PHD Projects of the Millimeter and Submillimeter Astronomy

Director: Prof. Dr. Karl Menten

Group Website

Code: KM01

The chemistry and physics of the diffuse interstellar medium

The Heterodyne Instrument for the Far-Infrared (HIFI) abord Herschel opened a whole new era of studies of the diffuse interstellar medium (ISM). Utilizing Herschel’s superb sensitivity combined with its high spectral resolution receivers operating in a low thermal background space environment, HIFI revolutionized observations of light hydrides, many of which have their ground-state rotational transitions in the submillimeter and far infrared range. As the building blocks of larger molecules, the (mostly) di- or triatomic species detected by HIFI and (also by APEX and SOFIA) are of central astrochemical interest. In addition, they triggered new interest in the physics and chemistry of diffuse and translucent clouds, for example in their role as interfaces between the cold (and warm) neutral atomic and the denser, cold molecular phases of the ISM in our, but also in external galaxies.

Building on the success of Herschel, new opportunities arise with ground-based and airborne observations of hydrides: in the submillimeter range, hydrides such as 13CH+, OH+, and SH+ can be studied using the APEX telescope with new receivers and the exceptional atmospheric conditions on the Chajnantor Plateau in northern Chile. Access to even higher frequencies is provided by the airborne Stratospheric Observatory for Infrared Astronomy (SOFIA) and the GREAT receiver and allows observations of CH, SH and OH, to name just a few of the simplest hydrides. A thorough analysis of such observations will lead to a comprehensive characterization of hydrides in diffuse clouds throughout our Galaxy.

Possible dissertation projects comprise observational studies with, predominantly, SOFIA and APEX, but also with other telescopes as well modeling of the data and bringing them into context with a glabal view of the Milky Way galaxy's ISM.

Contact: Prof. Dr. Karl Menten (kmenten@mpifr-bonn.mpg.de)
Site: Bonn, Max-Planck-Institut für Radioastronomie

Code: KM02

Effelsberg K-band fingerprints of star forming regions

The unprecendented sensitivity and large bandwidth (8GHz) of the new Effelsberg K-band receiver, covering 18-26 GHz in frequency, offer new opportunities to study the physical and chemical conditions of star forming regions and mant other interesting sources with unbiased line surveys. These surveys give access to probes of temperature, density and chemistry that can be used to characterize the evolutionary stages of the regions. The project will be very complementary to line survey projects conducted with the IRAM 30m and APEX 12m telescopes in the millimeter and submillimeter wavelength range, respetively.

The K-band contains many interesting lines, amongst them the many transitions of ammonia (including 15NH3 and non-metastable lines), as well as lines from carbon chains like HC3N, HC5N (for both also isotopologues and vibrationally excited levels), from molecules like methanol, CCS, C3H2, C6H and several recombination lines and maser transitions (water, methanol, ammonia), make K-band line surveys very appealing for molecular fingerprints, that can be used to rapidly characterize the main charactistics and the evolutioniary stage of the regions, then leading to a new “K-band spectral classification” of star forming regions.

For such surveys, a sophisticated data reduction pipeline, capable of processing and calibrating the large amount of data will be needed. The PhD candidate will participate in setting up this pipeline to prepare for the analysis of the wealth of molecular line data. A background in software engineering and experience with data reduction of radio astronomical data would be a plus.

Contact: Dr. Friedrich Wyrowski (wyrowski@mpifr.de), Dr. Benjamin Winkel (bwinkel@mpifr.de), Dr. A. Kraus (akraus@mpifr.de) Prof. Dr. Karl Menten (kmenten@mpifr-bonn.mpg.de)
Site: Bonn, Max-Planck-Institut für Radioastronomie

Code: KM03

Massive molecular outflows

The detailed physical processes at the origin of high-mass stars (here defined as ionizing OB stars; i.e., earlier than B3 or M*> 8 M_sol) are still to be fully recognized and understood. Whether they form through a scaled-up version of the low-mass star formation process or by means of a specific process is still an open issue. Observations seem to contradict both scenarios as the level of turbulence in massive dense cores is not enough for the first scenario nor the level of fragmentation is as high as predicted by alternative models.

Important insights in the mechanisms that lead to the formation of massive stars may come from observations of a large statical sample of deeply embedded massive young stellar objects (YSOs) aimed at characterising how they accrete material from their surrounding envelopes. While in principle detection of circumstellar disks is the ultimate test to verify whether massive star formation is a scaled-up version of low-mass star formation, circumstellardisks are still a challenge for observations given the average distance of massive YSOs and their high level of multiplicity. On the other hand, jets and outflows are a direct consequence of accretion onto the protostar, they have linear sizes much larger than those of disks and are associated with emission from some molecules such as SiO that are associated unambiguously only with shocks.

Project aims: The PhD project will focus on the analysis and interpretation of existing Herschel, SOFIA and APEX data. These data will allow to determine the excitation conditions and chemistry within the molecular outflows. In addition, we are currently performing high-angular resolution observations of a sub-sample of sources with the ALMA and Plateau de Bure interferometers. These are the most powerful facilities in the mm/submm wavelength range: the new data will allow to obtain a census of molecular outflows in each source, and study their properties as function of the properties of the emitting source. The aim of this sub-project is to derive properties of massive molecular outflows (collimation, physics and energetics) in a statical sample of sources and compare with the same properties of molecular outflows from low-mass YSOs to verify whether massive molecular outflows are a scaled-up version of their low-mass counterparts or whether their properties change at a given mass and luminosity of the central object.

Bibliography:
Arce et al. 2007, Protostars and Planets V, 245
Bontemps et al. 2010, A&A, 524, A18
Cesaroni et al 2007, Protostars and Planets V, 197
Leurini et al 2013, A&A, 554, A35 Leurini et al 2013, A&A, 554, A35

Contact: Dr. Silvia Leurini (sleurini@mpifr-bonn.mpg.de), Dr. Friedrich Wyrowski (wyrowski@mpifr- bonn.mpg.de), Prof. Dr. Karl Menten (kmenten@mpifr-bonn.mpg.de)
Site: Bonn, Max-Planck-Institut für Radioastronomie, Millimeter and Submillimeter Astronomy Group

Code: KM04

A comprehensive Galactic plane radio wavelength star formation survey

Understanding the circumstances of massive star formation is one of the great challenges of modern astronomy. In the last years, our view of massive star forming regions has dramatically been changed by Galactic plane surveys covering centimeter to infrared wavelengths. These surveys enable us for the first time to study ALL evolutionary stages of massive star formation in an unbiased way. With the exciting results of the new submm/FIR surveys from the ground (ATLASGAL) and space (Hi-GAL) the massive and cold dust clumps from which massive cluster form are now detected in an unbiased way. Complementary, the EVLA will allow incredibly powerful and comprehensive radio- wavelength surveys of, both, the ionized and the molecular tracers of star formation in the Galactic plane.

In this project, the extremely wideband (4-8 GHz) new C-band receivers of the EVLA will be used for an unbiased survey to find and characterize star-forming regions in the Galaxy.  This survey of the Galactic plane, that is now ongoing, will detect tell-tale tracers of star formation: compact, ultra-, and hyper-compact Hii regions and molecular masers which trace different stages of early stellar evolution and will pinpoint the very centers of the early phase of
star-forming activity. Combined with the submm/infrared surveys it will offer a nearly complete census of the number, luminosities and masses of massive star forming clusters in a large range of evolutionary stages and provide a unique dataset with true legacy value for a global perspective on star formation in our Galaxy.

Contact: Dr. Friedrich Wyrowski (wyrowski@mpifr- bonn.mpg.de), Prof. Dr. Karl Menten (kmenten@mpifr-bonn.mpg.de)

Site: Bonn, Max-Planck-Institut für Radioastronomie, Millimeter and Submillimeter Astronomy Group

Code: KM05

A 350 micron Galactic Plane survey of the inner Milky Way

The very successful APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) has revealed for the first time the structure of the cold interstellar medium over several 100 sq. deg. The survey was conducted with LABOCA at the APEX telescope to conduct an unbiased census of massive star forming clumps and their different evolutionary stages in the inner Galaxy.

 Soon a new, much larger bolometer camera will be commissioned at the APEX telescope, the A-MKID dual color camera with ~3500 pixel at 870 and ~20000 pixel at 350 micrion. At the short wavelengths, this instrument will allow to resolve sources of 0.1 pc size within 3 kpc towards giant star forming complexes.  When combining the A-MKID data with the Herschel/Hi-GAL survey at 60 to 600 micron, it will be possible to:

 • derive evolutionary stages for a representative sample of star forming clumps

 • compute dust emissivity and temperature over a large star forming complex

 • analyze how the physical conditions vary within one giant complex

 • study the fragmentation of clumps into cores that can give birth to individual stars

 Given its high angular resolution and unbiased nature, such a survey

will provide a legacy and pathfinder for years to come.

Contact: Dr. Friedrich Wyrowski (wyrowski@mpifr- bonn.mpg.de), Prof. Dr.Karl Menten (kmenten@mpifr-bonn.mpg.de)

 Site: Bonn, Max-Planck-Institut für Radioastronomie, Millimeter and Submillimeter Astronomy Group

Code: KM06

Physical and chemical conditions in giant molecular clouds

Massive stars form in dense clumps within giant molecular clouds (GMCs), but how do these clouds form and evolve, how do the dense clumps form within them and what are the conditions for star formation within these dense clumps? To address these questions the MPIfR operates powerful heterodyne cameras for line observations, such as the upcoming new LAsMA array for observations at 345GHz and the CHAMP+ array (690 and 810 GHz), both at APEX, complemented by the upGREAT array on SOFIA for THz observations of important fine structure cooling lines. The high mapping speed of these cameras enables to map giant molecular clouds on degree scales in a variety of molecules. Such a chemical inventory provides a new view on the large scale properties of molecular clouds. Furthermore, by combining results from the different cameras the excitation and cooling of the clouds can be constrained to form a comprehensive picture of the formation and condition in GMCs.

Some of scientific questions to tackle with these observations are: What is the dynamics of the clouds and the embedded clumps? How strongly are the chemical conditions in the clouds altered by interaction processes, either from the outside of the clouds or by feedback from the ongoing star formation in the clouds? Can some of the chemical variations be used in conjunction with chemical models as chemical clocks to put different clumps in the clouds into an evolutionary sequence? How do these large-scale chemical properties of Galactic GMCs compare with observations of their extra-galactic counterparts that are now feasible with the high sensitivity and angular resolution of ALMA?

Contact: Dr. Friedrich Wyrowski (wyrowski@mpifr-bonn.mpg.de), Prof. Dr.Karl Menten (kmenten@mpifr-bonn.mpg.de)
Site: Bonn, Max-Planck-Institut für Radioastronomie, Millimeter and Submillimeter Astronomy Group

Code: KM07

Massive star clusters in the making

The origin of stellar masses, in particular of massive stars, is a fundamental open issue in modern astrophysics. Do the highest mass stars all form in clusters, and what physical conditions are required to give birth to rich clusters? High angular resolution studies of the most active and luminous sites in our galaxy provide critical testbeds for currently debated theoretical scenarios in the understanding of star formation processes.

The objective of this PhD project is to use mm/submm interferometric datasets to study the small-scale structures massive clumps, such as the W51 Main star forming complex, which gives birth to a rich cluster. In particular, this ambitious project will focus on the physical properties from the small, protostellar scales to their larger, parsec scale environment, as well as study and compare the chemical properties of individual protostars. Confronting the results to models will help to constrain the link between the small scale star formation processes and the global properties of the molecular cloud.

Bibliography:

- Csengeri et al., 2014, A&A, 565, 75
- Csengeri et al., 2011, A&A, 527, 135
- Csengeri et al., 2010, ApJL, 740, 5
- Ginsburg et al., 2015, A&A, 573, 106

Contact: Dr. Timea Csengeri (csengeri@mpifr-bonn.mpg.de), Dr. Friedrich Wyrowski, Prof. Dr. Karl Menten (kmenten@mpifr-bonn.mpg.de)
Site: Bonn, Max-Planck-Institut für Radioastronomie, Millimeter and Submillimeter Astronomy Group

Code: KM08

Properties of relativistic jets of microquasars

The goal is to contribute to a better  understanding of the physical processes producing relativistic jets in microquasars.
Several issues are still open.  When become steady jets able to develop a flat spectrum? What is the connection between steady jets and transient jets? What is the relationship between transient  jets and very high gamma-ray emission? The better understanding will be gained by model simulations compared with radio and gamma ray observations.

contact: PD Dr/ Maria Massi (mmassi@mpifr-bonn.mpg.de)

Code: KM09

The Cepheus A Star formation and proper Motion (CHASM) Survey


While low-mass stars are known to form both in isolation (e.g., in Taurus) and in clusters (e.g., Orion Nebula), high-mass stars (> 8 M⊙) preferentially form in associations of a few tens to a few thousands of low- and high-mass stars (e.g., Stahler et al. 2000). Therefore, regions which give birth to massive stars are a preferred laboratory 1) to give us clues on the star formation mechanisms over a wide range of masses, and 2) to explore the initial conditions of cluster formation. From the point of view of the young stellar objects (YSOs) as a whole, a fundamental parameter to constrain is their velocity dispersion (σ) within the natal clump, which can be inferred from a direct measurement of the proper motions of the cluster members. In the context of star formation theories (e.g., Tan et al. 2014), knowing whether the most massive objects have high proper motions (> 2−5km/s) relative to the clump gas, or alternatively negligible random motions, is
fundamental to discern whether they mainly accrete mass from their immediate surroundings (i.e., the pre-stellar core, < 0.1pc – as in the Core-Accretion model), or their final mass can be clump-fed (i.e., the mass reservoir is supplied outside a 0.1pc radius from the star – as in the Competitive-Accretion model). With this in mind, we have started a large project (The CHASM Survey) to provide, for the  first time, a direct measurement of the full-space motions and 3D positions of several low- and high-mass YSOs within the second, nearest (to the Sun), high-mass star-forming region: Cepheus A.

Project Plan: this PhD project will focus on the analysis and interpretation of multi-epoch, astrometric, Very Long Baseline Array (VLBA) observations, at both C (5cm) and K (1cm) bands, towards Cepheus A. These observations will start on December 2016, last for the following 2 years, and will provide a unique dataset of accurate  parallaxes and proper motions of both T Tauri and high-mass YSOs, by means of radio  continuum and spectral line (maser) data, respectively. Eventually, these results will be used to assess the magnitude and direction of the relative proper motions of the YSOs, and to understand, in the context of star formation theories, whether or not the most massive object (Cepheus A HW2) of the cluster can accrete from the whole clump.  The successful candidate is expected to gain a strong expertise on the calibration  of astrometric Very Long Baseline Interferometry (VLBI) data, for parallaxes and  proper motion studies, which are the most powerful application of milli-arcsecond (mas) resolution observations to Galactic targets (e.g., Reid & Honma 2014).


Bibliography:
Reid, M. J., & Honma, M. 2014, ARA& A, 52, 339
Stahler et al. 2000, PPIV, 327
Tan et al. 2014, PPVI, 149

Contact: Dr. Alberto Sanna (asanna@mpifr.de), Prof. Dr. K.M. Menten (kmenten@mpifr.de)

 
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