Mon. Not. R. Astron. Soc., 473, 440-446 (2018/January-1)
XMM-Newton study of the supersoft symbiotic system Draco C1.
SAEEDI S., SASAKI M. and DUCCI L.
Abstract (from CDS):
We present the results of the analysis of thirty-one XMM-Newton observations of the symbiotic star Draco C1 located in the Draco dwarf spheroidal galaxy. This object had been identified as a supersoft source based on ROSAT data. We analysed X-ray, ultraviolet (UV) and optical data taken with XMM-Newton in order to obtain the physical parameters and the geometry of the system. We have also performed the first X-ray timing analysis of Draco C1. The X-ray spectrum is well fitted with a blackbody model with a temperature of (1.8 ± 0.3) x 105 K. We obtained a bolometric luminosity of >=1038 erg s–1 for the white dwarf. The X-ray spectrum and luminosity suggest stable nuclear burning on the surface of the white dwarf. The low column density derived from the X-ray spectrum is consistent with the lack of nebular lines found in previous UV studies. The long-term variability in the optical and the UV suggests that the system is not observed face-on and that the variability is caused by the reflection effect. For the red giant companion, we estimate a radius of ∼110 R☉ and an upper limit <=1.5 M☉ for its mass assuming Roche lobe overflow.