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1.
Rita Loidl Josef Hron Susanne Höfner Uffe G. ørgensen Bernhard Aringer Franz Kerschbaum 《Astrophysics and Space Science》1997,251(1-2):243-246
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. 相似文献
2.
3.
Vladas Vansevičius Audrius Bridžius Ramutis Drazdys 《Astrophysics and Space Science》2002,280(1-2):31-39
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. 相似文献
4.
S. Casertano M. G. Lattanzi M. A. C. Perryman A. Spagna 《Astrophysics and Space Science》1996,241(1):89-104
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. 相似文献
5.
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. 相似文献
6.
Viktoras Deveikis Audrius Bridžius Vladas Vansevičius 《Astrophysics and Space Science》2002,280(1-2):47-50
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. 相似文献
7.
M.A.C. Perryman 《Astrophysics and Space Science》2002,280(1-2):1-10
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. 相似文献
8.
Jokūbas Sūdžius Saulius Raudeliūnas Arūnas Kučinskas Audrius Bridžius Vladas Vansevičius 《Astrophysics and Space Science》2002,280(1-2):109-114
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
B-V = 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. 相似文献
9.
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.) 相似文献
10.
Algirdas Kazlauskas Vladas Vansevičius Audrius Bridžius Ramutis Drazdys Romualdas Kalytis 《Astrophysics and Space Science》2002,280(1-2):57-62
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. 相似文献
11.
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. 相似文献
12.
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. 相似文献
13.
Arūnas Kučinskas Vladas Vansevičius Toshihiko Tanabé 《Astrophysics and Space Science》2002,280(1-2):151-157
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. 相似文献
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15.
Paolo Saracco Sandro D'Odorico Alan Moorwood Jean G. Cuby 《Astrophysics and Space Science》2001,276(2-4):991-998
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. 相似文献
16.
Jun Yang Xiang Liu Zhi-Qiang Shen National Astronomical Observatories/Urumqi Observatory Chinese Academy of Sciences Urumqi Shanghai Astronomical Observatory Chinese Academy of Sciences Shanghai Graduate University of the Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2005,5(6):563-570
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. 相似文献
17.
Thomas H. BURBINE Timothy J. McCOY Larry R. NITTLER Gretchen K. BENEDIX Edward A. CLOUTIS Tamara L. Dickinson 《Meteoritics & planetary science》2002,37(9):1233-1244
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. 相似文献
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19.
L. N. Yalyalieva A. A. Chemel E. V. Glushkova A. K. Dambis A. D. Klinichev 《Astrophysical Bulletin》2018,73(3):335-343
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 Rr = Ar/Er?i for each cluster computed via the color-difference method based on IPHAS r, i, and Hα-band, 2MASS J-, H-, and Ks-band, WISE W1-band, and Pan-STARRS i-, z-, and y-band data. The inferred Rr values vary significantly from cluster to cluster spanning the Rr = 3.1–5.2 interval with a mean and standard deviation equal to 〈Rr〉 = 3.99 and σRr = 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). 相似文献
20.
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. 相似文献