Many stars are surrounded by gaseous and dusty disk. The gaseous disk regions often display forbidden emission lines and produce measurable amounts of molecular emission, e.g., in CO. The dust parts cause on the one hand strong continuum emission noticeable via an infrared excess, but also spectral features corresponding to vibrational transitions in small dust particles.

Our investigations aim at finding tracers for all disk regions. Hence, we study the circumstellar disks over the complete wavelength range, extending from the optical to the infrared. The optical range hosts several forbidden emission lines that were identified as valuable tracers for the innermost disk regions, i.e., close to the star. For the molecular disk regions, we studied so far the CO band emission in great detail, in order to constrain the disk parameters such as density and temperature, but also to derive proper kinematical information (Keplerian rotation versus outflow).

We study the disks of evolved massive stars using both observations in different wavelength regions, but we also developed our theoretical models and numerical codes. Below is a selection of our results on

Ionized and neutral atomic disk region

We found that several sets of optical forbidden emission lines can be used as valuable tracers for the structure and the kinematics of the innermost disk regions. These are the lines of [OI] and [CaII].

[OI] - Kraus, Borges Fernandes & de Araújo, 2007, A&A 463, 627 & Kraus, Borges Fernandes & de Araújo, 2010, A&A 517, A30

[CaII] - Aret, Kraus, Muratore, Borges Fernandes, 2012, MNRAS, 423, 284

Molecular disk region

A description of the code developed to model CO band emission from disks and winds is described in the following publication:

CO band emission from MWC 349 - Kraus, Krügel, Thum, & Geballe, 2000, A&A, 362, 158

Applications to the molecular disks of evolved massive stars can be found in a variety of publications, e.g.,

CPD-52 9243 - Cidale, Borges Fernandes, Andruchow, Arias, Kraus, Chesneau, Kanaan, Curé, de Wit, & Muratore, 2012, A&A, 548, A72

GG Car - Kraus, Oksala, Nickeler, Muratore, Borges Fernandes, Aret, Cidale, de Wit, 2013, A&A, 549, A28

The CO bands are also found to be ideal age indicators

The 13Carbon footprint of B[e] supergiants - Kraus, 2009, A&A, 494, 253 & Liermann, Kraus, Schnurr, & Borges Fernandes, 2010, MNRAS, 408, L6

Dusty disks

Detailed descriptions of the radiative transfer codes developed and used to study the structure of the dusty disks is described in the following two publications:

SEDs of flared dust disks - Kraus, 2003, in Open Issues in Local Star Formation, p. 279

The dusty disk of CD-42 11721 - Borges Fernandes, Kraus, Lorenz Martins, & de Araújo, 2007, MNRAS, 377, 1343