共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
I. I. Romanyuk E. A. Semenko I. A. Yakunin D. O. Kudryavtsev A. V. Moiseeva 《Astrophysical Bulletin》2017,72(2):165-177
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
3.
Yu. Yu. Balega V. V. Dyachenko A. F. Maksimov E. V. Malogolovets D. A. Rastegaev I. I. Romanyuk 《Astrophysical Bulletin》2012,67(1):44-56
We present the results of speckle interferometry of a sample of 117 chemically peculiar stars with global magnetic fields.
The observations were made in December 2009 at the BTA with a spatial resolution of about 0.02″ in the visual spectral region.
Twenty-nine stars were resolved into individual components, 14 of them for the first time (HD965, HD5797, HD8855, HD10783,
HD16605, HD21699, HD35502, HD51418, HD64486, HD79158, HD103498, HD108651, HD213918, HD293764). In twelve cases a companion
turned out to be 2–4
m
fainter than the main component—a magnetic star. Young hot Bp stars HD35502 and HD213918 are exceptions, since their companions
are fainter by about 1
m
. In all cases, the linear distance from a star to its companion at the epoch of observations in the picture plane exceeded
109 km. Eighty-eight magnetic CP stars revealed no secondary components within our study. Thus, the fraction of speckle interferometric
binaries in our sample amounts to 25%. 相似文献
4.
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
5.
We have detected new HD absorption systems at high redshifts, z
abs = 2.626 and z
abs = 1.777, identified in the spectra of the quasars J0812+3208 and Q1331+170, respectively. Each of these systems consists
of two subsystems. The HD column densities have been determined: log N
HDA = 15.70 ± 0.07 for z
A = 2.626443(2) and log N
HDB = 12.98 ± 0.22 for z
B = 2.626276(2) in the spectrum of J0812+3208 and log N
HDC = 14.83 ± 0.15 for z
C = 1.77637(2) and log N
HDD = 14.61 ± 0.20 for z
D = 1.77670(3) in the spectrum of Q1331+170. The measured HD/H2 ratio for three of these subsystems has been found to be considerably higher than its values typical of clouds in our Galaxy.We
discuss the problem of determining the primordial deuterium abundance, which is most sensitive to the baryon density of the
Universe Ωb. Using a well-known model for the chemistry of a molecular cloud, we have estimated the isotopic ratio D/H=HD/2H2 = (2.97 ± 0.55) × 10−5 and the corresponding baryon density Ωb
h
2 = 0.0205−0.0020+0.0025. This value is in good agreement with Ωb
h
2 = 0.0226−0.00060.0006 obtained by analyzing the cosmic microwave background radiation anisotropy. However, in high-redshift clouds, under conditions
of low metallicity and low dust content, hydrogen may be incompletely molecularized even in the case of self-shielding. In
this situation, the HD/2H2 ratio may not correspond to the actual D/H isotopic ratio. We have estimated the cloud molecularization dynamics and the
influence of cosmological evolutionary effects on it. 相似文献
6.
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
7.
J. C. Pandey K. P. Singh R. Sagar S. A. Drake 《Journal of Astrophysics and Astronomy》2002,23(1-2):9-14
We present photometric observations of four stars that are optical counterparts of soft X-ray/EUV sources, namely 1ES 0829+15.9,
1ES0920-13.6, 2RE J1 10159+223509 and 1ES 1737+61.2. We have discovered periodic variability in two of the stars, viz., MCC
527 (1ES 0829+15.9; Period = 0
d
.828 ± 0.0047) and HD 81032 (1ES 0920-13.6; Period = ∼ 57.02 ± 0.560 days). HD 95559 (2RE J1 10159+223509) is found to show
a period of 3
d
. HD 160934 (1ES1737+61.2) also shows photometric variability but needs to be monitored further for finding its period. These
stars most likely belong to the class of chromospherically active stars. 相似文献
8.
The GALEX General Data Release 4/5 includes 174 spectroscopic tiles, obtained from slitless grism observations, for a total of more
than 60 000 ultraviolet spectra. We have determined statistical properties of the sample of GALEX stars. We have defined a suitable system of spectroscopic indices, which measure the main mid-UV features at the GALEX low spectral resolution and we have employed it to determine the atmospheric parameters of stars in the range 4500≲T
eff≲9000 K. Our preliminary results indicate that the majority of the sample is formed by main sequence F- and G-type stars,
with metallicity [M/H]≳−1 dex. 相似文献
9.
Yu. V. Glagolevskij 《Astrophysical Bulletin》2010,65(1):34-41
We model the magnetic fields of four magnetic stars using published longitudinal (Be) field measurements. The structure of
the magnetic field of each of the four stars is close to that of the central dipole. Unfortunately, the number of measurements
for each star is insufficient for accurate finding of the field parameters, and therefore we find no dipole shift exceeding
its error Δa ≈ 0.1, expressed as a fraction of the stellar radius. Our data support the opinion that the results of modeling depend most
strongly on the adopted inclination of the star’s rotation axis i. 相似文献
10.
Yu. V. Glagolevskij 《Astrophysics》2005,48(4):483-490
A model is constructed for the magnetic field of the star HD 187474, which has a very long axial rotation period P = 2345d. It turns out that the structure of the magnetic field is best described by a model of a displaced (Δα = 0.1) dipole inclined
to the axis of rotation by an angle β = 24°. The star is inclined to the line of sight by an angle i = 86°. Because of the
displaced dipole the magnitude of the magnetic field differs at the poles: Bp = +6300 and 11600 G. A Mercator map of the distribution
of the magnetic field over the surface is obtained. The 7 slowly rotating CP stars studied thus far have an average angle
β = 62°, which equals the average value for a random orientation of dipoles.
__________
Translated from Astrofizika, Vol. 48, No. 4, pp. 575–583 (November 2005). 相似文献
11.
The problem of lithium in chemically peculiar Ap-CP stars has been the subject of debate for many years. The main reason for
this is a lack of spectral observations of Ap stars in the neighborhood of the lithium resonance doublet Li I 6708 Å. An international
cooperation project on “Lithium in cool CP stars with magnetic fields” was started in 1996. Systematic observations of CP
stars in spectral regions of the 6708 Å and 6103 Å lines at the ZTSh (CrAO), CAT (ESO), Feros (ESO), and the 74″ telescope
of the Mount Stromlo Observatory (Australia) have been used to analyze spectra of several CP stars studied by the way the
6708 Å lithium line varies with the stars’ rotational phase. Monitoring of the spectra of the oscillating CP stars (group
I) HD 83368, HD 60435, and HD 3980, for which significant Doppler shifts of the Li I 6708 Å line are observed led to the discovery
of “lithium spots” on the surface of these stars whose positions are related to the magnetic field structure. Models of the
surfaces of these stars with the special program “ROTATE” based on the profiles of the Li I 6708 Å line are used to estimate
the size of the spots, their positions on the stars’ surface, and the lithium abundances in these spots. A detailed analysis
and modelling of the spectra of slowly rotating oscillating CP stars with strong, invariant lithium 6708 Å emission, including
blending with lines of the rare earth elements, reveals an enhanced lithium abundance, with the abundance determined from
the lithium 6103 Å line being higher than that determined from the 6708 Å line for all the stars. This may indicate vertical
stratification of lithium in the atmospheres of CP stars with an anomalous isotopic composition (6Li/7Li = 0.2–0.5). HD 101065, an ultraslow rotator (vsini ≈ 1.5) visible from the poles and with powerful oscillations which cause pulsating line broadening in its spectrum, is unique
among these stars. The amount of lithium in the atmosphere of HD 101065 logN(Li) = 3.1 on a scale of logN(H) = 12.0 and the isotope ratio 6Li/7Li ≈ 0.3. The high estimates of 6Li/7Li may be explained by the production of lithium in spallation reactions and the preservation of surface 6Li and 7Li by strong magnetic fields in the upper layers of the atmosphere near the magnetic poles.
__________
Translated from Astrofizika, Vol. 50, No. 3, pp. 463–492 (August 2007). 相似文献
12.
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
13.
《New Astronomy》2016
The atmospheric parameters and chemical abundances of two neglected A-type stars, 28 Peg and HD 202240, were derived using high resolution spectra obtained at the TÜBİTAK National Observatory. We determined the photospheric abundances of 11 elements for 28 Peg and 20 for HD 202240, using equivalent-width measurement and spectral synthesis methods. Their abundance patterns are in good agreement with those of chemically normal A-type stars having similar atmospheric parameters. We pinpoint the position of these stars on the H-R diagram and estimate their masses and ages as; 2.60 ± 0.10 M⊙ and 650 ± 50 Myr for 28 Peg and 4.50 ± 0.09 M⊙ and 150 ± 10 Myr for HD 202240. To compare our abundance determinations with those of stars having similar ages and atmospheric parameters, we select members of open clusters. We notice that our target stars exhibit similar abundance patterns with these members. 相似文献
14.
V. N. Frolov Yu. K. Ananjevskaja D. L. Gorshanov E. V. Polyakov 《Astronomy Letters》2010,36(5):338-348
We present the results of our comprehensive study of the Galactic open star cluster NGC 6866. The positions of stars in the
investigated region have been obtained with the “Fantasy” automatic measuring machine from 10 plates of the normal astrograph
at the Pulkovo Astronomical Observatory. The size of the investigated field is 40′ × 40′, the limiting magnitude is B ∼ 16·
m
6, and the maximum epoch difference is 79 yr. For 1202 field stars, we have determined the relative proper motions with an
rms error of 2.5 mas yr−1. Out of them, 423 stars may be considered cluster members with a probability P > 70% according to the astrometric criterion. Photometric diagrams have been used as an additional criterion. We have performed
two-color BV CCD photometry of stars with the Pulkovo ZA-320M mirror astrograph. The U magnitudes from the literature have also been used to construct the two-color diagrams. A total of 267 stars have turned
out to be members of NGC 6866 according to the two criteria. We present refined physical parameters of the cluster and its
age estimate (5.6 × 108 yr). The cluster membership of red and blue giants, variable, double, and multiple stars is considered. We have found an
almost complete coincidence of the positions of one of the stars in the region (a cluster nonmember) and a soft X-ray source
in the ROSAT catalog. The “Fantasy” automatic measuring machine is described in the Appendix. 相似文献
15.
Spectral observations of Ap-CP stars with the BTA (Special Astronomical Observatory, Russian Academy of Sciences) using the
NES echelle spectrometer have revealed several stars with an anomalous lithium abundance. The oscillating star HD 12098, which
is the first roAp star in the northern hemisphere of the sky, merits special attention. Strong, variable LiI 6708 Å line was
observed in the spectrum of this star. There are not enough observations for a reliable analysis by Doppler mapping, but there
are enough to indicate the presence of lithium spots on the surface of this star similar to the roAp stars HD 83368 and HD
60435, on whose surfaces spots with a high lithium abundance have been reliably detected. Parameters for a model of its atmosphere
have been chosen using the method of synthetic spectra based on atmospheric models including lines from the VALD list and
several additional blended REE lines calculated by the authors. The profile of the lithium LiI 6708 Å blend has been calculated
taking the magnetic field into account using the SYNTHM code. A lithium abundance has been determined for two phases of the
rotation of HD 12098 that is anomalously high compared to the solar and meteoritic abundances. The large difference in the
lithium abundance in the two phases (in two different regions on the star's surface) exceeds 0.5 dex and is very close to
that which we have found by analyzing the spectra of the roAp stars HD 83368 and HD 60435. Thus, we have discovered yet another
roAp star, HD 12098, with lithium spots on its surface.
Translated from Astrofizika, Vol. 51, No. 4, pp. 607–616 (November 2008). 相似文献
16.
G. Hildebrandt 《Astronomische Nachrichten》1975,296(6):277-280
The lightcurves in the UBV system are given for the four Ap stars HD 9531, HD 10221, HD 27309 and HD 184905 from 1968 to 1971. The measurements are represented by the periods od.6684, 3d.16, 2d.7098 and 1d.845031 respectively. 相似文献
17.
The abundances of 22 heavy elements from Sr to Pb have been determined for the halo star HD 29907 (T
eff = 5500 K, log g = 4.64) with [Fe/H] = −1.55 using high-quality VLT/UVES spectra (ESO, Chile). The star has a moderate enhancement of r-process elements (Eu-Tm) with [r/Fe] = 0.63. In the range from Ba to Yb, the derived abundance pattern agrees well with those for strongly r-process enhanced stars (r-II stars with [Eu/Fe] > 1 and [Ba/Eu] < 0), such as CS 22892-052 and CS 31082-001, as well as with
the scaled solar r-process curve and the r-process model HEW. Thus, Ba-Yb in HD 29907 originate in the r-process. Just as other moderately r-process enhanced stars studied in the literature, HD 29907 exhibits higher Sr, Y, and Zr abundances than those for r-II stars.
These results confirm the assumption by other authors about the existence of an additional Sr-Zr synthesis mechanism in the
early Galaxy before the onset of nucleosynthesis in asymptotic giant branch (AGB) stars. The same mechanism can be responsible
for the enhancement of Mo-Ag in the star being investigated compared to r-II stars. There are no grounds to suggest the presence
of s-nuclei of lead in the material of the star being investigated, because its measured abundance ratio log ɛ(Pb/Eu) = 1.20 lies within the range for the comparison stars: from log ɛ(Pb/Eu) = 0.17 (CS 31082-001) to < 1.55 (HE 1219-0312). Thus, even if there was a contribution of AGB stars to the heavy-element
enrichment of the interstellar medium at the epoch with [Fe/H] = −1.55, it was small, at the level of the abundance error. 相似文献
18.
We analyze the chemical composition of the atmospheres of a single K-type star HD 115404 and the secondary component of the
V471 Tau variable. We use the technique of modeling of synthetic spectra to analyze the high-resolution spectra of these stars,
taken with the RTT 150 Russian-Turkish telescope and find the abundances of 23 and 17 elements in the atmospheres of HD 115404
and V471 Tau, respectively. We demonstrate the lack of composition anomalies in the HD 115404 and show it to be consistent
with the published data, inferred from equivalent widths of spectral lines. We find the abundances of 15 elements from Na
to Ba to be consistent with the metallicity of the atmosphere of V471 Tau ([Fe/H] = −0.22 ± 0.12dex), which differs significantly
from the average metallicity of the Hyades cluster. We show the existence of strong carbon and oxygen overabundances (by more
than 1dex) due to the enrichment of the secondary by the nucleosynthesis products during the common-envelope stage of the
system. On the whole, we demonstrate that V471 Tau and the other precataclysmic variables share similar composition anomalies. 相似文献
19.
D.G. Turner V.V. Kovtyukh D.J. Majaess D.J. Lane K.E. Moncrieff 《Astronomische Nachrichten》2009,330(8):807-815
New and existing photometry for the G0 Ia supergiant HD 18391 is analyzed in order to confirm the nature of the variability previously detected in the star, which lies off the hot edge of the Cepheid instability strip. Small‐amplitude variability at a level of δV = 0.016 ± 0.002 is indicated, with a period of P = 123d.04 ± 0d.06. A weaker second signal may be present at P = 177d.84 ± 0d.18 with δV = 0.007 ± 0.002, likely corresponding to fundamental mode pulsation if the primary signal represents overtone pulsation (123.04/177.84 = 0.69). The star, with a spectroscopic reddening of EB–V = 1.02 ± 0.003, is associated with heavily‐reddened B‐type stars in its immediate vicinity that appear to be outlying members of an anonymous young cluster centered ∼10′ to the west and 1661 ± 73 pc distant. The cluster has nuclear and coronal radii of rn = 3.5′ and Rc = 14′, respectively, while the parameters for HD 18391 derived from membership in the cluster with its outlying B stars are consistent with those implied by its Cepheid‐like pulsation, provided that it follows the semi‐period‐luminosity relation expected of such objects. Its inferred luminosity as a cluster member is MV = –7.76 ± 0.10, its age (9 ± 1) × 106 years, and its evolutionary mass ∼19 M⊙. HD 18391 is not a classical Cepheid, yet it follows the Cepheid period‐luminosity relation closely, much like another Cepheid impostor, V810 Cen (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
20.
R. F. Griffin 《Journal of Astrophysics and Astronomy》2001,22(1):121-130
HD 111154 is a member of the Coma Cluster. It is here shown to be a somewhat unequal pair of stars of approximately solar
type. They are in an orbit that has a period of just under 27 days and quite a high eccentricity (0.442). Although the minimum
masses (1.08 and 1.00M
⊙) are large enough to encourage a search for eclipses, no such events have been detected. 相似文献