VELOcities of CEpheids (VELOCE). II. Systematic search for spectroscopic binary cepheids

Abstract

Classical Cepheids provide valuable insights into the evolution of stellar multiplicity among intermediate-mass stars. Here, we present a systematic investigation of single-lined spectroscopic binaries (SB1s) based on high-precision velocities measured by the VELOcities of CEpheids ( project. We detected ($29<!PCT!>$) SB1 systems among the Milky Way Cepheids in the first data release ($43<!PCT!>$) of which were not previously known to be SB1 systems. We determined 30 precise and tentative orbital solutions ($53<!PCT!>$) of which are reported for the first time. This large set of Cepheid orbits provides a detailed view of the eccentricity $e$ and orbital period distribution among evolved intermediate-mass stars, ranging from $e $ and $\,d. The orbital motion on timescales exceeding the 11 yr baseline was investigated using a template-fitting technique applied to literature data. Particularly interesting objects include a) R Cru, the Cepheid with the shortest orbital period in the Milky Way (sim 238\,d); b) ASAS J103158-5814.7, a short-period overtone Cepheid exhibiting time-dependent pulsation amplitudes as well as orbital motion; and c) 17 triple systems with outer visual companions, among other interesting objects. Most Cepheids (21/23) that exhibit evidence of a companion based on a proper motion anomaly are also spectroscopic binaries, whereas the remaining do not exhibit significant ($> 3 orbital radial velocity variations. quality flags, notably the renormalized unit weight error (RUWE), do not allow Cepheid binaries to be identified reliably although statistically the average RUWE of SB1 Cepheids is slightly higher than that of non-SB1 Cepheids. A comparison with photometric amplitudes in $G-$, $Bp$, and $Rp$ also does not allow one to identify spectroscopic binaries among the full sample, indicating that the photometric amplitudes in this wavelength range are not sufficiently informative of companion stars.