A two-arm gaseous spiral in the inner 200 pc of the early-type galaxy NGC 2974: signature of an inner bar   总被引：1，自引：0，他引：1  

Eric Emsellem  Paul Goudfrooij  Pierre Ferruit 《Monthly notices of the Royal Astronomical Society》2003,345(4):1297-1312

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The new model of a tidally disrupted star: further development and relativistic calculations     

P. B. Ivanov  M. A. Chernyakova  I. D. Novikov 《Monthly notices of the Royal Astronomical Society》2003,338(1):147-155

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利用自回归模型检测地球极移重力效应     

杨学峰  孙和平  徐建桥 《大地测量与地球动力学》2004,24(2):110-114

同时采用4个台站的国际超导重力仪长期连续重力观测资料和国际地球自转服务中心提供的同步地球自转参数，研究了极移引起的地球重力场变化特征。利用自回归模型估计了各序列的功率谱密度和积谱密度，结果表明极移导致的重力效应的主要能量集中在Chandler摆动和周年项附近，叠积后实际重力观测与极移重力信号理论值之间的差异分别为0．4％和3．9％，说明超导重力仪可有效监测极移导致的重力变化。  相似文献   

Near-Infrared Imaging Spectrophotometry Of Comet C/1995 O1 (Hale-Bopp) Near Perihelion     

Harker  David E.  Woodward  Charles E.  McMURTRY  Craig W.  Goetz  J. A.  Pipher  J. L.  Forrest  W. J. 《Earth, Moon, and Planets》1997,78(1-3):259-264

We present 1- to 5-μm broadband and CVF images of comet Hale-Bopp taken 1997 February 10.5 UT, 50 days before perihelion. All the images exhibit a nonspherical coma with a bright “ridge” in the direction of the dust tail approximately 10″ from the coma. Synthetic aperture spectrophotometry implies that the optically important grains are of a radius ≤0.4 μm; smallest radius for any comet seen to date. The variation of the integrated surface brightness with radial distance from the coma (ρ) in all the images closely follows the “steady state” ρ⁻¹ model for comet dust ablation (Gehrz and Ney, 1992). The near-infrared colors taken along the dust tail are not constant implying the dust grain properties vary with coma distance. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Relativist ic Corrections to the Thermal Sunyaev-Zel''''dovich Power Spectrum     

Hai-Ning LiNational Astronomical Observatories  Chinese Academy of Sciences  Beijing  lhnDepartment of Astronomy  Beijing Normal University  Beijing 《中国天文和天体物理学报》2003,3(5)

We present a quantitative estimate of the relativistic corrections to the thermal SZ power spectrum produced by the energetic electrons in massive clusters. The corrections are well within 10% for current experiments with working frequencies below v < 100 GHz, but become non-negligible at high frequencies v > 350 GHz. Moreover, the corrections appear to be slightly smaller at higher l or smaller angular scales. We conclude that there is no need to include the relativistic corrections in the theoretical study of the SZ power spectrum especially at low frequencies unless the SZ power spectrum is used for precision cosmology.  相似文献   

The rms peculiar velocity of galaxy clusters for different cluster masses and radii     

Ivan Suhhonenko  Mirt Gramann 《Monthly notices of the Royal Astronomical Society》2003,339(1):271-279

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A high-resolution radio study of neutral gas in the starburst galaxy NGC 520     

R. J. Beswick  A. Pedlar  M. S. Clemens  P. Alexander 《Monthly notices of the Royal Astronomical Society》2003,346(2):424-432

We present subarcsec angular resolution observations of the neutral gas in the nearby starburst galaxy NGC 520. The central kpc region of NGC 520 contains an area of significantly enhanced star formation. The radio continuum structure of this region resolves into ∼10 continuum components. By comparing the flux densities of the brightest of these components at 1.4 GHz with published 15-GHz data we infer that these components detected at 1.4 and 1.6 GHz are related to the starburst and are most likely to be collections of several supernova remnants within the beam. None of these components is consistent with emission from an active galactic nuclei. Both neutral hydrogen (H  i ) and hydroxyl (OH) absorption lines are observed against the continuum emission, along with a weak OH maser feature probably related to the star formation activity in this galaxy. Strong H  i absorption  ( N _H∼ 10²² atoms cm⁻²)  traces a velocity gradient of 0.5 km s⁻¹ pc⁻¹ across the central kpc of NGC 520. The H  i absorption velocity structure is consistent with the velocity gradients observed in both the OH absorption and in CO emission observations. The neutral gas velocity structure observed within the central kpc of NGC 520 is attributed to a kpc-scale ring or disc. It is also noted that the velocity gradients observed for these neutral gas components appear to differ with the velocity gradients observed from optical ionized emission lines. This apparent disagreement is discussed and attributed to the extinction of the optical emission from the actual centre of this source hence implying that optical ionized emission lines are only detected from regions with significantly different radii to those sampled by the observations presented here.  相似文献   

The dynamical evolution and star formation history of the Small Magellanic Cloud: effects of interactions with the Galaxy and the Large Magellanic Cloud     

Akira M. Yoshizawa  Masafumi Noguchi 《Monthly notices of the Royal Astronomical Society》2003,339(4):1135-1154

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The depolarization properties of powerful extragalactic radio sources as a function of cosmic epoch     

J. A. Goodlet  C. R. Kaiser 《Monthly notices of the Royal Astronomical Society》2005,359(4):1456-1468

We use the observed polarization properties of a sample of 26 powerful radio galaxies and radio-loud quasars to constrain the conditions in the Faraday screens local to the sources. We adopt the cosmological redshift, low-frequency radio luminosity and physical size of the large-scale radio structures as our 'fundamental' parameters. We find no correlation of the radio spectral index with any of the fundamental parameters. The observed rotation measure is also independent of these parameters, suggesting that most of the Faraday rotation occurs in the Galactic foreground. The difference between the rotation measures of the two lobes of an individual source, as well as the dispersion of the rotation measure, shows significant correlations with the source redshift, but not with the radio luminosity or source size. This is evidence that the small-scale structure observed in the rotation measure is caused by a Faraday screen local to the sources. The observed asymmetries between the lobes of our sources show no significant trends with each other or other source properties. Finally, we show that the commonly used model for the depolarization of synchrotron radio emission by foreground Faraday screens is inconsistent with our observations. We apply alternative models to our data and show that they require a strong increase of the dispersion of the rotation measure inside the Faraday screens with cosmological redshift. Correcting our observations with these models for redshift effects, we find a strong correlation of the depolarization measure with redshift and a significantly weaker correlation with radio luminosity. We do not find any (anti-)correlation of depolarization measure with source size. All our results are consistent with a decrease in the order of the magnetic field structure of the Faraday screen local to the sources for increasing cosmological redshift.  相似文献   

The continuum and narrow-line region of the narrow-line Seyfert 1 galaxy Mrk 766     

A. Rodríguez-Ardila †  M. Contini  S. M. Viegas 《Monthly notices of the Royal Astronomical Society》2005,357(1):220-234

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