The innermost regions of circumstellar discs

The innermost regions of circumstellar discs

Herbig Ae/Be stars are young stellar objects with masses in between low mass young stars (or T Tauri stars) and high mass young stars (the MYSOs mentioned above). As we consider stars of larger mass, their interior structure changes, and may make it more difficult to generate magnetic fields. These magnetic fields are important because they regulate how the young stars accrete material from surrounding circumstellar discs.

In order to investigate the inner regions of these discs, we used another spectrograph mounted on the VLT called X-Shooter. This instrument provides a very large wavelength coverage, from the UV and blue regions of the spectrum right across to the near-infrared. Collecting all of this information in ‘one shot’ is very useful, as any effects of source variability can be ignored.

Figure 1: The Herbig Ae/Be star IRAS 10082-5647 and below it an image showing the long wavelength coverage of VLT/X-Shooter (ESA/Hubble & NASA)

Figure 1: The Herbig Ae/Be star IRAS 10082-5647 and below it an image showing the long wavelength coverage of VLT/X-Shooter (ESA/Hubble & NASA)

Using our CO model, we showed that the CO bandhead emission can be well represented by small scale gaseous discs around the stars. We also examined the relationship between the CO bandheads mentioned above, and an atomic hydrogen emission line - Brackett γ (produced by even higher temperature processes) and found that these emission lines seem to be correlated, despite appearing to originate in different enviroments in the disc.

In a seperate study, the X-Shooter data mentioned above were used to determine a set of consistent stellar parameters and accretion rates for the ninty objects in the entire sample. This is the largest and most complete set of stellar parameters ever determined for Herbig Ae/Be stars. In addition, various differences between Ae and Be stars were found, suggesting the latter may be accreting in a different manner to low mass stars.

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Dr John D. Ilee
Postdoctoral Research Fellow