The variability of cosmic methanol masers in massive star forming regions.
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Date
2013-02-01
Authors
Maswanganye, Jabulani Paul
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Abstract
In this thesis, the background and technical theory of the receivers are discussed.
Methods used to search for periods, correlations, and delays in the time series of class
II methanol masers at 6668 MHz and 12178 MHz are presented together with the
observed variability of these sources. Background theory is given on, the processes
by which massive stars are formed. The theory of astronomical masers and methanol
maser excitation is given in detail.
The receiver testing and observation technique chapters describe: the results
and methods used to calibrate the two receivers, namely 2.5-cm and 4.5-cm, with
central frequencies of 6668 MHz and 12178 MHz respectively, as well as data cap-
ture methods for spectroscopic observations. The laboratory square law detector
or radiometer was also calibrated to ensure that the noise diode temperature was
accurately determined. There is 8.3 per cent deviation from an ideal square law
detector.
The time series and spectra for one methanol source, G351.42+0.64 which serves
as a control source at 6668 MHz and 12178 MHz, one irregularly varying methanol
source G351.78-0.54 at 6668 MHz, seven known quasi-periodic and periodic sources
(G9.62+0.20E, G12.89+0.49, G188.95+0.89 and G328.24-0.55, at both 6668 MHz
and 12178 MHz, and G331.13-0.24, G338.93-0.06, and G339.62-0.12, at 6668 MHz),
and seven new methanol maser source regions (G0.092+0.663, G6.189-0.358, G8.832-
0.028, G8.872-0.493, G348.617-1.162, G351.688+0.171 and G358.460-0.391, at both
6668 MHz and 12178 MHz) are shown and discussed. The seven new sources were
from the 6668-MHz Methanol Multi-Beam (MMB) survey Catalogues I and II. Periods were searched for using the Lomb-Scargle and epoch-folding methods. The
quasi-periodic and periodic sources show diverse waveforms and diverse periods be-
tween 29 and 511 days. From the seven new methanol maser sources, G8.872-0.493
(76 day period) and G358.460-0.391 (187 day period) both at 6668 MHz, were found
to be variable and they are possible new candidates for the periodic or quasi-periodic
group of sources.
The Colliding Wind Binary (CWB) model is proposed by van der Walt (2011)
as the source of the observed periodic variability in these regions. The properties
of the binary systems using the 29 and 511 day period are discussed as well as the
common features in the time series, such as long-term variations and flares. The
source of the periodicities has not been finally determined but the foundation has
been laid.