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This paper presents a catalog of the energy distribution in the spectra of 263 stars in the wavelength range from 0.4 to 100 m, which are at late stages of evolution and have been observed by the ISO space observatory. For each object in the catalog, estimates of the observed bolometric fluxes were derived from smoothed energy distribution curves. The catalog is available at https://infra.sai.msu.ru/sai%5flss%5fsed both as a table and in machine-readable format. It is shown that for the specified sample of objects, their ISO SWS spectra in the range 2.4–45 m correspond to the general shape of the continuum in only 60 of cases, and can be used without recalibration. A selection of carbon stars, accessible for the infrared observations from the MSU observatories has been made. For some of them the first brightness estimates in the , and bands were obtained with the new IR camera of the 2.5-m telescope of CMO. [ABSTRACT FROM AUTHOR]

The results of photometric, polarimetric, and spectroscopic observations of the young star ZZ Tau IRS in the visible and near-infrared bands are presented. Against the continuum of an M spectral type star about 50 emission lines of allowed (H I, He I, Na I, S II) and forbidden (O I, O II, O III, N I, N II, S II, Ca II, Fe II, Ni II) transitions were identified. It was found that from the autumn of 2020 to the beginning of 2023, the brightness of the star in the visible region decreased ) and then began to return to the initial level. As the visible brightness of the star declined, its color indices decreased in the visible region, but increased in the near-IR bands. At light minimum, the degree of polarization in the band reached approx 13 , and the equivalent widths of, e.g., the H and [S II] 6731 lines increased to 376 and 79 , respectively. Arguments are given in favor of ZZ Tau IRS being a UX Ori type star, and its variability being due to eclipses by dust clouds, which are inhomogeneities in the dusty disk wind. Forbidden lines are formed both in the disk wind and in the jet, the axis of what is oriented along . The jet mass-loss rate exceeds yr , what is abnormally large for a star with a mass less than . Apparently, the disk wind of ZZ Tau IRS is not axially symmetric, probably due to the azimuthal asymmetry of the protoplanetary disk found earlier from ALMA observations. [ABSTRACT FROM AUTHOR]

This paper presents a prototype of an infrared photometer, created at the Sternberg Astronomical Institute, Lomonosov Moscow State University (SAI MSU), based on the commercial infrared module Gavin-615A. The operating spectral range of the photometer is 3–5 m. Investigations of the photometer's detector have shown that its parameters coincide with those stated by the manufacturer. The nonlinearity of the detector does not exceed across the entire signal range, and coefficients for correction functions were determined. Additionally, we determined the readout noise , the conversion coefficient ADU, the signal magnitude of the bias frame ADU, and the dark current /s, which is the sum of the detector's dark current and the radiation from the entrance window of the detector module. The value of dark current was measured at a window temperature of C. Observations commenced with the photometer at the 2.5-m telescope of the Caucasian Mountain Observatory of MSU, with the first results presented in this paper. The unvignetted field of view was . In the band under good atmospheric conditions, an image quality close to the diffraction limit was achieved. Images of a star with brightness and were obtained over the 20-s exposure time and a ratio. It is shown that at high image quality with and exposure of 20 s it is possible to observe stars up to 9 and . The main module of the photometer was also used in measurements of the sky background brightness. [ABSTRACT FROM AUTHOR]

The results of measurements of background brightness in the near-infrared range (J, H, K bands), carried out in 2016–2023 at the Caucasus Mountain Observatory of Moscow State University was analyzed. It is shown that the instrumental background associated with the thermal radiation of the telescope is noticeable only in the band, and at operating temperatures its contribution mainly determines the level of the overall background in this band. The coefficients of a polynomial taking into account the contribution of instrumental and extra-atmospheric backgrounds are presented. It is shown that the brightness of the sky background does not depend on air temperature, but a weak dependence on the water vapor content is observed, close to that expected from model calculations: in the and bands, the background brightness decreases at a rate of mm, and in the band it grows at a rate of mm. The maximum amplitude of background brightness variability on short time scales ( min) has been estimated: % in the and bands and % in the band. The maximum contribution of Moon's radiation scattered in the atmosphere to the overall background level has been determined. It is shown that this contribution can be ignored at an angular distance from the Moon greater than even during a full moon. The average background surface brightness mag/arcsec2 in the J, H, and bands was calculated: , , and . [ABSTRACT FROM AUTHOR]

We present the results of the infrared photometric observations in the bands and infrared spectroscopic observations in the range 1–2.5 m for the carbon Mira star T Dra performed from 2019 to 2023. An analysis of the photometric observations shows the presence of both pulsational brightness fluctuations with an amplitude falling from in the band to in the and bands and a linear trend in the mean brightness with a value of in the band. In the infrared spectrum of T Dra we have identified the absorption bands of C H , HCN, CN, CO, and C molecules. The depth of the absorption band at 1.53 m has been found to depend on the star's brightness. We show that the CO m bands have a high contrast, suggesting their formation not in the stellar atmosphere but in the circumstellar dust envelope. We present the spectral energy distribution of T Dra in a wide spectral range from which the bolometric fluxes at maximum and minimum brightness have been estimated: and W m , respectively. For the distance to T Dra of 944 pc they correspond to the star's luminosity at maximum brightness and at minimum brightness . We have modeled the radiative transfer in the circumstellar envelope of T Dra and estimated the parameters of the star and the envelope: K, , AU, AU, , , and yr . [ABSTRACT FROM AUTHOR]

We explain the details of the photometric operation mode of the ASTRONICAM near-IR spectrograph camera mounted on the 2.5-m telescope of the Caucasian Mountain Observatory of the Sternberg Astronomical Institute and describe algorithms used for primary correction and overall pipeline reduction of the acquired data. We present the transformation equations from the 2MASS photometric system to the instrumental -band system. We derive color transformation coefficients between the instrumental photometric system and standard MKO-NIR (Mauna Kea Observatories Near-Infrared) system for the , , and -band filters and show that the camera system is close to the standard photometric system. We found that in the case of observations at zenith, average background brightness level, and seeing the stars with , , can be measured with a 3000-s exposure at the signal-to-noise ratio . [ABSTRACT FROM AUTHOR]

The morphology and kinematics of the matter in the vicinity of young stars ZZ Tau and ZZ Tau IRS are studied. It has been found that the emission nebula (the H filament) located southwest of these stars, as well as the Herbig–Haro object HH 393 projected onto it are moving away from ZZ Tau and ZZ Tau IRS with a radial velocity of about 50 km s . On the inner edge of the western part of the H filament, there is a cooler filament emiting in the molecular hydrogen line ( m) and in the dust continuum. In the northeastern part of the studied region, a new Herbig–Haro object is discovered and assigned the number HH 1232. The presence of several more new emission nebulae is suspected. The electron density in the studied regions of the H filament, as well as HH 393 and HH 1232 cm . Arguments are presented in favor of the fact that the dusty disk wind has created a gas-and-dust nebula around ZZ Tau IRS, along the symmetry axis of which there is a jet moving in the direction of HH 393. [ABSTRACT FROM AUTHOR]

The results of photometric and spectral observations of T CrB obtained in a wide range of wavelengths in 2011–2023 are presented. We use the near-IR light curves to determine a new ephemeris for the times of light minima when the red giant is located between the observer and the hot component. The flux ratio H /H varied from to in 2020–2023, which may be due to a change in the flux ratio between the X-ray and optical ranges. It is shown that the value of H /H anticorrelates with the rate of accretion onto the hot component of the system. Based on high-speed follow-up observations obtained on June 8, 2023, we detected a variability of the He II line with a characteristic time-scale of min, the amplitude of variability in the -band was . Simulations of the near-IR light curves accounting for the ellipsoidal effect allowed us to obtain the parameters of the binary system: the Roche lobe filling factor of the cool component , the mass ratio , the orbital inclination . A comparison of the light curve obtained in 2005–2023 with the 1946 outburst template made it possible to predict the date of the upcoming outburst—January 2024. [ABSTRACT FROM AUTHOR]

The observations and comprehensive study of intermediate initial mass stars at the late stages of evolution, and after the asymptotic giant branch (AGB) in particular, are of crucial importance to identify the common properties for the stars of given group and to reveal binaries among them. This work aims to investigate photometric and spectral peculiarities of a poorly studied post-AGB candidate and infrared source IRAS 07253–2001. We present the new multicolor photometry obtained with the telescopes of the Caucasian mountain observatory and analyse it together with the data acquired by the All Sky Automated Survey for SuperNovae. We report on the detection of multiperiod brightness variability caused by pulsations. A beating of close periods, the main one of 73 days and additional ones of 68 and 70 days, leads to amplitude variations. We have also detected a long-term sine trend in brightness with a period of nearly 1800 days. We suppose it to be orbital and IRAS 07253–2001 to be binary. Based on new low-resolution spectroscopic data obtained with the 2.5-m telescope of the Caucasian mountain observatory in 2020 and 2023 in the 3500–7500 wavelength range we have identified spectral lines and compiled a spectral atlas. We have found the [N II], [Ni II] and [S II] forbidden emission lines in the spectrum and discuss their origin. The H line has a variable double-peaked emission component. We have derived preliminary estimates of the star's parameters and detected a variation of radial velocity with a peak-to-peak amplitude of about 30 km s . [ABSTRACT FROM AUTHOR]

The paper presents results of studying the kinematics of the ionized gas in the galaxy of the Large Magellanic Cloud type NGC 7292 obtained with the 2.5-m telescope of the Caucasian Mountain Observatory (CMO SAI MSU) and the 6-m BTA telescope of the Special Astrophysical Observatory (SAO RAS). Analysis of the velocity fields of the ionized and neutral hydrogen showed that the kinematic center of NGC 7292 located at the center of the bar, northwest of the photometric center of the galaxy (the southeastern end of the bar) previously taken as the center of NGC 7292. In addition to the circular rotation of the gas, the radial motions associated with the bar play a significant role in the kinematics of the disk. The observed perturbations of the gaseous-disk kinematics induced by the ongoing star formation do not exceed those caused by the bar. It is possible that part of the non-circular motions (at the southeastern end of the bar which is the brightest H II region) may be related to the effects of the capture of a dwarf companion or a gaseous cloud. [ABSTRACT FROM AUTHOR]

We report the results of optical spectroscopy of eight highly variable X-ray sources—AGN candidates from all-sky survey of the eROSITA telescope of the Spectrum-Roentgen-Gamma Space Observatory—performed with the TDS spectrograph (3600–7500 Å, ) attached to the 2.5-m telescope of the Caucasian Mountain Observatory of Sternberg Astronomical Institute of M.V. Lomonosov Moscow State University. We determined the redshifts of the sources from the emission and absorption lines in their spectra. At least five objects can be classified as Seyfert galaxies. We performed pilot infrared photometry of three distant quasars with using the ASTRONIRCAM camera and show that on the " " diagram the distant quasars studied can be confidently distinguished from Galactic red and brown dwarfs. This result proves the possibility of preliminary classification of distant X-ray quasar candidates by their IR colors for further detailed spectroscopic study on large telescopes. [ABSTRACT FROM AUTHOR]

The main factors that influence the success of observations in the infrared range (central wavelengths of the photometric bands at 3.75 and 4.8 m) on the multipurpose optical telescope are considered. Estimates of the sky background brightness are obtained for the Caucasus Mountain Observatory (CMO) of Moscow State University: photons/(s pixel) in the 3.75 m band and photons/(s pixel) in the 4.8 m; and the instrumental background for the 2.5-m CMO telescope at С: photons/(s pixel) in the 3.75 m band and photons/(s pixel) in the 4.8 m band. It is shown that at this background signal level with the currently available commercial cameras in the 3–5 m spectral range, the telescope–camera coupling capabilities for observing faint objects will still be limited by the thermal background. For different observational conditions, estimates of the limiting magnitudes of objects available for observations in the 3.75 and 4.8 m ranges are obtained. For average observation conditions (instrument temperature of C and stellar image size of ), the limit is and , respectively. [ABSTRACT FROM AUTHOR]

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 for 15 new quasars detected in X-rays by the eROSITA telescope of the SRG orbital observatory during the first three all-sky surveys. The redshifts of the sources lie in the range 0.5–4.156. We have estimated the masses of the central supermassive black holes and the bolometric luminosities for eight quasars from the width of the C IV 1549 Å emission line and the continuum flux at 1350 Å. For these objects we have also estimated the ratio of the X-ray luminosity to the Eddington limit to be a few percent. At the same time, the bolometric-to-Eddington luminosity ratio for them has turned out to be in a fairly narrow range, 30–40 . A large ratio points to an active growth of the mass of the central black holes in these objects. [ABSTRACT FROM AUTHOR]

We present the results of a UBVRcIc and JHKLM photometric monitoring campaign conducted in 2016–2020, low-resolution spectroscopy, and an analysis of the ASAS-3 and ASAS-SN photometric data for the semiregular variable and post-AGB candidate AU Vul (IRAS 20160+2734). The star is shown to experience quasi-periodic brightness oscillations with a variable amplitude and periods of 67–75 and 145–150 days in different time intervals. Its spectrum at maximum light is classified as that of an early G supergiant. In this spectrum H , H , and higher Balmer lines are weakened, possibly, because of emission components, while the absorptions of s-process elements (Ba II, Sr II, and Y II) are slightly strengthened. An H emission has been detected in the spectrum on the ascending branch of the light curve. TiO absorption bands are observed in the spectra at different brightness levels with maximum intensity at minimum light. The spectral energy distribution in the range 0.44 ()–2.2 () m corresponds to spectral types from G2I at maximum to G8I at minimum light. An emission excess has been detected in the and bands. The spectral energy distribution in the range 0.44–90 m constructed from our own observations and WISE, MSX, IRAS, and AKARI data is satisfactorily described by the sum of three components: a star and dust envelopes with K and K. Using the distance based on the Gaia EDR3 parallax, pc, we have estimated the absolute magnitude, , and the luminosity, . A comparison with evolutionary models has shown that AU Vul may be at the very beginning of the post-AGB stage of evolution and have a mass . We note that the star has a number of properties that distinguish it from typical post-AGB objects and make it akin to RV Tau stars. [ABSTRACT FROM AUTHOR]

The Transient Double-beam Spectrograph (TDS) is designed for low-spectral-resolution optical observations of nonstationary and extragalactic sources at the 2.5-m telescope of the Caucasus Mountain Observatory (CMO) of SAI MSU. The spectra are recorded simultaneously in two channels, short-wavelength (360–577 nm, reciprocal dispersion 1.21 Å/pixel, resolution with a -wide working slit) and long-wavelength (567–746 nm, 0.87 Å/pixel, ) ones, with the light between them being split by a dichroic mirror with a 50 transmittance at 574 nm. In the "blue" channel, it is possible to automatically replace the main grating by an additional one with a double resolving power. Two CCD cameras based on E2V 42-10 detectors cooled down to C with a readout noise of 3 electrons at a readout rate of 50 kHz serve as detectors. The height of the entrance slit is 3 arcmin. The spectrograph incorporates a back-slit viewing camera and a calibration unit to record the line spectrum of a gas-discharge lamp and a continuum LED source ("flat field") to take into account the vignetting and slit width nonuniformity. The transmittance of the entire optical path without losses on the slit at the zenith is 20 and 35 in the "blue" and "red" channels, respectively. Excluding the atmosphere and the telescope, the efficiency of the TDS itself reaches 47 and 65 at maximum, respectively. The spectrograph is permanently mounted at the Cassegrain focus of the 2.5-m CMO SAI MSU telescope together with a wide-field photometric CCD-camera; the light is fed into the spectrograph by a flat diagonal mirror inserted into the optical path. Regular observations of nonstationary stars and extragalactic sources to with a signal-to-noise ratio above 5 in 2 h of observations have been carried out with the TDS since November 2019. [ABSTRACT FROM AUTHOR]

The algorithm for the reduction of spectroscopic observations with the ASTRONIRCAM camera-spectrograph installed at the 2.5-m telescope of the Sternberg Astronomical Institute of the Moscow State University is described. The instrument allows spectra of astronomical objects with long () and short () slits to be taken in the wavelength range from 1 to 2.5 m. The measured resolution reaches for a slit; the light efficiency of the system changes from 6 to in the working wavelength range in the long-slit mode and from 1 to in the cross-dispersion mode. The transmission is limited by the quality of the grisms used. We have estimated the fraction of scattered light and studied the mechanical flexures and temperature drifts of the structure. [ABSTRACT FROM AUTHOR]