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81.
Discovery of trans-neptunian object (TNO) satellites and determination of their orbits has recently enabled estimation of the size and albedo of several small TNOs, extending the size range of objects having known size and albedo down into the sub-100 km range. In this paper we compute albedo and size estimates or limits for 20 TNOs, using a consistent method for all binary objects and a consistent method for all objects having reported thermal fluxes. As is true for larger TNOs, the small objects show a remarkable diversity of albedos. Although the sample is limited, there do not yet appear to be any trends relating albedo to other observable properties or to dynamical class, with the possible exception of inclination. The observed albedo diversity of TNOs has important implications for computing the size-frequency distribution, the mass, and other global properties of the Kuiper belt derived from observations of objects' apparent magnitudes and may also point the way toward an improved compositional taxonomy based on albedo in addition to color. 相似文献
82.
C. Reynolds T.V. Cawthorne D.C. Gabuzda 《Monthly notices of the Royal Astronomical Society》2001,327(4):1071-1080
External Faraday rotation has been detected in both the core and the parsec-scale jet of BL Lac in a four-frequency very long baseline interferometry (VLBI) experiment. This unexpected result indicates the presence of significant amounts of thermal gas close to the nucleus of this object. The rotation measure (RM) in the jet components is constant, and differs from the currently accepted Galactic RM, indicating that this value (−205 rad m−2 ) is not applicable to the components in the parsec-scale jet. The similarity of the RM in these jet components leads us to suspect that the jet RM is caused by a foreground screen in our Galaxy, although we cannot rule out a combination of Galactic RM and RM local to the jet. If the jet RM is due solely to the Galaxy, this would mean that the currently accepted value of the foreground RM (−205 rad m−2 ) is not correct, either because the value changed between 1982 and 1997, or because the assumption of no intrinsic source rotation was incorrect, as it was at our later epoch of observation. Our observations suggest a value of .
After correcting for the foreground RM, the core value is −427 rad m−2 , which is unexpected since, owing to the weakness of their line emission, BL Lac objects are often assumed to be depleted in gas. The core RM appears to be variable, probably because of the presence of at least two polarized components close to the core the relative contributions of which vary with time. 相似文献
After correcting for the foreground RM, the core value is −427 rad m
83.
84.
85.
G. Beskin N. Borisov V. Komarova S. Mitronova S. Neizvestny V. Plokhotnichenko M. Popova 《Astrophysics and Space Science》1997,248(1-2):51-57
I summarize fully-sampled observations of the 3 mm emission from CO and HCN in the inner arcminute of NGC 1068. The CO emission
is distributed in the form of a molecular bar, coincident with the infrared bar, from which emanate two spiral arms. A relatively
weak concentration of CO line emission is found at the nucleus. By contrast, the HCN emission is strongly concentrated at
the center, with relatively weak emission in the region of the star-forming arms. The ratio of HCN to CO integrated intensities
is about 0.6 over the central r ≉ 175 pc and is the highest ratio measured in the center of any galaxy; the ratio reflects
the high thermal pressure (TK ~ 50 K, n[H2] ~ 4 × 106 cm-3) in the few hundred parsecs surrounding the nucleus.
The kinematics in the star-forming arms are well described by circular orbits, with ordered noncircular motions of < 30 km
s-1 that may be attributed to spiral density wave streaming. Interior to the bar, noncircular motions dominate the gas kinematics.
A model of the CO kinematics contrains any Inner Lindblad Resonance to be close to the location of the hundred-parsec scale
HCN ‘disk’. At the nucleus, the spatially unresolved CO emission shows a triplet velocity structure characteristic of kinematically
independent regions.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
86.
Yi Liu Juan Li Jun-Hui Fan 《中国天文和天体物理学报》2007,7(3):380-388
The post-1994observationsof the blazar OQ 530 in optical BV RI bands, and radio observations at 22GHz and 37GHz were collected. The date compensated discrete Fourier transform (DCDFT) and CLEANest methods were used to search for possible periodicities. Two possible periods of 456±100 days and 258±29 days were found in the optical bands. The existence of possible correlations between the optical and radio emissions was investigated by means of discrete correlation function (DCF) analysis, and no significant correlation was found. Some possible mechanisms for the periodic variability are discussed. 相似文献
87.
UAVRS影像空中三角测量实验研究 总被引:5,自引:0,他引:5
无人飞行器低空遥感系统(UAV Low Altitude Remote Sensing System简称UAVRS系统)适合于在阴云山区低空获取高分辨率垂直和倾斜影像,但获取的影像存在像幅小、数量多、基线短、重叠度不规则且倾角过大等问题,而这些问题,都是国内外现有的数字摄影测量系统面临的新问题。本文提出以带权观测值光束法平差解决UAVRS复杂影像区域网的空中三角测量问题的方法。其技术要点在于,从提高单模型定向的精度出发,以单模型定向元素为基础构建自由区域网,为带权观测值光束法平差提供有效初值。经试验表明,空三加密点的平面精度为0.386m,高程精度为0.525m,基本能达到1∶2000地形图测图的要求。 相似文献
88.
89.
Long TeV γ-ray campaigns have been carried out to study the spectrum, variability and duty cycle of the BL Lac object Markarian 421. These campaigns have given some evidence of the presence of protons in the jet: (i) Its spectral energy distribution which shows two main peaks; one at low energies (∼1 keV) and the other at high energies (hundreds of GeV), has been described by using synchrotron proton blazar model. (ii) The study of the variability at GeV γ-rays and X-rays has indicated no significant correlation. (iii) TeV γ-ray detections without activity in X-rays, called “orphan flares” have been observed in this object.Recently, The Telescope Array Collaboration reported the arrival of 72 ultra-high-energy cosmic rays with some of them possibly related to the direction of Markarian 421. The IceCube Collaboration reported the detection of 37 extraterrestrial neutrinos in the TeV–PeV energy range collected during three consecutive years. In particular, no neutrino track events were associated with this source. In this paper, we consider the proton–photon interactions to correlate the TeV γ-ray fluxes reported by long campaigns with the neutrino and ultra-high-energy cosmic ray observations around this blazar. Considering the results reported by The IceCube and Telescope Array Collaborations, we found that only from ∼25% to 70% of TeV fluxes described with a power law function with exponential cutoff can come from the proton–photon interactions. 相似文献
90.
According to the data of optical observations of the Tuorla Observatory in Finland, using the power spectrum method, DCF (Discrete Correlation Function) method, and Jurkevich method, respectively, we analyzed the periodicity of the long-term light variation of the BL Lac object 1ES 1959+650, and obtained its light period to be P =1.4±0.3 yr. Assuming that the origin of the periodicity is concerned with the accretion disk, we obtained the region where the instability of this source occurs being R =9.65 Rg, here Rg represents the Schwarzschild radius. 相似文献