The GENESIS Project S106 - on the Trail of the Formation of Massive Stars

December 3, 2018 /

How exactly do massive stars form in our Milky Way? Dr. Nicola Schneider from the University of Cologne and her international team pursues this question in the GENESIS project S106 by combining observations with SOFIA, the Stratospheric Observatory for Infrared Astronomy, with data from other observatories. These sort of studies are the main objectives of GENESIS, a German-French collaborative project between N. Schneider, R. Simon from the I. Physik. Institut, Cologne and S. Bontemps from the Laboratoire d’Astrophysique of Bordeaux. All stars, even ordinary ones like our Sun, are formed by interstellar gas and dust clouds. These clouds show a complex structure with filaments and clumps. The mass flow along the filaments ends in an accretion disk around the proto star. This disk gradually collects the surrounding matter and finally the star is formed inside. Triggered by this process additionally ionized gas is ejected perpendicular to the disk in so-called jets. In a low-mass star, these processes occur comparatively ordered in clearly distinguishable phases and altogether last about one million years. If the pressure inside the proto star is high enough, the hydrogen burning (the fusion of hydrogen nuclei to helium) is ignited - the new star is born.

star formation region S106
Image of the star formation region S106 in the constellation Cygnus
(the swan), taken by the Hubble Space Telescope. In the center is the
young, massive double star S106 IR, which is surrounded by dust, and
is responsible for the hourglass-like shape of the surrounding gas cloud
and the visible turbulence therein. Copyright: NASA & ESA

How exactly do massive stars form in our Milky Way? Dr. Nicola Schneider from the University of Cologne and her international team pursues this question in the GENESIS project S106 by combining observations with SOFIA, the Stratospheric Observatory for Infrared Astronomy, with data from other observatories. These sort of studies are the main objectives of GENESIS, a German-French collaborative project between N. Schneider, R. Simon from the I. Physik. Institut, Cologne and S. Bontemps from the Laboratoire d’Astrophysique of Bordeaux. All stars, even ordinary ones like our Sun, are formed by interstellar gas and dust clouds. These clouds show a complex structure with filaments and clumps. The mass flow along the filaments ends in an accretion disk around the proto star. This disk gradually collects the surrounding matter and finally the star is formed inside. Triggered by this process, additionally ionized gas is ejected perpendicular to the disk in so-called jets. In a low-mass star, these processes occur comparatively ordered in clearly distinguishable phases and altogether last about one million years. If the pressure inside the proto star is high enough, the hydrogen burning (the fusion of hydrogen nuclei to helium) is ignited - the new star is born.

Schematic representation / Animation of the S106 region
Schematic representation / animation (pleas click) of the S106 region
(Figure 3) projected onto an IR image of the region.
Copyright: M. Röllig & N. Schneider

Massive stars, on the other hand, presumably collapse within only a few thousand years and start their hydrogen burning, even while the accretion disk is still being formed - the different phases of star formation do not take place sequentially, but simultaneously and are difficult to study separately. And in order not to make it too easy for the researchers, the massive stars are usually not formed individually, but together with one or even several equally massive companions and with many low-mass stars together.
In order to better understand the different processes and phases involved in the formation of massive stars, the team headed by Nicola Schneider has now measured the neutral oxygen [OI] emission line at 63 μm with the German REceiver for Astronomy at Terahertz Frequencies (GREAT) onboard SOFIA in the star formation area S106 with high frequency accuracy. Using the high-resolution spectral data provided by this instrument, the astronomer can determine the different velocity distributions within the gas. A physical model adapted to this data then allows one to derive the spatial distribution of the element and other important physical parameters (e.g., density and temperature) of the overall system. Indeed, the data analyzed by Nicola Schneider confirm that at the center of S106 is a massive binary star system, and that this star formation area is in a fast and dynamic process of simultaneously accumulating and expelling material.

components of the S106 star formation area
The main components of the S106 star formation area: In the center
is  the massive double star around which the accretion flow 'winds'
and material is transported to a star in formation. Perpendicular to
this are ionized cavities, also called the HII region.
Copyright: M. Röllig N. Schneider

And there is still no end in sight: Observations with the 30  meter  telescope of the Institut de Radioastronomie Millimétrique (IRAM ) in the Spanish Sierra Nevada show that large amounts of cold gas are still plunging into the center of S106 and continue driving these turbulent processes. Shock fronts can additionally influence and change the structure of the star formation area. With the help of SOFIA data and forthcoming observations with the NOEMA interferometer from IRAM, Nicola Schneider now wants to investigate the extent to which shock fronts form on the impact of the hot, ejected gas on the incoming cold gas, and how important filaments are as mass transporters in the star formation

 
















single images of the [OI] line
The individual images on this map show how the [OI] emission
changes with speedCopyright: N. Schneider

In the scientific publication on the [OI] 63 μm observations of S106, Nicola Schneider also describes how she can generally derive the three-dimensional ionization, the density, and the velocity structure of a star formation region, only from high spectral resolution data. Because of the far-reaching importance of this template analysis, her article was selected to be the 'highlight paper' of the September issue of Astronomy and Astrophysics (A & A, 617 (2018) A45).





Further Links

Further SOFIA Links

Contact: Dörte Mehlert, Email: mehlert@dsi.uni-stuttgart.de; Tel.:0711 - 685-69632

GREAT/upGREAT, the „German Receiver for Astronomy at Terahertz Frequencies“, was developed and built by a consortium of German research institutes (MPI for Radio Astronomy, Bonn and KOSMA/Universität zu Köln, in collaboration with the DLR Institute for Planetary Research, Berlin, and the MPI for Solar System Research, Göttingen). The GREAT Principal Investigator (PI) is Jürgen Stutzki from Cologne University, Deputy Principal Investiogator (Co-PI) in Bernd Klein from MPIfR. The development of the instrument was financed by means of the participating institutes, Max Planck Society and German Research Society.

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