The African VLBI Network (AVN) is slowly becoming a reality. A couple of successful fringe test observations have been conducted even as single-dish maser monitoring observations constitute the main activity on the telescopes (HartRAO 26 m and Ghana 32 m). Some of the recent observational results from the AVN telescopes includes detection of velocity drifts in masers. Although MeerKAT is largely designed for high sensitivity continuum and HI science, its bands cover some masers and is already making impressive discoveries. The need to grow the critical mass of radio astronomers in the African continent persists. The NWU 4-dish interferometer, the Nigeria 3.7 m radio telescope and the African Millimeter Telescope (AMT) are some of the initiatives that will significantly improve the statistics of radio astronomers in Africa.

Many astrophysical phenomena can only be studied in detail for objects in our galaxy, the Milly Way, but we know much more about the structure of thousands of nearby galaxies than we do about our own Galaxy. Accurate distance measurements in the Milky Way underpin our ability to understand a wide range of astrophysical phenomena and this requires observations from both the northern and southern hemisphere. Our ability to measure accurate parallaxes to southern masers has been hampered a range of factors, in particular the absence of a dedicated, homogeneous VLBI array in the south. We have recently made significant advances in astrometric calibration techniques which allow us to achieve trigonometric parallax accuracies of around 10 micro-arcseconds (μas) for 6.7 GHz methanol masers with a hetrogeneous array of 4 antennas. We outline the details of this new “multiview” technique and present the first trigonometric parallax measurements that utilise this approach.

Mass loss is a key property to understand stellar evolution and in particular for low-metallicity environments. Our knowledge has improved dramatically over the last decades both for single and binary evolutionary models. However, episodic mass loss although definitely present observationally, is not included in the models, while its role is currently undetermined. A major hindrance is the lack of large enough samples of classified stars. We attempted to address this by applying an ensemble machine-learning approach using color indices (from IR/Spitzer and optical/Pan-STARRS photometry) as features and combining the probabilities from three different algorithms. We trained on M31 and M33 sources with known spectral classification, which we grouped into Blue/Yellow/Red/B[e] Supergiants, Luminous Blue Variables, classical Wolf-Rayet and background galaxies/AGNs. We then applied the classifier to about one million Spitzer point sources from 25 nearby galaxies, spanning a range of metallicites (). Equipped with spectral classifications we investigated the occurrence of these populations with metallicity.

The evolutionary link between Red Supergiants and Luminous Blue variables is interesting, but still poorly understood. We present the results of a study of the Galactic candidate luminous blue variable Wray 15-906, revealed via the detection of its infrared circumstellar shell (of ≍2 pc in diameter) with the Wide-field Infrared Survey Explorer (WISE) and the Herschel Space Observatory. Using the stellar atmosphere code CMFGEN and the Gaia parallax, we found that Wray 15-906 is a relatively low-luminosity, log(L/Lȯ) ≍ 5.4, star with a temperature of 25±2 kK. In the framework of single star evolution, the obtained results suggest that Wray 15-906 is a post-red supergiant star with an initial mass of ≍ 25Mȯ and that before exploding as a supernova it could transform for a short time into a WN11h star. The presence of a shell with a mass 2.9±0.5Me indicates that Wray 15-906 has suffered substantial mass loss in the recent past.

National Astronomical Research Institute of Thailand (Public Organization) initiated a national flagship project in 2017 for development of radio astronomy and geodesy in Thailand. In this project, a 40-m Thai National Radio Telescope (TNRT) and a 13-m VLBI Global Observing System (VGOS) radio telescope as its co-location are constructed in Chiang Mai. The 40-m TNRT is the largest telescope for radio astronomy in South-East Asia. Its flexible operation with a wide-coverage of observable frequencies 0.3-115 GHz will allow us to uniquely contribute to the time-domain astronomy as well as carry out unbiased surveys for a wide variety of science research fields, which were published in a white paper. Within the framework of collaboration with VLBI arrays in the world, TNRT will drastically improve the imaging quality and performances based on its unique geographical location, for both radio astronomy and geodetic VLBI studies in South-East Asia for the first time. On-going commissioning of TNRT particularly in the L-band system (1.0–1.8 GHz) is introduced as well as vision for establishment of forthcoming regional VLBI networks based on TNRT: Thai National VLBI Array and South-East Asian VLBI Network in collaboration with Indonesia, Malaysia, and Vietnam.

The ALMA Project is embarking on a partner-wide initiative to at least double, and ultimately quadruple the correlated bandwidth of ALMA by @2030. This initiative is called the ALMA Wideband Sensitivity Upgrade (WSU). In this contribution, I briefly describe the main aspects of the upgrade and status. Then I provide several examples of how the WSU will enhance (sub)millimeter maser science by affording the ability to observe more diagnostic maser transitions (and thermal lines) with a single observation.

Wolf-Rayet (WR) stars comprise a class of stars whose spectra are dominated by strong, broad emission lines that are associated with copious mass loss. In the massive-star regime, roughly 90% of the known WR stars are thought to have evolved off the main sequence. Dubbed classical WR (cWR) stars, these hydrogen-depleted objects represent a crucial evolutionary phase preceding core collapse into black holes, and offer a unique window into hot-star wind physics. Their formation is thought to be rooted in either intrinsic mass-loss or binary interactions. Results obtained from analyses using contemporary model atmospheres still fail to reconcile the derived properties of WR stars with predictions from stellar evolution. Importantly, stellar evolution models cannot reproduce the the bulk of cWR stars, a problem that becomes especially severe at subsolar metallicity. Next-generation model atmospheres and upcoming observational campaigns to hunt for undetected companions promise a venue for progress.

Imaging the bright maser emission produced by the various molecular species from 1.6 to 116 GHz provides a way to probe the kinematics of dense molecular gas at high angular resolution. Unimpeded by the high dust optical depths that affect shorter wavelength (sub)mm observations, the high brightness temperature of these emission lines have become an essential tool for understanding the process of massive star formation. Operating from 1.2–116 GHz, the next generation Very Large Array (ngVLA) of 263 antennas will provide the capabilities needed to fully exploit these powerful tracers, including the ability to resolve accretion and outflow motions down to scales as fine as ∼1-10 au in deeply embedded Galactic star-forming regions, and at sub-pc scales in nearby galaxies. I will summarize the proposed specifications of the ngVLA, describe the current status of the project, and offer examples of future experiments designed to image the vicinity of massive protostars in continuum, thermal lines, and maser lines simultaneously.

Line-driven stellar winds are ubiquitous among hot massive stars. In some cases they can become so strong, that the whole star is cloaked by an optically thick wind. The strong outflow gives rise to large emission lines, defining the class of so-called Wolf-Rayet (WR) stars. While being major players in the evolution of massive stars, the formation of heavy black holes, and the distribution of elements, the occurrence and nature of WR winds is still quite enigmatic.

A promising instrument towards a better theoretical understanding are stellar atmospheres allowing for a consistent inclusion of the hydrodynamics. By coupling stellar and wind parameters and the inclusion of a detailed non-LTE radiative transfer, they allow us to go beneath the observable layers and study the onset of WR-type winds. Establishing larger sets of models, we were able to make ground-breaking progress by identifying trends with mass and metallicity that deviate significantly from present empirical descriptions. Our modelling efforts reveal a complex picture for WR-type winds with strong, non-linear dependencies. Besides covering metallicity and mass, we further identify surface hydrogen as an important ingredient to retain WR-type mass loss at lower metallicity. Here, we present a summary of recent insights on the nature and onset of WR-type winds in massive stars including the consequences for stellar evolution, remaining open questions, and current efforts to overcome them.

Massive stars emit X-rays. Despite modest X-ray luminosities of single hot massive stars, the ongoing large observing campaigns combining X-ray and UV spectroscopy provide a tomographic view of stellar winds. It is now established that X-ray radiation is modulated with stellar rotation and shows the same period as discrete absorption components (DACs) in the UV resonance lines. The latter are associated with corotating interaction regions (CIRs) in stellar winds, therefore the mechanisms responsible for generation of X-rays and CIRs appear to be physically linked. Binary massive stars with accreting compact companions – high-mass X-ray binaries (HMXBs) – are routinely observed by modern X-ray observatories at Mpc distances. Joint observations in X-ray and UV allow to determine realistic properties of these systems. The brightest sources among HMXBs are ultraluminous X-ray sources (ULXs). Their powerful radiation is an important source of stellar feedback. HMXBs are the products of massive binary evolution and are typically found in the vicinity of young massive star clusters. The superstar clusters blow hot superbubbles which fill large areas in star-forming dwarf galaxies. Recent models show that X-ray emission from superbubbles is likely the dominant source of He ii ionization in metal-poor star-forming dwarf galaxies. To conclude, X-ray observations provide an important window for studying massive stars and their feedback near and far.

The Galactic ASKAP survey of OH (GASKAP-OH) is surveying the Milky Way Fourth Quadrant, the Galactic Centre, the Galactic Bulge and the Large Magellanic Cloud (LMC) in the 18-cm ground-state lines of the hydroxyl radical (OH), using Australia’s Square Kilometre Array Pathfinder (ASKAP) telescope. With an expected per-channel rms sensitivity of 36 mJy/beam in its shallowest regions, and a velocity channel width of 0.1 km s-1, GASKAP-OH is expected to discover hundreds of new star-formation and evolved star OH masers, as well as extensive absorption from quasi-thermal OH throughout the Galactic Plane. We here summarise the science goals and technical specifications of the survey, and report initial detection results from test observations. GASKAP-OH is expected to run for several years and is an open collaboration. Data products will be made available to the wider community as soon as they are verified.

We report on a study of 9 nearby primitive galaxies observed by Hubble’s COS far-UV spectrograph that can serve as templates of high-z galaxies to be observed by JWST. By “primitive galaxies,” we mean galaxies having a low stellar mass, and low gas metallicity, , whether they are local or at high redshift. We find that far-UV spectra of these galaxies show evidence of hard radiation, including X-rays. Following Thuan et al. (2004), we identify these galaxies as massive X-ray binaries containing a massive accreting stellar black hole. We further find that the lower the metallicity, the higher the probability of extremely strong X-radiation. Following Heger et al. (2003), we suggest that the accreting black hold is produced by direct collapse of stars having initial masses greater than 50 . The X-radiation produced by black hole disk directly affects the surrounding interstellar medium, and many of these effects are observable in far-UV spectra.

The 64-dish MeerKAT telescope was inaugurated in 2018 and has been conducting regular science operations since then. In the meantime, new observation modes have been under development. Spectral line modes are available, as well as L-, UHF- and S-band receivers. MeerKAT’s excellent sensitivity over a wide range of angular scales makes it an excellent choice for studies of HII regions, supernova remnants and planetary nebulae. In addition, an OH megamaser has been detected at z > 0.5 for the first time.

LLAMA (Large Latin America Millimeter/submillimeter Array) is a new radio observatory that is being constructed in a collaboration between Argentina and Brazil. It will consist of a 12 meters diameter antenna that is being installed in Alto Chorrillos at 4850 m of altitude, in the Salta province of Argentina. Alto Chorrillos is a high-quality astronomical site similar to Chajnantor (Chile), where ALMA observatory operates. When completed, LLAMA will allow line, continuum and linear polarization observations between 35 and 700 GHz, approximately. For the first light, LLAMA will be equipped with ALMA-like receivers at bands 5 (163 - 211 GHz), 6 (211 - 275 GHz) and 9 (602 - 720 GHz). LLAMA is being planned to be a versatile astronomical facility that will serve the scientific community for the exploration of scientific topics as diverse as the molecular evolution of the Universe, black holes and their accretion disks, astrophysical jets, stellar formation and evolution, the structure of our galaxy and the Sun, planetary atmospheres and extragalactic astronomy. In this work, I will present the LLAMA project and the perspectives for this new astronomical facility in the context of the investigation of galactic and extragalactic masers.

Wolf-Rayet stars are regarded as candidates for progenitors of core-collapse supernovae, and they are expected to be progenitors of long gamma-ray bursts. These types of stars are considered to be fast rotators. Their high rotation speed breaks the sphericity of the star and leads to an axisymmetric wind density structure. In such a case, the electron scattering takes place in a nonspherical environment, and as a result, we might expect an intrinsic polarization. We present a 2.5D radiation hydrodynamic stellar wind model of these stars. The model simulations account for the deformation of the stellar surface due to rotation, gravity darkening, and nonradial forces. We computed the polarization from the density variable of the hydrodynamic model, derived the upper limit of rotational velocities, and found no conflict with the previous studies of Wolf-Rayet stars.

We present our measurements of the amplitude of photometric and spectroscopic variability due to clumping in the wind of Wolf-Rayet (WR) stars. Photometric variability was assessed using TESS light-curves, while spectroscopic variations were obtained from almost 20 years of monitoring of nearly 100 classical (presumably single) stars. Our results show an apparent dependence of the variability amplitude with the stars’ surface temperature and/or terminal velocity. Our interpretation is that it supports the idea that the dominating driver of the clumps in WR winds is a sub-surface convection region.

We present the prospects from astrometric spectral line VLBI in the era of ngEHT. We review the potential targets, that span many interesting science cases. We summarise the approaches that have been demonstrated to work at lower frequencies and touch on the simulations that give us great confidence that these same approaches will continue to work at sub-mm wavelengths. We conclude that this is a worthwhile pursuit with a high probability of success.

We present the results of a magnitude-limited spectroscopic survey of Galactic Wolf-Rayet stars with the HERMES spectrograph mounted on the Mercator telescope. Using cross-correlation to measure radial velocities, we measured the observed binary fractions of the Galactic carbon- (WC) and nitrogen-rich (WN) Wolf-Rayet stars to be and . We used Monte-Carlo simulations with a Bayesian framework to derive the intrinsic multiplicity properties and found and . We find that the majority of WN binaries reside in short-period systems, similar to O stars. However, the orbital period distribution of the Galactic WC population peaks at 5000 d, a discrepancy that challenges our current understanding of binary evolution in Wolf-Rayet stars.

We are pleased to summarise the IAU Symposium 380, Cosmic Masers: Proper Motion toward the Next-Generation Large Projects held on March 2023 March 20-24 in Kagoshima City, Japan. It is the sixth symposium focusing on astrophysical masers broadly used in research of star formation and evolved stars, astrometric measurements of the Milky Way galaxy, as well as studies of extragalactic environments.