J/ApJS/226/18 5yr radial velocity measurements of 19 Cepheids (Anderson+, 2016) ================================================================================ Vetting Galactic Leavitt law calibrators using radial velocities: on the variability, binarity, and possible parallax error of 19 long-period Cepheids. Anderson R.I., Casertano S., Riess A.G., Melis C., Holl B., Semaan T., Papics P.I., Blanco-Cuaresma S., Eyer L., Mowlavi N., Palaversa L., Roelens M. =2016ApJS..226...18A (SIMBAD/NED BibCode) ================================================================================ ADC_Keywords: Stars, variable ; Radial velocities ; Binaries, spectroscopic Keywords: binaries: general; binaries: spectroscopic; distance scale; parallaxes stars: distances; stars: variables: Cepheids Abstract: We investigate the radial velocity (RV) variability and spectroscopic binarity of 19 Galactic long-period (P_puls_>~10d) classical Cepheid variable stars whose trigonometric parallaxes are being measured using the Hubble Space Telescope and Gaia. Our primary objective is to constrain possible parallax error due to undetected orbital motion. Using over 1600 high-precision RVs measured between 2011 and 2016, we find no indication of orbital motion on <~5yr timescales for 18 Cepheids and determine upper limits on allowed configurations for a range of input orbital periods. The results constrain the unsigned parallax error due to orbital motion to <2% for 16 stars, and <4% for 18. We improve the orbital solution of the known binary YZ Carinae and show that the astrometric model must take into account orbital motion to avoid significant error (~+/-100{mu}arcsec). We further investigate long-timescale (P_orb_>10yr) variations in pulsation-averaged velocity v_{gamma}_ via a template fitting approach using both new and literature RVs. We discover the spectroscopic binarity of XZ Car and CD Cyg, find first tentative evidence for AQ Car, and reveal KN Cen's orbital signature. Further (mostly tentative) evidence of time-variable v_{gamma}_ is found for SS CMa, VY Car, SZ Cyg, and X Pup. We briefly discuss considerations regarding a vetting process of Galactic Leavitt law calibrators and show that light contributions by companions are insignificant for most distance scale applications. Description: We here present a detailed investigation of spectroscopic binarity of the 19 Cepheids for which HST/WFC3 spatial scan parallaxes are being recorded (Riess+ 2014ApJ...785..161R; Casertano+ 2016ApJ...825...11C). We have secured time-series observations from three different high-resolution echelle spectrographs: Coralie (R~60000) at the Swiss 1.2m Euler telescope located at La Silla Observatory, Chile; Hermes (R~85000) at the Flemish 1.2m Mercator telescope located at the Roque de los Muchachos Observatory on La Palma, Canary Islands, Spain; Hamilton (R~60000) at the 3m Shane telescope located at Lick Observatory, California, USA. File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table1.dat 74 19 Basic information on the sample of Cepheids discussed here table2.dat 49 1630 RV data obtained for this program table3.dat 88 19 Results from RV curve modeling for all program Cepheids table4.dat 80 18 *Upper limits on wsini, the maximum unsigned projected parallax error estimated from upper limits on spectroscopic binarity table6.dat 62 33 Time-variable v{gamma} of new spectroscopic binaries based on RV template fitting table7.dat 63 41 Time-dependent v{gamma} based on RV template fitting for reported binary Cepheids table8.dat 62 19 Estimating typical photometric bias due to main sequence companions refs.dat 65 38 References -------------------------------------------------------------------------------- Note on table4.dat: The orbital elements for the spectroscopic binary YZ Carinae are given in table 5: ------------------------------------------------------------------------------ Porb e K Vgam T0-2.4M omega asini Fmass rms wsini d km/s km/s deg [10+6km] Msun km/s %w ------------------------------------------------------------------------------ 830.22 0.041 10.62 0.844 53422 195 117.1 0.093 0.39 26 +/-0.34 +/-0.010 +/-0.82 +/-0.063 +/-29 +/-12 +/-9.4 +/-0.041 ------------------------------------------------------------------------------ See section 4.2 for further explanations. -------------------------------------------------------------------------------- See also: B/gcvs : General Catalogue of Variable Stars (Samus+ 2007-2013) J/ApJ/826/56 : HST/WFC3 obs. of Cepheids in SN Ia host gal. (Riess+, 2016) J/ApJ/824/74 : OGLE LC classification of MC Cepheids (Garcia-Varela+, 2016) J/MNRAS/455/4231 : Coralie radial velocities for l Car (Anderson+, 2016) J/AJ/150/13 : Cepheid Radial Velocities (CRaV) project (Evans+, 2015) J/A+A/579/A68 : CANDID code for interferometric observations (Gallenne+, 2015) J/ApJ/804/144 : del Cephei new spectroscopic observations (Anderson+, 2015) J/MNRAS/446/4008 : RT Aur and SZ tau UBV light curves (Evans+, 2015) J/A+A/566/L10 : Cepheid radial velocity amplitude modulations (Anderson, 2014) J/MNRAS/434/2238 : Cepheids in open clusters (Anderson+, 2013) J/A+A/553/A24 : Models for rotating stars (Georgy+, 2013) J/AJ/144/187 : Iris photom. near southern Cepheids. V. AQ Pup (Turner+, 2012) J/A+A/546/A61 : Radial velocities for XHIP catalogue (de Bruijne+, 2012) J/A+A/537/A146 : Stellar models with rotation. 0.8