Beobachtungsergebnisse der Berliner Arbeitsgemeinschaft für Veränderliche Sterne e.V. (BAV)

In this 11th compilation of BAV results of observations are given from the years 1973 till 1975 for 217 observed minima of 56 eclipsing binaries, 173 maxima of 25 RR Lyrae stars, 624 results of 89 Mira stars, 182 results of 47 RV Tauri stars and irregular variables, 52 results of 27 eruptive variable stars and 12 maxima of four δ Cephei stars.     

Beobachtungsergebnisse der Berliner Arbeitsgemeinschaft für Veränderliche Sterne e.V. (BAV) (BAV-Mitteilungen Nr. 29)

In this 12th compilation of BAV results of observations are given from the years 1976 and 1977 for 231 observed minima of 58 eclipsing binaries, 108 maxima of 25 RR Lyrae stars, four maxima of four δ Cephei stars, four maxima of one δ Scuti star and 182 results of 23 longperiodic, semi-regular, irregular and RV Tauri stars.     

<Emphasis Type="Italic">BVRI</Emphasis> CCD-photometry of comparison stars in the neighborhoods of galaxies with active nuclei. III

Observations with a matrix photometer are reported. The stellar magnitudes in the BVRcIc bands are estimated for 80 comparison stars in the neighborhoods of 10 galaxies with active nuclei: 2 Seyfert galaxies, 4 quasars, and 4 BL Lac objects. The stellar magnitudes of the observed stars range from 11 to 19^m.5. For stars with magnitudes of 14–15^m the typical photometric errors are 0^m.011, 0^m.008, 0^m.006, and 0^m.007 in the B, V, R, and I bands, respectively. The BVRI magnitudes for most of these stars were not known previously. 14′ × 14′ finding charts for these stars are included. These results can be used for differential BVRI photometry of active galactic nuclei. __________ Translated from Astrofizika, Vol. 50, No. 1, pp. 57–72 (February 2007).     

Elemental abundance analyses with DAO spectrograms: XXX. The middle B through early A stars ξ2 Ceti (B9 III), 21 Aquilae (B8 II‐III), ι Aquilae (B5 III), and ι Delphini (A2V)

This series of high quality elemental abundance analyses of mostly main‐sequence band normal and peculiar B, A, and F stars defines their properties and provides data for the comparison with the analyses of somewhat similar stars and with theoretical predictions. Most use high dispersion and high S/N (≥ 200) spectrograms obtained with CCD detectors at the long camera of the Coudé spectrograph of the 1.22‐m Dominion Astrophysical Observatory telescope. Here we reanalyze 21 Aql with better quality spectra and increase the number of stars consistently analyzed in the spectral range B5 to A2 by analyzing three new stars for this series. In the early A stars the normal and non‐mCP stars have abundances with overlapping ranges. But more stars are needed especially in the B5 to B9 range. ξ² Cet on average has a solar composition with a few abundances outside the solar range while both 21 Aql and ι Aql have abundances marginally less than solar. The abundances of ι Del are greater than solar with a few elements such as Ca being less than solar. It is an Am star (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Titanium isotopic compositions of well‐characterized silicon carbide grains from Orgueil (CI): Implications for s‐process nucleosynthesis

Abstract— We have measured the titanium isotopic compositions of 23 silicon carbide grains from the Orgueil (CI) carbonaceous chondrites for which isotopic compositions of silicon, carbon, and nitrogen and aluminum‐magnesium systematics had been measured previously. Using the 16 most‐precise measurements, we estimate the relative contributions of stellar nucleosynthesis during the asymptotic giant branch (AGB) phase and the initial compositions of the parent stars to the compositions of the grains. To do this, we compare our data to the results of several published stellar models that employ different values for some important parameters. Our analysis confirms that s‐process synthesis during the AGB phase only slightly modified the titanium compositions in the envelopes of the stars where mainstream silicon carbide grains formed, as it did for silicon. Our analysis suggests that the parent stars of the >1 μm silicon carbide grains that we measured were generally somewhat more massive than the Sun (2–3 M_⊙) and had metallicities similar to or slightly higher than solar. Here we differ slightly from results of previous studies, which indicated masses at the lower end of the range 1.5–3 M_⊙ and metallicities near solar. We also conclude that models using a standard ¹³C pocket, which produces a good match for the main component of s‐process elements in the solar system, overestimate the contribution of the ¹³C pocket to s‐process nucleosynthesis of titanium found in silicon carbide grains. Although previous studies have suggested that the solar system has a significantly different titanium isotopic composition than the parent stars of silicon carbide grains, we find no compelling evidence that the Sun falls off of the array defined by those stars. We also conclude that the Sun does lie on the low‐metallicity end of the silicon and titanium arrays defined by mainstream silicon carbide grains.     

Beobachtungsergebnisse der Berliner Arbeitsgemeinschaft für veränderliche Sterne e. V. (BAV)

In this 8th compilation, the following results of observations are given: 207 observed minima of 56 eclipsing binaries, 100 maxima of 21 RR Lyrae- and δ Cephei-stars, 82 results of 32 Mira stars and long period variables, and 47 results of 9 RV Tauri stars, semiregular, and irregular variables, from the years 1966 up to 1968.     

Catalog of positions and <Emphasis Type="Italic">B</Emphasis>-magnitudes of stars in the circumpolar region of the Northern Sky Survey (FON) project

The catalog of equatorial coordinates α and δ and B-magnitudes of stars has been created at the Main Astronomical Observatory, National Academy of Sciences of Ukraine (MAO NASU), for the circumpolar region (from 58° to 90°) of the Northern Sky Survey (FON) project within the work on the rational use of resources accumulated in the JDA (Joint Digital Archive) of the Ukrainian Virtual Observatory (UkrVO). The total number of processed plates is 477. The plates were digitized with the using Microtek ScanMaker 9800XL TMA and Epson Expression 10000XL scanners (scanning mode was 1200 dpi, the linear size of plates was 30 × 30 cm or 13000 × 13000 px). The catalog includes 1 975 967 stars and galaxies with B of up to 16.5 ^m as of the epoch of 1985.28. The coordinates of stars and galaxies were obtained in the Tycho-2 reference system and B-magnitudes were obtained in the system of photoelectric standards. The internal errors of the catalog for all the objects are σ_αδ = 0.23′′ and σ _B = 0.12 ^m , and those for stars of the B range from 8 ^m –14 ^m , 0.11′′ and 0.06 ^m , respectively. The convergence between the calculated and reference positions is σ_αδ = 0.06′′ (for 171124 stars from Tycho-2), and that between the photoelectric stellar B-magnitudes is σ _B = 0.15m (for 5130 stars). The external error from the comparison with UCAC-4 are σ_αδ = 0.33′′ (1928367 stars and galaxies have been cross identified).     

Photometrische Untersuchungen im Zentralgebiet der Praesepe (NGC 2632)

In supplementing the photometric sequence in the central part of the Praesepe cluster and its extension to fainter stars a photographic photometry in UBV on plates of the 134/200/400 cm – Schmidt telescope of Karl-Schwarzschild-Observatory was done. The already known photometric data from stars obtained by HAFFNER , HECKMANN and WEIS were completed by (U – B) colours on the base of JOHNSON'S photoelectric photometry. Besides, a number of brighter and fainter stars, cluster members, white dwarfs inclusively and field stars were investigated to set up a photometric sequence down to V ≈ 18.^m9. A finding chart where all the measured stars are marked is given.     

Elemental abundance analyses with DAO spectrograms: XXXI. The early F supergiants ν Her (F2 II) and 41 Cyg (F5 Ib‐II)

This series of high quality elemental abundance analyses of mostly Main Sequence normal and peculiar B, A, and F stars defines their properties and provides data for the comparison with analyses of somewhat similar stars and with theoretical predictions. Most use high dispersion and high S/N (≥ 200) spectrograms obtained with CCD detectors at the long camera of the 1.22‐m Dominion Astrophysical Observatory telescope's coudé spectrograph. Here we expand the range of stars examined to include two relatively quiescent F supergiants. ν Her (F2 II) and 41 Cyg (F5 Ib‐II) are analyzed as consistently as possible with previous studies. These LTE fine analyses use the ATLAS9 and the WIDTH9 programs of R. L. Kurucz. High signal‐to‐noise spectrograms and high quality atomic data were employed. The derived values of these photometrically constant stars are somewhat different with the abundances of ν Her being somewhat metal‐poor and those of 41 Cyg being crudely solar‐like. Our analyses indicate that the basic results of Luck & Wepfer (1995) who also studied ν Her and 41 Cyg are not likely to be significantly changed by new studies of all their stars. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Kinematics of Stars from the TGAS (Gaia DR1) Catalogue

Based on the stellar proper motions of the TGAS (Gaia DR1) catalogue, we have analyzed the velocity field of main-sequence stars and red giants from the TGAS catalogue with heliocentric distances up to 1.5 kpc. We have obtained four variants of kinematic parameters corresponding to different methods of calculating the distances from the parallaxes of stars measured with large relative errors. We have established that within the Ogorodnikov–Milne model changing the variant of distances affects significantly only the solar velocity components relative to the chosen centroid of stars, provided that the solution is obtained in narrow ranges of distances (0.1 kpc). The estimates of all the remaining kinematic parameters change little. This allows the Oort coefficients and related Galactic rotation parameters as well as all the remaining Ogorodnikov–Milne model parameters (except for the solar terms) to be reliably estimated irrespective of the parallax measurement accuracy. The main results obtained from main-sequence stars in the range of distances from 0.1 to 1.5 kpc are: A = 16.29 ± 0.06 km s^?1 kpc^?1, B = ?11.90 ± 0.05 km s^?1 kpc^?1, C = ?2.99 ± 0.06 km s^?1 kpc^?1, K = ?4.04 ± 0.16 km s^?1 kpc^?1, and the Galactic rotation period P = 217.41 ± 0.60 Myr. The analogous results obtained from red giants in the range from 0.2 to 1.6 kpc are: the Oort constants A = 13.32 ± 0.09 km s^?1 kpc^?1, B = ?12.71 ± 0.06 km s^?1 kpc^?1, C = ?2.04 ± 0.08 km s^?1 kpc^?1, K = ?2.72 ± 0.19 km s^?1 kpc^?1, and the Galactic rotation period P = 236.03 ± 0.98 Myr. The Galactic rotation velocity gradient along the radius vector (the slope of the Galactic rotation curve) is ?4.32 ± 0.08 km s^?1 kpc^?1 for main-sequence stars and ?0.61 ± 0.11 km s^?1 kpc^?1 for red giants. This suggests that the Galactic rotation velocity determined from main-sequence stars decreases with increasing distance from the Galactic center faster than it does for red giants.     

Elemental abundance analyses with DAO spectrograms: XXXII. HR 6455 (A3 III), δ Aqr (A3 V), η Lep (F2 V), and 1 Boo (A1 V)

We examine the sharp‐lined stars HR 6455 (A3 III, v sin i = 8.7 km s^–1) and η Lep (F2 V, v sin i = 13.5 km s^–1) as well as δ Aqr (A3 V, v sin i = 81 km s^–1) and 1 Boo (A1 V, v sin i = 59 km s^–1) to increase the number consistently analyzed A and F stars using high dispersion and high S/N (≥200) spectrograms obtained with CCD detectors at the long Coudé camera of the 1.22‐m telescope of the Dominion Astrophysical Observatory. Such studies contribute to understanding systematic abundance differences between normal and non‐magnetic main‐sequence band chemically peculiar A and early F stars. LTE fine analyses of HR 6455, δ Aqr, and 1 Boo using Kurucz's ATLAS suite programs show the same general elemental abundance trends with differences in the metal richness. Light and iron‐peak element abundances are generally solar or overabundant while heavy element and rare earth element abundances are overabundant. HR 6455 is an evolved Am star while δ Aqr and 1 Boo show the phenomenon to different extents. Most derived abundances of η Lep are solar (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Age determination of the open cluster NGC 2287 (M41)

We have estimated the age of the open cluster NGC 2287 (M41) by taking into account the rotation of the member stars.TheUBV photoelectric measurement values were taken from Eggen (1974). Besides the Main-Sequence stars this cluster has seven red giants, all of them above the turn-off point.Having obtained the theoretical Hertzsprung-Russell diagram from observed colour-magnitude diagram, we have discussed two methods, given in the literature, to estimate the age of the cluster under consideration. The first method we have followed is to determine the turn-off point on the cluster Main-Sequence. The other is fitting the position of the red giants with the evolutionary tracks of rotating stars with different masses on the Hertzsprung-Russell diagram.We have estimated the cluster age based on the turn-off point as 3.10×10⁷ yr. From the fitting of the evolutionary tracks of rotating stars to the cluster Hertzsprung-Russell diagram, we infer that the age of the cluster is about 8.00×10⁷ yr.     

Results from the Wide Angle Search for Planets Prototype (WASP0) – II. Stellar variability in the Pegasus field

Recent wide field photometric surveys, which target a specific field for long durations, are ideal for studying both long- and short-period stellar variability. Here, we report on 75 variable stars detected during the observations of a field in Pegasus using the Wide Angle Search for Planets Prototype (WASP0) instrument, 73 of which are new discoveries. The variables detected include 16 δ Scuti stars, 34 eclipsing binaries, 3 BY Draconis stars and 4 RR Lyraes. We estimate that the fraction of stars in the field brighter than   V ∼ 13.5  exhibiting variable behaviour with an amplitude greater than 0.6 per cent rms is ∼0.4 per cent. These results are compared with other wide field stellar variability surveys, and implications for detecting transits due to extra-solar planets are discussed.     

Beobachtungsergebnisse der Berliner Arbeitsgemeinschaft für veränderliche Sterne e. V. (BAV)

In this 9th compilation of BAV results of observations are given from the years 1969 up to 1971 for 208 observed minima of 46 eclipsing binaries, 72 maxima of 22 RR Lyrae- and δ-Cephei-stars, 232 results of 66 Mira stars, 72 results of 12 RV Tauri-stars and 22 results of 3 irregular variables and U Geminorum-stars.     

Study of young open clusters as tracers of spiral features in our galaxy. Paper 4: Czernik 20 (OCl 427)

Photoelectric and photographic photometry of 72 stars was done in the field of the not-well-studied open cluster Czernik 20= OCl 427 in the direction of the Auriga constellation. Of these stars, a total of 43 have been found to be probable members down tom _v− 15.75 mag. There is apparently a variable extinction across the field of the cluster withE(B-V) ranging from 0.53 to 0.38 mag. The cluster stars show a range in their ages from 1.0 × 10⁷ to 7.1 × 10⁷ years, indicating that Czernik 20 is young enough to be considered as a spiral-arm tracer in the study of our Galaxy. The distance of this cluster is found to be 4.27 ±0.14 kpc and it is located inside the outer Perseus arm of the Milky Way     

Beobachtungsergebnisse der Berliner Arbeitsgemeinschaft für veränderliche Sterne e.V. (BAV)

In this 10th compilation of BAV results of observations are given from the year 1972 and some from the year 1969 for 187 observed minima of 50 eclipsing binaries, 84 maxima of 18 RR Lyrae- and δ Cephei-stars, 123 results of 55 Mira stars and 85 results of 15 RV Tauri-stars and irregular variables.     

The Wolf-Rayet stars at high (spatial) resolution

The Wolf-Rayet stars represent an advanced stage of evolution of the most massive stars. Their next immediate stadium will be supernova explosion. The most striking property of this very rare but exceptionally hot and bright objects is their extreme mass loss, of the order of 10^-5 solar mass per year. In turn of evolution before and during the Wolf-Rayet phase such stars eject a lot of matter (∼ 10 M_⊙) with velocity up to 3000 km/s that surrounds the min the form of gas and dust. In the case of binary Wolf-Rayet star such expanding envelope may interact with a companion (usually hot OB star) wind forming a tail extended for ∼ 100 AU. This spectacular phenomenon as well as some other connected with Wolf-Rayet stars that can be studied with high spatial resolution instruments (both astrometric and imaging) are reviewed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Flares of the H<Subscript>2</Subscript>O maser in W31(2)

We analyze our monitoring data for the water-vapor maser in the source W31(2), associated with a region of vigorous star formation, a cluster of OB stars. The monitoring was performed with the 22-m radio telescope at Pushchino Radio Astronomy Observatory during 1981–2004. The variability of the H₂O maser in W31(2) was found to be cyclic, with a mean period of 1.9 yr. Two flares were most intense (superflares): in 1985–1986 and 1998–1999. In each activity cycle, we observed up to several short flares, subpeaks. The fluxes of many emission features during the flares were correlated. We also observed successive activation of individual emission features in order of increasing or decreasing radial velocity, suggesting an ordered structure and, hence, a radial-velocity gradient of the medium. There is a clear correlation of the emission peaks of the main components in the spectra at radial velocities of ?1.7, ?1.3, 0.5, and 1.3 km s^?1 with activity cycles and of the emission at V_LSR < ?8 km s^?1 with short flares. During the superflares, the emission in the low-velocity part of the H₂O spectrum and a number of other phenomena related to coherent maser-emission properties were suppressed. The maser spots are assumed to form a compact structure, to have a common pumping source, and to be associated with an accretion flow onto the cluster of OB stars.     

Magnetic,chemically peculiar (CP2) stars in the SuperWASP survey

The magnetic chemically peculiar (CP2) stars of the upper main sequence are well‐suited for investigating the impact of magnetic fields on the surface layers of stars, which leads to abundance inhomogeneities (spots) resulting in photometric variability. The light changes are explained in terms of the oblique rotator model; the derived photometric periods thus correlate with the rotational periods of the stars. CP2 stars exhibiting this kind of variability are classified as α² Canum Venaticorum (ACV) variables. We have analysed around 3850000 individual photometric WASP measurements of magnetic chemically peculiar (CP2) stars and candidates selected from the catalogue of Ap, HgMn, and Am stars, with the ultimate goal of detecting new ACV variables. In total, we found 80 variables, from which 74 are reported here for the first time. The data allowed us to establish variability for 23 stars which had been reported as probably constant in the literature before. Light curve parameters were obtained for all stars by a least‐squares fit with the fundamental sine wave and its first harmonic. Because of the scarcity of Strömgren uvbyβ measurements and the lack of parallax measurements with an accuracy better than 20%, we are not able to give reliable astro‐physical parameters for the investigated objects. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Chemical evolution of the galaxy: Abundances of the light elements (sodium to calcium)

The abundances of the light (Na to Ca) elements in disc and halo stars are reviewed. New analyses are emphasized. Elements considered are the α-nuclei (Mg, Si, and Ca), and the odd-even nuclei (Na and Al, also²⁵Mg and²⁶Mg). The α-nuclei are overabundant (relative to Fe) in the old disc and halo stars. Halo stars ([Fe/H] < —1.2) have [α/Fe] ∼0.3 with extreme halo ([Fe/H] ≲ −2.0) stars showing possibly higher overabundances. The scatter in [α/Fe] at a given [Fe/H] is small. To within the observational errors, the abundance patterns for Mg, Si, and Ca are identical. For disc stars, the Na and Al abundances relative to Mg are almost independent of the [Fe/H]. Halo stars ([Fe/H] < −1) show [Na/Mg] < 0 and [AI/Mg] < 0, but the form of the mean relation and the scatter about the relation between [odd-even/Mg] and [Fe/H] remains uncertain.