THE SPINDLE: AN IRRADIATED DISK AND BENT PROTOSTELLAR JET IN ORION

Energy Technology Data Exchange (ETDEWEB)

Bally, John; Youngblood, Allison; Ginsburg, Adam, E-mail: John.Bally@colorado.edu, E-mail: Allison.Youngblood@colorado.edu, E-mail: Adam.Ginsburg@colorado.edu [Department of Astrophysical and Planetary Sciences, University of Colorado, UCB 389, Boulder, CO 80309 (United States)

2012-09-10

We present Hubble Space Telescope observations of a bent, pulsed Herbig-Haro jet, HH 1064, emerging from the young star Parenago 2042 embedded in the H II region NGC 1977 located about 30' north of the Orion Nebula. This outflow contains eight bow shocks in the redshifted western lobe and five bow shocks in the blueshifted eastern lobe. Shocks within a few thousand AU of the source star exhibit proper motions of {approx}160 km s{sup -1} but motions decrease with increasing distance. Parenago 2042 is embedded in a proplyd-a photoevaporating protoplanetary disk. A remarkable set of H{alpha} arcs resembling a spindle surround the redshifted (western) jet. The largest arc with a radius of 500 AU may trace the ionized edge of a circumstellar disk inclined by {approx}30 Degree-Sign . The spindle may be the photoionized edge of either a {approx}3 km s{sup -1} FUV-driven wind from the outer disk or a faster MHD-powered flow from an inner disk. The HH 1064 jet appears to be deflected north by photoablation of the south-facing side of a mostly neutral jet beam. V2412 Ori, located 1' west of Parenago 2042 drives a second bent flow, HH 1065. Both HH 1064 and 1065 are surrounded by LL Ori-type bows marking the boundary between the outflow cavity and the surrounding nebula.

Circumstellar and circumplanetary disks

Science.gov (United States)

Chiang, Eugene

2000-11-01

This thesis studies disks in three astrophysical contexts: (1)protoplanetary disks; (2)the Edgeworth-Kuiper Belt; and (3)planetary rings. We derive hydrostatic, radiative equilibrium models of passive protoplanetary disks surrounding T Tauri and Herbig Ae/Be stars. Each disk is encased by an optically thin layer of superheated dust grains. This layer is responsible for up to ~70% of the disk luminosity at wavelengths between ~5 and 60 μm. The heated disk flares and absorbs more stellar radiation at a given stellocentric distance than a flat disk would. Spectral energy distributions are computed and found to compare favorably with the observed flattish infrared excesses of several young stellar objects. Spectral features from dust grains in the superheated layer appear in emission if the disk is viewed nearly face-on. We present the results of a pencil-beam survey of the Kuiper Belt using the Keck 10-m telescope. Two new objects are discovered. Data from all surveys are pooled to construct the luminosity function from mR = 20 to 27. The cumulative number of objects per square degree, Σ(surface area but the largest bodies contain most of the mass. To order-of-magnitude, 0.2 M⊕ and 1 × 1010 comet progenitors lie between 30 and 50 AU. The classical Kuiper Belt appears truncated at a distance of 50 AU. We propose that rigid precession of narrow eccentric planetary rings surrounding Uranus and Saturn is maintained by a balance of forces due to ring self- gravity, planetary oblateness, and interparticle collisions. Collisional impulses play an especially dramatic role near ring edges. Pressure-induced accelerations are maximal near edges because there (1)velocity dispersions are enhanced by resonant satellite perturbations, and (2)the surface density declines steeply. Remarkably, collisional forces felt by material in the last ~100 m of a ~10 km wide ring can increase equilibrium masses up to a factor of ~100. New ring surface densities are derived which accord with

Basic properties of a stationary accretion disk surrounding a black hole

International Nuclear Information System (INIS)

Hoshi, Reiun

1977-01-01

The structure of a stationary accretion disk surrounding a black hole is studied by means of newly developed basic equations. The basic equations are derived under the assumption that the vertical distribution of disk matter is given by a polytrope. For a Keplerian accretion disk, basic equations reduce to a differential equation of the first order. We have found that solutions of an optically thick accretion disk converge to a limiting value, irrespective of the outer boundary condition. This gives the happy consequence that the inner structure of an optically thick accretion disk is determined irrespective of the outer boundary condition. On the contrary, an optically thin accretion disk shows bimodal behavior, that is, two physically distinct states exist depending on the outer boundary condition imposed at the outer edge of the accretion disk. (auth.)

WATER ICE AT THE SURFACE OF THE HD 100546 DISK

International Nuclear Information System (INIS)

Honda, M.; Kudo, T.; Terada, H.; Takato, N.; Takatsuki, S.; Nakamoto, T.; Inoue, A. K.; Fukagawa, M.; Tamura, M.

2016-01-01

We made near-infrared multicolor imaging observations of a disk around Herbig Be star HD 100546 using Gemini/NICI. K (2.2 μm), H 2 O ice (3.06 μm), and L′ (3.8 μm) disk images were obtained and we found a 3.1 μm absorption feature in the scattered light spectrum, likely due to water ice grains at the disk surface. We compared the observed depth of the ice absorption feature with the disk model based on Oka et al., including the water ice photodesorption effect by stellar UV photons. The observed absorption depth can be explained by both the disk models with and without the photodesorption effect within the measurement accuracy, but the model with photodesorption effects is slightly more favored, implying that the UV photons play an important role in the survival/destruction of ice grains at the Herbig Ae/Be disk surface. Further improvement to the accuracy of the observations of the water ice absorption depth is needed to constrain the disk models

WATER ICE AT THE SURFACE OF THE HD 100546 DISK

Energy Technology Data Exchange (ETDEWEB)

Honda, M. [Department of Physics, Kurume University School of Medicine, 67 Asahi-machi, Kurume, Fukuoka, 830-0011 (Japan); Kudo, T.; Terada, H.; Takato, N. [Subaru Telescope, National Astronomical Observatory of Japan, 650 North A’ohoku Place, Hilo, Hawaii 96720 (United States); Takatsuki, S.; Nakamoto, T. [Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro, Tokyo 152-8551 (Japan); Inoue, A. K. [College of General Education, Osaka Sangyo University, Daito, Osaka 574-8530 (Japan); Fukagawa, M.; Tamura, M. [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)

2016-04-10

We made near-infrared multicolor imaging observations of a disk around Herbig Be star HD 100546 using Gemini/NICI. K (2.2 μm), H{sub 2}O ice (3.06 μm), and L′ (3.8 μm) disk images were obtained and we found a 3.1 μm absorption feature in the scattered light spectrum, likely due to water ice grains at the disk surface. We compared the observed depth of the ice absorption feature with the disk model based on Oka et al., including the water ice photodesorption effect by stellar UV photons. The observed absorption depth can be explained by both the disk models with and without the photodesorption effect within the measurement accuracy, but the model with photodesorption effects is slightly more favored, implying that the UV photons play an important role in the survival/destruction of ice grains at the Herbig Ae/Be disk surface. Further improvement to the accuracy of the observations of the water ice absorption depth is needed to constrain the disk models.

JHKL photometry of three Herbig-Haro jet sources and a nebulous T Tauri star

International Nuclear Information System (INIS)

Vrba, F.J.; Rydgren, A.E.; Zak, D.S.; Computer Sciences Corp., Baltimore, MD; Rensselaer Polytechnic Institute, Troy, NY)

1985-01-01

Infrared sources have been detected at the positions of the Herbig-Haro jet sources HH 30, DG Tau B, and Haro 6-5 B in the Taurus dark cloud complex. The colors of these Herbig-Haro jet sources in the 1-4 micron wavelength range are comparable to those of the dustiest T Tauri stars, while the K magnitudes corrected for likely interstellar extinction are actually somewhat fainter than those oftypical T Tauri stars in this region. These observations are consistent with the view that these Herbig-Haro jet sources are low-mass premain-sequence stars. The nebulous T Tauri star Haro 6-5 was also observed and found to show both a large infrared excess and an intrinsic-polarization of about 3 percent in visible light. Thus this star seems to resemble HL Tau and DG Tau, which have been suggested as examples of young stars with circumstellar disks. 17 references

A STUDY OF RO-VIBRATIONAL OH EMISSION FROM HERBIG Ae/Be STARS

Energy Technology Data Exchange (ETDEWEB)

Brittain, Sean D.; Reynolds, Nickalas [Department of Physics and Astronomy, 118 Kinard Laboratory, Clemson University, Clemson, SC 29634-0978 (United States); Najita, Joan R. [National Optical Astronomy Observatory, 950 N. Cherry Ave., Tucson, AZ 85719 (United States); Carr, John S. [Naval Research Laboratory, Code 7211, Washington, DC 20375 (United States); Ádámkovics, Máté, E-mail: sbritt@clemson.edu [Department of Astronomy, University of California, Berkeley, CA 94720-3411 (United States)

2016-10-20

We present a study of ro-vibrational OH and CO emission from 21 disks around Herbig Ae/Be stars. We find that the OH and CO luminosities are proportional over a wide range of stellar ultraviolet luminosities. The OH and CO line profiles are also similar, indicating that they arise from roughly the same radial region of the disk. The CO and OH emission are both correlated with the far-ultraviolet luminosity of the stars, while the polycyclic aromatic hydrocarbon (PAH) luminosity is correlated with the longer wavelength ultraviolet luminosity of the stars. Although disk flaring affects the PAH luminosity, it is not a factor in the luminosity of the OH and CO emission. These properties are consistent with models of UV-irradiated disk atmospheres. We also find that the transition disks in our sample, which have large optically thin inner regions, have lower OH and CO luminosities than non-transition disk sources with similar ultraviolet luminosities. This result, while tentative given the small sample size, is consistent with the interpretation that transition disks lack a gaseous disk close to the star.

A new Herbig-Haro object in the Gum nebula and its associated star

International Nuclear Information System (INIS)

Graham, J.A.

1991-01-01

Photographic and spectroscopic observations are presented of some faint nebulosity which is associated with the strong IRAS point source 08211 - 4158. Two components are observed. One relatively compact and knotty region has a purely gaseous spectrum characteristic of a low-excitation Herbig-Haro object, while another area shows a spectrum with strong continuum radiation and superposed emission lines which suggest that it is scattering light from an embedded young star. Radial-velocity measurements show that this star is at rest with respect to its surroundings while the Herbig-Haro object has a mean velocity of -38 km/s with respect to its local standard of rest. The evidence favors but does not conclusively show that the source 1 in the area, identified by Campbell and Persson (1988), marks the position of the embedded star which powers the Herbig-Haro object. 13 refs

Gas dynamics in the inner few AU around the Herbig B[e] star MWC297. Indications of a disk wind from kinematic modeling and velocity-resolved interferometric imaging

Science.gov (United States)

Hone, Edward; Kraus, Stefan; Kreplin, Alexander; Hofmann, Karl-Heinz; Weigelt, Gerd; Harries, Tim; Kluska, Jacques

2017-10-01

Aims: Circumstellar accretion disks and outflows play an important role in star formation. By studying the continuum and Brγ-emitting region of the Herbig B[e] star MWC297 with high-spectral and high-spatial resolution we aim to gain insight into the wind-launching mechanisms in young stars. Methods: We present near-infrared AMBER (R = 12 000) and CRIRES (R = 100 000) observations of the Herbig B[e] star MWC297 in the hydrogen Brγ-line. Using the VLTI unit telescopes, we obtained a uv-coverage suitable for aperture synthesis imaging. We interpret our velocity-resolved images as well as the derived two-dimensional photocenter displacement vectors, and fit kinematic models to our visibility and phase data in order to constrain the gas velocity field on sub-AU scales. Results: The measured continuum visibilities constrain the orientation of the near-infrared-emitting dust disk, where we determine that the disk major axis is oriented along a position angle of 99.6 ± 4.8°. The near-infrared continuum emission is 3.6 × more compact than the expected dust-sublimation radius, possibly indicating the presence of highly refractory dust grains or optically thick gas emission in the inner disk. Our velocity-resolved channel maps and moment maps reveal the motion of the Brγ-emitting gas in six velocity channels, marking the first time that kinematic effects in the sub-AU inner regions of a protoplanetary disk could be directly imaged. We find a rotation-dominated velocity field, where the blue- and red-shifted emissions are displaced along a position angle of 24° ± 3° and the approaching part of the disk is offset west of the star. The visibility drop in the line as well as the strong non-zero phase signals can be modeled reasonably well assuming a Keplerian velocity field, although this model is not able to explain the 3σ difference that we measure between the position angle of the line photocenters and the position angle of the dust disk. We find that the fit can be

Multi-Wavelength Interferometric Observations of YSO Disks

Science.gov (United States)

Ragland, Sam; Akeson, R.; Armandroff, T.; Colavita, M.; Cotton, W.; Danchi, W.; Hillenbrand, L.; Millan-Gabet, R.; Ridgway, S. T.; Traub, W.; Wizinowich, P.

2010-01-01

We initiated a multi-color interferometric study of YSO disks in the K, L and N bands using the Keck Interferometer. The initial results on two Herbig Ae/Be stars will be presented. Our observations are sensitive to the radial distribution of temperature in the inner region of the YSO disks. The geometric models show that the apparent size increases linearly with wavelength, suggesting that the disk is extended with a temperature gradient. We will discuss our results in conjunction with the previous measurements of these targets.

THE DISK IMAGING SURVEY OF CHEMISTRY WITH SMA. I. TAURUS PROTOPLANETARY DISK DATA

International Nuclear Information System (INIS)

Oeberg, Karin I.; Qi Chunhua; Andrews, Sean M.; Espaillat, Catherine; Van Kempen, Tim A.; Wilner, David J.; Fogel, Jeffrey K. J.; Bergin, Edwin A.; Pascucci, Ilaria

2010-01-01

Chemistry plays an important role in the structure and evolution of protoplanetary disks, with implications for the composition of comets and planets. This is the first of a series of papers based on data from DISCS, a Submillimeter Array survey of the chemical composition of protoplanetary disks. The six Taurus sources in the program (DM Tau, AA Tau, LkCa 15, GM Aur, CQ Tau, and MWC 480) range in stellar spectral type from M1 to A4 and offer an opportunity to test the effects of stellar luminosity on the disk chemistry. The disks were observed in 10 different lines at ∼3'' resolution and an rms of ∼100 mJy beam -1 at ∼0.5 km s -1 . The four brightest lines are CO 2-1, HCO + 3-2, CN 2 33/4/2 - 1 22/3/1 , and HCN 3-2, and these are detected toward all sources (except for HCN toward CQ Tau). The weaker lines of CN 2 22 -1 11 , DCO + 3-2, N 2 H + 3-2, H 2 CO 3 03 -2 02 , and 4 14 -3 13 are detected toward two to three disks each, and DCN 3-2 only toward LkCa 15. CH 3 OH 4 21 -3 1 2 and c-C 3 H 2 are not detected. There is no obvious difference between the T Tauri and Herbig Ae sources with regard to CN and HCN intensities. In contrast, DCO + , DCN, N 2 H + , and H 2 CO are detected only toward the T Tauri stars, suggesting that the disks around Herbig Ae stars lack cold regions for long enough timescales to allow for efficient deuterium chemistry, CO freeze-out, and grain chemistry.

Protoplanetary disks around intermediate-mass stars: the asset of imaging in the mid-infrared

International Nuclear Information System (INIS)

Doucet, Coralie

2006-01-01

The accrued efficiency of the instruments in many wavelengths has allowed to show that most young stellar objects were surrounded by circumstellar matter distributed in a disk. Direct imaging of such systems is very difficult because of their narrow angular size and their weak luminosity in comparison with the star. Nowadays, 50 % of low-mass pre-main sequence stars, i.e. T Tauri stars, are surrounded by a disk. This proportion is less obvious for intermediate-mass stars, like Herbig Ae stars, that are less numerous and whose direct disk detection is more difficult. Until now, only the interpretation of the Spectral Energy Distribution (SED) of such objects allows to have access to the geometry of the disk. But the solutions are degenerated and several parameters fit the same SED. It is essential to have direct images of the objects, the only evidence of the presence of disks. This PhD allows to show that mid-infrared imaging could rise a part of the degeneracy of the disk's parameters linked to the fit of the SED for several objects and gives constraints on the minimum external radius and inclination of the disk. We present a new observation mode with VISIR, the mid-infrared imager and spectrometer on the VLT (ESO, Chile): the so-called BURST mode. This mode allows to reach the diffraction limit of the telescope. Thanks to mid-infrared imaging with this instrument, we were able, for the first time, to have access to the geometry of a disk (flared structure) around a massive star that was, until now, only deduced from the SED modelling. (author) [fr

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

Energy Technology Data Exchange (ETDEWEB)

Monnier, John D.; Aarnio, Alicia; Adams, Fred C.; Calvet, Nuria; Hartmann, Lee [Astronomy Department, University of Michigan, Ann Arbor, MI 48109 (United States); Harries, Tim J.; Hinkley, Sasha; Kraus, Stefan [University of Exeter, Exeter (United Kingdom); Andrews, Sean; Wilner, David [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 91023 (United States); Espaillat, Catherine [Boston University, Boston, MA (United States); McClure, Melissa [European Southern Observatory, Garching (Germany); Oppenheimer, Rebecca [American Museum of Natural History, New York (United States); Perrin, Marshall [Space Telescope Science Institute, Baltimore, MD (United States)

2017-03-20

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 and 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.

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

International Nuclear Information System (INIS)

Monnier, John D.; Aarnio, Alicia; Adams, Fred C.; Calvet, Nuria; Hartmann, Lee; Harries, Tim J.; Hinkley, Sasha; Kraus, Stefan; Andrews, Sean; Wilner, David; Espaillat, Catherine; McClure, Melissa; Oppenheimer, Rebecca; Perrin, Marshall

2017-01-01

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 and 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.

Observations of radio emission in the 18 cm hydroxyl lines in the direction of Herbig-Haro objects and reflection nebulae

International Nuclear Information System (INIS)

Pashchenko, M.I.; Rudnitskij, G.M.

1980-01-01

In 1978 observations of Herbig-Haro objects and R associations in the 1665 and 1667 MHz main lines of the ground state of the OH molecule have been carried out at the Large radio telescope of the Nancay Radio Astronomy Station (France). Out of the 63 objects searched, the OH emission has been observed in 36 directions. In most cases, the observed line profiles have a simple singlepeak structure, with the line widths of 1-3 km/s. This emission most probably originates in interstellar dust clouds surrounding the Herbig-Haro objects and R associations. Some consequences of the results obtained are briefly discussed. Results of observations show that the quantity of strong maser radio sources near Herbig-Haro objects is not large

HNC IN PROTOPLANETARY DISKS

International Nuclear Information System (INIS)

Graninger, Dawn; Öberg, Karin I.; Qi, Chunhua; Kastner, Joel

2015-01-01

The distributions and abundances of small organics in protoplanetary disks are potentially powerful probes of disk physics and chemistry. HNC is a common probe of dense interstellar regions and the target of this study. We use the Submillimeter Array (SMA) to observe HNC 3–2 toward the protoplanetary disks around the T Tauri star TW Hya and the Herbig Ae star HD 163296. HNC is detected toward both disks, constituting the first spatially resolved observations of HNC in disks. We also present SMA observations of HCN 3–2 and IRAM 30 m observations of HCN and HNC 1–0 toward HD 163296. The disk-averaged HNC/HCN emission ratio is 0.1–0.2 toward both disks. Toward TW Hya, the HNC emission is confined to a ring. The varying HNC abundance in the TW Hya disk demonstrates that HNC chemistry is strongly linked to the disk physical structure. In particular, the inner rim of the HNC ring can be explained by efficient destruction of HNC at elevated temperatures, similar to what is observed in the ISM. However, to realize the full potential of HNC as a disk tracer requires a combination of high SNR spatially resolved observations of HNC and HCN and disk-specific HNC chemical modeling

HNC IN PROTOPLANETARY DISKS

Energy Technology Data Exchange (ETDEWEB)

Graninger, Dawn; Öberg, Karin I.; Qi, Chunhua [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Kastner, Joel, E-mail: dgraninger@cfa.harvard.edu [Center for Imaging Science, School of Physics and Astronomy, and Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623 (United States)

2015-07-01

The distributions and abundances of small organics in protoplanetary disks are potentially powerful probes of disk physics and chemistry. HNC is a common probe of dense interstellar regions and the target of this study. We use the Submillimeter Array (SMA) to observe HNC 3–2 toward the protoplanetary disks around the T Tauri star TW Hya and the Herbig Ae star HD 163296. HNC is detected toward both disks, constituting the first spatially resolved observations of HNC in disks. We also present SMA observations of HCN 3–2 and IRAM 30 m observations of HCN and HNC 1–0 toward HD 163296. The disk-averaged HNC/HCN emission ratio is 0.1–0.2 toward both disks. Toward TW Hya, the HNC emission is confined to a ring. The varying HNC abundance in the TW Hya disk demonstrates that HNC chemistry is strongly linked to the disk physical structure. In particular, the inner rim of the HNC ring can be explained by efficient destruction of HNC at elevated temperatures, similar to what is observed in the ISM. However, to realize the full potential of HNC as a disk tracer requires a combination of high SNR spatially resolved observations of HNC and HCN and disk-specific HNC chemical modeling.

Nature and origin of Herbig-Haro objects

International Nuclear Information System (INIS)

Schwartz, R.D.; Arizona Univ., Tucson)

1985-01-01

A brief description of the nature of Herbig-Haro nebulae is given, and the shock-wave origin of the nebulae is discussed. Kinematical evidence suggests that Herbig-Haro objects are ejected in bipolar flows from young stars. Evidence from infrared observations of the stars that excite Herbig-Haro objects is summarized; these stars appear to be T Tauri stars. The origin of these nebulae is discussed emphasizing energy required to power them, and a number of questions are posed pertaining to outflow mechanisms associated with the exciting stars

X-rays from HD 100546- A Young Herbig Star Orbited by Giant Protoplanets

Science.gov (United States)

Skinner, Stephen

A protoplanetary system consisting of at least two giant planets has beendetected orbiting the young nearby Herbig Be star HD 100546. The inner protoplanet orbits inside a gap within 14 AU of the star and is exposed to strong stellar UV and X-ray radiation. The detection of very warm disk gas provides evidence that stellar heating is affecting physical conditions in the planet-forming environment. We obtained a deep 74 ksec X-ray observation of HD 100546 in 2015 with XMM-Newton yielding an excellent-quality spectrum. We propose here to analyze the XMM-Newton data to determine the X-ray ionization and heating rates in the disk. X-ray ionization and heating affect the thermal and chemical structure of the disk and are key parameters for constructing realistic planet formation models. We are requesting ADAP funding to support the analysis and publication of this valuable XMM-Newton data set, which is now in the public archive.

CYANIDE PHOTOCHEMISTRY AND NITROGEN FRACTIONATION IN THE MWC 480 DISK

Energy Technology Data Exchange (ETDEWEB)

Guzmán, V. V.; Öberg, K. I.; Loomis, R.; Qi, C., E-mail: vguzman@cfa.harvard.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

2015-11-20

HCN is a commonly observed molecule in Solar System bodies and in interstellar environments. Its abundance with respect to CN is a proposed tracer of UV exposure. HCN is also frequently used to probe the thermal history of objects, by measuring its degree of nitrogen fractionation. To address the utility of HCN as a probe of disks, we present Atacama Large (sub-) Millimeter Array observations of CN, HCN, H{sup 13}CN, and HC{sup 15}N toward the protoplanetary disk around Herbig Ae star MWC 480, and of CN and HCN toward the disk around T Tauri star DM Tau. Emission from all molecules is clearly detected and spatially resolved, including the first detection of HC{sup 15}N in a disk. Toward MWC 480, CN emission extends radially more than 1″ exterior to the observed cut-off of HCN emission. Quantitative modeling further reveals very different radial abundance profiles for CN and HCN, with best-fit outer cut-off radii of >300 AU and 110 ± 10 AU, respectively. This result is in agreement with model predictions of efficient HCN photodissociation into CN in the outer-part of the disk where the vertical gas and dust column densities are low. No such difference in CN and HCN emission profiles are observed toward DM Tau, suggestive of different photochemical structures in Herbig Ae and T Tauri disks. We use the HCN isotopologue data toward the MWC 480 disk to provide the first measurement of the {sup 14}N/{sup 15}N ratio in a disk. We find a low disk averaged {sup 14}N/{sup 15}N ratio of 200 ± 100, comparable to what is observed in cloud cores and comets, demonstrating interstellar inheritance and/or efficient nitrogen fractionation in this disk.

Herbig-Haro objects and T Tauri nebulae

International Nuclear Information System (INIS)

Boehm, K.H.

1975-01-01

The empirical information about Herbig-Haro objects and T Tauri nebulae is summarized. We emphasize especially the importance of the spectroscopic and spectrophotometric data. Relative and (preliminary) absolute emission line fluxes are presented and discussed. We consider the radial velocity data and the detection of a faint blue continuum in Herbig-Haro objects as important from a theoretical point of view. The direct interpretation of the emission line spectra is simple and leads to values of the electron temperature, electron density, density inhomogeneities, filling factors, degree of ionization and chemical abundances. The relevant procedures are discussed in some detail. The possible role of the Herbig-Haro objects in the early phases of stellar evolution is discussed. (orig./BJ) [de

MID-INFRARED IMAGING OF THE TRANSITIONAL DISK OF HD 169142: MEASURING THE SIZE OF THE GAP

Energy Technology Data Exchange (ETDEWEB)

Honda, M. [Department of Mathematics and Physics, Faculty of Science, Kanagawa University, 2946 Tsuchiya, Hiratsuka, Kanagawa 259-1293 (Japan); Maaskant, Koen; Waters, L. B. F. M.; Dominik, C.; Mulders, G. D. [Astronomical Institute Anton Pannekoek, University of Amsterdam, P.O. Box 94249, 1090 GE Amsterdam (Netherlands); Okamoto, Y. K. [Institute of Astrophysics and Planetary Sciences, Faculty of Science, Ibaraki University, 2-1-1 Bunkyo, Mito, Ibaraki 310-8512 (Japan); Kataza, H. [Department of Infrared Astrophysics, Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510 (Japan); Fukagawa, M. [Department of Earth and Space Science, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043 (Japan); Tielens, A. G. G. M. [Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands); Min, M. [Astronomical Institute Utrecht, Utrecht University, P.O. Box 80000, 3508 TA Utrecht (Netherlands); Yamashita, T. [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Fujiyoshi, T.; Fujiwara, H. [Subaru Telescope, National Astronomical Observatory of Japan, 650 North A' ohoku Place, Hilo, HI 96720 (United States); Miyata, T.; Sako, S. [Institute of Astronomy, School of Science, University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015 (Japan); Sakon, I.; Onaka, T. [Department of Astronomy, Graduate School of Science, University of Tokyo, Bunkyo-ku, Tokyo 113-0033 (Japan)

2012-06-20

The disk around the Herbig Ae star HD 169142 was imaged and resolved at 18.8 and 24.5 {mu}m using Subaru/COMICS. We interpret the observations using a two-dimensional radiative transfer model and find evidence for the presence of a large gap. The mid-infrared images trace dust that is emitted at the onset of a strong rise in the spectral energy distribution (SED) at 20 {mu}m, and are therefore very sensitive to the location and characteristics of the inner wall of the outer disk and its dust. We determine the location of the wall to be 23{sup +3}{sub -5} AU from the star. An extra component of hot dust must exist close to the star. We find that a hydrostatic optically thick inner disk does not produce enough flux in the near-infrared, and an optically thin, geometrically thick component is our solution to fit the SED. Considering the recent findings of gaps and holes in a number of Herbig Ae/Be group I disks, we suggest that such disk structures may be common in group I sources. Classification as group I should be considered a strong case for classification as a transitional disk, though improved imaging surveys are needed to support this speculation.

MID-INFRARED IMAGING OF THE TRANSITIONAL DISK OF HD 169142: MEASURING THE SIZE OF THE GAP

International Nuclear Information System (INIS)

Honda, M.; Maaskant, Koen; Waters, L. B. F. M.; Dominik, C.; Mulders, G. D.; Okamoto, Y. K.; Kataza, H.; Fukagawa, M.; Tielens, A. G. G. M.; Min, M.; Yamashita, T.; Fujiyoshi, T.; Fujiwara, H.; Miyata, T.; Sako, S.; Sakon, I.; Onaka, T.

2012-01-01

The disk around the Herbig Ae star HD 169142 was imaged and resolved at 18.8 and 24.5 μm using Subaru/COMICS. We interpret the observations using a two-dimensional radiative transfer model and find evidence for the presence of a large gap. The mid-infrared images trace dust that is emitted at the onset of a strong rise in the spectral energy distribution (SED) at 20 μm, and are therefore very sensitive to the location and characteristics of the inner wall of the outer disk and its dust. We determine the location of the wall to be 23 +3 –5 AU from the star. An extra component of hot dust must exist close to the star. We find that a hydrostatic optically thick inner disk does not produce enough flux in the near-infrared, and an optically thin, geometrically thick component is our solution to fit the SED. Considering the recent findings of gaps and holes in a number of Herbig Ae/Be group I disks, we suggest that such disk structures may be common in group I sources. Classification as group I should be considered a strong case for classification as a transitional disk, though improved imaging surveys are needed to support this speculation.

EVOLUTION OF THE DUST/GAS ENVIRONMENT AROUND HERBIG Ae/Be STARS

International Nuclear Information System (INIS)

Liu Tie; Zhang Huawei; Wu Yuefang; Qin Shengli; Miller, Martin

2011-01-01

Using the KOSMA 3 m telescope, 54 Herbig Ae/Be (HAe/Be) stars were surveyed in CO and 13 CO emission lines. The properties of the stars and their circumstellar environments were studied by fitting spectral energy distributions (SEDs). The mean line width of 13 CO (2-1) lines of this sample is 1.87 km s -1 . The average column density of H 2 is found to be 4.9 x 10 21 cm -2 for stars younger than 10 6 yr, while this drops to 2.5 x 10 21 cm -2 for those older than 10 6 yr. No significant difference is found among the SEDs of HAe and HBe stars of the same age. Infrared excess decreases with age, envelope masses and envelope accretion rates decease with age after 10 5 yr, the average disk mass of the sample is 3.3 x 10 -2 M sun , the disk accretion rate decreases more slowly than the envelope accretion rate, and a strong correlation between the CO line intensity and the envelope mass is found.

H2 emission from Herbig-Haro objects

International Nuclear Information System (INIS)

Elias, J.H.

1980-01-01

Molecular hydrogen emission lines have been detected in six Herbig-Haro objects. The line intensities suggest tha the H 2 emission arises in a moderate-density, shock-heated gas, consistent with evidence for a similar origin of the visible emission-line spectra in Herbig-Haro objects. Indirect arguments indicate that the typical H 2 line widths are less than 70 km s -1 and that typical helicentric radial velocities are no more than 30 km s -1 in magnitude

A statistical spectropolarimetric study of Herbig Ae/Be stars

Science.gov (United States)

Ababakr, K. M.; Oudmaijer, R. D.; Vink, J. S.

2017-11-01

We present H α linear spectropolarimetry of a large sample of Herbig Ae/Be stars. Together with newly obtained data for 17 objects, the sample contains 56 objects, the largest such sample to date. A change in linear polarization across the H α line is detected in 42 (75 per cent) objects, which confirms the previous finding that the circumstellar environment around these stars on small spatial scales has an asymmetric structure, which is typically identified with a disc. A second outcome of this research is that we confirm that Herbig Ae stars are similar to T Tauri stars in displaying a line polarization effect, while depolarization is more common among Herbig Be stars. This finding had been suggested previously to indicate that Herbig Ae stars form in the same manner than T Tauri stars through magnetospheric accretion. It appears that the transition between these two differing polarization line effects occurs around the B7-B8 spectral type. This would in turn not only suggest that Herbig Ae stars accrete in a similar fashion as lower mass stars, but also that this accretion mechanism switches to a different type of accretion for Herbig Be stars. We report that the magnitude of the line effect caused by electron scattering close to the stars does not exceed 2 per cent. Only a very weak correlation is found between the magnitude of the line effect and the spectral type or the strength of the H α line. This indicates that the detection of a line effect only relies on the geometry of the line-forming region and the geometry of the scattering electrons.

Discovery of a point-like source and a third spiral arm in the transition disk around the Herbig Ae star MWC 758

Science.gov (United States)

Reggiani, M.; Christiaens, V.; Absil, O.; Mawet, D.; Huby, E.; Choquet, E.; Gomez Gonzalez, C. A.; Ruane, G.; Femenia, B.; Serabyn, E.; Matthews, K.; Barraza, M.; Carlomagno, B.; Defrère, D.; Delacroix, C.; Habraken, S.; Jolivet, A.; Karlsson, M.; Orban de Xivry, G.; Piron, P.; Surdej, J.; Vargas Catalan, E.; Wertz, O.

2018-03-01

Context. Transition disks offer the extraordinary opportunity to look for newly born planets and to investigate the early stages of planet formation. Aim. In this context we observed the Herbig A5 star MWC 758 with the L'-band vector vortex coronagraph installed in the near-infrared camera and spectrograph NIRC2 at the Keck II telescope, with the aim of unveiling the nature of the spiral structure by constraining the presence of planetary companions in the system. Methods: Our high-contrast imaging observations show a bright (ΔL' = 7.0 ± 0.3 mag) point-like emission south of MWC 758 at a deprojected separation of 20 au (r = 0.''111 ± 0.''004) from the central star. We also recover the two spiral arms (southeast and northwest), already imaged by previous studies in polarized light, and discover a third arm to the southwest of the star. No additional companions were detected in the system down to 5 Jupiter masses beyond 0.''6 from the star. Results: We propose that the bright L'-band emission could be caused by the presence of an embedded and accreting protoplanet, although the possibility of it being an asymmetric disk feature cannot be excluded. The spiral structure is probably not related to the protoplanet candidate, unless on an inclined and eccentric orbit, and it could be due to one (or more) yet undetected planetary companions at the edge of or outside the spiral pattern. Future observations and additional simulations will be needed to shed light on the true nature of the point-like source and its link with the spiral arms. The reduced images (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/611/A74

Ionization of Polycyclic Aromatic Hydrocarbon Molecules around the Herbig Ae/be ENVIRONMENT*

Science.gov (United States)

Sakon, Itsuki; Onaka, Takashi; Okamoto, Yoshiko K.; Kataza, Hirokazu; Kaneda, Hidehiro; Honda, Mitsuhiko

We present the results of mid-infrared N-band spectroscopy of the Herbig Ae/Be system MWC1080 using the Cooled Mid-Infrared Camera and Spectrometer (COMICS) on board the 8 m Subaru Telescope. The MWC1080 has a geometry such that the diffuse nebulous structures surround the central Herbig B0 type star. We focus on the properties of polycyclic aromatic hydrocarbons (PAHs) and PAH-like species, which are thought to be the carriers of the unidentified infrared (UIR) bands in such environments. A series of UIR bands at 8.6, 11.0, 11.2, and 12.7 μm is detected throughout the system and we find a clear increase in the UIR 11.0 μm/11.2 μm ratio in the vicinity of the central star. Since the UIR 11.0 μm feature is attributed to a solo-CH out-of-plane wagging mode of cationic PAHs while the UIR 11.2 μm feature to a solo-CH out-of-plane bending mode of neutral PAHs, the large 11.0 μm/11.2 μm ratio directly indicates a promotion of the ionization of PAHs near the central star.

Optical polarization studies of Herbig-Haro objects: Pt. 4

International Nuclear Information System (INIS)

Scarrott, S.M.

1988-01-01

Optical polarization maps are presented for the various nebulosities of the HH34 complex in the L1641 dark cloud. The Herbig-Haro object HH34 and its associated optical jet are unpolarized but their source of excitation (HH34-IRS) is the illuminating star of a reflection nebula which envelops the jet and extends as far as HH34. The optical polarization of HH34-IRS suggests that it is surrounded by a circumstellar disc which collimates the outflows in some manner. There is other reflection nebulosity in the region illuminated by a faint star which we identify as the optical counterpart of HH34-IRS5. We have also discovered a small bipolar reflection nebula approximately 20 arcsec west of HH34-IRS. (author)

On the polarization of Herbig Ae/Be star radiation

Energy Technology Data Exchange (ETDEWEB)

Petrova, N I; Shevchenko, V S

1987-08-01

Results of multicolor UBVRI polarimetry of 14 Herbig Ae/Be stars including 7 stars for which observations of polarization have been made for the first time are presented. 6 bright Herbig Ae/Be stars (As 441, AS 442, LK H..cap alpha..134, LK H..cap alpha..135, Lk H..cap alpha..169 and V517 Cyg) which belong to star formation region connected with IC 5070 show the polarization from 1 to 4.5. per cent with similar theta (approx. 180 deg) (basically of interstellar nature). The polarimetrical variability of BD+46 deg 3471, BD+65 deg 1637, HD 200775 and Lk H..cap alpha..234 is confirmed. Mechanismes of polarization in Herbig Ae/Be stars in circumstellar formations are discussed.

C2D spitzer-IRS spectra of disks around T tauri stars : II. PAH emission features

NARCIS (Netherlands)

Geers, V. C.; Augereau, J. -C; Pontoppidan, K. M.; Dullemond, C. P.; Visser, R.; Kessler-Silacci, J. E.; Evans, N. J.; van Dishoeck, E. F.; Blake, G. A.; Boogert, A. C. A.; Lahuis, F.; Merin, B.

Aims. We search for Polycyclic Aromatic Hydrocarbon (PAH) features towards young low-mass (T Tauri) stars and compare them with surveys of intermediate mass (Herbig Ae/Be) stars. The presence and strength of the PAH features are interpreted with disk radiative transfer models exploring the PAH

Einstein X-ray observations of Herbig Ae/Be stars

Science.gov (United States)

Damiani, F.; Micela, G.; Sciortino, S.; Harnden, F. R., Jr.

1994-01-01

We have investigated the X-ray emission from Herbig Ae/Be stars, using the full set of Einstein Imaging Proportional Counter (IPC) observations. Of a total of 31 observed Herbig stars, 11 are confidently identified with X-ray sources, with four additonal dubious identifications. We have used maximum likelihood luminosity functions to study the distribution of X-ray luminosity, and we find that Be stars are significantly brighter in X-rays than Ae stars and that their X-ray luminosity is independent of projected rotational velocity v sin i. The X-ray emission is instead correlated with stellar bolometric luminosity and with effective temperature, and also with the kinetic luminosity of the stellar wind. These results seem to exclude a solar-like origin for the X-ray emission, a possibility suggested by the most recent models of Herbig stars' structure, and suggest an analogy with the X-ray emission of O (and early B) stars. We also observe correlations between X-ray luminosity and the emission at 2.2 microns (K band) and 25 microns, which strengthen the case for X-ray emission of Herbig stars originating in their circumstellar envelopes.

Few Skewed Results from IOTA Interferometer YSO Disk Survey

Science.gov (United States)

Monnier, J. D.; Millan-Gabet, R.; Berger, J.-P.; Pedretti, E.; Traub, W.; Schloerb, F. P.

2005-12-01

The 3-telescope IOTA interferometer is capable of measuring closure phases for dozens of Herbig Ae/Be stars in the near-infrared. The closure phase unambiguously identifies deviations from centro-symmetry (i.e., skew) in the brightness distribution, at the scale of 4 milliarcseconds (sub-AU physical scales) for our work. Indeed, hot dust emission from the inner circumstellar accretion disk is expected to be skewed for (generic) flared disks viewed at intermediate inclination angles, as has been observed for LkHa 101. Surprisingly, we find very little evidence for skewed disk emission in our IOTA3 sample, setting strong constraints on the geometry of the inner disk. In particular, we rule out the currently-popular model of a VERTICAL hot inner wall of dust at the sublimation radius. Instead, our data is more consistent with a curved inner wall that bends away from the midplane as might be expected from the pressure-dependence of dust sublimation or limited absorption of stellar luminosity in the disk midplane by gas.

Spiral Arms in the Asymmetrically Illuminated Disk of MWC 758 and Constraints on Giant Planets

Science.gov (United States)

Grady, C. A.; Muto, T.; Hashimoto, J.; Fukagawa, M.; Currie, T.; Biller, B.; Thalmann, C.; Sitko, M. L.; Russell, R.; Wisniewski, J.;

Observations of the 18-cm OH lines in Herbig--Haro objects and reflection nebulae

International Nuclear Information System (INIS)

Pashchenko, M.I.; Rudnitskii, G.M.

1980-01-01

In 1978 various Herbig--Haro objects and R-associations (containing reflection nebulae) were observed in the principal (1665, 1667 MHz) lines of the ground state of the hydroxyl molecule with the large radio telescope of the Station Radioastronomique de Nancay. OH emission was detected near 36 of the 63 objects examined. In most cases the line profiles have a simple, single-peaked structure, with a line width of 1--3 km/sec. The OH emission probably originates in interstellar dust clouds surrounding the HH objects and R-associations. Some implications of these results are discussed briefly

Dust Density Distribution and Imaging Analysis of Different Ice Lines in Protoplanetary Disks

Energy Technology Data Exchange (ETDEWEB)

Pinilla, P. [Department of Astronomy/Steward Observatory, The University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Pohl, A. [Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany); Stammler, S. M.; Birnstiel, T., E-mail: pinilla@email.arizona.edu [University Observatory, Faculty of Physics, Ludwig-Maximilians-Universität München, Scheinerstr. 1, D-81679 Münich (Germany)

2017-08-10

Recent high angular resolution observations of protoplanetary disks at different wavelengths have revealed several kinds of structures, including multiple bright and dark rings. Embedded planets are the most used explanation for such structures, but there are alternative models capable of shaping the dust in rings as it has been observed. We assume a disk around a Herbig star and investigate the effect that ice lines have on the dust evolution, following the growth, fragmentation, and dynamics of multiple dust size particles, covering from 1 μ m to 2 m sized objects. We use simplified prescriptions of the fragmentation velocity threshold, which is assumed to change radially at the location of one, two, or three ice lines. We assume changes at the radial location of main volatiles, specifically H{sub 2}O, CO{sub 2}, and NH{sub 3}. Radiative transfer calculations are done using the resulting dust density distributions in order to compare with current multiwavelength observations. We find that the structures in the dust density profiles and radial intensities at different wavelengths strongly depend on the disk viscosity. A clear gap of emission can be formed between ice lines and be surrounded by ring-like structures, in particular between the H{sub 2}O and CO{sub 2} (or CO). The gaps are expected to be shallower and narrower at millimeter emission than at near-infrared, opposite to model predictions of particle trapping. In our models, the total gas surface density is not expected to show strong variations, in contrast to other gap-forming scenarios such as embedded giant planets or radial variations of the disk viscosity.

CN rings in full protoplanetary disks around young stars as probes of disk structure

Science.gov (United States)

Cazzoletti, P.; van Dishoeck, E. F.; Visser, R.; Facchini, S.; Bruderer, S.

2018-01-01

Aims: Bright ring-like structure emission of the CN molecule has been observed in protoplanetary disks. We investigate whether such structures are due to the morphology of the disk itself or if they are instead an intrinsic feature of CN emission. With the intention of using CN as a diagnostic, we also address to which physical and chemical parameters CN is most sensitive. Methods: A set of disk models were run for different stellar spectra, masses, and physical structures via the 2D thermochemical code DALI. An updated chemical network that accounts for the most relevant CN reactions was adopted. Results: Ring-shaped emission is found to be a common feature of all adopted models; the highest abundance is found in the upper outer regions of the disk, and the column density peaks at 30-100 AU for T Tauri stars with standard accretion rates. Higher mass disks generally show brighter CN. Higher UV fields, such as those appropriate for T Tauri stars with high accretion rates or for Herbig Ae stars or for higher disk flaring, generally result in brighter and larger rings. These trends are due to the main formation paths of CN, which all start with vibrationally excited H_2^* molecules, that are produced through far ultraviolet (FUV) pumping of H2. The model results compare well with observed disk-integrated CN fluxes and the observed location of the CN ring for the TW Hya disk. Conclusions: CN rings are produced naturally in protoplanetary disks and do not require a specific underlying disk structure such as a dust cavity or gap. The strong link between FUV flux and CN emission can provide critical information regarding the vertical structure of the disk and the distribution of dust grains which affects the UV penetration, and could help to break some degeneracies in the SED fitting. In contrast with C2H or c-C3H2, the CN flux is not very sensitive to carbon and oxygen depletion.

Observations of the 63 micron forbidden O I line in Herbig-Haro objects

International Nuclear Information System (INIS)

Cohen, M.; Hollenbach, D.J.; Haas, M.R.; Erickson, E.F.

1988-01-01

The paper presents observations of the 63 micron forbidden O I line from Herbig-Haro objects and their exciting stars. Forbidden O I 63 micron emission is detected toward the HH-exciting stars T Tau, DG Tau, L1551 IRS 5, and toward the HH objects HH 7-11, HH 42A, and HH 43 which are displaced from their exciting stars. The forbidden O I emission is associated with these flows on the basis of its spatial coincidence and its negative radial velocities. If the exciting stars drive bipolar flows in which the 63 micron emission follows that at 6300 A, the absence of redshifted 63 micron lines from the three exciting stars might indicate that the disks hypothesized to overlie the receding lobes of these flows are still optically thick in the far-infrared. 50 references

Studies of Young, Star-forming Circumstellar Disks

Science.gov (United States)

Bae, Jaehan

2017-08-01

. When a planet forms in a disk, the gravitational interaction between the planet and disk can create structures, such as spiral arms and gaps. In Chapter 5, I compared the disk structures formed by planetary companions in numerical simulations with the observed structures in the disk surrounding an 8 Myr-old Herbig Ae star SAO 206462. Based on the experiments, I made predictions for the mass and position of a currently unrevealed planet, which can help guide future observations to search for more conclusive evidence for the existence of a planetary companion in the system. In Chapter 6, I showed for the first time in global simulation domains that spiral waves, driven for instance by planets or gravitational instability, can be unstable due to resonant interactions with inertial modes, breaking into turbulence. In Chapter 7, I showed that the spiral wave instability operates on the waves launched by planets and that the resulting turbulence can significantly stir up solid particles from the disk midplane. The stirring of solid particles can have influences on the observation appearance of the parent disk and on the subsequent assembly of planetary bodies in the disk. Finally, in Chapter 8, I investigated the dispersal of circumstellar disks via photoevaporative winds, finding that the photoevaporative loss alone, coupled with a range of initial angular momenta of protostellar clouds, can explain the observed decline of the disk frequency with increasing age. The findings and future possibilities are summarized in Chapter 9.

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

Science.gov (United States)

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.

Emission line spectra of Herbig-Haro objects

International Nuclear Information System (INIS)

Brugel, E.W.; Boehm, K.H.; Mannery, E.

1981-01-01

Spectrophotometric data have been obtained for 12 Herbig-Haro nebulae with the multichannel spectrometer on the Mt. Palomar 5.08 m telescope and with the image intensified dissector scanner on the Kitt Peak 2.13 m telescope. Optical emission line fluxes are presented for the following Herbig-Haro objects: H-H 1 (NW), H-H 1 (SE), H-H 2A, H-H 2G, H-H 2H, H-H 3, H-H 7, H-H 11, H-H 24A, H-H 30, H-H 32, and H-H 40. Values for the electron temperature and electron density have been determined for 10 of these condensations. Significant inhomogeneities in the line-forming regions of these H-H objects are indicated by the derived N/sub e/-T/sub e/ diagrams. Empirical two-component density models have been constructed to interpret the emission line spectra of the five brightest condensations. Slightly less satisfactory homogeneous models are presented for the remaining five objects

Herbig-Haro objects

International Nuclear Information System (INIS)

Schwartz, R.D.

1983-01-01

Progress in the understanding of Herbig-Haro (HH) objects is reviewed. The results of optical studies of the proper motions and alignments, variability, and polarization of HH objects and the results of spectroscopic studies are discussed. Ground-based infrared studies and far-infrared observations are reviewed. Findings on the properties of molecular clouds associated with HH objects, on gas flows associated with HH IR stars, on maser emission, and on radio continuum observations are considered. A history of proposed excitation mechanisms for HH objects is briefly presented, and the salient shock-wave calculations aimed at synthesizing the spectra of HH objects are summarized along with hypotheses that have been advanced about the origin of the objects. 141 references

A study of dust properties in the inner sub-au region of the Herbig Ae star HD 169142 with VLTI/PIONIER

Science.gov (United States)

Chen, L.; Kóspál, Á.; Ábrahám, P.; Kreplin, A.; Matter, A.; Weigelt, G.

2018-01-01

Context. An essential step to understanding protoplanetary evolution is the study of disks that contain gaps or inner holes. The pre-transitional disk around the Herbig star HD 169142 exhibits multi-gap disk structure, differentiated gas and dust distribution, planet candidates, and near-infrared fading in the past decades, which make it a valuable target for a case study of disk evolution. Aims: Using near-infrared interferometric observations with VLTI/PIONIER, we aim to study the dust properties in the inner sub-au region of the disk in the years 2011-2013, when the object is already in its near-infrared faint state. Methods: We first performed simple geometric modeling to characterize the size and shape of the NIR-emitting region. We then performed Monte-Carlo radiative transfer simulations on grids of models and compared the model predictions with the interferometric and photometric observations. Results: We find that the observations are consistent with optically thin gray dust lying at Rin 0.07 au, passively heated to T 1500 K. Models with sub-micron optically thin dust are excluded because such dust will be heated to much higher temperatures at similar distance. The observations can also be reproduced with a model consisting of optically thick dust at Rin 0.06 au, but this model is plausible only if refractory dust species enduring 2400 K exist in the inner disk. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programs 190.C-963 and 087.C-0709.

Time-dependent bow shocks and the condensation structure of Herbig-Haro objects

International Nuclear Information System (INIS)

Raga, A.C.; Bohm, K.H.

1987-01-01

Some Herbig-Haro objects show a structure which appears to look like a bow shock, but also show a number of condensations superposed on this bow-shaped structure. In the case of HH 1 and HH 2 considerably different proper motions have been measured for the individual condensations. It is, however, very hard to explain why the condensations remain so close to each other if they are indeed separate entities. In this paper it is shown that an interpretation of the whole Herbig-Haro object as a single, time-dependent bow shock provides a natural explanation for the occurrence of condensations (which in numerical calculations appear to be associated with thermal instabilities in the postshock flow) with different proper motions. To this effect, time-dependent, axisymmetric, nonadiabatic bow shock models have been developed from which predictions were obtained for spatially resolved H-alpha intensity maps, and then these predictions are compared qualitatively with observations of a few Herbig-Haro objects. 57 references

A Survey of CH3CN and HC3N in Protoplanetary Disks

Science.gov (United States)

Bergner, Jennifer B.; Guzmán, Viviana G.; Öberg, Karin I.; Loomis, Ryan A.; Pegues, Jamila

2018-04-01

The organic content of protoplanetary disks sets the initial compositions of planets and comets, thereby influencing subsequent chemistry that is possible in nascent planetary systems. We present observations of the complex nitrile-bearing species CH3CN and HC3N toward the disks around the T Tauri stars AS 209, IM Lup, LkCa 15, and V4046 Sgr as well as the Herbig Ae stars MWC 480 and HD 163296. HC3N is detected toward all disks except IM Lup, and CH3CN is detected toward V4046 Sgr, MWC 480, and HD 163296. Rotational temperatures derived for disks with multiple detected lines range from 29 to 73 K, indicating emission from the temperate molecular layer of the disk. V4046 Sgr and MWC 480 radial abundance profiles are constrained using a parametric model; the gas-phase CH3CN and HC3N abundances with respect to HCN are a few to tens of percent in the inner 100 au of the disk, signifying a rich nitrile chemistry at planet- and comet-forming disk radii. We find consistent relative abundances of CH3CN, HC3N, and HCN between our disk sample, protostellar envelopes, and solar system comets; this is suggestive of a robust nitrile chemistry with similar outcomes under a wide range of physical conditions.

New test of bow-shock models of Herbig-Haro objects

International Nuclear Information System (INIS)

Raga, A.C.; Bohm, K.H.; Solf, J.; Max-Planck-Institut fuer Astronomie, Heidelberg, West Germany)

1986-01-01

Long-slit, high-resolution spectroscopy of the Herbig-Haro oject HH 32 has shown that the emission-line profiles in all four condensations A, B, C, and D show high- and low-velocity components. The spatial maxima of these two components are always arranged in a double-layer pattern, with the maximum of the high-velocity component 0.6-1.0 arcsecs closer to the central star (AS 353A) than the low-velocity maximum. A study of the emission-line profiles predicted from a model of a radiating bow shock shows that such a double-layer structure appears naturally for this type of flow. In this case both the high-velocity and the low-velocity components come from the post-shock gas, in agreement with the theoretical prediction that it should be very difficult to detect the pre-shock gas observationally. The present results agree qualitatively well with observations of HH 32, strengthening the case for a bow-shock interpretation of this Herbig-Haro object. It is shown that the double-layer effect will be more easily observable for bow shocks which move at a relatively large angle with respect to the plane of the sky (i.e., for Herbig-Haro objects which have large radial velocities). 31 references

The spatial extent of polycyclic aromatic hydrocarbons emission in the Herbig star HD 179218

Science.gov (United States)

Taha, A. S.; Labadie, L.; Pantin, E.; Matter, A.; Alvarez, C.; Esquej, P.; Grellmann, R.; Rebolo, R.; Telesco, C.; Wolf, S.

2018-04-01

Aim. We investigate, in the mid-infrared, the spatial properties of the polycyclic aromatic hydrocarbons (PAHs) emission in the disk of HD 179218, an intermediate-mass Herbig star at 300 pc. Methods: We obtained mid-infrared images in the PAH-1, PAH-2 and Si-6 filters centered at 8.6, 11.3, and 12.5 μm, and N-band low-resolution spectra using CanariCam on the 10-m Gran Telescopio Canarias (GTC). We compared the point spread function (PSF) profiles measured in the PAH filters to the profile derived in the Si-6 filter, where the thermal continuum emission dominates. We performed radiative transfer modeling of the spectral energy distribution (SED) and produced synthetic images in the three filters to investigate different spatial scenarios. Results: Our data show that the disk emission is spatially resolved in the PAH-1 and PAH-2 filters, while unresolved in the Si-6 filter. Thanks to very good observing conditions, an average full width at half maximum (FWHM) of 0.232'', 0.280'' and 0.293'' is measured in the three filters, respectively. Gaussian disk fitting and quadratic subtraction of the science and calibrator PSFs suggests a lower-limit characteristic angular diameter of the emission of 100 mas, or 30 au. The photometric and spectroscopic results are compatible with previous findings. Our radiative transfer (RT) modeling of the continuum suggests that the resolved emission should result from PAH molecules on the disk atmosphere being UV-excited by the central star. Simple geometrical models of the PAH component compared to the underlying continuum point to a PAH emission uniformly extended out to the physical limits of the disk model. Furthermore, our RT best model of the continuum requires a negative exponent of the surface density power-law, in contrast with earlier modeling pointing to a positive exponent. Conclusions: We have spatially resolved - for the first time to our knowledge - the PAHs emission in the disk of HD 179218 and set constraints on its

Coevolution of Binaries and Circumbinary Gaseous Disks

Science.gov (United States)

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.

Exploring Disks Around Planets

Science.gov (United States)

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

A LIKELY CLOSE-IN LOW-MASS STELLAR COMPANION TO THE TRANSITIONAL DISK STAR HD 142527

International Nuclear Information System (INIS)

Biller, Beth; Benisty, Myriam; Chauvin, Gael; Olofsson, Johan; Pott, Jörg-Uwe; Müller, André; Bonnefoy, Mickaël; Henning, Thomas; Lacour, Sylvestre; Thebault, Philippe; Juhász, Attila; Sicilia-Aguilar, Aurora; Tuthill, Peter; Crida, Aurelien

2012-01-01

With the uniquely high contrast within 0.''1 (Δmag(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 (3σ 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 with an estimated mass of ∼0.1-0.4 M ☉ . 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.

Unusual H2O maser source near Herbig-Haro object number 11

International Nuclear Information System (INIS)

Lo, K.Y.; Morris, M.; Moran, J.M.; Haschick, A.D.

1976-01-01

Water emission spectra of an unusual source near Herbig-Haro (HH) 11 have been monitored over a 14-month period. Variations in the intensity and the radial velocity of the emission are noticeable on time scales as short as one day. At any given time, only one or two velocity components are present in the spectrum. The variations are such that each component appears and disappears at a fixed radial velocity, and new components appear at seemingly random velocities within a 40 km s -1 range. It is suggested that the exciting source is losing mass via a stellar wind, and that the H 2 O emission arises in the transition region between the cavity created by the stellar wind and the surrounding molecular medium. The proposed model can be tested by VLBI observations; an accurate position for the H 2 O maser source is required to determine the physical relationship between the maser source and the infrared or HH objects

DEEP MIPS OBSERVATIONS OF THE IC 348 NEBULA: CONSTRAINTS ON THE EVOLUTIONARY STATE OF ANEMIC CIRCUMSTELLAR DISKS AND THE PRIMORDIAL-TO-DEBRIS DISK TRANSITION

International Nuclear Information System (INIS)

Currie, Thayne; Kenyon, Scott J.

2009-01-01

We describe new, deep MIPS photometry and new high signal-to-noise optical spectroscopy of the 2.5 Myr old IC 348 Nebula. To probe the properties of the IC 348 disk population, we combine these data with previous optical/infrared photometry and spectroscopy to identify stars with gas accretion, to examine their mid-IR colors, and to model their spectral energy distributions. IC 348 contains many sources in different evolutionary states, including protostars and stars surrounded by primordial disks, two kinds of transitional disks, and debris disks. Most disks surrounding early/intermediate spectral-type stars (>1.4 M sun at 2.5 Myr) are debris disks; most disks surrounding solar and subsolar-mass stars are primordial disks. At the 1-2 σ level, more massive stars also have a smaller frequency of gas accretion and smaller mid-IR luminosities than lower-mass stars. These trends are suggestive of a stellar mass-dependent evolution of disks, where most disks around high/intermediate-mass stars shed their primordial disks on rapid, 2.5 Myr timescales. The frequency of MIPS-detected transitional disks is ∼15%-35% for stars plausibly more massive than 0.5 M sun . The relative frequency of transitional disks in IC 348 compared to that for 1 Myr old Taurus and 5 Myr old NGC 2362 is consistent with a transition timescale that is a significant fraction of the total primordial disk lifetime.

10 micron Spectroscopy with OSCIR: Silicate Minerology and The Origins of Disks & Protoplanetesimals

Science.gov (United States)

Woodward, Chick; Wooden, Diane; Harker, David; Rodgers, Bernadette; Butner, Harold

1999-02-01

The analysis of the silicate mineralogy of pre-main sequence Herbig Ae/Be (HeAeBe) stars to main sequence (beta)-Pic systems, probes the chemical and physical conditions in these potentially planet-forming environments, the condensation of dust from the gas-disk, and the aggregation and accretion of these solids into planetesimals and comets. We propose to obtain 10 micron OSCIR spectra of a selected list of HeAeBe and (beta)-Pic like systems. Use of our ground-based data, combined with the ISO SWS database, and our extensive analytical modeling efforts will permit us to develop a fundamental understanding of connections between silicate mineralogy and the origins and evolution of disks and protoplanetesimals. This program will provide a framework to extend our understanding of planetary formation processes and the mineralogy of dust in differing circumstellar environs and comets to be studied with the NASA STARDUST and SIRTF missions.

AN ORDERED MAGNETIC FIELD IN THE PROTOPLANETARY DISK OF AB Aur REVEALED BY MID-INFRARED POLARIMETRY

Energy Technology Data Exchange (ETDEWEB)

Li, Dan; Pantin, Eric; Telesco, Charles M.; Zhang, Han; Barnes, Peter J.; Mariñas, Naibí [Department of Astronomy, University of Florida, 211 Bryant Space Science Center, FL 32611 (United States); Wright, Christopher M. [School of Physical, Environmental, and Mathematical Sciences, University of New South Wales, Canberra, ACT 2610 (Australia); Packham, Chris, E-mail: d.li@ufl.edu [Physics and Astronomy Department, University of Texas at San Antonio, 1 UTSA Circle, San Antonio, TX 78249 (United States)

2016-11-20

Magnetic fields ( B -fields) play a key role in the formation and evolution of protoplanetary disks, but their properties are poorly understood due to the lack of observational constraints. Using CanariCam at the 10.4 m Gran Telescopio Canarias, we have mapped out the mid-infrared polarization of the protoplanetary disk around the Herbig Ae star AB Aur. We detect ∼0.44% polarization at 10.3 μ m from AB Aur's inner disk ( r  < 80 au), rising to ∼1.4% at larger radii. Our simulations imply that the mid-infrared polarization of the inner disk arises from dichroic emission of elongated particles aligned in a disk B -field. The field is well ordered on a spatial scale, commensurate with our resolution (∼50 au), and we infer a poloidal shape tilted from the rotational axis of the disk. The disk of AB Aur is optically thick at 10.3 μ m, so polarimetry at this wavelength is probing the B -field near the disk surface. Our observations therefore confirm that this layer, favored by some theoretical studies for developing magneto-rotational instability and its resultant viscosity, is indeed very likely to be magnetized. At radii beyond ∼80 au, the mid-infrared polarization results primarily from scattering by dust grains with sizes up to ∼1 μ m, a size indicating both grain growth and, probably, turbulent lofting of the particles from the disk mid-plane.

Survey of high-velocity molecular gas in the vicinity of Herbig-Haro objects. I

International Nuclear Information System (INIS)

Edwards, S.; Snell, R.L.

1983-01-01

A survey of high-velocity molecular gas toward 49 Herbig-Haro objects is presented. Observations of the 12 CO J = 1-0 transition obtained with the 14 m telescope of the Five College Radio Astronomy Observatory reveal three new spatially extended high-velocity molecular outflows. One is in the NGC 1333 region near HH 12, and two are in the NGC 7129 region, the first near LkHα 234 and the second near a far-infrared source. The relationship between optical Herbin-Haro emission knots and large-scale motions of the ambient molecular material is investigated, and the properties of high-velocity molecular outflows in the vicinity of Herbig-Haro objects are discussed. Of 11 energetic outflows in the vicinity of Herbig-Haro objects, eight are found in four pairs separated by 0.2-1.0 pc. We estimate that energetic outflows characterized by mass loss rates > or =10 -7 M/sub sun/ yr -1 occur for at least 10 4 yr once in the lifetime of all stars with masses greater than 1M/sub sun/

Chemical spots on the surface of the strongly magnetic Herbig Ae star HD 101412

DEFF Research Database (Denmark)

Järvinen, S. P.; Hubrig, S.; Schöller, M.

2016-01-01

Due to the knowledge of the rotation period and the presence of a rather strong surface magnetic field, the sharp-lined young Herbig Ae star HD 101412 with a rotation period of 42 d has become one of the most well-studied targets among the Herbig Ae stars. High-resolution HARPS polarimetric spectra...... that is opposite to the behaviour of the other elements studied. Since classical Ap stars usually show a relationship between the magnetic field geometry and the distribution of element spots, we used in our magnetic field measurements different line samples belonging to the three elements with the most numerous...

Molecular hydrogen mapping of Herbig-Haro 7-11; a filamentary bullet

International Nuclear Information System (INIS)

Lightfoot, J.F.; Glencross, W.M.

1986-01-01

A map is presented of the Q-branch H 2 line emission associated with Herbig-Haro 7-11. The molecules are shock-excited and the emitting area stretches 4 arcmin north-west from HH7-11 in a fairly sharp and straight line. The evidence suggests that the emission occurs where a spine of dense molecular gas is being struck by a jet from the young star SVS13. The origin of the Herbig-Haro objects is discussed. It is suggested that HH7-11 are the bow-shocks formed around a helical filament of dense gas moving at 200 km s -1 through the molecular cloud. The filament could be produced by a well-collimated precessing jet from SVS13. HH2. HH12 and HH101 may be explained in a similar way. (author)

Using He I λ10830 to Diagnose Mass Flows Around Herbig Ae/Be Stars

Science.gov (United States)

Cauley, Paul W.; Johns-Krull, Christopher M.

2015-01-01

The pre-main sequence Herbig Ae/Be stars (HAEBES) are the intermediate mass cousins of the low mass T Tauri stars (TTSs). However, it is not clear that the same accretion and mass outflow mechanisms operate identically in both mass regimes. Classical TTSs (CTTSs) accrete material from their disks along stellar magnetic field lines in a scenario called magnetospheric accretion. Magnetospheric accretion requires a strong stellar dipole field in order to truncate the inner gas disk. These fields are either absent or very weak on a large majority of HAEBES, challenging the view that magnetospheric accretion is the dominant accretion mechanism. If magnetospheric accretion does not operate similarly around HAEBES as it does around CTTSs, then strong magnetocentrifugal outflows, which are directly linked to accretion and are ubiquitous around CTTSs, may be driven less efficiently from HAEBE systems. Here we present high resolution spectroscopic observations of the He I λ10830 line in a sample of 48 HAEBES. He I λ10830 is an excellent tracer of both mass infall and outflow which is directly manifested as red and blue-shifted absorption in the profile morphologies. These features, among others, are common in our sample. The occurrence of both red and blue-shifted absorption profiles is less frequent, however, than is found in CTTSs. Statistical contingency tests confirm this difference at a significant level. In addition, we find strong evidence for smaller disk truncation radii in the objects displaying red-shifted absorption profiles. This is expected for HAEBES experiencing magnetospheric accretion based on their large rotation rates and weak magnetic field strengths. Finally, the low incidence of blue-shifted absorption in our sample compared to CTTSs and the complete lack of simultaneous red and blue-shifted absorption features suggests that magnetospheric accretion in HAEBES is less efficient at driving strong outflows. The stellar wind-like outflows that are

Two Herbig-Haro objects discovered by narrow-band CCD imagery

International Nuclear Information System (INIS)

Ogura, Katsuo

1990-01-01

Two new Herbig-Haro objects, HH 132 and HH 133, have been discovered by CCD imagery behind interference filters on and just off the forbidden S II lines in the red. They are located in Puppis R2 and in Vela R2. Possible locations of their exciting sources are discussed. 12 refs

Spectroscopic Peculiarity of the Herbig Be Star HD 259431

Science.gov (United States)

Pogodin, M. A.; Pavlovskij, S. E.; Drake, N. A.; Beskrovnaya, N. G.; Kozlova, O. V.; Alekseev, I. Yu.; Borges Fernandes, M.; Pereira, C. B.; Valyavin, G.

2017-06-01

High-resolution spectra of the Herbig Be star HD 259431 obtained in 2010-2016 at three observatories (Crimean AO, ESO in Chile, and OAN SPN in Mexico) are analysed. The object demonstrates a very rich emission line profile spectrum. The bulk of the lines exhibit double-peaked emission profiles and originate in the gaseous disk. The atmospheric lines are unusually shallow, and majority of them are distorted by the circumstellar (CS) contribution. Moreover, we have revealed that they are overlapped with an additional continuum emission. Using the observed ratio of the equivalent widths of two He I λ 4009 and 4026 lines, we estimated the spectral type of the object as B5 V. We also constructed the spectral energy distribution of the additional continuum using wide wings of the atmospheric Hβ-Hɛ lines free of the CS contribution. The continuum corresponds to the blue part of the black body spectrum. The Hβ - Hɛ Balmer emission lines show very variable profiles looking as either of P Cyg-type or a double-peaked emission line with a depression of the red wing. We found the period of this variability P = 2.630d and interpreted it as a sign of a rotating magnetosphere of the star with the magnetic axis inclined to the rotation axis. At different phases of rotation, the observer can see either an accretion flow at high magnetic latitudes or a wind zone at lower latitudes. We also estimated the inclination of the rotation axis i = 52°±1°.

THE HERBIG BE STAR V1818 ORI AND ITS ENVIRONMENT

Energy Technology Data Exchange (ETDEWEB)

Chiang, Hsin-Fang; Reipurth, Bo [Institute for Astronomy and NASA Astrobiology Institute, University of Hawaii at Manoa, 640 North Aohoku Place, Hilo, HI 96720 (United States); Hillenbrand, Lynne, E-mail: hchiang@ifa.hawaii.edu, E-mail: reipurth@ifa.hawaii.edu [Department of Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States)

2015-03-15

The little-studied Herbig Be star V1818 Ori is located in the direction of the southern L1641 cloud and the Mon R2 star-forming complex, and is most likely associated with the latter at a distance of ∼900 pc. A high-resolution spectrum is consistent with a spectral type around B7 V, with lines of Hα, the red Ca ii triplet, and several forbidden lines in emission. An All Sky Automated Survey V-band light curve spanning 9 yr reveals major variability with deep absorption episodes reminiscent of the UX Orionis stars. We have searched for additional young stars clustering around V1818 Ori using grism images and the 2MASS and Wide-field Infrared Survey Explorer catalogs, and have found almost two dozen fainter stars with evidence of youth. Direct images show that the bright star IRAS 05510–1025, only about 3 arcmin from V1818 Ori, is surrounded by a reflection nebula, indicating its association with a molecular cloud. A spectrum of the star shows no emission-lines, and it is found to be a close binary with late B and early G type components. Its radial velocity indicates that it is an interloper, accidentally passing through the cloud and not physically associated with V1818 Ori.

The OH maser near the Herbig-Haro object GGD37

International Nuclear Information System (INIS)

Norris, R.P.

1980-01-01

H 2 O masers are often associated with Herbig-Haro (HH) objects, but OH masers have been found near only one HH object, GGD37. The position of this maser has been measured and it is found to be coincident with the compact H II region from which the HH object was probably ejected. (author)

On the infrared emission of the exciting star of the Herbig-Haro objects 1 and 2

International Nuclear Information System (INIS)

Tapia, M.; Roth, M.; Carrasco, L.; Ruiz, M.T.

1987-01-01

Further evidence is presented indicating that the infrared emission at lambda > 3 μm, spatially coincident with the VLA source located midway between the Herbig-Haro objects 1 and 2, comes from warm circumstellar dust around the star most probably responsible for the excitation of these Herbig-Haro objects. The nearby extended emission dominating at shorter wavelengths comes from scattered stellar light, the shocked ionized nebulosity, or both. The visual extinction in the direction of the central star is 23 < or approx., Asub(V) < or approx., 63. (author)

AN M DWARF COMPANION AND ITS INDUCED SPIRAL ARMS IN THE HD 100453 PROTOPLANETARY DISK

Energy Technology Data Exchange (ETDEWEB)

Dong, Ruobing [Nuclear Science Division, Lawrence Berkeley National Lab, Berkeley, CA 94720 (United States); Zhu, Zhaohuan [Princeton University, Princeton, NJ 08544 (United States); Fung, Jeffrey; Chiang, Eugene [Department of Astronomy, University of California at Berkeley, Berkeley, CA 94720 (United States); Rafikov, Roman [Institute for Advanced Study, Princeton, NJ 08540 (United States); Wagner, Kevin, E-mail: rdong2013@berkeley.edu [Department of Astronomy/Steward Observatory, The University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)

2016-01-01

Recent VLT/SPHERE near-infrared imaging observations revealed two spiral arms with a near m = 2 rotational symmetry in the protoplanetary disk around the ∼1.7 M{sub ⊙} Herbig star HD 100453. A ∼0.3 M{sub ⊙} M dwarf companion, HD 100453 B, was also identified at a projected separation of 120 AU from the primary. In this Letter, we carry out hydrodynamic and radiative transfer simulations to examine the scattered light morphology of the HD 100453 disk as perturbed by the companion on a circular and coplanar orbit. We find that the companion truncates the disk at ∼45 AU in scattered light images, and excites two spiral arms in the remaining (circumprimary) disk with a near m = 2 rotational symmetry. Both the truncated disk size and the morphology of the spirals are in excellent agreement with the SPHERE observations at Y, J, H, and K1-bands, suggesting that the M dwarf companion is indeed responsible for the observed double-spiral-arm pattern. Our model suggests that the disk is close to face on (inclination angle ∼5°), and that the entire disk-companion system rotates counterclockwise on the sky. The HD 100453 observations, along with our modeling work, demonstrate that double spiral arm patterns in near-infrared scattered light images can be generically produced by companions, and support future observations to identify the companions responsible for the arms observed in the MWC 758 and SAO 206462 systems.

CHEMICAL IMAGING OF THE CO SNOW LINE IN THE HD 163296 DISK

Energy Technology Data Exchange (ETDEWEB)

Qi, Chunhua; Öberg, Karin I.; Andrews, Sean M.; Wilner, David J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Bergin, Edwin A. [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States); Hughes, A. Meredith [Van Vleck Observatory, Astronomy Department, Wesleyan University, 96 Foss Hill Drive, Middletown, CT 06459 (United States); Hogherheijde, Michiel [Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands); D’Alessio, Paola [Centro de Radioastronomi´a y Astrofísica, Universidad Nacional Autónoma de México, 58089 Morelia, Michoacán, México (Mexico)

2015-11-10

The condensation fronts (snow lines) of H{sub 2}O, CO, and other abundant volatiles in the midplane of a protoplanetary disk affect several aspects of planet formation. Locating the CO snow line, where the CO gas column density is expected to drop substantially, based solely on CO emission profiles, is challenging. This has prompted an exploration of chemical signatures of CO freeze-out. We present ALMA Cycle 1 observations of the N{sub 2}H{sup +} J = 3−2 and DCO{sup +} J = 4−3 emission lines toward the disk around the Herbig Ae star HD 163296 at ∼0.″5 (60 AU) resolution, and evaluate their utility as tracers of the CO snow line location. The N{sub 2}H{sup +} emission is distributed in a ring with an inner radius at 90 AU, corresponding to a midplane temperature of 25 K. This result is consistent with a new analysis of optically thin C{sup 18}O data, which implies a sharp drop in CO abundance at 90 AU. Thus N{sub 2}H{sup +} appears to be a robust tracer of the midplane CO snow line. The DCO{sup +} emission also has a ring morphology, but neither the inner nor the outer radius coincide with the CO snow line location of 90 AU, indicative of a complex relationship between DCO{sup +} emission and CO freeze-out in the disk midplane. Compared to TW Hya, CO freezes out at a higher temperature in the disk around HD 163296 (25 versus 17 K in the TW Hya disk), perhaps due to different ice compositions. This highlights the importance of actually measuring the CO snow line location, rather than assuming a constant CO freeze-out temperature for all disks.

Herbig-Haro objects: recent observational and theoretical developments

International Nuclear Information System (INIS)

Canto, J.

1981-01-01

A brief summary of our present observational and theoretical knowledge of Herbig-Haro objects is given. Special emphasis is given to the recent observational results in the radio frequency range and on the most recent models advanced to explain these objects. It is concluded that HH-objects are most probably intrinsic emission nebulae produced by the cooling of shock-heated material. The source of energy is likely to be a strong wind from a new born star which is displaced approximately 0.1 pc typically from the optical object. (Auth.)

HDE 323771: a new Herbig Ae star

International Nuclear Information System (INIS)

Persi, P.; Polcaro, V.F.; Viotti, R.

1991-01-01

From an analysis of the blue and red spectrum, and a study of the energy distribution from the optical up to the far infrared, we identify HDE 323771 as a new PMS Herbig Ae star. The P Cygni line profiles observed in the Balmer and Fe II lines indicate the presence of a stellar wind with a velocity of about 250-350 km s -1 . An upper limit of mass loss rate is derived from the observed upper limit for the Br γ luminosity. The near-IR images and the IR energy distribution indicate the presence of an extended circumstellar dust envelope with a temperature of about 1500 K. (author)

An ALMA Survey of DCN/H{sup 13}CN and DCO{sup +}/H{sup 13}CO{sup +} in Protoplanetary Disks

Energy Technology Data Exchange (ETDEWEB)

Huang, Jane; Öberg, Karin I.; Qi, Chunhua; Andrews, Sean M.; Guzmán, Viviana V.; Loomis, Ryan A.; Wilner, David J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Aikawa, Yuri; Furuya, Kenji [Center for Computational Sciences, The University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki 305-8577 (Japan); Van Dishoeck, Ewine F., E-mail: jane.huang@cfa.harvard.edu [Leiden Observatory, Leiden University, P.O. Box 9513, NL-2300 RA Leiden (Netherlands)

2017-02-01

The deuterium enrichment of molecules is sensitive to their formation environment. Constraining patterns of deuterium chemistry in protoplanetary disks is therefore useful for probing how material is inherited or reprocessed throughout the stages of star and planet formation. We present ALMA observations at ∼0.″6 resolution of DCO{sup +}, H{sup 13}CO{sup +}, DCN, and H{sup 13}CN in the full disks around T Tauri stars AS 209 and IM Lup, in the transition disks around T Tauri stars V4046 Sgr and LkCa 15, and in the full disks around Herbig Ae stars MWC 480 and HD 163296. We also present ALMA observations of HCN in the IM Lup disk. DCN, DCO{sup +}, and H{sup 13}CO{sup +} are detected in all disks, and H{sup 13}CN in all but the IM Lup disk. We find efficient deuterium fractionation for the sample, with estimates of disk-averaged DCO{sup +}/HCO{sup +} and DCN/HCN abundance ratios ranging from ∼0.02–0.06 and ∼0.005–0.08, respectively, which is comparable to values reported for other interstellar environments. The relative distributions of DCN and DCO{sup +} vary between disks, suggesting that multiple formation pathways may be needed to explain the diverse emission morphologies. In addition, gaps and rings observed in both H{sup 13}CO{sup +} and DCO{sup +} emission provide new evidence that DCO{sup +} bears a complex relationship with the location of the midplane CO snowline.

Misaligned disks in the binary protostar IRS 43

DEFF Research Database (Denmark)

Brinch, Christian; Jørgensen, Jes Kristian; Hogerheijde, Michiel R.

2016-01-01

and position angle and also with respect to the binary orbital plane. Each stellar component has an associated circumstellar disk while the binary is surrounded by a circumbinary disk. Together with archival VLA measurements of the stellar positions over 25 years, and assuming a circular orbit, we use our...

ALMA REVEALS THE ANATOMY OF THE mm-SIZED DUST AND MOLECULAR GAS IN THE HD 97048 DISK

Energy Technology Data Exchange (ETDEWEB)

Walsh, Catherine; Maud, Luke T. [Leiden Observatory, Leiden University, P.O. Box 9531, 2300 RA Leiden (Netherlands); Juhász, Attila [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Meeus, Gwendolyn [Departamento de Física Teórica, Universidad Autonoma de Madrid, Campus Cantoblanco, E-28049 Madrid (Spain); Dent, William R. F. [Joint ALMA Observatory (JAO), Alonso de Córdova 3107, Vitacura, Santiago (Chile); Aikawa, Yuri [Center for Computer Sciences, University of Tsukuba, 305-8577 Tsukuba (Japan); Millar, Tom J. [School of Mathematics and Physics, Queen’s University Belfast, University Road, Belfast BT7 1NN (United Kingdom); Nomura, Hideko, E-mail: cwalsh@strw.leidenuniv.nl, E-mail: c.walsh1@leeds.ac.uk [Department of Earth and Planetary Science, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, 152-8551 Tokyo (Japan)

2016-11-10

Transitional disks show a lack of excess emission at infrared wavelengths due to a large dust cavity, that is often corroborated by spatially resolved observations at ∼ mm wavelengths. We present the first spatially resolved ∼ mm-wavelength images of the disk around the Herbig Ae/Be star, HD 97048. Scattered light images show that the disk extends to ≈640 au. ALMA data reveal a circular-symmetric dusty disk extending to ≈350 au, and a molecular disk traced in CO J = 3-2 emission, extending to ≈750 au. The CO emission arises from a flared layer with an opening angle ≈30°–40°. HD 97048 is another source for which the large (∼ mm-sized) dust grains are more centrally concentrated than the small (∼ μ m-sized) grains and molecular gas, likely due to radial drift. The images and visibility data modeling suggest a decrement in continuum emission within ≈50 au, consistent with the cavity size determined from mid-infrared imaging (34 ± 4 au). The extracted continuum intensity profiles show ring-like structures with peaks at ≈50, 150, and 300 au, with associated gaps at ≈100 and 250 au. This structure should be confirmed in higher-resolution images (FWHM ≈ 10–20 au). These data confirm the classification of HD 97048 as a transitional disk that also possesses multiple ring-like structures in the dust continuum emission. Additional data are required at multiple and well-separated frequencies to fully characterize the disk structure, and thereby constrain the mechanism(s) responsible for sculpting the HD 97048 disk.

ALMA Reveals the Anatomy of the mm-sized Dust and Molecular Gas in the HD 97048 Disk

Science.gov (United States)

Walsh, Catherine; Juhász, Attila; Meeus, Gwendolyn; Dent, William R. F.; Maud, Luke T.; Aikawa, Yuri; Millar, Tom J.; Nomura, Hideko

2016-11-01

Transitional disks show a lack of excess emission at infrared wavelengths due to a large dust cavity, that is often corroborated by spatially resolved observations at ˜ mm wavelengths. We present the first spatially resolved ˜ mm-wavelength images of the disk around the Herbig Ae/Be star, HD 97048. Scattered light images show that the disk extends to ≈640 au. ALMA data reveal a circular-symmetric dusty disk extending to ≈350 au, and a molecular disk traced in CO J = 3-2 emission, extending to ≈750 au. The CO emission arises from a flared layer with an opening angle ≈30°-40°. HD 97048 is another source for which the large (˜ mm-sized) dust grains are more centrally concentrated than the small (˜μm-sized) grains and molecular gas, likely due to radial drift. The images and visibility data modeling suggest a decrement in continuum emission within ≈50 au, consistent with the cavity size determined from mid-infrared imaging (34 ± 4 au). The extracted continuum intensity profiles show ring-like structures with peaks at ≈50, 150, and 300 au, with associated gaps at ≈100 and 250 au. This structure should be confirmed in higher-resolution images (FWHM ≈ 10-20 au). These data confirm the classification of HD 97048 as a transitional disk that also possesses multiple ring-like structures in the dust continuum emission. Additional data are required at multiple and well-separated frequencies to fully characterize the disk structure, and thereby constrain the mechanism(s) responsible for sculpting the HD 97048 disk.

ALMA REVEALS THE ANATOMY OF THE mm-SIZED DUST AND MOLECULAR GAS IN THE HD 97048 DISK

International Nuclear Information System (INIS)

Walsh, Catherine; Maud, Luke T.; Juhász, Attila; Meeus, Gwendolyn; Dent, William R. F.; Aikawa, Yuri; Millar, Tom J.; Nomura, Hideko

2016-01-01

Transitional disks show a lack of excess emission at infrared wavelengths due to a large dust cavity, that is often corroborated by spatially resolved observations at ∼ mm wavelengths. We present the first spatially resolved ∼ mm-wavelength images of the disk around the Herbig Ae/Be star, HD 97048. Scattered light images show that the disk extends to ≈640 au. ALMA data reveal a circular-symmetric dusty disk extending to ≈350 au, and a molecular disk traced in CO J = 3-2 emission, extending to ≈750 au. The CO emission arises from a flared layer with an opening angle ≈30°–40°. HD 97048 is another source for which the large (∼ mm-sized) dust grains are more centrally concentrated than the small (∼ μ m-sized) grains and molecular gas, likely due to radial drift. The images and visibility data modeling suggest a decrement in continuum emission within ≈50 au, consistent with the cavity size determined from mid-infrared imaging (34 ± 4 au). The extracted continuum intensity profiles show ring-like structures with peaks at ≈50, 150, and 300 au, with associated gaps at ≈100 and 250 au. This structure should be confirmed in higher-resolution images (FWHM ≈ 10–20 au). These data confirm the classification of HD 97048 as a transitional disk that also possesses multiple ring-like structures in the dust continuum emission. Additional data are required at multiple and well-separated frequencies to fully characterize the disk structure, and thereby constrain the mechanism(s) responsible for sculpting the HD 97048 disk.

The electron density and temperature distributions predicted by bow shock models of Herbig-Haro objects

International Nuclear Information System (INIS)

Noriega-Crespo, A.; Bohm, K.H.; Raga, A.C.

1990-01-01

The observable spatial electron density and temperature distributions for series of simple bow shock models, which are of special interest in the study of Herbig-Haro (H-H) objects are computed. The spatial electron density and temperature distributions are derived from forbidden line ratios. It should be possible to use these results to recognize whether an observed electron density or temperature distribution can be attributed to a bow shock, as is the case in some Herbig-Haro objects. As an example, the empirical and predicted distributions for H-H 1 are compared. The predicted electron temperature distributions give the correct temperature range and they show very good diagnostic possibilities if the forbidden O III (4959 + 5007)/4363 wavelength ratio is used. 44 refs

A CO survey in planet-forming disks: Characterizing the gas content in the epoch of planet formation

Energy Technology Data Exchange (ETDEWEB)

Hales, A. S.; De Gregorio-Monsalvo, I.; Dent, W. F. R.; Phillips, N. [Atacama Large Millimeter/Submillimeter Array, Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura 763-0355 Santiago (Chile); Montesinos, B. [Department of Astrophysics, Centre for Astrobiology (CAB, CSIC-INTA), ESAC Campus, P.O. Box 78, E-28691 Villanueva de la Cañada, Madrid (Spain); Casassus, S.; Garay, G.; Mardones, D.; Pérez, S. [Departamento de Astronomía, Universidad de Chile, Camino El Observatorio 1515, Las Condes, Santiago (Chile); Dougados, C.; Ménard, F. [UMI-FCA, CNRS/INSU, France (UMI 3386) (France); Eiroa, C. [Departamento de Física Teórica, Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, E-28049 Madrid (Spain); Hughes, A. M. [Department of Astronomy, University of California, Berkeley, CA 94720 (United States); Palau, Aina [Institut de Ciéncies de l' Espai (CSIC-IEEC), Campus UAB-Facultat de Ciéncies, Torre C5-parell 2, E-08193 Bellaterra, Catalunya (Spain); Torrelles, J. M. [Institut de Ciències de l' Espai (CSIC-IEEC) and Institut de Ciències del Cosmos (UB-IEEC), Martí i Franquès 1, E-08028 Barcelona (Spain); Wilner, D., E-mail: ahales@alma.cl [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)

2014-09-01

We carried out a {sup 12}CO(3-2) survey of 52 southern stars with a wide range of IR excesses (L {sub IR}/L {sub *}) using the single-dish telescopes APEX and ASTE. The main aims were (1) to characterize the evolution of molecular gas in circumstellar disks using L {sub IR}/L {sub *} values as a proxy of disk dust evolution, and (2) to identify new gas-rich disk systems suitable for detailed study with ALMA. About 60% of the sample (31 systems) have L {sub IR}/L {sub *} > 0.01, typical of T Tauri or Herbig AeBe stars, and the rest (21 systems) have L {sub IR}/L {sub *} < 0.01, typical of debris disks. We detect CO(3-2) emission from 20 systems, and 18 (90%) of these have L {sub IR}/L {sub *} > 0.01. However, the spectra of only four of the newly detected systems appear free of contamination from background or foreground emission from molecular clouds. These include the early-type stars HD 104237 (A4/5V, 116 pc) and HD 98922 (A2 III, 507 pc, as determined in this work), where our observations reveal the presence of CO-rich circumstellar disks for the first time. Of the other detected sources, many could harbor gaseous circumstellar disks, but our data are inconclusive. For these two newly discovered gas-rich disks, we present radiative transfer models that simultaneously reproduce their spectral energy distributions and the {sup 12}CO(3-2) line profiles. For both of these systems, the data are fit well by geometrically flat disks, placing them in the small class of non-flaring disks with significant molecular gas reservoirs.

Brown dwarf disks with ALMA

Energy Technology Data Exchange (ETDEWEB)

Ricci, L.; Isella, A. [Department of Astronomy, California Institute of Technology, MC 249-17, Pasadena, CA 91125 (United States); Testi, L.; De Gregorio-Monsalvo, I. [European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching (Germany); Natta, A. [INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze (Italy); Scholz, A., E-mail: lricci@astro.caltech.edu [School of Cosmic Physics, Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2 (Ireland)

2014-08-10

We present Atacama Large Millimeter/submillimeter Array continuum and spectral line data at 0.89 mm and 3.2 mm for three disks surrounding young brown dwarfs and very low mass stars in the Taurus star forming region. Dust thermal emission is detected and spatially resolved for all the three disks, while CO(J = 3-2) emission is seen in two disks. We analyze the continuum visibilities and constrain the disks' physical structure in dust. The results of our analysis show that the disks are relatively large; the smallest one has an outer radius of about 70 AU. The inferred disk radii, radial profiles of the dust surface density, and disk to central object mass ratios lie within the ranges found for disks around more massive young stars. We derive from our observations the wavelength dependence of the millimeter dust opacity. In all the three disks, data are consistent with the presence of grains with at least millimeter sizes, as also found for disks around young stars, and confirm that the early stages of the solid growth toward planetesimals occur also around very low-mass objects. We discuss the implications of our findings on models of solids evolution in protoplanetary disks, the main mechanisms proposed for the formation of brown dwarfs and very low-mass stars, as well as the potential of finding rocky and giant planets around very low-mass objects.

The detection and study of pre-planetary disks

Science.gov (United States)

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.

RADIATION HYDRODYNAMICS MODELS OF THE INNER RIM IN PROTOPLANETARY DISKS

Energy Technology Data Exchange (ETDEWEB)

Flock, M.; Turner, N. J. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Fromang, S. [Laboratoire AIM, CEA/DSM-CNRS-Université Paris 7, Irfu/Service d’Astrophysique, CEA-Saclay, F-91191 Gif-sur-Yvette (France); Benisty, M., E-mail: mflock@caltech.edu [Université Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble (France)

2016-08-20

Many stars host planets orbiting within a few astronomical units (AU). The occurrence rate and distributions of masses and orbits vary greatly with the host star’s mass. These close planets’ origins are a mystery that motivates investigating protoplanetary disks’ central regions. A key factor governing the conditions near the star is the silicate sublimation front, which largely determines where the starlight is absorbed, and which is often called the inner rim. We present the first radiation hydrodynamical modeling of the sublimation front in the disks around the young intermediate-mass stars called Herbig Ae stars. The models are axisymmetric and include starlight heating; silicate grains sublimating and condensing to equilibrium at the local, time-dependent temperature and density; and accretion stresses parameterizing the results of MHD magnetorotational turbulence models. The results compare well with radiation hydrostatic solutions and prove to be dynamically stable. Passing the model disks into Monte Carlo radiative transfer calculations, we show that the models satisfy observational constraints on the inner rim’s location. A small optically thin halo of hot dust naturally arises between the inner rim and the star. The inner rim has a substantial radial extent, corresponding to several disk scale heights. While the front’s overall position varies with the stellar luminosity, its radial extent depends on the mass accretion rate. A pressure maximum develops near the location of thermal ionization at temperatures of about 1000 K. The pressure maximum is capable of halting solid pebbles’ radial drift and concentrating them in a zone where temperatures are sufficiently high for annealing to form crystalline silicates.

Optical polarization studies of Herbig-Haro objects: Pt. 5

International Nuclear Information System (INIS)

Scarrott, S.M.; Warren-Smith, R.F.

1988-01-01

Optical linear polarization maps are presented for the HH46/47 nebulosities in the ESO210-6A dark globule. HH46 is part of an optical bipolar nebula illuminated by an obscured source - HH46IRS. The polarization pattern in the immediate neighbourhood of the source suggests the presence of circumstellar disc oriented in such a manner that the well-collimated outflows propagate along the major axis of the disc before creating the Herbig-Haro knots HH47A/B/C on the periphery of the globule. (author)

Optical polarization studies of Herbig-Haro objects. Pt. 7

International Nuclear Information System (INIS)

Scarrott, S.M.; Gledhill, T.M.; Rolph, C.D.

1990-01-01

A small patch of optical nebulosity in the cometary globule CG30 is an amorphous reflection nebula containing a Herbig-Haro knot. The exciting and illuminating star, which we identify with the IR source IRAS 08076-3356/CG30IRS4, is deeply embedded in the globule and is not seen directly at optical wavelengths. Structure in the polarization data suggests that the optical nebula is formed by the illumination of the walls of a cavity excavated in the cloud during outflow activity from the embedded source. (author)

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

Science.gov (United States)

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

Observational study of Herbig-Haro nebulae

International Nuclear Information System (INIS)

Brugel, E.W.

1981-01-01

Spectrophotometric data have been obtained for twelve Herbig-Haro nebulae with the multichannel spectrometer on the Mt. Palomar 5.08 meter telescope and with the image intensified dissector scanner on the Kitt Peak 2.13 meter telescope. Energy distributions of the continuous spectra of the Herbig-Haro objects H-H 1 (NW), H-H 2A, H-H 2G, H-H 2H, H-H 24A and H-H 32 have been determined in the wavelength range 3300 to 8000A. The signal-to-noise ratio has been improved in comparison to an earlier attempt to measure the continuum in H-H 1 and H-H 2H. Reddening corrections are based on Miller's [SII] method. The [FeII] emission line spectra have also been utilized as a secondary method for determining the interstellar reddening. In all continua the flux F/sub lambda/ increases rapidly with decreasing wavelength after the small scale structure has been averaged out. A power law interpolation F/sub lambda/ proportional lambda/sup -n/ demonstrates that for all observed H-H objects n lies in the range between 2.04 (H-H 2A, H-H 2H) and 2.92 (H-H 32). The relation of these results to recent I.U.E. observations of H-H 1 is discussed. It is also found that the ratio of the total optical continuum flux to Hβ flux is almost the same for all observed H-H objects with the sole exception of H-H 24A in which the continuum is considerably stronger than in other objects. This fact leads to difficulties in the usual dust scattering hypothesis for the interpretation of H-H continua. It is argued, if these energy distributions are really due to dust scattering in stellar continua as has been usually assumed, the original source must be a hot object and cannot be a T Tauri star.An interpretation in terms of transition radiation (as suggested by Gurzadyan) does not seem to be possible because the observed rise of F/sub lambda/ towards the ultraviolet is too steep

Spatially and spectrally resolved 10 mu m emission in Herbig Ae/Be stars

NARCIS (Netherlands)

van Boekel, R; Waters, LBFM; Dominik, C; Dullemond, CP; Tielens, AGGM; de Koter, A

We present new mid-infrared spectroscopy of the emission from warm circumstellar dust grains in the Herbig Ae stars HD 100546. HD 97048 and HD 104237, with a spatial resolution Of of approximate to0."9. We find that the emission in the UIR bands at 8.6, 11.3 and (HD 97048 only) 12.7 mum is extended

Very low-excitation Herbig-Haro objects

International Nuclear Information System (INIS)

Boehm, K.H.; Brugel, E.W.; Mannery, E.

1980-01-01

Spectrophotometric observations show that H-H 7 and H-H 11 belong to a class of very low-excitation Herbig-Haro objects of which H-H 47 has been the only known example. Typical properties include line flux ratios [N I] (lambda5198+lambda5200)/Hβ and [S II] lambda/6717/Hα, which are both considerably larger than 1, very strong [O I] and [C I] lines, as well as relatively faint [O II] lines. So far no shock-wave models are available for these low-excitation objects. H-H 7 and H-H 11 have electron densities which are lower by about one order of magnitude, and electron temperatures which are slightly lower than those for high-excitation objects like H-H 1 and H-H 2. H-H 11 has a filling factor of about 1, much higher than other H-H objects

A spatial study of the mid-IR emission features in four Herbig Ae/Be stars

NARCIS (Netherlands)

Boersma, C.; Peeters, E.; Martin-Hernandez, N. L.; van der Wolk, G.; Verhoeff, A. P.; Tielens, A. G. G. M.; Waters, L. B. F. M.; Pel, J. W.

Context. Infrared (IR) spectroscopy and imaging provide a prime tool to study the characteristics of polycyclic aromatic hydrocarbon (PAH) molecules and the mineralogy in regions of star formation. Herbig Ae/Be stars are known to have varying amounts of natal cloud material present in their

Herniated disk disease

International Nuclear Information System (INIS)

Ross, J.S.; Masaryk, T.J.; Modic, M.T.; Bohlman, H.; Wilber, G.; Carter, J.

1988-01-01

Thirty patients with symptoms of disk herniation and no previous surgery were examined with Gd-DTPA-enhanced MR imaging. Studies obtained before and after administration of Gd-DTPA included the following sequences: sagittal and axial spin echo (SE) 500/17 (repetition time, msec/echo time, msec), sagittal SE 2,000/60, sagittal FLASH 200/13/60. Studies were interpreted separately for presence of extradural disease (EDD) characterized by morphology, mass effect, and enhancement. Post Gd-DTPA diagnoses were: normal, n = 1; herniation, n = 28; neoplasm, n = 1. Tissue diagnosis was obtained in 13. The Gd-DTPA examination correctly changed the diagnosis in one case, provided increased confidence in the diagnosis in four, and was equivalent to the precontrast study in eight. Increased conspicuity of EDD with Gd-DTPA was related to the enhancement of epidural space analogous to IV CT and enhancement of scar surrounding disk herniation. Histologically, this scar was identical to that seen in postoperative spines, Gd-DTPA appears to be a useful adjunct in cervical and thoracic degenerative disk disease

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

Energy Technology Data Exchange (ETDEWEB)

Macías, Enrique; Anglada, Guillem; Osorio, Mayra; Gómez, José F. [Instituto de Astrofísica de Andalucía (CSIC) Glorieta de la Astronomía s/n E-18008 Granada (Spain); Torrelles, José M. [Institut de Ciències de l’Espai (CSIC) and Institut de Ciències del Cosmos (UB)/IEEC, Can Magrans S/N, Cerdanyola del Vallès, Barcelona (Spain); Carrasco-González, Carlos; Rodríguez, Luis F.; Sierra, Anibal, E-mail: emacias@bu.edu [Instituto de Radioastronomía y Astrofísica UNAM, Apartado Postal 3-72 (Xangari), 58089 Morelia, Michoacán (Mexico)

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{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.

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

International Nuclear Information System (INIS)

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

2017-01-01

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 C 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.

A peculiar Herbig-Haro object located far outside Lynds 1641

International Nuclear Information System (INIS)

Ogura, Katsuo

1991-01-01

A peculiar Herbig-Haro object, named HH 131, has been discovered by low-dispersion slit spectroscopy and narrowband CCD imaging. It lies well outside the dark cloud Lynds (L) 1641 toward the southwest. Accordingly, it has no associated molecular cloud, but it may be related to a cloud of atomic hydrogen. Its morphology is also unique, showing a fairly high degree of axisymmetric structure as well as a sort of double helix. No likely candidates for its energy source have been found in the IRAS Point Source Catalog, or by slit spectroscopy and an objective-prism Schmidt survey of nearby stars. 24 refs

High velocity molecular gas near Herbig-Haro objects HH 7--11

International Nuclear Information System (INIS)

Snell, R.L.; Edwards, S.

1981-01-01

Observations of the J = 2-1 and J = 1-0 transitions of 12 CO and 13 CO reveal the presence of high velocity molecular gas associated with a low luminosity infrared source in the vicinity of the Herbig-Haro objects HH 7--11. The blueshifted and redshifted wings show peak intensities spatially separated by 1X5 (0.2 pc), suggesting an energetic bipolar outflow of gas from a young low mass star. The mass loss rate implied by these observations is 8 x 10 -6 M/sub sun/ yr -1

Spectral Variability of the Herbig Ae/Be Star HD 37806

Science.gov (United States)

Pogodin, M. A.; Pavlovskiy, S. E.; Kozlova, O. V.; Beskrovnaya, N. G.; Alekseev, I. Yu.; Valyavin, G. G.

2018-03-01

Results are reported from a spectroscopic study of the Herbig Ae/Be star HD 37806 from 2009 through 2017 using high resolution spectrographs at the Crimean Astrophysical Observatory and the OAN SPM Observatory in Mexico. 72 spectra of this object near the Hα, Hβ, HeI 5876 and D NaI lines are analyzed. The following results were obtained: 1. The type of spectral profile of the Hα line can change from P Cyg III to double emission and vice versa over a time scale on the order of a month. 2. Narrow absorption components are observed in the profiles of the Hα and D NaI lines with radial velocities that vary over a characteristic time on the order of a day. 3. On some days, the profiles of the Hβ, HeI 5876, and D NaI lines show signs of accretion of matter to the star with a characteristic lifetime of a few days. A possible interpretation of these phenomena was considered. The transformation of the Hα profile may be related to a change in the outer latitudinal width of the boundary of the wind zone. The narrow variable absorption lines may be caused by the rotation of local azimuthal inhomogeneities in the wind zone owing to the interaction of the disk with the star's magnetosphere in a propeller regime. Several current theoretical papers that predict the formation of similar inhomogeneous wind structures were examined. It is suggested that the episodes with signs of accretion in the spectral line profiles cannot be a consequence of the modulation of these profiles by the star's rotation but are more likely caused by sudden, brief changes in the accretion rate. These spectral observations of HD 37806 should be continued in a search for cyclical variability in the spectral parameters in order to identify direct signs of magnetospheric accretion and detect possible binary behavior in this object.

HH 222: A GIANT HERBIG-HARO FLOW FROM THE QUADRUPLE SYSTEM V380 ORI

Energy Technology Data Exchange (ETDEWEB)

Reipurth, Bo; Aspin, Colin; Connelley, M. S. [Institute for Astronomy, University of Hawaii at Manoa, 640 North Aohoku Place, Hilo, HI 96720 (United States); Bally, John [Center for Astrophysics and Space Astronomy, University of Colorado, Boulder, CO 80309 (United States); Geballe, T. R. [Gemini Observatory, 670 North Aohoku Place, Hilo, HI 96720 (United States); Kraus, Stefan [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-78, Cambridge, MA 02138 (United States); Appenzeller, Immo [Landessternwarte Heidelberg, Königstuhl 12, D-69117 Heidelberg (Germany); Burgasser, Adam, E-mail: reipurth@ifa.hawaii.edu, E-mail: caa@ifa.hawaii.edu, E-mail: msc@ifa.hawaii.edu, E-mail: John.Bally@colorado.edu, E-mail: tgeballe@gemini.edu, E-mail: stefan.kraus@cfa.harvard.edu, E-mail: iappenze@lsw.uni-heidelberg.de, E-mail: aburgasser@ucsd.edu [Center for Astrophysics and Space Science, University of California San Diego, La Jolla, CA 92093 (United States)

2013-11-01

HH 222 is a giant shocked region in the L1641 cloud, and is popularly known as the Orion Streamers or ''the waterfall'' on account of its unusual structure. At the center of these streamers are two infrared sources coincident with a nonthermal radio jet aligned along the principal streamer. The unique morphology of HH 222 has long been associated with this radio jet. However, new infrared images show that the two sources are distant elliptical galaxies, indicating that the radio jet is merely an improbable line-of-sight coincidence. Accurate proper motion measurements of HH 222 reveal that the shock structure is a giant bow shock moving directly away from the well-known, very young, Herbig Be star V380 Ori. The already known Herbig-Haro object HH 35 forms part of this flow. A new Herbig-Haro object, HH 1041, is found precisely in the opposite direction of HH 222 and is likely to form part of a counterflow. The total projected extent of this HH complex is 5.3 pc, making it among the largest HH flows known. A second outflow episode from V380 Ori is identified as a pair of HH objects, HH 1031 to the northwest and the already known HH 130 to the southeast, along an axis that deviates from that of HH 222/HH 1041 by only 3.°7. V380 Ori is a hierarchical quadruple system, including a faint companion of spectral type M5 or M6, which at an age of ∼1 Myr corresponds to an object straddling the stellar-to-brown dwarf boundary. We suggest that the HH 222 giant bow shock is a direct result of the dynamical interactions that led to the conversion from an initial non-hierarchical multiple system into a hierarchical configuration. This event occurred no more than 28,000 yr ago, as derived from the proper motions of the HH 222 giant bow shock.

Accretion Disks around Young Stars: An Observational Perspective

Science.gov (United States)

Ménard, F.; Bertout, C.

Accretion disks are pivotal elements in the formation and early evolution of solar-like stars. On top of supplying the raw material, their internal conditions also regulate the formation of planets. Their study therefore holds the key to solve this long standing mystery: how did our Solar System form? This chapter focuses on observational studies of the circumstellar environment, and in particular of circumstellar disks, associated with pre-main sequence solar-like stars. The direct measurement of disk parameters poses an obvious challenge: at the distance of the typical star forming regions ( e.g. 140 pc for Taurus), a planetary system like ours (with diameter simeq50 AU out to Pluto, but excluding the Kuiper belt which could extend much farther out) subtends only 0.35''. Yet its surface brightness is low in comparison to the bright central star and high angular and high contrast imaging techniques are required if one hopes to resolve and measure these protoplanetary disks. Fortunately, capable instruments providing 0.1'' resolution or better and high contrast have been available for just about 10 years now. They are covering a large part of the electromagnetic spectrum, from the UV/Optical with HST and the near-infrared from ground-based adaptive optics systems, to the millimetric range with long-baseline radio interferometers. It is therefore not surprising that our knowledge of the structure of the disks surrounding low-mass stars has made a gigantic leap forward in the last decade. In the following pages we will attempt to describe, in a historical perpective, the road that led to the idea that most solar-like stars are surrounded by an accretion disk at one point in their early life and how, nowadays, their structural and physical parameters can be estimated from direct observations. We will follow by a short discussion of a few of the constraints available regarding the evolution and dissipation of these disks. This last topic is particularly relevant today

Experimental chemonucleolysis with chymopapain in canine intervertebral disks

International Nuclear Information System (INIS)

Kudo, T.; Sumi, A.; Hashimoto, A.

1993-01-01

The present study describes the radiological and histological changes in the canine intervertebral disk after the experimental injection of chymopapain as the chemical reagent, and determines the appropriate dose of the enzyme for treatment of herniated disks. By radiography, narrowing of the disk space was observed within 2 weeks after the injection of chymopapain, and recovered to 74.1% in the 0.1 mg group, 61.1% in the 1.0 mg group and 71.7% in the 10.0 mg group at 12 weeks. The disk space recovery showed a tendency to delay with aging. Microscopically, proteoglycan positive matrix appeared and the nuclear space was reduced in each disk at 2 weeks after chymopapain injection. The nucleus pulposus contained an irregularly-defined mass consisting of clusters of degenerated notochordal cells surrounded by proliferated chondrocytes and collagen matrix. In each disk at 12 weeks after chymopapain injection, the center of the nucleus pulposus was replaced by fibrocartilage tissue. In the disk into which 10.0 mg chymopapain was injected, the nuclear space filled with dense fibrocartilage tissue without a regenerated matrix component and narrowing of the disk were maintained. It is suggested that canine chemonucleolysis with 10.0 mg of chymopapain reduces the interdiskal pressure. This treatment may therefore relieve the signs and symptoms of herniation of the nucleus pulposus, and may effect chemical disk decompression

IRAS observations of the exciting stars of Herbig-Haro objects. II. The Reipurth and Graham sample and low-resolution spectra

International Nuclear Information System (INIS)

Cohen, M.

1990-01-01

Using IRAS COADDed images, candidates are suggested for the exciting stars of Herbig-Haro objects from the Reipurth and Graham sample. The IRAS low-resolution spectrometer provides spectra for 20 of the 46 candidate stars so far identified as exciting young, unevolved H-H systems. These reveal 10-micron silicate absorption features, or are too red to show detectable flux near 10 microns. The histogram of bolometric luminosities for 46 young Herbig-Haro exciting stars has a median of 13 solar luminosities and a mode between 16 and 32 solar luminosities. Although the enlarged sample of known exciting stars has more of the higher luminosity objects than an earlier sample, the histogram still represents a generally low-luminosity distribution. 27 refs

A model for neutrino emission from nuclear accretion disks

Science.gov (United States)

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).

TH28 (Krautter's star) and its string of Herbig-Haro objects

International Nuclear Information System (INIS)

Graham, J.A.; Heyer, M.H.

1988-01-01

A high-quality spectrogram of the unusual T Tauri-like star Th28 and its string of Herbig-Haro (HH) objects has been obtained. New velocities and line intensities for the star and the gaseous knots are reported, and data are given for a third HH object located 87 arcsec to the SE along the same collimation axis as defined by the other features. Th28 has a heliocentric velocity of +5 km/s which is close to the velocity of the CO in the area. The star's spectral type is probably in the G8-K2 range. 24 references

An oxygen-rich dust disk surrounding an evolved star in the Red Rectangle

NARCIS (Netherlands)

Waters, LBFM; Waelkens, C; van Winckel, H; Molster, FJ; Tielens, AGGM; van Loon, JT; Morris, PW; Cami, J; Bouwman, J; de Koter, A; de Jong, T; de Graauw, T

1998-01-01

The Red Rectangle(1) is the prototype of a class of carbon-rich reflection nebulae surrounding low-mass stars in the final stages of evolution. The central star of this nebula has ejected most of its layers (during the red-giant phase), which now form the surrounding cloud, and is rapidly evolving

The characteristics of the IR emission features in the spectra of Herbig Ae stars : evidence for chemical evolution

NARCIS (Netherlands)

Boersma, C.; Bouwman, J.; Lahuis, F.; van Kerckhoven, C.; Tielens, A. G. G. M.; Waters, L. B. F. M.; Henning, T.

Context. Infrared ( IR) spectra provide a prime tool to study the characteristics of polycyclic aromatic hydrocarbon ( PAH) molecules in regions of star formation. Herbig Ae/Be stars are a class of young pre-main sequence stellar objects of intermediate mass. They are known to have varying amounts

DYNAMICS OF CIRCUMSTELLAR DISKS. III. THE CASE OF GG Tau A

International Nuclear Information System (INIS)

Nelson, Andrew F.; Marzari, F.

2016-01-01

We present two-dimensional hydrodynamic simulations using the Smoothed Particle Hydrodynamic code, VINE, to model a self-gravitating binary system. We model configurations in which a circumbinary torus+disk surrounds a pair of stars in orbit around each other and a circumstellar disk surrounds each star, similar to that observed for the GG Tau A system. We assume that the disks cool as blackbodies, using rates determined independently at each location in the disk by the time dependent temperature of the photosphere there. We assume heating due to hydrodynamical processes and to radiation from the two stars, using rates approximated from a measure of the radiation intercepted by the disk at its photosphere. We simulate a suite of systems configured with semimajor axes of either a = 62 AU (“wide”) or a = 32 AU (“close”), and with assumed orbital eccentricity of either e = 0 or e = 0.3. Each simulation follows the evolution for ∼6500–7500 yr, corresponding to about three orbits of the torus around the center of mass. Our simulations show that strong, sharply defined spiral structures are generated from the stirring action of the binary and that, in some cases, these structures fragment into 1–2 massive clumps. The torus quickly fragments into several dozen such fragments in configurations in which either the binary is replaced by a single star of equal mass, or radiative heating is neglected. The spiral structures extend inwards to the circumstellar environment as large scale material streams for which most material is found on trajectories that return it to the torus on a timescale of 1–200 yr, with only a small fraction accreting into the circumstellar environment. The spiral structures also propagate outwards through the torus, generating net outwards mass flow, and eventually losing coherence at large distances from the stars. The torus becomes significantly eccentric in shape over most of its evolution. In all configurations, accretion onto the

DYNAMICS OF CIRCUMSTELLAR DISKS. III. THE CASE OF GG Tau A

Energy Technology Data Exchange (ETDEWEB)

Nelson, Andrew F. [XCP-2, Mailstop T082, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Marzari, F., E-mail: andy.nelson@lanl.gov, E-mail: francesco.marzari@pd.infn.it [Università di Padova, Dipartimento di Fisica, via Marzolo 8, 35131 Padova (Italy)

2016-08-20

We present two-dimensional hydrodynamic simulations using the Smoothed Particle Hydrodynamic code, VINE, to model a self-gravitating binary system. We model configurations in which a circumbinary torus+disk surrounds a pair of stars in orbit around each other and a circumstellar disk surrounds each star, similar to that observed for the GG Tau A system. We assume that the disks cool as blackbodies, using rates determined independently at each location in the disk by the time dependent temperature of the photosphere there. We assume heating due to hydrodynamical processes and to radiation from the two stars, using rates approximated from a measure of the radiation intercepted by the disk at its photosphere. We simulate a suite of systems configured with semimajor axes of either a = 62 AU (“wide”) or a = 32 AU (“close”), and with assumed orbital eccentricity of either e = 0 or e = 0.3. Each simulation follows the evolution for ∼6500–7500 yr, corresponding to about three orbits of the torus around the center of mass. Our simulations show that strong, sharply defined spiral structures are generated from the stirring action of the binary and that, in some cases, these structures fragment into 1–2 massive clumps. The torus quickly fragments into several dozen such fragments in configurations in which either the binary is replaced by a single star of equal mass, or radiative heating is neglected. The spiral structures extend inwards to the circumstellar environment as large scale material streams for which most material is found on trajectories that return it to the torus on a timescale of 1–200 yr, with only a small fraction accreting into the circumstellar environment. The spiral structures also propagate outwards through the torus, generating net outwards mass flow, and eventually losing coherence at large distances from the stars. The torus becomes significantly eccentric in shape over most of its evolution. In all configurations, accretion onto the

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

Science.gov (United States)

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.

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

Science.gov (United States)

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†

Science.gov (United States)

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.

Observations of high-velocity molecular gas near Herbig-Haro objects: HH 24--27 and HH 1--2

International Nuclear Information System (INIS)

Snell, R.L.; Edwards, S.

1982-01-01

High-velocity CO has been detected in the vicinity of the Herbig-Haro objects HH 24--27. These observations indicate that there are two sources of high-velocity outflow; one centered on an infrared source near HH 26, and the second centered roughly 2' south of HH 24. The redshifted and blueshifted wings in both sources are spatially separated suggesting that the high-velocity gas is due to energetic bipolar outflow from young stars embedded in the molecular cloud. The association of Herbig-Haro objects with regions of high-velocity gas suggests a common origin for both in the interaction of a stellar wind with the ambient molecular cloud. The mass loss rates implied by our observations, assuming that the rate of mass loss has been constant throughout the dynamical lifetime of the bipolar lobes, are roughly 10 -6 M/sub sun/ yr -1 for both sources. We have also searched for high-velocity gas near HH 1--2 but found no evidence for mass outflow in this region

Constraining the disk masses of the class I binary protostar GV Tau

Energy Technology Data Exchange (ETDEWEB)

Sheehan, Patrick D.; Eisner, Josh A., E-mail: psheehan@email.arizona.edu [Steward Observatory, University of Arizona 933 North Cherry Avenue, Tucson, AZ 85721 (United States)

2014-08-10

We present new spatially resolved 1.3 mm imaging with CARMA of the GV Tau system. GV Tau is a Class I binary protostar system in the Taurus Molecular Cloud, the components of which are separated by 1.''2. Each protostar is surrounded by a protoplanetary disk, and the pair may be surrounded by a circumbinary envelope. We analyze the data using detailed radiative transfer modeling of the system. We create synthetic protostar model spectra, images, and visibilities and compare them with CARMA 1.3 mm visibilities, a Hubble Space Telescope near-infrared scattered light image, and broadband spectral energy distributions from the literature to study the disk masses and geometries of the GV Tau disks. We show that the protoplanetary disks around GV Tau fall near the lower end of estimates of the Minimum Mass Solar Nebula, and may have just enough mass to form giant planets. When added to the sample of Class I protostars from Eisner, we confirm that Class I protostars are on average more massive than their Class II counterparts. This suggests that substantial dust grain processing occurs between the Class I and Class II stages, and may help to explain why the Class II protostars do not appear to have, on average, enough mass in their disks to form giant planets.

Characterizing Protoplanetary Disks in a Young Binary in Orion

Science.gov (United States)

Powell, Jonas; Hughes, A. Meredith; Mann, Rita; Flaherty, Kevin; Di Francesco, James; Williams, Jonathan

2018-01-01

Planetary systems form in circumstellar disks of gas and dust surrounding young stars. One open question in the study of planet formation involves understanding how different environments affect the properties of the disks and planets they generate. Understanding the properties of disks in high-mass star forming regions (SFRs) is critical since most stars - probably including our Sun - form in those regions. By comparing the disks in high-mass SFRs to those in better-studied low-mass SFRs we can learn about the role environment plays in planet formation. Here we present 0.5" resolution observations of the young two-disk binary system V2434 Ori in the Orion Nebula from the Atacama Large Millimeter/submillimeter Array (ALMA) in molecular line tracers of CO(3-2), HCN(4-3), HCO+(4-3) and CS(7-6). We model each disk’s mass, radius, temperature structure, and molecular abundances, by creating synthetic images using an LTE ray-tracing code and comparing simulated observations with the ALMA data in the visibility domain. We then compare our results to a previous study of molecular line emission from a single Orion proplyd, modeled using similar methods, and to previously characterized disks in low-mass SFRs to investigate the role of environment in disk chemistry and planetary system formation.

Increased H2CO production in the outer disk around HD 163296

Science.gov (United States)

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

First Images from the PIONIER/VLTI optical interferometry imaging survey of Herbig Ae/Be stars

Science.gov (United States)

Kluska, Jacques; Malbet, Fabien; Berger, Jean-Philippe; Benisty, Myriam; Lazareff, Bernard; Le Bouquin, Jean-Baptiste; Baron, Fabien; Dominik, Carsten; Isella, Andrea; Juhasz, Attila; Kraus, Stefan; Lachaume, Régis; Ménard, François; Millan-Gabet, Rafael; Monnier, John; Pinte, Christophe; Thi, Wing-Fai; Thiébaut, Eric; Zins, Gérard

2013-07-01

The morphology of the close environment of herbig stars is being revealed step by step and appears to be quite complex. Many physical phenomena could interplay : the dust sublimation causing a puffed-up inner rim, a dusty halo, a dusty wind or an inner gaseous component. To investigate more deeply these regions, getting images at the first Astronomical Unit scale is crucial. This has become possible with near infrared instruments on the VLTi. We are carrying out the first Large Program survey of HAeBe stars with statistics on the geometry of these objects at the first astronomical unit scale and the first images of the very close environment of some of them. We have developed a new numerical method specific to young stellar objects which removes the stellar component reconstructing an image of the environment only. To do so we are using the differences in the spectral behaviour between the star and its environment. The images reveal the environement which is not polluted by the star and allow us to derive the best fit for the flux ratio and the spectral slope between the two components (stellar and environmental). We present the results of the survey with some statistics and the frist images of Herbig stars made by PIONIER on the VLTi.

Dust in protoplanetary disks: observations*

Directory of Open Access Journals (Sweden)

Waters L.B.F.M.

2015-01-01

Full Text Available Solid particles, usually referred to as dust, are a crucial component of interstellar matter and of planet forming disks surrounding young stars. Despite the relatively small mass fraction of ≈1% (in the solar neighborhood of our galaxy; this number may differ substantially in other galaxies that interstellar grains represent of the total mass budget of interstellar matter, dust grains play an important role in the physics and chemistry of interstellar matter. This is because of the opacity dust grains at short (optical, UV wavelengths, and the surface they provide for chemical reactions. In addition, dust grains play a pivotal role in the planet formation process: in the core accretion model of planet formation, the growth of dust grains from the microscopic size range to large, cm-sized or larger grains is the first step in planet formation. Not only the grain size distribution is affected by planet formation. Chemical and physical processes alter the structure and chemical composition of dust grains as they enter the protoplanetary disk and move closer to the forming star. Therefore, a lot can be learned about the way stars and planets are formed by observations of dust in protoplanetary disks. Ideally, one would like to measure the dust mass, the grain size distribution, grain structure (porosity, fluffiness, the chemical composition, and all of these as a function of position in the disk. Fortunately, several observational diagnostics are available to derive constrains on these quantities. In combination with rapidly increasing quality of the data (spatial and spectral resolution, a lot of progress has been made in our understanding of dust evolution in protoplanetary disks. An excellent review of dust evolution in protoplanetary disks can be found in Testi et al. (2014.

Feasibility of using PZT actuators to study the dynamic behavior of a rotating disk due to rotor-stator interaction.

Science.gov (United States)

Presas, Alexandre; Egusquiza, Eduard; Valero, Carme; Valentin, David; Seidel, Ulrich

2014-07-07

In this paper, PZT actuators are used to study the dynamic behavior of a rotating disk structure due to rotor-stator interaction excitation. The disk is studied with two different surrounding fluids-air and water. The study has been performed analytically and validated experimentally. For the theoretical analysis, the natural frequencies and the associated mode shapes of the rotating disk in air and water are obtained with the Kirchhoff-Love thin plate theory coupled with the interaction with the surrounding fluid. A model for the Rotor Stator Interaction that occurs in many rotating disk-like parts of turbomachinery such as compressors, hydraulic runners or alternators is presented. The dynamic behavior of the rotating disk due to this excitation is deduced. For the experimental analysis a test rig has been developed. It consists of a stainless steel disk (r = 198 mm and h = 8 mm) connected to a variable speed motor. Excitation and response are measured from the rotating system. For the rotating excitation four piezoelectric patches have been used. Calibrating the piezoelectric patches in amplitude and phase, different rotating excitation patterns are applied on the rotating disk in air and in water. Results show the feasibility of using PZT to control the response of the disk due to a rotor-stator interaction.

Feasibility of Using PZT Actuators to Study the Dynamic Behavior of a Rotating Disk due to Rotor-Stator Interaction

Directory of Open Access Journals (Sweden)

Alexandre Presas

2014-07-01

Full Text Available In this paper, PZT actuators are used to study the dynamic behavior of a rotating disk structure due to rotor-stator interaction excitation. The disk is studied with two different surrounding fluids—air and water. The study has been performed analytically and validated experimentally. For the theoretical analysis, the natural frequencies and the associated mode shapes of the rotating disk in air and water are obtained with the Kirchhoff-Love thin plate theory coupled with the interaction with the surrounding fluid. A model for the Rotor Stator Interaction that occurs in many rotating disk-like parts of turbomachinery such as compressors, hydraulic runners or alternators is presented. The dynamic behavior of the rotating disk due to this excitation is deduced. For the experimental analysis a test rig has been developed. It consists of a stainless steel disk (r = 198 mm and h = 8 mm connected to a variable speed motor. Excitation and response are measured from the rotating system. For the rotating excitation four piezoelectric patches have been used. Calibrating the piezoelectric patches in amplitude and phase, different rotating excitation patterns are applied on the rotating disk in air and in water. Results show the feasibility of using PZT to control the response of the disk due to a rotor-stator interaction.

CLUSTER DYNAMICS LARGELY SHAPES PROTOPLANETARY DISK SIZES

Energy Technology Data Exchange (ETDEWEB)

Vincke, Kirsten; Pfalzner, Susanne, E-mail: kvincke@mpifr-bonn.mpg.de [Max Planck Institute for Radio Astronomy, Auf dem Hügel 69, D-53121 Bonn (Germany)

2016-09-01

To what degree the cluster environment influences the sizes of protoplanetary disks surrounding young stars is still an open question. This is particularly true for the short-lived clusters typical for the solar neighborhood, in which the stellar density and therefore the influence of the cluster environment change considerably over the first 10 Myr. In previous studies, the effect of the gas on the cluster dynamics has often been neglected; this is remedied here. Using the code NBody6++, we study the stellar dynamics in different developmental phases—embedded, expulsion, and expansion—including the gas, and quantify the effect of fly-bys on the disk size. We concentrate on massive clusters (M {sub cl} ≥ 10{sup 3}–6 ∗ 10{sup 4} M {sub Sun}), which are representative for clusters like the Orion Nebula Cluster (ONC) or NGC 6611. We find that not only the stellar density but also the duration of the embedded phase matters. The densest clusters react fastest to the gas expulsion and drop quickly in density, here 98% of relevant encounters happen before gas expulsion. By contrast, disks in sparser clusters are initially less affected, but because these clusters expand more slowly, 13% of disks are truncated after gas expulsion. For ONC-like clusters, we find that disks larger than 500 au are usually affected by the environment, which corresponds to the observation that 200 au-sized disks are common. For NGC 6611-like clusters, disk sizes are cut-down on average to roughly 100 au. A testable hypothesis would be that the disks in the center of NGC 6611 should be on average ≈20 au and therefore considerably smaller than those in the ONC.

Narrowband imaging of the Herbig-Haro object HH 46/47

International Nuclear Information System (INIS)

Raga, A.C.; Mateo, M.

1987-01-01

Narrow-band CCD images of the HH 46/47 system were obtained in the light of the H-alpha, forbidden N II 6583-A forbidden S II 6717-A and forbidden S II 6731-A emission lines. The images include HH 46, HH 47B, and HH 47A. A calibration for these images was carried out that makes it possible to calculate line ratios, and then use these line ratios as diagnostics of the physical conditions in the radiating gas. The study shows that the bright condensation HH 47A has a higher electron density and a lower excitation spectrum than the jet that joins this condensation to the central source. This result does not agree with the observations of other morphologically similar Herbig-Haro objects. 36 references

General relativistic model for the gravitational field of active galactic nuclei surrounded by a disk

NARCIS (Netherlands)

Vogt, D.; Letelier, P.S.

2005-01-01

An exact but simple general relativistic model for the gravitational field of active galactic nuclei is constructed, based on the superposition in Weyl coordinates of a black hole, a Chazy-Curzon disk and two rods, which represent matter jets. The influence of the rods on the matter properties of

Disk

NARCIS (Netherlands)

P.A. Boncz (Peter); L. Liu (Lei); M. Tamer Özsu

2008-01-01

htmlabstractIn disk storage, data is recorded on planar, round and rotating surfaces (disks, discs, or platters). A disk drive is a peripheral device of a computer system, connected by some communication medium to a disk controller. The disk controller is a chip, typically connected to the CPU of

MID-INFRARED SPECTRA OF TRANSITIONAL DISKS IN THE CHAMAELEON I CLOUD

International Nuclear Information System (INIS)

Kim, K. H.; Watson, Dan M.; Manoj, P.; Forrest, W. J.; Sargent, B.; McClure, M. K.; Green, J. D.; Harrold, Samuel T.; Furlan, E.; Najita, J.; Espaillat, C.; Calvet, N.; Luhman, K. L.

2009-01-01

We present 5-40 μm 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 Chamaeleon 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.

Structure of Herbig-Haro object 43 and Orion dark cloud extinction

International Nuclear Information System (INIS)

Schwartz, R.D.; Dopita, M.A.; Cohen, M.; Mount Stromlo and Siding Spring Observatories, Canberra, Australia; NASA, Ames Research Center, Moffett Field; California Univ., Berkeley)

1985-01-01

New ultraviolet and optical observations of Herbig-Haro object No. 43 are reported. Continuum and emission-line fluxes in the wavelength range 1250 to 7350 A have been measured. The continuum fluxes are best matched by an enhanced H exp 0 two-photon component added to H free-bound emission, assuming a Theta Ori extinction curve with E(B - V) = 0.2, R = 5. The structure and dynamics of three components within the object are discussed. The object has a radiative output of not less than 0.23 solar luminosities in ultraviolet and optical radiation combined. The energy requirements are discussed in terms of the production of shock waves by a collimated, supersonic mass outflow from a nearby infrared source. 16 references

New Herbig-Haro objects in star-forming regions

Science.gov (United States)

Reipurth, BO; Graham, J. A.

1988-01-01

A list of 25 new Herbig-Haro objects, HH 58 to HH 82, in the Orion molecular clouds and in southern molecular cloud complexes has been compiled. CCD images in the S II 6717, 6731 forbidden lines are presented for the objects, together with a few spectra and some IR observations. The individual objects and, when identified, their energy sources are discussed. HH 65 is located in the red lobe of the bipolar outflow associated with the highly variable reflection nebula Re 50. HH 67 is a 22-arcsec long sinusoidal jet. HH 68/69 consists of a long, linear chain of four HH knots. HH 72 emerges from a 120-solar luminosity IRAS source embedded in a Bok globule. HH 79 is the first HH object discovered in the Ophiuchus clouds. HH 80/81 in Sagittarius are among the brightest HH objects known, have complex velocities, high excitation conditions and emerge from a 6000-solar luminosity young B-star. HH 82 is associated with the bright variable star S Coronae Australis.

High-resolution observations of IRAS 08544-4431. Detection of a disk orbiting a post-AGB star and of a slow disk wind

Science.gov (United States)

Bujarrabal, V.; Castro-Carrizo, A.; Winckel, H. Van; Alcolea, J.; Contreras, C. Sánchez; Santander-García, M.; Hillen, M.

2018-06-01

Context. Aims: In order to study the effects of rotating disks in the post-asymptotic giant branch (post-AGB) evolution, we observe a class of binary post-AGB stars that seem to be systematically surrounded by equatorial disks and slow outflows. Although the rotating dynamics had only been well identified in three cases, the study of such structures is thought to be fundamental to the understanding of the formation of disks in various phases of the late evolution of binary stars and the ejection of planetary nebulae from evolved stars. Methods: We present ALMA maps of 12CO and 13CO J = 3-2 lines in the source IRAS 08544-4431, which belongs to the above mentioned class of objects. We analyzed the data by means of nebula models, which account for the expectedly composite source and can reproduce the data. From our modeling, we estimated the main nebula parameters, including the structure and dynamics and the density and temperature distributions. We discuss the uncertainties of the derived values and, in particular, their dependence on the distance. Results: Our observations reveal the presence of an equatorial disk in rotation; a low-velocity outflow is also found, probably formed of gas expelled from the disk. The main characteristics of our observations and modeling of IRAS 08544-4431 are similar to those of better studied objects, confirming our interpretation. The disk rotation indicates a total central mass of about 1.8 M⊙, for a distance of 1100 pc. The disk is found to be relatively extended and has a typical diameter of 4 × 1016 cm. The total nebular mass is 2 × 10-2 M⊙, of which 90% corresponds to the disk. Assuming that the outflow is due to mass loss from the disk, we derive a disk lifetime of 10 000 yr. The disk angular momentum is found to be comparable to that of the binary system at present. Assuming that the disk angular momentum was transferred from the binary system, as expected, the high values of the disk angular momentum in this and other

THE EVOLUTION OF PROTOPLANETARY DISKS IN THE ARCHES CLUSTER

International Nuclear Information System (INIS)

Olczak, C.; Kaczmarek, T.; Pfalzner, S.; Harfst, S.; Portegies Zwart, S.

2012-01-01

Most stars form in a cluster environment. These stars are initially surrounded by disks from which potentially planetary systems form. Of all cluster environments, starburst clusters are probably the most hostile for planetary systems in our Galaxy. The intense stellar radiation and extreme density favor rapid destruction of circumstellar disks via photoevaporation and stellar encounters. Evolving a virialized model of the Arches cluster in the Galactic tidal field, we investigate the effect of stellar encounters on circumstellar disks in a prototypical starburst cluster. Despite its proximity to the deep gravitational potential of the Galactic center, only a moderate fraction of members escapes to form an extended pair of tidal tails. Our simulations show that encounters destroy one-third of the circumstellar disks in the cluster core within the first 2.5 Myr of evolution, preferentially affecting the least and most massive stars. A small fraction of these events causes rapid ejection and the formation of a weaker second pair of tidal tails that is overpopulated by disk-poor stars. Two predictions arise from our study. (1) If not destroyed by photoevaporation protoplanetary disks of massive late B- and early O-type stars represent the most likely hosts of planet formation in starburst clusters. (2) Multi-epoch K- and L-band photometry of the Arches cluster would provide the kinematically selected membership sample required to detect the additional pair of disk-poor tidal tails.

AN EXTREME ANALOGUE OF ϵ AURIGAE: AN M-GIANT ECLIPSED EVERY 69 YEARS BY A LARGE OPAQUE DISK SURROUNDING A SMALL HOT SOURCE

Energy Technology Data Exchange (ETDEWEB)

Rodriguez, Joseph E.; Stassun, Keivan G.; Lund, Michael B.; Conroy, Kyle E. [Department of Physics and Astronomy, Vanderbilt University, 6301 Stevenson Center, Nashville, TN 37235 (United States); Siverd, Robert J. [Las Cumbres Observatory Global Telescope Network, 6740 Cortona Drive, Suite 102, Santa Barbara, CA 93117 (United States); Pepper, Joshua [Department of Physics, Lehigh University, 16 Memorial Drive East, Bethlehem, PA 18015 (United States); Tang, Sumin [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Kafka, Stella [American Association of Variable Star Observers, 49 Bay State Road, Cambridge, MA 02138 (United States); Gaudi, B. Scott; Stevens, Daniel J.; Kochanek, Christopher S. [Department of Astronomy, The Ohio State University, Columbus, OH 43210 (United States); Beatty, Thomas G. [Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Lab, University Park, PA 16802 (United States); Shappee, Benjamin J. [Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)

2016-05-01

We present TYC 2505-672-1 as a newly discovered and remarkable eclipsing system comprising an M-type red giant that undergoes a ∼3.45 year long, near-total eclipse (depth of ∼4.5 mag) with a very long period of ∼69.1 years. TYC 2505-672-1 is now the longest-period eclipsing binary system yet discovered, more than twice as long as that of the currently longest-period system, ϵ Aurigae. We show from analysis of the light curve including both our own data and historical data spanning more than 120 years and from modeling of the spectral energy distribution, both before and during eclipse, that the red giant primary is orbited by a moderately hot source ( T {sub eff} ≈ 8000 K) that is itself surrounded by an extended, opaque circumstellar disk. From the measured ratio of luminosities, the radius of the hot companion must be in the range of 0.1–0.5 R {sub ⊙} (depending on the assumed radius of the red giant primary), which is an order of magnitude smaller than that for a main sequence A star and 1–2 orders of magnitude larger than that for a white dwarf. The companion is therefore most likely a “stripped red giant” subdwarf-B type star destined to become a He white dwarf. It is, however, somewhat cooler than most sdB stars, implying a very low mass for this “pre-He-WD” star. The opaque disk surrounding this hot source may be a remnant of the stripping of its former hydrogen envelope. However, it is puzzling how this object became stripped, given that it is at present so distant (orbital semimajor axis of ∼24 au) from the current red giant primary star. Extrapolating from our calculated ephemeris, the next eclipse should begin in early UT 2080 April and end in mid UT 2083 September (eclipse center UT 2081 December 24). In the meantime, radial velocity observations would establish the masses of the components, and high-cadence UV observations could potentially reveal oscillations of the hot companion that would further constrain its evolutionary

PETROLOGIC CONSTRAINTS ON AMORPHOUS AND CRYSTALLINE MAGNESIUM SILICATES: DUST FORMATION AND EVOLUTION IN SELECTED HERBIG Ae/Be SYSTEMS

International Nuclear Information System (INIS)

Rietmeijer, Frans J. M.; Nuth, Joseph A.

2013-01-01

The Infrared Space Observatory, Spitzer Space Telescope, and Herschel Space Observatory surveys provided a wealth of data on the Mg-silicate minerals (forsterite, enstatite), silica, and ''amorphous silicates with olivine and pyroxene stoichiometry'' around Herbig Ae/Be stars. These incredible findings do not resonate with the mainstream Earth Sciences because of (1) disconnecting ''astronomical nomenclature'' and the long existing mineralogical and petrologic terminology of minerals and amorphous materials, and (2) the fact that Earth scientists (formerly geologists) are bound by the ''Principle of Actualism'' that was put forward by James Hutton (1726-1797). This principle takes a process-oriented approach to understanding mineral and rock formation and evolution. This paper will (1) review and summarize the results of laboratory-based vapor phase condensation and thermal annealing experiments, (2) present the pathways of magnesiosilica condensates to Mg-silicate mineral (forsterite, enstatite) formation and processing, and (3) present mineralogical and petrologic implications of the properties and compositions of the infrared-observed crystalline and amorphous dust for the state of circumstellar disk evolution. That is, the IR-observation of smectite layer silicates in HD142527 suggests the break-up of asteroid-like parent bodies that had experienced aqueous alteration. We discuss the persistence of amorphous dust around some young stars and an ultrafast amorphous to crystalline dust transition in HD 163296 that leads to forsterite grains with numerous silica inclusions. These dust evolution processes to form forsterite, enstatite ± tridymite could occur due to amorphous magnesiosilica dust precursors with a serpentine- or smectite-dehydroxylate composition.

PETROLOGIC CONSTRAINTS ON AMORPHOUS AND CRYSTALLINE MAGNESIUM SILICATES: DUST FORMATION AND EVOLUTION IN SELECTED HERBIG Ae/Be SYSTEMS

Energy Technology Data Exchange (ETDEWEB)

Rietmeijer, Frans J. M. [Department of Earth and Planetary Sciences, MSC 03 2040, 1-University of New Mexico, Albuquerque, NM 87131-001 (United States); Nuth, Joseph A., E-mail: fransjmr@unm.edu [Astrochemistry Laboratory, Solar System Exploration Division, Code 691, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

2013-07-01

The Infrared Space Observatory, Spitzer Space Telescope, and Herschel Space Observatory surveys provided a wealth of data on the Mg-silicate minerals (forsterite, enstatite), silica, and ''amorphous silicates with olivine and pyroxene stoichiometry'' around Herbig Ae/Be stars. These incredible findings do not resonate with the mainstream Earth Sciences because of (1) disconnecting ''astronomical nomenclature'' and the long existing mineralogical and petrologic terminology of minerals and amorphous materials, and (2) the fact that Earth scientists (formerly geologists) are bound by the ''Principle of Actualism'' that was put forward by James Hutton (1726-1797). This principle takes a process-oriented approach to understanding mineral and rock formation and evolution. This paper will (1) review and summarize the results of laboratory-based vapor phase condensation and thermal annealing experiments, (2) present the pathways of magnesiosilica condensates to Mg-silicate mineral (forsterite, enstatite) formation and processing, and (3) present mineralogical and petrologic implications of the properties and compositions of the infrared-observed crystalline and amorphous dust for the state of circumstellar disk evolution. That is, the IR-observation of smectite layer silicates in HD142527 suggests the break-up of asteroid-like parent bodies that had experienced aqueous alteration. We discuss the persistence of amorphous dust around some young stars and an ultrafast amorphous to crystalline dust transition in HD 163296 that leads to forsterite grains with numerous silica inclusions. These dust evolution processes to form forsterite, enstatite {+-} tridymite could occur due to amorphous magnesiosilica dust precursors with a serpentine- or smectite-dehydroxylate composition.

Observations of zodiacal light of the isolated Herbig BF Ori Ae star

International Nuclear Information System (INIS)

Grinin, V.P.; Kiselev, N.N.; Minikulov, N.Kh.; AN Tadzhikskoj SSR, Dushanbe

1989-01-01

The isolated Herbig BF Ori Ae-star belongs to the subclass of young irreguLar variables with non-periodic Algol-type brightness variations. In the course of polarization and photometrical patrol observations carried out in 1987-88 in the Crimea and Sanglock, high linear polarization has been observed in deep minima. The analysis of the observations show, that the most probably a source of polarization is the scattered light from the circumstellar dust disklike envelope that is the analogue of the solar zodiacal light. It is concluded that the bimodal distribution oF positional angles of linear polarization in L 1641 reflects a complex structure of the magnetic field in this giant cloud

Fall-Back Disks in Long and Short GRBS

Science.gov (United States)

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.

HERBIG-HARO OBJECTS IN THE LUPUS I AND III MOLECULAR CLOUDS

International Nuclear Information System (INIS)

Wang Hongchi; Henning, Thomas

2009-01-01

We performed a deep search for Herbig-Haro (HH) objects toward the Lupus I and III clouds, covering a sky area of ∼ 1 and ∼ 0.5 deg 2 , respectively. In total, 11 new HH objects, HH 981--991, are discovered. The HH objects both in Lupus I and in Lupus III tend to be concentrated in small areas. The HH objects detected in Lupus I are located in a region of radius 0.26 pc near the young star Sz 68. The abundance of HH objects shows that this region of the cloud is active in on-going star formation. HH objects in the Lup III cloud are concentrated in the central part of the cloud around the Herbig Ae/Be stars HR 5999 and 6000. HH 981 and 982 in Lupus I are probably driven by the young brown dwarf SSTc2d J154457.9-342340 which has a mass of 50 M J . HH 990 and 991 in Lup III align well with the HH 600 jet emanating from the low-mass star Par-Lup3-4, and are probably excited by this low-mass star of spectral type M5. High proper motions for HH 228 W, E, and E2 are measured, which confirms that they are excited by the young star Th 28. In contrast, HH 78 exhibits no measurable proper motion in the time span of 18 years, indicating that HH 78 is unlikely part of the HH 228 flow. The HH objects in Lup I and III are generally weak in terms of brightness and dimension in comparison to HH objects we detected with the same technique in the R CrA and Cha I clouds. Through a comparison with the survey results from the Spitzer c2d program, we find that our optical survey is more sensitive, in terms of detection rate, than the Spitzer IRAC survey to high-velocity outflows in the Lup I and III clouds.

Probing Protoplanetary Disks: From Birth to Planets

Science.gov (United States)

Cox, Erin Guilfoil

2018-01-01

Disks are very important in the evolution of protostars and their subsequent planets. How early disks can form has implications for early planet formation. In the youngest protostars (i.e., Class 0 sources) magnetic fields can control disk growth. When the field is parallel to the collapsing core’s rotation axis, infalling material loses angular momentum and disks form in later stages. Sub-/millimeter polarization continuum observations of Class 0 sources at ~1000 au resolution support this idea. However, in the inner (~100 au), denser regions, it is unknown if the polarization only traces aligned dust grains. Recent theoretical studies have shown that self-scattering of thermal emission in the disk may contribute significantly to the polarization. Determining the scattering contribution in these sources is important to disentangle the magnetic field. At older times (the Class II phase), the disk structure can both act as a modulator and signpost of planet formation, if there is enough of a mass reservoir. In my dissertation talk, I will present results that bear on disk evolution at both young and late ages. I will present 8 mm polarization results of two Class 0 protostars (IRAS 4A and IC348 MMS) from the VLA at ~50 au resolution. The inferred magnetic field of IRAS 4A has a circular morphology, reminiscent of material being dragged into a rotating structure. I will show results from SOFIA polarization data of the area surrounding IRAS 4A at ~4000 au. I will also present ALMA 850 micron polarization data of ten protostars in the Perseus Molecular Cloud. Most of these sources show very ordered patterns and low (~0.5%) polarization in their inner regions, while having very disordered patterns and high polarization patterns in their extended emission that may suggest different mechanisms in the inner/outer regions. Finally, I will present results from our ALMA dust continuum survey of protoplanetary disks in Rho Ophiuchus; we measured both the sizes and fluxes of

Confined surface plasmon sensors based on strongly coupled disk-in-volcano arrays.

Science.gov (United States)

Ai, Bin; Wang, Limin; Möhwald, Helmuth; Yu, Ye; Zhang, Gang

2015-02-14

Disk-in-volcano arrays are reported to greatly enhance the sensing performance due to strong coupling in the nanogaps between the nanovolcanos and nanodisks. The designed structure, which is composed of a nanovolcano array film and a disk in each cavity, is fabricated by a simple and efficient colloidal lithography method. By tuning structural parameters, the disk-in-volcano arrays show greatly enhanced resonances in the nanogaps formed by the disks and the inner wall of the volcanos. Therefore they respond to the surrounding environment with a sensitivity as high as 977 nm per RIU and with excellent linear dependence on the refraction index. Moreover, through mastering the fabrication process, biological sensing can be easily confined to the cavities of the nanovolcanos. The local responsivity has the advantages of maximum surface plasmon energy density in the nanogaps, reducing the sensing background and saving expensive reagents. The disk-in-volcano arrays also possess great potential in applications of optical and electrical trapping and single-molecule analysis, because they enable establishment of electric fields across the gaps.

Extraplanar H II Regions in Spiral Galaxies. I. Low-metallicity Gas Accreting through the Disk-halo Interface of NGC 4013

Science.gov (United States)

Howk, J. Christopher; Rueff, Katherine M.; Lehner, Nicolas; Wotta, Christopher B.; Croxall, Kevin; Savage, Blair D.

2018-04-01

The interstellar thick disks of galaxies serve as the interface between the thin star-forming disk, where feedback-driven outflows originate, and the distant halo, the repository for accreted gas. We present optical emission line spectroscopy of a luminous, thick disk H II region located at z = 860 pc above the plane of the spiral galaxy NGC 4013 taken with the Multi-Object Double Spectrograph on the Large Binocular Telescope. This nebula, with an Hα luminosity ∼4–7 times that of the Orion nebula, surrounds a luminous cluster of young, hot stars that ionize the surrounding interstellar gas of the thick disk, providing a measure of the properties of that gas. We demonstrate that strong emission line methods can provide accurate measures of relative abundances between pairs of H II regions. From our emission line spectroscopy, we show that the metal content of the thick disk H II region is a factor of ≈2 lower than gas in H II regions at the midplane of this galaxy (with the relative abundance of O in the thick disk lower by ‑0.32 ± 0.09 dex). This implies incomplete mixing of material in the thick disk on small scales (hundreds of parsecs) and that there is accretion of low-metallicity gas through the thick disks of spirals. The inclusion of low-metallicity gas this close to the plane of NGC 4013 is reminiscent of the recently proposed “fountain-driven” accretion models.

SDP_golofs01_3: Stellar Disk Evolution

Science.gov (United States)

Olofsson, G.

2010-03-01

n a collaboration between the HSC, P. Harvey (Mission Scientist) and the three instrument consortia we propose to apply the full power of Herschel to investigate the properties of circum-stellar disks. The versatility of Herschel allows us to address several key questions: How do the disks evolve with time? Planets clearly form out of circum-stellar disks and there is growing evidence that the time scale is short, 1 - 10 Myr, for the main accretion phase. During this time period, the stellar radiation and stellar winds clean the disks from most of their dust and gas, eventually making them transparent. However, collisions and evaporation from comet- like bodies will continue to produce dust and gas. This activity declines with time, and we will pursue this scenario by observing a sample of IR excess stars of known age, ranging from a few million years to the age of the sun. Are there analogues to our Kuiper belt around nearby stars? The Kuiper belt is a dust belt surrounding the Sun, located outside the orbit of Neptune, which has a key role in stabilizing orbits of the KE-objects and this dynamical aspect makes it particularly interesting to search for stars that may host KE-belt analogues. Herschel offers a unique sensitivity beyond 100 m and we propose an extensive survey of nearby stars seeking cold dust emission. What will a closer IR look at the "Fabulous Four" (and some other resolved disks) reveal? Several nearby MS stars with IR excesses have circumstellar dust structures that can be resolved by Herschel. Imaging these structures in the six PACS+SPIRE bands will enable us to explore the dust properties, notably the size distribution and albedo.. What is the composition of young disks? We propose a detailed spectroscopic investigation of four bright disks, including a full spectral scan with PACS, an FTS scan at full resolution and HIFI observations of selected frequencies. The aim is to constrain the properties of both the dust and gas components.

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

International Nuclear Information System (INIS)

Kim, K. H.; Watson, Dan M.; Manoj, P.; Forrest, W. J.; Arnold, Laura; Najita, Joan; Furlan, Elise; Sargent, Benjamin; Espaillat, Catherine; Muzerolle, James; Megeath, S. T.; Calvet, Nuria; Green, Joel D.

2013-01-01

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'' age 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.

A Search for Debris Disks Around Variable Pulsars

Science.gov (United States)

Shannon, Ryan; Cordes, J.; Lazio, J.; Kramer, M.; Lyne, A.

2009-01-01

After a supernova explosion, a modest amount of material will fall back and form a disk surrounding the resultant neutron star. This material can aggregate into rocky debris and the disk can be stable for the entire 10 million year lifetime of a canonical (non-recycled) radio pulsar. Previously, we developed a model that unifies the different classes of radio variability observed in many older pulsars. In this model, rocky material migrates inwards towards the neutron star and is ablated inside the pulsar magnetosphere. This material alters the electrodynamics in the magnetosphere which can cause the observed quiescent and bursting states observed in nulling pulsars, intermittent pulsars, and rotating radio transients. With this model in mind, we observed three nulling pulsars and one intermittent pulsar that are good candidates to host debris disks detectable by the Spitzer IRAC. Here we report how our IRAC observations constrain disk geometry, with particular emphasis on configurations that can provide the in-fall rate to cause the observed radio variability. We place these observations in the context of other searches for debris disks around neutron stars, which had studied either very young or very old (recycled) pulsars. By observing older canonical pulsars, all major classes of radio pulsars have been observed, and we can assess the presence of debris disks as a function of pulsar type. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech.

Gas Velocities Reveal Newly Born Planets in a Disk

Science.gov (United States)

Kohler, Susanna

2018-06-01

Occasionally, science comes together beautifully for a discovery and sometimes this happens for more than one team at once! Today we explore how two independent collaborations of scientists simultaneously found the very first kinematic evidence for young planets forming in a protoplanetary disk. Though they explored the same disk, the two teams in fact discovered different planets.Evidence for PlanetsALMAs view of the dust in the protoplanetary disk surrounding the young star HD 163296. Todays studies explore not the dust, but the gas of this disk. [ALMA (ESO/NAOJ/NRAO); A. Isella; B. Saxton (NRAO/AUI/NSF)]Over the past three decades, weve detected around 4,000 fully formed exoplanets. Much more elusive, however, are the young planets still in the early stages of formation; only a handful of these have been discovered. More observations of early-stage exoplanets are needed in order to understand how these worlds are born in dusty protoplanetary-disk environments, how they grow their atmospheres, and how they evolve.Recent observations by the Atacama Large Millimeter/submillimeter Array (ALMA) have produced stunning images of protoplanetary disks. The unprecedented resolution of these images reveals substructure in the form of gaps and rings, hinting at the presence of planets that orbit within the disk and clear out their paths as they move. But there are also non-planet mechanisms that could produce such substructure, like grain growth around ice lines, or hydrodynamic instabilities in the disk.How can we definitively determine whether there are nascent planets embedded in these disks? Direct direction of a point source in a dust gap would be a strong confirmation, but now we have the next best thing: kinematic evidence for planets, from the motion of a disks gas.Observations of carbon monoxide line emission at +1km/s from the systemic velocity (left) vs. the outcome of a computer simulation (right) in the Pinte et al. study. A visible kink occurs in the flow

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

Science.gov (United States)

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.

Understanding Gas-Phase Ammonia Chemistry in Protoplanetary Disks

Science.gov (United States)

Chambers, Lauren; Oberg, Karin I.; Cleeves, Lauren Ilsedore

2017-01-01

Protoplanetary disks are dynamic regions of gas and dust around young stars, the remnants of star formation, that evolve and coagulate over millions of years in order to ultimately form planets. The chemical composition of protoplanetary disks is affected by both the chemical and physical conditions in which they develop, including the initial molecular abundances in the birth cloud, the spectrum and intensity of radiation from the host star and nearby systems, and mixing and turbulence within the disk. A more complete understanding of the chemical evolution of disks enables a more complete understanding of the chemical composition of planets that may form within them, and of their capability to support life. One element known to be essential for life on Earth is nitrogen, which often is present in the form of ammonia (NH3). Recent observations by Salinas et al. (2016) reveal a theoretical discrepancy in the gas-phase and ice-phase ammonia abundances in protoplanetary disks; while observations of comets and protostars estimate the ice-phase NH3/H2O ratio in disks to be 5%, Salinas reports a gas-phase NH3/H2O ratio of ~7-84% in the disk surrounding TW Hydra, a young nearby star. Through computational chemical modeling of the TW Hydra disk using a reaction network of over 5000 chemical reactions, I am investigating the possible sources of excess gas-phase NH3 by determining the primary reaction pathways of NH3 production; the downstream chemical effects of ionization by ultraviolet photons, X-rays, and cosmic rays; and the effects of altering the initial abundances of key molecules such as N and N2. Beyond providing a theoretical explanation for the NH3 ice/gas discrepancy, this new model may lead to fuller understanding of the gas-phase formation processes of all nitrogen hydrides (NHx), and thus fuller understanding of the nitrogen-bearing molecules that are fundamental for life as we know it.

Properties of Planet-Forming Prostellar Disks

Science.gov (United States)

Lindstrom, David (Technical Monitor); Lubow, Stephen

2005-01-01

The proposal achieved many of its objectives. The main area of investigation was the interaction of young planets with surrounding protostellar disks. The grant funds were used to support visits by CoIs and visitors: Gordon Ogilvie, Gennaro D Angelo, and Matthew Bate. Funds were used for travel and partial salary support for Lubow. We made important progress in two areas described in the original proposal: secular resonances (Section 3) and nonlinear waves in three dimensions (Section 5). In addition, we investigated several new areas: planet migration, orbital distribution of planets, and noncoorbital corotation resonances.

The Building History of XUV disks of M83& NGC2403 with TRGB Archaeology

Science.gov (United States)

Koda, Jin

2015-06-01

We propose deep HSC g & i-band imaging of two extended ultraviolet (XUV) disks of M83 and NGC2403. These galaxies have the prototype XUV disks with the largest size ( 1 deg and 30 arcmin). The Subaru HSC permits unprecedentedly deep imaging over these gigantic XUV disks, including sufficient surrounding areas which are used for sky subtraction and statistical estimation of background contamination. This project probes the building history of the XUV disks using archeological stellar populations, especially the tip of red giant branch (TRGB) stars (age 2-14 Gyr). Their presence and distribution over the XUV disks will reveal any star formation (SF) occurring over the past 2 Gyr, 4-6 Gyr, and beyond - i.e., the epochs preceding the recent (UV-traced) state of SF. Their color depends strongly on metallicity, thus providing an additional measure of star-gas recycling during the evolution of the XUV disks. In addition, we will detect young & massive main sequence stars (<100 Myr) and He-burning stars (100-500 Myr). Comparing various generations of stars, in terms of number densities and spatial distributions, will reveal the much-unexplored SF history in the XUV disks.

SIGNATURES OF GRAVITATIONAL INSTABILITY IN RESOLVED IMAGES OF PROTOSTELLAR DISKS

Energy Technology Data Exchange (ETDEWEB)

Dong, Ruobing [Lawrence Berkeley National Lab, Berkeley, CA 94720 (United States); Vorobyov, Eduard [Department of Astrophysics, The University of Vienna, Vienna, A-1180 (Austria); Pavlyuchenkov, Yaroslav [Institute of Astronomy, Russian Academy of Sciences, Moscow (Russian Federation); Chiang, Eugene [Department of Astronomy, University of California at Berkeley, Berkeley, CA 94720 (United States); Liu, Hauyu Baobab, E-mail: rdong2013@berkeley.edu [European Southern Observatory (ESO), Karl-Schwarzschild-Strasse 2, D-85748 Garching (Germany)

2016-06-01

Protostellar (class 0/I) disks, which have masses comparable to those of their nascent host stars and are fed continuously from their natal infalling envelopes, are prone to gravitational instability (GI). Motivated by advances in near-infrared (NIR) adaptive optics imaging and millimeter-wave interferometry, we explore the observational signatures of GI in disks using hydrodynamical and Monte Carlo radiative transfer simulations to synthesize NIR scattered light images and millimeter dust continuum maps. Spiral arms induced by GI, located at disk radii of hundreds of astronomical units, are local overdensities and have their photospheres displaced to higher altitudes above the disk midplane; therefore, arms scatter more NIR light from their central stars than inter-arm regions, and are detectable at distances up to 1 kpc by Gemini/GPI, VLT/SPHERE, and Subaru/HiCIAO/SCExAO. In contrast, collapsed clumps formed by disk fragmentation have such strong local gravitational fields that their scattering photospheres are at lower altitudes; such fragments appear fainter than their surroundings in NIR scattered light. Spiral arms and streamers recently imaged in four FU Ori systems at NIR wavelengths resemble GI-induced structures and support the interpretation that FUors are gravitationally unstable protostellar disks. At millimeter wavelengths, both spirals and clumps appear brighter in thermal emission than the ambient disk and can be detected by ALMA at distances up to 0.4 kpc with one hour integration times at ∼0.″1 resolution. Collapsed fragments having masses ≳1 M {sub J} can be detected by ALMA within ∼10 minutes.

Pion production In The Inner Disk Around Cygnus X-1

International Nuclear Information System (INIS)

Meirelles Filho, C.; Miyake, H.; Timoteo, V.S.; Lima, C.L.

2004-01-01

Neutron production via 4He breakup and p(p, nπ+)p is considered in the innermost region of an accretion disk surrounding a Kerr Black Hole. Close to the horizon, the contribution from p(p, nπ+)p to the neutron production is comparable to that from the breakup. It is shown that the viscosity generated by the collisions of the accreting matter with the neutrons may drive stationary accretion, for accretion rates below a critical value. In this case, solution to the disk equations is double-valued and for both solutions protons overnumber the pairs. We suggest that these solutions may mimic the states of high and low luminosity observed in Cygnus X-1

DETECTION OF CH{sub 4} IN THE GV TAU N PROTOPLANETARY DISK

Energy Technology Data Exchange (ETDEWEB)

Gibb, Erika L. [Department of Physics and Astronomy, University of Missouri -St Louis, 503 Benton Hall, One University Blvd, St Louis, MO 63121 (United States); Horne, David, E-mail: gibbe@umsl.edu [Department of Physics, Marietta College, Marietta, OH 45750 (United States)

2013-10-20

T Tauri stars are low mass young stars that may serve as analogs to the early solar system. Observations of organic molecules in the protoplanetary disks surrounding T Tauri stars are important for characterizing the chemical and physical processes that lead to planet formation. Searches for undetected molecules, particularly in the inner, planet forming regions of these disks are important for testing protoplanetary disk chemical models and for understanding the evolution of volatiles through the star and planet formation process. We used NIRSPEC on Keck 2 to perform a high resolution (λ/Δλ ∼ 25,000) L-band survey of T Tauri star GV Tau N. This object is one of two in which the simple organic molecules HCN and C{sub 2}H{sub 2} have been reported in absorption in the warm molecular layer of the protoplanetary disk. In this Letter, we report the first detection of methane, CH{sub 4}, in a protoplanetary disk. Specifically, we detected the ν{sub 3} band in absorption. We determined a rotational temperature of 750 ± 50 K and column density of (2.8 ± 0.2) × 10{sup 17} cm{sup –2}. Our results imply that CH{sub 4} originates in the warm molecular layer of the inner protoplanetary disk.

Variability of Disk Emission in Pre-Main Sequence and Related Stars. II. Variability in the Gas and Dust Emission of the Herbig Fe Star SAO 206462

Science.gov (United States)

Sitko, Michael L.; Day, Amanda N.; Kimes, Robin L.; Beerman, Lori C.; Martus, Cameron; Lynch, David K.; Russell, Ray W.; Grady, Carol A.; Schneider, Glenn; Lisse, Carey M.;

Connection between Herbig-Haro objects and flare stars in the neighborhood of the sun

International Nuclear Information System (INIS)

Giulbudagian, A.L.

1984-01-01

The origin of the K-M-dwarf flare stars observed with widely ranging spatial velocities in the solar neighborhood is investigated theoretically. It is proposed that these objects are Herbig-Haro objects (HHOs) which have lost their diffuse envelopes as they emerged from dark clouds. The number of HHOs in the Galaxy and their average lifetime are estimated as 150,000 and 3,000 yr, respectively, corresponding to a total of 5 x 10 to the 11th HHOs created in the Galaxy over 10 Gyr and in rough agreement with the number of low-mass flare stars (5 x 10 to the 10th) if some of them have ages of 1 Gyr or more

Improved bow shock models for Herbig-Haro objects - application to HH 2A-prime

International Nuclear Information System (INIS)

Raymond, J.C.; Hartmann, L.; Hartigan, P.

1988-01-01

An improved version of the bow shock theory previously applied to Herbig-Haro objects is presented. The modifications provide a more accurate calculation of the ionization state of material entering the bow shock. The revised preionization does not drastically affect the emission-line predictions for a 200 km/s bow shock model, though the effects will be more severe for slower shock velocities. The line profiles of the new models resemble the observed profiles somewhat more closely, and the relative emission-line intensities typically differ by 30 percent from those predicted by the older models. The models agree well with new IUE spectra and existing optical data for HH 2A-prime. 32 references

An Automated Scheme for the Large-Scale Survey of Herbig-Haro Objects

Science.gov (United States)

Deng, Licai; Yang, Ji; Zheng, Zhongyuan; Jiang, Zhaoji

2001-04-01

Owing to their spectral properties, Herbig-Haro (HH) objects can be discovered using photometric methods through a combination of filters, sampling the characteristic spectral lines and the nearby continuum. The data are commonly processed through direct visual inspection of the images. To make data reduction more efficient and the results more uniform and complete, an automated searching scheme for HH objects is developed to manipulate the images using IRAF. This approach helps to extract images with only intrinsic HH emissions. By using this scheme, the pointlike stellar sources and extended nebulous sources with continuum emission can be eliminated from the original images. The objects with only characteristic HH emission become prominent and can be easily picked up. In this paper our scheme is illustrated by a sample field and has been applied to our surveys for HH objects.

INVESTIGATING THE CIRCUMSTELLAR DISK OF THE Be SHELL STAR 48 LIBRAE

Energy Technology Data Exchange (ETDEWEB)

Silaj, J.; Jones, C. E. [Department of Physics and Astronomy, The University of Western Ontario, 1151 Richmond Street, London, Ontario, N6A 3K7 (Canada); Carciofi, A. C.; Escolano, C.; Bednarski, D. [Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universitária de São Paulo, Rua do Matão 1226, Cidade Universitária, 05508-900 São Paulo, SP Brazil (Brazil); Okazaki, A. T. [Faculty of Engineering, Hokkai-Gakuen University, Toyohira-ku, Sapporo 062-8605 (Japan); Tycner, C. [Department of Physics, Central Michigan University, Mt. Pleasant, MI 48859 (United States); Rivinius, T.; Klement, R. [European Organisation for Astronomical Research in the Southern Hemisphere, Casilla 19001, Santiago 19 (Chile)

2016-07-20

A global disk oscillation implemented in the viscous decretion disk (VDD) model has been used to reproduce most of the observed properties of the well known Be star ζ Tau. 48 Librae shares several similarities with ζ Tau—they are both early-type Be stars, display shell characteristics in their spectra, and exhibit cyclic V / R variations—but has some marked differences as well, such as a much denser and more extended disk, a much longer V / R cycle, and the absence of the so-called triple-peak features. We aim to reproduce the photometric, polarimetric, and spectroscopic observables of 48 Librae with a self-consistent model, and to test the global oscillation scenario for this target. Our calculations are carried out with the three-dimensional NLTE radiative transfer code HDUST. We employ a rotationally deformed, gravity-darkened central star surrounded by a disk whose unperturbed state is given by the VDD model. A two-dimensional global oscillation code is then used to calculate the disk perturbation and superimpose it on the unperturbed disk. A very good, self-consistent fit to the time-averaged properties of the disk is obtained with the VDD. The calculated perturbation has a period P = 12 years, which agrees with the observed period, and the behavior of the V / R cycle is well reproduced by the perturbed model. The perturbed model improves the fit to the photometric data and reproduces some features of the observed spectroscopic data. Some suggestions to improve the synthesized spectroscopy in a future work are given.

Identifying Likely Disk-hosting M dwarfs with Disk Detective

Science.gov (United States)

Silverberg, Steven; Wisniewski, John; Kuchner, Marc J.; Disk Detective Collaboration

2018-01-01

M dwarfs are critical targets for exoplanet searches. Debris disks often provide key information as to the formation and evolution of planetary systems around higher-mass stars, alongside the planet themselves. However, less than 300 M dwarf debris disks are known, despite M dwarfs making up 70% of the local neighborhood. The Disk Detective citizen science project has identified over 6000 new potential disk host stars from the AllWISE catalog over the past three years. Here, we present preliminary results of our search for new disk-hosting M dwarfs in the survey. Based on near-infrared color cuts and fitting stellar models to photometry, we have identified over 500 potential new M dwarf disk hosts, nearly doubling the known number of such systems. In this talk, we present our methodology, and outline our ongoing work to confirm systems as M dwarf disks.

CONSTRAINTS ON THE RADIAL VARIATION OF GRAIN GROWTH IN THE AS 209 CIRCUMSTELLAR DISK

International Nuclear Information System (INIS)

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

2012-01-01

We present dust continuum observations of the protoplanetary disk surrounding the pre-main-sequence star AS 209, spanning more than an order of magnitude in wavelength from 0.88 to 9.8 mm. The disk was observed with subarcsecond angular resolution (0.''2-0.''5) to investigate radial variations in its dust properties. At longer wavelengths, the disk emission structure is notably more compact, providing model-independent evidence for changes in the grain properties across the disk. We find that physical models which reproduce the disk emission require a radial dependence of the dust opacity κ ν . Assuming that the observed wavelength-dependent structure can be attributed to radial variations in the dust opacity spectral index (β), we find that β(R) increases from β 1.5 for R ∼> 80 AU, inconsistent with a constant value of β across the disk (at the 10σ level). Furthermore, if radial variations of κ ν are caused by particle growth, we find that the maximum size of the particle-size distribution (a max ) increases from submillimeter-sized grains in the outer disk (R ∼> 70 AU) to millimeter- and centimeter-sized grains in the inner disk regions (R ∼ max (R) with predictions from physical models of dust evolution in protoplanetary disks. For the dust composition and particle-size distribution investigated here, our observational constraints on a max (R) are consistent with models where the maximum grain size is limited by radial drift.

Variable extinction in HD 45677 and the evolution of dust grains in pre-main-sequence disks

Science.gov (United States)

Sitko, Michael L.; Halbedel, Elaine M.; Lawrence, Geoffrey F.; Smith, J. Allyn; Yanow, Ken

1994-01-01

Changes in the UV extinction and IR emission were sought in the Herbig Ae/Be star candidate HD 45677 (= FS CMa) by comparing UV, optical, and IR observations made approximately 10 yr apart. HD 45677 varied significantly, becoming more than 50% brighter in the UV and optical than it was a decade ago. A comparison of the observations between epochs indicates that if the variations are due to changes in dust obscuration, the dust acts as a gray absorber into the near-IR and must be depleted in grains smaller than 1 micron. This is similar to the results obtained on the circumstellar disks of stars like Vega and Beta Pic, and suggests that radiation pressure may be responsible for the small-grain depletion. In addition, the total IR flux seems to have declined, indicating a decrease in the total mass of the dust envelope that contributes to the IR emission in this part of the spectrum. Due to the anomalous nature of the extinction, the use of normal extinction curves to deredden the spectral energy distributions of stars with circumstellar dust may lead to significant errors and should be used with great caution.

ALMA Survey of Lupus Protoplanetary Disks. II. Gas Disk Radii

Science.gov (United States)

Ansdell, M.; Williams, J. P.; Trapman, L.; van Terwisga, S. E.; Facchini, S.; Manara, C. F.; van der Marel, N.; Miotello, A.; Tazzari, M.; Hogerheijde, M.; Guidi, G.; Testi, L.; van Dishoeck, E. F.

2018-05-01

We present Atacama Large Millimeter/Sub-Millimeter Array (ALMA) Band 6 observations of a complete sample of protoplanetary disks in the young (∼1–3 Myr) Lupus star-forming region, covering the 1.33 mm continuum and the 12CO, 13CO, and C18O J = 2–1 lines. The spatial resolution is ∼0.″25 with a medium 3σ continuum sensitivity of 0.30 mJy, corresponding to M dust ∼ 0.2 M ⊕. We apply Keplerian masking to enhance the signal-to-noise ratios of our 12CO zero-moment maps, enabling measurements of gas disk radii for 22 Lupus disks; we find that gas disks are universally larger than millimeter dust disks by a factor of two on average, likely due to a combination of the optically thick gas emission and the growth and inward drift of the dust. Using the gas disk radii, we calculate the dimensionless viscosity parameter, α visc, finding a broad distribution and no correlations with other disk or stellar parameters, suggesting that viscous processes have not yet established quasi-steady states in Lupus disks. By combining our 1.33 mm continuum fluxes with our previous 890 μm continuum observations, we also calculate the millimeter spectral index, α mm, for 70 Lupus disks; we find an anticorrelation between α mm and millimeter flux for low-mass disks (M dust ≲ 5), followed by a flattening as disks approach α mm ≈ 2, which could indicate faster grain growth in higher-mass disks, but may also reflect their larger optically thick components. In sum, this work demonstrates the continuous stream of new insights into disk evolution and planet formation that can be gleaned from unbiased ALMA disk surveys.

THICK-DISK EVOLUTION INDUCED BY THE GROWTH OF AN EMBEDDED THIN DISK

International Nuclear Information System (INIS)

Villalobos, Alvaro; Helmi, Amina; Kazantzidis, Stelios

2010-01-01

We perform collisionless N-body simulations to investigate the evolution of the structural and kinematical properties of simulated thick disks induced by the growth of an embedded thin disk. The thick disks used in the present study originate from cosmologically common 5:1 encounters between initially thin primary disk galaxies and infalling satellites. The growing thin disks are modeled as static gravitational potentials and we explore a variety of growing-disk parameters that are likely to influence the response of thick disks. We find that the final thick-disk properties depend strongly on the total mass and radial scale length of the growing thin disk, and much less sensitively on its growth timescale and vertical scale height as well as the initial sense of thick-disk rotation. Overall, the growth of an embedded thin disk can cause a substantial contraction in both the radial and vertical direction, resulting in a significant decrease in the scale lengths and scale heights of thick disks. Kinematically, a growing thin disk can induce a notable increase in the mean rotation and velocity dispersions of thick-disk stars. We conclude that the reformation of a thin disk via gas accretion may play a significant role in setting the structure and kinematics of thick disks, and thus it is an important ingredient in models of thick-disk formation.

ALMA OBSERVATIONS OF HD 141569’s CIRCUMSTELLAR DISK

Energy Technology Data Exchange (ETDEWEB)

White, J. A.; Boley, A. C. [Department of Physics and Astronomy, 6224 Agricultural Road, Vancouver, BC V6T 1Z1 (Canada); Hughes, A. M.; Flaherty, K. M. [Department of Astronomy, Van Vleck Observatory, Wesleyan University, 96 Foss Hill Drive, Middletown, CT 06459 (United States); Ford, E. [Center for Exoplanets and Habitable Worlds, 525 Davey Laboratory, The Pennsylvania State University, University Park, PA 16802-2111 (United States); Wilner, D.; Payne, M. [Harvard Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Corder, S., E-mail: jawhite@astro.ubc.ca [North American ALMA Science Center, National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA, 22903 (United States)

2016-09-20

We present ALMA band 7 (345 GHz) continuum and {sup 12}CO( J = 3-2) observations of the circumstellar disk surrounding HD 141569. At an age of about 5 Myr, the disk has a complex morphology that may be best interpreted as a nascent debris system with gas. Our 870 μ m ALMA continuum observations resolve a dust disk out to approximately 56 au from the star (assuming a distance of 116 pc) with 0.″38 resolution and 0.07 mJy beam{sup −1} sensitivity. We measure a continuum flux density for this inner material of 3.8 ± 0.4 mJy (including calibration uncertainties). The {sup 12}CO(3-2) gas is resolved kinematically and spatially from about 30 to 210 au. The integrated {sup 12}CO(3-2) line flux density is 15.7 ± 1.6 Jy km s{sup −1}. We estimate the mass of the millimeter debris and {sup 12}CO(3-2) gas to be ≳0.04 M {sub ⊕} and ∼2 × 10{sup −3} M {sub ⊕}, respectively. If the millimeter grains are part of a collisional cascade, then we infer that the inner disk (<50 au) has ∼160 M {sub ⊕} contained within objects less than 50 km in radius, depending on the planetesimal size distribution and density assumptions. Markov Chain Monte Carlo modeling of the system reveals a disk morphology with an inclination of 53.°4 centered around an M = 2.39 M {sub ⊙} host star ( M sin( i ) = 1.92 M {sub ⊙}). We discuss whether the gas in HD 141569's disk may be second generation. If it is, the system can be used to study the clearing stages of planet formation.

Oscillations of disks

CERN Document Server

Kato, Shoji

2016-01-01

This book presents the current state of research on disk oscillation theory, focusing on relativistic disks and tidally deformed disks. Since the launch of the Rossi X-ray Timing Explorer (RXTE) in 1996, many high-frequency quasiperiodic oscillations (HFQPOs) have been observed in X-ray binaries. Subsequently, similar quasi-periodic oscillations have been found in such relativistic objects as microquasars, ultra-luminous X-ray sources, and galactic nuclei. One of the most promising explanations of their origin is based on oscillations in relativistic disks, and a new field called discoseismology is currently developing. After reviewing observational aspects, the book presents the basic characteristics of disk oscillations, especially focusing on those in relativistic disks. Relativistic disks are essentially different from Newtonian disks in terms of several basic characteristics of their disk oscillations, including the radial distributions of epicyclic frequencies. In order to understand the basic processes...

HERSCHEL OBSERVATIONS AND UPDATED SPECTRAL ENERGY DISTRIBUTIONS OF FIVE SUNLIKE STARS WITH DEBRIS DISKS

International Nuclear Information System (INIS)

Dodson-Robinson, Sarah E.; Su, Kate Y. L.; Bryden, Geoff; Harvey, Paul; Green, Joel D.

2016-01-01

Observations from the Herschel Space Observatory have more than doubled the number of wide debris disks orbiting Sunlike stars to include over 30 systems with R  > 100 AU. Here, we present new Herschel PACS and reanalyzed Spitzer MIPS photometry of five Sunlike stars with wide debris disks, from Kuiper Belt size to R  > 150 AU. The disk surrounding HD 105211 is well resolved, with an angular extent of >14″ along the major axis, and the disks of HD 33636, HD 50554, and HD 52265 are extended beyond the PACS point-spread function size (50% of energy enclosed within radius 4.″23). HD 105211 also has a 24 μ m infrared excess, which was previously overlooked, because of a poorly constrained photospheric model. Archival Spitzer IRS observations indicate that the disks have small grains of minimum radius a min  ∼ 3 μ m, although a min is larger than the radiation-pressure blowout size in all systems. If modeled as single-temperature blackbodies, the disk temperatures would all be <60 K. Our radiative transfer models predict actual disk radii approximately twice the radius of a model blackbody disk. We find that the Herschel photometry traces dust near the source population of planetesimals. The disk luminosities are in the range 2 × 10 −5  ⩽  L / L ⊙  ⩽ 2 × 10 −4 , consistent with collisions in icy planetesimal belts stirred by Pluto-size dwarf planets.

HERSCHEL OBSERVATIONS AND UPDATED SPECTRAL ENERGY DISTRIBUTIONS OF FIVE SUNLIKE STARS WITH DEBRIS DISKS

Energy Technology Data Exchange (ETDEWEB)

Dodson-Robinson, Sarah E. [Department of Physics and Astronomy, University of Delaware, 217 Sharp Lab, Newark, DE 19716 (United States); Su, Kate Y. L. [Steward Observatory, Department of Astronomy, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Bryden, Geoff [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Harvey, Paul; Green, Joel D., E-mail: sdr@udel.edu [Astronomy Department, University of Texas, 2515 Speedway Drive C1400, Austin, TX 78712 (United States)

2016-12-20

Observations from the Herschel Space Observatory have more than doubled the number of wide debris disks orbiting Sunlike stars to include over 30 systems with R  > 100 AU. Here, we present new Herschel PACS and reanalyzed Spitzer MIPS photometry of five Sunlike stars with wide debris disks, from Kuiper Belt size to R  > 150 AU. The disk surrounding HD 105211 is well resolved, with an angular extent of >14″ along the major axis, and the disks of HD 33636, HD 50554, and HD 52265 are extended beyond the PACS point-spread function size (50% of energy enclosed within radius 4.″23). HD 105211 also has a 24 μ m infrared excess, which was previously overlooked, because of a poorly constrained photospheric model. Archival Spitzer IRS observations indicate that the disks have small grains of minimum radius a {sub min} ∼ 3 μ m, although a {sub min} is larger than the radiation-pressure blowout size in all systems. If modeled as single-temperature blackbodies, the disk temperatures would all be <60 K. Our radiative transfer models predict actual disk radii approximately twice the radius of a model blackbody disk. We find that the Herschel photometry traces dust near the source population of planetesimals. The disk luminosities are in the range 2 × 10{sup −5} ⩽  L / L {sub ⊙} ⩽ 2 × 10{sup −4}, consistent with collisions in icy planetesimal belts stirred by Pluto-size dwarf planets.

High spectral resolution observations of the H2 2.12 micron line in Herbig-Haro objects

International Nuclear Information System (INIS)

Zinnecker, H.; Mundt, R.; Geballe, T.R.; Zealey, W.J.

1989-01-01

High-spectral-resolution Fabry-Perot observations of the H 2 2.12-micron line emissions of several Herbig-Haro (HH) objects are discussed. It is shown that H 2 emission by the shock heating of external molecular gas in the wings of the bow shock associated with the working surface of a high-velocity jet may occur for HH objects associated with the jet's end. The shock heating of external molecular gas entrained in the flow by internal shocks occurring in the jet itself and/or in its boundary layer may be the H 2 emission mechanism for HH objects observed along the flow axis. 59 refs

An ALMA continuum survey of circumstellar disks in the upper Scorpius OB association

Energy Technology Data Exchange (ETDEWEB)

Carpenter, John M.; Ricci, Luca; Isella, Andrea [Department of Astronomy, California Institute of Technology, MC 249-17, Pasadena, CA 91125 (United States)

2014-05-20

We present ALMA 880 μm continuum observations of 20 K- and M-type stars in the Upper Scorpius OB association (Upper Sco) that are surrounded by protoplanetary disks. These data are used to measure the dust content in disks around low-mass stars (0.1-1.6 M {sub ☉}) at a stellar age of 5-11 Myr. Thirteen sources were detected in the 880 μm dust continuum at ≥3σ with inferred dust masses between 0.3 and 52 M {sub ⊕}. The dust masses tend to be higher around the more massive stars, but the significance is marginal in that the probability of no correlation is p ≈ 0.03. The evolution in the dust content in disks was assessed by comparing the Upper Sco observations with published continuum measurements of disks around ∼1-2 Myr stars in the Class II stage in the Taurus molecular cloud. While the dust masses in the Upper Sco disks are on average lower than in Taurus, any difference in the dust mass distributions is significant at less than 3σ. For stellar masses between 0.49 M {sub ☉} and 1.6 M {sub ☉}, the mean dust mass in disks is lower in Upper Sco relative to Taurus by Δlog M {sub dust} = 0.44 ± 0.26.

Magnetically Induced Disk Winds and Transport in the HL Tau Disk

International Nuclear Information System (INIS)

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

2017-01-01

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 × 10 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.

Magnetically Induced Disk Winds and Transport in the HL Tau Disk

Energy Technology Data Exchange (ETDEWEB)

Hasegawa, Yasuhiro; Flock, Mario; Turner, Neal J. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Okuzumi, Satoshi, E-mail: yasuhiro@caltech.edu [Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551 (Japan)

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 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 {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.

Chemistry of dense clumps near moving Herbig-Haro objects

Science.gov (United States)

Christie, H.; Viti, S.; Williams, D. A.; Girart, J. M.; Morata, O.

2011-09-01

Localized regions of enhanced emission from HCO+, NH3 and other species near Herbig-Haro objects (HHOs) have been interpreted as arising in a photochemistry stimulated by the HHO radiation on high-density quiescent clumps in molecular clouds. Static models of this process have been successful in accounting for the variety of molecular species arising ahead of the jet; however, recent observations show that the enhanced molecular emission is widespread along the jet as well as ahead. Hence, a realistic model must take into account the movement of the radiation field past the clump. It was previously unclear as to whether the short interaction time between the clump and the HHO in a moving source model would allow molecules such as HCO+ to reach high enough levels, and to survive for long enough to be observed. In this work we model a moving radiation source that approaches and passes a clump. The chemical picture is qualitatively unchanged by the addition of the moving source, strengthening the idea that enhancements are due to evaporation of molecules from dust grains. In addition, in the case of several molecules, the enhanced emission regions are longer lived. Some photochemically induced species, including methanol, are expected to maintain high abundances for ˜104 yr.

The Chemistry of Protostellar Jet-Disk Systems

Science.gov (United States)

Codella, Claudio

2017-11-01

The birth of a Sun-like star is a complex game played by several participants whose respective roles are not yet entirely clear. On the one hand, the star-to-be accretes matter from a collapsing envelope. The gravitational energy released in the process heats up the material surrounding the protostar, creating warm regions enriched by interstellar complex organic molecules (iCOMs, at least 6 atoms) called hot-corinos. On the other hand, the presence of angular momentum and magnetic fields leads to two consequences: (i) the formation of circumstellar disks; and (ii) substantial episodes of matter ejection, as e.g. collimated jets. Thanks to the combination of the high-sensitivities and high-angular resolu- tions provided by the advent of new telescopes such as ALMA and NOEMA, it is now possible to image in details the earliest stages of the Sun-like star formation, thus inspecting the inner ( effects connected with the accreting disk. In other words, it is time to study the protostellar jet-disk system as a whole. Several still unanswered questions can be addressed. What is the origin of the chemically enriched hot corinos: are they jet-driven shocked regions? What is the origin of the ejections: are they due to disk or stellar winds? Shocks are precious tool to attack these questions, given they enrich the gas phase with the species deposited onto the dust mantles and/or locked in the refractory dust cores. Basically, we have to deal with two kind of shocks: (i) high-velocity shocks produced by protostellar jets, and (ii) slow accretion shocks located close to the centrifugal barrier of the accretion disks. Both shocks are factories of iCOMs, which can be then efficiently used to follow both the kinematics and the chemistry of the inner protostellar systems. With this in mind, we will discuss recent results obtained in the framework of different observational campaigns at mm and sub-mm wavelengths.

SPECTRALLY RESOLVED PURE ROTATIONAL LINES OF WATER IN PROTOPLANETARY DISKS

International Nuclear Information System (INIS)

Pontoppidan, Klaus M.; Salyk, Colette; Blake, Geoffrey A.; Kaeufl, Hans Ulrich

2010-01-01

We present ground-based high-resolution N-band spectra (Δv = 15 km s -1 ) of pure rotational lines of water vapor in two protoplanetary disks surrounding the pre-main-sequence stars AS 205N and RNO 90, selected based on detections of rotational water lines by the Spitzer InfraRed Spectrograph. Using VISIR on the Very Large Telescope, we spectrally resolve individual lines and show that they have widths of 30-60 km s -1 , consistent with an origin in Keplerian disks at radii of ∼1 AU. The water lines have similar widths to those of the CO at 4.67 μm, indicating that the mid-infrared water lines trace similar radii. The rotational temperatures of the water are 540 and 600 K in the two disks, respectively. However, the line ratios show evidence of non-LTE excitation, with low-excitation line fluxes being overpredicted by two-dimensional disk LTE models. Due to the limited number of observed lines and the non-LTE line ratios, an accurate measure of the water ortho/para (O/P) ratio is not available, but a best estimate for AS 205N is O/P =4.5 ± 1.0, apparently ruling out a low-temperature origin of the water. The spectra demonstrate that high-resolution spectroscopy of rotational water lines is feasible from the ground, and further that ground-based high-resolution spectroscopy is likely to significantly improve our understanding of the inner disk chemistry revealed by recent Spitzer observations.

Contact statuses between functionally graded brake disk and pure pad disk

International Nuclear Information System (INIS)

Shahzamanian, M.M.; Sahari, B.B.; Bayat, M.; Mustapha, F.; Ismarrubie, Z.N.; Shahrjerdi, A.

2009-01-01

Full text: The contact statuses between functionally graded (FG) brake disks and pure pad disk are investigated by using finite element method (FEM). Two types of variation is considered for FG brake disk, the variation of materials are considered change in radial and thickness direction of disk. The material properties of these two types of FG brake disks are assumed to be represented by power-law distributions in the radius and thickness direction. The results are obtained and then compared. For the radial FG brake disk, the inner and outer surfaces are considered metal and ceramic respectively, and friction coefficient between metal surface and ceramic surface of FG brake dick with pad are considered 1.4 and 0.75 respectively. For the thickness FG brake disk the contact surface with pure pad brake disk is ceramic and the free surface is metal and friction coefficient between ceramic (contact) surface and pure pad brake disk is considered 0.75. In both types of FG brake disks the Coulomb contact friction is applied. Mechanical response of FG brake disks are compared and verified with the known results in the literatures. Three types of contact statuses are introduced as Sticking, Contact and Near Contact. The contact status between pad and disk for different values for pad thickness, grading index,n , and percentage of friction coefficient (λ) is shown. It can be seen that for all values of percentage of friction coefficient,λ , and grading indices, n, by increasing the thickness of pad cause the contact status changes from sticking to contact and then to near contact. (author)

182nd Symposium of the International Astronomical Union

CERN Document Server

Bertout, Claude

1997-01-01

Herbig-Haro objects were discovered 50 years ago, and during this half century they have developed from being mysterious small nebulae to be­ coming an important phenomenon in star formation. Indeed, HH flows are now recognized not only as fascinating astrophysical laboratories involving shock physics and chemistry, hydrodynamics and radiation processes, but it has gradually been realized that HH flows hold essential clues to the birth and early evolution of low mass stars. IAU Symposium No. 182 on Herbig-Haro Flows and the Birth of Low Mass Stars were held from January 20 to 24, 1997 in Chamonix in the french alps. A total of 178 researchers from 26 countries met to discuss our present level of understanding of Herbig-Haro flows and their relation to disk accretion events and T Tauri winds and other outflow phenomena like molecular outflows, embedded molecular hydrogen flows and radio jets. The present book contains the manuscripts from the oral contributions of the symposium. The poster papers were printed...

GIANT PLANET MIGRATION, DISK EVOLUTION, AND THE ORIGIN OF TRANSITIONAL DISKS

International Nuclear Information System (INIS)

Alexander, Richard D.; Armitage, Philip J.

2009-01-01

We present models of giant planet migration in evolving protoplanetary disks. Our disks evolve subject to viscous transport of angular momentum and photoevaporation, while planets undergo Type II migration. We use a Monte Carlo approach, running large numbers of models with a range in initial conditions. We find that relatively simple models can reproduce both the observed radial distribution of extrasolar giant planets, and the lifetimes and accretion histories of protoplanetary disks. The use of state-of-the-art photoevaporation models results in a degree of coupling between planet formation and disk clearing, which has not been found previously. Some accretion across planetary orbits is necessary if planets are to survive at radii ∼<1.5 AU, and if planets of Jupiter mass or greater are to survive in our models they must be able to form at late times, when the disk surface density in the formation region is low. Our model forms two different types of 'transitional' disks, embedded planets and clearing disks, which show markedly different properties. We find that the observable properties of these systems are broadly consistent with current observations, and highlight useful observational diagnostics. We predict that young transition disks are more likely to contain embedded giant planets, while older transition disks are more likely to be undergoing disk clearing.

HOT GAS HALOS AROUND DISK GALAXIES: CONFRONTING COSMOLOGICAL SIMULATIONS WITH OBSERVATIONS

International Nuclear Information System (INIS)

Rasmussen, Jesper; Sommer-Larsen, Jesper; Pedersen, Kristian; Toft, Sune; Grove, Lisbeth F.; Benson, Andrew; Bower, Richard G.

2009-01-01

Models of disk galaxy formation commonly predict the existence of an extended reservoir of accreted hot gas surrounding massive spirals at low redshift. As a test of these models, we use X-ray and Hα data of the two massive, quiescent edge-on spirals NGC 5746 and NGC 5170 to investigate the amount and origin of any hot gas in their halos. Contrary to our earlier claim, the Chandra analysis of NGC 5746, employing more recent calibration data, does not reveal any significant evidence for diffuse X-ray emission outside the optical disk, with a 3σ upper limit to the halo X-ray luminosity of 4 x 10 39 erg s -1 . An identical study of the less massive NGC 5170 also fails to detect any extraplanar X-ray emission. By extracting hot halo properties of disk galaxies formed in cosmological hydrodynamical simulations, we compare these results to expectations for cosmological accretion of hot gas by spirals. For Milky-Way-sized galaxies, these high-resolution simulations predict hot halo X-ray luminosities which are lower by a factor of ∼2 compared to our earlier results reported by Toft et al. We find the new simulation predictions to be consistent with our observational constraints for both NGC 5746 and NGC 5170, while also confirming that the hot gas detected so far around more actively star-forming spirals is in general probably associated with stellar activity in the disk. Observational results on quiescent disk galaxies at the high-mass end are nevertheless providing powerful constraints on theoretical predictions, and hence on the assumed input physics in numerical studies of disk galaxy formation and evolution.

Time-dependent simulations of disk-embedded planetary atmospheres

Science.gov (United States)

Stökl, A.; Dorfi, E. A.

2014-03-01

At the early stages of evolution of planetary systems, young Earth-like planets still embedded in the protoplanetary disk accumulate disk gas gravitationally into planetary atmospheres. The established way to study such atmospheres are hydrostatic models, even though in many cases the assumption of stationarity is unlikely to be fulfilled. Furthermore, such models rely on the specification of a planetary luminosity, attributed to a continuous, highly uncertain accretion of planetesimals onto the surface of the solid core. We present for the first time time-dependent, dynamic simulations of the accretion of nebula gas into an atmosphere around a proto-planet and the evolution of such embedded atmospheres while integrating the thermal energy budget of the solid core. The spherical symmetric models computed with the TAPIR-Code (short for The adaptive, implicit RHD-Code) range from the surface of the rocky core up to the Hill radius where the surrounding protoplanetary disk provides the boundary conditions. The TAPIR-Code includes the hydrodynamics equations, gray radiative transport and convective energy transport. The results indicate that diskembedded planetary atmospheres evolve along comparatively simple outlines and in particular settle, dependent on the mass of the solid core, at characteristic surface temperatures and planetary luminosities, quite independent on numerical parameters and initial conditions. For sufficiently massive cores, this evolution ultimately also leads to runaway accretion and the formation of a gas planet.

A New Paradigm for Gamma Ray Bursts: Long Term Accretion Rate Modulation by an External Accretion Disk

Science.gov (United States)

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.

A LARGE, MASSIVE, ROTATING DISK AROUND AN ISOLATED YOUNG STELLAR OBJECT

International Nuclear Information System (INIS)

Quanz, Sascha P.; Beuther, Henrik; Steinacker, Juergen; Linz, Hendrik; Krause, Oliver; Henning, Thomas; Birkmann, Stephan M.; Zhang Qizhou

2010-01-01

and the molecules' abundances are similar to those found in other circumstellar disks. We furthermore detected C 2 H toward the objects and discuss this finding in the context of star formation. Finally, we have performed radiative transfer modeling of the K-band scattered light image varying a disk plus outflow two-dimensional density profile and the stellar properties. The model approximately reproduces extent and location of the dark lane, and the basic appearance of the outflow. We discuss our findings in the context of circumstellar disks across all mass regimes and conclude that our discovery is an ideal laboratory to study the early phases in the evolution of massive circumstellar disks surrounding young stellar objects.

Using Vertical Structure to Infer the Total Mass Hidden in a Debris Disk

Science.gov (United States)

Daley, Cail; Hughes, A. Meredith; Carter, Evan; Flaherty, Kevin; Stafford Lambros, Zachary; Pan, Margaret; Schlichting, Hilke; Chiang, Eugene; Wilner, David; Dent, Bill; Carpenter, John; Andrews, Sean; MacGregor, Meredith Ann; Moor, Attila; Kospal, Agnes

2018-01-01

Disks of optically thin debris dust surround ≥ 20% of main sequence stars and mark the final stage of planetary system evolution. The features of debris disks encode dynamical interactions between the dust and any unseen planets embedded in the disk. The vertical distribution of the dust is particularly sensitive to the total mass of planetesimal bodies in the disk, and is therefore well suited for constraining the prevalence of otherwise unobservable Uranus and Neptune analogs. Inferences of mass from debris disk vertical structure have previously been applied to infrared and optical observations of several systems, but the smaller particles traced by short-wavelength observations are ‘puffed up’ by radiation pressure, yielding only upper limits on the total embedded mass. The large grains that dominate the emission at millimeter wavelengths are essentially impervious to the effects of stellar radiation, and therefore trace the underlying mass distribution more directly. Here we present 1.3mm dust continuum observations of the debris disk around the nearby M star AU Mic with the Atacama Large Millimeter/submillimeter Array (ALMA). The 3 au spatial resolution of the observations, combined with the favorable edge-on geometry of the system, allows us to measure the vertical structure of a debris disk at millimeter wavelengths for the first time. We analyze the data using a ray-tracing code that translates a 2-D density and temperature structure into a model sky image of the disk. This model image is then compared directly to the interferometric data in the visibility domain, and the model parameters are explored using a Markov Chain Monte Carlo routine. We measure a scale height-to-radius ratio of 0.03, which we then compare to a theoretical model of steady-state, size-dependent velocity distributions in the collisional cascade to infer a total mass within the disk of ∼ 1.7 Earth masses. These measurements rule out the presence of a gas giant or Neptune

CT-guided percutaneous laser disk decompression for cervical and lumbar disk hernia

International Nuclear Information System (INIS)

Shimizu, Kanichiro; Koyama, Tutomu; Harada, Junta; Abe, Toshiaki

2008-01-01

Percutaneous laser disk decompression under X-ray fluoroscopy was first reported in 1987 for minimally invasive therapy of lumbar disk hernia. In patients with disk hernia, laser vaporizes a small portion of the intervertebral disk thereby reducing the volume and pressure of the affected disk. We present the efficacy and safety of this procedure, and analysis of fair or poor response cases. In our study, 226 cases of lumbar disk hernia and 7 cases of cervical disk hernia were treated under CT guided PLDD. Japan Orthopedic Association (JOA) score and Mac-Nab criteria were investigated to evaluate the response to treatment. Improvement ratio based on the JOA score was calculated as follows. Overall success rate was 91.6% in cases lumber disk hernia, and 100% in cases of cervical disk hernia. We experienced two cases with two cases with postoperative complication. Both cases were treated conservatively. The majority of acute cases and post operative cases were reported to be 'good' on Mac-Nab criteria. Cases of fair or poor response on Mac-Nab criteria were lateral type, foraminal stenosis or large disk hernia. CT-guided PLDD is a safe and accurate procedure. The overall success rate can be increased by carefully selecting patients. (author)

Disk Storage Server

CERN Multimedia

This model was a disk storage server used in the Data Centre up until 2012. Each tray contains a hard disk drive (see the 5TB hard disk drive on the main disk display section - this actually fits into one of the trays). There are 16 trays in all per server. There are hundreds of these servers mounted on racks in the Data Centre, as can be seen.

Ultraviolet continuum and H2 fluorescent emission in Herbig-Haro objects 43 and 47

International Nuclear Information System (INIS)

Schwartz, R.D.

1983-01-01

The results of International Ultraviolet Explorer (IUE) short-wavelength spectra of the low-excitation Herbig-Haro objects HH 43 and HH 47 are reported. In HH 43 a number of emission lines in the Lyman band of H 2 from the excited state 1 μ + /sub u/, #betta#' = 1, J' = 4 are observed. The lines are produced by fluorescence from the H Lyα line which pumps the lower state 1 μ + /sub g/, #betta#'' = 2.J'' = 5 which in turn is excited by a low-velocity shock wave. No evidence of emission from highly ionized gas is present in the UV spectra. Both objects exhibit a UV continuum which peaks in the vicinity of 1500 A and which is probably caused by hydrogen two-photon emission enhanced by collisional excitation in a low-velocity shock

DISCOVERY OF AN Hα EMITTING DISK AROUND THE SUPERMASSIVE BLACK HOLE OF M31

International Nuclear Information System (INIS)

Menezes, R. B.; Steiner, J. E.; Ricci, T. V.

2013-01-01

Due to its proximity, the mass of the supermassive black hole in the nucleus of the Andromeda galaxy (M31), the most massive black hole in the Local Group of galaxies, has been measured by several methods involving the kinematics of a stellar disk which surrounds it. We report here the discovery of an eccentric Hα emitting disk around the black hole at the center of M31 and show how modeling this disk can provide an independent determination of the mass of the black hole. Our model implies a mass of 5.0 +0.8 –1.0 × 10 7 M ☉ for the central black hole, consistent with the average of determinations by methods involving stellar dynamics, and compatible (at 1σ level) with measurements obtained from the most detailed models of the stellar disk around the central black hole. This value is also consistent with the M-σ relation. In order to make a comparison, we applied our simulation on the stellar kinematics in the nucleus of M31 and concluded that the parameters obtained for the stellar disk are not formally compatible with the parameters obtained for the Hα emitting disk. This result suggests that the stellar and the Hα emitting disks are intrinsically different from each other. A plausible explanation is that the Hα emission is associated with a gaseous disk. This hypothesis is supported by the detection of traces of weaker nebular lines in the nuclear region of M31. However, we cannot exclude the possibility that the Hα emission is, at least partially, generated by stars.

Development of Disk Rover, wall-climbing robot using permanent magnet disk

International Nuclear Information System (INIS)

Hirose, Shigeo; Tsutsumitake; Hiroshi; Toyama, Ryousei; Kobayashi, Kengo.

1992-01-01

A new type of wall climbing robot, named Disk Rover, using permanent magnet disks are developed. The newly introduced permanent magnet disk is to rotate the magnet disk on the surface of wall with partly contacted posture. It allows to produce high magnetic attraction force compared with conventional permanent wheel which utilizes only a small portion of the magnet installed around the wheel. The optimum design of the magnetic wheel is done by using finit element method and it is shown that the magnetic attraction force vs. weight ratio can be designed about three times higher than conventional type magnet wheel. The developed Disk Rover is 25 kg in weight including controller and battery, about 685 mm in diameter, 239 mm in height and has a pair of permanent magnet disks. It is demonstrated by the experiments that the Disk Rover can move around on the surface of the wall quite smoothly by radio control and has payload of about its own weight. Several considerations are also done in order to surmount bead weld. (author)

Constraint on the infall of H I into big disk galaxies

International Nuclear Information System (INIS)

Bothun, G.D.

1985-01-01

Available 21-cm observations of late-type spirals from a variety of sources have been gathered together for purposes of constructing an H I luminosity function for spirals with M/sub B/ -1 ) has enabled increasingly larger volumes of space that surround the disk to become accessible to the Arecibo 21-cm beam. The data show absolutely no trend of increasing H I with redshift. There is likewise no tendency for an increase in observed H I mass over that predicted from the linear diameter of the galaxy, as the ratio of beam size to galaxy size increases. From these null results we can place an upper limit on the halo H I column density of N/sub H/ = 3 x 10 19 atoms cm -2 . In relative terms, the halo can contain no more than 1/3 the amount of H I already distributed in the disk. Based on these data, we argue that, if infall is still important at the present time in the evolution of big disk galaxies, then the reservoir should be detectable unless it is predominately in a form more exotic than atomic hydrogen

A SEARCH FOR HERBIG-HARO OBJECTS IN NGC 7023 AND BARNARD 175

International Nuclear Information System (INIS)

Rector, T. A.; Schweiker, H.

2013-01-01

Wide-field optical imaging was obtained of the cluster and reflection nebula NGC 7023 and the Bok globule B175. We report the discovery of four new Herbig-Haro (HH) objects in NGC 7023, the first HH objects to be found in this region. They were first detected by their Hα and [S II] emission but are also visible at 3.6 and 4.5 μm in archival Spitzer observations of this field. These HH objects are part of at least two distinct outflows. Both outflows are aligned with embedded 'Class I' young stellar objects in a tight group on the western edge of the nebula. One of the outflows may have a projected distance of 0.75 pc, which is a notable length for an embedded source. No new HH objects were discovered in B175. However, we reclassify the knot HH450X, in B175, as a background galaxy. The discovery that HH 450X is not a shock front weakens the argument that HH 450 and SNR G110.3+11.3 are co-located and interacting.

A SPITZER c2d LEGACY SURVEY TO IDENTIFY AND CHARACTERIZE DISKS WITH INNER DUST HOLES

International Nuclear Information System (INIS)

Merin, Bruno; Brown, Joanna M.; Herczeg, Gregory J.; Van Dishoeck, Ewine F.; Oliveira, Isa; Lahuis, Fred; Bottinelli, Sandrine; Augereau, Jean-Charles; Olofsson, Johan; Evans, Neal J.; Harvey, Paul M.; Cieza, Lucas; Spezzi, Loredana; Prusti, Timo; Alcala, Juan M.; Blake, Geoffrey A.; Bayo, Amelia; Geers, Vincent G.; Walter, Frederick M.; Chiu, Kuenley

2010-01-01

Understanding how disks dissipate is essential to studies of planet formation. However, identifying exactly how dust and gas dissipate is complicated due to the difficulty of finding objects that are clearly in the transition phase of losing their surrounding material. We use Spitzer Infrared Spectrograph (IRS) spectra to examine 35 photometrically selected candidate cold disks (disks with large inner dust holes). The infrared spectra are supplemented with optical spectra to determine stellar and accretion properties and 1.3 mm photometry to measure disk masses. Based on detailed spectral energy distribution modeling, we identify 15 new cold disks. The remaining 20 objects have IRS spectra that are consistent with disks without holes, disks that are observed close to edge-on, or stars with background emission. Based on these results, we determine reliable criteria to identify disks with inner holes from Spitzer photometry, and examine criteria already in the literature. Applying these criteria to the c2d surveyed star-forming regions gives a frequency of such objects of at least 4% and most likely of order 12% of the young stellar object population identified by Spitzer. We also examine the properties of these new cold disks in combination with cold disks from the literature. Hole sizes in this sample are generally smaller than in previously discovered disks and reflect a distribution in better agreement with exoplanet orbit radii. We find correlations between hole size and both disk and stellar masses. Silicate features, including crystalline features, are present in the overwhelming majority of the sample, although the 10 μm feature strength above the continuum declines for holes with radii larger than ∼7 AU. In contrast, polycyclic aromatic hydrocarbons are only detected in 2 out of 15 sources. Only a quarter of the cold disk sample shows no signs of accretion, making it unlikely that photoevaporation is the dominant hole-forming process in most cases.

Planet Formation in AB Aurigae: Imaging of the Inner Gaseous Spirals Observed inside the Dust Cavity

Energy Technology Data Exchange (ETDEWEB)

Tang, Ya-Wen; Gu, Pin-Gao; Ho, Paul T. P. [Academia Sinica, Institute of Astronomy and Astrophysics, Taipei, Taiwan (China); Guilloteau, Stephane; Dutrey, Anne; Chapillon, Edwige; Folco, Emmanuel di [Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, alle Geoffroy Saint-Hilaire, F-33615 Pessac (France); Muto, Takayuki [Department of Physics, National Taiwan University, Taiwan (China); Shen, Bo-Ting [Division of Liberal Arts, Kogakuin University, 1-24-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo 163-8677 (Japan); Inutsuka, Shu-ichiro [Department of Physics, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602 (Japan); Momose, Munetake [College of Science, Ibaraki University, 2-1-1 Bunkyo, Mito, Ibaraki 310-8512 (Japan); Pietu, Vincent [IRAM, 300 rue de la Piscine, Domaine Universitaire, F-38406 Saint-Martin-d’Hères (France); Fukagawa, Misato [Division of Particle and Astrophysical Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602 (Japan); Corder, Stuartt [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States); Ohashi, Nagayoshi [Subaru Telescope, National Astronomical Observatory of Japan, 650 North Aohoku Place, Hilo, HI 96720 (United States); Hashimoto, Jun, E-mail: ywtang@asiaa.sinica.edu.tw [Astrobiology Center of NINS 2-21-1, Osawa, Mitaka, Tokyo, 181-8588 (Japan)

2017-05-01

We report the results of ALMA observations of a protoplanetary disk surrounding the Herbig Ae star AB Aurigae. We obtained high-resolution (0.″1; 14 au) images in {sup 12}CO J = 2 − 1 emission and in the dust continuum at the wavelength of 1.3 mm. The continuum emission is detected at the center and at the ring with a radius ( r ) of ∼120 au. The CO emission is dominated by two prominent spirals within the dust ring. These spirals are trailing and appear to be about 4 times brighter than their surrounding medium. Their kinematics is consistent with Keplerian rotation at an inclination of 23°. The apparent two-arm-spiral pattern is best explained by tidal disturbances created by an unseen companion located at r of 60–80 au, with dust confined in the pressure bumps created outside this companion orbit. An additional companion at r of 30 au, coinciding with the peak CO brightness and a large pitch angle of the spiral, would help to explain the overall emptiness of the cavity. Alternative mechanisms to excite the spirals are discussed. The origin of the large pitch angle detected here remains puzzling.

Understanding Floppy Disks.

Science.gov (United States)

Valentine, Pamela

1980-01-01

The author describes the floppy disk with an analogy to the phonograph record, and discusses the advantages, disadvantages, and capabilities of hard-sectored and soft-sectored floppy disks. She concludes that, at present, the floppy disk will continue to be the primary choice of personal computer manufacturers and their customers. (KC)

OT1_ipascucc_1: Understanding the Origin of Transition Disks via Disk Mass Measurements

Science.gov (United States)

Pascucci, I.

2010-07-01

Transition disks are a distinguished group of few Myr-old systems caught in the phase of dispersing their inner dust disk. Three different processes have been proposed to explain this inside-out clearing: grain growth, photoevaporation driven by the central star, and dynamical clearing by a forming giant planet. Which of these processes lead to a transition disk? Distinguishing between them requires the combined knowledge of stellar accretion rates and disk masses. We propose here to use 43.8 hours of PACS spectroscopy to detect the [OI] 63 micron emission line from a sample of 21 well-known transition disks with measured mass accretion rates. We will use this line, in combination with ancillary CO millimeter lines, to measure their gas disk mass. Because gas dominates the mass of protoplanetary disks our approach and choice of lines will enable us to trace the bulk of the disk mass that resides beyond tens of AU from young stars. Our program will quadruple the number of transition disks currently observed with Herschel in this setting and for which disk masses can be measured. We will then place the transition and the ~100 classical/non-transition disks of similar age (from the Herschel KP "Gas in Protoplanetary Systems") in the mass accretion rate-disk mass diagram with two main goals: 1) reveal which gaps have been created by grain growth, photoevaporation, or giant planet formation and 2) from the statistics, determine the main disk dispersal mechanism leading to a transition disk.

DISCOVERY OF CRYSTALLIZED WATER ICE IN A SILHOUETTE DISK IN THE M43 REGION

Energy Technology Data Exchange (ETDEWEB)

Terada, Hiroshi [Subaru Telescope, National Astronomical Observatory of Japan, 650 North A' ohoku Place, Hilo, HI 96720 (United States); Tokunaga, Alan T., E-mail: terada@subaru.naoj.org [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu 96822 (United States)

2012-07-01

We present the 1.9-4.2 {mu}m spectra of the five bright (L {<=} 11.2) young stars associated with silhouette disks with a moderate to high inclination angle of 39 Degree-Sign -80 Degree-Sign in the M42 and M43 regions. The water ice absorption is seen toward d121-1925 and d216-0939, while the spectra of d182-316, d183-405, and d218-354 show no water ice feature around 3.1 {mu}m within the detection limits. By comparing the water ice features toward nearby stars, we find that the water ice absorption toward d121-1925 and d216-0939 most likely originates from the foreground material and the surrounding disk, respectively. The angle of the disk inclination is found to be mainly responsible for the difference of the optical depth of the water ice among the five young stars. Our results suggest that there is a critical inclination angle between 65 Degree-Sign and 75 Degree-Sign for the circumstellar disk where the water ice absorption becomes strong. The average density at the disk surface of d216-0939 was found to be 6.38 Multiplication-Sign 10{sup -18} g cm{sup -3}. The water ice absorption band in the d216-0939 disk is remarkable in that the maximum optical depth of the water ice band is at a longer wavelength than detected before. It indicates that the primary carrier of the feature is purely crystallized water ice at the surface of the d216-0939 disk with characteristic size of {approx}0.8 {mu}m, which suggests grain growth. This is the first direct detection of purely crystallized water ice in a silhouette disk.

DISCOVERY OF AN H{alpha} EMITTING DISK AROUND THE SUPERMASSIVE BLACK HOLE OF M31

Energy Technology Data Exchange (ETDEWEB)

Menezes, R. B.; Steiner, J. E.; Ricci, T. V., E-mail: robertobm@astro.iag.usp.br [Instituto de Astronomia Geofisica e Ciencias Atmosfericas, Universidade de Sao Paulo, Rua do Matao 1226, Cidade Universitaria, Sao Paulo, SP CEP 05508-090 (Brazil)

2013-01-10

Due to its proximity, the mass of the supermassive black hole in the nucleus of the Andromeda galaxy (M31), the most massive black hole in the Local Group of galaxies, has been measured by several methods involving the kinematics of a stellar disk which surrounds it. We report here the discovery of an eccentric H{alpha} emitting disk around the black hole at the center of M31 and show how modeling this disk can provide an independent determination of the mass of the black hole. Our model implies a mass of 5.0{sup +0.8}{sub -1.0} Multiplication-Sign 10{sup 7} M{sub Sun} for the central black hole, consistent with the average of determinations by methods involving stellar dynamics, and compatible (at 1{sigma} level) with measurements obtained from the most detailed models of the stellar disk around the central black hole. This value is also consistent with the M-{sigma} relation. In order to make a comparison, we applied our simulation on the stellar kinematics in the nucleus of M31 and concluded that the parameters obtained for the stellar disk are not formally compatible with the parameters obtained for the H{alpha} emitting disk. This result suggests that the stellar and the H{alpha} emitting disks are intrinsically different from each other. A plausible explanation is that the H{alpha} emission is associated with a gaseous disk. This hypothesis is supported by the detection of traces of weaker nebular lines in the nuclear region of M31. However, we cannot exclude the possibility that the H{alpha} emission is, at least partially, generated by stars.

Possible Analog for Early Solar System Disk Found

Science.gov (United States)

1998-10-01

, although tiny when compared to some suspected planet-forming systems recently discovered by other astronomical techniques, contains several compact clusters of water molecules that amplify microwave radio emissions in a manner similar to the way a laser amplifies light. By tracking the motions of these powerful, naturally occurring amplifiers, or "masers," the researchers could determine that a mass about the size of our Sun lies at the center of this disk. The researchers also detected a powerful radio jet, centered on the disk of water masers but perpendicular to it, shooting out of NGC 2071. Theorists have speculated that such jets are produced by accretion disks around very young stars, where flowing winds are driven outward by material that fails to fall onto the star. This may represent the smallest -- and perhaps earliest -- example of this disk-jet phenomenon seen to date. "We're pretty sure that systems like this, with disks of gas and dust surrounding a young star, turn into solar systems containing planets, moons and comets, but we don't know exactly how they do it," said Dr. Luis Rodriguez of the National Autonomous University of Mexico. "This particular object, because we can see all these phenomena and measure the rotation speeds and masses, is going to provide us an ideal laboratory for studying the mysterious process of planet formation." In addition to Torrelles and Ho, the other authors of the report published in the 1 October 1998 issue of the Astrophysical Journal were Drs. Jose F. Gomez of the Laboratory for Space and Astrophysics, Guillem Anglada of the Institute of Astrophysics of Andalucia, Spain, and Rodriguez and Dr. Salvador Curiel of the National Autonomous University of Mexico. The VLA is an instrument of the National Radio Astronomy Observatory, a facility of the National Science Foundation, operated under cooperative agreement by the Associated Universities, Inc.

EFFECT OF A STELLAR COMPANION ON THE MODELING OF HD 142527 INFRARED SED

OpenAIRE

Erick Nagel

2014-01-01

The discovery of a companion of the Herbig Ae/Be star HD 142527 motivates the study of the effect that it produces on the SED. The main change on the system configuration is the formation of a gap in the disk. Due to this change, a wall (outer edge of the gap), which is frontally illuminated by stellar radiation is formed. We present a model for the SED, considering all the components: a disk with two gaps (one produced by the stellar companion and the other by potential planets), three walls...

DISCOVERY OF CANDIDATE H2O DISK MASERS IN ACTIVE GALACTIC NUCLEI AND ESTIMATIONS OF CENTRIPETAL ACCELERATIONS

International Nuclear Information System (INIS)

Greenhill, Lincoln J.; Moran, James M.; Tilak, Avanti; Kondratko, Paul T.

2009-01-01

Based on spectroscopic signatures, about one-third of known H 2 O maser sources in active galactic nuclei (AGNs) are believed to arise in highly inclined accretion disks around central engines. These 'disk maser candidates' are of interest primarily because angular structure and rotation curves can be resolved with interferometers, enabling dynamical study. We identify five new disk maser candidates in studies with the Green Bank Telescope, bringing the total number published to 30. We discovered two (NGC 1320, NGC 17) in a survey of 40 inclined active galaxies (v sys -1 ). The remaining three disk maser candidates were identified in monitoring of known sources: NGC 449, NGC 2979, and NGC 3735. We also confirm a previously marginal case in UGC 4203. For the disk maser candidates reported here, inferred rotation speeds are 130-500 km s -1 . Monitoring of three more rapidly rotating candidate disks (CG 211, NGC 6264, VV 340A) has enabled measurement of likely orbital centripetal acceleration, and estimation of central masses ((2-7) x10 7 M sun ) and mean disk radii (0.2-0.4 pc). Accelerations may ultimately permit estimation of distances when combined with interferometer data. This is notable because the three AGNs are relatively distant (10,000 km s -1 sys -1 ), and fractional error in a derived Hubble constant, due to peculiar motion of the galaxies, would be small. As signposts of highly inclined geometries at galactocentric radii of ∼0.1-1 pc, disk masers also provide robust orientation references that allow analysis of (mis)alignment between AGNs and surrounding galactic stellar disks, even without extensive interferometric mapping. We find no preference among published disk maser candidates to lie in high-inclination galaxies. This provides independent support for conclusions that in late-type galaxies, central engine accretion disks and galactic plane orientations are not correlated.

Equilibrium configuration of a stratus floating above accretion disks: Full-disk calculation

Science.gov (United States)

Itanishi, Yusuke; Fukue, Jun

2017-06-01

We examine floating strati above a luminous accretion disk, supported by the radiative force from the entire disk, and calculate the equilibrium locus, which depends on the disk luminosity and the optical depth of the stratus. Due to the radiative transfer effect (albedo effect), the floating height of the stratus with a finite optical depth generally becomes high, compared with the particle case. In contrast to the case of the near-disk approximation, moreover, the floating height becomes yet higher in the present full-disk calculation, since the intense radiation from the inner disk is taken into account. As a result, when the disk luminosity normalized by the Eddington luminosity is ˜0.3 and the stratus optical depth is around unity, the stable configuration disappears at around r ˜ 50 rg, rg being the Schwarzschild radius, and the stratus would be blown off as a cloudy wind consisting of many strati with appropriate conditions. This luminosity is sufficiently smaller than the Eddington one, and the present results suggest that the radiation-driven cloudy wind can be easily blown off from the sub-Eddington disk, and this can explain various outflows observed in ultra-fast outflow objects as well as in broad-absorption-line quasars.

The effect of an accretion disk on coherent pulsed emission from weakly magnetized neutron stars

International Nuclear Information System (INIS)

Asaoka, Ikuko; Hoshi, Reiun.

1989-01-01

Using a simple model for hot spots formed on the magnetic polar regions we calculate the X-ray pulse profiles expected from bright low-mass X-ray binaries. We assume that neutron stars in close binary systems are surrounded by accretion disks extending down in the vicinity of their surfaces. Even partial eclipses of a hot spot by the accretion disk change the coherent pulsed fraction and, in some cases, the phase of pulsations by almost 180deg. Coherent pulsations are clearly seen even for sufficiently compact model neutron stars, if the hot spots emit isotropic or fan-beam radiation. In the case of pencil-beam radiation, coherent pulsations are also seen if the cap-opening angle is less than ∼60deg, while the inclination angle is larger than 68deg. Gravitational lensing alone does not smear coherent pulsations in moderately weak magnetized neutron stars in the presence of an absorbing accretion disk. (author)

Accretion Disks and Coronae in the X-Ray Flashlight

Science.gov (United States)

Degenaar, Nathalie; Ballantyne, David R.; Belloni, Tomaso; Chakraborty, Manoneeta; Chen, Yu-Peng; Ji, Long; Kretschmar, Peter; Kuulkers, Erik; Li, Jian; Maccarone, Thomas J.; Malzac, Julien; Zhang, Shu; Zhang, Shuang-Nan

2018-02-01

Plasma accreted onto the surface of a neutron star can ignite due to unstable thermonuclear burning and produce a bright flash of X-ray emission called a Type-I X-ray burst. Such events are very common; thousands have been observed to date from over a hundred accreting neutron stars. The intense, often Eddington-limited, radiation generated in these thermonuclear explosions can have a discernible effect on the surrounding accretion flow that consists of an accretion disk and a hot electron corona. Type-I X-ray bursts can therefore serve as direct, repeating probes of the internal dynamics of the accretion process. In this work we review and interpret the observational evidence for the impact that Type-I X-ray bursts have on accretion disks and coronae. We also provide an outlook of how to make further progress in this research field with prospective experiments and analysis techniques, and by exploiting the technical capabilities of the new and concept X-ray missions ASTROSAT, NICER, Insight-HXMT, eXTP, and STROBE-X.

SURVIVAL OF INTERSTELLAR MOLECULES TO PRESTELLAR DENSE CORE COLLAPSE AND EARLY PHASES OF DISK FORMATION

International Nuclear Information System (INIS)

Hincelin, U.; Wakelam, V.; Hersant, F.; Guilloteau, S.; Commerçon, B.

2013-01-01

An outstanding question of astrobiology is the link between the chemical composition of planets, comets, and other solar system bodies and the molecules formed in the interstellar medium. Understanding the chemical and physical evolution of the matter leading to the formation of protoplanetary disks is an important step for this. We provide some new clues to this long-standing problem using three-dimensional chemical simulations of the early phases of disk formation: we interfaced the full gas-grain chemical model Nautilus with the radiation-magnetohydrodynamic model RAMSES, for different configurations and intensities of the magnetic field. Our results show that the chemical content (gas and ices) is globally conserved during the collapsing process, from the parent molecular cloud to the young disk surrounding the first Larson core. A qualitative comparison with cometary composition suggests that comets are constituted of different phases, some molecules being direct tracers of interstellar chemistry, while others, including complex molecules, seem to have been formed in disks, where higher densities and temperatures allow for an active grain surface chemistry. The latter phase, and its connection with the formation of the first Larson core, remains to be modeled

2TB hard disk drive

CERN Multimedia

This particular object was used up until 2012 in the Data Centre. It slots into one of the Disk Server trays. Hard disks were invented in the 1950s. They started as large disks up to 20 inches in diameter holding just a few megabytes (link is external). They were originally called "fixed disks" or "Winchesters" (a code name used for a popular IBM product). They later became known as "hard disks" to distinguish them from "floppy disks (link is external)." Hard disks have a hard platter that holds the magnetic medium, as opposed to the flexible plastic film found in tapes and floppies.

DISK DETECTIVE: DISCOVERY OF NEW CIRCUMSTELLAR DISK CANDIDATES THROUGH CITIZEN SCIENCE

Energy Technology Data Exchange (ETDEWEB)

Kuchner, Marc J.; McElwain, Michael; Padgett, Deborah L. [NASA Goddard Space Flight Center Exoplanets and Stellar Astrophysics Laboratory, Code 667 Greenbelt, MD 21230 (United States); Silverberg, Steven M.; Wisniewski, John P. [Homer L. Dodge Department of Physics and Astronomy The University of Oklahoma 440 W. Brooks St. Norman, OK 73019 (United States); Bans, Alissa S. [Valparaiso University, Department of Physics and Astronomy, Neils Science Center, 1610 Campus Drive East, Valparaiso, IN 46383 (United States); Bhattacharjee, Shambo [International Space University 1 Rue Jean-Dominique Cassini F-67400 Illkirch-Graffenstaden (France); Kenyon, Scott J. [Smithsonian Astrophysical Observatory 60 Garden Street Cambridge, MA 02138 (United States); Debes, John H. [Space Telescope Science Institute 3700 San Martin Dr. Baltimore, MD 21218 (United States); Currie, Thayne [National Astronomical Observatory of Japan 650 N A’ohokhu Place Hilo, HI 96720 (United States); García, Luciano [Observatorio Astronómico de Córdoba Universidad Nacional de Córdoba Laprida 854, X5000BGR, Córdoba (Argentina); Jung, Dawoon [Korea Aerospace Research Institute Lunar Exploration Program Office 169-84 Gwahak-ro, Yuseong-gu, Daejeon 34133 (Korea, Republic of); Lintott, Chris [Denys Wilkinson Building Keble Road Oxford, OX1 3RH (United Kingdom); Rebull, Luisa M. [Infrared Processing and Analaysis Center Caltech M/S 314-6 1200 E. California Blvd. Pasadena, CA 91125 (United States); Nesvold, Erika, E-mail: Marc.Kuchner@nasa.gov, E-mail: michael.w.mcelwain@nasa.gov, E-mail: deborah.l.padgett@nasa.gov, E-mail: carol.a.grady@nasa.gov, E-mail: silverberg@ou.edu, E-mail: wisniewski@ou.edu [Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, DC 20015-1305 (United States); Collaboration: Disk Detective Collaboration; and others

2016-10-20

The Disk Detective citizen science project aims to find new stars with 22 μ m excess emission from circumstellar dust using data from NASA’s Wide-field Infrared Survey Explorer ( WISE ) mission. Initial cuts on the AllWISE catalog provide an input catalog of 277,686 sources. Volunteers then view images of each source online in 10 different bands to identify false positives (galaxies, interstellar matter, image artifacts, etc.). Sources that survive this online vetting are followed up with spectroscopy on the FLWO Tillinghast telescope. This approach should allow us to unleash the full potential of WISE for finding new debris disks and protoplanetary disks. We announce a first list of 37 new disk candidates discovered by the project, and we describe our vetting and follow-up process. One of these systems appears to contain the first debris disk discovered around a star with a white dwarf companion: HD 74389. We also report four newly discovered classical Be stars (HD 6612, HD 7406, HD 164137, and HD 218546) and a new detection of 22 μ m excess around the previously known debris disk host star HD 22128.

DISK DETECTIVE: DISCOVERY OF NEW CIRCUMSTELLAR DISK CANDIDATES THROUGH CITIZEN SCIENCE

International Nuclear Information System (INIS)

Kuchner, Marc J.; McElwain, Michael; Padgett, Deborah L.; Silverberg, Steven M.; Wisniewski, John P.; Bans, Alissa S.; Bhattacharjee, Shambo; Kenyon, Scott J.; Debes, John H.; Currie, Thayne; García, Luciano; Jung, Dawoon; Lintott, Chris; Rebull, Luisa M.; Nesvold, Erika

2016-01-01

The Disk Detective citizen science project aims to find new stars with 22 μ m excess emission from circumstellar dust using data from NASA’s Wide-field Infrared Survey Explorer ( WISE ) mission. Initial cuts on the AllWISE catalog provide an input catalog of 277,686 sources. Volunteers then view images of each source online in 10 different bands to identify false positives (galaxies, interstellar matter, image artifacts, etc.). Sources that survive this online vetting are followed up with spectroscopy on the FLWO Tillinghast telescope. This approach should allow us to unleash the full potential of WISE for finding new debris disks and protoplanetary disks. We announce a first list of 37 new disk candidates discovered by the project, and we describe our vetting and follow-up process. One of these systems appears to contain the first debris disk discovered around a star with a white dwarf companion: HD 74389. We also report four newly discovered classical Be stars (HD 6612, HD 7406, HD 164137, and HD 218546) and a new detection of 22 μ m excess around the previously known debris disk host star HD 22128.

Disk Detective: Discovery of New Circumstellar Disk Candidates Through Citizen Science

Science.gov (United States)

Kuchner, Marc J.; Silverberg, Steven M.; Bans, Alissa S.; Bhattacharjee, Shambo; Kenyon, Scott J.; Debes, John H.; Currie, Thayne; Garcia, Luciano; Jung, Dawoon; Lintott, Chris;

Herschel Studies of the Evolution and Environs of Young Stars in the DIGIT, WISH, and FOOSH Programs

Science.gov (United States)

Green, Joel D.; DIGIT OT Key Project Team; WISH GT Key Project Team; FOOSH OT1 Team

2012-01-01

The Herschel Space Observatory has enabled us to probe the physical conditions of outer disks, envelopes, and outflows of young stellar objects, including embedded objects, Herbig Ae/Be disks, and T Tauri disks. We will report on results from three projects, DIGIT, WISH, and FOOSH. The DIGIT (Dust, Ice, and Gas in Time) program (PI: Neal Evans) utilizes the full spectral range of the PACS instrument to explore simultaneously the solid and gas-phase chemistry around sources in all of these stages. WISH (Water in Star Forming Regions with Herschel, PI Ewine van Dishoeck) focuses on observations of key lines with HIFI and line scans of selected spectral regions with PACS. FOOSH (FU Orionis Objects Surveyed with Herschel, PI Joel Green) studies FU Orionis objects with full range PACS and SPIRE scans. DIGIT includes examples of low luminosity protostars, while FOOSH studies the high luminosity objects during outburst states. Rotational ladders of highly excited CO and OH emission are detected in both disks and protostars. The highly excited lines are more commonly seen in the embedded phases, where there appear to be two temperature components. Intriguingly, water is frequently detected in spectra of embedded sources, but not in the disk spectra. In addition to gas features, we explore the extent of the newly detected 69 um forsterite dust feature in both T Tauri and Herbig Ae/Be stars. When analyzed along with the Spitzer-detected dust features, these provide constraints on a population of colder crystalline material. We will present some models of individual sources, as well as some broad statistics of the emission from these stages of star and planet formation.

Accretion Disk Assembly During Common Envelope Evolution: Implications for Feedback and LIGO Binary Black Hole Formation

Energy Technology Data Exchange (ETDEWEB)

Murguia-Berthier, Ariadna; Ramirez-Ruiz, Enrico; Antoni, Andrea; Macias, Phillip [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); MacLeod, Morgan, E-mail: armurgui@ucsc.edu [School of Natural Sciences, Institute for Advanced Study, 1 Einstein Drive, Princeton, NJ 08540 (United States)

2017-08-20

During a common envelope (CE) episode in a binary system, the engulfed companion spirals to tighter orbital separations under the influence of drag from the surrounding envelope material. As this object sweeps through material with a steep radial gradient of density, net angular momentum is introduced into the flow, potentially leading to the formation of an accretion disk. The presence of a disk would have dramatic consequences for the outcome of the interaction because accretion might be accompanied by strong, polar outflows with enough energy to unbind the entire envelope. Without a detailed understanding of the necessary conditions for disk formation during CE, therefore, it is difficult to accurately predict the population of merging compact binaries. This paper examines the conditions for disk formation around objects embedded within CEs using the “wind tunnel” formalism developed by MacLeod et al. We find that the formation of disks is highly dependent on the compressibility of the envelope material. Disks form only in the most compressible of stellar envelope gas, found in envelopes’ outer layers in zones of partial ionization. These zones are largest in low-mass stellar envelopes, but comprise small portions of the envelope mass and radius in all cases. We conclude that disk formation and associated accretion feedback in CE is rare, and if it occurs, transitory. The implication for LIGO black hole binary assembly is that by avoiding strong accretion feedback, CE interactions should still result in the substantial orbital tightening needed to produce merging binaries.

Magnetohydrodynamics of accretion disks

International Nuclear Information System (INIS)

Torkelsson, U.

1994-04-01

The thesis consists of an introduction and summary, and five research papers. The introduction and summary provides the background in accretion disk physics and magnetohydrodynamics. The research papers describe numerical studies of magnetohydrodynamical processes in accretion disks. Paper 1 is a one-dimensional study of the effect of magnetic buoyancy on a flux tube in an accretion disk. The stabilizing influence of an accretion disk corona on the flux tube is demonstrated. Paper 2-4 present numerical simulations of mean-field dynamos in accretion disks. Paper 11 verifies the correctness of the numerical code by comparing linear models to previous work by other groups. The results are also extended to somewhat modified disk models. A transition from an oscillatory mode of negative parity for thick disks to a steady mode of even parity for thin disks is found. Preliminary results for nonlinear dynamos at very high dynamo numbers are also presented. Paper 3 describes the bifurcation behaviour of the nonlinear dynamos. For positive dynamo numbers it is found that the initial steady solution is replaced by an oscillatory solution of odd parity. For negative dynamo numbers the solution becomes chaotic at sufficiently high dynamo numbers. Paper 4 continues the studies of nonlinear dynamos, and it is demonstrated that a chaotic solution appears even for positive dynamo numbers, but that it returns to a steady solution of mixed parity at very high dynamo numbers. Paper 5 describes a first attempt at simulating the small-scale turbulence of an accretion disk in three dimensions. There is only find cases of decaying turbulence, but this is rather due to limitations of the simulations than that turbulence is really absent in accretion disks

Preparation of thin actinide metal disks using a multiple disk casting technique

International Nuclear Information System (INIS)

Conner, W.V.

1975-01-01

A casting technique has been developed for preparing multiple actinide metal disks which have a minimum thickness of 0.006 inch. This technique was based on an injection casting procedure which utilizes the weight of a tantalum metal rod to force the molten metal into the mold cavity. Using the proper mold design and casting parameters, it has been possible to prepare ten 1/2 inch diameter neptunium or plutonium metal disks in a single casting, This casting technique is capable of producing disks which are very uniform. The average thickness of the disks from a typical casting will vary no more than 0.001 inch and the variation in the thickness of the individual disks will range from 0.0001 to 0.0005 inch. (Auth.)

Preparation of thin actinide metal disks using a multiple disk casting technique

International Nuclear Information System (INIS)

Conner, W.V.

1976-01-01

A casting technique has been developed for preparing multiple actinide metal disks which have a minimum thickness of 0.006 inch. This technique was based on an injection casting procedure which utilizes the weight of a tantalum metal rod to force the molten metal into the mold cavity. Using the proper mold design and casting parameters, it has been possible to prepare ten 1/2 inch diameter neptunium or plutonium metal disks in a single casting. This casting technique is capable of producing disks which are very uniform. The average thickness of the disks from a typical casting will vary no more than 0.001 inch and the variation in the thickness of the individual disks will range from 0.0001 to 0.0005 inch. (author)

ON THE TRANSITIONAL DISK CLASS: LINKING OBSERVATIONS OF T TAURI STARS AND PHYSICAL DISK MODELS

International Nuclear Information System (INIS)

Espaillat, C.; Andrews, S.; Qi, C.; Wilner, D.; Ingleby, L.; Calvet, N.; Hernández, J.; Furlan, E.; D'Alessio, P.; Muzerolle, J.

2012-01-01

Two decades ago 'transitional disks' (TDs) described spectral energy distributions (SEDs) of T Tauri stars with small near-IR excesses, but significant mid- and far-IR excesses. Many inferred this indicated dust-free holes in disks possibly cleared by planets. Recently, this term has been applied disparately to objects whose Spitzer SEDs diverge from the expectations for a typical full disk (FD). Here, we use irradiated accretion disk models to fit the SEDs of 15 such disks in NGC 2068 and IC 348. One group has a 'dip' in infrared emission while the others' continuum emission decreases steadily at all wavelengths. We find that the former have an inner disk hole or gap at intermediate radii in the disk and we call these objects 'transitional disks' and 'pre-transitional disks' (PTDs), respectively. For the latter group, we can fit these SEDs with FD models and find that millimeter data are necessary to break the degeneracy between dust settling and disk mass. We suggest that the term 'transitional' only be applied to objects that display evidence for a radical change in the disk's radial structure. Using this definition, we find that TDs and PTDs tend to have lower mass accretion rates than FDs and that TDs have lower accretion rates than PTDs. These reduced accretion rates onto the star could be linked to forming planets. Future observations of TDs and PTDs will allow us to better quantify the signatures of planet formation in young disks.

Molecular Gas Clumps from the Destruction of Icy Bodies in the beta Pictoris Debris Disk

Science.gov (United States)

Dent, W. R. F.; Wyatt, M. C.; Roberge, A.; Augereau, J. -C.; Casassus, S.; Corder, S.; Greaves, J. S.; DeGregorio-Monsalvo, I.; Hales, A.; Jackson, A. P.;

Relativistic static thin dust disks with an inner edge: An infinite family of new exact solutions

International Nuclear Information System (INIS)

Gonzalez, Guillermo A.; Gutierrez-Pineres, Antonio C.; Vina-Cervantes, Viviana M.

2009-01-01

An infinite family of new exact solutions of the vacuum Einstein equations is presented. The solutions are static and axially symmetric and correspond to an infinite family of thin dust disks with a central inner edge. The metric functions of all the solutions can be explicitly computed, and can be expressed in a simple manner in terms of oblate spheroidal coordinates. The energy density of all the disks of the family is positive everywhere and well behaved, so that the corresponding energy-momentum tensor is in full agreement with all the energy conditions. Moreover, although the total mass of the disks is infinite, the solutions are asymptotically flat and the Riemann tensor is regular everywhere, as it is shown by computing the curvature scalars. Now, besides its importance as a new family of exact solutions of the vacuum Einstein equations, the main importance of this family of solutions is that it can be easily superposed with the Schwarzschild solution in order to describe thin disks surrounding a central black hole. Accordingly, a detailed analysis of this superposition will be presented in a subsequent paper.

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

Energy Technology Data Exchange (ETDEWEB)

Kim, K. H. [Korea Astronomy and Space Science Institute (KASI), 776, Daedeokdae-ro, Yuseong-gu, Daejeon 305-348 (Korea, Republic of); Watson, Dan M.; Manoj, P.; Forrest, W. J. [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States); Furlan, Elise [Infrared Processing and Analysis Center, Caltech, 770 S. Wilson Avenue, Pasadena, CA 91125 (United States); Najita, Joan [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Sargent, Benjamin [Center for Imaging Science and Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology, 54 Lomb Memorial Dr., Rochester, NY 14623 (United States); Hernández, Jesús [Centro de Investigaciones de Astronomía, Apdo. Postal 264, Mérida 5101-A (Venezuela, Bolivarian Republic of); Calvet, Nuria [Department of Astronomy, University of Michigan, 830 Dennison Building, 500 Church Street, Ann Arbor, MI 48109 (United States); Adame, Lucía [Facultad de Ciencias Físico-Matemáticas, Universidad Autónoma de Nuevo León, Av. Universidad S/N, San Nicolás de los Garza, Nuevo León, C.P. 66451, México (Mexico); Espaillat, Catherine [Department of Astronomy, Boston University, 725 Commonwealth Avenue, Boston, MA 02215 (United States); Megeath, S. T. [Ritter Astrophysical Research Center, Department of Physics and Astronomy, University of Toledo, 2801 W. Bancroft St., Toledo, OH 43606 (United States); Muzerolle, James, E-mail: quarkosmos@kasi.re.kr [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); and others

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 those 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.

Properties of molecular clouds containing Herbig-Haro objects

International Nuclear Information System (INIS)

Loren, R.B.; Evans, N.J. II; Knapp, G.R.

1979-01-01

We have studied the physical conditions in the molecular clouds associated with a large number of Herbig-Haro and related objects. Formaldehyde emission at 2 mm was detected in the direction of approx.15 out of 30 objects observed. Using the 2 mm H 2 CO emission and observations of 2 cm H 2 CO absorption, along the the 2.6 mm CO line, we calculate core densities of these molecular clouds. Dense cores are found near but not necessarily coincident with the HH objects. Known embedded infrared sources are more likely to be at the position of greatest density than are the HH objects themselves. The densities determined for the cloud cores are intermediate between the densities of cold, dark clouds such as L134 N and the hot clouds associated with H II regions. Thus, a continuous spectrum of densities is observed in molecular clouds. The temperature and density of the clouds in this study are not well correlated. The cores associated with HH 29 IR and T Tau are very dense (6 x 10 4 and 9 x 10 4 cm -3 ), yet have temperatures typical of cold dark clouds.The strong inverse correlation between X (H 2 CO) and density found by Wootten et al. is also found in the clouds associated with HH objects. This correlation also holds within a single cloud, indicating that the correlation is not due to differences in cloud age and evolution toward gas-phase chemical equilibrium. The decrease of X (H 2 CO) with density is more rapid than predicted by steady state ion-molecule chemistry and may be the result of increased depletion of molecules onto grain surfaces at higher density

PLANETESIMAL DISK MICROLENSING

International Nuclear Information System (INIS)

Heng, Kevin; Keeton, Charles R.

2009-01-01

Motivated by debris disk studies, we investigate the gravitational microlensing of background starlight by a planetesimal disk around a foreground star. We use dynamical survival models to construct a plausible example of a planetesimal disk and study its microlensing properties using established ideas of microlensing by small bodies. When a solar-type source star passes behind a planetesimal disk, the microlensing light curve may exhibit short-term, low-amplitude residuals caused by planetesimals several orders of magnitude below Earth mass. The minimum planetesimal mass probed depends on the photometric sensitivity and the size of the source star, and is lower when the planetesimal lens is located closer to us. Planetesimal lenses may be found more nearby than stellar lenses because the steepness of the planetesimal mass distribution changes how the microlensing signal depends on the lens/source distance ratio. Microlensing searches for planetesimals require essentially continuous monitoring programs that are already feasible and can potentially set constraints on models of debris disks, the progeny of the supposed extrasolar analogues of Kuiper Belts.

Dusty disks around young stars

NARCIS (Netherlands)

Verhoeff, A.

2009-01-01

Stars are formed through the collapse of giant molecular clouds. During this contraction the matter spins up and naturally forms a circumstellar disk. Once accretion comes to a halt, these disks are relatively stable. Some disks are known to last up to 10 Myrs. Most disks however, dissipate on

Debris Disks: Probing Planet Formation

OpenAIRE

Wyatt, Mark C.

2018-01-01

Debris disks are the dust disks found around ~20% of nearby main sequence stars in far-IR surveys. They can be considered as descendants of protoplanetary disks or components of planetary systems, providing valuable information on circumstellar disk evolution and the outcome of planet formation. The debris disk population can be explained by the steady collisional erosion of planetesimal belts; population models constrain where (10-100au) and in what quantity (>1Mearth) planetesimals (>10km i...

Fast, Capacious Disk Memory Device

Science.gov (United States)

Muller, Ronald M.

1990-01-01

Device for recording digital data on, and playing back data from, memory disks has high recording or playback rate and utilizes available recording area more fully. Two disks, each with own reading/writing head, used to record data at same time. Head on disk A operates on one of tracks numbered from outside in; head on disk B operates on track of same number in sequence from inside out. Underlying concept of device applicable to magnetic or optical disks.

Mass distributions in disk galaxies

NARCIS (Netherlands)

Martinsson, Thomas; Verheijen, Marc; Bershady, Matthew; Westfall, Kyle; Andersen, David; Swaters, Rob

We present results on luminous and dark matter mass distributions in disk galaxies from the DiskMass Survey. As expected for normal disk galaxies, stars dominate the baryonic mass budget in the inner region of the disk; however, at about four optical scale lengths (hR ) the atomic gas starts to

A search for strong, ordered magnetic fields in Herbig Ae/Be stars

Science.gov (United States)

Wade, G. A.; Bagnulo, S.; Drouin, D.; Landstreet, J. D.; Monin, D.

2007-04-01

The origin of magnetic fields in intermediate- and high-mass stars is fundamentally a mystery. Clues towards solving this basic astrophysical problem can likely be found at the pre-main-sequence (PMS) evolutionary stage. With this work, we perform the largest and most sensitive search for magnetic fields in PMS Herbig Ae/Be (HAeBe) stars. We seek to determine whether strong, ordered magnetic fields, similar to those of main-sequence Ap/Bp stars, can be detected in these objects, and if so, to determine the intensities, geometrical characteristics, and statistical incidence of such fields. 68 observations of 50 HAeBe stars have been obtained in circularly polarized light using the FORS1 spectropolarimeter at the ESO VLT. An analysis of both Balmer and metallic lines reveals the possible presence of weak longitudinal magnetic fields in photospheric lines of two HAeBe stars, HD 101412 and BF Ori. Results for two additional stars, CPD-53 295 and HD 36112, are suggestive of the presence of magnetic fields, but no firm conclusions can be drawn based on the available data. The intensity of the longitudinal fields detected in HD 101412 and BF Ori suggest that they correspond to globally ordered magnetic fields with surface intensities of order 1 kG. On the other hand, no magnetic field is detected in 4 other HAeBe stars in our sample in which magnetic fields had previously been confirmed. Monte Carlo simulations of the longitudinal field measurements of the undetected stars allow us to place an upper limit of about 300 G on the general presence of aligned magnetic dipole magnetic fields, and of about 500 G on perpendicular dipole fields. Taking into account the results of our survey and other published results, we find that the observed bulk incidence of magnetic HAeBe stars in our sample is 8-12 per cent, in good agreement with that of magnetic main-sequence stars of similar masses. We also find that the rms longitudinal field intensity of magnetically detected HAe

WIND-ACCRETION DISKS IN WIDE BINARIES, SECOND-GENERATION PROTOPLANETARY DISKS, AND ACCRETION ONTO WHITE DWARFS

International Nuclear Information System (INIS)

Perets, Hagai B.; Kenyon, Scott J.

2013-01-01

Mass transfer from an evolved donor star to its binary companion is a standard feature of stellar evolution in binaries. In wide binaries, the companion star captures some of the mass ejected in a wind by the primary star. The captured material forms an accretion disk. Here, we study the evolution of wind-accretion disks, using a numerical approach which allows us to follow the long-term evolution. For a broad range of initial conditions, we derive the radial density and temperature profiles of the disk. In most cases, wind accretion leads to long-lived stable disks over the lifetime of the asymptotic giant branch donor star. The disks have masses of a few times 10 –5 -10 –3 M ☉ , with surface density and temperature profiles that follow broken power laws. The total mass in the disk scales approximately linearly with the viscosity parameter used. Roughly, 50%-80% of the mass falling into the disk accretes onto the central star; the rest flows out through the outer edge of the disk into the stellar wind of the primary. For systems with large accretion rates, the secondary accretes as much as 0.1 M ☉ . When the secondary is a white dwarf, accretion naturally leads to nova and supernova eruptions. For all types of secondary star, the surface density and temperature profiles of massive disks resemble structures observed in protoplanetary disks, suggesting that coordinated observational programs might improve our understanding of uncertain disk physics.

A High-mass Protobinary System with Spatially Resolved Circumstellar Accretion Disks and Circumbinary Disk

Energy Technology Data Exchange (ETDEWEB)

Kraus, S.; Kluska, J.; Kreplin, A.; Bate, M.; Harries, T. J.; Hone, E.; Anugu, A. [School of Physics, Astrophysics Group, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom); Hofmann, K.-H.; Weigelt, G. [Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany); Monnier, J. D. [Department of Astronomy, University of Michigan, 311 West Hall, 1085 South University Avenue, Ann Arbor, MI 48109 (United States); De Wit, W. J. [ESO, Alonso de Cordova 3107, Vitacura, Santiago 19 (Chile); Wittkowski, M., E-mail: skraus@astro.ex.ac.uk [ESO, Karl-Schwarzschild-Str. 2, D-85748 Garching bei München (Germany)

2017-01-20

High-mass multiples might form via fragmentation of self-gravitational disks or alternative scenarios such as disk-assisted capture. However, only a few observational constraints exist on the architecture and disk structure of high-mass protobinaries and their accretion properties. Here, we report the discovery of a close (57.9 ± 0.2 mas = 170 au) high-mass protobinary, IRAS17216-3801, where our VLTI/GRAVITY+AMBER near-infrared interferometry allows us to image the circumstellar disks around the individual components with ∼3 mas resolution. We estimate the component masses to ∼20 and ∼18 M {sub ⊙} and find that the radial intensity profiles can be reproduced with an irradiated disk model, where the inner regions are excavated of dust, likely tracing the dust sublimation region in these disks. The circumstellar disks are strongly misaligned with respect to the binary separation vector, which indicates that the tidal forces did not have time to realign the disks, pointing toward a young dynamical age of the system. We constrain the distribution of the Br γ and CO-emitting gas using VLTI/GRAVITY spectro-interferometry and VLT/CRIRES spectro-astrometry and find that the secondary is accreting at a higher rate than the primary. VLT/NACO imaging shows L ′-band emission on (3–4)× larger scales than the binary separation, matching the expected dynamical truncation radius for the circumbinary disk. The IRAS17216-3801 system is ∼3× more massive and ∼5× more compact than other high-mass multiplies imaged at infrared wavelength and the first high-mass protobinary system where circumstellar and circumbinary dust disks could be spatially resolved. This opens exciting new opportunities for studying star–disk interactions and the role of multiplicity in high-mass star formation.

Source to Accretion Disk Tilt

OpenAIRE

Montgomery, M. M.; Martin, E. L.

2010-01-01

Many different system types retrogradely precess, and retrograde precession could be from a tidal torque by the secondary on a misaligned accretion disk. However, a source to cause and maintain disk tilt is unknown. In this work, we show that accretion disks can tilt due to a force called lift. Lift results from differing gas stream supersonic speeds over and under an accretion disk. Because lift acts at the disk's center of pressure, a torque is applied around a rotation axis passing through...

Evolution of magnetic disk subsystems

Science.gov (United States)

Kaneko, Satoru

1994-06-01

The higher recording density of magnetic disk realized today has brought larger storage capacity per unit and smaller form factors. If the required access performance per MB is constant, the performance of large subsystems has to be several times better. This article describes mainly the technology for improving the performance of the magnetic disk subsystems and the prospects of their future evolution. Also considered are 'crosscall pathing' which makes the data transfer channel more effective, 'disk cache' which improves performance coupling with solid state memory technology, and 'RAID' which improves the availability and integrity of disk subsystems by organizing multiple disk drives in a subsystem. As a result, it is concluded that since the performance of the subsystem is dominated by that of the disk cache, maximation of the performance of the disk cache subsystems is very important.

STELLAR MASS DEPENDENT DISK DISPERSAL

International Nuclear Information System (INIS)

Kennedy, Grant M.; Kenyon, Scott J.

2009-01-01

We use published optical spectral and infrared (IR) excess data from nine young clusters and associations to study the stellar mass dependent dispersal of circumstellar disks. All clusters older than ∼3 Myr show a decrease in disk fraction with increasing stellar mass for solar to higher mass stars. This result is significant at about the 1σ level in each cluster. For the complete set of clusters we reject the null hypothesis-that solar and intermediate-mass stars lose their disks at the same rate-with 95%-99.9% confidence. To interpret this behavior, we investigate the impact of grain growth, binary companions, and photoevaporation on the evolution of disk signatures. Changes in grain growth timescales at fixed disk temperature may explain why early-type stars with IR excesses appear to evolve faster than their later-type counterparts. Little evidence that binary companions affect disk evolution suggests that photoevaporation is the more likely mechanism for disk dispersal. A simple photoevaporation model provides a good fit to the observed disk fractions for solar and intermediate-mass stars. Although the current mass-dependent disk dispersal signal is not strong, larger and more complete samples of clusters with ages of 3-5 Myr can improve the significance and provide better tests of theoretical models. In addition, the orbits of extra-solar planets can constrain models of disk dispersal and migration. We suggest that the signature of stellar mass dependent disk dispersal due to photoevaporation may be present in the orbits of observed extra-solar planets. Planets orbiting hosts more massive than ∼1.6 M sun may have larger orbits because the disks in which they formed were dispersed before they could migrate.

Manipulation of magnetic vortex parameters in disk-on-disk nanostructures with various geometry

Directory of Open Access Journals (Sweden)

Maxim E. Stebliy

2015-03-01

Full Text Available Magnetic nanostructures in the form of a sandwich consisting of two permalloy (Py disks with diameters of 600 and 200 nm separated by a nonmagnetic interlayer are studied. Magnetization reversal of the disk-on-disk nanostructures depends on the distance between centers of the small and big disks and on orientation of an external magnetic field applied during measurements. It is found that manipulation of the magnetic vortex chirality and the trajectory of the vortex core in the big disk is only possible in asymmetric nanostructures. Experimentally studied peculiarities of a motion path of the vortex core and vortex parameters by the magneto-optical Kerr effect (MOKE magnetometer are supported by the magnetic force microscopy imaging and micromagnetic simulations.

Global Simulations of the Inner Regions of Protoplanetary Disks with Comprehensive Disk Microphysics

Energy Technology Data Exchange (ETDEWEB)

Bai, Xue-Ning, E-mail: xbai@cfa.harvard.edu [Institute for Theory and Computation, Harvard-Smithsonian Center for Astrophysics, 60 Garden St., MS-51, Cambridge, MA 02138 (United States)

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 magnetic 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.

Global Simulations of the Inner Regions of Protoplanetary Disks with Comprehensive Disk Microphysics

Science.gov (United States)

Bai, Xue-Ning

2017-08-01

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 magnetic 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.

Buoyancy limits on magnetic viscosity stress-law scalings in quasi stellar object accretion disk models

International Nuclear Information System (INIS)

Sakimoto, P.J.

1985-01-01

Quasi-Stellar Objects (QSOs) are apparently the excessively bright nuclei of distant galaxies. They are thought to be powered by accretion disks surrounding supermassive black holes: however, proof of this presumption is hampered by major uncertainties in the viscous stress necessary for accretion to occur. Models generally assume an and hoc stress law which scales the stress with the total pressure. Near the black hole, radiation pressure dominates gas pressure; scaling the stress with the radiation pressure results in disk models that are thermally unstable and optically thin. This dissertation shows that a radiation pressure scaling for the stress is not possible if the viscosity is due to turbulent magnetic Maxwell stresses. The argument is one of internal self-consistency. First, four model accretion disks that bound the reasonably expected ranges of viscous stress scalings and vertical structures are constructed. Magnetic flux tubes of various initial field strengths are then placed within these models, nd their buoyancy is modeled numerically. In disks using the radiation pressure stress law scaling, low opacities allow rapid heat flow into the flux tubes: the tubes are extremely buoyant, and magnetic fields strong enough to provide the required stress cannot be retained. If an alternative gas pressure scaling for the stress is assumed, then the disks are optically thick; flux tubes have corresponding lower buoyancy, and magnetic fields strong enough to provide the stress can be retained for dynamically significant time periods

VLA Observations of the Disk around the Young Brown Dwarf 2MASS J044427+2512

Energy Technology Data Exchange (ETDEWEB)

Ricci, L. [Department of Physics and Astronomy, Rice University, 6100 Main Street, Houston, TX 77005 (United States); Rome, H. [The Kinkaid School, 201 Kinkaid School Drive, Houston, TX 77024 (United States); Pinilla, P. [Department of Astronomy Steward Observatory, The University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Facchini, S. [Max-Planck-Institut fur Extraterrestrische Physik, Giessenbachstrasse 1, D-85748 Garching (Germany); Birnstiel, T. [University Observatory, Faculty of Physics, Ludwig-Maximilians-Universität München, Scheinerstr. 1, D-81679 Munich (Germany); Testi, L., E-mail: luca.ricci@rice.edu [European Southern Observatory (ESO) Headquarters, Karl-Schwarzschild-Str. 2, D-85748 Garching (Germany)

2017-09-01

We present multi-wavelength radio observations obtained with the VLA of the protoplanetary disk surrounding the young brown dwarf 2MASS J04442713+2512164 (2M0444) in the Taurus star-forming region. 2M0444 is the brightest known brown dwarf disk at millimeter wavelengths, making this an ideal target to probe radio emission from a young brown dwarf. Thermal emission from dust in the disk is detected at 6.8 and 9.1 mm, whereas the 1.36 cm measured flux is dominated by ionized gas emission. We combine these data with previous observations at shorter sub-mm and mm wavelengths to test the predictions of dust evolution models in gas-rich disks after adapting their parameters to the case of 2M0444. These models show that the radial drift mechanism affecting solids in a gaseous environment has to be either completely made inefficient, or significantly slowed down by very strong gas pressure bumps in order to explain the presence of mm/cm-sized grains in the outer regions of the 2M0444 disk. We also discuss the possible mechanisms for the origin of the ionized gas emission detected at 1.36 cm. The inferred radio luminosity for this emission is in line with the relation between radio and bolometric luminosity valid for for more massive and luminous young stellar objects, and extrapolated down to the very low luminosity of the 2M0444 brown dwarf.

EVOLUTION OF WARPED ACCRETION DISKS IN ACTIVE GALACTIC NUCLEI. I. ROLES OF FEEDING AT THE OUTER BOUNDARIES

International Nuclear Information System (INIS)

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

2013-01-01

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 10 6 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 10 6 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.

WIND-ACCRETION DISKS IN WIDE BINARIES, SECOND-GENERATION PROTOPLANETARY DISKS, AND ACCRETION ONTO WHITE DWARFS

Energy Technology Data Exchange (ETDEWEB)

Perets, Hagai B. [Technion-Israel Institute of Technology, Haifa (Israel); Kenyon, Scott J., E-mail: hperets@physics.technion.ac.il [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

2013-02-20

Mass transfer from an evolved donor star to its binary companion is a standard feature of stellar evolution in binaries. In wide binaries, the companion star captures some of the mass ejected in a wind by the primary star. The captured material forms an accretion disk. Here, we study the evolution of wind-accretion disks, using a numerical approach which allows us to follow the long-term evolution. For a broad range of initial conditions, we derive the radial density and temperature profiles of the disk. In most cases, wind accretion leads to long-lived stable disks over the lifetime of the asymptotic giant branch donor star. The disks have masses of a few times 10{sup -5}-10{sup -3} M {sub Sun }, with surface density and temperature profiles that follow broken power laws. The total mass in the disk scales approximately linearly with the viscosity parameter used. Roughly, 50%-80% of the mass falling into the disk accretes onto the central star; the rest flows out through the outer edge of the disk into the stellar wind of the primary. For systems with large accretion rates, the secondary accretes as much as 0.1 M {sub Sun }. When the secondary is a white dwarf, accretion naturally leads to nova and supernova eruptions. For all types of secondary star, the surface density and temperature profiles of massive disks resemble structures observed in protoplanetary disks, suggesting that coordinated observational programs might improve our understanding of uncertain disk physics.

Vibration of imperfect rotating disk

Directory of Open Access Journals (Sweden)

Půst L.

2011-12-01

Full Text Available This study is concerned with the theoretical and numerical calculations of the flexural vibrations of a bladed disk. The main focus of this study is to elaborate the basic background for diagnostic and identification methods for ascertaining the main properties of the real structure or an experimental model of turbine disks. The reduction of undesirable vibrations of blades is proposed by using damping heads, which on the experimental model of turbine disk are applied only on a limited number of blades. This partial setting of damping heads introduces imperfection in mass, stiffness and damping distribution on the periphery and leads to more complicated dynamic properties than those of a perfect disk. Calculation of FEM model and analytic—numerical solution of disk behaviour in the limited (two modes frequency range shows the splitting of resonance with an increasing speed of disk rotation. The spectrum of resonance is twice denser than that of a perfect disk.

RINGED ACCRETION DISKS: EQUILIBRIUM CONFIGURATIONS

Energy Technology Data Exchange (ETDEWEB)

Pugliese, D.; Stuchlík, Z., E-mail: d.pugliese.physics@gmail.com, E-mail: zdenek.stuchlik@physics.cz [Institute of Physics and Research Centre of Theoretical Physics and Astrophysics, Faculty of Philosophy and Science, Silesian University in Opava, Bezručovo náměstí 13, CZ-74601 Opava (Czech Republic)

2015-12-15

We investigate a model of a ringed accretion disk, made up by several rings rotating around a supermassive Kerr black hole attractor. Each toroid of the ringed disk is governed by the general relativity hydrodynamic Boyer condition of equilibrium configurations of rotating perfect fluids. Properties of the tori can then be determined by an appropriately defined effective potential reflecting the background Kerr geometry and the centrifugal effects. The ringed disks could be created in various regimes during the evolution of matter configurations around supermassive black holes. Therefore, both corotating and counterrotating rings have to be considered as being a constituent of the ringed disk. We provide constraints on the model parameters for the existence and stability of various ringed configurations and discuss occurrence of accretion onto the Kerr black hole and possible launching of jets from the ringed disk. We demonstrate that various ringed disks can be characterized by a maximum number of rings. We present also a perturbation analysis based on evolution of the oscillating components of the ringed disk. The dynamics of the unstable phases of the ringed disk evolution seems to be promising in relation to high-energy phenomena demonstrated in active galactic nuclei.

HERSCHEL OBSERVATIONS OF THE T CHA TRANSITION DISK: CONSTRAINING THE OUTER DISK PROPERTIES

International Nuclear Information System (INIS)

Cieza, Lucas A.; Olofsson, Johan; Henning, Thomas; Harvey, Paul M.; Evans II, Neal J.; Pinte, Christophe; Augereau, Jean-Charles; Ménard, Francois; Merín, Bruno; Najita, Joan

2011-01-01

T Cha is a nearby (d ∼ 100 pc) transition disk known to have an optically thin gap separating optically thick inner and outer disk components. Huélamo et al. recently reported the presence of a low-mass object candidate within the gap of the T Cha disk, giving credence to the suspected planetary origin of this gap. Here we present the Herschel photometry (70, 160, 250, 350, and 500 μm) of T Cha from the 'Dust, Ice, and Gas in Time' Key Program, which bridges the wavelength range between existing Spitzer and millimeter data and provide important constraints on the outer disk properties of this extraordinary system. We model the entire optical to millimeter wavelength spectral energy distribution (SED) of T Cha (19 data points between 0.36 and 3300 μm without any major gaps in wavelength coverage). T Cha shows a steep spectral slope in the far-IR, which we find clearly favors models with outer disks containing little or no dust beyond ∼40 AU. The full SED can be modeled equally well with either an outer disk that is very compact (only a few AU wide) or a much larger one that has a very steep surface density profile. That is, T Cha's outer disk seems to be either very small or very tenuous. Both scenarios suggest a highly unusual outer disk and have important but different implications for the nature of T Cha. Spatially resolved images are needed to distinguish between the two scenarios.

HERSCHEL OBSERVATIONS OF THE T CHA TRANSITION DISK: CONSTRAINING THE OUTER DISK PROPERTIES

Energy Technology Data Exchange (ETDEWEB)

Cieza, Lucas A. [Institute for Astronomy, University of Hawaii at Manoa, Honolulu, HI 96822 (United States); Olofsson, Johan; Henning, Thomas [Max Planck Institut fuer Astronomie, Koenigstuhl 17, 69117 Heidelberg (Germany); Harvey, Paul M.; Evans II, Neal J. [Department of Astronomy, University of Texas at Austin, Austin, TX 78712 (United States); Pinte, Christophe; Augereau, Jean-Charles; Menard, Francois [UJF-Grenoble 1/CNRS-INSU, Institut de Planetologie et d' Astrophysique de Grenoble (IPAG) UMR 5274, Grenoble, F-38041 (France); Merin, Bruno [Herschel Science Centre, European Space Agency (ESAC), P.O. Box 78, 28691 Villanueva de la Canada, Madrid (Spain); Najita, Joan, E-mail: lcieza@ifa.hawaii.edu [National Optical Astronomy Observatory, 950 N. Cherry Avenue, Tucson, AZ 86719 (United States)

2011-11-10

T Cha is a nearby (d {approx} 100 pc) transition disk known to have an optically thin gap separating optically thick inner and outer disk components. Huelamo et al. recently reported the presence of a low-mass object candidate within the gap of the T Cha disk, giving credence to the suspected planetary origin of this gap. Here we present the Herschel photometry (70, 160, 250, 350, and 500 {mu}m) of T Cha from the 'Dust, Ice, and Gas in Time' Key Program, which bridges the wavelength range between existing Spitzer and millimeter data and provide important constraints on the outer disk properties of this extraordinary system. We model the entire optical to millimeter wavelength spectral energy distribution (SED) of T Cha (19 data points between 0.36 and 3300 {mu}m without any major gaps in wavelength coverage). T Cha shows a steep spectral slope in the far-IR, which we find clearly favors models with outer disks containing little or no dust beyond {approx}40 AU. The full SED can be modeled equally well with either an outer disk that is very compact (only a few AU wide) or a much larger one that has a very steep surface density profile. That is, T Cha's outer disk seems to be either very small or very tenuous. Both scenarios suggest a highly unusual outer disk and have important but different implications for the nature of T Cha. Spatially resolved images are needed to distinguish between the two scenarios.

Near-infrared H2 emission from Herbig-Haro objects. I. A survey of low excitation objects

International Nuclear Information System (INIS)

Schwartz, R.D.; Cohen, M.; Williams, P.M.

1987-01-01

A survey for H 2 1-0 S(1) emission in 16 Herbig-Haro (HH) objects and three exciting stars for HH objects is reported. Eleven HH objects which show low-excitation optical spectra exhibit H 2 emission. One object (HH 43) is more than twice as bright as any previously reported HH object. In addition, spectra in the range 1.6-2.55 microns are reported for HH 43 and HH 120, and a 2.0-2.55 micron spectrum is presented for HH 26. The spectra yield estimates of the H 2 density and temperature ranges in these objects. The role of ultraviolet H 2 emission-line fluorescence in HH 43 with respect to cascading among excited vibrational states of the ground electronic state is discussed. Models which may account for the combined ultraviolet, optical, and near-IR spectra of HHs are briefly analyzed. 35 references

Audit: Automated Disk Investigation Toolkit

Directory of Open Access Journals (Sweden)

Umit Karabiyik

2014-09-01

Full Text Available Software tools designed for disk analysis play a critical role today in forensics investigations. However, these digital forensics tools are often difficult to use, usually task specific, and generally require professionally trained users with IT backgrounds. The relevant tools are also often open source requiring additional technical knowledge and proper configuration. This makes it difficult for investigators without some computer science background to easily conduct the needed disk analysis. In this paper, we present AUDIT, a novel automated disk investigation toolkit that supports investigations conducted by non-expert (in IT and disk technology and expert investigators. Our proof of concept design and implementation of AUDIT intelligently integrates open source tools and guides non-IT professionals while requiring minimal technical knowledge about the disk structures and file systems of the target disk image.

A high-resolution spectropolarimetric survey of Herbig Ae/Be stars - II. Rotation

Science.gov (United States)

Alecian, E.; Wade, G. A.; Catala, C.; Grunhut, J. H.; Landstreet, J. D.; Böhm, T.; Folsom, C. P.; Marsden, S.

2013-02-01

We report the analysis of the rotational properties of our sample of Herbig Ae/Be (HAeBe) and related stars for which we have obtained high-resolution spectropolarimetric observations. Using the projected rotational velocities measured at the surface of the stars, we have calculated the angular momentum of the sample and plotted it as a function of age. We have then compared the angular momentum and the v sin i distributions of the magnetic to the non-magnetic HAeBe stars. Finally, we have predicted v sin i of the non-magnetic, non-binary (`normal') stars in our sample when they reach the zero-age main sequence (ZAMS), and compared them to various catalogues of v sin i of main-sequence stars. First, we observe that magnetic HAeBe stars are much slower rotators than normal stars, indicating that they have been more efficiently braked than the normal stars. In fact, the magnetic stars have already lost most of their angular momentum, despite their young ages (lower than 1 Myr for some of them). Secondly, our analysis suggests that the low-mass (1.5 5 M⊙) are losing angular momentum. We propose that winds, which are expected to be stronger in massive stars, are at the origin of this phenomenon.

YottaYotta announces new world record set for TCP disk-to-disk bulk transfer

CERN Document Server

2002-01-01

The Yottabyte NetStorage(TM) Company, today announced a new world record for TCP disk-to-disk data transfer using the company's NetStorager(R) System. The record-breaking demonstration transferred 5 terabytes of data between Chicago, Il. to Vancouver, BC and Ottawa, ON, at a sustained average throughput of 11.1 gigabits per second. Peak throughput exceeded 11.6 gigabits per second, more than 15-times faster than previous records for TCP transfer from disk-to-disk (1 page).

IMAGING OF A TRANSITIONAL DISK GAP IN REFLECTED LIGHT: INDICATIONS OF PLANET FORMATION AROUND THE YOUNG SOLAR ANALOG LkCa 15

International Nuclear Information System (INIS)

Thalmann, C.; Goto, M.; Henning, T.; Carson, J.; Brandner, W.; Feldt, M.; Grady, C. A.; Wisniewski, J. P.; Janson, M.; Fukagawa, M.; Honda, M.; Mulders, G. D.; Min, M.; Moro-MartIn, A.; McElwain, M. W.; Hodapp, K. W.; Abe, L.; Egner, S.; Golota, T.; Fukue, T.

2010-01-01

We present H- and K s -band imaging data resolving the gap in the transitional disk around LkCa 15, revealing the surrounding nebulosity. We detect sharp elliptical contours delimiting the nebulosity on the inside as well as the outside, consistent with the shape, size, ellipticity, and orientation of starlight reflected from the far-side disk wall, whereas the near-side wall is shielded from view by the disk's optically thick bulk. We note that forward scattering of starlight on the near-side disk surface could provide an alternate interpretation of the nebulosity. In either case, this discovery provides confirmation of the disk geometry that has been proposed to explain the spectral energy distributions of such systems, comprising an optically thick disk with an inner truncation radius of ∼46 AU enclosing a largely evacuated gap. Our data show an offset of the nebulosity contours along the major axis, likely corresponding to a physical pericenter offset of the disk gap. This reinforces the leading theory that dynamical clearing by at least one orbiting body is the cause of the gap. Based on evolutionary models, our high-contrast imagery imposes an upper limit of 21 M Jup on companions at separations outside of 0.''1 and of 13 M Jup outside of 0.''2. Thus, we find that a planetary system around LkCa 15 is the most likely explanation for the disk architecture.

Disk-to-Disk network transfers at 100 Gb/s

Science.gov (United States)

Barczyk, Artur; Gable, Ian; Hay, Marilyn; Leavett-Brown, Colin; Legrand, Iosif; Lewall, Kim; McKee, Shawn; McWilliam, Donald; Mughal, Azher; Newman, Harvey; Rozsa, Sandor; Savard, Yvan; Sobie, Randall J.; Tam, Thomas; Voicu, Ramiro

2012-12-01

A 100 Gbps network was established between the California Institute of Technology conference booth at the Super Computing 2011 conference in Seattle, Washington and the computing center at the University of Victoria in Canada. A circuit was established over the BCNET, CANARIE and Super Computing (SCInet) networks using dedicated equipment. The small set of servers at the endpoints used a combination of 10GE and 40GE technologies, and SSD drives for data storage. The configuration of the network and the server configuration are discussed. We will show that the system was able to achieve disk-to-disk transfer rates of 60 Gbps and memory-to-memory rates in excess of 180 Gbps across the WAN. We will discuss the transfer tools, disk configurations, and monitoring tools used in the demonstration.

Disk-to-Disk network transfers at 100 Gb/s

International Nuclear Information System (INIS)

Barczyk, Artur; Legrand, Iosif; Mughal, Azher; Newman, Harvey; Rozsa, Sandor; Voicu, Ramiro; Gable, Ian; Leavett-Brown, Colin; Lewall, Kim; Savard, Yvan; Sobie, Randall J; Hay, Marilyn; McWilliam, Donald; McKee, Shawn; Tam, Thomas

2012-01-01

A 100 Gbps network was established between the California Institute of Technology conference booth at the Super Computing 2011 conference in Seattle, Washington and the computing center at the University of Victoria in Canada. A circuit was established over the BCNET, CANARIE and Super Computing (SCInet) networks using dedicated equipment. The small set of servers at the endpoints used a combination of 10GE and 40GE technologies, and SSD drives for data storage. The configuration of the network and the server configuration are discussed. We will show that the system was able to achieve disk-to-disk transfer rates of 60 Gbps and memory-to-memory rates in excess of 180 Gbps across the WAN. We will discuss the transfer tools, disk configurations, and monitoring tools used in the demonstration.

MODELING DUST EMISSION OF HL TAU DISK BASED ON PLANET–DISK INTERACTIONS

International Nuclear Information System (INIS)

Jin, Sheng; Ji, Jianghui; Li, Shengtai; Li, Hui; Isella, Andrea

2016-01-01

We use extensive global two-dimensional hydrodynamic disk gas+dust simulations with embedded planets, coupled with three-dimensional radiative transfer calculations, to model the dust ring and gap structures in the HL Tau protoplanetary disk observed with the Atacama Large Millimeter/Submillimeter Array (ALMA). We include the self-gravity of disk gas and dust components and make reasonable choices of disk parameters, assuming an already settled dust distribution and no planet migration. We can obtain quite adequate fits to the observed dust emission using three planets with masses of 0.35, 0.17, and 0.26 M Jup at 13.1, 33.0, and 68.6 AU, respectively. Implications for the planet formation as well as the limitations of this scenario are discussed

Fast disk array for image storage

Science.gov (United States)

Feng, Dan; Zhu, Zhichun; Jin, Hai; Zhang, Jiangling

1997-01-01

A fast disk array is designed for the large continuous image storage. It includes a high speed data architecture and the technology of data striping and organization on the disk array. The high speed data path which is constructed by two dual port RAM and some control circuit is configured to transfer data between a host system and a plurality of disk drives. The bandwidth can be more than 100 MB/s if the data path based on PCI (peripheral component interconnect). The organization of data stored on the disk array is similar to RAID 4. Data are striped on a plurality of disk, and each striping unit is equal to a track. I/O instructions are performed in parallel on the disk drives. An independent disk is used to store the parity information in the fast disk array architecture. By placing the parity generation circuit directly on the SCSI (or SCSI 2) bus, the parity information can be generated on the fly. It will affect little on the data writing in parallel on the other disks. The fast disk array architecture designed in the paper can meet the demands of the image storage.

Debris Disks in Aggregate: Using Hubble Space Telescope Coronagraphic Imagery to Understand the Scattered-Light Disk Detection Rate

Science.gov (United States)

Grady, Carol A.

2011-01-01

Despite more than a decade of coronagraphic imaging of debris disk candidate stars, only 16 have been imaged in scattered light. Since imaged disks provide our best insight into processes which sculpt disks, and can provide signposts of the presence of giant planets at distances which would elude radial velocity and transit surveys, we need to understand under what conditions we detect the disks in scattered light, how these disks differ from the majority of debris disks, and how to increase the yield of disks which are imaged with 0.1" angular resolution. In this talk, I will review what we have learned from a shallow HSTINICMOS NIR survey of debris disks, and present first results from our on-going HST /STIS optical imaging of bright scattered-light disks.

Disks around Failed Stars - a Question of Age

Science.gov (United States)

2002-08-01

First Ground-Based Mid-Infrared Observations of Brown Dwarfs [1] Summary A team of European astronomers [2] have observed eight Brown Dwarfs, i.e., small and faint objects also known as "failed stars", with the TIMMI2 infrared sensitive instrument at the ESO 3.6-m telescope on La Silla. From two of these, mid-infrared radiation is detected - for the first time ever from such objects with a ground-based telescope . While the younger Brown Dwarf, aged a few million years, is found to be surrounded by a dusty disk, no warm dust is present around the older ones. The new observations support the following formation hypothesis for Brown Dwarfs: they are born in the same way as "real" stars, by contraction in interstellar clouds of gas and dust . During the later stages of this process, the infalling material is transferred onto the star via a gas and dust disk . This disk - in which planets may possibly form - then disperses with time. PR Photo 17a/02 : Image of Brown Dwarf LP 944-20 PR Photo 17b/02 : Models of the disk around Brown Dwarf Cha HA 2 Brown Dwarfs are faint and cool objects Astronomical objects known as "Brown Dwarfs" are "failed stars" . Their comparatively small mass, less than about 7% of that of our Sun (or about 75 times the mass of planet Jupiter), is too small to achieve sufficiently high pressure and temperature at their centre to ignite energy-producing nuclear processes. Some astronomers also refer to Brown Dwarfs as a "missing link" between planets and stars, being neither one nor the other, yet with similarities to both. They do not burn hydrogen to helium as "real" stars do, but continue to emit faint light as they slowly contract and cool during millions of years. They end their inglorious life with a whimper and finally fade into eternal insignificance. Although Brown Dwarfs were theoretically predicted already in 1963, astronomers had to wait until 1995 for the first one to be discovered. This was mainly due to their extreme faintness as

The dynamics of Herbig-Haro objects HH46 and 47A and their remarkable connecting filament HH47B

International Nuclear Information System (INIS)

Meaburn, J.; Dyson, J.E.

1987-01-01

Echelle observations of the Hα and [S II] line profiles have been made with the Anglo-Australian Telescope along the emission-line filament (HH47B) which connects the Herbig-Haro objects HH46 and 47A. A red continuum source between HH46 and the 10μm peak has a +-200kms -1 wide Hα component centred on the rest velocity of the parent globule. Scattered radiation from an embedded T Tauri star is suggested. HH46 and 47A are receding away from the observer but the connecting filament exhibits some form of velocity ellipse. The bipolar configuration had been previously suggested by the discovery of the counter object HH47C with Vsub(HEL) = 100kms -1 . (author)

MOLECULAR GAS IN YOUNG DEBRIS DISKS

International Nuclear Information System (INIS)

Moor, A.; Abraham, P.; Kiss, Cs.; Juhasz, A.; Kospal, A.; Pascucci, I.; Apai, D.; Henning, Th.; Csengeri, T.; Grady, C.

2011-01-01

Gas-rich primordial disks and tenuous gas-poor debris disks are usually considered as two distinct evolutionary phases of the circumstellar matter. Interestingly, the debris disk around the young main-sequence star 49 Ceti possesses a substantial amount of molecular gas and possibly represents the missing link between the two phases. Motivated to understand the evolution of the gas component in circumstellar disks via finding more 49 Ceti-like systems, we carried out a CO J = 3-2 survey with the Atacama Pathfinder EXperiment, targeting 20 infrared-luminous debris disks. These systems fill the gap between primordial and old tenuous debris disks in terms of fractional luminosity. Here we report on the discovery of a second 49 Ceti-like disk around the 30 Myr old A3-type star HD21997, a member of the Columba Association. This system was also detected in the CO(2-1) transition, and the reliable age determination makes it an even clearer example of an old gas-bearing disk than 49 Ceti. While the fractional luminosities of HD21997 and 49 Ceti are not particularly high, these objects seem to harbor the most extended disks within our sample. The double-peaked profiles of HD21997 were reproduced by a Keplerian disk model combined with the LIME radiative transfer code. Based on their similarities, 49 Ceti and HD21997 may be the first representatives of a so far undefined new class of relatively old (∼>8 Myr), gaseous dust disks. From our results, neither primordial origin nor steady secondary production from icy planetesimals can unequivocally explain the presence of CO gas in the disk of HD21997.

Deformation and Life Analysis of Composite Flywheel Disk and Multi-disk Systems

Science.gov (United States)

Arnold, S. M.; Saleeb, A. F.; AlZoubi, N. R.

2001-01-01

In this study an attempt is made to put into perspective the problem of a rotating disk, be it a single disk or a number of concentric disks forming a unit. An analytical model capable of performing an elastic stress analysis for single/multiple, annular/solid, anisotropic/isotropic disk systems, subjected to both pressure surface tractions, body forces (in the form of temperature-changes and rotation fields) and interfacial misfits is derived and discussed. Results of an extensive parametric study are presented to clearly define the key design variables and their associated influence. In general the important parameters were identified as misfit, mean radius, thickness, material property and/or load gradation, and speed; all of which must be simultaneously optimized to achieve the "best" and most reliable design. Also, the important issue of defining proper performance/merit indices (based on the specific stored energy), in the presence of multiaxiality and material anisotropy is addressed. These merit indices are then utilized to discuss the difference between flywheels made from PMC and TMC materials with either an annular or solid geometry. Finally two major aspects of failure analysis, that is the static and cyclic limit (burst) speeds are addressed. In the case of static limit loads, upper, lower, and out-of-plane bounds for disks with constant thickness are presented for both the case of internal pressure loading (as one would see in a hydroburst test) and pure rotation (as in the case of a free spinning disk). The results (interaction diagrams) are displayed graphically in designer friendly format. For the case of fatigue, a representative fatigue/life master curve is illustrated in which the normalized limit speed versus number of applied cycles is given for a cladded TMC disk application.

Results of a Long-Term Spectral and Photometric Monitoring of the Herbig Ae Star HD 179218

Science.gov (United States)

Kozlova, O. V.; Alekseev, I. Yu.

2017-06-01

We present the results of the long-term spectroscopic and photometric monitoring of the Herbig Ae star HD 179218. The high-resolution spectra (R = 20000) were made on the 2.6-m telescope at the Crimean Astrophysical Observatory (CrAO) in the regions of Hα emission line. The photometric observations were obtained on 1.25-m telescope AZT-11 (CrAO) equipped with the UBVRI electrophotometer-polarimeter. Our results showed that Hα emission parameters demonstrate the long- term variability on the time scale about 4000 days. The same variability is observed in the change of the stellar brightness in V-band. The unusual behavior the V-I color index depending on the stellar brightness in the V-band can be concluded that around the star there is an additional source of IR-radiation. We believe that the obtained results can be explained by the presence in the vicinity of HD 179218 a low-mass component.

FOMALHAUT'S DEBRIS DISK AND PLANET: CONSTRAINING THE MASS OF FOMALHAUT B FROM DISK MORPHOLOGY

International Nuclear Information System (INIS)

Chiang, E.; Kalas, P.; Graham, J. R.; Kite, E.; Clampin, M.

2009-01-01

Following the optical imaging of exoplanet candidate Fomalhaut b (Fom b), we present a numerical model of how Fomalhaut's debris disk is gravitationally shaped by a single interior planet. The model is simple, adaptable to other debris disks, and can be extended to accommodate multiple planets. If Fom b is the dominant perturber of the belt, then to produce the observed disk morphology it must have a mass M pl J , an orbital semimajor axis a pl > 101.5 AU, and an orbital eccentricity e pl = 0.11-0.13. These conclusions are independent of Fom b's photometry. To not disrupt the disk, a greater mass for Fom b demands a smaller orbit farther removed from the disk; thus, future astrometric measurement of Fom b's orbit, combined with our model of planet-disk interaction, can be used to determine the mass more precisely. The inner edge of the debris disk at a ∼ 133 AU lies at the periphery of Fom b's chaotic zone, and the mean disk eccentricity of e ∼ 0.11 is secularly forced by the planet, supporting predictions made prior to the discovery of Fom b. However, previous mass constraints based on disk morphology rely on several oversimplifications. We explain why our constraint is more reliable. It is based on a global model of the disk that is not restricted to the planet's chaotic zone boundary. Moreover, we screen disk parent bodies for dynamical stability over the system age of ∼ 100 Myr, and model them separately from their dust grain progeny; the latter's orbits are strongly affected by radiation pressure and their lifetimes are limited to ∼ 0.1 Myr by destructive grain-grain collisions. The single planet model predicts that planet and disk orbits be apsidally aligned. Fomalhaut b's nominal space velocity does not bear this out, but the astrometric uncertainties may be large. If the apsidal misalignment proves real, our calculated upper mass limit of 3M J still holds. If the orbits are aligned, our model predicts M pl = 0.5M J , a pl = 115 AU, and e pl = 0

DISCOVERY OF AN EDGE-ON DEBRIS DISK WITH A DUST RING AND AN OUTER DISK WING-TILT ASYMMETRY

International Nuclear Information System (INIS)

Kasper, Markus; Apai, Dániel; Wagner, Kevin; Robberto, Massimo

2015-01-01

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 bow 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

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

Energy Technology Data Exchange (ETDEWEB)

Mawet, Dimitri; Bottom, Michael; Matthews, Keith [Department of Astronomy, California Institute of Technology, 1200 East California Boulevard, MC 249-17, Pasadena, CA 91125 (United States); Choquet, Élodie; Serabyn, Eugene [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Absil, Olivier; Huby, Elsa; Gonzalez, Carlos A. Gomez; Wertz, Olivier; Carlomagno, Brunella; Christiaens, Valentin; Defrère, Denis; Delacroix, Christian; Habraken, Serge; Jolivet, Aissa [Space sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, 19 Allée du Six Août, B-4000 Liège (Belgium); Femenia, Bruno [W. M. Keck Observatory, 65-1120 Mamalahoa Hwy., Kamuela, HI 96743 (United States); Lebreton, Jérémy [NASA Exoplanet Science Institute, California Institute of Technology, 770 South Wilson Avenue, Pasadena, CA 91125 (United States); Forsberg, Pontus; Karlsson, Mikael [Department of Engineering Sciences, Ångström Laboratory, Uppsala University, Box 534, SE-751 21 Uppsala (Sweden); Milli, Julien, E-mail: dmawet@astro.caltech.edu [European Southern Observatory, Alonso de Cordóva 3107, Vitacura, Santiago (Chile); and others

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 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 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 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.

CIRCUMSTELLAR DEBRIS DISKS: DIAGNOSING THE UNSEEN PERTURBER

Energy Technology Data Exchange (ETDEWEB)

Nesvold, Erika R. [Department of Terrestrial Magnetism, Carnegie Institution for Science, 5241 Broad Branch Rd., Washington, DC 20015 (United States); Naoz, Smadar; Vican, Laura [Department of Physics and Astronomy, UCLA, 475 Portola Plaza, Los Angeles, CA 90095 (United States); Farr, Will M. [School of Physics and Astronomy, University of Birmingham, Birmingham, B15 2TT (United Kingdom)

2016-07-20

The first indication of the presence of a circumstellar debris disk is usually the detection of excess infrared emission from the population of small dust grains orbiting the star. This dust is short-lived, requiring continual replenishment, and indicating that the disk must be excited by an unseen perturber. Previous theoretical studies have demonstrated that an eccentric planet orbiting interior to the disk will stir the larger bodies in the belt and produce dust via interparticle collisions. However, motivated by recent observations, we explore another possible mechanism for heating a debris disk: a stellar-mass perturber orbiting exterior to and inclined to the disk and exciting the disk particles’ eccentricities and inclinations via the Kozai–Lidov mechanism. We explore the consequences of an exterior perturber on the evolution of a debris disk using secular analysis and collisional N -body simulations. We demonstrate that a Kozai–Lidov excited disk can generate a dust disk via collisions and we compare the results of the Kozai–Lidov excited disk with a simulated disk perturbed by an interior eccentric planet. Finally, we propose two observational tests of a dust disk that can distinguish whether the dust was produced by an exterior brown dwarf or stellar companion or an interior eccentric planet.

A Resolved and Asymmetric Ring of PAHs within the Young Circumstellar Disk of IRS 48

Energy Technology Data Exchange (ETDEWEB)

Schworer, Guillaume; Lacour, Sylvestre; Du Foresto, Vincent Coudé [LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universits, UPMC Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cité (France); Huélamo, Nuria [Dpto. Astrofísica, Centro de Astrobiología (INTA-CSIC), ESAC Campus, P.O. Box 78, E-28691, Villanueva de la Cañada (Spain); Pinte, Christophe; Chauvin, Gaël [Univ. Grenoble Alpes, IPAG, F-38000 Grenoble, France CNRS, IPAG, F-38000 Grenoble (France); Ehrenreich, David [Observatoire de l’Université de Genève, 51 chemin des Maillettes, 1290 Versoix (Switzerland); Girard, Julien [European Southern Observatory, Alonso de Cordova 3107, Casilla 19001 Vitacura, Santiago 19 (Chile); Tuthill, Peter [Sydney Institute for Astronomy, School of Physics, The University of Sydney, NSW 2006 (Australia)

2017-06-20

For one decade, the spectral type and age of the ρ Oph object IRS-48 were subject to debate and mystery. Modeling its disk with mid-infrared to millimeter observations led to various explanations to account for the complex intricacy of dust holes and gas-depleted regions. We present multi-epoch high-angular-resolution interferometric near-infrared data of spatially resolved emissions in the first 15 au of IRS-48, known to have very strong polycyclic aromatic hydrocarbon (PAH) emissions within this dust-depleted region. We make use of new Sparse-Aperture-Masking data to instruct a revised radiative-transfer model, where spectral energy distribution fluxes and interferometry are jointly fitted. Neutral and ionized PAH, very small grains (VSG), and classical silicates are incorporated into the model; new stellar parameters and extinction laws are explored. A bright (42 L {sub ⊙}) and hence large (2.5 R {sub ⊙}) central star with A {sub v} = 12.5 mag and R {sub v} = 6.5 requires less near-infrared excess: the inner-most disk at ≈1 au is incompatible with the interferometric data. The revised stellar parameters place this system on a 4 Myr evolutionary track, four times younger than the previous estimations, which is in better agreement with the surrounding ρ Oph region and disk-lifetime observations. The disk-structure solution converges to a classical-grain outer disk from 55 au combined with an unsettled and fully resolved VSG and PAH ring, between 11 and 26 au. We find two overluminosities in the PAH ring at color-temperatures consistent with the radiative transfer simulations; one follows a Keplerian circular orbit at 14 au. We show a depletion of a factor of ≈5 of classical dust grains up to 0.3 mm compared to very small particles: the IRS-48 disk is nearly void of dust grains in the first 55 au. A 3.5 M {sub Jup} planet on a 40 au orbit can qualitatively explain the new disk structure.

The spatial intensity distribution of selected emission lines for Herbig-Haro 1 - Comparison between theory and observations

International Nuclear Information System (INIS)

Noriega-Crespo, A.; Bohm, K.H.; Raga, A.C.

1989-01-01

In this paper, it is shown that most of the spatial intensity distribution of 11 selected emission lines for Herbig-Haro 1 (including the forbidden S II emission lines at 6731 A and 4069 A, the forbidden O III line at 5007 A, and the forbidden O II line at 3727 A) can be explained by a bow shock with a shock velocity of about 150-200 km/sec at the stagnation point, and under the assumption that the gas entering the shock is fully preionized. The results are based on three spectrograms (with a total exposure time of 180 min) obtained consecutively. Specifically, the ratios of each of the forbidden lines to H-alpha were studied, which permitted a critical test of the model. The agreement between the theoretical predictions and the observations was found to be remarkable, considering the complex geometry that a bow shock could have. 38 refs

Head-Disk Interface Technology: Challenges and Approaches

Science.gov (United States)

Liu, Bo

Magnetic hard disk drive (HDD) technology is believed to be one of the most successful examples of modern mechatronics systems. The mechanical beauty of magnetic HDD includes simple but super high accuracy positioning head, positioning technology, high speed and stability spindle motor technology, and head-disk interface technology which keeps the millimeter sized slider flying over a disk surface at nanometer level slider-disk spacing. This paper addresses the challenges and possible approaches on how to further reduce the slider disk spacing whilst retaining the stability and robustness level of head-disk systems for future advanced magnetic disk drives.

An Optimal Strategy for Accurate Bulge-to-disk Decomposition of Disk Galaxies

Energy Technology Data Exchange (ETDEWEB)

Gao Hua [Department of Astronomy, School of Physics, Peking University, Beijing 100871 (China); Ho, Luis C. [Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871 (China)

2017-08-20

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

Science.gov (United States)

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

International Nuclear Information System (INIS)

Gao Hua; Ho, Luis C.

2017-01-01

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.

Foundations of Black Hole Accretion Disk Theory

Directory of Open Access Journals (Sweden)

Marek A. Abramowicz

2013-01-01

Full Text Available This review covers the main aspects of black hole accretion disk theory. We begin with the view that one of the main goals of the theory is to better understand the nature of black holes themselves. In this light we discuss how accretion disks might reveal some of the unique signatures of strong gravity: the event horizon, the innermost stable circular orbit, and the ergosphere. We then review, from a first-principles perspective, the physical processes at play in accretion disks. This leads us to the four primary accretion disk models that we review: Polish doughnuts (thick disks, Shakura-Sunyaev (thin disks, slim disks, and advection-dominated accretion flows (ADAFs. After presenting the models we discuss issues of stability, oscillations, and jets. Following our review of the analytic work, we take a parallel approach in reviewing numerical studies of black hole accretion disks. We finish with a few select applications that highlight particular astrophysical applications: measurements of black hole mass and spin, black hole vs. neutron star accretion disks, black hole accretion disk spectral states, and quasi-periodic oscillations (QPOs.

Foundations of Black Hole Accretion Disk Theory.

Science.gov (United States)

Abramowicz, Marek A; Fragile, P Chris

2013-01-01

This review covers the main aspects of black hole accretion disk theory. We begin with the view that one of the main goals of the theory is to better understand the nature of black holes themselves. In this light we discuss how accretion disks might reveal some of the unique signatures of strong gravity: the event horizon, the innermost stable circular orbit, and the ergosphere. We then review, from a first-principles perspective, the physical processes at play in accretion disks. This leads us to the four primary accretion disk models that we review: Polish doughnuts (thick disks), Shakura-Sunyaev (thin) disks, slim disks, and advection-dominated accretion flows (ADAFs). After presenting the models we discuss issues of stability, oscillations, and jets. Following our review of the analytic work, we take a parallel approach in reviewing numerical studies of black hole accretion disks. We finish with a few select applications that highlight particular astrophysical applications: measurements of black hole mass and spin, black hole vs. neutron star accretion disks, black hole accretion disk spectral states, and quasi-periodic oscillations (QPOs).

Relativistic, accreting disks

International Nuclear Information System (INIS)

Abramowicz, M.A; Jaroszynski, M.; Sikora, M.

1978-01-01

An analytic theory of the hydrodynamical structure of accreting disks (without self-gravitation but with pressure) orbiting around and axially symmetric, stationary, compact body (e.g. black hole) is presented. The inner edge of the marginally stable accreting disk (i.e. disk with constant angular momentum density) has a sharp cusp located on the equatorial plane between rsub(ms) and rsub(mb). The existence of the cusp is also typical for any angular momentum distribution. The physical importance of the cusp follows from the close analogy with the case of a close binary system (L 1 Lagrange point on the Roche lobe). The existence of the cusp is thus a crucial phenomenon in such problems as boundary condition for the viscous stresses, accretion rate etc. (orig.) [de

CT recognition of lateral lumbar disk herniation

International Nuclear Information System (INIS)

Williams, A.L.; Haughton, V.M.; Daniels, D.L.; Thornton, R.S.

1982-01-01

Although computed tomography (CT) has been shown to be useful in diagnosing posterolateral and central lumbar disk herniations, its effectiveness in demonstrating lateral herniated disks has not been emphasized. The myelographic recognition of those herniations may be difficult because root sheaths or dural sacs may not be deformed. A total of 274 CT scans interpreted as showing lumbar disk herniation was reviewed. Fourteen (5%) showed a lateral disk herniation. The CT features of a lateral herniated disk included: (1) focal protrusion of the disk margin within or lateral to the intervertebral foramen: (2) displacement of epidural fat within the intervertebral foramen; (3) absence of dural sac deformity; and (4) soft-tissue mass within or lateral to the intervertebral foramen. Because it can image the disk margin and free disk fragments irrespective of dural sac or root sheath deformity, CT may be more effective than myelography for demonstrating the presence and extent of lateral disk herniation

Grain surface chemistry in protoplanetary disks

International Nuclear Information System (INIS)

Reboussin, Laura

2015-01-01

Planetary formation occurs in the protoplanetary disks of gas and dust. Although dust represents only 1% of the total disk mass, it plays a fundamental role in disk chemical evolution since it acts as a catalyst for the formation of molecules. Understanding this chemistry is therefore essential to determine the initial conditions from which planets form. During my thesis, I studied grain-surface chemistry and its impact on the chemical evolution of molecular cloud, initial condition for disk formation, and protoplanetary disk. Thanks to numerical simulations, using the gas-grain code Nautilus, I showed the importance of diffusion reactions and gas-grain interactions for the abundances of gas-phase species. Model results combined with observations also showed the effects of the physical structure (in temperature, density, AV) on the molecular distribution in disks. (author)

The DiskMass Survey. II. Error Budget

Science.gov (United States)

Bershady, Matthew A.; Verheijen, Marc A. W.; Westfall, Kyle B.; Andersen, David R.; Swaters, Rob A.; Martinsson, Thomas

2010-06-01

We present a performance analysis of the DiskMass Survey. The survey uses collisionless tracers in the form of disk stars to measure the surface density of spiral disks, to provide an absolute calibration of the stellar mass-to-light ratio (Υ_{*}), and to yield robust estimates of the dark-matter halo density profile in the inner regions of galaxies. We find that a disk inclination range of 25°-35° is optimal for our measurements, consistent with our survey design to select nearly face-on galaxies. Uncertainties in disk scale heights are significant, but can be estimated from radial scale lengths to 25% now, and more precisely in the future. We detail the spectroscopic analysis used to derive line-of-sight velocity dispersions, precise at low surface-brightness, and accurate in the presence of composite stellar populations. Our methods take full advantage of large-grasp integral-field spectroscopy and an extensive library of observed stars. We show that the baryon-to-total mass fraction ({F}_bar) is not a well-defined observational quantity because it is coupled to the halo mass model. This remains true even when the disk mass is known and spatially extended rotation curves are available. In contrast, the fraction of the rotation speed supplied by the disk at 2.2 scale lengths (disk maximality) is a robust observational indicator of the baryonic disk contribution to the potential. We construct the error budget for the key quantities: dynamical disk mass surface density (Σdyn), disk stellar mass-to-light ratio (Υ^disk_{*}), and disk maximality ({F}_{*,max}^disk≡ V^disk_{*,max}/ V_c). Random and systematic errors in these quantities for individual galaxies will be ~25%, while survey precision for sample quartiles are reduced to 10%, largely devoid of systematic errors outside of distance uncertainties.

A COMMON SOURCE OF ACCRETION DISK TILT

International Nuclear Information System (INIS)

Montgomery, M. M.; Martin, E. L.

2010-01-01

Many different system types retrogradely precess, and retrograde precession could be from a tidal torque by the secondary on a misaligned accretion disk. However, a source that causes and maintains disk tilt is unknown. In this work, we show that accretion disks can tilt due to a force called lift. Lift results from differing gas stream supersonic speeds over and under an accretion disk. Because lift acts at the disk's center of pressure, a torque is applied around a rotation axis passing through the disk's center of mass. The disk responds to lift by pitching around the disk's line of nodes. If the gas stream flow ebbs, then lift also ebbs and the disk attempts to return to its original orientation. To first approximation, lift does not depend on magnetic fields or radiation sources but does depend on the mass and the surface area of the disk. Also, for disk tilt to be initiated, a minimum mass transfer rate must be exceeded. For example, a 10 -11 M sun disk around a 0.8 M sun compact central object requires a mass transfer rate greater than ∼ 8 x 10 -11 M sun yr -1 , a value well below the known mass transfer rates in cataclysmic variable dwarf novae systems that retrogradely precess and exhibit negative superhumps in their light curves and a value well below mass transfer rates in protostellar-forming systems.

Dynamic Young Stars and their Disks: A Temporal View of NGC 2264 with Spitzer and CoRoT*

Directory of Open Access Journals (Sweden)

Cody Ann Marie

2014-01-01

Full Text Available Variability is a signature feature of young stars. Among the well known light curve phenomena are periodic variations attributed to surface spots and irregular changes associated with accretion or circumstellar disk material. While decades of photometric monitoring have provided a framework for classifying young star variability, we still know surprisingly little about its underlying mechanisms and connections to the surrounding disks. In the past few years, dedicated photometric monitoring campaigns from the ground and space have revolutionized our view of young stars in the time domain. We present a selection of optical and infrared time series from several recent campaigns, highlighting the Coordinated Synoptic Investigation of NGC 2264 (“CSI 2264”– a joint30-day effort with the Spitzer, CoRoT, and MOST telescopes. The extraordinary photometric precision, high cadence, and long time baseline of these observations is now enabling correlation of variability properties at very different wavelengths, corresponding to locations from the stellar surface to the inner 0.1 AU of the disk. We present some results of the CSI 2264 program, including new classes of optical/infrared behavior. Further efforts to tie observed variability features to physical models will provide insights into the inner disk environment at a time when planet formation may be underway.

Covering and piercing disks with two centers

KAUST Repository

Ahn, Heekap; Kim, Sangsub; Knauer, Christian; Schlipf, Lena; Shin, Chansu; Vigneron, Antoine E.

2013-01-01

We give exact and approximation algorithms for two-center problems when the input is a set D of disks in the plane. We first study the problem of finding two smallest congruent disks such that each disk in D intersects one of these two disks. Then we study the problem of covering the set D by two smallest congruent disks. © 2012 Elsevier B.V.

Covering and piercing disks with two centers

KAUST Repository

Ahn, Heekap

2013-04-01

We give exact and approximation algorithms for two-center problems when the input is a set D of disks in the plane. We first study the problem of finding two smallest congruent disks such that each disk in D intersects one of these two disks. Then we study the problem of covering the set D by two smallest congruent disks. © 2012 Elsevier B.V.

HERSCHEL OBSERVATIONS OF THE T CHA TRANSITION DISK: CONSTRAINING THE OUTER DISK PROPERTIES

OpenAIRE

Cieza, Lucas A.; Olofsson, Johan; Harvey, Paul M.; Pinte, Christophe; Merin, Bruno; Augereau, Jean-Charles; Evans, Neal J., II; Najita, Joan; Henning, Thomas; Menard, Francois

2011-01-01

T Cha is a nearby (d = 100 pc) transition disk known to have an optically thin gap separating optically thick inner and outer disk components. Huelamo et al. (2011) recently reported the presence of a low-mass object candidate within the gap of the T Cha disk, giving credence to the suspected planetary origin of this gap. Here we present the Herschel photometry (70, 160, 250, 350, and 500 micron) of T Cha from the "Dust, Ice, and Gas in Time" (DIGIT) Key Program, which bridges the wavelength ...

EMBEDDED PROTOSTELLAR DISKS AROUND (SUB-)SOLAR STARS. II. DISK MASSES, SIZES, DENSITIES, TEMPERATURES, AND THE PLANET FORMATION PERSPECTIVE

International Nuclear Information System (INIS)

Vorobyov, Eduard I.

2011-01-01

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.

TOWARD A GLOBAL EVOLUTIONARY MODEL OF PROTOPLANETARY DISKS

Energy Technology Data Exchange (ETDEWEB)

Bai, Xue-Ning, E-mail: xbai@cfa.harvard.edu [Institute for Theory and Computation, Harvard-Smithsonian Center for Astrophysics, 60 Garden St., MS-51, Cambridge, MA 02138 (United States)

2016-04-20

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.

TOWARD A GLOBAL EVOLUTIONARY MODEL OF PROTOPLANETARY DISKS

International Nuclear Information System (INIS)

Bai, Xue-Ning

2016-01-01

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

Relativistic, accreting disks

Energy Technology Data Exchange (ETDEWEB)

Abramowicz, M A; Jaroszynski, M; Sikora, M [Polska Akademia Nauk, Warsaw

1978-02-01

An analytic theory of the hydrodynamical structure of accreting disks (without self-gravitation but with pressure) orbiting around an axially symmetric, stationary, compact body (e.g. black hole) is presented. The inner edge of the marginally stable accreting disk (i.e. disk with constant angular momentum density) has a sharp cusp located on the equatorial plane between r/sub ms/ and r/sub mb/. The existence of the cusp is also typical for any angular momentum distribution. The physical importance of the cusp follows from the close analogy with the case of a close binary system (L/sub 1/ Lagrange point on the Roche lobe). The existence of the cusp is thus a crucial phenomenon in such problems as boundary condition for the viscous stresses, accretion rate, etc.

IBM 3390 Hard Disk Platter

CERN Multimedia

1991-01-01

The 3390 disks rotated faster than those in the previous model 3380. Faster disk rotation reduced rotational delay (ie. the time required for the correct area of the disk surface to move to the point where data could be read or written). In the 3390's initial models, the average rotational delay was reduced to 7.1 milliseconds from 8.3 milliseconds for the 3380 family.

Characterization of the magnetic field of the Herbig Be star HD200775

Science.gov (United States)

Alecian, E.; Catala, C.; Wade, G. A.; Donati, J.-F.; Petit, P.; Landstreet, J. D.; Böhm, T.; Bouret, J.-C.; Bagnulo, S.; Folsom, C.; Grunhut, J.; Silvester, J.

2008-03-01

The origin of the magnetic fields observed in some intermediate-mass and high-mass main-sequence stars is still a matter of vigorous debate. The favoured hypothesis is a fossil field origin, in which the observed fields are the condensed remnants of magnetic fields present in the original molecular cloud from which the stars formed. According to this theory a few per cent of the pre-main-sequence (PMS) Herbig Ae/Be star should be magnetic with a magnetic topology similar to that of main-sequence intermediate-mass stars. After our recent discovery of four magnetic Herbig stars, we have decided to study in detail one of them, HD200775, to determine if its magnetic topology is similar to that of the main-sequence magnetic stars. With this aim, we monitored this star in Stokes I and V over more than 2yr, using the new spectropolarimeters ESPaDOnS at Canada-France-Hawaii Telescope (CFHT), and Narval at Bernard Lyot Telescope (TBL). By analysing the intensity spectrum we find that HD200775 is a double-lined spectroscopic binary system, whose secondary seems similar, in temperature, to the primary. We have carefully compared the observed spectrum to a synthetic one, and we found no evidence of abundance anomalies in its spectrum. We infer the luminosity ratio of the components from the Stokes I profiles. Then, using the temperature and luminosity of HD200775 found in the literature, we estimate the age, the mass and the radius of both components from their HR diagram positions. From our measurements of the radial velocities of both stars we determine the ephemeris and the orbital parameters of the system. A Stokes V Zeeman signature is clearly visible in most of the least-squares deconvolution profiles and varies on a time-scale on the order of 1d. We have fitted the 30 profiles simultaneously, using a χ2 minimization method, with a centred and a decentred-dipole model. The best-fitting model is obtained with a reduced χ2 = 1.0 and provides a rotation period of 4

Formation of Close-in Super-Earths in an Evolving Disk Due to Disk Winds

Science.gov (United States)

Ogihara, Masahiro; Kokubo, Eiichiro; Suzuki, Takeru; Morbidelli, Alessandro

2018-04-01

Planets with masses larger than Mars mass undergo rapid inward migration (type I migration) in a standard protoplanetary disk. Recent magnetohydrodynamical simulations revealed the presence of magnetically-driven disk winds, which would alter the disk profile and the type I migration in the close-in region (rEarths can be reproduced by simulations. We find that the type I migration is significantly suppressed in a disk with flat surface density profile. After planetary embryos undergo slow inward migration, they are captured in a resonant chain. The resonant chain undergoes late orbital instability during the gas depletion, leading to a non-resonant configuration. We also find that observed distributions of close-in super-Earths (e.g., period ratio, mass ratio) can be reproduced by results of simulations.

Hydrogen Cyanide In Protoplanetary Disks

Science.gov (United States)

Walker, Ashley L.; Oberg, Karin; Cleeves, L. Ilsedore

2018-01-01

The chemistry behind star and planet formation is extremely complex and important in the formation of habitable planets. Life requires molecules containing carbon, oxygen, and importantly, nitrogen. Hydrogen cyanide, or HCN, one of the main interstellar nitrogen carriers, is extremely dangerous here on Earth. However, it could be used as a vital tool for tracking the chemistry of potentially habitable planets. As we get closer to identifying other habitable planets, we must understand the beginnings of how those planets are formed in the early protoplanetary disk. This project investigates HCN chemistry in different locations in the disk, and what this might mean for forming planets at different distances from the star. HCN is a chemically diverse molecule. It is connected to the formation for other more complex molecules and is commonly used as a nitrogen tracer. Using computational chemical models we look at how the HCN abundance changes at different locations. We use realistic and physically motivated conditions for the gas in the protoplanetary disk: temperature, density, and radiation (UV flux). We analyze the reaction network, formation, and destruction of HCN molecules in the disk environment. The disk environment informs us about stability of habitable planets that are created based on HCN molecules. We reviewed and compared the difference in the molecules with a variety of locations in the disk and ultimately giving us a better understanding on how we view protoplanetary disks.

CO Gas Inside the Protoplanetary Disk Cavity in HD 142527: Disk Structure from ALMA

OpenAIRE

Perez, S.; Casassus, S.; Ménard, F.; Roman, P.; van der Plas, G.; Cieza, L.; Pinte, C.; Christiaens, Valentin; Hales, A. S.

2014-01-01

Inner cavities and annular gaps in circumstellar disks are possible signposts of giant planet formation. The young star HD 142527 hosts a massive protoplanetary disk with a large cavity that extends up to 140 AU from the central star, as seen in continuum images at infrared and millimeter wavelengths. Estimates of the survival of gas inside disk cavities are needed to discriminate between clearing scenarios. We present a spatially and spectrally resolved carbon monoxide isotopologue 2-1 line ...

The Tilt between Acretion Disk and Stellar Disk Shiyin Shen1,2 ...

Indian Academy of Sciences (India)

80 Nandan Road, Shanghai 200030, China. 2Key Lab for Astrophysics, Shanghai 200234, China. ∗ e-mail: ssy@shao.ac.cn. Abstract. The orientations .... shows the model prediction from the stellar dust model (section 5). 4. Result: The tilt between the accretion disk and stellar disk. We parameterize the inclinations of the ...

Cold disks : Spitzer spectroscopy of disks around young stars with large gaps

NARCIS (Netherlands)

Blake, G. A.; Dullemond, C. P.; Merin, B.; Augereau, J. C.; Boogert, A. C. A.; Evans, N. J.; Geers, V. C.; Lahuis, F.; Kessler-Silacci, J. E.; Pontoppidan, K. M.; van Dishoeck, E. F.; Brown, J.M.

2007-01-01

We have identified four circumstellar disks with a deficit of dust emission from their inner 15-50 AU. All four stars have F-G spectral type and were uncovered as part of the Spitzer Space Telescope "Cores to Disks" Legacy Program Infrared Spectrograph (IRS) first-look survey of similar to 100 pre -

Covering and piercing disks with two centers

KAUST Repository

Ahn, Heekap; Kim, Sangsub; Knauer, Christian; Schlipf, Lena; Shin, Chansu; Vigneron, Antoine E.

2011-01-01

We consider new versions of the two-center problem where the input consists of a set D of disks in the plane. We first study the problem of finding two smallest congruent disks such that each disk in intersects one of these two disks. Then we study the problem of covering the set D by two smallest congruent disks. We give exact and approximation algorithms for these versions. © 2011 Springer-Verlag.

Verbatim Floppy Disk

CERN Multimedia

1976-01-01

Introduced under the name "Verbatim", Latin for "literally", these disks that sized more than 5¼ inches have become almost universal on dedicated word processing systems and personal computers. This format was replaced more slowly by the 3½-inch format, introduced for the first time in 1982. Compared to today, these large format disks stored very little data. In reality, they could only contain a few pages of text.

ALMA OBSERVATIONS OF THE DEBRIS DISK AROUND THE YOUNG SOLAR ANALOG HD 107146

Energy Technology Data Exchange (ETDEWEB)

Ricci, L.; Carpenter, J. M.; Fu, B. [Department of Astronomy, California Institute of Technology, MC 249-17, Pasadena, CA 91125 (United States); Hughes, A. M. [Department of Astronomy, Wesleyan University, Van Vleck Observatory, 96 Foss Hill Drive, Midletown, CT 06457 (United States); Corder, S. [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States); Isella, A., E-mail: lricci@astro.caltech.edu [Department of Physics and Astronomy, Rice University, 6100 South Main, Houston, TX 77521-1892 (United States)

2015-01-10

We present the Atacama Large Millimeter/submillimeter Array (ALMA) continuum observations at a wavelength of 1.25 mm of the debris disk surrounding the ∼100 Myr old solar analog HD 107146. The continuum emission extends from about 30 to 150 AU from the central star with a decrease in the surface brightness at intermediate radii. We analyze the ALMA interferometric visibilities using debris disk models with radial profiles for the dust surface density parameterized as (1) a single power law, (2) a single power law with a gap, and (3) a double power law. We find that models with a gap of radial width ∼8 AU at a distance of ∼80 AU from the central star, as well as double power-law models with a dip in the dust surface density at ∼70 AU provide significantly better fits to the ALMA data than single power-law models. We discuss possible scenarios for the origin of the HD 107146 debris disk using models of planetesimal belts in which the formation of Pluto-sized objects trigger disruptive collisions of large bodies, as well as models that consider the interaction of a planetary system with a planetesimal belt and spatial variation of the dust opacity across the disk. If future observations with higher angular resolution and sensitivity confirm the fully depleted gap structure discussed here, a planet with a mass of approximately a few Earth masses in a nearly circular orbit at ∼80 AU from the central star would be a possible explanation for the presence of the gap.

ALMA OBSERVATIONS OF THE DEBRIS DISK AROUND THE YOUNG SOLAR ANALOG HD 107146

International Nuclear Information System (INIS)

Ricci, L.; Carpenter, J. M.; Fu, B.; Hughes, A. M.; Corder, S.; Isella, A.

2015-01-01

We present the Atacama Large Millimeter/submillimeter Array (ALMA) continuum observations at a wavelength of 1.25 mm of the debris disk surrounding the ∼100 Myr old solar analog HD 107146. The continuum emission extends from about 30 to 150 AU from the central star with a decrease in the surface brightness at intermediate radii. We analyze the ALMA interferometric visibilities using debris disk models with radial profiles for the dust surface density parameterized as (1) a single power law, (2) a single power law with a gap, and (3) a double power law. We find that models with a gap of radial width ∼8 AU at a distance of ∼80 AU from the central star, as well as double power-law models with a dip in the dust surface density at ∼70 AU provide significantly better fits to the ALMA data than single power-law models. We discuss possible scenarios for the origin of the HD 107146 debris disk using models of planetesimal belts in which the formation of Pluto-sized objects trigger disruptive collisions of large bodies, as well as models that consider the interaction of a planetary system with a planetesimal belt and spatial variation of the dust opacity across the disk. If future observations with higher angular resolution and sensitivity confirm the fully depleted gap structure discussed here, a planet with a mass of approximately a few Earth masses in a nearly circular orbit at ∼80 AU from the central star would be a possible explanation for the presence of the gap

Astrophysical disks Collective and Stochastic Phenomena

CERN Document Server

Fridman, Alexei M; Kovalenko, Ilya G

2006-01-01

The book deals with collective and stochastic processes in astrophysical discs involving theory, observations, and the results of modelling. Among others, it examines the spiral-vortex structure in galactic and accretion disks , stochastic and ordered structures in the developed turbulence. It also describes sources of turbulence in the accretion disks, internal structure of disk in the vicinity of a black hole, numerical modelling of Be envelopes in binaries, gaseous disks in spiral galaxies with shock waves formation, observation of accretion disks in a binary system and mass distribution of luminous matter in disk galaxies. The editors adaptly brought together collective and stochastic phenomena in the modern field of astrophysical discs, their formation, structure, and evolution involving the methodology to deal with, the results of observation and modelling, thereby advancing the study in this important branch of astrophysics and benefiting Professional Researchers, Lecturers, and Graduate Students.

Gravitational Instabilities in Circumstellar Disks

Science.gov (United States)

Kratter, Kaitlin; Lodato, Giuseppe

2016-09-01

Star and planet formation are the complex outcomes of gravitational collapse and angular momentum transport mediated by protostellar and protoplanetary disks. In this review, we focus on the role of gravitational instability in this process. We begin with a brief overview of the observational evidence for massive disks that might be subject to gravitational instability and then highlight the diverse ways in which the instability manifests itself in protostellar and protoplanetary disks: the generation of spiral arms, small-scale turbulence-like density fluctuations, and fragmentation of the disk itself. We present the analytic theory that describes the linear growth phase of the instability supplemented with a survey of numerical simulations that aim to capture the nonlinear evolution. We emphasize the role of thermodynamics and large-scale infall in controlling the outcome of the instability. Despite apparent controversies in the literature, we show a remarkable level of agreement between analytic predictions and numerical results. In the next part of our review, we focus on the astrophysical consequences of the instability. We show that the disks most likely to be gravitationally unstable are young and relatively massive compared with their host star, Md/M*≥0.1. They will develop quasi-stable spiral arms that process infall from the background cloud. Although instability is less likely at later times, once infall becomes less important, the manifestations of the instability are more varied. In this regime, the disk thermodynamics, often regulated by stellar irradiation, dictates the development and evolution of the instability. In some cases the instability may lead to fragmentation into bound companions. These companions are more likely to be brown dwarfs or stars than planetary mass objects. Finally, we highlight open questions related to the development of a turbulent cascade in thin disks and the role of mode-mode coupling in setting the maximum angular

Development of Powered Disk Type Sugar Cane Stubble Saver

Directory of Open Access Journals (Sweden)

Radite P.A.S.

2009-04-01

Full Text Available The objective of this research was to design, fabricate and test a prototype of sugar cane stubble saver based on powered disk mechanism. In this research, a heavy duty disk plow or disk harrow was used as a rotating knife to cut the sugarcane stubble. The parabolic disk was chosen because it is proven reliable as soil working tools and it is available in the market as spare part of disk plow or disk harrow unit. The prototype was mounted on the four wheel tractor’s three point hitch, and powered by PTO of the tractor. Two kinds of disks were used in these experiments, those were disk with regular edge or plain disk and disk with scalloped edge or scalloped disk. Both disks had diameter of 28 inch. Results of field test showed that powered disk mechanism could satisfy cut sugar cane’s stubble. However, scalloped disk type gave smoother stubble cuts compared to that of plain disk. Plain disk type gave broken stubble cut. Higher rotation (1000 rpm resulted better cuts as compared to lower rotation (500 rpm both either on plain disk and scalloped disk. The developed prototype could work below the soil surface at depth of 5 to 10 cm. With tilt angle setting 20O and disk angle 45O the width of cut was about 25 cm.

Accretion in Radiative Equipartition (AiRE) Disks

Energy Technology Data Exchange (ETDEWEB)

Yazdi, Yasaman K.; Afshordi, Niayesh, E-mail: yyazdi@pitp.ca, E-mail: nafshordi@pitp.ca [Perimeter Institute for Theoretical Physics, 31 Caroline Street N, Waterloo, ON N2L 2Y5 (Canada)

2017-07-01

Standard accretion disk theory predicts that the total pressure in disks at typical (sub-)Eddington accretion rates becomes radiation pressure dominated. However, radiation pressure dominated disks are thermally unstable. Since these disks are observed in approximate steady state over the instability timescale, our accretion models in the radiation-pressure-dominated regime (i.e., inner disk) need to be modified. Here, we present a modification to the Shakura and Sunyaev model, where the radiation pressure is in equipartition with the gas pressure in the inner region. We call these flows accretion in radiative equipartition (AiRE) disks. We introduce the basic features of AiRE disks and show how they modify disk properties such as the Toomre parameter and the central temperature. We then show that the accretion rate of AiRE disks is limited from above and below, by Toomre and nodal sonic point instabilities, respectively. The former leads to a strict upper limit on the mass of supermassive black holes as a function of cosmic time (and spin), while the latter could explain the transition between hard and soft states of X-ray binaries.

HIGH-RESOLUTION INFRARED IMAGING AND SPECTROSCOPY OF THE Z CANIS MAJORIS SYSTEM DURING QUIESCENCE AND OUTBURST

Energy Technology Data Exchange (ETDEWEB)

Hinkley, Sasha; Hillenbrand, Lynne; Crepp, Justin R. [Department of Astronomy, California Institute of Technology, 1200 E. California Blvd, MC 249-17, Pasadena, CA 91125 (United States); Oppenheimer, Ben R.; Zimmerman, Neil; Brenner, Douglas [Astrophysics Department, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024 (United States); Rice, Emily L. [Department of Engineering Science and Physics, College of Staten Island, City University of New York, 2800 Victory Bvld, Staten Island, NY 10314 (United States); Pueyo, Laurent [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Vasisht, Gautam; Roberts, Jennifer E.; Roberts, Lewis C. Jr.; Burruss, Rick; Wallace, J. Kent; Cady, Eric; Zhai, Chengxing [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109 (United States); Kraus, Adam L. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA, 02138 (United States); Ireland, Michael J. [Department of Physics and Astronomy, Macquarie University, New South Wales, NSW 2109 (Australia); Beichman, Charles [NASA Exoplanet Science Institute, California Institute of Technology, Pasadena, CA 91125 (United States); Dekany, Richard [Caltech Optical Observatories, California Institute of Technology, Pasadena, CA 91125 (United States); Parry, Ian R. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); and others

2013-01-20

We present adaptive optics photometry and spectra in the JHKL bands along with high spectral resolution K-band spectroscopy for each component of the Z Canis Majoris system. Our high angular resolution photometry of this very young ({approx}<1 Myr) binary, comprised of an FU Ori object and a Herbig Ae/Be star, was gathered shortly after the 2008 outburst while our high-resolution spectroscopy was gathered during a quiescent phase. Our photometry conclusively determines that the outburst was due solely to the embedded Herbig Ae/Be member, supporting results from earlier works, and that the optically visible FU Ori component decreased slightly ({approx}30%) in luminosity during the same period, consistent with previous works on the variability of FU Ori type systems. Further, our high-resolution K-band spectra definitively demonstrate that the 2.294 {mu}m CO absorption feature seen in composite spectra of the system is due solely to the FU Ori component, while a prominent CO emission feature at the same wavelength, long suspected to be associated with the innermost regions of a circumstellar accretion disk, can be assigned to the Herbig Ae/Be member. These findings clarify previous analyses of the origin of the CO emission in this complex system.

Modeling Protoplanetary Disks

Science.gov (United States)

Holman, Megan; Tubbs, Drake; Keller, L. D.

2018-01-01

Using spectra models with known parameters and comparing them to spectra gathered from real systems is often the only ways to find out what is going on in those real systems. This project uses the modeling programs of RADMC-3D to generate model spectra for systems containing protoplanetary disks. The parameters can be changed to simulate protoplanetary disks in different stages of planet formation, with different sized gaps in different areas of the disks, as well as protoplanetary disks that contain different types of dust. We are working on producing a grid of models that all have different variations in the parameters in order to generate a miniature database to use for comparisons to gathered spectra. The spectra produced from these simulations will be compared to spectra that have been gathered from systems in the Small Magellanic cloud in order to find out the contents and stage of development of that system. This allows us to see if and how planets are forming in the Small Magellanic cloud, a region which has much less metallicity than our own galaxy. The data we gather from comparisons between the model spectra and the spectra of systems in the Small Magellanic Cloud can then be applied to how planets may have formed in the early universe.

The Fabulous Four Debris Disks

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Werner, Michael; Stapelfeldt, Karl

2004-09-01

This program is a comprehensive study of the four bright debris disks that were spatially resolved by IRAS: Beta Pictoris, Epsilon Eridani, Fomalhaut, and Vega. All SIRTF instruments and observing modes will be used. The program has three major objectives: (1) Study of the disk spatial structure from MIPS and IRAC imaging; (2) Study of the dust grain composition using the IRS and MIPS SED mode; and (3) companion searches using IRAC. The data from this program should lead to a detailed understanding of these four systems, and will provide a foundation for understanding all of the debris disks to be studied with SIRTF. Images and spectra will be compared with models for disk structure and dust properties. Dynamical features indicative of substellar companions' effects on the disks will be searched for. This program will require supporting observations of PSF stars, some of which have been included explicitly. In the majority of cases, the spectral observations require a preferred orientation to align the slits along the disk position angles. Detector saturation issues are still being worked for this program, and will lead to AOR modifications in subsequent submissions. The results from this program will be analyzed collaboratively by the IRAC, IRS, and MIPS teams and by general GTOs Jura and Werner.

THE VLA VIEW OF THE HL TAU DISK: DISK MASS, GRAIN EVOLUTION, AND EARLY PLANET FORMATION

Energy Technology Data Exchange (ETDEWEB)

Carrasco-González, Carlos; Rodríguez, Luis F.; Galván-Madrid, Roberto [Instituto de Radioastronomía y Astrofísica UNAM, Apartado Postal 3-72 (Xangari), 58089 Morelia, Michoacán, México (Mexico); Henning, Thomas; Linz, Hendrik; Birnstiel, Til; Boekel, Roy van; Klahr, Hubert [Max-Planck-Institut für Astronomie Heidelberg, Königstuhl 17, D-69117 Heidelberg (Germany); Chandler, Claire J.; Pérez, Laura [National Radio Astronomy Observatory, P.O. Box O, 1003 Lopezville Road, Socorro, NM 87801-0387 (United States); Anglada, Guillem; Macias, Enrique; Osorio, Mayra [Instituto de Astrofísica de Andalucía (CSIC), Apartado 3004, E-18080 Granada (Spain); Flock, Mario [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Menten, Karl [Jansky Fellow of the National Radio Astronomy Observatory (United States); Testi, Leonardo [European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching bei München (Germany); Torrelles, José M. [Institut de Ciències de l’Espai (CSIC-IEEC) and Institut de Ciències del Cosmos (UB-IEEC), Martí i Franquès 1, E-08028 Barcelona (Spain); Zhu, Zhaohuan, E-mail: c.carrasco@crya.unam.mx, E-mail: l.rodriguez@crya.unam.mx, E-mail: r.galvan@crya.unam.mx, E-mail: henning@mpia.de, E-mail: linz@mpia.de [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)

2016-04-10

The first long-baseline ALMA campaign resolved the disk around the young star HL Tau into a number of axisymmetric bright and dark rings. Despite the very young age of HL Tau, these structures have been interpreted as signatures for the presence of (proto)planets. The ALMA images triggered numerous theoretical studies based on disk–planet interactions, magnetically driven disk structures, and grain evolution. Of special interest are the inner parts of disks, where terrestrial planets are expected to form. However, the emission from these regions in HL Tau turned out to be optically thick at all ALMA wavelengths, preventing the derivation of surface density profiles and grain-size distributions. Here, we present the most sensitive images of HL Tau obtained to date with the Karl G. Jansky Very Large Array at 7.0 mm wavelength with a spatial resolution comparable to the ALMA images. At this long wavelength, the dust emission from HL Tau is optically thin, allowing a comprehensive study of the inner disk. We obtain a total disk dust mass of (1–3) × 10{sup −3} M {sub ⊙}, depending on the assumed opacity and disk temperature. Our optically thin data also indicate fast grain growth, fragmentation, and formation of dense clumps in the inner densest parts of the disk. Our results suggest that the HL Tau disk may be actually in a very early stage of planetary formation, with planets not already formed in the gaps but in the process of future formation in the bright rings.

THE VLA VIEW OF THE HL TAU DISK: DISK MASS, GRAIN EVOLUTION, AND EARLY PLANET FORMATION

International Nuclear Information System (INIS)

Carrasco-González, Carlos; Rodríguez, Luis F.; Galván-Madrid, Roberto; Henning, Thomas; Linz, Hendrik; Birnstiel, Til; Boekel, Roy van; Klahr, Hubert; Chandler, Claire J.; Pérez, Laura; Anglada, Guillem; Macias, Enrique; Osorio, Mayra; Flock, Mario; Menten, Karl; Testi, Leonardo; Torrelles, José M.; Zhu, Zhaohuan

2016-01-01

The first long-baseline ALMA campaign resolved the disk around the young star HL Tau into a number of axisymmetric bright and dark rings. Despite the very young age of HL Tau, these structures have been interpreted as signatures for the presence of (proto)planets. The ALMA images triggered numerous theoretical studies based on disk–planet interactions, magnetically driven disk structures, and grain evolution. Of special interest are the inner parts of disks, where terrestrial planets are expected to form. However, the emission from these regions in HL Tau turned out to be optically thick at all ALMA wavelengths, preventing the derivation of surface density profiles and grain-size distributions. Here, we present the most sensitive images of HL Tau obtained to date with the Karl G. Jansky Very Large Array at 7.0 mm wavelength with a spatial resolution comparable to the ALMA images. At this long wavelength, the dust emission from HL Tau is optically thin, allowing a comprehensive study of the inner disk. We obtain a total disk dust mass of (1–3) × 10 −3 M ⊙ , depending on the assumed opacity and disk temperature. Our optically thin data also indicate fast grain growth, fragmentation, and formation of dense clumps in the inner densest parts of the disk. Our results suggest that the HL Tau disk may be actually in a very early stage of planetary formation, with planets not already formed in the gaps but in the process of future formation in the bright rings

CONSTRAINTS ON COMPTON-THICK WINDS FROM BLACK HOLE ACCRETION DISKS: CAN WE SEE THE INNER DISK?

International Nuclear Information System (INIS)

Reynolds, Christopher S.

2012-01-01

Strong evidence is emerging that winds can be driven from the central regions of accretion disks in both active galactic nuclei and Galactic black hole binaries. Direct evidence for highly ionized, Compton-thin inner-disk winds comes from observations of blueshifted (v ∼ 0.05-0.1c) iron-K X-ray absorption lines. However, it has been suggested that the inner regions of black hole accretion disks can also drive Compton-thick winds—such winds would enshroud the inner disk, preventing us from seeing direct signatures of the accretion disk (i.e., the photospheric thermal emission, or the Doppler/gravitationally broadened iron Kα line). Here, we show that, provided the source is sub-Eddington, the well-established wind-driving mechanisms fail to launch a Compton-thick wind from the inner disk. For the accelerated region of the wind to be Compton-thick, the momentum carried in the wind must exceed the available photon momentum by a factor of at least 2/λ, where λ is the Eddington ratio of the source, ruling out radiative acceleration unless the source is very close to the Eddington limit. Compton-thick winds also carry large mass fluxes, and a consideration of the connections between the wind and the disk shows this to be incompatible with magneto-centrifugal driving. Finally, thermal driving of the wind is ruled out on the basis of the large Compton radii that typify black hole systems. In the absence of some new acceleration mechanisms, we conclude that the inner regions of sub-Eddington accretion disks around black holes are indeed naked.

PLANETESIMAL AND PROTOPLANET DYNAMICS IN A TURBULENT PROTOPLANETARY DISK: IDEAL UNSTRATIFIED DISKS

International Nuclear Information System (INIS)

Yang, Chao-Chin; Mac Low, Mordecai-Mark; Menou, Kristen

2009-01-01

The dynamics of planetesimals and planetary cores may be strongly influenced by density perturbations driven by magneto-rotational turbulence in their natal protoplanetary gas disks. Using the local shearing box approximation, we perform numerical simulations of planetesimals moving as massless particles in a turbulent, magnetized, unstratified gas disk. Our fiducial disk model shows turbulent accretion characterized by a Shakura-Sunyaev viscosity parameter of α ∼ 10 -2 , with rms density perturbations of ∼10%. We measure the statistical evolution of particle orbital properties in our simulations including mean radius, eccentricity, and velocity dispersion. We confirm random walk growth in time of all three properties, the first time that this has been done with direct orbital integration in a local model. We find that the growth rate increases with the box size used at least up to boxes of eight scale heights in horizontal size. However, even our largest boxes show velocity dispersions sufficiently low that collisional destruction of planetesimals should be unimportant in the inner disk throughout its lifetime. Our direct integrations agree with earlier torque measurements showing that type I migration dominates over diffusive migration by stochastic torques for most objects in the planetary core and terrestrial planet mass range. Diffusive migration remains important for objects in the mass range of kilometer-sized planetesimals. Discrepancies in the derived magnitude of turbulence between local and global simulations of magneto-rotationally unstable disks remains an open issue, with important consequences for planet formation scenarios.

Circumstellar Gas in Young Planetary Debris Disks

Science.gov (United States)

Roberge, A.

Circumstellar (CS) disks orbiting young stars fall into two categories: primordial disks, composed of unprocessed interstellar dust and gas, and debris disks, produced by the destruction of solid planetary bodies. In the first class, the most abundant gas is H_2; in the second, it appears that the H_2 gas has disappeared, possibly through incorporation into gas giant planets. The lifetime of H_2 gas in a CS disk is therefore of great importance, as it dictates the timescale for the formation of giant planets. FUSE observations of H_2 in CS disk systems have shown that FUV absorption spectroscopy may sensitively probe for small amounts of gas along the line of sight to the star. Most importantly, the FUSE non-detection of H_2 gas in the Beta Pictoris disk suggests that the primordial gas lifetime is less than about 12 Myr, and that gas giant planets must form very quickly. However, this suggestion is based on one system, and needs to be tested in additional systems with a range of ages, especially since there are indications that age is not the only factor in the evolution of a CS disk. We propose for FUSE observations of 3 additional debris disk systems, Fomalhaut, HD3003, and HD2884. Fomalhaut is an intermediate age debris disk, one of the Fabulous Four CS disks first discovered in 1984. The other two disks are younger, with ages similar to that of Beta Pic. All three stars are brighter in the FUV than Beta Pic, permitting us to sensitively probe for traces of H_2 gas. We will also measure the amount of secondary atomic gas produced from planetary bodies in these disks, in an effort to understand the entire evolution of CS gas in young planetary systems.

A New M Dwarf Debris Disk Candidate in a Young Moving Group Discovered with Disk Detective

Science.gov (United States)

Silverberg, Steven M.; Kuchner, Marc J.; Wisniewski, John P.; Gagne, Jonathan; Bans, Alissa S.; Bhattacharjee, Shambo; Currie, Thayne R.; Debes, John R.; Biggs, Joseph R; Bosch, Milton

2016-01-01

We used the Disk Detective citizen science project and the BANYAN II Bayesian analysis tool to identify a new candidate member of a nearby young association with infrared excess. WISE J080822.18-644357.3, an M5.5-type debris disk system with significant excess at both 12 and 22 microns, is a likely member (approx.90% BANYAN II probability) of the approx.45 Myr old Carina association. Since this would be the oldest M dwarf debris disk detected in a moving group, this discovery could be an important constraint on our understanding of M dwarf debris disk evolution.

Circumstellar disks around binary stars in Taurus

International Nuclear Information System (INIS)

Akeson, R. L.; Jensen, E. L. N.

2014-01-01

We have conducted a survey of 17 wide (>100 AU) young binary systems in Taurus with the Atacama Large Millimeter Array (ALMA) at two wavelengths. The observations were designed to measure the masses of circumstellar disks in these systems as an aid to understanding the role of multiplicity in star and planet formation. The ALMA observations had sufficient resolution to localize emission within the binary system. Disk emission was detected around all primaries and 10 secondaries, with disk masses as low as 10 –4 M ☉ . We compare the properties of our sample to the population of known disks in Taurus and find that the disks from this binary sample match the scaling between stellar mass and millimeter flux of F mm ∝M ∗ 1.5--2.0 to within the scatter found in previous studies. We also compare the properties of the primaries to those of the secondaries and find that the secondary/primary stellar and disk mass ratios are not correlated; in three systems, the circumsecondary disk is more massive than the circumprimary disk, counter to some theoretical predictions.

Time-Dependent Simulations of the Formation and Evolution of Disk-Accreted Atmospheres Around Terrestrial Planets

Science.gov (United States)

Stoekl, Alexander; Dorfi, Ernst

2014-05-01

In the early, embedded phase of evolution of terrestrial planets, the planetary core accumulates gas from the circumstellar disk into a planetary envelope. This atmosphere is very significant for the further thermal evolution of the planet by forming an insulation around the rocky core. The disk-captured envelope is also the staring point for the atmospheric evolution where the atmosphere is modified by outgassing from the planetary core and atmospheric mass loss once the planet is exposed to the radiation field of the host star. The final amount of persistent atmosphere around the evolved planet very much characterizes the planet and is a key criterion for habitability. The established way to study disk accumulated atmospheres are hydrostatic models, even though in many cases the assumption of stationarity is unlikely to be fulfilled. We present, for the first time, time-dependent radiation hydrodynamics simulations of the accumulation process and the interaction between the disk-nebula gas and the planetary core. The calculations were performed with the TAPIR-Code (short for The adaptive, implicit RHD-Code) in spherical symmetry solving the equations of hydrodynamics, gray radiative transport, and convective energy transport. The models range from the surface of the solid core up to the Hill radius where the planetary envelope merges into the surrounding protoplanetary disk. Our results show that the time-scale of gas capturing and atmospheric growth strongly depends on the mass of the solid core. The amount of atmosphere accumulated during the lifetime of the protoplanetary disk (typically a few Myr) varies accordingly with the mass of the planet. Thus, a core with Mars-mass will end up with about 10 bar of atmosphere while for an Earth-mass core, the surface pressure reaches several 1000 bar. Even larger planets with several Earth masses quickly capture massive envelopes which in turn become gravitationally unstable leading to runaway accretion and the eventual

FIRST L-BAND INTERFEROMETRIC OBSERVATIONS OF A YOUNG STELLAR OBJECT: PROBING THE CIRCUMSTELLAR ENVIRONMENT OF MWC 419

International Nuclear Information System (INIS)

Ragland, S.; Armandroff, T.; Wizinowich, P. L.; Akeson, R. L.; Millan-Gabet, R.; Colavita, M. M.; Traub, W. A.; Vasisht, G.; Danchi, W. C.; Hillenbrand, L. A.; Ridgway, S. T.

2009-01-01

We present spatially resolved K- and L-band spectra (at spectral resolution R = 230 and R = 60, respectively) of MWC 419, a Herbig Ae/Be star. The data were obtained simultaneously with a new configuration of the 85 m baseline Keck Interferometer. Our observations are sensitive to the radial distribution of temperature in the inner region of the disk of MWC 419. We fit the visibility data with both simple geometric and more physical disk models. The geometric models (uniform disk and Gaussian) show that the apparent size increases linearly with wavelength in the 2-4 μm wavelength region, suggesting that the disk is extended with a temperature gradient. A model having a power-law temperature gradient with radius simultaneously fits our interferometric measurements and the spectral energy distribution data from the literature. The slope of the power law is close to that expected from an optically thick disk. Our spectrally dispersed interferometric measurements include the Br γ emission line. The measured disk size at and around Br γ suggests that emitting hydrogen gas is located inside (or within the inner regions) of the dust disk.

First L-Band Interferometric Observations of a Young Stellar Object: Probing the Circumstellar Environment of MWC 419

Science.gov (United States)

Ragland, S.; Akeson, R. L.; Armandroff, T.; Colavita, M. M.; Danchi, W. C.; Hillenbrand, L. A.; Millan-Gabet, R.; Ridgway, S. T.; Traub, W. A.; Vasisht, G.; Wizinowich, P. L.

2009-09-01

We present spatially resolved K- and L-band spectra (at spectral resolution R = 230 and R = 60, respectively) of MWC 419, a Herbig Ae/Be star. The data were obtained simultaneously with a new configuration of the 85 m baseline Keck Interferometer. Our observations are sensitive to the radial distribution of temperature in the inner region of the disk of MWC 419. We fit the visibility data with both simple geometric and more physical disk models. The geometric models (uniform disk and Gaussian) show that the apparent size increases linearly with wavelength in the 2-4 μm wavelength region, suggesting that the disk is extended with a temperature gradient. A model having a power-law temperature gradient with radius simultaneously fits our interferometric measurements and the spectral energy distribution data from the literature. The slope of the power law is close to that expected from an optically thick disk. Our spectrally dispersed interferometric measurements include the Br γ emission line. The measured disk size at and around Br γ suggests that emitting hydrogen gas is located inside (or within the inner regions) of the dust disk.

MIGRATION TRAPS IN DISKS AROUND SUPERMASSIVE BLACK HOLES

International Nuclear Information System (INIS)

Bellovary, Jillian M.; Low, Mordecai-Mark Mac; McKernan, Barry; Ford, K. E. Saavik

2016-01-01

Accretion disks around supermassive black holes (SMBHs) in active galactic nuclei (AGNs) contain stars, stellar mass black holes, and other stellar remnants, which perturb the disk gas gravitationally. The resulting density perturbations exert torques on the embedded masses causing them to migrate through the disk in a manner analogous to planets in protoplanetary disks. We determine the strength and direction of these torques using an empirical analytic description dependent on local disk gradients, applied to two different analytic, steady-state disk models of SMBH accretion disks. We find that there are radii in such disks where the gas torque changes sign, trapping migrating objects. Our analysis shows that major migration traps generally occur where the disk surface density gradient changes sign from positive to negative, around 20–300R g , where R g  = 2GM/c 2 is the Schwarzschild radius. At these traps, massive objects in the AGN disk can accumulate, collide, scatter, and accrete. Intermediate mass black hole formation is likely in these disk locations, which may lead to preferential gap and cavity creation at these radii. Our model thus has significant implications for SMBH growth as well as gravitational wave source populations

Modeling collisions in circumstellar debris disks

Science.gov (United States)

Nesvold, Erika

2015-10-01

Observations of resolved debris disks show a spectacular variety of features and asymmetries, including inner cavities and gaps, inclined secondary disks or warps, and eccentric, sharp-edged rings. Embedded exoplanets could create many of these features via gravitational perturbations, which sculpt the disk directly and by generating planetesimal collisions. In this thesis, I present the Superparticle Model/Algorithm for Collisions in Kuiper belts and debris disks (SMACK), a new method for simultaneously modeling, in 3-D, the collisional and dynamical evolution of planetesimals in a debris disk with planets. SMACK can simulate azimuthal asymmetries and how these asymmetries evolve over time. I show that SMACK is stable to numerical viscosity and numerical heating over 107 yr, and that it can reproduce analytic models of disk evolution. As an example of the algorithm's capabilities, I use SMACK to model the evolution of a debris ring containing a planet on an eccentric orbit and demonstrate that differential precession creates a spiral structure as the ring evolves, but collisions subsequently break up the spiral, leaving a narrower eccentric ring. To demonstrate SMACK's utility in studying debris disk physics, I apply SMACK to simulate a planet on a circular orbit near a ring of planetesimals that are experiencing destructive collisions. Previous simulations of a planet opening a gap in a collisionless debris disk have found that the width of the gap scales as the planet mass to the 2/7th power (alpha = 2/7). I find that gap sizes in a collisional disk still obey a power law scaling with planet mass, but that the index alpha of the power law depends on the age of the system t relative to the collisional timescale t coll of the disk by alpha = 0.32(t/ tcoll)-0.04, with inferred planet masses up to five times smaller than those predicted by the classical gap law. The increased gap sizes likely stem from the interaction between collisions and the mean motion

THREE-DIMENSIONAL DISK-PLANET TORQUES IN A LOCALLY ISOTHERMAL DISK

International Nuclear Information System (INIS)

D'Angelo, Gennaro; Lubow, Stephen H.

2010-01-01

We determine an expression for the Type I planet migration torque involving a locally isothermal disk, with moderate turbulent viscosity (5 x 10 -4 ∼< α ∼< 0.05), based on three-dimensional nonlinear hydrodynamical simulations. The radial gradients (in a dimensionless logarithmic form) of density and temperature are assumed to be constant near the planet. We find that the torque is roughly equally sensitive to the surface density and temperature radial gradients. Both gradients contribute to inward migration when they are negative. Our results indicate that two-dimensional calculations with a smoothed planet potential, used to account for the effects of the third dimension, do not accurately determine the effects of density and temperature gradients on the three-dimensional torque. The results suggest that substantially slowing or stopping planet migration by means of changes in disk opacity or shadowing is difficult and appears unlikely for a disk that is locally isothermal. The scalings of the torque and torque density with planet mass and gas sound speed follow the expectations of linear theory. We also determine an improved formula for the torque density distribution that can be used in one-dimensional long-term evolution studies of planets embedded in locally isothermal disks. This formula can be also applied in the presence of mildly varying radial gradients and of planets that open gaps. We illustrate its use in the case of migrating super-Earths and determine some conditions sufficient for survival.

Angular momentum transfer in steady disk accretion

International Nuclear Information System (INIS)

Gorbatskij, V.G.

1977-01-01

The conditions of steady disk accretion have been investigated. The disk axisymmetric model is considered. It is shown that the gas is let at the outer boundary of the disk with the azimuthal velocity which is slightly less than the Kepler circular one. Gas possesses the motion quality moment which is transferred from the outer layers of the disk to the surface of the star. The steady state of the disk preserved until the inflow of the moment to the star increases its rotation velocity up to magnitudes close to the critical one

Time-Dependent Variations of Accretion Disk

Directory of Open Access Journals (Sweden)

Hye-Weon Na

1987-06-01

Full Text Available In dward nova we assume the primary star as a white dwarf and the secondary as the late type star which filled Roche lobe. Mass flow from the secondary star leads to the formation of thin accretion disk around the white dwarf. We use the α parameter as viscosity to maintain the disk form and propose that the outburst in dwarf nova cause the steep increase of source term. With these assumptions we solve the basic equations of stellar structure using Newton-Raphson method. We show the physical parameters like temperature, density, pressure, opacity, surface density, height and flux to the radius of disk. Changing the value of α, we compare several parameters when mass flow rate is constant with those of when luminosity of disk is brightest. At the same time, we obtain time-dependent variations of luminosity and mass of disk. We propose the suitable range of α is 0.15-0.18 to the difference of luminosity. We compare several parameters of disk with those of the normal late type stars which have the same molecular weight of disk is lower. Maybe the outburst in dwarf nova is due to the variation of the α value instead of increment of mass flow from the secondary star.

MIRROR AND POINT SYMMETRIES IN A BALLISTIC JET FROM A BINARY SYSTEM

International Nuclear Information System (INIS)

Raga, A. C.; Esquivel, A.; Velazquez, P. F.; Haro-Corzo, S.; RodrIguez-Gonzalez, A.; Canto, J.; Riera, A.

2009-01-01

Models of accretion disks around a star in a binary system predict that the disk will have a retrograde precession with a period a factor of ∼10 times the orbital period. If the star+disk system ejects a bipolar outflow, this outflow will be subject to the effects of both the orbital motion and the precession. We present an analytic, ballistic model and a three-dimensional gasdynamical simulation of a bipolar outflow from a source in a circular orbit, and with a precessing outflow axis. We find that this combination results in a jet/counterjet system with a small spatial scale, reflection-symmetric spiral (resulting from the orbital motion) and a larger-scale, point-symmetric spiral (resulting from the longer period precession). These results provide interesting possibilities for modeling specific Herbig-Haro jets and bipolar planetary nebulae.

[Management of disk displacement with condylar fracture].

Science.gov (United States)

Yu, Shi-bin; Li, Zu-bing; Yang, Xue-wen; Zhao, Ji-hong; Dong, Yao-jun

2003-07-01

To investigate clinical features of disk displacement during the course of condylar fracture and to explore the techniques of disk reposition and suturation. 32 patients (10 females and 22 males) who had disk displacements with condylar fractures were followed up. Reduction and reposition of the dislocated disks simultaneously with fixation of fractures were performed. 7 patients underwent intermaxillary fixation with elastic bands for 1 to 2 weeks. The occlusions were satisfactory in all cases but one for the reason of ramus height loss. No TMJ symptom was found when examined 3 months post operation. Anterior disk displacements were most occurred with high condylar process fractures. Surgical reposition and suturation of disk play an important role for the later TMJ-function.

Dust evolution in protoplanetary disks

OpenAIRE

Gonzalez , Jean-François; Fouchet , Laure; T. Maddison , Sarah; Laibe , Guillaume

2007-01-01

6 pages, 5 figures, to appear in the Proceedings of IAU Symp. 249: Exoplanets: Detection, Formation and Dynamics (Suzhou, China); International audience; We investigate the behaviour of dust in protoplanetary disks under the action of gas drag using our 3D, two-fluid (gas+dust) SPH code. We present the evolution of the dust spatial distribution in global simulations of planetless disks as well as of disks containing an already formed planet. The resulting dust structures vary strongly with pa...

Fallback disks & magnetars: prospects & possibilities

Science.gov (United States)

Alpar, M. A.

Some bound matter in the form of a fallback disk may be an initial parameter of isolated neutron stars at birth which along with the initial rotation rate and dipole and higher multipole magnetic moments determines the evolution of neutron stars and the categories into which they fall This talk reviews the strengths and difficulties of fallback disk models in explaining properties of isolated neutron stars of different categories Evidence for and observational limits on fallback disks will also be discussed

Identification of β-SiC surrounded by relatable surrounding diamond ...

Indian Academy of Sciences (India)

β-SiC is identified in the presence of a relatable surrounding diamond medium using subtle, but discernible Raman ... Change in the nature of the surrounding material structure and its .... intensity implies very low graphite content in thin film. In.

MIGRATION TRAPS IN DISKS AROUND SUPERMASSIVE BLACK HOLES

Energy Technology Data Exchange (ETDEWEB)

Bellovary, Jillian M.; Low, Mordecai-Mark Mac; McKernan, Barry; Ford, K. E. Saavik [Department of Astrophysics, American Museum of Natural History, Central Park West at 79th Street, NY 10024 (United States)

2016-03-10

Accretion disks around supermassive black holes (SMBHs) in active galactic nuclei (AGNs) contain stars, stellar mass black holes, and other stellar remnants, which perturb the disk gas gravitationally. The resulting density perturbations exert torques on the embedded masses causing them to migrate through the disk in a manner analogous to planets in protoplanetary disks. We determine the strength and direction of these torques using an empirical analytic description dependent on local disk gradients, applied to two different analytic, steady-state disk models of SMBH accretion disks. We find that there are radii in such disks where the gas torque changes sign, trapping migrating objects. Our analysis shows that major migration traps generally occur where the disk surface density gradient changes sign from positive to negative, around 20–300R{sub g}, where R{sub g} = 2GM/c{sup 2} is the Schwarzschild radius. At these traps, massive objects in the AGN disk can accumulate, collide, scatter, and accrete. Intermediate mass black hole formation is likely in these disk locations, which may lead to preferential gap and cavity creation at these radii. Our model thus has significant implications for SMBH growth as well as gravitational wave source populations.

Circumstellar disks around binary stars in Taurus

Energy Technology Data Exchange (ETDEWEB)

Akeson, R. L. [NASA Exoplanet Science Institute, IPAC/Caltech, Pasadena, CA 91125 (United States); Jensen, E. L. N. [Swarthmore College, Department of Physics and Astronomy, Swarthmore, PA 19081 (United States)

2014-03-20

We have conducted a survey of 17 wide (>100 AU) young binary systems in Taurus with the Atacama Large Millimeter Array (ALMA) at two wavelengths. The observations were designed to measure the masses of circumstellar disks in these systems as an aid to understanding the role of multiplicity in star and planet formation. The ALMA observations had sufficient resolution to localize emission within the binary system. Disk emission was detected around all primaries and 10 secondaries, with disk masses as low as 10{sup –4} M {sub ☉}. We compare the properties of our sample to the population of known disks in Taurus and find that the disks from this binary sample match the scaling between stellar mass and millimeter flux of F{sub mm}∝M{sub ∗}{sup 1.5--2.0} to within the scatter found in previous studies. We also compare the properties of the primaries to those of the secondaries and find that the secondary/primary stellar and disk mass ratios are not correlated; in three systems, the circumsecondary disk is more massive than the circumprimary disk, counter to some theoretical predictions.

Evaluation of powder metallurgy superalloy disk materials

Science.gov (United States)

Evans, D. J.

1975-01-01

A program was conducted to develop nickel-base superalloy disk material using prealloyed powder metallurgy techniques. The program included fabrication of test specimens and subscale turbine disks from four different prealloyed powders (NASA-TRW-VIA, AF2-1DA, Mar-M-432 and MERL 80). Based on evaluation of these specimens and disks, two alloys (AF2-1DA and Mar-M-432) were selected for scale-up evaluation. Using fabricating experience gained in the subscale turbine disk effort, test specimens and full scale turbine disks were formed from the selected alloys. These specimens and disks were then subjected to a rigorous test program to evaluate their physical properties and determine their suitability for use in advanced performance turbine engines. A major objective of the program was to develop processes which would yield alloy properties that would be repeatable in producing jet engine disks from the same powder metallurgy alloys. The feasibility of manufacturing full scale gas turbine engine disks by thermomechanical processing of pre-alloyed metal powders was demonstrated. AF2-1DA was shown to possess tensile and creep-rupture properties in excess of those of Astroloy, one of the highest temperature capability disk alloys now in production. It was determined that metallographic evaluation after post-HIP elevated temperature exposure should be used to verify the effectiveness of consolidation of hot isostatically pressed billets.

Simultaneous measurements of disk vibration and pressure fluctuation in turbulent flow developing in a model hard disk drive

Energy Technology Data Exchange (ETDEWEB)

Kurashima, D.; Naka, Y.; Fukagata, K. [Department of Mechanical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522 (Japan); Obi, S., E-mail: obsn@mech.keio.ac.jp [Department of Mechanical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522 (Japan)

2011-06-15

The complex flow features inside hard disk drive models are investigated in an axisymmetric and a semi-open shroud configurations. For the axisymmetric case, we have employed both experimental and computational approaches. The experiment focuses on both flow dynamics and the disk vibration, where measurements of the fluctuating pressure and velocity are undertaken at some representative points. The correlation between the disk vibration and the fluctuating pressure in the turbulent flow between disks is evident from the spectral analysis. The experimentally observed fluctuating pressure and velocity are partly due to the disk vibration and its contribution could be estimated by comparing the experiment with the results of a large eddy simulation. For the semi-open shroud case, although the characteristic peaks attributable to the large-scale vortical structure are still observed in the power spectra, the pressure fluctuation and the disk vibration are suppressed when the arm is inserted.

MOLECULAR DISK PROPERTIES IN EARLY-TYPE GALAXIES

International Nuclear Information System (INIS)

Xu, X.; Walker, C.; Narayanan, D.

2010-01-01

We study the simulated CO emission from elliptical galaxies formed in the mergers of gas-rich disk galaxies. The cold gas not consumed in the merger-driven starburst quickly resettles into a disk-like configuration. By analyzing a variety of arbitrary merger orbits that produce a range of fast- to slow-rotating remnants, we find that molecular disk formation is a fairly common consequence of gas-rich galaxy mergers. Hence, if a molecular disk is observed in an early-type merger remnant, it is likely the result of a 'wet merger' rather than a 'dry merger'. We compare the physical properties from our simulated disks (e.g., size and mass) and find reasonably good agreement with recent observations. Finally, we discuss the detectability of these disks as an aid to future observations.

Rotation of gas above the galactic disk

International Nuclear Information System (INIS)

Gvaramadze, V.V.; Lominadze, D.G.

1988-01-01

The galactic disk is modeled by an oblate spheroid with confocal spherodial isodensity surfaces. An explicit analytic expression is found for the angular velocity of the gas outside the disk. The parameters of a three-component model of a spiral galaxy (oblate spheroid with central hole, bulge, and massive corona) are chosen in such a way as to obtain in the disk a two-hump rotation curve (as in the Galaxy, M 31, and M 81). It is shown that at heights absolute value z ≤ 2 kpc the gas rotates in the same manner as the disk. However, at greater heights the rotation curve ceases to have two humps. Allowance for the pressure gradient of the gas slightly changes the rotation curve directly above the disk (r r/sub disk/)

Dynamics of acoustically levitated disk samples.

Science.gov (United States)

Xie, W J; Wei, B

2004-10-01

The acoustic levitation force on disk samples and the dynamics of large water drops in a planar standing wave are studied by solving the acoustic scattering problem through incorporating the boundary element method. The dependence of levitation force amplitude on the equivalent radius R of disks deviates seriously from the R3 law predicted by King's theory, and a larger force can be obtained for thin disks. When the disk aspect ratio gamma is larger than a critical value gamma(*) ( approximately 1.9 ) and the disk radius a is smaller than the critical value a(*) (gamma) , the levitation force per unit volume of the sample will increase with the enlargement of the disk. The acoustic levitation force on thin-disk samples ( gammaacoustic field for stable levitation of a large water drop is to adjust the reflector-emitter interval H slightly above the resonant interval H(n) . The simulation shows that the drop is flattened and the central parts of its top and bottom surface become concave with the increase of sound pressure level, which agrees with the experimental observation. The main frequencies of the shape oscillation under different sound pressures are slightly larger than the Rayleigh frequency because of the large shape deformation. The simulated translational frequencies of the vertical vibration under normal gravity condition agree with the theoretical analysis.

Comparison of Rosco Neo-Sensitabs with Oxoid paper disks in EUCAST disk diffusion antimicrobial susceptibility testing on Mueller-Hinton agar

DEFF Research Database (Denmark)

Justesen, U S; Acar, Ziyap; Olsson, K

2013-01-01

This study compared Neo-Sensitabs with Oxoid paper disks using the European Committee on Antimicrobial Susceptibility Testing (EUCAST) disk diffusion antimicrobial susceptibility test on Mueller-Hinton agar. The EUCAST-recommended quality control strains (Escherichia coli ATCC 25922, Pseudomonas...... paper disks for EUCAST disk diffusion antimicrobial susceptibility testing on Mueller-Hinton agar....

Working with arrays of inexpensive EIDE disk drives

International Nuclear Information System (INIS)

Sanders, D.; Riley, C.; Cremaldi, L.; Summers, D.; Petravick, D.

2000-01-01

In today's marketplace, the cost per Terabyte of disks with EIDE interfaces is about a third that of disks with SCSI. Hence, three times as many particle physics events could be put online with EIDE. The modern EIDE interface includes many of the performance features that appeared earlier in SCSI. EIDE bus speeds approach 33 Megabytes/s and need only be shared between two disks rather than seven disks. The interal I/O rate of very fast (and expensive) SCSI disks is only 50% greater than EIDE disks. Hence, two EIDE disks whose combined cost is much less than one very fast SCSI disk can actually give more data throughput due to the advantage of multiple spindles and head actuators. The authors explore the use of 12 and 16 Gigabyte EIDE disks with motherboard and PCI bus card interfaces on a number of operating systems and CPUs. These include Red Hat Linux and Windows 95/98 on a Pentium, MacOS and Apple's Rhapsody/NeXT/UNIX on a PowerPC, and Sun Solaris on a UltraSparc 10 workstation

Ultrafast disk lasers and amplifiers

Science.gov (United States)

Sutter, Dirk H.; Kleinbauer, Jochen; Bauer, Dominik; Wolf, Martin; Tan, Chuong; Gebs, Raphael; Budnicki, Aleksander; Wagenblast, Philipp; Weiler, Sascha

2012-03-01

Disk lasers with multi-kW continuous wave (CW) output power are widely used in manufacturing, primarily for cutting and welding applications, notably in the automotive industry. The ytterbium disk technology combines high power (average and/or peak power), excellent beam quality, high efficiency, and high reliability with low investment and operating costs. Fundamental mode picosecond disk lasers are well established in micro machining at high throughput and perfect precision. Following the world's first market introduction of industrial grade 50 W picosecond lasers (TruMicro 5050) at the Photonics West 2008, the second generation of the TruMicro series 5000 now provides twice the average power (100 W at 1030 nm, or 60 W frequency doubled, green output) at a significantly reduced footprint. Mode-locked disk oscillators achieve by far the highest average power of any unamplified lasers, significantly exceeding the 100 W level in laboratory set-ups. With robust long resonators their multi-microjoule pulse energies begin to compete with typical ultrafast amplifiers. In addition, significant interest in disk technology has recently come from the extreme light laser community, aiming for ultra-high peak powers of petawatts and beyond.

Equilibrium figures for beta Lyrae type disks

International Nuclear Information System (INIS)

Wilson, R.E.

1981-01-01

Accumulated evidence for a geometrically and optically thick disk in the β Lyrae system has now established the disk's basic external configuration. Since the disk has been constant in its main properties over the historical interval of β Lyrae observations and also seems to have a basically well-defined photosphere, it is now time to being consideration of its sturcture. Here, we compute equilibrium figures for self-gravitating disks around stars in binary systems as a start toward eventual computation of complete disk models. A key role is played by centrifugally limited rotation of the central star, which would naturally arise late in the rapid phase of mass transfer. Beta Lyrae is thus postulated to be a double-contact binary, which makes possible nonarbitrary separation of star and disk into separate structures. The computed equilibrium figures are three-dimensional, as the gravitation of the second star is included. Under the approximation that the gravitational potential of the disk is that of a thin wire and that the local disk angular velocity is proportional to u/sup n/ (u = distance from rotation axis), we comptue the total potential and locate equipotential surfaces. The centrifugal potential is written in a particularly convenient form which permits one to change the rotation law discontinuously (for example, at the star-disk coupling point) while ensuring that centrifugal potential and centrifigual force are continuous functions of position. With such a one-parameter rotation law, one can find equilibrium disk figures with dimensions very similar to those found in β Lyrae, but considerations of internal consistency demand at least a two-parameter law

Recent development of disk lasers at TRUMPF

Science.gov (United States)

Schad, Sven-Silvius; Gottwald, Tina; Kuhn, Vincent; Ackermann, Matthias; Bauer, Dominik; Scharun, Michael; Killi, Alexander

2016-03-01

The disk laser is one of the most important laser concepts for today's industrial laser market. Offering high brilliance at low cost, high optical efficiency and great application flexibility the disk laser paved the way for many industrial laser applications. Over the past years power and brightness increased and the disk laser turned out to be a very versatile laser source, not only for welding but also for cutting. Both, the quality and speed of cutting are superior to CO2-based lasers for a vast majority of metals, and, most important, in a broad thickness range. In addition, due to the insensitivity against back reflections the disk laser is well suited for cutting highly reflective metal such as brass or copper. These advantages facilitate versatile cutting machines and explain the high and growing demand for disk lasers for applications besides welding applications that can be observed today. From a today's perspective the disk principle has not reached any fundamental limits regarding output power per disk or beam quality, and offers numerous advantages over other high power resonator concepts, especially over fiber lasers or direct diode lasers. This paper will give insight in the latest progress in kilowatt class cw disk laser technology at TRUMPF and will discuss recent power scaling results as well.

Radiative Transfer Modeling in Proto-planetary Disks

Science.gov (United States)

Kasper, David; Jang-Condell, Hannah; Kloster, Dylan

2016-01-01

Young Stellar Objects (YSOs) are rich astronomical research environments. Planets form in circumstellar disks of gas and dust around YSOs. With ever increasing capabilities of the observational instruments designed to look at these proto-planetary disks, most notably GPI, SPHERE, and ALMA, more accurate interfaces must be made to connect modeling of the disks with observation. PaRTY (Parallel Radiative Transfer in YSOs) is a code developed previously to model the observable density and temperature structure of such a disk by self-consistently calculating the structure of the disk based on radiative transfer physics. We present upgrades we are implementing to the PaRTY code to improve its accuracy and flexibility. These upgrades include: creating a two-sided disk model, implementing a spherical coordinate system, and implementing wavelength-dependent opacities. These upgrades will address problems in the PaRTY code of infinite optical thickness, calculation under/over-resolution, and wavelength-independent photon penetration depths, respectively. The upgraded code will be used to better model disk perturbations resulting from planet formation.

Herniated lumbar intervertebral disk

International Nuclear Information System (INIS)

Hochhauser, L.; Cacayorin, E.D.; Karcnik, T.J.; McGowan, D.P.; Clark, K.G.; Storrs, D.; Kieffer, S.A.

1988-01-01

From a series of 25 patients with low-back pain and sciatica who subsequently underwent surgical exploration, 24 lumbar herniated disks and one asymmetrically bulging disk were correctly diagnosed with use of a 0.5-T MR imaging unit. The radiologic findings on saggital images included a polypoid protrusion beyond the posterior margin of the vertebral bodies more clearly displayed with T1-weighted than with T-2 weighted sequences and a focal extension into the extradural space on axial views. In most, the signal intensity of HNP was isointense to the disk of origin. The study suggests that MR imaging is currently capable of accurately predicting an HNP. The diagnosis is based primarily on morphologic characteristics rather than signal intensity alterations

A 100 au Wide Bipolar Rotating Shell Emanating from the HH 212 Protostellar Disk: A Disk Wind?

Science.gov (United States)

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.

Chemical evolution of the galactic disk

International Nuclear Information System (INIS)

Wyse, R.F.G.; Gilmore, G.

1987-01-01

The distribution of enriched material in the stars and gas of their Galaxy contains information pertaining to the chemical evolution of the Milky Way from its formation epoch to the present day, and provides general constraints on theories of galaxy formation. The separate stellar components of the Galaxy cannot readily be understood if treated in isolation, but a reasonably self-consistent model for Galactic chemical evolution may be found if one considers together the chemical properties of the extreme spheroid, thick disk and thin disk populations of the Galaxy. The three major stellar components of the Galaxy are characterized by their distinct spatial distributions, metallicity structure, and kinematics, with the newly-identified thick disk being approximately three times more massive than the classical metal-poor, non-rotating extreme spheroid. Stellar evolution in the thick disk straightforwardly provides the desired pre-enrichment for resolution of the thin disk G dwarf problem

DUST DISTRIBUTION IN THE β PICTORIS CIRCUMSTELLAR DISKS

International Nuclear Information System (INIS)

Ahmic, Mirza; Croll, Bryce; Artymowicz, Pawel

2009-01-01

We present three-dimensional models of dust distribution around β Pictoris that produce the best fits to the Hubble Space Telescope/Advanced Camera for Surveys' images obtained by Golimowski and coworkers. We allow for the presence of either one or two separate axisymmetric dust disks. The density models are analytical, radial two power laws joined smoothly at a crossover radius with density exponentially decreasing away from the midplane of the disks. Two-disk models match the data best, yielding a reduced χ 2 of ∼1.2. Our two-disk model reproduces many of the asymmetries reported in the literature and suggests that it is the secondary (tilted) disk which is largely responsible for them. Our model suggests that the secondary disk is not constrained to the inner regions of the system (extending out to at least 250 AU) and that it has a slightly larger total area of dust than the primary, as a result of slower falloff of density with radius and height. This surprising result raises many questions about the origin and dynamics of such a pair of disks. The disks overlap, but can coexist owing to their low optical depths and therefore long mean collision times. We find that the two disks have dust replenishment times on the order of 10 4 yr at ∼100 AU, hinting at the presence of planetesimals that are responsible for the production of second generation dust. A plausible conjecture, which needs to be confirmed by physical modeling of the collisional dynamics of bodies in the disks, is that the two observed disks are derived from underlying planetesimal disks; such disks would be anchored by the gravitational influence of planets located at less than 70 AU from β Pic that are themselves in slightly inclined orbits.

Radiation-hydrodynamics of HII regions and molecular clouds

International Nuclear Information System (INIS)

Sandford, M.T. II; Whitaker, R.W.; Klein, R.I.

1981-01-01

Two-dimensional calculations of ionization-shock fronts surrounding neutral cloud clumps reveal that a radiation-driven implosion of the clump can occur. The implosion of a cloud clump results in the formation of density enhancements that may eventually form low mass stars. The smaller globules produced may become Herbig-Haro objects, or maser sources

Thermal Comptonization in standard accretion disks

International Nuclear Information System (INIS)

Maraschi, L.; Molendi, S.

1990-01-01

Using the theory of geometrically thin accretion disks (where the effects of viscosity are parametrized in terms of the total pressure, viscosity parameter, α) equations are presented for the innermost region of the disk (where the pressure is due to radiation, and the main source of opacity is Thompson scattering). It is important to stress that the four equations can be solved without making use of an equation for the temperature. This is not true for the other regions of the disk. An equation given is used to determine the temperature, assuming that the disk is homogeneous and isothermal in the vertical direction. (author)

Island universes structure and evolution of disk galaxies

CERN Document Server

DE JONG, R. S

2007-01-01

This book contains an up-to-date review of the structure and evolution of disk galaxies from both the observational and theoretical point of view. The book is the proceedings of the "Island Universes" conference held at the island of Terschelling, The Netherlands in July 2005, which attracted about 130 experts and students in the field. The conference was organized as a tribute to Dr. Piet C. van der Kruit for receiving the honorary Jacobus C. Kapteyn Professorship in Astronomy. The eight topical themes discussed at the meeting are reflected in these proceedings: 1) Properties of Stellar Disks, 2) Kinematics and Dynamics of Disk Galaxies, 3) Bars, Spiral Structure, and Secular Evolution in Disk Galaxies, 4) The Outskirts and Environment of Disk Galaxies, 5) Interstellar Matter, 6) (Evolution of) Star Formation in Galactic Disks, 7) Disk Galaxies through Cosmic Time, and 8) Formation Models of Disk Galaxies. These proceedings are concluded with a conference summary reflecting on the most significant recent pro...

RED FRACTION AMONG SATELLITE GALAXIES WITH DISK-LIKE LIGHT PROFILES: EVIDENCE FOR INFLOW IN THE H I DISK

International Nuclear Information System (INIS)

Hester, J. A.

2010-01-01

The relationships between color, characterized with respect to the g - r red sequence; stellar structure, as determined using the i-band Sersic index; and group membership are explored using the Sloan Digital Sky Survey (SDSS). The new results place novel constraints on theories of galaxy evolution, despite the strong correlation between color and stellar structure. Observed correlations are of three independent types-those based on stellar structure, on the color of disk-like galaxies, and on the color of elliptical galaxies. Of particular note, the fraction of galaxies residing on the red sequence measured among galaxies with disk-like light profiles is enhanced for satellite galaxies compared to central galaxies. This fraction increases with group mass. When these new results are considered, theoretical treatments of galaxy evolution that adopt a gas accretion model centered on the hot galactic halo cannot consistently account for all observations of disk galaxies. The hypothesis is advanced that inflow within the extended H I disk prolongs star formation in satellite galaxies. When combined with partial ram pressure stripping (RPS) of this disk, this new scenario is consistent with the observations. This is demonstrated by applying an analytical model of RPS of the extended H I disk to the SDSS groups. These results motivate incorporating more complex modes of gas accretion into models of galaxy evolution, including cold mode accretion, an improved treatment of gas dynamics within disks, and disk stripping.

On the Solar System-Debris Disk Connecction

OpenAIRE

Moro-Martin, Amaya

2007-01-01

This paper emphasizes the connection between solar and extra-solar debris disks: how models and observations of the Solar System are helping us understand the debris disk phenomenon, and vice versa, how debris disks are helping us place our Solar System into context.

EARTH, MOON, SUN, AND CV ACCRETION DISKS

International Nuclear Information System (INIS)

Montgomery, M. M.

2009-01-01

Net tidal torque by the secondary on a misaligned accretion disk, like the net tidal torque by the Moon and the Sun on the equatorial bulge of the spinning and tilted Earth, is suggested by others to be a source to retrograde precession in non-magnetic, accreting cataclysmic variable (CV) dwarf novae (DN) systems that show negative superhumps in their light curves. We investigate this idea in this work. We generate a generic theoretical expression for retrograde precession in spinning disks that are misaligned with the orbital plane. Our generic theoretical expression matches that which describes the retrograde precession of Earths' equinoxes. By making appropriate assumptions, we reduce our generic theoretical expression to those generated by others, or to those used by others, to describe retrograde precession in protostellar, protoplanetary, X-ray binary, non-magnetic CV DN, quasar, and black hole systems. We find that spinning, tilted CV DN systems cannot be described by a precessing ring or by a precessing rigid disk. We find that differential rotation and effects on the disk by the accretion stream must be addressed. Our analysis indicates that the best description of a retrogradely precessing spinning, tilted, CV DN accretion disk is a differentially rotating, tilted disk with an attached rotating, tilted ring located near the innermost disk annuli. In agreement with the observations and numerical simulations by others, we find that our numerically simulated CV DN accretion disks retrogradely precess as a unit. Our final, reduced expression for retrograde precession agrees well with our numerical simulation results and with selective observational systems that seem to have main-sequence secondaries. Our results suggest that a major source to retrograde precession is tidal torques like that by the Moon and the Sun on the Earth. In addition, these tidal torques should be common to a variety of systems where one member is spinning and tilted, regardless if

THE INNER DISK STRUCTURE, DISK-PLANET INTERACTIONS, AND TEMPORAL EVOLUTION IN THE β PICTORIS SYSTEM: A TWO-EPOCH HST/STIS CORONAGRAPHIC STUDY

Energy Technology Data Exchange (ETDEWEB)

Apai, Dániel; Schneider, Glenn [Department of Astronomy and Steward Observatory, The University of Arizona, Tucson, AZ 85721 (United States); Grady, Carol A. [Eureka Scientific, 2452 Delmer, Suite 100, Oakland CA 96002 (United States); Wyatt, Mark C. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Lagrange, Anne-Marie [Université Grenoble Alpes, IPAG, F-38000, Grenoble (France); Kuchner, Marc J.; Stark, Christopher J. [NASA Goddard Space Flight Center, Exoplanets and Stellar Astrophysics Laboratory, Code 667, Greenbelt, MD 20771 (United States); Lubow, Stephen H., E-mail: apai@arizona.edu [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

2015-02-20

We present deep Hubble Space Telescope/Space Telescope Imaging Spectrograph coronagraphic images of the β Pic debris disk obtained at two epochs separated by 15 yr. The new images and the re-reduction of the 1997 data provide the most sensitive and detailed views of the disk at optical wavelengths as well as the yet smallest inner working angle optical coronagraphic image of the disk. Our observations characterize the large-scale and inner-disk asymmetries and we identify multiple breaks in the disk radial surface brightness profile. We study in detail the radial and vertical disk structure and show that the disk is warped. We explore the disk at the location of the β Pic b super-Jupiter and find that the disk surface brightness slope is continuous between 0.''5 and 2.''0, arguing for no change at the separations where β Pic b orbits. The two epoch images constrain the disk's surface brightness evolution on orbital and radiation pressure blow-out timescales. We place an upper limit of 3% on the disk surface brightness change between 3'' and 5'', including the locations of the disk warp, and the CO and dust clumps. We discuss the new observations in the context of high-resolution multi-wavelength images and divide the disk asymmetries in two groups: axisymmetric and non-axisymmetric. The axisymmetric structures (warp, large-scale butterfly, etc.) are consistent with disk structure models that include interactions of a planetesimal belt and a non-coplanar giant planet. The non-axisymmetric features, however, require a different explanation.

THE DARK DISK OF THE MILKY WAY

International Nuclear Information System (INIS)

Purcell, Chris W.; Bullock, James S.; Kaplinghat, Manoj

2009-01-01

Massive satellite accretions onto early galactic disks can lead to the deposition of dark matter in disk-like configurations that co-rotate with the galaxy. This phenomenon has potentially dramatic consequences for dark matter detection experiments. We utilize focused, high-resolution simulations of accretion events onto disks designed to be Galaxy analogues, and compare the resultant disks to the morphological and kinematic properties of the Milky Way's thick disk in order to bracket the range of co-rotating accreted dark matter. In agreement with previous results, we find that the Milky Way's merger history must have been unusually quiescent compared to median Λ cold dark matter expectations and, therefore, its dark disk must be relatively small: the fraction of accreted dark disk material near the Sun is about 20% of the host halo density or smaller and the co-rotating dark matter fraction near the Sun, defined as particles moving with a rotational velocity lag less than 50 km s -1 , is enhanced by about 30% or less compared to a standard halo model. Such a dark disk could contribute dominantly to the low energy (of order keV for a dark matter particle with mass 100 GeV) nuclear recoil event rate of direct detection experiments, but it will not change the likelihood of detection significantly. These dark disks provide testable predictions of weakly interacting massive particle dark matter models and should be considered in detailed comparisons to experimental data. Our findings suggest that the dark disk of the Milky Way may provide a detectable signal for indirect detection experiments, contributing up to about 25% of the dark matter self-annihilation signal in the direction of the center of the Galaxy, lending the signal a noticeably oblate morphology.

A PRIMER ON UNIFYING DEBRIS DISK MORPHOLOGIES

International Nuclear Information System (INIS)

Lee, Eve J.; Chiang, Eugene

2016-01-01

A “minimum model” for debris disks consists of a narrow ring of parent bodies, secularly forced by a single planet on a possibly eccentric orbit, colliding to produce dust grains that are perturbed by stellar radiation pressure. We demonstrate how this minimum model can reproduce a wide variety of disk morphologies imaged in scattered starlight. Five broad categories of disk shape can be captured: “rings,” “needles,” “ships-and-wakes,” “bars,” and “moths (a.k.a. fans),” depending on the viewing geometry. Moths can also sport “double wings.” We explain the origin of morphological features from first principles, exploring the dependence on planet eccentricity, disk inclination dispersion, and the parent body orbital phases at which dust grains are born. A key determinant in disk appearance is the degree to which dust grain orbits are apsidally aligned. Our study of a simple steady-state (secularly relaxed) disk should serve as a reference for more detailed models tailored to individual systems. We use the intuition gained from our guidebook of disk morphologies to interpret, informally, the images of a number of real-world debris disks. These interpretations suggest that the farthest reaches of planetary systems are perturbed by eccentric planets, possibly just a few Earth masses each.

A Primer on Unifying Debris Disk Morphologies

Science.gov (United States)

Lee, Eve J.; Chiang, Eugene

2016-08-01

A “minimum model” for debris disks consists of a narrow ring of parent bodies, secularly forced by a single planet on a possibly eccentric orbit, colliding to produce dust grains that are perturbed by stellar radiation pressure. We demonstrate how this minimum model can reproduce a wide variety of disk morphologies imaged in scattered starlight. Five broad categories of disk shape can be captured: “rings,” “needles,” “ships-and-wakes,” “bars,” and “moths (a.k.a. fans),” depending on the viewing geometry. Moths can also sport “double wings.” We explain the origin of morphological features from first principles, exploring the dependence on planet eccentricity, disk inclination dispersion, and the parent body orbital phases at which dust grains are born. A key determinant in disk appearance is the degree to which dust grain orbits are apsidally aligned. Our study of a simple steady-state (secularly relaxed) disk should serve as a reference for more detailed models tailored to individual systems. We use the intuition gained from our guidebook of disk morphologies to interpret, informally, the images of a number of real-world debris disks. These interpretations suggest that the farthest reaches of planetary systems are perturbed by eccentric planets, possibly just a few Earth masses each.

A PRIMER ON UNIFYING DEBRIS DISK MORPHOLOGIES

Energy Technology Data Exchange (ETDEWEB)

Lee, Eve J.; Chiang, Eugene, E-mail: evelee@berkeley.edu, E-mail: echiang@astro.berkeley.edu [Department of Astronomy, University of California Berkeley, Berkeley, CA 94720-3411 (United States)

2016-08-20

A “minimum model” for debris disks consists of a narrow ring of parent bodies, secularly forced by a single planet on a possibly eccentric orbit, colliding to produce dust grains that are perturbed by stellar radiation pressure. We demonstrate how this minimum model can reproduce a wide variety of disk morphologies imaged in scattered starlight. Five broad categories of disk shape can be captured: “rings,” “needles,” “ships-and-wakes,” “bars,” and “moths (a.k.a. fans),” depending on the viewing geometry. Moths can also sport “double wings.” We explain the origin of morphological features from first principles, exploring the dependence on planet eccentricity, disk inclination dispersion, and the parent body orbital phases at which dust grains are born. A key determinant in disk appearance is the degree to which dust grain orbits are apsidally aligned. Our study of a simple steady-state (secularly relaxed) disk should serve as a reference for more detailed models tailored to individual systems. We use the intuition gained from our guidebook of disk morphologies to interpret, informally, the images of a number of real-world debris disks. These interpretations suggest that the farthest reaches of planetary systems are perturbed by eccentric planets, possibly just a few Earth masses each.

DISK IMAGING SURVEY OF CHEMISTRY WITH SMA. II. SOUTHERN SKY PROTOPLANETARY DISK DATA AND FULL SAMPLE STATISTICS

International Nuclear Information System (INIS)

Oeberg, Karin I.; Qi Chunhua; Andrews, Sean M.; Espaillat, Catherine; Wilner, David J.; Fogel, Jeffrey K. J.; Bergin, Edwin A.; Pascucci, Ilaria; Kastner, Joel H.

2011-01-01

This is the second in a series of papers based on data from DISCS, a Submillimeter Array observing program aimed at spatially and spectrally resolving the chemical composition of 12 protoplanetary disks. We present data on six Southern sky sources-IM Lup, SAO 206462 (HD 135344b), HD 142527, AS 209, AS 205, and V4046 Sgr-which complement the six sources in the Taurus star-forming region reported previously. CO 2-1 and HCO + 3-2 emission are detected and resolved in all disks and show velocity patterns consistent with Keplerian rotation. Where detected, the emission from DCO + 3-2, N 2 H + 3-2, H 2 CO 3 03 - 2 02 and 4 14 - 3 13 , HCN 3-2, and CN 2 33/4/2 - 1 22/3/1 are also generally spatially resolved. The detection rates are highest toward the M and K stars, while the F star SAO 206462 has only weak CN and HCN emission, and H 2 CO alone is detected toward HD 142527. These findings together with the statistics from the previous Taurus disks support the hypothesis that high detection rates of many small molecules depend on the presence of a cold and protected disk midplane, which is less common around F and A stars compared to M and K stars. Disk-averaged variations in the proposed radiation tracer CN/HCN are found to be small, despite a two orders of magnitude range of spectral types and accretion rates. In contrast, the resolved images suggest that the CN/HCN emission ratio varies with disk radius in at least two of the systems. There are no clear observational differences in the disk chemistry between the classical/full T Tauri disks and transitional disks. Furthermore, the observed line emission does not depend on the measured accretion luminosities or the number of infrared lines detected, which suggests that the chemistry outside of 100 AU is not coupled to the physical processes that drive the chemistry in the innermost few AU.

Chemistry in protoplanetary disks

Science.gov (United States)

Semenov, D. A.

2012-01-01

In this lecture I discuss recent progress in the understanding of the chemical evolution of protoplanetary disks that resemble our Solar system during the first ten million years. At the verge of planet formation, strong variations of temperature, density, and radiation intensities in these disks lead to a layered chemical structure. In hot, dilute and heavily irradiated atmosphere only simple radicals, atoms, and atomic ions can survive, formed and destroyed by gas-phase processes. Beneath the atmosphere a partly UV-shielded, warm molecular layer is located, where high-energy radiation drives rich chemistry, both in the gas phase and on dust surfaces. In a cold, dense, dark disk midplane many molecules are frozen out, forming thick icy mantles where surface chemistry is active and where complex (organic) species are synthesized.

8-inch IBM floppy disk

CERN Multimedia

1971-01-01

The 8-inch floppy disk was a magnetic storage disk for the data introduced commercially by IBM in 1971. It was designed by an IBM team as an inexpensive way to load data into the IBM System / 370. Plus it was a read-only bare disk containing 80 KB of data. The first read-write version was introduced in 1972 by Memorex and could contain 175 KB on 50 tracks (with 8 sectors per track). Other improvements have led to various coatings and increased capacities. Finally, it was surpassed by the mini diskette of 5.25 inches introduced in 1976.

Disk tides and accretion runaway

Science.gov (United States)

Ward, William R.; Hahn, Joseph M.

1995-01-01

It is suggested that tidal interaction of an accreting planetary embryo with the gaseous preplanetary disk may provide a mechanism to breach the so-called runaway limit during the formation of the giant planet cores. The disk tidal torque converts a would-be shepherding object into a 'predator,' which can continue to cannibalize the planetesimal disk. This is more likely to occur in the giant planet region than in the terrestrial zone, providing a natural cause for Jupiter to predate the inner planets and form within the O(10(exp 7) yr) lifetime of the nebula.

On Fallback Disks around Young Neutron Stars

Science.gov (United States)

Alpar, M. Ali; Ertan, Ü.; Erkut, M. H.

2006-08-01

Some bound matter in the form of a fallback disk may be an initial parameter of isolated neutron stars at birth, which, along with the initial rotation rate and dipole (and higher multipole) magnetic moments, determines the evolution of neutron stars and the categories into which they fall. This talk reviews the possibilities of fallback disk models in explaining properties of isolated neutron stars of different categories. Recent observations of a fallback disk and observational limits on fallback disks will also be discussed.

New Insights into the Nature of Transition Disks from a Complete Disk Survey of the Lupus Star-forming Region

Science.gov (United States)

van der Marel, Nienke; Williams, Jonathan P.; Ansdell, M.; Manara, Carlo F.; Miotello, Anna; Tazzari, Marco; Testi, Leonardo; Hogerheijde, Michiel; Bruderer, Simon; van Terwisga, Sierk E.; van Dishoeck, Ewine F.

2018-02-01

Transition disks with large dust cavities around young stars are promising targets for studying planet formation. Previous studies have revealed the presence of gas cavities inside the dust cavities, hinting at recently formed, giant planets. However, many of these studies are biased toward the brightest disks in the nearby star-forming regions, and it is not possible to derive reliable statistics that can be compared with exoplanet populations. We present the analysis of 11 transition disks with large cavities (≥20 au radius) from a complete disk survey of the Lupus star-forming region, using ALMA Band 7 observations at 0.″3 (22–30 au radius) resolution of the 345 GHz continuum, 13CO and C18O 3–2 observations, and the spectral energy distribution of each source. Gas and dust surface density profiles are derived using the physical–chemical modeling code DALI. This is the first study of transition disks of large cavities within a complete disk survey within a star-forming region. The dust cavity sizes range from 20 to 90 au radius, and in three cases, a gas cavity is resolved as well. The deep drops in gas density and large dust cavity sizes are consistent with clearing by giant planets. The fraction of transition disks with large cavities in Lupus is ≳ 11 % , which is inconsistent with exoplanet population studies of giant planets at wide orbits. Furthermore, we present a hypothesis of an evolutionary path for large massive disks evolving into transition disks with large cavities.

Zodiac II: Debris Disk Science from a Balloon

Science.gov (United States)

Bryden, Geoffrey; Traub, Wesley; Roberts, Lewis C., Jr.; Bruno, Robin; Unwin, Stephen; Backovsky, Stan; Brugarolas, Paul; Chakrabarti, Supriya; Chen, Pin; Hillenbrand, Lynne;

From circumstellar disks to planetary systems: observation and modeling of protoplanetary disks

OpenAIRE

Macías Quevedo, Enrique

2016-01-01

The existence of exoplanetary systems was first predicted after the discovery of accretion disks around young stars. Nowadays, with nearly 3500 exoplanets discovered, and almost 5000 more candidates identified by the Kepler space mission, planetary systems are now known to be ubiquitous around low-mass stars. The formation of these systems takes place during the stellar formation itself, from the dust and gas orbiting around the star in the protoplanetary disks. However, the process that lead...

Melting of polydisperse hard disks

NARCIS (Netherlands)

Pronk, S.; Frenkel, D.

2004-01-01

The melting of a polydisperse hard-disk system is investigated by Monte Carlo simulations in the semigrand canonical ensemble. This is done in the context of possible continuous melting by a dislocation-unbinding mechanism, as an extension of the two-dimensional hard-disk melting problem. We find

STAR FORMATION IN DISK GALAXIES. III. DOES STELLAR FEEDBACK RESULT IN CLOUD DEATH?

Energy Technology Data Exchange (ETDEWEB)

Tasker, Elizabeth J.; Wadsley, James; Pudritz, Ralph [Department of Physics and Astronomy, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4M1 (Canada)

2015-03-01

Stellar feedback, star formation, and gravitational interactions are major controlling forces in the evolution of giant molecular clouds (GMCs). To explore their relative roles, we examine the properties and evolution of GMCs forming in an isolated galactic disk simulation that includes both localized thermal feedback and photoelectric heating. The results are compared with the three previous simulations in this series, which consists of a model with no star formation, star formation but no form of feedback, and star formation with photoelectric heating in a set with steadily increasing physical effects. We find that the addition of localized thermal feedback greatly suppresses star formation but does not destroy the surrounding GMC, giving cloud properties closely resembling the run in which no stellar physics is included. The outflows from the feedback reduce the mass of the cloud but do not destroy it, allowing the cloud to survive its stellar children. This suggests that weak thermal feedback such as the lower bound expected for a supernova may play a relatively minor role in the galactic structure of quiescent Milky-Way-type galaxies, compared to gravitational interactions and disk shear.

STAR FORMATION IN DISK GALAXIES. III. DOES STELLAR FEEDBACK RESULT IN CLOUD DEATH?

International Nuclear Information System (INIS)

Tasker, Elizabeth J.; Wadsley, James; Pudritz, Ralph

2015-01-01

Stellar feedback, star formation, and gravitational interactions are major controlling forces in the evolution of giant molecular clouds (GMCs). To explore their relative roles, we examine the properties and evolution of GMCs forming in an isolated galactic disk simulation that includes both localized thermal feedback and photoelectric heating. The results are compared with the three previous simulations in this series, which consists of a model with no star formation, star formation but no form of feedback, and star formation with photoelectric heating in a set with steadily increasing physical effects. We find that the addition of localized thermal feedback greatly suppresses star formation but does not destroy the surrounding GMC, giving cloud properties closely resembling the run in which no stellar physics is included. The outflows from the feedback reduce the mass of the cloud but do not destroy it, allowing the cloud to survive its stellar children. This suggests that weak thermal feedback such as the lower bound expected for a supernova may play a relatively minor role in the galactic structure of quiescent Milky-Way-type galaxies, compared to gravitational interactions and disk shear

RADIALLY MAGNETIZED PROTOPLANETARY DISK: VERTICAL PROFILE

International Nuclear Information System (INIS)

Russo, Matthew; Thompson, Christopher

2015-01-01

This paper studies the response of a thin accretion disk to an external radial magnetic field. Our focus is on protoplanetary disks (PPDs), which are exposed during their later evolution to an intense, magnetized wind from the central star. A radial magnetic field is mixed into a thin surface layer, wound up by the disk shear, and pushed downward by a combination of turbulent mixing and ambipolar and ohmic drift. The toroidal field reaches much greater strengths than the seed vertical field that is usually invoked in PPD models, even becoming superthermal. Linear stability analysis indicates that the disk experiences the magnetorotational instability (MRI) at a higher magnetization than a vertically magnetized disk when both the effects of ambipolar and Hall drift are taken into account. Steady vertical profiles of density and magnetic field are obtained at several radii between 0.06 and 1 AU in response to a wind magnetic field B r ∼ (10 −4 –10 −2 )(r/ AU) −2 G. Careful attention is given to the radial and vertical ionization structure resulting from irradiation by stellar X-rays. The disk is more strongly magnetized closer to the star, where it can support a higher rate of mass transfer. As a result, the inner ∼1 AU of a PPD is found to evolve toward lower surface density. Mass transfer rates around 10 −8 M ⊙ yr −1 are obtained under conservative assumptions about the MRI-generated stress. The evolution of the disk and the implications for planet migration are investigated in the accompanying paper

The age of the galactic disk

International Nuclear Information System (INIS)

Sandage, A.

1988-07-01

The galactic disk is a dissipative structure and must, therefore be younger than the halo if galaxy formation generally proceeds by collapse. Just how much younger the oldest stars in the galactic disk are than the oldest halo stars remains an open question. A fast collapse (on a time scale no longer than the rotation period of the extended protogalaxy) permits an age gap of the order of approximately 10 to the 9th power years. A slow collapse, governed by the cooling rate of the partially pressure supported falling gas that formed into what is now the thick stellar disk, permits a longer age gap, claimed by some to be as long as 6 Gyr. Early methods of age dating the oldest components of the disk contain implicit assumptions concerning the details of the age-metallicity relation for stars in the solar neighborhood. The discovery that this relation for open clusters outside the solar circle is different that in the solar neighborhood (Geisler 1987), complicates the earlier arguments. The oldest stars in the galactic disk are at least as old as NGC 188. The new data by Janes on NGC 6791, shown first at this conference, suggest a disk age of at least 12.5 Gyr, as do data near the main sequence termination point of metal rich, high proper motion stars of low orbital eccentricity. Hence, a case can still be made that the oldest part of the galactic thick disk is similar in age to the halo globular clusters, if their ages are the same as 47 Tuc

Latest advances in high brightness disk lasers

Science.gov (United States)

Kuhn, Vincent; Gottwald, Tina; Stolzenburg, Christian; Schad, Sven-Silvius; Killi, Alexander; Ryba, Tracey

2015-02-01

In the last decade diode pumped solid state lasers have become an important tool for many industrial materials processing applications. They combine ease of operation with efficiency, robustness and low cost. This paper will give insight in latest progress in disk laser technology ranging from kW-class CW-Lasers over frequency converted lasers to ultra-short pulsed lasers. The disk laser enables high beam quality at high average power and at high peak power at the same time. The power from a single disk was scaled from 1 kW around the year 2000 up to more than 10 kW nowadays. Recently was demonstrated more than 4 kW of average power from a single disk close to fundamental mode beam quality (M²=1.38). Coupling of multiple disks in a common resonator results in even higher power. As an example we show 20 kW extracted from two disks of a common resonator. The disk also reduces optical nonlinearities making it ideally suited for short and ultrashort pulsed lasers. In a joint project between TRUMPF and IFSW Stuttgart more than 1.3 kW of average power at ps pulse duration and exceptionally good beam quality was recently demonstrated. The extremely low saturated gain makes the disk laser ideal for internal frequency conversion. We show >1 kW average power and >6 kW peak power in multi ms pulsed regime from an internally frequency doubled disk laser emitting at 515 nm (green). Also external frequency conversion can be done efficiently with ns pulses. >500 W of average UV power was demonstrated.

A study of the Herbig-Haro object HH 120 and the associated cometary globule CG 30

International Nuclear Information System (INIS)

Pettersson, B.

1984-01-01

Infrared and spectroscopic observations are presented of a new Herbig-Haro object, here named HH 120, in the cometary globule CG 30. The emission line spectrum indicates a very low degree of excitation of the same order as that found for HH 47, HH 7, and HH 11. From several spectra a radial velocity of -42 km -1 +-12 km s -1 is deduced and the electron temperature, Tsub(e), and electron number density, Nsub(e), are found to be 9100 K+-400 K and 1700 cm -3 +-600 cm -3 , respectively. A prominent continuum is shown to be composed of a collisionally enhanced two-photon continuum and a reflected late-type stellar component, probably originating in the hidden source of energy. Infrared scans of CG 30 revealed five sources, two of which are very close to HH 120. It is argued that one of them, CG 30-IRS4, is the source of energy producing HH 120 and an associated reflection nebula. The bolometric luminosity of CG 30-IRS4 is estimated to be at least 0.9 Lsub(sun), its mass 1.1 Msub(sun) and its radius 1.6 Rsub(sun). (orig.)

NASA Lunar and Meteorite Sample Disk Program

Science.gov (United States)

Foxworth, Suzanne

2017-01-01

The Lunar and Meteorite Sample Disk Program is designed for K-12 classroom educators who work in K-12 schools, museums, libraries, or planetariums. Educators have to be certified to borrow the Lunar and Meteorite Sample Disks by attending a NASA Certification Workshop provided by a NASA Authorized Sample Disk Certifier.

Herbig-haro objects and mid-infrared outflows in the VELA C molecular cloud

International Nuclear Information System (INIS)

Zhang, Miaomiao; Wang, Hongchi; Henning, Thomas

2014-01-01

We have performed a deep [S II] λλ6717/6731 wide field Herbig-Haro (HH) object survey toward the Vela C molecular cloud with a sky coverage of about 2 deg 2 . In total, 18 new HH objects, HH 1090-1107, are discovered and the two previously known HH objects, HH 73-74, are also detected in our [S II] images. We also present an investigation of mid-infrared outflows in the Vela C molecular cloud using the Wide-field Infrared Survey Explorer images taken from AllWISE data release. Using the method suggested by Zhang and Wang, 11 extended green objects (EGOs) are identified to be the mid-infrared outflows, including 6 new mid-infrared outflows that have not been detected previously at other wavelengths and 5 mid-infrared counterparts of the HH objects detected in this work. Using the AllWISE Source Catalog and the source classification scheme suggested by Koenig et al., we have identified 56 young stellar object (YSO) candidates in the Vela C molecular cloud. The possible driving sources of the HH objects and EGOs are discussed based on the morphology of HH objects and EGOs and the locations of HH objects, EGOs and YSO candidates. Finally we associate 12 HH objects and 5 EGOs with 10 YSOs and YSO candidates. The median length of the outflows in Vela C is 0.35 pc and the outflows seem to be oriented randomly.

The response of relativistic outflowing gas to the inner accretion disk of a black hole.

Science.gov (United States)

Parker, Michael L; Pinto, Ciro; Fabian, Andrew C; Lohfink, Anne; Buisson, Douglas J K; Alston, William N; Kara, Erin; Cackett, Edward M; Chiang, Chia-Ying; Dauser, Thomas; De Marco, Barbara; Gallo, Luigi C; Garcia, Javier; Harrison, Fiona A; King, Ashley L; Middleton, Matthew J; Miller, Jon M; Miniutti, Giovanni; Reynolds, Christopher S; Uttley, Phil; Vasudevan, Ranjan; Walton, Dominic J; Wilkins, Daniel R; Zoghbi, Abderahmen

2017-03-01

The brightness of an active galactic nucleus is set by the gas falling onto it from the galaxy, and the gas infall rate is regulated by the brightness of the active galactic nucleus; this feedback loop is the process by which supermassive black holes in the centres of galaxies may moderate the growth of their hosts. Gas outflows (in the form of disk winds) release huge quantities of energy into the interstellar medium, potentially clearing the surrounding gas. The most extreme (in terms of speed and energy) of these-the ultrafast outflows-are the subset of X-ray-detected outflows with velocities higher than 10,000 kilometres per second, believed to originate in relativistic (that is, near the speed of light) disk winds a few hundred gravitational radii from the black hole. The absorption features produced by these outflows are variable, but no clear link has been found between the behaviour of the X-ray continuum and the velocity or optical depth of the outflows, owing to the long timescales of quasar variability. Here we report the observation of multiple absorption lines from an extreme ultrafast gas flow in the X-ray spectrum of the active galactic nucleus IRAS 13224-3809, at 0.236 ± 0.006 times the speed of light (71,000 kilometres per second), where the absorption is strongly anti-correlated with the emission of X-rays from the inner regions of the accretion disk. If the gas flow is identified as a genuine outflow then it is in the fastest five per cent of such winds, and its variability is hundreds of times faster than in other variable winds, allowing us to observe in hours what would take months in a quasar. We find X-ray spectral signatures of the wind simultaneously in both low- and high-energy detectors, suggesting a single ionized outflow, linking the low- and high-energy absorption lines. That this disk wind is responding to the emission from the inner accretion disk demonstrates a connection between accretion processes occurring on very different

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

Science.gov (United States)

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

THE VLA NASCENT DISK AND MULTIPLICITY SURVEY: FIRST LOOK AT RESOLVED CANDIDATE DISKS AROUND CLASS 0 AND I PROTOSTARS IN THE PERSEUS MOLECULAR CLOUD

Energy Technology Data Exchange (ETDEWEB)

Segura-Cox, Dominique M.; Harris, Robert J.; Looney, Leslie W. [Department of Astronomy, University of Illinois, Urbana, IL 61801 (United States); Tobin, John J. [Leiden Observatory, Leiden University, P.O. Box 9513, 2000-RA Leiden (Netherlands); Li, Zhi-Yun [Department of Astronomy, University of Virginia, Charlottesville, VA 22903 (United States); Chandler, Claire; Perez, Laura [National Radio Astronomy Observatory, Socorro, NM 87801 (United States); Kratter, Kaitlin [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Dunham, Michael M. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Sadavoy, Sarah [Max-Planck-Institut für Astronomie, D-69117 Heidelberg (Germany); Melis, Carl, E-mail: segurac2@illinois.edu [Center for Astrophysics and Space Sciences, University of California, San Diego, CA 92093 (United States)

2016-02-01

We present the first dust emission results toward a sample of seven protostellar disk candidates around Class 0 and I sources in the Perseus molecular cloud from the VLA Nascent Disk and Multiplicity (VANDAM) survey with ∼0.″05 or 12 AU resolution. To examine the surface brightness profiles of these sources, we fit the Ka-band 8 mm dust-continuum data in the u, v-plane to a simple, parametrized model based on the Shakura–Sunyaev disk model. The candidate disks are well-fit by a model with a disk-shaped profile and have masses consistent with known Class 0 and I disks. The inner-disk surface densities of the VANDAM candidate disks have shallower density profiles compared to disks around more evolved Class II systems. The best-fit model radii of the seven early-result candidate disks are R{sub c} > 10 AU; at 8 mm, the radii reflect lower limits on the disk size since dust continuum emission is tied to grain size and large grains radially drift inwards. These relatively large disks, if confirmed kinematically, are inconsistent with theoretical models where the disk size is limited by strong magnetic braking to <10 AU at early times.

Developmental changes in the adhesive disk during Giardia differentiation.

Science.gov (United States)

Palm, Daniel; Weiland, Malin; McArthur, Andrew G; Winiecka-Krusnell, Jadwiga; Cipriano, Michael J; Birkeland, Shanda R; Pacocha, Sarah E; Davids, Barbara; Gillin, Frances; Linder, Ewert; Svärd, Staffan

2005-06-01

Giardia lamblia is a protozoan parasite infecting the upper mammalian small intestine. Infection relies upon the ability of the parasite to attach to the intestine via a unique cytoskeletal organelle, the ventral disk. We determined the composition and structure of the disk throughout the life cycle of the parasite and identified a new disk protein, SALP-1. SALP-1 is an immunodominant protein related to striated fiber-assemblin (SFA). The disk is disassembled during encystation and stored as four fragments in the immobile cyst. Serial Analysis of Gene Expression (SAGE) showed that the mRNA levels of the disk proteins decreased in encystation but two-dimensional protein gels showed that the protein levels were more constant. The parasite emerges without a functional disk but the four disk fragments are quickly reassembled into two new disks on the dividing, early excysting form. Thus, disk proteins are stored within the cyst, ready to be used in the rapid steps of excystation.

Spatially resolved investigation of competing nanocluster emission in quantum-disks-in-nanowires structure characterized by nanoscale cathodoluminescence

KAUST Repository

Prabaswara, Aditya; Stowe, David J.; Janjua, Bilal; Ng, Tien Khee; Anjum, Dalaver H.; Longo, Paolo; Zhao, Chao; Elafandy, Rami T.; Li, Xiaohang; Alyamani, Ahmed Y.; El-Desouki, Munir M.; Ooi, Boon S.

2017-01-01

We report on the study and characterization of nanoclusters-related recombination centers within quantum-disks-in-nanowires heterostructure by utilizing microphotoluminescence (mu-PL) and cathodoluminescence scanning transmission electron microscopy (CL-STEM). mu-PL measurement shows that the nanoclusters-related recombination center exhibits different temperature-dependent characteristics compared with the surrounding InGaN quantum-disksrelated recombination center. CL-STEM measurements reveal that these recombination centers mainly arise from irregularities within the quantum disks, with a strong, spatially localized emission when measured at low temperature. The spectra obtained from both CL-STEM and mu-PL correlate well with each other. Our work sheds light on the optical and structural properties of simultaneously coexisting recombination centers within nanowires heterostructures. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Spatially resolved investigation of competing nanocluster emission in quantum-disks-in-nanowires structure characterized by nanoscale cathodoluminescence

KAUST Repository

Prabaswara, Aditya

2017-06-30

We report on the study and characterization of nanoclusters-related recombination centers within quantum-disks-in-nanowires heterostructure by utilizing microphotoluminescence (mu-PL) and cathodoluminescence scanning transmission electron microscopy (CL-STEM). mu-PL measurement shows that the nanoclusters-related recombination center exhibits different temperature-dependent characteristics compared with the surrounding InGaN quantum-disksrelated recombination center. CL-STEM measurements reveal that these recombination centers mainly arise from irregularities within the quantum disks, with a strong, spatially localized emission when measured at low temperature. The spectra obtained from both CL-STEM and mu-PL correlate well with each other. Our work sheds light on the optical and structural properties of simultaneously coexisting recombination centers within nanowires heterostructures. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

The AMBRE project: The thick thin disk and thin thick disk of the Milky Way

Science.gov (United States)

Hayden, M. R.; Recio-Blanco, A.; de Laverny, P.; Mikolaitis, S.; Worley, C. C.

2017-11-01

We analyze 494 main sequence turnoff and subgiant stars from the AMBRE:HARPS survey. These stars have accurate astrometric information from Gaia DR1, providing reliable age estimates with relative uncertainties of ±1 or 2 Gyr and allowing precise orbital determinations. The sample is split based on chemistry into a low-[Mg/Fe] sequence, which are often identified as thin disk stellar populations, and high-[Mg/Fe] sequence, which are often associated with thick disk stellar populations. We find that the high-[Mg/Fe] chemical sequence has extended star formation for several Gyr and is coeval with the oldest stars of the low-[Mg/Fe] chemical sequence: both the low- and high-[Mg/Fe] sequences were forming stars at the same time. We find that the high-[Mg/Fe] stellar populations are only vertically extended for the oldest, most-metal poor and highest [Mg/Fe] stars. When comparing vertical velocity dispersion for the low- and high-[Mg/Fe] sequences, the high-[Mg/Fe] sequence has lower vertical velocity dispersion than the low-[Mg/Fe] sequence for stars of similar age. This means that identifying either group as thin or thick disk based on chemistry is misleading. The stars belonging to the high-[Mg/Fe] sequence have perigalacticons that originate in the inner disk, while the perigalacticons of stars on the low-[Mg/Fe] sequence are generally around the solar neighborhood. From the orbital properties of the stars, the high-[Mg/Fe] and low-[Mg/Fe] sequences are most likely a reflection of the chemical enrichment history of the inner and outer disk populations, respectively; radial mixing causes both populations to be observed in situ at the solar position. Based on these results, we emphasize that it is important to be clear in defining what populations are being referenced when using the terms thin and thick disk, and that ideally the term thick disk should be reserved for purely geometric definitions to avoid confusion and be consistent with definitions in external

The Evolution of Spiral Disks

Science.gov (United States)

Bershady, Matthew A.; Andersen, David R.

We report on aspects of an observational study to probe the mass assembly of large galaxy disks. In this contribution we focus on a new survey of integral-field Hα velocity-maps of nearby, face on disks. Preliminary results yield disk asymmetry amplitudes consistent with estimates based on the scatter in the local Tully-Fisher relation. We also show how the high quality of integral-field echelle spectroscopy enables determinations of kinematic inclinations to i ~20 °. This holds the promise that nearly-face-on galaxies can be included in the Tully-Fisher relation. Finally, we discuss the prospects for measuring dynamical asymmetries of distant galaxies.

The CDF Run II disk inventory manager

International Nuclear Information System (INIS)

Hubbard, Paul; Lammel, Stephan

2001-01-01

The Collider Detector at Fermilab (CDF) experiment records and analyses proton-antiproton interactions at a center-of-mass energy of 2 TeV. Run II of the Fermilab Tevatron started in April of this year. The duration of the run is expected to be over two years. One of the main data handling strategies of CDF for Run II is to hide all tape access from the user and to facilitate sharing of data and thus disk space. A disk inventory manager was designed and developed over the past years to keep track of the data on disk, to coordinate user access to the data, and to stage data back from tape to disk as needed. The CDF Run II disk inventory manager consists of a server process, a user and administrator command line interfaces, and a library with the routines of the client API. Data are managed in filesets which are groups of one or more files. The system keeps track of user access to the filesets and attempts to keep frequently accessed data on disk. Data that are not on disk are automatically staged back from tape as needed. For CDF the main staging method is based on the mt-tools package as tapes are written according to the ANSI standard

The Stability of Galaxy Disks

NARCIS (Netherlands)

Westfall, K. B.; Andersen, D. R.; Bershady, M. A.; Martinsson, T. P. K.; Swaters, R. A.; Verheijen, M. A. W.; Seigar, M.S.; Treuthardt, P.

2014-01-01

We calculate the stellar surface mass density (Σ*) and two-component (gas+stars) disk stability (QRW) for 25 late-type galaxies from the DiskMass Survey. These calculations are based on fits of a dynamical model to our ionized-gas and stellar kinematic data performed using a Markov Chain Monte Carlo

Hydraulic jumps in ''viscous'' accretion disks

International Nuclear Information System (INIS)

Michel, F.C.

1984-01-01

We propose that the dissipative process necessary for rapid accretion disk evolution is driven by hydraulic jump waves on the surface of the disk. These waves are excited by the asymmetric nature of the central rotator (e.g., neutron star magnetosphere) and spiral out into the disk to form a pattern corotating with the central object. Disk matter in turn is slowed slightly at each encounter with the jump and spirals inward. In this process, the disk is heated by true turbulence produced in the jumps. Additional effects, such as a systematic misalignment of the magnetic moment of the neutron star until it is nearly orthogonal, and systematic distortion of the magnetosphere in such a way as to form an even more asymmetric central ''paddle wheel'' may enhance the interaction with inflowing matter. The application to X-ray sources corresponds to the ''slow'' solutions of Ghosh and Lamb, and therefore to rms magnetic fields of about 4 x 10 10 gauss. Analogous phenomena have been proposed to act in the formation of galactic spiral structure

Chemical Evolution of a Protoplanetary Disk

Science.gov (United States)

Semenov, Dmitry A.

2011-12-01

In this paper we review recent progress in our understanding of the chemical evolution of protoplanetary disks. Current observational constraints and theoretical modeling on the chemical composition of gas and dust in these systems are presented. Strong variations of temperature, density, high-energy radiation intensities in these disks, both radially and vertically, result in a peculiar disk chemical structure, where a variety of processes are active. In hot, dilute and heavily irradiated atmosphere only the most photostable simple radicals and atoms and atomic ions exist, formed by gas-phase processes. Beneath the atmosphere a partly UV-shielded, warm molecular layer is located, where high-energy radiation drives rich ion-molecule and radical-radical chemistry, both in the gas phase and on dust surfaces. In a cold, dense, dark disk midplane many molecules are frozen out, forming thick icy mantles where surface chemistry is active and where complex polyatomic (organic) species are synthesized. Dynamical processes affect disk chemical composition by enriching it in abundances of complex species produced via slow surface processes, which will become detectable with ALMA.

Disk Evolution and the Fate of Water

Science.gov (United States)

Hartmann, Lee; Ciesla, Fred; Gressel, Oliver; Alexander, Richard

2017-10-01

We review the general theoretical concepts and observational constraints on the distribution and evolution of water vapor and ice in protoplanetary disks, with a focus on the Solar System. Water is expected to freeze out at distances greater than 1-3 AU from solar-type central stars; more precise estimates are difficult to obtain due to uncertainties in the complex processes involved in disk evolution, including dust growth, settling, and radial drift, and the level of turbulence and viscous dissipation within disks. Interferometric observations are now providing constraints on the positions of CO snow lines, but extrapolation to the unresolved regions where water ice sublimates will require much better theoretical understanding of mass and angular momentum transport in disks as well as more refined comparison of observations with sophisticated disk models.

A Pulsar and a Disk

Science.gov (United States)

Kohler, Susanna

2016-07-01

Recent, unusual X-ray observations from our galactic neighbor, the Small Magellanic Cloud, have led to an interesting model for SXP 214, a pulsar in a binary star system.Artists illustration of the magnetic field lines of a pulsar, a highly magnetized, rotating neutron star. [NASA]An Intriguing BinaryAn X-ray pulsar is a magnetized, rotating neutron star in a binary system with a stellar companion. Material is fed from the companion onto the neutron star, channeled by the objects magnetic fields onto a hotspot thats millions of degrees. This hotspot rotating past our line of sight is what produces the pulsations that we observe from X-ray pulsars.Located in the Small Magellanic Cloud, SXP 214 is a transient X-ray pulsar in a binary with a Be-type star. This star is spinning so quickly that material is thrown off of it to form a circumstellar disk.Recently, a team of authors led by JaeSub Hong (Harvard-Smithsonian Center for Astrophysics) have presented new Chandra X-ray observations of SXP 214, tracking it for 50 ks (~14 hours) in January 2013. These observations reveal some very unexpected behavior for this pulsar.X-ray PuzzleThe energy distribution of the X-ray emission from SXP 214 over time. Dark shades or blue colors indicate high counts, and light shades or yellow colors indicate low counts. Lower-energy X-ray emission appeared only later, after about 20 ks. [Hong et al. 2016]Three interesting pieces of information came from the Chandra observations:SXP 214s rotation period was measured to be 211.5 s an increase in the spin rate since the discovery measurement of a 214-second period. Pulsars usually spin down as they lose angular momentum over time so what caused this one to spin up?Its overall X-ray luminosity steadily increased over the 50 ks of observations.Its spectrum became gradually softer (lower energy) over time; in the first 20 ks, the spectrum only consisted of hard X-ray photons above 3 keV, but after 20 ks, softer X-ray photons below 2 ke

LUNAR ACCRETION FROM A ROCHE-INTERIOR FLUID DISK

Energy Technology Data Exchange (ETDEWEB)

Salmon, Julien; Canup, Robin M., E-mail: julien@boulder.swri.edu, E-mail: robin@boulder.swri.edu [Department of Space Studies, Southwest Research Institute, 1050 Walnut Street, Suite 300, Boulder, CO 80302 (United States)

2012-11-20

We use a hybrid numerical approach to simulate the formation of the Moon from an impact-generated disk, consisting of a fluid model for the disk inside the Roche limit and an N-body code to describe accretion outside the Roche limit. As the inner disk spreads due to a thermally regulated viscosity, material is delivered across the Roche limit and accretes into moonlets that are added to the N-body simulation. Contrary to an accretion timescale of a few months obtained with prior pure N-body codes, here the final stage of the Moon's growth is controlled by the slow spreading of the inner disk, resulting in a total lunar accretion timescale of {approx}10{sup 2} years. It has been proposed that the inner disk may compositionally equilibrate with the Earth through diffusive mixing, which offers a potential explanation for the identical oxygen isotope compositions of the Earth and Moon. However, the mass fraction of the final Moon that is derived from the inner disk is limited by resonant torques between the disk and exterior growing moons. For initial disks containing <2.5 lunar masses (M{sub Last-Quarter-Moon }), we find that a final Moon with mass > 0.8 M{sub Last-Quarter-Moon} contains {<=}60% material derived from the inner disk, with this material preferentially delivered to the Moon at the end of its accretion.

Stratified Simulations of Collisionless Accretion Disks

Energy Technology Data Exchange (ETDEWEB)

Hirabayashi, Kota; Hoshino, Masahiro, E-mail: hirabayashi-k@eps.s.u-tokyo.ac.jp [Department of Earth and Planetary Science, The University of Tokyo, Tokyo, 113-0033 (Japan)

2017-06-10

This paper presents a series of stratified-shearing-box simulations of collisionless accretion disks in the recently developed framework of kinetic magnetohydrodynamics (MHD), which can handle finite non-gyrotropy of a pressure tensor. Although a fully kinetic simulation predicted a more efficient angular-momentum transport in collisionless disks than in the standard MHD regime, the enhanced transport has not been observed in past kinetic-MHD approaches to gyrotropic pressure anisotropy. For the purpose of investigating this missing link between the fully kinetic and MHD treatments, this paper explores the role of non-gyrotropic pressure and makes the first attempt to incorporate certain collisionless effects into disk-scale, stratified disk simulations. When the timescale of gyrotropization was longer than, or comparable to, the disk-rotation frequency of the orbit, we found that the finite non-gyrotropy selectively remaining in the vicinity of current sheets contributes to suppressing magnetic reconnection in the shearing-box system. This leads to increases both in the saturated amplitude of the MHD turbulence driven by magnetorotational instabilities and in the resultant efficiency of angular-momentum transport. Our results seem to favor the fast advection of magnetic fields toward the rotation axis of a central object, which is required to launch an ultra-relativistic jet from a black hole accretion system in, for example, a magnetically arrested disk state.

Noise characteristics of barium ferrite particulate rigid disks

Science.gov (United States)

Kodama, Naoki; Inoue, Hitoshi; Spratt, Geoffrey; Uesaka, Yasutaro; Katsumoto, Masayuki

1991-04-01

This paper discusses the relationship between the noise characteristics and magnetic properties of longitudinal barium ferrite (Ba-F) rigid disks with different switching field distributions (SFD). The magnetomotive force dependencies of reverse dc-erase (RDC) noise are measured and compared with SFD values. Coated disks with acicular magnetic particles have dips and thin-film disks peaks in the RDC. In Ba-F disks, both cases are observed depending on the SFD values, though the depths or heights of the RDC noise are much smaller than those of coated disks with acicular particles or thin-film disks. Disks with small SFD values have peaks, and disks with large SFD values have dips. In order to find the relationship between noise properties and magnetic properties, interparticle interactions in Ba-F disks are investigated. Reverse dc remanence Id(H) and ac-demagnetized isothermal remanence Ir(H) are measured. Both are normalized by the saturation remanence. The deviation from the noninteracting system, ΔM = Id(H) - [1ΔM=Id(H)-[1- 2Ir(H)] and an interaction field factor (IFF) given by (H'r - Hr)/Hc, are derived from these remanent properties. Here, H'r is the field corresponding to 50% of the remanent magnetization, Hr is remanence coercivity. In Ba-F disks, ΔM shows positive interactions, and the peak heights of ΔM increase and IFF decrease with decreasing SFD values. Positive interactions between Ba-F particles seem to be caused by particle stacking. Therefore, particle stacking results in small SFD values and peak-type RDC noise.

THE LONG-TERM EVOLUTION OF PHOTOEVAPORATING PROTOPLANETARY DISKS

Energy Technology Data Exchange (ETDEWEB)

Bae, Jaehan; Hartmann, Lee [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48105 (United States); Zhu Zhaohuan [Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Peyton Hall, Princeton, NJ 08544 (United States); Gammie, Charles, E-mail: jaehbae@umich.edu, E-mail: lhartm@umich.edu, E-mail: zhuzh@astro.princeton.edu, E-mail: gammie@illinois.edu [Department of Astronomy, University of Illinois Urbana-Champaign, 1002 W. Green Street, Urbana, IL 61801 (United States)

2013-09-01

We perform calculations of our one-dimensional, two-zone disk model to study the long-term evolution of the circumstellar disk. In particular, we adopt published photoevaporation prescriptions and examine whether the photoevaporative loss alone, coupled with a range of initial angular momenta of the protostellar cloud, can explain the observed decline of the frequency of optically thick dusty disks with increasing age. In the parameter space we explore, disks have accreting and/or non-accreting transitional phases lasting for {approx}< 20% of their lifetime, which is in reasonable agreement with observed statistics. Assuming that photoevaporation controls disk clearing, we find that the initial angular momentum distribution of clouds needs to be weighted in favor of slowly rotating protostellar cloud cores. Again, assuming inner disk dispersal by photoevaporation, we conjecture that this skewed angular momentum distribution is a result of fragmentation into binary or multiple stellar systems in rapidly rotating cores. Accreting and non-accreting transitional disks show different evolutionary paths on the M-dot-R{sub wall} plane, which possibly explains the different observed properties between the two populations. However, we further find that scaling the photoevaporation rates downward by a factor of 10 makes it difficult to clear the disks on the observed timescales, showing that the precise value of the photoevaporative loss is crucial to setting the clearing times. While our results apply only to pure photoevaporative loss (plus disk accretion), there may be implications for models in which planets clear disks preferentially at radii of the order of 10 AU.

Three-body correlations and conditional forces in suspensions of active hard disks

Science.gov (United States)

Härtel, Andreas; Richard, David; Speck, Thomas

2018-01-01

Self-propelled Brownian particles show rich out-of-equilibrium physics, for instance, the motility-induced phase separation (MIPS). While decades of studying the structure of liquids have established a deep understanding of passive systems, not much is known about correlations in active suspensions. In this work we derive an approximate analytic theory for three-body correlations and forces in systems of active Brownian disks starting from the many-body Smoluchowski equation. We use our theory to predict the conditional forces that act on a tagged particle and their dependence on the propulsion speed of self-propelled disks. We identify preferred directions of these forces in relation to the direction of propulsion and the positions of the surrounding particles. We further relate our theory to the effective swimming speed of the active disks, which is relevant for the physics of MIPS. To test and validate our theory, we additionally run particle-resolved computer simulations, for which we explicitly calculate the three-body forces. In this context, we discuss the modeling of active Brownian swimmers with nearly hard interaction potentials. We find very good agreement between our simulations and numerical solutions of our theory, especially for the nonequilibrium pair-distribution function. For our analytical results, we carefully discuss their range of validity in the context of the different levels of approximation we applied. This discussion allows us to study the individual contribution of particles to three-body forces and to the emerging structure. Thus, our work sheds light on the collective behavior, provides the basis for further studies of correlations in active suspensions, and makes a step towards an emerging liquid state theory.

RADIALLY MAGNETIZED PROTOPLANETARY DISK: VERTICAL PROFILE

Energy Technology Data Exchange (ETDEWEB)

Russo, Matthew [Department of Physics, University of Toronto, 60 St. George St., Toronto, ON M5S 1A7 (Canada); Thompson, Christopher [Canadian Institute for Theoretical Astrophysics, 60 St. George St., Toronto, ON M5S 3H8 (Canada)

2015-11-10

This paper studies the response of a thin accretion disk to an external radial magnetic field. Our focus is on protoplanetary disks (PPDs), which are exposed during their later evolution to an intense, magnetized wind from the central star. A radial magnetic field is mixed into a thin surface layer, wound up by the disk shear, and pushed downward by a combination of turbulent mixing and ambipolar and ohmic drift. The toroidal field reaches much greater strengths than the seed vertical field that is usually invoked in PPD models, even becoming superthermal. Linear stability analysis indicates that the disk experiences the magnetorotational instability (MRI) at a higher magnetization than a vertically magnetized disk when both the effects of ambipolar and Hall drift are taken into account. Steady vertical profiles of density and magnetic field are obtained at several radii between 0.06 and 1 AU in response to a wind magnetic field B{sub r} ∼ (10{sup −4}–10{sup −2})(r/ AU){sup −2} G. Careful attention is given to the radial and vertical ionization structure resulting from irradiation by stellar X-rays. The disk is more strongly magnetized closer to the star, where it can support a higher rate of mass transfer. As a result, the inner ∼1 AU of a PPD is found to evolve toward lower surface density. Mass transfer rates around 10{sup −8} M{sub ⊙} yr{sup −1} are obtained under conservative assumptions about the MRI-generated stress. The evolution of the disk and the implications for planet migration are investigated in the accompanying paper.

Can disk be removed in a disk-and-washer structure

International Nuclear Information System (INIS)

Inagaki, Shigemi.

1981-06-01

A modified disk-and-washer structure, so to speak a coaxial coupled cavity structure, is proposed. It has not protrusions called disks at the inner surface of the cylinder. The thickness of the washer outer rim increases so much that it rather looks like a chain of accelerating cavities having slit around the outermost wall and through the slit they are coupled in a cylindrical cavity. SUPERFISH calculations show that both accelerating and coupling mode can be made confluent** in π-mode* operation and that the effective shunt impedance obtained under certain condition is 27 Mohm/m which is 10% less than that of KEK PF single cavity or scaled LASL side-coupled cavity. (author)

Composite polymer: Glass edge cladding for laser disks

Science.gov (United States)

Powell, H.T.; Wolfe, C.A.; Campbell, J.H.; Murray, J.E.; Riley, M.O.; Lyon, R.E.; Jessop, E.S.

1987-11-02

Large neodymium glass laser disks for disk amplifiers such as those used in the Nova laser require an edge cladding which absorbs at 1 micrometer. This cladding prevents edge reflections from causing parasitic oscillations which would otherwise deplete the gain. Nova now utilizes volume-absorbing monolithic-glass claddings which are fused at high temperature to the disks. These perform quite well but are expensive to produce. Absorbing glass strips are adhesively bonded to the edges of polygonal disks using a bonding agent whose index of refraction matches that of both the laser and absorbing glass. Optical finishing occurs after the strips are attached. Laser disks constructed with such claddings have shown identical gain performance to the previous Nova disks and have been tested for hundreds of shots without significant degradation. 18 figs.

Composite polymer-glass edge cladding for laser disks

Science.gov (United States)

Powell, Howard T.; Riley, Michael O.; Wolfe, Charles R.; Lyon, Richard E.; Campbell, John H.; Jessop, Edward S.; Murray, James E.

1989-01-01

Large neodymium glass laser disks for disk amplifiers such as those used in the Nova laser require an edge cladding which absorbs at 1 micrometer. This cladding prevents edge reflections from causing parasitic oscillations which would otherwise deplete the gain. Nova now utilizes volume-absorbing monolithic-glass claddings which are fused at high temperature to the disks. These perform quite well but are expensive to produce. Absorbing glass strips are adhesively bonded to the edges of polygonal disks using a bonding agent whose index of refraction matches that of both the laser and absorbing glass. Optical finishing occurs after the strips are attached. Laser disks constructed with such claddings have shown identical gain performance to the previous Nova disks and have been tested for hundreds of shots without significant degradation.

A 29-Year-Old Harken Disk Mitral Valve

Science.gov (United States)

Hsi, David H.; Ryan, Gerald F.; Taft, Janice; Arnone, Thomas J.

2003-01-01

An 81-year-old woman was evaluated for prosthetic mitral valve function. She had received a Harken disk mitral valve 29 years earlier due to severe mitral valve disease. This particular valve prosthesis is known for premature disk edge wear and erosion. The patient's 2-dimensional Doppler echocardiogram showed the distinctive appearance of a disk mitral valve prosthesis. Color Doppler in diastole showed a unique crown appearance, with initial flow acceleration around the disk followed by convergence to laminar flow in the left ventricle. Cineradiographic imaging revealed normal valve function and minimal disk erosion. We believe this to be the longest reported follow-up of a surviving patient with a rare Harken disk valve. We present images with unique echocardiographic and cineangiographic features. (Tex Heart Inst J 2003;30:319–21) PMID:14677746

PROTOPLANETARY DISK RESONANCES AND TYPE I MIGRATION

International Nuclear Information System (INIS)

Tsang, David

2011-01-01

Waves reflected by the inner edge of a protoplanetary disk are shown to significantly modify Type I migration, even allowing the trapping of planets near the inner disk edge for small planets in a range of disk parameters. This may inform the distribution of planets close to their central stars, as observed recently by the Kepler mission.

Chemical constraints on the formation of the Galactic thick disk

Directory of Open Access Journals (Sweden)

Feltzing S.

2012-02-01

Full Text Available We highlight some results from our detailed abundance analysis study of 703 kinematically selected F and G dwarf stars in the solar neighbourhood. The analysis is based on spectra of high-resolution (R = 45000 to 110 000 and high signal-to-noise (S/N ≈ 150 to 300. The main findings include: (1 at a given metallicity, the thick disk abundance trends are more α-enhanced than those of the thin disk; (2 the metal-rich limit of the thick disk reaches at least solar metallicities; (3 the metal-poor limit of the thin disk is around [Fe/H] ≈−0.8; (4 the thick disk shows an age-metallicity gradient; (5 the thin disk does not show an age-metallicity gradient; (6 the most metal-rich thick disk stars at [Fe/H] ≈ 0 are significantly older than the most metal-poor thin disk stars at [Fe/H] ≈−0.7; (7 based on our elemental abundances we find that kinematical criteria produce thin and thick disk stellar samples that are biased in the sense that stars from the low-velocity tail of the thick disk are classified as thin disk stars, and stars from the high-velocity tail of the thin disk are classified as thick disk stars; (8 age criteria appears to produce thin and thick disk stellar samples with less contamination.

Premixed direct injection disk

Science.gov (United States)

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.

Vibration of imperfect rotating disk

Czech Academy of Sciences Publication Activity Database

Půst, Ladislav; Pešek, Luděk

2011-01-01

Roč. 5, č. 2 (2011), s. 205-216 ISSN 1802-680X R&D Projects: GA ČR GA101/09/1166 Institutional research plan: CEZ:AV0Z20760514 Keywords : bladed disk * imperfect disk * travelling waves Subject RIV: BI - Acoustics http://www.kme.zcu.cz/acm/index.php/acm/article/view/86

GIANT HERBIG-HARO FLOWS IN L1228: A SECOND LOOK

International Nuclear Information System (INIS)

Devine, D.; Chiriboga, D.; Smart, K.; Bally, J.

2009-01-01

We present second epoch narrowband Hα and [S II] images of the giant Herbig-Haro flows HH199 and HH200 in the L1228 molecular cloud. Proper motions for several members of the HH200 flow were determined by comparing the new images to similar narrowband images taken 13 years earlier. Based on our measurements, the HH200 flow is inclined by 15 deg. to the plane of the sky and has a steady, fixed outflow axis with P.A. = 49 deg. There is a general nonlinear decline in the proper motions with increasing distance from the source, and it appears that successive eruption episodes have cleared out a relatively free channel through the L1228 cloud. The bright knot HH200B6 is located at the end of the channel along the edge of L1228, and appears to be tracing the location where the outflow erupts from the cloud. We did not detect any proper motions for HH200B6, and suggest that it is the plug of material that has been bored out by the cumulative effects of numerous eruptions along a steady outflow axis. The proper motions combined with the spacing of the HH200 knots along the flow axis are consistent with a velocity variable outflow, which erupts periodically on timescales of the order of 600 years. The relatively small size of the knots combined with the large proper motions and derived bow-shock speeds would seem to rule out the presence of a less collimated wind component. We also discuss the HH199 flow, which is radically different from HH200. The members of the HH199 flow exhibited large changes in the morphology and emission, and were not suitable for determining proper motions. The HH200 and HH199 flows appear to be the opposite ends of the spectrum of giant HH flows.

PLANETESIMAL AND PROTOPLANET DYNAMICS IN A TURBULENT PROTOPLANETARY DISK: IDEAL STRATIFIED DISKS

International Nuclear Information System (INIS)

Yang, Chao-Chin; Mac Low, Mordecai-Mark; Menou, Kristen

2012-01-01

Due to the gravitational influence of density fluctuations driven by magneto-rotational instability in the gas disk, planetesimals and protoplanets undergo diffusive radial migration as well as changes in other orbital properties. The magnitude of the effect on particle orbits can have important consequences for planet formation scenarios. We use the local-shearing-box approximation to simulate an ideal, isothermal, magnetized gas disk with vertical density stratification and simultaneously evolve numerous massless particles moving under the gravitational field of the gas and the host star. We measure the evolution of the particle orbital properties, including mean radius, eccentricity, inclination, and velocity dispersion, and its dependence on the disk properties and the particle initial conditions. Although the results converge with resolution for fixed box dimensions, we find the response of the particles to the gravity of the turbulent gas correlates with the horizontal box size, up to 16 disk scale heights. This correlation indicates that caution should be exercised when interpreting local-shearing-box models involving gravitational physics of magneto-rotational turbulence. Based on heuristic arguments, nevertheless, the criterion L h /R ∼ O(1), where L h is the horizontal box size and R is the distance to the host star, is proposed to possibly circumvent this conundrum. If this criterion holds, we can still conclude that magneto-rotational turbulence seems likely to be ineffective at driving either diffusive migration or collisional erosion under most circumstances.

The Vela pulsar with an active fallback disk

Energy Technology Data Exchange (ETDEWEB)

Özsükan, Gökçe; Ekşi, K. Yavuz [Faculty of Science and Letters, Department of Physics, İstanbul Technical University, Maslak 34469, İstanbul (Turkey); Hambaryan, Valeri; Neuhäuser, Ralph; Hohle, Markus M.; Ginski, Christian [Astrophysikalisches Institut und Universitäts-Sternwarte, Universität Jena, Schillergäßchen 2-3, 07745 Jena (Germany); Werner, Klaus, E-mail: eksi@itu.edu.tr [Institute for Astronomy and Astrophysics, Kepler Center for Astro and Particle Physics, Eberhard Karls University, Sand 1, D-72076 Tübingen (Germany)

2014-11-20

Fallback disks are expected to form around young neutron stars. The presence of these disks can be revealed by their blackbody spectrum in the infrared, optical, and UV bands. We present a re-reduction of the archival optical and infrared data of the Vela pulsar, together with the existing infrared and UV spectrum of Vela, and model their unpulsed components with the blackbody spectrum of a supernova debris disk. We invoke the quiescent disk solution of Sunyaev and Shakura for the description of the disk in the propeller stage and find the inner radius of the disk to be inside the light cylinder radius. We perform a high-resolution X-ray analysis with XMM-Newton and find a narrow absorption feature at 0.57 keV that can be interpreted as the K {sub α} line of He-like oxygen (O VII). The strength of the line indicates an element over-abundance in our line of sight exceeding the amounts that would be expected from interstellar medium. The spectral feature may originate from the pulsar wind nebula and may be partly caused by the reprocessed X-ray radiation by the fallback disk. We discuss the lower-than-three braking index of Vela as partially due to the contribution of the propeller torques. Our results suggest that the pulsar mechanism can work simultaneously with the propeller processes and that the debris disks can survive the radiation pressure for at least ∼10{sup 4} yr. As Vela is a relatively close object, and a prototypical pulsar, the presence of a disk, if confirmed, may indicate the ubiquity of debris disks around young neutron stars.

Sinuous oscillations and steady warps of polytropic disks

International Nuclear Information System (INIS)

Balmforth, N.J.; Spiegel, E.A.

1995-05-01

In an asymptotic development of the equations governing the equilibria and linear stability of rapidly rotating polytropes we employed the slender aspect of these objects to reduce the three-dimensional partial differential equations to a somewhat simpler, ordinary integro-differential form. The earlier calculations dealt with isolated objects that were in centrifugal balance, that is the centrifugal acceleration of the configuration was balanced largely by self gravity with small contributions from the pressure gradient. Another interesting situation is that in which the polytrope rotates subject to externally imposed gravitational fields. In astrophysics, this is common in the theory of galactic dynamics because disks are unlikely to be isolated objects. The dark halos associated with disks also provide one possible explanation of the apparent warping of many galaxies. If the axis of the highly flattened disk is not aligned with that of the much less flattened halo, then the resultant torque of the halo gravity on the disk might provide a nonaxisymmetric distortion or disk warp. Motivated by these possibilities we shall here build models of polytropic disks of small but finite thickness which are subjected to prescribed, external gravitational fields. First we estimate how a symmetrical potential distorts the structure of the disk, then we examine its sinuous oscillations to confirm that they freely decay, hence suggesting that a warp must be externally forced. Finally, we consider steady warps of the disk plane when the axis of the disk does not coincide with that of the halo

Vibration and flutter of mistuned bladed-disk assemblies

Science.gov (United States)

Kaza, K. R. V.; Kielb, R. E.

1984-01-01

An analytical model for investigating vibration and flutter of mistuned bladed disk assemblies is presented. This model accounts for elastic, inertial and aerodynamic coupling between bending and torsional motions of each individual blade, elastic and inertial couplings between the blades and the disk, and aerodynamic coupling among the blades. The disk was modeled as a circular plate with constant thickness and each blade was represented by a twisted, slender, straight, nonuniform, elastic beam with a symmetric cross section. The elastic axis, inertia axis, and the tension axis were taken to be noncoincident and the structural warping of the section was explicitly considered. The blade aerodynamic loading in the subsonic and supersonic flow regimes was obtained from two-dimensional unsteady, cascade theories. All the possible standing wave modes of the disk and traveling wave modes of the blades were included. The equations of motion were derived by using the energy method in conjunction with the assumed mode shapes for the disk and the blades. Continuities of displacement and slope at the blade-disk junction were maintained. The equations were solved to investigate the effects of blade-disk coupling and blade frequency mistuning on vibration and flutter. Results showed that the flexibility of practical disks such as those used for current generation turbofans did not have a significant influence on either the tuned or mistuned flutter characteristics. However, the disk flexibility may have a strong influence on some of the system frequencies and on forced response.

Thin accretion disks in stationary axisymmetric wormhole spacetimes

International Nuclear Information System (INIS)

Harko, Tiberiu; Kovacs, Zoltan; Lobo, Francisco S. N.

2009-01-01

In this paper, we study the physical properties and the equilibrium thermal radiation emission characteristics of matter forming thin accretion disks in stationary axially symmetric wormhole spacetimes. The thin disk models are constructed by taking different values of the wormhole's angular velocity, and the time averaged energy flux, the disk temperature, and the emission spectra of the accretion disks are obtained. Comparing the mass accretion in a rotating wormhole geometry with the one of a Kerr black hole, we verify that the intensity of the flux emerging from the disk surface is greater for wormholes than for rotating black holes with the same geometrical mass and accretion rate. We also present the conversion efficiency of the accreting mass into radiation, and show that the rotating wormholes provide a much more efficient engine for the transformation of the accreting mass into radiation than the Kerr black holes. Therefore specific signatures appear in the electromagnetic spectrum of thin disks around rotating wormholes, thus leading to the possibility of distinguishing wormhole geometries by using astrophysical observations of the emission spectra from accretion disks.

THE LONG-TERM EVOLUTION OF PHOTOEVAPORATING PROTOPLANETARY DISKS

International Nuclear Information System (INIS)

Bae, Jaehan; Hartmann, Lee; Zhu Zhaohuan; Gammie, Charles

2013-01-01

We perform calculations of our one-dimensional, two-zone disk model to study the long-term evolution of the circumstellar disk. In particular, we adopt published photoevaporation prescriptions and examine whether the photoevaporative loss alone, coupled with a range of initial angular momenta of the protostellar cloud, can explain the observed decline of the frequency of optically thick dusty disks with increasing age. In the parameter space we explore, disks have accreting and/or non-accreting transitional phases lasting for ∼ wall plane, which possibly explains the different observed properties between the two populations. However, we further find that scaling the photoevaporation rates downward by a factor of 10 makes it difficult to clear the disks on the observed timescales, showing that the precise value of the photoevaporative loss is crucial to setting the clearing times. While our results apply only to pure photoevaporative loss (plus disk accretion), there may be implications for models in which planets clear disks preferentially at radii of the order of 10 AU

Probing Disk Stratification by Combining X-ray and Disk Inclination Data for Taurus-Auriga

Science.gov (United States)

Arraki, Kenza S.; Daly, B.; Harding, M.; McCleary, J.; Cox, A. W.; Grady, C. A.; Woodgate, B. E.; Hamaguchi, K.; Wisniewski, J. P.; Brakken-Thal, S.; Hilton, G.; Bonfield, D.; Williger, G. M.

2010-01-01

Photoelectric neutral Hydrogen absorption, N(H), is a probe of the gas and dust column towards the star. Kastner et al. (2005) found a correlation between N(H) and proplyd aspect ratio in the Orion nebula cluster. We extend this study to Taurus-Auriga by combining publicly available N(H) data from the XMM-Newton Extended Survey of the Taurus molecular cloud (XEST), with published disk inclination data obtained from HST coronagraphic imagery and mm interferometry. Additional inclinations were derived from jet proper motion and radial velocity data obtained from archival HST imagery and the Apache Point Observatory 3.5m telescope's Goddard Fabry-Perot and DIS long-slit spectrograph. Both N(H) and extinction have linear relations with system inclination, where the extinction has a smaller slope than the N(H) trend. Correlations with system inclination demonstrate that the bulk of both N(H) and extinction arise in the disk rather than in remnant envelopes, nearby molecular cloud material, or foreground material. The deficit in extinction compared with predictions for ISM-like gas to dust ratios is consistent with grain growth and settling toward the disk midplane and stratification in disks occurring by 2 Myr. However, the disks remain gas-rich, indicating that giant planet formation is still feasible. We gratefully acknowledge the support of the NASA Motivating Undergraduates in Science and Technology (MUST) Project and of NASA's APRA program under WBS#399131.02.06.02.32. A grant of Director's Discretionary Time funded observing time at the Apache Point Observatory.

Magnetic hard disks for audio-visual use; AV yo jiki disk baitai

Energy Technology Data Exchange (ETDEWEB)

Tei, Y.; Sakaguchi, S.; Uwazumi, H. [Fuji Electric Co. Ltd., Tokyo (Japan)

1999-11-10

Computers, consumer, and communications are converging and fusing. The key device in homes in the near future will be an audiovisual hard disk drive (AV-HDD). The reason is that there is no other AV cash memory with high capacity, high speed, and a low price than the HDD. Fuji Electric has early started developing an AV magnetic hard disk, a core-functional element of the AV-HDD, to take the initiative in the market. This paper describes the state of plastic medium development, which is regarded as a next-generation strategic commodity. (author)

Accretion disks in active galactic nuclei

International Nuclear Information System (INIS)

Shields, G.A.

1989-01-01

Active galactic nuclei (AGN) have taunted astrophysicists for a quarter century. How do these objects produce huge luminosities---in some cases, far outshining our galaxy---from a region perhaps no larger than the solar system? Accretion onto supermassive black holes has been widely considered the best buy in theories of AGN. Much work has gone into accretion disk theory, searches for black holes in galactic nuclei, and observational tests. These efforts have not proved the disk model, but there is progress. Evidence for black holes in the nuclei of nearby galaxies is provided by observations of stellar velocities, and radiation from the disk's hot surface may be observed in the ultraviolet (UV) and neighboring spectral bands. In the review, the author describe some of the recent work on accretion disks in AGN, with an emphasis on points of contact between theory and observation

First Large-scale Herbig-Haro Jet Driven by a Proto-brown Dwarf

Science.gov (United States)

Riaz, B.; Briceño, C.; Whelan, E. T.; Heathcote, S.

2017-07-01

We report the discovery of a new Herbig-Haro jet, HH 1165, in SOAR narrow-band imaging of the vicinity of the σ Orionis cluster. HH 1165 shows a spectacular extended and collimated spatial structure, with a projected length of 0.26 pc, a bent C-shaped morphology, multiple knots, and fragmented bow shocks at the apparent ends of the flow. The Hα image shows a bright halo with a clumpy distribution of material seen around the driving source, and curved reflection nebulosity tracing the outflow cavities. The driving source of HH 1165 is a Class I proto-brown dwarf, Mayrit 1701117 (M1701117), with a total (dust+gas) mass of ˜36 M Jup and a bolometric luminosity of ˜0.1 L ⊙. High-resolution VLT/UVES spectra of M1701117 show a wealth of emission lines indicative of strong outflow and accretion activity. SOAR/Goodman low-resolution spectra along the jet axis show an asymmetrical morphology for HH 1165. We find a puzzling picture wherein the northwest part exhibits a classical HH jet running into a pre-dominantly neutral medium, while the southern part resembles an externally irradiated jet. The C-shaped bending in HH 1165 may be produced by the combined effects from the massive stars in the ionization front to the east, the σ Orionis core to the west, and the close proximity to the B2-type star HR 1950. HH 1165 shows all of the signatures to be considered as a scaled-down version of parsec-length HH jets, and can be termed as the first sub-stellar analog of a protostellar HH jet system.

Continuum Reverberation Mapping of AGN Accretion Disks

Energy Technology Data Exchange (ETDEWEB)

Fausnaugh, Michael M. [Department of Astronomy, Ohio State University, Columbus, OH (United States); MIT Kavli Institute for Astrophysics and Space Research, Cambridge, MA (United States); Peterson, Bradley M. [Department of Astronomy, Ohio State University, Columbus, OH (United States); Center for Cosmology and AstroParticle Physics, Ohio State University, Columbus, OH (United States); Space Telescope Science Institute, Baltimore, MD (United States); Starkey, David A. [SUPA Physics and Astronomy, University of St. Andrews, Scotland (United Kingdom); Department of Astronomy, University of Illinois at Urbana-Champaign, Urbana, IL (United States); Horne, Keith, E-mail: faus@mit.edu [SUPA Physics and Astronomy, University of St. Andrews, Scotland (United Kingdom); Collaboration: the AGN STORM Collaboration

2017-12-05

We show recent detections of inter-band continuum lags in three AGN (NGC 5548, NGC 2617, and MCG+08-11-011), which provide new constraints on the temperature profiles and absolute sizes of the accretion disks. We find lags larger than would be predicted for standard geometrically thin, optically thick accretion disks by factors of 2.3–3.3. For NGC 5548, the data span UV through optical/near-IR wavelengths, and we are able to discern a steeper temperature profile than the T ~ R{sup −3/4} expected for a standard thin disk. Using a physical model, we are also able to estimate the inclinations of the disks for two objects. These results are similar to those found from gravitational microlensing of strongly lensed quasars, and provide a complementary approach for investigating the accretion disk structure in local, low luminosity AGN.

Hydrodynamical winds from a geometrically thin disk

International Nuclear Information System (INIS)

Fukue, Jun

1989-01-01

Hydrodynamical winds emanating from the surface of a geometrically thin disk under the gravitational field of the central object are examined. The attention is focused on the transonic nature of the flow. For a given configuration of streamlines, the flow fields are divided into three regions: the inner region where the gas near the disk plane is gravitationally bound to form a corona; the intermediate wind region where multiple critical points appear and the gas flows out from the disk passing through critical points; and the outer region where the gas is unbound to escape to infinity without passing through critical points. This behavior of disk winds is due to the shape of the gravitational potential of the central object along the streamline and due to the energy source distribution at the flow base on the disk plane where the potential in finite. (author)

Free-fall dynamics of a pair of rigidly linked disks

Science.gov (United States)

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.

Spitzer IRS Spectroscopy of the 10 Myr-Old EF Cha Debris Disk: Evidence for Phyllosilicate-Rich Dust in the Terrestrial Zone

Science.gov (United States)

Currie, Thayne; Lisse, Carey M.; Sicillia-Aguilar, Aurora; Rieke, George H.; Su, Kate Y. L.

2011-01-01

We describe Spitzer IRS spectroscopic observations of the approx. 10 Myr-old star, EF Chao Compositional modeling of the spectra from 5 micron to 35 micron confirms that it is surrounded by a luminous debris disk with L(sub D)/L(sub *) approx. 10(exp -3), containing dust with temperatures between 225 K and 430 K characteristic of the terrestrial zone. The EF Cha spectrum shows evidence for many solid-state features, unlike most cold, low-luminosity debris disks but like some other 10-20 Myr-old luminous, warm debris disks (e.g. HD 113766A). The EF Cha debris disk is unusually rich in a species or combination of species whose emissivities resemble that of finely-powdered, laboratory-measured phyllosilicate species (talc, saponite, and smectite), which are likely produced by aqueous alteration of primordial anhydrous rocky materials. The dust and, by inference, the parent bodies of the debris also contain abundant amorphous silicates and metal sulfides, and possibly water ice. The dust's total olivine to pyroxene ratio of approx. 2 also provides evidence of aqueous alteration. The large mass volume of grains with sizes comparable to or below the radiation blow-out limit implies that planetesimals may be colliding at a rate high enough to yield the emitting dust but not so high as to devolatize the planetesimals via impact processing. Because phyllosilicates are produced by the interactions between anhydrous rock and warm, reactive water, EF Cha's disk is a likely signpost for water delivery to the terrestrial zone of a young planetary system.

On Hydromagnetic Stresses in Accretion Disk Boundary Layers

DEFF Research Database (Denmark)

Pessah, Martin Elias; Chan, Chi-kwan

2012-01-01

Detailed calculations of the physical structure of accretion disk boundary layers, and thus their inferred observational properties, rely on the assumption that angular momentum transport is opposite to the radial angular frequency gradient of the disk. The standard model for turbulent shear...... of efficient angular momentum transport in the inner disk regions. This suggests that the detailed structure of turbulent MHD accretion disk boundary layers could differ appreciably from those derived within the standard framework of turbulent shear viscosity...

Radial Transport and Meridional Circulation in Accretion Disks

Energy Technology Data Exchange (ETDEWEB)

Philippov, Alexander A. [Department of Astrophysical Sciences, Princeton University, Ivy Lane, Princeton, NJ 08540 (United States); Rafikov, Roman R., E-mail: sashaph@princeton.edu [Institute for Advanced Study, Einstein Drive, Princeton, NJ 08540 (United States)

2017-03-10

Radial transport of particles, elements and fluid driven by internal stresses in three-dimensional (3D) astrophysical accretion disks is an important phenomenon, potentially relevant for the outward dust transport in protoplanetary disks, origin of the refractory particles in comets, isotopic equilibration in the Earth–Moon system, etc. To gain better insight into these processes, we explore the dependence of meridional circulation in 3D disks with shear viscosity on their thermal stratification, and demonstrate a strong effect of the latter on the radial flow. Previous locally isothermal studies have normally found a pattern of the radial outflow near the midplane, switching to inflow higher up. Here we show, both analytically and numerically, that a flow that is inward at all altitudes is possible in disks with entropy and temperature steeply increasing with height. Such thermodynamic conditions may be typical in the optically thin, viscously heated accretion disks. Disks in which these conditions do not hold should feature radial outflow near the midplane, as long as their internal stress is provided by the shear viscosity. Our results can also be used for designing hydrodynamical disk simulations with a prescribed pattern of the meridional circulation.

THE NATURE OF TRANSITION CIRCUMSTELLAR DISKS. II. SOUTHERN MOLECULAR CLOUDS

Energy Technology Data Exchange (ETDEWEB)

Romero, Gisela A.; Schreiber, Matthias R.; Rebassa-Mansergas, Alberto [Departamento de Fisica y Astronomia, Universidad de Valparaiso, Valparaiso (Chile); Cieza, Lucas A. [Institute for Astronomy, University of Hawaii at Manoa, Honolulu, HI 96822 (United States); Merin, Bruno [Herschel Science Centre, ESAC (ESA), P.O. Box 78, 28691 Villanueva de la Canada, Madrid (Spain); Smith Castelli, Analia V. [Consejo Nacional de Investigaciones Cientificas y Tecnicas, Rivadavia 1917, C1033AAJ Buenos Aires (Argentina); Allen, Lori E. [Department of Astronomy, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721-0065 (United States); Morrell, Nidia [Las Campanas Observatory, Carnegie Observatories, Casilla 601, La Serena (Chile)

2012-04-10

Transition disk objects are pre-main-sequence stars with little or no near-IR excess and significant far-IR excess, implying inner opacity holes in their disks. Here we present a multifrequency study of transition disk candidates located in Lupus I, III, IV, V, VI, Corona Australis, and Scorpius. Complementing the information provided by Spitzer with adaptive optics (AO) imaging (NaCo, VLT), submillimeter photometry (APEX), and echelle spectroscopy (Magellan, Du Pont Telescopes), we estimate the multiplicity, disk mass, and accretion rate for each object in our sample in order to identify the mechanism potentially responsible for its inner hole. We find that our transition disks show a rich diversity in their spectral energy distribution morphology, have disk masses ranging from {approx}<1 to 10 M{sub JUP}, and accretion rates ranging from {approx}<10{sup -11} to 10{sup -7.7} M{sub Sun} yr{sup -1}. Of the 17 bona fide transition disks in our sample, three, nine, three, and two objects are consistent with giant planet formation, grain growth, photoevaporation, and debris disks, respectively. Two disks could be circumbinary, which offers tidal truncation as an alternative origin of the inner hole. We find the same heterogeneity of the transition disk population in Lupus III, IV, and Corona Australis as in our previous analysis of transition disks in Ophiuchus while all transition disk candidates selected in Lupus V, VI turned out to be contaminating background asymptotic giant branch stars. All transition disks classified as photoevaporating disks have small disk masses, which indicates that photoevaporation must be less efficient than predicted by most recent models. The three systems that are excellent candidates for harboring giant planets potentially represent invaluable laboratories to study planet formation with the Atacama Large Millimeter/Submillimeter Array.

THE NATURE OF TRANSITION CIRCUMSTELLAR DISKS. II. SOUTHERN MOLECULAR CLOUDS

International Nuclear Information System (INIS)

Romero, Gisela A.; Schreiber, Matthias R.; Rebassa-Mansergas, Alberto; Cieza, Lucas A.; Merín, Bruno; Smith Castelli, Analía V.; Allen, Lori E.; Morrell, Nidia

2012-01-01

Transition disk objects are pre-main-sequence stars with little or no near-IR excess and significant far-IR excess, implying inner opacity holes in their disks. Here we present a multifrequency study of transition disk candidates located in Lupus I, III, IV, V, VI, Corona Australis, and Scorpius. Complementing the information provided by Spitzer with adaptive optics (AO) imaging (NaCo, VLT), submillimeter photometry (APEX), and echelle spectroscopy (Magellan, Du Pont Telescopes), we estimate the multiplicity, disk mass, and accretion rate for each object in our sample in order to identify the mechanism potentially responsible for its inner hole. We find that our transition disks show a rich diversity in their spectral energy distribution morphology, have disk masses ranging from ∼ JUP , and accretion rates ranging from ∼ –11 to 10 –7.7 M ☉ yr –1 . Of the 17 bona fide transition disks in our sample, three, nine, three, and two objects are consistent with giant planet formation, grain growth, photoevaporation, and debris disks, respectively. Two disks could be circumbinary, which offers tidal truncation as an alternative origin of the inner hole. We find the same heterogeneity of the transition disk population in Lupus III, IV, and Corona Australis as in our previous analysis of transition disks in Ophiuchus while all transition disk candidates selected in Lupus V, VI turned out to be contaminating background asymptotic giant branch stars. All transition disks classified as photoevaporating disks have small disk masses, which indicates that photoevaporation must be less efficient than predicted by most recent models. The three systems that are excellent candidates for harboring giant planets potentially represent invaluable laboratories to study planet formation with the Atacama Large Millimeter/Submillimeter Array.

Theory of Disk Accretion onto Magnetic Stars

Directory of Open Access Journals (Sweden)

Lai Dong

2014-01-01

Full Text Available Disk accretion onto magnetic stars occurs in a variety of systems, including accreting neutron stars (with both high and low magnetic fields, white dwarfs, and protostars. We review some of the key physical processes in magnetosphere-disk interaction, highlighting the theoretical uncertainties. We also discuss some applications to the observations of accreting neutron star and protostellar systems, as well as possible connections to protoplanetary disks and exoplanets.

New models of general relativistic static thick disks

NARCIS (Netherlands)

Vogt, D.; Letelier, P.S.

2005-01-01

New families of exact general relativistic thick disks are constructed using the "displace, cut, fill, and reflect" method. A class of functions used to fill the disks is derived imposing conditions on the first and second derivatives to generate physically acceptable disks. The analysis of the

A WISE survey of circumstellar disks in Taurus

International Nuclear Information System (INIS)

Esplin, T. L.; Luhman, K. L.; Mamajek, E. E.

2014-01-01

We have compiled photometry at 3.4, 4.6, 12, and 22 μm from the all-sky survey performed by the Wide-field Infrared Survey Explorer (WISE) for all known members of the Taurus complex of dark clouds. Using these data and photometry from the Spitzer Space Telescope, we have identified members with infrared excess emission from circumstellar disks and have estimated the evolutionary stages of the detected disks, which include 31 new full disks and 16 new candidate transitional, evolved, evolved transitional, and debris disks. We have also used the WISE All-Sky Source Catalog to search for new disk-bearing members of Taurus based on their red infrared colors. Through optical and near-infrared spectroscopy, we have confirmed 26 new members with spectral types of M1-M7. The census of disk-bearing stars in Taurus should now be largely complete for spectral types earlier than ∼M8 (M ≳ 0.03 M ☉ ).

A WISE survey of circumstellar disks in Taurus

Energy Technology Data Exchange (ETDEWEB)

Esplin, T. L.; Luhman, K. L. [Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States); Mamajek, E. E., E-mail: taran.esplin@psu.edu [Department of Physics and Astronomy, The University of Rochester, Rochester, NY 14627 (United States)

2014-04-01

We have compiled photometry at 3.4, 4.6, 12, and 22 μm from the all-sky survey performed by the Wide-field Infrared Survey Explorer (WISE) for all known members of the Taurus complex of dark clouds. Using these data and photometry from the Spitzer Space Telescope, we have identified members with infrared excess emission from circumstellar disks and have estimated the evolutionary stages of the detected disks, which include 31 new full disks and 16 new candidate transitional, evolved, evolved transitional, and debris disks. We have also used the WISE All-Sky Source Catalog to search for new disk-bearing members of Taurus based on their red infrared colors. Through optical and near-infrared spectroscopy, we have confirmed 26 new members with spectral types of M1-M7. The census of disk-bearing stars in Taurus should now be largely complete for spectral types earlier than ∼M8 (M ≳ 0.03 M {sub ☉}).

Determination of elastic stresses in gas-turbine disks

Science.gov (United States)

Manson, S S

1947-01-01

A method is presented for the calculation of elastic stresses in symmetrical disks typical of those of a high-temperature gas turbine. The method is essentially a finite-difference solution of the equilibrium and compatibility equations for elastic stresses in a symmetrical disk. Account can be taken of point-to-point variations in disk thickness, in temperature, in elastic modulus, in coefficient of thermal expansion, in material density, and in Poisson's ratio. No numerical integration or trial-and-error procedures are involved and the computations can be performed in rapid and routine fashion by nontechnical computers with little engineering supervision. Checks on problems for which exact mathematical solutions are known indicate that the method yields results of high accuracy. Illustrative examples are presented to show the manner of treating solid disks, disks with central holes, and disks constructed either of a single material or two or more welded materials. The effect of shrink fitting is taken into account by a very simple device.

Analytical solutions to orthotropic variable thickness disk problems

Directory of Open Access Journals (Sweden)

Ahmet N. ERASLAN

2016-02-01

Full Text Available An analytical model is developed to estimate the mechanical response of nonisothermal, orthotropic, variable thickness disks under a variety of boundary conditions. Combining basic mechanical equations of disk geometry with the equations of orthotropic material, the elastic equation of the disk is obtained. This equation is transformed into a standard hypergeometric differential equation by means of a suitable transformation. An analytical solution is then obtained in terms of hypergeometric functions. The boundary conditions used to complete the solutions simulate rotating annular disks with two free surfaces, stationary annular disks with pressurized inner and free outer surfaces, and free inner and pressurized outer surfaces. The results of the solutions to each of these cases are presented in graphical forms. It is observed that, for the three cases investigated the elastic orthotropy parameter turns out to be an important parameter affecting the elastic behaviorKeywords: Orthotropic disk, Variable thickness, Thermoelasticity, Hypergeometric equation

Herschel/SPIRE observations of the dusty disk of NGC 4244

NARCIS (Netherlands)

Holwerda, B. W.; Bianchi, S.; Boker, T.; Radburn-Smith, D.; de Jong, R. S.; Baes, M.; van der Kruit, P. C.; Xilouris, M.; Gordon, K. D.; Dalcanton, J. J.

We present Herschel/SPIRE images at 250, 350, and 500 mu m of NGC 4244, a typical low-mass, disk-only and edge-on spiral galaxy. The dust disk is clumpy and shows signs of truncation at the break radius of the stellar disk. This disk coincides with the densest part of the Hi disk. We compare the

Three-dimensional discrete element method simulation of core disking

Science.gov (United States)

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.

Empirical Temperature Measurement in Protoplanetary Disks

Science.gov (United States)

Weaver, Erik; Isella, Andrea; Boehler, Yann

2018-02-01

The accurate measurement of temperature in protoplanetary disks is critical to understanding many key features of disk evolution and planet formation, from disk chemistry and dynamics, to planetesimal formation. This paper explores the techniques available to determine temperatures from observations of single, optically thick molecular emission lines. Specific attention is given to issues such as the inclusion of optically thin emission, problems resulting from continuum subtraction, and complications of real observations. Effort is also made to detail the exact nature and morphology of the region emitting a given line. To properly study and quantify these effects, this paper considers a range of disk models, from simple pedagogical models to very detailed models including full radiative transfer. Finally, we show how the use of the wrong methods can lead to potentially severe misinterpretations of data, leading to incorrect measurements of disk temperature profiles. We show that the best way to estimate the temperature of emitting gas is to analyze the line peak emission map without subtracting continuum emission. Continuum subtraction, which is commonly applied to observations of line emission, systematically leads to underestimation of the gas temperature. We further show that once observational effects such as beam dilution and noise are accounted for, the line brightness temperature derived from the peak emission is reliably within 10%–15% of the physical temperature of the emitting region, assuming optically thick emission. The methodology described in this paper will be applied in future works to constrain the temperature, and related physical quantities, in protoplanetary disks observed with ALMA.

Effect of massive disks on bulge isophotes

International Nuclear Information System (INIS)

Monet, D.G.; Richstone, D.O.; Schechter, P.L.

1981-01-01

Massive disks produce flattened equipotentials. Unless the stars in a galaxy bulge are preferentially hotter in the z direction than in the plane, the isophotes will be at least as flat as the equipotentials. The comparison of two galaxy models having flat rotation curves with the available surface photometry for five external galaxies does not restrict the mass fraction which might reside in the disk. However, star counts in our own Galaxy indicate that unless the disk terminates close to the solar circle, no more than half the mass within that circle lies in the disk. The remaining half must lie either in the bulge or, more probably, in a third dark, round, dynamically distinct component

Gravitomagnetic acceleration from black hole accretion disks

International Nuclear Information System (INIS)

Poirier, J; Mathews, G J

2016-01-01

We demonstrate how the motion of the neutral masses in an accretion disk orbiting a black hole creates a general-relativistic magnetic-like (gravitomagnetic) field that vertically accelerates neutral particles near an accretion disk upward and then inward toward the axis of the accretion disk. Even though this gravitomagnetic field is not the only mechanism contributing to the production of jets, it presents a novel means to identify one general relativistic effect from a much more complicated problem. In addition, as the accelerated material above or below the accretion disk nears the axis with a nearly vertical direction, a frame-dragging effect twists the trajectories around the axis thus contributing to the collimation of the jet. (note)

Gravitomagnetic acceleration from black hole accretion disks

Science.gov (United States)

Poirier, J.; Mathews, G. J.

2016-05-01

We demonstrate how the motion of the neutral masses in an accretion disk orbiting a black hole creates a general-relativistic magnetic-like (gravitomagnetic) field that vertically accelerates neutral particles near an accretion disk upward and then inward toward the axis of the accretion disk. Even though this gravitomagnetic field is not the only mechanism contributing to the production of jets, it presents a novel means to identify one general relativistic effect from a much more complicated problem. In addition, as the accelerated material above or below the accretion disk nears the axis with a nearly vertical direction, a frame-dragging effect twists the trajectories around the axis thus contributing to the collimation of the jet.

Synthesis of disk-rod-disk liquid crystal trimers by using click chemistry

Institute of Scientific and Technical Information of China (English)

无

2010-01-01

A series of disk-rod-disk liquid crystal trimers were synthesized.CuI-NEt3 catalyzed alkyne azide cycloaddition in toluene at room temperature connected two triphenylene discogens to a biphenyl rod-shaped mesogen.The trimers were characterized by using 1H NMR,IR,and high resolution mass spectrometry.The mesomorphic properties were investigated using polarized optical microscopy(POM) ,differential scanning calorimetry(DSC) ,and wide-angle X-ray diffraction.The results showed that the trimers exhibited rectangular columnar mesophase(Colr) .The length of the flexible spacer connecting the three segments has prominent influence on the phase transition temperatures of the trimers.

Stability of a chemically active floating disk

Science.gov (United States)

Vandadi, Vahid; Jafari Kang, Saeed; Rothstein, Jonathan; Masoud, Hassan

2017-11-01

We theoretically study the translational stability of a chemically active disk located at a flat liquid-gas interface. The initially immobile circular disk uniformly releases an interface-active agent that locally changes the surface tension and is insoluble in the bulk. If left unperturbed, the stationary disk remains motionless as the agent is discharged. Neglecting the inertial effects, we numerically test whether a perturbation in the translational velocity of the disk can lead to its spontaneous and self-sustained motion. Such a perturbation gives rise to an asymmetric distribution of the released factor that could trigger and sustain the Marangoni propulsion of the disk. An implicit Fourier-Chebyshev spectral method is employed to solve the advection-diffusion equation for the concentration of the active agent. The solution, given a linear equation of state for the surface tension, provides the shear stress distribution at the interface. This and the no-slip condition on the wetted surface of the disk are then used at each time step to semi-analytically determine the Stokes flow in the semi-infinite liquid layer. Overall, the findings of our investigation pave the way for pinpointing the conditions under which interface-bound active particles become dynamically unstable.

Childhood to adolescence: dust and gas clearing in protoplanetary disks

Science.gov (United States)

Brown, Joanna Margaret

Disks are ubiquitous around young stars. Over time, disks dissipate, revealing planets that formed hidden by their natal dust. Since direct detection of young planets at small orbital radii is currently impossible, other tracers of planet formation must be found. One sign of disk evolution, potentially linked to planet formation, is the opening of a gap or inner hole in the disk. In this thesis, I have identified and characterized several cold disks with large inner gaps but retaining massive primordial outer disks. While cold disks are not common, with ~5% of disks showing signs of inner gaps, they provide proof that at least some disks evolve from the inside-out. These large gaps are equivalent to dust clearing from inside the Earth's orbit to Neptune's orbit or even the inner Kuiper belt. Unlike more evolved systems like our own, the central star is often still accreting and a large outer disk remains. I identified four cold disks in Spitzer 5-40 μm spectra and modeled these disks using a 2-D radiative transfer code to determine the gap properties. Outer gap radii of 20-45 AU were derived. However, spectrophotometric identification is indirect and model-dependent. To validate this interpretation, I observed three disks with a submillimeter interferometer and obtained the first direct images of the central holes. The images agree well with the gap sizes derived from the spectrophotometry. One system, LkH&alpha 330, has a very steep outer gap edge which seems more consistent with gravitational perturbation rather than gradual processes, such as grain growth and settling. Roughly 70% of cold disks show CO v=1&rarr 0 gas emission from the inner 1 AU and therefore are unlikely to have evolved due to photoevaporation. The derived rotation temperatures are significantly lower for the cold disks than disks without gaps. Unresolved (sub)millimeter photometry shows that cold disks have steeper colors, indicating that they are optically thin at these wavelengths, unlike

Modeling the η Corvi debris disk from the sub-AU scale to its outermost regions

Science.gov (United States)

Lebreton, J.; Beichman, C. A.; Bryden, G.; Defrère, D.; Mennesson, Bertr; Millan-Gabet, R.

2014-03-01

Dusty debris disks surrounding main sequence stars are thought to be analogues to thepopulations of small bodies of the Solar System (asteroids, comets/icy bodies and dust grains), however with often much higher masses and associated dust production rates. Mecanisms such as massive collisions or LHB-like events must therefore be invoked to justify their existence. This is especially striking for the nearby F2V star η Corvi that shows a very strong mid- and far-infrared excess despite an estimated age of ~1.4 Gyr (Lisse et al. 2012, Wyatt et al. 2005). We present new observations of the η Crv debris disk obtained in the far-infrared with Herschel/PACS and SPIRE and in the mid-infrared with the Keck Interferometer Nuller (Millan-Gabet et al. 2011). The Herschel/PACS images at 70, 100 and 160 μm reveal a well resolved belt of cold material at ~130 AU, as well as an unresolved component in the innermost parts of the system. This warmer counterpart is resolved in the mid-infrared as a strong null excess originating from within the ~2x4 AU field-of-view of the interferometer, which is reminiscent of the architecture of the Fomalhaut debris disk (Mennesson et al. 2012, Lebreton et al. 2013). The signature of warm silicate dust is also very clear in Spitzer/IRS high-resolution spectra (Chen et al. 2006) at intermediate wavelengths (10-35 μm). We undertake to establish a consistent model of the debris disk from the sub-AU scale to its outermost regions using the GRaTer radiative transfer code (Augereau et al. 1999a, Lebreton et al. 2013) by adjusting simultaneously the interferometric nulls, the resolved Herschel images and the spectro-photometric data against a large parameter space. Our analysis providesaccurate estimates of the fundamental parameters of the disk: its surface density profile, grain size distribution and mass, making it possible to unveil the origin of the dust and the relation between the cold (~50 K) Kuiper-like belt and the warm (~500 K) exo

THE KOZAI-LIDOV MECHANISM IN HYDRODYNAMICAL DISKS

International Nuclear Information System (INIS)

Martin, Rebecca G.; Nixon, Chris; Armitage, Philip J.; Lubow, Stephen H.; Price, Daniel J.; Doğan, Suzan; King, Andrew

2014-01-01

We use three-dimensional hydrodynamical simulations to show that a highly misaligned accretion disk around one component of a binary system can exhibit global Kozai-Lidov cycles, where the inclination and eccentricity of the disk are interchanged periodically. This has important implications for accreting systems on all scales, for example, the formation of planets and satellites in circumstellar and circumplanetary disks, outbursts in X-ray binary systems, and accretion onto supermassive black holes

Disk access controller for Multi 8 computer

International Nuclear Information System (INIS)

Segalard, Jean

1970-01-01

After having presented the initial characteristics and weaknesses of the software provided for the control of a memory disk coupled with a Multi 8 computer, the author reports the development and improvement of this controller software. He presents the different constitutive parts of the computer and the operation of the disk coupling and of the direct access to memory. He reports the development of the disk access controller: software organisation, loader, subprograms and statements

On Shocks Driven by High-mass Planets in Radiatively Inefficient Disks. II. Three-dimensional Global Disk Simulations