Rotational Modulation Research Articles

Abstract 12792: Reentrant Drivers Are Distinguished From Passive Rotors by Sequential Computer Simulation of Ablation Using Personalized Non-Paroxysmal Atrial Fibrillation Heart Models Based on Late Gadolinium Enhancement Magnetic Resonance Imaging (LGE-MRI)

Introduction: Although rotor modulation targeting atrial fibrillation (AF) drivers or substrates has been proposed as one of the effective ablation strategies for non-paroxysmal AF (Non-PAF), previous meta-analyses demonstrated that ablation added to pulmonary vein isolation (PVI) did not result in the expected outcome. This is because the optimal method of detection of rotors and ablation strategy remain unclear. Recently, rotor detection using LGE-MRI-based computer simulations has been shown to be effective for Non-PAF ablation in clinical practice. Our study aimed to establish the minimal ablation strategy that, while correctly finding the rotors, also avoids iatrogenic atrial tachyarrhythmias due to excessive ablation. Hypothesis: By prioritizing and classifying detected rotors, reentrant drivers (RDs) of AF rather than passive rotors (PRs) could be identified, thereby offering an optimal ablation strategy. Methods: Personalized computational modeling of AF ablation was performed in 10 Non-PAF patient models based on fibrosis data from LGE-MRI. In each bi-atrial model, all rotors induced outside of PVI were investigated, and a number of ablation strategies were examined sequentially to classify rotors and achieve minimal ablation (figure). A rotor that terminated following ablation of another rotor was defined as PR. A rotor that persisted and needed to be ablated to achieve non-inducibility of the substrate was defined as RD. Results: Seven patients had rotors outside of PVI, with 6 having both PRs and RDs. Overall, 35 rotors were induced, 13 in left atrium and 22 in the right; 17 were RDs and 18 PRs. In addition, the density of fibrosis in the sites of RDs was significantly higher than in those of PRs (p=0.031). Conclusion: The sequential computer simulation strategy to predict ablation targets using a personalized AF model is promising in detecting different types of rotors and establishing the optimal minimum-lesion ablation strategy.

KIC 6951642: A confirmed Kepler γ Doradus – δ Scuti star with intermediate to fast rotation in a possible single-lined binary system

Context. KIC 6951642 has been reported as a candidate hybrid pulsator of type-γ Doradus – δ Scuti from observations of the first quarters of the Kepler mission. The regular patterns seen in the Fourier spectra of the Kepler and Transiting Exoplanet Survey Satellite TESS light curves and the sinusoidal modulation of its surface brightness suggest the additional presence of rotational modulation and stellar activity, respectively. Aims. We aim to investigate the pulsating nature of KIC 6951642 and to search for the signature of rotation and/or activity in the light curves. Methods. We performed an iterative frequency search of both Fourier spectra, and searched for regular patterns in them. We applied spectrum synthesis to determine the atmospheric stellar parameters. Since KIC 6951642 was reported to belong to a spectroscopic binary system, we fitted the time delays derived from the light curves with the radial velocities obtained from published as well as new spectra in an attempt to improve the quality of the first orbit. Results. Follow-up spectroscopy showed that KIC 6951642 is a fast-rotating F0-type star in a possible single-lined binary with a period of ∼4.8 yr. In the low-frequency regime, we identified the frequencies of 0.721 d−1 as well as of 0.0087 d−1. We attribute the first frequency to stellar rotation, and the second one to stellar activity with a cycle of length of 3.2 yr. We also detected g modes, with the strongest mode located at 2.238 d−1, as well as three asymmetric multiplets (with a mean spacing of 0.675 ± 0.044 d−1). In the high-frequency regime, we detected frequencies of type-δ Scuti, with the strongest mode located at 13.96 d−1, as well as seven asymmetric multiplets (with a mean spacing of 0.665 ± 0.084 d−1). We subsequently identified a few more frequencies that appear to be combinations of a g or p mode and one of the higher cited frequencies not due to pulsations. Conclusions. We propose that KIC 6951642 accomadates for a fast-rotating γ Dor – δ Sct hybrid star with various rotationally split multiplets of g and p modes and that it also displays a cycle lasting years of (possible) stellar activity.

Radial Velocity Survey for Planets around Young stars (RVSPY)

Context. The occurrence rate and period distribution of (giant) planets around young stars is still not as well constrained as for older main-sequence stars. This is mostly due to the intrinsic activity-related complications and the avoidance of young stars in many large planet search programmes. Yet, dynamical restructuring processes in planetary systems may last significantly longer than the actual planet formation phase and may well extend long into the debris disc phase, such that the planet populations around young stars may differ from those observed around main-sequence stars. Aims. We introduce our Radial Velocity Survey for Planets around Young stars (RVSPY), which is closely related to the NaCo-ISPY direct imaging survey, characterise our target stars, and search for substellar companions at orbital separations smaller than a few au from the host star. Methods. We used the FEROS spectrograph, mounted to the MPG/ESO 2.2 m telescope in Chile, to obtain high signal-to-noise spectra and time series of precise radial velocities (RVs) of 111 stars, most of which are surrounded by debris discs. Our target stars have spectral types between early F and late K, a median age of 400 Myr, and a median distance of 45 pc. During the initial reconnaissance phase of our survey, we determined stellar parameters and used high-cadence observations to characterise the intrinsic stellar activity, searched for hot companions with orbital periods of up to 10 days, and derived the detection thresholds for longer-period companions. In our analysis we, have included archival spectroscopic data, spectral energy distribution, and data for photometric time series from the TESS mission. Results. For all target stars we determined their basic stellar parameters and present the results of the high-cadence RV survey and activity characterisation. We have achieved a median single-measurement RV precision of 6 m s−1 and derived the short-term intrinsic RV scatter of our targets (median 23 m s−1), which is mostly caused by stellar activity and decays with an age from >100 m s−1 at <20 Myr to <20 m s−1 at >500 Myr. We analysed time series periodograms of the high-cadence RV data and the shape of the individual cross-correlation functions. We discovered six previously unknown close companions with orbital periods between 10 and 100 days, three of which are low-mass stars, and three are in the brown dwarf mass regime. We detected no hot companion with an orbital period <10 days down to a median mass limit of ~1 MJup for stars younger than 500 Myr, which is still compatible with the established occurrence rate of such companions around main-sequence stars. We found significant RV periodicities between 1.3 and 4.5 days for 14 stars, which are, however, all caused by rotational modulation due to starspots. We also analysed the data for TESS photometric time series and found significant periodicities for most of the stars. For 11 stars, the photometric periods are also clearly detected in the RV data. We also derived stellar rotation periods ranging from 1 to 10 days for 91 stars, mostly from the TESS data. From the intrinsic activity-related short-term RV jitter, we derived the expected mass-detection thresholds for longer-period companions, and selected 84 targets for the longer-term RV monitoring.

Multifractal characterization as a function of timescale in the light curves with planetary signal observed by the Kepler mission

We investigate the evolution of five multifractal indicators of the Kepler Mission light curves of the moderately young Sun-like Kepler-30 star accompanied by a three-planet system. We focus not only on the fact that the rotational modulation has multifractality properties but also on some studies on these properties based on scale. Then, we systematically investigate the dynamic behaviors of the small and large fluctuations in two types of light curves (PDC and SAP). Those fluctuations indicate that the properties of stellar noise and rotation modulation are highlighted when we apply the Multifractal Detrended Moving Average (MFDMA) algorithm. Our results also demonstrated that the multifractality of the light curve is due to both long-range correlation and broad probability density function, but the main source of multifractality is the long-range correlation. This new approach can be used to develop theoretical and computational models for various stellar magnetic activity-related phenomena and their interactions with the planets, and it can greatly simplify spot modeling from current TESS and future PLATO data.

Wavelength-switchable dual-wavelength thulium-doped fiber laser utilizing photonic crystal fiber

A dual-wavelength thulium-doped fiber laser with a wide switchable single-wavelength range is demonstrated by employing a polarization-maintaining photonic crystal fiber. A new type of comb filter is designed and its spectrum is simulated. A nonlinear polarization rotation module is inserted into the laser cavity to suppress intense gain competition. An output power instability as low as 0.84 dB has been attained. The switchable range of single-wavelength operation is 43.64 nm, and the slope efficiency is 1.79%, attained by optimizing the splicer parameter between the polarization-maintaining photonic crystal fiber and the single-mode fiber. There are five regions of dual-wavelength output from 1978.04 to 1986.51 nm, and the maximum and minimum wavelength intervals are 6.11 nm and 1.9 nm.

Detectability of Rotational Modulation in Kepler Sun-like Stars as a Function of Age

We examine how the fraction f of stars for which rotational modulation has been detected in Kepler light curves depends on the stellar mass M ⋆ and age t ⋆. Our sample consists of ≈850 FGK stars hosting transiting planet candidates detected from the prime Kepler mission. For these stars, atmospheric parameters have been derived using high-resolution spectra from the California-Kepler survey, and rotational modulation has been searched in Kepler light curves homogeneously. We fit stellar models to the atmospheric parameters, Gaia parallax, and Two Micron All Sky Survey magnitude of these stars and obtain samples drawn from the posterior probability distributions for their masses and ages under a given, uninformative prior. We combine them with the result of rotational modulation search to simultaneously infer the mass–age distribution of the sample as well as f(M ⋆, t ⋆), in a manner that fully takes into account mass and age uncertainties of individual stars. We find that f remains near unity up to t ⋆ ∼ 3 Gyr and drops to almost zero by t ⋆ ∼ 5 Gyr, although the trend is less clearly detected for stars with ≲0.9 M ⊙ due to weaker age constraints. This finding is consistent with a view that the detection of rotational modulation is limited by photometric precision to younger stars that exhibit higher-amplitude modulation, and suggests that the detectability of rotational modulation in Kepler light curves is insensitive to metallicity and activity cycles for stars younger than the Sun.

Eclipse of the V773 Tau B circumbinary disc

Context. Young multiple stellar systems can host both circumstellar and circumbinary discs composed of gas and dust, and the orientations of circumbinary discs can be sculpted by the orientation and eccentricity of the central binaries. Studying multiple binary systems and their associated discs enables our understanding of the size and distribution of the planetary systems that subsequently form around them. Aims. A deep (~70%) and extended (~150 days) eclipse was seen towards the young multiple stellar system V773 Tau in 2010. We interpret it as being due to the passage of a circumbinary disc around the B components moving in front of the A components. Our aim is to characterise the orientation and structure of the disc, to refine the orbits of the sub-components, and to predict when the next eclipse will occur. Methods. We combined the photometry from several ground-based surveys, constructed a model for the light curve of the eclipse, and used high angular resolution imaging to refine the orbits of the three spatially resolved components of the system: A, B, and C. A frequency analysis of the light curves, including from the TESS satellite, enabled the characterisation of the rotational periods of the Aa and Ab stars. Results. A toy model of the circumbinary disc shows that it extends out to approximately 5 au around the B binary and has an inclination of 73° with respect to the orbital plane of AB, where the lower bound of the radius of the disc is constrained by the geometry of the AB orbit and the upper bound is set by the stability of the disc. We identify several frequencies in the photometric data that we attribute to rotational modulation of the Aa and Ab stellar companions. We produced the first determination of the orbit of the more distant C component around the AB system and limited its inclination to 93°. Conclusions. The high inclination and large diameter of the disc, together with the expected inclination of the disc from theory, suggest that B is an almost equal-mass, moderately eccentric binary. We identify the rotational periods of the Aa and Ab stars and a third frequency in the light curve that we attribute to the orbital period of the stars in the B binary. We predict that the next eclipse will occur around 2037, during which both detailed photometric and spectroscopic monitoring will characterise the disc in greater detail.

Analysis of eight magnetic chemically peculiar stars with rotational modulation

ABSTRACT Since the end of 2018, the Transiting Exoplanet Survey Satellite (TESS) has provided stellar photometry to the astronomical community. We have used TESS data to study rotational modulation in the light curves of a sample of chemically peculiar stars with measured large-scale magnetic fields (mCP stars). In general, mCP stars show inhomogeneous distributions of elements in their atmospheres that lead to spectroscopic (line profile) and photometric (light curve) variations commensurate with the rotational period. We analyzed the available TESS data from 50 sectors for eight targets after post-processing them in order to minimize systematic instrumental trends. Analysis of the light curves allowed us to determine rotational periods for all eight of our targets. For each star, we provide a phase diagram calculated using the derived period from the light curves and from the available measurements of the disc-averaged longitudinal magnetic field 〈Bz〉. In most cases, the phased light curve and 〈Bz〉 measurements show consistent variability. Using our rotation periods, and global stellar parameters derived from fitting Balmer line profiles, and from Geneva and Strömgren–Crawford photometry, we determined the equatorial rotational velocities and calculated the respective critical rotational fractions veq/vcrit. We have shown from our sample that the critical rotational fraction decreases with stellar age, at a rate consistent with the magnetic braking observed in the larger population of mCP stars.

KIC 3440495: A Rapidly Rotating δ Scuti-γ Doradus Hybrid Pulsator in a Binary System

In this paper, we study the pulsation properties of KIC 3440495 using Kepler and TESS data. A Fourier analysis of the light curve reveals 24 pulsation modes as well as 29 frequencies associated with rotation. The rotation frequency is derived to be f rot = 2.322909(2) day−1, and the rotational modulation is determined to be caused by starspots. A large frequency separation of Δν = 54.5 μHz is found by using a Fourier transform, the autocorrelation function, a histogram of frequency differences, and an échelle diagram. We use the large separation to estimate the refined stellar parameters of the star to be v = [239, 279] km s−1, M = [1.5, 1.65] M ⊙, R equator = [2.03, 2.30] R ⊙, R polar = [1.72, 1.78] R ⊙, and ω = [0.61, 0.77]. The phase modulations of the pulsating frequencies show a long-term trend which may be attributed to an orbital effect of a binary system; hence, the star may be a fast rotating pulsator in a binary system. KIC 3440495 has an amplitude spectrum similar to Altair, and is identified as a potential sister of Altair. Based on studies of Altair, KIC 3330495 is presumably a young star at a similar evolutionary stage.

Rotation of hot normal, peculiar and Be stars from space photometry

ABSTRACT The periods of 34 376 main-sequence stars hotter than 6000 K are derived from Kepler, K2, and TESS light curves. From the effective temperatures and GAIA DR3 luminosities, the radii, and hence the equatorial rotational velocities, can be estimated. Comparison with the projected rotational velocities shows that the photometric periods are indistinguishable from the rotational periods. Rotational light modulation in cool stars appears to continue to the hottest B stars. In fact, it is the most common type of light variation and is seen in 20–50 per cent of F, A, and B stars. The rotation rates of Am, Ap, and Bp stars do not appear to be very different from those of non-peculiar stars. Mixing of the surface layers by rotation cannot be the sole reason why element diffusion is not present in stars with normal surface abundances. The rotation rate of Be stars is well below the rate required to trigger mass-loss by non-radial pulsation. Surface activity leading to ejection of material into co-rotating clouds is suggested as the mass-loss mechanism. The rotational amplitudes of non-Be stars increases rapidly with effective temperature, possibly due to an increasing proportion of incipient Be stars in the sample. The simplest way to explain these results is to assume that surface convection is present in all main-sequence stars, from the coolest M star to the hottest B star.

Influence of gyro axis sequence configuration on the accuracy of alignment and navigation in a nested rotation inertial navigation system

It is analyzed that for a nested rotation inertial navigation system (NRINS) constructed from three ring fiber optic gyros nested within each other the main residual errors after rotation modulation are gyro angle random walk (ARW) and non-modulated gyro drift. It is pointed out that different orientations of the gyro sensitive axis lead to different equivalent ARWs, and the non-modulated gyro drift caused by the nested installation of three ring gyros is also different. The mechanism of generation of non-modulated drift in the embedded system and the general relationship with the axis sequence configuration are expounded. The equivalent ARW and non-modulated gyro drift in the inner frame rotation modulation mode and their influence on the alignment and navigation of the system are analyzed and deduced. Finally, taking the two typical applications of short-time and long-time navigation as examples, the influence of different gyro axis sequence configuration schemes on the navigation accuracy of the NRINS is verified through static navigation experiments, and the best axis sequence configuration scheme under the two applications is determined. By optimizing the gyro axis sequence configuration, the accuracy of navigation can be improved by about two times, which is of great significance. This work has important reference value for further improving the accuracy of NRINS and maximizing the accuracy advantage of gyros in different applications.

Flares and rotation of M dwarfs with habitable zones accessible to TESS planet detections

Context. More than 4000 exoplanets have been discovered to date, providing the search for a place capable of hosting life with a large number of targets. With the Transiting Exoplanet Survey Satellite (TESS) having completed its primary mission in July 2020, the number of planets confirmed by follow-up observations is growing further. Crucial for planetary habitability is not only a suitable distance of the planet to its host star, but also the star’s properties. Stellar magnetic activity, and especially flare events, expose planets to a high photon flux and potentially erode their atmospheres. Here especially the poorly constrained high-energy UV and X-ray domain is relevant. Aims. We characterize the magnetic activity of M dwarfs to provide the planet community with information on the energy input from the star; in particular, in addition to the frequency of optical flares directly observed with TESS, we aim at estimating the corresponding X-ray flare frequencies, making use of the small pool of known events observed simultaneously in both wavebands. Methods. We identified 112 M dwarfs with a TESS magnitude ≤11.5 for which TESS can probe the full habitable zone for transits. These 112 stars have 1276 two-minute cadence TESS LCs from the primary mission, which we searched for rotational modulation and flares. We study the link between rotation and flares and between flare properties, for example the flare amplitude-duration relation and cumulative flare energy frequency distributions (FFDs). Assuming that each optical flare is associated with a flare in the X-ray band, and making use of published simultaneous Kepler/K2 and XMM-Newton flare studies, we estimate the X-ray energy released by our detected TESS flare events. Our calibration also involves the relation between flare energies in the TESS and K2 bands. Results. We detected more than 2500 optical flare events on a fraction of about 32% of our targets and found reliable rotation periods only for 12 stars, which is a fraction of about 11%. For these 12 targets, we present cumulative FFDs and FFD power law fits. We construct FFDs in the X-ray band by calibrating optical flare energies to the X-rays. In the absence of directly observed X-ray FFDs for main-sequence stars, our predictions can serve for estimates of the high-energy input to the planet of a typical fast-rotating early- or mid-M dwarf.

Reflections and focusing of inertial waves in a tilted librating cube

A fluid-filled cube rotating about an axis passing through the midpoints of opposite edges is subjected to small librations (i.e. modulation of the mean rotation). Low viscosity regimes, with Ekman number as small as $10^{-8}$ and equally small relative forcing amplitude, are explored numerically. The full inertial range of forcing frequencies, from 0 to twice the mean rotation rate are considered. The response flows are dominated by inertial wavebeams emitted from edges and/or vertices, depending on the forcing frequency. How these reflect on the cube's walls and focus onto edges and vertices lead to intricate patterns. Most of the results can be reconciled using linear inviscid ray-tracing theory with careful attention to wavebeam emissions and reflections. However, even at the low Ekman number and relative forcing amplitude considered, other effects are discernible which are not captured by ray tracing. These include a symmetry breaking due to viscous effects and a progressive wave, retrograde to the mean rotation and localized in the boundary layers of the cube, due to nonlinear effects and the librational forcing.

A numerical study of double-diffusive convection in the anisotropic porous layer under rotational modulation with internal heat generation

Double-diffusive convection in a non-uniformly rotating anisotropic fluid layer with internal heating is investigated. The normal mode technique is used to obtain the critical stationary and oscillatory Rayleigh numbers. The analysis for the nonlinear case is based on minimal truncated double Fourier series which gives rise to the nonlinear Lorenz type equations. A local quasilinearization block hybrid method (LQBHM) is employed to solve the coupled nonlinear Lorenz type equations. The solution obtained using this method is compared with solutions obtained using the ode45 solver. The numerical results indicate that the LQBHM is accurate, efficient, and flexible. A weakly nonlinear analysis is used to investigate the rate of heat and mass transfer in the fluid system. The effects of time varying rotation, internal heat generation, anisotropy parameters, concentration Rayleigh, Vadasz, and Lewis numbers on the heat and mass transfer are shown graphically. Among other results, the quantitative relationships for rotational modulation amplitude and internal heat generation are [Nu/Sh]δ1=0.2<<[Nu/Sh]δ1=1.1 and [Nu/Sh]Ri=5<<[Nu/Sh]Ri=30 respectively. Therefore, modulation amplitude and internal heating have been found to enhance the rate of heat mass transfer hence advancing the onset of thermal convection in the system.

An Improved Online Fast Self-Calibration Method for Dual-Axis RINS Based on Backtracking Scheme.

In the field of high accuracy dual-axis rotational inertial navigation system (RINS), the calibration accuracy of the gyroscopes and accelerometers is of great importance. Although rotation modulation can suppress the navigation error caused by scale factor error and bias error in a static condition, it cannot suppress the scale factor errors thoroughly during the maneuvering process of the vehicle due to the two degrees of rotation freedom. The self-calibration method has been studied by many researchers. However, traditional calibration methods need several hours to converge, which is unable to meet the demand for quick response to positioning and orientation. To solve the above problems, we do the following work in this study: (1) we propose a 39-dimensional online calibration Kalman filtering (KF) model to estimate all calibration parameters; (2) Error relationship between calibration parameters error and navigation error are derived; (3) A backtracking filtering scheme is proposed to shorten the calibration process. Experimental results indicate that the proposed method can shorten the calibration process and improve the calibration accuracy simultaneously.

Vetting the “Lobster” Diagram: Searching for Unseen Companions in Wide Binaries Using NASA Space Exoplanet Missions

Over the past decade, the number of known wide-binary systems has expanded exponentially, thanks to the release of data from the Gaia Mission. Some of these wide-binary systems are actually higher-order multiples, where one of the components is an unresolved binary itself. One way to search for these systems is by identifying the overluminous components in the systems. In this study, we examine 4947 K+K wide-binary pairs from the SUPERWIDE catalog, and quantify the relative colors and luminosities of the components to find evidence for additional unresolved companions. The method is best illustrated in a graph that we call the “Lobster” diagram. To confirm that the identified overluminous components are close binary systems, we cross-match our wide binaries with the TESS, K2, and Kepler archives, and search for signs of eclipses and fast stellar rotation modulation in the light curves. We find that 78.9% ± 20.7% of the wide binaries that contain an eclipsing system are identified as overluminous in the “Lobster” diagram, and that 73.5% ± 12.4% of the wide binaries that contain a component showing fast rotation (P < 5 days) also show an overluminous component. From these results, we calculate a revised lower limit on the higher-order multiplicity fraction for K+K wide binaries of 40.0% ± 1.6%. We also examine the higher-order multiplicity fraction as a function of projected physical separation and metallicity. The fraction is unusually constant as a function of projected physical separation, while we see no statistically significant evidence that the fraction varies with metallicity.

The CARMENES search for exoplanets around M dwarfs

Context. The Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Échelle Spectrographs (CARMENES) instrument is searching for periodic radial-velocity (RV) variations of M dwarfs, which are induced by orbiting planets. However, there are other potential sources of such variations, including rotational modulation caused by stellar activity. Aims. We aim to investigate four M dwarfs (Ross 318, YZ CMi, TYC 3529-1437-1, and EV Lac) with different activity levels and spectral sub-types. Our goal is to compare the periodicities seen in 22 activity indicators and the stellar RVs, and to examine their stability over time. Methods. For each star, we calculated generalised Lomb-Scargle periodograms of pseudo-equivalent widths of chromospheric lines, indices of photospheric bands, the differential line width as a measure of the width of the average photospheric absorption line, the RV, the chromatic index that describes the wavelength dependence of the RV, and parameters of the cross-correlation function. We also calculated periodograms for subsets of the data and compared our results to TESS photometry. Results. We find the rotation periods of all four stars to manifest themselves in the RV and photospheric indicators, particularly the TiO 7050 index, whereas the chromospheric lines show clear signals only at lower activity levels. For EV Lac and TYC 3529-1437-1, we find episodes during which indicators vary with the rotation period, and episodes during which they vary with half the rotation period, similarly to photometric light curves. Conclusions. The changing periodicities reflect the evolution of stellar activity features on the stellar surface. We therefore conclude that our results not only emphasise the importance of carefully analysing indicators complementary to the RV in RV surveys, but they also suggest that it is also useful to search for signals in activity indicators in subsets of the dataset, because an activity signal that is present in the RV may not be visible in the activity indicators all the time, in particular for the most active stars.

On the Evolution of Rotational Modulation Amplitude in Solar-mass Main-sequence Stars

We investigate the relation between rotation periods P rot and photometric modulation amplitudes R per for ≈4000 Sun-like main-sequence stars observed by Kepler, using P rot and R per from McQuillan et al., effective temperature T eff from LAMOST DR6, and parallax data from Gaia EDR3. As has been suggested in previous works, we find that P rot scaled by the convective turnover time τ c, or the Rossby number Ro, serves as a good predictor of R per: R per plateaus at around 1% in relative flux for 0.2 ≲ Ro/Ro⊙ ≲ 0.4, and decays steeply with increasing Ro for 0.4 ≲ Ro/Ro⊙ ≲ 0.8, where Ro⊙ denotes Ro of the Sun. In the latter regime we find ∼ −4.5 to −2.5, although the value is sensitive to detection bias against weak modulation and may depend on other parameters including T eff and surface metallicity. The existing X-ray and Ca ii H and K flux data also show transitions at Ro/Ro⊙ ∼ 0.4, suggesting that all these transitions share the same physical origin. We also find that the rapid decrease of R per with increasing Ro causes rotational modulation of fainter Kepler stars with Ro/Ro⊙ ≳ 0.6 to be buried under the photometric noise. This effect sets the longest P rot detected in the McQuillan et al. sample as a function of T eff and obscures the signature of stalled spin down that has been proposed to set in around Ro/Ro⊙ ∼ 1.

Single-Axis Rotation Modulation Transverse SINS Based on Virtual Sphere Model in Polar Region

The measurement error of the inertial measurement unit (IMU) seriously affects the navigation accuracy of the strap-down inertial navigation system (SINS) in polar region. In order to improve navigation precision, a self-compensation method of the single-axis rotation modulation transverse SINS based on virtual sphere model is proposed in this paper. Based on the principle of single-axis rotation modulation and the mechanism of error propagation of transverse navigation system, the error characteristics of system errors were analyzed, such as constant bias, scale factor error, installation error and random walk. Finally, the simulation and experiment are designed to validate the performance of the proposed method. The navigation results demonstrate that the navigation errors of inertial navigation system, especially constant error, can be effectively restrained by the proposed single-axis rotation modulation transverse SINS based on virtual sphere model, enhancing accuracy in long-endurance navigation in polar region.

Ultra-lightweight FPGA-based RC5 designs via data-dependent rotation block optimization

Lightweight cryptography provides security to resource-constrained applications, such as embedded systems and Internet of Things (IoT) devices. This work explores an ultra-lightweight implementation of RC5 block cipher, via two levels of serialization. We also exploit a resource-sharing optimization technique for the data-dependent rotation (DDR) module, since it is the most computationally intensive component of the RC5 block cipher. We present two RC5 hardware structures: (i) an 8-bit serial RC5 architecture using a dual-part DDR unit; this design occupies only 54 slices on a Spartan-6 FPGA device and is 69% superior in terms of Throughput-per-Slice (TPS) compared to the smallest 8-bit AES FPGA implementation, (ii) a novel bit-serial RC5 architecture based on shift-register LUT (SRL) primitives; this design consumes only 20 Spartan-6 slices and shows 81% improvement in throughput performance at the expense of only 5% additional area resources compared to the smallest bit-serial AES design reported. The proposed DDR-based optimizations and efficient time scheduling make our proposed designs outperform most of the state-of-the-art lightweight block cipher designs in terms of hardware efficiency (with regard to TPS).