Based on 583 radial velocity (RV) measurements we obtained at the Three College Observatory (TCO, North Carolina, USA) in 2015–2024, (including 396 not previously analyzed from 2020–2024) as well as on 236 RV data from the German amateur R. Bücke (2011–2022), we calculated the pulsation period and amplitude of the Cepheid Polaris Aa system (α UMi). The analysis showed that the pulsation period was stable within a few minutes in 2020–2024. During this time, the pulsation amplitude was increasing and reached the 1960s level (4–6 km s−1), when its sharp decline began. Since its new growth began after Polaris Ab, the system secondary component, passed a periastron, we concluded that the observed amplitude changes were due to its orbital motion. It is clear that Polaris Aa is returning to normal pulsating activity.

Context. The oldest stars in the Milky Way are metal-poor with [Fe/H] < -1.0, displaying peculiar elemental abundances compared to solar values. The relative variations in the chemical compositions among stars is also increasing with decreasing stellar metallicity, allowing for the pure signature of unique nucleosynthesis processes to be revealed. The study of the r-process is, for instance, one of the main goals of stellar archaeology and metal-poor stars exhibit an unexpected complexity in the stellar production of the r-process elements in the early Galaxy. Aims. In this work, we report the atmospheric parameters, main dynamic properties, and the abundances of four metal-poor stars: HE 1523-0901, HD 6268, HD 121135, and HD 195636 (-1.5 > [Fe/H] > -3.0). Methods. The abundances were derived from spectra obtained with the HRS echelle spectrograph at the Southern African Large Telescope, using both local and non-local thermodynamic equilibrium (LTE and NLTE) approaches, with the average error between 0.10 and 0.20 dex. Results. Based on their kinematical properties, we show that HE 1523-0901 and HD 195636 are halo stars with typical high velocities. In particular, HD 121135 displays a peculiar kinematical behaviour, making it unclear whether it is a halo or an accreted star. Furthermore, HD 6268 is possibly a rare prototype of very metal-poor thick disk stars. The abundances derived for our stars are compared with theoretical stellar models and with other stars with similar metallicity values from the literature. Conclusions. HD 121135 is Al-poor and Sc-poor, compared to stars observed in the same metallicity range (-1.62 > [Fe/H] > -1.12). The most metal-poor stars in our sample, HE 1523-0901, HD 6268, and HD 195636, exhibit anomalies that are better explained by supernova models from fast-rotating stellar progenitors for elements up to the Fe group. Compared to other stars in the same metal-licity range, their common biggest anomaly is represented by the low Sc abundances. If we consider the elements beyond Zn, HE 1523-0901 can be classified as an r-II star, HD 6268 as an r-I candidate, and HD 195636 and HD 121135 exhibiting a borderline r-process enrichment between limited-r and r-I star. Significant relative differences are observed between the r-process signatures in these stars.

Results are reviewed of a long-term program of binary systems observing since 2013 at the 0.81 m telescope of the Three College Observatory in North Carolina, USA, with an e ' chelle spectrograph at a medium spectral resolution. The target list includes recognized and suspected binary systems with normal stars (no spectral lines in emission), classical Be stars, and objects with the B[e] phenomenon. The results include refinement of the orbital elements of bright binaries previously observed with photographic plates, further evidence for phased -locked peak intensity variations of double -peaked line profiles in Be binaries, and recent discoveries of binaries among objects with the B[e] phenomenon.

Radial abundance gradients provide sound constraints for chemo-dynamical models of galaxies. Azimuthal variations of abundance ratios are solid diagnostics to understand their chemical enrichment. In this paper we investigate azimuthal variations of abundances in the Milky Way using Cepheids. We provide the detailed chemical composition (25 elements) of 105 Classical Cepheids from high-resolution SALT spectra observed by the MAGIC project. Negative abundance gradients, with abundances decreasing from the inner to the outer disc, have been reported both in the Milky Way and in external galaxies, and our results are in full agreement with literature results. We find azimuthal variations of the oxygen abundance [O/H]. While a large number of external spirals show negligible azimuthal variations, the Milky Way seems to be one of the few galaxies with noticeable [O/H] azimuthal asymmetries. They reach 0.2 dex in the inner Galaxy and in the outer disc, where they are the largest, thus supporting similar findings for nearby spiral galaxies as well as recent 2D chemo-dynamical models.

HD327083 is a member of a small group of supergiants exhibiting the B[e] phenomenon. It was found to be a binary system with an early-B and an early-F supergiant components. However the fundamental and orbital parameters of the system were not accurately known. We determined a new set of the system parameters that include the orbital period and the components’ masses using a combination of photometric and spectroscopic data. A new orbital period of 107.7 days was found from both the spectral line positional variations and the visual light curve. Absorption lines of the cool component show a radial velocity semi-amplitude of 48.3 kms −1 , similar to that of emission lines that originate around the hot component. The system shows partial eclipses. We estimated the components’ masses to be nearly equal and close to 6-8 M ? . The masses turned out to be smaller then the evolutionary masses that may be a consequence of a recent mass-transfer.

Optical high-resolution spectroscopic observations of the emission-line star MWC645 are presented. The spectrum exhibits strong variable double-peaked Balmer emission lines as well as low-excitation emission lines of FeII, [FeII], and [OI] which are signatures of the B[e] phenomenon, while lines of helium have not been found. In addition to the emission lines, for the first time we identified absorption lines of neutral metals (e.g., LiI 6708 A, CaI 6717 A, and a number of FeI and TiI lines) that indicate the presence of a cool component in the system. The heliocentric radial velocity measured in our best spectrum was found to be −65.1±1.0 kms −1 for the emission lines and −23.2±0.4 kms −1 for the absorption lines. Using a combination of photometric and spectroscopic data as well as the Gaia EDR3 distance (D=6.5±0.9 kpc), we disentangled the component contributions and estimated their temperatures and luminosities (∼15000 K and ∼4000 K, log L/L ? = 3.8±0.2 and 2.8±0.2 for the hot and cool component, respectively).

Atmospheric parameters and elemental abundances of metal-poor Population II star TYC5594-576-1 ([Fe/H] = –2.8) have been studied, including the elements of neutron (n-) capture processes, as an important part of the enrichment sources of early Galaxy. Na, Mg, Al, Co, Sr, Y, Zr, Mo, Ba, La, Ce, Pr, Sm, Eu, Gd, Dy, Os, and Th abundances were determined using the synthetic spectrum method, taken into account the hyperfine structure (HFS) for the Ba II, La II and Eu II lines. The abundances of Si, Ca, Sc, N were determined based on the equivalent widths of their lines. The carbon abundance was obtained by the molecular synthesis fitting for the CH region of 4300-4330 ÅÅ. For the abundances determinations of C, Na, Mg, Al, Ba, and Th the NLTE corrections have been applied.We have determined the abundances of several n- capture elements for the first time and found that the behaviour of these elements abundances shows a significant trend with increasing atomic number. The elements ratios of [Eu/Fe] = 1.85, [Ba/Eu] = –1.24, [Sr/Ba] = –1.04 confirm the status of TYC5594-576-1 as a r-process enrichment star, with lower strontium [Sr/Fe] = –0.33 and higher thorium [Th/Fe] = 1.28 abundances. The obtained europium and thorium excesses testifies to the early enrichment of the Galaxy by the r-process elements as a result of the merger of neutron stars or black holes. The carbon abundance confirms the effect of canonical additional mixing in this star.

Confident main-sequence (MS) members of the Collinder 394 open cluster are perfect objects to check the correctness of their distances, obtained from the GAIA GR2 (2018) catalogue. The differences in the distances to the open cluster Collinder 394, determined by photometry and from the GAIA parallaxes have raised doubts about the correctness of the latter. Therefore we used spectroscopically determined T eff and loggvalues for these stars from Usenko et al. (2019) and tried to solve the inverse problem: determine radii of these stars using the derived distances and calibrations “T eff - radius” for MS stars and compare with similar ones. For this purpose we used the calibrations from Torres et al. (2010), based on the nearest MS eclipsing binaries and compilations for MS stars from Mamajek (2018). As a result, we obtained relationships that connect T eff , logg, radii, masses, and distances for the confident Collinder 394 MS stars. We have confirmed the correctness of the GAIA DR2 (2018) distances for these stars and determined their radii and masses. The latter estimates turned out to be close to those of the evolutionary masses calculated by the PARSEC model

Low metallicity star HD121135 ([Fe/H] = -1.5) have been investigated spectroscopically. Its atmos- pheric parameters and elemental abundances have been determined, including elements of neutron (n-) capture processes, which are the keys in the study of early Galaxy enrichment. Na, Mg, Ni, Co, Sr, Y, Zr, Mo, Ba, La, Ce, Pr, Sm, Eu, Gd, Dy, Ho, Os, Th abundances were calculated using the synthetic spectrum method, factoring in the hy- perfine structure (HFS) for the Eu II lines. Si, Ca, Sc abun- dances were determined using the equivalent widths of their lines. The carbon content was computed by the molec- ular synthesis fitting for the region of CH (4300-4330 ÅÅ). For the abundances determinations of C, Na, Mg, Ba, and Th the NLTE corrections have been applied. We have determined for the first time the abundances of several n-capture elements and found that the behaviors of these elements do not show a significant trend with increasing atomic number. The elements ratios of [Eu/Fe] = 0.06, [Ba/Eu] = 0.13, [Sr/Ba] = - 0.05 do not support the HD121135 status as a r-process enrichment star. We have obtained the thorium abundance [Th/Fe] = 0.26. The car- bon content confirms the effect of canonical additional mixing in this star.

We present the results of a spectroscopic and photometric investigation of 18 probable members of the open cluster Collinder 220, which contains the Cepheid UW Car. Besides the Cepheid, we studied tree K-giants, two B-giants, and twelve B-A-F main sequence stars. Radial velocities (RV), v sin i, Teff , and log g were determined using spectroscopic model fitting and atmosphere models. We have derived color-excesses, reddenings, and intrinsic colors for these stars using their Teff and log g from comparison to the atmosphere models, especially for hot stars. Proper motions, RV, and the GAIA DR2 2018 parallaxes allowed us to determine their membership in the cluster and absolute magnitudes. We found that seven stars along with the Cepheid can be the cluster members with a high confidence. The parallaxes and reddenings of the 7 confident cluster members led to the distances in a range of 1900–2800 pc, while the other stars are probably foreground objects. All the members have [Fe/H] near 0.1 dex. The B-giant HD90435 located near the cluster’s “turn-off” point has a low projected rotational velocity, and this fact allows us to determine its chemical composition to compare with that of the Cepheid UW Car. The CNO abundances of HD90435 are nearly solar, while the Cepheid shows a deficit of carbon, an overabundance of nitrogen, a nearly solar oxygen, and an overabundance of sodium. The confident cluster member, K-supergiant CPD −57◦3199, has CNOand Na abundances close to those of UW Car.

The all-sky survey conducted by the InfraRed Astronomical Satellite (IRAS) in the 1980’s discovered many objects with infrared excesses whose nature has not been explored until recently. IRAS07080+0605 is one of those identified in the visual spectral range with an early-type star, which shows the B[e] phenomenon. The object is puzzling, because it exhibits one of the strongest infrared excesses associated with a star of one of the lowest surface temperatures (∼8500 K) among objects with the B[e] phenomenon, an apparent combination of spectral features of dwarfs and supergiants, and the absence of a surrounding optical nebula. Our photometric and spectroscopic study shows that the object’s properties are similar to those of the famous Red Rectangle proto-planetary nebula. In this paper we describe our findings and hypotheses about the nature and evolutionary status of IRAS07080+0605

Thirty three spectra of the Polaris system obtained in August–December 2019 and February–April 2020 at the 0.81m telescope of the Three College Observatory (TCO, North Carolina, USA) were used to determine the radial velocities (RV) and effective temperature of the Cepheid Polaris Aa. These new data have been added to the entire Polaris system RV data collection (over 2,500 measurements) to compute a new orbit of the Polaris Aa companion. Furthermore we have used our eight observational datasets taken in 2015–2020 and eight datasets taken in 2011–2018 by Anderson (2019) to check for possible influence of the orbital motion of Polaris Ab on the Polaris Aa pulsational activity. It was found that the mean pulsational period in 2015–2020 was quite stable (3.976±0.012 days), while the pulsational amplitude showed evident changes: a growth before HJD 2457350 with a following decrease. This fact could be due to the Polaris Ab passing through the periastron.

We report the discovery of two new lithium-rich Cepheids in theMilkyWay (A(Li) approximate to 2.9 dex) among the targets of the MAGIC spectroscopic survey with the Southern African Large Telescope spectrographs. The 6707 angstrom Li feature is usually not detectable in the atmosphere of Cepheids. Only three Cepheids (two in the Milky Way and one in the Large Magellanic Cloud) had been reported so far with high lithium abundances.We examine the possibility that the Li-rich Cepheids are evolving towards the red giant branch, crossing the instability strip for the first time, as well as other possible scenarios. The two stars are mixed-mode Cepheids pulsating simultaneously in the first and in the second overtone modes. We briefly discuss the possible connection between their unusual chemical composition and their pulsational properties.

Objects with the B[e] phenomenon exhibit permitted and forbidden emission lines due to the presence of circumstellar ionized gas and large infrared excesses due to processing of the stellar radiation by circumstellar dust. There are five groups of stars that show this phenomenon (pre-main-sequence Herbig Ae/Be stars, symbiotic systems, proto-planetary nebulae, some supergiant, and FS CMa type objects). The latter group is the most recently discovered and the least explored. The leading hypothesis about the group nature implies that they are mostly intermediate-mass binary sys- tems, whose circumstellar medium was created during a strong mass-transfer phase due to a Roche lobe overflow of the more massive star in the system. We have been conducting a large program of spectroscopic and photometric observations of many objects and candidates to this group. The current report is devoted to the preliminary results of our ongoing study of two objects with similar underlying early B-type stars, FS CMa (the group prototype) and MO Cam. The objects show different emission-line profiles and infrared excesses which are most likely due to different tilt angles of their non-spherical envelopes with respect to the line of sight. Variability of spectral lines is discussed here.

We present the results of a spectro- scopic and photometric investigation of 20 objects from the open cluster Collinder 394, which contains the Cepheid BB Sgr. Besides the Cepheid, we studied tree K-giants, four B-giants, and twelve B-A-F main sequence stars. Radial velocities (RV), vsini, T eff , logg, were determined using spectroscopic model fitting and atmosphere models. We have derived the color-excesses, reddenings, and intrinsic colors for these stars using their T eff and logg from compar- ison to the atmosphere models, especially for hot stars. Proper motions, RV and GAIA DR2 2018 parallax/distance values for these stars allowed us to determine their membership in the cluster and absolute magnitudes. We found that seven stars do not belong to the cluster. The parallaxes and reddenings of 13 confidently cluster members led to the distances in a range of 630–800 pc, although the majority of them (8 objects) are located at a mean distance of 657.7±66.7 pc, and 5 objects with the Cepheid could probably belong to the cluster’s corona. All the members have [Fe/H] near 0.1 dex. The main sequence B-star No. 76 (HD 174307) has a low rotational velocity projection, and this fact allows us to determine its chemical composition to compare with that of the Cepheid BB Sgr. Its CNO and Na abundances are close to the solar one, while the Cepheid show a deficit of carbon, an overabundance of nitrogen, nearly solar oxygen, and an overabundance of sodium. Three foreground K-giants have different C abundances (from a deficit to the solar), and Na (from the solar to an overabundance) as well as a solar-like O content. The foreground F7-8 V star No. 75 (CPD −20 ◦ 7218) was revealed to be a Li-rich star, while the A7 V star No. 69 (BD −20 ◦ 5290) has an anomalous deficit of CNO with overabundances of some α, r- and s-process elements.

We present the results of an analysis of 20 spectra of α UMi (Polaris) obtained in September 2018 – January 2019 using 0.81m telescope of the Three College Observatory (TCO), North Carolina, USA. Frequency analysis displays an increase of the pulsational period up to 3.68 min in comparison to the August - December 2017 - January - May 2018 observational sets, and it come to 3.973216 days. The systemic velocity (γ – velocity) is equal to −11.75 kms −1 . The radial velocity amplitude rose to 3.50 kms −1 and actually returned to the previous values of 3.43, 3.31, and 3.81 kms −1 , respectively, found from the August - December 2016, January - March 2017 and August - December 2017 sets. The radial velocity’s amplitude growth tendency still remains. The average T eff = 6051±22 K shows a growth toward the value found from the 2005 – 2007 observational sets and probably has a tendency toward the T eff growth. The joint TCO and Hermes radial velocity measurements during the last four years show the changes of Polaris’ pulsational amplitude.

We briefly describe the large observational project MAGIC aimed at mass spectroscopic studies of stars of different subsystems of our Galaxy. The project was carried out on the Southern African Large Telescope (hereafter referred to as SALT) with efficient use of its capabilities, site’s climate, and spectroscopic instruments. We discuss in detail the issues of high-resolution spectroscopy when studying the chemical composition of Galactic Cepheids. Observations of these objects with HRS echelle spectrograph of SALT telescope started in 2016 and currently the number of such observations exceeds one hundred. Spectra were acquired in the medium-resolution mode ( R ~36 500–39 000)with a high signalto-noise ratio ( S/N ~50–220). All obtained echelle images acquired were reduced with a package that we developed based on standard MIDAS system. We describe standard reduction steps using the Cepheid RSNor as a test object. Based on the data of spectroscopic observations we determined the atmospheric parameters and the abundances of 31 chemical elements (36 neutral atoms and ions) whose absorption lines are observed in the spectrum of RSNor. We performed all computations using two methods and showed that echelle spectra acquired in the medium-resolution mode of HRS can be used to study the chemical composition of Cepheids with good accuracy and that the results agree with the results of other studies within the quoted errors.

For the classical Cepheid V1033 Cyg we have constructed an O—C diagram spanning a time interval of 117 years. The O—C diagram has the shape of a parabola, which has made it possible to determine for the first time the quadratic light elements and to calculate the rate of evolutionary increase in the period dP/dt = 18.19 (±0.08) syr −1 , in agreement with the results of theoretical calculations for the first crossing of the instability strip. Thus, V1033 Cyg is the second actually observed Cepheid (after α UMi) that crosses the instability strip for the first time.

We present the results of an analysis of the spectra of nine so called Polaris cluster A−FV stars obtained during 2016 - 2018. Radial velocities (RV) and GAIA DR 18 parallaxes-distances for these stars allow us to determine their membership in the cluster and to construct its 3D kinematic model. However Teff for four stars determined spectroscopically give cause for doubts about the GAIA DR 18 parallaxes accuracy. The comparison between their MV and distances with the those from Pecaut & Mamajek (2013) calibrations shows significant differences for the objects with parallaxes less than 8 mas. The differences in distances increase exponentially with decreasing parallax. These facts indicate an unreliability of the GAIA DR2 parallx measurements of less than 10 mas. We estimated the distance to Polaris B to be 104.2 pc.