Synthetic Spectra of Long-Period Variables: A First Comparison with ISO Observations

Exploratory synthetic spectra were computed for carbon-rich long-period variables. We used dynamic model atmospheres of Höfner &; Dorfi (1997) and calculated partial pressures, absorption- and scattering coefficients as input for the spectral synthesis code of Jørgensen et al. (1992). First ISO SWS-observations of the carbon-Mira T Dra are compared with our synthetic spectra.     

GAIA Photometric System: Evaluation of Performance

We present a method and results of evaluation of the photometric systems (PSs) proposed for the GAIA mission. The method, however, can be applied for the analysis of virtually any multicolour PS designed for the global investigation of the Galactic stellar populations. Performance of the 1F, 2A and 3G PSs is evaluated taking into account their ability to simultaneously determine the main stellar parameters,T _eff, log g, [M/H] and E _B-V, for a large variety of stars down to G ∼ 20. The representative Galactic stellar populations were constructed and employed for evaluation of the PSs. Despite the fact that the 2A and 3G PSs perform significantly better than the 1F (presently adopted as a baseline PS for GAIA), we conclude that still there is no photometric system proposed to date, which would allow to achieve the scientific objectives of the GAIA mission. This revised version was published online in July 2006 with corrections to the Cover Date.     

Astrometry from space: GAIA and planet detection

The proposed baseline GAIA mission will be able to detect the astrometric signature of Jupiter-size planets around of the order of a million stars, using either global or narrow-angle astrometry. If the mission can realize the higher astrometric accuracy that photon statistics allows for bright stars, lower-mass planets (from Earth size to ten times larger) can be found around ten to a few hundred stars.     

α-process Elements in the Galaxy: A Possible GAIA Contribution

The sensitivity of stellar spectra to α/Fe abundance changes is investigated with the aim to be detected photometrically and employed for the scientific goals of the GAIA mission. A grid of plane parallel, line blanketed, flux constant, LTE model atmospheres with different [α/Fe] ratios was calculated. As a first step, the modeled stellar energy fluxes for solar-type stars and giants were computed and intercompared. The spectral sensitivity to α/Fe abundance changes is noticeable and has to be taken into account when selecting photometric filters for GAIA. The Ca II H and K lines and Mg I b triplet are the most sensitive direct indicators ofα/Fe abundance changes. This revised version was published online in July 2006 with corrections to the Cover Date.     

GAIA Photometric System: Simulation of Photometric Observations

We present a software package developed for modelling of the GAIA photometric observations. The modelling procedure is very flexible and fully controlled via the parameter file. Therefore, configuration of the GAIA telescopes and photometric systems, as well as the object samples under investigation, can be adjusted easily. This revised version was published online in July 2006 with corrections to the Cover Date.     

GAIA: An Astrometric and Photometric Survey of our Galaxy

In October 2000, the GAIA astrometric mission was approved as one of the next two `cornerstones' of ESA's science programme, with a launch date target of 2010–12. GAIA will provide positional, radial velocity, and photometric measurements with the accuracies needed to produce a stereoscopic and kinematic census of about one billion stars throughout our Galaxy (and into the Local Group), amounting to about 1 per cent of the Galactic stellar population. GAIA's main scientific goal is to clarify the origin and history of our Galaxy, from a quantitative census of the stellar populations. It will advance questions such as when the stars in our Galaxy formed, when and how it was assembled, and its distribution of dark matter. The survey aims for completeness toV =20 mag, with accuracies of 10 μas at 15 mag. This revised version was published online in July 2006 with corrections to the Cover Date.     

3-D Structure of the Galactic Interstellar Matter: A Contribution from GAIA

We investigate the possibilities for tracing interstellar extinction with the ESA's astrometric space mission GAIA. The analysis is based on detailed simulations of the GAIA photometry, which are used to derive the distribution of interstellar matter in a modelled Galaxy. We find that `small' diffuse clouds (diameter D = 4 pc, E <sub>B-V</sub> = 0.06) will be easily traced with GAIA up to the distances of ∼ 800 pc. `Large' diffuse interstellar clouds (D = 10 pc, E _B-V = 0.13) will be located up to the distances of ∼ 2.5 kpc. This holds for the reddening tracers of spectral types O – K2 brighter than V = 17. Inmost cases, due to their low spatial density, the early type stars (O– A2) cannot provide reliable information about the distribution of interstellar matter. None of the reddening tracers measured by GAIA will provide reliable identification of the individual interstellar clouds beyond the distances of ∼ 3 kpc. Therefore, we conclude that the information available from photometric observations will be not sufficient for the detailed reconstruction of the 3-D distribution of Galactic interstellar matter. It is therefore extremely important to define the new strategies which would allow to combine all the available information, including the earlier space- and/or ground-based investigations, together with the information which will be provided by GAIA itself (parallaxes, E _B-V etc.). This revised version was published online in July 2006 with corrections to the Cover Date.     

Astrometry from Space: New Design of the GAIA Mission

An interferometric astrometric mission, aiming at accuracies at around the10 microarcsec level, was recommended as a high priority concept within thenew ESA Horizon 2000+ scientific programme. The original outline concept forsuch a mission, GAIA, presented its general feasibility but did not addressmany questions of implementation or optimisation. Another concept of aninterferometer for a scanning astrometric satellite is presented. It containsa simpler optical telescope and a more efficient detector system. The designutilizes the full resolution of all light in the dispersed fringes of aFizeau interferometer. A preliminary optimization of the satellite indicatesthat two telescope units with a baseline of 100 cm will achieve a precisionof 3, 8, 22, 68, 302 microarcsec for parallaxes of stars with V = 12, 14, 16, 18, 20 mag, respectively, from a 5 year mission. Simultaneousspectrophotometry of the entire spectrum of each star will be obtained with aresolution corresponding to intermediate band photometry. The expectedprecision of this photometry is about 0.003 mag for V = 16. The performance is good in crowded fields, at least up to one star per 5 arcsec2. A Hipparcos-type beam combiner of 150 cm width is placed in front of atelescope with 4 square apertures of 50 cm. The assumed focal length is f = 60 m and the field 0.5 degree diameter. The detector consists of CCDs used for time delayed integration (drift-scan.)     

On the Tolerances of Filters for GAIA Medium Band Photometric System

We investigate the effects arising from the filter transmission curve differences across the filter area in the 3G medium-band photometric system proposed for GAIA. We discuss the accuracy of the transformations to the standard photometric system and the precision of the determination of physical parameters for various types of stars using the 4-D classification procedure. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthetic Spectra of the Fe VIII – Fe XVI Emission Lines for Electron Non-Thermal Distributions

A certain class of non-thermal electron distributions can exhibit more mono-energetic shape and a higher peak than the Maxwellian distribution. This type of electron distribution can be observed mainly in flaring plasmas. We have studied the influence of this kind of electron energy distribution on the excitation equilibrium of Fe VIII – Fe XVI in the solar corona. The changes in synthetic spectra of the emission lines belonging to these ions due to this non-thermal distribution are shown. The possibilities of finding the shape of the energy distribution function of electrons from the Fe line ratios are also discussed. The results can be used for diagnostics of coronal plasmas where the deviations of particle energy distributions from the Maxwellian one can be significant.     

Colours and Composition of the Centaurs

Centaurs are widely believed to come from the Edgeworth-Kuiper belt, located beyond the orbit of Neptune. From here they can be injected into the inner part of the Solar System through planetary perturbations or mutual collisions. Due to their origin and dynamical evolution, Centaurs are supposed to constitute a transition population of objects from the large reservoir of Trans-Neptunian Objects (TNOs) to the active bodies of the inner Solar System. On the basis of the present knowledge of the physical properties of Centaurs and TNOs a similarity between the two populations appears evident. This is the strongest observational constraint supporting the theory of common origin.     

Asymptotic Giant Branch Stars as Tracers of Star Formation Histories: the GAIA Context

We discuss a possible use of the asymptotic giant branch (AGB) stars for tracing star formation histories on the Galactic and extragalactic distance scales with the ESA's astrometric space mission GAIA. Extensive numerical simulations demonstrate that metallicities (Δ [M/H] ≲ 0.3) can be obtained for the AGB stars with GAIA up to the distances of ∼ 200 kpc, if no interstellar extinction is present. Reliable population ages can be also obtained from the AGB stars if their T _eff are constrained precisely. We show that precise effective temperatures can be obtained by fitting observed spectral energy distributions of the AGB stars with theoretical fluxes calculated from the synthetic spectra. A combination of the derived effective temperatures with the bolometric luminosities allows to derive precise population ages for a wide range of ages and metallicities over the large distance scales. This demonstrates that AGB stars can be employed very effectively for tracing star formation histories with GAIA, allowing to refine the global evolutionary scenarios of stellar populations in the Milky Way and the galaxies beyond. This revised version was published online in July 2006 with corrections to the Cover Date.     

高分辨率恒星光谱处理与元素丰度分析软件平台

精确的元素丰度分析通常是建立在高分辨率光谱的基础上的。为了提高光谱数据的处理效率和能够以友好的界面来进行光谱处理与丰度分析,开发了一套软件平台。利用这个平台,可以对一维光谱进行自动化和交互式处理,可以计算丰度并进行丰度分析,可以将得到的丰度结果录入到数据库中,然后根据研究需要到数据库中进行查询和提取,生成丰度的分析图表。     

Counts, Sizes and Colours of Faint Infrared-Selected Galaxies

Deep J- and K _s-band images covering a 5 × 5 arcmin area centred on the NTT Deep Field have been obtained during the Science Verification of SOFI at the NTT. These images were made available via the Web in early June, 1998. The preliminary results we have obtained by the analysis of these data are the following: (i) the counts continue to rise with no evidence of a turnover or of a flattening down to the limits of the survey (K _s = 22.5 and J = 24 mag); (ii) we find a slope d log(N)/dm≈ 0.37, in agreement with most of the faintest surveys but much steeper than the Hawaii survey; (iii) fainter than K _s ≈ 19and J ≈ 20 mag, the median J-K colour of galaxies shows a break in its reddening trend turning toward bluer colours; (iv) faint bluer galaxies also display a larger compactness index, and a smaller apparent size. This revised version was published online in July 2006 with corrections to the Cover Date.     

A Composite Model for GHz Peaked Spectra of Radio Sources

GHz-Peaked Spectrum (GPS) radio sources are powerful and compact sources with convex spectra. With increasing observational findings, it has been realized that either Synchrotron Self-Absorption (SSA) alone or Free-Free Absorption (FFA) alone is not enough to account for all the spectral features. We present a model consisting of an SSA region partially covered by FFA plasma, and derive a composite spectral formula. By applying the model to a sample of 19 GPS sources having strong absorption, it is found that the external FFA process makes the SSA peak frequency linearly shift to a higher (observed) peak frequency. The shift indicates that the FFA does play a role at the frequency close to the observed peak frequency.     

Spectra of extremely reduced assemblages: Implications for Mercury

Abstract— We investigate the possibility that Mercury's crust is very reduced with FeO concentrations of less than ?0.1 wt%. We believe that such a surface could have a composition of enstatite, plagioclase, diopside, and sulfide, similar to the mineral assemblages found in aubritic meteorites. To test this hypothesis, we investigated the spectra of aubrites and their constituent minerals as analogs for the surface of Mercury. We found that some sulfides have distinctive absorption features in their spectra shortwards of ?0.6 μm that may be apparent in the spectrum of such an object. Determination of the surface composition of Mercury using orbital x‐ray spectroscopy should easily distinguish between a lunar highlands and enstatite basalt composition since these materials have significant differences in concentrations of Al, Mg, S, and Fe. The strongest argument against Mercury having an enstatite basalt composition is its extreme spectral redness. Significant reddening of the surface of an object (such as Mercury) is believed to require reduction of FeO to nanophase iron, thus requiring a few percent FeO in the material prior to alteration.     

一种用于射电频谱分析的高速FFT实现算法

提出了一种用于高速射电频谱分析的FFT实现算法,基于奇偶分开的FFT变换算法.采用N点FFT变换来实现4N点实信号的FFT变换,从而在FPGA(现场可编程门阵列)硬件里实现了高速FFT变换算法.仿真分析表明,新算法得到了良好的效果,明显地提高了硬件的利用效率.     

A Comprehensive Study of 94 Open Clusters Based on the Data from IPHAS,GAIA DR2, and Other Sky Surveys

We determine the color excesses, photometric distances, ages, astrometric parallaxes and proper motions for 94 open clusters in the northern part of the Milky Way. We estimate the color excesses and photometric distances based on the data from IPHAS photometric survey of the northern Galactic plane using individual total-to-selective extinction ratios R_r = A_r/E_r?i for each cluster computed via the color-difference method based on IPHAS r, i, and Hα-band, 2MASS J-, H-, and K_s-band, WISE W1-band, and Pan-STARRS i-, z-, and y-band data. The inferred R_r values vary significantly from cluster to cluster spanning the R_r = 3.1–5.2 interval with a mean and standard deviation equal to 〈R_r〉 = 3.99 and σR_r = 0.34, respectively.We identified cluster members using (1) absolute proper motions determined from individual-epoch positions of stars retrieved from IPHAS, 2MASS,URAT1, ALLWISE,UCAC5, and Gaia DR1 catalogs and positions of stars on individual Palomar Sky Survey plates reconstructed based on the data provided in USNO-B1.0 catalog and (2) absolute proper motions provided in Gaia DR2 catalog, and computed the averageGaia DR2 trigonometric parallaxes and propermotions of the clusters. Themean formal error of the inferred astrometric parallaxes of clusters is of about 7 μas, however, a comparison of astrometric and photometric parallaxes of our cluster sample implies that Gaia DR2 parallaxes are, on the average, systematically underestimated by 45 ± 9 μas. This result agrees with estimates obtained by other authors using other objects. At the same time, we find our photometric distance scale to be correct within the quoted errors (the inferred correction factor is equal to unity to within a standard error of 0.025).     

A Synthetic Interdisciplinary “Chronological Frieze”: an Attempt

This chapter introduces the chronological and interdisciplinary “frieze” which presents the main events relevant (in our opinion) to the problem of the emergence of life on Earth. This selection of events is directly connected to the previous chapters of this book.The frieze may be found in print as an insert at the back of the print publication. This supplementary material is also available in the online version of this article at and is accesssible for authorized users.