Promotionskolloquium
Sarwar Khan	SCHEDULED

MPIfR

High-mass stars (> 8 Msun) play a vital role in shaping galaxies and the interstellar medium (ISM) through their intense radiation, stellar winds, and eventual supernova explosions. Yet, key questions about how they form, influence their surroundings, and regulate future star formation remain open. Studying these stars is challenging as they are rare, short-lived, and form deep inside dusty, distant clouds. Statistical, unbiased surveys are therefore essential, and recent technological advances have made this possible. The first part of this talk presents a blind search for HII regions — ionized regions created by the intense ultraviolet radiation of high mass stars — conducted using radio recombination line and continuum emission from the GLObal view on STAR formation (GLOSTAR) survey. This analysis cataloged 244 Galactic HII regions and derived their physical properties and associations with mid infrared and dust emission to shed light on their evolution. To probe how high mass stars influence their natal environments, we investigated molecular gas properties as traced by H2CO (an important densitometer and thermometer) transitions. While the bulk of the H2CO emission arises from the background source, several targets exhibit multiple components. The secondary components typically showcase broader linewidth tracing higher temperatures, indicative of supersonic, nonthermal motions and turbulent gas probing HII region feedback. Together, these results attempt to provide a comprehensive view of high mass star formation, linking the properties of HII regions and their molecular environments across Galactic scales.

	Special Colloquium
Dr. Frederic Jaron	SCHEDULED

TU Vienna

The geodetic and astrometric application of VLBI is a powerful technique for the realization of global reference frames and the measurement of Earth orientation parameters. Source structure is one of the remaining unmodeled errors that prevent the technique from reaching its ultimate accuracy goals. We have developed a method to remove the influence of source structure from the output of the DiFX software correlator that fits into the common geodetic processing pipeline. In this talk I will present our approach and its application to observational data of the VLBI Global Observing System (VGOS). Improvement of closure group delays and post-fit residuals is obtained for selected sources when reliable image information is available.

	Main Colloquium
Dr. Jaroslav Haas	SCHEDULED

Charles University, Prague

The centre of our Galaxy hosts a supermassive black hole called Sgr A*. Its nature has been tested in various ways and is now considered proven beyond any reasonable doubt. The properties of the population of the less massive black holes in this region are, however, far less certain. In my talk, I will present a specific way to probe the distribution of the generally expected stellar-mass black holes in the innermost fraction of a parsec of the Galactic centre. For a much larger scale of a few hundred parsec around Sgr A*, I will then discuss an efficient novel formation channel for the provocatively elusive intermediate-mass black holes.

	Promotionskolloquium
Ivalu Barlach Christensen	SCHEDULED

MPIfR

The physical state of the interstellar medium (ISM) is essential for understanding the intricate processes involved in massive star formation within galaxies. The nearby (d about 1.5 kpc) molecular cloud, Cygnus-X, harbors multiples sites of high-mass star-formation, allowing us to probe the various stages as stars form and how the chemistry evolve. Within the Cygnus Allscale Survey of Chemistry and Dynamical Environments (CASCADE), we aim to explore the large-scale distribution of deuterated molecules in Cygnus-X. A plethora of star-forming clumps are observed with the CASCADE survey, where clumps are believed to evolve from quiescent infrared-dark clouds to high-mass protostellar objects to hot molecular cores to ultra-compact HII regions. The most active and dense region within Cygnus-X is the DR21 filament, harboring the prominent Hii region DR21 Main with the most intense outflow of the Milky Way. The degree of deuteration, R, can significantly enhance over the elemental D/H-ratio (10^−) depending on physical parameters such as temperature, density, and ionization fraction. Deuterated molecules and their molecular D/H-ratios are important diagnostic tools to study the physical conditions of star-forming regions. This thesis focuses on probing the deuterated fractions of Cygnus-X. Along the DR21 filament, the deuterated fraction of DCO+, DNC, and DCN exhibit morphological variations, caused by the local physical conditions. Active star-formation along the filamentary structure initiate shock chemistry in these high density region, destroying DCO+, and consequently decreasing R(DCO+). Furthermore, the lower density regions are exposed to FUV, in which the formation of HCO+ is halted, consequently increasing the R(DCO+). Finally, to further understand how deuterated fractions behave as clumps evolve, we investigate 67 clumps. Utilizing CASCADE observation of the ubiquitous H2CO complemented with higher J-transitions with the APEX telescope, we determine the physical conditions of 67 clumps in Cygnus-X. The methodology of determining the H2 volume density is efficient in probing the bulk of the gas within 0.2 pc of the clumps. With the physical conditions constrained, we model the chemical evolution of these clumps utilizing the plethora of molecules covered with CASCADE, including the 6 deuterated fractions. We find that the two deuterated fractions decrease and increase, respectively, as the clumps evolve and become hotter.

	Special Colloquium
Prof. Tom Megeath	SCHEDULED

University of Toledo, Ohio

TBD