bluuebunny/crossref_metadata_2025 huggingface dataset:
The Structure of the Inner Circumstellar Shell in Miras
Authors: Hinkle Kenneth H. , Lebzelter Thomas
Published: January 2020

We have measured CO line profiles in a time series of 42 high-resolution 1.6 − 2.5 μm spectra of R Cas. The low-excitation CO first overtone lines have a contribution from a ∼1000 K region. We show that this region undergoes a periodic changes on time scales many times longer than the photospheric pulsation. Comparison with interferometry and models suggests that the ∼1000 K region is at ∼2 R* and cospatial with the region of SiO masers and grain condensation. The CO lines are entirely in absorption requiring formation in a layer thin compared to the stellar diameter. The CO excitation temperature has been measured as low as 600 K suggesting that grains with a variety of compositions condense at ∼2 R*.
On the circumstellar effects on the Li and Ca abundances in massive Galactic O-rich AGB stars
Authors: Pérez-Mesa V. , Zamora O. , García-Hernández D. A. , Ossorio Y. , Masseron T. , Plez B. , Manchado A. , Karakas A. I. , Lugaro M.
Published: January 2020

We explore the circumstellar effects on the Li and Ca abundances determination in a complete sample of massive Galactic AGB stars. The Li abundance is an indicator of the hot bottom burning (HBB) activation, while the total Ca abundance could be affected by overproduction of the short-lived radionuclide 41Ca by the s-process. Li abundances were previously studied with hydrostatic models, while Ca abundances are determined here for the first time. The pseudo-dynamical abundances of Li and Ca are very similar to the hydrostatic ones, indicating that circumstellar effects are almost negligible. The new Li abundances confirm the (super-)Li-rich character of the sample Li-detected stars, supporting the HBB activation in massive Galactic AGB stars. Most sample stars display nearly solar Ca abundances that are consistent with predictions from the s-process nucleosynthesis models. A minority of the sample stars show a significant Ca depletion. Possible reasons for their (unexpected) low Ca content are given.
On cylindrically symmetric solutions of polarized radiative transfer equation
Authors: Freimanis Juris
Published: January 2020

While the observed polarization maps of spatially resolved post-AGB objects usually require numerical modelling of radiative transfer, it is useful to have known analytical solutions of the polarized radiative transfer equation (PRTE) as benchmarks of computer codes in the simplest model cases. We consider two such solutions: cylindrically symmetric Green’s function for an infinite medium and cylindrically symmetric inner eigenfunctions of PRTE.
Observations of the Ultraviolet-Bright Star Barnard 29 in the Globular Cluster M13 (NGC 6205)
Authors: Dixon William V. , Chayer Pierre , Reid I. N. , Bertolami Marcelo Miguel Miller
Published: January 2020

We have analyzed FUSE, COS, GHRS, and Keck/HIRES spectra of the UV-bright star Barnard 29 in M13. Fits to the star’s optical spectrum yield Teff = 20,000 ± 100 K and log g = 3.00 ± 0.01. Using modern stellar-atmosphere models, we are able to reproduce the complex shape of the Balmer H.. feature. We derive photospheric abundances of He, C, N, O, Mg, Al, Si, P, S, Cl, Ar, Ti, Cr, Fe, Ni, and Ge. Barnard 29 exhibits an abundance pattern typical of the first-generation stars in M13, enhanced in oxygen and depleted in aluminum. We see no evidence of significant chemical evolution since the star left the RGB; in particular, it did not undergo third dredge-up. Previous workers found that the star’s FUV spectra yield an iron abundance about 0.5 dex lower than its optical spectrum, but the iron abundances derived from all of our spectra are consistent with one another and with the cluster value. We attribute this difference to our use of model atmospheres without microturbulence. By comparing our best-fit model with the star’s optical magnitudes, we derive a mass M*/M=0.40 − 0.49 and luminosity log L*/L⊙=3.20 − 3.29, depending on the cluster distance. Comparison with stellar-evolution models suggests that Barnard 29 evolved from a ZAHB star of mass M*/M⊙∼0.50, placing it near the boundary between the extreme and blue horizontal branches.
Dynamics, temperature, chemistry, and dust: Ingredients for a self-consistent AGB wind
Authors: Boulangier J. , Gobrecht D. , Decin L.
Published: January 2020

Understanding 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

Silicon 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

The 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

Stars 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

UV 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

Low- 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

. 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

LSST (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

The 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

The 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

A 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

Condensation 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

The 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

The 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

AGB 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

We 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

Recent 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

We 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

We 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

Certain 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

We 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

We 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

Since 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

We 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.
AGB population as probes of galaxy structure and evolution
Authors: Javadi Atefeh , van Loon Jacco Th.
Published: January 2020

The evolution of galaxies is driven by the birth and death of stars. AGB stars are at the end points of their evolution and therefore their luminosities directly reflect their birth mass; this enables us to reconstruct the star formation history. These cool stars also produce dust grains that play an important role in the temperature regulation of the interstellar medium (ISM), chemistry, and the formation of planets. These stars can be resolved in all of the nearby galaxies. Therefore, the Local Group of galaxies offers us a superb near-field cosmology site. Here we can reconstruct the formation histories, and probe the structure and dynamics, of spiral galaxies, of the many dwarf satellite galaxies surrounding the Milky Way and Andromeda, and of isolated dwarf galaxies. It also offers a variety of environments in which to study the detailed processes of galaxy evolution through studying the mass-loss mechanism and dust production by cool evolved stars. In this paper, I will first review our recent efforts to identify mass-losing Asymptotic Giant Branch (AGB) stars and red supergiants (RSGs) in Local Group galaxies and to correlate spatial distributions of the AGB stars of different mass with galactic structures. Then, I will outline our methodology to reconstruct the star formation histories using variable pulsating AGB stars and RSGs and present the results for rates of mass–loss and dust production by pulsating AGB stars and their analysis in terms of stellar evolution and galaxy evolution.
A systematic survey of grain growth in discs around post-AGB binaries with PACS and SPIRE photometry
Authors: Dsilva K. , Van Winckel H. , Kluska J.
Published: January 2020

Post-AGB stars are the final stage of evolution of low-intermediate mass stars (M < 8 Mʘ). Those in binary systems have stable circumbinary discs. Using data from Herschel (PACS/SPIRE), we extend the SEDs of 50 galactic post-AGB binary systems to sub-millimetre wavelengths and use the slope of the SED as a diagnostic tool to probe the presence of large grains. Using a Monte Carlo radiative transfer code (MCMax), we create a large grid of models to quantify the observed spectral indices, and use the presence of large grains in the disc as a proxy for evolution.
AGB Stars: Remaining Problems
Authors: Lattanzio John
Published: January 2020

I present a subjective list of what I think are the most serious problems in the modelling of AGB stars. Because AGB stars represent the last phase of stellar evolution, they suffer from the accumulation of the effects of uncertainties in all the earlier phases. The complexity of AGB evolution adds further uncertainties specific to the evolutionary behaviour of those stars. Most of the problems are associated with mixing, specifically the boundaries of mixed regions. The nature of the “extra-mixing” remains a mystery, let alone how to model it reliably. Other problems are briefly mentioned and I finish with some hopes of making progress in the future.
Carbon and oxygen isotopes in AGB stars. From the cores of AGB stars to presolar dust
Authors: Lebzelter Thomas , Hinkle Kenneth , Straniero Oscar
Published: January 2020

Isotopic ratios are a powerful tool for gaining insights into stellar evolution and nucleosynthesis. The isotopic ratios of the key elements carbon and oxygen are perfectly suited to investigate the pristine composition of red giants, the conditions in their interiors, and the mixing in their extended atmospheres. Of course the dust ejected from red giants in their final evolution also contains isotopically tagged material. This red giant dust is present in the solar system as presolar dust grains. We have measured isotopic ratios of carbon and oxygen in spectra from a large sample of AGB stars including both Miras and semiregular variables. We show how the derived ratios compare with expectations from stellar models and with measurements in presolar grains. Comparison of isotopes that are affected by different types of nucleosynthesis provides insights into galactic evolution.
GK Car and GZ Nor: Two low-luminous, depleted RV Tauri stars
Authors: Gezer I. , Van Winckel H. , Manick R. , Kamath D.
Published: January 2020

RV Tauri stars are luminous population II Cepheids which show a characteristic light curve of alternating deep and shallow minima. There are 126 RV Tauri variables in our Galaxy. Using WISE [3.4]-[4.6], [12]-[22] diagram we show that Galactic RV Tauri stars show three main types of IR properties in their SEDs; disc-type, non-IR and uncertain, which does not show a clear characteristic in the SED. We also show that there is a strong correlation between disc-type SED and binarity (Gezer et al. 2015). RV Tauri stars were linked to post AGB stars in early studies (Jura 1986), however, recent studies show that their evolutionary nature is more complex than previously thought (Kamath & Van Winckel 2014, and Manick et al. 2018). In this study, we intentionally selected two RV Tauri stars, GK Car (disc-type) and GZ Nor (uncertain), with different IR characteristics to compare their chemical and photometric properties.
Infrared light curves of dusty & metal-poor AGB stars
Authors: Goldman Steven R. , Boyer Martha ,   the DUSTiNGS team
Published: January 2020

The effects of metallicity on both the dust production and mass loss of evolved stars have consequences for stellar masses, stellar lifetimes, progenitors of core-collapse SNe, and the origin of dust in the ISM. With the DUST in Nearby Galaxies with Spitzer (DUSTiNGS) survey, we have discovered samples of dusty evolved AGB stars out to the edge of the Local Group with metallicities down to 0.6% solar. This makes them the nearest analogs of AGB stars in high-redshift galaxies. We present new infrared light curves of the dustiest AGB stars in 10 galaxies from the DUSTiNGS survey and show how the infrared Period-Luminosity (PL) relation is affected by dust and metallicity. These results have implications for the efficiency of AGB dust production at high-redshift and for the use of the Mira PL relation as a distance indicator.
A DARWIN C-star model grid with new dust opacities
Authors: Eriksson Kjell , Höfner Susanne , Aringer Bernhard
Published: January 2020

We have improved the treatment of dust opacity from the small-particle limit approximation to size-dependent which leads to models with smaller grains, lower dust-to-gas ratios, but about the same mass-loss rates and outflow velocities. The K-magnitudes get brighter, whereas the V-magnitudes can be either brighter or dimmer depending on the wind properties.
Evolutionary timescales from the AGB to the CSPNe phase
Authors: Miller Bertolami Marcelo M.
Published: January 2020

The transition from the asymptotic giant branch (AGB) to the final white dwarf (WD) stage is arguably the least understood phase in the evolution of single low- and intermediate-mass stars (0.8 ≲MZAMS/M⊙≲ 8…10). Here we briefly review the progress in the last 50 years of the modeling of stars during the post-AGB phase. We show that although the main features, like the extreme mass dependency of post-AGB timescales were already present in the earliest post-AGB models, the quantitative values of the computed post-AGB timescales changed every time new physics was included in the modeling of post-AGB stars and their progenitors. Then we discuss the predictions and uncertainties of the latest available models regarding the evolutionary timescales of post-AGB stars.
Looking for new water-fountain stars
Authors: Uscanga L. , Gómez J. F. , Yung B. H. K. , Imai H. , Rizzo J. R. , Suárez O. , Miranda L. F. , Trinidad M. A. , Anglada G. , Torrelles J. M.
Published: January 2020

We carried out simultaneous observations of H2O and OH masers, and radio continuum at 1.3 cm with the Karl G. Jansky Very Large Array (VLA) towards 4 water-fountain candidates. Water fountains (WFs) are evolved stars, in the AGB and post-AGB phase, with collimated jets traced by high-velocity H2O masers. Up to now, only 15 sources have been confirmed as WFs through interferometric observations. We are interested in the discovery and study of new WFs. A higher number of these sources is important to understand their properties as a group, because they may represent one of the first manifestations of collimated mass-loss in evolved stars. These observations will provide information about the role of magnetic fields in the launching of jets in WFs. Our aim is to ascertain the WF nature of these candidates, and investigate the spatial distribution of the H2O and OH masers.
The Nearby Evolved Stars Survey: Project description and initial results
Authors: Scicluna Peter
Published: January 2020

The Nearby Evolved Stars Survey aims to observe over 400 evolved stars within 2 kpc, to determine why, and how much, our Galaxy cares about AGB stars. This contribution presents a brief introduction to the survey and data. NESS is an open project. Anyone is welcome to get involved and we aim to make as much data and code available to the community as possible.
On the nature and mass loss of Bulge OH/IR stars
Authors: Blommaert Joris A. D. L. , Groenewegen Martin A. T. , Justtanont Kay , Decin L.
Published: January 2020

We report on the successful search for CO (2-1) and (3-2) emission associated with OH/IR stars in the Galactic Bulge. We observed a sample of eight extremely red AGB stars with the APEX telescope and detected seven. The sources were selected at sufficient high Galactic latitude to avoid interference by interstellar CO, which hampered previous studies of inner galaxy stars. We also collected photometric data and Spitzer IRS spectroscopy to construct the SEDs, which were analysed through radiative transfer modelling. We derived variability periods of our stars from the VVV and WISE surveys. Through dynamical modelling we then retrieve the total mass loss rates (MLR) and the gas-to-dust ratios. The luminosities range between approximately 4,000 and 5,500 L⊙ and periods are below 700 days. The total MLR ranges between 10−5 and 10−4 M⊙ yr−1. The results are presented in Blommaert et al. 2018 and summarized below.
A step further on the physical, kinematic and excitation properties of PNe
Authors: Rocha Gonçalves Denise , Akras Stavros
Published: January 2020

PNe are known to be photoionized objects. However they also have low-ionization structures (LIS) with different excitation behavior. We are only now starting to answer why most LIS have lower electron densities than the PN shells hosting them, and whether or not their intense emission in low-ionization lines is the key to their main excitation mechanism. Can LIS line ratios, chemical abundances and kinematics enlight the interplay between the different excitation and formation processes in PNe? Based on the spectra of five PNe with LIS and using new diagnostic diagrams from shock models, we demonstrate that LIS’s main excitation is due to shocks, whereas the other components are mainly photoionized. We propose new diagnostic diagrams involving a few emission lines ([N II], [O III], [S II]) and fshocks/f*, where fshocks and f* are the ionization photon fluxes due to the shocks and to the central star ionizing continuum, respectively.
Dust Structure Around Asymptotic Giant Branch Stars
Authors: Upadhyay Devendra Raj , Khanal Lochan , Hamal Priyanka , Aryal Binil
Published: January 2020

This paper presents mass, temperature profile, and the variation of Planck’s function in different regions around asymptotic giant branch (AGB) stars. The physics of the interstellar medium (ISM) is extremely complex because the medium is very inhomogeneous and is made of regions with fairly diverse physical conditions. We studied the dust environment such as flux, temperature, mass, and inclination angle of the cavity structure around C-rich asymptotic giant branch stars in 60 μm and 100 μm wavelengths band using Infrared Astronomical Survey. We observed the data of AGB stars named IRAS 01142+6306 and IRAS 04369+4501. Flexible image transport system image was downloaded from Sky View Observatory; we obtained the surrounding flux density using software Aladin v2.5. The average dust color temperature and mass are found to be 25.08 K, 23.20 K and 4.73 × ;1026 kg (0.00024 M⊙), 2.58 × 1028 kg (0.013 M⊙), respectively. The dust color temperature ranges from 18.76 K ± 3.16 K to 33.21K ± K and 22.84 K ± 0.18 K to 24.48 K ± 0.63 K. The isolated cavity like structure around the AGB stars has an extension of 45.67 pc × 17.02 pc and 42.25 pc × 17.76 pc, respectively. The core region is found to be edge-on having an inclination angle of 79.46° and 73.99°, respectively.
Near IR and visual polarimetry of the Planetary Nebula M2-9
Authors: Navarro Silvana G. , Serrano Omar , Luna Abraham , Devaraj Rangaswami , Corral Luis J. , Ramírez Vélez Julio , Hiriart David
Published: January 2020

Bipolar and more complex morphologies observed in planetary nebulae have been explained by two principal hypotheses: by the existence of a companion producing a circumstellar disk, by the effects of a magnetic field, or by a combination of both. The polarimetric analysis of these objects could give information about the presence of dust grains aligned with any preferential direction, due to a magnetic field or to the action of radiative torques (RAT). We performed polarimetric observations of some planetary nebulae in order to detect linear polarization and (in the best scenario) to detect the signature of an accretion disk in these objects. We observed in the visual region with POLIMA at the San Pedro Mártir observatory, and with POLICAN the NIR polarimeter in the Guillermo Haro observatory. We present the result of these observations in one of these objects: the PN M2-9.
ALMA spectrum of the extreme OH/IR star OH 26.5+0.6
Authors: Justtanont K. , Muller S. , Barlow M. J. , Engels D. , García-Hernández D. A. , Groenewegen M. A. T. , Matsuura M. , Olofsson H. , Teyssier D. , Marti-Vidal I. , Khouri T. , Van de Sande M. , Homan W. , Danilovich T. , de Koter A. , Decin L. , Waters L. B. F. M. , Stancliffe R. , Vlemmings W. , Royer P. , Kerschbaum F. , Paladini C. , Blommaert J. , de Nutte R.
Published: January 2020

We present ALMA band 7 data of the extreme OH/IR star, OH 26.5+0.6. In addition to lines of CO and its isotopologues, the circumstellar envelope also exhibits a number of emission lines due to metal-containing molecules, e.g., NaCl and KCl. A lack of C18O is expected, but a non-detection of C17O is puzzling given the strengths of H217O in Herschel spectra of the star. However, a line associated with Si17O is detected. We also report a tentative detection of a gas-phase emission line of MgS. The ALMA spectrum of this object reveals intriguing features which may be used to investigate chemical processes and dust formation during a high mass-loss phase.
SMA Spectral Line Survey of the Proto-Planetary Nebula CRL 618
Authors: Patel Nimesh A. , Gottlieb Carl , Young Ken , Kaminski Tomasz , McCarthy Michael , Menten Karl , Lee Chin-Fei , Gupta Harshal
Published: January 2020

Carbon-rich Asymptotic Giant Branch (AGB) stars are major sources of gas and dust in the interstellar medium. During the brief (∼1000 yr) period in the evolution from AGB to the Planetary Nebula (PN) stage, the molecular composition evolves from mainly diatomic and small polyatomic species to more complex molecules. Using the Submillimeter Array (SMA), we have carried out a spectral line survey of CRL 618, covering a frequency range of 281.9 to 359.4 GHz. More than 1000 lines were detected in the ∼60 GHz range, most of them assigned to HC3N and c-C3H2, and their isotopologues. About 200 lines are unassigned. Lines of CO, HCO+, and CS show the fast outflow wings, while the majority of line emission arises from a compact region of ∼1” diameter. We have analyzed the lines of HC3N, c-C3H2, CH3CN, and their isotopologues with rotation temperature diagrams.
Fine Three‐Dimensional VHF Lightning Mapping Using Waveform Cross‐Correlation TOA Method
Authors: Liu Bo , Shi Lihua , Qiu Shi , Liu Hengyi , Dong Wansheng , Li Yun , Sun Zheng
Published: January 2020

Waveform cross‐correlation approach was first applied to three‐dimensional very high frequency (VHF) lightning mapping. A Hilbert transform of the original waveform and a three‐step cross‐correlation parsing process were employed to compute the time differences with a small 10‐μs time window for the final time‐of‐arrival (TOA) positioning. The lightning channel continuity was significantly improved, and its fine structure, including the K process, was clearly distinguished with speeds of up to 1.1 × 107 m/s. The two overlapped K processes indicate the high location accuracy of the time‐of‐arrival, based on the waveform correlation method. The median (mean) values of the positioning precision with the proposed method were evaluated by duplicate located sources and estimated as σx = 20 m (26 m), σy = 19 m (28 m), and σz = 54 m (67 m).
Is the Regional Precipitation Predictable in Decadal Scale? A Possible Approach for the Decadal Prediction of the Summer Precipitation Over North China
Authors: Huang Yanyan , Wang Huijun
Published: January 2020

A skillful decadal precipitation (DP) prediction is beneficial for infrastructure implementation, water management, and sustainable development, which currently face many challenges. In this study, a new increment method is applied to the decadal prediction of summer precipitation during 1961–2014 over North China, which has suffered water resource scarcity and increased droughts in recent decades. There are three steps in the increment method. First, the DP over North China is obtained by applying a 5‐year running mean. Second, the 3‐year decadal increment (DI) of the DP (DP at the current year minus the DP at the 3 years before, DI_DP) is predicted by a statistical model with the leading 3‐year DI of sea surface temperature anomalies over the North Atlantic and the leading 4‐year DI of the sea ice concentration over the East Siberian Sea. Third, the well‐predicted DI_DP is added to the observed DP at 3 years ago to obtain the final DP prediction. With realistic DP prediction, including correct regime shifts, the increment method provides a promising and valuable approach to decadal climate prediction.
Magnetic Properties of Asteroid (162173) Ryugu
Authors: Hercik David , Auster Hans‐Ulrich , Constantinescu Dragos , Blum Jürgen , Fornaçon Karl‐Heinz , Fujimoto Masaki , Gebauer Kathrin , Grundmann Jan‐Thimo , Güttler Carsten , Hillenmaier Olaf , Ho Tra‐Mi , Hördt Andreas , Krause Christian , Kührt Ekkehard , Lorda Laurence , Matsuoka Ayako , Motschmann Uwe , Moussi‐Soffys Aurélie , Richter Ingo , Sasaki Kaname , Scholten Frank , Stoll Bernd , Weiss Benjamin P. , Wolff Friederike , Glassmeier Karl‐Heinz
Published: January 2020

Observations of the magnetization state of asteroids indicate diverse properties. Values between 1.9 
 10
Am
/kg (Eros) and 10
Am
/kg (Braille) have been reported. A more detailed understanding of asteroidal magnetic properties allows far‐reaching conclusions of the magnetization mechanism as well as the strength of the magnetic field of the solar system regions the asteroid formed in. The Hayabusa2 mission with its lander Mobile Asteroid Surface Scout is equipped with a magnetometer experiment, MasMag. MasMag is a state‐of‐the‐art three‐axis fluxgate magnetometer, successfully operated also on Philae, the Rosetta mission lander. MasMag has enabled, after Eros for the second time ever, to determine the magnetic field of an asteroid during descent and on‐surface operations. The new observations show that Ryugu, a low‐albedo C‐type asteroid, has no detectable global magnetization, and any local magnetization is either small (
 Am
/kg) or on very small (subcentimeter) scales. This implies, for example, that energetic solar wind particles could reach and alter the surface unimpeded by strong asteroidal magnetic fields, such as minimagnetospheres in case of the Moon.