We present an analysis of multi-wavelength observations from various datasets and Galactic plane surveys to study the star formation process in the W42 complex. A bipolar appearance of W42 complex is evident due to the ionizing feedback from the O5-O6 type star in a medium that is highly inhomogeneous. The VLT/NACO adaptive-optics K and L images (resolutions ∼0. 2-0. 1) resolved this ionizing source into multiple point-like sources below ∼5000 AU scale. The position angle ∼15 • of W42 molecular cloud is consistent with the H-band starlight mean polarization angle which in turn is close to the Galactic magnetic field, suggesting the influence of Galactic field on the evolution of the W42 molecular cloud. Herschel sub-millimeter data analysis reveals three clumps located along the waist axis of the bipolar nebula, with the peak column densities of ∼3-5 × 10 22 cm −2 corresponding to visual extinctions of A V ∼32-53.5 mag. The Herschel temperature map traces a temperature gradient in W42, revealing regions of 20 K, 25 K, and 30-36 K. Herschel maps reveal embedded filaments (length ∼1-3 pc) which appear to be radially pointed to the denser clump associated with the O5-O6 star, forming a hub-filament system. 512 candidate young stellar objects (YSOs) are identified in the complex, ∼40% of which are present in clusters distributed mainly within the molecular cloud including the Herschel filaments. Our datasets suggest that the YSO clusters including the massive stars are located at the junction of the filaments, similar to those seen in Rosette Molecular Cloud.

We have carried out an extensive multi-wavelength study to investigate the star formation process in the S235 complex. The S235 complex has a sphere-like shell appearance at wavelengths longer than 2 µm and harbors an O9.5V type star approximately at its center. Near-infrared extinction map traces eight subregions (having A V > 8 mag), and five of them appear to be distributed in an almost regularly spaced manner along the sphere-like shell surrounding the ionized emission. This picture is also supported by the integrated 12 CO and 13 CO intensity maps and by Bolocam 1.1 mm continuum emission. The position-velocity analysis of CO reveals an almost semi-ring like structure, suggesting an expanding H ii region. We find that the Bolocam clump masses increase as we move away from the location of the ionizing star. This correlation is seen only for those clumps which are distributed near the edges of the shell. Photometric analysis reveals 435 young stellar objects (YSOs), 59% of which are found in clusters. Six subregions (including five located near the edges of the shell) are very well correlated with the dust clumps, CO gas, and YSOs. The average values of Mach numbers derived using NH 3 data for three (East 1, East 2, and Central E) out of these six subregions are 2.9, 2.3, and 2.9, indicating these subregions are supersonic. The molecular outflows are detected in these three subregions, further confirming the on-going star formation activity. Together, all these results are interpreted as observational evidence of positive feedback of a massive star.

We present the Spitzer‐Infrared Array Camera (IRAC) images of the S235 star‐forming complex that includes the east 1, east 2, central, S235A and S235B regions. In addition, we present the near‐infrared images of the S235A and S235B regions. The IRAC photometry reveals on‐going star formation, with 86 Class 0/I and 144 Class II young stellar objects (YSOs) in the entire S235 complex. Nearly 73 per cent of these YSOs are present in clusters with a maximum surface density of 120 YSOs pc−2 (in the vicinity of S235A and S235B regions). A few YSOs, possibly in an arc‐like formation, are identified towards the south of S235A region, which may be considered evidence for magnetically supercritical collapse. One of the sources in the arc‐like formation, namely S235AB‐MIR, seems to be a young, massive star that is still accreting matter. Spectral energy distribution (SED) modelling of some of the newly identified YSOs confirms the classification made on the basis of IRAC colours. The IRAC ratio map of Ch2/Ch4 traces clearly the Brα emission associated with the H ii region of S235A within the horseshoe envelope. Outside the horseshoe structure, the ratio map indicates shock‐excited H2 emission. Brα emission is also seen around S235B (from the ratio map). The ratio map of Ch2/Ch4 reveals that the source ‘e2s3’ in the east 2 region may be associated with shock‐excited H2 emission outflow or jet. The SED modelling of this new source indicates that it is a very young massive star that is not yet able to drive an H ii region.

The signatures of the counter‐electrojet that occurs in the afternoon hours as recorded on the ground and satellite‐borne magnetometers during the magnetically quiet days, clearly indicate reversal of the jet current in a narrow latitude region centered around the dip equator. The latitudinal variation of the vertical (Z) and northward (H) components of the earth's magnetic field reveal that the decrease and reversal of the eastward toroidal current of the jet is maximum around the dip equator. By numerically solving the equations governing the electrojet including the terms due to local winds it is shown that vertically upward winds of 15 ‐ 20 m/s are most effective in producing the counter‐electrojet. The profile of vertical winds adopted in the model calculations was actually measured during twilight hours. It is shown that the latitudinal variations of H and Z observed during the counter‐electrojet can be reproduced satisfactorily by the vertical wind hypothesis. A rocket experiment is suggested to verify the presence of vertical winds during the counter‐electrojet.

Mid-infrared (MIR) shells or bubbles around expanding H ii regions have received much attention due to their ability to initiate a new generation of star formation. We present multi-wavelength observations around two bubbles associated with a southern massive star-forming (MSF) region G8.14+0.23, to investigate the triggered star formation signature on the edges of the bubbles by the expansion of the H ii region. We have found observational signatures of the collected molecular and cold dust material along the bubbles and the 12 CO(J=3-2) velocity map reveals that the molecular gas in the bubbles is physically associated around the G8.14+0.23 region. We have detected 244 young stellar objects (YSOs) in the region and about 37% of these YSOs occur in clusters. Interestingly, these YSO clusters are associated with the collected material on the edges of the bubbles. We have found good agreement between the dynamical age of the H ii region and the kinematical time scale of bubbles (from the 12 CO(J=3-2) line data) with the fragmentation time of the accumulated molecular materials to explain possible "collect-and-collapse" process around the G8.14+0.23 region. However, one can not entirely rule out the possibility of triggered star formation by compression of the pre-existing dense clumps by the shock wave. We have also found two massive embedded YSOs (about 10 and 22 M ) which are associated with the dense fragmented clump at the interface of the bubbles. We conclude that the expansion of the H ii region is also leading to the formation of these two young massive embedded YSOs in the G8.14+0.23 region.