| 1. |
- Bautista, M A, et al.
(författare)
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Excitation of Sr II lines in Eta Carinae
- 2002
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 331:4, s. 875-879
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Tidskriftsartikel (refereegranskat)abstract
- We study the nature of the peculiar [Sr II] and Sr II emission filament found in the ejecta of Eta Carinae. To this purpose we carry out abinitio calculations of radiative transition probabilities and electron impact excitation rate coefficients for Sr II. Then we build a multilevel model for the system which is used to investigate the physical condition of the filament and the nature of the observed allowed and forbidden Sr II optical emission. It is found that the observed spectrum is consistent with the lines being pumped by the continuum radiation field in a mostly neutral region with electron density near 107cm-3 . Under these conditions, the observed emission can be explained without the need for a large Sr overabundance.
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| 2. |
- Beer, Martin E, et al.
(författare)
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Red giant depletion in globular cluster cores
- 2004
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 348:2, s. 679-686
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the observed depletion of red giants in the cores ofpost-core-collapse globular clusters. In particular, the evolutionaryscenario we consider is a binary consisting of two low-mass stars whichundergoes two common-envelope phases. The first common-envelope phaseoccurs when the primary is a red giant resulting in a helium white dwarfand main-sequence star in a detached binary. The second common-envelopephase occurs shortly after the secondary becomes a red giant. During thesecond common-envelope phase, the degenerate helium cores mergeresulting in a core mass greater than the helium burning limit and theformation of a horizontal branch star. We show that stellar encountersenhance this evolutionary route in post-core-collapse clusters. Theseencounters increase the population of binary secondaries which wouldhave evolved on to the red giant branch in the recent past.
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| 3. |
- Biemont, E, et al.
(författare)
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Measurement of radiative lifetimes and determination of transition probabilities of astrophysical interest in HoIII
- 2001
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 328:4, s. 1085-1090
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Tidskriftsartikel (refereegranskat)abstract
- Lifetimes of six levels belonging to the 4f(10)6p configuration of Ho III have been measured for the first time using the time-resolved laser-induced fluorescence method. They are compared with multiconfigurational pseudo-relativistic Hartree-Fock calculations. A very good agreement is found. Using the experimental lifetimes and theoretical branching fractions, a first set of transition probabilities of astrophysical interest has been obtained for this ion.
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| 4. |
- Biemont, E, et al.
(författare)
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New f-values in neutral lead obtained by time-resolved laser spectroscopy, and astrophysical applications
- 2000
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 312:1, s. 116-122
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Tidskriftsartikel (refereegranskat)abstract
- Natural radiative lifetimes have been measured for three odd-parity levels of neutral lead using time-resolved UV laser-induced fluorescence from a laser-produced plasma. These new lifetimes, as well as additional recent values obtained by laser spectroscopy, combined with theoretical branching ratios deduced from a relativistic Hartree-Fock calculation taking core polarization effects into account, have allowed the deduction of a new set of accurate f-values of astrophysical interest. Using the new lifetime value for 6p7s (1/2, 1/2)(0)degrees, a refined value of the lead abundance in the solar photosphere is deduced: A(Pb) = 2.00 +/- 0.06 on the usual logarithmic scale, allowing the resolution of the long-standing discrepancy previously observed between the solar photosphere and meteorites.
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| 5. |
- Biemont, E, et al.
(författare)
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Radiative lifetime measurements and transition probabilities of astrophysical interest in ErIII
- 2001
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 321:3, s. 481-486
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Tidskriftsartikel (refereegranskat)abstract
- Radiative lifetimes of seven excited states of Er iii have been measured using time-resolved laser-induced fluorescence following two-photon excitation. Relativistic Hartree-Fock calculations taking core-polarization effects into account are found to be in excellent agreement with the experimental results. A large set of new calculated transition probabilities is presented for many transitions of astrophysical interest. These results will be useful for investigating the composition of chemically peculiar stars.
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| 6. |
- Chugai, Nikolai N., et al.
(författare)
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The Type IIn supernova 1994W : evidence for the explosive ejection of a circumstellar envelope
- 2004
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 352, s. 1213-1231
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Tidskriftsartikel (refereegranskat)abstract
- We present and analyse spectra of the Type IIn supernova (SN) 1994W obtained between 18 and 203d after explosion. During the luminous phase (first 100d) the line profiles are composed of three major components: (i) narrow P-Cygni lines with the absorption minima at -700kms-1 (ii) broad emission lines with blue velocity at zero intensity ~4000km s-1 and (iii) broad, smooth wings extending out to at least ~5000kms-1, most apparent in Hα. These components are identified with an expanding circumstellar (CS) envelope, shocked cool gas in the forward post-shock region, and multiple Thomson scattering in the CS envelope, respectively. The absence of broad P-Cygni lines from the SN is the result of the formation of an optically thick, cool, dense shell at the interface of the ejecta and the CS envelope. Models of the SN deceleration and Thomson scattering wings are used to recover the density (n~ 109cm-3), radial extent [~(4-5) × 1015cm] and Thomson optical depth (τT>~ 2.5) of the CS envelope during the first month. The plateau-like SN light curve is reproduced by a hydrodynamical model and is found to be powered by a combination of internal energy leakage after the explosion of an extended pre-SN (~1015cm) and subsequent luminosity from CS interaction. The pre-explosion kinematics of the CS envelope is recovered, and is close to homologous expansion with outer velocity ~1100kms-1 and a kinematic age of ~1.5yr. The high mass (~0.4Msolar) and kinetic energy (~2 × 1048erg) of the CS envelope, combined with low age, strongly suggest that the CS envelope was explosively ejected ~1.5yr prior to the SN explosion.
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| 7. |
- Davies, Melvyn B, et al.
(författare)
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Blue straggler production in globular clusters
- 2004
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 349:1, s. 129-134
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Tidskriftsartikel (refereegranskat)abstract
- Recent Hubble Space Telescope observations of a large sample of globular clusters reveal that every cluster contains between 40 and 400 blue stragglers.The population does not correlate with either stellar collision rate (as would be expected if all blue stragglers were formed via collisions) or total mass (as would be expected if all blue stragglers were formed via the unhindered evolution of a subset of the stellar population). In this paper, we support the idea that blue stragglers are made through both channels. The number produced via collisions tends to increase with cluster mass. In this paper we show how the current population produced from primordial binaries decreases with increasing cluster mass;exchange encounters with third, single stars in the most massivec lusters tend to reduce the fraction of binaries containing a primary close to the current turn-off mass. Rather, their primaries tend to be somewhat more massive (~1-3 Msolar) and have evolved off the main sequence, filling their Roche lobes in the past, often converting their secondaries into blue stragglers (but more than 1 Gyr or so ago and thus they are no longer visible as blue stragglers). We show that this decline in the primordial blue straggler population is likely to be offset by the increase in the number of blue stragglers produced via collisions. The predicted total blue straggler population is therefore relatively independent of cluster mass, thus matching the observed population. This result does not depend on any particular assumed blue straggler lifetime.
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| 8. |
- Flynn, Chris, et al.
(författare)
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White dwarfs and Galactic dark matter
- 2003
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 339:3, s. 817-824
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Tidskriftsartikel (refereegranskat)abstract
- We discuss the recent discovery by Oppenheimer et al. of old, cool white dwarf stars, which may be the first direct detection of Galactic halo dark matter. We argue here that the contribution of more mundane white dwarfs of the stellar halo and thick disc would contribute sufficiently to explain the new high velocity white dwarfs without invoking putative white dwarfs of the dark halo. This by no means rules out that dark matter has been found, but it does constrain the overall contribution by white dwarfs brighter than MR
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| 9. |
- Hibbert, A, et al.
(författare)
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3s(2)3p-3s3p(2) transitions in SIV
- 2002
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 333:4, s. 885-893
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Tidskriftsartikel (refereegranskat)abstract
- We use both the civ3 and mchf codes to calculate oscillator strengths of allowed and intercombination lines in the 3s(2) 3p-3s3p(2) multiplets. Valence, core-valence and some core-core correlation effects are included. The two approaches give results in excellent agreement. Core effects are particularly important for the intercombination lines, though relatively minor for allowed transitions. We obtain a branching ratio of 1.42 with an estimated accuracy of 0.02 for the transitions, compared with an experimental value of 1.12+/-0.1. The A -values of the intercombination lines are substantially different from those of previous calculations.
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| 10. |
- Keenan, FP, et al.
(författare)
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The O IV and S IV intercombination lines in the ultraviolet spectra of astrophysical sources
- 2002
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 337:3, s. 901-909
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Tidskriftsartikel (refereegranskat)abstract
- New electron density diagnostic line ratios are presented for the O IV 2s(2)2p P-2-2s2p(24)P and S IV 3s(2)3p P-2-3s3p(24)P intercombination lines around 1400 Angstrom comparison of these with observational data for the symbiotic star RR Telescopii (RR Tel), obtained with the Space Telescope Imaging Spectrograph (STIS), reveals generally very good agreement between theory and observation. However the S IV P-2(3/2)-P-4(1/2) transition at 1423.824 Angstrom is found to be blended with an unknown feature at 1423.774 Angstrom. The linewidth for the latter indicates that the feature arises from a species with a large ionization potential. In addition, the S IV P-2(1/2)-P-4(3/2) transition at 1398.044 Angstrom is identified for the first time (to our knowledge) in an astrophysical source other than the Sun, and an improved wavelength of 1397.166 Angstrom is measured for the O IV P-2(1/2)-P-4(3/2) line. The O IV and S IV line ratios in a sunspot plume spectrum, obtained with the Solar Ultraviolet Measurements of the Emitted Radiation (SUMER) instrument on the Solar and Heliospheric Observatory, are found to be consistent, and remove discrepancies noted in previous comparisons of these two ions.
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| 11. |
- Xu, Huailiang, et al.
(författare)
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Theoretical and experimental lifetime and oscillator strength determination in singly ionized neodymium (Nd II)
- 2003
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 346:2, s. 433-440
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Tidskriftsartikel (refereegranskat)abstract
- Radiative lifetime measurements were performed with time-resolved laser-induced fluorescence techniques for 24 levels of Nd II in the energy range 20 500- 32 500 cm(-1). For 17 levels, no previous experimental data exist. These results have allowed the testing of new theoretical calculations with the relativistic Hartree-Fock method taking configuration interactions and core-polarization effects into account, and a satisfying agreement has been found for this complex ion. A new set of calculated oscillator strengths, accurate within a few per cent for the strongest transitions, is presented for 107 lines of astrophysical interest appearing in the wavelength range 358.0-1100.0 nm. These results will be useful to evaluate abundance values of neodymium in chemically peculiar stars in relation with cosmochronology.
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| 12. |
- Chugai, N. N., et al.
(författare)
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Circumstellar interaction of the type Ia supernova 2002ic
- 2004
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 355, s. 627-637
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Tidskriftsartikel (refereegranskat)abstract
- We propose a model to account for the bolometric light curve, the quasi-continuum and the CaII emission features of the peculiar type Ia supernova (SN) 2002ic, which exploded in a dense circumstellar envelope. The model suggests that the SN Ia had the maximum possible kinetic energy and that the ejecta expand in an approximately spherically symmetric (possibly clumpy) circumstellar environment. The CaII and the quasi-continuum are emitted by shocked SN ejecta that underwent deformation and fragmentation in the intershock layer. Modelling of the CaII triplet implies that the contribution of the OI 8446-Åline is about 25 per cent of the 8500-Åfeature on day 234, which permits us to recover the flux in the CaII 8579-Åtriplet from the flux of 8500-Åblend reported by Deng et al. We use the CaII doublet and triplet fluxes on day 234 to derive the electron temperature (~ 4400 K) in the CaII line-emitting zone and the ratio of the total area of dense fragments to the area of the shell, S/S0~ 102. We argue that CaII bands and the quasi-continuum originate from different zones of the shocked ejecta that reflect the abundance stratification of the supernova.
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| 13. |
- Pozzo, M., et al.
(författare)
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On the source of the late-time infrared luminosity of SN 1998S and other Type II supernovae
- 2004
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 352, s. 457-477
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Tidskriftsartikel (refereegranskat)abstract
- We present late-time near-infrared (NIR) and optical observations of the Type IIn SN 1998S. The NIR photometry spans 333-1242 d after explosion, while the NIR and optical spectra cover 333-1191 and 305-1093 d, respectively. The NIR photometry extends to the M' band (4.7 μm), making SN 1998S only the second ever supernova for which such a long IR wavelength has been detected. The shape and evolution of the Hα and HeI 1.083-μm line profiles indicate a powerful interaction with a progenitor wind, as well as providing evidence of dust condensation within the ejecta. The latest optical spectrum suggests that the wind had been flowing for at least 430 yr. The intensity and rise of the HK continuum towards longer wavelengths together with the relatively bright L' and M' magnitudes show that the NIR emission was due to hot dust newly formed in the ejecta and/or pre-existing dust in the progenitor circumstellar medium (CSM). The NIR spectral energy distribution (SED) at about 1 yr is well described by a single-temperature blackbody spectrum at about 1200 K. The temperature declines over subsequent epochs. After ~2 yr, the blackbody matches are less successful, probably indicating an increasing range of temperatures in the emission regions. Fits to the SEDs achieved with blackbodies weighted with λ-1 or λ-2 emissivity are almost always less successful. Possible origins for the NIR emission are considered. Significant radioactive heating of ejecta dust is ruled out, as is shock/X-ray-precursor heating of CSM dust. More plausible sources are (a) an IR echo from CSM dust driven by the ultraviolet/optical peak luminosity, and (b) emission from newly-condensed dust which formed within a cool, dense shell produced by the ejecta shock/CSM interaction. We argue that the evidence favours the condensing dust hypothesis, although an IR echo is not ruled out. Within the condensing-dust scenario, the IR luminosity indicates the presence of at least 10-3 Msolar of dust in the ejecta, and probably considerably more. Finally, we show that the late-time (K-L')0 evolution of Type II supernovae may provide a useful tool for determining the presence or absence of a massive CSM around their progenitor stars.
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| 14. |
- Romeo, Alessandro, 1961, et al.
(författare)
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A wavelet add-on code for new-generation N-body simulations and data de-noising (JOFILUREN)
- 2004
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 354:4, s. 1208-1222
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Tidskriftsartikel (refereegranskat)abstract
- Wavelets are a new and powerful mathematical tool, whose most celebrated applications are data compression and de‐noising. In a previous paper, we have shown that wavelets can be used for removing noise efficiently from cosmological, galaxy and plasma N‐body simulations. The expected two‐orders‐of‐magnitude higher performance means, in terms of the well‐known Moore's law, an advance of more than one decade in the future. In this paper, we describe a wavelet add‐on code designed for such an application. Our code can be included in common grid‐based N‐body codes, is written in fortran, is portable and is available on request from the first author. The code can also be applied for removing noise from standard data, such as signals and images.
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| 15. |
- Antonuccio-Delogu, V., et al.
(författare)
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Properties of galaxy haloes in clusters and voids
- 2002
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Ingår i: Monthly Notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 332:1, s. 7-20
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Tidskriftsartikel (refereegranskat)abstract
- We use the results of a high-resolution N -body simulation to investigate the role of the environment on the formation and evolution of galaxy-sized haloes. Starting from a set of constrained initial conditions, we have produced a final configuration hosting a double cluster in one octant and a large void extending over two octants of the simulation box. In this paper we concentrate on gravitationally bound galaxy-sized haloes extracted from these two regions and from a third region hosting a single, relaxed cluster without substructure. Exploiting the high mass resolution of our simulation (m body =2.1×109 h -1 Msolar ), we construct halo samples probing more than two decades in mass, starting from a rather small mass threshold: 5×1010 h -1 Msolar =34.2r 0 , where r 0 is the core radius of the TIS solution). We do, however, find a dependence of this relationship on the environment, like for the P (lambda ) statistics. These facts hint at a possible role of tidal fields in determining the statistical properties of haloes.
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| 16. |
- Romeo, Alessandro, 1961, et al.
(författare)
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N-body simulations with two-orders-of-magnitude higher performance using wavelets
- 2003
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Ingår i: Monthly notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 342:2, s. 337-344
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Tidskriftsartikel (refereegranskat)abstract
- Noise is a problem of major concern for N-body simulations of structure formation in the early Universe, and of galaxies and plasmas. Here for the first time we use wavelets to remove noise from N-body simulations of disc galaxies, and show that they become equivalent to simulations with two orders of magnitude more particles. We expect a comparable improvement in performance for cosmological and plasma simulations. Our wavelet code will be described in a following paper, and will then be available on request.
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| 17. |
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| 18. |
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| 19. |
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| 20. |
- Pandey, G, et al.
(författare)
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Abundance analyses of cool extreme helium stars
- 2001
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Ingår i: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY. - : BLACKWELL SCIENCE LTD. - 0035-8711. ; 324:4, s. 937-959
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Tidskriftsartikel (refereegranskat)abstract
- Extreme helium stars (EHes) with effective temperatures from 8000 to 13 000 K are among the coolest EHes and overlap the hotter R CrB stars in effective temperature. The cool EHes may represent an evolutionary link between the hot EHes and the R CrB stars
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| 21. |
- Rickman, H, et al.
(författare)
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From the Oort cloud to observable short-period comets - I. The initial stage of cometary capture
- 2001
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Ingår i: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY. - : BLACKWELL SCIENCE LTD. - 0035-8711. ; 325:4, s. 1303-1311
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the first stage of the dynamical evolution of Oort cloud comets entering the planetary region for the first time. To this purpose, we integrate numerically the motions of a large number of fictitious comets pertaining to two samples, both w
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| 22. |
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| 23. |
- Tyne, VH, et al.
(författare)
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The continuing saga of Sakurai's object (V4334 Sgr): dust production and helium line emission
- 2000
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Ingår i: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY. - : BLACKWELL SCIENCE LTD. - 0035-8711. ; 315:3, s. 595-599
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Tidskriftsartikel (refereegranskat)abstract
- We report further UKIRT spectroscopic observations of Sakurai's object (V4334 Sgr) made in 1999 April/May in the 1-4.75 mu m range, and find that the emission is dominated by amorphous carbon at T-d similar to 600 K. The estimated maximum grain size is 0.
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| 24. |
- Zhang, Zhiguo, et al.
(författare)
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Experimental and theoretical studies of DyIII: radiative lifetimes and oscillator strengths of astrophysical interest
- 2002
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Ingår i: Monthly Notices of the Royal Astronomical Society. - 1365-2966. ; 334:1, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- The lifetimes of three short-lived levels belonging to the 4f(9) 6p configuration and of two long-lived levels of the 4f(9) 5d configuration of Dy iii have been measured for the first time using time-resolved laser-induced fluorescence techniques. They are in good agreement with theoretical values calculated within the framework of a pseudo-relativistic configuration interaction approximation. Using the experimental lifetimes and the theoretical branching fractions, a first set of transition probabilities of astrophysical interest has been obtained for Dy III.
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