Heating and cooling processes in disks

The research leading to these results has received funding from the European Union Seventh Framework Programme FP7-2011 under grant agreement no 284405. 10th Lecture from Summer School “Protoplanetary Disks: Theory and Modelling Meet Observations”This chapter summarises current theoretical concepts and methods to determine the gas temperature structure in protoplanetary disks by balancing all relevant heating and cooling rates. The processes considered are non-LTE line heating/cooling based on the escape probability method, photo-ionisation heating and recombination cooling, free-free heating/cooling, dust thermal accommodation and high-energy heating processes such as X-ray and cosmic ray heating, dust photoelectric and PAH heating, a number of particular follow-up heating processes starting with the UV excitation of H2, and the release of binding energy in exothermal reactions. The resulting thermal structure of protoplanetary disks is described and discussed.Publisher PDFPeer reviewe

Preface

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Tracing the Physical Conditions in Active Galactic Nuclei with Time-Dependent Chemistry

We present an extension of the code ProDiMo that allows for a modeling of processes pertinent to active galactic nuclei and to an ambient chemistry that is time dependent. We present a proof-of-concept and focus on a few astrophysically relevant species, e.g., H+, H2+ and H3+; C+ and N+; C and O; CO and H2O; OH+, H2O+ and H3O+; HCN and HCO+. We find that the freeze-out of water is strongly suppressed and that this affects the bulk of the oxygen and carbon chemistry occurring in AGN. The commonly used AGN tracer HCN/HCO+ is strongly time-dependent, with ratios that vary over orders of magnitude for times longer than 10^4 years. Through ALMA observations this ratio can be used to probe how the narrow-line region evolves under large fluctuations in the SMBH accretion rate. Strong evolutionary trends, on time scales of 10^4-10^8 years, are also found in species such as H3O+, CO, and H2O. These reflect, respectively, time dependent effects in the ionization balance, the transient nature of the production of molecular gas, and the freeze-out/sublimation of water.Comment: Accepted for publication at the Journal of Physical Chemistry A "Oka Festschrift: Celebrating 45 Years of Astrochemistry

The atmospheres of rocky exoplanets : I. Outgassing of common rock and the stability of liquid water

Funding: O.H. acknowledges the PhD stipend from the University of St Andrews’ Centre for Exoplanet Science.Context. Little is known about the interaction between atmospheres and crusts of exoplanets so far, but future space missions and ground-based instruments are expected to detect molecular features in the spectra of hot rocky exoplanets. Aims. We aim to understand the composition of the gas in an exoplanet atmosphere which is in equilibrium with a planetary crust. Methods. The molecular composition of the gas above a surface made of a mixture of solid and liquid materials was determined by assuming phase equilibrium for given pressure, temperature, and element abundances. We study total element abundances that represent different parts of the Earth’s crust (continental crust, bulk silicate Earth, mid oceanic ridge basalt), CI chondrites and abundances measured in polluted white dwarfs. Results. For temperatures between ~600 and ~3500 K, the near-crust atmospheres of all considered total element abundances are mainly composed of H2O, CO2, and SO2 and in some cases of O2 and H2. For temperatures ≲500 K, only N2-rich or CH4-rich atmospheres remain. For ≳3500 K, the atmospheric gas is mainly composed of atoms (O, Na, Mg, and Fe), metal oxides (SiO, NaO, MgO, CaO, AlO, and FeO), and some metal hydroxides (KOH and NaOH). The inclusion of phyllosilicates as potential condensed species is crucial for lower temperatures, as they can remove water from the gas phase below about 700 K and inhibit the presence of liquid water. Conclusions. Measurements of the atmospheric composition could, in principle, characterise the rock composition of exoplanet crusts. H2O, O2 and CH4 are natural products from the outgassing of different kinds of rocks that had time to equilibrate. These are discussed as biomarkers, but they do emerge naturally as a result of the thermodynamic interaction between the crust and atmosphere. Only the simultaneous detection of all three molecules might be a sufficient biosignature, as it is inconsistent with chemical equilibrium.Publisher PDFPeer reviewe

Continuum and line modelling of discs around young stars. I. 300000 disc models for Herschel/GASPS

We have combined the thermo-chemical disc code ProDiMo with the Monte Carlo radiative transfer code MCFOST to calculate a grid of ~300000 circumstellar disc models, systematically varying 11 stellar, disc and dust parameters including the total disc mass, several disc shape parameters and the dust-to-gas ratio. For each model, dust continuum and line radiative transfer calculations are carried out for 29 far IR, sub-mm and mm lines of [OI], [CII], 12CO and o/p-H2O under 5 inclinations. The grid allows to study the influence of the input parameters on the observables, to make statistical predictions for different types of circumstellar discs, and to find systematic trends and correlations between the parameters, the continuum fluxes, and the line fluxes. The model grid, comprising the calculated disc temperatures and chemical structures, the computed SEDs, line fluxes and profiles, will be used in particular for the data interpretation of the Herschel open time key programme GASPS. The calculated line fluxes show a strong dependence on the assumed UV excess of the central star, and on the disc flaring. The fraction of models predicting [OI] and [CII] fine-structure lines fluxes above Herschel/PACS and Spica/SAFARI detection limits are calculated as function of disc mass. The possibility of deriving the disc gas mass from line observations is discussed.Comment: accepted by MNRAS. 5 pages, 4 figures, 3 table

Forming planets around stars with non-solar composition

Contains fulltext : 238006.pdf (Publisher’s version ) (Open Access)Europlanet Science Congres

The protoplanetary disk of FT Tauri: multi-wavelength data analysis and modeling

Investigating the evolution of protoplanetary disks is crucial for our understanding of star and planet formation. Several theoretical and observational studies have been performed in the last decades to advance this knowledge. FT Tauri is a young star in the Taurus star forming region that was included in a number of spectroscopic and photometric surveys. We investigate the properties of the star, the circumstellar disk, and the accretion and ejection processes and propose a consistent gas and dust model also as a reference for future observational studies. We performed a multi-wavelength data analysis to derive the basic stellar and disk properties, as well as mass accretion/outflow rate from TNG-Dolores, WHT-Liris, NOT-Notcam, Keck-Nirspec, and Herschel-Pacs spectra. From the literature, we compiled a complete Spectral Energy Distribution. We then performed detailed disk modeling using the MCFOST and ProDiMo codes. Multi-wavelengths spectroscopic and photometric measurements were compared with the reddened predictions of the codes in order to constrain the disk properties. This object can serve as a benchmark for primordial disks with significant mass accretion rate, high gas content and typical size.Comment: 16 pages, 9 figures, accepted for publication in A&