Distinguishing between symbiotic stars and planetary nebulae

Abstract

Context. Number of known symbiotic stars (SySt) is still significantly lower than their predicted population. One of the main problems in finding complete population of SySt is the fact that their spectrum can be confused with other objects, such as planetary nebulae (PNe) or dense H ii regions. The problem is reinforced by a fact that in significant fraction of established SySt the emission lines used to distinguish them from other objects are not present. Aims. We aim at finding new diagnostic diagrams that could help separate SySt from PNe. Additionally, we examine known sample of extragalactic PNe for candidate SySt. Methods. We employed emission line fluxes of known SySt and PNe from the literature. Results. We found that among the forbidden lines in the optical region of spectrum, only the [O iii] and [N ii] lines can be used as a tool for distinguishing between SySt and PNe, which is consistent with the fact that they have the highest critical densities. The most useful diagnostic that we propose is based on He i lines which are more common and stronger in SySt than forbidden lines. All these useful diagnostic diagrams are electron density indicators that better distinguishes PNe and ionized symbiotic nebulae. Moreover, we found six new candidate SySt in the Large Magellanic Cloud and one in M81. If confirmed, the candidate in M81 would be the furthest known SySt thus far.

Spectroscopic and photometric analysis of symbiotic candidates -- I. Ten candidates on classical symbiotic stars

“…Recently, Akras et al (2019b) proposed a set of IR criteria for classifying the symbiotic stars based on the IR photometry from 2MASS and WISE. Iłkiewicz & Mikołajewska (2017) presented spectroscopic criteria based on the ratio of emission line fluxes to distinguish between planetary nebulae and symbiotic stars, extending the diagnostic diagrams of Gutierrez-Moreno et al (1995) which are applicable only if [O ] emission lines are observed together with Balmer lines. In our recent work (Merc et al 2020), we have proposed to employ the position in the Gaia DR2 HR diagram, or the unusual X-ray-to-optical flux ratios as criteria to discard disputable symbiotic candidates and, to a lesser extent, to identify promising systems.…”

Optical emission line spectra of symbiotic binaries

“…planetary nebulae, Be stars and young stellar objects (e.g. Gutierrez-Moreno et al 1995;Rodríguez-Flores et al 2014;Iłkiewicz & Mikołajewska 2017). We have investigated how our emission models of symbiotic binaries fit to these previously presented line ratio classification diagrams and how the line ratios depend on the massloss rate and orbital separation.…”

“…Gutierrez-Moreno et al (1995) used the [O ] and Balmer emission lines for the classification, but this method is not always applicable, because the [O ] are not always detected. Iłkiewicz & Mikołajewska (2017) explored various other emission lines including [N ], [O ], [Ne ], and He lines, in order to distinguish planetary nebulae from symbiotic binaries. They demonstrated that this set of lines provides an efficient diagnostics for symbiotic binaries.…”

“…Proga et al (1994) analysed the He 𝜆𝜆5876, 6678, 7065 emission lines and showed that these lines provide a useful diagnostic tool for the symbiotic binaries and they can be used to separate between S-and D-type symbiotics. Iłkiewicz & Mikołajewska (2017) showed that these lines can also be used to separate symbiotic binaries from planetary nebulae. The He line ratios in symbiotic binaries differ considerably from the standard Case B approximation due to the metastability of the 2 3 S level and collisional effects and thus these line ratios are very sensitive to the physical conditions in the highest density regions (Schmid & Schild 1990).…”

Symbiotic Stars in the APOGEE Survey: The Case of LIN 358 and SMC N73 (LIN 445a)

“…SySts are further classified as S-type, for those where the mass donor is a normal giant star, and D-type, for systems where the donor is a Mira variable surrounded by a warm dust envelope (Webster & Allen 1975). SySts are use-shown that D-type SySts can, in fact, be distinguished from PNe by the strength of forbidden lines (O III and N III) and various He I lines in the optical region of the spectrum (Gutierrez-Moreno et al 1995;I lkiewicz & Miko lajewska 2017). Meanwhile, S-type SySts are typically identified by the presence of photospheric absorption features (TiO, VO, C 2 , CN) in the observed spectrum of the cool companion, in addition to presence of strong emission lines from He II and Hα, as well as from high-excitation ions (Fe VII, O VI; e.g., Belczyński et al 2000).…”