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\begin{document}
\IBVShead{5584}{21 December 2004}

\IBVStitletl{Discovery of Spectral Variability of}{ Post-AGB Star SAO\,40039} 

\IBVSauth{Klochkova, V. G.; Chentsov, E. L.; Panchuk, V. E.; Yushkin, M. V.}


\IBVSinsto{Special Astrophysical Observatory of
           the Russian Academy of Sciences,
           Karachai-Cirkassian Republic,
           Nizhnij Arkhyz, 369167, Russia, e-mail: valenta@sao.ru}


\SIMBADobj{SAO 40039}
\IBVStyp{ post-AGB } 
\IBVSkey{spectroscopy}

\IBVSabs{For the first time a significant variability of optical spectrum}
\IBVSabs{of post-AGB star SAO 40039 is detected. Variable absorption and}
\IBVSabs{emission components are present both in the HI and numerous metallic}
\IBVSabs{lines (FeII, SiII, etc). Stellar radial velocity is variable also.}


\begintext

We present the first results obtained in the course of spectroscopic
monitoring of the poorly-studied post-AGB star SAO\,40039.
A high-luminosity star SAO\,40039 (${\rm B = 10\fmm1}$
(Fujii et al., 2002)) is located close to the galactic plane
in the direction close to the anticenter of Galaxy
(${\rm l = 159\fdeg8}$, ${\rm b = 4\fdeg8}$).
Based on BVRIJHK photometry, Fujii et al. (2002) classified the star
as A4\,{\sc i}a. It is identified with the IR-source IRAS\,05040\,+\,4820. 
Its double-peaked spectral energy distribution and its
position in the IRAS color-color diagram confirm the post-AGB status.
There is no ${\rm H_2O}$, SiO or CO maser associated with the
source IRAS\,05040\,+\,4820 (Wouterloot \& Brand, 1989; Wouterloot et al.
1993). According to the Lewis (1989) chronological sequence, this
means that SAO\,40039 is close to the PN stage. This conclusion is also 
confirmed  by the sufficiently high temperature of the central
star and a low temperature of the dusty envelope (Fujii et al., 2002). 


Our spectral observations of SAO\,40039 were made at the 6-m
telescope of the Special Astrophysical Observatory with the
echelle-spectrograph NES (Nasmyth focus, 2K$\times$2K CCD-chip,
${\rm R \ge 60000}$ (Panchuk et al. 2002,
{\tt http://www.sao.ru/hq/ssl/NES.html}). The journal of observations is
presented in Table\,1. The data reduction process (cosmic ray trace
removal, background subtraction, and spectral order extraction) were
done under the standard ECHELLE context of the MIDAS package. The
cosmic ray traces were removed by median averaging of two subsequent
spectra. A hollow cathode Th-Ar lamp was used for wavelength
calibration. The radial velocities were measured by matching the
original and mirrored profiles of individual lines. A typical error
in the $V_r$ measurements for a single line is about 1\,km\,s$^{-1}$. 

\vskip 1cm

\begin{center}
{Table\,1: Observing log for SAO\,40039}
\vskip 3mm
\begin{tabular}{ccccr}
\hline\noalign{\smallskip}
Date &Exposure & Spectral range & Resolving   & $\overline{S/N}$\\
     &time, s  & \AA{}      & power, R&    \\
\noalign{\smallskip}
\hline\noalign{\smallskip}
02/12/2002 & 2$\times$3600 & 4520--6000 & 60000 & 75  \\
09/09/2003 & 2$\times$3600 & 4520--6000 & 60000 & 100  \\
10/01/2004 & 2$\times$3600 & 5280--6760 & 75000 & 85  \\
08/03/2004 & 2$\times$3600 & 5280--6760 & 75000 & 115  \\
\hline\noalign{\smallskip}
\end{tabular}
\end{center}

\IBVSfig{10cm}{5584-f1.eps}{A fragment of two spectra of SAO\,40039: 08/03/2004 --  solid line, 10/01/2004 -- dotted.\label{2spectra}}
\IBVSfigKey{5584-f1.eps}{SAO 40039}{spectrum}

The main peculiarity of the SAO\,40039 spectrum is the presence of
complex emission-absorption profiles of ${\rm H\alpha}$ and some
metallic lines. In addition, comparing spectra obtained at
different epochs, we reveal strong variability both in numerous
metallic lines (Fig.\,\ref{2spectra}, Fig.\,\ref{lines}) and in
${\rm H\alpha}$ (Fig.\,\ref{Halpha}). 


\vskip 1cm

\centerline{Table\,2:  Heliocentric $V_r$ (km\,s$^{-1}$) in the spectra of SAO\,40039}
\vskip 3mm
\begin{table}
\begin{tabular}{lllll}
\hline
Ion (Mult.)&02/12/2002&09/09/2003&10/01/2004&08/03/2004 \\
\hline
\multicolumn{5}{l}{Cores of absorption lines:} \\
\vspace{-5mm}\\
Fe\,{\sc II}, Cr\,{\sc II}, etc. (${\rm r \rightarrow 1}$)&$-14.8$& $-6.8$& $-15.3$&$-8.2$\\
H$\alpha$              & ---    & ---     & $-27$ & $-28$ \\    
H$\beta$               &$-14.8$ & $-10.6$ & ---   & ---   \\
\hline
Wings of weak absorptions   &&&& \\ 
at ${\rm r = 0.90 \div 0.95}$&$-14$   & $-9.5$  &$-15.5$& $-13.0$ \\  
\hline 
\multicolumn{5}{l}{Maximum extension of blue wings:}\\
Fe\,{\sc II}(42)               & $-70$ & $-61$  & $-65:$ & $-70$  \\
H$\alpha$              & ---    & ---   & $-65:$ & $-57:$ \\    
\hline
\multicolumn{5}{l}{Emission lines:}\\
\vspace{-5mm}\\
Fe\,{\sc II}(40, 46)           &  ---  & ---    & ---     & $-18$  \\
H$\alpha$              & ---   &  ---   & $-15$ & $-13:$   \\
\hline
I.S.\,NaI (1)&$-25$, $-3$&$-26$, $-2$ &$-27$, $-2.5$ & $-28$, $-2$ \\
DIB         & ---       & ---  & $-3:$   &   $-2.5:$          \\     
\hline
\end{tabular}
\end{table}

\newpage


\IBVSfig{12cm}{5584-f2.eps}{Temporal variability of selected lines in the SAO\,40039 spectra. 02/12/2002 -- solid line, 09/09/2003 -- dotted, 10/01/2004 -- dashed short, 08/03/2004 -- dash-dot.\label{lines}}
\IBVSfigKey{5584-f2.eps}{SAO 40039}{spectrum}


The heliocentric $V_r$ values derived from absorption and emission lines
and/or their components at different epochs are shown in Table\,2. Our
present time coverage does not allow us to comment on possible
reasons for the variability found. Significantly variable $V_r$ were
revealed in most of the absorption lines (except for $V_r$ values
determined on the wings of the weak absorptions at depth
${\rm r = 0.90 \div 0.95}$).
As seen in Fig.\,\ref{lines}, variability in the central part of the line
profiles ($ V_r \approx -20$\,km\,s$^{-1}$) could be caused by
variable emission. These variations are especially remarkable in the
Fe\,{\sc II}\,(40) lines. In the blue wings of the 
strongest Fe\,{\sc II}\,(42) lines, however, variability is caused by
variable  absorption along the line of sight.
As a first approximation, the value ${\rm V_r \approx -13}$\,km\,s$^{-1}$
that follows from the wings of weak (${\rm 0.75 < r < 0.92}$) absorption lines
could be adopted as a systemic velocity ${\rm V_{sys}}$
(${\rm V_{lsr} \approx -20}$\,km\,s$^{-1}$). 


Using high resolution spectra, we classified SAO\,40039 as a A4\,{\sc i}b
star (${\rm Mv \approx -5^m}$), which is consistent with the result
published by Fujii et al. (2002). The determination of the stellar 
luminosity leads us to the distance value of ${\rm d \approx
4}$\,kpc. This distance fits very well with the systemic velocity of
${\rm V_{lsr} \approx -20}$\,km\,s$^{-1}$. Besides, as follows from
Table\,2, a velocity component of 
${\rm V_r \approx -25 \div -28}$\,km\,s$^{-1}$ is present in the
interstellar NaD lines (Fig.\,\ref{Halpha}).
According to M\"unch (1957), distant stars HD\,232299,
${\rm BD+43^{\circ}1168}$ and HD\,232947  which exist at galactic latitudes
close to SAO\,40039, have similar double-peaked NaD line profiles
with components at 
${\rm V_r \approx -(20 \div 38)}$ and $-(1 \div 3)$\,km\,s$^{-1}$ having
intensities approaching those in the SAO\,40039 spectra.


\IBVSfig{7cm}{5584-f3.eps}{The same as in Fig.\,\ref{lines} but for Na\,{\sc i}\,5895\,\AA{} and H$\alpha$.\label{Halpha}}
\IBVSfigKey{5584-f3.eps}{SAO 40039}{spectrum}

Since the spectrum of SAO\,40039 contains many absorption lines
without visible emission components, it is possible to estimate
metalicity and abundances of selected chemical elements in its
atmosphere. However, we have to keep in mind that both the model
parameters and chemical composition, determined for such a luminous
star with the unstable and extended gaseous-dusty envelope in the
framework of a static plane-parallel atmospheric model under the LTE
approach, can be considered as a first approximation only. The
comparison of spectra of SAO\,40039 with a grid of theoretical spectra
that were calculated by us permits us to obtain the following model
parameters for the star: ${\rm T_{eff} \approx 8000}$\,K,
${\rm \log g \approx 1.0}$,   ${\rm \xi_t \approx 6}$\,km\,s$^{-1}$,
${\rm [Fe/H]_{\odot} = -0.3}$ and C, O overabundances. In summary,
stellar parameters and chemical abundances pattern of SAO\,40039 
resemble to a PPN candidate HD\,187885\,=\,IRAS19500$-$1709
(Van Winckel et al., 1996). 


\medskip

{\bf Acknowledgements:} We acknowledge financial support from the
Russian Foundation for Basic Research (project No.\,02--02--16085),
from the Department of Physics Sciences of  RAS and from the Russia
President's  Foundation for young scientists (No.\,MK-874.2004.2). 



\references

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{\bf 385}, 884 

Lewis, B.M., 1989, {\it Astrophys. J.}, {\bf 338}, 234 

M\"unch, G., 1957, {\it Astrophys. J.}, {\bf 125}, 42. 

Panchuk, V.E., Piskunov, N.E.,  Klochkova, V.G., Yushkin, M.V.,
    Ermakov, S.V., 2002, {\it Preprint of the Special Astrophys. Observ.},
    No.\,169

Van Winckel, H., Waelkens, C., Waters, L.B.F.M., 1996,
{\it Astron. \& Astrophys.}, {\bf 306}, 37L

Wouterloot, J.G.A.,   Brand, J., 1989, {\it Astron. \& Astrophys. Suppl. Ser.},
  {\bf 80}, 149

Wouterloot, J.G.A., Brand, J., Fiegle, K., 1993, {\it Astron. \& Astrophys. Suppl. Ser.},
  {\bf 98}, 589

\endreferences


\end{document}


