A&A press release: Young stellar objects: the source of gas emission around [..] (10 October 2008)
- Details
- Published on 08 October 2008
A&A press release
Released on October 10th, 2008
|
Young stellar objects: the source of gas emission around Herbig Ae/Be
stars |
Based on the articles:
“Spatially resolving the hot CO around the young Be star 51 Ophiuchi”, by E. Tatulli et al.
and
“The origin of hydrogen line emission for five Herbig Ae/Be stars spatially resolved by VLTI/AMBER spectro-interferometry”, by S. Kraus et al.
Published in Astronomy & Astrophysics , 2008, vol. 489-3, pp. 1151-1173
This week, Astronomy
& Astrophysics is publishing new high-resolution
observations of the gas component surrounding six young stars with the
AMBER/VLTI instrument (ESO, Chile). Astronomers were able to measure
the spatial distribution of the hydrogen and CO gas emission in the
inner disks around six Herbig Ae/Be stars. They found that the gas
emission can clearly trace the infall of matter onto the star or the
ejection of gas from the system.
This week, Astronomy
& Astrophysics is publishing new observations with
AMBER/VLTI of the gas component in the vicinity of young stars. An
international team of astronomers led by E. Tatulli (Grenoble, France)
and S. Kraus (Bonn, Germany) [1] used the unique capability of the VLT
near-infrared interferometer, coupled with spectroscopy, to probe the
gaseous environment of Herbig Ae/Be stars. These are young stars of
intermediate mass (approximately 2 to 10 solar masses), which are still
contracting and often show strong line emissions.
In recent years, young stars have been widely studied with
near-infrared interferometers, allowing astronomers to study
their close environment with high spatial resolution (see for example
the A&A
special feature on AMBER/VLTI first results, published in
March 2007). So far, near-infrared interferometry has been used mostly
to probe the dust that closely surrounds young stellar objects.
However, dust is only 1% of the total mass of protoplanetary disks,
while gas is their main component (99%) and may be responsible for the
structure of forming planetary disks. High-resolution observations of
emission spectral lines are then required to trace this gaseous
component. Various processes have been proposed as the source of
emission lines. For example, they might come from an accreting gaseous
inner disk or might be due to either magnetospheric accretion processes
or to a stellar wind. Most of these processes would take place close to
the star (less than 1 AU), and are therefore not accessible with direct
imaging facilities.
Using the capabilities of AMBER/VLTI, including milli-arcsecond spatial
resolution [2], the team has now been able to trace the inner gaseous
environment of six Herbig Ae/Be stars. They measured the geometry and
position of the emitting regions surrounding these stars, for several
diagnostic emission lines [3]. For two Herbig Be stars, they find that
the emission line is probably associated with mass infall; in one case
(51 Ophiuchi), the emission line could originate within a dust-free hot
gaseous disk. In the other one (HD 98922), the emitting region is very
compact and might originate from magnetospheric accretion, through
which the material is transported from the disk to the stellar surface.
For the four other Herbig Ae/Be stars that have been observed, the
emission line would be related to mass outflow, with gas lifted from
the surface of a circumstellar disk and then ejected from the stellar
system.
Until now, the origin of the gas emission from these young stars was
still being 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. Applying the new high-resolution
feature of the AMBER instrument to gas emission observations, the team
was then able to show that the gas emission can distinctly trace the
physical processes acting close to the star.
Fig. 1 - Artist's impression of the environment of a young star, showing the geometry of the dust disc in the outer area
and the hot gas disc closer to the central star.
© ESO/L. Calçada. Full resolution versions of this picture are available on the ESO web site
[1] The team includes S. Kraus, K.-H. Hofmann, A. Meilland, N. Nardetto, T. Preibisch, D. Schertl, G. Weigelt (MPI, Bonn, Germany), E. Tatulli (INAF, Italy / Laboratoire d'Astrophysique de Grenoble, France), M. Benisty, J.-P. Berger, F. Malbet, F. Ménard (Laboratoire d'Astrophysique de Grenoble, France), O. Chesneau, P. Stee, (OCA, France), A. Natta (INAF, Italy), M. Smith (Univ. of Kent, UK), C. Gil, L. Testi (ESO), and S. Robbe-Dubois (Université de Nice, France).
[2] Observing the Moon with milli-arcsecond resolution, one should be able to distinguish details about 2 meters in size.
[3] They used the Brackett-γ line of hydrogen at 2.166 μm and the CO emission feature at 2.3 μm as diagnostic lines.
Spatially resolving the hot CO around the young Be star 51 Ophiuchi, by E. Tatulli, F. Malbet, F. Menard, C. Gil, L. Testi, A. Natta, S. Kraus, P. Stee, and S. Robbe-Dubois.
The origin of hydrogen line emission for five Herbig Ae/Be stars spatially resolved by VLTI/AMBER spectro-interferometry, by S. Kraus, K.-H. Hofmann, M. Benisty, J.-P. Berger, O. Chesneau, A. Isella, F. Malbet, A. Meilland, A. Nardetto, A. Natta, Th. Preibisch, D. Schertl, M. Smith, P. Stee, E. Tatulli, L. Testi, and G. Weigelt.
Published in Astronomy & Astrophysics, 2008, volume 489-3, pp. 1151-1173.
Free version of the articles in PDF format: Tatulli et al. and Kraus et al.
The European Southern Observatory and the Max-Planck-Institute für Radioastronomie have also published press releases on this work.
Contacts:
- Science:
Dr Stefan
Kraus
Max-Planck-Institute for Radio Astronomy
Bonn, Germany
Email: skraus (at) mpifr-bonn.mpg.de
Phone: +49 (0)228 525 395
Dr. Eric Tatulli
Observatoire de Grenoble
France
Email: etatulli (at) obs.ujf-grenoble.fr
Phone: +33 (0)4 76 63 57 75
- Press office:
Dr.
Jennifer Martin
Journal Astronomy & Astrophysics
61, avenue de l'Observatoire
75014 Paris, France
Email: aanda.paris (at) obspm.fr
Phone: +33 1 43 29 05 41
© Astronomy & Astrophysics 2008