We are investigating the extended outflow from G25.82–W1, which is one of the members of the high-mass protocluster G25.82–0.17. The aim is to study the star-forming environment of G25.82–W1. To identify the outflow, we obtained CO 2-1 data using the Atacama Large Millimeter/submillimeter Array.

We have identified several spatial and spectral outflows, including: 1) an extended N1–S1 CO outflow, driven by a high-mass young stellar object (HM-YSO) named G25.82–W1; 2) an elongated SE–NW outflow powered by G25.82–W2; 3) a compact and curved N2–S2 CO outflow originating from G25.82–E; and 4) a pair of knotty lobes centered on G25.82–W.

Furthermore, the innermost region of the N1–S1 CO outflow, traced by the 22 GHz H2O maser, reveals a complex spatial and velocity structure within a 2” from its launching point.

To accurately calculate the properties of the N1–S1 CO outflow, we have utilized an accurate distance measurement of d=4.5 kpc, derived from the annual parallax of the H2O masers. The outflow rate and force are comparable to those observed in outflows from other HM-YSOs. The physical properties of the N1–S1 CO outflow follow a trend connecting the low and high-mass regimes, supporting the idea that the star-forming mode in G25.82–W1 is likely a scaled-up version of low-mass star formation.

Recent ALMA observations detected protostellar outflows in 70-μm dark infrared dark clouds (IRDCs). These sources are candidates for the initial stages of high-mass star formation. We launched a new survey for free-free emission from outflow shocks using the Yamaguchi Interferometer (YI) at 8 GHz. We aim to catalog “proto-high-mass protostar” candidates that are still in the low to intermediate-mass phase. We selected starless-like clumps without any 70-μm point source from Traficante et al. (2015). We currently detected 82 sources from 167 clumps. 37 of them are fainter than 20 mJy (down to a few mJy). They tend to associate with colder and denser clumps that are suitable for star formation. This fact suggests that, at least, some of them trace star-formation activities. The highest-density clumps are, in fact, associated with several masers and molecular outflows. Furthermore, some of them have already shown a signature of ongoing cluster formation.

The 6.7 GHz methanol maser emitted by a high-mass star forming region G33.641-0.228 is known to exhibit fast flux density variability on timescales of less than one day. The mechanism of this variability, called burst, has not been known. We observed the circular polarization of this maser. As a result, we found that only the spectral components representing burst exhibit strong circular polarization exceeding 10%. This suggests that the two phenomena of the burst and circular polarization are related to each other.

Long-term monitoring observations of the 6.7 GHz methanol masers by Hitachi 32-m operated by Ibaraki University, which are named as “the Ibaraki 6.7 GHz Methanol Maser Monitor (iMet)”, have revealed that the periods of the flux variability of 6.7 GHz methanol masers in the five high-mass star-forming regions G05.900-0.430, G06.795-0.257, G10.472+0.027, G12.209-0.102 and G13.657-0.599 are over 1000 days. These periods are approximately twice the longest known period of 6.7 GHz methanol masers of 668 days for G196.45-1.68. The facts that the flux variation patterns show symmetric sine curves and that the luminosity of the central protostar and periods of maser flux variation are consistent with the expected period-luminosity (PL) relation suggest that the mechanism of maser flux variability of G05.900-0.430, G10.472+0.027 and G12.209-0.102 can be explained by protostellar pulsation instability. From the period-luminosity relation, central stars of these three sources are expected to be very high-mass protostars with a mass of : ∼40 M⊚ and a mass accretion rate of : ∼2×10-2 M⊚yr-1. On the other hand, G06.795-0.257 and G13.657-0.599 have luminosities that are an order of magnitude smaller than that expected from PL relation, and the variation patterns are intermittent, suggesting a variation mechanism of these sources originated from binary system.

Context: Theoretical scenarios describe the phenomenon of mass accumulation by high-mass young stellar objects (HMYSOs) through disk accretion. Aims: To find out whether the rotation of the core around hyper-compact (HC) HII regions is common Methods: The molecular core G301.1364-00.2249A was selected as the subject of investigation. Observations were carried out on CH3CN, SO2, H29α radio recombination line and continuum emission. Analysis involved the “Moment 0, 1, 2" and “Population-diagram” methods. Result: The structures of G301.1364-00.2249A exhibited clear definition. CH3CN moment 0 images revealed multiple enhanced emission regions and an absorption area. The moment 1 image depicted a velocity gradient from southeast to northwest. Conclusion: The molecular gas has a rotational motion in the direction from the southeast to northwest. The rotational temperature was measured at 293 K.

We compare detailed observations of multiple H2O maser transitions around the red supergiant star VY CMa with models to constrain the physical conditions in the complex outflows. The temperature profile is consistent with a variable mass loss rate but the masers are mostly concentrated in dense clumps. High-excitation lines trace localised outflows near the star.

High brightness and low interstellar extinction allow the 6.7 GHz methanol (CH3OH) masers to carry the information about what happens in the vicinity of the High-Mass Young Stellar Objects (HMYSOs). Monitoring this transition provides an only one opportunity to catch rare, unusual phenomena. In this paper, I describe three of them: quasi-periodic flares of the red-shifted emission in Cep A HW2, accretion burst in S255-NIRS3 and reappearance of the methanol maser flare in G24.329+0.144.

We report the detections of NH3(3,3) and 25 GHz and 278.3 GHz class I CH3OH maser emission associated with the outflow of the Extended Green Object G19.01–0.03 in sub-arcsecond resolution Atacama Large Millimeter/submillimeter Array (ALMA) and Karl G. Jansky Very Large Array (VLA) observations. For masers associated with the outer outflow lobes (> 12.5 ″ from the central massive young stellar object; MYSO), the spatial distribution of the NH3(3,3) masers is statistically indistinguishable from that of previously known 44 GHz Class I CH3OH masers, strengthening the connection of NH3(3,3) masers to outflow shocks. In sub-arcsecond resolution VLA observations, we resolve the 6.7 GHz Class II CH3OH maser emission towards the MYSO into a partial, inclined ring, with a velocity gradient consistent with the rotationally supported circumstellar disc traced by thermal gas emission.

We report on a direct comparison of VLBI maser data and ALMA thermal-emission data for the high-mass protostar G353.273+0.641. We detected a gravitationally-unstable disk by dust and a high-velocity jet traced by a thermal CO line by ALMA long-baselines (LB). 6.7 GHz CH3OH masers trace infalling streamlines inside the disk. The innermost maser ring indicates another compact accretion disk of 30 au. Such a nested system could be caused by angular momentum transfer by the spiral arms. 22 GHz H2O masers trace the jet-accelerating region, which are directly connecting the CO jet and the protostar. The recurrent maser flares imply episodic jet ejections per 1–2 yr, while typical separation of CO knots indicates a variation of outflow rate per 100 yr. Our study demonstrates that VLBI maser observations are still a powerful tool to explore detailed structures nearby high-mass protostars by combining ALMA LB.

Most massive stars (up to 100%) are thought to be in binary systems. The multiplicity of massive stars seems to be intrinsically linked to their formation and evolution, and so Massive Young Stellar Objects are key in observing this early stage of star formation. We have surveyed hundreds of MYSOs across the Galaxy from the RMS catalogue, using UKIDSS and VVV point source data. Preliminary results show binary fractions of 44±3% for the UKIDSS sample and 32±3% for the VVV sample. In addition we use the K-band magnitudes as a proxy for the companion mass, and find a significant fraction of the detected companions have estimated mass ratios greater than 0.5, which suggests a deviation from the capture formation scenario.

An overview is provided of the scientific goals of the Magellanic Cloud component of the STScI Directors Discretionary UV initiative ULLYSES, together with the complementary spectroscopic survey XShootU (VLT/Xshooter) and other ancillary datasets. Together, ULLYSES and XShootU permit the first comprehensive, homogeneous study of wind densities and velocities in metal-poor massive stars, plus UV/optical spectroscopic libraries for population synthesis models and a large number of interstellar sight-lines towards the Magellanic Clouds.

The aim of this survey is the homogeneous characterization of a large sample of H ii regions with active star formation in order to detect observational trends supporting the two main models of massive star formation.

In this contribution we present the results from a1 homogeneous quantitative spectroscopic analysis of ∼400 Galactic O-type stars targeted by the IACOB and OWN surveys. The ultimate objective is to perform a modern reassessment of one of the long-standing problems in the field of massive stars: the elusive detection of mid O-type stars close to the “canonical” theoretical ZAMS. We first provide statistically significant evidence of the existence of a clear lack of stars in our sample populating the region of the spectroscopic HR diagram approximately delimited by the theoretical ZAMS, the ∼ 40 and ∼ 70 M⊙ single evolutionary tracks and the 2 Myr isochrone. We then evaluate if this empirical result could be a result of possible limitations of our analysis strategy and/or the existence of potential observational biases affecting the compiled sample. Once both explanations are investigated, we evaluate the possibility that a modification of the efficiency of mass accretion during the star formation process could lead to a new (corrected) theoretical ZAMS in better accordance with our empirical results.

Luminous Blue Variable stars (LBVs) are rare and enigmatic. Often cited as evolutionary stages in the single-star evolution, the idea that binary evolution produces the LBV state was already considered, 30 years ago.

It is now commonly accepted that a significant part of massive stars are born in multiple systems. One aspect that also emerged is that massive stars have on average at least two companions, i.e. they are triples. This immediately implies that a number of LBVs should have evolved as part of multiple systems.

While some LBVs are confirmed as binaries, different methods were used to derive their multiplicity, with different results. We report on a systematic search for multiplicity using spectroscopy, interferometry in a sample of 20 LBVs. Spectroscopy provides us with a bias-corrected binary fraction of $\[62_{ - 24}^{ + 38}\]$%, and a percentage of 50–70% is found from interferometry. This has a high impact on the way that these objects might be formed.

In this contribution, we explore the question on the formation of multiple massive stellar systems via disk fragmentation with the help of the highest-resolution simulations to date of a fragmenting disk in the context of massive star formation. The simulations start from a collapsing cloud of 200 solar masses, followed by the formation of an accretion disk that develops spiral arms and fragments. Due to the high resolution of our grid, we are able to self-consistently form the fragments without the need for a subgrid module such as sink particles. We track the formed fragments into the first stages of companion formation, which allows us to give an estimate of the multiplicity of the final system due to disk fragmentation. We find in total around ∼6 fragments, some at orbits of ∼ 1000 au, and some close (possibly spectroscopic) companions.

Mass loss through stellar winds plays a dominant role in the evolution of massive stars. Very massive stars (VMSs, > 100Mȯ) display Wolf-Rayet spectral morphologies (WNh) whilst on the main-sequence. Bestenlehner (2020) extended the elegant and widely used stellar wind theory by Castor, Abbott & Klein (1975) from the optically thin (O star) to the optically thick main-sequence (WNh) wind regime. The new mass-loss description is able to explain the empirical mass-loss dependence on the Eddington parameter and is suitable for incorporation into stellar evolution models for massive and very massive stars. The prescription can be calibrated with the transition mass-loss rate defined in Vink & Gräfener (2012). Based on the stellar sample presented in Bestenlehner et al. (2014) we derive a mass-loss recipe for the Large Magellanic Cloud using the new theoretical mass-loss prescription of Bestenlehner (2020).

Upcoming large-scale spectroscopic surveys such as WEAVE and 4MOST will provide thousands of spectra of massive stars, which need to be analysed in an efficient and homogeneous way. Studies on massive stars are usually based on samples of a few hundred objects which pushes current spectroscopic analysis tools to their limits because visual inspection is necessary to verify the spectroscopic fit.

The novel spectroscopic analysis pipeline takes advantage of the statistics that large samples provide, and determines the model error to account for imperfections in stellar atmosphere codes due to simplified, wrong or missing physics. Considering observational plus model uncertainties improve spectroscopic fits. The pipeline utilises the entire spectrum rather than selected diagnostic lines allowing a wider range of temperature from B to early O stars to be analysed. A small fraction of stars like peculiar, contaminated or spectroscopic binaries require visual inspection, which are identified through their larger uncertainties.

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.

We compare pre-supernova observations with synthetic photometry from stellar evolution models to infer the progenitor properties of the seven known progenitors of Type Ib and IIb supernovae. Our results are roughly consistent with a hydrogen mass threshold of for a Type II appearance.

Our knowledge of massive star evolution is limited by uncertainties linked with multi-dimensional processes taking place in stellar interiors. Important examples are convective boundary mixing (CBM) and entrainment, which are implemented in 1D stellar evolution models assuming simplified prescriptions. 3D hydrodynamics models can improve these prescriptions by studying realistic multi-D processes for a short timerange (minutes or hours). In these proceedings, we present results coming from a new set of high-resolution hydrodynamics simulations of a neon-burning shell in a massive star, and discuss how the entrainment law can be calibrated from 3D models and then used to improve 1D stellar evolution prescriptions.