The SFB 1601 organises frequent scientific colloquia. Guests are Welcome!

Venue:

(a) University of Cologne, Physics Institutes (Zülpicher Str. 77), Lecture Hall III, 3:00 pm
The colloquia will start off with a coffee/tea reception at 02:45 pm in front of the lecture hall.

(b) University of Bonn, Argelander Institute for Astronomy (Auf dem Hügel 71), AIfA Lecture Hall

Previous Colloquia


April 8, 2024
Olivier Berné
CNRS senior scientist, IRAP Research Institute in Astrophysics and Planetology, Toulouse, France
Illuminating planet formation: the role of ultraviolet radiation from massive stars in the physics and chemistry

Abstract

The formation and evolution of (exo-)planets stands as a central question in astronomy, particuarly in the context of the JWST mission. The earliest stages of these processes take place in protoplanetary disks of gas and dust around young stars. It has become clear that most of these disks originate within stellar clusters, subjecting them  to intense ultraviolet (UV) radiation from the most massive members of these clusters. Despite its relevance to planet formation theories (our proto-Solar System disk formed in a cluster) very little is known about the role of this external UV radiation in the formation, evolution, and chemical composition of embryonic planetary systems. The unprecedented capabilities of JWST coupled with models relying on laboratory and theoretical spectroscopy now enables us to characterize protoplanetary disks irradiated by UV from the cluster uniquely. In this presentation, I will describe recent advancements in the field, illustrating how UV photons can disrupt the gas within protoplanetary disks, potentially impeding the formation of giant planets, while also serving to activate gas-phase organic chemistry through the formation of the methyl cation, observed for the first time with JWST. 
(Cologne, Host: Oskar Asvany)

April 15, 2024
Brian Hays
Univ. Lille, CNRS, UMR 8523 – PhLAM – Physique des Lasers Atomes et Molécules, France
Dynamic rotational spectroscopy to investigate gas phase molecular processes relevant to the interstellar medium

Abstract

Astronomical observations of molecules are buoyed by laboratory astrophysics investigations of a variety of processes. Observations of the interstellar medium need spectral line positions to find molecules, rates of reaction to explain to feed chemical models, and collisional (de)excitation rates to predict the abundance of molecules under the peculiar conditions of space. Laboratory astrophysics measurements or predictions can provide all this information using a wide variety of techniques. Given the strong link between rotational spectroscopy and astrochemistry through several microwave, millimeter, and sub-millimeter telescopes, the role of rotational spectroscopy can be expanded beyond its traditional role of providing spectral line positions in laboratory measurements. I will discuss new experiments that push rotational spectroscopy into the detection of products of reaction and validation of collisional (de)excitation rates all in support of astrochemistry.
(Cologne, Host: Stephan Schlemmer)

April 22, 2024
Anthony Whitworth
CHART, School of Physics & Astronomy, Cardiff University, UK
A Star Is Born



Abstract

The commonest stars in the Universe are probably M Dwarfs. This talk is about how M Dwarfs and Sun-like stars might form and why they are so common. I shall try to convince you – and myself – of the following (hypo)theses. [1] Their formation has nothing to do with the Singular Isothermal Sphere. [2] The Sun is a rather massive star, not in the sense that it will ever excite an HII region or explode as a supernova, but in the sense that there are many more stars with lower mass than with higher mass. [3] The Sun is somewhat unusual in being single. [4] The peak of the Core Mass Function at one or two solar masses, and the (low residual) levels of turbulence in prestellar cores, are a consequence of thermodynamics, specifically the interplay between molecular-line cooling and dust cooling. [5] This same thermodynamics explains the threshold for star formation at AV ≳  8 (Σ  ≳  200 M pc−2), V⊙ and the ubiquity of structures (cores, filaments, sheets) with linear size of order 0.1 pc. [6] A typical prestellar core must spawn between 4 and 5 stars if it is to deliver the observed binary fraction as a function of primary mass, or the proportion of higher-order multiples. [7] The efficiency of star formation in a prestellar core is very high, notionally of order 100%. OK, some of these theses are not very contentious, but I think that some of them might ‘shift the dial’ a little bit.
(Cologne, Host: Stefanie Walch-Gassner)

April 29, 2024
Daniel Seifried
I. Physics Institute, University of Cologne
Magnetic fields & Chemistry in 3D, ISM simulations

Abstract

In my talk I will present recent results from state-of-the-art simulations of molecular clouds and star formation. I will focus on the interplay of magnetic fields, turbulence and chemistry and their effect on the structure evolution in clouds and the subsequent star formation process. Specifically, I will show how magnetic field lead to a stabilisation of clouds on larger scales, whereas on smaller scales gravity takes over. I will discuss how this effect is reflected in the chemical composition of the clouds and the structure of magnetic fields. Furthermore, I will present a novel analysis of the 3D morphology of substructures contained in the clouds, which show a intriguing transition from sheet-like structures to filamentary structures, in excellent agreement with recent observations. Lastly, I will connect the results of these simulations to actual observations by discussing synthetic observations created from the simulations. Specifically I will focus on dust polarisation maps and discuss what we can learn from them about the underlying 3D magnetic field structure and how accurately magnetic field properties can be inferred from such observations.

May 6, 2024
Peter Schilke, Beth Jones
I. Physics Institute, University of Cologne
A census of high-mass star-forming regions in the Galaxy with ALMAGAL

Abstract

The ALMA Large Program ALMAGAL has observed over 1000 high-mass star forming clumps and unveiled more than 6000 protostellar cores embedded within. For the first time, homogeneous interferometric spectral line data are now available toward a significant fraction of the total Galactic population of high-mass star formation sites. Determining the properties of protostellar cores within the Galaxy is vital to draw robust conclusions and truly understand the pathway to Galactic high-mass stars.
We present the first results of the survey, concentrating on the determination of temperatures from fitting of methyl cyanide lines.  Temperatures are critical for determining important parameters such as luminosity and mass.  We then explore the evolutionary state of the protostars, the fraction of clump luminosity powered solely by the cores, and quantify the correlation with other star formation features such as HII regions.  Since some ALMAGAL sources are in the lower metallicity outer Galaxy, we also connect to CRC project A1, and to next week’s talk.

The very high spatial resolution of the ALMAGAL data creates challenges of the data fitting and interpretation that are absent in most previous data sets. Hence, we explore Machine Learning methods to recover underlying density and temperature profiles.
(Cologne)

May 13, 2024
Agata Karska, Dario Colombo, Eleonore Dann
Max Planck Institute for Radio Astronomy, Bonn; Argelander Institute for Astronomy, University of Bonn; I. Physics Institute, University of Cologne
The outer Galaxy: structure, star formation, and chemistry

Abstract

Star formation is ubiquitous in the Galaxy, but the physical and chemical conditions in star-forming sites might differ as a function of galactocentric radius. Due to the negative metallicity gradient, the efficiency of gas cooling and dust shielding decreases in more distant regions. A lower interstellar radiation field and a decrease in cosmic-ray fluxes lead to a decrease in gas heating and ultimately cause lower gas and dust temperatures in the outer Galaxy. The balance between these processes sets the physical conditions of the gas and dust and likely affects star-formation rates and efficiencies. In this talk, we will present the first research highlights of the recently completed APEX legacy survey “Outer Galaxy High Resolution Survey” (OGHReS), which covers 100 deg^2 in the 3rd Galactic quadrant in the 2-1 transition of CO and its rare isotopologues. We will discuss important characteristics of the structure of the outer Galaxy, highlighting the differences with the inner Galaxy. We observed that large-scale filaments in the outer Galaxy are fundamentally quiescent objects, with a mass one order of magnitude lower compared to similar size filaments in the inner Galaxy. Additionally, outer galaxy filaments are found exclusively in inter-arm regions, which might point towards a different formation mechanism with respect to the inner Galaxy. The most prominent filament in the outer Galaxy, Falcor, is the only exception, being a site of efficient star formation and a host of the hot core candidate. Finally, we will present preliminary results of the follow-up studies of selected  star-forming clumps in additional molecular and atomic lines, and discuss their gradients across the Milky Way. We will initiate the discussion to what extent the outer Galaxy can act as a laboratory of star formation in a low-metallicity environment, and propose the next steps necessary to interpret star formation in diverse ecosystems.

May 27, 2024 – online
Sudeshna Patra
Indian Institute of Science Education and Research (IISER), Tirupati, India 
The Outer Milky Way: Laboratory for the Effects of Metallicity

Abstract

Metals play a pivotal role in shaping star formation processes, influencing gas cooling, condensation, and stellar evolution. Metallicity gradually decreases as we move outward in the Galaxy, falling between the values observed in the LMC and the inner Galactic disk. The outer region of the Milky Way presents a distinctive opportunity for investigating the impact of low metallicity on the formation of stars, where the metallicity reaches 0.3 times thesolar- metallicity. This part of the disk is an excellent proxy for other low-metallicity systems, at the same time offering easier and clearer observations of molecular clouds than nearby galaxies.
In this talk, first, I will discuss the role of metallicity in shaping protoplanetary disk evolution. We have calculated disk fraction (i.e., the percentage of stars having disks) for 10 young and sub-solar metallicity clusters in the outer Milky Way with RG range of 10-13 kpc. We find that low-metallicity clusters exhibit a lower disk fraction compared to solar-metallicity clusters. We also observe the positive correlation between cluster disk fraction and metallicity for two different age groups. We emphasize that both cluster age and metallicity significantly affect the fraction of stars with evidence of inner disks.
In the second part of the talk, I will discuss the effect of metallicity on the mass-luminosity conversion factor (𝛼𝑡𝑜𝑡) from dense gas (HCN, HCO+). Recent recognition that the mass-luminosity conversion factor from CO is not constant, but instead varies with metallicity, begs the question. We have analyzed 17 outer galaxy clouds, along with 6 inner galaxy clouds and 5 local clouds. We have found that 𝛼𝑡𝑜𝑡 (𝐻𝐶𝑁) is 3 times higher in the outer Galaxy than in the inner Galaxy after correcting for metallicity. I will also discuss how this metallicity correction contributes to explaining the relatively slow star formation in the Central Molecular Zone.
(ONLINE, Host: Agata Karska)

June 3, 2024
Clément Lauzin
Université catholique de Louvain, Belgium
High-resolution spectroscopic measurements on methanol and other reference molecules for fundamental physics, chemistry and astrophysics.

Abstract

High-resolution spectroscopic measurements performed in the laboratory enable the determination of molecular parameters and the identification of molecular species in different environments. The detection of new species and an estimation of its density allow in a second step to constrain astrophysical/chemical models. Very precise laboratory measurements may also challenge our understanding of quantum chemistry and fundamental physics.

Several high-resolution spectrometers were built recently in Louvain-la-Neuve. Those instruments work in different spectral ranges, microwave, near-infrared and UV to measure different molecular systems such as isolated molecules, neutral van der Waals complexes and molecular ions. During this talk, we will introduce a buffer gas cooling cell (20K) which is combined to a cavity ringdown spectrometer working in the near-infrared range. The set-up is illustrated in Figure 1. This instrument has been specifically designed to obtain reference measurements on complex molecules such as CH3OH probed in the overtone range. Our recent results concerning methanol will be shown and the tools developed to tackle the complex spectral signature will be detailed. Part of the complex spectral signature of methanol is also illustrated in Figure 1. Several potential upgrades of this instrument, for instance combining it with a home-built femtosecond laser to reach higher precision will be presented. Further, I will present action photodissociation spectroscopy measurements and the associated analysis concerning ionic species such as N2O+. To finish, our results concerning the study of molecular aggregation at the molecular scale will be presented. 

Figure 1: The Experimental set-up combining a buffer gas cooling cell and a cavity ringdown spectrometer is presented in the upper panel. Laser light is injected in a high-finesse optical cavity and the lifetime of the photons inside this cavity is measured as a function of the laser frequency. The lower panel presents the spectrum of methanol measured in the 2OH overtone range at a temperature of 25 K. 


(Cologne, Host: Oskar Asvany)

June 10, 2024
Sven Thorwirth & Luis Bonah
I. Physics Institute, University of Cologne
Spectroscopy of vibrationally excited COMs for radio astronomy

Abstract

A full understanding of the spectroscopic signatures of line-rich astronomical sources such as hot molecular cores requires dedicated studies of complex organic molecules, COMs, in the laboratory. Notoriously, COMs feature dense pure rotational spectra already in their ground vibrational states but also possess energetically low-lying vibrational modes further contributing to line density. 
In addition, the parent isotopic species of COMs can be so abundant astronomically that even rare isotopic species may be observed with ease also in their vibrationally excited states. This poses severe challenges on laboratory spectroscopy.
Besides the sheer number of isotopic species deserving spectroscopic characterization, the observation and interpretation of corresponding pure rotational spectra is often (very) challenging spectroscopically. 
In the course of this talk, we will show how application of specifically tailored experimental approaches and analysis software may support spectroscopic study of COMs and introduce recent studies carried out in the framework of CRC 1601.
(Cologne)

July 8, 2024
Emma Bordier
I. Physics Institute, University of Cologne
On the origin of companions around massive O-type stars: the high angular resolution view

Abstract

The high incidence of multiples and particularly close binaries among main sequence massive stars, challenges current understanding of their formation. To understand how such close systems are built, we need to obtain strong constrains on the origin of the pairing mechanism and the birth orbital properties. Different scenarios operating at different scales try to explain the formation of these multiples such as turbulent/core fragmentation, disk fragmentation (in which inward migration can occur) and the capture of an unbound body or similar dynamical effects that may happen later on in the formation process. With the ultimate goal to better understand multiplicity origins and properties at birth, I will demonstrate the crucial role of high-angular observations such as interferometry (VLTI/GRAVITY and PIONIER) and high-contrast imaging (VLT/NACO) to investigate key ingredients in massive star formation processes. The combination of these techniques provides valuable statistics on young high-mass multiple systems with physical separations ranging from 1 to 35,000 AU.
By determining physical properties such as multiplicity frequencies, mass ratios, and physical separation distributions, we can link our findings to the most promising pathways for the formation of massive multiples. In our quest to understand the origins of multiplicity, we compare our results with those of other stellar populations across different mass regimes and evolutionary stages, within a consistent parameter space. Finally, in the context of the SFB1601, this talk will also highlight some of our team’s latest and early results on multiplicity in young massive stars.

July 15, 2024
Bérenger Gans
Institut des Sciences Moléculaires d’Orsay, CNRS & University of Paris-Saclay, France
Investigation of interstellar radical photoionization by VUV photoelectron spectroscopy

Abstract

Despite their significance in astrophysical environments, a large number of cations of free radicals are spectroscopically poorly characterized in the gas phase, due to experimental challenges. Photoionization spectroscopy holds great potential in this area, though it remains difficult because it requires efficient radical sources and tunable VUV radiations with high-enough spectral resolution.
In this talk, I will describe two different techniques employed to tackle this subject: threshold photoelectron spectroscopy (TPES) coupled with synchrotron radiation, and pulsed-field-ionization zero-kinetic-electron photoelectron spectroscopy (PFI ZEKE PES) coupled with a tunable VUV laser.
In the first part, I will briefly present results on carbon- and/or silicon-bearing radicals using a flow tube reactor coupled with the DELICIOUS 3 photoelectron/photoion coincidence spectrometer of the DESIRS beamline at SOLEIL French synchrotron facility.
In the second part, I will introduce a versatile laser setup that we recently built at ISMO to perform PFI-ZEKE spectroscopy of free radicals, allowing either large spectral coverages with vibrational resolution (~3 cm-1) or narrow spectroscopic investigations with rotational resolution (<0.1 cm-1). Results on the CH3 radical that confirmed the recent detection by JWST of the methyl radical cation (CH3+) in a protoplanetary disk within the Orion star-forming region will be presented.
(Cologne, Host: Oskar Asvany)


  • October 08, 2024 – Susanne Pfalzner
  • October 15, 2024 – Alexey Potapov
  • October 22, 2024 – SFB1601-PL
  • October 29, 2024
  • November 05, 2024 – SFB1601-PL
  • November 12, 2024
  • November 19, 2024 – Urs Graf
  • November 26, 2024 – Nuria Marcelino (Host Wonju Kim)
  • December 3, 2024 – SFB1601-PL
  • December 10, 2024 – Daniel Obenchain (Host Stephan Schlemmer)
  • December 17, 2024 – SFB1601-PL
  • January 7, 2025
  • January 14, 2025 – SFB1601-PL
  • January 21, 2025
  • January 28, 2025 – SFB1601-PL

October 15, 2024
Alexey Potapov
Analytical Mineralogy group, Institute of Geosciences, Friedrich Schiller University, Jena
Laboratory Astrophysics and Solid-state Astrochemistry

Abstract

Laboratory astrophysics bridges studies of atomic and molecular species in interstellar and circumstellar media and planetary atmospheres conducted through astronomical observations, and studies of these species or their analogues that we can create in the laboratory and probe in situ. Many laboratory experiments are devoted to studies of solid-state or surface reactions that lead to a greater complexity (comparing to the gas phase) of molecular species. Complex organic and prebiotic molecules can be formed through surface reaction pathways linking astrophysics/astrochemistry with the big scientific question – the origin of Life on Earth.In my talk, I will provide a brief introduction to laboratory astrophysics and to cosmic surfaces, will present a new view of cosmic dust grains, and will discuss results of experiments on the catalytic formation of molecules thereon.  

Schematic figure showing dust grains (in grey) mixed with ice molecules (in blue) and the main sources of their processing in astrophysical environments (from Potapov et al., Phys. Rev. Lett., 2020, 124,221103).


(Cologne, Host: Stephan Schlemmer)