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361. NGC 5866 Chandra X-Ray Point Source Catalog
ID:
ivo://nasa.heasarc/ngc5866cxo
Title:
NGC 5866 Chandra X-Ray Point Source Catalog
Short Name:
NGC5866CXO
Date:
18 Apr 2025
Publisher:
NASA/GSFC HEASARC
Description:
S0 galaxies are often thought to be passively evolved from spirals after star formation is quenched. To explore what is actually occurring in such galaxies, the authors conducted a multi-wavelength case study of NGC 5866 - a nearby edge-on S0 galaxy in a relatively isolated environment. This study shows strong evidence for dynamic activities in the interstellar medium, which are most likely driven by supernova explosions in the galactic disk and bulge. Understanding these activities can have strong implications for studying the evolution of such galaxies. The authors utilized Chandra, Hubble Space Telescope, and Spitzer data as well as ground-based observations to characterize the content, structure, and physical state of the medium and its interplay with the stellar component in NGC 5866. These reveal the presence of diffuse X-ray-emitting hot gas, which extends as far as 3.5 kpc away from the galactic plane and can be heated easily by Type Ia SNe in the bulge. The Chandra/ACIS observation of NGC 5866 was taken on 2002 November 14. The authors reprocessed the archived data for their study. See Figure 1 in the reference paper for the Chandra/ACIS-S image of NGC 5866 in the 0.3-7 keV band. This table contains the detected X-ray point sources listed in table 2 of this paper. This table was created by the HEASARC in May 2018 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJ/706/693">CDS Catalog J/ApJ/706/693</a> file table2.dat, the list of detected X-ray sources in the Chandra observation of NGC 5866. This is a service provided by NASA HEASARC .
362. NGC 6791 Chandra X-Ray Point Source Catalog
ID:
ivo://nasa.heasarc/ngc6791cxo
Title:
NGC 6791 Chandra X-Ray Point Source Catalog
Short Name:
NGC6791CXO
Date:
18 Apr 2025
Publisher:
NASA/GSFC HEASARC
Description:
This table contains some of the results from the first X-ray study of NGC 6791, one of the oldest open clusters known (8 Gyr). This Chandra observation was aimed at uncovering the population of close interacting binaries down to an X-ray luminosity (L<sub>X</sub>) of ~1 x 10<sup>30</sup> erg/s (0.3-7 keV). The authors detect 86 sources within 8 arcminutes of the cluster center, including 59 inside the half-mass radius of 4.42 arcminutes. centered on 19<sup>h</sup> 20<sup>m</sup> 53<sup>s</sup>, +37<sup>o</sup> 46' 18" (J2000.0). They identify 20 sources with proper-motion cluster members, which are a mix of cataclysmic variables (CVs), active binaries (ABs), and binaries containing sub-subgiants. With follow-up optical spectroscopy, the authors confirm the nature of one CV. They also discover one new, X-ray variable candidate CV with Balmer and He II emission lines in its optical spectrum; this is the first X-ray-selected CV in an open cluster. The number of CVs per unit mass is consistent with the field, suggesting that the 3-4 CVs observed in NGC 6791 are primordial. The authors compare the X-ray properties of NGC 6791 with those of a few old open clusters (NGC 6819, M67) and globular clusters (47 Tuc, NGC 6397). It is puzzling that the number of ABs brighter than 1 x 10<sup>30</sup> erg/s normalized by cluster mass is lower in NGC 6791 than in M 67 by a factor ~3-7. CVs, ABs, and sub-subgiants brighter than 1 x 10<sup>30</sup> erg/s are under-represented per unit mass in the globular clusters compared to the oldest open clusters, and this accounts for the lower total X-ray luminosity per unit mass of the former. This indicates that the net effect of dynamical encounters may be the destruction of even some of the hardest (i.e., X-ray-emitting) binaries. The authors observed NGC 6791 with the Advanced CCD Imaging Spectrometer (ACIS) on Chandra from 2004 July 1 20:51 UTC until July 2 10:49 UTC for a total exposure time of 48.2ks (ObsID 4510). They obtained low-resolution spectra of candidate optical counterparts to guide the classification of the X-ray sources. A total of 16 candidate counterparts brighter than V ~18.3 were observed with the FAST long-slit spectrograph on the 1.5m Tillinghast telescope on Mt. Hopkins on nine nights between 2005 June 7 to September 2 (coverage from 3480 to 7400 Angstrom and a 3 Angstrom resolution). Candidate optical counterparts fainter than V ~17 were observed with the fiber-fed multi-object spectrograph Hectospec on the 6.5m Multi-Mirror Telescope. A total of 16 candidate counterparts were observed on the nights of 2005 May 13 and July 4-6 (spectra that cover 3700 to 9150 Angstrom with a 6-Angstrom resolution). The authors performed source detections in broad (0.3-7.0 keV), soft (0.3-2.0 keV) and hard (2.0-7.0 keV) energy bands, also used in their Chandra study of M 67 (van den Berg et al. 2004, A&A, 418. 509), so as to facilitate comparison. The CIAO detection routine wavdetect was run for scales of 1.0 to 11.3 pixels, in steps increasing by a factor of sqrt(2), with the larger scales appropriate for large off-axis angles where the point-spread function (PSF) becomes significantly broader. The authors computed exposure maps for the response at 1 keV to account for spatial variations of the sensitivity. The wavdetect detection threshold was set to 10<sup>-6</sup>, from which the authors expect two spurious detections per detection scale (so 16 spurious detections in total) in the area that they consider here. Combination of the broad, soft, and hard-band source lists results in a master catalog of 86 distinct sources within 8 arcmin of the cluster center, of which 59 lie inside the half-mass radius r<sub>h</sub>. To investigate the validity of the sources, the authors also ran wavdetect with a threshold of 10<sup>-7</sup> or an expected number of spurious sources of 1.6. The 14 sources not detected in this run are marked with a value of the source_flag parameter of 'T' in this table (replacing the '*' symbol used in the original table). This table was created by the HEASARC in August 2015 based on the <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJ/770/98">CDS Catalog J/ApJ/770/98</a> files table1.dat and table2.dat. This is a service provided by NASA HEASARC .
363. NGC 2264 Chandra X-Ray Point Source Catalog 2
ID:
ivo://nasa.heasarc/ngc2264cx2
Title:
NGC 2264 Chandra X-Ray Point Source Catalog 2
Short Name:
NGC2264CX2
Date:
18 Apr 2025
Publisher:
NASA/GSFC HEASARC
Description:
With the goal of improving the member census of the NGC 2264 star-forming region and studying the origin of X-ray activity in young pre-main sequence (PMS) stars, the authors analyzed a deep, 100 ks long, Chandra ACIS observation covering a 17' x 17' field in the 3 Myr old star-forming region (SFR) NGC 2264. The preferential detection in X-rays of low-mass PMS stars gives strong indications of their membership. The authors study X-ray activity as a function of stellar and circumstellar characteristics by correlating the X-ray luminosities, temperatures, and absorptions with optical and near-infrared (NIR) data from the literature. The authors detected 420 X-ray point sources in the observation above a 4.6-sigma significance threshold using the PWDetect software. Optical and NIR counterparts were found in the literature for 85% of the sources. The authors argue that more than 90% of these counterparts are NGC 2264 members, thereby significantly increasing the known low-mass cluster population by about 100 objects. Among the sources without counterpart, about 50% are probably associated with members, several of which are expected to be previously unknown protostellar objects. With regard to activity, several previous findings are confirmed: X-ray luminosity is related to stellar mass, although with a large scatter; L<sub>x</sub>/L<sub>bol</sub> is close to, but almost invariably below, the saturation level of 10<sup>-3</sup>, especially when considering the quiescent X-ray emission. A comparison between classical T Tauri stars (CTTS) and weak-line T Tauri stars (WTTS) shows several differences: CTTS have, at any given mass, activity levels that are both lower and more scattered than WTTS; emission from CTTS may also be more time variable and is on average slightly harder than for WTTS. However, there is evidence in some CTTS of extremely cool, ~0.1 - 0.2 keV, plasma which the authors speculate is due to plasma heated by accretion shocks. The X-ray spectra of the 199 sources with more than 50 detected photons were analyzed by the authors. Spectral fits were performed with XSPEC 11.3 and with several shell and TCL scripts to automate the process. For each source, they fit the data in the [0.5 - 7.0] keV energy interval with several model spectra: one and two isothermal components (APEC), subject to photoelectric absorption from interstellar and circumstellar material (WABS). Plasma abundances for one-temperature (1T) models were fixed at 0.3 times the solar abundances, while they were both fixed at that value and treated as a free parameter for the two-temperature (2T) models. The absorbing column densities, N<sub>H</sub>, were both left as a free parameter and fixed at values corresponding to the optically/NIR determined extinctions, when available: N<sub>H</sub> = 1.6 x 10<sup>21</sup> A<sub>V</sub>. This table contains the X-ray, optical and NIR data for the 420 detected X-ray sources; it does not contain the master catalog of 1598 optical/NIR sources within the ACIS FOV which was presented in Table 3 of the reference paper, available at <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/A+A/455/903/table3.dat">https://cdsarc.cds.unistra.fr/ftp/cats/J/A+A/455/903/table3.dat</a> This table was created by the HEASARC in March 2007 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/A+A/455/903">CDS Catalog J/A+A/455/903</a> files table1.dat, table4.dat and table6.dat. This is a service provided by NASA HEASARC .
364. NGC 2264 Chandra X-Ray Point Source Catalog
ID:
ivo://nasa.heasarc/ngc2264cxo
Title:
NGC 2264 Chandra X-Ray Point Source Catalog
Short Name:
NGC2264CXO
Date:
18 Apr 2025
Publisher:
NASA/GSFC HEASARC
Description:
The NGC 2264 Chandra X-Ray Point Source Catalog contains the results of a Chandra observation of a field in the NGC 2264 star-forming region. The observation was made with Chandra's Advanced CCD Imaging Spectrometer imaging array (ACIS-I) on 2002 February 9, and has an exposure time of 48.1 ks. The catalog contains 263 sources, and includes X-ray luminosity, optical and infrared photometry, and X-ray variability information. The authors found 41 variable sources, 14 of which have a flare-like light curve, and two of which have a pattern of a steady increase or decrease over a 10-hr period. The optical and infrared photometry for the stars identified as X-ray sources are consistent with most of these objects being pre-main sequence stars with ages younger than 3 Myr. The authors found that 213 (81%) of the 263 X-ray sources have optical and/or infrared counterparts, most, but probably not all, of which are likely to be member stars of NGC 2264. There are 51 X-ray sources that lack optical or infrared counterparts: the authors believe that these are most likely extragalactic objects (active galaxies). This table was created by the HEASARC in February 2007 based on CDS table J/AJ/127/2659, files table1.dat, table4.dat and table5.dat. This is a service provided by NASA HEASARC .
365. NGC 3293 Chandra X-Ray Point Source Catalog
ID:
ivo://nasa.heasarc/ngc3293cxo
Title:
NGC 3293 Chandra X-Ray Point Source Catalog
Short Name:
NGC3293CXO
Date:
18 Apr 2025
Publisher:
NASA/GSFC HEASARC
Description:
NGC 3293 is a young stellar cluster at the northwestern periphery of the Carina Nebula Complex that has remained poorly explored until now. The authors wanted to characterize the stellar population of NGC 3293 in order to evaluate key parameters of the cluster population like the age and the mass function, and to test claims of an abnormal initial mass function (IMF) and a deficit of <= 2.5*M<sub>sun</sub> stars. Thus, they performed a deep (71 ksec) X-ray observation of NGC 3293 with Chandra in which they detected 1026 individual X-ray point sources. These X-ray data directly probe the low-mass (M <= 2*M<sub>sun</sub>) stellar population by means of the strong X-ray emission of young low-mass stars. The authors have identified counterparts for 74% of the X-ray sources in their deep near-infrared images. These data clearly show that NGC 3293 hosts a large population of ~ 1*M<sub>sun</sub> stars, refuting claims of a lack of M <= 2.5*M<sub>sun</sub> stars. The analysis of the color-magnitude diagram suggests an age of ~8-10 Myr for the low-mass population of the cluster. There are at least 511 X-ray detected stars with color-magnitude positions that are consistent with young stellar members within 7 arcminutes from the cluster center. The number ratio of X-ray detected stars in the 1-2 solar mass range versus the M >= 5*M<sub>sun</sub> stars (known from optical spectroscopy) is well consistent with the expectation from a normal field initial mass function. Most of the early B-type stars and ~20% of the later B-type stars are detected as X-ray sources. These data shows that NGC 3293 is one of the most populous stellar clusters in the entire Carina Nebula Complex (only excelled by Tr 14, and very similar to Tr 16 and Tr 15). The cluster has probably harbored several O-type stars, the supernova explosions of which may have had an important impact on the early evolution of the Carina Nebula Complex. The authors used the Chandra X-ray Observatory to perform a deep pointing of the cluster NGC 3293 with the Imaging Array of the Chandra Advanced CCD Imaging Spectrometer (ACIS-I). The 71-ksec observation was performed as an open time project with ObsID 16648 (PI: T. Preibisch) during Chandra Observing Cycle 15 in October 2015 (start date: 2015-10-07 T10:14:23, end date: 2015-10-08 T06:43:28). The imaging array ACIS-I provides a field of view of 17' x 17' on the sky (which corresponds to a scale of 11.3 x 11.3pc at the cluster distance of 2.3 kpc), and has a pixel size of 0.492". The aimpoint of the observation was RA(J2000) = 10<sup>h</sup> 35<sup>m</sup> 50.07<sup>s</sup>, Dec(J2000) = -58<sup>o</sup> 14' 00", which is close to the optical center of the cluster (see Fig. 1 in the reference paper). The pointing roll angle (i.e., the orientation of the detector with respect to the celestial North direction) was 140.19<sup>o</sup>. In addition to ACIS-I, one CCD detector (CCD 7 = S3) of the spectroscopic array ACIS-S was also operational during this pointing. It covers an 8.3' x 8.3' area on the sky southwest of the cluster center. While the ACIS-I chips are front-illuminated (FI), the S3 chip is back-illuminated (BI), and thus its response extends to energies below that accessible by the FI chips. This causes a substantially higher level of background in the S3 chip. Furthermore, the PSF is seriously degraded at the rather large off-axis angles of the S3 chip. These two effects led to a considerably higher detection limit for point sources in the area covered by the S3 chip compared to the region covered by the ACIS-I array. Nevertheless, the S3 data were included in the data analysis and source detection, and contributed four point sources to the total source list. At the distance of 2.3 kpc, the expected ACIS point source sensitivity limit for a three-count detection on-axis in a 71-ks observation corresponds to a minimum X-ray luminosity of L<sub>x</sub> ~ 10<sup>29.7</sup> erg s<sup>-1</sup> in the 0.5-8.0 keV energy band, assuming an extinction of A<sub>V</sub> ~ 1 mag (N<sub>H</sub> ~ 2 x 10<sup>21</sup> cm<sup>-2</sup>) typical for the stars in the central region of NGC 3293, and a thermal plasma with kT = 1 keV (which is a typical value for young stars). Using the empirical relation between X-ray luminosity and stellar mass and the temporal evolution of X-ray luminosity from the sample of young stars in the Orion Nebula Cluster, which was very well studied in the Chandra Orion Ultradeep Project (Preibisch et al. 2005, ApJS, 160, 401; Preibisch & Feigelson 2005, ApJS, 160, 390), the authors expected to detect ~90% of the ~ 1*M<sub>sun</sub> stars in the central region of the young cluster NGC 3293. The X-ray properties of the 97 B-type stars in the ACIS-I field towards the cluster (24 of which are detected as X-ray sources) are not included in this HEASARC table, but are listed in Table 3 of the reference paper, which is also reproduced below: <pre> ESL No.* Star Name X-ray Spectral Type X-ray Luminosity (L<sub>x</sub>) log (L<sub>x</sub>/L<sub>bol</sub>) Src No. erg/s 49 B2.5 V < 4.33e+30 < -5.88 33 HDE 303073 B8 III < 7.15e+30 < -6.31 65 ALS 20075 B5 III-V < 2.12e+30 < -5.88 77 B6-7 V < 1.42e+30 < -5.91 96 ALS 20084 B6-7 III < 9.09e+29 < -5.96 87 47 B5 V 4.62e+30 -5.11 38 B2.5 V < 7.16e+29 < -6.94 68 78 B9 III 4.79e+30 72 B8 IIp < 6.87e+29 69 B5 V < 3.89e+29 < -6.47 22 HDE 303075 B0.5-1.5n < 6.22e+29 < -7.77 109 B5 V < 5.05e+29 < -6.06 93 B6-7 V < 5.16e+29 < -6.17 116 B6-7 V < 4.74e+29 < -5.88 73 B6-7 V < 3.87e+29 < -6.38 10 CPD-57 3500 395 B1 III 7.35e+29 -7.89 121 ALS 20096 B8: III < 4.84e+29 50 B3 Vn < 5.01e+29 < -6.71 2 HD 91943 418 B0.7 Ib 4.11e+30 -8.15 41 V438 Car B2.5 V < 3.94e+29 < -7.21 48 CPD-57 3505 461 B2.5 V 1.39e+30 -6.67 3 CPD-57 3506A 490 B1 III 5.37e+30 -7.63 125 B8 III-V < 8.62e+29 < -5.48 19 V405 Car 523 B1 V 6.77e+29 -7.88 34 CPD-57 3509 535 B2 IIIh 6.71e+29 -7.54 1 HD 91969 542 B0 Iab 2.78e+31 -7.52 106 565 B6-7 V 1.20e+30 -5.54 53 CPD-57 3512 B3 V < 3.61e+29 < -6.70 98 598 B8 III-V 1.31e+30 -5.65 30 CPD-57 3514 601 B2 V 1.99e+30 -6.64 123 604 B8 III 3.79e+30 -4.98 8 HD 91983 626 B1 III 1.36e+30 -7.78 32 CPD-57 3518 B0.5-B1.5 Vn < 1.20e+30 < -7.14 61 B5 V < 3.87e+29 < -6.56 5 CPD-57 3521 679 B1 III 3.45e+30 -7.61 28 CPD-57 3520 B2 V < 4.16e+29 < -7.46 113 B6-7 V < 4.09e+29 < -6.01 11 CPD-57 3526 703 B1: 2.29e+30 6 CPD-57 3526B 710 B1 III 2.29e+30 -7.73 84 B5 V < 3.99e+29 < -6.33 31 CPD-57 3528 B2 V < 1.50e+30 < -6.66 29 CPD-57 3531 B0.5-B1.5 Vn < 5.99e+29 < -7.56 59 B5 III-Vn < 8.23e+29 < -6.61 80 B5 V < 1.31e+30 < -5.98 13 HD 92024 831 B1 III 6.59e+29 -7.82 108 850 B6-7 V 3.65e+30 -5.09 95 884 B6-7 V 1.49e+30 -5.66 67 B3 V < 1.20e+30 < -6.42 97 B6-7 III < 6.34e+29 < -6.01 94 927 B5 V 4.42e+30 -5.35 85 B5 V < 1.47e+30 < -5.80 4 CPD-57 3523 697 B1 III 3.40e+30 -7.57 7 HD 92044 908 B1 III 2.20e+30 -7.94 14 CPD-57 3524A 704 B0.5 IIIn 5.46e+30 -7.27 </pre> * The ESL number is the source number of the star as given in Evans et al. (2005, A&A, 437, 467). This table was created by the HEASARC in September 2017 based upon the <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/A+A/605/A85">CDS Catalog J/A+A/605/A85</a> files table1.dat and table2.dat. This is a service provided by NASA HEASARC .
366. NGC 6231 Chandra X-Ray Point Source Catalog
ID:
ivo://nasa.heasarc/ngc6231cxo
Title:
NGC 6231 Chandra X-Ray Point Source Catalog
Short Name:
NGC6231CXO
Date:
18 Apr 2025
Publisher:
NASA/GSFC HEASARC
Description:
NGC 6231 is a massive young star cluster, near the center of the Sco OB1 association. While its OB members are well studied, its low-mass population has received little attention. In the reference paper, the authors present high-spatial resolution Chandra ACIS-I X-ray data, wherein they detect 1,613 point X-ray sources. Their main aim was to clarify the global properties of NGC 6231 down to low masses through a detailed membership assessment, and to study the cluster stars' spatial distribution, the origin of their X-ray emission, the cluster age and formation history, and its initial mass function. The authors use X-ray data, complemented by optical and IR data, to establish cluster membership. The spatial distribution of different stellar subgroups also provides highly significant constraints on cluster membership, as does the distribution of X-ray hardness. In their study, the authors perform spectral modeling of group-stacked X-ray source spectra. The X-ray properties of the sources detected in the Chandra observations of NGC 6231, and their cross-identifications in the catalogs of Sung, Sana, and Bessell (2013 AJ, 145, 37; hereafter SSB); VPHAS+ (Drew et al., 2014, MNRAS, 440, 2036); and 2MASS (<a href="https://cdsarc.cds.unistra.fr/ftp/cats/II/246">CDS Cat. II/246</a>), and information about membership, H-alpha or IR excess, mass and luminosity are also provided. SSB derive a distance modulus for NGC 6231 of 11.0 (1,585 pc), a reddening E(B - V) = 0.47, and a nearly normal reddening law with R = 3.2. The present authors adopt these values for this work. NGC 6231 was observed twice in X-rays with the ACIS-I detector on-board the Chandra X-ray Observatory on 2005, July 3 to 4 (ObsId 5372) and 16 to 17 (ObsID 6291), respectively. The two pointings share the same center (aimpoint) but were performed with a different roll angle. Effective exposure times for the observations were 76.19 and 44.39 ks, respectively, making the total exposure time 120.58 ks. The data were filtered to retain the energy band 0.3 - 8.0 keV, and the full-field lightcurves were inspected to search for high-background periods, but none were found. Exposure maps were computed using standard CIAO software tasks. To these prepared datasets, the authors applied the source detection software PWDetect, a wavelet-based detection algorithm developed at INAF-Osservatorio Astronomico di Palermo. The PWDetect version used here is a modified one, able to detect sources in combined datasets, thus taking full advantage of the deep total exposure. The detection threshold was chosen such as to yield ten spurious detections in the field of view (FOV), for the given background counts. This is a more relaxed constraint than the more usual limit of one spurious detection per field, but is justified when the lowered threshold allows the detection of more than one hundred additional faint sources, as it was the case here or in the COUP Program's Orion data. This HEASARC table contains the list of 1,613 detected X-ray point sources and information about their optical and IR counterparts, where known. It does not contain the 275 additional candidate cluster members (where their candidacy was based on their having H-alpha or IR excesses) which lack X-ray counterparts and that were also listed in Table B.2 of the reference paper. This table was created by the HEASARC in December 2016 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/A+A/596/A82">CDS Catalog J/A+A/596/A82</a> file tableb.dat, which is the merger of tables B.1 (the list of 1,613 X-ray sources) and B.2 (the list of 1,888 optical and near-IR identifications of X-ray sources and of IR- and H-alpha-excess stars) from the reference paper, but excluding the 275 stars listed in the latter whose candidacy was based on their having H-alpha or IR excesses and which lack X-ray counterparts. # This is a service provided by NASA HEASARC .
367. NGC 4636 Chandra X-Ray Point Source Catalog
ID:
ivo://nasa.heasarc/ngc4636cxo
Title:
NGC 4636 Chandra X-Ray Point Source Catalog
Short Name:
NGC4636CXO
Date:
18 Apr 2025
Publisher:
NASA/GSFC HEASARC
Description:
This catalog lists the X-ray point-source population in the nearby Virgo elliptical galaxy NGC 4636 from three Chandra X-ray observations. These observations, totaling ~193 ks after time filtering, were taken with the Advanced CCD Imaging Camera (ACIS) over a three-year period. Using a wavelet decomposition detection algorithm, the authors detected 318 individual point sources. For their analysis, they used a subset of 277 detections with >= net 10 counts (a limiting luminosity of approximately 1.2 x 10<sup>37</sup> erg s<sup>-1</sup> in the 0.5-2 keV band, outside the central 1.5 arcminutes bright galaxy core). This table contains this subset of 277 X-ray sources. The authors discuss the radial distribution of the point sources. Between 1.5 and 6 arcminutes from the center, 25% of the sources are likely to be background sources (active galactic nuclei (AGNs)) and 75% to be low-mass X-ray binaries (LMXBs) within the galaxy, while at radial distances greater than 6 arcminutes, background sources (AGN) will dominate the point sources. The authors explore short and long-term variability (over timescales of 1 day to three years) for X-ray point sources in this elliptical galaxy. 54 sources (24%) in the common ACIS fields of view show significant variability between observations. Of these, 37 are detected with at least 10 net counts in only one observation and thus may be "transient." In addition, ~10% of the sources in each observation show significant short-term variability. The cumulative luminosity function (LF) for the point sources in NGC 4636 can be represented as a power law of slope Alpha = 1.14 +/- 0.03. The authors do not detect, but estimate an upper limit of ~4.5 x 10<sup>37</sup> erg s<sup>-1</sup> to the current X-ray luminosity of, the historical supernova SN1939A. They find 77 matches between X-ray point sources and globular cluster (GC) candidates found in deep optical images of NGC 4636. In the annulus from 1.5 to 6 arcminutes of the galaxy center, 48 of the 129 X-ray point sources (37%) with >=10 net counts are matched with GC candidates. Since they expect 25% of these sources to be background AGN, the percentage matched with GCs could be as high as 50%. Of these matched sources, the authors find that ~70% are associated with the redder GC candidates, those that are thought to have near-solar metal abundance. The fraction of GC candidates with an X-ray point source match decreases with decreasing GC luminosity. The authors do not find a correlation between the X-ray luminosities of the matched point sources and the luminosity or color of the host GC candidates. The LFs of the X-ray point sources matched with GCs and those that are unmatched have similar slopes over 1.8 x 10<sup>37</sup> erg s<sup>-1</sup> <= L<sub>x</sub> <= 1 x 10<sup>38</sup> erg s<sup>-1</sup>. This table was created by the HEASARC in July 2009 based on electronic versions of Tables 2 and 3 from the paper obtained from the ApJ web site, but excluding the 7 entries in Table 3 which corresponded to weaker X-ray sources which were not listed in Table 2. 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 .
368. NGC 2237 Chandra X-Ray Point Source Catalog
ID:
ivo://nasa.heasarc/ngc2237cxo
Title:
NGC 2237 Chandra X-Ray Point Source Catalog
Short Name:
NGC2237CXO
Date:
18 Apr 2025
Publisher:
NASA/GSFC HEASARC
Description:
The authors have obtained high spatial resolution Chandra X-ray images of the NGC 2237 young stellar cluster on the periphery of the Rosette Nebula. They detect 168 X-ray sources, 80% of which have stellar counterparts in USNO, Two Micron All Sky Survey, and deep FLAMINGOS images. These constitute the first census of the cluster members with 0.2 <~ M <~ 2 M<sub>sun</sub>. Star locations in near-infrared color-magnitude diagrams indicate a cluster age of around 2 Myr with a visual extinction of 1 <~ AV <~ 3 at 1.4 kpc, the distance of the Rosette Nebula's main cluster NGC 2244. The authors derive the K-band luminosity function and the X-ray luminosity function of the cluster, which indicate a population of ~ 400-600 stars. The X-ray-selected sample shows a K-excess disk frequency of 13%. The young Class II counterparts are aligned in an arc ~3 pc long suggestive of a triggered formation process induced by the O stars in NGC 2244. The diskless Class III sources are more dispersed. Several X-ray emitting stars are located inside the molecular cloud and around gaseous pillars projecting from the cloud. These stars, together with a previously unreported optical outflow originating inside the cloud, indicate that star formation is continuing at a low level and the cluster is still growing. This X-ray view of young stars on the western side of the Rosette Nebula complements the authors' earlier studies of the central cluster NGC 2244 and the embedded clusters on the eastern side of the Nebula. The large-scale distribution of the clusters and molecular material is consistent with a scenario in which the rich central NGC 2244 cluster formed first, and its expanding H II region triggered the formation of the now-unobscured satellite clusters Rosette Molecular Cloud (RMC) XA and NGC 2237. A large swept-up shell of material around the H II region is now in a second phase of collect-and-collapse fragmentation, leading to the recent formation of subclusters. Other clusters deeper in the molecular cloud appear unaffected by the Rosette Nebula expansion. Some sources which have information from published catalogs are listed by their source_number value below, where for convenience, [OI81] = Ogura & Ishida (1981, PASJ, 33, 149), [MJD95] = Massey, Johnson, & Degioia-Eastwood (1995, ApJ, 454, 151) and [BC02] = Berghofer & Christian (2002, A&A, 384, 890): <pre> 53 = [OI81] 14 = [MJD95] 104; spectral type B1V; pmRA=11.0 mas/yr, pmDE=-2.8 mas/yr; 54 = [OI81] 10 = [MJD95] 108; spectral type B2V; pmRA=-2.3 mas/yr, pmDE=-11.9 mas/yr; 61 = V539 Mon [OI81] 13 = [MJD95] 110; MSX6C G206.1821-02.3456; pmRA=2.8 mas/yr, pmDE=0.4 mas/yr; 71 = [OI81] 12 = [MJD95] 102; pmRA=6.8 mas/yr, pmDE=0.6 mas/yr; 128 = [OI81] 35 = [MJD95] 471; spectral type A2:; pmRA=-0.8 mas/yr, pmDE=3.6 mas/yr; 138 = [OI81] 36 = [MJD95] 497; spectral type B5; pmRA=6.5 mas/yr, pmDE=2.1 mas/yr; 141 = [MJD95] 498; pmRA=-3.0 mas/yr, pmDE=1.9 mas/yr; 149 = [BC02] 11; known X-ray source; log(Lx(ROSAT/PSPC))=31.01 erg/s; pmRA=0.6 mas/yr, pmDE=-12.6 mas/yr; 161 = [MJD95] 653; pmRA=-1.0 mas/yr, pmDE=-5.4 mas/yr </pre> This table was created by the HEASARC in July 2010 based on electronic versions of Tables 1, 2, 3 and 4 of the reference paper which were obtained from the electronic ApJ web site. To distinguish between the 130 X-ray sources in the primary sample (Table 1 of the reference paper) and the 38 X-ray sources in the tentative sample (Table 2 of the reference paper), the HEASARC has created a parameter called source_sample which is set to 'P' for the primary sources and to 'T' for the tentative sources. This is a service provided by NASA HEASARC .
369. NGC 6334 Chandra X-Ray Point Source Catalog
ID:
ivo://nasa.heasarc/ngc6334cxo
Title:
NGC 6334 Chandra X-Ray Point Source Catalog
Short Name:
NGC6334CXO
Date:
18 Apr 2025
Publisher:
NASA/GSFC HEASARC
Description:
The full stellar population of NGC 6334, one of the most spectacular regions of massive star formation in the nearby Galaxy, has not been well sampled in past studies. The authors have analyzed a mosaic of two Chandra X-ray Observatory images of the region using sensitive data analysis methods, giving a list of 1607 faint X-ray sources with arcsecond positions and approximate line-of-sight absorption. About 95% of these are expected to be cluster members, most lower mass pre-main-sequence stars. Extrapolating to low X-ray levels, the total stellar population is estimated to be 20,000 - 30,000 pre-main-sequence stars. The X-ray sources show a complicated spatial pattern with ~10 distinct star clusters. The heavily obscured clusters are mostly associated with previously known far-infrared sources and radio H II regions. The lightly obscured clusters are mostly newly identified in the X-ray images. Dozens of likely OB stars are found, both in clusters and dispersed throughout the region, suggesting that star formation in the complex has proceeded over millions of years. A number of extraordinarily heavily absorbed X-ray sources are associated with the active regions of star formation. This table was created by the HEASARC in August 2009 based on the electronic version of table 1 from the above reference which were obtained from the AJ web site. This is a service provided by NASA HEASARC .
370. NGC 752 Chandra X-Ray Point Source Catalog
ID:
ivo://nasa.heasarc/ngc752cxo
Title:
NGC 752 Chandra X-Ray Point Source Catalog
Short Name:
NGC752CXO
Date:
18 Apr 2025
Publisher:
NASA/GSFC HEASARC
Description:
This table provides a list of X-ray sources detected in a ~140 ks Chandra X-ray observation of the open cluster NGC 752. For the sources with 2MASS counterparts, the values of their magnitudes in the J, H and K bands are also given. Very little is known about the evolution of stellar activity between the ages of the Hyades (0.8 Gyr) and the Sun (4.6 Gyr). To gain information on the typical level of coronal activity at a star's intermediate age, the authors have studied the X-ray emission from stars in the 1.9 Gyr-old open cluster NGC 752. They analyzed a ~ 140 ks Chandra observation of NGC 752 and a ~50 ks XMM-Newton observation of the same cluster. They detected 262 X-ray sources in the Chandra data and 145 sources in the XMM-Newton observation. Around 90% of the catalogued cluster members within Chandra's field of view are detected in the X-ray observation. The X-ray luminosity of all observed cluster members (28 stars) and of 11 cluster member candidates was derived. These data indicate that, at an age of 1.9 Gyr, the typical X-ray luminosity L<sub>x</sub> of the cluster members with masses of 0.8 to 1.2 solar masses is 1.3 x 10<sup>28</sup> erg s<sup>-1</sup>, which is approximately a factor of 6 times less intense than that observed in the younger Hyades. Given that L<sub>x</sub> is proportional to the square of a star's rotational rate, the median L<sub>x</sub> of NGC 752 is consistent, for t >= 1 Gyr, with a decaying rate in rotational velocities v<sub>rot</sub> ~ t<sup>-alpha</sup> with alpha ~ 0.75, steeper than the Skumanich relation (alpha ~ 0.5) and significantly steeper than that observed between the Pleiades and the Hyades (where alpha <0.3), suggesting that a change in the rotational regimes of the stellar interiors is taking place at an age of ~ 1 Gyr. The 135 ks observation of NGC 752 was performed by the Chandra ACIS camera on September 29, 2003 starting at 21:11:59 UT. The X-ray source detection was performed on the event list using the Wavelet Transform detection algorithm developed at Palermo Astronomical Observatory PWDETECT, available at <a href="http://oapa.astropa.unipa.it/progetti_ricerca/PWDetect">http://oapa.astropa.unipa.it/progetti_ricerca/PWDetect</a>. Initially, the energy range 0.2 - 10 keV was selected and the threshold for source detection was taken as to ensure a maximum of 1-2 spurious sources per field. 169 sources were detected in this way. The analysis of these sources hardness ratios showed, however, that all the catalogued stars in the field had low hardness ratios, HR < ~ 0.2, where HR is the number of photons in the 2 - 8 keV band over the number in the 0.5 - 2 keV band. Thus, to maximize the detection of stellar sources, PWDETECT was applied to the event list in the energy range from 0.5 - 2 keV. Using a detection threshold which ensures less than 1 spurious source per field leads to the detection of 188 sources, while lowering this threshold to 10 spurious sources per field, allows 262 sources to be identified in this energy range. This is a significant increase (well above the number expected if all the additional sources were spurious), thus the authors retained this list of 262 sources as their final list of sources in the NGC 752 field, with the caveat that ~ 10 sources among them are likely spurious. Note that the existence of ~ 10 spurious sources in the list is not so much of a problem in this context, because cluster members or candidate members are identified by the existence of a visible or near-IR counterpart. The authors searched for 2MASS counterparts to the X-ray sources using the 2MASS Point Source Catalogue (PSC) and a search radius of 3 arcsec and found a counterpart for 43 sources. Searching within the Point Source Reject Table of the 2MASS Extended Mission leads to the further identification of 1 counterpart (source number 87). This table was created by the HEASARC in October 2008 based on the electronic version of Table 6 from the reference paper which was obtained from the CDS website, i.e., their catalog J/A+A/490/113 file table6.dat. This is a service provided by NASA HEASARC .