J/ApJ/847/127ivo://CDS.VizieR/J/ApJ/847/127doi:10.26093/cds/vizier.18470127CDSPandey G.Lambert D.L.2018-09-25T13:18:40Z2018-07-03T10:08:58ZCDS support team

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

cds-question@unistra.frchemical-abundancespeculiar-variable-starsline-intensitiesvisible-astronomyspectroscopyOptical high-resolution spectra of V652 Her and HD 144941, the two extreme helium stars with exceptionally low C/He ratios, have been subjected to a non-LTE abundance analysis using the tools TLUSTY and SYNSPEC. Defining atmospheric parameters were obtained from a grid of non-LTE atmospheres and a variety of spectroscopic indicators including HeI and HeII line profiles, and the ionization equilibrium of ion pairs such as CII/CIII and NII/NIII. The various indicators provide a consistent set of atmospheric parameters: Teff=25000+/-300K, logg=3.10+/-0.12(cgs), and {xi}=13+/-2km/s are provided for V652 Her, and Teff=22000+/-600K, logg=3.45+/-0.15(cgs), and {xi}=10km/s are provided for HD 144941. In contrast to the non-LTE analyses, the LTE analyses-LTE atmospheres and an LTE line analysis-with the available indicators do not provide a consistent set of atmospheric parameters. The principal non-LTE effect on the elemental abundances is on the neon abundance. It is generally considered that these extreme helium stars with their very low C/He ratio result from the merger of two helium white dwarfs. Indeed, the derived composition of V652 Her is in excellent agreement with predictions by Zhang & Jeffery (2012MNRAS.419..452Z), who model the slow merger of helium white dwarfs; a slow merger results in the merged star having the composition of the accreted white dwarf. In the case of HD 144941, which appears to have evolved from metal-poor stars, a slow merger is incompatible with the observed composition but variations of the merger rate may account for the observed composition. More detailed theoretical studies of the merger of a pair of helium white dwarfs are to be encouraged.2017ApJ...847..127Phttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/847/127CatalogResearchIsServedByTAP VizieR generic servicerelated-toB/vsx : AAVSO International Variable Star Index VSX (Watson+, 2006-2014)J/ApJS/224/2 : K2 EPIC stellar properties for 138600 targets (Huber+, 2016)J/AJ/143/28 : Analysis of B6-A9 stars from INES UV spectra (Freire+, 2012)J/MNRAS/420/757 : STEREO magnetic chemically peculiar stars (Wraight+, 2012)J/A+A/469/799 : Torun catalog of post-AGB and related objects (Szczerba+, 2007)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/847/127https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/847/127http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/847/127https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/847/127https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/847/127http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/847/127GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapOpticaldefaultJ/ApJ/847/127/table145Summary of atmospheric parameters and photospheric abundances (tables 1, 4 and 5)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNameStar namemeta.id;meta.maincharAna"non-LTE" or "LTE" analysesmeta.notecharTeff[21000/25300]? Effective temperatureKphys.temperature.effectiveintnullablee_Teff[300/600]? Teff uncertaintyKstat.error;phys.temperature.effectiveintnullablelogg[3.1/3.5]? log of surface gravitylog(cm.s**-2)phys.gravityfloatnullablee_logg[0.1/0.2]? logg uncertaintylog(cm.s**-2)stat.errorfloatnullableVt[10/13]? Microturbulent velocitykm/sphys.velocintnullablee_Vt[2]? Vt uncertaintykm/sstat.errorintnullablevsini[10]? Rotational velocity (or lower range)km/sphys.veloc.rotatintnullablevsini2? Upper range of vsinikm/sphys.veloc.rotatintnullableH[9.5/12] H abundancephys.abundfloatHe[10.9/11.5] He abundancephys.abundfloatC[6.6/8.4] C abundancephys.abundfloatN[6.4/9] N abundancephys.abundfloatO[7/8.7] O abundancephys.abundfloatNe[7.2/8.6] Ne abundancephys.abundfloatMg[5.8/7.6] Mg abundancephys.abundfloatAl[5.1/6.5]? Al abundancephys.abundfloatnullableSi[6/7.5] Si abundancephys.abundfloatP[5.4/5.5]? P abundancephys.abundfloatnullableS[6/7.4] S abundancephys.abundfloatAr[6.4/7]? Ar abundancephys.abundfloatnullablel_Fe[<= ] Limit flag on Femeta.code.error;phys.abund.FecharFe[6.2/7.5] Fe abundancephys.abundfloatEWsDisplay the measured equivalent widths (Table 2 or Table 3)meta.ref.urlcharJ/ApJ/847/127/table2Measured equivalent widths (EW) and NLTE/LTE photospheric line for V652 HerIonIonphys.atmol.ionStagecharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintTypeMeasurement type: "Line" or "Mean"meta.notecharlambda[3796/7033]? wavelength, Angstroms0.1nmem.wldoublenullablef_lambdaFlag on lambda (1)meta.codecharExPot[8.2/35.7]? Excitation potentialeVphys.atmol.excitationfloatnullablelog(gf)[-3,1.2]? Logarithm of oscillator strengthphys.atmol.oscStrengthfloatnullabler_log(gf)[c] Source for log(gf) (2)meta.ref;pos.framecharl_EWLimit flag on EWmeta.code.error;spect.line.eqWidthcharEW[7/316]? Equivalent width0.0001nmspect.line.eqWidthintnullablef_EW[s ] flag on EW, s=Syntheticmeta.codecharl_eps-nlteLimit flag on eps-nltemeta.code.errorchareps-nlte[5.7/10.5]? Abundance derived from this line (3)phys.abundfloatnullablee_eps-nlte[0/0.3]? 1{sigma} scatter in mean valuestat.errorfloatnullablel_eps-lteLimit flag on eps-ltemeta.code.errorchareps-lte[4.9/10.5]? Abundance derived from this line (4)phys.abundfloatnullablee_eps-lte[0/0.4]? 1{sigma} scatter in mean valuestat.errorfloatnullableJ/ApJ/847/127/table3Measured equivalent widths (EW) and NLTE/LTE photospheric line for HD 144941recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintTypeMeasurement type: "Line" or "Mean"meta.notecharIonIonphys.atmol.ionStagecharlambda[3796/7033]? wavelength, Angstroms0.1nmem.wldoublenullablef_lambdaFlag on lambda (1)meta.codecharExPot[8.2/35.7]? Excitation potentialeVphys.atmol.excitationfloatnullablelog(gf)[-3,1.2]? Logarithm of oscillator strengthphys.atmol.oscStrengthfloatnullabler_log(gf)[c] Source for log(gf) (2)meta.ref;pos.framecharl_EWLimit flag on EWmeta.code.error;spect.line.eqWidthcharEW[7/316]? Equivalent width0.0001nmspect.line.eqWidthintnullablef_EW[s ] flag on EW, s=Syntheticmeta.codecharl_eps-nlteLimit flag on eps-nltemeta.code.errorchareps-nlte[5.7/10.5]? Abundance derived from this line (3)phys.abundfloatnullablee_eps-nlte[0/0.3]? 1{sigma} scatter in mean valuestat.errorfloatnullablel_eps-lteLimit flag on eps-ltemeta.code.errorchareps-lte[4.9/10.5]? Abundance derived from this line (4)phys.abundfloatnullablee_eps-lte[0/0.4]? 1{sigma} scatter in mean valuestat.errorfloatnullable