A B S T R A C TThis paper presents a global analysis of the 2MASS (Two Micron All Sky Survey) data as observed in seven fields at different galactic latitudes in our Galaxy. The data allow the preliminary determination of the scale parameters, which lead to strong constraints on the radial and vertical structure of the galactic thin and thick disc. The interpretation of star counts and colour distributions of stars in the near-infrared with the synthetic stellar population model gives strong evidence that the galactic thin disc density scalelength (h R ) is rather short 2X8^0X3 kpcX The galactic thick disc population is revisited in the light of new data. We find the thick disc to have a local density of 3X5^2X0 per cent of the thin disc, exponential scaleheight (h z ) of 860^200 pc and exponential scalelength (h R ) of 3X7^0 X8 0X5 kpcX

(abridged) We develop a model which describes the coevolution of the mass function of dense cores and of the IMF in a protocluster clump. In the model, cores injected in the clump evolve under the effect of gas accretion. Accretion onto the cores follows a time-dependent accretion rate that describes accretion in a turbulent medium. Once the accretion timescales of cores exceed their contraction timescales, they are turned into stars. We include the effect of feedback by the newly formed massive stars through their stellar winds. A fraction of the wind's energy is assumed to counter gravity and disperse the gas from the protocluster and as a consequence, quench further star formation. The latter effect sets the final IMF of the cluster. We apply our model to a clump that is expected to resemble the progenitor clump of the Orion Nebula Cluster (ONC). Our model is able to reproduce both the shape and normalization of the ONC's IMF and the mass function of dense cores in Orion. The complex features of the ONC's IMF,i.e., a shallow slope in the mass range ~0.3-2.5 Msol,a steeper slope in the mass range ~2.5-12 Msol, and a nearly flat tail at the high mass end are reproduced. The model predicts a 'rapid' star formation process with an age spread for the stars of 2.3 10^5 yr which is consistent with the fact that 80% of the ONC's stars have ages of <=0.3 Myr. The model predicts a primordial mass segregation with the most massive stars being born in the region between 2-4 times the core radius of the cluster. In parallel, the model also reproduces, simultaneously, the mass function of dense cores in Orion. We study the effects of varying the model parameters on the resulting IMF and show that the IMF of stellar clusters is expected to show significant variations, provided variations in the clumps and cores properties exist.Comment: accepted to MNRAS. 22 pages, 17 figures. 2 new sections added to better present the model parameters and compare to previous work. Some figures are now better presented. Main conclusions unchange

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 optical photometric and polarimetric observations of stars towards NGC 1931 with the aim to derive the cluster parameters such as distance, reddening, age and luminosity/mass function as well as to understand the dust properties and star formation in the region. The distance to the cluster is found to be 2.3±0.3 kpc and the reddening E(B − V ) in the region is found to be variable. The stellar density contours reveal two clustering in the region. The observations suggest differing reddening law within the cluster region. Polarization efficiency of the dust grains towards the direction of the cluster is found to be less than that for the general diffuse interstellar medium (ISM). The slope of the mass function (-0.98±0.22) in the southern region in the mass range 0.8 < M/M ⊙ < 9.8 is found to be shallower in comparison to that in the northern region (-1.26±0.23), which is comparable to the Salpeter value (-1.35). The K-band luminosity function (KLF) of the region is found to be comparable to the average value of slope (∼0.4) for young clusters obtained by Lada & Lada (2003), however, the slope of the KLF is steeper in the northern region as compared to the southern region. The region is probably ionized by two B2 main-sequence type stars. The mean age of the young stellar objects (YSOs) is found to be 2±1 Myr which suggests that the identified YSOs could be younger than the ionizing sources of the region. The morphology of the region, the distribution of the YSOs as well as ages of the YSOs and ionizing sources indicate a triggered star formation in the region.

We present observational data for two main components (S255IR and S255N) of the S255 high mass star forming region in continuum and molecular lines obtained at 1.3 mm and 1.1 mm with the SMA, at 1.3 cm with the VLA and at 23 and 50 cm with the GMRT. The angular resolution was from ∼ 2 to ∼ 5 for all instruments. With the SMA we detected a total of about 50 spectral lines of 20 different molecules (including isotopologues). About half of the lines and half of the species (in particular N 2 H + , SiO, C 34 S, DCN, DNC, DCO + , HC 3 N, H 2 CO, H 2 CS, SO 2 ) have not been previously reported in S255IR and partly in S255N at high angular resolution. Our data reveal several new clumps in the S255IR and S255N areas by their millimeter wave continuum emission. Masses of these clumps are estimated at a few solar masses. The line widths greatly exceed expected thermal widths. These clumps have practically no association with NIR or radio continuum sources, implying a very early stage of evolution. At the same time, our SiO data indicate the presence of high-velocity outflows related to some of these clumps. In some cases, strong molecular emission at velocities of the quiescent gas has no detectable counterpart in the continuum. We discuss the main features of the distribution of NH 3 , N 2 H + , and deuterated molecules. We estimate properties of decimeter wave radio continuum sources and their relationship with the molecular material.

We have performed a detailed analysis of the Czernik 3 (Cz3) open cluster by using deep near-infrared photometry taken with TIRCAM2 on 3.6m Devasthal optical telescope along with the recently available high quality proper motion data from the Gaia DR2 and deep photometric data from Pan-STARRS1. The cluster has a highly elongated morphology with fractal distribution of stars. The core and cluster radii of the cluster are estimated as 0.5 pc and 1.2 pc, respectively. We have identified 45 stars as cluster members using the Gaia proper motion data. The distance and age of the cluster are found to be 3.5 ± 0.9 kpc and $0.9^{+0.3}_{-0.1}$ Gyr, respectively. The slope of the mass function `Γ′ in the cluster region, in the mass range ∼0.95 &lt;M/M⊙&lt;2.2, is found to be −1.01 ± 0.43. The cluster shows the signatures of mass-segregation and is dynamically relaxed (dynamical age=10 Myr). This along with its small size, big tidal radius, low density/large separation of stars, and elongated and distorted morphology, indicate that the Cz3 is a loosely bound disintegrating cluster under the influence of external tidal interactions.

Optical and NIR observations of the type Ia supernova SN 2014J in M82 are presented. The observed light curves are found to be similar to normal SNe Ia, with a decline rate parameter ∆m 15 (B) = 1.08 ± 0.03. The supernova reached B-band maximum on JD 2456690.14, at an apparent magnitude m B (max) = 11.94. The optical spectra show a red continuum with deep interstellar Na i absorption, but otherwise resemble those of normal SNe Ia. The Si ii λ6355 feature indicates a velocity of ∼ 12 000 km s −1 at B-band maximum, which places SN 2014J at the border of the Normal Velocity and High Velocity group of SNe Ia. The velocity evolution of SN 2014J places it in the Low Velocity Gradient subclass, whereas the equivalent widths of Si ii features near B-band maximum place it at the border of the Core Normal and Broad Line subclasses of SNe Ia. An analytic model fit to the bolometric light curve indicates that a total of ∼ 1.3 M ⊙ was ejected in the explosion, and the ejected 56 Ni mass M N i ∼ 0.6 M ⊙ . The low [Fe iii] λ4701 to [Fe ii] λ5200 ratio in the nebular spectra of SN 2014J hints towards clumpiness in the ejecta. Optical broadband, linear polarimetric observations of SN 2014J obtained on four epochs indicate an almost constant polarization (P R ∼2.7 per cent; θ ∼37 • ), which suggests that the polarization signal is of interstellar origin.

We present a multiwavelength study of the NGC 281 complex, which contains the young cluster IC 1590 at the center, using deep wide-field optical UBV I c photometry, slitless spectroscopy along with archival data sets in the near-infrared (NIR) and X-ray regions. The extent of IC 1590 is estimated to be 6.5 pc. The cluster region shows a relatively small amount of differential reddening. The majority of the identified young stellar objects (YSOs) are low-mass PMS stars having age < 1-2 Myr and mass 0.5-3.5 Mˇ. The slope (Γ) of the mass function for IC 1590, in the mass range 2 < M=MˇÄ 54, is found to be 1.11˙0.15. The slope of the K-band luminosity function (0.37˙0.07) is similar to the average value ( 0.4) reported for young clusters. The distribution of gas and dust obtained from the IRAS, CO, and radio maps indicates clumpy structures around the central cluster. The radial distribution of the young stellar objects, their ages, Δ(H K) NIR-excess, and the fraction of classical T Tauri stars suggest triggered star formation at the periphery of the cluster region. However, deeper optical, NIR, and MIR observations are needed to have a conclusive view of the star-formation scenario in the region. The properties of the Class 0/I and Class II sources detected by using the Spitzer mid-infrared observations indicate that a majority of the Class II sources are X-ray emitting stars, whereas X-ray emission is absent from the Class 0/I sources. The spatial distribution of Class 0/I and Class II sources reveals the presence of three sub-clusters in the NGC 281 West region.