2008 (IPP)
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Item Photometric and Spectroscopic study of a highly reddened type Ia supernova SN 2003hx in NGC 2076(2008-01-28) Misra, Kuntal; Sahu, D. K.We present UBV RI CCD photometry and optical spectra of the type Ia supernova SN 2003hx which appeared in the galaxy NGC 2076, obtained till ∼ 146 days after the epoch of B band maximum. The supernova reached at maximum brightness in B band on JD 245 2893 ± 1.0 with an apparent magnitude of 14.92 ± 0.01 mag which was estimated by making template fits to the light curves. SN 2003hx is an example of a highly reddened supernova with E(B −V ) = 0.56 ± 0.23. We estimate Rv = 1.97 ± 0.54 which indicates the small size of dust particles as compared to their galactic counterparts. The luminosity decline rate is ∆m15(B) = 1.17 ± 0.12 mag and the absolute B band magnitude obtained from the luminosity versus decline rate relation (Phillips et al. 1999) is MB max = -19.20 ± 0.18 mag. The peak bolometric luminosity indicates that ∼ 0.66 M⊙ mass of 56 Ni was ejected by the supernova. The spectral evolution indicates the supernova to be a normal type Ia event.Item HD molecules at high redshift: A low astration factor of deuterium in a solar-metallicity DLA system at z=2.418(2008-08) Noterdaeme, P.; Srianand, R.We present the detection of deuterated molecular hydrogen (HD) in the remote Universe in a damped Lyman-α cloud at zabs = 2.418 toward the quasar SDSS J143912.04+111740.5. This is a unique system in which H2 and CO molecules are also detected. The chemical enrichment of this gas derived from Zn ii and S ii is as high as in the Sun. We measure N(HD)/2N(H2) = 1.5+0.6 −0.4 × 10−5, which is significantly higher than the same ratio measured in the Galaxy and close to the primordial D/H ratio estimated from the WMAP constraint on the baryonic matter density (Ωb). This indicates a low astration factor of deuterium that contrasts with the unusually high chemical enrichment of the gas. This can be interpreted as the consequence of an intense infall of primordial gas onto the associated galaxy. Detection of HD molecules at high-z also opens the possibility to obtain an independent constraint on the cosmological-time variability of , the proton-to-electron mass ratio.Item First detection of CO in a high-redshift damped Lyman - Alpha system(2008-04) Srianand, R.We present the first detection of carbon monoxide (CO) in a damped Lyman-α system (DLA) at zabs =2.41837 toward SDSS J143912.04+111740.5. We also detected H2 and HD molecules. The measured total column densities (in log units) of H i, H2, and CO are 20.10±0.10, 19.38±0.10, and 13.89±0.02, respectively. The molecular fraction, f = 2N(H2)/(N(H i)+2N(H2)) = 0.27+0.10 −0.08, is the highest among all known DLAs. The abundances relative to solar of S, Zn, Si, and Fe are −0.03±0.12, +0.16±0.11, −0.86±0.11, and −1.32±0.11, respectively, indicating a high metal enrichment and a depletion pattern onto dust-grains similar to the cold ISM of our Galaxy. The measured N(CO)/N(H2) = 3×10−6 is much less than the conventional CO/H2 ratio used to convert the CO emission into gaseous mass but is consistent with what is measured along translucent sightlines in the Galaxy. The CO rotational excitation temperatures are higher than those measured in our Galactic ISM for similar kinetic temperature and density. Using the C i fine structure absorption lines, we show that this is a consequence of the excitation being dominated by radiative pumping by the cosmic microwave background radiation (CMBR). From the CO excitation temperatures, we derive TCMBR = 9.15±0.72 K, while 9.315±0.007 K is expected from the hot big-bang theory. This is the most precise high-redshift measurement of TCMBR and the first confirmation of the theory using molecular transitions at high redshift.Item Detection of the 2175\AA~ extinction feature and 21-cm absorption in two MgII systems at z~1.3(2008-09) Srianand, R.We have discovered two dusty intervening Mg ii absorption systems at z ∼ 1.3 in the Sloan Digital Sky Survey (SDSS) database. The overall spectra of both QSOs are red (u-K>4.5 mag) and are well modelled by the composite QSO spectrum reddened by the extinction curve from the Large Magellanic Cloud(LMC2) Supershell redshifted to the rest-frame of the Mg ii systems. In particular, we detect clearly the presence of the UV extinction bump at λrest ∼ 2175 ˚ A. Absorption lines of weak transitions like Si iiλ1808, Cr iiλ2056, Cr ii+Zn iiλ2062, Mn iiλ2594, Ca iiλ3934 and Ti iiλ1910 from these systems are detected even in the low signal-to-noise ratio and low resolution SDSS spectra, suggesting high column densities of these species. The depletion pattern inferred from these absorption lines is consistent with that seen in the cold neutral medium of the LMC. Using the LMC AV vs. N(H i) relationship we derive N(H i)∼ 6×1021 cm−2 in both systems. Metallicities are close to solar. Giant Metrewave Radio Telescope (GMRT) observations of these two relatively weak radio loud QSOs (fν ∼ 50 mJy) resulted in the detection of 21-cm absorption in both cases.We show that the spin temperature of the gas is of the order of or smaller than 500 K. These systems provide a unique opportunity to search for molecules and diffuse interstellar bands at z > 1.