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Topic: Protoplanetary disk

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	boss (proptoplanetary disks) (Site not responding. Last check: 2007-10-08)
		Disk temperatures drop sufficiently with vertical height or radial position, or with decreased disk mass or disk mass accretion rates, to permit the plausible incorporation of both ~ 1200 K and < 700 K components in chondritic meteorites.
		Surface densities of low mass disks appear to be inadequate for the disk to evolve through gravitational torques, and the models tend to be largely stable with respect to convection, which could otherwise lead to turbulence and significant viscous torques.
		Thermal ionization of K and Na may allow the generation of significant magnetic fields near the midplane in the inner disk, while cosmic rays and short-lived nuclides ionize the outer disk, perhaps eliminating the possibility of a field-free gap between these two regions and allowing continued magnetically-driven inflow of disk mass to the protostar.
	www.obspm.fr /encycl/papers/boss1.html (383 words)

	protoplanetary disk
		The existence of such disks was long suspected (see planetary systems, formation) but was confirmed by direct imaging in 1994 when C. Robert O'Dell and colleagues of Rice University used the Hubble Space Telescope (HST) to examine newborn stars in the Orion Nebula.
		Evidence for dusty disks, 8 to 16 times the diameter of Neptune's orbit, was found in all six in the form of dark bands, believed to be dust lanes, crossing the bright areas around each star.
		Two of the most spectacular edge-on disks surround HH 30 and the "Butterfly Star," both of which are narrow in their central parts but gently flare at distances of about 100 astronomical units.
	www.daviddarling.info /encyclopedia/P/protoplandisk.html (979 words)

	Protoplanetary disc - Wikipedia, the free encyclopedia
		A protoplanetary disc (also protoplanetary disk, proplyd) is an accretion disc surrounding a T Tauri star.
		As the cloud shrinks, conservation of angular momentum causes the random motions originally present in the cloud to become one coherent rotation.
		Gravitational interactions may cause the dust and gas in the disk to condense into planetesimals.
	en.wikipedia.org /wiki/Protoplanetary_disc (277 words)

	Subaru Telescope, NAOJ
		New high resolution near-infrared direct imaging of the protoplanetary disk surrounding the star AB Aurigae shows that this planetary nursery is not the comparatively featureless and smooth place that astronomers had once assumed, but a place where gas and dust swirl in a complex spiral pattern.
		Protoplanetary disks are only as large as a solar system, a small place on astronomical scales, and observing such small structures from distances of several hundred light years away is a challenge (Note 1).
		By looking at the disk with the super sharp resolution of 0.1 arcseconds and in infrared wavelengths that are not heavily influenced by material outside the star and the disks, the detailed structure of a protoplanetary disks is finally becoming directly observable.
	www.naoj.org /Pressrelease/2004/04/18/index.html (1620 words)

	Protoplanetary disk (Site not responding. Last check: 2007-10-08)
		Disk Checker 2000 Scans disk surface, files, and folders for errors with disk image working ability.
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		BPP Disk Ultra-secure and ultra-fast volume encryption BPP Disk creates encrypted disk drives which can be mounted at any time.
	www.serebella.com /encyclopedia/article-Protoplanetary_disk.html (414 words)

	Astronomers Discover Edge-on Protoplanetary Disk in Quadruple Star System
		The disk appears as a dark lane down the middle of the object, and the star is hidden behind it.
		This morphology is the distinct signature of a protoplanetary disk that is being viewed edge-on and is blocking the light from the star at its center.
		By analyzing the infrared images of the edge-on disk and the quadruple star system, the research team can learn about both the physical properties of disks from which planets form, and the way in which stars are born in multiple star systems.
	www.noao.edu /outreach/press/pr02/pr0201.html (1015 words)

	Movies from numerical simulations of gap opening and planet migration (Site not responding. Last check: 2007-10-08)
		Meanwhile, the response of a viscous protoplanetary disk is calculated using a high resolution 2D hydrodynamic simulation, and displayed in an almost corotating frame.
		The surface density profile of the disk (shown as function of radius in the inset graph) is not significantly modified by the presence of the planet at this stage.
		The overall exchange of angular momentum between the planet and disk is now governed by the viscous evolution of the disk, and the planet is expected to migrate in the same sense as the disk gas (usually inward at small radii) while maintaining its position within a gap.
	jilawww.colorado.edu /~pja/planet_migration.html (489 words)

	Protoplanetary disc -- Facts, Info, and Encyclopedia article (Site not responding. Last check: 2007-10-08)
		A protoplanetary disc (also protoplanetary disk, proplyd) is an (Click link for more info and facts about accretion disc) accretion disc surrounding a (Click link for more info and facts about T Tauri star) T Tauri star.
		Gravitational interactions may cause the dust and gas in the disk to condense into (One of many small solid celestial bodies thought to have existed at an early stage in the development of the solar system) planetesimals.
		This process competes against the (Click link for more info and facts about stellar wind) stellar wind, which drives the gas out of the system, and (An increase by natural growth or addition) accretion, which pulls material into the central T Tauri star.
	www.absoluteastronomy.com /encyclopedia/p/pr/protoplanetary_disc.htm (473 words)

	An "Ideal Laboratory" For Studying Planet Formation
		The team of astronomers was able to measure the rotation of a disk seen around a young star by tracking water masers - clusters of super-heated molecules that amplify radio emission -- within it.
		Theorists have speculated that such jets are produced by accretion disks around very young stars, where flowing winds are driven outward by material that fails to fall onto the star.
		The disk is centered with the radio continuum jet which is emanating from the central star.
	www.nrao.edu /pr/1998/essdisk (746 words)

	Edge-on Protoplanetary Disk In The Orion Nebula
		Resembling an interstellar Frisbee, this is a disk of dust seen edge-on around a newborn star in the Orion nebula, located 1,500 light-years away.
		Because the disk is edge-on, the star is largely hidden inside, in this striking Hubble Space Telescope picture.
		However, clearly visible in this image are nebulosities above and below the plane of the disk; these betray the presence of the otherwise invisible central star, which cannot be seen directly due to dust in the edge-on disk.
	www.solarviews.com /cap/ds/orion4.htm (240 words)

	NAI: News Stories (Site not responding. Last check: 2007-10-08)
		"In the disk instability mechanism, the action occurs in a disk of gas and dust which is orbiting around a star," says Boss.
		Scientists now generally believe that protoplanetary disks of gas and dust last only a few million years because that is what they have observed from studies of distant newborn stars.
		It could be that our own Sun's disk lasted much longer than average, and therefore the planets in our solar system had a much longer period of time during which to form.
	nai.arc.nasa.gov /news_stories/news_detail.cfm?ID=160 (2045 words)

	AVS/Express in application to astrophysical hydrodynamics (Site not responding. Last check: 2007-10-08)
		In this simulation the process of tidal gap formation in a protoplanetary disk is followed.
		The orbital radius of the planet is equal to 0.4 of the outer radius of the disk.
		A problem of mass flow in the immediate vicinity of a planet embedded in a protoplanetary disk is studied numerically in two dimensions.
	www.camk.edu.pl /~pci/AVS/pdisk.html (327 words)

	Nat' Academies Press, Planetary Sciences: American and Soviet Research/Proceedings from the U.S.-U.S.S.R. Workshop on ...
		The removal of angular momentum to the periphery (necessary for the formation of the Sun and protoplanetary disk) is possible at the formation stage in the center of the contracting cloud (protosolar nebula) of the stellar-like core (Sun's embryo).
		This paper discusses a disk formation model during collapse of the protosolar nebula with J ~ 1052g cm2s-i, yielding a low-mass protoplan- etary disL The disk begins to form at the growth stage of the stellar-like core and expands during accretion to the present dimensions of the solar system.
		In addition to the internal heat source (viscous dissipation), there is an external one which affects the temperature distribution in the disk: radiation (diffused in the accretion envelope) of the shock wave front at the core and in the nearest portion of the disk.
	www.nap.edu /books/0309043336/html/44.html (4826 words)

	Spaceflight Now \| Breaking News \| More Sun-like stars may have planetary systems
		They propose that most older T Tauri stars haven't lost their disks at all: The disk material has simply changed into a form that is nearly invisible to Earth-based telescopes.
		The dense disks of dust and gas surrounding classical T Tauri stars are easily visible because dust glows brightly in the infrared region of the spectrum.
		They decided that their best bet was to search for evidence of molecular hydrogen, the main constituent of the protoplanetary disk, which should persist much longer than the dust grains and carbon monoxide.
	spaceflightnow.com /news/n0212/17planetary (1486 words)

	Origins Ed. Forum: FAQs- How do planetary systems form?
		Instead, some of the material was confined to a flat, spinning disk, called a protoplanetary disk, around the young Sun.
		As they grew larger, their gravitational forces increased, attracting more matter from the disk and gradually building up kilometer-sized bodies called planetesimals, some of which in turn formed the nuclei of the planets as we know them today.
		This protoplanetary disk was thus the transition state between our stellar ancestors and the planetary objects that evolved from it.
	origins.stsci.edu /faq/planetary-systems.html (330 words)

	[No title]
		\par A protoplanetary disk in the Orion Nebula.
		It seems to me that the technology is not quite there yet to answer whether disk instability would lead to the formation of planets like Jupiter." \line \line But the discoveries of planets in other solar systems, Boss argues, have illustrated hidden flaws in the core-accretion model.
		The Sun's protoplanetary disk may have lasted much longer than average, giving our planets a much longer period of time in which to form.
	www.astrobio.net /news/rtf.php?sid=145&d=Astrobio145&ext=Astrobio145.doc (1909 words)

	Universe Today - Oldest Planetary Disk Discovered
		Planetary disks like this have been seen before, but never around a star which is so old; it's possible it'll never form planets.
		Most protoplanetary disks last only a few million years, while the oldest previously known disks have ages of about 10 million years.
		The disk in question orbits a pair of red dwarf stars in the Stephenson 34 system, located approximately 350 light-years away in the constellation Taurus.
	www.universetoday.com /am/publish/25_million_years_dust_disk_form_planets.html (622 words)

	Science News: Planet formation on the fast track: growing up in a hurry (Site not responding. Last check: 2007-10-08)
		Direct telescope observations suggest that protoplanetary disks don't last more than about 7 million years, and studies of the environment in which stars form suggest that many disks may evaporate in much less time.
		He was surprised to find that gravity could cause the swirling disk, after just a few orbits about its parent star, to suddenly fragment into clumps as big as a modest-size planet.
		Mayer argues that his group has shown that a protoplanetary disk can evolve through a sequence of milder instabilities, coming to a point where the disk fragments into planet forming clumps.
	www.findarticles.com /p/articles/mi_m1200/is_4_163/ai_97235661 (1376 words)

	HubbleSite - Hubble Picture Adds to Planet-Making Recipe - 6/2/1999
		The Hubble telescope has snapped a nearly face-on view of a swirling disk of dust and gas surrounding a developing star called AB Aurigae.
		The image, taken in visible light by the Space Telescope Imaging Spectrograph, shows unprecedented detail in the disk, including clumps of dust and gas that may be the seeds of planet formation.
		The rest of the disk material is illuminated by light reflected from the gas and dust surrounding the star.
	oposite.stsci.edu /pubinfo/pr/1999/21 (234 words)

	Protoplanetary disk (Site not responding. Last check: 2007-10-08)
		A protoplanetary disc (also protoplanetary disk, proplyd) is a disc of dust and gas which orbits a protostar, within a solarnebula.
		As the cloud shrinks, conservation of angular momentum causes the random motions originally present in the cloudto become one coherent rotation.
		This process competes against the stellarwind, which drives the gas out of the system, and accretion, which pullsmaterial into the central protostar.
	www.therfcc.org /protoplanetary-disk-34593.html (160 words)

	Mark Petersen (Site not responding. Last check: 2007-10-08)
		My thesis work consisted of several parts: A slanted quasi-geostrophic (QG) model used to study geophysical turbulence; a study of vortex cores, circulation cells, and filaments in QG turbulence; and a protoplanetary disk model of the gas that surrounds young stars.
		Protoplanetary disk models are used to study Rossby waves, shear instabilities, and vortex formation in gas disks around young stars that eventually lead to planetary formation.
		Linear analysis of this system shows that the conditions of radiative damping and a radial temperature gradient results in baroclinic instabilities which lead to vortices in the disk.
	cnls.lanl.gov /~petersen/ppd.html (175 words)

	[28.01] Protoplanetary disk formation and evolution models: DM Tau and GM Aur (Site not responding. Last check: 2007-10-08)
		Early disk formation is studied in the standard scenario of slowly rotating isothermal collapsing spheres and is strongly dependent on the initial angular momentum and the collapse accretion rate.
		We also study the disk evolution under the Beta parameterization of turbulence, recently proposed for sheared flows on protoplanetary disks.
		The large value of present disk mass and the relatively small observed accretion rate of this system may also be indicative of the presence of an inner gas giant planet.
	www.aas.org /publications/baas/v34n3/dps2002/122.htm (360 words)

	Physical parameters of the Keplerian protoplanetary disk of DM Tau (Site not responding. Last check: 2007-10-08)
		The disk is large, with an outer radius of 850 AU.
		The intrinsic local velocity dispersion in the disk is found to be essentially thermal, with a turbulent component of less than 30 % of the thermal width.
		Parameters derived from this observation are used to confirm the molecular abundances and depletion factors estimated for several simple organic molecules by Dutrey et al (1997) for DMTau.
	iram.fr /IRAMFR/ARN/oct98/node17.html (205 words)

	Exploring New Worlds
		The inner part of the disk, which lies between the star and the planet, spins faster than the outer part, just as the inner planets in the solar system revolve around the sun faster than the outer ones.
		In taking up angular momentum from the inner part of the disk and losing it to the outer part, a massive planet clears a gap around it: The more massive the planet—relative to the mass of the star it orbits—the larger the gap.
		For instance, because a planet that arises from a clump of gas does not have a solid core, the protoplanetary disk need not have an abundance of heavy elements, such as silica and iron, to form a core.
	www.sciencenews.org /sn_arc98/8_8_98/bob1.htm (2391 words)

	[No title] (Site not responding. Last check: 2007-10-08)
		Title: The Distribution of Water in Protoplanetary Disks Fred Ciesla NASA Ames Abstract: The distribution of water in the solar nebula is important to understand for a number of reasons.
		I have developed a model which tracks the evolution of water in a viscous protoplanetary disk as vapor and solids are created and destroyed due to collisions, accretion, condensation, and vaporization.
		The transport of water-bearing species due to diffusion and gas drag induced migration are tracked to understand how the distribution of water changes in an evolving protoplanetary disk.
	www.ifa.hawaii.edu /colloquia/abstracts/ciesla.txt (159 words)

	SPACE.com -- Dusty Rings May Mark Planetary Systems
		The amount of light reflected from the ring can be used to measure the vast number of dust grains within and therefore the amount of material available to form planets, as well as the amount that might form.
		Recent innovations in studying disks around stars using powerful infrared telescopes, including the Hubble Space Telescope, have generated a new sub-field in astrophysics in the past few months, Marcy said.
		Now astronomers are studying disks and rings around stars thought to be generating planets to learn their temperature and density and use that information to learn more about planet formation, he said.
	www.space.com /scienceastronomy/generalscience/dust_rings_991026.html (857 words)

	HubbleSite - Astronomers Have Found a New Twist in a Suspected Proto-Planetary Disk - 1/7/1998
		A telltale new warp uncovered in a vast, thin disk of dust encircling the star Beta Pictoris may be caused by the gravitational tug of a bypassing star or companion brown dwarf.
		These conclusions are based on Hubble telescope pictures that reveal the dim outermost reaches of the disk, which are 7 billion miles from the central star.
		An unusual flaring at the top of the right side of the disk reveals that dust has been pulled above the dense plane of the disk beyond what is observed on the left side.
	hubblesite.org /newscenter/newsdesk/archive/releases/1998/03 (210 words)

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