X-Rays in Cepheids: Identifying Low-mass Companions of Intermediate-mass Stars - INSU - Institut national des sciences de l'Univers Access content directly
Journal Articles The Astrophysical Journal Year : 2022

X-Rays in Cepheids: Identifying Low-mass Companions of Intermediate-mass Stars


X-ray observations have been made of a sample of 20 classical Cepheids, including two new observations (Polaris and 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 four 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 initial mass function (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 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. *Based on observations obtained with the Chandra X-ray Observatory.
Fichier principal
Vignette du fichier
Evans_2022_ApJ_938_153.pdf (1.02 Mo) Télécharger le fichier
Origin : Publisher files allowed on an open archive

Dates and versions

insu-03874879 , version 1 (28-11-2022)


Attribution - CC BY 4.0



Nancy Remage Evans, Scott Engle, Ignazio Pillitteri, Edward Guinan, H. Moritz Günther, et al.. X-Rays in Cepheids: Identifying Low-mass Companions of Intermediate-mass Stars. The Astrophysical Journal, 2022, 938, ⟨10.3847/1538-4357/ac6fdf⟩. ⟨insu-03874879⟩
32 View
6 Download



Gmail Facebook Twitter LinkedIn More