检索结果-南通市图书馆

Steps Towards a Fully Automated Classification and Redshiftmeasurement Pipeline for LAMOST Spectra. I. Continuum level and wavelength estimation for galaxies

在线全文

学校读者我要写书评

暂无评论

chinese Journal of Astronomy and Astrophysics 2001年第6期1卷 563-572页

作者： A-Li Luo and Yong-Heng Zhao national astronomical observatories, chinese academy of sciences, beijing 100012 national astronomical observatories Chinese Academy of Sciences Beijing 100012

The Large Sky-Area Multi-Object Spectroscopic Telescope (LAMOST) under construction by the national astronomical observatories will yield up to four thousand multi-fiber spectra of stars and galaxies per field. The present series of papers describes the automated data-reduction pipeline currently being designed in order to cope with the anticipated flood of spectrographic data. In this preliminary paper, we present an automated method for estimating the continuum level, the positions of strong lines and the 4000 A break in galaxy spectra. In order to obtain detailed information on the continuum, we use a wavelet filter bank. After continuum fitting, our software searches for a 4000 A break and distinguishes between emission-line galaxies (ELGs) and non-ELGs according to whether the break is small or large. It then searches for strong lines and measures the intensities of emission lines and the equivalent widths of absorption lines. For non-ELGs, the absorption lines are identified automatically yielding redshift measurements.

关键词： methods: data analysis - techniques: spectroscopic - galaxies: emission lines - galaxies: absorption lines

Annual Modulation in Intraday Variability Timescales of Extragalactic Radio Sources

在线全文

学校读者我要写书评

暂无评论

chinese Journal of Astronomy and Astrophysics 2001年第2期1卷 133-143页

作者： Shan-Jie Qian and Xi-Zhen Zhang (beijing astronomical Observatory, national astronomical observatories, chinese academy of sciences, beijing 100012) beijing astronomical Observatory National Astronomical Observatories Chinese Academy of Sciences Beijing 100012

Annual modulations in timescales of intraday variability (IDV hereafter) are discussed for six extragalactic sources: 0716+714, 0917+624, 0954+65, 1749+70, 1803+78 and 2007+77. The timescales calculated from scintillation theory are compared with the observational data . It is emphasized that systematic observations are required to identify the phenomenon and to determine the motion of the interstellar medium with respect to the Local Standard of Rest. In addition, significant deviations from the annual modulation could be due to intrinsic variations.

关键词： scattering - ISM: kinematics - BL Lacertae objects: individual: 0716+71 - quasars: individual: 0917+62 - radiation mechanisms: non-thermal

Discovery of an Optical Jet in the Rosette Nebula: Rosette HH2

在线全文

学校读者我要写书评

暂无评论

chinese Journal of Astronomy and Astrophysics 2003年第6期3卷 495-498页

作者： Jin-Zeng Linational astronomical observatories, chinese academy of sciences, beijing 100012 national astronomical observatories Chinese Academy of Sciences Beijing 100012

We report on the discovery of an optical jet - Rosette HH2 - in the RosetteNebula. The jet system bears unique features for residing at the center of a giant HII region, andits energy source is visible with apparently very low extinction along the line of sight. Unlikemost other Herbig-Haro jets, this jet indicates a high-excitation origin, and its extended portionshows a seemingly intact structure, instead of normally a shocked working surface, which isattributed to photoablation.

关键词： stars: formation stars: pre-main sequence herbig-haro objects ISM: jetsand outflows

Detectability of rotation-powered pulsars in future hard X-ray surveys

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2009年第11期9卷 1241-1258页

作者： Wei Wang national astronomical observatories Chinese Academy of Sciences Beijing 100012 China

Recent INTEGRAL/IBIS hard X-ray surveys have detected about 10 young pulsars. We show hard X-ray properties of these 10 young pulsars, which have a luminosity of 10^33 - 10^37 erg s^-1 and a photon index of 1.6-2.1 in the energy range of 20-100 keV. The correlation between X-ray luminosity and spin-down power of Lx ∝ Lsd^1.31 suggests that the hard X-ray emission in rotation-powered pulsars is dominated by the pulsar wind nebula （PWN） component. Assuming spectral properties are similar in 20-100keV and 2-10 keV for both the pulsar and PWN components, the hard X-ray luminosity and flux of 39 known young X-ray pulsars and 8 millisecond pulsars are obtained, and a correlation of Lx ∝ Lsd^1.5 is derived. About 20 known young X-ray pulsars and 1 millisecond pulsars could be detected with future INTEGRAL and HXMT surveys. We also carry out Monte Carlo simulations of hard X-ray pulsars in the Galaxy and the Gould Belt, assuming values for the pulsar birth rate, initial position, proper motion velocity, period, and magnetic field distribution and evolution based on observational statistics and the Lx - Lsd reltions：Lx ∝Lsd^1.31 and Lx∝Lsd^1.5 More than 40 young pulsars （mostly in the Galactic plane） could be detected after ten years of INTEGRAL surveys and the launch of HXMT. So, the young pulsars would be a significant part of the hard X-ray source population in the sky, and will contribute to unidentified hard X-ray sources in present and future hard X-ray surveys by INTEGRAL and HXMT.

关键词： pulsars general -- stars neutron -- X-rays stars -- radiation mechanisms nontherrnal

IRAS 01005+7910:a High Galactic Latitude Post-AGB Star

在线全文

学校读者我要写书评

暂无评论

chinese Journal of Astronomy and Astrophysics 2002年第3期2卷 193-196页

作者： Jing-Yao Hunational astronomical observatories, chinese academy of sciences, beijing 100012 national astronomical observatories Chinese Academy of Sciences Beijing 100012

IRAS 01005+7910 is a cold IRAS source. We present its optical identification, photometric and spectroscopic observation results. Its optical counterpart is classified as a B2Ie star with V magnitude 10.85. Its Hα line shows the P Cygni profile. According to its location in the Galaxy (b = 16.6), we consider it to be a post-AGB star or a proto-planetary nebula.

关键词： stars: post-AGB - infrared: stars - stars: evolution

Ionization state of cosmic hydrogen by early stars and quasars

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2009年第6期9卷 665-681页

作者： Xiao-Chun Mao1,2 1 national astronomical observatories, chinese academy of sciences, beijing 100012, china 2 Graduate University of chinese academy of sciences, beijing 100049, china national astronomical observatories Chinese Academy of Sciences Graduate University of chinese academy of sciences

Cosmic hydrogen is reionized and maintained in its highly ionized state by the ultraviolet emission attributed to an early generation of stars and quasars. The Lyα opacity observed in absorption spectra of high-redshift quasars permits more stringent constraints on the ionization state of cosmic hydrogen. Based on density perturbation and structure formation theory, we develop an analytic model to trace the evolution of the ionization state in the post-overlap epoch of reionization, in which the bias factor is taken into account. For quasars, we represent an improved luminosity function by utilizing a hybrid approach for the halo formation rate that is in reasonable agreement with the published measurements at 2 ≤ z ≤ 6. Comparison with the classic Press-Schechter mass function of dark matter halos, we demonstrate that the biased mass distribution indeed enhances star formation efficiency in the overdense environment by more than 25 per cent following the overlap of ionized bubbles. In addition, an alternative way is introduced to derive robust estimates of the mean free path for ionizing photons. In our model, star-forming galaxies are likely to dominate the ionizing background radiation beyond z = 3, and quasars contribute equally above a redshift of z ～ 2.5. From 5 ≤ z ≤ 6, the lack of evolution in photoionization rate can thus be explained by the relatively flat evolution in star formation efficiency, although the mean free path of ionizing photons increases rapidly. Moreover, in the redshift interval z ～ 2 - 6, the expected mean free path and Gunn-Peterson optical depth obviously evolve by a factor of ～ 500 and ～50 respectively. We find that the relative values of critical overdensities for hydrogen ionization and collapse could be 430% at z ≈2 and 2% at z ≈6, suggesting a rapid overlap process in the overdense regions around instant quasars following reionization. We further illustrate that the absolute estimates of the fraction of neutral hydrogen computed fr

关键词： cosmology theory -- formation galaxies -- quasars general -- diffuse radiation -- intergalactic medium

What does the Sun tell and hint now?

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2009年第9期9卷 959-965页

作者： Ke-Jun Li1,2 1 national astronomical observatories /Yunnan Observatory,chinese academy of sciences,Kunming 650011,china 2 Key Laboratory of Solar Activity,national astronomical observatories,chinese academy of sciences,beijing 100012,china national astronomical observatories / Yunnan Observatory Chinese Academy of Sciences Key Laboratory of Solar Activity National Astronomical Observatories Chinese Academy of Sciences

Some historical records, which have held since the beginning of modern solar activity cycles, are being broken by the present Sun： cycle 23 records the longest cycle length and fall time; latitudes of high-latitude sunspots belonging to a new cycle around the minimum time of the cycle are statistically the lowest at present, compared with those of other cycles; there are only one or no sunspots in a month appearing at high latitudes for 58 months, which is the first time that such a long duration has been observed. The solar dynamo is believed to be slowing down due to：（1） the minimum smoothed monthly mean sunspot number is the smallest since cycle 16 onwards, and even probably among all modern solar cycles; and （2） once the time interval between the first observations of two neighboring sunspot groups is larger than 14 d, it should be approximately regarded as an observation of no sunspots on the visible solar disk, called a spotless event. Spotless events occur with the highest frequency around the minimum time of cycle 24, and the longest spotless event also appears around the minimum time for observations of the Sun since cycle 16. Cycle 24 is expected to have the lowest level of sunspot activity from cycle 16 onwards and even probably for all of the modern solar cycles.

关键词： Sun: activity -- Sun: general -- sunspots

Inhomogeneity in Spectral Transmission of the Coated UB VRI Filters of BFOSC and its Influence on Photometry

在线全文

学校读者我要写书评

暂无评论

chinese Journal of Astronomy and Astrophysics 2002年第6期2卷 563-575页

作者： Bao-An Yao and Liu Huang1 Shanghai astronomical Observatory, chinese academy of sciences, Shanghai 2000302 national astronomical observatories, chinese academy of sciences, beijing 100012 Shanghai astronomical Observatory Chinese Academy of Sciences Shanghai 200030 national astronomical observatories Chinese Academy of Sciences Beijing 100012

In order to realize the Johnson UBV and Kron-Cousins RI photometric systems in BFOSC, glass filters were purchased according to the Bessell prescription. All the filters are anti-reflection coated,on both sides to increase the transmission. By comparing two dome flat-field exposures taken through any one of these filters set in two orientations 90degrees apart, inhomogeneities in the filter transmission is clearly demonstrated. Using a PDS microphotometer, we have confirmed that the form of their spectral transmission curve varied from point to point on the filters. This kind of inhomogeneity cannot be eliminated by dividing by flat-fielding exposure and must be ascribed to inhomogeneities in the coating. This is not some accidental defect in coating, it is in the existing coating technique because all the filters (including the narrow-band interference ones) for the BFOSC and a Hbeta filter made by another manufacturer showed a similar pattern. We found that for the studies of variable stars with amplitudes less than 0.05 mag. or studies aiming at establishing accurate C-M diagrams of star clusters, the usual uncoated Schott glass filters of Bessell's prescription are to be preferred.

关键词： methods : data analysis techniques : photometric

Pulsars in FIRST Observations

在线全文

学校读者我要写书评

暂无评论

chinese Journal of Astronomy and Astrophysics 2002年第2期2卷 146-150页

作者： Xiang-Hua Li and Jin-Lin Han national astronomical observatories, chinese academy of sciences, beijing 100012 national astronomical observatories Chinese Academy of Sciences Beijing 100012

We identify 16 pulsars from the Survey of Faint Images of the Radio Sky at Twenty-cm (FIRST) at 1.4 GHz. Their positions and total flux densities are extracted from the FIRST catalog. By comparing the source positions with those in the PSR catalog, we obtain better determined positions of PSR J1022+1001, J1518+4904, J1652+2651, and proper motion upper limits of PSR J0751+1807, J1012+5307, and J1640+2224. The proper motions of the other ten pulsars are consistent with the catalog values.

关键词： pulsar: general -stars: neutron