Solutions to the field equations and the deceleration parameter

We utilise a form for the Hubble parameter to generate a number of solutions to the Einstein field equations with variable cosmological constant and variable gravitational constant. The Hubble law utilised yields a constant value for the deceleration parameter. A variety of solutions is presented in the Robertson-Walker spacetimes. A generalisation of the cosmic scale factor is utilised in the anisotropic Bianchi I spacetime to illustrate that new solutions may also be found in spacetimes with less symmetry than Robertson-Walker. We also show that the constant deceleration parameter used is consistent with alternate theories of gravity by considering the scalar-tensor theory of Lau and Prokhovnik with ak = 0 Robertson-Walker background.     

Contribution to the observation of the photospheric oscillations

Observations of the 300 s photospheric oscillation on large solar surfaces (up to 520 in diameter) using a sodium optical resonance cell seem to show that the power at long horizontal wavelengths is larger than previous results would indicate. In order to get more information about the spatial distribution of the energy, a new observational method has been perfected, which will allow us to obtain the spatiotemporal power spectrum.In some of our observations, a long-period oscillation (about 40 min) appears, with an amplitude comparable to that of the 300-s oscillation, and which seems to be correlated with the occurence of chromospheric flares.     

Optimum trajectories for spacecraft mission to asteroid Apophis with a return to the Earth

A topical task for astronautics is to prepare a mission to the asteroid Apophis that is approaching the Earth. Determination of energetically favorable trajectories for a spacecraft involved in this mission with a return to the Earth has been considered. Two possible variants of engines for this mission are analyzed. The first variant employs electric engines with low jet thrust, while the second variant employs a spacecraft accelerated and controlled by only high-thrust engines. It is shown that both variants can be used in the mission to Apophis, but the use of electric engines with low thrust allows the project characteristics to be significantly improved.     

Trying to enlarge the sky coverage of the FAST

The proposed FAST project is a novel giant spherical radio telescope, with active elements which form a temporary paraboloid to track radio objects in the sky. Efforts have been made to extend the limited sky coverage that is a characteristic disadvantage of Arecibo-style radio telescopes. Three measures under investigation are introduced in this paper. The expected performance of the telescope is described, and a brief comparison is made with some of the largest existing radio telescopes. This revised version was published online in July 2006 with corrections to the Cover Date.     

How to compare the surface of Io to laboratory samples

Since one does not know the photometric functions of various parts of Io, one cannot convert the observed geometric albedo of the satellite to a parameter more directly measurable in the laboratory. One must therefore convert laboratory reflectances to geometric albedos before quantitative comparisons between Io's surface and a laboratory sample are made. This procedure involves determining the wavelength dependence of the sample's photometric function. For substances such as sulfur, whose reflectance varies strongly with wavelength, it is incorrect to assume that the photometric function, and hence the ratio (laboratory reflectance/geometric albedo) is independent of wavelength. To illustrate this point, measurements of the color dependence of this ratio for sulfur are presented for the specific case in which the measured laboratory reflectance is the sample's normal reflectance. In general, unless the laboratory reflectance is precisely the geometric albedo, a wavelength-dependent correction factor must be determined before the laboratory sample can be compared quantitatively with Io's surface.     

Reply to the paper

Leblanc and de la Noë used the set of data published by Mercier and Rosenberg (1974) on the type III burst at 169 MHz. They conclude that type III bursts are associated with low density coronal structures and occur in low density regions.We show that their methods cannot lead to firm conclusions; we point out some inconsistencies in their results.     

Probing the Quiet Solar Atmosphere from the Photosphere to the Corona

We investigate the morphology and temporal variability of a quiet-Sun network region in different solar layers. The emission in several extreme ultraviolet (EUV) spectral lines through both raster and slot time-series, recorded by the EUV Imaging Spectrometer (EIS) on board the Hinode spacecraft is studied along with \(\mbox{H}\upalpha\) observations and high-resolution spectropolarimetric observations of the photospheric magnetic field. The photospheric magnetic field is extrapolated up to the corona, showing a multitude of large- and small-scale structures. We show for the first time that the smallest magnetic structures at both the network and internetwork contribute significantly to the emission in EUV lines, with temperatures ranging from \(8\times 10^{4}~\mbox{K}\) to \(6\times 10^{5}~\mbox{K}\). Two components of transition region emission are present, one associated with small-scale loops that do not reach coronal temperatures, and another component that acts as an interface between coronal and chromospheric plasma. Both components are associated with persistent chromospheric structures. The temporal variability of the EUV intensity at the network region is also associated with chromospheric motions, pointing to a connection between transition region and chromospheric features. Intensity enhancements in the EUV transition region lines are preferentially produced by \(\mbox{H}\upalpha\) upflows. Examination of two individual chromospheric jets shows that their evolution is associated with intensity variations in transition region and coronal temperatures.     

Resolving the Elysium Controversy: An open invitation to explain the evidence

The origin of Mars’ Elysium-Amazonis plain has been the subject of debate for three decades, with a flood-volcanic origin the majority view today. Stratigraphical observations indicate that this view, based mainly on form analogy with Earth, is in error. A general unwillingness to engage with these observations in published work is detrimental not only to wider perceptions of planetary geology, often viewed as little more than the science of resemblance as a consequence, but also to superposed theories of surface chronology and source of the young martian meteorites, which are characterised by inconsistency and paradox as a result. Adherents to the volcanic hypothesis must convincingly explain how the observed field-relations are consistent with a lava surface across this region, or accept that these deposits are not what they currently believe them to be.     

A Cosmological Explanation to the Pioneer Anomaly

An earlier paper introduced a new cosmological theory based on the proposition that all four metrical coefficients of space and time change with the cosmological expansion. Such a universal scale expansion would preserve the four-dimensional spacetime geometry and therefore by general relativity most physical relationships. In addition, if the scale expansion were exponential with time, all epochs would be equivalent. The theory resolves several outstanding problems with the standard model based on the Big Bang concept and better agrees with observations. Four independent observational programs support the SEC theory, which also provides an explanation to the Pioneer anomaly. A possible resolution to the recently discovered discrepancies between optical observations of the planets and their ephemerides is proposed.     

Extending the Eigenvector 1 space to the optical variability of quasars

We introduce a new physical parameter, the optical variability amplitude, to the well-established Eigenvector 1 space of quasars and test a sample of long-term B-band light curves of 42 Palomar-Green quasars monitored by Giveon et al. We find that the optical variability amplitude strongly correlates with the intensity ratio of Fell to Hβ,Hβwidth and peak luminosity at 5007A. We briefly discuss the physical meaning of our findings and suggest that the Eddington ratio may be a key factor in determining a quasar's variability.     

Distance to the anti-center shell

Heiles (1984) has identified a large angular diameter (30°), anomalous velocity H I structure in the anti-center region of the Galaxy. The distance to this structure is the key to understanding of the energetics and, hence, the origin. Distance estimates based on indirect arguments have ranged from less than 100 pc to a few kiloparsecs. We report the absence of any anomalous velocity Ca K absorption features in high sensitivity echelle spectra towards 17 stars located within the boundaries of this structure. We conclude that the structure is definitely beyond 500 pc and barring unusually low Ca II abundance is more distant than 2.5 kpc. This results supports the hypothesis that the anti-center structure is the result of collision of high-velocity clouds with the galactic H I disk.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.     

Validity of the isobaric assumption to the solar corona

Many coronal heating mechanisms have been suggested to balance the losses from this tenuous medium by radiation, conduction, and plasma mass flows. A previous paper (Walsh, Bell, and Hood, 1995) considered a time-dependent heating supply where the plasma evolved isobarically along the loop length. The validity of this assumption is investigated by including the inertial terms in the fluid equations making it necessary to track the sound waves propagating in a coronal loop structure due to changes in the heating rate with time. It is found that the temperature changes along the loop are mainly governed by the variations in the heating so that the thermal evolution can be approximated to a high degree by the simple isobaric case. A typical isobaric evolution of the plasma properties is reproduced when the acoustic time scale is short enough. However, the cooling of a hot temperature equilibrium to a cool one creates supersonic flows which are not allowed for in this model.     

30m环形干涉望远镜

简要介绍了云南天文台对下一代地面大型天文光学望远镜进行的初步研究，依据这些研究结果我们提出研制一个新概念的大型地面望远镜：30m环形干涉望远镜（Ringy Interferometric Telescope），它既有单口径望远镜那样的直接成像能力和分辨率，又可以进行综合孔径模式的高分辨率成像，该计划显著地不同于经典的地面大型望远镜，对其中关键技术的研究正在积极进行之中。     

Evidence the Galactic contribution to the IceCube astrophysical neutrino flux

We show that the Galactic latitude distribution of IceCube astrophysical neutrino events with energies above 100 TeV is inconsistent with the isotropic model of the astrophysical neutrino flux. Namely, the Galactic latitude distribution of the events shows an excess at low latitudes |b| < 10° and a deficit at high Galactic latitude |b| ≳50°. We use Monte–Carlo simulations to show that the inconsistency of the isotropic signal model with the data is at ≳3σ level, after the account of trial factors related to the choice of the low-energy threshold and Galactic latitude binning in our analysis.     

阿昌族天文初探

阿昌族有独立的语言而没有文字,是否有传统的天文内容,过去还未有人进行发掘。我们首次从实地调查的结果得知,阿昌人中流传的对宇宙的解释,属于天文学发展初期的认识。大约从明朝改用农历后,还保留有4个传统节日和部分原始信仰。从六月火把节和十月会街节推断,其原用历法是将一年分成10个月的“十月太阳历”,两个节日是源于“十月历”的冬夏两次过新年。崇拜太阳而不崇拜月亮可作为旁证。     

Quantum Approach to Neutron Stars Leading to Configurations With Local Anisotropy and Mass Above the Oppenheimer-Volkoff Limit

The theory of stars consisting of non-interacting neutrons at zero Kelvin isrevisited starting from a quantum formulation. The Dirac equation is solvedin a curved space-time with spherical symmetry and N single-particle quantumstates are filled with N neutrons in such a way that the mass of the star isa minimum constrained by Einstein's equations of general relativity. Thisrule leads to quantum ground states with local isotropy (i.e. isotropicpressure) for masses below the Oppenheimer-Volkoff limit, but quantum groundstates with local anisotropy above it. The calculations suggest that thereare stable neutron stars with mass well above the currently accepted limit.     

Using the minimum spanning tree to trace mass segregation

We present a new method to detect and quantify mass segregation in star clusters. It compares the minimum spanning tree (MST) of massive stars with that of random stars. If mass segregation is present, the MST length of the most massive stars will be shorter than that of random stars. This difference can be quantified (with an associated significance) to measure the degree of mass segregation. We test the method on simulated clusters in both 2D and 3D and show that the method works as expected.
We apply the method to the Orion Nebula Cluster (ONC) and show that the method is able to detect the mass segregation in the Trapezium with a 'mass segregation ratio (MSR)'  Λ_MSR= 8.0 ± 3.5  (where  Λ_MSR= 1  is no mass segregation) down to  16 M_⊙  , and also that the ONC is mass segregated at a lower level  (∼2.0 ± 0.5)  down to  5 M_⊙  . Below  5 M_⊙  we find no evidence for any further mass segregation in the ONC.     

Multiplex approach to the photometric detection of planets

If the hypothesis is correct that most solar-like stars have planetary systems and have planets in inner orbits, then approximately 1% of these stars should have planets with orbital planes close enough to our line of sight to show transits. To get a statistically significant estimate of the fraction of stars that have planets in inner orbits, it is necessary to monitor thousands of stars continuously for a period of several years. To accomplish this requires the use of a multi-channel photometer system. We present here several multi-channel methods that have been used for ground-based observations and a concept for applying multi-channel photometry to the detection of numerous Earth-sized planets.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A.     

Limits to the accuracy of the 10.7 cm flux

The 10.7 cm flux data, which are widely used as an index of solar activity, are actually spot measurements of the solar flux density at 10.7 cm wavelength, made three times each day, usually at 17:00, 20:00, and 23:00 UT. These values, or the 20:00 UT determination alone, are frequently used as the average flux for that day. Since each spot measurement takes about one hour to make, and the Sun's emissions at that wavelength can vary over time scales shorter than the intervals between the measurements, the data are unavoidably undersampled. Radio emissions from transient events, such as flares, are defined as contaminants of the flux, and largely-empirical procedures have evolved which are used to filter them from the data. The utility of theF _10.7 index over more than 40 years suggests that the consequences of the under-sampling and the use of largely-empirical data filters are not serious. However, as new applications of the flux data appear, and existing ones become more quantitative, we need to better understand the accuracy of data as estimates of the 10.7 cm flux index, and to know how much precision we can reasonably expect to attain. In this paper we describe part of a study aimed at estimating how good the spot measurements are as estimators of the ‘daily-average’ flux. By a combination of measurement and modelling, the contributions to the flux monitor output truly due to the Sun are separated from the non-solar signals. We then derive the daily average 10.7 cm flux values and compare them with the spot measurements. We find that in general, the spot measurements are usually within a percent or so of the daily-average fluxes.     

UV Capabilities to Probe the Formation of Planetary Systems: From the ISM to Planets

Planetary systems are angular momentum reservoirs generated during star formation. Solutions to three of the most important problems in contemporary astrophysics are needed to understand the entire process of planetary system formation: The physics of the ISM. Stars form from dense molecular clouds that contain ∼ 30% of the total interstellar medium (ISM) mass. The structure, properties and lifetimes of molecular clouds are determined by the overall dynamics and evolution of a very complex system – the ISM. Understanding the physics of the ISM is of prime importance not only for Galactic but also for extragalactic and cosmological studies. Most of the ISM volume (∼ 65%) is filled with diffuse gas at temperatures between 3000 and 300 000 K, representing about 50% of the ISM mass. The physics of accretion and outflow. Powerful outflows are known to regulate angular momentum transport during star formation, the so-called accretion–outflow engine. Elementary physical considerations show that, to be efficient, the acceleration region for the outflows must be located close to the star (within 1 AU) where the gravitational field is strong. According to recent numerical simulations, this is also the region where terrestrial planets could form after 1 Myr. One should keep in mind that today the only evidence for life in the Universe comes from a planet located in this inner disk region (at 1 AU) from its parent star. The temperature of the accretion–outflow engine is between 3000 and 10 ⁷ K. After 1 Myr, during the classical T Tauri stage, extinction is small and the engine becomes naked and can be observed at ultraviolet wavelengths. The physics of planet formation. Observations of volatiles released by dust, planetesimals and comets provide an extremely powerful tool for determining the relative abundances of the vaporizing species and for studying the photochemical and physical processes acting in the inner parts of young planetary systems. This region is illuminated by the strong UV radiation field produced by the star and the accretion–outflow engine. Absorption spectroscopy provides the most sensitive tool for determining the properties of the circumstellar gas as well as the characteristics of the atmospheres of the inner planets transiting the stellar disk. UV radiation also pumps the electronic transitions of the most abundant molecules (H ₂, CO, etc.) that are observed in the UV.Here we argue that access to the UV spectral range is essential for making progress in this field, since the resonance lines of the most abundant atoms and ions at temperatures between 3000 and 300 000 K, together with the electronic transitions of the most abundant molecules (H ₂, CO, OH, CS, S ₂, CO ₂ ⁺, C ₂, O ₂, O₃, etc.) are at UV wavelengths. A powerful UV-optical instrument would provide an efficient mean for measuring the abundance of ozone in the atmosphere of the thousands of transiting planets expected to be detected by the next space missions (GAIA, Corot, Kepler, etc.). Thus, a follow-up UV mission would be optimal for identifying Earth-like candidates.