H2O MASER OBSERVATIONS IN G354.61+0.47 WITH KAVA

• Main Author: Hafieduddin, Mohammad
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/63008
• Institution: Institut Teknologi Bandung

Massive stars have significant impact both in the local and cosmological scale. In this thesis, massive stars are defined as those that will end as type-II supernova (greater than 8M!). According to classic star-formation models, this class of star could not be formed because the strong radiative pressure exerted by these stars would blow away accreting gases. Alternative models had been proposed to bypass this problem. There are core accretion model, competitive accretion model and merger/collison model. Unfortunately, observational data needed to ascertain the correctness of a massive-star formation model are lacking because the rarity of massive stars and the high level of extinction from gases and dust that envelope their formation processes. The advance of radio interferometry techniques, especially VLBI (Very Long Baseline Interferometry), helps to overcome these issues by providing us the capability to observe structure tracers with high angular resolution. In this thesis, we use combination of data taken by KaVA (KVN and VERA Array, which consisted of KVN (Korean VLBI Network) and VERA (VLBI Exploration for Radio Astrometry)), EAVN (East Asian VLBI Network) and ALMA (Atacama Large Millimeter/submillimeter Array) to probe the structure of a massive star-formation region G354.61+0.47. The main objective of this thesis is to map the distribution and proper motion of the 22 GHz H2O masers in G354.61+0.47 from KaVa data and compare them with observational results obtained previously. We will focus on the 6.7 GHz CH3OH methanol maser data taken with EAVN and both CO and C17O transition spectra data taken with ALMA. Calibration and imaging procedures of the data were done using AIPS and CASA software packages. We found that the maser distributions fit nicely in ALMA continuum map and CO(J=3- 2) line integrated emission map. Comparison to these two lend some credence to the hypothesis that the H2O maser distribution traces combination of infall and outflow structure in G354.61 and CH3OH maser distribution is related to circumstellar disk in this object.