Astronomy & Astrophysics

All Figures

$\begin{figure} \par\includegraphics[width=8cm,clip]{4598fig1.eps} \end{figure}$ Figure 1: Sketch of the surface chemical processes involved in the growth and evaporation of an island of solid material s at the surface of a dirty dust grain. The total surface area $A_{\rm tot}$ of the grain collects molecules which are then transported by hopping to meet on the island's surface area $A_{\rm s}$ , where the actual chemisorption process can take place.
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In the text

$\begin{figure} \includegraphics[width=8.2cm]{4598fig2.eps} \end{figure}$ Figure 2: Local hydro- and thermodynamical processes in a dust-forming gas as affected by expansion waves (dashed : 0.01 s, solid: 0.15 s, dotted: 5 s). 1st row: l.h.s. density $\rho$ , r.h.s. pressure p [dimensionless]. 2nd row: l.h.s. temperature T, r.h.s. velocity u [dimensionless]. 3rd row: l.h.s. nucleation rate $J_*/n_{\langle{\rm H}\rangle}$ [1/s], r.h.s. net growth velocity $\chi ^{\rm net}$ [cm/s]. Parameter: $T_{\rm ref}=1900$ K, $T_{\rm RE}=0.9\times T_{\rm ref}=1710~$ K, $\rho _{\rm ref}=10^{-3.5}$ g/cm³ ( $p_{\rm gas}=2.15\times 10^7$ dyn/cm², $n_{\rm \langle H \rangle, ref}=1.35\times 10^{20}$ cm^-3, $\rm M=0.1$ (Mach number), $t_{\rm ref}=3.2365$ s, $l_{\rm ref}=10^5$ cm).
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In the text

$\begin{figure} \par\mbox{\includegraphics[width=5.02cm,clip]{4598fig3a.eps}\qqua... ...3b.eps}\qquad \includegraphics[width=5.4cm,clip]{4598fig3c.eps} }\end{figure}$ Figure 3: Local details of the dust formation process and the evolution of the chemical abundances in the gas phase. The colours/line-styles indicate the dust species (and assigned elements) as follows. Dark blue/full: TiO₂[s] (Ti); brown/short dash-dot: SiO₂[s] (Si); green/long dash-dot: Fe[s] (Fe); orange/long dashed: Mg₂SiO₄[s] (Mg), light blue/dotted: Al₂O₃[s] (Al); red/dashed: [no assigned dust species] (O). 1st row: supersaturation ratios S (^*), 2nd row: inverse surface area non-equilibrium factors $1/b^{~\rm s}_{\rm surf}$ , 3rd row: factor determining growth or evaporation $1 - 1/(S~b^{~\rm s}_{\rm surf})$ (^*), 4th row: element abundances in the gas phase, 5th row: mean dust particle size $\langle a\rangle$ [cm]. (^*) Note, we plot S^1/2 for Al₂O₃[s] and Mg₂SiO₄[s] according to Appendix B.
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In the text

$\begin{figure} \par\mbox{\includegraphics[width=4.4cm,clip]{4598fig4a.eps}\includegraphics[width=4.31cm,clip]{4598fig4b.eps} }\end{figure}$ Figure 4: Dust volume fractions, expressed by $1/b_{\rm surf}^{~\rm s} = V_{\rm s}/V_{\rm tot}$ , at the point of constructive wave interaction (x=0.25) as function of time ( bottom panels) and corresponding cumulative volumes $\sum V_{\rm s}/V_{\rm tot}$ ( top panels). Orange/open squares: $\rm Mg_2SiO_4$ , brown/stars: $\rm Mg_2SiO_4 + SiO_2$ , green/open triangels: $\rm Mg_2SiO_4 + SiO_2 + Fe$ , light blue/filled triangles: $\rm Mg_2SiO_4 + SiO_2 + Fe + Al_2O_3$ , dark blue/open circles: $\rm Mg_2SiO_4 + SiO_2 + Fe + Al_2O_3 + TiO_2$ . Left: short-term behaviour, right: long-term behaviour. In the beginning, when dust is not yet present and $V_{\rm tot}=0$ , we put numerically $b_{\rm surf}^{\rm s}=1$ .
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In the text

$\begin{figure} \par\includegraphics[width=14.2cm,clip]{4598fig5.eps} \end{figure}$ Figure 5: Gas phase chemistry: particle densities $n_{\rm y}$ [cm^-3] as function of temperature T at $\rho =10^{-3.5}$ g cm^-3 ( $p_{\rm gas}=2.15\times 10^7$ dyn/cm², $n_{\rm \langle H \rangle, ref}=1.35\times 10^{20}$ cm^-3) for solar element abundances (l.h.s.) and for element abundances as present at late stages of the dust formation model (r.h.s.). These results are calculated with the complete chemical equilibrium code.
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In the text

$\begin{figure} \par\mbox{\includegraphics[width=8.3cm,clip]{4598fig6a.eps}\quad \includegraphics[width=8.3cm,clip]{4598fig6b.eps} }\par\end{figure}$ Figure 6: Evolution of temperature, dust, and chemistry at the centre of wave interaction (x=0.25, l.h.s.: short-term - r.h.s.: long-term). Left panels on l.h.s.: 1st row: temperature T [1900 K], 2nd row: nucleation rate per hydrogen nuclei $J_*/n_{\langle{\rm H}\rangle}~$ [1/s], 3rd row: number of dust particles $n_{\rm d}~$ [1/cm³], 4th row: mean grain radius $\langle a\rangle~$ [cm], 5th row: degree of condensation $f_{\rm x}(t)=1-\epsilon _{\rm x}(t)/\epsilon _{\rm x,0}$ (red filled squares: O - orange filled hexagons: Mg - brown filled squares: Si - green crosses: Fe - cyan triangles: Al - dark blue open hexagons: Ti). Left panels on r.h.s.: 1st row: temperature T [1900 K], 2nd row: number of dust particles $n_{\rm d}~$ [1/cm³], 3rd row: mean grain radius $\langle a\rangle~$ [cm], 4th row: element abundances $\epsilon _{\rm x}$ 5th row: degree of condensation $f_{\rm x}(t)$ (same colour code). Right panels: number density of molecules $n_{\rm y}$ [cm^-3]. Note that the scaling on the l.h.s. and the r.h.s. is different.
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In the text

$\begin{figure} \par\mbox{\includegraphics[width=10.2cm,clip]{4598fig7a.eps}\qqua... ...ncludegraphics[width=5cm,clip,bb=39 150 291 685 ]{4598fig7b.eps} }\end{figure}$ Figure 7: Same as l.h.s of Figs. 6 and 4, but for $T_{\rm RE}=0.5\times T_{\rm ref}=950~$ K, simulating an convective element that ascends to a higher atmospheric latitude. Left: time evolution of temperature, dust, and chemistry. Right: time evolution of the cumulative volumes $\sum V_{\rm s}/V_{\rm tot}$ ( top) and the solid volume fractions $1/b_{\rm surf}^{~\rm s} = V_{\rm s}/V_{\rm tot}$ ( bottom).
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In the text

$\begin{figure} \par\mbox{\includegraphics[width=4.02cm,clip]{4598fig8a.eps}\quad \includegraphics[width=4.5cm,clip]{4598fig8b.eps} }\end{figure}$ Figure 8: Influence of reaction kinetics on the cumulative volume fraction $\sum V_{\rm s}/V_{\rm tot}$ ( top: open squares: $\rm Mg_2SiO_4$ , Stars: $\rm Mg_2SiO_4 + SiO_2$ , Open triangles: $\rm Mg_2SiO_4 + SiO_2 + Fe$ , Filled triangles: $\rm Mg_2SiO_4 + SiO_2 + Fe + Al_2O_3$ , Open circles: $\rm Mg_2SiO_4 + SiO_2 + Fe + Al_2O_3 + TiO_2$ .) and the degree of condensation $f_{\rm x}$ ( bottom). Different cases are colour coded: case #0 - dark blue, case #1 - light blue (just below orange), case #2 - orange, case #3 - red (Table 2).
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In the text

$\begin{figure} \par\epsfig{file=4598fig9.eps, width=4.5cm} \end{figure}$ Figure B.1: Thought experiment to obtain the reference state $^\circ$ .

In the text

$\begin{figure} \includegraphics[width=8.7cm]{4598fig10.eps} \end{figure}$ Figure B.2: Monomer supersaturation ratios S (solid lines) and reaction supersaturation ratios S_r (dashed lines) separately for all considered solids s as function of temperature T at fixed hydrogen nuclei density $n_{\langle{\rm H}\rangle}=10^{18}~\rm cm^{-3}$ . $\sqrt {S}$ is shown for comparison by the red dashed lines.

In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{4598fig1.eps} \end{figure}$	Figure 1: Sketch of the surface chemical processes involved in the growth and evaporation of an island of solid material s at the surface of a dirty dust grain. The total surface area $A_{\rm tot}$ of the grain collects molecules which are then transported by hopping to meet on the island's surface area $A_{\rm s}$ , where the actual chemisorption process can take place.
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