Abstracts

A phoenix rises from the ashes: WOH G64 is still a red supergiant, for now

van Loon Jacco Th, Ohnaka Keiichi

ABSTRACT
For a long time, WOH G64 was known as the most extreme red supergiant outside our Galaxy. However, in a matter of years it has faded, its pulsations have become suppressed and the spectrum has become dominated by emission lines from ionized gas, a far cry from the Mira-like pulsation and late M-type spectrum it used to display. Around the same time, a hot dust cloud was discovered using the Very Large Telescope interferometer. WOH G64 has been claimed to have turned into a yellow hypergiant, which could signal a pre-supernova post-red supergiant evolution. Here we present spectra of WOH G64 obtained with the Southern African Large Telescope between November 2024 and December 2025. Molecular absorption bands from TiO are seen at all times. This implies that WOH G64 is currently a red supergiant and may never have ceased to be. However, the shallow, resolved bands and possible detection of VO hint at a highly extended atmosphere. The continuum appears to be varying, while the line emission shows a different behaviour, suggesting two separate components in the system. Meanwhile, atomic absorption lines are deepening. This places important constraints on scenarios for the dramatic events that are unfolding.

Reference : 2026 Monthly Notices of the Royal Astronomical Society (Letter), 546, 12
URL : https://academic.oup.com/mnras/article/doi/10.1093/mnras/stag012/8416424

A surprisingly large asymmetric ejection from Mira A

Khouri T., Vlemmings W. H. T., Raudales Oseguera D. A., Tafoya D., Olofsson H., Maercker C. Paladini M., Saberi M., Gorai P., Danilovich T.

Stars with masses between roughly 1 and 8 M_⊙ end their lives on the asymptotic giant branch (AGB), when intense mass loss takes place, with major consequences for the chemical evolution of the universe. The mechanism responsible for the outflows is generally accepted to be radiation pressure acting on dust grains that form in the dense extended atmospheres of AGB stars. Dust formation is enabled, or at least dramatically enhanced, by the action of convection and stellar pulsations. The complex physics underlying convection, stellar pulsations, and dust nucleation precludes predicting AGB mass loss from first principles.
Our aim was to characterize the recent mass ejections of the AGB star Mira A using observations of the inner envelope. In particular, we studied two lobes observed to be expanding away from Mira A to obtain empirical insights into the mass-ejection process.
We investigated the evolution of the lobes using images of polarized light obtained at six epochs using the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) on the Very Large Telescope and of molecular emission at two epochs obtained with the Atacama Large Millimeter/submillimeter Array (ALMA). Six lines of SO_2 were used to investigate the excitation temperature and column density of SO_2 in the lobes. We used the 13 CO J=3-2 line and radiative transfer models to constrain the column density of the gas, which allowed us to infer the abundances of SO, SO_2, AlO, AlF, and PO in the lobes.
While dust seems confined almost exclusively to the edges of the lobes, gas fills the lobes and displays higher densities than expected at the observed radial distances based on the large-scale mass-loss rate of Mira A, with a total gas mass in the lobes of ∼ 2 M_⊙. We find the expansion of the lobes to be consistent with both a constant velocity (ejection time in 2010 or 2011) or a decelerating expansion (ejection time in 2012). If ejection events with a similar magnitude happen periodically, we derive periods between 50 and 200 years to account for the mass-loss rate of Mira A. This periodicity is very uncertain because of the complexity of the circumstellar environment that hampers accurate determinations of the mass-loss rate. We find abundances in the lobes of ∼ 1.5 and ∼ 2.5 for SO and SO_2, respectively, when accounting for radiative transfer effects and of 2 10^ -5 10^ -6 10^ -6 6.5 and 4 for AlO, AlF, and PO assuming LTE and optically thin emission. The strong variation in brightness of the different features identified in the polarized-light images is puzzling. We suggest that an asymmetric stellar radiation field preferentially illuminates specific regions of the circumstellar envelope at a given time, producing a lighthouse-like effect.

Reference : 2026 Astronomy & Astrophysics, in press, arXiv:2602.03159
URL : https://www.aanda.org/10.1051/0004-6361/202557159

The intermediate neutron capture process: VI. Proton ingestion and i-process in rotating magnetic asymptotic giant branch stars

Choplin A., Siess L., Goriely S., Eggenberger P., Moyano F. D.

Context. The intermediate neutron-capture process (i-process) can occur during proton ingestion events (PIEs), which may take place in the early evolutionary phases of asymptotic giant branch (AGB) stars.

Aims. We investigate the impact of rotational and magnetic mixing on i-process nucleosynthesis in low-metallicity, low-mass AGB stars.

Methods. We computed AGB models with [Fe/H] = −2.5 and −1.7 and initial masses of 1 and 1.5 M _⊙ using the STAREVOL code, including a network of 1160 nuclei coupled to transport equations. Rotating models incorporate a calibrated Tayler-Spruit (TS) dynamo to account for core rotation rates inferred from asteroseismic observations of solar-metallicity sub-giants and giants. Initial rotation velocities of 0, 30, and 90 km s ⁻¹ were considered, along with varying assumptions for magnetic mixing.

Results. Rotation without magnetic fields strongly suppresses the i-process due to the production of primary ¹⁴ N, which is subsequently converted into ²² Ne – a potent neutron poison during the PIE. Including magnetic fields via the TS dynamo restores the models close to their non-rotating counterparts: strong core-envelope coupling suppresses shear mixing and prevents primary ¹⁴ N synthesis, yielding i-process nucleosynthesis similar to non-rotating models. We also find that rotational mixing during the AGB phase is insufficient to affect the occurrence of PIEs.

Conclusions. Proton ingestion event-driven nucleosynthesis proceeds similarly in asteroseismic-calibrated magnetic rotating AGB stars and non-rotating stars, producing identical abundance patterns.

Reference : 2026 Astronomy & Astrophysics, 706, A44
URL : https://www.aanda.org/10.1051/0004-6361/202557649

Halo Photometry and Asteroseismology for 98 of the Brightest Stars Observed by TESS

J. Rudrasingam, T. R. Bedding, B. J. S. Pope, M. G. Pedersen, M. N. Lund, T. R. White, D. Hey

The Transiting Exoplanet Survey Satellite (TESS) mission has facilitated studies of asteroseismology, eclipsing binaries, and transits in many stars. However, the brightest stars saturate TESS, yet they are the most amenable to photon-hungry high-resolution studies and have long observational histories. In this work, we adapted the halo photometry used in K2 to extract light curves from the unsaturated halo pixels of the star’s point spread function. We used this method to extract light curves for 98 of the brightest stars observed by TESS in Sectors 1-93. These bright stars include 15 red giants, five δ Scuti variables, eight stochastic low-frequency variables, eight eclipsing binaries, and 46 other variables. We measured νmax for 13 red giants using pyMON and Δν for one of them, β Gem (Pollux). For five of them, this represents the first time that oscillations were detected. We derived their stellar masses using the measured νmax and previous interferometric and radiometric angular diameters. We also discovered δ Scuti and γ Doradus variability in α Cep, possible asteroseismic binary signatures in ϵ Car, and a new eclipsing binary, γ And. Furthermore, we identified 18 stars in our sample that will be observed by the future PLAnetary Transits and Oscillations of stars (PLATO) mission, and 69 stars that have Stellar Observations Network Group (SONG) observations, including some simultaneous with TESS. The light curves are publicly available on the Mikulski Archive for Space Telescopes.

Reference : Accepted for publication in MNRAS
URL : https://arxiv.org/abs/2602.22472

The Nearby Evolved Stars Survey

Wallström S. H. J., Scicluna P., Srinivasan S., Wouterloot J. G .A., McDonald I., Decock L., Wijshoff M., Chen R., Torres D., Umans L., Willebrords B., Kemper F., Rau G., Feng S., Jeste M., Kaminski T., Li D., Liu F. C., Trejo-Cruz A., Chawner H., Goldman S., MacIsaac H., Tang J., Zeegers S. T., Danilovich T., Matsuura M., Menten K. M., van Loon J. Th, Cami J., Clark C. J. R., Dharmawardena T. E., Greaves J., He Jinhua, Imai H., Jones O. C., Kim H., Marshall J. P., Shinnaga H., Wesson R.

Low- to intermediate-mass (∼ 0.8−8 M _⊙ ) evolved stars contribute significantly to the chemical enrichment of the interstellar medium in the local Universe. It is therefore crucial to accurately measure the mass return in their final evolutionary stages. The Nearby Evolved Stars Survey (NESS) is a large multi-telescope project targeting a volume-limited sample of ∼ 850 stars within 3 kpc in order to derive the dust and gas return rates in the solar neighbourhood, and to constrain the physics underlying these processes. We present an initial analysis of the CO-line observations, including detection statistics, carbon isotopic ratios, initial mass-loss rates, and gas-to-dust ratios. We describe a new data reduction pipeline for homogeneity, which we use to analyse the available NESS CO data from the James Clerk Maxwell Telescope, measuring line parameters and calculating empirical gas mass-loss rates. We present the first release of the available data on 485 sources, one of the largest homogeneous samples of CO data to date. Comparison with a large combined literature sample finds that high mass-loss rate and especially carbon-rich sources are over-represented in literature, while NESS is probing significantly more sources at low mass-loss rates, detecting 59 sources in CO for the first time and providing useful upper limits on non-detections. CO line detection rates are 81% for the CO(2−1) line and 75% for CO(3−2). The majority (82%) of detected lines conform to the expected soft parabola shape, while eleven sources show a double wind. Calculated mass-loss rates show power-law relations with both the dust-production rates and expansion velocities, up to a mass-loss rate saturation value ∼ 5 × 10 ⁻⁶ M _⊙ yr ⁻¹ . Median gas-to-dust ratios of 250 and 680 are found for oxygen-rich and carbon-rich sources, respectively. Our analysis of CO observations in this first data release highlights the importance of our volume-limited approach in characterizing the local AGB population as a whole.

Reference : 2025 Astronomy & Astrophysics, 704, A276
URL : https://www.aanda.org/10.1051/0004-6361/202556298

The JWST MIRI view of the planetary nebula NGC 6302 – I. A UV-irradiated torus and a hot bubble triggering PAH formation

Matsuura Mikako, Volk Kevin, Kavanagh Patrick, Balick Bruce, Wesson Roger, Zijlstra Albert A, Dinerstein Harriet L, Peeters Els, Sterling N C, Cami Jan, Barlow M J, Kastner Joel, Walsh Jeremy R, Waters L B F M, Hirano Naomi, Aleman Isabel, Bernard-Salas Jeronimo, Bhatt Charmi, Blommaert Joris, Clark Nicholas, Jones Olivia, Justtanont Kay, Kemper F, Kraemer Kathleen E, Lagadec Eric, Laming J Martin, Molster F J, Moraga Baez Paula, Monteiro H, Richards Anita M S, Sahai Raghvendra, Sloan G C, Torki Maryam, van Hoof Peter A M, Wright Nicholas J, Wilson Finnbar, Csukai Alexander

NGC 6302 is a spectacular bipolar planetary nebula (PN) whose spectrum exhibits fast outflows and highly ionized emission lines, indicating the presence of a very hot central star ($\sim$220 000 K). Its infrared spectrum reveals a mixed oxygen and carbon dust chemistry, displaying both silicate and polycyclic aromatic hydrocarbon (PAH) features. Using the James Webb Space Telescope Mid-Infrared Instrument and Medium Resolution Spectrometer, a mosaic map was obtained over the core of NGC 6302, covering the wavelength range of 5–28 $\mu$m and spanning an area of $\sim$18.5 arcsec $\times$ 15arcsec. The spatially resolved spectrum reveals $\sim$200 molecular and ionized lines from species requiring ionization potentials of up to 205 eV. The spatial distributions highlight a complex structure at the nebula’s centre. Highly ionized species such as [Mg vii] and [Si vii] show compact structures, while lower ionization species such as H$^+$ extend much farther outwards, forming filament-defined rims that delineate a bubble. Within the bubble, the H$^+$ and H$_2$ emission coincide, while the PAH emission appears farther out, indicating an ionization structure distinct from typical photodissociation regions, such as the Orion Bar. This may be the first identification of a PAH formation site in a PN. This PN appears to be shaped not by a steady, continuous outflow, but by a series of dynamic, impulsive bubble ejections, creating local conditions conducive to PAH formation. A dusty torus surrounds the core, primarily composed of large ($\mu$m-sized) silicate grains with crystalline components. The long-lived torus contains a substantial mass of material, which could support an equilibrium chemistry and a slow dust-formation process.

Reference : 2025 Monthly Notices of the Royal Astronomical Society, 542, 1287-1307
URL : https://academic.oup.com/mnras/article/542/2/1287/8241385

H I line observations of 151 evolved stars made with the Nançay Radio Telescope

Gérard E., van Driel W., Matthews L. D., Le Bertre T., Martin J.-M., Riêu N. Q.

We present an analysis of the results of 21-cm HI line observations of the circumstellar envelopes (CSEs) of a sample of 151 evolved stars, consisting predominantly (85%) of asymptotic giant branch (AGB) stars. This is the first time an analysis could be carried out for the neutral hydrogen constituent of a substantial sample of CSEs of AGB stars. We obtained our observations mainly with the Nançay Radio Telescope (NRT), resulting in 34 clear detections and 21 possible detections. Among the 106 AGB type stars with non-confused HI spectra, 75% are O-rich and 22% are C-rich, while 41% are SRb type semi-regular variables and 38% are Miras. We found no significant biases in the selection or observations of different types of AGB stars. The total HI masses of the detected AGB stars range from 0.002 to 0.1 M⊙, with a mean value of 0.02 M⊙. The mean total HI masses are not significantly different for stars of different types of variability (Miras and semi-regulars). However, there is a difference between O- and C-rich AGB stars, which is due to only three C-rich stars with exceptionally high HI masses (>0.1 M⊙). If we disregard them, thereno significant difference among these types. We compared the total masses of atomic and molecular hydrogen in 34 AGB star CSEs, with the latter estimated from far-infrared imaging of dust, which extends out to about the same radii as the HI. We found that, on average, the H2 masses are 20 times larger than the HI masses. However, in eight objects, the hydrogen in the CSE is essentially completely atomic. We examined the possible dependence of our results, in particular the H2/HI total mass ratio, on the effective temperature (Teff ) of the central star. We find that the HI detection rate of CSEs tends to increase steadily with Teff, but we find no obvious correlation between the H2/HI mass ratio and Teff over the range 2100–3300 K. Here, we discuss this result in the context of the theoretical prediction that the hydrogen in their CSEs should be mainly atomic for AGB stars warmer than about 2500 K, and mainly molecular for cooler stars. However, the limited fraction in our sample of stars with well-determined temperatures lying below 2500 K prevented us from definitively confirming or refuting the predictions of this model. We discuss a number of effects that might explain the predominantly molecular nature of CSEs, irrespective of stellar temperature. Advancing their interpretation would require further development of mass outflow models for AGB stars of different effective temperatures, as well as comprehensive sets of Teff measurements of this highly time-variable class of stars. We also compared the HI and CO(1–0) line emission of AGB CSEs. The latter emission originates from much smaller radii (<0.01 pc) than the HI (0.75 pc for the resolved sources), and no H2 masses can be determined from it. There is a large spread in the CO:HI integrated line flux ratio (by more than a factor of 100). We found that CO:HI flux ratios generally increase with the H2 :HI mass ratio.

Reference : 2025 Astronomy & Astrophysics, 704, A186
URL : https://www.aanda.org/10.1051/0004-6361/202556118

Direct imaging of mass transfer and circumcompanion structures in π ¹ Gru with VLTI/MATISSE

Drevon J., Paladini C., Höfner S., Planquart L., Siess L., Jorissen A., Montargés M., Vlemmings W., Khouri T., Olofsson H., Alonso-Hernandez J., De Beck E., Fonfria J. P., Hron J., Matter A., Nardetto N., Ohnaka K., Sanchez-Contreras C., Weigelt G., Wittkowski M., Bojnordi Arbab B., Aringer B., Baron F., Chiavassa A., Cruzalébes P., Danchi W. C., Kerschbaum F., Leftley J., Lagadec E., Lopez B., Lykou F., Millour F., Rau G., Sanchez-Bermudez J., Thévenin F., Van Eck S., Velilla-Prieto L.

We investigate how the presence of a binary companion appears to affect dust and molecule formation in the circumstellar environment of a star on the asymptotic giant branch (AGB).

L - and N -band observations obtained over the course of one month with the multi aperTure mid-infrared spectroScopic experiment instrument (MATISSE) at the very large telescope interferometer (VLTI) were used to constrain the distribution of dust and molecules in the close environment of π1Gru through image reconstruction. The reconstructed images were fit to the interferometric observables, that is, the visibilities and closure phases, using the two Python-based tools Python for MiRA (PYRA) and mean astrophysical images with PYRA (MYTHRA) built around the multi-aperture image reconstruction algorithm (MiRA).

Our observations support (i) a wind Roche-lobe overflow (WRLOF) scenario, where mass transfer from the AGB star to its companion produces a possible circumcompanion disk in the L band around π1GruC, with a central cavity that likely traces dust sublimation and a circumcompanion envelope in the N band. (ii) A main-sequence nature for the companion: Because both Atacama large millimeter/submillimeter array (ALMA) and the VLTI/MATISSE N-band observations show emission, we favor a thermal infrared emission from the main-sequence star over free-free emission from a with dwarf companion. Finally, (iii) a plume-like structure extending from π1Gru C, likely marking the onset of the spiral observed at larger scales. Together, this provides direct evidence that links small-scale mass transfer and disk formation through WRLOF to the global circumstellar morphology.

These results highlight the atmospheric deformation induced by the companion, reveal ongoing mass transfer between the evolved star and its companion, and indicate a circumcompanion disk-like structure.

Reference : 2026 Astronomy & Astrophysics, 706, L1
URL : https://www.aanda.org/10.1051/0004-6361/202558298

The SB9 catalogue : status, comparison with non-single stars from Gaia DR3 and evolution to SBX

Merle T, Jorissen A, Alexandre S, Desuter J, Loup C, Tokovinin A, Traven G, Van der Swaelmen M, Van Eck S, Van de Steene G, Southworth J, Sadowski G

Abstract
The Ninth Catalogue of Spectroscopic Binary Orbits (S$_\mathrmB^9$) is a comprehensive compilation of spectroscopic binaries (SBs) with orbital parameters sourced from the literature, comprising approximately 4000 systems with about 2800 single-lined and 1200 double-lined binaries. This work presents the latest status of the S$_\mathrmB^9$ catalogue after over two decades of development since its online inception in 2004. In particular, we expose the statistical properties of SBs in terms of orbital period distributions and eccentricity-period diagrams per spectral type and evolutionary stage. We perform a careful cross-match with the Gaia Data Release 3 (DR3) to update astrometric parameters and compare with the Gaia DR3 Non-Single Star (NSS) catalogue. Our cross-matching approach uses positional separations, magnitudes, and proper-motion back-propagation to identify counterparts. The final S$_\mathrmB^9$ version updated by D. Pourbaix (2021-03-02) includes 4003 SB systems, some in higher-order multiples: 152 in triples, 71 in quadruples and 14 in higher-order systems. Among these 4003 SB, 3976 have matching Gaia DR3 identifiers, while 21 are too bright and six too faint for Gaia detection. red Ten S$_\mathrmB^9$ systems with periods larger than 1180 d (including a spectroscopic triple) have been spatially resolved by GaiaDR3. We identify a common sample of 827 S$_\mathrmB^9$ binaries cross-matched with Gaia NSS, among which 655 are considered as reliable, based on relative period and absolute eccentricity differences not exceeding 10 %. The limited overlap (21 % of S$_\mathrmB^9$) is primarily due to selection cuts in NSS SB1 analysis, brightness limits, temporal baselines, and partial orbital solutions in the Gaia NSS catalogue. This study highlights the strengths and limitations of both catalogues and establishes a clean benchmark sample for future binary star research. Our work marks the transition of S$_\mathrmB^9$ into S$_\mathrmB^X$, The eXtended Catalogue of Spectroscopic Binary Orbits⋆, featuring a modern relational database, improved web interface, and Virtual Observatory access standards, aiming to enhance accessibility, data quality, and analysis capabilities for the binary and multiple star community.

Reference : 2026 Monthly Notices of the Royal Astronomical Society
URL : https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag351/8499613

Asteroseismology of Carbon-deficient Red Giants: Merger Products of Hierarchical Triple Systems?

Maben Sunayana, Campbell Simon W., Bedding Timothy R., Zhao Gang, Howell Madeline, Kumar Yerra Bharat, Reddy Bacham E.

Abstract
Carbon-deficient giants (CDGs) are a rare and chemically peculiar class of stars whose origins remain under active investigation. We present an asteroseismic analysis of the entire known CDG population, selecting 129 stars observed by Kepler, K2, and TESS to obtain seismic constraints. We detect solar-like oscillations in 43 CDGs. By measuring ν max and applying seismic scaling relations, we determine precise masses for these stars, finding that 79% are low mass ( M ≲ 2 M _⊙ ). The luminosity distribution is bimodal, and the CDGs separate into three chemically and evolutionarily distinct groups, characterized by clear trends in sodium and CNO abundances, α -element enhancement, and kinematics. We find that two of these groups are only distinguished by their initial α -element abundances, thus effectively reducing the number of groups to two. Lithium enrichment is common across all groups, linking CDGs to lithium-rich giants and suggesting a shared evolutionary origin. We find that the spectroscopic log g is systematically offset from seismic values. Group 1 CDG patterns are most consistent with formation through core He-flash mixing, while the more massive and more chemically processed Groups 2 and 2 α likely formed through mergers involving helium white dwarfs, possibly in hierarchical triples. Pollution from asymptotic giant branch stars appears very unlikely, given the unchanged [C+N+O] abundance across all groups.

Reference : 2025 The Astrophysical Journal, 994, 19
URL : https://iopscience.iop.org/article/10.3847/1538-4357/ae071c

ATOMIUM: Continuum emission and evidence of dust enhancement from binary motion

Danilovich T., Samaratunge N., Mori Y. L., Richards A. M. S., Baudry A., Etoka S., Montargès M., Kervella P., McDonald I., Gottlieb C. A., Wallace A., Price D. J., Decin L., Bolte J., Ceulemans T., De Ceuster F., de Koter A., Dionese D., El Mellah I., Esseldeurs M., Gray M., Herpin F., Khouri T., Lagadec E., Landri C., Marinho L., Menten K. M., Millar T. J., Müller H. S. P., Pimpanuwat B., Plane J. M. C., Sahai R., Siess L., Van de Sande M., Vermeulen O., Wong K. T., Yates J., Zijlstra A.

Context. Low- and intermediate-mass stars on the asymptotic giant branch (AGB) account for a significant portion of the dust and chemical enrichment in their host galaxy. Understanding the dust formation process of these stars and their more massive counterparts, the red supergiants, is essential for quantifying galactic chemical evolution.

Aims. To improve our understanding of the dust nucleation and growth process, we aim to better constrain stellar properties at millimetre wavelengths. To characterise how this process varies with the mass-loss rate and pulsation period, we studied a sample of oxygen-rich and S-type evolved stars.

Methods. Here we present ALMA observations of the continuum emission around a sample of 17 stars from the ATOMIUM survey. We analysed the stellar parameters at 1.24 mm and the dust distributions at high angular resolutions.

Results. From our analysis of the stellar contributions to the continuum flux, we find that the semi-regular variables all have smaller physical radii and fainter monochromatic luminosities than the Mira variables. Comparing these properties with pulsation periods, we find a positive trend between the stellar radius and period only for the Mira variables with periods of more than 300 days, and we find and a positive trend between the period and the monochromatic luminosity only for the red supergiants and the most extreme AGB stars with periods of more than 500 days. We find that the continuum emission at 1.24 mm can be classified into four groups; (i) ‘featureless’ continuum emission is confined to the (unresolved) regions close to the star for five stars in our sample, (ii) relatively uniform extended flux is seen for four stars, (iii) tentative elongated features are seen for three stars, and (iv) the remaining five stars have unique or unusual morphological features in their continuum maps. These features can be explained by the fact that 10 of the 14 AGB stars in our sample have binary companions.

Conclusions. Based on our results, we conclude that there are two modes of dust formation: well-established pulsation-enhanced dust formation and our newly proposed companion-enhanced dust formation. If the companion is located close to the AGB star, in the wind acceleration region, then additional dust formed in the wake of the companion can increase the amount of mass lost through the dust-driven wind. This explains the different dust morphologies seen around our stars and partly accounts for the large scatter in literature mass-loss rates, especially among semi-regular stars with small pulsation periods.

Reference : 2025 Astronomy & Astrophysics, 704, A341
URL : https://www.aanda.org/10.1051/0004-6361/202554878

Sense and sensitivity – I. Uncertainty analysis of the gas-phase chemistry in AGB outflows

Van de Sande M, Gueguen M, Danilovich T, Millar T J

Chemical reaction networks are central to all chemical models. Each rate coefficient has an associated uncertainty, which is generally not taken into account when calculating the chemistry. We performed the first uncertainty analysis of a chemical model of C- and O-rich asymptotic giant branch (AGB) outflows using the Rate22 reaction network. Quantifying the error on the model predictions enables us to determine the need for adding complexity to the model. Using a Monte Carlo sampling method, we quantified the impact of the uncertainties on the chemical kinetic data on the predicted fractional abundances and column densities. The errors are caused by a complex interplay of reactions forming and destroying each species. Parent species show an error on their envelope sizes, which is not caused by the uncertainty on their photodissociation rate, but rather the chemistry reforming the parent after its photodissociation. Using photodissociation models to estimate the envelope size might be an oversimplification. The error on the CO envelope impacts retrieved mass-loss rates by up to a factor of two. For daughter species, the error on the peak fractional abundance ranges from a factor of a few to three orders of magnitude, and is on average about 10 per cent of its value. This error is positively correlated with the error on the column density. The standard model suffices for many species, e.g. the radial distribution of cyanopolyynes and hydrocarbon radicals around IRC +10216. However, including spherical asymmetries, dust-gas chemistry, and photochemistry induced by a close-by stellar companion are still necessary to explain certain observations.

Reference : 2025 MNRAS Volume 545, Issue 3, id.staf2049
URL : https://academic.oup.com/mnras/article/doi/10.1093/mnras/staf2049/8342143

X TrA through the eyes of MATISSE: More evidence of clumpy molecular layers around C-type asymptotic giant branch stars

Răstău V., Paladini C., Drevon J., Hron J., Kerschbaum F., Wittkowski M., Fonfria J. P., Montargès M., Khouri T., Vlemmings W., Olofsson H., Ohnaka K., Alonso-Hernandez J., Sánchez Contreras C., Velilla-Prieto L., Danchi W. C., Rau G., Lykou F., Sanchez-Bermudez J., Lopez B., Höfner S., Aringer B., Planquart L., Cruzalèbes P., Weigelt G.

Aims . The goal of this study is to further the understanding of the wind formation mechanism in asymptotic giant branch (AGB) stars through the analysis of the close environment (within a few stellar radii) of the carbon star X TrA.

Methods . X TrA was observed for the first time with the Mid-Infrared SpectroScopic Experiment instrument (MATISSE) in the L and N bands in low spectral resolution mode (R=30), and its close surroundings were mapped in specific wavelength ranges corresponding to specific molecules (C ₂ H ₂ and HCN, at 3.1 and 3.8 μm) and dust (amorphous carbon and, for example, SiC at 11.3 μm), via image reconstruction techniques.

Results . The angular diameter of the star ranges from 10 mas in the L band pseudo-continuum (3.5 μm) to 20 mas at 3.1 and 11.3 μm. The reconstructed images show some mild elongated features (along the east-west direction) and asymmetric protrusions, which are most evident around 3.1 μm. Imaging results highlight the clumpy nature of the circumstellar environment, starting from the photospheric region up to more distant layers.

Conclusions . The angular diameters found for X TrA in the image data are in agreement with previous photospheric diameter estimates (following VLTI/MIDI 8–13 μm observations), and their wavelength dependence is similar to values found for other carbon stars observed with MATISSE (R Scl and V Hya). The 3.1 μm images presented here show highly asymmetric features, another case of a C-rich star with irregular morphologies close to the stellar disk; this supports the notion that the C ₂ H ₂ + HCN abundance distribution usually originates from a clumpy layer around carbon stars.

Reference : 2026 Astronomy & Astrophysics, 705, A127
URL : https://www.aanda.org/10.1051/0004-6361/202557477

Betelgeuse: Detection of the Expanding Wake of the Companion Star

A. K. Dupree, P. Cristofari, M. MacLeod, K. Kravchenko

Recent analyses conclude that Betelgeuse, a red supergiant star (HD 39801), likely has a companion object with a period of ∼2000 days orbiting at only 2.3 R⋆, deep in the chromosphere of the supergiant. A probable detection of such a companion, named Siwarha, has just occurred from speckle imaging. This study finds that Betelgeuse spectra in the optical region and ultraviolet exhibit signatures of variable circumstellar absorption and chromospheric outflows. These variations are consistent with the ∼2000 days period of the companion object. Circumstellar absorption evident in optical Mn I lines, and mass outflow marked by ultraviolet Fe II, Si I, and Mg I lines increase after the transit of the companion across the disk of Betelgeuse. Following the eclipse of the companion, the absorption and outflow slowly decrease in advance of the next transit. The occurrence and variation of this plasma appear consistent with the presence of a trailing and expanding wake caused by a companion star orbiting within the atmosphere of Betelgeuse.

Reference : 2026, ApJ, 998, ID50
URL : https://iopscience.iop.org/article/10.3847/1538-4357/ae2ed5/pdf

Eppur si eclissa: Eccentric low-mass companions and time-in-dust selection to explain long secondary periods

Decin L., Vermeulen O., Esseldeurs M., Driessen F. A., Landri C., Dionese D., Siess L., Skowron D. M.

Context. Long secondary periods (LSPs) are observed in about one-third of pulsating red giants, yet this phenomenon remains unexplained. Four key observational constraints anchor the discussion: (i) a ∼30% occurrence rate in semi-regular variable AGB stars (SRVs) with a much lower rate (or complete absence thereof) in regularly pulsating Mira-type AGB stars (Miras); (ii) ∼50% of LSP stars show a secondary mid-infrared (MIR) minimum; (iii) Keplerian fits to radial-velocity (RV) curves favour the argument of periastron ω  > 180°; and (iv) the RV-light curve phase lag clusters around − π /2.

Aims. We test whether a close-in, eccentric low-mass companion that only spends part of its orbit within the giant’s dust-formation (wind-launching) zone can match all four empirical facts.

Methods. Guided by observed RV amplitudes and periods of ∼500–1500 days, we adopted a companion mass of M ₂  ∈ [0.08, 0.25] M _⊙ , orbital separation of a  ∈ [1.5, 3] au, and eccentricty of e  ≤ 0.6. Next, we took the dust condensation radius of R _cond  ∼ 2.5 − 3 au for SRVs (larger for Miras when scaling with luminosity). We computed the time-in-dust fraction f _dust (time with r  ≥  R _cond ) and applied line-of-sight criteria: an LSP requires an orbital inclination of i  ≥  i _LSP and f _dust  ≥  f _min , while a secondary MIR minimum interpreted as secondary eclipse further requires i  ≥  i _ecl  >  i _LSP and a superior conjunction. We tested the first three empirical facts analytically, then modelled the RV-light phase offset with 3D hydrodynamical simulations.

Results. Our proposed scenario explains the observed excess of ω  > 180°. For SRV-like parameters, we obtained an LSP detectability of ∼31.6 ± 0.1%, while Mira-type conditions yield ∼3.0 ± 0.1%; for both scenarios, the conditional secondary MIR eclipse fraction is ∼44%. Our hydrodynamical models place the optical-depth peak just downstream of the companion near apastron, then shift it to ∼90 − 225° phase offsets later in the orbit. This result is consistent with the RV-light offsets.

Conclusions. A time-in-dust geometric selection for low-mass companions in close eccentric orbits is sufficient to explain the four key empirical facts constraining the LSP mechanism.

Reference : 2025 Astronomy & Astrophysics, 703, L23
URL : https://www.aanda.org/10.1051/0004-6361/202557634

Infrared period-luminosity relations of Galactic Miras based on multi-epoch photometry and the Gaia parallax uncertainty

Uttenthaler, S., Lebzelter, T., Meingast, S.

Miras and other long-period variable (LPV) stars on the AGB follow period-luminosity (PL) relations. These relations have been difficult to study for Galactic LPVs because their distances were poorly known in the past. We aim to establish the PL relations of solar-neighbourhood Miras for several near-IR photometric bands. To this end, we used multi-epoch photometry from the DIRBE and unTimely/WISE catalogues, Gaia parallax distances, and contemporary pulsation periods obtained from optical observations of a well-selected sample of solar-neighbourhood Miras. We show that clearly defined PL relations in the nine investigated near-IR bands emerge from our data, and we report the slopes and zero-point magnitudes. We find that Galactic Miras are fainter in the near-IR than their Large Magellanic Cloud siblings. We derive average period-temperature, period-bolometric-luminosity, and period-radius relations from fits to synthetic SEDs constructed from the PL relations. By applying AGB evolutionary models, the scatter of stars around the PL sequences can also be used to test whether the parallax uncertainties quoted in the Gaia catalogue are realistic. Furthermore, we performed such tests based on a comparison with parallaxes obtained with the VLBI and with a sample of LPVs in the globular cluster 47 Tuc. We conclude that, for Galactic Miras with a fractional parallax uncertainty of <0.1 in the Gaia catalogue, the parallax uncertainty is underestimated by factors between 1.0 and 1.7, and most likely by $\sim1.3$. For more uncertain parallaxes, we find evidence that the distances (parallaxes) are generally overestimated (underestimated). Nevertheless, we find strong evidence that the large error-inflation factors reported for AGB stars in the literature are unrealistic. Our results lend confidence to the parallax measurements of these highly extended, variable stars.

Reference : 2026 14 pages, 10 figures, submitted to A&A
URL : https://arxiv.org/abs/2602.14775

Hidden massive eclipsing binaries in red supergiant systems: The hierarchical triple system KQ Puppis and other candidates

Jadlovský, D., Molnár, L., Ercolino, A., Bernini-Peron, M., Mérand, A., Krtička, J., Wang, L., Ádám, R. Z., Baade, D., Bayo, A., González-Torà, G., Granzer, T., Janík, J., Kolář, J., Kravchenko, K., Langer, N., Oskinova, L. M., Pauli, D., Ramachandran, V., Rubio, A. C., Sander, A. A. C., Strassmeier, K. G., Weber, M., Wittkowski, M., Brahm, R., Schaffenroth, V., Vanzi, L., Skarka, M.

The majority of massive stars are part of binary systems that may interact during their evolution. However, not many RSGs are known binaries, and only a few have constrained orbital parameters. We search the available TESS photometry for eclipsing companions of RSGs. We focus on the best candidate, VV Cephei type binary KQ Pup, which is made up of a RSG, KQ Pup A, and a B-type companion, KQ Pup B (orbital period of 26 yr). We use photometry, spectroscopy, and newly taken interferometric data with VLTI-GRAVITY. Using TESS, we discovered eclipses with a period of 17.2596d, associated with KQ Pup B, making it a Ba+Bb binary. The detection of the hydrogen Brγ line with VLTI-GRAVITY enabled us to track the orbital motion of the Ba+Bb pair relative to A and determine the astrometric orbit of A+B. The dynamical masses agree with independent estimates from asteroseismology and evolutionary models. The results give a mass of ∼10M⊙ for the RSG KQ Pup A and ∼14M⊙ for the sum of the hot components Ba+Bb. We determined an orbital parallax of π=1.24+0.05−0.04mas, which is the first such parallax measurement for a RSG. KQ Pup represents a unique demonstration of mass transfer mechanism in wide eccentric RSG systems. The variability of Balmer emission lines and the detection of Brγ are a strong signature of accretion to Ba+Bb near periastron. With the RSG filling its Roche lobe only by ∼70% at periastron, the mass transfer is instead driven by accretion from its extended atmosphere via the Wind Roche Lobe Overflow. The accretion disk dissipates by apastron. Overall, we discovered that several previously assumed RSG binaries host eclipsing inner systems, corresponding to ∼10% of all known Galactic RSG binaries. This suggests that many of the remaining RSG binaries may also be hierarchical triples.

Reference : submitted to A&A, comments welcome
URL : https://arxiv.org/abs/2509.25168

The dusty envelopes of asymptotic giant branch stars with ultraviolet excesses

Alonso-Hernández, Jaime, Sánchez Contreras, Carmen, Sahai, Raghvendra, Sanz-Forcada, Jorge

Aims. In a first study, we characterised the properties of the gas component in the circumstellar envelopes surrounding a sample of 29 AGB stars with UV excesses. Now we intend to complement this information with an analysis of the dust component and compare the estimated parameters with those previously inferred from larger samples of AGB stars. Methods. We modelled the spectral energy distributions of the sample using dust radiative transfer models. In some cases, we complemented the analysis with Herschel/PACS radial surface brightness profiles. Results. We derived mass-loss rates and gas-to-dust ratios, which are in the typical ranges for AGB stars. We found that the stellar and mass-loss parameters follow similar trends than those presented in the literature. There is an anticorrelation between the gas-to-dust ratio and the UV emission, although it is weaker than its correlations with pulsation and mass-loss. We also estimated the dust attenuation produced by the dust at UV wavelengths and describe its effects on the intrinsic UV emission. Conclusions. Stellar and mass-loss parameters of UV emitting AGB stars follow similar trends as found for larger samples of AGB stars. High-angular resolution observations are required to explore the dust forming regions and identify the presence of stellar companions. Circumstellar dust attenuation might play a dominant role in the observed UV emission, and needs to be accounted to estimate the intrinsic UV emission.

Reference : Accepted in Astronomy & Astrophysics
URL : https://arxiv.org/abs/2603.19815

Understanding post-red giant branch binaries through stable mass transfer

Moltzer C. A. S., Pols O. R., Van Winckel H., Temmink K. D., Wijdeveld M. W.

Context. Post-red giant branch (post-RGB) and post-asymptotic giant branch (post-AGB) binaries consist of a primary star that has recently evolved off either the RGB or AGB after losing the majority of its envelope and a main-sequence companion. They are distinguished by having luminosities below and above the tip of the RGB, respectively. These systems are characterised by the presence of a stable, dusty circumbinary disc, identified by a near-IR excess. Observed Galactic post-AGB and post-RGB binaries have orbital periods and eccentricities that are at odds with binary population synthesis models.

Aims. In this work, we focus on post-RGB binaries. We investigate whether stable mass transfer can explain the orbital periods of such binaries by comparing stable mass transfer models with the known sample of 38 Galactic post-RGB binaries.

Methods. We systematically determined the luminosities of the Galactic post-RGB and post-AGB binary sample using spectral energy distribution fitting. We computed evolution models for low- and intermediate-mass binaries with RGB donors at two metallicities using the detailed stellar evolution code, MESA. We selected the stable mass transfer models that result in primaries with effective temperatures within the observed range of post-RGB binaries (4000 − 8500 K).

Results. From our model grids, we find that low-mass post-RGB binaries are expected to follow strict luminosity–orbital period relations. The Galactic post-RGB binaries appear consistent with these luminosity–orbital period relations if we assume that their orbits remained eccentric during mass transfer and that the donor star filled its Roche lobe at periastron. However, our models are unable to explain the eccentricities themselves. Furthermore, the post-mass-transfer ages of observed post-RGB binaries estimated using our models are significantly longer than the predicted dissipation timescales of their circumbinary discs.

Conclusions. The stable mass transfer formation channel appears to explain the orbital periods of Galactic post-RGB binaries. This formation scenario could be tested more extensively by obtaining the orbits of additional Galactic systems, as well as those of the numerous candidates in the Magellanic Clouds, through long-term radial velocity monitoring. Additionally, we expect that Gaia Data Release 4 will improve the luminosities of Galactic post-RGB binaries, which will allow for a more accurate comparison with post-RGB luminosity–orbital period relations.

Reference : 2025 Astronomy & Astrophysics, 703, A294
URL : https://www.aanda.org/10.1051/0004-6361/202556437

Detection of CH 3+ in the O-rich Planetary Nebula NGC 6302

Charmi Bhatt, Jan Cami, Els Peeters, Nicholas Clark, Paula Moraga Baez, Kevin Volk, G. C. Sloan, Joel H. Kastner, Harriet L. Dinerstein, Mikako Matsuura, Bruce Balick, Kathleen E. Kraemer, Kay Justtanont, Olivia Jones, Raghvendra Sahai, Isabel Aleman, Michael J. Barlow, Jeronimo Bernard-Salas, Joris Blommaert, Naomi Hirano, Patrick Kavanagh, Francisca Kemper, Eric Lagadec, J. Martin Laming, Frank Molster, Hektor Monteiro, Anita M. S. Richards, N. C. Sterling, Maryam Torki, Peter A. M. van Hoof, Jeremy R. Walsh, L. B. F. M. Waters, Roger Wesson, Finnbar Wilson, Nicholas J. Wright, and Albert A. Zijlstra

Planetary nebulae are sites where ejected stellar material evolves into complex molecules, but the precise physical conditions and chemical routes that govern these processes are unclear. The presence of abundant carbon-rich molecules in O-rich environments poses particular challenges. Here we report the first detection of methyl cation (CH3+) in any planetary nebula, observed in the O-rich nebula NGC 6302 using JWST MIRI/MRS observations. CH3+ is a key driver of organic chemistry in UV-irradiated environments. Spatially resolved observations reveal that CH3+ is co-located with 12CO, H2, H II, HCO+, and Polycyclic aromatic hydrocarbons (PAHs). LTE modelling of the CH3+ emission yields excitation temperatures of 500-800K in the inner bubble and torus, rising to 1000-2000K in the outer bubble of NGC 6302, with column densities ranging from 10^11 to 10^13 cm^-2. This detection demonstrates that hydrocarbon radical chemistry must be incorporated into planetary nebulae chemical models. Further near-IR observations are crucial to map different chemical networks operating in these environments.

Reference : Bhatt, C. et al. 2025, Astrophysical Journal, 995, 67
URL : https://iopscience.iop.org/article/10.3847/1538-4357/ae1020

Detection of CO 2 ice in the planetary nebula NGC 6302

Charmi Bhatt, Simon W. Cao, Jan Cami, Nicholas Clark, Pascale Ehrenfreund, Els Peeters, Mikako Matsuura, G. C. Sloan, Harriet L. Dinerstein, Patrick Kavanagh, Kevin Volk, Isabel Aleman, Michael J. Barlow, Kay Justannont, Kathleen E. Kraemer, Joel H. Kastner, Francisca Kemper, Hektor Monteiro, Raghvendra Sahai, N. C. Sterling, Jeremy R. Walsh, L. B. F. M. Waters, Albert Zijlstra

Using JWST/MIRI observations, we report the detection of CO ice in the dusty torus of the planetary nebula NGC 6302, an environment generally considered hostile to fragile molecular species and ices due to intense UV irradiation. This detection accompanies cold (20-50 K) gas-phase CO along the same sightlines. The ice absorption profile exhibits a double-peak profile, a characteristic of pure, crystalline CO ice. The CO gas-to-ice ratio is more than an order of magnitude higher than in young stellar objects, pointing to distinct ice formation or processing mechanisms in evolved stellar environments. This discovery demonstrates that the dusty torus provides sufficient shielding to harbour ice chemistry, and that ice-mediated surface reactions must be incorporated into chemical models of planetary nebulae.

Reference : Bhatt et al. 2026, in publication (A&A Letters)
URL : https://arxiv.org/pdf/2602.22366

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

The Impact of Binaries on Stellar Evolution (ImBaSE2027)

Dear colleagues,

We are pleased to announce the next meeting in the ImBaSE (The Impact of Binaries on Stellar Evolution) conference series, devoted to binary and stellar evolution, including observational, theoretical, and population studies of interacting and non-interacting systems.

The next ImBaSE conference will take place in Tenerife, Spain, from July 12th to 16th, 2027.

Conference website: https://meetings.iac.es/imbase2027/

If you work on binary, stellar evolution, or related topics, please mark the conference dates in your calendar. If you would like to receive future announcements, please fill in the Expression of Interest form available on the website to be added to the mailing list. More information about the scientific program, venue, and registration will be announced in due course through that mailing list.

We are planning an in-person meeting with approximately 120–180 participants. We would appreciate it if you could forward this message to colleagues who might be interested.

Looking forward to seeing you there,
Ana Escorza, Jaroslav Merc & Michael Abdul-Masih
The ImBaSE 2027 Organisers