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تسجيل مستخدم جديدOptical and near-IR photometric study of the open cluster NGC 637 and NGC 957
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We present UBVRI CCD photometry in the region of the open clusters NGC 637 and NGC 957. The radii are found to be 4.2 arcmin and 4.3 arcmin. Their reddenings E(B-V) are 0.64+/-0.05 mag and 0.71+/-0.05 mag and their distances, from main sequence fitting are 2.5+/-0.2 kpc and 2.2+/-0.2 kpc. Comparison with Z=0.02 isochrones leads to an age of 10+/-5 Myr for both clusters. Combining our photometry with 2MASS JHK shows the reddening law in these directions to be normal. Mass function slopes of x=1.65+/-0.20 and 1.31+/-0.50 are derived for the clusters, both of which are found to be dynamically relaxed. Spectral and photometric characteristics of three Be stars, two in NGC 957 and one (newly discovered) in NGC 637 indicate them to be of Classical Be type.
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< -2$ are evolving off the main sequence; stars with $-2 < M_{V} < +2$ are located on the main sequence and stars with $M_{V} > +2$ are placed above it. According to our analysis, the cluster distance is $d = 2750 pm 250 pc$ ($V_{0}-M_{V} = 12.2 pm 0.2$) and its nuclear age is $8 pm 1 Myr$. NGC 3293 contains an important fraction of pre--main sequence (PMS) stars distributed along a parallel band to the ZAMS with masses from 1 to $2.5 cal M_{sun}$ and a mean contraction age of $10 Myr$. This last value does not differ too much from the nuclear age estimate. Actually, if we take into account the many factors that may affect the PMS star positions onto the colour--magnitude diagram, both ages can be perfectly reconciled. The star formation rate, on the other hand, suggests that NGC 3293 stars formed surely in one single event, therefore favouring a coeval process of star formation. Besides, using the $H_{alpha}$ data, we detected nineteen stars with signs of having $H_{alpha}$ emission in the region of NGC 3293, giving another indication that the star formation process is still active in the region. The computed initial mass function for the cluster has a slope value $x = 1.2 pm 0.2$, a bit flatter than the typical slope for field stars and similar to the values found for other young open clusters.
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