On the development of infrared radiation from an expanding nova shell

We discuss the precipitation and growth of grains in carbon-rich nova ejecta with a view to understanding the evolution of infrared luminosity of such objects. An initial phase of rapid grain growth is followed by an extended period of slower growth due to thinning out of the expanding gas. The period of rapid grain growth is attended by an equally rapid rise of infrared luminosity which reaches a maximum and thereafter declines more slowly after grains have grown to a significant fraction of their final radius. This behaviour of luminosity and also a rapid decline of grain temperature from 2000–900 K predicted in an optically thin model is shown to be in good agreement with data for Nova Serpentis 1970. Comparison of our model calculations with observations provide tentative estimates of various parameters of interest for dust grains condensing in Nova Serpentis 1970.     

Sudden grain nucleation and growth in supernova and nova ejecta

The thermal conditions leading to the rapid nucleation and growth of dust in astronomical explosions are examined. The contribution herein to nucleation physics lies only in the clarification of the ambient conditions where it apparently occurs. In both nova and interior shells of supernovae, dust precipitates in gas densities of order of 10^–14 g cm^–3 a few months after the explosion. The ambient conditions differ widely, however. Supernova condensation occurs in a thermal equilibrium, with photons, ions, electrons and grains having equal temperatures. In novae huge disequilibria exist, with photon and electron temperatures near 5×10⁴ K, photon energy density near 750 K, and forming refractory grains near 1800 K. In neither type of explosion can the condensed matter easily maintain chemical equilibrium with the total system. Interesting isotopic anomalies are trapped in both types of refractory condensate in the interstellar medium. The nova provides the best astronomical laboratory for observing the condensation.Invited contribution to the Proceedings of a Workshop onThermodynamics and Kinetics of Dust Formation in the Space Medium, held at the Lunar and Planetary Institute, Houston, 6–8 September, 1978.     

The host galaxies of nearby Seyfert 1 nuclei

We use optical and infrared imaging data of a complete hard X-ray selected sample of AGN to investigate the host galaxies of nearby Seyfert 1 nuclei. We disentangle the emission due to the unresolved point source and the resolved host galaxy by means of luminosity profile fitting. The stellar colours in the nucleus are redder inB — V andV — K than in normal spiral bulges or current stellar evolutionary models, probably due to dust obscuration.J — H colour is quite normal butH — K usually very red, probably indicating a large contribution from reradiating hot dust to the IR colours. No significant difference in IR colours oi the stellar component is found with respect to a comparison sample of Liners and starbursts, except that the reradiating dust in Seyferts tends to be hotter and lie closer to the nucleus.B — V colour gets slightly bluer towards the nucleus, whereasV — K andJ — K have red gradients.B — V andJ — K gradients are not correlated and are likely to be caused by different mechanisms. There is a clear correlation between the AGN and host luminosity. Finally, we present optical colour ratio maps of two Seyfert nuclei, NGC 3227 and NGC 7469. The blue, ringlike or elongated structure in the maps and its correspondence with molecular CO geometry is interpreted as evidence for circumnuclear star formation in these AGN.     

Modèle d'éjection de matière des novae

We have found that the gas of the premaximum, diffuse-enhanced and orion systems is produced by the nova itself and is ejected by shock waves in the form of discrete layers. The principal envelope originates in the gas responsible for the premaximum system, as a result of considerable, sudden increase of the radiation pressure of Lα, a certain time after the beginning of the nova explosion. The radiation pressure accelerates a part of the premaximum envelope and it is this accelerated part of the premaximum envelope that forms the principal envelope of nova. This acceleration is then transferred to the outer regions of the envelope. The mass of the principal envelope therefore increases continuously. We have rejected all the previous theories that have been proposed for the formation of the principal envelope, because the authors of the theories have supposed that the principal envelope is formed at the moment of the luminosity maximum, while in the case of Nova Delphini 1967, we have found that the principal envelope was formed about 125 days before the luminosity maximum. By accepting that the premaximum, diffuse-enhanced and orion layers are ejected by shock waves and that the principal system is produced by radiation pressure, we can interpret the luminosity curve and the variation of the radial velocity of each system as a function of time and the observed sporadic changes of luminosity or radial velocity. We have found that the luminosity comes from the gas associated with the principal envelope and that its mass is about 80% of the mass of the all matters ejected by a nova, during its activity. We have discussed the cause of the nova explosion and have concluded that there is no satisfactory theory of novae.     

Investigation of galaxy and quasar luminosity evolution in the model of standard cosmology

It is shown that the Hubble curvem(z) for galaxies and quasars averaged over a large volume of data forms in the first approximation a single continuous curve in the interval of red shifts 10^–2.5z4.5, which is satisfactorily described by the dependence .A large deviation of the observed mean dependence from the theoretical one predicted by the standard cosmology is explained by the evolution of the galaxy and especially quasar luminosity. The corresponding mid-statistical function of the absolute luminosity variation for the last 4/5 times of existence in the Universe is equal toM(z)–M(z ₀)=logz/z ₀+2z–0.4z ².The luminosity of the most far distant from the observed quasars on the average by 5–6 stellar magnitudes high than the luminosity of near galaxies and quasars. It is obtained that even the most far distant quasars atz5 are in the maximum of luminosity, or their extinction has just began, thus the quasar formation should be expected forz>(5–6). The relative rate of the luminosity decrease of galaxies and near quasars is rather accurately amounts in the recent epoch 7% per 10⁹ years. The obtained average Hubble curve of galaxies and quasars is evidently the main cause of their evolution in the Universe.     

Periodic motions around pulsating stars

The periodic motion of a test particle (dust, grain, or a larger body) around a pulsating star with a luminosity oscillation of small amplitude (featured by a small parameterB) is being studied. The perturbations of all orbital elements are determined to first order inB, by using Delaunay-type canonical variables and a method whose bases were put forth by von Zeipel. According to the value of the ratio oscillation frequency/dynamic frequency, three possible situations are pointed out: nonresonant (NR), quasi-resonant (QR), and resonant (R). The solution of motion equations shows that only in the (QR) and (R) cases there are orbital parameters (argument of periastron and mean anomaly) affected by secular perturbations. These solutions (which indicate a secularly stable motion in a first approximation) are valid over prediction times of orderB ^–1 in the (NR) case andB ^–1/2 in the (QR) and (R) cases. The theory may be applied to various astronomical situations.     

Simulations of superhumps and superoutbursts

We numerically study the tidal instability of accretion discs in close binary systems using a two-dimensional SPH code. We find that the precession rate of tidally unstable, eccentric discs does not only depend upon the binary mass ratio q . Although the (prograde) disc precession rate increases with the strength of the tidal potential, we find that increasing the shear viscosity ν also has a significant prograde effect. Increasing the disc temperature has a retrograde impact upon the precession rate.   We find that motion relative to the binary potential results in superhump-like, periodic luminosity variations in the outer reaches of an eccentric disc. The nature and location of the luminosity modulation are functions of ν. Light curves most similar to observations are obtained for ν values appropriate for a dwarf nova in outburst.   We investigate the thermal–tidal instability model for superoutburst. A dwarf nova outburst is simulated by instantaneously increasing ν, which causes a rapid radial expansion of the disc. Should the disc encounter the 3: 1 eccentric inner Lindblad resonance and become tidally unstable, then tidal torques become much more efficient at removing angular momentum from the disc. The disc then shrinks and M _d increases. The resulting increase in disc luminosity is found to be consistent with the excess luminosity of a superoutburst.     

CCD photometry of seyfert galaxies

Morphology and elliptically averaged luminosity profiles have been derived from CCD surface photometry of thirteen seyfert galaxies. ApparentV andI magnitudes,V-I colour index, as well as absolute Mv and MI magnitudes have been calculatedV andI luminosity profiles of Mk 10, Mk 79, Mk 358, Mk 618, Mk 352, and Mk 110, are adjusted by the usual model bulge plus disk with structural parameters comparable to those observed in normal spirals. The averaged luminosity profiles of Mk 50, Mk 124, Mk 348, and 3C227 are fitted byr ^–1/4 law with structural parameters similar to those observed in ellipticals and red compact galaxies. Mk 42 and NGC 985 show disturbed luminosity profiles.     

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.     

Infrared spectroscopy of Nova Cassiopeiae 1993 – IV. A closer look at the dust

Nova Cassiopeiae 1993 (V705 Cas) was an archetypical dust-forming nova. It displayed a deep minimum in the visual light curve, and spectroscopic evidence for carbon, hydrocarbon and silicate dust. We report the results of fitting the infrared (IR) spectral energy distribution (SED) with the dusty code, which we use to determine the properties and geometry of the emitting dust. The emission is well described as originating in a thin shell whose dust has a carbon:silicate ratio of 2:1 by number (  ∼1.26:1  by mass) and a relatively flat size distribution. The 9.7- and 18-μm silicate features are consistent with freshly condensed dust and, while the lower limit to the grain size distribution is not well constrained, the largest grains have dimensions  ∼0.06 μm  ; unless the grains in V705 Cas were anomalously small, the sizes of grains produced in nova eruptions may previously have been overestimated in novae with optically thick dust shells. Laboratory work by Grishko & Duley may provide clues to the apparently unique nature of nova unidentified infrared (UIR) features.     

Investigation of late-type stars in the FBS survey. I. M stars

The spectral subtypes and luminosity classes are given for 15 comparatively faint M stars found on plates of the First Byurakan Spectroscopic Survey. Two of them are classified as M dwarfs. Most of the new M stars are probably Mirids.Translated from Astrofizika, Vol. 37, No. 1, pp. 73–82, January–February, 1994.     

Dust and Molecules in Nova Environments

The current status of our knowledge about the formation and evolution of dust and molecules in the environments of classical novae is reviewed. We discuss the chemistry that leads to the formation of diatomic molecules and nucleation sites, dust formation in nova winds, the properties and the processing of dust in nova environments, and the eventual fate of the dust. We also discuss the environment of nova progenitors, and what this can tell us about the pre-nova evolution of close binary systems. This revised version was published online in September 2006 with corrections to the Cover Date.     

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.     

Multicolor Photometry of Nova Lacertae 1910 = DI Lac in 1962-2002

We present an analysis of the behavior of nova DI Lac 52 years after the outburst and over the next 40 years. Similar to a dwarf nova, DI Lac demonstrates flare activity with a characteristic time of 36 days and an amplitude of about 0 ^m .6. A flare profile is asymmetrical, the rise in brightness lasting about five days and the fading lasting about twenty days. Shorter flares sometimes occur between the main ones. The flares can be divided into three types in accordance with their behavior on magnitude–color diagrams. The ascending and descending branches of flares of the first type practically coincide on the diagrams, the second type describe counterclockwise loops, and the third type describe clockwise loops. The first and second types of flares can be explained within the framework of the theory of thermal instability as arising first in the outer and inner parts of the accretion disk, respectively. The nature of flares of the third type is still unclear.     

Astron observations of the Rapid Burster MXB 1730-335 and constraints on burster parameters from spectra of trailing bursts

We report on eight X-ray bursts detected by ASTRON from the Rapid Burster (RB) on 13 and 28 April and 16 August, 1983. Six of them (trailing bursts), with durations of 1.5–2 min, rise times of 5–10 s and intervals of 1–1.5 hours, exhibit spectral softening during the burst decay and may be related to the type I bursts. Two of the bursts (triangle bursts) observed on 28 April at interval of 28 min with much longer rise times (30–50 s) and longer durations (3 min), do not show distinct spectral softening. Persistent flux from RB on 16 August was estimated asF _p(2.0–2.4)×10^–9 erg cm^–2 s^–1. Spectral evolution of two trailing bursts was investigated by fitting their spectra in consecutive time intervals with the blackbody (BB), isothermal scattering photosphere (SP) and thermal bremsstrahlung (TB) models. Around the burst maxima the SP model fits the data best whereas in the burst tails the TB model is generally better. The BB model is worse than at least one of the two others. Interpretation of the burst spectra in terms of the BB radiation leads to improbably small neutron star mass and radius (M<0.86M ,R _NS<5 km) if the peak luminosity does not exceed the Eddington limit. Interpretation of the spectra around the burst maxima (3–15 s from the burst onset) in terms of an isothermal SP yields reasonable constraints onM,R _NS, and distanceD. For instance, for the hydrogen photosphere we obtainedM=(1.0–2.1)M R _NS=(7.1–16.4) km ifD=11 kpc. If one postulatesM=1.4M , thenD=(8.5–13) kpc for hydrogen photosphere; if, besides,D=11 kpc, thenR _NS=(8.1–13.3) km. It follows also from the SP-interpretation that the photosphere radius may increase up to 20–30 km in maxima of the trailing bursts when the luminosity becomes close to the Eddington luminosity.     

Nova Vulpeculae 1968 No. 2 (Kohoutek)

Nova Vul 1968 No. 2 (Kohoutek) has been studied on Asiago material obtained before and after the announcement of discovery. The nova, fainter than 20 magnitude at minimum, brightened on July 16. The maximum (9.25 B) was reached on July 19. From the light curve the star can be classified as a normal fast nova. Objective prism spectra taken near maximum display the presence of absorption systems with radial velocities from –550 to –2200 km/sec. On slit spectrograms obtained at the end of October, the nova was found in the nebular stage with wide emission bands of H, Hei, Heii,Nii,Niii and forbidden lines ofOiii,Nii,Oi. The degree of excitation is slowly increasing.The nova is strongly reddened by interstellar absorption.     

Luminosity function for galaxies and cosmology

Formulae for two classical cosmological tests,N(z) andN(m) are obtained with the luminosity function taken into account. From the testN(m) and Jarvis and Tyson observational data, characteristic absolute magnitude of galaxiesM ^*=–20.05 and mean extragalactic absorptionA=4×10^–4 mag Mpc^–1 have been found.     

Short-period intensity fluctuations of integral sunlight

An attempt has been made to detect short-period solar luminosity fluctuations in the vicinity of 5 min, analogous to the observed velocity oscillation. Using silicon photodiodes to monitor integral sunlight, an upper limit for the amplitude of the intensity fluctuations of 3 x 10^-5 rms was found.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

9,6-Year periodicity of symbiotic nova RT Ser (1909) during the outburst decay from 1940 to 1994

The behavior of the symbiotic nova RT Ser from 1940 to 1994 from photographic observations made at the Gissar Observatory (1940–1978) and BVR-band observations at the Crimean Observatory (1983–1994) is analyzed. The outburst lightcurve shows a linear decline at a rate of 0^m.06 per year. It appears from the nature of the outburst attenuation that the fading, having already lasted about 80 yr, is still continuing. Judging from the color indices, the principal contribution to the visible light from the system is made by a cool, late-type red giant and hot gas the source of which is, as yet, unknown. The photometric variability observed in the BVR bands with a characteristic time of 10 yr is confirmed by photographic observations of 1928–1978. The period determined from all the data is 9.6 yr and is most likely orbital.Translated fromAstrofizika, Vol. 39, No. 1, pp. 31–40, January–March, 1996.     

The luminosity function of halo white dwarfs

Recently, Liebertet al. (1989) have obtained an approximate observational luminosity function for halo white dwarfs. Certainly, this first attempt will be improved by the forthcoming Very Large Telescopes. Here we construct theoretical luminosity functions of such stars and we examine their dependence on the age of the halo. Finally, we show that accurate observational luminosity functions could provide useful information about the evolution of the galaxy.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.