G. C. MacLeod

Masers in Massive Star-forming Regions Associated with the Brightest Steep-Spectrum IRAS Point Sources

Twenty-four bright, steep-spectrum far-infrared IRAS point sources, which were originally discussed by Hughes & MacLeod, have been searched for hydroxyl, water, and methanol masers and for formaldehyde absorption features. Distances and spectral types for the stars exciting these masers were estimated using radio continuum, IRAS spectra, and maser velocity data. It is found that 21 of the 24 sources are regions of massive star formation containing stars earlier than type B2. We report the discovery of five new OH masers, one new 6.7 GHz CH3OH maser, and two new 12.2 GHz CH3OH masers toward these IRAS sources. By contrast, no 4.765 GHz excited-OH masers were found toward these sources. This sample contains only star-forming regions; there are no planetary or reflection nebulae or extragalactic sources present, as seen in samples with less extreme IRAS colors.

6.7 GHz Methanol Masers Associated with IRAS-Selected Sources

New detections of eight 6.7 GHz methanol masers have been made toward three samples of IRAS-selected objects. Two of the methanol maser sources have associated 1.6 GHz hydroxyl masers, and one has an associated 12.2 GHz methanol maser. The detection rate of the methanol masers is strongly dependent upon the IRAS colors of the sources. This dependence may arise from the conditions required for masing and reflect evolutionary changes in the star-forming regions. The reddest IRAS sources are the youngest.

Improved selection criteria for H ii regions, based on IRAS sources

We present new criteria for selecting HII regions from the Infrared Astronomical Satellite (IRAS) Point Source Catalogue (PSC), based on an HII region catalogue derived manually from the all-sky Wide-field Infrared Survey Explorer (WISE). The criteria are used to augment the number of HII region candidates in theMilkyWay. The criteria are defined by the linear decision boundary of two samples: IRAS point sources associated with known HII regions, which serve as the HII region sample, and IRAS point sources at high Galactic latitudes, which serve as the non-H II region sample. Amachine learning classifier, specifically a support vector machine, is used to determine the decision boundary. We investigate all combinations of four IRAS bands and suggest that the optimal criterion is log (F-60/F-12) >= (-0.19 x log (F-100/F-25) + 1.52), with detections at 60 and 100 mu m. This selects 3041 HII region candidates from the IRAS PSC. We find that IRAS HII region candidates show evidence of evolution on the two-colour diagram. Merging the WISE HII catalogue with IRAS HII region candidates, we estimate a lower limit of approximately 10 200 for the number of HII regions in the Milky Way.

Methanol masers in the southern Galaxy

We have detected 6.6-GHz A+-methanol masers towards all nineteen 12.2-GHz E-methanol masers at declinations below -42°. We also searched all known OH masers in the longitude range 260° to 345° and detected 52 of 88. The detection rate of 6.6-GHz methanol masers is four times higher in the Norma area of the Galaxy than in the Carina arm. Although this may be partly due to sensitivity limitations, it may also be a product of the radial metallicity gradient in the Galaxy.

A masing event in NGC 6334I: contemporaneous flaring of hydroxyl, methanol, and water masers

As a product of the maser monitoring program with the 26m telescope of the Hartebeesthoek Radio Astronomy Observatory (HartRAO), we present an unprecedented, contemporaneous flaring event of 10 maser transitions in hydroxyl, methanol, and water that began in 2015 January in the massive star-forming region NGC6334I in the velocity range -10 to -2 km/s. The 6.7 GHz methanol and 22.2 GHz water masers began flaring within 22 days of each other, while the 12.2 GHz methanol and 1665 MHz hydroxyl masers flared 80 and 113 days later respectively. The 1665 MHz, 6.7 GHz, and 22.2 GHz masers have all remained in their flared state for nearly 3 years. The brightest flaring components increased by factors of 66, 21, 26, and 20 in the 12.2 and 6.7 GHz methanol, 1665 MHz hydroxyl and 22.2 GHz water maser transitions respectively; some weaker components increased by up to a factor of 145. We also report new maser emission in the 1720, 6031, and 6035 MHz OH lines and the 23.1 GHz methanol line, along with the detection of only the fifth 4660 MHz OH maser. We note the correlation of this event with the extraordinary (sub)millimeter continuum outburst from the massive protostellar system NGC6334I-MM1 and discuss the implications of the observed time lags between different maser velocity components on the nature of the outburst. Finally, we identify two earlier epoch maser flaring events likely associated with this object, which suggest a recurring accretive phenomenon that generates powerful radiative outbursts.

Spectroscopic research with the Hartebeesthoek radio telescope

Research into star-forming regions, evolved HII regions, late-type stars with circumstellar dust shells and comet Halley using spectroscopic observations made with the Hartebeesthoek radio telescope is reviewed.

Masers in star-forming regions associated with cold, bright IRAS sources

Twenty-four regions of massive star-formation have been searched for OH, H2O, 6.6-GHz and 12.2-GHz CH3OH masers. Chosen from the IRAS Point Source Catalog by their infrared colours, these objects are the coolest objects in the catalog. Masers were detected towards all but two of these IRAS sources. Seven sources were observed in the 12CO (J=1−0) line and all show evidence of molecular outflow. In six of the CO sources we have found maser emission with peaks in both the red and the blue wings of the outflow. We infer that the conditions for masing in these regions are probably produced by the mechanical energy of the outflowing material.