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Ewine F Van Dishoeck - One of the best experts on this subject based on the ideXlab platform.

  • cometary compositions compared with protoplanetary disk midplane Chemical Evolution an emerging Chemical Evolution taxonomy for comets
    Astronomy and Astrophysics, 2019
    Co-Authors: Christian Eistrup, Catherine Walsh, Ewine F Van Dishoeck
    Abstract:

    [Abridged] With a growing number of molecules observed in many comets, and an improved understanding of Chemical Evolution in protoplanetary disk midplanes, comparisons can be made between models and observations that could potentially constrain the formation histories of comets. A $\chi^{2}$-method was used to determine maximum likelihood surfaces for 14 different comets that formed at a given time (up to 8 Myr) and place (out to beyond the CO iceline) in the pre-solar nebula midplane. This was done using observed volatile abundances for the 14 comets and the Evolution of volatile abundances from Chemical modelling of disk midplanes. Considering all parent species (ten molecules) in a scenario that assumed reset initial chemistry, the $\chi^{2}$ likelihood surfaces show a characteristic trail in the parameter space with high likelihood of formation around 30 AU at early times and 12 AU at later times for ten comets. This trail roughly traces the vicinity of the CO iceline in time. The formation histories for all comets were thereby constrained to the vicinity of the CO iceline, assuming that the chemistry was partially reset early in the pre-solar nebula. This is found, both when considering carbon-, oxygen-, and sulphur-bearing molecules (ten in total), and when only considering carbon- and oxygen-bearing molecules (seven in total). Since these 14 comets did not previously fall into the same taxonomical categories together, this Chemical constraint may be proposed as an alternative taxonomy for comets. Based on the most likely time for each of these comets to have formed during the disk Chemical Evolution, a formation time classification for the 14 comets is suggested.

  • cometary compositions compared with protoplanetary disk midplane Chemical Evolution an emerging Chemical Evolution taxonomy for comets
    Astronomy and Astrophysics, 2019
    Co-Authors: Catherine Walsh, Christian Eistrup, Ewine F Van Dishoeck
    Abstract:

    Context. Comets are planetesimals left over from the formation of planets in the solar system. With a growing number of observed molecular abundances in many comets, and an improved understanding of Chemical Evolution in protoplanetary disk midplanes, comparisons can be made between models and observations that could potentially constrain the formation histories of comets.Aims. Our aim is to carry out the first statistical comparison between cometary volatile ice abundances and modelled evolving abundances in a protoplanetary disk midplane.Methods. A χ 2 -method was used to determine maximum likelihood surfaces for 14 different comets that formed at a given time (up to 8 Myr) and place (out to beyond the CO iceline) in the pre-solar nebula midplane. This was done using observed volatile abundances for the 14 comets and the Evolution of volatile abundances from Chemical modelling of disk midplanes. Two assumptions for the Chemical modelling starting conditions (cloud inheritance or Chemical reset), as well as two different sets of cometary molecules (parent species, with or without sulphur species) were investigated.Results. Considering all parent species (ten molecules) in the reset scenario, χ 2 likelihood surfaces show a characteristic trail in the parameter space with high likelihood of formation around 30 AU at early times and 12 AU at later times for ten comets. This trail roughly traces the vicinity of the CO iceline in time.Conclusions. A statistical comparison between observed and modelled Chemical abundances in comets and comet-forming regions could be a powerful tool for constraining cometary formation histories. The formation histories for all comets were constrained to the vicinity of the CO iceline, assuming that the chemistry was partially reset early in the pre-solar nebula. This is found, both when considering carbon-, oxygen-, and sulphur-bearing molecules (ten in total), and when only considering carbon- and oxygen-bearing molecules (seven in total). Since these 14 comets did not previously fall into the same taxonomical categories together, this Chemical constraint may be proposed as an alternative taxonomy for comets. Based on the most likely time for each of these comets to have formed during the disk Chemical Evolution, a formation time classification for the 14 comets is suggested.

  • setting the volatile composition of exo planet building material does Chemical Evolution in disk midplanes matter
    Astronomy and Astrophysics, 2016
    Co-Authors: Christian Eistrup, Catherine Walsh, Ewine F Van Dishoeck
    Abstract:

    Context. The atmospheres of extrasolar planets are thought to be built largely through accretion of pebbles and planetesimals. Such pebbles are also the building blocks of comets. The Chemical composition of their volatiles are usually taken to be inherited from the ices in the collapsing cloud. However, chemistry in the protoplanetary disk midplane can modify the composition of ices and gases.Aims. To investigate if and how Chemical Evolution affects the abundances and distributions of key volatile species in the midplane of a protoplanetary disk in the 0.2–30 AU range. Methods. A disk model used in planet population synthesis models is adopted, providing temperature, density and ionisation rate at different radial distances in the disk midplane. A full Chemical network including gas-phase, gas-grain interactions and grain-surface chemistry is used to evolve chemistry in time, for 1 Myr. Both molecular (inheritance from the parent cloud) and atomic (Chemical reset) initial conditions are investigated.Results. Great diversity is observed in the relative abundance ratios of the main considered species: H2 O, CO, CO2 , CH4 , O2 , NH3 and N2 . The choice of ionisation level, the choice of initial abundances, as well as the extent of Chemical reaction types included are all factors that affect the Chemical Evolution. The only exception is the inheritance scenario with a low ionisation level, which results in negligible changes compared with the initial abundances, regardless of whether or not grain-surface chemistry is included. The grain temperature plays an important role, especially in the critical 20–28 K region where atomic H no longer sticks long enough to the surface to react, but atomic O does. Above 28 K, efficient grain-surface production of CO2 ice is seen, as well as O2 gas and ice under certain conditions, at the expense of H2 O and CO. H2 O ice is produced on grain surfaces only below 28 K. For high ionisation levels at intermediate disk radii, CH4 gas is destroyed and converted into CO and CO2 (in contrast with previous models), and similarly NH3 gas is converted into N2 . At large radii around 30 AU, CH4 ice is enhanced leading to a low gaseous CO abundance. As a result, the overall C/O ratios for gas and ice change significantly with radius and with model assumptions. For high ionisation levels, Chemical processing becomes significant after a few times 105 yr.Conclusions. Chemistry in the disk midplane needs to be considered in the determination of the volatile composition of planetesimals. In the inner yr.

  • setting the volatile composition of exo planet building material does Chemical Evolution in disk midplanes matter
    Astronomy and Astrophysics, 2016
    Co-Authors: Christian Eistrup, Catherine Walsh, Ewine F Van Dishoeck
    Abstract:

    Context. The atmospheres of extrasolar planets are thought to be built largely through accretion of pebbles and planetesimals. Such pebbles are also the building blocks of comets. The Chemical composition of their volatiles are usually taken to be inherited from the ices in the collapsing cloud. However, chemistry in the protoplanetary disk midplane can modify the composition of ices and gases. Aims. To investigate if and how Chemical Evolution affects the abundances and distributions of key volatile species in the midplane of a protoplanetary disk in the 0.2–30 AU range. Methods. A disk model used in planet population synthesis models is adopted, providing temperature, density and ionisation rate at different radial distances in the disk midplane. A full Chemical network including gas-phase, gas-grain interactions and grain-surface chemistry is used to evolve chemistry in time, for 1 Myr. Both molecular (inheritance from the parent cloud) and atomic (Chemical reset) initial conditions are investigated. Results. Great diversity is observed in the relative abundance ratios of the main considered species: H2O, CO, CO2, CH4, O2, NH3 and N2. The choice of ionisation level, the choice of initial abundances, as well as the extent of Chemical reaction types included are all factors that affect the Chemical Evolution. The only exception is the inheritance scenario with a low ionisation level, which results in negligible changes compared with the initial abundances, regardless of whether or not grain-surface chemistry is included. The grain temperature plays an important role, especially in the critical 20–28 K region where atomic H no longer sticks long enough to the surface to react, but atomic O does. Above 28 K, efficient grain-surface production of CO2 ice is seen, as well as O2 gas and ice under certain conditions, at the expense of H2O and CO. H2O ice is produced on grain surfaces only below 28 K. For high ionisation levels at intermediate disk radii, CH4 gas is destroyed and converted into CO and CO2 (in contrast with previous models), and similarly NH3 gas is converted into N2. At large radii around 30 AU, CH4 ice is enhanced leading to a low gaseous CO abundance. As a result, the overall C/O ratios for gas and ice change significantly with radius and with model assumptions. For high ionisation levels, Chemical processing becomes significant after a few times 105 yr. Conclusions. Chemistry in the disk midplane needs to be considered in the determination of the volatile composition of planetesimals. In the inner <30 AU disk, interstellar ice abundances are preserved only if the ionisation level is low, or if these species are included in larger bodies within 105 yr.

  • setting the volatile composition of exo planet building material does Chemical Evolution in disk midplanes matter
    arXiv: Earth and Planetary Astrophysics, 2016
    Co-Authors: Christian Eistrup, Catherine Walsh, Ewine F Van Dishoeck
    Abstract:

    [Abridged] Chemical Evolution in the protoplanetary disk midplane can modify the composition of ices and gases. We have investigated if and how Chemical Evolution affects the abundances and distributions of key volatile species in the midplane of a protoplanetary disk in the 0.2-30 AU range. A full Chemical network including gas-phase, gas-grain interactions and grain-surface chemistry is used to evolve chemistry in time, for 1 Myr. Great diversity is observed in the relative abundance ratios of the main considered species: H2O, CO, CO2, CH4, O2, NH3 and N2. The choice of ionisation level, the choice of initial abundances, as well as the extent of Chemical reaction types included are all factors that affect the Chemical Evolution. The only exception is the inheritance scenario with a low ionisation level, which results in negligible changes compared with the initial abundances, regardless of whether grain-surface chemistry is included. The Chemical processing changes the C/O ratios for gas and ice significantly with radius and with model assumptions. For high ionisation levels, Chemical processing becomes significant after a few times $10^{5}$~yrs. It is concluded that Chemical Evolution in the disk midplane needs to be considered in the determination of the volatile composition of planetesimals.

F Matteucci - One of the best experts on this subject based on the ideXlab platform.

  • the fall of a giant Chemical Evolution of enceladus alias the gaia sausage
    Monthly Notices of the Royal Astronomical Society: Letters, 2019
    Co-Authors: Fiorenzo Vincenzo, F Matteucci, A Miglio, E Spitoni, F Calura, Victor Silva Aguirre, G Cescutti
    Abstract:

    We present the first Chemical Evolution model for Enceladus, alias the Gaia Sausage, to investigate the star formation history of one of the most massive satellites accreted by the Milky Way during a major merger event. Our best Chemical Evolution model for Enceladus nicely fits the observed stellar [$\alpha$/Fe]-[Fe/H] Chemical abundance trends, and reproduces the observed stellar metallicity distribution function, by assuming low star formation efficiency, fast infall time scale, and mild outflow intensity. We predict a median age for Enceladus stars $12.33^{+0.92}_{-1.36}$ Gyr, and - at the time of the merger with our Galaxy ($\approx10$ Gyr ago from Helmi et al.) - we predict for Enceladus a total stellar mass $M_{\star} \approx 5 \times 10^{9}\,\text{M}_{\odot}$. By looking at the predictions of our best model, we discuss that merger events between the Galaxy and systems like Enceladus may have inhibited the gas accretion onto the Galaxy disc at high redshifts, heating up the gas in the halo. This scenario could explain the extended period of quenching in the star formation activity of our Galaxy about 10 Gyr ago, which is predicted by Milky Way Chemical Evolution models, in order to reproduce the observed bimodality in [$\alpha$/Fe]-[Fe/H] between thick- and thin-disc stars.

  • effects of the radial inflow of gas and galactic fountains on the Chemical Evolution of m 31
    Astronomy and Astrophysics, 2013
    Co-Authors: E Spitoni, F Matteucci, M M Marconuchida
    Abstract:

    Context. Galactic fountains and radial gas flows are very important in gredients in modeling the Chemical Evolution of galactic disks. Aims. Our aim here is to study the effects of galactic fountains and radial gas flows in the chemica l Evolution of the disk of Andromeda (M31) galaxy. Methods. We adopt a ballistic method to study the effects of galactic fountains on the Chemical enrichment of the M31 disk. In particular, we study the effects of the landing coordinate of the fountains and the time delay in the pollution of the interstellar gas. To study the effects of radial flows we adopt a very detailed Chemical evoluti on model. Our aim is to study the formation of abundance gradients along the M31 disk and also compare our results with the Milky Way. Results. We find that the landing coordinate for the fountains in M31 is no more than 1 kpc from the starting point, thus producing negligible effect on the Chemical Evolution of the disk. We find that the dela y time in the enrichment process due to fountains is no longer than 100 Myr and this timescale also produces negligible effects on the results. Then, we compute the Chemical Evolution of the M31 disk with radial gas flows produced by the infall of ext ragalactic material and fountains. We find that a moderate in side-out formation of the disk coupled with radial flows of variable sp eed can very well reproduce the observed gradient. We discuss also the effects of other parameters such a threshold in the gas density f or star formation and an effi ciency of star formation varying with the galactic radius. Conclusions. We conclude that galactic fountains do not affect the Chemical Evolution of the M31 disk. The inclusion of radial gas flows together with an inside-out formation of the disk, prod uces a very good agreement with observations. On the other hand, if radial flows are not considered, one should assume a threshol d in the star formation and a variable star formation effi ciency, besides the inside-out formation to reproduce the data. We conclude that the most important physical processes in creating disk gradients are the inside-out formation and the radial gas flows. More data o n abundance gradients both locally and at high redshift are necessary to confirm this conclusion.

  • the effects of radial inflow of gas and galactic fountains on the Chemical Evolution of m31
    arXiv: Cosmology and Nongalactic Astrophysics, 2013
    Co-Authors: E Spitoni, F Matteucci, M M Marconuchida
    Abstract:

    Galactic fountains and radial gas flows are very important ingredients in modeling the Chemical Evolution of galactic disks. Our aim here is to study the effects of galactic fountains and radial gas flows in the Chemical Evolution of the disk of M31. We adopt a ballistic method to study the effects of galactic fountains on the Chemical enrichment of the M31 disk. We find that the landing coordinate for the fountains in M31 is no more than 1 kpc from the starting point, thus producing negligible effect on the Chemical Evolution of the disk. We find that the delay time in the enrichment process due to fountains is no longer than 100 Myr and this timescale also produces negligible effects on the results. Then, we compute the Chemical Evolution of the M31 disk with radial gas flows produced by the infall of extragalactic material and fountains. We find that a moderate inside-out formation of the disk coupled with radial flows of variable speed can very well reproduce the observed gradient. We discuss also the effects of other parameters such a threshold in the gas density for star formation and an efficiency of star formation varying with the galactic radius. We conclude that the most important physical processes in creating disk gradients are the inside-out formation and the radial gas flows. More data on abundance gradients both locally and at high redshift are necessary to confirm this conclusion.

  • quantifying the uncertainties of Chemical Evolution studies ii stellar yields
    Astronomy and Astrophysics, 2010
    Co-Authors: F Matteucci, D Romano, Amanda I Karakas, M Tosi
    Abstract:

    Context. Galactic Chemical Evolution models are useful tools for interpreting the large body of high-quality observational data on the Chemical composition of stars and gas in galaxies that have become available in recent years. Aims. This is the second paper of a series that aims at quantifying the uncertainties in Chemical Evolution model predictions related to the underlying model assumptions. Specifically, it deals with the uncertainties due to the choice of the stellar yields. Methods. We adopted a widely used model for the Chemical Evolution of the Galaxy to test the effects of changing the stellar nucleosynthesis prescriptions on the predicted Evolution of several Chemical species. Up-to-date results from stellar Evolutionary models were carefully taken into account. Results. We find that, except for a handful of elements whose nucleosynthesis in stars is well understood by now, large uncertainties still affect model predictions. This is especially true for the majority of the iron-peak elements, but also for much more abundant species such as carbon and nitrogen. The main causes of the mismatch we find among the outputs of different models assuming different stellar yields and among model predictions and observations are (i) the adopted location of the mass cut in models of type II supernova explosions; (ii) the adopted strength and extent of hot bottom burning in models of asymptotic giant branch stars; (iii) the neglection of the effects of rotation on the Chemical composition of the stellar surfaces; (iv) the adopted rates of mass loss and of (v) nuclear reactions; and (vi) the different treatments of convection. Conclusions. Our results suggest that it is mandatory to include processes such as hot bottom burning in intermediate-mass stars and rotation in stars of all masses in accurate studies of stellar Evolution and nucleosynthesis. In spite of their importance, both these processes still have to be better understood and characterized. As for massive stars, presupernova models computed with mass loss and rotation are available in the literature, but they still wait for a self-consistent coupling with the results of explosive nucleosynthesis computations.

  • quantifying the uncertainties of Chemical Evolution studies ii stellar yields
    arXiv: Astrophysics of Galaxies, 2010
    Co-Authors: F Matteucci, D Romano, Amanda I Karakas, M Tosi
    Abstract:

    This is the second paper of a series which aims at quantifying the uncertainties in Chemical Evolution model predictions related to the underlying model assumptions. Specifically, it deals with the uncertainties due to the choice of the stellar yields. We adopt a widely used model for the Chemical Evolution of the Galaxy and test the effects of changing the stellar nucleosynthesis prescriptions on the predicted Evolution of several Chemical species. We find that, except for a handful of elements whose nucleosynthesis in stars is well understood by now, large uncertainties still affect the model predictions. This is especially true for the majority of the iron-peak elements, but also for much more abundant species such as carbon and nitrogen. The main causes of the mismatch we find among the outputs of different models assuming different stellar yields and among model predictions and observations are: (i) the adopted location of the mass cut in models of type II supernova explosions; (ii) the adopted strength and extent of hot bottom burning in models of asymptotic giant branch stars; (iii) the neglection of the effects of rotation on the Chemical composition of the stellar surfaces; (iv) the adopted rates of mass loss and of (v) nuclear reactions, and (vi) the different treatments of convection. Our results suggest that it is mandatory to include processes such as hot bottom burning in intermediate-mass stars and rotation in stars of all masses in accurate studies of stellar Evolution and nucleosynthesis. In spite of their importance, both these processes still have to be better understood and characterized. As for massive stars, presupernova models computed with mass loss and rotation are available in the literature, but they still wait for a self-consistent coupling with the results of explosive nucleosynthesis computations.

Christian Eistrup - One of the best experts on this subject based on the ideXlab platform.

  • cometary compositions compared with protoplanetary disk midplane Chemical Evolution an emerging Chemical Evolution taxonomy for comets
    Astronomy and Astrophysics, 2019
    Co-Authors: Christian Eistrup, Catherine Walsh, Ewine F Van Dishoeck
    Abstract:

    [Abridged] With a growing number of molecules observed in many comets, and an improved understanding of Chemical Evolution in protoplanetary disk midplanes, comparisons can be made between models and observations that could potentially constrain the formation histories of comets. A $\chi^{2}$-method was used to determine maximum likelihood surfaces for 14 different comets that formed at a given time (up to 8 Myr) and place (out to beyond the CO iceline) in the pre-solar nebula midplane. This was done using observed volatile abundances for the 14 comets and the Evolution of volatile abundances from Chemical modelling of disk midplanes. Considering all parent species (ten molecules) in a scenario that assumed reset initial chemistry, the $\chi^{2}$ likelihood surfaces show a characteristic trail in the parameter space with high likelihood of formation around 30 AU at early times and 12 AU at later times for ten comets. This trail roughly traces the vicinity of the CO iceline in time. The formation histories for all comets were thereby constrained to the vicinity of the CO iceline, assuming that the chemistry was partially reset early in the pre-solar nebula. This is found, both when considering carbon-, oxygen-, and sulphur-bearing molecules (ten in total), and when only considering carbon- and oxygen-bearing molecules (seven in total). Since these 14 comets did not previously fall into the same taxonomical categories together, this Chemical constraint may be proposed as an alternative taxonomy for comets. Based on the most likely time for each of these comets to have formed during the disk Chemical Evolution, a formation time classification for the 14 comets is suggested.

  • cometary compositions compared with protoplanetary disk midplane Chemical Evolution an emerging Chemical Evolution taxonomy for comets
    Astronomy and Astrophysics, 2019
    Co-Authors: Catherine Walsh, Christian Eistrup, Ewine F Van Dishoeck
    Abstract:

    Context. Comets are planetesimals left over from the formation of planets in the solar system. With a growing number of observed molecular abundances in many comets, and an improved understanding of Chemical Evolution in protoplanetary disk midplanes, comparisons can be made between models and observations that could potentially constrain the formation histories of comets.Aims. Our aim is to carry out the first statistical comparison between cometary volatile ice abundances and modelled evolving abundances in a protoplanetary disk midplane.Methods. A χ 2 -method was used to determine maximum likelihood surfaces for 14 different comets that formed at a given time (up to 8 Myr) and place (out to beyond the CO iceline) in the pre-solar nebula midplane. This was done using observed volatile abundances for the 14 comets and the Evolution of volatile abundances from Chemical modelling of disk midplanes. Two assumptions for the Chemical modelling starting conditions (cloud inheritance or Chemical reset), as well as two different sets of cometary molecules (parent species, with or without sulphur species) were investigated.Results. Considering all parent species (ten molecules) in the reset scenario, χ 2 likelihood surfaces show a characteristic trail in the parameter space with high likelihood of formation around 30 AU at early times and 12 AU at later times for ten comets. This trail roughly traces the vicinity of the CO iceline in time.Conclusions. A statistical comparison between observed and modelled Chemical abundances in comets and comet-forming regions could be a powerful tool for constraining cometary formation histories. The formation histories for all comets were constrained to the vicinity of the CO iceline, assuming that the chemistry was partially reset early in the pre-solar nebula. This is found, both when considering carbon-, oxygen-, and sulphur-bearing molecules (ten in total), and when only considering carbon- and oxygen-bearing molecules (seven in total). Since these 14 comets did not previously fall into the same taxonomical categories together, this Chemical constraint may be proposed as an alternative taxonomy for comets. Based on the most likely time for each of these comets to have formed during the disk Chemical Evolution, a formation time classification for the 14 comets is suggested.

  • setting the volatile composition of exo planet building material does Chemical Evolution in disk midplanes matter
    Astronomy and Astrophysics, 2016
    Co-Authors: Christian Eistrup, Catherine Walsh, Ewine F Van Dishoeck
    Abstract:

    Context. The atmospheres of extrasolar planets are thought to be built largely through accretion of pebbles and planetesimals. Such pebbles are also the building blocks of comets. The Chemical composition of their volatiles are usually taken to be inherited from the ices in the collapsing cloud. However, chemistry in the protoplanetary disk midplane can modify the composition of ices and gases.Aims. To investigate if and how Chemical Evolution affects the abundances and distributions of key volatile species in the midplane of a protoplanetary disk in the 0.2–30 AU range. Methods. A disk model used in planet population synthesis models is adopted, providing temperature, density and ionisation rate at different radial distances in the disk midplane. A full Chemical network including gas-phase, gas-grain interactions and grain-surface chemistry is used to evolve chemistry in time, for 1 Myr. Both molecular (inheritance from the parent cloud) and atomic (Chemical reset) initial conditions are investigated.Results. Great diversity is observed in the relative abundance ratios of the main considered species: H2 O, CO, CO2 , CH4 , O2 , NH3 and N2 . The choice of ionisation level, the choice of initial abundances, as well as the extent of Chemical reaction types included are all factors that affect the Chemical Evolution. The only exception is the inheritance scenario with a low ionisation level, which results in negligible changes compared with the initial abundances, regardless of whether or not grain-surface chemistry is included. The grain temperature plays an important role, especially in the critical 20–28 K region where atomic H no longer sticks long enough to the surface to react, but atomic O does. Above 28 K, efficient grain-surface production of CO2 ice is seen, as well as O2 gas and ice under certain conditions, at the expense of H2 O and CO. H2 O ice is produced on grain surfaces only below 28 K. For high ionisation levels at intermediate disk radii, CH4 gas is destroyed and converted into CO and CO2 (in contrast with previous models), and similarly NH3 gas is converted into N2 . At large radii around 30 AU, CH4 ice is enhanced leading to a low gaseous CO abundance. As a result, the overall C/O ratios for gas and ice change significantly with radius and with model assumptions. For high ionisation levels, Chemical processing becomes significant after a few times 105 yr.Conclusions. Chemistry in the disk midplane needs to be considered in the determination of the volatile composition of planetesimals. In the inner yr.

  • setting the volatile composition of exo planet building material does Chemical Evolution in disk midplanes matter
    Astronomy and Astrophysics, 2016
    Co-Authors: Christian Eistrup, Catherine Walsh, Ewine F Van Dishoeck
    Abstract:

    Context. The atmospheres of extrasolar planets are thought to be built largely through accretion of pebbles and planetesimals. Such pebbles are also the building blocks of comets. The Chemical composition of their volatiles are usually taken to be inherited from the ices in the collapsing cloud. However, chemistry in the protoplanetary disk midplane can modify the composition of ices and gases. Aims. To investigate if and how Chemical Evolution affects the abundances and distributions of key volatile species in the midplane of a protoplanetary disk in the 0.2–30 AU range. Methods. A disk model used in planet population synthesis models is adopted, providing temperature, density and ionisation rate at different radial distances in the disk midplane. A full Chemical network including gas-phase, gas-grain interactions and grain-surface chemistry is used to evolve chemistry in time, for 1 Myr. Both molecular (inheritance from the parent cloud) and atomic (Chemical reset) initial conditions are investigated. Results. Great diversity is observed in the relative abundance ratios of the main considered species: H2O, CO, CO2, CH4, O2, NH3 and N2. The choice of ionisation level, the choice of initial abundances, as well as the extent of Chemical reaction types included are all factors that affect the Chemical Evolution. The only exception is the inheritance scenario with a low ionisation level, which results in negligible changes compared with the initial abundances, regardless of whether or not grain-surface chemistry is included. The grain temperature plays an important role, especially in the critical 20–28 K region where atomic H no longer sticks long enough to the surface to react, but atomic O does. Above 28 K, efficient grain-surface production of CO2 ice is seen, as well as O2 gas and ice under certain conditions, at the expense of H2O and CO. H2O ice is produced on grain surfaces only below 28 K. For high ionisation levels at intermediate disk radii, CH4 gas is destroyed and converted into CO and CO2 (in contrast with previous models), and similarly NH3 gas is converted into N2. At large radii around 30 AU, CH4 ice is enhanced leading to a low gaseous CO abundance. As a result, the overall C/O ratios for gas and ice change significantly with radius and with model assumptions. For high ionisation levels, Chemical processing becomes significant after a few times 105 yr. Conclusions. Chemistry in the disk midplane needs to be considered in the determination of the volatile composition of planetesimals. In the inner <30 AU disk, interstellar ice abundances are preserved only if the ionisation level is low, or if these species are included in larger bodies within 105 yr.

  • setting the volatile composition of exo planet building material does Chemical Evolution in disk midplanes matter
    arXiv: Earth and Planetary Astrophysics, 2016
    Co-Authors: Christian Eistrup, Catherine Walsh, Ewine F Van Dishoeck
    Abstract:

    [Abridged] Chemical Evolution in the protoplanetary disk midplane can modify the composition of ices and gases. We have investigated if and how Chemical Evolution affects the abundances and distributions of key volatile species in the midplane of a protoplanetary disk in the 0.2-30 AU range. A full Chemical network including gas-phase, gas-grain interactions and grain-surface chemistry is used to evolve chemistry in time, for 1 Myr. Great diversity is observed in the relative abundance ratios of the main considered species: H2O, CO, CO2, CH4, O2, NH3 and N2. The choice of ionisation level, the choice of initial abundances, as well as the extent of Chemical reaction types included are all factors that affect the Chemical Evolution. The only exception is the inheritance scenario with a low ionisation level, which results in negligible changes compared with the initial abundances, regardless of whether grain-surface chemistry is included. The Chemical processing changes the C/O ratios for gas and ice significantly with radius and with model assumptions. For high ionisation levels, Chemical processing becomes significant after a few times $10^{5}$~yrs. It is concluded that Chemical Evolution in the disk midplane needs to be considered in the determination of the volatile composition of planetesimals.

Catherine Walsh - One of the best experts on this subject based on the ideXlab platform.

  • cometary compositions compared with protoplanetary disk midplane Chemical Evolution an emerging Chemical Evolution taxonomy for comets
    Astronomy and Astrophysics, 2019
    Co-Authors: Christian Eistrup, Catherine Walsh, Ewine F Van Dishoeck
    Abstract:

    [Abridged] With a growing number of molecules observed in many comets, and an improved understanding of Chemical Evolution in protoplanetary disk midplanes, comparisons can be made between models and observations that could potentially constrain the formation histories of comets. A $\chi^{2}$-method was used to determine maximum likelihood surfaces for 14 different comets that formed at a given time (up to 8 Myr) and place (out to beyond the CO iceline) in the pre-solar nebula midplane. This was done using observed volatile abundances for the 14 comets and the Evolution of volatile abundances from Chemical modelling of disk midplanes. Considering all parent species (ten molecules) in a scenario that assumed reset initial chemistry, the $\chi^{2}$ likelihood surfaces show a characteristic trail in the parameter space with high likelihood of formation around 30 AU at early times and 12 AU at later times for ten comets. This trail roughly traces the vicinity of the CO iceline in time. The formation histories for all comets were thereby constrained to the vicinity of the CO iceline, assuming that the chemistry was partially reset early in the pre-solar nebula. This is found, both when considering carbon-, oxygen-, and sulphur-bearing molecules (ten in total), and when only considering carbon- and oxygen-bearing molecules (seven in total). Since these 14 comets did not previously fall into the same taxonomical categories together, this Chemical constraint may be proposed as an alternative taxonomy for comets. Based on the most likely time for each of these comets to have formed during the disk Chemical Evolution, a formation time classification for the 14 comets is suggested.

  • cometary compositions compared with protoplanetary disk midplane Chemical Evolution an emerging Chemical Evolution taxonomy for comets
    Astronomy and Astrophysics, 2019
    Co-Authors: Catherine Walsh, Christian Eistrup, Ewine F Van Dishoeck
    Abstract:

    Context. Comets are planetesimals left over from the formation of planets in the solar system. With a growing number of observed molecular abundances in many comets, and an improved understanding of Chemical Evolution in protoplanetary disk midplanes, comparisons can be made between models and observations that could potentially constrain the formation histories of comets.Aims. Our aim is to carry out the first statistical comparison between cometary volatile ice abundances and modelled evolving abundances in a protoplanetary disk midplane.Methods. A χ 2 -method was used to determine maximum likelihood surfaces for 14 different comets that formed at a given time (up to 8 Myr) and place (out to beyond the CO iceline) in the pre-solar nebula midplane. This was done using observed volatile abundances for the 14 comets and the Evolution of volatile abundances from Chemical modelling of disk midplanes. Two assumptions for the Chemical modelling starting conditions (cloud inheritance or Chemical reset), as well as two different sets of cometary molecules (parent species, with or without sulphur species) were investigated.Results. Considering all parent species (ten molecules) in the reset scenario, χ 2 likelihood surfaces show a characteristic trail in the parameter space with high likelihood of formation around 30 AU at early times and 12 AU at later times for ten comets. This trail roughly traces the vicinity of the CO iceline in time.Conclusions. A statistical comparison between observed and modelled Chemical abundances in comets and comet-forming regions could be a powerful tool for constraining cometary formation histories. The formation histories for all comets were constrained to the vicinity of the CO iceline, assuming that the chemistry was partially reset early in the pre-solar nebula. This is found, both when considering carbon-, oxygen-, and sulphur-bearing molecules (ten in total), and when only considering carbon- and oxygen-bearing molecules (seven in total). Since these 14 comets did not previously fall into the same taxonomical categories together, this Chemical constraint may be proposed as an alternative taxonomy for comets. Based on the most likely time for each of these comets to have formed during the disk Chemical Evolution, a formation time classification for the 14 comets is suggested.

  • setting the volatile composition of exo planet building material does Chemical Evolution in disk midplanes matter
    Astronomy and Astrophysics, 2016
    Co-Authors: Christian Eistrup, Catherine Walsh, Ewine F Van Dishoeck
    Abstract:

    Context. The atmospheres of extrasolar planets are thought to be built largely through accretion of pebbles and planetesimals. Such pebbles are also the building blocks of comets. The Chemical composition of their volatiles are usually taken to be inherited from the ices in the collapsing cloud. However, chemistry in the protoplanetary disk midplane can modify the composition of ices and gases.Aims. To investigate if and how Chemical Evolution affects the abundances and distributions of key volatile species in the midplane of a protoplanetary disk in the 0.2–30 AU range. Methods. A disk model used in planet population synthesis models is adopted, providing temperature, density and ionisation rate at different radial distances in the disk midplane. A full Chemical network including gas-phase, gas-grain interactions and grain-surface chemistry is used to evolve chemistry in time, for 1 Myr. Both molecular (inheritance from the parent cloud) and atomic (Chemical reset) initial conditions are investigated.Results. Great diversity is observed in the relative abundance ratios of the main considered species: H2 O, CO, CO2 , CH4 , O2 , NH3 and N2 . The choice of ionisation level, the choice of initial abundances, as well as the extent of Chemical reaction types included are all factors that affect the Chemical Evolution. The only exception is the inheritance scenario with a low ionisation level, which results in negligible changes compared with the initial abundances, regardless of whether or not grain-surface chemistry is included. The grain temperature plays an important role, especially in the critical 20–28 K region where atomic H no longer sticks long enough to the surface to react, but atomic O does. Above 28 K, efficient grain-surface production of CO2 ice is seen, as well as O2 gas and ice under certain conditions, at the expense of H2 O and CO. H2 O ice is produced on grain surfaces only below 28 K. For high ionisation levels at intermediate disk radii, CH4 gas is destroyed and converted into CO and CO2 (in contrast with previous models), and similarly NH3 gas is converted into N2 . At large radii around 30 AU, CH4 ice is enhanced leading to a low gaseous CO abundance. As a result, the overall C/O ratios for gas and ice change significantly with radius and with model assumptions. For high ionisation levels, Chemical processing becomes significant after a few times 105 yr.Conclusions. Chemistry in the disk midplane needs to be considered in the determination of the volatile composition of planetesimals. In the inner yr.

  • setting the volatile composition of exo planet building material does Chemical Evolution in disk midplanes matter
    Astronomy and Astrophysics, 2016
    Co-Authors: Christian Eistrup, Catherine Walsh, Ewine F Van Dishoeck
    Abstract:

    Context. The atmospheres of extrasolar planets are thought to be built largely through accretion of pebbles and planetesimals. Such pebbles are also the building blocks of comets. The Chemical composition of their volatiles are usually taken to be inherited from the ices in the collapsing cloud. However, chemistry in the protoplanetary disk midplane can modify the composition of ices and gases. Aims. To investigate if and how Chemical Evolution affects the abundances and distributions of key volatile species in the midplane of a protoplanetary disk in the 0.2–30 AU range. Methods. A disk model used in planet population synthesis models is adopted, providing temperature, density and ionisation rate at different radial distances in the disk midplane. A full Chemical network including gas-phase, gas-grain interactions and grain-surface chemistry is used to evolve chemistry in time, for 1 Myr. Both molecular (inheritance from the parent cloud) and atomic (Chemical reset) initial conditions are investigated. Results. Great diversity is observed in the relative abundance ratios of the main considered species: H2O, CO, CO2, CH4, O2, NH3 and N2. The choice of ionisation level, the choice of initial abundances, as well as the extent of Chemical reaction types included are all factors that affect the Chemical Evolution. The only exception is the inheritance scenario with a low ionisation level, which results in negligible changes compared with the initial abundances, regardless of whether or not grain-surface chemistry is included. The grain temperature plays an important role, especially in the critical 20–28 K region where atomic H no longer sticks long enough to the surface to react, but atomic O does. Above 28 K, efficient grain-surface production of CO2 ice is seen, as well as O2 gas and ice under certain conditions, at the expense of H2O and CO. H2O ice is produced on grain surfaces only below 28 K. For high ionisation levels at intermediate disk radii, CH4 gas is destroyed and converted into CO and CO2 (in contrast with previous models), and similarly NH3 gas is converted into N2. At large radii around 30 AU, CH4 ice is enhanced leading to a low gaseous CO abundance. As a result, the overall C/O ratios for gas and ice change significantly with radius and with model assumptions. For high ionisation levels, Chemical processing becomes significant after a few times 105 yr. Conclusions. Chemistry in the disk midplane needs to be considered in the determination of the volatile composition of planetesimals. In the inner <30 AU disk, interstellar ice abundances are preserved only if the ionisation level is low, or if these species are included in larger bodies within 105 yr.

  • setting the volatile composition of exo planet building material does Chemical Evolution in disk midplanes matter
    arXiv: Earth and Planetary Astrophysics, 2016
    Co-Authors: Christian Eistrup, Catherine Walsh, Ewine F Van Dishoeck
    Abstract:

    [Abridged] Chemical Evolution in the protoplanetary disk midplane can modify the composition of ices and gases. We have investigated if and how Chemical Evolution affects the abundances and distributions of key volatile species in the midplane of a protoplanetary disk in the 0.2-30 AU range. A full Chemical network including gas-phase, gas-grain interactions and grain-surface chemistry is used to evolve chemistry in time, for 1 Myr. Great diversity is observed in the relative abundance ratios of the main considered species: H2O, CO, CO2, CH4, O2, NH3 and N2. The choice of ionisation level, the choice of initial abundances, as well as the extent of Chemical reaction types included are all factors that affect the Chemical Evolution. The only exception is the inheritance scenario with a low ionisation level, which results in negligible changes compared with the initial abundances, regardless of whether grain-surface chemistry is included. The Chemical processing changes the C/O ratios for gas and ice significantly with radius and with model assumptions. For high ionisation levels, Chemical processing becomes significant after a few times $10^{5}$~yrs. It is concluded that Chemical Evolution in the disk midplane needs to be considered in the determination of the volatile composition of planetesimals.

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  • inflow outflow yields and stellar population mixing in Chemical Evolution models
    arXiv: Astrophysics of Galaxies, 2016
    Co-Authors: Brett H Andrews, David H Weinberg, Ralph Schonrich, Jennifer A Johnson
    Abstract:

    Chemical Evolution models are powerful tools for interpreting stellar abundance surveys and understanding galaxy Evolution. However, their predictions depend heavily on the treatment of inflow, outflow, star formation efficiency (SFE), the stellar initial mass function, the Type Ia supernova delay time distribution, stellar yields, and stellar population mixing. Using flexCE, a flexible one-zone Chemical Evolution code, we investigate the effects of and trade-offs between parameters. Two critical parameters are SFE and the outflow mass-loading parameter, which shift the knee in [O/Fe]-[Fe/H] and the equilibrium abundances that the simulations asymptotically approach, respectively. One-zone models with simple star formation histories follow narrow tracks in [O/Fe]-[Fe/H] unlike the observed bimodality (separate high-alpha and low-alpha sequences) in this plane. A mix of one-zone models with inflow timescale and outflow mass-loading parameter variations, motivated by the inside-out galaxy formation scenario with radial mixing, reproduces the two sequences better than a one-zone model with two infall epochs. We present [X/Fe]-[Fe/H] tracks for 20 elements assuming three different supernova yield models and find some significant discrepancies with solar neighborhood observations, especially for elements with strongly metallicity-dependent yields. We apply principal component abundance analysis (PCAA) to the simulations and existing data to reveal the main correlations amongst abundances and quantify their contributions to variation in abundance space. For the stellar population mixing scenario, the abundances of alpha-elements and elements with metallicity-dependent yields dominate the first and second principal components, respectively, and collectively explain 99% of the variance in the model. flexCE is a python package available at this https URL.

  • radial flows and angular momentum conservation in galactic Chemical Evolution
    Monthly Notices of the Royal Astronomical Society, 2012
    Co-Authors: Thomas Bilitewski, Ralph Schonrich
    Abstract:

    We study the effects of radial flows on Galactic Chemical Evolution. A simple analytic scheme is developed prescribing the coupling of infall from the intergalactic medium and radial flows within the disc based on angular momentum conservation. We show that model parameters are tightly constrained by the observed [Fe/H]-abundance gradient in the Galactic disc. By this comparison the average rotational velocity of the onfalling material can be constrained to 0.7 ≤ v/Vc ≤ 0.75, or respectively ∼160 km s−1 when assuming a constant disc circular velocity of Vc = 220 km s−1. We test the robustness of this value against the influence of other processes. For a very simple model of inside-out formation this value changes only by Δv/Vc ∼ 0.1, i.e. ∼20 km s−1, and significantly less on more realistic scenarios, showing that inside-out formation does not alone explain the abundance gradient. Effects of other uncertain parameters, e.g. star formation history and star formation efficiency, have very small impact. Other drivers of inflow beyond our explicit modelling are assessed by adding a fixed inflow across the whole disc. The churning amplitude only mildly affects the results mostly by slightly flattening the metallicity gradient in the inner disc. A new process causing radial gas flows due to the ejection of material by stars moving on non-circular orbits is studied and seems to contribute negligibly to the total flows. We further show that gaseous outer discs cannot be the main source feeding the persistent star formation in the inner regions by a direct inflow.

  • radial flows and angular momentum conservation in galactic Chemical Evolution
    arXiv: Astrophysics of Galaxies, 2012
    Co-Authors: Thomas Bilitewski, Ralph Schonrich
    Abstract:

    We study the effects of radial flows on Galactic Chemical Evolution. A simple analytic scheme is developed prescribing the coupling of infall from the intergalactic medium and radial flows within the disc based on angular momentum conservation. We show that model parameters are tightly constrained by the observed [Fe/H]-abundance gradient in the Galactic disc. By this comparison the average rotational velocity of the onfalling material can be constrained to 0.7 < v/V_c < 0.75, or respectively ~ 160 km/s when assuming a constant disc circular velocity of V_c = 220 km/s. We test the robustness of this value against the influence of other processes. For a very simple model of inside-out formation this value changes only by \Delta v/V_c ~ 0.1, i.e. ~ 20 km/s, and significantly less on more realistic scenarios, showing that inside-out formation does not alone explain the abundance gradient. Effects of other uncertain parameters, e.g. star formation history and star formation efficiency have very small impact. Other drivers of inflow beyond our explicit modelling are assessed by adding a fixed inflow across the whole disc. The churning amplitude only mildly affects the results mostly by slightly flattening the metallicity gradient in the inner disc. A new process causing radial gas flows due to the ejection of material by stars moving on non-circular orbits is studied and seems to contribute negligibly to the total flows. We further show that gaseous outer discs cannot be the main source feeding the persistent star formation in the inner regions by a direct inflow.

  • Chemical Evolution with radial mixing
    Monthly Notices of the Royal Astronomical Society, 2009
    Co-Authors: Ralph Schonrich, James Binney
    Abstract:

    Models of the Chemical Evolution of our Galaxy are extended to include radial migration of stars and flow of gas through the disc. The models track the production of both iron and α-elements. A model is chosen that provides an excellent fit to the metallicity distribution of stars in the Geneva-Copenhagen survey (GCS) of the solar neighbourhood and a good fit to the local Hess diagram. The model provides a good fit to the distribution of GCS stars in the age-metallicity plane, although this plane was not used in the fitting process. Although this model's star formation rate is monotonically declining, its disc naturally splits into an α-enhanced thick disc and a normal thin disc. In particular, the model's distribution of stars in the ([O/Fe], [Fe/H]) plane resembles that of Galactic stars in displaying a ridge line for each disc. The thin-disc's ridge line is entirely due to stellar migration, and there is the characteristic variation of stellar angular momentum along it that has been noted by Haywood in survey data. Radial mixing of stellar populations with high σ z from inner regions of the disc to the solar neighbourhood provides a natural explanation of why measurements yield a steeper increase of σ z with age than predicted by theory. The metallicity gradient in the interstellar medium is predicted to be steeper than in earlier models, but appears to be in good agreement with data for both our Galaxy and external galaxies. The models are inconsistent with a cut-off in the star formation rate at low gas surface densities. The absolute magnitude of the disc is given as a function of time in several photometric bands, and radial colour profiles are plotted for representative times.