J/A+A/712/A116ivo://CDS.VizieR/J/A+A/712/A116CDSHernandez-Diaz S.Stelzer B.Munoz-Giraldo D.2026-08-10T08:51:18Z2026-08-10T09:45:01ZCDS support team

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

cds-question@unistra.frcataclysmic-variable-starsphotometryvisible-astronomyaccretionspectroscopynarrow-band-photometryatomic-spectroscopyCataclysmic variable stars (CVs) evolve towards shorter orbital periods (Porb) until they reach a minimum Porb of ~80 min. Beyond this point, the donor star becomes out of thermal equilibrium or increasingly degenerate, causing the system to "bounce back" to longer Porb values. Such highly evolved systems are known as period-bouncers. Although 40-80% of all CVs are expected to have reached this stage, period-bouncers represent only 3-25% of the observed CV population. This is likely a consequence of their intrinsic faintness associated with lower mass-transfer rates. Establishing new diagnostics to unveil this missing population of evolved CVs is therefore crucial. We investigate whether period-bounce CVs can be distinguished from short-period pre-bounce CVs through their Balmer decrements using optical spectra from the Sloan Digital Sky Survey (SDSS). Differences in their Balmer decrements are expected to trace the distinct physical conditions in the accretion discs of period-bouncers resulting from their lower mass-transfer rates. Two samples of non-magnetic CVs with public SDSS optical spectra were constructed: one of short-period pre-bounce CVs and another of period-bounce CVs. For systems showing Balmer absorption from the white dwarf (WD), hydrogen-dominated atmosphere models were fitted and subtracted to correct for the WD component. H{alpha}, H{beta}, and H{gamma} fluxes were measured. We then investigated statistical relations between the Balmer decrements, the H{beta} line luminosity, and Porb, and compared the measured Balmer decrements with theoretical predictions from accretion disc models. Short-period pre-bounce CVs show flat Balmer decrements, i.e. Balmer line ratios close to unity, consistent with optically thick line emission and local thermodynamic equilibrium accretion disc models. In contrast, systems near and beyond the period minimum exhibit progressively steeper decrements (H{alpha}/H{beta}>1 and H{gamma}/H{beta}<1). This behaviour is attributed to their lower mass accretion rates. Balmer decrements can effectively be used to discriminate between short-period pre-bouncers and period-bouncers. The observed steeper Balmer decrements in period-bouncers are consistent with more extended optically thin regions and a more pronounced radial stratification of the physical conditions within their accretion discs. Our logistic-regression classifier based on the H{gamma}/H{beta} and H{alpha}/H{beta} ratios offers a robust and efficient tool for identifying period-bouncer candidates in optical spectroscopic surveys.2026A&A...712A.116Hhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/712/A116CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toI/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)I/352 : Distances to 1.47 billion stars in Gaia EDR3J/MNRAS/524/4867 : CVs from SDSS (Inight+, 2023)J/A+A/687/A305 : CV eROSITA-enhanced multi-wavelength cat.https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/712/A116https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/712/A116http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/712/A116https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/712/A116https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/712/A116http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/712/A116GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/712/A116/tableb1 (properties and Balmer emission-line measurements for 57 short-period CVs derived from SDSS optical spectra)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/712/A116/tableb1?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/712/A116/tableb1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/712/A116/tableb1?GETtext/xml+votable180.050000true133.838221264838111.30418662943620.0055555555555555566/2172 4174 4296 4453 4650 4723 4988 4999 5191 5210 5485 5596 5727 5918 5932 6052 6076 6643 7199 7211 7320 7371 7518 8359 8559 9165 9467 10232 11072 12288 12625 17515 18520 18844 18859 19870 19937 25934 26157 26316 26588 26995 27004 27419 27524 27671 27779 28082 28104 28127 28194 31331 31699 32432 32436 324801.9867573869263685e-19 3.916500758235022e-19https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/712/A116?format=asciiOpticaldefaultJ/A+A/712/A116/tableb1properties and Balmer emission-line measurements for 57 short-period CVs derived from SDSS optical spectrarecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintSimbadSimbad column added by the CDSmeta.ref.urlcharSystemObject's common namemeta.id;meta.maincharGaiaDR3Gaia ID from data release 3 (3)meta.idRA_ICRSGaia DR3 Right Ascension (ICRS) at Ep=2016.0degpos.eq.ra;meta.mainDE_ICRSGaia DR3 Declination (ICRS) at Ep=2016.0degpos.eq.dec;meta.mainSDSSnameSDSS namemeta.idcharPlateSDSS spectroscopic plate numbermeta.id;instr.plateintFibreSDSS fibre identification numbermeta.noteintMJDModified Julian Date of the SDSS spectroscopic observationtime.epochintBPmagGaia BP mean magnitudemagphot.mag;em.opt.BdoubleRPmagGaia RP mean magnitudemagphot.mag;em.opt.RdoubleGmagGaia G mean magnitudemagphot.mag;em.optdoubleDistDistance to the object (1)pcpos.distancedoublee_DistLower uncertainty in Dist (1)pcstat.errordoubleE_DistUpper uncertainty in Dist (1)pcstat.error;stat.maxdoubleTypeCataclysmic variable type (3) (4) (2)src.classcharPorbOrbital period of the system (3)mintime.perioddoubleFHaH{alpha} line flux (10^-17^erg/cm^2^/s)1e-20W.m**-2phot.flux;spect.linefloate_FHaUncertainty in FHa (10^-17^erg/cm^2^/s)1e-20W.m**-2stat.errorfloatFHbH{beta} line flux (10^-17^erg/cm^2^/s)1e-20W.m**-2phot.flux;em.line.Hbetafloate_FHbUncertainty in FHb (10^-17^erg/cm^2^/s)1e-20W.m**-2stat.errorfloatFHg? H{gamma} line flux (10^-17^erg/cm^2^/s)1e-20W.m**-2phot.flux;spect.linefloatnullablee_FHg? Uncertainty in FHg (10^-17^erg/cm^2^/s)1e-20W.m**-2stat.errorfloatnullableLHaH{alpha} line luminosity (10^+27^erg/s)1e+20Wphys.luminosity;em.line.Halphafloate_LHaLower uncertainty in LHa (10^+27^erg/s)1e+20Wstat.errorfloatE_LHaUpper uncertainty in LHa (10^+27^erg/s)1e+20Wstat.error;stat.maxfloatLHbH{beta} line luminosity (10^+27^erg/s)1e+20Wphys.luminosity;em.line.Hbetafloate_LHbLower uncertainty in LHb (10^+27^erg/s)1e+20Wstat.errorfloatE_LHbUpper uncertainty in LHb (10^+27^erg/s)1e+20Wstat.error;stat.maxfloatLHg? H{gamma} line luminosity (10^+27^erg/s)1e+20Wphys.luminosityfloatnullablee_LHg? Lower uncertainty in LHg (10^+27^erg/s)1e+20Wstat.errorfloatnullableE_LHg? Upper uncertainty in LHg (10^+27^erg/s)1e+20Wstat.error;stat.maxfloatnullableHa/HbRatio between H{alpha} and H{beta} linesphys.abund;spect.line;arith.ratiofloate_Ha/HbUncertainty in Halpha/Hbetastat.error;phys.abundfloatHg/Hb? Ratio between H{gamma} and H{beta} linesspect.line.intensity;arith.ratiofloatnullablee_Hg/Hb? Uncertainty in Hgamma/Hbetastat.error;phys.abundfloatnullablePPB? Period-Bouncer probability from the logistic regression model (expressed as a percentage)%statfloatnullable