Guided flows in coronal magnetic flux tubes

There is evidence for coronal plasma flows to break down into fragments and to be laminar. We investigate this effect by modeling flows confined along magnetic channels. We consider a full MHD model of a solar atmosphere box with a dipole magnetic field. We compare the propagation of a cylindrical flow perfectly aligned to the field to that of another one with a slight misalignment. We assume a flow speed of 200 km/s, and an ambient magnetic field of 30 G. We find that while the aligned flow maintains its cylindrical symmetry while it travels along the magnetic tube, the misaligned one is rapidly squashed on one side, becoming laminar and eventually fragmented because of the interaction and backreaction of the magnetic field. This model could explain an observation of erupted fragments that fall back as thin and elongated strands and end up onto the solar surface in a hedge-like configuration, made by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. The initial alignment of plasma flow plays an important role in determining the possible laminar structure and fragmentation of flows while they travel along magnetic channels.Comment: 11 pages, 8 figures, accepted for publication, movies available upon request to the first autho

Thermal structure of hot non-flaring corona from Hinode/EIS

In previous studies a very hot plasma component has been diagnosed in solar active regions through the images in three different narrow-band channels of SDO/AIA. This diagnostic from EUV imaging data has also been supported by the matching morphology of the emission in the hot Ca XVII line, as observed with Hinode/EIS. This evidence is debated because of unknown distribution of the emission measure along the line of sight. Here we investigate in detail the thermal distribution of one of such regions using EUV spectroscopic data. In an active region observed with SDO/AIA, Hinode/EIS and XRT, we select a subregion with a very hot plasma component and another cooler one for comparison. The average spectrum is extracted for both, and 14 intense lines are selected for analysis, that probe the 5.5 < log T < 7 temperature range uniformly. From these lines the emission measure distributions are reconstructed with the MCMC method. Results are cross-checked with comparison of the two subregions, with a different inversion method, with the morphology of the images, and with the addition of fluxes measured with from narrow and broad-band imagers. We find that, whereas the cool region has a flat and featureless distribution that drops at temperature log T >= 6.3, the distribution of the hot region shows a well-defined peak at log T = 6.6 and gradually decreasing trends on both sides, thus supporting the very hot nature of the hot component diagnosed with imagers. The other cross-checks are consistent with this result. This study provides a completion of the analysis of active region components, and the resulting scenario supports the presence of a minor very hot plasma component in the core, with temperatures log T > 6.6.Comment: 12 pages, 8 figures, accepted for publicatio

Globular Clusters in the Magellanic Clouds.I:BV CCD-Photometry for 11 Clusters

We present BV CCD-data for 11 intermediate-age LMC clusters; the main conclusions are: 1. in the (V_to, V_cl,m) and (V-to, (V_to-V_cl,m)) planes the models yield a good overall description of the data; 2. with the current sample, it is impossible to firmly choose between "classical" and "overshooting" models; 3. the separation in colour between the MS band and the Red He-burning Clump is smaller than predicted by theoretical tracks; 4. the existence of the so-called "RGB phase-transition (Renzini and Buzzoni 1986) seems to be confirmed.Comment: 62 pages, 37 figures and tables 6 to 16 available on request, uuencoded compressed postscript file with tables 1-5 and 17-18 included, BAP 08-1994-020-OA

Rate-Control or Rhythm-Contol: Where do we stand?

Atrial fibrillation is the most common sustained rhythm disturbance and its prevalence is increasing worldwide due to the progressive aging of the population. Current guidelines clearly depict the gold standard management of acute symptomatic atrial fibrillation but the best-long term approach for first or recurrent atrial fibrillation is still debated with regard to quality of life, risk of new hospitalizations, and possible disabling complications, such as thromboembolic stroke, major bleeds and death. Some authors propose that regaining sinus rhythm in all cases, thus re-establishing a physiologic cardiac function not requiring a prolonged antithrombotic therapy, avoids the threat of intracranial or extracranial haemorrhages due to Vitamin K antagonists or aspirin. On the contrary, advocates of a rate control approach with an accurate antithrombotic prophylaxis propose that such a strategy may avoid the risk of cardiovascular and non cardiovascular side effects related to antiarrhythmic drugs. This review aims to explore the state of our knowledge in order to summarize evidences and issues that need to be furthermore clarified

Gemini optical observations of binary millisecond-pulsars

Milli-second pulsars (MSPs) are rapidly spinning neutron stars, with spin periods P_s <= 10 ms, which have been most likely spun up after a phase of matter accretion from a companion star. In this work we present the results of the search for the companion stars of four binary milli-second pulsars, carried out with archival data from the Gemini South telescope. Based upon a very good positional coincidence with the pulsar radio coordinates, we likely identified the companion stars to three MSPs, namely PSRJ0614-3329 (g=21.95 +- 0.05), J1231-1411 (g=25.40 +-0.23), and J2017+0603 (g=24.72 +- 0.28). For the last pulsar (PSRJ0613-0200) the identification was hampered by the presence of a bright star (g=16 +- 0.03) at \sim 2" from the pulsar radio coordinates and we could only set 3-sigma upper limits of g=25.0, r= 24.3, and i= 24.2 on the magnitudes of its companion star. The candidate companion stars to PSRJ0614-3329, J1231-1411, and J2017+0603 can be tentatively identified as He white dwarfs (WDs) on the basis of their optical colours and brightness and the comparison with stellar model tracks. From the comparison of our multi-band photometry with stellar model tracks we also obtained possible ranges on the mass, temperature, and gravity of the candidate WD companions to these three MSPs. Optical spectroscopy observations are needed to confirm their possible classification as He WDs and accurately measure their stellar parameters.Comment: 17 pages, 7 figures, 6 tables, accepted for publication in MNRA

Bright hot impacts by erupted fragments falling back on the Sun: magnetic channelling

Dense plasma fragments were observed to fall back on the solar surface by the Solar Dynamics Observatory after an eruption on 7 June 2011, producing strong EUV brightenings. Previous studies investigated impacts in regions of weak magnetic field. Here we model the $\sim~300$ km/s impact of fragments channelled by the magnetic field close to active regions. In the observations, the magnetic channel brightens before the fragment impact. We use a 3D-MHD model of spherical blobs downfalling in a magnetized atmosphere. The blob parameters are constrained from the observation. We run numerical simulations with different ambient density and magnetic field intensity. We compare the model emission in the 171\AA~ channel of the Atmospheric Imaging Assembly with the observed one. We find that a model of downfall channelled in a $\sim~1$MK coronal loop confined by a magnetic field of $\sim~10-20$G, best explains qualitatively and quantitatively the observed evolution. The blobs are highly deformed, further fragmented, when the ram pressure becomes comparable to the local magnetic pressure and they are deviated to be channelled by the field, because of the differential stress applied by the perturbed magnetic field. Ahead of them, in the relatively dense coronal medium, shock fronts propagate, heat and brighten the channel between the cold falling plasma and the solar surface. This study shows a new mechanism which brightens downflows channelled by the magnetic field, such as in accreting young stars, and also works as a probe of the ambient atmosphere, providing information about the local plasma density and magnetic field.Comment: 17 pages, 14 figure

Optical, near-IR and XX-ray observations of SN 2015J and its host galaxy

SN 2015J was discovered on April 27th 2015 and is classified as a type IIn supernova. At first, it appeared to be an orphan SN candidate, i.e. without any clear identification of its host galaxy. Here, we present the analysis of the observations carried out {by the VLT 8-m class telescope with the FORS2 camera in the R band and the Magellan telescope (6.5 m) equipped with the IMACS Short-Camera (V and I filters) and the FourStar camera (Ks filter)}. We show that SN 2015J resides in what appears to be a very compact galaxy establishing a relation between the SN event and its natural host. We also present and discuss archival and new $X$-ray data centred on SN 2015J. At the time of the supernova explosion, Swift/XRT observations were made and a weak X-ray source was detected at the location of SN 2015J. Almost one year later, the same source was unambiguously identified during serendipitous observations by Swift/XRT and $XMM$-Newton, clearly showing an enhancement of the 0.3-10 keV band flux by a factor $\simeq 30$ with respect to the initial state. Swift/XRT observations show that the source is still active in the $X$-rays at a level of $\simeq 0.05$ counts s$^{-1}$. The unabsorbed X-ray luminosity derived from the {\it XMM}-Newton slew and SWIFT observations, $L_{x}\simeq 5\times10^{41}$ erg s$^{-1}$, places SN 2015J among the brightest young supernovae in X-rays.Comment: The Astrophysical Journal, Volume 850, Number

On the importance of background subtraction in the analysis of coronal loops observed with TRACE

In the framework of TRACE coronal observations, we compare the analysis and diagnostics of a loop after subtracting the background with two different and independent methods. The dataset includes sequences of images in the 171 A, 195 A filter bands of TRACE. One background subtraction method consists in taking as background values those obtained from interpolation between concentric strips around the analyzed loop. The other method is a pixel-to-pixel subtraction of the final image when the loop had completely faded out, already used by Reale & Ciaravella 2006. We compare the emission distributions along the loop obtained with the two methods and find that they are considerably different. We find differences as well in the related derive filter ratio and temperature profiles. In particular, the pixel-to-pixel subtraction leads to coherent diagnostics of a cooling loop. With the other subtraction the diagnostics are much less clear. The background subtraction is a delicate issue in the analysis of a loop. The pixel-to-pixel subtraction appears to be more reliable, but its application is not always possible. Subtraction from interpolation between surrounding regions can produce higher systematic errors, because of intersecting structures and of the large amount of subtracted emission in TRACE observations.Comment: 9 pages, 9 figure

The extended structure of the dwarf irregular galaxies Sextans A and Sextans B. Signatures of tidal distortion in the outskirts of the Local Group

We present a detailed study of the stellar and HI structure of the dwarf irregular galaxies SextansA and SextansB, members of the NGC3109 association. We use newly obtained deep (r~26.5) and wide field g,r photometry to extend the Surface Brightness (SB) profiles of the two galaxies down to mu_V~ 31.0 mag/arcsec^2. We find that both galaxies are significantly more extended than what previously traced with surface photometry, out to ~4 kpc from their centers along their major axis. Older stars are found to have more extended distribution with respect to younger populations. We obtain the first estimate of the mean metallicity for the old stars in SexB, from the color distribution of the Red Giant Branch, =-1.6. The SB profiles show significant changes of slope and cannot be fitted with a single Sersic model. Both galaxies have HI discs as massive as their respective stellar components. In both cases the HI discs display solid-body rotation with maximum amplitude of ~50 km/s (albeit with significant uncertainty due to the poorly constrained inclination), implying a dynamical mass ~10^{9}~M_sun, a mass-to-light ratio M/L_V~25 and a dark-to-barionic mass ratio of ~10. The distribution of the stellar components is more extended than the gaseous disc in both galaxies. We find that the main, approximately round-shaped, stellar body of Sex~A is surrounded by an elongated low-SB stellar halo that can be interpreted as a tidal tail, similar to that found in another member of the same association (Antlia). We discuss these, as well as other evidences of tidal disturbance, in the framework of a past passage of the NGC3109 association close to the Milky Way, that has been hypothesized by several authors and is also supported by the recently discovered filamentary configuration of the association itself.Comment: Accepted for publication by A&A. PdfLateX, 16 pages, 11 figures, 2 appendice

Osteobiografía de dos Cazadores de ambientes marinos de la Isla Grande de Tierra del Fuego

La propuesta del presente trabajo consiste en realizar el análisis osteobiografíco de dos individuos provenientes de la Isla Grande de Tierra del Fuego, porción Argentina. Uno de ellos fue hallado en una excavación cercana al cementerio de la estancia Harberton, Canal Beagle; el otro proviene de un sitio de Bahía Valentín, Península Mitre. Dado que los valores de la composición isotópica de carbono y nitrógeno, ya publicadas en otras contribuciones, resultan muy similares en ambos individuos, aquí hacemos foco en diversos indicadores fisiológicos y patológicos de los dos esqueletos y sus aparatos masticatorios hallando marcadas diferencias entre ellos. Se sugiere que las mismas, posiblemente, puedan estar relacionadas con situaciones de aislamiento geográfico y temporal propias de cada uno de los individuos.We intend to make a bone biography of two individuals from the Isla Grande de Tierra del Fuego, Argentina portion. One of them was found in an excavation near the cemetery of the Estancia Harberton, Beagle Channel, and the other from a site of Bahía Valentín, Península Mitre. The results of the isotopic composition of carbon and nitrogen are very similar between individuals. We analyze the various physiological and pathological indicators of the two skeletons and masticatory apparatus, finding marked differences.Fil: Kozameh, Livia F.. Universidad Nacional de Rosario; ArgentinaFil: Testa, Nora. Universidad Nacional de Rosario; ArgentinaFil: Tessone, Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geocronología y Geología Isotopica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geocronología y Geología Isotópica; Argentin