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    ULTRAVIOLET STELLAR SPECTRAL CLASSIFICATION USING A MULTILEVEL TREE NEURAL NETWORK
    (Elsevier Science Ltd, 1995-01-25) Gulati, R.K; Gupta, R; Gothoskar, P; et.al
    Here we present a pattern classification technique based on an Artificial Neural Network (ANN) in a multi-level tree configuration to classify ultraviolet stellar spectra from the IUE Low-Dispersion Spectra Reference Atlas. Preliminary results of this technique show that 94% of the spectra have been classified correctly with an accuracy of one sub-class. A conventional 9~2 minimization scheme has also been applied to the data to compare the classification obtained from these schemes with that of the IUE catalog classification.
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    Star Formation Activity in the Galactic H ii Complex S255-S257
    (2011-06-09) Ojha, D.K.; Samal, M.R; Pandey, A.K.; et.al
    We present results on the star-formation activity of an optically obscured region containing an embedded cluster (S255-IR) and molecular gas between two evolved H ii regions S255 and S257. We have studied the complex using optical, near-infrared (NIR) imaging, optical spectroscopy and radio continnum mapping at 15 GHz, along with Spitzer-IRAC results. It is found that the main exciting sources of the evolved H ii regions S255 and S257 and the compact H ii regions associated with S255-IR are of O9.5 - B3 V nature, consistent with previous observations. Our NIR observations reveal 109 likely young stellar object (YSO) candidates in an area of 40.9 40.9 centered on S255-IR, which include 69 new YSO candidates. To see the global star formation, we constructed the V 􀀀I=V diagram for 51 optically identified IRAC YSOs in an area of 130 130 centered on S255-IR. We suggest that these YSOs have an approximate age between 0.1 - 4 Myr, indicating a non-coeval star formation. Using spectral energy distribution (SED) models, we constrained physical properties and evolutionary status of 31 and 16 YSO candidates outside and inside the gas ridge, respectively. The models suggest that the sources associated within the gas ridge are of younger population (mean age 1.2 Myr) than the sources outside the gas ridge (mean age 2.5 Myr). The positions of the young sources inside the gas ridge at the interface of the H ii regions S255 and S257, favor a site of induced star formation