IUCAA Preprints

Permanent URI for this communityhttp://localhost:4000/handle/11007/149

Browse

Filters

20052

Settings

Has files: YesSubject: search.filters.subject.Clouds

Search Results

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Physical conditions in the ISM towards HD185418
    (2005-06-01) Shaw, Gargi; Srianand, R.
    We have developed a complete model of the hydrogen molecule as part of the spectral simulation code Cloudy. Our goal is to apply this to spectra of high-redshift star-forming regions where H2 absorption is seen, but where few other details are known, to understand its implication for star formation. The microphysics of H2 is intricate, and it is important to validate these numerical simulations in better-understood environments. This paper studies a well-defined line-of-sight through the Galactic interstellar medium (ISM) as a test of the microphysics and methods we use. We present a self-consistent calculation of the observed absorption-line spectrum to derive the physical conditions in the ISM towards HD185418, a ine-of-sight with many observables. We deduce density, temperature, local radiation field, cosmic ray ionization rate, chemical composition and compare these conclusions with conditions deduced from analytical calculations. We find a higher density, similar abundances, and require a cosmic ray flux enhanced over the Galactic background value, consistent with enhancements redicted by MHD simulations.
  • No Thumbnail Available
    Item
    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.