NGC6231CXO ivo://nasa.heasarc/ngc6231cxo NASA/GSFC HEASARC Damiani et al. 2026-10-09 NASA/GSFC HEASARC help desk heasarc-vo at athena.gsfc.nasa.gov Survey Source 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 . 2016A&A...596A..82D https://heasarc.gsfc.nasa.gov/W3Browse/all/ngc6231cxo.html Catalog Research served-by HEASARC TAP https://heasarc.gsfc.nasa.gov/xamin/vo/cone?showoffsets&table=ngc6231cxo& GET text/xml 180 99999 true 253.48715 -42.0052 0.0166666666666667 https://heasarc.gsfc.nasa.gov/xamin/vo/tap https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/getvotable.pl?name=ngc6231cxo GET text/xml https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/w3query.pl?tablehead=name=heasarc_ngc6231cxo&Action=More+Options&Action=Parameter+Search&ConeAdd=1 CHANDRA 0.0166666666666667 X-ray public ngc6231cxo NGC 6231 Chandra X-Ray Point Source Catalog name IAU X-Ray Source Designation (CXOU JHHMMSS.s+DDMMSS) meta.id;meta.main char nullable ra Right Ascension degree pos.eq.ra;meta.main double nullable dec Declination degree pos.eq.dec;meta.main double nullable error_radius Position Error arcsec stat.error;pos double nullable count_rate X-Ray Count Rate ct/s phot.count;em.X-ray double nullable count_rate_error Error in X-Ray Count Rate ct/s stat.error;phot.count;em.X-ray double nullable log_lx Logarithm of the X-Ray Luminosity log(erg/s) phys.luminosity;em.X-ray double nullable twomass_name 2MASS Identifier (2MASS JHHMMSSss+DDMMSSs) meta.id.cross char nullable jmag 2MASS J Magnitude (Cutri et al., 2003, Cat. II/246) mag phot.mag;em.IR.J double nullable vmag SSB V Magnitude mag phot.mag;em.opt.V double nullable hardness_ratio_2 Hardness Ratio 2: Bands [1.2-2.2], [2.2-8.0]keV phot.flux;arith.ratio;em.X-ray double nullable log_lx_quiescent Logarithm of the Quiescent X-Ray Luminosity log(erg/s) phys.luminosity;em.X-ray double nullable lii Galactic Longitude degree pos.galactic.lon double nullable vphas_name VPHAS+ Identifier (VPHAS JHHMMSS.s+DDMMSS.s) meta.id.cross char nullable imag VPHAS+ i Magnitude mag phot.mag;em.opt.I double nullable sbb_halpha_index SSB H-Alpha Index mag meta.code;em.line.Halpha double nullable log_lbol Logarithm of the Bolometric Luminosity log(Solar_Luminosity) phys.luminosity double nullable vi_color SSB V-I Color mag phot.color;em.opt.V;em.opt.I double nullable hardness_ratio_1 Hardness Ratio 1: Bands [0.3-1.2], [1.2-2.2]keV phot.flux;arith.ratio;em.X-ray double nullable rmag VPHAS+ r Magnitude mag phot.mag;em.opt.R double nullable sbb_source_number Identifier in SBB (Sung et al., 2013, Cat. J/AJ/145/37) meta.id.cross int nullable vphas_halpha_mag VPHAS+ H-Alpha Magnitude mag phot.mag;em.line.Halpha double nullable stellar_group Group from Color-Magnitude Diagram meta.code short nullable mass Derived Star Mass Solar_Mass phys.mass double nullable counts Total X-Ray Detected Counts ct phot;em.X-ray double nullable ks_prob_not_constant Probability of Not Being Constant percent stat.probability double nullable bii Galactic Latitude degree pos.galactic.lat double nullable halpha_excess_flag Flag [Y] Indicates H-Alpha Excess meta.note;phot.color.excess;em.line.Halpha char nullable source_number Sequential Identification Number for Each Source in the Catalog meta.id;src short nullable hmag 2MASS H Magnitude mag phot.mag;em.IR.H double nullable kmag 2MASS K Magnitude mag phot.mag;em.IR.K double nullable ir_excess_flag Flag [Y] Indicates IR Excess meta.note;phot.color.excess;em.IR char nullable "__x_ra_dec" System unit vector column double nullable "__y_ra_dec" System unit vector column double nullable "__z_ra_dec" System unit vector column double nullable "__row" System index column char nullable