Using nicmos arrays to study galaxies

The 256×256 HgCdTe arrays developed for the NICMOS (Near-Infrared Camera and Multi-object Spectrometer) project have proven to be very capable devices for extragalactic imaging. This paper describes a sampling of extragalactic results from NICMOS arrays. A brief summary of the history of the development of these arrays, and their outstanding performance characteristics is also given.     

The impact of radio source structure on European geodetic VLBI measurements

European geodetic very long baseline interferometry (VLBI) sessions (also known as EUROPE sessions) have been carried out on a regular basis for the past 15 years to study relative crustal motions within Europe. These sessions are based on observations of extragalactic radio sources, which serve as distant fiducial marks to establish an accurate and stable celestial reference frame for long-term geodetic measurements. The radio sources, however, are not always point-like on milliarcsecond scales, as VLBI imaging has revealed. In this work, we quantify the magnitude of the expected effect of intrinsic source structure on geodetic bandwidth synthesis delay VLBI measurements for a subset of 14 sources regularly observed during the EUROPE sessions. These sources have been imaged at both X-band (8.4 GHz) and S-band (2.3 GHz) based on dedicated observations acquired with the European VLBI Network (EVN) in November 1996. The results of this calculation indicate that the reference source 0457+024 causes significant structural effects in measurements obtained on European VLBI baselines (about 10 picoseconds on average), whereas most of the other sources produce effects that are only occasionally larger than a few picoseconds. Applying the derived source structure models to the data of the EUROPE5-96 session carried out at the same epoch as the EVN experiment shows no noticeable changes in the estimated VLBI station locations.     

TACTIC Imaging γ-Ray Telescope: A Simulation Study of the Effect of Switched-off Pixels on Its Quality Factor

The 349-pixel Cerenkov Light Imaging Camera of the -raytelescope array, TACTIC, has been recently commissioned at Mt.Abu, India. This telescope is being used for gamma-ray sourceobservations at photon energies above 0.5 TeV. Comprehensivesimulation studies, using the CORSIKA air-shower code, are inprogress to predict and optimize the performance of the TACTIC.In this short note, we study the expected performance of theImaging Element of the TACTIC under conditions of a pixelswitch-off, forced either by the well-known star-rotationphenomenon or by a defective instrumentation channel. Thechanges in the image parameters, and the resulting telescopequality factor, are studied after simulating two representativecases of pixel shut-down.     

Impact of aerosols and adverse atmospheric conditions on the data quality for spectral analysis of the H.E.S.S. telescopes

The Earth’s atmosphere is an integral part of the detector in ground-based imaging atmospheric Cherenkov telescope (IACT) experiments and has to be taken into account in the calibration. Atmospheric and hardware-related deviations from simulated conditions can result in the mis-reconstruction of primary particle energies and therefore of source spectra. During the eight years of observations with the High Energy Stereoscopic System (H.E.S.S.) in Namibia, the overall yield in Cherenkov photons has varied strongly with time due to gradual hardware aging, together with adjustments of the hardware components, and natural, as well as anthropogenic, variations of the atmospheric transparency. Here we present robust data selection criteria that minimize these effects over the full data set of the H.E.S.S. experiment and introduce the Cherenkov transparency coefficient as a new atmospheric monitoring quantity. The influence of atmospheric transparency, as quantified by this coefficient, on energy reconstruction and spectral parameters is examined and its correlation with the aerosol optical depth (AOD) of independent MISR satellite measurements and local measurements of atmospheric clarity is investigated.     

Acta Geologica Sinica （English Edition） Calls For Submission of Review Papers

正Acta Geologica Sinica(English Edition)is a bimonthly,SCI-indexed academic journal produced by the Geological Society of China.Having an impact factor ranging from 1.5 to 2.15,it has long been indexed by many international databases and websites,such as SCI,CA,BIG,etc.Internationally,the journal cooperates with John WileySons Co.Ltd to publish the electronic version;all papers can be downloaded online.Contributors wishing to submit,read,enquire and     

Acta Geologica Sinica (English Edition) Calls For Submission of Review Papers

正Acta Geologica Sinica(English Edition) is a bimonthly,SCI-indexed academic journal produced by the Geological Society of China.Having an impact factor ranging from 1.5 to 2.15,it has long been indexed by many international databases and websites,such as SCI,CA,BIG,etc.Internationally,the journal cooperates with John WileySons Co.Ltd to publish the electronic version;all papers can be downloaded online.Contributors wishing to submit,read,enquire and     

"日中乌"辨析

从观测资料可认证史载“日中乌”是指太阳黑子,而“阳乌载日”则是日全食时的日冕。二者并非神话,而是写实文字。     

Maurice Loewy and the equatorial Coudé in Vienna

Moritz (Maurice) Loewy was born in Vienna, studied in Vienna and emigrated to France because he was a Jew and could not get a position in Vienna. In Paris he became director of the observatory. Our investigation removes the ambiguity on Maurice Loewy's birthplace, and we conclude that he was born in Vienna in 1833 (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dwingeloo – the golden radio telescope

The Dwingeloo 25‐m telesope, inaugurated in 1956, has played a major role in research for half a century. We trace its history back to its conception in 1944, and summarize its main achievements. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)