The “four sigma” limit for significant periodicities

Most of the pulsations which have been observed in sdB stars have very low amplitudes. Detection of modes from photometric observations is usually performed by noting the most prominent peaks in a periodogram or, equivalently, an amplitude spectrum. A common strategy is to assume that peaks which exceed four times the mean noise level correspond to significant periodicities. The efficiency of the assumption is investigated by simulation. It is found that the actual significance levels corresponding to the four sigma limit may vary by orders of magnitude, depending on the exact data configuration.     

The 2–4-μm spectrum of Saturn's rings

Observations of the rings of Saturn at 2–4 μm reveal the presence of a 3.6-μm peak in the infrared reflectivity. This peak is consistent with a particle size of ? 50 μm, and a composition of pure H₂O ice. The quoted size may only be indicative of the textural scale of frost on the surface of larger particles. The presence of small amounts of CH₄ in the form of a clathrate, however, cannot be ruled out by our measurements.     

The origin of afternoon “auroral” radar echoes

One of the puzzling, and hitherto unexplained, properties of VHF backscatter from the auroral electrojet is the occurrence of a thin, horizontal and remarkably uniform backscattering layer during the afternoon period. If the backscattering regions are in fact twostream plasma instabilities, it is shown that the properties of the afternoon backscatter can be explained by invoking an electric field perpendicular to the magnetic field.     

The role of proton injection processes in the nonlinear evolution of “pearls”

Given a constant number of resonant protons in a field tube the unstable wave amplitude reaches a steady value rapidly due to nonlinear effects. Observations show that the pearl amplitudes grow gradually for a long time. Consistency with observations is obtained by taking into account the processes of proton injection.     

The use of micropulsation “whistlers” in the study of the outer magnetosphere

Certain types of micropulsation dynamic spectra show a series of rising tones thought to be caused by dispersion in the magnetosphere. Based on this idea and a previous analysis it is shown that these spectra can be used to evaluate the plasma density in the outer magnetosphere (five to eight Earth radii) in a way analogous to that used for VLF whistlers. The method is applied to micropulsations observed at Hobart in April, 1964. The results indicate a substantial decrease in plasma density beyond about five Earth radii in broad agreement with previous VLF work.     

The design,construction and performance of a large Hα and [Nii] interference filter for the SRC 48-inch Schmidt

The design, construction and performance of a 15-in. square mosaic interference filter is described. This is designed to improve the sensitivity of the SRC 48-in. Schmidt for the detection of gaseous nebulae in the light of H and [Nii] by approximately seven times. Its bandwidth with Kodak 098-04 emulsion is 105 Å but when combined with 103aE emulsion the effective bandwidth is around 80 Å.     

Search for variable sources using data of “Cold” surveys

We search for variable sources, using the data of the surveys conducted on the RATAN-600 radio telescope in 1980–1994 at 3.94 GHz. To test the radio sources of the RCR (RATAN Cold Refined) catalog for variability, we estimated the long-term variability indices V of the studied objects, their relative variability amplitudes V _χ , and the χ ² probabilities p. Out of about two hundred considered sources, 41 proved to have positive long-term variability indices, suggesting that these sources may be variable. Fifteen objects can be considered to be reliably variable according to the χ ² criterion p > 0.98, three of these sources have χ ² probabilities p ≥ 0.999. The corresponding probabilities for six sources lie in the 0.95 < p < 0.98 interval, and those of the remaining 20 objects in the 0.73 ≤ p < 0.95 interval. Twenty four of 41 objects are variable or possibly variable in the optical range, and five objects are known variable radio sources. We construct the light curves and spectra for the sources with positive long-term variability indices.     

The peculiar case of the “double-humped” super-luminous supernova SN 2006oz

SN 2006oz is a super-luminous supernova with a mysterious bright precursor that has resisted explanation in standard models.However,such a precursor has been predicted in the dual-shock quark nova model of super-luminous supernovae–the precursor is the supernova event while the main light curve of the super-luminous supernova is powered by the Quark-Nova（explosive transition of the neutron star to a quark star）.As the supernova is fading,the Quark-Nova re-energizes the supernova ejecta,producing a＂double-humped＂light curve.We show that the quark nova model successfully reproduces the observed light curve of SN 2006oz.     

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.