An international team of astronomers led by E. Tatulli (Grenoble, France) and S. Kraus (Bonn, Germany)  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 , 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 . 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.
 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).
 Observing the Moon with milli-arcsecond resolution, one should be able to distinguish details about 2 meters in size.
 They used the Brackett-Γ line of hydrogen at 2.166 µm and the CO emission feature at 2.3 µm as diagnostic lines.
Significantly more productivity in USP lasers
06.12.2016 | Fraunhofer-Institut für Lasertechnik ILT
Shape matters when light meets atom
05.12.2016 | Centre for Quantum Technologies at the National University of Singapore
In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.
Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
16.11.2016 | Event News
01.11.2016 | Event News
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07.12.2016 | Health and Medicine
07.12.2016 | Life Sciences
07.12.2016 | Health and Medicine