Thesis projects in high-mass star
formation and the interstellar medium
Max-Planck-Institute
for
Astronomy (MPIA),
Heidelberg/Germany
Attention: Prof. 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, ALMA) - now allows to resolve
the innermost regions of massive star-forming regions and thus study the
physical processes in detail. These processes are for example studied with
the IRAM NOEMA
large program CORE, or most
recently also with JWST. In addition
to these small-scale structure, the group also works on larger spatial
scales associated with the formation of clouds as well as the Milky Way
structure as a whole. For these questions, we are part of larger survey
collaborations as well, for example, ATLASGAL
or THOR that are conducted with
other instruments like APEX,
VLA or Herschel.
Ongoing
PhD
thesis projects:
Dynamical
accretion flows (Molly Wells, start September 2021)
The dynamical
processes during cloud and star formation are still poorly constrained.
Are clouds collapsing globally or are filamentary accretion processes an
indispensable part of the picture? This project will characterize the
kinematical and physical properties of accretion flows from cloud to core
scales by means of large observing programs conducted at ALMA & NOEMA.
Characterizing
physical and chemical properties of young protostars with JWST
(Simon Reyes-Reyes, start September 2023)
What
are the physical and chemical properties of the warm/hot dense gas close
to the forming (high-mass) protostars? The advent of JWST now allows us
to characterize these properties in great detail. This thesis will start
from a European MIRI consortium guaranteed time program targeting a
sample of protostars with the MIRI MRS IFU. This project will
investigate the properties of the accretion and outflow processes.
Furthermore, atomic and molecular gas lines as well as ice
features covered by MIRI will reveal the dense core properties closely
associated with the protostars and their disks.
Upcoming
PhD thesis projects:
Finished
PhD
thesis projects:
Molecular
cloud formation processes in the Milky Way (Jonas Syed, star
September 2019-July 2023)
How do molecular clouds
form and how does the molecular gas convert to the atomic phase? How
much does environment, e.g., spiral arms or interarm regions, affect
these processes? These questions will be addressed based on large-scale
surveys in the atomic and molecular gas of our Milky Way. The atomic
phase can be studied by means of the THOR
project (The HI/OH/Recombination line survey of the Milky Way) observed
with the Very Large Array (VLA). The THOR HI data will be analyzed in
detail and set into context with complementary surveys of other gas
tracers in the Milky Way. This northern hemisphere project will be
complemented by studies of southern Giant Molecular Filaments by means
of the new 13CO/C18O(2-1) survey SEDIGISM conducted with APEX.
High-mass
core and disk characetrization from mid-infrared (JWST)
to mm wavelength (NOEMA)
(Caroline Gieser,
September 2018-July 2022)
Star
formation proceeds from very cold gas clumps to hot molecular
cores and stars, and hence the star formation process automatically
covers a broad range of temperatures. Therefore, studying star
formation in general, and high-mass star formation in particular,
requires multi-wavelength studies to sample the different phases and
entities within the star-forming region. Therefore, this PhD project is
planed to investigate different physical processes during high-mass star
formation, all related to the physical and chemical properties of the
dense cores and potential accretion disks. The project will start with
investigations of the core and disk properties at mm wavelengths based
on the IRAM NOEMA
large program CORE. Then, after
the launch of JWST to happen in the first half of 2016, the project is
suppose to slowly shift to the warmer gas and dust properties visible at
mid-infrared wavelength based on a guaranteed time project with JWST.
The
formation of disks during the early evolution of high-mass stars (Aida Ahmadi, December 2015-Januar 2020)
What
are
the properties of the gas during high-mass star formation? Where and how
do massive accretion disks form? What are the actual infall rates - and
related accretion rates - of the gas? How does the gas accrete through
embedded hypercompact HII regions? These are some of the questions related
to a newly established large program CORE
at the Plateau de Bure Interferometer (NOEMA,
formerly PdBI): Fragmentation and disk formation during high-mass star
formation. This program studies a sample of 18 high-mass star-forming
regions in the 1mm and 870mum band in the line and continuum emission at
almost unprecedented spatial resolution of 0.2-0.3''. corresponding to
linear scales of down to ~150AU for the closest target regions. Within
this program, the student will focus in particular on the kinematics of
the gas and the formation of accretion disks. This project includes all
steps from data reduction to analysis interpretation and setting into
context with theoretical models. The
whole project is embedded in a large international collaboration.
Molecular
and atomic gas in the Milky Way (Michael
Rugel, November 2014-November 2018)
What are the relative
properties of the molecular and atomic gas in the Milky Way? How do
their properties vary with for example the Galactoccentric radius of the
Galactic latitude? Employing the Galacticplane survey "The
HI/OH/Recombination line survey of the Milky Way" (THOR)
that observes our Milky Way
with the Very Large Array (VLA) between longitudes of 15 and 67
degrees and latitudes <+_1 degree) in
the
emission of the atomichydrogen (HI), four OH and 19 radio recombination
lines, as well as the continuum emission, we can study the different
phases of theinterstellar medium (ISM) in great depth. This allows not
just studies of individual clouds but also investigations of the general
propertieswith respect to location in our home galaxy. In addition to
these scientific studies, Michael will also be involved in the data
reductionand analysis of this large survey. The
whole project is embedded in a large international collaboration.
Cloud
formation based on HI emission from the THOR survey (Simon Bihr, October 2012-April 2016)
Understanding
the
formation of molecular clouds from the more diffuse atomic medium is
central to the understanding of star formation in general. We are
currently conducting "The HI/OH/Recombination line survey of the Milky
Way" (THOR) which observes with the
Very Large Array (VLA)
a large fraction of the Galactic plane (between longitudes of 15 and 67
degrees and latitudes <+_1 degree) in the emission of the atomic
hydrogen (HI), four OH and 19 radio recombination lines, as well as the
continuum emission. This survey will allow us to address a plethora of
scientific question associated with the formation of clouds, the embedded
star formation, emerging HII regions as well as the end of the stars life.
The thesis project from Simon Bihr is specifically targeting the cloud
formation aspect of the project employing the HI data, and correlating
them with complementary surveys, e.g., CO observations of the molecular
phase. Questions to be addressed are: How does the molecular gas form out
of the atomic phase? Do we find kinematic transition signatures between
the different phases? How does the atomic to molecular mass ratios vary
with the density of the medium? In addition to these science projects,
Simon will be deeply involved in the execution of such a large
project from the planing via data reduction and analysis to the final
interpretation. The whole project is embedded in a large
international collaboration.
Chemical
sub-structure of high-mass star-forming regions (Siyi Feng, September 2011- February
2015)
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.
Mapping the chemistry of the interstellar
medium (Thomas Gerner, April 2011 - October 2014)
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.
Massive star formation on Galactic scales (Jochen
Tackenberg, October 2009 - April 2013)
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.
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.
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.
Associated PhD thesis projects:
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)
Diploma/Master
thesis projects:
Complex
kinematics in 10 filamentary infrared dark clouds
(David-Sebastian Kalb, June 2022- July 2023)
Filamentary accretion flows in Cygnus X's
DR20 (Miriam Sawczuck, May 2021- August 2022)
HI cloud formation - Studying the ISM by
mean of HI self absorption (Jonas Syed, 2018-2019)
Chemical complexity of AFGL2591
(Caroline Gieser, 2017-2018)
Fragmentation, rotation and outflows in
the high-mass star-forming region IRAS23033+5951 (Felix Bosco,
2015-2016)
Kinematics, temperature and turbulence of
IRDCs (Simon Bihr, July 2011 - July 2012)
Bachelor
thesis projects:
Filamentary
accretion flows in high-mass star-forming clouds (Jan-Erik
Schneider 2023)
Magnetic fields in stellar feedback
bubbles probed by the Planck-353 GHz polarization observations
(Henrik Ruh
2018)
Temperature and kinematics of massive
star-forming clumps (Jonas Syed, 2017)
Interferometric outflow studies of the
massive star formation region IRAS19410+2336 (Felix Widmann,
March to July 2014)
Interferometric imaging procedures (Tobias Schierhuber, March to
July 2014)
Characterization of Infrared Dark Clouds (Roxana Chira, March to
July 2011)