Context.
Clouds are ubiquitous in exoplanet atmospheres and they represent a challenge for the model interpretation of their spectra. When generating a large number of model spectra, complex cloud ...models often prove too costly numerically, whereas more efficient models may be overly simplified.
Aims.
We aim to constrain the atmospheric properties of the directly imaged planet HR 8799e with a free retrieval approach.
Methods.
We used our radiative transfer code petitRADTRANS for generating the spectra, which we coupled to the PyMultiNest tool. We added the effect of multiple scattering which is important for treating clouds. Two cloud model parameterizations are tested: the first incorporates the mixing and settling of condensates, the second simply parameterizes the functional form of the opacity.
Results.
In mock retrievals, using an inadequate cloud model may result in atmospheres that are more isothermal and less cloudy than the input. Applying our framework on observations of HR 8799e made with the GPI, SPHERE, and GRAVITY, we find a cloudy atmosphere governed by disequilibrium chemistry, confirming previous analyses. We retrieve that C/O = 0.60
−0.08
+0.07
. Other models have not yet produced a well constrained C/O value for this planet. The retrieved C/O values of both cloud models are consistent, while leading to different atmospheric structures: either cloudy or more isothermal and less cloudy. Fitting the observations with the self-consistent Exo-REM model leads to comparable results, without constraining C/O.
Conclusions.
With data from the most sensitive instruments, retrieval analyses of directly imaged planets are possible. The inferred C/O ratio of HR 8799e is independent of the cloud model and thus appears to be a robust. This C/O is consistent with stellar, which could indicate that the HR 8799e formed outside the CO
2
or CO iceline. As it is the innermost planet of the system, this constraint could apply to all HR 8799 planets.
Ices on pebbles in protoplanetary discs Topchieva, A; Molyarova, T; Akimkin, V ...
Monthly notices of the Royal Astronomical Society,
04/2024, Letnik:
530, Številka:
3
Journal Article
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ABSTRACT The formation of solid macroscopic grains (pebbles) in protoplanetary discs is the first step towards planet formation. We aim to study the distribution of pebbles and the chemical ...composition of their ice mantles in a young protoplanetary disc. We use the two-dimensional hydrodynamical code feosad in the thin-disc approximation, which is designed to model the global evolution of a self-gravitating viscous protoplanetary disc taking into account dust coagulation and fragmentation, thermal balance, and phase transitions and transport of the main volatiles (H2O, CO2, CH4, and CO), which can reside in the gas, on small dust ($\lt 1\, \mu\mathrm{ m}$), on grown dust ($\gt 1\, \mu\mathrm{ m}$) and on pebbles. We model the dynamics of the protoplanetary disc from the cloud collapse to the 500 kyr moment. We determine the spatial distribution of pebbles and composition of their ice mantles and estimate the mass of volatiles on pebbles, grown dust, and small dust. We show that pebbles form as early as 50 kyr after the disc formation and exist until the end of simulation (500 kyr), providing prerequisites for planet formation. All pebbles formed in the model are covered by icy mantles. Using a model considering accretion and desorption of volatiles on to dust/pebbles, we find that the ice mantles on pebbles consist mainly of H2O and CO2, and are carbon-depleted compared to gas and ices on small and grown dust, which contain more CO and CH4. This suggests a possible dominance of oxygen in the composition of planets formed from pebbles under these conditions.
The formation of solid macroscopic grains (pebbles) in protoplanetary discs is the first step toward planet formation. We aim to study the distribution of pebbles and the chemical composition of ...their ice mantles in a young protoplanetary disc. We use the two-dimensional hydrodynamical code FEOSAD in the thin-disc approximation, which is designed to model the global evolution of a self-gravitating viscous protoplanetary disc taking into account dust coagulation and fragmentation, thermal balance, and phase transitions and transport of the main volatiles (H\(_2\)O, CO\(_{2}\), CH\(_{4}\) and CO), which can reside in the gas, on small dust (\(<1\) \(\mu\)m), on grown dust (\(>1\) \(\mu\)m) and on pebbles. We model the dynamics of the protoplanetary disc from the cloud collapse to the 500 kyr moment. We determine the spatial distribution of pebbles and composition of their ice mantles and estimate the mass of volatiles on pebbles, grown dust and small dust. We show that pebbles form as early as 50 kyr after the disc formation and exist until the end of simulation (500 kyr), providing prerequisites for planet formation. All pebbles formed in the model are covered by icy mantles. Using a model considering accretion and desorption of volatiles onto dust/pebbles, we find that the ice mantles on pebbles consist mainly of H\(_2\)O and CO\(_{2}\), and are carbon-depleted compared to gas and ices on small and grown dust, which contain more CO and CH\(_4\). This suggests a possible dominance of oxygen in the composition of planets formed from pebbles under these conditions.
Clouds are ubiquitous in exoplanet atmospheres and represent a challenge for the model interpretation of their spectra. Complex cloud models are too numerically costly for generating a large number ...of spectra, while more efficient models may be too strongly simplified. We aim to constrain the atmospheric properties of the directly imaged planet HR 8799e with a free retrieval approach. We use our radiative transfer code petitRADTRANS for generating spectra, which we couple to the PyMultiNest tool. We added the effect of multiple scattering which is important for treating clouds. Two cloud model parameterizations are tested: the first incorporates the mixing and settling of condensates, the second simply parameterizes the functional form of the opacity. In mock retrievals, using an inadequate cloud model may result in atmospheres that are more isothermal and less cloudy than the input. Applying our framework on observations of HR 8799e made with the GPI, SPHERE and GRAVITY, we find a cloudy atmosphere governed by disequilibrium chemistry, confirming previous analyses. We retrieve that \({\rm C/O}=0.60_{-0.08}^{+0.07}\). Other models have not yet produced a well constrained C/O value for this planet. The retrieved C/O values of both cloud models are consistent, while leading to different atmospheric structures: cloudy, or more isothermal and less cloudy. Fitting the observations with the self-consistent Exo-REM model leads to comparable results, while not constraining C/O. With data from the most sensitive instruments, retrieval analyses of directly imaged planets are possible. The inferred C/O ratio of HR 8799e is independent of the cloud model and thus appears to be a robust. This C/O is consistent with stellar, which could indicate that the HR 8799e formed outside the CO\(_2\) or CO iceline. As it is the innermost planet of the system, this constraint could apply to all HR 8799 planets.
Abstract
Constraining planet formation based on the atmospheric composition of exoplanets is a fundamental goal of the exoplanet community. Existing studies commonly try to constrain atmospheric ...abundances, or to analyze what abundance patterns a given description of planet formation predicts. However, there is also a pressing need to develop methodologies that investigate how to transform atmospheric compositions into planetary formation inferences. In this study we summarize the complexities and uncertainties of state-of-the-art planet formation models and how they influence planetary atmospheric compositions. We introduce a methodology that explores the effect of different formation model assumptions when interpreting atmospheric compositions. We apply this framework to the directly imaged planet HR 8799e. Based on its atmospheric composition, this planet may have migrated significantly during its formation. We show that including the chemical evolution of the protoplanetary disk leads to a reduced need for migration. Moreover, we find that pebble accretion can reproduce the planet’s composition, but some of our tested setups lead to too low atmospheric metallicities, even when considering that evaporating pebbles may enrich the disk gas. We conclude that the definitive inversion from atmospheric abundances to planet formation for a given planet may be challenging, but a qualitative understanding of the effects of different formation models is possible, opening up pathways for new investigations.
Protoplanetary disk mass is a key parameter controlling the process of planetary system formation. CO molecular emission is often used as a tracer of gas mass in the disk. In this study, we consider ...the ability of CO to trace the gas mass over a wide range of disk structural parameters, and we search for chemical species that could possibly be used as alternative mass tracers to CO. Specifically, we apply detailed astrochemical modeling to a large set of models of protoplanetary disks around low-mass stars to select molecules with abundances correlated with the disk mass and being relatively insensitive to other disk properties. We do not consider sophisticated dust evolution models, restricting ourselves to the standard astrochemical assumption of 0.1 m dust. We find that CO is indeed the best molecular tracer for total gas mass, despite the fact that it is not the main carbon carrier, provided reasonable assumptions about CO abundance in the disk are used. Typically, chemical reprocessing lowers the abundance of CO by a factor of 3, compared to the case where photodissociation and freeze-out are the only ways of CO depletion. On average, only 13% C atoms reside in gas-phase CO, albeit with variations from 2% to 30%. CO2, H2O, and H2CO can potentially serve as alternative mass tracers, with the latter two only applicable if disk structural parameters are known.
Chemical Signatures of the FU Ori Outbursts Molyarova, Tamara; Akimkin, Vitaly; Semenov, Dmitry ...
The Astrophysical journal,
10/2018, Letnik:
866, Številka:
1
Journal Article
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Odprti dostop
The FU Ori-type young stellar objects are characterized by a sudden increase in luminosity by 1-2 orders of magnitude followed by a slow return to the pre-outburst state on timescales of ∼10-100 yr. ...The outburst strongly affects the entire disk, changing its thermal structure and radiation field. In this paper, using a detailed physical-chemical model, we study the impact of the FU Ori outburst on the disk chemical inventory. Our main goal is to identify gas-phase molecular tracers of the outburst activity that could be observed after the outburst with modern telescopes such as ALMA and NOEMA. We find that the majority of molecules experience a considerable increase in total disk gas-phase abundances due to the outburst, mainly due to the sublimation of their ices. Their return to the pre-outburst chemical state takes different amounts of time, from nearly instantaneous to very long. Among the former, we identify CO, NH3, C2H6, C3H4, etc. Their abundance evolution tightly follows the luminosity curve. For CO, the abundance increase does not exceed an order of magnitude, while for other tracers, the abundances increase by 2-5 orders of magnitude. Other molecules, like H2CO and NH2OH, have longer retention timescales, remaining in the gas phase for ∼10-103 yr after the end of the outburst. Thus, H2CO could be used as an indicator of the previous outbursts in the post-outburst FU Ori systems. We investigate the corresponding time-dependent chemistry in detail and present the most favorable transitions and ALMA configurations for future observations.
Abstract
The chemical influence of luminosity outbursts on the environments of young solar-type stars is explored. Species are categorized into several types according to their response to the ...outburst. The first and second types imply chemical changes only during the outburst (with slightly different behaviours). These response types are mostly observed close to the star and are caused by icy mantle evaporation. However, mantles recover after the outburst almost immediately. A notable exception is benzene ice, which is accumulated on dust surfaces during and after the outburst, so that its abundance exceeds the pre-outburst level by orders of magnitude. The third type of response is mostly seen at the disc periphery and implies alteration of abundances during the outburst and preservation of these ‘abnormal’ abundances for centuries. This behaviour is typical of organic compounds, like HCOOCH3, CH3CN, and CH2CO. Their presence in the dark disc regions can be a manifestation of the past outburst. CO and CO2 only trace past outbursts at the remote disc regions. The outburst changes the C/O ratio, but it quickly returns to the pre-outburst value almost everywhere in the disc. An important factor determining the sensitivity of molecular composition to the outburst is the dust size distribution. The duration of the pre-outburst stage and of the outburst itself influence the chemical effects, if the burst duration is shorter than 50 yr and the duration of the quiescent phase between the bursts is shorter than 100 kyr.
Aims . We study a new mechanism of dust accumulation and planetesimal formation in a gravitationally unstable disk with suppressed magnetorotational instability and we compare it with the classical ...dead zone in a layered disk model. Methods . We used numerical hydrodynamics simulations in the thin-disk limit ( FEOSAD code) to model the formation and long-term evolution of gravitationally unstable disks, including dust dynamics and growth. Results . We found that in gravitationally unstable disks with a radially varying strength of gravitational instability (GI), an inner region (of several astronomical units) of low mass and angular momentum transport is formed. This region is characterized by a low effective value for the α GI parameter, often used to describe the efficiency of mass transport by GI in young protoplanetary disks. The inner region is also similar in terms of characteristics to the dead zone in the layered disk model. As the disk forms and evolves, the GI-induced dead zone accumulates a massive dust ring, which is susceptible to the development of the streaming instability. The model and observationally inferred dust masses and radii may differ significantly in gravitationally unstable disks with massive inner dust rings. Conclusions . The early occurrence of the GI-induced dust ring, followed by the development of the streaming instability suggest that this mechanism may be behind the formation of the first generation of planetesimals in the inner terrestrial zone of the disk. The proposed mechanism, however, crucially depends on the susceptibility of the disk to gravitational instability and requires the magnetorotational instability to be suppressed.
Abstract
The snowlines of various volatile species in protoplanetary disks are associated with abrupt changes in gas composition and dust physical properties. Volatiles may affect dust growth, as ...they cover grains with icy mantles that can change the fragmentation velocity of the grains. In turn, dust coagulation, fragmentation, and drift through the gas disk can contribute to the redistribution of volatiles between the ice and gas phases. Here we present the hydrodynamic model FEOSAD for protoplanetary disks with two dust populations and volatile dynamics. We compute the spatial distributions of major volatile molecules (H
2
O, CO
2
, CH
4
, and CO) in the gas, on small and grown dust, and analyze the composition of icy mantles over the initial 0.5 Myr of disk evolution. We show that most of the ice arrives to the surface of the grown dust through coagulation with small grains. Spiral structures and dust rings forming in the disk, as well as photodissociation in the outer regions, lead to the formation of complex snowline shapes and multiple snowlines for each volatile species. During the considered disk evolution, the snowlines shift closer to the star, with their final position being a factor of 4–5 smaller than that at the disk formation epoch. We demonstrate that volatiles tend to collect in the vicinity of their snowlines, both in the ice and gas phases, leading to the formation of thick icy mantles potentially important for dust dynamics. The dust size is affected by a lower fragmentation velocity of bare grains in the model with a higher turbulent viscosity.
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