Spectral variability of IL cephei

The results of six years of spectroscopic studies of the Herbig Be star IL Cep (HD216629) are reported. Various spectral parameters of the Hα and Hβ emission lines and those of the He I λ 5876 Å absorption feature are found for the first time to have exhibited slow variations in 2006–2011 and to have reached their extrema in 2009–2010. The Na I D1 and D2 lines reproduce, in a weaker form, the Hα radialvelocity variations. It is suggested that the variations found in the spectrum of the star may be due to the presence of additional bodies in the system.     

Étude du système AX Mon

We have divided this investigation into four main parts. In the first part, we study the ways in which the envelope affects the composition and the spectral variations, and the orbital motion acts on the envelope absorption intensities and how the extent of the envelope constantly decreases during the 11 yr of our observations. This phenomenon regarding AX Mon has not been previously reported in the literature. However, it explains the appearance of the α Cygni spectrum which occurs according to an arbitrary integral multiple of the orbital periods. Two absorbing envelopes seem to exist: an exterior shell of hydrogen and an interior metallic shell, which appears only when the last hydrogen line of the Balmer series of the envelope is H 27. In the second part, the study of the line Feii λ 4233 shows the influence of the orbital motion on the profile and, in particular, its effect on the absorption in the envelope. The decrease of the extent of the envelope is shown by means of a series of ‘isophase curves’, which indicates that there is maximum emission whenever, there is maximum envelope extension. The existence of satellite components to the red or violet gives evidence for the existence of heterogeneous velocity layers, contracting more rapidly than the bulk of the envelope during the cycle 100 and expanding more rapidly during cycle 116. The study of theV/R ratio shows that this ratio is independent of the orbital motion and always remains bigger than one. Some layers fall down to the photosphere as the envelope decreases (cycle 100 to 108). These layers participate in the general motion of the envelope (cycles 109 to 112) and then are strongly accelerated towards the border when the general contraction in the envelope increases again (cycles 112 to 116). The nature of the radial velocities indicates a pulsation of the emission layers which is connected with the orbital motion. The direction of the acceleration in the internal layers is reversed from apastron to periastron, while at the same time the acceleration of the internal layers increases. These motions cause changes in the density which could explain the variations of intensity in the spectrum of the envelope. In the third part, we study the photometric variations referring to three time-scales:

1. very short time-scale variations (≤4 hr). These variations can be important, reaching 0.1 mag, and can be described by a model matter ejection in very hot gaseous streams.
2. short time-scale variations (>1 day). These variations are connected with the intensity of the satellite absorptions of the line Feii λ 4233 and could be interpreted as absorption variations in the low layers of the envelope.
3. long time-scale variations (≤3 yr). We observe a perceptible decrease of the amplitude of (b) type variations, but no change in their mean value. We can then determine the AX Mon indices (V=6.77;B?V=+0.33;U?B=?0.66). The amplitude of the variations seems to increase as the envelope increases.

In the fourth part, we show that the spectral type of the hotter star can be estimated to be B0.5 V and for the cold star to be K2 II. The mass-ratio is estimated by choosing the velocity curve of the α Cygni spectrum to represent the B star, this choice leading to results which agree very well with the observations. In the resulting model, the secondary star fills the Roche's lobe and mass exchange can occur between the K star and the B star. The large value of the inclination (i=79°) leads to a quasiequatorial observation and explains why, in spite of the small eccentricity, we can observe tidal effects and the resulting spectral changes. The study of the evolution of the system by means of the theories by Crawford and Plavec shows that the mass exchange began with the commencement of nuclear reactions at the border of the B star. During this evolution, the role of the two components has changed, the original primary becoming the secondary. In this assumption, the present system has exchanged about half of the permitted mass. The emissive zone radius is estimated to be 70R _⊙ by means of Sobolev's theory. This zone is entirely contained within the Roche's lobe of the star and is very sensitive to the gravitational action of the K star.     

Wind dynamics and circumstellar extinction variations in the T Tauri star RY Tau

The wind interaction with the dusty environment of the classical T Tauri star RY Tau has been investigated. During two seasons from 2013 to 2015, we carried out a spectroscopicmonitoring of this star with simultaneous BV R photometry. A correlation between the stellar brightness and the radial velocity of the wind determined from the Hα and Na D line profiles has been found. The irregular stellar brightness variations are shown to be caused by extinction in a dusty disk wind at a distance of about 0.2 AU from the star. We hypothesize that the circumstellar extinction variations result from a cyclic rearrangement of the magnetosphere and coronal mass ejections, which affect the dusty disk wind near the inner boundary of the circumstellar disk.     

Rapid spectral variability of ɛ PerA

The results of high-resolution spectropolari metric observations (R = 60 000) of the B0.5-type subgiant ? PerA are reported. Regular components of line profile variations with the frequencies 3.82–12.99 d^?1 are found. A possible relation between the non-radial pulsations of the star and the observed regular variations of the line profiles is shown. A wavelet analysis of the difference of line profiles in the spectrum of ? PerA is performed. The amplitude of the wavelet spectrum is found to have two maxima at 10–20 and 50–60 km/s velocity scales. It is suggested that the first maxi mum corresponds to the amplitude of fluctuations in the velocity field of large-scale motions in the non-radially pulsating photosphere of the star, whereas the second maximum is associated with the variation of the half widths of spectral line profiles. An upper limit for the effective magnetic field of the star is inferred.     

Very peculiar wind from BD+53°2790, the optical counterpart to 4U 2206+54

BD+53°2790, an O9.5V star, is the optical counterpart to the HMXRB 4U 2206+54. This system was classified initially as a BeX, but observational evidence soon stressed the need to revise this classification. The permanent asymmetry in the Hα line profiles (in contrast with the cyclic variations shown by Be stars), the variations in the profile of this line in time scales of hours (while time scales from weeks to months are expected in Be stars), and the lack of correlation between IR observables and Hα line parameters, strongly suggest that, while BD+53°2790 contains a circumstellar disc, it is not like the one present in Be stars (Blay et al. 2006). Furthermore, there is evidence of overabundance of He in BD+53°2790. Together with the presence of an anomalous wind, found through UV spectroscopy, the possibility to link this star with the group of He rich stars is open. We will discuss the work done with IUE data from BD+53°2790 and the unexpected finding of a slow and dense wind, very rare for an O9.5V star.     

HD 45583—a chemically peculiar star with an unusual curve of longitudinal magnetic field variations

The results of a complex study of the chemically peculiar star HD 45583 are reported. Observations were made using the Main Stellar Spectrograph equipped with a circular polarization analyzer and NES echelle spectrograph of the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. Our measurements of Zeeman spectra show that the star exhibits unusual variations of the longitudinal component of magnetic field with a secondary minimum. The period of spectral and magnetic variability coincides with the rotation period, which is equal to 1.^d177000. Two possible causes of the secondary minimum are discussed: spots with higher than ambient content of some chemical elements on the star’s surface or complex structure of the stellar magnetic field. The parameters of the star’s atmosphere are determined (T _eff = 13000 K, log g = 4.0), as well as the abundances of some elements: the star shows a 1–2 dex overabundance of Fe, Si, and Cr, helium is underabundant by about 2 dex with respect to the Sun.     

Some peculiarities of the variability of the positional and photometric line parameters in the spectrum of HD 93521. Differential rotation of the star

The variability of positional and photometric parameters of the lines in the spectrum of HD 93521 is analyzed using CCD spectra taken with the PFES echelle spectrograph of the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS). To study the velocity field of the star’s atmosphere, the radial velocity variations are measured separately for the blue and red halves of the absorption profile at different levels of residual line intensity. The amplitude and phase of temporal variations of radial velocity differ for the two halves of the absorption profile. In case of strong HeI, Hβ, andHα lines the amplitude depends on intensity r. The time scales (P) of radial velocity variations and the mean halfwidths \(\overline {FW H M} \) differ for different lines and correlate fairly well with their central depths. The increase of P and decrease of \(\overline {FW H M} \) from weak to strong lines are due to the differential nature of the rotation of the star. Our analysis proofs that HD 93521 is a run-away star and this fact explains its location at a distance of about 2.0 kpc above the Galactic plane.     

Evidence for the pulsational origin of the Long Secondary Periods: The red supergiant star V424 Lac (HD 216946)

The results of a long-term UBV photometric monitoring of the red supergiant (RSG) star V424 Lac are presented. V424 Lac shows multiperiodic brightness variations which can be attributed to pulsational oscillations. A much longer period (P = 1601 d), that allows us to classify this star as a long secondary period variable star (LSPV) has been also detected. The B − V and U − B color variations related to the long secondary period (LSP) are similar to those related to the shorter periods, supporting the pulsational nature of LSP. The long period brightness variation of V424 Lac is accompanied by a near-UV (NUV) excess, which was spectroscopically detected in a previous study [Massey, P., Plez, B., Levesque, E.M., et al., 2005. ApJ 634, 1286] and which is now found to be variable from photometry. On the basis of the results found for V424 Lac, the NUV excess recently found in a number of RSGs may be due not solely to circumstellar dust but may also have a contribution from a still undetected LSP variability.     

Long-term variations in the β Cephei stars 16 (EN) Lac and ν Eri

We present results of an investigation of the long-term variations of the amplitudes of the three strongest modes of 16 (EN) Lac and of the period of the strongest mode of ν Eri. We show that in the case of the first star there are feasible explanations of the observed variations. The explanations involve non-linear interaction between pulsation modes (the first two observed modes) and beating between two non-interacting modes of constant amplitudes (the third observed mode). In the case of the second star, however, we can only indicate the difficulty of accounting for the long-term period variation.     

Study of the optical variability of T Tau in the period 1962–2003

We present the results of our long-term U BV R observations of the star T Tauri performed at Mt. Maidanak Observatory from 1986 until 2003. These data, together with previous photoelectric observations of other authors, suggest that the long-term variations of the light curve are not periodic, but have a cycle with a time scale of 6–9 yr. The light curve also exhibits slower variations with time scales of ～30–40 yr. We confirm the existence of periodic brightness variations with a period of \(P = 2\mathop .\limits^d 798\) over many years; this process is peculiar in that the phase and shape of the phase curve change from season to season. We analyze the color behavior of the star. We found evidence of a strong flare occurred on October 5, 1999, when the brightness of the star reached \(9\mathop .\limits^m 22\). This is the strongest flare recorded during its photoelectric observations.     

UBVRI photometry of the eclipsing symbiotic system CI Cygni in 1996–1999

The UBVRI photometry of the eclipsing symbiotic star CI Cyg in 1996–1999 is presented. The system continued to be in quiescence during this period. The shape of the minima in its light curves attributable to eclipses of the compact star with an accretion disk by the red giant is the same as that in 1988–1995. An analysis of our observations and those of other researchers, which span a total of 27 years, has revealed a cyclic variability of the out-of-eclipse photometric properties of CI Cyg on a time scale of about 10.7±0.6 years with the clearest manifestation in the U-B color. The fact that the system’s out-of-eclipse light variations in U, on the one hand, and in BVRI, on the other, occur in antiphase suggests that the titanium red giant plays a significant role in this cyclic process. However, with its contribution to the total U flux being no larger than 10%, the observed light fluctuations of CI Cyg in this band must be caused not only by variability of the giant but also by light variations of the hot component. The presence of a 10.7-year cycle in the system’s active and quiescent states suggests that some precession phenomenon is responsible for it. Precession of the accretion disk, which would cause both the observed brightness of the primary component and the effect of its radiation on the titanium red giant to vary, can serve as an example of such a phenomenon.     

A study of the magnetic field in FK Com

We present the results of our new spectropolarimetric observations of FKCom aimed to measure the longitudinal component B _z of its magnetic field. The most interesting interpretation of our results suggests that the B _z value has significantly decreased compared to the 2008 observations of this star. Such a decrease of the longitudinal component of the magnetic field can be similar to the secular variations of B _z registered earlier for another chromospherically active star II Peg. On the other hand, assuming the existence of B _z variations with the rotation phase, we suggest that the variations of the phase curve B _z from 2008 to 2012 originated because of the strengthening of the negative polarity spot, its domination, and as a result-a generally more symmetric distribution of magnetic regions.     

New results of magnetic field measurements for BP Tau

We present measurements of the longitudinal magnetic field component B _‖ of the young star BP Tau in the He I 5876 emission line formation region, i.e., in the accretion flow near the stellar surface. The values obtained (?1.7 kG and ?1.0 kG in 2000 and 2001, respectively) agree with the results of similar measurements by other authors. At the same time, we show that the previously obtained field strength at the magnetic pole, B _p, and the inclination of the magnetic axis to the rotation axis, β, are untrustworthy. In our opinion, based on the B _‖ measurements available to date, it is not possible to conclude whether the star’s magnetic field is a dipole one or has a more complex configuration and to solve the question of whether this field is stationary. However, we argue that at least in the He I 5876 line formation region, the star’s magnetic field is not stationary and can be restructured in a time of the order of several hours. Nonstationary small-scale magnetic fields of active regions on the stellar surface and/or magnetospheric field line reconnection due to the twisting of these field lines as the star rotates could be responsible for the short-term magnetic field variability. It seems highly likely that there are no strictly periodic variations in brightness and emission line profiles in BP Tau due to the irregular restructuring of the star’s magnetic field.     

Orbital variations and outbursts of the unusual variable star V1129 Centauri

The variable star V1129 Cen is classified in the GCVS as being of β Lyr type. Unusual for such stars, it exhibits outbursts roughly once a year, lasting for ∼ 40 days. For this reason, a relationship to the dwarf novae has been suspected. Here, for the first time a detailed analysis of the light curve of the system is presented. Based on observations with high time resolution obtained at the Observatório do Pico dos Dias and on the long term ASAS light curve the orbital variations of the system are studied. They are dominated by ellipsoidal variations and partial eclipses of a probably slightly evolved F2 star in a binary with an orbital period of 21^h 26^m. Comparison with the characteristics of dwarf novae show that the observational properties of V1129 Cen can be explained if it is just another dwarf novae, albeit with an unusually bright and early type mass donor which outshines the accretion disk and the mass gainer to a degree that many normal photometric and spectroscopic hallmarks of cataclysmic variables remain undetected.     

Photometric and spectroscopic evolution of the symbiotic nova V1016 Cygni after its outburst

We have constructed the light curves of the symbiotic nova V1016 Cyg for the period 1971–2007 in a homogeneous photometric system close to UBV using our observations with the Zeiss-600 SAI telescope. Based on the observational data obtained with the 125-cm SAI telescope in 2000–2007, we have performed absolute spectrophotometry of the star in the range λ3700–9300 Å. The derived line intensities are compared with the data of other authors in the preceding years (1965–1988). The behavior of nebular lines showed the variations in electron density and, probably, electron temperature in the [OIII] emission region caused by a variable stellar wind from the hot component. All the available observations of the star confirm the theoretical conclusion that the nova-like outburst of V1016 Cyg was produced by a thermonuclear flash in the accreted envelope of a white dwarf.     

Similarities and differences in the spectral behavior of W Ser and UX Mon in the ultraviolet

We present ultraviolet spectra of two eclipsing interacting binary systems, W Ser and UX Mon, with good coverage over the 14.16-day and 5.9-day orbital periods, respectively, using observations taken by the International Ultraviolet Explorer (IUE) during the period between 1978–1993 and 1981–1991. Two profiles of W Ser and UX Mon showing variations of line fluxes at two orbital phases are presented. This paper focuses on the N V emission line at 1240 Å, C II emission line at 1336 Å, C IV emission line at 1550 Å, O III emission line at 1666 Å and the Si III emission line at 1892 Å, produced in an extended gaseous envelope around the mass-gaining component by calculating spectral line fluxes. Our results show that there are variations of line fluxes with time, similar to the light curves found for both W Ser and UX Mon. We attribute these spectral variations to eclipse effects and to variations in the mass transfer rate. These results from the IUE observations support the thick disk model around the primary star in which variations of mass transfer affect the observed radiation from the gaseous envelope around the hot star. Future, high-resolution imaging is recommended to confirm the inferred asymmetrical circumstellar envelopes.     

Light variations in the candidate for protoplanetary objects HD 179821=V1427 Aql in 1899–1999

We present photoelectric and photographic observations of the supergiant HD 179821 with a large infrared excess, a candidate for protoplanetary objects. Over, ten years of our UBV observations, the star exhibited semiregular light variations with amplitudes $\Delta V = 0\mathop .\limits^m 10$ , $\Delta B = 0\mathop .\limits^m 15$ , and $\Delta U = 0\mathop .\limits^m 25$ , as well as systematic color and light variations. From 1990 until 1996, the yearly mean U-B and B-V color indices decreased by 0.25 and 0.15, respectively. After 1996, the motion of the star in the two-color (B-V)-(U-B) diagram upward and to the left slowed down. The color excess that we derived from our observations, by assuming that the star’s spectral type was F3 I in the 1990s, is E(B-V)=1.0. The photographic observations of HD 179821 from 1899 until 1989 show that its brightness m _pg generally increased while significantly fluctuating. An analysis of the observational data suggests that HD 179821 is most likely a post-AGB star of intermediate or low mass.     

Slitless spectrograph for small telescopes: First results

A slitless UBVR spectrograph has been built for use on small telescopes. Test observations on the Zeiss-600 telescope at the Terskol peak demonstrated that the spectrograph is an efficient instrument for studying high-speed processes in variable stars with a high temporal resolution. The spectrograph resolving power R ≈ 100 in the vicinity of λ = 480 nm and the error in the determination of the wavelength is approximately 3 nm. The spectrograph provides a moderate signal-to-noise ratio for stars up to 16 ^m . It permits one to measure equivalent widths of unblended lines down to 0.1 nm. The developed special software based on the theory of quantum statistics makes it possible to detect relative variations in the spectrum of approximately 10^?5–10^?6 of the bolometric flux of the star. Observations with the spectrograph made it possible to detect variations of emissions in Balmer lines and Ca II H, K lines in the EV Lac flare star in the subsecond range. The spectroscopic monitoring permits one to study stellar flares with small amplitude, to carry out a comprehensive colorimetric analysis of flare plasma, and to determine temperatures and sizes of flares in the light intensity maximum. Observations of the transit of the HAT-P-1 B exoplanet demonstrate that the chromospheric activity power of the parent star does not vary during the transit. The slitless spectrograph with a low resolving capacity opens new prospects in studying active processes occurring on stars’ surfaces.     

FG Sge at the stage of dust shell ejection

New photometric observations of the variable star FG Sge, a rapidly evolving planetary nebula nucleus, were performed in 2003–2008. On 230 nights, we obtained 86 UBV and 155 BV RI (or R _c , I _c ) magnitude estimates. The maximum amplitude of the V-band light variations was >8 ^m . Six deep minima and four high maxima were observed. Analysis of the light curve has shown that the pulsation period of the star remained constant since 1991 and was P = 115 days. We have studied the wavelength dependence of the extinction at various phases of the light curve. The blueing of the B-V color at deep minima is interpreted as the result of light scattering in the circumstellar dust shell of the star formed by preceding dust ejections since 1992. Our spectroscopic observations performed on nine nights in 2003–2007 with the 125-cm telescope at the Crimean Station of the Sternberg Institute have confirmed the previously detected intensity variations of the Swan bands and the sodium doublet with brightness. It is noted that the Swan bands originate in the upper atmosphere, the star’s extended envelope, while the sodium doublet originates mainly in the circumstellar shell of FG Sge. We suggest that the star is currently located in the temperature-luminosity diagram at the turning point of the horizontal track of cooling in the direction of hot stars—evolution caused by the last helium shell flash at the planetary nebula stage.     

Anisotropic illumination of a circumbinary disk in the presence of a low-mass companion

The model of a young star with a protoplanetary disk and a low-mass companion (q ≤ 0.1) moving in a circular orbit inclined to the disk plane is considered. Hydrodynamic models of such a system have been calculated by the SPH method. The perturbations in the disk caused by the orbital motion of the companion are shown to lead to a strong dependence of the disk illumination conditions on azimuth (because of extinction variations between the star and the disk surface) and, as a result, to the appearance of a large-scale asymmetry in the disk images. Calculations show that the dependence of the disk illumination on azimuth is stronger in the central part of the disk than on the periphery. The bright and dark (shadow) regions are located asymmetrically relative to the line of nodes. The sizes of these regions and their positions on the disk depend on model parameters and orbital phase. During the orbital motion, the bright and dark regions do not follow the companion but execute small-amplitude oscillations relative to some direction. The model properties described above open up new possibilities for detecting low-mass companions in the vicinity of young stars. Stars with protoplanetary disks seen face-on or at low inclinations i are best suited for this purpose.