J/A+A/693/L11ivo://CDS.VizieR/J/A+A/693/L11doi:10.26093/cds/vizier.36939011CDSAros-Bunster C.Schreiber M.R.Toloza O.Hernandez M.S.Belloni D.,El-Badry K.Vanderbosch Z.Lagos-Vilches F.Gansicke T.B.Koester D.2025-03-03T20:01:55Z2025-01-10T09:22:40ZCDS support team

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

cds-question@unistra.frmultiple-starswhite-dwarf-starsspectroscopyvisible-astronomyThe white dwarf (WD) binary SDSS J1257+5428 comprises an extremely low-mass WD with a mass of 0.1-0.24M_{sun}_ and a more massive companion of ~1M_{sun}_ that is more than 0.6Gyr younger. The origin of this system has been termed paradoxical because current theories for the formation of WD binaries are unable to explain its existence. Any additional observational constraint on the formation of SDSS J1257+5428 might provide important insights into double WD formation in general. We present the discovery of a tertiary WD, which makes SDSS J1257+5428 the third known triple WD. We used KECK/LRIS spectroscopy, Gaia and SDSS photometry, and WD atmosphere models to characterize the distant tertiary (projected separation ~8000au). We find the tertiary WD to be cool (6200-6400K) and massive (log(g)=8.88-8.97), which translates to a cooling age of >~4Gyr. This cooling age represents a lower limit on the total age of the triple system. While at first glance it seems likely that the inner binary formed through a stable mass transfer phase followed by common envelope evolution, reproducing the stellar mass and period required for the progenitor of the ~1M_{sun}_WD in the inner binary through stable mass transfer seems impossible. We therefore speculate that the system might be the descendant of a cataclysmic variable with an evolved donor.2025A&A...693L..11Ahttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/693/L11CatalogResearchIsServedByTAP VizieR generic servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/693/L11https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/693/L11http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/693/L11https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/693/L11https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/693/L11http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/693/L11GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapOpticaldefaultJ/A+A/693/L11/spectrumCalibrated spectrum of the tertiary WDrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintlambdaWavelength in Angstroems0.1nmem.wldoubleFlux? Calibrated flux density10mW.m**-2.nm**-1phot.flux.densitydoublenullableSkyFluxSky flux density10mW.m**-2.nm**-1phot.flux.density;obs.fielddoublee_FluxUncertainty in the flux density10mW.m**-2.nm**-1stat.error;phot.fluxdoubleXposX position on the CCDpixpos.cartesian.x;instr.detintYposY position on the CCDpixpos.cartesian.y;instr.detfloatResponseResponse functionstat.fit.paramdoubleFlagData flagmeta.code.errorfloat