New high-resolution observations with the VLT Interferometer of the European Southern Observatory in Chile reveal gas infall and outflow processes in the direct environment of six young stars. The origin of the gas emission from these stars is still strongly debated, since earlier investigations could not resolve the gas distribution close to the star. An international team of astronomers, led by Stefan Kraus from the Max Planck Institute for Radio Astronomy in Bonn, Germany and Eric Tatulli from the Observatoire de Grenoble in France used the AMBER instrument to measure the geometry of atomic and molecular gas in the inner disk regions. Surprisingly, they found that the gas emission can trace very distinct physical mechanisms. These processes include infall of material onto the star as well as gas which is ejected from the system, likely in a disk wind. The results are published in this week’s issue of “Astronomy & Astrophysics”.
An international team of astronomers led by Stefan Kraus from the Max Planck Institute for Radio Astronomy in Bonn, Germany, and Eric Tatulli from the Observatoire de Grenoble, France, used the unique capability of the VLT near-infrared interferometer, coupled with spectroscopy, to probe the gaseous environment of a specific type of young stars called Herbig Ae/Be stars. These are young stars of intermediate mass (approximately 2 to 10 solar masses) which are still contracting and which often show strong line emission.
In recent years, young stars have been widely studied with near-infrared interferometers, allowing astronomers to study their close environment with high spatial resolution. “But so far, near-infrared interferometry has been mostly used to probe the dust that closely surrounds young stars,” says Eric Tatulli. “However, dust is only one percent of the total mass of the discs, while gas is their main component and may define the final architecture of forming planetary systems.”
High-resolution observations of emission spectral lines are required to trace this gaseous component. Various processes have been proposed as the source of emission lines. For example, the emission lines might come from an accreting gaseous inner disk or might be due to magnetospheric accretion processes or a stellar wind. Most of these processes take place close to the star (less than 1 AU, or the distance between Earth and the Sun) and are therefore not accessible with direct imaging facilities.
An international team of astronomers led by Stefan Kraus from the Max Planck Institute for Radio Astronomy in Bonn, Germany, and Eric Tatulli from the Observatoire de Grenoble, France, used the unique capability of the VLT near-infrared interferometer, coupled with spectroscopy, to probe the gaseous environment of a specific type of young stars called Herbig Ae/Be stars. These are young stars of intermediate mass (approximately 2 to 10 solar masses) which are still contracting and which often show strong line emission.
In recent years, young stars have been widely studied with near-infrared interferometers, allowing astronomers to study their close environment with high spatial resolution. “But so far, near-infrared interferometry has been mostly used to probe the dust that closely surrounds young stars,” says Eric Tatulli. “However, dust is only one percent of the total mass of the discs, while gas is their main component and may define the final architecture of forming planetary systems.”
High-resolution observations of emission spectral lines are required to trace this gaseous component. Various processes have been proposed as the source of emission lines. For example, the emission lines might come from an accreting gaseous inner disk or might be due to magnetospheric accretion processes or a stellar wind. Most of these processes take place close to the star (less than 1 AU, or the distance between Earth and the Sun) and are therefore not accessible with direct imaging facilities.
*Original Papers: *
The origin of hydrogen line emission for five Herbig Ae/Be stars spatially resolved by VLTI/AMBER spectro-interferometry, Kraus, S.; Hofmann, K.-H.; Benisty, M.; Berger, J.-P.; Chesneau, O.; Isella, A.; Malbet, F.; Meilland, A.; Nardetto, N.; Natta, A.; Preibisch, T.; Schertl, D.; Smith, M.; Stee, P.; Tatulli, E.; Testi, L.; Weigelt, G. , Astronomy & Astrophysics Volume 489, Issue 3, 2008, pp.1157-1173, and Spatially resolving the hot CO around the young Be star 51 Ophiuchi, Tatulli, E.; Malbet, F.; Menard, F.; Gil, C.; Testi, L.; Natta, A.; Kraus, S.; Stee, P.; Robbe-Dubois, S., Astronomy and Astrophysics, Volume 489, Issue 3, 2008, pp.1151-1155.
*Contact: *
* Dr. Stefan Kraus,
Max-Planck-Institut fuer Radioastronomie, Bonn.
Fon: +49 228 525 395
E-mail: skraus@mpifr.de
* Dr. Eric Tatulli,
Observatoire de Grenoble, France.
Fon: +33 4 76 63 57 75
E-mail: etatulli@obs.ujf-grenoble.fr
* Dr. Norbert Junkes,
Public Outreach,
Max-Planck-Institut fuer Radioastronomie, Bonn.
Fon: +49-228-525-399
E-mail: njunkes@mpifr.de
