| 1. |
- Franz, Jan, 1973, et al.
(författare)
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Formation of carbon-monoxide by radiative association : a quantum-dynamical study
- 2011
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 414, s. 3547-3550
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Tidskriftsartikel (refereegranskat)abstract
- Rate coefficients for the formation of carbon monoxide (CO) by radiative association of carbon and oxygen atoms are computed using quantum dynamical simulations. At temperatures above 10 K CO radiative association is dominated by C(3P) and O(3P) approaching on the A1Π potential energy curve. The rate coefficient is estimated as k=A(T/300 K)αexp−β/T with A= 1.39 × 10−18 cm3 s−1, α=−0.016 and β= 92.2 for temperatures between 6 and 127.2 K, and A= 1.36 × 10−17 cm3 s−1, α= 0.41 and β= 340 for temperatures between 127.2 and 15 000 K. Furthermore we computed the rate coefficients for approaching on the X1Σ+ curve. For temperatures below 200 K it is between 0.7 × 10−22 and 4 × 10−22 cm3 s−1.
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| 2. |
- Green, J. A., et al.
(författare)
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The 6-GHz multibeam maser survey-I. Techniques
- 2009
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 392:2, s. 783-794
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Tidskriftsartikel (refereegranskat)
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| 3. |
- Holmlid, Leif, 1942
(författare)
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The diffuse interstellar band carriers in interstellar space: all intense bands calculated from He doubly excited states embedded in Rydberg Matter
- 2008
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 384:2, s. 764-774
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Tidskriftsartikel (refereegranskat)abstract
- The interpretation of the almost 300 diffuse interstellar bands (DIBs) is one of the most long-standing problems in interstellar spectra. The only model showing agreement with a large number of DIBs (>60 bands) is based on transitions in doubly excited atoms embedded in the condensed phase named Rydberg Matter (RM). A similar model is now used to precisely calculate all intense bands from the high-resolution survey by Galazutdinov et al., 63 bands in total. Thus, the RM model interprets at present 120 DIBs accurately in a consistent manner, almost half of the number of DIBs. The origin of almost all intense DIBs is shown to be absorption during electron transitions between co-planar doubly excited He atoms inside RM, and from singly excited He atoms to doubly excited He atoms inside RM. The average error in the assignments is 4 cm−1 (1.4 Å), comparable to the band width. The intense but broad DIB 578.0 nm is part of a series of 10 bands interpreted as RM transitions from n" = 5 to the conduction band limit. The shape of DIB 579.7 nm is consistent with a rotational band from symmetric top RM clusters at approximately 100 K. Good agreement with observational results like band shapes and correlations among various bands is found.
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| 4. |
- 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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| 5. |
- Andreasson, Håkan, 1966, et al.
(författare)
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On the rotation curves for axially symmetric disk solutions of the Vlasov-Poisson system
- 2015
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 446:4, s. 3932-3942
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Tidskriftsartikel (refereegranskat)abstract
- A large class of flat axially symmetric solutions to the Vlasov–Poisson system is constructed with the property that the corresponding rotation curves are approximately flat, slightly decreasing or slightly increasing. The rotation curves are compared with measurements from real galaxies and satisfactory agreement is obtained. These facts raise the question whether the observed rotation curves for disc galaxies may be explained without introducing dark matter. Furthermore, it is shown that for the ansatz we consider stars on circular orbits do not exist in the neighbourhood of the boundary of the steady state.
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| 6. |
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| 7. |
- Bakala, P., et al.
(författare)
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Power density spectra of modes of orbital motion in strongly curved space-time: obtaining the observable signal
- 2014
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 439:2, s. 1933-1939
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Tidskriftsartikel (refereegranskat)abstract
- High-frequency quasi-periodic oscillations (HF QPOs) appear in the X-ray variability of several accreting low-mass binaries. In a series of works, it was suggested that these QPOs may have connection to inhomogeneities orbiting close to an inner edge of the accretion disc. In this paper, we explore the appearance of an observable signal generated by small radiating circular hotspots moving along quasi-elliptic trajectories close to the innermost stable circular orbit in the Schwarzschild space-time. Our consideration takes into account the capabilities of observatories that have been operating in the past two decades represented by the Rossi X-ray Timing Explorer (RXTE) and the proposed future instruments represented by the Large Observatory for X-ray Timing (LOFT). For these purposes, we choose such model parameters that lead to light curves comparable to those observed in Galactic black hole sources, in particular the microquasar GRS 1915+105. We find that when a weak signal corresponding to the hotspot Keplerian frequency is around the limits of the RXTE detectability, the LOFT observations can clearly reveal its first and second harmonics. Moreover, in some specific situations the radial epicyclic frequency of the spot can be detected as well. Finally, we also compare the signal produced by the spots to the signal produced by axisymmetric epicyclic disc-oscillation modes and discuss the key differences that could be identified via the proposed future technology. We conclude that the ability to recognize the harmonic content of the signal can help to distinguish between the different proposed physical models. RAMOWICZ MA, 1991, ASTRONOMY & ASTROPHYSICS, V245, P454 RAMOWICZ MA, 1992, NATURE, V356, P41 RAMOWICZ MA, 2003, PASJ, V55, P466
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| 8. |
- Burdakova, Daria, et al.
(författare)
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Formation of Na-containing complex molecules in the gas phase in dense molecular clouds: quantum study of the Na+ + H-2 and Na+ + D-2 radiative association step
- 2019
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 485:4, s. 5874-5879
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Tidskriftsartikel (refereegranskat)abstract
- The Na+ -H-2 radiative association ( RA) is the first and limiting step in the models of formation of NaH in the gas phase. Also, the accurate evaluation of the RA rate is required to be included in chemical models of dense molecular clouds. In this work, a quantum study of the formation of the Na+ -H-2 and Na+ -D-2 complexes by radiative association is presented. We use a 3D potential energy surface published recently and a quantum dynamical method based on the driven equation formalism. The values obtained for the radiative association rates are compared with previous evaluations based on approximate methods and the possible role played by these two processes in the gas phase chemistry of dense molecular clouds is discussed.
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| 9. |
- Douglas, K. M., et al.
(författare)
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Experimental study of the removal of excited state phosphorus atoms by H2O and H-2: implications for the formation of PO in stellar winds
- 2022
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 515:1, s. 99-109
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Tidskriftsartikel (refereegranskat)abstract
- The reactions of the low-lying metastable states of atomic phosphorus, P(D-2) and P(P-2), with H2O and H-2 were studied by the pulsed laser photolysis at 248 nm of PCl3, combined with laser-induced fluorescence detection of P(D-2), P(P-2), and PO. Rate coefficients between 291 and 740 K were measured, along with a yield for the production of PO from P(D-2 or P-2) + H2O of (35 +/- 15) %. H-2 reacts with both excited P states relatively efficiently; physical (i.e. collisional) quenching, rather than chemical reaction to produced PH + H, is shown to be the more likely pathway. A comprehensive phosphorus chemistry network is then developed using a combination of electronic structure theory calculations and a Master Equation treatment of reactions taking place over complex potential energy surfaces. The resulting model shows that at the high temperatures within two stellar radii of a MIRA variable AGB star in oxygen-rich conditions, collisional excitation of ground-state P(S-4) to P(D-2), followed by reaction with H2O, is a significant pathway for producing PO (in addition to the reaction between P(S-4) and OH). The model also demonstrates that the PN fractional abundance in a steady (non-pulsating) outflow is underpredicted by about 2 orders of magnitude. However, under shocked conditions where sufficient thermal dissociation of N-2 occurs at temperatures above 4000 K, the resulting N atoms convert a substantial fraction of PO into PN.
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| 10. |
- Eklund, Henrik, et al.
(författare)
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Evolution of eccentricity and inclination of hot protoplanets embedded in radiative discs
- 2017
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 469:1, s. 206-217
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Tidskriftsartikel (refereegranskat)abstract
- We study the evolution of the eccentricity and inclination of protoplanetary embryos and low-mass protoplanets (from a fraction of an Earth mass to a few Earth masses) embedded in a protoplanetary disc, by means of three-dimensional hydrodynamics calculations with radiative transfer in the diffusion limit. When the protoplanets radiate in the surrounding disc the energy released by the accretion of solids, their eccentricity and inclination experience a growth towards values that depend on the luminosity-to-mass ratio of the planet, which are comparable to the disc's aspect ratio and which are reached over time-scales of a few thousand years. This growth is triggered by the appearance of a hot, underdense region in the vicinity of the planet. The growth rate of the eccentricity is typically three times larger than that of the inclination. In long-term calculations, we find that the excitation of eccentricity and the excitation of inclination are not independent. In the particular case in which a planet has initially a very small eccentricity and inclination, the eccentricity largely overruns the inclination. When the eccentricity reaches its asymptotic value, the growth of inclination is quenched, yielding an eccentric orbit with a very low inclination. As a side result, we find that the eccentricity and inclination of non-luminous planets are damped more vigorously in radiative discs than in isothermal discs.
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