Simulation of Water Vapor Photodissociation during Dust Storm Season on Mars

Solar System Research - Within the framework of this work, using a three-dimensional numerical model of the general circulation of the Martian atmosphere MAOAM (Martian Atmosphere: Observation and...     

Optical Identification of Four Hard X-ray Sources from the INTEGRAL Sky Surveys

Astronomy Letters - We continue the study begun in Karasev et al. (2018) and present the results of our optical identifications of four hard X-ray sources from the INTEGRAL sky surveys. Having...     

Estimates of gravity wave drag on Mars: Indication of a possible lower thermospheric wind reversal

Spectral gravity wave parameterization suitable for planetary thermospheres applied to wind and temperature from Mars Climate Database reveals enormously strong drag incompatible with the wind distribution. It points out to a possible wind reversal in the 110-140 km layer similar to the one in the Earth’s lower thermosphere.     

The water cycle in the general circulation model of the martian atmosphere

Within the numerical general-circulation model of the Martian atmosphere MAOAM (Martian Atmosphere: Observation and Modeling), we have developed the water cycle block, which is an essential component of modern general circulation models of the Martian atmosphere. The MAOAM model has a spectral dynamic core and successfully predicts the temperature regime on Mars through the use of physical parameterizations typical of both terrestrial and Martian models. We have achieved stable computation for three Martian years, while maintaining a conservative advection scheme taking into account the water–ice phase transitions, water exchange between the atmosphere and surface, and corrections for the vertical velocities of ice particles due to sedimentation. The studies show a strong dependence of the amount of water that is actively involved in the water cycle on the initial data, model temperatures, and the mechanism of water exchange between the atmosphere and the surface. The general pattern and seasonal asymmetry of the water cycle depends on the size of ice particles, the albedo, and the thermal inertia of the planet’s surface. One of the modeling tasks, which results from a comparison of the model data with those of the TES experiment on board Mars Global Surveyor, is the increase in the total mass of water vapor in the model in the aphelion season and decrease in the mass of water ice clouds at the poles. The surface evaporation scheme, which takes into account the turbulent rise of water vapor, on the one hand, leads to the most complete evaporation of ice from the surface in the summer season in the northern hemisphere and, on the other hand, supersaturates the atmosphere with ice due to the vigorous evaporation, which leads to worse consistency between the amount of the precipitated atmospheric ice and the experimental data. The full evaporation of ice from the surface increases the model sensitivity to the size of the polar cap; therefore, the increase in the latter leads to better results. The use of a more accurate dust scenario changes the model temperatures, which also strongly affects the water cycle.     

Long-term numerical theories of comet motion

We propose a method of constructing numerical theories of comet motion that cover long time intervals. The method involves the determination of individual values of the constants A ₁, A ₂, and A ₃ (radial, transversal, and normal components of nongravitational acceleration) and photocenter shifts for each appearance with the presence of a sufficient quantity of observations. Moreover, in the case of close planetary approaches, bursts of brightness, or heavy shifts in the cometary gas production maxima against the perihelion when standard models of nongravitational acceleration cannot provide an accurate presentation of the observations, we propose the use of instant velocity measurements. This method was used to construct a unified numerical theory of motion of the Kopff comet in the interval of 1906–2002. The theory encompassed 16 appearances of the comet with the mean error of unit weight σ = 1.40.     

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.