Brightness Variation and Proper Motions of Three Objects in the Cygnus Region

The results of an investigation of three peculiar objects in the Cygnus region are given. One of them was already known to be a Herbig-Haro object. In accordance with its observational characteristics, the second object is, in all probability, a T Tauri star. The physical character of the last object is not yet entirely clear, but from the properties of its emission in the near infrared range it is probably also a T Tauri star. The proper motions of the objects have been measured. It is shown that all three objects are members of a tight system of the Trapezium type and evidently are the results of the successive fragmentation of an original protostellar body.     

Nature of microstructure in pulsar radio emission

We present a model for microstructure in pulsar radio emission. We propose that micropulses result from alteration of the radio wave generation region by nearly transverse drift waves propagating across the pulsar magnetic field and encircling the bundle of the open magnetic field lines. It is demonstrated that such waves can modify the curvature of the field lines significantly. This, in turn, affects strongly fulfilment of the resonance conditions necessary for the excitation of radio waves. The time-scale of micropulses is therefore determined by the wavelength of the drift waves. The main features of the microstructure are naturally explained within the framework of this model.     

The mass of the white dwarf in the recurrent nova U Scorpii

We present spectroscopy of the eclipsing recurrent nova U Sco. The radial velocity semi-amplitude of the primary star was found to be     from the motion of the wings of the He  ii λ 4686-Å emission line. By detecting weak absorption features from the secondary star, we find its radial velocity semi-amplitude to be     . From these parameters, we obtain a mass of     for the white dwarf primary star and a mass of     for the secondary star. The radius of the secondary is calculated to be     , confirming that it is evolved. The inclination of the system is calculated to be     , consistent with the deep eclipse seen in the light-curves. The helium emission lines are double-peaked, with the blueshifted regions of the disc being eclipsed prior to the redshifted regions, clearly indicating the presence of an accretion disc. The high mass of the white dwarf is consistent with the thermonuclear runaway model of recurrent nova outbursts, and confirms that U Sco is the best Type Ia supernova progenitor currently known. We predict that U Sco is likely to explode within ∼700 000 yr.     

The first World Atlas of the artificial night sky brightness

We present the first World Atlas of the zenith artificial night sky brightness at sea level. Based on radiance-calibrated high-resolution DMSP satellite data and on accurate modelling of light propagation in the atmosphere, it provides a nearly global picture of how mankind is proceeding to envelop itself in a luminous fog. Comparing the Atlas with the United States Department of Energy (DOE) population density data base, we determined the fraction of population who are living under a sky of given brightness. About two-thirds of the World population and 99 per cent of the population in the United States (excluding Alaska and Hawaii) and European Union live in areas where the night sky is above the threshold set for polluted status. Assuming average eye functionality, about one-fifth of the World population, more than two-thirds of the United States population and more than one half of the European Union population have already lost naked eye visibility of the Milky Way. Finally, about one-tenth of the World population, more than 40 per cent of the United States population and one sixth of the European Union population no longer view the heavens with the eye adapted to night vision, because of the sky brightness.     

Parallax distortion by the weak microlensing effect

Parallax measurements allow distances to celestial objects to be determined. Together with measurements of their position on the celestial sphere, they give a full three-dimensional picture of the location of the objects relative to the observer. The distortion of the parallax value of a distant source affected by weak microlensing is considered. This means that the weak microlensing leads to distortion of the distance scale. The gravitational deflection causes a retrograde apparent motion of the image, which is revealed as a negative parallax. It is shown that the distortions may significantly change the parallax values when they amount to several microseconds of arc. In particular, at this level many measured values of parallaxes should be negative.     

The electron pressure in the outer atmosphere of ε Eri (K2 V)

Observations of ε Eri (K2 V) have been made with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope . The spectra obtained show a number of emission lines which can be used to determine, or place limits on, the electron density and pressure. Values of the electron pressure are required in order to make quantitative models of the transition region and inner corona from absolute line fluxes, and to constrain semi-empirical models of the chromosphere. Using line flux ratios in Si  iii and O  iv a mean electron pressure of P _e= N _e T _e=4.8×10¹⁵ cm⁻³ K is derived. This value is compatible with the lower and upper limits to P _e found from flux ratios in C  iii , O  v and Fe  xii . Some inconsistencies which may be because of small uncertainties in the atomic data used are discussed.     

Evidence of climatic warming in the southern Urals region derived from borehole temperatures and meteorological data

Thirty borehole temperature–depth profiles in the central and southern Urals, Russia were scrutinized for evidence of ground surface temperature histories. We explored two inversion schemes: a simple ramp inversion in which solutions are parameterized in terms of an onset time and magnitude of change and a more sophisticated functional space inverse algorithm in which the functional form of the solution is left unspecified. To enhance and potentially identify latitudinal differences in the ground surface temperature signal, we subdivided the data into three groups based on geographic proximity and simultaneously inverted the borehole temperature–depth logs. The simultaneous inversions highlighted 13 temperature–depth logs that could not both fit a common ground surface temperature history and a priori models within reasonable bounds. Our results confirm that this is an effective way to reduce site-specific noise from an ensemble of boreholes. Each inversion scheme gives comparable results indicating locally variable warming on the order of 1°C starting between 1800 and 1900 AD. Similarly surface air temperature records from 12 nearby meteorological stations exhibit locally variable warming also on the order of 1°C of warming during the 20th century. To explore the degree to which borehole temperatures and surface air temperature (SAT) time series are responding to the same signal, we average the SAT data into the same three groups and used these averages as a forcing function at the Earth's surface to generate synthetic transient temperature profiles. Root mean square (RMS) misfits between these synthetic temperature profiles and averaged temperature–depth profiles are low, suggesting that first-order curvature in borehole temperatures and variations in SAT records are correlated.     

Trace-element contents and cathodoluminescence of “trapiche” rubies from Mong Hsu, Myanmar (Burma): geological significance

Summary ?Mong Hsu rubies of the “trapiche” type are sporadically seen in the gem market. However, they have never been described in the field. The study of the nature of solid inclusions, the variation of trace-element contents, as well as the cathodoluminescence behaviour of six “trapiche” rubies permit the conclusion that these rubies crystallised in the same geological environment (marble-type deposit) as the normal rubies from Mong Hsu: (1) Cr and V are the main chromophorous elements in both ruby types; they act, together with Ti, as activators or quenchers for cathodoluminescence; (2) calcite, dolomite, rutile, mica, diaspore, apatite, chlorite, and feldspar are solid inclusions found in both ruby types; (3) the presence of bastn?site in trapiche ruby and fluorite in non-trapiche ruby indicates the circulation of F-bearing fluids during ruby deposition; (4) the distribution of trace-element contents in the crystal is similar for both ruby types. In the Cr₂O₃ vs. Fe₂O₃ and Cr₂O₃ vs. Fe₂O₃/TiO₂ diagrams, the population fields of Mong Hsu “trapiche” and non-“trapiche” rubies overlap. They are distinct from those of rubies and sapphires hosted in basalts from South-east Asia. Received October 30, 2001; revised version accepted March 25, 2002