Method for studying the spatial-temporal structure of wave-like disturbances in the ionosphere

The method for studying the spatial-temporal structure and propagation characteristics of traveling ionospheric disturbances, using the spectral and cross-correlation analysis of electron density disturbances at different altitudes, obtained with the incoherent scatter radar and vertical sounding ionosonde, is considered. Different algorithms for detecting traveling ionospheric disturbances and calculating the total vector of the disturbance propagation velocity are presented. The results of the method application have been considered in detail, using September 11, 2005, as an example.     

Optical Spectroscopy of Quasars Discovered by SRG/eROSITA with a 2.5-m Telescope at the Caucasus Mountain Observatory of SAI MSU

Astronomy Letters - Based on observations with the transient double-beam spectrograph (TDS) at the 2.5-m telescope of the Caucasus Mountain Observatory of SAI MSU, we have determined the redshifts...     

An Upper Limit on Nickel Overabundance in the Supercritical Accretion Disk Wind of SS 433 from X-ray Spectroscopy

We analyze a long (with a total exposure time of 120 ks) X-ray observation of the unique Galactic microquasar SS 433 carried out by the XMM-Newton space observatory with the goal of searching for the fluorescent line of neutral (or weakly ionized) nickel at energy 7.5 keV. We consider two models for the formation of fluorescent lines in the spectrum of SS 433: (1) through the reflection of radiation from a putative central X-ray source off the optically thick neutral gas of the supercritical disk “funnel” walls; and (2) due to the scattering of the radiation coming from the hottest parts of the jets in the optically thin wind of the system. We show that for these two cases the flux of the Ni I K_α fluorescent line is expected to be 0.45 of the flux of the Fe I K_α fluorescent line at 6.4 keV for the relative nickel overabundance Z_Ni/Z = 10 observed in the jets of SS 433. For the continuum model without the absorption edge of neutral iron, we have found an upper limit on the flux of the narrow Ni I K_α fluorescent line of 0.9 × 10^?5 phot s^?1 cm^?2 (90% confidence level). In the continuum model with the absorption edge we have determined an upper limit on the flux of the Ni I K_α line at the level of 2.5×10^?5 phot s^?1 cm^?2. At the same time, the flux of the fluorescent iron line has been measured to be 9.9 _8.4 ^11.2 × 10^?5 phot s^?1 cm^?2. This result implies that the nickel overabundance in the accretion disk wind should be at least a factor of 1.5 times smal than the corresponding nickel overabundance observed in the jets of SS 433.     

Extreme Storm Surges in the Gulf of Finland: Frequency-Spectral Properties and the Influence of Low-Frequency Sea Level Oscillations

Oceanology - An analysis of hourly tide gauge observation data yields time-frequency estimates of storm surges in the Gulf of Finland. Spectral analysis of long-term series made it possible to...     

Estimation of the Nucleus Size of Comet Shoemaker-Levy 9 under the Assumption of Its Step-by-Step Disintegration

The orbital dynamics of comet Shoemaker-Levy 9 was considered. The size of the nucleus before its disintegration was estimated using positional observations of individual fragments of the comet and taking into account the time when the fragment falls on Jupiter were observed. The center of inertia of the parent body was assumed to coincide with the center of fragment H at the moment of disintegration. The diameter of the parent body was estimated under different assumptions about the moments of disintegration. Thus, if the nucleus of the comet was disintegrated at the moment when fragment H was passing the perijovion, the diameter of the nucleus is equal to 1.39 km; if the nucleus was disintegrated two hours before the perijovion passage, the estimate of the nucleus diameter must be increased up to 9.03 km. The period of revolution of the comet nucleus was estimated assuming that the comet rotated about the axis perpendicular to its orbital plane. The calculations allowed us to assume that fragmentation of the nucleus began approximately an hour before the comet passed the perijovion and the diameter of the parent nucleus was about 4 km.     

Comparison of the electron density variations measured with instruments of the ISZF SO RAN radar complex under the conditions of different geomagnetic disturbance

The variations in the electron density measured with the incoherent scatter radar, DPS-4 digisonde, and FMCW ionosonde are compared in this work. The main regularities in differences are explained by the effect of different-scale ionospheric irregularities. Considerable morning gradients of electron density result in that ionosondes give increased values as compared to the incoherent scatter radar data. Electron density disturbances measured with different instruments can be of correlated and uncorrelated character. Uncorrelated disturbances are explained by intense medium-scale ionospheric irregularities. Correlated disturbances are caused by large-scale irregularities. Observation of such disturbances can be used to determine the velocity and direction of a disturbance.     

On the concept of the russian information and analytical center for asteroid and comet hazards

The concept is presented of the Russian information and analytical center for asteroid and comet hazards (IAC ACH) as a part of the national IAC for space threats. An overview is given of the center’s goals and objectives, as well as the requirements for the center, its structure, and the possible cooperation between the institutes of the Russian Academy of Sciences and other organizations in the creation of the center.