Do mesogranules exist?

Applying spatial and temporal averaging techniques to several long sequences of Dopplergrams obtained at the solar disk center and near the limb, we confirmed the persistent supergranule velocity pattern. After excluding the 5-min oscillation and supergranule velocity fields from the disk center Doppler data, we find that the velocity structure shows a typical scale of 7 Mm, consistent with the scale of mesogranules found by November, Toomre, and Gebbie (1981) and November et al. (1982). However, this velocity pattern does not show properties of the cellular convection. It is not coherent for more than one hour, the period during which the raw Doppler images are averaged to remove the 5-min oscillation. Furthermore, we did not find convection patterns in the scale of mesogranules from the Doppler data obtained near the solar limb. We propose that the mesogranule velocity structure found by November et al. might be the uncorrected part of the 5-min oscillation and granule velocity.     

Full-disk observations of solar oscillations from the geographic South Pole: Latest results

This paper presents the latest results obtained from the analysis of the full-disk Doppler shift observations obtained at the geographic South Pole in 1981. About 80 normal modes of oscillation (l = 0–3) have now been identified. Their frequencies range from 1886 Hz (l = 1, n = 12) to 5074.5 Hz (l = 2, n = 35), and their amplitudes are as low as 2.5 cm s^-1. Amplitude modulation occurs with periods of 1–2 days, and the individual oscillations appear to be excited randomly and independently. In cases where other groups have observed some of the modes identified by us, the agreement in frequency is good.Proceedings of the 66th IAU Colloquium: Problems in Solar and Stellar Oscillations, held at the Crimean Astrophysical Observatory, U.S.S.R., 1–5 September, 1981.     

The action of the satellite 1981 S13, and the optical depth profile of the Encke-gap ringlet in the Saturn A ring

The radial optical depth profile of the Encke ringlet obtained by the occultation experiment of the Voyager photopolarimeter (PPS data) is explained to be caused by the gravitational action of the recently discovered stallite 1981 S13 and a second smaller moonlet orbiting near one of its either libration points — L₄ or L₅. To this aim the results of previous and new numerical particle simulations as well as an extension of the scattering theory concerning a single moonlet to a pair of satellites have been used leading to a triple-peaked ringlet near the orbits of the moonlets. The width and the shape of that ringlet and its separate peaks depend on the mass ratio of both moonlets and on their orbital eccentricites. The best resemblance between the PPS data and the theoretical profile is obtained if the mass ratio of the either moonlets takes M₂/M_1981S13 ≈ (0.8 … 3.0) × 10⁻² and the eccentricities hold: e_1981S13 < h_1981S13; e₂ ≈ h₂ (the values h are the Hill scales of either moonlets defined by h_1981S13/2 ≈ (M_1981S13/2/3M_h)^1/3, M_h = Saturn mass). Furthermore, our results yield a size of 1981 S13 of < 15 km in diameter.     

Is there an oblique magnetic rotator inside the Sun?

The size of the rotational splitting recently observed (Claverie et al., 1981) is correlated with the 12.2^d variation in the measurements of solar oblateness observed by Dicke (1976) and implies a convection zone of depth of 0.1 R . The near equality of amplitudes of global velocity oscillations (Claverie et al., 1981) of the various m components of the l = 1 and l = 2 modes as seen from the Earth viewing the Sun nearly along the equator is unexpected for pure rotational splitting. It is suggested that a magnetic perturbation is present and an oblique asymmetric magnetic rotator with magnetic fields of a few million gauss is responsible. A more detailed account was submitted to Nature.Proceedings of the 66th IAU Colloquium: Problems in Solar and Stellar Oscillations, held at the Crimean Astrophysical Observatory, U.S.S.R., 1–5 September, 1981.     

Concerning time variation observations of the global magnetic field of the Sun

This paper is devoted to an analysis of some technique questions inherent in the problem of detection of weak periodic variations of the magnetograph signal in observations of large-scale magnetic fields on the Sun. Namely, using observational data obtained at the Sayan observatory STOP telescope (Grigoryevet al., 1981; Grigoryev and Demidov, 1987), we address the question of the dependence of signal strength variations in observations of the global magnetic field of the Sun on some other parameters recorded during observations: brightness, the position of the zero level, and the ratio of intensities of the splitting components. It is pointed out that, although the influence of these parameter variations can occur at several frequencies, the least reliable are long-period oscillations of the magnetic field with periodsP >L/2, whereL is the realization length. The most reliable for the data being analyzed are field variations with periods of 29 and 80 min, and the proximity of the latter to the harmonic of the well-known 160-min pulsations of the Sun suggests their possible relationship, but further investigations are needed.     

160-min oscillations of the Sun as the mean of study of its internal structure

The investigation of the models of the contemporary Sun with a mixed core has shown that the amplitude of some gravity modes of oscillations of the star can be mainly concentrated in the central region. This phenomenon takes place if the node of the amplitude of radial displacement coincides with the boundary of the mixed core. In this case the core can be regarded as a driving generator of the oscillations, determining their period and phase. It is suggested as the explanation of the observational properties of the 160-min oscillation.

     

New light on solar infrared intensity oscillations

The detection of large-amplitude infrared solar intensity oscillations in the 5-min region is reported. Using a broad-band multichannel photometer, the peak-to-peak intensity variation at 2.23 m is found to be as high as 2.4% for a circular aperture of 1 arc min and 0.8% in the full disk observations, i.e., remarkably higher than at the other four observed wavelength regions.The spatially-integrated power spectrum shows the 5-min oscillation plus a strong feature near 4 mHz. This feature coincides in frequency with the fundamental p-mode resonance of the chromosphere. However, a power-spectrum autocorrelation as well as a second-order Fourier transform of the data suggest that a high-frequency tail of the 5-min power spectrum is a more likely interpretation of this feature.     

The 160 minutes oscillations

We describe basic observational data regarding the 160-min oscillations of the Sun as well as the implications for helioseismology. The most acceptable theoretical interpretation seems to be a resonant interaction of gravity g-mode oscillations of the solar model with a slight modification to the equilibrium structure (with low heavy element abundance).It is noted also that there is significant 160-min commensurability over the solar system; e.g., spin rates of main and minor planets prefer, statistically, to be integer multiples of the 160-min period. The same period appears to be the most characteristic period (in the range studied from about 110 to 830 min) for the distribution of orbital periods of close binary stars. Allowing for these facts various non-classical suggestions as to possible nature of the 160-min period are briefly reviewed.     

The measurement of long-period oscillations at Sacramento Peak Observatory and South Pole

A program to measure long-period brightness oscillations at the solar limb has been pursued at Sacramento Peak Observatory for several years. Past improvements in observing technique and data analysis are reviewed. The encouraging results aid in the verification of the reality and the origin of oscillatory signals. However, the main stumbling block to this and other observational programs is the length of observing sequences imposed by the day/night cycle. The South Pole has received considerable attention as a site where extended observations might be possible. Currently, the Sacramento Peak program is developing a South Pole telescope designed for the observing technique and data analysis proven in Sunspot. A review of pertinent South Pole site parameters is given here for other workers who may be considering South Pole observations. Observing sequences longer than 150 hr are possible, though rare. Data sets of this duration are very attractive for solar oscillation studies.Proceedings of the 66th IAU Colloquium: Problems in Solar and Stellar Oscillations, held at the Crimean Astrophysical Observatory, U.S.S.R., 1–5 September, 1981.Operated by the Association of Universities for Research in Astronomy, Inc., under contract AST 78-17292 with the National Science Foundation.Summer Research Assistant at Sacramento Peak Observatory.     

Discovery of a coherent oscillation with a 1.07 h period in the suspected cataclysmic variable FBS 1220+753 (Dra 7)

We report results of extensive photometry of the suspected cataclysmic variable FBS 1220+753. The observations were obtained over 28 nights in 2010, 2011 and 2012. The total duration of the observations was 160 h. We clearly detected the highly coherent oscillation with a period of 1.0712887±0.0000013 h and a stable semi-amplitude of 0.03 mag. In a time scale of years, the oscillation period is very stable (dP/dt<(4.1±1.4)×10^?10). The light curves of FBS 1220+753 show no obvious flickering. The significant brightness changes on large time intervals are also absent. Therefore, it is unlikely that FBS 1220+753 is a cataclysmic variable. The period is compatible with oscillations seen in δ Sct variables. But its high stability and the unchangeable oscillation amplitude suggest that the oscillation cannot be caused by multiperiodic stellar pulsations. The average pulse shape of the oscillation is very sinusoidal with slightly sharper maxima compared with minima, but it is somewhat changeable from year to year. The light curves obtained in 2011 and folded with the doubled oscillation period reveal that the adjacent oscillation cycles have slightly different depths of the minima and different steepness of the rise and decline. This behaviour resembles the behaviour of the binary subdwarf–white dwarf systems, in which the variability is caused by ellipsoidal variations. However, the folded light curve obtained from the data of 2010 reveal nearly equal shapes of the adjacent oscillation cycles, and this does not conform to such an interpretation. Thus, the nature of the oscillation seen in FBS 1220+753 remains puzzling. To solve this puzzle, detailed spectroscopic observations are needed.     

The OSCROX stellar oscillaton code

This paper describes the OSCROX stellar oscillation code for the calculation of the adiabatic oscillations of low degree ? of a spherical star. There are two principal versions: one in Lagrangian variables (oscroxL), the second in Eulerian variables (oscroxE). The Lagrangian code does not require values of the Brunt Väisälä frequency or equivalently the density gradient. For ?=1 the oscillation equations have both an exact integral and an exact partial wave solution, and codes oscroxL1 and oscroxE1 incorporate these exact solutions. The difference in the frequencies obtained with the various codes gives some estimate of the uncertainty in the results due both to limited accuracy of hydrostatic support of the stellar model, and the limited accuracy of the integration of the oscillation equations. We compare the results of the different methods by calculating the frequencies in the range 20–2500 μHz of a model of a 1.5 M_⊙ main-sequence star (ModelJC) kindly provided by J. Christensen-Dalsgaard for the purposes of cross comparison of codes, a modified version of this model (ModelJCA) with improved hydrostatic support, and of a highly accurate n=3 polytropic model of a star with the same mass and radius. For the polytropic model the frequencies as calculated by all codes agree to within 0.001 μHz, whereas for the 1.5 M_⊙ main sequence model the frequency differences reach a maximum of 0.04 μHz, due primarily to the limited accuracy of hydrostatic support in the model; this is reduced to 0.01 μHz for ModelJCA.     

Penumbral oscillations in Na D lines

Penumbral oscillations were measured in two opposite parts in the penumbra of a spot, using photographic spectra of Na D lines. Power spectra of velocities show the presence of the 5-min oscillation with lowv _rms.Coherence and phase analyses between the velocity fluctuations of the lines are also studied.The results seem to show that the 5-min oscillation is still surviving as a standing or evanescent wave at the height of formation of Na D lines.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

Oscillations in the 45 – 5000 MHz Radio Spectrum of the 18 April 2014 Flare

Using a new type of oscillation map, made from the radio spectra by the wavelet technique, we study the 18 April 2014 M7.3 flare (SOL2014-04-18T13:03:00L245C017). We find a quasi-periodic character of this flare with periods in the range 65?–?115 seconds. At the very beginning of this flare, in connection with the drifting pulsation structure (plasmoid ejection), we find that the 65?–?115 s oscillation phase slowly drifts towards lower frequencies, which indicates an upward propagating wave initiated at the start of the magnetic reconnection. Many periods (1?–?200 seconds) are found in the drifting pulsation structure, which documents multi-scale and multi-periodic processes. On this drifting structure, fiber bursts with a characteristic period of about one second are superimposed, whose frequency drift is similar to that of the drifting 65?–?115 s oscillation phase. We also checked periods found in this flare by the EUV Imaging Spectrometer (EIS)/Hinode and Interface Region Imaging Spectrograph (IRIS) observations. We recognize the type III bursts (electron beams) as proposed, but their time coincidence with the EIS and IRIS peaks is not very good. The reason probably is that the radio spectrum is a whole-disk record consisting of all bursts from any location, while the EIS and IRIS peaks are emitted only from locations of slits in the EIS and IRIS observations.     

The most resonant pulsation frequency of δ Scuti stars

Pulsation of the Sun with a period of P₀ ≈ 160 min discovered about two decades ago, is still waiting explanation. In view of the hypothesis about its cosmological origin, and attempting to find signature of this P₀ periodicity among other (short-period variable) stars, the pulsation frequencies of δ Sct stars are subjected to specific analysis. With a confidence level ≈ 3.8σ it is found that the frequency v₀ = P₀⁻¹ ≈ 104 m̈Hz, within the error limits, appears indeed to be the most “resonant” one for the total sample of 318 pulsating stars of δ Sct type (the most commensurable, or “synchronizing”, period for all these stars occurs to be 162 ± 4 min). We conjecture that a) the P₀ oscillation might be connected with periodic fluctuations of gravity field (metrics), and b) the primary excitation mechanism of pulsations of δ Sct stars, reffected by this “ubiquitous” P₀ resonance, must be attributed perhaps to superfast rotation of their inner cores (their rates tend to be in near-resonance with the “universal” v₀ frequency). The arguments are given favouring a cosmoogical nature of the P₀ oscillation.     

Solar oscillations observed in the total irradiance

The total solar irradiance measurements obtained by the active-cavity radiometer on board the Solar Maximum Mission have been analyzed for evidence of global oscillations. We find that the most energetic low-degree p-mode oscillations in the five-minute band have amplitudes of a few parts per million of the total irradiance, and we positively detect modes with l = 0, 1, and 2. The distribution in l differs from that of the velocity spectrum, with relatively more power at lower l values. The individual modes have narrow line widths, corresponding to values of Q greater than a few thousand, or lifetimes of at least a week. We do not detect the 160-min oscillation in the power spectrum, and place an upper limit of 5 parts per million (99.9% confidence) on its amplitude.     

The lunar farside: The nature of highlands east of Mare Smythii

Available lunar orbital data were studied in detail to determine the nature and origin of geochemical variation in a portion of the farside highlands east of the Smythii basin. Such data exist for the elements Al, Mg, Fe, Ti, and Th (Clark and Hawke, 1981; Davis, 1980; Metzger et al., 1977). As in our previous studies (Clarke and Hawke, 1981, 1987), averages and ranges of concentrations for these elements are calculated and correlated for photogeologically defined units associated with features such as Babcock, King, Al-Khwarezmi, Langemak, Pasteur, and Sklodowska and with the region as a whole. In addition, comparisons are made between this and other highland regions which have been investigated by other workers in a similar manner (Andre et al., 1977; Haines et al., 1978; Maxwell and Andre, 1981). The region is shown to be distinctively enriched in the anorthositic end-members of the ANT-suite. Anomalies which have been reported for this region (Hawke et al., 1985) are confirmed by this study. An area south of Pasteur shows enrichment in some mafic components, giving evidence for the presence of buried mare basalt, and lending support to the hypothesis that volcanic activity may be fairly widespread even in the farside highlands. The units just southeast of Mare Smythii appear to be geochemically related to the area partly surrounding the Smythii on the west (Clark and Hawke, 1987). Considerable geochemical heterogeneity exists in this area, as in areas of the nearside highlands (Clark and Hawke, 1981, 1982, 1987; Hawke et al., 1985).     

Low-l 5-min oscillation observations

Medium resolution CCD-spectrograph observations have been obtained that are suitable for studying long spatial wavelength 5-min oscillations. We find evidence that at wavelengths of order one solar radius the oscillation field is not isotropic. It is also not well described by modes of uniform excitation. The velocity power density per spherical harmonic increases with decreasing l to 1.1 × 10³ cm² s^–2 per 3.5 × 10^–4 Hz angular frequency bandwidth at l = 4. These results are inconsistent with the data of Fossat and Ricort (1975) as analyzed by Christensen-Dalsgaard and Gough (1982), who found a substantially constant modal amplitude at intermediate l values. It is interesting that other calculations have seen a similar dependence at small l in the growth rate of p-modes due to the -mechanism.Visiting Astronomer, Sacramento Peak Observatory.     

Evidence for a small,high-Z,iron-like solar core

The high-Z core (HZC) model of the Sun, supported in Rouse (1985) by superior agreements of nonradial g-mode periods of oscillation with long period observations, is used to calculate frequencies of oscillation in the five-minute band (5MB). Allowing for the fact that the present HZC model profile does not include an upper photosphere and self-consistent chromosphere, the HZC model of the Sun is also supported by the very good agreements of the 5MB nonradial frequencies of oscillation with observations for HZC l degrees 0 to 19 and orders n 20, and the good agreement of the HZC purely radial frequencies of oscillation with about the same n-orders with observations previously identified as l = 0 oscillations. Two important aspects of these agreements are (1) the nonradial frequencies were calculated with the equations that neglect the gravitational perturbation (the Cowling approximation), and (2) the radial frequencies were calculated with the equation that includes the gravitational perturbation. The present agreements suggest that for solar-type stars, the gravitational perturbation may not affect the nonradial p-modes of oscillation as much as it affects the radial modes and the nonradial g-modes. More research will be performed.     

Inclined asymmetric librations in exterior resonances

Librational motion in Celestial Mechanics is generally associated with the existence of stable resonant configurations and signified by the existence of stable periodic solutions and oscillation of critical (resonant) angles. When such an oscillation takes place around a value different than 0 or \(\pi \), the libration is called asymmetric. In the context of the planar circular restricted three-body problem, asymmetric librations have been identified for the exterior mean motion resonances (MMRs) 1:2, 1:3, etc., as well as for co-orbital motion (1:1). In exterior MMRs the massless body is the outer one. In this paper, we study asymmetric librations in the three-dimensional space. We employ the computational approach of Markellos (Mon Not R Astron Soc 184:273–281,  https://doi.org/10.1093/mnras/184.2.273, 1978) and compute families of asymmetric periodic orbits and their stability. Stable asymmetric periodic orbits are surrounded in phase space by domains of initial conditions which correspond to stable evolution and librating resonant angles. Our computations were focused on the spatial circular restricted three-body model of the Sun–Neptune–TNO system (TNO = trans-Neptunian object). We compare our results with numerical integrations of observed TNOs, which reveal that some of them perform 1:2 resonant, inclined asymmetric librations. For the stable 1:2 TNO librators, we find that their libration seems to be related to the vertically stable planar asymmetric orbits of our model, rather than the three-dimensional ones found in the present study.     

Oscillations in Solar Faculae. III. The Phase Relations Between Chromospheric and Photospheric Line-of-Sight Velocities

An analysis of line-of-sight velocity oscillation in nine solar faculae was undertaken with the aim of studying phase relations between chromospheric (He?i 10830?Å line) and photospheric (Si?i 10827 Å line) five-minute oscillations. We found that the time lag of the chromospheric signal relative to photospheric one varies from ?12 to 100 seconds and is about 50 seconds on average. We assume that the small observed lag can have three possible explanations: i) convergence of formation levels of He?i 10830?Å and Si?i 10827?Å in faculae; ii) significant increase of five-minute oscillation propagation velocity above faculae; iii) simultaneous presence of standing and travelling waves.