Astrophysical Bulletin最新文献

Observations of exoplanets in the ultraviolet (UV) wavelength range provide data about the structure of the exoplanetary atmosphere, as well as the atmospheric escape rate. Observations by the Hubble Space Telescope (HST) carried out in the spectral H Ly(alpha) line for the exoplanet (pi) Men c did not reveal any absorption in the blue and red wings of the line. However, due to the peculiarities of the HST orbit, these observations do not allow us to speak unambiguously about the presence or absence of hydrogen in the exoplanetary atmosphere; they only provide an estimate of the upper limit of the mass velocity for hydrogen in the atmosphere. The exoplanet (pi) Men c falls on the outer boundary of the Fulton division from the sub-Neptune side, which implies the presence of hydrogen in the exoplanetary atmosphere. Based on the assumption that (pi) Men c has a primary hydrogen-helium envelope, we performed kinetic modeling of non-thermal processes in the upper atmosphere of the exoplanet (pi) Men c. We considered the processes of suprathermal particle production in exothermic photochemistry under the action of hard ultraviolet (UV) radiation from the host star, as well as the effect of the stellar wind proton flux penetrating the atmosphere. The non-thermal atmospheric escape caused by the exposure to the hard radiation of the host star turned out to be comparable with the estimates of the escaping atmospheric flux due to the thermal processes. The energy of the stellar wind protons penetrating into the atmosphere is completely spent on heating the atmosphere.

In this work, we investigate the possibility of observing cusps—hot, pointed structures above solar flare loops—using the Mg XII spectroheliograph onboard the ‘‘CORONAS-F’’ satellite. This instrument produced monochromatic images of the solar corona in the Mg XII (lambda) 8.42 (text{AA}) line, which is formed at temperatures exceeding 4 MK. Observations of cusp tips, which are otherwise challenging due to the dominance of the cool coronal background, can aid in the analysis of reconnection dynamics and magnetic field topology. We examined three cusps observed using the Mg XII spectroheliograph and compared them with observations from the Extreme Ultraviolet Imaging Telescope (EIT) and the Soft X-ray Telescope (SXT). We concluded that EIT can observe cusps only when they are located on the limb, while the visibility of cusps in SXT images depends on the relative positioning of the cusps and adjacent coronal structures. In contrast, Mg XII images are free from these issues and are the most suitable for studying cusps. The characteristic sizes and lifetimes of the analyzed cusps are 300–500 Mm and 4–16 hours, respectively. For two cusps, motion of the cusp tip (i.e., the X-point) was observed over 2–3 hours, with characteristic speeds of 10–40 km s({}^{-1}). This suggests that reconnection can occur on timescales of several hours after the impulsive phase of the flare. Using the measured cusp tip velocities, we estimated the magnetic reconnection rate: (M_{A}approx 0.13).

We investigated the velocity field of the ionized gas and a star-formation ring in the lenticular galaxy NGC 6798 with a global counter-rotating gas disk. 3D spectroscopy data from the scanning Fabry–Perot interferometer of the 6-m BTA telescope of SAO RAS, as well as the data of narrow-band photometry in the emission lines H(alpha) and [N II] (lambda) 6583 from the MaNGaL mapper of the 2.5-m KGO telescope of SAI MSU were obtained and analyzed. We come to a conclusion that the case of NGC 6798 is consistent with one of the scenarios proposed earlier to explain the origin of lenticular galaxies—the orbital angular momentum of the cold outer gas accreted by the galaxy is too high, preventing it from penetrating into the central disk of the galaxy, where, being compressed by gravitation inside the stellar disk, it could begin to form stars. The weak current star formation that we did detect in NGC 6798 obviously began much later than the event of the formation of a large gas disk. The bar in the center of NGC 6798, and possibly the associated wave of radial gas contraction that we are now detecting in the ring complex of H II regions, is a consequence of a particular event in the life of the galaxy that took place no more than 1.5–2 Gyr ago.

Interstellar dust particles are swept up during the expansion of a supernova (SN) remnant, penetrate behind the shock wave front, where they are heated and destroyed in the hot gas. This leads to a change in the emission properties of such particles. The paper considers the evolution of the infrared (IR) luminosity of an SN remnant expanding in an inhomogeneous interstellar medium with a lognormal distribution of density perturbations. The IR luminosity of the swept up interstellar dust increases rapidly during the first few thousand years after the SN explosion and reaches a maximum. It then decreases due to the destruction of particles in the hot gas and a drop in their emissivity in the cooling gas of the shell. The dependence of the evolution of the IR luminosity of the dust in the remnant on the gas density dispersion ahead of the shock wave front from the SN is shown. It was found that the band centered at 70 (mu)m can be considered as the most optimal for studying late remnants, since the maximum IR luminosity is located within its limits for a significant time (40–50 kyr). During the evolution, the dust temperature changes from 70 to 20 K and weakly depends on the level of inhomogeneity of the medium. During the radiative phase, strong lines of metal ions appear in the remnant spectra against the dust continuum. Their luminosity grows rapidly and exceeds the luminosity of dust in the continuum under the line by approximately 10–10({}^{3}) times. The moment of achieving high luminosity in the lines depends significantly on the inhomogeneity of the medium. The possibilities of observing IR emission both in the dust continuum and in the lines are discussed. It is expected that their ratios will allow us to estimate the magnitude of inhomogeneity of the medium in which the remnant is expanding.

The review describes the evolution of high-resolution spectroscopic equipment mounted on the moving part of the alt-azimuth mount of the 6-m BTA telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. We list the main problems identified during operation of various detector types and execution of various observational programs. Restrictions on programs are identified that arise from various requirements for the positional stability of spectrographs. Prospects for reconstruction projects for Nasmyth focus instruments are assessed.

We present the results of spectroscopic observations of nine symbiotic star candidates in the 360–735 nm wavelength range carried out with the TDS spectrograph of the 2.5-m SAI MSU CMO telescope. Eight selected sample stars were classified as red giants of the M3–M6 spectral types. Light curve analysis revealed that all nine stars can be attributed to SRA- and SRB-type variables (based on the classification of the General Catalog of Variable Stars–GCVS). It is shown that one of the stars, V520 And, can be classified as a symbiotic star. Its spectrum reveals H I, He I, Fe II emission lines, weak lines of [O III] (lambda) 5007, [Ne III] (lambda) 3869, and He II (lambda) 4686, and a Balmer jump in emission. The emission spectrum is found to be variable on both the long and very short timescales. A high-resolution spectrum ((R=25000)) obtained with the new CMO spectrograph showed the double-peaked shape of the H(alpha) line and the presence of an absorption component in it. The October 14, 2023 photometric monitoring revealed a flickering in the (B) band with an amplitude of (0overset{textrm{m}}{.}8) on a timescale of 10–15 minutes. The luminosity, effective temperature, and radius of the V520 And cool component were determined: (L=1400{-}2200;L_{odot}), (T_{textrm{eff}}=3200) K, and (R=120{-}155;R_{odot}), respectively. Evidence for the presence in the system of an accretion disk with the luminosity (L<10;L_{odot}) was also found.

The paper presents the results of study of the exoplanet systems HD 189733, HAT-P-13, HAT-P-16 and HAT-P-65. The multi-color photometric observations of exoplanet transits in the listed systems were carried out in blue and red rays using the equipment of the Caucasian Mountain Observatory and the Crimean Astronomical Station of the SAI MSU. Based on the results, light curves were plotted, from which the radii of the exoplanets were determined. The shown difference in the radii of the exoplanets in different filters may indicate the presence of atmospheres in the exoplanets under study.

We describe the general remaining unclear issues of the star-formation process that could be studied using the millimeter radio telescope on the Suffa plateau (Uzbekistan). A description of possible objects of study is given. The possibilities of solving scientific problems in studying these objects using various instruments are assessed: the 70-m RT-70 radio telescope, a smaller-diameter antenna (15–20 m), and an antenna array consisting of small (3–8 m) antennas.

This paper is the second in a series of papers dedicated to the analysis of spectral and photometric observations of the Herbig Ae/Be star HD 179218. The variations in the H(alpha) and H(beta) line profiles in the star’s spectrum and the variations in its brightness and color indices in the (UBVRI) system are investigated. Regular variations of the profiles with periods from 37 to 737 days at a significance level of (10^{-4}) were revealed. Two of the found spectral periods agree with the photometric ones within the error limits. The regular spectral and photometric variability we discovered may indicate a presence of a companion or an exoplanet/exoplanets around the star, and may also be associated with the precession of the accretion disk and variation of the accretion rate.