An Analysis of the Condensation Temperature of Elements of Extrasolar Planetary Systems

Using high signal-to-noise ratio spectra of extrasolar planet-hosting stars, we obtained the atmospheric parameters, accurate metallicities and the differential abundance for 15 elements (C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Ni and Ba). In a search for possible signatures of metal-rich material accreting onto the parent stars, we found that , for a given element, there is no significant trend of increasing [X/H] with increasing condensation temperature Tc. In our sample of planet-harboring stars, the volatile and refractory elements behave similarly, and we can not confirm if there exists any significant dependence on the condensation temperature Tc.     

Planet Host Stars：Mass,Age and Kinematics

1 INTRODUCTION In the past years, we were thrilled to the reports of discoveries of many planets around stars.These planetary systems outside the solar system (if exist) provide not only an independenttest of the formation theory of the solar system but also a chance to search for extraterrestriallife in the universe. Many studies have been made to identify the particularities of these stars,among which spectroscopic studies (e.g. Gonzalez et al. 2001; Santos et al. 2001; Zhao etaL. 2001…     

Rotation Periods of Nine ROSAT Selected Solar-Type Stars

We monitored 16 X-ray selected young solar-type stars for light variation and found appreciable periodic light variability with amplitudes of a few hundredths of a magni-tude in nine of the objects. Using the method of Phase Dispersion Minimization (PDM) and Fourier analysis (software PERIOD04), the rotation periods of these stars were determined from the photometric data. The rotation periods of all nine stars are shorter than about 3days. It is suggested that, as with the Pleiades cluster, small amplitude light variations are quite common among young solar-type stars with rotation periods around 3 days or less. This gives further evidence for the spin up of solar-type stars predicted by models of angular momentum evolution of pre-main sequence stars.     

Distribution of SiO and OH Maser Stars in the Galactic Plane

The observational results of the Nobeyama 45-m SiO maser survey and the Arecibo 305-m OH maser survey are assembled for an analysis of the distribution and kinematics of late-type stars in the Galactic plane.It is found that neither SiO maser stars nor OH maser stars show any concentration to the spiral arms,which imply that they do not belong to the arm population and quite possibly they are low-mass stars in late stage of evolution.A rotational curve is also derived for these objects and a few features which may be real are discussed and compared with those derived from planetary nebulae and AGB stars.     

Non－LTE Analysis of the Sodium Abundance of Metal－Poor Stars in the Galactic Disk and Halo

We performed an extensive non-LTE analysis of the neutral sodiumlines of Na I 5683/5688, 5890/5896, 6154/6161, and 8183/8195 in disk/halo starsof types F-K covering a wide metallicity range (-4 [Fe/H] +0.4), using ourown data as well as data collected from the literature. For comparatively metal-rich disk stars (-1 [Fe/H] +0.4) where the weaker 6154/6161 lines are thebest abundance indicators, we confirmed [Na/Fe] ～ 0 with an "upturn" (i.e., ashallow/broad dip around -0.5 [Fe/H] 0) as already reported in previousstudies. For the metal-deficient halo stars, where the much stronger 5890/5896 or8183/8195 lines subject to considerable (negative) non-LTE corrections amountingto 0.5 dex have to be used, our analysis suggests mildly "subsolar" [Na/Fe] valuesdown to ～ -0.4 (with a somewhat large scatter of ～±0.2 dex) on the average at thetypical halo metallicity of [Fe/H] ～ -2, followed by a rise again to a near-solar ratioof [Na/Fe] ～ 0 at the very metal-poor regime [Fe/H] ～ -3 to -4. These resultsare discussed in comparison with the previous observational studies along with thetheoretical predictions from the available chemical evolution models.     

A rigorous statistical test for the existence of supermetallicity in F, G and K dwarfs

In this paper, the first statistically rigorous test is performed to determine whether there are dwarfs in the solar neighbourhood with [Fe/H] > +0.2 dex. The possibility that no such stars exist is rejected with a confidence limit exceeding 99.994 per cent. If the threshold value is raised to +0.38 dex, the corresponding hypothesis is rejected with a confidence limit of 98.5 per cent. It is tentatively found that this upper limit does not depend on the presence or absence of planets orbiting metal-rich stars. In a result that is unchanged from a previous paper, the upper limit for the known metallicities of giants is found to be about 0.2 dex lower than the limit for dwarfs. Stars that might be observed to improve the upper metallicity limit for dwarfs are listed.     

A statistical search for supermetallicity in F, G and K stars

High-dispersion and low-resolution data are combined to search for super-metal-rich (SMR) FGK stars in the solar neighbourhood and Baade's Window. The data are assessed by using statistical analysis, with their rms errors playing a key role. A star is considered to be SMR if its value of     , while 'borderline' SMR status may be assigned if     . Borderline SMR status is assigned to μ Leo and three other giants, but no full-fledged SMR giants are found in either Baade's Window or the solar neighbourhood. By contrast, the existence of SMR class     stars turns out to be well established, with values found for [Fe/H] that are as large as ∼+0.4 dex. It is concluded that this apparent contrast between class     stars and giants should not be interpreted in astrophysical terms at present because of marked shortcomings in the available data base for giants. Recommendations are made about future research that may cure this problem and extend present knowledge about SMR dwarfs.     

A search for Ca ii emission enhancement in stars resulting from nearby giant planets

We present a search for periodicities ( P _chr) in the chromospheric Ca  ii infrared triplet emission of several stars ( τ Boo, 51 Peg, υ And, ρ ¹ Cnc, ρ CrB, 70 Vir and GL 876) which may be directly attributable to interaction with close-in giant planets. Activity enhancements could arise from increased non-radiative heating and dynamo action in planet-induced tidal bulges (with P _chr≈ P _orb/2), or from interactions between the stellar and planetary magnetic fields (with P _chr≈ P _orb). We compare both P _chr and the phase dependence of the activity with the planetary orbital period P _orb, the orbital phase, and models. No significant P _chr or phase dependence attributable to planets can be clearly identified. We place approximate upper limits on the amplitude of any planet-induced activity. We identify a possible stellar rotation period for GL 876, and support previous period determinations for four other stars. We discuss the results and possible directions of future research.     

类太阳色球活动恒星的高色散光谱观测和锂丰度

基于对9颗类太阳色球活动恒星高信噪比的高色散光谱观测, 测量了这些恒星锂线(入 = 6707.8 A'')的等值宽度, 计算了这些恒星表层锂元素丰度. 通过研究这些类太阳色球活动恒星锂丰度和X射线光度之间的关系, 发现X射线光度 强的类太阳色球活动恒星锂丰度值大于X射线较弱的恒星. 也就是说活动性较强的类太阳色球活动恒星其锂丰度较高, 活动性较弱的类太阳色球活动恒星其锂丰度较低. 考虑到主序的类太阳恒星锂元素和恒星自转速度随着恒星年龄的增加逐渐减少, 以及随着类太阳色球活动恒星自转速度的减小, 色球活动又逐渐变弱. 因此类似于锂丰度, 类太阳色球活动恒星自转速度的大小和恒星的 活动水平也同样可以表明恒星的年龄.     

球状星团中低光度红巨星的脉动稳定性

利用一种非定常的恒星非局部对流理论,对球状星团中低光度的红巨星进行了线性非绝热脉动理论计算．结果表明,对所有温度高于约5400 K模型的基音到4阶泛音都是脉动稳定的．随着恒星光度的增大,低阶泛音也变得脉动不稳定．对中低光度的红巨星,脉动稳定性非常低,接近中性稳定．因此他们将是不变星或非常小振幅的短周期变星(P<2天)．     

A search for planets transiting the M-dwarf debris disc host, AU Microscopii

We present high-cadence, high-precision multiband photometry of the young, M1Ve, debris disc star, AU Microscopii. The data were obtained in three continuum filters spanning a wavelength range from 4500 to 6600 Å, plus Hα, over 28 nights in 2005. The light curves show intrinsic stellar variability due to star-spots with an amplitude in the blue band of 0.051 mag and a period of 4.847 d. In addition, three large flares were detected in the data which all occur near the minimum brightness of the star. We remove the intrinsic stellar variability and combine the light curves of all the filters in order to search for transits by possible planetary companions orbiting in the plane of the nearly edge-on debris disc. The combined final light curve has a sampling of 0.35 min and a standard deviation of 6.8 mmag. We performed Monte Carlo simulations by adding fake transits to the observed light curve and find with 95 per cent significance that there are no Jupiter mass planets orbiting in the plane of the debris disc on circular orbits with periods,   P ≤ 5  d. In addition, there are no young Neptune like planets (with radii 2.5 times smaller than the young Jupiter) on circular orbits with periods,   P ≤ 3  d.     

Magnetospheric radio emission from extrasolar giant planets: the role of the host stars

We present a new analysis of the expected magnetospheric radio emission from extrasolar giant planets (EGPs) for a distance limited sample of the nearest known extrasolar planets. Using recent results on the correlation between stellar X-ray flux and mass-loss rates from nearby stars, we estimate the expected mass-loss rates of the host stars of extrasolar planets that lie within 20 pc of the Earth. We find that some of the host stars have mass-loss rates that are more than 100 times that of the Sun and, given the expected dependence of the planetary magnetospheric radio flux on stellar wind properties, this has a very substantial effect. Using these results and extrapolations of the likely magnetic properties of the extrasolar planets, we infer their likely radio properties.
We compile a list of the most promising radio targets and conclude that the planets orbiting Tau Bootes, Gliese 86, Upsilon Andromeda and HD 1237 (as well as HD 179949) are the most promising candidates, with expected flux levels that should be detectable in the near future with upcoming telescope arrays. The expected emission peak from these candidate radio emitting planets is typically ∼40–50 MHz. We also discuss a range of observational considerations for detecting EGPs.     

Lithium Abundance of Metal－poor Stars

High-resolution, high signal-to-noise ratio spectra have been obtained for 32 metal-poor stars. The equivalent widths of Li A6708 A were measured and the lithium abundances were derived. The average lithium abundance of 21 stars on the lithium plateau is 2.33±0.02 dex. The Lithium plateau exhibits a marginal trend along metallicity, dA(Li)/d[Fe/H] ?0.12±0.06, and no clear trend with the effective temperature. The trend indicates that the abundance of lithium plateau may not be primordial and that a part of the lithium was produced in Galactic Chemical Evolution (GCE).     

Population Synthesis for Mira Variables

By means of a population synthesis code, we investigate the Mira variables. Their birth rate (over 0.65 yr-1) and their number (-130000) in the Galaxy are estimated. For all possible Mira variables, ranges of their initial masses, pulsating periods, mass losses and lifetimes are given. We check our model with the observed Mira variables near the Sun and our results prove to be valid.     

Spin Evolution of Neutron Stars in OB／X-ray Binaries

We have investigated the relation between the orbital period Porb and the spin period Ps of neutron stars in OB/X-ray binaries. By simulating the time-development of the mass loss rate and radius expansion of a 20A⊙ donor star, we have calculated the detailed spin evolution of the neutron star before steady wind accretion occurs (that is, when the break spin period is reached), or when the OB star begins evolving off the main sequence or has filled its Roche lobe. Our results are compatible with the observations of OB/X-ray binaries. We find that in relatively narrow systems with orbital periods less than tens of days, neutron stars with initial magnetic field B0 stronger than about 3×1012 G can reach the break spin period to allow steady wind accretion in the main sequence time, whereas neutron stars with B0 < 3×1012 G and/or in wide systems would still be in one of the pulsar, rapid rotator or propeller phases when the companion evolves off the main sequence or fills its Roche lobe. Our results may     

Non-LTE Analysis of the Sodium Abundance of Metal- Poor Stars in the Galactic Disk and Halo

We performed an extensive non-LTE analysis of the neutral sodium lines of Na I 5683/5688, 5890/5896, 6154/6161, and 8183/8195 in disk/halo stars of types F-K covering a wide metallicity range (-4 (?) [Fe/H] (?) +0.4), using our own data as well as data collected from the literature. For comparatively metal-rich disk stars (-1(?) [Fe/H] (?) +0.4) where the weaker 6154/6161 lines are the best abundance indicators, we confirmed [Na/Fe]- 0 with an "upturn" (i.e., a shallow/broad dip around -0.5 (?) [Fe/H](?) 0) as already reported in previous studies. For the metal-deficient halo stars, where the much stronger 5890/5896 or 8183/8195 lines subject to considerable (negative) non-LTE corrections amounting to 0.5 dex have to be used, our analysis suggests mildly "subsolar" [Na/Fe] values down to--0.4 (with a somewhat large scatter of-±0.2 dex) on the average at the typical halo metallicity of [Fe/H] --2, followed by a rise again to a near-solar ratio of [Na/Fe] - 0 at the very metal-poor regime [Fe/H]--3 to -4     

Radioactive Ages of Metal-Poor Halo Stars

The abundances of long-lived radioactive elements Th and U observed in metal-poor halo stars can be used as chronometers to determine the age of individual stars, and hence set a lower limit on the age of the Galaxy and hence of the universe. This radioactive dating requires the zero-decay productions of Th and U, which involves complicated r-process nucleosynthesis calculations. Several parametric r-process models have been used to calculate the initial abundance ratios of Th/Eu and U/Th, but, due to the sharp sensitivity of these models to nuclear physics inputs, the calculations have relatively large uncertainties which lead to large uncertainties in the age determinations. In order to reduce these uncertainties, we present a simple method to estimate the initial productions of Th and U, which only depends on the solar system abundances and the stellar abundances of stable r-process elements. From our calculations of the initial abundance ratios of Th/Eu and U/Th, we re-estimate the ages of those ver     

Mira Symbiotic Stars

1 INTRODUCTION Symbiotic stars (SSs) are interacting binaries consisting of a cool giant, a hot compact companion and an H II region (Berman 1932; Boyarchuk 1967; Boyarchuk 1968). The cool component is a red giant (RG) that belongs either to the first gia…     

Newly Identified Silicate Carbon Stars from IRAS Low-Resolution Spectra

The discovery of silicate carbon star poses a challenge to the theory of stellar evolution in the late stage, hence it is important to look for more silicate carbon stars. To this end we have carried out cross-identifications between the new IRAS Low-Resolution Spectrum (LRS) database and the new carbon star catalog, CGCS3. We have found nine new silicate carbon stars with silicate features around 10μm and/or 18μm. These newly identified stars are located in the Regions IIIa and VII in the IRAS two-color diagram, which means they indeed have typical far infrared colors of silicate carbon stars. The infrared properties of each of these sources are discussed.