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Results of the first spectroscopic observations at the 1.5-m Russian–Turkish telescope for the X-ray sources discovered by the eROSITA telescope onboard the SRG space observatory and identified by the SRGz machine learning system as candidates for distant X-ray quasars are presented. Seven objects have been confirmed as quasars at redshifts $$z=2.7{-}4.2$$ and two sources, which were included in the program of optical observations aimed at testing and adjusting SRGz and had a significant uncertainty in the photometric redshift, have turned out to be Seyfert galaxies at $$z\approx 0.6$$ .

This paper presents the results that confirm the sublimation activity at the perihelion of the primitive main-belt asteroids 779 Nina, 704 Interamnia, and 145 Adeona; this activity was first discovered in September 2012 (Busarev et al., 2015; Busarev et al., 2016). The new spectrophotometric and/or UBVRI photometric observations of Nina, Interamnia, and Adeona were carried out in 2016–2018 during a regular perihelion passage of these asteroids. Additionally, probable spectral signs of weak sublimation activity were discovered on another two primitive main-belt asteroids, 51 Nemausa and 65 Cybele. In this study, we discuss the conditions for the occurrence of a periodic and/or continuous sublimation process on main-belt asteroids with low-temperature mineralogy; in particular, the conditions that are associated with their formation close to the “snow line” or beyond. We also consider general evolution processes that are able sustain a sufficiently high concentration of water ice close to the surface of the bodies in question and, therefore, their continuous sublimation activity, or lead to the recurrence of extinct activity.

The X-ray binary Her X-1 consists of an accreting neutron star and the optical component HZ Her. The 35-day X-ray superorbital variability of this system is known since its discovery in 1972 by the Uhuru satellite and is believed to be caused by forced precession of a warped accretion disk tilted to the orbital plane. We argue that the observed features of the 35-day optical variability of HZ Her can be explained by free precession of the neutron star with a period close to that of the forced disk. The model parameters include a) the X-ray luminosity of the neutron star; b) the optical flux from the accretion disk; c) the tilt of the inner and outer edges of the accretion disk. A possible synchronization mechanism based on the coupling between the neutron star free precession and the dynamical action of non-stationary gas streams is discussed., 12 pages, 11 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society Main Journal

At the age of about 1 year, the spectra of most Type Ia supernovae are dominated by strong forbidden nebular emission lines of FeII and FeIII. Later observations (at about 2 years) of the nearby SN 2011fe showed an unexpected shift of ionization to FeI and FeII. Spectra of the very nearby SN Ia 2014J at an intermediate phase (1 - 1.5 years) that are presented here show a progressive decline of FeIII emission, while FeI is not yet strong. The decrease in ionization can be explained if the degree of clumping in the ejecta increases significantly at ~1.5 years, at least in the Fe-dominated zone. Models suggest that clumps remain coherent after about one year, behaving like shrapnel. The high density in the clumps, combined with the decreasing heating rate, would then cause recombination. These data may witness the phase of transition from relatively smooth ejecta to the very clumpy morphology that is typical of SN remnants. The origin of the increased clumping may be the development of local magnetic fields., Accepted for publication in MNRAS

We present three low-mass and one solar mass companions found around four intermediate-mass giants HD1695, HD120235, HD145316 and HD200004 from precise radial velocity measurements using the 1.5 m Russian-Turkish Telescope (RTT150) at the TUBITAK National Observatory of Turkey (TUG). The stellar parameters, which are effective temperature ( T eff ), surface gravity (logg) and metallicity ( [ Fe / H ] ), as well as rotational velocity (vsini) are obtained from spectral analysis. From the estimated stellar masses, the orbital parameters of the companions are also derived. We find two types of Keplerian solutions for the companion of HD120235: (1) periods 5522 days and eccentricity of e ∼ 0.93 , and (2) periods 1566 days and eccentricity of e ∼ 0.83 . From the abundances analysis HD1695 is found to be a metal-rich star with [ Fe / H ] > 0.1 , while HD200004 is a metal poor star with [ Fe / H ] - 0.2 . The other two stars, HD120235 and HD145316, have solar-like abundances with [ Fe / H ] ∼ 0.0 . Our stellar parameters and orbital solutions show that all of these stars are evolved intermediate-mass giants.

WOS: 000416942200014, For over 10 years, we have carried out a precise radial velocity (RV) survey to find substellar companions around evolved G, K-type stars to extend our knowledge of planet formation and evolution. We performed high precision RV measurements for the giant star HD 208897 using an iodine (l(2)) absorption cell. The measurements were made at TUBlTAK National Observatory (TUG; RTT150) and Okayama Astrophysical Observatory (OAO). For the origin of the periodic variation seen in the RV data of the star, we adopted a Keplerian motion caused by an unseen companion. We found that the star hosts a planet with a minimum mass of m(2) sin i = 1.40 M-J, which is relatively low compared to those of known planets orbiting evolved intermediate-mass stars. The planet is in a nearly circular orbit with a period of P = 353 days at about 1 AU distance from the host star. The star is metal rich and located at the early phase of ascent along the red giant branch. The photometric observations of the star at Ankara University Kreiken Observatory (AUKR) and the HlPPARCOS photometry show no sign of variation with periods associated with the RV variation. Neither bisector velocity analysis nor analysis of the Ca II and H alpha lines shows any correlation with the RV measurements., JSPS KAKENHIMinistry of Education, Culture, Sports, Science and Technology, Japan (MEXT)Japan Society for the Promotion of ScienceGrants-in-Aid for Scientific Research (KAKENHI) [JP23244038, JP16H02169]; Scientific and Technological Research Council of Turkey (TUBlTAK) [114F099]; [3.6714.2017/8.9], This work was supported by The Scientific and Technological Research Council of Turkey (TUBlTAK), the project number of 114F099. Authors thank to TUG, KFU, and AST for partial support in using RTT150 (Russian-Turkish 1.5-m telescope in Antalya). This work was also supported by JSPS KAKENHI Grant Numbers JP23244038, JP16H02169. This work was funded by the subsidy 3.6714.2017/8.9 allocated to Kazan Federal University for the state assignment in the sphere of scientific activities.

We present the results of our long-term photometric and spectroscopic observations at the Russian-Turkish RTT-150 telescope for the optical counterpart to one of the best-known sources, representatives of the class of fast X-ray transients, IGR J17544-2619. Based on our optical data, we have determined for the first time the orbital and physical parameters of the binary system by the methods of Doppler spectroscopy. We have computed theoretical spectra of the optical counterpart by applying non-LTE corrections for selected lines and obtained the parameters of the stellar atmosphere and the optical star ($T_{\rm eff}=33\,000$ K, $\log\,g=3.85$, $R=9.5\ R_{\odot},$ and $M=23\ M_{\odot}$). The latter suggest that the optical star is not a supergiant as has been thought previously., 13 pages, 11 figures, 4 tables