TGCat, The Chandra Transmission Grating Catalog and Archive: Systems, Desgin and Accessibility

The recently released Chandra Transmission Grating Catalog and Archive, TGCat, presents a fully dynamic on-line catalog allowing users to browse and categorize Chandra gratings observations quickly and easily, generate custom plots of resulting response corrected spectra on-line without the need for special software and to download analysis ready products from multiple observations in one convenient operation. TGCat has been registered as a VO resource with the NVO providing direct access to the catalogs interface. The catalog is supported by a back-end designed to automatically fetch newly public data, process, archive and catalog them, At the same time utilizing an advanced queue system integrated into the archive's MySQL database allowing large processing projects to take advantage of an unlimited number of CPUs across a network for rapid completion. A unique feature of the catalog is that all of the high level functions used to retrieve inputs from the Chandra archive and to generate the final data products are available to the user in an ISIS written library with detailed documentation. Here we present a structural overview of the Systems, Design, and Accessibility features of the catalog and archive.United States. National Aeronautics and Space Administration (Chandra X-ray Center (CXC) NASA contract NAS8-03060)United States. National Aeronautics and Space Administration (Smithsonian Astrophysical Observatory (SAO) contract SV3-73016 for the Chandra X-Ray Center and Science Instruments

The velocity ellipsoid in the Galactic disc using Gaia DR1

The stellar velocity ellipsoid of the solar neighbour (d < 200 pc) is re-examined using intermediate-old mono-abundance stellar groups with high-quality chemistry data together with parallaxes and proper motions from Gaia DR1. We find the average velocity dispersion values for the three space velocity components for the thin and thick discs of (σU, σV, σW)thin = (33 ± 4, 28 ± 2, 23 ± 2) and (σU, σV, σW)thick = (57 ± 6, 38 ± 5, 37 ± 4) km s-1, respectively. The mean values of the ratio between the semi-axes of the velocity ellipsoid for the thin disc are found to be σV/σU = 0.70 ± 0.13 and σW/σU is 0.64 ± 0.08, while for the thick disc σV/σU = 0.67 ± 0.11 and σW/σU is 0.66 ± 0.11. Inputting these dispersions into the linear Strömberg relation for the thin disc groups, we find the Sun's velocity with respect to the Local Standard of Rest in Galactic rotation to be V⊙ = 13.9 ± 3.4 kms-1. A relation is found between the vertex deviation and the chemical abundances for the thin disc, ranging from -5 to +40° as iron abundance increases. For the thick disc we find a vertex deviation of luv ~- 15°. The tilt angle (luw) in the U-W plane for the thin disc groups ranges from -10 to +15°, but there is no evident relation between luw and the mean abundances. However, we find a weak relation for luw as a function of iron abundances and a-elements for most of the groups in the thick disc, where the tilt angle decreases from -5 to -20° when [Fe/H] decreases and [α/Fe] increases. The velocity anisotropy parameter is independent of the chemical group abundances and its value is nearly constant for both discs (β ~ 0.5), suggesting that the combined disc is dynamically relaxed.BA and SRM acknowledge support from National Science Foundation grant AST-1616636

The Chandra Source Catalog

The Chandra Source Catalog (CSC) is a general purpose virtual X-ray astrophysics facility that provides access to a carefully selected set of generally useful quantities for individual X-ray sources, and is designed to satisfy the needs of a broad-based group of scientists, including those who may be less familiar with astronomical data analysis in the X-ray regime. The first release of the CSC includes information about 94,676 distinct X-ray sources detected in a subset of public ACIS imaging observations from roughly the first eight years of the Chandra mission. This release of the catalog includes point and compact sources with observed spatial extents <~ 30''. The catalog (1) provides access to the best estimates of the X-ray source properties for detected sources, with good scientific fidelity, and directly supports scientific analysis using the individual source data; (2) facilitates analysis of a wide range of statistical properties for classes of X-ray sources; and (3) provides efficient access to calibrated observational data and ancillary data products for individual X-ray sources, so that users can perform detailed further analysis using existing tools. The catalog includes real X-ray sources detected with flux estimates that are at least 3 times their estimated 1 sigma uncertainties in at least one energy band, while maintaining the number of spurious sources at a level of <~ 1 false source per field for a 100 ks observation. For each detected source, the CSC provides commonly tabulated quantities, including source position, extent, multi-band fluxes, hardness ratios, and variability statistics, derived from the observations in which the source is detected. In addition to these traditional catalog elements, for each X-ray source the CSC includes an extensive set of file-based data products that can be manipulated interactively.Comment: To appear in The Astrophysical Journal Supplement Series, 53 pages, 27 figure

Statistical Characterization of the Chandra Source Catalog

The first release of the Chandra Source Catalog (CSC) contains ~95,000 X-ray sources in a total area of ~0.75% of the entire sky, using data from ~3,900 separate ACIS observations of a multitude of different types of X-ray sources. In order to maximize the scientific benefit of such a large, heterogeneous data-set, careful characterization of the statistical properties of the catalog, i.e., completeness, sensitivity, false source rate, and accuracy of source properties, is required. Characterization efforts of other, large Chandra catalogs, such as the ChaMP Point Source Catalog (Kim et al. 2007) or the 2 Mega-second Deep Field Surveys (Alexander et al. 2003), while informative, cannot serve this purpose, since the CSC analysis procedures are significantly different and the range of allowable data is much less restrictive. We describe here the characterization process for the CSC. This process includes both a comparison of real CSC results with those of other, deeper Chandra catalogs of the same targets and extensive simulations of blank-sky and point source populations.Comment: To be published in the Astrophysical Journal Supplement Series (Fig. 52 replaced with a version which astro-ph can convert to PDF without issues.

Quantitative chemical tagging: empirical constraints on the identification of dispersed coeval stellar groups

Thesis by publication.At foot of title: Astronomy, Astrophysics and strophonics Research Centre.Bibliography: pages 96-101.1. Introduction -- 2. Chemical tagging -- 3. Stellar spectroscopy and abundance analysis -- 4. Empirical chemical tagging -- 5. The first blind chemical tagging experiment -- 6. Summary and conclusions.Though it has been established that open clusters have tight abundance scatter, the empirical evidence for the viability of chemical tagging has for the most part gone unstudied. With a large survey dedicated to tagging - GALAH - just on the horizon, we perform several empirical investigations of this technique. An empirical coeval probability function, which quantifies the likelihood that a pair of stars originated from the same star formation event, is developed and characterised. We then perform a real world test by conducting the first ever blind chemical tagging experiment, with several important implications.The long term evolution and the origin of the Galactic stellar disc are the subjects of intense study. Much is surmised about the evolution of galaxies in general by studying those at cosmic scales, yet there are still significant issues in explaining phenomena in our own Galaxy. It is only a single case, but of universal importance due to our ability to resolve individual stars and stellar populations. Amongst the important open questions are the origin (or indeed the reality) of the thin and thick stellar discs, the role of intra-disc stellar migrations, the merger history, in-situ star formation history and the chemical evolution of the disc. Kinematic information, though crucial to understanding the Galactic environment, is short lived in the disc and thus astronomers are turning to stellar chemical abundances, which remain unchanged for most of a star's lifetime, to reveal history. In particular, the technique of chemical tagging may be able to use this "fossil" information to link groups of stars in the disc which have formed concurrently from the same molecular cloud, but have since dispersed. Though it has been established that open clusters have tight abundance scatter, the empirical evidence for the viability of chemical tagging has for the most part gone unstudied. With a large survey dedicated to tagging - GALAH - just on the horizon, we perform several empirical investigations of this technique. An empirical coeval probability function, which quantifies the likelihood that a pair of stars originated from the same star formation event, is developed and characterised. We then perform a real world test by conducting the first ever blind chemical tagging experiment, with several important implications.Mode of access: World wide web1 online resource (vi, 101 pages) illustrations (some colour

Open SciServer: A Sustainable Data-Driven Science Platform

The Open SciServer project implements a transition to sustainability for the SciServer collaborative data-driven science platform. SciServer is a high-impact, highly successful DIBB (data infrastructure building block) with a well-developed existing code base; an established user community; and demonstrated impact on scientific discovery, research, and education. SciServer has grown from a platform for transformational impact in astronomy to one that creates significant impact in multiple science domains including – but not limited to - materials science and engineering; turbulence; oceanography; and precision medicine and genomics. To facilitate the transition to sustainability, we will work with the NSF Science Gateways Community Institute and deepen our interaction with the community. The transition plan will migrate the SciServer code base from closed to open source, enabling expansion of the user community to provide continued evolution of the platform as technologies and science drivers grow. The second major thrust of the transition plan is the creation of simple, rapid cloud deployment and management options to suit the broad range of current and future SciServer users. The SciServer transition to sustainability will also generalize its educational tools to allow all users to integrate SciServer with curricular efforts, accelerating translation of education to research and workforce development in data-intensive science domains. </p

Detailed X-ray line properties of θ² Ori A in quiescence

We investigate X-ray emission properties of the peculiar X-ray source θ² Ori A in the Orion Trapezium region using more than 500 ks of HETGS spectral data in the quiescent state. The amount of exposure provides tight constraints on several important diagnostics involving O, Ne, Mg, and Si line flux ratios from He-like ion triplets, resonance line ratios of the H- and He-like lines, and line widths. Accounting for the influence of the strong UV radiation field of the O9.5V star, we can now place the He-like line origin well within two stellar radii of the O-star's surface. The lines are resolved with average line widths of 341 ± 38 km s⁻¹. In the framework of standard wind models, this likely implies a rather weak wind with moderate post-shock velocities. The emission measure distribution of the X-ray spectrum, as reported previously, includes very high temperature components which are not easily explained in this framework. The X-ray properties are also not consistent with coronal emissions from an unseen low-mass companion nor with typical signatures from colliding wind interactions. The properties are more consistent with X-ray signatures observed in the massive Trapezium star θ¹ Ori C which has recently been successfully modeled with a magnetically confined wind model.8 page(s