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Abstract—We present the results of observations of radial velocity variability in stars with exoplanets. Observations of a number of stars with characteristic stellar magnitudes from 8.54m to 10.5m were carried out using a new high-resolution (R = 35 000–120 000) fiber-fed spectrograph mounted at the foundation of the 6-m BTA telescope, in the mode of resolutions from R = 45 000 to R = 65 000 with a simultaneous registration of the calibration spectrum of a thorium–argon hollow cathode lamp. The achieved characteristic measurement accuracies ranged from a few to several tens of m s−1. In the future, the thorium-argon lamp will be supplemented with a Fabri–Perot etalon to reach the radial velocity measurement accuracy in stars up to 1 m s−1. [ABSTRACT FROM AUTHOR]

Isolated cool white dwarf stars more often have strong magnetic fields than young, hotter white dwarfs, which has been a puzzle because magnetic fields are expected to decay with time but a cool surface suggests that the star is old. In addition, some white dwarfs with strong fields vary in brightness as they rotate, which has been variously attributed to surface brightness inhomogeneities similar to sunspots, chemical inhomogeneities and other magneto-optical effects. Here we describe optical observations of the brightness and magnetic field of the cool white dwarf WD 1953-011 taken over about eight years, and the results of an analysis of its surface temperature and magnetic field distribution. We find that the magnetic field suppresses atmospheric convection, leading to dark spots in the most magnetized areas. We also find that strong fields are sufficient to suppress convection over the entire surface in cool magnetic white dwarfs, which inhibits their cooling evolution relative to weakly magnetic and non-magnetic white dwarfs, making them appear younger than they truly are. This explains the long-standing mystery of why magnetic fields are more common amongst cool white dwarfs, and implies that the currently accepted ages of strongly magnetic white dwarfs are systematically too young. [ABSTRACT FROM AUTHOR]

The method and results of measuring the shear elastic modulus of a rubberlike polymer by the deformation of a plane elastic layer are described. For shear deformations not exceeding 0.5 of the layer thickness, the shear modulus is constant and its value is in agreement with the value determined by pressing a rigid ball against the polymer layer. For deformations exceeding 0.5 of the layer thickness, the stress-strain dependence becomes nonlinear. The coefficient of shear viscosity is determined from the shear wave form generated by focused ultrasound in a homogeneous polymer sample. [ABSTRACT FROM AUTHOR]

We have studied variability of the spectral lines of the OB star δOri A—the brightest component of the δOri triple system. Forty spectra with signal-to-noise ratios ≈500–800 and a time resolution of four minutes were obtained. We detected variability in the HeIIλ4686, HeIλ4713, and H β absorption and the CIIIλ5696 emission profiles. The amplitude of the variability is ≈(0.5–1)% of the continuum intensity. The dynamical wavelet spectrum of the profile variations reveals large-scale components in the interval 25–50 km/s that move within the- V sin i to V sin i band for the primary star of the system, Aa1, with a band crossing time of 4h–5h. However, some of the variable features go outside the band, presumably due to either imhomogeneities in the stellar wind from δOri Aa1 or nonradial pulsations of the weaker components of the system, Aa2 or Ab. The detected variability may be cyclic with a period of ≈4h. We suggest that it is associated with nonradial pulsations of the primary in the sector mode ( l,m) = (2, −2). [ABSTRACT FROM AUTHOR]

We present results of Zeeman CCD measurements of DA white dwarfs carried out with the 6-m telescope of the Special Astrophysical Observatory in 1995-2000. The accuracy of the measurements ranges from 0.5 to 15 kG. Magnetic fields were detected in three of the 26 observed white dwarfs. We have confirmed the existence of magnetic fields on WD 1953-011 (B[sub e] = 28 ± 6 kG) and 40 Eri B (B[sub e](min) = -2.8 kG, B[sub e](max) = 1.8 kG). The data are discussed in the context of a statistical study of the occurrence of magnetic white dwarfs. [ABSTRACT FROM AUTHOR]

The light curves for almost 50 thousand stars with magnitudes have been obtained over 2.5 years at SAO RAS in the process of conducting an exoplanet survey in roughly -sized fields around the white dwarfs WD 0009 501 and GRW 708247. In this paper we present a catalog of variable stars that have been found in the considered regions. Periodogram analysis was used as the main variation search method. The catalog includes 150 periodic variable stars: 113 of them have been known previously, and for the remaining 37 variations have been discovered for the first time. These stars were classified according to the nature of the variations into four eclipsing variable and three pulsating types, as well as rotating stars. We present the periods and variation amplitudes in the range of and , determined from the investigated data. [ABSTRACT FROM AUTHOR]

We report an independent Doppler confirmation of the TESS planet candidate orbiting an F-type main-sequence star TOI−1408 located 140 pc away. We present a set of radial velocities obtained with a high-resolution fibre-optic spectrograph FFOREST mounted at the SAO RAS 6-m telescope (BTA-6). Our self-consistent analysis of these Doppler data and TESS photometry suggests a grazing transit such that the planet obscures its host star by only a portion of the visible disc. Because of this degeneracy, the radius of TOI−1408.01 appears ill-determined with lower limit about ∼1 R Jup, significantly larger than in the current TESS solution. We also derive the planet mass of 1.69 ± 0.20  M Jup and the orbital period ∼4.425 d, thus making this object a typical hot Jupiter, but with a significant orbital eccentricity of 0.259 ± 0.026. Our solution may suggest that the planet is likely to experience a high tidal eccentricity migration at the stage of intense orbital rounding, or may indicate possible presence of other unseen companions in the system, yet to be detected. [ABSTRACT FROM AUTHOR]

We report eight new exoplanet candidates discovered at the Special Astrophysical Observatory of the Russian Academy of Sciences using the transit technique. Photometric observations were performed with a 50-cm robotic telescope during the second half of 2020. Transits with depths of and periods were detected in – stars. All the stars considered are dwarfs with radii (with an uncertainty of up to for a single star). We use simulations to estimate the candidate radii (all are greater than 1.4 times the Jovian radius), semi-major axes of their orbits (0.012–0.035 AU), and other orbital parameters. We report the transit light curves for two stars obtained in 2022 based on individual observations. [ABSTRACT FROM AUTHOR]

The article titled "Erratum: Doppler confirmation of TESS planet candidate TOI1408.01: grazing transit and likely eccentric orbit" was published in the Monthly Notices of the Royal Astronomical Society: Letters in 2023. The authors of the paper discovered that there were multiple duplicated transit lightcurves in their analysis due to a mistake. They reanalyzed the correct dataset and found that there were mostly insignificant changes to the results, with the orbital period being the most notable change. The corrected table is provided in the article. [Extracted from the article]

We observed the bright O6If(n) supergiant λ Cep in 1997 with the 6-m optical telescope of the Special Astrophysical Observatory and in 2007 with the 1.8-m telescope of the Bohyunsan Optical Astronomy Observatory (South Korea). A total of 90 spectra of the star were acquired, with good time resolution (10 minutes), signal-to-noise ratios 150-300, and spectral resolutions of 45 000-60 000. We detected line-profile variations of H, HeI, and HeII lines. It is suggested that the detected variations are due to non-radial photospheric pulsations and the star's rotation (rotational profile modulation). [ABSTRACT FROM AUTHOR]

We observed the bright supergiant ρ Leo (B1 lab) in January–February 2004 using the 6-m telescope of the Special Astrophysical Observatory (Russia) and the 1.8-m telescope of the Bohyunsan Optical Astronomy Observatory (South Korea). 47 spectra with high time resolution (4–10 min), signal-to-noise ratios 300–1000, and spectral resolutions 45 000–60 000 were obtained. We detected variability in the HeI, SiII, SiIII, and NII line profiles, which may be due to rotational modulation of the profiles and photospheric pulsations of ρ Leo. The possible influence of the stellar magnetic field on the line-profile variations is discussed. [ABSTRACT FROM AUTHOR]

This is an analysis of certain aspects of using the CLEAN algorithm for Fourier analysis of short segments of time series and of time series consisting of short segments of length ΔT separated by very long irregular gaps. It is assumed that the time series contain a harmonic component of amplitude A with a period longer than the length of the longest of the segments of the time series plus white noise with dispersion N2. Reliability plots are constructed for determining the ranges of the parameters ( ν, ϕ) for which the CLEAN procedure can be used to determine the values of ν, the frequency, and ϕ, the phase of the harmonic component, with a given accuracy. The results of this analysis are used to search for harmonic components in the variation of the Hβ line profile in spectra of the triple star δ Ori A obtained in 2004 with the BTA telescope at the Special Astrophysical Observatory of the Russian Academy of Sciences. [ABSTRACT FROM AUTHOR]

We present the results of a search for and analysis of line-profile variations in the spectrum of the star ι Her. The observations were acquired with the 1.8 m telescope of the Bohyunsan Optical Astronomy Observatory (Republic of Korea) in May–June 2004. We obtained 69 spectra of the star with signal-to-noise ratios ≈300 and a time resolution of 5–7 min. Profile variability was revealed for six lines of HI, HeI, and SiIII, in the central parts of the lines. The variability amplitude is ≈(1–2)% in units of the intensity of the adjacent continuum. Evidence was found for cyclic variations of the lines, with periods from ≈7h to ≈2.9d. We conclude that ι Her belongs to the group of slowly pulsating stars. [ABSTRACT FROM AUTHOR]

We describe the results of our magnetometric monitoring of two white dwarfs: 40 Eri B and WD 0009+501. We found periodic variations in the longitudinal magnetic field of 40 Eri B. The field variability with an amplitude of ∼4 kG and a zero mean is discussed in terms of an oblique rotator model. The rotation period is ∼5 h 17 min, but there is another period of 2 h 25 min that may be related to nondipolar field components. The published projected rotational velocities of 40 Eri B measured from a narrow non-LTE Hα peak (V sin i ≲ 8 km s[sup –1]) are in good agreement with our measurements of the magnetic field and the rotation period. The combined effect of magnetic and rotational broadening of the central Hα component constrains the rotation period, P >= 5.2 h. We discovered the rotation period (1.83 h) of the magnetic white dwarf WD 0009+501. The period was found from the periodically varying magnetic field of the star with a mean = –42.3 ± 5.4 kG and a half-amplitude of 32.0 ± 6.8 kG.© 2003 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

Abstract—Within the program for studying the variability of slow-rotating magnetic stars, we carried out magnetic monitoring of the Ap star HD 110066 (AX CVn), the expected variability period of which was estimated as 13.4 yrs. Based on our measurements of the magnetic field performed with the 1-m SAO RAS telescope and the literature data, we assumed that the most likely period of this star days; we also estimated the parameters of the oblique rotator model describing the magnetic variability of the star HD 110066. In order to determine its chemical abundance, a high-resolution spectrum with () was obtained using the fiber-fed spectrometer of the 6-m telescope of SAO RAS. The chemical abundance estimates completely coincided with those from the spectrum obtained with a similar resolution with the ESPaDOnS spectrometer (CFHT, Mauna Kea, Hawaii). [ABSTRACT FROM AUTHOR]

Abstract—We report the results of laboratory tests of the first version of the high-resolution fiber-fed spectrograph designed for the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS). During laboratory tests a spectral resolution of about 70 000 was achieved. The peak efficiency of the entire optical path of the spectrograph (without light losses at the CCD, primary mirror of the 6-m telescope, and in the atmosphere) at 620 nm and with the equivalent slit widths of the 1″.5 and 0″.75 are equal to 8% and 4%, respectively. The resolving power R = 70 000 and 100 000 can be reached with the sky aperture 0″.75 and 0″.4 respectively. In the current version of the spectrograph these regimes of operation are implemented by mechanic aperturing of the slit. A dedicated projecting camera has been developed and is currently manufactured to operate with a collimated 200-mm diameter beam, which will make it possible to increase the spectral resolution up to 100 000. A two-beam image slicer will be used to maintain the luminous efficiency of the instrument at least at the 6% level. [ABSTRACT FROM AUTHOR]

The determination of fundamental parameters of stars is one of the main tasks of astrophysics. For magnetic chemically peculiar stars, this problem is complicated by the anomalous chemical composition of their atmospheres, which requires special analysis methods. We present the results of the effective temperature, surface gravity, abundance, and radius determinations for three CP stars HD 188041, HD 111133, and HD 204411. Our analysis is based on a self-consistent model fitting of high-resolution spectra and spectrophotometric observations over a wide wavelength range, taking into account the anomalous chemical composition of atmospheres and the inhomogeneous vertical distribution for three chemical elements: Ca, Cr, and Fe. For two stars, HD 188041 and HD 204411, we also performed interferometric observations that provided us with the direct estimates of stellar radii. Comparison of the radii determined from the analysis of spectroscopic/spectrophotometric observations with direct measurements of the radii by interferometry methods for seven CP stars shows that the radii agree within the limits of measurement errors, which proves indirect spectroscopic analysis capable of proving reliable determinations of the fundamental parameters of fainter Ap stars that are not possible to study with modern interferometric facilities. [ABSTRACT FROM AUTHOR]

Abstract—We present the measurements of masses of two exoplanets and one exoplanet candidate: the candidate we earlier confirmed in the KOI-974 system, a new TESS candidate in the TOI-1797 system, and the well-known hot Jupiter MASCARA-3b. The observations were carried out using the first prototype of the high-resolution fiber-opticspectrograph of the 6-m BTA telescope, and with the BOES spectrograph of Bohyunsan Optical Astronomy Observatory of the Korea Astronomy and Space Science Institute. The MASCARA-3b mass estimates are presented to demonstrate the performance of the new BTA spectrograph and do not differ from the measurements of other authors within the errors. The KOI-974 mass estimate upper constraint is new. Assuming a circular orbit, the exoplanet mass does not exceed 0.16 MJup. More complex orbital shapes are not visible at the radial velocity half-amplitude level of more than 20 m s−1, which classifies this exoplanet as the neptunes. Only four observations were obtained for the planetary candidate TOI-1797.01, which is insufficient for its confident classification. Meanwhile, the candidate's radial velocity values based on these four observations rule out its stellar nature. [ABSTRACT FROM AUTHOR]

We present the results of long term high-resolution spectral and spectro-polarimetric observations of the classic spectroscopic binary star β Coronae Borealis, which is also well known for its chemical peculiarity and strong magnetic field. One of the main objectives of these observations was to check some suggestions of the presence of a third low-mass component in the system. Analysing our own radial velocity (RV) measurements of β Coronae Borealis obtained between 2004 and 2013 together with other RV and astrometric data taken from the literature, we have considerably improved the orbital elements of the star. Using residual RVs obtained after subtracting the orbit from the observed RV, we detected a significant periodic signal consistent with the well-known 18.4868-d rotation/magnetic period of the star. The shape of the residual RVs folded with the rotation period exhibits a bimodal structure. In order to clarify the origin of the residual RV variation, we model the RV variation due to rotational modulation Zeeman patterns in the spectral lines of β Coronae Borealis spectra. The results of this analysis and the investigation of chemical inhomogeneities in the spectra of β Coronae Borealis convincingly support the ‘magnetic’ nature of the observed RV variations. [ABSTRACT FROM AUTHOR]

We present the results of ground based observations and model analysis of transits of exoplanets WASP-33b, WASP-43b, WASP-104b, and HD 219134b. Broadband transmission spectra (dependence of the observed radii on wavelength) have been plotted for all exoplanets, ranging from the near-UV to the IR region. We show that the transmission spectrum of WASP-33b is, within errors, flat in the range of 3800 Å to 12 000 Å. The derived broadband spectrum of WASP-43b is also flat in the first approximation, although other authors have reported the presence of absorption lines of various chemical elements in the narrow bands. Model spectra of WASP-43b taken from the literature and based on IR data allowed us to obtain a direct estimate of its nighttime temperature. We present and analyze the results of ground based observations which confirm the discovery of a transiting super-Earth in the HD 219134 star system. Signs of this planet’s existence were discovered earlier during the radial velocity analysis of the star, as well as transit observations with the Spitzer space telescope in the IR.At the estimated time, we registered a transit in the near-UV range several times. The transit depth measured in the U-band of the Johnson photometric system amounts to 0.13% ± 0.027%, which is deeper than the one based on Spitzer measurements. We discuss the possible causes of this difference. [ABSTRACT FROM AUTHOR]

We report the results of photometric observations of a number of magnetic white dwarfs in order to search for photometric variability in these stars. These V-band observations revealed significant variability in the classical highly magnetized white dwarf GRW+70◦8247 with a likely period from several days to several dozen days and a half-amplitude of about 0 04. Our observations also revealed the variability of the well-known white dwarf GD229. The half amplitude of its photometric variability is equal to about 0 005, and the likely period of this degenerate star lies in the 10-20 day interval. This variability is most likely due to the rotation of the stars considered.We also discuss the peculiarities of the photometric variability in a number of other white dwarfs. We present the updated 'magnetic field-rotation period' diagram for the white dwarfs. [ABSTRACT FROM AUTHOR]

We present first results of spectroscopic observations of transiting exoplanets in the Special Astrophysical Observatory of the Russian Academy of Sciences with the Main Stellar Spectrograph of the 6-m BTA telescope. For the exoplanetWASP-32b, we detected a significant variation of intensity and equivalent width in the Hα spectral line of the parent star at the time of a transit. The equivalent width of the line during transit is by 8-10% larger than outside the planet passage. Residual intensity in the core of the line reveals the following tendency: the line is by 10-15% deeper inside transit than outside it. Observations with the long-slit spectrograph of the Crimean Astrophysical Observatory at the 2.6-m ZTSh telescope also showed a transit event in the Hα line, although, with a smaller amplitude and shape inverted in relation to the data from the 6-m telescope. While in the observations with the BTA the Hα line becomes deeper during the transit, in the ZTSh observations, the residual intensity of the Hα line decreases during the transit. Reducing and analysis of the archive data of WASP-32b observations with the HARPS spectrograph also confirm the Hα line modulation at the time of the transit. The observed data give evidence of the envelope in WASP-32b filling the Roche lobe and a comet-like tail of changing geometry and orientation relative to the observer. These changes determine different depths and shapes of the Hα spectral line at the time of transits. [ABSTRACT FROM AUTHOR]

We report the results of a polarimetric and photometric study of the cool white dwarf WD1748+508. Observations were performed during four consecutive nights on the telescopes of the Crimean Astrophysical Observatory. As a result, polarization was detected in the V band at the level of −0.36 ± 0.087% and the star was found to be photometrically variable with a period ranging from five hours to about two days. Throughout the entire observing set the variability amplitude was constant and equal to about 10 ± 1 mmag. Non-zero circular polarization directly indicates that the white dwarf has a global magnetic field with a strength of 10 MG or higher.We interpret the photometric variations found in this study in terms of rotationally modulated variability of magnetic properties of the star's atmosphere. [ABSTRACT FROM AUTHOR]

The goal of the present study is the development and testing of a method for spectral detection of the light of host stars reflected from their exoplanets. The presented method is based on the analysis of dynamical spectra, which make it possible to obtain high signal-to-noise residual spectra after host star spectrum deduction. These residual spectra contain information on the light reflected from an exoplanet and on its albedo. The first results of such research for the exoplanet HD 189733b are presented in the paper. We obtained a series of a few dozens moderate-resolution spectra of the host star HD 189733. Individual spectra have a high signal-to-noise ratio (≈700) and cover a considerable part of the complete orbital cycle of the exoplanet. The use of the developed method allowed us to achieve a characteristic contrast of the reflected light detection at a level of 5 × 10 from the continuum. Investigation of the dynamic spectra with this characteristic value as a detection threshold has not revealed obvious evidence of the host star light reflected from the planet. Nevertheless, the obtained threshold is high, which demonstrates the necessity of the development of the method for the exoplanet monitoring studies. [ABSTRACT FROM AUTHOR]

We present the results of photometric observations of the weak magnetic white dwarf WD 0009+501. The observations were carried out for two years with the 1-m telescopes of the Special and Crimean Astrophysical Observatories. As a result of these observations, we detected regular V -band luminosity variations with a period of P ≈ 8 hours. The amplitude of the variability is stable on timescales greater than two years and amounts to 11 ± 1 mmag. The difference in the variability amplitude from observations with different telescopes is 1-3 mmag. The result is interpreted within the concept of a rotation-modulated variability of magnetic properties of the star's atmosphere. We also discuss a possible variability due to the presence of planetary companions around stars of this type. The results of monitoring were used to explore the capabilities of the telescopes for exoplanet investigation. We studied the dependences between the characteristic times of exposures, magnitudes of the objects, and a threshold level of the expected variability amplitudes for all the telescopes involved in our program. A program of exoplanet monitoring with the mentioned telescopes was drawn up for the next few years based on the results of the study. [ABSTRACT FROM AUTHOR]

We propose a project of a high-resolution ( R = 100 000) fiber-fed spectrograph for comprehensive studies of stellar atmospheres, exoplanet searches, asteroseismological studies, studies of stellar magnetism, active nuclei of bright galaxies, interstellar medium, etc. We present the optical scheme of the instrument. The operating wavelength region spans from 4000 to 7500 Å. We also present the optical scheme of the pre-fiber optic unit of the spectrograph. The unit supports four main modes of spectroscopic observations: the mode of traditional spectroscopy with the spectrum of the studied object taken along with the background spectrum in the immediate vicinity of the object; the mode of the simultaneous recording of the spectrum of the object and that of the wavelength standard; the mode of high-precision spectroscopy with an iodine cell, and the mode of spectropolarimetric observations with the measurement of all the Stokes parameters. [ABSTRACT FROM AUTHOR]

We present and interpret simultaneous new photometric and spectroscopic observations of the peculiar magnetic white dwarf WD 1953-011. The flux in the V-band filter and intensity of the Balmer spectral lines demonstrate variability with the rotation period of about 1.45 days. According to previous studies, this variability can be explained by the presence of a dark spot having a magnetic nature, analogous to a sunspot. Motivated by this idea, we examine possible physical relationships between the suggested dark spot and the strong-field magnetic structure (magnetic "spot" or "tube") recently identified on the surface of this star. Comparing the rotationally modulated flux with the variable spectral observables related to the magnetic "spot," we establish their correlation and therefore their physical relationship. Modeling the variable photometric flux assuming that it is associated with temperature variations in the stellar photosphere, we argue that the strong-field area and dark, low-temperature spot are comparable in size and located at the same latitudes, essentially overlapping each other with a possible slight longitudinal shift. In this paper, we also present a new, improved value of the star's rotational period and constrain the characteristics of the thermal inhomogeneity over the degenerate's surface. [ABSTRACT FROM AUTHOR]

Based on an analysis of the catalog of magnetic fields, we have investigated the statistical properties of the mean magnetic fields for OB stars. We show that the mean effective magnetic field B of a star can be used as a statistically significant characteristic of its magnetic field. No correlation has been found between the mean magnetic field strength B and projected rotational velocity of OB stars, which is consistent with the hypothesis about a fossil origin of the magnetic field. We have constructed the magnetic field distribution function for B stars, F( B), that has a power-law dependence on B with an exponent of ≈−1.82. We have found a sharp decrease in the function F( B) for B ⩽ 400 G that may be related to rapid dissipation of weak stellar surface magnetic fields. [ABSTRACT FROM AUTHOR]