Light curve shape variability of SZ cassiopeiae between 1978–1994

The aim of our investigation was toapproach the problem of identification for possiblevariability of light curve shape in case of theclassical Cepheid SZ Cassiopeiae. In order to performsuch a study we analysed eight observational data setsobtained through V photoelectrical photometry,covering a time base of 16 years. We applied theFourier decomposition technique to each data set; theobtained Fourier coefficients were used to calculatethe corresponding amplitude ratios and phasedifferences. Their time behavior were finally studiedin order to search for evidences of the variability ofthe light curve shape.     

Light curves of gas-eclipsed binary systems

Light curves have been calculated for the model of a binary system consisting of two spherical components, imbedded in a common spherically-symmetric, isotropically-scattering envelope with radially-varying opacity. The periodically-varying screening of stellar radiation by the envelope gives rise to regular light changes, which are similar to stellar eclipses during a superior conjunction of the components and in maxima resemble the light changes due to the reflection effect for Algol-type binaries, whereas for systems with nearly equal luminosities of the components they match light variations, caused by the gravitational distortions of stellar figures.It is shown that the light changes in AO Cas can be interpreted in terms of our model and we propose to call binaries of that type gas-eclipsed variables. The observed light curves RY Gem, RS CVn, VW Cep are compared with the model curves. It is indicated that the light curve of the Algol-type system RY Gem can be interpreted in the framework of the adopted model, provided that stellar eclipses are accompanied by the screening effect of the envelope.Asymmetry, local fluctuations, different widths of minima, and some other peculiarities of the observed light curves are discussed within the context of our model. It can be regarded as a certain optical counterpart of the Roche model, since the isophotes of the envelope resemble the Roche equipotentials in their behaviour.     

Observation and statistical analysis of ZZ Piscium

To examine the non-linear oscillation and period change of white dwarf variables, ZZ Psc is discussed observationally. As a result of data reduction we found two major periods, 680 seconds and 860 seconds, but could not find chaotic behavior of ZZ Psc.     

Ubvr light curves of 44i Bootis during 1978

In this paper theU, B, V, R light curves of the eclipsing variable 44i Boo, obtained during 1978, are represented and discussed.     

Light curves for off-centre ignition models of Type Ia supernovae

We compare observations of the high-redshift galaxy population to the predictions of the galaxy formation model of Croton et al. and De Lucia & Blaizot. This model, implemented on the Millennium Simulation of the concordance Lambda cold dark matter cosmogony, introduces 'radio mode' feedback from the central galaxies of groups and clusters in order to obtain quantitative agreement with the luminosity, colour, morphology and clustering properties of the present-day galaxy population. Here we construct deep light cone surveys in order to compare model predictions to the observed counts and redshift distributions of distant galaxies, as well as to their inferred luminosity and mass functions out to redshift 5. With the exception of the mass functions, all these properties are sensitive to modelling of dust obscuration. A simple but plausible treatment agrees moderately well with most of the data. The predicted abundance of relatively massive  (∼ M _*)  galaxies appears systematically high at high redshift, suggesting that such galaxies assemble earlier in this model than in the real Universe. An independent galaxy formation model implemented on the same simulation matches the observed mass functions slightly better, so the discrepancy probably reflects incomplete or inaccurate galaxy formation physics rather than problems with the underlying cosmogony.     

Light curves of relativistic charged neutron star

Gravitational lensing properties and the influence of the electric charge on the light curves of a slowly rotating neutron star whose exterior is described by the Reissner-Nordström metric are considered. The polar cap emission model is assumed. No effect of the magnetosphere except for its possible contribution to the total charge is taken into account. In general, the lensing effect is reduced by the charge and the light curves become more similar to those typical in flat space rather than to the Schwarzschild spacetime.     

Light curves of Asteroids (IV)

Light curves, based on photoelectric observations made in 1965 and 1978, are given for 11 asteroids. For 7 of them, periods have been determined (TABLE 1). Our period for (16) Psyche is different from some previous determinations.     

Vaporization of comet nuclei: Light curves and life times

We have examined the effects of vaporization from the nucleus of a comet and show that a latitude dependence of vaporization can, in some cases, explain asymmetries in cometary light curves. We also find that a non-uniform distribution of solar radiation over a comet can considerably shorten the vaporization lifetime compared to the results normally obtained by assuming that the nuclear surface is isothermal.Independent of any latitude effects, comets with CO₂-dominated nuclei and with perihelion distances less than 0.5 AU have vaporization lifetimes less than or comparable to their dynamical ejection times. This may explain the observed deficit of comets with small perihelion distances. Similarly comets with CO₂-dominated nuclei and perihelia near Jupiter's orbit have vaporization lifetimes that are shorter than the time for capture into short-period orbits. We suggest, therefore, that at least some new comets are composed in large part of CO₂, while only H₂O-dominated comets, with lower vaporization rates, can survive to be captured into short-period orbits.     

Light curves of the eclipsing systems of RS CVn-type

This work presents the light curves for rotating spotted stars generated by a computational code developed by us. This code is based in a model of the system and its analytical solution. The work also present an analysis of the photometric curve variations with the changes in the model's parameters.As a first result we have simulated a temporal evolution of the light curve when the photospheric spot varies its size and position and we reproduced some observational light curves of the II Peg star.Work supported by Dirección de Investigación, Universidad de La Serena, Chile.     

A photometric study of the Algol system Y Piscium

From the discussion of 417 photoelectric observations of this semi-detached Algol system, obtained in B and V during 82 nights in 1965–1971, the existence of a gas stream may be inferred for the following reasons: The scatter of the single observations is dependent on the orbital phase; the largest scatter occurs at the phases following both eclipses. The conventional photometric solution which is based on the long region rectification and neglects the photometric influences of the gas stream, gives for the two colours different geometric parameters of the system. However, the short region rectification allows a consistent photometric solution. According to this solution a short total phase exists, and the luminous regions caused by the impact of particles of the gas stream are hidden during the central part of the primary eclipse. Outside of eclipses, the additional light is seen during about half of the orbital period. From the variation of the visibility of the additional light during the primary eclipse it may be concluded that during about the first half of the observing time the luminous regions were situated at the high latitudes of the bright component, indicating the existence of magnetic fields on this component at this epoch, whilst later on the additional light came from an equatorial region on the following side of the massive component.Originally presented at the IAU Colloquium No. 16 held at the Univ. of Pennsylvenia, Philadelphia Pa., U.S.A. September 8–11, 1971.     

Light curves of jetted gamma-ray burst afterglows in circumstellar clouds

We present a Chandra observation of the powerful radio galaxy 3C 294 showing clear evidence for a surrounding intracluster medium. At a redshift of 1.786 this is the most distant cluster of galaxies yet detected in X-rays. The radio core is detected as a point source, which has a spectrum consistent with a heavily absorbed power law, implying an intrinsic 2–10 keV luminosity of ∼10⁴⁵ erg s⁻¹. A small excess of emission is associated with the southern radio hotspots. The soft, diffuse emission from the intracluster medium is centred on the radio source. It has an hourglass shape in the north–south direction, extending to radii of at least 100 kpc, well beyond the radio source. The X-ray spectrum of this extended component is fitted by a thermal model with temperature ∼5 keV, or by gas cooling from above 7 keV at rates of ∼ 400–700 M_⊙ yr⁻¹. The rest-frame 0.3–10 keV luminosity of the cluster is ∼ 4.5×10⁴⁴ erg s⁻¹. The existence of such a cluster is consistent with a low-density universe.     

Light curves of V711 Tauri (HR 1099)

V andB observations of V711 Tauri (HR 1099) for the year 1982–1983 are presented. The light curves made with the data of this season are compared with those of the previous observations of the 1981–1982 season. The single-peaked maximum light had shifted slightly and the peak amplitude had decreased to 0.04 mag. inV. No clear sign of colour,B–V, variation in comparison with the low temperature dark-spot is detected.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.     

Light curves of SN 1998A and comparison with similar unusual SNe

Following the proposal by Damineli that the central object of Eta Carinae may be an early-type binary, we perform numerical simulations of the X-ray emission from colliding stellar winds. A synthetic light curve has been generated which qualitatively agrees with the recent X-ray variability, and provides further support for the binary model. In particular, the model predicts a rise in the observed X-ray emission towards periastron, followed by a sharp drop and subsequent recovery. This is indeed what is seen in the RXTE light curve, although some problems concerning the X-ray spectrum at periastron still need to be explained. The simulations suggest that the width of the periastron dip will provide strong constraints on the binary and stellar wind properties of the components of Eta Car.     

Orbital Period Studies of the RS CVn-Type BinariesII. UV Piscium

Many available published times of light minima of the active binary system UV Psc have been collected and analyzed using a new method proposed by Kalimeris et al. (1994). Similar to what was seen in other RS CVn-type binaries, the orbital period of UV Psc oscillates with a period of about 61 years and an semi-amplitude of 0.21 ×10^-5 days. Two possible mechanisms (magnetic activity cycle mechanism and a light-time effect due to a hypothetical third body) that could modulated the orbital period behaviour are studied. We think that the cyclical period change in UV Psc can most probably be attributed to a magnetic activity cycle in the primary component. This revised version was published online in July 2006 with corrections to the Cover Date.     

Light curves of the trans-Neptunian objects 1996 TP66 and 1994 VK8

We have obtained a number of CCD images of two trans-Neptunian objects, 1994 VK8 and 1996 TP66, over two nights. The changes in magnitude of these objects have been examined, in a search for periodic variation. In the case of 1996 TP66, nothing other than random noise can be found to within the errors of ∼0.04 mag. Although a periodic signal is found for 1994 VK8, it appears to be an artefact, as the same frequency appears in the variation of sky brightness and is probably due to the sampling of the data. However, 1994 VK8 does exhibit a variation of ∼0.5 mag. This would suggest either significant non-sphericity or a change in surface composition over a large area. In either case 1994 VK8 warrants further investigation.     

The Chromospheric Radiation on the Circumstellar Shell of Tx Piscium

Using the chromospheric UV flux based on IUE data, we have undertaken a wavelength calculation of the rates of photodissociation and the a abundances of the relevant molecules CO, SiS, HCN and C₂H₂ for the inner region of the circumstellar shell of the carbon-rich star TX Psc. Shielding by heavy elements and dust was taken into account. Further, for CO, the line self-shielding as an additional shielding process was included. We find that the large influence of the shielding prevents the molecules from photodissociation in the internal layer of the shell of TX Psc. The possibility of detecting C₂H₂ via the equivalent widths of the infrared lines in the circumstellar shell is discussed. Finally, we estimate the antenna temperature and the luminosity of the fine-structure lines of [CI]609µ and [CII]158µ of the envelope of TX Psc, respectively.     

Two-colour photoelectric investigation of SZ Pisces

The RS CVn-type eclipsing binary SZ Psc was observed in two coloursB andV, in 1981. The rate of change of the period was calculated using two different least-squares procedures. The amplitudes of the light variations at outside eclipses are 0 _. ^m 181 and 0 _. ^m 213 inB andV colours, respectively. The light curves of the system have been solved using a new approximation. The radius of the cooler component is only 82% of its Roche-radius and the system is detached one.     

Evolutionary status of UV Piscium and its comparison with other short period RS CVn binaries

From the derived elements of UV Piscium, the evolutionary status of both of its components are compared with the Schaller et al. models and also with other main sequence systems having spectral types of late F to K range. From these models the ages of the components of UV Psc are determined. The Rossby number, which is a measure of chromospheric activity, has been derived from the convective turnover time scales and also from the age estimates.