Pulsation Phase Research Articles

High-resolution spectroscopy for Cepheids distance determination

Context. In recent years, infrared interferometry has revealed the presence of faint dusty circumstellar envelopes (CSE) around Cepheids. However the size, shape, chemical nature, and the interaction of the CSE with the star itself are still under investigation. The presence of a CSE might have an effect on the angular diameter estimates used in the interferometric Baade-Wesselink and surface-brightness methods of determining the distance of Cepheids. Aims. By studying Hα profiles as a function of the period, we investigate the permanent mass loss and the CSE around Cepheids. Our high spectral- and time-resolution data, combined with a very good S/N, will be useful in constraining future hydrodynamical models of Cepheids atmosphere and their close environment. Methods. We present HARPS �� high-resolution spectroscopy (R = 120 000) of eight galactic Cepheids: R Tra, S Cru, Y Sgr, β Dor, ζ Gem, RZ Vel, � Car, and RS Pup, providing a good period sampling (P = 3.39 d to P = 41.52 d). The Hα line profiles are described for all stars using a 2D (wavelength versus pulsation phase) representation. For each star, an average spectral line profile is derived, together with its first moment (γ-velocity) and its asymmetry (γ-asymmetry). Results. Short-period Cepheids show Hα line profiles following the pulsating envelope of the star, while long-period Cepheids show very complex line profiles and, in particular, large asymmetries. We find a new relationship between the period of Cepheids and their γ-velocities and -asymmetries. These results may be related to the dynamical structure of the atmosphere and to a permanent mass

Pulsation properties of the rapidly oscillating Ap star 10 Aquilae (HD 176232)

We have studied the pulsation behaviour of radial velocities of individual spectral lines of different chemical elements for the well known, bright rapidly oscillating Ap (roAp) star 10 Aql (HD 176232) based on high-quality Very Large Telescope spectra. We found that only lines of rare earth elements and the narrow Hα core show detectable rapid variations of radial velocity with the known photometric pulsation period, 11.7 min. The highest pulsation amplitudes of more than 0.5 km s−1 are found for rather weak lines of Tb iii and Dy iii. The pulsational phases obtained for lines of Tb iii and Dy iii differ by π rad, perhaps an indication of a radial node between their line-forming layers. Weak lines of Sm ii also display amplitudes near 0.5 km s−1. Surprisingly, the lines of Pr iii show the lowest detected pulsation amplitude in strong contrast with the majority of roAp stars for which this ion has some of the highest radial velocity amplitudes. Lines of Nd iii with different intensities have pulsation amplitudes different to the weaker lines that are formed more deeply in the atmosphere having higher amplitudes. Line bisectors for strong Nd iii line profiles show significant changes of phase, and even phase jumps for some lines, indicating complex variations in the pulsation phase as a function of atmospheric depth. The low-measured rotational velocity of this star indicates that there is little Doppler resolution of the line profiles, hence that the large range of pulsation amplitudes and phases of radial velocities determined for line bisectors are primarily caused by atmospheric depth effects.

Phase‐resolved Spectroscopy of the Vela Pulsar withXMM‐Newton

The ~104 yr old Vela Pulsar represents the bridge between the young Crab-like and the middle-aged rotation-powered pulsars. Its multiwavelength behavior is due to the superposition of different spectral components. We take advantage of the unprecedented harvest of photons collected by XMM-Newton to assess the Vela Pulsar spectral shape and to study the pulsar spectrum as a function of its rotational phase. As for the middle-aged pulsars Geminga, PSR B0656+14, and PSR B1055-52 (the ``Three Musketeers''), the phase-integrated spectrum of Vela is well described by a three-component model, consisting of two blackbodies (Tbb = [1.06 ± 0.03] × 106 K, Rbb = 5.1 km, TBB = 2.16 × 106 K, RBB = 0.73 km) plus a power law (γ = 2.2). The relative contributions of the three components are seen to vary as a function of the pulsar rotational phase. The two blackbodies have a shallow ~7%-9% modulation. The cooler blackbody, possibly related to the bulk of the neutron star surface, has a complex modulation, with two peaks per period, separated by ~0.35 in phase, the radio pulse occurring exactly in between. The hotter blackbody, possibly originating from a hot polar region, has a nearly sinusoidal modulation, with a single, broad maximum aligned with the second peak of the cooler blackbody, trailing the radio pulse by ~0.15 in phase. The nonthermal component, magnetospheric in origin, is present only during 20% of the pulsar phase and appears to be opposite to the radio pulse. XMM-Newton phase-resolved spectroscopy unveils the link between the thermally emitting surface of the neutron star and its charge-filled magnetosphere, probing emission geometry as a function of the pulsar rotation. This is a fundamental piece of information for future three-dimensional modeling of the pulsar magnetosphere.

The projection factor, period–radius relation, and surface–brightness colour relation in classical cepheids

Context. The projection factor (p -factor) is of crucial importance in linking radial velocity variations to radius variations in radially variable stars such as RR Lyrae of Cepheids. In turn, this is a crucial ingredient in the Baade-Wesselink method in obtaining distances to these stars using a surface–brightness (SB) colour relation.Aims. Our aim is to establish a relation between the p -factor and pulsation period based on six cepheids with interferometrically measured angular diameter variations and known distances. As a by-product, a period–radius (PR) relation is derived which in turn is used to derive the p -factor and distance for two stars. In addition, the data allows calibration of the SB colour relation.Methods. Literature values of the V -band, K -band and radial velocity curves are collected and fitted with Fourier series. For stars with known distances and measured angular diameters as a function of the pulsation phase, values for the radius and the p -factor can be obtained. A PR relation is derived based on five stars. For two cepheids, this PR relation is used to determine the radius and then solve for the p -factor and the distance. From the Fourier series, the V and K values at the times of the angular diameter measurements are derived, and the SB colour relation can be established. Allowance is made for the recent discovery of circumstellar material around some cepheids which influences both the derived angular diameters and the colours.Results. The PR relation derived is: log R = 0.686 log P + 1.134, slightly shallower than recently discussed PR-relations in the literature but in agreement with theory. Based on a total of eight stars with periods in the range 5–35 days there is no evidence that the p -factor depends on period, and the best-fitting constant value is p = 1.27 ± 0.05. The SB relation derived is log = 0.275 ()0 + 0.524, in excellent agreement with that derived by Kervella et al. (2004b, A&A, 428, 587).

Period–colour and amplitude–colour relations in classical Cepheid variables – V. The Small Magellanic Cloud Cepheid models

Period-colour (PC) and amplitude-colour (AC) relations at maximum, mean and minimum light are constructed from a large grid of full amplitude hydrodynamic models of Cepheids with a composition appropriate for the SMC (Small Magellanic Cloud). We compare these theoretical relations with those from observations. The theoretical relations are in general good agreement with their observational counterparts though there exist some discrepancy for short period (log [P] < 1) Cepheids. We outline a physical mechanism which can, in principle, be one factor to explain the observed PC/AC relations for the long and short period Cepheids in the Galaxy, LMC and SMC. Our explanation relies on the hydrogen ionization front-photosphere interaction and the way this interaction changes with pulsation period, pulsation phase and metallicity. Since the PC relation is connected with the period-luminosity (PL) relation, it is postulated that such a mechanism can also explain the observed properties of the PL relation in these three galaxies.

Pulsation in the presence of a strong magnetic field: the roAp star HD 166473★

Phase-resolved high-resolution, high signal-to-noise ratio (S/N) observations of the strongly magnetic roAp star HD 166473 are analysed. HD 166473 was selected as the target of this study because it has one of the strongest magnetic fields of all the roAp stars known with resolved magnetically split lines. Indeed, we show that enhanced pulsation diagnosis can be achieved from consideration of the different pulsation behaviour of the π and a Zeeman components of the resolved spectral lines. This study is based on a time-series of high spectral resolution observations obtained with the Ultraviolet and Visual Echelle Spectrograph of the Very Large Telescope of the European Southern Observatory. Radial velocity variations due to pulsation are observed in rare earth lines, with amplitudes up to 110 m -1 . The variations occur with three frequencies, already detected in photometry, but which can in this work be determined with better precision: 1.833, 1.886 and 1.928 mHz. The pulsation amplitudes and phases observed in the rare earth element lines vary with atmospheric height, as is the case in other roAp stars studied in detail. Lines of Fe and of other (mostly non-rare earth) elements do not show any variation to very high precision (1.5 m s -1 in the case of Fe). The low amplitudes of the observed variations do not allow the original goal of studying differences between the behaviour of the resolved Zeeman line components to be reached; the S/N achieved in the radial velocity determinations is insufficient to establish definitely the possible existence of such differences. Yet the analysis provides a tantalizing hint at the occurrence of variations of the mean magnetic field modulus with the pulsation frequency, with an amplitude of 21 ± 5 G.

Abundances in intermediate-mass AGB stars undergoing third dredge-up and hot-bottom burning

High-dispersion near-infrared spectra have been taken of seven highly evolved, variable, intermediate-mass (4-6 M ⊙ ) asymptotic giant branch (AGB) stars in the Large Magellanic Cloud and Small Magellanic Cloud in order to look for C, N and O variations that are expected to arise from third dredge-up and hot-bottom burning. The pulsation of the objects has been modelled, yielding stellar masses, and spectral synthesis calculations have been performed in order to derive abundances from the observed spectra. For two stars, abundances of C, N, O, Na, Al, Ti, Sc and Fe were derived and compared with the abundances predicted by detailed AGB models. Both stars show very large N enhancements and C deficiencies. These results provide the first observational confirmation of the long-predicted production of primary nitrogen by the combination of third dredge-up and hot-bottom burning in intermediate-mass AGB stars. It was not possible to derive abundances for the remaining five stars: three were too cool to model, while another two had strong shocks in their atmospheres which caused strong emission to fill the line cores and made abundance determination impossible. The latter occurrence allows us to predict the pulsation phase interval during which observations should be made if successful abundance analysis is to be possible.

Vertical structure of pulsations in roAp stars

Inhalt (u.a.): M. BREGER: Delta Scuti stars: Observational aspects; M.S. Cunha: Theory of rapidly oscillating Ap stars; M. SACHKOV et al.: Vertical structure of pulsations in roAp stars; G. HOUDEK: Theoretical asteroseismology of solar-like oscillations; B.L. POPIELSKI: Core modes as a seismic probe of mixing beyond the convective core; M. GODART: Temperature gradients in the core overshooting region; W.A. DZIEMBOWSKI – J. DASZYŃSKA-DASZKIEWICZ – A.A. PAMYATNYKH: Interpretation of the Be star HD 163868 oscillation spectrum based on the MOST observations; D. KILKENNY: Pulsating Hot Subdwarfs – An Observational Review; M.H. MONTGOMERY: Mapping Convection using Pulsating White Dwarf Stars; M. ROTH: The Network Activities in HELAS; I. KUDZEJ et al.: A New Slovak Observatory 500 km from Vienna; W.W. WEISS: Microsatellites; G. KOPACKI – S. FRANDSEN: RR Lyrae stars in M4

Exploration of the \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $P_{s}$ \end{document} ‐ \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $P_{\mathrm{orb}\,}$ \end{document} Relation for Wind‐fed X‐Ray Pulsars

We have investigated the relation between the orbital periods (Porb) and the spin periods (Ps) of wind-fed X-ray pulsars in high-mass X-ray binaries (HMXBs), based on population synthesis calculations of the spin evolution of neutron stars during the pre-HMXB stage. We show that most neutron stars either have steady accretion or still reside in the radio pulsar phase when the donor star starts to evolve off the main sequence. In the former case, the spin period can be decelerated to ~102-103 s, depending on the value of Porb. We briefly discuss possible origins of the Ps-Porb correlation in Be/X-ray binaries and the existence of HMXBs with main-sequence donors. We also investigate the evolution of the inclination angle between the magnetic and spin axes of neutron stars in a massive binary, suggesting secular alignment of the magnetic and spin axes during their evolution.

Algorithm of Ensemble Pulsar Time

An algorithm of the ensemble pulsar time based on the Wiener filtration method has been constructed. This algorithm has allowed the separation of the contributions of an atomic clock and a pulsar itself to the post-fit pulsar timing residuals. The method has been applied to the timing data of the millisecond pulsars PSR B1855+09 and PSR B1937+21 and allowed to filter out the atomic scale component from the pulsar phase variations. Direct comparison of the terrestrial time TT(BIPM96) and the ensemble pulsar time PTens has displayed that the difference TT(BIPM96) – PTens is within ±0.4 μs range. A new limit of gravitational wave background based on the difference TT(BIPM96) – PTens was established to be Ωgh2~10−10.

Further VLBA observations of SiO masers toward Mira variable stars

We present the results of continued monitoring of the SiO masers at 7 mm wavelength in several of the Mira variable stars reported in Cotton et al. (2004, A&A, 414, 275) (o Ceti = Mira, U Orionis = U Ori, R Aquarii = R Aqr) over a period of 16 months, extending the observations to several pulsation cycles. The observed size of the maser rings varied by 3–14% with time but show no clear correlation with pulsation phase. In all cases, the SiO masers appear just outside the dense molecular layer indicated by near-IR observations. Rotation (or large scale motion) is possibly detected in o Ceti with a period of 89 × sin(i) years. We find linear polarization up to ∼60% and at several epochs predominantly tangentially ordered polarization vectors indicate a radial magnetic field direction. Jet-like features are examined in o Ceti and R Aqr and in both cases, the magnetic field appears elongated with the masing structure. This suggests that the dynamic feature in the envelope is dragging the magnetic field or that the gas is constrained to follow magnetic field.

Extraction of Caprolactam with Toluene in a Pulsed Disc and Doughnut Column—Part II: Experimental Evaluation of the Hydraulic Characteristics

In Part I of this study a theoretical model was recommended describing the hydraulic characteristics, being Sauter drop diameter, hold‐up, operating regimes, and operational window, of caprolactam extraction in a pulsed disc and doughnut column. In order to confirm the theoretical model pilot plant experiments for the caprolactam forward and back‐extraction were performed to determine the hydraulic characteristics as a function of the operating conditions. The experimental conditions covered the industrial operating range. All hydraulic experiments were performed at equilibrium conditions in order to avoid the influence of mass transfer. In the determination of the operational window flooding because of too low pulsation was qualitatively observed, while it was found that at high pulsation phase inversion was limiting for the back‐extraction process and flooding for the forward extraction process. Application of the in Part I recommended theoretical model for the description of the obtained hydraulic data resulted in an accurate description after fitting the drop diameter, hold‐up, and phase inversion data.

Time Monitoring Observations of SiO J = 2–1 and J = 3–2 Maser Emission toward Late‐Type Stars

We present the results of simultaneous time monitoring observations of SiO J = 2-1 and J = 3-2 maser emission for 10 late-type stars (8 Mira variables, 1 OH/IR star, and 1 supergiant) with the 14 m radio telescope at Taeduk Radio Astronomy Observatory from 1999 January to 2001 February. The SiO v = 1, J = 2-1 and J = 3-2 maser emission was detected at almost all observational epochs. The SiO v = 2, J = 2-1 maser was detected from 4 late-type stars (VY CMa, R Cas, χ Cyg, R Leo) and the v = 2, J = 3-2 maser was detected from 7 stars (R Aqr, TX Cam, R Cas, χ Cyg, W Hya, R Leo, IK Tau). The v = 3, J = 2-1 and J = 3-2 masers were also detected from χ Cyg and TX Cam, respectively. Based on these observational data, line profile and peak velocity variations with respect to stellar velocity, antenna temperatures, and their ratio variations as a function of optical phase of central star were investigated. As main results, the line profile and the peak velocity variation of the v = 1, J = 3-2 maser with pulsation phase was found to differ from the v = 1, J = 2-1 transition. Similarly, the J = 2-1 and J = 3-2 transitions also differ between rovibrational transitions at a given pulsation phase. However, it is difficult to find significant correlations between the peak velocity variation relative to the stellar velocity of either the J = 3-2 or J = 2-1 transitions over pulsation phase, due to limited time sampling in these data. The peak and integrated antenna temperature (PT and IT) ratios among rotational ladders and vibrational states are investigated. These ratios between rotational ladders of the v = 1, J = 2-1, and J = 3-2 masers are averaged to be the peak antenna temperature ratio, PT(v = 1, J = 3-2)/PT(v = 1, J = 2-1) ≈ 0.29, and the integrated antenna temperature ratio, IT(v = 1, J = 3-2)/IT(v = 1, J = 2-1) ≈ 0.21, respectively. In the v = 2 state, these ratios are PT(v = 2, J = 3-2)/PT(v = 2, J = 2-1) ≈ 7.94 and IT(v = 2, J = 3-2)/IT(v = 2, J = 2-1) ≈ 8.50, respectively. The peak and integrated antenna temperature ratios between vibrational states are also averaged to be PT(v = 2, J = 3-2)/PT(v = 1, J = 3-2) ≈ 1.29, IT(v = 2, J = 3-2)/IT(v = 1, J = 3-2) ≈ 1.02, PT(v = 2, J = 2-1)/PT(v = 1, J = 2-1) ≈ 0.06, and IT(v = 2, J = 2-1)/IT(v = 1, J = 2-1) ≈ 0.05, respectively. These intensity ratios for the v = 2, J = 2-1 and v = 2, J = 3-2 masers suggest that line overlaps operating in the v = 2, J = 2-1 transition do not similarly affect the v = 2, J = 3-2 transition.

The discovery of a new type of upper atmospheric variability in the rapidly oscillating Ap stars with VLT high-resolution spectroscopy★

In a high-resolution spectroscopic survey of rapidly oscillating Ap (roAp) stars with the Ultraviolet and Visual Echelle Spectrograph on the Very Large Telescope of the European Southern Observatory, we find that almost all stars show significant variation of the radial velocity amplitudes - on a time-scale of a few pulsation cycles - for lines of the rare earth ion Pr III and in the core of the Ha line. These variations in the radial velocity amplitudes are described by new frequencies in the amplitude spectra that are not seen in broad-band photometric studies of the same stars. The Pr III lines form high in the atmosphere of these stars at continuum optical depths of log τ 5000 < -5 and tend to be concentrated towards the magnetic poles in many stars, and the core of the Ha line forms at continuum optical depths -5 ≤ log τ 5000 ≤ -2, whereas the photometry samples the atmosphere on average at continuum optical depths closer to log τ 5000 = 0 and averages over the visible hemisphere of the star. Therefore, there are three possible explanations for the newly discovered frequencies: (1) there are modes with nodes near to the level where the photometry samples that can be easily detected at the higher level of formation of the Pr III lines; or (2) there are higher degree, l, non-radial oblique pulsation modes that are detectable in the spectroscopy because the Pr III is concentrated towards the magnetic poles where such modes have their highest amplitudes, but average out over the visible hemisphere in the photometry which samples the star's surface more uniformly; or (3) there is significant growth and decay of the principal mode amplitudes on a time-scale of just a few pulsation cycles at the high level of formation of the Pr III lines and core of the Ha line. The third hypothesis implies that this level is within the magneto-acoustic boundary layer where energy is being dissipated by both outward acoustic running waves and inward magnetic slow waves. We suggest observations that can distinguish among these three possibilities. We propose that strong changes in pulsation phase seen with atmospheric height in roAp stars, in some cases more than n rad from the top to the bottom of a single spectral line, strongly affect the pulsation phases seen in photometry in various bandpasses which explains why phase differences between bandpasses for roAp stars have never been explicable with standard theories that assume single spherical harmonics within the observable atmosphere. We also discuss the photometric amplitude variations as a function of bandpass, and suggest that these are primarily caused by continuum variations, rather than by variability in the rare earth element lines. We propose further tests of this suggestion.

Period–colour and amplitude–colour relations in classical Cepheid variables – IV. The multiphase relations

Abstract The superb phase resolution and quality of the Optical Gravitational Lensing Experiment (OGLE) data on the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) Cepheids, together with existing data on Galactic Cepheids, are combined to study the period–colour (PC) and amplitude–colour (AC) relations as a function of pulsation phase. Our results confirm earlier work that the LMC PC relation (at mean light) is more consistent with two lines of differing slopes, separated at a period of 10 d. However, our multiphase PC relations reveal much new structure which can potentially increase our understanding of Cepheid variables. These multiphase PC relations provide insight into why the Galactic PC relation is linear but the LMC PC relation is non-linear. This is because the LMC PC relation is shallower for short (log P &amp;lt; 1) and steeper for long (log P &amp;gt; 1) period Cepheids than the corresponding Galactic PC relation. Both of the short- and long-period Cepheids in all three galaxies exhibit the steepest and shallowest slopes at phases around 0.75–0.85, respectively. A consequence is that the PC relation at phase ∼ 0.8 is highly non-linear. Further, the Galactic and LMC Cepheids with log P &amp;gt; 1 display a flat slope in the PC plane at phases close to the maximum light. When the LMC period–luminosity (PL) relation is studied as a function of phase, we confirm that it changes with the PC relation. The LMC PL relation in V and I band near the phase of 0.8 provides compelling evidence that this relation is also consistent with two lines of differing slopes joined at a period close to 10 d.

Convective heat transfer characteristics from combined mechanical and supply pulsed radial reattaching jets

The heat transfer characteristics of combined mechanically and supply pulsated radial reattaching jets, CPRJR, were documented as a function of nozzle exit angle (0° and 20°), non-dimensional gap height (0.05 and 0.13), non-dimensional flow guide height (0.8 and 1.16), mechanical pulsation rate (5 and 10 Hz), mechanical to supply pulsation rate (1:1, 1:2, 1:3, and 1:4), phase angle (0° and 180°), and Reynolds number (1683 and 2366). Air was forced through a supply pulsation mechanism and then through a pulsated nozzle diverter apparatus. The air impinged on a heated plate where instantaneous heat flux and surface temperature measurements were collected and analyzed on instantaneous, ensemble-averaged, and area-averaged bases. CPRJR heat transfer can be characterized as a frequency interference of mechanical and supply pulsation effects. Significant improvement, up to 72%, over the corresponding mechanical pulsation case was found to occur for a supply-to-mechanical ratio of 3:1 with a phase angle of 0°. In general, the increased heat transfer rates were associated with the an increase in surface-directed momentum caused by increased cycle “on” mass flow rate and corresponding entrainment.

Amplitude and phase of cerebrospinal fluid pulsations: experimental studies and review of the literature

A recently developed model of communicating hydrocephalus suggests that ventricular dilation may be related to the redistribution of pulsations in the cranium from the subarachnoid spaces (SASs) into the ventricles. Based on this model, the authors have developed a method for analyzing flow pulsatility in the brain by using the ratio of aqueductal to cervical subarachnoid stroke volume and the phase of cerebrospinal fluid (CSF) flow, which is obtained at multiple locations throughout the cranium, relative to the phase of arterial flow. Flow data were collected in a group of 15 healthy volunteers by using a series of images acquired with cardiac-gated, phase-contrast magnetic resonance imaging. The stroke volume ratio was 5.1 +/- 1.8% (mean +/- standard deviation). The phase lag in the aqueduct was -52.5 +/-16.5 degrees and the phase lag in the prepontine cistern was -22.1 +/- 8.2 degrees. The flow phase at the level of C-2 was -5.1 +/- 10.5 degrees, which was consistent with flow synchronous with the arterial pulse. The subarachnoid phase lag ventral to the pons was shown to decrease progressively to zero at the craniocervical junction. Flow in the posterior cervical SAS preceded the anterior space flow. Under normal conditions, pulsatile ventricular CSF flow is a small fraction of the net pulsatile CSF flow in the cranium. A thorough review of the literature supports the view that modified intracranial compliance can lead to redistribution of pulsations and increased intraventricular pulsations. The phase of CSF flow may also reflect the local and global compliance of the brain.

Study of the cyclotron feature in MXB 0656-072

We have monitored a type II outburst of the Be/X-ray binary MXB 0656-072 in a series of pointed RXTE observations during October through December 2003. The source spectrum shows a cyclotron resonance scattering feature at 32.8(-0.4)(+0.5) keV, corresponding to a magnetic field strength of 3.67(-0.04)(+ 0.06) x 10(12) G and is stable through the outburst and over the pulsar spin phase. The pulsar, with an average pulse period of 160.4 +/- 0.4 s, shows a spin-up of 0.45 s over the duration of the outburst. From optical data, the source distance is estimated to be 3.9 +/- 0.1 kpc and this is used to estimate the X-ray luminosity and a theoretical prediction of the pulsar spin-up during the outburst.

On the Spectroscopic Determination of Atmospheric Parameters and O/Fe Abundances of RR Lyrae Stars

Abstract In order to study how the conventional spectroscopic method based on the equivalent widths of the Fe I and Fe II lines effectively applies to determining the atmospheric parameters ($T_{\mathrm{eff}}, \log g, v_{\mathrm{t}}, [\mathrm{Fe/H}]$) of RR Lyrae variables and how accurately the abundances can be established from such constructed model atmospheres, we analyzed 15 high-dispersion spectrograms of RR Lyr, DX Del, DH Peg, and VY Ser taken at several different phases by using the HDS spectrograph of the Subaru Telescope, and examined the consistency of the resulting phase-to-phase abundances. Taking oxygen as the target element along with Fe, we determined its non-LTE abundance from the O I 6155–8 and 7771–5 triplets. It was found that consistent abundances were obtained for O as well as Fe to a level of $\sim 0.1 \,\mathrm{dex}$, irrespective of the pulsation phase, except for the special near-maximum high-temperature phase. This suggests that classical model atmospheres are reliably applicable to abundance determinations of RR Lyrae stars in most cases. While the oxygen abundances derived from O I 7771–5 well correlate with those from O I 6155–8, the former tends to be systematically larger by 0.1–0.2 dex than the latter, which may be interpreted as being due to the depth-dependence of the microturbulence increasing with height; i.e., the $v_{\mathrm{t}}$ value derived from deep-forming Fe lines of weak/medium-strength may not be simply applied to higher forming strong lines, such as O I 7771–5.

Mechanics of growth pulsations as the basis of growth and morphogenesis in colonial hydroids

Growth and shaping in colonial hydroids (Hydrozoa, Cnidaria) are realized due to the functioning of special colony elements, growing tips located at the terminuses of branched colony body. Unlike in plants, the growing tips of colonial hydroids are sites of active cell movements related to morphogenesis and lacking proliferation. The activity of hydroid growing tips is expressed as growth pulsations: cyclic repetitions of their apex extensions and retractions. The parameters of growth pulsations are species specific and related to the shape of a forming element. Here, the succession of cell movements and changes in mutual arrangement within the growing tip are described in detail at all pulsation phases. The role of the inner cell layer in the tip activity was demonstrated for the first time. Relationships between the growing tip parameters, length and diameter, and pulsations are discussed. A scheme is proposed for cyclic processes in both epithelial layers. An explanation is provided for the two-step mode of growth pulsations with relative independence of the main phases. It was proposed that successive activities of the tip ecto- and endoderm serve as driving forces provided there is a hard outer skeleton. This scheme makes it possible to explain some patterns of growth and morphogenesis in colonial hydroids, such as gradually increasing growth rate of a new tip and its maximum growth rate, differences in the parameters of growth pulsations between shoot and stolon tips, shoot base inclination towards the stolon tip, etc., and provides a basis for further improvement of the model of morphogenesis in hydroids.