Rotation Inclination Research Articles

Seismic behavior of looseness-induced inclined mortise and tenon joints in ancient timber structures: Experimental tests, multi-scale finite element model, and behavior degradation

The inclination damage of mortise and tenon (M-T) joints, caused by the looseness between the mortise and tenon, has an detrimental impact on the overall safety of structures. To investigate the effects of varying inclination rotation on the seismic behavior of ancient M-T joints, four 1/3.2-scaled straight M-T joints with different inclination rotation, one intact joint for comparison and three looseness-induced inclined joints, were cyclically tested. Typical failure modes of the damaged joints were identified. The influence of the tilt deterioration on the joint's hysteretic and rotational behavior was evaluated. The test results showed that with an increase in the inclination rotation, the size of the hysteretic loops of the inclined joints was increasingly smaller, the negative initial slippage and pinching effects were more apparent, the ultimate moment-resisting, initial elastic stiffness, and ductility of the specimens degraded significantly. Furthermore, the multi-scale finite element models of the looseness-induced inclined M-T joints were established using the ABAQUS. Based on the validated numerical model, the parameter analysis was performed. The influence of the frictional coefficient of wood, inclined rotation, and horizontal gap between the tenon and mortise on the joint's hysteretic behavior and energy dissipation mechanism was quantified. It is found that with a friction coefficient of 0.6, the positive and negative ultimate moments-resisting of the joint improved 65.99 % and 35.89 %, respectively; the joint's slip moment and energy dissipation increased by 12.18 and 3.78 times, respectively. With a 0.043 rad inclined rotation, the positive and negative ultimate moments of the joint decreased 23.32 % and 30.46 %, respectively; the joint's positive and negative initial elastic stiffnesses and cumulative energy dissipation reduced 49.12 %, 28.96 %, and 56.33 %, respectively. When the inclined rotation remained at 0.022 rad, the positive and negative ultimate moments of the joint including a 6 mm horizontal gap reduced 26.63 % and 34.20 %, respectively; the joint's positive and negative initial elastic stiffnesses, and accumulative energy dissipation decreased 42.42 %, 59.43 %, and 79.50 %, respectively.

Pulsations of Three Rapidly Oscillating Ap Stars TIC 96315731, TIC 72392575, and TIC 318007796

We analyze the frequencies of three known roAp stars, TIC 96315731, TIC 72392575, and TIC 318007796, using the light curves from the Transiting Exoplanet Survey Satellite. For TIC 96315731, the rotational and pulsational frequencies are 0.1498360 day−1 and 165.2609 day−1, respectively. In the case of TIC 72392575, the rotational frequency is 0.25551 day−1. We detect a quintuplet of pulsation frequencies with a center frequency of 135.9233 day−1, along with two signals within the second pair of rotational sidelobes of the quintuplet separated by the rotation frequency. These two signals may correspond to the frequencies of a dipole mode. In TIC 318007796, the rotational and pulsational frequencies are 0.2475021 day−1, 192.73995 day−1, and 196.33065 day−1, respectively. Based on the oblique pulsator model, we calculate the rotation inclination i and magnetic obliquity angle β for the stars, which provide the geometry of the pulsation modes. Combining the phases of the frequency quintuplets, the pulsation amplitude and phase modulation curves, and the results of spherical harmonic decomposition, we conclude that the pulsation modes of frequency quintuplets in TIC 96315731, TIC 72392575, and TIC 318007796 correspond to distorted dipole mode, distorted quadrupole mode, and distorted dipole mode, respectively.

SHARAD observations for layered ejecta deposits formed by late-Amazonian-aged impact craters at low latitudes of Mars

Frequent changes of the rotational inclination of Mars have driven global transitions of the cryosphere. Although glaciers of water ice may have extended to the equatorial region, current observations of surface deposits at latitudes lower than 30° show relative depletion in hydrogen. Thermal stability models predict that at these low latitudes, ancient water ice may be preserved below a desiccated regolith layer that is meters to hundreds of meters thick. However, confirmed detections of massive water ice and/or water ice remain sparse at low latitudes. Here we use sounding radar observations of late-Amazonian-aged impact craters with layered ejecta deposits at low latitudes to search for subsurface layering and interface properties to investigate the possible existence of subsurface water/water ice. Such craters are widespread at low latitudes, including the landing area of the Zhurong rover, Tianwen-1 mission. The layered ejecta deposits of selected craters have lateral sizes and thickness suitable for investigation by sounding radar. Compared to previously-reported, but rare, cases that contained obvious reflectors between the layered ejecta deposits and underlying materials, we detect no clear reflections in neither the layered ejecta deposits nor deeper materials, suggesting that these materials have similar dielectric properties across their interfaces. Referring to the surface permittivity of background terrains of the investigated craters, we derive a broad range of relative permittivity of ∼2–10 for materials in the layered ejecta deposits. We discuss the implications of these results in the context of past and present water ice at low latitudes of Mars.

Projected spin–orbit alignments from Kepler asteroseismology and Gaia astrometry

ABSTRACT The angle between the rotation and orbital axes of stars in binary systems – the obliquity – is an important indicator of how these systems form and evolve, but few such measurements exist. We combine the sample of astrometric orbital inclinations from Gaia Data Release 3 with a sample of solar-like oscillators in which rotational inclinations have been measured using asteroseismology. We supplement our sample with one binary whose visual orbit has been determined using speckle interferometry and present the projected spin–orbit alignments in five systems. We find that each system, and the overall sample, is consistent with alignment but there are important caveats. First, the asteroseismic rotational inclinations are fundamentally ambiguous and, secondly, we can only measure the projected (rather than true) obliquity. If rotational and orbital inclinations are independent and isotropically distributed, the likelihood of drawing our data by chance is less than a few per cent. Though small, our data set argues against uniformly random obliquities in binary systems. We speculate that dozens more measurements could be made using data from NASA’s Transiting Exoplanet Survey Satellite mission, mostly in red giants. ESA’s PLAnetary Transits and Oscillations mission will likely produce hundreds more spin–orbit measurements in systems with main-sequence and subgiant stars.

Photometric Properties and Stellar Parameters of the Rapidly Rotating Magnetic Early-B Star HD 345439

We first present the multicolor photometry results of the rapidly rotating magnetic star HD 345439 using the Nanshan One-meter Wide-field Telescope. From the photometric observations, we derive a rotational period of 0.7699 ± 0.0014 day. The light curves of HD 345439 are dominated by the double asymmetric S-wave feature that arises from the magnetic clouds. Pulsating behaviors are not observed in Sector 41 of the Transiting Exoplanet Survey Satellite. No evidence is found of the occurrence of centrifugal breakout events neither in the residual flux nor in the systematic variations at the extremum of the light curve. Based on the hypothesis of the Rigidly Rotating Magnetosphere model, we restrict the magnetic obliquity angle β and the rotational inclination angle i so that they satisfy the approximate relation β + i ≈ 105°. The color excess, extinction, and luminosity are determined to be E (B−V) = 0.745 ± 0.016 mag, A V = 2.31 ± 0.05 mag, and dex, respectively. Furthermore, we derive the effective temperature as T eff = 22 ± 1 kK and the surface gravity as log g = 4.00 ± 0.22. The mass , radius , and age Myr are estimated from the Hertzsprung–Russell diagram.

Erratum: Discovery of multiple p-mode pulsation frequencies in the roAp star, HD 86181

We report the frequency analysis of a known roAp star, HD 86181 (TIC 469246567), with new inferences from TESS data. We derive the rotation frequency to be νrot = 0.48753 ± 0.00001d−1. The pulsation frequency spectrum is rich, consisting of two doublets and one quintuplet, which we interpret to be oblique pulsation multiplets from consecutive, high-overtone dipole, quadrupole and dipole modes. The central frequency of the quintuplet is 232.7701d−1 (2.694 mHz). The phases of the sidelobes, the pulsation phase modulation, and a spherical harmonic decomposition all show that the quadrupole mode is distorted. Following the oblique pulsator model, we calculate the rotation inclination, i, and magnetic obliquity, β, of this star, which provide detailed information about the pulsation geometry. The i and β derived from the best fit of the pulsation amplitude and phase modulation to a theoretical model, including the magnetic field effect, slightly differ from those calculated for a pure quadrupole, indicating the contributions from l = 4, 6, 8, ... are small. Non-adiabatic models with different envelope convection conditions and physics configurations were considered for this star. It is shown that models with envelope convection almost fully suppressed can explain the excitation at the observed pulsation frequencies.

Discovery of multiple p-mode pulsation frequencies in the roAp star, HD 86181

ABSTRACT We report the frequency analysis of a known roAp star, HD 86181 (TIC 469246567), with new inferences from Transiting Exoplanet Survey Satellite (TESS) data. We derive the rotation frequency to be νrot = 0.48753 ± 0.00001 d−1. The pulsation frequency spectrum is rich, consisting of two doublets and one quintuplet, which we interpret to be oblique pulsation multiplets from consecutive, high-overtone dipole, quadrupole, and dipole modes. The central frequency of the quintuplet is 232.7701 d−1 (2.694 mHz). The phases of the sidelobes, the pulsation phase modulation, and a spherical harmonic decomposition all show that the quadrupole mode is distorted. Following the oblique pulsator model, we calculate the rotation inclination, i, and magnetic obliquity, β, of this star, which provide detailed information about the pulsation geometry. The i and β derived from the best fit of the pulsation amplitude and phase modulation to a theoretical model, including the magnetic field effect, slightly differ from those calculated for a pure quadrupole, indicating the contributions from ℓ = 4, 6, 8,... are small. Non-adiabatic models with different envelope convection conditions and physics configurations were considered for this star. It is shown that models with envelope convection almost fully suppressed can explain the excitation at the observed pulsation frequencies.

A study of the global magnetic activity of the star Kepler-17 using light curve inversion with bipartite regularization

A new method of light curve inversion with bipartite regularization (LIBR), which is complementary to the previous treatments by Bonomo and Lanza and Estrela and Valio, is used to reconstruct the physical properties of star spots on the solar-type star Kepler-17 by using the full Q1- Q17 data set. The Markov Chain Monte Carlo (MCMC) method was applied to find the best profile of the reconstructed surface. The known value of the rotation inclination of Kepler-17 allows the generation of a star spot model in a sequence of stellar rotation with a period of 12.26 d. Because of the nature of the light curve inversion, the spot model is limited to the equatorial region. We also investigated the starspot lifetimes of Kepler-17 utilizing the MCMC method. Combined with the LIBR inversion results, it was found that the star spots typically last from one to several stellar rotations. From the time evolution of the spot size, a magnetic cycle period of 437 d can be derived. This value is comparatively shorter than the solar cycle which might be a consequence of the younger age (∼ 1.78 Gyr) of Kepler-17. The light curve of Kepler-17 is characterized by the presence of large-amplitude variation caused by star spots but no superflare activity. An interesting possibility is that the magnetic energy stored in the star spot regions could have been constantly dissipated by electrodynamic interaction between the central star and the hot Jupiter, Kepler-17b, via a lower-level energy release process.

Pulsations of the Rapidly Oscillating Ap Star KIC 10685175 Revisited by TESS

Abstract KIC 10685175 (TIC 264509538) was discovered to be a rapidly oscillating Ap star from Kepler long-cadence data using super-Nyquist frequency analysis. It was reobserved by the Transiting Exoplanet Survey Satellite (TESS) with 2 minute cadence data in Sectors 14 and 15. We analyzed the TESS light curves, finding that the previously determined frequency is a Nyquist alias. The revised pulsation frequency is 191.5151 ± 0.0005 day−1 (P = 7.52 minutes) and the rotation frequency is 0.32229 ± 0.00005 day−1 (P rot = 3.1028 days). The star is an oblique pulsator with a pulsation amplitude modulated by the rotation, reaching a maximum pulsation amplitude at the time of the rotational light minimum. The oblique pulsation generates a frequency quintuplet split by exactly the rotation frequency. The phases of sidelobes, the pulsation phase modulation, and a spherical harmonic decomposition all show this star to be pulsating in a distorted quadrupole mode. Following the oblique pulsator model, we calculated the rotation inclination i and magnetic oblique β of this star, which provide detailed information of pulsation geometry. The i and β derived by the best fit of pulsation amplitude and phase modulation through a theoretical model differ from those calculated for a pure quadrupole, indicating the existence of strong magnetic distortion. The model also predicts the polar magnetic field strength is as high as about 6 kG which is predicted to be observed in a high-resolution spectrum of this star.

The stability of two interacting compositional plumes under the influence of inclined rotation

The linear stability of two interacting compositional plumes rotating uniformly about an axis inclined to the vertical is studied. The problem is governed by seven dimensionless parameters: The Grashoff number, , measuring the buoyancy force relative to the viscous force, the rotation parameter, , which measures the Coriolis force relative to the viscous force, the angle, , between the rotation vector and the vertical, the concentration strength , of the second plume relative to that of the first, the thicknesses, , of the two plumes and the distance, , between them (which have been made dimensionless using the salt-finger length scale). It is shown that rotation destabilises the neutral modes present in its absence. For a given set of the parameters (=), the growth rate increases with to a finite value as approaches infinity. The inclination of rotation to the horizontal is found to tend to stabilise a vertically rotating plume but succeeds only in reducing the magnitude of the growth rate while the order of magnitude remains the same. The introduction of a horizontal component of rotation also has a similar stabilising effect. The presence of a horizontal component of rotation also introduces a new mode which propagates horizontally across the vertical basic flow, provided the second plume acquires certain strength. The growth rate is of the same order of magnitude even when the rotation parameter increases indefinitely whatever values the other parameters take. The helicity of the unstable modes can take positive or negative values depending, in a complicated way, on the parameters. The helicity of the horizontally propagating wave is zero.

Light curves of stars and exoplanets: estimating inclination, obliquity and albedo

[Abridged] Distant stars and planets will remain spatially unresolved for the foreseeable future. It is nonetheless possible to infer aspects of their brightness markings and viewing geometries by analyzing disk-integrated rotational and orbital brightness variations. We compute the harmonic lightcurves, F_l^m(t), resulting from spherical harmonic maps of intensity or albedo, Y_l^m(theta,phi), where l and m are the total and longitudinal order. Notably, odd m>1 are present in an inclined lightcurve, but not seen by an equatorial observer. We therefore suggest that the Fourier spectrum of a thermal lightcurve may be sufficient to determine the orbital inclination of non-transiting short-period planets, the rotational inclination of stars and brown dwarfs, and the obliquity of directly imaged planets. In the best-case scenario of a nearly edge-on geometry, measuring the m=3 mode of a star's rotational lightcurve to within a factor of two provides an inclination estimate good to +/- 6 degrees, assuming stars have randomly distributed spots. Alternatively, if stars have brightness maps perfectly symmetric about the equator, their lightcurves will have no m=3 power, regardless of orientation. In general, inclination estimates will remain qualitative until detailed hydrodynamic simulations and/or occultation maps can be used as a calibrator. We further derive harmonic reflected lightcurves for tidally-locked planets; these are higher-order versions of the well-known Lambert phase curve. We show that a non-uniform planet may have an apparent albedo 25% lower than its intrinsic albedo, even if it exhibits precisely Lambertian phase variations. Lastly, we provide low-order analytic expressions for harmonic lightcurves that can be used for fitting observed photometry; as a general rule, edge-on solutions cannot simply be scaled by sin(i) to mimic inclined lightcurves.

HR 1613: A Slowly Rotating A Dwarf Spectroscopic Binary with Solar Abundances

From two sets of radial velocities we have obtained the orbital elements of HR 1613. This single-lined binary has an orbital period of 8.11128 days and a nearly circular orbit. The primary has an A9 V spectral type and a v sin i value of 11 km s-1, while the unseen secondary is likely a K or M dwarf. Spectral classifications and spectrum synthesis analysis indicate that the abundances of the primary are normal. We reject the possibility that the primary of HR 1613 is seen nearly pole-on and instead argue that its rotational inclination is at least 20°, resulting in an equatorial rotational velocity of 30 km s-1 or less. Slowly rotating A stars almost always have spectrum peculiarities, being classified as either Ap or Am stars, but HR 1613, with its essentially solar abundances, appears to be an exception.

The Hyades Binary θ2Tauri: Confronting Evolutionary Models with Optical Interferometry

We determine the masses and magnitude difference of the components of the Hyades spectroscopic binary θ2 Tauri. We find that both components appear to be less massive and/or brighter than predicted from some recent evolutionary models. The rapid rotation and unknown rotational inclination of both components introduce uncertainty in their luminosities and colors, but not enough to reconcile both of them with the evolutionary models. We measured the visual orbit with the Mark III optical interferometer and the Navy Prototype Optical Interferometer and combined it with the Hipparcos proper-motion-based parallax to find a total system mass Σ of 4.03 ± 0.20 ⊙. We also combined our visual orbit with three recent spectroscopic orbits to find three spectroscopically based estimates of Σ and compared these to the Σ from the visual orbit and parallax. We chose the spectroscopic orbit that agreed best and used its mass ratio to estimate individual masses A,B of 2.15 ± 0.12 and 1.87 ± 0.11 ⊙. From the interferometry, we determine Δm = 1.13 ± 0.05 mag across the 450-850 nm band. The parallax then implies absolute V magnitudes MA,B of 0.48 ± 0.05 and 1.61 ± 0.06 mag. If the components are rotating near breakup velocity and seen nearly pole-on, the true luminosities may be as faint as 1.03 and 2.13 mag; even in that case, however, the secondary is too blue by ∼0.07 mag in B - V.

The rapidly oscillating Ap star HD 99563 and its distorted dipole pulsation mode

We undertook a time-series photometric multi-site campaign for the rapidly oscillating Ap star HD 99563 and also acquired mean light observations over two seasons. The pulsations of the star, that show flatter light maxima than minima, can be described with a frequency quintuplet centred on 1557.653 microHertz and some first harmonics of these. The amplitude of the pulsation is modulated with the rotation period of the star that we determine with 2.91179 +/- 0.00007 d from the analysis of the stellar pulsation spectrum and of the mean light data. We break the distorted oscillation mode up into its pure spherical harmonic components and find it is dominated by the l=1 pulsation, and also has a notable l=3 contribution, with weak l=0 and 2 components. The geometrical configuration of the star allows one to see both pulsation poles for about the same amount of time; HD 99563 is only the fourth roAp star for which both pulsation poles are seen and only the third where the distortion of the pulsation modes was modelled. We point out that HD 99563 is very similar to the well-studied roAp star HR 3831. Finally, we note that the visual companion of HD 99563 is located in the Delta Scuti instability strip and may thus show pulsation. We show that if the companion was physical, the roAp star would be a 2.03 solar mass object, seen at a rotational inclination of 44 degrees, which then predicts a magnetic obliquity of 86.4 degrees.

Chromospherically Active Stars. XXI. The Giant, Single-lined Binaries HD 89546 and HD 113816

We have obtained spectroscopy and photometry of the chromospherically active, single-lined spectroscopic binaries HD 89546 and HD 113816. HD 89546 has a circular orbit with a period of 21.3596 days. Its primary has a spectral type of G9 III and is somewhat metal-poor with [Fe/H] ~ -0.5. HD 113816 has an orbit with a period of 23.6546 and a low eccentricity of 0.022. Its mass function is extremely small, 0.0007 M⊙, consistent with a very low inclination. The primary is a slightly metal-poor K2 III. A decade or more of photometric monitoring with an automatic telescope demonstrates that both systems display brightness variations due to rotational modulation of the visibility of photospheric star spots, as well as light-curve changes resulting from the redistribution of star spots by differential rotation and long-term changes in the filling factor of the spots. We determined rotation periods for each season when the observations were numerous enough. Our mean rotation periods of 21.3 and 24.1 days for HD 89546 and HD 113816, respectively, confirm that the giants in each system are synchronously rotating. The orbital elements and properties of the giant components of these two systems, including levels of surface magnetic activity, are quite similar. However, the two rotational inclinations are rather different, 57° for HD 89546 and 13° for HD 113816. Thus the latter giant is seen nearly pole on. We analyzed the light curves for similarities and differences that result from viewing these two systems from quite different inclinations.

Rain-induced slope instability in Hong Kong

Slope failures are common in Hong Kong. A wide spectrum of slope failures have been noted. Failures may differ in respect of thickness of failed mass, time of failure occurrence, rotational inclination, failure movement rate, mobility of debris, etc. Small failures significantly outnumber large ones. Due to their close proximity to buildings, however, small failures that collapse catastrophically without prior warning are of concern. Intense rainfall, soils that are largely non-cohesive upon saturation, steep terrain, and intense development are considered to be the major causes of the failures. Loss of pore-water suction, erosion, and pore-water pressure build-up at shallow depths are the most common ways through which rainwater affects the slope stability, as short-burst rainstorms are common. The scale of a failure event depends on the intensity, areal extent, position and duration of the triggering rainstorm. Antecedent rainfall has relatively little influence. The prediction of slope stability in Hong Kong is difficult because of the highly erratic nature of the hydrological influences and the inherent heterogeneity of local soils. While some of the hydrological and geological attributes cannot be accurately predicted and effectively controlled, the hazard can be mitigated by appropriate geotechnical control.

Chromospherically Active Stars. XVII. The Double-lined Binary 54 Camelopardalis (AE Lyncis)

New spectroscopic observations of the double-lined chromospherically active binary 54 Camelopardalis (=AE Lyncis) have been obtained, resulting in improved orbital elements and the determination of the fundamental properties of the system. 54 Cam has a period of 11.06794 days, an eccentricity of 0.125, and a mass ratio of 0.9945. The spectral types are F8 IV–V and G5 IV, positioning the components on opposite sides of the Hertzsprung gap. From a comparison with theoretical evolutionary tracks, the masses are estimated to be 1.60 and 1.59 M⊙ for the G and F stars, respectively, while the radii are 3.7 and 3.2 R⊙. Only the G star is chromospherically active. 54 Cam is particularly interesting since the F star is the brighter star at blue and red wavelengths, but the G star is slightly more massive and evolved. Both stars appear to be pseudosynchronously rotating, and the orbital and rotational inclinations are aligned. The lithium abundances of the two components are significantly different but consistent with standard theory, supporting the conclusion that both stars are more massive than the lithium-dip stars.

The oblique dipole pulsation mode of the rapidly oscillating Ap star HD 80316

New high-speed photometric observations of the rapidly oscillating Ap star HD 80316 suggest that its principal pulsation mode is an oblique dipole mode with a frequency of either 2251.68 or 2254.47 j..lHz (P=7.4 min). Rotationally split frequency triplets give two choices for the rotation period, Prot = 2.085 ± 0.005 or 4.163 ± 0.010 d, which agree with possible rotation periods derived independently from mean light observations. Both frequency triplet possibilities show the sum of the rotational inclination, i, and the magnetic obliquity, /3, to be greater than 90°. This makes HD 80316 only the third roAp star, after HR 3831 and HD 6532, to have a polarity-reversing dipole pulsation. The two possible rotation periods are so close to multiples of 1 d- 1 that alias problems in our single-site observations preclude a definite solution for the oscillations of this star. Further progress requires multisite observations, or long-term single-site observations to sample all rotation phases.

Chromospherically Active Stars. XIV. A Rediscussion of the Properties and Evolutionary State of HD 181943

The chromospherically active single star HD 181943 was previously proposed as either a pre-main-sequence star seen pole-on or a post-main-sequence subgiant that evolved from an Ap star similar to 53 Cam. It also was found to be a variable star with a 385 day period. We have used new spectroscopic and photometric observations to reevaluate the properties and evolutionary state of this unusual system. We conclude that HD 181943 is a single K1 V star that has recently arrived on the ZAMS. Its emission line fluxes are nearly identical to those of HD 82558= LQ Hya, while its log lithium abundance of 1.75 is somewhat smaller than that of similar Pleiades stars. Its low v sin i of 5 km s<SUP>-1</SUP> suggests that its rotational inclination axis is likely ≤12°. We estimate a distance of 46±6 pc or a parallax of 0.022". Space velocities indicate that it belongs to no known moving group. Our photometric observations, covering nearly 2300 days, confirm that HD 181943 is variable. However, they do not support the 385 day period but instead suggest a period of about 2000 days. When photometry from earlier epochs is included no single period fits all the data. We interpret this as evidence for changes in high latitude or polar spots. Portions of our photometric data analyzed for rotational modulation reveal no periodic short-term variations. Continued observation of the comparison star, HD 181219=V4153 Sgr, indicates that it is a constant star and so its variable-star classification should be revised. Variability previously ascribed to this star was the result of moonlight contamination.