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Post Info TOPIC: Herbig-Haro (HH) 211
Blobrana


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"This is a truly unique observation that will provide important information about the chemistry occurring in planet-forming regions, and may give us insights into the chemical reactions that made water and even life possible in our own solar system" - Achim Tappe, of the Harvard-Smithsonian Centre for Astrophysics, Cambridge, Mass.

A young star forms out of a thick, rotating cloud of gas and dust. Like the two ends of a spinning top, powerful jets of gas emerge from the top and bottom of the dusty cloud. As the cloud shrinks more and more under its own gravity, its star eventually ignites and the remaining dust and gas flatten into a pancake-like disk, from which planets will later form. By the time the star ignites and stops accumulating material from its cloud, the jets will have died out.

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Water is being blasted to pieces by a young star's laser-like jets, according to new observations from NASA's Spitzer Space Telescope.
The discovery provides a better understanding of how water -- an essential ingredient for life as we know it -- is processed in emerging solar systems.

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Blobrana


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Astronomers have found the best evidence yet of matter spiralling outward from a young, still-forming star in fountain-like jets. Due to the spiral motion, the jets help the star to grow by drawing angular momentum from the surrounding accretion disk.

"Theorists knew that a star has to shed angular momentum as it forms. Now, we see evidence to back up the theory" - astronomer Qizhou Zhang of the Harvard-Smithsonian Center for Astrophysics (CfA).

Angular momentum is the tendency for a spinning object to continue spinning. It applies to star formation because a star forms at the centre of a rotating disk of hydrogen gas. A star grows by gathering material from the disk. However, gas cannot fall inward toward the star until that gas sheds its excess angular momentum.
As hydrogen nears the star, a fraction of the gas is ejected outward perpendicular to the disk in opposite directions, like water from a fire hose, in a bipolar jet. If the gas spirals around the axis of the jet, then it will carry angular momentum with it away from the star.
Using the Submillimeter Array (SMA), an international team of astronomers observed an object called Herbig-Haro (HH) 211, located about 1,000 light-years away in the constellation Perseus. HH 211 is a bipolar jet travelling through interstellar space at supersonic speeds. The central protostar is about 20,000 years old with a mass only six percent the mass of our Sun. It eventually will grow into a star like the Sun.
The astronomers found clear evidence for rotation in the bipolar jet. Gas within the jet swirls around at speeds of more than 3,000 miles per hour, while also blasting away from the star at a velocity greater than 200,000 miles per hour.

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RA(2000) = 03h 43m 56.7s, Dec(2000) = +32  00 50.3


Title: Submillimeter arcsecond-resolution mapping of the highly collimated protostellar jet HH 211
Authors: Chin-Fei Lee, Paul T.P. Ho, Aina Palau, Naomi Hirano, Tyler L. Bourke, Hsien Shang, Qizhou Zhang

We have mapped the protostellar jet HH 211 in 342 GHz continuum, SiO (J=8-7), and CO (J=3-2) emission at ~ 1 resolution with the Submillimeter Array (SMA). Thermal dust emission is seen in continuum at the centre of the jet, tracing an envelope and a possible optically thick compact disk (with a size < 130 AU) around the protostar. A knotty jet is seen in CO and SiO as in H2, but extending closer to the protostar. It consists of a chain of knots on each side of the protostar, with an interknot spacing of  ~ 2-3 or 600-900 AU and the innermost pair of knots at only ~ 1.7 or 535 AU from the protostar. These knots likely trace unresolved internal (bow) shocks (i.e., working surfaces) in the jet, with a velocity range up to ~ 25 km/s. The two-sided mass-loss rate of the jet is estimated to be ~ (0.7-2.8) x 10^-6 solar masses yr^-1. The jet is episodic, precessing, and bending. A velocity gradient is seen consistently across two bright SiO knots (BK3 and RK2) perpendicular to the jet axis, with ~ 1.5 ± 0.8 km/s at ~ 30 ± 15 AU, suggesting a presence of a jet rotation. The launching radius of the jet, derived from the potential jet rotation, is ~ 0.15-0.06 AU in the inner disk.

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Blobrana


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Astronomers find jets everywhere when they look into space.
Small jets spout from newborn stars, while huge jets blast out of the centres of galaxies.
Yet despite their commonness, the processes that drive them remain shrouded in mystery.
Even relatively nearby stellar jets hide their origins behind almost impenetrable clouds of dust. All stars, including our sun, pass through a jet phase during their "childhood," so astronomers are eager to understand how jets form and how they may influence star and planet formation.



At this week's meeting on submillimeter astronomy in Cambridge, Mass., astronomers described the latest results from an international collaboration using the Submillimetre Array (SMA) atop Mauna Kea, Hawaii.
The SMA has begun to peer through the dust and home in on the sources of nearby stellar jets.
"Using the SMA, we can stare into the throat of the jet. We're getting close to seeing its launching point" - Paul Ho, SMA project scientist, Harvard-Smithsonian Centre for Astrophysics (CfA).

Astronomer Hsien Shang of the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) and her colleagues have created a model of jet formation that calculates temperatures, densities and brightness within stellar jets. SMA observations of a young star system prosaically named Herbig-Haro (HH) 211 have confirmed the validity of the model.

"Our model predicts what we will see about 100 astronomical units from the star. With the SMA, we can begin to look at the HH 211 system at the scale of the model and test those predictions. So far, everything checks out." - Hsien Shang.
HH 211 is located about 1,000 light-years away in the constellation Perseus.
Astronomers estimate that the small protostar hidden within HH 211 is less than 1,000 years old-a mere baby by astronomical standards, so young that it is still growing by accumulating matter from a surrounding disk of gas and dust.
The protostar eventually will become a low-mass star similar to the sun.
Although most of the matter in the disk will flow onto the star, some must be ejected outward to carry away excess angular momentum.
Complex physical processes funnel that ejected matter into dual jets that shoot outward in opposite directions.

hh211
Expand (681kb, 2400 x 2387)
Credit: A.A. Muench-Nasrallah, CfA

Position(2000): RA 03h 43m 57.5s , Dec 32° 00' 46"

Herbig-Haro 211 consists of two jets of material, visible at lower right, blasting from a young protostar hidden behind dust. The Submillimeter Array has looked deep within the inner regions of the jets, close to their launching point, in order to test predictions of jet formation models. This infrared image was taken using the FLAMINGOS camera, which was designed and constructed at the University of Florida. Credit: A.A. Muench-Nasrallah, CfA

"Jets form very close to a protostar, within about 5 million miles of its surface according to the model we applied. The SMA can help test the jet model on the youngest protostars using molecular tracers from within that innermost region." - Naomi Hirano (ASIAA).

SMA's successor, the planned ALMA project, should finally reveal the nature of the engine powering these jets by peering into the core where they form.
"The SMA has brought us tantalizingly close to our goal-the answer to the question of how jets form. ALMA will take us those final few steps" - Paul Ho.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Centre for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

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-- Edited by Blobrana at 07:59, 2007-12-27

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