Close binary systems in star-forming regions: EQ Ori in the Ori I association

Photoelectric (UBVR) observations of the eclipsing variable EQ Ori are presented. The ephemerides of primary minima are refined, and the range of the star’s light variations is determined. All light curves are solved by Lavrov’s direct method, and highly accurate photometric orbital elements are obtained for the system. The magnitudes and colors of each component are calculated and analyzed in two-color (U-B)-(B-V) and (U-B)-(V-R) diagrams. The system’s primary component is classified as a metallic-line Am star. The absolute parameters of the components are estimated, and the binary is classified as a detached system with a subgiant: A0 V and K2 IV. EQ Ori has a faint physical companion, which causes the epochs of primary minimum to be systematically displaced with a period of about 30 years. The expected parameters of the distant companion are estimated. The system’s components are at a pre-ZAMS evolutionary stage, with their age being 2×10⁶ years. EQ Ori is thought to be a member of the Ori I association.     

The Hβ and Hγ lines in the spectrum of V1057 Cyg

We present the equivalent widths of the Hβ and Hγ absorption lines in the spectrum of V1057 Cyg measured from 1978–1990 spectrograms. The mean equivalent widths of these lines decreased approximately twofold during 1978–1985 and somewhat increased during 1987–1990. Using published UBV photometry, we show that there has been a correlation between the Hβ equivalent width and the ?U-B? color since 1983, with ?W _λ(Hβ)? increasing with decreasing?U-B? Based on our spectroscopic and photometric observations in 1978–1990, we assume that V1057 Cyg has passed to a qualitatively new stage of its development after 1985.     

Nova Monocerotis 2002 (V838 Mon) at early outburst stages

We obtained U BV R photometric and spectroscopic observations during the outburst of V838 Mon. Before its outburst, the B brightness of the star had been stable ( $\tilde15.^m 85$ ) for 45 years. This was a blue star with the color index $(B - V)_0 = - 0\mathop .\limits^m 03 \pm 0\mathop .\limits^m 1$ and may have been a cataclysmic variable. In the middle of March 2002, the outburst amplitude reached $8\mathop .\limits^m 1$ in B. The star has the counterpart V 1006/7 in M 31 in luminosity at maximum and in spectrum. The unusual spectrum at the premaximum stage originated in the expanding photosphere of a cool K-type giant. The expansion velocity of the photosphere was 150 km s^?1; the maximum velocity in the expanding stellar envelope reached 500 km s^?1. The absorption components of neutral metal lines were enhanced by a factor of 3 or 4 compared to a normal K-type star. No overabundance of s-process elements was found. One day before the brightness peak, an intense Hα emission line with broad wings, FWZI=3100 km s^?1, and numerous lines of ionized metals appeared in V838 Mon, which is characteristic of normal classical novae. We show light, color, and spectral variations of the object.     

Absolute magnitudes and kinematic parameters of the subsystem of RR Lyrae variables

The statistical parallax technique is applied to a sample of 262 RRab Lyrae variables with published photoelectric photometry, metallicities, and radial velocities and with measured absolute proper motions. Hipparcos, PPM, NPM, and the Four-Million Star Catalog (Volchkov et al. 1992) were used as the sources of proper motions; the proper motions from the last three catalogs were reduced to the Hipparcos system. We determine parameters of the velocity distribution for halo [(U ₀, V ₀, W ₀) = (?9±12, ?214 ±10, ? 10, ?16±7) km s ^?1 and (σ _U , σ _V , σ _W ) = (164±11, 105±7, 95±7) km s ^?1] and thick-disk [(U ₀, V ₀, W ₀) = (?16±8, ?41±7, ?18±5) km s ^?1], and [(σ _U , σ _V , σ _W ) = (53±9, 42±8, 26±5) km s ^?1] RR Lyrae, as well as the intensity-averaged absolute magnitude for RR Lyrae of these populations: 〈M _V 〉 = 0.77 ± 0.10 and 〈M _V 〉 = +1.11 ± 0.25 for the halo and thickdisk objects, respectively. The metallicity dependence of the absolute magnitude of RR Lyrae is analyzed (〈M _V 〉 = (0.76 ± 0.12) + (0.26 ± 0.26) · ([Fe/H]+1.6)=1.17+0.26 · [Fe/H]). Our results are in satisfactory agreement with the ?M _V ?(RR)?[Fe/H]relation from Carney et al. (1992) (〈M _V 〉(RR)=1.01+0.15·[Fe/H]) obtained by Baade-Wesselink's method. They provide evidence for a short distance scale: the LMC distance modulus and the distance to the Galactic center are 18.22±0.11 and 7.4±0.5 kpc, respectively. The zero point of the distance scale and the kinematic parameters of the RR Lyrae populations are shown to be virtually independent of the source of absolute proper motions used and of whether they are reduced to the Hipparcos system or not.     

Minimum on the light curve of the classical symbiotic star AS 338 in 1999

We present our UBVRI photometry and spectroscopy of AS 338 performed in 1999–2000. Another eclipse of the hot component in this symbiotic binary system, the deepest one ever observed, occurred in September 1999. The U brightness declined by ～2^m, the Hβflux decreased by a factor of ～2.3, and the [O III]γ5007 flux did not change. The hot component is eclipsed at orbital phases ?≈0.045–0.057. The U-B color index begins to appreciably fluctuate during an eclipse of the hot component and its circumstellar envelope. About 100 days after a strong outburst of 1995, the mean UBV brightness of AS 338 declined linearly in the ensuing five years at the same rate in all bands (ΔU/Δt≈10^?3 mag/day). The brightness of the outer, uneclipsed parts of the circumstellar envelope also decreased, which is attributable to a reduction in the luminosity of the hot component against the rise in its temperature. The appearance of He II lines has not yet been recorded, though the optical brightness of AS 338 has already dropped by ～2^m after the outburst.     

Analysis of the HST ultraviolet spectra for T Tauri stars: RY Tau and HD 115043

The ultraviolet spectra of the stars RY Tau and HD 115043 from the Hubble Space Telescope are analyzed. RY Tau belongs to the classical T Tauri stars, while HD 115043 is a young (t~3×10⁸ years), chromospherically active star. The most intense emission lines were identified, and their fluxes were measured. Low-resolution spectra of RY Tau and HD 115043 in the wavelength range 1160–1760 Å exhibit almost the same set of emission lines. However, first, the luminosity of RY Tau in these lines is approximately a factor of 300 higher than that of HD 115043, and, second, the relative line intensities differ greatly. The intensity ratio of the C IV λ1550, Si IV λ1400, and NV λ1240 doublet components is close to 1: 2 in the spectra of both stars. Judging by the continuum energy distribution, the spectral type of RY Tau is later than that of HD 115043. Synchronous flux variability in the C IV λ1550 and He II λ1640 lines in a time of ~20 min was detected in RY Tau. The flux rise in these lines was accompanied by a redshift of the intensity peak in the profiles by~50 km s^?1. Intermediate-resolution spectra are used to study line profiles in the spectrum of RY Tau. In particular, the profiles of (optically thin) Si III]λ1892 and C III]λ1909 lines were found to be asymmetric and about 300 km s^?1 in width. The (optically thick) C IV λ1550 doublet lines have similar profiles. The Mg II λ2800 doublet lines are also asymmetric, but their shape is different: they consist of a broad (?750 km s^?1 at the base) emission component on which an interstellar absorption line shifted from the line symmetry center by about 20 km s^?1 is superimposed. The intensity ratio of the Mg II λ2800 doublet components is?1.4. Whether there are molecular hydrogen lines in the spectrum of RY Tau is still an open question. It is shown that the emission lines in the ultraviolet spectrum of RY Tau cannot originate in a hydrostatically equilibrium chromosphere. It is argued that quasi-steady accretion of circumstellar matter is responsible for the emission.     

Hydrodynamic processes of angular momentum transport in the interior of a rotating massive hydrogen-burning star

The evolution of a rotating star with a mass of 16M _⊙ at the hydrogen burning phase is considered together with the hydrodynamic processes of angular momentum transport in its interior. Shear turbulence is shown to limit the amplitude of the latitudinal variations in mean molecular weight on a surface of constant pressure in a layer with variable chemical composition. The resulting nonuniformity in the mean molecular weight distribution and the turbulent energy transport along the surface of constant pressure reduce the absolute value of the meridional circulation velocity. Nevertheless, meridional circulation remains the main mechanism of angular momentum transport in the radial direction in a layer with variable chemical composition. The intensity of the processes of angular momentum transport by meridional circulation and shear turbulence is determined by the angular momentum of the star. At a fairly high angular momentum, more specifically, at J = 3.69 × 10⁵² g cm² s^?1, the star during the second half of the hydrogen-burning phase in its convective core has characteristics typical of classical early Be stars.     

Eu III oscillator strengths and europium abundances in Ap stars

We present our calculations of the spectrum and oscillator strengths for the 4f⁷?(4f⁶5d+4f⁶6s) Eu III transitions. The calculations were performed with Cowan's RCN-RCG-RCE codes in the single-configuration approximation. A comparison of computed level lifetimes with experimental data for three levels shows that the scale of theoretical oscillator strengths could be overestimated by a factor of 3. The theoretical oscillator strengths of red Eu III lines are two orders of magnitude smaller than their astrophysical oscillator strengths derived by Ryabchikova et al. (1999) from the condition of ionization balance. The new oscillator strengths were tested by analyzing the Eu abundance using Eu II and Eu III lines in the spectra of hot peculiar stars (α² CVn is a typical representative) and cool peculiar stars (β CrB is a typical representative). First, we computed non-LTE corrections, which proved to be significant for α² CVn. We also analyzed the Eu II λ6645.11-Å line as well as ultraviolet and optical Eu III lines. We show that the new oscillator strengths together with the non-LTE corrections allow the contradiction between the Eu abundances derived by Ryabchikova et al. (1999) separately from optical Eu II and Eu III lines in α² CVn to be resolved. The new Eu abundance, log(Eu/N _tot)=?6.5, also faithfully describes the blended near-ultraviolet resonance Eu III lines. Using the new Eu III oscillator strengths to analyze the spectrum of the cool Ap star β CrB, we found a significant deviation of the n(Eu II)/n(Eu III) ratio from its equilibrium value. For a chemically homogeneous model atmosphere, to obtain the observed intensity of the Eu III λ 6666.35-Å line, the Eu abundance must be increased by two orders of magnitude compared to that required to describe the Eu II λ 6645.11-Å line. We discuss the possibility of explaining the observed intensities of Eu II and Eu III lines in the spectrum of β CrB by the presence of an inhomogeneous atmosphere with Eu concentrated in its uppermost layers. In such atmospheres, the role of non-LTE effects becomes dominant.     

Infrared observations of the star R Cas

We present our JHKLM photometry for R Cas performed during 1988–2000. The pulsation period of R Cas is $P \approx 429\mathop .\limits^d 6$ , with the maximum IR brightness lagging behind the maximum visual brightness by ～0.2 P. The amplitude of light variations appreciably decreases with increasing wavelength at λ≤3 μm. At λ>3 μm, this decrease virtually ceases. There is a step on the ascending branch of IR JHK brightness. The K-L color index increases linearly with K magnitude: $K - L = 0.304K + 1\mathop .\limits^m 20$ . The color temperature dependence, T _K-L =f(K), is also linear: T _K?L = ?622K + 1100 K. In going from minimum to maximum, the K flux (as well as the bolometric flux) from the star and its color temperature T _K-L increase by a factor of ～2.2 and ～1.3, respectively.     

Infrared photometry for five close binary systems

We present the JHKLM photometry for five close (W Ser) binary systems obtained in the period 1996–2004. Positive phase shifts (with respect of the adopted ephemerides) have been found in the orbital infrared light curves for three binaries, RX Cas, KX And, and β Lyr; the rates of increase in their periods are ～3.5 × 10^?4, ～1.6 × 10^?3, and ～1.4 × 10^?4 days yr^?1, respectively. We have performed the spectral classification of the components of the binaries under study and estimated their parameters.     

The orbital period of Nova Aquilae 1999 No. 2 (V1494 Aql)

The photometric monitoring of Nova V 1494 Aql at the Sternberg Astronomical Institute and at the Special Astrophysical Observatory in July and September 2002 has confirmed that the star is an eclipsing system. Its orbital period was improved, \(0\mathop .\limits^d 1346141(5)\). Light elements and eight mid-eclipse times are given. The light-curve shape suggests that the star is an intermediate polar.     

Effect of partial mixing of matter on the hydrodynamic angular momentum transport processes in massive main-sequence stars

We consider the evolution of a rotating star with a mass of 16M _⊙ and an angular momentum of 3.25 × 10⁵² g cm² s^?1, along with the hydrodynamic transport of angular momentum and chemical elements in its interiors. When the partial mixing of matter of the turbulent radiative envelope and the convective core is taken into account, the efficiency of the angular momentum transport by meridional circulation in the stellar interiors and the duration of the hydrogen burning phase increase. Depending on the Schmidt number in the turbulent radiative stellar envelope, the ratio of the equatorial rotational velocity to the circular one increases with time in the process of stellar evolution and can become typical of early-type Be stars during an additional evolution time of the star on the main sequence. Partial mixing of matter is a necessary condition under which the hydrodynamic transport processes can increase the angular momentum of the outer stellar layer to an extent that the equatorial rotational velocity begins to increase during the second half of the evolutionary phase of the star on the main sequence, as shown by observations of the brightest stars in open star clusters with ages of 10–25 Myr. When the turbulent Schmidt number is 0.4, the equatorial rotational velocity of the star increases during the second half of the hydrogen burning phase in the convective core from 330 to 450 km s^?1.     

An electronic version of the second volume of the General Catalogue of Variable Stars with improved coordinates

We present a new electronic version of the second volume of the fourth edition of the General Catalogue of Variable Stars (GCVS), which contains data on 13480 variable stars in the constellations Cygnus-Orion (the order of constellations in the Catalogue follows the Latin alphabet). The new version takes into account the Name Lists of Variable Stars from no. 67 to 76 for the same constellations. The main distinctive feature of the new version is that it contains improved equatorial J2000.0 coordinates for 13446 stars (including those for 5052 stars with an allowance made for proper motions), based on the identifications with positional catalogs using finding charts, as well as on our new measurements. We searched for a number of stars on original plates from the collections of several observatories and using digital sky survey images. The new version also includes a file of remarks to the second and third GCVS volumes. Apart from a complete update of the positional information, we took into account several corrections that were found to be necessary after the publication of the second GCVS volume (1985). We present a list of references to new Internet resources.     

Spectrum of the star BM Ori at minimum light

Two spectra of the star BM Ori were obtained with the 2.6-m Crimean Astrophysical Observatory telescope near its maximum eclipse phase. The light detector was a CCD array. The wavelength range 5305–5373 Å was chosen in such a way that it contained no strong primary lines. Optimum filtration of the spectra yielded a signal-to-noise ratio of ～300. Eighteen secondary lines are seen in the spectrum. Atmospheric parameters of the secondary star were determined: T _eff=5740 K and logg=3.0; the secondary was classified by these parameters as being of spectral type G2 III. The best agreement between observed and synthetic spectra is achieved for metallicity [M/H]=?0.5 and microturbulence ξ_t=0 km s^?1. The projected rotational velocity is Vsini=60 km s^?, in agreement with the synchronous velocity in the hypothesis that assumes a total eclipse by the secondary star. Atmospheric elemental abundances in the secondary are estimated. Nickel, chromium, and iron exhibit an underabundance of ～1 dex.     

Evolution of low-mass helium stars in semidetached binaries

We systematically investigate the evolution of low-mass (0.35, 0.40, and 0.65M _⊙) helium donors in semidetached binaries with white-dwarf accretors. The initial periods of the binaries are chosen in such a way that the helium abundance in the center of the models at the time of Roche lobe overflow varies between Y _c = 0.98 and Y _c ? 0.1. The results of our calculations can be used to analyze the formation scenarios and evolutionary status of AM CVn stars. We show that the minimum orbital periods of the semidetached binaries depend weakly on the total mass of the components and the evolutionary phase of the donor at the time of Roche lobe overflow and are 9–10 min. The differences in the mass transfer rates after P _orb reaches its minimum in the range P _orb ≈ 10–40 min do not exceed a factor of ～2.5. For P _orb ? 20 min, the mass-losing stars are weakly degenerate homogeneous cooling objects; the He, C, N, O, and Ne abundances depend on the evolutionary phase at which Roche lobe overflow occurred. For the binaries that are currently believed to be the most probable candidates for AM CVn stars with helium donors, Y ? 0.4, X _C ? 0.3, X _O ? 0.25, and X _N ? 0.5 × 10^?2. In the binaries under consideration, once P _orb ≈ 40 min has been reached, the mass loss time scale begins to exceed the thermal time scale of the donors, the latter begin to contract, their matter becomes degenerate, and the populations of AMCVn stars with white-dwarf and helium-star progenitors of their donors probably merge together.     

An electronic version of volume I of the General Catalogue of Variable Stars with improved coordinates

We present a new electronic version of the first volume of the General Catalogue of Variable Stars (GCVS), fourth edition, which contains data on 10558 variable stars in Andromeda-Crux (the constellations are ordered in the Catalog according to the Latin alphabet). This version incorporates the name lists of variable stars from no. 67 to no. 76 for the same constellations. The main distinctive feature of the new version is that it provides improved equatorial J2000.0 coordinates for 10349 stars (including those for 4587 stars corrected for proper motions). These are based on identifications with positional catalogs using finding charts and on our new measurements. We searched for a number of stars on original plates from the plate collections of several observatories. The version also includes a file of remarks to the first GCVS volume and a preliminary version of the file of bibliographic references to the entire fourth edition of the GCVS. Apart from a complete update of the positional information, the new version incorporates all the other corrections that were found to be necessary after the first GCVS volume was published (1985).     

Optical spectrum of the infrared source IRAS 20004+2955 (V1027 Cyg)

Based on high-dispersion echelle spectra taken with the 6-m Special Astrophysical Observatory telescope, we study the IR source IRAS 20004+2955 identified with the variable star V1027 Cyg. We have determined the star’s fundamental parameters (T _eff=5000 K, logg=1.0), metallicity ([Fe/H]=?0.2 dex), and atmospheric abundances of 16 elements. Its metallicity, carbon underabundance, and slight overabundance of the heavy elements Zr, Y, Ce, and Eu suggest that V1027 Cyg belongs to the Galactic disk population.     

Analysis of HST and IUE ultraviolet spectra for T Tauri stars: DF Tau

We analyze ultraviolet spectra of DF Tau, a binary system whose primary component is a classical T Tauri star. The spectra were obtained from the Hubble Space Telescope and the IUE satellite. The stellar emission in the wavelength range covered is shown to originate in an accretion shock wave. The gas infall velocity is ～250 km s^?1. The accreted-gas density is typically N ₀≤10¹¹ cm^?3, but it can occasionally be higher by one and a half orders of magnitude. The continuum intensity near λ=1900 Å was found to be virtually constant for such a significant change in N ₀. The star’s photometric variability is probably attributable to variations in accreted-gas density and velocity, as well as to variations in the area of a hot spot on the stellar surface and in its orientation relative to the observer. The mean accretion rate is $\dot M \sim 3 \times 10^{ - 9} M_ \odot yr^{ - 1}$ . The interstellar extinction for DF Tau is $A_V \simeq 0\mathop .\limits^m 5$ , the stellar radius is ≤2R _⊙, and the luminosity of the primary component is most likely no higher than 0.3 L _⊙. We argue that the distance to DF Tau is about 70 pc. Upper limits are placed on the primary’s coronal emission measure: EM(T=10⁷ K)<3×10⁵⁴ cm^?3 and EM(T=1.3×10⁶ K)<3×10⁵⁵ cm^?3. Absorption lines originating in the stellar wind were detected in the star’s spectrum. Molecular hydrogen lines have essentially the same radial velocity as the star, but their full width at half maximum is FWHM ?50 km s^?1. We failed to explain why the intensity ratio of the C IV λ1550 doublet components exceeds 2.