Cygnus OB2 Association Chandra X-Ray Point Source Catalog

Cygnus OB2 Association Chandra X-Ray Point Source Catalog CYGOB2CXO ivo://nasa.heasarc/cygob2cxo NASA/GSFC HEASARC Albacete Colombo et al. 2026-10-09 NASA/GSFC HEASARC help desk heasarc-vo at athena.gsfc.nasa.gov Survey Source The aim of this study is to identify the so far unknown low mass stellar population of the ~2 Myr old Cygnus OB2 star forming region, and to investigate the X-ray and near-IR stellar properties of its members. The authors analyzed a 97.7ks Chandra ACIS-I observation pointed at the core of the Cygnus OB2 region. Sources were detected using the PWDETECT code and were positionally correlated with optical and near-IR catalogs from the literature. Source events were extracted with the ACIS EXTRACT package. X-ray variability was characterized through the Kolmogorov-Smirnov test and spectra were fitted using absorbed APEC thermal plasma models. The authors detected 1003 X-ray sources. Of these, 775 have near-IR counterparts and are expected to be almost all associated with Cygnus OB2 members. From near-IR color-color and color-magnitude diagrams, they estimate a typical absorption toward Cygnus OB2 of AV ~ 7.0 mag. Although the region is young, very few stars (~ 4.4%) show disk-induced excesses in the near-IR. X-ray variability is detected in ~ 13% of the sources, but this fraction increases, up to 50%, with increasing source statistics. Flares account for at least 60% of the variability. Despite being generally bright, all but 2 of the 26 detected O-type and early B-type stars are not significantly variable. Typical X-ray spectral parameters are log NH ~ 22.25 (cm-2) and kT ~ 1.35 keV with 1-sigma dispersion of 0.2 dex and 0.4 keV, respectively. Variable and flaring sources have harder spectra with median kT = 3.3 and 3.8 keV, respectively. OB stars are typically softer (kT ~ 0.75 keV). X-ray luminosities range between 1030 and 1031 erg s-1 for intermediate-mass and low-mass stars, and between 2.5 x 1030 and 6.3 x 1033 erg s-1 for OB stars. Cygnus OB2 was observed with the ACIS detector on board the Chandra X-ray Observatory (CXO) on 2004 January 16 (Obs.Id. 4511; PI: E. Flaccomio). The ACIS-I 17' x 17' field of view is covered by 4 chips each with 1024 x 1024 pixels (scale 0.49 arcseconds per pixel). The observation was pointed towards J2000.0 (RA,Dec) = (20 33 12.2, +41 15 00.7). An SNR threshold of 4.5 sigma was chosen which resulted in an initial source list of 1054 sources, 51 of which were subsequently rejected as either instrumental artifacts or multiple detections of the same source with different spatial scales. An additional 10 of the 1003 X-ray sources in the present table are likely spurious statistical fluctuations rather than real sources. This table was created by the HEASARC in March 2008 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/A+A/464/211">CDS catalog J/A+A/464/211</a> files table1.dat, table2.dat and table3.dat. This is a service provided by NASA HEASARC . 2007A&A...464..211A https://heasarc.gsfc.nasa.gov/W3Browse/all/cygob2cxo.html Catalog Research served-by HEASARC TAP https://heasarc.gsfc.nasa.gov/xamin/vo/cone?showoffsets&table=cygob2cxo& GET text/xml 180 99999 true 308.38670833 41.0888 0.0166666666666667 https://heasarc.gsfc.nasa.gov/xamin/vo/tap https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/getvotable.pl?name=cygob2cxo GET text/xml https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/w3query.pl?tablehead=name=heasarc_cygob2cxo&Action=More+Options&Action=Parameter+Search&ConeAdd=1 CHANDRA 0.0166666666666667 X-ray public cygob2cxo Cygnus OB2 Association Chandra X-Ray Point Source Catalog name Source Designation (CXOCyg JHHMMSS.ss+DDMMSS.s) 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 off_axis Off-Axis Angle (arcmin) arcmin instr.offset double nullable error_radius RMS Uncertainty on Position (arcsec) arcsec stat.error;pos double nullable count_rate Total (0.5-8.0keV) Band Count Rate (ct/s) ct/s phot.count;em.X-ray double nullable hb_count_rate Hard (2.8-8.0keV) Band Count Rate (ct/s) ct/s phot.count;em.X-ray.medium double 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 fit_log_nh_error RMS Uncertainty on log(NH) cm^-2 stat.error;phys.columnDensity;stat.fit.param double nullable snr Significance of Detection stat.snr double nullable source_number Sequential Identification Number for Each X-Ray Source in Catalog meta.id;src short nullable jmag_flag J Band Photometric Quality Flag meta.code;phot.mag;em.IR.J char nullable hmag_error RMS Uncertainty on H Magnitude mag stat.error;phot.mag;em.IR.H double nullable fit_reduced_chi2 Reduced Chi^2 Value for the Spectral Fit stat.fit.chi2 double nullable psf_fraction PSF Fraction of Source Events within the Extraction Area, Assuming E=1.49keV instr.det.psf double nullable jmag_error RMS Uncertainty on J Magnitude mag stat.error;phot.mag;em.IR.J double nullable ks_mag_flag Ks Band Photometric Quality Flag meta.code;phot.mag;em.IR.K char nullable median_energy Median Photon Energy (keV) keV phys.energy double nullable bii Galactic Latitude degree pos.galactic.lat double nullable fit_apec_kt_error RMS Uncertainty on Plasma Temperature (keV) keV stat.error;phys.temperature;stat.fit.param double nullable exposure Exposure Time (s) s time.duration;obs.exposure double nullable flare_flag Flag [F] Indicates Flare-Like Sources meta.code char nullable extraction_area Source Extraction Area (pixels) pixel instr.det.psf int nullable vmag_extinction_flag Flag [U] Indicates Stars with Unconstrained AV meta.code;phys.absorption;em.opt.V char nullable log_prob_constant Logarithm of the KS-Test Significance, log(P_KS_) stat.probability double nullable fit_apec_kt Plasma Temperature (keV) keV phys.temperature;stat.fit.param double nullable twomass_name 2MASS Source Designation (2MASS JHHMMSSss+DDMMSSs) meta.id.cross char nullable ks_mag_error RMS Uncertainty on Ks Magnitude mag stat.error;phot.mag;em.IR.K double nullable hmag 2MASS H Magnitude mag phot.mag;em.IR.H double nullable mb_count_rate Medium (1.7-2.8keV) Band Count Rate (ct/s) ct/s phot.count;em.X-ray.medium double nullable fit_log_nh Logarithm of Best Fit Hydrogen Column Density (in cm^-2) log(H-atoms/cm^2) phys.columnDensity;stat.fit.param double nullable cxo_2mass_offset Offset between Chandra and 2MASS Sources (arcsec) arcsec pos.angDistance;em.X-ray;em.IR double nullable sb_count_rate Soft (0.5-1.7keV) Band Count Rate (ct/s) ct/s phot.count;em.X-ray.soft double nullable counts Background-Corrected Extracted Source Counts in the 0.5-8.0keV Band (ct/photon) ct phot;em.X-ray int nullable hmag_flag H Band Photometric Quality Flag meta.code;phot.mag;em.IR.H char nullable fit_dof Degree of Freedom for the Spectral Fit stat.fit.dof short nullable vmag_extinction Absorption in V Band mag phys.absorption;em.opt.V double nullable fit_log_em Logarithm of Emission Measure (in cm^-3) cm^-3 phys.emissMeasure;stat.fit.param double nullable alt_name Alternative Source Designation Based on Catalog Source Number meta.id char nullable ks_mag 2MASS Ks Magnitude mag phot.mag;em.IR.K double nullable jmag 2MASS J Magnitude mag phot.mag;em.IR.J double nullable lii Galactic Longitude degree pos.galactic.lon double nullable