J/A+A/566/L10ivo://CDS.VizieR/J/A+A/566/L10doi:10.26093/cds/vizier.35669010CDSAnderson R.I.2017-07-04T07:08:05Z2014-06-27T09:44:20ZCDS support team

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

cds-question@unistra.frvariable-starsgiant-starssupergiant-starsradial-velocityClassical Cepheids are crucial calibrators of the extragalactic distance scale. The Baade-Wesselink technique can be used to calibrate Cepheid distances using Cepheids in the Galaxy and the Magellanic Clouds. To report the discovery of modulations in radial velocity (RV) curves of four Galactic classical Cepheids and to investigate their impact as a systematic uncertainty for Baade-Wesselink distances. Highly precise Doppler measurements were obtained using the Coralie high-resolution spectrograph since 2011. Particular care was taken to sample all phase points in order to very accurately trace the RV curve during multiple epochs and to search for differences in linear radius variations derived from observations obtained at different epochs. Different timescales are sampled, ranging from cycle-to-cycle to months and years. The unprecedented combination of excellent phase coverage obtained during multiple epochs and high precision enabled the discovery of significant modulation in the RV curves of the short-period s-Cepheids QZ Normae and V335 Puppis, as well as the long-period fundamental mode Cepheids l Carinae and RS Puppis. The modulations manifest as shape and amplitude variations that vary smoothly over timescales of years for short-period Cepheids, and from one pulsation cycle to the next in the long-period Cepheids. The order of magnitude of the effect ranges from several hundred m/s to a few km/s. The resulting difference among linear radius variations derived using data from different epochs can lead to systematic errors of up to 15% for Baade-Wesselink-type distances, if the employed angular and linear radius variations are not determined contemporaneously. The different nature of the Cepheids exhibiting modulation in their RV curves suggests that this phenomenon is common. The observational baseline is not yet sufficient to conclude whether these modulations are periodic. In order to ensure the accuracy of Baade-Wesselink distances, angular and linear radius variations should always be determined contemporaneously.2014A&A...566L..10Ahttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/566/L10CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toIII/229 : Radial Velocities of Cepheids (Gorynya+ 1992-98)J/A+A/318/416 : Classical Cepheids RV + photometry (Pont+ 1997)J/A+A/323/775 : Cepheids radial velocities and coordinates (Mishurov+ 1997)J/AJ/115/635 : Cepheid radial velocities (Metzger+ 1998)J/A+A/341/818 : s-Cepheid velocity curves (Kienzle+, 1999)J/A+A/415/531 : Radial velocities of 10 Galactic Cepheids (Storm+, 2004)J/MNRAS/362/1167 : Radial velocities of 14 southern Cepheids (Petterson+, 2005)J/A+A/453/309 : HARPS observations of 9 galactic Cepheids (Nardetto+, 2006)J/A+A/489/1255 : HARPS observations of 8 galactic Cepheids (Nardetto+, 2008)J/A+A/502/951 : HARPS observations of 9 galactic Cepheids (Nardetto+, 2009)J/A+A/504/959 : Amplitudes of single-mode Cepheids (Klagyivik+, 2009)J/A+A/534/A94 : Milky Way Cepheids radial velocities (Storm+, 2011)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/566/L10https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/566/L10http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/566/L10https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/566/L10https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/566/L10http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/566/L10GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/566/L10/cepheids (Identifiers, coordinates, pulsation periods)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/566/L10/cepheids?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/566/L10/cepheids?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/566/L10/cepheids?GETtext/xml+votable180.050000true242.835417-54.3541670.0055555555555555566/37303 39410 40580 42153https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/566/L10?format=asciiOpticaldefaultJ/A+A/566/L10/lcarCoralie radial velocity data for l CarinaerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintBJDBarycentric Julian Date (BJD-2400000)time.epochdoubleRVBarycentric radial velocitykm/sphys.veloc;pos.barycenterdoublee_RVRadial velocity uncertaintykm/sstat.errorfloatJ/A+A/566/L10/rspupCoralie radial velocity data for RS PuppisrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintBJDBarycentric Julian Date (BJD-2400000)time.epochdoubleRVBarycentric radial velocitykm/sphys.veloc;pos.barycenterdoublee_RVRadial velocity uncertaintykm/sstat.errorfloatJ/A+A/566/L10/v335pupCoralie radial velocity data for V335 PuppisrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintBJDBarycentric Julian Date (BJD-2400000)time.epochdoubleRVBarycentric radial velocitykm/sphys.veloc;pos.barycenterdoublee_RVRadial velocity uncertaintykm/sstat.errorfloatJ/A+A/566/L10/cepheidsIdentifiers, coordinates, pulsation periodsHDHD numbermeta.idintrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNameCepheid name according to the GCVSmeta.id;meta.maincharRAJ2000Right ascension (J2000.0)pos.eq.ra;meta.mainDEJ2000Declination (J2000.0)pos.eq.dec;meta.mainPerPulsation perioddtime.perioddoubleVCShow the Radial Velocity curvesmeta.ref.urlcharFileNameName of the file with RV datameta.id;meta.filecharSimbadSimbad column added by the CDSmeta.ref.urlcharJ/A+A/566/L10/qznorCoralie radial velocity data for QZ NormaerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintBJDBarycentric Julian Date (BJD-2400000)time.epochdoubleRVBarycentric radial velocitykm/sphys.veloc;pos.barycenterdoublee_RVRadial velocity uncertaintykm/sstat.errorfloat