J/A+A/710/A243ivo://CDS.VizieR/J/A+A/710/A243CDSBao T.Ponti G.Xu X.-J.Morris M.R.Levin B.Mori K.Mandel S.,Locatelli N.Munoz-Darias T.Casares J.Torres M.A.P.2026-06-17T08:23:44Z2026-06-17T09:23:05ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frgalaxy-planesmilky-way-galaxyx-ray-sourcesx-ray-binary-starsThe origin of the highly ionized iron emission (FeXXV at 6.7keV) characterizing the Galactic ridge X-ray emission (GRXE) remains a fundamental puzzle in high-energy astrophysics. Although the GRXE continuum is largely resolved into discrete populations of cataclysmic variables and coronally active stars, these sources exhibit Fe XXV equivalent widths significantly lower than that of the total GRXE, leaving the intense iron line emission unexplained. In this work, we cross-correlated the XMM-Newton survey of the inner Galactic disk with Gaia DR3 astrometry to identify and characterize hard X-ray sources (>2keV) with reliable stellar counterparts. We selected 107 X-ray sources located within the red giant branch of the color-magnitude diagram, many of which are verified long-period variables. These sources exhibit high X-ray luminosities (Lx~10^31^-10^33^erg/s), significantly exceeding the typical coronal saturation levels of single giants. Their X-ray spectra are notably harder than those of quiescent stellar coronae, with plasma temperatures reaching up to kT ~6keV and a prominent emission feature at ~6.7keV. The combination of high Lx, hard spectra, and intense FeXXV emission identifies this population as accretion-powered binaries associated with late-type giants. Our analysis demonstrates that this population contributes ~20% of the total GRXE continuum and ~40% of its iron line emission, providing a key component to resolving the Galactic X-ray background puzzle.2026A&A...710A.243Bhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/710/A243CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/A+A/682/A34 : SRG/eROSITA all-sky survey catalogs (eRASS1) (Merloni+, 2024)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/710/A243https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/710/A243http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/710/A243https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/710/A243https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/710/A243http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/710/A243GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/710/A243/tablea1 (Source properties for 107 SySt candidates)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/710/A243/tablea1?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/710/A243/tablea1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/710/A243/tablea1?GETtext/xml+votable180.050000true265.1487-28.09490.0055555555555555565/7203 7206-7207 6/28803 28806-28807 28809 28811 28817-28819 28822-28823 28833 28837 28848-28849 28852 28874-28875 28878 28890 28897 28900 28902-28903 28912-28913 28915 28921 42450-42451 42454-42457 42460-424621.9867573869263685e-19 3.916500758235022e-19https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/710/A243?format=asciiX-raydefaultJ/A+A/710/A243/tablea1Source properties for 107 SySt candidatesrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintID[1/107] Source indexmeta.id;meta.mainintRAJ2000Right Ascension (J2000) from X-raydegpos.eq.ra;meta.mainDEJ2000Declination (J2000) from X-raydegpos.eq.dec;meta.mainSepSeparation between X-ray and Gaia positionarcsecpos.angDistancefloatGmagGaia DR3 G-band magnitude (1)magphot.mag;em.optfloatBP-RPGaia DR3 BP-RP color (1)magphot.color;em.opt.B;em.opt.RfloatDistGeometric distance from Gaia DR3kpcpos.angDistancefloatdmaxXMax detectable distance (X-ray sensitivity)kpcpos.angDistancefloatdmaxGMax detectable distance (Gaia sensitivity)kpcpos.angDistancefloatlogLXLog of X-ray luminosity (0.2-12keV)log(1e-07W)phys.luminosity;em.X-rayfloatpanyProbability that any association is correctstat.fit.goodnessfloatpiRelative probability of the matchstat.fit.goodnessfloatf_(r-Ha)v[*] Note '*' if (r-H{alpha})v>0.8(H{alpha} excess)meta.codechar(r-Ha)vVPHAS+ (r-Halpha) colormagphot.color;em.opt.R;em.line.Halphafloat(u-i)v? VPHAS+ (u-i) colormagphot.color;em.opt;em.optfloatnullable