Collisional Pumping of H${}_2$O and CH${}_3$OH Masers in C-Type Shock Waves

Abstract

The collisional pumping of H${}_2$O and CH${}_3$OH masers in magnetohydrodynamic nondissociative C-type shocks is considered. A grid of C-type shock models with speeds in the range $5-70$ km s${}^{-1}$ and preshock gas densities $n_{{\mathrm{H}}_2,0}=10^4-10^7$ cm${}^{-3}$ is constructed. The large velocity gradient approximation is used to solve the radiative transfer equation in molecular lines. The para-H${}_2$O 183.3 GHz and ortho-H${}_2$O 380.1 and 448.0 GHz transitions are shown to be inverted and to have an optical depth along the shock velocity $|\tau |\sim 1$ at relatively low gas densities in the maser zone, $n_{{\mathrm{H}}_2}\gtrsim 10^5-10^6$ cm${}^{-3}$. Higher gas densities, $n_{{\mathrm{H}}_2}\gtrsim 10^7$ cm${}^{-3}$, are needed for efficient pumping of the remaining H${}_2$O masers. Simultaneous generation of H${}_2$O and class I CH${}_3$OH maser emission in a shock is possible at preshock gas densities $n_{{\mathrm{H}}_2,0}\approx 10^5$ cm${}^{-3}$ and shock speeds in the range $u_{\mathrm{s}}\approx 17.5-22.5$ km s${}^{-1}$. The possibility of detecting class I CH${}_3$OH and para-H${}_2$O 183.3 GHz masers in star-forming regions and near supernova remnants is investigated.

19 pages, 6 figures, published in Astronomy Letters, 2022, Vol. 48, No. 6, pp. 345-359

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Cited by in corpus (1)

• Survey of (sub)mm water masers in low-mass star-forming regions