The range and valence of a real Smirnov function

NASA Astrophysics Data System (ADS)

Ferguson, Timothy; Ross, William T.

2018-02-01

We give a complete description of the possible ranges of real Smirnov functions (quotients of two bounded analytic functions on the open unit disk where the denominator is outer and such that the radial boundary values are real almost everywhere on the unit circle). Our techniques use the theory of unbounded symmetric Toeplitz operators, some general theory of unbounded symmetric operators, classical Hardy spaces, and an application of the uniformization theorem. In addition, we completely characterize the possible valences for these real Smirnov functions when the valence is finite. To do so we construct Riemann surfaces we call disk trees by welding together copies of the unit disk and its complement in the Riemann sphere. We also make use of certain trees we call valence trees that mirror the structure of disk trees.

Transitional Disks Associated with Intermediate-Mass Stars: Results of the SEEDS YSO Survey

NASA Technical Reports Server (NTRS)

Grady, C.; Fukagawa, M.; Maruta, Y.; Ohta, Y.; Wisniewski, J.; Hashimoto, J.; Okamoto, Y.; Momose, M.; Currie, T.; McElwain, M.;

The Disk and Jet of the Classical T Tauri Star AA Tau

NASA Technical Reports Server (NTRS)

Cox, A. W.; Grady, C. A.; Hamel, H.; Hornbeck, Jeremy; Russell, R.; Sitko, M.; Woodgate, B.

2013-01-01

Previous studies of the classical T Tauri star AA Tau have interpreted the UX Orionis-like photopolarimetric variability as being due to a warp in the inner disk caused by an inclined stellar magnetic dipolefield. We test that these effects are macroscopically observable in the inclination and alignment of the disk. We use the HST/STIS coronagraphic detection of the disk to measure the outer disk radius and inclination, and find that the inner disk is both misinclined and misaligned with respect to the outer disk. AA Tau drives a faint jet which is also misaligned with respect to the projection of the outer disk minor axis. The jet is also poorly collimated near the star. The measured inclination, 71+/-1deg, is above the inclination range suggested for stars with UX Orionis-like variability, indicating that dust grains in the disk have grown and settled toward the disk midplane.

Spectral domain optical coherence tomography imaging in optic disk pit associated with outer retinal dehiscence

PubMed Central

Wong, Chee Wai; Wong, Doric; Mathur, Ranjana

2014-01-01

A 37-year-old Bangladeshi male presented with an inferotemporal optic disk pit and serous macular detachment in the left eye. Imaging with spectral domain optical coherence tomography (OCT) revealed a multilayer macular schisis pattern with a small subfoveal outer retinal dehiscence. This case illustrates a rare phenotype of optic disk maculopathy with macular schisis and a small outer retinal layer dehiscence. Spectral domain OCT was a useful adjunct in delineating the retinal layers in optic disk pit maculopathy, and revealed a small area of outer retinal layer dehiscence that could only have been detected on high-resolution OCT. PMID:25349471

Herschel Observations of Protostellar and Young Stellar Objects in Nearby Molecular Clouds: The DIGIT Open Time Key Project

NASA Astrophysics Data System (ADS)

Green, Joel D.; DIGIT OTKP Team

2010-01-01

The DIGIT (Dust, Ice, and Gas In Time) Open Time Key Project utilizes the PACS spectrometer (57-210 um) onboard the Herschel Space Observatory to study the colder regions of young stellar objects and protostellar cores, complementary to recent observations from Spitzer and ground-based observatories. DIGIT focuses on 30 embedded sources and 64 disk sources, and includes supporting photometry from PACS and SPIRE, as well as spectroscopy from HIFI, selected from nearby molecular clouds. For the embedded sources, PACS spectroscopy will allow us to address the origin of [CI] and high-J CO lines observed with ISO-LWS. Our observations are sensitive to the presence of cold crystalline water ice, diopside, and carbonates. Additionally, PACS scans are 5x5 maps of the embedded sources and their outflows. Observations of more evolved disk sources will sample low and intermediate mass objects as well as a variety of spectral types from A to M. Many of these sources are extremely rich in mid-IR crystalline dust features, enabling us to test whether similar features can be detected at larger radii, via colder dust emission at longer wavelengths. If processed grains are present only in the inner disk (in the case of full disks) or from the emitting wall surface which marks the outer edge of the gap (in the case of transitional disks), there must be short timescales for dust processing; if processed grains are detected in the outer disk, radial transport must be rapid and efficient. Weak bands of forsterite and clino- and ortho-enstatite in the 60-75 um range provide information about the conditions under which these materials were formed. For the Science Demonstration Phase we are observing an embedded protostar (DK Cha) and a Herbig Ae/Be star (HD 100546), exemplars of the kind of science that DIGIT will achieve over the full program.

Magnetorotational instability in decretion disks of critically rotating stars and the outer structure of Be and Be/X-ray disks

NASA Astrophysics Data System (ADS)

Krtička, J.; Kurfürst, P.; Krtičková, I.

2015-01-01

Context. Evolutionary models of fast-rotating stars show that the stellar rotational velocity may approach the critical speed. Critically rotating stars cannot spin up more, therefore they lose their excess angular momentum through an equatorial outflowing disk. The radial extension of such disks is unknown, partly because we lack information about the radial variations of the viscosity. Aims: We study the magnetorotational instability, which is considered to be the origin of anomalous viscosity in outflowing disks. Methods: We used analytic calculations to study the stability of outflowing disks submerged in the magnetic field. Results: The magnetorotational instability develops close to the star if the plasma parameter is large enough. At large radii the instability disappears in the region where the disk orbital velocity is roughly equal to the sound speed. Conclusions: The magnetorotational instability is a plausible source of anomalous viscosity in outflowing disks. This is also true in the region where the disk radial velocity approaches the sound speed. The disk sonic radius can therefore be roughly considered as an effective outer disk radius, although disk material may escape from the star to the insterstellar medium. The radial profile of the angular momentum-loss rate already flattens there, consequently, the disk mass-loss rate can be calculated with the sonic radius as the effective disk outer radius. We discuss a possible observation determination of the outer disk radius by using Be and Be/X-ray binaries.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duffell, Paul C.; MacFadyen, Andrew I.; Farris, Brian D.

Most standard descriptions of Type II migration state that massive, gap-opening planets must migrate at the viscous drift rate. This is based on the idea that the disk is separated into an inner and outer region and gas is considered unable to cross the gap. In fact, gas easily crosses the gap on horseshoe orbits, nullifying this necessary premise which would set the migration rate. In this work, it is demonstrated using highly accurate numerical calculations that the actual migration rate is dependent on disk and planet parameters, and can be significantly larger or smaller than the viscous drift rate. Inmore » the limiting case of a disk much more massive than the secondary, the migration rate saturates to a constant that is sensitive to disk parameters and is not necessarily of the order of the viscous rate. In the opposite limit of a low-mass disk, the migration rate decreases linearly with disk mass. Steady-state solutions in the low disk mass limit show no pile-up outside the secondary's orbit, and no corresponding drainage of the inner disk.« less

A New Perspective on Galaxy Evolution from the Low Density Outskirts of Galaxies

NASA Astrophysics Data System (ADS)

Emery Watkins, Aaron

2017-01-01

In order to investigate the nature of galaxy outskirts, we carried out a deep imaging campaign of several nearby ($D\\lesssim$10Mpc) galaxies, across a range of environments. We found that most of the galaxies we imaged show red and non-star-forming outer disks, implying evolved stellar populations. Such populations in outer disks are expected as the result of radial migration, yet through Fourier analysis we found no evidence of extended spiral structure in these galaxies. Without star formation or outer spiral structure, it is difficult to determine how these outer disks formed. To investigate the effects of interactions on outer disks, we also observed the Leo I Group; however, while group environments are expected to promote frequent interactions, we found only three extremely faint tidal streams, implying a calm interaction history. As Leo I is fairly low density, this implies that loose groups are ineffective at producing intragroup light (IGL). In the famous interacting system M51, we found that its extended tidal features show similarly red colors as the typical outer disks we observed, implying that M51 had a similar outer disk prior to the interaction, and that the interaction induced no extended star formation, including in the system's HI tail. Therefore, to investigate the nature of star formation in low-density environments, we carried out deep narrow-band H$\\alpha$ imaging of M101 and M51.

Imaging the Disk and Jet of the Classical T Tauri Star AA Tau

NASA Astrophysics Data System (ADS)

Cox, Andrew; Grady, C.; Hammel, H. B.; Hornbeck, J.; Russell, R. W.; Sitko, M. L.; Woodgate, B. E.

2013-01-01

Previous studies of the classical T Tauri star AA Tau have interpreted the UX Orionis-like photo-polarimetric variability as being due to a warp in the inner disk caused by an inclined stellar magnetic dipole field. We test that these effects are macroscopically observable in the inclination and alignment of the disk. We use HST/STIS coronagraphic imagery to measure the V magnitude of the star for both STIS corona graphic observations, compare these data with optical photometry in the literature and find that unlike other classical T Tauri stars observed on the same HST program, the disk is most robustly detected at optical minimum light. We measure the outer disk radius, major axis position angle, and disk inclination, and find that the inner disk, as reported in the literature, is both mis-inclined and misaligned with respect to the outer disk. AA Tau drives a faint jet which is also misaligned with respect to the projection of the outer disk minor axis and which is poorly collimated near the star. The measured outer disk inclination, 71±1 degrees, is out of the inclination band suggested for stars with UX Orionis-like variability where no grain growth has occurred in the disk. The faintness of the disk, the small disk size, and visibility of the star and despite the high inclination, all indicate that the disk must have experienced grain growth and settling toward the disk midplane, which we verify by comparing the observed disk with model imagery from the literature.

The Shadow Knows: Using Shadows to Investigate the Structure of the Pretransitional Disk of HD 100453

DOE Office of Scientific and Technical Information (OSTI.GOV)

Long, Zachary C.; Fernandes, Rachel B.; Sitko, Michael

2017-03-20

We present Gemini Planet Imager polarized intensity imagery of HD 100453 in Y , J , and K 1 bands that reveals an inner gap (9–18 au), an outer disk (18–39 au) with two prominent spiral arms, and two azimuthally localized dark features that are also present in Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) total intensity images. Spectral energy distribution fitting further suggests that the radial gap extends to 1 au. The narrow, wedge-like shape of the dark features appears similar to predictions of shadows cast by an inner disk that is misaligned with respect to the outer disk. Using themore » Monte Carlo radiative transfer code HOCHUNCK3D, we construct a model of the disk that allows us to determine its physical properties in more detail. From the angular separation of the features, we measure the difference in inclination between the disks (45°) and their major axes, PA = 140° east of north for the outer disk, and 100° for the inner disk. We find an outer-disk inclination of 25° ± 10° from face-on, in broad agreement with the Wagner et al. measurement of 34°. SPHERE data in J and H bands indicate a reddish disk, which indicates that HD 100453 is evolving into a young debris disk.« less

The Shadow Knows: Using Shadows to Investigate the Structure of the Pretransitional Disk of HD 100453

NASA Astrophysics Data System (ADS)

Long, Zachary C.; Fernandes, Rachel B.; Sitko, Michael; Wagner, Kevin; Muto, Takayuki; Hashimoto, Jun; Follette, Katherine; Grady, Carol A.; Fukagawa, Misato; Hasegawa, Yasuhiro; Kluska, Jacques; Kraus, Stefan; Mayama, Satoshi; McElwain, Michael W.; Oh, Daehyon; Tamura, Motohide; Uyama, Taichi; Wisniewski, John P.; Yang, Yi

2017-03-01

We present Gemini Planet Imager polarized intensity imagery of HD 100453 in Y, J, and K1 bands that reveals an inner gap (9-18 au), an outer disk (18-39 au) with two prominent spiral arms, and two azimuthally localized dark features that are also present in Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) total intensity images. Spectral energy distribution fitting further suggests that the radial gap extends to 1 au. The narrow, wedge-like shape of the dark features appears similar to predictions of shadows cast by an inner disk that is misaligned with respect to the outer disk. Using the Monte Carlo radiative transfer code HOCHUNCK3D, we construct a model of the disk that allows us to determine its physical properties in more detail. From the angular separation of the features, we measure the difference in inclination between the disks (45°) and their major axes, PA = 140° east of north for the outer disk, and 100° for the inner disk. We find an outer-disk inclination of 25° ± 10° from face-on, in broad agreement with the Wagner et al. measurement of 34°. SPHERE data in J and H bands indicate a reddish disk, which indicates that HD 100453 is evolving into a young debris disk.

The Shadow Knows: Using Shadows to Investigate the Structure of the Pretransitional Disk of HD 100453

NASA Technical Reports Server (NTRS)

Long, Zachary C.; Fernandes, Rachel B.; Sitko, Michael; Wagner, Kevin; Muto, Takayuki; Hashimoto, Jun; Follette, Katherine; Grady, Carol A.; Fukagawa, Misato; Hasegawa, Yasuhiro;

Imaging the Disk and Jet of the Classical T Tauri Star AA Tau

NASA Technical Reports Server (NTRS)

Cox, Andrew W.; Grady, Carol A.; Hammel, Heidi B.; Hornbeck, Jeremy; Russell, Ray W.; Sitko, Michael L.; Woodgate, Bruce E.

2013-01-01

Previous studies of the classical T Tauri star AA Tau have interpreted the UX-Orionis-like photo-polarimetric variability as being due to a warp in the inner disk caused by an inclined stellar magnetic dipole field. We test that these effects are macroscopically observable in the inclination and alignment of the disk. We use Hubble Space Telescope (HST)/STIS coronagraphic imagery to measure the V magnitude of the star for both STIS coronagraphic observations, compare these data with optical photometry in the literature, and find that, unlike other classical T Tauri stars observed in the same HST program, the disk is most robustly detected in scattered light at stellar optical minimum light.We measure the outer disk radius, 1 inch.15 plus-minus 0 inch.10, major-axis position angle, and disk inclination and find that the inner disk, as reported in the literature, is both misinclined and misaligned with respect to the outer disk. AA Tau drives a faint jet, detected in both STIS observations and in follow-on Goddard Fabry-Perot imagery, which is also misaligned with respect to the projection of the outer disk minor axis and is poorly collimated near the star, but which can be traced 21 inches from the star in data from 2005. The measured outer disk inclination, 71deg plus-minus 1deg, is out of the range of inclinations suggested for stars with UX-Orionis-like variability when no grain growth has occurred in the disk. The faintness of the disk, small disk size, and detection of the star despite the high inclination all indicate that the dust disk must have experienced grain growth and settling toward the disk midplane, which we verify by comparing the observed disk with model imagery from the literature.

IMAGING THE DISK AND JET OF THE CLASSICAL T TAURI STAR AA TAU

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cox, Andrew W.; Grady, Carol A.; Hammel, Heidi B.

2013-01-01

Previous studies of the classical T Tauri star AA Tau have interpreted the UX-Orionis-like photo-polarimetric variability as being due to a warp in the inner disk caused by an inclined stellar magnetic dipole field. We test that these effects are macroscopically observable in the inclination and alignment of the disk. We use Hubble Space Telescope (HST)/STIS coronagraphic imagery to measure the V magnitude of the star for both STIS coronagraphic observations, compare these data with optical photometry in the literature, and find that, unlike other classical T Tauri stars observed in the same HST program, the disk is most robustlymore » detected in scattered light at stellar optical minimum light. We measure the outer disk radius, 1.''15 {+-} 0.''10, major-axis position angle, and disk inclination and find that the inner disk, as reported in the literature, is both misinclined and misaligned with respect to the outer disk. AA Tau drives a faint jet, detected in both STIS observations and in follow-on Goddard Fabry-Perot imagery, which is also misaligned with respect to the projection of the outer disk minor axis and is poorly collimated near the star, but which can be traced 21'' from the star in data from 2005. The measured outer disk inclination, 71 Degree-Sign {+-} 1 Degree-Sign , is out of the range of inclinations suggested for stars with UX-Orionis-like variability when no grain growth has occurred in the disk. The faintness of the disk, small disk size, and detection of the star despite the high inclination all indicate that the dust disk must have experienced grain growth and settling toward the disk midplane, which we verify by comparing the observed disk with model imagery from the literature.« less

Gravitational Instabilities in the Disks of Massive Protostars as an Explanation for Linear Distributions of Methanol Masers

NASA Astrophysics Data System (ADS)

Durisen, Richard H.; Mejia, Annie C.; Pickett, Brian K.; Hartquist, Thomas W.

2001-12-01

Evidence suggests that some masers associated with massive protostars may originate in the outer regions of large disks, at radii of hundreds to thousands of AU from the central mass. This is particularly true for methanol (CH3OH), for which linear distributions of masers are found with disklike kinematics. In three-dimensional hydrodynamics simulations we have made to study the effects of gravitational instabilities in the outer parts of disks around young low-mass stars, the nonlinear development of the instabilities leads to a complex of intersecting spiral shocks, clumps, and arclets within the disk and to significant time-dependent, nonaxisymmetric distortions of the disk surface. A rescaling of our disk simulations to the case of a massive protostar shows that conditions in the disturbed outer disk seem conducive to the appearance of masers if it is viewed edge-on.

HERSCHEL OBSERVATIONS OF GAS AND DUST IN THE UNUSUAL 49 Ceti DEBRIS DISK

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roberge, A.; Kamp, I.; Montesinos, B.

2013-07-01

We present far-IR/sub-mm imaging and spectroscopy of 49 Ceti, an unusual circumstellar disk around a nearby young A1V star. The system is famous for showing the dust properties of a debris disk, but the gas properties of a low-mass protoplanetary disk. The data were acquired with the Herschel Space Observatory PACS and SPIRE instruments, largely as part of the ''Gas in Protoplanetary Systems'' (GASPS) Open Time Key Programme. Disk dust emission is detected in images at 70, 160, 250, 350, and 500 {mu}m; 49 Cet is significantly extended in the 70 {mu}m image, spatially resolving the outer dust disk formore » the first time. Spectra covering small wavelength ranges centered on eight atomic and molecular emission lines were obtained, including [O I] 63 {mu}m and [C II] 158 {mu}m. The C II line was detected at the 5{sigma} level-the first detection of atomic emission from the disk. No other emission lines were seen, despite the fact that the O I line is the brightest one observed in Herschel protoplanetary disk spectra. We present an estimate of the amount of circumstellar atomic gas implied by the C II emission. The new far-IR/sub-mm data fills in a large gap in the previous spectral energy distribution (SED) of 49 Cet. A simple model of the new SED confirms the two-component structure of the disk: warm inner dust and cold outer dust that produces most of the observed excess. Finally, we discuss preliminary thermochemical modeling of the 49 Cet gas/dust disk and our attempts to match several observational results simultaneously. Although we are not yet successful in doing so, our investigations shed light on the evolutionary status of the 49 Cet gas, which might not be primordial gas but rather secondary gas coming from comets.« less

Herschel Observations of Gas and Dust in the Unusual 49 Ceti Debris Disk

NASA Technical Reports Server (NTRS)

Roberge, A.; Kamp, I.; Montesinos, B.; Dent, W. R. F.; Meeus, G.; Donaldson, J. K.; Olofsson, J.; Moor, A.; Augereau, J.-C.; Howard, C.;

Herschel Observations of Gas and Dust in the Unusual 49 Ceti Debris Disk

NASA Astrophysics Data System (ADS)

Roberge, A.; Kamp, I.; Montesinos, B.; Dent, W. R. F.; Meeus, G.; Donaldson, J. K.; Olofsson, J.; Moór, A.; Augereau, J.-C.; Howard, C.; Eiroa, C.; Thi, W.-F.; Ardila, D. R.; Sandell, G.; Woitke, P.

2013-07-01

We present far-IR/sub-mm imaging and spectroscopy of 49 Ceti, an unusual circumstellar disk around a nearby young A1V star. The system is famous for showing the dust properties of a debris disk, but the gas properties of a low-mass protoplanetary disk. The data were acquired with the Herschel Space Observatory PACS and SPIRE instruments, largely as part of the "Gas in Protoplanetary Systems" (GASPS) Open Time Key Programme. Disk dust emission is detected in images at 70, 160, 250, 350, and 500 μm 49 Cet is significantly extended in the 70 μm image, spatially resolving the outer dust disk for the first time. Spectra covering small wavelength ranges centered on eight atomic and molecular emission lines were obtained, including [O I] 63 μm and [C II] 158 μm. The C II line was detected at the 5σ level—the first detection of atomic emission from the disk. No other emission lines were seen, despite the fact that the O I line is the brightest one observed in Herschel protoplanetary disk spectra. We present an estimate of the amount of circumstellar atomic gas implied by the C II emission. The new far-IR/sub-mm data fills in a large gap in the previous spectral energy distribution (SED) of 49 Cet. A simple model of the new SED confirms the two-component structure of the disk: warm inner dust and cold outer dust that produces most of the observed excess. Finally, we discuss preliminary thermochemical modeling of the 49 Cet gas/dust disk and our attempts to match several observational results simultaneously. Although we are not yet successful in doing so, our investigations shed light on the evolutionary status of the 49 Cet gas, which might not be primordial gas but rather secondary gas coming from comets.

Lunar and Planetary Science XXXV: Origin of Planetary Systems

NASA Technical Reports Server (NTRS)

2004-01-01

The session titled Origin of Planetary Systems" included the following reports:Convective Cooling of Protoplanetary Disks and Rapid Giant Planet Formation; When Push Comes to Shove: Gap-opening, Disk Clearing and the In Situ Formation of Giant Planets; Late Injection of Radionuclides into Solar Nebula Analogs in Orion; Growth of Dust Particles and Accumulation of Centimeter-sized Objects in the Vicinity of a Pressure enhanced Region of a Solar Nebula; Fast, Repeatable Clumping of Solid Particles in Microgravity ; Chondrule Formation by Current Sheets in Protoplanetary Disks; Radial Migration of Phyllosilicates in the Solar Nebula; Accretion of the Outer Planets: Oligarchy or Monarchy?; Resonant Capture of Irregular Satellites by a Protoplanet ; On the Final Mass of Giant Planets ; Predicting the Atmospheric Composition of Extrasolar Giant Planets; Overturn of Unstably Stratified Fluids: Implications for the Early Evolution of Planetary Mantles; and The Evolution of an Impact-generated Partially-vaporized Circumplanetary Disk.

Revealing the Structure of a Pre-Transitional Disk: The Case of the Herbig F Star SAO 206462 (HD 135344B)

NASA Astrophysics Data System (ADS)

Grady, C. A.; Schneider, G.; Sitko, M. L.; Williger, G. M.; Hamaguchi, K.; Brittain, S. D.; Ablordeppey, K.; Apai, D.; Beerman, L.; Carpenter, W. J.; Collins, K. A.; Fukagawa, M.; Hammel, H. B.; Henning, Th.; Hines, D.; Kimes, R.; Lynch, D. K.; Ménard, F.; Pearson, R.; Russell, R. W.; Silverstone, M.; Smith, P. S.; Troutman, M.; Wilner, D.; Woodgate, B.; Clampin, M.

2009-07-01

SAO 206462 (HD 135344B) has previously been identified as a Herbig F star with a circumstellar disk with a dip in its infrared excess near 10 μm. In combination with a low accretion rate estimated from Br γ, it may represent a gapped, but otherwise primordial or "pre-transitional" disk. We test this hypothesis with Hubble Space Telescope coronagraphic imagery, FUV spectroscopy and imagery and archival X-ray data, and spectral energy distribution (SED) modeling constrained by the observed system inclination, disk outer radius, and outer disk radial surface brightness (SB) profile using the Whitney Monte Carlo Radiative Transfer Code. The essentially face-on (i lsim 20°) disk is detected in scattered light from 0farcs4 to 1farcs15 (56-160 AU), with a steep (r -9.6) radial SB profile from 0farcs6 to 0farcs93. Fitting the SB data requires a concave upward or anti-flared outer disk, indicating substantial dust grain growth and settling by 8 ± 4 Myr. The warm dust component is significantly variable in near to mid-IR excess and in temperature. At its warmest, it appears confined to a narrow belt from 0.08 to 0.2 AU. The steep SED for this dust component is consistent with grains with a<= 2.5 μm. For cosmic carbon to silicate dust composition, conspicuous 10 μm silicate emission would be expected and is not observed. This may indicate an elevated carbon to silicate ratio for the warm dust, which is not required to fit the outer disk. At its coolest, the warm dust can be fit with a disk from 0.14 to 0.31 AU, but with a higher inclination than either the outer disk or the gaseous disk, providing confirmation of the high inclination inferred from mid-IR interferometry. In tandem, the compositional and inclination difference between the warm dust and the outer dust disk suggests that the warm dust may be of second-generation origin, rather than a remnant of a primordial disk component. With its near face-on inclination, SAO 206462's disk is a prime location for planet searches. Based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

Masers in Disks due to Gravitational Instabilities

NASA Astrophysics Data System (ADS)

Mejia, A. C.; Durisen, R. H.; Pickett, B. K.; Hartquist, T. W.

2001-12-01

Evidence suggests that some masers associated with massive protostars may originate in the outer regions of large circumstellar disks, at radii of 100's to 1000's of AU from the central mass. This is particularly true for methanol (CH3OH), where linear distributions of masers are found with disk-like kinematics. In 3D hydrodynamics simulations we have made to study the effects of gravitational instabilities in the outer parts of disks around young low-mass stars, the nonlinear development of the instabilities leads to a complex of intersecting spiral shocks, clumps, and arclets within the disk and to significant time-dependent, nonaxisymmetric distortions of the disk surface. A rescaling of our disk simulations to the case of a massive protostar shows that conditions in the disturbed outer disk seem conducive to the appearance of masers if it is viewed edge-on. This work was supported by NASA Origins Program Grant NAGW5-4342, by the Alexander von Humboldt Foundation, and by NASA Planetary Geology and Geophysics Program Grant NAG5-10262.

Magnetocentrifugally Driven Flows from Young Stars and Disks. IV. The Accretion Funnel and Dead Zone

NASA Astrophysics Data System (ADS)

Ostriker, Eve C.; Shu, Frank H.

1995-07-01

We formulate the time-steady, axisymmetric problem of stellar magnetospheric inflow of gas from a surrounding accretion disk. The computational domain is bounded on the outside by a surface of given shape containing the open field lines associated with an induced disk wind. The mechanism for this wind has been investigated in previous publications in this journal. Our zeroth-order solution incorporates an acceptable accounting of the pressure balance between the magnetic field lines loaded with accreting gas (funnel flow) and those empty of matter (dead zone). In comparison with previous models, our funnel-flow/dead-zone solution has the following novel features: (1) Because of a natural tendency for the trapped stellar magnetic flux to pinch toward the corotation radius Rx (X-point of the effective potential), most of the interesting magnetohydrodynamics is initiated within a small neighborhood of Rx (X-region), where the Keplerian angular speed of rotation in the disk equals the spin rate of the star. (2) Unimpeded funnel flow from the inner portion of the X-region to the star can occur when the amount of trapped magnetic flux equals or exceeds 1.5 times the unperturbed dipole flux that would lie outside Rx in the absence of an accretion disk. (3). Near the equatorial plane, radial infall from the X-point is terminated at a "kink" point Rk = 0.74Rx that deflects the flow away from the midplane, mediating thereby between the field topology imposed by a magnetic fan of trapped flux at Rx and the geometry of a strong stellar dipole. (4) The excess angular momentum of accretion that would otherwise spin up the star rapidly is deposited by the magnetic torques of the funnel flow into the inner portion of the X-region of the disk. (5) An induced disk wind arises in the outer portion of the .X-region, where the stellar field lines have been blown open, and removes whatever excess angular momentum that viscous torques do not transport to the outer disk. (6) The interface between open field lines loaded with outflowing matter (connected to the disk) and those not loaded (connected to the star) forms a "helmet streamer," along which major mass-ejection and reconnection events may arise in response to changing boundary conditions (e.g., stellar magnetic cycles), much the way that such events occur in the active Sun. (7) Pressure balance across the dead-zone/wind interface will probably yield an asymptotically vertical (i.e., "jetlike") trajectory for the matter ejected along the helmet streamer, but mathematical demonstration of this fact is left for future studies. (8) In steady state the overall balance of angular momentum in the star/disk/ magnetosphere system fixes the fractions, f and 1 - f, of the disk mass accretion rate into the X-region carried away, respectively, by the wind and funnel flows.

Inside-out Planet Formation. IV. Pebble Evolution and Planet Formation Timescales

NASA Astrophysics Data System (ADS)

Hu, Xiao; Tan, Jonathan C.; Zhu, Zhaohuan; Chatterjee, Sourav; Birnstiel, Tilman; Youdin, Andrew N.; Mohanty, Subhanjoy

2018-04-01

Systems with tightly packed inner planets (STIPs) are very common. Chatterjee & Tan proposed Inside-out Planet Formation (IOPF), an in situ formation theory, to explain these planets. IOPF involves sequential planet formation from pebble-rich rings that are fed from the outer disk and trapped at the pressure maximum associated with the dead zone inner boundary (DZIB). Planet masses are set by their ability to open a gap and cause the DZIB to retreat outwards. We present models for the disk density and temperature structures that are relevant to the conditions of IOPF. For a wide range of DZIB conditions, we evaluate the gap-opening masses of planets in these disks that are expected to lead to the truncation of pebble accretion onto the forming planet. We then consider the evolution of dust and pebbles in the disk, estimating that pebbles typically grow to sizes of a few centimeters during their radial drift from several tens of astronomical units to the inner, ≲1 au scale disk. A large fraction of the accretion flux of solids is expected to be in such pebbles. This allows us to estimate the timescales for individual planet formation and the entire planetary system formation in the IOPF scenario. We find that to produce realistic STIPs within reasonable timescales similar to disk lifetimes requires disk accretion rates of ∼10‑9 M ⊙ yr‑1 and relatively low viscosity conditions in the DZIB region, i.e., a Shakura–Sunyaev parameter of α ∼ 10‑4.

ALMA continuum observations of the protoplanetary disk AS 209. Evidence of multiple gaps opened by a single planet

NASA Astrophysics Data System (ADS)

Fedele, D.; Tazzari, M.; Booth, R.; Testi, L.; Clarke, C. J.; Pascucci, I.; Kospal, A.; Semenov, D.; Bruderer, S.; Henning, Th.; Teague, R.

2018-02-01

This paper presents new high angular resolution ALMA 1.3 mm dust continuum observations of the protoplanetary system AS 209 in the Ophiuchus star forming region. The dust continuum emission is characterized by a main central core and two prominent rings at r = 75 au and r = 130 au intervaled by two gaps at r = 62 au and r = 103 au. The two gaps have different widths and depths, with the inner one being narrower and shallower. We determined the surface density of the millimeter dust grains using the 3D radiative transfer disk code DALI. According to our fiducial model the inner gap is partially filled with millimeter grains while the outer gap is largely devoid of dust. The inferred surface density is compared to 3D hydrodynamical simulations (FARGO-3D) of planet-disk interaction. The outer dust gap is consistent with the presence of a giant planet (Mplanet 0.7 MSaturn); the planet is responsible for the gap opening and for the pile-up of dust at the outer edge of the planet orbit. The simulations also show that the same planet could be the origin of the inner gap at r = 62 au. The relative position of the two dust gaps is close to the 2:1 resonance and we have investigated the possibility of a second planet inside the inner gap. The resulting surface density (including location, width and depth of the two dust gaps) are in agreement with the observations. The properties of the inner gap pose a strong constraint to the mass of the inner planet (Mplanet < 0.1 MJ). In both scenarios (single or pair of planets), the hydrodynamical simulations suggest a very low disk viscosity (α < 10‑4). Given the young age of the system (0.5-1 Myr), this result implies that the formation of giant planets occurs on a timescale of ≲1 Myr. The reduced image (FITS file) is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/610/A24

The early evolution of protostellar disks

NASA Technical Reports Server (NTRS)

Stahler, Steven W.; Korycansky, D. G.; Brothers, Maxwell J.; Touma, Jihad

1994-01-01

We consider the origin and intital growth of the disks that form around protostars during the collapse of rotating molecular cloud cores. These disks are assumed to be inviscid and pressure free, and to have masses small compared to those of their central stars. We find that there exist three distinct components-an outer disk, in which shocked gas moves with comparable azimuthal and radical velocities; and inner disk, where material follows nearly circular orbits, but spirals slowly toward the star because of the drag exerted by adjacent onfalling matter, and a turbulent ring adjoining the first two regions. Early in the evolution, i.e., soon after infalling matter begins to miss the star, only the outer disk is present, and the total mass acceration rate onto the protostar is undiminished. Once the outer disk boundary grows to more than 2.9 times the stellar radius, first the ring, and then the inner disk appear. Thereafter, the radii of all three components expand as t(exp 3). The mass of the ring increase with time and is always 13% of the total mass that has fallen from the cloud. Concurrently with the buildup of the inner disk and ring, the accretion rate onto the star falls off. However, the protostellar mass continue to rise, asymptotically as t(exp 1/4). We calculated the radiated flux from the inner and outer disk components due to the release of gravitational potential energy. The flux from the inner disk is dominant and rises steeply toward the stellar surface. We also determine the surface temperature of the inner disk as a function of radius. The total disk luminosity decreases slowly with time, while the contributions from the ring and inner disk both fall as t(exp -2).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tang, Ya-Wen; Dutrey, Anne; Guilloteau, Stéphane

We aim to unveil the observational imprint of physical mechanisms that govern planetary formation in the young, multiple system GG Tau A. We present ALMA observations of {sup 12}CO and {sup 13}CO 3–2 and 0.9 mm continuum emission with 0.″35 resolution. The {sup 12}CO 3–2 emission, found within the cavity of the circumternary dust ring (at radius <180 au) where no {sup 13}CO emission is detected, confirms the presence of CO gas near the circumstellar disk of GG Tau Aa. The outer disk and the recently detected hot spot lying at the outer edge of the dust ring are mappedmore » both in {sup 12}CO and {sup 13}CO. The gas emission in the outer disk can be radially decomposed as a series of slightly overlapping Gaussian rings, suggesting the presence of unresolved gaps or dips. The dip closest to the disk center lies at a radius very close to the hot spot location at ∼250–260 au. The CO excitation conditions indicate that the outer disk remains in the shadow of the ring. The hot spot probably results from local heating processes. The two latter points reinforce the hypothesis that the hot spot is created by an embedded proto-planet shepherding the outer disk.« less

Connecting the shadows: probing inner disk geometries using shadows in transitional disks

NASA Astrophysics Data System (ADS)

Min, M.; Stolker, T.; Dominik, C.; Benisty, M.

2017-08-01

Aims: Shadows in transitional disks are generally interpreted as signs of a misaligned inner disk. This disk is usually beyond the reach of current day high contrast imaging facilities. However, the location and morphology of the shadow features allow us to reconstruct the inner disk geometry. Methods: We derive analytic equations of the locations of the shadow features as a function of the orientation of the inner and outer disk and the height of the outer disk wall. In contrast to previous claims in the literature, we show that the position angle of the line connecting the shadows cannot be directly related to the position angle of the inner disk. Results: We show how the analytic framework derived here can be applied to transitional disks with shadow features. We use estimates of the outer disk height to put constraints on the inner disk orientation. In contrast with the results from Long et al. (2017, ApJ, 838, 62), we derive that for the disk surrounding HD 100453 the analytic estimates and interferometric observations result in a consistent picture of the orientation of the inner disk. Conclusions: The elegant consistency in our analytic framework between observation and theory strongly support both the interpretation of the shadow features as coming from a misaligned inner disk as well as the diagnostic value of near infrared interferometry for inner disk geometry.

Numerical Treatment of Thin Accretion Disk Dynamics around Rotating Black Holes

NASA Astrophysics Data System (ADS)

Yildiran, Deniz; Donmez, Orhan

In the present study, we perform the numerical simulation of a relativistic thin accretion disk around the nonrotating and rapidly rotating black holes using the general relativistic hydrodynamic code with Kerr in Kerr-Schild coordinate that describes the central rotating black hole. Since the high energy X-rays are produced close to the event horizon resulting the black hole-disk interaction, this interaction should be modeled in the relativistic region. We have set up two different initial conditions depending on the values of thermodynamical variables around the black hole. In the first setup, the computational domain is filled with constant parameters without injecting gas from the outer boundary. In the second, the computational domain is filled with the matter which is then injected from the outer boundary. The matter is assumed to be at rest far from the black hole. Both cases are modeled over a wide range of initial parameters such as the black hole angular momentum, adiabatic index, Mach number and asymptotic velocity of the fluid. It has been found that initial values and setups play an important role in determining the types of the shock cone and in designating the events on the accretion disk. The continuing injection from the outer boundary presents a tail shock to the steady state accretion disk. The opening angle of shock cone grows as long as the rotation parameter becomes larger. A more compressible fluid (bigger adiabatic index) also presents a bigger opening angle, a spherical shock around the rotating black hole, and less accumulated gas in the computational domain. While results from [J. A. Font, J. M. A. Ibanez and P. Papadopoulos, Mon. Not. R. Astron. Soc. 305 (1999) 920] indicate that the tail shock is warped around for the rotating hole, our study shows that it is the case not only for the warped tail shock but also for the spherical and elliptical shocks around the rotating black hole. The warping around the rotating black hole in our case is much smaller than the one by [J. A. Font, J. M. A. Ibanez and P. Papadopoulos, Mon. Not. R. Astron. Soc. 305 (1999) 920], due to the representation of results at the different coordinates. Contrary to the nonrotating black hole, the tail shock is slightly warped around the rotating black hole. The filled computational domain without any injection leads to an unstable accretion disk. However much of it reaches a steady state for a short period of time and presents quasi-periodic oscillation (QPO). Furthermore, the disk tends to loose mass during the whole dynamical evolution. The time-variability of these types of accretion flowing close to the black hole may clarify the light curves in Sgr A*.

THE EFFECTS OF EPISODIC STAR FORMATION ON THE FUV-NUV COLORS OF STAR FORMING REGIONS IN OUTER DISKS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barnes, Kate L.; Van Zee, Liese; Dowell, Jayce D., E-mail: barneskl@astro.indiana.edu, E-mail: vanzee@astro.indiana.edu, E-mail: jdowell@unm.edu

2013-09-20

We run stellar population synthesis models to examine the effects of a recently episodic star formation history (SFH) on UV and Hα colors of star forming regions. Specifically, the SFHs we use are an episodic sampling of an exponentially declining star formation rate (SFR; τ model) and are intended to simulate the SFHs in the outer disks of spiral galaxies. To enable comparison between our models and observational studies of star forming regions in outer disks, we include in our models sensitivity limits that are based on recent deep UV and Hα observations in the literature. We find significant dispersionmore » in the FUV-NUV colors of simulated star forming regions with frequencies of star formation episodes of 1 × 10{sup –8} to 4 × 10{sup –9} yr{sup –1}. The dispersion in UV colors is similar to that found in the outer disk of nearby spiral galaxies. As expected, we also find large variations in L{sub H{sub α}}/L{sub FUV}. We interpret our models within the context of inside-out disk growth, and find that a radially increasing τ and decreasing metallicity with an increasing radius will only produce modest FUV-NUV color gradients, which are significantly smaller than what is found for some nearby spiral galaxies. However, including moderate extinction gradients with our models can better match the observations with steeper UV color gradients. We estimate that the SFR at which the number of stars emitting FUV light becomes stochastic is ∼2 × 10{sup –6} M{sub ☉} yr{sup –1}, which is substantially lower than the SFR of many star forming regions in outer disks. Therefore, we conclude that stochasticity in the upper end of the initial mass function is not likely to be the dominant cause of dispersion in the FUV-NUV colors of star forming regions in outer disks. Finally, we note that if outer disks have had an episodic SFH similar to that used in this study, this should be taken into account when estimating gas depletion timescales and modeling chemical evolution of spiral galaxies.« less

Type II Migration and Giant Planet Survival

NASA Technical Reports Server (NTRS)

Ward, William R.

2003-01-01

Type II migration, in which a newly formed large planet opens a gap in its precursor circumstellar nebula and subsequently evolves with it, has been implicated as a delivery mechanism responsible for close stellar companions. Large scale migration is possible in a viscously spreading disk of surface density sigma (r,t) when most of it is sacrificed to the primary in order to promote a small portion of the disk to much higher angular momentum orbits. Embedded planets generally follow its evolution unless their own angular momentum is comparable to that of the disk. The fraction of the starting disk mass, M (sub d) = 2pi integral rsigma(r,0)dr, that is consumed by the star depends on the distance at which material escapes the disk's outer boundary. If the disk is allowed to expand indefinitely, virtually all of the disk will fall into the primary in order to send a vanishingly small portion to infinity. For such a case, it is difficult to explain the survival of any giant planets, including Jupiter and Saturn. Realistically, however, there are processes that could truncate a disk at a finite distance, r(sub d). Recent numerical modeling has illustrated that planets can survive in this case. We show here that much of these results can be understood by simple conservation arguments.

3-D MHD disk wind simulations of protostellar jets

NASA Astrophysics Data System (ADS)

Staff, Jan E.; Koning, Nico; Ouyed, Rachid; Tanaka, Kei; Tan, Jonathan C.

2016-01-01

We present the results of large scale, three-dimensional magnetohydrodynamics simulations of disk winds for different initial magnetic field configurations. The jets are followed from the source to distances, which are resolvable by HST and ALMA observations. Our simulations show that jets are heated along their length by many shocks. The mass of the protostar is a free parameter that can be inserted in the post processing of the data, and we apply the simulations to both low mass and high mass protostars. For the latter we also compute the expected diagnostics when the outflow is photoionized by the protostar. We compute the emission lines that are produced, and find excellent agreement with observations. For a one solar mass protostar, we find the jet width to be between 20 and 30 au while the maximum velocities perpendicular to the jet are found to be 100 km s-1. The initially less open magnetic field configuration simulations result in a wider, two-component jet; a cylindrically shaped outer jet surrounding a narrow and much faster, inner jet. For the initially most open magnetic field configuration the kink mode creates a narrow corkscrew-like jet without a clear Keplerian rotation profile and even regions where we observe rotation opposite to the disk (counter-rotating). This is not seen in the less open field configurations.

Dust modeling of the combined ALMA and SPHERE datasets of HD 163296. Is HD 163296 really a Meeus group II disk?

NASA Astrophysics Data System (ADS)

Muro-Arena, G. A.; Dominik, C.; Waters, L. B. F. M.; Min, M.; Klarmann, L.; Ginski, C.; Isella, A.; Benisty, M.; Pohl, A.; Garufi, A.; Hagelberg, J.; Langlois, M.; Menard, F.; Pinte, C.; Sezestre, E.; van der Plas, G.; Villenave, M.; Delboulbé, A.; Magnard, Y.; Möller-Nilsson, O.; Pragt, J.; Rabou, P.; Roelfsema, R.

2018-06-01

Context. Multiwavelength observations are indispensable in studying disk geometry and dust evolution processes in protoplanetary disks. Aims: We aim to construct a three-dimensional model of HD 163296 that is capable of reproducing simultaneously new observations of the disk surface in scattered light with the SPHERE instrument and thermal emission continuum observations of the disk midplane with ALMA. We want to determine why the spectral energy distribution of HD 163296 is intermediary between the otherwise well-separated group I and group II Herbig stars. Methods: The disk was modeled using the Monte Carlo radiative transfer code MCMax3D. The radial dust surface density profile was modeled after the ALMA observations, while the polarized scattered light observations were used to constrain the inclination of the inner disk component and turbulence and grain growth in the outer disk. Results: While three rings are observed in the disk midplane in millimeter thermal emission at 80, 124, and 200 AU, only the innermost of these is observed in polarized scattered light, indicating a lack of small dust grains on the surface of the outer disk. We provide two models that are capable of explaining this difference. The first model uses increased settling in the outer disk as a mechanism to bring the small dust grains on the surface of the disk closer to the midplane and into the shadow cast by the first ring. The second model uses depletion of the smallest dust grains in the outer disk as a mechanism for decreasing the optical depth at optical and near-infrared wavelengths. In the region outside the fragmentation-dominated regime, such depletion is expected from state-of-the-art dust evolution models. We studied the effect of creating an artificial inner cavity in our models, and conclude that HD 163296 might be a precursor to typical group I sources.

Hydrodynamical Modeling of Large Circumstellar Disks

NASA Astrophysics Data System (ADS)

Kurfürst, P.; Krtǐcka, J.

2016-11-01

Direct centrifugal ejection from a critically or near-critically rotating surface forms a gaseous equatorial decretion disk. Anomalous viscosity provides the efficient mechanism for transporting the angular momentum outwards. The outer part of the disk can extend up to a very large distance from the parent star. We study the evolution of density, radial and azimuthal velocity, and angular momentum loss rate of equatorial decretion disks out to very distant regions. We investigate how the physical characteristics of the disk depend on the distribution of temperature and viscosity. We also study the magnetorotational instability, which is considered to be the origin of anomalous viscosity in outflowing disks. We use analytical calculations to study the stability of outflowing disks submerged to the magnetic field. At large radii the instability disappears in the region where the disk orbital velocity is roughly equal to the sound speed. Therefore, the disk sonic radius can be roughly considered as an outer disk radius.

Disk filter

DOEpatents

Bergman, Werner

1986-01-01

An electric disk filter provides a high efficiency at high temperature. A hollow outer filter of fibrous stainless steel forms the ground electrode. A refractory filter material is placed between the outer electrode and the inner electrically isolated high voltage electrode. Air flows through the outer filter surfaces through the electrified refractory filter media and between the high voltage electrodes and is removed from a space in the high voltage electrode.

Disk filter

DOEpatents

Bergman, W.

1985-01-09

An electric disk filter provides a high efficiency at high temperature. A hollow outer filter of fibrous stainless steel forms the ground electrode. A refractory filter material is placed between the outer electrode and the inner electrically isolated high voltage electrode. Air flows through the outer filter surfaces through the electrified refractory filter media and between the high voltage electrodes and is removed from a space in the high voltage electrode.

Hydrocarbon Emission Rings in Protoplanetary Disks Induced by Dust Evolution

NASA Astrophysics Data System (ADS)

Bergin, Edwin A.; Du, Fujun; Cleeves, L. Ilsedore; Blake, G. A.; Schwarz, K.; Visser, R.; Zhang, K.

2016-11-01

We report observations of resolved C2H emission rings within the gas-rich protoplanetary disks of TW Hya and DM Tau using the Atacama Large Millimeter Array. In each case the emission ring is found to arise at the edge of the observable disk of millimeter-sized grains (pebbles) traced by submillimeter-wave continuum emission. In addition, we detect a C3H2 emission ring with an identical spatial distribution to C2H in the TW Hya disk. This suggests that these are hydrocarbon rings (I.e., not limited to C2H). Using a detailed thermo-chemical model we show that reproducing the emission from C2H requires a strong UV field and C/O > 1 in the upper disk atmosphere and outer disk, beyond the edge of the pebble disk. This naturally arises in a disk where the ice-coated dust mass is spatially stratified due to the combined effects of coagulation, gravitational settling and drift. This stratification causes the disk surface and outer disk to have a greater permeability to UV photons. Furthermore the concentration of ices that transport key volatile carriers of oxygen and carbon in the midplane, along with photochemical erosion of CO, leads to an elemental C/O ratio that exceeds unity in the UV-dominated disk. Thus the motions of the grains, and not the gas, lead to a rich hydrocarbon chemistry in disk surface layers and in the outer disk midplane.

Role of subunit assembly in autosomal dominant retinitis pigmentosa linked to mutations in peripherin 2.

PubMed

Molday, Robert S; Molday, Laurie L; Loewen, Christopher J R

2004-01-01

Peripherin 2 is a photoreceptor-specific membrane protein implicated in outer segment disk morphogenesis and linked to various retinopathies including autosomal dominant retinitis pigmentosa (ADRP). Peripherin 2 and ROM1 assemble as a mixture of core noncovalent homomeric and heteromeric tetramers that further link together through disulfide bonds to form higher order oligomers. These complexes are critical for disk rim formation and outer segment structure through interaction with the cGMP-gated channel and other photoreceptor proteins. We have examined the role of subunit assembly in peripherin 2 targeting to disks, outer segment structure, and photoreceptor degeneration by examining molecular and cellular properties of peripherin 2 mutants in COS-1 cells and transgenic Xenopus laevis rod photoreceptors. Wild-type (WT) and the ADRP-linked P216L mutant were transported and incorporated into newly formed outer segment disks of transgenic X. laevis. The P216L mutant, however, induced progressive outer segment instability and photoreceptor degeneration possibly through the introduction of a new N-linked oligosaccharide chain. In contrast, the C214S and L185P disease-linked, tetramerization-defective mutants, were retained in the inner segment, but did not affect outer segment structure or induce photoreceptor degeneration. Together, these results indicate that peripherin 2 mutations can cause ADRP either through a deficiency in WT peripherin 2 (C214S, 1.185P) or by a dominant negative effect on disk stability (P216L).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bergin, Edwin A.; Du, Fujun; Schwarz, K.

We report observations of resolved C{sub 2}H emission rings within the gas-rich protoplanetary disks of TW Hya and DM Tau using the Atacama Large Millimeter Array. In each case the emission ring is found to arise at the edge of the observable disk of millimeter-sized grains (pebbles) traced by submillimeter-wave continuum emission. In addition, we detect a C{sub 3}H{sub 2} emission ring with an identical spatial distribution to C{sub 2}H in the TW Hya disk. This suggests that these are hydrocarbon rings (i.e., not limited to C{sub 2}H). Using a detailed thermo-chemical model we show that reproducing the emission frommore » C{sub 2}H requires a strong UV field and C/O > 1 in the upper disk atmosphere and outer disk, beyond the edge of the pebble disk. This naturally arises in a disk where the ice-coated dust mass is spatially stratified due to the combined effects of coagulation, gravitational settling and drift. This stratification causes the disk surface and outer disk to have a greater permeability to UV photons. Furthermore the concentration of ices that transport key volatile carriers of oxygen and carbon in the midplane, along with photochemical erosion of CO, leads to an elemental C/O ratio that exceeds unity in the UV-dominated disk. Thus the motions of the grains, and not the gas, lead to a rich hydrocarbon chemistry in disk surface layers and in the outer disk midplane.« less

Modeling MHD accretion-ejection: episodic ejections of jets triggered by a mean-field disk dynamo

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stepanovs, Deniss; Fendt, Christian; Sheikhnezami, Somayeh, E-mail: deniss@stepanovs.org, E-mail: fendt@mpia.de

2014-11-20

We present MHD simulations exploring the launching, acceleration, and collimation of jets and disk winds. The evolution of the disk structure is consistently taken into account. Extending our earlier studies, we now consider the self-generation of the magnetic field by an α{sup 2}Ω mean-field dynamo. The disk magnetization remains on a rather low level, which helps to evolve the simulations for T > 10, 000 dynamical time steps on a domain extending 1500 inner disk radii. We find the magnetic field of the inner disk to be similar to the commonly found open field structure, favoring magneto-centrifugal launching. The outermore » disk field is highly inclined and predominantly radial. Here, differential rotation induces a strong toroidal component, which plays a key role in outflow launching. These outflows from the outer disk are slower, denser, and less collimated. If the dynamo action is not quenched, magnetic flux is continuously generated, diffuses outward through the disk, and fills the entire disk. We have invented a toy model triggering a time-dependent mean-field dynamo. The duty cycles of this dynamo lead to episodic ejections on similar timescales. When the dynamo is suppressed as the magnetization falls below a critical value, the generation of the outflows and also accretion is inhibited. The general result is that we can steer episodic ejection and large-scale jet knots by a disk-intrinsic dynamo that is time-dependent and regenerates the jet-launching magnetic field.« less

Evolution of Warped Accretion Disks in Active Galactic Nuclei. I. Roles of Feeding at the Outer Boundaries

NASA Astrophysics Data System (ADS)

Li, Yan-Rong; Wang, Jian-Min; Cheng, Cheng; Qiu, Jie

2013-02-01

We investigate the alignment processes of spinning black holes and their surrounding warped accretion disks in a frame of two different types of feeding at the outer boundaries. We consider (1) fixed flows in which gas is continually fed with a preferred angular momentum, and (2) free flows in which there is no gas supply and the disks diffuse freely at their outer edges. As expected, we find that for the cases of fixed flows the black hole disk systems always align on timescales of several 106 yr, irrespective of the initial inclinations. If the initial inclination angles are larger than π/2, the black hole accretion transits from retrograde to prograde fashion, and the accreted mass onto the black holes during these two phases is comparable. On the other hand, for the cases of free flows, both alignments and anti-alignments can occur, depending on the initial inclinations and the ratios of the angular momentum of the disks to that of the black holes. In such cases, the disks will be consumed within timescales of 106 yr by black holes accreting at the Eddington limit. We propose that there is a close connection between the black hole spin and the lifetime for which the feeding persists, which determines the observable episodic lifetimes of active galactic nuclei. We conclude that careful inclusion of the disk feeding at the outer boundaries is crucial for modeling the evolution of the black hole spin.

On the Outer Edges of Protoplanetary Dust Disks

NASA Astrophysics Data System (ADS)

Birnstiel, Tilman; Andrews, Sean M.

2014-01-01

The expectation that aerodynamic drag will force the solids in a gas-rich protoplanetary disk to spiral in toward the host star on short timescales is one of the fundamental problems in planet formation theory. The nominal efficiency of this radial drift process is in conflict with observations, suggesting that an empirical calibration of solid transport mechanisms in a disk is highly desirable. However, the fact that both radial drift and grain growth produce a similar particle size segregation in a disk (such that larger particles are preferentially concentrated closer to the star) makes it difficult to disentangle a clear signature of drift alone. We highlight a new approach, by showing that radial drift leaves a distinctive "fingerprint" in the dust surface density profile that is directly accessible to current observational facilities. Using an analytical framework for dust evolution, we demonstrate that the combined effects of drift and (viscous) gas drag naturally produce a sharp outer edge in the dust distribution (or, equivalently, a sharp decrease in the dust-to-gas mass ratio). This edge feature forms during the earliest phase in the evolution of disk solids, before grain growth in the outer disk has made much progress, and is preserved over longer timescales when both growth and transport effects are more substantial. The key features of these analytical models are reproduced in detailed numerical simulations, and are qualitatively consistent with recent millimeter-wave observations that find gas/dust size discrepancies and steep declines in dust continuum emission in the outer regions of protoplanetary disks.

A Radial Age Gradient in the Geometrically Thick Disk of the Milky Way

NASA Astrophysics Data System (ADS)

Martig, Marie; Minchev, Ivan; Ness, Melissa; Fouesneau, Morgan; Rix, Hans-Walter

2016-11-01

In the Milky Way, the thick disk can be defined using individual stellar abundances, kinematics, or age, or geometrically, as stars high above the midplane. In nearby galaxies, where only a geometric definition can be used, thick disks appear to have large radial scale lengths, and their red colors suggest that they are uniformly old. The Milky Way’s geometrically thick disk is also radially extended, but it is far from chemically uniform: α-enhanced stars are confined within the inner Galaxy. In simulated galaxies, where old stars are centrally concentrated, geometrically thick disks are radially extended, too. Younger stellar populations flare in the simulated disks’ outer regions, bringing those stars high above the midplane. The resulting geometrically thick disks therefore show a radial age gradient, from old in their central regions to younger in their outskirts. Based on our age estimates for a large sample of giant stars in the APOGEE survey, we can now test this scenario for the Milky Way. We find that the geometrically defined thick disk in the Milky Way has indeed a strong radial age gradient: the median age for red clump stars goes from ∼9 Gyr in the inner disk to 5 Gyr in the outer disk. We propose that at least some nearby galaxies could also have thick disks that are not uniformly old, and that geometrically thick disks might be complex structures resulting from different formation mechanisms in their inner and outer parts.

Extended Millimeter Emission in the HD 141569 Circumstellar Disk Detected with ALMA

NASA Astrophysics Data System (ADS)

White, Jacob Aaron; Boley, A. C.

2018-06-01

We present archival Atacama Large Millimeter/submillimeter Array (ALMA) observations of the HD 141569 circumstellar disk at 345, 230, and 100 GHz. These data detect extended millimeter emission that is exterior to the inner disk. We find through simultaneous visibility modeling of all three data sets that the system’s morphology is described well by a two-component disk model. The inner disk ranges from approximately 16–45 au with a spectral index of 1.81 (q = 2.95), and the outer disk ranges from 95 to 300 au with a spectral index of 2.28 (q = 3.21). Azimuthally averaged radial emission profiles derived from the continuum images at each frequency show potential emission that is consistent with the visibility modeling. The analysis presented here shows that at ∼5 Myr, HD 141569's grain size distribution is steeper and therefore possibly evolved in the outer disk than in the inner disk.

Clumps in the outer disk by disk instability: Why they are initially gas giants and the legacy of disruption

NASA Astrophysics Data System (ADS)

Boley, Aaron C.; Hayfield, Tristen; Mayer, Lucio; Durisen, Richard H.

2010-06-01

We explore the initial conditions for fragments in the extended regions (r≳50AU) of gravitationally unstable disks. We combine analytic estimates for the fragmentation of spiral arms with 3D SPH simulations to show that initial fragment masses are in the gas giant regime. These initial fragments will have substantial angular momentum, and should form disks with radii of a few AU. We show that clumps will survive for multiple orbits before they undergo a second, rapid collapse due to H 2 dissociation and that it is possible to destroy bound clumps by transporting them into the inner disk. The consequences of disrupted clumps for planet formation, dust processing, and disk evolution are discussed. We argue that it is possible to produce Earth-mass cores in the outer disk during the earliest phases of disk evolution.

Nebula Scale Mixing Between Non-Carbonaceous and Carbonaceous Chondrite Reservoirs: Testing the Grand Tack Model with Almahata Sitta Stones

NASA Technical Reports Server (NTRS)

Yin, Q.-Z.; Sanborn, M. E.; Goodrich, C. A.; Zolensky, M.; Fioretti, A. M.; Shaddad, M.; Kohl, I. E.; Young, E. D.

2018-01-01

There is an increasing number of Cr-O-Ti isotope studies that show that solar system materials are divided into two main populations, one carbonaceous chondrite (CC)-like and the other is non-carbonaceous (NCC)-like, with minimal mixing between them attributed to a gap opened in the propoplanetary disk due to Jupiter's formation. The Grand Tack model suggests that there should be a particular time in the disk history when this gap is breached and ensuring a subsequent large-scale mixing between S- and C-type asteroids (inner solar system and outer solar system materials), an idea supported by our recent work on chondrule (Delta)17O-(epsilon)54Cr isotope systematics.

Hubble and Spitzer Space Telescope Observations of the Debris Disk around the nearby K Dwarf HD 92945

NASA Astrophysics Data System (ADS)

Golimowski, D. A.; Krist, J. E.; Stapelfeldt, K. R.; Chen, C. H.; Ardila, D. R.; Bryden, G.; Clampin, M.; Ford, H. C.; Illingworth, G. D.; Plavchan, P.; Rieke, G. H.; Su, K. Y. L.

2011-07-01

We present the first resolved images of the debris disk around the nearby K dwarf HD 92945, obtained with the Hubble Space Telescope's (HST 's) Advanced Camera for Surveys. Our F606W (Broad V) and F814W (Broad I) coronagraphic images reveal an inclined, axisymmetric disk consisting of an inner ring about 2farcs0-3farcs0 (43-65 AU) from the star and an extended outer disk whose surface brightness declines slowly with increasing radius approximately 3farcs0-5farcs1 (65-110 AU) from the star. A precipitous drop in the surface brightness beyond 110 AU suggests that the outer disk is truncated at that distance. The radial surface-density profile is peaked at both the inner ring and the outer edge of the disk. The dust in the outer disk scatters neutrally but isotropically, and it has a low V-band albedo of 0.1. This combination of axisymmetry, ringed and extended morphology, and isotropic neutral scattering is unique among the 16 debris disks currently resolved in scattered light. We also present new infrared photometry and spectra of HD 92945 obtained with the Spitzer Space Telescope's Multiband Imaging Photometer and InfraRed Spectrograph. These data reveal no infrared excess from the disk shortward of 30 μm and constrain the width of the 70 μm source to lsim180 AU. Assuming that the dust comprises compact grains of astronomical silicate with a surface-density profile described by our scattered-light model of the disk, we successfully model the 24-350 μm emission with a minimum grain size of a min = 4.5 μm and a size distribution proportional to a -3.7 throughout the disk, but with maximum grain sizes of 900 μm in the inner ring and 50 μm in the outer disk. Together, our HST and Spitzer observations indicate a total dust mass of ~0.001M ⊕. However, our observations provide contradictory evidence of the dust's physical characteristics: its neutral V-I color and lack of 24 μm emission imply grains larger than a few microns, but its isotropic scattering and low albedo suggest a large population of submicron-sized grains. If grains smaller than a few microns are absent, then stellar radiation pressure may be the cause only if the dust is composed of highly absorptive materials like graphite. The dynamical causes of the sharply edged inner ring and outer disk are unclear, but recent models of dust creation and transport in the presence of migrating planets support the notion that the disk indicates an advanced state of planet formation around HD 92945. Based in part on guaranteed observing time awarded by the National Aeronautics and Space Administration (NASA) to the Advanced Camera for Surveys Investigation Definition Team and the Multiband Imaging Photometer for Spitzer Instrument Team.

Debris disks as signposts of terrestrial planet formation. II. Dependence of exoplanet architectures on giant planet and disk properties

NASA Astrophysics Data System (ADS)

Raymond, S. N.; Armitage, P. J.; Moro-Martín, A.; Booth, M.; Wyatt, M. C.; Armstrong, J. C.; Mandell, A. M.; Selsis, F.; West, A. A.

2012-05-01

We present models for the formation of terrestrial planets, and the collisional evolution of debris disks, in planetary systems that contain multiple marginally unstable gas giants. We previously showed that in such systems, the dynamics of the giant planets introduces a correlation between the presence of terrestrial planets and cold dust, i.e., debris disks, which is particularly pronounced at λ ~ 70 μm. Here we present new simulations that show that this connection is qualitatively robust to a range of parameters: the mass distribution of the giant planets, the width and mass distribution of the outer planetesimal disk, and the presence of gas in the disk when the giant planets become unstable. We discuss how variations in these parameters affect the evolution. We find that systems with equal-mass giant planets undergo the most violent instabilities, and that these destroy both terrestrial planets and the outer planetesimal disks that produce debris disks. In contrast, systems with low-mass giant planets efficiently produce both terrestrial planets and debris disks. A large fraction of systems with low-mass (M ≲ 30 M⊕) outermost giant planets have final planetary separations that, scaled to the planets' masses, are as large or larger than the Saturn-Uranus and Uranus-Neptune separations in the solar system. We find that the gaps between these planets are not only dynamically stable to test particles, but are frequently populated by planetesimals. The possibility of planetesimal belts between outer giant planets should be taken into account when interpreting debris disk SEDs. In addition, the presence of ~ Earth-mass "seeds" in outer planetesimal disks causes the disks to radially spread to colder temperatures, and leads to a slow depletion of the outer planetesimal disk from the inside out. We argue that this may explain the very low frequency of >1 Gyr-old solar-type stars with observed 24 μm excesses. Our simulations do not sample the full range of plausible initial conditions for planetary systems. However, among the configurations explored, the best candidates for hosting terrestrial planets at ~1 AU are stars older than 0.1-1 Gyr with bright debris disks at 70 μm but with no currently-known giant planets. These systems combine evidence for the presence of ample rocky building blocks, with giant planet properties that are least likely to undergo destructive dynamical evolution. Thus, we predict two correlations that should be detected by upcoming surveys: an anti-correlation between debris disks and eccentric giant planets and a positive correlation between debris disks and terrestrial planets. Three movies associated to Figs. 1, 3, and 7 are available in electronic form at http://www.aanda.org

Dielectric supported radio-frequency cavities

DOEpatents

Yu, David U. L.; Lee, Terry G.

2000-01-01

A device which improves the electrical and thermomechanical performance of an RF cavity, for example, in a disk-loaded accelerating structure. A washer made of polycrystalline diamond is brazed in the middle to a copper disk washer and at the outer edge to the plane wave transformer tank wall, thus dissipating heat from the copper disk to the outer tank wall while at the same time providing strong mechanical support to the metal disk. The washer structure eliminates the longitudinal connecting rods and cooling channels used in the currently available cavities, and as a result minimizes problems such as shunt impedance degradation and field distortion in the plane wave transformer, and mechanical deflection and uneven cooling of the disk assembly.

RESOLVING THE PLANET-HOSTING INNER REGIONS OF THE LkCa 15 DISK

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thalmann, C.; Garufi, A.; Quanz, S. P.

2016-09-10

LkCa 15 hosts a pre-transitional disk as well as at least one accreting protoplanet orbiting in its gap. Previous disk observations have focused mainly on the outer disk, which is cleared inward of ∼50 au. The planet candidates, on the other hand, reside at orbital radii around 15 au, where disk observations have been unreliable until recently. Here, we present new J -band imaging polarimetry of LkCa 15 with SPHERE IRDIS, yielding the most accurate and detailed scattered-light images of the disk to date down to the planet-hosting inner regions. We find what appear to be persistent asymmetric structures inmore » the scattering material at the location of the planet candidates, which could be responsible at least for parts of the signals measured with sparse-aperture masking. These images further allow us to trace the gap edge in scattered light at all position angles and search the inner and outer disks for morphological substructure. The outer disk appears smooth with slight azimuthal variations in polarized surface brightness, which may be due to shadowing from the inner disk or a two-peaked polarized phase function. We find that the near-side gap edge revealed by polarimetry matches the sharp crescent seen in previous ADI imaging very well. Finally, the ratio of polarized disk to stellar flux is more than six times larger in the J -band than in the RI bands.« less

Orbital evolution and accretion of protoplanets tidally interacting with a gas disk. I. Effects of interaction with planetesimals and other protoplanets

NASA Astrophysics Data System (ADS)

Kominami, Junko; Tanaka, Hidekazu; Ida, Shigeru

2005-11-01

We have performed N-body simulations on the stage of protoplanet formation from planetesimals, taking into account so-called "type-I migration," and damping of orbital eccentricities and inclinations, as a result of tidal interaction with a gas disk without gap formation. One of the most serious problems in formation of terrestrial planets and jovian planet cores is that the migration time scale predicted by the linear theory is shorter than the disk lifetime (10 6-10 7 years). In this paper, we investigate retardation of type-I migration of a protoplanet due to a torque from a planetesimal disk in which a gap is opened up by the protoplanet, and torques from other protoplanets which are formed in inner and outer regions. In the first series of runs, we carried out N-body simulations of the planetesimal disk, which ranges from 0.9 to 1.1 AU, with a protoplanet seed in order to clarify how much retardation can be induced by the planetesimal disk and how long such retardation can last. We simulated six cases with different migration speeds. We found that in all of our simulations, a clear gap is not maintained for more than 10 5 years in the planetesimal disk. For very fast migration, a gap cannot be created in the planetesimal disk. For migration slower than some critical speed, a gap does form. However, because of the growth of the surrounding planetesimals, gravitational perturbation of the planetesimals eventually becomes so strong that the planetesimals diffuse into the vicinity of the protoplanets, resulting in destruction of the gap. After the gap is destroyed, close encounters with the planetesimals rather accelerate the protoplanet migration. In this way, the migration cannot be retarded by the torque from the planetesimal disk, regardless of the migration speed. In the second series of runs, we simulated accretion of planetesimals in wide range of semimajor axis, 0.5 to 2-5 AU, starting with equal mass planetesimals without a protoplanet seed. Since formation of comparable-mass multiple protoplanets ("oligarchic growth") is expected, the interactions with other protoplanets have a potential to alter the migration speed. However, inner protoplanets migrate before outer ones are formed, so that the migration and the accretion process of a runaway protoplanet are not affected by the other protoplanets placed inner and outer regions of its orbit. From the results of these two series of simulations, we conclude that the existence of planetesimals and multiple protoplanets do not affect type-I migration and therefore the migration shall proceed as the linear theory has suggested.

Spreading dynamics of superposed liquid drops on a spinning disk

NASA Astrophysics Data System (ADS)

Sahoo, Subhadarshinee; Orpe, Ashish V.; Doshi, Pankaj

2018-01-01

We have experimentally studied simultaneous spreading of superposed drops of two Newtonian liquids on top of a horizontal spinning disk using the flow visualization technique. An inner drop of high surface tension liquid is placed centrally on the disk followed by a drop of outer liquid (lower surface tension) placed exactly above that. The disk is then rotated at a desired speed for a range of volume ratios of two liquids. Such an arrangement of two superposed liquid drops does not affect the spreading behavior of the outer liquid but influences that of the inner liquid significantly. The drop spreads to a larger extent and breaks into more fingers (Nf) as compared to the case where the same liquid is spreading in the absence of outer liquid. The experimentally observed number of fingers is compared with the prediction using available theory for single liquid. It is found that the theory over-predicts the value of Nf for the inner liquid while it is covered by an outer liquid. We provide a theoretical justification for this observation using linear stability analysis. Our analysis demonstrates that for small but finite surface tension ratio of the two liquids, the presence of the outer interface reduces the value of the most unstable wave number which is equivalent to the decrease in the number of fingers observed experimentally. Finally, sustained rotation of the disk leads to the formation of droplets at the tip of the fingers traveling outwards.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carraro, Giovanni; Vázquez, Rubén A.; Costa, Edgardo

In the third Galactic quadrant (180{sup ∘}⩽l⩽270{sup ∘}) of the Milky Way, the Galactic thin disk exhibits a significant warp—shown both by gas and young stars—bending down a few kiloparsecs below the formal Galactic plane (b=0{sup ∘}). This warp shows its maximum at l∼240{sup ∘}, in the direction of the Canis Major constellation. In a series of papers, we have traced the detailed structure of this region using open star clusters, putting particular emphasis on the spiral structure of the outer disk. We noted a conspicuous accumulation of young star clusters within 2–3 kpc from the Sun and close tomore » b = 0°, which we interpreted as the continuation of the Local (Orion) arm toward the outer disk. While most clusters (and young stars in their background) closely follow the warp of the disk, our decade-old survey of the spiral structure of this region led us to identify three clusters, Haffner 18 (1 and 2) and Haffner 19, which remain very close to b = 0° and lie at distances (4.5, ∼8.0, and 6.4 kpc) where most of the material is already significantly warped. Here, we report on a search for clusters that share the same properties as Haffner 18 and 19, and investigate the possible reasons for such an unexpected occurrence. We present UBVRI photometry of five young clusters, namely NGC 2345, NGC 2374, Trumpler 9, Haffner 20, and Haffner 21, which also lie close to the formal Galactic plane. With the exception of Haffner 20, in the background of these clusters we detected young stars that appear close to b=0{sup ∘} and are located at distances up to ∼8 kpc from the Sun, thus deviating significantly from the warp. These populations define a structure that distributes over almost the entire third Galactic quadrant. We discuss this structure in the context of a possible thin disk flaring, similar to the Galactic thick disk.« less

HST and Adaptive Optics Imaging of the Edge-on Circumtertiary Disk in the Young Triple System HV Tauri

NASA Astrophysics Data System (ADS)

Stapelfeldt, K. R.; Menard, F.; Brandner, W.; Padgett, D. L.; Krist, J. E.; Watson, A. M.

2000-12-01

Hubble Space Telescope images of the HV Tauri triple system show that HV Tau C appears as a compact bipolar nebula at visual wavelengths. Near-infrared adaptive optics observations made at the Canada France Hawaii Telescope show a similar morphology, and no directly visible star at wavelengths less than 2 microns. These results confirm the conclusions of Monin & Bouvier 2000, namely that HV Tau C is an optically thick circumstellar disk seen close to edge-on. The images are compared to scattered light models for circumstellar disks. We find that the HV Tau C disk has an outer radius of 85 AU, inclination of about 6 deg, gaussian scale height of 15 AU at its outer radius, and is flared. The thickness of the dark lane indicates a total disk mass about half that of Jupiter. There is clear evidence for declining dust opacity toward longer wavelengths, as the dust lane thickness shrinks by 30 between 0.8 and 2.2 microns; the trend is consistent with interstellar dust grains. Tidal truncation of the disk outer radius may have occurred in this system.

Mid-infrared interferometric variability of DG Tauri: Implications for the inner-disk structure

NASA Astrophysics Data System (ADS)

Varga, J.; Gabányi, K. É.; Ábrahám, P.; Chen, L.; Kóspál, Á.; Menu, J.; Ratzka, Th.; van Boekel, R.; Dullemond, C. P.; Henning, Th.; Jaffe, W.; Juhász, A.; Moór, A.; Mosoni, L.; Sipos, N.

2017-08-01

Context. DG Tau is a low-mass pre-main sequence star, whose strongly accreting protoplanetary disk exhibits a so-far enigmatic behavior: its mid-infrared thermal emission is strongly time-variable, even turning the 10 μm silicate feature from emission to absorption temporarily. Aims: We look for the reason for the spectral variability at high spatial resolution and at multiple epochs. Methods: Infrared interferometry can spatially resolve the thermal emission of the circumstellar disk, also giving information about dust processing. We study the temporal variability of the mid-infrared interferometric signal, observed with the VLTI/MIDI instrument at six epochs between 2011 and 2014. We fit a geometric disk model to the observed interferometric signal to obtain spatial information about the disk. We also model the mid-infrared spectra by template fitting to characterize the profile and time dependence of the silicate emission. We use physically motivated radiative transfer modeling to interpret the mid-infrared interferometric spectra. Results: The inner disk (r < 1-3 au) spectra exhibit a 10 μm absorption feature related to amorphous silicate grains. The outer disk (r > 1-3 au) spectra show a crystalline silicate feature in emission, similar to the spectra of comet Hale-Bopp. The striking difference between the inner and outer disk spectral feature is highly unusual among T Tauri stars. The mid-infrared variability is dominated by the outer disk. The strength of the silicate feature changed by more than a factor of two. Between 2011 and 2014 the half-light radius of the mid-infrared-emitting region decreased from 1.15 to 0.7 au. Conclusions: For the origin of the absorption we discuss four possible explanations: a cold obscuring envelope, an accretion heated inner disk, a temperature inversion on the disk surface and a misaligned inner geometry. The silicate emission in the outer disk can be explained by dusty material high above the disk plane, whose mass can change with time, possibly due to turbulence in the disk. Based on observations made with the ESO Very Large Telescope Interferometer at Paranal Observatory (Chile) under the programs 088.C-1007 (PI: L. Mosoni), 090.C-0040 (PI: Th. Ratzka), and 092.C-0086 (PI: Th. Ratzka).

Internal position and limit sensor for free piston machines

NASA Technical Reports Server (NTRS)

Holliday, Ezekiel S. (Inventor); Wood, James Gary (Inventor)

2012-01-01

A sensor for sensing the position of a reciprocating free piston in a free piston Stirling machine. The sensor has a disk mounted to an end face of the power piston coaxially with its cylinder and reciprocating with the piston The disk includes a rim around its outer perimeter formed of an electrically conductive material A coil is wound coaxially with the cylinder, spaced outwardly from the outer perimeter of the disk and mounted in fixed position relative to the pressure vessel, preferably on the exterior of the pressure vessel wall.

Equilibrium configurations of perfect fluid orbiting Schwarzschild-de Sitter black holes

NASA Astrophysics Data System (ADS)

Stuchlík, Z.; Slaný, P.; Hledík, S.

2000-11-01

The hydrodynamical structure of perfect fluid orbiting Schwarzschild-de Sitter black holes is investigated for configurations with uniform distribution of angular momentum density. It is shown that in the black-hole backgrounds admitting the existence of stable circular geodesics, closed equipotential surfaces with a cusp, allowing the existence of toroidal accretion disks, can exist. Two surfaces with a cusp exist for the angular momentum density smaller than the one corresponding to marginally bound circular geodesics; the equipotential surface corresponding to the marginally bound circular orbit has just two cusps. The outer cusp is located nearby the static radius where the gravitational attraction is compensated by the cosmological repulsion. Therefore, due to the presence of a repulsive cosmological constant, the outflow from thick accretion disks can be driven by the same mechanism as the accretion onto the black hole. Moreover, properties of open equipotential surfaces in vicinity of the axis of rotation suggest a strong collimation effects of the repulsive cosmological constant acting on jets produced by the accretion disks.

Formation of Large Regular Satellites of Giant Planets in an Extended Gaseous Nebula. 2; Satellite Migration And Survival

NASA Technical Reports Server (NTRS)

Mosqueira, I.; Estrada, P. R.

2000-01-01

Using an optically thick inner disk and an extended, optically thin outer disk as described in Mosqueira and Estrada, we compute the torque as a function of position in the subnebula, and show that although the torque exerted on the satellite is generally negative, which leads to inward migration as expected, there are regions of the disk where the torque is positive. For our model these regions of positive torque correspond roughly to the locations of Callisto and Iapetus. Though the outer location of zero torque depends on the (unknown) size of the transition region between the inner and outer disks, the result that Saturn's is found much farther out (at approximately 3r(sub c, sup S) where r(sub c, sup S) is Saturn's centrifugal radius) than Jupiter's (at approximately 2r(sub c, sup J), where r(sub c, sup J) is Jupiter's centrifugal radius) is mostly due to Saturn's less massive outer disk, and larger Hill radius. For a satellite to survive in the disk the timescale of satellite migration must be longer than the timescale for gas dissipation. For large satellites (approximately 1000 km) migration is dominated by the gas torque. We consider the possibility that the feedback reaction of the gas disk caused by the redistribution of gas surface density around satellites with masses larger than the inertial mass causes a large drop in the drift velocity of such objects, thus improving the likelihood that they will be left stranded following gas dissipation. We adapt the inviscid inertial mass criterion to include gas drag, and m-dependent non-local deposition of angular momentum.

A radio frequency coaxial feedthrough

DOEpatents

Owens, T.L.

1987-12-07

An improved radio frequency coaxial transmission line vacuum feedthrough is provided based on the use of a half-wavelength annular dielectric pressure barrier disk, or multiple disks comprising an effective half wavelength structure to eliminate reflection from the barrier surfaces. Gas-tight seals are formed about the outer and inner diameter surfaces of the barrier disk using a sealing technique which generates radial forces sufficient to form seals by forcing the conductor walls against the surfaces of the barrier disks in a manner which does not deform the radii of the inner and outer conductors, thereby preventing enhancement of the electric field at the barrier faces which limits the voltage and power handling capabilities of a feedthrough.

Radio frequency coaxial feedthrough

DOEpatents

Owens, Thomas L.

1989-01-17

An improved radio frequency coaxial transmission line vacuum feed-through provided based on the use of a half-wavelength annular dielectric pressure barrier disk, or multiple disks comprising an effective half wavelength structure to eliminate reflections from the barrier surfaces. Gas-tight seals are formed about the outer and inner diameter surfaces of the barrier disk using a sealing technique which generates radial forces sufficient to form seals by forcing the conductor walls against the surfaces of the barrier disks in a manner which does not deform the radii of the inner and outer conductors, thereby preventing enhancement of the electric field at the barrier faces which limits voltage and power handling capabilities of a feedthrough.

Interaction of the stream from L 1 with the outer edge of the accretion disk in a cataclysmic variable

NASA Astrophysics Data System (ADS)

Kaigorodov, P. V.; Bisikalo, D. V.; Kurbatov, E. P.

2017-08-01

Vertical oscillations of the gas at the outer edge of the accretion disk in a semi-detached binary due to interaction with the stream of matter from the inner Lagrangian point L 1 are considered. Mixing of the matter from the stream from L 1 with matter of the disk halo results in the formation of a system of two diverging shocks and a contact discontinuity, or so-called "hot line". The passage of matter through the region of the hot line leads to an increase in its vertical velocity and a thickening of the disk at phases 0.7-0.8. Subsequently, the matter moving along the outer edge of the disk also experiences vertical oscillations, forming secondary maxima at phases 0.2-0.4. It is shown that, for systems with component mass ratios of 0.6, these oscillations will be amplified with each passage of the matter through the hotline zone, while the observations will be quenched in systems with component mass ratios 0.07 and 7. The most favorable conditions for the flow of matter from the stream through the edge of the disk arise for component mass ratios 0.62. A theoretical relation between the phases of disk thickenings and the component mass ratio of the system is derived.

A Distant Solar System Artist Concept

NASA Image and Video Library

2004-12-09

This artist concept depicts a distant hypothetical solar system, similar in age to our own. Looking inward from the system outer fringes, a ring of dusty debris can be seen, and within it, planets circling a star the size of our Sun. This debris is all that remains of the planet-forming disk from which the planets evolved. Planets are formed when dusty material in a large disk surrounding a young star clumps together. Leftover material is eventually blown out by solar wind or pushed out by gravitational interactions with planets. Billions of years later, only an outer disk of debris remains. These outer debris disks are too faint to be imaged by visible-light telescopes. They are washed out by the glare of the Sun. However, NASA's Spitzer Space Telescope can detect their heat, or excess thermal emission, in infrared light. This allows astronomers to study the aftermath of planet building in distant solar systems like our own. http://photojournal.jpl.nasa.gov/catalog/PIA07096

OUTER-DISK POPULATIONS IN NGC 7793: EVIDENCE FOR STELLAR RADIAL MIGRATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Radburn-Smith, David J.; Dalcanton, Julianne J.; Roskar, Rok

2012-07-10

We analyzed the radial surface brightness profile of the spiral galaxy NGC 7793 using HST/ACS images from the GHOSTS survey and a new HST/WFC3 image across the disk break. We used the photometry of resolved stars to select distinct populations covering a wide range of stellar ages. We found breaks in the radial profiles of all stellar populations at 280'' ({approx}5.1 kpc). Beyond this disk break, the profiles become steeper for younger populations. This same trend is seen in numerical simulations where the outer disk is formed almost entirely by radial migration. We also found that the older stars ofmore » NGC 7793 extend significantly farther than the underlying H I disk. They are thus unlikely to have formed entirely at their current radii, unless the gas disk was substantially larger in the past. These observations thus provide evidence for substantial stellar radial migration in late-type disks.« less

WATER VAPOR IN THE PROTOPLANETARY DISK OF DG Tau

DOE Office of Scientific and Technical Information (OSTI.GOV)

Podio, L.; Dougados, C.; Thi, W.-F.

2013-03-20

Water is key in the evolution of protoplanetary disks and the formation of comets and icy/water planets. While high-excitation water lines originating in the hot inner disk have been detected in several T Tauri stars (TTSs), water vapor from the outer disk, where most water ice reservoirs are stored, was only reported in the nearby TTS TW Hya. We present spectrally resolved Herschel/HIFI observations of the young TTS DG Tau in the ortho- and para-water ground-state transitions at 557 and 1113 GHz. The lines show a narrow double-peaked profile, consistent with an origin in the outer disk, and are {approx}19-26more » times brighter than in TW Hya. In contrast, CO and [C II] lines are dominated by emission from the envelope/outflow, which makes H{sub 2}O lines a unique tracer of the disk of DG Tau. Disk modeling with the thermo-chemical code ProDiMo indicates that the strong UV field, due to the young age and strong accretion of DG Tau, irradiates a disk upper layer at 10-90 AU from the star, heating it up to temperatures of 600 K and producing the observed bright water lines. The models suggest a disk mass of 0.015-0.1 M{sub Sun }, consistent with the estimated minimum mass of the solar nebula before planet formation, and a water reservoir of {approx}10{sup 2}-10{sup 3} Earth oceans in vapor and {approx}100 times larger in the form of ice. Hence, this detection supports the scenario of ocean delivery on terrestrial planets by the impact of icy bodies forming in the outer disk.« less

Swivel Joint For Liquid Nitrogen

NASA Technical Reports Server (NTRS)

Milner, James F.

1988-01-01

Swivel joint allows liquid-nitrogen pipe to rotate through angle of 100 degree with respect to mating pipe. Functions without cracking hard foam insulation on lines. Pipe joint rotates on disks so mechanical stress not transmitted to thick insulation on pipes. Inner disks ride on fixed outer disks. Disks help to seal pressurized liquid nitrogen flowing through joint.

RESOLVED CO GAS INTERIOR TO THE DUST RINGS OF THE HD 141569 DISK

DOE Office of Scientific and Technical Information (OSTI.GOV)

Flaherty, Kevin M.; Hughes, A. Meredith; Zachary, Julia

2016-02-10

The disk around HD 141569 is one of a handful of systems whose weak infrared emission is consistent with a debris disk, but still has a significant reservoir of gas. Here we report spatially resolved millimeter observations of the CO(3-2) and CO(1-0) emission as seen with the Submillimeter Array and CARMA. We find that the excitation temperature for CO is lower than expected from cospatial blackbody grains, similar to previous observations of analogous systems, and derive a gas mass that lies between that of gas-rich primordial disks and gas-poor debris disks. The data also indicate a large inner hole inmore » the CO gas distribution and an outer radius that lies interior to the outer scattered light rings. This spatial distribution, with the dust rings just outside the gaseous disk, is consistent with the expected interactions between gas and dust in an optically thin disk. This indicates that gas can have a significant effect on the location of the dust within debris disks.« less

Evaporation of Accretion Disks around Black Holes: The Disk-Corona Transition and the Connection to the Advection-dominated Accretion Flow.

PubMed

Liu; Yuan; Meyer; Meyer-Hofmeister; Xie

1999-12-10

We apply the disk-corona evaporation model (Meyer & Meyer-Hofmeister) originally derived for dwarf novae to black hole systems. This model describes the transition of a thin cool outer disk to a hot coronal flow. The mass accretion rate determines the location of this transition. For a number of well-studied black hole binaries, we take the mass flow rates derived from a fit of the advection-dominated accretion flow (ADAF) model to the observed spectra (for a review, see Narayan, Mahadevan, & Quataert) and determine where the transition of accretion via a cool disk to a coronal flow/ADAF would be located for these rates. We compare this with the observed location of the inner disk edge, as estimated from the maximum velocity of the Halpha emission line. We find that the transition caused by evaporation agrees with this determination in stellar disks. We also show that the ADAF and the "thin outer disk + corona" are compatible in terms of the physics in the transition region.

Falling Outer Rotation Curves of Star-forming Galaxies at 0.6 ≲ z ≲ 2.6 Probed with KMOS3D and SINS/zC-SINF

NASA Astrophysics Data System (ADS)

Lang, Philipp; Förster Schreiber, Natascha M.; Genzel, Reinhard; Wuyts, Stijn; Wisnioski, Emily; Beifiori, Alessandra; Belli, Sirio; Bender, Ralf; Brammer, Gabe; Burkert, Andreas; Chan, Jeffrey; Davies, Ric; Fossati, Matteo; Galametz, Audrey; Kulkarni, Sandesh K.; Lutz, Dieter; Mendel, J. Trevor; Momcheva, Ivelina G.; Naab, Thorsten; Nelson, Erica J.; Saglia, Roberto P.; Seitz, Stella; Tacchella, Sandro; Tacconi, Linda J.; Tadaki, Ken-ichi; Übler, Hannah; van Dokkum, Pieter G.; Wilman, David J.

2017-05-01

We exploit the deep, resolved, Hα kinematic data from the KMOS3D and SINS/zC-SINF surveys to examine the largely unexplored outer-disk kinematics of star-forming galaxies (SFGs), out to the peak of cosmic star formation. Our sample contains 101 SFGs, representative of the more massive (9.3≲ {log}{M}* /{M}⊙ ≲ 11.5) main sequence population at 0.6 ≤ z ≤ 2.6. Through a novel stacking approach, we are able to constrain a representative rotation curve extending out to ˜4 effective radii. This average rotation curve exhibits a significant drop in rotation velocity beyond the turnover, with a slope of {{Δ }}V/{{Δ }}R=-{0.26}-0.09+0.10 in units of normalized coordinates V/V max and R/R turn. This result confirms that the fall-off seen in some individual galaxies is a common feature of our sample of high-z disks. The outer fall-off strikingly deviates from the flat or mildly rising rotation curves of local spiral galaxies that have similar masses. Through a comparison with models that include baryons and dark matter, we demonstrate that the falling stacked rotation curve is consistent with a high mass fraction of baryons, relative to the total dark matter halo (m d ≳ 0.05), in combination with a sizeable level of pressure support in the outer disk. These findings agree with recent studies demonstrating that high-z star-forming disks are strongly baryon-dominated within the disk scale, and furthermore suggest that pressure gradients caused by large, turbulent gas motions are present even in their outer disks. These results are largely independent of our model assumptions, such as the presence of stellar bulges, the effect of adiabatic contraction, and variations in halo concentration.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jacobson, Heather R.; Pilachowski, Catherine A.; Friel, Eileen D., E-mail: jacob189@msu.edu, E-mail: catyp@astro.indiana.edu, E-mail: edfriel@mac.com

We present a detailed chemical abundance study of evolved stars in 10 open clusters based on Hydra multi-object echelle spectra obtained with the WIYN 3.5 m telescope. From an analysis of both equivalent widths and spectrum synthesis, abundances have been determined for the elements Fe, Na, O, Mg, Si, Ca, Ti, Ni, Zr, and for two of the 10 clusters, Al and Cr. To our knowledge, this is the first detailed abundance analysis for clusters NGC 1245, NGC 2194, NGC 2355, and NGC 2425. These 10 clusters were selected for analysis because they span a Galactocentric distance range R{sub gc}more » {approx} 9-13 kpc, the approximate location of the transition between the inner and outer disks. Combined with cluster samples from our previous work and those of other studies in the literature, we explore abundance trends as a function of cluster R{sub gc}, age, and [Fe/H]. As found previously by us and other studies, the [Fe/H] distribution appears to decrease with increasing R{sub gc} to a distance of {approx}12 kpc and then flattens to a roughly constant value in the outer disk. Cluster average element [X/Fe] ratios appear to be independent of R{sub gc}, although the picture for [O/Fe] is more complicated with a clear trend of [O/Fe] with [Fe/H] and sample incompleteness. Other than oxygen, no other element [X/Fe] exhibits a clear trend with [Fe/H]; likewise, there does not appear to be any strong correlation between abundance and cluster age. We divided clusters into different age bins to explore temporal variations in the radial element distributions. The radial metallicity gradient appears to have flattened slightly as a function of time, as found by other studies. There is also some indication that the transition from the inner disk metallicity gradient to the {approx}constant [Fe/H] distribution of the outer disk occurs at different Galactocentric radii for different age bins. However, interpretation of the time evolution of radial abundance distributions is complicated by the unequal R{sub gc} and [Fe/H] ranges spanned by clusters in different age bins.« less

Chasing Shadows: Rotation of the Azimuthal Asymmetry in the TW Hya Disk

DOE Office of Scientific and Technical Information (OSTI.GOV)

Debes, John H.; Poteet, Charles A.; Hines, Dean

2017-02-01

We have obtained new images of the protoplanetary disk orbiting TW Hya in visible, total intensity light with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope ( HST ), using the newly commissioned BAR5 occulter. These HST /STIS observations achieved an inner working angle of ∼0.″2, or 11.7 au, probing the system at angular radii coincident with recent images of the disk obtained by ALMA and in polarized intensity near-infrared light. By comparing our new STIS images to those taken with STIS in 2000 and with NICMOS in 1998, 2004, and 2005, we demonstrate that TW Hya’smore » azimuthal surface brightness asymmetry moves coherently in position angle. Between 50 au and 141 au we measure a constant angular velocity in the azimuthal brightness asymmetry of 22.°7 yr{sup −1} in a counterclockwise direction, equivalent to a period of 15.9 yr assuming circular motion. Both the (short) inferred period and lack of radial dependence of the moving shadow pattern are inconsistent with Keplerian rotation at these disk radii. We hypothesize that the asymmetry arises from the fact that the disk interior to 1 au is inclined and precessing owing to a planetary companion, thus partially shadowing the outer disk. Further monitoring of this and other shadows on protoplanetary disks potentially opens a new avenue for indirectly observing the sites of planet formation.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kasper, Markus; Apai, Dániel; Wagner, Kevin

Using Very Large Telescope/SPHERE near-infrared dual-band imaging and integral field spectroscopy, we discovered an edge-on debris disk around the 17 Myr old A-type member of the Scorpius–Centaurus OB association HD 110058. The edge-on disk can be traced to about 0.″6 or 65 AU projected separation. In its northern and southern wings, the disk shows at all wavelengths two prominent, bright, and symmetrically placed knots at 0.″3 or 32 AU from the star. We interpret these knots as a ring of planetesimals whose collisions may produce most of the dust observed in the disk. We find no evidence for a bowmore » in the disk, but we identify a pair of symmetric, hooklike features in both wings. Based on similar features in the Beta Pictoris disk, we propose that this wing-tilt asymmetry traces either an outer planetesimal belt that is inclined with respect to the disk midplane or radiation-pressure-driven dust blown out from a yet unseen inner belt that is inclined with respect to the disk midplane. The misaligned inner or outer disk may be a result of interaction with a yet unseen planet. Overall, the disk geometry resembles the nearby disk around Beta Pictoris, albeit seen at smaller radial scales.« less

Disk-like Chemistry of the Triangulum-Andromeda Overdensity as Seen by APOGEE

NASA Astrophysics Data System (ADS)

Hayes, Christian R.; Majewski, Steven R.; Hasselquist, Sten; Beaton, Rachael L.; Cunha, Katia; Smith, Verne V.; Price-Whelan, Adrian M.; Anguiano, Borja; Beers, Timothy C.; Carrera, Ricardo; Fernández-Trincado, J. G.; Frinchaboy, Peter M.; García-Hernández, D. A.; Lane, Richard R.; Nidever, David L.; Nitschelm, Christian; Roman-Lopes, Alexandre; Zamora, Olga

2018-05-01

The nature of the Triangulum-Andromeda (TriAnd) system has been debated since the discovery of this distant, low-latitude Milky Way (MW) overdensity more than a decade ago. Explanations for its origin are either as a halo substructure from the disruption of a dwarf galaxy, or a distant extension of the Galactic disk. We test these hypotheses using the chemical abundances of a dozen TriAnd members from the Sloan Digital Sky Survey-IV’s (SDSS-IV’s) 14th Data Release (DR14) of Apache Point Observatory Galactic Evolution Experiment (APOGEE) data to compare to APOGEE abundances of stars with similar metallicity from both the Sagittarius (Sgr) dSph and the outer MW disk. We find that TriAnd stars are chemically distinct from Sgr across a variety of elements, (C+N), Mg, K, Ca, Mn, and Ni, with a separation in [X/Fe] of about 0.1 to 0.4 dex depending on the element. Instead, the TriAnd stars, with a median metallicity of about ‑0.8, exhibit chemical abundance ratios similar to those of the lowest metallicity ([Fe/H] ∼ ‑0.7) stars in the outer Galactic disk, and are consistent with expectations of extrapolated chemical gradients in the outer disk of the MW. These results suggest that TriAnd is associated with the MW disk, and, therefore, that the disk extends to this overdensity—i.e., past a Galactocentric radius of 24 kpc—albeit vertically perturbed about 7 kpc below the nominal disk midplane in this region of the Galaxy.

New Constraints on Turbulence and Embedded Planet Mass in the HD 163296 Disk from Planet–Disk Hydrodynamic Simulations

NASA Astrophysics Data System (ADS)

Liu, Shang-Fei; Jin, Sheng; Li, Shengtai; Isella, Andrea; Li, Hui

2018-04-01

Recent Atacama Large Millimeter and Submillimeter Array (ALMA) observations of the protoplanetary disk around the Herbig Ae star HD 163296 revealed three depleted dust gaps at 60, 100, and 160 au in the 1.3 mm continuum as well as CO depletion in the middle and outer dust gaps. However, no CO depletion was found in the inner dust gap. To examine the planet–disk interaction model, we present results of 2D two fluid (gas + dust) hydrodynamic simulations coupled with 3D radiative transfer simulations. To fit the high gas-to-dust ratio of the first gap, we find that the Shakura–Sunyaev viscosity parameter α must be very small (≲ {10}-4) in the inner disk. On the other hand, a relatively large α (∼ 7.5× {10}-3) is required to reproduce the dust surface density in the outer disk. We interpret the variation of α as an indicator of the transition from an inner dead zone to the outer magnetorotational instability (MRI) active zone. Within ∼100 au, the HD 163296 disk’s ionization level is low, and non-ideal magnetohydrodynamic effects could suppress the MRI, so the disk can be largely laminar. The disk’s ionization level gradually increases toward larger radii, and the outermost disk (r> 300 au) becomes turbulent due to MRI. Under this condition, we find that the observed dust continuum and CO gas line emissions can be reasonably fit by three half-Jovian-mass planets (0.46, 0.46, and 0.58 {M}{{J}}) at 59, 105, and 160 au, respectively.

STAR CLUSTER POPULATIONS IN THE OUTER DISKS OF NEARBY GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Herbert-Fort, Stephane; Zaritsky, Dennis; Moustakas, John

We present a Large Binocular Telescope imaging study that characterizes the star cluster component of nearby galaxy outer disks (beyond the optical radius R{sub 25}). Expanding on the pilot project of Herbert-Fort et al., we present deep ({approx}27.5 mag V-band point-source limiting magnitude) U- and V-band imaging of six galaxies: IC 4182, NGC 3351, NGC 4736, NGC 4826, NGC 5474, and NGC 6503. We find that the outer disk of each galaxy is populated with marginally resolved star clusters with masses {approx}10{sup 3} M{sub Sun} and ages up to {approx}1 Gyr (masses and ages are limited by the depth ofmore » our imaging and uncertainties are large given how photometry can be strongly affected by the presence or absence of a few stars in such low-mass systems), and that they are typically found out to at least 2 R{sub 25} but sometimes as far as 3-4 R{sub 25}-even beyond the apparent H I disk. The mean rate of cluster formation for 1 R{sub 25} {<=} R {<=} 1.5 R{sub 25} is at least one every {approx}2.5 Myr and the clusters are spatially correlated with the H I, most strongly with higher density gas near the periphery of the optical disk and with lower density neutral gas at the H I disk periphery. We hypothesize that the clusters near the edge of the optical disk are formed in the extension of spiral structure from the inner disk and are a fairly consistent phenomenon and that the clusters formed at the periphery of the H I disk are the result of accretion episodes.« less

Chemistry of the Triangulum-Andromeda Overdensity as Seen by APOGEE

NASA Astrophysics Data System (ADS)

Rochford Hayes, Christian; Majewski, Steven R.; Hasselquist, Sten; Beaton, Rachael; Cunha, Katia M. L.; Smith, Verne V.; Price-Whelan, Adrian M.; APOGEE Team

2018-06-01

The nature of the Triangulum-Andromeda (TriAnd) system has been debated since the discovery of this distant, low-latitude Milky Way (MW) overdensity more than a decade ago. Explanations for its origin are either as a halo substructure from the disruption of a dwarf galaxy or a distant extension of the Galactic disk. We test these hypotheses using chemical abundances of a dozen TriAnd members from the Sloan Digital Sky Survey’s 14th Data Release of Apache Point Observatory Galactic Evolution Experiment (APOGEE) data to compare to APOGEE abundances of stars with similar metallicity from both the Sagittarius (Sgr) dSph, and the outer MW disk. We find that TriAnd stars are chemically distinct from Sgr across a variety of elements, (C+N), Mg, K, Ca, Mn, and Ni, with a separation in [X/Fe] of about 0.1 to 0.4 dex depending on the element. Instead, the TriAnd stars, with a median metallicity of about -0.8, exhibit chemical abundance ratios similar to those of the lowest metallicity ([Fe/H] ~ -0.7) stars in the outer Galactic disk, and are consistent with expectations of extrapolated chemical gradients in the outer disk of the MW. These results suggest that TriAnd is associated with the MW disk, and, therefore, that the disk extends to this overdensity - i.e., past a Galactocentric radius of 24 kpc - albeit vertically perturbed about 7 kpc below the nominal disk midplane in this region of the Galaxy.

Increased H2CO production in the outer disk around HD 163296

NASA Astrophysics Data System (ADS)

Carney, M. T.; Hogerheijde, M. R.; Loomis, R. A.; Salinas, V. N.; Öberg, K. I.; Qi, C.; Wilner, D. J.

2017-09-01

Context. The gas and dust in circumstellar disks provide the raw materials to form planets. The study of organic molecules and their building blocks in such disks offers insight into the origin of the prebiotic environment of terrestrial planets. Aims: We aim to determine the distribution of formaldehyde, H2CO, in the disk around HD 163296 to assess the contribution of gas- and solid-phase formation routes of this simple organic. Methods: Three formaldehyde lines were observed (H2CO 303-202, H2CO 322-221, and H2CO 321-220) in the protoplanetary disk around the Herbig Ae star HD 163296 with ALMA at 0.5″ (60 AU) spatial resolution. Different parameterizations of the H2CO abundance were compared to the observed visibilities, using either a characteristic temperature, a characteristic radius or a radial power law index to describe the H2CO chemistry. Similar models were applied to ALMA Science Verification data of C18O. In each scenario, χ2 minimization on the visibilities was used to determine the best-fit model in each scenario. Results: H2CO 303-202 was readily detected via imaging, while the weaker H2CO 322-221 and H2CO 321-220 lines required matched filter analysis to detect. H2CO is present throughout most of the gaseous disk, extending out to 550 AU. An apparent 50 AU inner radius of the H2CO emission is likely caused by an optically thick dust continuum. The H2CO radial intensity profile shows a peak at 100 AU and a secondary bump at 300 AU, suggesting increased production in the outer disk. In all modeling scenarios, fits to the H2CO data show an increased abundance in the outer disk. The overall best-fit H2CO model shows a factor of two enhancement beyond a radius of 270 ± 20 AU, with an inner abundance (relative to H2) of 2 - 5 × 10-12. The H2CO emitting region has a lower limit on the kinetic temperature of T> 20 K. The C18O modeling suggests an order of magnitude depletion of C18O in the outer disk and an abundance of 4 - 12 × 10-8 in the inner disk. Conclusions: There is a desorption front seen in the H2CO emission that roughly coincides with the outer edge of the 1.3 millimeter continuum. The increase in H2CO outer disk emission could be a result of hydrogenation of CO ices on dust grains that are then sublimated via thermal desorption or UV photodesorption. Alternatively, there could be more efficient gas-phase production of H2CO beyond 300 AU if CO is photodisocciated in this region. The reduced datacube is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/605/A21

An optical study of stars and dust in the Andromeda galaxy

NASA Technical Reports Server (NTRS)

Walterbos, R. A. M.; Kennicutt, R. C., Jr.

1988-01-01

The distribution of light in M 31 is characterized on the basis of the UBVR surface photometry reported by Walterbos and Kennicutt (1987). The results of the data analysis are presented in extensive graphs, maps, and tables and discussed in detail, considering the outer disk regions, the decomposition into bulge and disk, the global disk and bulge colors, and dust and gas in two spiral arms. Principal findings examined include: (1) position-angle changes at radial distances beyond about 18 kpc (consistent with SW disk warping); (2) a bulge profile well described by an r exp 1/4 power law; (3) a bulge contribution to total light of about 40 percent; (4) increasing blueness in the outer disk (color gradient 0.02 mag/kpc in B-R); (5) an extinction law similar to that for the Galaxy; and (6) a significant correlation between dust and H I distributions.

Heat transfer in a rotating cavity with a stationary stepped casing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mirzaee, I.; Quinn, P.; Wilson, M.

1999-04-01

In the system considered here, corotating turbine disks are cooled by air supplied at the periphery of the system. The system comprises two corotating disks, connected by a rotating cylindrical hub and shrouded by a stepped, stationary cylindrical outer casing. Cooling air enters the system through holes in the periphery of one disk, and leaves through the clearances between the outer casing and the disks. The paper describes a combined computational and experimental study of the heat transfer in the above-described system. In the experiments, one rotating disk is heated, the hub and outer casing are insulated, and the othermore » disk is quasi-adiabatic. Thermocouples and fluxmeters attached to the heated disc enable the Nusselt numbers, Nu, to be determined for a wide range of rotational speeds and coolant flow rates. Computations are carried out using an axisymmetric elliptic solver incorporating the Launder-Sharma low-Reynolds-number {kappa}-{epsilon} turbulence model. The flow structure is shown to be complex and depends strongly on the so-called turbulent flow parameter, {lambda}{sub T}, which incorporates both rotational speed and flow rate. For a given value of {lambda}{sub T}, the computations show that Nu increases as Re{sub {phi}}, the rotational Reynolds number, increases. Despite the complexity of the flow, the agreement between the computed and measured Nusselt numbers is reasonably good.« less

Tracing Interactions of a Protoplanet with its Circumstellar Disk

NASA Astrophysics Data System (ADS)

Stapelfeldt, Karl

2017-08-01

A candidate companion to a very young star has been discovered in HST snapshot optical images. The object is projected at the outer radius of an edge-on protoplanetary disk and is aligned with the disk plane. Keck LGS photometry results indicate the object has the same temperature as brown dwarf GQ Lupi b but with 10x less luminosity - consistent with a planetary mass companion. Because the edge-on disk suppresses the light of the central star, the companion is uniquely accessible to follow-up studies with minimal starlight residuals. We propose HST/WFC3 imaging and spectroscopy of the system to 1) fully define the morphology of the disk scattered light, particularly at the disk outer edge near the companion; 2) search for Halpha emission from the companion as evidence that it is actively accreting; and 3) complete spectral characterization of the companion using G141 spectroscopy. Confirmation of a substellar spectrum, accretion, and disk interaction action would establish this object as a leading example of an accreting protoplanet at 100 AU and offer support to models for planet formation by gravitational instability.

The correlation between HCN/H2O flux ratios and disk mass: evidence for protoplanet formation

NASA Astrophysics Data System (ADS)

Rose, Caitlin; Salyk, Colette

2017-01-01

We analyze hydrogen cyanide (HCN) and water vapor flux ratios in protoplanetary disks as a way to trace planet formation. Analyzing only disks in the Taurus molecular cloud, Najita et al. (2013) found a tentative correlation between protoplanetary disk mass and the HCN/H2O line flux ratio in Spitzer-IRS emission spectra. They interpret this correlation to be a consequence of more massive disks forming planetesimals more efficiently than smaller disks, as the formation of large planetesimals may lock up water ice in the cool outer disk region and prevent it from migrating, drying out the inner disk. The sequestering of water (and therefore oxygen) in the outer disk may also increase the carbon-to- oxygen ratio in the inner disk, leading to enhanced organic molecule (e.g. HCN) emission. To confirm this trend, we expand the Najita et al. sample by calculating HCN/H2O line flux ratios for 8 more sources with known disk masses from clusters besides Taurus. We find agreement with the Najita et al. trend, suggesting that this is a widespread phenomenon. In addition, we find HCN/H2O line flux ratios for 17 more sources that await disk mass measurements, which should become commonplace in the ALMA era. Finally, we investigate linear fits and outliers to this trend, and discuss possible causes.

Physics and chemistry of the solar nebula.

PubMed

Lunine, J I

1997-06-01

The solar system is thought to have begun in a flattened disk of gas and dust referred to traditionally as the solar nebula. Such a construct seems to be a natural product of the collapse of dense parts of giant molecular clouds, the vast star-forming regions that pepper the Milky Way and other galaxies. Gravitational, magnetic and thermal forces within the solar nebula forced a gradual evolution of mass toward the center (where the sun formed) and angular momentum (borne by a small fraction of the mass) toward the outer more distant regions of the disk. This evolution was accompanied by heating and a strong temperature contrast from the hot, inner regions to the cold, more remote parts of the disk. The resulting chemistry in the disk determined the initial distribution of organic matter in the planets; most of the reduced carbon species, in condensed form, were located beyond the asteroid belt (the 'outer' solar system). The Earth could have received much of its inventory of pre-biological material from comets and other icy fragments of the process of planetary formation in the outer solar system.

Outer-disk reddening and gas-phase metallicities: The CALIFA connection

NASA Astrophysics Data System (ADS)

Marino, R. A.; Gil de Paz, A.; Sánchez, S. F.; Sánchez-Blázquez, P.; Cardiel, N.; Castillo-Morales, A.; Pascual, S.; Vílchez, J.; Kehrig, C.; Mollá, M.; Mendez-Abreu, J.; Catalán-Torrecilla, C.; Florido, E.; Perez, I.; Ruiz-Lara, T.; Ellis, S.; López-Sánchez, A. R.; González Delgado, R. M.; de Lorenzo-Cáceres, A.; García-Benito, R.; Galbany, L.; Zibetti, S.; Cortijo, C.; Kalinova, V.; Mast, D.; Iglesias-Páramo, J.; Papaderos, P.; Walcher, C. J.; Bland-Hawthorn, J.

2016-01-01

We study, for the first time in a statistically significant and well-defined sample, the relation between the outer-disk ionized-gas metallicity gradients and the presence of breaks in the surface brightness profiles of disk galaxies. Sloan Digital Sky Survey (SDSS) g'- and r'-band surface brightness, (g' - r') color, and ionized-gasoxygen abundance profiles for 324 galaxies within the Calar Alto Legacy Integral Field Area (CALIFA) survey are used for this purpose. We perform a detailed light-profile classification, finding that 84% of our disks show down- or up-bending profiles (Type II and Type III, respectively), while the remaining 16% are well fitted by one single exponential (Type I). The analysis of the color gradients at both sides of this break shows a U-shaped profile for most Type II galaxies with an average minimum (g' - r') color of ~0.5 mag and an ionized-gas metallicity flattening associated with it only in the case of low-mass galaxies. Comparatively, more massive systems show a rather uniform negative metallicity gradient. The correlation between metallicity flattening and stellar mass for these systems results in p-values as low as 0.01. Independent of the mechanism having shaped the outer light profiles of these galaxies, stellar migration or a previous episode of star formation in a shrinking star-forming disk, it is clear that the imprint in their ionized-gas metallicity was different for low- and high-mass Type II galaxies. In the case of Type III disks, a positive correlation between the change in color and abundance gradient is found (the null hypothesis is ruled out with a p-value of 0.02), with the outer disks of Type III galaxies with masses ≤1010 M⊙ showing a weak color reddening or even a bluing. This is interpreted as primarily due to a mass downsizing effect on the population of Type III galaxies that recently experienced an enhanced inside-out growth.

Long-lived Eccentric modes in Protoplanetary Disks

NASA Astrophysics Data System (ADS)

Lee, Wing-Kit; Dempsey, Adam M.; Lithwick, Yoram

2018-04-01

A theory is developed to understand global eccentric modes that are slowly precessing in protoplanetary disks. Using the typical self-similar density profiles, we found that these modes are trapped in the disk and are not sensitive to the uncertain boundary condition at the disk edge. This is contrary to common wisdom that the modes can only exist in disks with very sharp outer edge. Because of their discrete spectrum, once excited, a perturbed disk can stay eccentric for a long time until the mode is viscously damped. The physics behind the mode trapping depends ultimately on the relative importance of gas pressure and self-gravity, which is characterized by g = 1/ (Q h), where h is the disk aspect ratio and Q is the Toomre stability parameter. A very low mass disk (g ≪ 1) is pressure-dominated and supports pressure modes, in which the eccentricity is highest at the disk edge. The modes are trapped by a turning point due to the density drop in the outer disk. For a more massive disk with g of order of unity (Q~1/h~10-100), prograde modes are supported. Unlike the pressure modes, these modes are trapped by Q-barriers and result in a bump in the radial eccentricity profile. As the mode trapping is a generic phenomenon for typical disk profiles, the free linear eccentric modes are likely to be present in protoplanetary disks with a wide range of disk mass.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kraus, Stefan; Espaillat, Catherine; Wilner, David J.

Pre-transitional disks are protoplanetary disks with a gapped disk structure, potentially indicating the presence of young planets in these systems. In order to explore the structure of these objects and their gap-opening mechanism, we observed the pre-transitional disk V1247 Orionis using the Very Large Telescope Interferometer, the Keck Interferometer, Keck-II, Gemini South, and IRTF. This allows us to spatially resolve the AU-scale disk structure from near- to mid-infrared wavelengths (1.5-13 {mu}m), tracing material at different temperatures and over a wide range of stellocentric radii. Our observations reveal a narrow, optically thick inner-disk component (located at 0.18 AU from the star)more » that is separated from the optically thick outer disk (radii {approx}> 46 AU), providing unambiguous evidence for the existence of a gap in this pre-transitional disk. Surprisingly, we find that the gap region is filled with significant amounts of optically thin material with a carbon-dominated dust mineralogy. The presence of this optically thin gap material cannot be deduced solely from the spectral energy distribution, yet it is the dominant contributor at mid-infrared wavelengths. Furthermore, using Keck/NIRC2 aperture masking observations in the H, K', and L' bands, we detect asymmetries in the brightness distribution on scales of {approx}15-40 AU, i.e., within the gap region. The detected asymmetries are highly significant, yet their amplitude and direction changes with wavelength, which is not consistent with a companion interpretation but indicates an inhomogeneous distribution of the gap material. We interpret this as strong evidence for the presence of complex density structures, possibly reflecting the dynamical interaction of the disk material with sub-stellar mass bodies that are responsible for the gap clearing.« less

Flow visualization in radial flow through stationary and corotating parallel disks

NASA Astrophysics Data System (ADS)

Mochizuki, S.; Tanaka, M.; Yang, Wen-Jei

Paraffin mist is used here as a tracer to observe the patterns in the radial flow through both stationary and corotating parallel disks. The periodic and alternative generation of separation bubbles on both disks and the resulting flow fluctuation and turbulent flow in the radial channel are studied. Stall cells are visualized around the outer rim of the corotating disks.

Molecular basis for photoreceptor outer segment architecture

PubMed Central

Goldberg, Andrew F. X.; Moritz, Orson L.; Williams, David S.

2016-01-01

To serve vision, vertebrate rod and cone photoreceptors must detect photons, convert the light stimuli into cellular signals, and then convey the encoded information to downstream neurons. Rods and cones are sensory neurons that each rely on specialized ciliary organelles to detect light. These organelles, called outer segments, possess elaborate architectures that include many hundreds of light-sensitive membranous disks arrayed one atop another in precise register. These stacked disks capture light and initiate the chain of molecular and cellular events that underlie normal vision. Outer segment organization is challenged by an inherently dynamic nature; these organelles are subject to a renewal process that replaces a significant fraction of their disks (up to ~10%) on a daily basis. In addition, a broad range of environmental and genetic insults can disrupt outer segment morphology to impair photoreceptor function and viability. In this chapter, we survey the major progress that has been made for understanding the molecular basis of outer segment architecture. We also discuss key aspects of organelle lipid and protein composition, and highlight distributions, interactions, and potential structural functions of key OS-resident molecules, including: kinesin-2, actin, RP1, prominin-1, protocadherin 21, peripherin-2/rds, rom-1, glutamic acid-rich proteins, and rhodopsin. Finally, we identify key knowledge gaps and challenges that remain for understanding how normal outer segment architecture is established and maintained. PMID:27260426

Imaging Transitional Disks with TMT: Lessons Learned from the SEEDS Survey

NASA Technical Reports Server (NTRS)

Grady, Carol A.; Fukagawa, M.; Muto, T.; Hashimoto, J.

2014-01-01

TMT studies of the early phases of giant planet formation will build on studies carried out in this decade using 8-meter class telescopes. One such study is the Strategic Exploration of Exoplanets and Disks with Subaru transitional disk survey. We have found a wealth of indirect signatures of giant planet presence, including spiral arms, pericenter offsets of the outer disk from the star, and changes in disk color at the inner edge of the outer disk in intermediate-mass PMS star disks. T Tauri star transitional disks are less flamboyant, but are also dynamically colder: any spiral arms in these diskswill be more tightly wound. Imaging such features at the distance of the nearest star-forming regions requires higher angular resolution than achieved with HiCIAO+ AO188. Imaging such disks with extreme AO systems requires use of laser guide stars, and are infeasible with the extreme AO systems currently commissioning on 8-meter class telescopes. Similarly, the JWST and AFTAWFIRST coronagraphs being considered have inner working angles 0.2, and will occult the inner 28 atomic units of systems at d140pc, a region where both high-contrast imagery and ALMA data indicate that giant planets are located in transitional disks. However, studies of transitional disks associated with solar-mass stars and their planet complement are feasible with TMT using NFIRAOS.

Characterization of the Inner Disk around HD 141569 A from Keck/NIRC2 L-Band Vortex Coronagraphy

NASA Astrophysics Data System (ADS)

Mawet, Dimitri; Choquet, Élodie; Absil, Olivier; Huby, Elsa; Bottom, Michael; Serabyn, Eugene; Femenia, Bruno; Lebreton, Jérémy; Matthews, Keith; Gomez Gonzalez, Carlos A.; Wertz, Olivier; Carlomagno, Brunella; Christiaens, Valentin; Defrère, Denis; Delacroix, Christian; Forsberg, Pontus; Habraken, Serge; Jolivet, Aissa; Karlsson, Mikael; Milli, Julien; Pinte, Christophe; Piron, Pierre; Reggiani, Maddalena; Surdej, Jean; Vargas Catalan, Ernesto

2017-01-01

HD 141569 A is a pre-main sequence B9.5 Ve star surrounded by a prominent and complex circumstellar disk, likely still in a transition stage from protoplanetary to debris disk phase. Here, we present a new image of the third inner disk component of HD 141569 A made in the L‧ band (3.8 μm) during the commissioning of the vector vortex coronagraph that has recently been installed in the near-infrared imager and spectrograph NIRC2 behind the W.M. Keck Observatory Keck II adaptive optics system. We used reference point-spread function subtraction, which reveals the innermost disk component from the inner working distance of ≃23 au and up to ≃70 au. The spatial scale of our detection roughly corresponds to the optical and near-infrared scattered light, thermal Q, N, and 8.6 μm PAH emission reported earlier. We also see an outward progression in dust location from the L‧ band to the H band (Very Large Telescope/SPHERE image) to the visible (Hubble Space Telescope (HST)/STIS image), which is likely indicative of dust blowout. The warm disk component is nested deep inside the two outer belts imaged by HST-NICMOS in 1999 (at 406 and 245 au, respectively). We fit our new L‧-band image and spectral energy distribution of HD 141569 A with the radiative transfer code MCFOST. Our best-fit models favor pure olivine grains and are consistent with the composition of the outer belts. While our image shows a putative very faint point-like clump or source embedded in the inner disk, we did not detect any true companion within the gap between the inner disk and the first outer ring, at a sensitivity of a few Jupiter masses.

Tomographic Sounding of Protoplanetary and Transitional Disks: Using Inner Disk Variability at Near to Mid-IR Wavelengths to Probe Conditions in the Outer Disk

NASA Technical Reports Server (NTRS)

Grady, C. A.; Sitko, M.L.

2013-01-01

Spitzer synoptic monitoring of young stellar associations has demonstrated that variability among young stars and their disks is ubiquitous. The Spitzer studies have been limited by target visibility windows and cover only a short temporal baseline in years. A complementary approach is to focus on stars chosen for high-value observations (e.g. high-contrast imaging, interferometry, or access to wavelengths which are difficult to achieve from the ground) where the synoptic data can augment the imagery or interferometry as well as probing disk structure. In this talk, we discuss how synoptic data for two protoplanetary disks, MWC 480 and HD 163296, constrain the dust disk scale height, account for variable disk illumination, and can be used to locate emission features, such as the IR bands commonly associated with PAHs in the disk, as part of our SOFIA cycle 1 study. Similar variability is now known for several pre-transitional disks, where synoptic data can be used to identify inner disks which are not coplanar with the outer disk, and which may be relicts of giant planet-giant planet scattering events. Despite the logistical difficulties in arranging supporting, coordinated observations in tandem with high-value observations, such data have allowed us to place imagery in context, constrained structures in inner disks not accessible to direct imagery, and may be a tool for identifying systems where planet scattering events have occurred.

Inferring a Gap in the Group II Disk of the Herbig Ae/Be Star HD 142666

NASA Astrophysics Data System (ADS)

Ezra Rubinstein, Adam; Macías, Enrique; Espaillat, Catherine; Calvet, Nuria; Robinson, Connor; Zhang, Ke

2018-01-01

Disks around Herbig Ae/Be (HAeBe) stars have been classified into Group I or Group II, which are thought to be flared and flat disks respectively. Most Group I disks have been shown to have large gaps, suggesting ongoing planet formation, while no large gaps have been found in Group II disks. We analyzed the Group II disk of HD 142666 using irradiated accretion disk modeling of the broad-band spectral energy distribution along with the 1.3 millimeter spatial brightness distribution traced by Atacama Large Millimeter and Submillimeter Array (ALMA) observations. Our model is able to reproduce the available data, predicting a high degree of settling in the disk, which is consistent with the Group II classification of HD 142666. Although the ALMA observations did not have enough angular resolution to fully resolve the inner parts of the disk, the observed visibilities and synthesized image can only be reproduced when including a gap between ~5 to 12 au in our disk model. In addition, we also infer that the disk has an outer radius of ~65 au, which may be evidence of radial migration of dust or an unseen, low-mass companion that is truncating the outer disk. These results may suggest that Group II disks around HAeBe stars have gaps, possibly carved by young giant planets in the disk. Further ALMA observations of HD 142666 and other Group II disks are needed to discern if gaps are common in this class of objects, as well as to reveal their possible origin.

GAPS IN PROTOPLANETARY DISKS AS SIGNATURES OF PLANETS. II. INCLINED DISKS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jang-Condell, Hannah; Turner, Neal J.

2013-07-20

We examine the observational appearance of partial gaps being opened by planets in protoplanetary disks, considering the effects of the inclination relative to the line of sight. We model the disks with static {alpha}-models with detailed radiative transfer, parameterizing the shape and size of the partially cleared gaps based on the results of hydrodynamic simulations. As in previous work, starlight falling across the gap leads to high surface brightness contrasts. The gap's trough is darkened by both shadowing and cooling, relative to the uninterrupted disk. The gap's outer wall is brightened by direct illumination and also by heating, which puffsmore » it up so that it intercepts more starlight. In this paper, we examine the effects of inclination on resolved images of disks with and without gaps at a wide range of wavelengths. The scattering surface's offset from the disk midplane creates a brightness asymmetry along the axis of inclination, making the disk's near side appear brighter than the far side in scattered light. Finite disk thickness also causes the projected distances of equidistant points on the disk surface to be smaller on the near side of the disk as compared to the far side. Consequently, the gap shoulder on the near side of the disk should appear brighter and closer to the star than on the far side. However, if the angular resolution of the observation is coarser than the width of the brightened gap shoulder, then the gap shoulder on the far side may appear brighter because of its larger apparent size. We present a formula to recover the scale height and inclination angle of an imaged disk using simple geometric arguments and measuring disk asymmetries. Resolved images of circumstellar disks have revealed clearings and gaps, such as the transitional disk in LkCa 15. Models created using our synthetic imaging attempting to match the morphology of observed scattered light images of LkCa 15 indicate that the H-band flux deficit in the inner {approx}0.''5 of the disk can be explained with a planet if mass is greater than 0.5 Jupiter mass.« less

Formation of Planetary Populations I: Metallicity & Envelope Opacity Effects

NASA Astrophysics Data System (ADS)

Alessi, Matthew; Pudritz, Ralph E.

2018-05-01

We present a comprehensive body of simulations of the formation of exoplanetary populations that incorporate the role of planet traps in slowing planetary migration. The traps we include in our model are the water ice line, the disk heat transition, and the dead zone outer edge. We reduce our model parameter set to two physical parameters: the opacity of the accreting planetary atmospheres (κenv) and a measure of the efficiency of planetary accretion after gap opening (fmax). We perform planet population synthesis calculations based on the initial observed distributions of host star and disk properties - their disk masses, lifetimes, and stellar metallicities. We find the frequency of giant planet formation scales with disk metallicity, in agreement with the observed Jovian planet frequency-metallicity relation. We consider both X-ray and cosmic ray disk ionization models, whose differing ionization rates lead to different dead zone trap locations. In both cases, Jovian planets form in our model out to 2-3 AU, with a distribution at smaller radii dependent on the disk ionization source and the setting of envelope opacity. We find that low values of κenv (0.001-0.002 cm2 g-1) and X-ray disk ionization are necessary to obtain a separation between hot Jupiters near 0.1 AU, and warm Jupiters outside 0.6 AU, a feature present in the data. Our model also produces a large number of super Earths, but the majority are outside of 2 AU. As our model assumes a constant dust to gas ratio, we suggest that radial dust evolution must be taken into account to reproduce the observed super Earth population.

The inner-disk and stellar properties of the young stellar object WL 16

NASA Technical Reports Server (NTRS)

Carr, John S.; Tokunaga, Alan T.; Najita, Joan; Shu, Frank H.; Glassgold, Alfred E.

1993-01-01

We present kinematic evidence for a rapidly rotating circumstellar disk around the young stellar object WL 16, based on new high-velocity-resolution data of the v = 2-0 CO bandhead emission. A Keplerian disk provides an excellent fit to the observed profile and requires a projected velocity for the CO-emitting region of roughly 250 km/s at the inner radius and 140 km/s at the outer radius, giving a ratio of the inner to the outer radius of about 0.3. We show that satisfying the constraints imposed by the gas kinematics, the observed CO flux, and the total source luminosity requires the mass of WL 16 to lie between 1.4 and 2.5 solar mass. The inner disk radius for the CO emission must be less than 8 solar radii.

Planet-Planet Scattering in Planetesimal Disks. II. Predictions for Outer Extrasolar Planetary Systems

NASA Astrophysics Data System (ADS)

Raymond, Sean N.; Armitage, Philip J.; Gorelick, Noel

2010-03-01

We develop an idealized dynamical model to predict the typical properties of outer extrasolar planetary systems, at radii comparable to the Jupiter-to-Neptune region of the solar system. The model is based upon the hypothesis that dynamical evolution in outer planetary systems is controlled by a combination of planet-planet scattering and planetary interactions with an exterior disk of small bodies ("planetesimals"). Our results are based on 5000 long duration N-body simulations that follow the evolution of three planets from a few to 10 AU, together with a planetesimal disk containing 50 M ⊕ from 10 to 20 AU. For large planet masses (M >~ M Sat), the model recovers the observed eccentricity distribution of extrasolar planets. For lower-mass planets, the range of outcomes in models with disks is far greater than that which is seen in isolated planet-planet scattering. Common outcomes include strong scattering among massive planets, sudden jumps in eccentricity due to resonance crossings driven by divergent migration, and re-circularization of scattered low-mass planets in the outer disk. We present the distributions of the eccentricity and inclination that result, and discuss how they vary with planet mass and initial system architecture. In agreement with other studies, we find that the currently observed eccentricity distribution (derived primarily from planets at a <~ 3 AU) is consistent with isolated planet-planet scattering. We explain the observed mass dependence—which is in the opposite sense from that predicted by the simplest scattering models—as a consequence of strong correlations between planet masses in the same system. At somewhat larger radii, initial planetary mass correlations and disk effects can yield similar modest changes to the eccentricity distribution. Nonetheless, strong damping of eccentricity for low-mass planets at large radii appears to be a secure signature of the dynamical influence of disks. Radial velocity measurements capable of detecting planets with K ≈ 5 m s-1 and periods in excess of 10 years will provide constraints on this regime. Finally, we present an analysis of the predicted separation of planets in two-planet systems, and of the population of planets in mean-motion resonances (MMRs). We show that, if there are systems with ~ Jupiter-mass planets that avoid close encounters, the planetesimal disk acts as a damping mechanism and populates MMRs at a very high rate (50%-80%). In many cases, resonant chains (in particular the 4:2:1 Laplace resonance) are set up among all three planets. We expect such resonant chains to be common among massive planets in outer planetary systems.

Modulated mass-transfer model for superhumps in SU Ursae Majoris stars

NASA Technical Reports Server (NTRS)

Mineshige, Shin

1988-01-01

The response of a circular accretion disk to rapid modulation of the mass-transfer rate into the disk is explored in order to model superhumps in SU UMa stars. It is proposed that periodically enhanced flow may disrupt or heat up the outer disk and produce the dips noted just before the superhump peaks. The elliptical accretion-disk model with extended vertical disk structure can account for the observed characteristics of superhumps in these stars.

The protoplanetary system HD 100546 in Hα polarized light from SPHERE/ZIMPOL. A bar-like structure across the disk gap?

NASA Astrophysics Data System (ADS)

Mendigutía, I.; Oudmaijer, R. D.; Garufi, A.; Lumsden, S. L.; Huélamo, N.; Cheetham, A.; de Wit, W. J.; Norris, B.; Olguin, F. A.; Tuthill, P.

2017-12-01

Context. HD 100546 is one of the few known pre-main-sequence stars that may host a planetary system in its disk. Aims: This work aims to contribute to our understanding of HD 100546 by analyzing new polarimetric images with high spatial resolution. Methods: Using VLT/SPHERE/ZIMPOL with two filters in Hα and the adjacent continuum, we have probed the disk gap and the surface layers of the outer disk, covering a region <500 mas (<55 au at 109 pc) from the central star, at an angular resolution of 20 mas. Results: Our data show an asymmetry: the SE and NW regions of the outer disk are more polarized than the SW and NE regions. This asymmetry can be explained from a preferential scattering angle close to 90° and is consistent with previous polarization images. The outer disk in our observations extends from 13 ± 2 to 45 ± 9 au, with a position angle and inclination of 137 ± 5° and 44 ± 8°, respectively. The comparison with previous estimates suggests that the disk inclination could increase with the stellocentric distance, although the different measurements are still consistent within the error bars. In addition, no direct signature of the innermost candidate companion is detected from the polarimetric data, confirming recent results that were based on intensity imagery. We set an upper limit to its mass accretion rate <10-8 M⊙ yr-1 for a substellar mass of 15 MJup. Finally, we report the first detection (>3σ) of a 20 au bar-like structure that crosses the gap through the central region of HD 100546. Conclusions: In the absence of additional data, it is tentatively suggested that the bar could be dust dragged by infalling gas that radially flows from the outer disk to the inner region. This could represent an exceptional case in which a small-scale radial inflow is observed in a single system. If this scenario is confirmed, it could explain the presence of atomic gas in the inner disk that would otherwise accrete on to the central star on a timescale of a few months/years, as previously indicated from spectro-interferometric data, and could be related with additional (undetected) planets.

Planetesimal and Protoplanet Dynamics in a Turbulent Protoplanetary Disk

NASA Astrophysics Data System (ADS)

Yang, Chao-Chin; Mac Low, M.; Menou, K.

2010-01-01

In core accretion scenario of planet formation, kilometer-sized planetesimals are the building blocks toward planetary cores. Their dynamics, however, are strongly influenced by their natal protoplanetary gas disks. It is generally believed that these disks are turbulent, most likely due to magnetorotational instability. The resulting density perturbations in the gas render the movement of the particles a random process. Depending on its strength, this process might cause several interesting consequences in the course of planet formation, specifically the survivability of objects under rapid inward type-I migration and/or collisional destruction. Using the local-shearing-box approximation, we conduct numerical simulations of planetesimals moving in a turbulent, magnetized gas disk, either unstratified or vertically stratified. We produce a fiducial disk model with turbulent accretion of Shakura-Sunyaev alpha about 10-2 and root-mean-square density perturbation of about 10% and statistically characterize the evolution of the orbital properties of the particles moving in the disk. These measurements result in accurate calibration of the random process of particle orbital change, indicating noticeably smaller magnitudes than predicted by global simulations, although the results may depend on the size of the shearing box. We apply these results to revisit the survivability of planetesimals under collisional destruction or protoplanets under type-I migration. Planetesimals are probably secure from collisional destruction, except for kilometer-sized objects situated in the outer regions of a young protoplanetary disk. On the other hand, we confirm earlier studies of local models in that type-I migration probably dominates diffusive migration due to stochastic torques for most planetary cores and terrestrial planets. Discrepancies in the derived magnitude of turbulence between local and global simulations of magnetorotationally unstable disks remains an open issue, with important consequences for planet formation scenarios.

Assessment of disk MHD generators for a base load powerplant

NASA Technical Reports Server (NTRS)

Chubb, D. L.; Retallick, F. D.; Lu, C. L.; Stella, M.; Teare, J. D.; Loubsky, W. J.; Louis, J. F.; Misra, B.

1981-01-01

Results from a study of the disk MHD generator are presented. Both open and closed cycle disk systems were investigated. Costing of the open cycle disk components (nozzle, channel, diffuser, radiant boiler, magnet and power management) was done. However, no detailed costing was done for the closed cycle systems. Preliminary plant design for the open cycle systems was also completed. Based on the system study results, an economic assessment of the open cycle systems is presented. Costs of the open cycle disk conponents are less than comparable linear generator components. Also, costs of electricity for the open cycle disk systems are competitive with comparable linear systems. Advantages of the disk design simplicity are considered. Improvements in the channel availability or a reduction in the channel lifetime requirement are possible as a result of the disk design.

Studies of extra-solar Oort Clouds and the Kuiper Disk

NASA Technical Reports Server (NTRS)

Stern, S. Alan

1994-01-01

The March 1994 Semi-Annual report for Studies of Extra-Solar Oort Clouds and the Kuiper Disk is presented. We are conducting research designed to enhance our understanding of the evolution and detectability of comet clouds and disks. This area holds promise for also improving our understanding of outer solar system formation, the bombardment history of the planets, the transport of volatiles and organics from the outer solar system to the inner planets, and to the ultimate fate of comet clouds around the Sun and other stars. According to 'standard' theory, both the Kuiper Disk and Oort Cloud are (at least in part) natural products of the planetary accumulation stage of solar system formation. One expects such assemblages to be a common attribute of other solar systems. Therefore, searches for comet disks and clouds orbiting other stars offer a new method for inferring the presence of planetary systems. Our three-year effort consists of two major efforts: observational work to predict and search for the signatures of Oort Clouds and comet disks around other stars; and modeling studies of the formation and evolution of the Kuiper Disk (KD) and similar assemblages that may reside around other stars, including beta Pic.

Weak Turbulence in Protoplanetary Disks as Revealed by ALMA

NASA Astrophysics Data System (ADS)

Flaherty, Kevin; Hughes, A. Meredith; Simon, Jacob; Andrews, Sean; Bai, Xue-Ning; Wilner, David

2018-01-01

Gas kinematics are an important part of planet formation, influencing processes ranging from the growth of sub-micron grains to the migration of gas giant planets. Dynamical behavior can be traced with both synoptic observations of the mid-infrared excess, sensitive to the inner disk, and spatially resolved radio observations of gas emission, sensitive to the outer disk. I report on our ongoing efforts to constrain turbulence using ALMA observations of CO emission from protoplanetary disks. Building on our upper limit around HD 163296 (<0.05cs), we find evidence for weak turbulence around TW Hya (<0.08cs) indicating that weak non-thermal motion is not unique to HD 163296. I will also discuss observations of CO/13CO/C18O from around V4046 Sgr, DM Tau, and MWC 480 that will help to further expand the turbulence sample, as well as inform our understanding of CO photo-chemistry in the outer edges of these disks.

TRANSITIONAL DISKS AND THEIR ORIGINS: AN INFRARED SPECTROSCOPIC SURVEY OF ORION A

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, K. H.; Watson, Dan M.; Manoj, P.

Transitional disks are protoplanetary disks around young stars, with inner holes or gaps which are surrounded by optically thick outer, and often inner, disks. Here we present observations of 62 new transitional disks in the Orion A star-forming region. These were identified using the Spitzer Space Telescope's Infrared Spectrograph and followed up with determinations of stellar and accretion parameters using the Infrared Telescope Facility's SpeX. We combine these new observations with our previous results on transitional disks in Taurus, Chamaeleon I, Ophiuchus, and Perseus, and with archival X-ray observations. This produces a sample of 105 transitional disks of ''cluster'' agemore » 3 Myr or less, by far the largest hitherto assembled. We use this sample to search for trends between the radial structure in the disks and many other system properties, in order to place constraints on the possible origins of transitional disks. We see a clear progression of host-star accretion rate and the different disk morphologies. We confirm that transitional disks with complete central clearings have median accretion rates an order of magnitude smaller than radially continuous disks of the same population. Pre-transitional disks-those objects with gaps that separate inner and outer disks-have median accretion rates intermediate between the two. Our results from the search for statistically significant trends, especially related to M-dot , strongly support that in both cases the gaps are far more likely to be due to the gravitational influence of Jovian planets or brown dwarfs orbiting within the gaps, than to any of the photoevaporative, turbulent, or grain-growth processes that can lead to disk dissipation. We also find that the fraction of Class II YSOs which are transitional disks is large, 0.1-0.2, especially in the youngest associations.« less

[Sulfhydryl group distribution along the axis of the rod outer segment in the frog].

PubMed

Derevianchenko, T G; Fedorovich, I B; Ostrovskiĭ, M A

1985-10-01

The existence of SH-group concentration axial gradient in frog's retinal rod outer segments has been shown. A diminution of SH-groups in the outer segment apical part points to a damage of the vision pigment during the life span of the rod disks.

Investigating dust trapping in transition disks with millimeter-wave polarization

NASA Astrophysics Data System (ADS)

Pohl, A.; Kataoka, A.; Pinilla, P.; Dullemond, C. P.; Henning, Th.; Birnstiel, T.

2016-08-01

Context. Spatially resolved polarized (sub-)mm emission has been observed for example in the protoplanetary disk around HL Tau. Magnetically aligned grains are commonly interpreted as the source of polarization. However, self-scattering by large dust grains with a high enough albedo is another polarization mechanism, which is becoming a compelling method independent of the spectral index to constrain the dust grain size in protoplanetary disks. Aims: We study the dust polarization at mm wavelengths in the dust trapping scenario proposed for transition disks, when a giant planet opens a gap in the disk. We investigate the characteristic polarization patterns and their dependence on disk inclination, dust size evolution, planet position, and observing wavelength. Methods: We combine two-dimensional hydrodynamical simulations of planet-disk interactions with self-consistent dust growth models. These size-dependent dust density distributions are used for follow-up three-dimensional radiative transfer calculations to predict the polarization degree at ALMA bands due to scattered thermal emission. Results: Dust self-scattering has been proven to be a viable mechanism for producing polarized mm-wave radiation. We find that the polarization pattern of a disk with a planetary gap after 1 Myr of dust evolution shows a distinctive three-ring structure. Two narrow inner rings are located at the planet gap edges. A third wider ring of polarization is situated in the outer disk beyond 100 au. For increasing observing wavelengths, all three rings change their position slightly, where the innermost and outermost rings move inward. This distance is detectable when comparing the results at ALMA bands 3, 6, and 7. Within the highest polarized intensity regions the polarization vectors are oriented in the azimuthal direction. For an inclined disk there is an interplay between polarization originating from a flux gradient and inclination-induced quadrupole polarization. For intermediate inclined transition disks, the polarization degree is as high as ~2% at λ = 3.1 mm (band 3), which is well above the detection limit of future ALMA observations.

Saturn’s Formation and Early Evolution at the Origin of Jupiter’s Massive Moons

NASA Astrophysics Data System (ADS)

Ronnet, T.; Mousis, O.; Vernazza, P.; Lunine, J. I.; Crida, A.

2018-05-01

The four massive Galilean satellites are believed to have formed within a circumplanetary disk during the last stages of Jupiter’s formation. While the existence of a circum-Jovian disk is supported by hydrodynamic simulations, no consensus exists regarding the origin and delivery mechanisms of the building blocks of the forming satellites. The opening of a gap in the circumsolar disk would have efficiently isolated Jupiter from the main sources of solid material. However, a reservoir of planetesimals should have existed at the outer edge of Jupiter’s gap, where solids were trapped and accumulated over time. Here we show that the formation of Saturn’s core within this reservoir, or its prompt inward migration, allows planetesimals to be redistributed from this reservoir toward Jupiter and the inner Solar System, thereby providing enough material to form the Galilean satellites and to populate the Main Belt with primitive asteroids. We find that the orbit of planetesimals captured within the circum-Jovian disk are circularized through friction with gas in a compact system comparable to the current radial extent of the Galilean satellites. The decisive role of Saturn in the delivery mechanism has strong implications for the occurrence of massive moons around extrasolar giant planets as they would preferentially form around planets within multiple planet systems.

Calorimetric Studies of Bovine Rod Outer Segment Disk Membranes Support a Monomeric Unit for Both Rhodopsin and Opsin

PubMed Central

Edrington, Thomas C.; Bennett, Michael; Albert, Arlene D.

2008-01-01

The photoreceptor rhodopsin is a G-protein coupled receptor that has recently been proposed to exist as a dimer or higher order oligomer, in contrast to the previously described monomer, in retinal rod outer segment disk membranes. Rhodopsin exhibits considerably greater thermal stability than opsin (the bleached form of the receptor), which is reflected in an ∼15°C difference in the thermal denaturation temperatures (Tm) of rhodopsin and opsin as measured by differential scanning calorimetry. Here we use differential scanning calorimetry to investigate the effect of partial bleaching of disk membranes on the Tm of rhodopsin and of opsin in native disk membranes, as well as in cross-linked disk membranes in which rhodopsin dimers are known to be present. The Tms of rhodopsin and opsin are expected to be perturbed if mixed oligomers are present. The Tm remained constant for rhodopsin and opsin in native disks regardless of the level of bleaching. In contrast, the Tm of cross-linked rhodopsin in disk membranes was dependent on the extent of bleaching. The energy of activation for denaturation of rhodopsin and cross-linked rhodopsin was calculated. Cross-linking rhodopsin significantly decreased the energy of activation. We conclude that in native disk membranes, rhodopsin behaves predominantly as a monomer. PMID:18586850

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hendler, Nathanial P.; Mulders, Gijs D.; Pascucci, Ilaria

The properties of disks around brown dwarfs and very low mass stars (hereafter VLMOs) provide important boundary conditions on the process of planet formation and inform us about the numbers and masses of planets than can form in this regime. We use the Herschel Space Observatory PACS spectrometer to measure the continuum and [O i] 63 μ m line emission toward 11 VLMOs with known disks in the Taurus and Chamaeleon I star-forming regions. We fit radiative transfer models to the spectral energy distributions of these sources. Additionally, we carry out a grid of radiative transfer models run in amore » regime that connects the luminosity of our sources with brighter T Tauri stars. We find that VLMO disks with sizes 1.3–78 au, smaller than typical T Tauri disks, fit well the spectral energy distributions assuming that disk geometry and dust properties are stellar mass independent. Reducing the disk size increases the disk temperature, and we show that VLMOs do not follow previously derived disk temperature–stellar luminosity relationships if the disk outer radius scales with stellar mass. Only 2 out of 11 sources are detected in [O i] despite a better sensitivity than was achieved for T Tauri stars, suggesting that VLMO disks are underluminous. Using thermochemical models, we show that smaller disks can lead to the unexpected [O i] 63 μ m nondetections in our sample. The disk outer radius is an important factor in determining the gas and dust observables. Hence, spatially resolved observations with ALMA—to establish if and how disk radii scale with stellar mass—should be pursued further.« less

Embedded Protostellar Disks Around (Sub-)Solar Stars. II. Disk Masses, Sizes, Densities, Temperatures, and the Planet Formation Perspective

NASA Astrophysics Data System (ADS)

Vorobyov, Eduard I.

2011-03-01

We present basic properties of protostellar disks in the embedded phase of star formation (EPSF), which is difficult to probe observationally using available observational facilities. We use numerical hydrodynamics simulations of cloud core collapse and focus on disks formed around stars in the 0.03-1.0 M sun mass range. Our obtained disk masses scale near-linearly with the stellar mass. The mean and median disk masses in the Class 0 and I phases (M mean d,C0 = 0.12 M sun, M mdn d,C0 = 0.09 M sun and M mean d,CI = 0.18 M sun, M mdn d,CI = 0.15 M sun, respectively) are greater than those inferred from observations by (at least) a factor of 2-3. We demonstrate that this disagreement may (in part) be caused by the optically thick inner regions of protostellar disks, which do not contribute to millimeter dust flux. We find that disk masses and surface densities start to systematically exceed that of the minimum mass solar nebular for objects with stellar mass as low as M * = 0.05-0.1 M sun. Concurrently, disk radii start to grow beyond 100 AU, making gravitational fragmentation in the disk outer regions possible. Large disk masses, surface densities, and sizes suggest that giant planets may start forming as early as in the EPSF, either by means of core accretion (inner disk regions) or direct gravitational instability (outer disk regions), thus breaking a longstanding stereotype that the planet formation process begins in the Class II phase.

High-Resolution Near-Infrared Polarimetry of a Circumstellar Disk around UX Tau A

NASA Technical Reports Server (NTRS)

Serabyn, G.; Grady, C. A.; Currie, T.

2012-01-01

We present H-band polarimetric imagery of UX Tau A taken with HiCIAO/AO188 on the Subaru Telescope. UX Tau A has been classified as a pre-transitional disk object, with a gap structure separating its inner and outer disks. Our imagery taken with the 0.15" (21 AU) radius coronagraphic mask has revealed a strongly polarized circumstellar disk surrounding UX Tau A which extends to 120 AU, at a spatial resolution of 0.1" (14 AU). It is inclined by 46 degrees plus or minus 2 degrees as the west side is nearest. Although SED modeling and sub-millimeter imagery suggested the presence of a gap in the disk, with the inner edge of the outer disk estimated to be located at 25 - 30 AU, we detect no evidence of a gap at the limit of our inner working angle (23AU) at the near-infrared wavelength. We attribute the observed strong polarization (up to 66 %) to light scattering by dust grains in the disk. However, neither polarization models of the circumstellar disk based on Rayleigh scattering nor Mie scattering approximations were consistent with the observed azimuthal profile of the polarization degrees of the disk. Instead, a geometric optics model of the disk with nonspherical grains with the radii of 30 micrometers is consistent with the observed profile. We suggest that the dust grains have experienced frequent collisional coagulations and have grown in the circumstellar disk of UX Tau A.

High-Resolution Near-Infrared Polarimetry of a Circumstellar Disk around UX Tau A

NASA Astrophysics Data System (ADS)

Tanii, Ryoko; Itoh, Yoichi; Kudo, Tomoyuki; Hioki, Tomonori; Oasa, Yumiko; Gupta, Ranjan; Sen, Asoke K.; Wisniewski, John P.; Muto, Takayuki; Grady, Carol A.; Hashimoto, Jun; Fukagawa, Misato; Mayama, Satoshi; Hornbeck, Jeremy; Sitko, Michael L.; Russell, Ray W.; Werren, Chelsea; Curé, Michel; Currie, Thayne; Ohashi, Nagayoshi; Okamoto, Yoshiko; Momose, Munetake; Honda, Mitsuhiko; Inutsuka, Shu-ichi; Takeuchi, Taku; Dong, Ruobing; Abe, Lyu; Brandner, Wolfgang; Brandt, Timothy D.; Carson, Joseph; Egner, Sebastian E.; Feldt, Markus; Fukue, Tsubasa; Goto, Miwa; Guyon, Olivier; Hayano, Yutaka; Hayashi, Masahiko; Hayashi, Saeko S.; Henning, Thomas; Hodapp, Klaus W.; Ishii, Miki; Iye, Masanori; Janson, Markus; Kandori, Ryo; Knapp, Gillian R.; Kusakabe, Nobuhiko; Kuzuhara, Masayuki; Matsuo, Taro; McElwain, Michael W.; Miyama, Shoken; Morino, Jun-ichi; Moro-Martín, Amaya; Nishimura, Tetsuro; Pyo, Tae-Soo; Serabyn, Eugene; Suto, Hiroshi; Suzuki, Ryuji; Takami, Michihiro; Takato, Naruhisa; Terada, Hiroshi; Thalmann, Christian; Tomono, Daigo; Turner, Edwin L.; Watanabe, Makoto; Yamada, Toru; Takami, Hideki; Usuda, Tomonori; Tamura, Motohide

2012-12-01

We present H-band polarimetric imagery of UX Tau A taken with HiCIAO/AO188 on the Subaru Telescope. UX Tau A has been classified as a pre-transitional disk object, with a gap structure separating its inner and outer disks. Our imagery taken with the 0.''15 (21 AU) radius coronagraphic mask has revealed a strongly polarized circumstellar disk surrounding UX Tau A, which extends to 120 AU, at a spatial resolution of 0.''1 (14 AU). It is inclined by 46° ± 2°, since the west side is nearest. Although SED modeling and sub-millimeter imagery have suggested the presence of a gap in the disk, with the inner edge of the outer disk estimated to be located at 25-30 AU, we detect no evidence of a gap at the limit of our inner working angle (23 AU) at the near-infrared wavelength. We attribute the observed strong polarization (up to 66%) to light scattering by dust grains in the disk. However, neither polarization models of the circumstellar disk based on Rayleigh-scattering nor Mie-scattering approximations were consistent with the observed azimuthal profile of the polarization degrees of the disk. Instead, a geometric optics model of the disk with nonspherical grains with radii of 30μm is consistent with the observed profile. We suggest that the dust grains have experienced frequent collisional coagulations, and have grown in the circumstellar disk of UX Tau A.

Three-dimensional organization of nascent rod outer segment disk membranes.

PubMed

Volland, Stefanie; Hughes, Louise C; Kong, Christina; Burgess, Barry L; Linberg, Kenneth A; Luna, Gabriel; Zhou, Z Hong; Fisher, Steven K; Williams, David S

2015-12-01

The vertebrate photoreceptor cell contains an elaborate cilium that includes a stack of phototransductive membrane disks. The disk membranes are continually renewed, but how new disks are formed remains poorly understood. Here we used electron microscope tomography to obtain 3D visualization of the nascent disks of rod photoreceptors in three mammalian species, to gain insight into the process of disk morphogenesis. We observed that nascent disks are invariably continuous with the ciliary plasma membrane, although, owing to partial enclosure, they can appear to be internal in 2D profiles. Tomographic analyses of the basal-most region of the outer segment show changes in shape of the ciliary plasma membrane indicating an invagination, which is likely a first step in disk formation. The invagination flattens to create the proximal surface of an evaginating lamella, as well as membrane protrusions that extend between adjacent lamellae, thereby initiating a disk rim. Immediately distal to this initiation site, lamellae of increasing diameter are evident, indicating growth outward from the cilium. In agreement with a previous model, our data indicate that mature disks are formed once lamellae reach full diameter, and the growth of a rim encloses the space between adjacent surfaces of two lamellae. This study provides 3D data of nascent and mature rod photoreceptor disk membranes at unprecedented z-axis depth and resolution, and provides a basis for addressing fundamental questions, ranging from protein sorting in the photoreceptor cilium to photoreceptor electrophysiology.

Premixed direct injection disk

DOEpatents

York, William David; Ziminsky, Willy Steve; Johnson, Thomas Edward; Lacy, Benjamin; Zuo, Baifang; Uhm, Jong Ho

2013-04-23

A fuel/air mixing disk for use in a fuel/air mixing combustor assembly is provided. The disk includes a first face, a second face, and at least one fuel plenum disposed therebetween. A plurality of fuel/air mixing tubes extend through the pre-mixing disk, each mixing tube including an outer tube wall extending axially along a tube axis and in fluid communication with the at least one fuel plenum. At least a portion of the plurality of fuel/air mixing tubes further includes at least one fuel injection hole have a fuel injection hole diameter extending through said outer tube wall, the fuel injection hole having an injection angle relative to the tube axis. The invention provides good fuel air mixing with low combustion generated NOx and low flow pressure loss translating to a high gas turbine efficiency, that is durable, and resistant to flame holding and flash back.

Gas lines from the 5-Myr old optically thin disk around HD 141569A . Herschel observations and modeling

NASA Astrophysics Data System (ADS)

Thi, W.-F.; Pinte, C.; Pantin, E.; Augereau, J. C.; Meeus, G.; Ménard, F.; Martin-Zaïdi, C.; Woitke, P.; Riviere-Marichalar, P.; Kamp, I.; Carmona, A.; Sandell, G.; Eiroa, C.; Dent, W.; Montesinos, B.; Aresu, G.; Meijerink, R.; Spaans, M.; White, G.; Ardila, D.; Lebreton, J.; Mendigutía, I.; Brittain, S.

2014-01-01

Context. The gas- and dust dissipation processes in disks around young stars remain uncertain despite numerous studies. At the distance of ~99-116 pc, HD 141569A is one of the nearest HerbigAe stars that is surrounded by a tenuous disk, probably in transition between a massive primordial disk and a debris disk. Atomic and molecular gases have been found in the structured 5-Myr old HD 141569A disk, making HD 141569A the perfect object within which to directly study the gaseous atomic and molecular component. Aims: We wish to constrain the gas and dust mass in the disk around HD 141569A. Methods: We observed the fine-structure lines of O i at 63 and 145 μm and the C ii line at 157 μm with the PACS instrument onboard the Herschel Space Telescope as part of the open-time large program GASPS. We complemented the atomic line observations with archival Spitzer spectroscopic and photometric continuum data, a ground-based VLT-VISIR image at 8.6 μm, and 12CO fundamental ro-vibrational and pure rotational J = 3-2 observations. We simultaneously modeled the continuum emission and the line fluxes with the Monte Carlo radiative transfer code MCFOST and the thermo-chemical code ProDiMo to derive the disk gas- and dust properties assuming no dust settling. Results: The models suggest that the oxygen lines are emitted from the inner disk around HD 141569A, whereas the [C ii] line emission is more extended. The CO submillimeter flux is emitted mostly by the outer disk. Simultaneous modeling of the photometric and line data using a realistic disk structure suggests a dust mass derived from grains with a radius smaller than 1 mm of ~2.1 × 10-7M⊙ and from grains with a radius of up to 1 cm of 4.9 × 10-6M⊙. We constrained the polycyclic aromatic hydrocarbons (PAH) mass to be between 2 × 10-11 and 1.4 × 10-10M⊙ assuming circumcircumcoronene (C150H30) as the representative PAH. The associated PAH abundance relative to hydrogen is lower than those found in the interstellar medium (3 × 10-7) by two to three orders of magnitude. The disk around HD 141569A is less massive in gas (2.5 to 4.9 × 10-4M⊙ or 67 to 164 M⊕) and has a flat opening angle (<10%). Conclusions: We constrained simultaneously the silicate dust grain, PAH, and gas mass in a ~5-Myr old Herbig Ae disk. The disk-averaged gas-to-dust-mass is most likely around 100, which is the assumed value at the disk formation despite the uncertainties due to disagreements between the different gas tracers. If the disk was originally massive, the gas and the dust would have dissipated at the same rate. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 079.C-0602(A).Appendix A is available in electronic form at http://www.aanda.orgHerschel is an ESA space observatory with science instruments provided by Principal Investigator consortia. It is open for proposals for observing time from the worldwide astronomical community.

Hints for Small Disks around Very Low Mass Stars and Brown Dwarfs

NASA Astrophysics Data System (ADS)

Hendler, Nathanial P.; Mulders, Gijs D.; Pascucci, Ilaria; Greenwood, Aaron; Kamp, Inga; Henning, Thomas; Ménard, François; Dent, William R. F.; Evans, Neal J., II

2017-06-01

The properties of disks around brown dwarfs and very low mass stars (hereafter VLMOs) provide important boundary conditions on the process of planet formation and inform us about the numbers and masses of planets than can form in this regime. We use the Herschel Space Observatory PACS spectrometer to measure the continuum and [O I] 63 μm line emission toward 11 VLMOs with known disks in the Taurus and Chamaeleon I star-forming regions. We fit radiative transfer models to the spectral energy distributions of these sources. Additionally, we carry out a grid of radiative transfer models run in a regime that connects the luminosity of our sources with brighter T Tauri stars. We find that VLMO disks with sizes 1.3-78 au, smaller than typical T Tauri disks, fit well the spectral energy distributions assuming that disk geometry and dust properties are stellar mass independent. Reducing the disk size increases the disk temperature, and we show that VLMOs do not follow previously derived disk temperature-stellar luminosity relationships if the disk outer radius scales with stellar mass. Only 2 out of 11 sources are detected in [O I] despite a better sensitivity than was achieved for T Tauri stars, suggesting that VLMO disks are underluminous. Using thermochemical models, we show that smaller disks can lead to the unexpected [O I] 63 μm nondetections in our sample. The disk outer radius is an important factor in determining the gas and dust observables. Hence, spatially resolved observations with ALMA—to establish if and how disk radii scale with stellar mass—should be pursued further. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

External Photoevaporation of the Solar Nebula. II. Effects on Disk Structure and Evolution with Non-uniform Turbulent Viscosity due to the Magnetorotational Instability

NASA Astrophysics Data System (ADS)

Kalyaan, A.; Desch, S. J.; Monga, N.

2015-12-01

The structure and evolution of protoplanetary disks, especially the radial flows of gas through them, are sensitive to a number of factors. One that has been considered only occasionally in the literature is external photoevaporation by far-ultraviolet (FUV) radiation from nearby, massive stars, despite the fact that nearly half of disks will experience photoevaporation. Another effect apparently not considered in the literature is a spatially and temporally varying value of α in the disk (where the turbulent viscosity ν is α times the sound speed C times the disk scale height H). Here we use the formulation of Bai & Stone to relate α to the ionization fraction in the disk, assuming turbulent transport of angular momentum is due to the magnetorotational instability. We calculate the ionization fraction of the disk gas under various assumptions about ionization sources and dust grain properties. Disk evolution is most sensitive to the surface area of dust. We find that typically α ≲ 10-5 in the inner disk (<2 AU), rising to ˜10-1 beyond 20 AU. This drastically alters the structure of the disk and the flow of mass through it: while the outer disk rapidly viscously spreads, the inner disk hardly evolves; this leads to a steep surface density profile ({{Σ }}\\propto {r}-< p> with < p> ≈ 2-5 in the 5-30 AU region) that is made steeper by external photoevaporation. We also find that the combination of variable α and external photoevaporation eventually causes gas as close as 3 AU, previously accreting inward, to be drawn outward to the photoevaporated outer edge of the disk. These effects have drastic consequences for planet formation and volatile transport in protoplanetary disks.

Usher syndrome type 1–associated cadherins shape the photoreceptor outer segment

PubMed Central

Parain, Karine; Aghaie, Asadollah; Picaud, Serge

2017-01-01

Usher syndrome type 1 (USH1) causes combined hearing and sight defects, but how mutations in USH1 genes lead to retinal dystrophy in patients remains elusive. The USH1 protein complex is associated with calyceal processes, which are microvilli of unknown function surrounding the base of the photoreceptor outer segment. We show that in Xenopus tropicalis, these processes are connected to the outer-segment membrane by links composed of protocadherin-15 (USH1F protein). Protocadherin-15 deficiency, obtained by a knockdown approach, leads to impaired photoreceptor function and abnormally shaped photoreceptor outer segments. Rod basal outer disks displayed excessive outgrowth, and cone outer segments were curved, with lamellae of heterogeneous sizes, defects also observed upon knockdown of Cdh23, encoding cadherin-23 (USH1D protein). The calyceal processes were virtually absent in cones and displayed markedly reduced F-actin content in rods, suggesting that protocadherin-15–containing links are essential for their development and/or maintenance. We propose that calyceal processes, together with their associated links, control the sizing of rod disks and cone lamellae throughout their daily renewal. PMID:28495838

Usher syndrome type 1-associated cadherins shape the photoreceptor outer segment.

PubMed

Schietroma, Cataldo; Parain, Karine; Estivalet, Amrit; Aghaie, Asadollah; Boutet de Monvel, Jacques; Picaud, Serge; Sahel, José-Alain; Perron, Muriel; El-Amraoui, Aziz; Petit, Christine

2017-06-05

Usher syndrome type 1 (USH1) causes combined hearing and sight defects, but how mutations in USH1 genes lead to retinal dystrophy in patients remains elusive. The USH1 protein complex is associated with calyceal processes, which are microvilli of unknown function surrounding the base of the photoreceptor outer segment. We show that in Xenopus tropicalis , these processes are connected to the outer-segment membrane by links composed of protocadherin-15 (USH1F protein). Protocadherin-15 deficiency, obtained by a knockdown approach, leads to impaired photoreceptor function and abnormally shaped photoreceptor outer segments. Rod basal outer disks displayed excessive outgrowth, and cone outer segments were curved, with lamellae of heterogeneous sizes, defects also observed upon knockdown of Cdh23 , encoding cadherin-23 (USH1D protein). The calyceal processes were virtually absent in cones and displayed markedly reduced F-actin content in rods, suggesting that protocadherin-15-containing links are essential for their development and/or maintenance. We propose that calyceal processes, together with their associated links, control the sizing of rod disks and cone lamellae throughout their daily renewal. © 2017 Schietroma et al.

Imaging a Central Ionized Component, a Narrow Ring, and the CO Snowline in the Multigapped Disk of HD 169142

NASA Astrophysics Data System (ADS)

Macías, Enrique; Anglada, Guillem; Osorio, Mayra; Torrelles, José M.; Carrasco-González, Carlos; Gómez, José F.; Rodríguez, Luis F.; Sierra, Anibal

2017-04-01

We report Very Large Array observations at 7 mm, 9 mm, and 3 cm toward the pre-transitional disk of the Herbig Ae star HD 169142. These observations have allowed us to study the millimeter emission of this disk with the highest angular resolution so far (0.″12 × 0.″09, or 14 au × 11 au, at 7 mm). Our 7 and 9 mm images show a narrow ring of emission at a radius of ˜25 au tracing the outer edge of the inner gap. This ring presents an asymmetric morphology that could be produced by dynamical interactions between the disk and forming planets. Additionally, the azimuthally averaged radial intensity profiles of the 7 and 9 mm images confirm the presence of the previously reported gap at ˜45 au and reveal a new gap at ˜85 au. We analyzed archival DCO+(3-2) and C18O(2-1) ALMA observations, showing that the CO snowline is located very close to this third outer gap. This suggests that growth and accumulation of large dust grains close to the CO snowline could be the mechanism responsible for this proposed outer gap. Finally, a compact source of emission is detected at 7 mm, 9 mm, and 3 cm toward the center of the disk. Its flux density and spectral index indicate that it is dominated by free-free emission from ionized gas, which could be associated with the photoionization of the inner disk, an independent object, or an ionized jet.

Planetary migration in protoplanetary discs and outer Solar System architecture.

NASA Astrophysics Data System (ADS)

Crida, A.; Morbidelli, A.; Tsiganis, K.

2007-08-01

Planets form around stars in gaseous protoplanetary discs. Due to tidal effects, they perturb the gas distribution, which in turn affects their motion. If the planet is massive enough (see for instance Crida et al. 2006 for a criterion), it repels the gas efficiently and opens a gap around its orbit ; then, locked into its gap, the planet follows the disc viscous evolution, which generally consists in accretion onto the central star. This process is called type II migration and leads to the orbital decay of the planet on a timescale shorter than the disc lifetime. After a review of these processes, we will focus on the Solar System giant planets. Strong constraints suggest that they did not migrate significantly. Masset and Snellgrove (2001) have shown that the evolution of 2 giants planets in mean motion resonance in a common gap differs from the evolution of a single planet. For what concerns Jupiter and Saturn, we found that in some conditions on the disc parameter, they can avoid significant migration (Morbidelli and Crida 2007). Adding Uranus and Neptune to the system, six stable fully resonant configurations for the four giants in the gas disc appear. Of course, none of them correspond to the present configuration. However, after the gas disc phase, the system was surrounded by a planetesimal disk. Interactions with this debris disk make the planets slowly evolve, until an instability in reached. This destabilises the planetesimal disc and triggers the Late Heavy Bombardment, while the planets reach their actual position, like in the model by Tsiganis et al (2005) and Gomes et al (2005). Our simulations show a very satisfying case, opening the possibility for a dynamically consistent scenario of the outer Solar System evolution, starting from the gas phase.

Sequential planet formation in transition disks: The case of HD 100546

NASA Astrophysics Data System (ADS)

Pinilla, Paola; Birnsitel, Til; Walsh, Catherine; van Dishoeck, Ewine

2015-08-01

Transition disks are circumstellar disks with dust inner cavities and may reveal an intermediate step of the ongoing disk dispersal process, where planet formation might happen. The recent gas and dust observations of transition disks have given major support to the presence of massive planets in transition disks. The analysis of such observations help to constrain the properties of the potential unseen planets. An excellent candidate to analyse the dust evolution when planets are embedded in disks is the transition disk around the Herbig Ae star HD 100546. Near-infrared observations of HD 100546 suggested the presence on an inner planet at 10 AU distance from the star (e.g. Mulders et al. 2013), while an outer planet has been directly imaged at 70 AU distance, which may be in the act of formation (Quant et al. 2013, 2015; Currie et al. 2014). The two embedded planets can lead to remarkable dust structures due to the particle trapping at the edges of the gaps caved by such planets (e.g. Pinilla et al. 2012, 2015). Recent ALMA Cycle 0 observations of this disk reveal a two-ring like structure consistent with particle trapping induced by the two companions (Walsh et al. 2014). The comparison of these observations with dust evolution models, that include the coagulation and fragmentation of dust grains, suggest that the outer companion must be at least two million of years younger than the inner companion, revealing sequential planet formation in this disk (Pinilla et al. 2015, under revision).

Gemini spectroscopy of the outer disk star cluster BH176

NASA Astrophysics Data System (ADS)

Sharina, M. E.; Donzelli, C. J.; Davoust, E.; Shimansky, V. V.; Charbonnel, C.

2014-10-01

Context. BH176 is an old metal-rich star cluster. It is spatially and kinematically consistent with belonging to the Monoceros Ring. It is larger in size and more distant from the Galactic plane than typical open clusters, and it does not belong to the Galactic bulge. Aims: Our aim is to determine the origin of this unique object by accurately determining its distance, metallicity, and age. The best way to reach this goal is to combine spectroscopic and photometric methods. Methods: We present medium-resolution observations of red clump and red giant branch stars in BH176 obtained with the Gemini South Multi-Object Spectrograph. We derive radial velocities, metallicities, effective temperatures, and surface gravities of the observed stars and use these parameters to distinguish member stars from field objects. Results: We determine the following parameters for BH176: Vh = 0 ± 15 km s-1, [Fe/H] = -0.1 ± 0.1, age 7 ± 0.5 Gyr, E(V - I) = 0.79 ± 0.03, distance 15.2 ± 0.2 kpc, α-element abundance [α/Fe] ~ 0.25 dex (the mean of [Mg/Fe], and [Ca/Fe]). Conclusions: BH176 is a member of old Galactic open clusters that presumably belong to the thick disk. It may have originated as a massive star cluster after the encounter of the forming thin disk with a high-velocity gas cloud or as a satellite dwarf galaxy. Appendix A is available in electronic form at http://www.aanda.org

Dynamical Stability of Imaged Planetary Systems in Formation: Application to HL Tau

NASA Astrophysics Data System (ADS)

Tamayo, D.; Triaud, A. H. M. J.; Menou, K.; Rein, H.

2015-06-01

A recent Atacama Large Millimeter/Submillimeter Array image revealed several concentric gaps in the protoplanetary disk surrounding the young star HL Tau. We consider the hypothesis that these gaps are carved by planets, and present a general framework for understanding the dynamical stability of such systems over typical disk lifetimes, providing estimates for the maximum planetary masses. We collect these easily evaluated constraints into a workflow that can help guide the design and interpretation of new observational campaigns and numerical simulations of gap opening in such systems. We argue that the locations of resonances should be significantly shifted in massive disks like HL Tau, and that theoretical uncertainties in the exact offset, together with observational errors, imply a large uncertainty in the dynamical state and stability in such disks. This presents an important barrier to using systems like HL Tau as a proxy for the initial conditions following planet formation. An important observational avenue to breaking this degeneracy is to search for eccentric gaps, which could implicate resonantly interacting planets. Unfortunately, massive disks like HL Tau should induce swift pericenter precession that would smear out any such eccentric features of planetary origin. This motivates pushing toward more typical, less massive disks. For a nominal non-resonant model of the HL Tau system with five planets, we find a maximum mass for the outer three bodies of approximately 2 Neptune masses. In a resonant configuration, these planets can reach at least the mass of Saturn. The inner two planets’ masses are unconstrained by dynamical stability arguments.

CHARACTERIZATION OF THE INNER DISK AROUND HD 141569 A FROM KECK/NIRC2 L-BAND VORTEX CORONAGRAPHY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mawet, Dimitri; Bottom, Michael; Matthews, Keith

HD 141569 A is a pre-main sequence B9.5 Ve star surrounded by a prominent and complex circumstellar disk, likely still in a transition stage from protoplanetary to debris disk phase. Here, we present a new image of the third inner disk component of HD 141569 A made in the L ′ band (3.8 μ m) during the commissioning of the vector vortex coronagraph that has recently been installed in the near-infrared imager and spectrograph NIRC2 behind the W.M. Keck Observatory Keck II adaptive optics system. We used reference point-spread function subtraction, which reveals the innermost disk component from the innermore » working distance of ≃23 au and up to ≃70 au. The spatial scale of our detection roughly corresponds to the optical and near-infrared scattered light, thermal Q , N , and 8.6 μ m PAH emission reported earlier. We also see an outward progression in dust location from the L ′ band to the H band (Very Large Telescope/SPHERE image) to the visible ( Hubble Space Telescope ( HST )/STIS image), which is likely indicative of dust blowout. The warm disk component is nested deep inside the two outer belts imaged by HST-NICMOS in 1999 (at 406 and 245 au, respectively). We fit our new L ′-band image and spectral energy distribution of HD 141569 A with the radiative transfer code MCFOST. Our best-fit models favor pure olivine grains and are consistent with the composition of the outer belts. While our image shows a putative very faint point-like clump or source embedded in the inner disk, we did not detect any true companion within the gap between the inner disk and the first outer ring, at a sensitivity of a few Jupiter masses.« less

SMA Continuum Survey of Circumstellar Disks in Serpens

NASA Astrophysics Data System (ADS)

Law, Charles; Ricci, Luca; Andrews, Sean M.; Wilner, David J.; Qi, Chunhua

2017-06-01

The lifetime of disks surrounding pre-main-sequence stars is closely linked to planet formation and provides information on disk dispersal mechanisms and dissipation timescales. The potential for these optically thick, gas-rich disks to form planets is critically dependent on how much dust is available to be converted into terrestrial planets and rocky cores of giant planets. For this reason, an understanding of how dust mass varies with key properties such as stellar mass, age, and environment is critical for understanding planet formation. Millimeter wavelength observations, in which the dust emission is optically thin, are required to study the colder dust residing in the disk’s outer regions and to measure disk dust masses. Hence, we have obtained SMA 1.3 mm continuum observations of 62 Class II sources with suspected circumstellar disks in the Serpens star-forming region (SFR). Relative to the well-studied Taurus SFR, Serpens allows us to probe the distribution of dust masses for disks in a much denser and more clustered environment. Only 13 disks were detected in the continuum with the SMA. We calculate the total dust masses of these disks and compare their masses to those of disks in Taurus, Lupus, and Upper Scorpius. We do not find evidence of diminished dust masses in Serpens disks relative to those in Taurus despite the fact that disks in denser clusters may be expected to contain less dust mass due to stronger and more frequent tidal interactions that can disrupt the outer regions of disks. However, considering the low detection fraction, we likely detected only bright continuum sources and a more sensitive survey of Serpens would help clarify these results.

THE SPITZER INFRARED SPECTROGRAPH SURVEY OF PROTOPLANETARY DISKS IN ORION A. I. DISK PROPERTIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, K. H.; Watson, Dan M.; Manoj, P.

2016-09-01

We present our investigation of 319 Class II objects in Orion A observed by Spitzer /IRS. We also present the follow-up observations of 120 of these Class II objects in Orion A from the Infrared Telescope Facility/SpeX. We measure continuum spectral indices, equivalent widths, and integrated fluxes that pertain to disk structure and dust composition from IRS spectra of Class II objects in Orion A. We estimate mass accretion rates using hydrogen recombination lines in the SpeX spectra of our targets. Utilizing these properties, we compare the distributions of the disk and dust properties of Orion A disks with thosemore » of Taurus disks with respect to position within Orion A (Orion Nebular Cluster [ONC] and L1641) and with the subgroups by the inferred radial structures, such as transitional disks (TDs) versus radially continuous full disks (FDs). Our main findings are as follows. (1) Inner disks evolve faster than the outer disks. (2) The mass accretion rates of TDs and those of radially continuous FDs are statistically significantly displaced from each other. The median mass accretion rate of radially continuous disks in the ONC and L1641 is not very different from that in Taurus. (3) Less grain processing has occurred in the disks in the ONC compared to those in Taurus, based on analysis of the shape index of the 10 μ m silicate feature ( F {sub 11.3}/ F {sub 9.8}). (4) The 20–31 μ m continuum spectral index tracks the projected distance from the most luminous Trapezium star, θ {sup 1} Ori C. A possible explanation is UV ablation of the outer parts of disks.« less

Evidence for dust grain growth in young circumstellar disks.

PubMed

Throop, H B; Bally, J; Esposito, L W; McCaughrean, M J

2001-06-01

Hundreds of circumstellar disks in the Orion nebula are being rapidly destroyed by the intense ultraviolet radiation produced by nearby bright stars. These young, million-year-old disks may not survive long enough to form planetary systems. Nevertheless, the first stage of planet formation-the growth of dust grains into larger particles-may have begun in these systems. Observational evidence for these large particles in Orion's disks is presented. A model of grain evolution in externally irradiated protoplanetary disks is developed and predicts rapid particle size evolution and sharp outer disk boundaries. We discuss implications for the formation rates of planetary systems.

On the possibility of enrichment and differentiation in gas giants during birth by disk instability

NASA Astrophysics Data System (ADS)

Boley, Aaron C.; Durisen, Richard H.

2011-11-01

We investigate the coupling between solids and gas during the formation of gas giant planets by disk fragmentation in the outer regions of massive disks. We find that fragments can become differentiated at birth. Even if an entire clump does not survive, differentiation could create solids cores that survive to accrete gaseous envelopes later.

Studies of extra-solar OORT clouds and the Kuiper disk

NASA Technical Reports Server (NTRS)

Stern, S. Alan

1993-01-01

This is the second report for NAGW-3023, Studies of Extra-Solar Oort Clouds and the Kuiper Disk. We are conducting research designed to enhance our understanding of the evolution and detectability of comet clouds and disks. This area holds promise for also improving our understanding of outer solar system formation, the bombardment history of the planets, the transport of volatiles and organics from the outer solar system to the inner planets, and the ultimate fate of comet clouds around the Sun and other stars. According to 'standard' theory, both the Kuiper Disk and Oort Cloud are (at least in part) natural products of the planetary accumulation stage of solar system formation. One expects such assemblages to be a common attribute of other solar systems. Therefore, searches for comet disks and clouds orbiting other stars offer a new method for infering the presence of planetary systems. Our three-year effort consists of two major efforts: (1) observational work to predict and search for the signatures of Oort Clouds and comet disks around other stars; and (2) modelling studies of the formation and evolution of the Kuiper Disk (KD) and similar assemblages that may reside around other stars, including Beta Pic. These efforts are referred to as Task 1 and 2, respectively.

Studies of extra-solar Oort Clouds and the Kuiper Disk

NASA Technical Reports Server (NTRS)

Stern, Alan

1995-01-01

This is the September 1995 Semi-Annual report for Studies of Extra-Solar Oort Clouds and the Kuiper Disk. We are conducting research designed to enhance our understanding of the evolution and detectability of comet clouds and disks. This area holds promise for also improving our understanding of outer solar system formation the bombardment history of the planets, the transport of volatiles and organics from the outer solar system to the inner planets, and to the ultimate fate of comet clouds around the Sun and other stars. According to 'standard' theory, both the Kuiper Disk and the Oort Cloud are (at least in part) natural products of the planetary accumulation stage of solar system formation. One expects such assemblages to be a common attribute of other solar systems. Therefore, searches for comet disks and clouds orbiting other stars offer a new method for inferring the presence of planetary systems. This project consists of two major efforts: (1) observational work to predict and search for the signatures of Oort Clouds and comet disks around other stars; and (2) modelling studies of the formation and evolution of the Kuiper Disk (KD) and similar assemblages that may reside around other stars, including beta Pic. These efforts are referred to as Task 1 and 2.

Modeling the HD 32297 Debris Disk With Far-Infrared Herschel Data

NASA Technical Reports Server (NTRS)

Donaldson, J.K.; Lebreton, J.; Roberge, A.; Augereau, J.-C.; Krivov, A. V.

2013-01-01

HD 32297 is a young A-star (approx. 30 Myr) 112 pc away with a bright edge-on debris disk that has been resolved in scattered light. We observed the HD 32297 debris disk in the far-infrared and sub-millimeter with the Herschel Space Observatory PACS and SPIRE instruments, populating the spectral energy distribution (SED) from 63 to 500 micron..We aimed to determine the composition of dust grains in the HD 32297 disk through SED modeling, using geometrical constraints from the resolved imaging to break the degeneracies inherent in SED modeling. We found the best fitting SED model has two components: an outer ring centered around 110 AU, seen in the scattered light images, and an inner disk near the habitable zone of the star. The outer disk appears to be composed of grains>2 micron consisting of silicates, carbonaceous material, and water ice with an abundance ratio of 1:2:3 respectively and 90% porosity. These grains appear consistent with cometary grains, implying the underlying planetesimal population is dominated by comet-like bodies. We also discuss the 3.7 sigma detection of [C ii] emission at 158 micron with the Herschel PACS instrument, making HD 32297 one of only a handful of debris disks with circumstellar gas detected

Mid-infrared multi-wavelength imaging of Ophiuchus IRS 48 transitional disk†

NASA Astrophysics Data System (ADS)

Honda, Mitsuhiko; Okada, Kazushi; Miyata, Takashi; Mulders, Gijs D.; Swearingen, Jeremy R.; Kamizuka, Takashi; Ohsawa, Ryou; Fujiyoshi, Takuya; Fujiwara, Hideaki; Uchiyama, Mizuho; Yamashita, Takuya; Onaka, Takashi

2018-04-01

Transitional disks around the Herbig Ae/Be stars are fascinating targets in the contexts of disk evolution and planet formation. Oph IRS 48 is one of such Herbig Ae stars, which shows an inner dust cavity and azimuthally lopsided large dust distribution. We present new images of Oph IRS 48 at eight mid-infrared (MIR) wavelengths from 8.59 to 24.6 μm taken with COMICS mounted on the 8.2 m Subaru Telescope. The N-band (7 to 13 μm) images show that the flux distribution is centrally peaked with a slight spatial extent, while the Q-band (17 to 25 μm) images show asymmetric double peaks (east and west). Using 18.8- and 24.6 μm images, we derived the dust temperature at both east and west peaks to be 135 ± 22 K. Thus, the asymmetry may not be attributed to a difference in the temperature. Comparing our results with previous modeling works, we conclude that the inner disk is aligned to the outer disk. A shadow cast by the optically thick inner disk has a great influence on the morphology of MIR thermal emission from the outer disk.

Mid-infrared multi-wavelength imaging of Ophiuchus IRS 48 transitional disk†

NASA Astrophysics Data System (ADS)

Honda, Mitsuhiko; Okada, Kazushi; Miyata, Takashi; Mulders, Gijs D.; Swearingen, Jeremy R.; Kamizuka, Takashi; Ohsawa, Ryou; Fujiyoshi, Takuya; Fujiwara, Hideaki; Uchiyama, Mizuho; Yamashita, Takuya; Onaka, Takashi

2018-06-01

Transitional disks around the Herbig Ae/Be stars are fascinating targets in the contexts of disk evolution and planet formation. Oph IRS 48 is one of such Herbig Ae stars, which shows an inner dust cavity and azimuthally lopsided large dust distribution. We present new images of Oph IRS 48 at eight mid-infrared (MIR) wavelengths from 8.59 to 24.6 μm taken with COMICS mounted on the 8.2 m Subaru Telescope. The N-band (7 to 13 μm) images show that the flux distribution is centrally peaked with a slight spatial extent, while the Q-band (17 to 25 μm) images show asymmetric double peaks (east and west). Using 18.8- and 24.6 μm images, we derived the dust temperature at both east and west peaks to be 135 ± 22 K. Thus, the asymmetry may not be attributed to a difference in the temperature. Comparing our results with previous modeling works, we conclude that the inner disk is aligned to the outer disk. A shadow cast by the optically thick inner disk has a great influence on the morphology of MIR thermal emission from the outer disk.

High-Resolution Submillimeter and Near-Infrared Studies of the Transition Disk around Sz 91

NASA Technical Reports Server (NTRS)

Tsukagoshi, Takashi; Momose, Munetake; Hashimoto, Jun; Kudo, Tomoyuki; Andrews, Sean; Saito, Masao; Kitamura, Yoshimi; Ohashi, Nagayoshi; Wilner, David; Kawabe, Ryohei;

Super-Earths as Failed Cores in Orbital Migration Traps

NASA Astrophysics Data System (ADS)

Hasegawa, Yasuhiro

2016-11-01

I explore whether close-in super-Earths were formed as rocky bodies that failed to grow fast enough to become the cores of gas giants before the natal protostellar disk dispersed. I model the failed cores’ inward orbital migration in the low-mass or type I regime to stopping points at distances where the tidal interaction with the protostellar disk applies zero net torque. The three kinds of migration traps considered are those due to the dead zone's outer edge, the ice line, and the transition from accretion to starlight as the disk's main heat source. As the disk disperses, the traps move toward final positions near or just outside 1 au. Planets at this location exceeding about 3 M ⊕ open a gap, decouple from their host traps, and migrate inward in the high-mass or type II regime to reach the vicinity of the star. I synthesize the population of planets that formed in this scenario, finding that a fraction of the observed super-Earths could have been failed cores. Most super-Earths that formed this way have more than 4 M ⊕, so their orbits when the disks dispersed were governed by type II migration. These planets have solid cores surrounded by gaseous envelopes. Their subsequent photoevaporative mass loss is most effective for masses originally below about 6 M ⊕. The failed core scenario suggests a division of the observed super-Earth mass-radius diagram into five zones according to the inferred formation history.

ACCRETION KINEMATICS THROUGH THE WARPED TRANSITION DISK IN HD 142527 FROM RESOLVED CO(6–5) OBSERVATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Casassus, S.; Marino, S.; Pérez, S.

2015-10-01

The finding of residual gas in the large central cavity of the HD 142527 disk motivates questions regarding the origin of its non-Keplerian kinematics and possible connections with planet formation. We aim to understand the physical structure that underlies the intra-cavity gaseous flows, guided by new molecular-line data in CO(6–5) with unprecedented angular resolutions. Given the warped structure inferred from the identification of scattered-light shadows cast on the outer disk, the kinematics are consistent, to first order, with axisymmetric accretion onto the inner disk occurring at all azimuths. A steady-state accretion profile, fixed at the stellar accretion rate, explains themore » depth of the cavity as traced in CO isotopologues. The abrupt warp and evidence for near free-fall radial flows in HD 142527 resemble theoretical models for disk tearing, which could be driven by the reported low-mass companion, whose orbit may be contained in the plane of the inner disk. The companion’s high inclination with respect to the massive outer disk could drive Kozai oscillations over long timescales; high-eccentricity periods may perhaps account for the large cavity. While shadowing by the tilted disk could imprint an azimuthal modulation in the molecular-line maps, further observations are required to ascertain the significance of azimuthal structure in the density field inside the cavity of HD 142527.« less

Galactic Behavior for the Outer B Ring

NASA Image and Video Library

2010-11-01

Keeping a close watch on the outer portion of Saturn B ring, NASA Cassini spacecraft records the complex inward and outward movement of the edge of the ring. This ring movement resembles the suspected behavior of spiral disk galaxies.

On the metallicity gradients of the Galactic disk as revealed by LSS-GAC red clump stars

NASA Astrophysics Data System (ADS)

Huang, Yang; Liu, Xiao-Wei; Zhang, Hua-Wei; Yuan, Hai-Bo; Xiang, Mao-Sheng; Chen, Bing-Qiu; Ren, Juan-Juan; Sun, Ning-Chen; Wang, Chun; Zhang, Yong; Hou, Yong-Hui; Wang, Yue-Fei; Yang, Ming

2015-08-01

Using a sample of over 70 000 red clump (RC) stars with 5%-10% distance accuracy selected from the LAMOST Spectroscopic Survey of the Galactic Anti-center (LSS-GAC), we study the radial and vertical gradients of the Galactic disk(s) mainly in the anti-center direction, covering a significant volume of the disk in the range of projected Galactocentric radius 7 ≤ RGC ≤ 14 kpc and height from the Galactic midplane 0 ≤ |Z| ≤ 3 kpc. Our analysis shows that both the radial and vertical metallicity gradients are negative across much of the volume of the disk that is probed, and they exhibit significant spatial variations. Near the solar circle (7 ≤ RGC ≤ 115 kpc), the radial gradient has a moderately steep, negative slope of -0.08 dex kpc-1 near the midplane (|Z| < 0.1 kpc), and the slope flattens with increasing |Z|. In the outer disk (11.5 < RGC ≤ 14 kpc), the radial gradients have an essentially constant, much less steep slope of -0.01 dex kpc-1 at all heights above the plane, suggesting that the outer disk may have experienced an evolutionary path different from that of the inner disk. The vertical gradients are found to flatten largely with increasing RGC. However, the vertical gradient of the lower disk (0 ≤ |Z| ≤ 1 kpc) is found to flatten with RGC quicker than that of the upper disk (1 < |Z| ≤ 3 kpc). Our results should provide strong constraints on the theory of disk formation and evolution, as well as the underlying physical processes that shape the disk (e.g. gas flows, radial migration, and internal and external perturbations).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Espaillat, C.; D'Alessio, P.; Hernandez, J.

In the past few years, several disks with inner holes that are relatively empty of small dust grains have been detected and are known as transitional disks. Recently, Spitzer has identified a new class of 'pre-transitional disks' with gaps based on near-infrared photometry and mid-infrared spectra; these objects have an optically thick inner disk separated from an optically thick outer disk by an optically thin disk gap. A near-infrared spectrum provided the first confirmation of a gap in the pre-transitional disk of LkCa 15 by verifying that the near-infrared excess emission in this object was due to an optically thickmore » inner disk. Here, we investigate the difference between the nature of the inner regions of transitional and pre-transitional disks using the same veiling-based technique to extract the near-infrared excess emission above the stellar photosphere. However, in this work we use detailed disk models to fit the excess continua as opposed to the simple blackbody fits previously used. We show that the near-infrared excess emission of the previously identified pre-transitional disks of LkCa 15 and UX Tau A in the Taurus cloud as well as the newly identified pre-transitional disk of ROX 44 in Ophiuchus can be fit with an inner disk wall located at the dust destruction radius. We also present detailed modeling of the broadband spectral energy distributions of these objects, taking into account the effect of shadowing by the inner disk on the outer disk, but considering the finite size of the star, unlike other recent treatments. The near-infrared excess continua of these three pre-transitional disks, which can be explained by optically thick inner disks, are significantly different from that of the transitional disks of GM Aur, whose near-infrared excess continuum can be reproduced by emission from sub-micron-sized optically thin dust, and DM Tau, whose near-infrared spectrum is consistent with a disk hole that is relatively free of small dust. The structure of pre-transitional disks may be a sign of young planets forming in these disks and future studies of pre-transitional disks will provide constraints to aid in theoretical modeling of planet formation.« less

New constraints on the disk characteristics and companion candidates around T Chamaeleontis with VLT/SPHERE

NASA Astrophysics Data System (ADS)

Pohl, A.; Sissa, E.; Langlois, M.; Müller, A.; Ginski, C.; van Holstein, R. G.; Vigan, A.; Mesa, D.; Maire, A.-L.; Henning, Th.; Gratton, R.; Olofsson, J.; van Boekel, R.; Benisty, M.; Biller, B.; Boccaletti, A.; Chauvin, G.; Daemgen, S.; de Boer, J.; Desidera, S.; Dominik, C.; Garufi, A.; Janson, M.; Kral, Q.; Ménard, F.; Pinte, C.; Stolker, T.; Szulágyi, J.; Zurlo, A.; Bonnefoy, M.; Cheetham, A.; Cudel, M.; Feldt, M.; Kasper, M.; Lagrange, A.-M.; Perrot, C.; Wildi, F.

2017-09-01

Context. The transition disk around the T Tauri star T Cha possesses a large gap, making it a prime target for high-resolution imaging in the context of planet formation. Aims: We aim to find signs of disk evolutionary processes by studying the disk geometry and the dust grain properties at its surface, and to search for companion candidates. Methods: We analyze a set of VLT/SPHERE data at near-infrared and optical wavelengths. We performed polarimetric imaging of T Cha with IRDIS (1.6 μm) and ZIMPOL (0.5-0.9 μm), and obtained intensity images from IRDIS dual-band imaging with simultaneous spectro-imaging with IFS (0.9-1.3 μm). Results: The disk around T Cha is detected in all observing modes and its outer disk is resolved in scattered light with unprecedented angular resolution and signal-to-noise. The images reveal a highly inclined disk with a noticeable east-west brightness asymmetry. The significant amount of non-azimuthal polarization signal in the Uφ images, with a Uφ/Qφ peak-to-peak value of 14%, is in accordance with theoretical studies on multiple scattering in an inclined disk. Our optimal axisymmetric radiative transfer model considers two coplanar inner and outer disks, separated by a gap of 0.̋28 ( 30 au) in size, which is larger than previously thought. We derive a disk inclination of 69 deg and PA of 114 deg. In order to self-consistently reproduce the intensity and polarimetric images, the dust grains, responsible for the scattered light, need to be dominated by sizes of around ten microns. A point source is detected at an angular distance of 3.5'' from the central star. It is, however, found not to be co-moving. Conclusions: We confirm that the dominant source of emission is forward scattered light from the near edge of the outer disk. Our point source analysis rules out the presence of a companion with mass larger than 8.5 Mjup between 0.̋1 and 0.̋3. The detection limit decreases to 2 Mjup for 0.̋3 to 4.0''. Based on observations made with European Southern Observatory (ESO) telescopes at the Paranal Observatory in Chile, under program IDs 095.C-0298(B), 096.C-0248(B) and 096.C-0248(C).

An Earth with affinities to Enstatite Chondrites

NASA Astrophysics Data System (ADS)

McDonough, W. F.

2015-12-01

The Enstatite chondrite model for the Earth, as envisaged by Marc Javoy and colleagues, has strengths and weaknesses. The overwhelming evidence against layered mantle scenarios makes the existing enstatite Earth models unacceptable. Increasingly, stable and radiogenic isotope data for the Earth and the range of chondrites find that many (but not all) isotopic ratios are shared between the Earth and enstatite chondrites. This significant amount of overlap in isotope space compels one to reconsider the enstatite chondrite model for the Earth. During early solar system formation (circa +1 Ma) radial inward migration of the Jupiter and Saturn in the disk (e.g., Grand Tack model) would fully disrupted an asteroid belt, resulting in mixing and redistribution of preexisting components, while much later after the disk is gone (e.g., +100 Ma) gravitational scattering by these planets may have transported small bodies from the outer reaches of the solar system inward towards the rocky planets (Nice model). Astromineralogy reveals variations in the proportion of olivine to pyroxene in accretion disks, some with inner disk regions being richer in olivine relative to the disk wide composition, while other disks show the abundance of olivine is greater in the outer (vs the inner) part of the circumstellar disk, with differences in disk mineralogy being relating to type of star (e.g., T Tauri vs Herbig Ae/Be stars). The inner disk regions (a few AU) show higher abundances of large grains and generally higher crystallinity as compared to outer disk regions, suggesting grain growth occurs more rapidly in the inner disk regions. Recent results from geoneutrino measurements are most consistent with geochemical models that predict 20 TW of radiogenic power, less so with existing enstatite Earth models predicting less power in the planet. At 1 AU the Earth accreted a greater proportion of olivine to pyroxene (i.e., Mg/Si of pyrolite) than that available to the known enstatite chondrite parent body. The Earth accreted early in a reduced state, perhaps to the point of differentiating silicides into the core. Later accreted material was increasingly more oxidized. Stirring and mixing in the early solar system created opportunities for the Earth and enstatite chondrites to share some, but not all chemical and isotopic characteristics.

Imaging a Central Ionized Component, a Narrow Ring, and the CO Snowline in the Multigapped Disk of HD 169142

DOE Office of Scientific and Technical Information (OSTI.GOV)

Macías, Enrique; Anglada, Guillem; Osorio, Mayra

2017-04-01

We report Very Large Array observations at 7 mm, 9 mm, and 3 cm toward the pre-transitional disk of the Herbig Ae star HD 169142. These observations have allowed us to study the millimeter emission of this disk with the highest angular resolution so far (0.″12 × 0.″09, or 14 au × 11 au, at 7 mm). Our 7 and 9 mm images show a narrow ring of emission at a radius of ∼25 au tracing the outer edge of the inner gap. This ring presents an asymmetric morphology that could be produced by dynamical interactions between the disk andmore » forming planets. Additionally, the azimuthally averaged radial intensity profiles of the 7 and 9 mm images confirm the presence of the previously reported gap at ∼45 au and reveal a new gap at ∼85 au. We analyzed archival DCO{sup +}(3–2) and C{sup 18}O(2–1) ALMA observations, showing that the CO snowline is located very close to this third outer gap. This suggests that growth and accumulation of large dust grains close to the CO snowline could be the mechanism responsible for this proposed outer gap. Finally, a compact source of emission is detected at 7 mm, 9 mm, and 3 cm toward the center of the disk. Its flux density and spectral index indicate that it is dominated by free–free emission from ionized gas, which could be associated with the photoionization of the inner disk, an independent object, or an ionized jet.« less

THE STRUCTURE AND STELLAR CONTENT OF THE OUTER DISKS OF GALAXIES: A NEW VIEW FROM THE Pan-STARRS1 MEDIUM DEEP SURVEY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng, Zheng; Thilker, David A.; Heckman, Timothy M.

2015-02-20

We present the results of an analysis of Pan-STARRS1 Medium Deep Survey multi-band (grizy) images of a sample of 698 low-redshift disk galaxies that span broad ranges in stellar mass, star-formation rate, and bulge/disk ratio. We use population synthesis spectral energy distribution fitting techniques to explore the radial distribution of the light, color, surface mass density, mass/light ratio, and age of the stellar populations. We characterize the structure and stellar content of the galaxy disks out to radii of about twice Petrosian r {sub 90}, beyond which the halo light becomes significant. We measure normalized radial profiles for sub-samples ofmore » galaxies in three bins each of stellar mass and concentration. We also fit radial profiles to each galaxy. The majority of galaxies have down-bending radial surface brightness profiles in the bluer bands with a break radius at roughly r {sub 90}. However, they typically show single unbroken exponentials in the reddest bands and in the stellar surface mass density. We find that the mass/light ratio and stellar age radial profiles have a characteristic 'U' shape. There is a good correlation between the amplitude of the down-bend in the surface brightness profile and the rate of the increase in the M/L ratio in the outer disk. As we move from late- to early-type galaxies, the amplitude of the down-bend and the radial gradient in M/L both decrease. Our results imply a combination of stellar radial migration and suppression of recent star formation can account for the stellar populations of the outer disk.« less

Exploring Structures and Variability in the Pre-transitional Disk in HD 169142

NASA Astrophysics Data System (ADS)

Wagner, Kevin Robert; Sitko, Michael L.; Grady, Carol A.; Whitney, Barbara; Swearingen, Jeremy R.; Champney, Elizabeth H.; Johnson, Alexa N.; Warren, Chelsea C.; Russell, Ray W.; Schneider, Glenn; Momose, Muntake; Muto, Takayuki; Inoue, Akio K.; Lauroesch, James Thomas; Hornbeck, Jeremy; Brown, Alexander; Fukagawa, Misato; Currie, Thayne M.; Wisniewski, John P.; Woodgate, Bruce E.

2015-01-01

We present a theoretical modelling analysis of of the structures in the pre-transisitonal disk in HD 169142 using 3D Monte-Carlo radiative transfer simulation. The multi-epoch broadband spectral energy distribution (SED) exhibits clear evidence of changes to the inner (sub-AU) regions of the disk over a maximum timescale of 10 years with the additional constraint that the shadowing of the outer (>25 AU) disk is non-time-dependent. We find that changes to the inner dust rim (0.2 AU) cannot account for this behavior. Instead, we find that if the inner disk posses an optically thin body of small grains then changes to the outer edge of these structures may successfully reproduce the two states in the SED (analogous to what may be occurring due to accretion onto the central star or dynamical clearing by planets). Furthermore, we explore the density distributions of the outer disk structures as they are constrained by the SED and imaged surface brightness profiles, with the conclusion that a mid-plane density power law profile of r^{-2} and r^{-1} for the 35-70 AU and 70-250 AU regions, respectively, may reproduce the observations to the limit of our available complexity of structures within our modelling software. Finally, we find that a 0.3x density scaling of the 35-70 AU region reproduces the second gap imaged in the near-infrared and at 7 mm, strengthening the link to this structure being cleared by one or more planetary mass bodies.This work was supported by NASA ADAP grant NNX09AC73G, Hubble Space Telescope grant HST-GO-13032, the IR&D program at The Aerospace Corporation, and the University of Cincinnati Honors Program.

New insights on the formation and assembly of M83 from deep near-infrared imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barnes, Kate L.; Van Zee, Liese; Dale, Daniel A.

2014-07-10

We present results from new near-infrared (NIR) imaging from the Spitzer Space Telescope that trace the low surface brightness features of the outer disk and stellar stream in the nearby spiral galaxy, M83. Previous observations have shown that M83 hosts a faint stellar stream to the northwest and a star-forming disk that extends to ∼3 times the optical radius (R{sub 25}). By combining the NIR imaging with archival far-ultraviolet (FUV) and H I imaging, we study the star formation history of the system. The NIR surface brightness profile has a break at ∼5.'8 (equivalent to 8.1 kpc and 0.9 R{submore » 25}) with a shallower slope beyond this radius, which may result from the recent accretion of gas onto the outer disk and subsequent star formation. Additionally, the ratio of FUV to NIR flux increases with increasing radius in several arms throughout the extended star forming disk, indicating an increase in the ratio of the present to past star formation rate with increasing radius. This sort of inside-out disk formation is consistent with observations of gas infall onto the outer disk of M83. Finally, the flux, size, and shape of the stellar stream are measured and the origin of the stream is explored. The stream has a total NIR flux of 11.6 mJy, which implies a stellar mass of 1 × 10{sup 8} M{sub ☉} in an area subtending ∼80°. No FUV emission is detected in the stream at a level greater than the noise, confirming an intermediate-age or old stellar population in the stream.« less

THE GRAVITATIONAL INTERACTION BETWEEN PLANETS ON INCLINED ORBITS AND PROTOPLANETARY DISKS AS THE ORIGIN OF PRIMORDIAL SPIN–ORBIT MISALIGNMENTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matsakos, Titos; Königl, Arieh

Many of the observed spin–orbit alignment properties of exoplanets can be explained in the context of the primordial disk misalignment model, in which an initially aligned protoplanetary disk is torqued by a distant stellar companion on a misaligned orbit, resulting in a precessional motion that can lead to large-amplitude oscillations of the spin–orbit angle. We consider a variant of this model in which the companion is a giant planet with an orbital radius of a few astronomical units. Guided by the results of published numerical simulations, we model the dynamical evolution of this system by dividing the disk into inner andmore » outer parts—separated at the location of the planet—that behave as distinct, rigid disks. We show that the planet misaligns the inner disk even as the orientation of the outer disk remains unchanged. In addition to the oscillations induced by the precessional motion, whose amplitude is larger the smaller the initial inner-disk-to-planet mass ratio, the spin–orbit angle also exhibits a secular growth in this case—driven by ongoing mass depletion from the disk—that becomes significant when the inner disk’s angular momentum drops below that of the planet. Altogether, these two effects can produce significant misalignment angles for the inner disk, including retrograde configurations. We discuss these results within the framework of the Stranded Hot Jupiter scenario and consider their implications, including the interpretation of the alignment properties of debris disks.« less

United theory of planet formation (i): Tandem regime

NASA Astrophysics Data System (ADS)

Ebisuzaki, Toshikazu; Imaeda, Yusuke

2017-07-01

The present paper is the first one of a series of papers that present the new united theory of planet formation, which includes magneto-rotational instability and porous aggregation of solid particles in an consistent way. We here describe the ;tandem; planet formation regime, in which a solar system like planetary systems are likely to be produced. We have obtained a steady-state, 1-D model of the accretion disk of a protostar taking into account the magneto-rotational instability (MRI) and and porous aggregation of solid particles. We find that the disk is divided into an outer turbulent region (OTR), a MRI suppressed region (MSR), and an inner turbulent region (ITR). The outer turbulent region is fully turbulent because of MRI. However, in the range, rout(= 8 - 60 AU) from the central star, MRI is suppressed around the midplane of the gas disk and a quiet area without turbulence appears, because the degree of ionization of gas becomes low enough. The disk becomes fully turbulent again in the range rin(= 0.2 - 1 AU), which is called the inner turbulent region, because the midplane temperature become high enough (>1000 K) due to gravitational energy release. Planetesimals are formed through gravitational instability at the outer and inner MRI fronts (the boundaries between the MRI suppressed region (MSR) and the outer and inner turbuent regions) without particle enhancement in the original nebula composition, because of the radial concentration of the solid particles. At the outer MRI front, icy particles grow through low-velocity collisions into porous aggregates with low densities (down to ∼10-5 gcm-3). They eventually undergo gravitational instability to form icy planetesimals. On the other hand, rocky particles accumulate at the inner MRI front, since their drift velocities turn outward due to the local maximum in gas pressure. They undergo gravitational instability in a sub-disk of pebbles to form rocky planetesimals at the inner MRI front. They are likely to be volatile-free because of the high temperature (>1000 K) at this formation site. Such water-free rocky particles may explain the formation of enstatite chondrites, of which the Earth is likely to be primarily composed of. It is also consistent with the model in which the Earth was initially formed as a completely volatile-free planet. The water and other volatile elements came later through the accretion of icy particles by the occasional scatterings in the outer regions. Our new proposed tandem planet formation regime shows that planetesimals are formed at two distinct sites (outer and inner edges of the MRI suppressed region). The former is likely to be the source of outer gas giants and the latter inner rocky planets. The tandem regime also explains the gap in the distribution of solid components (2-4 AU), which is necessary to form a ;solar-system-like; planetary system, which has a relatively small Mars and a very small mass in the main asteroid belt. We found that this tandem regime dose not take place when the vertical magnetic field of the disk five times weaker compared with that we assumed in the present paper, since the outer MRI front shift outward beyond 100 AU. This suggests that yet other regimes exists in our united theory. It may explain the variation observed in exsoplanetary systems by variations in magnetic field and probably angular momentum of the parent molecular cloud.

NGC 1058: Gas motions in an extended, quiescent spiral disk

NASA Technical Reports Server (NTRS)

Hanson, Margaret Murray; Dickey, John M.; Helou, George

1990-01-01

Researchers investigate in detail the motion of gas in the galaxy NGC 1058 using the very large array (VLA) to map the emission in the 21-cm line. This galaxy is so nearly face-on that the contribution to the line width due to the variation of the rotational velocity across the D-array beam is small compared with the random z-motion of the gas. Researchers confirm results of earlier studies (Lewis 1987, A. and A. Suppl., 63, 515; van der Kruit and Shostak 1984, A. and A., 134, 258) of the galaxy's total neutral hydrogen (HI) and kinematics, including the fact that the rotation curve drops faster than Keplerian at the outer edge of the disk, which is interpreted as a fortuitous twist of the plane of rotation in the outer disk. However, their very high velocity resolution (2.58 km s(exp -1) after Hanning smoothing) coupled with good spatial resolution, allows researchers to measure more accurately the line width, and even to some extent its shape, throughout the disk. One of the most interesting results of this study is the remarkable constancy of the line width in the outer disk. From radius 90 to 210 seconds the Gaussian velocity dispersion (sigma sub nu) of the 21-cm line has a mean value of 5.7 km s(exp -1) (after correcting for the spectral resolution) with a dispersion of less than 0.9 km s(exp -1) (after correcting for the spectral resolution) with a dispersion of less than 0.9 km s(exp -1). Translating this directly into a kinetic temperature (Doppler temperature): T sub Dopp equals 121K (sigma sub mu exp 2/(km s(exp -1) (exp 2) gives 4000 K, with a dispersion of less than 1500 K over the outer disk. This constancy is observed even when comparing the spiral arms versus inter-arm regions, which in the radius range from 100 to 150 seconds the surface density modulates (defined as the ratio N sub peak -N sub trough/N sub peak + N sub trough) from 0.5 to 0.25 in the range 150 to 200 seconds.

High-resolution submillimeter and near-infrared studies of the transition disk around Sz 91

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tsukagoshi, Takashi; Momose, Munetake; Hashimoto, Jun

2014-03-10

To reveal the structures of a transition disk around a young stellar object in Lupus, Sz 91 , we have performed aperture synthesis 345 GHz continuum and CO(3-2) observations with the Submillimeter Array (∼1''-3'' resolution) and high-resolution imaging of polarized intensity at the K{sub s} -band using the HiCIAO instrument on the Subaru Telescope (0.''25 resolution). Our observations successfully resolved the inner and outer radii of the dust disk to be 65 and 170 AU, respectively, which indicates that Sz 91 is a transition disk source with one of the largest known inner holes. The model fitting analysis of themore » spectral energy distribution reveals an H{sub 2} mass of 2.4 × 10{sup –3} M {sub ☉} in the cold (T < 30 K) outer part at 65 AU 3 × 10{sup –9} M {sub ☉}) of hot (T ∼ 180 K) dust possibly remains inside the inner hole of the disk. The structure of the hot component could be interpreted as either an unresolved self-luminous companion body (not directly detected in our observations) or a narrow ring inside the inner hole. Significant CO(3-2) emission with a velocity gradient along the major axis of the dust disk is concentrated on the Sz 91 position, suggesting a rotating gas disk with a radius of 420 AU. The Sz 91 disk is possibly a rare disk in an evolutionary stage immediately after the formation of protoplanets because of the large inner hole and the lower disk mass than other transition disks studied thus far.« less

High-Resolution Submillimeter and Near-Infrared Studies of the Transition Disk Around Sz 91

NASA Technical Reports Server (NTRS)

Tsukagoshi, Takashi; Momose, Munetake; Abe, Lyu; Akiyama, Eiji; Brandner, Wolfgang; Brandt, Timothy D.; Carson, Joseph; Currie, Thayne; Egner, Sebastian E.; Goto, Miwa;

Regulation of black-hole accretion by a disk wind during a violent outburst of V404 Cygni

NASA Astrophysics Data System (ADS)

Muñoz-Darias, T.; Casares, J.; Mata Sánchez, D.; Fender, R. P.; Armas Padilla, M.; Linares, M.; Ponti, G.; Charles, P. A.; Mooley, K. P.; Rodriguez, J.

2016-06-01

Accretion of matter onto black holes is universally associated with strong radiative feedback and powerful outflows. In particular, black-hole transients have outflows whose properties are strongly coupled to those of the accretion flow. This includes X-ray winds of ionized material, expelled from the accretion disk encircling the black hole, and collimated radio jets. Very recently, a distinct optical variability pattern has been reported in the transient stellar-mass black hole V404 Cygni, and interpreted as disrupted mass flow into the inner regions of its large accretion disk. Here we report observations of a sustained outer accretion disk wind in V404 Cyg, which is unlike any seen hitherto. We find that the outflowing wind is neutral, has a large covering factor, expands at one per cent of the speed of light and triggers a nebular phase once accretion drops sharply and the ejecta become optically thin. The large expelled mass (>10-8 solar masses) indicates that the outburst was prematurely ended when a sizeable fraction of the outer disk was depleted by the wind, detaching the inner regions from the rest of the disk. The luminous, but brief, accretion phases shown by transients with large accretion disks imply that this outflow is probably a fundamental ingredient in regulating mass accretion onto black holes.

Direct imaging of an asymmetric debris disk in the HD 106906 planetary system

DOE PAGES

Kalas, Paul G.; Rajan, Abhijith; Wang, Jason J.; ...

2015-11-13

Here, we present the first scattered light detections of the HD 106906 debris disk using the Gemini/Gemini Planet Imager in the infrared and Hubble Space Telescope (HST)/Advanced Camera for Surveys in the optical. HD 106906 is a 13 Myr old F5V star in the Sco–Cen association, with a previously detected planet-mass candidate HD 106906b projected 650 AU from the host star. Our observations reveal a near edge-on debris disk that has a central cleared region with radius ~50 AU, and an outer extent >500 AU. The HST data show that the outer regions are highly asymmetric, resembling the "needle" morphologymore » seen for the HD 15115 debris disk. The planet candidate is oriented ~21° away from the position angle of the primary's debris disk, strongly suggesting non-coplanarity with the system. We hypothesize that HD 106906b could be dynamically involved in the perturbation of the primary's disk, and investigate whether or not there is evidence for a circumplanetary dust disk or cloud that is either primordial or captured from the primary. In conclusion, we show that both the existing optical properties and near-infrared colors of HD 106906b are weakly consistent with this possibility, motivating future work to test for the observational signatures of dust surrounding the planet.« less

Regulation of black-hole accretion by a disk wind during a violent outburst of V404 Cygni.

PubMed

Muñoz-Darias, T; Casares, J; Mata Sánchez, D; Fender, R P; Armas Padilla, M; Linares, M; Ponti, G; Charles, P A; Mooley, K P; Rodriguez, J

2016-06-02

Accretion of matter onto black holes is universally associated with strong radiative feedback and powerful outflows. In particular, black-hole transients have outflows whose properties are strongly coupled to those of the accretion flow. This includes X-ray winds of ionized material, expelled from the accretion disk encircling the black hole, and collimated radio jets. Very recently, a distinct optical variability pattern has been reported in the transient stellar-mass black hole V404 Cygni, and interpreted as disrupted mass flow into the inner regions of its large accretion disk. Here we report observations of a sustained outer accretion disk wind in V404 Cyg, which is unlike any seen hitherto. We find that the outflowing wind is neutral, has a large covering factor, expands at one per cent of the speed of light and triggers a nebular phase once accretion drops sharply and the ejecta become optically thin. The large expelled mass (>10(-8) solar masses) indicates that the outburst was prematurely ended when a sizeable fraction of the outer disk was depleted by the wind, detaching the inner regions from the rest of the disk. The luminous, but brief, accretion phases shown by transients with large accretion disks imply that this outflow is probably a fundamental ingredient in regulating mass accretion onto black holes.

Inner Super-Earths, Outer Gas Giants: How Pebble Isolation and Migration Feedback Keep Jupiters Cold

NASA Astrophysics Data System (ADS)

Fung, Jeffrey; Lee, Eve J.

2018-06-01

The majority of gas giants (planets of masses ≳102 M ⊕) are found to reside at distances beyond ∼1 au from their host stars. Within 1 au, the planetary population is dominated by super-Earths of 2–20 M ⊕. We show that this dichotomy between inner super-Earths and outer gas giants can be naturally explained should they form in nearly inviscid disks. In laminar disks, a planet can more easily repel disk gas away from its orbit. The feedback torque from the pile-up of gas inside the planet’s orbit slows down and eventually halts migration. A pressure bump outside the planet’s orbit traps pebbles and solids, starving the core. Gas giants are born cold and stay cold: more massive cores are preferentially formed at larger distances, and they barely migrate under disk feedback. We demonstrate this using two-dimensional hydrodynamical simulations of disk–planet interaction lasting up to 105 years: we track planet migration and pebble accretion until both come to an end by disk feedback. Whether cores undergo runaway gas accretion to become gas giants or not is determined by computing one-dimensional gas accretion models. Our simulations show that in an inviscid minimum mass solar nebula, gas giants do not form inside ∼0.5 au, nor can they migrate there while the disk is present. We also explore the dependence on disk mass and find that gas giants form further out in less massive disks.

Studies of Disks Around the Sun and Other Stars

NASA Technical Reports Server (NTRS)

Stern, S. Alan (Principal Investigator)

1996-01-01

We are conducting research designed to enhance our understanding of the evolution and detectability of comet clouds and disks. This area holds promise for also improving our understanding of outer solar system formation, the bombardment history of the planets, the transport of volatiles and organics from the outer solar system to the inner planets, and to the ultimate fate of comet clouds around the Sun and other stars. According to 'standard' theory, both the Kuiper Disk and the Oort Cloud are (at least in part) natural products of the planetary accumulation stage of solar system formation. One expects such assemblages to be a common attribute of other solar systems. Therefore, searches for comet disks and clouds orbiting other stars offer a new method for inferring the presence of planetary systems. This two-element program consists modeling collisions in the Kuiper Disk and the dust disks around other stars. The modeling effort focuses on moving from our simple, first-generation, Kuiper disk collision rate model, to a time-dependent, second-generation model that incorporates physical collisions, velocity evolution, dynamical erosion, and various dust transport mechanisms. This second generation model will be used to study the evolution of surface mass density and the object-size spectrum in the disk. The observational effort focuses on obtaining submm/mm-wave flux density measurements of 25-30 IR excess stars in order to better constrain the masses, spatial extents and structure of their dust ensembles.

Multimodal imaging in a case of bilateral outer retinitis associated with mumps infection.

PubMed

Kahloun, Rim; Ben Amor, Hager; Ksiaa, Imen; Zina, Sourour; Jelliti, Bechir; Ben Yahia, Salim; Khairallah, Moncef

2018-02-01

To report the results of multimodal imaging of acute outer retinitis associated to mumps infection. A patient with mumps-associated outer retinitis evaluated by color fundus photography, spectral domain optical coherence tomography (SD-OCT), optical coherence tomography angiography, fundus autofluorescence (FAF), fluorescein angiography (FA), and indocyanine green angiography (ICGA). We report a case of a 12-year-old boy who developed bilateral outer retinitis related to mumps. Ophthalmoscopy showed confluent areas of outer retinitis involving the posterior pole and the periphery with a centrifugal gyrate pattern. SD-OCT revealed a marked disorganization of the outer retinal layers with multiple highly reflective spicules. FA shows diffuse late hyperfluorescence with optic disk staining. ICGA shows macular and peripheral hyperfluorescent lesions with a geographical pattern in the late phases. The patient was treated with acyclovir and oral prednisone. Four weeks after presentation visual acuity remained unchanged, and retinal changes seen at the acute phase had resolved leading to extensive retinal atrophy and optic disk pallor. SD-OCT showed atrophy of the retinal pigment epithelial and outer retinal layers. FAF revealed scattered hyperautofluorescent lesions. Electrophysiology showed generalized retinal dysfunction. Mumps infection should be considered in the differential diagnosis of bilateral necrotizing outer retinitis in children and young adults. A multimodal imaging approach may help distinguish mumps-associated retinitis from other causes of viral retinitis and facilitate appropriate management.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kalas, Paul G.; Rajan, Abhijith; Wang, Jason J.

Here, we present the first scattered light detections of the HD 106906 debris disk using the Gemini/Gemini Planet Imager in the infrared and Hubble Space Telescope (HST)/Advanced Camera for Surveys in the optical. HD 106906 is a 13 Myr old F5V star in the Sco–Cen association, with a previously detected planet-mass candidate HD 106906b projected 650 AU from the host star. Our observations reveal a near edge-on debris disk that has a central cleared region with radius ~50 AU, and an outer extent >500 AU. The HST data show that the outer regions are highly asymmetric, resembling the "needle" morphologymore » seen for the HD 15115 debris disk. The planet candidate is oriented ~21° away from the position angle of the primary's debris disk, strongly suggesting non-coplanarity with the system. We hypothesize that HD 106906b could be dynamically involved in the perturbation of the primary's disk, and investigate whether or not there is evidence for a circumplanetary dust disk or cloud that is either primordial or captured from the primary. In conclusion, we show that both the existing optical properties and near-infrared colors of HD 106906b are weakly consistent with this possibility, motivating future work to test for the observational signatures of dust surrounding the planet.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kalas, Paul G.; Wang, Jason J.; Duchene, Gaspard

We present the first scattered light detections of the HD 106906 debris disk using the Gemini/Gemini Planet Imager in the infrared and Hubble Space Telescope (HST)/Advanced Camera for Surveys in the optical. HD 106906 is a 13 Myr old F5V star in the Sco–Cen association, with a previously detected planet-mass candidate HD 106906b projected 650 AU from the host star. Our observations reveal a near edge-on debris disk that has a central cleared region with radius ∼50 AU, and an outer extent >500 AU. The HST data show that the outer regions are highly asymmetric, resembling the “needle” morphology seenmore » for the HD 15115 debris disk. The planet candidate is oriented ∼21° away from the position angle of the primary’s debris disk, strongly suggesting non-coplanarity with the system. We hypothesize that HD 106906b could be dynamically involved in the perturbation of the primary’s disk, and investigate whether or not there is evidence for a circumplanetary dust disk or cloud that is either primordial or captured from the primary. We show that both the existing optical properties and near-infrared colors of HD 106906b are weakly consistent with this possibility, motivating future work to test for the observational signatures of dust surrounding the planet.« less

The Dragonfly Nearby Galaxies Survey. IV. A Giant Stellar Disk in NGC 2841

NASA Astrophysics Data System (ADS)

Zhang, Jielai; Abraham, Roberto; van Dokkum, Pieter; Merritt, Allison; Janssens, Steven

2018-03-01

Neutral gas is commonly believed to dominate over stars in the outskirts of galaxies, and investigations of the disk-halo interface are generally considered to be in the domain of radio astronomy. This may simply be a consequence of the fact that deep H I observations typically probe to a lower-mass surface density than visible wavelength data. This paper presents low-surface-brightness, optimized visible wavelength observations of the extreme outskirts of the nearby spiral galaxy NGC 2841. We report the discovery of an enormous low-surface brightness stellar disk in this object. When azimuthally averaged, the stellar disk can be traced out to a radius of ∼70 kpc (5 R 25 or 23 inner disk scale lengths). The structure in the stellar disk traces the morphology of H I emission and extended UV emission. Contrary to expectations, the stellar mass surface density does not fall below that of the gas mass surface density at any radius. In fact, at all radii greater than ∼20 kpc, the ratio of the stellar mass to gas mass surface density is a constant 3:1. Beyond ∼30 kpc, the low-surface-brightness stellar disk begins to warp, which may be an indication of a physical connection between the outskirts of the galaxy and infall from the circumgalactic medium. A combination of stellar migration, accretion, and in situ star formation might be responsible for building up the outer stellar disk, but whatever mechanisms formed the outer disk must also explain the constant ratio between stellar and gas mass in the outskirts of this galaxy.

On Shocks Driven by High-mass Planets in Radiatively Inefficient Disks. III. Observational Signatures in Thermal Emission and Scattered Light

NASA Astrophysics Data System (ADS)

Hord, Blake; Lyra, Wladimir; Flock, Mario; Turner, Neal J.; Mac Low, Mordecai-Mark

2017-11-01

Recent observations of the protoplanetary disk around the Herbig Be star HD 100546 show two bright features in infrared (H and {L}{\\prime } bands) at about 50 au,with one so far unexplained. We explore the observational signatures of a high-mass planet causing shock heating in order to determine if it could be the source of the unexplained infrared feature in HD 100546. More fundamentally, we identify and characterize planetary shocks as an extra, hitherto ignored, source of luminosity in transition disks. The RADMC-3D code is used to perform dust radiative transfer calculations on the hydrodynamical disk models, including volumetric heating. A stronger shock heating rate by a factor of 20 would be necessary to qualitatively reproduce the morphology of the second infrared source. Instead, we find that the outer edge of the gap carved by the planet heats up by about 50% relative to the initial reference temperature, which leads to an increase in the scale height. The bulge is illuminated by the central star, producing a lopsided feature in scattered light, as the outer gap edge shows an asymmetry in density and temperature attributable to a secondary spiral arm launched not from the Lindblad resonances but from the 2:1 resonance. We conclude that high-mass planets lead to shocks in disks that may be directly observed, particularly at wavelengths of 10 μm or longer, but that they are more likely to reveal their presence in scattered light by puffing up their outer gap edges and exciting multiple spiral arms.

Unlocking CO Depletion in Protoplanetary Disks. I. The Warm Molecular Layer

NASA Astrophysics Data System (ADS)

Schwarz, Kamber R.; Bergin, Edwin A.; Cleeves, L. Ilsedore; Zhang, Ke; Öberg, Karin I.; Blake, Geoffrey A.; Anderson, Dana

2018-03-01

CO is commonly used as a tracer of the total gas mass in both the interstellar medium and in protoplanetary disks. Recently, there has been much debate about the utility of CO as a mass tracer in disks. Observations of CO in protoplanetary disks reveal a range of CO abundances, with measurements of low CO to dust mass ratios in numerous systems. One possibility is that carbon is removed from CO via chemistry. However, the full range of physical conditions conducive to this chemical reprocessing is not well understood. We perform a systematic survey of the time dependent chemistry in protoplanetary disks for 198 models with a range of physical conditions. We vary dust grain size distribution, temperature, comic-ray and X-ray ionization rates, disk mass, and initial water abundance, detailing what physical conditions are necessary to activate the various CO depletion mechanisms in the warm molecular layer. We focus our analysis on the warm molecular layer in two regions: the outer disk (100 au) well outside the CO snowline and the inner disk (19 au) just inside the midplane CO snowline. After 1 Myr, we find that the majority of models have a CO abundance relative to H2 less than 10‑4 in the outer disk, while an abundance less than 10‑5 requires the presence of cosmic-rays. Inside the CO snowline, significant depletion of CO only occurs in models with a high cosmic-ray rate. If cosmic-rays are not present in young disks, it is difficult to chemically remove carbon from CO. Additionally, removing water prior to CO depletion impedes the chemical processing of CO. Chemical processing alone cannot explain current observations of low CO abundances. Other mechanisms must also be involved.

Differential distribution of proteins and lipids in detergent-resistant and detergent-soluble domains in rod outer segment plasma membranes and disks.

PubMed

Elliott, Michael H; Nash, Zack A; Takemori, Nobuaki; Fliesler, Steven J; McClellan, Mark E; Naash, Muna I

2008-01-01

Membrane heterogeneity plays a significant role in regulating signal transduction and other cellular activities. We examined the protein and lipid components associated with the detergent-resistant membrane (DRM) fractions from retinal rod outer segment (ROS) disk and plasma membrane-enriched preparations. Proteomics and correlative western blot analysis revealed the presence of alpha and beta subunits of the rod cGMP-gated ion channel and glucose transporter type 1, among other proteins. The glucose transporter was present exclusively in ROS plasma membrane (not disks) and was highly enriched in DRMs, as was the cGMP-gated channel beta-subunit. In contrast, the majority of rod opsin and ATP-binding cassette transporter A4 was localized to detergent-soluble domains in disks. As expected, the cholesterol : fatty acid mole ratio was higher in DRMs than in the corresponding parent membranes (disk and plasma membranes, respectively) and was also higher in disks compared to plasma membranes. Furthermore, the ratio of saturated : polyunsaturated fatty acids was also higher in DRMs compared to their respective parent membranes (disk and plasma membranes). These results confirm that DRMs prepared from both disks and plasma membranes are enriched in cholesterol and in saturated fatty acids compared to their parent membranes. The dominant fatty acids in DRMs were 16 : 0 and 18 : 0; 22 : 6n3 and 18 : 1 levels were threefold higher and twofold lower, respectively, in disk-derived DRMs compared to plasma membrane-derived DRMs. We estimate, based on fatty acid recovery that DRMs account for only approximately 8% of disks and approximately 12% of ROS plasma membrane.

The Dynamical Structure of HR 8799's Inner Debris Disk

NASA Astrophysics Data System (ADS)

Contro, B.; Wittenmyer, Robert A.; Horner, J.; Marshall, Jonathan P.

2015-06-01

The HR 8799 system, with its four giant planets and two debris belts, has an architecture closely mirroring that of our Solar system where the inner, warm asteroid belt and outer, cool Edgeworth-Kuiper belt bracket the giant planets. As such, it is a valuable laboratory for examining exoplanetary dynamics and debris disk-exoplanet interactions. Whilst the outer debris belt of HR 8799 has been well resolved by previous observations, the spatial extent of the inner disk remains unknown. This leaves a significant question mark over both the location of the planetesimals responsible for producing the belt's visible dust and the physical properties of those grains. We have performed the most extensive simulations to date of the inner, unresolved debris belt around HR 8799, using UNSW Australia's Katana supercomputing facility to follow the dynamical evolution of a model inner disk comprising 300,298 particles for a period of 60 Ma. These simulations have enabled the characterisation of the extent and structure of the inner disk in detail, and will in future allow us to provide a first estimate of the small-body impact rate and water delivery prospects for possible (as-yet undetected) terrestrial planet (s) in the inner system.

The Dynamical Structure of HR 8799's Inner Debris Disk.

PubMed

Contro, B; Wittenmyer, Robert A; Horner, J; Marshall, Jonathan P

2015-06-01

The HR 8799 system, with its four giant planets and two debris belts, has an architecture closely mirroring that of our Solar system where the inner, warm asteroid belt and outer, cool Edgeworth-Kuiper belt bracket the giant planets. As such, it is a valuable laboratory for examining exoplanetary dynamics and debris disk-exoplanet interactions. Whilst the outer debris belt of HR 8799 has been well resolved by previous observations, the spatial extent of the inner disk remains unknown. This leaves a significant question mark over both the location of the planetesimals responsible for producing the belt's visible dust and the physical properties of those grains. We have performed the most extensive simulations to date of the inner, unresolved debris belt around HR 8799, using UNSW Australia's Katana supercomputing facility to follow the dynamical evolution of a model inner disk comprising 300,298 particles for a period of 60 Ma. These simulations have enabled the characterisation of the extent and structure of the inner disk in detail, and will in future allow us to provide a first estimate of the small-body impact rate and water delivery prospects for possible (as-yet undetected) terrestrial planet (s) in the inner system.

Explaining the Birth of the Martian Moons

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2016-09-01

A new study examines the possibility that Marss two moons formed after a large body slammed into Mars, creating a disk of debris. This scenario might be the key to reconciling the moons orbital properties with their compositions.Conflicting EvidenceThe different orbital (left) and spectral (right) characteristics of the Martian moons in the three different formation scenarios. Click for a better look! Phobos and Deimoss orbital characteristics are best matched by formation around Mars (b and c), and their physical characteristics are best matched by formation in the outer region of an impact-generated accretion disk (rightmost panel of c). [Ronnet et al. 2016]How were Marss two moons, Phobos and Deimos, formed? There are three standing theories:Two already-formed, small bodies from the outer main asteroid belt were captured by Mars, intact.The bodies formed simultaneously with Mars, by accretion from the same materials.A large impact on Mars created an accretion disk of material from which the two bodies formed.Our observations of the Martian moons, unfortunately, provide conflicting evidence about which of these scenarios is correct. The physical properties of the moons low albedos, low densities are consistent with those of asteroids in our solar system, and are not consistent with Marss properties, suggesting that the co-accretion scenario is unlikely. On the other hand, the moons orbital properties low inclination, low eccentricity, prograde orbits are consistent with bodies that formed around Mars rather than being captured.In a recent study,a team of scientists led by Thomas Ronnet and Pierre Vernazza (Aix-Marseille University, Laboratory of Astrophysics of Marseille) has attempted to reconcile these conflictingobservations by focusing on the third option.Moons After a Large ImpactIn the thirdscenario, an impactor of perhaps a few percent of Marss mass smashed into Mars, forming a debris disk of hot material that encircled Mars. Perturbations in the disk then led to the formation of large clumps, which eventually agglomerated to form Phobos and Deimos.The authors find that Phobos and Deimos most likely formed in the outer regions of the accretion disk that was created by a large impact with Mars. [Adapted from Ronnet et al. 2016]In the study conducted by Ronnet, Vernazza, and collaborators, the authors investigated the composition and texture of the dust that would have crystallized in an impact-generated accretion disk making up Marss moons. They find that Phobos and Deimos could not have formed out of the extremely hot, magma-filled inner regions of such a disk, because this would have resulted in different compositions than we observe.Phobos and Deimos could have formed, however, in the very outer part of an impact-generated accretion disk, where the hot gas condensed directly into small solid grains instead of passing through the magma phase. Accretion of such tiny grains would naturally explain the similarity in physical properties we observe between Marss moons and some main-belt asteroids and yet this picture is also consistent with the moons current orbital parameters.The authors argue that the formation of the Martian moons from the outer regions of an impact-generated accretion disk is therefore a plausible scenario, neatly reconciling the observed physical properties of Phobos and Diemos with their orbital properties.CitationT. Ronnet et al 2016 ApJ 828 109. doi:10.3847/0004-637X/828/2/109

The Diversity of Carbon in Cometary Refractory Dust Particles

NASA Technical Reports Server (NTRS)

Wooden, D. H.

2018-01-01

When comparing the dark icy surfaces of outer solar system small bodies and the composition of carbonaceous chondrites derived from dark asteroids we find a significant discrepancy in the assessed amounts of elemental carbon: up to 80% amorphous carbon is used to model the dark surfaces of Kuiper Belt Objects and Centaurs whereas at most 5% of elemental carbon is found in carbonaceous chondrites. If we presume that regimes of comet nuclei formation are analogous to disk regimes where other outer solar system ice-rich bodies formed then we can turn to comet dust to gain insights into the diversity in the concentration and forms of carbon available in the outer disk. Comet dust offers important insights into the diversity in the amounts and forms of carbon that were incorporated into aggregate dust particles in the colder parts of the protoplanetary disk out of which comet nuclei accreted. Comet nuclei are amongst the most primitive bodies because they have remained cold and unequilibrated. Comet dust particles reveal the presence of forms of elemental carbon and of soluble and insoluble organic matter, and in a great diversity of concentrations from very little, e.g., Stardust samples of comet 81P/Wild 2, to 80% by volume for Ultra Carbonaceous Antarctic Micro Meteorites (UCAMMs). Cometary outbursts and/or jet activity also demonstrate variations in the concentration of carbon in the grains at different grain sizes within a single comet. We review the diversity of carbon-bearing dust grains in cometary samples, flyby measurements and deduced from remote-sensing to enrich the discussion about the diversity of carbonaceous matter available in the outer ice-rich disk at the time of comet nuclei formation.

Polarized Disk Emission from Herbig Ae/Be Stars Observed Using Gemini Planet Imager: HD 144432, HD 150193, HD 163296, and HD 169142

DOE Office of Scientific and Technical Information (OSTI.GOV)

Monnier, John D.; Aarnio, Alicia; Adams, Fred C.

In order to look for signs of ongoing planet formation in young disks, we carried out the first J -band polarized emission imaging of the Herbig Ae/Be stars HD 150193, HD 163296, and HD 169142 using the Gemini Planet Imager, along with new H band observations of HD 144432. We confirm the complex “double ring” structure for the nearly face-on system HD 169142 first seen in H -band, finding the outer ring to be substantially redder than the inner one in polarized intensity. Using radiative transfer modeling, we developed a physical model that explains the full spectral energy distribution andmore » J - and H -band surface brightness profiles, suggesting that the differential color of the two rings could come from reddened starlight traversing the inner wall and may not require differences in grain properties. In addition, we clearly detect an elongated, off-center ring in HD 163296 (MWC 275), locating the scattering surface to be 18 au above the midplane at a radial distance of 77 au, co-spatial with a ring seen at 1.3 mm by ALMA linked to the CO snow line. Lastly, we report a weak tentative detection of scattered light for HD 150193 (MWC 863) and a non-detection for HD 144432; the stellar companion known for each of these targets has likely disrupted the material in the outer disk of the primary star. For HD 163296 and HD 169142, the prominent outer rings we detect could be evidence for giant planet formation in the outer disk or a manifestation of large-scale dust growth processes possibly related to snow-line chemistry.« less

The HD 163296 Circumstellar Disk in Scattered Light: Evidence of Time-Variable Self-Shadowing

NASA Technical Reports Server (NTRS)

Wisniewski, John P.; Clampin, Mark; Grady, Carol A.; Ardila, David R.; Ford, Holland C.; Golimowski, David A.; Illingworth, Garth D.; Krist, John E.

2008-01-01

We present the first multi-color view of the scattered light disk of the Herbig Ae star HD 163296, based on coronagraphic observations from the Hubble Space Telescope Advanced Camera for Surveys (ACS). Radial profile fits of the surface brightness along the disk's semi-major axis indicates that the disk is not continuously flared, and extends to approx.540 AU. The disk's color (V-I)=1.1 at a radial distance of 3.5" is redder than the observed stellar color (V-I)=0.15. This red disk color might be indicative of either an evolution in the grain size distribution (i.e. grain growth) and/or composition, both of which would be consistent with the observed non-flared geometry of the outer disk. We also identify a single ansa morphological structure in our F435W ACS data, which is absent from earlier epoch F606W and F814W ACS data, but corresponds to one of the two ansa observed in archival HST STIS coronagraphic data. Following transformation to similar band-passes, we find that the scattered light disk of HD 163296 is 1 mag arcsec(sup -2) fainter at 3.5" in the STIS data than in the ACS data. Moreover, variations are seen in (i) the visibility of the ansa(e) structures, in (ii) the relative surface brightness of the ansa(e) structures, and in (iii) the (known) intrinsic polarization of the system. These results indicate that the scattered light from the HD 163296 disk is variable. We speculate that the inner disk wall, which Sitko et al. suggests has a variable scale height as diagnosed by near-IR SED variability, induces variable self-shadowing of the outer disk. We further speculate that the observed surface brightness variability of the ansa(e) structures may indicate that the inner disk wall is azimuthally asymmetric. Subject headings: circumstellar matter - stars: individual (HD 163296) - planetary systems: formation - planetary systems: protoplanetary disks

Connecting Stellar Substructures to the Oscillating Disk: Monoceros and A13

NASA Astrophysics Data System (ADS)

Sheffield, Allyson; Tzanidakis, Anastasios; Johnston, Kathryn; Price-Whelan, Adrian

2018-01-01

Recent observations of stellar substructures in the Milky Way have challenged our view of where the traditional disk ends. By assessing the stellar populations in a stellar feature, particularly the fraction of RR Lyrae to M giant stars, an accretion scenario can be ruled out in favor of a kicked-out disk origin. A more definitive distinction can be made with the inclusion of high-resolution abundances. I will present evidence that two low latitude stellar substructures, the Monoceros Ring and A13, originated in the Galactic disk and were kicked out to their current location, in the outer regions of the stellar disk, due to a dynamic perturbation to the disk.

Unraveling the Helix Nebula: Its Structure and Knots

NASA Astrophysics Data System (ADS)

O'Dell, C. R.; McCullough, Peter R.; Meixner, Margaret

2004-11-01

Through Hubble Space Telescope (HST) imaging of the inner part of the main ring of the Helix Nebula, together with CTIO 4 m images of the fainter outer parts, we have a view of unprecedented quality of the nearest bright planetary nebula. These images have allowed us to determine that the main ring of the nebula is composed of an inner disk of about 499" diameter (0.52 pc) surrounded by an outer ring (in reality a torus) of 742" diameter (0.77 pc) whose plane is highly inclined to the plane of the disk. This outer ring is surrounded by an outermost ring of 1500" (1.76 pc) diameter, which is flattened on the side colliding with the ambient interstellar medium. The inner disk has an extended distribution of low-density gas along its rotational axis of symmetry, and the disk is optically thick to ionizing radiation, as is the outer ring. Published radial velocities of the knots provide support for the two-component structure of the main ring of the nebula and for the idea that the knots found there are expanding along with the nebular material from which they recently originated. These velocities indicate a spatial expansion velocity of the inner disk of 40 and 32 km s-1 for the outer ring, which yields expansion ages of 6560 and 12,100 yr, respectively. The outermost ring may be partially ionized through scattered recombination continuum from the inner parts of the nebula, but shocks certainly are occurring in it. This outermost ring probably represents a third period of mass loss by the central star. There is one compact, outer object that is unexplained, showing shock structures indicating a different orientation of the gas flow from that of the nebula. There is a change in the morphology of the knots as a function of the distance from the local ionization front. This supports a scenario in which the knots are formed in or near the ionization front and are then sculpted by the stellar radiation from the central star as the ionization front advances beyond them. Based in part on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Based in part on observations obtained at the Cerro Tololo Inter-American Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a Cooperative Agreement with the National Science Foundation.

Hubble Space Telescope observations of the dwarf Nova Z Chamaeleontis through two eruption cycles

NASA Technical Reports Server (NTRS)

Robinson, E. L.; Wood, Janet H.; Bless, R. C.; Clemens, J. C.; Dolan, J. F.; Elliot, J. L.; Nelson, M. J.; Percival, J. W.; Taylor, M. J.; Van Citters, G. W.

1995-01-01

We have obtained the first high-speed photometry of the eclipsing dwarf nova Z Cha at ultraviolet wavelengths with the Hubble Space Telescope (HST). We observed the eclipse roughly every 4 days over two cycles of the normal eruptions of Z Cha, giving a uniquely complete coverage of its outburst cycle. The accretion disk dominated the ultraviolet light curve of Z Cha at the peak of an eruption; the white dwarf, the bright spot on the edge of the disk, and the boundary layer were all invisible. We were able to obtain an axisymmetric map of the accretion disk at this time only by adopting a flared disk with an opening angle of approximately 8 deg. The run of brightness temperature with radius in the disk at the peak of the eruption was too flat to be consistent with a steady state, optically thick accretion disk. The local rate of mass flow through the disk was approximately 5 x 10(exp -10) solar masses/yr near the center of the disk and approximately 5 x 10(exp -9) solar masses/yr near the outer edge. The white dwarf, the accretion disk, and the boundary layer were all significant contributors to the ultraviolet flux on the descending branches of the eruptions. The temperature of the white dwarf during decline was 18,300 K less than T(sub wd) less than 21,800 K, which is significantly greater than at minimum light. Six days after the maximum of an eruption Z Cha has faded to near minimum light at ultraviolet wavelenghts, but was still approximately 70% brighter at minimum light in the B band. About one-quarter of the excess flux in the B band came from the accretion disk. Thus, the accretion disk faded and became invisible at ultraviolet wavelengths before it faded at optical wavelenghts. The disk did, however, remain optically thick and obscured the lower half of the white dwarf at ultraviolet and possibly at optical wavelenghts for 2 weeks after the eruption ended. By the third week after eruptiuons the eclipse looked like a simple occultation of an unobscured, spherical white dwarf by a dark secondary star. The center of the accretion disk was, therfore, optically thin at ultraviolet wavelenghts and the boundary layer was too faint to be visible.

Herschel's "Cold Debris Disks": Background Galaxies or Quiescent Rims of Planetary Systems?

NASA Technical Reports Server (NTRS)

Krivov, A. V.; Eiroa, C.; Loehne, T.; Marshall, J. P.; Montesinos, B.; DelBurgo, C.; Absil, O.; Ardila, D.; Augereau, J.-C.; Bayo, A.;

Herschel's "Cold Debris Disks": Background Galaxies or Quiescent Rims of Planetary Systems?

NASA Astrophysics Data System (ADS)

Krivov, A. V.; Eiroa, C.; Löhne, T.; Marshall, J. P.; Montesinos, B.; del Burgo, C.; Absil, O.; Ardila, D.; Augereau, J.-C.; Bayo, A.; Bryden, G.; Danchi, W.; Ertel, S.; Lebreton, J.; Liseau, R.; Mora, A.; Mustill, A. J.; Mutschke, H.; Neuhäuser, R.; Pilbratt, G. L.; Roberge, A.; Schmidt, T. O. B.; Stapelfeldt, K. R.; Thébault, Ph.; Vitense, Ch.; White, G. J.; Wolf, S.

2013-07-01

Infrared excesses associated with debris disk host stars detected so far peak at wavelengths around ~100 μm or shorter. However, 6 out of 31 excess sources studied in the Herschel Open Time Key Programme, DUNES, have been seen to show significant—and in some cases extended—excess emission at 160 μm, which is larger than the 100 μm excess. This excess emission has been attributed to circumstellar dust and has been suggested to stem from debris disks colder than those known previously. Since the excess emission of the cold disk candidates is extremely weak, challenging even the unrivaled sensitivity of Herschel, it is prudent to carefully consider whether some or even all of them may represent unrelated galactic or extragalactic emission, or even instrumental noise. We re-address these issues using several distinct methods and conclude that it is highly unlikely that none of the candidates represents a true circumstellar disk. For true disks, both the dust temperatures inferred from the spectral energy distributions and the disk radii estimated from the images suggest that the dust is nearly as cold as a blackbody. This requires the grains to be larger than ~100 μm, even if they are rich in ices or are composed of any other material with a low absorption in the visible. The dearth of small grains is puzzling, since collisional models of debris disks predict that grains of all sizes down to several times the radiation pressure blowout limit should be present. We explore several conceivable scenarios: transport-dominated disks, disks of low dynamical excitation, and disks of unstirred primordial macroscopic grains. Our qualitative analysis and collisional simulations rule out the first two of these scenarios, but show the feasibility of the third one. We show that such disks can indeed survive for gigayears, largely preserving the primordial size distribution. They should be composed of macroscopic solids larger than millimeters, but smaller than a few kilometers in size. If larger planetesimals were present, then they would stir the disk, triggering a collisional cascade and thus causing production of small debris, which is not seen. Thus, planetesimal formation, at least in the outer regions of the systems, has stopped before "cometary" or "asteroidal" sizes were reached.

Disk-loss and disk-renewal phases in classical Be stars. II. Contrasting with stable and variable disks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Draper, Zachary H.; Wisniewski, John P.; Bjorkman, Karen S.

2014-05-10

Recent observational and theoretical studies of classical Be stars have established the utility of polarization color diagrams (PCDs) in helping to constrain the time-dependent mass decretion rates of these systems. We expand on our pilot observational study of this phenomenon, and report the detailed analysis of a long-term (1989-2004) spectropolarimetric survey of nine additional classical Be stars, including systems exhibiting evidence of partial disk-loss/disk-growth episodes as well as systems exhibiting long-term stable disks. After carefully characterizing and removing the interstellar polarization along the line of sight to each of these targets, we analyze their intrinsic polarization behavior. We find thatmore » many steady-state Be disks pause at the top of the PCD, as predicted by theory. We also observe sharp declines in the Balmer jump polarization for later spectral type, near edge-on steady-state disks, again as recently predicted by theory, likely caused when the base density of the disk is very high, and the outer region of the edge-on disk starts to self absorb a significant number of Balmer jump photons. The intrinsic V-band polarization and polarization position angle of γ Cas exhibits variations that seem to phase with the orbital period of a known one-armed density structure in this disk, similar to the theoretical predictions of Halonen and Jones. We also observe stochastic jumps in the intrinsic polarization across the Balmer jump of several known Be+sdO systems, and speculate that the thermal inflation of part of the outer region of these disks could be responsible for producing this observational phenomenon. Finally, we estimate the base densities of this sample of stars to be between ≈8 × 10{sup –11} and ≈4 × 10{sup –12} g cm{sup –3} during quasi steady state periods given there maximum observed polarization.« less

Variety in planetary systems

NASA Technical Reports Server (NTRS)

Wetherill, George W.

1993-01-01

Observation of circumstellar disks, regular satellite systems of outer planets, and planet-size objects orbiting pulsars support the supposition that formation of planetary systems is a robust, rather than a fragile, byproduct of the formation and evolution of stars. The extent to which these systems may be expected to resemble one another and our Solar System, either in overall structure or in detail remains uncertain. When the full range of possible stellar masses, disk masses, and initial specific angular momenta are considered, the possible variety of planetary configurations is very large. Numerical modeling indicates a difference between the formation of small, inner, terrestrial planets and the outer planets.

Cepheid variables in the flared outer disk of our galaxy.

PubMed

Feast, Michael W; Menzies, John W; Matsunaga, Noriyuki; Whitelock, Patricia A

2014-05-15

Flaring and warping of the disk of the Milky Way have been inferred from observations of atomic hydrogen but stars associated with flaring have not hitherto been reported. In the area beyond the Galactic centre the stars are largely hidden from view by dust, and the kinematic distances of the gas cannot be estimated. Thirty-two possible Cepheid stars (young pulsating variable stars) in the direction of the Galactic bulge were recently identified. With their well-calibrated period-luminosity relationships, Cepheid stars are useful distance indicators. When observations of these stars are made in two colours, so that their distance and reddening can be determined simultaneously, the problems of dust obscuration are minimized. Here we report that five of the candidates are classical Cepheid stars. These five stars are distributed from approximately one to two kiloparsecs above and below the plane of the Galaxy, at radial distances of about 13 to 22 kiloparsecs from the centre. The presence of these relatively young (less than 130 million years old) stars so far from the Galactic plane is puzzling, unless they are in the flared outer disk. If so, they may be associated with the outer molecular arm.

ABUNDANCES OF PLANETARY NEBULAE IN THE OUTER DISK OF M31

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kwitter, Karen B.; Lehman, Emma M. M.; Balick, Bruce

2012-07-01

We present spectroscopic observations and chemical abundances of 16 planetary nebulae (PNe) in the outer disk of M31. The [O III] {lambda}4363 line is detected in all objects, allowing a direct measurement of the nebular temperature essential for accurate abundance determinations. Our results show that the abundances in these M31 PNe display the same correlations and general behaviors as Type II PNe in the Milky Way. We also calculate photoionization models to derive estimates of central star properties. From these we infer that our sample PNe, all near the bright-end cutoff of the planetary nebula luminosity function, originated from starsmore » near 2 M{sub Sun }. Finally, under the assumption that these PNe are located in M31's disk, we plot the oxygen abundance gradient, which appears shallower than the gradient in the Milky Way.« less

Images of the Extended Outer Regions of the Debris Ring around HR 4796 A

NASA Technical Reports Server (NTRS)

Thalmann, C.; Janson, M.; Buenzli, E.; Brandt, T. D.; Wisniewski, J. P.; Moro-Martin, A.; Usuda, T.; Schneider, G.; Carson, J.; McElwain, M. W.;

Extra-mitochondrial aerobic metabolism in retinal rod outer segments: new perspectives in retinopathies.

PubMed

Panfoli, I; Calzia, D; Ravera, S; Morelli, A M; Traverso, C E

2012-04-01

Vertebrate retinal rods are photoreceptors for dim-light vision. They display extreme sensitivity to light thanks to a specialized subcellular organelle, the rod outer segment. This is filled with a stack of membranous disks, expressing the proteins involved in visual transduction, a very energy demanding process. Our previous proteomic and biochemical studies have shed new light on the chemical energy processes that supply ATP to the outer segment, suggesting the presence of an extra-mitochondrial aerobic metabolism in rod outer segment, devoid of mitochondria, which would account for a quantitatively adequate ATP supply for phototransduction. Here the functional presence of an oxidative phosphorylation in the rod outer limb is examined for its relationship to many physiological and pathological data on the rod outer segment. We hypothesize that the rod outer limb is at risk of oxidative stress, in any case of impairment in the respiratory chain functioning, or of blood supply. In fact, the electron transfer chain is a major source of reactive O(2) species, known to produce severe alteration to the membrane lipids, especially those of the outer segment that are rich in polyunsaturated fatty acids. We propose that the disk membrane may become the target of reactive oxygen species that may be released by the electron transport chain under pathologic conditions. For example, during aging reactive oxygen species production increases, while cellular antioxidant capacity decreases. Also the apoptosis of the rod observed after exposure to bright or continuous illumination can be explained considering that an overfunctioning of phototransduction may damage the disk membrane to a point at which cytochrome c escapes from the intradiskal space, where it is presently supposed to be, activating a putative caspase 9 and the apoptosome. A pathogenic mechanism for many inherited and acquired retinal degenerations, representing a major problem in clinical ophthalmology, is proposed: a number of rod pathologies would be promoted by impairment of energy supply and/or oxidative stress in the rod outer segment. In conclusion we suppose that the damaging role of oxygen, be it hypoxia or hyperoxia invoked in most of the blinding diseases, acquired and even hereditary is to be seeked for inside the photoreceptor outer segment that would conceal a potential for cell death that is still to be recognized. Copyright © 2012 Elsevier Ltd. All rights reserved.

A Circumstellar Disk around HD 169142 in the Mid-Infrared (N-Band)

NASA Astrophysics Data System (ADS)

Okamoto, Yoshiko Kataza; Kataza, Hirokazu; Honda, M.; Yamashita, T.; Fujiyoshi, T.; Miyata, T.; Sako, S.; Fujiwara, H.; Sakon, I.; Fukagawa, M.; Momose, M.; Onaka, T.

2017-07-01

The Herbig Ae star HD 169142 is one of the objects that show complex structure, such as multiple (innermost, middle, and outer) disks, gaps, and unresolved sources. We made N-band (8-13 μm) observations of HD 169142 with the Cooled Mid-Infrared Camera and Spectrometer on the 8.2 m Subaru Telescope. The images are spatially resolved out to an ˜1″ radius in all the observed bands. We made a simple disk model composed of an unresolved central source (representing the innermost disk/halo) and the ring at a radius r ˜ 25 au (corresponding to the inner wall or edge of a middle disk at ˜25-40 au). The radial intensity profile within the central region (≲0.″3 or ≲ 40 au) is well reproduced by the model. Furthermore, we subtracted the model image from the observed one to search for additional structures. In the model-subtracted images, we found an unresolved west source separated by 17.0 ± 2.9 au in the direction of position angle 260° ± 5° from the original emission peak, which is supposed to correspond to the position of the central star, and a bright east arc located at r ˜ 60 au. The west source is different from the L‧-band unresolved source recently found in coronagraphic observations. It could be a structure related to planet formation in the disk, such as a circumplanetary disk or clumpy disk structure. The east arc corresponds to the inner wall or edge of the outer disk. Based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

A Study of Inner Disk Gas around Young Stars in the Lupus Complex

NASA Astrophysics Data System (ADS)

Arulanantham, Nicole Annemarie; France, Kevin; Hoadley, Keri

2018-06-01

We present a study of molecular hydrogen at the surfaces of the disks around five young stars in the Lupus complex: RY Lupi, RU Lupi, MY Lupi, Sz 68, and TYC 7851. Each system was observed with the Cosmic Origins Spectrograph (COS) onboard the Hubble Space Telescope (HST), and we detect a population of fluorescent H2 in all five sources. The temperatures required for LyA fluorescence to proceed (T ~ 1500-2500 K) place the gas within ~15 AU of the central stars. We have used these features to extract the radial distribution of H2 in the inner disk, where planet formation may already be taking place. The objects presented here have very different outer disk morphologies, as seen by ALMA via 890 micron dust continuum emission, ranging from full disks with no signs of cavities to systems with large regions that are clearly depleted (e.g. TYC 7851, with a cavity extending to 75 and 60 AU in dust and gas, respectively). Our results are interpreted in conjunction with sub-mm data from the five systems in an effort to piece together a more complete picture of the overall disk structure. We have previously applied this multi-wavelength approach to RY Lupi, including 4.7 micron IR-CO emission in our analysis. These IR-CO and UV-H2 observations were combined with 10 micron silicate emission, the 890 micron dust continuum, and 1.3 mm CO observations from the literature to infer a gapped structure in the inner disk. This single system has served as a testing ground for the larger Lupus complex sample, which we compare here to examine any trends between the outer disk morphology and inner disk gas distributions.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bromley, Benjamin C.; Kenyon, Scott J., E-mail: bromley@physics.utah.edu, E-mail: skenyon@cfa.harvard.edu

Correlations in the orbits of several minor planets in the outer solar system suggest the presence of a remote, massive Planet Nine. With at least 10 times the mass of the Earth and a perihelion well beyond 100 au, Planet Nine poses a challenge to planet formation theory. Here we expand on a scenario in which the planet formed closer to the Sun and was gravitationally scattered by Jupiter or Saturn onto a very eccentric orbit in an extended gaseous disk. Dynamical friction with the gas then allowed the planet to settle in the outer solar system. We explore thismore » possibility with a set of numerical simulations. Depending on how the gas disk evolves, scattered super-Earths or small gas giants settle on a range of orbits, with perihelion distances as large as 300 au. Massive disks that clear from the inside out on million-year timescales yield orbits that allow a super-Earth or gas giant to shepherd the minor planets as observed. A massive planet can achieve a similar orbit in a persistent, low-mass disk over the lifetime of the solar system.« less

HD139614: the Interferometric Case for a Group-Ib Pre-Transitional Young Disk

NASA Technical Reports Server (NTRS)

Labadie, Lucas; Matter, Alexis; Kreplin, Alexander; Lopez, Bruno; Wolf, Sebastian; Weigelt, Gerd; Ertel, Steve; Berger, Jean-Philippe; Pott, Jorg-Uwe; Danchi, William C.

2014-01-01

The Herbig Ae star HD139614 is a group-Ib object, which featureless SED indicates disk flaring and a possible pre-transitional evolutionary stage. We present mid- and near-IR interferometric results collected with MIDI, AMBER and PIONIER with the aim of constraining the spatial structure of the 0.1-10 AU disk region and assess its possible multi-component structure. A two-component disk model composed of an optically thin 2-AU wide inner disk and an outer temperature-gradient disk starting at 5.6 AU reproduces well the observations. This is an additional argument to the idea that group-I HAeBe inner disks could be already in the disk-clearing transient stage. HD139614 will become a prime target for mid-IR interferometric imaging with the second-generation instrument MATISSE of the VLTI.

Exploring Dust around HD 142527 down to 0.″025 (4 au) Using SPHERE/ZIMPOL

DOE Office of Scientific and Technical Information (OSTI.GOV)

Avenhaus, H.; Quanz, S. P.; Schmid, H. M.

We have observed the protoplanetary disk of the well-known young Herbig star HD 142527 using ZIMPOL polarimetric differential imaging with the very broad band (∼600–900 nm) filter. We obtained two data sets in 2015 May and 2016 March. Our data allow us to explore dust scattering around the star down to a radius of ∼0.″025 (∼4 au). The well-known outer disk is clearly detected at higher resolution than before and shows previously unknown substructures, including spirals going inward into the cavity. Close to the star, dust scattering is detected at high signal-to-noise ratio, but it is unclear whether the signal represents the innermore » disk, which has been linked to the two prominent local minima in the scattering of the outer disk that are interpreted as shadows. An interpretation of an inclined inner disk combined with a dust halo is compatible with both our and previous observations, but other arrangements of the dust cannot be ruled out. Dust scattering is also present within the large gap between ∼30 and ∼140 au. The comparison of the two data sets suggests rapid evolution of the inner regions of the disk, potentially driven by the interaction with the close-in M-dwarf companion, around which no polarimetric signal is detected.« less

Origins Space Telescope: Planet-forming disks and exoplanets

NASA Astrophysics Data System (ADS)

Pontoppidan, Klaus; Origins Space Telescope Study Team

2017-01-01

The Origins Space Telescope (OST) is the mission concept for the Far-Infrared Surveyor, a study in development by NASA in preparation for the 2020 Astronomy and Astrophysics Decadal Survey. Origins is planned to be a large aperture, actively-cooled telescope covering a wide span of the mid- to far-infrared spectrum. Its imagers and spectrographs will enable a variety of surveys of the sky that will discover and characterize the most distant galaxies, Milky-Way, exoplanets, and the outer reaches of our Solar system. Origins will enable flagship-quality general observing programs led by the astronomical community in the 2030s. The Science and Technology Definition Team (STDT) would like to hear your science needs and ideas for this mission. The team can be contacted at firsurveyor_info@lists.ipac.caltech.edu. This presentation will provide a summary of the science case related to planet formation and exoplanets. Leveraging orders of magnitude of improvements in sensitivity, the Origins Telescope will reveal the path of water from the interstellar medium to the inner regions of planet-forming disks, and determine the total masses of disks around stars across the stellar mass range out to distances of 500 pc. It will measure the temperatures and search for basic chemical ingredients for life on rocky planets. Beyond this, the Origins Telescope will open a vast discovery space in the general areas of star formation, protoplanetary and debris disks, and cool exoplanets in habitable zones.

A Herschel-Detected Correlation between Planets and Debris Disks

NASA Astrophysics Data System (ADS)

Bryden, Geoffrey; Krist, J. E.; Stapelfeldt, K. R.; Kennedy, G.; Wyatt, M.; Beichman, C. A.; Eiroa, C.; Marshall, J.; Maldonado, J.; Montesinos, B.; Moro-Martin, A.; Matthews, B. C.; Fischer, D.; Ardila, D. R.; Kospal, A.; Rieke, G.; Su, K. Y.

2013-01-01

The Fomalhaut, beta Pic, and HR 8799 systems each have directly imaged planets and prominent debris disks, suggesting a direct link between the two phenomena. Unbiased surveys with Spitzer, however, failed to find a statistically significant correlation. We present results from SKARPS (the Search for Kuiper belts Around Radial-velocity Planet Stars) a Herschel far-IR survey for debris disks around solar-type stars known to have orbiting planets. The identified disks are generally cold and distant 50 K/100 AU), i.e. well separated from the radial-velocity-discovered planets. Nevertheless, we find a strong correlation between the inner planets and outer disks, with disks around planet-bearing stars tending to be much brighter than those not known to have planets.

MECHANISM FOR EXCITING PLANETARY INCLINATION AND ECCENTRICITY THROUGH A RESIDUAL GAS DISK

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen Yuanyuan; Liu Huigen; Zhao Gang

2013-05-20

According to the theory of Kozai resonance, the initial mutual inclination between a small body and a massive planet in an outer circular orbit is as high as {approx}39. Degree-Sign 2 for pumping the eccentricity of the inner small body. Here we show that with the presence of a residual gas disk outside two planetary orbits, the inclination can be reduced to as low as a few degrees. The presence of the disk changes the nodal precession rates and directions of the planet orbits. At the place where the two planets achieve the same nodal processing rate, vertical secular resonancemore » (VSR) occurs so that the mutual inclination of the two planets will be excited, which might further trigger the Kozai resonance between the two planets. However, in order to pump an inner Jupiter-like planet, the conditions required for the disk and the outer planet are relatively strict. We develop a set of evolution equations, which can fit the N-body simulation quite well but can be integrated within a much shorter time. By scanning the parameter spaces using the evolution equations, we find that a massive planet (10 M{sub J} ) at 30 AU with an inclination of 6 Degree-Sign to a massive disk (50 M{sub J} ) can finally enter the Kozai resonance with an inner Jupiter around the snowline. An inclination of 20 Degree-Sign of the outer planet to the disk is required for flipping the inner one to a retrograde orbit. In multiple planet systems, the mechanism can happen between two nonadjacent planets or can inspire a chain reaction among more than two planets. This mechanism could be the source of the observed giant planets in moderate eccentric and inclined orbits, or hot Jupiters in close-in, retrograde orbits after tidal damping.« less

Module isolation devices

DOEpatents

Carolan, Michael Francis; Cooke, John Albert; Buzinski, Michael David

2010-04-27

A gas flow isolation device includes a gas flow isolation valve movable from an opened condition to a closed condition. The module isolation valve in one embodiment includes a rupture disk in flow communication with a flow of gas when the module isolation valve is in an opened condition. The rupture disk ruptures when a predetermined pressure differential occurs across it causing the isolation valve to close. In one embodiment the valve is mechanically linked to the rupture disk to maintain the valve in an opened condition when the rupture disk is intact, and which permits the valve to move into a closed condition when the rupture disk ruptures. In another embodiment a crushable member maintains the valve in an open condition, and the flow of gas passed the valve upon rupturing of the rupture disk compresses the crushable member to close the isolation valve.

Exploring Disks Around Planets

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-07-01

Giant planets are thought to form in circumstellar disks surrounding young stars, but material may also accrete into a smaller disk around the planet. Weve never detected one of these circumplanetary disks before but thanks to new simulations, we now have a better idea of what to look for.Image from previous work simulating a Jupiter-mass planet forming inside a circumstellar disk. The planet has its own circumplanetary disk of accreted material. [Frdric Masset]Elusive DisksIn the formation of giant planets, we think the final phase consists of accretion onto the planet from a disk that surrounds it. This circumplanetary disk is important to understand, since it both regulates the late gas accretion and forms the birthplace of future satellites of the planet.Weve yet to detect a circumplanetary disk thus far, because the resolution needed to spot one has been out of reach. Now, however, were entering an era where the disk and its kinematics may be observable with high-powered telescopes (like the Atacama Large Millimeter Array).To prepare for such observations, we need models that predict the basic characteristics of these disks like the mass, temperature, and kinematic properties. Now a researcher at the ETH Zrich Institute for Astronomy in Switzerland, Judit Szulgyi, has worked toward this goal.Simulating CoolingSzulgyi performs a series of 3D global radiative hydrodynamic simulations of 1, 3, 5, and 10 Jupiter-mass (MJ) giant planets and their surrounding circumplanetary disks, embedded within the larger circumstellar disk around the central star.Density (left column), temperature (center), and normalized angular momentum (right) for a 1 MJ planet over temperatures cooling from 10,000 K (top) to 1,000 K (bottom). At high temperatures, a spherical circumplanetary envelope surrounds the planet, but as the planet cools, the envelope transitions around 64,000 K to a flattened disk. [Szulgyi 2017]This work explores the effects of different planet temperatures and masses on the properties of the disks. Szulgyi specifically examines a range of planetary temperatures between 10,000 K and 1,000 K for the 1 MJ planet. Since the planet cools as it radiates away its formation heat, the different temperatures represent an evolutionary sequence over time.Predicted CharacteristicsSzulgyis work produced a number of intriguing observations, including the following:For the 1 MJ planet, a spherical circumplanetary envelope forms at high temperatures, flattening into a disk as the planet cools. Higher-mass planets form disks even at high temperatures.The disk has a steep temperature profile from inside to outside, and the whole disk is too hot for water to remain frozen. This suggests that satellites couldnt form in the disk earlier than 1 Myr after the planet birth. The outskirts of the disk cool first as the planet cools, indicating that satellites may eventually form in these outer parts and then migrate inward.The planets open gaps in the circumstellar disk as they orbit. As a planet radiates away its formation heat, the gap it opens becomes deeper and wider (though this is a small effect). For high-mass planets (5 MJ), the gap eccentricity increases, which creates a hostile environment for satellite formation.Szulgyi discusses a number of features of these disks that we can plan to search for in the future with our increasing telescope power including signatures in direct imaging and observations of their kinematics. The results from these simulations will help us both to detect these circumplanetary disks and to understand our observations when we do. These future observations will then allow us to learn about late-stage giant-planet formation as well as the formation of their satellites.CitationJ. Szulgyi 2017 ApJ 842 103. doi:10.3847/1538-4357/aa7515

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kikuchi, Akihiro; Higuchi, Arika; Ida, Shigeru, E-mail: kikuchi.a@geo.titech.ac.jp, E-mail: higuchia@geo.titech.ac.jp, E-mail: ida@elsi.jp

Recently, gas giant planets in nearly circular orbits with large semimajor axes (a ∼ 30-1000 AU) have been detected by direct imaging. We have investigated orbital evolution in a formation scenario for such planets, based on a core accretion model. (1) Icy cores accrete from planetesimals at ≲ 30 AU, (2) they are scattered outward by an emerging nearby gas giant to acquire highly eccentric orbits, and (3) their orbits are circularized through the accretion of disk gas in outer regions, where they spend most of their time. We analytically derived equations to describe the orbital circularization through gas accretion.more » Numerical integrations of these equations show that the eccentricity decreases by a factor of more than 5 while the planetary mass increases by a factor of 10. Because runaway gas accretion increases planetary mass by ∼10-300, the orbits are sufficiently circularized. On the other hand, a is reduced at most only by a factor of two, leaving the planets in the outer regions. If the relative velocity damping by shock is considered, the circularization slows down, but is still efficient enough. Therefore, this scenario potentially accounts for the formation of observed distant jupiters in nearly circular orbits. If the apocenter distances of the scattered cores are larger than the disk sizes, their a shrink to a quarter of the disk sizes; the a-distribution of distant giants could reflect the outer edges of the disks in a similar way that those of hot jupiters may reflect inner edges.« less

Detailed Structure of the Outer Disk Around HD 169142 with Polarized Light in H-band

NASA Technical Reports Server (NTRS)

Momose, Munetake; Morita, Ayaka; Fukagawa, Misato; Muto, Takayuki; Takeuchi, Taku; Hashimoto, Jun; Honda, Mitsuhiko; Kudo, Tomoyuki; Okamoto, Yoshiko K.; Kanagawa, Kazuhiro D.;

VIVA (VLA Imaging of Virgo in Atomic gas): H I Stripping in Virgo Galaxies

NASA Astrophysics Data System (ADS)

Chung, A.; van Gorkom, J. H.; Crowl, H.; Kenney, J. D. P.; Vollmer, B.

2008-08-01

We present results of a new Very Large Array survey of 53 Virgo galaxies (48 spirals and 5 dwarf/irregular systems). The goal is to study how the H I gas properties are affected by the cluster environment. The survey covers galaxies in a wide range of densities from the center of the cluster to more than 3 Mpc from M 87. The gas is imaged down to a column-density sensitivity of a few times 1019cm-2. We find examples of gas stripping at all stages. Within ˜0.5 Mpc from M 87, most galaxies are severely H I stripped. The H I disks are truncated to well within the optical disks. While the H I looks asymmetric, the outer stellar disks look undisturbed. The fact that only the gas and not the stars has been stripped suggests that those galaxies have been affected by the hot and dense cluster gas. Interestingly we also find a few truncated disks at large projected distances from the center. Although some of these may have been stripped while crossing the cluster core, a detailed population-synthesis study of the outer disk of one of these shows that star formation was terminated recently. The time since stripping is too short for the galaxy to have traveled from the core to its current location. So at least one galaxy has lost its gas from the outer disk by another mechanism than ram-pressure stripping in the dense cluster core. At intermediate- to low-density regions (>0.6 Mpc) we find H I tails with various lengths. We find seven galaxies with long one-sided H I tails pointing away from M 87. The galaxies are at 0.6-1 Mpc from M 87. Since these galaxies are only mildly H I deficient and the tails point away from M 87, these galaxies are probably falling into the cluster for the first time on highly radial orbits. For all but two of the galaxies the estimated ram pressure at their location in the cluster would be sufficient to pull out the H I in the very outer disks. One galaxy also looks optically disturbed and a simulation suggests that a combination of ram pressure plus a tidal interaction has pulled out the tail. In the outskirts of the cluster we find several examples of tidally interacting galaxies. We possibly see evidence for some accretion of gas as well. Lastly, the merging of subclusters with Virgo can cause bulk motions of the ICM. We see one example of a galaxy far out that appears to be ram-pressure stripped by a dynamic ICM. In summary, our results show that galaxies are already affected in the low-density outer regions of the cluster through ram-pressure stripping and tidal interactions, or a combination of both.

Jupiter's magnetosphere and radiation belts

NASA Technical Reports Server (NTRS)

Kennel, C. F.; Coroniti, F. V.

1979-01-01

Radioastronomy and Pioneer data reveal the Jovian magnetosphere as a rotating magnetized source of relativistic particles and radio emission, comparable to astrophysical cosmic ray and radio sources, such as pulsars. According to Pioneer data, the magnetic field in the outer magnetosphere is radially extended into a highly time variable disk-shaped configuration which differs fundamentally from the earth's magnetosphere. The outer disk region, and the energetic particles confined in it, are modulated by Jupiter's 10 hr rotation period. The entire outer magnetosphere appears to change drastically on time scales of a few days to a week. In addition to its known modulation of the Jovian decametric radio bursts, Io was found to absorb some radiation belt particles and to accelerate others, and most importantly, to be a source of neutral atoms, and by inference, a heavy ion plasma which may significantly affect the hydrodynamic flow in the magnetosphere. Another important Pioneer finding is that the Jovian outer magnetosphere generates, or permits to escape, fluxes of relativistic electrons of such intensities that Jupiter may be regarded as the dominant source of 1 to 30 MeV cosmic ray electrons in the heliosphere.

Mid-infrared interferometric variability of DG Tau: implications for the inner-disk structure .

NASA Astrophysics Data System (ADS)

Ábrahám, P.; Varga, J.; Gabányi, K. É.; Chen, L.; Kóspál, Á.; Ratzka, Th.; van Boekel, R.; Mosoni, L.; Henning, Th.

DG Tau is a low-mass young star whose strongly accreting disk shows a variable 10 mu m silicate feature, that may even turn temporarily from emission to absorption. Aiming to find the physical reason of this variability, we analysed multiepoch VLTI/MIDI interferometric observations. We found that the inner disk within 3 au radius exhibits a 10 mu m absorption feature related to amorphous silicate grains, while the outer disk displays a variable crystalline feature in emission, similar in shape to the spectrum of comet Hale-Bopp. The variability may be related to a fluctuating amount of dusty material above the disk surface, possibly due to turbulence.

The Thermal Regulation of Gravitational Instabilities in Protoplanetary Disks

NASA Astrophysics Data System (ADS)

Pickett, Brian K.; Mejía, Annie C.; Durisen, Richard H.; Cassen, Patrick M.; Berry, Donald K.; Link, Robert P.

2003-06-01

We present a series of high-resolution, three-dimensional hydrodynamics simulations of a gravitationally unstable solar nebula model. The influences of both azimuthal grid resolution and the treatment of thermal processes on the origin and evolution of gravitational instabilities are investigated. In the first set of simulations, we vary the azimuthal resolution for a locally isothermal simulation, doubling and quadrupling the resolution used in a previous study; the largest number of grid points is (256,256,64) in cylindrical coordinates (r,ϕ,z). At this resolution, the disk breaks apart into a dozen short-lived condensations. Although our previous calculations underresolved the number and growth rate of clumps in the disk, the overall qualitative, but fundamental, conclusion remains: fragmentation under the locally isothermal condition in numerical simulations does not in itself lead to the survival of clumps to become gaseous giant protoplanets. Since local isothermality represents an extreme assumption about thermal processes in the disk, we also present several extended simulations in which heating from an artificial viscosity scheme and cooling from a simple volumetric cooling function are applied to two different models of the solar nebula. The models are differentiated primarily by disk temperature: a high-Q model generated directly by our self-consistent field equilibrium code and a low-Q model generated by cooling the high-Q model in a two-dimensional version of our hydrodynamics code. Here, ``high-Q'' and ``low-Q'' refer to the minimum values of the Toomre stability parameter Q in each disk, Qmin=1.8 and 0.9, respectively. Previous simulations, by ourselves as well as others, have focused on initial states that are already gravitationally unstable, i.e., models similar to the low-Q model. This paper presents for the first time the numerical evolution of an essentially stable initial equilibrium state (the high-Q model) to a severely unstable one by cooling. The additional heating and cooling are applied to each model over the outer half of the disk or the entire disk. The models are subject to the rapid growth of a four-armed spiral instability; the subsequent evolution of the models depends on the thermal behavior of the disk. The cooling function tends to overwhelm the heating included in our artificial viscosity prescription, and as a result the spiral structure strengthens. The spiral disturbances transport mass at prodigious rates during the early nonlinear stages of development and significantly alter the disk's vertical surface. Although dense condensations of material can appear, their character depends on the extent of the volumetric cooling in the disk. In the simulation of the high-Q model with heating and cooling applied throughout the disk, thin, dense rings form at radii ranging from 1 to 3 AU and steadily increase in mass; later companion formation may occur in these rings as cooling drives them toward instability. When heating and cooling are applied only over the outer radial half of the disk, however, a succession of single condensations appears near 5 AU. Each clump has roughly the mass of Saturn, and some survive a complete orbit. Since the clumps form near the artificial boundary in the treatment of the disk gas physics, the production of a clump in this case is a numerical artifact. Nevertheless, radially abrupt transitions in disk gas characteristics, for example, in opacity, might mimic the artificial boundary effects in our simulations and favor the production of stable companions in actual protostellar and protoplanetary disks. The ultimate survival of condensations as eventual stellar or substellar companions to the central star is still largely an open question.

A disk of scattered icy objects and the origin of Jupiter-family comets.

PubMed

Duncan, M J; Levison, H F

1997-06-13

Orbital integrations carried out for 4 billion years produced a disk of scattered objects beyond the orbit of Neptune. Objects in this disk can be distinguished from Kuiper belt objects by a greater range of eccentricities and inclinations. This disk was formed in the simulations by encounters with Neptune during the early evolution of the outer solar system. After particles first encountered Neptune, the simulations show that about 1 percent of the particles survive in this disk for the age of the solar system. A disk currently containing as few as approximately 6 x 10(8) objects could supply all of the observed Jupiter-family comets. Two recently discovered objects, 1996 RQ20 and 1996 TL66, have orbital elements similar to those predicted for objects in this disk, suggesting that they are thus far the only members of this disk to be identified.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu Zhaohuan; Stone, James M.; Rafikov, Roman R., E-mail: zhzhu@astro.princeton.edu, E-mail: jstone@astro.princeton.edu, E-mail: rrr@astro.princeton.edu

Some regions in protoplanetary disks are turbulent, while some regions are quiescent (e.g. the dead zone). In order to study how planets open gaps in both inviscid hydrodynamic disk (e.g. the dead zone) and the disk subject to magnetorotational instability (MRI), we carried out both shearing box two-dimensional inviscid hydrodynamical simulations and three-dimensional unstratified magnetohydrodynamical (MHD) simulations (having net vertical magnetic fields) with a planet at the box center. We found that, due to the nonlinear wave steepening, even a low mass planet can open gaps in both cases, in contradiction to the ''thermal criterion'' for gap opening. In ordermore » to understand if we can represent the MRI turbulent stress with the viscous {alpha} prescription for studying gap opening, we compare gap properties in MRI-turbulent disks to those in viscous HD disks having the same stress, and found that the same mass planet opens a significantly deeper and wider gap in net vertical flux MHD disks than in viscous HD disks. This difference arises due to the efficient magnetic field transport into the gap region in MRI disks, leading to a larger effective {alpha} within the gap. Thus, across the gap, the Maxwell stress profile is smoother than the gap density profile, and a deeper gap is needed for the Maxwell stress gradient to balance the planetary torque density. Comparison with previous results from net toroidal flux/zero flux MHD simulations indicates that the magnetic field geometry plays an important role in the gap opening process. We also found that long-lived density features (termed zonal flows) produced by the MRI can affect planet migration. Overall, our results suggest that gaps can be commonly produced by low mass planets in realistic protoplanetary disks, and caution the use of a constant {alpha}-viscosity to model gaps in protoplanetary disks.« less

Spiral density waves in a young protoplanetary disk.

PubMed

Pérez, Laura M; Carpenter, John M; Andrews, Sean M; Ricci, Luca; Isella, Andrea; Linz, Hendrik; Sargent, Anneila I; Wilner, David J; Henning, Thomas; Deller, Adam T; Chandler, Claire J; Dullemond, Cornelis P; Lazio, Joseph; Menten, Karl M; Corder, Stuartt A; Storm, Shaye; Testi, Leonardo; Tazzari, Marco; Kwon, Woojin; Calvet, Nuria; Greaves, Jane S; Harris, Robert J; Mundy, Lee G

2016-09-30

Gravitational forces are expected to excite spiral density waves in protoplanetary disks, disks of gas and dust orbiting young stars. However, previous observations that showed spiral structure were not able to probe disk midplanes, where most of the mass is concentrated and where planet formation takes place. Using the Atacama Large Millimeter/submillimeter Array, we detected a pair of trailing symmetric spiral arms in the protoplanetary disk surrounding the young star Elias 2-27. The arms extend to the disk outer regions and can be traced down to the midplane. These millimeter-wave observations also reveal an emission gap closer to the star than the spiral arms. We argue that the observed spirals trace shocks of spiral density waves in the midplane of this young disk. Copyright © 2016, American Association for the Advancement of Science.

Freeze-fracture studies of photoreceptor membranes: new observations bearing upon the distribution of cholesterol

PubMed Central

1983-01-01

We performed electron microscopy of replicas from freeze-fractured retinas exposed during or after fixation to the cholesterol-binding antibiotic, filipin. We observed characteristic filipin-induced perturbations throughout the disk and plasma membranes of retinal rod outer segments of various species. It is evident that a prolonged exposure to filipin in fixative enhances rather than reduces presumptive cholesterol detection in the vertebrate photoreceptor cell. In agreement with the pattern seen in our previous study (Andrews, L.D., and A. I. Cohen, 1979, J. Cell Biol., 81:215-228), filipin- binding in membranes exhibiting particle-free patches seemed largely confined to these patches. Favorably fractured photoreceptors exhibited marked filipin-binding in apical inner segment plasma membrane topologically confluent with and proximate to the outer segment plasma membrane, which was comparatively free of filipin binding. A possible boundary between these differing membrane domains was suggested in a number of replicas exhibiting lower filipin binding to the apical plasma membrane of the inner segment in the area surrounding the cilium. This area contains a structure (Andrews, L. D., 1982, Freeze- fracture studies of vertebrate photoreceptors, In Structure of the Eye, J. G. Hollyfield and E. Acosta Vidrio, editors, Elsevier/North-Holland, New York, 11-23) that resembles the active zones of the nerve terminals for the frog neuromuscular junction. These observations lead us to hypothesize that these structures may function to direct vesicle fusion to occur near them, in a domain of membrane more closely resembling outer than inner segment plasma membrane. The above evidence supports the views that (a) all disk membranes contain cholesterol, but the particle-free patches present in some disks trap cholesterol from contiguous particulate membrane regions; (b) contiguous inner and outer segment membranes may greatly differ in cholesterol content; and (c) the suggested higher cholesterol in the inner segment than in the outer segment plasma membrane may help direct newly inserted photopigment molecules to the outer segment. PMID:6411740

Live-Cell Imaging of Phagosome Motility in Primary Mouse RPE Cells.

PubMed

Hazim, Roni; Jiang, Mei; Esteve-Rudd, Julian; Diemer, Tanja; Lopes, Vanda S; Williams, David S

2016-01-01

The retinal pigment epithelium (RPE) is a post-mitotic epithelial monolayer situated between the light-sensitive photoreceptors and the choriocapillaris. Given its vital functions for healthy vision, the RPE is a primary target for insults that result in blinding diseases, including age-related macular degeneration (AMD). One such function is the phagocytosis and digestion of shed photoreceptor outer segments. In the present study, we examined the process of trafficking of outer segment disk membranes in live cultures of primary mouse RPE, using high speed spinning disk confocal microscopy. This approach has enabled us to track phagosomes, and determine parameters of their motility, which are important for their efficient degradation.

Structure of the Iconic Vega Debris Disk

NASA Astrophysics Data System (ADS)

Su, Kate

2015-10-01

Debris structures provide the best means to explore planets down to ice-giant masses in the outer (>5 AU) parts of extrasolar planetary systems. It is thought that the iconic Vega debris disk composes of two separate belts shepherded by unseen planets, similar to the Solar System. We will probe this possibility with SOFIA at 35 microns by: 1.) documenting the structure of the debris with sufficient resolution to distinguish a separate warm belt from the alternative model of dust flowing inward from the outer debris ring; and 2.) testing for traces of dust in its 15-60 AU zone and thus probing the possibility that ice giant planets may be shepherding the debris belts.

A Resolved Debris Disk Around the Candidate Planet-hosting Star HD 95086

NASA Technical Reports Server (NTRS)

Moor, A.; Abraham, P.; Kospal, A.; Szabo, Gy. M.; Apai, D.; Balog, Z.; Csengeri, T.; Grady, C.; Henning, Th.; Juhasz, J.;

Differences in the protein composition of bovine retinal rod outer segment disk and plasma membranes isolated by a ricin-gold-dextran density perturbation method

PubMed Central

1987-01-01

The plasma membrane and disk membranes of bovine retinal rod outer segments (ROS) have been purified by a novel density-gradient perturbation method for analysis of their protein compositions. Purified ROS were treated with neuraminidase to expose galactose residues on plasma membrane-specific glycoproteins and labeled with ricin-gold-dextran particles. After the ROS were lysed in hypotonic buffer, the plasma membrane was dissociated from the disks by either mild trypsin digestion or prolonged exposure to low ionic strength buffer. The dense ricin-gold-dextran-labeled plasma membrane was separated from disks by sucrose gradient centrifugation. Electron microscopy was used to follow this fractionation procedure. The dense red pellet primarily consisted of inverted plasma membrane vesicles containing gold particles; the membrane fraction of density 1.13 g/cc consisted of unlabeled intact disks and vesicles. Ricin-binding studies indicated that the plasma membrane from trypsin-treated ROS was purified between 10-15-fold. The protein composition of plasma membranes and disks was significantly different as analyzed by SDS gels and Western blots labeled with lectins and monoclonal antibodies. ROS plasma membrane exhibited three major proteins of 36 (rhodopsin), 38, and 52 kD, three ricin-binding glycoproteins of 230, 160, and 110 kD, and numerous minor proteins in the range of 14-270 kD. In disk membranes rhodopsin appeared as the only major protein. A 220-kD concanavalin A-binding glycoprotein and peripherin, a rim-specific protein, were also present along with minor proteins of 43 and 57-63 kD. Radioimmune assays indicated that the ROS plasma membrane contained about half as much rhodopsin as disk membranes. PMID:2447095

Radiation Hydrodynamics Simulations of Photoevaporation of Protoplanetary Disks by Ultraviolet Radiation: Metallicity Dependence

NASA Astrophysics Data System (ADS)

Nakatani, Riouhei; Hosokawa, Takashi; Yoshida, Naoki; Nomura, Hideko; Kuiper, Rolf

2018-04-01

Protoplanetary disks are thought to have lifetimes of several million yr in the solar neighborhood, but recent observations suggest that the disk lifetimes are shorter in a low-metallicity environment. We perform a suite of radiation hydrodynamics simulations of photoevaporating protoplanetary disks to study their long-term evolution of ∼10,000 yr and the metallicity dependence of mass-loss rates. Our simulations follow hydrodynamics, extreme and far-ultraviolet (FUV) radiative transfer, and nonequilibrium chemistry in a self-consistent manner. Dust-grain temperatures are also calculated consistently by solving the radiative transfer of the stellar irradiation and grain (re-)emission. We vary the disk metallicity over a wide range of {10}-4 {Z}ȯ ≤slant Z≤slant 10 {Z}ȯ . The photoevaporation rate is lower with higher metallicity in the range of {10}-1 {Z}ȯ ≲ Z≲ 10 {Z}ȯ , because dust shielding effectively prevents FUV photons from penetrating and heating the dense regions of the disk. The photoevaporation rate sharply declines at even lower metallicities in {10}-2 {Z}ȯ ≲ Z≲ {10}-1 {Z}ȯ , because FUV photoelectric heating becomes less effective than dust–gas collisional cooling. The temperature in the neutral region decreases, and photoevaporative flows are excited only in an outer region of the disk. At {10}-4 {Z}ȯ ≤slant Z≲ {10}-2 {Z}ȯ , H I photoionization heating acts as a dominant gas heating process and drives photoevaporative flows with a roughly constant rate. The typical disk lifetime is shorter at Z = 0.3 {Z}ȯ than at Z={Z}ȯ , being consistent with recent observations of the extreme outer galaxy.

The impact of galaxy geometry and mass evolution on the survival of star clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Madrid, Juan P.; Hurley, Jarrod R.; Martig, Marie

2014-04-01

Direct N-body simulations of globular clusters in a realistic Milky-Way-like potential are carried out using the code NBODY6 to determine the impact of the host galaxy disk mass and geometry on the survival of star clusters. A relation between disk mass and star-cluster dissolution timescale is derived. These N-body models show that doubling the mass of the disk from 5 × 10{sup 10} M {sub ☉} to 10 × 10{sup 10} M {sub ☉} halves the dissolution time of a satellite star cluster orbiting the host galaxy at 6 kpc from the galactic center. Different geometries in a disk ofmore » identical mass can determine either the survival or dissolution of a star cluster orbiting within the inner 6 kpc of the galactic center. Furthermore, disk geometry has measurable effects on the mass loss of star clusters up to 15 kpc from the galactic center. N-body simulations performed with a fine output time step show that at each disk crossing the outer layers of star clusters experiences an increase in velocity dispersion of ∼5% of the average velocity dispersion in the outer section of star clusters. This leads to an enhancement of mass loss—a clearly discernable effect of disk shocking. By running models with different inclinations, we determine that star clusters with an orbit that is perpendicular to the Galactic plane have larger mass loss rates than do clusters that evolve in the Galactic plane or in an inclined orbit.« less

The Outer Disks of Herbig Stars From the UV to NIR

NASA Technical Reports Server (NTRS)

Grady, C.; Fukagawa, M.; Maruta, Y.; Ohta, Y.; Wisniewski, J.; Hashimoto, J.; Okamoto, Y.; Momose, M.; Currie, T.; Mcelwain, M.;

On the Possibility of Enrichment and Differentiation in Gas Giants During Birth by Disk Instability

NASA Astrophysics Data System (ADS)

Boley, Aaron C.; Durisen, Richard H.

2010-11-01

We investigate the coupling between rock-size solids and gas during the formation of gas giant planets by disk fragmentation in the outer regions of massive disks. In this study, we use three-dimensional radiative hydrodynamic simulations and model solids as a spatial distribution of particles. We assume that half of the total solid fraction is in small grains and half in large solids. The former are perfectly entrained with the gas and set the opacity in the disk, while the latter are allowed to respond to gas drag forces, with the back reaction on the gas taken into account. To explore the maximum effects of gas-solid interactions, we first consider 10 cm size particles. We then compare these results to a simulation with 1 km size particles, which explores the low-drag regime. We show that (1) disk instability planets have the potential to form large cores due to aerodynamic capturing of rock-size solids in spiral arms before fragmentation; (2) temporary clumps can concentrate tens of M ⊕ of solids in very localized regions before clump disruption; (3) the formation of permanent clumps, even in the outer disk, is dependent on the grain-size distribution, i.e., the opacity; (4) nonaxisymmetric structure in the disk can create disk regions that have a solids-to-gas ratio greater than unity; (5) the solid distribution may affect the fragmentation process; (6) proto-gas giants and proto-brown dwarfs can start as differentiated objects prior to the H2 collapse phase; (7) spiral arms in a gravitationally unstable disk are able to stop the inward drift of rock-size solids, even redistributing them to larger radii; and (8) large solids can form spiral arms that are offset from the gaseous spiral arms. We conclude that planet embryo formation can be strongly affected by the growth of solids during the earliest stages of disk accretion.

A gaseous metal disk around a white dwarf.

PubMed

Gänsicke, B T; Marsh, T R; Southworth, J; Rebassa-Mansergas, A

2006-12-22

The destiny of planetary systems through the late evolution of their host stars is very uncertain. We report a metal-rich gas disk around a moderately hot and young white dwarf. A dynamical model of the double-peaked emission lines constrains the outer disk radius to just 1.2 solar radii. The likely origin of the disk is a tidally disrupted asteroid, which has been destabilized from its initial orbit at a distance of more than 1000 solar radii by the interaction with a relatively massive planetesimal object or a planet. The white dwarf mass of 0.77 solar mass implies that planetary systems may form around high-mass stars.

Dynamical Upheaval in Ice Giant Formation: A Solution to the Fine-tuning Problem in the Formation Story

NASA Astrophysics Data System (ADS)

Frelikh, Renata; Murray-Clay, Ruth

2018-04-01

We report on our recent theoretical work, where we suggest that a protoplanetary disk dynamical instability may have played a crucial role in determining the atmospheric size of the solar system’s ice giants. In contrast to the gas giants, the intermediate-size ice giants never underwent runaway gas accretion in a full gas disk. However, as their substantial core masses are comparable to those of the gas giants, they would have gone runaway, given enough time. In the standard scenario, the ice giants stay at roughly their current size for most of the disk lifetime, undergoing period of slow gas accretion onto ~full-sized cores that formed early-on. The gas disk dissipates before the ice giants accumulate too much gas, but we believe this is fine tuned. A considerable amount of solids is observed in outer disks in mm-to-cm sized particles (pebbles). Assisted by gas drag, these pebbles rapidly accrete onto cores. This would cause the growing ice giants to exceed their current core masses, and quickly turn into gas giants. To resolve this problem, we propose that Uranus and Neptune stayed small for the bulk of the disk lifetime. They only finished their core and atmospheric growth in a short timeframe just as the disk gas dissipated, accreting most of their gas from a disk depleted to ~1% of its original mass. The ice giants have atmospheric mass fractions comparable to the disk gas-to-solid ratio of this depleted disk. This coincides with a disk dynamical upheaval onset by the depletion of gas. We propose that the cores started growing closer-in, where they were kept small by proximity to Jupiter and Saturn. As the gas cleared, the cores were kicked out by the gas giants. Then, they finished their core growth and accreted their atmospheres from the remaining, sparse gas at their current locations. We predict that the gas giants may play a key role in forming intermediate-size atmospheres in the outer disk.

Vacuum breaker valve assembly

DOEpatents

Thompson, J.L.; Upton, H.A.

1999-04-27

Breaker valve assemblies for a simplified boiling water nuclear reactor are described. The breaker valve assembly, in one form, includes a valve body and a breaker valve. The valve body includes an interior chamber, and an inlet passage extends from the chamber and through an inlet opening to facilitate transporting particles from outside of the valve body to the interior chamber. The breaker valve is positioned in the chamber and is configured to substantially seal the inlet opening. Particularly, the breaker valve includes a disk which is sized to cover the inlet opening. The disk is movably coupled to the valve body and is configured to move substantially concentrically with respect to the valve opening between a first position, where the disk completely covers the inlet opening, and a second position, where the disk does not completely cover the inlet opening. 1 fig.

Vacuum breaker valve assembly

DOEpatents

Thompson, Jeffrey L.; Upton, Hubert Allen

1999-04-27

Breaker valve assemblies for a simplified boiling water nuclear reactor are described. The breaker valve assembly, in one form, includes a valve body and a breaker valve. The valve body includes an interior chamber, and an inlet passage extends from the chamber and through an inlet opening to facilitate transporting particles from outside of the valve body to the interior chamber. The breaker valve is positioned in the chamber and is configured to substantially seal the inlet opening. Particularly, the breaker valve includes a disk which is sized to cover the inlet opening. The disk is movably coupled to the valve body and is configured to move substantially concentrically with respect to the valve opening between a first position, where the disk completely covers the inlet opening, and a second position, where the disk does not completely cover the inlet opening.

Millimetre spectral indices of transition disks and their relation to the cavity radius

NASA Astrophysics Data System (ADS)

Pinilla, P.; Benisty, M.; Birnstiel, T.; Ricci, L.; Isella, A.; Natta, A.; Dullemond, C. P.; Quiroga-Nuñez, L. H.; Henning, T.; Testi, L.

2014-04-01

Context. Transition disks are protoplanetary disks with inner depleted dust cavities that are excellent candidates for investigating the dust evolution when there is a pressure bump. A pressure bump at the outer edge of the cavity allows dust grains from the outer regions to stop their rapid inward migration towards the star and to efficiently grow to millimetre sizes. Dynamical interactions with planet(s) have been one of the most exciting theories to explain the clearing of the inner disk. Aims: We look for evidence of millimetre dust particles in transition disks by measuring their spectral index αmm with new and available photometric data. We investigate the influence of the size of the dust depleted cavity on the disk integrated millimetre spectral index. Methods: We present the 3-mm (100 GHz) photometric observations carried out with the Plateau de Bure Interferometer of four transition disks: LkHα 330, UX Tau A, LRLL 31, and LRLL 67. We used the available values of their fluxes at 345 GHz to calculate their spectral index, as well as the spectral index for a sample of twenty transition disks. We compared the observations with two kinds of models. In the first set of models, we considered coagulation and fragmentation of dust in a disk in which a cavity is formed by a massive planet located at different positions. The second set of models assumes disks with truncated inner parts at different radii and with power-law dust-size distributions, where the maximum size of grains is calculated considering turbulence as the source of destructive collisions. Results: We show that the integrated spectral index is higher for transition disks (TD) than for regular protoplanetary disks (PD) with mean values of bar{αmmTD} = 2.70 ± 0.13 and bar{αmmPD} = 2.20 ± 0.07 respectively. For transition disks, the probability that the measured spectral index is positively correlated with the cavity radius is 95%. High angular resolution imaging of transition disks is needed to distinguish between the dust trapping scenario and the truncated disk case. The final PdBI data used in the paper are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/564/A51

Contribution of collagen fibers to the compressive stiffness of cartilaginous tissues.

PubMed

Römgens, Anne M; van Donkelaar, Corrinus C; Ito, Keita

2013-11-01

Cartilaginous tissues such as the intervertebral disk are predominantly loaded under compression. Yet, they contain abundant collagen fibers, which are generally assumed to contribute to tensile loading only. Fiber tension is thought to originate from swelling of the proteoglycan-rich nucleus. However, in aged or degenerate disk, proteoglycans are depleted, whereas collagen content changes little. The question then rises to which extend the collagen may contribute to the compressive stiffness of the tissue. We hypothesized that this contribution is significant at high strain magnitudes and that the effect depends on fiber orientation. In addition, we aimed to determine the compression of the matrix. Bovine inner and outer annulus fibrosus specimens were subjected to incremental confined compression tests up to 60 % strain in radial and circumferential direction. The compressive aggregate modulus was determined per 10 % strain increment. The biochemical composition of the compressed specimens and uncompressed adjacent tissue was determined to compute solid matrix compression. The stiffness of all specimens increased nonlinearly with strain. The collagen-rich outer annulus was significantly stiffer than the inner annulus above 20 % compressive strain. Orientation influenced the modulus in the collagen-rich outer annulus. Finally, it was shown that the solid matrix was significantly compressed above 30 % strain. Therefore, we concluded that collagen fibers significantly contribute to the compressive stiffness of the intervertebral disk at high strains. This is valuable for understanding the compressive behavior of collagen-reinforced tissues in general, and may be particularly relevant for aging or degenerate disks, which become more fibrous and less hydrated.

Thermal shields for gas turbine rotor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ross, Christopher W.; Acar, Bulent

A turbomachine including a rotor having an axis and a plurality of disks positioned adjacent to each other in the axial direction, each disk including opposing axially facing surfaces and a circumferentially extending radially facing surface located between the axially facing surfaces. At least one row of blades is positioned on each of the disks, and the blades include an airfoil extending radially outward from the disk A non-segmented circumferentially continuous ring structure includes an outer rim defining a thermal barrier extending axially in overlapping relation over a portion of the radially facing surface of at least one disk, andmore » extending to a location adjacent to a blade on the disk A compliant element is located between a radially inner circumferential portion of the ring structure and a flange structure that extends axially from an axially facing surface of the disk.« less

A 3D Numerical Study of Gravitational Instabilities in Young Circumbinary Disks

NASA Astrophysics Data System (ADS)

Cai, Kai; Michael, Scott; Durisen, Richard

2013-07-01

Gravitational instabilities (GIs) in protoplanetary disks have been suggested as one of the major formation mechanisms of giant planets. Theoretical and computational studies have indicated that certain family of GIs can be excited in a circumbinary disk, which could lead to enhanced protoplanet formation (e.g., Sellwood & Lin 1989, Boss 2006). We have carried out a 3D simulation of a gravitationally unstable circumbinary disk around a young Sun-like star and a 0.02-Msun companion, both inside the central hole of the disk. Here we present a preliminary comparison between this simulation and a similarly simulated circumstellar disk around a solar-mass star but without the low-mass companion. The GIs stimulated by the binary and those that arise spontaneously are quite different in structure and strength. However, no fragmentation is observed, even after many orbital periods as measured in the outer disk.

Modeling Protoplanetary Disks to Characterize the Evolution of their Structure

NASA Astrophysics Data System (ADS)

Allen, Magdelena; van der Marel, Nienke; Williams, Jonathan

2018-01-01

Stars form from gravitationally collapsing clouds of gas and dust. Most young stars retain a protoplanetary disk for a few million years. This disk’s dust reemits stellar flux in the infrared, producing a spectral energy distribution (SED) observable by Spitzer and other telescopes. To understand the inner clearing of dust cavities and evolution in the SED, we used the Chiang & Goldreich two-layer approximation. We first wrote a python script based on refinements by Dullemond that includes a hot, puffed inner rim, shadowed mid region, flaring outer disk, and a variable inner cavity. This was then coupled with a Markov Chain Monte Carlo procedure to fit the observed SEDs of disks in the star forming Lupus region. The fitting procedure recovers physical characteristics of the disk including temperature, size, mass, and surface density. We compare the characteristics of circumstellar disks without holes and more evolved transition disks with cleared inner regions.

Ultra-low field MRI food inspection system prototype

NASA Astrophysics Data System (ADS)

Kawagoe, Satoshi; Toyota, Hirotomo; Hatta, Junichi; Ariyoshi, Seiichiro; Tanaka, Saburo

2016-11-01

We develop an ultra-low field (ULF) magnetic resonance imaging (MRI) system using a high-temperature superconducting quantum interference device (HTS-SQUID) for food inspection. A two-dimensional (2D)-MR image is reconstructed from the grid processing raw data using the 2D fast Fourier transform method. In a previous study, we combined an LC resonator with the ULF-MRI system to improve the detection area of the HTS-SQUID. The sensitivity was improved, but since the experiments were performed in a semi-open magnetically shielded room (MSR), external noise was a problem. In this study, we develop a compact magnetically shielded box (CMSB), which has a small open window for transfer of a pre-polarized sample. Experiments were performed in the CMSB and 2D-MR images were compared with images taken in the semi-open MSR. A clear image of a disk-shaped water sample is obtained, with an outer dimension closer to that of the real sample than in the image taken in the semi-open MSR. Furthermore, the 2D-MR image of a multiple cell water sample is clearly reconstructed. These results show the applicability of the ULF-MRI system in food inspection.

Coevolution of Binaries and Circumbinary Gaseous Disks

NASA Astrophysics Data System (ADS)

Fleming, David; Quinn, Thomas R.

2018-04-01

The recent discoveries of circumbinary planets by Kepler raise questions for contemporary planet formation models. Understanding how these planets form requires characterizing their formation environment, the circumbinary protoplanetary disk, and how the disk and binary interact. The central binary excites resonances in the surrounding protoplanetary disk that drive evolution in both the binary orbital elements and in the disk. To probe how these interactions impact both binary eccentricity and disk structure evolution, we ran N-body smooth particle hydrodynamics (SPH) simulations of gaseous protoplanetary disks surrounding binaries based on Kepler 38 for 10^4 binary orbital periods for several initial binary eccentricities. We find that nearly circular binaries weakly couple to the disk via a parametric instability and excite disk eccentricity growth. Eccentric binaries strongly couple to the disk causing eccentricity growth for both the disk and binary. Disks around sufficiently eccentric binaries strongly couple to the disk and develop an m = 1 spiral wave launched from the 1:3 eccentric outer Lindblad resonance (EOLR). This wave corresponds to an alignment of gas particle longitude of periastrons. We find that in all simulations, the binary semi-major axis decays due to dissipation from the viscous disk.

Properties of the outer regions of spiral disks: abundances, colors and ages

NASA Astrophysics Data System (ADS)

Mollá, Mercedes; Díaz, Angeles I.; Gibson, Brad K.; Cavichia, Oscar; López-Sánchez, Ángel-R.

2017-03-01

We summarize the results obtained from our suite of chemical evolution models for spiral disks, computed for different total masses and star formation efficiencies. Once the gas, stars and star formation radial distributions are reproduced, we analyze the Oxygen abundances radial profiles for gas and stars, in addition to stellar averaged ages and global metallicity. We examine scenarios for the potential origin of the apparent flattening of abundance gradients in the outskirts of disk galaxies, in particular the role of molecular gas formation prescriptions.

The Nonbarred Double-Ringed Galaxy, PGC 1000714

NASA Astrophysics Data System (ADS)

Seigar, Marc; Mutlu Pakdil, Burcin; Mangedarage, Mithila; Treuthardt, Patrick M.

2017-01-01

Hoag-type galaxies are rare peculiar systems which bear strong resemblance to Hoag's Object with an elliptical-like core, a detached outer ring, and no signs of a bar or stellar disk. They represent extreme cases and help us understand the formation of galaxies in general by providing clues on formation mechanisms. The nature of outer rings in Hoag-type galaxies is still debated and may be related either to slow secular evolution, such as dissolution of a barlike structure or to environmental processes, such as galaxy-galaxy interactions or gas infall. Due to a fairly superficial resemblance to Hoag's Object, PGC 1000714 is a good target for detailed study of the peculiar structure of this type. We present the first photometric study of PGC 1000714 that has not yet been described in the literature. Our aim is to evaluate its structure and properties as well as understand the origin of outer rings in such galaxies. Surface photometry of the central body is performed using near-UV, BVRI and JHK images. Based on the photometric data, the nearly round central body follows a de Vaucouleurs profile almost all the way to the center. The detailed photometry reveals a reddish inner ring-shaped structure that shares the same center as the central body. However, no sign of a bar or stellar disk is detected. The outer ring appears as a bump in the surface brightness profile with a peak brightness of 25.8 mag/arcsec^{2} in the B-band and shows no sharp outer boundary. By reconstructing the observed SED for the central body and the rings, we recover the stellar population properties of the galaxy components. Our work suggests different formation histories for the inner and outer rings. We rule out the secular evolution model as being a formation mechanism for the outer ring. The colors of the outer ring are consistent with a feature that may have experienced a burst of star formation due to a possible recent accretion event. In addition, our work supports that the central body may be formed by a relatively dry major merger or in a single, short and highly effective star formation burst, and the inner ring may be formed as a result of intergalactic medium accretion or secular evolution of a possible gaseous disk

Gaps, rings, and non-axisymmetric structures in protoplanetary disks. From simulations to ALMA observations

NASA Astrophysics Data System (ADS)

Flock, M.; Ruge, J. P.; Dzyurkevich, N.; Henning, Th.; Klahr, H.; Wolf, S.

2015-02-01

Aims: Recent observations by the Atacama Large Millimeter/submillimeter Array (ALMA) of disks around young stars revealed distinct asymmetries in the dust continuum emission. In this work we wish to study axisymmetric and non-axisymmetric structures that are generated by the magneto-rotational instability in the outer regions of protoplanetary disks. We combine the results of state-of-the-art numerical simulations with post-processing radiative transfer (RT) to generate synthetic maps and predictions for ALMA. Methods: We performed non-ideal global 3D magneto-hydrodynamic (MHD) stratified simulations of the dead-zone outer edge using the FARGO MHD code PLUTO. The stellar and disk parameters were taken from a parameterized disk model applied for fitting high-angular resolution multi-wavelength observations of various circumstellar disks. We considered a stellar mass of M∗ = 0.5 M⊙ and a total disk mass of about 0.085 M∗. The 2D initial temperature and density profiles were calculated consistently from a given surface density profile and Monte Carlo radiative transfer. The 2D Ohmic resistivity profile was calculated using a dust chemistry model. We considered two values for the dust-to-gas mass ratio, 10-2 and 10-4, which resulted in two different levels of magnetic coupling. The initial magnetic field was a vertical net flux field. The radiative transfer simulations were performed with the Monte Carlo-based 3D continuum RT code MC3D. The resulting dust reemission provided the basis for the simulation of observations with ALMA. Results: All models quickly turned into a turbulent state. The fiducial model with a dust-to-gas mass ratio of 10-2 developed a large gap followed by a jump in surface density located at the dead-zone outer edge. The jump in density and pressure was strong enough to stop the radial drift of particles at this location. In addition, we observed the generation of vortices by the Rossby wave instability at the jump location close to 60 AU. The vortices were steadily generated and destroyed at a cycle of 40 local orbits. The RT results and simulated ALMA observations predict that it is feasible to observe these large-scale structures that appear in magnetized disks without planets. Neither the turbulent fluctuations in the disk nor specific times of the model can be distinguished on the basis of high-angular resolution submillimeter observations alone. The same applies to the distinction between gaps at the dead-zone edges and planetary gaps, to the distinction between turbulent and simple unperturbed disks, and to the asymmetry created by the vortex.

Free-fall dynamics of a pair of rigidly linked disks

NASA Astrophysics Data System (ADS)

Kim, Taehyun; Chang, Jaehyeock; Kim, Daegyoum

2018-03-01

We investigate experimentally the free-fall motion of a pair of identical disks rigidly connected to each other. The three-dimensional coordinates of the pair of falling disks were constructed to quantitatively describe its trajectory, and the flow structure formed by the disk pair was identified by using dye visualization. The rigidly linked disk pair exhibits a novel falling pattern that creates a helical path with a conical configuration in which the lower disk rotates in a wider radius than the upper disk with respect to a vertical axis. The helical motion occurs consistently for the range of disk separation examined in this study. The dye visualization reveals that a strong, noticeable helical vortex core is generated from the outer tip of the lower disk during the helical motion. With an increasing length ratio, which is the ratio of the disk separation to the diameter of the disks, the nutation angle and the rate of change in the precession angle that characterize the combined helical and conical kinematics decrease linearly, whereas the pitch of the helical path increases linearly. Although all disk pairs undergo this helical motion, the horizontal-drift patterns of the disk pair depend on the length ratio.

A kinematic determination of the structure of the double ring planetary nebula NGC 2392, the Eskimo

DOE Office of Scientific and Technical Information (OSTI.GOV)

O'dell, C.R.; Weiner, L.D.; Chu, Yoyhua

Slit spectra and existing velocity cube data have been used to determine the structure of the double ring PN NGC 2392. The inner shell is a stellar wind-sculpted prolate spheroid with a ratio of axes of 2:1 and the approaching end of the long axis pointed 20 deg from the line of sight in P.A. = 200 deg. The outer ring is caused by an outer disk with density dropping off with distance from the central star and with distance from its plane, which is the same as the equatorial band of high density in the inner shell. The outermore » disk contains a ring of higher density knots at a distance of 16 arcsec and is losing material through free expansion, forming an outer envelope of increasing velocity. Forbidden S II spectra are used to determine the densities in all of the major regions of the nebula. It is argued that the filamentary cores at the centers of the knots seen in the outer ring originate in the sublimation of bodies formed at the same time as the parent star. 26 refs.« less

The accretion of migrating giant planets

NASA Astrophysics Data System (ADS)

Dürmann, Christoph; Kley, Wilhelm

2017-02-01

Aims: Most studies concerning the growth and evolution of massive planets focus either on their accretion or their migration only. In this work we study both processes concurrently to investigate how they might mutually affect one another. Methods: We modeled a two-dimensional disk with a steady accretion flow onto the central star and embedded a Jupiter mass planet at 5.2 au. The disk is locally isothermal and viscosity is modeled using a constant α. The planet is held on a fixed orbit for a few hundred orbits to allow the disk to adapt and carve a gap. After this period, the planet is released and free to move according to the gravitational interaction with the gas disk. The mass accretion onto the planet is modeled by removing a fraction of gas from the inner Hill sphere, and the removed mass and momentum can be added to the planet. Results: Our results show that a fast migrating planet is able to accrete more gas than a slower migrating planet. Utilizing a tracer fluid we analyzed the origin of the accreted gas originating predominantly from the inner disk for a fast migrating planet. In the case of slower migration, the fraction of gas from the outer disk increases. We also found that even for very high accretion rates, in some cases gas crosses the planetary gap from the inner to the outer disk. Our simulations show that the crossing of gas changes during the migration process as the migration rate slows down. Therefore, classical type II migration where the planet migrates with the viscous drift rate and no gas crosses the gap is no general process but may only occur for special parameters and at a certain time during the orbital evolution of the planet.

51 OPHIUCHUS: A POSSIBLE BETA PICTORIS ANALOG MEASURED WITH THE KECK INTERFEROMETER NULLER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stark, Christopher C.; Kuchner, Marc J.; Traub, Wesley A.

2009-10-01

We present observations of the 51 Ophiuchi circumstellar disk made with the Keck interferometer operating in nulling mode at N band. We model these data simultaneously with VLTI-MIDI visibility data and a Spitzer IRS spectrum using a variety of optically thin dust cloud models and an edge-on optically thick disk model. We find that single-component optically thin disk models and optically thick disk models are inadequate to reproduce the observations, but an optically thin two-component disk model can reproduce all of the major spectral and interferometric features. Our preferred disk model consists of an inner disk of blackbody grains extendingmore » to {approx}4 AU and an outer disk of small silicate grains extending out to {approx}1200 AU. Our model is consistent with an inner 'birth' disk of continually colliding parent bodies producing an extended envelope of ejected small grains. This picture resembles the disks around Vega, AU Microscopii, and beta Pictoris, supporting the idea that 51 Ophiuchius may be a beta Pictoris analog.« less

Stability and Occurrence Rate Constraints on the Planetary Sculpting Hypothesis for “Transitional” Disks

NASA Astrophysics Data System (ADS)

Dong, Ruobing; Dawson, Rebekah

2016-07-01

Transitional disks, protoplanetary disks with deep and wide central gaps, may be the result of planetary sculpting. By comparing numerical planet-opening-gap models with observed gaps, we find systems of 3-6 giant planets are needed in order to open gaps with the observed depths and widths. We explore the dynamical stability of such multi-planet systems using N-body simulations that incorporate prescriptions for gas effects. We find they can be stable over a typical disk lifetime, with the help of eccentricity damping from the residual gap gas that facilitates planets locking into mean motion resonances. However, in order to account for the occurrence rate of transitional disks, the planet sculpting scenario demands gap-opening-friendly disk conditions, in particular, a disk viscosity α ≲ 0.001. In addition, the demography of giant planets at ˜3-30 au separations, poorly constrained by current data, has to largely follow occurrence rates extrapolated outward from radial velocity surveys, not the lower occurrence rates extrapolated inward from direct imaging surveys. Even with the most optimistic occurrence rates, transitional disks cannot be a common phase that most gas disks experience at the end of their life, as popularly assumed, simply because there are not enough planets to open these gaps. Finally, as consequences of demanding almost all giant planets at large separations participate in transitional disk sculpting, the majority of such planets must form early and end up in a chain of mean motion resonances at the end of disk lifetime.

A model for neutrino emission from nuclear accretion disks

NASA Astrophysics Data System (ADS)

Deaton, Michael

2015-04-01

Compact object mergers involving at least one neutron star can produce short-lived black hole accretion engines. Over tens to hundreds of milliseconds such an engine consumes a disk of hot, nuclear-density fluid, and drives changes to its surrounding environment through luminous emission of neutrinos. The neutrino emission may drive an ultrarelativistic jet, may peel off the disk's outer layers as a wind, may irradiate those winds or other forms of ejecta and thereby change their composition, may change the composition and thermodynamic state of the disk itself, and may oscillate in its flavor content. We present the full spatial-, angular-, and energy-dependence of the neutrino distribution function around a realistic model of a nuclear accretion disk, to inform future explorations of these types of behaviors. Spectral Einstein Code (SpEC).

Early scattering of the solar protoplanetary disk recorded in meteoritic chondrules

PubMed Central

Marrocchi, Yves; Chaussidon, Marc; Piani, Laurette; Libourel, Guy

2016-01-01

Meteoritic chondrules are submillimeter spherules representing the major constituent of nondifferentiated planetesimals formed in the solar protoplanetary disk. The link between the dynamics of the disk and the origin of chondrules remains enigmatic. Collisions between planetesimals formed at different heliocentric distances were frequent early in the evolution of the disk. We show that the presence, in some chondrules, of previously unrecognized magnetites of magmatic origin implies the formation of these chondrules under impact-generated oxidizing conditions. The three oxygen isotopes systematic of magmatic magnetites and silicates can only be explained by invoking an impact between silicate-rich and ice-rich planetesimals. This suggests that these peculiar chondrules are by-products of the early mixing in the disk of populations of planetesimals from the inner and outer solar system. PMID:27419237

Modeling Protostar Envelopes and Disks Seen With ALMA: A Focus on L1527 Kinematics

NASA Astrophysics Data System (ADS)

Terebey, Susan; Flores Rivera, Lizxandra; Willacy, Karen

2018-06-01

ALMA probes continuum and spectral line emission from protostars that comes from both the envelope and circumstellar disk. The dust and gas emit on a variety of spatial scales, ranging from sub-arcseconds for disks to roughly 10 arcseconds for envelopes for nearby protostars. We present models of what ALMA should detect that incorporate a self-consistent collapse solution, radiative transfer, and realistic dust properties. Molecular abundances are also calculated; we present results for CO and isotopologues for the Class 0 source L1527. Results for the outer disk show that there can be significant differences from standard assumptions due to the effect of CO freeze out and non-Keplerian dynamics.

Gas in Debris Disks and the Volatiles of Terrestrial Planet Formation

NASA Technical Reports Server (NTRS)

Kuchner, Marc

2010-01-01

Debris disks are a kind of protoplanetary disk that likely corresponds to the epoch of terrestrial planet and outer planet formation. Previously pictured to be gas-free, some debris disks are now revealing gas components, sometimes with strikingly non-solar abundance patterns. Understanding the nature and distribution of this gas may eventually help us understand the origin of volatiles on the Earth, the carbon depletion of the asteroids, and even the origin of life. I'll describe what we know about these systems observationally, some of the leading hypotheses about the sources and sinks of the gas, and how these new astronomical discoveries may bear on solar-system science.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Osorio, Mayra; Anglada, Guillem; Macías, Enrique

We present Very Large Array observations at 7 mm that trace the thermal emission of large dust grains in the HD 169142 protoplanetary disk. Our images show a ring of enhanced emission of radius ∼25-30 AU, whose inner region is devoid of detectable 7 mm emission. We interpret this ring as tracing the rim of an inner cavity or gap, possibly created by a planet or a substellar companion. The ring appears asymmetric, with the western part significantly brighter than the eastern one. This azimuthal asymmetry is reminiscent of the lopsided structures that are expected to be produced as a consequence of trappingmore » of large dust grains. Our observations also reveal an outer annular gap at radii from ∼40 to ∼70 AU. Unlike other sources, the radii of the inner cavity, the ring, and the outer gap observed in the 7 mm images, which trace preferentially the distribution of large (millimeter/centimeter sized) dust grains, coincide with those obtained from a previous near-infrared polarimetric image, which traces scattered light from small (micron-sized) dust grains. We model the broadband spectral energy distribution and the 7 mm images to constrain the disk physical structure. From this modeling we infer the presence of a small (radius ∼0.6 AU) residual disk inside the central cavity, indicating that the HD 169142 disk is a pre-transitional disk. The distribution of dust in three annuli with gaps in between them suggests that the disk in HD 169142 is being disrupted by at least two planets or substellar objects.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cieza, Lucas A.; Mathews, Geoffrey S.; Kraus, Adam L.

We present deep Sparse Aperture Masking (SAM) observations obtained with the ESO Very Large Telescope of the pre-transitional disk object FL Cha (SpT = K8, d = 160 pc), the disk of which is known to have a wide optically thin gap separating optically thick inner and outer disk components. We find non-zero closure phases, indicating a significant flux asymmetry in the K{sub S} -band emission (e.g., a departure from a single point source detection). We also present radiative transfer modeling of the spectral energy distribution of the FL Cha system and find that the gap extends from 0.06{sup +0.05}{submore » -0.01} AU to 8.3 {+-} 1.3 AU. We demonstrate that the non-zero closure phases can be explained almost equally well by starlight scattered off the inner edge of the outer disk or by a (sub)stellar companion. Single-epoch, single-wavelength SAM observations of transitional disks with large cavities that could become resolved should thus be interpreted with caution, taking the disk and its properties into consideration. In the context of a binary model, the signal is most consistent with a high-contrast ({Delta}K{sub S} {approx} 4.8 mag) source at a {approx}40 mas (6 AU) projected separation. However, the flux ratio and separation parameters remain highly degenerate and a much brighter source ({Delta}K{sub S} {approx} 1 mag) at 15 mas (2.4 AU) can also reproduce the signal. Second-epoch, multi-wavelength observations are needed to establish the nature of the SAM detection in FL Cha.« less

On the Impact Origin of Phobos and Deimos. II. True Polar Wander and Disk Evolution

NASA Astrophysics Data System (ADS)

Hyodo, Ryuki; Rosenblatt, Pascal; Genda, Hidenori; Charnoz, Sébastien

2017-12-01

Phobos and Deimos are the two small Martian moons, orbiting almost on the equatorial plane of Mars. Recent works have shown that they can accrete within an impact-generated inner dense and outer light disk, and that the same impact potentially forms the Borealis basin, a large northern hemisphere basin on the current Mars. However, there is no a priori reason for the impact to take place close to the north pole (Borealis present location), nor to generate a debris disk in the equatorial plane of Mars (in which Phobos and Deimos orbit). In this paper, we investigate these remaining issues on the giant impact origin of the Martian moons. First, we show that the mass deficit created by the Borealis impact basin induces a global reorientation of the planet to realign its main moment of inertia with the rotation pole (True Polar Wander). This moves the location of the Borealis basin toward its current location. Next, using analytical arguments, we investigate the detailed dynamical evolution of the eccentric inclined disk from the equatorial plane of Mars that is formed by the Martian-moon-forming impact. We find that, as a result of precession of disk particles due to the Martian dynamical flattening J 2 term of its gravity field and particle–particle inelastic collisions, eccentricity and inclination are damped and an inner dense and outer light equatorial circular disk is eventually formed. Our results strengthen the giant impact origin of Phobos and Deimos that can finally be tested by a future sample return mission such as JAXA’s Martian Moons eXploration mission.

PSOCT studies of intervertebral disk

NASA Astrophysics Data System (ADS)

Matcher, Stephen J.; Winlove, Peter C.; Gangnus, Sergey V.

2004-07-01

Polarization-sensitive optical coherence tomography (PSOCT) is an emerging optical imaging technique that is sensitive to the birefringence properties of tissues. It thus has applications in studying the large-scale ordering of collagen fibers within connective tissues. This ordering not only provides useful insights into the relationship between structure and function for various anatomical structures but also is an indicator of pathology. Intervertebral disk is an elastic tissue of the spine and possesses a 3-D collagen structure well suited to study using PSOCT. Since the outer layer of the disk has a lamellar structure with collagen fibers oriented in a trellis-like arrangement between lamellae, the birefringence fast-axis shows pronounced variations with depth, on a spatial scale of about 100 μm. The lamellar thickness varies with age and possibly with disease. We have used a polarisation-sensitive optical coherence tomography system to measure the birefringence properties of freshly excised, hydrated bovine caudal intervertebral disk and compared this with equine flexor tendon. Our results clearly demonstrate the ability of PSOCT to detect the outer three lamellae, down to a depth of at least 700 μm, via discontinuities in the depth-resolved retardance. We have applied a simple semi-empirical model based on Jones calculus to quantify the variation in the fast-axis orientation with depth. Our data and modeling is in broad agreement with previous studies using x-ray diffraction and polarization microscopy applied to histological sections of dehydrated disk. Our results imply that PSOCT may prove a useful tool to study collagen organisation within intervertebral disk in vitro and possibly in vivo and its variation with age and disease.

RESONANT CLUMPING AND SUBSTRUCTURE IN GALACTIC DISKS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Molloy, Matthew; Smith, Martin C.; Shen, Juntai

2015-05-10

We describe a method to extract resonant orbits from N-body simulations, exploiting the fact that they close in frames rotating with a constant pattern speed. Our method is applied to the N-body simulation of the Milky Way by Shen et al. This simulation hosts a massive bar, which drives strong resonances and persistent angular momentum exchange. Resonant orbits are found throughout the disk, both close to the bar and out to the very edges of the disk. Using Fourier spectrograms, we demonstrate that the bar is driving kinematic substructure even in the very outer parts of the disk. We identifymore » two major orbit families in the outskirts of the disk, one of which makes significant contributions to the kinematic landscape, namely, the m:l = 3:−2 family, resonating with the bar. A mechanism is described that produces bimodal distributions of Galactocentric radial velocities at selected azimuths in the outer disk. It occurs as a result of the temporal coherence of particles on the 3:−2 resonant orbits, which causes them to arrive simultaneously at pericenter or apocenter. This resonant clumping, due to the in-phase motion of the particles through their epicycle, leads to both inward and outward moving groups that belong to the same orbital family and consequently produce bimodal radial velocity distributions. This is a possible explanation of the bimodal velocity distributions observed toward the Galactic anticenter by Liu et al. Another consequence is that transient overdensities appear and dissipate (in a symmetric fashion), resulting in a periodic pulsing of the disk’s surface density.« less

Variable Dynamics in the Inner Disk of HD 135344B Revealed with Multi-epoch Scattered Light Imaging

NASA Astrophysics Data System (ADS)

Stolker, Tomas; Sitko, Mike; Lazareff, Bernard; Benisty, Myriam; Dominik, Carsten; Waters, Rens; Min, Michiel; Perez, Sebastian; Milli, Julien; Garufi, Antonio; de Boer, Jozua; Ginski, Christian; Kraus, Stefan; Berger, Jean-Philippe; Avenhaus, Henning

2017-11-01

We present multi-epoch Very Large Telescope/Spectro-Polarimetric High-contrast Exoplanet REsearch (VLT/SPHERE) observations of the protoplanetary disk around HD 135344B (SAO 206462). The J-band scattered light imagery reveal, with high spatial resolution (˜41 mas, 6.4 au), the disk surface beyond ˜20 au. Temporal variations are identified in the azimuthal brightness distributions of all epochs, presumably related to the asymmetrically shading dust distribution in the inner disk. These shadows manifest themselves as narrow lanes, cast by localized density enhancements, and broader features which possibly trace the larger scale dynamics of the inner disk. We acquired visible and near-infrared photometry which shows variations up to 10% in the JHK bands, possibly correlated with the presence of the shadows. Analysis of archival Very Large Telescope Interferometer/Precision Integrated-Optics Near-infrared Imaging ExpeRiment (VLTI/PIONIER) H-band visibilities constrain the orientation of the inner disk to I=18\\buildrel{\\circ}\\over{.} {2}-4.1+3.4 and {PA}=57\\buildrel{\\circ}\\over{.} 3+/- 5\\buildrel{\\circ}\\over{.} 7, consistent with an alignment with the outer disk or a minor disk warp of several degrees. The latter scenario could explain the broad, quasi-stationary shadowing in north-northwest direction in case the inclination of the outer disk is slightly larger. The correlation between the shadowing and the near-infrared excess is quantified with a grid of radiative transfer models. The variability of the scattered light contrast requires extended variations in the inner disk atmosphere (H/r≲ 0.2). Possible mechanisms that may cause asymmetric variations in the optical depth ({{Δ }}τ ≲ 1) through the atmosphere of the inner disk include turbulent fluctuations, planetesimal collisions, or a dusty disk wind, possibly enhanced by a minor disk warp. A fine temporal sampling is required to follow day-to-day changes of the shadow patterns which may be a face-on variant of the UX Orionis phenomenon. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programmes 087.C-0702(A,B), 087.C-0458(B,C), 087.C-0703(B), 088.C-0670(B), 088.D-0185(A), 088.C-0763(D), 089.C-0211(A), 091.C-0570(A), 095.C-0273(A), 097.C-0885(A), 097.C-0702(A), and 297.C-5023(A).

Observational and research progress of the M51 galaxy

NASA Astrophysics Data System (ADS)

Chen, Zhu; Williams, Peter

2006-12-01

The M51 system consists of a grand-design spiral galaxy and a relatively large close companion, NGC 5195. Because M51 (=NGC 5194) is nearby and nearly face-on to us, its structure can be observed in great detail and with a minimum of obscuration from dust. As a result, this galaxy has been thoroughly observed at wavelengths from radio to X-ray. Due to the rich archive of observational data, its structure, dynamical process, star formation mechanism and some other important properties have been analyzed by many authors. In the center of M51, there is a Seyfert 2 or LINER type AGN which radius is 100 pc. The mass within 70 pc in the center is (4~7)×106 Msun, this indicates there may be a black hole there. The disk of M51 can be divided into two parts, the inner disk around the nucleus cuts off at 1350 pc, from this radius to 10 kpc is the outer disk. In contrast, the companion, NGC 5195 is small and faint, and heavy dust from the arm of M51 in the foreground obscures its optical radiation. M51 has many interesting properties different from other normal galaxies, such as the wide open spiral arm, the long HI tidal tail and the huge distorted gas ring around the outer disk, these may be related to the interaction effects. Actually, the dynamical modeling history of M51 is long, in the early stage of astronomical numerical simulation, Toomre & Toomre have given a simple simulation of M51 to study its tidal effect. In 1990, the discovery of M51's long HI tidal tail made the astrophysicists shift the preferred collision time of M51 and NGC 5195 to somewhat later times in order to give the tail more time to develop. More recently, Salo and Laurikainen suggested that a multiple-passage model might be more appropriate for the system, such a scenario appears to do a better job of explaining NGC 5194's HI velocity field, but the predicted structure of the HI tidal tail is more complex than its observation. In this paper, the authers review literature of multi-wavelength observations and recent research results of M51, discuss the improvements and drawbacks of its simulation results and also summarize the available observations of NGC 5195.

Comparison Simulations of Gas Giant Planet Formation via Disk Instability

NASA Astrophysics Data System (ADS)

Pickett, Megan K.; Cai, K.; Durisen, R.; Milne, M.

2011-01-01

There has been disagreement about whether cooling in protoplanetary disks can be sufficiently fast to induce the formation of gas giant protoplanets via gravitational instabilities. Simulations by our own group and others indicate that this method of planet formation does not work for disks around young, low-mass stars inside several tens of AU, while simulations by other groups show fragmentation into protoplanetary clumps in this region. To allow direct comparison in hopes of isolating the cause of the differences, we here present a comparison high-resolution three-dimensional hydrodynamics simulation of a protoplanetary disk,using an improved version of one of our own radiative schemes. We find that the disk does not fragment in our code but instead quickly settles into a state with only low amplitude nonaxisymmetric structure, which persists for at least several outer disk rotations. Further, we see no rapid radiative or convective cooling.

β Pictoris' inner disk in polarized light and new orbital parameters for β Pictoris b

DOE PAGES

Millar-Blanchaer, Maxwell A.; Graham, James R.; Pueyo, Laurent; ...

2015-09-16

Here, we present H-band observations of β Pic with the Gemini Planet Imager's (GPI's) polarimetry mode that reveal the debris disk between ~0farcs3 (6 AU) and ~1farcs7 (33 AU), while simultaneously detecting β Pic b. The polarized disk image was fit with a dust density model combined with a Henyey–Greenstein scattering phase function. The best-fit model indicates a disk inclined to the line of sight (more » $$\\phi =85\\buildrel{\\circ}\\over{.} {27}_{-0.19}^{+0.26}$$) with a position angle (PA) $${\\theta }_{\\mathrm{PA}}=30\\buildrel{\\circ}\\over{.} {35}_{-0.28}^{+0.29}$$ (slightly offset from the main outer disk, $${\\theta }_{\\mathrm{PA}}\\approx 29^\\circ $$), that extends from an inner disk radius of $${23.6}_{-0.6}^{+0.9}\\;\\mathrm{AU}$$ to well outside GPI's field of view.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morales, F. Y.; Bryden, G.; Werner, M. W.

We present dual-band Herschel /PACS imaging for 59 main-sequence stars with known warm dust ( T {sub warm} ∼ 200 K), characterized by Spitzer . Of 57 debris disks detected at Herschel wavelengths (70 and/or 100 and 160 μ m), about half have spectral energy distributions (SEDs) that suggest two-ring disk architectures mirroring that of the asteroid–Kuiper Belt geometry; the rest are consistent with single belts of warm, asteroidal material. Herschel observations spatially resolve the outer/cold dust component around 14 A-type and 4 solar-type stars with two-belt systems, 15 of which for the first time. Resolved disks are typically observedmore » with radii >100 AU, larger than expected from a simple blackbody fit. Despite the absence of narrow spectral features for ice, we find that the shape of the continuum, combined with resolved outer/cold dust locations, can help constrain the grain size distribution and hint at the dust’s composition for each resolved system. Based on the combined Spitzer /IRS+Multiband Imaging Photometer (5-to-70 μ m) and Herschel /PACS (70-to-160 μ m) data set, and under the assumption of idealized spherical grains, we find that over half of resolved outer/cold belts are best fit with a mixed ice/rock composition. Minimum grain sizes are most often equal to the expected radiative blowout limit, regardless of composition. Three of four resolved systems around the solar-type stars, however, tend to have larger minimum grains compared to expectation from blowout ( f {sub MB} = a {sub min}/ a {sub BOS} ∼ 5). We also probe the disk architecture of 39 Herschel -unresolved systems by modeling their SEDs uniformly, and find them to be consistent with 31 single- and 8 two-belt debris systems.« less

Inner disk clearing around the Herbig Ae star HD 139614: Evidence for a planet-induced gap?

NASA Astrophysics Data System (ADS)

Matter, A.; Labadie, L.; Augereau, J. C.; Kluska, J.; Crida, A.; Carmona, A.; Gonzalez, J. F.; Thi, W. F.; Le Bouquin, J.-B.; Olofsson, J.; Lopez, B.

2016-02-01

Spatially resolving the inner dust cavity (or gap) of the so-called (pre-)transitional disks is a key to understanding the connection between the processes of planetary formation and disk dispersal. The disk around the Herbig star HD 139614 is of particular interest since it presents a pretransitional nature with an au-sized gap structure that is spatially resolved by mid-infrared interferometry in the dust distribution. With the aid of new near-infrared interferometric observations, we aim to characterize the 0.1-10 au region of the HD 139614 disk further and then identify viable mechanisms for the inner disk clearing. We report the first multiwavelength modeling of the interferometric data acquired on HD 139614 with the VLTI instruments PIONIER, AMBER, and MIDI, complemented by Herschel/PACS photometric measurements. We first performed a geometrical modeling of the new near-infrared interferometric data, followed by radiative transfer modeling of the complete dataset using the code RADMC3D. We confirm the presence of a gap structure in the warm μm-sized dust distribution, extending from about 2.5 au to 6 au, and constrained the properties of the inner dust component: e.g., a radially increasing dust surface density profile, and a depletion in dust of ~103 relative to the outer disk. Since self-shadowing and photoevaporation appears unlikely to be responsible for the au-sized gap of HD 139614, we thus tested if dynamical clearing could be a viable mechanism using hydrodynamical simulations to predict the structure of the gaseous disk. Indeed, a narrow au-sized gap is consistent with the expected effect of the interaction between a single giant planet and the disk. Assuming that small dust grains are well coupled to the gas, we found that an approximately 3 Mjup planet located at ~4.5 au from the star could, in less than 1 Myr, reproduce most of the aspects of the dust surface density profile, while no significant depletion (in gas) occurred in the inner disk, in contrast to the dust. However, this "dust-depleted" inner disk could be explained by the expected dust filtration by the gap and the efficient dust growth/fragmentation occurring in the inner disk regions. Our results support the hypothesis of a giant planet opening a gap and shaping the inner region of the HD 139614 disk. This makes HD 139614 an exciting candidate specifically for witnessing planet-disk interaction. Based on observations collected at the European Southern Observatory, Chile (ESO IDs : 385.C-0886, 087.C-0811, 089.C-0456, and 190.C-0963).

Shadows cast on the transition disk of HD 135344B. Multiwavelength VLT/SPHERE polarimetric differential imaging

NASA Astrophysics Data System (ADS)

Stolker, T.; Dominik, C.; Avenhaus, H.; Min, M.; de Boer, J.; Ginski, C.; Schmid, H. M.; Juhasz, A.; Bazzon, A.; Waters, L. B. F. M.; Garufi, A.; Augereau, J.-C.; Benisty, M.; Boccaletti, A.; Henning, Th.; Langlois, M.; Maire, A.-L.; Ménard, F.; Meyer, M. R.; Pinte, C.; Quanz, S. P.; Thalmann, C.; Beuzit, J.-L.; Carbillet, M.; Costille, A.; Dohlen, K.; Feldt, M.; Gisler, D.; Mouillet, D.; Pavlov, A.; Perret, D.; Petit, C.; Pragt, J.; Rochat, S.; Roelfsema, R.; Salasnich, B.; Soenke, C.; Wildi, F.

2016-11-01

Context. The protoplanetary disk around the F-type star HD 135344B (SAO 206462) is in a transition stage and shows many intriguing structures both in scattered light and thermal (sub-)millimeter emission which are possibly related to planet formation processes. Aims: We aim to study the morphology and surface brightness of the disk in scattered light to gain insight into the innermost disk regions, the formation of protoplanets, planet-disk interactions traced in the surface and midplane layers, and the dust grain properties of the disk surface. Methods: We have carried out high-contrast polarimetric differential imaging (PDI) observations with VLT/SPHERE and obtained polarized scattered light images with ZIMPOL in the R and I-bands and with IRDIS in the Y and J-bands. The scattered light images and surface brightness profiles are used to study in detail structures in the disk surface and brightness variations. We have constructed a 3D radiative transfer model to support the interpretation of several detected shadow features. Results: The scattered light images reveal with unprecedented angular resolution and sensitivity the spiral arms as well as the 25 au cavity of the disk. Multiple shadow features are discovered on the outer disk with one shadow only being present during the second observation epoch. A positive surface brightness gradient is observed in the stellar irradiation corrected (r2-scaled) images in southwest direction possibly due to an azimuthally asymmetric perturbation of the temperature and/or surface density by the passing spiral arms. The disk integrated polarized flux, normalized to the stellar flux, shows a positive trend towards longer wavelengths which we attribute to large (2πa ≳ λ) aggregate dust grains in the disk surface. Part of the non-azimuthal polarization signal in the Uφ image of the J-band observation can be attributed to multiple scattering in the disk. Conclusions: The detected shadow features and their possible variability have the potential to provide insight into the structure of and processes occurring in the innermost disk regions. Possible explanations for the presence of the shadows include a 22° misaligned inner disk, a warped disk region that connects the inner disk with the outer disk, and variable or transient phenomena such as a perturbation of the inner disk or an asymmetric accretion flow. The spiral arms are best explained by one or multiple protoplanets in the exterior of the disk although no gap is detected beyond the spiral arms up to 1.''0. Based on observations collected at the European Southern Observatory, Chile, ESO No. 095.C-0273(A) and 095.C-0273(D).

DEVELOPMENT OF A LAMINATED DISK FOR THE SPIN TEK ROTARY MICROFILTER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Herman, D.

2011-06-03

Funded by the Department of Energy Office of Environmental Management, EM-31, the Savannah River National Laboratory (SRNL) partnered with SpinTek Filtration{trademark} to develop a filter disk that would withstand a reverse pressure or flow during operation of the rotary microfilter. The ability to withstand a reverse pressure and flow eliminates a potential accident scenario that could have resulted in damage to the filter membranes. While the original welded filter disks have been shown to withstand and reverse pressure/flow in the static condition, the filter disk design discussed in this report will allow a reverse pressure/flow while the disks are rotating.more » In addition, the laminated disk increases the flexibility during filter startup and cleaning operations. The new filter disk developed by SRNL and SpinTek is manufactured with a more open structure significantly reducing internal flow restrictions in the disk. The prototype was tested at the University of Maryland and demonstrated to withstand the reverse pressure due to the centrifugal action of the rotary filter. The tested water flux of the disk was demonstrated to be 1.34 gpm in a single disk test. By comparison, the water flux of the current disk was 0.49 gpm per disk during a 25 disk test. The disk also demonstrated rejection of solids by filtering a 5 wt % Strontium Carbonate slurry with a filtrate clarity of less the 1.4 Nephelometric Turbidity Units (NTU) throughout the two hour test. The Savannah River National Laboratory (SRNL) has been working with SpinTek Filtration{trademark} to adapt the rotary microfilter for radioactive service in the Department of Energy (DOE) Complex. One potential weakness is the loose nature of the membrane on the filter disks. The current disk is constructed by welding the membrane at the outer edge of the disk. The seal for the center of the membrane is accomplished by an o-ring in compression for the assembled stack. The remainder of the membrane is free floating on the disk. This construction requires that a positive pressure be applied to the rotary filter tank to prevent the membrane from rising from the disk structure and potentially contacting the filter turbulence promoter. In addition, one accident scenario is a reverse flow through the filtrate line due to mis-alignment of valves resulting in the membrane rising from the disk structure. The structural integrity of the current disk has been investigated, and shown that the disk can withstand a significant reverse pressure in a static condition. However, the disk will likely incur damage if the filter stack is rotated during a reverse pressure. The development of a laminated disk would have several significant benefits for the operation of the rotary filter including the prevention of a compromise in filter disk integrity during a reverse flow accident, increasing operational flexibility, and increasing the self cleaning ability of the filter. A laminated disk would allow the filter rotor operation prior to a positive pressure in the filter tank. This would prevent the initial dead-head of the filter and prevent the resulting initial filter cake buildup. The laminated disk would allow rotor operation with cleaning fluid, eliminating the need for a recirculation pump. Additionally, a laminated disk would allow a reverse flow of fluid through the membrane pores removing trapped particles.« less

Strongly baryon-dominated disk galaxies at the peak of galaxy formation ten billion years ago

NASA Astrophysics Data System (ADS)

Genzel, R.; Schreiber, N. M. Förster; Übler, H.; Lang, P.; Naab, T.; Bender, R.; Tacconi, L. J.; Wisnioski, E.; Wuyts, S.; Alexander, T.; Beifiori, A.; Belli, S.; Brammer, G.; Burkert, A.; Carollo, C. M.; Chan, J.; Davies, R.; Fossati, M.; Galametz, A.; Genel, S.; Gerhard, O.; Lutz, D.; Mendel, J. T.; Momcheva, I.; Nelson, E. J.; Renzini, A.; Saglia, R.; Sternberg, A.; Tacchella, S.; Tadaki, K.; Wilman, D.

2017-03-01

In the cold dark matter cosmology, the baryonic components of galaxies—stars and gas—are thought to be mixed with and embedded in non-baryonic and non-relativistic dark matter, which dominates the total mass of the galaxy and its dark-matter halo. In the local (low-redshift) Universe, the mass of dark matter within a galactic disk increases with disk radius, becoming appreciable and then dominant in the outer, baryonic regions of the disks of star-forming galaxies. This results in rotation velocities of the visible matter within the disk that are constant or increasing with disk radius—a hallmark of the dark-matter model. Comparisons between the dynamical mass, inferred from these velocities in rotational equilibrium, and the sum of the stellar and cold-gas mass at the peak epoch of galaxy formation ten billion years ago, inferred from ancillary data, suggest high baryon fractions in the inner, star-forming regions of the disks. Although this implied baryon fraction may be larger than in the local Universe, the systematic uncertainties (owing to the chosen stellar initial-mass function and the calibration of gas masses) render such comparisons inconclusive in terms of the mass of dark matter. Here we report rotation curves (showing rotation velocity as a function of disk radius) for the outer disks of six massive star-forming galaxies, and find that the rotation velocities are not constant, but decrease with radius. We propose that this trend arises because of a combination of two main factors: first, a large fraction of the massive high-redshift galaxy population was strongly baryon-dominated, with dark matter playing a smaller part than in the local Universe; and second, the large velocity dispersion in high-redshift disks introduces a substantial pressure term that leads to a decrease in rotation velocity with increasing radius. The effect of both factors appears to increase with redshift. Qualitatively, the observations suggest that baryons in the early (high-redshift) Universe efficiently condensed at the centres of dark-matter haloes when gas fractions were high and dark matter was less concentrated.

Strongly baryon-dominated disk galaxies at the peak of galaxy formation ten billion years ago.

PubMed

Genzel, R; Schreiber, N M Förster; Übler, H; Lang, P; Naab, T; Bender, R; Tacconi, L J; Wisnioski, E; Wuyts, S; Alexander, T; Beifiori, A; Belli, S; Brammer, G; Burkert, A; Carollo, C M; Chan, J; Davies, R; Fossati, M; Galametz, A; Genel, S; Gerhard, O; Lutz, D; Mendel, J T; Momcheva, I; Nelson, E J; Renzini, A; Saglia, R; Sternberg, A; Tacchella, S; Tadaki, K; Wilman, D

2017-03-15

In the cold dark matter cosmology, the baryonic components of galaxies-stars and gas-are thought to be mixed with and embedded in non-baryonic and non-relativistic dark matter, which dominates the total mass of the galaxy and its dark-matter halo. In the local (low-redshift) Universe, the mass of dark matter within a galactic disk increases with disk radius, becoming appreciable and then dominant in the outer, baryonic regions of the disks of star-forming galaxies. This results in rotation velocities of the visible matter within the disk that are constant or increasing with disk radius-a hallmark of the dark-matter model. Comparisons between the dynamical mass, inferred from these velocities in rotational equilibrium, and the sum of the stellar and cold-gas mass at the peak epoch of galaxy formation ten billion years ago, inferred from ancillary data, suggest high baryon fractions in the inner, star-forming regions of the disks. Although this implied baryon fraction may be larger than in the local Universe, the systematic uncertainties (owing to the chosen stellar initial-mass function and the calibration of gas masses) render such comparisons inconclusive in terms of the mass of dark matter. Here we report rotation curves (showing rotation velocity as a function of disk radius) for the outer disks of six massive star-forming galaxies, and find that the rotation velocities are not constant, but decrease with radius. We propose that this trend arises because of a combination of two main factors: first, a large fraction of the massive high-redshift galaxy population was strongly baryon-dominated, with dark matter playing a smaller part than in the local Universe; and second, the large velocity dispersion in high-redshift disks introduces a substantial pressure term that leads to a decrease in rotation velocity with increasing radius. The effect of both factors appears to increase with redshift. Qualitatively, the observations suggest that baryons in the early (high-redshift) Universe efficiently condensed at the centres of dark-matter haloes when gas fractions were high and dark matter was less concentrated.

You’re Cut Off: HD and MHD Simulations of Truncated Accretion Disks

NASA Astrophysics Data System (ADS)

Hogg, J. Drew; Reynolds, Christopher S.

2017-01-01

Truncated accretion disks are commonly invoked to explain the spectro-temporal variability from accreting black holes in both small systems, i.e. state transitions in galactic black hole binaries (GBHBs), and large systems, i.e. low-luminosity active galactic nuclei (LLAGNs). In the canonical truncated disk model of moderately low accretion rate systems, gas in the inner region of the accretion disk occupies a hot, radiatively inefficient phase, which leads to a geometrically thick disk, while the gas in the outer region occupies a cooler, radiatively efficient phase that resides in the standard geometrically thin disk. Observationally, there is strong empirical evidence to support this phenomenological model, but a detailed understanding of the disk behavior is lacking. We present well-resolved hydrodynamic (HD) and magnetohydrodynamic (MHD) numerical models that use a toy cooling prescription to produce the first sustained truncated accretion disks. Using these simulations, we study the dynamics, angular momentum transport, and energetics of a truncated disk in the two different regimes. We compare the behaviors of the HD and MHD disks and emphasize the need to incorporate a full MHD treatment in any discussion of truncated accretion disk evolution.

Murchison CM2 chondrite at nanoscale: evidence for hydrated minerals in the protoplanetary disk

NASA Astrophysics Data System (ADS)

Trigo-Rodriguez, J. M.; Vila-Ruaix, A.; Alonso-Azcárate, J.; Abad, M. M.

2017-03-01

The most pristine chondrites are undifferentiated meteorites with highly unequilibrated mineral grains that accreted from the protoplanetary disk about 4.6 Gyrs ago. Here we focus our attention in the study of Murchison, one of the most primitive carbonaceous chondrites belonging to the CM2 group. Despite of being aqueously altered, Murchison matrix is extraordinarily complex at nanoscale, and its study can hold clues to understand the origin of the water incorporated in the parent bodies of carbonaceous chondrites. Murchison comes from an undifferentiated carbon-rich asteroid which formed from the accretion of solid particles formed in the outer protoplanetary disk. Their rock-forming materials felt into the plane of the system where they mixed with organics, and probably with hydrated minerals. Our UHRTEM (ultra-high resolution transmission electron microscopy) data demonstrate that Murchison fine-grained matrix consists of a complex mixture of many ingredients, including chondrule and CAI fragments, stellar grains, phyllosilicates and organic compounds. We describe here some mineral and textural features that exemplify how pristine, and diverse is Murchison matrix. Our results indicate that the study of carbonaceous chondrites at nanoscale can provide a significant progress in our understanding of the accretion of materials and the preservation of presolar grains in the outer regions of the protoplanetary disk.

Terahertz plasmon-induced transparency based on asymmetric dual-disk resonators coupled to a semiconductor InSb waveguide and its biosensor application

NASA Astrophysics Data System (ADS)

Shahamat, Yadollah; Vahedi, Mohammad

2017-06-01

An ultracompact double eight-shaped plasmonic structure for the realization of plasmon-induced transparency (PIT) in the terahertz (THz) region has been studied. The device consists of a semiconductor-insulator-semiconductor bus waveguide coupled to the dual-disk resonators. Indium antimonide is employed to excite SPP in the THz region. The transmission characteristics of the proposed device are simulated numerically by the finite-difference time-domain method. In addition, a theoretical analysis based on the coupled-mode theory for transmission features is presented and compared with the numerical results. Results are in good agreement. Also, the dependence of PIT frequency characteristics on the radius of the outer disk is discussed in detail. In addition, by removing one of the outer disk resonators, double-PIT peaks can be observed in the transmission spectrum, and the physical mechanism of the appeared peaks is investigated. Finally, an application of the proposed structure for distinguishing different states of DNA molecules is discussed. Results show that the maximum sensitivity with 654 GHz/RIU-1 could be obtained for a single PIT structure. The frequency shifts equal to 37 and 99 GHz could be observed for the denatured and the hybridized DNA states, respectively.

On The Possibility of Enrichment and Differentiation in Gas Giants During Birth by Disk Instability

NASA Astrophysics Data System (ADS)

Boley, Aaron C.; Durisen, R. H.

2011-01-01

We investigate the coupling between rock-size solids and gas during the formation of gas giant planets by disk fragmentation in the outer regions of massive disks. In this study, we use three-dimensional radiative hydrodynamics simulations and model solids as a spatial distribution of particles. We assume that half of the total solid fraction is in small grains and half in large solids. The former are perfectly entrained with the gas and set the opacity, while the latter are allowed to respond to gas drag forces. To explore the maximum effects of gas-solid interactions, we first consider 10cm-size particles. We then compare these results to a simulation with 1km-size particles, which explores the low-drag regime.We show that (1) disk instability planets have the potential to form large cores due to aerodynamic capturing of rock-size solids in spiral arms before fragmentation; (2) that temporary clumps can concentrate tens of M⊕ of solids in very localized regions before clump disruption; (3) that the formation of permanent clumps, even in the outer disk, is dependent on the opacity; (4) that nonaxisymmetric structure in the disk can create disk regions that have a solids-to-gas ratio greater than unity; (5) that the solid distribution may affect the fragmentation process; (6) that proto-gas giants and proto-brown dwarfs can start as differentiated objects prior to the H2 collapse phase; (7) that spiral arms in a gravitationally unstable disk are able to stop the inward drift of rock-size solids, even redistributing them to larger radii; and, (8) that large solids can form spiral arms that are offset from the gaseous spiral arms. ACB's support was provided in part under contract with the California Institute of Technology (Caltech) funded by NASA through the Sagan Fellowship Program. RHD was supported by NASA Origins of Solar Systems grant NNX08AK36G.

Disk Chemistry and Cometary Composition

NASA Astrophysics Data System (ADS)

Markwick, A. J.; Charnley, S. B.

2003-05-01

We will describe current chemical modelling of disks similar to the protosolar nebula. Calculations are being undertaken to determine the spatial and temporal chemistry of the gas and dust within the 5-40AU comet-forming region of the nebula. These theoretical studies aim to determine the contribution of pristine and partially-processed interstellar material from the cool outer nebula, as compared to that obtained from outward radial mixing of matter from the hot inner nebula. Reference Molecular distributions in the inner regions of protostellar disks, Markwick, A. J., Ilgner, M., Millar, T. J., Henning, Th. (2002), Astron. Astrophys., 385, 632.

Disk Chemistry and Cometary Composition

NASA Astrophysics Data System (ADS)

Markwick, A. J.; Charnley, S. B.

2005-01-01

We will describe current chemical modelling of disks similar to the protosolar nebula. Calculations are being undertaken to determine the spatial and temporal chemistry of the gas and dust within the 5-40AU comet-forming region of the nebula. These theoretical studies aim to determine the contribution of pristine and partially-processed interstellar material from the cool outer nebula as compared to that obtained from outward radial mixing of matter from the hot inner nebula. Reference Molecular distributions in the inner regions of protostellar disks Markwick A. J. Ilgner M. Millar T. J. Henning Th. (2002) Astron. Astrophys. 385 632

Binary-disk interaction. II. Gap-opening criteria for unequal-mass binaries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Del Valle, Luciano; Escala, Andrés, E-mail: ldelvalleb@gmail.com

We study the interaction of an unequal-mass binary with an isothermal circumbinary disk, motivated by the theoretical and observational evidence that after a major merger of gas-rich galaxies, a massive gaseous disk with a supermassive black hole binary will be formed in the nuclear region. We focus on the gravitational torques that the binary exerts on the disk and how these torques can drive the formation of a gap in the disk. This exchange of angular momentum between the binary and the disk is mainly driven by the gravitational interaction between the binary and a strong nonaxisymmetric density perturbation thatmore » is produced in the disk, in response to the presence of the binary. Using smoothed particle hydrodynamics numerical simulations, we test two gap-opening criteria, one that assumes the geometry of the density perturbation is an ellipsoid/thick spiral and another that assumes a flat spiral geometry for the density perturbation. We find that the flat spiral gap-opening criterion successfully predicts which simulations will have a gap in the disk and which will not. We also study the limiting cases predicted by the gap-opening criteria. Since the viscosity in our simulations is considerably smaller than the expected value in the nuclear regions of gas-rich merging galaxies, we conclude that in such environments the formation of a circumbinary gap is unlikely.« less

How robust are our views of Milky Way stellar populations before Gaia?

NASA Astrophysics Data System (ADS)

Haywood, M.

2014-07-01

One year before the first release of the first data from Gaia, how robust are our views of the Milky Way stellar populations? Recent results have shown that limits, differences and/or continuities between populations are not where we thought they were just a few years ago. The outer disk (> 10kpc) has properties essentially different from the inner (thin+thick) disk, while the bulge is best explained in terms of disk populations, with a negligible or inexistent classical bulge, suggesting that the Milky Way is a pure disk galaxy. Much less contingent than previously envisaged, the thick disk is probably the main phase of stellar mass creation in the MW, and the parent population of the thin disk. These results lead to fundamental changes in our views on the stellar mass growth of the Galaxy, secular mass redistribution in the disk, and imply a change of paradigm of the chemical evolution. I review these different advances, and discuss some of the key questions.

EXTERNAL PHOTOEVAPORATION OF THE SOLAR NEBULA: JUPITER's NOBLE GAS ENRICHMENTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Monga, Nikhil; Desch, Steven

We present a model explaining the elemental enrichments in Jupiter's atmosphere, particularly the noble gases Ar, Kr, and Xe. While He, Ne, and O are depleted, seven other elements show similar enrichments (∼3 times solar, relative to H). Being volatile, Ar is difficult to fractionate from H{sub 2}. We argue that external photoevaporation by far-ultraviolet (FUV) radiation from nearby massive stars removed H{sub 2}, He, and Ne from the solar nebula, but Ar and other species were retained because photoevaporation occurred at large heliocentric distances where temperatures were cold enough (≲ 30 K) to trap them in amorphous water ice. Asmore » the solar nebula lost H, it became relatively and uniformly enriched in other species. Our model improves on the similar model of Guillot and Hueso. We recognize that cold temperatures alone do not trap volatiles; continuous water vapor production is also necessary. We demonstrate that FUV fluxes that photoevaporated the disk generated sufficient water vapor in regions ≲ 30 K to trap gas-phase species in amorphous water ice in solar proportions. We find more efficient chemical fractionation in the outer disk: whereas the model of Guillot and Hueso predicts a factor of three enrichment when only <2% of the disk mass remains, we find the same enrichments when 30% of the disk mass remains. Finally, we predict the presence of ∼0.1 M {sub ⊕} of water vapor in the outer solar nebula and protoplanetary disks in H II regions.« less

Formation of a White-Light Jet Within a Quadrupolar Magnetic Configuration

NASA Astrophysics Data System (ADS)

Filippov, Boris; Koutchmy, Serge; Tavabi, Ehsan

2013-08-01

We analyze multi-wavelength and multi-viewpoint observations of a large-scale event viewed on 7 April 2011, originating from an active-region complex. The activity leads to a white-light jet being formed in the outer corona. The topology and evolution of the coronal structures were imaged in high resolution using the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). In addition, large field-of-view images of the corona were obtained using the Sun Watcher using Active Pixel System detector and Image Processing (SWAP) telescope onboard the PRoject for Onboard Autonomy (PROBA2) microsatellite, providing evidence for the connectivity of the coronal structures with outer coronal features that were imaged with the Large Angle Spectrometric Coronagraph (LASCO) C2 on the S olar and Heliospheric Observatory (SOHO). The data sets reveal an Eiffel-tower type jet configuration extending into a narrow jet in the outer corona. The event starts from the growth of a dark area in the central part of the structure. The darkening was also observed in projection on the disk by the Solar TErrestrial RElations Observatory-Ahead (STEREO-A) spacecraft from a different point of view. We assume that the dark volume in the corona descends from a coronal cavity of a flux rope that moved up higher in the corona but still failed to erupt. The quadrupolar magnetic configuration corresponds to a saddle-like shape of the dark volume and provides a possibility for the plasma to escape along the open field lines into the outer corona, forming the white-light jet.

The Cosmic Battery in Astrophysical Accretion Disks

NASA Astrophysics Data System (ADS)

Contopoulos, Ioannis; Nathanail, Antonios; Katsanikas, Matthaios

2015-06-01

The aberrated radiation pressure at the inner edge of the accretion disk around an astrophysical black hole imparts a relative azimuthal velocity on the electrons with respect to the ions which gives rise to a ring electric current that generates large-scale poloidal magnetic field loops. This is the Cosmic Battery established by Contopoulos and Kazanas in 1998. In the present work we perform realistic numerical simulations of this important astrophysical mechanism in advection-dominated accretion flows, ADAFs. We confirm the original prediction that the inner parts of the loops are continuously advected toward the central black hole and contribute to the growth of the large-scale magnetic field, whereas the outer parts of the loops are continuously diffusing outward through the turbulent accretion flow. This process of inward advection of the axial field and outward diffusion of the return field proceeds all the way to equipartition, thus generating astrophysically significant magnetic fields on astrophysically relevant timescales. We confirm that there exists a critical value of the magnetic Prandtl number between unity and 10 in the outer disk above which the Cosmic Battery mechanism is suppressed.

A mysterious dust clump in a disk around an evolved binary star system.

PubMed

Jura, M; Turner, J

1998-09-10

The discovery of planets in orbit around the pulsar PSR1257+12 shows that planets may form around post-main-sequence stars. Other evolved stars, such as HD44179 (an evolved star which is part of the binary system that has expelled the gas and dust that make the Red Rectangle nebula), possess gravitationally bound orbiting dust disks. It is possible that planets might form from gravitational collapse in such disks. Here we report high-angular-resolution observations at millimetre and submillimetre wavelengths of the dusk disk associated with the Red Rectangle. We find a dust clump with an estimated mass near that of Jupiter in the outer region of the disk. The clump is larger than our Solar System, and far beyond where planet formation would normally be expected, so its nature is at present unclear.

The Mass Distribution in Disk Galaxies

NASA Astrophysics Data System (ADS)

Courteau, Stéphane; Dutton, Aaron A.

We present the relative fraction of baryons and dark matter at various radii in galaxies. For spiral galaxies, this fraction measured in a galaxy's inner parts is typically baryon-dominated (maximal) and dark-matter dominated (sub-maximal) in the outskirts. The transition from maximal to sub-maximal baryons occurs within the inner parts of low-mass disk galaxies (with V tot <= 200 km s-1) and in the outer disk for more massive systems. The mean mass fractions for late- and early-type galaxies vary significantly at the same fiducial radius and circular velocity, suggesting a range of galaxy formation mechanisms. A more detailed discussion, and resolution of the so-called ``maximal disk problem'', is presented in Courteau & Dutton, ApJL, 801, 20.

The unusual carbon star HD 59643 - Alternative models

NASA Technical Reports Server (NTRS)

Johnson, H. R.; Eaton, J. A.; Querci, F. R.; Querci, M.; Baumert, J. H.

1988-01-01

A binary model for the carbon star HD 59643 is discussed in which the secondary spectrum is formed in an accretion disk. If this hot, ultraviolet-emitting disk radiates like a 20,000 K black-body, it must be 0.03 solar radii or less across at minimum emission. Large widths of C IV multiplet UV1 on high-resolution spectra indicate its formation in the inner parts of a disk. The semiforbidden C III and Si III lines, however, are much narrower and could be formed in the outer parts of a disk or in the carbon star's chromosphere. The electron density in the region of formation of C III is about 10 to the 10th/cu cm.

Probing Signatures of a Distant Planet around the Young T-Tauri Star CI Tau Hosting a Possible Hot Jupiter

NASA Astrophysics Data System (ADS)

Konishi, Mihoko; Hashimoto, Jun; Hori, Yasunori

2018-06-01

We search for signatures of a distant planet around the two million-year-old classical T-Tauri star CI Tau hosting a hot-Jupiter candidate ({M}{{p}}\\sin i∼ 8.1 {M}Jupiter}) in an eccentric orbit (e ∼ 0.3). To probe the existence of an outer perturber, we reanalyzed 1.3 mm dust continuum observations of the protoplanetary disk around CI Tau obtained by the Atacama Large Millimeter/submillimeter Array (ALMA). We found a gap structure at ∼0.″8 in CI Tau’s disk. Our visibility fitting assuming an axisymmetric surface brightness profile suggested that the gap is located at a deprojected radius of 104.5 ± 1.6 au and has a width of 36.9 ± 2.9 au. The brightness temperature around the gap was calculated to be ∼2.3 K lower than that of the ambient disk. Gap-opening mechanisms such as secular gravitational instability (GI) and dust trapping can explain the gap morphology in the CI Tau disk. The scenario that an unseen planet created the observed gap structure cannot be ruled out, although the coexistence of an eccentric hot Jupiter and a distant planet around the young CI Tau would be challenging for gravitational scattering scenarios. The mass of the planet was estimated to be between ∼0.25 M Jupiter and ∼0.8 M Jupiter from the gap width and depth ({0.41}-0.06+0.04) in the modeled surface brightness image, which is lower than the current detection limits of high-contrast direct imaging. The young classical T-Tauri CI Tau may be a unique system for exploring the existence of a potential distant planet as well as the origin of an eccentric hot Jupiter.

What is the Mass of a Gap-opening Planet?

NASA Astrophysics Data System (ADS)

Dong, Ruobing; Fung, Jeffrey

2017-02-01

High-contrast imaging instruments such as GPI and SPHERE are discovering gap structures in protoplanetary disks at an ever faster pace. Some of these gaps may be opened by planets forming in the disks. In order to constrain planet formation models using disk observations, it is crucial to find a robust way to quantitatively back out the properties of the gap-opening planets, in particular their masses, from the observed gap properties, such as their depths and widths. Combining 2D and 3D hydrodynamics simulations with 3D radiative transfer simulations, we investigate the morphology of planet-opened gaps in near-infrared scattered-light images. Quantitatively, we obtain correlations that directly link intrinsic gap depths and widths in the gas surface density to observed depths and widths in images of disks at modest inclinations under finite angular resolution. Subsequently, the properties of the surface density gaps enable us to derive the disk scale height at the location of the gap h, and to constrain the quantity Mp2/α, where Mp is the mass of the gap-opening planet and α characterizes the viscosity in the gap. As examples, we examine the gaps recently imaged by VLT/SPHERE, Gemini/GPI, and Subaru/HiCIAO in HD 97048, TW Hya, HD 169142, LkCa 15, and RX J1615.3-3255. Scale heights of the disks and possible masses of the gap-opening planets are derived assuming each gap is opened by a single planet. Assuming α = 10‑3, the derived planet masses in all cases are roughly between 0.1 and 1 MJ.

The SEEDS of Planet Formation: Observations of Transitional Disks

NASA Technical Reports Server (NTRS)

Grady, Carol A.

2011-01-01

As part of its 5-year study, the Strategic Exploration of Exoplanets and Disk Systems (SEEDS) has already observed a number of YSOs with circumstellar disks, including 13 0.5-8 Myr old A-M stars with indications that they host wide gaps or central cavities in their circumstellar disks in millimeter or far-IR observations, or from deficits in warm dust thermal emission. For 8 of the disks, the 0.15" inner working angle of HiCIAO+A0188 samples material in the millimeter or mid-IR identified cavity. In one case we report detection of a previously unrecognized wide gap. For the remaining 4 stars, the SEEDS data sample the outer disk: in 3 cases, we present the first NIR imagery of the disks. The data for the youngest sample members 1-2 Myr) closely resemble coeval primordial disks. After approximately 3 Myr, the transitional disks show a wealth of structure including spiral features, rings, divots, and in some cases, largely cleared gaps in the disks which are not seen in coeval primordial disks. Some of these structural features are predicted consequences of Jovian-mass planets having formed in the disk, while others are novel features. We discuss the implications for massive planet formation timescales and mechanisms.

The SEEDS of Planet Formation: Observations of Transitional Disks

NASA Technical Reports Server (NTRS)

Grady, Carol

2011-01-01

As part of its 5-year study, the Strategic Exploration of Exoplanets and Disk Systems (SEEDS) has already observed a number of YSOs with circumstellar disks, including 13 0.5- 8 Myr old A-M stars with indications that they host wide gaps or central cavities in their circumstellar disks in millimeter or far-IR observations, or from deficits in warm dust thermal emission. For 8 of the disks, the 0.15" inner working angle of HiCIAO+A0188 samples material in the millimeter or mid-IR identified cavity. In one case we reprt detection of a previously unrecognized wide gap. For the remaining 4 stars, the SEEDS data sample the outer disk: in 3 cases, we present the first NIR imagery of the disks. The data for the youngest sample members (less than 1-2 Myr) closely resemble coeval primordial disks. After approximately 3 Myr, the transitional disks show a wealth of structure including spiral features, rings, divots, and in some cases, largely cleared gaps in the disks which are not seen in coeval primordial disks. Some of these structural features are predicted consequences of lovianmass planets having formed in the disk, while others are novel features. We discuss the implications for massive planet formation timescales and mechanisms.

What Are M31 Disk Planetary Nebulae Trying to Tell Us?

NASA Astrophysics Data System (ADS)

Kwitter, Karen B.; Balick, Bruce; Henry, Richard B. C.; Corradi, Romano L. M.

2015-01-01

Over the past eight years we have observed optical spectra of planetary nebulae (PNe) in the disk of M31 using DIS on the 3.5-m ARC telescope at Apache Point Observatory and OSIRIS on the 10.4-m GTC on La Palma. We have so far studied more than two dozen objects over a projected galactocentric radius range from 5 - 33 kpc; this corresponds to a deprojected in-disk range of 15 - 106 kpc. Using ELSA, a five-level atom package, we have derived nebular diagnostics and ionic and total nebular abundances of He and O, as well as estimates for other elements. The average 12+log(O/H) for 23 disk PNe we have observed is 8.6, or about 80% of the solar value. The inferred oxygen abundance gradient across the disk is surprisingly shallow (~ -0.004 dex/kpc) out to R(deprojected)~60 kpc. CLOUDY models we have computed for many of these objects indicate central star masses whose main-sequence progenitors are estimated to be in the range of 1.7-2.5 solar masses, with lifetimes under ~2 Gyr. The existence of such young, relatively massive, and metal-rich stars past the outer edge of the spiral arms at ~18 kpc and the H I warp at ~30 kpc (beyond which stellar [Fe/H] < -1) is unexpected, and disagrees with standard models of outer galaxy assembly via assimilation of metal-poor dwarf galaxies. Star formation from inner-disk ISM ejected by a putative gravitational encounter between M31 and M33 about 3 GY ago (Bernard et al. 2012, ApJ 420, 2625) supplies a possible explanation.

Formation of TRAPPIST-1

NASA Astrophysics Data System (ADS)

Ormel, C. W.; Liu, B.; Schoonenberg, D.

2017-09-01

We present a model for the formation of the recently-discovered TRAPPIST-1 planetary system. In our scenario planets form in the interior regions, by accretion of mm to cm-size particles (pebbles) that drifted from the outer disk. This scenario has several advantages: it connects to the observation that disks are made up of pebbles, it is efficient, it explains why the TRAPPIST-1 planets are ˜Earth mass, and it provides a rationale for the system's architecture.

Cost/benefit analysis of advanced materials technologies for future aircraft turbine engines

NASA Technical Reports Server (NTRS)

Bisset, J. W.

1976-01-01

The cost/benefits of advance commercial gas turbine materials are described. Development costs, estimated payoffs and probabilities of success are discussed. The materials technologies investigated are: (1) single crystal turbine blades, (2) high strength hot isostatic pressed turbine disk, (3) advanced oxide dispersion strengthened burner liner, (4) bore entry cooled hot isostatic pressed turbine disk, (5) turbine blade tip - outer airseal system, and (6) advance turbine blade alloys.

Emission Lines from the Gas Disk Around TW Hydra and the Origin of the Inner Hole

NASA Technical Reports Server (NTRS)

Gorti, U.; Hollenbach, D.; Najita, J.; Pascucci, I.

2011-01-01

We compare line emission calculated from theoretical disk models with optical to submillimeter wavelength observational data of the gas disk surrounding TW Hya and infer the spatial distribution of mass in the gas disk. The model disk that best matches observations has a gas mass ranging from approx.10(exp -4) to 10(exp -5) M for 0.06AU < r < 3.5 AU and approx. 0.06M for 3.5AU < r < 200 AU. We find that the inner dust hole (r < 3.5 AU) in the disk must be depleted of gas by approx. 1-2 orders of magnitude compared with the extrapolated surface density distribution of the outer disk. Grain growth alone is therefore not a viable explanation for the dust hole. CO vibrational emission arises within r approx. 0.5 AU from thermal excitation of gas. [O i] 6300Å and 5577Å forbidden lines and OH mid-infrared emission are mainly due to prompt emission following UV photodissociation of OH and water at r < or approx. 0.1 AU and at r approx. 4 AU. [Ne ii] emission is consistent with an origin in X-ray heated neutral gas at r < or approx. 10 AU, and may not require the presence of a significant extreme-ultraviolet (h? > 13.6 eV) flux from TW Hya. H2 pure rotational line emission comes primarily from r approx. 1 to 30 AU. [Oi] 63microns, HCO+, and CO pure rotational lines all arise from the outer disk at r approx. 30-120 AU. We discuss planet formation and photoevaporation as causes for the decrease in surface density of gas and dust inside 4 AU. If a planet is present, our results suggest a planet mass approx. 4-7MJ situated at 3 AU. Using our photoevaporation models and the best surface density profile match to observations, we estimate a current photoevaporative mass loss rate of 4x10(exp -9M)/yr and a remaining disk lifetime of approx.5 million years.

The Dynamics and Implications of Gap Clearing via Planets in Planetesimal (Debris) Disks

NASA Astrophysics Data System (ADS)

Morrison, Sarah Jane

Exoplanets and debris disks are examples of solar systems other than our own. As the dusty reservoirs of colliding planetesimals, debris disks provide indicators of planetary system evolution on orbital distance scales beyond those probed by the most prolific exoplanet detection methods, and on timescales 10 r to 10 Gyr. The Solar System possesses both planets and small bodies, and through studying the gravitational interactions between both, we gain insight into the Solar System's past. As we enter the era of resolved observations of debris disks residing around other stars, I add to our theoretical understanding of the dynamical interactions between debris, planets, and combinations thereof. I quantify how single planets clear material in their vicinity and how long this process takes for the entire planetary mass regime. I use these relationships to assess the lowest mass planet that could clear a gap in observed debris disks over the system's lifetime. In the distant outer reaches of gaps in young debris systems, this minimum planet mass can exceed Neptune's. To complement the discoveries of wide-orbit, massive, exoplanets by direct imaging surveys, I assess the dynamical stability of high mass multi-planet systems to estimate how many high mass planets could be packed into young, gapped debris disks. I compare these expectations to the planet detection rates of direct imaging surveys and find that high mass planets are not the primary culprits for forming gaps in young debris disk systems. As an alternative model for forming gaps in planetesimal disks with planets, I assess the efficacy of creating gaps with divergently migrating pairs of planets. I find that migrating planets could produce observed gaps and elude detection. Moreover, the inferred planet masses when neglecting migration for such gaps could be expected to be observable by direct imaging surveys for young, nearby systems. Wide gaps in young systems would likely still require more than two planets even with plantesimal-driven migration. These efforts begin to probe the types of potential planets carving gaps in disks of different evolutionary stages and at wide orbit separations on scales similar to our outer Solar System.

Comparison of central axis and jet ring coolant supply for turbine disk cooling on a SSME-HPOTP model

NASA Technical Reports Server (NTRS)

Kim, Y. W.; Metzger, D. E.

1992-01-01

The test facility, test methods and results are presented for an experimental study modeling the cooling of turbine disks in the blade attachment regions with multiple impinging jets, in a configuration simulating the disk cooling method employed on the Space Shuttle Main Engine oxygen turbopump. The study's objective was to provide a comparison of detailed local convection heat transfer rates obtained for a single center-supply of disk coolant with those obtained with the present flight configuration where disk coolant is supplied through an array of 19 jets located near the disk outer radius. Specially constructed disk models were used in a program designed to evaluate possible benefits and identify any possible detrimental effects involved in employing an alternate disk cooling scheme. The study involved the design, construction and testing of two full scale rotating model disks, one plane and smooth for baseline testing and the second contoured to the present flight configuration, together with the corresponding plane and contoured stator disks. Local heat transfer rates are determined from the color display of encapsulated liquid crystals coated on the disk in conjunction with use of a computer vision system. The test program was composed of a wide variety of disk speeds, flowrates, and geometrical configurations, including testing for the effects of disk boltheads and gas ingestion from the gas path region radially outboard of the disk-cavity.

Herschel evidence for disk flattening or gas depletion in transitional disks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Keane, J. T.; Pascucci, I.; Espaillat, C.

Transitional disks are protoplanetary disks characterized by reduced near- and mid-infrared emission, with respect to full disks. This characteristic spectral energy distribution indicates the presence of an optically thin inner cavity within the dust disk believed to mark the disappearance of the primordial massive disk. We present new Herschel Space Observatory PACS spectra of [O I] 63.18 μm for 21 transitional disks. Our survey complements the larger Herschel GASPS program ({sup G}as in Protoplanetary Systems{sup )} by quadrupling the number of transitional disks observed with PACS in this wavelength. [O I] 63.18 μm traces material in the outer regions ofmore » the disk, beyond the inner cavity of most transitional disks. We find that transitional disks have [O I] 63.18 μm line luminosities ∼2 times fainter than their full disk counterparts. We self-consistently determine various stellar properties (e.g., bolometric luminosity, FUV excess, etc.) and disk properties (e.g., disk dust mass, etc.) that could influence the [O I] 63.18 μm line luminosity, and we find no correlations that can explain the lower [O I] 63.18 μm line luminosities in transitional disks. Using a grid of thermo-chemical protoplanetary disk models, we conclude that either transitional disks are less flared than full disks or they possess lower gas-to-dust ratios due to a depletion of gas mass. This result suggests that transitional disks are more evolved than their full disk counterparts, possibly even at large radii.« less

Deuterium fractionation of water in the Solar nebula

NASA Astrophysics Data System (ADS)

Albertsson, Tobias; Semenov, Dmitry; Henning, Thomas

2013-07-01

Water evaporates in the inner regions of protoplanetary disks and is frozen onto grains in the outer regions. Therefore its presence in vast quantities on Earth is puzzling. Subsequent delivery through bombardment by primitive bodies formed in the outer icy regions is the favored mechanism. By studying water D/H ratios one hopes to understand whether the water was mainly delivered by comets or asteroids. Using an extended deuterium chemistry network coupled to a 2D chemo-dynamical disk model, we investigate the evolution of the D/H ratio of water in the young Solar nebula. We find that both the laminar and mixing Solar nebula models show the Earth's ocean water D/H ratio at 2-3 AU. In addition, the 2D-mixing model explains better the water D/H values observed in the Oort- and Jupiter-family comets.

Modeling Jupiter's current disc - Pioneer 10 outbound

NASA Astrophysics Data System (ADS)

Jones, D. E.; Melville, J. G.; Blake, M. L.

1980-07-01

A model of the magnetic field of the Jovian current disk is presented. The model uses Euler functions and the Biot-Savart law applied to a series of concentric, but not necessarily coplanar current rings. It was found that the best fit to the Pioneer 10 outbound perturbation magnetic field data is obtained if the current disk is twisted, and also bent to tend toward parallelism with the Jovigraphic equator. The inner and outer radii of the disk appear to be about 7 and 150 Jovian radii, respectively; because of the observed current disk penetrations, the bent disk also requires a deformation in the form of a bump or wrinkle whose axis tends to exhibit spiraling. Modeling of the azimuthal field shows that it is due to a thin radial current sheet, but it may actually be due in large part to penetration of a tail current sheet as suggested by Voyager observations.

Modeling of the heat distribution in the intervertebral disk.

PubMed

Persson, Johan; Hansen, Eskil; Lidgren, Lars; McCarthy, Ian

2005-05-01

The heat transfer equation was used to model the heat distribution in an intervertebral disk during ultrasound (US) exposure. The influence of thermal and acoustic parameters was studied to get a quantitative understanding of the heat transfer in the system. Heating of collagen to 65 degrees C or above will lead to denaturation and is believed to stabilize and contract the outer part of the disk in a herniated disk. In our model, the US intensity was approximated by a Gaussian distribution and nonlinear propagation was excluded. The effect of self-heating and cooling of the transducer was also studied. The simulations were performed using the finite element method. From this model, it can be concluded that it is possible to heat parts of the disk to treatment temperature using a focused 5-mm diameter US probe. The physical constraints on the piezocrystal set the limit of the size of the treatment volume.

Inner and outer star forming regions over the disks of spiral galaxies. I. Sample characterization

NASA Astrophysics Data System (ADS)

Rodríguez-Baras, M.; Díaz, A. I.; Rosales-Ortega, F. F.; Sánchez, S. F.

2018-01-01

Context. The knowledge of abundance distributions is central to understanding the formation and evolution of galaxies. Most of the relations employed for the derivation of gas abundances have so far been derived from observations of outer disk H ii regions, despite the known differences between inner and outer regions. Aims: Using integral field spectroscopy (IFS) observations we aim to perform a systematic study and comparison of two inner and outer H ii regions samples. The spatial resolution of the IFS, the number of objects and the homogeneity and coherence of the observations allow a complete characterization of the main observational properties and differences of the regions. Methods: We analyzed a sample of 725 inner H ii regions and a sample of 671 outer H ii regions, all of them detected and extracted from the observations of a sample of 263 nearby, isolated, spiral galaxies observed by the CALIFA survey. Results: We find that inner H ii regions show smaller equivalent widths, greater extinction and luminosities, along with greater values of [N ii] λ6583/Hα and [O ii] λ3727/[O iii] λ5007 emission-line ratios, indicating higher metallicities and lower ionization parameters. Inner regions have also redder colors and higher photometric and ionizing masses, although MionMphot is slighty higher for the outer regions. Conclusions: This work shows important observational differences between inner and outer H ii regions in star forming galaxies not previously studied in detail. These differences indicate that inner regions have more evolved stellar populations and are in a later evolution state with respect to outer regions, which goes in line with the inside-out galaxy formation paradigm. Table 4 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/609/A102

Ringed Structures of the HD 163296 Protoplanetary Disk Revealed by ALMA

NASA Astrophysics Data System (ADS)

Isella, Andrea; Guidi, Greta; Testi, Leonardo; Liu, Shangfei; Li, Hui; Li, Shengtai; Weaver, Erik; Boehler, Yann; Carperter, John M.; De Gregorio-Monsalvo, Itziar; Manara, Carlo F.; Natta, Antonella; Pérez, Laura M.; Ricci, Luca; Sargent, Anneila; Tazzari, Marco; Turner, Neal

2016-12-01

We present Atacama Large Millimeter and Submillimeter Array observations of the protoplanetary disk around the Herbig Ae star HD 163296 that trace the spatial distribution of millimeter-sized particles and cold molecular gas on spatial scales as small as 25 astronomical units (A.U.). The image of the disk recorded in the 1.3 mm continuum emission reveals three dark concentric rings that indicate the presence of dust depleted gaps at about 60, 100, and 160 A.U. from the central star. The maps of the 12CO, 13CO, and C 18O J =2 -1 emission do not show such structures but reveal a change in the slope of the radial intensity profile across the positions of the dark rings in the continuum image. By comparing the observations with theoretical models for the disk emission, we find that the density of CO molecules is reduced inside the middle and outer dust gaps. However, in the inner ring there is no evidence of CO depletion. From the measurements of the dust and gas densities, we deduce that the gas-to-dust ratio varies across the disk and, in particular, it increases by at least a factor 5 within the inner dust gap compared to adjacent regions of the disk. The depletion of both dust and gas suggests that the middle and outer rings could be due to the gravitational torque exerted by two Saturn-mass planets orbiting at 100 and 160 A.U. from the star. On the other hand, the inner dust gap could result from dust accumulation at the edge of a magnetorotational instability dead zone, or from dust opacity variations at the edge of the CO frost line. Observations of the dust emission at higher angular resolution and of molecules that probe dense gas are required to establish more precisely the origins of the dark rings observed in the HD 163296 disk.

Ringed Structures of the HD 163296 Protoplanetary Disk Revealed by ALMA.

PubMed

Isella, Andrea; Guidi, Greta; Testi, Leonardo; Liu, Shangfei; Li, Hui; Li, Shengtai; Weaver, Erik; Boehler, Yann; Carperter, John M; De Gregorio-Monsalvo, Itziar; Manara, Carlo F; Natta, Antonella; Pérez, Laura M; Ricci, Luca; Sargent, Anneila; Tazzari, Marco; Turner, Neal

2016-12-16

We present Atacama Large Millimeter and Submillimeter Array observations of the protoplanetary disk around the Herbig Ae star HD 163296 that trace the spatial distribution of millimeter-sized particles and cold molecular gas on spatial scales as small as 25 astronomical units (A.U.). The image of the disk recorded in the 1.3 mm continuum emission reveals three dark concentric rings that indicate the presence of dust depleted gaps at about 60, 100, and 160 A.U. from the central star. The maps of the ^{12}CO, ^{13}CO, and C^{18}O J=2-1 emission do not show such structures but reveal a change in the slope of the radial intensity profile across the positions of the dark rings in the continuum image. By comparing the observations with theoretical models for the disk emission, we find that the density of CO molecules is reduced inside the middle and outer dust gaps. However, in the inner ring there is no evidence of CO depletion. From the measurements of the dust and gas densities, we deduce that the gas-to-dust ratio varies across the disk and, in particular, it increases by at least a factor 5 within the inner dust gap compared to adjacent regions of the disk. The depletion of both dust and gas suggests that the middle and outer rings could be due to the gravitational torque exerted by two Saturn-mass planets orbiting at 100 and 160 A.U. from the star. On the other hand, the inner dust gap could result from dust accumulation at the edge of a magnetorotational instability dead zone, or from dust opacity variations at the edge of the CO frost line. Observations of the dust emission at higher angular resolution and of molecules that probe dense gas are required to establish more precisely the origins of the dark rings observed in the HD 163296 disk.

Some aspects of the cosmogonic outward migration of Neptune. Co-planar migration

NASA Astrophysics Data System (ADS)

Neslušan, L.; Jakubík, M.

2013-10-01

Considering a simple model of the cosmogonic outward migration of Neptune, we investigate if the assumption of an extremely low orbital inclination of small bodies in a once-existing proto-planetary disk could influence the structure of reservoirs of the objects in the trans-Neptunian region. We found no significant influence. Our models predict only the existence of the mean-motion resonances (MMRs) with Neptune 2:3, 3:5, 1:2, and an anemic scattered disk (MMRs 3:4, 5:7, and 9:11 are also indicated). To explain the classical Edgeworth-Kuiper belt, relatively abundant 4:7 and 2:5 MMRs, and the more numerous scattered disk, we need to assume that, e.g., the outer boundary of the original proto-planetary disk considerably exceeded the distance of the current Neptune's orbit (Neptune probably ended its migration at the distance, where the disk's density started to be sub-critical), or that some Pluto-sized objects resided inside the MMRs and in the distant parts of the original proto-planetary disk.

Low-temperature crystallization of silicate dust in circumstellar disks.

PubMed

Molster, F J; Yamamura, I; Waters, L B; Tielens, A G; de Graauw, T; de Jong, T; de Koter, A; Malfait, K; van den Ancker, M E; van Winckel, H; Voors, R H; Waelkens, C

1999-10-07

Silicate dust in the interstellar medium is observed to be amorphous, yet silicate dust in comets and interplanetary dust particles is sometimes partially crystalline. The dust in disks that are thought to be forming planets around some young stars also appears to be partially crystalline. These observations suggest that as the dust goes from the precursor clouds to a planetary system, it must undergo some processing, but the nature and extent of this processing remain unknown. Here we report observations of highly crystalline silicate dust in the disks surrounding binary red-giant stars. The dust was created in amorphous form in the outer atmospheres of the red giants, and therefore must be processed in the disks to become crystalline. The temperatures in these disks are too low for the grains to anneal; therefore, some low-temperature process must be responsible. As the physical properties of the disks around young stars and red giants are similar, our results suggest that low-temperature crystallization of silicate grains also can occur in protoplanetary systems.

The twofold debris disk around HD 113766 A. Warm and cold dust as seen with VLTI/MIDI and Herschel/PACS

NASA Astrophysics Data System (ADS)

Olofsson, J.; Henning, Th.; Nielbock, M.; Augereau, J.-C.; Juhàsz, A.; Oliveira, I.; Absil, O.; Tamanai, A.

2013-03-01

Context. Warm debris disks are a sub-sample of the large population of debris disks, and display excess emission in the mid-infrared. Around solar-type stars, very few objects (~2% of all debris disks) show emission features in mid-IR spectroscopic observations that are attributed to small, warm silicate dust grains. The origin of this warm dust could be explained either by a recent catastrophic collision between several bodies or by transport from an outer belt similar to the Kuiper belt in the solar system. Aims: We present and analyze new far-IR Herschel/PACS photometric observations, supplemented by new and archival ground-based data in the mid-IR (VLTI/MIDI and VLT/VISIR), for one of these rare systems: the 10-16 Myr old debris disk around HD 113766 A. We improve an existing model to account for these new observations. Methods: We implemented the contribution of an outer planetesimal belt in the Debra code, and successfully used it to model the spectral energy distribution (SED) as well as complementary observations, notably MIDI data. We better constrain the spatial distribution of the dust and its composition. Results: We underline the limitations of SED modeling and the need for spatially resolved observations. We improve existing models and increase our understanding of the disk around HD 113766 A. We find that the system is best described by an inner disk located within the first AU, well constrained by the MIDI data, and an outer disk located between 9-13 AU. In the inner dust belt, our previous finding of Fe-rich crystalline olivine grains still holds. We do not observe time variability of the emission features over at least an eight-year time span in an environment subjected to strong radiation pressure. Conclusions: The time stability of the emission features indicates that μm-sized dust grains are constantly replenished from the same reservoir, with a possible depletion of sub- μm-sized grains. We suggest that the emission features may arise from multi-composition aggregates. We discuss possible scenarios concerning the origin of the warm dust observed around HD 113766 A. The compactness of the innermost regions as probed by the MIDI visibilities and the dust composition suggest that we are witnessing the results of (at least) one collision between partially differentiated bodies, in an environment possibly rendered unstable by terrestrial planetary formation. Based on Herschel observations, OBSIDs: 1342227026, 1342227027, 1342237934, and 1342237935. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Based on VISIR observations collected at the VLT (European Southern Observatory, Paranal, Chile) with program 089.C-0322(A).

What is the Mass of a Gap-opening Planet?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dong, Ruobing; Fung, Jeffrey, E-mail: rdong@email.arizona.edu

High-contrast imaging instruments such as GPI and SPHERE are discovering gap structures in protoplanetary disks at an ever faster pace. Some of these gaps may be opened by planets forming in the disks. In order to constrain planet formation models using disk observations, it is crucial to find a robust way to quantitatively back out the properties of the gap-opening planets, in particular their masses, from the observed gap properties, such as their depths and widths. Combining 2D and 3D hydrodynamics simulations with 3D radiative transfer simulations, we investigate the morphology of planet-opened gaps in near-infrared scattered-light images. Quantitatively, wemore » obtain correlations that directly link intrinsic gap depths and widths in the gas surface density to observed depths and widths in images of disks at modest inclinations under finite angular resolution. Subsequently, the properties of the surface density gaps enable us to derive the disk scale height at the location of the gap h , and to constrain the quantity M {sub p}{sup 2}/ α , where M {sub p} is the mass of the gap-opening planet and α characterizes the viscosity in the gap. As examples, we examine the gaps recently imaged by VLT/SPHERE, Gemini/GPI, and Subaru/HiCIAO in HD 97048, TW Hya, HD 169142, LkCa 15, and RX J1615.3-3255. Scale heights of the disks and possible masses of the gap-opening planets are derived assuming each gap is opened by a single planet. Assuming α = 10{sup −3}, the derived planet masses in all cases are roughly between 0.1 and 1 M {sub J}.« less

Studies of Disks Around the Sun and Other Stars

NASA Technical Reports Server (NTRS)

Stern, S. Alan

1997-01-01

This is a NASA Origins of Solar Systems research program, and this NASA Headquarters grant has now been transferred to a new grant at NASA GSFC (NAG5-4082). Thus the need for this 'Final Report' on a project that is not, in fact, complete. We are conducting research designed to enhance our understanding of the evolution and detectability of comet clouds and disks. This area holds promise for also improving our understanding of outer solar system formation, the bombardment history of the planets, the transport of volatiles and organics from the outer solar system to the inner planets, and to the ultimate fate of comet clouds around the Sun and other stars. According to "standard" theory, both the Kuiper Belt and the Oort Cloud are (at least in part) natural products of the planetary accumulation stage of solar system formation. One expects such assemblages to be a common attribute of other solar systems. Our program consists of modeling collisions in the Kuiper Belt and the dust disks around other stars. The modeling effort focuses on moving from our simple, first-generation, Kuiper Belt collision rate model, to a time-dependent, second-generation model that incorporates physical collisions, velocity evolution, dynamical erosion, and various dust transport mechanisms. This second generation model is to be used to study the evolution of surface mass density and the object-size spectrum in the disk.

A Low Mass for Mars from Jupiter's Early Gas-Driven Migration

NASA Technical Reports Server (NTRS)

Walsh, Kevin J.; Morbidelli, Alessandro; Raymond, Sean N.; O'Brien, David P.; Mandell, Avi M.

2011-01-01

Jupiter and Saturn formed in a few million years from a gas-dominated protoplanetary disk, and were susceptible to gas-driven migration of their orbits on timescales of only approximately 100,000 years. Hydrodynamic simulations show that these giant planets can undergo a two-stage, inward-then-outward, migration. The terrestrial planets finished accreting much later and their characteristics, including Mars' small mass, are best reproduced by starting from a planetesimal disk with an outer edge at about one astronomical unit from the Sun (1 AU is the Earth-Sun distance). Here we report simulations of the early Solar System that show how the inward migration of Jupiter to 1.5 AU, and its subsequent outward migration, lead to a planetesimal disk truncated at 1 AU; the terrestrial planets then form from this disk over the next 30-50 million years, with an Earth/Mars mass ratio consistent with observations. Scattering by Jupiter initially empties but then repopulates the asteroid belt, with inner-belt bodies originating between 1 and 3 AU and outer-belt bodies originating between and beyond the giant planets. This explains the significant compositional differences across the asteroid belt. The key aspect missing from previous models of terrestrial planet formation is the substantial radial migration of the giant planets, which suggests that their behaviour is more similar to that inferred for extrasolar planets than previously thought.

X-Ray Quasi-periodic Oscillations in the Lense–Thirring Precession Model. I. Variability of Relativistic Continuum

NASA Astrophysics Data System (ADS)

You, Bei; Bursa, Michal; Życki, Piotr T.

2018-05-01

We develop a Monte Carlo code to compute the Compton-scattered X-ray flux arising from a hot inner flow that undergoes Lense–Thirring precession. The hot flow intercepts seed photons from an outer truncated thin disk. A fraction of the Comptonized photons will illuminate the disk, and the reflected/reprocessed photons will contribute to the observed spectrum. The total spectrum, including disk thermal emission, hot flow Comptonization, and disk reflection, is modeled within the framework of general relativity, taking light bending and gravitational redshift into account. The simulations are performed in the context of the Lense–Thirring precession model for the low-frequency quasi-periodic oscillations, so the inner flow is assumed to precess, leading to periodic modulation of the emitted radiation. In this work, we concentrate on the energy-dependent X-ray variability of the model and, in particular, on the evolution of the variability during the spectral transition from hard to soft state, which is implemented by the decrease of the truncation radius of the outer disk toward the innermost stable circular orbit. In the hard state, where the Comptonizing flow is geometrically thick, the Comptonization is weakly variable with a fractional variability amplitude of ≤10% in the soft state, where the Comptonizing flow is cooled down and thus becomes geometrically thin, the fractional variability of the Comptonization is highly variable, increasing with photon energy. The fractional variability of the reflection increases with energy, and the reflection emission for low spin is counterintuitively more variable than the one for high spin.

HCO+ Detection of Dust-depleted Gas in the Inner Hole of the LkCa 15 Pre-transitional Disk

NASA Astrophysics Data System (ADS)

Drabek-Maunder, E.; Mohanty, S.; Greaves, J.; Kamp, I.; Meijerink, R.; Spaans, M.; Thi, W.-F.; Woitke, P.

2016-12-01

LkCa 15 is an extensively studied star in the Taurus region, known for its pre-transitional disk with a large inner cavity in the dust continuum and normal gas accretion rate. The most popular hypothesis to explain the LkCa 15 data invokes one or more planets to carve out the inner cavity, while gas continues to flow across the gap from the outer disk onto the central star. We present spatially unresolved HCO+ J=4\\to 3 observations of the LkCa 15 disk from the James Clerk Maxwell telescope (JCMT) and model the data with the ProDiMo code. We find that: (1) HCO+ line-wings are clearly detected, certifying the presence of gas in the cavity within ≲50 au of the star. (2) Reproducing the observed line-wing flux requires both a significant suppression of cavity dust (by a factor ≳104 compared to the interstellar medium (ISM)) and a substantial increase in the gas scale-height within the cavity (H 0/R 0 ˜ 0.6). An ISM dust-to-gas ratio (d:g = 10-2) yields too little line-wing flux, regardless of the scale-height or cavity gas geometry, while a smaller scale-height also under-predicts the flux even with a reduced d:g. (3) The cavity gas mass is consistent with the surface density profile of the outer disk extended inwards to the sublimation radius (corresponding to mass M d ˜ 0.03 M ⊙), and masses lower by a factor ≳10 appear to be ruled out.

The Thermal Regulation of Gravitational Instabilities in Protoplanetary Disks. II. Extended Simulations with Varied Cooling Rates

NASA Astrophysics Data System (ADS)

Mejía, Annie C.; Durisen, Richard H.; Pickett, Megan K.; Cai, Kai

2005-02-01

In order to investigate mass transport and planet formation through gravitational instabilities (GIs), we have extended our three-dimensional hydrodynamic simulations of protoplanetary disks from a previous paper. Our goal is to determine the asymptotic behavior of GIs and how it is affected by different constant cooling times. Initially, Rdisk=40 AU, Mdisk=0.07 Msolar, M*=0.5 Msolar, and Qmin=1.5. Sustained cooling, with tcool=2 ORPs (outer rotation periods; 1ORP~250 yr), drives the disk to instability in about 4 ORPs. This calculation is followed for 23.5 ORPs. After 12 ORPs, the disk settles into a quasi-steady state with sustained nonlinear instabilities, an average Q=1.44 over the outer disk, a well-defined power law Σ(r), and a roughly steady M~5×10-7 Msolar yr-1. The transport is driven by global low-order spiral modes. We restart the calculation at 11.2 ORPs with tcool=1 and 1/4 ORPs. The latter case is also run at high azimuthal resolution. We find that shorter cooling times lead to increased M-values, denser and thinner spiral structures, and more violent dynamic behavior. The asymptotic total internal energy and the azimuthally averaged Q(r) are insensitive to tcool. Fragmentation occurs only in the high-resolution tcool=1/4 ORP case; however, none of the fragments survive for even a quarter of an orbit. Ringlike density enhancements appear and grow near the boundary between GI-active and GI-inactive regions. We discuss the possible implications of these rings for gas giant planet formation.

Shape of LOSVDs in Barred Disks: Implications for Future IFU Surveys

NASA Astrophysics Data System (ADS)

Li, Zhao-Yu; Shen, Juntai; Bureau, Martin; Zhou, Yingying; Du, Min; Debattista, Victor P.

2018-02-01

The shape of line-of-sight velocity distributions (LOSVDs) carries important information about the internal dynamics of galaxies. The skewness of LOSVDs represents their asymmetric deviation from a Gaussian profile. Correlations between the skewness parameter (h 3) and the mean velocity (\\overline{V}) of a Gauss–Hermite series reflect the underlying stellar orbital configurations of different morphological components. Using two self-consistent N-body simulations of disk galaxies with different bar strengths, we investigate {h}3-\\overline{V} correlations at different inclination angles. Similar to previous studies, we find anticorrelations in the disk area, and positive correlations in the bar area when viewed edge-on. However, at intermediate inclinations, the outer parts of bars exhibit anticorrelations, while the core areas dominated by the boxy/peanut-shaped (B/PS) bulges still maintain weak positive correlations. When viewed edge-on, particles in the foreground/background disk (the wing region) in the bar area constitute the main velocity peak, whereas the particles in the bar contribute to the high-velocity tail, generating the {h}3-\\overline{V} correlation. If we remove the wing particles, the LOSVDs of the particles in the outer part of the bar only exhibit a low-velocity tail, resulting in a negative {h}3-\\overline{V} correlation, whereas the core areas in the central region still show weakly positive correlations. We discuss implications for IFU observations on bars, and show that the variation of the {h}3-\\overline{V} correlation in the disk galaxy may be used as a kinematic indicator of the bar and the B/PS bulge.

The Size Distribution Of Cluster Galaxies

NASA Astrophysics Data System (ADS)

Kuchner, U.; Ziegler, B.; Bamford, S.; Verdugo, M.; Haeussler, B.

2017-06-01

We establish a sample of 560 spectroscopically confirmed cluster members of MACS J1206.2- 0847 at z = 0.45 and utilize multi-wavelength and multi-component Sersic profile fitting to provide luminosities and sizes for the key structural components bulge and disk. While the difference between field and cluster galaxy properties are mostly due to a preference for cluster members to be early-type (quiescent, bulge-dominated), we see evidence for an outer disk fading and a sharp rise in the number of red disks with smaller effective radii at the tidally active cluster region around R200. Even though red disks are already virialized according to their velocity distribution, they are clearly not part of the old population found in the innermost region; they represent an important population of transitional objects in clusters.

Calcium Sensing by Recoverin: Effect of Protein Conformation on Ion Affinity.

PubMed

Timr, Štěpán; Kadlec, Jan; Srb, Pavel; Ollila, O H Samuli; Jungwirth, Pavel

2018-04-05

The detailed functional mechanism of recoverin, which acts as a myristoyl switch at the rod outer-segment disk membrane, is elucidated by direct and replica-exchange molecular dynamics. In accord with NMR structural evidence and calcium binding assays, simulations point to the key role of enhanced calcium binding to the EF3 loop of the semiopen state of recoverin as compared to the closed state. This 2-4-order decrease in calcium dissociation constant stabilizes the semiopen state in response to the increase of cytosolic calcium concentration in the vicinity of recoverin. A second calcium ion then binds to the EF2 loop and, consequently, the structure of the protein changes from the semiopen to the open state. The latter has the myristoyl chain extruded to the cytosol, ready to act as a membrane anchor of recoverin.

Oscillations at B Ring Edge

NASA Image and Video Library

2010-11-01

This image obtained by NASA Cassini spacecraft of the outer edge of Saturn?s B ring, reveals the combined effects of a tugging moon and oscillations that can naturally occur in disks like Saturn rings and spiral galaxies.

Attachment device for an inflatable protective cushion

DOEpatents

Nelsen, J.M.; Luna, D.A.; Gwinn, K.W.

1997-11-18

An inflatable cushion assembly for use with an inflator comprises an inflatable cushion having an inner surface, outer surface, and at least one protrusion extending from one of the inner or outer surfaces. The inflatable cushion defines an opening between the inner surface and the outer surface for receiving the inflator. An attachment member contacts the one of the inner or outer surfaces adjacent the opening and includes a groove for receiving the protrusion, the attachment member securing the inflator within the opening. 22 figs.

Attachment device for an inflatable protective cushion

DOEpatents

Nelsen, J.M.; Luna, D.A.; Gwinn, K.W.

1998-12-08

An inflatable cushion assembly for use with an inflator comprises an inflatable cushion having an inner surface, outer surface, and at least one protrusion extending from one of the inner or outer surfaces. The inflatable cushion defines an opening between the inner surface and the outer surface for receiving the inflator. An attachment member contacts the one of the inner or outer surfaces adjacent the opening and includes a groove for receiving the protrusion, the attachment member securing the inflator within the opening. 22 figs.

Towards a Global Evolutionary Model of Protoplanetary Disks

NASA Astrophysics Data System (ADS)

Bai, Xue-Ning

2016-04-01

A global picture of the evolution of protoplanetary disks (PPDs) is key to understanding almost every aspect of planet formation, where standard α-disk models have been continually employed for their simplicity. In the meantime, disk mass loss has been conventionally attributed to photoevaporation, which controls disk dispersal. However, a paradigm shift toward accretion driven by magnetized disk winds has taken place in recent years, thanks to studies of non-ideal magnetohydrodynamic effects in PPDs. I present a framework of global PPD evolution aiming to incorporate these advances, highlighting the role of wind-driven accretion and wind mass loss. Disk evolution is found to be largely dominated by wind-driven processes, and viscous spreading is suppressed. The timescale of disk evolution is controlled primarily by the amount of external magnetic flux threading the disks, and how rapidly the disk loses the flux. Rapid disk dispersal can be achieved if the disk is able to hold most of its magnetic flux during the evolution. In addition, because wind launching requires a sufficient level of ionization at the disk surface (mainly via external far-UV (FUV) radiation), wind kinematics is also affected by the FUV penetration depth and disk geometry. For a typical disk lifetime of a few million years, the disk loses approximately the same amount of mass through the wind as through accretion onto the protostar, and most of the wind mass loss proceeds from the outer disk via a slow wind. Fractional wind mass loss increases with increasing disk lifetime. Significant wind mass loss likely substantially enhances the dust-to-gas mass ratio and promotes planet formation.

Modeling transiting circumstellar disks: characterizing the newly discovered eclipsing disk system OGLE LMC-ECL-11893

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scott, Erin L.; Mamajek, Eric E.; Pecaut, Mark J.

2014-12-10

We investigate the nature of the unusual eclipsing star OGLE LMC-ECL-11893 (OGLE J05172127-6900558) in the Large Magellanic Cloud recently reported by Dong et al. The eclipse period for this star is 468 days, and the eclipses exhibit a minimum of ∼1.4 mag, preceded by a plateau of ∼0.8 mag. Spectra and optical/IR photometry are consistent with the eclipsed star being a lightly reddened B9III star of inferred age ∼150 Myr and mass ∼4 M {sub ☉}. The disk appears to have an outer radius of ∼0.2 AU with predicted temperatures of ∼1100-1400 K. We model the eclipses as being duemore » to either a transiting geometrically thin dust disk or gaseous accretion disk around a secondary object; the debris disk produces a better fit. We speculate on the origin of such a dense circumstellar dust disk structure orbiting a relatively old low-mass companion, and on the similarities of this system to the previously discovered EE Cep.« less

A Semiautomatic Pipeline for Be Star Light Curves

NASA Astrophysics Data System (ADS)

Rímulo, L. R.; Carciofi, A. C.; Rivinius, T.; Okazaki, A.

2016-11-01

Observational and theoretical studies from the last decade have shown that the Viscous Decretion Disk (VDD) scenario, in which turbulent viscosity is the physical mechanism responsible for the transport of material and angular momentum ejected from the star to the outer regions of the disk, is the only viable model for explaining the circumstellar disks of Be stars. In the α-disk approach applied to the VDD, the dimensionless parameter α is a measure of the turbulent viscosity. Recently, combining the time-dependent evolution of a VDD α-disk with non-LTE radiative transfer calculations, the first measurement of the α parameter was made, for the disk dissipation of the Be star ω CMa. It was found that α≍ 1 for that Be disk. The main motivation of this present work is the statistical determination of the α parameter. For this purpose, we present a pipeline that will allow the semiautomatic determination of the α parameter of several dozens of light curves of Be stars available from photometric surveys, In this contribution, we describe the pipeline, outlining the main staps required for the semiautomatic analysis of light curves

Emergence and stability of intermediate open vesicles in disk-to-vesicle transitions.

PubMed

Li, Jianfeng; Zhang, Hongdong; Qiu, Feng; Shi, An-Chang

2013-07-01

The transition between two basic structures, a disk and an enclosed vesicle, of a finite membrane is studied by examining the minimum energy path (MEP) connecting these two states. The MEP is constructed using the string method applied to continuum elastic membrane models. The results reveal that, besides the commonly observed disk and vesicle, open vesicles (bowl-shaped vesicles or vesicles with a pore) can become stable or metastable shapes. The emergence, stability, and probability distribution of these open vesicles are analyzed. It is demonstrated that open vesicles can be stabilized by higher-order elastic energies. The estimated probability distribution of the different structures is in good agreement with available experiments.

The Gaia-ESO Survey and CSI 2264: Substructures, disks, and sequential star formation in the young open cluster NGC 2264

NASA Astrophysics Data System (ADS)

Venuti, L.; Prisinzano, L.; Sacco, G. G.; Flaccomio, E.; Bonito, R.; Damiani, F.; Micela, G.; Guarcello, M. G.; Randich, S.; Stauffer, J. R.; Cody, A. M.; Jeffries, R. D.; Alencar, S. H. P.; Alfaro, E. J.; Lanzafame, A. C.; Pancino, E.; Bayo, A.; Carraro, G.; Costado, M. T.; Frasca, A.; Jofré, P.; Morbidelli, L.; Sousa, S. G.; Zaggia, S.

2018-01-01

Context. Reconstructing the structure and history of young clusters is pivotal to understanding the mechanisms and timescales of early stellar evolution and planet formation. Recent studies suggest that star clusters often exhibit a hierarchical structure, possibly resulting from several star formation episodes occurring sequentially rather than a monolithic cloud collapse. Aims: We aim to explore the structure of the open cluster and star-forming region NGC 2264 ( 3 Myr), which is one of the youngest, richest and most accessible star clusters in the local spiral arm of our Galaxy; we link the spatial distribution of cluster members to other stellar properties such as age and evolutionary stage to probe the star formation history within the region. Methods: We combined spectroscopic data obtained as part of the Gaia-ESO Survey (GES) with multi-wavelength photometric data from the Coordinated Synoptic Investigation of NGC 2264 (CSI 2264) campaign. We examined a sample of 655 cluster members, with masses between 0.2 and 1.8 M⊙ and including both disk-bearing and disk-free young stars. We used Teff estimates from GES and g,r,i photometry from CSI 2264 to derive individual extinction and stellar parameters. Results: We find a significant age spread of 4-5 Myr among cluster members. Disk-bearing objects are statistically associated with younger isochronal ages than disk-free sources. The cluster has a hierarchical structure, with two main blocks along its latitudinal extension. The northern half develops around the O-type binary star S Mon; the southern half, close to the tip of the Cone Nebula, contains the most embedded regions of NGC 2264, populated mainly by objects with disks and ongoing accretion. The median ages of objects at different locations within the cluster, and the spatial distribution of disked and non-disked sources, suggest that star formation began in the north of the cluster, over 5 Myr ago, and was ignited in its southern region a few Myr later. Star formation is likely still ongoing in the most embedded regions of the cluster, while the outer regions host a widespread population of more evolved objects; these may be the result of an earlier star formation episode followed by outward migration on timescales of a few Myr. We find a detectable lag between the typical age of disk-bearing objects and that of accreting objects in the inner regions of NGC 2264: the first tend to be older than the second, but younger than disk-free sources at similar locations within the cluster. This supports earlier findings that the characteristic timescales of disk accretion are shorter than those of disk dispersal, and smaller than the average age of NGC 2264 (i.e., ≲3 Myr). At the same time, we note that disks in the north of the cluster tend to be shorter-lived ( 2.5 Myr) than elsewhere; this may reflect the impact of massive stars within the region (notably S Mon), that trigger rapid disk dispersal. Conclusions: Our results, consistent with earlier studies on NGC 2264 and other young clusters, support the idea of a star formation process that takes place sequentially over a prolonged span in a given region. A complete understanding of the dynamics of formation and evolution of star clusters requires accurate astrometric and kinematic characterization of its population; significant advance in this field is foreseen in the upcoming years thanks to the ongoing Gaia mission, coupled with extensive ground-based surveys like GES. Full Table B.1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/609/A10

A Hot White Dwarf SDSS J134430.11+032423.1 with a Planetary Debris Disk

NASA Astrophysics Data System (ADS)

Li, Lifang; Zhang, Fenghui; Kong, Xiaoyang; Han, Quanwang; Li, Jiansha

2017-02-01

We discovered a debris disk around hot white dwarf (WD) SDSS J134430.11+032423.1 (SDSS J1344+0324). The effective temperature [{T}{eff} = 26,071(±163) K], surface gravity [{log}g=7.88(2)], and mass [M=0.58(1) {M}⊙ ] of this WD have been redetermined based on the analysis of its SDSS spectrum. We found that SDSS J1344+0324 is currently the hottest WD with a debris disk. Two spectra observed by SDSS at different times show that this object is similar to SDSS J1228+1040 with variable near-IR Ca II triplet emissions from a gaseous disk. The parameters of the debris disk are derived from the IR excess analysis of SDSS J1344+0324. We found that the disk is the coolest of all debris disks around WDs, and that the inner and outer radii are very close to the tide radius of the WD. Thus, the debris disk is very narrow (about 0.22 {R}⊙ ). This implies that it might be a newly formed disk resulting from the tidal disruption of a rocky planetary body that has just entered the tide volume of the WD. This might provide strong observational evidence for the formation of debris disks around WDs.

Measurement of Circumstellar Disk Sizes in the Upper Scorpius OB Association with ALMA

NASA Astrophysics Data System (ADS)

Barenfeld, Scott A.; Carpenter, John M.; Sargent, Anneila I.; Isella, Andrea; Ricci, Luca

2017-12-01

We present detailed modeling of the spatial distributions of gas and dust in 57 circumstellar disks in the Upper Scorpius OB Association observed with ALMA at submillimeter wavelengths. We fit power-law models to the dust surface density and CO J = 3–2 surface brightness to measure the radial extent of dust and gas in these disks. We found that these disks are extremely compact: the 25 highest signal-to-noise disks have a median dust outer radius of 21 au, assuming an {R}-1 dust surface density profile. Our lack of CO detections in the majority of our sample is consistent with these small disk sizes assuming the dust and CO share the same spatial distribution. Of seven disks in our sample with well-constrained dust and CO radii, four appear to be more extended in CO, although this may simply be due to the higher optical depth of the CO. Comparison of the Upper Sco results with recent analyses of disks in Taurus, Ophiuchus, and Lupus suggests that the dust disks in Upper Sco may be approximately three times smaller in size than their younger counterparts, although we caution that a more uniform analysis of the data across all regions is needed. We discuss the implications of these results for disk evolution.

Three-dimensional discrete element method simulation of core disking

NASA Astrophysics Data System (ADS)

Wu, Shunchuan; Wu, Haoyan; Kemeny, John

2018-04-01

The phenomenon of core disking is commonly seen in deep drilling of highly stressed regions in the Earth's crust. Given its close relationship with the in situ stress state, the presence and features of core disking can be used to interpret the stresses when traditional in situ stress measuring techniques are not available. The core disking process was simulated in this paper using the three-dimensional discrete element method software PFC3D (particle flow code). In particular, PFC3D is used to examine the evolution of fracture initiation, propagation and coalescence associated with core disking under various stress states. In this paper, four unresolved problems concerning core disking are investigated with a series of numerical simulations. These simulations also provide some verification of existing results by other researchers: (1) Core disking occurs when the maximum principal stress is about 6.5 times the tensile strength. (2) For most stress situations, core disking occurs from the outer surface, except for the thrust faulting stress regime, where the fractures were found to initiate from the inner part. (3) The anisotropy of the two horizontal principal stresses has an effect on the core disking morphology. (4) The thickness of core disk has a positive relationship with radial stress and a negative relationship with axial stresses.

Lamina cribrosa position and Bruch's membrane opening differences between anterior ischemic optic neuropathy and open-angle glaucoma.

PubMed

Rebolleda, Gema; Pérez-Sarriegui, Ane; Díez-Álvarez, Laura; De Juan, Victoria; Muñoz-Negrete, Francisco J

2018-06-01

To compare the optic nerve head morphology among primary open-angle glaucoma, non-arteritic anterior ischemic optic neuropathy eyes, their fellow healthy eyes and control eyes, using spectral-domain optical coherence tomography with enhanced depth imaging. Observational cross-sectional study including 88 eyes of 68 patients. In this study, 23 non-arteritic anterior ischemic optic neuropathy eyes, 17 fellow unaffected eyes, 25 primary open-angle glaucoma eyes, and 23 age-matched control eyes were included. Peripapillary retinal nerve fiber layer thickness and optic disk area were evaluated. Bruch's membrane opening diameter, optic cup depth, anterior lamina cribrosa depth, and prelaminar tissue thickness were assessed. Non-arteritic anterior ischemic optic neuropathy and primary open-angle glaucoma eyes had similar visual field mean deviation and peripapillary retinal nerve fiber layer thickness (P = 0.6 and P = 0.56, respectively). Bruch's membrane opening diameter was significantly larger in primary open-angle glaucoma eyes than in control eyes (P = 0.02). Lamina cribrosa and disk cup were deeper in eyes with primary open-angle glaucoma than both control and non-arteritic anterior ischemic optic neuropathy eyes (P < 0.001). Prelaminar tissue thickness was significantly thinner in primary open-angle glaucoma eyes than in non-arteritic anterior ischemic optic neuropathy eyes (P < 0.001). Lamina cribrosa was shallower in both non-arteritic anterior ischemic optic neuropathy and unaffected fellow eyes compared to healthy eyes (P < 0.001 and P = 0.04, respectively). No differences were found in the optic disk area. A forward lamina cribrosa placement and not a smaller disk could be involved in the pathogenesis of non-arteritic anterior ischemic optic neuropathy. A significantly larger Bruch's membrane opening diameter was found in primary open-angle glaucoma eyes compared with control eyes. This issue has clinical implications because Bruch's membrane opening has been considered a stable reference for disk-related measures.

An almost head-on collision as the origin of two off-centre rings in the Andromeda galaxy.

PubMed

Block, D L; Bournaud, F; Combes, F; Groess, R; Barmby, P; Ashby, M L N; Fazio, G G; Pahre, M A; Willner, S P

2006-10-19

The unusual morphology of the Andromeda galaxy (Messier 31, the closest spiral galaxy to the Milky Way) has long been an enigma. Although regarded for decades as showing little evidence of a violent history, M31 has a well-known outer ring of star formation at a radius of ten kiloparsecs whose centre is offset from the galaxy nucleus. In addition, the outer galaxy disk is warped, as seen at both optical and radio wavelengths. The halo contains numerous loops and ripples. Here we report the presence of a second, inner dust ring with projected dimensions of 1.5 x 1 kiloparsecs and offset by about half a kiloparsec from the centre of the galaxy (based upon an analysis of previously-obtained data). The two rings appear to be density waves propagating in the disk. Numerical simulations indicate that both rings result from a companion galaxy plunging through the centre of the disk of M31. The most likely interloper is M32. Head-on collisions between galaxies are rare, but it appears nonetheless that one took place 210 million years ago in our Local Group of galaxies.

Sublimation of icy planetesimals and the delivery of water to the habitable zone around solar type stars

NASA Astrophysics Data System (ADS)

Brunini, Adrián; López, María Cristina

2018-06-01

We present a semi analytic model to evaluate the delivery of water to the habitable zone around a solar type star carried by icy planetesimals born beyond the snow line. The model includes sublimation of ice, gas drag and scattering by an outer giant planet located near the snow line. The sublimation model is general and could be applicable to planetary synthesis models or N-Body simulations of the formation of planetary systems. We perform a short series of simulations to asses the potential relevance of sublimation of volatiles in the process of delivery of water to the inner regions of a planetary system during early stages of its formation. We could anticipate that erosion by sublimation would prevent the arrival of much water to the habitable zone of protoplanetary disks in the form of icy planetesimals. Close encounters with a massive planet orbiting near the outer edge of the snow line could make possible for planetesimals to reach the habitable zone somewhat less eroded. However, only large planetesimals could provide appreciable amounts of water. Massive disks and sharp gas surface density profiles favor icy planetesimals to reach inner regions of a protoplanetary disk.

Constraining the Structure of the Transition Disk HD 135344B (SAO 206462) by Simultaneous Modeling of Multiwavelength Gas and Dust Observations

NASA Technical Reports Server (NTRS)

Carmona, A.; Pinte, C.; Thi, W. F.; Benisty, M.; Menard, F.; Grady, C.; Kamp, I.; Woitke, P.; Olofsson, J.; Roberge, A.;

The Nature and Cause of Spectral Variability in LMC X-1

NASA Technical Reports Server (NTRS)

Ruhlen, L.; Smith, D. M.; Scank, J. H.

2011-01-01

We present the results of a long-term observation campaign of the extragalactic wind-accreting black-hole X-ray binary LMC X-1, using the Proportional Counter Array on the Rossi X-Ray Timing Explorer (RXTE). The observations show that LMC X-1's accretion disk exhibits an anomalous temperature-luminosity relation. We use deep archival RXTE observations to show that large movements across the temperature-luminosity space occupied by the system can take place on time scales as short as half an hour. These changes cannot be adequately explained by perturbations that propagate from the outer disk on a viscous timescale. We propose instead that the apparent disk variations reflect rapid fluctuations within the Compton up-scattering coronal material, which occults the inner parts of the disk. The expected relationship between the observed disk luminosity and apparent disk temperature derived from the variable occultation model is quantitatively shown to be in good agreement with the observations. Two other observations support this picture: an inverse correlation between the flux in the power-law spectral component and the fitted inner disk temperature, and a near-constant total photon flux, suggesting that the inner disk is not ejected when a lower temperature is observed.

The inclination of the dwarf irregular galaxy Holmberg II

NASA Astrophysics Data System (ADS)

Sánchez-Salcedo, F. J.; Hidalgo-Gámez, A. M.; Martínez-García, E. E.

2014-10-01

We provide constraints on the inclination angle of the H I disk of the dwarf irregular galaxy Holmberg II (Ho II) from a stability analysis of the outer gaseous disk. We point out that a mean inclination angle of 27(°) and thus a flat circular velocity of ≈ 60 km s(-1) , is required to have a level of gravitational stability similar to that found in other galaxies. Adopting this inclination angle, we find that Ho II lies on the right location in the baryonic Tully-Fisher relation. Moreover, for this inclination, its rotation curve is consistent with MOND. However, the corresponding analysis of the stability under MOND indicates that this galaxy could be problematic for MOND because its outer parts are marginally unstable in this gravity theory. We urge MOND simulators to study numerically the non-linear stability of gas-rich dwarf galaxies since this may provide a new key test for MOND.

The Coast Artillery Journal. Volume 66, Number 2, February 1927

DTIC Science & Technology

1927-02-01

bicycle gear and chain , step-up 1 to 5, con- necting the disk with the elevating drum. As a result one turn of the range disk covers the outer two...our seacoast cities, navy yards, a!ld habors are reasonably protected against bombardment, because we would otherwise be forced to chain down our...type and the sliding sleeve type. Spare parts, such as the rear bands, etc., are continually heing suplied for these two types and it would be

Turbine nozzle/nozzle support structure

DOEpatents

Boyd, Gary L.; Shaffer, James E.

1997-01-01

An axial flow turbine's nozzle/nozzle support structure having a cantilevered nozzle outer structure including an outer shroud and airfoil vanes extending radially inwardly therefrom, an inner shroud radially adjacent the inner end of the airfoil vanes and cooperatively disposed relative to the outer shroud to provide an annular fluid flow path, an inner and an outer support ring respectively arranged radially inside the inner shroud and axially adjacent a portion of the outer shroud, and pins extending through such portion and into the outer support ring. The inner support ring or inner shroud has a groove therein bounded by end walls for receiving and being axially abuttable with a locating projection from the adjacent airfoil vane, inner shroud, or inner support ring. The nozzle outer structure may comprise segments each of which has a single protrusion which is axially engageable with the outer support ring or, alternatively, a first and second protrusion which are arcuately and axially separated and which include axial openings therein whereby first and second protrusions on respective, arcuately adjacent nozzle segments have axial openings therein which are alignable with connector openings in the outer support ring and within each of such aligned openings a pin is receivable. The inner shroud may, likewise, comprise segments which, when assembled in operating configuration, have a 360 degree expanse.

Turbine nozzle/nozzle support structure

DOEpatents

Boyd, G.L.; Shaffer, J.E.

1997-01-07

An axial flow turbine`s nozzle/nozzle support structure is described having a cantilevered nozzle outer structure including an outer shroud and airfoil vanes extending radially inwardly therefrom, an inner shroud radially adjacent the inner end of the airfoil vanes and cooperatively disposed relative to the outer shroud to provide an annular fluid flow path, an inner and an outer support ring respectively arranged radially inside the inner shroud and axially adjacent a portion of the outer shroud, and pins extending through such portion and into the outer support ring. The inner support ring or inner shroud has a groove therein bounded by end walls for receiving and being axially abuttable with a locating projection from the adjacent airfoil vane, inner shroud, or inner support ring. The nozzle outer structure may comprise segments each of which has a single protrusion which is axially engageable with the outer support ring or, alternatively, a first and second protrusion which are arcuately and axially separated and which include axial openings therein whereby first and second protrusions on respective, arcuately adjacent nozzle segments have axial openings therein which are alignable with connector openings in the outer support ring and within each of such aligned openings a pin is receivable. The inner shroud may, likewise, comprise segments which, when assembled in operating configuration, have a 360 degree expanse. 6 figs.

Turbine nozzle/nozzle support structure

DOEpatents

Boyd, Gary L.; Shaffer, James E.

1996-01-01

An axial flow turbine's nozzle/nozzle support structure having a cantilevered nozzle outer structure including an outer shroud and airfoil vanes extending radially inwardly therefrom, an inner shroud radially adjacent the inner end of the airfoil vanes and cooperatively disposed relative to the outer shroud to provide an annular fluid flow path, an inner and an outer support ring respectively arranged radially inside the inner shroud and axially adjacent a portion of the outer shroud, and pins extending through such portion and into the outer support ring. The inner support ring or inner shroud has a groove therein bounded by end walls for receiving and being axially abuttable with a locating projection from the adjacent airfoil vane, inner shroud, or inner support ring. The nozzle outer structure may comprise segments each of which has a single protrusion which is axially engageable with the outer support ring or, alternatively, a first and second protrusion which are arcuately and axially separated and which include axial openings therein whereby first and second protrusions on respective, arcuately adjacent nozzle segments have axial openings therein which are alignable with connector openings in the outer support ring and within each of such aligned openings a pin is receivable. The inner shroud may, likewise, comprise segments which, when assembled in operating configuration, have a 360 degree expanse.

Turbine nozzle/nozzle support structure

DOEpatents

Boyd, G.L.; Shaffer, J.E.

1996-09-10

An axial flow turbine`s nozzle/nozzle support structure is described having a cantilevered nozzle outer structure including an outer shroud and airfoil vanes extending radially inwardly therefrom, an inner shroud radially adjacent the inner end of the airfoil vanes and cooperatively disposed relative to the outer shroud to provide an annular fluid flow path, an inner and an outer support ring respectively arranged radially inside the inner shroud and axially adjacent a portion of the outer shroud, and pins extending through such portion and into the outer support ring. The inner support ring or inner shroud has a groove therein bounded by end walls for receiving and being axially abuttable with a locating projection from the adjacent airfoil vane, inner shroud, or inner support ring. The nozzle outer structure may comprise segments each of which has a single protrusion which is axially engageable with the outer support ring or, alternatively, a first and second protrusion which are arcuately and axially separated and which include axial openings therein whereby first and second protrusions on respective, arcuately adjacent nozzle segments have axial openings therein which are alignable with connector openings in the outer support ring and within each of such aligned openings a pin is receivable. The inner shroud may, likewise, comprise segments which, when assembled in operating configuration, have a 360 degree expanse. 6 figs.

Turbine nozzle/nozzle support structure

DOEpatents

Boyd, Gary L.; Shaffer, James E.

1995-01-01

An axial flow turbine's nozzle/nozzle support structure having a cantilevered nozzle outer structure including an outer shroud and airfoil vanes extending radially inwardly therefrom, an inner shroud radially adjacent the inner end of the airfoil vanes and cooperatively disposed relative to the outer shroud to provide an annular fluid flow path, an inner and an outer support ring respectively arranged radially inside the inner shroud and axially adjacent a portion of the outer shroud, and pins extending through such portion and into the outer support ring. The inner support ring or inner shroud has a groove therein bounded by end walls for receiving and being axially abuttable with a locating projection from the adjacent airfoil vane, inner shroud, or inner support ring. The nozzle outer structure may comprise segments each of which has a single protrusion which is axially engageable with the outer support ring or, alternatively, a first and second protrusion which are arcuately and axially separated and which include axial openings therein whereby first and second protrusions on respective, arcuately adjacent nozzle segments have axial openings therein which are alignable with connector openings in the outer support ring and within each of such aligned openings a pin is receivable. The inner shroud may, likewise, comprise segments which, when assembled in operating configuration, have a 360 degree expanse.

Turbine nozzle/nozzle support structure

DOEpatents

Boyd, G.L.; Shaffer, J.E.

1995-08-15

An axial flow turbine`s nozzle/nozzle support structure is described having a cantilevered nozzle outer structure including an outer shroud and airfoil vanes extending radially inwardly therefrom, an inner shroud radially adjacent the inner end of the airfoil vanes and cooperatively disposed relative to the outer shroud to provide an annular fluid flow path, an inner and an outer support ring respectively arranged radially inside the inner shroud and axially adjacent a portion of the outer shroud, and pins extending through such portion and into the outer support ring. The inner support ring or inner shroud has a groove therein bounded by end walls for receiving and being axially abuttable with a locating projection from the adjacent airfoil vane, inner shroud, or inner support ring. The nozzle outer structure may comprise segments each of which has a single protrusion which is axially engageable with the outer support ring or, alternatively, a first and second protrusion which are arcuately and axially separated and which include axial openings therein whereby first and second protrusions on respective, arcuately adjacent nozzle segments have axial openings therein which are alignable with connector openings in the outer support ring and within each of such aligned openings a pin is receivable. The inner shroud may, likewise, comprise segments which, when assembled in operating configuration, have a 360 degree expanse. 6 figs.

NASA's Solar Eclipse Composite Image July 11, 2010

NASA Image and Video Library

2017-12-08

Eclipse 2010 Composite A solar eclipse photo (gray and white) from the Williams College Expedition to Easter Island in the South Pacific (July 11, 2010) was embedded with an image of the Sun’s outer corona taken by the Large Angle Spectrometric Coronagraph (LASCO) on the SOHO spacecraft and shown in red false color. LASCO uses a disk to blot out the bright sun and the inner corona so that the faint outer corona can be monitored and studied. Further, the dark silhouette of the moon was covered with an image of the Sun taken in extreme ultraviolet light at about the same time by the Atmospheric Imaging Assembly on Solar Dynamics Observatory (SDO). The composite brings out the correlation of structures in the inner and outer corona. Credits: Williams College Eclipse Expedition -- Jay M. Pasachoff, Muzhou Lu, and Craig Malamut; SOHO’s LASCO image courtesy of NASA/ESA; solar disk image from NASA’s SDO; compositing by Steele Hill, NASA Goddard Space Flight Center. NASA Goddard Space Flight Center is home to the nation's largest organization of combined scientists, engineers and technologists that build spacecraft, instruments and new technology to study the Earth, the sun, our solar system, and the universe.

Formation Location of Enceladus and Comets from D/H Measurements

NASA Astrophysics Data System (ADS)

Petit, J.-M.; Mousis, O.; Kavelaars, J. J.

2012-04-01

The building blocks of Enceladus could have formed in Saturn's subnebula, thus bearing no connection with planetesimals condensed in Saturn's feeding zone. We have shown that the D/H ratio in H2O in Saturn's sub-nebula reaches the protosolar value in about 1,000 yr, well before ice forms again at Enceladus' location (several 10,000 yr). However, the D/H ratio measured by the Ion and Neutral Mass Spectrometer aboard the Cassini spacecraft in Saturn's satellite Enceladus is remarkably similar to the values observed in the nearly-isotropic comets. Hence the building blocks of Enceladus formed in the solar nebula. Nearly-isotropic comets originate from the Oort cloud. Delivery of material into the Oort cloud reservoir is controlled by Uranus-Neptune scattering. The D/H ratio in comets is therefore representative of that of the location of Uranus-Neptune at the time of formation of the Oort cloud. Since D/H strongly depends on heliocentric distance in the solar nebula, the similarity of D/H ratios links the primordial source region of the nearly-isotropic comets with the formation location of Enceladus. This precludes these comets from having formed beyond ~15 AU from the Sun. which in turn implies that Uranus and Neptune were originally closer to Saturn's location during the feeding of the Oort cloud, likely in the 12-15 AU region. Such a configuration is consistent with the Nice model of evolution of the outer Solar System. 103P/Hartley 2 being D-poor compared to these bodies questions the current models. A fraction of ecliptic comets could have formed at closer distances from the Sun than assumed here and has been ejected outward and then display a low R/H ratio. However, they would only represent a small fraction of all ecliptic comets. The high level of deuteration predicted in ecliptic comets from the description of the isotopic exchange between H2 and H2O in the gas phase of the disk is based on classical models of the solar nebula (the alpha-turbulent model) in which the disk's temperature, pressure and density decrease monotonically with increasing heliocentric distance. These models do not consider the possible presence of sporadic and local phenomena such as shock waves that have been invoked to speed up the formation of planetesimals and trigger the crystallization of initially amorphous silicates prior to their incorporation in comets. Shock waves in the outer nebula could have locally increased the disk's temperature and pressure conditions and might have significantly decreased the deuteration level of the H2O ice formed at this place. A possibly extended, both in time and space, major heating could have been induced by the inflow of the presolar cloud or envelop onto the outer part of the accretion disk at the time of the disk's formation. The influence of this mechanism on the outer disk's thermodynamic conditions and chemistry remains to be investigated.

The warped disk of Centaurus A in the near-infrared

NASA Technical Reports Server (NTRS)

Quillen, A. C.; Graham, James R.; Frogel, Jay A.

1993-01-01

We present infrared images of Cen A (NGC 5128) in the J, H, and K bands. The infrared morphology is primarily determined by the presence of a thin absorptive warped disk. By integrating the light of the underlying prolate galaxy through such a disk, we construct models which we compare with infrared and X-ray data. The geometry of the warped disk needed to fit the IR data is consistent with a warped disk which has evolved as a result of differential precession in a prolate potential. The disk has an inclination, with respect to the principal axis of the underlying elliptical galaxy, that is higher at larger radii than in the inner region. A scenario is proposed where a small gas-rich galaxy infalling under the force of dynamical friction is tidally stripped. Stripping occurs at different times during its infall. The orientation of the resulting gas disk depends upon the angular momentum of the infalling galaxy. We find that the resulting precession angle of the disk is well described by the precession model, but that the inclination angle may vary as a function of radius. We propose an orbit for the infalling galaxy that is consistent with the geometry of the warped disk needed to fit our infrared data, and rotation observed in the outer part of the galaxy.

Investigating FP Tau’s protoplanetary disk structure through modeling

NASA Astrophysics Data System (ADS)

Brinjikji, Marah; Espaillat, Catherine

2017-01-01

This project presents a study aiming to understand the structure of the protoplanetary disk around FP Tau, a very young, very low mass star in the Taurus star-forming region. We have gathered existing optical, Spitzer, Herschel and submillimeter observations to construct the spectral energy distribution (SED) of FP Tau. We have used the D’Alessio et al (2006) physically self-consistent irradiated accretion disk model including dust settling to model the disk of FP Tau. Using this method, the best fit for the SED of FP Tau is a model that includes a gap located 10-20 AU away from the star. This gap is filled with optically thin dust that separates the optically thick dust in the outer disk from the optically thick dust in the inner disk. These characteristics indicate that FP Tau’s protostellar system is best classified as a pre-transitional disk. Near-infrared interferometry in the K-Band from Willson et al 2016 indicates that FP Tau has a small gap located 10-20 AU from the star, which is consistent with the model we produced, lending further support to the pre-transitional disk interpretation. The most likely explanation for the existence of a gap in the disk is a forming planet.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, K. H.; Watson, Dan M.; Manoj, P.

We present 5-40 {mu}m Spitzer Infrared Spectrograph spectra of a collection of transitional disks, objects for which the spectral energy distribution (SED) indicates central clearings (holes) or gaps in the dust distribution, in the Chamaeleon I star-forming region. Like their counterparts in the Taurus-Auriga star-forming region that we have previously observed, the spectra of these young objects (1-3 Myr old) reveal that the central clearings or gaps are very sharp-edged, and are surrounded by optically thick dusty disks similar to those around other classical T Tauri stars in the Chamaeleon I association. Also like the Taurus transitional disks, the Chamaeleonmore » I transitional disks have extremely large depletion factors for small dust grains in their gaps, compared to the full accretion disks whose SEDs are represented by the median SED of Class II objects in the region. We find that the fraction of transitional disks in the Chamaeleon I cloud is somewhat higher than that in the Taurus-Auriga cloud, possibly indicating that the frequency of transitional disks, on average, increases with cluster age. We also find a significant correlation between the stellar mass and the radius of the outer edge of the gap. We discuss the disk structures implied by the spectra and the constraints they place on gap-formation mechanisms in protoplanetary disks.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shahamat, Narjes; Abbassi, Shahram, E-mail: abbassi@um.ac.ir

In the present work we study self-gravity effects on the vertical structure of a magnetized neutrino-dominated accretion disk as a central engine for gamma-ray bursts (GRBs). Some of the disk physical timescales that are supposed to play a pivotal role in the late-time evolutions of the disk, such as viscous, cooling, and diffusion timescales, have been studied. We are interested in investigating the possibility of the occurrence of X-ray flares, observed in late-time GRBs’ extended emission through the “magnetic barrier” and “fragmentation” processes in our model. The results lead us to interpret self-gravity as an amplifier for Blandford–Payne luminosity (BPmore » power) and the generated magnetic field, but a suppressor for neutrino luminosity and magnetic barrier processes via highlighting the fragmentation mechanism in the outer disk, especially for the higher mass accretion rates.« less

Magnetically Induced Disk Winds and Transport in the HL Tau Disk

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hasegawa, Yasuhiro; Flock, Mario; Turner, Neal J.

2017-08-10

The mechanism of angular momentum transport in protoplanetary disks is fundamental to understanding the distributions of gas and dust in the disks. The unprecedented ALMA observations taken toward HL Tau at high spatial resolution and subsequent radiative transfer modeling reveal that a high degree of dust settling is currently achieved in the outer part of the HL Tau disk. Previous observations, however, suggest a high disk accretion rate onto the central star. This configuration is not necessarily intuitive in the framework of the conventional viscous disk model, since efficient accretion generally requires a high level of turbulence, which can suppressmore » dust settling considerably. We develop a simplified, semi-analytical disk model to examine under what condition these two properties can be realized in a single model. Recent, non-ideal MHD simulations are utilized to realistically model the angular momentum transport both radially via MHD turbulence and vertically via magnetically induced disk winds. We find that the HL Tau disk configuration can be reproduced well when disk winds are properly taken into account. While the resulting disk properties are likely consistent with other observational results, such an ideal situation can be established only if the plasma β at the disk midplane is β {sub 0} ≃ 2 × 10{sup 4} under the assumption of steady accretion. Equivalently, the vertical magnetic flux at 100 au is about 0.2 mG. More detailed modeling is needed to fully identify the origin of the disk accretion and quantitatively examine plausible mechanisms behind the observed gap structures in the HL Tau disk.« less

Magnetically Induced Disk Winds and Transport in the HL Tau Disk

NASA Astrophysics Data System (ADS)

Hasegawa, Yasuhiro; Okuzumi, Satoshi; Flock, Mario; Turner, Neal J.

2017-08-01

The mechanism of angular momentum transport in protoplanetary disks is fundamental to understanding the distributions of gas and dust in the disks. The unprecedented ALMA observations taken toward HL Tau at high spatial resolution and subsequent radiative transfer modeling reveal that a high degree of dust settling is currently achieved in the outer part of the HL Tau disk. Previous observations, however, suggest a high disk accretion rate onto the central star. This configuration is not necessarily intuitive in the framework of the conventional viscous disk model, since efficient accretion generally requires a high level of turbulence, which can suppress dust settling considerably. We develop a simplified, semi-analytical disk model to examine under what condition these two properties can be realized in a single model. Recent, non-ideal MHD simulations are utilized to realistically model the angular momentum transport both radially via MHD turbulence and vertically via magnetically induced disk winds. We find that the HL Tau disk configuration can be reproduced well when disk winds are properly taken into account. While the resulting disk properties are likely consistent with other observational results, such an ideal situation can be established only if the plasma β at the disk midplane is β 0 ≃ 2 × 104 under the assumption of steady accretion. Equivalently, the vertical magnetic flux at 100 au is about 0.2 mG. More detailed modeling is needed to fully identify the origin of the disk accretion and quantitatively examine plausible mechanisms behind the observed gap structures in the HL Tau disk.

Apparatus for premixing in a gas turbine engine

DOEpatents

McCormick, Keith Alan; Smith, Duane A.

2002-01-01

An apparatus for mixing fuel with oxidizing agent is disclosed comprising an outer body and an inner body. The outer body has an interior surface extending between an inlet end toward an outlet end. The interior surface includes a first plurality of openings. The inner body has an exterior surface extending between the first end and the second end of the inner body. The exterior surface of the inner body includes a second plurality of openings. At least a portion of the exterior surface of the inner body is positioned within the outer body to define a mixing channel between the exterior surface of the inner body and the interior surface of the outer body. In one form the first and second plurality of openings substantially longitudinally span at least one of the outer body and the inner body. In another form the first and second plurality of openings are substantially radially oriented. In yet another form the first and second plurality of openings are offset from one another.

A Complete ALMA Map of the Fomalhaut Debris Disk

DOE Office of Scientific and Technical Information (OSTI.GOV)

MacGregor, Meredith A.; Wilner, David J.; Matrà, Luca

We present ALMA mosaic observations at 1.3 mm (223 GHz) of the Fomalhaut system with a sensitivity of 14 μ Jy/beam. These observations provide the first millimeter map of the continuum dust emission from the complete outer debris disk with uniform sensitivity, enabling the first conclusive detection of apocenter glow. We adopt an MCMC modeling approach that accounts for the eccentric orbital parameters of a collection of particles within the disk. The outer belt is radially confined with an inner edge of 136.3 ± 0.9 au and width of 13.5 ± 1.8 au. We determine a best-fit eccentricity of 0.12more » ± 0.01. Assuming a size distribution power-law index of q = 3.46 ± 0.09, we constrain the dust absorptivity power-law index β to be 0.9 < β < 1.5. The geometry of the disk is robustly constrained with inclination 65.°6 ± 0.°3, position angle 337.°9 ± 0.°3, and argument of periastron 22.°5 ± 4.°3. Our observations do not confirm any of the azimuthal features found in previous imaging studies of the disk with Hubble Space Telescope , SCUBA, and ALMA. However, we cannot rule out structures ≤10 au in size or that only affect smaller grains. The central star is clearly detected with a flux density of 0.75 ± 0.02 mJy, significantly lower than predicted by current photospheric models. We discuss the implications of these observations for the directly imaged Fomalhaut b and the inner dust belt detected at infrared wavelengths.« less

HD 106906 b: A PLANETARY-MASS COMPANION OUTSIDE A MASSIVE DEBRIS DISK

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bailey, Vanessa; Reiter, Megan; Morzinski, Katie

2014-01-01

We report the discovery of a planetary-mass companion, HD 106906 b, with the new Magellan Adaptive Optics (MagAO) + Clio2 system. The companion is detected with Clio2 in three bands: J, K{sub S} , and L', and lies at a projected separation of 7.''1 (650 AU). It is confirmed to be comoving with its 13 ± 2 Myr F5 host using Hubble Space Telescope Advanced Camera for Surveys astrometry over a time baseline of 8.3 yr. DUSTY and COND evolutionary models predict that the companion's luminosity corresponds to a mass of 11 ± 2 M {sub Jup}, making it one ofmore » the most widely separated planetary-mass companions known. We classify its Magellan/Folded-Port InfraRed Echellette J/H/K spectrum as L2.5 ± 1; the triangular H-band morphology suggests an intermediate surface gravity. HD 106906 A, a pre-main-sequence Lower Centaurus Crux member, was initially targeted because it hosts a massive debris disk detected via infrared excess emission in unresolved Spitzer imaging and spectroscopy. The disk emission is best fit by a single component at 95 K, corresponding to an inner edge of 15-20 AU and an outer edge of up to 120 AU. If the companion is on an eccentric (e > 0.65) orbit, it could be interacting with the outer edge of the disk. Close-in, planet-like formation followed by scattering to the current location would likely disrupt the disk and is disfavored. Furthermore, we find no additional companions, though we could detect similar-mass objects at projected separations >35 AU. In situ formation in a binary-star-like process is more probable, although the companion-to-primary mass ratio, at <1%, is unusually small.« less

GASP. IV. A Muse View of Extreme Ram-pressure-stripping in the Plane of the Sky: The Case of Jellyfish Galaxy JO204

NASA Astrophysics Data System (ADS)

Gullieuszik, Marco; Poggianti, Bianca M.; Moretti, Alessia; Fritz, Jacopo; Jaffé, Yara L.; Hau, George; Bischko, Jan C.; Bellhouse, Callum; Bettoni, Daniela; Fasano, Giovanni; Vulcani, Benedetta; D’Onofrio, Mauro; Biviano, Andrea

2017-09-01

In the context of the GAs Stripping Phenomena in galaxies with Muse (GASP) survey, we present the characterization of JO204, a jellyfish galaxy in A957, a relatively low-mass cluster with M=4.4× {10}14 {M}ȯ . This galaxy shows a tail of ionized gas that extends up to 30 kpc from the main body in the opposite direction of the cluster center. No gas emission is detected in the galaxy outer disk, suggesting that gas-stripping is proceeding outside-in. The stellar component is distributed as a regular disk galaxy; the stellar kinematics shows a symmetric rotation curve with a maximum radial velocity of 200 km s‑1 out to 20 kpc from the galaxy center. The radial velocity of the gas component in the central part of the disk follows the distribution of the stellar component; the gas kinematics in the tail retains the rotation of the galaxy disk, indicating that JO204 is moving at high speed in the intracluster medium. Both the emission and radial-velocity maps of the gas and stellar components indicate ram-pressure as the most likely primary mechanism for gas-stripping, as expected given that JO204 is close to the cluster center and it is likely at the first infall in the cluster. The spatially resolved star formation history of JO204 provides evidence that the onset of ram-pressure-stripping occurred in the last 500 Myr, quenching the star formation activity in the outer disk, where the gas has been already completely stripped. Our conclusions are supported by a set of hydrodynamic simulations.

On the impact origin of Phobos and Deimos

NASA Astrophysics Data System (ADS)

Genda, Hidenori; Hyodo, Ryuki; Chanorz, Sebastian; Rosenblatt, Pascal

2017-10-01

Phobos and Deimos, the two small satellites of Mars, are thought either to be captured asteroids or to have accreted in an impact-induced debris disk. Recently, we succeeded in making them in a framework of the giant impact scenario [1]. In our canonical simulation, large moons form from the material in the dense inner disk and then migrate outwards due to gravitational interactions with the remnant disk. As the large inner moons migrate outward, their orbital resonances sweep up and gather materials distributed within a thin outer disk, facilitating accretion of two small satellites whose sizes are similar to Phobos and Deimos. The large inner moons fall back to Mars after about 5 million years due to tidal pull of Mars, and the two small outer satellites evolve into current Phobos- and Deimos-like orbits.In addition, we recently perform high-resolution SPH giant impact simulations using sophisticated equation of states (M-ANEOS). We investigate the thermodynamic and physical aspects of the impact-induced disk [2], such as degrees of melting and vaporization of materials, mixing ratio of Mars and impactor’s materials, and expected particle sizes that form Phobos and Deimos. Our results will give useful information for planning a future sample return mission to Martian moons, such as JAXA’s MMX (Martian Moons eXploration) mission.[1] Rosenblatt, P., Charnoz, S., Dunseath, K.M., Terao-Dunseath, M., Trinh, A., Hyodo, R., Genda, H., Toupin, S., 2016. Accretion of Phobos and Deimos in an extended debris disc stirred by transient moons. Nature Geoscience 9, 581-583.[2] Hyodo, R., Genda, H., Charnoz, S., Rosenblatt, P., 2017, On the impact origin of Phobos and Deimos I: Thermodynamic and physical aspects. ApJ accepted (arXiv:1707.06282).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lieman-Sifry, Jesse; Hughes, A. Meredith; Flaherty, Kevin M.

We present a CO(2-1) and 1240 μ m continuum survey of 23 debris disks with spectral types B9-G1, observed at an angular resolution of 0.″5–1″ with the Atacama Large Millimeter/Submillimeter Array (ALMA). The sample was selected for large infrared excess and age ∼10 Myr, to characterize the prevalence of molecular gas emission in young debris disks. We identify three CO-rich debris disks, plus two additional tentative (3 σ) CO detections. Twenty disks were detected in the continuum at the >3 σ level. For the 12 disks in the sample that are spatially resolved by our observations, we perform an independentmore » analysis of the interferometric continuum visibilities to constrain the basic dust disk geometry, as well as a simultaneous analysis of the visibilities and broadband spectral energy distribution to constrain the characteristic grain size and disk mass. The gas-rich debris disks exhibit preferentially larger outer radii in their dust disks, and a higher prevalence of characteristic grain sizes smaller than the blowout size. The gas-rich disks do not exhibit preferentially larger dust masses, contrary to expectations for a scenario in which a higher cometary destruction rate would be expected to result in a larger mass of both CO and dust. The three debris disks in our sample with strong CO detections are all around A stars: the conditions in disks around intermediate-mass stars appear to be the most conducive to the survival or formation of CO.« less

A low mass for Mars from Jupiter's early gas-driven migration.

PubMed

Walsh, Kevin J; Morbidelli, Alessandro; Raymond, Sean N; O'Brien, David P; Mandell, Avi M

2011-06-05

Jupiter and Saturn formed in a few million years (ref. 1) from a gas-dominated protoplanetary disk, and were susceptible to gas-driven migration of their orbits on timescales of only ∼100,000 years (ref. 2). Hydrodynamic simulations show that these giant planets can undergo a two-stage, inward-then-outward, migration. The terrestrial planets finished accreting much later, and their characteristics, including Mars' small mass, are best reproduced by starting from a planetesimal disk with an outer edge at about one astronomical unit from the Sun (1 au is the Earth-Sun distance). Here we report simulations of the early Solar System that show how the inward migration of Jupiter to 1.5 au, and its subsequent outward migration, lead to a planetesimal disk truncated at 1 au; the terrestrial planets then form from this disk over the next 30-50 million years, with an Earth/Mars mass ratio consistent with observations. Scattering by Jupiter initially empties but then repopulates the asteroid belt, with inner-belt bodies originating between 1 and 3 au and outer-belt bodies originating between and beyond the giant planets. This explains the significant compositional differences across the asteroid belt. The key aspect missing from previous models of terrestrial planet formation is the substantial radial migration of the giant planets, which suggests that their behaviour is more similar to that inferred for extrasolar planets than previously thought. ©2011 Macmillan Publishers Limited. All rights reserved

ON A GIANT IMPACT ORIGIN OF CHARON, NIX, AND HYDRA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Canup, Robin M., E-mail: robin@boulder.swri.edu

It is generally believed that Charon was formed as a result of a large, grazing collision with Pluto that supplied the Pluto-Charon system with its high angular momentum. It has also been proposed that Pluto's small outer moons, Nix and Hydra, formed from debris from the Charon-forming impact, although the viability of this scenario remains unclear. Here I use smooth particle hydrodynamics impact simulations to show that it is possible to simultaneously form an intact Charon and an accompanying debris disk from a single impact. The successful cases involve colliding objects that are partially differentiated prior to impact, having thinmore » outer ice mantles overlying a uniform composition rock-ice core. The composition of the resulting debris disks varies from a mixture of rock and ice (similar to the bulk composition of Pluto and Charon) to a pure ice disk. If Nix and Hydra were formed from such an impact-generated disk, their densities should be less than or similar to that of Charon and Pluto, and the small moons could be composed entirely of ice. If they were instead formed from captured material, a mixed rock-ice composition and densities similar to that of Charon and Pluto would be expected. Improved constraints on the properties of Nix and Hydra through occultations and/or the New Horizons encounter may thus help to distinguish between these two modes of origin, particularly if the small moons are found to have ice-like densities.« less

A TREND BETWEEN COLD DEBRIS DISK TEMPERATURE AND STELLAR TYPE: IMPLICATIONS FOR THE FORMATION AND EVOLUTION OF WIDE-ORBIT PLANETS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ballering, Nicholas P.; Rieke, George H.; Su, Kate Y. L.

2013-09-20

Cold debris disks trace the limits of planet formation or migration in the outer regions of planetary systems, and thus have the potential to answer many of the outstanding questions in wide-orbit planet formation and evolution. We characterized the infrared excess spectral energy distributions of 174 cold debris disks around 546 main-sequence stars observed by both the Spitzer Infrared Spectrograph and the Multiband Imaging Photometer for Spitzer. We found a trend between the temperature of the inner edges of cold debris disks and the stellar type of the stars they orbit. This argues against the importance of strictly temperature-dependent processesmore » (e.g., non-water ice lines) in setting the dimensions of cold debris disks. Also, we found no evidence that delayed stirring causes the trend. The trend may result from outward planet migration that traces the extent of the primordial protoplanetary disk, or it may result from planet formation that halts at an orbital radius limited by the efficiency of core accretion.« less

THE PDS 66 CIRCUMSTELLAR DISK AS SEEN IN POLARIZED LIGHT WITH THE GEMINI PLANET IMAGER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wolff, Schuyler G.; Greenbaum, Alexandra Z.; Perrin, Marshall

2016-02-10

We present H- and K-band imaging polarimetry for the PDS 66 circumstellar disk obtained during the commissioning of the Gemini Planet Imager (GPI). Polarization images reveal a clear detection of the disk in to the 0.″12 inner working angle (IWA) in the H band, almost three times closer to the star than the previous Hubble Space Telescope (HST) observations with NICMOS and STIS (0.″35 effective IWA). The centro-symmetric polarization vectors confirm that the bright inner disk detection is due to circumstellar scattered light. A more diffuse disk extends to a bright outer ring centered at 80 AU. We discuss several physicalmore » mechanisms capable of producing the observed ring + gap structure. GPI data confirm enhanced scattering on the east side of the disk that is inferred to be nearer to us. We also detect a lateral asymmetry in the south possibly due to shadowing from material within the IWA. This likely corresponds to a temporally variable azimuthal asymmetry observed in HST/STIS coronagraphic imaging.« less

Radial Surface Density Profiles of Gas and Dust in the Debris Disk Around 49 Ceti

NASA Technical Reports Server (NTRS)

Hughes, A. Meredith; Lieman-Sifry, Jesse; Flaherty, Kevin M.; Daley, Cail M.; Roberge, Aki; Kospal, Agnes; Moor, Attila; Kamp, Inga; Wilner, David J.; Andrews, Sean M.;

The great dichotomy of the Solar System: Small terrestrial embryos and massive giant planet cores

NASA Astrophysics Data System (ADS)

Morbidelli, A.; Lambrechts, M.; Jacobson, S.; Bitsch, B.

2015-09-01

The basic structure of the Solar System is set by the presence of low-mass terrestrial planets in its inner part and giant planets in its outer part. This is the result of the formation of a system of multiple embryos with approximately the mass of Mars in the inner disk and of a few multi-Earth-mass cores in the outer disk, within the lifetime of the gaseous component of the protoplanetary disk. What was the origin of this dichotomy in the mass distribution of embryos/cores? We show in this paper that the classic processes of runaway and oligarchic growth from a disk of planetesimals cannot explain this dichotomy, even if the original surface density of solids increased at the snowline. Instead, the accretion of drifting pebbles by embryos and cores can explain the dichotomy, provided that some assumptions hold true. We propose that the mass-flow of pebbles is two-times lower and the characteristic size of the pebbles is approximately ten times smaller within the snowline than beyond the snowline (respectively at heliocentric distance r rice , where rice is the snowline heliocentric distance), due to ice sublimation and the splitting of icy pebbles into a collection of chondrule-size silicate grains. In this case, objects of original sub-lunar mass would grow at drastically different rates in the two regions of the disk. Within the snowline these bodies would reach approximately the mass of Mars while beyond the snowline they would grow to ∼ 20 Earth masses. The results may change quantitatively with changes to the assumed parameters, but the establishment of a clear dichotomy in the mass distribution of protoplanets appears robust provided that there is enough turbulence in the disk to prevent the sedimentation of the silicate grains into a very thin layer.

A 5 Micron of beta Pictoris B at a Sub-Jupiter Projected Separation: Evidence for a Misalignment Between the Planet and the Inner, Warped Disk

NASA Technical Reports Server (NTRS)

Currie, Thayne; Thalmann, Christian; Matsumura, Soko; Madhusudhan, Nikku; Burrows, Adam; Kuchner, Marc

2011-01-01

We present and analyze a new M' detection of the young exoplanet Beta Pictoris b from 2008 VLT/NaCo data at a separation of approx. = 4 AU and a high signal-to-noise rereduction of L' data taken in December 2Q09. Based on our orbital analysis, the planet's orbit is viewed almost perfectly edge-on (i approx. 89 degrees) and has a Saturn-like semimajor axis of 9.50AU(+3.93 AU)/-(1.7AU) . Intriguingly, the planet's orbit is aligned with the major axis of the outer disk (Omega approx.31 degrees) but probably misaligned with the warp/inclined disk at 80 AU often cited as a signpost for the planet's existence. Our results motivate new studies to clarify how Beta Pic b sculpts debris disk structures and whether a second planet is required to explain the warp/inclined disk

Near-resonant excitation and propagation of eccentric density waves by external forcing. [in accretion disks

NASA Technical Reports Server (NTRS)

Ostriker, Eve C.; Shu, Frank H.; Adams, Fred C.

1992-01-01

An overview is presented of the astronomical evidence that relatively massive, distended, gaseous disks form as a natural by-product of the process of star formation, and also the numerical evidence that SLING-amplified eccentric modes in the outer parts of such disks can drive one-armed spiral density waves in the inner parts by near-resonant excitation and propagation. An ordinary differential equation (ODE) of the second order that approximately governs the nonlocalized forcing of waves in a disk satisfying Lindblad resonance almost everywhere is derived. When transformed and appended with an extra model term, this ODE implies, for free waves, the usual asymptotic results of the WKBJ dispersion relationship and the propagation Goldreich-Tremaine (1978) formula for the resonant torque exerted on a localized Lindblad resonance. An analytical solution is given for the rate of energy and angular momentum transfer by nonlocalized near-resonant forcing in the case when the disk has power-law dependences on the radius of the surface density and temperature.

The Minimum-Mass Surface Density of the Solar Nebula using the Disk Evolution Equation

NASA Technical Reports Server (NTRS)

Davis, Sanford S.

2005-01-01

The Hayashi minimum-mass power law representation of the pre-solar nebula (Hayashi 1981, Prog. Theo. Phys.70,35) is revisited using analytic solutions of the disk evolution equation. A new cumulative-planetary-mass-model (an integrated form of the surface density) is shown to predict a smoother surface density compared with methods based on direct estimates of surface density from planetary data. First, a best-fit transcendental function is applied directly to the cumulative planetary mass data with the surface density obtained by direct differentiation. Next a solution to the time-dependent disk evolution equation is parametrically adapted to the planetary data. The latter model indicates a decay rate of r -1/2 in the inner disk followed by a rapid decay which results in a sharper outer boundary than predicted by the minimum mass model. The model is shown to be a good approximation to the finite-size early Solar Nebula and by extension to extra solar protoplanetary disks.

Interstellar Explorer Observations of the Solar System's Debris Disks

NASA Astrophysics Data System (ADS)

Lisse, C. M.; McNutt, R. L., Jr.; Brandt, P. C.

2017-12-01

Planetesimal belts and debris disks full of dust are known as the "signposts of planet formation" in exosystems. The overall brightness of a disk provides information on the amount of sourcing planetesimal material, while asymmetries in the shape of the disk can be used to search for perturbing planets. The solar system is known to house two such belts, the Asteroid belt and the Kuiper Belt; and at least one debris cloud, the Zodiacal Cloud, sourced by planetisimal collisions and Kuiper Belt comet evaporative sublimation. However these are poorly understood in toto because we live inside of them. E.g., while we know of the two planetesimal belt systems, it is not clear how much, if any, dust is produced from the Kuiper belt since the near-Sun comet contributions dominate near-Earth space. Understanding how much dust is produced in the Kuiper belt would give us a much better idea of the total number of bodies in the belt, especially the smallest ones, and their dynamical collisional state. Even for the close in Zodiacal cloud, questions remain concerning its overall shape and orientation with respect to the ecliptic and invariable planes of the solar system - they aren't explainable from the perturbations caused by the known planets alone. In this paper we explore the possibilities of using an Interstellar Explorer telescope placed at 200 AU from the sun to observe the brightness, shape, and extent of the solar system's debris disk(s). We should be able to measure the entire extent of the inner, near-earth zodiacal cloud; whether it connects smoothly into an outer cloud, or if there is a second outer cloud sourced by the Kuiper belt and isolated by the outer planets, as predicted by Stark & Kuchner (2009, 2010) and Poppe et al. (2012, 2016; Figure 1). VISNIR imagery will inform about the dust cloud's density, while MIR cameras will provide thermal imaging photometry related to the cloud's dust particle size and composition. Observing at high phase angle by looking back towards the sun from 200 AU, we will be able to perform deep searches for the presence of rings and dust clouds around discrete sources, and thus we will be able to search for possible strong individual sources of the debris clouds - like the Haumea family collisional fragments, or the rings of the Centaur Chariklo, or dust emitted from spallation off the 6 known bodies of the Pluto system.

Numerical Modeling of Tidal Effects in Polytropic Accretion Disks

NASA Technical Reports Server (NTRS)

Godon, Patrick

1997-01-01

A two-dimensional time-dependent hybrid Fourier-Chebyshev method of collocation is developed and used for the study of tidal effects in accretion disks, under the assumptions of a polytropic equation of state and a standard alpha viscosity prescription. Under the influence of the m = 1 azimuthal component of the tidal potential, viscous oscillations in the outer disk excite an m = 1 eccentric instability in the disk. While the m = 2 azimuthal component of the tidal potential excites a Papaloizou-Pringle instability in the inner disk (a saturated m = 2 azimuthal mode), with an elliptic pattern rotating at about a fraction (approx. = 1/3) of the local Keplerian velocity in the inner disk. The period of the elliptic mode corresponds well to the periods of the short-period oscillations observed in cataclysmic variables. In cold disks (r(Omega)/c(sub s) = M approx. = 40) we also find a critical value of the viscosity parameter (alpha approx. = 0.01), below which shock dissipation dominates and is balanced by the wave amplification due to the wave action conservation. In this case the double spiral shock propagates all the way to the inner boundary with a Mach number M(sub s) approx. = 1.3.

Shaping Disk Galaxy Stellar Populations via Internal and External Processes

NASA Astrophysics Data System (ADS)

Roškar, Rok

2015-03-01

In recent years, effects such as the radial migration of stars in disks have been recognized as important drivers of the properties of stellar populations. Radial migration arises due to perturbative effects of disk structures such as bars and spiral arms, and can deposit stars formed in disks to regions far from their birthplaces. Migrant stars can significantly affect the demographics of their new locales, especially in low-density regions such as in the outer disks. However, in the cosmological environment, other effects such as mergers and filamentary gas accretion also influence the disk formation process. Understanding the relative importance of these processes on the detailed evolution of stellar population signatures is crucial for reconstructing the history of the Milky Way and other nearby galaxies. In the Milky Way disk in particular, the formation of the thickened component has recently attracted much attention due to its potential to serve as a diagnostic of the galaxy's early history. Some recent work suggests, however, that the vertical structure of Milky Way stellar populations is consistent with models that build up the thickened component through migration. I discuss these developments in the context of cosmological galaxy formation.

Observation of the Central Part of the Beta-Pictoris Disk with an Anti-Blooming CCD

NASA Astrophysics Data System (ADS)

Lecavelier Des Etangs, A.; Perrin, G.; Ferlet, R.; Vidal Madjar, A.; Colas, F.; Buil, C.; Sevre, F.; Arlot, J. E.; Beust, H.; Lagrange Henri, A. M.; Lecacheux, J.; Deleuil, M.; Gry, C.

1993-07-01

β Pictoris (A5V) possesses a circumstellar disk of gas and dust which is oriented edge-on to Earth. Possibly a planet may be indirectly responsible for spectroscopic events, presently interpreted as the signature of the vaporisation of comet-like bodies when grazing the star, and may have cleared up dust particles in the inner zone. Previous coronographic studies coupled with IRAS and ground based IR observations also seem to indicate that the inner regions of the disk may be possibly dust free. We have extended the coronographic studies closer to the star in order to directly observe this zone, through a different observational technique based on the use of an anti- blooming CCD. These new observations, recorded at La Silla (Chile), revealed the structure of the disk down to two arcsec from the star (30 AU from the star). A different nature of dust particles seems to be present in the inner regions of the disk, in possible relation with a planetary formation process. Also an inverted asymmetry is observed in the inner region of the disk when compared to the outer one, a structure possibly related to a non homogeneous distribution of the dust within the disk.

A New Paradigm for Gamma Ray Bursts: Long Term Accretion Rate Modulation by an External Accretion Disk

NASA Technical Reports Server (NTRS)

Cannizzo, John; Gehrels, Neil

2009-01-01

We present a new way of looking at the very long term evolution of GRBs in which the disk of material surrounding the putative black hole powering the GRB jet modulates the mass flow, and hence the efficacy of the process that extracts rotational energy from the black hole and inner accretion disk. The pre-Swift paradigm of achromatic, shallow-to-steep "breaks" in the long term GRB light curves has not been borne out by detailed Swift data amassed in the past several years. We argue that, given the initial existence of a fall-back disk near the progenitor, an unavoidable consequence will be the formation of an "external disk" whose outer edge continually moves to larger radii due to angular momentum transport and lack of a confining torque. The mass reservoir at large radii moves outward with time and gives a natural power law decay to the GRB light curves. In this model, the different canonical power law decay segments in the GRB identified by Zhang et al. and Nousek et al. represent different physical states of the accretion disk. We identify a physical disk state with each power law segment.

Barred Ring Galaxy NGC 1291

NASA Image and Video Library

2005-05-05

This ultraviolet image left and visual image right from NASA Galaxy Evolution Explorer is of the barred ring galaxy NGC 1291. The VIS image is dominated by the inner disk and bar. The UV image is dominated by the low surface brightness outer arms.

THE EVOLUTION OF INNER DISK GAS IN TRANSITION DISKS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hoadley, K.; France, K.; McJunkin, M.

2015-10-10

Investigating the molecular gas in the inner regions of protoplanetary disks (PPDs) provides insight into how the molecular disk environment changes during the transition from primordial to debris disk systems. We conduct a small survey of molecular hydrogen (H{sub 2}) fluorescent emission, using 14 well-studied Classical T Tauri stars at two distinct dust disk evolutionary stages, to explore how the structure of the inner molecular disk changes as the optically thick warm dust dissipates. We simulate the observed Hi-Lyman α-pumped H{sub 2} disk fluorescence by creating a 2D radiative transfer model that describes the radial distributions of H{sub 2} emissionmore » in the disk atmosphere and compare these to observations from the Hubble Space Telescope. We find the radial distributions that best describe the observed H{sub 2} FUV emission arising in primordial disk targets (full dust disk) are demonstrably different than those of transition disks (little-to-no warm dust observed). For each best-fit model, we estimate inner and outer disk emission boundaries (r{sub in} and r{sub out}), describing where the bulk of the observed H{sub 2} emission arises in each disk, and we examine correlations between these and several observational disk evolution indicators, such as n{sub 13–31}, r{sub in,} {sub CO}, and the mass accretion rate. We find strong, positive correlations between the H{sub 2} radial distributions and the slope of the dust spectral energy distribution, implying the behavior of the molecular disk atmosphere changes as the inner dust clears in evolving PPDs. Overall, we find that H{sub 2} inner radii are ∼4 times larger in transition systems, while the bulk of the H{sub 2} emission originates inside the dust gap radius for all transitional sources.« less

Multiple rings in the transition disk and companion candidates around RX J1615.3-3255. High contrast imaging with VLT/SPHERE

NASA Astrophysics Data System (ADS)

de Boer, J.; Salter, G.; Benisty, M.; Vigan, A.; Boccaletti, A.; Pinilla, P.; Ginski, C.; Juhasz, A.; Maire, A.-L.; Messina, S.; Desidera, S.; Cheetham, A.; Girard, J. H.; Wahhaj, Z.; Langlois, M.; Bonnefoy, M.; Beuzit, J.-L.; Buenzli, E.; Chauvin, G.; Dominik, C.; Feldt, M.; Gratton, R.; Hagelberg, J.; Isella, A.; Janson, M.; Keller, C. U.; Lagrange, A.-M.; Lannier, J.; Menard, F.; Mesa, D.; Mouillet, D.; Mugrauer, M.; Peretti, S.; Perrot, C.; Sissa, E.; Snik, F.; Vogt, N.; Zurlo, A.; SPHERE Consortium

2016-11-01

Context. The effects of a planet sculpting the disk from which it formed are most likely to be found in disks that are in transition between being classical protoplanetary and debris disks. Recent direct imaging of transition disks has revealed structures such as dust rings, gaps, and spiral arms, but an unambiguous link between these structures and sculpting planets is yet to be found. Aims: We aim to find signs of ongoing planet-disk interaction and study the distribution of small grains at the surface of the transition disk around RX J1615.3-3255 (RX J1615). Methods: We observed RX J1615 with VLT/SPHERE. From these observations, we obtained polarimetric imaging with ZIMPOL (R'-band) and IRDIS (J), and IRDIS (H2H3) dual-band imaging with simultaneous spatially resolved spectra with the IFS (YJ). Results: We image the disk for the first time in scattered light and detect two arcs, two rings, a gap and an inner disk with marginal evidence for an inner cavity. The shapes of the arcs suggest that they are probably segments of full rings. Ellipse fitting for the two rings and inner disk yield a disk inclination I = 47 ± 2° and find semi-major axes of 1.50 ± 0.01'' (278 au), 1.06 ± 0.01'' (196 au) and 0.30 ± 0.01'' (56 au), respectively. We determine the scattering surface height above the midplane, based on the projected ring center offsets. Nine point sources are detected between 2.1'' and 8.0'' separation and considered as companion candidates. With NACO data we recover four of the nine point sources, which we determine to be not co-moving, and therefore unbound to the system. Conclusions: We present the first detection of the transition disk of RX J1615 in scattered light. The height of the rings indicate limited flaring of the disk surface, which enables partial self-shadowing in the disk. The outermost arc either traces the bottom of the disk or it is another ring with semi-major axis ≳ 2.35'' (435 au). We explore both scenarios, extrapolating the complete shape of the feature, which will allow us to distinguish between the two in future observations. The most attractive scenario, where the arc traces the bottom of the outer ring, requires the disk to be truncated at r ≈ 360 au. If the closest companion candidate is indeed orbiting the disk at 540 au, then it would be the most likely cause for such truncation. This companion candidate, as well as the remaining four, all require follow up observations to determine if they are bound to the system. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme IDs 095.C-0298(A), 095.C-0298(B), and 095.C-0693(A) during guaranteed and open time observations of the SPHERE consortium, and on NACO observations: program IDs: 085.C-0012(A), 087.C-0111(A), and 089.C-0133(A). The reduced images as FITS files are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/595/A114

The value of maximum jaw motion measurements for distinguishing between common temporomandibular disorder subgroups.

PubMed

Masumi, S; Kim, Y J; Clark, G T

2002-05-01

The purpose of this study was to determine if mandibular motion measurements could be used to distinguish between common temporomandibular disorder (TMD) subgroups that were established on the basis of only clinical signs and symptoms. Patients were 41 consecutive TMD clinic patients (31 women and 10 men). These patients were divided into 6 typical TMD subgroups. The subgroups were patients with (1) arthromyalgia, (2) arthromyalgia with disk condyle incoordination, (3) disk condyle incoordination only, (4) osteoarthritis, (5) suspected disk displacement without reduction, or (6) other diagnoses. There were no subjects in the other-diagnosis subgroup and only 1 subject with suspected disk displacement without reduction who was dropped without further consideration. The data for mean age showed that the osteoarthritis subgroup (n = 12) was statistically older (17 years) than the disk-condyle-incoordination-only subgroup (n = 11). The mean age of the other 2 groups, arthromyalgia (n = 11) and arthromyalgia with disk condyle incoordination (n = 6), was between the osteoarthritis and the disk-condyle-incoordination-only subgroups. For the 4 TMD subgroups whose data were analyzed, the mean differences between similar jaw opening measurements ranged from 6 to 8 mm with a standard deviation of approximately 8 to 10 mm. The mean left lateral motions were 0.5 to 1.3 mm larger than observed on the right. The widest mean jaw opening (56 mm) occurred in the disk-condyle-incoordination-only group. These differences were not found to be statistically significant. Analysis of opening, lateral and protrusive jaw motion data showed these measurements could not reliably differentiate between patients with osteoarthritis, arthromyalgia, arthromyalgia with disk condyle incoordination and disk condyle incoordination only.

Dynamical models to explain observations with SPHERE in planetary systems with double debris belts

NASA Astrophysics Data System (ADS)

Lazzoni, C.; Desidera, S.; Marzari, F.; Boccaletti, A.; Langlois, M.; Mesa, D.; Gratton, R.; Kral, Q.; Pawellek, N.; Olofsson, J.; Bonnefoy, M.; Chauvin, G.; Lagrange, A. M.; Vigan, A.; Sissa, E.; Antichi, J.; Avenhaus, H.; Baruffolo, A.; Baudino, J. L.; Bazzon, A.; Beuzit, J. L.; Biller, B.; Bonavita, M.; Brandner, W.; Bruno, P.; Buenzli, E.; Cantalloube, F.; Cascone, E.; Cheetham, A.; Claudi, R. U.; Cudel, M.; Daemgen, S.; De Caprio, V.; Delorme, P.; Fantinel, D.; Farisato, G.; Feldt, M.; Galicher, R.; Ginski, C.; Girard, J.; Giro, E.; Janson, M.; Hagelberg, J.; Henning, T.; Incorvaia, S.; Kasper, M.; Kopytova, T.; LeCoroller, H.; Lessio, L.; Ligi, R.; Maire, A. L.; Ménard, F.; Meyer, M.; Milli, J.; Mouillet, D.; Peretti, S.; Perrot, C.; Rouan, D.; Samland, M.; Salasnich, B.; Salter, G.; Schmidt, T.; Scuderi, S.; Sezestre, E.; Turatto, M.; Udry, S.; Wildi, F.; Zurlo, A.

2018-03-01

Context. A large number of systems harboring a debris disk show evidence for a double belt architecture. One hypothesis for explaining the gap between the debris belts in these disks is the presence of one or more planets dynamically carving it. For this reason these disks represent prime targets for searching planets using direct imaging instruments, like the Spectro-Polarimetric High-constrast Exoplanet Research (SPHERE) at the Very Large Telescope. Aim. The goal of this work is to investigate this scenario in systems harboring debris disks divided into two components, placed, respectively, in the inner and outer parts of the system. All the targets in the sample were observed with the SPHERE instrument, which performs high-contrast direct imaging, during the SHINE guaranteed time observations. Positions of the inner and outer belts were estimated by spectral energy distribution fitting of the infrared excesses or, when available, from resolved images of the disk. Very few planets have been observed so far in debris disks gaps and we intended to test if such non-detections depend on the observational limits of the present instruments. This aim is achieved by deriving theoretical predictions of masses, eccentricities, and semi-major axes of planets able to open the observed gaps and comparing such parameters with detection limits obtained with SPHERE. Methods: The relation between the gap and the planet is due to the chaotic zone neighboring the orbit of the planet. The radial extent of this zone depends on the mass ratio between the planet and the star, on the semi-major axis, and on the eccentricity of the planet, and it can be estimated analytically. We first tested the different analytical predictions using a numerical tool for the detection of chaotic behavior and then selected the best formula for estimating a planet's physical and dynamical properties required to open the observed gap. We then apply the formalism to the case of one single planet on a circular or eccentric orbit. We then consider multi-planetary systems: two and three equal-mass planets on circular orbits and two equal-mass planets on eccentric orbits in a packed configuration. As a final step, we compare each couple of values (Mp, ap), derived from the dynamical analysis of single and multiple planetary models, with the detection limits obtained with SPHERE. Results: For one single planet on a circular orbit we obtain conclusive results that allow us to exclude such a hypothesis since in most cases this configuration requires massive planets which should have been detected by our observations. Unsatisfactory is also the case of one single planet on an eccentric orbit for which we obtained high masses and/or eccentricities which are still at odds with observations. Introducing multi planetary architectures is encouraging because for the case of three packed equal-mass planets on circular orbits we obtain quite low masses for the perturbing planets which would remain undetected by our SPHERE observations. The case of two equal-mass planets on eccentric orbits is also of interest since it suggests the possible presence of planets with masses lower than the detection limits and with moderate eccentricity. Our results show that the apparent lack of planets in gaps between double belts could be explained by the presence of a system of two or more planets possibly of low mass and on eccentric orbits whose sizes are below the present detection limits. Based on observations collected at Paranal Observatory, ESO (Chile) Program ID: 095.C-0298, 096.C-0241, 097.C-0865, and 198.C-0209.

The IRS 1 circumstellar disk, and the origin of the jet and CO outflow in B5

NASA Technical Reports Server (NTRS)

Langer, W. D.; Velusamy, T.; Xie, T.; Levin, S. M. (Principal Investigator)

1996-01-01

We report the discovery of the inner edge of the high velocity CO outflow associated with the bipolar jet originating from IRS 1 in Barnard 5 and the first ever resolution of its circumstellar disk in the 2.6 mm dust continuum and C18O. From high spatial resolution observations made with the Owens Valley Millimeter Array we are able to locate the origin of the outflow to within approximately 500 AU on either side of IRS 1 and apparently at the edge of, or possibly within, its circumstellar disk. The orientation of the continuum disk is perpendicular to the highly collimated jet outflow recently seen in optical emission at much farther distances. The disk has been detected in C18O giving a disk mass approximately 0.16 M (solar). Our HCO+ and HCN maps indicate significant chemical differentiation in the circumstellar region on small scales with HCO+ tracing an extended disk of material. The 12CO interferometer maps of the outflow show two conelike features originating at IRS 1, the blue one fanning open to the northeast and the red one to the southwest. The vertices of the cones are on either side of the circumstellar disk and have a projected opening angle of about 90 degrees. The intrinsic opening angle is in the range of 60 degrees-90 degrees which leads to significant interaction between outflow and infall.

Effect of External Photoevaporation on the Radial Transport of Volatiles and the Water Snowline in the Solar Nebula

NASA Astrophysics Data System (ADS)

Kalyaan, Anusha; Desch, Steven

2017-01-01

The Sun was likely born in a high mass star forming region [1]. Such a birth environment with a proximity to a nearby O or B star would photoevaporate the sun’s protoplanetary disk and cause an outward mass flow from the outer edge, as well as truncation of the disk, as seen in the Orion proplyds (although not as intensely)[2]. Photoevaporation likely explains the currently observed ~47 AU edge of the Kuiper Belt in our solar system [3], and more compellingly, the origin of certain short-lived radionuclides (such as Fe60), which cannot be successfully explained by a nebular origin [4][5]. Such a mass loss mechanism should affect the radial transport processes in the snowline region and along with temperature, has the potential to alter the location of the snowline.In this context, and in the light of recent ALMA observational results indicative of non-traditional behavior of snowlines and volatile transport in disks [6][7], this work studies what effect a photoevaporative mass loss from the outer disk may have on the volatile transport around the snowline region between ~1-10 AU in the disk. We build on the model of [8] and explore the effects of a steep photoevaporated non-uniform $\\alpha$ disk on radial transport of volatiles and small icy solids by incorporating the advection-diffusion equations as in [9] and condensation/evaporation of volatiles. We present results of these simulations, including volatile mass fluxes, ice/rock ratios, and snow line locations, in protoplanetary disks like the solar nebula.References: [1] Adams, F.C., 2010, ARAA 48,47 [2] Henney, W.J., & O’Dell, C.R., 1999, AJ, 118, 2350 [3] Trujillo,C.A. & Brown,M.E., 2001, ApJL,554,L95 [4] Hester, J.J., & Desch, S.J., 2005,ASPC, 341,107 [5] Wadhwa, M. et al. , 2007, Protostars & Planets V, 835 [5 [6] Cieza, L.A., et al., 2016, Nature,535,258 [7] Huang, J, et al. et al., 2016, ApJL, 823, L18 [8] Kalyaan, A., et al., 2015, ApJ, 815, 112 [9] Desch, S.J., et al., (in review).

N-Body Simulations of Planetary Accretion Around M Dwarf Stars

NASA Astrophysics Data System (ADS)

Ogihara, Masahiro; Ida, Shigeru

2009-07-01

We have investigated planetary accretion from planetesimals in terrestrial planet regions inside the ice line around M dwarf stars through N-body simulations including tidal interactions with disk gas. Because of low luminosity of M dwarfs, habitable zones (HZs) are located in inner regions (~0.1 AU). In the close-in HZ, type-I migration and the orbital decay induced by eccentricity damping are efficient according to the high disk gas density in the small orbital radii. Since the orbital decay is terminated around the disk inner edge and the disk edge is close to the HZ, the protoplanets accumulated near the disk edge affect formation of planets in the HZ. Ice lines are also in relatively inner regions at ~0.3 AU. Due to the small orbital radii, icy protoplanets accrete rapidly and undergo type-I migration before disk depletion. The rapid orbital decay, the proximity of the disk inner edge, and large amount of inflow of icy protoplanets are characteristic in planetary accretion in terrestrial planet regions around M dwarfs. In the case of full efficiency of type-I migration predicted by the linear theory, we found that protoplanets that migrate to the vicinity of the host star undergo close scatterings and collisions, and four to six planets eventually remain in mutual mean-motion resonances and their orbits have small eccentricities (lsim0.01) and they are stable both before and after disk gas decays. In the case of slow migration, the resonant capture is so efficient that densely packed ~40 small protoplanets remain in mutual mean-motion resonances. In this case, they start orbit crossing, after the disk gas decays and eccentricity damping due to tidal interaction with gas is no more effective. Through merging of the protoplanets, several planets in widely separated non-resonant orbits with relatively large eccentricities (~0.05) are formed. Thus, the final orbital configurations (separations, resonant or non-resonant, eccentricity, and distribution) of the terrestrial planets around M dwarfs sensitively depend on strength of type-I migration. We also found that large amount of water-ice is delivered by type-I migration from outer regions and final planets near the inner disk edge around M dwarfs are generally abundant in water-ice except for the innermost one that is shielded by the outer planets, unless type-I migration speed is reduced by a factor of more than 100 from that predicted by the linear theory.

Recent developments on SU UMa stars - theory vs. observation

NASA Astrophysics Data System (ADS)

Cannizzo, John K.

2015-01-01

Kepler light curves of short period dwarf novae have resparked interest in the nature of superoutbursts and led to the question: Is the thermal-tidal instability needed, or can the plain vanilla version of the accretion disk limit cycle do the job all by itself? A detailed time-resolved study of an eclipsing SU UMa system during superoutburst onset should settle the question - if there is a dramatic contraction of the disk at superoutburst onset, Osaki's thermal-tidal model would be preferred; if not, the plain disk instability model would be sufficient. I will present recent results that support the contention by Osaki & Kato that the time varying negative superhump frequencies can be taken as a surrogate for the outer disk radius variations. Finally, it may be necessaryto look beyond the short period dwarf novae to gain perspective on the nature of embedded precursors in long outbursts.

Debris disks as signposts of terrestrial planet formation

NASA Astrophysics Data System (ADS)

Raymond, S. N.; Armitage, P. J.; Moro-Martín, A.; Booth, M.; Wyatt, M. C.; Armstrong, J. C.; Mandell, A. M.; Selsis, F.; West, A. A.

2011-06-01

There exists strong circumstantial evidence from their eccentric orbits that most of the known extra-solar planetary systems are the survivors of violent dynamical instabilities. Here we explore the effect of giant planet instabilities on the formation and survival of terrestrial planets. We numerically simulate the evolution of planetary systems around Sun-like stars that include three components: (i) an inner disk of planetesimals and planetary embryos; (ii) three giant planets at Jupiter-Saturn distances; and (iii) an outer disk of planetesimals comparable to estimates of the primitive Kuiper belt. We calculate the dust production and spectral energy distribution of each system by assuming that each planetesimal particle represents an ensemble of smaller bodies in collisional equilibrium. Our main result is a strong correlation between the evolution of the inner and outer parts of planetary systems, i.e. between the presence of terrestrial planets and debris disks. Strong giant planet instabilities - that produce very eccentric surviving planets - destroy all rocky material in the system, including fully-formed terrestrial planets if the instabilities occur late, and also destroy the icy planetesimal population. Stable or weakly unstable systems allow terrestrial planets to accrete in their inner regions and significant dust to be produced in their outer regions, detectable at mid-infrared wavelengths as debris disks. Stars older than ~100 Myr with bright cold dust emission (in particular at λ ~ 70 μm) signpost dynamically calm environments that were conducive to efficient terrestrial accretion. Such emission is present around ~16% of billion-year old Solar-type stars. Our simulations yield numerous secondary results: 1) the typical eccentricities of as-yet undetected terrestrial planets are ~0.1 but there exists a novel class of terrestrial planet system whose single planet undergoes large amplitude oscillations in orbital eccentricity and inclination; 2) by scaling our systems to match the observed semimajor axis distribution of giant exoplanets, we predict that terrestrial exoplanets in the same systems should be a few times more abundant at ~0.5 AU than giant or terrestrial exoplanets at 1 AU; 3) the Solar System appears to be unusual in terms of its combination of a rich terrestrial planet system and a low dust content. This may be explained by the weak, outward-directed instability that is thought to have caused the late heavy bombardment. The movie associated to Fig. 2 is available in electronic form at http://www.aanda.org

Exploring the Surface Brightness Breaks and Star Formation in Disk Galaxies

NASA Astrophysics Data System (ADS)

Malko, Bradley Ann; Hunter, Deidre Ann

2018-06-01

Stellar surface brightness profiles of both spirals and dwarf irregular galaxies often show breaks in which the exponential fall-off abruptly changes slope. Most often the profile is down-bending (Type II) in the outer disk, but sometimes it is up-bending (Type III). Stellar disks extend a long ways beyond the profile breaks, but we do not understand what happens physically at the breaks. To explore this we are examining the star formation activity, as traced with FUV emission, interior to the break compared to that exterior to the break in both dwarf irregulars and spiral galaxies. We present the results for the spiral galaxy NGC 2500 and compare it to the LITTLE THINGS dwarf irregular galaxies.

Refractive index sensing with Fano resonances in silicon oligomers

PubMed Central

Chong, Katie E.; Orton, Henry W.; Decker, Manuel; Miroshnichenko, Andrey E.; Brener, Igal; Kivshar, Yuri S.

2017-01-01

We demonstrate experimentally refractive index sensing with localized Fano resonances in silicon oligomers, consisting of six disks surrounding a central one of slightly different diameter. Owing to the low absorption and narrow Fano-resonant spectral features appearing as a result of the interference of the modes of the outer and the central disks, we demonstrate refractive index sensitivity of more than 150 nm RIU−1 with a figure of merit of 3.8. This article is part of the themed issue ‘New horizons for nanophotonics’. PMID:28220001

Description of a new species of Microhyla from Bali, Indonesia (Amphibia, Anura).

PubMed

Matsui, Masafumi; Hamidy, Amir; Eto, Koshiro

2013-01-01

We describe a microhylid frog from Bali, Indonesia as a new species, Microhyla orientalis sp. nov. It belongs to the M. achatina group and is close to M. mantheyi, M. malang, and M. borneensis. It is distinguished from its congeners by a combination of the following characters: small size (adult males about 16-17 mm in SVL); a faint vertebral stripe present; a black lateral stripe from behind eye to half length of trunk; snout rounded in profile; eyelid without supraciliary spines; first finger less than one-fifth of third; tips of three outer fingers weakly dilated, forming weak disks, dorsally with median longitudinal groove; outer palmar tubercle single; tibiotarsal articulation reaching up to center of eye; tips of toes distinctly dilated into disks, dorsally with median longitudinal groove; inner and outer metatarsal tubercles present; four or more phalanges on inner and outer sides of fourth toe, and three phalanges on inner side of fifth toe free of web; and tail of larva with a black marking at middle. The male advertisement call of the new species consists of a series of notes each lasts for 0.01-0.08 s and composed of 3-5 pulses with a dominant frequency of 3.2-3.6 kHz. Uncorrected sequence divergences between M. orientalis and all homologous 16S rRNA sequences available were > 6.6%. At present, the new species is known from rice fields between 435-815 m elevation in Wongaya Gede and Batukaru.

77 FR 11017 - Airworthiness Directives; Pratt & Whitney (PW) Models PW4074 and PW4077 Turbofan Engines

Federal Register 2010, 2011, 2012, 2013, 2014

2012-02-24

... (BSI) or eddy current inspection (ECI) of the disk outer rim front rail for cracks prior to... date of this AD. (ii) Perform a borescope inspection (BSI) or eddy current inspection (ECI) of the...

Submillimeter Array {sup 12}CO (2-1) Imaging of the NGC 6946 Giant Molecular Clouds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Ya-Lin; Sakamoto, Kazushi; Pan, Hsi-An, E-mail: yalinwu@email.arizona.edu

2017-04-10

We present a {sup 12}CO (2–1) mosaic map of the spiral galaxy NGC 6946 by combining data from the Submillimeter Array and the IRAM 30 m telescope. We identify 390 giant molecular clouds (GMCs) from the nucleus to 4.5 kpc in the disk. GMCs in the inner 1 kpc are generally more luminous and turbulent, some of which have luminosities >10{sup 6} K km s{sup −1} pc{sup 2} and velocity dispersions >10 km s{sup −1}. Large-scale bar-driven dynamics likely regulate GMC properties in the nuclear region. Similar to the Milky Way and other disk galaxies, GMC mass function of NGCmore » 6946 has a shallower slope (index > −2) in the inner region, and a steeper slope (index < −2) in the outer region. This difference in mass spectra may be indicative of different cloud formation pathways: gravitational instabilities might play a major role in the nuclear region, while cloud coalescence might be dominant in the outer disk. Finally, the NGC 6946 clouds are similar to those in M33 in terms of statistical properties, but they are generally less luminous and turbulent than the M51 clouds.« less

Featured Image: A New Look at Fomalhaut

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-06-01

ALMA continuum image overlaid as contours on the Hubble STIS image of Fomalhaut. [MacGregor et al. 2017]This stunning image of the Fomalhaut star system was taken by the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. This image maps the 1.3-mm continuum emission from the dust around the central star, revealing a ring that marks the outer edge of the planet-forming debris disk surrounding the star. In a new study, a team of scientists led by Meredith MacGregor (Harvard-Smithsonian Center for Astrophysics) examines these ALMA observations of Fomalhaut, which beautifully complement former Hubble images of the system. ALMAs images provide the first robust detection of apocenter glow the brightening of the ring at the point farthest away from the central star, a side effect of the rings large eccentricity. The authors use ALMAsobservations to measure properties of the disk, such as its span (roughly 136 x 14 AU), eccentricity (e 0.12), and inclination angle ( 66). They then explore the implications for Fomalhaut b, the planet located near the outer disk. To read more about the teams observations, check out the paper below.CitationMeredith A. MacGregor et al 2017 ApJ 842 8. doi:10.3847/1538-4357/aa71ae

The simulation of the outer Oort cloud formation. The first giga-year of the evolution

NASA Astrophysics Data System (ADS)

Dybczyński, P. A.; Leto, G.; Jakubík, M.; Paulech, T.; Neslušan, L.

2008-08-01

Aims: Considering a model of an initial disk of planetesimals that consists of 10 038 test particles, we simulate the formation of distant-comet reservoirs for the first 1 Gyr. Since only the outer part of the Oort cloud can be formed within this period, we analyse the efficiency of the formation process and describe approximately the structure of the part formed. Methods: The dynamical evolution of the particles is followed by numerical integration of their orbits. We consider the perturbations by four giant planets on their current orbits and with their current masses, in addition to perturbations by the Galactic tide and passing stars. Results: In our simulation, the population size of the outer Oort cloud reaches its maximum value at about 210 Myr. After a subsequent, rapid decrease, it becomes almost stable (with only a moderate decrease) from about 500 Myr. At 1 Gyr, the population size decreases to about 40% of its maximum value. The efficiency of the formation is low. Only about 0.3% of the particles studied still reside in the outer Oort cloud after 1 Gyr. The space density of particles in the comet cloud, beyond the heliocentric distance, r, of 25 000 AU is proportional to r-s, where s = 4.08 ± 0.34. From about 50 Myr to the end of the simulation, the orbits of the Oort cloud comets are not distributed randomly, but high galactic inclinations of the orbital planes are strongly dominant. Among all of the outer perturbers considered, this is most likely caused by the dominant, disk component of the Galactic tide. Movies (cf. caption to Fig. 1) are only available at http://www.aanda.org

A Study on the Characteristics of the Structure of Vega's Debris Disk

NASA Astrophysics Data System (ADS)

Lu, Tao; Ji, Jiang-hui

2013-10-01

The clumpy structure in the Vega's debris disk was reported at millimeter wavelengths previously, and attributed to the concentration of dust grains trapped in resonances with a potential high-eccentricity planet. However, current imaging at multi-wavelengths with higher sensitivity indicates that the Vega's debris disk has a smooth structure. But a planet orbiting Vega could not be neglected, and the present-day observations may place a severe constraint on the orbital parameters for the potential planet. Herein, we utilize the modi- fied MERCURY codes to numerically simulate the Vega system, which consists of a debris disk and a planet. In our simulations, the initial inner and outer boundaries of the debris disk are assumed to be 80 AU and 120 AU, respectively. The dust grains in the disk have the sizes from 10 μm to 100 μm, and the nearly coplanar orbits. From the outcomes, we show that the evolution of debris disk is consistent with recent observations, if there is no planet orbiting Vega. However, if Vega owns a planet with a high eccentricity (e.g., e = 0.6), the planet's semi- major axis cannot be larger than 60 AU, otherwise, an aggregation phenomenon will occur in the debris disk due to the existence of the postulated planet. In addition, the 2:1 mean motion resonances may play a significant role in forming the structure of debris disk.

Piston manometer as an absolute standard for vacuum-gage calibration in the range 2 to 500 millitorr

NASA Technical Reports Server (NTRS)

Warshawsky, I.

1972-01-01

A thin disk is suspended, with very small annular clearance, in a cylindrical opening in the base plate of a calibration chamber. A continuous flow of calibration gas passes through the chamber and annular opening to a downstream high vacuum pump. The ratio of pressures on the two faces of the disk is very large, so that the upstream pressure is substantially equal to net force on the disk divided by disk area. This force is measured with a dynamometer that is calibrated in place with dead weights. A probable error of + or - (0.2 millitorr plus 0.2 percent) is attainable when downstream pressure is known to 10 percent.

Three-dimensional reconstruction of TMJ MR images: a technical note and case report.

PubMed

Kitai, Noriyuki; Eriksson, Lars; Kreiborg, Sven; Wagner, Aase; Takada, Kenji

2004-01-01

MR images of the temporomandibular joint at occlusion and at various stages of mouth opening were registered and reconstructed three-dimensionally before and after a modified condylotomy in a patient with painful disk displacement. Following the condylotomy, the condyle/disk relationship had become normalized in all three planes of space at closed mouth and during mouth opening. The post-operative distances of the condylar and diskal paths had increased when compared with the preoperative distances. The three-dimensional visualizing method may, besides providing diagnostic advantages, be a valuable tool for qualitative and quantitative documentation of the efficiency of different treatment methods for normalization of the disk/condyle relationship in patients with TMJ disk displacement.

An inducible amphipathic helix within the intrinsically disordered C terminus can participate in membrane curvature generation by peripherin-2/rds.

PubMed

Milstein, Michelle L; Kimler, Victoria A; Ghatak, Chiranjib; Ladokhin, Alexey S; Goldberg, Andrew F X

2017-05-12

Peripherin-2/rds is required for biogenesis of vertebrate photoreceptor outer segment organelles. Its localization at the high-curvature rim domains of outer segment disk membranes suggests that it may act to shape these structures; however, the molecular function of this protein is not yet resolved. Here, we apply biochemical, biophysical, and imaging techniques to elucidate the role(s) played by the protein's intrinsically disordered C-terminal domain and an incipient amphipathic α-helix contained within it. We investigated a deletion mutant lacking only this α-helix in stable cell lines and Xenopus laevis photoreceptors. We also studied a soluble form of the full-length ∼7-kDa cytoplasmic C terminus in cultured cells and purified from Escherichia coli The α-helical motif was not required for protein biosynthesis, tetrameric subunit assembly, tetramer polymerization, localization at disk rims, interaction with GARP2, or the generation of membrane curvature. Interestingly, however, loss of the helical motif up-regulated membrane curvature generation in cellulo , introducing the possibility that it may regulate this activity in photoreceptors. Furthermore, the incipient α-helix (within the purified soluble C terminus) partitioned into membranes only when its acidic residues were neutralized by protonation. This suggests that within the context of full-length peripherin-2/rds, partitioning would most likely occur at a bilayer interfacial region, potentially adjacent to the protein's transmembrane domains. In sum, this study significantly strengthens the evidence that peripherin-2/rds functions directly to shape the high-curvature rim domains of the outer segment disk and suggests that the protein's C terminus may modulate membrane curvature-generating activity present in other protein domains. © 2017 by The American Society for Biochemistry and Molecular Biology, Inc.

ALMA Dust Polarization Observations of Two Young Edge-on Protostellar Disks

NASA Astrophysics Data System (ADS)

Lee, Chin-Fei; Li, Zhi-Yun; Ching, Tao-Chung; Lai, Shih-Ping; Yang, Haifeng

2018-02-01

Polarized emission is detected in two young nearly edge-on protostellar disks in 343 GHz continuum at ∼50 au (∼0.″12) resolution with Atacama Large Millimeter/submillimeter Array. One disk is in HH 212 (Class 0) and the other in the HH 111 (early Class I) protostellar system. The polarization fraction is ∼1%. The disk in HH 212 has a radius of ∼60 au. The emission is mainly detected from the nearside of the disk. The polarization orientations are almost perpendicular to the disk major axis, consistent with either self-scattering or emission by grains aligned with a poloidal field around the outer edge of the disk because of the optical depth effect and temperature gradient; the presence of a poloidal field would facilitate the launching of a disk wind, for which there is already tentative evidence in the same source. The disk of HH 111 VLA 1 has a larger radius of ∼220 au and is thus more resolved. The polarization orientations are almost perpendicular to the disk major axis in the nearside, but more along the major axis in the farside, forming roughly half of an elliptical pattern there. It appears that toroidal and poloidal magnetic field may explain the polarization on the near and far sides of the disk, respectively. However, it is also possible that the polarization is due to self-scattering. In addition, alignment of dust grains by radiation flux may play a role in the farside. Our observations reveal a diversity of disk polarization patterns that should be taken into account in future modeling efforts.

ON THE STAR FORMATION LAW FOR SPIRAL AND IRREGULAR GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Elmegreen, Bruce G., E-mail: bge@us.ibm.com

2015-12-01

A dynamical model for star formation on a galactic scale is proposed in which the interstellar medium is constantly condensing to star-forming clouds on the dynamical time of the average midplane density, and the clouds are constantly being disrupted on the dynamical timescale appropriate for their higher density. In this model, the areal star formation rate scales with the 1.5 power of the total gas column density throughout the main regions of spiral galaxies, and with a steeper power, 2, in the far outer regions and in dwarf irregular galaxies because of the flaring disks. At the same time, theremore » is a molecular star formation law that is linear in the main and outer parts of disks and in dIrrs because the duration of individual structures in the molecular phase is also the dynamical timescale, canceling the additional 0.5 power of surface density. The total gas consumption time scales directly with the midplane dynamical time, quenching star formation in the inner regions if there is no accretion, and sustaining star formation for ∼100 Gyr or more in the outer regions with no qualitative change in gas stability or molecular cloud properties. The ULIRG track follows from high densities in galaxy collisions.« less

Uranus and Neptune: Refugees from the Jupiter-Saturn zone?

NASA Astrophysics Data System (ADS)

Thommes, E. W.; Duncan, M. J.; Levison, H. F.

1999-09-01

Plantesimal accretion models of planet formation have been quite successful at reproducing the terrestrial region of the Solar System. However, in the outer Solar System these models run into problems, and it becomes very difficult to grow bodies to the current mass of the ``ice giants," Uranus and Neptune. Here we present an alternative scenario to in-situ formation of the ice giants. In addition to the Jupiter and Saturn solid cores, several more bodies of mass ~ 10 MEarth or more are likely to have formed in the region between 4 and 10 AU. As Jupiter's core, and perhaps Saturn's, accreted nebular gas, the other nearby bodies must have been scattered outward. Dynamical friction with the trans-Saturnian part of the planetesimal disk would have acted to decouple these ``failed cores" from their scatterer, and to circularize their orbits. Numerical simulations presented here show that systems very similar to our outer Solar System (including Uranus, Neptune, the Kuiper belt, and the scattered disk) are a natural product of this process.

OUTER GALACTIC DISKS AND A QUANTITATIVE TEST OF GRAVITY AT LOW ACCELERATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zaritsky, Dennis; Psaltis, Dimitrios, E-mail: dzaritsky@as.arizona.ed, E-mail: psaltis@as.arizona.ed

We use the recent measurement of the velocity dispersion of star-forming, outer-disk knots by Herbert-Fort et al. in the nearly face-on galaxy NGC 628, in combination with other data from the literature, to execute a straightforward test of gravity at low accelerations. Specifically, the rotation curve at large radius sets the degree of non-standard acceleration and then the predicted scale height of the knots at that radius provides the test of the scenario. For our demonstration, we presume that the H{alpha} knots, which are young (age < 10 Myr), are distributed like the gas from which they have recently formedmore » and find a marginal (>97% confidence) discrepancy with a modified gravity scenario given the current data. More interestingly, we demonstrate that there is no inherent limitation that prevents such a test from reaching possible discrimination at the >4{sigma} level with a reasonable investment of observational resources.« less

The ATCA CABB Line Survey on Centaurus A: Properties of the Molecular Gas from the Dust Lanes to the Central Engine

NASA Astrophysics Data System (ADS)

Ott, Juergen; Koribalski, Baerbel; Henkel, Christian; Edwards, Philip; Norris, Ray; Meier, David; Feain, Ilana; Curran, Steve; Martin-Pintado, Jesus; Beelen, Alexandre; Aalto, Susanne; Combes, Francoise; Israel, Frank; Muller, Sebastien; Espada, Daniel; Guelin, Michel; Black, John Harry; V-Trung, Dinh; Impellizzeri, Caterina M. V.; Persson, Carina

2011-10-01

Centaurus A with its host NGC5128 is the most nearby radio galaxy. Its molecular spectrum exhibits three prominent features: a) gas that is located in the outer disk and dust lanes, b) absorption lines that are supposedly close to the central AGN, and c) gas in emission from the nucleus. We propose to perform an extensive line survey toward CenA using the exciting new capabilities of CABB. The broad basebands and narrow zoom bands of CABB are ideal to capture the full breath of the CenA spectral features. Our multi-band line observations will allow us to derive the exact physical conditions of each component as well as the chemistry involved. We will therefore obtain a comprehensive view of the physics imprinted on the molecular spectrum of a radio galaxy and its host, reaching from the central supermassive black hole, through the accretion region and the inner disk to the outer dust lanes.

Polluted White Dwarf (Artist's Concept)

NASA Image and Video Library

2017-11-01

This artist's concept shows an exoplanet and debris disk orbiting a polluted white dwarf. White dwarfs are dim, dense remnants of stars similar to the Sun that have exhausted their nuclear fuel and blown off their outer layers. By "pollution," astronomers mean heavy elements invading the photospheres -- the outer atmospheres -- of these stars. The leading explanation is that exoplanets could push small rocky bodies toward the star, whose powerful gravity would pulverize them into dust. That dust, containing heavy elements from the torn-apart body, would then fall on the star. NASA's Spitzer Space Telescope has been instrumental in expanding the field of polluted white dwarfs orbited by hot, dusty disks. Since launch in 2004, Spitzer has confirmed about 40 of these special stars. Another space telescope, NASA's Wide-field Infrared Survey Explorer (WISE), also detected a handful, bringing the total up to about four dozen known today. Because these objects are so faint, infrared light is crucial to identifying them. https://photojournal.jpl.nasa.gov/catalog/PIA22084

On the Formation of Multiple Concentric Rings and Gaps in Protoplanetary Disks

NASA Astrophysics Data System (ADS)

Bae, Jaehan; Zhu, Zhaohuan; Hartmann, Lee

2017-12-01

As spiral waves driven by a planet in a gaseous disk steepen into a shock, they deposit angular momentum, opening a gap in the disk. This has been well studied using both linear theory and numerical simulations, but so far only for the primary spiral arm: the one directly attached to the planet. Using 2D hydrodynamic simulations, we show that the secondary and tertiary arms driven by a planet can also open gaps as they steepen into shocks. The depths of the secondary/tertiary gaps in surface density grow with time in a low-viscosity disk (α =5× {10}-5), so even low-mass planets (e.g., super-Earth or mini-Neptune-mass) embedded in the disk can open multiple observable gaps, provided that sufficient time has passed. Applying our results to the HL Tau disk, we show that a single 30 Earth-mass planet embedded in the ring at 68.8 au (B5) can reasonably well reproduce the positions of the two major gaps at 13.2 and 32.3 au (D1 and D2), and roughly reproduce two other major gaps at 64.2 and 74.7 au (D5 and D6) seen in the mm continuum. The positions of secondary/tertiary gaps are found to be sensitive to the planetary mass and the disk temperature profile, so with accurate observational measurements of the temperature structure, the positions of multiple gaps can be used to constrain the mass of the planet. We also comment on the gaps seen in the TW Hya and HD 163296 disk.

DETECTION AND CHARACTERIZATION OF EXTRASOLAR PLANETS THROUGH MEAN-MOTION RESONANCES. I. SIMULATIONS OF HYPOTHETICAL DEBRIS DISKS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tabeshian, Maryam; Wiegert, Paul A., E-mail: mtabeshi@uwo.ca

2016-02-20

The gravitational influence of a planet on a nearby disk provides a powerful tool for detecting and studying extrasolar planetary systems. Here we demonstrate that gaps can be opened in dynamically cold debris disks at the mean-motion resonances of an orbiting planet. The gaps are opened away from the orbit of the planet itself, revealing that not all disk gaps need contain a planetary body. These gaps are large and deep enough to be detectable in resolved disk images for a wide range of reasonable disk-planet parameters, though we are not aware of any such gaps detected to date. Themore » gap shape and size are diagnostic of the planet location, eccentricity and mass, and allow one to infer the existence of unseen planets, as well as many important parameters of both seen and unseen planets in these systems. We present expressions to allow the planetary mass and semimajor axis to be calculated from observed gap width and location.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Quintana, Elisa V.; Lissauer, Jack J., E-mail: elisa.quintana@nasa.gov

Models of planet formation have shown that giant planets have a large impact on the number, masses, and orbits of terrestrial planets that form. In addition, they play an important role in delivering volatiles from material that formed exterior to the snow line (the region in the disk beyond which water ice can condense) to the inner region of the disk where terrestrial planets can maintain liquid water on their surfaces. We present simulations of the late stages of terrestrial planet formation from a disk of protoplanets around a solar-type star and we include a massive planet (from 1 Mmore » {sub ⊕} to 1 M {sub J}) in Jupiter's orbit at ∼5.2 AU in all but one set of simulations. Two initial disk models are examined with the same mass distribution and total initial water content, but with different distributions of water content. We compare the accretion rates and final water mass fraction of the planets that form. Remarkably, all of the planets that formed in our simulations without giant planets were water-rich, showing that giant planet companions are not required to deliver volatiles to terrestrial planets in the habitable zone. In contrast, an outer planet at least several times the mass of Earth may be needed to clear distant regions of debris truncating the epoch of frequent large impacts. Observations of exoplanets from radial velocity surveys suggest that outer Jupiter-like planets may be scarce, therefore, the results presented here suggest that there may be more habitable planets residing in our galaxy than previously thought.« less

Radial Surface Density Profiles of Gas and Dust in the Debris Disk around 49 Ceti

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hughes, A. Meredith; Lieman-Sifry, Jesse; Flaherty, Kevin M.

We present ∼0.″4 resolution images of CO(3–2) and associated continuum emission from the gas-bearing debris disk around the nearby A star 49 Ceti, observed with the Atacama Large Millimeter/Submillimeter Array (ALMA). We analyze the ALMA visibilities in tandem with the broadband spectral energy distribution to measure the radial surface density profiles of dust and gas emission from the system. The dust surface density decreases with radius between ∼100 and 310 au, with a marginally significant enhancement of surface density at a radius of ∼110 au. The SED requires an inner disk of small grains in addition to the outer diskmore » of larger grains resolved by ALMA. The gas disk exhibits a surface density profile that increases with radius, contrary to most previous spatially resolved observations of circumstellar gas disks. While ∼80% of the CO flux is well described by an axisymmetric power-law disk in Keplerian rotation about the central star, residuals at ∼20% of the peak flux exhibit a departure from axisymmetry suggestive of spiral arms or a warp in the gas disk. The radial extent of the gas disk (∼220 au) is smaller than that of the dust disk (∼300 au), consistent with recent observations of other gas-bearing debris disks. While there are so far only three broad debris disks with well characterized radial dust profiles at millimeter wavelengths, 49 Ceti’s disk shows a markedly different structure from two radially resolved gas-poor debris disks, implying that the physical processes generating and sculpting the gas and dust are fundamentally different.« less

The Dynamics of Truncated Black Hole Accretion Disks. I. Viscous Hydrodynamic Case

NASA Astrophysics Data System (ADS)

Hogg, J. Drew; Reynolds, Christopher S.

2017-07-01

Truncated accretion disks are commonly invoked to explain the spectro-temporal variability in accreting black holes in both small systems, I.e., state transitions in galactic black hole binaries (GBHBs), and large systems, I.e., low-luminosity active galactic nuclei (LLAGNs). In the canonical truncated disk model of moderately low accretion rate systems, gas in the inner region of the accretion disk occupies a hot, radiatively inefficient phase, which leads to a geometrically thick disk, while the gas in the outer region occupies a cooler, radiatively efficient phase that resides in the standard geometrically thin disk. Observationally, there is strong empirical evidence to support this phenomenological model, but a detailed understanding of the dynamics of truncated disks is lacking. We present a well-resolved viscous, hydrodynamic simulation that uses an ad hoc cooling prescription to drive a thermal instability and, hence, produce the first sustained truncated accretion disk. With this simulation, we perform a study of the dynamics, angular momentum transport, and energetics of a truncated disk. We find that the time variability introduced by the quasi-periodic transition of gas from efficient cooling to inefficient cooling impacts the evolution of the simulated disk. A consequence of the thermal instability is that an outflow is launched from the hot/cold gas interface, which drives large, sub-Keplerian convective cells into the disk atmosphere. The convective cells introduce a viscous θ - ϕ stress that is less than the generic r - ϕ viscous stress component, but greatly influences the evolution of the disk. In the truncated disk, we find that the bulk of the accreted gas is in the hot phase.

The Dynamics of Truncated Black Hole Accretion Disks. I. Viscous Hydrodynamic Case

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hogg, J. Drew; Reynolds, Christopher S.

Truncated accretion disks are commonly invoked to explain the spectro-temporal variability in accreting black holes in both small systems, i.e., state transitions in galactic black hole binaries (GBHBs), and large systems, i.e., low-luminosity active galactic nuclei (LLAGNs). In the canonical truncated disk model of moderately low accretion rate systems, gas in the inner region of the accretion disk occupies a hot, radiatively inefficient phase, which leads to a geometrically thick disk, while the gas in the outer region occupies a cooler, radiatively efficient phase that resides in the standard geometrically thin disk. Observationally, there is strong empirical evidence to supportmore » this phenomenological model, but a detailed understanding of the dynamics of truncated disks is lacking. We present a well-resolved viscous, hydrodynamic simulation that uses an ad hoc cooling prescription to drive a thermal instability and, hence, produce the first sustained truncated accretion disk. With this simulation, we perform a study of the dynamics, angular momentum transport, and energetics of a truncated disk. We find that the time variability introduced by the quasi-periodic transition of gas from efficient cooling to inefficient cooling impacts the evolution of the simulated disk. A consequence of the thermal instability is that an outflow is launched from the hot/cold gas interface, which drives large, sub-Keplerian convective cells into the disk atmosphere. The convective cells introduce a viscous θ − ϕ stress that is less than the generic r − ϕ viscous stress component, but greatly influences the evolution of the disk. In the truncated disk, we find that the bulk of the accreted gas is in the hot phase.« less

ECCENTRICITY TRAP: TRAPPING OF RESONANTLY INTERACTING PLANETS NEAR THE DISK INNER EDGE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ogihara, Masahiro; Ida, Shigeru; Duncan, Martin J., E-mail: ogihara@geo.titech.ac.j, E-mail: ida@geo.titech.ac.j, E-mail: duncan@astro.queensu.c

2010-10-01

Using orbital integration and analytical arguments, we have found a new mechanism (an 'eccentricity trap') to halt type I migration of planets near the inner edge of a protoplanetary disk. Because asymmetric eccentricity damping due to disk-planet interaction on the innermost planet at the disk edge plays a crucial role in the trap, this mechanism requires continuous eccentricity excitation and hence works for a resonantly interacting convoy of planets. This trap is so strong that the edge torque exerted on the innermost planet can completely halt type I migrations of many outer planets through mutual resonant perturbations. Consequently, the convoymore » stays outside the disk edge, as a whole. We have derived a semi-analytical formula for the condition for the eccentricity trap and predict how many planets are likely to be trapped. We found that several planets or more should be trapped by this mechanism in protoplanetary disks that have cavities. It can be responsible for the formation of non-resonant, multiple, close-in super-Earth systems extending beyond 0.1 AU. Such systems are being revealed by radial velocity observations to be quite common around solar-type stars.« less

The Effect of Varied Initial Conditions on the Evolution of Protoplanetary Disks

NASA Astrophysics Data System (ADS)

Michael, Scott A.; Durisen, R. H.; Boley, A. C.

2006-12-01

We present a series of three-dimensional hydrodynamics simulations of gravitationally unstable protoplanetary disks with globally constant cooling times. The purpose of these simulations is to study the effects of varying the initial surface density profile, equation of state, and cooling time. All non-fragmenting disks exhibit the same phases of evolution described by Mejía et al. (2005) axisymmetric cooling, a burst in a well-defined multi-armed mode, and a transition to an asymptotic behavior in which heating and cooling are roughly balanced over much of the disk. The burst tends to be weaker for initial surface density profiles that fall more steeply with r. Regardless of initial surface density profile, the outer disk redistributes its mass to follow an approximate Σ ∝ r-5/2 power law. Comparison of different equations of state show that, for a given cooling time, a disk with γ = 7/5 is more likely to fragment than one with γ = 5/3. By varying the cooling time with both equations of state, we are able to confirm the tcoolΩ < 8.25 and 5.14 fragmentation criterion for γ = 7/5 and 5/3, respectively, as found by Rice et al. (2005).

The fate of scattered planets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bromley, Benjamin C.; Kenyon, Scott J., E-mail: bromley@physics.utah.edu, E-mail: skenyon@cfa.harvard.edu

2014-12-01

As gas giant planets evolve, they may scatter other planets far from their original orbits to produce hot Jupiters or rogue planets that are not gravitationally bound to any star. Here, we consider planets cast out to large orbital distances on eccentric, bound orbits through a gaseous disk. With simple numerical models, we show that super-Earths can interact with the gas through dynamical friction to settle in the remote outer regions of a planetary system. Outcomes depend on planet mass, the initial scattered orbit, and the evolution of the time-dependent disk. Efficient orbital damping by dynamical friction requires planets atmore » least as massive as the Earth. More massive, longer-lived disks damp eccentricities more efficiently than less massive, short-lived ones. Transition disks with an expanding inner cavity can circularize orbits at larger distances than disks that experience a global (homologous) decay in surface density. Thus, orbits of remote planets may reveal the evolutionary history of their primordial gas disks. A remote planet with an orbital distance ∼100 AU from the Sun is plausible and might explain correlations in the orbital parameters of several distant trans-Neptunian objects.« less

Gas Cavities inside Dust Cavities in Disks Inferred from ALMA Observations

NASA Astrophysics Data System (ADS)

van der Marel, Nienke; van Dishoeck, Ewine F.; Bruderer, Simon; Pinilla, Paola; van Kempen, Tim; Perez, Laura; Isella, Andrea

2016-01-01

Protoplanetary disks with cavities in their dust distribution, also named transitional disks, are expected to be in the middle of active evolution and possibly planet formation. In recent years, millimeter-dust rings observed by ALMA have been suggested to have their origin in dust traps, caused by pressure bumps. One of the ways to generate these is by the presence of planets, which lower the gas density along their orbit and create pressure bumps at the edge. We present spatially resolved ALMA Cycle 0 and Cycle 1 observations of CO and CO isotopologues of several famous transitional disks. Gas is found to be present inside the dust cavities, but at a reduced level compared with the gas surface density profile of the outer disk. The dust and gas emission are quantified using the physical-chemical modeling code DALI. In the majority of these disks we find clear evidence for a drop in gas density of at least a factor of 10 inside the cavity, whereas the dust density drops by at least a factor 1000. The CO isotopologue observations reveal that the gas cavities are significantly smaller than the dust cavities. These gas structures suggest clearing by one or more planetary-mass companions.

Radial decoupling of small and large dust grains in the transitional disk RX J1615.3-3255

NASA Technical Reports Server (NTRS)

Kooistra, Robin; Kamp, Inga; Fukagawa, Misato; Menard, Francois; Momose, Munetake; Tsukagoshi, Takashi; Kudo, Tomoyuki; Kusakabe, Nobuhiko; Hashimoto, Jun; Abe, Lyu;

Radial decoupling of small and large dust grains in the transitional disk RX J1615.3-3255

NASA Astrophysics Data System (ADS)

Kooistra, Robin; Kamp, Inga; Fukagawa, Misato; Ménard, François; Momose, Munetake; Tsukagoshi, Takashi; Kudo, Tomoyuki; Kusakabe, Nobuhiko; Hashimoto, Jun; Abe, Lyu; Brandner, Wolfgang; Brandt, Timothy D.; Carson, Joseph C.; Egner, Sebastian E.; Feldt, Markus; Goto, Miwa; Grady, Carol A.; Guyon, Olivier; Hayano, Yutaka; Hayashi, Masahiko; Hayashi, Saeko S.; Henning, Thomas; Hodapp, Klaus W.; Ishii, Miki; Iye, Masanori; Janson, Markus; Kandori, Ryo; Knapp, Gillian R.; Kuzuhara, Masayuki; Kwon, Jungmi; Matsuo, Taro; McElwain, Michael W.; Miyama, Shoken; Morino, Jun-Ichi; Moro-Martin, Amaya; Nishimura, Tetsuo; Pyo, Tae-Soo; Serabyn, Eugene; Suenaga, Takuya; Suto, Hiroshi; Suzuki, Ryuji; Takahashi, Yasuhiro H.; Takami, Michihiro; Takato, Naruhisa; Terada, Hiroshi; Thalmann, Christian; Tomono, Daigo; Turner, Edwin L.; Watanabe, Makoto; Wisniewski, John; Yamada, Toru; Takami, Hideki; Usuda, Tomonori; Tamura, Motohide; Currie, Thayne; Akiyama, Eiji; Mayama, Satoshi; Follette, Katherine B.; Nakagawa, Takao

2017-01-01

We present H-band (1.6 μm) scattered light observations of the transitional disk RX J1615.3-3255, located in the 1 Myr old Lupus association. From a polarized intensity image, taken with the HiCIAO instrument of the Subaru Telescope, we deduce the position angle and the inclination angle of the disk. The disk is found to extend out to 68 ± 12 AU in scattered light and no clear structure is observed. Our inner working angle of 24 AU does not allow us to detect a central decrease in intensity similar to that seen at 30 AU in the 880 μm continuum observations. We compare the observations with multiple disk models based on the spectral energy distribution (SED) and submm interferometry and find that an inner rim of the outer disk at 30 AU containing small silicate grains produces a polarized intensity signal which is an order of magnitude larger than observed. We show that a model in which the small dust grains extend smoothly into the cavity found for large grains is closer to the actual H-band observations. A comparison of models with different dust size distributions suggests that the dust in the disk might have undergone significant processing compared to the interstellar medium.

Chemical Abundances of Planetary Nebulae in the Substructures of M31. II. The Extended Sample and a Comparison Study with the Outer-disk Group

NASA Astrophysics Data System (ADS)

Fang, Xuan; García-Benito, Rubén; Guerrero, Martín A.; Zhang, Yong; Liu, Xiaowei; Morisset, Christophe; Karakas, Amanda I.; Miller Bertolami, Marcelo M.; Yuan, Haibo; Cabrera-Lavers, Antonio

2018-01-01

We report deep spectroscopy of 10 planetary nebulae (PNe) in the Andromeda Galaxy (M31) using the 10.4 m Gran Telescopio Canarias (GTC). Our targets reside in different regions of M31, including halo streams and the dwarf satellite M32, and kinematically deviate from the extended disk. The temperature-sensitive [O III] λ4363 line is observed in all PNe. For four PNe, the GTC spectra extend beyond 1 μm, enabling the explicit detection of the [S III] λ6312 and λλ9069, 9531 lines and thus determination of the [S III] temperature. Abundance ratios are derived and generally consistent with AGB model predictions. Our PNe probably all evolved from low-mass (<2 M ⊙) stars, as analyzed with the most up-to-date post-AGB evolutionary models, and their main-sequence ages are mostly ∼2–5 Gyr. Compared to the underlying, smooth, metal-poor halo of M31, our targets are uniformly metal rich ([O/H] ≳ ‑0.4), and seem to resemble the younger population in the stream. We thus speculate that our halo PNe formed in the Giant Stream’s progenitor through extended star formation. Alternatively, they might have formed from the same metal-rich gas as did the outer-disk PNe but were displaced into their present locations as a result of galactic interactions. These interpretations are, although speculative, qualitatively in line with the current picture, as inferred from previous wide-field photometric surveys, that M31's halo is the result of complex interactions and merger processes. The behavior of the N/O of the combined sample of the outer-disk and our halo/substructure PNe signifies that hot bottom burning might actually occur at <3 M ⊙ but careful assessment is needed. Based on observations made with the Gran Telescopio Canarias, installed at the Spanish Observatorio del Roque de los Muchachos of Instituto de Astrofísica de Canarias, in the island of La Palma. The observations presented in this paper are associated with GTC programs #GTC66-16A and #GTC25-16B.

Multiwavelength search for protoplanetary disks

NASA Technical Reports Server (NTRS)

Neuhaeuser, Ralph; Schmidt-Kaler, Theodor

1994-01-01

Infrared emission of circumstellar dust was observed for almost one hundred T Tauri stars. This dust is interpreted to be part of a protoplanetary disk orbiting the central star. T Tauri stars are young stellar objects and evolve into solar type stars. Planets are believed to form in these disks. The spectral energy distribution of a disk depends on its temperature profile. Different disk regions emit at different wavelengths. The disk-star boundary layer is hot and emits H(alpha) radiation. Inner disk regions at around 1 AU with a temperature of a few hundred Kelvin can be probed in near infrared wavelength regimes. Outer disk regions at around 100 AU distance from the star are colder and emit far infrared and sub-millimeter radiation. Also, X-ray emission from the stellar surface can reveal information on disk properties. Emission from the stellar surface and the boundary layer may be shielded by circumstellar gas and dust. T Tauri stars with low H(alpha) emission, i.e. no boundary layer, show stronger X-ray emission than classical T Tauri stars, because the inner disk regions of weak emission-line T Tauri stars may be clear of material. In this paper, first ROSAT all sky survey results on the X-ray emission of T Tauri stars and correlations between X-ray luminosity and properties of T Tauri disks are presented. Due to atmospheric absorption, X-ray and most infrared observations cannot be carried out on Earth, but from Earth orbiting satellites (e.g. IRAS, ROSAT, ISO) or from lunar based observatories, which would have special advantages such as a stable environment.

A comparative study of single-temperature and two-temperature accretion flows around black holes

NASA Astrophysics Data System (ADS)

Dihingia, Indu Kalpa; Das, Santabrata; Mandal, Samir

2018-02-01

We study the properties of sub-Keplerian accretion disk around a stationary black hole, considering bremsstrahlung, synchrotron and Comptonization of synchrotron photons as radiative cooling mechanisms active in the disk. We obtain the solutions of two-temperature global accretion flow (TTAF) and compare it with the results obtained from single-temperature (STAF) model. We observe that flow properties, in particular, the radial profile of electron and ion temperatures differ noticeably in the adopted models for flows with identical boundary conditions fixed at the outer edge of the disk. Since the electron temperature is one of the key factors to regulate the radiative processes, we argue that physically motivated description of electron temperature needs to be considered in studying the astrophysical phenomena around black holes.

The Architecture of the LkCa 15 Transitional Disk Revealed by High-contrast Imaging

NASA Technical Reports Server (NTRS)

Thalmann, C.; Mulders, G. D.; Hodapp, K.; Janson, M.; Grady, C. A.; Min, M.; deJuanOvelar, M.; Carson, J.; Brandt, T.; Bonnefoy, M.;

The Architecture of the LkCa 15 Transitional Disk Revealed By High-Contrast Imaging

NASA Technical Reports Server (NTRS)

Thalmann, C.; Mulders, G. D.; Hodapp, K.; Janson, M.; Grady, C.A.; Min, M.; de Juan Ovelar, M.; Carson, J.; Brandt, T.; Bonnefoy, M.;

A Study on the Characteristics of the Structure of Vega's Debris Disk

NASA Astrophysics Data System (ADS)

Lu, T.; Ji, J. H.

2013-03-01

Clumpy structure in the Vega's debris disk has been previously reported at millimeter wavelengths and attributed to the concentrations of dust grains trapped in resonances with a potential planet. However, current imaging at multi-wavelengths with higher sensitivity is against the former observed structure. The disk is now revealed to have a smooth structure. A planet orbiting Vega could not be neglected,but the present-day observations may place a severe constraint on the orbital parameters for the potential planet. Herein, we utilize modified MERCURY codes to numerically simulate Vega system, consisting of debris disk and a planet. In our simulations, the initial inner and outer boundaries of the debris disk are assumed to be 80~AU and 120~AU, respectively. The radius of dust grains distributes in the range from 10 μm to 100 μm, in nearly coplanar orbits. From the outcomes, we show that the evolution of debris disk is consistent with recent observations, if there is no planet orbiting Vega. However, if Vega owns a planet with a high eccentricity (e.g., e=0.6), the planetary semi-major axis cannot be larger than 60~AU, otherwise, the structure of debris disk will congregate due to the existence of the postulated planet. The 2:1 mean motion resonances may play a significant role in sculpting the debris disk.

The detection and study of pre-planetary disks

NASA Technical Reports Server (NTRS)

Sargent, A. I.; Beckwith, S. V. W.

1994-01-01

A variety of evidence suggests that at least 50% of low-mass stars are surrounded by disks of the gas and dust similar to the nebula that surrounded the Sun before the formation of the planets. The properties of these disks may bear strongly on the way in which planetary systems form and evolve. As a result of major instrumental developments over the last decade, it is now possible to detect and study the circumstellar environments of the very young, solar-type stars in some detail, and to compare the results with theoretical models of the early solar system. For example, millimeter-wave aperture synthesis imaging provides a direct means of studying in detail the morphology, temperature and density distributions, velocity field and chemical constituents in the outer disks, while high resolution, near infrared spectroscopy probes the inner, warmer parts; the emergence of gaps in the disks, possibly reflecting the formation of planets, may be reflected in the variation of their dust continuum emission with wavelength. We review progress to date and discuss likely directions for future research.

An inner warp in the DoAr 44 T Tauri transition disk

NASA Astrophysics Data System (ADS)

Casassus, Simon; Avenhaus, Henning; Pérez, Sebastián; Navarro, Víctor; Cárcamo, Miguel; Marino, Sebastián; Cieza, Lucas; Quanz, Sascha P.; Alarcón, Felipe; Zurlo, Alice; Osses, Axel; Rannou, Fernando R.; Román, Pablo E.; Barraza, Marcelo

2018-04-01

Optical/IR images of transition disks (TDs) have revealed deep intensity decrements in the rings of HAeBes HD 142527 and HD 100453, that can be interpreted as shadowing from sharply tilted inner disks, such that the outer disks are directly exposed to stellar light. Here we report similar dips in SPHERE+IRDIS differential polarized imaging (DPI) of TTauri DoAr 44. With a fairly axially symmetric ring in the sub mm radio continuum, DoAr 44 is likely also a warped system. We constrain the warp geometry by comparing radiative transfer predictions with the DPI data in H band (Qϕ(H)) and with a re-processing of archival 336 GHz ALMA observations. The observed DPI shadows have coincident radio counterparts, but the intensity drops are much deeper in Qϕ(H) (˜88%), compared to the shallow drops at 336 GHz (˜24%). Radiative transfer predictions with an inner disk tilt of ˜30 ± 5 deg approximately account for the observations. ALMA long-baseline observations should allow the observation of the warped gas kinematics inside the cavity of DoAr 44.

DUST DYNAMICS IN PROTOPLANETARY DISK WINDS DRIVEN BY MAGNETOROTATIONAL TURBULENCE: A MECHANISM FOR FLOATING DUST GRAINS WITH CHARACTERISTIC SIZES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miyake, Tomoya; Suzuki, Takeru K.; Inutsuka, Shu-ichiro, E-mail: miyake.tomoya@e.mbox.nagoya-u.ac.jp, E-mail: stakeru@nagoya-u.jp

We investigate the dynamics of dust grains of various sizes in protoplanetary disk winds driven by magnetorotational turbulence, by simulating the time evolution of the dust grain distribution in the vertical direction. Small dust grains, which are well-coupled to the gas, are dragged upward with the upflowing gas, while large grains remain near the midplane of a disk. Intermediate-size grains float near the sonic point of the disk wind located at several scale heights from the midplane, where the grains are loosely coupled to the background gas. For the minimum mass solar nebula at 1 au, dust grains with sizemore » of 25–45 μm float around 4 scale heights from the midplane. Considering the dependence on the distance from the central star, smaller-size grains remain only in an outer region of the disk, while larger-size grains are distributed in a broader region. We also discuss the implications of our result for observations of dusty material around young stellar objects.« less

A LIKELY CLOSE-IN LOW-MASS STELLAR COMPANION TO THE TRANSITIONAL DISK STAR HD 142527

DOE Office of Scientific and Technical Information (OSTI.GOV)

Biller, Beth; Benisty, Myriam; Chauvin, Gael

2012-07-10

With the uniquely high contrast within 0.''1 ({Delta}mag(L') = 5-6.5 mag) available using Sparse Aperture Masking with NACO at Very Large Telescope, we detected asymmetry in the flux from the Herbig Fe star HD 142527 with a barycenter emission situated at a projected separation of 88 {+-} 5 mas (12.8 {+-} 1.5 AU at 145 pc) and flux ratios in H, K, and L' of 0.016 {+-} 0.007, 0.012 {+-} 0.008, and 0.0086 {+-} 0.0011, respectively (3{sigma} errors), relative to the primary star and disk. After extensive closure-phase modeling, we interpret this detection as a close-in, low-mass stellar companion withmore » an estimated mass of {approx}0.1-0.4 M{sub Sun }. HD 142527 has a complex disk structure, with an inner gap imaged in both the near and mid-IR as well as a spiral feature in the outer disk in the near-IR. This newly detected low-mass stellar companion may provide a critical explanation of the observed disk structure.« less

30 CFR 291.1 - What is MMS's authority to collect information?

Code of Federal Regulations, 2011 CFR

2011-07-01

..., DEPARTMENT OF THE INTERIOR APPEALS OPEN AND NONDISCRIMINATORY ACCESS TO OIL AND GAS PIPELINES UNDER THE OUTER... been denied open and nondiscriminatory access to Outer Continental Shelf (OCS) pipelines as sections of...

Hubble Space Telescope Scattered-light Imaging and Modeling of the Edge-on Protoplanetary Disk ESO-Hα 569

NASA Astrophysics Data System (ADS)

Wolff, Schuyler G.; Perrin, Marshall D.; Stapelfeldt, Karl; Duchêne, Gaspard; Ménard, Francois; Padgett, Deborah; Pinte, Christophe; Pueyo, Laurent; Fischer, William J.

2017-12-01

We present new Hubble Space Telescope (HST) Advanced Camera for Surveys observations and detailed models for a recently discovered edge-on protoplanetary disk around ESO-Hα 569 (a low-mass T Tauri star in the Cha I star-forming region). Using radiative transfer models, we probe the distribution of the grains and overall shape of the disk (inclination, scale height, dust mass, flaring exponent, and surface/volume density exponent) by model fitting to multiwavelength (F606W and F814W) HST observations together with a literature-compiled spectral energy distribution. A new tool set was developed for finding optimal fits of MCFOST radiative transfer models using the MCMC code emcee to efficiently explore the high-dimensional parameter space. It is able to self-consistently and simultaneously fit a wide variety of observables in order to place constraints on the physical properties of a given disk, while also rigorously assessing the uncertainties in those derived properties. We confirm that ESO-Hα 569 is an optically thick nearly edge-on protoplanetary disk. The shape of the disk is well-described by a flared disk model with an exponentially tapered outer edge, consistent with models previously advocated on theoretical grounds and supported by millimeter interferometry. The scattered-light images and spectral energy distribution are best fit by an unusually high total disk mass (gas+dust assuming a ratio of 100:1) with a disk-to-star mass ratio of 0.16.

Galactic Warps in Triaxial Halos

NASA Astrophysics Data System (ADS)

Jeon, Myoungwon; Kim, Sungsoo S.; Ann, Hong Bae

2009-05-01

We study the behavior of galactic disks in triaxial halos both numerically and analytically to see if warps can be excited and sustained in triaxial potentials. We consider the following two scenarios: (1) galactic disks that are initially tilted relative to the equatorial plane of the halo (for a pedagogical purpose), and (2) tilted infall of dark matter relative to the equatorial plane of the disk and the halo. With numerical simulations of 100,000 disk particles in a fixed halo potential, we find that in triaxial halos, warps can be excited and sustained just as in spherical or axisymmetric halos but they show some oscillatory behavior and even can be transformed to a polar-ring system if the halo has a prolate-like triaxiality. The nonaxisymmetric component of the halo causes the disk to nutate, and the differential nutation between the inner and outer parts of the disk generally makes the magnitude of the warp slightly diminish and fluctuate. We also find that warps are relatively weaker in oblate and oblate-like triaxial halos, and since these halos are the halo configurations of disk galaxies inferred by cosmological simulations, our results are consistent with the fact that most of the observed warps are quite weak. We derive approximate formulae for the torques exerted on the disk by the triaxial halo and the dark matter torus, and with these formulae we successfully describe the behavior of the disks in our simulations. The techniques used in deriving these formulae could be applied for realistic halos with more complex structures.

The Large-scale Magnetic Fields of Thin Accretion Disks

NASA Astrophysics Data System (ADS)

Cao, Xinwu; Spruit, Hendrik C.

2013-03-01

Large-scale magnetic field threading an accretion disk is a key ingredient in the jet formation model. The most attractive scenario for the origin of such a large-scale field is the advection of the field by the gas in the accretion disk from the interstellar medium or a companion star. However, it is realized that outward diffusion of the accreted field is fast compared with the inward accretion velocity in a geometrically thin accretion disk if the value of the Prandtl number P m is around unity. In this work, we revisit this problem considering the angular momentum of the disk to be removed predominantly by the magnetically driven outflows. The radial velocity of the disk is significantly increased due to the presence of the outflows. Using a simplified model for the vertical disk structure, we find that even moderately weak fields can cause sufficient angular momentum loss via a magnetic wind to balance outward diffusion. There are two equilibrium points, one at low field strengths corresponding to a plasma-beta at the midplane of order several hundred, and one for strong accreted fields, β ~ 1. We surmise that the first is relevant for the accretion of weak, possibly external, fields through the outer parts of the disk, while the latter one could explain the tendency, observed in full three-dimensional numerical simulations, of strong flux bundles at the centers of disk to stay confined in spite of strong magnetororational instability turbulence surrounding them.

Metallicity Distribution of Disk Stars and the Formation History of the Milky Way

NASA Astrophysics Data System (ADS)

Toyouchi, Daisuke; Chiba, Masashi

2018-03-01

We investigate the formation history of the stellar disk component in the Milky Way (MW) based on our new chemical evolution model. Our model considers several fundamental baryonic processes, including gas infall, reaccretion of outflowing gas, and radial migration of disk stars. Each of these baryonic processes in the disk evolution is characterized by model parameters that are determined by fitting to various observational data of the stellar disk in the MW, including the radial dependence of the metallicity distribution function (MDF) of the disk stars, which has recently been derived in the APOGEE survey. We succeeded to obtain the best set of model parameters that well reproduces the observed radial dependences of the mean, standard deviation, skewness, and kurtosis of the MDFs for the disk stars. We analyze the basic properties of our model results in detail to gain new insights into the important baryonic processes in the formation history of the MW. One of the remarkable findings is that outflowing gas, containing many heavy elements, preferentially reaccretes onto the outer disk parts, and this recycling process of metal-enriched gas is a key ingredient for reproducing the observed narrower MDFs at larger radii. Moreover, important implications for the radial dependence of gas infall and the influence of radial migration on the MDFs are also inferred from our model calculation. Thus, the MDF of disk stars is a useful clue for studying the formation history of the MW.

Giant Planet Formation by Disk Instability: A Comparison Simulation with an Improved Radiative Scheme

NASA Astrophysics Data System (ADS)

Cai, Kai; Pickett, Megan K.; Durisen, Richard H.; Milne, Anne M.

2010-06-01

There has been disagreement about whether cooling in protoplanetary disks can be sufficiently fast to induce the formation of gas giant protoplanets via gravitational instabilities. Simulations by our own group and others indicate that this method of planet formation does not work for disks around young, low-mass stars inside several tens of AU, while simulations by other groups show fragmentation into protoplanetary clumps in this region. To allow direct comparison in hopes of isolating the cause of the differences, we here present a high-resolution three-dimensional hydrodynamics simulation of a protoplanetary disk, where the disk model, initial perturbation, and simulation conditions are essentially identical to those used in a recent set of simulations by Boss in 2007, hereafter B07. As in earlier papers by the same author, B07 purports to show that cooling is fast enough to produce protoplanetary clumps. Here, we evolve the same B07 disk using an improved version of one of our own radiative schemes and find that the disk does not fragment in our code but instead quickly settles into a state with only low amplitude nonaxisymmetric structure, which persists for at least several outer disk rotations. We see no rapid radiative or convective cooling. We conclude that the differences in results are due to different treatments of regions at and above the disk photosphere, and we explain at least one way in which the scheme in B07 may lead to artificially fast cooling.

Disk Masses around Solar-mass Stars are Underestimated by CO Observations

NASA Astrophysics Data System (ADS)

Yu, Mo; Evans, Neal J., II; Dodson-Robinson, Sarah E.; Willacy, Karen; Turner, Neal J.

2017-05-01

Gas in protostellar disks provides the raw material for giant planet formation and controls the dynamics of the planetesimal-building dust grains. Accurate gas mass measurements help map the observed properties of planet-forming disks onto the formation environments of known exoplanets. Rare isotopologues of carbon monoxide (CO) have been used as gas mass tracers for disks in the Lupus star-forming region, with an assumed interstellar CO/H2 abundance ratio. Unfortunately, observations of T-Tauri disks show that CO abundance is not interstellar, a finding reproduced by models that show CO abundance decreasing both with distance from the star and as a function of time. Here, we present radiative transfer simulations that assess the accuracy of CO-based disk mass measurements. We find that the combination of CO chemical depletion in the outer disk and optically thick emission from the inner disk leads observers to underestimate gas mass by more than an order of magnitude if they use the standard assumptions of interstellar CO/H2 ratio and optically thin emission. Furthermore, CO abundance changes on million-year timescales, introducing an age/mass degeneracy into observations. To reach a factor of a few accuracy for CO-based disk mass measurements, we suggest that observers and modelers adopt the following strategies: (1) select low-J transitions; (2) observe multiple CO isotopologues and use either intensity ratios or normalized line profiles to diagnose CO chemical depletion; and (3) use spatially resolved observations to measure the CO-abundance distribution.

Rotating flexible drag mill

DOEpatents

Pepper, W.B.

1984-05-09

A rotating parachute for decelerating objects travelling through atmosphere at subsonic or supersonic deployment speeds includes a circular canopy having a plurality of circumferentially arranged flexible panels projecting radially from a solid central disk. A slot extends radially between adjacent panels to the outer periphery of the canopy. Upon deployment, the solid disk diverts air radially to rapidly inflate the panels into a position of maximum diameter. Air impinging on the panels adjacent the panel slots rotates the parachute during its descent. Centrifugal force flattens the canopy into a constant maximum diameter during terminal descent for maximum drag and deceleration.

Advanced Forensic Format: an Open Extensible Format for Disk Imaging

NASA Astrophysics Data System (ADS)

Garfinkel, Simson; Malan, David; Dubec, Karl-Alexander; Stevens, Christopher; Pham, Cecile

This paper describes the Advanced Forensic Format (AFF), which is designed as an alternative to current proprietary disk image formats. AFF offers two significant benefits. First, it is more flexible because it allows extensive metadata to be stored with images. Second, AFF images consume less disk space than images in other formats (e.g., EnCase images). This paper also describes the Advanced Disk Imager, a new program for acquiring disk images that compares favorably with existing alternatives.

75 FR 26681 - Airworthiness Directives; Turbomeca S.A. Arriel 2B and 2B1 Turboshaft Engines

Federal Register 2010, 2011, 2012, 2013, 2014

2010-05-12

... displacement of the HP blade relative to the disk in case of blade lock rupture or opening, therefore... repetitive borescope inspection of the engine for rearward displacement of the high-pressure turbine (HP... axial displacement of the HP blade relative to the disk in case of blade lock rupture or opening...

75 FR 59065 - Airworthiness Directives; Turboméca S.A. Arriel 2B and 2B1 Turboshaft Engines

Federal Register 2010, 2011, 2012, 2013, 2014

2010-09-27

... displacement of the HP blade relative to the disk in case of blade lock rupture or opening, therefore... limit axial displacement of the HP blade relative to the disk in case of blade lock rupture or opening... and the HP blade platform. Introduction of these dampers has demonstrated to limit axial displacement...

A GLIMPSE of Star Formation in the Outer Galaxy

NASA Astrophysics Data System (ADS)

Winston, Elaine; Hora, Joseph L.; Tolls, Volker

2018-01-01

The wealth of infrared data provided by recent infrared missions such as Spitzer, Herschel, and WISE has yet to be fully mined in the study of star formation in the outer galaxy. The nearby galaxy and massive star forming regions towards the galactic center have been extensively studied. However the outer regions of the Milky Way, where the metallicity is intermediate in value between the inner galactic disk and the Magellanic Clouds, has not been systematically studied. We are using Spitzer/IRAC’s GLIMPSE (Galactic Legacy Infrared Mid-plane Survey Extraordinaire) observations of the galactic plane at 3.6, 4.5, 5.8, and 8.0 microns to identify young stellar objects (YSOs) via their disk emission in the mid-infrared. A tiered clustering analysis is then performed: preliminary large scale clustering is identified across the field using a Density-Based Spatial Clustering of Applications with Noise (DBSCAN) technique. Smaller scale sub clustering within these regions is performed using an implementation of the Minimum Spanning Tree (MST) technique. The YSOs are then compared to known objects in the SIMBAD catalogue and their photometry and cluster membership is augmented using available Herschel and WISE photometry. We compare our results to those in the inner galaxy to determine how dynamical processes and environmental factors affect the star formation efficiency. These results will have applications to the study of star formation in other galaxies, where only global properties can be determined. We will present here the results of our initial investigation into star formation in the outer galaxy using the Spitzer/GLIMPSE observations of the SMOG field.

Dynamics and Origin of the 2:1 Orbital Resonances of the GJ 876 Planets

NASA Astrophysics Data System (ADS)

Lee, Man Hoi; Peale, S. J.

2002-03-01

The discovery by Marcy and coworkers of two planets in 2:1 orbital resonance about the star GJ 876 has been supplemented by a dynamical fit to the data by Laughlin & Chambers, which places the planets in coplanar orbits deep in three resonances at the 2:1 mean-motion commensurability. The selection of this almost singular state by the dynamical fit means that the resonances are almost certainly real, and with the small amplitudes of libration of the resonance variables, indefinitely stable. Several unusual properties of the 2:1 resonances are revealed by the GJ 876 system. The libration of both lowest order mean-motion resonance variables and the secular resonance variable, θ1=λ1- 2λ2+ϖ1, θ2=λ1- 2λ2+ϖ2, and θ3=ϖ1-ϖ2, about 0° (where λ1,2 are the mean longitudes of the inner and outer planet and ϖ1,2 are the longitudes of periapse) differs from the familiar geometry of the Io-Europa pair, where θ2 and θ3 librate about 180°. By considering the condition that ϖ1=ϖ2 for stable simultaneous librations of θ1 and θ2, we show that the GJ 876 geometry results from the large orbital eccentricities ei, whereas the very small eccentricities in the Io-Europa system lead to the latter's geometry. Surprisingly, the GJ 876 configuration, with θ1, θ2, and θ3 all librating, remains stable for e1 up to 0.86 and for amplitude of libration of θ1 approaching 45° with the current eccentricities-further supporting the indefinite stability of the existing system. Any process that drives originally widely separated orbits toward each other could result in capture into the observed resonances at the 2:1 commensurability. We find that forced inward migration of the outer planet of the GJ 876 system results in certain capture into the observed resonances if initially e1<~0.06 and e2<~0.03 and the migration rate |a2/a2|<~3×10- 2(a2/AU)-3/2yr-1. Larger eccentricities lead to likely capture into higher order resonances before the 2:1 commensurability is reached. The planets are sufficiently massive to open gaps in the nebular disk surrounding the young GJ 876 and to clear the disk material between them, and the resulting planet-nebular interaction typically forces the outer planet to migrate inward on the disk viscous timescale, whose inverse is about 3 orders of magnitude less than the above upper bound on |a2/a2| for certain capture. If there is no eccentricity damping, eccentricity growth is rapid with continued migration within the resonance, with ei exceeding the observed values after a further reduction in the semimajor axes ai of only 7%. With eccentricity damping ei/ei=-K|ai/ai|, the eccentricities reach equilibrium values that remain constant for arbitrarily long migration within the resonances. The equilibrium eccentricities are close to the observed eccentricities for K~100 if there is migration and damping of the outer planet only, but for K~10 if there is also migration and damping of the inner planet. This result is independent of the magnitude or functional form of the migration rate ai as long as ei/ei=-K|ai/ai|. Although existing analytic estimates of the effects of planet-nebula interaction are consistent with this form of eccentricity damping for certain disk parameter values, it is as yet unclear that such interaction can produce the large value of K required to obtain the observed eccentricities. The alternative eccentricity damping by tidal dissipation within the star or the planets is completely negligible, so the observed dynamical properties of the GJ 876 system may require an unlikely fine-tuning of the time of resonance capture to be near the end of the nebula lifetime.

WISE Views of Centaurs & Scattered Disk Objects

NASA Technical Reports Server (NTRS)

Bauer, J. M.; Walker, R.; Mainzer, A.; Blauvelt, E.; Masiero, J.; Grav, T.; Cutri, R.; Dailey, J.; Lisse, C. M.; Fernandez, Y. R.;

H I in the Shell Elliptical Galaxy NGC 3656

NASA Astrophysics Data System (ADS)

Balcells, Marc; van Gorkom, J. H.; Sancisi, Renzo; del Burgo, Carlos

2001-10-01

Very Large Array7 neutral hydrogen observations of the shell elliptical galaxy NGC 3656 reveal an edge-on, warped minor-axis gaseous disk (MHI~2×109 Msolar) extending 7 kpc. H I is also found outside the optical image, on two complexes to the northeast and northwest that seem to trace one or two tidal tails, or possibly an outer broken H I disk or ring. These complexes link with the outer edges of the inner disk and appear displaced with respect to the two optical tails in the galaxy. The disk kinematics is strongly lopsided, suggesting recent or ongoing accretion. Integral-field optical fiber spectroscopy at the region of the bright southern shell of NGC 3656 has provided a determination of the stellar velocities of the shell. The shell, at 9 kpc from the center, has traces of H I with velocities bracketing the stellar velocities, providing evidence for a dynamical association of H I and stars at the shell. Within the errors the stars have systemic velocity, suggesting a possible phase-wrapping origin for the shell. We probed a region of 40'×40' (480 kpc×480 kpc)×1160 km s-1 down to an H I mass sensitivity (6 σ) of 3×107 Msolar and detect five dwarf galaxies with H I masses ranging from 2×108 to 2×109 Msolar, all within 180 kpc of NGC 3656 and all within the velocity range (450 km s-1) of the H I of NGC 3656. The dwarfs had been previously cataloged, but none had a known redshift. For the NGC 3656 group to be bound requires a total mass of (3-7.4)×1012 Msolar, yielding a mass-to-light ratio from 125 to 300. The overall H I picture presented by NGC 3656 supports the hypothesis of a disk-disk merger origin or possibly an ongoing process of multiple mergers with nearby dwarfs. Based on observations made with the William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group of Telescopes in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.

Breeding Super-Earths and Birthing Super-puffs in Transitional Disks

NASA Astrophysics Data System (ADS)

Lee, Eve J.; Chiang, Eugene

2016-02-01

The riddle posed by super-Earths (1-4R⊕, 2-20M⊕) is that they are not Jupiters: their core masses are large enough to trigger runaway gas accretion, yet somehow super-Earths accreted atmospheres that weigh only a few percent of their total mass. We show that this puzzle is solved if super-Earths formed late, as the last vestiges of their parent gas disks were about to clear. This scenario would seem to present fine-tuning problems, but we show that there are none. Ambient gas densities can span many (in one case up to 9) orders of magnitude, and super-Earths can still robustly emerge after ˜0.1-1 Myr with percent-by-weight atmospheres. Super-Earth cores are naturally bred in gas-poor environments where gas dynamical friction has weakened sufficiently to allow constituent protocores to gravitationally stir one another and merge. So little gas is present at the time of core assembly that cores hardly migrate by disk torques: formation of super-Earths can be in situ. The basic picture—that close-in super-Earths form in a gas-poor (but not gas-empty) inner disk, fed continuously by gas that bleeds inward from a more massive outer disk—recalls the largely evacuated but still accreting inner cavities of transitional protoplanetary disks. We also address the inverse problem presented by super-puffs: an uncommon class of short-period planets seemingly too voluminous for their small masses (4-10R⊕, 2-6M⊕). Super-puffs most easily acquire their thick atmospheres as dust-free, rapidly cooling worlds outside ˜1 AU where nebular gas is colder, less dense, and therefore less opaque. Unlike super-Earths, which can form in situ, super-puffs probably migrated in to their current orbits; they are expected to form the outer links of mean-motion resonant chains, and to exhibit greater water content. We close by confronting observations and itemizing remaining questions.

Floating nut retention system

NASA Technical Reports Server (NTRS)

Charles, J. F.; Theakston, H. A. (Inventor)

1980-01-01

A floating nut retention system includes a nut with a central aperture. An inner retainer plate has an opening which is fixedly aligned with the nut aperture. An outer retainer member is formed of a base plate having an opening and a surface adjacent to a surface of the inner retainer plate. The outer retainer member includes a securing mechanism for retaining the inner retainer plate adjacent to the outer retainer member. The securing mechanism enables the inner retainer plate to float with respect to the outer retainer number, while simultaneously forming a bearing surface for inner retainer plate.

A 100 au Wide Bipolar Rotating Shell Emanating from the HH 212 Protostellar Disk: A Disk Wind?

NASA Astrophysics Data System (ADS)

Lee, Chin-Fei; Li, Zhi-Yun; Codella, Claudio; Ho, Paul T. P.; Podio, Linda; Hirano, Naomi; Shang, Hsien; Turner, Neal J.; Zhang, Qizhou

2018-03-01

HH 212 is a Class 0 protostellar system found to host a “hamburger”-shaped dusty disk with a rotating disk atmosphere and a collimated SiO jet at a distance of ∼400 pc. Recently, a compact rotating outflow has been detected in SO and SO2 toward the center along the jet axis at ∼52 au (0.″13) resolution. Here we resolve the compact outflow into a small-scale wide-opening rotating outflow shell and a collimated jet, with the observations in the same S-bearing molecules at ∼16 au (0.″04) resolution. The collimated jet is aligned with the SiO jet, tracing the shock interactions in the jet. The wide-opening outflow shell is seen extending out from the inner disk around the SiO jet and has a width of ∼100 au. It is not only expanding away from the center, but also rotating around the jet axis. The specific angular momentum of the outflow shell is ∼40 au km s‑1. Simple modeling of the observed kinematics suggests that the rotating outflow shell can trace either a disk wind or disk material pushed away by an unseen wind from the inner disk or protostar. We also resolve the disk atmosphere in the same S-bearing molecules, confirming the Keplerian rotation there.

Josephson current in ballistic graphene Corbino disk

NASA Astrophysics Data System (ADS)

Abdollahipour, Babak; Mohammadkhani, Ramin; Khalilzadeh, Mina

2018-06-01

We solve Dirac-Bogoliubov-De-Gennes (DBdG) equation in a superconductor-normal graphene-superconductor (SGS) junction with Corbino disk structure to investigate the Josephson current through this junction. We find that the critical current Ic has a nonzero value at Dirac point in which the concentration of the carriers is zero. We show this nonzero critical current depends on the system geometry and it decreases monotonically to zero by decreasing the ratio of the inner to outer radii of the Corbino disk (R1 /R2), while in the limit of R1 /R2 → 1 it scales like a diffusive Corbino disk. The product of the critical current and the normal-state resistance IcRN increases by increasing R1 /R2 and attains the same value for the wide and short rectangular structure at the limit of R1 /R2 → 1 at zero doping. These results reveals the pseudodiffusive behavior of the graphene Corbino Josephson junction similar to the rectangular structure at the zero doping.

First Keck Nulling Observations of a Young Stellar Object: Probing the Circumstellar Environment of the Herbig Ae star MWC 325

NASA Technical Reports Server (NTRS)

Ragland, S.; Ohnaka, K.; Hillenbrand, L.; Ridgway, S. T.; Colavita, M. M.; Akeson, R. L.; Cotton, W.; Danichi, W. C.; Hrynevych, M.; Milan-Gabet, R.;

Global Simulations of the Inner Regions of Protoplanetary Disks with Comprehensive Disk Microphysics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bai, Xue-Ning, E-mail: xbai@cfa.harvard.edu

2017-08-10

The gas dynamics of weakly ionized protoplanetary disks (PPDs) are largely governed by the coupling between gas and magnetic fields, described by three non-ideal magnetohydrodynamical (MHD) effects (Ohmic, Hall, ambipolar). Previous local simulations incorporating these processes have revealed that the inner regions of PPDs are largely laminar and accompanied by wind-driven accretion. We conduct 2D axisymmetric, fully global MHD simulations of these regions (∼1–20 au), taking into account all non-ideal MHD effects, with tabulated diffusion coefficients and approximate treatment of external ionization and heating. With the net vertical field aligned with disk rotation, the Hall-shear instability strongly amplifies horizontal magneticmore » field, making the overall dynamics dependent on initial field configuration. Following disk formation, the disk likely relaxes into an inner zone characterized by asymmetric field configuration across the midplane, which smoothly transitions to a more symmetric outer zone. Angular momentum transport is driven by both MHD winds and laminar Maxwell stress, with both accretion and decretion flows present at different heights, and modestly asymmetric winds from the two disk sides. With anti-aligned field polarity, weakly magnetized disks settle into an asymmetric field configuration with supersonic accretion flow concentrated at one side of the disk surface, and highly asymmetric winds between the two disk sides. In all cases, the wind is magneto-thermal in nature, characterized by a mass loss rate exceeding the accretion rate. More strongly magnetized disks give more symmetric field configuration and flow structures. Deeper far-UV penetration leads to stronger and less stable outflows. Implications for observations and planet formation are also discussed.« less

A Triple Protostar System in L1448 IRS3B Formed via Fragmentation of a Gravitationally Unstable Disk

NASA Astrophysics Data System (ADS)

Tobin, John J.; Kratter, Kaitlin M.; Persson, Magnus; Looney, Leslie; Dunham, Michael; Segura-Cox, Dominique; Li, Zhi-Yun; Chandler, Claire J.; Sadavoy, Sarah; Harris, Robert J.; Melis, Carl; Perez, Laura M.

2017-01-01

Binary and multiple star systems are a frequent outcome of the star formation process; most stars form as part of a binary/multiple protostar system. A possible pathway to the formation of close (< 500 AU) binary/multiple star systems is fragmentation of a massive protostellar disk due to gravitational instability. We observed the triple protostar system L1448 IRS3B with ALMA at 1.3 mm in dust continuum and molecular lines to determine if this triple protostar system, where all companions are separated by < 200 AU, is likely to have formed via disk fragmentation. From the dust continuum emission, we find a massive, 0.39 solar mass disk surrounding the three protostars with spiral structure. The disk is centered on two protostars that are separated by 61 AU and the third protostar is located in the outer disk at 183 AU. The tertiary companion is coincident with a spiral arm, and it is the brightest source of emission in the disk, surrounded by ~0.09 solar masses of disk material. Molecular line observations from 13CO and C18O confirm that the kinematic center of mass is coincident with the two central protostars and that the disk is consistent with being in Keplerian rotation; the combined mass of the two close protostars is ~1 solar mass. We demonstrate that the disk around L1448 IRS3B remains marginally unstable at radii between 150~AU and 320~AU, overlapping with the location of the tertiary protostar. This is consistent with models for a protostellar disk that has recently undergone gravitational instability, spawning the companion stars.

First Detection of Methanol in a Class O Protostellar Disk

NASA Technical Reports Server (NTRS)

Velusamy, T.; Langer, William D.; Goldsmith, Paul F.

2000-01-01

We report the detection of emission from methanol in a compact source coincident with the position of the L1157 infrared source, which we attribute to molecules in the disk surrounding this young, Class O protostellar object. In addition, we identify a spectral feature in the outflow corresponding to an ethanol transition. Using the Caltech Owens Valley Millimeter Array with a synthesized beam size of 2", we detect spatially unresolved methanol in the 2(sub k) - 1(sub k) transitions at 3mm, which is coincident in position with the peak of the continuum emission. The gas phase methanol could be located in the central region (< 100 AU radius) of a flat disk, or in an extended heated surface layer (approx. 200 AU radius) of a flared disk. The fractional abundance of methanol X(CH3OH) is approx. 2 x l0(exp -8) in the flat disk model, and 3 x l0(exp -7) for the flared disk. The fractional abundance is small in the disk as a whole, but considerably larger in the warm portions. This difference indicates that substantial chemical processing probably takes place in the disk via depletion and desorption. The methanol desorbed from the grains in the warm surface layers returns to the icy grain mantles in the cooler interior of the disk, where it is available to become part of the composition of solar system-like bodies, such as comets, formed in the outer circumstellar region. This first millimeter-wavelength detection of a complex organic molecule in a young protostellar disk has implications for disk structure and chemical evolution and for potential use as a temperature probe. The research of TV and WL was conducted at the Jet Propulsion Laboratory, California Institute of Technology with support from the National Aeronautics and Space Administration.

Large thermal protection system panel

NASA Technical Reports Server (NTRS)

Weinberg, David J. (Inventor); Myers, Franklin K. (Inventor); Tran, Tu T. (Inventor)

2003-01-01

A protective panel for a reusable launch vehicle provides enhanced moisture protection, simplified maintenance, and increased temperature resistance. The protective panel includes an outer ceramic matrix composite (CMC) panel, and an insulative bag assembly coupled to the outer CMC panel for isolating the launch vehicle from elevated temperatures and moisture. A standoff attachment system attaches the outer CMC panel and the bag assembly to the primary structure of the launch vehicle. The insulative bag assembly includes a foil bag having a first opening shrink fitted to the outer CMC panel such that the first opening and the outer CMC panel form a water tight seal at temperatures below a desired temperature threshold. Fibrous insulation is contained within the foil bag for protecting the launch vehicle from elevated temperatures. The insulative bag assembly further includes a back panel coupled to a second opening of the foil bag such that the fibrous insulation is encapsulated by the back panel, the foil bag, and the outer CMC panel. The use of a CMC material for the outer panel in conjunction with the insulative bag assembly eliminates the need for waterproofing processes, and ultimately allows for more efficient reentry profiles.

ALMA observations of AGN fuelling. The case of PKS B1718-649

NASA Astrophysics Data System (ADS)

Maccagni, F. M.; Morganti, R.; Oosterloo, T. A.; Oonk, J. B. R.; Emonts, B. H. C.

2018-06-01

We present ALMA observations of the 12CO (2-1) line of the newly born (tradio 102 years) active galactic nucleus (AGN), PKS B1718-649. These observations reveal that the carbon monoxide in the innermost 15 kpc of the galaxy is distributed in a complex warped disk. In the outer parts of this disk, the CO gas follows the rotation of the dust lane and of the stellar body of the galaxy hosting the radio source. In the innermost kiloparsec, the gas abruptly changes orientation and forms a circumnuclear disk (r ≲ 700 pc) with its major axis perpendicular to that of the outer disk. Against the compact radio emission of PKS B1718-649 (r 2 pc), we detect an absorption line at red-shifted velocities with respect to the systemic velocity (Δv = +365 ± 22 km s-1). This absorbing CO gas could trace molecular clouds falling onto the central super-massive black hole. A comparison with the near-infrared H2 1-0 S(1) observations shows that the clouds must be close to the black hole (r ≲ 75 pc). The physical conditions of these clouds are different from the gas at larger radii, and are in good agreement with the predictions for the conditions of the gas when cold chaotic accretion triggers an active galactic nucleus. These observations on the centre of PKS B1718-649 provide one of the best indications that a population of cold clouds is falling towards a radio AGN, likely fuelling its activity. The reduced datacube is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/614/A42

Dual effect of local anesthetics on the function of excitable rod outer segment disk membrane

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mashimo, T.; Abe, K.; Yoshiya, I.

1986-04-01

The effects of local anesthetics and a divalent cation, Ca2+, on the function of rhodopsin were estimated from the measurements of light-induced proton uptake. The light-induced proton uptake by rhodopsin in the rod outer segment disk membrane was enhanced at lower pH (4) but depressed at higher pHs (6 to 8) by the tertiary amine local anesthetics lidocaine, bupivacaine, tetracaine, and dibucaine. The order of local anesthetic-induced depression of the proton uptake followed that of their clinical anesthetic potencies. The depression of the proton uptake versus the concentration of the uncharged form of local anesthetic nearly describes the same curvemore » for small and large dose of added anesthetic. Furthermore, a neutral local anesthetic, benzocaine, depressed the proton uptake at all pHs between 4 and 7. These results indicate that the depression of the proton uptake is due to the effect of only the uncharged form. It is hypothesized that the uncharged form of local anesthetics interacts hydrophobically with the rhodopsin in the disk membrane. The dual effect of local anesthetics on the proton uptake, on the other hand, suggests that the activation of the function of rhodopsin may be caused by the charged form. There was no significant change in the light-induced proton uptake by rhodopsin when 1 mM of Ca2+ was introduced into the disk membrane at varying pHs in the absence or presence of local anesthetics. This fact indicates that Ca2+ ion does not influence the diprotonating process of metarhodopsin; neither does it interfere with the local anesthetic-induced changes in the rhodopsin molecule.« less

Analytic Expressions for the Inner-rim Structure of Passively Heated Protoplanetary Disks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ueda, Takahiro; Okuzumi, Satoshi; Flock, Mario, E-mail: t_ueda@geo.titech.ac.jp

We analytically derive the expressions for the structure of the inner region of protoplanetary disks based on the results from the recent hydrodynamical simulations. The inner part of a disk can be divided into four regions: a dust-free region with a gas temperature in the optically thin limit, an optically thin dust halo, an optically thick condensation front, and the classical, optically thick region, in order from the innermost to the outermost. We derive the dust-to-gas mass ratio profile in the dust halo using the fact that partial dust condensation regulates the temperature relative to the dust evaporation temperature. Beyondmore » the dust halo, there is an optically thick condensation front where all the available silicate gas condenses out. The curvature of the condensation surface is determined by the condition that the surface temperature must be nearly equal to the characteristic temperature ∼1200 K. We derive the midplane temperature in the outer two regions using the two-layer approximation, with the additional heating by the condensation front for the outermost region. As a result, the overall temperature profile is step-like, with steep gradients at the borders between the outer three regions. The borders might act as planet traps where the inward migration of planets due to gravitational interaction with the gas disk stops. The temperature at the border between the two outermost regions coincides with the temperature needed to activate magnetorotational instability, suggesting that the inner edge of the dead zone must lie at this border. The radius of the dead zone inner edge predicted from our solution is ∼2–3 times larger than that expected from the classical optically thick temperature.« less

Analytic Expressions for the Inner-rim Structure of Passively Heated Protoplanetary Disks

NASA Astrophysics Data System (ADS)

Ueda, Takahiro; Okuzumi, Satoshi; Flock, Mario

2017-07-01

We analytically derive the expressions for the structure of the inner region of protoplanetary disks based on the results from the recent hydrodynamical simulations. The inner part of a disk can be divided into four regions: a dust-free region with a gas temperature in the optically thin limit, an optically thin dust halo, an optically thick condensation front, and the classical, optically thick region, in order from the innermost to the outermost. We derive the dust-to-gas mass ratio profile in the dust halo using the fact that partial dust condensation regulates the temperature relative to the dust evaporation temperature. Beyond the dust halo, there is an optically thick condensation front where all the available silicate gas condenses out. The curvature of the condensation surface is determined by the condition that the surface temperature must be nearly equal to the characteristic temperature ˜1200 K. We derive the midplane temperature in the outer two regions using the two-layer approximation, with the additional heating by the condensation front for the outermost region. As a result, the overall temperature profile is step-like, with steep gradients at the borders between the outer three regions. The borders might act as planet traps where the inward migration of planets due to gravitational interaction with the gas disk stops. The temperature at the border between the two outermost regions coincides with the temperature needed to activate magnetorotational instability, suggesting that the inner edge of the dead zone must lie at this border. The radius of the dead zone inner edge predicted from our solution is ˜2-3 times larger than that expected from the classical optically thick temperature.

DETERMINATION OF CENTRAL ENGINE POSITION AND ACCRETION DISK STRUCTURE IN NGC 4261 BY CORE SHIFT MEASUREMENTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haga, Takafumi; Doi, Akihiro; Murata, Yasuhiro

2015-07-01

We report multifrequency phase-referenced observations of the nearby radio galaxy NGC 4261, which has prominent two-sided jets, using the Very Long Baseline Array at 1.4–43 GHz. We measured radio core positions showing observing frequency dependences (known as “core shift”) in both approaching jets and counterjets. The limit of the core position as the frequency approaches infinity, which suggests a jet base, is separated by 82 ± 16 μas upstream in projection, corresponding to (310 ± 60)R{sub s} (R{sub s}: Schwarzschild radius) as a deprojected distance, from the 43 GHz core in the approaching jet. In addition, the innermost component atmore » the counterjet side appeared to approach the same position at infinity of the frequency, indicating that cores on both sides are approaching the same position, suggesting a spatial coincidence with the central engine. Applying a phase-referencing technique, we also obtained spectral index maps, which indicate that emission from the counterjet is affected by free–free absorption (FFA). The result of the core shift profile on the counterjet also requires FFA because the core positions at 5–15 GHz cannot be explained by a simple core shift model based on synchrotron self-absorption (SSA). Our result is apparently consistent with the SSA core shift with an additional disk-like absorber over the counterjet side. Core shift and opacity profiles at the counterjet side suggest a two-component accretion: a radiatively inefficient accretion flow at the inner region and a truncated thin disk in the outer region. We proposed a possible solution about density and temperature profiles in the outer disk on the basis of the radio observation.« less

SKARPS: The Search for Kuiper Belts around Radial-Velocity Planet Stars

NASA Technical Reports Server (NTRS)

Bryden, Geoffrey; Marshall, Jonathan; Stapelfeldt, Karl; Su, Kate; Wyatt, Mark

2011-01-01

The Search for Kuiper belts Around Radial-velocity Planet Stars - SKARPS -is a Herschel survey of solar-type stars known to have orbiting planets. When complete, the 100-star SKARPS sample will be large enough for a meaningful statistical comparison against stars not known to have planets. (This control sample has already been observed by Herschel's DUst around NEarby Stars - DUNES - key program). Initial results include previously known disks that are resolved for the first time and newly discovered disks that are fainter and colder than those typically detected by Spitzer. So far, with only half of the sample in hand, there is no measured correlation between inner RV planets and cold outer debris. While this is consistent with the results from Spitzer, it is in contrast with the relationship suggested by the prominent debris disks in imaged-planet systems.

A high-speed, large-capacity, 'jukebox' optical disk system

NASA Technical Reports Server (NTRS)

Ammon, G. J.; Calabria, J. A.; Thomas, D. T.

1985-01-01

Two optical disk 'jukebox' mass storage systems which provide access to any data in a store of 10 to the 13th bits (1250G bytes) within six seconds have been developed. The optical disk jukebox system is divided into two units, including a hardware/software controller and a disk drive. The controller provides flexibility and adaptability, through a ROM-based microcode-driven data processor and a ROM-based software-driven control processor. The cartridge storage module contains 125 optical disks housed in protective cartridges. Attention is given to a conceptual view of the disk drive unit, the NASA optical disk system, the NASA database management system configuration, the NASA optical disk system interface, and an open systems interconnect reference model.

Smearing of mass accretion rate variation by viscous processes in accretion disks in compact binary systems

NASA Astrophysics Data System (ADS)

Ghosh, A.; Chakrabarti, Sandip K.

2016-09-01

Variation of mass supply rate from the companion can be smeared out by viscous processes inside an accretion disk. Hence, by the time the flow reaches the inner edge, the variation in X-rays need not reflect the true variation of the mass supply rate at the outer edge. However, if the viscosity fluctuates around a mean value, one would expect the viscous time scale t_{{visc}} also to spread around a mean value. In high mass X-ray binaries, which are thought to be primarily wind-fed, the size of the viscous Keplerian disk is smaller and thus such a spread could be lower as compared to the low mass X-ray binaries which are primarily fed by Roche lobe overflow. If there is an increasing or decreasing trend in viscosity, the interval between enhanced emission would be modified systematically. In the absence of a detailed knowledge about the variation of mass supply rates at the outer edge, we study ideal circumstances where modulation must take place exactly in orbital time scales, such as when there is an ellipticity in the orbit. We study a few compact binaries using long term All Sky monitor (ASM) data (1.5-12 keV) of Rossi X-ray Timing Explorer (RXTE) and all sky survey data (15-50 keV) of Swift satellites by different methods to look for such smearing effects and to infer what these results can tell us about the viscous processes inside the respective disks. We employ three different methods to seek imprints of periodicity on the X-ray variation and found that in all the cases, the location of the peak in the power density spectra is consistent with the orbital frequencies. Interestingly, in high mass X-ray binaries the peaks are sharp with high rms values, consistent with a small Keplerian disk in a wind fed system. However, in low mass X-ray binaries with larger Keplerian disk component, the peaks are spreaded out with much lower rms values. X-ray reflections, or superhump phenomena which may also cause such X-ray modulations would not be affected by the size of the Keplerian disk component. Our result thus confirms different sizes of Keplerian disks in these two important classes of binaries. If the orbital periods of any binary system is not known, they may be obtained with reasonable accuracy for HMXBs and with lesser accuracy for LMXBs by our method.

Mapping a stellar disk into a boxy bulge: The outside-in part of the Milky Way bulge formation

NASA Astrophysics Data System (ADS)

Di Matteo, P.; Haywood, M.; Gómez, A.; van Damme, L.; Combes, F.; Hallé, A.; Semelin, B.; Lehnert, M. D.; Katz, D.

2014-07-01

By means of idealized, dissipationless N-body simulations that follow the formation and subsequent buckling of a stellar bar, we study the characteristics of boxy/peanut-shaped bulges and compare them with the properties of the stellar populations in the Milky Way (MW) bulge. The main results of our modeling, valid for the general family of boxy/peanut shaped bulges, are the following: (i) Because of the spatial redistribution in the disk initiated at the epoch of bar formation, stars from the innermost regions to the outer Lindblad resonance (OLR) of the stellar bar are mapped into a boxy bulge. (ii) The contribution of stars to the local bulge density depends on their birth radius: stars born in the innermost disk tend to dominate the innermost regions of the boxy bulge, while stars originating closer to the OLR are preferably found in the outer regions of the boxy/peanut structure. (iii) Stellar birth radii are imprinted in the bulge kinematics: the larger the birth radii of stars ending up in the bulge, the greater their rotational support and the higher their line-of-sight velocity dispersions (but note that this last trend depends on the bar viewing angle). (iv) The higher the classical bulge-over-disk ratio, the larger its fractional contribution of stars at large vertical distance from the galaxy midplane. Comparing these results with the properties of the stellar populations of the MW bulge recently revealed by the ARGOS survey, we conclude that (I) the two most metal-rich populations of the MW bulge, labeled A and B in the ARGOS survey, originate in the disk, with the population of A having formed on average closer to the Galaxy center than the population of component B; (II) a massive (B/D ~ 0.25) classical spheroid can be excluded for the MW, thus confirming previous findings that the MW bulge is composed of populations that mostly have a disk origin. On the basis of their chemical and kinematic characteristics, the results of our modeling suggest that the populations A, B, and C, as defined by the ARGOS survey, can be associated, respectively, with the inner thin disk, to the young thick and to the old thick disk, following the nomenclature that we recently suggested for stars in the solar neighborhood. Appendix A is available in electronic form at http://www.aanda.org

Dancing Twins: Stellar Hierarchies That Formed Sequentially?

NASA Astrophysics Data System (ADS)

Tokovinin, Andrei

2018-04-01

This paper draws attention to the class of resolved triple stars with moderate ratios of inner and outer periods (possibly in a mean motion resonance) and nearly circular, mutually aligned orbits. Moreover, stars in the inner pair are twins with almost identical masses, while the mass sum of the inner pair is comparable to the mass of the outer component. Such systems could be formed either sequentially (inside-out) by disk fragmentation with subsequent accretion and migration, or by a cascade hierarchical fragmentation of a rotating cloud. Orbits of the outer and inner subsystems are computed or updated in four such hierarchies: LHS 1070 (GJ 2005, periods 77.6 and 17.25 years), HIP 9497 (80 and 14.4 years), HIP 25240 (1200 and 47.0 years), and HIP 78842 (131 and 10.5 years).

Two chemically similar stellar overdensities on opposite sides of the plane of the Galactic disk

DOE PAGES

Bergemann, Maria; Sesar, Branimir; Cohen, Judith G.; ...

2018-02-26

Our Galaxy is thought to have undergone an active evolutionary history dominated by star formation, the accretion of cold gas, and, in particular, mergers up to 10 gigayear ago. The stellar halo reveals rich fossil evidence of these interactions in the form of stellar streams, substructures, and chemically distinct stellar components. The impact of dwarf galaxy mergers on the content and morphology of the Galactic disk is still being explored. Recent studies have identified kinematically distinct stellar substructures and moving groups, which may have extragalactic origin. However, there is mounting evidence that stellar overdensities at the outer disk/halo interface couldmore » have been caused by the interaction of a dwarf galaxy with the disk. Here we report detailed spectroscopic analysis of 14 stars drawn from two stellar overdensities, each lying about 5 kiloparsecs above and below the Galactic plane - locations suggestive of association with the stellar halo. However, we find that the chemical compositions of these stars are almost identical, both within and between these groups, and closely match the abundance patterns of the Milky Way disk stars. This study hence provides compelling evidence that these stars originate from the disk and the overdensities they are part of were created by tidal interactions of the disk with passing or merging dwarf galaxies.« less

Isotopic evidence for primordial molecular cloud material in metal-rich carbonaceous chondrites.

PubMed

Van Kooten, Elishevah M M E; Wielandt, Daniel; Schiller, Martin; Nagashima, Kazuhide; Thomen, Aurélien; Larsen, Kirsten K; Olsen, Mia B; Nordlund, Åke; Krot, Alexander N; Bizzarro, Martin

2016-02-23

The short-lived (26)Al radionuclide is thought to have been admixed into the initially (26)Al-poor protosolar molecular cloud before or contemporaneously with its collapse. Bulk inner Solar System reservoirs record positively correlated variability in mass-independent (54)Cr and (26)Mg*, the decay product of (26)Al. This correlation is interpreted as reflecting progressive thermal processing of in-falling (26)Al-rich molecular cloud material in the inner Solar System. The thermally unprocessed molecular cloud matter reflecting the nucleosynthetic makeup of the molecular cloud before the last addition of stellar-derived (26)Al has not been identified yet but may be preserved in planetesimals that accreted in the outer Solar System. We show that metal-rich carbonaceous chondrites and their components have a unique isotopic signature extending from an inner Solar System composition toward a (26)Mg*-depleted and (54)Cr-enriched component. This composition is consistent with that expected for thermally unprocessed primordial molecular cloud material before its pollution by stellar-derived (26)Al. The (26)Mg* and (54)Cr compositions of bulk metal-rich chondrites require significant amounts (25-50%) of primordial molecular cloud matter in their precursor material. Given that such high fractions of primordial molecular cloud material are expected to survive only in the outer Solar System, we infer that, similarly to cometary bodies, metal-rich carbonaceous chondrites are samples of planetesimals that accreted beyond the orbits of the gas giants. The lack of evidence for this material in other chondrite groups requires isolation from the outer Solar System, possibly by the opening of disk gaps from the early formation of gas giants.

Isotopic evidence for primordial molecular cloud material in metal-rich carbonaceous chondrites

PubMed Central

Van Kooten, Elishevah M. M. E.; Wielandt, Daniel; Schiller, Martin; Nagashima, Kazuhide; Thomen, Aurélien; Olsen, Mia B.; Nordlund, Åke; Krot, Alexander N.; Bizzarro, Martin

2016-01-01

The short-lived 26Al radionuclide is thought to have been admixed into the initially 26Al-poor protosolar molecular cloud before or contemporaneously with its collapse. Bulk inner Solar System reservoirs record positively correlated variability in mass-independent 54Cr and 26Mg*, the decay product of 26Al. This correlation is interpreted as reflecting progressive thermal processing of in-falling 26Al-rich molecular cloud material in the inner Solar System. The thermally unprocessed molecular cloud matter reflecting the nucleosynthetic makeup of the molecular cloud before the last addition of stellar-derived 26Al has not been identified yet but may be preserved in planetesimals that accreted in the outer Solar System. We show that metal-rich carbonaceous chondrites and their components have a unique isotopic signature extending from an inner Solar System composition toward a 26Mg*-depleted and 54Cr-enriched component. This composition is consistent with that expected for thermally unprocessed primordial molecular cloud material before its pollution by stellar-derived 26Al. The 26Mg* and 54Cr compositions of bulk metal-rich chondrites require significant amounts (25–50%) of primordial molecular cloud matter in their precursor material. Given that such high fractions of primordial molecular cloud material are expected to survive only in the outer Solar System, we infer that, similarly to cometary bodies, metal-rich carbonaceous chondrites are samples of planetesimals that accreted beyond the orbits of the gas giants. The lack of evidence for this material in other chondrite groups requires isolation from the outer Solar System, possibly by the opening of disk gaps from the early formation of gas giants. PMID:26858438

Probing the Gaseous Disk of T Tau N with CN 5-4 Lines

NASA Technical Reports Server (NTRS)

Podio, L.; Kamp, I.; Codella, C.; Nisini, B.; Aresu, G.; Brittain, S.; Cabrit, S.; Dougados, C.; Grady, C.; Meijerink, R.;

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Mo; Evans II, Neal J.; Dodson-Robinson, Sarah E.

Gas in protostellar disks provides the raw material for giant planet formation and controls the dynamics of the planetesimal-building dust grains. Accurate gas mass measurements help map the observed properties of planet-forming disks onto the formation environments of known exoplanets. Rare isotopologues of carbon monoxide (CO) have been used as gas mass tracers for disks in the Lupus star-forming region, with an assumed interstellar CO/H{sub 2} abundance ratio. Unfortunately, observations of T-Tauri disks show that CO abundance is not interstellar, a finding reproduced by models that show CO abundance decreasing both with distance from the star and as a functionmore » of time. Here, we present radiative transfer simulations that assess the accuracy of CO-based disk mass measurements. We find that the combination of CO chemical depletion in the outer disk and optically thick emission from the inner disk leads observers to underestimate gas mass by more than an order of magnitude if they use the standard assumptions of interstellar CO/H{sub 2} ratio and optically thin emission. Furthermore, CO abundance changes on million-year timescales, introducing an age/mass degeneracy into observations. To reach a factor of a few accuracy for CO-based disk mass measurements, we suggest that observers and modelers adopt the following strategies: (1) select low- J transitions; (2) observe multiple CO isotopologues and use either intensity ratios or normalized line profiles to diagnose CO chemical depletion; and (3) use spatially resolved observations to measure the CO-abundance distribution.« less

Migration of Gas Giant Planets in a Gravitationally Unstable Disk

NASA Astrophysics Data System (ADS)

Desai, Karna Mahadev; Steiman-Cameron, Thomas Y.; Michael, Scott; Durisen, Richard H.

2017-01-01

Understanding the migration of giant planets in gravitationally unstable protoplanetary disks is important for understanding planetary system architecture, especially the existence of planets orbiting close to and at large distances from their stars. Migration rates can determine the efficiency of planet formation and survival rates of planets. We present results from simulations of 0.3, 1, and 3 Jupiter-mass planets in a 0.14 M⊙ protoplanetary disk around a 1 M⊙ star, where the disk is marginally unstable to gravitational instabilities (GIs). Each planet is simulated separately. We use CHYMERA, a radiative 3D hydrodynamics code developed by the Indiana University Hydrodynamics Group. The simulations include radiative cooling governed by realistic dust opacities. The planets are inserted into the disk, once the disk has settled into its quasi-steady GI-active phase. We simulate each of the 0.3, 1, and 3 Jupiter-mass planets by inserting it at three different locations in the disk, at the corotation radius and at the inner and outer Lindblad resonances. No matter where placed, the 3 Jupiter-mass planets tend to drift inexorably inward but with a rate that slows after many orbital periods. The 1 Jupiter-mass planets migrate mostly inward, but their motion can be delayed or reversed near the corotation of the two-armed wave. The 0.3 Jupiter-mass planets are much less predictable and frequently migrate outward. We analyze how the density of matter and waves in the disk at different azimuthal locations affect the migration.

Multi-scale simulations of black hole accretion in barred galaxies. Self-gravitating disk models

NASA Astrophysics Data System (ADS)

Jung, M.; Illenseer, T. F.; Duschl, W. J.

2018-06-01

Due to the non-axisymmetric potential of the central bar, in addition to their characteristic arms and bar, barred spiral galaxies form a variety of structures within the thin gas disk, such as nuclear rings, inner spirals, and dust lanes. These structures in the inner kiloparsec are extremely important in order to explain and understand the rate of black hole feeding. The aim of this work is to investigate the influence of stellar bars in spiral galaxies on the thin self-gravitating gas disk. We focus on the accretion of gas onto the central supermassive black hole and its time-dependent evolution. We conducted multi-scale simulations simultaneously resolving the galactic disk and the accretion disk around the central black hole. In all the simulations we varied the initial gas disk mass. As an additional parameter we chose either the gas temperature for isothermal simulations or the cooling timescale for non-isothermal simulations. Accretion was either driven by a gravitationally unstable or clumpy accretion disk or by energy dissipation in strong shocks. Most of the simulations show a strong dependence of the accretion rate at the outer boundary of the central accretion disk (r < 300 pc) on the gas flow at kiloparsec scales. The final black hole masses reach up to 109 M⊙ after 1.6 Gyr. Our models show the expected influence of the Eddington limit and a decline in growth rate at the corresponding sub-Eddington limit.

Steamy Solar System

NASA Technical Reports Server (NTRS)

2007-01-01

[figure removed for brevity, see original site] Annotated Version

This diagram illustrates the earliest journeys of water in a young, forming star system. Stars are born out of icy cocoons of gas and dust. As the cocoon collapses under its own weight in an inside-out fashion, a stellar embryo forms at the center surrounded by a dense, dusty disk. The stellar embryo 'feeds' from the disk for a few million years, while material in the disk begins to clump together to form planets.

NASA's Spitzer Space Telescope was able to probe a crucial phase of this stellar evolution - a time when the cocoon is vigorously falling onto the pre-planetary disk. The infrared telescope detected water vapor as it smacks down on a disk circling a forming star called NGC 1333-IRAS 4B. This vapor started out as ice in the outer envelope, but vaporized upon its arrival at the disk.

By analyzing the water in the system, astronomers were also able learn about other characteristics of the disk, such as its size, density and temperature.

How did Spitzer see the water vapor deep in the NGC 1333-IRAS 4B system? This is most likely because the system is oriented in just the right way, such that its thicker disk is seen face-on from our Earthly perspective. In this 'face-on' orientation, Spitzer can peer through a window carved by an outflow of material from the embryonic star. This system in this drawing is shown in the opposite 'edge-on' configuration.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bergemann, Maria; Sesar, Branimir; Cohen, Judith G.

Our Galaxy is thought to have undergone an active evolutionary history dominated by star formation, the accretion of cold gas, and, in particular, mergers up to 10 gigayear ago. The stellar halo reveals rich fossil evidence of these interactions in the form of stellar streams, substructures, and chemically distinct stellar components. The impact of dwarf galaxy mergers on the content and morphology of the Galactic disk is still being explored. Recent studies have identified kinematically distinct stellar substructures and moving groups, which may have extragalactic origin. However, there is mounting evidence that stellar overdensities at the outer disk/halo interface couldmore » have been caused by the interaction of a dwarf galaxy with the disk. Here we report detailed spectroscopic analysis of 14 stars drawn from two stellar overdensities, each lying about 5 kiloparsecs above and below the Galactic plane - locations suggestive of association with the stellar halo. However, we find that the chemical compositions of these stars are almost identical, both within and between these groups, and closely match the abundance patterns of the Milky Way disk stars. This study hence provides compelling evidence that these stars originate from the disk and the overdensities they are part of were created by tidal interactions of the disk with passing or merging dwarf galaxies.« less

Eccentricity Evolution of Migrating Planets

NASA Technical Reports Server (NTRS)

Murray, N.; Paskowitz, M.; Holman, M.

2002-01-01

We examine the eccentricity evolution of a system of two planets locked in a mean motion resonance, in which either the outer or both planets lose energy and angular momentum. The sink of energy and angular momentum could be a gas or planetesimal disk. We analytically calculate the eccentricity damping rate in the case of a single planet migrating through a planetesimal disk. When the planetesimal disk is cold (the average eccentricity is much less than 1), the circularization time is comparable to the inward migration time, as previous calculations have found for the case of a gas disk. If the planetesimal disk is hot, the migration time can be an order of magnitude shorter. We show that the eccentricity of both planetary bodies can grow to large values, particularly if the inner body does not directly exchange energy or angular momentum with the disk. We present the results of numerical integrations of two migrating resonant planets showing rapid growth of eccentricity. We also present integrations in which a Jupiter-mass planet is forced to migrate inward through a system of 5-10 roughly Earth-mass planets. The migrating planets can eject or accrete the smaller bodies; roughly 5% of the mass (averaged over all the integrations) accretes onto the central star. The results are discussed in the context of the currently known extrasolar planetary systems.

Fall-Back Disks in Long and Short GRBS

NASA Technical Reports Server (NTRS)

Cannizo, John K.; Troja, E.; Gehrels, N.

2011-01-01

We present numerical time-dependent calculations for fall-back disks relevant for GRBs in which the disk of material surrounding the black hole (BH) powering the GRB jet modulates the mass flow, and hence the strength of the jet. Given the initial existence of a small mass appr oximately less than 10(exp -4) M(solar) near the progenitor with a circularization radius approximately 10(exp 10) - 10(exp 11) cm, an una voidable consequence will be the formation of an "external disk" whose outer edge continually moves to larger radii due to angular momentum transport and lack of a confining torque. For long GRBs, if the mass distribution in the initial fall-back disk traces the progenitor envelope, then a radius approximates 10(exp 11) cm gives a time scale app roximately 10(exp 4) s for the X-ray plateau. For late times t > 10(exp 7) s a steepening due to a cooling front in the disk may have obser vational support in GRB 060729. For short GRBs, one expects most of t he mass initially to lie at small radii < 10(exp 8) cm; however the presence of even a trace amount approximately 10(exp -9) M(solar) of hi gh angular material can give a brief plateau in the light curve.

Migration and growth of protoplanetary embryos. I. Convergence of embryos in protoplanetary disks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Xiaojia; Lin, Douglas N. C.; Liu, Beibei

2014-12-10

According to the core accretion scenario, planets form in protostellar disks through the condensation of dust, coagulation of planetesimals, and emergence of protoplanetary embryos. At a few AU in a minimum mass nebula, embryos' growth is quenched by dynamical isolation due to the depletion of planetesimals in their feeding zone. However, embryos with masses (M{sub p} ) in the range of a few Earth masses (M {sub ⊕}) migrate toward a transition radius between the inner viscously heated and outer irradiated regions of their natal disk. Their limiting isolation mass increases with the planetesimals surface density. When M{sub p} >more » 10 M {sub ⊕}, embryos efficiently accrete gas and evolve into cores of gas giants. We use a numerical simulation to show that despite stream line interference, convergent embryos essentially retain the strength of non-interacting embryos' Lindblad and corotation torques by their natal disks. In disks with modest surface density (or equivalently accretion rates), embryos capture each other in their mutual mean motion resonances and form a convoy of super-Earths. In more massive disks, they could overcome these resonant barriers to undergo repeated close encounters, including cohesive collisions that enable the formation of massive cores.« less

PAH Emission from Disks around Intermediate-Mass Stars: The Peculiar Aroma of Hydrocarbons Orbiting Herbig Ae/Be Stars

NASA Astrophysics Data System (ADS)

Keller, L. D.; Sloan, G. C.

2009-12-01

Over half of the intermediate-mass young stellar objects in the Galaxy (e.g. Herbig Ae/Be stars or HAeBe) have high-contrast emission in the mid-infrared spectral features of polycyclic aromatic hydrocarbons (PAHs) above the continuum produced by thermal emission from dust in the circumstellar disks. We have examined the PAH emission in detail for 30 HAeBe stars observed with the Spitzer IRS. We have identified some trends that, should they survive in a larger sample of HAeBe stars, will allow us to infer large-scale disk geometry (both inner and outer) and the degree of photo-processing of organic molecular material in HAeBe disks: HAeBe stars apparently have distinctive PAH spectra among the many other astronomical environments that are characterized by strong PAH emission; strong PAH emission is not necessarily an indicator of a particular disk geometry; PAH spectra of HAeBe stars change systematically with stellar effective temperature; PAH in HAeBe disks are ionized. As part of a Spitzer archival project we are applying our spectral analysis methods to an even larger sample of HAeBe stars observed with the IRS and currently available in the Spitzer archive. Here we report preliminary results as we begin the larger study.

A Resolved Near-Infrared Image of the Inner Cavity in the GM Aur Transitional Disk

NASA Technical Reports Server (NTRS)

Oh, Daehyeon; Hashimoto, Jun; Carson, Joseph C.; Janson, Markus; Kwon, Jungmi; Nakagawa, Takao; Mayama, Satoshi; Uyama, Taichi; Grady, Carol A.; McElwain, Michael W.

2016-01-01

We present high-contrast H-band polarized intensity (PI) images of the transitional disk around the young solar like star GM Aur. The near-infrared direct imaging of the disk was derived by polarimetric differential imaging using the Subaru 8.2 m Telescope and HiCIAO. An angular resolution and an inner working angle of 0 07 and radius approximately 0 05, respectively, were obtained. We clearly resolved a large inner cavity, with a measured radius of 18+/ 2 au, which is smaller than that of a submillimeter interferometric image (28 au). This discrepancy in the cavity radii at near-infrared and submillimeter wavelengths may be caused by a 34M(sub Jup) planet about 20 au away from the star, near the edge of the cavity. The presence of a near-infrared inner cavity is a strong constraint on hypotheses for inner cavity formation in a transitional disk. A dust filtration mechanism has been proposed to explain the large cavity in the submillimeter image, but our results suggest that this mechanism must be combined with an additional process. We found that the PI slope of the outer disk is significantly different from the intensity slope obtained from HSTNICMOS, and this difference may indicate the grain growth process in the disk.

The Evolution of CO in Protoplanetary Disks During Planet Formation

NASA Astrophysics Data System (ADS)

Schwarz, Kamber; Bergin, Edwin

2018-01-01

CO has long been used as a tracer of gas mass. However, recent observations have revealed a low CO to dust mass ratio in numerous protoplanetary disks. In at least some of these systems it is the CO, rather than the total gas mass, which is missing. During my PhD I have used models of protoplanetary disk chemistry as well as millimeter observations to explore the causes and extent of CO depletion in disks. My ALMA observations of CO isotopologues in the TW Hya protoplanetary disk revealed that CO is under-abundant in that system by nearly two orders of magnitude, failing to return to ISM abundances even inside the midplane CO snow line. I have also explored the physical conditions needed to remove carbon from gas phase CO via chemically process using a large grid of chemical models. My analysis reveals that in the warm molecular layer, a wide range of physical conditions can result in an order of magnitude reduction of CO in the outer disk. In the inner disk, ionization, such as from cosmic rays, is needed for chemical reprocessing to occur. However, it is very difficult for chemical processes alone to result in two orders of magnitude of depletion, such as is seen in TW Hya and inferred for other disks. In the midplane, where planets form, it is even more difficult to remove carbon from CO without invoking cosmic rays. My work shows that while CO is missing from the gas in protoplanetary disks, chemistry is unlikely to be the sole cause.

Multiple Paths of Deuterium Fractionation in Protoplanetary Disks

NASA Astrophysics Data System (ADS)

Aikawa, Yuri; Furuya, Kenji; Hincelin, Ugo; Herbst, Eric

2018-03-01

We investigate deuterium chemistry coupled with the nuclear spin-state chemistry of H2 and {{{H}}}3+ in protoplanetary disks. Multiple paths of deuterium fractionation are found; exchange reactions with D atoms, such as HCO+ + D, are effective in addition to those with HD. In a disk model with grain sizes appropriate for dark clouds, the freeze-out of molecules is severe in the outer midplane, while the disk surface is shielded from UV radiation. Gaseous molecules, including DCO+, thus become abundant at the disk surface, which tends to make their column density distribution relatively flat. If the dust grains have grown to millimeter size, the freeze-out rate of neutral species is reduced and the abundances of gaseous molecules, including DCO+ and N2D+, are enhanced in the cold midplane. Turbulent diffusion transports D atoms and radicals at the disk surface to the midplane, and stable ice species in the midplane to the disk surface. The effects of turbulence on chemistry are thus multifold; while DCO+ and N2D+ abundances increase or decrease depending on the regions, HCN and DCN in the gas and ice are greatly reduced at the innermost radii, compared to the model without turbulence. When cosmic rays penetrate the disk, the ortho-to-para ratio (OPR) of H2 is found to be thermal in the disk, except in the cold (≲10 K) midplane. We also analyze the OPR of {{{H}}}3+ and H2D+, as well as the main reactions of H2D+, DCO+, and N2D+, in order to analytically derive their abundances in the cold midplane.

Security of patient data when decommissioning ultrasound systems.

PubMed

Moggridge, James

2017-02-01

Although ultrasound systems generally archive to Picture Archiving and Communication Systems (PACS), their archiving workflow typically involves storage to an internal hard disk before data are transferred onwards. Deleting records from the local system will delete entries in the database and from the file allocation table or equivalent but, as with a PC, files can be recovered. Great care is taken with disposal of media from a healthcare organisation to prevent data breaches, but ultrasound systems are routinely returned to lease companies, sold on or donated to third parties without such controls. In this project, five methods of hard disk erasure were tested on nine ultrasound systems being decommissioned: the system's own delete function; full reinstallation of system software; the manufacturer's own disk wiping service; open source disk wiping software for full and just blank space erasure. Attempts were then made to recover data using open source recovery tools. All methods deleted patient data as viewable from the ultrasound system and from browsing the disk from a PC. However, patient identifiable data (PID) could be recovered following the system's own deletion and the reinstallation methods. No PID could be recovered after using the manufacturer's wiping service or the open source wiping software. The typical method of reinstalling an ultrasound system's software may not prevent PID from being recovered. When transferring ownership, care should be taken that an ultrasound system's hard disk has been wiped to a sufficient level, particularly if the scanner is to be returned with approved parts and in a fully working state.

Properties of resonant trans-Neptunian objects based on Herschel Space Observatory data

NASA Astrophysics Data System (ADS)

Farkas Anikó, Takácsné; Kiss, Csaba; Mueller, Thomas G.; Mommert, Michael; Vilenius, Esa

2016-10-01

The goal of our work is to characterise the physical characteristics of resonant, detached and scattered disk objects in the trans-Neptunian region, observed in the framework of the "TNOs are Cool!" Herschel Open Time Key Program. Based on thermal emission measurements with the Herschel/PACS and Spitzer/MIPS instruments we were able to determine size, albedo, and surface thermal properties for 23 objects using radiometric modelling techniques. This is the first analysis in which the physical properties of objects in the outer resonances are determined for a larger sample. In addition to the results for individual objects, we have compared these characteristic with the bulk properties of other populations of the trans-Neptunian region. The newly analysed objects show e.g. a large variety of beaming factors, indicating diverse surfaces, and in general they follow the albedo-colour clustering identified earlier for Kuiper belt objects and Centaurs, further strengthening the evidence for a compositional discontinuity in the young solar system.

High thermal conductivity connector having high electrical isolation

DOEpatents

Nieman, Ralph C.; Gonczy, John D.; Nicol, Thomas H.

1995-01-01

A method and article for providing a low-thermal-resistance, high-electrical-isolation heat intercept connection. The connection method involves clamping, by thermal interference fit, an electrically isolating cylinder between an outer metallic ring and an inner metallic disk. The connection provides durable coupling of a heat sink and a heat source.

Discrimination of Inner- and Outer-Sphere Electrode Reactions by Cyclic Voltammetry Experiments

ERIC Educational Resources Information Center

Tanimoto, Sachiko; Ichimura, Akio

2013-01-01

A laboratory experiment for undergraduate students who are studying homogeneous and heterogeneous electron-transfer reactions is described. Heterogeneous or electrode reaction kinetics can be examined by using the electrochemical reduction of three Fe[superscript III]/Fe[superscript II] redox couples at platinum and glassy carbon disk electrodes.…

Capture of irregular satellites at Jupiter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nesvorný, David; Vokrouhlický, David; Deienno, Rogerio

The irregular satellites of outer planets are thought to have been captured from heliocentric orbits. The exact nature of the capture process, however, remains uncertain. We examine the possibility that irregular satellites were captured from the planetesimal disk during the early solar system instability when encounters between the outer planets occurred. Nesvorný et al. already showed that the irregular satellites of Saturn, Uranus, and Neptune were plausibly captured during planetary encounters. Here we find that the current instability models present favorable conditions for capture of irregular satellites at Jupiter as well, mainly because Jupiter undergoes a phase of close encountersmore » with an ice giant. We show that the orbital distribution of bodies captured during planetary encounters provides a good match to the observed distribution of irregular satellites at Jupiter. The capture efficiency for each particle in the original transplanetary disk is found to be (1.3-3.6) × 10{sup –8}. This is roughly enough to explain the observed population of jovian irregular moons. We also confirm Nesvorný et al.'s results for the irregular satellites of Saturn, Uranus, and Neptune.« less

Three-dimensional modeling of radiative disks in binaries

NASA Astrophysics Data System (ADS)

Picogna, G.; Marzari, F.

2013-08-01

Context. Circumstellar disks in binaries are perturbed by the companion gravity causing significant alterations of the disk morphology. Spiral waves due to the companion tidal force also develop in the vertical direction and affect the disk temperature profile. These effects may significantly influence the process of planet formation. Aims: We perform 3D numerical simulations of disks in binaries with different initial dynamical configurations and physical parameters. Our goal is to investigate their evolution and their propensity to grow planets. Methods: We use an improved version of the SPH code VINE modified to better account for momentum and energy conservation via variable smoothing and softening length. The energy equation includes a flux-limited radiative transfer algorithm. The disk cooling is obtained with the use of "boundary particles" populating the outer surfaces of the disk and radiating to infinity. We model a system made of star/disk + star/disk where the secondary star (and relative disk) is less massive than the primary. Results: The numerical simulations performed for different values of binary separation and disk density show that trailing spiral shock waves develop when the stars approach their pericenter. Strong hydraulic jumps occur at the shock front, in particular for small separation binaries, creating breaking waves, and a consistent mass stream between the two disks. Both shock waves and mass transfer cause significant heating of the disk. At apocenter these perturbations are reduced and the disks are cooled down and less eccentric. Conclusions: The disk morphology is substantially affected by the companion perturbations, in particular in the vertical direction. The hydraulic jumps may slow down or even halt the dust coagulation process. The disk is significantly heated up by spiral waves and mass transfer, and the high gas temperature may prevent the ice condensation by moving the "snow line" outward. The disordered motion triggered by the spiral waves may, on the other hand, favor direct formation of large planetesimals from pebbles. The strength of the hydraulic jumps, disk heating, and mass exchange depends on the binary separation, and for larger semi-major axes, the tidal spiral pattern is substantially reduced. The environment then appears less hostile to planet formation.

Rotary-To-Axial Motion Converter For Valve

NASA Technical Reports Server (NTRS)

Reinicke, Robert H.; Mohtar, Rafic

1991-01-01

Nearly frictionless mechanism converts rotary motion into axial motion. Designed for use in electronically variable pressure-regulator valve. Changes rotary motion imparted by motor into translation that opens and closes valve poppet. Cables spaced equidistantly around edge of fixed disk support movable disk. As movable disk rotated, cables twist, lifting it. When rotated in opposite direction, cables untwist, lowering it. Spider disk helps to prevent cables from tangling. Requires no lubrication and insensitive to contamination in fluid flowing through valve.

Electrostatic shape-shifting ion optics

DOEpatents

Dahl, David A.; Scott, Jill R.; Appelhans, Anthony D.

2006-05-02

Electrostatic shape-shifting ion optics includes an outer electrode that defines an interior region between first and second opposed open ends. A first inner electrode is positioned within the interior region of the outer electrode at about the first open end. A second inner electrode is positioned within the interior region of the outer electrode at about the second open end. A first end cap electrode is positioned at about a first open end of the first inner electrode so that the first end cap electrode substantially encloses the first open end of the first inner electrode. A second end cap electrode is positioned at about a second open end of the second inner electrode so that the second end cap electrode substantially encloses the second open end of the second inner electrode. A voltage source operatively connected to each of the electrodes applies voltage functions to each of the electrodes to produce an electric field within an interior space enclosed by the electrodes.

Probing midplane CO abundance and gas temperature with DCO+ in the protoplanetary disk around HD 169142

NASA Astrophysics Data System (ADS)

Carney, M. T.; Fedele, D.; Hogerheijde, M. R.; Favre, C.; Walsh, C.; Bruderer, S.; Miotello, A.; Murillo, N. M.; Klaassen, P. D.; Henning, Th.; van Dishoeck, E. F.

2018-06-01

Context. Physical and chemical processes in protoplanetary disks affect the disk structure and the midplane environment within which planets form. The simple deuterated molecular cation DCO+ has been proposed to act as a tracer of the disk midplane conditions. Aims: This work aims to understand which midplane conditions are probed by the DCO+ emission in the disk around the Herbig Ae star HD 169142. We explore the sensitivity of the DCO+ formation pathways to gas temperature and CO abundance. Methods: The DCO+ J = 3-2 transition was observed with Atacama Large Millimeter/submillimeter Array at a spatial resolution of 0.3'' (35 AU at 117 pc). We modeled the DCO+ emission in HD 169142 with a physical disk structure adapted from the literature, and employed a simple deuterium chemical network to investigate the formation of DCO+ through the cold deuterium fractionation pathway via H2D+. Parameterized models are used to modify the gas temperature and CO abundance structure of the disk midplane to test their effect on DCO+ production. Contributions from the warm deuterium fractionation pathway via CH2D+ are approximated using a constant abundance in the intermediate disk layers. Results: The DCO+ line is detected in the HD 169142 disk with a total integrated line flux of 730 ± 73 mJy km s-1. The radial intensity profile reveals a warm, inner component of the DCO+ emission at radii ≲30 AU and a broad, ring-like structure from 50-230 AU with a peak at 100 AU just beyond the edge of the millimeter grain distribution. Parameterized models show that alterations to the midplane gas temperature and CO abundance are both needed to recover the observed DCO+ radial intensity profile. The alterations are relative to the fiducial physical structure of the literature model constrained by dust and CO observations. The best-fit model contains a shadowed, cold midplane in the region z/r < 0.1 with an 8 K decrease in Tgas and a factor of five CO depletion just beyond the millimeter grains (r = 83 AU), and a 2 K decrease in Tgas for r > 120 AU. The warm deuterium fractionation pathway is implemented as a constant DCO+ abundance of 2.0 × 10-12 between 30-70 K and contributes >85% to the DCO+ emission at r < 83 AU in the best-fit model. Conclusions: The DCO+ emission probes a reservoir of cold material in the HD 169142 outer disk that is not probed by the millimeter continuum, the spectral energy distribution, nor the emission from the 12 CO, 13 CO, or C18O J = 2-1 lines. The DCO+ emission is a sensitive probe of gas temperature and CO abundance near the disk midplane and provides information about the outer disk beyond the millimeter continuum distribution that is largely absent in abundant gaseous tracers such as CO isotopologues. The reduced datacubes (FITS files) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/614/A106

On the AU Microscopii debris disk. Density profiles, grain properties, and dust dynamics

NASA Astrophysics Data System (ADS)

Augereau, J.-C.; Beust, H.

2006-09-01

Context: . AU Mic is a young M-type star surrounded by an edge-on optically thin debris disk that shares many common observational properties with the disk around β Pictoris. In particular, the scattered light surface brightness profile falls off as ˜ r-5 outside 120 AU for β Pictoris and 35 AU for AU Mic. In both cases, the disk color rises as the distance increases beyond these reference radii. Aims: . In this paper, we present the first comprehensive analysis of the AU Mic disk properties since the system was resolved by Kalas et al. (2004, Science, 303, 1990). We explore whether the dynamical model, which successfully reproduces the β Pictoris brightness profile (e.g., Augereau et al. 2001, A&A, 370, 447), could apply to AU Mic. Methods: . We calculate the surface density profile of the AU Mic disk by performing the inversion of the near-IR and visible scattered light brightness profiles measured by Liu (2004, Science, 305, 1442) and Krist et al. (2005, AJ, 129, 1008), respectively. We discuss the grain properties by analysing the blue color of the disk in the visible (Krist et al. 2005) and by fitting the disk spectral energy distribution. Finally, we evaluate the radiation and wind forces on the grains. The impact of the recurrent X-ray and UV-flares on the dust dynamics is also discussed. Results: . We show that irrespective of the mean scattering asymmetry factor of the grains, most of the emission arises from an asymmetric, collisionally-dominated region that peaks close to the surface brightness break around 35 AU. The elementary scatterers at visible wavelengths are found to be sub-micronic, but the inferred size distribution underestimates the number of large grains, resulting in sub-millimeter emissions that are too low compared to the observations. From our inversion procedure, we find that the V- to H-band scattering cross sections ratio increases outside 40 AU, in line with the observed color gradient of the disk. This behavior is expected if the grains have not been produced locally, but placed in orbits of high eccentricity by a size-dependent pressure force, resulting in a paucity of large grains beyond the outer edge of the parent bodies' disk. Because of the low luminosity of AU Mic, radiation pressure is inefficient to diffuse the smallest grains in the outer disk, even when the flares are taken into account. Conversely, we show that a standard, solar-like stellar wind generates a pressure force onto the dust particles that behaves much like a radiation pressure force. With an assumed dot{M} ≃ 3×102 dot{M}⊙, the wind pressure overcomes the radiation pressure, and this effect is enhanced by the stellar flares. This greatly contributes to populating the extended AU Mic debris disk and explains the similarity between the β Pictoris and AU Mic brightness profiles. In both cases, the color gradient beyond 120 AU for β Pictoris and 35 AU for AU Mic, is believed to be a direct consequence of the dust dynamics.

The Cluster Population of UGC 2885

NASA Astrophysics Data System (ADS)

Holwerda, Benne

2017-08-01

UGC 2885 was discoverd to be the most extended disk galaxy [250 kpc diameter] by Vera Rubin in the 1980's. We ask for HST observations of UGC 2885 as it is close enough to resolve the GC population with HST but it is a substantially more extended disk than any studied before. LCDM galaxy assembly implies that the GC population comes from small accreted systems and the disk -and the clusters associated with it- predominantly from gas accretion (matching angular momentum to the disk). Several scaling relations between the GC population and parent galaxy have been observed but these differ for disk and spheroidal (massive) galaxies.We propose to observe this galaxy with HST in 4 point WFC3 mosaic with coordinated ACS parallels to probe both the disk and outer halo component of the GC population. GC populations have been studied extensively using HST color mosaics of local disk galaxies and these can serve as comparison samples. How UGC 2885 cluster populations relate to its stellar and halo mass, luminosity and with radius will reveal the formation history of extra-ordinary disk.Our goals are twofold: our science goal is to map the luminosity, (some) size, and color distributions of the stellar and globular clusters in and around this disk. In absolute terms, we expect to find many GC but the relative relation of the GC population to this galaxy's mass (stellar and halo) and size will shed light on its formation history; similar to a group or cluster central elliptical or to a field galaxy (albeit one with a disk 10x the Milky Way's size)? Our secondary motive is to make an HST tribute image to the late Vera Rubin.

Extreme Asymmetry in the Polarized Disk of V1247 Orionis

NASA Technical Reports Server (NTRS)

Ohta, Yurina; Fukagawa, Misato; Sitko, Michael; Muto, Takayuki; Kraus, Stefan; Grady, Carol A.; Wisniewski, John A.; Swearingen, Jeremy R.; Shibai, Hiroshi; McElwain, Michael W.

2016-01-01

We present the first near-infrared scattered-light detection of the transitional disk around V1247 Ori, which was obtained using high-resolution polarimetric differential imaging observations with Subaru/HiCIAO. Our imaging in the H band reveals the disk morphology at separations of approx.0.14-0.86 (54-330 au) from the central star. The polarized intensity image shows a remarkable arc-like structure toward the southeast of the star, whereas the fainter northwest region does not exhibit any notable features. The shape of the arm is consistent with an arc of 0.28 +/- 0.09 in radius (108 au from the star), although the possibility of a spiral arm with a small pitch angle cannot be excluded. V1247 Ori features an exceptionally large azimuthal contrast in scattered, polarized light; the radial peak of the southeastern arc is about three times brighter than the northwestern disk measured at the same distance from the star. Combined with the previous indication of an inhomogeneous density distribution in the gap at 46 au, the notable asymmetry in the outer disk suggests the presence of unseen companions and/or planet-forming processes ongoing in the arc.

DIRECT IMAGING OF FINE STRUCTURES IN GIANT PLANET-FORMING REGIONS OF THE PROTOPLANETARY DISK AROUND AB AURIGAE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hashimoto, J.; Tamura, M.; Fukue, T.

We report high-resolution 1.6 {mu}m polarized intensity (PI) images of the circumstellar disk around the Herbig Ae star AB Aur at a radial distance of 22 AU (0.''15) up to 554 AU (3.''85), which have been obtained by the high-contrast instrument HiCIAO with the dual-beam polarimetry. We revealed complicated and asymmetrical structures in the inner part ({approx}<140 AU) of the disk while confirming the previously reported outer (r {approx}> 200 AU) spiral structure. We have imaged a double ring structure at {approx}40 and {approx}100 AU and a ring-like gap between the two. We found a significant discrepancy of inclination anglesmore » between two rings, which may indicate that the disk of AB Aur is warped. Furthermore, we found seven dips (the typical size is {approx}45 AU or less) within two rings, as well as three prominent PI peaks at {approx}40 AU. The observed structures, including a bumpy double ring, a ring-like gap, and a warped disk in the innermost regions, provide essential information for understanding the formation mechanism of recently detected wide-orbit (r > 20 AU) planets.« less

DIRECT IMAGING AND SPECTROSCOPY OF A YOUNG EXTRASOLAR KUIPER BELT IN THE NEAREST OB ASSOCIATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Currie, Thayne; Lisse, Carey M.; Kuchner, Marc

2015-07-01

We describe the discovery of a bright, young Kuiper belt–like debris disk around HD 115600, a ∼1.4–1.5 M{sub ⊙}, ∼15 Myr old member of the Sco–Cen OB Association. Our H-band coronagraphy/integral field spectroscopy from the Gemini Planet Imager shows the ring has a (luminosity-scaled) semimajor axis of (∼22 AU) ∼ 48 AU, similar to the current Kuiper belt. The disk appears to have neutral-scattering dust, is eccentric (e ∼ 0.1–0.2), and could be sculpted by analogs to the outer solar system planets. Spectroscopy of the disk ansae reveal a slightly blue to gray disk color, consistent with major Kuiper beltmore » chemical constituents, where water ice is a very plausible dominant constituent. Besides being the first object discovered with the next generation of extreme adaptive optics systems (i.e., SCExAO, GPI, SPHERE), HD 115600's debris ring and planetary system provide a key reference point for the early evolution of the solar system, the structure, and composition of the Kuiper belt and the interaction between debris disks and planets.« less

A Venus-mass Planet Orbiting a Brown Dwarf: A Missing Link between Planets and Moons

NASA Astrophysics Data System (ADS)

Udalski, A.; Jung, Y. K.; Han, C.; Gould, A.; Kozłowski, S.; Skowron, J.; Poleski, R.; Soszyński, I.; Pietrukowicz, P.; Mróz, P.; Szymański, M. K.; Wyrzykowski, Ł.; Ulaczyk, K.; Pietrzyński, G.; Shvartzvald, Y.; Maoz, D.; Kaspi, S.; Gaudi, B. S.; Hwang, K.-H.; Choi, J.-Y.; Shin, I.-G.; Park, H.; Bozza, V.

2015-10-01

The co-planarity of solar system planets led Kant to suggest that they formed from an accretion disk, and the discovery of hundreds of such disks around young stars as well as hundreds of co-planar planetary systems by the Kepler satellite demonstrate that this formation mechanism is extremely widespread. Many moons in the solar system, such as the Galilean moons of Jupiter, also formed out of the accretion disks that coalesced into the giant planets. Here we report the discovery of an intermediate system, OGLE-2013-BLG-0723LB/Bb, composed of a Venus-mass planet orbiting a brown dwarf, which may be viewed either as a scaled-down version of a planet plus a star or as a scaled-up version of a moon plus a planet orbiting a star. The latter analogy can be further extended since they orbit in the potential of a larger, stellar body. For ice-rock companions formed in the outer parts of accretion disks, like Uranus and Callisto, the scaled masses and separations of the three types of systems are similar, leading us to suggest that the formation processes of companions within accretion disks around stars, brown dwarfs, and planets are similar.

Formation of Outer Planets: Overview

NASA Technical Reports Server (NTRS)

Lissauer, Jack

2003-01-01

An overview of current theories of planetary formation, with emphasis on giant planets is presented. The most detailed models are based upon observation of our own Solar System and of young stars and their environments. Terrestrial planets are believe to grow via pairwise accretion until the spacing of planetary orbits becomes large enough that the configuration is stable for the age of the system. According to the prevailing core instability model, giant planets begin their growth by the accumulation of small solid bodies, as do terrestrial planets. However, unlike terrestrial planets, the growing giant cores become massive enough that they are able to accumulate substantial amounts of gas before the protoplanetary disk disspates. The primary questions regarding the core instability model is whether planets with small cores can accrete gaseous enveloples within the lifetimes of gaseous protoplanetary disks. The main alternative giant planet formation model is the disk instability model, in which gaseous planets form directly via gravitational instabilities within protoplanetary disks. Formation of giant planets via gas instability has never been demonstrated for realistic disk conditions. Moreover, this model has difficulty explaining the supersolar abundances of heavy elements in Jupiter and Saturn, and it does not explain the orgin of planets like Uranus and Neptune.

Milky Way's thick and thin disk: Is there a distinct thick disk?

NASA Astrophysics Data System (ADS)

Kawata, D.; Chiappini, C.

2016-09-01

This article is based on our discussion session on Milky Way models at the 592 WE-Heraeus Seminar, Reconstructing the Milky Way's History: Spectroscopic Surveys, Asteroseismology and Chemodynamical Models. The discussion focused on the following question: "Are there distinct thick and thin disks?". The answer to this question depends on the definition one adopts for thin and thick disks. The participants of this discussion converged to the idea that there are at least two different types of disks in the Milky Way. However, there are still important open questions on how to best define these two types of disks (chemically, kinematically, geometrically or by age?). The question of what is the origin of the distinct disks remains open. The future Galactic surveys which are highlighted in this conference should help us answering these questions. The almost one-hour debate involving researchers in the field representing different modelling approaches (Galactic models such as TRILEGAL, Besançon and Galaxia, chemical evolution models, extended distribution functions method, chemodynamics in the cosmological context, and self-consistent cosmological simulations) illustrated how important is to have all these parallel approaches. All approaches have their advantages and shortcomings (also discussed), and different approaches are useful to address specific points that might help us answering the more general question above.

Shaft/shaft-seal interface characteristics of a multiple disk centrifugal blood pump.

PubMed

Manning, K B; Miller, G E

1999-06-01

A multiple disk centrifugal pump (MDCP) is under investigation as a potential left ventricular assist device. As is the case with most shaft driven pumps, leakage problems around the shaft/shaft seal interface are of major interest. If leakage were to occur during or after implantation, potential events such as blood loss, clotting, blood damage, and/or infections might result in adverse effects for the patient. Because these effects could be quite disastrous, potential shaft and shaft seal materials have been investigated to determine the most appropriate course to limit these effects. Teflon and nylon shaft seals were analyzed as potential candidates along with a stainless steel shaft and a Melonite coated shaft. The materials and shafts were evaluated under various time durations (15, 30, 45, and 60 min), motor speeds (800, 1,000, 1,200, and 1,400 rpm), and outer diameters (1/2 and 3/4 inches). The motor speed and geometrical configurations were typical for the MDCP under normal physiologic conditions. An air and water study was conducted to analyze the inner diameter wear, the inner temperature values, and the outer temperature values. Statistical comparisons were computed for the shaft seal materials, the shafts, and the outer diameters along with the inner and outer temperatures. The conclusions made from the results indicate that both the tested shaft seal materials and shaft materials are not ideal candidates to be used for the MDCP. Teflon experienced a significant amount of wear in air and water studies. Nylon did experience little wear, but heat generation was an evident problem. A water study on nylon was not conducted because of its molecular structure.

Colours of the Outer Solar System Origins Survey: An Update

NASA Astrophysics Data System (ADS)

Schwamb, Megan E.; Fraser, Wesley C.; Pike, Rosemary E.; Bannister, Michele T.; Marsset, Michaël; Kavelaars, J. J.; Benecchi, Susan; Delsanti, Audrey C.; Lehner, Matthew J.; Wang, Shiang-Yu; Thirouin, Audrey; Nesvorný, David

2018-01-01

The vast majority of the known dwarf-planet sized bodies are bright enough to be studied through optical and infrared spectroscopy. As a result, we have an understanding of the surface properties for the largest Kuiper belt objects (KBOs) which retain their primordial inventory of volatile ices. For the typically smaller > 22 mag KBO, we must rely instead on what colors reveal by proxy; yet this picture remains incomplete. Most KBO physical property studies examine the hodgepodge set of objects discovered by various surveys with different and varying detection biases that make it difficult if not impossible to reliably estimate the sizes of the different surface color groupings (compositional classes) residing in the modern-day Kuiper belt.The Colours of the Outer Solar System Origins Survey (Col-OSSOS) probes the surface properties within the Kuiper belt primarily through near simultaneous g,r and J colors with the Gemini North Telescope and u-band with Canada-France-Hawaii Telescope. The project aims to target ~100 KBOs brighter than 23.6 r‧ mag found by the Outer Solar System Origins Survey (OSSOS), a survey with a well-measured detection efficiency. Thus, Col-OSSOS provides the first brightness-complete, compositional-dynamical map of the Outer Solar System, probing in a new light the radial color distribution in the primordial planetesimal disk from which KBOs originated. We will provide an update on the current status of the program highlighting results from the first two years of the survey; including size estimates of the two color KBO subgroups (the red and neutral surfaces) within the dynamically excited Kuiper belt and implications for the early planetesimal disk composition based on neutral-colored binaries found in the cold classical Kuiper belt.

Circus Family of Stars (Artist's Concept)

NASA Technical Reports Server (NTRS)

2005-01-01

[figure removed for brevity, see original site] Quick Time Movie for PIA03521 Circus Family of Stars

This artist's animation shows the clockwork-like orbits of a triple-star system called HD 188753, which was discovered to harbor a gas giant, or 'hot Jupiter,' planet. The planet zips around the system's main star (yellow, center) every 3.3 days, while the main star is circled every 25.7 years by a dancing duo of stars (yellow and orange, outer orbit). The star pair is locked in a 156-day orbit.

This eccentric star family is a cramped bunch; the distance between the main star and the outer pair of stars is about the same as that between the Sun and Saturn. Though multiple-star systems like this one are common in the universe, astronomers were surprised to find a planet living in such tight quarters.

One reason for the surprise has to do with theories of hot Jupiter formation. Astronomers believe that these planets begin life at the outer fringes of their stars, in thick dusty disks called protoplanetary disks, before migrating inward. The discovery of a world under three suns throws this theory into question. As seen in this animation, there is not much room at this system's outer edges for a hot Jupiter to grow.

The discovery was made using the Keck I telescope atop Mauna Kea mountain in Hawaii. The triple-star system is located 149 light-years away in the constellation Cygnus.

The sizes and orbital periods in the animation are not shown to scale. The relative motions are shown with respect to the main star.

SPIN EVOLUTION OF ACCRETING YOUNG STARS. I. EFFECT OF MAGNETIC STAR-DISK COUPLING

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matt, Sean P.; Greene, Thomas P.; Pinzon, Giovanni

2010-05-10

We present a model for the rotational evolution of a young, solar mass star interacting with an accretion disk. The model incorporates a description of the angular momentum transfer between the star and the disk due to a magnetic connection, and includes changes in the star's mass and radius and a decreasing accretion rate. The model also includes, for the first time in a spin evolution model, the opening of the stellar magnetic field lines, as expected to arise from twisting via star-disk differential rotation. In order to isolate the effect that this has on the star-disk interaction torques, wemore » neglect the influence of torques that may arise from open field regions connected to the star or disk. For a range of magnetic field strengths, accretion rates, and initial spin rates, we compute the stellar spin rates of pre-main-sequence stars as they evolve on the Hayashi track to an age of 3 Myr. How much the field opening affects the spin depends on the strength of the coupling of the magnetic field to the disk. For the relatively strong coupling (i.e., high magnetic Reynolds number) expected in real systems, all models predict spin periods of less than {approx}3 days, in the age range of 1-3 Myr. Furthermore, these systems typically do not reach an equilibrium spin rate within 3 Myr, so that the spin at any given time depends upon the choice of initial spin rate. This corroborates earlier suggestions that, in order to explain the full range of observed rotation periods of approximately 1-10 days, additional processes, such as the angular momentum loss from powerful stellar winds, are necessary.« less

Identification of transitional disks in Chamaeleon with Herschel

NASA Astrophysics Data System (ADS)

Ribas, Á.; Merín, B.; Bouy, H.; Alves de Oliveira, C.; Ardila, D. R.; Puga, E.; Kóspál, Á.; Spezzi, L.; Cox, N. L. J.; Prusti, T.; Pilbratt, G. L.; André, Ph.; Matrà, L.; Vavrek, R.

2013-04-01

Context. Transitional disks are circumstellar disks with inner holes that in some cases are produced by planets and/or substellar companions in these systems. For this reason, these disks are extremely important for the study of planetary system formation. Aims: The Herschel Space Observatory provides an unique opportunity for studying the outer regions of protoplanetary disks. In this work we update previous knowledge on the transitional disks in the Chamaeleon I and II regions with data from the Herschel Gould Belt Survey. Methods: We propose a new method for transitional disk classification based on the WISE 12 μm - PACS 70 μm color, together with inspection of the Herschel images. We applied this method to the population of Class II sources in the Chamaeleon region and studied the spectral energy distributions of the transitional disks in the sample. We also built the median spectral energy distribution of Class II objects in these regions for comparison with transitional disks. Results: The proposed method allows a clear separation of the known transitional disks from the Class II sources. We find six transitional disks, all previously known, and identify five objects previously thought to be transitional as possibly non-transitional. We find higher fluxes at the PACS wavelengths in the sample of transitional disks than those of Class II objects. Conclusions: We show the Herschel 70 μm band to be a robust and efficient tool for transitional disk identification. The sensitivity and spatial resolution of Herschel reveals a significant contamination level among the previously identified transitional disk candidates for the two regions, which calls for a revision of previous samples of transitional disks in other regions. The systematic excess found at the PACS bands could be either a result of the mechanism that produces the transitional phase, or an indication of different evolutionary paths for transitional disks and Class II sources. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendix A is available in electronic form at http://www.aanda.org

Featured Image: Simulating Planetary Gaps

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-03-01

The authors model of howthe above disk would look as we observe it in a scattered-light image. The morphology of the gap can be used to estimate the mass of the planet that caused it. [Dong Fung 2017]The above image from a computer simulation reveals the dust structure of a protoplanetary disk (with the star obscured in the center) as a newly formed planet orbits within it. A recent study by Ruobing Dong (Steward Observatory, University of Arizona) and Jeffrey Fung (University of California, Berkeley) examines how we can determine mass of such a planet based on our observations of the gap that the planet opens in the disk as it orbits. The authors models help us to better understand how our observations of gaps might change if the disk is inclined relative to our line of sight, and how we can still constrain the mass of the gap-opening planet and the viscosity of the disk from the scattered-light images we have recently begun to obtain of distant protoplanetary disks. For more information, check out the paper below!CitationRuobing Dong () and Jeffrey Fung () 2017 ApJ 835 146. doi:10.3847/1538-4357/835/2/146

The Gaia-ESO Survey: Probes of the inner disk abundance gradient

NASA Astrophysics Data System (ADS)

Jacobson, H. R.; Friel, E. D.; Jílková, L.; Magrini, L.; Bragaglia, A.; Vallenari, A.; Tosi, M.; Randich, S.; Donati, P.; Cantat-Gaudin, T.; Sordo, R.; Smiljanic, R.; Overbeek, J. C.; Carraro, G.; Tautvaišienė, G.; San Roman, I.; Villanova, S.; Geisler, D.; Muñoz, C.; Jiménez-Esteban, F.; Tang, B.; Gilmore, G.; Alfaro, E. J.; Bensby, T.; Flaccomio, E.; Koposov, S. E.; Korn, A. J.; Pancino, E.; Recio-Blanco, A.; Casey, A. R.; Costado, M. T.; Franciosini, E.; Heiter, U.; Hill, V.; Hourihane, A.; Lardo, C.; de Laverny, P.; Lewis, J.; Monaco, L.; Morbidelli, L.; Sacco, G. G.; Sousa, S. G.; Worley, C. C.; Zaggia, S.

2016-06-01

Context. The nature of the metallicity gradient inside the solar circle (RGC < 8 kpc) is poorly understood, but studies of Cepheids and a small sample of open clusters suggest that it steepens in the inner disk. Aims: We investigate the metallicity gradient of the inner disk using a sample of inner disk open clusters that is three times larger than has previously been studied in the literature to better characterize the gradient in this part of the disk. Methods: We used the Gaia-ESO Survey (GES) [Fe/H] values and stellar parameters for stars in 12 open clusters in the inner disk from GES-UVES data. Cluster mean [Fe/H] values were determined based on a membership analysis for each cluster. Where necessary, distances and ages to clusters were determined via comparison to theoretical isochrones. Results: The GES open clusters exhibit a radial metallicity gradient of -0.10 ± 0.02 dex kpc-1, consistent with the gradient measured by other literature studies of field red giant stars and open clusters in the range RGC ~ 6-12 kpc. We also measure a trend of increasing [Fe/H] with increasing cluster age, as has also been found in the literature. Conclusions: We find no evidence for a steepening of the inner disk metallicity gradient inside the solar circle as earlier studies indicated. The age-metallicity relation shown by the clusters is consistent with that predicted by chemical evolution models that include the effects of radial migration, but a more detailed comparison between cluster observations and models would be premature. Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 188.B-3002 and 193.B-0936. These data products have been processed by the Cambridge Astronomy Survey Unit (CASU) at the Institute of Astronomy, University of Cambridge, and by the FLAMES/UVES reduction team at INAF/Osservatorio Astrofisico di Arcetri. These data have been obtained from the Gaia-ESO Survey Data Archive, prepared and hosted by the Wide Field Astronomy Unit, Institute for Astronomy, University of Edinburgh, which is funded by the UK Science and Technology Facilities Council.Full Table 2 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/591/A37

Millimeter image of the HL Tau Disk: gaps opened by planets?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Hui

2015-10-20

Several observed features which favor planet-induced gaps in the disk are pointed out. Parameters of a two-fluid simulation model are listed, and some model results are shown. It is concluded that (1) interaction between planets, gas, and dust can explain the main features in the ALMA observation; (2) the millimeter image of a disk is determined by the dust profile, which in turn is influenced by planetary masses, viscosity, disk self-gravity, etc.; and (3) models that focus on the complex physics between gas and dust (and planets) are crucial in interpreting the (sub)millimeter images of disks.

[CII] emission from NGC 4258 with SOFIA/FIFI-LS

NASA Astrophysics Data System (ADS)

Fadda, Dario; Appleton, Philip N.; Diaz Santos, Tanio; Togi, Aditya; Ogle, Patrick

2018-06-01

We present the [CII]157.7μm map of the NGC 4258 (M106) galaxy obtained with the FIFI-LS spectrometer onboard SOFIA.M106 contains an active nucleus classified as type 1.9 Seyfert with a warped inner rotating disk of water-vapor masers which allowed for the first high accuracy measurements of the mass of a supermassive black hole in any galaxy. A relativistic jet is thought to be responsible for anomalous radio-continuum spiral arms, which appear several kpc from the center, and extend outwards through the outer disk. These arms do not correlate with the galaxy's underlying stellar spiral structure, and their presence suggest that in the past, the jet has strongly interacted with the galaxy's outer disk , exciting synchrotron radiation. Since that time, a new burst of activity seems to have occurred, creating a compact jet at the core of the galaxy, and two radio hotspots further out associated with optical "bow-shocks". The position angle of this new "active" jet is different from that needed to excited the outer radio arms, presumably because the jet has precessed, perhaps as a result of precession of the axis of the inner warped accretion disk.Our observations reveal three main sources of [CII] emission: two associated with large regions of gas at the ends of the active jet, and a third minor axis filament associated with linear clumps of star formation and dust seen in HST images offset from the nucleus. We combine the SOFIA observations with previous Spitzer mid-IR, Chandra X-ray and VLA radio observations to explore the nature of the detected [CII] emission. In regions along the northern active jet, we see a significant deficiency in the [CII]/FIR ratio, and higher ratios near the ends of the jet. This implies that the jet has changed the conditions of the gas along its length. In several places near the jet, the [CII] emission shows very broad lines, suggestive of enhanced turbulence. Additionally, the minor-axis filament we discovered may represent gas in-falling towards the nucleus perpendicular to the jet. The results provide clues about how radio jets in active galaxies can influence the star formation properties of their host galaxies.

Rotary piston engine equipped with an improved air or fuel injection opening

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sasaki, Y.

An improved air or fuel injection opening is described for a rotary piston engine having a trochoidal inner surface of a center housing and an eccentrically rotating polygonal rotor. The air or fuel injection opening provided in a side housing wall is confined within a region limited so as to be outside of an outer envelope of traces of a side seal and inside an outer corner seal, with the opening having a contour smaller than that of the corner seal.

Evidence for unseen companions around T Tauri stars

NASA Technical Reports Server (NTRS)

Marsh, Kenneth A.; Mahoney, Michael J.

1992-01-01

The observed spectral energy distributions of HK Tau, T Tau, and R Y Tau exhibit shallow (but significant) dips at mid-infrared wavelengths. This behavior can be explained by the existence of discrete gaps in their circumstellar disks since, if the temperature in the disks decreases monotonically outward, a gap would result in a range of "missing" temperatures. The gap centers for the three objects occur at radial distances of 0.5, 1.4, and 1.6 AU, respectively, while the corresponding ratios of outer to inner radii of the gaps are 6:1, 7:1, and 15:1, respectively. Larger mid-infrared dips are observed for SU Aur and GM Aur and are interpreted as correspondingly larger gaps, with almost complete clearing of the inner region of the disk in the latter case. The gaps in all cases are consistent with the tidal effects of either companion stars or planets.

The 3 micron spectrum of the classical Be star Beta Monocerotis A

NASA Technical Reports Server (NTRS)

Sellgren, K.; Smith, R. G.

1992-01-01

A 3.1-3.7-micron spectrum of the classical Be star Beta Mon A is presented at a resolution of lambda/Delta-lambda of 700-800. The spectrum shows strong hydrogen recombination lines, including Pf-delta and a series of Humphreys lines from Hu 19 to Hu 28. The relative recombination line strengths suggest that Pf-delta has a large optical depth. The Humphreys lines have relative strengths consistent with case B and may be optically thin. The line widths observed are broader than the Balmer lines and similar in width to Fe II lines, consistent with a disk model in which optically thinner lines arise primarily from a faster rotating inner disk, while optically thicker lines come mainly from a slower rotating outer disk. The apparent lack of Stark broadening of the Humphreys lines is used to place an upper limit on the circumstellar electron density of about 10 exp 12/cu cm.

Interaction of NGC 2276 with the NGC 2300 group - Fabry-Perot observations of the H-alpha velocity field

NASA Technical Reports Server (NTRS)

Gruendl, Robert A.; Vogel, Stuart N.; Davis, David S.; Mulchaey, John S.

1993-01-01

We report kinematic observations of H-alpha emission from the spiral galaxy NGC 2276 obtained with a Fabry-Perot Camera. The 'bow shock' appearance and enhanced star formation in NGC 2276 have been attributed by Mulchaey et al. (1993) to a ram-pressure interaction with the dense IGM detected in ROSAT observations of the NGC 2300 group of galaxies. Along the 'bow shock' limb of the galaxy, we observe strong H-alpha emission and significant kinematic perturbations located immediately interior to an abrupt decrease in the scale length of the optical disk. Although ram-pressure forces may be important in the evolution of the outer gaseous disk, the peculiar kinematics and the truncation in the stellar disk are difficult to explain in a ram-pressure model; a more likely cause is tidal interaction, probably with the elliptical galaxy NGC 2300.

Active black holes: Relevant plasma structures, regimes and processes involving all phase space

NASA Astrophysics Data System (ADS)

Coppi, Bruno

2011-03-01

The presented theory is motivated by the growing body of experimental information on the characteristics, connected with relevant spectral, time, and space resolutions, of the radiation emission from objects considered as rotating black holes. In the immediate surroundings of these objects, three plasma regions are identified: an innermost Buffer Region, an intermediate Three-regime Region, and a Structured Peripheral Region. In the last region, a Composite Disk Structure made of a sequence of plasma rings corresponding to the formation of closed magnetic surfaces is considered to be present and to allow intermittent accretion flows along the relevant separatrices. The nonlinear ``Master Equation'' describing composite disk structures is derived and solved in appropriate asymptotic limits. A ring configuration, depending on the state of the plasma at the microscopic level: (i) can be excluded from forming given the strongly nonthermal nature of the electron distribution (in momentum space) within the Three-regime Region allowing the onset of a spiral structure; the observed High Frequency Quasi Periodic Oscillations are associated with these tridimensional structures; (ii) may be allowed to propagate to the outer edge of the Buffer Region where successive rings carrying currents in opposite directions are ejected vertically (in opposite directions) and originate the observed jets; or (iii) penetrates in the Three-regime Region and is dissipated before reaching the outer edge of the Buffer Region. The absence of a coherent composite disk structure guiding accretion in the presence of a significant magnetic field background is suggested to characterize quiescent black holes.

OUTWARD MOTION OF POROUS DUST AGGREGATES BY STELLAR RADIATION PRESSURE IN PROTOPLANETARY DISKS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tazaki, Ryo; Nomura, Hideko, E-mail: rtazaki@kusastro.kyoto-u.ac.jp

2015-02-01

We study the dust motion at the surface layer of protoplanetary disks. Dust grains in the surface layer migrate outward owing to angular momentum transport via gas-drag force induced by the stellar radiation pressure. In this study we calculate the mass flux of the outward motion of compact grains and porous dust aggregates by the radiation pressure. The radiation pressure force for porous dust aggregates is calculated using the T-Matrix Method for the Clusters of Spheres. First, we confirm that porous dust aggregates are forced by strong radiation pressure even if they grow to be larger aggregates, in contrast tomore » homogeneous and spherical compact grains, for which radiation pressure efficiency becomes lower when their sizes increase. In addition, we find that the outward mass flux of porous dust aggregates with monomer size of 0.1 μm is larger than that of compact grains by an order of magnitude at the disk radius of 1 AU, when their sizes are several microns. This implies that large compact grains like calcium-aluminum-rich inclusions are hardly transported to the outer region by stellar radiation pressure, whereas porous dust aggregates like chondritic-porous interplanetary dust particles are efficiently transported to the comet formation region. Crystalline silicates are possibly transported in porous dust aggregates by stellar radiation pressure from the inner hot region to the outer cold cometary region in the protosolar nebula.« less

ABUNDANCES OF RED GIANTS IN OLD OPEN CLUSTERS. V. Be 31, Be 32, Be 39, M 67, NGC 188, AND NGC 1193

DOE Office of Scientific and Technical Information (OSTI.GOV)

Friel, Eileen D.; Jacobson, Heather R.; Pilachowski, Catherine A., E-mail: friel@lowell.ed, E-mail: jacob189@msu.ed, E-mail: catyp@astro.indiana.ed

2010-05-15

We present a detailed abundance analysis based on high resolution spectroscopy for 16 stars in the old open clusters Be 31, Be 32, Be 39, M 67, NGC 188, and NGC 1193. Average cluster metallicities of [Fe/H] = -0.30 {+-} 0.02, -0.21 {+-} 0.01, +0.03 {+-} 0.07, +0.12 {+-} 0.02, and -0.22 {+-} 0.14 (s.d.) have been found for Be 32, Be 39, M 67, NGC 188, and NGC 1193, respectively. The two stars observed in the field of Be 31 have disparate radial velocities and elemental abundance patterns, and also disagree with the possible Be 31 star studied bymore » Yong et al. We conclude that membership has yet to be established for this important cluster, and therefore no element abundances measured here or in previous studies of Be 31 should be taken as definitive cluster abundances. A careful comparison of our results for the clusters M 67 and Be 32 to those of other studies shows general good agreement and identifies systematic differences resulting from different analyses. After combination of our results with those of other studies for clusters spanning the full R{sub gc} range of the thin disk, we explore the abundance distributions as a function of R{sub gc} and age for the elements Fe, O, Na, Mg, Al, Si, Ca, Ti, and Ni. As found in previous work, the [Fe/H] gradient appears to be continuous up to R{sub gc} {approx} 13 kpc before flattening in the outer disk. [X/Fe] ratios show a scatter of 0.2-0.3 dex at all R{sub gc}, for all elements considered. The [X/Fe] values of the six clusters analyzed here are consistent with those of other clusters of similar metallicity and Galactocentric location. Our whole cluster sample shows trends of increasing [O/Fe] and [Al/Fe] with age, although these trends vanish with the inclusion of other clusters from the literature. Larger, homogeneous open cluster samples are necessary to verify the existence and magnitude of abundance trends with age.« less

Dust-Corrected Star Formation Rates in Galaxies with Outer Rings

NASA Astrophysics Data System (ADS)

Kostiuk, I.; Silchenko, O.

2018-03-01

The star formation rates SFR, as well as the SFR surface densities ΣSFR and absolute stellar magnitudes MAB, are determined and corrected for interinsic dust absorption for 34 disk galaxies of early morphological types with an outer ring structure and ultraviolet emission from the ring. These characteristic are determined for the outer ring structures and for the galaxies as a whole. Data from the space telescopes GALEX (in the NUV and FUV ultraviolet ranges) and WISE (in the W4 22 μm infrared band) are used. The average relative deviation in the corrected SFR and ΣSFR derived from the NUV and FUV bands is only 19.0%, so their averaged values are used for statistical consideration. The relations between the dust-corrected SFR characteristics, UV colours, the galaxy morphological type, absolute magnitude are illustrated.

The effect of transverse crack upon parametric instability of a rotor-bearing system with an asymmetric disk

NASA Astrophysics Data System (ADS)

Han, Qinkai; Chu, Fulei

2012-12-01

It is well known that either the asymmetric disk or transverse crack brings parametric inertia (or stiffness) excitation to the rotor-bearing system. When both of them appear in a rotor system, the parametric instability behaviors have not gained sufficient attentions. Thus, the effect of transverse crack upon parametric instability of a rotor-bearing system with an asymmetric disk is studied. First, the finite element equations of motion are established for the asymmetric rotor system. Both the open and breathing transverse cracks are taken into account in the model. Then, the discrete state transition matrix (DSTM) method is introduced for numerically acquiring the instability regions. Based upon these, some computations for a practical asymmetric rotor system with open or breathing transverse crack are conducted, respectively. Variations of the primary and combination instability regions induced by the asymmetric disk with the crack depth are observed, and the effect of the orientation angle between the crack and asymmetric disk on various instability regions are discussed in detail. It is shown that for the asymmetric angle around 0, the existence of transverse (either open or breathing) crack has attenuation effect upon the instability regions. Under certain crack depth, the instability regions could be vanished by the transverse crack. When the asymmetric angle is around π/2, increasing the crack depth would enhance the instability regions.

Tornado type wind turbines

DOEpatents

Hsu, Cheng-Ting

1984-01-01

A tornado type wind turbine has a vertically disposed wind collecting tower with spaced apart inner and outer walls and a central bore. The upper end of the tower is open while the lower end of the structure is in communication with a wind intake chamber. An opening in the wind chamber is positioned over a turbine which is in driving communication with an electrical generator. An opening between the inner and outer walls at the lower end of the tower permits radially flowing air to enter the space between the inner and outer walls while a vertically disposed opening in the wind collecting tower permits tangentially flowing air to enter the central bore. A porous portion of the inner wall permits the radially flowing air to interact with the tangentially flowing air so as to create an intensified vortex flow which exits out of the top opening of the tower so as to create a low pressure core and thus draw air through the opening of the wind intake chamber so as to drive the turbine.

Security of patient data when decommissioning ultrasound systems

PubMed Central

2017-01-01

Background Although ultrasound systems generally archive to Picture Archiving and Communication Systems (PACS), their archiving workflow typically involves storage to an internal hard disk before data are transferred onwards. Deleting records from the local system will delete entries in the database and from the file allocation table or equivalent but, as with a PC, files can be recovered. Great care is taken with disposal of media from a healthcare organisation to prevent data breaches, but ultrasound systems are routinely returned to lease companies, sold on or donated to third parties without such controls. Methods In this project, five methods of hard disk erasure were tested on nine ultrasound systems being decommissioned: the system’s own delete function; full reinstallation of system software; the manufacturer’s own disk wiping service; open source disk wiping software for full and just blank space erasure. Attempts were then made to recover data using open source recovery tools. Results All methods deleted patient data as viewable from the ultrasound system and from browsing the disk from a PC. However, patient identifiable data (PID) could be recovered following the system’s own deletion and the reinstallation methods. No PID could be recovered after using the manufacturer’s wiping service or the open source wiping software. Conclusion The typical method of reinstalling an ultrasound system’s software may not prevent PID from being recovered. When transferring ownership, care should be taken that an ultrasound system’s hard disk has been wiped to a sufficient level, particularly if the scanner is to be returned with approved parts and in a fully working state. PMID:28228821

Infrared study of transitional disks in Ophiuchus with Herschel

NASA Astrophysics Data System (ADS)

Rebollido, Isabel; Merín, Bruno; Ribas, Álvaro; Bustamante, Ignacio; Bouy, Hervé; Riviere-Marichalar, Pablo; Prusti, Timo; Pilbratt, Göran L.; André, Philippe; Ábrahám, Péter

2015-09-01

Context. Observations of nearby star-forming regions with the Herschel Space Observatory complement our view of the protoplanetary disks in Ophiuchus with information about the outer disks. Aims: The main goal of this project is to provide new far-infrared fluxes for the known disks in the core region of Ophiuchus and to identify potential transitional disks using data from Herschel. Methods: We obtained PACS and SPIRE photometry of previously spectroscopically confirmed young stellar objects (YSO) in the region and analysed their spectral energy distributions. Results: From an initial sample of 261 objects with spectral types in Ophiuchus, we detect 49 disks in at least one Herschel band. We provide new far-infrared fluxes for these objects. One of them is clearly a new transitional disk candidate. Conclusions: The data from Herschel Space Observatory provides fluxes that complement previous infrared data and that we use to identify a new transitional disk candidate. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Final reduced Herschel maps are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/581/A30Appendix A is available in electronic form at http://www.aanda.orgAll tables are also available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/581/A30

Dust in circumstellar disks

NASA Astrophysics Data System (ADS)

Rodmann, Jens

2006-02-01

This thesis presents observational and theoretical studies of the size and spatial distribution of dust particles in circumstellar disks. Using millimetre interferometric observations of optically thick disks around T Tauri stars, I provide conclusive evidence for the presence of millimetre- to centimetre-sized dust aggregates. These findings demonstrate that dust grain growth to pebble-sized dust particles is completed within less than 1 Myr in the outer disks around low-mass pre-main-sequence stars. The modelling of the infrared spectral energy distributions of several solar-type main-sequence stars and their associated circumstellar debris disks reveals the ubiquity of inner gaps devoid of substantial amounts of dust among Vega-type infrared excess sources. It is argued that the absence of circumstellar material in the inner disks is most likely the result of the gravitational influence of a large planet and/or a lack of dust-producing minor bodies in the dust-free region. Finally, I describe a numerical model to simulate the dynamical evolution of dust particles in debris disks, taking into account the gravitational perturbations by planets, photon radiation pressure, and dissipative drag forces due to the Poynting-Robertson effect and stellar wind. The validity of the code it established by several tests and comparison to semi-analytic approximations. The debris disk model is applied to simulate the main structural features of a ring of circumstellar material around the main-sequence star HD 181327. The best agreement between model and observation is achieved for dust grains a few tens of microns in size locked in the 1:1 resonance with a Jupiter-mass planet (or above) on a circular orbit.

An Optimal Strategy for Accurate Bulge-to-disk Decomposition of Disk Galaxies

NASA Astrophysics Data System (ADS)

Gao, Hua; Ho, Luis C.

2017-08-01

The development of two-dimensional (2D) bulge-to-disk decomposition techniques has shown their advantages over traditional one-dimensional (1D) techniques, especially for galaxies with non-axisymmetric features. However, the full potential of 2D techniques has yet to be fully exploited. Secondary morphological features in nearby disk galaxies, such as bars, lenses, rings, disk breaks, and spiral arms, are seldom accounted for in 2D image decompositions, even though some image-fitting codes, such as GALFIT, are capable of handling them. We present detailed, 2D multi-model and multi-component decomposition of high-quality R-band images of a representative sample of nearby disk galaxies selected from the Carnegie-Irvine Galaxy Survey, using the latest version of GALFIT. The sample consists of five barred and five unbarred galaxies, spanning Hubble types from S0 to Sc. Traditional 1D decomposition is also presented for comparison. In detailed case studies of the 10 galaxies, we successfully model the secondary morphological features. Through a comparison of best-fit parameters obtained from different input surface brightness models, we identify morphological features that significantly impact bulge measurements. We show that nuclear and inner lenses/rings and disk breaks must be properly taken into account to obtain accurate bulge parameters, whereas outer lenses/rings and spiral arms have a negligible effect. We provide an optimal strategy to measure bulge parameters of typical disk galaxies, as well as prescriptions to estimate realistic uncertainties of them, which will benefit subsequent decomposition of a larger galaxy sample.

An Optimal Strategy for Accurate Bulge-to-disk Decomposition of Disk Galaxies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao Hua; Ho, Luis C.

The development of two-dimensional (2D) bulge-to-disk decomposition techniques has shown their advantages over traditional one-dimensional (1D) techniques, especially for galaxies with non-axisymmetric features. However, the full potential of 2D techniques has yet to be fully exploited. Secondary morphological features in nearby disk galaxies, such as bars, lenses, rings, disk breaks, and spiral arms, are seldom accounted for in 2D image decompositions, even though some image-fitting codes, such as GALFIT, are capable of handling them. We present detailed, 2D multi-model and multi-component decomposition of high-quality R -band images of a representative sample of nearby disk galaxies selected from the Carnegie-Irvine Galaxymore » Survey, using the latest version of GALFIT. The sample consists of five barred and five unbarred galaxies, spanning Hubble types from S0 to Sc. Traditional 1D decomposition is also presented for comparison. In detailed case studies of the 10 galaxies, we successfully model the secondary morphological features. Through a comparison of best-fit parameters obtained from different input surface brightness models, we identify morphological features that significantly impact bulge measurements. We show that nuclear and inner lenses/rings and disk breaks must be properly taken into account to obtain accurate bulge parameters, whereas outer lenses/rings and spiral arms have a negligible effect. We provide an optimal strategy to measure bulge parameters of typical disk galaxies, as well as prescriptions to estimate realistic uncertainties of them, which will benefit subsequent decomposition of a larger galaxy sample.« less

Wind-Driven Global Evolution of Protoplanetary Disks

NASA Astrophysics Data System (ADS)

Bai, Xue-Ning

It has been realized in the recent years that magnetized disk winds disk- likely play a decisive role in the global evolution of protoplanetary disks protoplanetary evolution (PPDs). Motivated by recent local simulations local , we first describe a global magnetized disk wind model, from which wind-driven accretion rate -rate wind-driven and wind mass loss rate can be reliably estimated. Both rates are shown to strongly depend on the amount of magnetic flux magnetic threading the disk. Wind kinematics is also affected by thermodynamics in the wind zone (particularly far UV heating/ionization), and the mass loss process loss- can be better termed as "magneto-photoevaporation." We then construct a framework of PPD global evolution global that incorporates wind-driven and viscously driven accretion viscously-driven as well as wind mass loss. For typical PPD accretion rates, the required field strength would lead to wind mass loss rate at least comparable to disk accretion rate, and mass loss is most significant in the outer disk (beyond ˜ 10 AU). Finally, we discuss the transport of magnetic flux in PPDs, which largely governs the long-term evolution long-term of PPDs.

System and method for multi-stage bypass, low operating temperature suppressor for automatic weapons

DOEpatents

Moss, William C.; Anderson, Andrew T.

2015-06-09

The present disclosure relates to a suppressor for use with a weapon. The suppressor may be formed to have a body portion having a bore extending concentric with a bore axis of the weapon barrel. An opening in the bore extends at least substantially circumferentially around the bore. A flow path communicates with the opening and defines a channel for redirecting gasses flowing in the bore out from the bore, through the opening, into a rearward direction in the flow path. The flow path raises a pressure at the opening to generate a Mach disk within the bore at a location approximately coincident with the opening. The Mach disk forms as a virtual baffle to divert at least a portion of the gasses into the opening and into the flow path.

Turbine stator vane segment having internal cooling circuits

DOEpatents

Jones, Raymond Joseph; Burns, James Lee; Bojappa, Parvangada Ganapathy; Jones, Schotsch Margaret

2003-01-01

A turbine stator vane includes outer and inner walls each having outer and inner chambers and a vane extending between the outer and inner walls. The vane includes first, second, third, fourth and fifth cavities for flowing a cooling medium. The cooling medium enters the outer chamber of the outer wall, flows through an impingement plate for impingement cooling of the outer band wall defining in part the hot gas path and through openings in the first, second and fourth cavities for flow radially inwardly, cooling the vane. The spent cooling medium flows into the inner wall and inner chamber for flow through an impingement plate radially outwardly to cool the inner wall. The spent cooling medium flows through the third cavity for egress from the turbine vane segment from the outer wall. The first, second or third cavities contain inserts having impingement openings for impingement cooling of the vane walls. The fifth cavity provides air cooling for the trailing edge.