Universität zu Köln

Roellig, M. and Ossenkopf-Okada, V (2022). The KOSMA-tau PDR model I. Recent updates to the numerical model of photo-dissociated regions. Astron. Astrophys., 664. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

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Abstract

Numerical models of photodissociation regions (PDRs) are an essential tool to quantitatively understand observations of massive star forming regions through simulations. Few mature PDR models are available and the Cologne KOSMA-tau PDR model is the only sophisticated model that uses a spherical cloud geometry, thereby allowing us to simulate clumpy PDRs. We present the current status of the code as a reference for modelers and for observers that plan to apply KOSMA-tau to interpret their data. For the numerical solution of the chemical problem, we present a superior Newton-Raphson stepping algorithm and discuss strategies to numerically stabilize the problem and speed up the iterations. The chemistry in KOSMA-tau is upgraded to include the full surface chemistry in an up-to-date formulation and we discuss a novel computation of branching ratios in chemical desorption reactions. The high dust temperature in PDRs leads to a selective freeze-out of oxygen-bearing ice species due to their higher condensation temperatures and we study changes in the ice mantle structures depending on the PDR parameters, in particular the impinging ultraviolet field. Selective freeze-out can produce enhanced C abundances and higher gas temperatures, resulting in a fine-structure line emission of atomic carbon [C i] enhanced by up to 50% if surface reactions are considered. We show how recent Atacama Large Millimeter Array (ALMA) observations of HCO+ emission in the Orion Bar with high spatial resolution on the scale of individual clumps can be interpreted in the context of nonstationary, clumpy PDR ensembles. Additionally, we introduce WL-PDR, a simple plane-parallel PDR model written in Mathematica to act as a numerical testing environment of PDR modeling aspects.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Roellig, M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Ossenkopf-Okada, V UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-660730
DOI:	10.1051/0004-6361/202141854
Journal or Publication Title:	Astron. Astrophys.
Volume:	664
Date:	2022
Publisher:	EDP SCIENCES S A
Place of Publication:	LES ULIS CEDEX A
ISSN:	1432-0746
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language STAR-FORMING REGIONS; FINE-STRUCTURE EXCITATION; TO-MOLECULAR TRANSITION; GAS-GRAIN CHEMISTRY; C-II EMISSION; NONEQUILIBRIUM PHOTODISSOCIATION REGIONS; SPONTANEOUS RADIATIVE DISSOCIATION; VIBRATIONALLY EXCITED H-2; DENSE INTERSTELLAR CLOUDS; MU-M EMISSION Multiple languages Astronomy & Astrophysics Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/66073