- ID:
- ivo://nasa.heasarc/rcw38cxo
- Title:
- RCW 38 Chandra X-Ray Point Source Catalog
- Short Name:
- RCW38CXO
- Date:
- 18 Apr 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- This table contains the results of a 96.7-ks Chandra observation of one of the youngest, most embedded, and most massive young stellar clusters studied to this date in X-rays, namely the embedded young cluster, RCW 38. 460 X-ray sources were detected in the field, of which 360 are confirmed to be associated with the RCW 38 cluster. The cluster members range in luminosity from 10<sup>30</sup> to 10<sup>33.5</sup> erg/s. Over 10% of the cluster members with over 100 counts were found to exhibit flares, while about 15% of the cluster members with over 30 counts were variable. Of the sources identified as cluster members, 160 have near-infrared (NIR) counterparts either in the Two Micron All Sky Survey (2MASS) database or which were detected via Very Large Telescope observations. Of these, about 20% appear to have optically thick disks. An additional 353 cluster members were identified through NIR observations, of which at least 50% possess optically thick disks. Over 100 X-ray sources were fit as absorbed Raymond-Smith-type plasmas and the authors found that the column to the cluster members varies from 10<sup>21.5</sup> to 10<sup>23</sup> cm<sup>-2</sup>. Comparing the gas to dust absorption signatures in these stars they found N<sub>H</sub> = A<sub>V</sub> (2 x 10<sup>21</sup>) cm<sup>-2</sup>. They also found that the cluster contains 31 candidate OB stars and is centered about 10" (0.1 pc) west of the primary source of its ionization, the O5 star IRS 2. The cluster has a peak central density of about 400 X-ray sources pc<sup>-2</sup>. The authors estimate that the total cluster membership exceeds 2000 stars. The Chandra observation of RCW 38 took place on 2001 December 10-11 and lasted 96.7 ks. It used Advanced CCD Imaging Spectrometer (ACIS) chips 0, 1, 2, 3, 6 and 7 in very faint mode. The combined field of view (FOV) of the 4 chips in the imaging array (0-3, ACIS-I) is 16.9' x 16.9'. The aimpoint of the array was 8 59 19.20, -47 30 22.0 (J2000.0), and Chandra's roll angle was 51 degrees. The source detection algorithm PWDetect was run on the cleaned events list across the entire ACIS-I array, and found 460 sources, including 31 sources with more than 200 net counts, 49 sources with 100-200 net counts, 71 sources with 50-100 net counts, and 78 sources with 20-50 net counts. NIR matches were found for 349 of the 460 X-ray sources, including 294 of the 360 cluster members and 55 of the 100 nonmembers. This table was created by the HEASARC in February 2007 based on the merger of Tables 1, 10 and 11 from the reference paper which were obtained from the AJ website. It does not include the results from either the quartile analysis of the sources which were presented in Tables 2 and 3 or of the spectral analysis of some of the sources which were presented in Tables 5 through 9 of the reference paper. This is a service provided by NASA HEASARC .
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- ID:
- ivo://nasa.heasarc/rcw49cxo
- Title:
- RCW 49 Chandra X-Ray Point Source Catalog
- Short Name:
- RCW49CXO
- Date:
- 18 Apr 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- This table contains the list of X-ray sources detected in a high-resolution X-ray imaging study of the stellar population in the Galactic massive star-forming region RCW 49 and its central OB association Westerlund 2. The authors obtained a ~ 40 ks X-ray image of a ~ 17' x 17' field using the Chandra X-Ray Observatory and deep NIR images using the Infrared Survey Facility in a concentric ~ 8.3' x 8.3' region. They detected 468 X-ray sources with a photometric significance >=1.0 and a 1% or less chance of being a background fluctuation, and identified optical, near-infrared (NIR), and Spitzer mid-infrared (MIR) counterparts for 379 of them. The unprecedented spatial resolution and sensitivity of the X-ray image, enhanced by optical and infrared imaging data, yielded the following results: (1) The central OB association Westerlund 2 is resolved for the first time in the X-ray band. X-ray emission is detected from all spectroscopically identified early-type stars in this region. (2) Most (~ 86%) X-ray sources with optical or infrared identifications are cluster members in comparison with a control field in the Galactic plane. (3) A loose constraint (2-5 kpc) for the distance to RCW 49 is derived from the mean X-ray luminosity of T Tauri stars. (4) The cluster X-ray population consists of low-mass pre-main-sequence and early-type stars as obtained from X-ray and NIR photometry. About 30 new OB star candidates are identified. (5) The authors estimate a cluster radius of 6' - 7' based on the X-ray surface number density profiles. (6) A large fraction (~ 90%) of cluster members are identified individually using complimentary X-ray and MIR excess emission. (7) The brightest five X-ray sources, two Wolf-Rayet stars and three O stars, have hard thermal spectra. The X-ray observation of RCW 49 was carried out using the Advanced CCD Imaging Spectrometer (ACIS) on board the Chandra X-Ray Observatory from 2003 August 23 UT 18:20 to August 24 UT 4:54. Four imaging array (ACIS-I) chips covered a 17 by 17 arcminutes field centered at (R.A., Dec.) = (10h24m00.5s, -57d 45' 18") in the equinox J2000.0 for a 36.7 ks exposure. ACIS-I covers the 0.5 - 8.0 keV energy band with a spectral resolution of ~ 150 eV at 6 keV and a point-spread function (PSF) radius of ~ 0.5" within ~ 2' of the on-axis position, degrading to ~ 6" at a 10' off-axis angle. The data were taken with the very faint telemetry mode and the timed exposure CCD operation with a frame time of 3.2 s. Sources with photometric significance of larger than 2 were fitted with an absorbed thin thermal plasma model. The abundance was fixed to be 0.3 times the solar value. Fits lacking uncertainties, fits with large uncertainties, and fits with frozen parameters should be viewed merely as splines to the data to obtain rough estimates of the X-ray luminosities: the listed parameter values are considered unreliable in such cases. The authors also conducted NIR observations on 2004 December 25 and 28 using the Simultaneous three-color Infrared Imager for Unbiased Surveys (SIRIUS) mounted on the Cassegrain focus of the IRSF 1.4 m telescope at the South African Astronomical Observatory. SIRIUS is a NIR imager capable of obtaining simultaneous images in the J, H, and K<sub>s</sub> bands. The instrument is equipped with three HAWAII arrays of 1024 by 1024 pixels. The pixel scale of 0.45" is an excellent match with the on-axis spatial resolution of Chandra. The authors covered 8.3 by 8.3 arcminute fields at two positions, one aimed at RCW 49 (10h24m01.9s, -57d 45' 31") and the other at a control region. This table was created by the HEASARC in October 2007 based on the versions of Tables 1, 2, and 3 from the paper which were obtained from the electronic ApJ website. This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/rcw108cxo
- Title:
- RCW 108 Star Formation Region Chandra X-Ray Point Source Catalog
- Short Name:
- RCW108CXO
- Date:
- 18 Apr 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- This table contains some of the results of an approximately 90 ks Chandra observation of a complex region that hosts multiple sites of recent and active star formation in ARA OB1a. The field is centered on the embedded cluster RCW 108-IR and includes a large portion of the open cluster NGC 6193. The authors detected over 420 X-ray sources in the field and combined these data with deep near-IR, Spitzer/IRAC and Midcourse Space Experiment (MSX) mid-IR data. They find that about 360 of the X-ray sources have near-IR counterparts. They divide the region into five parts based on the X-ray point source characteristics and extended 8 micron emission. The most clearly defined regions are the central region, identified by embedded sources with high luminosities in the both the near-IR and X-ray as well as high X-ray temperatures (~3 keV), and the eastern region, identified by low extinction and ~1 keV X-ray temperatures. Other regions, identified by their directional relationship to RCW 108-IR, are less uniform, representing combinations of the first two regions, independent star formation epochs, or both. The cluster members range in X-ray luminosity from 10<sup>29</sup> to 10<sup>33</sup> erg s<sup>-1</sup>. Over 18% of the cluster members with over 100 counts exhibit flares. All sources with over 350 counts are variable. Overall about 10% (16% in RCW 108-IR) appear to have optically thick disks as derived from their position in the (J - H), (H - K) diagram. The disk fraction becomes much higher when IRAC data are employed. The largest fraction of X-ray sources is best described as possessing some disk material via a more detailed extinction fitting. The authors fit the bulk of the X-ray spectra as absorbed Raymond-Smith-type plasmas, and find that the column to the RCW 108-IR members varies from 10<sup>21</sup> to 10<sup>23</sup> cm<sup>-2</sup>. They find that the field contains 41 candidate O or B stars, and estimate that the total number of pre-main-sequence stars in the field is about 1600 +/- 200. Approximately 800 are confined to the 3' (~1.1 pc) central region. The field was observed by Chandra on 2004 October 25 starting at 02:37 UT for 92.2 ks of total time and 88.8 ks of so-called "good-time" (ObsId 4503). The ACIS was used in the nominal imaging array (chips I0-I3) which provides a field of view of approximately 17' by 17' (~6.5 pc on a side). The aimpoint was at RA, Dec = 16:39:58.7, -48:51:54.4 (J2000.0). In addition, the S2 and S3 chips were on and located over IRAS 16379-4856. About 20 point sources were detected associated with this object; however, the analysis of these data is not presented here because they are far off-axis. This table was created by the HEASARC in June 2008 based on electronic versions of Tables 1, 2, 5, 7, 10 and 11 from the reference paper which were obtained from the Astronomical Journal web site. This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/rhoophcxo
- Title:
- Rho Ophiuchi SFR Chandra X-Ray Point Source Catalog
- Short Name:
- RHOOPHCXO
- Date:
- 18 Apr 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- This catalog of X-ray sources represents some of the results of a systematic study of X-ray flares from low-mass young stellar objects, using two deep exposure Chandra observations of the main region of the rho Ophiuchi star-forming cloud. From 195 X-ray sources, including class I-III pre-main sequence sources and some young brown dwarfs, a total of 71 X-ray flares were detected. The Chandra X-ray Observatory (Weisskopf et al., 2002PASP..114....1W) observed the central region of rho Oph twice with a deep exposure of the ACIS-I array, consisting of four abutted X-ray CCDs. The first observation (here and after, obs. BF) covered the south-east 17.4' x 17.4' area, including cores B, C, E, and F, while the second observation (obs. A) covered the north-west area centered on core A (Loren et al., 1990ApJ...365..269L). This table contains data and the results of spectral and timing analyses on the 195 sources detected in the two rho Oph fields, 9 of which were detected in both fields and are therefore listed twice (A-61=BF-2, A-64=BF-4, A-65=BF-5, A-69=BF-7, A-75=BF-11, A-77=BF-15, A-78=BF-16, A-79=BF-17, and A-81 = BF-19). Sources which flared have multiple entries, with one entry (typically, but not always) listing the properties of the quiescent emission, and additional entries for individual flares which were analyzed separately. For the very faint sources for which the temperatures obtained from X-ray spectral analyses were not constrained, there are typically two entries in this table per source, one of which gives the results of a spectral analysis in which the temperature was fixed at 1 keV (11.6 MK) and the other in which the temperature was instead fixed at 5 keV (58 MK). Thus, there are more entries (306) in this HEASARC table than the number (195) of detected rho Oph X-ray sources. This table was created by the HEASARC in February 2007 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/PASJ/55/653">CDS Catalog J/PASJ/55/653</a> files table2.dat and table3.dat. This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/ros13hrcxo
- Title:
- ROSAT/XMM-Newton 13-hour Field Chandra X-Ray Source Catalog
- Short Name:
- ROS13HRCXO
- Date:
- 18 Apr 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- This table contains some of the results from a Chandra ACIS-I survey of a high-latitude region at RA, Dec = 13 hours, +38 degrees which was earlier observed with ROSAT and which had recently been observed by XMM-Newton for 200 ks. XMM-Newton was expected to provide good-quality X-ray spectra for over 200 sources with fluxes around the knee of the log N /log S distribution, which are responsible for the bulk of the X-ray background. The main aim of the Chandra observations was to provide arcsecond, or better, positions, and hence reliable identifications, for the XMM-Newton sources. The ACIS-I observations were arranged in a mosaic of four 30-ks pointings, covering almost all of the 15-arcminute radius XMM-Newton/ROSAT field. 214 Chandra sources were detected above a Cash likelihood statistic of 25, which approximates to a 5-sigma significance, to a limiting flux of ~ 1.3 x 10<sup>-15</sup>erg/cm<sup>2</sup>/s (0.5 - 7 keV). Optical counterparts were derived from a Subaru SuprimeCam image reaching to R ~ 27. The very large majority of the Chandra sources have an optical counterpart, with the distribution peaking at 23 < R < 24, although 14 have no counterpart to R = 27. The fraction of X-ray sources with no identification brighter than R = 27 is similar to that found in deeper Chandra surveys. The majority of the identifications are with galaxies. As found in other Chandra surveys, there is a very wide range of optical magnitudes for a given X-ray flux, implying a range of emission mechanisms, and many sources have high L<sub>X</sub>/L<sub>opt</sub> ratios, implying absorption at moderate redshift. Comparison with the earlier ROSAT survey shows that the accuracy of the ROSAT positions agrees very well with the predictions from simulations by McHardy et al. and that the large majority of the identifications were correct. This table was created by the HEASARC in July 2013 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/MNRAS/342/802">CDS Catalog J/MNRAS/342/802</a> files table2.dat and table5.dat. This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/rosettecxo
- Title:
- Rosette Molecular Cloud Chandra X-Ray Point Source Catalog
- Short Name:
- ROSETTECXO
- Date:
- 18 Apr 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- The authors of this study have explored the young stellar populations in the Rosette Molecular Cloud (RMC) region with high spatial resolution X-ray images from the Chandra X-ray Observatory, which are effective in locating weak-lined T Tauri stars as well as disk-bearing young stars. A total of 395 X-ray point sources are detected, 299 of which (76%) have an optical or near-infrared (NIR) counterpart identified from deep FLAMINGOS images. From X-ray and mass sensitivity limits, the authors infer a total population of ~1700 young stars in the survey region. Based on smoothed stellar surface density maps, they investigate the spatial distribution of the X-ray sources and define three distinctive structures and substructures within them. Structures B and C are associated with previously known embedded IR clusters, while structure A is a new X-ray-identified unobscured cluster. A high-mass protostar RMCX 89 = IRAS 06306+0437 and its associated sparse cluster are studied. The different subregions are not coeval but do not show a simple spatial-age pattern. Disk fractions vary between subregions and are generally <~ 20% of the total stellar population inferred from the X-ray survey. The data are consistent with speculations that triggered star formation around the H II region is present in the RMC, but do not support a simple sequential triggering process through the cloud interior. While a significant fraction of young stars are located in a distributed population throughout the RMC region, it is not clear if they originated in clustered environments. This HEASARC table contains the 348 primary sources listed in Table 1 of the reference paper, as well as the 47 tentative sources listed in Table 2 (the latter having a likelihood > 10<sup>-3</sup> of being a spurious background fluctuation based on Poisson statistics), to make a total of 395 X-ray sources. The information on optical and infrared counterparts to these X-ray sources which was provided in Table 4 of the reference paper has also been included herein. In order to allow users to clearly identify these 2 samples, the HEASARC has created a parameter source_sample which is set to 'P' for the Table 1 primary sources and to 'T' for the Table 2 tentative sources. This HEASARC table also contains the X-ray spectroscopic information derived for 158 sources which have photometric significance (the snr parameter) >= 2.0 which was presented in Table 3 of the reference paper. All spectral fits used the "wabs(apec)" model in XSPEC and assumed 0.3 * Z_Sun abundances. The quoted emission measures and X-ray luminosities assume a distance to the Rosette molecular cloud of 1.4 kpc. This table was created by the HEASARC in July 2009 based on the merger of electronic versions of tables 1, 2, 3 and 4 from the above reference which were obtained from the ApJ web site. This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/selhcgcxo
- Title:
- Selected Hickson Compact Groups Chandra X-Ray Point Source Catalog
- Short Name:
- SELHCGCXO
- Date:
- 18 Apr 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- This table contains the Chandra X-ray point source catalogs for 9 Hickson Compact Groups (HCGs, 37 galaxies) at distances of 34 to 89 Mpc. The authors perform detailed X-ray point source detection and photometry and interpret the point source population by means of simulated hardness ratios. They thus estimate X-ray luminosities (L<sub>X</sub>) for all sources, most of which are too weak for reliable spectral fitting. For all sources, they provide counts, count rates, power-law indices (Gamma), hardness ratios, and L<sub>X</sub>, in the full (0.5-8.0 keV), soft (0.5-2.0 keV) and hard (2-8 keV) bands. In their paper, the authors use optical emission-line ratios from the literature to re-classify 24 galaxies as star-forming, accreting onto a supermassive black hole (AGNs), transition objects, or low-ionization nuclear emission regions. Two-thirds of their galaxies have nuclear X-ray sources with Swift/UVOT counterparts. Two nuclei have full-band X-ray luminosities >= 10<sup>42</sup> erg s<sup>-1</sup>, are strong multi-wavelength AGNs, and follow the known alpha<sub>OX</sub> - nu L_nu(near-UV)_ correlation for strong AGNs. Otherwise, most nuclei are X-ray faint, consistent with either a low-luminosity AGN or a nuclear X-ray binary population, and fall into the 'non-AGN' locus in alpha<sub>OX</sub> - nu L_nu(near-UV)_ space, which also hosts other normal galaxies. Each group was observed at the aim point of the back-illuminated S3 CCD of Chandra's Advanced CCD Imaging Spectrometer (ACIS), with the exception of HCG 90, which was observed with the ACIS-I array. The details of the 9 Chandra observations analyzed herein are given in Table 1 of the reference paper. The full details of the X-ray analysis and point source detection procedures are given in Section 3 of the reference paper. This table was created by the HEASARC in June 2014 based on electronic versions of Tables 2 and 3 from the reference paper which were obtained from the ApJS web site. Some of the values for the name parameter in the HEASARC's implementation of this table were corrected in April 2018. This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/smcdfscxo
- Title:
- Small Magellanic Cloud Deep Fields X-Ray Point Source Catalog
- Short Name:
- SMCDFSCXO
- Date:
- 18 Apr 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- This table contains the results of a pair of 100 ks Chandra observations of the Small Magellanic Cloud (SMC) to survey high-mass X-ray binaries (HMXBs), stars, and low-mass X-ray binaries (LMXBs)/cataclysmic variables down to L<sub>X</sub> = 4.3 x 10<sup>32</sup> erg s<sup>-1</sup>. The two SMC Deep Fields (DFs) are located in the most active star-forming region of the SMC bar, with Deep Field-1 positioned at the most pulsar-rich location identified from previous surveys. Two new pulsars were discovered in outburst, CXOU J004929.7-731058 (P = 892 s) and CXOU J005252.2-721715 (P = 326 s), and three new HMXB candidates were identified. Of the 15 Be-pulsars now known in the field, 13 were detected, with pulsations seen in 9 of them. Ephemerides demonstrate that 6 of the 10 pulsars known to exhibit regular outbursts were seen outside their periastron phase, and quiescent X-ray emission at L<sub>X</sub> = 10<sup>(33-34)</sup> erg s<sup>-1</sup> is shown to be common. Comparison with ROSAT, ASCA, and XMM-Newton catalogs resulted in positive identification of several previously ambiguous sources. Bright optical counterparts exist for 40 of the X-ray sources, of which 33 are consistent with early-type stars (M<sub>V</sub> < -2, B-V < 0.2), and are the subject of a companion paper to the reference paper. The results point to an underlying HMXB population density up to double that of active systems. The full catalog of 394 point sources is presented in this table; detailed analyses of the source timing and spectral properties are available in the reference paper. The aim-points for these Chandra observations were as follows: DF1 had J2000.0 coordinates of 00 53 34.50 -72 26 43.2 and DF2 had J2000.0 coordinates of 00 50 41.40 -73 16 10.3. This table was created by the HEASARC in August 2010 based on the electronic version of Table 2 from the reference paper which was obtained from the ApJ web site. This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/smcwingcxo
- Title:
- Small Magellanic Cloud Wing Survey Chandra X-Ray Point Source Catalog
- Short Name:
- SMCWINGCXO
- Date:
- 18 Apr 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- The authors have detected 523 X-ray sources in a survey of the Small Magellanic Cloud (SMC) Wing with the Chandra X-ray Observatory. By cross-correlating the X-ray data with optical and near-infrared catalogs, they have found 300 matches. Using a technique that combines X-ray colors and X-ray to optical flux ratios, they have been able to assign preliminary classifications to 265 of the objects. The identifications include 4 pulsars, 1 high-mass X-ray binary (HMXB) candidate, 34 stars and 185 active galactic nuclei (AGN). In addition, the authors have classified 32 sources as hard AGN which are likely absorbed by local gas and dust, and 9 soft AGN whose nature is still unclear. Considering the abundance of HMXBs discovered so far in the Bar of the SMC the number that have been detected in the Wing is low. Observations in the Wing of the SMC were made from 2005 July to 2006 March with Chandra. The survey consisted of 20 fields, with exposure times ranging from 8.6 - 10.3 ks. X-ray parameters for 523 sources detected in the Wing of the SMC with Chandra are presented. For each source equatorial coordinates, positional error, net counts (total counts minus background counts) in the 0.5 - 8.0 keV band, signal-to-noise of the detection and source flux in the 0.5 - 8.0 keV band are given. The median, compressed median and normalized quartile ratio of the photon energy distribution, determined using quantile analysis, are given for sources with three or more counts. For the sources that have optical counterparts the V- and R-band magnitudes, B-V color, X-ray to optical flux ratios based on the V- and R-band magnitudes, and a preliminary classification for the sources are given. This table was created by the HEASARC in June 2008 based on the <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/MNRAS/383/330">CDS Catalog J/MNRAS/383/330</a> file table2.dat. This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/spicescxo
- Title:
- SPICES Lynx Field Chandra X-Ray Source Catalog
- Short Name:
- SPICESCXO
- Date:
- 18 Apr 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- This table contains the first results on field X-ray sources detected in a deep, 184.7 ks observation with the Advanced CCD Imaging Spectrometer (ACIS-I) on the Chandra X-Ray Observatory. The observations target the Lynx field (J2000.0 RA = 08h 48m and Dec = +44d 54') of SPICES, the Spectroscopic Photometric Infrared-Chosen Extragalactic Survey, which contains three known X-ray-emitting clusters at redshifts of z = 0.57, 1.26, and 1.27. Not including the known clusters, in the 17' x 17' ACIS-I field the authors detect 132 sources in the 0.5 - 2 keV (soft) X-ray band down to a 2.1-sigma limiting flux of ~ 1.7 x 10<sup>-16</sup> erg/cm<sup>2</sup>/s and 11 sources in the 2 - 10 keV (hard) X-ray band down to a 2.1-sigma limiting flux of ~ 1.3 x 10<sup>-15</sup> erg/cm<sup>2</sup>/s. The combined catalog contains a total of 153 X-ray sources, of which 42 are detected only in the soft band and 21 are detected only in the hard band. Confirming previous Chandra results, the authors find that the fainter sources have harder X-ray spectra, providing a consistent solution to the long-standing "spectral paradox". From deep optical and near-infrared follow-up data, 77% of the X-ray sources have optical counterparts to I = 24, and 71% of the X-ray sources have near-infrared counterparts to K<sub>s</sub> = 20. Four of the 24 sources in the near-IR field are associated with extremely red objects (EROs; I - K<sub>s</sub> >= 4). The authors have obtained spectroscopic redshifts with the Keck telescopes of 18 of the Lynx Chandra sources. These sources comprise a mix of broad-lined active galaxies, apparently normal galaxies, and two late-type Galactic dwarfs. Intriguingly, one Galactic source (number 72) is identified with an M7 dwarf exhibiting non-transient, hard X-ray emission. Thirteen of the Chandra sources are located within regions for which the authors have Hubble Space Telescope imaging. Nine of the sources are detected, showing a range of morphologies: several show compact cores embedded within diffuse emission, while others are spatially extended showing typical galaxy morphologies. Two of the Chandra sources in this subsample appear to be associated with mergers. ACIS-I observations of the Lynx field were obtained on 2000 May 3 (65 ks; OBS-ID 1708) and 2000 May 4 (125 ks; OBS-ID 927). Time intervals with background rates larger than 3 sigma over the quiescent value of ~ 0.30 counts s<sup>-1</sup> per chip in the 0.3 - 10 keV band were removed. This procedure gave 60.7 ks of effective exposure out of the first observation and 124 ks out of the second, for a total of 184.7 ks. The two observations are almost coincident on the sky, so that the total coverage is 298 arcmin<sup>2</sup>. The aim point for the observations was RA = 08h 48m 54.79s, Dec = +44d 54' 32.9" (J2000.0), and both exposures were obtained in the faint mode when ACIS was at a temperature of -120 C. The Galactic absorbing column for this field is N<sub>H</sub> = 2 x 10<sup>20</sup> cm<sup>-2</sup>. The position angle of the observations was 258.45 degrees. Cosmology-dependent parameters are calculated for two models: an Einstein-de Sitter (EdS) universe consistent with previous work in this field (H<sub>0</sub> = 50 h<sub>50</sub> km s<sup>-1</sup> Mpc<sup>-1</sup>, Omega<sub>M</sub> = 1, and Omega<sub>Lambda</sub> = 0) and the dark energy cosmology (DEC) universe favored by recent work on high-redshift supernovae and fluctuations in the cosmic microwave background (H<sub>0</sub> = 65 km s<sup>-1</sup> Mpc<sup>-1</sup>, Omega<sub>M</sub> = 0.35, and Omega<sub>Lambda</sub> = 0.65). This table was created by the HEASARC in April 2007 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/AJ/123/2223">CDS catalog J/AJ/123/2223</a> files table1.dat, table2.dat and table3.dat. This is a service provided by NASA HEASARC .
