Abstract
Globular clusters (GCs) are natural laboratories where stellar and chemical evolution can be studied in detail. In addition, their chemical patterns and kinematics can tell us to which ...Galactic structure (disc, bulge, halo or extragalactic) the cluster belongs to. NGC 5927 is one of most metal-rich GCs in the Galaxy and its kinematics links it to the thick disc. We present abundance analysis based on high-resolution spectra of seven giant stars. The data were obtained using Fibre Large Array Multi Element Spectrograph/Ultraviolet Echelle Spectrograph (UVES) spectrograph mounted on ut2 telescope of the European Southern Observatory. The principal objective of this work is to perform a wide and detailed chemical abundance analysis of the cluster and look for possible Multiple Populations (MPs). We determined stellar parameters and measured 22 elements corresponding to light (Na, Al), alpha (O, Mg, Si, Ca, Ti), iron-peak (Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn), and heavy elements (Y, Zr, Ba, Ce, Nd, Eu). We found a mean iron content of Fe/H = −0.47 ± 0.02 (error on the mean). We confirm the existence of MPs in this GC with an O–Na anti-correlation, and moderate spread in Al abundances. We estimate a mean α/Fe = 0.25 ± 0.08. Iron-peak elements show no significant spread. The Ba/Eu ratios indicate a predominant contribution from SNeII for the formation of the cluster.
Due to the short residence time of air in supersonic combustors, achieving efficient mixing in compressible turbulent reactive flows is crucial for the design of supersonic ramjet (Scramjet) engines. ...In this respect, improving the understanding of shock-scalar mixing interactions is of fundamental importance for such supersonic combustion applications. In these compressible flows, the interaction between the turbulence and the shock wave is reciprocal, and the coupling between them is very strong. A basic understanding of the physics of such complex interactions has already been obtained through the analysis of relevant simplified flow configurations, including propagation of the shock wave in density-stratified media, shock-wave–mixing-layer interaction, and shock-wave–vortex interaction. Amplification of velocity fluctuations and substantial changes in turbulence characteristic length scales are the most well-known outcomes of shock–turbulence interaction, which may also deeply influence scalar mixing between fuel and oxidizer. The effects of the shock wave on the turbulence have been widely characterized through the use of so-called amplification factors, and similar quantities are introduced herein to characterize the influence of the shock wave on scalar mixing. One of the primary goals of the present study is indeed to extend previous analyses to the case of shock-scalar mixing interaction, which is directly relevant to supersonic combustion applications. It is expected that the shock wave will affect the scalar dissipation rate (SDR) dynamics. Special emphasis is placed on the modification of the so-called turbulence–scalar interaction as a leading-order contribution to the production of mean SDR, i.e., a quantity that defines the mixing rate and efficiency. To the best of the authors’ knowledge, this issue has never been addressed in detail in the literature, and the objective of the present study is to scrutinize this influence. The turbulent mixing of a passive (i.e., chemically inert) scalar in the presence of a shock wave is thus investigated using high-resolution numerical simulations. The starting point of the analysis relies on the transport equations of the variance of the mixture fraction, i.e., a fuel inlet tracer that quantifies the mixing between fuel and oxidizer. The influence of the shock wave is investigated for three distinct values of the shock Mach number
M
, and the obtained results are compared to reference solutions featuring no shock wave. The computed solutions show that the shock wave significantly modifies the scalar field topology. The larger the value of
M
, the stronger is the amplification of the alignment of the scalar gradient with the most compressive principal direction of the strain-rate tensor, which signifies the enhancement of scalar mixing with the shock Mach number.
To significantly improve the frequency references used in radio-astronomy and the precision measurements in atomic physics, we provide frequency dissemination through a 642-km coherent optical fiber ...link. On the frequency transfer, we obtained a frequency instability of
3
×
10
-
19
at 1,000 s in terms of Allan deviation on a 5-mHz measurement bandwidth, and an accuracy of
5
×
10
-
19
. The ultimate link performance has been evaluated by doubling the link to 1,284 km, demonstrating a new characterization technique based on the double round trip on a single fiber. This method is an alternative to previously demonstrated techniques for link characterization. In particular, the use of a single fiber may be beneficial to long hauls realizations in view of a continental fiber network for frequency and time metrology, as it avoids the doubling of the amplifiers, with a subsequent reduction in costs and maintenance. A detailed analysis of the results is presented, regarding the phase noise, the cycle-slips detection and removal and the instability evaluation. The observed noise power spectrum is seldom found in the literature; hence, the expression of the Allan deviation is theoretically derived and the results confirm the expectations.
The Juno spacecraft acquired direct observations of the jovian magnetosphere and auroral emissions from a vantage point above the poles. Juno’s capture orbit spanned the jovian magnetosphere from bow ...shock to the planet, providing magnetic field, charged particle, and wave phenomena context for Juno’s passage over the poles and traverse of Jupiter’s hazardous inner radiation belts. Juno’s energetic particle and plasma detectors measured electrons precipitating in the polar regions, exciting intense aurorae, observed simultaneously by the ultraviolet and infrared imaging spectrographs. Juno transited beneath the most intense parts of the radiation belts, passed about 4000 kilometers above the cloud tops at closest approach, well inside the jovian rings, and recorded the electrical signatures of high-velocity impacts with small particles as it traversed the equator.
On 27 August 2016, the Juno spacecraft acquired science observations of Jupiter, passing less than 5000 kilometers above the equatorial cloud tops. Images of Jupiter's poles show a chaotic scene, ...unlike Saturn's poles. Microwave sounding reveals weather features at pressures deeper than 100 bars, dominated by an ammonia-rich, narrow low-latitude plume resembling a deeper, wider version of Earth's Hadley cell. Near-infrared mapping reveals the relative humidity within prominent downwelling regions. Juno's measured gravity field differs substantially from the last available estimate and is one order of magnitude more precise. This has implications for the distribution of heavy elements in the interior, including the existence and mass of Jupiter's core. The observed magnetic field exhibits smaller spatial variations than expected, indicative of a rich harmonic content.
We characterize the precipitating electrons accelerated in the Europa‐magnetosphere interaction by analyzing in situ measurements and remote sensing observations recorded during 10 crossings of the ...flux tubes connected to Europa's auroral footprint tail by Juno. The electron downward energy flux, ranging from 34 to 0.8 mW/m2, exhibits an exponential decay as a function of downtail distance, with an e‐folding factor of 7.4°. Electrons are accelerated at energies between 0.3 and 25 keV, with a characteristic energy that decreases downtail. The electron distributions form non‐monotonic spectra in the near tail (i.e., within an angular separation of less than 4°) that become broadband in the far tail. The size of the interaction region at the equator is estimated to be 4.2 ± 0.9 Europa radii, consistent with previous estimates based on theory and UV observations.
Plain Language Summary
The space environment close to Jupiter is dominated by the magnetic field of the giant planet in a so‐called magnetosphere. The four Galilean moons, including Europa, orbit deep inside the Jovian magnetosphere and therefore constantly interact with the rapidly rotating plasma flow made of charged particles trapped by the magnetic field of the giant planet. The interaction between moons and plasma generates electromagnetic waves, accelerate particles and produce emissions at various wavelengths, including bright UV auroral spots and tails in the atmosphere of Jupiter. In this work, we present 10 events where the Juno spacecraft observed both in situ and remotely the acceleration of electrons due to the interaction between the icy moon Europa and the magnetospheric environment. We characterize the properties of the accelerated electrons. In particular, we find that acceleration is maximum near the moon itself, and that two distinct families of electron distributions exist.
Key Points
Juno unambiguously observed 10 events of downward electron acceleration from Europa at various downtail separations with the moon
Precipitating energy fluxes decrease exponentially as a function of downtail distance from the moon, with an e‐folding of 7.4°
Two types of electron distributions exist: non‐monotonic in the near tail and broadband in the far tail
A spherical harmonic model of the magnetic field of Jupiter is obtained from vector magnetic field observations acquired by the Juno spacecraft during 32 of its first 33 polar orbits. These Prime ...Mission orbits sample Jupiter's magnetic field nearly uniformly in longitude (∼11° separation) as measured at equator crossing. The planetary magnetic field is represented with a degree 30 spherical harmonic and the external field is approximated near the origin with a simple external spherical harmonic of degree 1. Partial solution of the underdetermined inverse problem using generalized inverse techniques yields a model (“JRM33”) of the planetary magnetic field with spherical harmonic coefficients reasonably well determined through degree and order 13. Useful information regarding the field extends through degree 18, well fit by a Lowes' spectrum with a dynamo core radius of 0.81 Rj, presumably the outer radius of the convective metallic hydrogen region. This new model provides a most detailed view of a planetary dynamo and evidence of advection of the magnetic field by deep zonal winds in the vicinity of the Great Blue Spot (GBS), an isolated and intense patch of flux near Jupiter's equator. Comparison of the JRM33 and JRM09 models suggests secular variation of the field in the vicinity of the GBS during Juno's nearly 5 years of operation in orbit about Jupiter. The observed secular variation is consistent with the penetration of zonal winds to a depth of ∼3,500 km where a flow velocity of ∼0.04 ms−1 is required to match the observations.
Plain Language Summary
Characterizing the planetary magnetic field of Jupiter is one of the primary science objectives of the Juno Mission. Is the magnetic field generated within the outer envelope consisting mostly of molecular hydrogen, or is it generated at depth where hydrogen becomes metallic under great pressure? The Juno spacecraft, in polar orbit about Jupiter since July 2016, just completed its baseline mapping mission of 33 orbits, providing global coverage of Jupiter's magnetic field near the planet. A detailed representation of the field has emerged, suggesting that Jupiter's magnetic field is generated by dynamo action at depth (beneath 0.81 Rj) in convective metallic hydrogen. A change in Jupiter's magnetic field over time (“secular variation”) was identified by comparison of the model field with that of an earlier model. The secular variation appeared on the flanks of an isolated magnetic patch (the “Great Blue Spot” (GBS)) and can be explained by the eastward motion of the field of the GBS, carried by zonal winds at a depth (∼3,500 km) where molecular hydrogen is sufficiently electrically conductive to grip the magnetic field.
Key Points
The Juno spacecraft sampled Jupiter's vector magnetic field along 32 polar passes separated by ∼11° longitude at the equator
A degree 18 spherical harmonic model of Jupiter's magnetic field is obtained by partial solution of a degree 30 linear system
The new model is consistent with dynamo action in metallic hydrogen, advection of the field by deep zonal winds, and secular variation
We report the analysis of short‐term ground‐based observations of the exospheric Na emission (D1 and D2 lines) from Mercury, which was characterized by two high‐latitude peaks confined near the ...magnetospheric cusp footprints. During a series of scheduled observations from the Télescope Héliographique pour l'Etude du Magnétisme et des Instabilités Solaires (THEMIS) telescope, achieved by scanning the whole planet, we implemented a series of extra measurements by recording the Na emission from a narrow north‐south strip only, centered above the two emission peaks. Our aim was to inspect the existence of short‐term variations, which were never analyzed before from ground‐based observations, and their possible correlation with interplanetary magnetic field variations. Though Mercury possesses a miniature magnetosphere, characterized by fast reconnection events that develop on a timescale of few minutes, ground‐based observations show that the exospheric Na emission pattern can be globally stable for a prolonged period (some days) and also exhibits fluctuations in the time range of tens of minutes.
Key Points
Short‐term variations of the double‐peak pattern are inspected for the first time by means of ad hoc fixed‐slit acquisitions
A first evidence of short‐term hemispheric variations is reported
No clear correlation between Na emission and in situ IMF data was found
Sodium and, in a lesser way, potassium atomic components of surface-bounded exospheres are among the brightest elements that can be observed from the Earth in our Solar System. Both species have been ...intensively observed around Mercury, the Moon and the Galilean Moons. During the last decade, new observations have been obtained thanks to space missions carrying remote and in situ instrumentation that provide a completely original view of these species in the exospheres of Mercury and the Moon. They challenged our understanding and modelling of these exospheres and opened new directions of research by suggesting the need to better take into account the relationship between the surface-exosphere and the magnetosphere. In this paper, we first review the large set of observations of Mercury and the Moon Sodium and Potassium exospheres. In the second part, we list what it tells us on the sources and sinks of these exospheres focusing in particular on the role of their magnetospheres of these objects and then discuss, in a third section, how these observations help us to understand and identify the key drivers of these exospheres.
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