Light curve analysis for eclipsing systems with exoplanets. The system HD 209458

We have analyzed precision light curves for HD 209458, a binary with an exoplanet. The parameters obtained at different epochs and different wavelengths are in good mutual agreement when confidence regions are used to calculate the uncertainty intervals. We demonstrate the effectiveness and reliability of our new method for estimating the uncertainty intervals. Reliable estimates are provided for the linear and quadratic limb-darkening coefficients of the star and their confidence intervals (uncertainties). We find that the wavelength dependence for the limb-darkening coefficients at λ = 3201?9708 Å differs significantly from the corresponding theoretical relation based on thin model stellar atmospheres.     

Analysis of light curves of eclipsing systems with exoplanets: HD 189733

High-accuracy multicolor light curves of the binary system HD 189733, which contains an exoplanet, are analyzed. We have determined the radii of the star and the planet in the binary system, as well as the orbital inclination. The limb-darkening coefficients of the stellar disk were obtained in 10 filters in the wavelength interval λλ = 5500?10 500 Å. The uncertainties of the fitted parameters were estimated using the differential-correction and confidence-area methods. The wavelength dependence of the limb-darkening coefficients is compared to the corresponding theoretical function for a model thin stellar atmosphere. We confirm the wavelength dependence of the exoplanet’s radius found by Pont et al. (at the 1σ level). The exoplanet radius increases with decreasing wavelength, which seems to argue for the presence of an atmosphere around the planet.     

Light curve analysis for eclipsing systems with exoplanets. The systems Kepler-5b,Kepler-6b,and Kepler-7b

High-accuracy light curves for the binaries with exoplanets Kepler-5b, Kepler-6b, and Kepler-7b have been analyzed. The radii of the stars and the planets and the orbital inclinations of the binaries are derived. Reliable estimates of the linear and quadratic limb-darkening coefficients and their confidence intervals (uncertainties) are presented.     

The eclipsing WN3(h)+O5V binary BAT99-129: Light curve analysis and parameters of its components

We have analyzed the broad-band light curve of the massive eclipsing binary BAT99-129, which is located in the Large Magellanic Cloud and consists of WN3(h) and O5V components. The light curve was obtained as part of the MACHO project. The dense extended atmosphere of the Wolf-Rayet (WR) star makes it impossible to apply a standard parametric model, such as that of Wilson and Devinney, to analyze the light curve. We reconstructed the distributions of the brightness and absorption across the disk of the WR component by directly solving the integral equations describing the eclipses in the system. Our analysis yields reliable estimates of the system’s orbital parameters and the parameters of its components. The orbital inclination is 78°, the size of the orbit 28.5 R _⊙, and the radius of the O component R _O = 7.1 R _⊙. The size of the WR core, which is opaque in the optical continuum, is R _WR = 3.4 R _⊙, and the brightness temperature at the center of the WR-component disk is T _br = 45 000 K. We discuss possible uncertainties in the parameters obtained. The derived information is used to draw conclusions about the system’s evolutionary status.     

PN G068.1+11.0: A young pre-cataclysmic variable with an extremely hot primary

An analysis of spectroscopic and photometric data for the young pre-cataclysmic variable (PCV) PN G068.1+11.0, which passed through its common-envelope stage relatively recently, is presented. The spectroscopic and photometric data were obtained with the 6-m telescope and Zeiss-1000 telescope of the Special Astrophysical Observatory. The light curves show sinusoidal brightness variations with the orbital-period time scale and brightness-variation amplitudes of Δm = 1_.^m41, 1_.^m62, and 1_.^m57 in the B, V, and R bands, respectively. The system’s spectrum exhibits weak HI (Hβ–Hδ) andHeII λλ4541, 4686, 5411 Å absorption lines during the phases of minimum brightness, as well as HI, HeII, CIII, CIV, NIII, and OII emission lines whose intensity variations are synchronized with variations of the integrated brightness of the system. The emission-line formation in the spectra can be fully explained by the effects of fluorescence of the ultraviolet light from the primary at the surface of the cool star. All the characteristics of the optical light of PN G068.1+11.0 confirm that it is a young PCV containing sdO subdwarf. The radial velocities were measured from a blend of lines of moderately light elements, CIII+NIII λ4640 Å, which is formed at the surface of the secondary due to reflection effects. The ephemeris of the system has been improved through a joint analysis of the radial-velocity curves and light curves of pre-cataclysmic variable, using modelling of the reflection effects. The fundamental parameters of PN G068.1+11.0 have been determined using two evolutionary tracks for planetary-nebula nuclei of different masses (0.7 M_⊙and 0.78M_⊙). The model spectra for the system and a comparison with the observations demonstrate the possibility of refining the components’ effective temperatures if the quality of the spectra used is improved.     

IR photometry and a model of a dust shell in V2108 Ophiuchi

We present the results of JHKLM photometry of the oxygen Mira variable V2108 Oph acquired in 2000–2004. The period of brightness variations is refined (570 ± 3 days), and light and color curves in the near-IR are presented. The mean fluxes, color temperatures, and sizes for two blackbodies representing the combined radiation of the star and dust shell at minimum and maximum brightness are estimated. Additional IRAS data were used to compute a model with a spherically symmetric dust shell of silicate grains; the best-fit model has a radius for its inner boundary of 2.4 × 10¹⁴ cm, a dust temperature at this boundary of 1150 K, an optical depth of the shell at 0.55 μm of 16.8, and implies a distance to the star of 980 pc. We estimate the mass-loss rate for V2108 Oph to be 1.2 × 10⁻⁵ M _⊙/yr. Original Russian Text ? M.B. Bogdanov, O.G. Taranova, V.I. Shenavrin, 2006, published in Astronomicheskiĭ Zhurnal, 2006, Vol. 83, No. 5, pp. 437–442.     

Interpretation of light curves of the cataclysmic variable OY Car in a model with shockless interaction between a gaseous stream and the disk

To determine the parameters of the accretion disk and shock-wave region responsible for the formation of the orbital peak in the light curve of the binary system OY Car (an SU UMa-type variable), we have analyzed its U BV R and JK light curves using two gas-dynamical models with different regions of shock interaction: one with a hot line along the stream from the Lagrange point L1 and one with a hot spot on the accretion disk. The hot-line model can better describe the quiescent state of the system: the maximum X² for the optical light curves does not exceed 207, whereas the minimum residual for the hot-spot model is X²>290. The shape of the eclipse is almost identical in both models; the main differences are in interpreting out-of-eclipse portions of the light curves, whose shape can varyin the transition from one orbital cycle to another. The hot-spot model is not able to describe variations of the system’s brightness at orbital phases ?～0.1–0.6. The rather complex behavior of the observed flux in this phase interval can be explained in the hot-line model as being due to variations of the temperature and size of the system. Based on the analysis of a sequence of 20 B curves of OY Car, we conclude that the flux variations in the primary minimum are due to variations of the luminosity of the accretion disk, whereas the flux variability in the vicinity of the orbital peak is due to the combined effect of the radiation of the disk and hot line. The JK light curves of OY Car in the quiescent state and during a small flare also indicate preference for the hot-line model, since the primaryminimum and the flux near quadratures calculated using the hot-spot model are not consistent with the observations.     

Observable effects during gravitational microlensing of stars by NUT objects

We consider observable effects during the gravitational microlensing of stars of finite angular size with a given brightness distribution across their disks by exotic objects whose space-time environment is described with the NUT metric. We demonstrate that, under certain conditions, the microlensing light curves and chromatic effects due to the wavelength dependence of the disk brightness distributions can differ considerably from those observed for a Schwarzschild gravitational lens, so that their analysis can facilitate the identification of such objects.     

Changes in the parameters of the accretion disk around the dwarf nova SDSS J090350.73+330036.1 during an outburst

R-band photometric light curves of the eruptive eclipsing binary SDSS J090350.73+330036.1 obtained during a superoutburst in May 2010 (JD 2455341-2455347) are analyzed. Observations covering an interval near the outburst maximum and the post-maximum decrease by 0.7 ^m are presented. Oscillations (superhumps) whose period differs from the orbital period by several percent are observed in the light curve together with eclipses, suggesting that the studied system is a SU UMa dwarf nova. A ??spiral arm?? model is used to fit the light curves and determine the parameters of the accretion disk and other components of the binary system. Together with a hot line, this model takes into account, geometrical inhomogeneities on the surface of the accretion disk, namely, two thickenings at its outer edge that decrease exponentially in the vertical direction with approach toward the white dwarf. The increase in the R-band flux from the system during the superoutburst mainly results from the enhanced luminosity of the accretion disk due to the increase in its radius by up to ??0.44a ₀ at the outburst maximum (a ₀ is the component separation), as well as a shallower radial temperature decrease law than in the canonical case. As the superoutburst faded, the disk radius decreased smoothly at the end of our observation (to ??0.33a ₀), the thickness of its outer edge and temperature of its boundary layer decreased, and the parameter ?? _g approached its canonical value. Deviations from the mean brightness of the system as a function of the superhump period P _sh are analyzed for each out-of-eclipse set of observations. Various factors affecting the appearance and amplitudes of superhumps in the orbital light curves are considered.     

Limb darkening of the Call K line wings. Comparison with the average quiet Sun models

The detailed measurements of Call K line profiles along a diameter of the solar disk are presented. The obtained limb-darkening curves are used to test three semi-empirical models for the quiet Sun assuming moderate resolution. The calculations were carried out using the non-LTE code MULTI, taking into account a partial frequency redistribution. A comparative analysis of the measured and computed curves shows that the behavior of the Call K profiles from the center to the limb is sensitive to the temperature distributions of the semi-empirical models. The SRPM 305 model published by Fontenla et al. (2007) best reproduces the observed limb darkening in the region from the photosphere to the lower chromosphere; however, the agreement of this model with the observations at the line center is worse than for the other models, since this model was not assigned to describe hot chromospheric layers.     

Spot activity of the binary CG Cyg: Observations during maximum spottedness

We present the results of new multicolor photometry of the chromospherically active binary CG Cyg acquired in 2005–2009 (136 hours of observations). The light curves for each season reveal rotational brightness modulation due to spots that varies in amplitude and phase from season to season. We have determined the longitudes of spotted areas: for each season, they were located on the primary, close to the line joining the centers of the components. The longitude distribution of spots was analyzed for 44 years of observations of CG Cyg using all data available in the literature. The active longitudes of CG Cyg are not fixed at the quadratures, as was believed earlier: most of the time (1965–2003), the spots were concentrated at two active longitudes at the quadratures, at orbital phases 0.28±0.06 and 0.70±0.08, but, during a shorter time after 2004, they were located along the line joining the component centers, at orbital phases 0.50 ± 0.04 and 0.93 ± 0.03. We detected a switch of the active longitude by 180° during 1.5 months in 2008, accompanied by an increase in the amplitude of the rotational brightness modulation and only a slight increase in the star’s spotted area (by 5%). Our analysis of archive data reveals that switches of the active longitude during time intervals of 1–1.5 months were observed three times during the entire observational history of CG Cyg (in 1991, as well as in our observations of 2003 and 2008). All these switches were accompanied by similar phenomena: an increase in the amplitude of the rotational brightness modulation (by 0.06 ^m , 0.02 ^m , and 0.04 ^m ) and an increase in the spotted area (by 79%, 11%, and 5%). We used a zonal spot model to reconstruct the parameters of the spotted regions on CG Cyg. At all our observing epochs, the spots were located at low latitudes, in a region that was symmetric about the equator, 10° to 14° wide on either side. The spots are cooler than the surrounding photosphere by 2000 K. The spotted area varied only slightly from season to season, comprising 13%–15% of the surface area of the star, close to the historic spottedness maximum for the CG Cyg system.     

Analysis of photometric light curves solution for massive contact OB binary stars. LY Aurigae,BH Centauri,SV Centauri

We searched for signs of the presence of circumstellar gaseous matter in photometric data for massive contact early-type binaries by analyzing residual curves (the dependence of the difference between the observed and theoretical brightness variations on the orbital-period phase) for three such stars. The residual curves make it possible to estimate the influence of gas in the common envelope on the observed light curves for different phase intervals and to qualitatively describe the character of the distortion of the light from the system’s components. Changes of the residual curves from filter to filter indicate varying conditions in the circumstellar matter. Changes of the residual curves from one observation epoch to another indicate varying conditions in the circumstellar matter. We compared the residual curves obtained for different photometric bands and epochs via a correlation analysis. The distortion of light from the components of LY Aurigae in the ultraviolet differs from that in the visual. The distortion of light from the components of SV Centauri is appreciable, but not selective, and does not vary in time, while the distortion of light from BH Centauri possesses a strong selective component. A comparison of the radii computed for the components of BH Centauri and SV Centauri shows that the gas distribution near these binaries varies in time.     

The intermediate-age pre-cataclysmic variables SDSS J172406+562003 and RE J2013+4002

We have analyzed the physical status of the pre-cataclysmic variables SDSSJ172406+562003 and RE J2013+4002, which have evolved after their common-envelope stage a time t = 10⁶?10⁷ years. Spectroscopy and photometry of these systems were performed with the 6-m and 1-m telescopes of the Special Astrophysical Observatory. We demonstrate that emission lines in the spectra were formed solely by the reflection of radiation emitted by the white dwarfs on the surfaces of their cool companions, under conditions close to local thermodynamic equilibrium. These effects are also responsible for most of the objects?? photometric variability amplitude. However, comparing the light curves of SDSS 172406 from different epochs, we find aperiodic brightness variations, probably due to spottedness of the surface of the secondary. Jointly analyzing the spectra, radial-velocity curves, and light curves of the pre-cataclysmic variables and modeling the reflection effects, we have derived their fundamental parameters. We demonstrate that the secondaries in these systems are consistent with evolutionary models for main-sequence stars and do not have the luminosity excesses characteristic of cool stars in young pre-cataclysmic variables.     

Spots and active longitudes on the star V815 Her

We have analyzed light curves from the MOST satellite for the two active dwarfs ɛ Eri and κ Cet. Our maps of the stellar surface-temperature inhomogeneities were obtained with no a priori assumptions about the shape, configuration, and number of spots. We find variations of the surface-temperature inhomogeneities with time, also on time scales about equal to their rotation periods. We consider a model of a spotted star with two types of surface inhomogeneities—spots and related plage fields—and demonstrate that the best agreement between the theoretical and observed light curves is achieved for small ratios of the plage-field area to the area of cool spots. This conclusion indicates that long-term brightness variations of stars younger than the Sun are mainly due to variable spots on their surfaces, while the contribution from plage fields becomes more significant for older stars.     

The brightness distribution over a stellar disk derived from observations of microlensing by a binary system

Using a model-independent technique, we have reconstructed a one-dimensional strip distribution of the brightness over a stellar disk from observations of microlensing of a Galactic bulge star by a caustic of the binary gravitational lens OGLE-1999-BUL-23, obtained by the international PLANET group. The ill-posed inverse problem was solved using a regularization method taking into account the non-negativity of the brightness distribution. The radial brightness distribution was searched for on a compact set of convex-upward, monotonically non-increasing, non-negative functions, assuming that the source is circularly symmetrical. The reconstructed brightness distribution is compared with the results of model fitting and limb-darkening calculations based on models of stellar atmospheres.     

Search for and study of hot circumstellar dust envelopes

Long-term (1984–2008) JHKLM photometry for 254 objects is presented. The observations were carried out in the standard JHKLM photometric system using an original method and a modern IR photometer designed and built at the Sternberg Astronomical Institute. Our program of studies included searches for and studies of relatively hot circumstellar dust envelopes. The most important results obtained using these observations include the following. We have detected relatively hot dust envelopes in a number of objects for the first time, including the RCB star UV Cas, RX Cas, several classical symbiotic stars, etc. A model has been calculated for the dust envelope of FG Sge, which formed around the star as a result of several successive cycles of dust condensation beginning in Autumn 1992. Several dust-condensation episodes have been traced in the envelopes of symbiotic systems (CH Cyg, V1016 Cyg, HM Sge, etc.), as well as the role of the hot component in the formation of the dust envelopes. We have established from variations of the IR emission that the cool components in the symbiotic novae V1016 Cyg and HM Sge, and possibly CH Cyg, are Miras. The binarity of V1016 Cyg and HM Sge has also been firmly established. The variability of a whole series of object has been studied, including the stellar components of close binary systems and several dozen Mira and semi-regular variables. The ellipsoidality of the components in the RX Cas system (a prototype W Ser star) and the cool component in the symbiotic systems CI Cyg and BF Cyg has been firmly established. We have obtained the first IR light curve for the eclipsing system V444 Cyg (WN5+O6), and determined the wavelength dependence of the obtained parameters of the WN5 star. Analysis of the IR light curves of several novae indicate the condensation of dust envelopes in the transition periods of Cygnus 1992, Aquila 1993, and Aquila 1995. The IR light curve of R CrB has been obtained over a long period and analyzed. IR observations of the nova-like variable V4334 Sgr have been carried out over four years, over which the star passed through four stages during its motion along its post-AGB evolutionary track; the star’s bolometric flux and optical depth of its dust envelope have been estimated, and the structure and mass of the dust layer determined. We have analyzed the IR variability of the symbiotic star V407 Cyg over 14 years, and found its cool component to be a Mira with a period of 745 days. The observed pulsations and trend are associated with the luminosity and temperature variations of the Mira, as well as the optical depth of the dust envelope. The size of the dust grains and mass-loss rate of the Mira have been determined. We have obtained JHKL light curves for the Seyfert galaxy NGC 4151 over 23 years. The IR brightness of the galaxy grew from 1985 through 1996 (by ∼0.9 ^m at 1.25 μm, ∼1 ^m at 1.65 μm, ∼1.1 ^m at 2.2 μm, and ∼1.3 ^m at 3.5 μm), while the galaxy simultaneously reddened. The “cool” variable source in NGC 4151 was still in the active state in 1998, although its luminosity had decreased by approximately 15%–20%. If the “cool” component of the variable source in this galaxy is a dust envelope heated by the central “hot” source, it should be optically thin to the radiation of this source: its mean optical depth is in the range 0.05–0.15. Emission from dust particles heated to temperatures of 600–800 K was observed in the near IR at a distance of several parsecs from the nucleus during the period of activity in 1995–1998; the inferred mass of emitting dust was 5–20 M _⊙. In 1994–2003, we observed a tendency for NGC 4151 to become bluer at 1.25–1.65 μm while simultaneously reddening at 2.2–3.5 μm. Beginning in Autumn 2000, the galaxy began to emerge from a minimum, which lasted from March 2000 through April 2001 in the IR; a flare of the galactic nucleus was observed and followed in detail in the IR in this same period. We confirm the IR variability of the nucleus of the Seyfert galaxy NGC 1068, which can be located in various stages of activity. The variability of NGC 1068 is associated with a complex source. A periodic component has been detected in the J brightness variations of the oxygen Mira V2108 Oph; we have shown that this star is immersed in a fairly dense dust envelope, and have calculated amodel for this envelope. We have calculated an (axially symmetrical) dust-envelope model for the carbon semi-regular variable RWLMi with a density distribution characteristic for the “superwind” stage. This envelope model is able to reproduce the observed fluxes over the entire observable spectrum, and displays a good agreement with the observational data. The three hot supergiants V482 Cas, QZ Sge, and HD 338926 may be variable in the IR. Long-term photometry of eight planetary nebulae in the near IR (1.25–5 μm) has enabled us to firmly establish the IR brightness and color variability of these nebulae on time scales from several tens of days to six-to-eight years. We have analyzed long-term JK photometry of the X-ray binary Cyg X-1 (V1357 Cyg). Periodicity with a characteristic time scale of ∼11.5 years is visible in the JK brightness variations of Cyg X-1 in 1984–2007, possibly due to periodic variations of the temperature, radius and luminosity of the optical component of the binary with P ∼11.5 yr. Fourteen-year IR light curves of five RV Tau stars (R Sge, RV Tau, AC Her, V Vul, and R Sct) and the yellow supergiant and protoplanetary-nebula candidate V1027 Cyg have been analyzed. A spherically symmetrical dust-envelope model has been calculated for V1027 Cyg.     

Multicolor photoelectric WBVR observations of the close binary system HZ Her = Her X-1 in 1986–1988. Method and observations

We present results of four-color (WBVR) photoelectric observations of the close binary HZ Her = Her X-1 in 1986–1988. As a rule, the duration of the observations exceeded two 35-day X-ray orbital periods in the 1986–1988 observing seasons. The accuracy and length of the photoelectric observations facilitated multi-faceted studies, which enabled us to define several fine photometric effects in the light curves of the binary more precisely and attempt to interpret them in a model for the matter flow from the optical component to the accretion disk around the neutron star. This model provides a satisfactory explanation for the inhomogeneity of the gas flow and “hot spot,” as well as the existence of distinct “splashes” moving in their own Keplerian orbits around the outer parts of the Keplerian disk. We present series of light curves for all the observing seasons, as well as color-color diagrams that reflect the physics of various photometric effects. The transformation coefficients for each of the instrumental systems for the three observatories at which the observations were carried out are given. Atmospheric extinction was taken into account duringmulti-color observations of the object, with subsequent correction for atmospheric effects with accuracies ranging from 0.003 ^m to 0.005 ^m for air masses up to M(z) = 2.     

The dwarf nova MN Dra: Periodic processes at various phases of the supercycle

We analyze photometry of the dwarf nova MN Dra carried out using various instruments at four observatories on 18 nights between May 20 and June 28, 2009. The observations cover a variety of activity states of the system: a superoutburst, three normal outbursts, and quiescence. Analysis of the system’s light curve during the superoutburst decline reveals positive superhumps that recur, on average, with a period of 0.105 days and are due to the direct apsidal precession of the accretion disk. These are observed until the end of the superoutburst, but their period decreases at a rate of −24.5 × 10⁻⁵ of the period per period. Both the positive-superhump period and its derivative are in good agreement with estimates made during previous superoutbursts. At the brightness minimum and in normal outbursts, MN Dra displays brightness variations with a period of 0.096 days, whose amplitude is much larger during the brightness minimum (0.8 ^m –1.5 ^m ) than during normal outbursts (0.1 ^m –0.2 ^m ). We suggest that these brightness variations could be negative superhumps due to nodal precession of the oblique accretion disk.     

A Search for long-period brightness variations of the T Tauri stars T Tau,DI Cep,and SU Aur

We have searched for protostellar or protoplanetary structures in the vicinity of young T Tauri stars using a technique that is able to distinguish long-period components of the observed light curves. We perform a statistical spectral analysis of the one-year mean light curves of three selected stars (T Tau, DI Cep, and SU Aur) and plot synthetic light curves for the most reliable period of each star. In a first approximation, the results show a good coincidence between our synthetic light curves and the original light curves, supporting the hypothesis that protostellar or protoplanetary structures are present in the studied systems. An analysis of the 0.36–20 µm spectral energy distributions of the program stars also leads to the conclusion that infrared anomalies for young stars are most likely due to thermal radiation from not-yet-formed companions in the vicinity of the star.