Olga S. Bayandina

High-mass protostars are deeply embedded in dust inside their natal cores and are not easily detectable. However, maser emission at centimeter wavelengths, owing to its high brightness, enables us to study gas kinematics in protostars' circumstellar regions. We aim to understand the origin of the ring-like structures outlined by the 6.7 GHz methanol maser emission in six high-mass young stellar objects by performing a sensitive search of the associated radio-continuum emission and derive its properties. We used the Karl G. Jansky Very Large Array in the A configuration at C and K bands in order to image radio-continuum as well as 6.7 GHz methanol and 22 GHz water maser emission. We present the first images of the thermal jets towards four targets in our sample, G23.389+00.185, G23.657-00.127, G28.817+00.365, and G30.400-00.296. In a further target, G23.207-00.377, the complex K band continuum emission makes it unclear whether the detected peaks trace jet knots from a single young protostar or mark multiple compact young protostars. The remaining source G31.047+00.356 shows radio continuum emission associated with an evolved H II region.

High-mass protostars are deeply embedded in dust inside their natal cores and are not easily detectable. However, maser emission at centimeter wavelengths, owing to its high brightness, enables us to study gas kinematics in protostars’ circumstellar regions. We aim to understand the origin of the ringlike structures outlined by the 6.7 GHz methanol maser emission in six high-mass young stellar objects by performing a sensitive search of the associated radio-continuum emission and derive its properties. We used the Karl G. Jansky Very Large Array in the A configuration at C and K bands in order to image radio-continuum as well as 6.7 GHz methanol and 22 GHz water maser emission. We present the first images of the thermal jets toward four targets in our sample, G23.389+00.185, G23.657−00.127, G28.817+00.365, and G30.400−00.296. In a further target, G23.207$-$00.377, the complex K band continuum emission makes it unclear whether the detected peaks trace jet knots from a single young protostar or mark multiple compact young protostars. The remaining source G31.047+00.356 shows radio continuum emission associated with an evolved H II region.

Context. Intermediate-mass protostars can be the preferred targets to study star formation, since they allow us to inquire how the stars form in clustered environments at a relatively close distance from us. Aims. Our aim is to investigate the formation, interaction with the local environment, and propagation of the protostellar jets inside the young stellar object (YSO) cluster G105.42+9.88 (alias LkHα 234). This is one of the least luminous targets of the Protostellar Outflows at the EarliesT Stages (POETS) survey, which has been recently carried out to study young outflow emission on scales of 10–100 au. Methods. We studied the jet launching regions at radii of ≤100 au by employing three different sets of very long baseline interferometry (VLBI) observations of the 22 GHz water masers spanning a time of ≈22 yr. We complemented the VLBI maser data with sensitive multi-band NSF’s Karl G. Jansky Very Large Array (JVLA) continuum observations to image the ionized component of the outflow at scales of 100–1000 au and sensitive Large Binocular Telescope (LBT) H₂ 2.12 µm observations to track the jets at scales of 0.1–1 pc. Results. Our combined observations allow us to study the protostellar outflows from the intermediate-mass binary system VLA 3A and 3B, separated by ≈0.″22, and from VLA 2, an intermediate-mass YSO placed ≈1″ to northwest of VLA 3. In each of these three YSOs, the presence of a thermal jet is suggested by previous Very Large Array (VLA) and our JVLA radio continuum observations. Toward VLA 2 the 2001 and 2011 Very Long Baseline Array (VLBA) observations consistently show that the water masers are tracing a compact (size ≈400 au) bipolar collimated (PA ≈ 70°) outflow, i.e., a jet. The analysis of the 3D flow velocities proves that the jet is magneto-centrifugally launched in a magnetohydrodynamic (MHD) disk wind (DW). We infer launch radii in the range 10–50 au for the streamlines traced by the water masers. The global VLBI 2023 water maser observations indicate that the jet propagation can be hindered by a very dense clump placed northeast of VLA 2 and that is consistent with the large-scale LBT H₂ emission, tracing only the southwest lobe of the VLA 2 jet. Instead, the parallel (PA ≈ 55^°−57^°) jets emitted by the nearby YSOs VLA 3A and 3B can be reliably tracked with the H₂ emission at scales of a few 10″ to both the southwest and the northeast. In particular, northeast of VLA 3 the direction of these two jets crosses a linear chain of spaced H₂ knots, which is a clear signature of an episodic jet. In VLA 3B the spatial distribution and intensity of the water masers change significantly between the VLBA 2011 and global VLBI 2023 observations, likely reflecting a different state (active in 2011 and quiescent in 2023) of wind ejection. The variable ejection from VLA 3B could be the origin of the episodic jet observed at larger scales. Conclusions. This work shows that the combination of VLBI observations of the 22 GHz water masers with sensitive high-angular-resolution radio continuum and near-infrared H₂ 2.12 µm observations permit to investigate the launching region of protostellar outflows, to trace their interaction with the surrounding environment, and track their paths at larger scales.

Context. Magnetohydrodynamic disk-winds are thought to play a key role in the formation of massive stars by providing the fine-tuning between accretion and ejection, where excess angular momentum is redirected away from the disk, allowing further mass growth of a young protostar. However, only a limited number of disk-wind sources have been detected to date. To better constrain the exact mechanism of this phenomenon, expanding the sample is critical. Aims. We performed a detailed analysis of the disk-wind candidate G11.92-0.61 MM1 by estimating the physical parameters of the massive protostellar system and constraining the wind-launching mechanism. Methods. Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 observations of G11.92-0.61 MM1 were conducted in September 2021 with ALMA’s longest baselines, which provided a synthesised beam of ~30 mas. We obtained high-resolution images of the CH₃CN (υ₈=1 and υ=0), CH₃OH, SO₂, and SO molecular lines, as well as the 1.3 mm continuum. Results. Our high-resolution molecular data allowed us to refine the parameters of the disk-outflow system in MM1. The rotating disk is resolved into two regions with distinct kinematics: the inner region (300 au), traced by mid-velocity CH₃CN emission, rotates in a sub-Keplerian regime. The central source is estimated to be ~20 M_⊙, which is about half the mass estimated in previous lower-resolution studies. A strong collimated outflow is traced by SO and SO₂ emission up to ~3400 au around MM1a. The SO and SO₂ emissions show a rotation-dominated velocity pattern, a constant specific angular momentum, and a Keplerian profile that suggests a magneto-centrifugal disk-wind origin with launching radii of ~50–100 au. Conclusions. G11.92-0.61 MM1 appears to be one of the clearest cases of molecular line-traced disk-winds detected around massive protostars.

Context. Understanding the launching mechanism of winds and jets remains one of the fundamental challenges in astrophysics. The Protostellar Outflows at the EarliesT Stages (POETS) survey has recently mapped the 3D velocity field of the protostellar winds in a sample (37) of luminous young stellar objects (YSOs) at scales of 10–100 au via very long baseline interferometry (VLBI) observations of the 22 GHz water masers. In most of the targets, the distribution of the 3D maser velocities can be explained in terms of a magnetohydrodynamic (MHD) disk wind (DW). Aims. Our goal is to assess the launching mechanism of the protostellar wind in the YSO IRAS 21078+5211, the most promising MHD DW candidate from the POETS survey. Methods. We have performed multi-epoch Very Long Baseline Array (VLBA) observations of the 22 GHz water masers in IRAS 21078+5211 to determine the 3D velocities of the gas flowing along several wind streamlines previously identified at a linear resolution of ~1 au. Results. Near the YSO at small separations along (xl ≤ 150 au) and across (R ≤ 40 au) the jet axis, water masers trace three individual DW streamlines. By exploiting the 3D kinematic information of the masers, we determined the launch radii of these streamlines with an accuracy of ~1 au, and they lie in the range of 10–50 au. At increasingly greater distances along the jet (110 au ≤ xl ≤ 220 au), the outflowing gas speeds up while it collimates close to the jet axis. Magneto-centrifugal launching in a radially extended MHD DW appears to be the only viable process to explain the fast (up to 60 km s⁻¹) and collimated (down to 10°) velocities of the wind in correspondence with launch radii ranging between 10 and 50 au. At larger separations from the jet axis (R ≥ 100 au), the water masers trace a slow (≤20 km s⁻¹), radially expanding arched shock-front with kinematics inconsistent with magneto-centrifugal launching. Our resistive-magnetohydrodynamical simulations indicate that this shock-front could be driven by magnetic pressure. Conclusions. The results obtained in IRAS 21078+5211 demonstrate that VLBI observations of the 22 GHz water masers can reliably determine the launching mechanism of protostellar winds.

We present results on simultaneous observations of Class I methanol masers at 25, 36, and 44 GHz towards 22 Galactic targets carried out with the Effelsberg 100-m telescope. The study investigates relations between the hyperfine (HF) structure of the torsion-rotation transitions in CH₃OH and maser activity. By analyzing the radial velocity shifts between different maser lines together with the patterns of the HF structure based on laboratory measurements and quantum-chemical calculations, we find that in any source only one specific HF transition forms the maser emission and that this transition changes from source to source. The physical conditions leading to this selective behavior are still unclear. Using accurate laboratory rest frequencies for the 25 GHz transitions, we have refined the centre frequencies for the HF multiplets at 36, 44, and 95 GHz: |$f_{36} = (36169.2488\pm 0.0002_{\rm stat} \pm 0.0004_{\rm sys})$| MHz. |$f_{44} = (44069.4176\pm 0.0002_{\rm stat} \pm 0.0004_{\rm sys})$| MHz, and |$f_{95} = (95169.4414\pm 0.0003_{\rm stat} \pm 0.0004_{\rm sys})$| MHz. Comparison with previous observations of 44 GHz masers performed 6-10 years ago with a Korean 21-m KVN telescope towards the same targets confirms the kinematic stability of Class I maser line profiles during this time interval and reveals a systematic radial velocity shift of 0.013 ± 0.005 km s⁻¹ between the two telescopes.

Context. Maser flares are particularly significant in the study of massive star formation as they not only signal but also provide unique insights into transient phenomena such as accretion bursts. Aims. With this project, we aim to investigate the context of the ongoing 6.7 GHz methanol maser flare in the little-known massive star-forming region G11.497-1.485. Methods We carried out two epochs of the Karl G. Jansky Very Large Array (VLA) observation for 6.7 GHz and 12 GHz class II methanol, 22 GHz water masers, and continuum in the C, Ku, and K bands. Results. The VLA overview revealed the presence of five distinct radio-continuum sources (CM1-4 and N) in G11.497-1.485. The central source, CM1, is found to show signs of accretion disc fragmentation, highlighted by the centimetre-continuum-traced fragments, and is found to drive a high-energy jet, the ends of which are marked by non-thermal knots CM2 and CM3. CM1 showed a gradual flaring of methanol masers and a fading of a 22 GHz water maser, which might be signalling an accretion burst. The two remaining sources of the region, CM4 and N, make up one of the most compact jet and disc–jet systems found to date. Conclusions. The obtained data reveal, for the first time, the structure of the G11.497-1.485 region. The change in fluxes of the maser and the continuum emission confirm a transient event and reveal its impact on multiple sources in the region.

Infrared dark clouds (IRDCs) represent the earliest stage of high-mass star formation and host molecular cores at different states of activity from quiet state without any IR-signature of star formation to active state with IR-signatures and pronounced maser activity. Many IRDCs show indications of shocked gas associated with protostar outflows and can contain class I methanol masers (cIMMs). The aim of this study is to probe different types of cores in IRDCs with cIMMs and thermal molecular emission and to investigate the relationship between presence of cIMMs and physical conditions in IRDCs. For a sample of 37 molecular cores, using the 20-m Onsala radio telescope, we collected molecular line data at 44, 85 and 97 GHz for more than 15 species including CH₃OH, CH₃CCH, CS. Kinetic temperature of the gas and molecular column densities were obtained. Methanol emission at 44 GHz was detected in 29 sources, with 4 sources are being new discoveries. None of the cores in quiescent state show emission at 44 GHz. Our results testify that cIMM emission is a reliable marker of advanced state of molecular cores. The higher detection rate for intermediate and IR-quiet sources suggests that cIMMs most readily trace the early stages of star formation characterized by moderate IR-signatures. We found that masers with higher flux densities tend to be associated with emission in the CH₃CCH lines with higher integrated intensities. Sources undetected at 44 GHz have 4 times lower integrated intensities of CH₃CCH and exhibit poorer molecular spectra than the most sources with cIMMs.