In this paper we study the evolution of the core and corona of nine open clusters using the projected radial density profiles derived from homogeneous CCD photometric data obtained with the 105 cm Kiso Schmidt telescope. The age and galactocentric distance of the target clusters vary from 16 to 2000 Myr and 9 to 10.8 kpc, respectively. Barring Be 62, which is a young open cluster, other clusters show a uniform reddening across the cluster region. The reddening in Be 62 varies from E(B À V ) min ¼ 0:70 mag to E(B À V ) max ¼ 1:00 mag. The coronae of six of the clusters in the present sample are found to be elongated; however, on the basis of the present sample it is not possible to establish any correlation between the age and shape of the core. The elongated core in the case of the young cluster Be 62 may reflect the initial conditions in the parental molecular cloud. The other results of the present study are as follows:(1) Core radius r c and corona size r cn /cluster radius r cl are linearly correlated.(2) The r c , r cn , and r cl are linearly correlated with the number of stars in that region. (3) In the age range 10Y1000 Myr, the core and corona shrink with age. (4) We find that in the galactocentric distance range 9Y10 kpc, the core and corona/cluster extent of the clusters increase with the galactocentric distance.

We present a comprehensive multiwavelength study of the star‐forming region NGC 1893 to explore the effects of massive stars on low‐mass star formation. Using near‐infrared colours, slitless spectroscopy and narrow‐band Hα photometry in the cluster region we have identified candidate young stellar objects (YSOs) distributed in a pattern from the cluster to one of the nearby nebulae Sim 129. The V, (V−I) colour–magnitude diagram of the YSOs indicates that majority of these objects have ages between 1 and 5 Myr. The spread in the ages of the YSOs may indicate a non‐coeval star formation in the cluster. The slope of the K‐band luminosity function for the cluster is estimated to be 0.34 ± 0.07, which agrees well with the average value (∼0.4) reported for young clusters. For the entire observed mass range 0.6 < M/M⊙≤ 17.7 the value of the slope of the initial mass function, ‘Γ’, comes out to be −1.27 ± 0.08, which is in agreement with the Salpeter value of −1.35 in the solar neighbourhood. However, the value of ‘Γ’ for pre‐main‐sequence phase stars (mass range 0.6 < M/M⊙≤ 2.0) is found to be −0.88 ± 0.09 which is shallower than the value (−1.71 ± 0.20) obtained for main‐sequence stars having mass range 2.5 < M/M⊙≤ 17.7 indicating a break in the slope of the mass function at ∼2 M⊙. Estimated ‘Γ’ values indicate an effect of mass segregation for main‐sequence stars, in the sense that massive stars are preferentially located towards the cluster centre. The estimated dynamical evolution time is found to be greater than the age of the cluster, therefore, the observed mass segregation in the cluster may be the imprint of the star formation process. There is evidence for triggered star formation in the region, which seems to govern initial morphology of the cluster.

We present $UBVI_c$ CCD photometry of the young open cluster Stock 8 with the aim to study the basic properties and star formation scenario in this region. The radius of the cluster is found to be $\sim 6^{\prime}$ ($\sim 3.6$ pc) and the reddening within the cluster region varies from $E(B-V)=0.40$ to 0.60 mag. The cluster is located at a distance of $2.05 \pm 0.10$ kpc. Using H$\alpha$ slitless spectroscopy and 2MASS NIR data we identified H$\alpha$ emission and NIR excess young stellar objects (YSOs), respectively. The colour-magnitude diagrams of these YSOs reveal that majority of these objects have ages between 1 to 5 Myr indicating a non-coeval star formation in the cluster. Massive stars in the cluster region reveal an average age of $\le$ 2 Myr. In the cluster region ($r \le 6^\prime$) the slope of the mass function (MF), $\Gamma$, in the mass range $\sim 1.0 \le M/M_\odot < 13.4$ can be represented by a power law having a slope of $-1.38\pm0.12$, which agrees well with Salpeter value (-1.35). In the mass range $0.3 \le M/M_\odot < 1.0$, the MF is also found to follow a power law with a shallower slope of $\Gamma = -0.58\pm 0.23$ indicating a break in the slope of the IMF at $\sim 1 M_\odot$. The slope of the $K$-band luminosity function for the cluster ($r \le 6^\prime$) is found to be $0.31\pm0.02$, which is smaller than the average value ($\sim$ 0.4) obtained for embedded star clusters. A significant number of YSOs are distributed along a Nebulous Stream towards the east side of the cluster. A small cluster is embedded in the Nebulous Stream. The YSOs lying in the Nebulous Stream and in the embedded cluster are found to be younger than the stars in the cluster Stock 8. It appears that star formation activity in the Nebulous Stream and embedded cluster may be independent from that of Stock 8.Comment: 48 pages, 29 figures, accepted for publication in MNRA

Aims. The properties of young stellar clusters (YSCs) in M 33, identified from the center out to about twice the size of the bright star-forming disk, are investigated to determine possible spatial and time variations of the star formation process in this Local Group blue galaxy. Methods. 915 MIR sources have been extracted from the Spitzer 24 μm image. Upon inspection of Hα and GALEX images and exclusion of evolved AGB stars, a sample of 648 objects is selected as candidate YSCs and their luminosity function is examined. The spectral energy distribution of each object, based on aperture photometry, is compared with Starburst99 models to derive age, mass and A V of individual clusters. In the analysis we allow for different values of the upper mass cutoff of the stellar initial mass function (IMF), the porosity of the ISM, and the dustiness of HII regions. We also examine the influence of different dust models and include corrections for incompleteness of the IMF. Results. We find discrete MIR sources as far as the extent of the warped HI disk, i.e. 16 kpc from the galaxy center. Their surface density has a steep radial decline beyond 4.5 kpc, and flattens out beyond the optical radius at 8.5 kpc. We are able to identify YSCs out to 12 kpc. At large galactocentric radii, the paucity of luminous clusters and the relevance of hot dust emission become evident from the analysis of the bolometric and MIR luminosity functions. The YSC mass and size are correlated with a log-log slope of 2.09±0.01, similar to that measured for giant molecular clouds in M 33 and the Milky Way, which represent the protocluster environment. Most of the YSCs in our sample have A V ∼ 0−1 mag and ages between 3 and 10 Myr. In the inner regions of M 33 the clusters span a wide range of mass (10 2 < M < 3 × 10 5 M ) and luminosity (10 38 < L bol < 3 × 10 41 erg s −1 ), while at galactocentric radii larger than ∼4 kpc we find a deficiency of massive clusters. Beyond 7 kpc, where the Hα surface brightness drops significantly, the dominant YSC population has M < 10 3 M and a slightly older age (10 Myr). This implies the occurrence of star formation events about 10 Myr ago as far as 10−12 kpc from the center of M 33. The cluster L FUV vs. L Hα relation is non-linear for L FUV < 10 39 erg s −1 , in agreement with randomly sampled models of the IMF which, furthermore, shows no appreciable variation throughout the M 33 disk.