IUCAA Preprints

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    Large-scale magnetic fields in Bok globules
    (IUCAA, 2015-02) Bertrang, G.; Wolf, S.; Das, H.S.
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    Spectroscopy of the recurrent nova V3890 sagittarii 18 days after the 1990 outburst
    (2014-11-23) Anupama, G. C.; Sethi, S.
    The spectrum of the recurrent nova V3890 Sgr, obtained from the Vainu Bappu Observatory 18 d after the 1990 outburst maximum, is presented. The nova was in the coronal line phase. The spectrum is similar to that of the recurrent nova RS Oph. An extinction E(B - V) = 1.1 is derived from the B - V colours, and from Balmer and He I line ratios. From the maximum magnitude-rate-of-decline relations for a nova, MV = -8.6 mag is estimated, which places the nova at a distance of about 5 kpc. Balmer line fluxes are used to derive the density, ˜109 cm-3, and the mass of the ejected ionized shell, ˜10-7 Msun. The temperature and radius estimates for the ionizing source are 3 × 105 K and 0.06 Rsun. A helium abundance of 0.23 is estimated. Applying expansion models in which the fast moving nova eject interact with a slow moving pre-outburst wind, we conclude that the eject expanded into an inhomogeneous stellar wind.
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    Manybody treatment of white dwarf and neutron stars on the brane
    (2005-07-01) Azam, Mofazzal; Sami, M.
    Brane-World models suggest modification of Newton’s law of gravity on the 3-brane at submillimeter scales. The brane-world induced corrections are in higher powers of inverse distance and appear as additional terms with the Newtonian potential. The average inter-particle distance in white dwarf and neutron stars are 10−10 cms and 10−13 cms respectively, and therefore, the effect of submillimeter corrections needs to be investigated. We show, by carrying out simple manybody calculations, that the mass and mass-radius relationship of the white dwarf and neutron stars are not effected by submillimeter corrections. However, our analysis shows that the correction terms in the effective theory give rise to force akin to surface tension in normal liquids.
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    Cosmological cosmic rays and the observed Li6 plateau in metal poor halo stars
    (2005-01-01) Rollinde, Emmanuel; Elisabeth, Vangioni-Flam; Olive, Keith A
    Very recent observations of the 6Li isotope in halo stars reveal a 6Li plateau about 1000 times above the predicted BBN abundance. We calculate the evolution of 6Li versus redshift generated from an initial burst of cosmological cosmic rays (CCRs) up to the formation of the Galaxy. We show that the pregalactic production of the 6Li isotope can account for the 6Li plateau observed in metal poor halo stars without additional overproduction of 7Li. The derived relation between the amplitude of the CCR energy spectra and the redshift of the initial CCR production puts constraints on the physics and history of the objects, such as pop III stars, responsible for these early cosmic rays. Consequently, we consider the evolution of 6Li in the Galaxy. Since 6Li is also produced in Galactic cosmic ray nucleosynthesis, we argue that halo stars with metalIicities between [Fe/H) = -2 and -1, must be somewhat depleted in 6Li.
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    Optical spectroscopy of candidates of young stellar objects in NGC 1333
    (2010-12-31) Itoh, Yoichi; et al.; Gupta, Ranjan; Oasa, Yumiko
    We carried out low-resolution optical spectroscopy of 14 low-luminosity young stellar object (YSO) candidates in the NGC 1333 cluster. These objects were previously identified by the near-infrared imaging survey. Eleven objects were confirmed as YSOs by the H line emission. Strengths of the H emission are correlated with the near-infrared excesses of the objects. Spectral types of all YSOs are estimated to be M-type, indicative of low-mass. Comparisons of the results of our spectroscopic observations and the previous photometric observations with evolutionary tracks on the HR diagram suggest two objects to be young brown dwarfs.