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.     

PG 1316+678: A young pre-cataclysmic binary with weak reflection effects

The PG 1316+678 star is classified as a pre-cataclysmic binary, as is evidenced by its photometric and spectroscopic observations. Its orbital period is determined to be P _orb = 3.3803^d, which coincides with the photometric period. The intensities of the emission HI and HeI lines are shown to vary synchronously with the brightness of the object (Δm _V = 0.065 ^m , Δm _R = 0.08 ^m ). These variations arise as the UV radiation from the DAO white dwarf is reflected from the surface of the cold companion. The parameters of the binary are estimated and the time of its evolution after the common-envelope phase is determined to be t ≈ 240 000 years. Thus, PG 1316+678 is a young pre-cataclysmic NN Ser variable with the smallest known photometric reflection effect.     

Analysis of reflection effects in HS 2333+3927

The results of photometric and spectroscopic observations of the pre-cataclysmic variable HS 2333+3927, which is a HW Vir binary system, are analyzed. The parameters of the sdB subdwarf companion (T _eff = 37 500 ± 500 K, log g = 5.7 ± 0.05) and the chemical composition of its atmosphere are refined using a spectrum of the binary system obtained at minimum brightness. Reflection effects can fully explain the observed brightness variations of HS 2333+3927, changes in the HI and HeI line profiles, and distortions of the radial-velocity curve of the primary star. A new method for determining the component-mass ratios in HW Vir binaries, based on their radial-velocity curves and models of irradiated atmospheres, is proposed. The set of parameters obtained for the binary components corresponds to models of horizontal-branch sdB subdwarfs and main-sequence stars.     

Analysis of MOST light curves of the active stars <Emphasis Type="Italic">ɛ</Emphasis> Eri AND <Emphasis Type="Italic">κ</Emphasis> Cet

We have analyzed light curves from the MOST satellite for the two active dwarfs ? 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.     

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.     

Observations of eclipses of UU Sge

We have performed spectroscopy and photometry of eclipses of the pre-cataclysmic variable UUSge using the 6-m telescope of the Special AstrophysicalObservatory and the 1.5-mRussian-Turkish telescope. Our analysis of variations of the B-V and V-R color indices during the eclipses indicates that the temperature of the secondary is T _eff,2 = 6000?6300 K. A similar value, T _eff,2 = 6200 ± 200 K, follows from our comparison of the observed spectrum of UU Sge at the total eclipse phase and theoretical spectra of late-type stars. We identify 27 absorption lines of 11 chemical elements in the secondary??s spectrum. Their abnormal intensities indicate possible high-velocity turbulent motions (up to ?? _turb = 10.0 km/s) in the atmosphere of the star and the presence of hot gas above its surface.     

The impact of reflection effects on the parameters of the old pre-cataclysmic variables MS Peg and LM Com

We have determined the main parameters of the old precataclysmic variable stars MS Peg and LM Com. The radial velocities of the components, reflection effects in the spectra, and light curves of the systems are studied based on model stellar atmospheres subject to external irradiation. Forty-seven moderate-resolution spectra for MS Peg and 57 for LM Com obtained with the 6-m telescope of the Special Astrophysical Observatory are used to derive the refined orbital periods of 0.1736660 days and 0.2586873 days, respectively; the orbital eccentricities do not exceed e=0.04. The mass (M _w =0.49e_⊙) and radius (e _w =0.015R_⊙) of the MS Peg primary calculated using the gravitational redshift correspond to those for a cooling carbon white dwarf with a thin hydrogen envelope. The parameters of the red dwarf (M _r =0.19M_⊙, T_eff=3560 K, R _r =0.18R_⊙) are close to those derived from evolutionary tracks for main-sequence M stars with solar chemical composition. The radius (R _r =0.22R_⊙) and temperature (T_eff=3650 K) of the LM Com secondary exceed theoretical estimates for main-sequence stars with masses of M _r =0.17M_⊙. The luminosity excess of the red dwarf in LM Com can be explained by a prolonged (T>5×10⁶ yrs) relaxation of the M star to its normal state after the binary leaves the common-envelope stage. For both systems, theoretical U, B, V, and R light curves and spectra calculated using the adopted sets of parameters are generally consistent with the observations. This confirms the radiative origin of the hot spots, the unimportance of horizontal radiative transport, and the absence of large-scale velocity fields with high values (V_trans>50 km/s) at the surfaces of the secondaries. Most of the emission lines in the spectra of these objects are formed under conditions close to thermalization, enabling modeling of their pro files in an LTE approximation. A strong λ3905 Å emission line has been identified as the 3s²3p4s 1P⁰-3s²3p² 1S SiI λ3905.52 Å line formed in the atmosphere of the hot spot. The observed intensity can be explained by non-LTE “superionization” of SiI atoms by soft UV radiation from the white dwarf. We suggest a technique for identifying binaries whose cool components are subject to UV irradiation based on observations of λ3905 Å emission in their spectra.     

CaII line formation in the spectra of irradiated atmospheres

We have studied the effect of external radiation on the formation of LTE and non-LTECaII lines in the spectra of A-M-star atmospheres. Three frequency distributions were chosen for the external radiation: X-ray radiation specified by the power law \(I_v^ + = I_{0^v } ^{ - 0.6} \) at 1–16.5 keV and UV radiation specified by blackbody distributions with the temperatures T_rad=50000 and 15000 K. We analyze the influence of variations in the irradiating flux and its angle of incidence on the profiles and equivalent widths of the λλ3933, 3968 Å resonance doublet and the λλ8498, 8542, 8662 Å infrared triplet. For any type of external radiation, allowing for deviations from LTE decreases the reflection effects for the CaII lines. We conclude that the CaII profiles do not display emission components in the spectra of optically thick stellar atmospheres irradiated by X-rays. Therefore, CaII emission lines observed in the radiation of cataclysmic variables must be formed in an optically thin plasma. CaII emission lines are likely to form in the spectra of stars with UV irradiation if CaII is the dominant ionization state in atmospheric layers close to the depths at which the continuum is formed. As a result, the spectra of symbiotic variables with hot primaries can contain CaII lines originating on the surfaces of the M-giants and supergiant secondaries due to reflection effects. These lines can be used to analyze the reflection effects and the temperature structure in the atmospheres of the secondaries only if non-LTE effects are included. In the spectra of close binaries with cool white dwarfs, CaII emission lines originate in the irradiated atmospheres of the secondaries under conditions close to thermalization. These lines can be used to study the reflection effects and calcium abundances even in an LTE approximation. We calculated the profiles and equivalent widths of CaII lines in the spectra of the four precataclysmic variables BE UMa, EG UMa, MS Peg, and HR Cam. The observed and theoretical reflection effects in the λλ3933, 8542 Å emission lines for the specified parameters of the systems and a solar calcium abundance in the atmospheres of the red dwarfs are in good agreement.     

The evolutionary status of UX CVn

We have analyzed available spectroscopic and photometric observations of the close binary UX CVn using model atmospheres. Theoretical spectra and light curves were derived from models of a precataclysmic variable and a close binary consisting of degenerate stars. We have used the 6-m telescope of the Special Astrophysical Observatory to obtain ten moderate-resolution spectra at three orbital phases. Our analysis of the radial-velocity curve shows that the orbital period of the system has been stable over 40 yrs, and the variations of the intensities of lines of various elements at different phases and radial velocities indicates an absence of the reflection effect. As a result, we have classified UX CVn as a detached close binary consisting of a hot, low-luminosity sub-dwarf primary and a white-dwarf secondary.     

Chemical composition of δ Scuti stars: 1. AO CVn, CP Boo, KW Aur

We used high-resolution echelle spectra acquired with the 1.5-m Russian-Turkish Telescope to determine the fundamental atmospheric parameters and abundances of 30 chemical elements for three ?? Scuti stars: AOCVn, CP Boo, and KWAur. The chemical compositions we find for these stars are similar to those for Am-star atmospheres, though some anomalies of up to 0.6?C0.7 dex are observed for light and heavy elements. We consider the effect of the adopted stellar parameters (effective temperature, log g, microturbulent velocity) and the amplitude of pulsational variations on the derived elemental abundances.     

Analysis of the spectral energy distributions of four cool R CrB stars near the brightness maximum

The effective temperatures T _eff and carbon and nitrogen abundances in the atmospheres of the cool R CrB stars ES Aql, SV Sge, Z UMi, and NSV 11154 have been determined by modeling their spectral energy distributions in the optical and near-infrared. The hydrogen-deficient model atmospheres were computed using the SAM12 code in the classical approximation, taking into account sources of opacity characteristic of the atmospheres of R CrB stars. The influence of the hydrogen deficiency on theoretical stellar spectra is analyzed. The resulting effective-temperature estimates for ES Aql, SV Sge, Z UMi, and NSV 11154 are in the range T _eff = 4600–5200 K. The carbon abundances log n(C) in the atmospheres of ES Aql, SV Sge, and Z UMi are 8.9–10.1, corresponding to [C/Fe] values typical of the atmospheres of R CrB stars. The nitrogen abundances are lower than those determined in other studies, and differ considerably from star to star. The mean [N/Fe] value for these three stars is ≈1.5 dex lowthan the mean [N/Fe] for known warm R CrB stars. Abnormally high estimates were obtained for the atmosphere of NSV 11154: log n(C) = 10.8 and log n(N) = 10.0. The approximate log g estimates agree with the conclusion from photometric observations that cool R CrB stars have lower luminosities than hotter R CrB stars.     

The nature of the unique precataclysmic variable V664 Cas with two-peaked Balmer lines in its spectrum

We analyze photometric and spectroscopic observations of the close binary system V664 Cas. All the characteristics of its radiation are consistent with the star being a cataclysmic variable with powerful reflection effects. The orbital period is refined (P=0.5816475 d) and the ephemerides of the system determined. The U, B, V, R light curves of V664 Cas display sinusoidal variations with similar amplitudes near Δm=1.1^m. This suggests that a hot spot on the surface of the secondary always dominates the optical radiation of the system. The spectra contain emission lines, two-peaked hydrogen lines, and narrow lines of helium and heavy elements in high ionization states, whose intensities vary synchronously with the brightness. The HeII λ4686 Å line has broad absorption wings that form in the atmosphere of the O subdwarf. The mass function, f(m)=0.007M_⊙, is the lowest among all precataclysmic variables: the mass of the secondary exceeds the mass of the primary by more than a factor of 1.6. A full set of fundamental parameters for V664 Cas is determined based on modeling of the spectra and light curves, taking into account reflection effects in the system. Most of the emission lines are formed under conditions of appreciable deviations from local thermodynamic equilibrium. The possibility of carrying out correct modeling of the Balmer-line profiles assuming the stellar radiation is absorbed in a planetary nebula is demonstrated.     

Fe2+-Fe3+ interactions in tourmaline

The color and spectroscopic properties of ironbearing tourmalines (elbaite, dravite, uvite, schorl) do not vary smoothly with iron concentration. Such behavior has often been ascribed to intervalence charge transfer between Fe²⁺ and Fe³⁺ which produces a new, intense absorption band in the visible portion of the spectrum. In the case of tourmaline, an entirely different manifestation of the interaction between Fe²⁺ and Fe³⁺ occurs in which the Fe²⁺ bands are intensified without an intense, new absorption band. At low iron concentrations, the intensity of light absorption from Fe²⁺ is about the same for E∥c and E⊥c polarizations, but at high iron concentrations, the intensity of the E⊥c polarization increases more than ten times as much as E∥c. This difference is related to intensification of Fe²⁺ absorption by adjacent Fe³⁺. Extrapolations indicate that pairs of Fe²⁺-Fe³⁺ have Fe²⁺ absorption intensity ～200 times as great as isolated Fe²⁺. Enhanced Fe²⁺ absorption bands are recognized in tourmaline by their intensity increase at 78 K of up to 50%. Enhancement of Fe²⁺ absorption intensity provides a severe limitration on the accuracy of determinations of Fe²⁺ concentration and site occupancy by optical spectroscopic methods. Details of the assignment of tourmaline spectra in the optical region are reconsidered.     

The physical parameters and orbit of the eclipsing binary system GSC 4596 1254 = SAO 3282

We have obtained the first U BV R photoelectric light curves for a recently discovered eclipsing binary with a period of 9.33 ^d and an appreciable eccentricity (e = 0.08). We have used these data to determine the photometric elements of the system for a model with two spherical stars with linear limb darkening. The high accuracy of the observations enabled determination of the absolute parameters of the components using available calibrations. The masses of the components are 1.28 and 1.08 M _⊙, and their ages are two billion years. The present orientation of the orbital ellipse is unfavorable for studies of the apsidal rotation, which is essentially due to relativistic effects.     

Physical parameters and orbit of the eclipsing binary BD +66 1663 = GSC 4479 412

We have obtained the first UBV(RI) _C photoelectric light curves of the recently discovered eclipsing binary BD +66 1663 = GSC 4479 412 (P = 7.04^d, V = 10.14). We have derived relative and absolute parameters of the binary, and analyzed the interstellar extinction towards the object. Though the star is located in the field of the young open cluster Be 59, we demonstrate that it is not a member.     

Physical parameters of the eclipsing binary V798 Cep

The first high-accuracy CCD UBV RI(RI)_C light curves for the recently discovered eclipsing binary V798 Cep (P = 16 ^d .08, V = 11 ^m . 8) are presented; this star is included in our program of eclipsing systems with considerable eccentricities. A photometric solution for the light curves and physical characteristics of the component stars are derived. The orbital eccentricity is quite high, e = 0.437. The longitude of periastron is close to 180°, making studies of the apsidal motion difficult. V798 Cep may be a hierarchical system.     

Spots and the Activity of Stars in the Hyades Cluster from Observations with the Kepler Space Telescope (K2)

Observations of the K2 mission (continuing the program of the Kepler Space Telescope) are used to estimate the spot coverage S (the fractional area of spots on the surface of an active star) for stars of the Hyades cluster. The analysis is based on data on the photometric variations of 47 confirmed single cluster members, together with their atmospheric parameters, masses, and rotation periods. The resulting values of S for these Hyades objects are lower than those stars of the Pleiades cluster (on average, by ΔS ~ 0.05?0.06). A comparison of the results of studies of cool, low-mass dwarfs in the Hyades and Pleiades clusters, as well as the results of a study of 1570 M stars from the main field observed in the Kepler SpaceMission, indicates that the Hyades stars are more evolved than the Pleiades stars, and demonstrate lower activity. The activity of seven solar-type Hyades stars (S = 0.013 ± 0.006) almost approaches the activity level of the present-day Sun, and is lower than the activity of solar-mass stars in the Pleiades (S = 0.031 ± 0.003). Solar-type stars in the Hyades rotate faster than the Sun (〈P〉 = 8.6 ^d ), but slower than similar Pleiades stars.     

Spots on the surfaces of late-type stars

The spottedness of two stars characterized by significant photometric variability is studied using published data: the recently discovered variable ASAS 063656-0521.0, whose V variability reaches 0.8 ^m , and XXTri (HD12545), which is among the most active RSCVn stars (in 1997–1998, the amplitude of its V variability was 0.63 ^m ). The spots cover up to 44% of the total visible surface S of ASAS 063656-0521.0. The mean estimated spottedness of XX Tri was 32%, and varied from29% to 36%. An analysis of the dependence of the spottedness on the properties of spotted stars, primarily their effective temperatures, is also presented. A modification of a simplifiedmethod for estimating the spottedness S, i.e., the fractional surface area of the spots, is applied to a sample of 48 late-type stars. The dependences of the spottedness on the effective temperature of the stars and the rotational velocity projected onto the line of sight are derived. Two groups of objects can be distinguished. The first contains stars displaying the typical dependence of S on the effective temperature (their maximum value of S is 20–25% for stars with temperatures 4500–5000 K, and S decreases for solar-type stars and cool M dwarfs). The second group is formed of the most active stars, which have temperatures of 3700–5200 K and S values from 25% to 50%. Our preliminary conclusion is that spottedness is not related to the period of the stellar rotation. The previously studied variable V410 Tau is used to consider the shortcomings of the method applied compared to the results of light-curve modeling.     

Long-term optical and radio monitoring of the quasars S5 0716+714 and 4C 38.41 on various time scales

We present the results of long-term radio and optical monitoring of two radio-loud quasars. The aim of the work was to study the objects?? variability on various time scales and search for correlations between the radio and optical emission. The monitoring was performed in 2002?C2010. The radio observations were carried out using the 22-m telescope of the Crimean AstrophysicalObservatory, 26-m telescope of the University of Michigan Radio Astronomy Observatory, and 14-m telescope of the Metsahovi Radio Observatory at 4.8, 8.0, 14.5, 22.2, and 36.8 GHz. The optical observations were obtained in the B, V,R bands using the Zeiss-1000 telescope of the Special Astrophysical Observatory with a CCD photometer. Light curves of the quasars 4C 38.41 (1633+382) and S5 0716+714 are presented. Radio flares of 4C 38.41 with amplitudes of 0.5?C1.0 Jy at 4.8 and 8 GHz and 1?C3 Jy at 22.2 and 36.8 GHz were detected on time scales of about 100 days. The amplitude of the optical brightness variations varied between 0.5 ^m and 1.5 ^m over about 200 days. The amplitudes of the flux variations for S5 0716+714 for the period of two months were 0.5?C1.6 Jy at centimeter and 1?C7 Jy at millimeter wavelengths. The amplitudes of flares in the optical reached 2 ^m in the B and V filters and 2.5 ^m in the R filter, on time scales of 200 days. The color indices of these objects did not change during the period covered by observations, i.e., the objects did not become bluer when they brightened. The detected delays between the variations atmillimeter and centimeter wavelengths are several days, which is within the interval between observations during the long-term monitoring. The absence of a distinct correlation between the optical and radio brightness variations was probably due to the presence of substantial time delays between the phenomena occurring in these different wavelength ranges.