Thesis projects in high-mass star formation
Max-Planck-Institute for Astronomy (MPIA), Heidelberg/Germany
Attention: Dr. Henrik Beuther

This group studies the early evolutionary phases of high-mass star formation using state of the art (sub)millimeter wavelength interferometers as well as ground- and space-based single-dish instrunments. Massive star formation is one of the most lively evolving parts of star formation research where many exiting questions remain to be tackled. One of the main underlying question in massive star formation is whether the most massive stars form via similar physical processes like their low-mass counterparts, or whether completely different processes, for example, the coalescence and merging of intermediate-mass protostars, are important as well. The availability of (Sub)Millimeter Interferometers - already existing instruments as well as future arrays (e.g., PdBI, SMA, CARMA, ALMA) - now allows to resolve the innermost regions of massive star-forming regions and thus study the physical processes in detail.

Ongoing PhD thesis projects:

Massive star formation on Galactic scales (Jochen Tackenberg, start October 2009)
Often studies of (massive) star formation are biased by initial sample selection criteria. However, to get a general understanding of the early evolution of young massive stars, it is important to overcome any selection bias and to study all different evolutionary stages in a statistical sense. The advent of Galactic plane surveys from near-/mid-/far-infrared wavelengths to the mm regime now allows for the first time such unbiased studies of massive star-forming regions on Galactic scales. This PhD project will start with the data from the submm wavelengths Galactic plane survey ATLASGAL (conducted with the APEX telescope in Chile) and cross-correlate a relative large fraction of the sky with the complementary mid- to far-infrared surveys avalaible from the Spitzer Space Telescope surveys GLIMPSE and MIPSGAL. These data will allow to disentangle the different evolutionary stages and hence tackle many different questions, for example it will constrain the relative time-scales during the evolution of massive stars. Follow-up steps of this project will include interefrometric case-studies of individual sources as well as analyzing complementary data from the Herschel satellite.

Mapping the chemistry of the interstellar medium (Thomas Gerner, start April 2011)
The thesis project will start at large spatial scales and investigate a sample of molecular cloud complexes at different evolutionary stages in a few selected molecular species. Part of the data are already gathered prior to the thesis, and the student can straightaway dive into the data reduction and analysis. On top of that, he/she will write additional proposals to enhance the large-scale sample (2-3 more sources) with APEX, the IRAM 30m telescope and Mopra, as well as to observe dedicated sub-regions in additional spectral setups. Based on the derived results, he/she will select a few specific targets and investigate the small-scale properties with interferometers. While outcomes like the ionization fraction can be used as input parameters for theoretical models, measured abundances can be directly compared with the modeling result conducted by another student in parallel. Furthermore, the resulting spatial and kinematic information will be related to the models via the radiative transfer modeling. On top of that, we will conduct broader chemical studies of massive star-forming regions at different evolutionary stages. While the results from that study will directly constrain the changing chemical properties throughout the evolution, they again can be set into context with the modeling results from the theoretical student.

Chemical sub-structure of high-mass star-forming regions (Siyi Feng, start September 2011)
How do the chemical properties vary within high-mass star-forming regions? The birth sites of massive stars are highly complex structures consisting of several individual gas and dust cores embedded in a less dense gas clump envelope. Furthermore, substructures like outflows and disks exist, and especially the outflows trigger shocks that can change the chemical properties of parts of the regions. Most previous chemical studies rather dealt with integrated properties from single-dish surveys, however, to disentangle the small-scale structure, interferometric observations at high-spatial-resolution will be essential. Therefore, the student will analyze and interprete interferometric observations of young high-mass star-forming regions, and set the results into context of chemical models. The observational data come from existing instruments like the SMA and PdBI, but also from the forthcoming next generation array ALMA. Furthermore, the student will likely also work with radiative transfer tools to properly model the data.

Associated thesis project:

Theorectical investigations of accretion disks and outflows/jets in high-mass star formation (Bhargav Vaidya, co-supervised with Christian Fendt)

Clustered high-mass star formation (Yuan Wang, exchange student from Nanjing University, China)

Upcoming PhD thesis projects:


Finished PhD thesis projects:

Fragmentation of massive star-forming clusters (Javier Rodon, July 2006 - November 2009)
The Initial Mass Function (IMF), i.e., the universal mass distribution of cluster stars and field stars, is one of the fundamental observational properties of almost all observed stellar distributions. However, until today it is not clear why the IMF is universal and at what time of the stellar cluster evolution the IMF forms. Since almost all massive stars form in a clustered mode, massive star-forming regions are the ideal environment to study the early evolution of the IMF. Furthermore, the two main theories of massive star formation - disk accretion and early fragmentation of the massive gas cores versus the coalescence and merging model - predict different shapes of the protocluster mass functions at early evolutionary stages. To resolve the dense gas and dust of the deeply embedded very young massive star-forming clusters, high-spatial resolution in the (sub)mm wavelength regime is necessary, thus requiring again (sub)mm interferometric observations. The thesis candidate is expected to observe various young massive star-forming regions in different evolutionary stages. The analysis of a statistically significant sample should allow to derive protocluster mass functions of the different regions and thus constrain whether the IMF is determined at the very beginning of massive star formation or whether  different processes during the cluster formation process contribute to the shape of the IMF. To solve the formation history of such an important universal characteristic like the IMF will be an exciting overal goal of this project.

Disks in massive star formation (Cassie Fallscheer, August 2006 - May 2010)
The last few years have accumulated large amounts of indirect evidence that at least early B and late O stars (up to probably 20Msun) form via similar disk-accretion proecesses like their low-mass counterparts. However, all these studies were rather indirect, and the time is ripe to investigate the underlying expected accretion disks in more detail. The advent of the above mentioned (sub)mm intereferometers now allows for the first time to resolve the dense gas and dust around the central massive protostars, and hence carefully tackle these questions investigating the small-scale structure of the massive star-forming regions. Furthermore, even the most massive stars (up to 100Msun) may harbor massive disks, but their physics could be very different to their low-mass counterparts changing the actual accretion processes. This thesis project is expected to observe a sample of massive disk candidates, and investigate the physical properties and the evolution of these objects. A potential evolutionary sequence as well as expetected differences between disks around objects of different masses are possible exciting perspectives of this project. The understanding of massive accretion disks is often considered as the missing link in the understanding of massive star formation.

Diploma/Master thesis projects:

Kinematics, temperature and turbulence of IRDCs (Simon Bihr, start July 2011)

Bachelor thesis projects:

Characterization of Infrared Dark Clouds (Roxana Chira, March to July 2011)