Massive Asymptotic Giant Branch Research Articles

Models for the lithium abundances of multiple populations in globular clusters and the possible role of the big bang lithium

Globular cluster stars show chemical abundance patterns typical of hot-CNO processing, and photometric evidence for the presence of multiple populations. Lithium is easily destroyed by proton capture in stellar environments, so determining its abundance may be crucial to discriminate among different models proposed to account for the origin of the gas from which the multiple populations form. In order to reproduce the observed O–Na anticorrelation and other patterns typical of multiple populations, the formation of second-generation stars must occur from the nuclearly processed stellar ejecta, responsible for the chemical anomalies, diluted with pristine gas having the composition of first-generation stars. This gas is a remnant of the first phases of star formation, or it has been re-accreted on the cluster core after the end of the Type II supernova explosions. As a consequence, the lithium abundance in the unprocessed gas — which is very likely to be equal to the lithium abundance emerging from the big bang — affects the lithium chemical patterns among the cluster stars. This paper focuses on a scenario in which processed gas is provided by asymptotic giant branch (AGB) stars. We examine the predictions of this scenario for the lithium abundances of multiple populations. We study the role of the non-negligible lithium abundance in the ejecta of massive AGB stars [A(Li)∼], and, at the same time, we explore how our models can constrain the extremely large — and very model dependent — lithium yields predicted by recent super-AGB models. We show that the super-AGB yields may be tested by examining the lithium abundances in a large set of blue main-sequence stars in ω Cen and/or NGC 2808. In addition, we examine the different model results obtained by assuming for the pristine gas either the big bang abundance predicted by the standard models [A(Li)=2.6−2.7] or the abundance detected at the surface of Population II stars [A(Li)=2.2−2.3], and we show that, once a chemical model is well constrained by a comparison with the observations, the O–Li distribution could perhaps be used to shed light on the primordial lithium abundance.

Reaction rates for thes-process neutron source22Ne+α

The 22Ne({\alpha},n)25Mg reaction is an important source of neutrons for the s-process. In massive stars responsible for the weak component of the s-process, 22Ne({\alpha},n)25Mg is the dominant source of neutrons, both during core helium burning and in shell carbon burning. For the main s-process component produced in Asymptotic Giant Branch (AGB) stars, the 13C({\alpha},n)16O reaction is the dominant source of neutrons operating during the interpulse period, with the 22Ne+{\alpha} source affecting mainly the s-process branchings during a thermal pulse. Rate uncertainties in the competing 22Ne({\alpha},n)25Mg and 22Ne({\alpha},{\gamma})26Mg reactions result in large variations of s-process nucleosynthesis. Here, we present up-to-date and statistically rigorous 22Ne+{\alpha} reaction rates using recent experimental results and Monte Carlo sampling. Our new rates are used in post-processing nucleosynthesis calculations both for massive stars and AGB stars. We demonstrate that the nucleosynthesis uncertainties arising from the new rates are dramatically reduced in comparison to previously published results, but several ambiguities in the present data must still be addressed. Recommendations for further study to resolve these issues are provided.

The role of super-asymptotic giant branch ejecta in the abundance patterns of multiple populations in globular clusters

In order to account for the chemical composition of a stellar second generation (SG), Globular Clusters (GCs) evolution models based on the asymptotic giant branch (AGB) scenario so far included only the yields available for the massive AGB stars, while the possible role of super-AGB ejecta was either extrapolated or not considered. In this work, we explore the role of super-AGB ejecta using yields recently calculated by Ventura and D'Antona. Models of clusters showing extended Na-O anticorrelations, like NGC 2808, indicate that a SG formation history similar to that outlined in our previous work is required: formation of an Extreme population with very large helium content from the pure ejecta of super-AGB stars, followed by formation of an Intermediate population by dilution of stellar ejecta with pristine gas. The very O-poor Na-rich Extreme stars can be accounted for once deep-mixing is assumed in SG giants forming in a gas with helium abundance Y> 0.34, which significantly reduces the atmospheric oxygen content, while preserving the sodium abundance. On the other hand, for clusters showing a mild O-Na anticorrelation, like M 4, the use of the new yields broadens the range of SG formation routes leading to abundance patterns consistent with observations. It is shown that models in which SG stars form only from super-AGB ejecta promptly diluted with pristine gas can reproduce the observations. We discuss the variety of small helium variations occurring in this model and its relevance for the horizontal branch morphology. In some of these models the duration of the SG formation episode can be as short as \sim10 Myr; the formation time of the SG is thus compatible with the survival of a cooling flow in the GC, previous to the explosion of the SG core collapse supernovae. We also explore models with formation of multiple populations in individual bursts, each lasting no longer than \sim10 Myr.

A POSSIBLE PHYSICAL CONNECTION BETWEEN HELIUM-RICH STELLAR POPULATIONS OF MASSIVE GLOBULAR CLUSTERS AND THE UV UPTURN OF GALACTIC SPHEROIDS

We discuss a possible physical connection between helium-rich (Y > 0.35) stellar populations of massive globular clusters (GCs) and the ultraviolet (UV) upturn of galactic spheroids by using analytical and numerical models. In our model, all stars are initially formed as bound or unbound star clusters (SCs) formed from giant molecular clouds (GMCs) and the SCs can finally become GCs, open clusters, and field stars depending on physical properties of their host GMCs. An essential ingredient of the model is that helium-rich stars are formed almost purely from gas ejected from massive asymptotic giant branch (AGB) stars. The helium-rich star formation is assumed to occur within massive SCs if the masses of the progenitor GMCs are larger than a threshold mass (M_thres). These massive SCs can finally become either massive GCs or helium-rich field stars depending on whether they are disintegrated or not. Using this model, we show that if the initial mass functions (IMFs) in galactic spheroids are mildly top-heavy, then the mass fractions of helium-rich main-sequence stars (F_He) can be as large as ~ 0.1 for M_thres=10^7 M_sun. F_He is found to depend on IMFs and M_thres such that it can be larger for shallower IMFs and smaller M_thres. The inner regions of galactic spheroids show larger F_He in almost all models. Based on these results, we suggest that if the UV upturn of elliptical galaxies is due to the larger fractions of helium-rich stars, then the origin can be closely associated with top-heavy IMFs in the galaxies.

PROBING SUBSTELLAR COMPANIONS OF ASYMPTOTIC GIANT BRANCH STARS THROUGH SPIRALS AND ARCS

Recent observations of strikingly well-defined spirals in the circumstellar envelopes of asymptotic giant branch (AGB) stars point to the existence of binary companions in these objects. In the case of planet or brown dwarf mass companions, we investigate the observational properties of the spiral-onion shell wakes due to the gravitational interaction of these companions with the outflowing circumstellar matter. Three dimensional hydrodynamical simulations at high resolution show that the substellar mass objects produce detectable signatures at 100 AU distance, for the wake induced by a Jupiter to brown dwarf mass object orbiting a solar mass AGB star. In particular, the arm pattern propagates with a speed depending on the local wind and sound speeds, implying possible variations in the arm separation in the wind acceleration region and/or in a slow wind with significant temperature variation. The pattern propagation speeds of the inner and outer boundaries differ by twice the sound speed, leading to the overlap of high density boundaries in slow winds and producing a subpattern of the spiral arm feature. Vertically, the wake forms concentric arcs with angular sizes anticorrelated to the wind Mach number. We provide an empirical formula for the peak density enhancement as a function of the mass, orbital distance, and velocity of the object as well as the wind and local sound speeds. In typical condition of AGB envelopes, the arm-interarm density contrast can be greater than 30 % of the background density within a distance of ~10(M_p/M_J) AU for the object mass M_p in units of Jupiter mass M_J. These results suggest that such features may probe unseen substellar mass objects embedded in the winds of AGB stars and may be useful in planning future high sensitivity/resolution observations with ALMA.

Type Ia supernovae from very long delayed explosion of core-white dwarf merger

We study the spinning down time scale of rapidly rotating white dwarfs (WDs) in the frame of the core-degenerate (CD) scenario for type Ia supernovae (SNe Ia). In the CD scenario the Chandrasekhar or super-Chandrasekhar mass WD is formed at the termination of the common envelope phase or during the planetary nebula phase, from a merger of a WD companion with the hot core of a massive asymptotic giant branch star. In the CD scenario the rapidly rotating WD is formed shortly after the stellar formation episode, and the delay from stellar formation to explosion is basically determined by the spin-down time of the rapidly rotating merger remnant. We find that gravitational radiation is inefficient in spinning down WDs, while the magneto-dipole radiation torque can lead to delay times that are required to explain SNe Ia.

Revision of the15N(p,γ)16O reaction rate and oxygen abundance in H-burning zones

The NO cycle takes place in the deepest layer of a H-burning core or shell, when the temperature exceeds T {\simeq} 30 {\cdot} 106 K. The O depletion observed in some globular cluster giant stars, always associated with a Na enhancement, may be due to either a deep mixing during the RGB (red giant branch) phase of the star or to the pollution of the primordial gas by an early population of massive AGB (asymptotic giant branch) stars, whose chemical composition was modified by the hot bottom burning. In both cases, the NO cycle is responsible for the O depletion. The activation of this cycle depends on the rate of the 15N(p,{\gamma})16O reaction. A precise evaluation of this reaction rate at temperatures as low as experienced in H-burning zones in stellar interiors is mandatory to understand the observed O abundances. We present a new measurement of the 15N(p,{\gamma})16O reaction performed at LUNA covering for the first time the center of mass energy range 70-370 keV, which corresponds to stellar temperatures between 65 {\cdot} 106 K and 780 {\cdot}106 K. This range includes the 15N(p,{\gamma})16O Gamow-peak energy of explosive H-burning taking place in the external layer of a nova and the one of the hot bottom burning (HBB) nucleosynthesis occurring in massive AGB stars. With the present data, we are also able to confirm the result of the previous R-matrix extrapolation. In particular, in the temperature range of astrophysical interest, the new rate is about a factor of 2 smaller than reported in the widely adopted compilation of reaction rates (NACRE or CF88) and the uncertainty is now reduced down to the 10% level.

A circumbinary disc in the final stages of common envelope and the core-degenerate scenario for Type Ia supernovae

We study the final stages of the common envelope (CE) evolution and find that a substantial fraction of the ejected mass does not reach the escape velocity. To reach this conclusion we use a self-similar solution under simplifying assumptions. Most of the gravitational energy of a companion white dwarf (WD) is released in the envelope of a massive asymptotic giant branch (AGB) or the red giant branch (RGB) star in a very short time. This rapid energy release forms a blast wave in the envelope. We follow the blast wave propagation from the centre of the AGB outwards, and show that ∼1–10 per cent of the ejected envelope remains bound to the remnant binary system. We suggest that due to angular momentum conservation and further interaction with the binary system, the fall-back material forms a circumbinary disc around the post-AGB Core and the companion WD. The interaction of the circumbinary disc with the binary system will reduce the orbital separation much more than expected of the dynamical phase (where the envelope is ejected) of the CE alone. The smaller orbital separation favours a merger at the end of the CE phase or a short time after, while the core is still hot. This is another channel for the formation of a massive WD with super-Chandrasekhar mass that might explode as a Type Ia supernova. We term this the core-degenerate (CD) scenario.

The Core-Degenerate Scenario for Type Ia Supernovae

AbstractIn the core-degenerate (CD) scenario for the formation of Type Ia supernovae (SNe Ia) the Chandrasekhar or super-Chandrasekhar mass white dwarf (WD) is formed at the termination of the common envelope phase or during the planetary nebula phase, from a merger of a WD companion with the hot core of a massive asymptotic giant branch (AGB) star. The WD is destroyed and accreted onto the more massive core. In the CD scenario the rapidly rotating WD is formed shortly after the stellar formation episode, and the delay from stellar formation to explosion is basically determined by the spin-down time of the rapidly rotating merger remnant. The spin-down is due to the magneto-dipole radiation torque. Several properties of the CD scenario make it attractive compared with the double-degenerate (DD) scenario. (1) Off-center ignition of carbon during the merger process is not likely to occur. (2) No large envelope is formed. Hence avoiding too much mass loss that might bring the merger remnant below the critical mass. (3) This model explains the finding that more luminous SNe Ia occur preferentially in star forming galaxies.

THE OXYGEN VERSUS SODIUM (ANTI)CORRELATION(S) IN ω Cen

Recent exam of large samples of omega Cen giants shows that it shares with mono-metallic globular clusters the presence of the sodium versus oxygen anticorrelation, within each subset of stars with iron content in the range -1.9<~[Fe/H]<~-1.3. These findings suggest that, while the second generation formation history in omega Cen is more complex than that of mono-metallic clusters, it shares some key steps with those simpler cluster. In addition, the giants in the range -1.3<[Fe/H]<~-0.7 show a direct O--Na correlation, at moderately low O, but Na up to 20 times solar. These peculiar Na abundances are not shared by stars in other environments often assumed to undergo a similar chemical evolution, such as in the field of the Sagittarius dwarf galaxy. These O and Na abundances match well the yields of the massive asymptotic giant branch stars (AGB) in the same range of metallicity, suggesting that the stars at [Fe/H]>-1.3 in omega Cen are likely to have formed directly from the pure ejecta of massive AGBs of the same metallicities. This is possible if the massive AGBs of [Fe/H]>-1.3 in the progenitor system evolve when all the pristine gas surrounding the cluster has been exhausted by the previous star formation events, or the proto--cluster interaction with the Galaxy caused the loss of a significant fraction of its mass, or of its dark matter halo, and the supernova ejecta have been able to clear the gas out of the system. The absence of dilution in the metal richer populations lends further support to a scenario of the formation of second generation stars in cooling flows from massive AGB progenitors. We suggest that the entire formation of omega Cen took place in a few 10^8yr, and discuss the problem of a prompt formation of s--process elements.

A deep insight into the Mg-Al-Si nucleosynthesis in massive asymptotic giant branch and super-asymptotic giant branch stars

The stars in globular clusters are known to differ in their surface chemistry: the spectroscopic investigations in the last decades outlined the presence of star-to-star differences in the abundances of the light elements, up to aluminium (and possibly silicon), suggesting that some stars were contaminated by an advanced proton-capture nucleosynthesis. The AGB stars are one of the most promising candidates in producing the pollution of the intra-cluster medium, via the ejection of gas processed by Hot Bottom Burning, from which new stellar generations are formed. This work is focused on the degree of nucleosynthesis involving magnesium, aluminium and silicon that these sources may experience. The key ingredient to determine the degree of magnesium depletion, and the amount of aluminium that can be produced, is the rate of proton capture on Mg25, forming Al26; an increase in this cross-section by a factor 2 with respect to the highest value allowed by the NACRE compilation allows to reproduce the extent of the Mg-depletion observed, and is in qualitative agreement with the positive Al-Si correlation observed in a few clusters. The main uncertainties associated with the macro- and micro-physics input, are discussed and commented, and the comparison with recent spectroscopic results for the globular cluster showing some degree of Mg-Al anticorrelation and Al-Si correlation is presented.

The evolutionary state of Miras with changing pulsation periods

Context: Miras are long-period variables thought to be in the asymptotic giant branch (AGB) phase of evolution. In about one percent of known Miras, the pulsation period is changing. It has been speculated that this changing period is the consequence of a recent thermal pulse in these stars. Aims: We aim to clarify the evolutionary state of these stars, and to determine in particular whether or not they are in the thermally-pulsing (TP-)AGB phase. Methods: One important piece of information that has been neglected so far when determining the evolutionary state is the presence of the radio-active s-process element technetium (Tc). We obtained high-resolution, high signal-to-noise-ratio optical spectra of a dozen prominent Mira variables with changing pulsation period to search for this indicator of TPs and dredge-up. We also use the spectra to measure lithium (Li) abundances. Furthermore, we establish the evolutionary states of our sample stars by means of their present-day periods and luminosities. Results: Among the twelve sample stars observed in this programme, five were found to show absorption lines of Tc. BH Cru is found to be a carbon-star, its period increase in the past decades possibly having stopped by now. We report a possible switch in the pulsation mode of T UMi from Mira-like to semi-regular variability in the past two years. R Nor, on the other hand, is probably a fairly massive AGB star, which could be true for all meandering Miras. Finally, we assign RU Vul to the metal-poor thick disk with properties very similar to the short-period, metal-poor Miras. Conclusions: We conclude that there is no clear correlation between period change class and Tc presence. The stars that are most likely to have experienced a recent TP are BH Cru and R Hya, although their rates of period change are quite different.

INTERMEDIATE-MASS BLACK HOLES IN EARLY GLOBULAR CLUSTERS

Spectroscopic and photometric observations show that many globular clusters host multiple stellar populations, challenging the common paradigm that globular clusters are "simple stellar populations" composed of stars of uniform age and chemical composition. The chemical abundances of second-generation (SG) stars constrain the sources of gas out of which these stars must have formed, indicating that the gas must contain matter processed through the high-temperature CNO cycle. First-generation massive Asymptotic Giant Branch (AGB) stars have been proposed as the source of this gas. In a previous study, by means of hydrodynamical and N-body simulations, we have shown that the AGB ejecta collect in a cooling flow in the cluster core, where the gas reaches high densities, ultimately forming a centrally concentrated subsystem of SG stars. In this Letter we show that the high gas density can also lead to significant accretion onto a pre-existing seed black hole. We show that gas accretion can increase the black hole mass by up to a factor of 100. The details of the gas dynamics are important in determining the actual black hole growth. Assuming a near-universal seed black hole mass and small cluster-to-cluster variations in the duration of the SG formation phase, the outcome of our scenario is one in which the present intermediate-mass black hole (IMBH) mass may have only a weak dependence on the current cluster properties. The scenario presented provides a natural mechanism for the formation of an IMBH at the cluster center during the SG star-formation phase.

The role of lithium production in massive AGB and super-AGB stars for the understanding of multiple populations in globular clusters

Abstract Lithium is made up in the envelopes of massive asymptotic giant branch (AGB) stars through the process of Hot Bottom Burning. In globular clusters, this processing is one possible source of the hot-CNO burning whose nuclear products are then ejected into the intracluster medium and take part in the formation of a second stellar generation, explaining the peculiar distribution of chemical elements among the cluster stars. We discuss the lithium yields from AGB stars in the mass range 3 to ∼6.3 M⊙, and from super-AGB stars of masses in the range 6.5–9 M⊙ for metallicity Z= 10−3. The qualitative behaviour of these yields is discussed in terms of the physical structure of the different masses. Although many uncertainties affect the other yields of these stars (e.g. O, Na and Mg), even larger uncertainties affect the lithium yield, as it depends dramatically on the adopted description of mass-loss. When we adopt our standard mass-loss formulation, very large yields are obtained especially for the super-AGB stars, and we discuss their possible role on the lithium abundance of second generation stars in globular clusters.

A giant dusty bipolar structure around the planetary nebula NGC 1514

The transition from spherically symmetric asymptotic giant branch mass loss to aspherical planetary nebulae is an intriguing problem of stellar astrophysics. On 12 μm maps of the Infrared Astronomical Satellite (IRAS), we detected a huge (2.6 pc) dust emission region around the evolved planetary nebula NGC 1514. On 100 and 60 μm IRAS maps, we additionally found two giant (2.1 and 0.9 pc) bipolar dust emission structures centred on NGC 1514; we suspect that each of these regions is physically connected to the planetary nebula. The bipolar structures are slightly tilted with respect to each other, possibly due to precession. The total mass (dust + gas) of all structures is 2.2 ± 1.4 M ⊙ . We argue that NGC 1514 and its dusty surroundings represent one of the very few known cases where the preserved history of all main mass-loss phases of a star of intermediate initial mass can be seen.

Lithium factories in the Galaxy: novae and AGB stars

AbstractWe review the state of the art in modelling lithium production, through the Cameron–Fowler mechanism, in two stellar sites: during nova explosions and in the envelopes of massive asymptotic giant branch (AGB) stars. We also show preliminary results concerning the computation of lithium yields from super–AGBs, and suggest that super–AGBs of metallicity close to solar may be the most important galactic lithium producers. Finally, we discuss how lithium abundances may help to understand the modalities of formation of the “second generation” stars in globular clusters.

Observations of Lithium in red giant stars

AbstractConnections between observations of the lithium abundance in various types of red giants and stellar evolution are discussed here. The emphasis is on three main topics; 1) the depletion of Li as stars ascend the red giant branch for the first time, 2) the synthesis of 7Li in luminous and massive asymptotic giant branch stars via the mechanism of hot-bottom burning, and 3) the possible multiple sources of excess Li abundances found in a tiny fraction of various types of G and K giants.

Rb-RICH ASYMPTOTIC GIANT BRANCH STARS IN THE MAGELLANIC CLOUDS

We present high-resolution (R~60,000) optical spectra of a carefully selected sample of heavily obscured and presumably massive O-rich Asymptotic Giant Branch (AGB) stars in the Magellanic Clouds (MCs). We report the discovery of strong Rb I lines at 7800 A in four Rb-rich LMC stars at luminosities equal to or greater than the standard adopted luminosity limit for AGB stars (Mbol~-7.1), confirming that "Hot Bottom Burning" (HBB) may produce a flux excess in the more massive AGB stars. In the SMC sample, just one of the five stars with Mbol<-7.1 was detected in Rb; the other stars may be massive red supergiants. The Rb-rich LMC AGB stars might have stellar masses of at least ~6-7 Msun. Our abundance analysis show that these Rb-rich stars are extremely enriched in Rb by up to 10^3-10^5 times solar but seem to have only mild Zr enhancements. The high Rb/Zr ratios, if real, represent a severe problem for the s-process, even if the 22Ne source is operational as expected for massive AGB stars; it is not possible to synthesize copious amounts of Rb without also overproducing Zr. The solution to the problem may lie with an incomplete present understanding of the atmospheres of luminous AGB stars.

NanoSIMS analysis and Auger electron spectroscopy of silicate and oxide stardust from the carbonaceous chondrite Acfer 094

We have detected 138 presolar silicate, 20 presolar oxide and three presolar complex grains within the carbonaceous chondrite Acfer 094 by NanoSIMS oxygen isotope mapping. These grains were further investigated by scanning electron microscopy (SEM) and Auger electron spectroscopy for morphological and chemical details and their distribution within the meteorite matrix. The three complex grains consist of Al-rich oxides (grossite and hibonite) attached to non-stoichiometric Si-rich silicates. Refractory Al-rich oxides therefore serve as seed nuclei for silicates to condense onto, which is proposed by condensation theory and astronomical observations. However, in the majority of presolar silicates we did not find any indications for large subgrains. Most of the grains (80%) belong to O isotope Group I ( 17O-enriched) and come from 1 to 2.5 M ⊙ asymptotic giant branch (AGB) stars of close-to-solar or slightly lower-than-solar metallicity. About 60% of these grains are irregular in shape; ∼40% display elliptical morphologies together with smooth, platy surfaces. Three grains with large 17O enrichments ( 17O/ 16O > 3 × 10 −3) have highly irregular shapes and are very small (<250 nm); these grains may have formed in binary star systems or around higher mass ( ∼ 3 M ⊙ ) AGB stars. About 10% of the presolar silicates in this study can be assigned to the O isotope Group IV, which most likely originate from type II supernovae (SNeII). These grains are also generally smaller than 300 nm and are often irregular in shape (88%), consistent with the SNII origin scenario. The presolar grains are generally evenly distributed within the matrix on an mm scale, although in one case a statistically significant clustering of five grains in one 10 × 10 μm 2 sized field is observed. This could be an important hint that the distribution of presolar material in the parental molecular cloud was heterogeneous on a very fine scale. The matrix-normalized abundance of silicate stardust in Acfer 094 is 163 ± 14 ppm, which is among the highest abundance of O-rich stardust in primitive meteorites. Oxide stardust comprises 26 ± 6 ppm of the matrix. Auger Nanoprobe measurements of 69 presolar silicates and oxides (30 on a quantitative, 39 on a qualitative basis) indicate that most of the grains are Fe-rich (Mg/(Mg + Fe) of 0.82 and lower), which is either due to non-equilibrium condensation, secondary alteration, or both. (Mg + Fe)/Si ratios of the silicates are mostly non-stoichiometric and scatter around pyroxene-like rather than olivine-like compositions, which is consistent with recent Auger and transmission electron microscopy observations and astrophysical predictions. Mg-rich grains (Mg/(Mg + Fe) > 0.5) more likely exhibit elliptical, smooth surfaces (14 out of 18 grains), which is an indication that these grains have not been strongly altered since their circumstellar condensation. We identified only one grain similar to the “glass with embedded metal and sulfides” (GEMS) with a statistically significant sulfur content (>2–3 at.%). It remains unclear why the typical high-sulfur GEMS grains are only found in interplanetary dust particles, but have not yet been unequivocally identified in primitive meteorites.

The role of massive AGB stars in the early solar system composition

Abstract— We demonstrate that a massive asymptotic giant branch (AGB) star is a good candidate as the main source of short‐lived radionuclides in the early solar system. Recent identification of massive (4–8 M⊙) AGB stars in the galaxy, which are both lithium‐ and rubidium‐rich, demonstrates that these stars experience proton captures at the base of the convective envelope (hot bottom burning), together with high‐neutron density nucleosynthesis with 22Ne as a neutron source in the He shell and efficient dredge‐up of the processed material. A model of a 6.5 M⊙ star of solar metallicity can simultaneously match the abundances of 26Al, 41Ca, 60Fe, and 107Pd inferred to have been present in the solar nebula by using a dilution factor of 1 part of AGB material per 300 parts of original solar nebula material, and taking into account a time interval between injection of the short‐lived nuclides and consolidation of the first meteorites equal to 0.53 Myr. Such a polluting source does not overproduce 53Mn, as supernova models do, and only marginally affects isotopic ratios of stable elements. It is usually argued that it is unlikely that the short‐lived radionuclides in the early solar system came from an AGB star because these stars are rarely found in star forming regions, however, we think that further interdisciplinary studies are needed to address the fundamental problem of the birth of our solar system.