| 1. |
- Gustafsson, Magnus
(författare)
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Diatom-diatom interactions with light : Applications and line shape theoretical aspects
- 2008
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Ingår i: Spectral line shapes, volume 15. - Melville, NY : American Institute of Physics (AIP). - 9780735405882 ; 15, s. 297-301
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Konferensbidrag (refereegranskat)abstract
- Recent advances in calculations of collision-induced absorption- and Raman-spectra in pure diatomic gases are presented. An extensive calculation of H2-H2 absorption from 40 K to 400 K has provided improved understanding of the atmosphere of Uranus. A highly advanced close-coupling calculation of H2-H2 light scattering has verified that the line shapes are affected by interference between the permanent H2 and the H2-H2 interaction-induced polarizabilities. A few directions that the research in astrophysical applications of collision-induced absorption is taking are also described. For instance, H2-H 2 dipole and potential surfaces for vibrations higher than v = 1 are currently being developed to enable simulations of collision-induced absorption at temperatures relevant for white dwarf atmospheres. For low temperature N 2-N2 absorption there is unresolved discrepancy between measurement and simulation. A possible solution to this puzzle is suggested
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| 2. |
- Gustafsson, Magnus, 1969-
(författare)
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Hydrogen dimer features in low temperature collision-induced spectra
- 2017
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Ingår i: Journal of Physics, Conference Series. - : Institute of Physics (IOP). - 1742-6588 .- 1742-6596. ; 810:1
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Tidskriftsartikel (refereegranskat)abstract
- The absorption of radiation in pure hydrogen (H2) gas around the S(0) and S(1) rotational transitions is computed at 20 K and compared with laboratory data. All transitions involving free state are included in the calculations of the absolute absorption. These calculations are done with an isotropic approximation for the H2–H2 pair potential. Agreement with the experiment is observed around the S(0) transition, while the computational approach appears to be slightly worse around the S(1) transition. The positions for bound-to-bound transitions are computed including the full anisotropic pair potential. The anisotropy seems to be crucial to achieve agreement with the measured bound-to-bound transition frequencies. However, those transitions contribute little to the total absorption. The present computed absolute absorptions will provide improved input for radiative transfer models of planetary atmospheres.
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| 3. |
- Zámečníková, Martina, et al.
(författare)
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Formation of CO+ by radiative association II
- 2020
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966. ; 492:3, s. 3794-3802
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Tidskriftsartikel (refereegranskat)abstract
- Radiative association of an oxygen atom with a carbon cation is investigated using quantal and semiclassical methods. The total rate coefficient for spontaneous radiative association of O(2s22p4, 3P) with C+(2s22p, 2P) on the doublet manifold is determined from the corresponding cross-sections. The cross-sections for the 12 Σ - → A2 II, 22 Σ - → A2II, and C2 Δ → A2II continuum-bound processes are calculated either semiclassically, in combination with the Breit-Wigner approach, or fully quantum mechanically. In the temperature range 10-10 000 K, our recommended total rate coefficient, obtained from these calculations and the data of Zámecniková et al. (2019), slowly increases from 7.5 × 10-18 cm3s-1 to 2.1 × 10-17 cm3s-1. Corresponding aspects of the CO+ and CO formations in SN 1987A are discussed
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| 4. |
- Grenman, Tiia, et al.
(författare)
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Dusty globules in the Crab Nebula
- 2017
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 599
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Tidskriftsartikel (refereegranskat)abstract
- Context. Dust grains are widespread in the Crab Nebula. A number of small, dusty globules, are visible as dark spots against the background of continuous synchrotron emission in optical images. Aims. Our aim is to catalogue such dusty globules and investigate their properties. Methods. From existing broad-band images obtained with the Hubble Space Telescope, we located 92 globules, for which we derived positions, dimensions, orientations, extinctions, masses, proper motions, and their distributions. Results. The globules have mean radii ranging from 400 to 2000 AU and are not resolved in current infrared images of the nebula. The extinction law for dust grains in these globules matches a normal interstellar extinction law. Derived masses of dust range from 1 to 60 × 10-6M⊙, and the total mass contained in globules constitute a fraction of approximately 2% or less of the total dust content of the nebula. The globules are spread over the outer part of the nebula, and a fraction of them coincide in position with emission filaments, where we find elongated globules that are aligned with these filaments. Only 10% of the globules are coincident in position with the numerous H2-emitting knots found in previous studies. All globules move outwards from the centre with transversal velocities of 60 to 1600 km s-1, along with the general expansion of the remnant. We discuss various hypotheses for the formation of globules in the Crab Nebula
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| 5. |
- Grenman, Tiia, et al.
(författare)
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History of Globulettes in the Milky Way
- 2018
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Ingår i: Astrophysics and Space Science. - : Springer. - 0004-640X .- 1572-946X. ; 363:2
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Tidskriftsartikel (refereegranskat)abstract
- Globulettes are small (radii $< 10$ kAU) dark dust clouds, seen against the background of bright nebulae.A majority of the objects have planetary mass.These objects may be a source of brown dwarfs and free floating planetary mass objects in the galaxy.In this paper we investigate how many globulettes could have formed in the Milky Way and how they could contribute to the total population of free floating planets.In order to do that we examine H-alpha images of 27 H~II regions. In these images, we find 778 globulettes.We find that a conservative value of the number of globulettes formed is $5.7\times 10^{10}$.If 10 \% of the globulettes form free floating planets then they have contributed with $5.7\times 10^{9}$ free floating planets in the Milky Way. A less conservative number of globulettes would mean that the globulettes could contribute $2.0\times 10^{10}$ free floating planets.Thus the globulettes could represent a non-negligible source of free floating planets in the Milky Way.
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| 6. |
- Grenman, Tiia, et al.
(författare)
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The tiny globulettes in the Carina nebula
- 2014
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 565, s. A107-
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Tidskriftsartikel (refereegranskat)abstract
- Context. Small molecular cloudlets are abundant in many H II regions surrounding newborn stellar clusters. In optical images these so-called globulettes appear as dark silhouettes against the bright nebular background. Aims. We aim to make an inventory of the population of globulettes in the Carina nebula complex, and to derive sizes and masses for comparisons with similar objects found in other H II regions. Methods. The globulettes were identified from H alpha images collected at the Hubble Space Telescope. Results. We have located close to 300 globulettes in the Carina complex, more than in any other region surveyed so far. The objects appear as well-confined dense clumps and, as a rule, lack thinner envelopes and tails. Objects with bright rims are in the minority, but more abundant than in other regions surveyed. Some globulettes are slightly elongated with their major axes oriented in the direction of young clusters in the complex. Many objects are quite isolated and reside at projected distances >1.5 pc from other molecular structures in the neighbourhood. No globulette coincides in position with recognized pre-main-sequence objects in the area. The objects are systematically much smaller, less massive, and much denser than those surveyed in other H II regions. Practically all globulettes are of planetary mass, and most have masses less than one Jupiter mass. The average number densities exceed 105 cm 3 in several objects. We have found a statistical relation between density and radius (mass) in the sense that the smallest objects are also the densest. Conclusions. The population of small globulettes in Carina appears to represent a more advanced evolutionary state than those investigated in other H II regions. The objects are subject to erosion in the intense radiation field, which would lead to a removal of any thinner envelope and an unveiling of the core, which becomes more compact with time. We discuss the possibility that the core may become gravitationally unstable, in which case free-floating planetary mass objects can form.
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| 7. |
- Gustafsson, Magnus, et al.
(författare)
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Radiative association rate constant for the formation of CO: the importance of the first excited (1)Sigma(+) state
- 2015
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 448:3, s. 2562-2565
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Tidskriftsartikel (refereegranskat)abstract
- The thermal rate constant for production of carbon monoxide, in its electronic ground state, through radiative association of carbon (C) and oxygen (O) atoms is computed. A combination of quantum and classical dynamics methods are employed. In particular, we investigate the importance of the mechanism where C and O approach each other on the 2(1)Sigma(+) potential energy curve. Accounting for this reaction turns out to add about 75 per cent to the rate constant at 10 000 K. We expect the results to be important for studies of the chemistry in interstellar gas, particularly in metal-rich ejecta of supernovae. Since a significant isotope effect has been predicted previously both stable carbon isotopes C-12 and C-13 are considered in the present study.
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| 8. |
- Haikala, L., et al.
(författare)
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Radio observations of globulettes in the Carina nebula
- 2017
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 602, s. 61-
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Tidskriftsartikel (refereegranskat)abstract
- Context. The Carina nebula hosts a large number of globulettes. An optical study of these tiny molecular clouds shows that the majority are of planetary mass, but there are also those with masses of several tens up to a few hundred Jupiter masses. Aims: We seek to search for, and hopefully detect, molecular line emission from some of the more massive objects; in case of successful detection we aim to map their motion in the Carina nebula complex and derive certain physical properties. Methods: We carried out radio observations of molecular line emission in 12CO and 13CO (2-1) and (3-2) of 12 globulettes in addition to positions in adjacent shell structures using APEX. Results: All selected objects were detected with radial velocities shifted relative to the emission from related shell structures and background molecular clouds. Globulettes along the western part of an extended dust shell show a small spread in velocity with small velocity shifts relative to the shell. This system of globulettes and shell structures in the foreground of the bright nebulosity surrounding the cluster Trumpler 14 is expanding with a few km s-1 relative to the cluster. A couple of isolated globulettes in the area move at similar speed. Compared to similar studies of the molecular line emission from globulettes in the Rosette nebula, we find that the integrated line intensity ratios and line widths are very different. The results show that the Carina objects have a different density/temperature structure than those in the Rosette nebula. In comparison the apparent size of the Carina globulettes is smaller, owing to the larger distance, and the corresponding beam filling factors are small. For this reason we were unable to carry out a more detailed modelling of the structure of the Carina objects in the way as performed for the Rosette objects. Conclusions: The Carina globulettes observed are compact and denser than objects of similar mass in the Rosette nebula. The distribution and velocities of these globulettes suggest that they have originated from eroding shells and elephant trunks. Some globulettes in the Trumpler 14 region are quite isolated and located far from any shell structures. These objects move at a similar speed as the globulettes along the shell, suggesting that they once formed from cloud fragments related to the same foreground shell.
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| 9. |
- Hansson, Johan, et al.
(författare)
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Nonlinear Effects of Gravity in Cosmology
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We investigate some nonlinear effects of gravity in cosmology. Possible physically interesting consequences include: non-requirement ofdark matter and dark energy, asymmetric gravitational matter-creation,emergent homogeneity/isotropy & asymptotic flatness, resolution of“cosmic coincidence” Ωm∼Ω, effective cutoff of gravitational inter-action at the scale of cosmic voids.
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| 10. |
- Hansson, Johan, et al.
(författare)
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Nonlinear Effects of Gravity in Cosmology
- 2018
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Ingår i: Advanced Studies in Theoretical Physics. - : Hikari Ltd. - 1313-1311 .- 1314-7609. ; 12:4, s. 157-172
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Tidskriftsartikel (refereegranskat)abstract
- We consider some nonlinear effects of gravity in cosmology. Possible physically interesting consequences include: non-requirement of dark matter and dark energy, asymmetric gravitational matter-creation, emergent homogeneity/isotropy & asymptotic flatness, resolution of "cosmic coincidence" Omega_m \sim Omega_lambda, effective cutoff of gravitational interaction at the scale of cosmic voids.
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