恒星初始质量分布函数对伽玛暴爆发率的影响     

许丛易  韦大明 《天文学报》2008,49(4)

伽玛射线暴的产生机制比较公认的是:长暴产生于大质量恒星死亡;短暴产生于密近双星合并.因此人们很自然地推测长暴和恒星形成率直接成比例,但是最近数据分析表明这并不能很好地拟合观测.考虑到只有质量大于某一临界质量的大质量恒星才可能产生长暴,因此恒星初始质量分布函数对长暴的产生率会有较大影响.考虑用恒星初始质量分布函数来解释长暴观测个数随红移的分布,得到了比较好的结果.  相似文献   

High resolution submillimeter observations of massive protostars     

C. L. Brogan  T. R. Hunter  R. Indebetouw  C. J. Chandler  Y. L. Shirley  R. Rao  A. P. Sarma 《Astrophysics and Space Science》2008,313(1-3):53-57

We describe results from recent Submillimeter Array observations of massive protostellar objects (CepheusA-East, NGC7538 IRS1, and G5.89-0.39) with resolutions ranging from 0.8″ to 2″. A wide range of spectral and continuum properties are observed, with one unifying theme: at these resolutions all of the studied sources reveal multiple submillimeter cores. Some are observed to have cm-wavelength counterparts, and others not, suggesting a range of evolutionary stages coexisting in close proximity. In the presence of such complexity and multiplicity of sources, these data suggest that the interpretation of diagnostics such as kinematic velocity gradients and temperatures that are strongly dependent on spatial resolution should be approached cautiously.  相似文献   

Complex organic molecules in an early stage of protostellar evolution     

Nami Sakai  Takeshi Sakai  Satoshi Yamamoto 《Astrophysics and Space Science》2008,313(1-3):153-157

We have detected the rotational lines of HCOOCH₃ toward a Class 0 low-mass protostar, NGC1333 IRAS4B, which is reported to be extremely young according to the dynamical age of the molecular outflow (a few 100 yr). This suggests that the complex organic molecules appear from the very early stage of protostellar evolution. On the other hand, the complex organic molecules are not detected in a more evolved protostar, L1527. We have also found a similar trend in a massive star forming region, NGC2264. The HCOOCH₃ emission is almost absent toward IRS1, whereas it is concentrated near MMS3, which is younger than IRS1. In addition, the HCOOCH₃ intensity peak is slightly shifted from the dust emission peak, as is seen in the Orion KL Compact Ridge, giving an important clue to solve its origin.  相似文献   

On nova Scorpii 2007 N.1 (V1280 Sco)     

Hanindyo Kuncarayakti  Desima Kristyowati  Chatief Kunjaya 《Astrophysics and Space Science》2008,314(1-3):209-212

We present the results of our photometric and spectroscopic observations of Nova Sco 2007 N.1 (V1280 Sco). The photometric data was represented by a single data point in the light curve since the observation was carried out only for one night. The spectra cover two different phases of the object’s evolution during the outburst, i.e. pre-maximum and post-maximum. Measurements of the P-Cygni profile on Na I ‘D’ line (5889 Å) was derived as the velocity of shell expansion, yielding 1567.43±174.14 km s^?1. We conclude that V1280 Sco is a fast Fe II-type nova.  相似文献   

A Study of the Solar-Like Properties of β Hydri     

Maria Pia Di Mauro  Jørgen Christensen-Dalsgaard  Lucio Paternò 《Astrophysics and Space Science》2003,284(1):229-232

We investigate properties of the internal structure of HR2021, better known as Hydri, a G2 IV subgiant with mass close to solar and for which observations by Bedding et al. (2001) have shown the presence of solar-like oscillations.We have computed models of Hydri,based on updated global parameters,and compared the computed frequencies for the models with the observed oscillation spectrum.  相似文献   

X-ray astronomy of stellar coronae     

Manuel Güdel 《Astronomy and Astrophysics Review》2004,12(2-3):71-237

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Late-type X-ray Emitting Binaries in the Solar Neighborhood and in Star Forming Regions     

Antonio Frasca  Ettore Marilli  Patrick Guillout  Rubens Freire Ferrero  Elvira Covino  Juan M. Alcalá 《Astrophysics and Space Science》2006,304(1-4):17-20

We present a spectroscopic and photometric follow-up of binary stars, discovered in a sample of X-ray sources, aimed at a deep characterization of the stellar X-ray population in the solar neighborhood and in Star Forming Regions (SFRs). The sources have been selected from the RasTyc sample, obtained by the cross-correlation between the ROSAT all-sky survey and Tycho catalogues (Guillout et al., 1999). Thanks to the high resolution spectroscopy, we have obtained good radial velocity curves, whose solutions provided us with the mass ratios and minimum masses of the components. We have also obtained an accurate spectral classification with codes specifically developed by us. In addition, we could obtain information on the age of the sources through the Lii-6708 line and on the chromospheric activity level through the Hα line.We show also some results on very young pre-main sequence (PMS) binaries discovered as optical counterparts of X-ray sources in SFRs. The spectroscopic and photometric monitoring has allowed us to determine the orbital and physical parameters and the rotation periods, that are of great importance for testing the models of PMS evolution.  相似文献   

恒星大气物理参量的非参数估计方法   总被引：1，自引：0，他引：1  

张健楠  吴福朝  罗阿理  赵永恒 《天文学报》2005,46(4):406-415

恒星大气物理参量（有效温度、表面重力、化学丰度）是导致恒星光谱差异的主要因素．恒星大气物理参量的自动测量是LAMOST等大规模巡天望远镜所产生的海量天体光谱数据自动处理中一个重要研究内容．针对测量大样本的恒星光谱数据估计每个恒星的大气物理参量，提出了一种基于变窗宽核函数的估计算法：变窗宽算法是对固定窗宽算法的改进，分为3个步骤：（1）将历史恒星光谱数据进行PCA处理，得到光谱的低维特征数据；（2）利用特征数据与其物理参数的对应关系，建立一种变窗宽的非参数估计模型；（3）利用该估计模型，直接计算待测恒星光谱的3个物理参量（有效温度、表面重力、金属丰度）．实验结果表明：该方法与固定窗宽估计模型以及在其他文献中报道的方法相比，具有较高的估计精度和鲁棒性．  相似文献   

CO interferometric observations of M1-92 (the minkowski's footprint)     

V. Bujarrabal  J. Alcolea  R. Neri  M. Grewing 《Astrophysics and Space Science》1995,224(1-2):433-434

We present high spatial resolution observations of the CO emission at 2.6mm in the protoplanetary nebula M1-92 (Minkowski's Footprint), obtained with the Plateau de Bure interferometer. The total mass corresponding to the CO measured intensity is estimated to be large, of about 0.1–0.2 solar masses. The cartography is particularly rich and revealing. From the measured position-velocity distribution of brightness, we conclude that a strong dynamical interaction between the AGB and post-AGB winds is present.  相似文献   

Transitions to and from stable discs in cataclysmic variable stars     

Brian Warner 《Astrophysics and Space Science》1995,230(1-2):83-94

The observational properties of Z Cam stars, nova-like variables and nova remnants are discussed in terms of the disc instability model. The effects of irradiation on the secondary star, giving rise to high and low states of mass transfer, and on the inner disc, suppressing or greatly reducing the disc instability, are used to explain the light curves of VY Scl stars. Irradiation may also play a part in producing low amplitude modulations in brightness of nova-likes on time scales of tens of days.  相似文献