2006 (IPP)
Permanent URI for this collectionhttp://localhost:4000/handle/11007/335
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12 results
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Item Velocity-metallicity correlation for high-z DLA galaxies: Evidence for a mass-metallicity relation?(2006-06-08) Ledoux, C.; Petitjean, Patrick; Fynbo, J. P. U.; et al.Item Re-analysis of the three-year wilkinson microwave anisotropy probe temperature power spectrum and likelihood(2006-10-02) Eriksen, H. K.; Huey, Greg; Saha, Rajib; et al.We analyze the three-year WMAP temperature anisotropy data seeking to confirm the power spectrum and likelihoods published by the WMAP team. We apply five independent implementations of four algorithms to the power spectrum estimation and two implementations to the parameter estimation. Our single most important result is that we broadly confirm the WMAP power spectrum and analysis. Still, we do find two small but potentially important discrepancies: On large angular scales there is a small power excess in the WMAP spectrum (5–10% at ℓ . 30) primarily due to likelihood approximation issues between 13 ≤ ℓ . 30. On small angular scales there is a systematic difference between the V- and W-band spectra (few percent at ℓ & 300). Recently, the latter discrepancy was explained by Huffenberger et al. (2006) in terms of over-subtraction of unresolved point sources. As far as the low-ℓ bias is concerned, most parameters are affected by a few tenths of a sigma. The most important effect is seen in ns. For the combination of WMAP, Acbar and BOOMERanG, the significance of ns = 1 drops from ∼ 2.7σ to ∼ 2.3σ when correcting for this bias. We propose a few simple improvements to the low-ℓ WMAP likelihood code, and introduce two important extensions to the Gibbs sampling method that allows for proper sampling of the low signal-to-noise regime. Finally, we make the products from the Gibbs sampling analysis publically available, thereby providing a fast and simple route to the exact likelihood without the need of expensive matrix inversions.Item Search for 1₁₁ - 1₁ₒ and 2₁₁ - 2₁₂ transitions of H₂CCO, H₂CCC, and H₂CCCC, in cosmic objects(2006-01-10) Chandra, S.; Musrif, P. G.; Dharmkare, Ram M.; et al.Item Quantum effects, soft singularities and the fate of the universe in a braneworld cosmology(2006-03-24) Tretjakov, P. V.; Toporensky, A.; Shtanov, Yuri; et al.Item Properties of dust in early-type galaxies(2006-11-12) Patil, M. K.; Pandey, S. K.; Sahu, D. K.; et al.We report optical extinction properties of dust for a sample of 26 early-type galaxies based on the analysis of their multicolour CCD observations. The wavelength dependence of dust extinction for these galaxies is determined and the extinction curves are found to run parallel to the Galactic extinction curve, which implies that the properties of dust in the extragalactic environment are quite similar to those of the Milky Way. For the sample galaxies, value of the parameter RV, the ratio of total extinction in V band to selective extinction in B & V bands, lies in the range 2.03 - 3.46 with an average of 3.02, compared to its canonical value of 3.1 for the Milky Way. A dependence of RV on dust morphology of the host galaxy is also noticed in the sense that galaxies with a well defined dust lane show tendency to have smaller RV values compared to the galaxies with disturbed dust morphology. The dust content of these galaxies estimated using total optical extinction is found to lie in the range 104 to 106 M⊙, an order of magnitude smaller than those derived from IRAS flux densities, indicating that a significant fraction of dust intermixed with stars remains undetected by the optical method. We examine the relationship between dust mass derived from IRAS flux and the X-ray luminosity of the host galaxies.The issue of the origin of dust in early-type galaxies is also discussed.Item On the variation of the fine-structure constant : Very high resolution spectrum of QSO HE 0515-4414(2006-01-10) Chand, Hum; Srianand, R.; Petitjean, Patrick; et al.We present a detailed analysis of a very high resolution (R ≈ 112, 000) spectrum of the quasar HE 0515−4414 obtained using the High Accuracy Radial velocity Planet Searcher (HARPS) mounted on the ESO 3.6 m telescope at the La Silla observatory. The main aim is to use HARPS spectrum of very high wavelength calibration accuracy (better than 1 mÅ), to constrain the variation of α = e² /~c and investigate any possible systematic inaccuracies in the wavelength calibration of the UV Echelle Spectrograph (UVES) mounted on the ESO Very Large Telescope (VLT). Methods. A cross-correlation analysis between the Th-Ar lamp spectra obtained with HARPS and UVES is carried out to detect any possible shift between the two spectra. Absolute wavelength calibration accuracies, and how that translate to the uncertainties in ∆ α/α are computed using Gaussian fits for both lamp spectra. The value of ∆α/α at Zabs = 1.1508 is obtained using Many Multiplet method, and simultaneous Voigt profile fits of HARPS and UVES spectra. Results. We find the shift between the HARPS and UVES spectra has mean around zero with a dispersion of σ ≃ 1 mÅ. This is shown to be well within the wavelength calibration accuracy of UVES (i.e σ ≃ 4 mÅ). We show that the uncertainties in the wavelength calibration induce an error of about, ∆α/α ≤ 10−⁶ , in the determination of the variation of the fine-structure constant. Thus, the results of non-evolving ∆α/α reported in the literature based on UVES/VLT data should not be heavily influenced by problems related to wavelength calibration uncertainties. Our higher resolution spectrum of the zabs = 1.1508 Damped Lyman-α system toward HE 0515−4414 reveals more components compared to the UVES spectrum. Using only Fe II lines of zabs = 1.1508 system, we obtain ∆α/α = (0.05 ± 0.24) × 10−⁵ . This result is consistent with the earlier measurement for this system using the UVES spectrum alone.Item Non subjective approach to the GP algorithm for analysing noisy time series(2006-01-10) Harikrishnan, K. P.; Misra, Ranjeev; Ambika, G.; et al.We present an adaptation of the standard Grassberger-Proccacia (GP) algorithm for estimating the Correlation Dimension of a time series in a non subjective manner. The validity and accuracy of this approach is tested using di erent types of time series, such as, those from standard chaotic systems, pure white and colored noise and chaotic systems added with noise. The e ectiveness of the scheme in analysing noisy time series, particularly those involving colored noise, is investigated. An interesting result we have obtained is that, for the same percentage of noise addition, data with colored noise is more distinguishable from the corresponding surrogates, than data with white noise. As examples for real life applications, analysis of data from an astrophysical X-ray object and human brain EEG, are presented.Item Non-linear behaviour of the black hole system GRS 1915+ 105(2006-02-05) Misra, Ranjeev; Harikrishnan, K. P.; Ambika, G.; et al.Using non-lin~ar ti?Ie seri.e~ analysis, along with surrogate data analysis, it is shown that the various types of lon~ t~rI? varla~lbty exhibited by the black hole system GRS 1915+105, can be explained in terms of a ~et~rmlmstlc.n?n-bnear system with some inherent stochastic noise. Evidence is provided for a non-linear limit cycle ongm of one of.the low f~eque~cy QPO detected in the source, while some other types of variability could. be due ~oan underlying low dimensional chaotic system. These results imply that the partial differential equanons which govern the magneto- ~drodynamic flow of the inner accretion disk, can be approximated by a by a small number ( ~ 3 - 5) of non-linear but ordinary differential equations. While this analysis does not reveal the exact nature of these approximate equations, they may be obtained in the future, after results of magneto-hydrodynamic simulation of realistic accretion disks become available.Item Non-circular beam correction to the CMB power spectrum(2006-08-24) Souradeep, Tarun; Mitra, Sanjit; Sengupta, Anand; et al.In the era of high precision CMB measurements, systematic effects are beginning to limit the ability to extract subtler cosmological information. The non-circularity of the experimental beam has become progressively important as CMB experiments strive to attain higher angular resolution and sensitivity. The effect of non-circular beam on the power spectrum is important at multipoles larger than the beam-width. For recent experiments with high angular resolution, optimal methods of power spectrum estimation are computationally prohibitive and sub-optimal approaches, such as the Pseudo-Cl method, are used. We provide an analytic framework for correcting the power spectrum for the effect of beam non-circularity and non-uniform sky coverage (including incomplete/masked sky maps). The approach is perturbative in the distortion of the beam from non-circularity allowing for rapid computations when the beam is mildly non-circular. When non-circular beam effect is important, we advocate that it is computationally advantageous to employ ‘soft’ azimuthally apodized masks whose spherical harmonic transform die down fast with m.Item Metallicity as a criterion to select H2 bearing damped lyman-alpha systems(2006-07-17) Petitjean, Patrick; Ledoux, C.; Noterdaeme, P.; et al.