High-resolution imaging spectroscopy of two micro-pores and an arch filament system in a small emerging-flux region

Aims. The purpose of this investigation is to characterize the temporal evolution of an emerging flux region, the associated photospheric and chromospheric flow fields, and the properties of the accompanying arch filament system. Methods. This study is based on imaging spectroscopy with the G\"ottingen Fabry-P\'erot Interferometer at the Vacuum Tower Telescope, on 2008 August 7. Cloud model (CM) inversions of line scans in the strong chromospheric absorption H$\alpha$ line yielded CM parameters, which describe the cool plasma contained in the arch filament system. Results. The observations cover the decay and convergence of two micro-pores with diameters of less than one arcsecond and provide decay rates for intensity and area. The photospheric horizontal flow speed is suppressed near the two micro-pores indicating that the magnetic field is sufficiently strong to affect the convective energy transport. The micro-pores are accompanied by an arch filament system, where small-scale loops connect two regions with H$\alpha$ line-core brightenings containing an emerging flux region with opposite polarities. The chromospheric velocity of the cloud material is predominantly directed downwards near the footpoints of the loops with velocities of up to 12 km/s, whereas loop tops show upward motions of about 3 km/s. Conclusions. Micro-pores are the smallest magnetic field concentrations leaving a photometric signature in the photosphere. In the observed case, they are accompanied by a miniature arch filament system indicative of newly emerging flux in the form of $\Omega$-loops. Flux emergence and decay take place on a time-scale of about two days, whereas the photometric decay of the micro-pores is much more rapid (a few hours), which is consistent with the incipient submergence of $\Omega$-loops. The results are representative for the smallest emerging flux regions still recognizable as such.Comment: 15 pages, 16 figures, 3 tables, published in A&

Viscoelastic model for the dynamic structure of binary systems

This paper presents the viscoelastic model for the Ashcroft-Langreth dynamic structure factors of liquid binary mixtures. We also provide expressions for the Bhatia-Thornton dynamic structure factors and, within these expressions, show how the model reproduces both the dynamic and the self-dynamic structure factors corresponding to a one-component system in the appropriate limits (pseudobinary system or zero concentration of one component). In particular we analyze the behavior of the concentration-concentration dynamic structure factor and longitudinal current, and their corresponding counterparts in the one-component limit, namely, the self dynamic structure factor and self longitudinal current. The results for several lithium alloys with different ordering tendencies are compared with computer simulations data, leading to a good qualitative agreement, and showing the natural appearance in the model of the fast sound phenomenon.Comment: 20 pages, 19 figures, submitted to PR

Integral field observations of the blue compact galaxy Haro14. Star formation and feedback in dwarf galaxies

(Abridged) Low-luminosity, gas-rich blue compact galaxies (BCG) are ideal laboratories to investigate many aspects of the star formation in galaxies. We study the morphology, stellar content, kinematics, and the nebular excitation and ionization mechanism in the BCG Haro 14 by means of integral field observations with VIMOS in the VLT. From these data we build maps in continuum and in the brighter emission lines, produce line-ratio maps, and obtain the velocity and velocity dispersion fields. We also generate the integrated spectrum of the major HII regions and young stellar clusters identified in the maps to determine reliable physical parameters and oxygen abundances. We find as follows: i) the current star formation in Haro 14 is spatially extended with the major HII regions placed along a linear structure, elongated in the north-south direction, and in a horseshoe-like curvilinear feature that extends about 760 pc eastward; the continuum emission is more concentrated and peaks close to the galaxy center; ii) two different episodes of star formation are present: the recent starburst, with ages $\leq$ 6 Myrs and the intermediate-age clusters, with ages between 10 and 30 Myrs; these stellar components rest on a several Gyr old underlying host galaxy; iii) the H$\alpha$/H$\beta$ pattern is inhomogeneous, with excess color values varying from E(B-V)=0.04 up to E(B-V)=1.09; iv) shocks play a significant role in the galaxy; and v) the velocity field displays a complicated pattern with regions of material moving toward us in the east and north galaxy areas. The morphology of Haro 14, its irregular velocity field, and the presence of shocks speak in favor of a scenario of triggered star formation. Ages of the knots are consistent with the ongoing burst being triggered by the collective action of stellar winds and supernovae originated in the central clusters.Comment: 18 pages, 17 figures. Accepted for publication in A&

Pion production within the hybrid relativistic plane wave impulse approximation model at MiniBooNE and MINERvA kinematics

The hybrid model for electroweak single-pion production (SPP) off the nucleon, presented in [Gonz\'alez-Jim\'enez et al., Phys. Rev. D 95, 113007 (2017)], is extended here to the case of incoherent pion-production on the nucleus. Combining a low-energy model with a Regge approach, this model provides valid predictions in the entire energy region of interest for current and future accelerator-based neutrino-oscillation experiments. The Relativistic Mean-Field model is used for the description of the bound nucleons while the outgoing hadrons are considered as plane waves. This approach, known as Relativistic Plane-Wave Impulse Approximation (RPWIA), is a first step towards the development of more sophisticated models, it is also a test of our current understanding of the elementary reaction. We focus on the charged-current $\nu$($\bar\nu$)-nucleus interaction at MiniBooNE and MINERvA kinematics. The effect on the cross sections of the final-state interactions, which affect the outgoing hadrons on their way out of the nucleus, is judged by comparing our results with those from the NuWro Monte Carlo event generator. We find that the hybrid-RPWIA predictions largely underestimate the MiniBooNE data. In the case of MINERvA, our results fall below the $\nu$-induced 1$\pi^0$ production data, while a better agreement is found for $\nu$-induced 1$\pi^+$ and $\bar\nu$-induced 1$\pi^0$ production.Comment: 13 pages, 10 figure

Probing star formation and feedback in dwarf galaxies. Integral field view of the blue compact galaxy Tololo 1937-423

(Abridged) Blue compact galaxies (BCG) are gas-rich, low-mass, small systems that form stars at unusually high rates. This makes them excellent laboratories for investigating the process of star-formation (SF) at galactic scales and the effects of massive stellar feedback on the interstellar (and intergalactic) medium. We analyzed the BCG Tololo 1937-423 using optical integral field spectroscopy with VIMOS at the Very Large Telescope to probe its morphology, stellar content, nebular excitation and ionization properties, and the kinematics of its warm ionized gas. We found that Tololo 1937-423 is currently undergoing an extended starburst, with nine major $H\alpha$ clumps. The galaxy presents a single continuum peak that is not cospatial with any knot in emission lines, indicating at least two relatively recent episodes of SF. The inhomogeneous dust distribution reaches its maximum roughly at the position of the continuum peak. We found shocked regions in the galaxy outer regions and at the edges of the SF knots. The oxygen abundance is similar in all the SF regions, suggesting a chemically homogeneous ionized interstellar medium over spatial scales of several kpc. The ionized gas kinematics displays an overall regular rotation around a northwest-southeast axis. The morphology of the galaxy and the two different episodes of SF suggest a scenario of triggered (induced by supernova shock waves) SF acting in Tololo 1937-423. The inferred ages for the different SF episodes (~13-80 Myr for the central post-starburst and 5-7 Myr for the ongoing SF) are consistent with triggered SF, with the most recent SF episode caused by the collective effect of stellar winds and supernova explosions from the central post-starburst. The velocity dispersion pattern, with higher velocity dispersions found at the edges of the SF regions, and shocked regions in the galaxy, also favor this scenario.Comment: 16 pages, 18 figures. Accepted for publication in A&