M. J. Gaylard

Periodic class II methanol masers in G9.62+0.20E

We present the light curves of the 6.7 and 12.2 GHz methanol masers in the star forming region G9.62+0.20E for a time span of more than 2600 days. The earlier reported period of 244 days is confirmed. The results of monitoring the 107 GHz methanol maser for two flares are also presented. The results show that flaring occurs in all three masing transitions. It is shown that the average flare profiles of the three masing transitions are similar. The 12.2 GHz masers are the most variable of the three masers with the largest relative amplitude having a value of 2.4. The flux densities for the different masing transitions are found to return to the same level during the low phase of the masers, suggesting that the source of the periodic flaring is situated outside the masing region, and that the physical conditions in the masing region are relatively stable. On the basis of the shape of the light curve we excluded stellar pulsations as the underlying mechanism for the periodicity. It is argued that a colliding wind binary can account for the observed periodicity and provide a mechanism to qualitatively explain periodicity in the seed photon flux and/or the pumping radiation field. It is also argued that the dust cooling time is too short to explain the decay time of about 100 days of the maser flare. A further analysis has shown that for the intervals from days 48 to 66 and from days 67 to 135 the decay of the maser light curve can be interpreted as due to the recombination of a thermal hydrogen plasma with densities of approximately 1.6× 10 6 cm 3 and 6.0× 10 5 cm 3 respectively.

Short-period variability in the Class II methanol maser source G12.89+0.49 (IRAS 18089-1732)

Time series are presented for the class II methanol maser source G12.89+0.49, which has been monitored for nine years at the Hartebeesthoek Radio Astronomy Observatory. The 12.2 and 6.7 GHz methanol masers were seen to exhibit rapid, correlated variations on timescales of less than a month. Daily monitoring has revealed that the variations have a periodic component with a period of 29.5 days. The period seems to be stable over the 110 cycles spanned by the time series. There are variations from cycle to cycle, with t he peak of the flare occurring anywhere within an eleven day window but the minima occur at the same phase of the cycle. Time delays of up to 5.7 days are seen between spectral features at 6.7 GHz and a delay of 1.1 day is seen between the dominant 12.2 GHz spectral feature and its 6.7 GHz counterpart.

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.

Very Long Baseline Array imaging of a periodic 12.2-GHz methanol maser flare in G9.62+0.20E

The class II methanol maser source G9.62+0.20E undergoes periodic flares at both 6.7 and 12.2 GHz. The flare starting in 2001 October was observed at seven epochs over three months using the Very Long Baseline Array (VLBA) at 12.2 GHz. High angular resolution images (beam size ∼1.7 × 0.6 mas) were obtained, enabling us to observe changes in 16 individual maser components. It was found that while existing maser spots increased in flux density, no new spots developed and no changes in morphology were observed. This rules out any mechanism which disturbs the masing region itself, implying that the flares are caused by a change in either the seed or pump photon levels. A time delay of one to two weeks was observed between groups of maser features. These delays can be explained by light travel time between maser groups. The regularity of the flares can possibly be explained by a binary system. Ke yw ords: masers ‐ stars: formation ‐ ISM: clouds ‐ H II regions ‐ radio lines: ISM.

Periodicity in Class II methanol masers in high-mass star-forming regions

We report the results of 10 years of monitoring of six regularly varying 6.7 GHz methanol masers using the Hartebeesthoek 26m telescope. Observations were done at intervals of 1--2 weeks, with faster sampling during flaring episodes. Four of the sources were also monitored at 12.2 GHz and show correlated variations. We find the Lomb-Scargle periodogram to be the most sensitive method to search for periodicity but possibly prone to false detections. Periods range from 132.8 days (with 26 cycles observed) to 509 days (with 7 cycles observed). Five of the sources show arguably periodic variations, while G331.13-0.24 shows strong periodicity in one peak, with large and variable delays in other peaks.

Newly discovered methanol masers associated with IRAS sources

Results are reported from a search for methanol maser emission in the 12.2-GHz 2(0)-3(-1) E transition toward a sample of newly discovered 1665-MHz OH masers associated with IRAS FIR sources. Six methanol maser sources associated with H II regions were detected with a success rate similar to previous surveys of star-formation regions. The association of CH3OH and OH masers is briefly discussed. A strong correlation between the radio and FIR flux densities appears to favor a radiative pumping mechanism for the CH3OH masers. 17 references.

New Periodic 6.7 GHz Class II Methanol Maser Associated with G358.460-0.391

Jabulani Maswanganye would like to express his gratitude for the bursaries from the National Astrophysics Space Science Programme, Hartebeesthoek Radio Astronomy Observatory, the North-West University doctoral scholarships and the South African SKA Project via the NRF.

Discovery of periodic class II methanol masers associated with G339.986−0.425 region

Ten new class II methanol masers from the 6.7-GHz Methanol Multibeam survey catalogues III and IV were selected for a monitoring programme at both 6.7 and 12.2 GHz with the 26m Hartebeesthoek Radio Astronomy Observatory (HartRAO) radio telescope for two years and nine months, from August 2012 to May 2015. In the sample, only masers associated with G339.986-0.425 were found to show periodic variability at both 6.7 and 12.2 GHz. The existence of periodic variation was tested with four independent methods. The analytical method gave the best estimation of the period, which was 246

How do methanol masers manage to appear in the youngest star vicinities and isolated molecular clumps

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