Sub-millimetre observations of periodic methanol maser sources

MSc (Astrophysical Sciences), North-West University, Potchefstroom Campus

One of the properties of high-mass star forming regions is that they are associated with masers. A small group of these star forming regions contain periodic methanol masers. A significant aspect of the periodic methanol masers are their variety of light curves. Two types of periodic maser light curves are well defined, namely, masers that have a light curve with a sharp rise in the maser flux density, reaching a peak, followed by a slow decay and masers that have a light curve of which the profile resembles an absolute cosine function. These differences in the light curve shapes could point to different mechanisms responsible for the periodic variability. This study uses sub-millimetre observations of these regions, associated with periodic methanol masers with different types of light curves, to search for differences or similarities in these regions. The Sub-Millimetre Array observations of G22.357+0.066 and G25.411+0.105 and the Atacama Large Millimetre/Sub- Millimetre Array observations of G9.62+0.20E reveal clear geometric differences between the sources. All three sources are associated with outflows. G22.357+ 0.066 and G9.62+0.19E have bipolar outflows almost in the plane of the sky and G25.411+0.105 has a bipolar outflow almost perpendicular to the plane of the sky. Since outflows are present in the sources it implies that they should also have disks, meaning that the disks of G22.357+0.066 and G9.62+0.19E would have similar orientations and the disk of G25.411+0.105 would have a different orientation. Thus, this suggests that the difference in the shape of the periodic methanol maser light curves might be a viewing angle effect.

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