J/A+A/704/A326ivo://CDS.VizieR/J/A+A/704/A326CDSCulpan R.Dorsch M.Pelisoli I.Schaffenroth V.Geier S.Heber U.,Kubatova B.Dawson H.Pritzkuleit M.Bhat A.Cabezas M.Maryeva O.,Kubat J.Kurpas M.Vostretcova E.Vos J.Mattig F.Hainich R.2026-03-02T06:25:50Z2025-12-19T09:16:42ZCDS support team

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

cds-question@unistra.frmilky-way-galaxymultiple-starsradial-velocityvisible-astronomyBlue horizontal-branch (BHB) stars are evolved low-mass objects that have completed their core hydrogen burning main-sequence (MS) stage and have lost significant mass during the red giant phase culminating in the helium flash. They are, hence, very old objects that can be used as markers in studying galactic structure and formation history. Their formation requires significant mass loss during the red-giant phase, but the role of stellar interactions in this process remains unclear. Knowing the fraction of BHBs that exist in binary or higher multiple systems where mass transfer may occur will enhance our understanding of their stellar evolution. We determine the fraction of BHBs in binary systems over a wide range of separations in the inner Galactic Halo to constrain mass-loss mechanisms and evolutionary pathways. Using a catalogue of 22336 BHB candidates from Gaia DR3, we analysed radial velocity variations found in spectra (263 spectra of 89 targets) acquired using the Ondvrejov Echelle spectrograph attached to the Perek 2m telescope at the Astronomical Institute of the Czech Academy of Sciences together with archival spectra from the Ultraviolet and Visual Echelle Spectrograph (UVES) and Fiber-fed Extended Range Optical Spectrograph (FEROS). We searched for wide common proper motion pairs, binary candidates with enhanced astrometric noise, and binaries with astrometric orbital solutions in Gaia DR3. Archival light curves from Gaia DR3 and the Zwicky Transient Facility (ZTF) were checked for binary induced variations. Synthetic SEDs and binary detection probabilities were modelled to account for selection effects.} We find a binary fraction of <2.2% (1 sigma confidence), far lower than the rates for their main-sequence (MS) and red-giant branch (RGB) progenitors 30 to 50%. This suggests that BHBs are either not descendants of binary systems, or that existing companions do not survive the BHB formation process. The negligible binary fraction implies single-star evolution could dominate BHB formation, contrasting with EHB stars where binarity is critical. Our results challenge models of mass loss on the RGB and highlight the need for alternative mechanisms.2025A&A...704A.326Chttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/704/A326CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/704/A326https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/704/A326http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/704/A326https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/704/A326https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/704/A326http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/704/A326GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/704/A326/tablea1 (Spectral analysis results, per-spectrum RVs)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/704/A326/tablea1?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/704/A326/tablea1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/704/A326/tablea1?GETtext/xml+votable180.050000true14.1624581-9.42847310.0055555555555555566/5 1018 1388 2248 2962 4322 4373 4971 5145 5156 5181 5287 5837 6100 6167 6170 6451 6622 7436 7532 8591 9233 10282 10669 10811 10904 10962 11235 11566 12446 12468 13038-13039 13098 13335 13359 13651 14874 14944 15021 15097 15235 15331 15341 17239 17580 17955 18031 18627 18963 19123 19160 19566 19848 19940 20431 21928 22634 23618 24002 24351 25590 25897 25964 26993 27374 27398 27464 27512 30157 30177 30663 31195 31356 31462 31583 32333 36696 36770 44992https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/704/A326?format=asciiOpticaldefaultJ/A+A/704/A326/tablea1Spectral analysis results, per-spectrum RVsrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNameSimbad IDmeta.id;meta.maincharTypeStar type (BHB or MS)src.classcharNOESNumber of OES spectra acquiredmeta.numberintNUVES/FEROSNumber of UVES and FEROS spectra usedmeta.numberintSimbadSimbad column added by the CDSmeta.ref.urlcharBJDBarycentric Julian Date (1)dtime.epochdoubleRV? Radial velocity from the individual spectrumkm/sphys.veloc;pos.heliocentricfloatnullablee_RV? Standard error on the radial velocity from the individual spectrumkm/sstat.errorfloatnullableVrotmeanWeighted mean rotational velocity plus minus one standard errorkm/sphys.veloc.rotatfloate_VrotmeanStandard error on the rotational velocity from the individual spectrumkm/sstat.errorfloatRVmeanWeighted mean rotational velocity plus minus one standard errorkm/sstat.error;phys.veloc.rotat;stat.fit.omcfloate_RVmeanStandard error on the rotational velocity from the individual spectrumkm/sstat.errorfloat_RARight Ascension (J2000) from SIMBAD (not part of the original data)degpos.eq.ra;meta.main_DEDeclination (J2000) from SIMBAD (not part of the original data)degpos.eq.dec;meta.main