East-west asymmetry of Saturn's rings

The energy distribution curves of eleven Ap stars, three Am stars, four normal A stars and one F0 V magnetic star have been obtained between 478 nm and 680 nm. For four of the Ap stars, two Am stars and all the four normal A stars, the effective temperatures are believed to have been estimated for the first time. For the rest, these estimates are expected to be an improvement over previously available values.It is concluded that the Ap and Am stars are not much different from the normal A stars in so far as their temperatures are concerned.     

J-type carbon stars in the Large Magellanic Cloud

A sample of 1497 carbon stars in the Large Magellanic Cloud (LMC) has been observed in the red part of the spectrum with the 2dF facility on the Anglo-Australian Telescope. Of these, 156 have been identified as J-type (i.e. ¹³C-rich) carbon stars using a technique which provides a clear distinction between J stars and the normal N-type carbon stars that comprise the bulk of the sample, and yields few borderline cases. A simple two-dimensional classification of the spectra, based on their spectral slopes in different wavelength regions, has been constructed and found to be related to the more conventional c and j indices, modified to suit the spectral regions observed. Most of the J stars form a photometric sequence in the   K − ( J − K )  colour–magnitude diagram, parallel to and 0.6 mag fainter than the N-star sequence. A subset of the J stars (about 13 per cent) are brighter than this J-star sequence; most of these are spectroscopically different from the other J stars. The bright J stars have stronger CN bands than the other J stars and are found strongly concentrated in the central regions of the LMC. Most of the rather few stars in common with Hartwick and Cowley's sample of suspected CH stars are J stars. Overall, the proportion of carbon stars identified as J stars is somewhat lower than has been found in the Galaxy. The Na D lines are weaker in the LMC J stars than in either the Galactic J stars or the LMC N stars, and do not seem to depend on temperature.     

Non-LTE sodium abundance in galactic thick- and thin-disk red giants

The non-LTE sodium abundance has been determined from the Na I 6154 and 6161 Å lines for 38 thin-disk stars (15 of them are Ba II stars), 15 thick-disk stars, 13 Hercules-stream stars, and 13 stars that cannot be attributed neither to the thick Galactic disk nor to the thin one. The Na I model atom has been constructed using the most accurate present-day atomic data. For the Na I 6154 and 6161 Å lines, the non-LTEabundance corrections are from ?0.06 to ?0.24 dex, depending on the stellar parameters. No differences in [Na/Fe] abundance between the thick and thin disks have been detected; the derived ratios are close to the solar ones. The existence of a [Na/Fe] overabundance in the Ba II stars has been confirmed. The Hercules-stream stars exhibit nearly solar [Na/Fe] ratios. The results obtained can be used to test the sodium nucleosynthesis models.     

A catalogue of RR Lyrae stars from the Northern Sky Variability Survey

A search for RR Lyrae stars has been conducted in the publicly available data of the Northern Sky Variability Survey. Candidates have been selected by the statistical properties of their variation; the standard deviation, skewness and kurtosis with appropriate limits determined from a sample 314 known RRab and RRc stars listed in the General Catalogue of Variable Stars. From the period analysis and light-curve shape of over 3000 candidates 785 RR Lyrae have been identified of which 188 are previously unknown. The light curves were examined for the Blazhko effect and several new stars showing this were found. Six double-mode RR Lyrae stars were also found of which two are new discoveries. Some previously known variables have been reclassified as RR Lyrae stars and similarly some RR Lyrae stars have been found to be other types of variable, or not variable at all.     

Masses of binary stars for general orbits

The masses of a pair of stars in the visual binary system have been estimated. The angle between the orbital plane of the stars and the plane of the sky has been taken into account. Inclination of the major axes of the orbits of the stars with the line of interaction between the orbital plane and the plane of the sky has also been considered. These two inclinations are also computed in terms of the observed quantities. Major and minor axes of actual orbits of the stars are determined.     

Mt. Suhora M dwarf survey - Detection of eight short-period variable stars

The Mt. Suhora M dwarf survey searching for pulsations in low mass main sequence stars has acquired CCD photometry of 46 M dwarf stars during the first year of the project (Baran et al., 2011). As a by-product of this search hundreds field stars have been checked for variability. This paper presents our initial result of a search for periodic variables in field stars observed in the course of the survey. On the basis of the periodicity and the shape of the light curves, eight new variables has been detected, among which five are δ Scuti stars and three likely RR Lyrae stars. Although variation in one of the stars has been previously detected, it was classified incorrectly. To support our classification, in August 2010, we performed spectroscopic observations to derive spectral types and luminosity classes for all eight variable stars.     

Identification of temperature anomaly RR Lyrae stars in LAMOST survey,misclassification and binarities

RR Lyrae stars,a well-known type of pulsating variable stars,have been known about for more than a century.A large amount of photometric data on RR Lyrae stars has been accumulated by space-and ground-based sky surveys,but the spectral data are relatively poor.Fortunately,the LAMOST sky survey project provides an opportunity to view them from the point of view of spectra.We collect the atmospheric parameters of 1685 RR Lyrae stars provided by the LAMOST catalog,and carry out research by using the reliable T_(eff).We find that there is a clear correlation between their Teff and pulsation periods,which is consistent with the pulsation and evolution theories of RR Lyrae stars.In addition,we focus on those RR Lyrae stars with abnormal temperatures.After analyzing the data from several photometric surveys,we find that some of these temperature anomalies are misclassified variable stars(e.g.,eclipsing binaries,pulsating stars on main sequence),and some are RR Lyrae binary candidates.For the latter,the temperatures of potential companions should be lower and their luminosities should not be neglected(e.g.,red giant stars).We obtain that the ratio of temperature anomaly stars to all the sample stars is 4%,which means that the impact on the further analysis(e.g.,kinematics analysis) is low.We also present the catalogs of spectral anomaly RR Lyrae stars.     

Radial Velocities of Six Early Type Evolved Stars

Many early-type main sequence stars are known spectroscopic binaries, while early type spectroscopic binaries with evolved components are rather rare and well-determined masses are available only in some cases. For this reason a program to study stars with suspected variable velocity among early-type evolved stars has been initiated some time ago. In the present paper 54 coudé spectra for a sub-group formed of six early-type stars, namely HD 7902, HD 28446, HD 42087, HD 187983, HD 195592 and HD 208501 have been measured and the results of these plates have been presented.     

Effect of Coriolis force on the shapes of rotating stars and stars in binary systems

In this paper an attempt has been made to determine the effect of Coriolis force on the shapes of Roche equipotential surfaces of rotating stars and stars in binary systems. Equations of Roche equipotential surfaces have been obtained for rotating and binary stars which take into account the effects of Coriolis force besides the centrifugal and gravitational forces. Shapes of Roche equipotentials and values of Roche limits are obtained for different values of angular velocity of rotation for rotating stars and for different values of mass ratios for the binary stars. The obtained results have been compared with the corresponding results in which the effect of Coriolis force has not been considered.     

Variability and evolution in various classes of post‐AGB stars

We aim to compare properties of early‐type post‐asymptotic giant‐branch (post‐AGB) stars, including normal first‐time B‐type post‐AGB stars, and extreme helium stars (EHes). Hipparcos photometry for 12 post‐AGB stars and 7 EHe stars has been analyzed; 5 post‐AGB stars are clearly variable. The Hipparcos data are not sufficiently sensitive to detect variability in any of the EHes. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Binary population synthesis and sdBs at different metallicities

One of the ways by which subdwarf B stars are thought to form is through binary star interactions. The metallicity of the sdB progenitor stars in such binary systems should not seem to be a major factor in the formation of sdB stars. However, given the different environments in which sdB stars are found, binary population synthesis simulations have been conducted in order to examine how metallicity might be a subtle factor in the formation of sdB stars in such environments. This is then applied to clusters of stars and to the UV Upturn phenomenon.     

Velocity Space of Galactic O-B Stars

Based on the Hipparcos proper motions and available radial velocity data of O-B stars, we have re-examined the local kinematical structure of the young disk population of-1500 O-B stars not including the Gould-belt stars. A systematic warping motion of the stars about the direction to the Galactic center has been reconfirmed. A negative K-term implying a systematic contraction of stars in the solar vicinity has been detected. Two different distance scales are used in order to find out their impact on the kinematical parameters, and we conclude that the adopted distance scale plays an important role in characterizing the kinematical parameters at the present level of the measurement uncertainty.     

Variable stars in the globular cluster NGC 4590 (M68)

We present results of time series photometry to search for variable stars in the field of metal-poor globular cluster NGC 4590 (M68). Periods have been revised for 40 known variables and no significant changes were found. A considerable change in Blazhko effect for V25 has been detected. Among nine newly discovered variable candidates, 5 stars are of RRc Bailey type variables while 4 stars are unclassified. The variable stars V10, V21, V50 and V51 are found to be cluster members based on the radial velocity data taken from literature.     

Giant CP Stars?

This study is part of an investigation of the possibility of using chemically peculiar (CP) stars to map local galactic structure. Correct luminosities of these stars are therefore crucial. CP stars are generally regarded as main-sequence or near-main-sequence objects. However, some CP stars have been classified as giants. A selection of stars, classified in literature as CP giants, are compared to normal stars in the same effective temperature interval and to ordinary ‘non giant’ CP stars. We find no clear confirmation of a higher luminosity for ‘CP giants’, than for CP stars in general. In addition, CP characteristics seem to be individual properties not repeated in a component star or other cluster members.     

On the radii of Ap and Am stars

The radii of several Ap and Am stars have been compared with those of the normal A stars of the Main Sequence. Though the brighter Ap stars have a little larger radii than the Main-Sequence stars, they may not be much different from those of the slightly evolved normal A stars. The Am stars have radii with which they appear to be merging with those of the cooler A stars of the Main Sequence. The Ap stars have radii predominantly in the range of 1.8 to 3.4R _⊙, while the Am stars are mainly concentrated between 1.8 and 2.2R _⊙.     

Classification of Red Stars with Spectral Absorption Bands Observed in the Near-Infrared Range

The results of a spectral classification of 257 M stars observed in the Cepheus region are given. Their equatorial coordinates, photographic stellar magnitudes, and spectral subtypes were determined. These stars are giants and supergiants, in all probability. None of them appear in a catalog of variable stars. It is assumed that variability might be detected in many of them upon further study. Fifty-two of the stars have been identified with infrared sources.     

Single Be stars as binary ejecta?

Among the mechanisms suggested for the creation of discs around Be stars is interaction with binary companions. This idea has largely been dismissed, because the majority of Be stars have no observed companion. This difficulty can be circumvented if single Be stars are actually ejected from binary systems (owing, for instance, to the supernova of the companion). Using Hipparcos data, we show that this explanation is not likely, by comparing the velocity distributions of Be stars with those of normal B stars. We find that the distributions are consistent to within 1 σ uncertainties, and thus do not support the formation of single Be stars through binary breakup.     

Spectrophotometric study of Be stars

A large sample of Be stars has been studied spectrophotometrically in the visible region. The continuum energy distribution data for 23 Be stars included in the list of Harmanecet al. (1983) are presented and discussed in the wavelength range 3200 Å–8000 Å. For 15 Be stars the observations reported in the present work are new. By comparing the observed continua with models, the effective temperatures of these stars have been estimated. It is found that, in general, Be stars have lower effective temperature than the corresponding normal B stars. The present study shows that the early-Be stars (B0–B5) possess near-ultraviolet and near-infrared excess emissions more frequently than the late-Be stars (B5–B9). The seven new Be stars are detected to show pole-on characteristics.     

Spectrophotometric studies of Ap stars

Based on the observed energy distribution curves of about a hundred Ap stars, the various relationships among their physical parameters: namely, the temperature, colour index, bolometric correction and bolometric magnitude have been studied. The hotter Ap stars have been found to be apparently bluer than their normal counterparts, which is possibly due to the broad continuum features at 4200 and 5200 that are generally present in Ap stars only. The bolometric corrections are independent of parallax measurements; the Ap stars as well as the normal stars follow the same sequence of bolometric corrections when related to temperature. The Ap stars appear to beslightly evolved and their position in the HR diagram indicates the hydrogen shell burning phase. The mass range of Ap stars is similar to that of normal A stars.     

Stellar Rotation and Activity

This review is limited to solar-type stars (late-F to early-K main sequence stars) and to recent developments in the study of the evolution of angular momentum in those stars. Observations of rotation in young clusters are discussed, together with the models that have been put forth to account for what is seen. One key question is whether or not the convective envelopes of solar-type stars decouple from the radiative cores when the stars near the Zero-Age Main Sequence. That question cannot yet be answered, but forthcoming observations are likely to address the issue. Another significant open question is the degree to which any one cluster of stars is typical of all stars at that age, and that too is near to being resolved as we reach deeper into the Galaxy at high spectroscopic resolution. Finally, some general properties of activity in solar-type stars are presented. This revised version was published online in July 2006 with corrections to the Cover Date.