Quasi-periodic Signatures Research Articles

Modons on tidally synchronized extrasolar planets

ABSTRACT We investigate modons on tidally synchronized extrasolar planet atmospheres. Modons are dynamic, coherent flow structures composed of a pair of storms with opposite signs of vorticity. Modons are important because they can divert flows and lead to recognizable weather patterns. On synchronized planets, powered by the intense irradiation from the host star, large modons reach planetary-scale in size and exhibit quasi-periodic life-cycles – chaotically moving around the planet, breaking and reforming many times over long durations (e.g. thousands of planet days). Additionally, the modons transport and mix planetary-scale patches of hot and cold air around the planet, leading to high-amplitude and quasi-periodic signatures in the disc-averaged temperature flux. Hence, they induce variations of the ‘hotspot’ longitude to either side of the planet’s substellar point – consistent with observations at different epochs. The variability behaviour in our simulations broadly underscores the importance of accurately capturing vortex dynamics in extrasolar planet atmosphere modelling, particularly in understanding current observations.

EPIC 246851721 b: A Tropical Jupiter Transiting a Rapidly Rotating Star in a Well-aligned Orbit

Abstract We report the discovery of EPIC 246851721 b, a “tropical” Jupiter in a 6.18-day orbit around the bright (V = 11.439) star EPIC 246851721 (TYC 1283-739-1). We present a detailed analysis of the system using K2 and ground-based photometry, radial velocities, Doppler tomography, and adaptive optics imaging. From our global models, we infer that the host star is a rapidly rotating ( = 74.92 ) F dwarf with = 6202 K, and . EPIC 246851721 b has a radius of 1.051 ± 0.044 , and a mass of 3.0 . Doppler tomography reveals an aligned spin–orbit geometry, with a projected obliquity of , making EPIC 246851721 the fourth hottest star to host a Jovian planet with P > 5 days and a known obliquity. Using quasi-periodic signatures in its light curve that appear to be spot modulations, we estimate the star’s rotation period, and thereby infer the true obliquity of the system to be . We argue that this near-zero obliquity is likely to be primordial rather than a result of tidal damping. The host star also has a bound stellar companion, a 0.4 M dwarf at a projected separation of 2100 au, but the companion is likely incapable of emplacing EPIC 246851721 b in its current orbit via high-eccentricity Kozai-Lidov migration.

Transit probability of precessing circumstellar planets in binaries and exomoons

Over two decades of exoplanetology have yielded thousands of discoveries, yet some types of systems are yet to be observed. Circumstellar planets around one star in a binary have been found, but not for tight binaries (< 5 AU). Additionally, extra-solar moons are yet to be found. This paper motivates finding both types of three-body system by calculating analytic and numerical probabilities for all transit configurations, accounting for any mutual inclination and orbital precession. The precession and relative three-body motion can increase the transit probability to as high as tens of per cent, and make it inherently time-dependent over a precession period as short as 5-10 yr. Circumstellar planets in such tight binaries present a tempting observational challenge: enhanced transit probabilities but with a quasi-periodic signature that may be difficult to identify. This may help explain their present non-detection, or maybe they simply do not exist. Whilst this paper considers binaries of all orientations, it is demonstrated how eclipsing binaries favourably bias the transit probabilities, sometimes to the point of being guaranteed. Transits of exomoons exhibit a similar behaviour under precession, but unfortunately only have one star to transit rather than two.

Temperature fluctuations superimposed on background temperature change

Proxy data allows the temperature of the Earth to be mapped over long periods of time. In this work the temperature fluctuations for over 200 proxy data sets were examined and from this set 50 sets were analyzed to test for periodic and quasi-periodic fluctuations in the data sets. Temperature reconstructions over 4 different time scales were analyzed to see if patterns emerged. Data were put into four time intervals; 4,000 years, 14,000 years, 1,000,000 years, and 3,000,000 years and analyzed with a goal to understanding periodic and quasi-periodic patterns in global temperature change superimposed on a “background” average temperature change. Quasi-periodic signatures were identified that predate the Industrial Revolution, during much of which direct data on temperature are not available. These data indicate that Earth temperatures have undergone a number of periodic and quasi-periodic intervals that contain both global warming and global cooling cycles. The fluctuations are superimposed on a background of temperature change that has a declining slope during the two periods, pre-ice age and post ice age with a transition about 12,000 BCE. The data are divided into “events” that span the time periods 3,000,000 BCE to “0” CE, 1,000,000 BCE to “0” CE, 12,000 BCE to 2,000 CE and 2,000 BCE to 2,000 CE. An equation using a quasi-periodic (frequency modulated sine waves) patterns was developed to analyze the date sets for quasi-periodic patterns. “Periodicities” which show reasonable agreement with the predictions of Milankovitch and other investigators were found in the data sets.

NEARBY PLANETARY SYSTEMS AS LENSES DURING PREDICTED CLOSE PASSAGES TO BACKGROUND STARS

The Einstein rings and proper motions of nearby stars tend to be large. Thus, every year some foreground stars within a few hundred parsecs of Earth induce gravitational lensing events in background stars. In some of these cases, the events may exhibit evidence of planets orbiting the nearby star. In fact, planets can even be discovered during relatively distant passages. Here, we study the lensing signatures associated with planets orbiting nearby high-proper-motion stars. We find the following. (1) Wide-orbit planets can be detected for all distances of closest approach between the foreground and background stars, potentially producing independent events long before and/or after the closest approach. (2) Close-orbit planets can be detected for intermediate distances of closest approach, producing quasiperiodic signatures that may occur days or weeks before and after the stellar-lens event. (3) Planets in the so-called 'zone for resonant lensing' can significantly increase the magnification when the distance of closest approach is small, making the stellar-lens event easier to detect, while simultaneously providing evidence for planets. Because approaches close enough to allow planets to be detected can be predicted, we can plan observing strategies to take advantage of the theoretical framework built in this paper, which describes the sequence of expected effects in terms of a sequence of detection regimes.

Time signatures of impulsively generated coronal fast wave trains

Impulsively generated short-period fast magneto-acoustic wave trains, guided by solar and stellar coronal loops, are numerically modelled. In the developed stage of the evolution, the wave trains have a characteristic quasi-periodic signature. The quasi-periodicity results from the geometrical dispersion of the guided fast modes, determined by the transverse profile of the loop. A typical feature of the signature is a tadpole wavelet spectrum: a narrow-spectrum tail precedes a broad-band head. The instantaneous period of the oscillations in the wave train decreases gradually with time. The period and the spectral amplitude evolution are shown to be determined by the steepness of the transverse density profile and the density contrast ratio in the loop. The propagating wave trains recently discovered with the Solar Eclipse Coronal Imaging System (SECIS) instrument are noted to have similar wavelet spectral features, which strengthens the interpretation of SECIS results as guided fast wave trains.

Excitation and Damping of Low‐Degree Solarp‐Modes during Activity Cycle 23: Analysis of GOLF and VIRGO Sun Photometer Data

We have used observations made by the Global Oscillations at Low Frequency (GOLF) and the Variability of Irradiance and Gravity Oscillations Sun Photometer (VIRGO/SPM) instruments on board the ESA/NASA Solar and Heliospheric Observatory satellite to study variations in the excitation and damping of low angular degree (low-l) solar p-modes on the rising phase of activity cycle 23. Our analysis includes a correction procedure that for the first time allows GOLF data to be treated as a single homogeneous set, thereby compensating for the change of operational configuration partway through the mission. Over the range 2.5 ≤ ν ≤ 3.5 mHz, we uncover an increase in damping and decrease in mode power that is consistent with previous findings. Furthermore, an excellent level of agreement is found between the variations extracted from the GOLF and VIRGO/SPM data. We find no net long-term changes to the modal energy supply rate. However, an analysis of the residuals uncovers the presence of a quasi-periodic signature of period ≈1.5 yr (most pronounced for SPM). While it is true that several workers claim to have uncovered similar periodicities in other phenomena related to the near-surface layers of the Sun here, we are at present more inclined to attribute our finding to an artifact of the mode-fitting procedure. We also uncover a significant change in the asymmetry of mode peaks in the GOLF data, as found in previous studies of much longer data sets. These assumed that the dominant contribution to this arose from the switch in operating configuration partway through the mission (which altered the depth in the solar atmosphere sampled by the instrument). However, our preliminary analysis of data collected over the 100 day period beginning 2002 November 19—when the instrument switched back to its original configuration—suggests that this change may have a solar cycle component.

Spatially quasiperiodic plasma and electromagnetic signatures in the poleward boundary of the auroral oval: Observations on the morningside

We present observational characteristics of the spatially quasiperiodic signatures of plasma and electric and magnetic fields observed in the poleward boundary of the morningside auroral oval by two polar‐orbiting satellites: Akebono and DMSP F9. The two satellites observed the proton discrete signatures at different altitudes (∼5000 km (Akebono) and ∼800 km (DMSP F9)) during nearly the same intervals. The data indicate that the ion (proton) signatures repetitively appeared and had a good correlation with occurrence of spiky electrons associated with upward components of small‐scale field‐aligned currents and variations of electric fields. We conclude that the repetitive (quasiperiodic) proton signatures had spatially energy‐dispersed signatures, which were not due to transient effect, on the basis of a comparison of the simultaneous observations at the different altitudes. Characteristic energy of each dispersed trace decreased with decreasing latitude, and the energy‐dispersed signatures frequently overlapped each other. A global plasma convection reversal often occurred during the quasiperiodic proton signatures. Sequential observations show that the region with these proton signatures was latitudinally wide and extended significantly to higher latitudes under northward interplanetary magnetic field conditions. It is plausible that instabilities in the tail‐flank boundary of the magnetosphere, represented by the Kelvin‐Helmholtz instability, are driven by the interaction between the solar wind and the central plasma sheet and then could produce the precipitating ions and the electrons accompanied by the variations of the electric and magnetic fields.

Dynamical phenomena in Fibonacci semiconductor superlattices.

We present a detailed study of the dynamics of electronic wavepackets in Fibonacci semiconductor superlattices, both in flat band conditions and subject to homogeneous electric fields perpendicular to the layers. Coherent propagation of electrons is described by means of a scalar Hamiltonian using the effective-mass approximation. We have found that an initial Gaussian wavepacket is filtered selectively when passing through the superlattice. This means that only those components of the wavepacket whose wavenumber belong to allowed subminibands of the fractal-like energy spectrum can propagate over the entire superlattice. The Fourier pattern of the transmitted part of the wavepacket presents clear evidences of fractality reproducing those of the underlying energy spectrum. This phenomenon persists even in the presence of unintentional disorder due to growth imperfections. Finally, we have demonstrated that periodic coherent-field induced oscillations (Bloch oscillations), which we are able to observe in our simulations of periodic superlattices, are replaced in Fibonacci superlattices by more complex oscillations displaying quasiperiodic signatures, thus sheding more light onto the very peculiar nature of the electronic states in these systems.