A study of class II methanol maser condensations in the star-forming region W48

The methanol-line spectra in two maser condensations at velocities ～41 and ～45 km/s in the star-forming region W48 have been studied. The intensity of the 2₀-3_?1 E (12.2 GHz) line is anticorrelated with that of the 5₁-6₀ A ⁺ (6.7 GHz) line: the intensity of the 5₁-6₀ A ⁺ (6.7 GHz) line is greater at ～41 km/s than at ～45 km/s, while the opposite is true of the 2₀-3_?1 E (12 GHz) line. The remaining class II methanol lines in this source demonstrate the same behavior as the 2₀-3_?1 E (12 GHz) line. This contradicts current concepts about the maser line intensities in various methanol transitions: according to model calculations, the intensities of all class II lines should vary in phase. This effect is confirmed for a large homogeneous sample of 67 sources. Possible explanations of the observed effect are proposed; one suggests the possible role of “transpumping” of the methanol-level populations in the maser condensations. The relationships between the variations of the 2₀-3_?1 E (12 GHz) and 5₁-6₀ A ⁺ (6.7 GHz) line intensities, which are present for all 67 sources considered, may indicate that the condensations are at different distances from the pumping source. The presence of condensations at various distances from the pumping source in all 67 sources can be understood if they are ice planets revolving in different orbits around massive stars or protostars.