@invited talk in Vienna:
 
”What can interferometry tell us about an AGB star ?” (flash version)
(March 14th, 2011, Observatory of Vienna)

Abstract: Asymptotic Giant Branch (AGB) stars are the main distributors of dust into the interstellar medium. The wind of these stars is driven by strong stellar pulsation in combination with radiation pressure on dust. High-resolution mid-IR interferometry is sensitive to the structure of the stellar atmosphere and the properties of the dust shell.
I will give a short introduction to AGB stars and the interferometric measurement principle, and will present the results obtained for four oxygen-rich AGB stars observed over the course of more than two years. The measured angular diameters in the mid-IR of these stars appear to be about two times larger than their photospheric diameters. The overall larger diameter originates from a warm molecular layer of water, and a detected gradual increase throughout the mid-IR can be attributed to a contribution of a spatially resolved close aluminia dust shell. It was also found that the observed angular diameters are smaller at visual minimum than at visual maximum, leading to the speculation that more dust forms at visual minimum.

   download (english, 4.7 MB, pdf)
 

@LSW Group meeting:
 
”Cosmic Dust, Planet Formation & AGB Stars” (flash version)
(November 13th, 2009, Heidelberg)

Abstract: I give an overview on cosmic dust properties and a short introduction why dust plays a role in planet formation. In the second part, the dust production in AGB stars is explained in more detail and my work with the AGB star W Hya is described.

   download (english, 2.0 MB, pdf)
 

@LSW Monday meeting and @IMPRS retreat:
 
”What can interferometry tell us about an AGB star ?” (flash version)
(March 11th and March 16th, 2009, LSW Heidelberg and Retreat at Black Forest)

Abstract: We observed the dusty circumstellar environments of Asymptotic Giant Branch (AGB) stars with MIDI, a MID-Infrared (~10 μm) interferometer with a spectral resolution between 30 and 230. In principle, such observations will allow us to fit for the stellar diameter and structure of the dense stellar winds, in particular the location of the dust formation layer and its dependence on pulsation cycle, mass loss rate, and chemistry.

I give a short introduction to interferometry, the meaning of visibilities, and the data-reduction process. I then fit our V Hya data to a preliminary model, composed of a uniform disk and circular ring. Thus far, these data are insufficient to study the dependence on pulsation phase or model an asymmetric dust shell but give very reasonable results for the size of the dust layer. With upcoming model improvements and new data this will lead to a better understanding of the late stage of evolved stars.

   download (english, 3.4 MB, pdf)
 

@LSW Monday meeting and @IMPRS research seminar:
 
”Simulations of Imperfect PRIMA
Fringe-Sensing Units and Calibration Strategies” (flash version)
(January 1st and April 10th, 2008, Heidelberg)

Abstract: I give a brief introduction about the PRIMA interferometer and its related planet search program ESPRI. In the second part I show our error simulations for the Fringe-Sensing Units (FSUs) and its possible calibration strategies.

   download (english, 1.6 MB, pdf)
 

@IMPRS literature seminar:
 
”Tidal Streams in the Milky Way System” (flash version)
(January 31st, 2008, IMPRS, Heidelberg)

Abstract: I give a brief introduction to SDSS survey. In the main part I present some results from recently observed tidal streams in our Milky Way, especially from the Sagittarius and Orphan stream.

   download (english, 4.1 MB, pdf)