A rare reflection effect eclipsing sdB+dM binary: 2M 1533+3759

In this paper, we report a rare reflection effect eclipsing sdB+dM binary, 2M?1533+3759. It is the seventh eclipsing sdB+dM binary that has been discovered to date. This system has an orbital period of 0.16177042 day and a velocity semi-amplitude of 71.1 km?s^?1. Using a grid of zero-metallicity NLTE model atmospheres, we derived T _eff=29250 K, log?g=5.58 and [He/H]=?2.37 from spectra taken near the reflection effection minimum. Lightcurve modeling resulted in a system mass ratio of 0.301 and an orbital inclination angle of 86.6°. The derived primary mass for 2M?1533+3759, 0.376±0.055 M _⊙, is significantly lower than the canonical mass (0.48 M _⊙) found for most previously investigated sdB stars. This implies an initial progenitor mass >1.8 M _⊙, at least a main sequence A star and perhaps even one massive enough to undergo non-degenerate helium ignition.     

Constraining the degree of the dominant mode in QQ Vir

We present early results of the application of a method which uses multicolor photometry and spectroscopy for ? discrimination. This method has been successfully applied to the pulsating hot subdwarf Balloon?090100001. Here we apply the method to QQ?Vir (PG1325+101). This star was observed spectroscopically and photometrically in 2008. Details on spectroscopy can be found in Telting et al. (Astrophys. Space Sci. 2010, this volume), while photometry and preliminary results on ? discrimination are provided here. The main aim of this work was to compare the value of the ? parameter derived for the main mode in QQ?Vir to previously published values derived by using different methods.     

Close encounters of a rotating star with planets in parabolic orbits of varying inclination and the formation of hot Jupiters

In this paper we extend the theory of close encounters of a giant planet on a parabolic orbit with a central star developed in our previous work (Ivanov and Papaloizou in MNRAS 347:437, 2004; MNRAS 376:682, 2007) to include the effects of tides induced on the central star. Stellar rotation and orbits with arbitrary inclination to the stellar rotation axis are considered. We obtain results both from an analytic treatment that incorporates first order corrections to normal mode frequencies arising from stellar rotation and numerical treatments that are in satisfactory agreement over the parameter space of interest. These results are applied to the initial phase of the tidal circularisation problem. We find that both tides induced in the star and planet can lead to a significant decrease of the orbital semi-major axis for orbits having periastron distances smaller than 5?C6 stellar radii with tides in the star being much stronger for retrograde orbits compared to prograde orbits. Assuming that combined action of dynamic and quasi-static tides could lead to the total circularisation of orbits this corresponds to observed periods up to 4?C5 days. We use the simple Skumanich law to characterise the rotational history of the star supposing that the star has its rotational period equal to one month at the age of 5 Gyr. The strength of tidal interactions is characterised by circularisation time scale, t _ev , which is defined as a typical time scale of evolution of the planet??s semi-major axis due to tides. This is considered as a function of orbital period P _obs , which the planet obtains after the process of tidal circularisation has been completed. We find that the ratio of the initial circularisation time scales corresponding to prograde and retrograde orbits, respectively, is of order 1.5?C2 for a planet of one Jupiter mass having P _obs ~ 4 days. The ratio grows with the mass of the planet, being of order five for a five Jupiter mass planet with the same P _orb . Note, however, this result might change for more realistic stellar rotation histories. Thus, the effect of stellar rotation may provide a bias in the formation of planetary systems having planets on close orbits around their host stars, as a consequence of planet?Cplanet scattering, which favours systems with retrograde orbits. The results reported in the paper may also be applied to the problem of tidal capture of stars in young stellar clusters.     

V2324 Cyg—an F-type star with fast wind

High-resolution optical spectroscopy of the V2324 Cyg variable star associated with the IR source IRAS 20572+4919 is performed for the first time. More than 200 absorption features (mostly Fe II, Ti II, Cr II, Y II, Ba II, and Y II) are identified in the wavelength interval from 4549 to 7880 Å. The spectral type and rotation velocity of the star are found to be F0 III and V sin i = 69 km/s, respectively. Neutral-hydrogen and NaI D lines have complex P Cyg-type profiles. Neither systematic trend of radial velocity V_r with line depth R_o nor temporal variability of V_r have been found. We found that the value for the average heliocentric radial velocity is V_r = ?16.8 ± 0.6 km/s. The radial velocities inferred from the cores of the absorption components of the Hβ and NaI wind lines vary from ?140 to ?225 km/s (and the expansion velocities of the corresponding layers, from about 120 to 210 km/s). The maximum expansion velocity is found for the blue component of the split Hα absorption: 450 km/s for December 12, 1995. The method of model atmospheres is used to determine the following parameters of the star: effective temperature T _eff = 7500 K, surface gravity log g = 2.0, microturbulence velocity ξ _t = 6.0 km/s, and metallicity, which is equal to the solar value. The main peculiarity of the chemical composition of the star is the overabundance of lithium and sodium. The results cast some doubt on the classification of V2324 Cyg as a post-AGB star.     

The Nature of the Faint Radio Source Population and Star Formation History derived from Sub-MJY Surveys

We present new results on the nature of the faint radio galaxy population obtained from a deep identification study in the Marano Field. This work represents the highest identification fractions attained to date in literature for sub-mJy radio samples. Star-forming galaxies constitute a significant fraction of the optical counterparts of sub-mJy radio sources, although they are not the dominant identification class (as formerly believed). We also present a new determination of the co-moving star formation density from z=0 to z?0.35 using the radio luminosity function of star-forming galaxies. For the local determination, we used a sample of 231 spiral galaxies taken from the B≤12 Revised Shapley-Ames Catalogue, while for the non-local determination, we used a sample of87 star-forming galaxies taken from the Benn et al. (1993) sample. The inferred local star formation rate is about twice as great as the H_α estimate, while the intermediate 0.05<z<0.35 star formation rate is consistent with coeval ultraviolet and H_α estimates. This is due to large-scale structure, rarely accounted for in estimates of the cosmic star formation history; the situation could improve significantly with deep moderate-area radio surveys.     

氦白矮星与小质量主序星并合及脉动热亚矮星的形成

sdBVrs型热亚矮星是一类特殊的热亚矮星,观测显示它们同时具有p模和g模的脉动.目前这一类热亚矮星的演化起源仍然缺乏完备的解释.对氦白矮星与小质量主序星并合模型进行详细计算表明,并合模型的结果符合sdBVrs型热亚矮星的表面有效温度、重力加速度等观测特征,并且能够激发出稳定的p模和g模脉动.因此,氦白矮星与小质量主序星并合是形成sdBVrs型热亚矮星可能的渠道之一.     

Magnetic fields and rotation of the white dwarfs 40 Eri B and WD 0009+501

We describe the results of our magnetometric monitoring of two white dwarfs: 40 Eri B and WD 0009+501. We found periodic variations in the longitudinal magnetic field of 40 Eri B. The field variability with an amplitude of ～4 kG and a zero mean is discussed in terms of an oblique rotator model. The rotation period is ～5 h 17 min, but there is another period of 2 h 25 min that may be related to nondipolar field components. The published projected rotational velocities of 40 Eri B measured from a narrow non-LTE Hα peak V sin i?8 km s^?1 are in good agreement with our measurements of the magnetic field and the rotation period. The combined effect of magnetic and rotational broadening of the central Hα component constrains the rotation period, P? 5.2 h. We discovered the rotation period (1.83 h) of the magnetic white dwarf WD 0009+501. The period was found from the periodically varying magnetic field of the star with a mean 〈B_e〉 = ?42.3±5.4 kG and a half-amplitude of 32.0±6.8 kG.     

Open clusters IC 4665 and Cr 359 and a probable birthplace of the pulsar PSR B1929+10

Based on the epicyclic approximation, we have simulated the motion of the young open star clusters IC 4665 and Collinder 359. The separation between the cluster centers is shown to have been minimal 7 Myr ago, 36 pc. We have established a close evolutionary connection between IC 4665 and the Scorpius-Centaurus association — the separation between the centers of these structures was ≈200 pc 15 Myr ago. In addition, the center of IC 4665 at this time was near two well-known regions of coronal gas: the Local Bubble and the North Polar Spur. The star HIP 86768 is shown to be one of the candidates for a binary (in the past) with the pulsar PSR B1929+10. At the model radial velocity of the pulsar V _r = 2 ± 50 km s^?1, a close encounter of this pair occurs in the vicinity of IC 4665 at a time of ?1.1 Myr. At the same time, using currently available data for the pulsar B1929+10 at its model radial velocity V _r = 200 ± 50 km s^?1, we show that the hypothesis of Hoogerwerf et al. (2001) about the breakup of the ζ Oph-B1929+10 binary in the vicinity of Upper Scorpius (US) about 0.9 Myr ago is more plausible.     

High-mass X-ray binaries and recent star formation history of the Small Magellanic Cloud

We study the relation between high-mass X-ray binary (HMXB) population and recent star formation history (SFH) for the Small Magellanic Cloud (SMC). Using archival optical SMC observations, we have approximated the color-magnitude diagrams of the stellar population by model stellar populations and, in this way, reconstructed the spatially resolved SFH of the galaxy over the past 100 Myr. We analyze the errors and stability of this method for determining the recent SFH and show that uncertainties in the models of massive stars at late evolutionary stages are the main factor that limits its accuracy. By combining the SFH with the spatial distribution of HMXBs obtained from XMM-Newton observations, we have derived the dependence of the HMXB number on the time elapsed since the star formation event. The number of young systems with ages ? 10 Myr is shown to be smaller than the prediction based on the type-II supernova rate. The HMXB number reaches its maximum ～20–50 Myr after the star formation event. This may be attributable, at least partly, to a low luminosity threshold in the population of X-ray sources studied, L _min ～ 10³⁴ erg s^?1. Be/X systems make a dominant contribution to this population, while the contribution from HMXBs with black holes is relatively small.     

Velocity Law in the Extended Photosphere of the WN5 Star in the Eclipsing Binary V444 Cygni

An algorithm for the solution of Fredholm's equations of the first kind describing light curves of WR + O binary systems on a set of nonnegative monotonically decreasing convex functions is developed. The algorithm is applied to the narrow-band continuum The λ4244 Ålight curve of the eclipsing binary V444 Cygni (WN5 + O6). Reliable information about the distribution of the linear absorption coefficientα (r) and the velocity law in the extended photosphere of the WN5 star is obtained from the analysis. Recent accurate spectrophotometric estimate of the luminosity ratio of the components in the binary was used to establish the relationship between the two geometrical parameters of the model: the radius of the O6 star and the orbital inclination. It is shown that the flow of matter in the WN5 photosphere is accelerating and that the value of the acceleration is relatively low. The expansion velocity at the distance r ? 3.8R _⊙ (at which_τ4244(r) ? 1) reaches a few hundreds km/s, i.e., the flow at this point is supersonic.     

Magnetic field measurement of the star HD 35298

Based on the spectropolarimetric data obtained at the 6-m telescope, a study of the magnetic field and physical parameters of the magnetic He-weak star HD 35298 was performed. A comparison of the results of magnetic field measurements by various methods has been carried out. The star’s magnetic field varies in the range from ?3 to +3 kG. The field geometry is explained in terms of the oblique rotator model. The obtained magnetic field variation curve can be described by a central dipole with the dipole axis inclined to the axis of rotation by β = 60°, and the magnetic field strength at the pole of B _p = 11.5 kG. The data on the variability of spectral lines of some metals are presented, allowing to make an assumption that the stellar surface is heavily spotted.     

The radio galaxy RC J1148+0455

Based on data from the MIT-GB-VLA 4850-MHz survey, we investigate the radio structure of RC J1148+0455 with a steep radio spectrum (α=?1.04) from the COLD catalog. The radio source consists of two components, each having a complex structure. We analyze an optical identification of the source by using 6-m telescope images. The centroid of the radio source falls on a group of eight galaxies at a 24 ^m level in R.     

Density dependence of the line source functions in scattering media

We have calculated source functions in a scattering medium in which the density changes according to the law ofN _e (r)～r ⁿ wheren takes the value from ?3 to +3(1) andN _e (r) is the electron density. We have assumed that the media consist of electrons and we have also considered a geometrically extended media in which the outer radii are 2, 3, 5 times the inner radius. The source functions obtained are completely due to electron scattering. It is found that the source function varies considerably for different variations of density changes fromn=?3 to +3. In the case of density variation withn=?3 and ?2, the source functions do not increase with optical depth considerably, but whenn=?1, 0, they rise slowly with the increase in optical depths and whenn=1 to 3 there is a steep rise in the source functions with the optical depth increasing towards the center of the star.     

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.     

Non-LTE modeling of narrow emission components of He and Ca lines in optical spectra of classical T Tauri stars

Using LTE calculations of the structure of T Tauri stellar atmospheres heated by radiation from an accretion shock (Dodin and Lamzin 2012), we have calculated the spectrum of the hot spot emerging on the stellar surface by taking into account non-LTE effects for He I, He II, Ca I, and Ca II. Assuming the pre-shock gas density N ₀ and velocity V ₀ to be the same at all points of the accretion stream cross section, we have calculated the spectrum of the star+circular spot system at various N ₀, V ₀, and parameters characterizing the star and the spot. Using nine stars as an example, we show that the theoretical optical spectra reproduce well the observed veiling of photospheric absorption lines as well as the profiles and intensities of the so-called narrow components of He II and Ca I emission lines with an appropriate choice of parameters. The accreted gas density in all of the investigated stars except DK Tau has been found to be N ₀ > 10¹² cm^?3. We have managed to choose the parameters for eight stars at a calcium abundance in the accreted gas ξ _Ca equal to the solar one, but we have been able to achieve agreement between the calculations and observations for TW Hya only by assuming ξ _Ca to be approximately a factor of 3 lower than the solar one. The estimated parameters do not depend on interstellar extinction, because they have been determined from the spectra normalized to the continuum level. The calculated intensity of Ca II lines has turned out to be lower than the observed one, but this contradiction can be eliminated by assuming that, in addition to the accreted gas with a high density N ₀, a more rarefied gas also falls onto the star. The theoretical equivalent widths and relative intensities of the subordinate He I lines disagree significantly with the observations. This is apparently because non-LTE effects should be taken into account when calculating the structure of the upper layers of the hot spot, the accuracy of the cross sections for collisional processes from upper levels is insufficient, and the spot inhomogeneity should probably be taken into account.     

Magnetic stars with wide depressions in the continuum. 2. The silicon star with a complex field structure HD 27404

Observations of the chemically peculiar star HD 27404 with the 6-m SAO RAS telescope showed a strong magnetic field with the longitudinal field component varying in a complicated way in the range of ?2.5 to 1 kG. Fundamental parameters of the star (T_eff = 11 300 K, log g = 3.9) were estimated analyzing photometric indices in the Geneva and in the Stro¨ mgren–Crawford photometric systems. We detected weak radial velocity variations which can be due to the presence of a close star companion or chemical spots in the photosphere. Rapid estimation of the key chemical element abundance allows us to refer HD 27404 to a SiCr or Si+ chemically peculiar A0–B9 star.     

On the Evolutionary State of High-Latitude Variable V534 Lyr

Based on the high spectral resolution monitoring conducted at the 6-m BTA telescope, we study the optical spectrum of the high-latitude variable V534 Lyr. Heliocentric radial velocities V_r corresponding to the positions of all metal absorption components, as well as the Na I D and Hα lines were measured during all the observational sets. The analysis of the velocity field examining the lines of various nature revealed a low-amplitude variability of V_r based on the lines with a high excitation potential, which are formed in deep layers of the stellar atmosphere, and allowed to estimate the systemic velocity of V_sys ≈ ?125 kms^?1 (V_lsr ≈ ?105 kms^?1). The distance estimate of d ≈ 6 kpc for the star leads to its absolute magnitude of \(M_V \approx - 5_ \cdot ^m 3\), what corresponds to the spectral classification. The previously undetected spectral phenomenon was revealed for this star: at certain times a splitting of the profiles of low-excited absorptions is observed, reaching ΔV_r = 20–50 kms^?1. A combination of the parameters: reduced metallicity [Met/H]_⊙ = ?0.28, high nitrogen abundance [N/Fe] = +1.10, large spatial velocity, high luminosity, a strong variability of the emission-absorption profiles of HI lines, splitting of metal absorptions at different times of observations and the variability of the velocity field in the atmosphere allow to classify V534 Lyr as a pulsating star in the thick disk of our Galaxy.     

Magnetic stars with wide depressions in the continuum. 1. The Ap star with strong silicon lines HD5601

Based on observations with the 6-m SAO RAS telescope, we have found that chemically peculiar star with a large depression of the continuum at λ5200 Å and strengthened silicon lines in the spectrum has a strong magnetic field. The longitudinal field component B_e has a negative polarity and varies from ?300 G to ?2000 G with a period of 1.756 days. Photometric variations of brightness take place with the same period. We determined the variability of the radial velocity at times of about tens of years pointing to a possible binarity of the object. We have built a magnetic model of this star, determined the inclination angles of the rotation axis to the line of sight i = 20° and of the dipole axis to the rotation axis β = 116°, and the field strength at the pole is B_p = 10 kG. We carried out a chemical composition analysis and found a lack of helium for almost an order of magnitude, some overabundance of silicon and metal elements for more than an order of magnitude, particularly, cobalt for three orders of magnitude.     

Terrestrial planet formation surrounding close binary stars

Most stars reside in binary/multiple star systems; however, previous models of planet formation have studied growth of bodies orbiting an isolated single star. Disk material has been observed around both components of some young close binary star systems. Additionally, it has been shown that if planets form at the right places within such disks, they can remain dynamically stable for very long times. Herein, we numerically simulate the late stages of terrestrial planet growth in circumbinary disks around ‘close’ binary star systems with stellar separations 0.05 AU?aB?0.4 AU and binary eccentricities 0?eB?0.8. In each simulation, the sum of the masses of the two stars is 1 M_⊙, and giant planets are included. The initial disk of planetary embryos is the same as that used for simulating the late stages of terrestrial planet formation within our Solar System by Chambers [Chambers, J.E., 2001. Icarus 152, 205-224], and around each individual component of the α Centauri AB binary star system by Quintana et al. [Quintana, E.V., Lissauer, J.J., Chambers, J.E., Duncan, M.J., 2002. Astrophys. J. 576, 982-996]. Multiple simulations are performed for each binary star system under study, and our results are statistically compared to a set of planet formation simulations in the Sun-Jupiter-Saturn system that begin with essentially the same initial disk of protoplanets. The planetary systems formed around binaries with apastron distances QB≡aB(1+eB)?0.2 AU are very similar to those around single stars, whereas those with larger maximum separations tend to be sparcer, with fewer planets, especially interior to 1 AU. We also provide formulae that can be used to scale results of planetary accretion simulations to various systems with different total stellar mass, disk sizes, and planetesimal masses and densities.     

Gas emission spectrum in the Irr galaxy IC 10

Observations of the dwarf Irr galaxy IC 10 have been performed at the 6-m Special Astrophysical Observatory telescope with the SCORPIO focal reducer in the mode of a slit spectrograph. The ionized-gas emission spectrum in the region of intense current star formation has been investigated. The relative oxygen, N⁺, and S⁺ abundances in about twenty H II regions and the synchrotron superbubble have been estimated. The galaxy-averaged oxygen abundance is 12 + log(O/H) = 8.17 ± 0.35 and the metallicity is Z = 0.18 ± 0.14Z _⊙. The metallicity found by comparing diagnostic diagrams with photoionization models is shown to be less reliable than its estimate based on strong oxygen lines.