The accretion of brown dwarfs and planets by giant stars – II. Solar-mass stars on the red giant branch

This paper extends our previous study of planet/brown dwarf accretion by giant stars to solar-mass stars located on the red giant branch. The model assumes that the planet is dissipated at the bottom of the convective envelope of the giant star. The evolution of the giant is then followed in detail. We analyse the effects of different accretion rates and different initial conditions. The computations indicate that the accretion process is accompanied by a substantial expansion of the star, and, in the case of high accretion rates, hot bottom burning can be activated. The possible observational signatures that accompany the engulfing of a planet are also extensively investigated. They include the ejection of a shell and a subsequent phase of IR emission, an increase in the ⁷Li surface abundance and a potential stellar metallicity enrichment, spin-up of the star because of the deposition of orbital angular momentum, the possible generation of magnetic fields and the related X-ray activity caused by the development of shear at the base of the convective envelope, and the effects on the morphology of the horizontal branch in globular clusters. We propose that the IR excess and high Li abundance observed in 4–8 per cent of the G and K giants originate from the accretion of a giant planet, a brown dwarf or a very low-mass star.     

Do the physical properties of Ap binaries depend on their orbital elements?

We reveal sufficient evidence that the physical characteristics of Ap stars are related to binarity. The Ap star peculiarity [represented by the  Δ( V 1- G )  value and magnetic field strength] diminishes with eccentricity, and it may also increase with orbital period ( P _orb). This pattern, however, does not hold for large orbital periods. A striking gap that occurs in the orbital period distribution of Ap binaries at 160–600 d might well mark a discontinuity in the above-mentioned behaviour. There is also an interesting indication that the Ap star eccentricities are relatively lower than those of corresponding B9–A2 normal binaries for   P _orb>10 d  . All this gives serious support to the pioneering idea of Abt & Snowden concerning a possible interplay between the magnetism of Ap stars and their binarity. Nevertheless, we argue instead in favour of another mechanism, namely that it is binarity that affects magnetism and not the opposite, and suggest the presence of a new magnetohydrodynamical mechanism induced by the stellar companion and stretching to surprisingly large P _orb.     

吸附态轻烃的解吸与分析

吸附态轻烃是沉积岩层中轻烃的主要赋存状态之一,主要来源于油气藏轻烃源,其吸附的物理化学状态及组成和含量上的特征代表着极其丰富和重要的地球化学信息,采用不同的方法和手段使沉积岩样品中的吸附态轻烃解吸出来,然后分析其组成和含量,就可以从不同的角度来了解和认识样品所对应层位及下伏地层的含油气信息。     

Confirmation of simultaneous p and g mode excitation in HD 8801 and γ Peg from time-resolved multicolour photometry of six candidate 'hybrid' pulsators

We carried out a multicolour time-series photometric study of six stars claimed as 'hybrid' p and g mode pulsators in the literature. γ Peg was confirmed to show short-period oscillations of the β Cep type and simultaneous long-period pulsations typical of Slowly Pulsating B (SPB) stars. From the measured amplitude ratios in the Strömgren uvy passbands, the stronger of the two short period pulsation modes was identified as radial; the second is  ℓ= 1  . Three of the four SPB-type modes are most likely  ℓ= 1  or 2. Comparison with theoretical model calculations suggests that γ Peg is either a  ∼8.5 M_⊙  radial fundamental mode pulsator or a  ∼9.6 M_⊙  first radial overtone pulsator. HD 8801 was corroborated as a 'hybrid'δ Sct/γ Dor star; four pulsation modes of the γ Dor type were detected, and two modes of the δ Sct type were confirmed. Two pulsational signals between the frequency domains of these two known classes of variables were confirmed and another was newly detected. These are either previously unknown types of pulsation or do not originate from HD 8801. The O-type star HD 13745 showed small-amplitude slow variability on a time-scale of 3.2 d. This object may be related to the suspected new type of supergiant SPB stars, but a rotational origin of its light variations cannot be ruled out at this point. 53 Psc is an SPB star for which two pulsation frequencies were determined and identified with low spherical degree. Small-amplitude variability was formally detected for 53 Ari but is suspected not to be intrinsic. The behaviour of ι Her is consistent with non-variability during our observations, and we could not confirm light variations of the comparison star 34 Psc previously suspected. The use of signal-to-noise criteria in the analysis of data sets with strong aliasing is critically discussed.     

化学改性土的工程分类研究

在已有研究成果和课题组工作的基础上,确立了化学改性土的分类原则,并将其分为5类:即无机类改性土、有机类改性土、无机有机复合类改性土、化学物理类改性土和污染土;给出了各类土的定义,并对它们的成因、工程性质、机理、用途以及优缺点进行了比较详细的分析.研究表明:5类化学改性土具有各自的工程性质特点和形成机理,并适用于不同的工程用途;其改性效果取决于改性材料的性质、被改性土的性质以及改性工艺等,其中化学-物理类改性土的工程性质最具有优势,而污染土一般不能满足工程的环境和强度要求,需要采取一定的措施后,才能作为工程材料使用.化学改性土在环境岩土工程领域中具有广阔的应用前景.     

CEMP星HE1005-1439中子俘获元素天体物理来源的研究

HE1005-1439是一颗金属丰度极低([Fe/H] ~ - 3.0)的碳增丰贫金属星(Carbon Enhanced Metal-Poor,CEMP), 该星的s-过程元素显著超丰([Ba/Fe] = 1.16±0.31, [Pb/Fe] = 1.98±0.19), 而r-过程元素温和超丰([Eu/Fe] = 0.46±0.22), 使用单一的s-过程模型和i-过程模型均不能拟合该星中子俘获丰度分布. 采用丰度分解的方法探究该星化学元素的天体物理来源可有助于理解CEMP星的形成和化学演化. 利用s-过程和r-过程的混合模型对其中子俘获元素的丰度分布进行拟合, 发现该星的中子俘获元素主要来源于低质量低金属丰度AGB伴星的s-过程核合成, 而r-过程核合成也有贡献.     

Elemental abundance analyses with DAO spectrograms – XXII. The B9–A3 stars λ Ursae Majoris, 59 Herculis, 14 Cygni and 29 Cygni

Elemental abundances of the moderately rotating B9–A3 stars λ UMa, 59 Her, 14 Cyg and 29 Cyg have been derived in a consistent manner with previous studies of this series from spectrograms obtained with Reticon and CCD detectors. The derived elemental abundances show that λ UMa is a mild Am star, while 59 Her is slightly metal-rich. Although 14 Cyg has values closer to solar than these stars, its subsolar Ca and Sc abundances indicate that it might be the hottest known hot-Am star. 29 Cyg is a metal-poor λ Boo star.     

Optical Spectroscopy of V4334 Sgr: 1996–2000

Due to a combination of rapid expansion and changes in chemical composition, the optical spectrum of V4334 Sgr changed rapidly between discovery in 1996 Februaryand extinction during 1999. As one of the most rapidly evolving stars ever observed, optical spectroscopy must answer a range of important questions.The development of the optical spectrum and its implications are discussedthrough a review of published literature. A previously unpublished sequence of spectra from near discovery through 1996 demonstrates the thermal evolution of V4334 Sgr, while detailed analysis of an unpublished echelle spectrumobtained in 1996 May raises questions about the model atmospheres used to date.As a result, requirements for future models of the atmosphere of V4334 Sgr are analysed. The future evolution of V4334 Sgr and the dispersion of its dustycocoon are briefly discussed.