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

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 first-order RGS spectra of the three sources. Spectral modeling of the EPIC-pn data discloses unprecedented characteristics; for instance, the best fit to the EPIC-pn spectrum of the β-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 β-type symbiotic star HM Sge, which we suggest is produced by periodic mass ejections such as jets. Consequently, we suggest that a simple β-type classification no longer applies to HM Sge. Finally, the spectrum of the β/δ-type symbiotic star NQ Gem cannot 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 β/δ-type symbiotic stars are needed in order to peer into the accretion process from such systems.