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| PRI (MPIfR) 10/2008 (1) | Press Release | October 10, 2008 |
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".
Figure 1:
Artist's impression of the environment of a young stellar object (YSO),
showing the geometry of the dust disk in the outer area and the hot gas disk
closer to the central star.
The extension of the gas disk is smaller than the distance between Earth and
the Sun in the solar system.
Image & Copyright: ESO/L. Calçada, ESO PR 35-08, October 10, 2008 (Click image for higher resolution).
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.
Figure 2:
The Paranal platform showing the four main VLT 8.2 m telescopes, as well the
four 1.8 m auxiliary telescopes.
Image: ESO photo, January 2007.
(Click image for higher resolution).
Using the ability of the VLTI and the AMBER instrument allowed the astronomers to see details equivalent to the dot at the end of this sentence from a distance of 1000 kilometres and, thus, to study the inner gaseous environments of the six young stars with unprecedented resolution.
"Until now, the origin of the gas emission from these young stars was still debated, because in most earlier investigations of the gas component, the spatial resolution was not high enough to study the gas distribution close to the star," says Stefan Kraus. "The researchers had very different ideas about the physical processes traced by the gas. By combining spectroscopy and interferometry, the VLTI now gives us the opportunity to distinguish between the physical mechanisms responsible for the observed gas emission."
The team measured the geometry and position of the emitting regions surrounding these stars for several diagnostic emission lines. In two of the stars, the emission lines are probably associated with mass infall, either originating within a dust-free, hot gaseous disk or within a very compact emitting region, through which the material is transported from the disk to the stellar surface. For the other four target stars, the line emission seems to be related to mass outflow, with gas lifted from the surface of a circumstellar disk and then ejected from the stellar system.
"Future observations using VLTI spectro-interferometry will allow
us to determine both the geometry and motion of the gas
and might reveal whether the observed line emission is caused by a
jet launched from the disk or by a stellar wind", concludes Stefan Kraus.
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.; Ménard, 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.
Astronomers get best view yet of infant stars at feeding time, ESO Science Release 35/08, October 10, 2008.
Zoom sur le disque de gaz autour des étoiles jeunes, foyer de naissance des planètes, Press Release Observatoire de Grenoble, October 10, 2008.
Young stellar objects: the source of gas emission around Herbig Ae/Be stars, A&A Press Release, October 10, 2008.
The Growing-up of a Star, ESO Press Release 03/08, January 29, 2008.
Shedding New Light on the Life Cycle of Stars, MPIfR & MPG Press Release 02/2007, February 21, 2007.
AMBER Looks Into the Cradle of Planets,
MPIfR & MPG Press Release 2005, November 28, 2005.
Max Planck Institute for Radio Astronomy (MPIfR).
Infrared Interferometry Group at MPIfR.
Laboratoire d'Astrophysique de Grenoble (LAOG).
European Southern Observatory (ESO).
Very Large Telescope Interferometer (VLTI) of ESO.
Astronomical Multi-BEam combineR (AMBER) at ESO/Paranal.
Dr. Stefan Kraus,
Max-Planck-Institut für Radioastronomie, Bonn.
Fon: +49 228 525 395
E-mail: skraus (at)
mpifr.de
Dr. Eric Tatulli,
Observatoire de Grenoble, France.
Fon: +33 4 76 63 57 75
E-mail: etatulli (at)
obs.ujf-grenoble.fr
Dr. Norbert Junkes,
Public Outreach,
Max-Planck-Institut für Radioastronomie, Bonn.
Fon: +49-228-525-399
E-mail: njunkes (at)
mpifr.de