Miracle-dz/UniFAR-FTUs huggingface dataset:
Consistent Iron Abundances Derived from Neutral and Singly Ionized Iron Lines in Ultraviolet and Optical Spectra of Six Warm Metal-poor Stars

Neutral Fe lines in metal-poor stars yield conflicting abundances depending on whether and how deviations from local thermodynamic equilibrium (LTE) are considered. We have collected new high-resolution and high signal-to-noise ultraviolet (UV) spectra of three warm dwarf stars with [Fe/H] ≈ −2.9 with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. We locate archival UV spectra for three other warm dwarfs with [Fe/H] ≈ −3.3, −2.2, and −1.6, supplemented with optical spectra for all six stars. We calculate stellar parameters using methods that are largely independent of the spectra, adopting broadband photometry, color–temperature relations, Gaia parallaxes, and assumed masses. We use the LTE line analysis code MOOG to derive Fe abundances from hundreds of Fe i and Fe ii lines with wavelengths from 2290 to 6430 Å. The [Fe/H] ratios derived separately from Fe i and Fe ii lines agree in all six stars, with [Fe ii/H]–[Fe i/H] ranging from +0.00 ± 0.07 to −0.12 ± 0.09 dex, when strong lines and Fe i lines with lower excitation potential <1.2 eV are excluded. This constrains the extent of any deviations from LTE that may occur within this parameter range. While our result confirms non-LTE calculations for some warm, metal-poor dwarfs, it may not be generalizable to more metal-poor dwarfs, where deviations from LTE are predicted to be larger. We also investigate trends of systematically lower abundances derived from Fe i lines in the Balmer continuum region (≈3100–3700 Å), and we conclude that no proposed explanation for this effect can fully account for the observations presently available.
Kinematic spin decoherence of a wave packet in a gravitational field

The spin state of a wave packet of a spin-1/2 particle in a gravitational field is a mixed state, obtained by integrating out the momentum degree of freedom. The entropy of this spin mixed state depends on the deviation of spacetime from the flatness. In terms of a succession of local inertial frames, it is shown that spin decoherence occurs even if the particle is uniformly moving or static in a gravitational field.
Limit of Temporal Resolution in Atomic Force Microscopy: Speed of Imaging with Atomically Engineered Tips While Preserving Picometer-Range Spatial Resolution

With recent advances in dynamic scanning probe microscopy techniques, it is now a routine to image the sub-molecular structure of molecules with atomically-engineered tips which are prepared via controlled modification of the tip termination and are chemically well-defined. The enhanced spatial resolution is possible as atomically-engineered tips can preserve their integrity in the repulsive interaction regime. Although the mechanism of improved spatial resolution has been investigated both experimentally and theoretically, the ultimate temporal resolution while preserving picometer scale spatial resolution still remains an open question. Here, we computationally analyze the temporal resolution of atomic force microscopy imaging with atomically-engineered tips. Our computational results reveal that non-metal terminated tips, e.g. oxygen-terminated copper, are well-suited for enhanced temporal resolution up to video rate imaging velocities while preserving picometer range spatial resolution. Contrarily, the highest-attainable spatial resolution of atomically-engineered tips with low-stiffness, e.g. CO-terminated, deteriorate with increasing imaging velocity. Our results reveal that when atomically-engineered tips terminated with molecules are in use, imaging velocities in the order of nanometers per second at most are inevitable even for atomically flat surfaces to retain atomic resolution and avoid slip-stick motion. In addition to shedding light on the temporal resolution of atomic force microscopy imaging with atomically-engineered tips, our numerical results provide an outlook to the scalability of atom-by-atom fabrication using scanning probe microscopy techniques.
The Soft X-Ray Afterglow of Gamma-Ray Bursts: A Stringent Test for the Fireball Model

I consider the recent discovery of a soft X-ray source inside the error box of the gamma-ray burst GB 960720 by the SAX, ASCA, and ROSAT satellites, in terms of the fireball model. I show that the ejecta shell, which after causing the burst is cold and dense but still relativistic, keeps plowing through the interstellar medium, heating up the just-shocked matter, which then emits X-rays. I compute the radiation emitted by this matter. I show that, up to about 2 months after the burst, in the cosmological scenario a soft X-ray (0.1-10 keV) flux of at least ≈ 10-13 erg s-1 cm-2, well within current observational capabilities, is generated, explaining the observations of the three satellites. Instead, in the Galactic Halo scenario a flux 3 orders of magnitude lower is expected. Detection of this nonthermal, declining flux in a statistically significant number of objects would simultaneously establish the fireball model and the cosmological nature of gamma-ray bursts.
The Exotic Zoo of Millisecond Pulsars in Globular Clusters: a multi-wavelength study

This work is focused on the study of millisecond pulsars in globular cluster by using multi-wavelength observations. Radio observations have been used to search for and timing the pulsars. An alternative method to search for very faint pulsars is first presented and then successfully applied to observations of stellar system Terzan 5, leading to the discovery of three new pulsars. The update of the timing solutions of 9 pulsars in M28 is then presented. The timing solutions now cover a data span of 10 years and provide spin, astrometric and orbital properties for all the systems. For the case of the eccentric binaries M28C and M28D, post-Keplerian corrections to the orbit have been measured in order to derive the masses of the binary components. The measurement of the pulsar proper motions allowed to constrain the cluster motion as a whole and its orbit around the Galaxy. Finally, the pulsar spin and orbital period derivatives have been used to measure their accelerations induced by the cluster potential field. Optical observations have been used to search for millisecond pulsar optical counterparts. Six new companion stars have been discovered. In particular, four companions turned out to be He white dwarfs. One companion turned out to be a faint and non-degenerate object, strongly affected by heating of the stellar side exposed to the pulsar flux. Finally, one companion is a main-sequence star which shows Hα emission likely due to a low-level mass transfer. Furthermore, we identified the companion star to a transient low-mass X-ray binary. This companion turned out to be a sub-giant branch star and therefore this system is likely in a very early phase of the mass accretion stage. Conclusion are drawn in the final chapter, where the evolution of millisecond pulsars is discussed and possible future developments are suggested.
The Post-pericenter Evolution of the Galactic Center Source G2

In early 2014, the fast-moving near-infrared source G2 reached its closest approach to the supermassive black hole Sgr A* in the Galactic center. We report on the evolution of the ionized gaseous component and the dusty component of G2 immediately after this event, revealed by new observations obtained in 2015 and 2016 with the SINFONI integral field spectrograph and the NACO imager at the ESO VLT. The spatially resolved dynamics of the Brγ line emission can be accounted for by the ballistic motion and tidal shearing of a test-particle cloud that has followed a highly eccentric Keplerian orbit around the black hole for the last 12 years. The non-detection of a drag force or any strong hydrodynamic interaction with the hot gas in the inner accretion zone limits the ambient density to less than a few at the distance of closest approach ( ), assuming G2 is a spherical cloud moving through a stationary and homogeneous atmosphere. The dust continuum emission is unresolved in L′-band, but stays consistent with the location of the Brγ emission. The total luminosity of the Brγ and L′ emission has remained constant to within the measurement uncertainty. The nature and origin of G2 are likely related to that of the precursor source G1, since their orbital evolution is similar, though not identical. Both objects are also likely related to a trailing tail structure, which is continuously connected to G2 over a large range in position and radial velocity.
A note on the adjoint of a perturbed operator

Let X and F be Banach spaces. By an operator from X to F we mean a linear operator with domain D(T)QX and range R(T)QY. An operator T from X to F is said to be a Fredholm operator if T is closed, the null space N(T) has finite dimension, and the range R(T) is closed and has finite codimension in F. We denote by $(X, F) the set of all Fredholm operators from X to F. If TE:$(X, F), the index of T is defined to be
Two channels for the formation of compact dwarf galaxies in clusters of galaxies

We have identified two channels for the formation of compact dwarf galaxies in the Illustris simulation by reconstructing mass and distance histories of candidates located in the vicinity of the simulation's most massive cluster galaxies. One channel is tidal stripping of Milky Way mass galaxies that form outside of clusters and eventually sink into them, spiraling in toward central massive objects. Second channel of formation is an in-situ formation (in reference to the parent cluster) of dwarf mass galaxies, with negligible evolution and limited change in stellar mass. We find 19 compact dwarf galaxies at the centers of 14 clusters, consistent with observations. 30% of them have external origin while 70% are formed in-situ.
Optical Spectroscopy of Supernova 1993J During Its First 2500 Days

We present 42 low-resolution spectra of supernova (SN) 1993J, our complete collection from the Lick and Keck observatories, from day 3 after explosion to day 2454, as well as one Keck high-dispersion spectrum from day 383. SN 1993J began as an apparent SN II, albeit an unusual one. After a few weeks, a dramatic transition took place, as prominent helium lines emerged in the spectrum. SN 1993J had metamorphosed from a SN II to a SN IIb. Nebular spectra of SN 1993J closely resemble those of SNe Ib and Ic, but with a persistent Hα line. At very late times, the Hα emission line dominated the spectrum, but with an unusual, boxlike profile. This is interpreted as an indication of circumstellar interaction.
Interacting holographic dark energy

We demonstrate that a transition from decelerated to accelerated cosmic expansion arises as a pure interaction phenomenon if pressureless dark matter is coupled to holographic dark energy whose infrared cutoff scale is set by the Hubble length. In a spatially flat universe the ratio of the energy densities of both components remains constant through this transition, while it is subject to slow variations for non-zero spatial curvature. The coincidence problem is dynamized and reformulated in terms of the interaction rate. An early matter era is recovered since for negligible interaction at high redshifts the dark energy itself behaves as matter. A simple model for this dynamics is shown to fit the SN Ia data. The constant background energy density ratio simplifies the perturbation analysis which is characterized by non-adiabatic features.
Heating Effects from Driven Transverse and Alfvén Waves in Coronal Loops

Recent numerical studies revealed that transverse motions of coronal loops can induce the Kelvin–Helmholtz instability (KHI). This process could be important in coronal heating because it leads to dissipation of energy at small spatial scale plasma interactions. Meanwhile, small-amplitude decayless oscillations in coronal loops have been discovered recently in observations of SDO/AIA. We model such oscillations in coronal loops and study wave heating effects, considering a kink and Alfvén driver separately and a mixed driver at the bottom of flux tubes. Both the transverse and Alfvén oscillations can lead to the KHI. Meanwhile, the Alfvén oscillations established in loops will experience phase mixing. Both processes will generate small spatial scale structures, which can help the dissipation of wave energy. Indeed, we observe the increase of internal energy and temperature in loop regions. The heating is more pronounced for the simulation containing the mixed kink and Alfvén driver. This means that the mixed wave modes can lead to a more efficient energy dissipation in the turbulent state of the plasma and that the KHI eddies act as an agent to dissipate energy in other wave modes. Furthermore, we also obtained forward-modeling results using the FoMo code. We obtained forward models that are very similar to the observations of decayless oscillations. Due to the limited resolution of instruments, neither Alfvén modes nor the fine structures are observable. Therefore, this numerical study shows that Alfvén modes probably can coexist with kink modes, leading to enhanced heating.
The dynamical evolution of globular clusters

The fundamental physical ideas underlying the dynamical behavior of globular star clusters are reviewed. The results of detailed numerical experiments involving large N-body stellar systems are summarized and compared with observations. Intuitive arguments and crude, analytic derivations of many of the major results are provided. The topics treated represent, in effect, a chronological history of the dynamical life of a globular cluster: from its birth in the early universe through core contraction to a compact state, to ultimate dissolution in the galactic tidal field. The approach is nonrigorous and pedagogical rather than mathematical and the paper is intended as an introduction to recent developments in stellar dynamical theory.
Effective action model of dynamically scalarizing binary neutron stars

Gravitational waves can be used to test general relativity (GR) in the highly dynamical strong-field regime. Scalar-tensor theories of gravity are natural alternatives to GR that can manifest nonperturbative phenomena in neutron stars (NSs). One such phenomenon, known as dynamical scalarization, occurs in coalescing binary NS systems. Ground-based gravitational-wave detectors may be sensitive to this effect, and thus could potentially further constrain scalar-tensor theories. This type of analysis requires waveform models of dynamically scalarizing systems; in this work we devise an analytic model of dynamical scalarization using an effective action approach. For the first time, we compute the Newtonian-order Hamiltonian describing the dynamics of a dynamically scalarizing binary in a self-consistent manner. Despite only working to leading order, the model accurately predicts the frequency at which dynamical scalarization occurs. In conjunction with Landau theory, our model allows one to definitively establish dynamical scalarization as a second-order phase transition. We also connect dynamical scalarization to the related phenomena of spontaneous scalarization and induced scalarization; these phenomena are naturally encompassed into our effective action approach.
Constraints on halo formation from cross-correlations with correlated variables

Cross-correlations between biased tracers and the dark matter field encode information about the physical variables which characterize these tracers. However, if the physical variables of interest are correlated with one another, then extracting this information is not as straightforward as one might naively have thought. We show how to exploit these correlations so as to estimate scale-independent bias factors of all orders in a model-independent way. We also show that failure to account for this will lead to incorrect conclusions about which variables matter and which do not. Morever, accounting for this allows one to use the scale dependence of bias to constrain the physics of halo formation; to date the argument has been phrased the other way around. We illustrate by showing that the scale dependence of linear and nonlinear bias, measured on nonlinear scales, can be used to provide consistent estimates of how the critical density for halo formation depends on halo mass. Our methods work even when the bias is nonlocal and stochastic, such as when, in addition to the spherically averaged density field and its derivatives, the quadrupolar shear field also matters for halo formation. In such models, the nonlocal bias factors are closely related to the more familiar local nonlinear bias factors, which are much easier to measure. Our analysis emphasizes the fact that biased tracers are biased because they do not sample fields (density, velocity, shear, etc.) at all positions in space in the same way that the dark matter does.
Dimension type characteristics for invariant sets of dynamical systems

CONTENTS Introduction Part I. Definition and basic properties of dimension and capacity characteristics § 1. Construction of dimension and capacity characteristics § 2. Properties of dimension and capacity characteristics Part II. Examples of dimension and capacity characteristics § 3. Classical dimension and capacity characteristics § 4. Topological pressure and topological entropy § 5. Metric entropy characteristics § 6. Dimension and capacity characteristics relative to a mapping Appendix A. A variational principle for non-compact sets Appendix B. Dynamical invariants of Takens Appendix C. Caratheodory-measurable sets References
Dynamic Stability of a Spinning Beam Carrying an Axial Dead Load

Abstract The linear dynamic behaviour of a uniform beam with its cross-section having at least two symmetry axes (the shear centre is coincident with the centroid), rotating with constant velocity about its longitudinal axis and carrying an axial dead load is analyzed. Internal damping is also considered by means of the viscoelastic behaviour of the beam material described by the Voigt-Kelvin model. The stability of the solution is investigated by characterizing the eigenvalues under the action of the two external control parameters (spin velocity and axial load). In this way instability and stability regions are distinguished in a map as the control parameters vary. Both (linear) divergence and flutter instabilities arise for certain ranges of compressive axial load. The inclusion of internal damping results in qualitative changes in the stability of the motion if compared with the undamped case. The particular case of a beam with J x = J y is also included.
Probing the formation history of the nuclear star cluster at the Galactic Centre with millisecond pulsars

The origin of the Nuclear Star Cluster in the centre of our Galaxy is still unknown. One possibility is that it formed after the disruption of stellar clusters that spiralled into the Galactic Centre due to dynamical friction. We trace the formation of the Nuclear Star Cluster around the central black hole, using state-of-the-art N-body simulations, and follow the dynamics of the neutron stars born in the clusters. We then estimate the number of Millisecond Pulsars (MSPs) that are released in the Nuclear Star Cluster, during its formation. The assembly and tidal dismemberment of globular clusters lead to a population of MSPs distributed over a radius of about 20 pc, with a peak near 3 pc. No clustering is found on the sub-parsec scale. We simulate the detectability of this population with future radio telescopes like the MeerKAT radio telescope and SKA1, and find that about of order ten MSPs can be observed over this large volume, with a paucity of MSPs within the central parsec. This helps discriminating this scenario from the in-situ formation model for the Nuclear Star Cluster that would predict an over abundance of MSPs closer to the black hole. We then discuss the potential contribution of our MSP population to the gamma-ray excess at the Galactic Centre.
Nova Populations

In this article we review the current status of the stellar population assignment for novae. Observations in the Milky Way and in external galaxies point out the existence of two nova populations: fast and bright novae, mainly originated from massive white dwarfs and associated with the thin disk/spiralarm stellar population, and slow and faint novae, originated from lighter white dwarfs and associated with thick-disk/bulge population.
Charm hadrons from fragmentation and B decays in e+e- annihilation at sqrt[s]=10.6 GeV

We present an analysis of charm quark fragmentation at 10.6 GeV, based on a data sample of 103 fb collected by the Belle detector at the KEKB accelerator. We consider fragmentation into the main charmed hadron ground states, namely \DZ, \DP, \Ds and \LC, as well as the excited states \DSZ and \DSP. The fragmentation functions are important to measure as they describe processes at a low energy scale, where calculations in perturbation theory lead to large uncertainties. Fragmentation functions can also be used as input distributions for Monte Carlo generators. Additionally, we determine the average number of these charmed hadrons produced per B decay at the \Ys resonance and measure the distribution of their production angle in \epem annihilation events and in B decays.
Time-dependent theory of solar meridional flows

We explore consequences for the solar dynamo of a newly-developed physical hypothesis describing a weak coupling of the orbital and rotational motions of extended bodies. The coupling is given by - c ((dL/dt) x omega sub alpha) x r, where dL/dt represents the rate of change of barycentric orbital angular momentum, omega sub alpha is the angular velocity of rotation, r is a position vector identifying a particular location in a coordinate system rotating with the Sun, and c is a coupling efficiency coefficient. This form of coupling has no dependence on tides. The coupling expression defines a non-axisymmetric global-scale acceleration field that varies both in space and with time. Meridional components of acceleration typically dominate in equatorial and middle latitudes, while zonal accelerations become increasingly significant at higher latitudes. A comparison of the waveform of the putative dynamical forcing function with the time series for measured solar meridional flow speeds from Sunspot Cycle 23 yields correlations significant at the 99.9% level. We introduce the possibility of a destructive interaction between the predicted large-scale flows (due to orbit-spin coupling) and the dynamo mechanism(s) of the 22-year magnetic activity cycle; observations in recent cycles of higher meridional flow speeds during episodes of reduced solar sunspot activity may be explained as a consequence of differences between the phasing of the magnetic cycle and the phase of the forcing function. Algorithms are provided for calculating meridional and zonal orbit-spin coupling accelerations within the Sun as a function of latitude, longitude, depth, and time.