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1.
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
2.
Based on spectra taken with a 6-m telescope, we analyzed the abundances of chemical elements in the He-weak stars HD 21699
and HD 217833, estimated their surface magnetic fields (Bs = 4000 and 4500 G, respectively) from the magnetic intensification of spectral lines, and determined their microturbulences
(V
t = 0.80 and 0.75 km s−1, respectively). The low values of V
t show that the stellar atmospheres are stabilized by a magnetic field, which explains the presence of diffusion processes
that lead to chemical anomalies. Helium is strongly underabundant, and its deficiency is −1.50 and −1.81 dex in HD 21699 and
HD 217833, respectively. We used model atmospheres to determine the effective temperatures, T
eff = 16 000 and 15 450 K, and surface gravities, log g = 4.15 and 3.88, for the stars from the Hδ line, implying that they lie on the main sequence near the stars of luminosity
class V. 相似文献
3.
Based on high-dispersion echelle spectra taken with the 6-m Special Astrophysical Observatory telescope, we study the IR source IRAS 20004+2955 identified with the variable star V1027 Cyg. We have determined the star’s fundamental parameters (T eff=5000 K, logg=1.0), metallicity ([Fe/H]=?0.2 dex), and atmospheric abundances of 16 elements. Its metallicity, carbon underabundance, and slight overabundance of the heavy elements Zr, Y, Ce, and Eu suggest that V1027 Cyg belongs to the Galactic disk population. 相似文献
4.
L. S. Lyubimkov 《Bulletin of the Crimean Astrophysical Observatory》2014,110(1):9-16
The studies of the abundances of superheavy chemical elements in magnetic stars conducted at the Crimean Astrophysical Observatory were facilitated by the launch of the Astron space station in 1983. This spacecraft observed the ultraviolet spectra of such stars. The present brief review is focused on the abundances of superheavy elements (Pt, Au, Hg, Tl, Pb, Bi, Th, and U) in the atmospheres of magnetic Ap and HgMn stars. These results were obtained basing on the visible and ultraviolet spectra of stars. The data accumulated over more than 30 years show that these stars are characterized by significant overabundances (up to 6–7 dex) of such elements. The following important fact is noted: the superheavy element anomalies follow the trend in the anomalies that are characteristic of less heavy elements. Therefore, it may be assumed that all these anomalies (including the significant overabundances of superheavy elements) share a common explanation. Certain unresolved problems are discussed briefly. 相似文献
5.
C.J. Mooney W.R.J. Rolleston F.P. Keenan P.L. Dufton D.L. Pollacco H.R. Magee 《Monthly notices of the Royal Astronomical Society》2001,326(3):1101-1109
We present a model-atmosphere analysis for the bright ( V ∼13) star ZNG-1, in the globular cluster M10. From high-resolution ( R ∼40 000) optical spectra we confirm ZNG-1 to be a post-asymptotic giant branch (post-AGB) star. The derived atmospheric parameters are T eff =26 500±1000 K and log g =3.6±0.2 dex . A differential abundance analysis reveals a chemical composition typical of hot post-AGB objects, with ZNG-1 being generally metal poor, although helium is approximately solar. The most interesting feature is the large carbon underabundance of more than 1.3 dex. This carbon deficiency, along with an observed nitrogen enhancement relative to other elements, may suggest that ZNG-1 evolved off the AGB before the third dredge-up occurred. Also, iron depletions observed in other similar stars suggest that gas–dust fractionation in the AGB progenitor could be responsible for the observed composition of these objects. However, we need not invoke either scenario since the chemical composition of ZNG-1 is in good agreement with abundances found for a Population II star of the same metallicity. 相似文献
6.
7.
We present the results of our abundance analysis for the atmosphere of the chemically peculiar Ap star HD 8441. HD 8441 is interesting in that the lines of rare-earth elements in its spectrum are weak and the longitudinal magnetic field component is small, being only several hundred gauss. Our estimates of the evolutionary status for HD 8441 have confirmed that it belongs to the group of Ap stars with weak lines of rare-earth elements in their spectra that leave the main sequence. A stratification analysis of the atmosphere of HD 8441 assuming a stepwise distribution of elements with depth reveals a nonuniform distribution of Si, Ca, Cr,Mn, and Fe with a significant increase in elemental abundances in deeper layers. The derived distribution qualitatively agrees with predictions of the theory of diffusive separation of elements under the action of radiation pressure forces and gravity. Comparison of the chemical composition and evolutionary status of HD 8441 with those of the stars HD 66318 and HD 144897 with strong magnetic fields shows that their atmospheres differ mainly by the abundances of rare-earth elements. The iron-peak elements exhibit large overabundances irrespective of the magnetic field strength. 相似文献
8.
We study the chemical evolution of population I and population II secondaries in cataclysmic variables (CVs) assuming that during nova explosions a part of the high metallicity nova ejecta is intercepted by the secondary and mixed into its convective envelope. We derive analytic expressions for the chemical composition of the envelope of the secondary as a function of the chemical composition of the nova ejecta X i,ej and the cross-section of the secondary σ . For population I CVs we find that the increase of the metallicity of the secondary is comparable to its initial metallicity only if σ is larger by an order of magnitude than the geometrical cross-section. A significant accumulation is therefore possible only in those species that are highly overabundant in the nova ejecta. Because the changes in the abundances of even those species depend strongly on the poorly known cross-section σ , the predictive power of our model is weak for population I CVs as long as σ is not well determined. In the case of population II CVs the accumulation of heavy elements by this process dominates over the initial metallicity of the secondary even for values of σ that are smaller by an order of magnitude than the geometrical cross-section. Thus, within a short time after turn-on of mass transfer, the relative metal abundances in the envelope of the secondary reflect those in the nova ejecta. This is nearly independent of the cross-section σ . 相似文献
9.
I. S. Savanov 《Astrophysics》1996,39(2):107-111
The abundances of 12 elements in the atmosphere of the "F str 4077" star HD 177645 have been determined from new spectroscopic observations with the CCD camera and the model atmosphere method. The overabundance of nitrogen found for this star indicates its possible relation to barium dwarfs with anomalies in the chemical composition of their atmospheres due to mass transfer from the more evolved companion in a binary system. As an object related to Ba stars and CH subgiants, HD 177645 with an effective temperature Teff=7150K may also have anomalies in the chemical composition characteristic of diffusion processes in chemically peculiar stars of the upper main sequence, as may be indicated by the overabundance of sulfur in its atmosphere.Translated fromAstrofizika, Vol. 39, No. 2, pp. 201–209, April–June, 1996. 相似文献
10.
We have derived the abundances of the rare-earth elements (REEs) Ce, Pr, Nd, and Eu in the atmospheres of 26 magnetic peculiar (Ap) stars in the range of effective temperatures 7000–10 000 K from spectra with resolutions R = 48 000 and 80 000 and investigated the dependence of the CePrNdEu anomalies (the difference in the element abundances determined separately from lines of the first and second ionization stages) on the effective temperature. The REE anomaly is shown to decrease with increasing effective temperature virtually to the point of disappearance for all of the investigated elements, except Eu. For the best-studied element Nd the Nd anomaly has also been found to decrease with increasing magnetic field strength for cool stars. For hot stars there is no Nd anomaly in a wide range of magnetic field strengths. Since the presence of anomalies in cool Ap stars is associated with the REE concentration in the upper atmospheric layers, the lower boundary of the REE layer apparently sinks into deeper layers with increasing effective temperature and magnetic field, causing the anomalies to disappear. We have detected an anticorrelation between the abundances of iron-peak elements and rare-earth elements, which serves as additional evidence for different stratification of these elements in the atmospheres of Ap stars. 相似文献
11.
L. A. Yakovina Ya. V. Pavlenko K. Abia A. E. Rozenbush 《Kinematics and Physics of Celestial Bodies》2011,27(5):233-248
We determine lithium abundances in atmospheres of three carbon stars from synthetic spectrum fitting in the λλ 668–674 nm
range using the Li I λ 670.8 nm resonance doublet. To produce synthetic spectra, we use a modified list of atomic lines from
the VALD database and three alternative line lists of CN and C2 molecules which are modifications of line lists from the Jorgensen’s website () and from the Kurucz database (1993, CD-ROM nos. 1–23). The spectral lines from these lists were tested by matching synthetic
spectra to observed spectra of the sun, Arcturus, and early R star HD 100764. We perform analysis of the blends involving
the Li I λ 670.8 nm doublet in spectra of N stars AW Cyg and UX Dra. The lithium abundances in HD 100764, AW Cyg, and UX Dra
are estimated to be lgN(Li) ≈ 2, −1.4, and −0.9, respectively. Discrepancies of lithium abundances lgN(Li) obtained with the help of molecular line lists do not seem to exceed 0.2 dex. 相似文献
12.
In the last decade, the photospheric solar metallicity as determined from spectroscopy experienced a remarkable downward revision.
Part of this effect can be attributed to an improvement of atomic data and the inclusion of NLTE computations, but also the
use of hydrodynamical model atmospheres seemed to play a role. This “decrease” with time of the metallicity of the solar photosphere
increased the disagreement with the results from helioseismology. With a CO
5
BOLD 3D model of the solar atmosphere, the CIFIST team at the Paris Observatory re-determined the photospheric solar abundances
of several elements, among them C, N, and O. The spectroscopic abundances are obtained by fitting the equivalent width and/or
the profile of observed spectral lines with synthetic spectra computed from the 3D model atmosphere. We conclude that the
effects of granular fluctuations depend on the characteristics of the individual lines, but are found to be relevant only
in a few particular cases. 3D effects are not responsible for the systematic lowering of the solar abundances in recent years.
The solar metallicity resulting from this analysis is Z=0.0153, Z/X=0.0209. 相似文献
13.
Sunetra Giridhar A. Arellano Ferro Aruna Goswami 《Journal of Astrophysics and Astronomy》1991,12(1):27-37
The long period classical cepheid RZ Vel (HD 73502) is known to be a member of an OB association, Vel OB1 in Vela, and a high
metallicity is ascribed to it by the photometric work of Eggen (1982). We have done an abundance analysis for this long period
(P = 20.4 days) and hence young (age ≈ 1.80×107 yr) classical cepheid using high resolution CCD spectra with good S/N ratio. We have used a detailed model atmosphere method
to derive the abundances of the light elements C, O, A1, S and of many Fe-peak elements and a few s-process elements. Our
present work indicates near solar abundance for most of the elements for RZ Vel and hence we do not confirm the high metallicity
derived photometrically by Eggen (1982) for this star 相似文献
14.
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
15.
V. S. Menzhevitski N. N. Shimanskaya V. V. Shimansky N. A. Sakhibullin 《Astrophysical Bulletin》2013,68(3):285-299
In this paper we construct and analyze the uniform non-LTE distributions of the aluminium ([Al/Fe]-[Fe/H]) and sodium ([Na/Fe]-[Fe/H]) abundances in the sample of 160 stars of the disk and halo of our Galaxy with metallicities within ?4.07 ≤ [Fe/H] ≤ 0.28. The values of metallicity [Fe/H] and microturbulence velocity ξ turb indices are determined from the equivalent widths of the Fe II and Fe I lines. We estimated the sodium and aluminium abundances using a 21-level model of the Na I atom and a 39-level model of the Al I atom. The resulting LTE distributions of [Na/Fe]-[Fe/H] and [Al/Fe]-[Fe/H] do not correspond to the theoretical predictions of their evolution, suggesting that a non-LTE approach has to be applied to determine the abundances of these elements. The account of non-LTE corrections reduces by 0.05–0.15 dex the abundances of sodium, determined from the subordinate lines in the stars of the disk with [Fe/H] ≥ ?2.0, and by 0.05–0.70 dex (with a strong dependence on metallicity) the abundances of [Na/Fe], determined by the resonance lines in the stars of the halo with [Fe/H] ≤ ?2.0. The non-LTE corrections of the aluminium abundances are strictly positive and increase from 0.0–0.1 dex for the stars of the thin disk (?0.7 ≤ [Fe/H] ≤ 0.28) to 0.03–0.3 dex for the stars of the thick disk (?1.5 ≤ [Fe/H] ≤ ?0.7) and 0.06–1.2 dex for the stars of the halo ([Fe/H] ≤ ?2.0). The resulting non-LTE abundances of [Na/Fe] reveal a scatter of individual values up to Δ[Na/Fe] = 0.4 dex for the stars of close metallicities. The observed non-LTE distribution of [Na/Fe]-[Fe/H] within 0.15 dex coincides with the theoretical distributions of Samland and Kobayashi et al. The non-LTE aluminium abundances are characterized by a weak scatter of values (up to Δ[Al/Fe] = 0.2 dex) for the stars of all metallicities. The constructed non-LTE distribution of [Al/Fe]-[Fe/H] is in a satisfactory agreement to 0.2 dex with the theoretical data of Kobayashi et al., but strongly differs (up to 0.4 dex) from the predictions of Samland. 相似文献
16.
F. Primas 《Astrophysics and Space Science》1999,265(1-4):67-70
A new sample of 7 stars ranging in metallicity from [Fe/H] = −2.0 to [Fe/H] = −0.75 has been analyzed in the boron spectral
region. The targets were selected according to the availability (in the literature) of their lithium and beryllium abundances,
because the simultaneous knowledge of LiBeB in the same targets is a powerful diagnostic for testing depletion and internal
mixing predicted by different stellar structure models. Two stars (HD 94028 and HD 194598), characterized by similar Li contents,
are found to have also similar B abundances, despite a 0.3 dex difference in their Be abundances claimed by Thorburn and Hobbs
(1996). Four stars out of 7 are characterized by strongly depleted Li and Be abundances: 2 of them (HD 2665 and HD 3795) are
also significantly B-depleted, while two others (HD 106516 and HD 221377) have near normal B abundances despite being depleted
by a factor ≥ 10 in both Li and Be abundances. These stars place strong constraints on the nature and depth of the mixing
processes responsible for their light element abundances. The 7th star (HD 160617) shows the remarkable aspect of deficient
B, probably deficient Be, and completely normal Li. No stellar destruction mechanism can explain this. Rather, chemical inhomogeneities
in the halo could be the cause.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
17.
E. A. Semenko M. E. Sachkov T. A. Ryabchikova D. O. Kudryavtsev N. E. Piskunov 《Astronomy Letters》2008,34(6):413-422
We present the results of our abundance analysis for the magnetic chemically peculiar star HD 115708 based on high-resolution spectra. The atmospheric chemical composition of HD 115708 (T eff = 7550 K) is shown to be typical of cool Ap stars with a significant ionization disequilibrium for the first and second rare earth ions, which is commonly observed in the atmospheres of pulsating Ap (roAp) stars. Our study of the vertical distribution of elements has shown that Mg, Ca, Cr, and Fe concentrate in deeper atmospheric layers, with their abundances decreasing sharply in the upper layers. The jumps in abundance are 1.5–3 orders of magnitude. Silicon is distributed in depth almost uniformly in the atmosphere of HD 115708. The derived empirical Cr and Fe distributions agree qualitatively with the results of diffusion calculations. Since the atmospheric chemical peculiarities in HD 115708 correspond to roAp stars, we have performed a spectroscopic monitoring to find nonradial pulsations. We have been able to determine only an upper limit for the amplitude of the possible radial velocity pulsations, ～100 m s?1, due to the insufficient temporal resolution and instability of the main stellar spectrograph (MSS) of the 6-m telescope. 相似文献
18.
T. I. Gorbaneva T. V. Mishenina C. Soubiran 《Kinematics and Physics of Celestial Bodies》2012,28(3):121-127
Abundances of europium for 112 FGK dwarf stars of thick and thin disks have been determined in the metallicity range of ?1.0 < [Fe/H] < +0.3. Spectra of the studied stars have been obtained using the 1.93-m telescope of Haute-Provence Observatory (France) with spectral resolution R = 42000 and signal-to-noise ratio S/N = 100?300. Eu content has been calculated with assumption of LTE using the synthetic spectrum approach with detailed consideration of superfine structure. Analysis of europium abundances as a function of metallicity in kinematically selected stars of the Galactic thick and thin disks revealed different values in the disks. Comparison of europium abundances with magnesium abundances makes it possible to assume that at [Fe/H] < ?0.2 dex the origins of these elements are similar and at [Fe/H] > ?0.2 dex they are, probably, different. 相似文献
19.
Data from our compiled catalog of spectroscopically determined magnesium abundances in stars with accurate parallaxes are used to select thin-disk dwarfs and subgiants according to kinematic criteria. We analyze the relations between the relative magnesium abundances in stars, [Mg/Fe], and their metallicities, Galactic orbital elements, and ages. The [Mg/Fe] ratios in the thin disk at any metallicity in the range ?1.0 dex <[Fe/H] < ?0.4 dex are shown to be smaller than those in the thick disk, implying that the thin-disk stars are, on average, younger than the thick-disk stars. The relative magnesium abundances in such metal-poor thin-disk stars have been found to systematically decrease with increasing stellar orbital radii in such a way that magnesium overabundances ([Mg/Fe] > 0.2 dex) are essentially observed only in the stars whose orbits lie almost entirely within the solar circle. At the same time, the range of metallicities in magnesium-poor stars is displaced from ?0.5 dex < [Fe/H] < +0.3 dex to ?0.7 dex < [Fe/H] < +0.2 dex as their orbital radii increase. This behavior suggests that, first, the star formation rate decreases with increasing Galactocentric distance and, second, there was no star formation for some time outside the solar circle, while this process was continuous within the solar circle. The decrease in the star formation rate with increasing Galactocentric distance is responsible for the existence of a negative radial metallicity gradient (grad R[Fe/H] = ?0.05 ± 0.01 kpc?1) in the disk, which shows a tendency to increase with decreasing age. At the same time, the relative magnesium abundance exhibits no radial gradient. We have confirmed the existence of a steep negative vertical metallicity gradient (grad Z[Fe/H] = ?0.29 ± 0.06 kpc?1) and detected a significant positive vertical gradient in relative magnesium abundance (grad Z[Mg/Fe] = 0.13 ± 0.02 kpc?1); both gradients increase appreciably in absolute value with decreasing age. We have found that there is not only an age-metallicity relation, but also an age-magnesium abundance relation, in the thin disk. We surmise that the thin disk has a multicomponent structure, but the existence of a negative trend in the star formation rate along the Galactocentric radius does not allow the stars of its various components to be identified in the immediate solar neighborhood. 相似文献
20.
Data from our compiled catalog of spectroscopically determined magnesium abundances in dwarfs and subgiants with accurate parallaxes are used to select Galactic halo stars according to kinematic criteria and to identify presumably accreted stars among them. Accreted stars are shown to constitute the majority in the Galactic halo. They came into the Galaxy from disrupted dwarf satellite galaxies. We analyze the relations between the relative magnesium abundances, metallicities, and Galactic orbital elements for protodisk and accreted halo stars. We show that the relative magnesium abundances in protodisk halo stars are virtually independent of metallicity and lie within a fairly narrow range, while presumably accreted stars demonstrate a large spread in relative magnesium abundances up to negative [Mg/Fe]. This behavior of protodisk halo stars suggests that the interstellar matter in the early Galaxy mixed well at the halo formation phase. The mean metallicity of magnesium-poor ([Mg/Fe] < 0.2 dex) accreted stars has been found to be displaced toward the negative values when passing from stars with low azimuthal velocities (|Θ| < 50 km s?1) to those with high ones at Δ[Fe/H] ≈ ?0.5 dex. The mean apogalactic radii and inclinations of the orbits also increase with increasing absolute value of |Θ|, while their eccentricities decrease. As a result, negative radial and vertical gradients in relative magnesium abundances are observed in the accreted halo in the absence of correlations between the [Mg/Fe] ratios and other orbital elements, while these correlations are found at a high significance level for genetically related Galactic stars. Based on the above properties of accreted stars and our additional arguments, we surmise that as the masses of dwarf galaxies decrease, the maximum SN II masses and, hence, the yield of α-elements in them also decrease. In this case, the relation between the [Mg/Fe] ratios and the inclinations and sizes of the orbits of accreted stars is in complete agreement with numerical simulations of dynamical processes during the interaction of galaxies. Thus, the behavior of the magnesium abundance in accreted stars suggests that the satellite galaxies are disrupted and lose their stars en masse only after dynamical friction reduces significantly the sizes of their orbits and drags them into the Galactic plane. Less massive satellite galaxies are disrupted even before their orbits change appreciably under tidal forces. 相似文献