SETI [ASTRO] Hubble Images May Shed Light on Importance of Novae in Galactic Evolution


Larry Klaes (lklaes@bbn.com)
Fri, 04 Jun 1999 15:51:47 -0400


>X-Authentication-Warning: brickbat12.mindspring.com: majordom set sender to owner-astro using -f >Date: Thu, 3 Jun 1999 22:01:40 GMT >From: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov> >To: astro@lists.mindspring.com >Subject: [ASTRO] Hubble Images May Shed Light on Importance of Novae in Galactic Evolution >Sender: owner-astro@brickbat12.mindspring.com >Reply-To: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov> > >College of Liberal Arts and Sciences >Arizona State University > >Contact: James Hathaway, 480-965-6375, Hathaway@asu.edu > >Embargoed until 9:20 a.m. CDT, June 3, 1999 > >EDITORS: False color gif images can be obtained over the internet at >http://wapiti.uwyo.edu/hst-nova on June 3, 1999 at 9:20 a.m. CDT. > >Hubble Images May Shed Light on Importance of Novae in Galactic Evolution > >Astronomers today released new Hubble Space Telescope images that show >gas shells ejected into space at regular intervals by an unusual type of white >dwarf star. The images may reveal important information about the role novae >play in the evolution of our galaxy, including the distribution of heavier >elements and the development of planetary systems. > >The images, produced by the Hubble Space Telescope's Near Infrared Camera >Multi-Object Spectrograph (NICMOS), are the first images of gas shells >produced by novae that are members of a class of double star systems called >Cataclysmic Variables. > >Cataclysmic Variables typically involve a white dwarf (a sun-mass star that >has burnt down its internal fuel and has collapsed to a dense, earth-size >sphere) in very close proximity to a larger and cooler star. The strong >gravity tides from the white dwarf drag hydrogen gas off the larger star. >This gas spirals down onto the surface of the white dwarf and accumulates >as a deeper and deeper hydrogen shell around the white dwarf core, which is >primarily carbon, oxygen and other heavier elements. > >When enough hydrogen has accumulated on the white dwarf's surface (after >about 10,000 years), thermonuclear fusion reactions begin and gradually >intensify until finally (much later) temperatures rise to the point where >they cause a nova explosion in the hydrogen shell, blowing it and part of >the white dwarf core into space -- and then the process begins all over >again. > >NICMOS has imaged thick, clumpy gas shells -- the remnants of Cataclysmic >Variable novae -- from three systems, QV Vul, QU Vul (both in the >constellation Vulpecula), and V1974 Cyg (in the constellation Cygnus). "Our >pictures show filaments, blobs, streams, and other structures that can only >be seen by the Hubble," said team member Chick Woodward from the University >of Wyoming. "We can analyze these pictures and determine how much gas is >blown into space by the various systems that we are studying. Before, we >could only guess how the gas was distributed in space and now we can see >that our previous guesses were not very good." > >In fact, the images provide important data which can be used to test the >accuracy of some key theories concerning novae and galactic evolution. In >their analysis, the team plans to compare the ejected shells in the images >to computer simulations of nova explosions. "Studies of these novae will be >critical in improving our calculations and will help us better understand >the cause and evolution of these explosions," said team member Sumner >Starrfield from Arizona State University. > >"For example, these observations imply that a great deal more material >is ejected in a nova explosion than was predicted by our calculations, and >that could make nova far more important in the evolution of the chemical >elements in our galaxy than was previously believed," said Starrfield. > >Novae have long been understood as part of the processes which contribute >to element production in our galaxy. Astronomers generally believe that >only hydrogen and helium were formed in the Big Bang event which formed >the universe; all other chemical elements are formed by processes in stars. >Thus the proportion of elements such as carbon, oxygen and iron has slowly >grown over the lifetime of the galaxy. > >According to team member James Truran from the University of Chicago, >much of the gaseous material in the galaxy comes from supernova explosions >involving stars like the sun or more massive stars, "and there are certain >important isotopes that can only be produced by novae." > >"We know from other studies of the novae we're looking at that the ejected >material is very unlike the gas on the surface of our sun," said Starrfield. >"The nova gas is enriched in elements such as carbon, nitrogen, oxygen, >neon, magnesium, and aluminum." But, Starrfield argues, that does not mean >that material from novae were not involved in the evolution of our solar >system. > >"It is possible that some of the aluminum in our own solar system came >from nova explosions. There is evidence that novae eject radioactive >aluminum and there is also evidence that radioactive aluminum once >existed in our solar system but has since decayed," said Starfield. > >"Furthermore, dust grains often condense in the shells ejected by such >novae," noted team member Robert Gehrz from the University of Minnesota. >"Their infrared spectral signature shows that dust they make is similar in >size to the small dust grains released from comets in our solar system. > >"It is therefore possible that novae are among the stars that produce the >solid grains that are the building blocks of planets. Like the gas produced >by novae, these grains end up in the gas and dust clouds that produce new >stellar and planetary systems," Gehrz said. > >Two of the three novae imaged, QV Vul and QU Vul, formed dust in their gas >shells. "We hope that the structures revealed by the NICMOS novae images >will help us to understand where the dust forms in nova shells and why >some novae produce grains while others do not," Gehrz added. > >"During the 1980's, QV Vul was found to produce four types of astrophysical >grains at various times during a two-year period following its eruption." >The dust that formed contained carbon, silicates, silicon carbide, and >hydrocarbons -- "stardust" similar to material found in our solar systems >meteorites, and material that was probably present in our solar system >when the planets were forming. > >"Our earlier models of QV Vul suggested that the carbon dust components >formed in fast-moving polar flumes, and that the silicates formed in a >slow-moving equatorial ring," Gehrz said. "We hope the NICMOS images >will enable us to evaluate the correctness of this model." > >The Hubble nova program is also laying the groundwork for greatly expanded >further study of novae in the universe. "Most of what astronomers know >about how novae effect the chemical evolution of galaxies is limited to >studies of novae in the Milky Way," noted team member Matthew Greenhouse >from the NASA Goddard Space Flight Center. "The heavy elements ejected by >these novae explosions produced bright infrared emission lines -- an infrared >signature that will allow the Infrared Spectrograph instrument aboard the >upcoming NASA Space Infrared Telescope Facility (scheduled for launch in >2001) to discover and study novae in a wide range of galaxies for the first >time." > >The international research team which planned and analyzed these >observations included Chick Woodward and Kunegunda Belle of the University >of Wyoming, Nye Evans and Stuart Eyres of the University of Kaele in >England, Robert Gehrz and Michael Schuster of the University of Minnesota, >Matthew Greenhouse of NASA Goddard Space Flight Center, Joachim Krautter >of the State Observatory and University of Heidelberg in Germany, Sumner >Starrfield of Arizona State University, and James Truran of the University >of Chicago. > >The work was supported by NASA and the Space Telescope Science Institute. > >For more information, contact: > >Chick Woodward, University of Wyoming >307-766-2706, chelsea@tana.uwyo.edu > >Robert Gehrz, University of Minnesota >612-624-7806, rgehrz@ast1.spa.umn.edu > >Sumner Starrfield, Arizona State University >480-965-7569, starrfie@nova.la.asu.edu > >



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