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1.
A. Thoul R. Scuflaire B. Vatovez A. Noels P. Magain M. Briquet M.-A. Dupret 《Astrophysics and Space Science》2003,284(1):241-244
Models of Cen A & B have been computed using the masses determinedby Pourbaix et al. (2002) and the data derived from the spectroscopicanalysis of Neuforge and Magain (1997). The seismological dataobtained by Bouchy and Carrier (2001, 2002) do help improveour knowledge of the evolutionary status of the system. All the constraintsare satisfied with a model which gives an age of about 6 Gyr for the binary. 相似文献
2.
V. P. Malanushenko 《Astrophysics》1996,39(3):208-215
Measurements of radial velocities from the SiII 6347A and 6371Alines and the HeI 6678A line based on observations of 1989–1994 are examined. The variability of the line shapes over the 96.6-day orbital period is analyzed. Evidence for a second component is found from lines in the spectrum of And which correspond to the silicon lines 6347 and 6371A. The preliminary value for the rotational velocity of the secondary component is 100–120 km/sec. Analysis of the variability of the radial velocities of the HeI 6678A line during the night has given the rotational period of the star of Prot=Id.012344 and indicates an inhomogeneous distribution either of the helium abundance or of the physical conditions over the surface. Thus, we have the first evidence for the existence of spots on the surface of an HgMn star.Translated fromAstrofizika, Vol. 39, No. 3, pp. 375–384, July–September, 1996. 相似文献
3.
M. I. Nouh S. M. Saad B. Korany M. A. Elkhamisy 《Journal of Astrophysics and Astronomy》2013,34(3):193-205
The eclipsing binary α CrB, is a well-known double-lined spectroscopic binary. The system is considered unique among main-sequence systems with respect to its small mass ratio and large magnitude difference between the components. Our aim in the present paper is to compute the orbital parameters and to model the atmospheric parameters of the system. Synthetic spectral analysis of both the individual and disentangled spectra has been performed and yielded effective temperatures T eff?=?10000±250 K, surface gravities logg?=?4±0.25 and projected rotational velocities $\emph{v}$ sini?=?110±5 km/sec for the primary component, and T eff?=?6000±250 K and logg?=?4.5±0.25 for the secondary component. Evolutionary state of the system is investigated using stellar models. 相似文献
4.
M.R. Sanad 《New Astronomy》2010,15(1):52-57
We present a spectroscopic study of Mg II k&h emission lines in the 2000–3000 Å region of 91 high resolution IUE spectra of α Orionis obtained during the period 1978–1996. There are absorption and emission components on the blue sides of the k&h emission lines, these components may be coming from the dust envelope located inside the extended atmosphere of α Orionis. A set of 91 Mg II k&h emission lines have been identified and measured to determine their fluxes and widths. We found that there is a spectral variability for these physical parameters with phase, similar to that found for the light curve, which we attribute to the changes of density and temperature of the regions from which these emission lines are coming, as a result of the semi-regular pulsation and the variability of mass loss of the red supergiant.Also we present a study of C II and Fe II emission features in the 2000–3000 Å region of 55 high resolution IUE spectra during the period 1978–1996. A set of 55 C II and Fe II emission lines have been identified and measured to determine their fluxes and widths. We found the same result as with the Mg II emission lines. 相似文献
5.
CCD spectra taken with the PFES and CEGS echelle spectrographs attached to the 6-m Special Astrophysical Observatory (Russian Academy of Sciences) telescope and the 2-m Shamakha Astrophysical Observatory (National Academy of Sciences of Azerbaijan) telescope, respectively, were used to study the line-profile variations in the spectrum of the hot supergiant α Cam. No fast (≤1.5 h) line-profile and radial-velocity variations were found. Some of the systematic effects that cause spurious variability are considered. The Hα-profile variability appears symmetric relative to the radial velocity of the star’s center of mass and is attributable to variable blueshifted and redshifted emission and/or absorption components superimposed on a variable photospheric profile. The Hα line shows evidence of a large-scale mass ejection from the stellar surface, which is also traceable in other spectral lines. The He II 4686 line exhibits an inverse P Cyg profile, while the red wing of the He I 5876 line shows weak and variable emission. The fast (on characteristic time scales of shorter than an hour) variability of the He II 4686 profile that was previously revealed by our observations (Kholtygin et al. 2000) is called into question. A comparison of the observational data on the variability of ultraviolet and optical line profiles for the supergiant αCam suggests that nonradial motions are mainly responsible for the radial-velocity and line-profile variability. 相似文献
6.
Possible configurations of the planetary systems of the binary stars α Cen A–BandEZAqr A–C are analyzed. The P-type orbits—circumbinary ones, i.e., the orbits around both stars of the binary, are studied. The choice of these systems is dictated by the fact that α Cen is closest to us in the Galaxy, while EZ Aqr is the closest system whose circumbinary planets, as it turns out, may reside in the “habitability zone.” The analysis has been performed within the framework of the planar restricted three-body problem. The stability diagrams of circumbinary motion have been constructed: on representative sets of initial data (in the pericentric distance–eccentricity plane), we have computed the Lyapunov spectra of planetary motion and identified the domains of regular and chaotic motion through their statistical analysis. Based on present views of the dynamics and architecture of circumbinary planetary systems, we have determined the most probable planetary orbits to be at the centers of the main resonance cells, at the boundary of the dynamical chaos domain around the parent binary star, which allows the semimajor axes of the orbits to be predicted. In the case of EZ Aqr, the orbit of the circumbinary planet is near the habitability zone and, given that the boundary of this zone is uncertain, may belong to it. 相似文献
7.
We study the dynamics of a wide multiple system α Centauri + Proxima. The total energy of the system was estimated according to the available observational data on masses, coordinates, proper motions, and radial velocities of its components. To account for the effect of the observational data errors on the result, we have implemented the Monte Carlo method. From N = 106 statistical tests we show that with the probability of about 90% the motion is hyperbolic, i.e., α Cen AB and Proxima will after a while diverge from each other by a considerable distance. We also perform numerical modeling of dynamic evolution of the wide pair α Cen AB + Proxima in the regular field of the Galaxy. The trajectory of relative motion is constructed. The components diverge from each other by a distance of 20 pc over the time scale of about 200 Myr. The critical parameter for determining the dynamic status of the system is the radial velocity of the C component (Proxima), known with an error of 200 ms?1. For a reliable determination of the nature of motions in the system, we have to decrease the radial velocity error by at least an order of magnitude. 相似文献
8.
N. Seehafer 《Solar physics》1978,58(2):215-223
At first it is shown that a magnetic field being force-free, i.e. satisfying × B = B, with = constant ( 0) in the whole exterior of the Sun cannot have a finite energy content and cannot be determined uniquely from only one magnetic field component given at the photosphere. Then the boundary value problem for a semi-infinite column of arbitrary cross section is solved by a Green's function method. 相似文献
9.
A. Kh. Rzaev 《Astrophysical Bulletin》2008,63(1):23-33
The temporal variations of the radial velocity and profile of the Hα line in the spectrum of α Cyg are analyzed based on 240 CCD spectra taken with the coude spectrograph attached to the 2-m telescope of Shamaha Astrophysical Observatory of the National Academy of Sciences of Azerbaijan in 1998–2000. The results obtained are inconsistent with the conclusion made by the Heidelberg group concerning the behavior of the variability of the Hα-line profile [1]. The observed pattern of radial-velocity variations is due to nonradial pulsations and differs for the blue and red halves of the absorption profile. The pulsation parameters differ for different levels of residual intensity for both halves of the absorption profile. The amplitude and period increase from the core toward the wing of the line for the red half of the absorption profile, and, on the contrary, decrease toward the line wing for the blue half of the profile. Absorption features are observed on the blue half of the absorption profile. Their emergence and disappearance, as well as minor migrations are indicative of the clumpy structure of the stellar envelope. The similarity of the variability behavior of the absorption and emission profiles indicates that the latter too owe their variability to nonradial pulsations. Thus the variability of the stellar wind in its formation regions is partly due to the nonradial pulsations of the underlying layers of the atmosphere. On the whole, the variability of the position and photometric parameters of the absorption and emission components of the profile is indicative of the nonstationary nature and asymmetric shape of the stellar wind. 相似文献
10.
We present ultraviolet spectra of the α Sco AB binary system taken by the International Ultraviolet Explorer during the period from 1979 to 1995. An investigation is carried out on the spectral variability of Mg II k and h emission lines arising from the chromosphere of α Sco A (Van der Hucht et al., 1979). There are absorption and emission components on the blue sides of the Mg II k and h lines, which are formed in the cool circumstellar gas shells around two stars (Bernat and Lambert, 1976).This work is based on calculations of line fluxes and line widths for the aforementioned spectral lines. We found that there is spectral variability for these physical parameters with pulsation phase, which we attribute to the changes of density and temperature of the chromosphere of α Sco A as a result of the semi-regular pulsation and the variability of mass loss of the red supergiant (Reimers et al., 2008). The observed values of the k-to-h ratio are approximately one, implying that the k and h emission lines originate from an optically thick atmosphere. 相似文献
11.
Zhong-Lue Wen Yan-Bin Yang Qi-Rong Yuan Xu Zhou Jun Ma Zhao-Ji Jiang National Astronomical Observatories Chinese Academy of Sciences Beijing Department of Physics Nanjing Normal University Nanjing 《中国天文和天体物理学报》2007,7(1):71-80
1 INTRODUCTION As the largest gravitational bound systems in the universe, clusters of galaxies are important laboratories for understanding the evolution of galaxies, and for constraining cosmological quantities (Bahcall 1988; Postman et al. 1992; Brunne… 相似文献
12.
V. I. Ferronsky S. A. Denisik S. V. Ferronsky 《Celestial Mechanics and Dynamical Astronomy》1979,20(1):69-81
The applicability of the properties of central configurations proceeding from the many-body problem to study of gaseous sphere cloud evolution during its gravitational contraction is justified. It is shown that the product runs to a constant value in the asymptotic time limit of simultaneous collision of all the particles of the cloud where is a form-factor of the potential energy and is a form-factor of the moment of inertia.The spherical bodies as well as ellipsoids of rotation and general ellipsoids with a one-dimensional mass distribution (k),k[0, 1] are found to possess the property =const.
. , - , , ., , - =const., , (k),k[0, 1].相似文献
13.
uvby
photometry has been done for early-type stars in the surroundings of the shell star Ori. The reddening maps show the presence of irregularly distributed absorbing material.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain. 相似文献
14.
15.
The simultaneous photometric and spectroscopic observations of the spotted G dwarf AP149 in the young open cluster α Persei are analyzed here.We reconstruct the observed light curves with a two-starspot model by means of a light curve modeling technique,and find that the active regions shift oppositely along longitude on a time scale of one day.Combining with the observational data obtained by other groups,we discuss the evolution of spotted regions in the photosphere,and find that its starspots evolve not ... 相似文献
16.
Based on 21 spectra with resolutions from 12 000 to 42 000 taken in 1997–2016 for the yellow supergiant α Aqr (which is believed to be nonvariable in the Cepheid instability strip), we have determined its effective temperature Teff and radial velocities from metal and hydrogen absorption lines. Blue and red components that account for 20–25% of the total number of lines used have been detected in the profiles of these lines. The effective temperature and radial velocities estimated from metal lines and their components do not show any noticeable variations, while the radial velocities determined from hydrogen lines show variations that are largest for the Hα line, with an amplitude of more than 10 km s?1. These variations resemble periodic (～100 days) and sporadic ones. The presence of variable red components in the hydrogen line cores confirms that there is a circumstellar envelope around the supergiant. The radial velocities of these components exhibit a behavior similar to that of the hydrogen lines but with larger amplitudes (it is twice that for the R component of the Hα line). Such an unusual variability as well as the presence of blue components in metal lines and the star’s position at the red edge of the Cepheid instability strip can be explained by a possible residual pulsational activity in the upper atmospheric layers of the star, which “swings” the envelope with a larger amplitude when passing into a less dense medium. The multicomponent structure of the Na I D doublet lines and their variations over long time intervals may be indicative of a chromospheric activity and a change in the stellar wind intensity. These processes can affect the sporadic variations of the radial velocities in the upper atmospheric layers of the star and its envelope. We raise the question about a revision of the classification of α Aqr as a yellow nonvariable supergiant. 相似文献
17.
We investigated the generation of dynamo waves in the solar convection zone through a numerical simulation. We integrated the axisymmetric α–Ω kinematic dynamo equations in a spherical geometry, where the α- and Ω-profiles depend on the spatial coordinates. The model results show that the fundamental parameter that determines the behavior of the system is the product between the characteristic intensities of the α and Ω contributions. In particular, we found three different regimes in which the system exhibits different behaviors: a regime without a dynamo effect, one with an exponential amplification of the magnetic field, and one with dynamo waves. 相似文献
18.
There are very few reports of flare signatures in the solar irradiance at H i Lyman α at 121.5 nm, i.e. the strongest line of the solar spectrum. The LYRA radiometer onboard PROBA2 has observed several flares for which unambiguous signatures have been found in its Lyman-α channel. Here we present a brief overview of these observations followed by a detailed study of one of them: the M2 flare that occurred on 8 February 2010. For this flare, the flux in the LYRA Lyman-α channel increased by 0.6 %, which represents about twice the energy radiated in the GOES soft X-ray channel and is comparable with the energy radiated in the He ii line at 30.4 nm. The Lyman-α emission represents only a minor part of the total radiated energy of this flare, for which a white-light continuum was detected. Additionally, we found that the Lyman-α flare profile follows the gradual phase but peaks before other wavelengths. This M2 flare was very localized and had a very brief impulsive phase, but more statistics are needed to determine if these factors influence the presence of a Lyman-α flare signal strong enough to appear in the solar irradiance. 相似文献
19.
《天文和天体物理学研究(英文版)》2020,(8)
One-dimensional(1 D) model atmospheres are still the most commonly used tool for the determination of stellar chemical composition. Convection in the model is usually treated by mixing-length theory(MLT). The mixing-length parameter α is generally calibrated from the Sun and applied to all other stars.The metal-poor giant, HD 122563, is an important benchmark star to test stellar atmosphere and interior physics. We investigate the influence of the convection mixing-length parameter α on the determination of chemical abundances of Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Co, Ni, Sr, Y, Zr and Ba in the case of HD 122563, taking advantage of a high resolution and high signal-to-noise ratio HARPS spectrum. The abundance discrepancies ?[X/H] that occur due to α variation rarely exceed 0.05 dex and most are less than 0.03 dex. We calculate the discrepancy ?[X/H] using a line-by-line differential analysis. The abundance discrepancies do not have direct relation with either line strength or the excitation potential. For 1 D stellar atmospheric analysis of HD 122563, the accuracy of abundance determination does not strongly depend on the choice of mixing-length parameter α(causing average discrepancies of 0.03 dex), while the uncertainties in the effective temperature and surface gravity play a more important role. 相似文献
20.
Maria Pia Di Mauro Jørgen Christensen-Dalsgaard Lucio Paternò 《Astrophysics and Space Science》2003,284(1):229-232
We investigate properties of the internal structure of HR2021, better known as Hydri, a G2 IV subgiant with mass close to solar and for which observations by Bedding et al. (2001) have shown the presence of solar-like oscillations.We have computed models of Hydri,based on updated global parameters,and compared the computed frequencies for the models with the observed oscillation spectrum. 相似文献