An XMM-Newton view of the Symbiotic Stars HM Sge, NQ Gem, and PU Vul

Abstract

We present the analysis of archival XMM-Newton observations of the symbiotic stars HM Sge, NQ Gem, and PU Vul. The EPIC-pn spectra hint at the presence of emission lines, which are further confirmed in the 1st order RGS spectra of the three sources. Spectral modeling of the EPIC-pn data disclose unprecedented characteristics, for instance, the best fit to the EPIC-pn spectrum of the $\beta$-type symbiotic star PU Vul reveals the presence of two plasma components. We report the discovery of an extremely soft spectral component in the EPIC-pn spectrum of the $\beta$-type symbiotic star HM Sge which we suggest is produced by periodic mass ejections such as jets. Consequently, we suggest that a simple $\beta$-type classification no longer applies to HM Sge. Finally, the spectrum of the $\beta/\delta$-type symbiotic star NQ Gem can not be fitted by a two-temperature plasma model as performed by previous authors. The model requires extra components to fit the 1.0-4.0 keV energy range. More sophisticated models to $\beta/\delta$-type symbiotic stars are needed in order to peer into the accretion process from such systems.