Exosat observations of X-rays from classical novae during outburst stage

The initial discovery of soft X-rays from Nova Muscae 1983 was followed by eight additional observations of the three brightest novae whose outburst stage coincided with the lifetime ofEXOSAT satellite; namely three more observations of Nova Muscae 1983, three observations of Nova Vulpeculae 1984#1 (PW Vul), and two observations of Nova Vulpeculae 1984#2. Through these observations we sampled the soft X-ray light curve of classical novae from optical maximum to 900 days after. The observations seem best explained by the constant bolometric luminosity model of a hot white dwarf remnant. Although the measurements suffer from limited statistics, very broad energy bandpass, and incomplete sampling of any single nova, their constraints on the theories of nova outburst are significant. One constraint is that the lifetime of the white dwarf remnant in Nova Muscae 1983 is 2 to 3 years, which leads to the conclusion that the burned envelope massM _burn should be of the order of . The second constraint is that the maximum temperature, of the white dwarf remnant should approximately be within 200 000 K to 400 000 K. We estimate that a white dwarf remnant evolving like the central star of a planetary nebula, with core mass of 0.8 to 0.9M , core luminosity of 2×10⁴ L , and envelope mass of 10^–6 M , can explain the general characteristics of the X-ray measurements for Nova Muscae 1983. In order to have 1.1M core mass, estimated from the early observations of bolometric luminosity in the UV to infrared range, a wind withM5×10^–7 M yr^–1 appears to be necessary. The few observations of Nova Vulpeculae 1984 #1 and Nova Vulpeculae 1984#2, during the first year after outburst, give a risetime and intensity that is consistent with a constant bolometric luminosity model.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.     

Rapid mass accretion in the symbiotic star AG Dra

The mass accretion process onto the hot component of AG Dra and its explosive phenomena are discussed. The hot component seems to be a massive white dwarf (M>1 M). The mass accretion rate is estimated to be about 10^–7M/year. Many properties of the explosive phenomena agree with those of mild hydrogen flashes expected from this rapid mass accretion.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.     

Interacting winds in classical nova outbursts

Classical nova outbursts occur in binary systems containing a white dwarf accretor and a Roche-lobe-filling main-sequence star. The outburst is due to a thermonuclear runaway in the accreted material on the surface of the white dwarf, and results in the ejection of up to 10^–4 M of material at velocities of several hundred to a few thousand kilometres per second. There is now strong evidence that the mass ejection takes place via a wind with secularly increasing velocity. The fast ejecta catches up with slower moving material ejected earlier in the outburst, forming a layer of shock-heated gas which gives rise to a short burst of soft X-ray emission. This emission was observed in V838 Her (Nova Herculis 1991), and was succesfully accounted for by the interacting winds model. In this paper, we present 2.5-D numerical hydrodynamics calculations of interacting winds in novae which consider the effects of the binary system on shaping the mass-loss, and show that many of the features seen in the optical shells of novae many years after outburst can be accounted for.This author is supported by a PPARC research assistantship     

Multi-frequency observations of the 1985 outburst of RS ophiuchi

The 1985 outburst of the bright, recurrent nova RS Oph was almost simultaneously observed at X-ray, UV, optical, IR and radio frequencies at many epochs. The abundances in the ejected shell and the development of the bolometric luminosity as a function of time suggest that the cause of the outburst is a nuclear runaway on a massive white dwarf.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Development, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.     

Constraints of the neutrino magnetic moment from white dwarf cooling

The neutrino magnetic moment provides an additional energy emission in stars. It will accelerate the white dwarf cooling process and reduce the life time of the white dwarf, but it causes a conflict with the observation. We use observational constraints to derive an upper limit for the neutrino magnetic moment: 4.0×10^–12 _B      

A full cycle in the evolution of a classical nova

A classical nova model was evolved through a complete cycle, i.e. accretion leading to cutburst, mass loss and again accretion, ending in another outburst, by means of an implicit Lagrangian hydrodynamic code, which included diffusion (concentration, pressure and thermal terms), as well as an extensive nuclear reactions network between 28 isotopes of C, N, O, F, Ne, Na, Mg and Al. The initial model was a 1.25 M C–O white dwarf (WD) and the accretion rate assumed was 10^–11 M/yr. For more details of this calculation, see Prialnik (1986).The accreted matter was assumed to have normal composition (X=0.70, Z=0.03). Nevertheless, due to diffusion and convection, a significant amount of core material was mixed into the accreted matter, raising Z by a factor of 10. The model's evolution closely resembled that of a fast nova eruption, with a peak bolometric luminosity of 2.9×10⁵ L, a time of decline by 3^m of 25 days, an ejected mass of 6.5×10^–6 M and a maximum velocity of 3800 km/sec.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.     

Precollapse evolution of accreting CO white dwarfs

We calculate how accretion affects the evolution of carbon-oxygen white dwarfs up to thermonuclear runaway. The influence of internal temperature (including the possibility of solidification) as well as that of other initial conditions (accretion rate, total mass) are taken into account. We examine in some detail the influence of the adopted pycnonuclear reaction rate and of the lattice impurities on the ignition conditions. The consequences of having a completely ordered C-O crystal instead of a disordered one are also analyzed.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.     

The May 1985 superoutburst of OY Carinae: I. Structure of the outer disk from optical and IR observations

We present optical and IR observations of the dwarf nova OY Car during the May 1985 superoutburst. From them we find that the superhump has a temperature of 8000K and an area of order half the size of the red dwarf or accretion disk. We also compare the behaviour during two simultaneous optical/IR observations. Whilst the light curves in the two pass bands are similar during one observation, in the other observation they show marked differences that may be due to a cool region in the outer disk.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.     

Periodic variations in the spectrum of the dwarf nova WX Hyi in outburst and minimum

We present the analysis of spectrograms obtained during quiescence and during an ordinary outburst of the SU UMa type dwarf nova WX Hyi (ESO 3.6m telescope, B&C spectrograph with Image Disector Scanner, 171 Åmm^–1, range 4000–7000 Å, time resolution 6min.). The radial velocities of these spectra have been discussed by Schoembs and Vogt (1981) who also derived the orbital elements of WX Hyi. The phasesmax refer to these elements. All velocities discussed here are with respect to the white dwarf, not to the center of mass of the binary system.Inquiescent state we did not find significant radial velocity variations. The equivalent widths W of the He I emission lines revealed periodic variations with an amplitude of 30%, maximal values of W were observed atmax=0.0...0.2. In contrast, the equivalent widths of the Balmer lines were not variable.Duringoutburst we found periodic radial velocity variations of the emission peak of H, H and He I 5875 with an amplitude of100 km s^–1,max0.5. Also the broad Balmer absorption lines revealed periodic radial velocity variations, with a similar amplitude (max=0.3...0.5). The equivalent width of the H central emission peak varies with an amplitude of30%,max0.85. No variations of the equivalent width of the Balmer absorption lines were found.The outburst observations suggest that the preceeding part of the disc is brighter than the following one (in orbital motion). This is probably due to heating of the preceeding part by collisions with circumbinary matter, which seems to have an enhanced density in outburst as compared to the quiescent state. The emission lines are formed in outer layers or in a halo around the disc. The equivalent width variations can be interpreted in terms of interactions between this halo and the optically thick part of the disc.A more detailed discussion of the data is being published elsewhere.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     

Перенос резонансного излучения И случайные ълуждания Фотонов

. . .

---

Transfer of resonance radiation in infinite medium is considered as a process of random walks of photons. Close relation is shown to exist between the problems of transfer of line radiation and the stable distributions of the probability theory. This relation is used as a basis of a new method for the investigation of the asymptotic properties of the radiation field far from the sources.

---

---

,      

Study of the X-ray selected BL Lac object 1727+502

In this paper, accretion disc and synchrotron emission models have been used to analyse simultaneous IR-optical-UV data of the BL Lac object 1727+502. In the following, some of its properties have been discussed. It is shown that the temperature of the disc is about 19, 000°k, the mass of the central black hole isM ₈ 5.4, and the accretion ratio is 10^–3 M /yr.     

Метагалактические протоны сверхвысоких энергий

, . 2.7°- . . . E3×10¹⁹ (1.6) .     

Theoretical spectra of cataclysmic variables

We present two methods of modelling accretion disks in dwarf novae. The first one determines self-consistently the structure of a disk together with the radiation field. The computed theoretical spectra agree well with the observations of the dwarf nova WX Hyi in quiescence as well as in superoutburst. The second method is a modification of Tylenda's (1981) approach. We have used it to calculate models of disks around main-sequence accretors. The most interesting result is that no unique solution exists for a moderate mass flux around 10^–6 Myr^–1. Such disks are thus probably unstable.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.     

Accretion disk instabilities

Basic properties of accretion disk instabilities are summarized. We first explain the standard disk model by Shakura and Sunyaev. In this model, the dominant sources of viscosity are assumed to be chaotic magnetic fields and turbulence in gas flow, and the magnitude of viscosity is prescribed by so-called model. It is then possible to build a particular disk model. In the framework of the standard model, accretion disks are stationary, but when some of the basic assumptions are relaxed, various kinds of instabilities appear. In particular, we focus on the thermal limit-cycle instability caused by partial ionization of hydrogen (and helium). We demonstrate that the disk instability model well accounts for the basic observed features of outbursts of dwarf novae and X-ray nova. We then introduce other kinds of instabilities based on the viscosity model. They are suspected to produce time variabilities observed on a wide range of timescales in close binaries and active galactic nuclei.     

Ускорение релятивистских электронов в плазменных реакторах и нелинейные спектры космических радиоисточников

( , 1977; , 1977). , , , . .     

Структура и эволюция Сверхмассивных вращающихся магнитных политроп

. - . . , . - . - , , , -. ., , .

---

The structure of rotating magnetic polytropes is considered in Roche approximation. Investigation of the influence of poloidal as well as toroidal magnetic fields on the conditions of the beginning of matter outflow due to rotational instability is carried out. The influence of the turbulent convection and twisting of magnetic force-lines on the time of smoothing of differential rotation is considered. The estimate of the magneto-turbulence energy generated by differential rotation is presented. Both maximum possible energy output and duration of the quasi-statical evolution phase up to the appearance of hydrodynamic instability due to the effects of general relativity are calculated for supermassive magnetic polytropes of index three with uniform or differential rotation. The radius-mass relation is obtained for supermassive differentially-rotating magnetic polytropes referring to the longest part of the quasi-statistical evolution stage; some consequences are pointed out, including the period-luminosity relation.The evolution of the considered models of supermassive rotating magnetic polytropes with different character of rotation and different geometry of a magnetic field is discussed.The results obtained are summarized in the last section.

---

---

English translation will appear in the next issue ofAstrophys. Space Sci.

---

Receipt delayed by postal strike in Great Britain     

The asymptotic limit of the form-factors α and β product for celestial bodies

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].

     

Рассеяние света на анизотропных частицах

, — . , , . , , .     

Scanner observations of gamma Cassiopeiae

The photoelectric spectrophotometric scans of Cas have been analysed to find the stellar and envelope parameters. The absolute energy distribution of Cas covering the wavelength interval 350–700 nm have been given. Its effective temperature and gravity have been estimated by a comparison of the observed energy distribution curves with appropriate model atmospheres. The temperature has also been determined by Zanstra's method from the total energy emitted in the H-line. The mass, radius, luminosity, photospheric electron density and mass-ejection rate for Cas have been derived. An estimate of the extension of the stellar envelope has been made by use of the dilution factor obtained from the Balmer decrement. Electron density and electron temperature in the envelope are estimated.