To search for and study the instabilities in the atmospheres of selected post-AGB stars, we have performed a long-term high-resolution spectroscopy ( R≥ 60 000 ) with the NES spectrograph of the 6-m BTA telescope. Low-amplitude pulsations, splitting and/or asymmetry of the absorption profiles with a low excitation potential (mainly absorptions of s -process metals), as well as variability of a complex H_α profile have been registered in the optical spectra of single stars associated with the IR sources IRASz02229+6208, IRAS 04296+3429, IRAS 07134+1005, IRAS 07430+1115, IRAS 19500 - 1709, IRAS 22223+4327, and IRAS 23304+6147 that had previously undergone the third mixing. The maximum pulsation amplitude A_V_r was detected for the stars in the IRAS 07134+1005 and IRAS 19500 - 1709 systems, which have the maximum temperatures among the stars in the studied sample. Stratification of radial velocity in the atmosphere was found for two stars in the sample. The luminosity of the studied stars was estimated based on the intensity of the IR oxygen triplet O I λ 7774. Moreover, a luminosity of log L/L_⊙≈ 3.1 was obtained for the star in the IRAS 07430+1115 system within the range of typical post-AGB star luminosity values, which eliminates the paradox of the luminosity and the initial mass of this object.

In order to study the instability of the spectrograph, temperature and positional monitoring of the quartz echelle spectrograph NES, located on the Nasmyth-2 focus platform of the 6- meter BTA telescope, was carried out. Over the course of just over two days, three series of exposures of the comparison spectrum lamp were obtained. In each series of exposures, the spectrum of the comparison lamp was recorded at intervals of 15 minutes and the readings of temperature sensors installed on the periphery of the NES were recorded. A correlation analysis of the obtained data was carried out. Based on the totality of the results, it was concluded that the main reason for the instability of the NES spectrograph is the thermal deformation of the pre-slit part.

The development of a corrector for low-frequency variations in the star image at the input of ESPriF—the echelle spectropolarimeter of the BTA primary focus—is reported. New technical solutions have made it possible to extend the operating frequency range to 10 Hz for stars brighter than 13^m .

High resolution optical spectra (R = 60 000) of the dormant LBV star P Cyg were obtained on the BTA telescope in the wavelength range Δλ = 477- 780 nm. After performing a detailed identification of different types lines (photospheric absorptions, permitted and forbidden emissions, components of lines with profiles of P Cyg type), we studied the variability of their profiles and patterns of radial velocities. The average radial velocity from positions of forbidden emissions ([N II] 5754.64, [Fe II] 5261.62, [Fe II] 7155.14 and [Ni II] 7377.83 Å) is accepted as the system V_sys = - 34 ± 1.4 km/s. About a dozen photospheric absorptions of CNO-triad ions and Si III are found, their stable position, V_r(abs) = - 73.8 km/s, shifted relative to V_sys at about - 40 km/s, indicates that these absorbtions are formed in the pseudophotosphere region. The high-excitation emissions ([O I] 5577, 6300, 6363 Å, [O III] 4959 and 5007 Å, as well as He II 4686 Å) are absent in the spectra. The radial velocity V_r(DIBs) = - 11.8 km/s according to the position of numerous DIBs is consistent with the position of the interstellar components of the D-lines Na I and K I forming in the galactic Perseus arm. An excess of color E(B- V) = 0.34 ±0.03^m and interstellar absorption A_v = 1.09^m were determined by measurements of equivalent widths of nine DIBs.

Having obtained high-resolution optical spectra with the NES spectrograph of the 6-m telescope BTA, we investigated the variability of the spectral features and radial velocity for a cold star which passed the asymptotic branch of giants and is associated with the IRAS 07430+1115 source. The optical spectrum of this post-AGB star with altered chemical composition is purely absorbtional, emissions and other peculiarities are absent in the spectrum. From the measurements of the positions of many metal absorbtions (mainly ions of heavy $s$-process metals) a weak variability of the radial velocity was revealed. The velocity varies with the average value $V_r=37.0$ km/s and the standard deviation $\Delta V_r \approx 0.8$ km/s, which may be a consequence of low-amplitude pulsations in the atmosphere of a far evolved star. The position of the H$\alpha$ line core varies within 40.5–43.8 km/s. Based on measurements of the positions of the rotational components of the (0;0), (1;0) and (2;0) Swan bands of the molecule C$_2$ origin in the circumstellar envelope, the average radial velocity $V_r{\rm (Swan)}=21$ km/s and the expansion velocity typical for post-AGB stars envelope $V_{\rm exp} \approx 16$ km/s are determinated. Using the intensity of the infrared triplet of oxygen, we estimated the luminosity of the central star of the IRAS 07430 system $\log L/L_{\odot} \approx 3.1$ which is within the range of values for post-AGB stars.

High-resolution optical spectra of the B[e] star CI Cam were obtained on arbitrary dates 2002–2023 using the 6-meter BTA telescope with the echelle spectrograph NES. The variability over time of the powerful emissions of Hα and He I profiles is found. For two-peak emissions with “rectangular” profiles, the intensity ratio of blue-shifted and red-shifted peaks is V/R⩾ 1 , except one date. A decrease in the intensity of all double-peaked emissions with “rectangular” profiles was revealed as they moved away in time from the 1998 outburst. The average radial velocity for emissions of this type for all observation dates varies in the range V_r(emis- d) = - (50.8 ÷ 55.7) ± 0.2 km/s. The half-amplitude of the change (standard deviation) is equal to ΔV_r = 2.5 km/s. The velocity for single-peaked ion emissions (Si III, Al III, Fe III) differs little from the values of V_r(emis- d) , but the measurement accuracy for these emissions is worse: the average error for different dates ranges from 0.4 to 1.3 km/s. The systemic velocity is assumed to be V_sys = - 55.4 ± 0.6 km/s according to the stable position of the forbidden emission [N II] 5755 Å. The position of single-peak emissions [O III] 4959 and 5007 Å is also stable: V_r([O III]) = - 54.2 ± 0.4 km/s. Emissions [O I] 5577, 6300, 6363 Å, [Ca II] 7291 and 7324 Å are absent from the spectra. Appearance of the emission near 4686 Å is an infrequent event, its intensity rarely exceeds the noise level. Only a wide asymmetric emission with an intensity of about 16

The article discusses the challenges and solutions associated with high-resolution spectroscopy on alt-azimuth mount telescopes, particularly focusing on the 6-meter BTA (Big Telescope Alt-Azimutal) and its Nasmyth focus. The main attention is given to the instability of spectra caused by the design features of the telescope and the equipment used. Special attention is paid to the issues of temperature non-uniformity and its impact on observation quality. Various stages of equipment development and testing are described along with the results of applying new technologies and methods to achieve high spectral resolution.

Аннотация. Сообщается о разработке нескольких проектов, направленных на повышение эффективности спектроскопии звезд на

Аннотация.Развитие наземной астрономии СССР, увенчавшееся проектами БТА и РАТАН, происходило в системе научно-организационных отношений, формировавшейся ещё в период довоенного становления и развития отечественных научно-технических проектов.В 20-е годы прошлого века была сформулирована и развивалась концепция ГРАФО (Горной Российской астрофизической обсерватории).Попытки реализации этого проекта в 30-е годы завершились организацией оте

High-resolution spectra of the LBV candidate Schulte 12 in the Cyg OB2 association were obtained at the 6-m BTA telescope with the NES echelle spectrograph on the arbitrary dates in 2001–2022. Variability of the emission profile of Hα and absorptions of He I, Si II with time was found. Based on the radial velocity measurements at 10 observation dates, radial velocity variability with an amplitude of $$\Delta {{V}_{r}} \approx $$ 8 km/s relative to the average value of the heliocentric velocity $${{V}_{r}} = - 15.6 \pm 2.6$$ km/s was revealed. This indicates the presence of a companion in the system. Based on the reliable intensity measurements of a sample of DIBs, color excess $$E(B - V) = 1.74 \pm {{0.03}^{m}}$$ was found. This results in the interstellar extinction value $${{A}_{{\text{v}}}} \approx {{5.6}^{m}}$$ that is only about half of the total extinction. Taking modern Schulte 12 parameters, including Gaia EDR3 parallax, we estimated its absolute magnitude as Mv ≈ $$ - {{9.2}^{m}}$$ and luminosity $${\text{log}}(L{\text{/}}{{L}_{ \odot }}) \approx 5.5$$ , which does not exceed the Humphreys–Davidson limit.

We present a survey of the results of photometric and spectral observations of a nebula AFGL 2688 in the system of post-AGB star V1610 Cyg. Apart from the analysis of the published results, our new spectral observations of the star at the BTA over 2002–2022 are also given consideration. A new understanding of the kinematics of gas and dust in the lobes of the nebula has been obtained. The totality of published data, registered in a wide range of wavelengths, allows us to consider AFGL 2688 as a prototype nebula for the stars undergoing the post-AGB stage. An assumption on the variation of the chemical composition of the central star is made. We discuss the prospects for studying the object in the optical range.

We present the second part of the review of spectroscopic observations of Mira variables in the optical and near infrared. The role of various structures (atmosphere, envelopes) in the formation of the optical spectrum is estimated. The thickness of the molecular layer that creates the observed effects of distortion of the emission spectra is estimated based on two model approximations. Assuming that a significant part of the optical spectrum is formed in the circumstellar envelopes, the known photometric and spectroscopic effects are discussed.

Over the past two decades the echelle spectrograph NES of the 6-m telescope was used to perform high resolution spectroscopy of far evolved stars spanning a wide range of initial masses. The studies cover a diversity of stars with high mass-loss rates during the preceding and current stages of evolution. All these stars have extended atmospheres and structured circumstellar envelopes produced by strong stellar winds. We have studied luminous blue variables near the Eddington limit; hot supergiants with B[e] phenomenon in spectra, which are very likely intermediate-mass binary systems soon after the fast mass exchange stage; a group of yellow hypergiants, as well as an extensive sample of low-mass post-AGB supergiants. The diverse nature of the types of these stars whose common feature is the presence of a circumstellar envelope makes the spectroscopy of such objects a comprehensive task. Such studies consist of many etapes, which include not only determining the peculiarities of their atmospheric chemical composition and understanding the role of supergiants in the enrichment of the interstellar medium with freshly synthesized elements, but also the determination of the evolution status of the objects considered, as well as search for and analysis of spectroscopic manifestations of kinematic processes in their extended and unstable atmospheres and gas-dust envelopes. We spectroscopically monitored selected objects to study in detail the instability of the kinematic state of the atmospheres of the stars considered. This review reports briefly the most significant observational obtained within the framework of the programs in 1998--2021.

Рассматривается возможность спектрофотометрии звезд, выполняемой одновременно с наблюдениями на спектрографах высокого разрешения БТА. В разработке использован многолетний опыт спектроскопических наблюдений на БТА, а также опыт работ по спектрографам проекта Спектр-УФ. The possibility of spectrophotometry of stars performed simultaneously with observations on high-resolution BTA spectrographs is considered. The development used our experience obtained during many years of spectral observations at the BTA, as well as experience in the spectrographs of the Spektr-UV project.

A high-resolution diffraction-grating spectrograph has been developed for round-the-clock monitoring of the Earth atmosphere in the optical range. The spectrograph is equipped with a tracking device and an optical fiber for detecting direct solar radiation. The spectrograph is used to determine the water vapor content by individual band lines in the red and near IR spectrum ranges.

Abstract—In the optical spectra of the cold post-AGB supergiant GSC $$04050$$ – $$02366$$ , obtained with the 6‑m BTA telescope with a resolution of $$R \geqslant 60{\kern 1pt} 000$$ on arbitrary dates over $$2019$$ – $$2021$$ , a radial velocity variability is found: heliocentric $${{V}_{r}}$$ based on the positional measurements of a set of metal absorptions varies from date to date with a standard deviation of $$\Delta {{V}_{r}} \approx 1.4$$ km s–1 about the average value of $${{V}_{r}} = 24.75$$ km s–1, which may stem out of the low-amplitude pulsations in the atmosphere. The spectra of the star are purely absorption type, there are no obvious emissions. Intensity variability of most of absorptions and Swan bands of the C2 molecule was discovered. A slight asymmetry of the H $$\alpha $$ profile is observed at some observation dates. The position of its absorption core varies within $$27.3$$ – $$30.6$$ km s–1. Splitting into two components (or asymmetry) of strong low-excitation absorptions (Y II, Zr II, Ba II, La II, Ce II, Nd II) was found. The position of the long-wavelength component coincides with the position of other photospheric absorptions, which confirms its formation in the atmosphere of the star. The position of the shortwave component is close to the position of the rotational features of Swan bands, which indicates its formation in the circumstellar envelope expanding at a velocity of about $${{V}_{{{\text{exp}}}}} = 16$$ km s–1.

Abstract—Two modifications of the Fabry–Perot interferometer were developed that use oblique incidence planar fronts from the source: Fabry–Perot interferometer with an open beam input and Fabry–Perot interferometer with an open beam output. The modifications differ only in the direction of the rays. The first modification has already been used as a basic element of the solar interference spectrograph layout (Kulagin, 1980) and the stellar interference spectrograph layout (Kulagin and Panchuk, 2017). The second modification has no analogues. Estimates of the increase in the illumination of interference patterns in the modifications are given. The same formula describes the dependence of the intensity of the outgoing radiation on the interference phase in both devices. However, the properties of the modifications differ dramatically. Possible applications of the two modifications combined with a diffraction grating are described.

Abstract —Over the past two decades NES spectrograph attached to the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences was used to perform spectroscopy of stars at advanced stages of evolution spanning a wide range of masses. The studies cover a variety of star types with high mass-loss rates during the preceding and current stages of evolution. All these stars have extended atmospheres and structured circumstellar envelopes produced by strong stellar winds. We have studied luminous blue variables (LBVs) near the Eddington limit; hot supergiants exhibiting B[e] phenomenon, which are very likely intermediate-mass binary systems soon after the fast mass exchange stage; a group of yellow hypergiants, as well as an extensive sample of low-mass post-AGB supergiants. The diverse nature of the types of these stars whose common feature is the presence of a envelope makes the spectroscopy of such objects a comprehensive task. Such studies consist of many etapes, which include not only determining the specifics of the chemical composition and understanding the role of supergiants in the enrichment of the interstellar medium with freshly synthesized elements, but also the determination of the evolutionary stage of the objects considered, as well as search for and analysis of spectroscopic manifestations of kinematic processes in their extended and unstable atmospheres and gas-dust envelopes. We spectroscopically monitored selected objects to study in detail the instability of the kinematic state of the atmospheres of the stars considered. Studies of stars at neighboring evolutionary stages have been initiated. This review reports the most significant observational obtained within the framework of the $$1998$$ – $$2021$$ programs.

The optical spectra of the B-supergiant LS III +52°24 (IRAS 22023+5249) obtained at the 6-m BTA telescope with a resolution $${\text{R}} \geqslant 60{\kern 1pt} {\kern 1pt} 000$$ in 2010–2021 revealed signs of wind variability and velocity stratification in the extended atmosphere. The neutral hydrogen lines H $$\alpha $$ and H $$\beta $$ have a P Cyg profile; their wind absorption component changes position in the range from $${{V}_{ \odot }} = - 270$$ to $$ - 290$$ km/s. The H $$\alpha $$ emission intensity reaches record-high values with respect to the local continuum: $$I{\text{/}}{{I}_{{{\text{cont}}}}} \geqslant 70$$ . The stationary radial velocity according to the positions of symmetric forbidden emissions and pemitted metal emissions is taken as the systemic velocity $${{V}_{{{\text{sys}}}}} = - 149.6 \pm 0.7$$ km/s. For the first time for this star, a time variability of the radial velocity in the range from $${{V}_{ \odot }} = - 127.2$$ to $$ - 178.3$$ km/s was found based on the positions of absorptions of NII and OII ions, which indicates the possible presence of a companion and/or atmospheric pulsations. The variability of the oxygen triplet profile $$W$$ (OI 7774) due to the appearance of unstable emission was recorded. The set of interstellar absorptions of the NaI D-line profile in the range from $${{V}_{ \odot }} = - 10.0$$ to $$ - 167.2$$ km/s is formed in the Local Arm and subsequent arms of the Galaxy. The distance to the star, $$d > 5.3$$ kpc, combined with the high velocity indicates that the star is located in the interarm space of the Galaxy beyond the Scutum–Crux arm.

We present the first part of the survey of the results of spectroscopic observations of mirides in the optical and near infrared ranges. The main phenomenological schemes and models are listed. The published results are supplemented by spectroscopic observations and calculations performed at the SAO RAS.