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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.

Although the star-formation process has been studied for decades, many important aspects of the physics involved remain unsolved. Recent advancements in instrumentation in the infrared, far-infrared, and sub-millimeter-wavelength regimes have contributed to a significantly improved understanding of processes in the interstellar medium (ISM) leading to star formation. The future of research on the ISM and star formation looks exciting with instruments like the JWST, ALMA, etc., already contributing to the topic by gathering high-resolution high-sensitivity data and with several larger ground- and space-bound facilities either being planned or constructed. India has a sizable number of astronomers engaged in research on topics related to the ISM and star formation. In this white paper invited by the Astronomical Society of India to prepare a vision document for Indian astronomy, we review the Indian contributions to the global understanding of the star-formation process and suggest areas that require focused efforts both in creating observing facilities and in the theoretical front in India, to improve the impact of our research in the coming decades. [ABSTRACT FROM AUTHOR]

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]

Using multi-wavelength data sets, we studied the star-formation activity in H ii region Sh 2-61 (hereafter S61). We identified a clustering in the region and estimated the membership using the Gaia proper motion data. The physical environment of S61 is inspected using infrared to radio wavelength images. We also determined the Lyman continuum flux associated with the H ii region and found that the H ii region is formed by at least two massive stars (S1 and S2). We also analyzed the 12 CO ( J = 3 –2) JCMT data of S61, and a shell structure accompanying three molecular clumps are observed towards S61. We found that the ionized gas in S61 is surrounded by dust and a molecular shell. Many young stellar objects and three molecular clumps are observed at the interface of the ionized gas and surrounding gas. The pressure at the interface is higher than in a typical cool molecular cloud. [ABSTRACT FROM AUTHOR]

Using optical photometric observations from 1.3-m Devasthal Fast Optical Telescope and deep near-infrared (NIR) photometric observations from TANSPEC mounted on 3.6-m Devasthal Optical Telescope, along with the multi-wavelength archival data, we present our study of open cluster Kronberger 55 to understand the star-formation scenario in the region. The distance, extinction and age of the cluster Kronberger 55 are estimated as ∼ 3.5 kpc, E (B - V) ∼ 1.0 mag and ≲ 5 Myr, respectively. We identified Young Stellar Objects (YSOs) based on their excess infrared (IR) emission using the two-color diagrams (TCDs). The mid-infrared (MIR) images reveal the presence of extended structure of dust and gas emission along with the outflow activities in the region with two peaks, one at the location of cluster Kronberger 55 and another at 5 ′. 35 southwards to it. The association of radio continuum emission with the southern peak, hints towards the formation of massive star/s. The Herschel sub-millimeter maps reveal the presence of two clumps connected with a filamentary structure in this region, and such configuration is also evident in the 12 CO(1–0) emission map. Our study suggests that this region might be a hub-filament system undergoing star formation due to the 'end-dominated collapse scenario'. [ABSTRACT FROM AUTHOR]

We have performed a detailed analysis on the Teutsch 76 (T76) open cluster using the deep near-infrared (NIR) observations taken with the TANSPEC instrument mounted on the 3.6m Devasthal optical telescope along with the recently available high quality proper motion data from the Gaia data release 3 and deep photometric data from Pan-STARRS1 survey. We have found that the T76 cluster is having a central density concentration with circular morphology, probably due to the star-formation processes. The radius of the T76 cluster is found to be 45 ″ (1.24 pc) and 28 stars within this radius were marked as highly probable cluster members. We have found that the cluster is located at a distance of 5.7 ± 1.0 kpc and is having an age of 50 ± 10 Myr. The mass function slope (Γ ) in the cluster region in the mass range of ∼ 0.75 < M / M ⊙ < 5.8 is estimated as - 1.3 ± 0.2 , which is similar to the value of −1.35 given by Salpeter (1955). The cluster is not showing any signatures of mass-segregation and is currently undergoing dynamical relaxation. [ABSTRACT FROM AUTHOR]

We present a study of the molecular cloud in Sh2-112 massive star forming region using the 3-2 transition of CO isotopologues: CO, 13 CO and C 18 O; supplemented in part by CGPS H i line emission and MSX data. Sh2-112 is an optically visible region powered by an O8V type massive star BD + 45 3216, and hosts two Red MSX Survey sources: G083.7962 + 03.3058 and G083.7071 + 03.2817, classified as H ii region and young stellar object, respectively. Reduced spectral data products from the James Clerk Maxwell Telescope archive, centered on the two RMS objects with ∼ 7 ′ × 7 ′ field-of-view each, were utilized for the purpose. The 13 CO(3-2) channel map of the region shows the molecular cloud to have filamentary extensions directed away from the massive star, which also seems to be at the edge of a cavity like structure. Multiple molecular cloud protrusions into this cavity structure, host local peaks of emission. The integrated emission map of the region constructed from only those emission clumps, detected above 5 σ level in the position–position–velocity space affirms the same. MSX sources were found distributed along the cavity boundary, where the gas has been compressed. Spectral extraction at these positions yielded high Mach numbers and low ratios of thermal to non-thermal pressures, suggesting a dominance of supersonic and non-thermal motion in the cloud. [ABSTRACT FROM AUTHOR]

Bright-rimmed clouds (BRCs) are excellent laboratories to explore the radiation-driven implosion mode of star formation because they show evidence of triggered star formation. In our previous study, BRC 18 has been found to accelerate away from the direction of the ionizing H  ii region because of the well-known 'Rocket Effect'. Based on the assumption that both BRC 18 and the candidate young stellar objects (YSOs) are kinematically coupled and using the latest Gaia EDR3 measurements, we found that the relative proper motions of the candidate YSOs exhibit a tendency of moving away from the ionizing source. Using BRC 18 as a prototype, we made our further analysis for 21 more BRCs, a majority of which showed a similar trend. For most of the BRCs, the median angle of the relative proper motion of the candidate YSOs is similar to the angle of on-sky direction from the ionizing source to the central IRAS source of the BRC. Based on the Pearson's and Spearman's correlation coefficients, we found a strong correlation between these two angles, which is further supported by the Kolmogorov–Smirnov (K−S) test on them. The strong correlation between these two angles supports the 'Rocket Effect' in the BRCs on the sky plane. [ABSTRACT FROM AUTHOR]

The structure of our Galaxy has been studied from ultraviolet (UV) star counts obtained with the Ultra-Violet Imaging Telescope (UVIT) on board the AstroSat satellite, in Far-UV (FUV) and Near-UV (NUV) bands. The F154W (BaF2) and N263M (NUVB4) filters were used in the FUV and NUV bands, respectively. The point sources are separated from the extra-galactic sources of UVIT observations using infrared (IR) color cut method. The observed UVIT star counts match well with the simulations obtained from the Besançon model of stellar population synthesis towards several Galactic directions. We also estimated the scale length and scale height of the thick disc and the scale height of the thin disc using the space density function and the exponential density law for the stars of intermediate galactic latitudes. The scale length of the thick disc ranges from 3.11 to 5.40 kpc whereas the scale height ranges from 530 ± 32 pc to 630 ± 29 pc. The scale height of the thin disc comes out to be in the range of 230 ± 20 pc to 330 ± 11 pc. [ABSTRACT FROM AUTHOR]

Context. Pre-main-sequence variability characteristics can be used to probe the physical processes leading to the formation and initial evolution of both stars and planets. Aims. The photometric variability of pre-main-sequence stars is studied at optical wavelengths to explore star–disk interactions, accretion, spots, and other physical mechanisms associated with young stellar objects. Methods. We observed a field of 16′ × 16′ in the star-forming region Pelican Nebula (IC 5070) at BVRI wavelengths for 90 nights spread over one year in 2012−2013. More than 250 epochs in the VRI bands are used to identify and classify variables up to V ∼ 21 mag. Their physical association with the cluster IC 5070 is established based on the parallaxes and proper motions from the Gaia second data release (DR2). Multiwavelength photometric data are used to estimate physical parameters based on the isochrone fitting and spectral energy distributions. Results. We present a catalog of optical time-series photometry with periods, mean magnitudes, and classifications for 95 variable stars including 67 pre-main-sequence variables towards star-forming region IC 5070. The pre-main-sequence variables are further classified as candidate classical T Tauri and weak-line T Tauri stars based on their light curve variations and the locations on the color-color and color-magnitude diagrams using optical and infrared data together with Gaia DR2 astrometry. Classical T Tauri stars display variability amplitudes up to three times the maximum fluctuation in disk-free weak-line T Tauri stars, which show strong periodic variations. Short-term variability is missed in our photometry within single nights. Several classical T Tauri stars display long-lasting (≥10 days) single or multiple fading and brightening events of up to two magnitudes at optical wavelengths. The typical mass and age of the pre-main-sequence variables from the isochrone fitting and spectral energy distributions are estimated to be ≤1 M⊙ and ∼2 Myr, respectively. We do not find any correlation between the optical amplitudes or periods with the physical parameters (mass and age) of pre-main-sequence stars. Conclusions. The low-mass pre-main-sequence stars in the Pelican Nebula region display distinct variability and color trends and nearly 30% of the variables exhibit strong periodic signatures attributed to cold spot modulations. In the case of accretion bursts and extinction events, the average amplitudes are larger than one magnitude at optical wavelengths. These optical magnitude fluctuations are stable on a timescale of one year. [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]