Pulsation Period Research Articles

Revisiting the Magnetic Field Distribution of Normal Pulsars: Implications for the Multiple Origins for Neutron Stars

In this study, we revisit the magnetic field (B-field) distribution of normal pulsars, motivated by the fact that the number of known pulsars has exceeded 3300. Here, we divided the normal pulsar samples into three subgroups by constant lines of characteristic age τ ch, i.e., young, middle-aged, and old pulsars. We note that τ ch is not used as the time indicator in this study; instead, it just served as cutting lines to divide the pulsar samples. Then, we applied several statistical tests, i.e., the Anderson–Darling, Shapiro–Wilk, Kolmogorov–Smirnov, and Mann–Whitney–Wilcoxon tests, to the selected normal pulsar samples (N = 1970) and to a data set of 32 neutron stars (NSs) in high-mass X-ray binaries (HMXBs) for comparison purposes. We obtained that (i) the conclusion on the characteristic B field (B ch) log-normal distribution for the normal pulsars by the previous studies is no longer appropriate, while only young pulsars (N = 24, τ ch < 15 kyr) follow a log-normal distribution, indicating that only the B ch of young pulsars is close to real B fields. (ii) In the directly measured B-field range of NS-HMXBs (∼1012–1013 G), the B ch of young pulsars (N = 15) and the real B fields of NS-HMXBs (N = 32) are inferred to be log-normal, and they are further verified to come from the same distribution, implying that there is no significant decay for real B fields, at least within the timescale of ∼10 Myr for normal pulsars. (iii) Statistically, young pulsars (N = 24) are inferred to be self-contained, suggesting that the initial spin period of pulsars is less than 515 ms. (iv) The B ch distributions of three normal pulsar subsamples are different, hinting at the existence of multiple origins for NSs.

Variability in Protoplanetary Nebulae. IX. Evidence for Evolution in a Decade

We have carried out a new photometric V,R C study of 12 protoplanetary nebulae, objects in the short-lived transition between the asymptotic giant branch and planetary nebula phases of stellar evolution. These had been the subjects of an earlier study, using data from 1994−2007, that found that all 12 varied periodically, with pulsation periods in the range of ∼38 to ∼150 days. They are all carbon-rich, with F−G spectral types. We combined our new (2008–2018) data with publicly available All-Sky Automated Survey for Supernovae data and determined new periods for their variability. The older and newer period values were compared to investigate evidence of period change, for which there is theoretical support that it might be detectable in a decade or two in some cases. Such a detection is challenging since the light curves are complicated, with multiple periods, changing amplitudes, and evidence of shocks. Nevertheless, we found one, and possibly two, such cases, which are associated with the higher-temperature stars in the sample (7250 and 8000 K). These results are most consistent with the evolution of stars at the lower end of the mass range of carbon stars, ∼1.5–2 M ☉. Several of the stars show longer-term trends of increasing (six cases) or decreasing (one case) brightness, which we think is most likely due to changes in the circumstellar dust opacity. There is one case of a possible ∼1.8 yr period in addition to the shorter pulsation. This is interpreted as possible evidence of an orbiting companion.

Pressure field characteristics of underwater detonation gas jet below and above free water surface

An underwater detonation tube (DT) experiment is carried out to investigate the pressure field characteristics of the detonation gas jet propagating under and above a free surface. In the experiment, a 0.78 L DT filled with 0.12 MPa methane-oxygen mixture is detonated. The evolution of jet shape and pressure field are recorded using high-speed photography, pressure sensors, hydrophones and microphones. There are mainly three bubble pulsation periods determined from the bubble evolution and field pressure evolution, and the bubble shape tends to be stable after the pulsation ends. The fast Fourier Transform and Wavelet Transform method are adopted to analyze the frequency characteristics and energy distribution of the pressure signals. The energy of the bubble pulsation and the energy of the shock wave have different contributions in different media. Specifically, the high-frequency energy formed by reverberation contributes more in water, while the low-frequency energy formed by bubble pulsation is the main part of the energy in the air. The shock wave formed by the decoupling of the detonation wave attenuates sharply during its propagation. The distribution characteristics of the detonation acoustic signal in the air are analyzed using the band-pass filter pair, and the transmission coefficient is defined to study the ability of the detonation acoustic signal to transmit through the water–air interface. The result indicates that the low-frequency signals, such as bubble pulsations, can transmit out of the water–air interface at a larger transmission angle more easily than the high-frequency signals. The signal of bubble pulsation has a stronger transmission ability through the water–air interface compared to the shock wave. Combining the bubble evolution and pressure evolution is helpful to analyze the different signal components in the water and air, which plays an important role in the analysis of the pressure field characteristics.

Analysis of the axial force distribution characteristics of multistage pumps and its correlation with hydraulic property

As the centrifugal pump is running, the fluid usually flows into the impeller along pump shaft, and the fluid flows out radially by the force of the impeller. The force is mutual, so the impeller is also subjected to the reaction force of the fluid, but the distribution of this force on the blades is uneven. In addition, the front and rear shrouds of the impeller are asymmetric, which are the main causes of axial force. This paper adopts numerical calculation method studying the mechanism of axial force of impeller at all stages of multistage pump at various working conditions, and exploring the formation mechanism of shroud pressure differential force and blade twisting axial force and its variation laws of similarities and differences, analyzing the steady state and transient characteristics between axial force and hydraulic property of double-casing multistage pump. The results show that the rotational angular velocity of the fluid in the front and rear pump chamber at each stage impeller is distributed along the axial direction in three regions, the regions are pump body boundary layer, core region, and impeller boundary layer. The working surface and back surface of the blade twist have the high and low axial force area, and its distribution is staggered, at the same number of stages, the greater the flow rate, the smaller the blade twisting axial force. The shroud pressure differential force with the increase of impeller stages presents a linear increasing trend, conforms to the principle of linear superposition of cover pressure differential force. The total axial force pulsation of multi-stage pump is related to the number of secondary impeller blades, its primary frequency coincides with the secondary impeller blade frequency, increasing the flow rate can reduce the multi-stage pump axial force pulsation amplitude. The pulsation period of single-stage impeller head and efficiency are related to the number of impeller blades, the smaller the number of impeller stages, the stronger the pressure dynamic, and static interference effect of the impeller inlet and outlet. Rotation of the secondary impeller causes dynamic and static interference, which is the main reason for the pulsation of the axial force coefficient in double-casing multistage pumps, the pulsation intensity is related to the periodic generation and shedding of the blade vortex. The results of the study can be used as a reference for optimizing the axial force of double-casing multistage pumps.

The Nature of Anomalous Period Increase in the Pulsating Variable V725 Sgr

The evolutionary tracks of stars with masses on the main sequence $$0.84\;M_{\odot}\leq M_{\textrm{ZAMS}}\leq 0.95\;M_{\odot}$$ and initial metal abundances $$Z=0.006$$ and $$0.01$$ were computed under various assumptions about the mass loss rate at the red giant stage as well as at the AGB and the post-AGB stages. Among 160 evolutionary sequences we selected nearly 30 sequences where the final thermal flash of the helium shell source occurs in the early post-AGB stage when the ratio of the hydrogen envelope mass to the stellar mass ranges from 0.01 to 0.08. Selected evolutionary sequences were used for calculation of initial and inner boundary conditions used in solution of the equations of radiation hydrodynamics and turbulent convection describing evolution of stellar pulsations after the helium flash. Among about three dozen hydrodynamic models we found the three ones demonstrating almost eightfold increase of the pulsation period observed in V725 Sgr during the last century as well as the gradual transformation of fairly regular pulsations with period $$\Pi\approx 12$$ day to semi–regular non-linear oscillations with period $$80\lesssim\Pi\lesssim 90\text{ day}$$ . We conclude that the anomalous growth of the pulsation period in V725 Sgr is due to the final thermal flash of the helium shell source that occurred in the early post-AGB star with mass $$M\approx 0.53\;M_{\odot}$$ and the mass of the hydrogen envelope ranging from $$0.013$$ to $$0.019\;M_{\odot}$$ .

An 18.9 min blue large-amplitude pulsator crossing the ‘Hertzsprung gap’ of hot subdwarfs

Blue large-amplitude pulsators (BLAPs) represent a new and rare class of hot pulsating stars with unusually large amplitudes and short periods. Up to now, only 24 confirmed BLAPs have been identified from more than one billion monitored stars, including a group with pulsation period longer than $\sim 20$ min (classical BLAPs, hereafter) and the other group with pulsation period below $\sim 8$ min. The evolutionary path that could give rise to such kinds of stellar configurations is unclear. Here we report on a comprehensive study of the peculiar BLAP discovered by the Tsinghua University - Ma Huateng Telescopes for Survey (TMTS), TMTS J035143.63+584504.2 (TMTS-BLAP-1). This new BLAP has an 18.9 min pulsation period and is similar to the BLAPs with a low surface gravity and an extended helium-enriched envelope, suggesting that it is a low-gravity BLAP at the shortest-period end. In particular, the long-term monitoring data reveal that this pulsating star has an unusually large rate of period change, P_dot/P=2.2e-6/yr. Such a significant and positive value challenges its origins from both helium-core pre-white-dwarfs and core helium-burning subdwarfs, but is consistent with that derived from shell helium-burning subdwarfs. The particular pulsation period and unusual rate of period change indicate that TMTS-BLAP-1 is at a short-lived (~10^6 yr) phase of shell-helium ignition before the stable shell-helium burning; in other words, TMTS-BLAP-1 is going through a "Hertzsprung gap" of hot subdwarfs.

RRab variables with identical light-curve shapes at different pulsation periods

ABSTRACT In this paper, we report on the detection of RRab stars with quasi-identical-shape light curves but period differences as large as 0.05–0.21 d using the Galactic bulge data of the OGLE-IV survey. We have examined stars with shorter periods than the Oosterhoff I ridge of the bulge. These stars generally have smaller amplitudes and larger Fourier phase-differences than the typical bulge RRab stars have at the same period. Many of these ‘anomalous’ stars have good-quality light curves without any sign of the Blazhko modulation. Examining their Fourier parameters revealed that several of these stars show very similar light curve to the typical bulge RR Lyrae. We found hundreds of quasi-identical-shape light-curve pairs with different periods between the ‘anomalous’- and the ‘normal’-position RRab stars based on the OGLE I-band data. The OGLE V-band, and the archive VVV and MACHO surveys Ks-, b- and r-band data of these stars were also checked for light-curve-shape similarity. Finally, 149 pairs with identical-shape light curves in each available photometric band were identified. Calculating the physical properties of the variables using empirical formulae, on average, −0.5 dex, −0.13 mag, 0.67, and 165 K differences between the [Fe/H], MV, R/R⊙, and Teff values of the members of the pairs are derived, being the short-period stars less metal-poor, fainter, smaller, and hotter than the long-period variables. To explain the existence of variables with different physical properties and pulsation periods but with identical-shape light curves is a challenging task for modelling.

Zwicky Transient Facility and Globular Clusters: The Period–Luminosity and Period–Wesenheit Relations for Type II Cepheids

We present the first gri-band period–luminosity (PL) and period–Wesenheit (PW) relations for 37 Type II Cepheids (TIICs) located in 18 globular clusters based on photometric data from the Zwicky Transient Facility. We also updated BVIJHK-band absolute magnitudes for 58 TIICs in 24 globular clusters using the latest homogeneous distances to the globular clusters. The slopes of g/r/i- and B/V/I-band PL relations are found to be statistically consistent when using the same sample of distance and reddening. We employed the calibration of ri-band PL/PW relations in globular clusters to estimate a distance to M31 based on a sample of ∼270 TIICs from the PAndromeda project. The distance modulus to M31, obtained using calibrated ri-band PW relation, agrees well with the recent determination based on classical Cepheids. However, distance moduli derived using the calibrated r- and i-band PL relations are systematically smaller by ∼0.2 mag, suggesting there are possible additional systematic errors on the PL relations. Finally, we also derive the period–color (PC) relations and for the first time the period–Q-index (PQ) relations, where the Q-index is reddening free, for our sample of TIICs. The PC relations based on (r − i) and near-infrared colors and the PQ relations are found to be relatively independent of the pulsation periods.

Feedback effects of pesticides flow atomization on the operating characteristics of pulsed engines

Traditional pulse-jet fogger have problems such as poor atomization or unstable operation. A pulse-jet fogger test device with an adjustable liquid flow rate was designed. Four experimental settings were used, no spraying and spraying with three liquid flow rates (11 L/h, 14 L/h, and 20 L/h). Pressure waveform in the combustion chamber and smoke inhalation depth tests showed following results: under different chemical fluid flow conditions, influences of the thermal atomization of the chemical liquid were observed in the pulse engine. Feedback effects were mainly changes in parameters and during each pulsation period, the turning time of the airflow in the pulse engine had different effects. The fuel consumption rate and pressure peak-to-peak value under 20 L/h chemical fluid flow were higher than other working conditions, and the positive and negative pressure amplitude fluctuated the least and had the best pressure stability. The 14 L/h chemical liquid flow demonstrated the worst stability, with the most significant fluctuations in pressure amplitude and large cyclical changes and poor consistency of the maximum depth of smoke inhalation in each cycle in the atomization section, with a high maximum relative difference of 34.6%, causing significant turbulence in the airflow oscillation system.

Chemical properties of the central part of the Galactic nuclear stellar disc. Abundances in four classical Cepheids revisited

ABSTRACT This paper is a revised abundance analysis of four yellow supergiant stars Cepheids which are located in the Galactic nucleus. The results are based on the spectra secured with the help of Subaru telescope, which are of the better quality comparing to previously analysed spectra taken with the Infrared Telescope Facility. A significantly improved method of the effective temperature determination of program stars, which is based on the calibrating relations between the temperature and line depth ratios, was applied. The present results confirmed our previous finding about the solar metallicity level at the Galaxy centre. It is very likely that the four stars of our program were born from an interstellar medium having homogeneous chemical properties, since all the stars are located close to each other, have close pulsation periods, and hence the age. However, one of the stars has a somewhat increased abundance of all studied elements compared to the abundance in the other three stars. A possible reason of this fact is discussed.

Ten-micron Emission in a Color–magnitude Diagram of M Giant Variables

Infrared color–magnitude diagrams are presented for variable M giants within the Two-Micron Sky Survey for which 10 μm dust emission was detected in IRAS low-resolution spectra. Dust emission is mostly limited to a definable region in absolute M Ks magnitude and (J − K s ) color, and to pulsation periods greater than 50 days.

XMM–Newton observations of PSR J0554+3107: pulsing thermal emission from a cooling high-mass neutron star

ABSTRACT XMM–Newton observations of the middle-aged radio-quiet γ-ray pulsar J0554+3107 allowed us, for the first time, firmly identify it in X-rays by detection of pulsations with the pulsar period. In the 0.2–2 keV band, the pulse profile shows two peaks separated by about a half of the rotation phase with the pulsed fraction of 25 ± 6 per cent. The profile and spectrum in this band can be mainly described by thermal emission from the neutron star with the hydrogen atmosphere, dipole magnetic field of ∼1013 G, and non-uniform surface temperature. Non-thermal emission from the pulsar magnetosphere is marginally detected at higher photon energies. The spectral fit with the atmosphere+power-law model implies that J0554+3107 is a rather heavy and cool neutron star with the mass of 1.6–2.1 M⊙, the radius of ≈13 km, and the redshifted effective temperature of ≈50 eV. The spectrum shows an absorption line of unknown nature at ≈350 eV. Given the extinction–distance relation, the pulsar is located at ≈2 kpc and has the redshifted bolometric thermal luminosity of ≈2 × 1032 erg s−1. We discuss cooling scenarios for J0554+3107 considering plausible equations of state of superdense matter inside the star, different compositions of the heat-blanketing envelope, and various ages.

Numerical investigation of pulsating flow structures and heat transfer enhancement performance in spherical corrugated helical tube

• Pulsating flow benefits heat transfer of helical tube with spherical corrugation. • Flow field and local heat transfer characteristic of a pulsating cycle are analyzed. • Optimum dimensionless pulsating frequency for thermal performance is Wo = 35. • Overall thermal performance parameter TP is in the range of 1.06–1.13. In this study, the innovative technology of a square wave pulsating flow combining with a spherical corrugated wall structure was applied in a helical tube to enhance heat transfer. Subsequently, the unsteady flow structure and heat transfer characteristics were numerically investigated. The accuracy of the numerical results was verified using experimental data and results in the open literature. For constant values of the geometrical parameters of the spherical corrugated helical tube, the effects of pulsating parameters on the heat transfer enhancement performance were explored, including dimensionless frequency ( Wo ) and dimensionless amplitude ( A ¯ ). The results indicated that the disturbance induced by the pulsating flow improved the local flow field inside the spherical corrugation. In addition, the intensity of the secondary flow and the turbulent kinetic energy of mainstream were simultaneously enhanced. Further, during more than 60% of one pulsation period, the average Nusselt number ( Nu m ) was noticeably greater than that in steady flow with the same average velocity. The maximum value of Nu m occurred at the end of the first half cycle and was increased by 38.5%. The optimum dimensionless pulsation frequency was Wo = 35 within the studied range. The Nusselt number and the friction factor increased with increase in the dimensionless amplitude. However, the comprehensive heat transfer enhancement performance was better under smaller A ¯ value. Furthermore, within the scope of the Dean number ( De ) De = 2936–4894, the overall thermal performance ( TP ) parameter was in the range of 1.06–1.13.

Long-period Pulsars as Possible Outcomes of Supernova Fallback Accretion

For about half a century, the radio pulsar population was observed to spin in the ∼0.002–12 s range, with different pulsar classes having a spin-period evolution that differs substantially depending on their magnetic fields or past accretion history. The recent detection of several slowly rotating pulsars has reopened the long-standing question of the exact physics, and observational biases, driving the upper bound of the period range of the pulsar population. In this work, we perform a parameter study of the spin-period evolution of pulsars interacting with supernova fallback matter and specifically look at the fallback accretion disk scenario. Depending on the initial conditions at formation, this evolution can differ substantially from the typical dipolar spin-down, resulting in pulsars that show spin periods longer than their coeval peers. By using general assumptions for the pulsar spin period and magnetic field at birth, initial fallback accretion rates, and including magnetic field decay, we find that very long spin periods (≳100 s) can be reached in the presence of strong, magnetar-like magnetic fields (≳1014 G) and moderate initial fallback accretion rates (∼1022−1027 g s−1). In addition, we study the cases of two recently discovered periodic radio sources, the pulsar PSR J0901–4046 (P = 75.9 s) and the radio transient GLEAM-X J162759.5–523504.3 (P = 1091 s), in light of our model. We conclude that the supernova fallback scenario could represent a viable channel to produce a population of long-period isolated pulsars that only recent observation campaigns are starting to unveil.

On Trapped Modes in Variable White Dwarfs as Probes of the 12C(α, γ)16O Reaction Rate

We seek signatures of the current experimental 12C reaction rate probability distribution function in the pulsation periods of carbon–oxygen white dwarf (WD) models. We find that adiabatic g-modes trapped by the interior carbon-rich layer offer potentially useful signatures of this reaction rate probability distribution function. Probing the carbon-rich region is relevant because it forms during the evolution of low-mass stars under radiative helium-burning conditions, mitigating the impact of convective mixing processes. We make direct quantitative connections between the pulsation periods of the identified trapped g-modes in variable WD models and the current experimental 12C reaction rate probability distribution function. We find an average spread in relative period shifts of ΔP/P ≃ ±2% for the identified trapped g-modes over the ±3σ uncertainty in the 12C reaction rate probability distribution function—across the effective temperature range of observed DAV and DBV WDs and for different WD masses, helium shell masses, and hydrogen shell masses. The g-mode pulsation periods of observed WDs are typically given to six to seven significant figures of precision. This suggests that an astrophysical constraint on the 12C reaction rate could, in principle, be extractable from the period spectrum of observed variable WDs.

Numerical study on heat transfer enhancement by viscoelastic fluid pulsating laminar flow in rectangular microchannel heat sinks

Efficient heat transfer technique at microscale is a long-term demand for development of microelectronic device. Simple-structured microchannel heat sinks (MHSs) have the advantages of easier fabrication processes and profound applicability, which are however limited by the laminar flow with lower heat transfer efficiency. Against this backdrop, a new type of heat transfer enhancement (HTE) techniques by viscoelastic fluid pulsating laminar flow (VPL flow) is proposed and evaluated from different aspects in this research. First of all, the effects of VPL flow on the thermal performance in a rectangular microchannel heat sink (RMHS) are numerically studied with the focus on the parametric effects on HTE. It indicates that the overall heat transfer performance can be significantly augmented by VPL flow and possesses an optimal enhancement under cases of exerted pulsation frequencies closed to the characteristic frequency of viscoelastic fluid flow. The characteristic frequency is determined from the Poiseuille start-up flow of the viscoelastic fluid flow and can be summarized by a power-law function with the relationship of Reynold number (Re) and Elasticity number (El). Moreover, the optimal HTE of RMHS increases with external pulsation amplitude and El but decreases with Re, which can also be summed up with them in a power-law function. Then, by analyzing of flow performance, the reversal flow and the resonance effects by VPL flow are regarded as the reasons for the HTE, which results from a balance between relaxation time of viscoelastic microstructures deformation and external pulsation period. Finally, the law of HTE by VPL flow is extended and verified in a carefully designed leaf-type microchannel heat sink (LMHS), suggesting a promising micro-scale heat transfer enhancement technology by VPL flow which however still needs further investigations on the optimal operating conditions in the future.

A computational conjugate heat transfer study of a rectangular minichannel undergoing sinusoidal flow pulsations

The development of current and next generation high performance electronic devices has led to smaller components in more densely packed spaces. The increasing power levels have resulted in ever-increasing heat flux densities which necessitates the evolution of new liquid-based heat exchange technologies. Pulsating flow in single-phase cooling systems is viewed as a potential solution to the problems involving high heat flux densities. A review of published literature indicates a lack of time-resolved and space-resolved links between the hydrodynamic pulsating characteristics and associated heat transfer perturbations. The scope of this work involves the development of a validated three-dimensional conjugate heat transfer computational model to investigate hydrodynamically and thermally fully developed pulsating flows in a heated rectangular minichannel. Simulations were performed for a sinusoidal waveform with a fixed pulsation amplitude for varying pulsation frequencies in the range of 0.02 Hz to 25 Hz, corresponding to Womersley numbers in the range of 0.5 ≤Wo≤ 18.33. Low pulsation frequencies exhibited the well known parabolic profile for the fluctuating hydrodynamic and thermal parameters, i.e., velocity, wall shear, and wall temperature. As a result, the axial pressure gradient, velocity, and wall shear stress profiles were in phase and similar results were obtained for the oscillating wall and bulk fluid temperatures. For the inertia dominated high frequency flows, an increase in axial pressure gradient leads to a phase lag of π/2 when compared with the velocity and wall shear profiles. The shorter time period pulsations exhibit unique attributes in the form of flow reversal effects at local near wall regions. High near wall thermal gradients were observed as a result of stronger viscous effects due to a narrowing thermal boundary layer; consequently the transverse diffusion of heat was ineffective. A phase lag and a subsequent drop in the peak magnitudes existed between the oscillating bulk and wall temperatures for high frequency flows. Fluctuations in near wall heat flux profiles showed a dependency on the imposed pulsation frequencies. For the chosen pulsation profile and frequencies, the overall time averaged thermal performance indicates that pulsating flow performs worse than steady flow for a flow rate amplitude of 1. The highest thermal performance was achieved for Wo=5.1 while maintaining a low friction factor.

Evaluating the V-band Photometric Metallicity with Fundamental Mode RR Lyrae in the Kepler Field

The aim of this work is to evaluate the performance of photometric metallicity [Fe/H], determined based on V-band light curves photometrically transformed from the gr-band light curves. We tested this by using a set of homogeneous samples of fundamental mode RR Lyrae located in the Kepler field. It was found that the color term is necessary in such photometric transformation. We demonstrated that when including the color term the determined photometric [Fe/H] are in good agreement with the spectroscopic [Fe/H], either based on the calibrated or the transformed V-band light curves. We also tested the impact of Blazhko RR Lyrae in determining the photometric [Fe/H], and found that Blazhko RR Lyrae can give consistent photometric [Fe/H]. Finally, we derived independent gVr-band [Fe/H]–ϕ 31–P relations (where ϕ 31 and P are the Fourier parameter and pulsation period, respectively) using our light curves. The V-band relation is in good agreement with the most recent determination given in the literature.

Modelling of multimode radially pulsating high-amplitude δ Scuti stars from the OGLE Galactic bulge sample

ABSTRACT Thanks to relatively firm mode identification, possible based only on period ratios, high-amplitude δ Scuti stars pulsating in at least three radial modes are promising targets for asteroseismic inference. In this study, we used the most numerous sample of HADS from the OGLE inner bulge fields that likely pulsate in either three or four radial modes simultaneously. We have computed a grid of pulsation models along evolutionary tracks and determined the physical parameters of stars by matching their pulsation periods and period ratios. For 176 HADS, we determined physical parameters, i.e. masses, luminosities, effective temperatures, metallicities, and ages. We present the distribution of physical parameters and discuss their properties. We selected 16 candidates for SX Phoenicis stars.

MeerKAT Observations of the Reversing Drifting Subpulses in PSR J1750-3503

We present an analysis of the subpulse drift in PSR J1750−3503, which is characterized by abrupt transitions of drift direction. As the pulsar does not exhibit other mode changes or clear nulling, it is an ideal candidate system for studying the phenomenon of drift direction change. For ∼80% of the time, the subpulses are characterized by positive drift—from early to later longitudes—while the drift direction is negative in the other ∼20%. The subpulse separation for single pulses with positive drift, P 2 = (18.8 ± 0.1)°, is higher than for single pulses with negative drift, P 2 = (17.5 ± 0.2)°. When the drift is stable, the measured repetition time of the drift pattern is P 3 obs = (43.5 ± 0.4)P, where P is the pulsar period. We show that the observed data can be reproduced by a carousel models with subpulse rotation around the magnetic axis using a purely dipolar configuration of the surface magnetic field. The observed drift characteristics can be modeled assuming that the actual repetition time P 3 < 2P, such that we observe its aliased value. A small variation in P 3, of the order of 6% (or less assuming higher alias orders), is enough to reproduce the characteristic drift direction changes we observe.