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Träfflista för sökning "WFRF:(Viti S.) srt2:(2005-2009)"

Sökning: WFRF:(Viti S.) > (2005-2009)

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1.
  • Blackwell-Whitehead, R. J., et al. (författare)
  • Experimental TiI oscillator strengths and their application to cool star analysis
  • 2006
  • Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 373:4, s. 1603-1609
  • Tidskriftsartikel (refereegranskat)abstract
    • We report experimental oscillator strengths for 88 Ti I transitions covering the wavelength range 465-3892 nm, 67 of which had no previous experimental values. Radiative lifetimes for 13 energy levels, including the low energy levels 3d(2)(F-3) 4s4p ((3)p) z(5)D(j)degrees have been measured using time-resolved laser-induced fluorescence. Intensity-calibrated Ti I spectra have been measured using Fourier transform spectroscopy to determine branching fractions for the decay channels of these levels. The branching fractions are combined with the radiative lifetimes to yield absolute transition probabilities and oscillator strengths. Our measurements include 50 transitions in the previously unobserved infrared region lambda > 1.0 mu m, a region of particular interest to the analysis of cool stars and brown dwarfs.
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2.
  • Jones, HRA, et al. (författare)
  • Status of the physics of substellar objects project
  • 2005
  • Ingår i: Astronomical Notes - Astronomische Nachrichten. - : Wiley. - 0004-6337. ; 326:10, s. 920-924
  • Tidskriftsartikel (refereegranskat)abstract
    • A full understanding of the properties of substellar objects is one of the major challenges facing astrophysics. Since their discovery in 1995, hundreds of brown dwarfs and extrasolar planets have been discovered. While these discoveries have enabled important comparisons with theory, observational progress has been much more rapid than the theoretical understanding of cool atmospheres. The reliable determination of mass, abundances, gravities and temperatures is not yet possible. The key problem is that substellar objects emit their observable radiation in the infrared region of the spectrum where our knowledge of atomic, molecular and line broadening data is poor. Here we report on the status of our PoSSO (Physics of SubStellar Objects) project. In order to understand brown dwarfs and extrasolar planets increasing more like those in our solar system, we are studying a wide range of processes. Here we give an update on the project and sketch an outline of atoms, molecules and processes requiring study.
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3.
  • Röllig, M., et al. (författare)
  • A photon dominated region code comparison study
  • 2007
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 467:No. 1 (May III 2007), s. 187-206
  • Tidskriftsartikel (refereegranskat)abstract
    • Aims.We present a comparison between independent computer codes, modeling the physics and chemistry of interstellar photon dominated regions (PDRs). Our goal was to understand the mutual differences in the PDR codes and their effects on the physical and chemical structure of the model clouds, and to converge the output of different codes to a common solution.Methods. A number of benchmark models have been created, covering low and high gas densities n = 103,105.5 cm-3 and far ultraviolet intensities $\chi$ = 10, 105 in units of the Draine field (FUV: 6
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4.
  • Thi, W. F., et al. (författare)
  • ISO observation of molecular hydrogen and fine-structure lines in the photodissociation region IC 63
  • 2009
  • Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 400:2, s. 622-628
  • Tidskriftsartikel (refereegranskat)abstract
    • We wish to constrain the main physical properties of the photodissociation region (PDR) IC63. We present the results of a survey for the lowest pure-rotational lines of H2 with the Short Wavelength Spectrometer and for the major fine-structure cooling lines of OI at 63 and 145μm and CII at 157.7μm with the Long Wavelength Spectrometer on board the Infrared Space Observatory (ISO) in the high-density PDR IC63. The observations are compared with available photochemical models based on optical absorption and/or millimetre emission line data with and without enhanced H2 formation rate on grain surfaces. The cloud density nH is constrained by the fine-structure lines. The models include both collisional excitation and ultraviolet (UV) pumping of the H2 ro-vibrational levels. Molecular pure-rotational lines up to S(5) are detected. The inferred column density of warm H2 at 106 +/- 11K is (5.9 +/- 1.8)+0.9-0.7 × 1021cm-2, while that of the hot component at 685 +/- 68K is (1.2 +/- 0.4) × 1019cm-2. Fine-structure lines are also detected in the far-infrared spectrum of IC63. The fine-structure lines constrain the density of the PDR to be (1-5) × 103cm-3. The impinging UV field on the PDR is enhanced by a factor of 103 compared to the mean interstellar field and is consistent with direct measurements in the UV. PDR models that include an enhanced H2 formation at high dust temperature give higher H2 intensities than models without enhancement. However, the predicted intensities are still lower than the observed intensities.
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