Young stellar objects: The source of gas emission around Herbig Ae/Be stars

Oct 10, 2008

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) 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.

Source: Astronomy & Astrophysics

Explore further: 'Perfect storm' quenching star formation around a supermassive black hole

add to favorites email to friend print save as pdf

Related Stories

Magnetic fields on solar-type stars

Dec 12, 2014

The Sun rotates slowly, about once every 24 days at its equator although the hot gas at every latitude rotates at a slightly different rate. Rotation helps to drive the mechanisms that power stellar magnetic ...

Effects of accretion disks around newborn stars

Dec 08, 2014

Stars are born in dense, cool clouds of molecular gas and dust. When the local density is high enough, the matter can gravitationally collapse to form a new star, a so-called young stellar object (YSO). In ...

Hubble spies charming spiral galaxy bursting with stars

Dec 09, 2014

( —The NASA/ESA Hubble Space Telescope observes some of the most beautiful galaxies in our skies—spirals sparkling with bright stellar nurseries, violent duos ripping gas and stars away from ...

Herschel observes Andromeda's past and future stars

Dec 01, 2014

Recently, the infrared Herschel Space Observatory, has taken a series of beautiful high-resolution infrared images of Andromeda. It is the first time we can see M31, at these wavelengths, at such a high resolution. ...

Recommended for you

The hot blue stars of Messier 47

Dec 17, 2014

Messier 47 is located approximately 1600 light-years from Earth, in the constellation of Puppis (the poop deck of the mythological ship Argo). It was first noticed some time before 1654 by Italian astronomer ...

Why is space black?

Dec 16, 2014

Imagine you're in space. Just the floating part, not the peeing into a vacuum hose or eating that funky "ice cream" from foil bags part. If you looked at the Sun, it would be bright and your retinas would ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.