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

TL;DR

This paper analyzes XMM-Newton observations of symbiotic stars HM Sge, NQ Gem, and PU Vul, revealing new spectral features, plasma components, and challenging existing classifications and models of these systems.

Contribution

It provides the first detailed spectral modeling of these stars, discovering an extremely soft component in HM Sge and highlighting the need for more complex models for NQ Gem.

Findings

Detection of emission lines in spectra.

Discovery of a soft spectral component in HM Sge.

NQ Gem spectra require complex modeling beyond two-temperature plasma.

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.