J/ApJ/804/144ivo://CDS.VizieR/J/ApJ/804/144doi:10.26093/cds/vizier.18040144CDSAnderson R.I.Sahlmann J.Holl B.Eyer L.Palaversa L.Mowlavi N.,Suveges M.Roelens M.2017-07-04T07:09:14Z2015-09-25T13:02:35ZCDS support team

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

cds-question@unistra.frspectroscopic-binary-starsvariable-starsradial-velocityClassical Cepheid variable stars are crucial calibrators of the cosmic distance scale thanks to a relation between their pulsation periods and luminosities. Their archetype, {delta} Cephei, is an important calibrator for this relation. In this paper, we show that {delta}Cephei is a spectroscopic binary based on newly obtained high-precision radial velocities. We combine these new data with literature data to determine the orbit, which has period 2201 days, semi-amplitude 1.5km/s, and high eccentricity (e=0.647). We re-analyze Hipparcos intermediate astrometric data to measure {delta} Cephei's parallax (varpri=4.09+/-0.16mas) and find tentative evidence for an orbital signature, although we cannot claim detection. We estimate that Gaia will fully determine the astrometric orbit. Using the available information from spectroscopy, velocimetry, astrometry, and Geneva stellar evolution models (M_{delta}Cep_~5.0-5.25M_{sun}_), we constrain the companion mass to within 0.2M_{sun}_<M_2_<1.2. We discuss the potential of ongoing and previous interactions between the companion and {delta} Cephei near pericenter passage, informing reported observations of circumstellar material and bow shock. The orbit may have undergone significant changes due to a Kozai-Lidov mechanism driven by the outer (visual and astrometric) companion HD213307. Our discovery of {delta} Cephei's nature as a spectroscopic binary exposes a hidden companion and reveals a rich and dynamical history of the archetype of classical Cepheid variables.2015ApJ...804..144Ahttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/804/144CatalogResearchIsServedByTAP VizieR generic servicerelated-toIII/254 : 2nd Cat. of RVs with Astrometric Data (Kharchenko+, 2007)III/252 : Pulkovo radial velocities for 35493 HIP stars (Gontcharov, 2006)III/192 : Radial Velocities measured at PPO by FEHRENBACH (Fehrenbach+ 1996)J/AJ/150/13 : Cepheid Radial Velocities (CRaV) project (Evans+, 2015)J/AN/336/70 : Vel & proper motions of Galactic Cepheids (Mel'nik+, 2015)J/A+A/566/L10 : Cepheid RV amplitude modulations (Anderson, 2014)J/A+A/561/A126 : RV and vsini of southern stars (de Medeiros+, 2014)J/MNRAS/434/2238 : Cepheids in open clusters (Anderson+, 2013)J/MNRAS/434/870 : Radial velocity curves of 3 Cepheids (Szabados+, 2013)J/A+A/553/A24 : Models for rotating stars (Georgy+, 2013)J/A+A/537/A146 : Stellar models with rotation. 0.8<M<120 (Ekstrom+, 2012)J/A+A/525/A95 : Search for brown-dwarf companions of stars (Sahlmann+, 2011)J/AJ/142/136 : Spectroscopy of Cepheids. l=30-250{deg} (Luck+, 2011)J/A+A/504/959 : Amplitudes of single-mode Cepheids (Klagyivik+, 2009)J/AN/328/889 : Mean Radial Velocities of open clusters (Kharchenko+, 2007)J/A+A/453/155 : Extended envelopes around Gal. Cepheids II. (Merand+, 2006)J/ApJS/156/227 : Radial velocities of 16 Galactic Cepheids (Barnes+, 2005)J/AJ/130/1880 : Cepheids with periods between 3 & 6 days (Andrievsky+, 2005)J/A+A/430/165 : Radial velocities for 6691 K and M giants (Famaey+, 2005)J/A+A/415/531 : Radial velocities of 10 Galactic Cepheids (Storm+, 2004)J/A+A/381/32 : Galactic Cepheid abundances (Andrievsky+, 2002)J/A+AS/137/451 : Radial velocities. IX. (Grenier+, 1999)J/A+AS/108/25 : Cepheids fundamental parameters II. (Bersier+, 1994)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/804/144https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/804/144http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/804/144https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/804/144https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/804/144http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/804/144GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapOpticaldefaultJ/ApJ/804/144/table2List of radial velocity standard starsrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintHDStandard Star Identifier (8 stars)meta.id;meta.mainintBJDBarycentric Julian Date; BJD-2400000dtime.epochdoubleRVel[-64.7/29.9] Barycentric Radial Velocity (1)km/sphys.veloc;pos.barycenterfloate_RVel[0.003/0.07] Uncertainty in RVelkm/sstat.error;spect.dopplerVelocfloatJ/ApJ/804/144/table1The new Hermes radial velocity data of {delta} CeprecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintBJDBarycentric Julian Date; BJD-2400000dtime.epochdoublePhasePulsation phase (1)time.phasedoubleRVel[-34.8/4] Barycentric Radial Velocity (2)km/sphys.veloc;pos.barycenterfloate_RVel[0.018] Uncertainty in RVel (3)km/sstat.error;spect.dopplerVelocfloat