Abstracts

Astrometric modeling of unresolved variable binary systems. II. Application to Gaia epoch astrometry of nearby pulsating and convective red giants

L. Decin, K. Sivkova, P. Kervella, A. Chiavassa, E. Beguin

(Abbreviated) The interpretation of high-precision astrometry for intrinsically variable stars remains challenging, particularly for unresolved binary systems containing asymptotic giant branch (AGB) stars. In such systems, large-amplitude pulsations and evolving convective surface structures induce time-dependent photocentre displacements that perturb the observed orbital motion. At the same time, Gaia DR4 epoch astrometry offers the prospect of deriving accurate orbital solutions and parallaxes for nearby unresolved AGB binaries.
Building upon the variability-induced mover (VIM) framework, we extend the astrometric model for unresolved evolved binaries by combining Keplerian photocentre motion, pulsation-induced flux-dependent photocentre shifts, and convection-induced photocentre motion. In the forward simulations, convection is represented either by stochastic photocentre displacements drawn from an exponential correlation function or by photocentre time series extracted from 3D radiation-hydrodynamic simulations. We then test a retrieval framework that fits the orbital and VIM signal while incorporating a red-noise covariance matrix to account for correlated astrometric residuals produced by convection. We show that Gaia epoch astrometry can recover reliable orbital and astrometric parameters for unresolved AGB binaries despite strong pulsation- and convection-induced photocentre variability. Pulsation-induced variability produces a coherent VIM signal that can be modeled jointly with the Keplerian photocentre orbit, while convection-induced photocentre motion behaves primarily as temporally correlated astrometric noise. Retrievals that ignore this correlated component lead to biased proper motions and parallaxes, whereas the inclusion of a physically motivated red-noise covariance model enables accurate recovery of the underlying orbital solution and astrometric parameters.

Reference : accepted for publication in A&A
URL : https://ui.adsabs.harvard.edu/abs/2026arXiv260830641D/abstract

On the Origin of a Dusty Circumstellar Medium around Red Supergiants

Sujit, Das, Sarangi, Arkaprabha, Sengupta, Sutirtha

Red supergiant (RSG) stars are widely recognized as significant sources of dust, enriching the interstellar medium. However, the physical conditions that regulate dust nucleation in their winds remain poorly constrained. We investigate the formation of molecules and dust in RSG and explore how enhanced mass loss can produce a dense, dust-rich circumstellar medium (CSM) before core collapse. We couple time-dependent mass loss with non-equilibrium chemistry to model the formation of molecules and dust precursors using mass loss rates ranging from 10^−6 to 10^−2 M⊙ yr^−1 and both constant and accelerating wind profiles. Molecules such as CO, H2O, SiO, HCN, CS, SO, NH3, H2, and O2 form efficiently in the CSM, with masses varying between 10^−15 – 10^−2 M⊙. O-rich dust, namely silicates and alumina, dominates the dust composition. The total dust mass ranges between 10^−8 and 3×10^−3 M⊙. Accelerated winds produce more dust and allow dust formation closer to the stellar surface. The resulting fluxes exhibit strong mid-infrared excesses. The 9.7 and 18 µm silicate features appear in either emission or absorption depending on the optical depth of the circumstellar medium. The time dependent mass-loss history of our SN 2023ixf progenitor models results in a gradual increase in CSM dust mass toward explosion. A clumpy CSM provides a substantially better match to the observed optical and infrared fluxes, demonstrating the importance of time-dependent mass loss, CSM structure, and wind acceleration in shaping the observable properties of red supergiant progenitors.

Reference : 2026 Submitted to The Astrophysical Journal
URL : https://arxiv.org/abs/2608.28344

Accretion in Binary Systems with Slow Stellar Winds

J. A. Toalá, E. Tejeda, R. F. Maldonado, and D. A. Vasquez-Torres

Wind accretion in binary systems is commonly described using the Bondi–Hoyle–Lyttleton (BHL) formalism. However, its standard implementation fails in the slow-wind regime, where the wind velocity of the donor star (Vw) is comparable to or smaller than the orbital velocity of the accretor (Vo). Tejeda & Toalá recently proposed a geometrical correction to the BHL formalism that accounts for the wind aberration caused by the binary’s orbital motion, which tilts the accretion cylinder and reduces its effective cross-section. Here we present a suite of smoothed particle hydrodynamic simulations performed with PHANTOM to test the geometric correction to the wind accretion in binary systems, with particular interest in systems operating in the slow-wind regime. We explore circular configurations and directly measure mass accretion efficiencies from the simulations. Our results confirm that the standard BHL prescription systematically overestimates accretion rates for Vw / Vo < 1, while the geometrically corrected model agrees with the simulated efficiencies with remarkable accuracy. A key finding is that the velocity relevant for accretion estimates is not the value derived from the unperturbed stellar wind, but the local gas velocity measured upstream of the accretor. The gravitational potential of the accretor perturbs the flow, altering the effective relative velocity and modifying the accretion efficiency, particularly for compact orbits. These results provide strong numerical support for the geometrically corrected framework and establish a physically motivated basis for modeling wind-fed accretion in interacting binaries, including symbiotic systems.

Reference : Accepted to Revista Mexicana de Astronomía y Astrofísica
URL : https://arxiv.org/abs/2603.01090

An extensive grid of DARWIN models for M-type AGB stars II. Effects of pulsation periods on wind properties

E. Siderud, K. Eriksson, S. Höfner and A. Ahmad

Mass loss from asymptotic giant branch (AGB) stars is the result of a complex interplay between pulsation, atmospheric dynamics, dust formation, and radiative acceleration. Pulsation periods are a key input in dynamical atmosphere and wind models, and different prescriptions for assigning periods based on stellar parameters may lead to systematic differences in the predicted wind properties. To better constrain this critical parameter, we investigated how the choice of pulsation period affects the wind properties of dynamical atmosphere and wind models of M-type AGB stars by comparing models based on an empirical period-luminosity (P-L) relation with corresponding ones that adopt a period-mean density relation derived from 3D pulsation models. We analysed two grids of DARWIN models that cover a range of current stellar masses, luminosities, and effective temperatures. For each grid, pulsation periods were assigned using either the P-L relation or the period-mean density relation, allowing for a direct comparison of the resulting dynamical structures and wind properties for pairs of models differing by period only. Independent of the adopted period prescription, the time-averaged wind properties correlate strongly with L⋆/M⋆. The pulsation period affects the atmospheric dynamics through changes in the relative timing of shock propagation and dust formation, which affect both wind formation and the resulting wind properties. Shorter periods favour the onset of a wind, and models differing only in pulsation period can exhibit significantly different wind properties. The period-mean density relation provides a physically motivated alternative to the empirical P-L relation by accounting for stellar parameters beyond luminosity, and enables a more direct comparison between DARWIN models and observed Mira variables.

Reference : A&A, Volume 713, September 2026, A210, 11 pages
URL : https://www.aanda.org/articles/aa/full_html/2026/09/aa60957-26/aa60957-26.html

A near-IR survey of luminous asymptotic giant branch stars in the satellites and stellar halo of M31

Jess M. Howell, Annette M. N. Ferguson, Olivia C. Jones, Mike J. Irwin, Maria-Rosa L. Cioni, Geraint F. Lewis, Nicolas F. Martin, Alan W. McConnachie

We investigate the dwarf spheroidal (dSph) satellites and stellar halo of M31 using near-infrared imaging from the Wide-Field Camera on the UKIRT 3.8 m telescope. Our homogeneous analysis covers the stellar extents of 12 dSphs, as well as their surrounding halo field populations. We identify carbon-rich (C) and oxygen-rich (M) thermally-pulsing AGB stars (TP-AGBs) using colour-magnitude and colour-colour diagrams, which also allows for effective contaminant rejection. TP-AGB stars are detected in eight of the 12 dSphs, indicating small intermediate-age populations in a substantial fraction of the sample; they are also found in considerable numbers throughout most of M31’s stellar halo. By combining 316 new detections with a revised classification of objects previously reported in the literature, we increase the TP-AGB candidate population in the dSphs from 82 to 359. We use the resulting dSph and halo AGB samples to compute C/M ratios and infer metallicities in the dSphs and adjacent halo fields with non-zero AGB counts. A clear metallicity gradient is observed in the M31 stellar halo out to 150 kpc, consistent with that found using other tracers. Using literature star formation histories from main-sequence turn-off photometry, we find a tight correlation between the number of C stars in the dSphs and the stellar mass formed in the last 0.5—3 Gyr. This study underscores the promise of AGB stars as quantitative tracers of intermediate-age star formation, particularly in intrinsically faint systems, and provides a catalogue of candidate TP-AGB stars for follow-up.

Reference : Accepted by MNRAS
URL : https://arxiv.org/abs/2609.20810

Annoucements

Wing emission lines in cool, evolved stars, revisited.

Progress in ultra-high resolution near-UV spectroscopy has enabled for a re-examination of so-called “wing emission lines” that appear in the broad absorption wings of the Ca II H & K lines, initially seen in cool, lower gravity stars [1]. In recent years, ESO’s Ultraviolet-Visible Spectrometer (UVES) has assembled an outstanding archive of cool evolved star spectra, observed with resolution of 65,000 and higher [2].
In comparison with older, photographic era spectra, these newer digital data reveal not only wing emission line profile details, but also wavelength shift anomalies that potentially distinguish some features from underlying absorption components only seen in higher gravity cool stars.
Similar features are seen in the solar spectrum as emission reversals near the solar limb, due to line of sight optical depth and chromospheric temperature reversal. Hypothetically, the extended atmospheres of evolved stars could result in ‘limb emission’ seen across the entire stellar disk, and as such, trace convection-related inhomogeneities. Narrow-band spectro-interferometric instrumentation and methods have advanced sufficiently to allow for examination of this possibility.
Signing off, with my gratitude, to the cool evolved star research community. – Robert.Stencel@du.edu, 2026.
Co-Editor of the 1987 Cool Stars 5 Workshop, Boulder - https://link.springer.com/book/10.1007/3-540-18653-0
[1] Stencel, R. 1977, http s://ui.adsabs.harvard.edu/abs/1977ApJ...215..176S/abstract
[2] UVES data, https://archive.eso.org/scienceportal/
.

Opening the vault: KU Leuven launches the HERMES spectral archive to the global astronomy community

The Institute of Astronomy at KU Leuven announces the public release of the HERMES spectral archive, opening more than 16 years of high-resolution stellar observations to the international scientific community. With roughly 150.000 science-grade spectra now available, the archive represents one of the most extensive and homogeneous collections of high-resolution optical spectra assembled to date. The data were collected with the HERMES spectrograph on the 1.2-m Mercator Telescope, located at the Roque de los Muchachos Observatory on La Palma (Spain), and form one of the cornerstones of KU Leuven’s contributions to stellar astrophysics over the last 16 years.

The HERMES archive can be accessed via the web interface at https://mercatorvo.ster.kuleuven.be/hermes/q/web/form or through Virtual Observatory tools at https://mercatorvo.ster.kuleuven.be/tap.

More information can be found here.

Solvay-Torino XV Workshop on AGB Stars: Registration and Abstract submission open

Dear colleagues,

We are pleased to announce that abstract submission and registration are now open for the Solvay–Torino XV Workshop on AGB Stars, which will take place in Brussels from 24–28 May 2027.
Please visit the conference website for further details: https://fys.kuleuven.be/ster/events/conferences/2027/solvay-torino-workshop

The abstract submission deadline is 1 December 2026, while registration and payment will remain open until 31 January 2027.

We very much hope to welcome many of you to Brussels!

Kind regards,
LOC team

ESO/ALMA Fellowship Programme 2026 / 2027

ESO’s prestigious postdoctoral fellowship programme in both Garching (Germany) and Santiago (Chile) offers outstanding early-career scientists the opportunity to further develop their independent research programmes. From exoplanets to cosmology, observational, theoretical and fundamental astrophysics, these are all areas where ESO Fellows can benefit from a highly dynamic scientific environment, at some of the most advanced ground-based telescopes in the world. Do watch ESOCast 165 to hear what previous ESO fellows have to say about the fellowship programme or watch the virtual tour to ESO’s premises from 2020 or https://www.youtube.com/watch?v=dK4q_OLvZ7Q where young scientists could ask questions about the fellowship programme.

Located in one of the most active research centres in Europe, the three-year long Garching fellowship offers plenty of opportunities to start new collaborations. Fellows are expected to engage in functional work for up to 25% of their time, equipping them with essential professional skills in diverse areas.

Fellows in Chile, on the other hand, interact with visiting astronomers from all areas of research and can easily collaborate with the Chilean astronomical community or with astronomers at other international observatories in the country. ESO Fellows in Chile contribute to ALMA or VLT duties up to a level of 80 nights per year during the first three years, while the fourth year is dedicated exclusively to scientific research.

Candidates are asked to apply online through the ESO Recruitment Portal. The application must be done using the ESO Application Form. Separate application forms must be completed for Garching and Santiago fellowships. The closing date for the 2026 fellowships is 15 October 2026.

1st announcement: ALMA at 15 years conference open for abstract submissions

1st announcement: ALMA at 15 years conference

Rationale
We are pleased to announce that the international conference "ALMA at 15 Years: Science, Synergies, and the Road Ahead" will be held in person from Feb. 22–26, 2027, at Academia Sinica’s Nangang campus in Taipei, Taiwan. The conference will highlight ALMA’s latest results, especially since the last Pan-ALMA conference held in 2023 and identify exciting directions for future ALMA research.

The program will feature invited and contributed science presentations, along with updates on the Wideband Sensitivity Upgrade (WSU), tutorial sessions on the archival and CARTA systems, and discussions of future ALMA prospects. Talks and posters presenting scientific work using ALMA and/or its synergies with other facilities across all areas of astronomy are welcome. Please visit the official conference website: https://2027alma.org

Important Dates
Abstract Submission Opens: June 15, 2026
Abstract Submission Deadline: September 15, 2026
Early-Bird Online-registration Opens: September 30, 2026
Notification of Abstract Acceptance: Late Oct./Early Nov., 2026
Early Bird Online-registration Deadline: November 27, 2026
Online Registration Deadline: January 20, 2027

SOC
John Carpenter (JAO, Chile), Paola Caselli (MPE, Germany), Marilyn Cruces (UC Chile, Chile), Leen Decin (KU Leuven, Belgium), Maria Diaz Trigo (ESO, Germany), Bunyo Hatsukade (NAOJ, Japan), Rodrigo Herrera-Camus (Universidad de Concepción, Chile), Jongsoo Kim (KASI, Korea), Lihwai Lin (ASIAA, Taiwan; Chair), Leslie Looney (UIUC, USA), Brett McGuire (MIT, USA), Jennifer Donovan Meyer (NRAO/NAASC, USA)

LOC
Cindy Chiu (ASIAA), Tien-Hao Hsieh (TARA), Sheng-Jun Lin (ASIAA), Yu-Nung Su (ASIAA), Ya-Wen Tang (ASIAA), Wei-Hao Wang (ASIAA; Chair)

Contact
Should you have any further inquiries, please feel free to contact the ALMA 2027 Abstract Submission & Registration Office (email: reg@2027alma.org)

We look forward to seeing you in Taipei!

Best regards,
Lihwai Lin (on behalf of SOC)