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1.
The existence of condensed carbon in the form of liquid droplets and graphite grains is found in white dwarf atmospheres with parametersg=108 cm s–2, H/He10–3, andT eff6000 K on the basis of model atmospheres techniques. It is shown that the condensation layers are dynamically stable and, consequently, that white dwarfs cannot supply the condensed particles to the interstellar medium. Possible observable effects are considered.  相似文献   

2.
The relationships among the various physical parameters-namely, the effective temperatures, radii and bolometric magnitudes, determined on the basis of the energy distribution curves of 25 Am stars — have been studied. Their effective temperatures are in the range of 7200 K to 9700 K; the radii, 1.5R to 2.5R ; the bolometric magnitudes, 0.75 mag. to 2.25 mag.; and the masses, 1.5M to 2.25M . The Am stars in general, appear redder than their normal counterparts, the blanketing in the blue andUV regions being the major cause. For the relatively cooler stars, the (B-V) colours are found to be less affected by blanketing. They are located in the neighbourhood of the upper edge of the zero-age Main Sequence band and show a fairly wide range in the evolutionary status among themselves. The bolometric corrections which are independent of the uncertainties in the parallax measurements, follow the same trend as that of the Ap stars, with reference to the temperature.  相似文献   

3.
Four different models for a K-giant atmosphere (T e=4500K, logg=2) have been computed. Each model is characterized by the inclusion of different opacity sources (H, H–, (H), metals, blanketing effect, He–) in order to obtain an evaluation of the model sensitivity concerning the atmospheric structure and the emergent flux. The results show that hydrogen, metals and blanketing effect must be taken into account to achieve self-consistent and reliable models.A picture of the influence of the frequency distribution of the absorption coefficient on the model features is also shown.
Sommario Sono stati calcolati quattro differenti modelli di una stella gigante K(T e=4500K, logg=2). Ogni modello è caratterizzato dalla inclusione di differenti sorgenti di opacità (H, H–, (H), metalli, effetto blanketing, He–) per ottenere una valutazione della sensibilità del modello per quel che riguarda la struttura atmosferica ed il flusso emergente. I risultati ottenuti mostrano che per costruire modelli auto-consistenti e con un buon grado di affidabilità occorre tener conto almeno delle seguenti sorgenti di opacità: H, metalli, effetto blanketing.Si mostra inoltre come sia possibile una descrizione schematica dell'influenza del coefficiente di assorbimento sulle varie caratteristiche del modello.
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4.
According to the tangential method the productAR 0 is determined with 145.7 km s–1 from measurements of the line profiles of the 21-cm line of the neutral hydrogen by Weaver and Williams (1973). The recent individual measurements of Oort's constantA and of the distanceR 0 of the Sun from the galactic centre yields 138.5 km s–1. The mean value 142.1 kms–1 leads toA=14.56 km s–1 kpc–1 andR 0=9.76 kpc. At the galactocentric distanceR nearR 0 the angular velocity is represented by (R)=25.84–2.98 (R–9.76)+0.075 (R–9.76)2. The mass of the Galaxy amounts to 1-92×1011 .

Herrn Kollegen Prof. Dr W. Gleisberg zum 70. Geburtstag am 26.12.1973 gewidmet.

Mitteilungen Serie A.  相似文献   

5.
The effective temperatures radii and bolometric magnitudes of Ap, Am and normal A stars have been estimated from their energy distribution curves between 478 nm and 680 nm. All the Am stars and one Ap star (i.e. CrB) were found to be affected by line blanketing, a rough estimation of which in the respective (B-V) colours has been found out in each case.The range in effective temperature is 0.45–0.60 in terms of (=5040/T e), while it is 1.8–4.8R in the case of radius, that in bolometric magnitude being from-0m.67 to+1m.61. An approximate estimate of the masses shows that they are between 1.5 and 3.0M . All these estimates are in agreement with those of the normal A stars. The Ap and Am stars are found to be slightly evolved and, therefore, are probably in the hydrogen shell-burning phase.  相似文献   

6.
The radial nonlinear pulsations of a model withM=0.8M ,M bol=–6 mag andT eff=5500 K have been studied. The pulsations are shown to exist in the form of the standing wave only in the innermost layers withR<0.2R ph. In the outer layers, the standing wave transforms into running waves, the frequency of which decreases with an increasingR. the pulsation period at the photosphere is found to be twice as long as the pulsation period atR<0.2R ph. The difference between the pulsation periods causes alternation of deep and shallow minima in the temporal dependences of the kinetic energy and radii and can be used to explain the nature of RV Tau variables. It is shown that at the distanceR>3R ph, the time-independent mass flux caused by shocks takes place. The rate of mass loss is found to beM10–4 M yr–1.  相似文献   

7.
Strong absorption satellite lines of CaI 6572 were found on spectrograms taken on three successive days just after the fourth contact of the 1971–72 eclipse of Zeta Aurigae. The radial velocities of the satellite lines are –88 km s–1, –74 km s–1, and –180 km–1, respectively, relative to the K-type primary star (K4 Ib). These absorptions should be due to a circumstellar cloud in which the column density of neutral calcium atoms is 1×1017 cm–2 and the turbulent velocities come to 20–50 km s–1. It is suggested that the cloud may be formed by the rocket-effect of the Lyman quanta of the B-type component (B6 V). We estimate the density in the cloud to be 2×1011 atoms cm–3 fors=10R K and 2×1010 atoms cm–3 fors=102 R K, wheres denotes the distance of the cloud from the K star andR K the K star's radius. The mass loss rate of the K-type component is also estimated to be about 10–7 M yr–1, assuming that the expansion of the K star occurs isotropically.  相似文献   

8.
Measurements of the Paschen discontinuity in stars withT eff104K leads to the conclusion that theD P/DB ratio increases with temperature faster than expected. The increase ofD P/DB with (logg)–1 is also steep.
Résumé Les mesures de la discontinuité de Paschen dans les étoiles deT eff104K nous montrent que le rapportD P/DB augmente avec la température plus rapidement que prevu. L'augment deD P/DB avec (logg)–1 est aussi remarquable.
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9.
A limb, two-ribbon H flare on June 4, 1991, associated with a white-light flare and followed by an emission spray and post-flare loops, is studied. A region of rapidly enhanced brightness at the bottom of the H ribbon above the white-light flare is revealed. The energy released by the white-light flare at eff = 4100 is estimated to be about 1.5 × 1028 erg s–1.  相似文献   

10.
We analyze the hypothesis of quantization in bands for the angular momenta of binary systems and for the maount of actionA c in stable and pulsating stars. This parameter isA c=Mv eff R eff, where the effective velocity corresponds to the kinetic energy in the stellar interior and the effective radius corresponds to the potential energyGM 2/R eff. Analogous parameters can be defined for a pulsating star withm=M where is the rate of the massm participating in the oscillation to the total massM andv osc,R osc the effective velocity and oscillation radius.From an elementary dimensional analysis one has thetA c (energy x time) (period)1/3 independently ifA c corresponds to the angular momentum in a binary system, or to the oscillation in a pulsating star or the inner energy and its time-scaleP eff in a stable star.From evolving stellar models one has that P effP eff(solar)1.22 hr a near-invariant for the Main Sequence and for the range of masses 0.6M <M<1.6M .With this one can give scalesn k=kn 1 withk integers andn 1=(P/P 1)1/3 withP 1=P eff1.22 hr. In these scales proportional toA c, one sees that the periods in binary and pulsating stars are clustered in discrete unitsn 1,n 2,n 3, etc.This can be seen in pulsating Scuti, Cephei, RR Lyrae, W Virginis, Cephei, semi-regular variables, and Miras and in binary stars as cataclysmic binaries, W Ursa Majoris, Algols, and Lyrae with the corresponding subgroups in all these materials. Phase functions (n k) in RR Lyrae and Cephei are also associated with discrete levelsn k.the suggested scenario is that the potential energies and the amounts of actionE p(t), Ac(t) are indeed time-dependent, but the stars remain more time in determinated most proble states. The Main Sequence itself is an example of this. These most probable states in binary systems, or pulsating or stable stars, must be associated with velocities sub-multiplesc/ F , given by the velocity of light and the fine structure constant.Additional tests for such a hypothesis are suggested when the sufficient amount of observational data are available. They can made with oscillation velocities in pulsating stars and velocity differences of pairs of galaxies.  相似文献   

11.
It is shown that the infrared flux method for determining stellar effective temperatures (Blackwell and Shallis 1977; Blackwell, Petford and Shallis 1980) can be applied to cool carbon stars. Although the spectra of cool carbon stars are highly line blanketed, the spectral region between 3 and 4 μm (L-band in the infrared photometry system) is found to be relatively free from strong line absorption. The ratioR L of bolometric flux toL flux can then be used as a measure of effective temperature. On the basis of the predicted line-blanketed flux based on model atmospheres, with an empirical correction for the effect of 3 μm absorption due to polyatomic species (HCN, C2H2), it is shown thatR L is roughly proportional to T3 eff. The high sensitivity ofR L to Teff makes it a very good measure of effective temperature, and the usual difficulty due to differential line blanketing effect in the analyses of photometric indices of cool carbon stars can be minimized. It is found that the majority of N-type carbon stars with small variability (SRb and Lb variables) are confined to the effective temperature range between 2400 and 3200 K, in contrast to M-giant stars (M0 III - M6 III, including SRb and Lb variables) that are confined to the effective temperature range between 3200 and 3900 K. The effective temperatures based on the infrared flux method show good agreement with those derived directly from angular diameter measurements of 5 carbon stars. On the basis of the new effective temperature scale for carbon stars, it is shown that the well known C-classification does not represent a temperature sequence. On the other hand, colour temperatures based on various photometric indices all show good correlations with our derived effective temperatures. An erratum to this article is available at .  相似文献   

12.
IntegratedUBV colours have been computed for synthetic clusters older than one billion years and for two chemical composition: (a)Y=0.30;Z=10–4 and (b)Y=0.30;Z=10–2, taking into account the contribution to the integrated light of Main Sequence, subgiant, red giant and horizontal branch stars. It has been found that integrated colours depend onZ and allow an estimate of the metal content, however not generally. Horizontal branch stars contribute to the integrated colours of clusters not significantly and the contribution of stars in more advanced phases (e.g., asymptotic branch stars) is almost negligible.Old clusters in LMC and SMC have been studied in terms of colour calibrations and this analysis has been supplemented, when possible, by photometric and spectroscopic data of individual stars. It was found that in the LMC clusters withZ=10–2 andt>5×109 yr are lacking, clusters with relatively blue colours are similar, both in age and chemical composition, to the halo galactic globular clusters. Moreover, there is a group of clusters with 1×109t5×109. In the SMC clusters withZ=10–2 andt>5×109 yr are lacking and clusters with 1×109t5×109 are rare. Clusters with relatively blue colours are interpreted with the following parameters:t=5×109 yr, 10–4Z10–3 andY=0.20.The implication of these results on the chemical history of the two galaxies is discussed.  相似文献   

13.
The minimum-propellant deterministic guidance law for bounded-thrust, constant jetexhaust velocity, spacecrafts is developed using the neighboring extremal theory. Minimization of the first-order variation in cost between a multi-burn nominal extremal and the perturbed trajectory eliminates all correction strategies except small changes in the nominal thrust-on, thrust-off times and small rotations of the thrust vector. Optimal values of these corrective controls for fixed values of initial state deviations, x 0, are found by minimizing the second variation in cost subject to the variational state and adjoint equations — an accessory minimum problem. The solution takes the linear feedback form u=A –1 22 A 21x 0, where the matricesA 22 andA 21 are functions only of transition matrices calculated along the nominal trajectory. The solution is applied to a three-burn Earth-Mars transfer.  相似文献   

14.
The Crosa and Boynton (1980) empirical model for discrete mass transfer in Her X-1 is further developed. The photometric features of the light curve (peaks of an hour duration and 0.3–0.7 m amplitude, steps near orbital phase =0); and the linear polarization bursts are assumed to be due to the formation and eclipses of the plasma blobs produced by discrete transfer of matter from optical star surface and its interaction with the accretion disc rim. The long lifetime (20h) of the cold (3×104 K) blob extending up to 1011 cm above the disc plane, as well as the deep X-ray flickerings (300 s) during the X-ray absorption dips are assumed to arise from a dispersal of accreting matter by the Rayleigh-Taylor instability in a blob moving through a hot corona of the disk atT c =3×106 K andn c =3×1011 cm–3. Thermal equilibrium in the corona and in the blobs are supported by X-ray flux. Within the first few hours after its formation a blob disintegrates into drops withr=5×109 cm,T=3×104 K, andn=3×1013 cm–3 which move then along Keplerian orbits. Frictional interactions of the drops with the corona destroy them on a 20h time-scale. The proposed model makes it possible to interpret the diverse observational facts and to predict numerous observational displays in the optical, UV, and X-ray bands. The first results of our optical-spectrum observations of blobs are briefly described.  相似文献   

15.
Vibrational transition probabilities, namely Franck—Condon factors and -centroids have been evaluated by an approximate analytical method for the (A–X), (A–X), and (A–X) system of YO molecule. Morse potential energy curves forX 2+,A 22,A22, andA22, states of YO have been constructed using the latest spectroscopic data. The value of -centroids for the band have been found to decrease linearly with the corresponding wavelengths. We show results for two new transitions of (A–X) and (A–X) and five new bands of (A–X) of YO in the umbral spectrum of the Sun.  相似文献   

16.
Photometry of HD 155638=V792 Her has been analyzed to determine the elements of this totally eclipsing RS CVn binary. The light variation outside eclipse was found to have a period of 27d.07±0d.07, which is slightly different from the 27d.5384±0d.0045 orbital period. Analysis of the eclipses was achieved by a modification of the Russell-Merrill technique. With the aid of radial velocity measures, absolute elements were obtained for the hot and cool stars, respectively;R h=2.58R ,R c=12.28R ,M h=1.40M ,M c=1.46M ,i=80o.61 and velocity semi-amplitudesK c=48.36 km s–1±0.79 km s–1, andK h=50.50 km s–1±0.33 km s–1. The apparent magnitudes areV h=9 m .73 andV c=8 m .48. The distance to HD 155638 was estimated to be 310 parsecs.  相似文献   

17.
The 5-dimensional Jordan-Brans-Dicke cosmologies in vacuum are found for the Bianchi type I metric, their relation with general relativity cosmologies is studied. Two solutions are possible, both produce effective pressure and energy density in the 4-dimensional G.R.-universes. One is a power-law relation, with two cases, the first one is forp eff=eff and the other forp eff=eff(– 1 < < 1) has a behaviour as the open flat universe. The second solution is an exponential only valid forp eff=–eff. In all cases the three-space expansion reaches infinity ast and the fifth dimension can be made to decrease approaching zero. The scalar field can increase or decrease with time.  相似文献   

18.
Parameters of the distant galaxy clusters of 3C295 (z=0.46) and Cl 0024+1654 (z=0.39) are compared with the predictions made using galaxies of the local clusters Coma (z=0.023) and DC 0329–52 (z=0.057) taking theK-effect into account. The distributions of colour and morphological type, and the amplitudesF +/F– of the 0 4000 discontinuity are examined and no evidence for evolution of the galaxies and the clusters can be seen.  相似文献   

19.
The pulsed plasma probe technique has been expanded to include simultaneous determinations of absolute electron density, density fluctuations, electron temperature, and mean-ion-mass with resolution limited only by probe geometry, sheath size, and telemetry. The technique has been designed to test for coupling of electron density variations and ion composition irregularities in multi-component plasmas by the comparison of electron density fluctuation power spectraP N(k) and a newly-developed diagnostic parameter, the mean-ion-mass fluctuation spectraM i/M iP M(k). In addition, the experiment extends satellite-borne irregularity spectral analyses down to the 5–20 m range while attempting to identify F-region plasma instability processes on the basis of characteristics inN e,T e, N e,P N,M i, andP M. Initial results demonstrate the expanded diagnostic capability for high spatial resolution measurements of mean-ion-mass and provide experimental evidence for the role of ion composition in multi-stepped plasma instability processes. Specific results include a spectral indexX n inP N=A nf–X n of 1.6–2.9 over the wavelength range from 1 km to 6 m under conditions identified with an unstable equatorial nighttime ionosphere. Simultaneous measurements ofM i/M i(P M=A M f –X m) andN e/N e(P N=A n f –X n) have shown a general behavior tending to lower power (A m<A n) and softer spectra (X m<X n) in ion mass fluctuations when compared with fluctuations in total plasma density. Limited analyses of the two power spectral elements raise hopes for the differentiation between plasma mechanisms that can lead to similar indices inP N.Paper originally submitted to the journalSpace Science Instrumentation.  相似文献   

20.
The data of the line series CH3CN 8(K) – 7(K) K = 0 – 7 and line CS J = 3 – 2 were taken simultaneously. At beam size of 16 the emissions of CH3CN and CS have a common center position located near IRc2 with deviations -8 and 5. The observed data show that in Orion KL core the integrated intensities of the two species have double peaks separated by a space of 14. The 2-dimension Gaussian fitting plots (FWHM) are ellipses ofD maj = 26 andD min = 22 for CH3CN 8(K) – 7(K) K = 3 – 6 andDmaj = 39 Dmin = 31 for CS J = 3 – 2 at a distance about 450 pc. Towards the multiple line emission region of CH3CN 8(K) – 7(K) K = 3 – 6, using a simplified very large velocity gradient model to solve the statistical equilibrium and radiative transfer equations, we find to fit the observed results, the optimum physical parameters and kinetic temperatureT k 120 K, densityn(H a) 1.2 × 105 cm–3, velocity gradientV gr 92 km s–1 pc–1 and the local abundance of CH3CNF ab 3 × 10–8. However towards the region of single line emission of CS J = 3 – 2 we have to use LTE and the optical thin approximation on the assumption ofT k= 120 K to obtain the lower limits of column density and then, an averaged abundance of CS of 6 × 10–8.  相似文献   

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