A Photometric Investigation of the Eclipsing System OO Aql

The paper is concerning with the light curve analysis of an active binary system of OO Aql. Basic orbital and physical parameters of this system were estimated by analysing photometric observations by Lafta and Grainger (1985) and Essam et al. (1992). Both groups of observations gave quite different light curves with a conspicuous asymmetry arising from unequal height of successive maxima. A slightly changed programme by Djuraevi (1992a) was applied. The programme was based on the Roche model and it included an option of overcontact configuration and active (bright or dark) spotted regions on the system's components. An inverse-problem method by Djuraevi (1992b) was used to estimate the parameters of the system and active regions. The light-curve analysis suggested a significant change in the system. For Lafta and Grainger's light curves our analysis showed the presence of a dark spotted area near the polar region of the primary component. This dark area covered about 22% of the primary's hemisphere. Essam et al.'s light curves had very complex shape. In this case the mechanism of the mass transfer and the exchange of the thermal energy between the components could produce a bright-spot (bs) area on the secondary, near the Lagrange equilibrium point L₁ around the neck region between the stars. To explain a sharp increase of the system's brightness in the B filter immediately after the secondary minimum, we had to introduce also a hot-spot (hs) area of a high temperature contrast on the secondary. With the increase of the brightness in the V-filter being of much lower intensity, this hot spot region could be taken as a local eruption. The behaviour of the B–V colour index with the orbital phase is in favour of this hypothesis also. The obtained results show that the light-curve changes are due to development and moving of active spot regions on the components.     

Solar coronal streamers

The solar disk locations of 13 coronal streamers were determined from a combination of eclipse, K-coronameter (1 1/8r1 1/2 R ), and balloon-borne coronagraph (2<r<6 R ) observations taken during 1964 and 1965. Of this sample, three were observed twice on photographs taken over intervals of four and 28 days. Most of these streamers could be structurally associated with K-coronameter enhancements to establish their disk locations.Those features having known disk locations all lay above some stage of chromospheric disk activity in the form of active regions and prominences. The average lifetime of three K-coronameter streamer-enhancements, for which all or nearly all of their lifetimes were known, was about 4 solar rotations. Rotation rates for the lower latitude streamer-enhancements (30°) were essentially identical to the underlying surface. One high latitude feature ( 50°) which overlay a quiescent prominence had a rate equivalent to the surface rate at 30° latitude. In general those K-coronameter enhancements associated with streamers came into existence over time periods of 14 days and disappeared by gradually blending into the background coronal pattern. All the observed structures are explained by a model consisting of localized, high density features (streamers) which overlie disk activity and are imbedded in a uniform but weaker azimuthally-symmetric quiet corona.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

An analysis of active close binaries (CB) based on photometric measurements

For the purpose of analysing light curves of active CB with an accretion disc being at the evolutional phase of an intensive matter exchange between the components a model for light-curve synthesis has been realized where the attention is given to systems like W Ser not sufficiently examined yet with regard that in them the accretion disc is formed around an ordinary star. In the paper one uses the elements presented in the first paper of this series. The model can successfully describe the essential characteristics of the observed light curves due to existence of an accretion disc and a hot spot, as well as those originated in the temperature distribution along the disc radius. The system components are considered in the framework of the nonsynchronous Roche model and the accretion disc of a constant thickness lies in the orbital plane around the star capturing the matter of the neighbouring component.The primary surrounded by the disc is situated relatively well within the Roche oval and its rotation can be significantly nonsynchronous. Near the Lagrange equilibrium pointL ₁ flows from the secondary (which fills the Roche limit) the gas stream nourishing the disc. In the zone where the stream touches the lateral side of the disc a hot spot is formed.The proposed model enables estimating of the basic orbital and physical parameters of active type W Ser CB (Djuraevi, 1991) on the basis of photometric measurements by applying the inverse-problem method.     

Analysis of red and infrared wide-band photometry of Algol

The basic physical picture of the Algol system is reviewed, and, using collected red and infrared observations, photometric curve fits are investigated by applying numerical quadratures to determine theoretical light curves appropriate to Roche model stars. The contact nature of Algol B appears to be confirmed, and effective temperatures of the three components areT _A=11 400°,T _B=5300°,T _C=7600°. In terms of a Lambert's law approach to the reflection effect, the effective heat-albedo is required to be reduced from unity to one half; and it is also found that the averaged gravity-darkening coefficient is close to a value appropriate for a diffusion type of heat-transfer mechanism operating in sub-photospheric layers.     

Spot modelling and elements of the RS CVn eclipsing binary WY Cancri

Results of analysis of photoelectric observations of the RS CVn eclipsing binary WY Cancri in the standard passbands ofUBV during 1973-74, 1976-79 and inUBVRI during 1984-86 are reported. A preliminary analysis of the eclipses suggested the primary eclipse to be transit. A study of the percentage contribution of the distortion wave amplitudes in all the colours with respect to the luminosities of both components, showed the hotter component to be the source of the distortion wave. The clean (wave removed) light curves of different epochs have not merged, suggesting residual effects of spot activity. The reason for this is attributed to the presence of either (1) polar spots or (2) small spots uniformly distributed all over the surface of the hotter component. This additional variation is found to have a periodicity of about 50 years or more. The distortion waves in yellow colour are modelled according to Budding’s (1977) method. For getting the best fit of the observations and theory, it was found necessary to assume three or four spots on the surface of the hot component. Out of these four spot groups, three are found to have direct motion with migration periods of 1.01, 1.01 and 2.51 years while the fourth one has a retrograde motion with a migration period of 3.01 years. From these periods and the latitudes of the spots derived from the model a co-rotating latitude of 4ℴ is obtained. The temperatures of these spots are found to be lower than that of the photosphere by about 700ℴK to 800ℴK. Assuming the light curve of 1985-86, which is the brightest of all the observed seasons, to be least affected by the spots, the light curves of the other seasons are all brought up to the quadrature level of this season by applying suitable corrections. The merged curves in theUBVRI colours are analysed for the elements by the Wilson-Devinney method. This analysis yielded the following absolute elements:

Preliminary results from the spectra of V471 tauri

The findings about this unusual eclipsing variable which possesses a white-dwarf component are reported. It was found that the H and K absorption lines of Caii are strongly pressure-broadened, and exhibit two double-reversal emission components. The radial velocities derived from the central strong emission components of Caii (H and K) are in agreement with the mean radial velocity curve obtained from the metallic absorption lines of the existing elements, whereas H (4340.47 Å) does not conform with the mean radial velocity curve. In certain orbital phases the H (6562.82 Å) line occurs in emission.     

The First Byurakan Spectral Sky Survey. Late-type stars. VI. The zone+69°≤δ≤+77°

We present the sixth list of red stars selected from the plates of the First Byurakan Spectral Sky Survey. These objects are located in the zone3 ^h 45 ^m 18 ^h and+69°+77°. The list contains data on 42 new objects. We suggest that there exists a dust cloud around 2 of them.Translated fromAstrofizika, Vol. 38, No. 2, 1995.     

Information limit optimization techniques applied to AB Doradus

UBVRI light curves of the rapidly rotating chromospherically active single star AB Doradus were modeled using circular starspots. Several different methods were employed to calculate corresponding temperatures, resulting in a range of values slightly beyond 1000 K below the photosphere. Grid searches varying the spot latitudes were performed at a range of inclinations in the expectation that an optimum combination of these parameters could be found. However, the best fits, in a ² sense, for each inclination tested, were essentially the same. When minimum spot area is included as an additional criterion an inclination of 70 deg appears to be preferred, in reasonable agreement with literature values. A spot evolution sequence is discussed for this data. An analysis of Rucinski's (1982) data is also presented in support of a call for further accurate photometry of this system.     

Rocket-coronagraph photometry of the 7 March, 1970 corona from 3 to 8.5 R s

A rocket-borne coronagraph utilizing external occulting disks was used to photograph the solar corona from 3 to 9 R _s at 1931 UT on 7 March, 1970. Comparison of the rocket and ground-based observations shows a one-to-one correspondence between major streamers from the inner to the outer corona. In particular streamers over the poles are clearly visible against the background corona from 3 to 8 R _s. These rocket data had a scattered light level of 1.2 × 10^–10 B _s. The derived quiet equatorial and polar K + F corona was within 10% of the absolute brightness of standard coronal models and displayed identical radial gradients to those models. The photometric profiles of the NE limb streamer were analyzed assuming a model in which the core density follows a Gaussian distribution in directions perpendicular to the radius vector. This streamer was assumed to be rooted on the visible disk at 55 to 60° from the plane-of-the-sky as based on K-coronameter and XUV data. An uncertainty of as much as a factor of three still remains for the value of the axis density owing to uncertainty in the line-of-sight dimension of the streamer.     

An analysis of close binaries (CB) based on photometric measurements (VIII)

The author considers current problems in the determination of the orbital and physical parameters for active close binaries (CB) of W Ser type based on the interpretation of photometric observations (Djuraevi, 1991). In this particular case, one analyses the light curves of CB SX Cas in the framework of the accretion-disc model explained in the second paper of this series (Djuraevi, 1992a). The light curve is analysed by applying the inverse-problem method described in the third paper of the series (Djuraevi, 1992b). On the basis of the observational material in theB andV filters (Shao, 1967), the light curves, the fundamental orbital and physical parameters of the system are estimated. In the paper a graphical illustration of the obtained solutions is also given. The obtained results confirm the general picture about the active processes in CB of W Ser type.     

Circumstellar matter in the symbiotic binary EG and

We present a quantitative model of a proposed common slowly expanding envelope corotating with a symbiotic binary system. The geometry of the envelope is defined by the equipotential surface containing the Lagrangian pointL ₂. The model was applied to the symbiotic binary EG And. The orbital inclination,i = 45°, and mass ratio of the cool to the hot component,q = 2.8–3.0, are determined. The nature of the primary as well as the secondary minima in the light curves, development of the line profiles, radial velocities and equivalent widths of the H line through an orbital revolution are explained by this model.     

Motions in the solar atmosphere associated with the white light flare of 11 July 1978

Series of white light heliograms and oft- and on-band H filtergrams have been obtained, with an average spatial resolution of 1, to study the flare active McMath region 15403 on 11 July, 1978. A great number of accurate heliographic positions were determined for the umbrae, the white light flare patches and several bright H flare knots, as well as along the principal zero filament and an arch prominence. Using the measured heliographic coordinates of these objects their motions could be analyzed in some detail. The velocities of several different objects could be deduced from the coordinates. Since the heliocentric angle of the region was about 45°, the variation in apparent heliographic coordinates also enabled some variations in heights to be determined.It is pointed out that the flare when fully developed, consisted almost entirely of loops. The zero filament which was activated prior to the flare ran between two umbrae of common penumbra and opposite polarity, one belonging to an old, the other to a new spot group. The white light flare developed on both sides of the filament where it passed between these two umbrae; it was also the place where the flare started. Observational evidence appears to indicate that the erupted filament re-formed from below.An indication has been found that there was a link between the motion of some umbrae and the major flare occurrence.     

The angle of inclination of the sunspot symmetry axis to the solar surface

The Wilson effect, used before only as a method of determining the physical depression of sunspots, is used here to estimate a quite different parameter - the sunspot symmetry axis inclination angle to the solar surface, this explains the observed negative Wilson effect.On the basis of photoheliograms taken with three telescopes of the High-Altitude Solar observatory Peak Alma-Ata, the Wilson effect for the whole solar disk is investigated, the east and west parts of the disk being studied separately. 111 sunspots of regular shape at different heliocentric angles were measured, eight of them being under observations from one limb to the other. To study the dependence of the Wilson effect on the heliocentric angle, all observations within an angular interval of 10° were averaged. The dependence thus derived is described by two sinusoids having the zero point shifted along both axes. The shift of the zero Wilson effect to the west, i.e., a shift along the heliocentric angle axis, can be caused by the deviation of the sunspot axis to the east from the normal to the solar surface. On the line of sight-normal plane the angle corresponding to this deviation is =34°±14°.     

An analysis of close binaries (CB) based on photometric measurements

The subject of the paper is the problem of stellar differntial rotation in close binaries (CB) ofRS CV n type. The differential-rotation parameters we find on the basis of the migration of the depression in the light curves caused by the spot effect over the orbital phase. For that purpose, a simple model (Bussoet al., 1985) and inverse-problem procedure, based on the Marquardt (1963) algorithm, are used. To verify the obtained solutions, the SIMPLEX algorithm (Torczon, 1991) is applied, suitable for the nonlinear parameter optimisation. This algorithm enables a correct solution of the nonlinear equation system describing the differential rotation. The procedure is applied in the determination of the parameters of differential rotation forCV Cam, VV Mon andSS Boo binaries.     

Determinacy of the eclipse elements from a part of the light curves of eclipsing binaries

A part of the light curves of two detached (CD Tau and V909 Cyg) and one semi-detached (Algol) binaries have been analysed with the emphasis on the determinacy of the parameters of different systems from a part of their eclipse curves. A model light curve for whichr ₁=0.050,r ₂=0.150,i=90°, andL ₁=0.800 were chosen, has also been considered for a further clarification of the determinacy problem of the eclipse parameters. Some insight into the determinacy is gained by varying one parameter and adjusting the others for the best fit to the light curves in the considered eclipse phases. It was realised that the determinacy problem of the unknown parameters is stored in the determinacy of the type of the eclipse minima. The attempts of the solutions with a false choice of initial elements result in finding (i) no minimum of ² to give any acceptable solution, (ii) rapid departure from the false start and convergence on the correct solution, or (iii) a false solution mostly with a true inclinationi, but wrong sense of the ratio of the radii.     

The Supercritical Accretion Disk of SS 433

The structure of the SS 433 supercritical accretion disk derived from spectral and photometric data is described. In the disk plane, gas outflows at a velocity of about 100-150 km/s, while above the disk plane, the velocity increases sharply and reaches 1500 km/s at polar angle 60°. The outer parts of the accretion disk are involved in the precessional motion, which means that the slaved disk precession model is correct. There is complex periodic variability in the radial velocities of SS 433. Apart from the well-known precessional and orbital variability, the strongest cycle is 1/7 of the precession period, P7 = 23.228 ± 0.005 days. This is interpreted as evidence for a spiral shock in the accretion disk. The He II 4686 line consists of two components: a stream-formed narrow Gaussian profile and a broad double-peaked one. The latter is completely eclipsed at phase 0.0. Its blue and red peaks are probably emitted in gaseous cocoons around the bases of the relativistic jets. A correct value of the mass function has been found, which shows that the optical star is massive. The relativistic star's mass is estimated to be Mx 6M.     

Radial migration of planetesimals

Planetesimals orbiting a protostar in a circumstellar disk are affected by gravitational interaction among themselves and by gas drag force due to disk gas. Within the Kyoto model of planetesimal accretion, the migration rate is interpreted as the inverse of the planetary formation time scale. Here, we study time scales of gravitational interaction and gas drag force and their influence on planetesimal migration in detail. Evaluating observations of 86 T Tauri stars (Beckwithet al., 1990), we find the mean radial temperature profile of circumstellar disks. The disk mass is taken to be 0.01M in accordance with minimum mass models and observed T Tauri disks. The time scale of gravitational interaction between planetesimals is studied analogously to Chandrasekhar's stellar dynamics. Hence, Chandrasekhar's coefficient , defined as the fraction between the mean separation of planetesimals and the impact parameter, plays an important role in determining the migration rate. We find ln to lie between 5 and 10 within the protosolar disk. Our result is that, at the stage of disk evolution considered here, gas drag force affects the radial migration of planetesimals by a few orders of magnitude more than gravitational interaction.Paper presented at the Conference on Planetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A.     

Photospheric and chromospheric activity of the short period X-ray and Algol eclipsing binary UX CrB

We present six \(\mbox{V}R_{c}I_{c}\) light curves of UX CrB from observations carried out from 2011–2015. We also obtained three optical spectra using the 2.16-m optical telescope and LAMOST survey at the national astronomical observatories. We classified its spectral type as \(\mbox{G2}\pm\mbox{2V}\). We noticed that there are strong absorptions in the H_α, H_β, Ca ii H&K and infrared triplet lines in the observed spectra. By subtracting away the photospheric contribution, we also noticed that there are small excess emissions in these chromospheric active lines, which indicate there are weak chromospheric activities. We tried and obtained four photometric solutions with different spot positions from our full and high time-resolution light curves in 2012, using the updated Wilson-Devinney code. The model with two spots on the primary produced the best result for explaining the observed light curves from 2012. Moreover, we explained all other light curves based on our photometric solution using our 2012 light curves. There are two active longitudes at about 68^° and 255^°. We noticed that the starspots have both long-time (years) and short-time (about two months) variation by analyzing the light curves and its starspot parameters. There is also an obvious oscillation of light curve maximum between 0.25 and 0.75 phases by analyzing the values of \(\mbox{Max.~I} - \mbox{Max.~II}\). We conclude UX CrB are the evolved main-sequence stars with strong photometric and chromospheric activities.     

The effect of an optically thin region on stability of an accretion disk around a supermassive black hole

We analyse conditions of the innermost portion of an accretion disk and establish a set of equations for this region. A stable innermost region may exist, which can probably explain the observed UV and X-ray spectra, avoiding the unstable emission. We then discuss the detailed radial structure of a disk around a black hole for typical AGN parameters and obtain different kinds of- relationships for different regions of a disk. On the basis of this, we discuss the stability. A new type of cycle is present, which we call a double S shaped cycle. In this cycle, the extent of accretion rate variability is much larger than that in dwarf nova cycles. This probably solves the problem of violent variability of AGN. In the meantime, the very high accretion rate at the hottest state in limit cycles in the unstable region may provide continuous injection of matter to the jet and power the relativistic motion of the jet.     

Radio light curve of the periodic radio star LSI+61°303 AT 3.6 CM wavelength

Two radio light curves of the periodic radio star LSI+61°303 have been obtained. They show radio outbursts of different strength and the phase of the peak intensity is different for both light curves.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.