Hubble Space Telescope Snapshot Survey for Resolved Companions of Galactic Cepheids: Final Results

Abstract

Cepheids in multiple systems provide information on the outcome of the formation of massive stars. They can also lead to exotic end-stage objects. This study concludes our survey of 70 galactic Cepheids using the {\it Hubble Space Telescope\} (\HST) Wide Field Camera~3 (WFC3) with images at two wavelengths to identify companions closer than $5\arcsec$. In the entire WFC3 survey we identify 16 probable companions for 13 Cepheids. The seven Cepheids having resolved candidate companions within $2"$ all have the surprising property of themselves being spectroscopic binaries (as compared with a 29\% incidence of spectroscopic binaries in the general Cepheid population). That is a strong suggestion that an inner binary is linked to the scenario of a third companion within a few hundred~AU\null. This characteristic is continued for more widely separated companions. Under a model where the outer companion is formed first, it is unlikely that it can anticipate a subsequent inner binary. Rather it is more likely that a triple system has undergone dynamical interaction, resulting in one star moving outward to its current location. {\it Chandra\} and {\it Gaia\} data as well as radial velocities and \HSTSTIS and {\it IUE\} spectra are used to derive properties of the components of the Cepheid systems. The colors of the companion candidates show a change in distribution at approximately 2000~AU separations, from a range including both hot and cool colors for closer companions, to only low-mass companions for wider separations.

Accepted by ApJ

References in corpus (14)

• The Gaia mission
• Binary interaction dominates the evolution of massive stars
• Southern Massive Stars at High Angular Resolution: Observational Campaign and Companion Detection
• Multiplicity of Galactic Cepheids and RR Lyrae stars from Gaia DR2 - I. Binarity from proper motion anomaly
• GPI PSF subtraction with TLOCI: the next evolution in exoplanet/disk high-contrast imaging
• Wide binaries are rare in open clusters
• Baade-Wesselink distances and the effect of metallicity in classical cepheids
• Speckle interferometry at SOAR in 2018
• Binary Properties from Cepheid Radial Velocities (CRaV)
• The Secret Lives of Cepheids: $\delta$ Cep -- the Prototype of a New Class of Pulsating X-ray Variable Stars
• Multiplicity of Galactic Cepheids from long-baseline interferometry. IV. New detected companions from MIRC and PIONIER observations
• Massive Star Multiplicity: The Cepheid W Sgr
• The Angular Separation of the Components of the Cepheid AW Per
• Searching for visual companions of close Cepheids. VLT/NACO lucky imaging of Y~Oph, FF~Aql, X~Sgr, W~Sgr and $\eta$~Aql