Comprehensive study of Mira variables

• Kateřina Neumannová

Mira variables represent late evolutionary stages of asymptotic giant branch stars and exhibit complex photometric and spectroscopic behaviour. We investigate Mira variables in the Milky Way and the Magellanic Clouds, including objects located in open and globular clusters. The main goal is to create a comprehensive catalogue of Mira stars and compare their properties in different stellar environments. We analyse their distribution, variability characteristics, and long-term time-series behaviour in order to identify both common trends and significant differences between individual groups of Mira variables. Special attention is devoted to the distinction between oxygen-rich (O-rich) and carbon-rich (C-rich) Miras using spectroscopic and photometric data, and to evaluating whether photometric classification alone is sufficiently reliable. We also investigate the presence of secondary periods in selected objects and study the influence of circumstellar dust on observed variability and classification. Finally, we discuss possible misclassifications of Mira variables in existing catalogues and their implications for studies of stellar populations and late stellar evolution.

What’s behind the brightness changes of Antares?

• Klára Lelkes (HUN-REN CSFK)

Antares is one of the nearest red supergiant and is similar to Betelgeuse in many aspects, yet it has received considerably less attention. We constructed the longest and most precise light curve of Antares to date using nine years of photometric observations from the Solar Mass Ejection Imager (SMEI) space instrument, which gave us an unprecedented view of the light variations of the star. We complemented these data with long-term radial velocity measurements from the STELLA telescope and from the literature. The corrected light curve and radial velocity measurements reveal several periodic signals, including a long secondary period of about 2000 days and multiple radial pulsation modes. Based on the phase difference between the photometric and radial velocity variations, we suggest that the long secondary period may be caused by a low-mass, close companion, analogous to Betelgeuse. Finally, analysis of the radial pulsations and comparison with stellar models allow us to estimate the physical parameters and distance of Antares independently of previous methods.

ALMA + VLTI imaging of cool evolved stars at high angular and spectral resolution

• Daniel Jadlovský (ESO & Masaryk University, Czech Republic)

The unique capabilities of the VLTI and ALMA instruments allow us to study the poorly constrained mass-loss process of AGB stars and red supergiants (RSGs). For stars of suitable size, VLTI can resolve their surface and dust formation zone at high spatial resolution, while ALMA can also provide high-resolution kinematical information. In this work, we exploit the capabilities of both instruments when used together. For a sample of AGB stars, we obtained imaging observations in near-infrared with VLTI-PIONIER and VLTI-MATISSE, as well as high-frequency vibrational and rotational transitions of SiO masers (J=6-5, 7-6) with ALMA at the longest baselines. Combined, we can trace features from the stellar surface out into the dust formation zone and uniquely test and further constrain 1D and 3D models. Meanwhile, these are some of the first SiO maser observations at this high frequency and high spatial resolution. The enhanced maser position accuracy, thanks to high S/N component fitting, unveils unexpected maser structures. I will also briefly discuss our recent results on AGB and RSG stars using VLTI-GRAVITY time series observations. Namely, I will demonstrate that we can constrain their pulsation properties, while we can also unveil their interacting companions and determine orbital parameters.

Super-AGB stars: fundamentals and recent progress

• Pilar Gil-Pons

Super-Asymptotic Giant Branch (super-AGB) stars are intermediate-mass giants of approximately 8-10 Msun, and correspond to the most massive objects that will not undergo a core-collapse supernova explosion. They burn carbon under degenerate conditions and develop oxygen-neon (ONe) cores. Due to an inverted temperature profile in their innermost regions and the prevailing degeneracy, carbon burning proceeds via off-centre flashes, giving rise to associated convective zones and eventually leading to the inward propagation of the carbon-burning flame. Most super-AGB stars evolve into the thermally-pulsing super-AGB (TP-SAGB) phase and ultimately end their lives as ONe white dwarfs. However, the cores of the most massive ones undergo electron captures on neon and magnesium. Deprived of the electron degeneracy pressure that sustains them, such cores are expected to collapse, triggering an electron-capture supernova (ECSN) explosion. Despite their predictable theoretical framework, super-AGB stars still harbor intriguing mysteries. For instance, no ECSN has been definitively confirmed observationally to date. The exact efficiency of stellar wind mass loss during the TP-SAGB remains highly uncertain, which alters theoretical predictions of ECSN rates. Furthermore, the nucleosynthesis associated with the "dredge-out” (a proton-ingestion episode occurring at the end of core carbon burning in the most massive super-AGBs) remains poorly understood. Finally, recent re-evaluations of carbon-burning rates may narrow the predicted initial mass ranges that lead to ONe core formation, shifting our understanding of the boundary between white dwarf progenitors and supernovae.

Type II Cepheids in the Rubin-LSST Era

• Susmita Das

We present theoretical period-luminosity (PL), period-Wesenheit (PW), and period-radius (PR) relations for BL Herculis stars (the shortest period Type II Cepheids), with a focus on their application to the Rubin-LSST survey. Using non-linear convective MESA-RSP models spanning periods of 1–4 days, metallicities (–2.0 ≤ [Fe/H] ≤ 0.0 dex), masses of 0.5–0.8 M⊙, and the full instability strip, we investigate their multi-wavelength pulsation properties. We find no significant metallicity dependence in the PL relations, supporting a universal PL relation for BL Her stars. To assess the connection between the models and forthcoming time-domain observations, we employ a robust light-curve optimization method to identify best-fitting model-observed pairs for BL Her stars in the Large Magellanic Cloud using the Gaia bands. We also provide the first theoretical predictions in the Rubin-LSST passbands, laying the groundwork for using Type II Cepheids as distance indicators in the Rubin era.

Nonlinear Dynamical Phenomena in AGB and Post-AGB Pulsators

• Emese Plachy (Konkoly Observatory, HUN-REN CSFK)

RV Tauri stars and semiregular variables are among the pulsating stars whose irregular variability has been interpreted as a manifestation of nonlinear dynamical phenomena, including deterministic chaos arising from mode interactions. Evidence for such behaviour has been reported in a small number of objects based on long-term ground-based observations and, more recently, high-precision Kepler photometry. The growing availability of space-based observations opens new opportunities to investigate these phenomena in larger samples. We discuss the potential of TESS and the upcoming PLATO mission for studying nonlinear dynamics and irregular variability in AGB and post-AGB pulsators.

The TESS view of RV Tauri and semiregular variables: coverage, quality and limitations

• Marcell L. Kovács (Hun-Ren Csfk Konkoly Observatory)

The Transiting Exoplanet Survey Satellite (TESS) has accumulated an unprecedented photometric dataset for pulsating stars across the entire sky. RV Tauri stars and a subset of semiregular variables (SRVs) are asymptotic giant branch (AGB) and post-AGB pulsators. The former are characterized by fundamental pulsation with periods of 20–80 days and amplitudes of 1–4 magnitudes, while SRVs often exhibit simultaneous pulsation in fundamental and overtone modes, with periods extending from tens to several hundred days. The scientific value of TESS observations for these stars depends strongly on the available time baseline. While most targets are observed for only a single 27-day sector, stars located in overlapping sectors may be monitored for several months, with coverage approaching one year in the Continuous Viewing Zones (CVZs). Light curve quality further depends on target brightness and source crowding, as well as on the ability to mitigate instrumental systematics. We examine the available data with particular attention to the AGB stars of the Large Magellanic Cloud (LMC), which lies within the southern CVZ and therefore benefits from extended temporal coverage, while also presenting challenges due to severe crowding. Our study aims to provide a practical overview of the strengths and limitations of TESS observations for RV Tauri and semiregular variables and to identify the most promising targets and datasets for future studies of long-period stellar variability.

Searching for tidally excited oscillations in LSP variable stars

• Piotr Kołaczek-Szymański (Astronomical Observatory, University of Warsaw)

One of the leading theories regarding the origin of the long secondary period (LSP) phenomenon in luminous red giants is binarity. In such a scenario, the red giant resides in a close binary system with a substellar object or a very low-mass star. In turn, the radial velocity curves of LSP stars suggest that a potential **companion has an eccentric orbit**. This may lead to the driving of so-called **tidally excited oscillations (TEOs)** in the red giant, which are observed in about 10% of close eccentric binary systems, including those containing evolved stars. TEOs are excited when the periodically varying tidal potential induced by the companion drives pulsations with frequencies coinciding with integer multiples of the orbital frequency. Since the explanation of the LSP phenomenon still remains inconclusive, we decided to search for possible TEO modes in relatively bright LSP stars and identified promising candidate(s). The presence of **TEO modes in LSP variables may serve as another independent piece of evidence supporting the binarity hypothesis** for these variables.

Observing the thermal pulse of RU Vulpeculae

• Balázs Zoltán Kertész (Konkoly Observatory, HUN-REN CSFK)

Low- and intermediate-mass stars experience a series of thermal pulses after reaching the asymptotic giant branch. Currently, three stars are suspected to be undergoing a thermal pulse: the variable stars T UMi, R Hya, and RU Vul. While detailed analyses have already been conducted for the first two, no such modeling has yet been performed for RU Vulpeculae. Since the both the amplitude and period of RU Vul have significantly decreased over the last decades, we started long-term multicolor observations from Piszkéstető Observatory on a weekly basis in January 2022. I extracted five years of standardized photometry of the star and performed a detailed frequency analysis of the pulsation. Based on this, I successfully confirmed our hypothesis that the star has recently transitioned from single-mode into double-mode pulsation. This is fully analogous with the behavior observed in T UMi, which recently began a thermal pulse. Subsequently, I examined the long-term evolution of RU Vul's pulsation period. By utilizing archival observational data, I mapped the evolution of the pulsation period over nearly 130 years, determined the exact time of the onset of the thermal pulse, the rate of period change since then, and the time of first excitation of the first overtone. This work lays the groundwork for modeling the thermal pulse of the star via combined evolutionary and seismic models, which will allow for the determination of several physical parameters, including the mass of RU Vul.

Eppur binaria non é esclusa: Gaia astrometry does not disfavor a binary origin for Long Secondary Periods}

• Patryk Iwanek (Astronomical Observatory, University of Warsaw)

Long Secondary Periods (LSPs) remain one of the major unresolved phenomena among red giant variables. An independent reassessment of the nearby LSP candidates analyzed by Shariat et al. (2026) is presented, based on long-term All Sky Automated Survey (ASAS) photometry and Gaia Focused Product Release (Gaia FPR) radial velocity data. Inspection of 221 candidates within 1.5 kpc from the Sun shows that only 103 objects, or about 47%, exhibit convincing LSP-like behavior, while the remaining stars are more naturally interpreted as semi-regular variables with irregular or multi-periodic pulsations. This substantial contamination limits the usefulness of the sample as a representative sequence-D population. In addition, gaiamock simulations show that even nearby LSP are not necessarily expected to display elevated Gaia RUWE values; therefore, the observed distance–RUWE relation does not provide evidence against the binary interpretation of LSPs.

Multiwavelength characterization of post-AGB binary systems

• Iván Gallardo Cava (Observatorio Astronómico Nacional (OAN-IGN))

The transition from late-stage stellar evolution to circumbinary disk dynamics is nowhere more evident than in binary post-AGB systems. Far from being passive remnants of mass loss, these systems are active laboratories where gas rotation, dust growth, and outflows interact in a complex dance. Our multiwavelength campaign, spanning IRAM-30m, GBT, NOEMA, MeerKAT, and ALMA, unveils the physical and chemical anatomy of these environments. We find a striking radial segregation of dust grains and chemical gradients driven by binary interaction. While MeerKAT observations identify free-free emission from fast disk winds, ALMA’s sub-AU resolution reveals the 'smoking gun' of second-generation planet formation: asymmetric, ring-like structures indicative of dust trapping. A central finding of this work is the identification of a fundamental physical dichotomy. By analyzing the disk-to-total mass ratio, we distinguish between disk-dominated systems, characterized by settled dust and stable Keplerian dynamics, and outflow-dominated sources, where mass ejection prevail. This framework not only explains the observed diversity of post-AGB binaries but also positions these long-lived disks as the definitive cradles where new planets may emerge from the ashes of evolved stars.

Linking stellar parameters and pulsations

• Iain McDonald (University of Manchester)

Pulsations, stellar evolution and instantaneous stellar properties are intrinsically linked by complex physics. Of these, pulsations are the easiest to measure. Here, I will present both the Nearby Evolved Stars Survey's efforts to measure the temperatures, luminosities and mass-loss rates of AGB stars and link them to their stellar pulsations, and my own work on using stellar pulsations to extract statistical masses and ages for AGB stars. By linking these studies together, we can start to empirically bridge some of gaps still remaining in our understanding of AGB stars.

What can mass loss observations and models tell us about the properties of mass-losing AGB stars?

• Henry Prager (University of Iowa)

Asymptotic Giant Branch (AGB) stars are the near-end state of low-to-intermediate mass stars (we have focused on stars between $0.6\ \mathrm{M_{\odot}}$ and $2.0\ \mathrm{M_{\odot}}$). Through combined effects of opacity driven pulsations and dust formation, these stars develop a strong pulsation and dust driven stellar wind and consequently experience significant mass loss, ultimately losing their stellar envelopes and becoming white dwarfs. Surveys of nearby galaxies tell us the observable properties of these mass-losing stars, and ultimately we should be able to replicate the properties of these populations using atmospheric models. We have been investigating the effects of modifying parameters of atmospheric models generated using George Bowen’s atmospheric pulsation code on the properties of the resulting grid of stellar of models. Initial results suggested extreme modifications to both the driving amplitude and dust properties were necessary to produce stars with the observed mass-loss rates at observed luminosities and pulsation periods. However, continued investigation has shown that modification of radius-mass-luminosity and pulsation-mass-radius relations to better match the results of dynamic 3D models of these stars significantly improves agreement between the properties of the modeled atmospheres and observations. Further, these modified constraints lead to self-consistent determinations of which stars should be losing mass from multiple methods. This implies we will need 3D models to correctly determine the relations between stellar mass, luminosity, radius, and pulsation period on the AGB.

Toward 3D Reconstruction of Spiral Structures in Evolved Stellar Envelopes

• Yun-A Jo (Korea Astronomy and Space Science Institute (KASI))

High-resolution interferometric observations have revealed a variety of spiral-shell structures in the circumstellar envelopes of evolved stars, likely linked to binary interaction and asymmetric mass loss. Interpreting the three-dimensional geometry of these expanding structures from position-position-velocity data, however, remains challenging due to projection effects and structural complexity. We present an ongoing effort to develop a tracing framework for identifying coherent spiral features by combining spatial and kinematic information in interferometric data cubes. The goal of this approach is to move beyond qualitative two-dimensional channel-map inspection toward a more systematic characterization of circumstellar spiral structures. In this contribution, we discuss the current status of the methodology, its limitations, and possible future applications to evolved-star systems exhibiting complex envelope morphologies. Such approaches may provide a useful basis for future comparisons with hydrodynamical models and for investigating the role of binary interaction in shaping circumstellar environments.

Spectroscopy of Planetary Nebulae as a Tool for Investigating s-Process Enrichments

• Nicholas Sterling (University of West Georgia, USA)

Planetary nebulae (PNe), the descendants of AGB stars, are characterized by carbon, nitrogen, and neutron(n)-capture element (atomic number Z > 30) enrichments that result from AGB nucleosynthesis. In particular, n-capture elements can be formed via the s-process during the thermally-pulsing AGB, and their abundances hold clues to poorly-understood processes in AGB stars including the treatment of convection, mass loss, and mixing across convective boundaries. Measuring the amount of freshly synthesized n-capture elements emerging from AGB stars constitutes critical input for modeling galactic chemical evolution. Many of the elements observed in PNe (e.g., Se, Kr, Te, and Xe) cannot be detected in AGB stars. These species lie on or near r-process peaks, and nebular abundances provide key information regarding how the s-process contributes to their production in the Universe. In this talk I will discuss results of recent and ongoing investigations that aim to determine accurate and precise abundances of n-capture elements in PNe. Our group has conducted multi-wavelength spectroscopic observations of Galactic and Magellanic Cloud PNe that have detected multiple ionization states of n-capture elements. This reduces uncertainties in correcting for unobserved ions, enabling the determination of accurate elemental abundances and enrichment factors from observations that do not include lines of all relevant ions of a given element. These studies place new constraints on s-process nucleosynthesis in stars with metallicities 10% solar up to solar, and indirectly on r-process enrichments in the present-day Universe.

Beyond the iron peak: Galactic evolution of molybdenum, ruthenium and zirconium through open clusters

• Natalia Alvarez Baena (Università di Roma "Tor Vergata")

Open clusters (OCs) are gravitationally bound stellar systems with masses up to ∼10^4 M⊙ ranging from several hundreds to tens of thousands members, that share between them properties such as age, kinematics and initial chemical composition. This makes them powerful tracers of the chemical evolution of the Galactic disc, as their ages and distances can be precisely determined. As part of the Stellar Population Astrophysics (SPA) project, we analysed high-resolution spectra of 95 giant stars in 32 OCs obtained with the HARPS-N spectrograph at the Telescopio Nazionale Galileo (TNG). We determined the Mo, Ru, and Zr abundances for 81 stars across 30 OCs through spectral synthesis with TSFitPy under LTE conditions. We compare these new chemical patterns with those of key reference elements (Y, Sr, Eu), which were previously derived by our group, aiming to disentangle the distinct contributions from various nucleosynthetic processes. This study provides the first Ru abundances for a large open cluster sample, alongside new measurements for Mo and Zr. We observe tight correlations between Mo, Ru, and other s-process elements (Sr, Y, Zr), with slopes near unity, suggesting common enrichment timescales. Conversely, relations with the r-process element Eu show significant deviations, implying additional nucleosynthetic contributions. Crucially, chemical planes involving [Mo/Ru] and [s/Mo] ratios suggest systematic offsets when compared to theoretical s-process predictions.

Companion-induced dust formation in AGB winds

• Davide Dionese (ULB (Brussels) (main), UW (Warsaw))

The origin of the Long Secondary Period (LSP) phenomenon remains one of the outstanding questions in the study of AGB stars, with binary interactions representing one of the leading scenarios. Three-dimensional hydrodynamic simulations provide a powerful tool for testing this hypothesis by predicting how a companion shapes the stellar wind and the resulting circumstellar environment. We present ongoing developments of a 3D modelling framework based on the SPH code Phantom that follows the interaction between the AGB outflow and a companion while including low-temperature radiative cooling, and dust formation and evaporation. The models allow us to investigate how binary properties, such as orbital separation and companion mass, influence the wind morphology and dust distribution around the system. These simulations provide theoretical predictions that can be directly compared with observations, helping to assess whether binary-induced dusty environments can reproduce the properties observed in LSP systems.

The photometric and spectroscopic monitoring of four LSP variable stars.

• Dorota Skowron (Astronomical Observatory, University of Warsaw)

The mechanism behind Long Secondary Periods (LSPs) in variable red giants remains unexplained, although recent evidence suggests they may be caused by periodic obscuration from a dusty cloud associated with a close-orbiting substellar companion, supported by observations of secondary eclipses in the mid-infrared. As one of the tests of this hypothesis, we conducted a two-year monitoring campaign of four LSP stars exhibiting mid-infrared secondary minima, for which we have collected high quality lightcurves and high-resolution spectra at multiple phases of their LSP variability cycle. We present a phase-dependent analysis of spectral diagnostics tracing the stellar atmosphere and circumstellar environment. These data allow us to investigate the structure, kinematics, and variability of the obscuring material and to assess its consistency with an orbiting dusty structure associated with a substellar companion.

AGB Stars in Sextans A: Linking Dust Production, Chemical Evolution, and Variability at Low Metallicity

• Claudio Gavetti (University of Roma Tre)

The extremely metal-poor dwarf galaxy Sextans A provides a unique laboratory for investigating the evolution of asymptotic giant branch (AGB) stars under conditions resembling those of the early Universe. In this contribution, I present a characterization of the evolved stellar population of Sextans A based on a comparison between JWST photometry and state-of-the-art stellar evolution and dust-formation models. This approach enables a comprehensive characterization of the observed sources, in terms of distribution of mass, chemical composition, and formation epoch of the progenitors, as well as the current evolutionary stage and dust production rate. Although the present analysis is based on single-epoch observations, stellar variability is expected to play a key role in shaping the observed properties of AGB stars and in the interpretation of their luminosities, mass-loss rates, and dust production efficiencies. I will also briefly discuss the possible impact of binary interactions, which may modify mass-loss histories and circumstellar dust properties, contributing to some of the most peculiar dusty sources. In this context, the AGB population of Sextans A offers a valuable opportunity to explore the possible connections between chemical composition, dust production, stellar variability, and binary interaction, contributing to a more comprehensive characterization of AGB populations in galaxies.

The nuances of identifying RV Tauri stars

• Monika I Jurkovic Malagurski (Astronomical Observatory of Belgrade)

RV Tauri stars are a subtype of Type II Cepheids pulsating stars. They are identifiable by their periods, which range from 30 to 150 days and alternating brightness during pulsation. Evolutionary the RV Tauri stars are in a post Asymptotic Giant Branch (AGB) phase. Because they occupy a position on the Hertzsprung - Russell diagram that other stars can cross their identification needs some input. Many RV Tauri stars are found in binary systems which further complicates their light curves. In this talk we will present light curves, luminosities, temperature and finding of dust from spectral energy distribution fittings and possible binary identifications of the RV Tauri stars in the Magellanic Clouds.

Mauve Science Programme: Year 1 Goals & Early Results

• Arianna Saba (Blue Skies Space)

Mauve is a small satellite designed and operated by Blue Skies Space to study stellar activity and variability, exoplanet hosts, hot stars, and exotic populations in binaries. The satellite features a 13 cm telescope and is designed to obtain spectrophotometric data of bright stars across the 200–700 nm wavelength range at a low resolution. Mauve launched on 28 November 2025 and obtained first light on 9 February 2026. The data from the satellite will be delivered through a three-year collaborative science programme, providing researchers with thousands of observational hours each year to perform time-domain astronomy at different timescales. Researchers participating in the science programme define the science goals with flexibility to update the observational plan as and when required. The science themes identified for the first year of operations are available here: https://doi.org/10.1093/rasti/rzag018. During the commissioning phase, Mauve observed multiple targets to characterise early performance and calibrate the instrument. In this presentation, we will showcase the proposed science themes, initial performance of the satellite, analysis and interpretations of the commissioning observations and how to participate in the programme. Learn more about Mauve: https://bssl.space/mauve.

A pilot study of pPNe variability with TESS

• María Rubio Viana (Universidad Complutense de Madrid)

We present a pilot photometric variability study of a sample of 22 evolved post-AGB and pre-planetary nebulae candidates using data from the NASA Transiting Exoplanet Survey Satellite (TESS). These short-lived evolutionary stages are crucial for understanding the morphological and dynamical transformation from asymptotic giant branch (AGB) stars to planetary nebulae (PNe), particularly the role of binarity and pulsations. The analysis was carried out using TESS high precission photometric light curves with a cadence of two-minutes, and different tools were employed to assess the possible contamination affecting the light curves (TESScont, TESS_localize). We inspected and characterized the light curves of the targets in order to identify signatures of periodic variability potentially associated with binarity, pulsations, or other dynamic processes occurring in these objects. Our sample reveals a diverse range of short-timescale variability behaviours, including objects showing binary interactions, stellar pulsations (periodic or stochastic) or a combination of both phenomena. A detailed bibliographic review was also performed for each target to place the observed variability in the context of previous studies and to assess the ppPN/post-AGB classification. This work demonstrates the potential of the TESS photometry mission for studying short-timescale variability in evolved stars during the transition between the AGB and planetary nebulae phases, and provides a set of promising candidates for future spectroscopic and multiwavelength follow-up observations.

Imaging the Origin of RVb Variability in Post-AGB Binary Systems

• Narsireddy Anugu (Georgia State University)

RV Tauri stars are pulsating post-AGB binaries. In addition to their pulsations, many of them show long-term brightness variations known as the RVb phenomenon. This variability is usually explained as variable obscuration of the central binary by a circumbinary disk, but the required binary–disk geometry has not been directly imaged in detail. I will present high-angular-resolution CHARA interferometric observations of RV Tau, U Mon, and AC Her. These observations resolve the inner binary systems and allow us to combine interferometric astrometry with radial velocities to determine their three-dimensional orbits. For RV Tau, we resolve a circumbinary disk whose orientation is consistent with the binary orbit. This geometry explains the RVb variability: as the post-AGB star moves around the orbit, its light passes through different parts of the inclined disk, producing the observed long-term modulation. For U Mon and AC Her, we also resolve compact emission around the companion stars, which we interpret as circum-companion disks. These disks are likely linked to accretion onto the companions and may be connected to jet launching in these systems. Together, these observations show how long-baseline interferometry can directly test the binary–disk picture for RV Tauri and related post-AGB systems.

An Introduction to Alpha Cygni Variables: Space Photometry and Evolutionary Context

• Joyce Guzik (Los Alamos National Laboratory)

Alpha Cygni variables are O-, B-, and A-type supergiants that show low-amplitude irregular or quasi-period photometric variability on timescales of days to weeks. There is not a consensus on their causes of variability or evolutionary state, and they may not be a homogeneous class. 185 alpha Cygni variables are listed in the AAVSO Variable Star Index (VSX), including the well-known bright stars Deneb and Rigel. Because alpha Cygni variables are not strictly periodic, long time-series observations are necessary to characterize their behavior. We will show example light curves from the Transiting Exoplanet Survey Satellite (TESS) and 8.6-year light curves recently processed from the Solar Mass Ejection Imager (SMEI) satellite in Earth orbit between 2003 and 2011. We also discuss the locations of alpha Cygni variables across the upper Hertzsprung-Russell Diagram in relation to other classes of pulsating stars and discuss whether some may have masses and evolutionary states relevant to future evolution into super-AGB stars. Continued study of their photometric variability and stellar parameters may help clarify the causes of their variation and their place in later stellar evolution.

The evolution and formation of ultramassive white dwarf stars

• Ana Carolina Antonini Santa Rosa (UFRGS)

Although the highest possible mass for a white dwarf star (WD) is a well-established limit, known as the Chandrasekhar Mass (Mch = 1.4 M☉), the progenitor mass for such a white dwarf is much more contentious, as differences in the treatment of convection alone can create a variation in progenitor mass of ~2M☉. Furthermore, modeling a sequence through the end of the Super Asymptotic Giant Branch (SAGB) is extremely computationally expensive and requires overcoming several instabilities. Consequently, very few works have been dedicated to modeling the full evolution of ultramassive WDs. And yet, establishing an accurate initial-final mass relation and more fully understanding the characteristics of ultramassive white dwarfs remains imperative if we aim to better constrain the chemical evolution of the Galaxy, the rates for core-collapse supernovae events, and the very nature of type Ia supernovae. In this work, we use the stellar evolution code MESA, in version r24.08.1, to compute the evolution and final fate of stars with initial masses 6-9M☉ and metallicity Z=0.02, from the pre-ZAMS until low luminosities (L < 10^-4 L) in the white dwarf cooling curve. As a result, we find massive and ultramassive WDs with masses ranging from 0.927-1.313M, and either CO (Mwd 1.015M) or ONe (Mwd 1.088M) cores. The 7.5M sequence was the lowest mass explored to undergo carbon burning. At the lower end of our grid (Mwd 1.088M), our models are H-rich, while for masses larger than this, our models are more representative of H-deficient WDs. We discuss and detail each step of the progenitor’s evolution, providing core masses and ages at different stages, carbon ignition and thermal pulse characteristics, as well as crystallization temperatures and cooling ages. This is the first grid of UMWD that accounts for the evolution both during the TP-SAGB stage and post-AGB.

Variability properties of Galactic O- and C-rich AGB stars as seen by Gaia

• Fran Jiménez-Esteban (CAB (INTA-CSIC))

We constructed the 'Gaia Catalogue of Galactic AGB stars', a well-characterized dataset of AGB stars with highly reliable Gaia identifications derived from a meticulous cross-matching procedure. The full catalogue combines several samples originating from different compilations of AGB star candidates, and is representative of AGB stars with both O- and C-rich chemistries. The full sample includes approximately 4,700 O-rich and 3,200 C-rich AGB stars. Using photometry compiled from several catalogues available in the Virtual Observatory, covering the range from the far-infrared to the optical, we constructed the spectral energy distributions (SEDs). Bolometric flux estimates were obtained by fitting the SEDs with theoretical models, and for those sources with reliable parallax measurements in Gaia DR3, we derived their stellar luminosities. Finally, we obtained their variability properties from Gaia DR3 epoch photometry. In this talk, I will present the results of this study, with special emphasis on the comparison between the properties shown by O- and C-rich Galactic AGB populations. We will also discuss the possible period-luminosity-amplitude relationships.

Low-temperature opacity effects on the pulsation properties of carbon-rich AGB stars

• Lynn Buchele (Institute of Science and Technology Austria)

Carbon-rich AGB stars are the primary source of carbon in the universe. Oxygen-rich AGB stars are generally characterized by the presence of TiO in their visible spectra whereas carbon-rich AGB stars present mainly C2 and CN in visible spectra. We present MESA models combined with output from GRYE of advanced AGB stars focusing on the third dredge-up and the enhancement of the C/O ratio. Opacity tables supplied by Ferguson et al. (2005) are based on oxygen-rich abundances and may not be appropriate for carbon-rich environments. As the C/O ratio increases, the amount of H2O decreases in favor of carbon species such as CN, HCN, and CO. This affects the low-temperature opacities in a significant way and impacts other aspects of MESA models. Using GYRE, we compute pulsation periods for different low-temperature opacity calculations to evaluate how parameters such as the stellar age of onset AGB phase and maximum pulsation period changes. Our analysis reveals that systematically varying the initial stellar mass and metallicity induces non-linear trends in period difference and age shift that arise due to changing opacities.

The Evolution of Mira Variables on the Period-Luminosity Diagram -- the Solution to the carbon star mystery

• Riku Urago

We construct a Period-Luminosity (Period-$M_{\rm bol}$) diagram for Mira variables in the Milky Way (MW) and compare it with those in the Large and Small Magellanic Clouds (LMC and SMC) in order to investigate the evolution of asymptotic giant branch (AGB) stars. The sample of MW Miras is taken from the General Catalogue of Variable Stars. Distances are estimated using the 3.4$\mu$m Period-Luminosity relation derived from LMC Miras and calibrated with VLBI parallaxes of MW Miras. The C-rich/O-rich classification is performed using a two-color diagram based on mid- and far-infrared photometry. In the Period-Luminosity diagram, O-rich and C-rich Miras show different distributions. MW O-rich Miras evolve from the Entrance Line, determined by the transition from the first-overtone mode to the fundamental mode, to the Terminal Line, beyond which the stars become optically invisible. O-rich Miras occupy the region between these lines rather evenly. These lines are determined rather sharply, independently of metallicity. In the LMC, the distribution of lower-mass O-rich Miras overlaps that of MW Miras, although the corresponding mass range is significantly different. Stars above the occupation region of lower-mass O-rich stars should become carbon stars through the Third Dredge-Up. In actuality, however, carbon stars are observed at lower luminosities than expected. This is due to extinction caused by the circumstellar dust envelope, and the stars reduce their luminosities through backwarming. This indicates that they do not form as low-luminosity objects but become fainter after becoming carbon stars. This is the solution to the carbon star mystery. The present work reveals that, in studying the evolution of AGB stars, we should properly take into account the effects of dust in the circumstellar envelope.

Equatorial Enhancement in the Dustiest OH/IR Stars in the Galactic Bulge

• Steven Goldman (Space Telescope Science Institute)

AGB stars play a crucial role in enriching the ISM, yet the highest mass-loss phase remains poorly understood. We present mid-IR spectroscopic observations from VISIR on the VLT for 21 of the most luminous and reddened oxygen-rich AGB stars in the Galactic Bulge. All targets exhibit the 10 μm silicate and 11.3 μm crystalline forsterite features in absorption, indicating dusty circumstellar environments. The presence of crystalline features suggests either extended envelopes or high-density dust formation regions. Using radiative transfer modeling of the SEDs combined with 1612 MHz OH maser wind speeds, we find significant discrepancies between observed and modeled outflow properties. The 16 sources with measured pulsation periods also appear on sequence D of the mid-IR period-luminosity relation, associated with the long secondary period.. Taken together, the high optical depths, crystalline features, discrepancies between observed and modeled wind speeds, pulsation periods longer than other fundamental-mode pulsators, and SED and pulsation properties similar to those with known equatorially enhanced circumstellar envelopes (e.g. OH 26.5+0.6) lead us to believe that all of these sources are likely to be equatorially enhanced. We propose that previous estimates of mass-loss rates in these types of stars have likely been overestimated due to inappropriate assumptions of geometry in modeling.

Long secondary periods among J-type carbon stars

• Lea Planquart (Chalmers University of Technology)

About 30% of long-period variables exhibit a long secondary period (LSP) in their light curve. Their origin is still unclear. About 15% of carbon stars are enriched in 13C and lack s-process elements. They are labeled as J-type stars. These chemical peculiarities challenge standard AGB models, suggesting that J-type stars may follow a different evolutionary sequence. In this talk, I will bring these two mysterious a priori unrelated subclasses together. We report, for the first time, the detection of LSP among J-type carbon stars and provided physical constraints on the circum-stellar/-companion environment of a star experiencing a LSP. The dense spectral monitoring has allowed us to characterize the phase-dependent variability in the gas and dust densities along the line of sight. In the binary framework, the current prevailing scenario to explain the LSP, these periodic increases of column density further supported the presence of a trailing structure - such as an expanding wake - created by a close substellar companion. These retrieved quantities and orbital configurations provide material for direct comparison with hydrodynamic simulations of AGB stars with a nearby substellar companion. Furthermore, the detection of LSP among the J-type stars raised new open questions about the impact of binary interactions on their evolutionary status.

A variability census of the 'Bright OH/IR star sample'

• Dieter Engels (Hamburger Sternwarte, University of Hamburg)

Extreme OH/IR stars are in the final phase of Asymptotic Giant Branch evolution, characterised by high mass-loss rates. This gives rise to the creation of circumstellar envelopes of gas and dust of high optical depth, leading to complete obscuration in the optical wavelength range. These stars are likely descendants from intermediate-mass stars, in which hot-bottom burning prevents their conversion to carbon-rich chemistry. This in turn, allows the formation of O-rich molecules, some of them (OH, H$_2$O and SiO) are sources of luminous maser emission. The masers allow to pinpoint these stars across the Galaxy. We recently completed an OH-1612 MHz monitoring program at the Nancay Radio Telescope of about 114 stars making up the 'Bright OH/IR star sample'. We found 82 Mira-like large-amplitude periodic variables with periods of $1.1-6.8$ years, and 30 'non-variable' OH/IR stars showing at most small-amplitude irregular fluctuations. Among the variable stars, 30 OH/IR stars are 'extreme', i.e. their periods exceed 1100 days ($\sim$3 yr). The 'non-variable' OH/IR stars are thought to have left the AGB and entered the early post-AGB phase, while the central stars are not yet visible again. We will discuss the OH/IR star properties in relation to the period-luminosity relation of Mira variables, and in context with current models of AGB evolution and AGB-post-AGB transition.

The GalRSG project: mapping the properties and variability of Galactic red supergiants

• Lorenzo Roberti (INAF-Osservatorio astronomico di Palermo)

We present GalRSG, a new catalogue providing a homogeneous physical characterization of hundreds of Galactic red supergiant (RSG) stars. This dataset stems from a long-term, panchromatic, high-cadence monitoring campaign targeting the Scutum–Crux region with VST@Paranal and REM@La Silla. To derive robust parameters (such as effective temperature, extinction, luminosity, radius, mass-loss properties, and distances), we utilize MCMC-based spectral energy distribution fitting from the optical to the mid-infrared. By combining MARCS stellar atmospheres with DUSTY circumstellar dust models and applying a multidimensional kernel-density analysis to the posteriors, we ensure highly reliable parameter inference. Our analysis reveals that roughly 50% of the sample hosts a dense circumstellar medium, while about 80% of the sources seem to be intrinsically variable. Our observed sample contains a large number of RSGs alongside a substantial population of Asymptotic Giant Branch (AGB) stars, and we will extract detailed light curves for both groups. Having such a rich, dual-population sample provides an excellent opportunity to study massive stars and core-collapse supernova (CCSN) progenitors, while directly mapping the physical and observational boundaries that separate them. In particular, some of the RSGs in our sample may actually be precursors to massive AGB stars, still residing in their core helium-burning phase. This high prevalence of dynamic circumstellar environments underscores why systematic, high-cadence monitoring is vital to separating classical stellar pulsations from genuine, pre-collapse anomalies across both populations.

Constraining AGB binary properties using full 3D spatially resolved radiative transfer

• Olivier Verhamme (KASI)

Spatially resolved observations have shown that AGB stars are frequently accompanied by spiral dust rings. These observed structures have been reproduced with hydrodynamical (HD) models by introducing a secondary star into the system. However, for almost all of the observed AGB stars with spiral structures we are lacking constrained binary parameters such as the secondary mass, inclination, position angle, etc. Previous spectral studies on these type of stars have been performed but usually assume spherical symmetry. This overlooks the asymmetry in the abundance profiles caused by the binary and does not address the spiral structure surrounding these stars. We perform detailed 3D radiative transfer on full 3D HD models and fit the resulting spectra to spatially resolved ALMA observations of CO, 13CO, SiC, ans SiS spectral lines. As the spiral is computed self-consistently in the HD model, the spatially integrated spectral lines give us limits on the inclination and position angle of the system. Moreover, by fitting the spectral data of different spatially resolved subregions we can get a full 3D map of the molecular abundance. The presence or absence of certain molecules indicates the UV emission of the secondary, strongly constraining the type (main sequence, red/white dwarf) and mass of the secondary. We will show the results of this highly in-depth radiative transfer modelling on the binary AGB-star AFGL 3068.

Binary stellar nucleosynthesis at the population level

• Alex Kemp

Binary stellar evolution is an intrinsic part of our universe, and it is increasingly clear that we ignore it to our peril. One aspect of stellar astrophysics that remains heavily reliant on single stellar evolution models is that of galactic chemical evolution, where our understanding continues to rely almost exclusively on stellar yields computed from models of single stars, especially for low mass stellar evolution. In this talk, I will present a brief overview of the current state of the art of binary stellar nucleosynthesis, highlighting the work that I am about to undertake at Konkoly Observatory.