Stars and their formation

  • Star formation – Ian Bonnell, Claudia Cyganowski, Kenny Wood
  • Stellar magnetospheres & winds – Moira Jardine
  • Brown dwarfs & atmospheres – Christiane Helling, Aleks Scholz
  • Protoplanetary discs – Peter Woitke, Aleks Scholz, Kenny Wood
  • Massive star formation – Ian Bonnell, Claudia Cyganowski
  • Stellar clusters – Ian Bonnell, Claudia Cyganowski

 

Star formation

Ian Bonnell, Claudia Cyganowski, Kenny Wood

Galaxies such as our own are constantly forming new stars, primarily in dense clouds of gas and dust. Gravity, acting to collapse the material in the clouds, is variously helped and hindered by turbulence, pressure, magnetism, and potentially feedback from previously-formed stars. The interplay of forces makes it a complex process and it is still not certain how they determine the final properties of the resulting stars and stellar clusters. In an effort to understand this, the St Andrews research group combines observations of star forming regions with hydrodynamical and radiative transfer simulations of the process. Thus we can examine the process at the largest scales of entire galaxies in order to understand how star forming clouds are themselves formed, and at the smallest scales where we can follow the formation of individual stars.

star formation

Two simulations of stars forming within a cold, dense and turbulent cloud.

The image above shows the results of two simulations of stars forming within a cold, dense and turbulent cloud. The stars are shown as white points. Both simulations were created from the same original setup with the cloud enshrouded by a warm envelope. The cloud shown on the right lost its envelope during its evolution as might be expected if it were exposed to an external source of feedback. As a result, the cloud on the right has formed far fewer stars than the one on the left which retained its envelope, revealing some of the star forming process’s dependency on the containment effect provided by the envelope.

 

 

Stellar magnetospheres & winds

Moira Jardine

Depiction of the sun's magnetic fields over an image captured by NASA's Solar Dynamics Observatory.(Credits: NASA/SDO/AIA/LMSAL)

Depiction of the sun’s magnetic fields over an image captured by NASA’s Solar Dynamics Observatory. (Credits: NASA/SDO/AIA/LMSAL)

In its youth, our Sun probably had a magnetic field that was more active than it is today, resulting in larger flares, a hotter corona and more powerful radio and X-ray emission. This field would have had a significant impact on planet formation and on the way the Sun has been spun down from its initial phase of rapid rotation. We are modelling the generation of magnetic fields deep within young stars and the way these fields are structured in the outer stellar corona. From Zeeman-Doppler images of the surface magnetic fields of young Suns we can extrapolate the coronal field to show the open field lines (where a wind might escape) and the closed field lines where stellar prominences may form (see figure). By studying the structure of these fields for a range of stars as they spin down with age, we hope to learn more about the early stages of stellar evolution.
We are also studying magnetic fields in evolved stars. The field in a planetary nebula is thought to act as a ‘tube’ that forces gas out along the rotation axis. This mechanism might explain why envelopes are spherical in AGB stars, but become elongated when the star evolves into the planetary nebula stage. In the first such object to be detected, NGC 7027, the polarization direction is perpendicular to the jets, suggesting the presence of a magnetic ‘torus’ or tube that is squeezing the gas flow.