Principal investigator / group head
Project C1 of the SFB 956: Conditions and Impact of Star Formation - Astrophysics, Instrumentation and Laboratory Research collects the theoretical and modelling efforts to understand the radiative impact from young stars on their environment. We develop a model for the surfaces of molecular clouds affected by UV radiation from young stars, so-called photon-dominated regions. It will allow to interpret the far-infrared observations of star-forming regions and determine the role of radiative triggering of star-formation.
The DFG-funded project is integrated in the Priority program 1573 "Physics of the Interstellar Medium" in collaboration with partners in Munich, Heidelberg, Bonn, and other universities. We systematically compare statistical properties of large scale mapping observations of ISM clouds in the different tracers with simulated observations based on turbulence models. The focus is on the observational bias introduced by limitations of any measured data set and the phase transition from atomic to molecular gas at cloud boundaries and other chemical transitions.
In the Herschel key project we performed FIR spectroscopy of the "Warm And Dense ISM" to improve our understanding of the physical and chemical processes controlling the interaction between stars and their environment. The program covered 136h of Herschel time and the results are still analysed by a large international consortium of more than 30 members. Observational results have been published in a number of papers.
The Herschel Guaranteed Time program and subsequent SOFIA/GREAT observations study the chemical fractionation in photon-dominated regions through the reaction 13C+ + CO → 13CO + C+. By accurately measuring the abundance of 13C isotopologues, we try to confirm the predicted fractionation structure in PDRs. Observations of 13C+ rather allowed to measure optical depths of the main idotope line. Best results for fractionation are obteined from 13CH.
The Herschel guaranteed time program "Herschel/HIFI Observations of EXtraOrdinary Sources: The Orion and Sagittarrius B2 Starforming Regions" devotes 60h observing time to the Orion Bar, the most prominent nearby photon-dominated region. I am active in the coordination of the data analysis, the interpretation of the data, and the modelling of this source.
My program to simulate the line radiative transfer in molecular clouds has been presented in detail in Ossenkopf, Trojan & Stutzki (2001). It is currently extended by Meltem Akyilmaz and Thomas Möller to include the effects of infrared continuum pumping through interstellar dust and the modelling of a full spectral-energy distribution from line and continuum emission.
We are minor partners in the planned 25m submm telescope at the Cerro Chajnantor at an altitude of 5600m. Currently, I am working in the science definition group for ISM studies and in the software development group covering the topics of quality assurance, observing modes, testing, and instrument interfaces.
In the ASTRONET FP7 project a "Coherent set of Astrophysical Tools for Spectroscopy" we developed the automatic fitter tool MAGIX for spectroscopic observations. Current activities cover the determination of optimized functions of merit for different problems.
Principal investigator / group head
The project was funded through the DFG from 2008 to 2011. We analysed new observations of photon-dominated regions (PDRs) and improved the KOSMA-tau model for the physics and chemistry of PDRs to investigate the physical and chemical processes in these regions. The results have been pulished in 9 papers. They are summarized in the report to the DFG.
The instrument control center for the HIFI instrument onboard Herschel has a distributed structure with the central node at SRON Groningen and several national sub-nodes. The German HIFI ICC node, located at the I. Physics Institute, is responsible for supporting the German HIFI user community, a set of instrument calibration activities, and the continuous monitoring of the instrument hardware delivered by German institutes, in particular the band 2 mixer, the local oscillator subsystem, and the wide-band spectrometer.
I developed all the astronomical observing modes for HIFI that are used in regular astronomical observations. Their design combines techniques well tested at ground-based radio observatories with a new timing approach based on the drift performance of the instrument. This maximizes the observing efficiency based on the scientific goals of the users defined through the HSPOT frontend. The observing modes are continuously updated, improved and debugged. In February 2012, mission configuration #100 in the lifetime of Herschel was delivered.
The Herschel Open Time Priority 1 program tried to resolve the chemical evolution of oxygen hydrides in radiatively heated dense clouds. By studying the abundances of OH+, H2O+, H3O+, OH, and H2O we want to determine the amount of H2O+ that is produced in those clouds by ice evaporation and subsequent ionization of the material like in comets. The results entered the systematic study of Nich Indiolo.
SOFIA observations of photon-dominated regions
In the science demonstration phase of the GREAT instrument I submitted two successful proposals dedicated to the mapping of CII and high-J CO in two PDRs. The results of the guaranteed time observations of M17SW have been published by Perez-Beaupuits et al. (2012), those from the open time observations of Cep B by Mookerjea et al. (2012).
Theory of line transfer
When systematically studying the usual approximations in line radiative transfer, I found that several of those are hardly justified. Therefore, I developed some extensions for the concept of complete redistribution and the large velocity gradient approximation in regions with inhomogeneous densities and postulated criteria for the applicability of the standard approximations.
Within the survey, introduced by Plume, Fuller, et al. (2007) we performed spectral mapping of 5 bright sources in the 345GHz band at the James Clark Maxwell Telescope on Mauna Kea. I was deeply involved in the analysis of the observations of the Orion Bar published by van der Wiel et al. (2009).
During the years at SRON Groningen I was involved in the tests of the HIFI hardware at instrument level, in integration and in thermal vacuum at ESTEC. The focus of my studies was on the instrument stability. For the data analysis a large set of HIFI user scripts have been written that became part of the official Herschel Common Software System.MPG Research Group "Dust in Star-Forming Regions" in Jena, I dealt with the evolution and optical properties of interstellar dust in molecular clouds and I am still open to all questions regarding these topics. This includes the optical constants of the involved materials, the scattering bevaviour of irregular particles, and the dynamics and coagulation of dust particles.
Created: Dr. V. Ossenkopf|
Last change: 4/12/2012