1 #LyX 1.1 created this file. For more info see http://www.lyx.org/
14 \paperorientation portrait
17 \paragraph_separation indent
19 \quotes_language english
23 \paperpagestyle default
27 06(03.11.1;16.06.1;19.06.1;19.37.1;19.53.1;19.63.1)
30 Hydrodynamics of giant planet formation
35 \begin_inset Formula \( \kappa \)
45 Institute for Astronomy (IfA), University of Vienna, Türkenschanzstrasse
53 wuchterl@amok.ast.univie.ac.at
56 Received September 15, 1996 / Accepted March 16, 1997
59 To investigate the physical nature of the `nuc\SpecialChar \-
60 leated instability' of proto
62 \begin_inset LatexCommand \cite{mizuno}
66 ), the stability of layers in static, radiative gas spheres is analysed
67 on the basis of Baker's
68 \begin_inset LatexCommand \cite{baker}
72 standard one-zone model.
73 It is shown that stability depends only upon the equations of state, the
74 opacities and the local thermodynamic state in the layer.
75 Stability and instability can therefore be expressed in the form of stability
76 equations of state which are universal for a given composition.
79 The stability equations of state are calculated for solar composition and
80 are displayed in the domain
81 \begin_inset Formula \( -14\leq \lg \rho /[\mathrm{g}\, \mathrm{cm}^{-3}]\leq 0 \)
85 \begin_inset Formula \( 8.8\leq \lg e/[\mathrm{erg}\, \mathrm{g}^{-1}]\leq 17.7 \)
89 These displays may be used to determine the one-zone stability of layers
90 in stellar or planetary structure models by directly reading off the value
91 of the stability equations for the thermodynamic state of these layers,
92 specified by state quantities as density
93 \begin_inset Formula \( \rho \)
97 \begin_inset Formula \( T \)
100 or specific internal energy
101 \begin_inset Formula \( e \)
105 Regions of instability in the
106 \begin_inset Formula \( (\rho \, e) \)
109 -plane are described and related to the underlying microphysical processes.
110 Vibrational instability is found to be a common phenomenon at temperatures
111 lower than the second He ionisation zone.
113 \begin_inset Formula \( \kappa \)
116 -mechanism is widespread under `cool' conditions.
125 giant planet formation --
126 \begin_inset Formula \( \kappa \)
129 -mechanism -- stability of gas spheres
139 nucleated instability
141 (also called core instability) hypothesis of giant planet formation, a
142 critical mass for static core envelope protoplanets has been found.
144 \begin_inset LatexCommand \cite{mizuno}
148 ) determined the critical mass of the core to be about
149 \begin_inset Formula \( 12\, M_{\oplus } \)
153 \begin_inset Formula \( M_{\oplus }=5.975\, 10^{27}\, \mathrm{g} \)
156 is the Earth mass), which is independent of the outer boundary conditions
157 and therefore independent of the location in the solar nebula.
158 This critical value for the core mass corresponds closely to the cores
159 of today's giant planets.
162 Although no hydrodynamical study has been available many workers conjectured
163 that a collapse or rapid contraction will ensue after accumulating the
165 The main motivation for this article is to investigate the stability of
166 the static envelope at the critical mass.
167 With this aim the local, linear stability of static radiative gas spheres
168 is investigated on the basis of Baker's (
169 \begin_inset LatexCommand \cite{baker}
173 ) standard one-zone model.
174 The nonlinear, hydrodynamic evolution of the protogiant planet beyond the
175 critical mass, as calculated by Wuchterl (
176 \begin_inset LatexCommand \cite{wuchterl}
180 ), will be described in a forthcoming article.
183 The fact that Wuchterl (
184 \begin_inset LatexCommand \cite{wuchterl}
188 ) found the excitation of hydrodynamical waves in his models raises considerable
189 interest on the transition from static to dynamic evolutionary phases of
190 the protogiant planet at the critical mass.
191 The waves play a crucial role in the development of the so-called nucleated
192 instability in the nucleated instability hypothesis.
193 They lead to the formation of shock waves and massive outflow phenomena.
194 The protoplanet evolves into a new quasi-equilibrium structure with a
198 envelope, after the mass loss phase has declined.
201 Phenomena similar to the ones described above for giant planet formation
202 have been found in hydrodynamical models concerning star formation where
203 protostellar cores explode (Tscharnuter
204 \begin_inset LatexCommand \cite{tscarnuter}
209 \begin_inset LatexCommand \cite{balluch}
213 ), whereas earlier studies found quasi-steady collapse flows.
214 The similarities in the (micro)physics, i.e., constitutive relations of protostel
215 lar cores and protogiant planets serve as a further motivation for this
219 Baker's standard one-zone model
222 \begin_float wide-fig
237 \begin_inset Formula \( \Gamma \)
242 \begin_inset Formula \( \Gamma _{1} \)
245 is plotted as a function of
246 \begin_inset Formula \( \lg \)
250 \begin_inset Formula \( [\mathrm{erg}\, \mathrm{g}^{-1}] \)
254 \begin_inset Formula \( \lg \)
258 \begin_inset Formula \( [\mathrm{g}\, \mathrm{cm}^{-3}] \)
262 \begin_inset LatexCommand \label{FigGam}
270 In this section the one-zone model of Baker (
271 \begin_inset LatexCommand \cite{baker}
275 ), originally used to study the Cepheïd pulsation mechanism, will be briefly
277 The resulting stability criteria will be rewritten in terms of local state
278 variables, local timescales and constitutive relations.
282 \begin_inset LatexCommand \cite{baker}
286 ) investigates the stability of thin layers in self-gravitating, spherical
287 gas clouds with the following properties:
290 hydrostatic equilibrium,
296 energy transport by grey radiation diffusion.
299 For the one-zone-model Baker obtains necessary conditions for dynamical,
300 secular and vibrational (or pulsational) stability [Eqs.\SpecialChar ~
314 \begin_inset LatexCommand \cite{baker}
319 Using Baker's notation:
320 \begin_inset Formula \begin{eqnarray*}
321 M_{\mathrm{r}} & & \mathrm{mass}\, \mathrm{internal}\, \mathrm{to}\, \mathrm{the}\, \mathrm{radius}\, r\\
322 m & & \mathrm{mass}\, \mathrm{of}\, \mathrm{the}\, \mathrm{zone}\\
323 r_{0} & & \mathrm{unperturbed}\, \mathrm{zone}\, \mathrm{radius}\\
324 \rho _{0} & & \mathrm{unperturbed}\, \mathrm{density}\, \mathrm{in}\, \mathrm{the}\, \mathrm{zone}\\
325 T_{0} & & \mathrm{unperturbed}\, \mathrm{temperature}\, \mathrm{in}\, \mathrm{the}\, \mathrm{zone}\\
326 L_{r0} & & \mathrm{unperturbed}\, \mathrm{luminosity}\\
327 E_{\mathrm{th}} & & \mathrm{thermal}\, \mathrm{energy}\, \mathrm{of}\, \mathrm{the}\, \mathrm{zone}
332 and with the definitions of the
336 (see Fig.\SpecialChar ~
338 \begin_inset LatexCommand \ref{FigGam}
346 \begin_inset Formula \begin{equation}
347 \tau _{\mathrm{co}}=\frac{E_{\mathrm{th}}}{L_{r0}}\, ,
358 \begin_inset Formula \begin{equation}
359 \tau _{\mathrm{ff}}=\sqrt{\frac{3\pi }{32G}\frac{4\pi r_{0}^{3}}{3M_{\mathrm{r}}}\, ,}
365 \begin_inset Formula \( K \)
369 \begin_inset Formula \( \sigma _{0} \)
372 have the following form:
373 \begin_inset Formula \begin{eqnarray}
374 \sigma _{0} & = & \frac{\pi }{\sqrt{8}}\frac{1}{\tau _{\mathrm{ff}}}\\
375 K & = & \frac{\sqrt{32}}{\pi }\frac{1}{\delta }\frac{\tau _{\mathrm{ff}}}{\tau _{\mathrm{co}}}\, ;
381 \begin_inset Formula \( E_{\mathrm{th}}\approx m(P_{0}/\rho _{0}) \)
388 \begin_inset Formula \begin{equation}
390 \delta =-\left( \frac{\partial \ln \rho }{\partial \ln T}\right) _{P}\\
397 is a thermodynamical quantity which is of order
398 \begin_inset Formula \( 1 \)
402 \begin_inset Formula \( 1 \)
405 for nonreacting mixtures of classical perfect gases.
406 The physical meaning of
407 \begin_inset Formula \( \sigma _{0} \)
411 \begin_inset Formula \( K \)
414 is clearly visible in the equations above.
416 \begin_inset Formula \( \sigma _{0} \)
419 represents a frequency of the order one per free-fall time.
421 \begin_inset Formula \( K \)
424 is proportional to the ratio of the free-fall time and the cooling time.
425 Substituting into Baker's criteria, using thermodynamic identities and
426 definitions of thermodynamic quantities,
427 \begin_inset Formula \[
428 \Gamma _{1}=\left( \frac{\partial \ln P}{\partial \ln \rho }\right) _{S}\, ,\: \chi _{\rho }=\left( \frac{\partial \ln P}{\partial \ln \rho }\right) _{T}\, ,\: \kappa _{P}=\left( \frac{\partial \ln \kappa }{\partial \ln P}\right) _{T}\]
436 \begin_inset Formula \[
437 \nabla _{\mathrm{ad}}=\left( \frac{\partial \ln T}{\partial \ln P}\right) _{S}\, ,\: \chi _{T}=\left( \frac{\partial \ln P}{\partial \ln T}\right) _{\rho }\, ,\: \kappa _{T}=\left( \frac{\partial \ln \kappa }{\partial \ln P}\right) _{T}\]
441 one obtains, after some pages of algebra, the conditions for
449 \begin_inset Formula \begin{eqnarray}
450 \frac{\pi ^{2}}{8}\frac{1}{\tau _{\mathrm{ff}}^{2}}(3\Gamma _{1}-4) & > & 0\label{ZSDynSta} \\
451 \frac{\pi ^{2}}{\tau _{\mathrm{co}}\tau _{\mathrm{ff}}^{2}}\Gamma _{1}\nabla _{\mathrm{ad}}\left[ \frac{1-3/4\chi _{\rho }}{\chi _{T}}(\kappa _{T}-4)+\kappa _{P}+1\right] & > & 0\label{ZSSecSta} \\
452 \frac{\pi ^{2}}{4}\frac{3}{\tau _{\mathrm{co}}\tau _{\mathrm{ff}}^{2}}\Gamma _{1}^{2}\nabla _{\mathrm{ad}}\left[ 4\nabla _{\mathrm{ad}}-(\nabla _{\mathrm{ad}}\kappa _{T}+\kappa _{P})-\frac{4}{3\Gamma _{1}}\right] & > & 0\label{ZSVibSta}
457 For a physical discussion of the stability criteria see Baker (
458 \begin_inset LatexCommand \cite{baker}
463 \begin_inset LatexCommand \cite{cox}
470 We observe that these criteria for dynamical, secular and vibrational stability,
471 respectively, can be factorized into
474 a factor containing local timescales only,
477 a factor containing only constitutive relations and their derivatives.
480 The first factors, depending on only timescales, are positive by definition.
481 The signs of the left hand sides of the inequalities\SpecialChar ~
483 \begin_inset LatexCommand \ref{ZSDynSta}
488 \begin_inset LatexCommand \ref{ZSSecSta}
493 \begin_inset LatexCommand \ref{ZSVibSta}
497 ) therefore depend exclusively on the second factors containing the constitutive
499 Since they depend only on state variables, the stability criteria themselves
502 functions of the thermodynamic state in the local zone
505 The one-zone stability can therefore be determined from a simple equation
506 of state, given for example, as a function of density and temperature.
507 Once the microphysics, i.e.
508 the thermodynamics and opacities (see Table\SpecialChar ~
510 \begin_inset LatexCommand \ref{KapSou}
514 ), are specified (in practice by specifying a chemical composition) the
515 one-zone stability can be inferred if the thermodynamic state is specified.
516 The zone -- or in other words the layer -- will be stable or unstable in
517 whatever object it is imbedded as long as it satisfies the one-zone-model
519 Only the specific growth rates (depending upon the time scales) will be
520 different for layers in different objects.
527 \begin_inset LatexCommand \label{KapSou}
536 <lyxtabular version="2" rows="4" columns="2">
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538 <column alignment="left" valignment="top" leftline="false" rightline="false" width="" special="">
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549 <cell multicolumn="0" alignment="center" valignment="top" topline="true" bottomline="false" leftline="true" rightline="true" rotate="false" usebox="none" width="" special="">
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559 <cell multicolumn="0" alignment="center" valignment="top" topline="true" bottomline="false" leftline="true" rightline="false" rotate="false" usebox="none" width="" special="">
564 Yorke 1979, Yorke 1980a
567 <cell multicolumn="0" alignment="center" valignment="top" topline="true" bottomline="false" leftline="true" rightline="true" rotate="false" usebox="none" width="" special="">
573 \begin_inset Formula \( \leq 1700^{\mathrm{a}} \)
580 <row topline="false" bottomline="false" newpage="false">
581 <cell multicolumn="0" alignment="center" valignment="top" topline="true" bottomline="false" leftline="true" rightline="false" rotate="false" usebox="none" width="" special="">
589 <cell multicolumn="0" alignment="center" valignment="top" topline="true" bottomline="false" leftline="true" rightline="true" rotate="false" usebox="none" width="" special="">
595 \begin_inset Formula \( 1700\leq T\leq 5000 \)
602 <row topline="false" bottomline="true" newpage="false">
603 <cell multicolumn="0" alignment="center" valignment="top" topline="true" bottomline="false" leftline="true" rightline="false" rotate="false" usebox="none" width="" special="">
611 <cell multicolumn="0" alignment="center" valignment="top" topline="true" bottomline="false" leftline="true" rightline="true" rotate="false" usebox="none" width="" special="">
617 \begin_inset Formula \( 5000\leq \)
630 \added_space_top medskip*
632 \begin_inset Formula \( ^{\textrm{a}} \)
637 \begin_float wide-tab
640 Regions of secular instability
641 \begin_inset LatexCommand \label{TabSecInst}
654 We will now write down the sign (and therefore stability) determining parts
655 of the left-hand sides of the inequalities (
656 \begin_inset LatexCommand \ref{ZSDynSta}
661 \begin_inset LatexCommand \ref{ZSSecSta}
666 \begin_inset LatexCommand \ref{ZSVibSta}
672 stability equations of state
677 The sign determining part of inequality\SpecialChar ~
679 \begin_inset LatexCommand \ref{ZSDynSta}
684 \begin_inset Formula \( 3\Gamma _{1}-4 \)
687 and it reduces to the criterion for dynamical stability
691 \begin_inset Formula \begin{equation}
692 \Gamma _{1}>\frac{4}{3}
697 Stability of the thermodynamical equilibrium demands
698 \begin_inset Formula \begin{equation}
699 \chi _{\rho }>0,\: \: c_{v}>0\, ,
708 \begin_inset Formula \begin{equation}
714 holds for a wide range of physical situations.
719 \begin_inset Formula \begin{eqnarray}
720 \Gamma _{3}-1=\frac{P}{\rho T}\frac{\chi _{T}}{c_{v}} & > & 0\\
721 \Gamma _{1}=\chi _{\rho }+\chi _{T}(\Gamma _{3}-1) & > & 0\\
722 \nabla _{\mathrm{ad}}=\frac{\Gamma _{3}-1}{\Gamma _{1}} & > & 0
727 we find the sign determining terms in inequalities\SpecialChar ~
729 \begin_inset LatexCommand \ref{ZSSecSta}
734 \begin_inset LatexCommand \ref{ZSVibSta}
738 ) respectively and obtain the following form of the criteria for dynamical,
739 secular and vibrational
747 \begin_inset Formula \begin{eqnarray}
748 3\Gamma _{1}-4=:\, S_{\mathrm{dyn}}> & 0 & \label{DynSta} \\
749 \frac{1-3/4\chi _{\rho }}{\chi _{T}}(\kappa _{T}-4)+\kappa _{P}+1=:\, S_{\mathrm{sec}}> & 0 & \label{SecSta} \\
750 4\nabla _{\mathrm{ad}}-(\nabla _{\mathrm{ad}}\kappa _{T}+\kappa _{P}-\frac{4}{3\Gamma _{1}}=:\, S_{\mathrm{vib}}> & 0 & \label{VibSta}
755 The constitutive relations are to be evaluated for the unperturbed thermodynamic
757 \begin_inset Formula \( (\rho _{0},T_{0}) \)
761 We see that the one-zone stability of the layer depends only on the constitutiv
763 \begin_inset Formula \( \Gamma _{1} \)
767 \begin_inset Formula \( \nabla _{\mathrm{ad}} \)
771 \begin_inset Formula \( \chi _{T},\, \chi _{\rho } \)
775 \begin_inset Formula \( \kappa _{P},\, \kappa _{T} \)
779 These depend only on the unperturbed thermodynamical state of the layer.
780 Therefore the above relations define the one-zone-stability equations of
782 \begin_inset Formula \( S_{\mathrm{dyn}},\, S_{\mathrm{sec}} \)
786 \begin_inset Formula \( S_{\mathrm{vib}} \)
790 See Fig.\SpecialChar ~
792 \begin_inset LatexCommand \ref{FigVibStab}
797 \begin_inset Formula \( S_{\mathrm{vib}} \)
801 Regions of secular instability are listed in Table\SpecialChar ~
803 \begin_inset LatexCommand \ref{TabSecInst}
820 Vibrational stability equation of state
821 \begin_inset Formula \( S_{\mathrm{vib}}(\lg e,\lg \rho ) \)
826 \begin_inset Formula \( >0 \)
829 means vibrational stability.
830 \begin_inset LatexCommand \label{FigVibStab}
841 The conditions for the stability of static, radiative layers in gas spheres,
842 as described by Baker's (
843 \begin_inset LatexCommand \cite{baker}
847 ) standard one-zone model, can be expressed as stability equations of state.
848 These stability equations of state depend only on the local thermodynamic
852 If the constitutive relations -- equations of state and Rosseland mean opacities
853 -- are specified, the stability equations of state can be evaluated without
854 specifying properties of the layer.
857 For solar composition gas the
858 \begin_inset Formula \( \kappa \)
861 -mechanism is working in the regions of the ice and dust features in the
863 \begin_inset Formula \( \mathrm{H}_{2} \)
866 dissociation and the combined H, first He ionization zone, as indicated
867 by vibrational instability.
868 These regions of instability are much larger in extent and degree of instabilit
869 y than the second He ionization zone that drives the Cepheïd pulsations.
870 \layout Acknowledgement
872 Part of this work was supported by the German
875 sche For\SpecialChar \-
876 schungs\SpecialChar \-
881 project number Ts\SpecialChar ~
884 \bibitem [1966]{baker}
886 Baker N., 1966, in: Stellar Evolution, eds.\SpecialChar ~
892 Cameron, Plenum, New York, p.\SpecialChar ~
895 \bibitem [1988]{balluch}
897 Balluch M., 1988, A&A 200, 58
902 P., 1980, Theory of Stellar Pulsation, Princeton University Press, Princeton,
906 \bibitem [1969]{cox69}
910 N., 1969, Academia Nauk, Scientific Information 15, 1
912 \bibitem [1971]{kruegel}
914 Krügel E., 1971, Der Rosselandsche Mittelwert bei tiefen Temperaturen, Diplom--Th
915 esis, Univ.\SpecialChar ~
918 \bibitem [1980]{mizuno}
920 Mizuno H., 1980, Prog.
925 \bibitem [1987]{tscarnuter}
928 M., 1987, A&A 188, 55
930 \bibitem [1989]{wuchterl}
932 Wuchterl G., 1989, Zur Entstehung der Gasplaneten.
938 sche Gas\SpecialChar \-
941 gen auf Pro\SpecialChar \-
945 ten, Dissertation, Univ.
948 \bibitem [1979]{yorke79}
951 W., 1979, A&A 80, 215
953 \bibitem [1980a]{yorke80a}
956 W., 1980a, A&A 86, 286