Intermediate‐term variations in solar radius during solar cycle 23

In this study, we look for the mid‐term variations in the daily average data of solar radius measurements made at the Solar Astrolabe Station of TUBITAK National Observatory (TUG) during solar cycle 23 for a time interval from 2000 February 26 to 2006 November 15. Due to the weather conditions and seasonal effect dependent on the latitude, the data series has the temporal gaps. For spectral analysis of the data series, thus, we use the Date Compensated Discrete Fourier Transform (DCDFT) and the CLEANest algorithm, which are powerful methods for irregularly spaced data. The CLEANest spectra of the solar radius data exhibit several significant mid‐term periodicities at 393.2, 338.9, 206.5, 195.2, 172.3 and 125.4 days which are consistent with periods detected in several solar time series by several authors during different solar cycles. The knowledge relating to the origin of solar radius variations is not yet present. To see whether these variations will repeat in next cycles and to understand how the amplitudes of such variations change with different phases of the solar cycles, we need more systematic efforts and the long‐term homogeneous data. Since most of the periodicities detected in the present study are frequently seen in solar activity indicators, it is thought that the physical mechanisms driving the periodicities of solar activity may also be effective in solar radius variations (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

New magnetic field measurements of β Cephei stars and slowly pulsating B stars

We present the results of the continuation of our magnetic survey with FORS 1 at the VLT of a sample of B‐type stars consisting of confirmed or candidate β Cephei stars and Slowly Pulsating B (hereafter SPB) stars, along with a small number of normal B‐type stars. A weak mean longitudinal magnetic field of the order of a few hundred Gauss was detected in three β Cephei stars and two stars suspected to be β Cephei stars, in five SPB stars and eight stars suspected to be SPB stars. Additionally, a longitudinal magnetic field at a level larger than 3σ has been diagnosed in two normal B‐type stars, the nitrogen‐rich early B‐type star HD 52089 and in the B5 IV star HD 153716. Roughly one third of β Cephei stars have detected magnetic fields: Out of 13 β Cephei stars studied to date with FORS 1, four stars possess weak magnetic fields, and out of the sample of six suspected β Cephei stars two show a weak magnetic field. The fraction of magnetic SPBs and candidate SPBs is found to be higher: Roughly half of the 34 SPB stars have been found to be magnetic and among the 16 candidate SPBs eight stars possess magnetic fields. In an attempt to understand why only a fraction of pulsating stars exhibit magnetic fields, we studied the position of magnetic and non‐magnetic pulsating stars in the H‐R diagram. We find that their domains in the H‐R diagram largely overlap, and no clear picture emerges as to the possible evolution of the magnetic field across the main sequence. It is possible that stronger fields tend to be found in stars with lower pulsating frequencies and smaller pulsating amplitudes. A somewhat similar trend is found if we consider a correlation between the field strength and the v sin i ‐values, i.e. stronger magnetic fields tend to be found in more slowly rotating stars (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Parametrization of single and binary stars

Stellar masses and ages are not directly observable parameters, and the methods used to determine them are based on the calibrating relations. In particular, the mass–luminosity relation, based on the masses of less than 200 well-studied binaries, is virtually the only way to estimate the mass of single stars. Thus, the development of methods for estimating stellar masses with accuracy comparable to direct methods is a problem of vital importance.
Here, we describe a method for estimating stellar masses and ages, which is based on the geometric similarity of evolutionary tracks for the stars at the same evolutionary stage in the Hertzsprung–Russell (HR) diagram. To examine the proposed approach, it has been applied to various test data sets. Application of the method, using synthetic stellar spectra Basel Stellar Library (of theoretical spectra; BaSeL), demonstrates that it allows determination of masses and ages of stars with a predictable distribution of uncertainties.
This statistical approach allows us to demonstrate the viability of the method using it on the set of double-lined eclipsing binaries with intermediate-mass and low-mass components which allows us to compare calculated characteristics with observational ones. As a result, the uncertainties of the stellar masses estimated with the proposed method are comparable with the accuracy of ones obtained from direct observations. This allows us to recommend the method for mass estimates of masses of single stars by the localization in the HR diagram.
As for the ages, the estimates for intermediate-mass stars are more reliable, while those obtained for low-mass stars are very uncertain, due both to slower movement of these stars in the HR diagram with age at stages close to the main sequence and to certain disagreements between theoretical models for this mass range.     

Model-based pattern speed estimates for 38 barred galaxies

We have modelled 38 barred galaxies by using near-infrared and optical data from the Ohio State University Bright Spiral Galaxy Survey. We constructed the gravitational potentials of the galaxies from H -band photometry, assuming a constant mass-to-light ratio. The halo component we choose corresponds to the so-called universal rotation curve. In each case, we used the response of gaseous and stellar particle disc to rigidly rotating potential to determine the pattern speed.
We find that the pattern speed of the bar depends roughly on the morphological type. The average value of corotation resonance radius to bar radius,     , increases from 1.15 ± 0.25 in types SB0/a–SBab to 1.44 ± 0.29 in SBb and 1.82 ± 0.63 in SBbc–SBc. Within the error estimates for the pattern speed and bar radius, all galaxies of type SBab or earlier have a fast bar     , whereas the bars in later type galaxies include both fast and slow rotators. Of 16 later type galaxies with a nominal value of     , there are five cases, where the fast-rotating bar is ruled out by the adopted error estimates.
We also study the correlation between the parameter     and other galactic properties. The clearest correlation is with the bar size: the slowest bars are also the shortest bars when compared to the galaxy size. A weaker correlation is seen with bar strength in a sense that slow bars tend to be weaker. These correlations leave room for a possibility that the determined pattern speed in many galaxies corresponds to actually that of the spiral, which rotates more slowly than the bar. No clear correlation is seen with either the galaxy luminosity or the colour.     

Covariance of dark energy parameters and sound speed constraints from large H i surveys

An interesting probe of the nature of dark energy is the measure of its sound speed, c _s. We review the significance for constraining sound speed models of dark energy using large neutral hydrogen (H  i ) surveys with the square kilometre array (SKA). Our analysis considers the effect on the sound speed measurement that arises from the covariance of c _s with the dark energy density, Ω_de, and a time-varying equation of state,   w ( a ) = w ₀+ (1 − a ) w _a   . We find that the approximate degeneracy between dark energy parameters that arises in power spectrum observations is lifted through redshift tomography of the H  i -galaxy angular power spectrum, resulting in sound speed constraints that are not severely degraded. The cross-correlation of the galaxy and the integrated Sachs Wolfe (ISW) effect spectra contributes approximately 10 per cent of the information that is needed to distinguish variations in the dark energy parameters, and most of the discriminating signal comes from the galaxy auto-correlation spectrum. We also find that the sound speed constraints are weakly sensitive to the H  i bias model. These constraints do not improve substantially for a significantly deeper H  i survey since most of the clustering sensitivity to sound speed variations arises from   z ≲ 1.5  . A detection of models with sound speeds close to zero,   c _s≲ 0.01,  is possible for dark energy models with   w ≳−0.9  .     

Environmental dependence of stellar mass,SFR, and SSFR for the Luminous Red Galaxy (LRG) sample of the SDSS DR7

Using the Luminous Red Galaxy (LRG) sample of the Sloan Digital Sky Survey Data Release 7 (SDSS DR7), we investigate the environmental dependence of stellar mass, star formation rate (SFR) and specific star formation rate (SSFR) of LRGs. It is found that stellar mass of LRGs nearly is independent of local environments, and that the environmental dependence of SFR and SSFR in the LRG sample is much weaker than the one in the Main galaxy sample. One possible explanation is that galaxy color and morphology are a pair of galaxy properties most predictive of local environments, while LRGs are a group of galaxies that are likely to be luminous, red and of early types (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

测井方法测定含煤地层的岩石弹性参数

本文论述了利用声波全波列数字测井资料提取横波的两种方法:子波逼近法和相似相关法。根据测井获得的纵波、横波和密度资料,计算了岩石的弹性模量,所得结果有足够的精度,为煤矿生产和建设提供了有用的岩石物理力学参数。文中还讨论了用静态法和动态法所测得的弹性模量存在的某些差别。