A signature of the donor star in the extra-galactic X-ray binary LMC X−2

Two nights of phase-resolved medium-resolution Very Large Telescope spectroscopy of the extra-galactic low-mass X-ray binary LMC X−2 have revealed a 0.32 ± 0.02 d spectroscopic period in the radial velocity curve of the He  ii λ4686 emission line that we interpret as the orbital period. However, similar to previous findings, this radial velocity curve shows a longer term variation that is most likely due to the presence of a precessing accretion disc in LMC X−2. This is strengthened by He  ii λ4686 Doppler maps that show a bright spot that is moving from night to night. Furthermore, we detect narrow emission lines in the Bowen region of LMC X−2, with a velocity of   K _em= 351 ± 28 km s⁻¹  , that we tentatively interpret as coming from the irradiated side of the donor star. Since K _em must be smaller than K ₂, this leads to the first upper limit on the mass function of LMC X−2 of   f ( M ₁) ≥ 0.86  M_⊙  (95 per cent confidence), and the first constraints on its system parameters.     

Self-regulated gravitational accretion in protostellar discs

We present a numerical model for the evolution of a protostellar disc that has formed self-consistently from the collapse of a molecular cloud core. The global evolution of the disc is followed for several million years after its formation. The capture of a wide range of spatial and temporal scales is made possible by use of the thin-disc approximation. We focus on the role of gravitational torques in transporting mass inward and angular momentum outward during different evolutionary phases of a protostellar disc with disc-to-star mass ratio of order 0.1. In the early phase, when the infall of matter from the surrounding envelope is substantial, mass is transported inward by the gravitational torques from spiral arms that are a manifestation of the envelope-induced gravitational instability in the disc. In the late phase, when the gas reservoir of the envelope is depleted, the distinct spiral structure is replaced by ongoing irregular non-axisymmetric density perturbations. The amplitude of these density perturbations decreases with time, though this process is moderated by swing amplification aided by the existence of the disc's sharp outer edge. Our global modelling of the protostellar disc reveals that there is typically a residual non-zero gravitational torque from these density perturbations, i.e. their effects do not exactly cancel out in each region. In particular, the net gravitational torque in the inner disc tends to be negative during first several million years of the evolution, while the outer disc has a net positive gravitational torque. Our global model of a self-consistently formed disc shows that it is also self-regulated in the late phase, so that it is near the Toomre stability limit, with a near-uniform Toomre parameter Q ≈ 1.5–2.0. Since the disc also has near-Keplerian rotation, and comparatively weak temperature variation, it maintains a near-power-law surface density profile proportional to r ^−3/2.     

Rieger quasi-periodicity in solar indices

Using wavelet analysis and Fourier analysis, the temporal behavior of ??156-day quasi-periodicity (Rieger quasi-periodicity, RQ) is investigated for series of daily solar indices: Wolf numbers W for 161 years (from 1849), the flux F_10.7 of the Sun??s radio emission at a frequency of 2800 MHz for 63 years (from 1947), the number of X-ray flares N _X for 29 years (from 1981), and the number of optical flares N _?? for 11 years in cycle 21. The N _?? series are studied for four quadrants of the solar disk. It is found for the W series that there is no stable dependence of the amplitude RQ on the cycle phase and the W value. It is associated with the fact that, corresponding to a period of around eight years, in the power spectrum changes in the amplitude of the Rieger quasiperiodicity of the index W are dominated by the peak. Moreover, the peaks corresponding to the 11-year cyclicity are also significant. The comparative study of the temporal behavior of the Rieger quasi-periodicity amplitude of the indices W, F_10.7, and N _X has shown that the quasi-periodicity covers the processes, occurring in active regions on the Sun at different altitudes, almost simultaneously. It is found that for N _??, the lag of variations of the Rieger quasi-periodicity amplitude for series of the Sun??s western hemisphere, relative to those for series of the eastern hemisphere, is on average less than for the flare series. Thus, if the flare occurrence is modulated by the Rieger quasi-periodicity process as a wave propagating over the Sun??s disc, then the wave is not a retrograde one. Different interpretations of the nature of the Rieger quasi-periodicity are discussed including the hypothesis of Rossby waves.     

Observations of extrasolar planet transits with the automated telescopes of the Pulkovo Astronomical Observatory

Exoplanet observations have been performed on the automated Pulkovo Observatory telescopes. We have obtained 33 transit light curves for 16 known exoplanets and six transit observations for three exoplanet candidates discovered by the Kepler telescope. Based on our observations, we have reliably confirmed the existence of an exoplanet with an extremely large radius, R _pl = 1.83 ± 0.16R _Jup, in the system KOI 256 and detected a strong deviation of its orbital revolution from the theoretically predicted one. During the transit of the exoplanet WASP-12b across the stellar disk, we detected bursts that could be caused by the planet transit across spots on the star or by the presence of a satellite around this exoplanet. We detected possible periodic variations in the duration of the exoplanet transit across the stellar disk with time for HAT-P-12b that could be caused by variations in orbital inclination. The transit duration and depth, the central transit time, and the radius and orbital inclination of the planet have been estimated. The equilibrium temperature and albedo have been estimated for several exoplanets.     

Evolution of oxygen and nitrogen abundances in SDSS galaxies

New expressions for ON and NS calibrations (we call them ON11 and NS11 calibrations) for the determination of oxygen and nitrogen abundances in HII regions are proposed. New criteria for the division of HII regions into three classes (hot, warm, and cold) are also proposed. ON11 and NS11 calibrations provide more accurate determination of oxygen and nitrogen abundances from integrated emission spectra, in comparison with ON and NS calibrations. Oxygen and nitrogen abundances are estimated for a sample of 57 470 SDSS galaxies using ON11 and NS11 calibrations. Strongline flux measurements for SDSS spectra of these galaxies are taken from the MPA/JHU catalog. A ??mass-metallicity?? diagram for several redshift ranges is constructed. It is found that the interstellar medium of galaxies with high masses log(M/M _??) > 11.3 was hardly enriched with either oxygen or nitrogen over the last 4 Gyrs (corresponding to the redshift interval z = 0?C0.4). This indicates that an active stage of star formation in massive galaxies was completed more than 4 Gyrs ago. For galaxies of lower masses, changes in oxygen and nitrogen abundances over the time period under consideration increase as galaxy mass decreases.     

Radiocarbon on Titan

Abstract— We explore the likely production and fate of ¹⁴C in the thick nitrogen atmosphere of Saturn's moon Titan and investigate the constraints that measurements of ¹⁴C might place on Titan's photochemical, atmospheric transport and surface‐atmosphere interaction processes. Titan's atmosphere is thick enough that cosmic‐ray flux limits the production of ¹⁴C: absence of a strong magnetic field and the increased distance from the Sun suggest production rates of ?9 atom/cm²/s, ?4x higher than Earth. The fate and detectability of ¹⁴C depends on the chemical species into which it is incorporated: as methane it would be hopelessly diluted even in only the atmosphere. However, in the more likely case that the ¹⁴C attaches to the haze that rains out onto the surface (as tholin, HCN or acetylene and their polymers), haze in the atmosphere or recently deposited on the surface would be quite radioactive. Such radioactivity may lead to a significant enhancement in the electrical conductivity of the atmosphere which will be measured by the Huygens probe. Measurements with simple detectors on future missions could place useful constraints on the mass deposition rates of photochemical material on the surface and identify locations where surface deposits of such material are “freshest”.     

Production of krypton and xenon isotopes in thick stony and iron targets isotropically irradiated with 1600 MeV protons

Abstract— Two spherical targets made of gabbro with a radius of 25 cm and of steel with a radius of 10 cm were irradiated isotropically with 1600 MeV protons at the SATURNE synchrotron at Laboratoire National Saturne (LNS)/CEN Saclay, in order to simulate the production of nuclides in meteorites induced by galactic cosmic‐ray protons in space. These experiments supply depth‐dependent production rate data for a wide range of radioactive and stable isotopes in up to 28 target elements. In this paper, we report results for ⁷⁸Kr, ^80–86Kr isotopes in Rb, Sr, Y and Zr and for ¹²⁴Xe, ¹²⁶Xe, ^128–132Xe, ¹³⁴Xe, ¹³⁶Xe isotopes in Ba and La. Krypton and xenon concentrations have been measured at different depths in the spheres by using conventional mass spectrometry. Based on Monte‐Carlo techniques, theoretical production rates are calculated by folding depth‐dependent spectra of primary and secondary protons and secondary neutrons with the excitation functions of the relevant nuclear reactions. The comparison of the model calculation results with experimental data in the thick target experiments performed at LNS and previously at CERN have allowed adjustments of the poorly known excitation functions of neutron‐induced reactions. Thus, for the two experiments at SATURNE, excellent agreement is obtained between experimental and calculated production rates for most Kr and Xe isotopes in all investigated target elements. Only Xe production in Ba in the gabbro is underestimated by the calculations by ?25%. This work validates the approach of the thin‐target model calculations of cosmogenic nuclide production rates in the attempt of modeling the interaction of galactic cosmic‐ray protons with stony and iron meteorites in space as well as with lunar samples.     

Karl Knorre,the first astronomer of Nikolaev Observatory (on the occasion of his bicentenary)

Karl Friedrich Knorre (1801–1883) was the son of Ernst Knorre, an astronomy professor at Dorpat university. During his education at Dorpat university, he became acquainted with Wilhelm Struve, the future director of Pulkovo observatory. Because of Knorre's passion for astronomy, Struve recommended him to the post of director of the planned naval observatory in Nikolaev. From its foundation in 1821, Karl Knorre was director of the Nikolaev Naval (and later Astronomical) Observatory. He carried out star position observations with the meridian circle, worked as an astronomy instructor for sea navigators, compiled the fifth section of the star charts of the Berlin Academy of Sciences and lead all hydrographic determinations on the Azov and Black seas. In 1871, Karl Nikolaev Observatory, and moved to Berlin.