We present a new set of models for intermediate mass AGB stars (4.0, 5.0 and, 6.0 M ⊙ ) at different metallicities (-2.15≤[Fe/H]≤+0.15). This integrates the existing set of models for low mass AGB stars (1.3≤M/M ⊙ ≤3.0) already included in the FRUITY database. We describe the physical and chemical evolution of the computed models from the Main Sequence up to the end of the AGB phase. Due to less efficient third dredge up episodes, models with large core masses show modest surface enhancements. The latter is due to the fact that the interpulse phases are short and, then, Thermal Pulses are weak. Moreover, the high temperature at the base of the convective envelope prevents it to deeply penetrate the radiative underlying layers. Depending on the initial stellar mass, the heavy elements nucleosynthesis is dominated by different neutron sources. In particular, the s-process distributions of the more massive models are dominated by the 22 Ne(α,n) 25 Mg reaction, which is efficiently activated during Thermal Pulses. At low metallicities, our models undergo hot bottom burning and hot third dredge up. We compare our theoretical final core masses to available white dwarf observations. Moreover, we quantify the weight that intermediate mass models have on the carbon stars luminosity function. Finally, we present the upgrade of the FRUITY web interface, now also including the physical quantities of the TP-AGB phase of all the models included in the database (ph-FRUITY).Subject headings: Stars: AGB and post-AGB -Physical data and processes: Nuclear reactions, nucleosynthesis, abundances found by varying the metallicity and the initial stellar mass. In fact, the three s-process peaks 2 receive different contributions depending on the physical environmental conditions (radiative or convective burning) and on the neutron-to-seed ratio (which is related to the metallicity).In this paper we also illustrate a new web interface (ph-FRUITY), to access tables containing the evolution of the most relevant physical quantities of our models. This paper is structured as follows. In §2 we describe the main features of our stellar evolutionary code, focusing on the most recent upgrades. In §3 we highlight the evolutionary phases prior to the AGB, which is analyzed in §4. In §5 we show the potentiality of our new web ph-FRUITY interface. The nucleosynthesis of all FRUITY models is discussed in detail in §6. Finally, in §7we report the discussion and our conclusions. The modelsAs already outlined, models presented in this paper (4.0-5.0-6.0 M ⊙ ) integrate the already existing set available on the FRUITY database (Cristallo et al. 2011), currently hosting Low Mass Stars AGB models (hereafter LMS-AGB; 1.3-1.5-2.0-2.5-3.0) with different initial metallicities (-2.15≤[Fe/H]≤+0.15). We add a further metallicity (Z = 0.002, corresponding to [Fe/H]=-0.85)in order to better sample the peak in the lead production (see below). In Table 1 we report all the models included in the FRUITY database (in bold the models added with this work), by specifying...

Aims. We model the synthesis of molecules and dust in the inner wind of the oxygen-rich Mira-type star IK Tau by considering the effects of periodic shocks induced by the stellar pulsation on the gas and by following the non-equilibrium chemistry in the shocked gas layers between 1 R and 10 R . We consider a very complete set of molecules and dust clusters, and combine the nucleation phase of dust formation with the condensation of these clusters into dust grains. We also test the impact of increasing the local gas density. Our derived molecular abundances and dust properties are compared to the most recent observational data. Methods. A semi-analytical formalism based on parameterised fluid equations is used to describe the gas density, velocity, and temperature in the inner wind. The chemistry is described by using a chemical kinetic network of reactions and the condensation mechanism is described by a Brownian formalism. A set of stiff, ordinary, coupled differential equations is solved, and molecular abundances, dust cluster abundances, grain size distributions and dust masses are derived. Results. The shocks drive an active non-equilibrium chemistry in the dust formation zone of IK Tau where the collision destruction of CO in the post-shock gas triggers the formation of C-bearing species such as HCN and CS. Most of the modelled molecular abundances agree well with the latest values derived from Herschel data, except for SO 2 and NH 3 , whose formation may not occur in the inner wind. Clusters of alumina, Al 2 O 3 , are produced within 2 R and lead to a population of alumina grains close to the stellar surface. Clusters of silicates (Mg 2 SiO 4 ) form at larger radii (r > 3 R ), where their nucleation is triggered by the formation of HSiO and H 2 SiO. They efficiently condense and reach their final grain size distribution between ∼6 R and 8 R with a major population of medium size grains peaking at ∼200 Å. This two dust-shell configuration agrees with recent interferometric observations. The derived dust-to-gas mass ratio for IK Tau is in the range 1-6 × 10 −3 and agrees with values derived from observations of O-rich Mira-type stars. Conclusions. Our results confirm the importance of periodic shocks in chemically shaping the inner wind of AGB stars and providing gas conditions conducive to the efficient synthesis of molecules and dust by non-equilibrium processes. They indicate that the wind acceleration will possibly develop in the radius range 4-8 R in IK Tau.

Context. The condensation of inorganic dust grains in the winds of evolved stars is poorly understood. As of today, it is not yet known which molecular clusters form the first dust grains in oxygen-rich (C/O < 1) asymptotic giant branch (AGB) winds. Aluminium oxides and iron-free silicates are often put forward as promising candidates for the first dust seeds. Aims. We aim to constrain the dust formation histories in the winds of oxygen-rich AGB stars. Methods. We obtained Atacama Large Millimeter/sub-millimeter array (ALMA) observations with a spatial resolution of 120 × 150 mas tracing the dust formation region of the low mass-loss rate AGB star, R Dor, and the high mass-loss rate AGB star, IK Tau. We detected emission line profiles of AlO, AlOH, and AlCl in the ALMA data and used these line profiles to derive a lower limit of atomic aluminium incorporated in molecules. This constrains the aluminium budget that can condense into grains. Results. Radiative transfer models constrain the fractional abundances of AlO, AlOH, and AlCl in IK Tau and R Dor. We show that the gas-phase aluminium chemistry is completely different in both stars with a remarkable difference in the AlO and AlOH abundance stratification. The amount of aluminium locked up in these three molecules is small, ≤1.1 × 10 −7 w.r.t. H 2 , for both stars, i.e. only ≤2% of the total aluminium budget. An important result is that AlO and AlOH, which are the direct precursors of alumina (Al 2 O 3 ) grains, are detected well beyond the onset of the dust condensation, which proves that the aluminium oxide condensation cycle is not fully efficient. The ALMA observations allow us to quantitatively assess the current generation of theoretical dynamical-chemical models for AGB winds. We discuss how the current proposed scenario of aluminium dust condensation for low mass-loss rate AGB stars within a few stellar radii from the star, in particular for R Dor and W Hya, poses a challenge if one wishes to explain both the dust spectral features in the spectral energy distribution (SED) in interferometric data and in the polarized light signal. In particular, the estimated grain temperature of Al 2 O 3 is too high for the grains to retain their amorphous structure. We advocate that large gas-phase (Al 2 O 3 ) n clusters (n > 34) can be the potential agents of the broad 11 µm feature in the SED and in the interferometric data and we propose potential formation mechanisms for these large clusters.