Molecular lines from protoplanetary nebulae: observations with ALMA     

Valentín Bujarrabal 《Astrophysics and Space Science》2008,313(1-3):209-214

Planetary nebulae (PNe) are formed in a very fast process. In just about 1000 years, the nebula evolves from a spherical and slowly expanding AGB envelope to a PN, with usually axial symmetry and high axial velocities. Molecular lines are known to probe most of the nebular material in young PNe and protoplanetary nebulae (PPNe), and are therefore very useful to study such an impressive evolution. Many quantitative results on these objects have been so obtained, including general structure, total mass and density distribution, kinetic temperatures, velocity fields, etc. Existing observations probe both the gas accelerated by post-AGB shocks and the quiescent components. But the study of crucial regions to understand PN formation (recently shocked shells, regions heated by the stellar UV and inner rotating disks) requires observations at higher frequency and with better spatial resolution.   相似文献   

Two strong radio bursts at high and medium Galactic latitude     

S. Kida  K. Niinuma  S. Suzuki  T. Tanaka  R. Nakanura  K. Takefuji  N. Matsumura  M. Kuniyoshi  T. Daishido 《New Astronomy》2008,13(7):519-525

The Nasu Observatory, which is composed of eight 20 m elements, was constructed for observing radio transients over a wide field at 1400 MHz. We report on two radio transients detected in consecutive drift scanning observations at declination 32° over a period of about two months. One of the two transients, WJN J1039+3200, appeared at =10^h39^m40^s±10^s, δ=32°±0.4° on March 4, 2005, and the other one, WJN J0645+3200, appeared at =06^h45^m25^s±10^s, δ=32°±0.4° on March 24, 2005. Both exhibited flux densities in excess of 1 Jy, and the burst durations were up to two days. Since there are few examples of radio transients outside the Galactic plane, these are very important observations. We have previously reported on four radio transients with features that look like the two transients detected this time. Of these six WJN transients in total, five had a duration of up to two days, and one up to three days. Four of the transients were detected at high Galactic latitude of b > 30°. Counterparts of the six WJN transients included X-ray sources in four events and had a consistency of 66%. The consistency of γ-ray, PGC Galaxy, NVSS, and FIRST sources was concentrated at about 50%. We were not able to find any special features in the counterparts. The distribution was verified by making a log N–log S plot using data for the four previously detected transients and the new ones. As a result, the distribution of the radio transients that we observed might have an isotropic distribution not dependent on Galactic longitude and Galactic latitude. The detection probability was calculated based on the assumption of an isotropic distribution. The 2σ upper probability limit for detection of transients of 1000 mJy or more is 0.0049 [deg⁻² yr⁻¹]. We cannot yet identify these two radio transients, because their features are different from any radio bursts observed in the past.  相似文献   

Fast rotation of neutron stars and equation of state of dense matter     

Pawe&#x; Haensel  Julian L. Zdunik  Micha&#x; Bejger 《New Astronomy Reviews》2008,51(10-12):785

Fast rotation of compact stars (at sub-millisecond period) and, in particular, their stability, are sensitive to the equation of state (EOS) of dense matter. Recent observations of XTE J1739-285 suggest that it contains a neutron star rotating at 1122 Hz. At such rotational frequency the effects of rotation on star’s structure are significant. We study the interplay of fast rotation, EOS, and gravitational mass of a sub-millisecond pulsar. We discuss the EOS dependence of spin-up to a sub-millisecond period, via mass accretion from a disk in a low-mass X-ray binary.  相似文献   

Element Abundance Analysis of HD 140283 and Astrophysics Sources of Weak r-process Elements     

MA Wen-juan  LI Hong-jie  Zhang Lu  ZHANG Bo 《Chinese Astronomy and Astrophysics》2021,45(1):58-66

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Photospheric variability of O stars     

A. W. Fullerton 《Astrophysics and Space Science》1994,221(1-2):105-114

The characteristics of the line profile variations observed in optical transitions of O-type stars are reviewed. For a few well-observed stars, there is compelling evidence that the variations are due to photospheric velocity fields from one or more modes of nonradial pulsation. However, the origin of the line profile variations observed in most O stars is not yet established. To date, there is little empirical evidence to suggest that the variability in optical absorption lines of O stars is causally linked to the stellar wind variability commonly observed in their UV resonance lines.  相似文献   

Young eccentric binary KL CMa revisited in the light of spectroscopy     

《New Astronomy》2015

The absolute dimensions of the components of the eccentric eclipsing binary KL CMa have been determined. The solution of light and radial velocity curves of high ($\mathrm{\Delta }\lambda =0.14$ Å) and intermediate ($\mathrm{\Delta }\lambda =1.1$ Å) resolution spectra yielded masses M₁ = 3.55 ± 0.27 M_⊙, M₂ = 2.95 ± 0.24 M_⊙ and radii R₁ = 2.37 ± 0.09 R_⊙, R₂ = 1.70 ± 0.1 R_⊙ for primary and secondary components, respectively. The system consists of two late B-type components at a distance of 220 ± 20 pc for an estimated reddening of $E(B-V)=0.127$.The present study provides an illustration of spectroscopy’s crucial role in the analysis of binary systems in eccentric orbits. The eccentricity of the orbit ($e=0.20$) of KL CMa is found to be bigger than the value given in the literature ($e=0.14$). The apsidal motion rate of the system has been updated to a new value of $\dot{w}=0°.0199\pm 0.0002{\text{cycle}}^{-1}$, which indicates an apsidal motion period of $U=87\pm 1$ yrs, two times slower than given in the literature. Using the absolute dimensions of the components yielded a relatively weak relativistic contribution of ${\dot{w}}_{\mathit{rel}}=0°.0013{\text{cycle}}^{-1}$. The observed internal-structure component ($\log k_{2\text{,}\mathit{obs}}=-2.22\pm 0.01$) is found to be in agreement with its theoretical value ($\log k_{2\text{,}\mathit{theo}}=-2.23$).Both components of the system are found very close to the zero-age main-sequence and theoretical isochrones indicate a young age ($\tau =50$ Myr) for the system. Analysis of the spectral lines yields a faster rotation ($V_{\mathit{rot}1\text{,}2}=100$ km s⁻¹) for the components than their synchronization velocities ($V_{\mathit{rot}\text{,}\mathit{syn}1}=68$ km s⁻¹, $V_{\mathit{rot}\text{,}\mathit{syn}1}=49$ km s⁻¹).  相似文献   

Two contact binaries at different evolutionary stages in the globular cluster NGC 6397     

《New Astronomy》2013

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An atlas of Zeeman polarisation in the Stokes IQUV spectrum of β Coronae Borealis     

G. A. Wade  J. -F. Donati  J. D. Landstreet   《New Astronomy》2000,5(8):455-482

We present an atlas of the Zeeman spectral line polarisation throughout the visible spectrum of the cool F0p star β CrB based on MuSiCoS spectropolarimetry. Stokes I, V, Q and U spectra covering the full 4500–6600 Å MuSiCoS intermediate bandpass are shown at sufficient display resolution so as to be suitable for the identification of individual spectral features. This is foreseen as being useful, for example, in the planning of very high resolution spectropolarimetric studies of Ap star Zeeman signatures using high-dispersion instruments likely to have significantly smaller spectral bandwidth.  相似文献   

The 1978 outburst of the recurrent nova WZ Sagittae     

Hao Xiang-liang  Mei Bao 《Chinese Astronomy and Astrophysics》1987,11(4):288-290

We give the results of photographic observations of the recurrent nova WZ Sge during its 1978 outburst, between December 5 and 25, using the double astrograph of Beijing Observatory. We discuss the observed properties and calculate the total energy released during the outburst to be about 1.07 (+40) erg. We estimate that the next outburst will occur around the year 2011.  相似文献   

Supernovae     

J. W. Menzies 《Astrophysics and Space Science》1996,235(2):185-193

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