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311.
P. Palmeri P. Quinet É. Biémont A. V. Yushchenko A. Jorissen S. Van Eck 《Monthly notices of the Royal Astronomical Society》2007,374(1):63-71
Using three independent theoretical approaches (CA, HFR + CP, AUTOSTRUCTURE), oscillator strengths have been calculated for a set of Tc ii transitions of astrophysical interest and the reliability of their absolute scale has been assessed. The examination of the spectra emitted by some Ap stars has allowed the identification of Tc ii transitions in HD 125248. This Tc ii detection should however await confirmation from spectral synthesis relying on dedicated model atmospheres. New partition functions are also provided for Tc i , Tc ii and Tc iii for temperatures ranging between 4000 and 13 000 K. 相似文献
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L.C. Watson J.D. Pritchard J.B. Hearnshaw P.M. Kilmartin A.C. Gilmore 《Monthly notices of the Royal Astronomical Society》2001,325(1):143-150
The visual triple system HD 9770 (BB Scl) has been the subject of a four-year programme of UVB ( RI )C photometry and H α échelle spectroscopy. Analysis of the data obtained over that period shows that star B, and probably also star A, of HD 9770 is a binary. The A system comprises a K1V star, which may be in a binary system with another K dwarf. The B system is an eclipsing binary of the BY Dra type in which both stars are chromospherically active. An orbital period of 0.476 525±0.000 013 d has been derived from the light curve in V . Physical parameters derived from analysis of the light curves in UBV ( RI )C are presented. 相似文献
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We consider the adequacy of various solar coronal heating models. We show that the correlation between the intensity of the coronal Fe XIV 530.5 nm green line and the calculated magnetic field strength in the solar corona can be a useful tool for this purpose. We have established this correlation for coronal structures and magnetic fields of large spatial and temporal scales. The correlation found exhibits a strong dependence on both solar cycle phase and heliolatitude. The efficiency of a particular coronal heating mechanism is probably determined by the relative area occupied by low and high loops (including open structures). The direct current models based on slow field dissipation (DC) and the wave models based on Alfvén and magnetosonic wave dissipation (AC) are more efficient in the equatorial and polar zones, respectively. 相似文献
317.
G. Y. Liang G. Zhao J. R. Shi 《Monthly notices of the Royal Astronomical Society》2006,368(1):196-202
Theoretical electron density sensitive line ratios R 1 – R 6 of Si x soft X-ray emission lines are presented. We found that these line ratios are sensitive to electron density n e , and the ratio R 1 is insensitive to electron temperature T e . For reliable determination of the electron density of laboratory and astrophysical plasmas, atomic data, such as electron impact excitation rates, are very important. Our results reveal that the discrepancy of the line ratios from different atomic data calculated with the distorted wave (DW) approximation and the R-matrix method is up to 19 per cent at n e = 2 × 108 cm−3 . We applied the theoretical intensity ratio R 1 to the Low Energy Transmission Grating Spectrometer (LETGS) spectrum of the solar-like star Procyon. By comparing the observed value (1.29) with the theoretical calculation, the derived electron density n e is 2.6 × 108 cm−3 , which is consistent with that derived from (C v < 8.3 × 108 cm−3 ) . When the temperature structure of the Procyon corona is taken into account, the derived electron density increases from n e = 2.6 × 108 to 2.8 × 108 cm−3 . 相似文献
318.
A number of high resolution and high signal-to-noise ratio spectra of mildly metal-poor stars were obtained with the coudé echelle spectrograph attached to the 2.16m telescope at Xinglong Observation Base of Beijing Astronomical Observatory. The spectra of seven mildly metal-poor stars were processed with the MIDAS software package, and the equivalent widths of their spectral lines were measured. The measured equivalent widths together with an error analysis are presented. 相似文献
319.
Hydrogen Lyman α (Lyα) is our primary emission-line window into high-redshift galaxies. Despite an extensive literature, Lyα radiative transfer in the most realistic case of a dusty, multiphase medium has received surprisingly little detailed theoretical attention. We investigate Lyα resonant scattering through an ensemble of dusty, moving, optically thick gas clumps. We treat each clump as a scattering particle and use Monte Carlo simulations of surface scattering to quantify continuum and Lyα surface scattering angles, absorption probabilities, and frequency redistribution, as a function of the gas dust content. This atomistic approach speeds up the simulations by many orders of magnitude, making possible calculations which are otherwise intractable. Our fitting formulae can be readily adapted for fast radiative transfer in numerical simulations. With these surface scattering results, we develop an analytic framework for estimating escape fractions and line widths as a function of gas geometry, motion, and dust content. Our simple analytic model shows good agreement with full Monte Carlo simulations. We show that the key geometric parameter is the average number of surface scatters for escape in the absence of absorption, , and we provide fitting formulae for several geometries of astrophysical interest. We consider the following two interesting applications. (i) Equivalent widths ( EWs ). Lyα can preferentially escape from a dusty multiphase interstellar medium if most of the dust lies in cold neutral clouds, which Lyα photons cannot penetrate. This might explain the anomalously high EWs sometimes seen in high-redshift/submillimetre sources. (ii) Multiphase galactic outflows . We show the characteristic profile is asymmetric with a broad red tail, and relate the profile features to the outflow speed and gas geometry. Many future applications are envisaged. 相似文献
320.