Suzaku observation of the classical nova V2491 Cyg in quiescence

We present Suzaku XIS observation of V2491 Cyg (Nova Cyg 2008 No. 2) obtained in quiescence, more than two years after the outburst. The nova was detected as a very luminous source in a wide spectral range from soft to hard X-rays. A very soft blackbody-like component peaking at 0.5 keV indicates that either we observe remaining, localized hydrogen burning on the surface of the white dwarf, or accretion onto a magnetized polar cap. In the second case, V2491 Cyg is a candidate "soft intermediate polar". We obtained the best fit for the X-ray spectra with several components: two of thermal plasma, a blackbody and a complex absorber. The later is typical of intermediate polars. The X-ray light-curve shows a modulation with a $\sim$38 min period. The amplitude of this modulation is strongly energy dependent and reaches maximum in the 0.8--2.0 keV range. We discuss the origin of the X-ray emission and pulsations, and the likelihood of the intermediate polar scenario.Comment: 8 pages, 7 figures, accepted to Astrophysical Journa

Diversity and Classification of Isopods Crustaceans (Isopoda, Crustacea) Assemblages of Admiralty Bay (King George Island, Antarctic)

Skorupiaki z rzędu równonogów (Isopoda) Latreille, 1817 są ważnym elementem zoobentosu morskiego (Gallardo i Castillo 1969; Jazdzewski i in. 1986), i stanowią jedną z najbogatszych w gatunki grup makrozoobentosu Oceanu Południowego (Clarke i Johnston 2003; De Broyer i in. 2011). Celem pracy była ocena bogactwa gatunkowego równonogów miękkiego dna Zatoki Admiralicji, analiza rozmieszczenia i różnorodności zgrupowań Isopoda miękkiego dna Zatoki Admiralicji oraz ocena bogactwa gatunkowego i różnorodności fauny Isopoda aparatów czepnych brunatnicy Himantothalls grandifolius. Materiał badawczy pochodzi z Zatoki Admiralicji (Wyspy Króla Jerzego) Antarktyka. Do analiz wykorzystano łącznie 152 próby ilościowe, jakościowe oraz z aparatów czepnych H. grandifolius. Stwierdzono 70 gatunków równonogów z czego 31 gatunków, nie było odnotowanych w tej zatoce. Isopoda nie tworzą na miękkim dnie Zatoki Admiralicji wyraźnych zgrupowań fauny, związanych z bardzo ograniczonymi obszarami dna, charakteryzującymi się bardzo podobnymi parametrami fizyko-chemicznymi. Różnorodność Isopoda miękkiego dna, w silnie zaburzonej przez lodowce zatoce glacjalnej, była niższa niż w ujściowej części Fiordu Ezcurry. Aparaty czepne H. grandifolius są zasiedlane przez specyficzne zgrupowanie Isopoda, silnie zdominowane przez Caecognathia antarctica i obecny tylko w tym siedlisku Cymodocella tubicauda. Nie wykazano zależności pomiędzy objętością aparatu czepnego H. grandifolius a zagęszczeniem gatunków, zagęszczeniem osobników i liczbą gatunków. Zaobserwowano zmiany w strukturze zgrupowań Isopoda pomiędzy latami osiemdziesiątymi XX wieku, a rokiem 2007. Crustaceans isopod (Isopoda) Latreille, 1817 are an important part of zoobenthos sea (Gallardo and Castillo 1969 JAŻDŻEWSKI et al. 1986), and represent one of the richest in species groups macrozoobenthos of the Southern Ocean (Clarke and Johnston 2003; De Broyer et al. 2011). The aim of the study was to assess species richness Isopoda of soft bottom of Admiralty Bay, analyzing the distribution and diversity Isopoda communieties of soft bottom of Admiralty Bay and evaluation of species richness and diversity of Isopoda fauna of holdfasts of macroalgae Himantothalls grandifolius. The research material comes from Admiralty Bay (King George Island) Antarctica. For the analysis used a total of 152 attempts quantitative, qualitative and holdfast samples of H. grandifolius. It was found 70 species Isopoda, of which 31 species was recorded in this the bay first time. Isopoda not form on the soft bottom of Admiralty Bay distinct groupings fauna associated with very limited areas of the bottom, characterized by very similar physico-chemical parameters. The diversity of the Isopoda soft bottom, in a strongly disturbed by glaciers glacial bay, was lower than in the estuary part of the Ezcurra Inlet. Holdfasts of H. grandifolius are inhabited by specific grouping of the Isopoda, strongly dominated by Caecognathia antarctica and present only in this habitat Cymodocella tubicauda. No significant correlation between the volume of holdfast of H. grandifolius and density of species, density of individuals and number of species. Observed changes in the structure of the Isopoda groupings between the eighties of the twentieth century, and 2007.CAREX Transfer of Knowledge Grant, CeDAMar Short Visit Gran

X-ray observations of VY Scl type nova-like binaries in the high and low state

Four VY Scl-type nova-like systems were observed in X-rays during both the low and the high optical states. We examined Chandra, ROSAT, Swift and Suzaku archival observations of BZ Cam, MV Lyr, TT Ari, and V794 Aql. The X-ray flux of BZ Cam is higher during the low state, but there is no supersoft X-ray source (SSS) as hypothesized in previous articles. No SSS was detected in the low state of the any of the other systems, with the X-ray flux decreasing by a factor between 2 and 50. The best fit to the Swift X-ray spectra is obtained with a multi-component model of plasma in collisional ionization equilibrium. The high state high resolution spectra of TT Ari taken with Chandra ACIS-S and the HETG gratings show a rich emission line spectrum, with prominent lines of in Mg, Si, Ne, and S. The complexity of this spectrum seems to have origin in more than one region, or more than one single physical mechanism. While several emission lines are consistent with a cooling flow in an accretion stream, there is at least an additional component. We discuss the origin of this component, which is probably arising in a wind from the system. We also examine the possibility that the VY Scl systems may be intermediate polars, and that while the boundary layer of the accretion disk emits only in the extreme ultraviolet, part of the X-ray flux may be due to magnetically driven accretion.Comment: 13 pages, 8 figures, 7 tables. Accepted for publication by MNRA

Constraining the Accretion Geometry of the Intermediate Polar EX Hya Using NuSTAR, Swift, and Chandra Observations

In magnetically accreting white dwarfs, the height above the white dwarf surface where the standing shock is formed is intimately related with the accretion rate and the white dwarf mass. However, it is difficult to measure. We obtained new data with NuSTAR and Swift that, together with archival Chandra data, allow us to constrain the height of the shock in the intermediate polar EX Hya. We conclude that the shock has to form at least at a distance of about one white dwarf radius from the surface in order to explain the weak Fe Kα 6.4 keV line, the absence of a reflection hump in the high-energy continuum, and the energy dependence of the white dwarf spin pulsed fraction. Additionally, the NuSTAR data allowed us to measure the true, uncontaminated hard X-ray (12-40 keV) flux, whose measurement was contaminated by the nearby galaxy cluster Abell 3528 in non-imaging X-ray instruments.Fil: Luna, Gerardo Juan Manuel. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Mukai, K.. National Aeronautics and Space Administration; Estados UnidosFil: Orio, M.. Università di Padova; ItaliaFil: Zemko, P.. Università di Padova; Itali

X-Ray Observations of VY Scl-Type Nova-Like Binaries in the High and Low State

Four VY Scl-type nova-like systems were observed in X-rays both during the low and the high optical states. They are BZ Cam, MV Lyr, TT Ari, and V794 Aql. Using archival ROSAT, Swift and SUZAKU observations we found that the X-ray flux for BZ Cam is higher during the low state, but there is no supersoft X-ray source (SSS) that would indicate the thermonuclear burning predicted in a previous article. The X-ray flux is lower by a factor 2–10 in the low than the high state in other systems, and does not reflect the drop in ˙M inferred from optical and UV data. The best fit model for the X-ray spectra is a collisionally ionized plasma model. The X-ray flux may originate in a shocked wind or in accretion onto polar caps in intermediate polar systems that continues even during the low state

V4743 Sgr, a magnetic nova?

Two XMM Newton observations of Nova V4743 Sgr (Nova Sgr 2002) were performed shortly after it returned to quiescence, 2 and 3.5 years after the explosion. The X-ray light curves revealed a modulation with a frequency of ~0.75 mHz, indicating that V4743 Sgr is most probably an intermediate polar (IP). The X-ray spectra have characteristics in common with known IPs, with a hard thermal plasma component that can be fitted only assuming a partially covering absorber. In 2004 the X-ray spectrum had also a supersoft blackbody-like component, whose temperature was close to that of the white dwarf (WD) in the supersoft X-ray phase following the outburst, but with flux by at least two orders of magnitude lower. In quiescent IPs, a soft X-ray flux component originates at times in the polar regions irradiated by an accretion column, but the supersoft component of V4743 Sgr disappeared in 2006, indicating a possible origin different from accretion. We suggest that it may have been due to an atmospheric temperature gradient on the WD surface, or to continuing localized thermonuclear burning at the bottom of the envelope, before complete turn-off. An optical spectrum obtained with SALT 11.5 years after the outburst showed a prominent He II 4686A line and the Bowen blend, which reveal a very hot region, but with peak temperature shifted to the ultraviolet (UV) range. V4743 Sgr is the third post-outburst nova and IP candidate showing a low-luminosity supersoft component in the X-ray flux a few years after the outburst.Comment: 9 pages, 5 figures, accepted to MNRA

Strain and strain-hardening analysis of formed parts produced by multi-pass metal spinning

U članku se daju rezultati eksperimentalnog istraživanja usmjerenog na analizu radijalne i tangencijalne raspodjele deformacije i utjecaja otvrđivanja plastičnom deformacijom površinskih slojeva šupljih dijelova od metalnog lima proizvedenih višeslojnim utiskivanjem (rotacijskim oblikovanjem) metala. Korišteni su tanki limovi od čelika EN 10025-94 (ISO 630-80), debljine 1 mm. Rezultati istraživanja potvrđuju minimalni utjecaj anizotropije materijala na radijalnu i tangencijalnu raspodjelu deformacija i relativno značajan utjecaj anizotropije materijala na otvrđivanja plastičnom deformacijom površinskih slojeva utiskivanih dijelova. Ustanovljeno je da veće otvrđivanje plastičnom deformacijom postoji u smjeru 90° prema smjeru valjanja lima nego u smjeru 0°.The paper presents results of experimental study focused on the analysis of radial and hoop strain distributions and effect of strain-hardening of the surface layers of sheet metal hollow parts produced by multi-pass metal spinning. The thin sheets of 1 mm thickness, steel EN 10025-94 (ISO 630-80), were used for experimental study. The results of the study confirm minimal influence of the anisotropy of material on radial and hoop strain distributions and the relatively significant influence of the material anisotropy on the strain-hardening of the spun part\u27s surface layers. It is found higher strain-hardening in the direction 90° refer to the rolling direction of the sheet compared to the direction 0°