Gaia, an unprecedented observatory for Solar System dynamics

The mission Gaia by European Space Agency (ESA) is expected to fly at the end of 2011 and to perform an all-sky, magnitude-limited survey for 5 years. The probe will not use an input catalogue, and will get high accuracy astrometry and photometry for all sources of magnitude V<20. Low-resolution spectra will also be available. Moving Solar System objects will be observed as well, and their observations will be processed by a specific pipeline in order to retrieve the physical and dynamical characteristics of each object. In this contribution we will mainly focus on the impact of Gaia observations on asteroid dynamics. A dramatic improvement of orbital elements is expected, as well as the measurement of subtle effects such as those related to general relativity (GR). Gaia observations will also be supported by a network of ground-based observation sites, capable of providing follow-up for newly discovered objects that will not receive an adequate coverage from space. Specific strategies for follow-up are being planned and tested. These will need to take into account the peculiar observing geometry (large parallax effect due to the orbit of Gaia around L2) and the time constraints dictated by data processing.     

Application of INSAT satellite cloud-imagery data for site evaluation work of proposed GRACE observatory

The weather-imageries from the INSAT group of satellites provide reliable and concurrent multistation cloud-cover data — an important input for a proper selection of an observatory site for optical, infra-red and γ-ray astronomy work. Using these data, it is shown that Gurushikar, Mt. Abu, promises to be an excellent site for setting up the proposed GRACE facility for high-sensitivity Gamma-Ray Astrophysics Cerenkov Experiments.     

Site selection for a radio astronomy observatory in Turkey: atmospherical, meteorological, and radio frequency analyses

Selecting the future site for a large Turkish radio telescope is a key issue. The National Radio Astronomy Observatory is now in the stage of construction at a site near Karaman City, in Turkey. A single-dish parabolic radio antenna of 30?C40 m will be installed near a building that will contain offices, laboratories, and living accommodations. After a systematic survey of atmospheric, meteorological, and radio frequency interference (RFI) analyses, site selection studies were performed in a predetermined location in Turkey during 2007 and 2008. In this paper, we described the experimental procedure and the RFI measurements on our potential candidate??s sites in Turkey, covering the frequency band from 1 to 40 GHz.     

Generation of an optimal target list for the exoplanet characterisation observatory (EChO)

The Exoplanet Characterisation Observatory (EChO) has been studied as a space mission concept by the European Space Agency in the context of the M3 selection process. Through direct measurement of the atmospheric chemical composition of hundreds of exoplanets, EChO would address fundamental questions such as: What are exoplanets made of? How do planets form and evolve? What is the origin of exoplanet diversity? More specifically, EChO is a dedicated survey mission for transit and eclipse spectroscopy capable of observing a large, diverse and well-defined planetary sample within its four to six year mission lifetime. In this paper we use the end-to-end instrument simulator EChOSim to model the currently discovered targets, to gauge which targets are observable and assess the EChO performances obtainable for each observing tier and time. We show that EChO would be capable of observing over 170 relativity diverse planets if it were launched today, and the wealth of optimal targets for EChO expected to be discovered in the next 10 years by space and ground-based facilities is simply overwhelming. In addition, we build on previous molecular detectability studies to show what molecules and abundances will be detectable by EChO for a selection of real targets with various molecular compositions and abundances. EChO’s unique contribution to exoplanetary science will be in identifying the main constituents of hundreds of exoplanets in various mass/temperature regimes, meaning that we will be looking no longer at individual cases but at populations. Such a universal view is critical if we truly want to understand the processes of planet formation and evolution in various environments. In this paper we present a selection of key results. The full results are available in Online Resource 1.     

The FAST/SKA site selection in Guizhou province

Many karst depressions with diameters of 300 m to 500 m, suitable for constructing Arecibo-style radio telescopes, were identified in the south of Guizhou Province by Remote Sensing (RS) and Geographic Information System (GIS) technologies together with field investigations. Fundamental topography and landform databases were established for 391candidate depressions, and using GIS the3-dimensional images of depressions, at a scale of 1:10000, were then simulated to fit a spherical antenna. This revised version was published online in July 2006 with corrections to the Cover Date.     

A Proposal for Establishing A Gravitational-Wave Detector Interferometer in Pakistan

The proposed ‘Gravitational-Wave Antenna Detector InteRferometer (GWADIR)’ will be a 3 km × 3 km Fabry-Perot type laser interferometer. The laser oscillator to be used will be a DL excited Nd-YAG laser with a minimum output of 100 Watts. The optical system will consist of 25 cm diameter Recycler, Beam Splitter, and Near/End Mirrors for each of two Ducts. The mirror system will be suspended by fine wires to isolate the system from the seismic noises of the earth. The output light emerging from the interferometer will be split into 8 beams and sent to 8 different interference detectors. These detectors will measure the interference intensities for the recombined light from the separate legs of the interferometer. The effective amplification due to the interferometer cavities will allow measurements of displacements to better than 10 times the wavelength of the laser light. A high vacuum of 10-8 Torrs will be maintained throughout the system, using turbo-molecular and ion pumps. The detector is designed to reach strain sensitivities from gravitational sources of h<10-23 (Hz)- 1/2 with a broad-band and narrow-band measurement capability in the range of frequencies from 50 Hz to 10 ⁴ Hz, thus allowing it to detect ‘standard’ signals from such sources as coalescing neutron stars or black-holes out to the edge of the universe. If enough funding became available, the project is expected to complete by the middle of the next decade. This revised version was published online in July 2006 with corrections to the Cover Date.     

Strategies for selection of small γ-ray showers using the Imaging Atmospheric Cherenkov Technique

Methods of selecting small candidate γ-ray events obtained using the Imaging Atmospheric Cherenkov Technique are presented. Three approaches are described: a variant of the standard ‘Supercuts’ analysis technique, a parameter weights approach, and a neural network approach. A cut on the parameter combination Length/Size is developed and shown to be effective at rejecting background due to muons. The techniques are applied to observations of Markarian 421 taken during 1995 and 1996 with the Whipple 10 m reflector. The efficiency and stability of the three approaches are compared, and the Supercuts variant is shown to be the most robust. A signal is detected in the energy range 170 GeV to 300 GeV at a significance level of 6.5 σ, in 7 hours of observation (the standard analysis gives 15.2 σ for E > 300 GeV). This represents the first significant detection of a source at an energy threshold below 200 GeV using the Whipple 10 m system.     

Comparing X-ray color selection in separating X-ray binary classes using color-color-intensity diagrams

X-ray binaries exhibit a wide range of properties but there are few accepted methods to determine the nature of the compact object. Color-Color-Intensity diagrams have been suggested as a means of distinguishing between systems containing black holes from those containing neutron stars. However, this technique has been verified with data from only one instrument (RXTE/ASM) with a single set of X-ray colors defined using data available only in pre-determined energy bands. We test a selection of X-ray colors with a more sensitive instrument to determine the reliability of this method. We use data from the MAXI/Gas Slit Camera, which allows users to specify energy-bands. We test X-ray colors that have been previously defined in the literature as well as ones that we define specifically in this paper. A representative set of systems are used to construct Color-Color-Intensity diagrams in each set of colors to determine which are best for separating different classes. For studying individual sources certain bands are more effective than others. For a specified energy range, the separation of soft states in black hole binaries was possible only where both soft and hard colors included information from the lowest energy band. We confirm that Color-Color-Intensity diagrams can distinguish between systems containing black holes or neutron stars in all X-ray colors tested; this suggests an universality in the accretion processes governing these different classes. We suggest possible physical processes driving different classes of X-ray binaries to different locations in Color-Color-Intensity diagrams.     

A Moon orbiting observatory for the measurement of the elemental and isotopic composition in the primary cosmic radiation

We describe a project for the measurement of elemental composition of the primary cosmic radiation to be performed by a space observatory orbiting around the Moon. The absence of atmosphere and the low intrinsic magnetic field of the Moon give access to the very low energy component of the cosmic radiation, allowing the search for rare events.The quest for antinuclei, the determination of the lunar lepton albedo and the abundance measurement of galactic radioactive clocks (Be¹⁰, C¹⁴, Al²⁶) are the major tasks of the ANTARES apparatus (ANTimatter Assessment RESearch).We report details of the instrument design, the expected performance for single detectors, their capability to accomplish the proposed measurements and the characteristics of the space mission.     

Optimal softening for force calculations in collisionless N-body simulations

In N -body simulations the force calculated between particles representing a given mass distribution is usually softened, to diminish the effect of graininess. In this paper we study the effect of such a smoothing, with the aim of finding an optimal value of the softening parameter. As already shown by Merritt, for too small a softening the estimates of the forces will be too noisy, while for too large a softening the force estimates are systematically misrepresented. In between there is an optimal softening, for which the forces in the configuration best approach the true forces. The value of this optimal softening depends both on the mass distribution and on the number of particles used to represent it. For a higher number of particles the optimal softening is smaller. More concentrated mass distributions necessitate smaller softening, but the softened forces are never as good an approximation of the true forces as for non-centrally concentrated configurations. We give good estimates of the optimal softening for homogeneous spheres, Plummer spheres and Dehnen spheres. We also give a rough estimate of this quantity for other mass distributions, based on the harmonic mean distance to the k th neighbour ( k =1,…,12), the mean being taken over all particles in the configuration. Comparing homogeneous Ferrers' ellipsoids of different shapes we show that the axial ratios do not influence the value of the optimal softening. Finally we compare two different types of softening, a spline softening and a generalization of the standard Plummer softening to higher values of the exponent. We find that the spline softening fares roughly as well as the higher powers of the power-law softening and both give a better representation of the forces than the standard Plummer softening.     

Weak gravitational lensing in different cosmologies, using an algorithm for shear in three dimensions

We present the results of weak gravitational lensing statistics in four different cosmological N -body simulations. The data have been generated using an algorithm for the three-dimensional shear, which makes use of a variable softening facility for the N -body particle masses, and enables a physical interpretation for the large-scale structure to be made. Working in three dimensions also allows the correct use of the appropriate angular diameter distances.
Our results are presented on the basis of the filled-beam approximation in view of the variable particle softening scheme in our algorithm. The importance of the smoothness of matter in the Universe for the weak lensing results is discussed in some detail.
The low-density cosmology with a cosmological constant appears to give the broadest distributions for all the statistics computed for sources at high redshifts. In particular, the range in magnification values for this cosmology has implications for the determination of the cosmological parameters from high-redshift type Ia supernovae. The possibility of determining the density parameter from the non-Gaussianity in the probability distribution for the convergence is discussed.     

Fall days of the SNC meteorites: Evidence for an SNC meteoroid stream,and a common site of origin

Abstract— Four of the SNC meteorites of putative Martian origin are falls. Two of these fell on October 3: Chassigny in 1815 and Zagami in 1962. The probability of this coincidence arising from random fall days is approximately 1 in 60. If this coincidence is not the result of chance, it suggests that some of the SNC meteorites are derived from a meteoroid stream. In that Chassigny and Zagami span nearly the full range of SNC lithologies and histories, the coincidence of fall days is consistent with suggestions that all of the SNCs came from a single site (impact crater) on their parent planet.     

用线性化分离法计算膨胀恒星大气的谱线形成

本文研究了具有宏观运动的膨胀恒星大气中的辐射转移过程。详细介绍如何利用线性化分离法计算运动大气谱线形成。并采用线性化分离法计算了εＯｒｉ星的Ｈα线ＰＣｙｇｎｉ轮廓。     

SPEXTRA: Optimal extraction code for long-slit spectra in crowded fields

We present a code for the optimal extraction of long-slit 2D spectra in crowded stellar fields. Its main advantage and difference from the existing spectrum extraction codes is the presence of a graphical user interface (GUI) and a convenient visualization system of data and extraction parameters. On the whole, the package is designed to study stars in crowded fields of nearby galaxies and star clusters in galaxies. Apart from the spectrum extraction for several stars which are closely located or superimposed, it allows the spectra of objects to be extracted with subtraction of superimposed nebulae of different shapes and different degrees of ionization. The package can also be used to study single stars in the case of a strong background. In the current version, the optimal extraction of 2D spectra with an aperture and the Gaussian function as PSF (point spread function) is proposed. In the future, the package will be supplemented with the possibility to build a PSF based on a Moffat function. We present the details of GUI, illustrate main features of the package, and show results of extraction of the several interesting spectra of objects from different telescopes.