Browsing by Author "Mukai, T."

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    Analysis of the distribution of background star polarization in dark clouds
    (2005-04-01) Sen, A.K.; Mukai, T.; Gupta, Ranjan; et al.
    The polarization observed for stars background to dark clouds (Bok Globules) is often used as diagnostic to study the ongoing star formation processes in these clouds. Such polarization maps in the optical have been reported for eight nearby clouds CB3, CB25, CB39, CB52, CB54, CB58, CB62 and CB246 in one of our previous work (Sen et al 2000). With a view to understand the origin of this polarization, in the present work attempts are made to look for any possible relation between this observed polarization and other physical parameters in the cloud (like temperature, turbulence etc.). The observed polarization does not seem to be clearly related to the dust and gas temperatures (Td and Tg) in the cloud as expected from Davis-Greenstein grain alignment mechanism (Davis & Greenstein 1952). However, the average observed polarization (pav) appears to be related to the turbulence ∆V (measured by 12CO line width) by the mathematical relation pav = 2.95 exp(−0.24∆V ). The possible relation between the direction of polarization vector and other physical parameters are also discussed. For this analysis in addition to the data on above eight dark clouds, the data on CB4 (Kane et al. 1995) are also included for comparison.
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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.