bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamics, temperature, chemistry, and dust: Ingredients for a self-consistent AGB wind
Authors: Boulangier J. , Gobrecht D. , Decin L. 
Published: January 2020

AbstractUnderstanding Asymptotic Giant Branch (AGB) stars is important as they play a vital role in the chemical life cycle of galaxies. AGB stars are in a phase of their life time where they have almost ran out of fuel and are losing vast amounts of material to their surroundings, via stellar winds. As this is an evolutionary phase of low mass stars, almost all stars go through this phase making them one of the main contributors to the chemical enrichment of galaxies. It is therefore important to understand what kind of material is being lost by these stars, and how much and how fast. This work summarises the steps we have taken towards developing a self-consistent AGB wind model. We improve on current models by firstly coupling chemical and hydrodynamical evolution, and secondly by upgrading the nucleation theory framework to investigate the creation of TiO2, SiO, MgO, and Al2O3 clusters.
Circumstellar chemistry of Si-C bearing molecules in the C-rich AGB star IRC+10216
Authors: Velilla-Prieto L. , Cernicharo J. , Agúndez M. , Fonfría J. P. , Castro-Carrizo A. , Quintana-Lacaci G. , Marcelino N. , McCarthy M. C. , Gottlieb C. A. , Sánchez Contreras C. , Young K. H. , Patel N. A. , Joblin C. , Martín-Gago J. A. 
Published: January 2020

AbstractSilicon carbide together with amorphous carbon are the main components of dust grains in the atmospheres of C-rich AGB stars. Small gaseous Si-C bearing molecules (such as SiC, SiCSi, and SiC2) are efficiently formed close to the stellar photosphere. They likely condense onto dust seeds owing to their highly refractory nature at the lower temperatures (i.e., below about 2500 K) in the dust growth zone which extends a few stellar radii from the photosphere. Beyond this region, the abundances of Si-C bearing molecules are expected to decrease until they are eventually reformed in the outer shells of the circumstellar envelope, owing to the interaction between the gas and the interstellar UV radiation field. Our goal is to understand the time-dependent chemical evolution of Si-C bond carriers probed by molecular spectral line emission in the circumstellar envelope of IRC+10216 at millimeter wavelengths.
The chemistry in clumpy AGB outflows
Authors: Van de Sande M. , Sundqvist J. O. , Millar T. J. , Keller D. , Decin L. 
Published: January 2020

AbstractThe chemistry within the outflow of an AGB star is determined by its elemental C/O abundance ratio. Thanks to the advent of high angular resolution observations, it is clear that most outflows do not have a smooth density distribution, but are inhomogeneous or “clumpy”. We have developed a chemical model that takes into account the effect of a clumpy outflow on its gas-phase chemistry by using a theoretical porosity formalism. The clumpiness of the model increases the inner wind abundances of all so-called unexpected species, i.e. species that are not predicted to be present assuming an initial thermodynamic equilibrium chemistry. By applying the model to the distribution of cyanopolyynes and hydrocarbon radicals within the outflow of IRC+10216, we find that the chemistry traces the underlying density distribution.
Newly discovered Planetary Nebulae population in Andromeda (M31): PN Luminosity function and implications for the late stages of stellar evolution
Authors: Bhattacharya Souradeep , Arnaboldi Magda , Hartke Johanna , Gerhard Ortwin , Comte Valentin , McConnachie Alan , Harris William E. 
Published: January 2020

AbstractStars with masses between ∼0.7 and 8 M⊙ end their lives as Planetary Nebulae (PNe). With the MegaCam at CFHT, we have carried out a survey of the central 16 sq. degrees of Andromeda (M31) reaching the outer disk and halo, using a narrow-band [OIII]5007 and a broad-band g filter. This survey extends previous PN samples both in uniform area coverage and depth. We identify ∼4000 PNe in M31, of which ∼3000 are new discoveries. We detect PNe down to ∼6 mag below the bright cut-off of the PN luminosity function (PNLF), ∼2 mag deeper than in previous works. We detect a steep rise in the number of PNe at ∼4.5 mag fainter than the bright cut-off. It persists as we go radially outwards and is steeper than that seen in the Magellanic clouds. We explore possible reasons for this rise, which give insights into the stellar population of M31.
The Impact of UV Radiation on Circumstellar Chemistry
Authors: Saberi Maryam , Vlemmings Wouter , Millar Tom , De Beck Elvire 
Published: January 2020

AbstractUV radiation plays a critical role in the chemistry of circumstellar envelopes (CSEs) around evolved stars on the asymptotic giant branch (AGB). However, the effects of all potential sources of UV radiation have not been included in models. We present preliminary results of adding an internal source of UV to the CSE chemistry and predict large enhancements of atomic and ionic species arising from photo-destruction of parent species. Observations of atomic carbon towards the UV-bright AGB star o Cet are consistent with the modelling. In addition, we calculate the precise depth dependence of the CO photodissociation rate in an expanding CSE. We incorporate this within a chemical network active in the outflows of AGB stars, which includes 933 species and 15182 reactions. Our results show that the CO envelope size is about 30% smaller at half abundance than the most commonly used radius reported by Mamon et al. (1988).
S-process Elements in Binary Central Stars of Planetary Nebulae
Authors: Löbling Lisa , Boffin Henri 
Published: January 2020

AbstractLow- and intermediate-mass stars experience a phase of carbon enrichment and slow neutron-capture nucleosynthesis (s-process) on the asymptotic giant branch. An interesting element is the radioactive technetium, whose presence is a clear indication that nucleosynthesis happened recently. Analysing the element abundances not only in the hot evolved stars at the center of planetary nebulae helps to derive constraints for the evolution of these stars. Doing so also in their companions if they are in a binary, provides information on the mass-transfer history.
What Young Massive Clusters in the Magellanic Clouds teach us about Old Galactic Globular Clusters?
Authors: D’Antona Francesca , Ventura Paolo , Dotter Aaron , Ekström Sylvia , Tailo Marco 
Published: January 2020

Abstract. The Asymptotic Giant Branch (AGB) scenario ascribes the multiple populations in old Galactic Globular Clusters (GGC) to episodes of star formation in the gas contaminated by the ejecta of massive AGBs and super-AGBs of a first stellar population. The mass of these AGBs (4-8 M⊙) today populate the Young Massive Clusters (YMC) of the Magellanic Clouds, where rapid rotation and its slowing down play an important role in shaping the color-magnitude diagram features. Consequently, we must reconsider whether the rotational evolution of these masses affects the yields, and whether the resulting abundances are compatible with the chemical patterns observed in GGC. We show the first results of a differential analysis, by computing the hot bottom burning evolution of non-rotating models with increased CNO-Na abundances at the second dredge-up, following the results of MESA rotational models.
LSST: making movies of AGB stars
Authors: Ivezić Željko , Suberlak Krzysztof , Boberg Owen M. 
Published: January 2020

AbstractLSST (www.lsst.org) will be a large, wide-field ground-based system designed to obtain repeated images covering the sky visible from Cerro Pachón in northern Chile. The telescope will have an 8.4m (6.5m effective) primary mirror, a 9.6 sq.deg. field of view, and a 3.2 Gigapixel camera. In a continuous observing campaign, LSST will cover the entire observable sky every three nights to a depth of V ∼ 25 per visit (using 30-second exposures and ugrizy filter set), with exquisitely accurate astrometry and photometry. Close to a half of the sky will be visited about 800 times during the nominal 10-year survey. The project is in the construction phase with first light expected in 2020 and the beginning of regular survey operations by 2022. We describe how these data will impact AGB star research and discuss how the system could be further optimized by utilizing narrow-band TiO and CN filters.
A Tough Egg to Crack
Authors: Lim Jeremy , van-Trung Dinh- 
Published: January 2020

AbstractThe sculpting of the Egg Nebula continues to defy a coherent explanation. Bipolar outflows from the center of the nebula have created bipolar optical lobes that are illuminated by searchlight beams; multiple bipolar outflows orthogonal to the lobes create the appearance of a dark lane; and quasi-circular arcs are imprinted on an approximately spherically-symmetric wind from the progenitorAGB-star. Here, we use archival data from ALMA to study at high angular resolution dust and molecular gas at the center of the nebula. We find that: (i) dust is concentrated in multiple blobs that outline the base of the northern optical lobe; (ii) dense molecular gas forms the wall of a channel swept up and compressed by the outflows that created the bipolar optical lobes; (iii) the expansion and illumination center of the nebula lies at or close to center of the outflow channel. We present a simple working model for the Egg Nebula, and highlight the difficulties that any model face for explaining all the features seen in this nebula.
Planetary nebulae in the (extra)-galactic context: Probing chemical evolution in star-forming galaxies
Authors: Stanghellini Letizia 
Published: January 2020

AbstractThe populations of planetary nebulae (PNe) probe metallicity and chemical content (and its evolution) of the parent galaxy, giving clues to galaxy formation and evolution. This sub-field of extra-galactic PN research has been particularly active in the recent years. Comparison of data and models yielded estimates of global cosmic enrichment and provided constraints to galaxy formation history. In external spiral galaxies, the chemical contents of PNe and H II regions can be compared to disclose possible evolution of the radial metallicity gradient, which is, in turn, a powerful constraint to galactic chemical evolutionary models. In the Milky Way, recent PN progenitor dating and new chemical abundances offer an updated look into our own Galaxy. Collectively, Galactic and extra-galactic radial metallicity gradients from emission-line probes (PNe and H II regions) can be compared to have a cosmological outlook on galactic evolution.
On the onset of dust formation in AGB stars
Authors: Gobrecht David , Bromley Stefan T. , Plane John M. C. , Decin Leen , Cristallo Sergio 
Published: January 2020

AbstractA promising candidate to initiate dust formation in oxygen-rich AGB stars is alumina (Al2O3) showing an emission feature around ∼13μm attributed to Al−O stretching and bending modes (Posch+99,Sloan+03). The counterpart to alumina in carbon-rich AGB atmospheres is the highly refractory silicon carbide (SiC) showing a characteristic feature around 11.3μm (Treffers74). Alumina and SiC grains are thought to represent the first condensates to emerge in AGB stellar atmospheres. We follow a bottom-up approach, starting with the smallest stoichiometric clusters (i.e. Al4O6, Si2C2), successively building up larger-sized clusters. We present new results of quantum-mechanical structure calculations of (Al2O3)n, n = 1−10 and (SiC)n clusters with n = 1−16, including potential energies, rotational constants, and structure-specific vibrational spectra. We demonstrate the energetic viability of homogeneous nucleation scenarios where monomers (Al2O3 and SiC) or dimers (Al4O6 and Si2C2) are successively added. We find significant differences between our quantum theory based results and nanoparticle properties derived from (classical) nucleation theory.
Molecular dust precursors in envelopes of oxygen-rich AGB stars and red supergiants
Authors: Kamiński Tomasz 
Published: January 2020

AbstractCondensation of circumstellar dust begins with formation of molecular clusters close to the stellar photosphere. These clusters are predicted to act as condensation cores at lower temperatures and allow efficient dust formation farther away from the star. Recent observations of metal oxides, such as AlO, AlOH, TiO, and TiO2, whose emission can be traced at high angular resolutions with ALMA, have allowed first observational studies of the condensation process in oxygen-rich stars. We are now in the era when depletion of gas-phase species into dust can be observed directly. I review the most recent observations that allow us to identify gas species involved in the formation of inorganic dust of AGB stars and red supergiants. I also discuss challenges we face in interpreting the observations, especially those related to non-equilibrium gas excitation and the high complexity of stellar atmospheres in the dust-formation zone.
Lumpy stars and bumpy winds
Authors: Liljegren Sofie , Höfner Susanne , Freytag Bernd , Bladh Sara 
Published: January 2020

AbstractThe wind-driving process of AGB stars is thought to be a two-step process: first matter is levitated by shock waves, and then accelerated outwards by radiation pressure on newly condensed dust grains. When modelling such a wind, spherical symmetry is usually assumed. This is in stark contrast with recent observations, which shows significant non-spherical structures. Giant convection cells cover the surface of the star, and matter is being ejected into the atmosphere where it condenses into lumpy dust clouds. We try to quantify the differences between what is simulated in the 3D star-in-a-box models (CO5BOLD code) and the 1D dynamical atmosphere and wind models (DARWIN code). The impact of having a non-spherical star on the wind properties is also investigated. We find that the inherent non-spherical behaviour of AGB stars might induce a dust-driven weak wind already early on the AGB, and including that the star is anisotropic when simulating the wind leads to large time variations in the density of the outflow. Such variations might be observable as small-scale structures in the circumstellar envelope.
The role of AGB stars in the evolution of globular clusters
Authors: Ventura Paolo , D’Antona Franca , Di Criscienzo Marcella , Dell’Agli Flavia , Tailo Marco 
Published: January 2020

AbstractThe results from high-resolution spectroscopy and accurate photometry have challenged the traditional paradigm that stars in globular clusters (GC) are simple stellar populations, rather suggesting that these structures harbor distinct groups of stars, differing in the chemical composition, particularly in the abundances of the light elements, from helium to silicon. Because this behavior is not shared by field stars, it is generally believed that some self-enrichment mechanism must have acted in GC, such that new stellar generations formed from the ashes of stars belonging to the original population. In this review, after presenting the state-of-the-art of the observations of GC stars, we discuss the possibility that the pollution of the intra-cluster medium was provided by the winds of AGB stars of initial mass above ∼3 M⊙. These objects evolve with time scales of 40 − 100 Myr and contaminate their surroundings with gas processed by p-capture nucleosynthesis, in agreement with the chemical patterns traced by GC stars.
The Maser-emitting Structure and Time Variability of the SiS Lines J=14−13 and 15-14 in IRC+10216
Authors: Fonfría J. P. , Fernández-López M. , Pardo J. R. , Agúndez M. , Sánchez Contreras C. , Velilla-Prieto L. , Cernicharo J. , Santander-García M. , Quintana-Lacaci G. , Castro-Carrizo A. , Curiel S. 
Published: January 2020

AbstractAGB stars are important contributors of processed matter to the ISM. However, the physical and chemical mechanisms involved in its ejection are still poorly known. This process is expected to have remarkable effects in the innermost envelope, where the dust grains are formed, the gas is accelerated, the chemistry is active, and the radiative excitation becomes important. A good tracer of this region in C-rich stars is SiS, an abundant refractory molecule that can display maser lines, very sensitive to changes in the physical conditions. We present high angular resolution interferometer observations (HPBW ≳0.″.25) of the v = 0 J = 14 – 13 and 15 – 14 SiS maser lines towards the archetypal AGB star IRC+10216, carried out with CARMA and ALMA to explore the inner 1” region around the central star. We also present an ambitious monitoring of these lines along one single pulsation period carried out with the IRAM 30 m telescope.
A critical test to disentangle the role of overshooting and rotation in stars
Authors: Costa G. , Girardi L. , Bressan A. , Marigo P. , Chen Y. , Kanniah B. , Lanza A. , Rodrigues T. S. 
Published: January 2020

AbstractWe study the mixing in low-intermediate massive stars using eclipsing binaries. We compute stellar evolutionary models with a varying convective core overshooting parameter and different rotation rates. Using a Bayesian estimation method, we found that the coexistence of the two phenomena may be a reasonable explanation of the observed extra-mixing.
Zooming into the complex dusty envelopes of C-rich AGB stars
Authors: Lykou Foteini , Hron Josef , Klotz Daniela 
Published: January 2020

AbstractRecent advances in high-angular resolution instruments (VLT and VLTI, ALMA) have enabled us to delve deep into the circumstellar envelopes of AGB stars from the optical to the sub-mm wavelengths, thus allowing us to study in detail the gas and dust formation zones (e.g., their geometry, chemistry and kinematics). This work focuses on four (4) C-rich AGB stars observed with a high-angular resolution technique in the near-infrared: a multi-wavelength tomographic study of the dusty layers of the circumstellar envelopes of these C-rich stars, i.e. the variations in the morphology and temperature distribution.
Astrometric observation of the Galactic LPVs with VERA; Mira and OH/IR stars
Authors: Nakagawa Akiharu , Kurayama Tomoharu , Orosz Gabor , Oyama Tomoaki , Nagayama Takumi , Omodaka Toshihiro 
Published: January 2020

AbstractWe present studies of Long Period Variables (LPVs) in our Galaxy based on astrometric VLBI observations of H2O and SiO masers. The Galactic Miras and OH/IR stars are our main targets. For Miras, we present the distribution of the LPVs on the MK – log P plane. Galactic Miras show consistency with PLR in the LMC except for some fainter sources. Parallaxes of the LPVs determined from VLBI and Gaia are compared. There seems to be some offset.
Mass Loss History of Evolved Stars (MLHES) Excavated by AKARI
Authors: Ueta Toshiya , Torres Andrew J. , Izumiura Hideyuki , Yamamura Issei 
Published: January 2020

AbstractWe performed a far-IR imaging survey of the circumstellar dust shells of 144 evolved stars as a mission program of the AKARI infrared astronomical satellite. Our objectives were to characterize the far-IR surface brightness distributions of the cold dust component in the circumstellar dust shells. We found that (1) far-IR emission was detected from all but one object, (2) roughly 60–70 % of the target sources showed some extension, (3) 29 sources were newly resolved in the far-IR in the vicinity of the target sources, (4) the results of photometry measurements were reasonable with respect to the entries in the AKARI/FIS Bright Source Catalogue, and (5) an IR two-color diagram would place the target sources in a roughly linear distribution that may correlate with the age of the circumstellar dust shell.
Asymptotic Giant Branch Variables in Nearby Galaxies
Authors: Whitelock Patricia A. 
Published: January 2020

AbstractCertain types of large amplitude AGB variable are proving to be powerful distance indicators that will rival Cepheids in the James Webb Space Telescope era of high precision infrared photometry. These are predominantly found in old populations and have low mass progenitors. At the other end of the AGB mass-scale, large amplitude variables, particularly those undergoing hot bottom burning, are the most luminous representatives of their population. These stars are < 1 Gyr old, are often losing mass copiously and are vital to our understanding of the integrated light of distant galaxies as well as to chemical enrichment. However, the evolution of such very luminous AGB variables is rapid and remains poorly understood. Here I discuss recent infrared observations of both low- and intermediate-mass Mira variables in the Local Group and beyond.
When binaries keep track of recent nucleosynthesis
Authors: Karinkuzhi D. , Van Eck S. , Jorissen A. , Goriely S. , Siess L. , Merle T. , Escorza A. , Van der Swaelmen M. , Boffin H. M. J. , Masseron T. , Shetye S. , Plez B. 
Published: January 2020

AbstractWe determine Zr and Nb elemental abundances in barium stars to probe the operation temperature of the s-process that occurred in the companion asymptotic giant branch (AGB) stars. Along with Zr and Nb, we derive the abundances of a large number of heavy elements. They provide constraints on the s-process operation temperature and therefore on the s-process neutron source. The results are then compared with stellar evolution and nucleosynthesis models. We compare the nucleosynthetic profile of the present sample stars with those of CEMP-s, CEMP-rs and CEMP-r stars. One barium star of our sample is potentially identified as the highest-metallicity CEMP-rs star yet discovered.
s-process abundances of Primary stars in the Sirius-like Systems: Constraints on pollution from AGB stars
Authors: Bharat Kumar Y. , Kong X-M. , Zhao G. , Zhao J-K. 
Published: January 2020

AbstractWe present the results from the abundance analysis of 21 primary stars in Sirius-like systems with various masses of white dwarf companions and orbital separation to understand the origin and nature of Ba stars. Three new Ba dwarfs are found for which masses are relatively low compared to Ba giants. Large fraction of the sample are found to be non-Ba stars, however, some of them have required WD mass and/or close orbital separation. Observed s-process abundances in Ba dwarfs are in good agreement with AGB models of respective WD companion mass, however, it required different pollution factors.
The loss of large amplitude pulsations at the end of AGB evolution
Authors: Engels D. , Etoka S. , Gérard E. 
Published: January 2020

AbstractSince 2013, we are performing with the Nancay Radio Telescope (NRT) a monitoring program of > 100 Galactic disk OH/IR stars, having bright 1612-MHz OH maser emission. The variations of the maser emission are used to probe the underlying stellar variability. We wish to understand how the large-amplitude variations are lost during the AGB – post-AGB transition. The fading out of pulsations with steadily declining amplitudes seems to be a viable process.
Does 3rd dredge-up reduce AGB mass-loss?
Authors: Uttenthaler Stefan , McDonald Iain , Bernhard Klaus , Cristallo Sergio , Gobrecht David 
Published: January 2020

AbstractWe follow up on a previous finding that Miras containing the third dredge-up (3DUP) indicator technetium (Tc) in their atmosphere form a different sequence of K – [22] colour as a function of pulsation period than Miras without Tc. A near-to-mid-infrared colour such as K – [22] is a good probe for the dust mass-loss rate (MLR) of these AGB stars. Contrary to what one might naïvely expect, Tc-poor Miras show redderK – [22] colours (i.e. higher dust MLRs) than Tc-rich Miras at a given period. In the follow-up work, the previous sample is extended and the analysis is expanded towards other colours and ISO dust spectra to check if the previous finding is due to a specific dust feature in the 22 μm band. We also investigate if the same two sequences can be revealed in the gas MLR. Different hypotheses to explain the observation of two sequences in the P vs. K – [22] diagram are discussed and tested, but so far none of them convincingly explains the observations.