Herschel Planetary Nebula Survey (HerPlaNS): Hydrogen Recombination Laser Lines in Mz 3

TL;DR

This study reports the detection of hydrogen recombination laser lines in the planetary nebula Mz 3, suggesting laser amplification effects in its core, which is unusual for such nebulae and similar to phenomena observed in MWC 349A.

Contribution

First detection of laser-enhanced hydrogen recombination lines in Mz 3, revealing laser effects in planetary nebulae cores and expanding understanding of nebular emission processes.

Findings

Detection of 12 HRLs in Mz 3's spectrum.

Evidence of laser amplification in Mz 3's core.

Similarity of Mz 3's core emission to MWC 349A.

Abstract

The bipolar nebula Menzel 3 (Mz 3) was observed as part of the \textit{Herschel} Planetary Nebula Survey (\textit{HerPlaNS}), which used the PACS and SPIRE instruments aboard the \textit{Herschel Space Observatory} to study a sample of planetary nebulae (PNe). In this paper, one of the series describing \textit{HerPlaNS} results, we report the detection of H I recombination lines (HRLs) in the spectrum of Mz 3. Inspection of the spectrum reveals the presence of 12 HRLs in the 55 to 680 $\mu$m range covered by the PACS and SPIRE instruments (H11$\alpha$ to H21$\alpha$ and H14$\beta$). The presence of HRLs in this range is unusual for PNe and has not been reported in Mz 3 before. Our analysis indicates that the HRLs we observed are enhanced by laser effect occurring in the core of Mz 3. Our arguments for this are: (i) the available Mz 3 optical to submillimetre HRL $\alpha$ line intensity ratios are not well reproduced by the spontaneous emission of optically thin ionized gas, as would be typical for nebular gas in PNe; (ii) the compact core of Mz 3 is responsible for a large fraction of the Herschel HRLs emission; (iii) the line intensity ratios for Mz 3 are very similar to those in the core emission of the well known star MWC 349A, where laser effect is responsible for the enhancement of HRLs in the Herschel wavelength range; (iv) the physical characteristics relevant to cause laser effect in the core of MWC 349A are very similar to those in the core of Mz 3.