University Of Tasmania
Krishnan_whole_thesis.pdf (3.94 MB)

6.7 GHz maser astrometry with the Australian long baseline array

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posted on 2023-05-27, 11:42 authored by Krishnan, V
Astrometry is the science of measuring the positions of astronomical objects in the sky, and as such forms a practical bedrock for astrophysics in general. This is because it is only when a source's position is unambiguously known, can it be observed while it transits across the sky or be detected at different wavelengths. One of the first discoveries as a result of astrometry was in differentiating between the planets in our Solar System and the stars in the Milky Way. Early astronomers would have noted the arcminute/day rate of proper motion of the nearby planets with respect to the distant celestial objects fixed in the sky with the passage of time. With the advancement of telescopes the arcsecond/year proper motions for the fastest moving nearby stars was resolved as well. In comparing comets or asteroid size objects of a few kilometres, to galaxies spanning hundreds of thousands of light-years, it becomes apparent that the absolute size of astronomical objects extends across dimensions spanning many orders of magnitude. Despite this, the distances to these objects render many of them regardless of size to be minuscule pinpoints, when viewed from the Earth. The accuracy with which an object's position can be known is governed by the diffraction limit ˜í‚àèd ‚Äöv¢v† ˜í¬™/D of the observing system and improvements in astrometric resolution have led to astronomical discoveries including Earth's precession, stellar aberration, atmospheric refraction, particle jets from black holes, the rate of expansion of planetary nebulae, detailed structure of circumstellar disks and out outflows from protostars, high-energy jets from quasars and the orbits of exoplanets around distant stars. The focus of this thesis is on the impact of accurate astrometry to measure trigonometric stellar parallaxes (from now on parallax) towards masers in high-mass star formation regions (HMSFRs) in the Milky Way galaxy using the Australian Long Baseline Array (LBA).


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Copyright 2016 the Author Chapter 3 appears to be the equivalent of a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly notices of the Royal Astronomical Society following peer review. The version of record: V. Krishnan, S. P. Ellingsen, M. A. Voronkov, S. L. Breen , 2013, The first high-resolution observations of 19.9-GHz methanol masers, MNRAS, 433, 3346-3363 is available online at doi:10.1093/mnras/stt1017 Chapter 7 appears to be the equivalent of a post-print version of an article published as: Krishnan, V. et al. 2015. First parallax measurements towards a 6.7 GHz methanol maser with the Australian long baseline array - distance to G339.884-1.259, Astrophysical journal, 805(2), 1-12

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