Robert J. Hanisch

Denition of the Flexible Image Transport System (FITS)

The Flexible Image Transport System { FITS { has been in use in the astronomical community for over two decades. A newly updated version of the standard has recently been approved by the International Astronomical Union FITS Working Group. This new version of the standard appears here in its entirety. As a preface we briefly describe the process by which the standard evolves and revisions are approved, and note two minor changes to NOST 100{2.0 which were adopted by the IAU FWG.

Cosmic-Ray Rejection and Readout Efficiency for Large-Area Arrays

We present an algorithm to optimally process uniformly sampled array image data obtained with a nondestructive readout. The algorithm discards full wells, removes cosmic-ray (particle) hits and other glitches, and makes a nearly optimum estimate of the signal on each pixel. The algorithm also compresses the data. The computer requirements are modest, and the results are robust. The results are shown and compared to results of Fowler-sampled and -processed data. Nonideal detector performance may require some additional code, but this is not expected to cost much processing time. Known types of detector faults are addressed.

Imaging of z ~ 2 QSO Host Galaxies with the Hubble Space Telescope

We report on deep imaging in two filters with the planetary camera of the Hubble Space Telescope of five QSOs at redshift of ~2, with a range of optical and radio luminosity. The observations included a suite of point-spread function (PSF) observations that were used to construct new PSF models, described elsewhere by Dumont et al. The new PSF models were used to remove the QSO nucleus from the images. We find that the host galaxies have resolved flux of the order of 10% of the QSO nuclei and are generally luminous and blue, indicating active star formation. While most have clearly irregular morphologies, the bulk of the flux can be modeled approximately by an R1/4 law. However, all host galaxies also have an additional approximately exponential luminosity profile beyond a radius of about 08, as also seen in ground-based data with larger telescopes. The QSOs all have a number of nearby faint blue companions that may be young galaxies at the QSO redshift. We discuss implications for evolution of the host galaxies, their spheroidal populations, and central black holes.

Automated Classification of ROSAT Sources Using Heterogeneous Multiwavelength Source Catalogs

We describe an online system for automated classification of X-ray sources, ClassX, and we present preliminary results of classification of the three major catalogs of ROSAT sources, ROSAT All-Sky Survey (RASS) Bright Source Catalog, RASS Faint Source Catalog, and WGACAT, into six class categories: stars, white dwarfs, X-ray binaries, galaxies, active galactic nuclei, and clusters of galaxies. ClassX is based on a machine-learning technology. It represents a system of classifiers, each classifier consisting of a considerable number of oblique decision trees. These trees are built as the classifier is trained to recognize various classes of objects using a training sample of sources of known object types. Each source is characterized by a preselected set of parameters, or attributes; the same set is then used as the classifier conducts classification of sources of unknown identity. The ClassX pipeline features an automatic search for X-ray source counterparts among heterogeneous data sets in online data archives using Virtual Observatory protocols; it retrieves from those archives all the attributes required by the selected classifier and inputs them to the classifier. The user input to ClassX is typically a file with target coordinates, optionally complemented with target IDs. The output contains the class name, attributes, and class probabilities for all classified targets. We discuss ways to characterize and assess the classifier quality and performance, and we present the respective validation procedures. On the basis of both internal validation and external verification, we conclude that the ClassX classifiers yield reasonable and reliable classifications for ROSAT sources and have the potential to broaden class representation significantly for rare object types.

Validation of Up-the-Ramp Sampling with Cosmic-Ray Rejection on Infrared Detectors

We examine cosmic-ray rejection methodology on data collected from InSb and Si:As detectors. The application of an up-the-ramp sampling technique with cosmic-ray identification and mitigation is the focus of this study. This technique is valuable for space-based observatories which are exposed to high-radiation environments. We validate the up-the-ramp approach on radiation-test data sets with InSb and Si:As detectors which were generated for SIRTF. The up-the-ramp sampling method studied in this paper is over 99.9% effective at removing cosmic rays and preserves the structure and photometric quality of the image to well within the measurement error.

A VLA 20 CM survey of poor groups of galaxies

The paper reports on VLA 20 cm observations of an extensive sample of galaxies in 139 poor groups. These groups, composed of galaxies down to the limit of the Zwicky et al. (CGCG) catalog, were chosen using a percolation algorithm set at a high surface-density threshold. Approximately 50 percent of the groups have measured redshifts. These groups were surveyed using a snapshot mode of the VLA with a resolution of about 13 arcsec. Analysis of the resulting radio and optical properties reveals that the presence of a nearby companion galaxy has an important role in generating radio emission in a galaxy. CCD observations of two radio-loud, disturbed galaxies with companions are presented and are used to discuss models of radio-source production. Nine tailed radio galaxies are found in the poor groups, which is much more than had been expected from previous work on rich clusters and from theoretical models. The paper discusses previous statistical biases and proposes a method for bending head-tail sources in poor groups. From the confinement of extended radio features associated with tailed sources, the presence of a substantial intracluster medium that should radiate significantly at soft-X-ray energies is predicted. 56 references.

NETWORK RESOURCES FOR ASTRONOMERS

The amount of data produced by large observational facilities and space missions has led to the archiving and on-line accessibility of much of this data, available to the entire astronomical community. This allows a much wider multi-frequency approach to astronomical research than previously possible. Here we provide an overview of these services, and give a basic description of their contents and possibilities for accessing them. Apart from services providing observational data, many of those providing general information, e.g., on addresses, bibliographies, software etc. are also described. The field is rapidly growing with improved network technology, and our attempt to keep the report as complete and up-to-date as possible will inevitably be outdated shortly. We will endeavor to maintain an updated version of this document on-line.The amount of data produced by large observational facilities and space missions has led to the archiving and on-line accessibility of much of this data, available to the entire astronomical community. This allows a much wider multi-frequency approach to astronomical research than previously possible. Here we provide an overview of these services, and give a basic description of their contents and possibilities for accessing them. Apart from services providing observational data, many of those providing general information, e.g. on addresses, bibliographies, software etc. are also described. The field is rapidly growing with improved network technology, and our attempt to keep the report as complete and up-to-date as possible will inevitably be outdated shortly. We will endeavor to maintain an updated version of this document on-line.

The organization and management of the Virtual Astronomical Observatory

The U.S. Virtual Astronomical Observatory (VAO; http://www.us-vao.org/) has been in operation since May 2010. Its goal is to enable new science through efficient integration of distributed multi-wavelength data. This paper describes the management and organization of the VAO, and emphasizes the techniques used to ensure efficiency in a distributed organization. Management methods include using an annual program plan as the basis for establishing contracts with member organizations, regular communication, and monitoring of processes.

DATA STANDARDS FOR THE INTERNATIONAL VIRTUAL OBSERVATORY

A primary goal of the International Virtual Observatory Alliance, which brings together Virtual Observatory Projects from 16 national and international development projects, is to develop, evaluate, test, and agree upon standards for astronomical data formatting, data discovery, and data delivery. In the three years that the IVOA has been in existence, substantial progress has been made on standards for tabular data, imaging data, spectroscopic data, and large-scale databases and on managing the metadata that describe data collections and data access services. In this paper, I describe how the IVOA operates and give my views as to why such a broadly based international collaboration has been able to make such rapid progress.

The National Virtual Observatory

The National Virtual Observatory is a distributed computational facility that will provide access to the “virtual sky”—the federation of astronomical data archives, object catalogs, and associated information services. The NVO’s “virtual telescope” is a common framework for requesting, retrieving, and manipulating information from diverse, distributed resources. The NVO will make it possible to seamlessly integrate data from the new all-sky surveys, enabling cross-correlations between multi-Terabyte catalogs and providing transparent access to the underlying image or spectral data. Success requires high performance computational systems, high bandwidth network services, agreed upon standards for the exchange of metadata, and collaboration among astronomers, astronomical data and information service providers, information technology specialists, funding agencies, and industry. International cooperation at the onset will help to assure that the NVO simultaneously becomes a global facility.