Akademik Veri Yönetim Sistemi
Tezin Türü: Yüksek Lisans
Tezin Yürütüldüğü Kurum: Universiteit Leiden, Faculty of Science, Leiden Observatory, Hollanda
Tezin Onay Tarihi: 2012
Tezin Dili: İngilizce
Öğrenci: Jaya Ramchandani
Asıl Danışman (Eş Danışmanlı Tezler İçin): Ewine Van Dishoeck
Eş Danışman: Umut Yıldız
Açık Arşiv Koleksiyonu: AVESİS Açık Erişim Koleksiyonu
Özet:
To further star and planetary formation studies, it is important to trace the physical and chemical evolution of gas and dust in star forming regions. This thesis introduces the LOMASS database, a public web-based archive of single-dish submillimetre spectra of molecules observed in young stellar objects by the astrochemistry group at Sterrewacht Leiden. The database will host observations from the James Clerk Maxwell Telescope and the Atacama Pathfinder EXperiment telescope for 22 molecules across 30 low-mass protostar sources. The immediate scientific benefit of LOMASS is public access to a large collection of line observations to compare and evaluate star formation models. LOMASS is currently populated with HCO+ (4−3) transition data. Using the HCO+ (4−3) data from LOMASS, this thesis analyses the central spectra of sources at different evolutionary stages (12 Class 0 and 13 Class I sources), and compares the results with those obtained for an optically thicker H2O (110−101) line for the same sources. Water is a key tracer of dynamics and chemistry in low-mass star-forming regions, especially outflows and jets, and HCO+ is a known tracer for envelope and protostellar collapse. The aim of the comparison is to investigate whether HCO+ traces the same trends as observed for H2O. A narrow emission of HCO+ is observed in the 25 sources under comparison, while water is dominated by profiles with broad and medium emissions. Both molecules show inverse and regular P-Cygni profiles, indicative of infalling and expanding envelopes, respectively. The behaviour of HCO+ follows that of water in terms of its presence in the quiescent envelope, absorption layer, and infalling envelope for both Class 0 and Class I sources. For water, the peak temperature , line width vmax, and integrated intensity ∫TMB dv all decrease from Class 0 to I, while for HCO+, similar values are found for , a slight decrease in vmax and an increase in ∫TMB dv is found. The error margins need to be taken into consideration for a more detailed analysis. Both H2O but HCO+ are present and excited in the outflow cavity wall where expansion occurs and in the infalling envelope. Expansion is detected in more Class I than Class 0 sources for both H2O but HCO+ and infall is detected in more Class 0 than Class I sources for both H2O but HCO+. To form a complete picture of the role of water and other molecules in star formation, further studies are required with a larger sample size of molecular profiles. The LOMASS database is expected to serve as a useful means to this end.