Abstracts

Parallaxes and Proper Motions of Long Period Variable Stars Determined from VLBI and Gaia DR3

Nakagawa Akiharu, Kurayama Tomoharu, Sudou Hiroshi, Orosz Gabor

Annual parallaxes of Galactic long period variable stars (LPVs) are essential for determining their distances and intrinsic properties, but their measurement remains challenging because of their large stellar sizes, circumstellar matter, and time-variable surface brightness asymmetry. In this study, we compare astrometric measurements obtained from very long baseline interferometry (VLBI) and Gaia Data Release 3 (DR3) for 43 Galactic LPVs. The parallaxes from the two methods are generally consistent within uncertainties for about half of the sample, although Gaia DR3 parallaxes tend to be slightly smaller than the VLBI values. This is consistent with previously reported systematic offsets. The behavior of parallax uncertainties differs between the two techniques: VLBI parallax errors increase with increasing parallax, whereas Gaia DR3 errors remain nearly constant. Consequently, VLBI measurements are more effective for LPVs with parallaxes smaller than approximately 2 mas, corresponding to distances beyond 500 pc. Proper motions are also compared, showing general agreement with a 2-sigma dispersion of approximately 13 km s−1, consistent with typical AGB outflow velocities. These results demonstrate the complementarity between VLBI and Gaia astrometry. We also find that the dispersion of parallax residuals becomes slightly larger for sources with pulsation periods around one year, suggesting a coupling of timescales between the stellar pulsation and the annual parallax.

Reference : 2026 Galaxies, 14, 26
URL : https://www.mdpi.com/2075-4434/14/2/26

Crystallization of stardust analogs under an electron flux atmosphere

Shohan Rakibul A, Cly Cody, Speck Angela, Sargent Benjamin, Nuth III Joseph A, Whittington Alan, Ponce Arturo

Abstract
The atomic microstructural evolution of circumstellar dust grains, which seed the interstellar medium, remains poorly understood. Amorphous alumina and its crystalline polymorphs, including corundum, have been found in the circumstellar shell of evolved stars. Evidence includes both astronomical observations of mid-infrared spectroscopic features and laboratory analyses of presolar grains. In this work, we show that electron fluxes can stimulate crystallization of amorphous alumina stardust analog materials using transmission electron microscopy (TEM). Crystallization experiments conducted at varying electron energies and flux conditions demonstrate a critical threshold cumulative electron dose of approximately 1024 e-/m2 for crystallization, suggesting that the crystallization process can occur through atomic rearrangement due to electron interaction with the amorphous matrix. Throughout the crystallization process, time-resolved diffraction reveals the transition from amorphous to a transitional η-Al2O3 phase. The same transitional phase was confirmed to occur via thermal annealing at 800C, while annealing at 1300 C produced the stable crystalline phase α-Al2O3 (corundum). In both processes, the structural evolution through atomic rearrangement was characterized by quantifying average interatomic distance between neighboring atoms using the electron pair distribution function analysis. Extrapolating to astronomical timescales, our findings suggest that electron bombardment may play a significant role in the crystallization of stardust grains, highlighting its potential importance in astrophysical environments, such as the circumstellar envelopes of planetary nebulae.

Reference : 2026 PNAS Nexus, ,
URL : https://academic.oup.com/pnasnexus/advance-article/doi/10.1093/pnasnexus/pgag095/8586729

Ages and masses of asymptotic giant branch stars from the period-luminosity diagram

I. McDonald

A method of determining ages and masses of asymptotic giant branch (AGB) stars between 0.8 and 6 solar masses is demonstrated, based on comparing the star’s position in the period—absolute-magnitude diagram to theoretical evolutionary models. For samples of Milky Way stars, the method provides errors (statistical and systematic, respectively) of order of +29/-35 and +/- 15% in age, +14/-7 and +/- 7%in initial mass and +17/-11 and +/- 27% in current mass. However, its applicability to individual stars depends strongly on both their position in the P-L diagram and the uncertainty of that position. This method is applied to published samples of AGB stars from the Gaia, NESS, DEATHSTAR and ATOMIUM surveys. These surveys’ statistical ensembles are compared to expectations from stellar evolutionary models, finding that most AGB samples are biased towards stars of younger ages and higher masses. An average mass for Milky Way AGB stars is found to be 1.1 solar masses, while mass returned to the interstellar medium by AGB stars typically comes from 1.2 solar-mass stars with mass-loss rates of order 2-3 x 10^-6 solar masses per year.

Reference : Accepted in MNRAS
URL : https://arxiv.org/abs/2604.10656

M1-92: Asymptotic giant branch interruption and isotopic ratio paradox. Chemistry and morpho-kinematics from improved shapemol modelling

Masa E., Alcolea J., Santander-García M., Bujarrabal V., Sánchez Contreras C., Castro-Carrizo A., Steffen W., Koning N.

The shaping of planetary nebulae on their evolution from asymptotic giant branch circumstellar envelopes to their final, most often axisymmetrical, form is still a process with many unknown details. The key to understanding the whole shaping process is the study of the transition objects called pre-planetary nebulae (pPNe). In this context, modelling tools must be kept to the standard of radio telescope capabilities, so we can make the most of the data they collect.
In this work we first present the newest update of the and modelling tools, adding ten new molecular species to be reproduced together with other general improvements. Later, we put this new update into practice to study a pPN with a rich chemistry that can provide valuable information on its origin and shaping.
We created a 3D morpho-kinematical model of the nebula in that is able to reproduce 23 line profiles from the IRAM 30m telescope and HIFI/HSO and five maps from IRAM NOEMA. The observational dataset is reproduced simultaneously under the same physical conditions, adjusting only the relative abundance of the different species.
We obtained a full description of the nebula’s physical and chemical properties, and we provide the total estimates for mass (0.79 linear momentum (4.10 $), and kinetic energy (6.48$ erg) as well as their detailed distribution across the nebula. We also analysed the isotopic ratios, finding robust discrepancies (values of 10 versus 30) in the g·cm·s -1 45 ratio across structures depending on their age.

Reference : 2026 Astronomy & Astrophysics, in press
URL : https://www.aanda.org/10.1051/0004-6361/202555741

VLTI-GRAVITY measurements of cool evolved stars: II. Pulsation properties and mass-loss process of the Mira star R Car and the red supergiant VX Sgr

Jadlovský, D., Wittkowski, M., Chiavassa, A., Kravchenko, K., Freytag, B., Höfner, S., Krtička, J., Paladini, C., Rau, G., Brož, M., Granzer, T., Weber, M.

The mass-loss process of red supergiant (RSG) and asymptotic giant branch (AGB) stars and its relation to variability is poorly constrained. We study two evolved stars, the Mira-type AGB star R Car and the extreme RSG VX Sgr. Our sample comprises 54 VLTI-GRAVITY snapshots taken over 7 years, being the largest VLTI time-series dataset to date. We determine the angular diameter as a function of time. The radii of the photosphere ($R_\star$) and atomic atmospheric layers are variable and relate to the light curve with phase shifts, showing a maximum radius near visual brightness minima. The more extended CO layers show longer, irregular periods and maximum extensions of $\sim 1.3-1.7 \: R_\star$ for R Car, and of $\sim 1.5-2.2 \: R_\star$ for VX Sgr. Comparison with CO5BOLD simulations revealed a similar behavior. Furthermore, during 2020-2021, VX Sgr exhibited an extreme mass-loss event similar to that of Betelgeuse, preceded by two strong shocks and culminating with the extreme expansion of H$_2$O and CO layers, both up to $\sim 2.2 \: R_\star$. During this event, we detected Brackett $γ$ and Balmer emission lines, both of which are signatures of a shock propagating through the atmosphere. The Mira R Car showed a photospheric radius $R_\star = 280 \pm 25 \: \rm R_\odot$, with a fundamental mode (FM) pulsation amplitude $\sim13 \%$ of $R_\star $. During its active cycle, the RSG VX Sgr showed $R_\star = 1556 \pm 110 \: \rm R_\odot$ with FM amplitude $ \sim13 \%$ of $R_\star $, the same as R Car. During its quiescent cycle, it showed $R_\star= 1456 \pm 108 \: \rm R_\odot$ and low-amplitude pulsations near the first overtone, only $\sim4 \%$ of $R_\star $. This supports a steady mass loss for Miras related to stable, large-amplitude FM pulsation, whereas the mass-loss process for RSGs may be dominated by extreme events connected to changes in the pulsation mode.

Reference : 2026 Accepted for publication in A&A
URL : https://arxiv.org/abs/2604.21621

HST-STIS Spectra of Antares (α Scorpii: M1.5 Iab)—Type II Supernova Progenitor and Betelgeuse’s Chromospheric Twin

Graham M. Harper, Thomas R. Ayres, Keiichi Ohnaka, Edward F. Guinan, and Curtis DeWitt

We present the first Hubble Space Telescope - Space Telescope Imaging Spectrograph (HST-STIS) far-ultraviolet (FUV) and near-ultraviolet (NUV) high-resolution spectra of the red supergiant (RSG) Antares (M1.5 Iab), isolated from its long-period B-star binary companion, and compare them to spectra of Betelgeuse (M2 Iab) to assess the similarities and differences in chromospheric heating and atmospheric dynamics. While Betelgeuse has two well-known circumstellar CO outflows, previous radio and infrared observations of Antares did not detect the presence of circumstellar CO. The Antares FUV STIS spectra reveal CO electronic Fourth-Positive absorption bands formed exterior to the chromosphere. The derived column density is 4 orders of magnitude smaller than the CO MOLsphere located interior to 1.7R*. The numerous NUV Fe II emission lines show classical wind-scattering profiles, with velocities close to the star of v(wind) ≃ 19 km s−1, consistent with that previously inferred from absorption spectra observed against the B star at a projected radius of ∼150R*. Surprisingly, the NUV semi-forbidden emission lines show evidence of wind scattering, indicative of the massive column densities present in the winds of low-surface-gravity RSGs. Differential comparison with Betelgeuse of chromospheric fluxes from emission lines excited by electron collisions, electron collisions combined with photospheric photoexcitation, and coincidental line pumping reveals similar levels of chromospheric heating. C ii] indicates comparable chromospheric electron densities and column densities. With its well-constrained distance and stellar parameters, Antares provides a good source for understanding the processes driving RSG outflows. Chromospherically, Antares is effectively a twin of Betelgeuse.

Reference : 2025 ApJ 1002, 80
URL : https://iopscience.iop.org/article/10.3847/1538-4357/ae581b

Evolving low- and intermediate-mass binaries: Departures from classical theory

Siess Lionel

This review explores the physical mechanisms driving the evolution of low- and intermediate-mass binary star systems, with particular emphasis on emerging mechanisms that challenge classical paradigms. We begin by describing the principal formation channels and orbital properties of binary systems. A critical reassessment of the Roche lobe formalism is presented, focusing on systems with eccentric orbits and asynchronous rotation, where deviations from traditional approximations become significant. We then review current theoretical models of mass and angular momentum exchange via Roche-lobe overflow, incorporating results from recent hydrodynamical simulations of wind accretion. The review also reports advances in tidal dissipation theory. Finally, we explore mechanisms capable of sustaining or exciting orbital eccentricity, including perturbations induced by mass transfer and interactions with circumbinary disks. These discussions aim to outline underexplored facets of binary evolution, offering new perspectives for theoretical and observational studies.

Reference : 2026 New Astronomy Reviews, 102, 101748
URL : https://linkinghub.elsevier.com/retrieve/pii/S1387647326000023

Annoucements

AGB stars and stellar pulsation workshop announcement

Dear All,

I am pleased to announce that the registration and abstract submission is open for the AGB stars and stellar pulsation workshop. The event will be held in hybrid form, on zoom and in person at Konkoly Observatory in Budapest, Hungary, 5-7 October 2026.

The aim of the workshop is to bring together researchers from the different fields of AGB and stellar pulsation to discuss the open questions related to AGB stars, especially connecting their variability and different classifications.
Registration and abstract submission is open until 31th May at the workshop webpage: https://indico.global/event/16549/
If you have any questions regarding the workshop, you can contact us at agbpulsation2026@konkoly.hu

Please feel free to forward this announcement to anyone who may be interested.

Best regards,
Borbála Cseh
On behalf of the organizing committee

First Announcement - Solvay-Torino XV Workshop on AGB Stars (May 2027)

Dear colleagues,

We are pleased to announce the next edition of the Torino Workshop: the Solvay–Torino XV Workshop on AGB Stars.
The workshop will take place in Brussels, Belgium, from 24 to 28 May 2027.

The Solvay–Torino XV Workshop on AGB Stars will bring together researchers working on the physics, nucleosynthesis, and observational properties of AGB stars and related evolved phases. The meeting will provide a focused forum to discuss recent advances in stellar evolution, mixing, heavy-element production, mass loss, binary evolution, and the broader role of evolved stars in Galactic chemical evolution.

The conference website is: https://fys.kuleuven.be/ster/events/conferences/2027/solvay-torino-workshop

To stay updated with future announcements, please complete the Early Mailing List form available on the website in order to be added to the mailing list. Further information on the scientific programme and registration will be circulated through that mailing list in due course.

We would be grateful if you could also forward this announcement to colleagues who may be interested.

We look forward to welcoming you to Brussels.
The Organising Committee