CCD astronomical applications for X-ray temporal studies

Charge coupled devices (CCDs) are under active investigation as imaging detectors in future X-ray astronomy satellites. The exploitation of such detectors holds great promise because of their capability to perform simultaneous imaging and spectroscopy. Unfortunately, standard readout techniques give a temporal resolution insufficient to study X-ray sources showing variability on timescales less than few seconds. In this paper alternative, non-imaging readout modes are investigated, in order to achieve millisecond temporal resolution for point-like sources. Simulation results are presented for the EPIC camera, the focal plane instrument for ESA's mission XMM, showing that the required temporal capabilities can be reached without loss of energy resolution.Work performed in part at the IFC/CNR, Milan, supported by a special EPIC grant from LABEN S.p.A.     

An image converter-intensifier detector for high-resolution astronomical spectroscopy in the balloon ultraviolet

A rugged and compact image converter-intensifier camera has been developed for a balloon-borne spectrograph used in a programme of UV astronomical interference spectroscopy. Details are given of the construction of this new detector and of relevant performance characteristics in comparison with direct photography.     

Electron density variations during ultraviolet transient events

% High-resolution temporal observations performed with the SUMER spectrometer on SOHO provide an opportunity to investigate the electron density variations in the `quiet-Sun' solar transition region due to UV transient events. Two datasets obtained in the density sensitive lines belonging to the Oiv 1400 Å multiplet were searched for such events, leading to the identification of two explosive events, on 10 July 1996 and 31 May 1997. In both cases, the Oiv 1401.16/1404.81 density-sensitive line intensity ratio shows a clear variation, corresponding to enhancements in the electron density by factors of 3. This is fully consistent with recent 2.5D MHD simulations. The 10 July 1996 dataset also provided us with the opportunity to monitor the behavior of the electron density through an UV blinker. Despite an increase of a factor of two in the line intensities, no variation of the electron density was found. This suggests that the intensity enhancement is due to an increase in the filling factor.     

A new spectrum analyzer for radio astronomical studies with the radio telescope RATAN-600

The spectral measuring facility with a new Fourier analyzer for use with the radio telescope RATAN-600 is described and its experimental data are reported.     

Super resolution for astronomical observations

In order to obtain detailed information from multiple telescope observations a general blind super-resolution (SR) reconstruction approach for astronomical images is proposed in this paper. A pixel-reliability-based SR reconstruction algorithm is described and implemented, where the developed process incorporates flat field correction, automatic star searching and centering, iterative star matching, and sub-pixel image registration. Images captured by the 1-m telescope at Yunnan Observatory are used to test the proposed technique. The results of these experiments indicate that, following SR reconstruction, faint stars are more distinct, bright stars have sharper profiles, and the backgrounds have higher details; thus these results benefit from the high-precision star centering and image registration provided by the developed method. Application of the proposed approach not only provides more opportunities for new discoveries from astronomical image sequences, but will also contribute to enhancing the capabilities of most spatial or ground-based telescopes.     

Research on Wide-field Imaging Techniques for Low-frequency Radio Arraytwo

Wide-field imaging of low-frequency radio telescopes is subject to a number of difficult problems. One particularly pernicious problem is the non-coplanar baseline effect. It will lead to distortion of the final image when the phase of $w$-direction called $w$-term is ignored. The image degradation effects are amplified for the telescopes with a wide field of view. This paper summarizes and analyzes several $w$-term correction methods and their technical principles. Their advantages and disadvantages are analyzed after comparing their computational cost and computational complexity. We conduct simulations with two of these methods, i.e., faceting and $w$-projection, based on the configuration of the first-phase Square Kilometre Array (SKA) low-frequency array. The resulted images are also compared with the result of the two-dimensional Fourier transform method. The results show that the image quality and correctness derived from both faceting and $w$-projection are better than the two-dimensional Fourier transform method in wide-field imaging. The effects of the number of facets and the $w$-direction step length on the image quality and running time are evaluated. The results indicate that the number of facets and the $w$-direction step length must be reasonable. Finally, we analyze the effect of data size on the running times of the faceting and $w$-projection algorithms. The results show that the faceting and $w$-projection algorithms need to be optimized before the huge amount of data processing. The research of the present paper initiates the analysis of wide-field imaging techniques and their applications in the existing and future low-frequency arrays, and will foster their applications in even broader fields.     

Machine Learning for Improving Stellar Image-based Alignment in Wide-field Telescopes

Stellar images will deteriorate dramatically when the sensitive elements of wide-field survey telescopes are misaligned during an observation,and active alignme...     

Prospects for astronomical development in South Africa

Because of its geographical location and (astronomically) excellent climate South Africa can make an unique contribution to international astronomical research. An assessment of recent developments in telescope technology has shown that an advanced technology telescope of 4m-class can be constructed which will out-perform most existing 4m-class telescopes. Detailed consideration is given to the construction of such a telescope for optical/infrared astronomy, the new science that this will enable and the selection of a site of sufficiently good quality to justify the erection of such a telescope. If a telescope of this nature is sited in southern Africa it would provide the premier astronomical facility in Africa for decades to come.     

Detrending time series for astronomical variability surveys

We present a detrending algorithm for the removal of trends in time series. Trends in time series could be caused by various systematic and random noise sources such as cloud passages, changes of airmass, telescope vibration, CCD noise or defects of photometry. Those trends undermine the intrinsic signals of stars and should be removed. We determine the trends from subsets of stars that are highly correlated among themselves. These subsets are selected based on a hierarchical tree clustering algorithm. A bottom-up merging algorithm based on the departure from normal distribution in the correlation is developed to identify subsets, which we call clusters. After identification of clusters, we determine a trend per cluster by weighted sum of normalized light curves. We then use quadratic programming to detrend all individual light curves based on these determined trends. Experimental results with synthetic light curves containing artificial trends and events are presented. Results from other detrending methods are also compared. The developed algorithm can be applied to time series for trend removal in both narrow and wide field astronomy.     

AstroGrid-D: Grid technology for astronomical science

We present status and results of AstroGrid-D, a joint effort of astrophysicists and computer scientists to employ grid technology for scientific applications. AstroGrid-D provides access to a network of distributed machines with a set of commands as well as software interfaces. It allows simple use of computer and storage facilities and to schedule or monitor compute tasks and data management. It is based on the Globus Toolkit middleware (GT4).Chapter 1 describes the context which led to the demand for advanced software solutions in Astrophysics, and we state the goals of the project.We then present characteristic astrophysical applications that have been implemented on AstroGrid-D in chapter 2. We describe simulations of different complexity, compute-intensive calculations running on multiple sites (Section 2.1), and advanced applications for specific scientific purposes (Section 2.2), such as a connection to robotic telescopes (Section 2.2.3). We can show from these examples how grid execution improves e.g. the scientific workflow.Chapter 3 explains the software tools and services that we adapted or newly developed. Section 3.1 is focused on the administrative aspects of the infrastructure, to manage users and monitor activity. Section 3.2 characterises the central components of our architecture: The AstroGrid-D information service to collect and store metadata, a file management system, the data management system, and a job manager for automatic submission of compute tasks.We summarise the successfully established infrastructure in chapter 4, concluding with our future plans to establish AstroGrid-D as a platform of modern e-Astronomy.     

Software design for panoramic astronomical pipeline processing

We describe the software requirement and design specifications for all-sky panoramic astronomical pipelines. The described software aims to meet the specific needs of superwide-angle optics, and includes cosmic-ray hit rejection, image compression, star recognition, sky opacity analysis, transient detection and a web server allowing access to real-time and archived data. The presented software is being regularly used for the pipeline processing of 11 all-sky cameras located in some of the world's premier observatories. We encourage all-sky camera operators to use our software and/or our hosting services and become part of the global Night Sky Live network.     

Automatic guide for the Raduga astronomical spectrograph

An automatic mirror guide has been designed and made for the Raduga fiber-optic echelle spectrograph. The new device was built into one of the parts of the spectrograph and allows the work of observers to be facilitated significantly. The automatic guide efficiently removes stellar image oscillations at frequencies of 0–2 Hz, which compensates almost completely for errors in setting the polar axis of a telescope and in its clockwork drive. The guide can be used on any telescope with a focal length of more than 5 m and has operated on two different telescopes. Over two observing seasons, several hundred stellar spectra were taken with the Raduga spectrograph using the automatic guide.     

A high-resolution Fabry-Pérot spectrometer for emission line studies in planetary nebulae and other extended astronomical objects

We describe here a scanning piezo-electric Fabry-Pérot spectrometer operating in the photoncounting mode whose plate spacing and parallelism are maintained by a servo-controlled system, ensuring high accuracy, for the study of emission lines from extended astronomical objects in the spectral range 4500–7000 Å. Details of the optical set-up and the Data Acquisition System (DAS) are described. Its performance at the Cassegrain focus of the 1 m telescope at Kavalur is discussed. Some line profiles on planetary nebulae studied with the above spectrometer are also presented.     

Advanced null Maksutov test for astronomical aspherical mirrors

The advanced null Maksutov test for concave aspherical mirrors using single reflection from the concave spherical reference mirror is proposed. The test is free of the disadvantages of the original Maksutov test and is preferable for high-precision testing of mirrors using bulky testing equipment.     

TIRCAM: A mid-IR camera for astronomical imaging

We present the main characteristics of a new mid-IR camera, TIRCAM, operating at the 1.5 m Italian Infrared Telescope.     

Air-clad fibres for astronomical instrumentation: focal-ratio degradation

Focal-ratio degradation (FRD) of light launched into high-numerical aperture (NA) single-annulus all-silica undoped air-clad fibres at an NA of 0.54 is reported. The measured annular light distribution remained Gaussian after 30 m of propagation, but the angular FWHM of the output annulus doubled from 4° after 1 m propagation to 8.5° after 30 m, which is significantly larger than that reported of standard doped-silica fibres (NA < 0.22). No significant diffractive effects were observed. The design of air-clad fibres for broad-band, high-NA astrophotonics applications is discussed.     

Horizon synthesis for archaeo‐astronomical purposes

In this paper I describe a simple numerical procedure to compute synthetic horizon altitude profiles for any given site. The method makes use of a simplified model of local Earth's curvature, and it is based on the availability of digital elevation models describing the topography of the area surrounding the site under study. Examples constructed using the Shuttle Radar Topographic Mission (SRTM) data (with 90 m horizontal resolution) are illustrated, and compared to direct theodolite measurements. The proposed method appears to be reliable and applicable in all cases when the distance to the local horizon is larger than ∼10 km, yielding a rms accuracy of ∼0.1 degrees (both in azimuth and elevation). Higher accuracies can be achieved with higher resolution digital elevation models, like those produced by many modern national geodetic surveys (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)