IRS: The Infrared Spectrograph on SIRTF

The Universidad Politécnica de Madrid participates in the MINISAT 01 program as the experiment CPLM responsible. This experiment aims at the study of the fluid behaviour in reduced gravity conditions. The interest of this study is and has been widely recognised by the scientific community and has potential applications in the pharmaceutical and microelectronic technologies (crystal growth), among others. The scientific team which has developed the CPLM experiment has a wide experience in this field and had participate in the performance of a large number of experiments on the fluid behaviour in reduced gravity conditions in flight (Spacelab missions, TEXUS sounding rockets, KC-135 and Caravelle aeroplanes, drop towers, as well as on earth labs (neutralbuoyancy and small scale simulations). The experimental equipment used in CPLMis a version of the payload developed for experimentation on drop towers and on board microsatellites as the UPM-Sat 1, adapted to fly on board MINISAT 01.     

Observing with SIRTF: Opportunities for the Scientific Community

The Space InfraRed Telescope Facility (SIRTF) is the fourth and finalelement in NASA's family of orbiting Great Observatories. SIRTFconsists of a 0.85-meter diameter telescope and three cryogenically-cooledscience instruments capable of observing from the near- to the far-infrared,between 3 and 180 m. Incorporating the latest in large-format infrareddetector arrays, SIRTF offers orders-of-magnitude improvements in capabilityover existing facilities. Launch is scheduled for December 2001, with ananticipated lifetime of up to 5 years. SIRTF will observe targets rangingfrom small, icy bodies in the outer Solar System to the most luminousknown objects in the distant reaches of the Universe. SIRTF representsan important scientific and technical bridge to NASA's new Origins program,and is managed for NASA by the Jet Propulsion Laboratory, CaliforniaInstitute of Technology.     

Observing and Calibration Strategies for FIR Imaging with SIRTF

We present data from a 16×32 array of unstressed Ge:Gadetectors, showing the long time constant responses and hook effectcharacteristic of these devices. This array is half the size of the70 m imaging array planned for MIPS, the Multiband ImagingPhotometer for SIRTF. We present simulations of the FIR (farinfrared) sky as viewed by a MIPS array, including realistic noiseeffects and extraction of point sources with a standard photometrypackage, showing that the photometric goals of MIPS are attainablewith the current array performance and using standard analysistechniques. Previous calculations by Heim et al. (1998) haddetermined that MIPS would achieve 5- detections of 1 mJy at 70 m in 2000 s; the simulations presented hereobtain results consistent with those calculations.     

Confusion limit resulting from galaxies: using the Infrared Array Camera on board SIRTF

Recent ISO data have allowed, for the first time, observationally based estimates for source confusion in mid-infrared surveys. We use the extragalactic source counts from ISOCAM in conjunction with K -band counts to predict the confusion resulting from galaxies in deep mid-infrared observations. We specifically concentrate on the near-future Space Infrared Telescope Facility ( SIRTF ) mission, and calculate expected confusion for the Infrared Array Camera (IRAC) on board SIRTF . A defining scientific goal of the IRAC instrument will be the study of high-redshift galaxies using a deep, confusion-limited wide-field survey at 3–10 μm . A deep survey can reach 3-μJy sources with reasonable confidence in the shorter wavelength IRAC bands. Truly confusion-limited images with the 8 μm will be difficult to obtain because of practical time constraints, unless infrared galaxies exhibit very strong evolution beyond the deepest current observations. We find L * galaxies to be detectable to z =3–3.5 at 8 μm, which is slightly more pessimistic than found in 1999 by Simpson & Eisenhardt.     

Active Adaptive Arrays: The ASTRON Approach to SKA

It has been argued, for a number of reasons, that the next generation radio telescope should be a multi-element interferometer with a collecting area of about 1 km². The remaining parameters of such an instrument – frequency range, angular resolution, instantaneous bandwidth, etc. – will be science driven. The requirements for propagation studies are briefly discussed, and it is pointed out how variable-source confusion may differ from the normal variety. Finally, the Dutch project to achieve a large collecting area using adaptive arrays of active antennas is described. A systematic approach has been adopted, with the construction of arrays of increasing complexity to test design features at each state. Recently, development of a low frequency array (LOFAR) has become an additional option. It would facilitate tests of some of the larger instrument's features, and provide real data on the influence of the ionosphere and interfering sources. This revised version was published online in July 2006 with corrections to the Cover Date.     

A Golden Era for Astronomy: The Advent of CCDs and Infrared Arrays

The advent of solid-state imaging devices transformed astronomy. Beginning with the introduction into astronomy of charge-coupled devices in 1976, followed a decade later by infrared arrays, astronomers gained access to near-perfect imaging devices. The consequences have been nothing short of revolutionary, perhaps especially so in the infrared. Witness, for example, the spectacular pictures from the Hubble Space Telescope cameras, or the impressive infrared imagery from the 2MASS project. Within the last decade CCD formats deployed or planned for use in ground-based cameras have become huge. Infrared mosaics, stimulated by the Next Generation Space Telescope, are coming soon. In addition, new technologies such as CMOS (Complementary Metal Oxide Semiconductors) and STJs (Superconductiong Tunnel Junctions) are being developed and the future of astronomical detectors looks very exciting, especially in an era of giant telescopes performing at their diffraction-limit. This revised version was published online in July 2006 with corrections to the Cover Date.     

Conversion Gain and Interpixel Capacitance of Cmos Hybrid Focal Plane Arrays

The conversion gain of optical and infrared focal plane CMOS hybrid arrays is a fundamental parameter, whose value computes into the derivation of other parameters characterizing the performance of a detector. The widespread “noise squared versus signal” method used to obtain the conversion gain can overestimate the nodal capacitance of the detector pixel by more than 20% for infrared arrays and by more than 100% for Si-PIN diode arrays. This is because this method does not take account of the capacitive coupling between neighboring pixels. A simple technique has been developed to measure the nodal capacitance directly by comparing the voltage change of an external calibrated capacitor with the voltage change on the nodal capacitor of the detector pixel. The method is elaborated in detail and has been verified with a Si-PIN diode array hybridized to a Hawaii-2RG multiplexer using an Fe ⁵⁵ X-ray source. It is also in good agreement with a stochastic method based on 2D autocorrelation.     

Efficiency Analysis of Focal Plane Arrays in Deep Dishes

In this paper we demonstrate the practical analysis of a dense Focal Plane Array (FPA) for a deep dish radio telescope. The analytical model is used to optimize efficiency and bandwidth of deep dish system by varying design parameters such as feed size and FPA aperture field. A prototype FPA was evaluated on the Westerbork Synthesis Radio Telescope (WSRT) and the resulting efficiency is discussed.     

The BL Lac heart of Centaurus A

We have observed emission from the nucleus of the closest radio galaxy, Centaurus A, from the radio to the gamma-ray band. We construct, for the first time, its overall spectral energy distribution (SED) which appears to be intriguingly similar to those of blazars, showing two broad peaks located in the far-infrared band and at ∼0.1 MeV respectively. The whole nuclear emission of Centaurus A is successfully reproduced with a synchrotron self-Compton model. The estimated physical parameters of the emitting source are similar to those of BL Lacs, except for a much smaller beaming factor, as qualitatively expected when a relativistic jet is orientated at a large angle to the line of sight. These results represent strong evidence that Centaurus A is indeed a misoriented BL Lac, and provide strong support in favour of the unification scheme for low-luminosity radio-loud active galactic nuclei. Modelling of the SED of Centaurus A also provides further and independent indications of the presence of velocity structures in sub-parsec-scale jets.     

Readout Techniques for Drift and Low Frequency Noise Rejection in Infrared Arrays

Three different methods are presented to subtract thermal drifts and low-frequency noise from the signal of infrared array. The first is dead pixels with open Indium bumps, the second is reference output as implemented on the Hawaii2 multiplexer, and the third is dark pixels to emulate reference cells having a capacity connected to the gate of the unit cell field-effect transistor (FET). The third method is the most effective and yields a reduction in readout noise from15.4–9.4 erms. A novel method will be described to extend this readout technique to the Aladdin 1 K × 1 K InSb array. This revised version was published online in July 2006 with corrections to the Cover Date.     

基于以太网的CSRH天线阵控制系统研究方案

中国频谱日像仪(Chinese Spectral Radioheliograph,CSRH)一期工程包括40面天线(400 MHz ～2 GHz)组成的天线阵,二期工程包括60面天线(2～15 GHz).天线统一控制包括天线指向调整、目标源跟踪、射电定标等.无论何种情况,所有的天线均需统一协调工作.对CSRH天线阵列整体控制进行了研究,提出了一种基于以太网的CSRH天线阵控制方案,并对可能遇到的关键问题进行分析.     

Artificial Neural Network Approach for Reconstruction of Event Arrival-Direction in Wide-Angle Atmospheric Cerenkov Detector Arrays: A Feasibility Study

A feasibility study has been carried out to assess the potentialof an Artificial Neural Network (ANN) for determiningthe direction of incidence of an Atmospheric Cerenkov Event(ACE) from the arrival-time information registered by aspaced-array of wide-angle Cerenkov detectors. Theresults obtained so far, using both, simulated and experimental data, indicate that a properly-trained net can yield a degree of accuracy which is comparable with what is achieved through the conventional ²-minimization, wavefront-fitting procedure.     

Measurements of Beam Pattern Perturbation in Corrugated Feed Horn Arrays for CMB Observations

An experimental study on the perturbation of the angular response of a W-band corrugated horn produced by nearby feeds, reproducing a typical situation of multi-feed arrays commonly used in high sensitivity Cosmic Microwave Background instruments, is reported in this paper. The effects for different positions of the scattering horn in the two principal polarisation planes were measured. We analyze the effects on both the side-lobe level and on the main beam. In particular, these results allowed us to validate design criterion for the multi-frequency focal array of the ESA PLANCK mission.This revised version was published online in July 2005. The first author’s e-mail address was removed.     

Gravitational waves from resolvable massive black hole binary systems and observations with Pulsar Timing Arrays

Massive black holes are key components of the assembly and evolution of cosmic structures, and a number of surveys are currently on going or planned to probe the demographics of these objects and to gain insight into the relevant physical processes. Pulsar Timing Arrays (PTAs) currently provide the only means to observe gravitational radiation from massive black hole binary systems with masses  ≳10⁷ M_⊙  . The whole cosmic population produces a stochastic background that could be detectable with upcoming PTAs. Sources sufficiently close and/or massive generate gravitational radiation that significantly exceeds the level of the background and could be individually resolved. We consider a wide range of massive black hole binary assembly scenarios, investigate the distribution of the main physical parameters of the sources, such as masses and redshift, and explore the consequences for PTAs observations. Depending on the specific massive black hole population model, we estimate that on average at least one resolvable source produces timing residuals in the range  ∼5–50 ns  . PTAs, and in particular the future Square Kilometre Array, can plausibly detect these unique systems, although the events are likely to be rare. These observations would naturally complement on the high-mass end of the massive black hole distribution function future surveys carried out by the Laser Interferometer Space Antenna .     

Cost Effective Frequency Ranges For Multi-Beam Dishes, Cylinders, Aperture Arrays, and Hybrids

Five out of six Square Kilometre Array (SKA) science programs need extensive surveys at frequencies below 1.4 GHz and only four need high-frequency observations. The latter ones drive to expensive high surface accuracy collecting area, while the former ask for multi-beam receiver systems and extensive post correlation processing. In this paper, we analyze the system cost of a SKA when the field-of-view (Fov) is extended from 1 deg² at 1.4 GHz to 200 deg² at 0.7 GHz for three different antenna concepts. We start our analysis by discussing the fundamental limitations and cost issues of wide-band focal plane arrays (FPA) in dishes and cylinders and of wide-band receptors in aperture arrays. We will show that a hybrid SKA in three different antenna technologies will give the highest effective sensitivity for all six key science programs.     

Evolution of ground-based gamma-ray astronomy from the early days to the Cherenkov Telescope Arrays

Most of what we know of cosmic gamma rays has come from spacecraft, but at energies above tens of GeV it has become possible to make observations with ground-based detectors of enormously greater collecting area. In recent years one such detector type, the cluster of imaging air Cherenkov telescopes, has reached a very productive state, whilst several alternative approaches have been explored, including converted solar power collectors and novel high-altitude particle shower detectors which promised to extend the energy range covered. Key examples of development from 1952 to 2011 are followed, noting the problems and discoveries that stimulated the current work, explaining the logic of the alternative approaches that were taken. The merits of the current major Cherenkov observatories and of other viable detectors are examined and compared, with examples of the astrophysical information they are beginning to provide. The detectors are still evolving, as we still do not understand the processes onto which the gamma rays provide a window. These include the acceleration of Galactic cosmic rays (in particular, the wide-band spectra of radiation from some individual supernova remnants are still hard to interpret), the highly relativistic and variable jets from active galactic nuclei, and aspects of the electrodynamics of pulsars. Larger groups of Cherenkov telescopes still offer the possibility of an increase in power of the technique for resolvable Galactic sources especially.     

A Study of the Effect of Geomagnetic Field on Extensive Air Showers with Small Arrays

We have studied Extensive Air Showers (EAS) with two small arraysof 1 m² scintillation detectors inTehran, 1200 m above sea level.The distribution of air showersin zenith and azimuth angles has been studied and a cosⁿΘdistribution with n = 7.2±0.2 was obtained for zenith angledistribution. An asymmetry has been observed in the azimuthaldistribution of EAS of cosmic rays because of magnetic field ofthe Earth. Amplitudes of the first and the second harmonics ofobserved distribution depend on zenith angle as A _I ≈ (0.02 + 0.35 sin²Θ)±0.02, and A _II ≈ (0.03 + 0.42 sin⁴Θ)±0.03. Meanwhile, the uncertainties arising from the instrument, transit location of shower particles in the scintillator and fluctuations in the shower front have been calculated.     

The sun and exoplanets: The solitude of man

Solar pulsations with a period of P ₀ = 9600.606(12) were discovered in 1974. A more recent discovery is that planetary distances in the solar system are subject to spatial resonance with the parameter L ₀ ?? cP ₀ ?? 9600 ls and that the P ₀ pulsation itself has cosmological significance (coherent cosmic oscillation, or the pace of absolute time of the universe; c is the speed of light). As of June 2011, 552 extrasolar planets have been discovered. Statistical analysis shows that the distribution of the semimajor axes of alien planets does not have L ₀ resonance. Moreover, it appears to have no resonance at all. This frustrates the 20th-century hopes for the existence of extraterrestrial civilizations and possible contact with them. They are simply not there. This explanation of the Fermi paradox, or the Great Silence, appears to rest on the triumph of the anthropic principle, which has been successfully implemented by nature within our planetary system. This leads to a vision whereby the cosmos seems to be created specially for us. The scale L ₀ indicates that the sun is a special quantum object, where L ₀ is a wave function parameter that is not subject to the rational principles of the classical world, but rather follows a peculiar, quantum logic.     

Ring and plasma: The enigmae of Enceladus

The E ring associated with the Kronian moon Enceladus has a lifetime of only a few thousand years against sputteringly by slow corotating O ions. The existence of the ring implies the necessity for a continuous supply of matter. Possible particle source mechanisms on Enceladus include meteoroidal impact ejection and geysering. Estimates of ejection rates of particulate debris following small meteoroid impact are on the order of 3 × 10^?18 g cm^?2 sec^?1, more than an order of magnitude too small to sustain the ring. A geyser source would need to generate a droplet supply at a rate of approximately 10^?16 g cm^?2 sec^? in order to account for a stable ring. Enceladus and the ring particles also directly supply both plasma and vapor to space via sputtering. The absence of a 60 eV plasma at the Voyager 2 Enceladus L-shell crossing, such as might have been expected from sputtering, cannot be explained by absorption and moderation of plasma ions by ring particles, because the ring is too diffuse. Evidently, the effective sputtering yield in the vicinity of Enceladus is on the order of, or smaller than, 0.4, about an order of magnitude less than the calculated value. Small scale surface roughness may account for some of this discrepancy.     

The chronology of Mercury's geological and geophysical evolution: The vulcanoid hypothesis

Previous discussions of Mercury's evolution have assumed that its cratering chronology is tied to that of the Moon, i.e., with Caloris forming about 3.9 Gyr ago as part of a late heavy bombardment that affected all of the terrestrial planets. That assumption requires that Mercury's core formed very early, because associated expansion features are not visible, and must have been erased before the cratering flux declined. Moreover, the modest amount of global shrinkage inferred from visible compressional features on Mercury's surface implies that the core is either largely molten at present, or had largely solidified before the end of the bombardment. The former interpretation requires a significant volatile content or implausibly large internal heat sources, while the latter raises questions about how to generate the planet's magnetic field. We have investigated whether constraints on Mercury's chronology could be relaxed by effects of a Mercury-specific bombarding population of planetesimals interior to its orbit, encountering the planet only occasionally due to secular perturbations. Such “vulcanoids” could have been a significant source of early cratering. However, those in orbits that can cross Mercury's are depleted by mutual collisions in ⪅1 Gyr, and can provide at most a modest extension of the period of heavy bombardment. Further inside Mercury's orbit, lower collisional velocities might allow survival of vulcanoids to the present. We report on a search for such bodies and on observational limits to such a population. We also review evidence that Mercury's intercrater plains are of volcanic origin and mainly predate Caloris, and that scarp formation (and global contraction) mainly postdates Caloris and has continued to recent times. If global lineaments are the product of tidal despinning, they constrain core formation to the first half of the planet's lifetime. While some questions and inconsistencies remain, the preponderance of evidence suggests that Mercury differentiated early, and at least half of its core volume is presently molten, probably due to a significant content of some light element such as sulfur.