Real-time signal processor for pulsar studies

This paper describes the design, tests and preliminary results of a real-time parallel signal processor built to aid a wide variety of pulsar observations. The signal processor reduces the distortions caused by the effects of dispersion, Faraday rotation, doppler acceleration and parallactic angle variations, at a sustained data rate of 32 Msamples/sec. It also folds the pulses coherently over the period and integrates adjacent samples in time and frequency to enhance the signal-to-noise ratio. The resulting data are recorded for further off-line analysis of the characteristics of pulsars and the intervening medium. The signal processing for analysis of pulsar signals is quite complex, imposing the need for a high computational throughput, typically of the order of a Giga operations per second (GOPS). Conventionally, the high computational demand restricts the flexibility to handle only a few types of pulsar observations. This instrument is designed to handle a wide variety of Pulsar observations with the Giant Metre Wave Radio Telescope (GMRT), and is flexible enough to be used in many other high-speed, signal processing applications. The technology used includes field-programmable-gate-array(FPGA) based data/code routing interfaces, PC-AT based control, diagnostics and data acquisition, digital signal processor (DSP) chip based parallel processing nodes and C language based control software and DSP-assembly programs for signal processing. The architecture and the software implementation of the parallel processor are fine-tuned to realize about 60 MOPS per DSP node and a multiple-instruction-multiple-data (MIMD) capability.     

Initial orbit determination using multiple observations

A novel approach for initial orbit determination based on multiple angles-only observations is presented. The proposed technique is iterative and uses Lagrangian coefficients, f and g. The proposed method does not show singularity for the coplanar cases. In addition, the method is capable of handling multiple observations, providing higher accuracy, whereas the level of the algorithm complexity and processor running time remain almost invariant. The technique presented is compared with the Double r-iteration and Gauss’ methods using data corrupted by noise to simulate true measurements. Results show that the proposed method is a valid alternative to the classical methods of orbit determination.     

1991年7月11日墨西哥日全食红外光谱观测及初步结果

本文概述１９９１年７月１１日日全食时中国日食观测队在墨西哥ＬａＰａｚ所作的近红外光谱观测情况及得到的初步结果。观测是用一强光力望远镜和一中小色散的光谱仪，配以ＣＣＤ摄象机、图象处理器、微机等组成的探测系统进行的。日全食时，在λ１０７１２－１０９７２波区共摄得极上层光球和色球的无缝光谱４１帧。日面外约１．０９６Ｒ处的有缝光谱３５帧。文中还介绍了拍得的色球、日珥资料概况。     

TV system for navigation and guidance

A TV system for navigation and guidance (TVSNG) has been designed for solving the navigation and scientific tasks of the Phobos-Grunt mission. It consists of two narrow-angle and two wide-angle television cameras. Each camera has a built-in processor for the real-time processing of received images. The program of TVSNG observations includes three modes: Imaging of Stars, Sequential Imaging, and Landing. The first two modes will be used to calibrate the TVSNG against the stars, to take images of Phobos and Mars, and to detect the dust rings of Mars. In the Landing mode, the height and velocity components of the spacecraft during the landing on Phobos will be measured, and an autonomous selection of the landing site will be made.     

Bayesian modelling of clusters of galaxies from multifrequency-pointed Sunyaev–Zel'dovich observations

We present a Bayesian approach to modelling galaxy clusters using multi-frequency pointed observations from telescopes that exploit the Sunyaev–Zel'dovich effect. We use the recently developed multinest technique to explore the high-dimensional parameter spaces and also to calculate the Bayesian evidence. This permits robust parameter estimation as well as model comparison. Tests on simulated Arcminute Microkelvin Imager observations of a cluster, in the presence of primary CMB signal, radio point sources (detected as well as an unresolved background) and receiver noise, show that our algorithm is able to analyse jointly the data from six frequency channels, sample the posterior space of the model and calculate the Bayesian evidence very efficiently on a single processor. We also illustrate the robustness of our detection process by applying it to a field with radio sources and primordial CMB but no cluster, and show that indeed no cluster is identified. The extension of our methodology to the detection and modelling of multiple clusters in multi-frequency SZ survey data will be described in a future work.     

A design for digital signal processing in a large field radio patrol camera

An FFT processor is being developed for the present pilot system of the large field radio patrol camera. A design of the processor is discussed.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.     

Chandra observations of neutron stars: an overview

We present an overview of Chandra X-ray Observatory observations of neutron stars. The outstanding spatial and spectral resolution of this great observatory have allowed for observations of unprecedented clarity and accuracy. Many of these observations have provided new insights into neutron star physics. We present an admittedly biased and overly brief review of these observations, highlighting some new discoveries made possible by the Observatory’s unique capabilities. This includes our analysis of recent multiwavelength observations of the putative pulsar and its pulsar-wind nebula in the IC443 SNR.      

Initial CHIP He I Observations of Solar Limb Activity

A new instrument capable of 3-min time resolution full-disk and limb observations in the Hei 1083 nm spectral line has been in operation at the High Altitude Observatory's Mauna Loa Solar Observatory (MLSO) since April 1996. We discuss instrument capabilities and performance and present some initial observations of limb activity from the first year of instrument operation. We compare limb Hei and Hα observations of quiescent and active prominences, comment on the role of Doppler shifts in interpreting the Hei observations, and illustrate the use of disk/limb Hei observations of a CME-associated eruptive filament in mass-ejection studies.     

UBV photometry of HR 1176

We present photoelectricUBV observations of the suspected Caii emission line star HR 1176. A period analysis of the observations by using the method of Shell-Metzner failed to yield any true period which is probably due to (i) the large gaps in the observations, (ii) low-amplitude variation, and (iii) the nonconstancy of the period, or there may be no regular light variation. A visual inspection of the present observations shows no systematic or abrupt variability except some scatter. However, a long period eclipsing nature of HR 1176 cannot be ruled out by this observations.     

Location of the rotation axis of a tumbling cylindrical earth satellite by using visual observations: Part II: Results

The method described in Part I of this paper has been applied to some observations of the satellite 76-115-B, in order to locate the rotation axis at various times between April 1977 and January 1978. The results are mostly consistent and suggest that the axis has drifted at a rate of 3–5°/day on some occasions. A continuous suggested track for the axis is not presented, because of the long intervals between some groups of observations.     

X-Ray Binaries in Nearby Galaxies

In the last few years Chandra observations have revolutionized the study of X-ray binaries by extending observed samples to extragalactic distances and stellar environments of varied star formation history. Here we summarize some of our results related to the interpretation of current observations of young star clusters and of elliptical galaxies.     

A systematic study of variability in a sample of ultraluminous X-ray sources

We present results from a study of short-term variability in 19 archival observations by XMM–Newton of 16 ultraluminous X-ray sources (ULXs). Eight observations (six sources) showed intrinsic variability with power spectra in the form of either a power-law or broken power-law-like continuum and in some cases quasi-periodic oscillations (QPOs). The remaining observations were used to place upper limits on the strength of possible variability hidden within. Seven observations (seven sources) yielded upper limits comparable to, or higher than, the values measured from those observations with detectable variations. These represented the seven faintest sources, all with   f_x < 3 × 10⁻¹² erg cm⁻² s⁻¹  . In contrast, there are four observations (three sources) that gave upper limits significantly lower than both the values measured from the ULX observations with detectable variations, and the values expected by comparison with luminous Galactic black hole X-ray binaries (BHBs) and active galactic nuclei (AGN) in the observed frequency bandpass (10⁻³–1 Hz). This is the case irrespective of whether one assumes characteristic frequencies appropriate for a stellar mass  (10 M_⊙)  or an intermediate mass  (1000 M_⊙)  black hole, and means that in some ULXs the variability is significantly suppressed compared to bright BHBs and AGN. We discuss ways to account for this unusual suppression in terms of both observational and intrinsic effects and whether these solutions are supported by our results.     

Stellar photometry in the region 1300–2000 Å, part II

Observations have been made at 1450Å of 94 early type stars. Comparison is made with other observations, and in general, good agreement has been found. Errors in absolute calibration of earlier observations have led to some disagreement. The presented data agree well with theoretical stellar models which include the effects of line blanketing.     

High spectral resolution X‐ray observations of AGN

A brief overview of some highlights of high spectral resolution X‐ray observations of AGN is given, mainly obtained with the RGS of XMM‐Newton. Future prospects for such observations with XMM‐Newton are given. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Weak-Field Magnetogram Calibration using Advanced Stokes Polarimeter Flux Density Maps – II. SOHO/MDI Full-Disk Mode Calibration

Cotemporal Nii 676.8 nm full-disk magnetograms from the Michelson Doppler Interferometer (MDI) instrument on SOHO and the Advanced Stokes Polarimeter (ASP) are quantitatively compared using observations of active region AR 8218, a large negative polarity sunspot group observed at S20 W22 on 13 May 1998. MDI produces flux density estimates based on a polarized line center-of-gravity algorithm using moderate spectral resolution filtergrams with approximately 4 arc sec angular resolution. The magnetograms are formed by an on-board image processor and sent to the ground where they are calibrated using an empirical model to produce flux density maps. The ASP uses high spectral resolution Stokes polarimetric observations to produce very high precision vector magnetic field maps at angular resolution values on the order of 1 arc sec in good seeing. We use ASP inversion results to create a reference ASP `longitudinal magnetic flux density map' with which to calibrate the MDI full-disk magnetograms. The magnetograms from each instrument are scaled to a common reference frame and co-aligned with an accuracy of about 1.6 arc sec. Regions of invalid data, poor field-of-view overlap, and sunspots are masked out in order to calibrate MDI predominately on the relatively vertical `weak-field' plage magnetic elements. Pixel-to-pixel statistical comparisons are used to determine an MDI magnetogram linear calibration relative to reference ASP flux density values. We find that the current Level-1.5 MDI full-disk calibration gives flux density values lower on average by a factor of 0.64±0.013 compared to the ASP reference in active region plage. In sunspot regions (penumbra and umbra) the factor is 0.69±0.007.     

Methods and statistics of TV observations of telescopic meteors

A review of TV and telescopic methods of meteor observations and of the problems of meteor astronomy addressed using these methods is presented. A meteor patrol developed at the Astronomical Observatory of Odessa National University and based on a Schmidt telescope and a TV detector is described. The meteor patrol allows meteor events to be recorded with a time resolution of 0.04 s. The investigated characteristics of the patrol are reported, and some aspects of the methods of observations and reduction employed are considered. The results of observations made during the period 2003–2004 are reported. A total of 368 meteors were recorded on 1093 individual frames during a total patrol time of 679 hours within a 36′ × 48′ field of view. The statistical data for meteor observations are reported, and classification of meteor images is presented. The specific features of some recorded meteor events are analyzed.     

Keck Observations of Solar System Objects: Perspectives for Extremely Large Telescopes

From differential tracking techniques, required for appulse observations of KBOs with Laser Guide Star Adaptive Optics (LGSAO), to developing methods for collecting spectra at the precise moment of a predicted impact, each Solar System observation conducted on a large telescope presents a unique set of challenges. We present operational details and some key science results from our science program, adaptive optics observations of main belt asteroids and near earth objects; as well as the technical and operational details of several Keck Solar System observations conducted by other teams: the impact of Shoemaker-Levy 9 on Jupiter, volcanoes on Io, the Deep Impact mission to Comet 9P/Tempel 1, and recent observations of Pluto’s moons Nix and Hydra. For each of these observations, we draw from our Keck experience to predict what challenges may lie ahead when similar observations are conducted on next generation telescopes.     

Dark matter: the connection with gamma-ray astrophysics

We review the status of indirect Dark Matter searches, focusing in particular on the connection with gamma-ray Astrophysics. After a brief introduction where we review the strong motivations for indirect searches, we tackle the question of how one can “discover” Dark Matter particles with astrophysical observations. To this purpose, I will discuss some recent conflicting claims that have generated some confusion in the field, and present new strategies that may provide robust enough evidence to claim discovery, based only on astrophysical observations.     

一种基于RTAI实时操作系统的相关跟踪处理机

引入倾斜校正自适应光学技术到月球激光测距中,详细介绍了倾斜校正自适应光学的相关跟踪原理,给出了一种基于实时操作系统RTAI的相关跟踪波前处理机的设计结果.该波前处理机采用绝对差分算法,使用通用CPU,基于Linux硬实时扩展系统BTAI实现对波前的实时处理.实验结果证明,它的相关跟踪处理帧频为1 KHz,并且具有集成度...