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1.
We consider dynamically consistent mean-field dynamos in a spherical shell of incompressible fluid. The generation of magnetic field and differential rotation is parameterized by the - and -effects, respectively. Extending previous investigations, we include now the cases of moderate and rapid rotation in the sense that the inverse Rossby number can approach or exceed unity: This can lead to disk-shaped -contours, which are in better accordance with recent results of helioseismology than cylindrical -contours. On the other hand, in order to obtain -dynamo cycles the Taylor number has to be so large, that eventually cylindrical -contours become unavoidable (cf. Taylor-Proudman theorem). We discuss the different possibilities in a state diagram, where the inverse Rossby number and the relative correlation length are taken as the elementary parameters for mean-field dynamos.  相似文献   

2.
An abundance analysis using photographic region spectrograms and fully line-blanketed model atmospheres has been performed for the chemically peculiar (CP) star HD 25823 model parameters were determined from H profile and photometric data. Its pattern of abundance shows that the heavier elements in HD 25823 are overabundant.  相似文献   

3.
In this paper of the series we analyze three stars listed among stars with discrepant v sin i: HD9531 and HD31592, which also show radial velocity variations inherent to spectroscopic binaries, and HD129174 which is an Mn-type star with a possible magnetic field. In HD9531 we confirm the radial velocity derived fromthe hydrogen lines as well as fromthe Ca II line at 3933 Å as variable. The profile of the calcium line also appears variable, and with the estimated magnetic induction Be = ?630 ± 1340 G, this suggests that the abundance of calcium possibly varies over the surface of the star. We identified the lines of the secondary component in the spectrum of HD31592 revealing thus it is an SB2 binary with B9.5V and A0V components. While the primary star rotates with v sin i = 50 km s?1, the secondary star is faster with v sin i = 170 km s?1. We find that only 60% of the Mn lines identified in the spectrum of HD129174 can be fitted with a unique abundance value, whereas the remaining lines are stronger or fainter. We also identified two Xe II lines at 5339.33 Å and 5419.15 Å and estimated their log g f.  相似文献   

4.
Based on high resolution spectroscopic observations hydrogen-line profiles of six Bootis stars: HD 31295, HD 101108, HD 105058, HD 106223, HD 142703 and HD 183324 are presented. Peculiar line profiles with weak cores and broad but shallow wings are found for four of the stars. Influence of metallicity parameter [Z/H] and effective temperature on the appearance of the observed hydrogen lines is discussed.  相似文献   

5.
The catalog of the classical WR stars which have the emission doublet Ovi 3811, 3834 in their optical spectra (the catalog of the WR-Ovi stars) and the results of the spectroscopic investigations of the WR-Ovi stars HD 16523, HD 17638, and HD 192103 are presented. Rapid spectral variability of the emission doublet Ovi 3811, 3834 in the spectra of WR-Ovi stars HD 16523, HD 17638, and of the emission band 3680-3780 Å in the spectra of the WR-Ovi star HD 16523 is observed. It is shown that spectral sub-types of the stars HD 16523 and HD 17638 as estimated from different criteria are uncertain. We argue that the WR-Ovi stars HD 16523 and HD 17638, the optical spectra of which display emission doublet Ovi 3811, 3834, may be considered as WO5 stars. The sub-type WO5 is proposed for the first time. Classification criteria of the WO5 sub-type are represented. The possible contribution of the ions Heii to the emission at 3811 Å and 3834 Å is investigated. Thez-distributions of WR-Ovi stars and WR stars with the probable relativistic companions are found to be similar.  相似文献   

6.
We present the results of magnetic field measurements of four chemically peculiar (CP) stars with helium abundance anomalies which are the members of the Orion stellar association OB1. The stars under study were classified as magnetic by other authors earlier. The present paper contains the results of the extensive study of the stars. Magnetic field measurements allowed us to conclude that HD36540 has a weak field and the longitudinal component B e does not exceed 500 G. The longitudinal field of HD36668 varies with the period P = 2. d 11884 and the amplitude from ?2 to +2 kG. The magnetic field of HD36916 has mainly negative polarity and varies within the range from 0 to ?1 kG with the period P = 1.d 565238. HD37058 is a magnetic star, the longitudinal field of which varies from ?1.2 to +0.8 kG with the period P = 14. d 659. The B e field variability pattern for the stars HD36916 and HD37058 is of a simple harmonic type. The longitudinal field of HD36668 is best described with two combined harmonic functions (“a doublewave”). The variability period of HD36540 is still undetermined. For all the stars from this paper, we measured radial velocities V r, axial rotation rates v e sin i, and determined basic parameters of atmospheres (effective temperatures T eff and gravity acceleration log g). We also estimated masses M, luminosities L, and radii R of the stars.  相似文献   

7.
High-resolution spectra of nine yellow nonvariable supergiants (NVSs) located within the canonical Cepheid instability strip from Sandage and Tammann (1969) (α Aqr, ? Leo, μ Per, ω Gem, BD+60 2532, HD 172365, HD 187299, HD 190113, and HD 200102) were taken with the 1-m Zeiss and 6-m BTA telescopes at the Special Astrophysical Observatory of the Russian Academy of Sciences in the 1990s. These have been used to determine the atmospheric parameters, chemical composition, radial velocities, reddenings, luminosities, distances, and radii. The spectroscopic estimates of T eff and the luminosities determined from the Hipparcos parallaxes have shown eight of the nine program NVSs on the T eff?log(L/L ⊙) diagram to be outside the canonical Cepheid instability strip. When the edges of the Cepheid instability strip from Bono et al. (2000) are used, out of the NVSs from the list on the diagram one is within the Cepheid instability strip but closer to the red edge, two are at the red edge, three are beyond the red edge, two are at the blue edge, and one is beyond the blue edge. The evolutionary masses of the objects have been estimated. The abundances of α-elements, r- and s-process elements for all program objects have turned out to be nearly solar. The СNO, Na, Mg, and Al abundance estimates have shown that eight of the nine NVSs from the list have already passed the first dredge-up. Judging by the abundances of the key elements and its position on the T eff?log(L/L ⊙) diagram, the lithium-rich supergiant HD 172365 is at the post-main-sequence evolutionary stage of gravitational helium core contraction and moves toward the first crossing of the Cepheid instability strip. The star ? Leo should be assigned to bright supergiants, while HD 187299 and HD 190113 may have already passed the second dredge-up and move to the asymptotic branch.  相似文献   

8.
Continuous spectra of the Be objects HD 50138 and HD 51585 have been investigated between 1.6 and 1.2 -1. The infrared gradient IR of HD 50138 (B5eV) is found to be 2.09±0.10, while the typical B5V star And indicates IR=1.17. A B5V (HD 16219) star located at about the same distance as HD 50138 has IR=1.29 and it is shown that interstellar reddening may account for IR between HD 16219 and And. The difference in gradient between HD 50138 and HD 16219 ( IR=0.8) may be explained by a continuous reemission in a lenticular envelope with a radius equal to 4R *. The peculiar object HD 51585 exhibits a B0.5 continuous spectrum, for which the value d logI /d(1/) should be 1.13 according to model atmospheres computations. The distance as derived from color excess leads to disagreement between measured and computed (for a B0.5 star) values of d logI /d(1/). The reddening may be explained by reemission in an envelope the radius of which is smaller than 5R*. In conclusion, the narrowness of the spectral range under consideration does not permit to decide whether the observed reddening is due to recombination to the third level of the hydrogen atom or whether it is part a thermal reemission in a circumstellar cloud at lower temperature, as it has been observed around 10 by various authors.

Les spectres utilisés dans ce travail ont été obtenus à l'aide des téléscopes de 193 cm et 120 cm de l'Observatoire de Haute-Provence (CNRS).  相似文献   

9.
We analyzed the chemical composition of the chemically peculiar (CP) star HD 0221=43 Cas using spectra taken with the NES spectrograph of the 6-m telescope with a spectral resolution of 45 000. The Hβ line profile corresponds most closely to Teff = 11 900 K and log g = 3.9. The rotational velocity is ve sin i = 27 ± 2 km s?1, and the microturbulence is ξt = 1 km s?1. The results of our abundance determination by the method of synthetic spectra show that the star has chemical anomalies typical of SrCrEu stars, although its effective magnetic field is weak, Be < 100 G. For silicon, we obtained an abundance distribution in atmospheric depth with a sharp jump of 1.5 dex at an optical depth of log τ5000 = ?0.3 and with silicon concentration in deep atmospheric layers. Similar distributions were found in the atmospheres of cooler stars with strong and weak magnetic fields. A comparison of the chemical peculiarities in HD 10221 with known CP stars with magnetic fields of various strengths leads us to conclude that a low rotational velocity rather than amagnetic field is the determining factor in the formation mechanism of chemical anomalies in the atmospheres of CP stars.  相似文献   

10.
Observations of the chemically peculiar star HD 27404 with the 6-m SAO RAS telescope showed a strong magnetic field with the longitudinal field component varying in a complicated way in the range of ?2.5 to 1 kG. Fundamental parameters of the star (Teff = 11 300 K, log g = 3.9) were estimated analyzing photometric indices in the Geneva and in the Stro¨ mgren–Crawford photometric systems. We detected weak radial velocity variations which can be due to the presence of a close star companion or chemical spots in the photosphere. Rapid estimation of the key chemical element abundance allows us to refer HD 27404 to a SiCr or Si+ chemically peculiar A0–B9 star.  相似文献   

11.
We report the discovery of brightness variability in the IR-excess early F supergiant HD 331319, a candidate post-AGB star. Over three years of systematic U BV observations, the star showed low-amplitude (up to in V) quasi-periodic brightness variations on a time scale of ∼45 days. A preliminary analysis of our photometry indicates that HD 331319 and other typical post-AGBF supergiants have a similar pattern of variability. A study of the extinction toward HD 331319 leads us to conclude that the fraction of the circumstellar extinction is small for this star. We present low-resolution spectroscopy for HD 331319 and discuss the spectral classification of post-AGB F supergiants using HD 331319, HD 161796, HD 187885, and HD 56126 as examples.  相似文献   

12.
HD 193182 is one of the most interesting stable shell stars and presents stable shell features which seems to be constant over decades. In this research we analyzed optical, ultraviolet and near-infrared spectra of this little-studied shell star. In the meantime we applied model calculations to the measured spectral parameters of HD 193182 in order to present a more complete view of its stellar and envelope characteristics.  相似文献   

13.
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14.
Circumstellar peculiarities of the A0-type Herbig stars are analyzed on the basis of high-resolution CCD spectroscopic data, obtained in 1991-1994 at the ESO and the Crimean Astrophysical Observatory (about 250 spectrograms). The results of investigation of the rapid line profile variability in H , H , HeI 5876 and DNa lines are presented for AB Aur, HD 163296, HD 36112 and HD 100546. The conclusion is made that the behaviour of these lines can be explained in the framework of the model containing an equatorially concentrated and azimuthally inhomogeneous stellar wind and an external cool shell occasionally losing matter in the form of infall on to the star.  相似文献   

15.
The results of observations of 159 stars at 1640 Å in Puppis made with the space telescope Glazar are presented. It is shown that the observed stars are members of different groups of stars situated at distances of about 120, 370, 700, 1250, 2400, and 4000 pc. The last two groups belong to the Pup OB1 and the Pup OB2 stellar associations.There is relatively little absorption in the observed region. The absorbing matter is mainly concentrated in small clouds.It is suggested that three stars — CP –27°4197, HD 60479, and HD 61672-are embedded in a dust envelope and that the star HD 60057 has a hot subdwarf companion.Forty-four of the observed stars are new OB or early A-type stars, spectral types of which were not known.  相似文献   

16.
A scanning spectropolarimeter has been constructed and used in a preliminary search for conspicuous features of the interstellar polarization curve between –1 = 1.58 –1 and 2.50 –1. The instrument was used at thef/4.5 prime focus of the 36 telescope of the Cambridge University Observatories. Scans were made on HD2905, HD21389, And and Tau with slitwidths of 50 Å and 100 Å.The commonly adopted method of correcting for instrumental polarisation by using observations of unpolarized stars has been applied. The normalized polarization curves corrected for instrumental polarization for HD2905 and HD21389 reveal a feature near –1 = 1.68 –1 which is most probably of insterstellar rather than instrumental origin.  相似文献   

17.
The spectrum of the peculiar O9 star HD 93521 is studied and compared with those of the standard stars 10 Lac and AE Aur. Several possibilities are examined which might explain the high galactic latitude of this star, corresponding toz>750 pc and its slight helium excess. It is suggested that HD 93521 is a runaway binary system composed of the O9 star plus a neutron star left over from a supernova explosion.  相似文献   

18.
New spectral observations of chemically peculiar (CP) magnetic stars were obtained using an NES echelle spectrometer with a BTA telescope in the Special Astrophysical Observatory (Russian Academy of Sciences). Several stars were shown to have anomalous Li abundances. Testing and monitoring the stars with Doppler shifts Vsini > 10 km/s indicated that the lithium 6708 Å line was variable in the spectra of some roaAP-CP stars. To distinguish variable features in the spectra, the dispersogram technique was used. The most peculiar among the stars studied is HD 12098. The strong and variable lithium 6708 Å line was detected in the spectrum of this star. The star has been shown to have greatly different lithium abundances in two rotation phases corresponding to opposite surface areas. As mentioned earlier, a similar behavior of the Li blend was found in the spectra of HD 83368 and HD 60435 which have lithium spots on their surface. Spectral observations of slowly rotating CP stars with the Doppler shifts Vsini < 10 km/s revealed the strong and nonvariable lithium 6708 Å line in the spectra of these stars. Quantitative spectral analysis using the Li I 6708 Å resonance doublet and the Li I 6103 Å line shows the lithium abundance, as determined by the 6103 Å line, to be somewhat greater than that determined by the 6708 Å line. A higher ratio of 6Li/7Li amounting to ～0.3–0.5 was found in these stars. 6Li production is assumed to be due to spallation reactions on the surface of magnetic CP stars; this isotope ratio remained in strong magnetic fields.  相似文献   

19.
Observations with the 6-m telescope revealed eight new magnetic, chemically peculiar stars: HD 29925, HD 40711, HD 115606, HD 168796, HD 178892, HD 196691, HD 209051, and BD+32°2827. Zeeman observations of all these objects have been carried out for the first time. We selected candidates by analyzing the depression profile at a wavelength of λ5200 Å. This technique for selecting candidate magnetic stars was shown to be efficient: we found magnetic fields in 14 of the 15 objects that we selected for our observations with a Zeeman analyzer. A maximum longitudinal field strength B e exceeding 8 kG was found in HD 178892; in HD 209051 and HD196691, B e reaches 3.3 and 2.2 kG, respectively. For the remaining stars, we obtained lower limits of the longitudinal field (more than several hundred G).  相似文献   

20.
The paper presents results of measurements of magnetic-field longitudinal components B e , radial velocities V r , and projections of the rotation velocity in the line of sight v e sin i for 74 objects, mainly main-sequence chemically peculiar stars and standard stars. Observations were carried out in 2011 at the 6-m BTA telescope using the Main Stellar Spectrograph (MSS) with a Zeeman analyzer. Seven new magnetic stars were discovered: HD38129, HD47152, HD50341, HD63347, HD188501, HD191287, and HD260858. Three more stars were suspected to have magnetic fields. Observations of magnetic standard stars and non-magnetic stars confirm the absence of any systematic errors capable of introducing distortions into the B e longitudinal-field measurement results. The paper gives comments on the research results for each of the 74 stars.  相似文献   

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