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Using new continuum and molecular line data from the Atacama Large Millimeter/submillimeter Array Three-millimeter Observations of Massive Star-forming Regions (ATOMS) survey and archival Very Large Array, 4.86 GHz data, we present direct observational evidence of hierarchical triggering relating three epochs of massive star formation in a ringlike H ii region, G24.47+0.49. We find from radio flux analysis that it is excited by a massive star(s) of spectral type O8.5V–O8V from the first epoch of star formation. The swept-up ionized ring structure shows evidence of secondary collapse, and within this ring, a burst of massive star formation is observed in different evolutionary phases, which constitutes the second epoch. ATOMS spectral line (e.g., HCO ^+ (1–0)) observations reveal an outer concentric molecular gas ring expanding at a velocity of ∼9 km s ^−1 , constituting the direct and unambiguous detection of an expanding molecular ring. It harbors twelve dense molecular cores with surface mass density greater than 0.05 g cm ^−2 , a threshold typical of massive star formation. Half of them are found to be subvirial and thus in gravitational collapse making them the third epoch of potential massive star-forming sites.

We present the results of deep radio observations of seven nearby large galaxies observed using the upgraded Giant Metrewave Radio Telescope (uGMRT) 0.3–0.5 GHz receivers with an angular resolution of ∼10″. The achieved sensitivities of these observations range from ≈15 to 50 μ Jy beam ^−1 , which is a factor of ≈3–4 lower than the previous observations at these frequencies. For two galaxies (NGC 3344 and NGC 3627) with moderate inclination angles, significant diffuse emissions are seen for the first time. The detected radio halos in the vertical direction are significantly larger in our 0.4 GHz maps compared to the observations at ∼1.5 GHz for four nearly edge-on galaxies—NGC 3623, NGC 4096, NGC 4594, and NGC 4631. For these four galaxies, significantly larger halos are also detected along the galaxy disk. For NGC 3623 and NGC 4594, we could detect elongated radio disks that were not seen before. We also present new uGMRT images of NGC 3344 and NGC 3623 at 1.3 GHz and a new VLA image of NGC 3627 at 1.5 GHz. We fitted an exponential function to the flux densities along different cross-cuts and found a significantly wider distribution at the 0.4 GHz uGMRT images compared to the high-frequency images at ∼1.5 GHz. Using maps at 0.144, 0.4, and ∼1.5 GHz, we made spectral index maps of the seven sample galaxies and found a steepening of the spectrum up to a value of ∼−1.5 in the halo regions of the galaxies.

We present a detailed study of the Sh2-87 H ii region using a multiwavelength data set in optical to radio bands. A Herschel column density map revealed that the host cloud is filamentary in nature, and together they formed a central dense hub. The extinction map generated using near-infrared photometric data also signifies the nonuniform distribution of the cloud and reveals its filamentary nature. We estimated a sizable variable extinction over the region up to A _V = 34.4 mag, with an average value of A _V = 3.4 mag. Using the various infrared color–color criteria, we identified 13 Class I and 202 Class II young stellar objects (YSOs) and 22 H α -emitting sources toward this region. Further analysis showed that the cluster is mainly composed of low-mass YSOs with a typical age of ∼3 Myr having masses in the range of 0.1–6.0 M _⊙ . The identified evolved YSOs (i.e., Class II YSOs) are primarily distributed along the filaments and in the outer parts of the cloud, while the recent star formation, inferred by the presence of Class I YSOs, ionized gas, and star-forming clumps, is observed in the hub region. The overall star formation scenario in the Sh2-87 region resembles the global hierarchical collapse model of star formation, where younger massive star formation activity is expected at the central hub along with the distribution of evolved low-mass YSOs in the filaments and the outer parts of the cloud.

We report on a multiwavelength study of the Wolf–Rayet star [KSF2015] 1381-19L, which is located in the solar metallicity region ( Z = 0.014) of the Milky Way, strongly obscured by interstellar dust. We perform a detailed characterization of the stellar atmosphere by fitting the spectral emission lines observed in the optical and near-infrared (NIR) bands, using CMFGEN. The best-fitted spectroscopic model indicates a highly luminous (10 ^5.89 L _⊙ ) star with a large radius (15 R _⊙ ) and effective temperature, wind terminal velocity, and chemical composition similar to those of Galactic WC9-dusty (WC9d)-type stars. The atmospheric ionization structure shows coexisting ionization states of different elements, simultaneously affecting the opacity and thermal electron balance. Fitting of the spectral energy data reveals high interstellar optical extinction ( A _V = 8.87), while the IR extinction is found to be comparatively lower ( ${A}_{{K}_{s}}=0.98$ ). We do not detect any excess emission at NIR wavelengths due to dust. Upon comparison of our results with the GENEVA single-star evolutionary models ( Z = 0.014), we identify the best possible progenitors (a rotating star of 67 M _⊙ and a nonrotating star of 90 M _⊙ ).

We use the H41 α recombination line to create templates of the millimeter free–free emission in the ALMA-IMF continuum maps, which allows us to separate it from dust emission. This method complements spectral-index information and extrapolation from centimeter-wavelength maps. We use the derived maps to estimate the properties of up to 34 H ii regions across the ALMA-IMF protoclusters. The hydrogen ionizing photon rate Q _0 and spectral types follow the evolutionary trend proposed by Motte et al. The youngest protoclusters lack detectable ionized gas, followed by protoclusters with increasing numbers of OB stars. The total Q _0 increases from ∼10 ^45 s ^−1 to >10 ^49 s ^−1 . We used the adjacent He41 α line to measure the relative number abundances of helium, finding values consistent with the Galactic interstellar medium, although a few outliers are discussed. A search for sites of maser amplification of the H41 α line returned negative results. We looked for possible correlations between the electron densities, emission measures, and Q _0 with H ii region size D . The latter is the best correlated, with Q _0 ∝ D ^2.49 ± 0.18 . This favors interpretations in which smaller ultracompact H ii regions are not necessarily the less dynamically evolved versions of larger ones but rather are ionized by less massive stars. Moderate correlations were found between the dynamical width Δ V _dyn with D and Q _0 . Δ V _dyn increases from about 1 to 2 times the ionized-gas sound speed. Finally, an outlier H ii region south of W43-MM2 is discussed. We suggest that this source could harbor an embedded stellar or disk wind.

We report the detection of high-frequency pulsations in WR 135 from short-cadence (10 minute) optical photometric and spectroscopic time series surveys. The harmonics up to the sixth order are detected from the integrated photometric flux variations, while the comparatively weaker eighth harmonic is detected from the strengths of the emission lines. We investigate the driving source of the stratified winds of WR 135 using the radiative transfer modeling code, CMFGEN, and find the physical conditions that can explain the propagation of such pulsations. From our study, we find that the optically thick subsonic layers of the atmosphere are close to the Eddington limit and are launched by the Fe opacity. The outer optically thin supersonic winds ( τ _ross = 0.1–0.01) are launched by the He II and C iv opacities. The stratified winds above the sonic point undergo velocity perturbation that can lead to clumps. In the optically thin supersonic winds, dense clumps of smaller size ( f _VFF = 0.27–0.3, where f _VFF is the volume filling factor) pulsate with higher-order harmonics. The larger clumps ( f _VFF = 0.2) oscillate with lower-order harmonics of the pulsation and affect the overall wind variability.

We present a molecular line study of the Sh2-138 (IRAS 22308+5812) hub-filament system with the aim of investigating its structure and kinematics. Archival CO molecular line data from the Canadian Galactic Plane Survey (CO( J = 1–0)) for the wider region (∼50′ × 50′) and the James Clerk Maxwell Telescope (CO(3–2), ^13 CO(3–2), and C ^18 O(3–2)) for the central portion (∼5′ × 5′) have been utilized. Analysis of the CO(1–0) spectra for the extended region in conjunction with the identification of the hub and filament using a column density map and the getsf tool, respectively, reveals a complex structure with the spectral extraction for the central position displaying multiple velocity components. Based on the Herschel 70 μ m warm dust emission, one of the filaments in the extended region was inferred to be associated with active star formation, and is host to a Bolocam 1.1 mm clump of ∼1606 M _☉ . An integrated intensity map of ^13 CO(3–2) emission, constructed from clumps detected at above 5 σ in position–position–velocity space, reveals three filamentary structures (labeled the western filament (W-f), southwestern filament (SW-f), and southeast filament (SE-f)) in the central portion. Velocity gradients observed in ^13 CO(3–2) position–velocity slices point to longitudinal gas flow along the filaments into the central region. Filaments W-f, SW-f, and SE-f were calculated to have observed line masses of ∼32, 33.5, and 50 M _☉ pc ^−1 , respectively. The cloud was found to be dominated by supersonic and nonthermal motions, with high Mach numbers (≳3) and a low thermal-to-nonthermal pressure ratio (∼0.01–0.1).

G10.21-0.31 is a 70 μ m dark high-mass starless core ( M > 300 M _⊙ within r < 0.15 pc) identified in the Spitzer, Herschel, and APEX continuum surveys, and is believed to harbor the initial stages of high-mass star formation. We present Atacama Large Millimeter/submillimeter Array (ALMA) and Submillimeter Array observations to resolve the internal structure of this promising high-mass starless core. Sensitive high-resolution ALMA 1.3 mm dust continuum emission reveals three cores of mass ranging within 11–18 M _⊙ , characterized by a turbulent fragmentation. Cores 1, 2, and 3 represent a coherent evolution of three different stages, characterized by outflows (CO and SiO), gas temperature (H _2 CO), and deuteration (N _2 D ^+ /N _2 H ^+ ). We confirm the potential for formation of high-mass stars in G10.21 and explore the evolution path of high-mass star formation. Yet, no high-mass prestellar core is present in G10.21. This suggests a dynamical star formation where cores grow in mass over time.

We present here the results of 8 yr of our near-simultaneous optical–near-infrared spectro-photometric monitoring of the bona fide FU Ori (FUor)-type candidate V2493 Cygnus (V2493 Cyg) starting from 2013 September to 2021 June. During our optical monitoring period (between 2015 October 16 and 2019 December 30), the V2493 Cyg is slowly dimming with an average dimming rate of ∼26.6 ± 5.6 mmag yr ^−1 in the V band. Our optical photometric colors show a significant reddening of the source post the second outburst pointing toward a gradual expansion of the emitting region post the second outburst. The mid-infrared colors, on the contrary, exhibit a blueing trend, which can be attributed to the brightening of the disk due to the outburst. Our spectroscopic monitoring shows a dramatic variation of the H α line as it transitioned from absorption feature to the emission feature and back. Such transition can possibly be explained by the variation in the wind structure in combination with accretion. Combining our time evolution spectra of the Ca ii infrared triplet lines with the previously published spectra of V2493 Cyg, we find that the accretion region has stabilized compared to the early days of the outburst. The evolution of the O i λ 7773 Å line also points toward the stabilization of the circumstellar disk post the second outburst.

We uncover a hub–filament system correlated with massive young stellar associations in G083.097+03.270. Diagnosed with simultaneous ^12 CO, ^13 CO, and C ^18 O line observations, the region is found to host two distinct and elongated filaments having separate velocity components, interacting spatially and kinematically, that appear to have seeded the formation of a dense hub at the intersection. A large velocity spread at the hub, in addition to a clear bridging feature connecting the filaments in velocity, indicate the merging of filaments. Along the filament axis, the velocity gradient reveals a global gas motion with an increasing velocity dispersion inward to the hub signifying turbulence. Altogether, the clustering of Class I sources, a high excitation temperature, a high column density, and the presence of a massive outflow at the central hub suggest enhanced star formation. We propose that the merging of large-scale filaments and velocity gradients along filaments are the driving factors in the mass accumulation process at the hub that have sequentially led to the massive star formation. With two giant filaments merging to coincide with a hub therein with ongoing star formation, this site serves as a benchmark for the “filaments to clusters” star-forming paradigm.

We present Period–Luminosity and Period–Luminosity–Color relations at maximum light for Mira variables in the Magellanic Clouds using time-series data from the Optical Gravitational Lensing Experiment (OGLE-III) and Gaia data release 2. The maximum-light relations exhibit a scatter typically up to ∼30% smaller than their mean-light counterparts. The apparent magnitudes of oxygen-rich Miras at maximum light display significantly smaller cycle-to-cycle variations than at minimum light. High-precision photometric data for Kepler Mira candidates also exhibit stable magnitude variations at the brightest epochs, while their multi-epoch spectra display strong Balmer emission lines and weak molecular absorption at maximum light. The stability of maximum-light magnitudes for Miras possibly occurs due to the decrease in the sensitivity to molecular bands at their warmest phase. At near-infrared wavelengths, the period–luminosity relations (PLRs) of Miras display similar dispersion at mean and maximum light with limited time-series data in the Magellanic Clouds. A kink in the oxygen-rich Mira PLRs is found at 300 days in the VI-bands, which shifts to longer periods (∼350 days) at near-infrared wavelengths. Oxygen-rich Mira PLRs at maximum light provide a relative distance modulus, Δμ = 0.48 ± 0.08 mag, between the Magellanic Clouds with a smaller statistical uncertainty than the mean-light relations. The maximum-light properties of Miras can be very useful for stellar atmosphere modeling and distance scale studies provided their stability and the universality can be established in other stellar environments in the era of extremely large telescopes. [ABSTRACT FROM AUTHOR]

We report on a multiwavelength study of the Wolf–Rayet star [KSF2015] 1381-19L, which is located in the solar metallicity region (Z = 0.014) of the Milky Way, strongly obscured by interstellar dust. We perform a detailed characterization of the stellar atmosphere by fitting the spectral emission lines observed in the optical and near-infrared (NIR) bands, using CMFGEN. The best-fitted spectroscopic model indicates a highly luminous (105.89 L ⊙) star with a large radius (15 R ⊙) and effective temperature, wind terminal velocity, and chemical composition similar to those of Galactic WC9-dusty (WC9d)-type stars. The atmospheric ionization structure shows coexisting ionization states of different elements, simultaneously affecting the opacity and thermal electron balance. Fitting of the spectral energy data reveals high interstellar optical extinction (A V = 8.87), while the IR extinction is found to be comparatively lower ( A K s = 0.98 ). We do not detect any excess emission at NIR wavelengths due to dust. Upon comparison of our results with the GENEVA single-star evolutionary models (Z = 0.014), we identify the best possible progenitors (a rotating star of 67 M ⊙ and a nonrotating star of 90 M ⊙). [ABSTRACT FROM AUTHOR]

We uncover a hub–filament system correlated with massive young stellar associations in G083.097+03.270. Diagnosed with simultaneous 12CO, 13CO, and C18O line observations, the region is found to host two distinct and elongated filaments having separate velocity components, interacting spatially and kinematically, that appear to have seeded the formation of a dense hub at the intersection. A large velocity spread at the hub, in addition to a clear bridging feature connecting the filaments in velocity, indicate the merging of filaments. Along the filament axis, the velocity gradient reveals a global gas motion with an increasing velocity dispersion inward to the hub signifying turbulence. Altogether, the clustering of Class I sources, a high excitation temperature, a high column density, and the presence of a massive outflow at the central hub suggest enhanced star formation. We propose that the merging of large-scale filaments and velocity gradients along filaments are the driving factors in the mass accumulation process at the hub that have sequentially led to the massive star formation. With two giant filaments merging to coincide with a hub therein with ongoing star formation, this site serves as a benchmark for the "filaments to clusters" star-forming paradigm. [ABSTRACT FROM AUTHOR]

We have performed a multi-wavelength analysis of a mid-infrared (MIR) bubble N37 and its surrounding environment. The selected 15′ × 15′ area around the bubble contains two molecular clouds (N37 cloud; 37–43 km s−1, and C25.29+0.31; 43–48 km s−1) along the line of sight. A total of seven OB stars are identified toward the bubble N37 using photometric criteria, and two of them are spectroscopically confirmed as O9V and B0V stars. The spectro-photometric distances of these two sources confirm their physical association with the bubble. The O9V star appears to be the primary ionizing source of the region, which is also in agreement with the desired Lyman continuum flux analysis estimated from the 20 cm data. The presence of the expanding H ii region is revealed in the N37 cloud, which could be responsible for the MIR bubble. Using the 13CO line data and photometric data, several cold molecular condensations as well as clusters of young stellar objects (YSOs) are identified in the N37 cloud, revealing ongoing star formation (SF) activities. However, the analysis of ages of YSOs and the dynamical age of the H ii region do not support the origin of SF due to the influence of OB stars. The position–velocity analysis of 13CO data reveals that two molecular clouds are interconnected by a bridge-like structure, favoring the onset of a cloud–cloud collision process. The SF activities (i.e., the formation of YSO clusters and OB stars) in the N37 cloud are possibly influenced by the cloud–cloud collision. [ABSTRACT FROM AUTHOR]