All Figures

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{h2447f1.ps} \end{figure}$ Figure 1: Apparent morphology of NGC 6741 in the medium-excitation line $\lambda$ 5007 $\AA\/$ of [O III] ( upper panel), and in the low-excitation line $\lambda$ 6584 $\rm\AA\/$ of [N II] ( lower panel). North is up and East to the left. HST-WFPC2 frames; programme GO 8773, P. I. Arsen Hajian.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{h2447f2.ps} \end{figure}$ Figure 2: Apparent I([N II])/I([O III]) distribution over NGC 6741 (same WFPC2 images as Fig. 1). The sharp, inhomogeneous layer at low-excitation ([N II]) framing the main nebula is punched, along and close to the apparent major axis, by a series of radial [O III] rays or jets penetrating into the faint, roundish halo.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{h2447f3.ps} \end{figure}$ Figure 3: Detailed spectral image of twelve ionic species in NGC 6741 at $\rm PA=15\hbox {$^\circ $ }$ (close to the apparent minor axis), arranged in order of increasing IP ( top-left to bottom-right). The original fluxes are multiplied by the factor given in parenthesis, to make each emission comparable with $\lambda$ 5007 $\rm\AA\/$ of [O III]. The blue-shifted gas is to the left. The top-left frame also shows the [O I] night-sky emission at $\lambda$ 6300.304 $\rm\AA\/$ . In the top-right frame the [O II] line at $\lambda$ 7319 $\rm\AA\/$ , partially blended with $\lambda$ 7320 $\rm\AA\/$ , has been suppressed (for details, see the text and Fig. 5).
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{h2447f4.ps} \end{figure}$ Figure 4: Same as Fig. 3, but for $\rm PA=75\hbox {$^\circ $ }$ (close to the apparent major axis of NGC 6741).
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{h2447f5.ps} \end{figure}$ Figure 5: De-blending procedure for the [O II] $\lambda \lambda$ 7319-7320 $\rm\AA\/$ doublet (using IRAF packages). Top panel: Image A = part of the echellogram (at $\rm PA=75\hbox {$^\circ $ }$ ) centered on $\lambda$ 7319 $\rm\AA\/$ . Middle panel: Image B = part of the echellogram (at $\rm PA=75\hbox {$^\circ $ }$ ) centered on $\lambda$ 7320 $\rm\AA\/$ . Bottom panel: Image C = Image A - (Image B/3.071), where 3.071 corresponds to I(7320)/I(7319).
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{h2447f6.ps} \end{figure}$ Figure 6: High-contrast [O III] and [N II] line profiles (in logarithmic scale) of NGC 6741 close to the apparent minor and major axes ( $\rm PA=15\hbox {$^\circ $ }$ and 75 $\hbox {$^\circ $ }$ , respectively) showing the faint halo and red-shifted tail. Same orientation as Figs. 3 and 4.
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In the text

$\begin{figure} \par\includegraphics[width=14cm,clip]{h2447f7.ps}\end{figure}$ Figure 7: Nebular tomography vs. spectral image connection. In this example we use the [O III] spectral images of NGC 6741 at $\rm PA=75\hbox {$^\circ $ }$ and $\rm PA=15\hbox {$^\circ $ }$ (same orientation as Figs. 3 and 4). Left panel: tomographic map of the nebular slice intercepted by a spectrograph slit aligned with the apparent major axis of an ellipsoidal PN denser at the equator than at the poles; a and b are the polar and equatorial axes, respectively, of the elliptical nebular slice. Central panel: spectral image of the nebular slice shown in the left panel; a' and b' are the polar and equatorial axes, respectively, of the spectral image. Right panel: [O III] tomographic reconstruction of NGC 6741 at $\rm PA=15\hbox {$^\circ $ }$ . See the text for details.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,height=8cm,clip]{h2447f8.eps} \end{figure}$ Figure 8: The cspl-zvpc relation for NGC 6741 at $\rm PA=15\hbox {$^\circ $ }$ , superimposed on the adopted expansion law $V_{\rm exp}$ (km s^-1 $) =13\times R\hbox {$^{\prime \prime }$ }$ , which is valid across the whole nebula, except in the innermost, highest-ionization, decelerated regions marked by [Ar V].
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In the text

$\begin{figure} \par\includegraphics[width=8cm,height=8cm,clip]{h2447f9.eps} \end{figure}$ Figure 9: Selected emission line profiles integrated along the slit for NGC 6741 at PA=15 $\hbox {$^\circ $ }$ , showing the spurious kinematical results provided by the recombination lines of He II. Symbols: continuous line = [Ar III] at $\lambda$ 7135 $\rm\AA\/$ ; dotted line = [Ar IV] at $\lambda$ 4740 $\rm\AA\/$ ; short-dashed line = [Ar V] at $\lambda$ 7005 $\rm\AA\/$ ; long-dashed line = He II at $\lambda$ 4686 $\rm\AA\/$ ; dotted-dashed line = He II at $\lambda$ 6560 $\rm\AA\/$ . For details, see the text.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{h2447f10.eps} \end{figure}$ Figure 10: Combined position-velocity maps in the nine observed PA of NGC 6741 at high (He II), medium ([O III]) and low ([N II]) excitation (multi-color maps in the electronic version of the paper; blue = He II, green = [O III], and red = [N II]), scaled according to the relation $V_{\rm exp}$ (km s $^{-1})=13\times R\hbox {$^{\prime \prime }$ }$ . The orientation of these tomographic maps is the same of Figs. 3 and 4.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{h2447f11.ps} \end{figure}$ Figure 11: F(H $\alpha$ )/F(H $\beta$ ) isophotal contours superimposed to the H $\beta$ spectral image for three representative PA of NGC 6741. Left panel: $\rm PA=15\hbox {$^\circ $ }$ (close to the apparent minor axis); central panel: $\rm PA=55\hbox {$^\circ $ }$ (intermediate direction); right panel: $\rm PA=75\hbox {$^\circ $ }$ (close to the apparent major axis). Same orientation as Figs. 3 and 4. The isophotal contours cover the range 5.20 (the outermost) to 7.60, with a constant step of 0.30.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,height=8cm,clip]{h2447f12.eps} \end{figure}$ Figure 12: Color-excess vs. distance relation in the direction of NGC 6741. Symbols: small dots = field stars; filled square = open cluster OCL 88; large dot = classical Cepheid V336 Aql.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,height=8.9cm,clip]{h2447f13.eps} \end{figure}$ Figure 13: Radial distribution of the physical conditions ( $T_{\rm e}$ and $N_{\rm e}$ ) at two selected directions of NGC 6741. Upper panel: the zvpc at $\rm PA=15\hbox {$^\circ $ }$ (close to the apparent minor axis); lower panel: the zvpc at $\rm PA=75\hbox {$^\circ $ }$ (close to the apparent major axis). Left ordinate scale: $T_{\rm e}$ [O III] (continuous line) and $T_{\rm e}$ [N II] (empty squares). Right ordinate scale: $N_{\rm e}$ (H $\alpha$ ) for D=2000 pc (dotted line), $N_{\rm e}$ [S II] (empty circles), and $N_{\rm e}$ [Ar IV] (filled circles).
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In the text

$\begin{figure} \par\includegraphics[width=8cm,height=9.8cm,clip]{h2447f14.eps} \end{figure}$ Figure 14: The $\frac{{\rm X}^{+i}}{{\rm O}^{++}}$ radial ionization structure of NGC 6741 in the zvpc at $\rm PA=15\hbox {$^\circ $ }$ (close to the apparent minor axis; upper panel), and $\rm PA=75\hbox {$^\circ $ }$ (close to the apparent major axis; lower panel). Same orientation as Fig. 13.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,height=10.6cm,clip]{h2447f15.eps} \end{figure}$ Figure 15: Model-nebula (CLOUDY) vs. true-nebula (NGC 6741, $\rm PA=15\hbox {$^\circ $ }$ , S-SW sector): physical conditions and radial ionization structure. Top panel: physical conditions in the model-nebula (to be compared with Fig. 13). Second panel: absolute flux distribution of H I $\lambda$ 6563 $\rm\AA\/$ , [N II] $\lambda$ 6584 $\rm\AA\/$ , and the ionic sequence of helium (He I $\lambda$ 5876 $\rm\AA\/$ and He II $\lambda$ 4686 $\rm\AA\/$ ) in the model nebula (thin symbols) and the true nebula (thick symbols). Third panel: absolute flux distribution for the ionic sequences of oxygen ([O I] $\lambda$ 6300 $\rm\AA\/$ , [O II] $\lambda$ 7320 $\rm\AA\/$ , and [O III] $\lambda$ 5007 $\rm\AA\/$ ) and sulphur ([S II] $\lambda$ 6717+6731 $\rm\AA\/$ , and [S III] $\lambda$ 6312 $\rm\AA\/$ ); same symbols as in the second panel. Bottom panel: absolute flux distribution for [Ne III] $\lambda$ 3968 $\rm\AA\/$ , and the ionic sequence of argon ([Ar III] $\lambda$ 7135 $\rm\AA\/$ , [Ar IV] $\lambda$ 4740 $\rm\AA\/$ , and [Ar V] $\lambda$ 7005 $\rm\AA\/$ ); same symbols as in the second and third panels.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{h2447f16.eps} \end{figure}$ Figure 16: Stereoscopic structure of NGC 6741 for a rotation around the North-South axis centered on the exciting star. Opaque reconstruction at high flux-cut for $\lambda$ 4686 ${\rm\AA}$ of He II, $\lambda$ 5007 ${\rm\AA}$ of [O III], and $\lambda$ 6584 ${\rm\AA}$ of [N II], as seen from thirteen directions separated by 15 $\hbox {$^\circ $ }$ . The line of sight is given by ( $\theta ,\psi$ ), where $\theta$ is the zenith angle and $\psi$ the azimuthal angle. Each horizontal pair represents a "direct'' stereoscopic pair (i.e. parallel eyes), and the whole figure provides twelve 3-D views of the nebula in as many directions, covering a straight angle (for details, see Ragazzoni et al. 2001). The (0, 0) images represent the rebuilt nebula as seen from Earth (North is up and East to the left). The complete series of nebular movies is shown in the electronic version of the paper (on-line data).
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{h2447f17.eps} \end{figure}$ Figure 17: Same as Fig. 16, but at low flux-cut.
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In the text

$\begin{figure} \par\includegraphics[width=16cm,clip]{h2447f18.eps} \end{figure}$ Figure 18: Optical appearance of NGC 6741 (multi-color in the electronic version of the paper; blue = He II, green = [O III], red = [N II]) for a rotation through the N-S axis centered on the exciting star. The left panel, (0, 0), corresponds to the re-built nebula as seen from the Earth (North is up and East to the left); projection( $\theta ,\psi$ ) = projection( $\theta \pm 180\hbox {$^\circ $ },\psi \pm 180\hbox {$^\circ $ }$ ). The complete (multi-color) movie is shown in the electronic version (on-line data).
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{h2447f1.ps} \end{figure}$	Figure 1: Apparent morphology of NGC 6741 in the medium-excitation line $\lambda$ 5007 $\AA\/$ of [O III] ( upper panel), and in the low-excitation line $\lambda$ 6584 $\rm\AA\/$ of [N II] ( lower panel). North is up and East to the left. HST-WFPC2 frames; programme GO 8773, P. I. Arsen Hajian.
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$\begin{figure} \par\includegraphics[width=8.8cm,clip]{h2447f2.ps} \end{figure}$	Figure 2: Apparent I([N II])/I([O III]) distribution over NGC 6741 (same WFPC2 images as Fig. 1). The sharp, inhomogeneous layer at low-excitation ([N II]) framing the main nebula is punched, along and close to the apparent major axis, by a series of radial [O III] rays or jets penetrating into the faint, roundish halo.
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$\begin{figure} \par\includegraphics[width=8.8cm,clip]{h2447f4.ps} \end{figure}$	Figure 4: Same as Fig. 3, but for $\rm PA=75\hbox {$^\circ $ }$ (close to the apparent major axis of NGC 6741).
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$\begin{figure} \par\includegraphics[width=8.8cm,clip]{h2447f6.ps} \end{figure}$	Figure 6: High-contrast [O III] and [N II] line profiles (in logarithmic scale) of NGC 6741 close to the apparent minor and major axes ( $\rm PA=15\hbox {$^\circ $ }$ and 75 $\hbox {$^\circ $ }$ , respectively) showing the faint halo and red-shifted tail. Same orientation as Figs. 3 and 4.
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$\begin{figure} \par\includegraphics[width=8cm,height=8cm,clip]{h2447f8.eps} \end{figure}$	Figure 8: The cspl-zvpc relation for NGC 6741 at $\rm PA=15\hbox {$^\circ $ }$ , superimposed on the adopted expansion law $V_{\rm exp}$ (km s^-1 $) =13\times R\hbox {$^{\prime \prime }$ }$ , which is valid across the whole nebula, except in the innermost, highest-ionization, decelerated regions marked by [Ar V].
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$\begin{figure} \par\includegraphics[width=8cm,height=8cm,clip]{h2447f12.eps} \end{figure}$	Figure 12: Color-excess vs. distance relation in the direction of NGC 6741. Symbols: small dots = field stars; filled square = open cluster OCL 88; large dot = classical Cepheid V336 Aql.
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$\begin{figure} \par\includegraphics[width=8cm,height=9.8cm,clip]{h2447f14.eps} \end{figure}$	Figure 14: The $\frac{{\rm X}^{+i}}{{\rm O}^{++}}$ radial ionization structure of NGC 6741 in the zvpc at $\rm PA=15\hbox {$^\circ $ }$ (close to the apparent minor axis; upper panel), and $\rm PA=75\hbox {$^\circ $ }$ (close to the apparent major axis; lower panel). Same orientation as Fig. 13.
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$\begin{figure} \par\includegraphics[width=8.8cm,clip]{h2447f17.eps} \end{figure}$	Figure 17: Same as Fig. 16, but at low flux-cut.
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