SETI [ASTRO] VLBA Scientists Study Birth of Sunlike Stars


Larry Klaes (lklaes@bbn.com)
Mon, 07 Jun 1999 21:04:54 -0400


>X-Authentication-Warning: brickbat12.mindspring.com: majordom set sender to owner-astro using -f >Date: Mon, 7 Jun 1999 19:18:35 GMT >From: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov> >To: astro@lists.mindspring.com >Subject: [ASTRO] VLBA Scientists Study Birth of Sunlike Stars >Sender: owner-astro@brickbat12.mindspring.com >Reply-To: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov> > >National Radio Astronomy Observatory >P.O. Box O >Socorro, New Mexico 87801 >http://www.nrao.edu > >Contact: >Dave Finley, Public Information Officer >(505) 835-7302 dfinley@nrao.edu > >FOR RELEASE: June 1, 1999 > >VLBA Scientists Study Birth of Sunlike Stars > >Three teams of scientists have used the National Science Foundation's Very >Long Baseline Array (VLBA) radio telescope to learn tantalizing new details >about how Sun-like stars are formed. Young stars, still growing by drawing >in nearby gas, also spew some of that material back into their surroundings, >like impatient infants that eat too quickly. The VLBA observations are >giving astronomers new insights on both processes -- the accretion of >material by the new stars and the outflows of material from them. > >"For the first time, we're actually seeing what happens right down next to >the star in these young systems," said Mark Claussen, of the National Radio >Astronomy Observatory (NRAO) in Socorro, NM. Claussen and other researchers >announced their findings at the American Astronomical Society's meeting in >Chicago. > >Material attracted by a young star's gravitational pull forms a flat, >orbiting disk, called an accretion disk, in which the material circles >closer and closer to the star until finally drawn into it. At the same time, >material is ejected in "jets" speeding from the poles of the accretion disk. >"The VLBA is showing us the first images of the region close to the star >where the material in these jets is accelerated and formed into the 'beams' >of the jet," Claussen said. > >"We don't understand the details of these processes well," Claussen said. >"These VLBA research projects are beginning to help unravel the mysteries >of how stars like the Sun form." > >The teams are observing clumps of water vapor that naturally amplify radio >emissions to see details smaller than the orbit of Mercury in young stellar >systems as well as track gas motions. The clumps of gas are called masers, >and amplify radio emission in much the same way that a laser amplifies >light emission. "These images are just fantastic," said Al Wootten of NRAO >in Charlottesville, VA. The maser clumps or "spots," emitting radio waves >at a specific wavelength, can be tracked as they move over time. In addition, >by measuring the Doppler shift in the wavelength of these emissions, >astronomers can determine the speed at which the gas is moving. > >In an object known as S106FIR, 2,000 light-years away in the constellation >Cygnus, a team of Japanese and U.S. VLBA observers led by Ray Furuya, a >graduate student from Japan's Nobeyama Radio Observatory, has tracked the >motion of material outward in the jet. This object, embedded in a dense >cloud of molecular gas, the material from which the star is forming, shows >maser spots moving in two directions as the jets emerge from both poles of >the accretion disk. "The water masers are the only way we can detect the >outflow from this young star," Furuya said. The VLBA observations can >discern details as small as half the distance from the Earth to the Sun. "We >can see outflow on scales the size of our Solar System. We think this object >is one of the youngest protostars known," Furuya said. > >In another object, dubbed IRAS 16293-2422, in the constellation Ophiuchus, >astronomers believe the water masers clearly show the outflowing jets of >a young star and may be tracing the accretion disk as well. The young star >is one of a pair of stars in a binary system some 500 light-years distant. >The water-vapor masers are seen around only one of the pair, however. "In >this system, we see outflow in the jet and also an elliptical ring of masers >that may be part of the accretion disk," said Wootten, leader of the team >observing this object. "The VLBA is showing us details as small as the size >of Mercury's orbit around the Sun, a great help in understanding the physics >going on there," Wootten said. > >A team composed largely of astronomers from the Harvard-Smithsonian Center >for Astrophysics in Cambridge, MA, also used the VLBA to study water masers >in a young stellar object 2,500 light-years away in Cepheus. This team sees >maser spots moving in opposite directions away from the young star on scales >of ten times the diameter of the solar system, presumably tracing the jet or >wind. On smaller scales, there is a circular loop of masers which the >astronomers believe surrounds the young stellar object. "The loop probably >represents the edge of a dusty shell of gas smaller than the Earth's orbit. >The star is several times the mass of the Sun and its heat evaporates >material closer in," said Nimesh Patel, leader of the team. > >The ability to see the details of stars still undergoing their formation >processes is extremely valuable to understanding the details of those >processes, according to Claussen, a member of the teams led by Furuya and >Wootten. "The VLBA images show detail about 100 times better than those >routinely available from other radio telescopes," Claussen said. "Studying >these systems by observing the clumps of water vapor that act as masers >is not particularly difficult with the VLBA. There are hundreds of young >stars that we can study this way, and that means that we have a tremendous >opportunity to learn just how stars similar to our Sun are formed and >interact with their surroundings in the early parts of their lives." > >The VLBA is a system of ten radio-telescope antennas, each 25 meters (82 >feet) in diameter, stretching some 5,000 miles from Mauna Kea in Hawaii to >St. Croix in the U.S. Virgin Islands. Operated from NRAO's Array Operations >Center in Socorro, NM, the > >VLBA offers astronomers the greatest resolving power, or ability to see fine >detail, of any telescope currently operational. The NRAO is a facility of >the National Science Foundation, operated under cooperative agreement by >Associated Universities, Inc. > > ### > >[IMAGE CAPTION: http://www.nrao.edu/pr/protoh2o.html] > >A newly forming Sun-like star, known as S106FIR. The lower left-hand panel >shows the dense molecular gas which supplies the natal material for the new >star. Note the size scale of the molecular clump of gas -- several thousand >Astronomical Units (A.U.). An Astronomical Unit is the distance from the >Earth to the Sun, or about 93 millioin miles. The top left panel shows the >water masers (purple dots) seen by the VLA in two oppositely directed >flows. The scale here is only tens of A.U. Astronomers assume, but have >not yet detected, the star in the center of the outlfow (represented by the >blue circle). One group of masers (to the southwest) has been observed over >three months with the VLBA at a resolution of less than half the distance >from the Earth to the Sun. The lower right panel shows the masers, color- >coded by observation date, in a very small "microjet" structure that >appears to delineate a shock where the outflowing jet fas runs into >other material surrounding the newly forming star. Credit: Ray Furuya, et >al., National Radio Astronomy Obsrvatory, Associated Universities, Inc. > >



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