In 2012–2014 we obtained 3296 CCD frames in the $$BVI_{c}$$ photometric system for the RR Lyrae star T Men with the 76-cm telescope of the South African Astronomical Observatory (SAAO, SAR) and the 1-m telescopes of the Las Cumbres Observatory Global Telescope (LCOGT). Our observations showed a slightly increased scatter of data points on the light curve, which allowed the Blazhko effect with a period $${\sim}18\overset{\textrm{d}}{.}49$$ to be detected. To study the variability of the pulsation period, we used all the available observations, including 1325 magnitude estimates from the digitized Harvard Astronomical Plate Collection (the DASCH project). This allowed us to construct an $$O-C$$ diagram spanning a time interval of 125 years and for the first time to detect at least three abrupt changes in the pulsation period.

We took a total of 635 B-, V-, and Ic-band CCD frames for the RRab Lyr type variable DVMon, which has a close bright visual companion with a separation of about 1.9′. Observations were made with the 76-cm telescope of the South African Astronomical Observatory (SAAO, South Africa) using SBIG CCD ST-10XME. For the first time, we obtained reliable separate PSF-photometry of both stars and determined their coordinates. We used all available data to construct the O — C diagram spanning a 110-year long time interval, which allowed us to reveal at least three sudden changes of the pulsation period around JD 2438000, 2453500, and 2456500. Our high resolution echelle spectra with the Southern African Large Telescope (SALT) showed that DV Mon belongs to type ab RR Lyrae variables of the Galactic thick disk.

We report on evidence that the highest specific star formation rate (SSFR) in dwarf galaxies in the local Universe is achieved while they pass the same stage of their chemical evolution corresponding to metallicity of similar to 1/3 Z(circle dot). It is supported by the observation that a strong star-burst event had occurred in early spheroids at the virtually same metallicity, imprinted in the peak metallicity of the sub-populations of metal-rich globular clusters (MRGCs).

In 2012–2014 we obtained 3641 CCD frames of the fields of the RR Lyrae (AB subtype, P = 0.583 days) variable DU Mon with BV I c filters using the 76-cm telescope of the South African Astronomical Observatory (SAAO) and the 1-m telescopes of the Las Cumbres Observatory Global Telescope Network (LCOGT). Our observations confirmed the presence of the Blazhko effect that we suspected previously and allowed its period to be determined, \({P_{Bl}} = 60_ \cdot ^d52 \pm 0_ \cdot ^d03\). Using all of the available observations, we constructed an O–C diagram spanning a time interval of 86 years that revealed at least one abrupt change in the pulsation period (a decrease by 15.26 s).

In 2005–2014 we acquired a total of 135, 137 and 134 measurements in \(B\)-, \(V\)- and \(I_{c}\)-filters, respectively, for the 5-days Cepheid ASAS 160125-5150.3. Our observations showed variations of light amplitude, which allowed us to suspect the presence of the Blazhko effect. Combining our measurements with ASAS-3 data allowed us to determine the period of the Blazhko effect \(P_{Bl}=1242^{d}\pm 10^{d}\), and now ASAS 160125-5150.3 is the second Galactic Cepheid (after V473 Lyr) with strong Blazhko effect pulsating in the first overtone.

In 2012–2014 we acquired 1569 CCD \(BVI_{c}\) frames for the RR Lyrae type variable SW Dor with the 76-cm telescope of the South African Astronomical Observatory (SAAO) and 1-m telescopes of Las Cumbres Observatory Global Telescope network (LCOGT). Our observations showed a large scatter in the resulting phased light curve, especially near maximum brightness, which allowed us to reveal the Blazhko effect with a period of \(\sim80.^{\hspace {-2pt}\mathrm {d}}9\). To study the pulsation period changes, we used all the available observations including the 1299 magnitude estimates from the digitized plate library of Harvard University (the DASCH project), which allowed us to construct the \(O-C\) diagram spanning a 125-year long time interval and discover for the first time at least three abrupt changes of the pulsation period.

На основании пространственного распределения самой полной на данный момент выборки цефеид с надежно определенными фотометрическими расстояниями (565 звезд), расположенных в пределах кпк от Солнца, исследована спиральная структура Галактики. Угол закрутки спиральных ветвей оценен в ; наиболее точная оценка, , получается в предположении существования глобального четырехрукавного спирального узора; определена фаза Солнца в спиральном узоре - . Путем сравнения положений спиральных рукавов, выявленных по пространственному распределению классических цефеид и галактических мазеров, по разности возрастов этих объектов сделана оценка угловой скорости вращения спирального узора - км/с/кпк.

We use data on space distribution of the currently most complete sample of Cepheids with reliable distances (565 stars), located within ~5 kpc from the Sun, to study the spiral pattern of the Milky Way galaxy. We estimate the pitch angle as 9°−10°; the most accurate estimate, i = 9.5° ± 0.1°, was obtained assuming the existence of a global four-armed spiral pattern; the solar phase angle in the spiral pattern is χ ⊙ = −121° ± 3°. Comparing positions of the spiral arms delineated by classical Cepheids and galactic masers, with the age difference of these objects in mind, we estimate the rotation angular speed of the spiral pattern to be Ω P = 25.2 ± 0.5 km s −1 kpc −1 .

In 2013–2014, we obtained 14959 CCD frames in the BV I c photometric system for 170 classical Cepheids from the General Catalogue of Variable Stars. We performed our observations with the 76-cm telescope of the South African Astronomical Observatory (SAAO, South Africa) using the SBIG ST-10XME CCD camera. The tables of observations, the plots of light curves, and the current light elements are presented.

We use ALLWISE data release W1- and W2-band epoch photometry collected by the Wide-Field Infrared Survey Explorer (WISE) to determine slopes of the period-luminosity relations for RR Lyrae stars in 15 globular clusters in the corresponding bands. We further combine these results with V- and K-band photometry of Galactic eld RR Lyrae stars to determine the metallicity slopes of the log P F -[Fe/H]-M K , log P F - [Fe/H]-M W1 , and log P F - [Fe/H]- M W2 period-metallicity-luminosity relations. We infer the zero points of these relations and determine the kinematical parameters of thick-disk and halo RR Lyraes via statistical parallax, and estimate the RR Lyrae-based distances to 18 Local-Group galaxies including the center of the Milky Way.

We have studied the high-resolution spectra taken with the 1.9-m telescope of the South African Astronomical Observatory for four supergiants that are deemed to be nonvariable and to lie beyond the red edge of the Cepheid instability strip (CIS): HD 192876, HD 194215, HD 206834, and HD 222574. The atmospheric parameters, reddenings, luminosities, distances, radii, and chemical composition have been determined for these stars. Based on these results, we have ascertained thatHD194215 is not a mainsequence star but an ordinary supergiant. All objects exhibit a nearly solar metallicity. The abundances of carbon and oxygen in HD 194215 and HD 206834 are nearly solar, while they are underabundant in HD 192876 and HD 222574. The abundances of sodium, magnesium, and aluminum are different for all objects, while those of the remaining elements are nearly solar. For HD 206834, the measured radial velocity exceeds its previously known values by a factor of 3, while the asymmetric knifelike profiles of the Ha and Hß absorption lines suggest the existence of an extended envelope around the star. Similar profiles of hydrogen absorption lines and strong lines of some metals with low lower-level excitation potentials have also been revealed in the spectrum of HD 222574. The positions of the supergiants on the effective temperature–luminosity diagram in comparison with the evolutionary tracks of the stars have shown their masses to lie within the range 3.4–4.3 M ⊙. HD 194215 and HD 206834 have crossed the CIS for the first time, with the latter object being near the stage of transformation into a red supergiant. HD 192876 and HD 222574 have already passed the first dredge-up and probably move from right to left, crossing the CIS for the second time. The position of HD 222574 near the red CIS edge is probably attributable to its Cepheid-like brightness and radial velocity variations.

Based on high-resolution spectra taken with the 1.9-m telescope of the South African Astronomical Observatory, we have determined the atmospheric parameters and chemical composition for three small-amplitude (AV Cir, BP Cir, and LR TrA), two classical (R TrA and S TrA), and one double-mode (U TrA) Cepheids. The averaged atmospheric parameters have been estimated for three Cepheids (AV Cir, BP Cir, and U TrA) observed at various pulsation phases. In all Cepheids, except U TrA, the metallicity has turned out to be higher than the solar one by 0.1–0.2 dex. The abundances of the key elements of the evolution of yellow supergiants (C, O, Na, Mg, Al) show that these objects have already passed the first dredge-up, while those of the remaining elements are nearly solar. Comparison of our results on the Cepheids from the list (except U TrA) with those of other authors shows significant differences in C and O abundance estimates for AV Cir, R TrA, S TrA, and LR TrA. For AV Cir and BP Cir, the H α line profiles are symmetric but with a slight asymmetry in the core at approximately the same phase near 0 · P 7: on the “blue” side for AV Cir and on the “red” one for BP Cir. BP Cir exhibits a distinct asymmetry in the absorption lines of neutral atoms and ions at various pulsation phases, which can be explained by nonradial first-overtone pulsations. The constancy of the H α absorption line profiles with pulsation phase for AV Cir and BP Cir may suggest the presence of a hydrogen envelope around them. For the double-mode Cepheid U TrA, an asymmetry is observed in the cores of the H α line and the absorption lines of neutral atoms and ions at various pulsation phases, which can be explained by nonradial pulsations in the Cepheid’s atmosphere. The absorption lines of neutral atoms and ions of metals in LR TrA closely resemble those in the well-known Cepheid BG Cru: secondary “blue” and “red” components whose line depths vary with pulsation phase are noticeable. This Cepheid can also pulsate in the first overtone and have an extended hydrogen envelope. Careful multiphase spectroscopic observations with a sufficiently high resolution are needed to test this assumption.