3C 273、3C 279与3C 345光变的比较与分析

Blazar 3C 345的红移以及从射电到X射线波段的能谱等方面与伽玛射线源3C 279很相似,但是EGRET却没有探测到来自3C 345的辐射.从光变幅度(8GHz、22GHz,37GHz和B波段),光学最小光变时标和不同波段间的时间延迟3个方面,比较3C 345与伽玛射线源3C 279和3C 273的异同,寻找3C 345没有伽玛射线的可能原因.分析结果显示:光变幅度,在射电波段,3C 345与3C 279的更相似,在光学波段,3C 279、3C 345和3C 273依次递减并观测到了天量级的光变;还发现3C 345的时延要比3C 279长很多,而与3C 273相近.基于3C 345与3C 273的其他观测特征的相似性,如都观测到了大兰包,红外光度相当,那么3C 345的伽玛辐射能谱可能与3C 273相似,伽玛光度也相当.简单计算表明,若3C 273处于3C 345的红移处时,即使处在爆发态EGRET也探测不到3C 273,这可能正是EGRET从未探测到3C 345的原因.     

Comparison and Analysis of the Light Variations of 3C 273, 3C 279 and 3C 345

The blazar 3C 345 is quite similar to the γ-ray blazar 3C 279 in respect of redshift, spectral energy distribution from the radio to the X-ray wave band, and so on. However, it was not detected by EGRET. We compared the differences and similarities between 3C 345 and the γ-ray sources 3C 279 and 3C 273 in respect of variation amplitudes (in the 8 GHz, 22 GHz, 37 GHz and B band), the smallest variation time scales in the optical and the time lags between different bands to search possible reason for the lack of the γ-ray radiation in 3C 345. From our analyses it is found that the variation amplitudes in the radio band for 3C 345 and 3C 279 are quite similar; the variation amplitudes in the optical wave band gradually decrease in the order 3C 279, 3C 345 and 3C 273, and variations on the order of days are found in these three sources. It is also found that the time lag in 3C 345 is much longer than that in 3C 279 and is approximately the same as that in 3C 273. Based on the similarity of other observational properties between 3C 345 and 3C 273, such as the presence of the big blue bump and their comparable infrared luminosities, it is proposed that the spectral energy distribution and the luminosity in the γ-ray band for 3C 345 are similar to those for 3C 273. It is indicated by our simple calculations that if 3C 273 has a similar redshift to that of 3C 345, then even at the burst state, EGRET could not detect any radiations from 3C 273. This might be the reason why 3C 345 had never been detected by EGRET.     

Synthetic phyllosilicates and the matrix material of C1 and C2 chondrites

Magnesium silicates and gels were synthesized from aqueous solution. A range of products with the Mg/Si ratio ranging from 2:1 to 1:1 was produced. Their composition and crystallinity were found to vary with the time scale available for formation. Structural similarities between these materials and the matrix silicates of Orgueil and Murchison were revealed through X-ray and infrared analysis.     

3C 345和3C 273的光变分析

用结构函数法,对两个经典的blazar 3C 273和3C 345的22 GHz、37 GHz和光学波段的数据进行了周期分析.结果显示,3C 273的周期性比较明显,22 GHz经分析存在7.0年和14.7年的周期,37 GHz存在7.2年和14.5年的周期,同时它的光学波段可能存在0.7年和8.7年的周期.3C 345的37 GHz存在比较明显的8.8年的周期,22 GHz和光学波段分别存在不太明显的9.3年和10.2年的周期.     

A VLBI Study of Compact Steep Spectrum Sources 3C43, 3C48 and 3C454

We used the VLBA(NRAO, USA) and made VLBI observations towards the compact steep spectrum sources 3C43, 3C48 and 3C454 at the central frequency 1.6 GHz, and obtained their total flux density maps and information on the structures of their components. By comparison with the previous data, we analyzed the variations of their flux densities as well as the displacements of their components. It is found that the total flux density of the source 3C43, as well as the flux densities and relative positions of its components are quite stable in 14 years. For the source 3C454, the total flux density and the flux densities of its components are also relatively stable, but two of the components moved away from the central core with superluminal velocities of 21.6c and 17.7c. Fitted to their flux densities at 4 L-band frequencies, the spectral indexes of the sources 3C43 and 3C454 were obtained to be 0.63 and 0.86, respectively, in good agreement with previous results, and consistent with the definition of α ≥0.5 for compact steep spectrum sources.     

The Sun,C12/C13 abundance ratio and neutrino emission

It is pointed out that the effect of neutrino emission process according to the photonneutrino coupling theory can be taken to interpret the observed ratio of C¹²/C¹³ abundance and other solar activities.     

Neutral-neutral reactions for the formation of C3O and C3S

We investigate, neutral-neutral radiative association reactions (C₂+CO) and (C₂+CS) for the formation of C₃O and C₃S respectively by DFT. Both the reactions are spin allowed and found to be exothermic and barrierless in nature. The product of these reactions are perfectly linear and the calculated rotational transitions are in good agreement with earlier published data. At the DFT/TZ2P level, the difference between the calculated rotational constant and experimental one is 0.064 % for C₃O and 0.16 % for C₃S. We also discussed the intrinsic and relative stability of these molecules.     

Structure investigations of 3C 196 and 3C 280 in the decameter waveband

Observational results are presented concerning the structure of the quasar 3C 196 and the radio galaxy 3C 280 at 20 and 25 MHz, obtained by the scintillation method with the URAN-1 interferometer. Angular dimensions of the scintillating components and extended regions of the sources have been evaluated. In the case of the quasar 3C 196, the effective angular size of the scintillating component equals 2±1 _. 5 and that of the extended region 18×25.The contribution of the compact component into the total radiation flux is 0.46±0.20. Spectra of the structural formations in 3C 196 have been obtained in the range 20–5000 MHz.For the radio galaxy 3C 280 the effective angular size of the scintillating component equals 1 _. 5±1 _. 2. and that of the extended region exceeds 10 _. The contribution into the total flux due to the scintillating part is 0.35±0.20.The data obtained are analyzed together with the results measured at higher frequencies. It is pointed out that in a wide frequency range, the effect of wave scattering in the interstellar medium does not exceed measurement errors,hence bringing about no increase in the compact component sizes of the sources observed.     

Haser model CN,C2 and C3 production rates in some comets

Emission fluxes of CN, C₂ and C₃ species observed in the coma of some comets are analysed in the framework of Haser model. CN, C₂ and C₃ production rates are determined using recently derived fluorescence efficiencies and dependence of CN, C₂ and C₃ production rates on the heliocentric distance is studied. Evidence for a burst type activity around January 15, 1974 in the post-perihelion period of comet Kohoutek (1973f) is observed.     

Calculations concerning interstellar isomeric abundance ratios for C3H and C3H2

The syntheses of interstellar c-C3H2, H2CCC, c-C3H, and HCCC, where "c" stands for the cyclic isomer, are thought to proceed via dissociative recombination of the precursor ions c-C3H3+ and H2CCCH+, which are themselves produced mainly via the radiative association reaction between C3H+ and H2. We have utilized ab initio methods to study the potential energy surface (PES) for the association of the linear ion C3H+ and H2 to form the isomers c-C3H3+ and H2CCCH+. The overall rate coefficient for radiative association has been calculated as a function of temperature via the phase space method. Our ab initio calculations show that the H2CCCH+ isomer is formed directly without an activation barrier from reactants, and that isomerization between the two isomers can occur readily via a low-energy pathway consisting of two transition states (saddle points on the PES) and one intermediate (local minimum on the PES). Calculations of the equilibrium coefficient for the isomerization H2CCCH+ <-> c-C3H3+ as a function of energy shows that equal abundances of these two ions should be produced as relaxation proceeds, in agreement with experimental measurements at high pressure. Our results confirm the important point that a simple ion-molecule association reaction can produce a cyclic hydrocarbon. If dissociative recombination reactions involving c-C3H3+ and H2CCCH+ maintain the carbon skeletal structure of the ions and produce roughly similar C3H/C3H2 branching ratios, then abundance ratios of unity are produced between the cyclic and noncyclic isomers of C3H and C3H2 via this mechanism. The large abundance ratio of c-C3H2 to H2CCC observed in TMC-1 can then be explained by differential destruction rates.     

Determination of sulphur-bearing components in C1 and C2 carbonaceous chondrites by stepped combustion

Abstract— Ten type 1 and 2 carbonaceous chondrites have been analysed by stepped combustion to determine the nature of their sulphur-bearing components. All samples show complex release patterns which, when combined with published petrographic observations, can be interpreted in terms of sulphur derived from a mixture of at least seven components (elemental sulphur, organic sulphur, sulphide, FESON or tochilinite and sulphates: gypsum, bloedite and epsomite). Estimated concentrations of individual components show that most of the sulphur in the meteorites exists in oxidised form. The concentrations of reduced and oxidised components can be used to derive approximate oxidised/reduced sulphur ratios for the meteorites. These ratios are indicators of the extent of aqueous alteration and increase in the order CM < CI. Formation of the different alteration products by aqueous processes active on the meteorite parent body appears to be the most likely origin.     

The12C/13C isotope ratio in comets,stars and interstellar matter

The¹²C/¹³C isotope ratio in the interstellar medium and in stellar atmospheres is discussed and compared to the value found in the solar system and especially in comets. The cometary value (100) tends to be slightly above the terrestrial value and is definitively higher than that for interstellar molecular clouds (about 30 to 50).This result implies that comets are not of interstellar origin; that the original isotopic abundances of the primitive solar nebula has been preserved in the cometary material; and that due to an enrichment of the interstellar medium in¹³C, the¹²C/¹³C isotope ratio has decreased by a factor of about 2.5 since the formation of the solar system (i.e., during the past 4.5×10⁹ years) — a result which is roughly in agreement with present theories of the chemical evolution of our Galaxy. The relatively high cometary carbon isotope ratio (as compared to the terrestrial value) indicates that some correction should be applied to the semi-empirical models describing the¹³C enrichment in the Galaxy.Paper dedicated to Professor Hannes Alfvén, on the occasion of his 70th birthday, 30 May, 1978.     

Telescope and instrument robotization at Dome C

This article reviews the situation for robotization of telescopes and instruments at the Antarctic station Concordia on Dome C. A brain‐storming meeting was held in Tenerife in March 2007 from which this review emerged.We describe and summarize the challenges for night‐time operations of various astronomical experiments at conditions “between Earth and Space” and conclude that robotization is likely a prerequisite for continuous astronomical data taking during the 2000‐hour night at Dome C. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The relative abundance of the carbon isotopes12C and13C in primary cosmic radiation

Mass measurements have been performed on stopping cosmic ray carbon nuclei in a nuclear emulsion stack, which was exposed to the primary radiation in a high altitude balloon flight. The mass determinations are based on measurements of mean track width and residual range in the range intervals 0<R<0.75 mm and 1<R<12 mm. The mean track width measurements have been performed with nuclear track photometers of special construction. The mass measurements in the interval 0<R<0.75 mm have given a nearly symmetrical mass distribution. The width of the distribution is equal to that expected for a distribution which contains only one isotope. The result indicates that one of the stable isotopes is appreciably more abundant than the other. The measurements in the range interval 1<R<12 mm gave the isotopic ratio¹³C/¹²C+¹³C)=0.08. The ratio has been extrapolated to the cosmic ray source. It is found to be smaller in the source than at the point of measurement. Different assumptions about the origin of the cosmic radiation are discussed with regard to the results obtained in this investigation.     

The C+, C,CO network in interstellar clouds

A chemical network determining the formation and destruction of C⁺, C, and CO and other species is set up and applied to spherical clouds in the normal interstellar radiation field. The spherical geometry adopted gives results which are different from those for slab models. The sensitivity of chemical species to chemical and astronomical parameters is explored. The relevance of this work to the observations is discussed.     

On the photochemical formation of CN,C2, and C3 radicals in cometary comae

The formation of cometary CN, C₂ and C₃ radicals is investigated in a photochemical reaction scheme. From an analysis of the observed brightness profiles of these radicals, it is shown that CN is formed as a primary product in the photolysis of its parent molecules, whereas C₂ and C₃ are formed via two-step photodissociation of their parents. We suggest that major parent of C₂ is different species from those of CN and C₃ on the basis of the difference of the variation with heliocentric distance of the sublimation rate of the parents of these radicals. Parent molecules and reaction schemes for the formation of these radicals are discussed.     

The Titan N/N and C/C isotopic ratios in HCN from Cassini/CIRS

We report the detection of H¹³CN and HC¹⁵N in mid-infrared spectra recorded by the Composite Infrared Spectrometer (CIRS) aboard Cassini, along with the determination of the ¹²C/¹³C and ¹⁴N/¹⁵N isotopic ratios. We analyzed two sets of limb spectra recorded near 13-15° S (Tb flyby) and 83° N (T4 flyby) at 0.5 cm⁻¹ resolution. The spectral range 1210-1310 cm⁻¹ was used to retrieve the temperature profile in the range 145-490 km at 13° S and 165-300 km at 83° N. These two temperature profiles were then incorporated in the atmospheric model to retrieve the abundance profile of H¹²C¹⁴N, H¹³CN and HC¹⁵N from their bands at 713, 706 and 711 cm⁻¹, respectively. The HCN abundance profile was retrieved in the range 90-460 km at 15° S and 165-305 km at 83° N. There is no evidence for vertical variations of the isotopic ratios. Constraining the isotopic abundance profiles to be proportional to the HCN one, we find at 15° S, and at 83° N, two values that are statistically consistent. A combination of these results yields a ¹²C/¹³C value equal to 75±12. This global result, as well as the 15° S one, envelop the value in Titan's methane (82.3±1) [Niemann, H.B., and 17 colleagues, 2005. Nature 438, 779-784] measured at 10° S and is slightly lower than the terrestrial inorganic standard value (89). The ¹⁴N/¹⁵N isotopic ratio is found equal to at 15° S and at 83° N. Combining the two values yields ¹⁴N/¹⁵N = 56 ± 8, which corresponds to an enrichment in ¹⁵N of about 4.9 compared with the terrestrial ratio. These results agree with the values obtained from previous ground-based millimeter observations [Hidayat, T., Marten, A., Bézard, B., Gautier, D., Owen, T., Matthews, H.E., Paubert, G., 1997. Icarus 126, 170-182; Marten, A., Hidayat, T., Biraud, Y., Moreno, R., 2002. Icarus 158, 532-544]. The ¹⁵N/¹⁴N ratio found in HCN is ∼3 times higher than in N₂ [Niemann, H.B., and 17 colleagues, 2005. Nature 438, 779-784], which implies a large fractionation process in the HCN photochemistry.