Toward a unified light curve model for multi-wavelength observations of V1974 Cygni (Nova Cygni 1992)
Izumi Hachisu
We present a unified model for optical, ultraviolet (UV), and X-ray light curves of V1974 Cygni (Nova Cygni 1992). Based on an optically thick wind model of nova outbursts, we have calculated light curves and searched for the best fit model that is consistent with optical, UV, and X-ray observations. Our best fit model is a white dwarf (WD) of mass $1.05~M_\sun$ with a chemical composition of $X=0.46$, $C+N+O=0.15$, and $Ne = 0.05$ by mass weight. Both supersoft X-ray and continuum UV 1455 \AA ~light curves are well reproduced. Supersoft X-rays emerged on day $\sim 250$ after outburst, which is naturally explained by our model: our optically thick winds cease on day 245 and supersoft X-rays emerge from self-absorption by the winds. The X-ray flux keeps a constant peak value for $\sim 300$ days followed by a quick decay on day $\sim 600$. The duration of X-ray flat peak is well reproduced by a steady hydrogen shell burning on the WD. Optical light curve is also explained by the same model if we introduce free-free emission from optically thin ejecta. A $t^{-1.5}$ slope of the observed optical and infrared fluxes is very close to the slope of our modeled free-free light curve during the optically thick wind phase. Once the wind stops, optical and infrared fluxes should follow a $t^{-3}$ slope, derived from a constant mass of expanding ejecta. An abrupt transition from a $t^{-1.5}$ slope to a $t^{-3}$ slope at day $\sim 200$ is naturally explained by the change from the wind phase to the post-wind phase on day $\sim 200$. The development of hard X-ray flux is also reasonably understood as shock-origin between the wind and the companion star. The distance to V1974 Cyg is estimated to be $\sim 1.7$~kpc with $E(B-V)= 0.32$ from the light curve fitting for the continuum UV 1455 \AA~.
ms.tex
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\shorttitle{Light Curve of V1974 Cygni}
\shortauthors{Hachisu \& Kato}

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\title{Toward a unified light curve model for multi-wavelength 
observations of V1974 Cygni (Nova Cygni 1992)}

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\author{Izumi Hachisu}
\affil{Department of Earth Science and Astronomy, 
College of Arts and Sciences, University of Tokyo,
Komaba, Meguro-ku, Tokyo 153-8902, Japan} 
\email{hachisu@chianti.c.u-tokyo.ac.jp}

\and

\author{Mariko Kato}
\affil{Department of Astronomy, Keio University, 
Hiyoshi, Kouhoku-ku, Yokohama 223-8521, Japan} 
\email{mariko@educ.cc.keio.ac.jp}

%\and
%
%\author{Taichi Kato}
%\affil{Department of Astronomy, Kyoto University, 
%Sakyo-ku, Kyoto 606-8502, Japan} 
%\email{tkato@kusastro.kyoto-u.ac.jp}
%
%% Notice that each of these authors has alternate affiliations, which
%% are identified by the \altaffilmark after each name.  Specify alternate
%% affiliation information with \altaffiltext, with one command per each
%% affiliation.

%\altaffiltext{1}{Visiting Astronomer, Cerro Tololo Inter-American Observatory.
%CTIO is operated by AURA, Inc.\ under contract to the National Science
%Foundation.}
%\altaffiltext{2}{Society of Fellows, Harvard University.}
%\altaffiltext{3}{present address: Center for Astrophysics,
%    60 Garden Street, Cambridge, MA 02138}
%\altaffiltext{4}{Visiting Programmer, Space Telescope Science Institute}
%\altaffiltext{5}{Patron, Alonso's Bar and Grill}


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\begin{abstract}
     We present a unified model for optical, ultraviolet (UV),
and X-ray light curves of V1974 Cygni (Nova Cygni 1992).
Based on an optically thick wind model of nova outbursts,
we have calculated light curves and searched for the best fit model
that is consistent with optical, UV, and X-ray observations.
Our best fit model is a white dwarf (WD) of mass $1.05~M_\sun$
with a chemical composition of $X=0.46$, $C+N+O=0.15$, 
and $Ne = 0.05$ by mass weight.
Both supersoft X-ray and continuum UV 1455 \AA ~light curves
are well reproduced.  Supersoft X-rays emerged on day $\sim 250$
after outburst, which is naturally explained by our model: our
optically thick winds cease on day 245 and supersoft X-rays emerge
from self-absorption by the winds.  The X-ray flux keeps a constant
peak value for $\sim 300$ days followed by a quick decay on day 
$\sim 600$.  The duration of X-ray flat peak is well reproduced
by a steady hydrogen shell burning on the WD.
Optical light curve is also explained by the same model if we 
introduce free-free emission from optically thin ejecta.
A $t^{-1.5}$ slope of the observed optical and infrared fluxes 
is very close to the slope of our modeled free-free light curve
during the optically thick wind phase.  Once the wind stops, 
optical and infrared fluxes should follow a $t^{-3}$ slope,
derived from a constant mass of expanding ejecta.
An abrupt transition from a $t^{-1.5}$ slope to a $t^{-3}$ slope 
at day $\sim 200$ is naturally explained by the change from 
the wind phase to the post-wind phase on day $\sim 200$.
The development of hard X-ray flux is also reasonably 
understood as shock-origin between the wind and the companion star.
The distance to V1974 Cyg is estimated to be $\sim 1.7$~kpc with
$E(B-V)= 0.32$ from the light curve fitting for the continuum 
UV 1455 \AA~.
\end{abstract}


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\keywords{novae, cataclysmic variables --- stars: individual (V1974~Cygni)
--- X-rays: stars}

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%% and \citet commands to identify citations.  The citations are
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\section{Introduction}
     It has been widely accepted that 
classical novae are a thermonuclear runaway event 
on a mass-accreting white dwarf (WD).
Characteristic properties on nova evolution have been
understood from its ignition through the end of nuclear burning
\citep[e.g.,][for a review]{war95}.
The next step we need is quantitative studies of individual objects.
For instance, fitting of multi-wavelength light curves with
theoretical models enables us to determine nova parameters.
Such a work has been developed in the recurrent novae 
\citep[e.g.,][]{hac01ka, hac01kb, hkkm00, hac03a},
but not yet in the classical novae except
a pioneering work on V1668 Cyg (Nova Cygni 1978) by \citet{kat94}.  

V1974 Cygni (Nova Cygni 1992) is a best example for such studies
because it was extensively observed in all the wavelengths from 
$\gamma$-ray to radio.  
Among various observational data, three bands of optical, 
continuum ultraviolet (UV) at 1455 \AA~, 
and X-ray are used for our present study.
Based on an optically thick wind model of nova 
outbursts \citep[e.g.,][]{kat94h},
we try to develop a unified model that yields light curves
for each wavelength band.  The next section introduces the light curve
analysis based on our optically thick wind model.  In \S 3, 
we describe light curve fittings with X-ray, UV, and optical bands.
Discussion follows in \S 4.  

%%% V1974 Cyg was discovered in outburst 
%%% on 1992 February 19.07 UT \citep{col92}
%%% and reached an optical maximum of $V= 4.4$ on 1992 February 21.17 UT.

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\section{Modeling of V1974 Cyg}

\subsection{Optically thick wind model}
     After a thermonuclear runaway sets in on a mass-accreting WD,
its envelope expands greatly to $R_{\rm ph} \gtrsim 100 ~R_\sun$
and settles in a steady-state.  The decay phase of nova can be 
followed by a sequence of steady state solutions \citep[e.g.,][]{kat94h}.  
Using the same method and numerical techniques as in \citet{kat94h},
we have calculated theoretical light curves.

     We solve a set of equations, i.e., the continuity, equation
of motion, radiative diffusion, and conservation of energy, 
from the bottom of the hydrogen-rich envelope through the photosphere,
under the condition that the solution goes through a critical point
of steady-state winds.  The winds are accelerated deep inside 
the photosphere so that they are called ``optically thick winds.''
We have used updated OPAL opacities \citep{igl96}.  
We simply assume that photons are emitted at the photosphere
as a blackbody with the photospheric temperature of $T_{\rm ph}$.
Physical properties of these wind solutions have already been
published \citep[e.g.,][]{hac01ka, hac01kb, hac04k, hkn96,
hkn99, hknu99, hkkm00, hac03a, kat83, kat97, kat99}.
It should be noticed that a large number of meshes, i.e., 
more than several thousands grids, are adopted for the wind solutions
in an expanded stage of $R_{\rm ph} \sim 100 ~R_\sun$.

     Optically thick winds stop after a large part of the envelope
is blown in the winds.  The envelope settles into a hydrostatic
equilibrium where its mass is decreasing in time by nuclear burning.
Then we solve equation of static balance instead of equation of motion.
When the nuclear burning decays, the WD enters a cooling phase, in
which the luminosity is supplied with heat flow from the ash of 
hydrogen burning.

\subsection{Multiwavelength light curves}
%     Two ejection processes of nova outbursts have been proposed
%so far: one is the shell ejection \citep[e.g.,][]{enn77}
%and the other is the optically 
%thick continuous wind \citep[e.g.,][]{fri66}.
%In the shell ejection model, perhaps 
%$10^{-5} - 10^{-4} M_\sun$ of matter is ejected at the very early
%phase of the outburst. As this shell expands away from the white dwarf
%(or the central binary system), the column density decreases and
%the emission becomes optically thin at ever longer wavelengths.
%The increase in the optical luminosity is interpreted by 
%the expansion of the photosphere, i.e., the expansion of
%the optically thick shell.  After the optical maximum,
%the shell becomes optically thin and the optical luminosity decreases
%because of the decrease
     In the optically thick wind model, a large part of 
the envelope is ejected continuously for a relatively 
long period \citep[e.g.,][]{kat94h}.  After the maximum expansion
of the photosphere, its photospheric radius gradually decreases
keeping the total luminosity ($L_{\rm ph}$) almost constant.
The photospheric temperature ($T_{\rm ph}$) increases in time
because of $L_{\rm ph} = 4 \pi R_{\rm ph}^2 \sigma T_{\rm ph}^4$.
The main emitting wavelength of radiation moves from optical
to supersoft X-ray through UV.
This causes the decrease in optical luminosity 
and the increase in UV.  Then the UV flux reaches a maximum.
Finally the supersoft X-ray flux increases after the UV flux decays.
These timescales depend on WD parameters such as the WD mass and
chemical composition of the envelope \citep{kat97}.
Thus, we can follow the development of optical, UV, and 
supersoft X-ray light curves by a single modeled sequence
of steady wind solutions.


\subsection{System parameters of optically thick wind model}
     The light curves of our optically thick wind model are
parameterized by the WD mass ($M_{\rm WD}$), 
the chemical composition of the envelope, and the envelope mass 
($\Delta M_{\rm env, 0}$) at the outburst (day 0).
We have searched for the best fit model by changing these parameters,
for example, in a step of $0.05~M_\sun$ for the WD mass, 
of $0.01$ for hydrogen mass content, $X$, and of 0.05 for carbon,
nitrogen, and oxygen mass content, $C+N+O$.  It should be noted
here that hydrogen content $X$ and carbon, nitrogen, and oxygen
content $C+N+O$ are important because they are main players
in the CNO cycle but neon content is not because neon is not
involved in the CNO cycle.  The metal abundance of $Z=0.02$
is adopted, in which carbon, nitrogen, oxygen, and neon
are also included with the solar composition ratio.
We assume neon mass content of $Ne = 0.05$ \citep[taken from][]{van05},
because neon mass content cannot be determined only from 
our light curve fitting. 

\placefigure{v1974cyg_softXray}
\placefigure{v1974cyg_softXray_r_t}


\section{Light curve fitting}
\subsection{Supersoft X-ray and UV 1455 \AA~ fluxes}
     {\it ROSAT} observation clearly shows that the supersoft
X-ray flux emerged on day $\sim 260$ after the outburst
and then decayed rapidly on day $\sim 600$ 
through a plateau phase of $\sim 300$ days \citep{kra96}.
Here, we define JD 2,448,665.0 as the outburst day,
8.67 days before the optical maximum (JD 2,488,673.67).
We have calculated many models, some of which are plotted 
in Figure \ref{v1974cyg_softXray} for the wavelength window
of $0.1 - 2.4$~keV.  Here, we have determined three parameters of
$M_{\rm WD}$, $X$, and $C+N+O$ by fitting three epochs with 
the observation, i.e., (1) when wind stops, (2) when hydrogen-burning
ends, and (3) when UV 1455 \AA~ flux reaches its maximum.  
We searched for the best fit model by eye.

     Our calculated X-ray fluxes in Figure \ref{v1974cyg_softXray}
show that the more massive the WD,
the shorter the duration of X-ray flat peak,
if the other two parameters are the same.
This is because a stronger gravity in more massive WDs
results in a smaller ignition mass.  As a result,
hydrogen is exhausted in a shorter period
\citep[see, e.g.,][for X-ray turn-off time]{kat97}.
On the other hand, if we increase hydrogen content,
we have a longer duration of hydrogen burning.
In this way, we choose the parameters that fit 
observed light curves.  The best fit model is $M_{\rm WD}= 1.05~M_\sun$,
$X=0.46$, $C+N+O= 0.15$, $Ne = 0.05$, 
and $\Delta M_{\rm env, 0} \approx 1.7 \times 10^{-5} M_\sun$, 
which is denoted by a thick solid line in Figure \ref{v1974cyg_softXray}.
Two epochs in the best-fit model are indicated by arrows:
(1) when the optically thick wind stops and 
(2) when the steady hydrogen-burning ends. 

Thin solid lines in Figure \ref{v1974cyg_softXray} depict
1.0, 1.1, and $1.2~M_\sun$ WDs with $X=0.35$, $C+N+O=0.30$, and
$Ne = 0.0$ while a thick solid line does the best-fit model 
of $1.05~M_\sun$ WD with $X=0.46$, $C+N+O=0.15$, and $Ne = 0.05$.
To see the effect of hydrogen content, we have added two other models 
with the same parameters as the best-fit
one except hydrogen content: $X=0.40$ ({\it dash-dotted line}) and
$X=0.53$ ({\it dotted line}).

     Figure \ref{v1974cyg_softXray} also shows that soft X-rays emerge
on day $\sim 250$.  In our model, soft X-rays appear after the wind
stops because the wind absorbs soft X-rays
\citep[e.g.,][]{sou96, hac03ka, hac03kb, hac03kc}.
The optically thick wind stops on day 245 just the time 
when the supersoft X-rays emerge.
After a plateau phase the X-ray flux quickly decreases 
as shown in Figure \ref{v1974cyg_softXray} because
the hydrogen shell-burning ends on day 558.

     The photospheric radius ($R_{\rm ph}$), temperature ($T_{\rm ph}$),
luminosity ($L_{\rm ph}$), and wind mass loss rate ({\it dashed line})
are plotted in Figure \ref{v1974cyg_softXray_r_t}.
Our results are roughly consistent with Balman et al.'s (1998) 
estimates for the photospheric radii and temperatures.
We should place the nova at a distance of 2.2~kpc to fit our
calculated X-ray flux with Balman et al.'s fluxes.
This distance is longer than that derived from the UV fitting
in Figure \ref{v1974cyg_uv1455}.  See discussion.

\placefigure{v1974cyg_uv1455}

     Figure \ref{v1974cyg_uv1455} depicts UV fluxes 
in a band of $\Delta \lambda=20$~\AA ~wide centered
at $\lambda=1455$~\AA , taken from \citet{cas04}.
The corresponding UV light curves are calculated 
for each model in Figure \ref{v1974cyg_softXray}.
Our best fitted $1.05~M_\sun$ WD model shows an excellent agreement
with the observation if we place the nova at a distance of 
1.7~kpc.  Here we adopt an absorption law given by \citet{sea79},
$A_\lambda= 8.3 E(B-V)= 2.65$,
together with an extinction of $E(B-V)= 0.32$ estimated by
\citet{cho97}.

\placefigure{tot_wind_ejected_visual}


\subsection{Optical fluxes}
     We cannot fit the observed visual light curve by our best fitted
model or even by other models with other sets of WD mass and envelope
chemical composition.  Therefore, we interpret that the optical flux
is dominated by free-free emission of the optically thin ejecta that
exist outside the photosphere.

     For the free-free emission of optically thin ejecta,
optical flux can be roughly estimated as
\begin{equation}
F_\lambda \propto \int N_e N_i d V 
\propto \int_{R_{\rm ph}}^\infty {\dot M_{\rm wind}^2 \over r^4} r^2 dr
\propto {\dot M_{\rm wind}^2 \over R_{\rm ph}}
\label{free-free-wind}
\end{equation}
during the optically thick wind phase,
where $F_\lambda$ is the flux at the
wavelength $\lambda$, $N_e$ and $N_i$ the number densities of 
electron and ion, $V$ the volume of the ejecta, 
$\dot M_{\rm wind}$ the wind massless rate.  Here, we use
the relation of $\rho_{\rm wind} = \dot M_{\rm wind}/ 4 \pi r^2 
v_{\rm wind}$, and $\rho_{\rm wind}$ and $v_{\rm wind}$ are 
the density and velocity of the wind, respectively.  
After the wind stops, we obtain
\begin{equation}
F_\lambda \propto \int N_e N_i d V 
\propto \rho^2 V \propto {M_{\rm ej}^2 \over V^2} V~
(\propto R^{-3} \propto t^{-3}),
\label{free-free-stop}
\end{equation}
\citep[e.g.,][]{woo97}, where $\rho$ is the density, $M_{\rm ej}$ 
the ejecta mass (in parenthesis, if $M_{\rm ej}$ is constant in time),
$R$ the radius of the ejecta ($V \propto R^3$), and $t$ the time after
the outburst.  Here, we substitute $\dot M_{\rm wind}$ and 
$R_{\rm ph}$ of our best fit model for those 
in equation(\ref{free-free-wind}).
We cannot uniquely specify the constant in equations 
(\ref{free-free-wind}) and (\ref{free-free-stop})
because radiative transfer is not calculated
outside the photosphere.  Instead,
we choose the constant to fit the light curve on day 43 denoted by A
(on the {\it thick solid line}) and on day 245 denoted 
by B (on the {\it dashed line})
in Figure \ref{tot_wind_ejected_visual}.  These two light curves
represent well the early/late parts of the observational data of AAVSO.

\citet{woo97} summarized the optical and infrared (IR) observations
of V1974 Cyg and concluded that 
$0.55 \mu$m $V$, $1.25 \mu$m $J$, $1.6 \mu$m $H$, and $2.3 \mu$m $K$
light curves all showed an abrupt transition from 
a $t^{-1.5}$ slope to a $t^{-3}$ slope at day $\sim 170$.
This $t^{-1.5}$ slope is very close to
the slope of our free-free light curve until day $\sim 100$.
After the wind stops, we have a slope of $t^{-3}$ 
as shown in Figure \ref{tot_wind_ejected_visual}.
This transition probably occurs when the optically thick
wind stops.  Therefore, our model is very consistent with
the temporal optical and IR observations.


%%%     Contrary to classical novae,
%%% light curves of recurrent novae, for example, U~Sco, can be 
%%% well reproduced only by the optically thick wind model 
%%% with the irradiation effects of the accretion disk 
%%% and the companion as demonstrated by \citet{hkkm00}.
%%% This is because ejecta masses of recurrent novae
%%% are as small as $\sim 1 \times 10^{-6} M_\sun$, 
%%% much smaller than ejecta masses of
%%% classical novae, typically $\sim 1 \times 10^{-4} M_\sun$.
%%% This indicates $10^{-4}$ times the free-free luminosities 
%%% of classical novae [see eq. (\ref{free-free-stop})] and, 
%%% therefore, 10 magnitudes darker in recurrent novae,
%%% that is, the free-free emission of optically thin ejecta is 
%%% not important in visual light curves of recurrent novae.


\section{Discussion}
%%%      The optically thin ejecta outside the photosphere
%%% contributes to optical flux but hardly to X-ray and UV fluxes.
%%% The electron temperature of the optically thin ejecta 
%%% was estimated to be 
%%% $T_{\rm e} \sim 11,000$~K by \citet{aus96} so that
%%% the main wavelengths of free-free emission are longer than
%%% $\lambda \gtrsim 4 h c / k T_{\rm e} \sim 0.35~\mu$m because
%%% the free-free energy spectrum is given by
%%% $\nu F_\nu \propto \nu \exp(- h \nu /k T)$.
%%% Therefore, the light curves of short wavelengths in Figures 
%%% \ref{v1974cyg_softXray}$-$\ref{v1974cyg_uv1455}
%%% are free from free-free emission which is important in long
%%% wavelengths.
%%% 
\subsection{Hard X-ray component}
     {\it ROSAT} observation shows that hard X-ray flux
increases on day $70-100$ and then decays on day $270-300$.
This hard component is suggested to be shock-origin
between ejecta \citep{kra96}.  Here we present another idea
that these hard X-rays are originated from a shock
between the optically thick wind and the companion as described below.

     V1974 Cyg is a binary system with an orbital period of 
$P_{\rm orb} = 0.0812585$~days \citep[e.g.,][]{dey94, ret97}.
\citet{par95} and \citet{ret97} estimated the companion mass
at $0.21 ~M_\sun$ from this orbital period.
Using these values we obtain the separation,
$a= 0.853 ~R_\sun$, the effective radii of each Roche lobe,
$R_1^* = 0.444 ~R_\sun$ and $R_2^* = 0.215 ~R_\sun$ for
the primary (WD) and the secondary component, respectively.
% AA=  0.853  RL1=  0.444  RL2=  0.215
Our optically thick wind model predicts that the companion star
emerges from the WD photosphere about day 80 
(for the photospheric radius, see Fig. \ref{v1974cyg_softXray_r_t}).

Before day $\sim 80$, the companion resides deep inside 
the WD photosphere and we do not detect hard X-rays.
After the companion emerges from the WD photosphere,
the shock front can be directly observed.
The optically thick wind stops on day 245
and we expect that the hard X-ray component decays after that.
This hard X-ray flux may show orbital modulations
if the inclination angle of binary is large enough.  However,
\citet{cho97} estimated it at $i \sim 39 \arcdeg$.
For such a small inclination angle, 
we are able to see main parts of the shock front at any binary phase,
because a bow-shock is formed off the surface of the companion 
\citep[see, e.g.,][]{shi86} and basically optically thin to hard X-rays.
Therefore, orbital modulation of hard X-ray flux is hardly observed,
which is consistent with the observation \citep{kra96}.


\citet{bal98} estimated the hydrogen column density of 
the hard X-ray component and concluded that it decreases,
by a factor of $\sim 10$,
from $N_{\rm H} \sim 10^{22.2}$ to $10^{21.3}$~cm$^{-2}$ between
day 70 and day 260, and almost constant after that.
In our optically thick wind model, the neutral hydrogen column
density is given by
\begin{equation}
N_{\rm H} \propto {{X} \over {m_{\rm H}}} \int_{r_{\rm s}}^\infty 
\rho_{\rm wind} d r
\approx {{\dot M_{\rm wind} X} \over {4 \pi a v_{\rm wind} m_{\rm H}}}
\propto \dot M_{\rm wind},
\end{equation}
where $m_{\rm H}$ is the
mass of hydrogen atom, $r_{\rm s}$ the position of the bow-shock from
the WD center, $a$ the separation of the binary, and
we roughly assume that the bow-shock front is at distance of
$r_{\rm s} = (0.5 - 0.7)a$
from the WD center.  Our wind mass loss rate
decreases from $\sim 10^{-5}$ to $\sim 10^{-6} M_\sun$~yr$^{-1}$
between day 70 and day 260 (see Fig. \ref{v1974cyg_softXray_r_t}),
which is very consistent with Balman et al.'s results.

\subsection{WD mass and chemical composition}
     Several groups estimated the WD mass of V1974 Cyg.
\citet{ret97} gave a mass of $M_{\rm WD} = 0.75 - 1.07 ~M_\sun$
based on the precessing disk model of superhump phenomenon.
A similar range of $0.75 - 1.1 ~M_\sun$ is also obtained by
\citet{par95} from various empirical relations on novae.
Very recently, \citet{sal05} found the WD mass to be $0.9 ~M_\sun$ for
50\% mixing of a solar composition envelope with a O-Ne degenerate
core, or $1.0 ~M_\sun$ for 25\% mixing,
by comparing the evolutional speed of post-wind phase of V1974 Cyg
with their post-wind phase of static envelope solutions.
Their values for the $1.0 ~M_\sun$ are roughly consistent with our results. 

     \citet{van05} criticized \citet{aus96} results and reanalyzed
chemical abundances of the ejecta from optical and UV spectra.
They obtained that He$= 1.2 \pm 0.2$, C$= 0.7 \pm 0.2$, N$= 44.9 \pm 11$,
O$= 12.8 \pm 7$, and Ne$= 41.5 \pm 17$ by number relative
to hydrogen and relative to solar.  In our notation,
these correspond to $X= 0.55$, $Y= 0.25$, $C+N+O= 0.12$,
$Ne = 0.06$, and $Z=0.02$ by mass weight.
The hydrogen content is a bit higher
but these values are very consistent with our results.

\subsection{Distance}
     We estimate the distance to V1974 Cyg 
from the UV 1455 \AA ~light curve fitting.
The absorption at $\lambda = 1455$ \AA ~ is calculated to be
$A_\lambda = 8.3 ~E(B-V) = 2.65$ \citep[e.g.,][]{sea79},
where we adopt the absorption at the visual band, 
$A_V = 3.1 ~E(B-V)= 0.99$ \citep{cho97}.  
Then we have a distance to the nova of $d \approx 1.7$~kpc.
For the X-ray band, \citet{bal98} obtained $(R_{\rm ph} / d )^2 =
(0.22-0.26) \times 10^{-25}$ on day 518 (corresponding to their day 511).
Using $R_{\rm ph} = 0.0115~R_\sun$ on day 518 of our best fit model,
we obtain the distance of $d = 1.6 - 1.7$~kpc, which is consistent 
with our distance estimation from the UV fitting.
On the other hand, our X-ray flux combined with Balman et al.'s (1998)
fluxes gives a rather large distance of 2.2~kpc.
This difference may come from the different model
parameters adopted in their atmosphere models: $1.2~M_\sun$ WD 
and $X= 0.54$, $Y= 0.21$, $Z= 0.02$, $C= 0.002$, $O= 0.103$, 
$N= 0.002$, and $Ne= 0.123$.  Their neon mass is much higher 
than the observation $Ne=0.06$ \citep{van05}.
Therefore we take the distance of $d = 1.7$~kpc.
These distances are all within the range listed in \citet{cho97},
$d= 1.3 - 3.5$~kpc with a most probable value of 1.8~kpc,
derived mainly from maximum magnitude-rate of decline (MMRD) relations.


%%%\placetable{system_parameters}


%% If you wish to include an acknowledgments section in your paper,
%% separate it off from the body of the text using the \acknowledgments
%% command.

%% Included in this acknowledgments section are examples of the
%% AASTeX hypertext markup commands. Use \url without the optional [HREF]
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%% use either \url or \anchor, with the HREF as the first argument and the
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\acknowledgments
     We thank A. Cassatella for providing us with their 
machine readable UV 1455 \AA ~data of V1974 Cygni and also 
AAVSO for the visual data of V1974 Cygni.  We are also grateful
to the anonymous referee for useful comments to improve the manuscript.
This research has been supported in part by the Grant-in-Aid for
Scientific Research (16540211, 16540219) 
of the Japan Society for the Promotion of Science.


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%%%%\section{Appendicial material}


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%\clearpage
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%\bibitem[Patterson (1984)]{pat84}
%Patterson, J. 1984, \apjs,  54, 443
%-493. The evolution of cataclysmic and low-mass X-ray binaries

%\bibitem[Payne-Gaposchkin (1957)]{pay57}
%Payne-Gaposchkin, C. 1957, The Galactic Novae (Amsterdam:
%North-Holland)

%\bibitem[Pereira et al. (1999)]{per99}
%Pereira, A., di Cicco, D., Vitorino, C., \& Green, D. W. E. 1999, 
%IAU circ., 7323
%Nova Aquilae 1999 No. 2

%\bibitem[Pavlenko et al. (2003)Pavlenko, Dudka, \& Baklanov]{pav03}
%Pavlenko, E. P., Dudka, O. I., \& Baklanov, A. V. 2003, Astrophysics, 
%46, 191
%-200, Multicolor Photometric Study of the NOVA V1494 Aql in 2002

%\bibitem[Prialnik \& Kovetz (1995)]{pri95}
%Prialnik, D., \& Kovetz, A. 1995, \apj, 445, 789

\bibitem[Retter et al. (1997)Retter, Leibowitz, \& Ofek]{ret97}
Retter, A., Leibowitz, E. M., \& Ofek, E. O. 1997, \mnras, 286, 745
%-756. Permanent superhumps in nova V1974 Cygni (1992)

%\bibitem[Rieke \& Lebofsky (1985)]{rie85}
%Rieke, G. H., \& Lebofsky, M. J. 1985, \apj, 288, 618
%-621, The interstellar extinction law from 1 to 13 microns

%%%\bibitem[Oka et al. (2002)]{oka02}
%%%Oka, K., Nagae, T., Matsuda, T., Fujiwara, H., \& Boffin, H. M. J.
%%%2002, \aap, in press (astro-ph/0208200)
%  Numerical Simulation of the Surface Flow of a Companion Star in a
%  Close Binary System

%\bibitem[Reinmuth (1925)]{rei25}
%Reinmuth, K. 1925, AN, 225, 385
%-, 

%\bibitem[Reinsch et al. (1996)]{rei96}
%Reinsch, K., van Teeseling, A., Beuermann, K., \& Abbott, T. M. C. 1996,
%\aap, 309, L11
%-L14, Optical low states of the supersoft X-ray source RX J0513.9-6951

%\bibitem[Reinsch et al. (2000)]{rei00}
%Reinsch, K., van Teeseling, A., King, A. R., \& Beuermann, K. 2000,
%\aap, 354, L37
%-L40, A limit-cycle model for the binary supersoft X-ray source 
%RX J0513.9-6951 

%\bibitem[Retter et al. (2000)]{ret00}
%Retter, A., Cook, L., Novak, R., Saxton, J. M., Jensen, L. T.,
%Korcakova, D., \& Janik, J. 2000, IAU Circ., 7537.
%V1494 Aquilae

%\bibitem[Rudy et al. (2002)]{rud02}
%Rudy, R. J., Venturini, C. C., Lynch, D. K., Mazuk, S., Puetter, R. C.
%2002, \apj, 573, 794
%-802, Near-Infrared Emission Lines of V723 Cassiopeiae 
%(Nova Cassiopeiae 1995)

\bibitem[Sala \& Hernanz (2005)]{sal05}
Sala, G., \& Hernanz, M. 2005, \aap, in press (astro-ph/0502092)
%Envelope models for the supersoft X-ray emission of V1974 Cyg

%\bibitem[Sawada et al. (1986)Sawada, Matsuda, \& Hachisu]{saw86}
%Sawada, K., Matsuda, T., \& Hachisu, I. 1986, \mnras, 219, 75
%-88, 
%Spiral shocks on a Roche lobe overflow in a semi-detached binary system

%\bibitem[Schaefer (2001a)]{sch01a}
%Schaefer, B. E. 2001a, IAU Circ. 7621
% CI AQUILAE  --- still bright

%\bibitem[Schaefer (2001b)]{sch01b}
%Schaefer, B. E. 2001b, IAU Circ. 7687
% CI AQUILAE  --- back to near quiescent phase

%\bibitem[Schaefer (2001c)]{sch01c}
%Schaefer, B. E. 2001c, IAU Circ. 7750
% CI AQUILAE  --- the 1941 possible outburst

%\bibitem[Schandl et al. (1997)Schandl, Meyer-Hofmeister, \& Meyer]{sch97}
%Schandl, S., Meyer-Hofmeister, E., \& Meyer, F. 1997, \aap, 318, 73
%Schandl, S., Meyer-Hofmeister, E. \& Meyer, F. 
%Visual light from the eclipsing supersoft X-ray source CAL 87.
%{\it Astron. Astrophys.} {\bf 318}, 73---80 (1997).

%\bibitem[Schmeja et al. (2000)Schmeja, Armsdorfer, \& Kimeswenger]{sch00}
%Schmeja, S., Armsdorfer, B., \& Kimeswenger, S. 2000, 
%Inf. Bull. Variable Stars, 4957
%Nova CI Aquilae in Decline

%\bibitem[Schenker (1999)]{sch99}
%Schenker, K. 1999, PhD thesis, Basel University 
%Radial pulsations in envelopes of classical novae

\bibitem[Seaton (1979)]{sea79}
Seaton, M. J. 1979, \mnras, 187, 73
%-76, Interstellar extinction in the UV

%\bibitem[Shakura \& Sunyaev (1973)]{sha73}
%Shakura, N. I., \& Sunyaev, R. A. 1973, \aap, 24, 337
%-355, Black holes in binary systems. Observational appearance.

\bibitem[Shima et al. (1986)Shima, Matsuda, \& Inaguchi]{shi86}
Shima, E., Matsuda, T., \& Inaguchi, T. 1986, \mnras, 221, 687
%-706.  Interaction between a stellar wind and an accretion flow

%\bibitem[\v{S}imon et al. (2001)\v{S}imon, Sobotka, Marek, \& Lehk\'y]{sim01}
%\v{S}imon, V., Sobotka, P., Marek, P., Lehk\'y, M.  2001, 
%Inf. Bull. Variable Stars, 5131
%Optical Monitoring of the X-ray Source QR And/RX J0019.8+2156

\bibitem[Southwell et al. (1996)]{sou96}
Southwell, K. A., Livio, M., Charles, P. A., O'Donoghue, D., 
\& Sutherland, W. J. 1996, \apj, 470, 1065
%-1074, The Nature of the Supersoft X-Ray Source RX J0513-69

%\bibitem[Starrfield et al. (1988)Starrfield, Sparks, \& Shaviv]{sta88}
%Starrfield, S., Sparks, W. M., \& Shaviv, G. 1988, \apjl, 325, L35
%Starrfield, S., Sparks, W. M. \& Shaviv, G. A model for the 1987
%outburst of the recurrent nova U Scorpii. {\it Astrophys. J.}
%{\bf 325}, L35---L38 (1988).

%\bibitem[Steeghs et al. (1997)Steeghs, Harlaftis, \& Horne]{ste97}
%Steeghs, D., Harlaftis, E. T., \& Horne, K. 1997, \mnras, 290, L28
%-L32
%Spiral structure in the accretion disc of the binary IP Pegasi

%\bibitem[Szkody (1994)]{szk95}
%Szkody, P. 1994, \aj, 108, 639
%--644, BVRJK observations of Northern Hemisphere old novae

%\bibitem[Takamizawa (2000)]{tak00}
%Takamizawa, K. 2000, IAU Circ., 7409
%Probable nova in Aquila

%\bibitem[Thoroughgood et al. (2001)]{tho01}
%Thoroughgood, T. D., Dhillon, V. S., Littlefair, S. P., Marsh, T. R.,
%\& Smith, D. A. 2001, \mnras, 327, 1323
%-1333. (astro-ph/0107477)
%The mass of the white dwarf in the recurrent nova U Scorpii

%\bibitem[van den Heuvel et al. (1992)]{heu92}
%van den Heuvel, E. P. J., Bhattacharya, D., Nomoto, K., \& Rappaport, 
%S. 1992, \aap, 262, 97
%%van den Heuvel, E. P. J., Bhattacharya, D., Nomoto, K., \& Rappaport, 
%%S. Accreting white dwarf models for CAL 83, CAL 87 and other
%%ultrasoft X-ray sources in the LMC. {\it Astron. Astrophys.} 
%%{\bf 262}, 97---105 (1992).

\bibitem[Vanlandingham et al. (2005)]{van05}
Vanlandingham, K. M., Schwarz, G.J., Shore, S.N., Starrfield, S.,
\&Wagner, R.M. 2005, \apj, submitted (astro-ph/0501648)
%  New Elemental Abundances for V1974 Cygni

%\bibitem[Warner (1989)]{war89}
%Warner, B. 1989, Classical Novae, eds. M. F. Bode \& A. Evans 
%(Chichester: John Wiley \& Sons Ltd.), p.1

\bibitem[Warner (1995)]{war95}
Warner, B. 1995, Cataclysmic variable stars, Cambridge, 
Cambridge University Press

%
%\bibitem[Webbink (1985)]{web85}
%Webbink, R. F. 1985, Interacting binary stars, eds. J. E. Pringle \&
%R. A. Wade (Cambridge: Cambridge Univ. Press), p.39
%-70, Stellar Evolution and Binaries
%
%\bibitem[Williams (2000)]{wil00db}
%Williams, D. B. 2000, Inf. Bull. Variable Stars, 4904
%CI Aquilae in 1917

\bibitem[Woodward et al. (1997)]{woo97}
Woodward, C. E., Gehrz, R. D., Jones, T. J., Lawrence, G. F., 
\& Skrutskie, M. F. 1997, \apj, 477, 817
%-824, The Temporal Evolution of the Near-Infrared Light Curves 
% of V1974 Cygni (Nova Cygni 1992)

%\bibitem[Woudt \& Warner (2003)]{wou03}
%Woudt, P. A., Warner, B. 2003, in the proceedings of IAU JD5, 
%`White Dwarfs: Galactic and Cosmological
%Probes', eds. Ed Sion, Stephane Vennes and Harry Shipman
%(astro-ph/0310494)
%AM CVn stars in the UCT CCD CV survey
%
\end{thebibliography}



%% In this first example, note that the \tabletypesize{}
%% command has been used to reduce the font size of the table.
%% Note also that the \label command needs to be placed 
%% inside the \tablecaption.


%% Text for table notes should follow after the \enddata but before
%% the \end{deluxetable}. Make sure there is at least one \tablenotemark
%% in the table for each \tablenotetext.

%% If you use the table environment, please indicate horizontal rules using
%% \tableline, not \hline.
%% Do not put multiple tabular environments within a single table.
%% The optional \label should appear inside the \caption command.

%% If the table is more than one page long, the width of the table can vary
%% from page to page when the default \tablewidth is used, as below.  The
%% individual table widths for each page will be written to the log file; a
%% maximum tablewidth for the table can be computed from these values.
%% The \tablewidth argument can then be reset and the file reprocessed, so
%% that the table is of uniform width throughout. Try getting the widths
%% from the log file and changing the \tablewidth parameter to see how
%% adjusting this value affects table formatting.

%% In this example, we have used the optional * argument to \\ to
%% instruct LaTeX to keep rows together on the same page. (See the
%% lines following the \cutinhead.) Using \\* to group together table
%% rows on the same page affects how the table breaks. Try taking
%% the *'s out and LaTeXing again to see the difference.

%% You can append references to a table using the \tablerefs command.

%% Tables may also be prepared as separate files. See the accompanying
%% sample file table.tex for an example of an external table file.
%% To include an external file in your main document, use the \input
%% command. Uncomment the line below to include table.tex in this
%% sample file. (Note that you will need to comment out the \documentclass,
%% \begin{document}, and \end{document} commands from table.tex if you want
%% to include it in this document.)

%% \input{table}

%%%%\clearpage
%\begin{deluxetable}{lll}
%\tabletypesize{\scriptsize}
%\tablecaption{Standard candle of premaximum halt
%\label{standard_candle}}
%\tablewidth{0pt}
%\tablehead{
%\colhead{WD mass} & 
%\colhead{$M_{V, {\rm peak}}$} & 
%\colhead{$M_{V, {\rm peak}}$} \\
%\colhead{($M_\sun$)} & 
%\colhead{($Z=0.02$)} & 
%\colhead{($C+O=0.3$)}
%} 
%\startdata
%0.59 & $-5.1$ & \nodata \\
%0.60 & $-5.1$ & $-5.2$ \\
%0.65 & $-5.2$ & \nodata \\
%0.70 & $-5.4$ & \nodata \\
%0.80 & $-5.6$ & $-5.7$ \\
%0.90 & $-5.7$ & $-5.8$ \\
%1.00 & $-5.8$ & $-6.0$ \\
%1.10 & $-5.9$ & $-6.2$ \\
%1.20 & $-6.0$ & $-6.3$ \\
%1.30 & $-6.2$ & \nodata \\
%1.35 & $-6.3$ & \nodata \\
%1.37 & $-6.3$ & \nodata
%%%%%%1.30 &%%%$V$-band absorption, $A_V$ & 1.86\tablenotemark{b} \\
%\enddata
%%%%%%\tablenotetext{b}{from extinction law of \citet{rie85}}
%\end{deluxetable}

%\clearpage
%\begin{deluxetable}{llll}
%\tabletypesize{\scriptsize}
%\tablecaption{Properties of two novae
%\label{system_parameters}}
%\tablewidth{0pt}
%\tablehead{
%\colhead{item} & 
%\colhead{} & 
%\colhead{V723 Cas} & 
%\colhead{V463 Sct}
%} 
%\startdata
%nova class & ... & very slow & fast \\
%%%%%%$t_2$ & ... & --- & 15 day\tablenotemark{a} \\
%WD mass & ... & $0.59 ~M_\sun$ & $1.1 ~M_\sun$ \\
%$M_{V, {\rm premax~halt}}$ & ... & $-5.1$ & $-6.2$ \\
%$v_{ph, {\rm flat~peak}}$ & ... & $20$~km~s$^{-1}$ & $150$~km~s$^{-1}$ \\
%$v_{ph, {\rm late~phase}}$ & ... & $500$~km~s$^{-1}$ & $1000$~km~s$^{-1}$ \\
%$\Delta M_{\rm ejecta}$ & ... & $3.6 \times 10^{-5} M_\sun$ & $6.0 \times 10^{-5} M_\sun$ \\
%super Eddington & ... & $1.8$ & $2.0$ \\
%$(m-M)_V$ & ... & $13.9$ & $12.1$ \\
%$E(B-V)$ & ... & $0.6$ & $0.8$\tablenotemark{a} \\
%distance & ... & $2.5$~kpc & $0.84$~kpc
%%%%%%1.30 &%%%$V$-band absorption, $A_V$ & 1.86\tablenotemark{b} \\
%\enddata
%\tablenotetext{a}{taken from \citet{kat02t}}
%%%%%%%\tablenotetext{b}{taken from \citet{rie85}}
%\end{deluxetable}

%% Use the figure environment and \plotone or \plottwo to include 
%% figures and captions in your electronic submission.

%% If you are not including electronic art with your submission, you may
%% mark up your captions using the \figcaption command. See the 
%% User Guide for details.
%%
%% No more than seven \figcaption commands are allowed per page, 
%% so if you have more than seven captions, insert a \clearpage 
%% after every seventh one. 


%% Tables should be submitted one per page, so put a \clearpage before
%% each one.

%% Two options are available to the author for producing tables:  the
%% deluxetable environment provided by the AASTeX package or the LaTeX
%% table environment.  Use of deluxetable is preferred.
%%

%% Three table samples follow, two marked up in the deluxetable environment,
%% one marked up as a LaTeX table.

\clearpage
\begin{figure}
%\epsscale{.5}
\plotone{f1.eps}
%\plotone{f1bw.eps}
%\plotone{v1974cyg_softXray_color.eps}
%\plotfiddle{evolution1.ps}{5.0cm}{270}{0.4}{0.4}{-170}{220}
\caption{
Calculated X-ray fluxes ($0.1-2.4$~keV) from white dwarf (WD)
photospheres are plotted against time for various WD masses and
chemical compositions together with {\it ROSAT} observation count rates 
\citep[{\it open and filled circles}: taken from][]{kra96}.
{\it Open circles}: dominated by soft X-rays.
{\it Filled circles}: dominated by hard X-rays.
{\it Open squares}: corrected X-ray fluxes \citep{bal98}.
The distance is assumed to be 2.2~kpc (see Discussion).
The epoch of the optical maximum corresponds to JD~2,448,673.67,
which is 8.67 days after the outburst.  
{\it Thin solid lines}: $1.0~M_\sun$,
$1.1~M_\sun$, and $1.2~M_\sun$ WDs with the envelope composition of
$X=0.35$, $C+N+O=0.30$, and $Ne=0.0$.
{\it Thick solid line}: the best-fit model of $1.05~M_\sun$ WD with
$X=0.46$, $C+N+O=0.15$, and $Ne = 0.05$.
Two other models are depicted for the same parameters as the best-fit
one except hydrogen content, $X=0.40$ ({\it dash-dotted line}) and
$X=0.53$ ({\it dotted line}).
Two epochs of the best-fit model are indicated by arrows.
\label{v1974cyg_softXray}}
\end{figure}


\clearpage
\begin{figure}
%\epsscale{.5}
\plotone{f2.eps}
%\plotone{f2bw.eps}
%\plotone{v1974cyg_softXray_r_t_color.eps}
%\plotfiddle{evolution1.ps}{5.0cm}{270}{0.4}{0.4}{-170}{220}
\caption{
Wind mass loss rate ({\it dashed line}),
photospheric temperature ($T_{\rm ph}$), 
photospheric radius ($R_{\rm ph}$), 
photospheric luminosity ($L_{\rm ph}$), and
X-ray flux ({\it thick solid line}) of
the best fit model ($M_{\rm WD}= 1.05~M_\sun$,
$X=0.46$, $C+N+O =0.15$, and $Ne =0.05$).
X-ray fluxes ({\it Open squares}), photospheric temperatures 
({\it Open triangles}), and photospheric radii ({\it Open diamonds}).
These are taken from \citet{bal98}.  Here, photospheric radii 
are calculated from $A_1 \equiv (R_{\rm ph} / d )^2$
in Balman et al.'s Table 1 with the distance of $d = 1.7$~kpc.
{\it Open and filled circles}: the same X-ray count rates as
in Fig. \ref{v1974cyg_softXray}.  See discussion for more details.
\label{v1974cyg_softXray_r_t}}
\end{figure}


\clearpage
\begin{figure}
%\epsscale{.5}
\plotone{f3.eps}
%\plotone{f3bw.eps}
%\plotone{v1974cyg_uv1455_color.eps}
%\plotfiddle{evolution1.ps}{5.0cm}{270}{0.4}{0.4}{-170}{220}
\caption{
Calculated UV ($\lambda = 1455$~\AA~) fluxes are plotted 
together with the {\it IUE} observations 
\citep[{\it open square}: taken from][]{cas04}.
These curves correspond to the four models ({\it solid lines})
in Fig. \ref{v1974cyg_softXray}.
The distance of $d=1.7$~kpc is assumed.  Here we use
Seaton's (1979) absorption law of $A_\lambda = 8.3~E(B-V)= 2.65$
with an extinction of $E(B-V)= 0.32$ \citep{cho97}.
\label{v1974cyg_uv1455}}
\end{figure}


\clearpage
\begin{figure}
%\epsscale{.5}
\plotone{f4.eps}
%\plotone{f4bw.eps}
%\plotone{tot_wind_ejected_visual_color.eps}
%\plotfiddle{evolution1.ps}{5.0cm}{270}{0.4}{0.4}{-170}{220}
\caption{
{\it Thick solid line:} visual magnitude of 
free-free emission from the optically thin ejecta, based on
equation (\ref{free-free-wind}): scaled to fit at day 43 (point A).
The flux decays with a slope of $\sim t^{-1.5}$ until day $\sim 100$.
{\it Dashed line:} free-free emission with a slope of $\sim t^{-3}$
after the wind stops: scaled to fit at day 224 (point B).
{\it Thin solid line:} ejected mass ($M_{\rm ej}$) from the WD by
the optically thick winds.  Here, we assume
JD~2,448,665.0 as the date of outburst.
{\it Small dots:} observational magnitudes taken from AAVSO archive.
Two epochs of the nova outburst are indicated by arrows:
the companion emerges from the WD photosphere and the
optically thick nova wind stops.
\label{tot_wind_ejected_visual}}
\end{figure}


%% The following command ends your manuscript. LaTeX will ignore any text
%% that appears after it.

\end{document}

astro-ph0506246.extracted_bib
\begin{thebibliography} is followed by an empty set of
%% curly braces.  If you forget this, LaTeX will generate the error
%% "Perhaps a missing \item?".
%%
%% thebibliography produces citations in the text using \bibitem-\cite
%% cross-referencing. Each reference is preceded by a
%% \bibitem command that defines in curly braces the KEY that corresponds
%% to the KEY in the \cite commands (see the first section above).
%% Make sure that you provide a unique KEY for every \bibitem or else the
%% paper will not LaTeX. The square brackets should contain
%% the citation text that LaTeX will insert in
%% place of the \cite commands.

%% We have used macros to produce journal name abbreviations.
%% AASTeX provides a number of these for the more frequently-cited journals.
%% See the Author Guide for a list of them.

%% Note that the style of the \bibitem labels (in []) is slightly
%% different from previous examples.  The natbib system solves a host
%% of citation expression problems, but it is necessary to clearly
%% delimit the year from the author name used in the citation.
%% See the natbib documentation for more details and options.

%\clearpage
\begin{thebibliography}{}
%\bibitem[Alcock et al. (1996)]{alc96}
%Alcock, C. et al. 1996, \mnras, 280, L49
%-L53, Optical variability of the Large Magellanic Cloud supersoft 
%source RX J0513.9-6951 from MACHO Project photometry
%
%\bibitem[Ayani (1999)]{aya99}
%Ayani, K. 1999, IAU circ., 7324
%V1494 Aquilae = Nova Aquilae 1999 No.2

\bibitem[Austin et al.'s (1996)]{aus96}
Austin, S. J., Wagner, R. M., Starrfield, S., Shore, S. N., 
Sonneborn, G., \& Bertram, R. 1996, \aj, 111, 869
%V1974 Cygni 1992: Optical and Ultraviolet Evolution and Analysis

%\bibitem[Bessell (1990)]{bes90}
%Bessell, M. S. 1990, \pasp, 102, 1181

\bibitem[Balman et al. (1998)Balman, Krautter, \& \"Ogelman]{bal98}
Balman, S., Krautter, J., \& \"Ogelman, H. 1998, \apj, 499, 395
% The X-Ray Spectral Evolution of Classical Nova V1974 Cygni 1992: 
% A Reanalysis of the ROSAT Data

%\bibitem[Bessell (1990)]{bes90}
%Bessell, M. S. 1990, \pasp, 102, 1181
%
%\bibitem[Bressan et al. (1993)]{bre93}
%Bressan, A., Fagotto, F., Bertelli, G., \& Chiosi, C. 1993, \aaps, 100, 647

%\bibitem[Barsukova \& Goranskii (2003)]{bar03}
%Barsukova, E. A., \& Goranskii, V. P. 2003, Astronomy Letters, 29, 195
%-198, The Orbital Period of Nova Aquilae 1999 No. 2 (V1494 Aql)

%\bibitem[Bos et al. (2001)]{bos01}
%Bos, M., Retter, A., Cook, L., \& Novak, R. 2001, IAU Circ., 7665
%V1494 Aquilae

%\bibitem[Bruch (1982)]{bru82}
%Bruch, A. 1982, \pasp, 94, 916

%\bibitem[Cassatella et al. (2002)Cassatella, Altamore, 
%\& Gonz\'alez-Riestra]{cas02}
%Cassatella, A., Altamore, A., \& Gonz\'alez-Riestra, R. 2002, 
%\aap, 384, 1023
%-1029, Classical novae in outburst: 
% The early evolution of the ultraviolet continuum

\bibitem[Cassatella et al. (2004)]{cas04}
Cassatella, A., Lamers, H. J. G. L. M., Rossi, C., Altamore, A.,
Gonz\'alez-Riestra, R. 2004, \aap, 420, 571
%-588, A study of the expanding envelope of Nova V1974 Cyg 1992
% based on IUE high resolution spectroscopy

\bibitem[Chochol et al. (1997)]{cho97}
Chochol, D., Grygar, J., Pribulla, T., Komzik, R., Hric, L., \& Elkin, V.
1997, \aap, 318, 908
%-924, The expansion of the envelope of Nova V1974 Cygni 
% and the distance problem

%\bibitem[Chochol \& Pribulla (1997)]{cho97}
%Chochol, D., \& Pribulla, T. 1997, Contributions of the Astronomical
%Observatory Skalnate Pleso, 27, 53
%-69, Photometric Study of Nova CAS 1995

%\bibitem[Chochol \& Pribulla (1998)]{cho98}
%Chochol, D., \& Pribulla, T. 1998, Contributions of the Astronomical
%Observatory Skalnate Pleso, 28, 121
%-141, Photometric variability of the slow nova V723 Cas

%\bibitem[Chochol et al. (2003)]{cho03}
%Chochol, D., Pribulla, T., Parimucha, \v{S}., \& Va\v{n}ko, M. 2003,
%Baltic Astronomy, 12, 610
%-615, Long-term photometry of very slow novae

%\bibitem[Collins (1992)]{col92}
%Collins, P. 1992, IAU Circ., 5454
%Nova Cygni 1992

%\bibitem[Cowley et al. (2002)]{cow02}
%Cowley, A.P., Schmidtke, P.C., Crampton, D., \& Hutchings, J.B. 2002, 
%\aj, 124, 2233
%-2237, A new orbital ephemeris and reinterpretation of spectroscopic 
% data for the supersoft X-ray binary RX J0513.9-6951
%
%\bibitem[Cowley et al. (1993)]{cow93}
%Cowley, A. P., Schmidtke, P. C., Hutchings, J. B., Crampton, D., \& 
%McGrath, T. K. 1993, \apj, 418, L63
%-L66, Detection, Identification, and Observed Properties of 
% Large Magellanic Cloud Supersoft X-Ray Sources

\bibitem[De Young \& Schmidt (1994)]{dey94}
De Young, J. A., \& Schmidt, R. E. 1994, \apj, 431, L47
%-L49.  The photometric period of V1974 Cygni (Nova Cygni 1992)

%\bibitem[Ennis et al. (1977)]{enn77}
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