X-ray and optical observations of 1RXS J154814.5-452845: a new intermediate polar with soft X-ray emission

We report the identification of the ROSAT all-sky survey source 1RXS J154814.5-452845as new intermediate polar and present the results from follow-up optical and X-ray observations. The source shows pulsations with a period of 693 s both in the optical and X-ray light curves and the detection of a synodic frequency strongly suggests that this is the rotation period of the white dwarf. Although the one day aliasing and the sparse optical data coverage does not allow to unambiguously identify the orbital period, the most likely values of 9.37 h and 6.72 h add 1RXS J154814.5-452845 to the intermediate polars with the longest orbital periods known. The optical spectrum displays features from the late type secondary and shows the presence of broad absorption lines at \Hbet and higher order Balmer lines which may be a signature of the white dwarf atmosphere, very similar to V 709 Cas. The average X-ray spectra as obtained by the EPIC instruments on board XMM-Newton show hard emission typical for this class of objects but also the presence of soft blackbody-like emission similar to that seen from soft intermediate polars and thought to arise from the white dwarf surface heated by the hard X-rays. The best fit model comprises thermal emission from multi-temperature plasma in collisional ionization equilibrium with a continuous temperature distribution up to a maximum of $\sim$60 keV, an Fe fluorescence line at 6.4 keV and with equivalent width of 260 eV and a blackbody component with kT of 86 eV. The hard X-ray emission is absorbed by matter covering 47% of the X-ray source with an equivalent hydrogen density of $\sim$\ohcm{23}. The remaining hard emission is absorbed by a much reduced column density of 1.5\hcm{21} as is the soft blackbody emission. (truncated)Comment: 14 pages, Latex, with 19 figures, accepted for publication in Astronomy and Astrophysic

Effect of oxygen concentration on nanoindentation-induced phase transformations in ion-implanted amorphous silicon

The effect of the local oxygen concentration in ion-implanted amorphous Si (a-Si) on nanoindentation-inducedphase transformations has been investigated. Implantation of oxygen into the a-Sifilms has been used to controllably introduce an approximately constant concentration of oxygen, ranging from ∼10¹⁸ to ∼10²¹ cm⁻³, over the depth range of the phase transformed zones. Nanoindentation was performed under conditions that ensure a phase transformed zone composed completely of Si-III/XII in the nominally oxygen-free a-Si. The effect of the local oxygen concentration has been investigated by analysis of the unloading curves, Raman microspectroscopy, and cross-sectional transmission electron microscopy (XTEM). The formation of Si-III/XII is suppressed with increasing oxygen concentration, favoring a greater volume of a-Si within the zones. The Raman microspectroscopy and XTEM verify that the volume of Si-III/XII decreases with increasing O concentration. With the smaller volumes of Si-III/XII, the pop-out normally observed on load versus penetration depth curves during unloading decreases in magnitude, becoming more kinklike and is barely discernable at high concentrations of oxygen. The probability of forming any high pressure phases is reduced from 1 to ∼0.1 for a concentration of 10²¹ cm⁻³. We suggest that the bonding of O with Si reduces the formation of Si-III/XII during unloading through a similar mechanism to that of oxygen-retarded solid phase crystallization of a-Si.This project is funded by the Australian Research Council and WRiota Pty Ltd

Phase transformations induced by spherical indentation in ion-implanted amorphous silicon

The deformation behavior of ion-implanted (unrelaxed) and annealed ion-implanted (relaxed) amorphous silicon(a-Si) under spherical indentation at room temperature has been investigated. It has been found that the mode of deformation depends critically on both the preparation of the amorphous film and the scale of the mechanical deformation.Ex situmeasurements, such as Raman microspectroscopy and cross-sectional transmission electron microscopy, as well as in situ electrical measurements reveal the occurrence of phase transformations in all relaxed a-Si films. The preferred deformation mode of unrelaxed a-Si is plastic flow, only under certain high load conditions can this state of a-Si be forced to transform. In situ electrical measurements have revealed more detail of the transformation process during both loading and unloading. We have used ELASTICA simulations to obtain estimates of the depth of the metallic phase as a function of load, and good agreement is found with the experiment. On unloading, a clear change in electrical conductivity is observed to correlate with a “pop-out” event on load versus penetration curves

AGN in the XMM-Newton first-light image as probes for the interstellar medium in the LMC

The XMM-Newton first-light image revealed X-ray point sources which show heavily absorbed power-law spectra. The spectral indices and the probable identification of a radio counterpart for the brightest source suggest AGN shining through the interstellar gas of the Large Magellanic Cloud (LMC). The column densities derived from the X-ray spectra in combination with HI measurements will allow to draw conclusions on HI to H_2 ratios in the LMC and compare these with values found for the galactic plane.Comment: 4 pages, LaTex, 4 figures, Accepted for publication in A&A Letter

The eclipsing bursting X-ray binary EXO 0748-676 revisited by XMM-Newton

The bright eclipsing and bursting low-mass X-ray binary EXO 0748-676 has been observed at several occasions by XMM-Newton during the initial calibration and performance verification (CAL/PV) phase. We present here the results obtained from observations with the EPIC cameras. Apart from several type-I X-ray bursts, the source shows a high degree of variability with the presence of soft flares. The wide energy coverage and high sensitivity of XMM-Newton allows for the first time a detailed description of the spectral variability. The source is found to be the superposition of a central (~2 10^8 cm) Comptonized emission, most probably a corona surrounding the inner edge of an accretion disk, associated with a more extended (~3 10^10 cm) thermal halo at a typical temperature of ~0.6 keV with an indication of non-solar abundances. Most of the variations of the source can be accounted for by a variable absorption affecting only the central comptonized component and reaching up to NH ~1.3 10^23 cm^{-2}. The characteristics of the surrounding halo are found compatible with an irradiated atmosphere of an accretion disc which intercepts the central emission due to the system high inclination.Comment: 6 pages, 4 figures, accepted for publication in A&A Letters, XMM special issu

The continued spectral and temporal evolution of RX J0720.4-3125

RX J0720.4-3125 is the most peculiar object among a group of seven isolated X-ray pulsars (the so-called "Magnificent Seven"), since it shows long-term variations of its spectral and temporal properties on time scales of years. This behaviour was explained by different authors either by free precession (with a seven or fourteen years period) or possibly a glitch that occurred around $\mathrm{MJD=52866\pm73 days}$. We analysed our most recent XMM-Newton and Chandra observations in order to further monitor the behaviour of this neutron star. With the new data sets, the timing behaviour of RX J0720.4-3125 suggests a single (sudden) event (e.g. a glitch) rather than a cyclic pattern as expected by free precession. The spectral parameters changed significantly around the proposed glitch time, but more gradual variations occurred already before the (putative) event. Since $\mathrm{MJD\approx53000 days}$ the spectra indicate a very slow cooling by $\sim$2 eV over 7 years.Comment: seven pages, three figures, three tables; accepted by MNRA

The highly ionized disk wind of GRO J1655-40

Aims: The galactic superluminal microquasar GRO J1655-40 started a new outburst in February 2005, after seven years in quiescence, rising to a high/soft state in March 2005. In this paper we study the X-ray spectra during this rise. Methods: We observed GRO J1655-40 with XMM-Newton, on 27 February 2005, in the low/hard state, and on three consecutive days in March 2005, during the rise of the source to its high/soft state. The EPIC-pn camera was used in the fast-read Burst mode to avoid photon pile-up. Results: First, we contributed to the improvement of the calibration of the EPIC-pn, since the high flux received from the source required some refinements in the correction of the Charge Transfer Efficiency of the camera.Second, we find that the X-ray spectrum of GRO J1655-40 is dominated in the high/soft state by the thermal emission from the accretion disk, with an inner radius of 13-14(D/3.2kpc)km and a maximum temperature of 1.3 keV. Two absorption lines are detected in the EPIC-pn spectra, at 6.7-6.8 and 7.8-8.0 keV, which can be identified either as blended Fe XXV and Fe XXVI K-alpha and K-beta lines, or as blueshifted Fe XXV. We find no orbital dependence on the X-ray properties, which provides an upper limit for the inclination of the system of 73 degr. The RGS spectrometers reveal interstellar absorption features at 17.2AA, 17.5AA (Fe L edges) and 23.54AA (OI K-alpha). Finally, while checking the interstellar origin of the OI line, we find a general correlation of the OI K-alpha line equivalent width with the hydrogen column density using several sources available in the literature.Comment: 10 pages, 7 figures, 4 tables. Revised version with important change

Analysis of the Energy Savings Potential in K-5 Schools in Hot and Humid Climates

This paper presents the analysis of the energy savings potential in K-5 schools in hot and humid climates. For the analysis, an existing K-5 school in Central Texas was selected as a case study school, and the building energy related data and information were collected. Based on the information, an hourly building energy simulation was developed using the DOE-2 program and calibrated with the measured building energy use. This final calibrated simulation was modified to be compliant to the ASHRAE Standard 90.1-1999 in order to be used as a base-case school. Then, several energy efficient measures that are appropriate for the school buildings in hot and humid climates were identified from previous studies and applied to the base-case school simulation to estimate the energy savings potential. The measures include high R-values for walls and roofs, high performance glazing, T-5 or T-8 fluorescent lamps, occupancy sensors for lighting control, and high efficient chillers and boilers

Analysis of Off-Grid, Off-Pipe Housing for Hot-Humid and Hot-Arid Climates

This paper investigates the feasibility of off-grid, off-pipe housing in hot-humid and hot-arid climates in the U.S. The study aims to eliminate the need for non-renewable sources of energy and municipal water in residences by using off-grid, off-pipe design approach. To accomplish this, a 2001 International Energy Conservation Code compliant house in Houston, TX and Phoenix, AZ was simulated to determine the base-case energy and water use. Based on the availability of on-site renewable energy and water sources (i.e., solar, wind and biomass and rainfall) in these locations, energy and water efficiency measures were selected in order to reduce the energy and water use to a level that could be met solely by on-site renewable resources. Finally, the sizing of the renewable energy and rainwater harvesting systems was performed to provide for daily needs as well as cumulative needs during the critical periods, in order to achieve complete self sufficiency in terms of energy and water use. The analysis was performed by integrating the results of DOE-2.1e, F-Chart and PV F-Chart programs, and cumulative rainwater supply and water demand analysis. The simulation results demonstrate the differences between the priorities for energy efficiency, water-efficiency and renewable energy measures in hot-humid and hot-arid climates

M 33 X-7: ChASeM33 reveals the first eclipsing black hole X-ray binary

The first observations conducted as part of the Chandra ACIS survey of M 33 (ChASeM33) sampled the eclipsing X-ray binary M 33 X-7 over a large part of the 3.45 d orbital period and have resolved eclipse ingress and egress for the first time. The occurrence of the X-ray eclipse allows us to determine an improved ephemeris of mid-eclipse and binary period as HJD (2453639.119+-0.005) +- N x (3.453014+-0.000020) and constrain the eclipse half angle to (26.5+-1.1) degree. There are indications for a shortening of the orbital period. The X-ray spectrum is best described by a disk blackbody spectrum typical for black hole X-ray binaries in the Galaxy. We find a flat power density spectrum and no significant regular pulsations were found in the frequency range of 10^{-4} to 0.15 Hz. HST WFPC2 images resolve the optical counterpart, which can be identified as an O6III star with the help of extinction and colour corrections derived from the X-ray absorption. Based on the optical light curve, the mass of the compact object in the system most likely exceeds 9 M_sun. This mass, the shape of the X-ray spectrum and the short term X-ray time variability identify M 33 X-7 as the first eclipsing black hole high mass X-ray binary.Comment: 14 pages, 5 figures, ApJ accepte