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Nucleosynthesis and Dust Production in AGB Stars: Open Issues and Future Perspectives

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A special issue of Galaxies (ISSN 2075-4434).

Deadline for manuscript submissions: closed (15 September 2024) | Viewed by 6328

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Special Issue Editors

Dr. Paolo Ventura

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Guest Editor

INAF–Osservatorio Astronomico di Roma, 00078 Monte Porzio Catone, Italy
Interests: stellar structure and evolution; stellar populations in clusters and galaxies
Special Issues, Collections and Topics in MDPI journals

Dr. Flavia Dell'Agli

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INAF–Osservatorio Astronomico di Roma, 00078 Monte Porzio Catone, Italy
Interests: stellar populations in clusters and galaxies; dust production from stars

Prof. Dr. Oscar Straniero

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Guest Editor

INAF–Osservatorio Astronomico d’Abruzzo, 64100 Teramo, Italy
Interests: stellar structure and evolution; nucleosynthesis in stellar interiors

Special Issue Information

Dear Colleagues,

This Special Issue of Galaxies will gather contributions to the XIV Torino Workshop, which will be held in Rome 10–14 June 2024. The conference, https://indico.ict.inaf.it/event/2523/overview, along with the tradition of the previous editions of the Torino workshop, will be focused on the physics and nucleosynthesis of asymptotic giant branch (AGB) stars and several related topics. The meeting will offer a valuable opportunity to discuss the state of the art of AGB, post-AGB and super AGB modeling, and the impact of current and future experimental efforts, above and below ground, to determine the rates of the relevant charged particle and neutron capture reactions, as well as the role of AGB stars in the chemical evolution of the Milky Way and other galaxies. The possibilities offered by the present and oncoming observational facilities (such as JWST, VLT, LAMOST, ELT, etc.), the study of dust formation in the wind of evolved stars and the meteoritic dust measurements, and hot topics in the field of theoretical and nuclear astrophysics will be also addressed. All the arguments mentioned above are extensively discussed in the literature, as witnessed by the high number of papers published on the individual topics addressed during the conference. However, to present and outline the synergy among the various research fields considered, it is of paramount importance to dedicate a Special Issue to the conference, as the workshop will offer the possibility of bringing together researchers from a variety of research fields, to address the current issues and discuss future directions via interdisciplinary approaches. These arguments will be presented in a series of oral presentations and poster sessions, and then published in the Special Issue of Galaxies.

There is no maximal length, and the suggested minimum is approx. 4000 words. Submitted papers should contain enough novel contents (except for reviews, which are acceptable from senior contributors). Please note that the three paper types recommended for this special issue are Article, Review, and Communication (limited number). For more details, including various article types, please visit https://www.mdpi.com/about/article_types.

Dr. Paolo Ventura
Dr. Flavia Dell'Agli
Prof. Dr. Oscar Straniero
Guest Editors

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Keywords

AGB and post-AGB evolution
dust production from AGB stars
nucleosynthesis in the interiors of AGB stars

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Published Papers (13 papers)

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Research

Jump to: Review

10 pages, 3558 KiB

Open AccessArticle

The New Deep-Underground Direct Measurement of ²²Ne(α, γ)²⁶Mg with EASγ: A Feasibility Study

by Daniela Mercogliano, Andreas Best and David Rapagnani

Galaxies 2024, 12(6), 79; https://doi.org/10.3390/galaxies12060079 - 20 Nov 2024

Viewed by 214

Abstract

²²Ne(α, γ)²⁶Mg is pivotal in the understanding of several open astrophysical questions, as the nucleosynthesis beyond Fe through the s-process, but its stellar reaction rate is still subject to large uncertainties. These mainly arise from its extremely low rate in the Gamow energy region, whose measurement is hampered by the unavoidable presence of the cosmic ray background noise. A possibility to overcome this issue is to perform the measurement in a quasi background-free environment, such as that offered by the underground Bellotti Ion Beam Facility at LNGS. This is the key idea of EASγ experiment. In this study, the signal from the de-excitation of the compound nucleus ²⁶Mg has been simulated and its detection has been investigated both on surface and deep-underground laboratories. The simulation results show the enhancement in sensitivity achieved by performing the measurement deep underground and with an additional shielding, yielding to unprecedented sensitivity. Full article

(This article belongs to the Special Issue Nucleosynthesis and Dust Production in AGB Stars: Open Issues and Future Perspectives)

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5 pages, 600 KiB

Open AccessCommunication

Stellar Ages of TESS Stars, Adopting Spectroscopic Data from Gaia GSP-Spec

by Elisa Denis, Patrick de Laverny, Andrea Miglio, Alejandra Recio-Blanco, Pedro Alonso Palicio, Josefina Montalban and Carlos Abia

Galaxies 2024, 12(6), 76; https://doi.org/10.3390/galaxies12060076 - 14 Nov 2024

Viewed by 261

Abstract

The Gaia DR3 GSP-spec/TESS (GST) catalog combines asteroseismic data from NASA’s TESS mission with spectroscopic data from ESA’s Gaia mission, and contains about 116,000 Red Clump and Red Giant Branch stars, surpassing previous datasets in size and precision. The Bayesian tool PARAM is used to estimate stellar ages using MESA models for, currently, 30,297 stars. This GST catalog, which includes kinematics and chemical information, is adopted for studying the Milky Way’s structure and evolution, in particular its thin and thick disk components. Full article

(This article belongs to the Special Issue Nucleosynthesis and Dust Production in AGB Stars: Open Issues and Future Perspectives)

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8 pages, 1261 KiB

Open AccessCommunication

Spectroscopy of a Sample of RV Tauri Stars Without IR Excess

by Kārlis Puķītis and Karina Korenika

Galaxies 2024, 12(6), 73; https://doi.org/10.3390/galaxies12060073 - 6 Nov 2024

Viewed by 305

Abstract

We observed high-resolution optical spectra of 11 RV Tauri stars without IR excess, with the primary goal of searching for chemical depletion patterns. Using equivalent widths of absorption lines, we calculated the photospheric parameters and chemical element abundances for five stars in the sample: HD 172810, V399 Cyg, AA Ari, V457 Cyg, and V894 Per. Only the abundance pattern of V457 Cyg suggests depletion. In the spectrum of this star, TiO lines are also observed in the emission, in addition to metal emissions. V457 Cyg is likely a binary system that was once surrounded by a circumbinary disc. In the spectrum of V894 Per, we find a set of spectral lines that appear to belong to another star, corroborating that it is an eclipsing variable rather than an RV Tauri star. The high overabundance of sodium may result from mass transfer within the binary system. Full article

(This article belongs to the Special Issue Nucleosynthesis and Dust Production in AGB Stars: Open Issues and Future Perspectives)

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14 pages, 1078 KiB

Open AccessArticle

A “Wonderful” Reference Dataset of Mira Variables

by Dana K. Baylis-Aguirre, Michelle J. Creech-Eakman and Gerard T. van Belle

Galaxies 2024, 12(6), 72; https://doi.org/10.3390/galaxies12060072 - 31 Oct 2024

Viewed by 410

Abstract

The conditions in Mira variable atmospheres make them wonderful laboratories to study a variety of stellar physics such as molecule–grain formation, dust production, shock chemistry, stellar winds, mass loss, opacity-driven pulsation, and shocks. We were awarded an NSF grant to analyze over a decade of synoptic observations from the Palomar Testbed Interferometer (PTI) of 106 Miras to curate a Mira Reference Dataset. The Miras included in this dataset include M-types, S-types, and C-types, and span a wide range of pulsation periods. PTI measured K-band angular sizes that when combined with a distance allow us to directly determine fundamental stellar parameters such as effective temperature, radial size, and bolometric flux. Supplementing observations with interferometric measurements of the stars opens the Mira laboratory to a wealth of different experiments. We provide two case studies to serve as examples of the power of the Mira Reference Dataset. The first case study describes combining PTI measurements with Spitzer IRS spectra of M-type Miras, which allowed us to fully characterize

{CO}_{2}

gas in their atmospheres. The second case study examines how PTI narrow-band data can be used to study phase-dependent pulsation effects on the stellar atmosphere. We provide a list of all the Miras (with coordinates) included in the set for anyone who would like to add them to their observing programs. All the data we produce and collate for this Mira Reference Dataset will be hosted and curated on a website open to the public so that other researchers and citizen scientists can participate in expanding the utility and body of knowledge on this set of “wonderful” stars. Full article

(This article belongs to the Special Issue Nucleosynthesis and Dust Production in AGB Stars: Open Issues and Future Perspectives)

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7 pages, 288 KiB

Open AccessCommunication

¹⁷O Destruction Rate in Stars

by David Rapagnani, Oscar Straniero and Gianluca Imbriani

Galaxies 2024, 12(6), 71; https://doi.org/10.3390/galaxies12060071 - 29 Oct 2024

Viewed by 357

Abstract

In recent years, several laboratory studies of CNO cycle-related nuclear reactions have been carried out. Nevertheless, extant models of stellar nucleosynthesis still adopt CNO reaction rates reported in old compilations, such as NACRE or CF88. In order to update these rates, we performed new calculations based on a Monte Carlo R-Matrix analysis. In more detail, a method was developed that is based on the collection of all the available data, including recent low-energy measurements obtained by the LUNA collaboration in the reduced background environment of the INFN-LNGS underground laboratory, on R-Matrix cross-section calculations with the AZURE2 code and on uncertainty evaluations with a Monte Carlo analysis. As a first scientific benchmark case, the reactions ¹⁷O

(p, γ)

¹⁸F and ¹⁷O

(p, α)

¹⁴N were investigated. Among the different stellar scenarios they can influence, the ¹⁶O/¹⁷O abundance ratio in RGB and AGB stars is the one that can be directly confirmed from spectroscopic measurements. The aim is to reduce the nuclear physics uncertainties, thus providing a useful tool to constrain deep mixing processes eventually taking place in these stars. In this work, we present the procedure we followed to calculate the ¹⁷O

(p, γ)

¹⁸F and the ¹⁷O

(p, α)

¹⁴N reaction stellar rates and preliminary comparisons with similar rates reported in widely used nuclear physics libraries are discussed. Full article

(This article belongs to the Special Issue Nucleosynthesis and Dust Production in AGB Stars: Open Issues and Future Perspectives)

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10 pages, 457 KiB

Open AccessArticle

The ¹⁷O/¹⁸O Ratio of Post-AGB Sources: Canonical and Non-Canonical Populations

by Javier Alcolea, Elisa Masa, Theo Khouri, Miguel Santander-García, Iván Gallardo Cava, Hans Olofsson, Carmen Sánchez Contreras, Valentín Bujarrabal, Wouter H. T. Vlemmings and Daniel Tafoya

Galaxies 2024, 12(6), 70; https://doi.org/10.3390/galaxies12060070 - 25 Oct 2024

Viewed by 432

Abstract

Stellar evolution models serve as tools to derive stellar parameters from elemental and isotopic abundance ratios. For low-to-intermediate mass evolved stars, C/O, ¹²C/¹³C, and ¹⁷O/¹⁸O ratios are proxies of the initial mass, a largely unknown parameter in post-AGB sources, yet fundamental to establish correlations with the main properties of their post-AGB envelopes, progressing in understanding their formation and evolution. In these sources, the C/O ratio can be constrained from the detection of C- or O-bearing species in addition to CO, while the ¹⁷O/¹⁸O ratio is straightforwardly determined from the C¹⁷O-to-C¹⁸O intensity ratio of rotational lines. However, the theory is at odds with the observations. We review the status of the question, including new accurate ¹⁷O/¹⁸O ratios for 11 targets (totaling 29). Comparing the results for the ¹⁷O/^$18$O ratios and C-rich/O-rich chemical composition, we find that ∼45% of the cases are canonical, i.e., the observations align with standard model predictions. O-rich non-canonical sources, with ^$17$O/^$18$O ratios above the expected, can be explained by a premature interruption of their AGB evolution as a consequence of a quasi-explosive ejection of a large fraction of the initial mass. For non-canonical C-rich sources, with ^$17$O/^$18$O ratios below predictions, we suggest the possibility they are extrinsic C-rich stars. Full article

(This article belongs to the Special Issue Nucleosynthesis and Dust Production in AGB Stars: Open Issues and Future Perspectives)

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6 pages, 2267 KiB

Open AccessArticle

The Ongoing Deep Underground Measurement of ²²Ne(α,n)²⁵Mg at the Ion Beam Facility of the INFN-LNGS

by Andreas Best, David Rapagnani and Daniela Mercogliano

Galaxies 2024, 12(6), 68; https://doi.org/10.3390/galaxies12060068 - 24 Oct 2024

Viewed by 423

Abstract

The ²²

Ne

(α, n)

²⁵

Mg

The ²²

Ne

(α, n)

²⁵

Mg

reaction is of major importance in nuclear astrophysics. It is the main neutron source for the weak s-process and as such is responsible for the nucleosynthesis of 60 < A < 90 elements. In addition, it provides a strong neutron burst during the later, hottest phases of the main s-process, which modifies the final nucleosynthesis products, especially at so-called branch points, which can be used to provide insight into the stellar interior at that time. The reaction rate needs to be known below ca. 900 keV, and due to the low cross-section at these energies, a direct measurement has so far proven to be severely hampered by external neutron background at the surface of the Earth. To solve this problem, a measurement campaign (the ERC-funded SHADES project) was recently started at the deep underground Gran Sasso National Laboratory (LNGS) in Italy. We provide an overview of the experiment status and an outlook into the near future. Full article

(This article belongs to the Special Issue Nucleosynthesis and Dust Production in AGB Stars: Open Issues and Future Perspectives)

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9 pages, 263 KiB

Open AccessArticle

The Initial-Final Mass Relation from Carbon Stars in Open Clusters

by Carlos Abia, Inma Domínguez, Paola Marigo, Sergio Cristallo and Oscar Straniero

Galaxies 2024, 12(6), 67; https://doi.org/10.3390/galaxies12060067 - 23 Oct 2024

Viewed by 455

Abstract

Recently, Marigo et al, identified a kink in the initial-final mass relation around initial masses of

M_{i n i} \approx 1.65 - 2.10

M_{⊙}

, based on Gaia DR2 and EDR3 data for white dwarfs in open clusters aged 1.5–2.5 Gyr. [...] Read more.

Recently, Marigo et al, identified a kink in the initial-final mass relation around initial masses of

M_{i n i} \approx 1.65 - 2.10

M_{⊙}

, based on Gaia DR2 and EDR3 data for white dwarfs in open clusters aged 1.5–2.5 Gyr. Notably, the white dwarfs associated with this kink, all from NGC 7789, exhibit masses of ∼0.70–0.74 M_⊙, usually associated with stars of

M_{i n i} \sim

3–4

M_{⊙}

. This kink in the M_ini mass range coincides with the theoretically accepted solar metallicity lowest-mass stars evolving into carbon stars during the AGB phase. According to Marigo et al., these carbon stars likely experienced shallow third dredge-up events, resulting in low photospheric C/O ratios and, consequently, middle stellar winds. Under such conditions, the AGB phase is prolonged, allowing for further core mass growth beyond typical predictions. If this occurs, it might provoke other anomalies, such as a non-standard surface chemical composition. We have conducted a chemical analysis of several carbon stars belonging to open clusters within the above cluster ages. Our chemical analysis reveals that the carbon stars found within the kink exhibit C/O ratios only slightly above the unity and the typical chemical composition expected for carbon stars of near solar metallicity, partially validating the above theoretical predictions. We also show that this kink in the IMFR strongly depends on the method used to derived the distances (luminosity) of these carbon stars. Full article

(This article belongs to the Special Issue Nucleosynthesis and Dust Production in AGB Stars: Open Issues and Future Perspectives)

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12 pages, 866 KiB

Open AccessArticle

Production of Lithium and Heavy Elements in AGB Stars Experiencing PIEs

by Arthur Choplin, Lionel Siess, Stephane Goriely and Sebastien Martinet

Galaxies 2024, 12(5), 66; https://doi.org/10.3390/galaxies12050066 - 18 Oct 2024

Viewed by 520

Abstract

Asymptotic giant branch (AGB) stars can experience proton ingestion events (PIEs), leading to a rich nucleosynthesis. During a PIE, the intermediate neutron capture process (i-process) develops, leading to the production of trans-iron elements. It is also suggested that lithium is produced during these [...] Read more.

1 < M_{ini} / M_{⊙} < 3

and

- 3 < [Fe / H] < 0

. We find that lithium is produced in all PIE models with surface abundances

3 <

A(Li)

< 5

. The surface enrichment and overall AGB lithium yield increases with decreasing stellar mass. The lithium enrichment is accompanied by a production of ¹³C with

3 <^{12}

C/¹³C

< 9

at the surface just after the PIE. AGB stars experiencing PIE may be related to J-type carbon stars whose main features are excesses of lithium and¹³C. In addition to Li and ¹³C, heavy elements (e.g., Sr, Ba, Eu, Pb) are significantly produced in low-metallicity stars up to [Fe/H]

≃ - 1

. The yields of our models are publicly available. Additionally, of interest to the Li nucleosynthesis, we provide an updated fitting formula for the ⁷Be(

e^{-}, ν_{e}

)⁷Li electron capture rate. Full article

(This article belongs to the Special Issue Nucleosynthesis and Dust Production in AGB Stars: Open Issues and Future Perspectives)

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10 pages, 2012 KiB

Open AccessArticle

M 1-92: The Death of an AGB Star Told by Its Isotopic Ratios

by Elisa Masa, Javier Alcolea, Miguel Santander-García, Valentín Bujarrabal, Carmen Sánchez Contreras and Arancha Castro-Carrizo

Galaxies 2024, 12(5), 63; https://doi.org/10.3390/galaxies12050063 - 10 Oct 2024

Cited by 1 | Viewed by 454

Abstract

Ongoing improvements in the sensitivity of sub-mm- and mm-range interferometers and single-dish radio telescopes allow for the increasingly detailed study of AGB and post-AGB objects in molecular species other than

{}^{12}{CO}

and

{}^{13}{CO}

. With a new update introduced in the [...] Read more.

{}^{12}{CO}

and

{}^{13}{CO}

. With a new update introduced in the modelling tool SHAPE + shapemol, we can now create morpho-kinematical models to reproduce observations of these AGB and post-AGB circumstellar shells in different molecular species, allowing for an accurate description of their physical features as well as their molecular abundances and isotopic ratios. The pre-planetary nebula M1-92 (Minkowski’s Footprint) is one of the most complex objects of this kind, with a wide range of physical conditions and more than 20 molecular species detected. We model this nebula, reproducing the observational data from IRAM-30m and HSO/HiFi spectra and NOEMA interferometric maps, trying to understand the unusual evolution of its central star in the last phases of its life. The results show interesting features that tell us the story of its death. According to standard evolution models, a

{}^{17}O

{}^{18}O

isotopic ratio of 1.6 implies a stellar initial mass of ∼1.7

M_{⊙}

. Such a star should have turned C-rich by the end of the AGB phase, in striking contrast to the O-rich nature of the nebula. The most plausible way of reconciling this discrepancy is that M1-92 resulted from a sudden massive ejection event, interrupting the AGB evolution of the central source and preventing its transformation into a C-rich star. We also detect a changing

{}^{12}C

{}^{13}C

ratio across the nebula, which is particularly relevant in the inner equatorial region traced by

{HCO}^{+}

and

H^{13}

{CO}^{+}

, indicating an isotopic ratio variation taking place at some point during the last 1200 yr. Full article

(This article belongs to the Special Issue Nucleosynthesis and Dust Production in AGB Stars: Open Issues and Future Perspectives)

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11 pages, 3346 KiB

Open AccessArticle

Exploring the Ionized Core of the Proto-Planetary Nebula CRL 618 and Its Vicinity with ALMA

by José Pablo Fonfría, Carmen Sánchez Contreras, Daniel Tafoya, Patricia Fernández-Ruiz, Arancha Castro-Carrizo, Javier Alcolea and Valentín Bujarrabal

Galaxies 2024, 12(5), 62; https://doi.org/10.3390/galaxies12050062 - 10 Oct 2024

Viewed by 481

Abstract

Proto- and young planetary nebulae comprise dense circumstellar envelopes made of molecular gas and dust, some of which hide compact ionized cores that host stellar systems with hot objects, and show high-velocity bipolar outflows launched from inside their cores by means of still unknown mechanisms. We present high-angular-resolution Atacama Large Millimeter/submillimeter Array (ALMA) observations (HPBW ≃ 30–50 mas) of CRL 618 at 1.35 mm covering the H30

α

recombination line as well as ≃150 molecular lines. The ionized core is resolved, showing a size of ≃0

.^{″} 8 \times 0 .^{″} 5

and is elongated along the east–west direction. This region exhibits a remarkable incomplete ring-like structure with two bright spots to the north and south that are separated by ≃

0_{.}^{″} 2

and shows deprojected velocity gradients ranging from 0.2 to 0.6 km

s^{- 1}

{au}^{- 1}

. The 1 mm wavelength continuum emission is mostly produced by free–free emission with a small contribution from dust with an average spectral index of 0.28 (

S_{ν} \propto ν^{α}

). The ionized core can roughly be modeled as a tilted hollow cylinder with a denser, incomplete equatorial band lacking its back side. Molecular emission traces the neutral component of the same structures enclosing the ionized matter. Full article

(This article belongs to the Special Issue Nucleosynthesis and Dust Production in AGB Stars: Open Issues and Future Perspectives)

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8 pages, 829 KiB

Open AccessArticle

Temporal Changes in the Infrared Spectra of Magellanic Carbon Stars

by G. C. Sloan, K. E. Kraemer, B. Aringer, J. Cami, K. Eriksson, S. Höfner, E. Lagadec, M. Matsuura, I. McDonald, E. Montiel, R. Sahai and A. A. Zijlstra

Galaxies 2024, 12(5), 61; https://doi.org/10.3390/galaxies12050061 - 9 Oct 2024

Viewed by 504

Abstract

The Medium-Resolution Spectrometer on the Mid-Infrared Instrument on the JWST obtained spectra of three carbon stars in the Large Magellanic Cloud. Two of the spectra differ significantly from spectra obtained ∼16–19 years earlier with the Infrared Spectrograph on the Spitzer Space Telescope. The one semi-regular variable among the three has changed little. The long-period Mira variable in the sample shows changes consistent with its pulsation cycle. The short-period Mira shows dramatic changes in the strength of its molecular absorption bands, with some bands growing weaker and some stronger. Whether these variations result from its pulsation cycle or its evolution is not clear. Full article

(This article belongs to the Special Issue Nucleosynthesis and Dust Production in AGB Stars: Open Issues and Future Perspectives)

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8 pages, 851 KiB

Open AccessReview

Synthesis of Organic and Inorganic Compounds in Asymptotic Giant Branch Stars

by Sun Kwok

Galaxies 2024, 12(5), 64; https://doi.org/10.3390/galaxies12050064 - 11 Oct 2024

Viewed by 503

Abstract

After the synthesis of carbon in the core of asymptotic giant branch (AGB) stars, carbon is dredged up to the surface by convection. Many carbon-based molecules are formed in the subsequently developed stellar wind. These include acetylene, which can link together to form benzene in post-AGB evolution. The emergence of the spectral signatures of aromatic and aliphatic compounds in the transition phase between AGB stars and planetary nebulae suggests that complex organic compounds can be formed in the circumstellar environment over very short (10³ yr) timescales. We suggest that the carrier of the family of unidentified infrared emission bands is an amorphous carbonaceous compound—mixed aromatic/aliphatic nanoparticles (MAONs). The implications of the synthesis of complex organics in evolved stars are discussed. Full article

(This article belongs to the Special Issue Nucleosynthesis and Dust Production in AGB Stars: Open Issues and Future Perspectives)

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