- ID:
- ivo://nasa.heasarc/cmaob1nir
- Title:
- CMa OB1 XMM-Newton Point Source Near-Infrared Counterpart Properties Catalog
- Short Name:
- CMAOB1NIR
- Date:
- 07 Mar 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- The Canis Major OB1 association has an intriguing scenario of star formation, especially in the region called Canis Major R1 (CMa R1) traditionally assigned to a reflection nebula, but in reality an ionized region. The authors focused on the young stellar population associated with CMa R1, for which previous results from ROSAT, optical, and near-infrared data had revealed two stellar groups with different ages, suggesting a possible mixing of populations originated from distinct star formation episodes (see the <a href="/W3Browse/rosat/cmar1xray.html">table CMAR1XRAY</a>). The observations performed with XMM-Newton resulted in a sample of 387 X-ray sources (187, 84, 37, and 79 in Fields E, C, S , and W, respectively), 340 of which have one or more NIR (2MASS) counterparts. This table contains the 2MASS photometry, estimates of age and mass, and infrared classification of members of the CMa R1 region and counterparts to X-ray sources, based on 2MASS and WISE data. The authors also used X-ray data to characterize the detected sources (387 sources) according to hardness ratios, light curves, and spectra (see the associated table <a href="/W3Browse/xmm-newton/cmaob1xmm.html">CMAOB1XMM</a>). For this work, four fields (each about 30-arcmin diameter with some overlap) were defined. These fields are located inside the arc-shaped ionized nebula, next to Z CMa - Field E (east); around GU CMa - Field W (west); and between both - Field C (center) and Field S (south), as shown in Figure 1 of the reference paper. <pre> RA(J2000) | Dec(J2000) | Designation(s) 07 04 18.3 | -11 27 24.0 | CMa cluster east (Field E) 07 02 58.4 | -11 34 44.7 | CMa cluster center (Field C) 07 02 29.5 | -11 47 12.4 | CMa cluster south (Field S) 07 01 23.0 | -11 19 56.6 | CMa cluster west (Field W) </pre> The authors have selected NIR counterparts by searching the 2MASS catalog for candidates located less that 10'' away from the nominal X-ray source positions. No counterpart was found for 45 sources. Candidates for which the distance seems to be incompatible with the CMaR1 molecular cloud were disregarded. This table includes the complete list of NIR counterparts, however the authors only consider as reliable those flagged as 'AAA' in the 2MASS catalog (i.e., with S/N > 10, magnitude errors <0.1 mag, and above the JHK completeness limits), given by the twomass_flags field in this table. There are 340 such reliable NIR counterparts for 290 X-ray sources, including 46 X-ray sources with multiple counterpart candidates. X-ray and NIR data have revealed that most (79%) of the XMM-Newton sources are probable members of CMa R1. The combination of the results from both analyses can confirm their young nature. On the other hand, 21% of the XMM-Newton sample are probably field objects. Among these, 6% (23/387) have infrared counterparts that probably are foreground stars and 4% (17/387) have counterparts that are too faint (bad quality data) without reliable classification. The other 11% of undefined sources (44/387) do not have 2MASS data because they are classified as possible background objects. The authors have seen that the XMM-Newton error boxes may include multiple NIR counterparts. In such cases, they restricted the comparative analysis to the 158 X-ray sources of their "best sample" that are associated with a single NIR counterpart, as described in Section 4.3 of the reference paper. A distance of 1 kpc to CMa OB1 is assumed for this table. This table was created by the HEASARC in October 2018 based upon the <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/A+A/609/A127">CDS Catalog J/A+A/609/A127</a> file tableb2.dat. This is a service provided by NASA HEASARC .
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Search Results
- ID:
- ivo://nasa.heasarc/cmaob1xmm
- Title:
- CMa OB1 XMM-Newton X-Ray Point Source Catalog
- Short Name:
- CMAOB1XMM
- Date:
- 07 Mar 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- The Canis Major OB1 association has an intriguing scenario of star formation, especially in the region called Canis Major R1 (CMa R1) traditionally assigned to a reflection nebula, but in reality an ionized region. The authors focused on the young stellar population associated with CMa R1, for which previous results from ROSAT, optical, and near-infrared data had revealed two stellar groups with different ages, suggesting a possible mixing of populations originated from distinct star formation episodes (see the <a href="/W3Browse/rosat/cmar1xray.html">table CMAR1XRAY</a>). The authors used X-ray data to characterize the detected sources according to hardness ratios, light curves, and spectra. They also provided estimates of mass and age, using the information from likely counterparts based on the 2MASS catalogue. The 2MASS-derived data on the counterparts, where matched, are provided in the <a href="/W3Browse/xmm-newton/cmaob1nir.html">associated table (CMAOB1NIR)</a>. This table contains a catalog of 387 XMM-Newton sources, of which 78% are confirmed as members or probable members of the CMa R1 association. Flares (or similar events) were observed for 13 sources and the spectra of 21 bright sources could be fitted by a thermal plasma model. Mean values of fits parameters were used to estimate X-ray luminosities. The authors found a minimum value of log(L<sub>X</sub> [erg/s]) = 29.43, indicating that the sample of low-mass stars (M<sub>*</sub> <= 0.5 M<sub>sun</sub>), which are faint X-ray emitters, is incomplete. Among the 250 objects selected as the complete subsample (defining a "best sample"), 171 are found to the east of the cloud, near Z CMa and dense molecular gas, of which 50% of them are young (<5Myr) and 30% are older (>10Myr). The opposite happens to the west, near GU CMa, in areas lacking molecular gas: among 79 objects, 30% are young and 50% are older. These findings confirm that a first episode of distributed star formation occurred in the whole studied region ~10Myr ago and dispersed the molecular gas, while a second, localized episode (<5Myr) took place in the regions where molecular gas is still present. For this work, four fields (each about 30-arcmin diameter with some overlap) were observed with the XMM-Newton satellite. These fields are located inside the arc-shaped ionized nebula, next to Z CMa - Field E (east); around GU CMa - Field W (west); and between both - Field C (center) and Field S (south), as shown in Figure 1 of the reference paper. These observations were performed with the EPIC cameras (MOS1, MOS2, and PN) in full frame mode with a medium filter. The C, W, and S fields had an exposure time without background corrections of about 30 ks while field E had 40 ks. <pre> RA(J2000) | Dec(J2000) | Designation(s) 07 04 18.3 | -11 27 24.0 | CMa cluster east (Field E) 07 02 58.4 | -11 34 44.7 | CMa cluster center (Field C) 07 02 29.5 | -11 47 12.4 | CMa cluster south (Field S) 07 01 23.0 | -11 19 56.6 | CMa cluster west (Field W) </pre> This table was created by the HEASARC in October 2018 based upon the <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/A+A/609/A127">CDS Catalog J/A+A/609/A127</a> file tableb1.dat. This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/ld7c151mhz
- Title:
- 7C 151-MHz Low-Declination Survey Catalog
- Short Name:
- LD7C151MHZ
- Date:
- 07 Mar 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- The Cambridge Low Frequency Synthesis Telescope (CLFST) has been used at 151 MHz to survey a region of 1393 square degrees, in the range of RA from 9<sup>h</sup> to 16<sup>h</sup>, and of Dec from 20<sup>o</sup> to 35<sup>o</sup>, with an angular resolution of 108 x 108cosec(Dec) arcsec<sup>2</sup>. The rms noise in the maps is in general ~ 35 - 55 mJy/beam, but varies considerably and exceeds this in some areas. The authors have extracted sources with signal-to-noise ratio > 5.5, a total of 5526 sources, and this table contains the catalog of their positions and flux densities. This table was created by the HEASARC in October 2010 based on CDS table J/MNRAS/282/779 file 7c_low.dat. This is a service provided by NASA HEASARC .
184. 20cm Radio Catalog
- ID:
- ivo://nasa.heasarc/north20cm
- Title:
- 20cm Radio Catalog
- Short Name:
- North20cm
- Date:
- 07 Mar 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- The 1.4-GHz Northern Sky Catalog - Version: 4 December 1991 This is the 20-cm Northern Sky Catalog of White, R. L. and Becker, R. H. (1992, Ap.J.Supp., in press) containing 30,239 sources detected from the Condon Greenbank images taken at 1.4 GHz over the declination range of -5 degrees to 82 degrees with a flux density limit of 100 mJy. This 20 cm catalog also contains the results of a cross-correlation with catalogs at 6 and 80 cm covering the northern sky between Dec=0 degrees and 70 degrees to give the spectral indices at three frequencies for about 20,000 sources. This is a service provided by NASA HEASARC .
185. 6cm Radio Catalog
- ID:
- ivo://nasa.heasarc/north6cm
- Title:
- 6cm Radio Catalog
- Short Name:
- North-6cm
- Date:
- 07 Mar 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- The NORTH6CM database is a catalog of 53,522 4.85-GHz sources generated by Becker, R. H., White, R. L., Edwards, A. L. 1991, ApJS 75, 1. It covers between 0 degrees and 75 degrees declination using observations taken with the NRAO Greenbank 300-ft telescope by Condon, Broderick and Seielstad (1989). The flux limit of the catalog is dependent on declination and ranges from approximately 40 mJy at 0 degrees to 20 mJy at 60 degrees. The source positions given in the catalog have a 95% confidence radius of approximately 50 arcsec. Spectral indices have been calculated for 29,051 sources which have counterparts in the Texas 365-MHz Northern Sky Survey. This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/dirbepsc
- Title:
- COBE DIRBE Point Source Catalog
- Short Name:
- DIRBEPSC
- Date:
- 07 Mar 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- This table contains the Cosmic Background Explorer (COBE) Diffuse Infrared Background Experiment (DIRBE) Point Source Catalog, an all-sky catalog containing infrared photometry in 10 bands from 1.25 microns to 240 microns for 11,788 of the brightest near and mid-infrared point sources in the sky. Since DIRBE had excellent temporal coverage (100-1900 independent measurements per object during the 10 month cryogenic mission in 1989 to 1990), the catalog also contains information about variability at each wavelength, including amplitudes of variation observed during the mission. Since the DIRBE spatial resolution is relatively poor (0.7 degrees), the authors carefully investigated the question of confusion, and flagged sources with infrared-bright companions within the DIRBE beam. In addition, they filtered the DIRBE light curves for data points affected by companions outside of the main DIRBE beam but within the `sky' portion of the scan. At high Galactic latitudes (|b| > 5 degrees), the catalog contains essentially all of the unconfused sources with flux densities greater than 90, 60, 60, 50, 90, and 165 Jy at 1.25, 2.2, 3.5, 4.9, 12, and 25 microns, respectively, corresponding to magnitude limits of approximately 3.1, 2.6, 1.7, 1.3, -1.3, and -3.5. At longer wavelengths and in the Galactic Plane, the completeness is less certain because of the large DIRBE beam and possible contributions from extended emission. For each source, for comparison, the names of the sources in other catalogs, their spectral types, variability types, IRAS and 2MASS photometry, SIMBAD spectral types and published variability types, and whether or not the sources are known OH/IR stars are also included. Unlike the IRAS and 2MASS Catalogs, the DIRBE Point Source Catalog was not constructed by searching the DIRBE database with a point source template and extracting sources based on S/N and confirmation criteria. The DIRBE Catalog was constructed using a target sample list obtained from other infrared catalogs. Since DIRBE is much less sensitive per scan than IRAS or 2MASS, essentially all of the point sources with high S/N light curves in the DIRBE database are already contained in IRAS, 2MASS, and/or MSX. Thus, for simplicity, the authors used these previous catalogs to select a sample for the DIRBE Point Source Catalog. Their initial sample included a total of 21,335 sources; the final catalog contains 11,788 sources. The initial sample was selected from the IRAS Point Source Catalog (1988), the 2MASS Point Source Catalog (Cutri 2003), and/or the MSX Point Source Catalog Version 1.2 (Egan et al. 1999, A&A, 349, 236) that satisfied at least one of the following criteria: (a) 2MASS J magnitude <= 4.51 (F<sub>1.25</sub> >= 25 Jy), (b) 2MASS K magnitude <= 3.81 (F<sub>2.2</sub> >= 20 Jy), (c) IRAS or MSX F<sub>12</sub> >= 15 Jy, or (d) IRAS or MSX F<sub>25</sub> >= 27.5 Jy. The 1.25 and 2.2 micron limits are equal to the average 1-sigma sensitivity per scan in the raw DIRBE light curves of Smith et al. (2002, AJ, 123, 948), while the 12 and 25 micron limits are 0.5 times the average noise levels per scan in that study. These low limits were selected in order to avoid missing variable stars that may have been faint during the 2MASS, IRAS, or MSX mission and to improve the completeness at 3.5 and 4.9 micron. Since the filtering process improves the average per measurement uncertainty, a sensitive selection criterion is warranted to include as many sources as possible. There were 7872 sources with 2MASS J <= 4.51, 20,492 sources with 2MASS K <= 3.81, 4969 sources with IRAS F12 >= 15 Jy, 40 sources in the MSX IRAS Gaps survey with MSX F12 >= 15 Jy, 2753 sources with IRAS F25 >= 27.5 Jy, and 18 sources in the MSX IRAS Gaps survey with MSX F25 >= 27.5 Jy. Thus, the initial list is dominated by stars selected by the 2MASS criteria. These lists were merged together to make a single target list, containing 21,335 sources. To merge the 2MASS and IRAS/MSX lists, the authors used a 60 arcsecond matching radius. If more than one 2MASS source was within 60 arcseconds of the IRAS position, they assumed that the brightest K band source was the match. Note that the authors did not include sources in their input list based on their 60 and/or 100 micron IRAS flux densities, as extended emission from cirrus becomes more significant at these wavelengths. This means that the DIRBE Point Source Catalog is biased against very cold objects, such as galaxies and molecular clouds. Since the authors only used the point source catalogs of 2MASS, IRAS, and MSX for source selection, their sample is also biased against extended objects. Note also that they are only targeting sources bright enough to detect their possible variability in the DIRBE database (i.e., sources that may be detected in a single DIRBE scan at at least one DIRBE wavelength). By co-adding the full light curves, it may be possible to detect fainter objects in the DIRBE database, but without variability information and with a higher likelihood of confusion. The COBE DIRBE Point Source Catalog as presented here contains the time-averaged DIRBE flux densities F<sub>nu</sub> in the 10 DIRBE bands for all 11,785 sources in the initial list that had a flux at minimum in the weekly averaged light curve in any of the six shortest DIRBE wavelengths greater than 3 times the average noise per data point, plus three additional sources (see Section 6 of the reference paper). These flux densities were calculated after filtering the light curves. The name of the object in the catalog from which it was originally selected from is also given (IRAS/MSX and/or 2MASS). This table was created by the HEASARC in April 2012 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJS/154/673">CDS Catalog J/ApJS/154/673</a> files table1.dat, table4.dat and table8.dat, and contains the DIRBE data for 11,788 of the brightest near- and mid-infrared point sources in the sky together with supporting data from 2MASS, IRAS, MSX and other catalogs. This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/cocd
- Title:
- COCD: Catalog of Open Cluster Data
- Short Name:
- COCD
- Date:
- 07 Mar 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- The Catalog of Open Cluster Data (COCD) is a result of studies of the wide neighborhoods of 513 open clusters and 7 compact associations carried out in the high-precision homogeneous All-Sky Compiled Catalog of 2.5 Million Stars (ASCC-2.5, Kharchenko 2001, <a href="https://cdsarc.cds.unistra.fr/ftp/cats/I/280">CDS Cat. <I/280></a>). On the basis of data on about 33,000 possible members (including about 10,000 most probable ones) and homogeneous methods of cluster parameter determination, the angular sizes of cluster cores and coronae, cluster heliocentric distances, mean proper motions, mean radial velocities and ages were established and collected in the COCD. These include cluster distances for 200 clusters, average cluster radial velocities for 94 clusters, and cluster ages for 195 clusters derived for the first time. Clusters in the catalogue are sequenced in their Right Ascension J2000 order. The Open Cluster Diagrams Atlas (OCDA) presents a set of open cluster diagrams used for the determination of parameters of the 513 open clusters and 7 compact associations, and is intended to illustrate the quality of the constructed cluster membership (Kharchenko et al. 2004, CDS Cat. <J/AN/325/740>), and the accuracy of the derived cluster parameters. Every diagram presents relation between various stellar data from the ASCC-2.5 in the area of the specific cluster. There are five diagrams provided for every cluster in the Atlas: the area map, the density profile, the vector point diagram, the magnitude equation diagram and the color-magnitude diagram. The OCDA PostScript plots (one file per cluster) are available as a remote data product for entries in this table. This table was created by the HEASARC in May 2011 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/A+A/438/1163">CDS Catalog J/A+A/438/1163</a> files cocd.dat and notes.dat. This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/cocdext1
- Title:
- COCD: Catalog of Open Cluster Data First Extension
- Short Name:
- COCDEXT1
- Date:
- 07 Mar 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- This table contains a list of 130 Galactic open clusters, found in the All-Sky Compiled Catalogue of 2.5 Million Stars (ASCC-2.5) and not included in the original Catalog of Open Cluster Data (COCD): it is known as the 1st Extension of the COCD (COCD-1). For these new clusters, the authors determined a homogeneous set of astrophysical parameters such as size, membership, motion, distance and age. In their previous work (the Browse table COCD based on the <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/A+A/438/1163">CDS Cat. J/A+A/438/1163</a>), 520 already-known open clusters out of a sample of 1700 clusters from the literature were confirmed in the ASCC-2.5 using independent, objective methods. Using these same methods, the whole sky was systematically screened for new clusters. The newly detected clusters show the same distribution over the sky as the known ones. It is found that without the a priori knowledge about existing clusters the authors' search lead to clusters which are, on average, brighter, have more members and cover larger angular radii than the 520 previously-known ones. On the basis of data on about 6,200 possible members (including about 2,200 most probable ones) and homogeneous methods of cluster parameter determination, the angular sizes of cluster cores and coronae, cluster heliocentric distances, colour-excesses, mean proper motions, and ages of 130 clusters and mean radial velocities of 69 clusters were established and collected in the COCD-1. Clusters in the catalogue are numbered in order of increasing J2000.0 Right Ascension. The 1st Extension of the Open Cluster Diagrams Atlas (OCDA-1) presents a set of open cluster diagrams used for the determination of parameters of the 130 newly discovered open clusters, and is intended to illustrate the quality of the constructed cluster membership, and the accuracy of the derived cluster parameters. Every diagram presents relations between various stellar data from the all sky catalog ASCC-2.5(Kharchenko, 2001, CDS Cat. <I/280>) in the area of the specific cluster. There are five diagrams provided for every cluster in the Atlas: the area map, the density profile, the vector point diagram, the "magnitude equation" (proper motion in each coordinate versus V magnitude) diagram, and the color-magnitude diagram. The 130 OCDA-1 PostScript plots (one file per cluster) are available as a remote data product for all of the entries in this table. This table was created by the HEASARC in May 2011 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/A+A/440/403/">CDS Catalog J/A+A/440/403/</a> files cluster.dat and notes.dat. This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/cr261cxo
- Title:
- Collinder 261 Chandra X-Ray Point Source Catalog
- Short Name:
- CR261CXO
- Date:
- 07 Mar 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- This table contains some of the results from the first X-ray study of Collinder 261 (Cr 261), which at an age of 7 Gyr is one of the oldest open clusters known in the Galaxy. This observation with the Chandra X-Ray Observatory was aimed at uncovering the close interacting binaries in Cr 261, and reached a limiting X-ray luminosity of L<sub>X</sub> ~ 4 x 10<sup>29</sup> erg s<sup>-1</sup> (0.3-7 keV) for stars in the cluster. The authors detected 107 sources within the cluster half-mass radius r<sub>h</sub>, and they estimate that among the sources with L<sub>X</sub> >~ 10<sup>30</sup> erg s<sup>-1</sup>, about 26 are associated with the cluster. They identify a mix of active binaries and candidate active binaries, candidate cataclysmic variables, and stars that have "straggled" from the main locus of CR 261 in the color-magnitude diagram. Based on a deep optical source catalog of the field, the authors estimate that Cr 261 has an approximate mass of 6500 M<sub>sun</sub>, roughly the same as the old open cluster NGC 6791. The X-ray emissivity of Cr 261 is similar to that of other old open clusters, supporting the trend that they are more luminous in X-rays per unit mass than old populations of higher (globular clusters) and lower (the local neighborhood) stellar density. This implies that the dynamical destruction of binaries in the densest environments is not solely responsible for the observed differences in X-ray emissivity. Cr 261 was observed with the Advanced CCD Imaging Spectrometer (ACIS) on board Chandra starting 2009 November 9 14:50 UTC, for a total exposure time of 53.8 ks (ObsID 11308). The observation was made in Very Faint, Timed exposure mode, with a single frame exposure time of 3.2 s. Kharchenko et al. (2013, A&A, 558, A53) estimate that the radius of Cr 261 is ~ 14.1 arcminutes. This is considerably larger than a single ACIS chip (8 4 x 8 4 arcminute<sup>2</sup>) and therefore the authors placed the center of the cluster (J2000.0 RA = 12<sup>h</sup> 38<sup>m</sup> 06.0<sup>s</sup>, Dec = -68<sup>o</sup> 22' 01" according to Kharchenko et al. 2013) close to the I3 aimpoint so that a larger contiguous part of the cluster could be imaged (see Figure 1 in the reference paper). The CCDs used were I0, I1, I2, and I3 from the ACIS-I array, and S2 and S3 from the ACIS-S array. The authors limited the X-ray analysis to the data from chips I0, I1, I2, and I3. The S2 and S3 chips lie far from the I3 aimpoint, giving rise to large positional errors on any sources detected on them. Such large errors make it hard to identify optical counterparts, and thus to classify the sources. Source detection was done in soft (0.3-2.0 keV), hard (2-7 keV) and broad (0.3-7 keV) energy bands. The CIAO source detection routine wavdetect was run for eight wavelet scales ranging from 1.0 to 11.3 pixels. The wavdetect detection threshold (sigthresh) was set at 10<sup>-7</sup>. The corresponding expected number of spurious detections per wavelet scale is 0.42 for all four ACIS chips combined, or 3.35 in total for all wavelet scales. The authors ran wavdetect for the three different energy bands and then cross-correlated the resulting source lists to obtain a master X-ray source list. They detected 113 distinct X-ray sources. To check if any real sources were missed, they ran wavdetect again with a detection threshold of 10<sup>-6</sup>, which increased the expected total number of spurious detections to 33.5, and found a total of 151 distinct X-ray sources with more than two counts (0.3-7 keV) in this case. The positions of 7 of the extra 38 sources were found to match those of short-period binaries discovered by Mazur et al. (1995, MNRAS, 273, 59; see Section 3.4). Close, interacting binaries are plausible real X-ray sources, and indeed the expected number of chance alignments between the Chandra detections and the binaries in the Mazur catalog is very low, as discussed in Section 3.5 of the reference paper. It is therefore likely that at least these seven additional sources are real, but given the ~ 34 spurious detections that are expected, the authors do not believe that there are many more real sources among the extra detections. They flagged the sources that are only found for sigthresh = 10<sup>-6</sup>, but kept them in the master source list. This HEASARC table contains the list of 151 X-ray sources found by wavdetect using a detection threshold of 10<sup>-6</sup> from Table 1 of the reference paper. Information about the 135 optical counterparts to these X-ray sources is available in the HEASARC table CR261OID (based on Table 2 of the reference paper) to which this current table has links. This table was created by the HEASARC in June 2017 based upon the machine-readable version of Table 1 from the reference paper, the catalog of Chandra sources in Cr 261, that was obtained from the ApJ web site. This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/cr261oid
- Title:
- Collinder 261 Chandra X-Ray Source Optical Counterparts Catalog
- Short Name:
- CR261OID
- Date:
- 07 Mar 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- This table contains some of the results from the first X-ray study of Collinder 261 (Cr 261), which at an age of 7 Gyr is one of the oldest open clusters known in the Galaxy. This observation with the Chandra X-Ray Observatory was aimed at uncovering the close interacting binaries in Cr 261, and reached a limiting X-ray luminosity of L<sub>X</sub> ~ 4 x 10<sup>29</sup> erg s<sup>-1</sup> (0.3-7 keV) for stars in the cluster. The authors detected 107 sources within the cluster half-mass radius r<sub>h</sub>, and they estimate that among the sources with L<sub>X</sub> >~ 10<sup>30</sup> erg s<sup>-1</sup>, about 26 are associated with the cluster. They identify a mix of active binaries and candidate active binaries, candidate cataclysmic variables, and stars that have "straggled" from the main locus of CR 261 in the color-magnitude diagram. Based on a deep optical source catalog of the field, the authors estimate that Cr 261 has an approximate mass of 6500 M<sub>sun</sub>, roughly the same as the old open cluster NGC 6791. The X-ray emissivity of Cr 261 is similar to that of other old open clusters, supporting the trend that they are more luminous in X-rays per unit mass than old populations of higher (globular clusters) and lower (the local neighborhood) stellar density. This implies that the dynamical destruction of binaries in the densest environments is not solely responsible for the observed differences in X-ray emissivity. Cr 261 was observed with the Advanced CCD Imaging Spectrometer (ACIS) on board Chandra starting 2009 November 9 14:50 UTC, for a total exposure time of 53.8 ks (ObsID 11308). The observation was made in Very Faint, Timed exposure mode, with a single frame exposure time of 3.2 s. Kharchenko et al. (2013, A&A, 558, A53) estimate that the radius of Cr 261 is ~ 14.1 arcminutes. This is considerably larger than a single ACIS chip (8 4 x 8 4 arcminute<sup>2</sup>) and therefore the authors placed the center of the cluster (J2000.0 RA = 12<sup>h</sup> 38<sup>m</sup> 06.0<sup>s</sup>, Dec = -68<sup>o</sup> 22' 01" according to Kharchenko et al. 2013) close to the I3 aimpoint so that a larger contiguous part of the cluster could be imaged (see Figure 1 in the reference paper). The CCDs used were I0, I1, I2, and I3 from the ACIS-I array, and S2 and S3 from the ACIS-S array. The authors limited the X-ray analysis to the data from chips I0, I1, I2, and I3. The S2 and S3 chips lie far from the I3 aimpoint, giving rise to large positional errors on any sources detected on them. Such large errors make it hard to identify optical counterparts, and thus to classify the sources. The authors retrieved optical images of Cr 261 in the B and V bands from the ESO public archive. These data were taken as part of the ESO Imaging Survey (EIS; program ID 164.O-0561). The observations of Cr 261 were made using the Wide Field Imager (WFI), mounted on the 2.2 m MPG/ESO telescope at La Silla, Chile. After correcting the X-ray source positions for the (almost negligible) boresight correction (0.06 =/- 0.07 arcseconds in RA and 0.09 +/- 0.08 arcseconds in Dec), the authors matched their X-ray source list with the entire optical source list, using 95% match radii. For 89 unique X-ray sources, they found 124 optical matches; of the latter, 104 are present in both the V and B images, while for 20 there is only a V or B detection. The authors also inspected the area around each X-ray source in the WFI images by eye, and discovered that five more X-ray sources have candidate optical counterparts that are saturated and therefore missing from their optical catalog. Finally, they added to the list of candidate counterparts six optical sources that lay just outside the 95% match radius, but inside the 3-sigma radius. In total, 98 of the 151 unique X-ray sources were thus matched to one or more optical sources. This HEASARC table contains the list of the 135 optical counterparts to 98 of the 151 X-ray sources from Table 2 of the reference paper. Information about the 151 X-ray sources is available in the HEASARC table CR261CXO (based on Table 1 of the reference paper) to which this current table has links. This table was created by the HEASARC in June 2017 primarily based upon the machine-readable version of Table 2 from the reference paper, the catalog of optical counterparts to Chandra sources in Cr 261, that was obtained from the ApJ web site. The information on the X-ray source positions was taken from the machine-readable version of Table 1 from the reference paper that was also obtained from the ApJ web site. This is a service provided by NASA HEASARC .
