W40SFRCXO ivo://nasa.heasarc/w40sfrcxo NASA/GSFC HEASARC Kuhn et al. 2026-04-03 NASA/GSFC HEASARC help desk heasarc-vo at athena.gsfc.nasa.gov Survey Source The young stellar cluster illuminating the W40 H II region, one of the nearest massive star-forming regions (SFRs), has been observed with the ACIS detector on board the Chandra X-ray Observatory. Due to its high obscuration, this is a poorly studied stellar cluster with only a handful of bright stars visible in the optical band, including three OB stars identified as primary excitation sources. The authors detect 225 X-ray sources, of which 85% are confidently identified as young stellar members of the region. Two potential distances of the cluster, 260 pc and 600 pc, are used in the paper. Supposing the X-ray luminosity function of SFRs to be universal, it supports a 600 pc distance as a lower limit for W40 and a total population of at least 600 stars down to 0.1 M<sub>sun</sub> under the assumption of a coeval population with a uniform obscuration. In fact, there is strong spatial variation in K<sub>s</sub>-band-excess disk fraction and non-uniform obscuration due to a dust lane that is identified in absorption in optical, infrared, and X-ray. The dust lane is likely part of a ring of material which includes the molecular core within W40. In contrast to the likely ongoing star formation in the dust lane, the molecular core is inactive. The star cluster has a spherical morphology, an isothermal sphere density profile, and mass segregation down to 1.5 M<sub>sun</sub>. However, other cluster properties, including a <= 1 Myr age estimate and ongoing star formation, indicate that the cluster is not dynamically relaxed. X-ray diffuse emission and a powerful flare from a young stellar object are also reported in the reference paper. This table was created by the HEASARC in March 2011 based on electronic versions of Tables, 1, 2 and 4 of the reference paper which were obtained from the ApJ web site. This is a service provided by NASA HEASARC . 2010ApJ...725.2485K https://heasarc.gsfc.nasa.gov/W3Browse/all/w40sfrcxo.html Catalog Research served-by HEASARC TAP https://heasarc.gsfc.nasa.gov/xamin/vo/cone?showoffsets&table=w40sfrcxo& GET text/xml 180 99999 true 277.841949 -2.247033 0.0166666666666667 https://heasarc.gsfc.nasa.gov/xamin/vo/tap https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/getvotable.pl?name=w40sfrcxo GET text/xml https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/w3query.pl?tablehead=name=heasarc_w40sfrcxo&Action=More+Options&Action=Parameter+Search&ConeAdd=1 CHANDRA 0.0166666666666667 X-ray public w40sfrcxo W 40 Star-Forming Region Chandra X-Ray Point Source Catalog log_lx_2_error Error in Log of Intrinsic Full-Band Luminosity log(erg/s) stat.error;phys.luminosity;em.X-ray double nullable "__row" System index column char nullable hmag 2MASS H-Band Magnitude mag phot.mag;em.IR.H double nullable log_nh_1 Log of Column Density Inferred log(cm^-2) phys.columnDensity double nullable name IAU Designation meta.id;meta.main char nullable ks_mag_error Error in K_S-Band Magnitude mag stat.error;phot.mag;em.IR.K double nullable alt_name Alternative Catalog-Based Source Designation meta.id char nullable log_hb_lx_2_error Error in Log of Intrinsic Hard-Band Luminosity log(erg/s) stat.error;phys.luminosity;em.X-ray.medium double nullable ukirt_flag UKIRT Flag meta.code short nullable twomass_flags 2MASS Photometry Quality and Confusion Flag meta.code char nullable exposure Effective Exposure (s) s time.duration;obs.exposure double nullable log_lx_obs Log of Apparent Full-Band Luminosity log(erg/s) phys.luminosity;em.X-ray double nullable source_anomaly_flag Flag Indicates Source Anomaly meta.code short nullable log_hb_lx_1 Log of Intrinsic Hard-Band Luminosity log(erg/s) phys.luminosity;em.X-ray.medium double nullable jmag 2MASS J-Band Magnitude mag phot.mag;em.IR.J double nullable off_axis Off-Axis Angle (arcmin) arcmin instr.offset double nullable dec Declination degree pos.eq.dec;meta.main double nullable source_number Sequential Identification Number for Each Source in Catalog meta.id;src short nullable source_variable_flag Variability Characterization meta.code;src.var short nullable median_energy Median Energy of Net Counts in Full Band (keV) keV phys.energy double nullable hmag_error Error in 2MASS H-Band Magnitude mag stat.error;phot.mag;em.IR.H double nullable av Visual Absorption from J vs. J-H Diagram (mag) mag phys.absorption;em.opt.V double nullable hb_counts Extracted Net Counts in the Hard Energy Band ct phot;em.X-ray.medium double nullable "__z_ra_dec" System unit vector column double nullable bii Galactic Latitude degree pos.galactic.lat double nullable lii Galactic Longitude degree pos.galactic.lon double nullable counts_error Average 1-Sigma Uncertainty in Net Counts ct stat.error;phot;em.X-ray double nullable psf_fraction PSF Fraction Enclosed within Extraction Region instr.det.psf double nullable "__x_ra_dec" System unit vector column double nullable counts Extracted Net Counts in Full Band ct phot;em.X-ray double nullable "__y_ra_dec" System unit vector column double nullable log_nh_2 Column Density Obtained log(cm^-2) phys.columnDensity double nullable ks_mag 2MASS K_S-Band Magnitude mag phot.mag;em.IR.K double nullable log_nh_2_error Error in Log of Column Density Obtained log(cm^-2) stat.error;phys.columnDensity double nullable error_radius Positional Error (arcsec) arcsec stat.error;pos double nullable stellar_mass_error Error in Mass from J vs. J-H Diagram Solar_Mass stat.error;phys.mass double nullable log_lx_1 Log of Intrinsic Full-Band Luminosity log(erg/s) phys.luminosity;em.X-ray double nullable apec_kt Plasma Temperature Inferred (keV) keV phys.temperature double nullable significance Source Significance stat.likelihood;em.X-ray double nullable stellar_mass Stellar Mass from J vs. J-H Diagram (Solar Masses) Solar_Mass phys.mass double nullable twomass_name 2MASS Source Designation meta.id.cross char nullable log_hb_lx_2 Intrinsic Hard-Band Luminosity log(erg/s) phys.luminosity;em.X-ray.medium double nullable jmag_error Error in 2MASS J-Band Magnitude mag stat.error;phot.mag;em.IR.J double nullable log_hb_lx_obs Log of Apparent Hard-Band Luminosity log(erg/s) phys.luminosity;em.X-ray.medium double nullable bck_counts Background Counts in the Extraction Region ct phot;instr.background;em.X-ray double nullable ra Right Ascension degree pos.eq.ra;meta.main double nullable membership_class Membership Class meta.code.class char nullable cxo_2mass_offset Chandra-2MASS Positional Offset (arcsec) arcsec pos.angDistance;em.X-ray;em.IR double nullable vla_id VLA Source Identification meta.id.cross short nullable log_lx_2 Intrinsic Full-Band Luminosity log(erg/s) phys.luminosity;em.X-ray double nullable