Rotational Excitation of Interstellar OCS: Non-LTE Line Analysis and Temperature–Density Diagnostics Using RADEX

Novák, Zalán (2025) Rotational Excitation of Interstellar OCS: Non-LTE Line Analysis and Temperature–Density Diagnostics Using RADEX. Bachelor's Thesis, Astronomy.

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Abstract

In this study, the potential of the OCS molecule was investigated as a tracer of temperature and density in different astrophysical environments through modeling of its rotational line emission using the non-LTE radiative transfer code RADEX. The work included analysis of modeled line intensities, diagnostics based on previous observations, and the development of a future observing proposal targeting the L1157 nebula. For the observations, the IRAM 30m telescope is proposed with an estimated total telescope time of 16 hours, and it aims to further test OCS as an environmental condition tracer in shocked molecular regions. The results suggest that rotational transitions of OCS can be used to constrain the kinetic temperature and density in molecular clouds, star-forming regions, and the Galactic Center, and may also serve as a temperature probe in protoplanetary disks. At temperatures and densities higher than ∼ 100 K and ∼ 106 cm−3 , the applicability of OCS is limited due to the lack of collisional rate coefficients and line transitions exceeding critical densities. Nevertheless, OCS remains a promising candidate for constraining environmental properties and could provide further insight into the conditions of the interstellar medium due to its unique property of having significantly closer rotational energy levels than other interstellar molecules. To draw more rigorous conclusions about OCS line diagnostics, additional observations across a broader range of environments are encouraged. Future studies would also benefit from using advanced radiative transfer codes like ProDiMo or LIME, which can account for three-dimensional structures, as well as temperature and density gradients in the complex molecular regions where OCS emission is modeled.

Item Type:	Thesis (Bachelor's Thesis)
Supervisor name:	Tak, F.F.S. van der
Degree programme:	Astronomy
Thesis type:	Bachelor's Thesis
Language:	English
Date Deposited:	11 Jul 2025 13:33
Last Modified:	25 Sep 2025 14:25
URI:	https://fse.studenttheses.ub.rug.nl/id/eprint/35794

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