“Hare and Hounds” Tests of Helioseismic Holography

We use the output of numerical wave-propagation simulations as synthetic data for “hare and hounds” tests of helioseismic holography. In the simple non-magnetic models examined here, we show that when the inversion method includes a consistent treatment of the filtering applied during the data analysis the inversions for the subsurface sound speed are qualitatively correct.     

The “FIP Effect” and the Origins of Solar Energetic Particles and of the Solar Wind

We find that the element abundances in solar energetic particles (SEPs) and in the slow solar wind (SSW), relative to those in the photosphere, show different patterns as a function of the first ionization potential (FIP) of the elements. Generally, the SEP and SSW abundances reflect abundance samples of the solar corona, where low-FIP elements, ionized in the chromosphere, are more efficiently conveyed upward to the corona than high-FIP elements that are initially neutral atoms. Abundances of the elements, especially C, P, and S, show a crossover from low to high FIP at \({\approx}\,10~\mbox{eV}\) in the SEPs but \({\approx}\,14~\mbox{eV}\) for the solar wind. Naively, this seems to suggest cooler plasma from sunspots beneath active regions. More likely, if the ponderomotive force of Alfvén waves preferentially conveys low-FIP ions into the corona, the source plasma that eventually will be shock-accelerated as SEPs originates in magnetic structures where Alfvén waves resonate with the loop length on closed magnetic field lines. This concentrates FIP fractionation near the top of the chromosphere. Meanwhile, the source of the SSW may lie near the base of diverging open-field lines surrounding, but outside of, active regions, where such resonance does not exist, allowing fractionation throughout the chromosphere. We also find that energetic particles accelerated from the solar wind itself by shock waves at corotating interaction regions, generally beyond 1 AU, confirm the FIP pattern of the solar wind.     

Possible presence of magnetic fields and iron content of atmospheres of “Metallic” Am-stars

Measurements with a CCD camera were made of two Fell lines at =6747.7 Å and 6149.2 Å in the spectra of 12 Am stars. The greater line strength of Fell 6147.7 Å relative to that of 6149.2 Å can be taken as evidence of a magnetic field in the atmosphere of the classical Am-star 15 Vul. Our observations support the conclusion of Mathys and Lanz [1] that a magnetic field is present in the atmosphere of yet another Am star, o Peg. For the rest of the stars studied the differences in the equivalent widths of the Fell lines can be explained by blending of the Fell line 6147.7 Å. Using the Fell line 6149.2 Å, which is free of blending, we estimate the iron content of the atmospheres of 12 Am stars with effective temperatures ranging from 7400 K to 9800 K. Our results indicate a star-to-star variation in log (Fe) of no less than 0.5 dex, a value greater than the measurement accuracy.Translated from Astrofizika, Vol. 37, No. 2, pp. 187–195, April–June, 1994.     

“Pure” supernovae and accelerated expansion of the Universe

A special class of type Ia supernovae that is not subject to ordinary and additional intragalactic gray absorption and chemical evolution has been identified. Analysis of the Hubble diagrams constructed for these supernovae confirms the accelerated expansion of the Universe irrespective of the chemical evolution and possible gray absorption in galaxies.     

Ultraviolet spectrum of FU Ori and a “Compromise” model of the FUor

We have analyzed the Hubble Space Telescope spectrum of the young star FU Ori in the range 2300–3100 Å. The long-wavelength part of the spectrum is similar to the spectrum of a supergiant with T _eff ? 5000–6000 K, but the range of wavelengths shorter than ?2600 Å is dominated by radiation from a region with T _eff ? 9000 K. We discuss the possibility of explaining these peculiarities of the spectrum, the Al II] 2669.2 emission line profile, and the results of X-ray observations for FU Ori in terms of an accretion disk model whose thickness increases as the star is approached starting from distances ?10¹² cm. Near the star, the disk has the shape of a cone in which only the part of its surface on the far (from the observer) side is visible. The suggested model is a kind of a compromise between the models of a thin α-disk and a supergiant: basically, this is an accretion model, but it resembles a supergiant in observational manifestations. Numerous absorption lines originating in the disk wind are superimposed on the disk spectrum. The wind is a cold (T ? 5000 K), dense (N _e ? 10¹¹ cm^?3) gas. The number of wind absorption lines in the ultraviolet spectrum of FU Ori increases with decreasing wavelength. This causes a rapid decline in intensity in the short-wavelength part of the spectrum. As a result, the maximum temperature in the disk estimated from low-resolution IUE spectra has been underestimated.     

Formation of “lightnings” in a neutron star magnetosphere and the nature of RRATs

The connection between the radio emission from “lightnings” produced by the absorption of high-energy photons from the cosmic gamma-ray background in a neutron star magnetosphere and radio bursts from rotating ratio transients (RRATs) is investigated. The lightning length reaches 1000 km; the lightning radius is 100 m and is comparable to the polar cap radius. If a closed magnetosphere is filled with a dense plasma, then lightnings are efficiently formed only in the region of open magnetic field lines. For the radio emission from a separate lightning to be observed, the polar cap of the neutron star must be directed toward the observer and, at the same time, the lightning must be formed. The maximum burst rate is related to the time of the plasma outflow from the polar cap region. The typical interval between two consecutive bursts is ∼100 s. The width of a single radio burst can be determined both by the width of the emission cone formed by the lightning emitting regions at some height above the neutron star surface and by a finite lightning lifetime. The width of the phase distribution for radio bursts from RRATs, along with the integrated pulse width, is determined by the width of the bundle of open magnetic field lines at the formation height of the radio emission. The results obtained are consistent with the currently available data and are indicative of a close connection between RRATs, intermittent pulsars, and extreme nullers.     

“Isotopic footprints” of gamma-ray and proton events and anomalous signal in radiocarbon in 775 AD

The production of the cosmogenic radionuclides ¹⁴C, ¹⁰Be, and ³⁶Cl in the Earth’s atmosphere under the action of powerful impulsive proton and gamma-ray events (superpowerful solar flares and Galactic gamma-ray bursts) is considered. The possible “isotopic footprint” in natural archives (the concentrations of these isotopes in dated polar ice cores and annual tree rings) has been calculated by taking into account geophysical processes. The results obtained have been applied to analyzing the anomalous increase in the concentration of radiocarbon measured in tree rings dated 774–775 AD. Arguments for the fact that the most likely cause of this increase is the high-energy emission from a Galactic gamma-ray burst are adduced.     

Spectral and photometric variability of the “runaway” star HD 214930

The paper contains the analysis of spectral and photometric variability of the “runaway” star HD 214930. The previously reported period of 4.7 day of the star’s radial velocity variability is confirmed. Optical photometric variability of the star has not been detected.     

Variable cosmological “constant” and motion of a test particle in a cloud of dust

We find that Einstein’s like field equations with coordinate-dependent cosmological “constant” Λ(x ⁱ ) imply a non geodesic law of motion for test particles moving in a continuous distribution of incoherent matter (“dust”). The deviation from the geodesic law depends on the derivatives ?Λ/? x ⁱ and, in the weak field approximation, causes an anomalous acceleration A～(Vc ²/γ ρ)?Λ/? t+(c ⁴/γ ρ)?Λ/? r where V=dr/dt, c=the speed of light, γ=8π G with G=the gravitational coupling, ρ=the mass density of the cloud, r and t are the radial and time coordinate respectively. Reasonable assumptions on Λ=Λ(t) give A<10^?8 cm/s² when ρ>10^?29 g/cm³ i.e. in all known astrophysical systems. A possible connection with the anomalous Pioneer acceleration is shortly discussed in the case of a cosmological “constant” coupled to matter.     

The seasonal variation of the newtonian constant of gravitation and its relationship with the “classical tests” of general relativity

The ratio between the Earth's perihelion advance (Δθ) _E and the solar gravitational red shift (GRS) (Δø _s e)a ₀/c ² has been rewritten using the assumption that the Newtonian constant of gravitationG varies seasonally and is given by the relationship, first found by Gasanalizade (1992b) for an aphelion-perihelion difference of (ΔG)_a?p . It is concluded that $$\begin{gathered} (\Delta \theta )_E = \frac{{3\pi }}{e}\frac{{(\Delta \phi _{sE} )_{A_0 } }}{{c^2 }}\frac{{(\Delta G)_{a - p} }}{{G_0 }} = 0.038388 \sec {\text{onds}} {\text{of}} {\text{arc}} {\text{per}} {\text{revolution,}} \hfill \\ \frac{{(\Delta G)_{a - p} }}{{G_0 }} = \frac{e}{{3\pi }}\frac{{(\Delta \theta )_E }}{{(\Delta \phi _{sE} )_{A_0 } /c^2 }} = 1.56116 \times 10^{ - 4} . \hfill \\ \end{gathered} $$ The results obtained here can be readily understood by using the Parametrized Post-Newtonian (PPN) formalism, which predicts an anisotropy in the “locally measured” value ofG, and without conflicting with the general relativity.     

The relationship of active comets, “extinct” comets,and dark asteroids

Spectrophotometric data on groups of asteroids in different types of orbits reveal different distributions of spectral properties, depending on whether the orbits are cometary or noncometary. In a list of 10 asteroids frequently suggested on purely dynamical grounds to be extinct or dormant comets, all have properties suggestive of spectral classes D, P, or C. Preliminary IRAS albedo results support this. Objects in these classes are very dark, reddish-black to neutral-black, and prevalent among the Trojans and outer belt. Two comets observed at low activity (visible nuclei) also have properties more consistent with D asteroids than any other class (very low reported geometric albedos of 0.02 and red colors). Consistent with these results are very low albedos reported for materials in more than a dozen comets; they average 0.05. Also, sampled cometary dust particles appear to consist of dark carbonaceous materials. Dramatically different are a control group of 13 Aten/Apollo/Amor objects selected from noncometary orbits. Most are in moderate-albedo classes: 8 or 9 appear to be of class S, and only 1 is in a low-albedo class (C). These are probably mostly objects perturbed out of the inner asteroid belt. The preponderence of S's in the noncometary group, together with the preponderence of ordinary chondrites among meteorites, may be evidence that such meteorites came from S asteroids. The data indicate that extinct, dormant, inactive, and minimally active comet nuclei have low albedos (p_v=a few percent) and very red to moderately red colors. As a group, their spectra are more similar to those of outer Solar System asteroids of classes D, P, and C, than to those of inner belt classes, though the observations are frequently not yet complete enough to assign definitively a spectral class. The results, taken together, support the view that dynamically identified “extinct comet candidates” are indeed outer Solar System objects probably of cometary origin. The results also support a scenario of Solar System formation in which dark carbonaceous dust dominated the spectrophotometric properties of planetesimals formed from about 2.7 AU out to at least the Trojan region at 5.2 AU. From 2.7 to at least 5.2 AU, and from class C to class D, the color of this dust reddens, apparently due to increasing amounts of red organic condensates. Comets are probably also colored to different degrees, by dust of this type, and may in some cases be even redder than D asteroids.     

Tidal gravitational forces: The infall of “new” comets and comet showers

The tidal gravitational field of the Galaxy directed into the galactic plane changes the angular momentum of comets in the Oort cloud. For comet orbits with semimajor axis greater than 2 × 10⁴ AU, the change of angular momentum in one orbit is sufficient to bring comets from the Oort cloud into the visible region, causing the infall of “new” comets. The limiting size orbit is weakly dependent on the angle between the major axis of the comet orbit and the galactic plane. The flux of comets into the inner Solar System caused by the galactic tidal field will be continuous and nearly isotropic. This effect appears to exclude any determination of the trajectories of passing stars by analysis of the angular distribution of new comets. The production of intense comet showers by the tidal field of a solar companion or of an interstellar cloud is considered. We show that the direction of a solar companion cannot be found from the present distribution of observable comets. The frequency of comet showers induced by encounters with interstellar clouds is found to be much lower than that from passing stars, and the tidal fields of interstellar clouds are not strong enough to cause comet showers of sufficient intensity to result in Earth impacts.     

Ionospheric and magnetospheric “plasmapauses”

During August 1972, Explorer 45 orbiting near the equatorial plane with an apogee of ～5.2 R_e traversed magnetic field lines in close proximity to those simultaneously traversed by the topside ionospheric satellite ISIS 2 near dusk in the L range 2.0–5.4. The locations of the Explorer 45 plasmapause crossings (determined by the saturation of the d.c. electric field double probe) during this month were compared to the latitudinal decreases of the H⁺ density observed on ISIS 2 (by the magnetic ion mass spectrometer) near the same magnetic field lines. The equatorially determined plasmapause field lines typically passed through or poleward of the minimum of the ionospheric light ion trough, with coincident satellite passes occurring for which the L separation between the plasmapause and trough field lines was between 1 and 2. Hence, the abruptly decreasing H⁺ density on the low latitude side of the ionospheric trough is not a near earth signature of the equatorial plasmapause. Vertical flows of the H⁺ ions in the light ion trough as detected by the magnetic ion mass spectrometer on ISIS were directed upward with velocities between 1 and 2 km s^?1 near dusk on these passes. These velocities decreased to lower values on the low latitude side of the H⁺ trough but did not show any noticeable change across the field lines corresponding to the magnetospheric plasmapause. The existence of upward accelerated H⁺ flows to possibly supersonic speeds during the refilling of magnetic flux tubes in the outer plasmasphere could produce an equatorial plasmapause whose field lines map into the ionosphere at latitudes which are poleward of the H⁺ density decrease.     

Influence of the Gravitational Fields of the Moon and the Sun on Long-Period Variations in the Proper Rotation of “Midas” Satellites

We report the results of an analysis of the variation of the proper rotation of several destabilized satellites over many-year long time intervals. The cause of the cyclic variations of the proper rotation period of “Midas-7” satellite, which has been orbiting the Earth since 1963 at an altitude of 3700 km, have long been unclear. These variations could not be explained either by the influence of the terrestrial atmosphere and terrestrial magnetic field, or by solar activity. Based on the results of 40-year long observations of “Midas-4,” “Midas-6,”, and “Midas-7” satellites it was established that their proper rotation exhibits not only dissipative braking variations, but also long-period variations with the periods of 477 days (“Midas-4”), 466 days (“Midas-6”), and 346 days (“Midas-7”) with different amplitudes. These variations in the case of the above satellites have well-defined resonance nature. An explanation of the processes found is proposed based on the results of this study and simulations of the observed orbital dynamics of the satellites. Long-period variations of the proper spacecraft rotation arise as a result of the combined effect of the gravitational fields of the Earth, Moon, and Sun depending on the orientation of their orbital planes in space. The amplitudes of such variations is determined by the inclination of satellite orbits to the equator: the closer it is to the pole (i.e., to 90?), the stronger the effect.     

Density distribution of solar wind protons and “loaded” ions in the shock layer ahead of a cometary ionosphere

We propose a simple method that allows the density fields of solar wind protons and heavy ions of cometary origin (“loaded” ions) in the solar wind-cometary ionosphere interaction region to be separated from the general density field calculated within the framework of a single-fluid model. The method is based on the assumption that the velocities of both components are identical. We analyze the density fields in the solar wind obtained in this way before and after the passage of the bow shock ahead of the cometary ionosphere and make a comparison with the distributions measured with various instruments onboard the Giotto spacecraft when it flew past Comet Halley and calculated on the basis of more complex multi-fluid models.     

Physical time and astronomical “time”

This sketch is based on the following line of thought. If we understand by (physical or dynamical) time the independent variable in the equations of motion, only quantities which are in a strictly linear relationship with this mechanical — physical time should properly be called time. This excludes therefore such concepts as e.g., sidereal time; in general that Earth Rotation Parameter which is one of the angles which define the orientation in space of a coordinate system fixed in a rigid model Earth. The relationships between these Eulerian angles and the ERP which follow from the theory of motion are discussed, also for the case that the reference system is an arbitrary noninertial system whose relationship (as a function of time) with an inertial system is known.     

A theoretical and empirical study of the response of the high latitude thermosphere to the sense of the “Y” component of the interplanetary magnetic field

The strength and direction of the Interplanetary Magnetic Field (IMF) controls the transfer of solar wind momentum and energy to the high latitude thermosphere in a direct fashion. The sense of “ Y” component of the IMF (BY) creates a significant asymmetry of the magnetospheric convection pattern as mapped onto the high latitude thermosphere and ionosphere. The resulting response of the polar thermospheric winds during periods when BY is either positive or negative is quite distinct, with pronounced changes in the relative strength of thermospheric winds in the dusk-dawn parts of the polar cap and in the dawn part of the auroral oval. In a study of four periods when there was a clear signature of BY, observed by the ISEE-3 satellite, with observations of polar winds and electric fields from the Dynamics Explorer-2 satellite and with wind observations by a ground-based Fabry-Perot interferometer located in Kiruna, Northern Sweden, it is possible to explain features of the high latitude thermospheric circulation using three dimensional global models including BY dependent, asymmetric, polar convection fields. Ground-based Fabry-Perot interferometers often observe anomalously low zonal wind velocities in the (Northern) dawn auroral oval during periods of extremely high geomagnetic activity when BY is positive. Conversely, for BY negative, there is an early transition from westward to southward and eastward winds in the evening auroral oval (excluding the effects of auroral substorms), and extremely large eastward (sunward) winds may be driven in the auroral oval after magnetic midnight. These observations are matched by the observation of strong anti-sunward polar-cap wind jets from the DE-2 satellite, on the dusk side with BY negative, and on the dawn side with BY positive.