The Spectroscopic Orbit of the Planetary Companion Transiting HD 209458

Three new silicon-bearing radicals of astrophysical interest, SiCCH and the two nearly isoenergetic isomers SiCN and SiNC, were detected in a laboratory discharge in their X2Pi ground states by Fourier transform microwave and millimeter-wave absorption spectroscopy. Hyperfine structure was observed in the low rotational transitions of the (2)Pi(1/2) ladder, and well-resolved Lambda-doubling was observed in both fine-structure ladders. With the spectroscopic constants derived from the laboratory measurements, the spectra of all three can be calculated to an uncertainty of less than 0.1 km s(-1) in equivalent radial velocity over the entire range of interest to radio astronomers. SiCN, with a dipole moment of 2.9 D, is probably the most promising of the three for astronomical discovery.     

Low-Mass Quark Stars

More and more observational hints of quark stars are proposed these years though pulsars are considered conventionally to be normal neutron stars. The existence of low-mass quark stars is a direct consequence of the possibility that pulsar-like stars are actually quark stars, because of the ability that quark matter can confine itself by color interaction. After a brief introduction to the study of quark stars, the various astrophysical implications of low-mass quark stars are investigated. It is addressed that some of the transient unidentified γ -ray sources are probably merging quark stars. The observability of low-mass quark stars is discussed.     

Interactive Winds in Low-Mass Evolved Stars

Hypersonic flows occur in the late evolutionary stages of low to intermediate mass stars (M _ZAMS < 8M⊙). We present, from an observational point of view, the story of the matter ejected and shaped by different stellar winds. From the end of the Asymptotic Giant Branch to the Planetary Nebulae phases, the temperature and density both of the star and of the gas and dust envelope show drastic variations over a few thousand of years. We present multiwavelength (X-ray to radio) signatures of the outflows, observed through spectra and images of the consecutive phases, and discuss some open questions (bipolar morphology, microstructures,...). This revised version was published online in July 2006 with corrections to the Cover Date.     

Low-Mass Neutron Stars with Rotation

Astronomy Letters - The properties of low-mass neutron stars with rigid rotation are considered. The possible evolution paths of such stars in a close binary system with mass transfer are...     

A New Code for Nonradial Stellar Pulsations and its Application to Low-Mass, Helium White Dwarfs

We present a finite difference code intended for computing linear, adiabatic, non radial pulsations of spherical stars. This code is based on a slight modification of the general Newton-Raphson technique in order to handle the relaxation of the eigenvalue(square of the eigenfrequency) of the modes and their corresponding eigenfunctions. This code has been tested computing the pulsation spectra of polytropic spheres finding a good agreement with previous work. Then, we have coupled this code to our evolutionary code and applied it to the computation of the pulsation spectrum of a low mass, pure-helium white dwarf of 0.3 M _⊙ for a wide range of effective temperatures. In making this calculation we have taken an evolutionary time step short enough such that eigenmodes corresponding to a given model are used as initial approximation to those of the next one. Specifically, we have computed periods, period spacing, eigenfunctions, weight functions, kinetic energies and variational periods for a wide range of modes. To our notice this is the first effort in studying the pulsation properties of helium white dwarfs. The solution we have found working with these realistic white dwarf models are in good accord with the predictions of the asymptotic theory of Tassoul (1980) for high order modes. This indicates that the code presented here is able to work adequately also with realistic stellar models. This revised version was published online in July 2006 with corrections to the Cover Date.     

Low-Mass Quark Stars or Quark White Dwarfs

An equation of state is considered that, in superdense nuclear matter, results in a phase transition of the first kind from the nucleon state to the quark state with a transition parameter > 3/2 ( = _Q /( _N + P ₀/c ²)). A calculation of the integrated parameters of superdense stars on the basis of this equation of state shows that on the stable branch of the dependence of stellar mass on central pressure (dM/dP _c > 0), in the low-mass range, following the formation of a tooth-shaped break (M = 0.08 M , R = 200 km) due to quark formation, a new local maximum with M _max = 0.082 M and R = 1251 km is also formed. The mass and radius of the quark core of such a star turn out to be M _core = 0.005 M and R _core = 1.7 km, respectively. Mass accretion in this model can result in two successive transitions to a neutron star with a quark core, with energy release like supernova outbursts.     

HD 183143: A hypergiant

We present spectroscopic evidence that the luminosity of HD 183143 is higher by one magnitude than thought previously. The star is yet another B6-8 Ia-0 white hypergiant of the Galaxy. Its absolute visual magnitude is close to ?8^m, and its distance is close to 2 kpc. We describe spectroscopic manifestations of the nonstationary behavior of its atmosphere and wind.     

Zehnfarbenphotometrie der vier Ap-Sterne HD 27309, HD 119213, HD 170000 und HD 192913

The results of a ten-colour photometry of the four Ap-stars HD 27309, HD 119213, HD 170000 and HD 192913 are given. The periods were determined to 2.7098, 2.433, 1.716 and 16.3 days. The amplitudewavelength relation shows a different behaviour for all of them.     

Magnetic field models of CP stars. II: HD11503, HD12098, HD12447, HD14437, HD34452, HD40312, HD178892

We model magnetic fields of seven magnetic stars using a program for studying the structure of magnetic fields in CP stars. It appears that five of them clearly manifest the structure of a central dipole, and the remaining two can be explained by a shifted dipole model. Our previous research and the results of this study demonstrate that the dipole orientation inside the stars relative to the rotation axis can vary from 0° to 90°, both for fast and slow rotators. We can not yet solve the question of the existence of a dominant orientation due to lack of statistics. Our modeling results are consistent with those calculated using Preston’s technique in the case of a dipole field configuration.     

A spectroscopic orbit for HD 115968

Photoelectric radial-velocity measurements show that the eighth-magnitude star HD 115968 is a spectroscopic binary with a period of 16.195 days. The star has a large proper motion, and is unlikely to have the luminosity corresponding to the spectral type of G8 III favoured by Zaitseva. It is most probably a late-G dwarf.     

Lichtelektrische Untersuchungen der vier Ap-Sterne HD 9531, HD 10221, HD 27309 und HD 184905

The lightcurves in the UBV system are given for the four Ap stars HD 9531, HD 10221, HD 27309 and HD 184905 from 1968 to 1971. The measurements are represented by the periods o^d.6684, 3^d.16, 2^d.7098 and 1^d.845031 respectively.     

Magnetic configurations of the fast CP rotators HD3360, HD4778, HD5737, HD112413, and HD215441

The method of “magnetic charges” is used to model magnetic fields of five rapidly rotating stars (P < 25^d) and to find the basic parameters of their magnetic fields. A table containing all the modeling results obtained using the adopted method as well as the parameters obtained for the same stars by other authors is presented. Significant discrepances are found in a number of cases, which can apparently be explained by insufficient accuracy of the estimated inclinations of the stars to the line of sight.     

一个小质量恒星形成区的物理和动力学性质

利用ＶＬＡ的观测，我们在猎户座分子云区，发现了１１个小质量分子云浓核。它们的平均有效半径为０．０３ｐｃ，平均质量为３．５Ｍ⊙，分布在呈丝状母云南北走向的轴线上。在浓核区３＇的范围内，测到有５ｋｍｓ－１ｐｃ－１的速度梯度，一个可能的解释是这个核区的慢速转旋。根据我们的ＮＨ３（１，１）的观测资料，并与尘埃的毫米波连续辐射和红外辐射比较，我们认为这个区域的大部浓核是还没有星核的年轻分子云核，正处于热动能与自引力的平衡阶段。     

On Low-Mass, Strange Quark Stars with a Crust

Low-mass strange stars with a crust are investigated within the framework of the bag model. The crust, which consists of degenerate electrons and atomic nuclei, has a limiting boundary density _cr , which is determined by the mass of the crust, and it cannot exceed the value _drip = 4.3·10¹¹ g/cm³, corresponding to the density at which neutrons drip from nuclei. For different values of _cr in the low-mass range (M 0.1 M) we calculate several series of configurations: we find the dependence of the stellar mass M on the central density _c for _cr = const, with 10⁹ g/cm³ _{cr drip} , and for each series we determine the parameters of the configuration for which the condition dM/d _c > 0 is violated. When the boundary density of the crust decreases to 10⁹ g/cm³, the minimum mass of a strange star decreases to M _min 10^-3 M, while the radius reaches 600 km.     

Magnetic field of CP stars in the Ori OB1 association. I. HD35456, HD35881, HD36313 A,HD36526

We present the results of magnetic field measurements of four chemically peculiar (CP) stars, the members of the Orion stellar association OB1. Observations were carried out with the circular polarization analyzer at the Main Stellar Spectrograph of the 6-m telescope. All the studied stars refer to the subtype of Bp stars with weak helium lines. Canadian astronomer E. F. Borra detected a magnetic field in three of them (HD35456, HD36313, and HD36526) from the Balmer line magnetometer observations. HD35881 was observed for the first time for the purpose to search for a magnetic field. We obtained the following results: HD35456 is a magnetic star with longitudinal field variation range from +300 to +650 G and a period of 4.9506 days; HD35881 is possible a new magnetic star, the longitudinal component of which varies from?1 to +1 kGwith a period of 0.6998 days, however, a small number of lines broadened by rotation does not allow us to conduct measurements more accurately; HD36313 is a binary star with the components similar in brightness, the primary component is a magnetic star with broad lines, the magnetic field of the secondary component (the star with narrow lines) was not detected. Measurements in the Hβ hydrogen line showed the variations of the longitudinal component from ?1.5 to +2 kG with a period of 1.17862 days; a strong longitudinal field was detected in HD36526 (from 0 to +3000 G) varying with a rotation period of the star of 3.081 days. In all the cases, we observe considerable discrepancies with the data on magnetic fields of these objects obtained earlier.     

中子星X射线双星中kHz QPO现象的理论解释

罗西X射线时变探测器(RXTE)在中子星小质量X射线双星中发现了千赫兹准周期振荡现象(kHzQPO)。kHzQPO的频率一般在几百到上千赫兹,其动力学时标与吸积盘最内部区域物质的运动时标一致,因此普遍认为kHz QPO产生于中子星表面附近区域,携带了来自中心中子星及周围强引力场信息,如质量、自转周期、角动量、半径、磁场等。kHz QpO现象的理解为研究强引力场和致密物质状态开启了一扇新的窗口。着重介绍基于kHz QPO的基本现象和相应的理论模型。     

Magnetic field models of CP stars HD18296, HD19832, HD22470, HD24712

We model the magnetic fields of four magnetic stars using published longitudinal (Be) field measurements. The structure of the magnetic field of each of the four stars is close to that of the central dipole. Unfortunately, the number of measurements for each star is insufficient for accurate finding of the field parameters, and therefore we find no dipole shift exceeding its error Δa ≈ 0.1, expressed as a fraction of the stellar radius. Our data support the opinion that the results of modeling depend most strongly on the adopted inclination of the star’s rotation axis i.