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1.
We present the results of determinations of age, helium abundance (Y), metallicity ([Fe/H]), and estimations of abundances of the elements: C, N, O, Mg, Ca, Ti, Cr, Ni, Sr, and Ba of four globular clusters in the neighborhood of the Andromeda galaxy ([SD2009]GC7,Mayall II, Mackey-GC1 (MGC1), and Bol 298 (MGC6)) and of six Galactic clusters. Medium-resolution long-slit integrated-light spectra from the clusters under study were used to determine the parameters.Observations of extra-galactic objects were carried out with the 6-m SAO RAS telescope using the SCORPIO-1 multimode focal reducer. Galactic globular clusters NGC6341 (M92), NGC6838 (M71), and NGC7078 were observed with the CARELEC spectrograph at the 1.93-m telescope of the Haute-Provence Observatory. The integratedlight spectra of Galactic globular clusters NGC104, NGC6121 (M4), and NGC7078 (M15) were taken from the spectral library by Schiavon.We selected the best isochrone for each cluster by comparison of the shapes and intensities of the observed and theoretical Balmer line profiles. 相似文献
2.
We determine the atmospheric parameters of the secondary in the close binary system FF Aqr and analyze its chemical composition.
A series of high-resolution spectra are taken at different orbital phases using the coude echelle spectrometer of the 1.5-m
Russian-Turkish Telescope (RTT150). We show that the absorption line intensity of heavy elements varies with phase due to
the spotty nature of the cool component. We determine the abundances of heavy elements in the star’s atmosphere by modelling
the synthetic spectra and performing a differential analysis of the chemical composition of FF Aqr relative to the solar composition.
Our analysis of the averaged spectrum of FF Aqr yielded 539 abundance estimates for 21 chemical elements. We found the metallicity
of the star ([Fe/H] = −0.11 ± 0.08) to be close solar, in agreement with the hypothesis that FF Aqr should belong to the Galactic disk. The
inferred chemical composition of the objects exhibits no anomalous abundances of the α-, r-, and s-process elements like those earlier found in other systems (IN Com, LW Hya, V471 Tau). The lack of such anomalies in FF Aqr
must be due to the fact that the elements heavier than 16
O cannot be synthesized in the core of the primary during the last stages of its evolution. 相似文献
3.
V. S. Menzhevitski N. N. Shimanskaya V. V. Shimansky D. O. Kudryavtsev 《Astrophysical Bulletin》2014,69(2):169-178
We study the effect of the photoionization cross sections for the ground state of Al I on the inferred aluminium abundance in stellar atmospheres. We match the theoretical and observed line profiles of the resonance λλ 3944.01, 3961.52 Å and subordinate λλ 6696.03, 6698.68 Å doublets in high-resolution spectra of the metal-poor solar-type stars HD22879 and HD201889. We determine the parameters of these stars from their photometric and spectroscopic data. Our computations show that the profiles can be matched and a single aluminium abundance inferred simultaneously from both groups of spectral lines only with low photoionization cross sections (about 10–12 Mb). Larger cross sections (about 58–65 Mb) make such fits impossible. We therefore conclude that small photoionization cross sections should be preferred for the determination of aluminium abundances in metal-poor stars. We redetermine the aluminium abundances in the atmospheres of halo stars. The resulting abundances prove to be lower by 0.1–0.15 dex than our earlier determinations which does not affect the conclusions based on our earlier estimates. In particular, the NLTE [Al/Fe]-[Fe/H] dependence, on the whole, agrees only qualitatively with the results of theoretical predictions. Therefore further refinement of the theory of nuclear synthesis of aluminium in the process of the chemical evolution of the Galaxy remains a task of current importance. 相似文献
4.
5.
We present the theoretical analysis of the Al I line formation in the spectra of late-type stars ignoring the assumption of
local thermodynamic equilibrium (LTE). The calculations were based on the 39-level aluminum atom model for one-dimensional
hydrostatic stellar atmosphere models with the parameters: T
eff from 4000 to 9000 K, log g = 0.0–4.5, and metallicity [A] = 0.0;–1.0;–2.0;–3.0;–4.0. The aluminum atom model and the method of calculations were tested by the study of line profiles
in the solar spectrum. We refined the oscillator strengths and Van-der-Vaals broadening constants C
6 of the investigated transitions. We conclude that the Al I atom is in the overionization state: the 3p level is underpopulated in the line formation region. This leads to the line weakening, as compared with the LTE results.
The overionization effect becomes more pronounced with increasing temperature and decreasing metallicity. We show that the
use of various atomic data (ionization cross-sections) for the low levels of Al I does not change the behavior of non-LTE
deviations, whereas the value of these deviations varies essentially. For nine selected Al I lines we calculated the grids
of theoretical non-LTE corrections (ΔX
NLTE = logɛ
NLTE − log ɛ
LTE) to the Al abundances determinedwith the LTE assumption. The non-LTE corrections are positive and significant for the stars
with temperatures T
eff > 6000 K. These corrections weakly depend on log g, and increase with declining stellar metallicity. 相似文献
6.
Jürgen Oberst Valéry Lainey Christophe Le Poncin-Lafitte Veronique Dehant Pascal Rosenblatt Stephan Ulamec Jens Biele J?rn Spurmann Ralph Kahle Volker Klein Ulrich Schreiber Anja Schlicht Nicolas Rambaux Philippe Laurent Beno?t Noyelles Bernard Foulon Alexander Zakharov Leonid Gurvits Denis Uchaev Scott Murchie Cheryl Reed Slava G. Turyshev Jesus Gil Mariella Graziano Konrad Willner Kai Wickhusen Andreas Pasewaldt Marita W?hlisch Harald Hoffmann 《Experimental Astronomy》2012,34(2):243-271
GETEMME (Gravity, Einstein??s Theory, and Exploration of the Martian Moons?? Environment), a mission which is being proposed in ESA??s Cosmic Vision program, shall be launched for Mars on a Soyuz Fregat in 2020. The spacecraft will initially rendezvous with Phobos and Deimos in order to carry out a comprehensive mapping and characterization of the two satellites and to deploy passive Laser retro-reflectors on their surfaces. In the second stage of the mission, the spacecraft will be transferred into a lower 1500-km Mars orbit, to carry out routine Laser range measurements to the reflectors on Phobos and Deimos. Also, asynchronous two-way Laser ranging measurements between the spacecraft and stations of the ILRS (International Laser Ranging Service) on Earth are foreseen. An onboard accelerometer will ensure a high accuracy for the spacecraft orbit determination. The inversion of all range and accelerometer data will allow us to determine or improve dramatically on a host of dynamic parameters of the Martian satellite system. From the complex motion and rotation of Phobos and Deimos we will obtain clues on internal structures and the origins of the satellites. Also, crucial data on the time-varying gravity field of Mars related to climate variation and internal structure will be obtained. Ranging measurements will also be essential to improve on several parameters in fundamental physics, such as the Post-Newtonian parameter ?? as well as time-rate changes of the gravitational constant and the Lense-Thirring effect. Measurements by GETEMME will firmly embed Mars and its satellites into the Solar System reference frame. 相似文献
7.
The properties of the stellar population of the unusual object NGC 2419 are studied; this is the most distant high-mass globular cluster of the Galaxy’s outer halo, and a spectrum taken with the 1.93-m telescope of the Haute Provence Observatory displays elemental abundance anomalies. Since traditional high-resolution spectroscopicmethods are applicable to bright stars only, spectroscopic information for the cluster’s stellar population as a whole, integrated along the spectrograph slit placed in various positions, is used. Population synthesis is carried out for the spectrum of NGC 2419 using synthetic spectra calculated from a grid of stellar model atmospheres, based on the theoretical isochrone from the literature that best fits the color-magnitude diagram of the cluster. The derived age (12.6 billion years), metallicity ([Fe/H] = ?2.25 dex), and abundances of helium (Y = 0.26) and other chemical elements (a total of 14) are in a good qualitative agreement with estimates from the literature made from high-resolution spectra of eight red giants in the cluster. The influence on the spectrum of deviations from local thermodynamic equilibrium is considered for several elements. The derived abundance of α-elements ([α/Fe] = 0.13 dex, as the mean of [O/Fe], [Mg/Fe], and [Ca/Fe]) differs from the mean value in the literature ([α/Fe] = 0.4 for the eight brightest red giants) and may be explained by recently discovered in NGC2419 large [a/Fe] dispersion. Further studies of the integrated properties of the stellar population in NGC 2419 using higher-resolution spectrographs in various wavelength ranges should help improve our understanding of the cluster’s chemical anomalies. 相似文献
8.
V. V. Shimansky S. A. Pozdnyakova N. V. Borisov I. F. Bikmaev V. V. Vlasyuk O. I. Spiridonova A. I. Galeev S. S. Mel’nikov 《Astrophysical Bulletin》2009,64(4):349-364
We analyze the physical state and the properties of the close binary systems HS 1857+5144 and Abell 65. We took the spectra
of both systems over a wide range of orbital phases with the 6-m telescope of the Special Astrophysical Observatory of the
Russian Academy of Sciences (SAO RAS) and obtained their multicolor light curves with the RTT150 and Zeiss-1000 telescopes
of the SAO RAS. We demonstrate that both Abell 65 and HS 1857+5144 are young precataclysmic variables (PV) with orbital periods
of P
orb
= 1.
d
003729 and P
orb
= 0.
d
26633331, respectively. The observed brightness and spectral variations during the orbital period are due to the radiation
of the cold component, which absorbs the short-wave radiation of the hot component and reemits it in the visual part of the
spectrum. A joint analysis of the brightness and radial velocity curves allowed us to find the possible and optimum sets of
their fundamental parameters. We found the luminosity excesses of the secondary components of HS 1857+5144 and Abell 65 with
respect to the corresponding Main Sequence stars to be typical for such objects. The excess luminosities of the secondary
components of all young PVs are indicative of their faster relaxation rate towards the quiescent state compared to the rates
estimated in earlier studies. 相似文献
9.
The formation of Na I lines in X-ray illuminated atmospheres is investigated by abandoning the assumption of local thermodynamic equilibrium (LTE). Calculations are performed on the basis of a 21-level Na I model atom for the LTE model atmospheres of irradiated F-G stars obtained with allowance for a reflection effect in the first approximation. The state of extreme “overrecombination” is shown to exist for the populations of all Na I levels in the case of external illumination. Absorption features in the profiles of “cool” and “normal” Na I lines have been found to be enhanced compared to the LTE approximation. Effects of the angle of incidence and intensity of the external radiation on the formation of level populations and line profiles when abandoning LTE are analyzed. The existence of overrecombination for Na I is explained by the small X-ray heating function and the large optical cooling function. Na I level populations are shown to depend weakly on the presence of “overionization” for Na II in the atmospheres of irradiated stars. 相似文献
10.
V. V. Shimansky D. N. Nurtdinova N. V. Borisov O. I. Spiridonova 《Astrophysical Bulletin》2011,66(4):442-448
Comprehensive observations of a close binary candidate WD 1437-008 are performed. The shape and amplitude of the observed
brightness variations are shown to be inconsistent with the hypothesis of reflection effects, and the photometric period of
the system, P
phot = 0.
d
2775, is found to differ from the period of spectral variations, P
sp = 0.
d
272060. As a result, WD 1437-008 has been preliminarily classified as a low-inclination cataclysmic variable. 相似文献