52 research outputs found
X-ray resonant photoexcitation: line widths and energies of K{\alpha} transitions in highly charged Fe ions
Photoabsorption by and fluorescence of the K{\alpha} transitions in highly
charged iron ions are essential mechanisms for X-ray radiation transfer in
astrophysical environments. We study photoabsorption due to the main K{\alpha}
transitions in highly charged iron ions from heliumlike to fluorinelike (Fe
24+...17+) using monochromatic X-rays around 6.6 keV at the PETRA III
synchrotron photon source. Natural linewidths were determined with hitherto
unattained accuracy. The observed transitions are of particular interest for
the understanding of photoexcited plasmas found in X-ray binaries and active
galactic nuclei.Comment: Revised versio
Mass Measurements of Neutron-Rich Gallium Isotopes Refine Production of Nuclei of the First r-Process Abundance Peak in Neutron Star Merger Calculations
We report mass measurements of neutron-rich Ga isotopes Ga with
TRIUMF's Ion Trap for Atomic and Nuclear science (TITAN). The measurements
determine the masses of Ga in good agreement with previous
measurements. The masses of Ga and Ga were measured for the first
time. Uncertainties between keV were reached. The new mass values
reduce the nuclear uncertainties associated with the production of A
84 isotopes by the \emph{r}-process for astrophysical conditions that might be
consistent with a binary neutron star (BNS) merger producing a blue kilonova.
Our nucleosynthesis simulations confirm that BNS merger may contribute to the
first abundance peak under moderate neutron-rich conditions with electron
fractions
Dawning of the N=32 shell closure seen through precision mass measurements of neutron-rich titanium isotopes
A precision mass investigation of the neutron-rich titanium isotopes
Ti was performed at TRIUMF's Ion Trap for Atomic and Nuclear science
(TITAN). The range of the measurements covers the shell closure and the
overall uncertainties of the Ti mass values were significantly
reduced. Our results confirm the existence of a weak shell effect at ,
establishing the abrupt onset of this shell closure. Our data were compared
with state-of-the-art \textit{ab-initio} shell model calculations which,
despite very successfully describing where the shell gap is strong,
overpredict its strength and extent in titanium and heavier isotones. These
measurements also represent the first scientific results of TITAN using the
newly commissioned Multiple-Reflection Time-of-Flight Mass Spectrometer
(MR-TOF-MS), substantiated by independent measurements from TITAN's Penning
trap mass spectrometer
Recommendations for Addressing Priority Io Science in the Next Decade
Io is a priority destination for solar system exploration. The scope and importance of science questions at Io necessitates a broad portfolio of research and analysis, telescopic observations, and planetary missions - including a dedicated New Frontiers class Io mission
The Science Case for Io Exploration
Io is a priority destination for solar system exploration, as it is the best natural laboratory to study the intertwined processes of tidal heating, extreme volcanism, and atmosphere-magnetosphere interactions. Io exploration is relevant to understanding terrestrial worlds (including the early Earth), ocean worlds, and exoplanets across the cosmos
Ueber Nervenatrophie in der ersten Schneckenwindung: Physiologische und psthologische Bedeutung derselben
Dissipation in the deep interiors of Ganymede and Europa
Jupiter's satellites are subject to strong tidal forces which result in variations of the gravitational potential and deformations of the satellites' surfaces on the diurnal tidal cycle. Tidal flexing in the deep interiors can be a significant heat source for the satellites' thermal-orbital evolution. Whereas typical structure models of Europa consist of a core, a silicate mantle, an ocean and an outer ice-I shell [1], pressures inside Ganymede are sufficient for high-pressure ice phases to occur between the silicate mantle and the ocean [2]. With current data it is unknown whether the deep interiors (i.e., Europa's silicate shell and Ganymede's silicate mantle and/or high-pressure ice layer) are dissipative. Other possibilities would be that the dissipation rates are in general very low (unlikely at least for Europa due to recent observations) or that dissipative processes are mainly occurring in the ice-I shell and/or ocean. Thus, for evaluations of the heating state of these satellites, it is important to measure the magnitude of the interior dissipation. However, observation of the interior layers such as high-pressure ice layers is more challenging than that of the surface ice-I layer. Here we suggest a method to constrain the dissipation states of the deep interiors of Ganymede and Europa by altimetry and gravity measurements from an orbiting or multi-flyby spacecraft. Tidal variations are generally described by the Love numbers k2 and h2 for the tide-induced potential variation due to internal mass redistribution and the radial surface displacement, respectively. The phase-lags of these complex numbers contain information about the rheological and dissipative states of the satellites. For the satellites we assume a decoupling of the outer ice-shell from the deep interior by a liquid subsurface water ocean. We show that, in this case, the phase-lag difference between the lags of k2 and h2 can provide information on the rheological and thermal state of the deep interiors if the viscosities of the deeper layers are small (the phase-lag difference is almost independent of the dissipation in the surface layer). In case of Ganymede, phase-lag differences can reach values of a few degrees for high-pressure ice viscosities of 1e13-1e14 Pa s (around the lower boundary at its melting temperature) and would indicate a highly dissipative state of the deep interior. In this case, in contrast to the phase lags itself, the phase-lag difference is dominated by dissipation in the high-pressure ice layer rather than dissipation within the ice-I shell. These phase lags would be detectable from spacecraft in orbit around the satellite [3]. For Europa the phase-lag difference could reach values exceeding 20 deg if the silicate mantle contains melt and phase-lag measurements could help distinguish between (1) a hot dissipative (melt-containing) silicate mantle which would in thermal equilibrium correspond to a very thin outer ice-I shell and (2) a cold deep interior implying that dissipation would mainly occur in a thick (several tens of km) outer ice-I shell. These measurements are highly relevant for ESA's Jupiter Icy Moons Explorer (JUICE) and NASA's Europa Multiple Flyby Mission, both targeted for the Jupiter system. References: [1] Schubert, G., F. Sohl and H. Hussmann 2009. Interior of Europa. In: Europa, (R.T. Pappalardo, W.B. McKinnon, K. Khurana, Eds.), University of Arizona Press, pp. 353 - 368. [2] Schubert G., J. D. Anderson, T. Spohn, and W. B. McKinnon 2004. Interior composition, structure, and dynamics of the Galilean satellites. In: F. Bagenal, T. E. Dowling, and W. B. McKinnon (eds.) Jupiter. The Planet, Satellites, and Magnetosphere, pp. 281-306. Cambridge University Press. [3] Hussmann, H., D. Shoji, G. Steinbrügge, A. Stark, F. Sohl 2016. Constraints on dissipation in the deep interiors of Ganymede and Europa from tidal phase-lags. Cel. Mech. Dyn. Astr. 126, 131 - 144
Measurement Methods for Ganymede's Librations from Laser Altimetry Observations
We investigate the potential for the Ganymede Laser Altimeter (GALA) on board the JUICE (JUpiter ICy moons Explorer) mission to measure the tidal deformations and the rotational state of Ganymede, in particular physical librations. A subsurface ocean would cause the upper ice shell to librate decoupled from its interior. Two distinct iterative least-squares inversion routines have been implemented to estimate simultaneously for the topography, the orientation of the rotation pole, the mean rotation and the libration amplitudes and tidal deformations using synthetic laser altimetry data. We follow the approach of a global expansion of spherical harmonics and as a second method the parametrization in 2D B-splines. Results indicatet hat a global ocean could only be found for a very thin ice shell thickness, if the ice shell is elastic and fully decoupled of the interior. However, to prove the non-existence of an ocean is difficult due to small libration amplitudes and their possibly ambiguous interpretation. In this case independent observations, such as the Love numbers, provide more unique constraints on the interior structure
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