Sher 25: pulsating but apparently alone

The blue supergiant Sher25 is surrounded by an asymmetric, hourglass-shaped circumstellar nebula, which shows similarities to the triple-ring structure seen around SN1987A. From optical spectroscopy over six consecutive nights, we detect periodic radial velocity variations in the stellar spectrum of Sher25 with a peak-to-peak amplitude of ~12 km/s on a timescale of about 6 days, confirming the tentative detec-tion of similar variations by Hendry et al. From consideration of the amplitude and timescale of the signal, coupled with observed line profile variations, we propose that the physical origin of these variations is related to pulsations in the stellar atmosphere, rejecting the previous hypothesis of a massive, short-period binary companion. The radial velocities of two other blue supergiants with similar bipolar nebulae, SBW1 and HD 168625, were also monitored over the course of six nights, but these did not display any significant radial velocity variations.Comment: 9 pages, 7 figures. Accepted for publication in MNRA

Effect of dark matter halo substructures on galaxy rotation curves

The effect of halo substructures on galaxy rotation curves is investigated in this paper using a simple model of dark matter clustering. A dark matter halo density profile is developed based only on the scale free nature of clustering that leads to a statistically self-similar distribution of the substructures at galactic scale. Semi-analytical method is used to derive rotation curves for such a clumpy dark matter density profile. It is found that the halo substructures significantly affect the galaxy velocity field. Based on the fractal geometry of the halo, this self-consistent model predicts an NFW-like rotation curve and a scale free power spectrum of the rotation velocity fluctuations.Comment: 6 pages, 3 figures. Accepted for publication in ApJ. The definitive version will be available at http://iopscience.iop.org

The role of Rayleigh-Taylor instabilities in filament threads

Many solar filaments and prominences show short-lived horizontal threads lying parallel to the photosphere. In this work the possible link between Rayleigh-Taylor instabilities and thread lifetimes is investigated. This is done by calculating the eigenmodes of a thread modelled as a Cartesian slab under the presence of gravity. An analytical dispersion relation is derived using the incompressible assumption for the magnetohydrodynamic (MHD) perturbations. The system allows a mode that is always stable, independently of the value of the Alfv\'en speed in the thread. The character of this mode varies from being localised at the upper interface of the slab when the magnetic field is weak, to having a global nature and resembling the transverse kink mode when the magnetic field is strong. On the contrary, the slab model permits another mode that is unstable and localised at the lower interface when the magnetic field is weak. The growth rates of this mode can be very short, of the order of minutes for typical thread conditions. This Rayleigh-Taylor unstable mode becomes stable when the magnetic field is increased, and in the limit of strong magnetic field it is essentially a sausage magnetic mode. The gravity force might have a strong effect on the modes of oscillation of threads, depending on the value of the Alfv\'en speed. In the case of threads in quiescent filaments, where the Alfv\'en speed is presumably low, very short lifetimes are expected according to the slab model. In active region prominences, the stabilising effect of the magnetic tension might be enough to suppress the Rayleigh-Taylor instability for a wide range of wavelengths

Depreciación de activos y su incidencia en el sistema de presupuesto anual del Ministerio del Interior Región Callao, año 2018

El presente trabajo de investigación, tiene por objetivo, determinar que la depreciación de activos incide en el sistema de Presupuesto anual del Ministerio del Interior Región Callao, año 2018. Es importante que el Ministerio del Interior pueda reconocer los importes y cálculos de las depreciaciones, sobre el valor de las adquisiciones conforme a las disposiciones legales que están en vigencia para que el presupuesto anual pueda ser llevado de manera transparente. Para desarrollar ésta investigación se recopiló diversos textos, artículos y escritos de autores que abordaron sobre las variables presentadas: Depreciación de Activos y Sistema de presupuesto. Esta investigación se desarrolló con el diseño de investigación No experimental, asimismo es de tipo Básica, presentando un enfoque cuantitativo y nivel explicativo. La muestra se calculó a partir del método de muestreo probabilístico, donde el muestreo aleatorio simple y la fórmula aplicada dieron como resultado a 36 personas que laboran en el área Gerencia, Planeamiento operativo, Secretaria, Manejo del roud, Logística, Recursos humanos, Oficina de administración, Oficina de bienestar y Staff apoyo general, que son las que conforman el grupo muestral. La técnica utilizada fue la encuesta y el instrumento fue el cuestionario aplicado a la muestra. El instrumento fue validado a través de la medición de validez de expertos y para la confiabilidad, se aplicó el coeficiente de alfa de Cronbach, dando un resultado general de 0.962, asimismo para la primera variable fue de 0.952y para la segunda variable fue de 0.931. Al finalizar, se llegó a la siguiente conclusión: el cálculo adecuado en la depreciación de activos incide razonablemente en el sistema de Presupuesto anual del Ministerio del Interior Región Callao, año 2018; de acuerdo a la prueba de chi-cuadrado de Pearson, el cual revela un valor de 118,393, ya que el valor de x2 c es mayor al xt 2 (118,393>55,758), entonces se rechaza la hipótesis nula H0 y se acepta la hipótesis alterna H1

The VLT-FLAMES Tarantula Survey XXII. Multiplicity properties of the B-type stars

We investigate the multiplicity properties of 408 B-type stars observed in the 30 Doradus region of the Large Magellanic Cloud with multi-epoch spectroscopy from the VLT-FLAMES Tarantula Survey (VFTS). We use a cross-correlation method to estimate relative radial velocities from the helium and metal absorption lines for each of our targets. Objects with significant radial-velocity variations (and with an amplitude larger than 16 km/s) are classified as spectroscopic binaries. We find an observed spectroscopic binary fraction (defined by periods of 0.1) for the B-type stars, f_B(obs) = 0.25 +/- 0.02, which appears constant across the field of view, except for the two older clusters (Hodge 301 and SL 639). These two clusters have significantly lower fractions of 0.08 +/- 0.08 and 0.10 +/- 0.09, respectively. Using synthetic populations and a model of our observed epochs and their potential biases, we constrain the intrinsic multiplicity properties of the dwarf and giant (i.e. relatively unevolved) B-type stars in 30 Dor. We obtain a present-day binary fraction f_B(true) = 0.58 +/- 0.11, with a flat period distribution. Within the uncertainties, the multiplicity properties of the B-type stars agree with those for the O stars in 30 Dor from the VFTS.Comment: Accepted by A&

Phantom thermodynamics

This paper deals with the thermodynamic properties of a phantom field in a flat Friedmann-Robertson-Walker universe. General expressions for the temperature and entropy of a general dark-energy field with equation of state $p=\omega\rho$ are derived from which we have deduced that, whereas the temperature of a cosmic phantom fluid ($\omega<-1$) is definite negative, its entropy is always positive. We interpret that result in terms of the intrinsic quantum nature of the phantom field and apply it to (i) attain a consistent explanation for some recent results concerning the evolution of black holes which,induced by accreting phantom energy, gradually loss their mass to finally vanish exactly at the big rip, and (ii) introduce the concept of cosmological information and its relation with life and the anthropic principle. Some quantum statistical-thermodynamic properties of the quantum quantum field are also considered that include a generalized Wien law and the prediction of some novel phenomena such as the stimulated absorption of phantom energy and the anti-laser effect.Comment: 19 pages, LaTex, 2 figures, accepted for publication in Nuclear Physics

The VLT-FLAMES Tarantula Survey XXIII. Two massive double-lined binaries in 30 Doradus

Aims. We investigate the characteristics of two newly discovered short-period, double-lined, massive binary systems in the Large Magellanic Cloud, VFTS 450 (O9.7 II–Ib + O7::) and VFTS 652 (B1 Ib + O9: III:). Methods. We perform model-atmosphere analyses to characterise the photospheric properties of both members of each binary (denoting the “primary” as the spectroscopically more conspicuous component). Radial velocities and optical photometry are used to estimate the binary-system parameters. Results. We estimate Teff = 27 kK, log g = 2.9 (cgs) for the VFTS 450 primary spectrum (34 kK, 3.6: for the secondary spectrum); and Teff = 22 kK, log g = 2.8 for the VFTS 652 primary spectrum (35 kK, 3.7: for the secondary spectrum). Both primaries show surface nitrogen enrichments (of more than 1 dex for VFTS 652), and probable moderate oxygen depletions relative to reference LMC abundances. We determine orbital periods of 6.89 d and 8.59 d for VFTS 450 and VFTS 652, respectively, and argue that the primaries must be close to filling their Roche lobes. Supposing this to be the case, we estimate component masses in the range ∼20–50 M⊙. Conclusions. The secondary spectra are associated with the more massive components, suggesting that both systems are high-mass analogues of classical Algol systems, undergoing case-A mass transfer. Difficulties in reconciling the spectroscopic analyses with the light-curves and with evolutionary considerations suggest that the secondary spectra are contaminated by (or arise in) accretion disks

Photoionized gas in hydrostatic equilibrium: the role of gravity

We present a method to include the effects of gravity in the plasma physics code Cloudy. More precisely, a term is added to the desired gas pressure in order to enforce hydrostatic equilibrium, accounting for both the self-gravity of the gas and the presence of an optional external potential. As a test case, a plane-parallel model of the vertical structure of the Milky Way disk near the solar neighbourhood is considered. It is shown that the gravitational force determines the scale height of the disk, and it plays a critical role in setting its overall chemical composition. However, other variables, such as the shape of incident continuum and the intensity of the Galactic magnetic field, strongly affect the predicted structure.Comment: 9 pages, 8 figures, MNRAS in pres

A new search strategy for microquasar candidates using NVSS/2MASS and XMM-Newton data

Microquasars are ideal natural laboratories for understanding accretion/ejection processes, studying the physics of relativistic jets, and testing gravitational phenomena. Nevertheless, these objects are difficult to find in our Galaxy. The main goal of this work is to increase the number of known systems of this kind. We have developed an improved search strategy based on positional cross-identification with very restrictive selection criteria to find new MQs, taking advantage of more sensitive modern radio and X-ray data. We find 86 sources with positional coincidence in the NVSS/XMM catalogs at |b|<10 deg. Among them, 24 are well-known objects and the remaining 62 sources are unidentified. For the fully coincident sources, whenever possible, we analyzed color-color and hardness ratio diagrams and found that at least 3 of them display high-mass X-ray binary characteristics, making them potential microquasar candidates.Comment: 9 pages, 3 figures, accepted for publication in A&

Tres fases del crecimiento económico argentino

Nuevos enfoques en la historia económica de España y de América Latina. Homenaje a Robert W. Fogel y Douglas C. North, Premios Nobel de Economía 1993Editada en la Universidad Carlos IIIEl empeoramiento de los resultados económicos relativos de Argentina puede atribuirse, en gran parte, a las desfavorables condiciones existentes para la acumulación de capital a partir de 1913. En la primera fase (antes de 1913) el éxito de la Belle Époque se debió a las espectaculares tasas de acumulación. En la segunda fase (1913-década de 1930) la baja tasa nacional de ahorro limitó la tasa de acumulación de capital. En la tercera fase (década de 1930-década de 1950) se adoptó una política de sustitución de las importaciones y el precio relativo de los bienes de capital importados que eran clave experimentó una brusca subida. Ahí comenzó el retraso: al principio, debido a que el ahorro era insuficiente ahorro y, más tarde, a que los altos precios de los bienes de capital importados redujeron los incentivos para realizar actividades de inversión que son las precursoras del crecimiento.Much of Argentina's decline in relative economic performance can be attributed to deleterious conditions for capital accumulation after 1913. In the first phase (pre-1913), the success of the Belle Époque was due to spectacular rates of accumulation. In the second phase (1913-1930s), low domestic savings rates constrained the rate of capital accumulation. In the third phase (1930s-1950s) import-substitution policies were implemented and the relative price of key imported capital goods rose sharply. Retardation ensued: at first because of insufficient saving; later because price disincentives channelled funds away from investment activities which are the precursor of growth.Publicad