The Energy Dependence of Neutron Star Surface Modes and X-ray Burst Oscillations

We calculate the photon energy dependence of the pulsed amplitude of neutron star (NS) surface modes. Simple approximations demonstrate that it depends most strongly on the bursting NS surface temperature. This result compares well with full integrations that include Doppler shifts from rotation and general relativistic corrections to photon propagation. We show that the energy dependence of type I X-ray burst oscillations agrees with that of a surface mode, lending further support to the hypothesis that they originate from surface waves. The energy dependence of the pulsed emission is rather insensitive to the NS inclination, mass and radius, or type of mode, thus hindering constraints on these parameters. We also show that, for this energy-amplitude relation, the majority of the signal (relative to the noise) comes in the 2-25 keV band, so that the current burst oscillation searches with the Rossi X-Ray Timing Explorer are close to optimal. The critical test of the mode hypothesis for X-ray burst oscillations would be a measurement of the energy dependence of burst oscillations from an accreting millisecond pulsar.Comment: Accepted for publication in The Astrophysical Journal, 6 pages, 5 figures (revised version: no changes to text, just edited author list

Motional frequency shifts of trapped ions in the Lamb-Dicke regime

First order Doppler effects are usually ignored in laser driven trapped ions when the recoil frequency is much smaller than the trapping frequency (Lamb-Dicke regime). This means that the central, carrier excitation band is supposed to be unaffected by vibronic transitions in which the vibrational number changes. While this is strictly true in the Lamb-Dicke limit (infinitely tight confinement), the vibronic transitions do play a role in the Lamb-Dicke regime. In this paper we quantify the asymptotic behaviour of their effect with respect to the Lamb-Dicke parameter. In particular, we give analytical expressions for the frequency shift, ``pulling'' or ``pushing'', produced in the carrier absorption band by the vibronic transitions both for Rabi and Ramsey schemes. This shift is shown to be independent of the initial vibrational state.Comment: 9 pages, 6 figure

Time-resolved X-Shooter spectra and RXTE light curves of the ultra-compact X-ray binary candidate 4U 0614+091

In this paper we present X-Shooter time resolved spectroscopy and RXTE PCA light curves of the ultra-compact X-ray binary candidate 4U 0614+091. The X-Shooter data are compared to the GMOS data analyzed previously by Nelemans et al. (2004). We confirm the presence of C III and O II emission features at ~ 4650 {\AA} and ~ 5000 {\AA}. The emission lines do not show evident Doppler shifts that could be attributed to the motion of the donor star/hot spot around the center of mass of the binary. We note a weak periodic signal in the red-wing/blue-wing flux ratio of the emission feature at ~ 4650 {\AA}. The signal occurs at P = 30.23 +/- 0.03 min in the X-Shooter and at P = 30.468 +/- 0.006 min in the GMOS spectra when the source was in the low/hard state. Due to aliasing effects the period in the GMOS and X-Shooter data could well be the same. We deem it likely that the orbital period is thus close to 30 min, however, as several photometric periods have been reported for this source in the literature already, further confirmation of the 30 min period is warranted. We compare the surface area of the donor star and the disc of 4U 0614+091 with the surface area of the donor star and the disc in typical hydrogen-rich low-mass X-ray binaries and the class of AM Canum Venaticorum stars and argue that the optical emission in 4U 0614+091 is likely dominated by the disc emission. Additionally, we search for periodic signals in all the publicly available RXTE PCA light curves of 4U 0614+091 which could be associated with the orbital period of this source. A modulation at the orbital period with an amplitude of ~ 10% such as those that have been found in other ultra-compact X-ray binaries (4U 0513-40, 4U 1820-30) is not present in 4U 0614+091.Comment: Accepted for publication in MNRAS, 11 pages, 7 figure

Atomic Spectral Features During Thermonuclear Flashes on Neutron Stars

The gravitational redshift measured by Cottam, Paerels and Mendez for the neutron star (NS) in the low-mass X-ray binary EXO 0748-676 depends on the identification of an absorption line during a type I burst as the H$\alpha$ line from hydrogenic Fe. We show that Fe is present above the photosphere as long as $\dot M>4\times 10^{-13}M_\odot {\rm yr^{-1}}$ during the burst. In this limit, the total Fe column is $N_{\rm Fe}\approx 3\times 10^{19}{\rm cm^{-2}}$ for incident material of solar abundances and only depends on the nuclear physics of the proton spallation. The Fe destruction creates many heavy elements with $Z<26$ which may imprint photo-ionization edges on the NS spectra during a radius expansion event or in a burst cooling tail. Detecting these features in concert with those from Fe would confirm a redshift measurement. We also begin to address the radiative transfer problem, and find that a concentrated Fe layer with $kT=1.2-1.4 {\rm keV}$ and column $N_{\rm Fe}= 7-20 \times 10^{20} {\rm cm}^{-2}$ (depending on the line depth) above the hotter continuum photosphere is required to create the H$\alpha$ line of the observed strength. This estimate must be refined by considerations of non-LTE effects as well as resonant line transport. Until these are carried out, we cannot say whether the Fe column from accretion and spallation is in conflict with the observations. We also show that hydrogenic Fe might remain in the photosphere due to radiative levitation from the high burst flux.Comment: Substantially revised version, to appear in Ap J Letter

Reactivity difference between protolytic forms of some macrocyclic chromium(III) complexes in ligand substitution and electron transfer processes

The review provides insight into the mechanism of ligand substitution and electron transfer (from chromium( III) to iron(III)) by comparison of the reactivity of some tetraazamacrocyclic chromium(III) complexes in the conjugate acid-base forms. Use of two geometrical isomers made possible to estimate the influence of geometry and protolytic reactions in trans and cis position towards the leaving group on the rate enhancement. Studies on the reaction rates in different media demonstrated the role played by outer sphere interactions in a monodentate ligand substitution

The characterisation of the microstructure and mechanical properties of diamond - like carbon (DLC) for endoprosthesis

The paper presents the results of research of DLC coating of a - C:H type obtained by using a technique of physical vapor deposition (PVD) on the surface of CoCrMo alloy, commonly used for the elements of the endoprosthesis. The surface has been observed using a scanning electron microscope (SEM). Analysis of the chemical composition and distribution of the different elements were performed using glow discharge optical emission spectrometry analysis (GDOES). It has been shown that the DLC elements are characterized by high hardness and good adhesion to the substrate

The characterisation of pure titanium for biomedical applications

The paper presents results of research on the use of pure titanium medical implants, dental and orthopedics – as pins hip replacements. The properties of metal biomaterials, including their hardness, determine the usefulness of the material and are one of the criteria for its use. They depend on their chemical composition and structure. Studies included the observation of the microstructure and mechanical properties of pure titanium. The observations surface were carried out using a scanning electron microscope SEM. The optical profiler was used to depict the geometric structure of the surface, and to carry out the nanoindentation tests a nano hardness tester was used