Jupiter approaching asteroids and their possibilities for activity

Jupiter‐family comets (JFCs) may often, closely and/or slowly approach Jupiter. A list of their close approaches within 0.21 AU from Jupiter between 1970 and 2030 is presented to determine the typical changes in some of their orbital elements and their relation to any triggered activity. A few JFCs from the list were temporary satellites of Jupiter. There are also several JFCs which originally had asteroidal provisional designations due to their low activity at discovery. But Jupiter is also approached by asteroids. The presented list of their approaches within 0.60 AU from Jupiter between 1960 and 2040, together with their orbital changes can be compared with the list of comets. Some of the orbital changes are large enough to cause an extremely low or short‐lived activity. Usually, quick and dedicated observations by large‐aperture telescopes are missing to confirm or refute it. Currently, the most important cometary candidate among Jupiter approaching asteroids is 2004 FY140. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Role of the solar wind parameters in changing orbital motion of the Earth’s satellites

The investigation of the solar wind and geomagnetic activity parameters' effect on variations of the orbital motion periods of artificial satellites has been continued. The periods of orbital motion of uncontrolled satellites from the database of the Ukrainian network of optical stations (UNOS) for 2012–2014 was used. The data have been compared with the values of geomagnetic planetary index K and the energy spectra of protons and electrons obtained by the GEOS satellites in events during which the orbital periods have changed. It is shown that, in the energy spectra of the proton and electron fluxes, there is no effect of softening the spectrum with time at the time of the flare appearance. This indicates the possibility of particle accumulation above the active region (AR), which entails further continuous energy emission of the solar flare from AR. Dependences have been obtained between the geomagnetic activity and the solar wind speed at a given interplanetary magnetic field strength during the periods under study for the changes in the orbital motion periods of satellites. The corresponding correlation coefficients are 0.93–0.96.     

Orbital period modulation and magnetic cycles in close binaries

We discuss the observed orbital period modulations in close binaries, and focus on the mechanism proposed by Applegate relating the changes of the stellar internal rotation associated with a magnetic activity cycle with the variation of the gravitational quadrupole moment of the active component; the variation of this quadrupole moment in turn forces the orbital motion of the binary stars to follow the activity level of the active star. We generalize this approach by considering the details of this interaction, and develop some illustrative examples in which the problem can be easily solved in analytical form. Starting from such results, we consider the interplay between rotation and magnetic field generation in the framework of different types of dynamo models, which have been proposed to explain solar and stellar activity. We show how the observed orbital period modulation in active binaries may provide new constraints for discriminating between such models. In particular, we study the case of the prototype active binary RS Canum Venaticorum, and suggest that torsional oscillations — driven by a stellar magnetic dynamo — may account for the observed behaviour of this star. Further possible applications of the relationship between magnetic activity and orbital period modulation, related to the recent discovery of binary systems containing a radio pulsar and a convecting upper main-sequence or a late-type low-mass companion, are discussed.     

Orbital Period Studies of RS CVn-type binaries III. BH Virginis

The changes in the orbital period of the short-period RS CVn-type binaryBH Vir are studied based on the analysis of the O-C curve formed by allphotoelectric times of light minimum. It was discovered that the orbitalperiod of BH Vir may show a periodic variation with a period of 9.12years. A weak evidence also indicating a small amplitude oscillation witha period of 52.7 years in the change of the orbital period. Two possiblemechanisms (light times effects due to two hypothetical additional bodiesand magnetic activity cycle) that could explained the period behavior arestudied. The periodic changes in the orbital period can be explained asdue either to magnetic activity cycles in the two components or to thelight-times effects of the additional bodies.     

The non-synchronous systems among RS CVN stars

An RS CVn star is considered as non-synchronous if its orbital period differs by more than 4% from its photometric period. Of 88 systems examined according to this criterion, 67 are synchronous, 21 are non-synchronous. For the 21 non-synchronous systems, we find their spectral types are most around KO-2 III, that their orbital eccentricities are larger and their chromospheric activity lower than the average level.     

EN photographic Perseids

Many Perseid meteors were photographed in the Czech part of the European Fireball Network during the activity of the new strong and sharp maximum on August 12, 1993. Basic data on many of them were evaluated and radiants, atmospheric trajectories and some orbital elements are presented here and compared with atmospheric and orbital data of regular Perseids, which were photographed outside the new activity in 1993 and preceding years. No substantial difference between these two groups of Perseid meteors was found.     

云南-香港宽视场巡天新发现的一个磁活动双星系统

云南-香港宽视场巡天新发现了一个磁活动双星系统,其轨道周期为0.60286 d.利用云南天文台1 m光学望远镜附加CCD (Charge-Coupled Device)相机,观测得到了这个双星系统的V、Rc双色光变曲线,结果表明该系统食外存在明显的测光畸变.借助云南天文台丽江2.4 m望远镜附加云南暗弱天体光谱成像仪(Yunnan Faint Object Spectrograph and Camera, YFOSC)对该双星系统的分光观测,测定了该双星系统主星的视向速度曲线并发现该系统的主星表面存在着强烈的色球活动,从而证明系统的光变曲线畸变源自主星的黑子活动.使用W-D (Wilson-Devinney)程序分析上述观测得到的光变曲线和视向速度曲线,得到了该双星系统的轨道参数以及黑子参数.最后,对该系统的特性进行了讨论并对未来的工作进行了展望.     

Magnetic activity and dynamics of close binaries

The connection between orbital period modulation and magnetic activity in close binaries is reviewed with an emphasis on the comparison between observational data for RS CVn systems and recently proposed theoretical models. The orbital period changes occurring on timescales of the order of a few decades can be accounted for by means of a standing torsional Alfven wave in the convection zone of the magnetically active components of such systems. Two resonant excitation mechanisms based on the coupling between the wave and an αΩ dynamo are discussed from a qualitative point of view. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Effect of Atmospheric Drag on Satellite Orbits During the Bastille Day Event

Geomagnetic storms driven by solar eruptions are known to have significant effects on the total density of the upper atmosphere in the altitude range 250–1000 km. This in turn causes a measurable effect on the orbits of resident space objects in this altitude range. We analyzed a sample of these orbits, both from sensor data and from orbital element sets, during the period surrounding the 14 July 2000 solar activity. We present information concerning the effects of this event on the orbits of resident space objects and how well accepted atmospheric models were able to represent it. As part of this analysis, we describe a technique for extracting atmospheric density information from orbital element sets. On daily time scales, the effect of geomagnetic activity appears to be more important than that of prompt radiation. However, the limitations in time and amplitude quantization of the accepted solar indices are evident. A limited comparison is also made with previous solar storm events.     

A New Magnetically Active Binary System Discovered in Yunnan-Hong Kong Wide Field Survey

We present a newly discovered magnetically active binary system detected by Yunnan-Hong Kong wide field survey, with an orbital period of 0.60286 days. Two color photometry for the system was performed using the 1 m Cassegrain telescope of Yunnan Observatories with its CCD (Charge-Coupled Device) camera. In the observed light curves, there are clearly different light maxima existed in the out-of-eclipse regions. We made spectroscopic observations for the binary system using the 2.4 m telescope and YFOSC (Yunnan Faint Object Spectrograph and Camera) of Lijiang station of Yunnan Observatories, China. The radial velocity curve was derived for primary star of the binary system. The primary star exhibited strong chromospheric activity, which confirms that the distortion of the light curves results from the starspot activity on the primary star. Through analyzing the light curves and RV (Radial Velocity) curve mentioned above by means of the W-D (Wilson-Devinney) code, orbital parameters and starspot configuration of the binary system are obtained. Finally, we have discussed the properties of the binary system, and given the prospects on the future work.     

Orbital variations of satellite 1976-87a and a determination of the air density at heights of 205 – 220 km

We Investigate the orbital changes of the satellite 1976-87A (the sixth Chinese satellite) during its lifetime and from its orbital decay rate determine the air density at heights 205–220 km. The density we obtained is, on the average, over 20% greater than that in the CIRA 1972 model. We discuss in detail the correlation between changes in the density and in the geomagnetic activity, and the relationships between the geomagnetic effect and the latitude and the local solar time.     

Orbital Period Studies of the RS CVn-Type BinariesII. UV Piscium

Many available published times of light minima of the active binary system UV Psc have been collected and analyzed using a new method proposed by Kalimeris et al. (1994). Similar to what was seen in other RS CVn-type binaries, the orbital period of UV Psc oscillates with a period of about 61 years and an semi-amplitude of 0.21 ×10^-5 days. Two possible mechanisms (magnetic activity cycle mechanism and a light-time effect due to a hypothetical third body) that could modulated the orbital period behaviour are studied. We think that the cyclical period change in UV Psc can most probably be attributed to a magnetic activity cycle in the primary component. This revised version was published online in July 2006 with corrections to the Cover Date.     

Reanalysis of the orbital period variations of two DLMR overcontact binaries:FG Hya and GR Vir

We investigate orbital period changes of two deep, low mass ratio(DLMR) overcontact W UMa-type binaries, FG Hya and GR Vir. It is found that the orbital period of FG Hya shows a cyclic change with a period of P_(mod)= 54.44 yr. The cyclic oscillation may be due to a third body in an eccentric orbit, while the orbital period of GR Vir shows a periodic variation with a period of P_(mod)= 28.56 yr and an amplitude of A = 0.0352 d. The periodic variation of GR Vir can be interpreted as a result of either the light-time effect of an unseen third body or the magnetic activity cycle.     

A note on the Delta Aurigid meteor stream

Seven doubly photographed meteors reported in the literature are shown to be members of the Delta Aurigids, which now appear to extend from September 29 to October 18. Visual observations from the second half of activity in 1980 reveal a zenith hourly rate of no more than 2 or 3. The mean orbital elements of the stream point to an unknown short period (115 years) retrogade comet as a parent.     

Fast and accurate computational tools for gravitational waveforms from binary stars with any orbital eccentricity

The relevance of orbital eccentricity in the detection of gravitational radiation from (steady state) binary stars is emphasized. Computationally effective (fast and accurate) tools for constructing gravitational wave templates from binary stars with any orbital eccentricity are introduced including tight estimation criteria of the pertinent truncation and approximation errors.     

Orbital dynamics and equilibrium points around an asteroid with gravitational orbit–attitude coupling perturbation

The strongly perturbed dynamical environment near asteroids has been a great challenge for the mission design. Besides the non-spherical gravity, solar radiation pressure, and solar tide, the orbital motion actually suffers from another perturbation caused by the gravitational orbit–attitude coupling of the spacecraft. This gravitational orbit–attitude coupling perturbation (GOACP) has its origin in the fact that the gravity acting on a non-spherical extended body, the real case of the spacecraft, is actually different from that acting on a point mass, the approximation of the spacecraft in the orbital dynamics. We intend to take into account GOACP besides the non-spherical gravity to improve the previous close-proximity orbital dynamics. GOACP depends on the spacecraft attitude, which is assumed to be controlled ideally with respect to the asteroid in this study. Then, we focus on the orbital motion perturbed by the non-spherical gravity and GOACP with the given attitude. This new orbital model can be called the attitude-restricted orbital dynamics, where restricted means that the orbital motion is studied as a restricted problem at a given attitude. In the present paper, equilibrium points of the attitude-restricted orbital dynamics in the second degree and order gravity field of a uniformly rotating asteroid are investigated. Two kinds of equilibria are obtained: on and off the asteroid equatorial principal axis. These equilibria are different from and more diverse than those in the classical orbital dynamics without GOACP. In the case of a large spacecraft, the off-axis equilibrium points can exist at an arbitrary longitude in the equatorial plane. These results are useful for close-proximity operations, such as the asteroid body-fixed hovering.     

Activity Profile of the Sextantid Meteor Shower

The detailed activity profile of the Sextandids - one of the day-time meteor showers - is poorly known and still unclear. Using the forward-scatter radio technique we have successfully been able to obtain further detailed overall activity profile of the Sextantids for seven consecutive years: 1991–1997. Analysis confirmed the Sextantid activity duration in solar longitude (J2000) of at least 184–193° and the maximum solar longitude at 188.35 ± 0.10° with a full width at half maximum (FWHM) of 2.0 ± 0.2°. Performing the numerical integrations, we also substantiated a possibility of the association between Apollo-type asteroid (3200) Phaethon and the Sextantids. Furthermore, we roughly estimated relative maximum flux rate of Sextantids : Geminids as 1 : 3 amplitude ratio. Depending upon the flux rates and the time lags of the orbital evolution with Phaethon, we conclude that the Sextantids are at a more progressive stage of orbital evolution than the Geminids if both meteor streams are really associated with Phaethon. This revised version was published online in July 2006 with corrections to the Cover Date.     

Tidally driven stress accumulation and shear failure of Enceladus's tiger stripes

Straddling the south polar region of Saturn's moon Enceladus, the four principal “tiger stripe” fractures are a likely source of tectonic activity and plume generation. Here we investigate tidally driven stress conditions at the tiger stripe fractures through a combined analysis of shear and normal diurnal tidal stresses and accounting for additional stress at depth due to the overburden pressure. We compute Coulomb failure conditions to assess failure location, timing, and direction (right- vs left-lateral slip) throughout the Enceladus orbital cycle and explore a suite of model parameters that inhibit or promote shear failure at the tiger stripes. We find that low coefficients of friction (μf=0.1-0.2) and shallow overburden depths (z=2-4 km) permit shear failure along the tiger stripe faults, and that right- and/or left-lateral slip responses are possible. We integrate these conditions into a 3D time-dependent fault dislocation model to evaluate tectonic displacements and stress variations at depth during a tiger stripe orbital cycle. Depending on the sequence of stress accumulation and subsequent fault slip, which varies as a function of fault location and orientation, frictional coefficient, and fault depth, we estimate resolved shear stress accumulation of ∼70 kPa prior to fault failure, which produces modeled strike-slip displacements on the order of ∼0.5 m in the horizontal direction and ∼5 mm in the vertical direction per slip event. Our models also indicate that net displacements on the order of 0.1 m per orbital cycle, in both right- and left-lateral directions, are possible for particular fault geometries and frictional parameters. Tectonic activity inferred from these analyses correlates with observed plume activity and temperature anomalies at Enceladus's south polar region. Moreover, these analyses provide important details of stress accumulation and the faulting cycle for icy satellites subjected to diurnal tidal stress.     

The semi-annual variation in air density for 1974–1978 from the orbit of 1972-05B

Values of air density at 712 epochs between August 1973 and September 1978 have been determined using orbital elements of 1972-05B with orbital decay rates from NORAD bulletins. Normalised to a series of fixed heights and cleared of the effects of solar activity, geomagnetic activity and the diurnal variation, the residual air density was analysed for the semi-annual variation. This variation exhibited maxima usually in April and October and minima usually in January and July.

For 1974–1978, this study revealed near-identical values of the April and October maxima and a July minimum 12% stronger than the January minimum. Further, the shape and phase of the variation exhibited an irregular pattern from year-to-year. Overall the amplitude of the variation was considerably greater than that given in the atmospheric models (CIRA, 1972; Jacchia, 1977). Other observations included the presence of subsidiary minima and maxima in late May and June respectively during 1977 and 1978 and a general increase in air density from mid 1977 onwards, relative to the atmospheric models.     

Are the W Ursae Majoris-type systems EK Comae Berenices and UX Eridani surrounded by circumstellar matter?

The variations of the orbital periods of two nearly neglected W UMa-type eclipsing binaries, EK Comae Berenices and UX Eridani, are presented through a detailed analysis of the O–C diagrams. It is found that the orbital period of EK Com is decreasing and the period of UX Eridani is increasing, and several sudden jumps have occurred in the orbital periods of both binaries. We analyze the mechanism(s), which might underlie the changes of the orbital periods of both systems, and obtain some new results. The long-term decrease of the orbital period of EK Comae Berenices might be caused by the decrease of the orbital angular momentum due to a magnetic stellar wind (MSW) or by mass transfer from the more massive to the less massive component. The secular increase in the orbital period of UX Eridani might be caused by mass transfer from the less massive to the more massive star. The possible mechanisms, which underlie the sudden changes in the orbital periods of the close binary systems are as the followings: (1) the variations of the structure due to the variation of the magnetic field; (2) the rapid mass exchange between the close binaries and their circumstellar matter. Finally, the evolutionary status of the systems EK Comae Berenices and UX Eridani is discussed.