再探伽玛射线暴中能量与脉冲宽度的依赖关系

探索来源于BATSE(http://cossc:gsfc:nasa:gov/batse)的GRB(Gamma-Ray Burst,伽玛射线暴)观测数据的半峰宽度(FWHM)与能量之间的关系,基于64个用KRL函数模型(即,文[1]中的(22)式)能很好地拟合的FRDE(Fast Rise and Exponential Decay,快速上升指数下降)型脉冲样本。发现64个样本中有63个的半峰宽度(FWHM)与能量之间的关系属于平台—幂率—平台型结构或峰型结构。64个样本的半峰宽度(FWHM)与能量之间的关系在观测中可详细分为5种类型:a)有34个样本为幂率形式关系;b)18个样本为低能段平台关系;c)有7个样本为高能段平台关系;d)4个样本为峰型结构关系;e)另外有1个样本为其他结构。结果表明:GRB观测数据的半峰宽度(FWHM)与能量之间的确存在有幂率的关系。此结果进一步确认了文[2](Qin etal 2005)的观点,即半峰宽度(FWHM)与能量之间的关系是由于火球模型的多普勒效应(Doppler effect)导致的。     

Measures of Jupiter photographs—1974/1975 apparition

The 1974/1975 Jupiter apparition is described. Photographic images have been measured and zonal velocities are given for all spots observed on four or more dates. Global and localized zonal flow patterns are graphically presented. Methane absorption band imagery at 890 nm indicates that white ovals and red spots are high in altitude, and blue features are cloud-free areas. The motions of blue features are complex and unlike the motions of other features. Interactions or associations between spots at five adjacent atmospheric currents have been observed. Zonal motion within an equatorial plume has been observed. Evidence is presented for a probable source of red spots in the North Tropical Zone.     

Photometric observations of nine Shakhbazian compact groups

By observations with the 1.5m telescope at San Pedro Martir (OAN, UNAM, Mexico) the BVR magnitudes are determined for 66 member galaxies in Shakhbazian Compact Galaxy Groups ShCG 40, ShCG 176, ShCG 270, ShCG 278, ShCG 310, and ShCG 342. Three other groups were observed in two or only in one band. Seven galaxies in ShCG 298 were observed in B and R, six galaxies in ShCG 95 were observed in V, and seven galaxies in ShCG 345 were observed in V and R. The distribution of brightness of observed galaxies is determined. Signs of interaction between galaxies are detected in some groups.     

Methods of searching for planets around pulsars

We analyse different methods of searching for planets around neutron stars by timing observations of pulsars. To this end, we study a few interesting models describing TOA residual variations that are observed, or could be observed, and which can mimic planets. We carry out a detailed theoretical analysis of the behaviour of these methods in the situations mentioned. We show that it is very helpful to look at these phenomena as some kind of quasi-periodic variations of residuals of time of arrival of pulsar pulses. We demonstrate that such a model-independent approach leads to promising conclusions that can be useful when analysing timing observations of pulsars to find planets or to prove that observed phenomena are of planetary origin.     

Curious Magnetic Changes in a Quiet Region

We describe the evolution of weak magnetic fields in a quiet region observed at the Big Bear Solar Observatory on 1 October 1996. We observed puzzling changes in which one polarity changed without corresponding increases or decreases in the other. In the rest of the same field, no special changes were observed, and a search of nearby days revealed no similar changes. We do not wish to call Maxwell's laws into question, we simply state that there are surprising effects that we cannot understand with current models.     

Submillimeter lightcurves of Vesta

Thermal lightcurves of Asteroid Vesta with significant amplitude have been observed at 870 μm (345 GHz) using the MPIfR 19-channel bolometer of the Heinrich–Hertz Submillimeter Telescope. Shape and albedo are not sufficient to explain the magnitude of this variation, which we relate to global variations in thermal inertia and/or other thermophysical parameters. Vesta's lightcurve has been observed over several epochs with the same general shape. However, there are some changes in morphology that may in part be related to viewing geometry and/or asteroid season. Inconsistent night-to-night variations exhibit the inherent difficulties in photometry at this wavelength. We are able to match the observed brightness temperatures with a relatively simple thermal model that integrates beneath the surface and assumes reasonable values of thermal inertia, loss tangent and refractive index, and without having to assume low values of emissivity in the submillimeter. High flux portions of the submillimeter lightcurve are found to correspond to regions with weak mafic bands observed in Hubble Space Telescope images.     

Photospheric variability of O stars

The characteristics of the line profile variations observed in optical transitions of O-type stars are reviewed. For a few well-observed stars, there is compelling evidence that the variations are due to photospheric velocity fields from one or more modes of nonradial pulsation. However, the origin of the line profile variations observed in most O stars is not yet established. To date, there is little empirical evidence to suggest that the variability in optical absorption lines of O stars is causally linked to the stellar wind variability commonly observed in their UV resonance lines.     

On a magnetohydrodynamical process of mass loss in AGB stars

A spherically, time independent model is constructed to explain the mass loss observed in cool giants. It is suggested that a random magnetic field frozen within the gas is capable of ejecting matter from the photosphere of AGB (Mira or OH/IR) stars. The velocities at infinity of the ejected material are comparable to the observed velocities of expansion in circumstellar envelopes.     

Lessons of Comet Hale-Bopp for Coma Chemistry: Observations and Theory

Many new cometary molecules — both parents and daughters — were detected in the exceptionally productive comet C/1995 O1 (Hale-Bopp).The space distribution of several of these species could be investigated from radio interferometry or from long-slit spectroscopy in the infrared. The distinction between parent species — directly sublimated from nucleus ices — and secondary species — resulting from chemical processing in the coma or produced by a secondary source — is not always clear. It is important to assess whether or not observed minor species (HCOOCH₃, HCOOH...) could be synthesized by chemical reactions favoured by the high density of the coma of comet Hale-Bopp. Chemical modelling by Rodgers and Charnley suggests that this is notthe case. CO and H₂CO are abundant cometary species which partly come from distributed sources. The nature of these sources is still a mystery. A special case, now well documented, is that of HNC, for which the abundance evolution with heliocentric distance could be observed in comet Hale-Bopp and which was observed in several much less productive comets.     

Multi-model Bayesian assessment of climate change in the northern annular mode

A typical question in climate change analysis is whether a certain observed climate characteristic, like a pronounced anomaly or an interdecadal trend, is an indicator of anthropogenic climate change or still in the range of natural variability. Many climatic features are described by one-dimensional index time series, like for instance the global mean temperature or circulation indices. Here, we present a Bayesian classification approach applied to the time series of the northern annular mode (NAM), which is the leading mode of Northern Hemisphere climate variability. After a pronounced negative phase during the 1950s and 1960s, the observed NAM index reveals a distinct positive trend, which is also simulated by various climate model simulations under enhanced greenhouse conditions. The objective of this study is to decide whether the observed temporal evolution of the NAM may be an indicator of global warming. Given a set of prior probabilities for disturbed and undisturbed climate scenarios, the Bayesian decision theorem decides whether the observed NAM trend is classified in a control climate, a greenhouse-gas plus sulphate aerosol climate or a purely greenhouse-gas induced climate as derived from multi-model ensemble simulations.The three climate scenarios are well separated from each other in terms of the 30-year NAM trends. The multi-model ensembles contain a weak but statistically significant climate change signal in the form of an intensification of the NAM. The Bayesian classification suggests that the greenhouse-gas scenario is the most probable explanation for the observed NAM trend since 1960, even if a high prior probability is assigned to the control climate. However, there are still large uncertainties in this classification result because some periods at the end of the 19th century and during the “warm” 1920s are also classified in an anthropogenic climate, although natural forcings are likely responsible for this early NAM intensification. This demonstrates a basic shortcoming of the Bayesian decision theorem when it is based on one-dimensional index time series like the NAM index.     

A white dwarf in the state of an ejector

We analyze the possibility of observational identification of white dwarfs in the state of an ejector. Among the distinctive features of this class of objects are a high rate of rotational energy loss comparable to or higher than the observed luminosity of the object and nonthermal gamma-ray and/or radio spectra. The manifestations of the white dwarf in the close binary system AE Aquarii closely match these criteria. We show that most of the peculiar manifestations of this object in the hard spectral range and the observed pattern of mass transfer in the system can be explained in terms of a model in which the state of the white dwarf is classified as an ejector.     

Massive stars and the intergalactic medium

We review the results of an X-ray (ASCA) survey of intergalactic medium metallicities in 33 groups and clusters of galaxies. The observed picture could be explained either by adopting top heavy IMF for galaxies observed at high environment overdensities or by metal-rich SN II driven winds.     

Properties of energetic electrons of magnetospheric origin in the magnetosheath and in the solar wind—correlation with geomagnetic activity

Bursts of energetic electrons (from >40keV up to 2MeV) as distinct from the magnetopause electron layer observed by Domingo et al. (1977) have been observed in the magnetosheath and in the solar wind by HEOS-2 at high-latitudes. Although these electrons are occasionally found close to the bow shock and simultaneously with low frequency (magnetosonic) upstream waves our observations strongly indicate that these electrons are of exterior cusp origin. Indeed, the flux intensity is highest in the exterior cusp region and decreases as the spacecraft moves away from it both tailward or upward. The energy spectrum becomes harder with increasing radial distance from the exterior cusp. The measured anisotropy indicates that the particles are propagating away from the exterior cusp. The magnetic field points to the exterior cusp region when these electrons are observed, being, for solar wind observations, centred at longitude 0° or 180° rather than along the spiral and in the magnetosheath, being usually different from the 90° or 270° orientation typical of that region. We exclude, therefore, that acceleration in the bow shock is the source of these particles because $\text{B}$ is not tangent to the shock when bursts are observed. We have also found a one to one correlation between geomagnetic storms' recovery phases and intense, continuous observations of >40 keV electrons in the magnetosheath, while, on the other hand, during geomagnetically quiet (Dst) periods bursts are observed only if AE is much larger than average.     

Non-rigid rotation of solar spicules

Hα profiles of chromospheric spicules computed for a variety of rotational behavior are compared with an observed profile, which was derived by averaging 11 Hα profiles taken near times of maximum spicule intensity. If turbulent velocity is small or equals zero, calculated profiles are in good agreement with the observed one under the conditions that rotation is non-rigid (faster rotation further away from the axis of the spicule) and the source function decreases in the direction from the spicule axis to the periphery. The comparison of calculated and observed tilts of spicule spectra relative to the direction of dispersion seems to corraborate the non-rigid character of spicular rotation.     

Calculations of two-dimensional models of the lower solar chromosphere

Several two-dimensional models of the lower solar chromosphere are computed using relative RMS line centre intensity variations and mean limb darkening curves observed in Mg b and NaD. These calculations indicate that the small scale fluctuations observed at line centre in these lines may result from density and electron temperature fluctuations in the lower chromosphere, while the large scale fluctuations may result from either fluctuations in the deeper lying continuum or horizontal and vertical differential velocity fields.     

Comet Hale-Bopp,Circumstellar Dust,and the Interstellar Medium

The infrared spectrum of comet Hale-Bopp, as observed with the Infrared Space Observatory (ISO), presents astonishing similarities with those of the dusty disks surrounding young stars. The prominent spectral features of crystalline silicates that occur in comets, have been observed in the circumstellar media of young and old stars, yet not in the interstellar medium. We suggest from the analogy with the young-star spectra that the crystalline nature of the silicates in comet Hale-Bopp dates from the early evolution of the solar system, and also that an Oort Cloud or Kuiper Belt is presently forming around young stars observed by ISO. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the ephemeris of the eclipsing polar HU Aquarii

The magnetic cataclysmic variable HU Aquarii displayed pronounced quasi‐periodic modulations of its eclipse timing. These were interpreted in terms of the light‐travel time (LTT) effect caused by a circumbinary planet or planetary system. We report new photometric observations that revealed another precise eclipse timing for the October 2013 epoch, the first obtained in a high accretion state after many years in low or intermediate states. The eclipse was observed to occur earlier by 95.3 ± 2.0 s or 62.8 ± 2.0 s than expected for an assumed linear or quadratic ephemeris, respectively. The implied apparent strong evolution of the orbital period calls for a revision of the current planetary model or the planetary parameters. The object deserves further monitoring to uncover the true nature of the observed variability and to constrain the properties of the proposed planet or planetary system. The new observations prove that advanced amateur equipment can successfully be used in the growing field of planet search in wide circumbinary orbits via the LTT effect. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Valleys on Hecates Tholus, Mars: origin by basal melting of summit snowpack

Valley networks observed on the martian surface are found mostly on Noachian-aged highlands units, but a few occur on younger volcanic edifices. Enigmatically, they do not occur on all younger volcanoes of similar age or location. Using new data, we reanalyze the radially arrayed valleys on the flanks of Hecates Tholus, a Hesperian-aged shield volcano, and test the hypothesis that these valleys might have formed via basal melting of summit snowpack. We find that magmatic intrusions with reasonable geometries provide sufficient heat flux to cause basal melting of snowpack, with the resulting meltwater interpreted to be responsible for incision of the observed valleys. Valley morphology is similar to valleys observed adjacent to seasonally melting Antarctic Dry Valley glaciers formed on comparable slopes, supporting the hypothesis of a snowmelt origin. These relatively young valley networks are thus plausibly interpreted to form under circumstances in which summit snow accumulation was melted during one or more episodes of high localized heat flux.     

Kolmogorov–Smirnov test as a tool to study the distribution of ultra-high energy cosmic ray sources

We analyse in detail the two-dimensional Kolmogorov–Smirnov test as a tool to learn about the distribution of the sources of the ultra-high energy cosmic rays. We confront, in particular, models based on active galactic nuclei observed in X-rays, galaxies observed in H  i and isotropic distributions, discussing how this method can be used not only to reject isotropy but also to support or reject specific source models, extending results obtained recently in the literature.     

Pre-enriched, not primordial ellipticals

We follow the chemical evolution of a galaxy through star formation and its feedback into the interstellar medium (ISM), starting from primordial gas and allowing for gas to inflow into the region being modelled. We attempt to reproduce observed spectral line strengths for early-type galaxies in order to constrain their star formation histories (SFH). The efficiencies and times of star formation are varied, as are the amount and duration of inflow. We evaluate the chemical enrichment and the mass of stars made with time. Single stellar population (SSP) data are then used to predict line strengths for composite stellar populations. The results are compared with observed line strengths in 10 ellipticals, including some features which help to break the problem of age–metallicity degeneracy in old stellar populations. We find that the elliptical galaxies modelled require high metallicity SSPs (> 3 Z⊙) at later times. In addition, the strong lines observed cannot be produced by an initial starburst in primordial gas, even if a large amount of inflow is allowed for during the first few × 10⁸ yr. This is because some pre-enrichment is required for lines in the bulk of the stars to approach the observed line strengths in ellipticals. These strong lines are better modelled by a system with a delayed burst of star formation, following an early SFH which can be a burst or more steady star formation. Such a model is representative of star formation in normal ellipticals or spirals, respectively, followed by a starburst and gas inflow during a merger or strong interaction with a gas-rich galaxy. Alternatively, a single initial burst of normal stars with a Salpeter initial mass function could produce the observed strong lines if it followed some pre-enrichment process which did not form long-lived stars (e.g. population III stars).