since the photometric 
ephemeris is not known with the required precision to establish a 
possible phase lag.

\references

Haefner, R., 1999, {\it IBVS}, No.\ 4706

Shafter, A.W., Szkody, P., Thorstensen, J., 1986, {\it ApJ}, {\bf 308}, 765

Shafter, A.W., Abbott, T.M.C., 1989,  {\it ApJ}, {\bf 339}, L75

Shafter, A.W., Misselt, K.A., 2006,  {\it ApJ}, {\bf 644}, 1104

Stockman, H.S., Schmidt, G.D., Berriman, G., Libert, J., Moore, R.L.,
  Wickramasinghe, D.T., 1992,   {\it ApJ}, {\bf 401}, 628

Verbunt, F., Bunk, W. H., Ritter, H., Pfeffermann, E., 1997, {\it
  A\&A},  {\bf 327}, 602

\endreferences 

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