The Influence of Specimen Thickness on the High Temperature Corrosion Behavior of CMSX-4 during Thermal-Cycling Exposure

CMSX-4 is a single-crystalline Ni-base superalloy designed to be used at very high temperatures and high mechanical loadings. Its excellent corrosion resistance is due to external alumina-scale formation, which however can become less protective under thermal-cycling conditions. The metallic substrate in combination with its superficial oxide scale has to be considered as a composite suffering high stresses. Factors like different coefficients of thermal expansion between oxide and substrate during temperature changes or growing stresses affect the integrity of the oxide scale. This must also be strongly influenced by the thickness of the oxide scale and the substrate as well as the ability to relief such stresses, e.g., by creep deformation. In order to quantify these effects, thin-walled specimens of different thickness (t = 100500 lm) were prepared. Discontinuous measurements of their mass changes were carried out under thermal-cycling conditions at a hot dwell temperature of 1100 C up to 300 thermal cycles. Thin-walled specimens revealed a much lower oxide-spallation rate compared to thick-walled specimens, while thinwalled specimens might show a premature depletion of scale-forming elements. In order to determine which of these competetive factor is more detrimental in terms of a component’s lifetime, the degradation by internal precipitation was studied using scanning electron microscopy (SEM) in combination with energy-dispersive X-ray spectroscopy (EDS). Additionally, a recently developed statistical spallation model was applied to experimental data [D. Poquillon and D. Monceau, Oxidation of Metals, 59, 409–431 (2003)]. The model describes the overall mass change by oxide scale spallation during thermal cycling exposure and is a useful simulation tool for oxide scale spallation processes accounting for variations in the specimen geometry. The evolution of the net-mass change vs. the number of thermal cycles seems to be strongly dependent on the sample thickness

Refined Neutron-Star Mass Determinations for Six Eclipsing X-Ray Pulsar Binaries

We present an improved method for determining the mass of neutron stars in eclipsing X-ray pulsar binaries and apply the method to six systems, namely Vela X-1, 4U 1538-52, SMC X-1, LMC X-4, Cen X-3, and Her X-1. In previous studies to determine neutron star mass, the X-ray eclipse duration has been approximated analytically by assuming the companion star is spherical with an effective Roche lobe radius. We use a numerical code based on Roche geometry with various optimizers to analyze the published data for these systems, which we supplement with new spectroscopic and photometric data for 4U 1538-52. This allows us to model the eclipse duration more accurately and thus calculate an improved value for the neutron star mass. The derived neutron star mass also depends on the assumed Roche lobe filling factor beta of the companion star, where beta = 1 indicates a completely filled Roche lobe. In previous work a range of beta between 0.9 and 1.0 was usually adopted. We use optical ellipsoidal lightcurve data to constrain beta. We find neutron star masses of 1.77 +/- 0.08 M_{sun} for Vela X-1, 0.87 +/- 0.07 M_{sun} for 4U 1538-52 (eccentric orbit), 1.00 +/- 0.10 M_{sun} for 4U 1538-52 (circular orbit), 1.04 +/- 0.09 M_{sun} for SMC X-1, 1.29 +/- 0.05 M_{sun} for LMC X-4, 1.49 +/- 0.08 M_{sun} for Cen X-3, and 1.07 +/- 0.36 M_{sun} for Her X-1. We discuss the limits of the approximations that were used to derive the earlier mass determinations, and we comment on the implications our new masses have for observationally refining the upper and lower bounds of the neutron star mass distribution.Comment: 10 figures, accepted for publication in The Astrophysical Journa

The investigation of additive manufacturing and moldable materials to produce railway ballast grain analogs

The size and shape of individual grains, play an important role in the mechanical behavior of granular materials such as the strength and stability of railway ballast. The aim of this research is to study materials from which uniform, reproducible grains with irregular convex geometry can be created by molding and additive manufacturing technologies in order to create reproducible artificial assemblies that can be used in experiments. Packings with determined grain shape results more controlled investigations contrarily to using natural grains with random geometry. Specimens were made from railway ballast materials, materials used in the construction industry, additively manufactured and molded polymers, and certain low-strength materials. Uniaxial compression and bending tests were conducted on these specimens. The mechanical properties of typical railway ballast materials (basalt and andesite) were compared with the properties of artificially produced materials. The results show that for grain reproduction the molding technology is recommended with the use of polyester-crushed stone composite and ceramic powder. Furthermore, the additive manufacturing was recommended with PolyJet or Multi Jet Fusion technology as they have the feasibility to produce grains with similar material properties to the properties of basalt and andesite

Are we far from testing general relativity with the transiting extrasolar planet HD 209458b `Osiris'?

In this paper we investigate the possibility of measuring the general relativistic gravitoelectric contribution P^(GE) to the orbital period P of the transiting exoplanet HD 209458b 'Osiris'. It turns out that the predicted magnitude of such an effect is \sim 0.1 s, while the most recent determinations of the orbital period of HD 209458b with the photometric transit method are accurate to \sim 0.01 s. The present analysis shows that the major limiting factor is the \sim 1 m s^-1 sensitivity in the measurement of the projected semiamplitude of the star's radial velocity K. Indeed, it affects the determination of the mass m of the planet which, in turn, induces a systematic error in the Keplerian period P^(0) of \sim 8 s. It is of crucial importance because P^(0) should be subtracted from the measured period in order to extract the relativistic correction. The present-day uncertainty in $m$ does not yet make necessary the inclusion of relativistic corrections in the data-reduction process of the determination of the system's parameters. The present situation could change only if improvements of one-two orders of magnitude in the ground-based Doppler spectroscopy technique occurred.Comment: LaTex2e, 11 pages, 18 references, no figures, no tables. Section 5 improved. Small corrections. To appear in New Astronom

X-Ray Emission from the Jets of XTE J1550-564

We report on X-ray observations of the the large-scale jets recently discovered in the radio and detected in X-rays from the black hole candidate X-ray transient and microquasar XTE J1550-564. On 11 March 2002, X-ray emission was detected 23 arcsec to the West of the black hole candidate and was extended along the jet axis with a full width at half maximum of 1.2 arcsec and a full width at 10% of maximum intensity of 5 arcsec. The morphology of the X-ray emission matched well to that of the radio emission at the same epoch. The jet moved by 0.52 +/- 0.13 arcsec between 11 March and 19 June 2002. The apparent speed during that interval was 5.2 +/- 1.3 mas/day. This is significantly less than the average apparent speed of 18.1 +/- 0.4 mas/day from 1998 to 2002, assuming that the jet was ejected in September 1998, and indicates that the jet has decelerated. The X-ray spectrum is adequately described by a powerlaw with a photon index near 1.8 subject to interstellar absorption. The unabsorbed X-ray flux was 3.4 x 10^-13 erg cm^-2 s^-1 in the 0.3-8 keV band in March 2002, and decreased to 2.9 x 10^-13 erg cm^-2 s^-1 in June. We also detect X-rays from the eastern jet in March 2002 and show that it has decelerated and dimmed since the previous detections in 2000.Comment: accepted for publication in ApJ, 11 pages, several figures in colo

Formation of the black-hole binary M33 X-7 via mass-exchange in a tight massive system

M33 X-7 is among the most massive X-Ray binary stellar systems known, hosting a rapidly spinning 15.65 Msun black hole orbiting an underluminous 70 Msun Main Sequence companion in a slightly eccentric 3.45 day orbit. Although post-main-sequence mass transfer explains the masses and tight orbit, it leaves unexplained the observed X-Ray luminosity, star's underluminosity, black hole's spin, and eccentricity. A common envelope phase, or rotational mixing, could explain the orbit, but the former would lead to a merger and the latter to an overluminous companion. A merger would also ensue if mass transfer to the black hole were invoked for its spin-up. Here we report that, if M33 X-7 started as a primary of 85-99 Msun and a secondary of 28-32 Msun, in a 2.8-3.1 day orbit, its observed properties can be consistently explained. In this model, the Main Sequence primary transferred part of its envelope to the secondary and lost the rest in a wind; it ended its life as a ~16 Msun He star with a Fe-Ni core which collapsed to a black hole (with or without an accompanying supernova). The release of binding energy and, possibly, collapse asymmetries "kicked" the nascent black hole into an eccentric orbit. Wind accretion explains the X-Ray luminosity, while the black hole spin can be natal.Comment: Manuscript: 18 pages, 2 tables, 2 figure. Supplementary Information: 34 pages, 6 figures. Advance Online Publication (AOP) on http://www.nature.com/nature on October 20, 2010. To Appear in Nature on November 4, 201

Dynamical Masses for the Large Magellanic Cloud Massive Binary System [L72] LH 54-425

We present results from an optical spectroscopic investigation of the massive binary system [L72] LH~54-425 in the LH 54 OB association in the Large Magellanic Cloud. We revise the ephemeris of [L72] LH 54-425 and find an orbital period of 2.247409 +/- 0.000010 days. We find spectral types of O3 V for the primary and O5 V for the secondary. We made a combined solution of the radial velocities and previously published V-band photometry to determine the inclination for two system configurations, i = 52 degrees for the configuration of the secondary star being more tidally distorted and i = 55 degrees for the primary as the more tidally distorted star. We argue that the latter case is more probable, and this solution yields masses and radii of M_1 = 47 +/- 2 M_Sun and R_1 = 11.4 +/- 0.1 R_Sun for the primary, and M_2 = 28 +/- 1 M_Sun and R_2 = 8.1 +/- 0.1 R_Sun for the secondary. Our analysis places LH 54-425 amongst the most massive stars known. Based on the position of the two stars plotted on a theoretical HR diagram, we find the age of the system to be about 1.5 Myr.Comment: 21 pages, 6 figures. Accepted in ApJ. To appear vol. 683, Aug. 10t

Low-Mass Eclipsing Binaries in the Initial Kepler Data Release

We identify 231 objects in the newly released Cycle 0 dataset from the Kepler Mission as double-eclipse, detached eclipsing binary systems with Teff < 5500 K and orbital periods shorter than ~32 days. We model each light curve using the JKTEBOP code with a genetic algorithm to obtain precise values for each system. We identify 95 new systems with both components below 1.0 M_sun and eclipses of at least 0.1 magnitudes, suitable for ground-based follow-up. Of these, 14 have periods less than 1.0 day, 52 have periods between 1.0 and 10.0 days, and 29 have periods greater than 10.0 days. This new sample of main-sequence, low-mass, double-eclipse, detached eclipsing binary candidates more than doubles the number of previously known systems, and extends the sample into the completely heretofore unexplored P > 10.0 day period regime. We find preliminary evidence from these systems that the radii of low-mass stars in binary systems decrease with period. This supports the theory that binary spin-up is the primary cause of inflated radii in low-mass binary systems, although a full analysis of each system with radial-velocity and multi-color light curves is needed to fully explore this hypothesis. As well, we present 7 new transiting planet candidates that do not appear among the recently released list of 706 candidates by the Kepler team, nor in the Kepler False Positive Catalog, along with several other new and interesting systems. We also present novel techniques for the identification, period analysis, and modeling of eclipsing binaries.Comment: 22 pages in emulateapj format. 9 figures, 4 tables, 2 appendices. Accepted to AJ. Includes a significant addition of new material since last arXiv submission and an updated method for estimating masses and radi

Spurious Eccentricities of Distorted Binary Components

I discuss the effect of physical distortion on the velocities of close binary components and how we may use the resulting distortion of velocity curves to constrain some properties of binary systems, such as inclination and mass ratio. Precise new velocities for 5 Cet convincingly detect these distortions with their theoretically predicted phase dependence. We can even use such distortions of velocity curves to test Lucy's theory of convective gravity darkening. The observed distortions for TT Hya and 5 Cet require the contact components of those systems to be gravity darkened, probably somewhat more than predicted by Lucy's theory but clearly not as much as expected for a radiative star. These results imply there is no credible evidence for eccentric orbits in binaries with contact components. I also present some speculative analyses of the observed properties of a binary encased in a non-rotating common envelope, if such an object could actually exist, and discuss how the limb darkening of some recently calculated model atmospheres for giant stars may bias my resuts for velocity-curve distortions, as well as other results from a wide range of analyses of binary stars.Comment: 14 pp, 2 tables, 12 fig; under review by Ap