Statistical masses of Abell clusters

The analysis of a homogeneous sample of 108 Abell clusters has led to an average peculiar velocity for the center of mass motion of these clusters of 610±750 km s^–1. From this result, an upper limit for the average mass of the Abell clusters of (1.6±2.4)×10¹⁵ M was obtained under the assumption that the peculiar motion is due to the excess of neighbours with respect to an uniform background. A lower limit of (2.42.9) x 10¹⁴ h ^-10.4 M was derived if one assumes that the peculiar velocity results from the mutual acceleration with the nearest neighbour.     

Neutron stars and general equation of nuclear matter

It has been shown that the mass of neutron stars obtained from equations of state based on nuclear theory depend upon the number of baryons assembled in it but not on the type of interactions considered. On examining the behaviour of different equations of state based on nuclear theories, a simple polytropic equation of state,P = (K/N)(p –p _s)^N is proposed. The results obtained forN=1.75 cover the entire range of neutron star masses obtained from the equations of state based on nuclear theories and give a maximum mass of 2.8M . Depending upon various mechanisms for energy output the mass of Crab pulsar is estimated to range from 0.32M to 1.5M . The relation connecting the coordinate mass,M, and the rest mass,M ₀, may be written asM/M 0.93 (M ₀/M)^0.9.     

Red spectroscopy of IP Pegasi

Time resolved spectroscopy of the dwarf nova IP Pegasi in the range 7670–8320Å shows absorption lines originating from the cool secondary. A radial velocity curve for this component has been derived by cross-correlation with a normal M star. The curve has semi-amplitude K₂=288.3±4 km s^–1, and is slightly distorted. This distortion is equivalent to an orbit with an apparent eccentricity of 0.075±0.024. The mass function of the primary is 0.394±0.016M. From this we derive constraints on the component masses of 0.621<1.14M and 0.172<0.71M. The red star has a radius in the range 0.322<0.51R and is probably on the main sequence.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986     

Mass accretion onto massive white dwarfs

We have studied the thermonuclear runaways which develop on white dwarfs of 1.205M and 1.358M accreting hydrogen rich material at 10^–10 M yr^–1. It is found that ignition of this material occurs at densities in excess of about 10⁴ gm cm^–3 and that the critical accumulated mass required to initiate the runaway is 0.7(1.5)×10^–4 M for a 1.358(1.205)M white dwarf.     

Structure of close binaries

Internal models have been obtained for uniformly rotating synchronous close binary systems using a modified double approximation scheme. We have considered primaries of 10M , 5M , and 2M with mass ratios of 0.0 to 1.0 in steps of 0.1, and some results are given for a 1M primary with a mass ratio of 1.0. A maximum luminosity reduction of 2.3% was found for a 10M primary with a mass ratio of 1.0 and 7.7% for a mass ratio of 0.0. The corresponding values for 5M are 2.0% and 7.0%, and for 2M they are 1.6% and 5.3%, respectively. These values were not found to be sensitive to small changes in composition. The maximum equatorial velocity varies from 399 km s^–1 for 2M to 567 km s^–1 for 10M when the mass ratio is zero, but these velocities decrease by 200–300 km s^–1 if the mass ratio is unity. The effect of gravity darkening on the apparent position of the primary in the theoretical H-R diagram was investigated. It was determined that an unresolved close binary of unit mass ratio can lie up to 0.9 magnitudes (depending on inclination) above the main sequence, whereas if the effects of distortion are ignored this number is at most 0.75 magnitudes. There seems to be some observational support for the larger value. Two models of the secondaries are given and their dimensions are compared with their critical Roche lobes.     

Low-Mass Quark Stars or Quark White Dwarfs

An equation of state is considered that, in superdense nuclear matter, results in a phase transition of the first kind from the nucleon state to the quark state with a transition parameter > 3/2 ( = _Q /( _N + P ₀/c ²)). A calculation of the integrated parameters of superdense stars on the basis of this equation of state shows that on the stable branch of the dependence of stellar mass on central pressure (dM/dP _c > 0), in the low-mass range, following the formation of a tooth-shaped break (M = 0.08 M , R = 200 km) due to quark formation, a new local maximum with M _max = 0.082 M and R = 1251 km is also formed. The mass and radius of the quark core of such a star turn out to be M _core = 0.005 M and R _core = 1.7 km, respectively. Mass accretion in this model can result in two successive transitions to a neutron star with a quark core, with energy release like supernova outbursts.     

Quasi-stationary solar wind in ray structures of the streamer belt

It is shown on the basis of analyzing the LASCO/SOHO data that the main quasi-stationary solar wind (SW), with a typical lifetime of up to 10 days, flows in the rays of the streamer belt. Depending on R, its velocity increases gradually from V3 km s^–1 at R1.3 R to V170 km s^–1 at R15 R . We have detected and investigated the movement of the leading edge of the main solar wind at the stage when it occupied the ray, i.e., at the formative stage of a quasi-stationary plasma flow in the ray. It is shown that the width of the leading edge of the main SW increases almost linearly with its distance from the Sun. It is further shown that the initial velocity of the inhomogeneities (`blobs') that travel in the streamer belt rays increases with the distance from the Sun at which they originate, and is approximately equal to the velocity of the main solar wind which carries them away. The characteristic width of the leading edge of the `blob' R , and remains almost unchanging as it moves away from the Sun. Estimates indicate that the main SW in the brightest rays of the streamer belt to within distances at least of order R3 R represents a flow of collisional magnetized plasma along a radial magnetic field.     

Echelle-mepsicron time-resolved spectroscopy of the dwarf nova SS Cygni

High dispersion time-resolved spectrograms of the dwarf nova SS Cygni, obtained with the Echelle-Mepsicron system, show double peaked emission lines with a complex profile. The intensity of the H line appears to be modulated by the orbital period. Radial velocity measurements of the wings of H and of the absorption line system of the late-type star yield semiamplitude values of K_em=101±6 km s^–1 and K_ab=151±7 km s^–1, respectively. Radial velocity measurements of the blue and red peaks and of the central absorption of H reveal a synchronous movement with the broad wings, although there is some evidence of a narrow component probably associated with a hot spot in the disk or a chromospheric emission line from the secondary star. The H modulation, the double profile and recently discovered UBV light variations support an inclination angle i 50°. The masses of the primary are M_p=0.60 M and M_s=0.40 M, respectively. A detailed analysis of the absorption lines reveals a spectral type of K2V.Paper presented at the IAU Colloquium No. 93 Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.     

Nonlinear pulsations of a very luminous star

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.     

The accretion of matter by a collapsing star in the presence of a magnetic field. II. Selfconsistent stationary picture

The stationary two-dimensional magnetohydrodynamic solution for the accretion of the matter without pressure into a gravitating centre of a black hole is obtained. It is assumed that the magnetic field far from the collapsed star is homogeneous and its influence on the flow is negligible. Around the star, at the plane perpendicular to the direction of the magnetic field, the dense quasistationary disc is formed, the structure of which in a large extent is determined by dissipation processes. The structure is calculated for (a) a laminar disc with the Coulomb mechanism of dissipation; and (b) a turbulent disc.The estimations of the parameters of the shock which result from the infall of the matter onto the disc are given. In the last section the numerical estimation and approximate character of the radiation spectrum of the disc and the shock are obtained for two cases of 10M and 10⁵ M . The luminosity of collapsed objects withM=10M appears to be about solar, thus its observation is possibly only at the distances less than 300–1000 pc. The collapsed objects in the Galaxy withM=10⁵ M could constitute very bright sources in spectral regions from optical up to X-ray. The spectra of a laminar and a turbulent disc for 10M black hole are very different. The laminar disc radiates primarily in the ultraviolet. The turbulent disc radiates a large part of its flux in the infrared. Therefore, one cannot exclude the possibility that some of the galactic infrared star-like sources are individual black holes in the accretion state.     

Three-component fluid model of the universe of critical density

A three-component fluid model of the Universe during the recombination era is analysed for = _c ( _c is the critical density). In addition to the well-known instability of the Jeans mode at 10⁹ M , we find two more unstable modes at 10¹² M .     

V 505 Mon: One of the most massive binaries

From 59 spectra collected at Asiago from 1969 to 1976, we obtain the spectroscopic orbit of the binary V 505 Mon. The rather long periodP=53.7805 days and semiamplitudeK ₁=83±4 km s^–1 of the primary component imply a fairly large mass of the secondary (m ₂3.2±0.4m ). Apparently also lines of this latter have been recorded, thus indicating highly massive components (m ₁50,R ₁=26,m ₂27,R ₂=14, in solar units) in a detached system (separation 255R ). The already reported variation of 0.15 mag., with period about one day, together with H emission, we detected, point toward a possible massive X-ray progenitor.     

TWO-FLUID MODEL FOR HEATING OF THE SOLAR CORONA AND ACCELERATION OF THE SOLAR WIND BY HIGH-FREQUENCY ALFVÉN WAVES

A model of the solar corona and wind is developed which includes for the first time the heating and acceleration effects of high-frequency Alfvén waves in the frequency range between 1 Hz and 1 kHz. The waves are assumed to be generated by the small-scale magnetic activity in the chromospheric network. The wave dissipation near the gyro-frequency, which decreases with increasing solar distance, leads to strong coronal heating. The resulting heating function is different from other artificial heating functions used in previous model calculations. The associated thermal pressure-gradient force and wave pressure-gradient force together can accelerate the wind to high velocities, such as those observed by Helios and Ulysses. Classical Coulomb heat conduction is also considered and turns out to play a role in shaping the temperature profiles of the heated protons. The time-dependent two-fluid (electrons and protons) model equations and the time-dependent wave-spectrum equation are numerically integrated versus solar distance out to about 0.3 AU. The solutions finally converge and settle on time-stationary profiles which are discussed in detail. The model computations can be made to fit the observed density profiles of a polar coronal hole and polar plume with the sonic point occurring at 2.4 R and 3.2 R , respectively. The solar wind speeds obtained at 63 R are 740 km s^-1 and 540 km s^-1; the mass flux is 2.1 and 2.2 × 10⁸ cm^-2 s^-1 (normalized to 1 AU), respectively. The proton temperature increases from a value of 4 × 10⁵ K at the lower boundary to 2 × 10⁶ K in the corona near 2 R .     

Das ProduktAR 0 und Weitere Galaktische Parameter

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 .

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

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Mitteilungen Serie A.     

Solar brightness distribution at 8.6 mm from interferometer observations

The radial brightness distribution of the quiet Sun at 8.6 mm is synthesized from observations using a sixteen element east-west interferometer in Nagoya. The observed brightness is flat from the disk center to 0.8R . A slight darkening appeared between 0.8R and the limb. No evidence of the bright ring near the limb is found. The radio radius at 8.6 mm is 1.015±0.005R . In addition there exists a coronal component just outside the radio limb.     

The metallic-line close binary system IW persei

TheUBV photoelectric light curve of IW Per as an ellipsoidal variable was obtained and a number of spectrograms were taken with dispersion of 10 Å mm^–1. New spectroscopic orbital elements are determined for this single-line spectroscopic binary to beK ₁=99.3 km s^–1, =0.2 km s^–1,a sini=1.80R andf(m)=0.093m . From analysis of the light curve, the geometric ellipticity coefficient of the distorted components is determined to beZ=0.037.Applying the second-order theory of light variation due to distorted components (Kopal and Kitamura, 1968), the orbital inclination and fractional radius of the primary component can be deduced simultaneously to bei=63° andr ₁=0.294. By takingm ₁=2.0m for the mass of the primary component with spectral type A5Vm, the mass of the secondary can be also deduced to bem ₂=1.08m , which would correspond to a G0-type if it is a Main-Sequence star. These elements indicate that the system is a non-eclipsing detached close binary.From intensity measurements of the lines Caii-K, Srii 4215 and Scii 4320 on twenty-eight good spectrograms taken at various phases, those intensities and the intensity ratio Sc/Sr are found to vary systematically with phase. From these variations the distribution of the local metallicity on the surface of the Am primary component is discussed in connection with the distribution of the local surface temperature.     

The parameters of planetary nebulae and their central stars derived from observations

On the basis of data on planetary nebula (PN) central star temperatures obtained by measurements in the ultraviolet (UV) range, the empirical calibration dependence between the number of Lyman photons emitted by a central starS and PN diameterD, is constructed. The temperatures of 118 PN central stars are estimated with this dependence. It is shown that the central star masses are distributed in a wide interval from 0.5 to 1.2M . About 60% of all stars have masses <0.6M , about 25% have masses >0.6M and the remainder have masses 0.6M . The averaged empirical tracks of evolution of low-mass (<0.6M ) and massive (>0.6M ) central stars differing considerably from each other are constructed. It is shown that the majority of central stars may possess hot chromospheres (T>2×10⁵ K) which spread for several tens of radii of the central star. The PN originates as a result of ionization of the matter ejected by a red giant at the superwind stage. The cause for this ionization is the UV radiation of the PN central star.     

Anisotropic angular broadening in the solar wind

We present Very Large Array observations at wavelengths of 2, 3.5, 6, and 20 cm, of angular broadening of radio sources due to the solar wind in the region 2–16 solar radii. Angular broadening is anisotropic with axial ratios in the range 2–16. Larger axial ratios are observed preferentially at smaller solar distances. Assuming that anisotropy is due to scattering blobs elongated along magnetic field lines, the distribution of position angles of the elliptically broadened images indicates that the field lines are non-radial even at the largest heliocentric distances observed here. At 5R , the major axis scattering angle is 0.7 at =6 cm and it varies with heliocentric distance asR ^–1.6. The level of turbulence, characterized by the wave structure function at a scale of 10 km along the major axis, normalized to =20 cm, has a value 20±7 at 5R and varies with heliocentric distance asR ^–3. Comprison with earlier results suggest that the level of turbulence is higher during solar maximum. Assuming a power-law spectrum of electron density fluctuations, the fitted spectral exponents have values in the range 2.8–3.4 for scales sizes between 2–35 km. The data suggests temporal fluctuations (of up to 10%) in the spectral exponent on a time scale of a few tens of minutes. The observed structure functions at different solar distances do not show any evidence for an inner scale; the upper limits are 1 km at 2R and 4 km at 13R . These upper limits are in conflict with earlier determinations and may suggest a reduced inner scale during solar maximum.     

Relativistic evolution of 103 M ⊙ star

A fully relativistic evolution of 10³ M is described for initial composition ofY=Z=0. Our results show that (a) a great part of the star is in radiative equilibrium, (b) the maximal red-shift for main-sequence 10³ M stars is significantly less than for isentropic models, and (c) a very low amount of CNO elements (<10^–8 by mass) is formed at any stage before hydrogen is completely consumed and hence such stars cannot be the progenitors of Population II stars.     

Vega: Data analysis of the observations

The observational data analysis indicates that the star is enveloped into a nebula considerably stretched along the equatorial plane. Vega is a star with B9.5IV-V characteristics withT _e =10.105±230 K andR=2.69±0.25R. The cover deforms energy distribution in Vega spectrum. As a result, the energy from with distribution corresponding to an A0V star is imitated in the direction towards the observer.