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- Thorn, D. B., et al.
(författare)
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Polarization and anisotropic emission of K-shell radiation from heavy few electron ions
- 2011
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Ingår i: Canadian journal of physics (Print). - 0008-4204 .- 1208-6045. ; 89:5, s. 513-519
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Tidskriftsartikel (refereegranskat)abstract
- The population of magnetic sublevels in hydrogen-like uranium ions has been investigated in relativistic ion-atom collisions by observing the subsequent X-ray emission. Using the gas target at the experimental storage ring facility we observed the angular emission of Lyman-alpha radiation from hydrogen-like uranium ions. The alignment parameter for three different interaction energies was measured and found to agree well with theory. In addition, the use of different gas targets allowed for the electron-impact excitation process to be observed.
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- Reggiani, M, et al.
(författare)
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Discovery of a point-like source and a third spiral arm in the transition disk around the Herbig Ae star MWC 758
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 611
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Tidskriftsartikel (refereegranskat)abstract
- Context. Transition disks offer the extraordinary opportunity to look for newly born planets and to investigate the early stages of planet formation. Aims. In this context we observed the Herbig A5 star MWC 758 with the L'-band vector vortex coronagraph installed in the near-infrared camera and spectrograph NIRC2 at the Keck II telescope, with the aim of unveiling the nature of the spiral structure by constraining the presence of planetary companions in the system. Methods. Our high-contrast imaging observations show a bright (Delta L' = 7.0 +/- 0.3 mag) point-like emission south of MWC 758 at a deprojected separation of similar to 20 au (r = 0 ''.111 +/- 0 ''.004) from the central star. We also recover the two spiral arms (southeast and northwest), already imaged by previous studies in polarized light, and discover a third arm to the southwest of the star. No additional companions were detected in the system down to 5 Jupiter masses beyond 0 ''.6 from the star. Results. We propose that the bright L'-band emission could be caused by the presence of an embedded and accreting protoplanet, although the possibility of it being an asymmetric disk feature cannot be excluded. The spiral structure is probably not related to the protoplanet candidate, unless on an inclined and eccentric orbit, and it could be due to one (or more) yet undetected planetary companions at the edge of or outside the spiral pattern. Future observations and additional simulations will be needed to shed light on the true nature of the point-like source and its link with the spiral arms.
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- Orban, Istvan, 1980-, et al.
(författare)
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Excitation and recombination studies with silicon and sulphur ions at an EBIT
- 2024
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Ingår i: Journal of Physics B. - 0953-4075 .- 1361-6455. ; 57:9
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of electron-impact excitation and recombination rate coefficients of highly charged Si and S ions at the Stockholm electron beam ion trap are reported. The experimental method was a combination of photon detection from the trapped ions during probing and subsequently extraction and time-of-flight (TOF) charge analysis of these ions. The TOF technique allows to measure recombination rate coefficients separately for every charge state, and together with the photon spectra of these ions also the excitation rate coefficients. In this paper, we present more details of the experimental procedure and summarize the experimental results in comparison with two different state-of-the-art calculations of recombination and excitation rates for Si10+–Si13+ and S12+–S15+ ions. One of these uses a relativistic configuration interaction approach (flexible atomic code) and the other is a relativistic many-body perturbation theory. A good to excellent agreement with both of them is found in energy and resonance strength for the investigated ions.
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- Wang, Jason J., et al.
(författare)
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Keck/NIRC2 L'-Band Imaging of Jovian-Mass Accreting Protoplanets around PDS 70
- 2020
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Ingår i: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 159:6
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Tidskriftsartikel (refereegranskat)abstract
- We present L'-band imaging of the PDS 70 planetary system with Keck/NIRC2 using the new infrared pyramid wave front sensor. We detected both PDS 70 b and c in our images, as well as the front rim of the circumstellar disk. After subtracting off a model of the disk, we measured the astrometry and photometry of both planets. Placing priors based on the dynamics of the system, we estimated PDS 70 b to have a semimajor axis of au and PDS 70 c to have a semimajor axis of au (95% credible interval). We fit the spectral energy distribution (SED) of both planets. For PDS 70 b, we were able to place better constraints on the red half of its SED than previous studies and inferred the radius of the photosphere to be 2–3 R Jup. The SED of PDS 70 c is less well constrained, with a range of total luminosities spanning an order of magnitude. With our inferred radii and luminosities, we used evolutionary models of accreting protoplanets to derive a mass of PDS 70 b between 2 and 4 M Jup and a mean mass accretion rate between 3 × 10−7 and 8 × 10−7 M Jup/yr. For PDS 70 c, we computed a mass between 1 and 3 M Jup and mean mass accretion rate between 1 × 10−7 and 5 × 10−7 M Jup/yr. The mass accretion rates imply dust accretion timescales short enough to hide strong molecular absorption features in both planets' SEDs.
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