Nucleosynthesis and molecular processes in the late stages of Stellar Evolution

    General
    Description

    Low- to intermediate-mass (M < 8 solar masses, Ms) stars represent the majority of stars in the Cosmos. They finish their lives on the Asymptotic Giant Branch (AGB) - just before they form planetary nebulae (PNe) - where they experience complex nucleosynthetic and molecular processes. AGB stars are important contributors to the enrichment of the interstellar medium where new stars/planets are born (including our own Early Solar System, ESS), and to the chemical evolution of stellar systems like globular clusters (GCs) and galaxies. In particular, the more massive (M > 4-5 Ms) AGB stars synthesize very different (radio)isotopes from those formed by lower mass AGB stars and Supernova detonations, as a consequence of different nucleosynthesis mechanisms. Evolved stars in the transition phase between AGB stars and PNe also form diverse organic compounds like PAHs, and fullerene and graphene molecular nanostructures, being a wonderful laboratory for Astrochemistry. On-going massive surveys like SDSS-IV/APOGEE-2 and the upcoming James Webb Space Telescope (JWST) represent a fundamental step forward to understand the nucleosynthesis and molecular processes in evolved stars. We aim to explore the nucleosynthesis of light and heavy (radio)isotopes in AGB stars and how they contribute to the ESS radioactive inventory as well as to the formation and evolution of GCs and galaxies. We also aim at understanding the top-down formation process of fullerene and graphene molecular nanostructures in evolved stars. Finally, it is intended to perform data mining with the Gaia satellite, in order to study the AGB- PNe evolutionary phase. In addition we aim to use the GALEX database to discover binary central stars in Galactic PNe.

    Principal investigator

    1. During 2020, we have published 37 papers in high-impact international refereed astronomical journals (including one invited review) and 2 papers in the Chemistry -Physics journal FNCN.

    2. Phosphorus-rich stars with an extremely peculiar chemical abundance pattern have been discovered for the first time, challenging the theoretical nucleosynthesis predictions.

    3. It was demonstrated that the P-rich star progenitors represent a new site for s-process nucleosynthesis, with important implications for the chemical evolution of our Galaxy.

    Related publications

    • Properties of central stars of planetary nebulae with distances in Gaia DR2
      Context. We have compiled a catalogue of central stars of planetary nebulae (CSPN) with reliable distances and positions obtained from Gaia Data Release 2 (DR2) astrometry. Distances derived from parallaxes allow us to analyse the galactic distribution and estimate other parameters such as sizes, kinematical ages, bolometric magnitudes, and
      González-Santamaría, I. et al.

      Advertised on:

      10
      2019
      Citations
      22
    • Discovery of a nitrogen-enhanced mildly metal-poor binary system: Possible evidence for pollution from an extinct AGB star
      We report the serendipitous discovery of a nitrogen-rich, mildly metal-poor ([Fe/H] = -1.08) giant star in a single-lined spectroscopic binary system found in the SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE-2) survey, Data Release 14 (DR14). Previous work has assumed that two percent of halo giants with unusual elemental
      Fernández-Trincado, José G. et al.

      Advertised on:

      11
      2019
      Citations
      25
    • Homogeneous analysis of globular clusters from the APOGEE survey with the BACCHUS code - II. The Southern clusters and overview
      We investigate the Fe, C, N, O, Mg, Al, Si, K, Ca, Ce, and Nd abundances of 2283 red giant stars in 31 globular clusters from high-resolution spectra observed in both the northern and Southern hemisphere by the SDSS-IV APOGEE-2 survey. This unprecedented homogeneous data set, largest to date, allows us to discuss the intrinsic Fe spread, the shape
      Mészáros, Szabolcs et al.

      Advertised on:

      2
      2020
      Citations
      111
    • Life in the fast lane: a direct view of the dynamics, formation, and evolution of the Milky Way's bar
      Studies of the ages, abundances, and motions of individual stars in the Milky Way provide one of the best ways to study the evolution of disc galaxies over cosmic time. The formation of the Milky Way's barred inner region in particular is a crucial piece of the puzzle of disc galaxy evolution. Using data from APOGEE and Gaia, we present maps of the
      Bovy, Jo et al.

      Advertised on:

      12
      2019
      Citations
      149
    • Spatial variations in the Milky Way disc metallicity-age relation
      Stellar ages are a crucial component to studying the evolution of the Milky Way. Using Gaia DR2 distance estimates, it is now possible to estimate stellar ages for a larger volume of evolved stars through isochrone matching. This work presents [M/H]-age and [α/M]-age relations derived for different spatial locations in the Milky Way disc. These
      Feuillet, Diane K. et al.

      Advertised on:

      10
      2019
      Citations
      63
    • The Gaia-ESO survey: Calibrating a relationship between age and the [C/N] abundance ratio with open clusters
      Context. In the era of large high-resolution spectroscopic surveys such as Gaia-ESO and APOGEE, high-quality spectra can contribute to our understanding of the Galactic chemical evolution by providing abundances of elements that belong to the different nucleosynthesis channels, and also by providing constraints to one of the most elusive
      Casali, G. et al.

      Advertised on:

      9
      2019
      Citations
      52
    • Far infrared spectroscopy and other spectral and thermal properties of [Li@C60]PF6
      The endohedral fullerene [Li@C60]+PF6− was characterized by differential scanning calorimetry (DSC), by electronic absorption spectroscopy in the spectral range from 195 to 800 nm and by FT-IR and far-infrared spectroscopy. [Li@C60]+PF6− shows a sharp melting point with the onset at 86 °C and peak at 90 °C and melting enthalpy of 9.5 kJ/mol. The
      Cataldo, Franco et al.

      Advertised on:

      9
      2019
      Citations
      6
    • Toluene pyrolysis in an electric ARC: Products analysis
      Toluene pyrolysis in a submerged carbon arc produced at least 72 different molecular species as detected by gas-chromatography coupled with mass spectrometry (GC-MS). The most abundant products found were bibenzyl (1,2-diphenylethane), naphthalene and biphenylene. Furthermore, also diethynylbenzene isomers, fluorene, diphenymethane, indene and
      Cataldo, Franco et al.

      Advertised on:

      6
      2019
      Citations
      7
    • H-band discovery of additional second-generation stars in the Galactic bulge globular cluster NGC 6522 as observed by APOGEE and Gaia
      We present an elemental abundance analysis of high-resolution spectra for five giant stars spatially located within the innermost regions of the bulge globular cluster NGC 6522 and derive Fe, Mg, Al, C, N, O, Si, and Ce abundances based on H-band spectra taken with the multi-object APOGEE-north spectrograph from the SDSS-IV Apache Point Observatory
      Fernández-Trincado, J. G. et al.

      Advertised on:

      7
      2019
      Citations
      38
    • ExoMol molecular line lists - XXXIII. The spectrum of Titanium Oxide
      Accurate line lists are crucial for correctly modelling a variety of astrophysical phenomena, including stellar photospheres and the atmospheres of extrasolar planets. This paper presents a new line database TOTO for the main isotopologues of titanium oxide (TiO): ^{46}Ti^{16}O, ^{47}Ti^{16}O, ^{48}Ti^{16}O, ^{49}Ti^{16}O, and ^{50}Ti^{16}O. The ^
      McKemmish, Laura K. et al.

      Advertised on:

      9
      2019
      Citations
      169
    • Do evolved stars in the LMC show dual dust chemistry?
      We study a group of evolved M-stars in the Large Magellanic Cloud, characterized by a peculiar spectral energy distribution. While the 9.7 μm feature arises from silicate particles, the whole infrared data seem to suggest the presence of an additional featureless dust species. We propose that the circumstellar envelopes of these sources are
      Marini, E. et al.

      Advertised on:

      9
      2019
      Citations
      4
    • TOI-150: A Transiting Hot Jupiter in the TESS Southern CVZ
      We report the detection of a hot Jupiter ({M}p={1.75}-0.17+0.14 {M}{{J}}, R p = 1.38 ± 0.04 R J) orbiting a middle-aged star ({log}g={4.152}-0.043+0.030) in the Transiting Exoplanet Survey Satellite (TESS) southern continuous viewing zone (β = ‑79.°59). We confirm the planetary nature of the candidate TOI-150.01 using radial velocity observations
      Cañas, Caleb I. et al.

      Advertised on:

      6
      2019
      Citations
      14
    • The metal-rich halo tail extended in |z|: a characterization with Gaia DR2 and APOGEE
      We report an analysis of the metal-rich tail ([Fe/H] > -0.75) of stars located at distances from the Galactic plane up to |z| ˜ 10 kpc, observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE). We examine the chemistry, kinematics, and dynamics of this metal-rich sample using chemical abundances and radial velocities provided
      Schuster, William J. et al.

      Advertised on:

      7
      2019
      Citations
      21
    • Reduction of the maximum mass-loss rate of OH/IR stars due to unnoticed binary interaction
      In 1981, the idea of a superwind that ends the life of cool giant stars was proposed1. Extreme oxygen-rich giants, OH/IR stars, develop superwinds with the highest mass-loss rates known so far, up to a few 10-4 solar masses (M⊙) per year2-12, informing our understanding of the maximum mass-loss rate achieved during the asymptotic giant branch (AGB)
      Decin, L. et al.

      Advertised on:

      2
      2019
      Citations
      25
    • AGB dust and gas ejecta in extremely metal-poor environments
      We present asymptotic giant branch (AGB) models of metallicity Z = 10-4 and 3 × 10-4, with the aim of understanding how the gas enrichment and the dust production change in very metal-poor environments and to assess the general contribution of AGB stars to the cosmic dust yield. The stellar yields and the dust produced are determined by the change
      Dell'Agli, F. et al.

      Advertised on:

      7
      2019
      Citations
      19
    • Chemical analysis of CH stars - III. Atmospheric parameters and elemental abundances
      Elemental abundances of CH stars can provide observational constraints for theoretical studies on the nucleosynthesis and evolution of low- and intermediate-mass stars. However, available abundance data in literature are quite scanty. In our pursuit to generate a homogeneous data base of elemental abundances of CH stars we have performed a detailed
      Purandardas, M. et al.

      Advertised on:

      7
      2019
      Citations
      21
    • High-resolution spectroscopy of Boyajian's star during optical dimming events
      Boyajian's star is an apparently normal main-sequence F-type star with a very unusual light curve. The dipping activity of the star, discovered during the Kepler mission, presents deep, asymmetric, and aperiodic events. Here we present high-resolution spectroscopic follow-up during some dimming events recorded post-Kepler observations, from ground
      Martínez González, M. J. et al.

      Advertised on:

      6
      2019
      Citations
      3
    • Exploring circumstellar effects on the lithium and calcium abundances in massive Galactic O-rich AGB stars
      Context. We previously explored the circumstellar effects on Rb and Zr abundances in a sample (21) of massive Galactic O-rich asymptotic giant branch (AGB) stars. Here we are interested in clarifying the role of the extended atmosphere in the case of Li and Ca. Li is an important indicator of hot bottom burning while the total Ca abundances in
      Pérez-Mesa, V. et al.

      Advertised on:

      3
      2019
      Citations
      4
    • Chemical Abundances of Main-sequence, Turnoff, Subgiant, and Red Giant Stars from APOGEE Spectra. II. Atomic Diffusion in M67 Stars
      Chemical abundances for 15 elements (C, N, O, Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, Fe, and Ni) are presented for 83 stellar members of the 4 Gyr old solar-metallicity open cluster M67. The sample contains stars spanning a wide range of evolutionary phases, from G dwarfs to red clump stars. The abundances were derived from near-IR (λ1.5–1.7 μm)
      Souto, D. et al.

      Advertised on:

      3
      2019
      Citations
      68
    • Chemical Cartography with APOGEE: Multi-element Abundance Ratios
      We map the trends of elemental abundance ratios across the Galactic disk, spanning R=3{--}15 {kpc} and midplane distance | Z| =0{--}2 {kpc}, for 15 elements in a sample of 20,485 stars measured by the SDSS/APOGEE survey (O, Na, Mg, Al, Si, P, S, K, Ca, V, Cr, Mn, Fe, Co, Ni). Adopting Mg rather than Fe as our reference element, and separating stars
      Weinberg, D. H. et al.

      Advertised on:

      3
      2019
      Citations
      112

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