2022/05/16 by Nancy Remage Evans, Scott G. Engle, Evans, Nancy Remage +26 · 1 citation
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #FOS: Physical sciences #Solar and Stellar Astrophysics (astro-ph.SR) #Stellar, planetary, and galactic studies
paper · pdf · doi:10.48550/arxiv.2205.07967
openalex publication_date 2022/05/16 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
X-ray observations have been made of a sample of 20 classical Cepheids, including two new observations (Polaris and \it l Car) reported here. The occurrence of X-ray flux around the pulsation cycle is discussed. Three Cepheids are detected (δ Cep, β Dor, and Polaris). X-rays have also been detected from the low--mass F, G, and K companions of 4 Cepheids (V473 Lyr, R Cru, V659 Cen, and W Sgr), and one hot companion (S Mus). Upper limits on the X-ray flux of the remaining Cepheids provide an estimate that 28% have low mass companions. This fraction of low--mass companions in intermediate mass Cepheids is significantly lower than expected from random pairing with the field IMF. Combining the companion fraction from X-rays with that from ultraviolet observations results in a binary/multiple fraction of 57% ±12% for Cepheids with the ratios q > 0.1 and separations a > 1 au. This is a lower limit since M stars are not included. X-ray observations detect less massive companions than other existing studies of intermediate mass stars. Our measured occurrence rate of unresolved, low-mass companions to Cepheids suggests that intermediate-period binaries derive from a combination of disk and core fragmentation and accretion. This yields a hybrid mass-ratio distribution that is skewed toward small values compared to a uniform distribution but is still top-heavy compared to random pairings drawn from the IMF.