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\IBVShead{4251}{26 September 1995}
\centerline{\ft PU Vul DURING THE BRIGHTNESS WEAKENING OF 1993-1994}
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We recently (Andrillat and Houziaux, 1994, hereafter referred as 
AH94) reviewed spectral features of the symbiotic nova PU Vulpeculae 
during its nebular phase between 1989 June and 1992 October. 
Observations of this object have been resumed in 1993 July, 1994 June 
and 1995 June with the same instrumentation as in AH94. We report 
here on these spectra.

Monochromatic magnitudes at wavelengths where the continuum 
may be easily located between 375 and 900 nm show a significant drop 
(about 1.2 mag.) from the violet limit up to 700\,nm between 1993 July 
and 1994 June. Figure 1 shows the composite aspect of the continuum 
corrected for an E(B$-$V)=0.4 interstellar extinction. Above 700\,nm the 
continuum is due to the M6\,III component, deeply cut by strong TiO 
bands, while at shorter wavelengths the photon flux originates in a 
hotter source, presumably the hot wind ejected from the compact object. 
The drop in the blue continuum can be explained by the eclipse already 
mentioned by Nussbaumer and Vogel (1994) from the IUE observations 
and confirmed by Garnavich (1994), who also notes in early 1994  April 
that the increase in equivalent width of H$\beta$ may be due to a drop in the 
continuum around 480\,nm.
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Figure 1. Continuous spectrum in 1993 July (solid line)
         and during the eclipse in 1994 June (dashes)
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Figure 2. Variations of the absolute fluxes around 4700\AA\ from August 15, 1992 to 
June 2, 1994. Note the collapse of HeII during the eclipse and the stability of the 
HeI line in spite of the drop of the continuum at the time of the eclipse.
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Figure 3. Variations of the absolute fluxes in the 7000\AA\ region between August 12, 
1992, and July 2, 1993 and during the eclipse phase on June 18, 1994. The continuum 
level drops by a factor of about 3 between August 1992 and July 1993 but remains unaltered by the eclipse. Remark that the drop of NIV at 7120\AA\ is similar to the behavior of the HeII line in Figure 2.
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The nebular spectrum has been observed between 375 and 900\,nm. 
As in 1992, (see AH94), a large proportion of the lines belong to the Fe$^+$ 
and Fe$^{++}$ ions. Fluxes determined in 1994 June are in good agreement 
with the values given by Kolotikov et al. (1995). Discordances are 
observed mostly in the cases of blends, as our resolution permits to 
separate components unresolved on the low resolution Asiago B\&C + CCD 
spectra. In general, [Fe III] lines slowly drop in intensity, while the 
[AIV] line at 474 nm increases, as it is apparent in Figure 2. On the 
spectrum secured during the brightness drop of 1993-1994, we observe 
the disappearence of the wind features, as already mentioned by 
Garnavich and Trummel (1994).
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\centerline{Table 1}
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\begin{tabular}{lrr}
\hline
 Date&	flux in HeII\,468.6 &	FWHM\\	
     & in 10$^{-12}$ erg.s$^{-1}$&in km, s$^{-1}$\\
\hline
\\	
91 Oct 25 &	1.09&	  820\\	
92 Aug 15&	2.52&	  833\\	
92 Sept  9&	2.71&	  953\\	
93 July  6&	3.30&	1150\\	
93 July 24&	4.18&	1200\\	
94 June 17&	$<$ 0.1&--\\	
95 June 17&	7.33&	1535\\
\hline
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These ``WR'' features which have disappeared include He\,II at 
454.2 and 468.6\,nm, C\,II at 711.7\,nm, C\,IV at 580.1-581.2 and 722.6\,nm, 
N III at 420.0, 451.5, 452.3, 464.0 and 489.7\,nm, and finally N\,IV lines at 
405.0, 579.4, 638.3, 710.9-712.3\,nm. Let us remark that during the 
1992-1995 interval the He\,I 471.4 and 706.5\,nm remain quite 
stable in flux. On the contrary, the [A\,IV] line at 474.0\,nm, absent in 
1992 (Figure 2), is stronger than the [Fe\,II] neighbouring lines. On the other 
side, we note that, except for the 1993-1994 luminosity drop, the He\,II 
$\lambda$ 468.6\,nm line increases both in flux and in FWHM, as reported in Table 1.

The parabolic shape of the He\,II line remains all trough the observed 
period of time, however its red wing is altered by the [Fe\,III] line at 
470.1\,nm: well separated on the 1991 October spectrum, this line is just 
visible as a shoulder on the 1995 June spectrum. Morever, it seems that 
between 1994 June and 1995 June, a narrow ``spike'' has developed 
on top of the wind component. Such a feature was observed, although 
ill-defined on a 1992 September 11 spectrum, although it could not be 
seen on August 15, 1992 (see Figure 2). This spike shows in 1995 June a 
$-$150 km.s$^{-1}$ shift with respect to the wind component. A similar 
behavior is also observed in the N\,III line at 464\,nm. In 1991 October, a strong and wide complex (2.12 10$^{-12}$ 
ergs s$^{-1}$ ) is dominated by a wide 464nm line. In 1992 August, its 
intensity has increased to 2.75 10$^{-12}$ ergs s$^{-1}$ but three narrow spikes develop on top of the broad emission, corresponding to the 3$^2$P\degr - 3$^2$D\degr 
multiplet components. During the eclipse phase, the broad feature drops 
(as it is the case for the N\,IV line at 712\,nm, see Figure 3), while the 
narrow components increase in strength (Figure 2). In 1995 June, when the 
broad line moderately reappears, the strongest N\,III components reach 
over 7 times the local continuum.

It is clear that the ``hot'' nebular spectrum of PU Vul has not yet 
reached its full development, while the wind features steadily reinforce 
their strength, indicating an increase of the wind density. The 
development of nebular components in the N\,III 464.0 nm  and in the 
He\,II 468.6\,nm lines shows that the nebular temperature is also 
increasing between 1992 and 1995.
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\beginauthors
Yvette ANDRILLAT
Universit\'e de Montpellier II
Laboratoire d'Astronomie
F 34095 Montpellier CEDEX 5
France
\authorsrightcol
L\'eo HOUZIAUX
D\'epartement d'Astrophysique
Universit\'e de Mons-Hainaut
B 7000 Mons
Belgium
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\endauthors
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\references

Andrillat, Y. and Houziaux, L., 1994,  {\it M.N.R.A.S.}, {\bf 271}, 875

Garnavich, P., 1994, {\it IAU Circ.}, No.\,5969

Garnavich, P. and Trummel, S.R., 1994, {\it IAU Circ.}, No.\,6089

Kolotikov, E.A., Munari, U., Yudin, B.F., 1995, {\it M.N.R.A.S.}, {\bf 275}, 185

Nussbaumer, H., Vogel, M., 1994, {\it IAU Circ.}, No.\,5960 

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