| 1. |
- Biemont, E, et al.
(författare)
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Radiative lifetimes, branching fractions and transition probabilities in Ge I - solar implications
- 1999
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 303:4, s. 721-726
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Tidskriftsartikel (refereegranskat)abstract
- New radiative lifetimes have been measured for the 5s (3)P(0,1,2)degrees and 5s (1)P(1)degrees levels of Ge I using a laser-produced plasma subject to selective laser excitation. A diffraction grating based emission spectrometer of moderately high resolution has been used to remeasure the branching ratios of the 4p-5s depopulating transitions. The oscillator strengths of astrophysical interest, which have been derived from these new data, are compared with theoretical values calculated within a pseudo-relativistic Hartree-Fock approach. The new set of f-values has been compared with the few results available in the literature, which are generally characterized by a large scatter and a low accuracy. The solar photospheric abundance of germanium deduced from the new atomic data of the present work is A(Ge) = 3.58 +/- 0.05, on the usual logarithmic scale, in agreement with the meteoritic value.
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| 2. |
- Harper, GM, et al.
(författare)
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Lines of O IV and S IV in the Goddard High-Resolution Spectrograph spectrum of RR Tel: constraints on atomic data
- 1999
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 303:3, s. 41-46
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Tidskriftsartikel (refereegranskat)abstract
- High signal-to-noise ratio spectra of RR Tel obtained at medium resolution with the Goddard High-Resolution Spectrograph (GHRS) on the Hubble Space Telescope (HST) are used to test available atomic data for the O IV 2s(2)2p P-2-2s2p(2) P-4 multiplet (UV 0.01). The fine-structure intervals of the 2s2p(2) P-4 term given by Moore (1983) appear to need revision. The flux ratios of lines within multiplet UV (0.01), which have a common upper level, depend only on transition probabilities. The observed flux ratio of lines from the P-4(3/2) level differs from that predicted by theory, but this difference cannot be attributed to a blend with a line of S IV]. At the electron densities in the RR Tel nebula, other flux ratios give information on the relative electron excitation rates between the P-2 and P-4 fine-structure levels. Using the collision strengths calculated by Zhang, Graziani & Pradhan, the rate to the P-4(5/2) level, relative to the rates to the other J states, appears to be underestimated by similar to 10 per cent, which is within the expected uncertainty of 20 per cent. We also discuss the S IV 3s(2)3p P-2-3s3p(2) P-4 multiplet.
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| 3. |
- Ronnback, J., et al.
(författare)
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Host galaxies of intermediate redshift radio-loud and radio-quiet quasars
- 1996
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Ingår i: Monthly notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 283:1, s. 282-296296
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Tidskriftsartikel (refereegranskat)abstract
- In a search for host galaxies associated with quasars, the authors present results from deep CCD imaging using the European Southern Observatory 3.5-m New Technology Telescope. Altogether 21 targets, 12 radio-loud and nine radio-quiet quasars, were observed in R, and additional V and Gunn i images were collected for a subgroup of these. The quasar redshifts are between 0.4 and 0.8, a range largely unexplored in previous studies. At these redshifts the R band corresponds to a rest-frame wavelength between 4600 and 3600 Aring. Thus, the authors are primarily probing the light from young stellar components of the presumed host galaxies. To separate out the light originating from the host object the authors remove the quasar contribution by scaling the point spread function (PSF). The PSF is a combination of an empirical PSF model, derived from stars lying in the same field as the quasars (used for the core of the PSF), and an analytical model for the wings of the PSF. After PSF subtraction of the QSO image the authors identify extended residual objects in 17 targets (nine in radio-loud and eight in radio-quiet quasars), of which a few are only marginal detections. These objects are large and luminous and their colours are relatively blue. Their V-R colours are consistent with a stellar population typical of late-type spirals and irregular galaxies. The blue colours could be caused by recent star formation events or by scattering of the QSO light
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| 4. |
- Adams, JA, et al.
(författare)
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Cosmic microwave background anisotropy in the decaying neutrino cosmology
- 1998
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Ingår i: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY. - : BLACKWELL SCIENCE LTD. - 0035-8711. ; 301:1, s. 210-214
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- It is attractive to suppose for several astrophysical reasons that the Universe has close to the critical density in light (similar to 30 eV) neutrinos which decay radiatively with a lifetime of similar to 10(23) s. In such a cosmology the Universe is re-
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| 5. |
- BERGVALL, N, et al.
(författare)
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ESO-146-G14, A RETARDED DISC GALAXY
- 1995
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Ingår i: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY. - : BLACKWELL SCIENCE LTD. - 0035-8711. ; 273:3, s. 603-614
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Tidskriftsartikel (refereegranskat)abstract
- In our search for nearby young and unevolved galaxies we encountered ESO 146 - G14, a blue low-surface-brightness late-type disc galaxy with remarkable properties. The analysis of the chemical abundances of the brightest Hn regions yields an oxygen abunda
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| 6. |
- Pijpers, Frank P, et al.
(författare)
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A modified R(1)circle times R(1) method for helioseismic rotation inversions
- 1996
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Ingår i: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY. - : BLACKWELL SCIENCE LTD. - 0035-8711. ; 279:2, s. 498-510
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Tidskriftsartikel (refereegranskat)abstract
- We present an efficient method for two-dimensional (2D) inversions for the solar rotation rate using the Subtractive Optimally Localized Averages (SOLA) method and a modification of the R(1) x R(1) technique proposed by Sekii. The SOLA method is based on
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| 7. |
- Ronnback, Jari, et al.
(författare)
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Host galaxies of intermediate redshift radio-loud and radio-quiet quasars
- 1996
-
Ingår i: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY. - : BLACKWELL SCIENCE LTD. - 0035-8711. ; 283:1, s. 282-296
-
Tidskriftsartikel (refereegranskat)abstract
- In a search for host galaxies associated with quasars, we present results from deep CCD imaging using the European Southern Observatory (ESO) 3.5-m New Technology Telescope (NTT). 21 targets, 12 radio-loud and nine radio-quiet quasars, were observed in R,
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