Kraus, Michaela: Modeling of the Near Infrared Emission From the Peculiar B[e]-Star MWC349. - Bonn, 2000. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
Online-Ausgabe in bonndoc:
author = {{Michaela Kraus}},
title = {Modeling of the Near Infrared Emission From the Peculiar B[e]-Star MWC349},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2000,
note = {The aim of this thesis is to investigate the first overtone band emission of CO from the peculiar B[e] star MWC 349. With the United Kingdom Infrared Telescope (UKIRT) in Hawaii, low resolution observations were made to determine the overall shape of the total band emission, and high resolution observations covering the (2->0) and (3->1) band heads to derive the velocity and optical depth of the CO gas.
Apart from the underlying continuum the observed spectra also show the existence of several hydrogen recombination lines contaminating the CO band spectrum. These contributions have to be discussed first to determine their influence on the total spectrum. Consequently, the thesis consists of three parts: The modeling of the continuum emission, the investigation of the Pfund line emission, and the discussion of the CO gas emitting the first overtone bands.
The continuum emission consists of several contributions. The radio range is dominated by free--free emission and the visible/ultraviolet part by free--bound emission, both occuring within the ionized wind zone. For the calculations, a wind model is discussed that allows the determination of several parameters like the electron temperature and radial distribution, and an estimate of the dimensions of the ionized stellar wind.
The infrared excess emission, on the other hand, is caused by circumstellar dust. The dust is arranged in a nearly edge--on circumstellar disk, and the contribution of this disk to the total continuum emission spectrum is modeled. The shape and strength of the disk spectrum strongly depends on the temperature and surface density distributions, the disk size and the inclination angle.
In the second part the contamination by the Pfund lines which arise in the ionized wind is discussed. Following Menzel's case B recombination theory, the emission is assumed to be optically thin. It is shown that the level population of the recombining hydrogen atoms are in local thermodynamical equilibrium. The model parameters that give the best fit agree with those found from the modeling of the continuum emission from the ionized wind.
The remaining part of the thesis deals with the hot CO gas. CO band emission is found in several young stellar objects, high--luminosity stars, and supergiants, all of them having large amounts of dust, especially in conjunction with a circumstellar disk. The (2->0) band head which contains all the velocity information of the CO gas, has already been found to be a good tracer of the inner edge of circumstellar disks. Since the existence of a circumstellar disk around MWC 349 is quite sure, it seems to be the natural location of the CO gas.
Detailed calculations of different model scenarios are performed to locate the CO band emitting gas in the environment of MWC 349, because the (2->0) band head shows no clear indication of pure rotational broadening. The most favoured scenario for the CO gas being located at the inner edge of the gas and dust disk proposes the existence of a disk bulge which absorbs radiation coming from the near part of the inner edge. The observer therefore only detects emission from a sector on the far side having a rather small radial velocity. Such a scenario opens prospects for future observations and more detailed model calculations.},

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