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 Advanced CCD Imaging Spectrometer 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 1σ 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, including source images, event lists, light curves, and spectra from each observation in which a source is detected.

The recently launched Chandra X-Ray Observatory (CXO) was designed to have the sharpest angular resolution yet of any X-ray telescope. Detailed modeling and metrology of the optics followed by extensive testing at the X-Ray Calibration Facility at the Marshall Space Flight Center in Huntsville, Alabama indicated that the optics were performing exceedingly well. While our analysis accounted for distortion of the mirrors due to gravity and the effects of finite distance and size of the X-ray generator, it was only on-orbit that we expected to directly observe the specified half arc-second performance.We present here results of the on-orbit calibration of the point spread function (PSF), comparing it with our predictions. We discuss how the PSF varies with source location in the telescope field of view, as well as with the spectral energy distribution of the source.

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 ∼3900 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 or the 2 Mega-second Deep Field Surveys, 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.

of (+) -isomenthy1 p-bromophenylcarbamate, CloH190~CO*NH~C6H4Br are orthorhombic, space group P212,21. and unit cell dimensions a = 25.58 (5)A, b = 13.18(2) A, c = 16.70(3) A. There are 12 molecules in the unit cell, 3 in each asymmetric unit. The structure was solved by the heavy-atom method, and refined by block-diagonal least-squares to R 0.087 for 2927 reflections. In the crystalline state, the isomenthol of the three molecules in the asymmetric unit exist in two different types of chair conformations. Two have the methyl substituent a t C(1) axial, while the p-bromophenylcarbamate and the isopropyl substituents at C(3) and C(4) are both equatorial. The third molecule has the alternate chair conformation, i.e., methyl equatorial at C(1). p-bromophenylcarbamate axial at C(3). and isopropyl axial at C(4). l H and 13C n.m.r. spectra of isomenthol in carbon disulphide and dimethyl sulphoxide solutions show it exhibits conformational mobility involving the two chair forms. The isomenthol conformer with the hydroxy-and the isopropyl-groups equatorial is the major component, that with methyl equatorial and the other two substituents axial the minor. The absolute configurations at the asymmetric carbons as derived from anomalous dispersion method are 1 R,3S,4R. There is no flattening observed in the cyclohexane ring as a whole, only some distortions a t the substituted positions. The p-bromophenylcarbamate chain is almost planar forming angles of 53" 43'. 53' 13'. and 81 ' 10' with the planes of the isomenthol for molecules (A), (B), and (C).

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