We investigate the presence and spatial characteristics of the jet base emission in M87* at 230 GHz, enabled by the significantly enhanced (u,v) coverage in the 2021 Event Horizon Telescope (EHT) observations. The integration of the 12−m Kitt Peak Telescope (USA) and NOEMA (France) stations into the array introduces two critical intermediate-length baselines to SMT (USA) and IRAM 30−m (Spain), providing sensitivity to emission structures at spatial scales of ∼250 μas and ∼2500 μas (∼ 0.02 pc and ∼ 0.02 pc). Without these new baselines, previous EHT observations of the source in 2017 and 2018 lacked the capability to constrain emission on large scales, where a “missing flux” of order ∼1 Jy is expected to reside. To probe these scales, we analyzed closure phases–robust against station-based gain calibration errors–and model the jet base emission using a simple Gaussian component offset from the compact ring emission at spatial separations > 100 μas. Our analysis revealed a Gaussian feature centered at (ΔRA ≈ 320 μas, ΔDec. ≈ 60 μ as), projected separation of ≈ 5500 AU, with an estimated flux density of only ∼60 mJy, implying that most of the missing flux identified in previous EHT studies had to originate from different, larger scales. Brighter emission at the relevant spatial scales is firmly ruled out, and the data do not favor more complex models. This component aligns with the inferred position of the large-scale jet and is therefore physically consistent with the emission of the jet base. While our findings point to detectable jet base emission at 230 GHz, the limited coverage provided by only two intermediate baselines limits our ability to robustly reconstruct its morphology. Consequently, we treated the recovered Gaussian as an upper limit on the jet base flux density. Future EHT observations with expanded intermediate baseline coverage will be essential to constrain the structure and nature of this component with higher precision.

Sagittarius A* ( the supermassive black hole at the center of the Milky Way, provides a unique laboratory to study accretion dynamics and plasma processes near the event horizon. We investigated the variability and polarization properties of using ALMA observations during the 2018 Event Horizon Telescope campaign. We analyzed high-cadence full-polarization light curves from ALMA at millimeter wavelengths, performed time-series analysis, and investigated the temporal behavior during an X-ray flare observed by on 2018 April 24. The variability characteristics are compared with expectations from standard accretion flow models. Chandra We find low variability in total intensity (σ/μ < 10%), but significantly higher variability in linear and circular polarization (∼ 30% and ∼ 50%, respectively). A time-series analysis reveals red-noise variability, with power spectral densities between -2 and -3 across all Stokes parameters. Polarized intensity shows stable intra-day timescales, while total intensity exhibits more variable timescales, suggesting distinct emission regions, with polarization likely arising from a coherent structure. On April 24, a statistically significant inter-band delay in polarized intensity coincides with a near-simultaneous X-ray and millimeter peak that deviates from the typical delayed flare scenario. This event also features enhanced millimeter variability and coherent polarization loop evolution. The observed simultaneity challenges standard models of transient synchrotron emission with cooling delays, favoring instead a scenario of continuous energy injection in an optically thin region. Our results offer new constraints on the physical mechanisms driving variability in and provide key observational input for refining theoretical models of accretion and plasma behavior in the vicinity of supermassive black holes.

We present first results from SIMPLIFI (Study of Interstellar Magnetic Polarization: a Legacy Investigation of Filaments), a SOFIA/HAWC+ 214 mu m polarimetric survey of Galactic molecular cloud filaments. We trace magnetic field morphology from the DR21 Main Ridge into surrounding subfilaments at similar to 0.1 pc resolution, extending polarimetric detections for the first time beyond high-column-density regions probed by prior submillimeter observations. We compare the plane-of-sky orientations of the magnetic field, B-pos , the projected gravitational acceleration, g(pos) , and the intensity gradient rotated by 90 degrees, del I-perpendicular to . The relative orientation of Bpos and del I-perpendicular to transitions from preferentially parallel in subfilaments to perpendicular in the DR21 Main Ridge at N(H-2) similar to 2 & times; 10(22) cm(-2), consistent with thresholds seen with Planck and expected in clouds formed from strongly magnetized, sub-Alfv & eacute;nic, magnetically subcritical gas ( M-A less than or similar to 1 , M/Phi(B)<[M/Phi(B)](cr) ). We find that the relative alignment between orientations shows region-to-region and pixel-to-pixel variations at fixed column density. Column density alone is thus not sufficient to encode changes in magnetic field structure. Theoretical models must account for additional drivers. Our central finding is that g(pos) and B-pos remain aligned throughout the cloud regardless of column density or environment, unlike the environment-dependent behavior of B-pos versus del I-perpendicular to and gpos versus del I-perpendicular to . This persistent alignment is consistent with magnetically guided accretion: subfilaments channel material along field lines at several 10(-3) M circle dot yr(-1), sufficient to assemble the Ridge within similar to 10(6) yr and sustain high-mass star formation. This framework also explains why observed radial velocities (approximate to 2 km s(-1)) fall well below freefall expectations (approximate to 8 km s(-1)): with the field nearly in the plane of the sky, only a small fraction of the accretion velocity projects along the line of sight.

Event Horizon Telescope (EHT) images of the supermassive black hole M87* depict an asymmetric ring of emission. General relativistic magnetohydrodynamic (GRMHD) models of M87* and its accretion disk predict that the amplitude and location of the ring's peak brightness asymmetry should fluctuate due to turbulence in the source plasma. We compare the observed distribution of brightness asymmetry amplitudes to the simulated distribution in GRMHD models, across varying black hole spin a(*). We show that, for strongly magnetized (MAD) models, three epochs of EHT data marginally disfavor divided by a(*)divided by less than or similar to 0.2. This is consistent with the Blandford-Znajek model for M87's jet, which predicts that M87* should have nonzero spin. We show quantitatively how future observations could improve spin constraints and discuss how improved spin constraints could distinguish between differing jet-launching mechanisms and black hole growth scenarios.

In very-long baseline interferometric arrays, nearly co-located stations probe the largest scales and typically cannot resolve the observed source. In the absence of a large-scale structure, closure phases constructed with these stations are zero and, since they are independent of station-based errors, they can be used to probe data issues. Here, we show how these trivial closure phases become nonzero with a brightness distribution on smaller scales than their short baseline would suggest. When applied to sources that are made up of a bright compact and large-scale diffuse component, the trivial closure phases directly measure the centroid relative to the compact source and higher-order image moments. We present a technique to measure these image moments with minimal model assumptions and validate it on synthetic Event Horizon Telescope (EHT) data. We then apply this technique to 2017 and 2018 EHT observations of M87* and find a weak preference for extended emission in the direction of the large-scale jet. We also apply it to 2021 EHT data and measure the source centroid about 1 mas northwest of the compact ring, which is consistent with the jet observed at lower frequencies.

Oxygen isotope abundances and their ratios are fingerprints of stellar evolution, and therefore provide a powerful tool in tracing the enrichment history of galaxies. However, their behavior in low-metallicity dwarf galaxies remains largely unexplored. The Small Magellanic Cloud (SMC), a nearby analog of young high-redshift galaxies, offers an ideal laboratory to investigate this regime. Using the Atacama Compact Array, we observed the J = 2 → 1 transitions of ^12 CO, ^13 CO, C ^18 O, and C ^17 O from the massive star-forming region LIRS 36 (aka N12A), achieving the first detection of C ^17 O in the SMC. This detection enables the first direct measurement of the ^18 O/ ^17 O abundance ratio of 0.87 ± 0.26 in this galaxy, which is substantially lower than all values in the literature, including molecular clouds in the Milky Way and other galaxies. Such a low ratio of ^18 O/ ^17 O, together with a high ^13 CO/C ^18 O ratio, indicates chemical enrichment dominated by low-mass stars, consistent with the observed paucity of high-mass stars in the SMC. We suggest that the SMC is governed by a top-light integrated galaxy-wide initial mass function, predicted by the SMC’s persistently low star formation activities.

Context. The 2017 observing campaign of the Event Horizon Telescope (EHT) delivered the first very long baseline interferometry (VLBI) images at the observing frequency of 230 GHz, leading to a number of unique studies on black holes and relativistic jets from active galactic nuclei (AGN). In total, eighteen sources were observed, including the main science targets, Sgr A* and M 87, and various calibrators. Sixteen sources were AGN. Aims. We investigated the morphology of the sixteen AGN in the EHT 2017 data set, focusing on the properties of the VLBI cores: size, flux density, and brightness temperature. We studied their dependence on the observing frequency in order to compare it with the Blandford-Konigl (BK) jet model. In particular, we aimed to study the signatures of jet acceleration and magnetic energy conversion. Methods. We modeled the source structure of seven AGN in the EHT 2017 data set using linearly polarized circular Gaussian components (1749+096, 1055+018, BL Lac, J0132-1654, J0006-0623, CTA 102, and 3C 454.3) and collected results for the other nine AGN from dedicated EHT publications, complemented by lower frequency data in the 2-86 GHz range. Combining these data into a multifrequency EHT+ data set, we studied the dependences of the VLBI core component flux density, size, and brightness temperature on the frequency measured in the AGN host frame (and hence on the distance from the central black hole), characterizing them with power law fits. We compared the observations with the BK jet model and estimated the magnetic field strength dependence on the distance from the central black hole. Results. Our observations spanning event horizon to parsec scales indicate a deviation from the standard BK model, particularly in the decrease of the brightness temperature with the observing frequency. Only some of the discrepancies may be alleviated by tweaking the model parameters or the jet collimation profile. Either bulk acceleration of the jet material, energy transfer from the magnetic field to the particles, or both are required to explain the observations. For our sample, we estimate a general radial dependence of the Doppler factor delta proportional to r(<= 0.5). This interpretation is consistent with a magnetically accelerated sub-parsec jet. We also estimate a steep decrease of the magnetic field strength with radius B proportional to r(-3), hinting at jet acceleration or efficient magnetic energy dissipation.

Context. High-mass stellar embryos are embedded in warm envelopes that provide mass reservoirs for the accretion process onto final stars. Feedback from star formation activities in return impacts the properties of the envelopes, offering us a unique opportunity to investigate star formation processes. Aims. Our goals are to characterise the properties of warm envelopes of proto- or young stellar objects at different evolutionary stages based on the morphology and kinematics of submillimetre emission from the (CO)-C-13 (6-5) line and to examine their relations with star formation processes. Methods. Using the Atacama Pathfinder EXperiment (APEX) telescope, we obtained maps of (CO)-C-13 (6-5) emission with an angular size of 80 '' x 80 '' (ranging from 0.3 pc x 0.3 pc to 4.9 pc x 4.9 pc in physical size) of 99 massive clumps from the ATLASGAL survey of submillimetre dust continuum emission. Our maps are classified based on morphological complexities, and the radial structure of (CO)-C-13 (6-5) emission is characterised for simple single-core sources. In addition, the velocity centroids of (CO)-C-13 (6-5) emission are compared to small- and large-scale gas kinematics (traced by (CO)-C-12 (6-5) and (CO)-C-13 (2-1) emission, respectively), aiming to shed light on the origin of envelope kinematics. Results. (CO)-C-13 (6-5) emission is detected towards sources in all stages of high-mass star formation, with a detection rate of 83% for the whole sample. The detection rate, line width, and peak brightness temperature increase with evolutionary stage, and the line luminosity is strongly correlated with the bolometric luminosity and the clump mass. These results indicate that the excitation of (CO)-C-13 (6-5) emission is closely related to star formation processes. In addition, the radial distributions of (CO)-C-13 (6-5) emission for single-core sources can be well fitted by power-law functions, suggesting a relatively simple envelope structure for the majority of our sources (52 out of 99). The slopes of the radial distributions are systematically steeper for the most evolved group of sources (that host HII regions), which likely results from enhancements in density and/or temperature at the central parts of the warm envelopes. As for the (CO)-C-13 (6-5) kinematics, linear velocity gradients are common among the single-core sources (44 out of 52), and the measured mean velocity gradients are on average 3 km s(-1) pc(-1). Our comparison of the (CO)-C-13 (6-5), (CO)-C-12 (6-5), and (CO)-C-13 (2-1) kinematics suggests that the origin of the linear velocity gradients in the warm envelopes is complex and unclear for many sources. Conclusions. (CO)-C-13 (6-5) emission is ubiquitous in a wide variety of massive clumps, ranging from young sources where protostars have not yet been formed to evolved sources with fully developed HII regions. The excitation of (CO)-C-13 (6-5) emission in warm envelopes is likely impacted by different processes at different epochs of high-mass star formation, while the origin of the (CO)-C-13 (6-5) kinematics remains elusive and needs further investigation.

Despite being only the 19th most abundant element in the interstellar medium, chlorine's reactivity and volatility give rise to a unique interstellar chemistry, favouring the formation of several chlorine-bearing hydrides. Further, the ^35Cl/ ^37Cl ratio probes nucleosynthesis across the Galaxy. Yet, studies of Cl-bearing molecules have remained limited to a few sightlines due to observational challenges. We systematically investigated the Galactic distribution of HCl and the [H^35Cl]/[H^37Cl] ratio in high-mass star-forming regions. As a probe of a region's nucleosynthesis history, this ratio may constrain predictions of Galactic chemical evolution models. We observed the ground-state J=1-0 lines of H^35Cl and H^37Cl toward 28 high-mass star-forming regions with SEPIA660 on APEX, more than doubling the number of known HCl detections and revealing with XCLASS models emission from both cores and outflows. H^35Cl was detected in all sources, H^37Cl in all but two, with spectral line profiles ranging from those with only emission to complex emission-absorption mixtures. We find column densities of the order of 10^13 cm^-2 for H^35Cl and isotopic ratios between 1.6 and 3.5 in emission-only sources. The derived [H^35Cl]/[H^37Cl] aligns with Galactic chemical evolution models and shows no trend with Galactocentric radius. However, local variations may reflect recent nucleosynthesis. Overall, the results suggest that most Galactic chlorine was synthesized during epochs of lower average metallicity in the Galaxy. Notably, we detect H^35Cl emission arising from outflows - particularly explosive ones - hinting at its presence in a broader range of environments. The present single-dish observations cannot reveal the origin of HCl in outflows; necessitating interferometric follow-up observations.

We present JWST NIRCam imaging targeting 13 z similar to 3 infrared-luminous (L-IR similar to 5 x 10(12)L(circle dot)) galaxies from the ALESS survey with uniquely deep, high-resolution (0.'' 08-0.'' 16) Atacama Large Millimeter/submillimeter Array 870 mu m imaging. The 2.0-4.4 mu m (observed frame) NIRCam imaging reveals the rest-frame near-infrared stellar emission in these submillimeter-selected galaxies at the same (sub)kiloparsec resolution as the 870 mu m dust continuum. The newly revealed stellar morphologies show striking similarities with the dust continuum morphologies at 870 mu m, with the centers and position angles agreeing for most sources, clearly illustrating that the spatial offsets reported previously between the 870 mu m and Hubble Space Telescope morphologies were due to strong differential dust obscuration. The F444W sizes are 78% +/- 21% larger than those measured at 870 mu m, in contrast to recent results from hydrodynamical simulations that predict larger 870 mu m sizes. We report evidence for significant dust obscuration in F444W for the highest-redshift sources, emphasizing the importance of longer-wavelength MIRI imaging. The majority of the sources show evidence that they are undergoing mergers/interactions, including tidal tails/plumes-some of which are also detected at 870 mu m. We find a clear correlation between NIRCam colors and 870 mu m surface brightness on similar to 1 kpc scales, indicating that the galaxies are primarily red due to dust-not stellar age-and we show that the dust structure on similar to kpc scales is broadly similar to that in nearby galaxies. Finally, we find no strong stellar bars in the rest-frame near-infrared, suggesting the extended bar-like features seen at 870 mu m are highly obscured and/or gas-dominated structures that are likely early precursors to significant bulge growth.

We investigate the origin of the elliptical ring structure observed in the images of the supermassive black hole M87*, aiming to disentangle contributions from gravitational, astrophysical, and imaging effects. Leveraging the enhanced capabilities of the Event Horizon Telescope (EHT)'s 2018 array, including improved (u,v)-coverage from the Greenland Telescope, we measured the ring's ellipticity using five independent imaging methods, obtaining a consistent average value of tau = 0.08(-0.02)(+0.03) with a position angle of xi = 50.1(-7.6)(+6.2) degrees. To interpret this measurement, we compared it to general relativistic magnetohydrodynamic (GRMHD) simulations spanning a wide range of physical parameters including the thermal or nonthermal electron distribution function, spins, and ion-to-electron temperature ratios in both low- and high-density regions. We find no statistically significant correlation between spin and ellipticity in GRMHD images. Instead, we identify a correlation between ellipticity and the fraction of non-ring emission, particularly in nonthermal models and models with higher jet emission. These results indicate that the ellipticity measured from the M87* emission structure is consistent with that expected from simulations of turbulent accretion flows around black holes, where it is dominated by astrophysical effects rather than gravitational ones. Future high-resolution imaging, including space very long baseline interferometry and long-term monitoring, will be essential to isolate gravitational signatures from astrophysical effects.

Close companions influence stellar evolution through tidal interactions, mass transfer and mass-loss effects. While such companions are detected around young stellar objects, main-sequence stars, red giants and compact objects, direct observational evidence of close-in companions around asymptotic giant branch (AGB) stars has remained elusive. Here we present (sub)millimetre time-domain imaging spectroscopy revealing the Keplerian motion of a close-in companion around the AGB star pi 1 Gruis. The companion, slightly more massive than the AGB star, is likely a main-sequence star. Unlike more evolved stars with companions at comparable distances, the companion of pi 1 Gruis follows a circular orbit, suggesting an eccentricity-generating mechanism during the late- or post-AGB phase. Our analysis suggests that model-predicted circularization rates may be underestimated. Our results highlight the potential of multi-epoch (sub)millimetre interferometry in detecting the Keplerian motion of close companions to giant stars and open avenues for our understanding of tidal interaction physics and binary evolution.

Context. High-mass stellar embryos are embedded in warm envelopes that provide mass reservoirs for the accretion process onto final stars. Feedback from star formation activities in return impacts the properties of the envelopes, offering us a unique opportunity to investigate star formation processes. Aims. Our goals are to characterise the properties of warm envelopes of proto- or young stellar objects at different evolutionary stages based on the morphology and kinematics of submillimetre emission from the 13CO (6–5) line and to examine their relations with star formation processes. Methods. Using the Atacama Pathfinder EXperiment (APEX) telescope, we obtained maps of 13CO (6–5) emission with an angular size of 80″ × 80″ (ranging from 0.3 pc × 0.3 pc to 4.9 pc × 4.9 pc in physical size) of 99 massive clumps from the ATLASGAL survey of submillimetre dust continuum emission. Our maps are classified based on morphological complexities, and the radial structure of 13CO (6–5) emission is characterised for simple single-core sources. In addition, the velocity centroids of 13CO (6–5) emission are compared to small- and large-scale gas kinematics (traced by 12CO (6–5) and 13CO (2–1) emission, respectively), aiming to shed light on the origin of envelope kinematics. Results. 13CO (6–5) emission is detected towards sources in all stages of high-mass star formation, with a detection rate of 83% for the whole sample. The detection rate, line width, and peak brightness temperature increase with evolutionary stage, and the line luminosity is strongly correlated with the bolometric luminosity and the clump mass. These results indicate that the excitation of 13CO (6–5) emission is closely related to star formation processes. In addition, the radial distributions of 13CO (6–5) emission for single-core sources can be well fitted by power-law functions, suggesting a relatively simple envelope structure for the majority of our sources (52 out of 99). The slopes of the radial distributions are systematically steeper for the most evolved group of sources (that host HII regions), which likely results from enhancements in density and/or temperature at the central parts of the warm envelopes. As for the 13CO (6–5) kinematics, linear velocity gradients are common among the single-core sources (44 out of 52), and the measured mean velocity gradients are on average 3 km s−1 pc−1. Our comparison of the 13CO (6−5), 12CO (6−5), and 13CO(2−1) kinematics suggests that the origin of the linear velocity gradients in the warm envelopes is complex and unclear for many sources. Conclusions. 13CO (6–5) emission is ubiquitous in a wide variety of massive clumps, ranging from young sources where protostars have not yet been formed to evolved sources with fully developed HII regions. The excitation of 13CO (6–5) emission in warm envelopes is likely impacted by different processes at different epochs of high-mass star formation, while the origin of the 13CO (6–5) kinematics remains elusive and needs further investigation.

We present a new method for modelling the kinematics of galaxies from interferometric observations by performing the optimization of the kinematic model parameters directly in visibility-space instead of the conventional approach of fitting velocity fields produced with the CLEAN algorithm in real-space. We demonstrate our method on ALMA observations of $^{12}$CO (2$-$1), (3$-$2) or (4$-$3) emission lines from an initial sample of 30 massive 850$\mu$m-selected dusty star-forming galaxies with far-infrared luminosities $\gtrsim$$\,10^{12}\,$L$_{\odot}$ in the redshift range $z \sim\,$1.2$-$4.7. Using the results from our modelling analysis for the 12 sources with the highest signal-to-noise emission lines and disk-like kinematics, we conclude the following: (i) Our sample prefers a CO-to-$H_2$ conversion factor, of $\alpha_{\rm CO} = 0.92 \pm 0.36$; (ii) These far-infrared luminous galaxies follow a similar Tully$-$Fisher relation between the circularized velocity, $V_{\rm circ}$, and baryonic mass, $M_{\rm b}$, as more typical star-forming samples at high redshift, but extend this relation to much higher masses $-$ showing that these are some of the most massive disk-like galaxies in the Universe; (iii) Finally, we demonstrate support for an evolutionary link between massive high-redshift dusty star-forming galaxies and the formation of local early-type galaxies using the both the distributions of the baryonic and kinematic masses of these two populations on the $M_{\rm b}\,-\,\sigma$ plane and their relative space densities.

Context. The Cygnus-X complex is a massive (a few 10(6) M-circle dot molecular gas mass), nearby (1.4 kpc) star-forming region with several OB associations. Of these, Cyg OB2 is the largest, with at least 169 OB stars. DR18 is the largest globule near the OB2 association, making it a perfect target for investigating the influence of ultraviolet radiation on molecular clouds. Aims. By analyzing emission from different molecular species, we aim to study the molecular gas structures toward DR18 using high angular-resolution molecular line observations. Methods. As part of the Cygnus Allscale Survey of Chemistry and Dynamical Environments (CASCADE) program, we carried out 3.6 millimeter (mm) continuum and spectral line high-resolution observations (similar to 3-4 '') toward DR18, covering several molecular species (e.g., HCN, HNC, H2CO, N2H+, SiO, C2H, deuterated species, etc.) with the Northern Extended Millimeter Array (NOEMA) and the Institut de Radioastronomie Millimetrique (IRAM) 30 m telescope. In addition, multi-wavelength archival datasets from midinfrared (MIR) to centimeter (cm) wavelengths were used to provide a comprehensive analysis of the region. Results. The spectral index analysis shows significant contamination of the 3.6 mm continuum by free-free emission from ionized gas. A comparison of the 3.6 mm and 6cm continuum emission confirms that a B2 star (DR18-05) shapes the cometary HII region in the DR18 cavity, with ionized gas escaping toward the OB2 association. On the other hand, the extended 3.6 mm and 6 cm continuum emission are likely to trace photoevaporating ionized gas from ultraviolet radiation from the Cyg OB2 association - not from DR18- 05. To study the feedback of the B2 star and the OB2 association on surrounding molecular regions, we analyzed the HCO+, HCN, HNC, N2H+, and SiO emission lines. The shell structure around DR18-05 indicates photodissociation regions (PDRs) formed by the expanding HII region and photo-erosion from DR18-05 and OB2 stars. We also identified 18 compact cores with N2H+ emission, half of which are gravitationally bound (virial parameter, alpha(vir), less than or similar to 2.0), and mostly located in colder regions (T-HCN/HNC < 30 K) behind the PDRs. The SiO emission is found only in PDRs, with narrow-line widths (similar to 0.8-2.0 km s(-1)) and lower abundances (X(SiO) similar to 5 x 10(-11)-1 x 10(-10)). Comparing with the UV irradiated shock models, we suggest that the SiO emission partially encompassing the HII region arises from the molecular gas region, marginally compressed by low-velocity shocks with similar to 5 km s(-1), irradiated by external UV radiation (G(0) similar to 10(2)-10(3)), as they traverse through a medium with n(H) similar to 10(4) to 10(5) cm(-3). These shocks can be generated by the initial expansion of the HII region and potentially by stellar winds.

Context. Theoretical models of early accretion during the formation process of massive stars have predicted that H II regions exhibit radio variability on timescales of decades. However, large-scale searches for such temporal variations with sufficient sensitivity have not yet been carried out. Aims. Our aim is to identify H II regions with variable radio wavelength fluxes and to investigate the properties of the identified objects, especially those with the highest level of variability. Methods. We compared the peak flux densities of 86 ultracompact H II (UC H II) regions measured by the GLOSTAR and CORNISH surveys and identified variables that show flux variations higher than 30% over the similar to 8 yr timespan between these surveys. Results. We found a sample of 38 variable UC H II regions, which is the largest sample identified to date. The overall occurrence of variability is 44 +/- 5%, suggesting that variation in UC H II regions is significantly more common than prediction. The variable UC H II regions are found to be younger than nonvariable UC H II regions, all of them meeting the size criterion of hypercompact (HC) H II regions. We studied the seven UC H II regions that show the highest variability (the "Top7") with variations >100%. The Top7 variable UC H II regions are optically thick at 4-8 GHz and compact, suggesting they are in a very early evolutionary stage of HC H II or UC H II regions. There is a significant correlation between variability and the spectral index of the radio emission. No dependence is observed between the variations and the properties of the sources' natal clumps traced by submillimeter continuum emission from dust, although variable H II regions are found in clumps at an earlier evolutionary stage.

Aims. OH 231.8+4.2 , also known as the Rotten Egg or Calabash nebula is a protoplanetary nebula which is seen in the direction of the open cluster M 46. While an association of the nebula with the cluster has been suggested in the past, this has been never confirmed. Here, we present accurate trigonometric parallax and proper motion measurements using VLBI observations of masers in the nebula and Gaia DR3 data for the cluster. Methods. We observed 22 GHz H2O and 43 GHz SiO masers around OH 231.8+4.2 using the Very Long Baseline Array at 4 epochs over 1 year. We also calculated the parallax and proper motion of the open star cluster M 46 using Gaia DR3 data. Results. Based on astrometric monitoring for 1 year, we measured an annual parallax of OH 231.8+4.2 to be 0.65 +­ 0.01 mas (stat.) +­ 0.02 mas (syst.), corresponding to a distance of 1.54 +­ 0.05 kpc. This agrees well with the parallax of M 46 from the Gaia DR3 data, which is 0.639 +­ 0.001 mas (stat.) +­ 0.010 mas (syst.). We re-estimated the luminosity of OH 231.8+4.2 to be 1.4 x 10^4 L_sol. However, there is a 15 km/s velocity difference between OH 231.8+4.2 and M 46 which could be caused by a past merger event.

We present the first wide-field extragalactic continuum catalogue with the MeerKAT S-band (2.5 GHz), of the radio-selected DEEP2 field. The combined image over the S1 (1.96-2.84 GHz) and S4 (2.62-3.50 GHz) sub-bands has an angular resolution of 6.8 arcsec x 3.6 arcsec (4.0 arcsec x 2.4 arcsec) at a robust weighting of R = 0.3 (R = -0.5) and a sensitivity of 4.7 (7.5) mu Jy beam(-1 )with an on-source integration time of 70 min and a minimum of 52 of the 64 antennas, for respective observations. We present the differential source counts for this field, as well as a morphological comparison of resolved sources between S-band and archival MeerKAT L-band images. We find consistent source counts with the literature and provide spectral indices fitted over a combined frequency range of 1.8 GHz. These observations provide an important first demonstration of the capabilities of MeerKAT S-band imaging with relatively short integration times, as well as a comparison with existing S-band surveys, highlighting the rich scientific potential with future MeerKAT S-band surveys.

Near the center of our Milky Way is a bar-like structure and the so-called Expanding 3 kpc arms. We currently have limited knowledge of this important region, since we are about 8.2 kpc from the center and cannot directly observe it at optical wavelengths, owing to strong extinction from interstellar dust. Here we present extremely precise very long baseline interferometry measurements of H _2 O maser sources from the BeSSeL Survey, where extinction is not a problem, which accurately determine the three-dimensional locations and motions of three massive young stars. Combined with previous measurements, these stars delineate a trail of orbits outlining the Milky Way’s Galactic bar. We present the first measurements capturing the dynamics of quasi-elliptical (X1) orbits around the Galactic bar. Our findings provide evidence substantiating the existence of such orbits populated by massive young stars. Our measurements of the position and velocity of a number of massive young stars, previously identified with the Expanding 3 kpc arms, show that they are more likely located in the X1 orbits about the Galactic bar. Also, some stars previously assigned to the Norma spiral arm appear to be in these orbits, which suggests that this spiral arm does not extend past the end of the bar.

The Cygnus-X complex is a massive, nearby (1.4 kpc) star-forming region with several OB associations. As part of the Cygnus Allscale Survey of Chemistry and Dynamical Environments (CASCADE) program, we carried out 3.6 millimeter (mm) continuum and spectral line high-resolution observations (∼ 3 - 4”) toward DR18, covering several molecular species with the Northern Extended Millimeter Array (NOEMA) and the Institut de Radioastronomie Millimétrique (IRAM) 30m telescope. In addition, multi-wavelength archival datasets were used to provide a comprehensive analysis of the region. A comparison of the 3.6mm and 6 cm continuum emission confirms that a B2 star (DR18-05) shapes the cometary HII region in the DR18 cavity, with ionized gas escaping toward the OB2 association. On the other hand, the extended 3.6mm and 6 cm continuum emission are likely to trace photoevaporating ionized gas from ultraviolet radiation from the Cyg OB2 association, not from DR18-05. The shell structure around DR18-05 indicates photodissociation regions (PDRs) formed by the expanding HII region and photo-erosion from DR18-05 and OB2 stars. We also identified 18 compact cores with N_2H^+ emission, half of which are gravitationally bound and mostly located in colder regions behind the PDRs. The SiO emission is found only in PDRs, with narrow-line widths ( 0.8 - 2.0 km s^-1) and lower abundances (X(SiO) ∼ 5×10^-11 - 1×10^-10). Comparing with the UV irradiated shock models, we suggest that the SiO emission partially encompassing the HII region arises from the molecular gas region, marginally compressed by low-velocity shocks with ∼ 5 km s^-1, irradiated by external UV radiation (G_ 0∼ 10^2 - 10^3), as they traverse through a medium with n_ H∼ 10^4 to 10^5 cm^-3.