Professor Ranjan Gupta

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    Filling Gaps in Indo-US Stellar Spectral Library using Principal Component Analysis
    (Stellar Populations as Building Blocks of Galaxies Proceedings IAU Symposium, 2006-07-12) Singh, Harinder P; Singh, S. Jotin; Gupta, Ranjan; et
    The Indo-US coud´e feed stellar spectral library (CFLIB) published recently by Valdes et al. (2004) contains spectra of 1273 stars in the spectral region 3460 to 9464 ˚A at a resolution of 1 ˚A. About 500 stars in this database have gaps ranging from a few ˚A to several tens of ˚A in this wavelength range. We use a variation of Principal Component Analysis (PCA) technique to fill gaps of up to 5˚A in a subset of spectra from the CFLIB. We hope to exploit the full potential of the scheme and attempt to fill larger gaps in stellar spectra in a subsequent study.
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    A Near-Infrared Stellar Spectral Library: II. K-Band Spectra
    (Bull. Astr. Soc. India, 2007-05-31) Ranade, Ranade C; Singh, Harinder P.; Gupta, Ranjan; et
    This paper is the second in the series of papers on near-infrared (NIR) stellar spectral library produced by reducing the observations carried out with 1.2 meter Gurushikhar Infrared Telescope (GIRT), at Mt. Abu, India using a NICMOS3 HgCdTe 256×256 NIR array based spectrometer. In paper I (Ranade et al. 2004), H-band spectra of 135 stars at a resolution of 16°A were presented. The K-band library being released now consists of 114 stars covering spectral types O7–M7 and luminosity classes I–V. The spectra have a moderate resolution of 22°A in the K band and have been continuum shape corrected to their respective effective temperatures. We hope to release the remaining J-band spectra soon. The complete H and K-Band library
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    Proposal for UV observations of star forming clouds
    (Bull. Astr. Soc. India, 2007-03-02) Sen, A.K.; Mukai, T.; Gupta, R; et
    The small, compact dark clouds (also known as Bok Globules), are undergoing gravitational collapse that can result in the production of low mass stars. Light from background stars is scattered in forward direction by magnetically aligned dichroic dust grains. The degree and direction of align- ment is proportional to the strength and direction of ambient magnetic ¯eld in the cloud. Background star polarimetry provides the technique to probe this ¯eld. In order to relate the physical conditions within the cloud to the back- ground star polarization and to know the dust properties, we need to determine E(B ¡V ) for each background star and relate it to the corresponding observed polarization (p). However, observed data, do not always show a correlation between polarization and extinction. Due to this the question arises whether the grains that produce polarization also produce observed extinction? The observation that the polarization is not related to the extinction, can be explained if polarization and extinction are caused by two di®erent grain populations. Polarization is mainly caused by short grains, whereas the extinction is caused by larger ones. Based on these ¯ndings, justi¯cations are made here to detect these small grains (0.0035-0.01 ¹m) in the star forming clouds through UV observations to be made by TAUVEX. These particles can be best detected through the UV observations, as they show far-UV excess and characteristic features of 2175 ºA bump. We propose imaging of these clouds through the three bandpass ¯lters of TAUVEX. We expect to resolve many unanswered questions associated with star forming clouds, through this set of proposed observations.