First detailed optical spectroscopic observations of the supernova remnants G107.7-5.1 and G150.3+4.5

Abstract

We present optical spectroscopic observations of the supernova remnants (SNRs) G107.7$-$5.1 and G150.3+4.5, each spanning nearly 3 degree. Both remnants were recently examined in the optical band through a deep H$α$ and [OIII] emission-line imaging survey, which led to the discovery of G107.7$-$5.1. Using long-slit spectra obtained with the 1.5-m Russian-Turkish Telescope (RTT150), we investigate the physical conditions of the pre-shock and post-shock gas in the optical filamentary regions of the SNRs. The SNR nature of G107.7$-$5.1 is confirmed by the measured [SII]/H$α$ and [NII]/H$α$ ratios, which range from 0.56 to 0.86 and from 0.7 to 1.4, respectively. A similar conclusion is reached for G150.3+4.5, where the observed [SII]/H$α$ (0.43-0.92) and [NII]/H$α$ (0.49-1.29) ratios likewise support a shock-excitation origin. Further confirmation of the shock-excited nature of both SNRs comes from their consistency with recent diagnostic diagrams based on multiple emission-line ratios. The [OIII]/H$β$ line ratios measured in both remnants indicate shocks with complete recombination zones and are consistent with shock velocities of $\gtrsim$100 km s$^{-1}$. The electron densities ($n_{\rm e}$), derived from the [SII] $λ$6716/$λ$6731 line ratios, exhibit substantial variation in the spectra of both SNRs. Additionally, extinction variations observed across the remnants suggest the presence of significant dust structures along the line of sight. We conclude that these two remnants display remarkable similarities across multiple diagnostic spectral properties, consistent with previous reports indicating comparable GeV gamma-ray characteristics.

Figures (5)

• Figure 1: H$\alpha$ image ($\sim$3.2 $\times$ 3.2 deg$^{2}$) of G107.7$-$5.1 from Fesen2024, revealing well-defined filamentary emission distributed across the northwestern, eastern, and southern regions. The slit positions (NW1, NW2, NW3, E1, and S1) for the spectroscopy are marked with green lines, and the aperture centres of each slit are indicated by crosses.
• Figure 2: H$\alpha$ plus RGB image ($\sim$3.5 $\times$ 2.4 deg$^{2}$) from Fesen2024, showing prominent filaments along the southern region of G150.3+4.5. The slit positions (S1$-$S8) for the spectroscopy are marked with green lines, and the aperture centres of each slit are indicated by crosses.
• Figure 3: RTT150 long-slit spectra obtained at three positions in the northwestern region (NW1, NW2, and NW3), one position in the eastern region (E1), and one position in the southern region (S1) of G107.7$-$5.1, covering the wavelength range 4500$-$7000 Å. Fluxes are in $10^{-16}$ erg cm$^{-2}$ s$^{-1}$ Å$^{-1}$.
• Figure 4: RTT150 long-slit spectra obtained at positions S1$-$S8 in the southern region of G150.3+4.5, covering the wavelength range 4500$-$7000 Å. Fluxes are in $10^{-16}$ erg cm$^{-2}$ s$^{-1}$ Å$^{-1}$.
• Figure 5: 2D diagnostic diagrams adapted from Kopsacheili2020. All diagnostic data were obtained directly from the link provided by Kopsacheili2024 and are overlaid with our spectroscopic measurements of G107.7$-$5.1 (navy blue) and G150.3+4.5 (green). The blue shaded region denotes the parameter space characteristic of shock-excited gas.