- ID:
- ivo://nasa.heasarc/abell
- Title:
- Abell Clusters
- Short Name:
- Abell
- Date:
- 02 May 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- The ABELL database contains information from a catalog of clusters of galaxies, each having at least 30 members within the magnitude range m3 to m3+2 (m3 is the magnitude of the third brightest cluster member) and each with a nominal redshift less than 0.2. The database contains the revised Northern Abell catalog, the Southern Abell catalog, and the Supplementary Southern Abell catalog; the catalogs are published as tables 3, 4 and 5 of Abell, Corwin & Orowin (1989). This database table was created by J. Osborne of Leicester from the STADAT SCAR file abelb.dat. The original SCAR version was created by Diana Parsons on 12 March 1990. This is a service provided by NASA HEASARC .
« Previous |
1 - 10 of 91
|
Next »
Number of results to display per page
Search Results
- ID:
- ivo://nasa.heasarc/abellzcat
- Title:
- Abell Clusters Measured Redshifts Catalog
- Short Name:
- ABELLZCAT
- Date:
- 02 May 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- The all-sky ACO (Abell, Corwin and Olowin 1989, ApJS, 70, 1) Catalog of 4073 rich clusters of galaxies and 1175 southern poor or distant S-clusters has been searched for published redshifts. Data for 1059 of them were found and classified into various quality classes, e.g. to reduce the problem of foreground contamination of redshifts. Taking the ACO selection criteria for redshifts, a total of 992 entries remain, 21 percent more than ACO. Redshifts for rich clusters are now virtually complete out to a redshift z of 0.05 in the north and of 0.04 in the south. In the north, the magnitude-redshift (m_10 - z) relation agrees with that of Kalinkov et al. (1985, Astr. Nachr., 306, 283). For the southern rich clusters, minor adjustments to the m_10 - z relation of ACO are suggested, while for the S-clusters the redshifts are about 30 percent lower than estimated. This table was created by the HEASARC in May 2010 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/VII/165A">CDS Catalog VII/165A</a> file catalog.dat. This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/qorgcat
- Title:
- All-Sky Optical Catalog of Radio/X-Ray Sources
- Short Name:
- QuasarOrg
- Date:
- 02 May 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- The Quasars.org (QORG) Catalog is an all-sky optical catalog of radio/X-ray sources. The QORG Catalog aligns and overlays the year 2001/2 releases of the ROSAT HRI, RASS, PSPC and WGA X-ray catalogs, the NVSS (2002), FIRST (2003) and SUMSS (2003) radio catalogs, the Veron QSO catalog (2003) and various galaxy/star reference catalogs onto the optical APM and USNO-A catalogs. This catalog displays calculated percentage probabilities for each optical, radio/X-ray associated object of its likelihood of being a quasar, galaxy, star, or erroneous radio/X-ray association. This table contains the main Master QORG catalog (master.dat) and contains all 501,756 radio/X-ray associated optical objects and known quasars which are optically detected in APM/USNO-A. Up to six radio/X-ray catalog identifications are presented for each optical object, plus any double radio lobes (21,498 of these). These are superimposed (and laterally fitted) onto a 670,925,779-object optical background which combines APM and USNO-A data. Other subsets of this master catalog are available at the CDS, including the Free-Lunch catalog, a concise easy-to-read variant of the Master catalog showcasing just one X-ray and/or radio identification for each object, a subset catalog of QSO candidates, and a subset catalog of known QSOs/galaxies/stars. Objects presented in this catalog are those optical APM/USNO-A objects which are associated with X-ray/radio detections, or any optically-found catalogued QSO/AGN/Bl Lac objects, which have confidence levels >40% of being radio/X-ray emitting optical objects. There are 501,756 objects included in all (including 48,285 catalogued quasars), representing the 99.4% coverage of the sky which is available from the APM and USNO-A. Each object is shown as one entry giving the position in equatorial coordinates, red and blue optical magnitudes (recalibrated) and PSF class, calculated probabilities of the object being, separately, a quasar, galaxy, star, or erroneous radio/X-ray association, any radio identification from each of the NVSS, FIRST and SUMSS surveys, including candidate double-lobe detections, any X-ray identification from each of the ROSAT HRI, RASS, PSPC and WGA surveys, including fluxes and field shifts of those identifications, plus, if already catalogued, the object name and redshift where applicable. The QORG catalog and supporting data can be accessed from the catalog home page at <a href="http://quasars.org/qorg-data.htm">http://quasars.org/qorg-data.htm</a> Questions or comments on the catalog contents may be directed to the first author Eric Flesch at eric@flesch.org. The authors request that researchers using this catalog make a small acknowledgement of such use in any published papers which thereby result. This table was created by the HEASARC in November 2004 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/A+A/427/387">CDS Catalog J/A+A/427/387</a> file master.dat.gz. This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/allwiseagn
- Title:
- AllWISE Catalog of Mid-IR AGNs
- Short Name:
- ALLWISEAGN
- Date:
- 02 May 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- This table contains an all-sky sample of ~1.4 million active galactic nuclei (AGNs) meeting a two-color infrared photometric selection criterion for AGNs as applied to sources from the Wide-field Infrared Survey Explorer final catalog release (AllWISE). The authors assess the spatial distribution and optical properties of their sample and find that the results are consistent with expectations for AGNs. These sources have a mean density of ~38 AGNs per square degree on the sky, and their apparent magnitude distribution peaks at g ~ 20, extending to objects as faint as g ~ 26. The authors test the AGN selection criterion against a large sample of optically identified stars and determine the "leakage" (that is, the probability that a star detected in an optical survey will be misidentified as a quasi-stellar object (QSO) in their sample) rate to be <= 4.0 x 10<sup>-5</sup>. They conclude that their sample contains almost no optically identified stars (<= 0.041%), making this sample highly promising for future celestial reference frame work as it significantly increases the number of all-sky, compact extragalactic objects. The authors further compare their sample to catalogs of known AGNs/QSOs and find a completeness value of >= 84% (that is, the probability of correctly identifying a known AGN/QSO is at least 84%) for AGNs brighter than a limiting magnitude of R <= 19. This sample includes approximately 1.1 million previously uncataloged AGNs. The WISE survey is an all-sky mid-IR survey at 3.4, 4.6, 12, and 22 microns (W1, W2, W3, and W4, respectively) conducted between 2010 January 7 and August 6, during the cryogenic mission phase, and first made available to the public on 2011 April 14. WISE has angular resolutions of 6.1, 6.4, 6.5, and 12.0 arcseconds in its four bands, respectively. The AllWISE data release, which was used for this work, incorporates data from the WISE Full Cryogenic, 3-Band Cryo, and NEOWISE Post-Cryo survey (Mainzer et al. 2014, ApJ, 792, 30) phases, which were co-added to achieve a depth of coverage ~0.4 mag deeper than previous data releases. AllWISE contains the positions, apparent motions, magnitudes, and point-spread function (PSF)-profile fit information for almost 748 million objects. Astrometric calibration of sources in the WISE catalog was done by correlation with bright stars from the 2MASS point source catalog, and the astrometric accuracy for sources in the AllWISE release was further improved by taking into account the proper motions of these reference stars, taken from the fourth USNO CCD Astrograph Catalog (UCAC4, Zacharias et al. 2013, AJ, 145, 44). A comparison with ICRF sources shows that AllWISE Catalog sources in the brightness range of 8 < W1 < 12 mag have positional accuracies to within 50 mas, and half of these sources have positional accuracies to within 20 mas. For more details on the WISE mission, see Wright et al. (2010, AJ, 140, 1868). The authors took all sources from the AllWISE catalog following Equations (3) and (4) from Mateos et al. (2012, MNRAS, 426, 3271) and they require that all of their sources have S/N >= 5 in the first three bands, as recommended in Mateos et al. (2012); as a further constraint, they limit their results to those with cc_flags = "0000," meaning that the sources are unaffected by known artifacts such as diffraction spikes, persistence, halos, or optical ghosts. In order to characterize the optical properties of their sample, the authors cross-matched it to SDSS-DR12, which is the final data release of SDSS-III (Eisenstein et al. 2011, AJ, 142, 72), within a radial tolerance of R < 1", obtaining 424,366 matches. To determine the fraction of false positive positional matches (that is, incorrectly correlating an object in their sample with a different SDSS object due to random positional agreement), they performed the same match on a scrambled version of their sample coordinates, determining that less than 1% of other cross-matches are false positive positional matches between the two catalogs. The authors also cross-matched their sample sources with he second release of the Large Quasar Astrometric Catalog (LQAC-2; Souchay et al. 2012, A&A, 537, A99), which contains 187,504 quasars, including radio-selected quasars from the ICRF2, optically selected quasars from SDSS, and infrared-selected quasars from 2MASS, and thus represents a robust sample of quasars over a wide range of wavelengths. They find that 93,403 quasars from LQAC-2 have clean detections. The majority of non-detections are due to sources in LQAC-2 that are too faint, having R >~ 19. This table was created by the HEASARC in January 2016 based on the machine-readable version of Table 1 from the reference paper which was obtained from the ApJS web site. This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/acceptcat
- Title:
- Archive of Chandra Cluster Entropy Profile Tables (ACCEPT) Catalog
- Short Name:
- ACCEPTCAT
- Date:
- 02 May 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- This table, the Archive of Chandra Cluster Entropy Profile Tables (ACCEPT) Catalog, contains the radial entropy profiles of the intracluster medium (ICM) for a collection of 239 clusters taken from the Chandra X-ray Observatory's Data Archive. Entropy is of great interest because it controls ICM global properties and records the thermal history of a cluster. The authors find that most ICM entropy profiles are well fitted by a model which is a power law at large radii and approaches a constant value at small radii: K(r) = K<sub>0</sub> + K<sub>100</sub> (r/100 kpc)<sup>alpha</sup>, where K<sub>0</sub> quantifies the typical excess of core entropy above the best-fitting power law found at larger radii. The authors also show that the K<sub>0</sub> distributions of both the full archival sample and the primary Highest X-Ray Flux Galaxy Cluster Sample of Reiprich (2001, Ph.D. thesis) are bimodal with a distinct gap between K<sub>0</sub> ~ 30 - 50 keV cm<sup>2</sup> and population peaks at K<sub>0</sub> ~ 15 keV cm<sup>2</sup> and K<sub>0</sub> ~ 150 keV cm<sup>2</sup>. The effects of point-spread function smearing and angular resolution on best-fit K<sub>0</sub> values are investigated using mock Chandra observations and degraded entropy profiles, respectively. The authors find that neither of these effects is sufficient to explain the entropy-profile flattening they measure at small radii. The influence of profile curvature and the number of radial bins on the best-fit K<sub>0</sub> is also considered, and they find no indication that K<sub>0</sub> is significantly impacted by either. All data and results associated with this work are publicly available via the project web site <a href="http://www.pa.msu.edu/astro/MC2/accept/">http://www.pa.msu.edu/astro/MC2/accept/</a>. The sample is collected from observations taken with the Chandra X-ray Observatory and which were publicly available in the CDA (Chandra Data Archive) as of 2008 August. This table was created by the HEASARC in January 2012 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJS/182/12">CDS Catalog J/ApJS/182/12</a> files table1.dat and table5.dat. This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/ascaegclus
- Title:
- ASCA Elliptical Galaxies and Galaxy Clusters Catalog
- Short Name:
- ASCAEGCLUS
- Date:
- 02 May 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- Utilizing ASCA archival data of about 300 objects - elliptical galaxies, groups, and clusters of galaxies - the authors performed systematic measurements of the X-ray properties of hot gas in their systems, and compiled them in this study. The steepness (power-law slope) of the luminosity-temperature (L-T) relation, L<sub>X</sub> ~ kT<sup>alpha</sup>, in the range of kT ~ 1.5 - 15 keV is alpha = 3.17 +/- 0.15, consistent with previous measurements. In the relation, the authors find two breaks at around intracluster medium (ICM) temperatures of 1 keV and 4 keV: alpha = 2.34 +/- 0.29 above 4 keV, 3.74 +/- 0.32 in the 1.5 to 5 keV range, and 4.03 +/- 1.07 below 1.5 keV. Two such breaks are also evident in the temperature and size relation. The steepness in the L-T relation at kT > 4 keV is consistent with the scale-relation derived from the CDM model, indicating that the gravitational effect is dominant in richer clusters, while poorer clusters suffer non-gravity effects. The steep L-T relation below 1 keV is mostly attributed to X-ray faint systems of elliptical galaxies and galaxy groups. The authors find that the ICM mass within the scaling radius R<sub>1500</sub> (the radius within which the averaged mass density is 1500 times higher than the critical density) follows the relation of M<sub>gas</sub> ~ T<sup>(2.33+/-0.07)</sup> from X-ray faint galaxies to rich clusters. Thus, the authors speculate that even such X-ray faint systems contain large-scale hot gas, which is too faint to detect. For this project, the authors utilized all of the ASCA data of elliptical galaxies and clusters of galaxies. Several clusters were observed more than once, and they chose the observation with the longest exposure. The total number of objects that the authors identified as elliptical galaxies and clusters was 313, and these are listed in this table. Some of the objects could not be utilized for deriving various correlations, due to either having an unknown redshift (17 objects), an insignificant detection (13 objects listed below), or contamination of the environmental X-ray emission, such as cluster emission around non-cD elliptical galaxies (10 objects: NGC 4472, NGC 4406, NGC 4374, NGC 1404, NGC 499, NGC 6034, NGC 2865, NGC 4291, CL 2236-04 and RX J1031.6-2607). Thus, the authors analyzed the ASCA data for 292 objects, among which were ~ 50 elliptical galaxies and galaxy groups. In this study, the authors assumed the Hubble constant to be 50 h<sub>50</sub> km s<sup>-1</sup> Mpc<sup>-1</sup> and q<sub>0</sub> to be 0. Table 1 of the reference paper (reproduced below) lists the 13 clusters for which only 90% confidence level upper limits to the flux in the observer's frame are available: <pre> Name Flux (0.5 - 2 keV) Upper Limit (erg/s/cm<sup>2</sup>) NGC 5018 9.8 x 10<sup>14</sup> GHO 1322+3114 1.3 x 10<sup>13</sup> J1888.16CL 5.9 x 10<sup>14</sup> CL 0317+1521 4.5 x 10<sup>14</sup> MS 1512.4+3647 1.0 x 10<sup>12</sup> PRG 38 6.9 x 10<sup>14</sup> SCGG 205 6.9 x 10<sup>14</sup> RGH 101 9.1 x 10<sup>14</sup> 3C 184 8.5 x 10<sup>14</sup> RX J1756.5+6512 1.6 x 10<sup>13</sup> 3C 324 5.4 x 10<sup>14</sup> PDCS 01 2.8 x 10<sup>14</sup> MS 0147.8-3941 5.0 x 10<sup>14</sup> </pre> This table was created by the HEASARC in December 2011 based on CDA Catalog J/PASJ/56/965 files table3.dat, table4.dat, table5.dat, table6.dat and table7.dat. This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/arxa
- Title:
- Atlas of Radio/X-Ray Associations (ARXA)
- Short Name:
- ARXA
- Date:
- 02 May 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- The Atlas of Radio/X-Ray Associations (ARXA) is a compendium of all cataloged or APM/USNO-A optical objects which are found to be associated with XMM-Newton, Chandra, RASS, HRI, PSPC or WGACAT X-ray detections, or with NVSS, FIRST or SUMSS radio detections. All detections are listed, plus double radio lobes where found. The source number counts are: <pre> Optical objects - 602,570. NVSS - 266,148 core associations, plus 8309 double lobes. FIRST - 173,383 core associations, plus 12,844 double lobes. SUMSS - 59,138 core associations, plus 2529 double lobes. XMM associations - 57,778. Chandra associations - 32,951. ROSAT RASS - 47,486. ROSAT HRI - 15,523. ROSAT PSPC - 35,607. WGA - 24,226. </pre> Each optical object is given as one entry in this catalog, containing the sky coordinates, the object name (from the literature where available), APM and USNO-A sourced red and blue photometry, redshift, the source catalogs for the name and redshift, the calculated odds that the object is a quasar, galaxy, star, or erroneous association, and the radio & X-ray identifiers, up to 10 of them possible although usually just 1 or 2. This catalog supersedes the previous similar compilation by the same author, the Quasars.org (QORG) Catalog, called QORGCAT in the HEASARC's Browse (see <a href="http://quasars.org/qorg-data.htm">http://quasars.org/qorg-data.htm</a>). Questions or comments on ARXA may be directed to eric@flesch.org. See also: <pre> APM home page <a href="http://www.ast.cam.ac.uk/~apmcat">http://www.ast.cam.ac.uk/~apmcat</a> USNO-A home page <a href="http://www.nofs.navy.mil/">http://www.nofs.navy.mil/</a> NVSS home page <a href="http://www.cv.nrao.edu/nvss/">http://www.cv.nrao.edu/nvss/</a> FIRST home page <a href="http://sundog.stsci.edu/">http://sundog.stsci.edu/</a> SUMSS home page <a href="http://www.astrop.physics.usyd.edu.au/SUMSS/index.html">http://www.astrop.physics.usyd.edu.au/SUMSS/index.html</a> XMM-Newton home page <a href="http://xmmssc-www.star.le.ac.uk">http://xmmssc-www.star.le.ac.uk</a> HRI & PSPC home page <a href="http://www.mpe.mpg.de/ROSAT/">http://www.mpe.mpg.de/ROSAT/</a> WGA home page <a href="http://wgacat.gsfc.nasa.gov/wgacat/wgacat.html">http://wgacat.gsfc.nasa.gov/wgacat/wgacat.html</a> RASS-FSC home page <a href="http://www.xray.mpe.mpg.de/rosat/survey/rass-fsc">http://www.xray.mpe.mpg.de/rosat/survey/rass-fsc</a> RASS-BSC home page <a href="http://www.xray.mpe.mpg.de/rosat/survey/rass-bsc">http://www.xray.mpe.mpg.de/rosat/survey/rass-bsc</a> Chandra home page <a href="http://chandra.harvard.edu">http://chandra.harvard.edu</a> XAssist home page <a href="http://xassist.pha.jhu.edu/zope/xassist">http://xassist.pha.jhu.edu/zope/xassist</a> (XMMX & CXOX sources are from XAssist) </pre> If using this catalog in published research, please add a small mention in the acknowledgements. This table is based on research which made use of the NASA/IPAC Extragalactic Database (NED) operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. This online catalog was created by the HEASARC in January 2010 based on a machine-readable table obtained from the author's ARXA web site at <a href="http://quasars.org/arxa.htm">http://quasars.org/arxa.htm</a>. This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/baxgalclus
- Title:
- BAX X-Ray Galaxy Clusters and Groups Catalog
- Short Name:
- BAXGalClus
- Date:
- 02 May 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- This table contains the BAX X-Ray Galaxy Clusters and Groups Catalog. BAX (`Base de Donnees Amas de Galaxies X': see <a href="http://bax.ast.obs-mip.fr/">http://bax.ast.obs-mip.fr/</a> for more details) is a multi-wavelength database dedicated to X-ray clusters and groups of galaxies which allows detailed information retrieval. BAX is designed to support astronomical research by providing access to published measurements of the main physical quantities and to the related bibliographic references: basic data stored in the database are cluster/group identifiers, equatorial coordinates, redshift, flux, X-ray luminosity (in the ROSAT band) and temperature, and (in the online version at <a href="http://bax.ast.obs-mip.fr/">http://bax.ast.obs-mip.fr/</a>) links to additional linked parameters (in X-rays, such as spatial profile parameters, as well as SZ parameters of the hot gas, lensing measurements, and data at other wavelengths, such as the optical and radio bands). The clusters and groups in the online BAX database can be queried by the basic parameters as well as the linked parameters or combinations of these. The authors expect BAX to become an important tool for the astronomical community. BAX will optimize various aspects of the scientific analysis of X-ray clusters and groups of galaxies, from proposal planning to data collection, interpretation and publication, from both ground based facilities like MEGACAM (CFHT), VIRMOS (VLT) and from space missions like XMM-Newton, Chandra and Planck. This table was created by the HEASARC in October 2004 based on CDS table B/bax/bax.dat. This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/cgmw
- Title:
- Candidate Galaxies Behind the Milky Way
- Short Name:
- CG
- Date:
- 02 May 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- This catalog gathers the searches for galaxies of apparent size greater than 0.1 mm on film (6.7" in angular size) lieing behind the Milky Way from photographic surveys in the near-infrared. The four volumes (CGMW1, CGMW2, CGMW3, and CGMW4) cover the galactic longitude ranges from -7 to +43 degrees, and from 210 to 250 degrees. The two volumes, CGMW1 and CGMW2, giving about 7000 galaxies behind the Milky Way between l = 210 degrees and 250 degrees, represent a systematic search for galaxies by means of 32 film copies of the UK Schmidt Southern Infrared Atlas on the Milky Way covering about 900 square degrees. In the search galaxies with apparent sizes greater than 0.1mm on film (6.7 arcsec in size) were detected by visual inspection. The material and procedure of search are described as well as the detectability of galaxies in paper I and paper II appended before Vol. 1 and Vol. 2 of the catalog, respectively, which have been published in Publ. Astron. Soc Japan, Vol. 42 (1990) and Vol. 43 (1991). The parameters of catalogued galaxies are also explained in paper I. Cross-identifications with other catalogs are also given. The third volume CGMW3 lists about 5300 galaxy candidates having sizes larger than 0.1 arcminutes that were found in a search of Schmidt atlases covering a Milky Way region of about 800 square degrees around l = 8 to 43 degrees, and b = -17 to +17 degrees. This surveyed region is located between the northern Local void and the Ophiuchus void. The fourth volume CGMW4 lists about 7150 galaxies and galaxy candidates having sizes larger than 0.1 arcminutes that were found in a search of Schmidt atlases covering a Milky Way region of about 260 square degrees around l = -7 to +16 degrees, and b = -19 to -1 degrees, i.e., a field in Sagittarius in the Galactic Center region. This database was created by the HEASARC in October 1999 based on a machine-readable version that was obtained from the CDS Data Center. This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/eingalcat
- Title:
- CatalogofGalaxiesObservedbytheEinsteinObservatoryIPC&HRI
- Short Name:
- Einstein/Gal
- Date:
- 02 May 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- This is a catalog of galaxies observed in the X-ray band with the Einstein Observatory imaging instruments, the Imaging Proportional Counter (IPC) and the High Resolution Imager (HRI). The catalog comprises 716 observations of 493 galaxies, including those that were targets of pointed observations, and galaxies from the Revised Shapley-Ames (RSA) Catalog of Bright Galaxies and the Second Revised Catalog (RC2) Catalog of Bright Galaxies that were serendipitously included in Einstein fields, plus X-ray data on 4 other galaxies (LMC, SMC, M 31 = NGC 224, and M 32 = NGC 221) taken from the literature, for a total of 720 entries. A total of 450 of these galaxies were imaged well within the instrumental fields, resulting in 238 detections and 212 3-sigma upper limits. The other galaxies were either at the edge of the visible field of view or were confused with other X-ray sources. This database was created by the HEASARC in January 2002 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJS/80/531">CDS Catalog J/ApJS/80/531</a>, tables gxatlas.dat and gxfluxes.dat. This is a service provided by NASA HEASARC .
