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Sample records for abundant circumstellar silica

  1. Abundant Circumstellar Silica Dust and SiO Gas Created by a Giant Hypervelocity Collision in the ~12 Myr HD172555 System

    Lisse, C M; Wyatt, M C; Morlok, A; Song, I; Bryden, G; Sheehan, P

    2009-01-01

    The fine dust detected by IR emission around the nearby Beta Pic analogue star HD172555 is very peculiar. The dust mineralogy is composed primarily of highly refractory, non-equilibrium materials, with approximately three-quarters of the Si atoms in silica (SiO2) species. Tektite and obsidian lab thermal emission spectra (non-equilibrium glassy silicas found in impact and magmatic systems) are required to fit the data. The best-fit model size distribution for the observed fine dust is dn/da = a-3.95 +/- 0.10. This steep a size distribution, with abundant micron-sized particles, argues for a fresh source of material within the last 0.1 Myr. The location of the dust with respect to the star is at 5.8 +/- 0.6 AU (equivalent to 1.9 +/- 0.2 AU from the Sun), within the terrestrial planet formation region but at the outer edge of any possible terrestrial habitability zone. The mass of fine dust is 4 x 10^19 - 2 x 10^20 kg, equivalent to a 150 - 200 km radius asteroid. Significant emission features centered at 4 and...

  2. Abundances and density structure of the inner circumstellar ring around SN 1987A

    Mattila, Seppo; Groeningsson, Per; Meikle, Peter; Stathakis, Raylee; Fransson, Claes; Cannon, Russell

    2010-01-01

    We present optical spectroscopic data of the inner circumstellar ring around SN 1987A from the Anglo-Australian Telescope (AAT) and the Very Large Telescope (VLT) between ~1400 and ~5000 days post-explosion. We also assembled the available optical and near-infrared line fluxes from the literature between ~300 and ~2000 days. These line light curves were fitted with a photoionization model to determine the density structure and the elemental abundances for the inner ring. We found densities ranging from 1x10^3 to 3x10^4 atoms cm^-3 and a total mass of the ionized gas of 0.058 Msun within the inner ring. Abundances inferred from the optical and near-infrared data were also complemented with estimates of Lundqvist & Fransson (1996) based on ultraviolet lines. This way we found an He/H-ratio (by number of atoms) of 0.17+-0.06, N/O-ratio of 1.5+-0.7, and the total (C+N+O)/(H+He) abundance about 1.6 times its LMC value or roughly 0.6 times the most recent solar value. An iron abundance of 0.20+-0.11 times solar...

  3. Circumstellar molecular composition of the oxygen-rich AGB star IK Tau: I. Observations and LTE chemical abundance analysis

    Kim, Hyunjoo; Menten, Karl M; Decin, Leen

    2010-01-01

    The aim of this paper is to study the molecular composition in the circumstellar envelope around the oxygen-rich star IK Tau. We observed IK Tau in several (sub)millimeter bands using the APEX telescope during three observing periods. To determine the spatial distribution of the $\\mathrm{^{12}CO(3-2)}$ emission, mapping observations were performed. To constrain the physical conditions in the circumstellar envelope, multiple rotational CO emission lines were modeled using a non local thermodynamic equilibrium radiative transfer code. The rotational temperatures and the abundances of the other molecules were obtained assuming local thermodynamic equilibrium. An oxygen-rich Asymptotic Giant Branch star has been surveyed in the submillimeter wavelength range. Thirty four transitions of twelve molecular species, including maser lines, were detected. The kinetic temperature of the envelope was determined and the molecular abundance fractions of the molecules were estimated. The deduced molecular abundances were com...

  4. Circumstellar water vapour in M-type AGB stars: Radiative transfer models, abundances and predictions for HIFI

    Maercker, Matthias; Olofsson, Hans; Bergman, Per; Ramstedt, Sofia

    2008-01-01

    Aims: By performing a detailed radiative transfer analysis, we determine fractional abundances of circumstellar H2O in the envelopes around six M-type asymptotic giant branch stars. The models are also used to predict H2O spectral line emission for the upcoming Herschel/HIFI mission. Methods: We use Infrared space observatory long wavelength spectrometer spectra to constrain the circumstellar fractional abundance distribution of ortho-H2O, using a non-local thermal equilibrium, and non-local, radiative transfer code based on the accelerated lambda iteration formalism. The mass-loss rates and kinetic temperature structures for the sample stars are determined through radiative transfer modelling of CO line emission based on the Monte-Carlo method. The density and temperature profiles of the circumstellar dust grains are determined through spectral energy distribution modelling using the publicly available code Dusty. Results: The determined ortho-H2O abundances lie between 1e-4 and 1.5e-3 relative to H2, with t...

  5. Rapid changes in diatom silica surface charge density, silanol abundance, and oxygen isotope values elucidate silica maturation processes in biogenic silica

    Wiedenheft, W.; Dodd, J. P.; Sunderlin, L.

    2014-12-01

    Oxygen isotope values of biogenic silica are increasingly used as proxies of paleoenvironmental conditions. Numerous studies have demonstrated a strong relationship between the diatom silica and the temperature/oxygen isotope value of the formation water; however, some studies have indicated that early diagenesis of biogenic silica may alter the oxygen isotope values by several permil. Quantification of the maturation process has proven difficult since the mechanisms that drive post-mortem changes in the silica oxygen isotope values have not been well characterized. New silica maturation data from marine diatoms, Stephanopyxis turris, cultured in a controlled laboratory experiment demonstrate rapid post-mortem decline in silica reactivity. A decrease in relative abundance of surface silanol groups coincides with a decrease in the surface charge density (excess proton concentration) of freshly harvested frustules. Over a maturation period of 20 days at 85ºC, S. turris samples in a 0.7 M NaCl solution at a pH of 8.0 demonstrate a rapid decrease in the surface charge density from -380 μmoles/g to -16 μmoles/g (Figure 1). FTIR analyses reveal a decrease in the abundance of silanol groups (Si-OH) in the diatom frustules occurs over the same time period. It is important to note that the surface charge density and silanol relative abundance appear to have an asymptotic change through time, indicating that further alteration/reactivity is greatly reduced. Preliminary data indicate that post-mortem increases in the oxygen isotope values of diatom silica observed here and in other studies are coincident with a reduction in the surface charge density and silanol abundance. These experiments demonstrate that rapid post-mortem alteration of biogenic silica is occurring and provide a possible mechanism for alteration of oxygen isotope values in biogenic silica.

  6. Confirmation of Circumstellar Phosphine

    Agúndez, M.; Cernicharo, J.; Decin, L.; Encrenaz, P.; Teyssier, D.

    2014-08-01

    Phosphine (PH3) was tentatively identified a few years ago in the carbon star envelopes IRC +10216 and CRL 2688 from observations of an emission line at 266.9 GHz attributable to the J = 1-0 rotational transition. We report the detection of the J = 2-1 rotational transition of PH3 in IRC +10216 using the HIFI instrument on board Herschel, which definitively confirms the identification of PH3. Radiative transfer calculations indicate that infrared pumping in excited vibrational states plays an important role in the excitation of PH3 in the envelope of IRC +10216, and that the observed lines are consistent with phosphine being formed anywhere between the star and 100 R * from the star, with an abundance of 10-8 relative to H2. The detection of PH3 challenges chemical models, none of which offer a satisfactory formation scenario. Although PH3 holds just 2% of the total available phosphorus in IRC +10216, it is, together with HCP, one of the major gas phase carriers of phosphorus in the inner circumstellar layers, suggesting that it could also be an important phosphorus species in other astronomical environments. This is the first unambiguous detection of PH3 outside the solar system, and is a further step toward a better understanding of the chemistry of phosphorus in space.

  7. CONFIRMATION OF CIRCUMSTELLAR PHOSPHINE

    Agúndez, M.; Cernicharo, J. [Instituto de Ciencia de Materiales de Madrid, CSIC, C/ Sor Juana Inés de la Cruz 3, E-28049 Cantoblanco (Spain); Decin, L. [Sterrenkundig Instituut Anton Pannekoek, University of Amsterdam, Science Park 904, NL-1098 Amsterdam (Netherlands); Encrenaz, P. [LERMA, Observatoire de Paris, 61 Av. de l' Observatoire, F-75014 Paris (France); Teyssier, D. [European Space Astronomy Centre, Urb. Villafranca del Castillo, P.O. Box 50727, E-28080 Madrid (Spain)

    2014-08-01

    Phosphine (PH{sub 3}) was tentatively identified a few years ago in the carbon star envelopes IRC +10216 and CRL 2688 from observations of an emission line at 266.9 GHz attributable to the J = 1-0 rotational transition. We report the detection of the J = 2-1 rotational transition of PH{sub 3} in IRC +10216 using the HIFI instrument on board Herschel, which definitively confirms the identification of PH{sub 3}. Radiative transfer calculations indicate that infrared pumping in excited vibrational states plays an important role in the excitation of PH{sub 3} in the envelope of IRC +10216, and that the observed lines are consistent with phosphine being formed anywhere between the star and 100 R {sub *} from the star, with an abundance of 10{sup –8} relative to H{sub 2}. The detection of PH{sub 3} challenges chemical models, none of which offer a satisfactory formation scenario. Although PH{sub 3} holds just 2% of the total available phosphorus in IRC +10216, it is, together with HCP, one of the major gas phase carriers of phosphorus in the inner circumstellar layers, suggesting that it could also be an important phosphorus species in other astronomical environments. This is the first unambiguous detection of PH{sub 3} outside the solar system, and is a further step toward a better understanding of the chemistry of phosphorus in space.

  8. Confirmation of circumstellar phosphine

    Agundez, M; Decin, L; Encrenaz, P; Teyssier, D

    2014-01-01

    Phosphine (PH3) was tentatively identified a few years ago in the carbon star envelopes IRC+10216 and CRL2688 from observations of an emission line at 266.9 GHz attributable to the J=1-0 rotational transition. We report the detection of the J=2-1 rotational transition of PH3 in IRC+10216 using the HIFI instrument on board Herschel, which definitively confirms the identification of PH3. Radiative transfer calculations indicate that infrared pumping to excited vibrational states plays an important role in the excitation of PH3 in the envelope of IRC+10216, and that the observed lines are consistent with phosphine being formed anywhere between the star and 100 R* from the star, with an abundance of 1e-8 relative to H2. The detection of PH3 challenges chemical models, none of which offers a satisfactory formation scenario. Although PH3 locks just 2 % of the total available phosphorus in IRC+10216, it is together with HCP, one of the major gas phase carriers of phosphorus in the inner circumstellar layers, suggest...

  9. Composite Circumstellar Dust Grains

    Gupta, Ranjan; Dutta, Rajeshwari

    2016-01-01

    We calculate the absorption efficiencies of composite silicate grains with inclusions of graphite and silicon carbide in the spectral range 5--25$\\rm \\mu m$. We study the variation in absorption profiles with volume fractions of inclusions. In particular we study the variation in the wavelength of peak absorption at 10 and 18$\\rm \\mu m$. We also study the variation of the absorption of porous silicate grains. We use the absorption efficiencies to calculate the infrared flux at various dust temperatures and compare with the observed infrared emission flux from the circumstellar dust around some M-Type \\& AGB stars obtained from IRAS and a few stars from Spitzer satellite. We interpret the observed data in terms of the circumstellar dust grain sizes; shape; composition and dust temperature.

  10. Silica in Protoplanetary Disks

    Sargent, B A; Tayrien, C; McClure, M K; Li, A; Basu, A R; Manoj, P; Watson, D M; Bohac, C J; Furlan, E; Kim, K H; Green, J D; Sloan, G C

    2008-01-01

    Mid-infrared spectra of a few T Tauri stars (TTS) taken with the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope show prominent narrow emission features indicating silica (crystalline silicon dioxide). Silica is not a major constituent of the interstellar medium; therefore, any silica present in the circumstellar protoplanetary disks of TTS must be largely the result of processing of primitive dust material in the disks surrouding these stars. We model the silica emission features in our spectra using the opacities of various polymorphs of silica and their amorphous versions computed from earth-based laboratory measurements. This modeling indicates that the two polymorphs of silica, tridymite and cristobalite, which form at successively higher temperatures and low pressures, are the dominant forms of silica in the TTS of our sample. These high temperature, low pressure polymorphs of silica present in protoplanetary disks are consistent with a grain composed mostly of tridymite named Ada found...

  11. SO2 and SO in circumstellar envelopes

    Guilloteau, S.; Lucas, R.; Omont, A.; Nguyen-Q-Rieu

    1986-09-01

    After its first detection in circumstellar envelopes (Lucas et al. 1986) SO2 has been systematically searched for with the IRAM 30-m telescope. It has been found in 3 new stars, with very strong lines in OH 231.8+4.2 (TA* ≈ 0.7 - 1.4K, Trot ≈ 25K, Δv ≈ 80 km s-1, TA*(SO2) > TA*(CO) ) and relatively strong ones in OH 26.5+0.6. SO has been detected for the first time in a circumstellar shell, in OH 231.8+4.2. H13CN has been observed in the same star, suggesting a very large abundance of 13C.

  12. A photospheric metal line profile analysis of hot DA white dwarfs with circumstellar material

    Dickinson, Nathan J; Welsh, Barry Y

    2012-01-01

    Some hot DA white dwarfs have circumstellar high ion absorption features in their spectra, in addition to those originating in the photosphere. In many cases, the line profiles of these absorbing components are unresolved. Given the importance of the atmospheric composition of white dwarfs to studies of stellar evolution, extra-solar planetary systems and the interstellar medium, we examine the effect of including circumstellar line profiles in the abundance estimates of photospheric metals in six DA stars. The photospheric C and Si abundances are reduced in five cases where the circumstellar contamination is strong, though the relative weakness of the circumstellar Si IV absorption introduces minimal contamination, resulting in a small change in abundance. The inability of previous, approximate models to reproduce the photospheric line profiles here demonstrates the need for a technique that accounts for the physical line profiles of both the circumstellar and photospheric lines when modelling these blended ...

  13. Chemical evolution of circumstellar matter around young stellar objects

    van Dishoeck, E. F.; Blake, G. A.

    1995-01-01

    Recent observational studies of the chemical composition of circumstellar matter around both high- and low-mass young stellar objects are reviewed. The molecular abundances are found to be a strong function of evolutionary state, but not of system mass or luminosity. The data are discussed with reference to recent theoretical models.

  14. Interstellar and circumstellar fullerenes

    Bernard-Salas, J; Jones, A P; Peeters, E; Micelotta, E R; Otsuka, M; Sloan, G C; Kemper, F; Groenewegen, M

    2014-01-01

    Fullerenes are a particularly stable class of carbon molecules in the shape of a hollow sphere or ellipsoid that might be formed in the outflows of carbon stars. Once injected into the interstellar medium (ISM), these stable species survive and are thus likely to be widespread in the Galaxy where they contribute to interstellar extinction, heating processes, and complex chemical reactions. In recent years, the fullerene species C60 (and to a lesser extent C70) have been detected in a wide variety of circumstellar and interstellar environments showing that when conditions are favourable, fullerenes are formed efficiently. Fullerenes are the first and only large aromatics firmly identified in space. The detection of fullerenes is thus crucial to provide clues as to the key chemical pathways leading to the formation of large complex organic molecules in space, and offers a great diagnostic tool to describe the environment in which they reside. Since fullerenes share many physical properties with PAHs, understand...

  15. The circumstellar structure around supernovae

    The time dependent ionization and temperature structure of the circumstellar medium around supernovae has been calculated, in order to interpret recent supernova radio observations. For a stellar wind origin of the circumstellar medium, the authors relate the time of radio turn-on to the progenitor mass loss rate. They also show that large column densities for the UV resonance lines are expected. The results are applied to SN 1979c, SN 1980K and SN 1987A

  16. The Rich Circumstellar Chemistry of SMP LMC 11

    Malek, Sarah E; Bernard-Salas, Jeronimo

    2011-01-01

    Carbon-rich evolved stars from the asymptotic giant branch to the planetary nebula phase are characterized by a rich and complex carbon chemistry in their circumstellar envelopes. A peculiar object is the preplanetary nebula SMP LMC 11, whose Spitzer-IRS spectrum shows remarkable and diverse molecular absorption bands. To study how the molecular composition in this object compares to our current understanding of circumstellar carbon chemistry, we modeled this molecular absorption. We find high abundances for a number of molecules, perhaps most notably benzene. We also confirm the presence of propyne (CH3C2H) in this spectrum. Of all the cyanopolyynes, only HC3N is evident; we can detect at best a marginal presence of HCN. From comparisons to various chemical models, we can conclude that SMP LMC 11 must have an unusual circumstellar environment (a torus rather than an outflow).

  17. Vortices in circumstellar disks

    Adams, F; Adams, Fred; Watkins, Richard

    1995-01-01

    We discuss the physics of vortices in the circumstellar disks associated with young stellar objects. We elucidate the basic physical properties of these localized storm systems. In particular, we consider point vortices, linear vortices, the effects of self-gravity, magnetic fields, and nonlinear aspects of the problem. We find that these vortices can exist in many different forms in the disks of young stellar objects and may play a role in the formation of binary companions and/or giant planets. Vortices may enhance giant planet formation via gravitational instability by allowing dust grains (heavy elements) to settle to the center on a short timescale; the gravitational instability itself is also enhanced because the vortices also create a larger local surface density in the disk. In addition, vortices can enhance energy dissipation in disks and thereby affect disk accretion. Finally, we consider the possibility that vortices of this type exist in molecular clouds and in the disk of the galaxy itself. On al...

  18. Silica Nephropathy

    N Ghahramani

    2010-06-01

    Full Text Available Occupational exposure to heavy metals, organic solvents and silica is associated with a variety of renal manifestations. Improved understanding of occupational renal disease provides insight into environmental renal disease, improving knowledge of disease pathogenesis. Silica (SiO2 is an abundant mineral found in sand, rock, and soil. Workers exposed to silica include sandblasters, miners, quarry workers, masons, ceramic workers and glass manufacturers. New cases of silicosis per year have been estimated in the US to be 3600–7300. Exposure to silica has been associated with tubulointerstitial disease, immune-mediated multisystem disease, chronic kidney disease and end-stage renal disease. A rare syndrome of painful, nodular skin lesions has been described in dialysis patients with excessive levels of silicon. Balkan endemic nephropathy is postulated to be due to chronic intoxication with drinking water polluted by silicates released during soil erosion. The mechanism of silica nephrotoxicity is thought to be through direct nephrotoxicity, as well as silica-induced autoimmune diseases such as scleroderma and systemic lupus erythematosus. The renal histopathology varies from focal to crescentic and necrotizing glomerulonephritis with aneurysm formation suggestive of polyarteritis nodosa. The treatment for silica nephrotoxicity is non-specific and depends on the mechanism and stage of the disease. It is quite clear that further research is needed, particularly to elucidate the pathogenesis of silica nephropathy. Considering the importance of diagnosing exposure-related renal disease at early stages, it is imperative to obtain a thorough occupational history in all patients with renal disease, with particular emphasis on exposure to silica, heavy metals, and solvents.

  19. Silica nephropathy.

    Ghahramani, N

    2010-07-01

    Occupational exposure to heavy metals, organic solvents and silica is associated with a variety of renal manifestations. Improved understanding of occupational renal disease provides insight into environmental renal disease, improving knowledge of disease pathogenesis. Silica (SiO2) is an abundant mineral found in sand, rock, and soil. Workers exposed to silica include sandblasters, miners, quarry workers, masons, ceramic workers and glass manufacturers. New cases of silicosis per year have been estimated in the US to be 3600-7300. Exposure to silica has been associated with tubulointerstitial disease, immune-mediated multisystem disease, chronic kidney disease and end-stage renal disease. A rare syndrome of painful, nodular skin lesions has been described in dialysis patients with excessive levels of silicon. Balkan endemic nephropathy is postulated to be due to chronic intoxication with drinking water polluted by silicates released during soil erosion. The mechanism of silica nephrotoxicity is thought to be through direct nephrotoxicity, as well as silica-induced autoimmune diseases such as scleroderma and systemic lupus erythematosus. The renal histopathology varies from focal to crescentic and necrotizing glomerulonephritis with aneurysm formation suggestive of polyarteritis nodosa. The treatment for silica nephrotoxicity is non-specific and depends on the mechanism and stage of the disease. It is quite clear that further research is needed, particularly to elucidate the pathogenesis of silica nephropathy. Considering the importance of diagnosing exposure-related renal disease at early stages, it is imperative to obtain a thorough occupational history in all patients with renal disease, with particular emphasis on exposure to silica, heavy metals, and solvents. PMID:23022796

  20. Processed and unprocessed ices in circumstellar disks

    Pontoppidan, K; Thi, W F; Van Dishoeck, E F

    2004-01-01

    We present 3-5 micron VLT-ISAAC spectroscopy searching for evidence of methanol ices in edge-on disks of young embedded stars. Examples include the disks of L1489 IRS in Taurus and CRBR 2422.8-3423 in Ophiuchus, the last of which has the highest column density of solid CO known toward a YSO. We find no unambiguous evidence for abundant methanol in the observed disks, but give strict upper limits. Several additional low-mass sources in the Serpens and Chameleon molecular clouds exhibit abundant solid methanol, although it is not clear if the ice is associated with a disk or with the envelope. These are the first detections of solid methanol in the circumstellar environments of embedded young low-mass stars providing evidence that complex molecular species previously observed only in the solid state toward high-mass star forming regions are also present near solar-type young stars. The constraints on the formation mechanisms of methanol and the chemical evolution of ices as the material is incorporated into cir...

  1. Circumstellar Nebulae in Young Supernova Remnants

    Chu, Y.-H.

    2000-01-01

    Supernovae descendent from massive stars explode in media that have been modified by their progenitors' mass loss and UV radiation. The supernova ejecta will first interact with the circumstellar material shed by the progenitors at late evolutionary stages, and then interact with the interstellar material. Circumstellar nebulae in supernova remnants can be diagnosed by their small expansion velocities and high [N II]/H$\\alpha$ ratios. The presence of circumstellar nebulae appears ubiquitous a...

  2. Polytype distribution in circumstellar silicon carbide.

    Daulton, T L; Bernatowicz, T J; Lewis, R S; Messenger, S; Stadermann, F J; Amari, S

    2002-06-01

    The inferred crystallographic class of circumstellar silicon carbide based on astronomical infrared spectra is controversial. We have directly determined the polytype distribution of circumstellar SiC from transmission electron microscopy of presolar silicon carbide from the Murchison carbonaceous meteorite. Only two polytypes (of a possible several hundred) were observed: cubic 3C and hexagonal 2H silicon carbide and their intergrowths. We conclude that this structural simplicity is a direct consequence of the low pressures in circumstellar outflows and the corresponding low silicon carbide condensation temperatures. PMID:12052956

  3. Circumstellar Molecular Spectra towards Evolved Stars

    Bakker, E J

    1997-01-01

    In this paper we discuss the relevance of, and possible scientific gains which can be acquired from studying circumstellar molecular spectra toward evolved stars. Where can we expect circumstellar molecular spectra, why would we want to study these spectra, which molecules might be present, and what can we learn from these studies? We present an overview of reported detections, and discuss some of the results.

  4. Tracing Planets in Circumstellar Discs

    Uribe Ana L.

    2013-04-01

    Full Text Available Planets are assumed to form in circumstellar discs around young stellar objects. The additional gravitational potential of a planet perturbs the disc and leads to characteristic structures, i.e. spiral waves and gaps, in the disc density profile. We perform a large-scale parameter study on the observability of these planet-induced structures in circumstellar discs in the (submm wavelength range for the Atacama Large (SubMillimeter Array (ALMA. On the basis of hydrodynamical and magneto-hydrodynamical simulations of star-disc-planet models we calculate the disc temperature structure and (submm images of these systems. These are used to derive simulated ALMA maps. Because appropriate objects are frequent in the Taurus-Auriga region, we focus on a distance of 140 pc and a declination of ≈ 20°. The explored range of star-disc-planet configurations consists of six hydrodynamical simulations (including magnetic fields and different planet masses, nine disc sizes with outer radii ranging from 9 AU to 225 AU, 15 total disc masses in the range between 2.67·10-7 M⊙ and 4.10·10-2 M⊙, six different central stars and two different grain size distributions, resulting in 10 000 disc models. At almost all scales and in particular down to a scale of a few AU, ALMA is able to trace disc structures induced by planet-disc interaction or the influence of magnetic fields in the wavelength range between 0.4...2.0 mm. In most cases, the optimum angular resolution is limited by the sensitivity of ALMA. However, within the range of typical masses of protoplane tary discs (0.1 M⊙...0.001 M⊙ the disc mass has a minor impact on the observability. At the distance of 140 pc it is possible to resolve discs down to 2.67·10-6 M⊙ and trace gaps in discs with 2.67·10-4 M⊙ with a signal-to-noise ratio greater than three. In general, it is more likely to trace planet-induced gaps in magneto-hydrodynamical disc models, because gaps are wider in the presence of

  5. Sulphur molecules in the circumstellar envelopes of M-type AGB stars

    Danilovich, Taissa; Black, J H; Olofsson, H; Justtanont, K

    2016-01-01

    The sulphur compounds SO and SO$_2$ have not been widely studied in the circumstellar envelopes of asymptotic giant branch (AGB) stars. By presenting and modelling a large number of SO and SO$_2$ lines in the low mass-loss rate M-type AGB star R Dor, and modelling the available lines of those molecules in a further four M-type AGB stars, we aim to determine their circumstellar abundances and distributions. We use a detailed radiative transfer analysis based on the accelerated lambda iteration method to model circumstellar SO and SO$_2$ line emission and molecular data files for both SO and SO$_2$ that are more extensive than those previously available. Using 17 SO lines and 98 SO2 lines to constrain our models for R Dor, we find an SO abundance of 6.7x10$^{-6}$ and an SO$_2$ abundance of 5x10$^{-6}$ with both species having high abundances close to the star. We also modelled $^{34}$SO and found an abundance of 3.1x10$^{-7}$, giving an $^{32}$SO/$^{34}$SO ratio of 21.6. We derive similar results for the circum...

  6. Carbon stars with oxygen-rich circumstellar material

    Jura, Michael; Hawkins, I.

    1991-01-01

    The IUE satellite was used to search for companions to two carbon-rich stars with oxygen-rich circumstellar envelopes, EU And and V778 Cyg. Depending upon the amount of interstellar extinction and distances (probably between 1 and 2 kpc from the Sun) to these two stars, upper limits were placed between approx. 1.5 and 6 solar mass to the mass of any main sequence companions. For the 'near' distance of 1 kpc, it seems unlikely that there are white dwarf companions because the detection would be expected of ultraviolet emission from accretion of red giant wind material onto the white dwarf. A new model is proposed to explain the oxygen-rich envelopes. If these stars have a high nitrogen abundance, the carbon that is in excess of the oxygen may be carried in the circumstellar envelopes in HCN rather than C2H2 which is a likely key seed molecule for the formation of carbon grains. Consequently, carbon particles may not form; instead, oxygen-rich silicate dust may nucleate from the SiO present in the outflow.

  7. White dwarf atmospheres and circumstellar environments

    Hoard, Donald W

    2012-01-01

    Written by selected astronomers at the forefront of their fields, this timely and novel book compiles the latest results from research on white dwarf stars, complementing existing literature by focusing on fascinating new developments in our understanding of the atmospheric and circumstellar environments of these stellar remnants. Complete with a thorough refresher on the observational characteristics and physical basis for white dwarf classification, this is a must-have resource for researchers interested in the late stages of stellar evolution, circumstellar dust and nebulae, and the future

  8. Sulphur molecules in the circumstellar envelopes of M-type AGB stars

    Danilovich, T.; De Beck, E.; Black, J. H.; Olofsson, H.; Justtanont, K.

    2016-04-01

    Aims: The sulphur compounds SO and SO2 have not been widely studied in the circumstellar envelopes of asymptotic giant branch (AGB) stars. By presenting and modelling a large number of SO and SO2 lines in the low mass-loss rate M-type AGB star R Dor, and modelling the available lines of those molecules in a further four M-type AGB stars, we aim to determine their circumstellar abundances and distributions. Methods: We use a detailed radiative transfer analysis based on the accelerated lambda iteration method to model circumstellar SO and SO2 line emission. We use molecular data files for both SO and SO2 that are more extensive than those previously available. Results: Using 17 SO lines and 98 SO2 lines to constrain our models for R Dor, we find an SO abundance of (6.7 ± 0.9) × 10-6 and an SO2 abundance of 5 × 10-6 with both species having high abundances close to the star. We also modelled 34SO and found an abundance of (3.1 ± 0.8) × 10-7, giving an 32SO/34SO ratio of 21.6 ± 8.5. We derive similar results for the circumstellar SO and SO2 abundances and their distributions for the low mass-loss rate object W Hya. For the higher mass-loss rate stars, we find shell-like SO distributions with peak abundances that decrease and peak abundance radii that increase with increasing mass-loss rate. The positions of the peak SO abundance agree very well with the photodissociation radii of H2O. We also modelled SO2 in two higher mass-loss rate stars but our models for these were less conclusive. Conclusions: We conclude that for the low mass-loss rate stars, the circumstellar SO and SO2 abundances are much higher than predicted by chemical models of the extended stellar atmosphere. These two species may also account for all the available sulphur. For the higher mass-loss rate stars we find evidence that SO is most efficiently formed in the circumstellar envelope, most likely through the photodissociation of H2O and the subsequent reaction between S and OH. The S

  9. Circumstellar debris and pollution at white dwarf stars

    Farihi, J.

    2016-04-01

    Circumstellar disks of planetary debris are now known or suspected to closely orbit hundreds of white dwarf stars. To date, both data and theory support disks that are entirely contained within the preceding giant stellar radii, and hence must have been produced during the white dwarf phase. This picture is strengthened by the signature of material falling onto the pristine stellar surfaces; disks are always detected together with atmospheric heavy elements. The physical link between this debris and the white dwarf host abundances enables unique insight into the bulk chemistry of extrasolar planetary systems via their remnants. This review summarizes the body of evidence supporting dynamically active planetary systems at a large fraction of all white dwarfs, the remnants of first generation, main-sequence planetary systems, and hence provide insight into initial conditions as well as long-term dynamics and evolution.

  10. Circumstellar Debris and Pollution at White Dwarf Stars

    Farihi, J

    2016-01-01

    Circumstellar disks of planetary debris are now known or suspected to closely orbit hundreds of white dwarf stars. To date, both data and theory support disks that are entirely contained within the preceding giant stellar radii, and hence must have been produced during the white dwarf phase. This picture is strengthened by the signature of material falling onto the pristine stellar surfaces; disks are always detected together with atmospheric heavy elements. The physical link between this debris and the white dwarf host abundances enables unique insight into the bulk chemistry of extrasolar planetary systems via their remnants. This review summarizes the body of evidence supporting dynamically active planetary systems at a large fraction of all white dwarfs, the remnants of first generation, main-sequence planetary systems, and hence provide insight into initial conditions as well as long-term dynamics and evolution.

  11. Detailed modelling of the circumstellar molecular line emission of the S-type AGB star W Aquilae

    Danilovich, T; Justtanont, K; Lombaert, R; Maercker, M; Olofsson, H; Ramstedt, S; Royer, P

    2014-01-01

    S-type AGB stars have a C/O ratio which suggests that they are transition objects between oxygen-rich M-type stars and carbon-rich C-type stars. As such, their circumstellar compositions of gas and dust are thought to be sensitive to their precise C/O ratio, and it is therefore of particular interest to examine their circumstellar properties. We present new Herschel HIFI and PACS sub-millimetre and far-infrared line observations of several molecular species towards the S-type AGB star W Aql. We use these observations, which probe a wide range of gas temperatures, to constrain the circumstellar properties of W Aql, including mass-loss rate and molecular abundances. We used radiative transfer codes to model the circumstellar dust and molecular line emission to determine circumstellar properties and molecular abundances. We assumed a spherically symmetric envelope formed by a constant mass-loss rate driven by an accelerating wind. Our model includes fully integrated H2O line cooling as part of the solution of th...

  12. Detailed Modelling of the Circumstellar Envelope of the S-type AGB Star W Aquilae

    Danilovich, T.; Bergman, P.; Justtanont, K.; Lombaert, R.; Maercker, M.; Olofsson, H.; Ramstedt, S.; Royer, P.

    2015-08-01

    We present new Herschel HIFI (de Graauw et al. 2010) and PACS (Poglitsch et al. 2010) sub-millimeter and far-infrared line observations of several molecular species towards the S-type AGB star W Aql. We use these observations, which probe a wide range of gas temperatures, to constrain the circumstellar properties of W Aql, including mass-loss rate and molecular abundances.

  13. Searching for signatures of planet formation in stars with circumstellar debris discs

    Maldonado, J.; Eiroa, C.; Villaver, E.; Montesinos, B.; Mora, A.

    2015-01-01

    Astronomy and Astrophysics 579 (2015): A20 reproduced with permission from Astronomy & Astrophysics Context. Tentative correlations between the presence of dusty circumstellar debris discs and low-mass planets have recently been presented. In parallel, detailed chemical abundance studies have reported different trends between samples of planet and non-planet hosts. Whether these chemical differences are indeed related to the presence of planets is still strongly debated. Aims. We aim t...

  14. The Mineralogy of Circumstellar Silicates Preserved in Cometary Dust

    Keller, L. P.; Messenger, S.

    2010-01-01

    Interplanetary dust particles (IDPs) contain a record of the building blocks of the solar system including presolar grains, molecular cloud material, and materials formed in the early solar nebula. Cometary IDPs have remained relatively unaltered since their accretion because of the lack of parent body thermal and aqueous alteration. We are using coordinated transmission electron microscope (TEM) and ion microprobe studies to establish the origins of the various components within cometary IDPs. Of particular interest is the nature and abundance of presolar silicates in these particles because astronomical observations suggest that crystalline and amorphous silicates are the dominant grain types produced in young main sequence stars and evolved O-rich stars. Five circumstellar grains have been identified including three amorphous silicate grains and two polycrystalline aggregates. All of these grains are between 0.2 and 0.5 micrometers in size. The isotopic compositions of all five presolar silicate grains fall within the range of presolar oxides and silicates, having large (17)O-enrichments and normal (18)O/(16)O ratios (Group 1 grains from AGB and RG stars). The amorphous silicates are chemically heterogeneous and contain nanophase FeNi metal and FeS grains in a Mg-silicate matrix. Two of the amorphous silicate grains are aggregates with subgrains showing variable Mg/Si ratios in chemical maps. The polycrystalline grains show annealed textures (equilibrium grains boundaries, uniform Mg/Fe ratios), and consist of 50-100 nm enstatite and pyrrhotite grains with lesser forsterite. One of the polycrystalline aggregates contains a subgrain of diopside. The polycrystalline aggregates form by subsolidus annealing of amorphous precursors. The bulk compositions of the five grains span a wide range in Mg/Si ratios from 0.4 to 1.2 (avg. 0.86). The average Fe/Si (0.40) and S/Si (0.21) ratios show a much narrower range of values and are approximately 50% of their solar

  15. Crystalline Silica Primer

    Staff- Branch of Industrial Minerals

    1992-01-01

    Crystalline silica is the scientific name for a group of minerals composed of silicon and oxygen. The term crystalline refers to the fact that the oxygen and silicon atoms are arranged in a threedimensional repeating pattern. This group of minerals has shaped human history since the beginning of civilization. From the sand used for making glass to the piezoelectric quartz crystals used in advanced communication systems, crystalline silica has been a part of our technological development. Crystalline silica's pervasiveness in our technology is matched only by its abundance in nature. It's found in samples from every geologic era and from every location around the globe. Scientists have known for decades that prolonged and excessive exposure to crystalline silica dust in mining environments can cause silicosis, a noncancerous lung disease. During the 1980's, studies were conducted that suggested that crystalline silica also was a carcinogen. As a result of these findings, crystalline silica has been regulated under the Occupational Safety and Health Administration's (OSHA) Hazard Communication Standard (HCS). Under HCS, OSHAregulated businesses that use materials containing 0.1% or more crystalline silica must follow Federal guidelines concerning hazard communication and worker training. Although the HCS does not require that samples be analyzed for crystalline silica, mineral suppliers or OSHAregulated

  16. Detailed modelling of the circumstellar molecular line emission of the S-type AGB star W Aquilae

    Danilovich, T.; Bergman, P.; Justtanont, K.; Lombaert, R.; Maercker, M.; Olofsson, H.; Ramstedt, S.; Royer, P.

    2014-09-01

    Context. S-type AGB stars have a C/O ratio which suggests that they are transition objects between oxygen-rich M-type stars and carbon-rich C-type stars. As such, their circumstellar compositions of gas and dust are thought to be sensitive to their precise C/O ratio, and it is therefore of particular interest to examine their circumstellar properties. Aims: We present new Herschel HIFI and PACS sub-millimetre and far-infrared line observations of several molecular species towards the S-type AGB star W Aql. We use these observations, which probe a wide range of gas temperatures, to constrain the circumstellar properties of W Aql, including mass-loss rate and molecular abundances. Methods: We used radiative transfer codes to model the circumstellar dust and molecular line emission to determine circumstellar properties and molecular abundances. We assumed a spherically symmetric envelope formed by a constant mass-loss rate driven by an accelerating wind. Our model includes fully integrated H2O line cooling as part of the solution of the energy balance. Results: We detect circumstellar molecular lines from CO, H2O, SiO, HCN, and, for the first time in an S-type AGB star, NH3. The radiative transfer calculations result in an estimated mass-loss rate for W Aql of 4.0 × 10-6 M⊙ yr-1 based on the 12CO lines. The estimated 12CO/13CO ratio is 29, which is in line with ratios previously derived for S-type AGB stars. We find an H2O abundance of 1.5 × 10-5, which is intermediate to the abundances expected for M and C stars, and an ortho/para ratio for H2O that is consistent with formation at warm temperatures. We find an HCN abundance of 3 × 10-6, and, although no CN lines are detected using HIFI, we are able to put some constraints on the abundance, 6 × 10-6, and distribution of CN in W Aql's circumstellar envelopeusing ground-based data. We find an SiO abundance of 3 × 10-6, and an NH3 abundance of 1.7 × 10-5, confined to a small envelope. If we include uncertainties

  17. The circumstellar envelope of AFGL 4106

    Van Loon, J T; Van Winckel, H; Waters, L B F M; Loon, Jacco Th. van; Winckel, Hans van

    1999-01-01

    We present new imaging and spectroscopy of the post-red supergiant binary AFGL 4106. Coronographic imaging in H-alpha reveals the shape and extent of the ionized region in the circumstellar envelope (CSE). Echelle spectroscopy with the slit covering almost the entire extent of the CSE is used to derive the physical conditions in the ionized region and the optical depth of the dust contained within the CSE. The dust shell around AFGL 4106 is clumpy and mixed with ionized gas. H-alpha and [N II] emission is brightest from a thin bow-shaped layer just outside of the detached dust shell. On-going mass loss is traced by [Ca II] emission and blue-shifted absorption in lines of low-ionization species. A simple model is used to interpret the spatial distribution of the circumstellar extinction and the dust emission in a consistent way.

  18. The complex circumstellar environment of HD142527

    Verhoeff, A P; Pantin, E; Waters, L B F M; Tielens, A G G M; Honda, M; Fujiwara, H; Bouwman, J; van Boekel, R; Dougherty, S M; de Koter, A; Dominik, C; Mulders, G D

    2011-01-01

    The recent findings of gas giant planets around young A-type stars suggest that disks surrounding Herbig Ae/Be stars will develop planetary systems. An interesting case is HD142527, for which previous observations revealed a complex circumstellar environment and an unusually high ratio of infrared to stellar luminosity. Its properties differ considerably from other Herbig Ae/Be stars. This suggests that the disk surrounding HD142527 is in an uncommon evolutionary stage. We aim for a better understanding of the geometry and evolutionary status of the circumstellar material around the Herbig Ae/Be star HD142527. We map the composition and spatial distribution of the dust around HD142527. We analyze SEST and ATCA millimeter data, VISIR N and Q-band imaging and spectroscopy. We gather additional relevant data from the literature. We use the radiative transfer code MCMax to construct a model of the geometry and density structure of the circumstellar matter, which fits all of the observables satisfactorily. We find...

  19. Oxygen Chemistry in the Circumstellar Envelope of the Carbon-Rich Star IRC+10216

    Agundez, M; Agundez, Marcelino; Cernicharo, Jose

    2006-01-01

    In this paper we study the oxygen chemistry in the C-rich circumstellar shells of IRC+10216. The recent discoveries of oxygen bearing species (water, hydroxyl radical and formaldehyde) toward this source challenge our current understanding of the chemistry in C-rich circumstellar envelopes. The presence of icy comets surrounding the star or catalysis on iron grain surfaces have been invoked to explain the presence of such unexpected species. This detailed study aims at evaluating the chances of producing O-bearing species in the C-rich circumstellar envelope only by gas phase chemical reactions. For the inner hot envelope, it is shown that although most of the oxygen is locked in CO near the photosphere (as expected for a C/O ratio greater than 1), some stellar radii far away species such as H2O and CO2 have large abundances under the assumption of thermochemical equilibrium. It is also shown how non-LTE chemistry makes very difficult the CO-->H2O,CO2 transformation predicted in LTE. Concerning the chemistry ...

  20. The infrared spectral features of circumstellar envelope of evolved low- and intermediate-mass stars

    2008-01-01

    The circumstellar envelope of evolved stars of low- and intermediate-mass is an important site for dust formation. In comparison with the interstellar medium, they have more types of organics and different types of inorganics. Various infrared features in the circumstellar envelope can reveal the composition and abundance of dust, as well as the chemical and physical conditions of the circumstellar shell. Infrared features and their carriers are different in the C-rich or O-rich environment, and the mixed-environment where the C-rich and O-rich circumstellar materials co-exist. The C-rich sources exhibit a series of spectral features which are attrib- uted to organic molecules. They also show two prominent features at 21 μm and 30 μm which emit a large portion of infrared radiation. The O-rich sources exhibit the strong 9.7 μm and 18 μm features attributed to the Si-O bending and O-Si-O stretching modes of amorphous silicate dust. With the ISO/SWS spectrometer, about 50 narrow bands are identified with the crystalline silicate grains, mainly forsterite and enstatite. In addition, a series of features, at 13 μm, 16.8 μm, 19.5 μm and 31.8 μm, appearing to be correlated with each other, are attributed to oxides. Some objects simultaneously show the C-rich and O-rich features, e.g. some C-rich sources have silicate features. There is no well-accepted interpretation for such mixed appearance, though a binary model is suggested.

  1. The infrared spectral features of circumstellar envelope of evolved low-and intermediate-mass stars

    ZHANG Ke; JIANG BiWei

    2008-01-01

    The circumstellar envelope of evolved stars of low-and intermediate-mass is an important site for dust formation. In comparison with the interstellar medium, they have more types of organics and different types of inorganics. Various infrared features in the circumstellar envelope can reveal the composition and abundance of dust, as well as the chemical and physical conditions of the circumstellar shell. Infrared features and their carriers are different in the C-rich or O-rich environment, and the mixed-environment where the C-rich and O-rich circumstellar materials co-exist. The C-rich sources exhibit a series of spectral features which are attrib-uted to organic molecules. They also show two prominent features at 21 μm and 30 μm which emit a large portion of infrared radiation. The O-rich sources exhibit the strong 9.7 μm and 18 μm features attributed to the Si-O bending and O-Si-O stretching modes of amorphous silicate dust. With the ISO/SWS spectrometer, about 50 narrow bands are identified with the crystalline silicate grains, mainly forsterite and enstatite. In addition, a series of features, at 13 μm, 16.8 μm, 19.5 μm and 31.8 μm, appearing to be correlated with each other, are attributed to oxides. Some objects simultaneously show the C-rich and O-rich features, e.g. some C-rich sources have silicate features. There is no well-accepted interpretation for such mixed appearance, though a binary model is suggested.

  2. Chemistry and distribution of daughter species in the circumstellar envelopes of O-rich AGB stars

    Li, Xiaohu; Millar, Tom J.; Heays, Alan N.; Walsh, Catherine; van Dishoeck, Ewine F.; Cherchneff, Isabelle

    2016-03-01

    Context. Thanks to the advent of Herschel and ALMA, new high-quality observations of molecules present in the circumstellar envelopes of asymptotic giant branch (AGB) stars are being reported that reveal large differences from the existing chemical models. New molecular data and more comprehensive models of the chemistry in circumstellar envelopes are now available. Aims: The aims are to determine and study the important formation and destruction pathways in the envelopes of O-rich AGB stars and to provide more reliable predictions of abundances, column densities, and radial distributions for potentially detectable species with physical conditions applicable to the envelope surrounding IK Tau. Methods: We use a large gas-phase chemical model of an AGB envelope including the effects of CO and N2 self-shielding in a spherical geometry and a newly compiled list of inner-circumstellar envelope parent species derived from detailed modeling and observations. We trace the dominant chemistry in the expanding envelope and investigate the chemistry as a probe for the physics of the AGB phase by studying variations of abundances with mass-loss rates and expansion velocities. Results: We find a pattern of daughter molecules forming from the photodissociation products of parent species with contributions from ion-neutral abstraction and dissociative recombination. The chemistry in the outer zones differs from that in traditional PDRs in that photoionization of daughter species plays a significant role. With the proper treatment of self-shielding, the N → N2 and C+→ CO transitions are shifted outward by factors of 7 and 2, respectively, compared with earlier models. An upper limit on the abundance of CH4 as a parent species of (≲2.5 × 10-6 with respect to H2) is found for IK Tau, and several potentially observable molecules with relatively simple chemical links to other parent species are determined. The assumed stellar mass-loss rate, in particular, has an impact on the

  3. On the origin of elemental abundances in the terrestrial planets

    Elser, Sebastian; Moore, Ben

    2012-01-01

    The abundances of elements in the Earth and the terrestrial planets provide the initial conditions for life and clues as to the history and formation of the Solar System. We follow the pioneering work of Bond et al. (2010) and combine circumstellar disk models, chemical equilibrium calculations and dynamical simulations of planet formation to study the bulk composition of rocky planets. We use condensation sequence calculations to estimate the initial abundance of solids in the circumstellar disk with properties determined from time dependent theoretical models. We combine this with dynamical simulations of planetesimal growth that trace the solids during the planet formation process. We calculate the elemental abundances in the resulting planets and explore how these vary with the choice of disk model and the initial conditions within the Solar Nebula. Although certain characteristics of the terrestrial planets in the Solar System could be reproduced, none of our models could reproduce the abundance properti...

  4. Circumstellar disks around binary stars in Taurus

    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 Fmm∝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.

  5. Circumstellar disks around binary stars in Taurus

    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.

  6. An MCMC Circumstellar Disks Modeling Tool

    Wolff, Schuyler; Perrin, Marshall D.; Mazoyer, Johan; Choquet, Elodie; Soummer, Remi; Ren, Bin; Pueyo, Laurent; Debes, John H.; Duchene, Gaspard; Pinte, Christophe; Menard, Francois

    2016-01-01

    We present an enhanced software framework for the Monte Carlo Markov Chain modeling of circumstellar disk observations, including spectral energy distributions and multi wavelength images from a variety of instruments (e.g. GPI, NICI, HST, WFIRST). The goal is to self-consistently and simultaneously fit a wide variety of observables in order to place constraints on the physical properties of a given disk, while also rigorously assessing the uncertainties in the derived properties. This modular code is designed to work with a collection of existing modeling tools, ranging from simple scripts to define the geometry for optically thin debris disks, to full radiative transfer modeling of complex grain structures in protoplanetary disks (using the MCFOST radiative transfer modeling code). The MCMC chain relies on direct chi squared comparison of model images/spectra to observations. We will include a discussion of how best to weight different observations in the modeling of a single disk and how to incorporate forward modeling from PCA PSF subtraction techniques. The code is open source, python, and available from github. Results for several disks at various evolutionary stages will be discussed.

  7. Circumstellar Debris Disks: Diagnosing the Unseen Perturber

    Nesvold, Erika R; Vican, Laura; Farr, Will M

    2016-01-01

    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 t...

  8. A database of circumstellar OH masers

    Engels, D

    2015-01-01

    We present a new database of circumstellar OH masers at 1612, 1665, and 1667 MHz in the Milky Way galaxy. The database (version 2.4) contains 13655 observations and 2341 different stars detected in at least one transition. Detections at 1612\\,MHz are considered to be complete until the end of 2014 as long as they were published in refereed papers. Detections of the main lines (1665 and 1667 MHz) and non-detections in all transitions are included only if published after 1983. The database contains flux densities and velocities of the two strongest maser peaks, the expansion velocity of the shell, and the radial velocity of the star. Links are provided for about 100 stars ($<$5\\% of all stars with OH masers) to interferometric observations and monitoring programs of the maser emission published since their beginnings in the 1970s. Access to the database is possible over the Web (www.hs.uni-hamburg.de/maserdb), allowing cone searches for individual sources and lists of sources. A general search is possible in...

  9. The circumstellar envelope of the C-rich post-AGB star HD 56126

    Hony, S; Waters, L B F M; De Koter, A

    2003-01-01

    We present a detailed study of the circumstellar envelope of the post-asymptotic giant branch ``21 micron object'' HD 56126. We build a detailed dust radiative transfer model of the circumstellar envelope in order to derive the dust composition and mass, and the mass-loss history of the star. To model the emission of the dust we use amorphous carbon, hydrogenated amorphous carbon, magnesium sulfide and titanium carbide. We present a detailed parametrisation of the optical properties of hydrogenated amorphous carbon as a function of H/C content. The mid-infrared imaging and spectroscopy is best reproduced by a single dust shell from 1.2 to 2.6 arcsec radius around the central star. This shell originates from a short period during which the mass-loss rate exceeded 10^(-4) M_sun/yr. We find that the strength of the ``21'' micron feature poses a problem for the TiC identification. The low abundance of Ti requires very high absorption cross-sections in the ultraviolet and visible wavelength range to explain the st...

  10. Laboratory Studies Of Circumstellar Carbonaceous Grain Formation

    Contreras, Cesar; Sciamma-O'Brien, Ella; Salama, Farid

    2014-06-01

    The study of the formation processes of dust is essential to understand the budget of extraterrestrial organic molecules. Although dust with all its components plays an important role in the evolution of interstellar (IS) chemistry and in the formation of organic molecules, little is known on the formation processes of carbonaceous dust. We report the progress that was recently achieved in this domain using NASA Ames’ COSmIC facility (Contreras & Salama 2013, ApJS, 208, 6). PAHs are important chemical building blocks of IS dust. They are detected in IDPs and in meteoritic samples. Additionally, observational, laboratory, and theoretical studies have shown that PAHs are an important, ubiquitous component of the ISM. The formation of PAHs from smaller molecules has not been extensively studied. Therefore, we have performed laboratory experiments to study the dynamic processes of carbon grain formation, starting from the smallest hydrocarbon molecules into the formation of larger PAH and further into nanograins. Studies of IS dust analogs formed from a variety of PAH and hydrocarbon precursors as well as species that include the atoms O, N, and S, have recently been performed in our laboratory using the COSmIC facility to provide conditions that simulate IS and circumstellar environments. The species formed in the COSmiC chamber through a pulsed discharge nozzle plasma source are detected and characterized with a cavity ringdown spectrometer coupled to a time-of-flight mass spectrometer, thus providing both spectroscopic and ion mass information in-situ. Analysis of solid soot particles was also conducted using scanning electron microscopy at the UCSC/NASA Ames’ MACS facility. The SEM analysis of the deposition of soot from methane and acetylene precursors seeded in argon plasmas provide examples on the types of nanoparticles and micrograins that are produced in these gas mixtures under our experimental conditions. From these measurements, we derive information on

  11. Studying Young Circumstellar Disks with ALMA

    Ménard, F. C.

    2005-12-01

    Accretion disks are pivotal elements in the formation and early evolution of solar-like stars. On top of supplying the raw material for stellar build-up, their internal conditions also regulate the formation of planets. Their study therefore holds the key to solve the mystery of the formation of our Solar System. This article focuses on observational studies of circumstellar disks associated with pre-main sequence solar-like stars and presents a few selected problems where ALMA will contribute in finding answers. At optical and near-infrared wavelengths, the direct measurement of disk parameters poses an obvious challenge: at the distance of typical star forming regions (e.g. ˜140 pc for Taurus), a planetary system like ours (with a diameter of ≃ 50 AU out to Pluto, but excluding the Kuiper belt) subtends only 0.35 arcsec. Moreover, its surface brightness is low in comparison to the bright central star. Hence, high angular resolution and high contrast imaging techniques are required if one hopes to resolve and measure such protoplanetary disks. Fortunately, potent imaging instruments have been available for about 10 years now. They cover a large part of the electromagnetic spectrum, from the UV/optical with HST, the near-infrared with ground-based adaptive optics systems to the millimeter range with long-baseline radio interferometers. It is therefore not surprising that our knowledge of the structure of disks surrounding low-mass stars has made a gigantic leap forward in the last decade. However, the angular resolution of current millimeter interferometers will remain significantly poorer than the resolution that is available at shorter wavelengths (˜ 0.1 arcsec) until ALMA provides the necessary long baselines. At that time, astronomers will have access to data of comparable resolution over a very large wavelength range, with unprecedented sensitivity. As a direct consequence, our understanding of the disk structure and evolution should improve just as much

  12. Erosion of circumstellar particle disks by interstellar dust

    Lissauer, Jack J.; Griffith, Caitlin A.

    1989-01-01

    Circumstellar particle disks appear to be a common phenomenon; however, their properties vary greatly. Models of the evolution of such systems focus on internal mechanisms such as interparticle collisions and Poynting-Robertson drag. Herein it is shown that 'sandblasting' by interstellar dust can be an important and even dominant contributor to the evolution of circumstellar particle disks. Stars spend up to about 3 percent of their main-sequence lifetimes within atomic clouds. Among an IRAS sample of 21 nearby main-sequence A stars, beta Pictoris has the brightest disk; it also possesses the smallest random velocity and therefore the slowest predicted erosion rate.

  13. Circumstellar envelopes and mass loss of red giant stars

    Mass loss from red giants is rediscussed on the basis of new observations of circumstellar absorption lines. The second ionization of Ca and the run of the expansion velocity with height above the stellar surface which are important for deriving mass loss rates of M giants have been determined. Deutsch's (1960) mass loss rates had to be revised considerably for early M giants. A review of the properties of expanding circumstellar envelopes of red giants as determined from optical, infrared, and microwave observations is given. (orig./BJ)

  14. Physical processes in circumstellar disks around young stars

    2011-01-01

    Circumstellar disks are vast expanses of dust that form around new stars in the earliest stages of their birth. Predicted by astronomers as early as the eighteenth century, they weren't observed until the late twentieth century, when interstellar imaging technology enabled us to see nascent stars hundreds of light years away. Since then, circumstellar disks have become an area of intense study among astrophysicists, largely because they are thought to be the forerunners of planetary systems like our own-the possible birthplaces of planets.            This volume brings

  15. Understanding the Chemical Complexity in Circumstellar Envelopes of C-rich AGB Stars: the Case of IRC +10216

    Agundez, M; Pardo, J R; Exposito, J P F; Guélin, M; Tenenbaum, E D; Ziurys, L M; Apponi, A J

    2007-01-01

    The circumstellar envelopes of carbon-rich AGB stars show a chemical complexity that is exemplified by the prototypical object IRC +10216, in which about 60 different molecules have been detected to date. Most of these species are carbon chains of the type CnH, CnH2, CnN, HCnN. We present the detection of new species (CH2CHCN, CH2CN, H2CS, CH3CCH and C3O) achieved thanks to the systematic observation of the full 3 mm window with the IRAM 30m telescope plus some ARO 12m observations. All these species, known to exist in the interstellar medium, are detected for the first time in a circumstellar envelope around an AGB star. These five molecules are most likely formed in the outer expanding envelope rather than in the stellar photosphere. A pure gas phase chemical model of the circumstellar envelope is reasonably successful in explaining the derived abundances, and additionally allows to elucidate the chemical formation routes and to predict the spatial distribution of the detected species.

  16. VOLATILE-RICH CIRCUMSTELLAR GAS IN THE UNUSUAL 49 CETI DEBRIS DISK

    Roberge, Aki; Grady, Carol A. [Exoplanets and Stellar Astrophysics Laboratory, NASA Goddard Space Flight Center, Code 667, Greenbelt, MD 20771 (United States); Welsh, Barry Y. [Eureka Scientific, 2452 Delmer, Suite 100, Oakland, CA 96002 (United States); Kamp, Inga [Kapteyn Astronomical Institute, University of Groningen, 9700 AV Groningen (Netherlands); Weinberger, Alycia J., E-mail: Aki.Roberge@nasa.gov [Department of Terrestrial Magnitism, Carnegie Institution for Science, 5241 Broad Branch Road NW, Washington, DC 20015 (United States)

    2014-11-20

    We present Hubble Space Telescope Space Telescope Imaging Spectrograph far-UV spectra of the edge-on disk around 49 Ceti, one of the very few debris disks showing submillimeter CO emission. Many atomic absorption lines are present in the spectra, most of which arise from circumstellar gas lying along the line-of-sight to the central star. We determined the line-of-sight C I column density, estimated the total carbon column density, and set limits on the O I column density. Surprisingly, no line-of-sight CO absorption was seen. We discuss possible explanations for this non-detection, and present preliminary estimates of the carbon abundances in the line-of-sight gas. The C/Fe ratio is much greater than the solar value, suggesting that 49 Cet harbors a volatile-rich gas disk similar to that of β Pictoris.

  17. VOLATILE-RICH CIRCUMSTELLAR GAS IN THE UNUSUAL 49 CETI DEBRIS DISK

    We present Hubble Space Telescope Space Telescope Imaging Spectrograph far-UV spectra of the edge-on disk around 49 Ceti, one of the very few debris disks showing submillimeter CO emission. Many atomic absorption lines are present in the spectra, most of which arise from circumstellar gas lying along the line-of-sight to the central star. We determined the line-of-sight C I column density, estimated the total carbon column density, and set limits on the O I column density. Surprisingly, no line-of-sight CO absorption was seen. We discuss possible explanations for this non-detection, and present preliminary estimates of the carbon abundances in the line-of-sight gas. The C/Fe ratio is much greater than the solar value, suggesting that 49 Cet harbors a volatile-rich gas disk similar to that of β Pictoris

  18. Volatile-Rich Circumstellar Gas in the Unusual 49 Ceti Debris Disk

    Roberge, Aki; Kamp, Inga; Weinberger, Alycia J; Grady, Carol A

    2014-01-01

    We present Hubble Space Telescope STIS far-UV spectra of the edge-on disk around 49 Ceti, one of the very few debris disks showing sub-mm CO emission. Many atomic absorption lines are present in the spectra, most of which arise from circumstellar gas lying along the line-of-sight to the central star. We determined the line-of-sight CI column density, estimated the total carbon column density, and set limits on the OI column density. Surprisingly, no line-of-sight CO absorption was seen. We discuss possible explanations for this non-detection, and present preliminary estimates of the carbon abundances in the line-of-sight gas. The C/Fe ratio is much greater than the solar value, suggesting that 49 Cet harbors a volatile-rich gas disk similar to that of Beta Pictoris.

  19. Hot Molecular Circumstellar Disk around Massive Protostar Orion Source I

    Hirota, Tomoya; Kurono, Yasutaka; Honma, Mareki

    2013-01-01

    We report new Atacama Large Millimeter/Submillimeter Array (ALMA) observations of a circumstellar disk around Source I in Orion KL, an archetype of massive protostar candidate. We detected two ortho-H$_{2}$O lines at 321 GHz ($10_{2,9}$-$9_{3,6}$) and 336 GHz ($\

  20. Circumstellar and explosion properties of Type Ibn supernovae

    Moriya, Takashi J

    2016-01-01

    We investigate circumstellar and explosion properties of Type Ibn supernovae (SNe) by analyzing their bolometric light curves. Bolometric light curves of Type Ibn SNe generally have a large contrast between peak luminosity and late-phase luminosity, which is much larger than those of 56Ni-powered SNe. Thus, most of them are likely powered by the interaction between SN ejecta and dense circumstellar media. In addition, Type Ibn SNe decline much faster than Type IIn SNe, and this indicates that the interaction in Type Ibn SNe ceases earlier than in Type IIn SNe. Thus, we argue that Type Ibn SN progenitors experience high mass-loss rates in a short period just before explosion, while Type IIn SN progenitors have high mass-loss rates sustained for a long time. Furthermore, we show that rise time and peak luminosity of Type Ibn and Type IIn SNe are similar and thus, they have similar explosion properties and circumstellar density. The similar circumstellar density in the two kinds of SNe may indicate that mass-los...

  1. Airborne silica levels in an urban area

    In order to evaluate the exposure levels of the general population we studied the concentrations of silica particles in the inhalable particulate fraction (PM10) in different meteorological-climate periods in an urban area of Rome. In order to determine the concentration and the granulometric spectrum of silica particles, PM10 sampled by a cascade impactor was analysed by X-ray diffractometry (XRD) and by scanning electron microscopy equipped with a thin-window system for X-ray microanalysis (SEM/EDX). Over the period September 2004-October 2005 the abundance of silica particles as evaluated by SEM/EDX ranged from 1.6 to 10.4% of the total PM10 particulate, with a weight concentration of free crystalline silica, evaluated by XRD, in the range 0.25-2.87 μg/m3. The mean diameter of silica particles ranged from 0.3 to 10.5 μm, with more than 87% of particles having a diameter of less than 2.5 μm. The correlations between SEM/EDX and XRD data seem to suggest that the airborne silica particles in the urban location studied were mainly in the form crystalline silica. A strong relationship was found between the meteorological-climate conditions and the concentration level of free crystalline silica. This result suggests that the Southern winds from the Sahara desert carry an important amount of silica particles into Mediterranean Europe

  2. 41Ca in Circumstellar Graphite from Supernovae

    Amari, S.; Zinner, E.; Lewis, R. S.

    1995-09-01

    anomalies (Fig. 1), with patterns that are consistent with that predicted for the O-rich zones of a 25 (sub)Solar Mass supernova [4] (shown as broad lines in the figure). Thus, ^41Ca in these two grains is likely to have been produced by neutron capture in these zones. One grain (KE3c-242) has a ^44Ca excess due to the decay of ^44Ti (T(sub)1/2=52a), with an inferred ^44Ti/^48Ti ratio of (3.6+/-1.4) x 10^-2. The presence of ^41Ca together with Ca isotopic anomalies in circumstellar graphite grains is evidence for mixing between the C-rich and O-rich zones. Furthermore, evidence for ^44Ti in a few low density graphite grains [6] strongly suggests contributions from the innermost zone to the ejecta from which the grains formed. Observations of SN 1987A [e.g., 7] and hydrodynamic calculations [e.g., 8] indicate the existence of clumps of variable compositions in SN ejecta. The large variety of isotopic compositions in low density graphite grains is evidence for extensive and heterogeneous mixing of SN ejecta, confirming the astronomical observations and the theoretical calculations. References: [1] Amari S. et al. (1994) LPS XXV, 27-28. [2] Zinner E. et al. (1995) LPS XXVI, 1561-1562. [3] Travaglio C. et al. (1995) in preparation. [4] Meyer B. S. et al. (1995) Meteoritics, 30, 319-324. [5] Woosley S. E. and Weaver T. A. (1995) Astrophys. J. Suppl., in press. [6] Amari S. et al. (1995) LPS XXVI, 37-38. [7] Hass M. R. et al. (1990) Astrophys. J., 360, 257-266. [8] Herant M. and Benz W. (1992) Astrophys. J., 387, 294-308.

  3. The polluted atmosphere of the white dwarf NLTT 25792 and the diversity of circumstellar environments

    Vennes, S

    2013-01-01

    We present an analysis of X-Shooter spectra of the polluted, hydrogen-rich white dwarf NLTT 25792. The spectra show strong lines of calcium (Ca H&K, near-infrared calcium triplet, and Ca I 4226 and numerous lines of iron along with magnesium and aluminum lines from which we draw the abundance pattern. Moreover, the photospheric Ca H&K lines are possibly blended with a circumstellar component shifted by -20 km/s relative to the photosphere. A comparison with a sample of four white dwarfs with similar parameters show considerable variations in their abundance patterns, particularly in the calcium to magnesium abundance ratio that varies by a factor of five within this sample. The observed variations, even after accounting for diffusion effects, imply similar variations in the putative accretion source. Also, we find that silicon and sodium are significantly underabundant in the atmosphere of NLTT 25792, a fact that may offer some clues on the nature of the accretion source.

  4. External Shaping of Circumstellar Envelopes of Evolved Stars

    Cox, N. L. J.

    2015-08-01

    The circumstellar envelopes of asymptotic giant branch (AGB) stars and red supergiants (RSGs) are complex chemical and physical environments, and the specifics of their mass-loss history are important for both stellar and galactic evolution. One key aspect in this is to understand how the circumstellar medium of these stars can be shaped and affected by both internal and external mechanisms. These influences can skew our view on the (dust) chemistry and mass-loss history of these stars, and hence their role in the chemical enrichment of galaxies. This contribution focuses on the external mechanism related to the interaction between the slow dusty stellar wind and the local ambient medium. I will discuss what recent observations and hydrodynamical simulations have revealed and how these can help us learn more about AGB stars and RSGs, as well as the interstellar medium (ISM).

  5. Bimodality of circumstellar disk evolution induced by Hall current

    Tsukamoto, Y; Okuzumi, S; Machida, M N; Inutsuka, S

    2015-01-01

    The formation process of circumstellar disks is still controversial because of the interplay of complex physical processes that occurs during the gravitational collapse of prestellar cores. In this study, we investigate the effect of the Hall current term on the formation of circumstellar disk using three-dimensional simulations. In our simulations, all non-ideal effects as well as the radiation transfer are considered. We show that the size of the disk is significantly affected by a simple difference in the inherent properties of the prestellar core, namely whether the rotation vector and the magnetic field are parallel or anti-parallel. In the former case, only a very small disk ($20$ AU) disk is formed in the early phase of protostar formation. We also show that the anti-rotating envelopes against the disk-rotation appear with a size of $\\gtrsim 200$ AU. We predict that the anti-rotating envelope will be found in the future observations.

  6. Archival Legacy Investigations of Circumstellar Environments: Overview and First Results

    Choquet, Élodie; Hagan, J Brendan; Gofas-Salas, Elena; Rajan, Abhijith; Chen, Christine; Perrin, Marshall D; Debes, John; Golimowski, David; Hines, Dean C; N'Diaye, Mamadou; Schneider, Glenn; Mawet, Dimitri; Marois, Christian; Soummer, Rémi

    2014-01-01

    We are currently conducting a comprehensive and consistent re-processing of archival HST-NICMOS coronagraphic surveys using advanced PSF subtraction methods, entitled the Archival Legacy Investigations of Circumstellar Environments program (ALICE, HST/AR 12652). This virtual campaign of about 400 targets has already produced numerous new detections of previously unidentified point sources and circumstellar structures. We present five newly spatially resolved debris disks revealed in scattered light by our analysis of the archival data. These images provide new views of material around young solar-type stars at ages corresponding to the period of terrestrial planet formation in our solar system. We have also detected several new candidate substellar companions, for which there are ongoing followup campaigns (HST/WFC3 and VLT/SINFONI in ADI mode). Since the methods developed as part of ALICE are directly applicable to future missions (JWST, AFTA coronagraph) we emphasize the importance of devising optimal PSF s...

  7. Circumstellar absorption in double detonation Type Ia supernovae

    Shen, Ken J; Foley, Ryan J

    2013-01-01

    Upon formation, degenerate He core white dwarfs are surrounded by a radiative H-rich layer primarily supported by ideal gas pressure. In this Letter, we examine the effect of this H-rich layer on mass transfer in He-C/O double white dwarf binaries that will eventually merge and possibly yield a Type Ia supernova (SN Ia) in the double detonation scenario. Because its thermal profile and equation of state differ from the underlying He core, the H-rich layer is transferred stably onto the C/O white dwarf prior to the He core's tidal disruption. We find that this material is ejected from the binary system and sweeps up the surrounding interstellar medium hundreds to thousands of years before the SN Ia. The close match between the resulting circumstellar medium profiles and values inferred from recent observations of circumstellar absorption in SNe Ia gives further credence to the resurgent double detonation scenario.

  8. CIRCUMSTELLAR ABSORPTION IN DOUBLE DETONATION TYPE Ia SUPERNOVAE

    Upon formation, degenerate He core white dwarfs are surrounded by a radiative H-rich layer primarily supported by ideal gas pressure. In this Letter, we examine the effect of this H-rich layer on mass transfer in He+C/O double white dwarf binaries that will eventually merge and possibly yield a Type Ia supernova (SN Ia) in the double detonation scenario. Because its thermal profile and equation of state differ from the underlying He core, the H-rich layer is transferred stably onto the C/O white dwarf prior to the He core's tidal disruption. We find that this material is ejected from the binary system and sweeps up the surrounding interstellar medium hundreds to thousands of years before the SN Ia. The close match between the resulting circumstellar medium profiles and values inferred from recent observations of circumstellar absorption in SNe Ia gives further credence to the resurgent double detonation scenario.

  9. X-raying circumstellar material around young stars

    Schneider, P C

    2015-01-01

    Young stars are surrounded by copious amounts of circumstellar material. Its composition, in particular its gas-to-dust ratio, is an important parameter. However, measuring this ratio is challenging, because gas mass estimates are often model dependent. X-ray absorption is sensitive to the gas along the line-of-sight while optical/near-IR extinction depends on the dust content. Therefore, the gas-to-dust ratio of an absorber is given by the ratio between X-ray and optical/near-IR extinction. We present three systems where we used X-ray and optical/near-IR data to constrain the gas-to-dust ratio of circumstellar material; from a dust-rich debris disk to gaseous protoplanetary disks.

  10. Four hundred million years of silica biomineralization in land plants

    Trembath-Reichert, Elizabeth; Wilson, Jonathan Paul; McGlynn, Shawn E.; Fischer, Woodward W.

    2015-01-01

    Biomineralization plays a fundamental role in the global silicon cycle. Grasses are known to mobilize significant quantities of Si in the form of silica biominerals and dominate the terrestrial realm today, but they have relatively recent origins and only rose to taxonomic and ecological prominence within the Cenozoic Era. This raises questions regarding when and how the biological silica cycle evolved. To address these questions, we examined silica abundances of extant members of early-diver...

  11. Rapid disappearance of a warm, dusty circumstellar disk

    Melis, Carl; Zuckerman, B.; Rhee, Joseph H.; Song, Inseok; Murphy, Simon J.; Bessell, Michael S.

    2012-01-01

    Stars form with gaseous and dusty circumstellar envelopes, which rapidly settle into disks that eventually give rise to planetary systems. Understanding the process by which these disks evolve is paramount in developing an accurate theory of planet formation that can account for the variety of planetary systems discovered so far. The formation of Earth-like planets through collisional accumulation of rocky objects within a disk has mainly been explored in theoretical and computational work in...

  12. On the excitation and formation of circumstellar fullerenes

    Bernard-Salas, J.; Cami, J.; E. Peeters; Jones, A.P.; Micelotta, E. R.; Groenewegen, M. A. T.

    2012-01-01

    We compare and analyze the Spitzer mid-infrared spectrum of three fullerene-rich planetary nebulae in the Milky Way and the Magellanic Clouds; Tc1, SMP SMC 16, and SMP LMC 56. The three planetary nebulae share many spectroscopic similarities. The strongest circumstellar emission bands correspond to the infrared active vibrational modes of the fullerene species C60 and little or no emission is present from Polycyclic Aromatic Hydrocarbons (PAHs). The strength of the fullerene bands in the thre...

  13. The progenitor of SN 2011ja: Clues from circumstellar interaction

    Chakraborti, Sayan; Ray, Alak; Smith, Randall; Ryder, Stuart; Yadav, Naveen; Sutaria, Firoza; Dwarkadas, Vikram V; Chandra, Poonam; Pooley, David; Roy, Rupak

    2013-01-01

    Massive stars, possibly red supergiants, which retain extended hydrogen envelopes until core collapse, produce Type II Plateau (IIP) supernovae. The ejecta from these explosions shock the circumstellar matter originating from the mass loss of the progenitor during the final phases of its life. This interaction accelerates particles to relativistic energies which then lose energy via synchrotron radiation in the shock-amplified magnetic fields and inverse Compton scattering against optical pho...

  14. Biogenic nanostructured silica

    2002-01-01

    Silicon is by far the most abundant element in the earth crust and also is an essential element for higher plants, yet its biology and mechanisms in plant tolerance of biotic and abiotic stresses are poorly understood. Based on the molecular mechanisms of the biosilicification in marine organisms such as diatoms and sponges, the cell wall template-mediated self-assembly of nanostructured silica in marine organisms and higher plants as well as the related organic molecules are discussed. Understanding of the templating and structure-directed effects of silicon-processing organic molecules not only offers the clue for synthesizing silicon-based materials, but also helps to recognize the anomaly of silicon in plant biology.

  15. Theoretical spectra of circumstellar dust shells around carbon-rich asymptotic giant branch stars

    Winters, J. M.; Dominik, C.; Sedlmayr, E.

    1994-01-01

    Realistic modeling of circumstellar dust shells around evolved stars has to include a physical treatment of the interaction among hydrodynamics, thermodynamics, radiative transfer, chemistry and dust formation and -growth. A self-consistent solution of this problem is presented in the case of stationary, spherical symmetric dust-driven winds. The resulting shell structure and the mass-loss rate are completely determined by the three fundamental stellar parameters stellar mass M(stellar), stellar luminosity L(stellar) and effective temperature T(sub eff) and by the element abundances epsilon(sub i). A detailed calculation of the transport coefficients of the dust component by means of the particle size distribution function and the solution of the non-grey radiative transfer problem provide realistic synthetic spectra of the dust shell models. We discuss the dependence of the resulting spectra on the stellar parameters in terms of infrared two color diagrams. Application of these model calculations to the prominent infrared object IRC +10216 yields best agreement with the observed spectrum and the visibility data at maximum light for the stellar parameters M(stellar) = 0.7 solar mass, L(stellar) = 2.4 x 10(exp 4) solar luminosity, T(stellar) = 2010K and a carbon to oxygen ratio of epsilon(sub c)/epsilon(sub o) = 1.40, which corresponds to a mass-loss rate of M-dot = 8 x 10(exp -5) solar mass/yr. In this model only amorphous carbon grains are considered as the main opacity source. From this model a distance to IRC +10216 of d = 170pc is deduced. The total mass contained in the circumstellar dust shell implies and initial main sequence mass of M(sub ZAMS) greater than or = 1.3 solar mass for IRC +10216.

  16. Cepheids at high angular resolution: circumstellar envelope and pulsation

    Gallenne, Alexandre

    2011-12-01

    In 2005, interferometric observations with VLTI/VINCI and CHARA/FLUOR revealed the existence of a circumstellar envelope (CSE) around some Cepheids. This surrounding material is particularly interesting for two reasons: it could have an impact on the distance estimates and could be linked to a past or on-going mass loss. The use of Baade-Wesselink methods for independent distance determinations could be significantly biased by the presence of these envelopes. Although their observations are difficult because of the high contrast between the photosphere of the star and the CSE, several observation techniques have the potential to improve our knowledge about their physical properties. In this thesis, I discuss in particular high angular resolution techniques that I applied to the study of several bright Galactic Cepheids. First, I used adaptive optic observations with NACO of the Cepheid RS Puppis, in order to deduce the flux ratio between the CSE and the photosphere of the star. In addition, I could carry out a statistical study of the speckle noise and inspect a possible asymmetry. Secondly, I analysed VISIR data to study the spectral energy distribution of a sample of Cepheids. These diffraction-limited images enabled me to carry out an accurate photometry in the N band and to detect an IR excess linked to the presence of a circumstellar component. On the other hand, applying a Fourier analysis I showed that some components are resolved. I then explored the K' band with the recombination instrument FLUOR for some bright Cepheids. Thanks to new set of data of Y Oph, I improved the study of its circumstellar envelope, using a ring-like model for the CSE. For two other Cepheids, U Vul and S Sge, I applied the interferometric Baade-Wesselink method in order to estimate their distance.

  17. Detection of circumstellar gas associated with GG Tauri

    Skrutskie, M. F.; Snell, R. L.; Strom, K. M.; Strom, S. E.; Edwards, S.; Fukui, Y.; Mizuno, A.; Hayashi, M.; Ohashi, N.

    1993-01-01

    Double-peaked (C-12)O (1-0) emission centered on the young T Tauri star GG Tau possesses a line profile which may be modeled on the assumption that CO emission arises in an extended circumstellar disk. While bounds on the observed gas mass can be estimated on this basis, it is suggested that a large amount of mass could lie within a small and optically thick region, escaping detection due to beam-dilution effects. In addition, CO may no longer accurately trace the gas mass due to its dissociation, or freezing into grains, or due to the locking-up of carbon into more complex molecules.

  18. Evidence for dust grain growth in young circumstellar disks

    Throop, H B; Esposito, L W; McCaughrean, M J; Throop, Henry B.; Bally, John; Esposito, Larry W.; Caughrean, Mark J. Mc

    2001-01-01

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

  19. Light-scattering models applied to circumstellar dust properties

    Radiation pressure force, Poynting-Robertson effect, and collisions are important to determine the size distribution of dust in circumstellar debris disks with the two former parameters depending on the light-scattering properties of grains. We here present Mie and discrete-dipole approximation (DDA) calculations to describe the optical properties of dust particles around β Pictoris, Vega, and Fomalhaut in order to study the influence of the radiation pressure force. We find that the differences between Mie and DDA calculations are lower than 30% for all porosities. Therefore, Mie calculations can be used to determine the cut-off limits which contribute to the size distribution for the different systems

  20. Four hundred million years of silica biomineralization in land plants

    Trembath-Reichert, Elizabeth; Wilson, Jonathan Paul; McGlynn, Shawn E.; Fischer, Woodward W.

    2015-04-01

    Biomineralization plays a fundamental role in the global silicon cycle. Grasses are known to mobilize significant quantities of Si in the form of silica biominerals and dominate the terrestrial realm today, but they have relatively recent origins and only rose to taxonomic and ecological prominence within the Cenozoic Era. This raises questions regarding when and how the biological silica cycle evolved. To address these questions, we examined silica abundances of extant members of early-diverging land plant clades, which show that silica biomineralization is widespread across terrestrial plant linages. Particularly high silica abundances are observed in lycophytes and early-diverging ferns. However, silica biomineralization is rare within later-evolving gymnosperms, implying a complex evolutionary history within the seed plants. Electron microscopy and X-ray spectroscopy show that the most common silica-mineralized tissues include the vascular system, epidermal cells, and stomata, which is consistent with the hypothesis that biomineralization in plants is frequently coupled to transpiration. Furthermore, sequence, phylogenetic, and structural analysis of nodulin 26-like intrinsic proteins from diverse plant genomes points to a plastic and ancient capacity for silica accumulation within terrestrial plants. The integration of these two comparative biology approaches demonstrates that silica biomineralization has been an important process for land plants over the course of their >400 My evolutionary history.

  1. The Circumstellar Disk of the Be Star $o$~Aquarii

    Sigut, T A A; Jansen, B; Zavala, R T

    2015-01-01

    Omicron Aquarii is late-type, Be shell star with a stable and nearly symmetric H$\\alpha$ emission line. We combine H$\\alpha$ interferometric observations obtained with the Navy Precision Optical Interferometer (NPOI) covering 2007 through 2014 with H$\\alpha$ spectroscopic observations over the same period and a 2008 observation of the system's near-infrared spectral energy distribution to constrain the properties of $o$~Aqr's circumstellar disk. All observations are consistent with a circumstellar disk seen at an inclination of $75\\pm\\,3^{\\circ}$ with a position angle on the sky of $110\\pm\\,8^{\\circ}$ measured E from N. From the best-fit disk density model, we find that 90\\% of the H$\\alpha$ emission arises from within $9.5$ stellar radii, and the mass associated with this H$\\alpha$ disk is $\\sim 1.8\\times10^{-10}$ of the stellar mass and the associated angular momentum, assuming Keplerian rotation for the disk, is $\\sim 1.6\\times10^{-8}$ of the total stellar angular momentum. The occurrence of a central quas...

  2. The interaction of supernovae and pulsars with circumstellar environment

    In Chapter One, self-similar solutions for the time-dependent behavior of a shocked, spherically, symmetric, relativistic fluid with tangential magnetic field in the case where the boundaries of the shocked fluid move at a constant velocity are found. These solutions can be applied to the evolution of the shocked-relativistic pulsar winds which are probably observed as Crab-like supernova remnants. Since the models include time evolution, they can be applied to young objects and may be relevant to a possible pulsar nebular in SN1987a. In Chapter Two, the development of models for the infrared echo from Type II supernovae arising from the heating of circumstellar dust is discussed. In these models, ellipsoidial dust distributions are considered (previous models considered only spherically symmetric dust distributions) since some red supergiants, the likely progenitors of most Type II supernovae, are known to have asymmetric circumstellar envelopes. The models show that an asymmetric dust distribution can have a substantial effect on the time evolution of the echo. In Chapter Three, the properties to be expected of the infrared and scattered light echoes from SN1987A are derived. These echoes are expected to arise from the dust formed within the wind given off by the progenitor during a previous red supergiant phase. The models take into account the emission and scattering properties of the dust grains, in particular silicate dust grains, and the observed supernova light curve. The predictions of the models are compared with the available observations

  3. Stellar orbit evolution in close circumstellar disc encounters

    Muñoz, Diego J; Vogelsberger, Mark; Hernquist, Lars; Springel, Volker

    2014-01-01

    The formation and early evolution of circumstellar discs often occurs within dense, newborn stellar clusters. For the first time, we apply the moving-mesh code AREPO, to circumstellar discs in 3-D, focusing on disc-disc interactions that result from stellar fly-bys. Although a small fraction of stars are expected to undergo close approaches, the outcomes of the most violent encounters might leave an imprint on the discs and host stars that will influence both their orbits and their ability to form planets. We first construct well-behaved 3-D models of self-gravitating discs, and then create a suite of numerical experiments of parabolic encounters, exploring the effects of pericenter separation r_p, disc orientation and disc-star mass ratio (M_d/M_*) on the orbital evolution of the host stars. Close encounters (2r_p<~ disc radius) can truncate discs on very short time scales. If discs are massive, close encounters facilitate enough orbital angular momentum extraction to induce stellar capture. We find that ...

  4. Modelling circumstellar discs with 3D radiation hydrodynamics

    Acreman, David M; Rundle, David A

    2009-01-01

    We present results from combining a grid-based radiative transfer code with a Smoothed Particle Hydrodynamics code to produce a flexible system for modelling radiation hydrodynamics. We use a benchmark model of a circumstellar disc to determine a robust method for constructing a gridded density distribution from SPH particles. The benchmark disc is then used to determine the accuracy of the radiative transfer results. We find that the SED and the temperature distribution within the disc are sensitive to the representation of the disc inner edge, which depends critically on both the grid and SPH resolution. The code is then used to model a circumstellar disc around a T-Tauri star. As the disc adjusts towards equilibrium vertical motions in the disc are induced resulting in scale height enhancements which intercept radiation from the central star. Vertical transport of radiation enables these perturbations to influence the mid-plane temperature of the disc. The vertical motions decay over time and the disc ulti...

  5. THE PROGENITOR OF SN 2011ja: CLUES FROM CIRCUMSTELLAR INTERACTION

    Massive stars, possibly red supergiants, which retain extended hydrogen envelopes until core collapse, produce Type II plateau (IIP) supernovae. The ejecta from these explosions shocks the circumstellar matter originating from the mass loss of the progenitor during the final phases of its life. This interaction accelerates particles to relativistic energies which then lose energy via synchrotron radiation in the shock-amplified magnetic fields and inverse Compton scattering against optical photons from the supernova. These processes produce different signatures in the radio and X-ray parts of the electromagnetic spectrum. Observed together, they allow us to break the degeneracy between shock acceleration and magnetic field amplification. In this work, we use X-rays observations from the Chandra and radio observations from the Australia Telescope Compact Array to study the relative importance of processes which accelerate particles and those which amplify magnetic fields in producing the non-thermal radiation from SN 2011ja. We use radio observations to constrain the explosion date. Multiple Chandra observations allow us to probe the history of variable mass loss from the progenitor. The ejecta expands into a low-density bubble followed by interaction with a higher density wind from a red supergiant consistent with MZAMS ∼> 12 M☉. Our results suggest that a fraction of Type IIP supernovae may interact with circumstellar media set up by non-steady winds

  6. 78 FR 14540 - Cyromazine, Silica Silicates (Silica Dioxide and Silica Gel), Glufosinate Ammonium, Dioctyl...

    2013-03-06

    ... AGENCY Cyromazine, Silica Silicates (Silica Dioxide and Silica Gel), Glufosinate Ammonium, Dioctyl Sodium... the registration review of cyromazine, silica silicates (silica dioxide and silica gel), glufosinate..., consistent with the notice published in the Federal Register of August 17, 2012, (77 FR 49792)...

  7. Herschel/HIFI observations of the circumstellar ammonia lines in IRC+10216

    Schmidt, M. R.; He, J. H.; Szczerba, R.; Bujarrabal, V.; Alcolea, J.; Cernicharo, J.; Decin, L.; Justtanont, K.; Teyssier, D.; Menten, K. M.; Neufeld, D. A.; Olofsson, H.; Planesas, P.; Marston, A. P.; Sobolev, A. M.; de Koter, A.; Schöier, F. L.

    2016-08-01

    Context. A discrepancy exists between the abundance of ammonia (NH3) derived previously for the circumstellar envelope (CSE) of IRC+10216 from far-IR submillimeter rotational lines and that inferred from radio inversion or mid-infrared (MIR) absorption transitions. Aims: To address the discrepancy described above, new high-resolution far-infrared (FIR) observations of both ortho- and para-NH3 transitions toward IRC+10216 were obtained with Herschel, with the goal of determining the ammonia abundance and constraining the distribution of NH3 in the envelope of IRC+10216. Methods: We used the Heterodyne Instrument for the Far Infrared (HIFI) on board Herschel to observe all rotational transitions up to the J = 3 level (three ortho- and six para-NH3 lines). We conducted non-LTE multilevel radiative transfer modelling, including the effects of near-infrared (NIR) radiative pumping through vibrational transitions. The computed emission line profiles are compared with the new HIFI data, the radio inversion transitions, and the MIR absorption lines in the ν2 band taken from the literature. Results: We found that NIR pumping is of key importance for understanding the excitation of rotational levels of NH3. The derived NH3 abundances relative to molecular hydrogen were (2.8 ± 0.5) × 10-8 for ortho-NH3 and for para-NH3, consistent with an ortho/para ratio of 1. These values are in a rough agreement with abundances derived from the inversion transitions, as well as with the total abundance of NH3 inferred from the MIR absorption lines. To explain the observed rotational transitions, ammonia must be formed near to the central star at a radius close to the end of the wind acceleration region, but no larger than about 20 stellar radii (1σ confidence level). Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. HIFI is the Herschel Heterodyne Instrument for the Far

  8. ALMA Observations of Circumstellar Disks in the Upper Scorpius OB Association

    Barenfeld, Scott A; Ricci, Luca; Isella, Andrea

    2016-01-01

    We present ALMA observations of 106 G-, K-, and M-type stars in the Upper Scorpius OB Association hosting circumstellar disks. With these data, we measure the 0.88 mm continuum and $^{12}$CO $J = 3-2$ line fluxes of disks around low mass ($0.14-1.66$ $M_{\\odot}$) stars at an age of 5-11 Myr. Of the 75 primordial disks in the sample, 53 are detected in the dust continuum and 26 in CO. Of the 31 disks classified as debris/evolved transitional disks, 5 are detected in the continuum and none in CO. The lack of CO emission in approximately half of the disks with detected continuum emission can be explained if CO is optically thick but has a compact emitting area ($\\lesssim 40$ AU), or if the CO is heavily depleted by a factor of at least $\\sim1000$ relative to interstellar medium abundances and is optically thin. The continuum measurements are used to estimate the dust mass of the disks. We find a correlation between disk dust mass and stellar host mass consistent with a power-law relation of $M_{dust}\\propto M_*^...

  9. Bursting SN 1996cr's Bubble: Hydrodynamic and X-ray Modeling of its Circumstellar Medium

    Dwarkadas, Vikram V; Bauer, Franz

    2010-01-01

    SN1996cr is one of the five closest SNe to explode in the past 30 years. Due to its fortuitous location in the Circinus Galaxy at ~ 3.7 Mpc, there is a wealth of recently acquired and serendipitous archival data available to piece together its evolution over the past decade, including a recent 485 ks Chandra HETG spectrum. In order to interpret this data, we have explored hydrodynamic simulations, followed by computations of simulated spectra and light curves under non-equilibrium ionization conditions, and directly compared them to the observations. Our simulated spectra manage to fit both the X-ray continuum and lines at 4 epochs satisfactorily, while our computed light curves are in good agreement with additional flux-monitoring data sets. These calculations allow us to infer the nature and structure of the circumstellar medium, the evolution of the SN shock wave, and the abundances of the ejecta and surrounding medium. The data imply that SN 1996cr exploded in a low-density medium before interacting with ...

  10. LABORATORY INVESTIGATIONS OF POLYCYCLIC AROMATIC HYDROCARBON FORMATION AND DESTRUCTION IN THE CIRCUMSTELLAR OUTFLOWS OF CARBON STARS

    The formation and destruction mechanisms of interstellar dust analogs formed from a variety of polycyclic aromatic hydrocarbon (PAH) and hydrocarbon molecular precursors are studied in the laboratory. We used the newly developed facility COSmIC, which simulates interstellar and circumstellar environments, to investigate both PAHs and species that include the cosmically abundant atoms O, N, and S. The species generated in a discharge plasma are detected, monitored, and characterized in situ using highly sensitive techniques that provide both spectral and ion mass information. We report here the first series of measurements obtained in these experiments which focus on the characterization of the most efficient molecular precursors in the chemical pathways that eventually lead to the formation of carbonaceous grains in the stellar envelopes of carbon stars. We compare and discuss the relative efficiencies of the various molecular precursors that lead to the formation of the building blocks of carbon grains. We discuss the most probable molecular precursors in terms of size and structure and the implications for the expected growth and destruction processes of interstellar carbonaceous dust

  11. LABORATORY INVESTIGATIONS OF POLYCYCLIC AROMATIC HYDROCARBON FORMATION AND DESTRUCTION IN THE CIRCUMSTELLAR OUTFLOWS OF CARBON STARS

    Contreras, Cesar S.; Salama, Farid, E-mail: cesar.contreras@nasa.gov, E-mail: Farid.Salama@nasa.gov [Space Science and Astrobiology Division, NASA-Ames Research Center, Moffett Field, CA 94035 (United States)

    2013-09-15

    The formation and destruction mechanisms of interstellar dust analogs formed from a variety of polycyclic aromatic hydrocarbon (PAH) and hydrocarbon molecular precursors are studied in the laboratory. We used the newly developed facility COSmIC, which simulates interstellar and circumstellar environments, to investigate both PAHs and species that include the cosmically abundant atoms O, N, and S. The species generated in a discharge plasma are detected, monitored, and characterized in situ using highly sensitive techniques that provide both spectral and ion mass information. We report here the first series of measurements obtained in these experiments which focus on the characterization of the most efficient molecular precursors in the chemical pathways that eventually lead to the formation of carbonaceous grains in the stellar envelopes of carbon stars. We compare and discuss the relative efficiencies of the various molecular precursors that lead to the formation of the building blocks of carbon grains. We discuss the most probable molecular precursors in terms of size and structure and the implications for the expected growth and destruction processes of interstellar carbonaceous dust.

  12. The photodissociation and chemistry of CO isotopologues: applications to interstellar clouds and circumstellar disks

    Visser, R; Black, J H

    2009-01-01

    Aims. Photodissociation by UV light is an important destruction mechanism for CO in many astrophysical environments, ranging from interstellar clouds to protoplanetary disks. The aim of this work is to gain a better understanding of the depth dependence and isotope-selective nature of this process. Methods. We present a photodissociation model based on recent spectroscopic data from the literature, which allows us to compute depth-dependent and isotope-selective photodissociation rates at higher accuracy than in previous work. The model includes self-shielding, mutual shielding and shielding by atomic and molecular hydrogen, and it is the first such model to include the rare isotopologues C17O and 13C17O. We couple it to a simple chemical network to analyse CO abundances in diffuse and translucent clouds, photon-dominated regions, and circumstellar disks. Results. The photodissociation rate in the unattenuated interstellar radiation field is 2.6e-10 s^-1, 30% higher than currently adopted values. Increasing t...

  13. Circumstellar Dust Shells: Clues to the Evolution of R Coronae Borealis Stars

    Montiel, Edward J.; Clayton, Geoffrey C.

    2016-06-01

    R Coronae Borealis (RCB) stars are an exotic group of extremely hydrogen- deficient, carbon-rich supergiants that are known for their spectacular declines in brightness (up to 8 mags) at irregular intervals. Two scenarios are currently competing to explain the origins of these stars. One suggests that RCB stars are the products after a binary white dwarf (WD) system merges. The other takes a single, evolved star and has it undergo a final, helium-shell flash (FF) and becoming a cool giant. Recently, observations of elemental abundances in RCB stars have strongly swung the argument in favor of the WD merger model. The FF scenario has maintained its relevancy by seemingly being the only model able to offer a suitable explanation for one RCB feature that merger model has historically struggled with explaining: the presence of cold, circumstellar dust envelopes which might be fossil planetary nebulae (PNe). In reality, the shells could actually be fossil PNe, material left over from the WD merger, or mass lost during the RCB phase, itself. I will present the results of my dissertation, which is to try and discern the nature and history of the far-IR dust shells around RCB stars to help understand the origin of these enigmatic stars. I will discuss our efforts to determine the mass, size, temperature, and morphology of these diffuse structures surrounding a sample of RCB stars using multi-wavelength observations ranging from the ultraviolet to the submillimeter. These observations have provided unprecedented wavelength coverage for both the central stars and their CSM. They have been examined by eye for morphology and have been used in the construction of maximum-light spectral energy distributions (SEDs). I will present the results of our Monte Carlo radiative transfer of the maximum-light SEDs. Finally, I will highlight our work investigating the HI abundance of the envelope of R Coronae Borealis, itself, using archival 21—cm observations from the Arecibo

  14. Flash-Heating of Circumstellar Clouds by $\\gamma$ Ray Bursts

    Dermer, C D; Dermer, Charles D.; Boettcher, Markus

    2000-01-01

    The blast-wave model for gamma-ray bursts (GRBs) has been called intoquestion by observations of spectra from GRBs that are harder than can beproduced through optically thin synchrotron emission. If GRBs originate fromthe collapse of massive stars, then circumstellar clouds near burst sourceswill be illuminated by intense gamma radiation, and the electrons in theseclouds will be rapidly scattered to energies as large as several hundred keV.Low-energy photons that subsequently pass through the hot plasma will bescattered to higher energies, hardening the intrisic spectrum. This effectresolves the "line-of-death" objection to the synchrotron shock model.Illuminated clouds near GRBs will form relativistic plasmas containing largenumbers of electron-positron pairs that can be detected within ~ 1-2 days ofthe explosion before expanding and dissipating. Localized regions of pairannihilation radiation in the Galaxy would reveal past GRB explosions.

  15. Magnetic field and early evolution of circumstellar disks

    Tsukamoto, Yusuke

    2016-01-01

    The magnetic field plays a central role in the formation and evolution of circumstellar disks. The magnetic field connects the rapidly rotating central region with the outer envelope and extracts angular momentum from the central region during gravitational collapse of the cloud core. This process is known as magnetic braking. Both analytical and multidimensional simulations have shown that disk formation is strongly suppressed by magnetic braking in moderately magnetized cloud cores in the ideal magnetohydrodynamic limit. On the other hand, recent observations have provided growing evidence of a relatively large disk several tens of astronomical units in size existing in some Class 0 young stellar objects. This introduces a serious discrepancy between the theoretical study and observations. Various physical mechanisms have been proposed to solve the problem of catastrophic magnetic braking, such as misalignment between the magnetic field and the rotation axis, turbulence, and non-ideal effect. In this paper,...

  16. Resolved images of self-gravitating circumstellar discs with ALMA

    Cossins, P; Testi, L

    2010-01-01

    In this paper we present simulated observations of massive self-gravitating circumstellar discs using the Atacama Large Millimetre/sub-millimetre Array (ALMA). Using a smoothed particle hydrodynamics model of a $0.2M_{\\odot}$ disc orbiting a $1M_{\\odot}$ protostar, with a cooling model appropriate for discs at temperatures below $\\sim 160$K and representative dust opacities, we have constructed maps of the expected emission at sub-mm wavelengths. We have then used the CASA ALMA simulator to generate simulated images and visibilities with various array configurations and observation frequencies, taking into account the expected thermal noise and atmospheric opacities. We find that at 345 GHz (870 $\\mu$m) spiral structures at a resolution of a few AU should be readily detectable in approximately face-on discs out to distances of the Taurus-Auriga star-forming complex.

  17. The progenitor of SN 2011ja: Clues from circumstellar interaction

    Chakraborti, Sayan; Smith, Randall; Ryder, Stuart; Yadav, Naveen; Sutaria, Firoza; Dwarkadas, Vikram V; Chandra, Poonam; Pooley, David; Roy, Rupak

    2013-01-01

    Massive stars, possibly red supergiants, which retain extended hydrogen envelopes until the time of core collapse produce Type IIP (Plateau) supernovae. The ejecta from these explosions shock the circumstellar matter originating from the mass loss of the progenitor during the final phases of its life. This interaction accelerates particles to relativistic energies which then lose energy via synchrotron radiation in the shock-amplified magnetic fields and inverse Compton scattering against optical photons from the supernova. These processes produce different signatures in the radio and X-ray part of the electromagnetic spectrum. Observed together, they allow us to break the degeneracy between shock acceleration and magnetic field amplification. In this work we use X-rays observations from the Chandra and radio observations from the ATCA to study the relative importance of particle acceleration and magnetic fields in producing the non-thermal radiation from SN 2011ja. We use radio observations to constrain the ...

  18. Archival Legacy Investigation of Circumstellar Environments (ALICE). Survey results

    Soummer, Remi; Choquet, Elodie; Pueyo, Laurent; Brendan Hagan, J.; Gofas-Salas, Elena; Rajan, Abhijith; Chen, Christine; Perrin, Marshall D.; Debes, John H.; Golimowski, David A.; Hines, Dean C.; N'Diaye, Mamadou; Schneider, Glenn; Mawet, Dimitri; Marois, Christian

    2016-01-01

    We report on the status of the ALICE project (Archival Legacy Investigation of Circumstellar Environments. HST/AR-12652), which consists in a consistent reanalysis of the entire HST-NICMOS coronagraphic archive with advanced post-processing techniques. Over the last two years, we have developed a sophisticated pipeline able to handle the data of the 400 stars of the archive. We present the results of the overall reduction campaign and discuss the first statistical analysis of the candidate detections. As we will deliver high-level science products to the STScI MAST archive, we are defining a new standard format for high-contrast science products, which will be compatible with every new high-contrast imaging instrument and used by the JWST coronagraphs. We present here an update and overview of the specifications of this standard.

  19. Beta Pic-like Circumstellar Gas Disk Around 2 And

    Cheng, Patricia

    2003-01-01

    This grant was awarded to support the data analysis and publication of results from our project entitled P Pic-like Circumstellar Gas Disk Around 2 And . We proposed to obtain FUSE observations of 2 And and study the characteristics and origin of its circumstellar gas. We observed 2 Andromedae with FUSE on 3-4 July 2001 in 11 exposures with a total exposure time of 21,289 seconds through the LWRS aperture. Our data were calibrated with Version 1.8.7 of the CALFUSE pipeline processing software. We corrected the wavelength scale for the heliocentric velocity error in this version of the CALFUSE software. The relative accuracy of the calibrated wavelength scale is +/- 9 km/s . We produced a co-added spectrum in the LiF 1B and LiF 2A channels (covering the 1100 to 1180 A region) by cross-correlating the 11 individual exposures and doing an exposure-time weighted average flux. The final co-added spectra have a signal-to-noise ratio in the stellar continuum near 1150 A of about 20. To obtain an absolute wavelength calibration, we cross-correlated our observed spectra with a model spectrum to obtain the best fit for the photospheric C I lines. Because the photospheric lines are very broad, this yields an absolute accuracy for the wavelength scale of approx.+/- 15 km/s. We then rebinned 5 original pixels to yield the optimal sampling of .033 A for each new pixel, because the calibrated spectra oversample the spectral resolution for FUSE+LWRS (R = 20,000 +/- 2,000).

  20. Lambda Boo Abundance Patterns: Accretion from Orbiting Sources

    Jura, M

    2015-01-01

    The abundance anomalies in lambda Boo stars are popularly explained by element-specific mass inflows at rates that are much greater than empirically-inferred bounds for interstellar accretion. Therefore, a lambda Boo star's thin outer envelope must derive from a companion star, planet, analogs to Kuiper Belt Objects or a circumstellar disk. Because radiation pressure on gas-phase ions might selectively allow the accretion of carbon, nitrogen, and oxygen and inhibit the inflow of elements such as iron, the source of the acquired matter need not contain dust. We propose that at least some lambda Boo stars accrete from the winds of hot Jupiters.

  1. Microporous silica membranes

    Boffa, Vittorio; Yue, Yuanzheng

    2012-01-01

    Hydrothermal stability is a crucial factor for the application of microporous silica-based membranes in industrial processes. Indeed, it is well established that steam exposure may cause densification and defect formation in microporous silica membranes, which are detrimental to both membrane...... permeability and selectivity. Numerous previous studies show that microporous transition metal doped-silica membranes are hydrothermally more stable than pure silica membranes, but less permeable. Here we present a quantitative study on the impact of type and concentration of transition metal ions on the...... microporous structure, stability and permeability of amorphous silica-based membranes, providing information on how to design chemical compositions and synthetic paths for the fabrication of silica-based membranes with a well accessible and highly stabile microporous structure....

  2. CPD–52 9243: Circumstellar Dust and Gas Properties Derived from Interferometric and Spectroscopic Data/footnotemark

    Cidale, L.S.; Borges Fernandes, M.; Kraus, Michaela; Andruchow, I.; Chesneau, O.; Kanaan, S.; Arias, M.L.; Curé, M.; de Wit, W.J.; Muratore, M.F.

    San Francisco: Astronomical Society of the Pacific, 2012 - (Carciofi, A.), s. 323-328. (ASP Conference Series. 464). ISBN 9781583818107. [Circumstellar Dynamics at High Resolution. Foz do Iguaçu (BR), 27.02.2012-02.03.2012] R&D Projects: GA ČR(CZ) GAP209/11/1198 Institutional research plan: CEZ:AV0Z10030501 Keywords : circumstellar dust * disk structure * kinematics Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

  3. A HIFI view on circumstellar H2O in M-type AGB stars: radiative transfer, velocity profiles, and H2O line cooling

    Maercker, M; Olofsson, H; De Beck, E; Justtanont, K; Lombaert, R; Royer, P

    2016-01-01

    We aim to constrain the temperature and velocity structures, and H2O abundances in the winds of a sample of M-type AGB stars. We further aim to determine the effect of H2O line cooling on the energy balance in the inner circumstellar envelope. We use two radiative-transfer codes to model molecular emission lines of CO and H2O towards four M-type AGB stars. We focus on spectrally resolved observations of CO and H2O from HIFI. The observations are complemented by ground-based CO observations, and spectrally unresolved CO and H2O observations with PAC. The observed line profiles constrain the velocity structure throughout the circumstellar envelopes (CSEs), while the CO intensities constrain the temperature structure in the CSEs. The H2O observations constrain the o-H2O and p-H2O abundances relative to H2. Finally, the radiative-transfer modelling allows to solve the energy balance in the CSE, in principle including also H2O line cooling. The fits to the line profiles only set moderate constraints on the velocit...

  4. Silica Refractory Bricks

    Yu Lingyan; Peng Xigao

    2011-01-01

    @@ 1.Scope This standard specifies the classification,technical requirements,test methods,quality appraisal procedures,packing,marking,transportation,storage,and quality certificate of silica refractory bricks.This standard is applicable to silica refractory bricks with single weight≤40 kg.

  5. Rapid disappearance of a warm, dusty circumstellar disk

    Melis, Carl; Rhee, Joseph H; Song, Inseok; Murphy, Simon J; Bessell, Michael S

    2012-01-01

    Stars form with gaseous and dusty circumstellar envelopes, which rapidly settle into disks that eventually give rise to planetary systems. Understanding the process by which these disks evolve is paramount in developing an accurate theory of planet formation that can account for the variety of planetary systems discovered so far. The formation of Earth-like planets through collisional accumulation of rocky objects within a disk has mainly been explored in theoretical and computational work in which post-collision ejecta evolution is typically ignored, although recent work has considered the fate of such material. Here we report observations of a young, Sun-like star (TYC 8241 2652 1) where infrared flux from post-collisional ejecta has decreased drastically, by a factor of about 30, over a period of less than two years. The star seems to have gone from hosting substantial quantities of dusty ejecta, in a region analogous to where the rocky planets orbit in the Solar System, to retaining at most a meagre amoun...

  6. Cepheids at high angular resolution: circumstellar envelope and pulsation

    Gallenne, Alexandre

    2011-01-01

    In 2005, interferometric observations with VLTI/VINCI and CHARA/FLUOR revealed the existence of a circumstellar envelope (CSE) around some Cepheids. This surrounding material is particularly interesting for two reasons: it could have an impact on the distance estimates and could be linked to a past or on-going mass loss. The use of Baade-Wesselink methods for independent distance determinations could be significantly biased by the presence of these envelopes. Although their observations are difficult because of the high contrast between the photosphere of the star and the CSE, several observation techniques have the potential to improve our knowledge about their physical properties. In this thesis, I discuss in particular high angular resolution techniques that I applied to the study of several bright Galactic Cepheids. First, I used adaptive optic observations with NACO of the Cepheid RS Puppis, in order to deduce the flux ratio between the CSE and the photosphere of the star. In addition, I could carry out ...

  7. Massive circumstellar envelope around type IIn supernova SN 1995G

    Chugai, N N

    2003-01-01

    We model the interaction of the supernova SN 1995G with a dense circumstellar (CS) gas in a thin shell approximation. A model fit of the observed bolometric light curve combined with data on the supernova expansion velocity provides an estimate of the density of the CS shell, its mass ($approx 1 M_{odot}$), and age ($approx 8$ years). It is shown that the derived CS gas density does not depend on the assumed mass of the supernova ejecta. This results from the high CS density, which ensures that the forward shock wave is essentially radiative. The derived CS density is consistent with the H$alpha$ luminosity and with the presence of the apparent effect of Thomson scattering in the red wing of this line. The mass of the CS envelope together with its expansion velocity indicates that the CS envelope was ejected as a result of violent energy release ($sim 6times10^{48}$ erg) eight years before the supernova outburst.

  8. Dust Migration and Morphology in Optically Thin Circumstellar Gas Disks

    Takeuchi, T; Takeuchi, Taku; Artymowicz, Pawel

    2001-01-01

    We analyze the dynamics of gas-dust coupling in the presence of stellar radiation pressure in circumstellar gas disks, which are in a transitional stage between the gas-dominated, optically thick, primordial nebulae, and the dust-dominated, optically thin Vega-type disks. Dust undergo radial migration, seeking a stable equilibrium orbit in corotation with gas. The migration of dust gives rise to radial fractionation of dust and creates a variety of possible observed disk morphologies, which we compute by considering the equilibrium between the dust production and the dust-dust collisions removing particles from their equilibrium orbits. Sand-sized and larger grains are distributed throughout most of the gas disk, with concentration near the gas pressure maximum in the inner disk. Smaller grains (typically in the range of 10 to 200 micron) concentrate in a prominent ring structure in the outer region of the gas disk (presumably at radius 100 AU), where gas density is rapidly declining with radius. The width an...

  9. ALIGNMENT OF PROTOSTARS AND CIRCUMSTELLAR DISKS DURING THE EMBEDDED PHASE

    Star formation proceeds via the collapse of a molecular cloud core over multiple dynamical timescales. Turbulence within cores results in a spatially non-uniform angular momentum of the cloud, causing a stochastic variation in the orientation of the disk forming from the collapsing material. In the absence of star-disk angular momentum coupling, such disk-tilting would provide a natural mechanism for the production of primordial spin-orbit misalignments in the resulting planetary systems. However, owing to high accretion rates in the embedded phase of star formation, the inner edge of the circumstellar disk extends down to the stellar surface, resulting in efficient gravitational and accretional angular momentum transfer between the star and the disk. Here, we demonstrate that the resulting gravitational coupling is sufficient to suppress any significant star-disk misalignment, with accretion playing a secondary role. The joint tilting of the star-disk system leads to a stochastic wandering of star-aligned bipolar outflows. Such wandering widens the effective opening angle of stellar outflows, allowing for more efficient clearing of the remainder of the protostar's gaseous envelope. Accordingly, the processes described in this work provide an additional mechanism responsible for sculpting the stellar initial mass function

  10. The chemical history of molecules in circumstellar disks. I. Ices

    Visser, R; Doty, S D; Dullemond, C P

    2009-01-01

    (Abridged) Aims & Methods. A two-dimensional, semi-analytical model is presented that follows, for the first time, the chemical evolution from a collapsing molecular cloud (a pre-stellar core) to a protostar and circumstellar disk. The model computes infall trajectories from any point in the cloud and tracks the radial and vertical motion of material in the viscously evolving disk. It includes a full time-dependent radiative transfer treatment of the dust temperature, which controls much of the chemistry. A small parameter grid is explored to understand the effects of the sound speed and the mass and rotation of the cloud. The freeze-out and evaporation of carbon monoxide (CO) and water (H2O), as well as the potential for forming complex organic molecules in ices, are considered as important first steps to illustrate the full chemistry. Results. Both species freeze out towards the centre before the collapse begins. Pure CO ice evaporates during the infall phase and re-adsorbs in those parts of the disk th...

  11. SN 2007od: A Type IIP SN with Circumstellar Interaction

    Andrews, J E; Clayton, Geoffrey C; Sugerman, B E K; Chatelain, J P; Clem, J; Welch, D L; Barlow, M J; Ercolano, B; Fabbri, J; Wesson, R; Meixner, M

    2010-01-01

    SN 2007od exhibits characteristics that have rarely been seen in a Type IIP supernova (SN). Optical V band photometry reveals a very steep brightness decline between the plateau and nebular phases of ~4.5 mag, likely due to SN 2007od containing a low mass of 56Ni. The optical spectra show an evolution from normal Type IIP with broad Halpha emission, to a complex, four component Halpha emission profile exhibiting asymmetries caused by dust extinction after day 232. This is similar to the spectral evolution of the Type IIn SN 1998S, although no early-time narrow (~200 km s-1) Halpha component was present in SN 2007od. In both SNe, the intermediate-width Halpha emission components are thought to arise in the interaction between the ejecta and its circumstellar medium (CSM). SN 2007od also shows a mid-IR excess due to new dust. The evolution of the Halpha profile and the presence of the mid-IR excess provide strong evidence that SN 2007od formed new dust before day 232. Late-time observations reveal a flattening ...

  12. The formation of polycyclic aromatic hydrocarbons in evolved circumstellar environments

    Cherchneff, Isabelle

    2010-01-01

    The formation of Polycyclic Aromatic Hydrocarbons in the circumstellar outflows of evolved stars is reviewed, with an emphasis on carbon stars on the Asymptotic Giant Branch. Evidence for PAHs present in their winds is provided by meteoritic studies and recent observations of the Unidentified Infrared bands. We detail the chemical processes leading to the closure of the first aromatic ring as well as the growth mechanisms leading to amorphous carbon grains. Existing studies on PAH formation in evolved stellar envelopes are reviewed and new results for the modelling of the inner wind of the archetype carbon star IRC+10216 are presented. Benzene, C6H6, forms close to the star, as well as water, H2O, as a result of non-equilibrium chemistry induced by the periodic passage of shocks. The growth process of aromatic rings may thus resemble that active in sooting flames due to the presence of radicals like hydroxyl, OH. Finally, we discuss possible formation processes for PAHs and aromatic compounds in the hydrogen-...

  13. The circumstellar environment of pre-SN Ia systems

    Harvey, E; Boumis, P; Kopsacheili, M; Akras, S; Sabin, L; Jurkic, T

    2016-01-01

    Here we explore the possible preexisting circumstellar debris of supernova type Ia systems. Classical, symbiotic and recurrent novae all accrete onto roughly solar mass white dwarfs from main sequence or Mira type companions and result in thermonuclear runaways and expulsion of the accreted material at high velocity. The expelled material forms a fast moving shell that eventually slows to planetary nebula expansion velocities within several hundred years. All such systems are recurrent and thousands of shells (each of about 0.001 Mo) snow plough into the environment. As these systems involve common envelope binaries the material is distributed in a non-spherical shell. These systems could be progenitors of some SN Ia and thus explode into environments with large amounts of accumulated gas and dust distributed in thin non-spherical shells. Such shells should be observable around 100 years after a SN Ia event in a radio flash as the SN Ia debris meets that of the ejected material of the systems previous incarna...

  14. ALMA Observations of HD141569's Circumstellar Disk

    White, J A; Hughes, A M; Flaherty, K M; Ford, E; Wilner, D; Corder, S; Payne, M

    2016-01-01

    We present ALMA band 7 (345 GHz) continuum and $^{12}$CO(J = 3-2) observations of the circumstellar disk surrounding HD141569. 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 $870\\rm~\\mu m$ ALMA continuum observations resolve a dust disk out to approximately $ 56 ~\\rm au$ from the star (assuming a distance of 116 pc) with $0."38$ resolution and $0.07 ~ \\rm mJy~beam^{-1}$ sensitivity. We measure a continuum flux density for this inner material of $3.8 \\pm 0.4 ~ \\rm mJy$ (including calibration uncertainties). The $^{12}$CO(3-2) gas is resolved kinematically and spatially from about 30 to 210 au. The integrated $^{12}$CO(3-2) line flux density is $15.7 \\pm 1.6~\\rm Jy~km~s^{-1}$. We estimate the mass of the millimeter debris and $^{12}$CO(3-2) gas to be $\\gtrsim0.04~\\rm M_{\\oplus}$ and $\\sim2\\times 10^{-3}~\\rm M_{\\oplus}$, respectively. If the millimeter grains are part of a collisional cascade, then we infer that the inner disk ($&...

  15. A statistical analysis of circumstellar material in Type Ia supernovae

    Maguire, Kate; Patat, Ferdinando; Gal-Yam, Avishay; Hook, Isobel M; Dhawan, Suhail; Howell, D Andrew; Mazzali, Paolo; Nugent, Peter E; Pan, Yen-Chen; Podsiadlowski, Philipp; Simon, Joshua D; Sternberg, Assaf; Valenti, Stefano; Baltay, Charles; Bersier, David; Blagorodnova, Nadejda; Chen, Ting-Wan; Ellman, Nancy; Feindt, Ulrich; Förster, Francisco; Fraser, Morgan; González-Gaitán, Santiago; Graham, Melissa L; Gutiérrez, Claudia; Hachinger, Stephan; Hadjiyska, Elena; Inserra, Cosimo; Knapic, Cristina; Laher, R R; Leloudas, Giorgos; Margheim, Steven; McKinnon, Ryan; Molinaro, Marco; Morrell, Nidia; Ofek, Eran O; Rabinowitz, David; Rest, Armin; Sand, David; Smareglia, Riccardo; Smartt, Stephen J; Taddia, Francesco; Walker, Emma S; Walton, Nicholas A; Young, David R

    2013-01-01

    A key tracer of the elusive progenitor systems of Type Ia supernovae (SNe Ia) is the detection of narrow blueshifted time-varying Na I D absorption lines, interpreted as evidence of circumstellar material (CSM) surrounding the progenitor system. The origin of this material is controversial, but the simplest explanation is that it results from previous mass loss in a system containing a white dwarf and a non-degenerate companion star. We present new single-epoch intermediate-resolution spectra of 17 low-redshift SNe Ia taken with XShooter on the ESO Very Large Telescope. Combining this sample with events from the literature, we confirm an excess (~20 per cent) of SNe Ia displaying blueshifted narrow Na I D absorption features compared to non-blueshifted Na I D features. The host galaxies of SNe Ia displaying blueshifted absorption profiles are skewed towards later-type galaxies, compared to SNe Ia that show no Na I D absorption, and SNe Ia displaying blueshifted narrow Na I D absorption features have broader l...

  16. Supernova spectra below strong circum-stellar interaction

    Leloudas, G; Johansson, J; Maeda, K; Moriya, T J; Nordin, J; Petrushevska, T; Silverman, J M; Sollerman, J; Stritzinger, M D; Taddia, F; Xu, D

    2013-01-01

    (abridged) We construct spectra of supernovae interacting strongly with a circum-stellar medium (CSM) by adding SN templates, a black-body continuum and an emission-line spectrum. In a Monte Carlo simulation we generate 500 spectra, distribute them to 10 different classifiers, and study how the different simulation parameters affect the appearance of the spectra. SNe IIn showing some structure over the continuum were characterized as 'SNe IInS'. It is demonstrated that the flux ratio of the underlying SN to the continuum fv is the most important parameter determining the spectral classification. Thermonuclear SNe get progressively classified as Ia-CSM, IInS and IIn as fv decreases. The transition between Ia-CSM and IInS occurs at fv~0.2-0.3. It is shown that SNe Ia-CSM are found at the magnitude range -19.5 > M > -21.6, in good agreement with observations, and that the faintest SN IIn that can hide a SN Ia has M = -20.1. The sample of SNe Ia-CSM shows an association with 91T-like SNe Ia. Our experiment does n...

  17. Polarization of circumstellar bow shocks due to electron scattering

    Shrestha, Manisha; Hoffman, J. L.; Neilson, H.; Ignace, R.

    2014-01-01

    Circumstellar material (CSM) provides a link between interacting supernovae and their massive progenitor stars. This CSM arises from stellar winds, outflows, or eruptions from a massive star before it explodes and can be detected around stars or supernovae with polarimetric observations. We use a Monte Carlo based radiative transfer code (SLIP) to investigate the polarization created by different models for the CSM surrounding a central source such as supernovae or massive stars. We vary parameters such as the shape, optical depth, temperature, and brightness of the CSM and compare the simulated flux and polarization behavior with observational data. We present results from new simulations that assume a bow shock shape for the CSM. Bow shocks are commonly observed around massive stars; this shape forms when a star moving more quickly than the speed of sound in the local interstellar medium emits a stellar wind that drives a shock wave into the ISM. Since a bow shock projects an aspherical shape onto the sky, light from the central source that scatters in the shock region becomes polarized. We present electron-scattering polarization maps for this geometry and discuss the behavior of observed polarization with viewing angle in the unresolved case.

  18. Molecular catastrophes and circumstellar SiO masers

    Stencel, Robert E.

    1993-01-01

    Understanding the complex SiO maser regions of highly evolved stars can be improved through multiwavelength studies of 'premaser' stars, such as M0-M4 giants and semiregular variables, which can be placed on normal H-R diagrams unlike most of the OH-IR stars. I argue that SiO masers are a key part of the transformation of hot stellar plasma into cold circumstellar silicate dust, in the outflows from evolved, oxygen rich stars. Evidence for this statement rests on the following: (1) red giant mass loss originates in a stochastic, amsotropic manner; (2) SiO maser maps of Miras and red supergiants show numerous maser spots within a few stellar radii; (3) molecules and dust naturally form in a cooling outflow; (4) the IRAS Low Resolution Spectrometer provided evidence for diverse and variable 10 micron silicate features in Miras, and these shapes correlate well with the proposed maser chronology, suggesting a formation and annealing sequence. The theory for the occurrence of SiO masers involving thermal instability, related 'new' physics, recent calculations and a prediction are discussed.

  19. Probing the circumstellar structure of pre-main sequence stars

    Vink, J S; Harries, T J; Oudmaijer, R D; Oudmaijer, Rene D.

    2003-01-01

    We present Halpha spectropolarimetry of a large sample of pre-main sequence (PMS) stars of low and intermediate mass, and argue that the technique is a powerful tool in studying the circumstellar geometry around these objects. For the intermediate mass (2 -- 15 Msun) Herbig Ae/Be stars we find that 16 out of 23 show a line effect, which immediately implies that flattening is common among these objects. Furthermore, we find a significant difference in Halpha spectropolarimetry behaviour between the Herbig Be and Ae groups. For the Herbig Be stars, the concept of an electron scattering disc is shown to be a useful concept to explain the depolarizations seen in this spectral range. At lower masses, more complex Halpha polarimetry behaviour starts to appear. The concept of a compact source of Halpha emission that is formed close to the stellar surface, for instance by hot spots due to magnetospheric accretion, is postulated as a working hypothesis to qualitatively explain the Halpha spectropolarimetry behaviour a...

  20. Photodissociation and chemistry of N2 in the circumstellar envelope of carbon-rich AGB stars

    Li, Xiaohu; Millar, Tom J.; Walsh, Catherine; Heays, Alan N.; van Dishoeck, Ewine F.

    2014-08-01

    Context. The envelopes of asymptotic giant branch (AGB) stars are irradiated externally by ultraviolet photons; hence, the chemistry is sensitive to the photodissociation of N2 and CO, which are major reservoirs of nitrogen and carbon, respectively. The photodissociation of N2 has recently been quantified by laboratory and theoretical studies. Improvements have also been made for CO photodissociation. Aims: For the first time, we use accurate N2 and CO photodissociation rates and shielding functions in a model of the circumstellar envelope of the carbon-rich AGB star, IRC +10216. Methods: We use a state-of-the-art chemical model of an AGB envelope, the latest CO and N2 photodissociation data, and a new method for implementing molecular shielding functions in full spherical geometry with isotropic incident radiation. We compare computed column densities and radial distributions of molecules with observations. Results: The transition of N2→ N (also, CO → C → C+) is shifted towards the outer envelope relative to previous models. This leads to different column densities and radial distributions of N-bearing species, especially those species whose formation/destruction processes largely depend on the availability of atomic or molecular nitrogen, for example, CnN (n = 1, 3, 5), CnN- (n = 1, 3, 5), HCnN (n = 1, 3, 5, 7, 9), H2CN and CH2CN. Conclusions: The chemistry of many species is directly or indirectly affected by the photodissociation of N2 and CO, especially in the outer shell of AGB stars where photodissociation is important. Thus, it is important to include N2 and CO shielding in astrochemical models of AGB envelopes and other irradiated environments. In general, while differences remain between our model of IRC +10216 and the observed molecular column densities, better agreement is found between the calculated and observed radii of peak abundance.

  1. At the interface of silica glass and compressed silica aerogel in Stardust track 10: Comet Wild 2 is not a goldmine

    Rietmeijer, Frans J. M.

    2016-03-01

    In Stardust tracks C2044,0,38, C2044,0,39, and C2044,0,42 (Brennan et al.) and Stardust track 10 (this work) gold is present in excess of its cosmochemical abundance. Ultra-thin sections of allocation FC6,0,10,0,26 (track 10) show a somewhat wavy, compressed silica aerogel/silica glass interface which challenges exact location identification, i.e., silica glass, compressed silica aerogel, or areas of overlap. In addition to domains of pure silica ranging from SiO2 to SiO3 glass, there is MgO-rich silica glass with a deep metastable composition, MgO = 14 ± 6 wt%, due to assimilation of Wild 2 Mg-silicate matter in silica melt. This magnesiosilica composition formed when temperatures during hypervelocity capture reached >2000 °C followed by ultrafast quenching of the magnesiosilica melt when it came into contact with compressed aerogel at ~155 °C. The compressed silica aerogel in track 10 has a continuous Au background as result of the melting point depression of gold particles silica aerogel matrix and in aggregates up to ~50 nm in size. No gold is found in MgO-rich silica glass. Gold in track 10 is present at the silica aerogel/silica glass interface. In the other tracks gold was likely near-surface contamination possibly from an autoclave used in processing of these particular aerogel tiles. So far gold contamination is documented in these four different tracks. Whether they are the only tiles with gold present in excess of its cosmochemical abundance or whether more tiles will show excess gold abundances is unknown.

  2. Silica, Silicosis, and Autoimmunity.

    Pollard, Kenneth Michael

    2016-01-01

    Inhalation of dust containing crystalline silica is associated with a number of acute and chronic diseases including systemic autoimmune diseases. Evidence for the link with autoimmune disease comes from epidemiological studies linking occupational exposure to crystalline silica dust with the systemic autoimmune diseases systemic lupus erythematosus, systemic sclerosis, and rheumatoid arthritis. Although little is known regarding the mechanism by which silica exposure leads to systemic autoimmune disease, there is a voluminous literature on silica exposure and silicosis that may help identify immune processes that precede development of autoimmunity. The pathophysiology of silicosis consists of deposition of silica particles in the alveoli of the lung. Ingestion of these particles by macrophages initiates an inflammatory response, which stimulates fibroblasts to proliferate and produce collagen. Silica particles are encased by collagen leading to fibrosis and the nodular lesions characteristic of the disease. The steps in the development of silicosis, including acute and chronic inflammation and fibrosis, have different molecular and cellular requirements, suggesting that silica-induced inflammation and fibrosis may be mechanistically separate. Significantly, it is unclear whether silica-induced inflammation and fibrosis contribute similarly to the development of autoimmunity. Nonetheless, the findings from human and animal model studies are consistent with an autoimmune pathogenesis that begins with activation of the innate immune system leading to proinflammatory cytokine production, pulmonary inflammation leading to activation of adaptive immunity, breaking of tolerance, and autoantibodies and tissue damage. The variable frequency of these immunological features following silica exposure suggests substantial genetic involvement and gene/environment interaction in silica-induced autoimmunity. However, numerous questions remain unanswered. PMID:27014276

  3. Silica, Silicosis and Autoimmunity.

    Kenneth Michael Pollard

    2016-03-01

    Full Text Available Inhalation of dust containing crystalline silica is associated with a number of acute and chronic diseases including systemic autoimmune diseases. Evidence for the link with autoimmune disease comes from epidemiological studies linking occupational exposure to crystalline silica dust with the systemic autoimmune diseases SLE, SSc and RA. Although little is known regarding the mechanism by which silica exposure leads to systemic autoimmune disease, there is a voluminous literature on silica exposure and silicosis that may help identify immune processes that precede development of autoimmunity. The pathophysiology of silicosis consists of deposition of silica particles in the alveoli of the lung. Ingestion of these particles by macrophages initiates an inflammatory response which stimulates fibroblasts to proliferate and produce collagen. Silica particles are encased by collagen leading to fibrosis and the nodular lesions characteristic of the disease. The steps in the development of silicosis, including acute and chronic inflammation and fibrosis, have different molecular and cellular requirements suggesting that silica-induced inflammation and fibrosis may be mechanistically separate. Significantly, it is unclear whether silica-induced inflammation and fibrosis contribute similarly to the development of autoimmunity. Nonetheless, the findings from human and animal model studies are consistent with an autoimmune pathogenesis that begins with activation of the innate immune system leading to proinflammatory cytokine production, pulmonary inflammation leading to activation of adaptive immunity, breaking of tolerance, autoantibodies and tissue damage. The variable frequency of these immunological features following silica exposure suggests substantial genetic involvement and gene/environment interaction in silica-induced autoimmunity. However numerous questions remain unanswered.

  4. Alkali Metal Modification of Silica Gel-Based Stationary Phase in Gas Chromatography

    Ashraf Yehia El-Naggar

    2013-01-01

    Modification of the precipitated silica gel was done by treatment with alkali metal (NaCl) before and after calcination. The silica surfaces before and after modification were confirmed by infrared spectroscopy in order to observe the strength and abundance of the acidic surface OH group bands which play an important role in the adsorption properties of polar and nonpolar solutes. The surface-modified silica gels were tested as GC solid stationary phases in terms of the separation efficiency ...

  5. New antifouling silica hydrogel.

    Beltrán-Osuna, Ángela A; Cao, Bin; Cheng, Gang; Jana, Sadhan C; Espe, Matthew P; Lama, Bimala

    2012-06-26

    In this work, a new antifouling silica hydrogel was developed for potential biomedical applications. A zwitterionic polymer, poly(carboxybetaine methacrylate) (pCBMA), was produced via atom-transfer radical polymerization and was appended to the hydrogel network in a two-step acid-base-catalyzed sol-gel process. The pCBMA silica aerogels were obtained by drying the hydrogels under supercritical conditions using CO(2). To understand the effect of pCBMA on the gel structure, pCBMA silica aerogels with different pCBMA contents were characterized using scanning electron microscopy (SEM), nuclear magnetic resonance (NMR) spectroscopy, and the surface area from Brauner-Emmet-Teller (BET) measurements. The antifouling property of pCBMA silica hydrogel to resist protein (fibrinogen) adsorption was measured using enzyme-linked immunosorbent assay (ELISA). SEM images revealed that the particle size and porosity of the silica network decreased at low pCBMA content and increased at above 33 wt % of the polymer. The presence of pCBMA increased the surface area of the material by 91% at a polymer content of 25 wt %. NMR results confirmed that pCBMA was incorporated completely into the silica structure at a polymer content below 20 wt %. A protein adsorption test revealed a reduction in fibrinogen adsorption by 83% at 25 wt % pCBMA content in the hydrogel compared to the fibrinogen adsorption in the unmodified silica hydrogel. PMID:22607091

  6. Isotopes in the interstellar medium and circumstellar envelopes

    Measurements of the present-day abundances of elements and isotopes, combined with model calculations, allow us to trace the history of nucleosynthesis in the universe. Throughout this review, emphasis will be placed on descriptions of the measurement processes and the interpretations needed to obtain actual isotope and element abundances from measurements. Comparisons of the abundances of isotopomers of a given element are less affected by systematic effects than are comparisons of the abundances of different elements. Thus ratios of isotopomers should be given a greater weight when data and models are compared. As is generally accepted, the universe began with an explosive event, the Big Bang. The nucleosynthesis associated with this event produced 'primordial' abundances of the 'light elements', deuterium, 3He, 4He, and 7Li. Subsequent stellar processing of the light elements has altered the relative abundances, and also produced heavier elements such as carbon, nitrogen and oxygen. Stellar nucleosynthesis products from solar and larger mass stars are expelled into the interstellar medium (ISM). The goal of studies of the abundances of the light elements is to estimate the primordial abundances, that is, the abundances produced in the Big Bang. It is believed that D is always net destroyed in stars; 3He and 7Li may be net produced, 4He is certainly net produced. In the Solar System itself, results are obtained from in situ measurements with space probes to Jupiter, measurements of solar wind constituents, the analysis of the content of meteorites, and spectral line measurements of the solar photosphere. For sources outside the Solar System, these data are based on spectral line measurements of gas-phase species. The ratio of gas-phase abundances of elements, such as carbon to lithium may be affected by differing amounts of condensation onto dust grains; however such a process will not affect the ratio of isotopes such as 6Li/7Li. The most reliable measurements

  7. Constraining silica diagenesis in methane-seep deposits

    Smrzka, Daniel; Kraemer, Stephan; Zwicker, Jennifer; Birgel, Daniel; Fischer, David; Kasten, Sabine; Goedert, James; Peckmann, Jörn

    2015-04-01

    Silicified fossils and silicified early diagenetic carbonate minerals as well as authigenic silica phases are common in ancient seep limestones. Silicification of calcareous fossils facilitates the preservation of even fine details and is therefore of great interest to paleontologists, permitting a reliable taxonomic identification of the chemosynthesis-based taxa that lived at ancient hydrocarbon seeps. Four methane-seep limestones of Paleozoic, Mesozoic, and Cenozoic age with abundant silica phases are compared in this study; one, an Eocene seep deposit on the north shore of the Columbia River at Knappton, western Washington State, USA, is described for the first time. Its lithology and fabrics, negative δ13Ccarbonate values as low as -27.6‰, and 13C-depleted biomarkers of archaea involved in the anaerobic oxidation of methane (AOM) reveal that the carbonate rock formed at a methane seep. The background sediments of the studied Phanerozoic seep limestones contain abundant siliceous microfossils, radiolarian tests in case of the Late Carboniferous Dwyka Group deposits from Namibia and the Late Triassic Graylock Butte deposits from eastern Oregon (USA), diatom frustules in case of the Eocene Knappton limestone and an Oligocene seep deposit from the Lincoln Creek Formation (western Washington State, USA). These microfossils are regarded as the source of dissolved silica, causing silicification and silica precipitation. All seep limestones used in this study are characterized by very similar paragenetic sequences. Silicified fossils include brachiopods and worm tubes, silica cements include microquartz, fibrous microcrystalline silica, and megaquartz. The silica cements formed after the AOM-derived cements ceased to precipitate but before equant calcite spar formed. Numerical experiments using the computer code PHREEQC were conducted to test the hypothesis that (1) AOM increases the pH of pore waters and that (2) this pH increase subsequently mobilizes biogenic

  8. A Collisional Algorithm for Modeling Circumstellar Debris Disks

    Nesvold, Erika; Kuchner, Marc

    2011-01-01

    Many planetary systems harbor circumstellar disks of dust and planetesimals thought to be debris left over from planet formation. These debris disks exhibit a range of morphological features which can arise from the gravitational perturbations of planets. Accurate models of these features, accounting for the interactions of the particles in a disk with each other and with whatever planets they contain, can act as signposts for planets in debris disks that otherwise could not be detected. Such models can also constrain the planet's mass and orbital parameters. Current models for many disks consider the gravitational and radiative effects of the star and planets on the disk, but neglect the morphological consequences of collisional interactions between the planetesimals. Many observed disk features are not satisfactorily explained by the current generation of models. I am developing a new kind of debris disk model that considers both the gravitational shaping of the disk by planets and the inelastic collisions between particles. I will use a hybrid N-body integrator to numerically solve the equations of motion for the particles and planets in the disk. To include the collisional effects, I begin with an algorithm that tests for collisions at each step of the orbit integration and readjusts the velocities of colliding particles. I am adapting this algorithm to the problem at hand by allowing each particle to represent a "swarm" of planetesimals with a range of masses. When the algorithm detects an encounter between swarms, two or three swarms are produced to approximate the range of possible trajectories of the daughter planetesimals. Here I present preliminary results from my collisional algorithm.

  9. Cellulose-silica aerogels.

    Demilecamps, Arnaud; Beauger, Christian; Hildenbrand, Claudia; Rigacci, Arnaud; Budtova, Tatiana

    2015-05-20

    Aerogels based on interpenetrated cellulose-silica networks were prepared and characterised. Wet coagulated cellulose was impregnated with silica phase, polyethoxydisiloxane, using two methods: (i) molecular diffusion and (ii) forced flow induced by pressure difference. The latter allowed an enormous decrease in the impregnation times, by almost three orders of magnitude, for a sample with the same geometry. In both cases, nanostructured silica gel was in situ formed inside cellulose matrix. Nitrogen adsorption analysis revealed an almost threefold increase in pores specific surface area, from cellulose aerogel alone to organic-inorganic composite. Morphology, thermal conductivity and mechanical properties under uniaxial compression were investigated. Thermal conductivity of composite aerogels was lower than that of cellulose aerogel due to the formation of superinsulating mesoporous silica inside cellulose pores. Furthermore, composite aerogels were stiffer than each of reference aerogels. PMID:25817671

  10. What Is Crystalline Silica?

    ... 1926.55, 1910.1000). OSHA also requires hazard communication training for workers exposed to crystalline silica, and ... identify, reduce, and eliminate health hazards associated with occupational ... safety and health? OSHA has various publications, standards, technical ...

  11. Connecting the evolution of thermally pulsing asymptotic giant branch stars to the chemistry in their circumstellar envelopes -- I. The case of hydrogen cyanide

    Marigo, Paola; Nanni, Ambra; Bressan, Alessandro; Girardi, Leo

    2015-01-01

    We investigate the formation of hydrogen cyanide (HCN) in the inner circumstellar envelopes of thermally pulsing asymptotic giant branch (TP-AGB) stars. A dynamic model for periodically shocked atmospheres, which includes an extended chemo-kinetic network, is for the first time coupled to detailed evolutionary tracks for the TP-AGB phase computed with the COLIBRI code. We carried out a calibration of the main shock parameters (the shock formation radius and the effective adiabatic index) using the circumstellar HCN abundances recently measured for a populous sample of pulsating TP-AGB stars. Our models recover the range of the observed HCN concentrations as a function of the mass-loss rates, and successfully reproduce the systematic increase of HCN moving along the M-S-C chemical sequence of TP-AGB stars, that traces the increase of the surface C/O ratio. The chemical calibration brings along two important implications: i) the first shock should emerge very close to the photosphere, and ii) shocks are expecte...

  12. Molecular Dynamics Simulations of Water Nanodroplets on Silica Surfaces

    Zambrano, Harvey A; Walther, Jens Honore; Jaffe, Richard L.

    2009-01-01

    Wetting is essential and ubiquitous in a variety of natural and technological processes.1,2,3 Silicon dioxides-water systems are abundant in nature and play fundamental roles in a vast variety of novel science and engineering activities such as silicon based devices, nanoscale lab on a chip systems...... amorphous silica-water systems....

  13. Silica in alkaline brines

    Jones, B.F.; Rettig, S.L.; Eugster, H.P.

    1967-01-01

    Analysis of sodium carbonate-bicarbonate brines from closed basins in volcanic terranes of Oregon and Kenya reveals silica contents of up to 2700 parts per million at pH's higher than 10. These high concentrations of SiO 2 can be attributed to reaction of waters with silicates, and subsequent evaporative concentration accompanied by a rise in pH. Supersaturation with respect to amorphous silica may occur and persist for brines that are out of contact with silicate muds and undersaturated with respect to trona; correlation of SiO2 with concentration of Na and total CO2 support this interpretation. Addition of moredilute waters to alkaline brines may lower the pH and cause inorganic precipitation of substantial amounts of silica.

  14. Cosmic petrology: comparison of circumstellar dust with solar system extraterrestrial materials

    Morlock, A.; Lisse, C. M.; Howard, K. T.

    2010-01-01

    Remote infrared observations allow us to obtain mineralogical information about micron-sized dust in circumstellar environments like young stellar objects (YSO). Comparison to laboratory infrared measurements of meteorites material from the time when our own Solar System was an YSO provides a link between astronomical observations with the known compositions of extraterrestrial materials in our Solar System.

  15. Daughter Fragmentation is Unlikely To Occur in Self-Gravitating Circumstellar Discs

    Forgan, Duncan

    2016-01-01

    Circumstellar discs are thought to be self-gravitating at very early times. If the disc is relatively cool, extended and accreting sufficiently rapidly, it can fragment into bound objects of order a few Jupiter masses and upwards. Given that the fragment's initial angular momentum is non-zero, and it will continue to accrete angular momentum from the surrounding circumstellar disc, we should expect that the fragment will also possess a relatively massive disc at early times. Therefore, we can ask: is disc fragmentation a hierarchical process? Or, can a disc fragment go on to produce its own self-gravitating circumfragmentary disc that produces daughter fragments? We investigate this using a set of nested 1D self-gravitating disc models. We calculate the radial structure of a marginally stable, self-gravitating circumstellar disc, and compute its propensity to fragmentation. We use this data to construct the local fragment properties at this radius. For each circumstellar disc model that results in fragmentati...

  16. Millimeter Continuum Measurements of Circumstellar Dust Around Very Young Low Mass Stars

    Terebey, S.; Chandler, C. J.; Andre, P.

    1992-01-01

    We investigate the question of disk formation during the protostar phase. We build on the results of Keene and Masson (1990) who analysis of L1551 showed themillimeter continuum emission comes from both an unresolved circumstellar conponent i.e. disk and an extended cloud core.

  17. Circumstellar CO Emission in S Stars I. Mass-Loss with Little or No Dust

    Sahai, R.; Liechti, S.

    1994-01-01

    47 S stars have been searched for circumstellar CO (J=1-0 and/or 2-1) emission, and 29 have been detected, including 4 which show no evidence of dust in their IRAS LRS spectra and one with possibly no Tc (and therefore not an AGB star).

  18. Precision Chemical Abundance Measurements

    Yong, David; Grundahl, Frank; Meléndez, Jorge;

    2012-01-01

    This talk covers preliminary work in which we apply a strictly differential line-by-line chemical abundance analysis to high quality UVES spectra of the globular cluster NGC 6752. We achieve extremely high precision in the measurement of relative abundance ratios. Our results indicate that the ob...

  19. Maximum abundant isotopes correlation

    The neutron excess of the most abundant isotopes of the element shows an overall linear dependence upon the neutron number for nuclei between neutron closed shells. This maximum abundant isotopes correlation supports the arguments for a common history of the elements during nucleosynthesis. (Auth.)

  20. Extracting silica from rice husk treated with potassium permanganate

    As an agro-waste material the rice husk is abundantly available is rice growing areas. In many areas rice husk after burning involves disposal problems because of higher quantities of silica present in it. Rice husk contains about 20 per cent silica, which is present in hydrated amorphous form. On thermal treatment the silica converts into crystobalite, which is a crystalline form of silica. However amorphous silica can be produced under controlled conditions ensuring high reactivity and large surface area. Leaching the rice husk with organic acids and alkalies removes the metallic impurities from its surface. How a dilute solution of potassium permanganate affects the rice husk is the subject of this research paper. The rice husk was treated with the dilute solution of potassium permanganate at room temperature and then analyzed by SEM, TGA and the ash by analytical treatment after burning under controlled temperature. The SEM results revealed that the protuberances of the rice husk were eaten away by the solution of potassium permanganate. Pyrolysis of rice husks showed that the thermal degradation of the treated rice husk was faster than the untreated rice husk where as analytical results confirmed the presence of more amorphous silica than untreated rice husk. (author)

  1. Molecular Dynamics Simulations of Water Droplets On Hydrophilic Silica Surfaces

    Zambrano, Harvey A; Walther, Jens Honore; Jaffe, Richard L.

    2009-01-01

    Wetting is essential and ubiquitous in a variety of natural and technological processes. Silicon dioxides-water systems are abundant in nature and play fundamental roles in a vast variety of novel science and engineering activities such as silicon based devices, nanoscale lab on a chip systems and......, nanobubles have been observed and proposed as the origin of long range ``hydrophobic'' forces even for hydrophilic silica-water interfaces unusual phenomena related to nanobubbles have been observed. In this work we study the role of air on the wetting of amorphous silica-water systems. We conduct molecular...

  2. Production of silica aerogel

    A production facility for silica aerogel has been set up in Lund. Aerogel is now produced in large quantities with the refractive indices of 1.03 and 1.05. The standard block size is 18 x 18 x 3 cm3. (Auth.)

  3. Preparation and characterization of rice hull silica products

    Rice hull is an abundant agricultural waste material which could be a renewable energy source when combusted. The combustion residue (called rice hull ash or RHA) contains a significant amount (20% of the hull) of potentially high grade silica. Silica gels prepared from rice hull were found to have properties comparable to two commercial desiccant silica gels (Blue Merck and FNG-A) in terms of chemical and amorphous structure, surface area, desiccant characteristics, microstructure and heats of adsorption. These properties were determined from water vapor adsorption measurements, electron microscopy, and from infrared and x-ray diffraction spectra. The acid treated rice hull gels were found to have fewer elemental impurities detected by qualitative x-ray fluorescence, compared to the commercial gels. Thermogravimetric analysis (TGA) data showed that this technique can also be used to indirectly compare impurity levels in the samples, in terms of the amorphous to crystalline phase transition. Using an improved acid treatment method, a silica gel sample was prepared from rice hull and compared to three commercial chromatographic silica gels using quantitative elemental x-ray fluorescence analysis. Elemental levels in the rice hull gel were within the range of levels or close to the detection limits of corresponding elements in the chromatographic gels. Water vapor adsorption, x-ray diffraction, infrared spectroscopy and scanning electron microscopy showed that the rice hull gel was similar to the commercial chromatographic silica gel Davison 12. Zeolites are crystalline aluminosilicates used as molecular sieves for purification and catalytic purposes. Zeolites X and Y were synthesized from rice hull silica gel and aluminum hydroxide. For comparison, controls were synthesized from commercial silica gel. The samples and controls exhibited characteristics infrared peaks corresponding to the vibrations of the TO4 (T=Si, Al) of the zeolite framework. The x-ray diffraction

  4. Searching for signatures of planet formation in stars with circumstellar debris discs

    Maldonado, J.; Eiroa, C.; Villaver, E.; Montesinos, B.; Mora, A.

    2015-07-01

    Context. Tentative correlations between the presence of dusty circumstellar debris discs and low-mass planets have recently been presented. In parallel, detailed chemical abundance studies have reported different trends between samples of planet and non-planet hosts. Whether these chemical differences are indeed related to the presence of planets is still strongly debated. Aims: We aim to test whether solar-type stars with debris discs show any chemical peculiarity that could be related to the planet formation process. Methods: We determine in a homogeneous way the metallicity, [Fe/H], and abundances of individual elements of a sample of 251 stars including stars with known debris discs, stars harbouring simultaneously debris discs and planets, stars hosting exclusively planets, and a comparison sample of stars without known discs or planets. High-resolution échelle spectra (R ~ 57 000) from 2-3 m class telescopes are used. Our methodology includes the calculation of the fundamental stellar parameters (Teff, log g, microturbulent velocity, and metallicity) by applying the iron ionisation and equilibrium conditions to several isolated Fe i and Fe ii lines, as well as individual abundances of C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, and Zn. Results: No significant differences have been found in metallicity, individual abundances or abundance-condensation temperature trends between stars with debris discs and stars with neither debris nor planets. Stars with debris discs and planets have the same metallicity behaviour as stars hosting planets, and they also show a similar ⟨[ X/Fe ] ⟩ - TC trend. Different behaviour in the ⟨[ X/Fe ] ⟩ - TC trends is found between the samples of stars without planets and the samples of planet hosts. In particular, when considering only refractory elements, negative slopes are shown in cool giant planet hosts, whilst positive ones are shown in stars hosting low-mass planets. The statistical significance of the

  5. Aniline incorporated silica nanobubbles

    M J Rosemary; V Suryanarayanan; Ian Maclaren; T Pradeep

    2006-09-01

    We report the synthesis of stearate functionalized nanobubbles of SiO2 with a few aniline molecules inside, represented as C6H5NH2@SiO2@stearate, exhibiting fluorescence with red-shifted emission. Stearic acid functionalization allows the materials to be handled just as free molecules, for dissolution, precipitation, storage etc. The methodology adopted involves adsorption of aniline on the surface of gold nanoparticles with subsequent growth of a silica shell through monolayers, followed by the selective removal of the metal core either using sodium cyanide or by a new reaction involving halocarbons. The material is stable and can be stored for extended periods without loss of fluorescence. Spectroscopic and voltammetric properties of the system were studied in order to understand the interaction of aniline with the shell as well as the monolayer, whilst transmission electron microscopy has been used to study the silica shell.

  6. Circumstellar dust shells around WN10-11 and WC8-10 stars: an evolutionary sequence

    In a recent IR photometric survey of late-type WC and WN stars, it was discovered that not only most WC8-10 stars have circumstellar dust shells, but that two extreme late-type WN stars also have strong IR excesses from circumstellar dust. The latter shells appear to have significantly different density distributions. The possibility of an evolutionary sequence is suggested. (Auth.)

  7. Formation Process of the Circumstellar Disk: Long-term Simulations in the Main Accretion Phase of Star Formation

    Machida, Masahiro N.; Inutsuka, Shu-ichiro; Matsumoto, Tomoaki

    2010-12-01

    The formation and evolution of the circumstellar disk in unmagnetized molecular clouds is investigated using three-dimensional hydrodynamic simulations from the prestellar core until the end of the main accretion phase. In collapsing cloud cores, the first (adiabatic) core with a size of gsim3 AU forms prior to the formation of the protostar. At its formation, the first core has a thick disk-like structure and is mainly supported by the thermal pressure. After the protostar formation, it decreases the thickness gradually and becomes supported by the centrifugal force. We found that the first core is a precursor of the circumstellar disk with a size of >3 AU. This means that unmagnetized protoplanetary disk smaller than thermodynamics of the collapsing gas, at the protostar formation epoch, the first core (or the circumstellar disk) has a mass of ~0.005-0.1 M sun, while the protostar has a mass of ~10-3 M sun. Thus, just after the protostar formation, the circumstellar disk is about 10-100 times more massive than the protostar. In the main accretion phase that lasts for ~105 yr, the circumstellar disk mass initially tends to dominate the protostellar mass. Such a massive disk is unstable to gravitational instability and tends to show fragmentation. Our calculations indicate that the low-mass companions may form in the circumstellar disk in the main accretion phase. In addition, the mass accretion rate onto the protostar shows a strong time variability that is caused by the torque from the low-mass companions and/or the spiral arms in the circumstellar disk. Such variability provides an important signature for detecting the substellar mass companion in the circumstellar disk around very young protostars.

  8. Interstellar and Circumstellar Optical & Ultraviolet Lines Towards SN1998S

    Bowen, D V; Meyer, D M; Blades, J C; Bowen, David V.; Roth, Katherine C.; Meyer, David M.

    1999-01-01

    We have observed SN1998S which exploded in NGC3877, with the UES at the WHT and with the E230M echelle of STIS aboard HST. Both data sets were obtained at two seperate epochs. From our own Galaxy we detect interstellar absorption lines of CaII, FeII, MgI, and probably MnII from the edge of the HVC Complex M. We derive gas-phase abundances which are very similar to warm disk clouds in the local ISM, which we believe argues against the HVC material having an extragalactic origin. At the velocity of NGC3877 we detect interstellar MgI, MgII, MnII, CaII, & NaI. Surprisingly, one component is seen to increase by a factor of ~1 dex in N(NaI) and N(MgI) between the two epochs over which the data were taken. Unusually, our data also show narrow Balmer, HeI, and metastable FeII P-Cygni profiles, with a narrow absorption component superimposed on the bottom of the profile's absorption trough. Both the broad and narrow components of the optical lines are seen to increase substantially in strength between the two epoc...

  9. Wind Dynamics and Circumstellar Extinction Variations in the T Tauri Star RY Tau

    Babina, Elena V; Petrov, Peter P

    2016-01-01

    The wind interaction with the dusty environment of the classical T Tauri star RY Tau has been investigated. During two seasons of 2013-2015 we carried out a spectroscopic and photometric (BVR) monitoring of the star. A correlation between the stellar brightness and the radial velocity of the wind determined from the H-alpha and Na D line profiles has been found for the first time. The irregular stellar brightness variations are shown to be caused by extinction in a dusty disk wind at a distance of about 0.2 AU from the star. We suppose, that variations of the circumstellar extinction results from cyclic rearrangements of the stellar magnetosphere and coronal mass ejections, which affect the dusty disk wind near the inner boundary of the circumstellar disk.

  10. Properties of the H-alpha-emitting Circumstellar Regions of Be Stars

    Tycner, C; Hajian, A R; Armstrong, J T; Benson, J A; Gilbreath, G C; Hutter, D J; Pauls, T A; White, N M; Tycner, Christopher; Lester, John B.; Hajian, Arsen R.

    2005-01-01

    Long-baseline interferometric observations obtained with the Navy Prototype Optical Interferometer of the H-alpha-emitting envelopes of the Be stars eta Tauri and beta Canis Minoris are presented. For compatibility with the previously published interferometric results in the literature of other Be stars, circularly symmetric and elliptical Gaussian models were fitted to the calibrated H-alpha observations. The models are sufficient in characterizing the angular distribution of the H-alpha-emitting circumstellar material associated with these Be stars. To study the correlations between the various model parameters and the stellar properties, the model parameters for eta Tau and beta CMi were combined with data for other Be stars from the literature. After accounting for the different distances to the sources and stellar continuum flux levels, it was possible to study the relationship between the net H-alpha emission and the physical extent of the H-alpha-emitting circumstellar region. A clear dependence of the...

  11. Circumstellar Habitable Zones to Ecodynamic Domains: A Preliminary Review and Suggested Future Directions

    Heath, Martin J

    2009-01-01

    The concept of the Circumstellar Habitable Zone has served the scientific community well for some decades. It slips easily off the tongue, and it would be hard to replace. Recently, however, several workers have postulated types of habitable bodies which might exist outside the classic circumstellar habitable zone (HZ). These include not only bodies which orbit at substantial distances from their parent stars, but also snowball worlds with geothermally-maintained internal oceans and even densely-atmosphered worlds with geothermally-maintained surface oceans, which have been ejected from unstable planetary systems into interstellar space. If habitability is not a unique and diagnostic property of the HZ, then the value of the term has been compromised in a fundamental way. At the same time, it has become evident that multiple environmental states, differing in important ways in their habitability, are possible even for geophysically similar planets subject to similar levels of insolation, within the classic HZ...

  12. From Protoplanetary Disks to Extrasolar Planets: Understanding the Life Cycle of Circumstellar Gas with Ultraviolet Spectroscopy

    France, Kevin; Ardila, David R; Bergin, Edwin A; Brown, Alexander; Burgh, Eric B; Calvet, Nuria; Chiang, Eugene; Cook, Timothy A; Désert, Jean-Michel; Ebbets, Dennis; Froning, Cynthia S; Green, James C; Hillenbrand, Lynne A; Johns-Krull, Christopher M; Koskinen, Tommi T; Linsky, Jeffrey L; Redfield, Seth; Roberge, Aki; Schindhelm, Eric R; Scowen, Paul A; Stapelfeldt, Karl R; Tumlinson, Jason

    2012-01-01

    Few scientific discoveries have captured the public imagination like the explosion of exoplanetary science during the past two decades. This work has fundamentally changed our picture of Earth's place in the Universe and led NASA to make significant investments towards understanding the demographics of exoplanetary systems and the conditions that lead to their formation. The story of the formation and evolution of exoplanetary systems is essentially the story of the circumstellar gas and dust that are initially present in the protostellar environment; in order to understand the variety of planetary systems observed, we need to understand the life cycle of circumstellar gas from its initial conditions in protoplanetary disks to its endpoint as planets and their atmospheres. In this white paper response to NASA's Request for Information "Science Objectives and Requirements for the Next NASA UV/Visible Astrophysics Mission Concepts (NNH12ZDA008L)", we describe scientific programs that would use the unique capabi...

  13. Circumstellar CO in OH/IR stars close to the Galactic Centre

    A pilot project is carried out to measure circumstellar CO emission from three OH/IR, stars close to the GC using the Nobeyama Millimeter Array at 115 GHz and the Sub-Millimeter Array at 230 GHz. An interferometer is necessary as a 'spatial filter' in this region of space because of the confusion with interstellar CO emission. The intention is to find out whether it is possible to later conduct a large-scale survey for mass-loss rates using, for example, ALMA. Thus an important parameter would be added to our understanding of the evolution of the Galactic Bulge. Sources have been detected towards two of the stars with 'correct' positions and radial velocities. However, for one of the stars the line profile is not what one expects for expanding circumstellar envelopes. This surprising result is discussed and our plans for future observations are presented

  14. 21 CFR 582.1711 - Silica aerogel.

    2010-04-01

    ... 21 Food and Drugs 6 2010-04-01 2010-04-01 false Silica aerogel. 582.1711 Section 582.1711 Food and....1711 Silica aerogel. (a) Product. Silica aerogel as a finely powdered microcellular silica foam having a minimum silica content of 89.5 percent. (b) (c) Limitations, restrictions, or explanation....

  15. 21 CFR 182.1711 - Silica aerogel.

    2010-04-01

    ... 21 Food and Drugs 3 2010-04-01 2009-04-01 true Silica aerogel. 182.1711 Section 182.1711 Food and....1711 Silica aerogel. (a) Product. Silica aerogel as a finely powdered microcellular silica foam having a minimum silica content of 89.5 percent. (b) (c) Limitations, restrictions, or explanation....

  16. Small SiC grains and a nitride grain of circumstellar origin from the Murchison meteorite: implications for stellar evolution and nucleosynthesis.

    Hoppe, P; Strebel, R; Eberhardt, P; Amari, S; Lewis, R S

    1996-03-01

    We report the results of SIMS isotopic analyses of carbon, nitrogen, oxygen, and silicon made on 849 small (approximately 1 micrometer) individual silicon carbide grains from the Murchison meteorite. The isotopic compositions of the major elements carbon and silicon of most grains (mainstream) are similar to those observed in larger grain studies suggesting an AGB star origin of these grains. In contrast, the trace element nitrogen shows a clear dependency on grain size. 14N/15N ratios increase with decreasing grain size, suggesting different stellar sources for grains of different size. Typically observed 14N/15N ratios in the small grains of this study are approximately 2700, clearly larger than the values expected from model calculations of AGB stars. In addition to the three dredge-up episodes characteristic for the evolution of AGB stars, extra-mixing of CNO-processed matter in low mass AGB stars appears to be a promising possibility in order to explain the high 14N/15N ratios of the small circumstellar SiC grains. A small fraction of grains shows a silicon isotopic signature not observed in larger circumstellar SiC grains from Murchison. Their stellar origin is still uncertain. The minor type A, B, Y, and X grains were found to be present at a level of a percent, which is similar to their abundance in the larger-grain SiC separates from Murchison. Oxygen isotopic compositions are normal within the experimental uncertainties of several 10%, indicating that oxygen of stellar origin is rare or even absent in the SiC grains. We conclude that most of the oxygen is a contaminant which was introduced into the SiC grains after their formation, e.g., during sample processing in the laboratory. We identified a nitride grain, most likely Si3N4 with little carbon, with highly anomalous isotopic compositions (12C/13C = 157 +/- 33, 14N/15N = 18 +/- 1, delta 29 Si = -43 +/- 56%, delta 30 Si = -271 +/- 50%). The isotopic patterns of carbon, nitrogen, and silicon resemble

  17. Observational Possibility of the "Snow Line" on the Surface of Circumstellar Disks with the Scattered Light

    Inoue, Akio K; Nakamoto, Taishi; Oka, Akinori

    2008-01-01

    We discuss how we obtain the spatial distribution of ice on the surface of the circumstellar disk around young stars. Ice in the disks plays a very important role in various issues, for instance, on the disk structure, on the planet formation, on the isotopic anomaly in meteorites, and on the origin of the sea on the Earth. Therefore, the spatially resolved observation of the condensation/sublimation front of ice, so-called ``snow line'' is strongly required. Here, we propose a new method for obtaining the spatially resolved ``snow line'' on the circumstellar disks by observing 3 \\micron H$_2$O ice feature in the scattered light. Based on radiative transfer considerations, we show that the feature is clearly imprinted in the spectrum of the scattered light from both optically thick and thin circumstellar disks. We also show that the scattered light and the H$_2$O ice feature from protoplanetary disks are detectable and spatially resolvable with the current instruments through a $H_2O$ narrowband filter around...

  18. Anisotropic inverse Compton scattering of photons from the circumstellar disc in PSR B1259-63

    van Soelen, B; Odendaal, A; Townsend, L J

    2012-01-01

    The gamma-ray binary system PSR B1259-63 consists of a 48 ms pulsar orbiting a Be star. The system is particularly interesting because it is the only gamma-ray binary system where the nature of the compact object is known. The non-thermal radiation from the system is powered by the spin-down luminosity of the pulsar and the unpulsed radiation originates from the stand-off shock front which forms between the pulsar and stellar wind. The Be star/optical companion in the system produces an excess infrared flux from the associated circumstellar disc. This infrared excess provides an additional photon source for inverse Compton scattering. We discuss the effects of the IR excess near periastron, for anisotropic inverse Compton scattering and associated gamma-ray production. We determine the infrared excess from the circumstellar disc using a modified version of a curve of growth method, which takes into account the changing optical depth through the circumstellar disc during the orbit. The model is constrained usi...

  19. Imaging the circumstellar environment of the young T Tauri star SU Aurigae

    Jeffers, S V; Canovas, H; Rodenhuis, M; Keller, C U

    2013-01-01

    The circumstellar environments of classical T Tauri stars are challenging to directly image because of their high star-to-disk contrast ratio. One method to overcome this is by using imaging polarimetry where scattered and consequently polarised starlight from the star's circumstellar disk can be separated from the unpolarised light of the central star. We present images of the circumstellar environment of SU Aur, a classical T Tauri star at the transition of T Tauri to Herbig stars. The images directly show that the disk extends out to ~500 au with an inclination angle of $\\sim$ 50$^\\circ$. Using interpretive models, we derived very small grains in the surface layers of its disk, with a very steep size- and surface-density distribution. Additionally, we resolved a large and extended nebulosity in our images that is most likely a remnant of the prenatal molecular cloud. The position angle of the disk, determined directly from our images, rules out a polar outflow or jet as the cause of this large-scale nebulo...

  20. Circumstellar Dust, PAHs, and Stellar Populations in Early-Type Galaxies: Insights from GALEX and WISE

    Simonian, Gregory V

    2016-01-01

    A majority of early-type galaxies contain interstellar dust, yet the origin of this dust, and why the dust sometimes exhibits unusual PAH ratios, remains a mystery. If the dust is internally produced, the most likely origin is the large number of AGB stars associated with the old stellar population. We present GALEX and WISE elliptical aperture photometry of $\\sim350$ early-type galaxies with Spitzer mid-infrared spectroscopy and/or ancillary data from ATLAS3D, to characterize their circumstellar dust and the shape of the radiation field that illuminates the interstellar PAHs. We find that circumstellar dust is ubiquitous in early-type galaxies, which indicates some tension between stellar population age estimates and models for circumstellar dust production in very old stellar populations. We also use dynamical masses from ATLAS3D to show that WISE W1 (3.4 $\\mu$m) mass-to-light ratios are inconsistent with model predictions for a single IMF, as found by previous work. While the stellar population differences...

  1. Infrared and X-Ray Evidence for Circumstellar Grain Destruction by the Blast Wave of Supernova 1987A

    Dwek, Eliahu; Arendt, Richard G.; Bouchet, Patrice; Burrows, David N.; Challis, Peter; Danziger, John; DeBuizer James M.; Gehrz, Robert D.; Kirshner, Robert P.; McCray, Richard; Park, Sangwok; Polomski, Elisha; Woodward, Charles

    2007-01-01

    Multiwavelength observations of supernova remnant (SNR) 1987A show that its morphology and luminosity are rapidly changing at X-ray, optical, infrared, and radio wavelengths as the blast wave from the explosion expands into the circumstellar equatorial ring, produced by mass loss from the progenitor star. The observed infrared (IR) radiation arises from the interaction of dust grains that formed in mass outflow with the soft X-ray emitting plasma component of the shocked gas. Spitzer IRS spectra at 5 - 30 microns taken on day 6190 since the explosion show that the emission arises from approx. 1.1 x 10(exp -6) solar mass of silicate grains radiating at a temperature of approx. 180+/-(15-20) K. Subsequent observations on day 7137 show that the IR flux had increased by a factor of 2 while maintaining an almost identical spectral shape. The observed IR-to-X-ray flux ratio (IRX) is consistent with that of a dusty plasma with standard LMC dust abundances. This flux ratio has decreased by a factor of approx. 2 between days 6190 and 7137, providing the first direct observation of the ongoing destruction of dust in an expanding SN blast wave on dynamic time scales. Detailed models consistent with the observed dust temperature, the ionization fluence of the soft X-ray emission component, and the evolution of IRX suggest that the radiating si1icate grains are immersed in a 3.5 x 10(exp 6) K plasma with a density of (0.3 - 1) x 10(exp 4)/cu cm, and have a size distribution that is confined to a narrow range of radii between 0.02 and 0.2 microns. Smaller grains may have been evaporated by the initial UV flash from the supernova.

  2. Orion A helium abundance

    The 22.4-GHz (H,He)66-alpha and 36.5-GHz (H,He)56-alpha radio recombination lines have been observed at several Jaffe-Pankonin positions in the central part of the Orion A source. The measured relative abundance of ionized helium increases with distance, averaging 11.6 percent at peripheral points. The observed behavior is interpreted by a blister-type model nebula, which implies that Orion A has a true He abundance of 12 percent, is moving with a radial velocity of 5 km/sec, and is expanding. 18 references

  3. Gel-silica science

    Sol-gel techniques can be used to produce two new types of optical silicas, termed Type V for the full density material and Type VI for the optically transparent porous material. This paper summarizes the processing differences between these six types of commercial silicas. The primary emphasis of this paper is to discuss the scientific basis for the processing of Types V and VI optical silica. First, however, the use of sol-gel processing of other systems will be briefly reviewed. The controlled hydrolysis of alkoxides has also been used to produce submicrometer TiO2, doped TiO2 (17), ZrO2 (18), doped ZrO2 (18), doped SiO2 (19), SrTiO3 (20), and corderite (20) powders. Emulsions have been employed to produce spherical powders of mixed cation oxides, such as yttrium aluminum garnets (YAG) and many other systems (20). Sol-gel powder processes have also been applied to fissile elements (21) where spray form sols UO2, and rigid gel spheres of UO-PuO2 are formed during passage through a column of heated liquid. Both crystalline and vitreous ceramic fibers have been prepared using the sol-gel method. Compositions include TiO2-SiO2 and ZrO2-SiO2 glass fibers (22), high purity SiO2 waveguide fibers (23), Al2O3, ZrO2, ThO2, MgO, TiO2, ZrSiO4, 3AlO3-2SiO2 fibers (24). Sol-gel derived alumina grains are important commercial products (25)

  4. FORMATION PROCESS OF THE CIRCUMSTELLAR DISK: LONG-TERM SIMULATIONS IN THE MAIN ACCRETION PHASE OF STAR FORMATION

    The formation and evolution of the circumstellar disk in unmagnetized molecular clouds is investigated using three-dimensional hydrodynamic simulations from the prestellar core until the end of the main accretion phase. In collapsing cloud cores, the first (adiabatic) core with a size of ∼>3 AU forms prior to the formation of the protostar. At its formation, the first core has a thick disk-like structure and is mainly supported by the thermal pressure. After the protostar formation, it decreases the thickness gradually and becomes supported by the centrifugal force. We found that the first core is a precursor of the circumstellar disk with a size of >3 AU. This means that unmagnetized protoplanetary disk smaller than sun, while the protostar has a mass of ∼10-3 Msun. Thus, just after the protostar formation, the circumstellar disk is about 10-100 times more massive than the protostar. In the main accretion phase that lasts for ∼105 yr, the circumstellar disk mass initially tends to dominate the protostellar mass. Such a massive disk is unstable to gravitational instability and tends to show fragmentation. Our calculations indicate that the low-mass companions may form in the circumstellar disk in the main accretion phase. In addition, the mass accretion rate onto the protostar shows a strong time variability that is caused by the torque from the low-mass companions and/or the spiral arms in the circumstellar disk. Such variability provides an important signature for detecting the substellar mass companion in the circumstellar disk around very young protostars.

  5. Silica aerogel Cherenkov counter

    A practical method for making silica aerogel Cherenkov counters has been developed at KEK, and some tests were performed to evaluate the performance of the counters. The method for making silica aerogel with refractive index between 1.01 and 1.06 is explained in detail. Chemical reaction with methanol, pressure and temperature conditions, and the structure of the autoclave are described together with the whole process. About 20 l aerogel is now produced per week at KEK. The dimensions of the aerogel module is 200 x 100 x 300 mm3. The aerogel with refractive index larger than 1.06 is produced from the aerogel with refractive index 1.06 by heating it up to about 900 deg C. The refractive index can be controlled by the temperature and duration of heating. Refractive index in relation to these conditions is listed in a table. However, the dispersion of the index is about ten times as large as that for the aerogel with lower index (<1.06). The wave length dependence of the transmission length of light for the aerogel was measured and compared with other data obtained at various laboratories. The performance of the counter was evaluated through the experiment with π beam. Average number of photoelectrons gathered is plotted in relation to momentum. It is deduced from the experiment that the saturation thickness of the aerogel is about 10 cm. Two examples of the practical use of the aerogel counter at KEK are also shortly described. (Aoki, K.)

  6. Electrochemically Formed Porous Silica

    Jean-Noël Chazalviel

    2011-04-01

    Full Text Available Controlled electrochemical formation of porous silica can be realized in dilute aqueous, neutral-pH, fluoride medium. Formation of a porous film is initiated by sweeping the potential applied to silicon to values higher than 20 V. Film formation, reaching a steady state, may be pursued in a wide range of potentials, including lower potentials. The origin of a threshold potential for porous film initiation has been explained quantitatively. All of the films appear mesoporous. Films grown at high potentials exhibit a variety of macrostructures superimposed on the mesoporosity. These macrostructures result from selective dissolution of silica induced by local pH lowering due to oxygen evolution. Films grown at potentials lower than 15 V appear uniform on the micrometer scale. However, all of the films also exhibit a stratified structure on the scale of a few tens of nanometres. This periodic structure can be traced back to the oscillatory behavior observed during the electrochemical dissolution of silicon in fluoride medium. It suggests that periodic breaking of the growing film may be responsible for this morphology.

  7. Retention of U(VI) onto silica in presence of model organic molecules

    Pham, T.T.H.; Mercier-Bion, F.; Drot, R.; Lagarde, G.; Simoni, E. [Groupe de Radiochimie, IPNO, Universite Paris 11, Orsay, 91406 (France); Lambert, J. [LCPME, 405 rue de Vandoeuvre, Villers-les-Nancy, 54600 (France)

    2008-07-01

    It is well-known that the organic matter influences the retention of ions onto mineral surfaces. However, the major part of concerned studies implies humic substances and complex solids. Another approach for identifying the sorption mechanisms is possible by studying simpler solids than those present in natural medium. So, silica is chosen as mineral surface because of its abundance in soils and of the presence of Si-O groups in clayey minerals. Uranium (VI) is selected as cation. Simple organic molecules like acetic (one carboxylic group) and oxalic (two carboxylic functions) acids are considered as models of the natural organic matter for understanding their role in the retention of U(VI) onto powders and slides of silica. Binary (organics/silica, U(VI)/silica) and ternary systems (organics/silica/U(VI)) are studied by complementary approaches. Sorption edges as function of pH are obtained by liquid scintillation methods and capillary electrophoresis. Different spectroscopic techniques are used to deduce the interactions between the organic matter and U(VI) sorbed onto the silica whose: Time-Resolved Laser induced Fluorescence Spectroscopy (TRLFS), X-ray Photoelectron Spectroscopy (XPS), Nuclear Microprobe Analysis (NMA). The results of the effect of these model organic molecules onto the U(VI) retention showed a good agreement between the different techniques. Concerning the acetic acid, there are not differences in the sorption percentages of uranyl (see the figure). All these results indicate that the uranyl-acetate complexes stay in the aqueous solution rather than sorbing onto the silica. On the contrary, oxalic acid influences the sorption of U(VI) onto the silica surface. The sorption percentage of U(VI) in the ternary system (oxalic acid/silica/U(VI)) is lower than the binary system (U(VI)/silica) (see the figure). So, the presence of oxalic acid decreases the sorption of U(VI) onto the silica surface. (authors)

  8. Silaffins in Silica Biomineralization and Biomimetic Silica Precipitation

    Carolin C. Lechner

    2015-08-01

    Full Text Available Biomineralization processes leading to complex solid structures of inorganic material in biological systems are constantly gaining attention in biotechnology and biomedical research. An outstanding example for biomineral morphogenesis is the formation of highly elaborate, nano-patterned silica shells by diatoms. Among the organic macromolecules that have been closely linked to the tightly controlled precipitation of silica in diatoms, silaffins play an extraordinary role. These peptides typically occur as complex posttranslationally modified variants and are directly involved in the silica deposition process in diatoms. However, even in vitro silaffin-based peptides alone, with and without posttranslational modifications, can efficiently mediate biomimetic silica precipitation leading to silica material with different properties as well as with encapsulated cargo molecules of a large size range. In this review, the biomineralization process of silica in diatoms is summarized with a specific focus on silaffins and their in vitro silica precipitation properties. Applications in the area of bio- and nanotechnology as well as in diagnostics and therapy are discussed.

  9. A pedagogy of abundance

    Weller, Martin

    2011-01-01

    The digitisation of content combined with a global network for delivery and an open system for sharing has seen radical changes in many industries. The economic model which has underpinned many content based industries has been based on an assumption of scarcity. With a digital, open, networked approach we are witnessing a shift to abundance of content, and subsequently new economic models are being developed which have this as an assumption. In this article the role of scarcity in developing...

  10. Abundances in galaxies

    Standard (or mildly inhomogeneous) Big Bang nucleosynthesis theory is well confirmed by abundance measurements of light elements up to 7Li and the resulting upper limit to the number of neutrino families confirmed in accelerator experiments. Extreme inhomogeneous models with a closure density in form of baryons seem to be ruled out and there is no evidence for a cosmic 'floor' to 9Be or heavier elements predicted in some versions of those models. Galaxies show a correlation between luminous mass and abundance of carbon and heavier elements, usually attributed to escape of hot gas from shallow potential wells. Uncertainties include the role of dark matter and biparametric behaviour of ellipticals. Spirals have radial gradients which may arise from a variety of causes. In our own Galaxy one can distinguish three stellar populations - disk, halo and bulge - characterised by differing metallicity distribution functions. Differential abundance effects are found among different elements in stars as a function of metallicity and presumably age, notably in the ratio of oxygen and α-particle elements to iron. These may eventually be exploitable to set a time scale for the formation of the halo, bulge and disk. (orig.)

  11. Interstellar Atomic Abundances

    Jenkins, E B

    2003-01-01

    A broad array of interstellar absorption features that appear in the ultraviolet spectra of bright sources allows us to measure the abundances and ionization states of many important heavy elements that exist as free atoms in the interstellar medium. By comparing these abundances with reference values in the Sun, we find that some elements have abundances relative to hydrogen that are approximately consistent with their respective solar values, while others are depleted by factors that range from a few up to around 1000. These depletions are caused by the atoms condensing into solid form onto dust grains. Their strengths are governed by the volatility of compounds that are produced, together with the densities and velocities of the gas clouds. We may characterize the depletion trends in terms of a limited set of parameters; ones derived here are based on measurements of 15 elements toward 144 stars with known values of N(H I) and N(H2). In turn, these parameters may be applied to studies of the production, de...

  12. ON ABSORPTION BY CIRCUMSTELLAR DUST, WITH THE PROGENITOR OF SN 2012aw AS A CASE STUDY

    We use the progenitor of SN 2012aw to illustrate the consequences of modeling circumstellar dust using Galactic (interstellar) extinction laws that (1) ignore dust emission in the near-IR and beyond, (2) average over dust compositions, and (3) mischaracterize the optical/UV absorption by assuming that scattered photons are lost to the observer. The primary consequences for the progenitor of SN 2012aw are that both the luminosity and the absorption are significantly overestimated. In particular, the stellar luminosity is most likely in the range 104.8 */L ☉ 5.0 and the star was not extremely massive for a Type IIP progenitor, with M * ☉. Given the properties of the circumstellar dust and the early X-ray/radio detections of SN 2012aw, the star was probably obscured by an ongoing wind with M-dot ∼10-5.5 to 10–5.0 M ☉ yr–1 at the time of the explosion, roughly consistent with the expected mass-loss rates for a star of its temperature (T* ≅ 3600+300–200 K) and luminosity. In the spirit of Galactic extinction laws, we supply simple interpolation formulae for circumstellar extinction by dusty graphitic and silicate shells as a function of wavelength (λ ≥ 0.3 μm) and total (absorption plus scattering) V-band optical depth (τV ≤ 20). These do not include the contributions of dust emission, but provide a simple, physical alternative to incorrectly using interstellar extinction laws.

  13. Silica aerogel core waveguide.

    Grogan, M D W; Leon-Saval, S G; England, R; Birks, T A

    2010-10-11

    We have selectively filled the core of hollow photonic crystal fibre with silica aerogel. Light is guided in the aerogel core, with a measured attenuation of 0.2 dB/cm at 1540 nm comparable to that of bulk aerogel. The structure guides light by different mechanisms depending on the wavelength. At long wavelengths the effective index of the microstructured cladding is below the aerogel index of 1.045 and guidance is by total internal reflection. At short wavelengths, where the effective cladding index exceeds 1.045, a photonic bandgap can guide the light instead. There is a small region of crossover, where both index- and bandgap-guided modes were simultaneously observed. PMID:20941148

  14. Detection of warm molecular hydrogen in the circumstellar disk around the Herbig Ae star HD97048

    Martin-Zaidi, C.; Lagage, P-. O.; Pantin, E.; Habart, E.

    2007-01-01

    We present high resolution spectroscopic mid-infrared observations of the circumstellar disk around the Herbig Ae star HD97048 with the VLT Imager and Spectrometer for the mid-InfraRed (VISIR). We detect the S(1) pure rotational line of molecular hydrogen (H2) at 17.035 microns arising from the disk around the star. This detection reinforces the claim that HD97048 is a young object surrounded by a flared disk at an early stage of evolution. The emitting warm gas is located within the inner 35...

  15. Apparent Stellar Wobble by a Planet in a Circumstellar Disk: Limitations on Planet Detection by Astrometry

    Takeuchi, Taku; Velusamy, T.; Lin, D.N.C.

    2004-01-01

    Astrometric detection of a stellar wobble on the plane of the sky will provide us a next breakthrough in searching extrasolar planets. The Space Interferometry Mission (SIM) is expected to achieve a high-precision astrometry as accurate as 1 micro-as, which is precise enough to discover a new-born Jupiter mass planet around a pre-main-sequence (PMS) star in the Taurus-Auriga star forming region. PMS stars, however, have circum-stellar disks that may be obstacles to the precise measurement of ...

  16. A Rigidly Rotating Magnetosphere Model for Circumstellar Emission from Magnetic OB Stars

    Townsend, R. H. D.; Owocki, S.P.

    2004-01-01

    We present a semi-analytical approach for modeling circumstellar emission from rotating hot stars with a strong dipole magnetic field tilted at an arbitrary angle to the rotation axis. By assuming the rigid-field limit in which material driven (e.g., in a wind outflow) from the star is forced to remain in strict rigid-body co-rotation, we are able to solve for the effective centrifugal-plus-gravitational potential along each field line, and thereby identify the location of potential minima wh...

  17. Radio Observations Reveal Unusual Circumstellar Environments for Some Type Ibc Supernova Progenitors

    Wellons, Sarah; Soderberg, Alicia M.; Chevalier, Roger A.

    2012-01-01

    We present extensive radio observations of the nearby Type Ibc supernovae 2004cc, 2004dk, and 2004gq spanning 8-1900 days after explosion. Using a dynamical model developed for synchrotron emission from a slightly decelerated shockwave, we estimate the velocity and energy of the fastest ejecta and the density profile of the circumstellar medium. The shockwaves of all three supernovae are characterized by non-relativistic velocities of v ~ (0.1-25)c and associated energies of E ~ (2-10) * 1e47...

  18. Archival Legacy Investigations of Circumstellar Environments (ALICE): Statistical assessment of point source detections

    Choquet, Élodie; Pueyo, Laurent; Soummer, Rémi; Perrin, Marshall D.; Hagan, J. Brendan; Gofas-Salas, Elena; Rajan, Abhijith; Aguilar, Jonathan

    2015-09-01

    The ALICE program, for Archival Legacy Investigation of Circumstellar Environment, is currently conducting a virtual survey of about 400 stars, by re-analyzing the HST-NICMOS coronagraphic archive with advanced post-processing techniques. We present here the strategy that we adopted to identify detections and potential candidates for follow-up observations, and we give a preliminary overview of our detections. We present a statistical analysis conducted to evaluate the confidence level on these detection and the completeness of our candidate search.

  19. Archival Legacy Investigations of Circumstellar Environments (ALICE): Statistical assessment of point source detections

    Choquet, É; Soummer, R; Perrin, M D; Hagan, J B; Gofas-Salas, E; Rajan, A; Aguilar, J

    2015-01-01

    The ALICE program, for Archival Legacy Investigation of Circumstellar Environment, is currently conducting a virtual survey of about 400 stars, by re-analyzing the HST-NICMOS coronagraphic archive with advanced post-processing techniques. We present here the strategy that we adopted to identify detections and potential candidates for follow-up observations, and we give a preliminary overview of our detections. We present a statistical analysis conducted to evaluate the confidence level on these detection and the completeness of our candidate search.

  20. 21 CFR 584.700 - Hydrophobic silicas.

    2010-04-01

    ... 21 Food and Drugs 6 2010-04-01 2010-04-01 false Hydrophobic silicas. 584.700 Section 584.700 Food... DRINKING WATER OF ANIMALS Listing of Specific Substances Affirmed as GRAS § 584.700 Hydrophobic silicas. (a) Product. Amorphous fumed hydrophobic silica or precipitated hydrophobic silica (CAS Reg. No....

  1. Silica/Polymer and Silica/Polymer/Fiber Composite Aerogels

    Ou, Danny; Stepanian, Christopher J.; Hu, Xiangjun

    2010-01-01

    Aerogels that consist, variously, of neat silica/polymer alloys and silica/polymer alloy matrices reinforced with fibers have been developed as materials for flexible thermal-insulation blankets. In comparison with prior aerogel blankets, these aerogel blankets are more durable and less dusty. These blankets are also better able to resist and recover from compression . an important advantage in that maintenance of thickness is essential to maintenance of high thermal-insulation performance. These blankets are especially suitable as core materials for vacuum- insulated panels and vacuum-insulated boxes of advanced, nearly seamless design. (Inasmuch as heat leakage at seams is much greater than heat leakage elsewhere through such structures, advanced designs for high insulation performance should provide for minimization of the sizes and numbers of seams.) A silica/polymer aerogel of the present type could be characterized, somewhat more precisely, as consisting of multiply bonded, linear polymer reinforcements within a silica aerogel matrix. Thus far, several different polymethacrylates (PMAs) have been incorporated into aerogel networks to increase resistance to crushing and to improve other mechanical properties while minimally affecting thermal conductivity and density. The polymethacrylate phases are strongly linked into the silica aerogel networks in these materials. Unlike in other organic/inorganic blended aerogels, the inorganic and organic phases are chemically bonded to each other, by both covalent and hydrogen bonds. In the process for making a silica/polymer alloy aerogel, the covalent bonds are introduced by prepolymerization of the methacrylate monomer with trimethoxysilylpropylmethacrylate, which serves as a phase cross-linker in that it contains both organic and inorganic monomer functional groups and hence acts as a connector between the organic and inorganic phases. Hydrogen bonds are formed between the silanol groups of the inorganic phase and the

  2. Silaffins in Silica Biomineralization and Biomimetic Silica Precipitation

    Lechner, Carolin C.; Becker, Christian F. W.

    2015-01-01

    Biomineralization processes leading to complex solid structures of inorganic material in biological systems are constantly gaining attention in biotechnology and biomedical research. An outstanding example for biomineral morphogenesis is the formation of highly elaborate, nano-patterned silica shells by diatoms. Among the organic macromolecules that have been closely linked to the tightly controlled precipitation of silica in diatoms, silaffins play an extraordinary role. These peptides typic...

  3. Facile preparation of mesoporous carbon-silica-coated graphene for the selective enrichment of endogenous peptides.

    Zhang, Quanqing; Zhang, Qinghe; Xiong, Zhichao; Wan, Hao; Chen, Xiaoting; Li, Hongmei; Zou, Hanfa

    2016-01-01

    A sandwich-like composite composed of ordered mesoporous carbon-silica shell-coated graphene (denoted as graphene@mSiO2-C) was prepared by an in-situ carbonation strategy. A mesoporous silica shell was synthesized by a sol-gel method, and cetyltrimethyl ammonium bromide inside the mesopores were in-situ carbonized as a carbon source to obtain a carbon-silica shell. The resulting mesoporous carbon-silica material with a sandwich structure possesses a high surface area (600 m(2) g(-1)), large pore volume (0.587 cm(3) g(-1)), highly ordered mesoporous pore (3 nm), and high carbon content (30%). This material shows not only high hydrophobicity of graphene and mesoporous carbon but also a hydrophilic silica framework that ensures excellent dispersibility in aqueous solution. The material can capture many more peptides from bovine serum albumin tryptic digests than mesoporous silica shell-coated graphene, demonstrating great enrichment efficiency for peptides. Furthermore, the prepared composite was applied to the enrichment of low-abundance endogenous peptides in human serum. Based on Matrix-Assisted Laser Desorption/ Ionization Time of Flight Mass Spectrometry identification, the graphene@mSiO2-C could efficiently size-exclude proteins and enriches the low-abundant peptides on the graphene and mesoporous carbon. And based on the LC-MS/MS results, 892 endogenous peptides were obtained by graphene@mSiO2-C, hinting at its great potential in peptides analysis. PMID:26695263

  4. Functionalized silica materials for electrocatalysis

    Vellaichamy Ganesan

    2015-02-01

    Electrocatalysis is an important phenomenon which is utilized in metal–air batteries, fuel cells, electrochemical sensors, etc. To increase the efficiency of the electrocatalytic process and to increase the electrochemical accessibility of the immobilized electrocatalysts, functionalized and non-functionalized mesoporous organo-silica (MCM41-type-materials) are used in this study. These materials possess several suitable properties to be durable catalysts and/or catalyst supports. Owing to the uniform dispersion of electrocatalysts (metal complex and/or metal nanoparticles (NPs)) on the functionalized and non-functionalized silica, an enormous increase in the redox current is observed. Long range channels of silica materials with pore diameter of 15–100 Å allowed metal NPs to accommodate in a specified manner in addition to other catalysts. The usefulness of MCM-41-type silica in increasing the efficiency of electrocatalysisis demonstrated by selecting oxygen, carbon dioxide and nitrite reduction reactions as examples

  5. Silica Brick for Coke Oven

    Wang Jing

    2007-01-01

    @@ 1 Scope This standard specifies the classification,specification,test method,quality appraisal procedure,labeling,packing,transportation,storage and quality certification of silica brick for coke oven.

  6. Silica reinforced triblock copolymer gels

    Theunissen, E.; Overbergh, N.; Reynaers, H.;

    2004-01-01

    scattering at very low q, but no structure and formfactor information. However, on heating above the viscoelastic to plastic transition, the 'typical' scattering pattern of the copolymer gel builds-up. All reinforced gels are strengthened by the addition of the reinforcing agent. The transitions from a...... viscoclastic rubber to a plastic fluid and from a plastic fluid to a viscoelastic liquid are shifted to more elevated temperatures when silica is added to the triblock copolymer gel. (C) 2004 Elsevier Ltd. All rights reserved.......The effect of silica and polymer coated silica particles as reinforcing agents on the structural and mechanical properties of polystyrene-poly(ethylene/butylene)-polystyrene (PS-PEB-PS) triblock gel has been investigated. Different types of chemically modified silica have been compared in order to...

  7. The silica cycle in a Northeast Pacific fjord; the role of biological resuspension

    Katz, Timor; Yahel, Gitai; Tunnicliffe, Verena; Herut, Barak; Whitney, Frank; Snelgrove, Paul V. R.; Lazar, Boaz

    2016-09-01

    This study is a quantitative assessment of the role fish-induced bio-resuspension plays in the silica cycle of coastal waters. We used new, published and archived oceanographic data to construct a comprehensive silica budget for Saanich Inlet (Vancouver Island, Canada), a highly productive Northeast Pacific fjord, where siliceous diatoms dominate primary productivity. Anoxia in the deep water of the inlet persists during most of the year, precluding animal life, whereas abundant groundfish continuously rework and resuspend bottom sediments in the shallower, oxygenated margins. This resuspension transfers settled biogenic silica fragments from the sediment, where they are immersed in porewater that is rich with dissolved silica, to the overlying water, where the much lower concentrations accelerate their dissolution rate. The budget shows that Saanich Inlet sediments constitute a sink for approximately 250 × 106 mol Si y-1. Most of this Si enters the inlet in advected, siliceous phytoplankton. Sediment resuspension by groundfish in the oxygenated margins of Saanich Inlet generates about 50% of the total flux of dissolved silica from the inlet seafloor. This resuspension also facilitates a massive transport of biogenic silica from the margins to the anoxic basin, where approximately 90% of all the biogenic silica is buried. The excess dissolution caused by fish activity reduces the burial efficiency of biogenic silica in the entire inlet sediments by about 20%. This case study emphasizes the link between the silica cycle and groundfish activity. Based on this study and because biological resuspension occurs in most regions of the ocean, we recommend that it will be taken into account when budgeting the silica cycle, and potentially other geochemical cycles, in marine environments.

  8. Strain-modulated electronic and thermal transport properties of two-dimensional O-silica

    Han, Yang; Qin, Guangzhao; Jungemann, Christoph; Hu, Ming

    2016-07-01

    Silica is one of the most abundant materials in the Earth’s crust and is a remarkably versatile and important engineering material in various modern science and technology. Recently, freestanding and well-ordered two-dimensional (2D) silica monolayers with octahedral (O-silica) building blocks were found to be theoretically stable by (Wang G et al 2015 J. Phys. Chem. C 119 15654–60). In this paper, by performing first-principles calculations, we systematically investigated the electronic and thermal transport properties of 2D O-silica and also studied how these properties can be tuned by simple mechanical stretching. Unstrained 2D O-silica is an insulator with an indirect band gap of 6.536 eV. The band gap decreases considerably with bilateral strain up to 29%, at which point a semiconductor–metal transition occurs. More importantly, the in-plane thermal conductivity of freestanding 2D O-silica is found to be unusually high, which is around 40 to 50 times higher than that of bulk α-quartz and more than two orders of magnitude higher than that of amorphous silica. The thermal conductivity of O-silica decreases by almost two orders of magnitude when the bilateral stretching strain reaches 10%. By analyzing the mode-dependent phonon properties and phonon-scattering channel, the phonon lifetime is found to be the dominant factor that leads to the dramatic decrease of the lattice thermal conductivity under strain. The very sensitive response of both band gap and phonon transport properties to the external mechanical strain will enable 2D O-silica to easily adapt to the different environment of realistic applications. Our study is expected to stimulate experimental exploration of further physical and chemical properties of 2D silica systems, and offers perspectives on modulating the electronic and thermal properties of related low-dimensional structures for applications such as thermoelectric, photovoltaic, and optoelectronic devices.

  9. The circumstellar envelope of IRC+10216 from milli-arcsecond to arcmin scales

    Leao, I C; Mekarnia, D; De Medeiros, J R; Vandame, B; Laverny, Patrick De; Vandame, Benoit

    2006-01-01

    Aims.Analysis of the innermost regions of the carbon-rich star IRC+10216 and of the outer layers of its circumstellar envelope have been performed in order to constrain its mass-loss history. Methods: .We analyzed the high dynamic range of near-infrared adaptive optics and the deep V-band images of the circumstellar envelope of IRC+10216 using high angular resolution, collected with the VLT/NACO and FORS1 instruments. Results: .From the near-infrared observations, we present maps of the sub-arcsecond structures, or clumps, in the innermost regions. The morphology of these clumps is found to strongly vary from J- to L-band. Their relative motion appears to be more complex than proposed in earlier works: they can be weakly accelerated, have a constant velocity, or even be motionless with respect to one another. From V-band imaging, we present a high spatial resolution map of the shell distribution in the outer layers of IRC+10216. Shells are resolved well up to a distance of about 90'' to the core of the nebula...

  10. A search of diffuse bands in fullerene planetary nebulae: evidence for diffuse circumstellar bands

    Diaz-Luis, J J; Rao, N Kameswara; Manchado, A; Cataldo, F

    2014-01-01

    Large fullerenes and fullerene-based molecules have been proposed as carriers of diffuse interstellar bands (DIBs). The recent detection of the most common fullerenes (C60 and C70) around some Planetary Nebulae (PNe) now enable us to study the DIBs towards fullerene-rich space environments. We search DIBs in the optical spectra towards three fullerene-containing PNe (Tc 1, M 1-20, and IC 418). Special attention is given to DIBs which are found to be unusually intense towards these fullerene sources. In particular, an unusually strong 4428A absorption feature is a common charateristic to fullerene PNe. Similarly to Tc 1, the strongest optical bands of neutral C60 are not detected towards IC 418. Our high-quality (S/N > 300) spectra for PN Tc 1 together with its large radial velocity permits us to search for the presence of diffuse bands of circumstellar origin which we refer to as diffuse circumstellar bands (DCBs). We report the first tentative detection of two DCBs at 4428 and 5780 A in the fullerene-rich ci...

  11. The Low Velocity Wind from the Circumstellar Matter Around the B9V Star sigma Herculis

    Chen, C H

    2003-01-01

    We have obtained FUSE spectra of sigma Her, a nearby binary system, with a main sequence primary, that has a Vega-like infrared excess. We observe absorption in the excited fine structure lines C II* at 1037 A, N II* at 1085 A, and N II** at 1086 A that are blueshifted by as much as ~30 km/sec with respect to the star. Since these features are considerably narrower than the stellar lines and broader than interstellar features, the C II and N II are circumstellar. We suggest that there is a radiatively driven wind, arising from the circumstellar matter, rather than accretion as occurs around beta Pic, because of sigma Her's high luminosity. Assuming that the gas is liberated by collisions between parent bodies at 20 AU, the approximate distance at which blackbody grains are in radiative equilibrium with the star and at which 3-body orbits become unstable, we infer dM/dt ~ 6 * 10^-12 M_{sun}/yr. This wind depletes the minimum mass of parent bodies in less than the estimated age of the system.

  12. Recurring Occultations of RW Aurigae by Coagulated Dust in the Tidally Disrupted Circumstellar Disk

    Rodriguez, Joseph E; Siverd, Robert J; Pepper, Joshua; Stassun, Keivan G; Gaudi, B Scott; Weintraub, David A; Beatty, Thomas G; Lund, Michael B; Stevens, Daniel J

    2015-01-01

    We present photometric observations of RW Aurigae, a Classical T Tauri system, that reveal two remarkable dimming events. These events are similar to that which we observed in 2010-2011, which was the first such deep dimming observed in RW Aur in a century's worth of photometric monitoring. We suggested the 2010-2011 dimming was the result of an occultation of the star by its tidally disrupted circumstellar disk. In 2012-2013, the RW Aur system dimmed by ~0.7 mag for ~40 days and in 2014/2015 the system dimmed by ~2 mag for >250 days. The ingress/egress duration measurements of the more recent events agree well with those from the 2010-2011 event, providing strong evidence that the new dimmings are kinematically associated with the same occulting source. Therefore, we suggest that both the 2012-2013 and 2014-2015 dimming events, measured using data from the Kilodegree Extremely Little Telescope and the Kutztown University Observatory, are also occultations of RW Aur A by tidally disrupted circumstellar materi...

  13. V409 Tau As Another AA Tau: Photometric Observations of Stellar Occultations by the Circumstellar Disk

    Rodriguez, Joseph E; Stassun, Keivan G; Siverd, Robert J; Cargile, Phillip; Weintraub, David A; Beatty, Thomas G; Gaudi, B Scott; Mamajek, Eric E; Sanchez, Nicole

    2015-01-01

    AA Tau is a well studied young stellar object that presents many of the photometric characteristics of a Classical T Tauri star (CTTS), including short-timescale stochastic variability attributed to spots and/or accretion as well as long duration dimming events attributed to occultations by vertical features (e.g., warps) in its circumstellar disk. We present new photometric observations of AA Tau from the Kilodegree Extremely Little Telescope North (KELT-North) which reveal a deep, extended dimming event in 2011, which we show supports the interpretation by Bouvier et al. (2013) of an occultation by a high-density feature in the circumstellar disk located >8 AU from the star. We also present KELT-North observations of V409 Tau, a relatively unstudied young stellar object also in Taurus-Auriga, showing short timescale erratic variability, along with two separate long and deep dimming events, one from January 2009 through late October 2010, and the other from March 2012 until at least September 2013. We interp...

  14. The frequency and infrared brightness of circumstellar discs at white dwarfs

    Rocchetto, M; Gaensicke, B T; Bergfors, C

    2014-01-01

    White dwarfs whose atmospheres are polluted by terrestrial-like planetary debris have become a powerful and unique tool to study evolved planetary systems. This paper presents results for an unbiased Spitzer IRAC search for circumstellar dust orbiting a homogeneous and well-defined sample of 134 single white dwarfs. The stars were selected without regard to atmospheric metal content but were chosen to have 1) hydrogen rich atmospheres, 2) 17 000 K < T_eff < 25 000 K and correspondingly young post main-sequence ages of 15-270Myr, and 3) sufficient far-ultraviolet brightness for a corresponding Hubble Space Telescope COS Snapshot. Five white dwarfs were found to host an infrared bright dust disc, three previously known, and two reported here for the first time, yielding a nominal 3.7% of white dwarfs in this post-main sequence age range with detectable circumstellar dust. Remarkably, complementary HST observations indicate that a fraction of 27% show metals in their photosphere that can only be explained ...

  15. Atomic and molecular hydrogen in the circumstellar envelopes of late-type stars

    Glassgold, A. E.; Huggins, P. J.

    1983-01-01

    The distribution of atomic and molecular hydrogen in the expanding circumstellar envelopes of cool evolved stars is discussed. The main concern is to evaluate the effects of photodestruction of H2 by galactic UV radiation, including shielding of the radiation by H2 itself and by dust in the envelope. One of the most important parameters is the H/H2 ratio which is frozen out in the upper atmosphere of the star. For stars with photospheric temperatures greater than about 2500 K, atmospheric models suggest that the outflowing hydrogen is mainly atomic, whereas cooler stars should be substantially molecular. In the latter case, photodissociation of H2 and heavy molecules contribute to the atomic hydrogen content of the outer envelope. The presented estimates indicate that atomic hydrogen is almost at the limit of detection in the C-rich star IRC + 10216, and may be detectable in warmer stars. Failure to detect it would have important implications for the general understanding of circumstellar envelopes.

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

    Tanii, Ryoko; Kudo, Tomoyuki; Hioki, Tomonori; Oasa, Yumiko; Gupta, Ranjan; Sen, A K; Wisniewski, J P; Muto, T; Grady, C A; Hashimoto, J; Fukagawa, M; Mayama, S; Hornbeck, J; Sitko, M; Russell, R; Werren, C; Cure, M; Currie, T; Ohashi, N; Okamoto, Y; Momose, M; Honda, M; Inutsuka, S -I; Takeuchi, T; Dong, R; Abe, L; Brandner, W; Brandt, T; Carson, J; Egner, S; Feldt, M; Fukue, T; Goto, M; Guyon, O; Hayano, Y; Hayashi, M; Hayashi, S S; Henning, T; Hodapp, K W; Ishii, M; Iye, M; Janson, M; Kandori, R; Knapp, G P; Kusakabe, N; Kuzuhara, M; Matsuo, T; McElwain, M W; Miyama, S; Morino, J -I; Moro-Martin, A; Nishimura, T; Pyo, T -S; Serabyn, G; Suto, H; Suzuki, R; Takami, M; Takato, N; Terada, H; Thalmann, C; Tomono, D; Turner, E L; Watanabe, M; Yamada, T; Takami, H; Usuda, T; Tamura, M

    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 \\pm 2 degree 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 (23 AU) at the near-infrared wavelength. We attribute the observed strong polarization (up to 66 %) to light scattering by dust grains in the disk. However, neither polarization models of the circumstellar disk based on Rayleigh scattering nor Mie scattering approximations were consistent w...

  17. 3-D Models of Embedded High-Mass Stars: Effects of a Clumpy Circumstellar Medium

    Indebetouw, R; Johnson, K E; wood, K

    2005-01-01

    We use 3-D radiative transfer models to show the effects of clumpy circumstellar material on the observed infrared colors of high mass stars embedded in molecular clouds. We highlight differences between 3-D clumpy and 1-D smooth models which can affect the interpretation of data. We discuss several important properties of the emergent spectral energy distribution (SED): More near-infrared light (scattered and direct from the central source) can escape than in smooth 1-D models. The near- and mid-infrared SED of the same object can vary significantly with viewing angle, depending on the clump geometry along the sightline. Even the wavelength-integrated flux can vary with angle by more than a factor of two. Objects with the same average circumstellar dust distribution can have very different near-and mid-IR SEDs depending on the clump geometry and the proximity of the most massive clump to the central source. Although clumpiness can cause similar objects to have very different SEDs, there are some observable t...

  18. Modelling the circumstellar medium in RS Ophiuchi and its link to Type Ia supernovae

    Booth, Richard A; Podsiadlowski, Philipp

    2016-01-01

    Recent interpretations of narrow, variable absorption lines detected in some Type Ia supernovae suggest that their progenitors are surrounded by dense, circumstellar material. Similar variations detected in the symbiotic recurrent nova system RS Oph, which undergoes thermonuclear outbursts every ~20 years, making it an ideal candidate to investigate the origin of these lines. To this end, we present simulations of multiple mass transfer-nova cycles in RS Oph. We find that the quiescent mass transfer produces a dense, equatorial outflow, i.e., concentrated towards the binary orbital plane, and an accretion disc forms around the white dwarf. The interaction of a spherical nova outburst with these aspherical circumstellar structures produces a bipolar outflow, similar to that seen in HST imaging of the 2006 outburst. In order to produce an ionization structure that is consistent with observations, a mass-loss rate of $5 \\times 10^{-7}\\,\\mathrm{M}_{\\odot}\\,\\mathrm{yr}^{-1}$ from the red giant is required. The sim...

  19. On the central symmetry of the circumstellar envelope of RS Cnc

    Nhung, Pham Tuyet; Winters, Jan Martin; Darriulat, Pierre; Gérard, Eric; Bertre, Thibaut Le

    2014-01-01

    We present a phenomenological study of CO(1-0) and CO(2-1) emission from the circumstellar envelope (CSE) of the Asymptotic Giant Branch (AGB) star RS\\,Cnc. It reveals departures from central symmetry that turn out to be efficient tools for the exploration of some of the CSE properties. We use a wind model including a bipolar flow with a typical wind velocity of $\\sim$8 km\\,s$^{-1}$ decreasing to $\\sim$2 km\\,s$^{-1}$ near the equator to describe Doppler velocity spectral maps obtained by merging data collected at the IRAM Plateau de Bure Interferometer and Pico Veleta single dish radio telescope. Parameters describing the wind morphology and kinematics are obtained, together with the radial dependence of the gas temperature in the domain of the circumstellar envelope probed by the CO observations. Significant north-south central asymmetries are revealed by the analysis, which we quantify using a simple phenomenological description. The origin of such asymmetries is unclear.

  20. Effects of stellar flybys on planetary systems: 3D modeling of the circumstellar disks damping effects

    Picogna, Giovanni

    2014-01-01

    Stellar flybys in star clusters are suspected to affect the orbital architecture of planetary systems causing eccentricity excitation and orbital misalignment between the planet orbit and the equatorial plane of the star. We explore whether the impulsive changes in the orbital elements of planets, caused by an hyperbolic stellar flyby, can be fully damped by the circumstellar disk surrounding the star. The time required to disperse stellar clusters is in fact comparable to circumstellar disk's lifetime. We have modelled in 3D a system made of a solar type star surrounded by a low density disk with a giant planet embedded in it approached on a hyperbolic encounter trajectory by a second star, of similar mass and with its own disk. We focus on extreme configurations where a very deep stellar flyby perturbs a Jovian planet on an external orbit. This allows to test in full the ability of the disk to erase the effects of the stellar encounter. We find that the amount of mass lost by the disk during the stellar fly...

  1. Photoevaporation of Circumstellar Disks due to External FUV Radiation in Stellar Aggregates

    Adams, F C; Laughlin, G; Gorti, U; Adams, Fred C.; Hollenbach, David; Laughlin, Gregory; Gorti, Uma

    2004-01-01

    When stars form in small groups (N = 100 - 500 members), their circumstellar disks are exposed to little EUV radiation but a great deal of FUV radiation from massive stars in the group. This paper calculates mass loss rates for circumstellar disks exposed to external FUV radiation. Previous work treated large disks and/or intense radiation fields in which the disk radius exceeds the critical radius (supercritical disks) where the sound speed in the FUV heated layer exceeds the escape speed. This paper shows that significant mass loss still takes place for subcritical systems. Some of the gas extends beyond the disk edge (above the disk surface) to larger distances where the temperature is higher, the escape speed is lower, and an outflow develops. The evaporation rate is a sensitive function of the stellar mass and disk radius, which determine the escape speed, and the external FUV flux, which determines the temperature structure of the flow. Disks around red dwarfs are readily evaporated and shrink to disk r...

  2. The Peculiar Balmer Decrement of SN 2009ip: Constraints on Circumstellar Geometry

    Levesque, Emily M; Ginsburg, Adam G; Bally, John; Keeney, Brian A

    2012-01-01

    We present optical and near-IR spectroscopic observations of the luminous blue variable SN 2009ip during its remarkable photometric evolution of 2012. The spectra sample three key points in the SN 2009ip lightcurve, corresponding to its initial brightening in August (2012-A) and its dramatic rebrightening in early October (2012-B). Based on line fluxes and velocities measured in our spectra, we find a surprisingly low I(H-alpha)/I(H-beta) ratio (~1.5) in the 2012-B spectra. Such a ratio implies either a rare Case B recombination scenario where H-alpha, but not H-beta, is optically thick, or an extremely high density for the circumstellar material of n_e > 10^(13) cm^(-3). The H-alpha line intensity yields a minimum radiating surface area of >~20,000 AU^2 in H-alpha at the peak of SN 2009ip's photometric evolution. Combined with the nature of this object's spectral evolution in 2012, a high circumstellar density and large radiating surface area imply the presence of a thin disk geometry around the central star...

  3. Tracing planet-induced structures in circumstellar disks using molecular lines

    Ober, F; Uribe, A L; Klahr, H H

    2015-01-01

    Circumstellar disks are considered to be the birthplace of planets. Specific structures like spiral arms, gaps, and cavities are characteristic indicators of planet-disk interaction. Investigating these structures can provide insights into the growth of protoplanets and the physical properties of the disk. We investigate the feasibility of using molecular lines to trace planet-induced structures in circumstellar disks. Based on 3D hydrodynamic simulations of planet-disk interactions, we perform self-consistent temperature calculations and produce N-LTE molecular line velocity-channel maps and spectra of these disks using our new N-LTE line radiative transfer code Mol3D. Subsequently, we simulate ALMA observations using the CASA simulator. We consider two nearly face-on inclinations, 5 disk masses, 7 disk radii, and 2 different typical pre-main-sequence host stars (T Tauri, Herbig Ae). We calculate up to 141 individual velocity-channel maps for five molecules/isotopoloques in a total of 32 rotational transitio...

  4. The PDS 66 Circumstellar Disk as seen in Polarized Light with the Gemini Planet Imager

    Wolff, Schuyler G; Millar-Blanchaer, Maxwell A; Nielsen, Eric L; Wang, Jason; Cardwell, Andrew; Chilcote, Jeffrey; Dong, Ruobing; Draper, Zachary H; Duchene, Gaspard; Fitzgerald, Michael P; Goodsell, Stephen J; Grady, Carol A; Graham, James R; Greenbaum, Alexandra Z; Hartung, Markus; Hibon, Pascale; Hines, Dean C; Hung, Li-Wei; Kalas, Paul; Macintosh, Bruce; Marchis, Franck; Marois, Christian; Pueyo, Laurent; Rantakyro, Fredrik T; Schneider, Glenn; Sivaramakrishnan, Anand; Wiktorowicz, Sloane J

    2016-01-01

    We present H and K band imaging polarimetry for the PDS 66 circumstellar disk obtained during the commissioning of the Gemini Planet Imager (GPI). Polarization images reveal a clear detection of the disk in to the 0.12'' inner working angle (IWA) in H band, almost 3 times as close to the star as the previous HST observations with NICMOS and STIS (0.35'' effective IWA). The centro-symmetric polarization vectors confirm that the bright inner disk detection is due to circumstellar scattered light. A more diffuse disk extends to a bright outer ring centered at 80 AU. We discuss several physical mechanisms capable of producing the observed ring + gap structure. GPI data confirm enhanced scattering on the East side of the disk which is inferred to be nearer to us. We also detect a lateral asymmetry in the South possibly due to shadowing from material within the inner working angle. This likely corresponds to a temporally variable azimuthal asymmetry observed in HST/STIS coronagraphic imaging.

  5. Radio Observations Reveal Unusual Circumstellar Environments for Some Type Ibc Supernova Progenitors

    Wellons, Sarah; Chevalier, Roger A

    2012-01-01

    We present extensive radio observations of the nearby Type Ibc supernovae 2004cc, 2004dk, and 2004gq spanning 8-1900 days after explosion. Using a dynamical model developed for synchrotron emission from a slightly decelerated shockwave, we estimate the velocity and energy of the fastest ejecta and the density profile of the circumstellar medium. The shockwaves of all three supernovae are characterized by non-relativistic velocities of v ~ (0.1-25)c and associated energies of E ~ (2-10) * 1e47 erg, in line with the expectations for a typical homologous explosion. Smooth circumstellar density profiles are indicated by the early radio data and we estimate the progenitor mass loss rates to be ~ (0.6-13) * 1e-5 M_sun/yr (wind velocity 10^3 km/s). These estimates approach the saturation limit (~1e-4 M_sun/yr) for line-driven winds from Wolf-Rayet stars, the favored progenitors of SNe Ibc including those associated with long-duration GRBs. Intriguingly, at later epochs all three supernovae show evidence for abrupt r...

  6. BANYAN. VIII. New Low-Mass Stars and Brown Dwarfs with Candidate Circumstellar Disks

    Boucher, Anne; Gagné, Jonathan; Malo, Lison; Faherty, Jacqueline K; Doyon, René; Chen, Christine H

    2016-01-01

    We present the results of a search for new circumstellar disks around low-mass stars and brown dwarfs with spectral types >K5 that are confirmed or candidate members of nearby young moving groups. Our search input sample was drawn from the BANYAN surveys of Malo et al. and Gagn\\'e et al. Two-Micron All-Sky Survey and Wide-field Infrared Survey Explorer data were used to detect near- to mid-infrared excesses that would reveal the presence of circumstellar disks. A total of 13 targets with convincing excesses were identified: four are new and nine were already known in the literature. The new candidates are 2MASS J05010082$-$4337102 (M4.5), J08561384$-$1342242 (M8$\\,\\gamma$), J12474428$-$3816464 (M9$\\,\\gamma$) and J02265658$-$5327032 (L0$\\,\\delta$), and are candidate members of the TW Hya ($\\sim10\\pm 3\\,$Myr), Columba ($\\sim 42^{+6}_{-4}\\,$Myr) and Tucana-Horologium ($\\sim 45\\pm 4\\,$Myr) associations, with masses of $120$ and $13-18\\,M_{\\mathrm{Jup}}$. The M8$-$L0 objects in Columba and Tucana-Horologium are po...

  7. Circumstellar C2, CN, and CH+ in the optical spectra of post-AGB stars

    Bakker, E J; Waters, L B F M; Schoenmaker, T; Bakker, Eric J.; Dishoeck, Ewine F. van; Schoenmaker, Ton

    1996-01-01

    We present optical high-resolution spectra of a sample of sixteen post-AGB stars and IRC +10216. Of the post-AGB stars, ten show C2 Phillips and Swan and CN Red System absorption, one CH+ emission, one CH+ absorption, and four without any molecules. We find typically Trot=43-399, 155-202, and 18-50 K, log N = 14.90-15.57, 14.35, and 15.03-16.47 cm-2 for C2, CH+, and CN respectively, and 0.620. The presence of C2 and CN absorption is correlated with cold dust (Tdust300K). All objects with the unidentified 21mum emission feature exhibit C2 and CN absorption, but not all objects with C2 and CN detections exhibit a 21mum feature. The derived expansion velocity, ranging from 5 to 44 km/s, is the same as that derived from CO millimeter line emission. This unambiguously proves that these lines are of circumstellar origin and are formed in the AGB ejecta (circumstellar shell expelled during the preceding AGB phase). Furthermore there seems to be a relation between the C2 molecular column density and the expansion vel...

  8. AGB stars in the LMC: evolution of dust in circumstellar envelopes

    Dell'Agli, F; Schneider, R; Di Criscienzo, M; García-Hernández, D A; Rossi, C; Brocato, E

    2014-01-01

    We calculated theoretical evolutionary sequences of asymptotic giant branch (AGB) stars, including formation and evolution of dust grains in their circumstellar envelope. By considering stellar populations of the Large Magellanic Cloud (LMC), we calculate synthetic colour-colour and colour-magnitude diagrams, which are compared with those obtained by the Spitzer Space Telescope. The comparison between observations and theoretical predictions outlines that extremely obscured carbon-stars and oxygen-rich sources experiencing hot bottom burning (HBB) occupy well defined, distinct regions in the colour-colour ($[3.6]-[4.5]$, $[5.8]-[8.0]$) diagram. The C-rich stars are distributed along a diagonal strip that we interpret as an evolutionary sequence, becoming progressively more obscured as the stellar surface layers enrich in carbon. Their circumstellar envelopes host solid carbon dust grains with size in the range $0.05 2$, are the descendants of stars with initial mass $M_{in} \\sim 2.5 - 3 M_{\\odot}$ in the ver...

  9. Magnetic silica colloids for catalysis

    Claesson, E.M.; Mehendale, N.C.; Klein Gebbink, R. J. M.; van Koten, G; Philipse, A. P.

    2007-01-01

    Monodisperse magnetizable colloidal silica particles in a stable dispersion have been functionalized with a homogeneous catalyst: a PCP–pincer Pd-complex. In a proof-of-principle experiment we demonstrate the catalytic activity of the colloids in a C–C bond formation reaction. Advantages of the magnetic silica carriers are the large surface-to-volume ratio and the easy recovery by magnetic separation. After magnetic separation, the catalyst-loaded particles are readily redispersed for further...

  10. Abundance, Excess, Waste

    Rox De Luca

    2016-02-01

    Her recent work focuses on the concepts of abundance, excess and waste. These concerns translate directly into vibrant and colourful garlands that she constructs from discarded plastics collected on Bondi Beach where she lives. The process of collecting is fastidious, as is the process of sorting and grading the plastics by colour and size. This initial gathering and sorting process is followed by threading the components onto strings of wire. When completed, these assemblages stand in stark contrast to the ease of disposability associated with the materials that arrive on the shoreline as evidence of our collective human neglect and destruction of the environment around us. The contrast is heightened by the fact that the constructed garlands embody the paradoxical beauty of our plastic waste byproducts, while also evoking the ways by which those byproducts similarly accumulate in randomly assorted patterns across the oceans and beaches of the planet.

  11. Molecular Dynamics Simulation of Water Nanodroplets on Silica Surfaces at High Air Pressures

    Zambrano, Harvey A; Jaffe, Richard Lawrence; Walther, Jens Honore

    2010-01-01

    Silicon dioxides-water systems are abundant in nature and play fundamental roles in a diversity of novel science and engineering applications. Although extensive research has been devoted to study the nature of the interaction between silica and water a complete understanding of the system has no...

  12. Dynamics of Circumstellar Disks. III. The Case of GG Tau A

    Nelson, Andrew F.; Marzari, F.

    2016-08-01

    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

  13. RADIO OBSERVATIONS REVEAL UNUSUAL CIRCUMSTELLAR ENVIRONMENTS FOR SOME TYPE Ibc SUPERNOVA PROGENITORS

    We present extensive radio observations of the nearby Type Ibc supernovae (SNe Ibc) 2004cc, 2004dk, and 2004gq spanning Δt ≈ 8-1900 days after explosion. Using a dynamical model developed for synchrotron emission from a slightly decelerated shock wave, we estimate the velocity and energy of the fastest ejecta and the density profile of the circumstellar medium. The shock waves of all three supernovae are characterized by non-relativistic velocities of v-bar approx. (0.1-25)c and associated energies of E ≈ (2-10) × 1047 erg, in line with the expectations for a typical homologous explosion. Smooth circumstellar density profiles are indicated by the early radio data and we estimate the progenitor mass-loss rates to be M-dot approx. (0.6-13) x 10-5 M☉ yr-1 (wind velocity, vw = 103 km s–1). These estimates approach the saturation limit ( M-dot ∼10-4 M☉ yr-1) for line-driven winds from Wolf-Rayet stars, the favored progenitors of SNe Ibc including those associated with long-duration gamma-ray bursts. Intriguingly, at later epochs all three supernovae show evidence for abrupt radio variability that we attribute to large density modulations (factor of ∼3-6) at circumstellar radii of r ≈ (1-50) × 1016 cm. If due to variable mass loss, these modulations are associated with progenitor activity on a timescale of ∼10-100 years before explosion. We consider these results in the context of variable mass-loss mechanisms including wind clumping, metallicity-independent continuum-driven ejections, and binary-induced modulations. It may also be possible that the SN shock waves are dynamically interacting with wind termination shocks; however, this requires the environment to be highly pressurized and/or the progenitor to be rapidly rotating prior to explosion. The proximity of the density modulations to the explosion sites may suggest a synchronization between unusual progenitor mass loss and the SN explosion, reminiscent of Type IIn supernovae. This study

  14. HST/STIS results on circumstellar disks and jets, future coronography and technology for IR multi-object spectroscopy

    Woodgate, Bruce E.

    2002-01-01

    Results of studies of circumstellar disks and jets obtained by HST/STIS visible coronagraphy and UV spectroscopy, and by ground-based Fabry-Perot coronagraphy will be presented. Future improvements in coronagraphy will be discussed. The development of microshutter arrays as programmable multi-object selectors for the NGST near IR spectrograph will be described.

  15. Formation Process of the Circumstellar Disk: Long-term Simulations in the Main Accretion Phase of Star Formation

    Machida, Masahiro N; Matsumoto, Tomoaki

    2010-01-01

    The formation and evolution of the circumstellar disk in unmagnetized molecular clouds is investigated using three-dimensional hydrodynamic simulations from the prestellar core until the end of the main accretion phase. In collapsing clouds, the first (adiabatic) core with a size of ~10AU forms prior to the formation of the protostar. At its formation, the first core has a thick disk-like structure, and is mainly supported by the thermal pressure. After the protostar formation, it decreases the thickness gradually, and becomes supported by the centrifugal force. We found that the first core is a precursor of the circumstellar disk. This indicates that the circumstellar disk is formed before the protostar formation with a size of ~10AU, which means that no protoplanetary disk smaller than <10AU exists. Reflecting the thermodynamics of the collapsing gas, at the protostar formation epoch, the circumstellar disk has a mass of ~0.01-0.1 solar mass, while the protostar has a mass of ~10^-3 solar mass. Thus, jus...

  16. Rice Husk Ash as a Renewable Source for the Production of Value Added Silica Gel and its Application: An Overview

    Ram Prasad

    2012-06-01

    Full Text Available In recent years, silica gels have developed a lot of interest due to their extraordinary properties and their existing and potential applications in science and technology. Silica gel has a wide range of applications such as a desiccant, as a preservation tool to control humidity, as an adsorbent, as a catalyst and as a cata-lyst support. Silica gel is a rigid three-dimensional network of colloidal silica, and is classified as: aqua-gel, alco-gel, xero-gel and aero-gel. Out of all known solid porous materials, aero-gels are particularly known for their high specific surface area, high porosity, low bulk density, high thermal insulation value, ultra low dielectric constant and low index of refraction. Because of these extraordinary properties silica aero-gel has many commercial applications such as thermal window insulation, acoustic barriers, super-capacitors and catalytic supports. However, monolithic silica aero-gel has been used extensively in high energy physics in Cherenkov radiation detectors and in shock wave studies at high pressures, inertial confinement fusion (ICF radio-luminescent and micrometeorites. Silica gel can be prepared by using various sol gel precursors but the rice husk (RH is considered as the cheapest source for silica gel production. Rice husk is a waste product abundantly available in rice producing countries during milling of rice. This review article aims at summarizing the developments carried out so far in synthesis, properties, characterization and method of determination of silica, silica gel, silica aero-gel and silica xero-gel. The effect of synthesis parameters such as pH, temperature of burning the rice husk, acid leaching prior to formation of rice husk ash (RHA on the properties of final product are also described. The attention is also paid on the application of RH, RHA, sil-ica, silica aero-gel and silica xero-gel. Development of economically viable processes for getting rice husk silica with specific

  17. Primordial Deuterium Abundance Measurements

    Levshakov, S A; Takahara, F; Levshakov, Sergei A.; Kegel, Wilhelm H.; Takahara, Fumio

    1997-01-01

    Deuterium abundances measured recently from QSO absorption-line systems lie in the range from 3 10^{-5} to 3 10^{-4}, which shed some questions on standard big bang theory. We show that this discordance may simply be an artifact caused by inadequate analysis ignoring spatial correlations in the velocity field in turbulent media. The generalized procedure (accounting for such correlations) is suggested to reconcile the D/H measurements. An example is presented based on two high-resolution observations of Q1009+2956 (low D/H) [1,2] and Q1718+4807 (high D/H) [8,9]. We show that both observations are compatible with D/H = 4.1 - 4.6 10^{-5}, and thus support SBBN. The estimated mean value = 4.4 10^{-5} corresponds to the baryon-to-photon ratio during SBBN eta = 4.4 10^{-10} which yields the present-day baryon density Omega_b h^2 = 0.015.

  18. Synthesis, characterization and catalytic activity of carbon-silica hybrid catalyst from rice straw

    Janaun, J.; Safie, N. N.; Siambun, N. J.

    2016-07-01

    The hybrid-carbon catalyst has been studied because of its promising potential to have high porosity and surface area to be used in biodiesel production. Silica has been used as the support to produce hybrid carbon catalyst due to its mesoporous structure and high surface area properties. The chemical synthesis of silica-carbon hybrid is expensive and involves more complicated preparation steps. The presence of natural silica in rice plants especially rice husk has received much attention in research because of the potential as a source for solid acid catalyst synthesis. But study on rice straw, which is available abundantly as agricultural waste is limited. In this study, rice straw undergone pyrolysis and functionalized using fuming sulphuric acid to anchor -SO3H groups. The presence of silica and the physiochemical properties of the catalyst produced were studied before and after sulphonation. The catalytic activity of hybrid carbon silica acid catalyst, (H-CSAC) in esterification of oleic acid with methanol was also studied. The results showed the presence of silica-carbon which had amorphous structure and highly porous. The carbon surface consisted of higher silica composition, had lower S element detected as compared to the surface that had high carbon content but lower silica composition. This was likely due to the fact that Si element which was bonded to oxygen was highly stable and unlikely to break the bond and react with -SO3H ions. H-CSAC conversions were 23.04 %, 35.52 % and 34.2 7% at 333.15 K, 343.15 K and 353.15 K, respectively. From this research, rice straw can be used as carbon precursor to produce hybrid carbon-silica catalyst and has shown catalytic activity in biodiesel production. Rate equation obtained is also presented.

  19. THE GAS/DUST RATIO OF CIRCUMSTELLAR DISKS: TESTING MODELS OF PLANETESIMAL FORMATION

    We present high-resolution, near-infrared NIRSPEC observations of CO absorption toward six class II T Tauri stars: AA Tau, DG Tau, IQ Tau, RY Tau, CW Tau, and Haro 6-5b. 12CO overtone absorption lines originating from the circumstellar disk of each object were used to calculate line-of-sight gas column densities toward each source. We measured the gas/dust ratio as a function of disk inclination, utilizing measured visual extinctions and inclinations for each star. The majority of our sources show further evidence for a correlation between the gas/dust column density ratio and disk inclination similar to that found by Rettig et al.

  20. A Compact Circumstellar Shell as the Source of High--velocity Features in SN 2011fe

    Mulligan, Brian W

    2015-01-01

    High--velocity features (HVF), especially of Ca II, are frequently seen in Type Ia supernovae observed prior to B-band maximum (Bmax). These HVF start at more than 25,000 km/s in the days after first light, and slow to about 18,000 km/s near Bmax. To recreate the Ca II near-infrared triplet (CaNIR) HVF in SN 2011fe, we consider the interaction between a Type Ia supernova and a compact circumstellar shell, employing a hydrodynamic 1-D simulation using FLASH. We generate synthetic spectra from the hydrodynamic results using syn++. We show that the CaNIR HVF and its velocity evolution is better explained by a supernova model interacting with a shell than a model without a shell, and briefly discuss the implications for progenitor models.

  1. Constraints on the Formation and Evolution of Circumstellar Disks in Rotating Magnetized Cloud Cores

    Basu, S

    1998-01-01

    We use magnetic collapse models to place some constraints on the formation and angular momentum evolution of circumstellar disks which are embedded in magnetized cloud cores. Previous models have shown that the early evolution of a magnetized cloud core is governed by ambipolar diffusion and magnetic braking, and that the core takes the form of a nonequilibrium flattened envelope which ultimately collapses dynamically to form a protostar. In this paper, we focus on the inner centrifugally-supported disk, which is formed only after a central protostar exists, and grows by dynamical accretion from the flattened envelope. We estimate a centrifugal radius for the collapse of mass shells within a rotating, magnetized cloud core. The centrifugal radius of the inner disk is related to its mass through the two important parameters characterizing the background medium: the background rotation rate $\\Omb$ and the background magnetic field strength $\\Bref$. We also revisit the issue of how rapidly mass is deposited onto...

  2. CO and HI emission from the circumstellar envelopes of some evolved stars

    Diep, P N; Nhung, P T; Tuan-Anh, P; Bertre, T Le; Winters, J M; Matthews, L D; Phuong, N T; Thao, N T; Darriulat, P

    2015-01-01

    Studies of the CO and HI radio emission of some evolved stars are presented using data collected by the IRAM Plateau de Bure interferometer and Pico Veleta telescope, the Nan\\c{c}ay Radio Telescope and the JVLA and ALMA arrays. Approximate axial symmetry of the physical and kinematic properties of the circumstellar envelope (CSE) are observed in CO emission, in particular, from RS Cnc, EP Aqr and the Red Rectangle. A common feature is the presence of a bipolar outflow causing an enhanced wind velocity in the polar directions. HI emission extends to larger radial distances than probed by CO emission and displays features related to the interaction between the stellar outflow and interstellar matter. With its unprecedented sensitivity, FAST will open a new window on such studies. Its potential in this domain is briefly illustrated.

  3. THE GAS/DUST RATIO OF CIRCUMSTELLAR DISKS: TESTING MODELS OF PLANETESIMAL FORMATION

    Horne, David [New York Center for Astrobiology, Rensselaer Polytechnic Institute, 110 Eighth Street, Troy, NY 12180-3590 (United States); Gibb, Erika [Department of Physics and Astronomy, University of Missouri-St. Louis, 8001 Natural Bridge Road, St. Louis, MO 63121 (United States); Rettig, Terrence W.; Tilley, David; Balsara, Dinshaw [Center for Astrophysics, University of Notre Dame, Notre Dame, IN 46556 (United States); Brittain, Sean [Department of Physics and Astronomy, Clemson University, Clemson, SC 29634-0978 (United States)

    2012-07-20

    We present high-resolution, near-infrared NIRSPEC observations of CO absorption toward six class II T Tauri stars: AA Tau, DG Tau, IQ Tau, RY Tau, CW Tau, and Haro 6-5b. {sup 12}CO overtone absorption lines originating from the circumstellar disk of each object were used to calculate line-of-sight gas column densities toward each source. We measured the gas/dust ratio as a function of disk inclination, utilizing measured visual extinctions and inclinations for each star. The majority of our sources show further evidence for a correlation between the gas/dust column density ratio and disk inclination similar to that found by Rettig et al.

  4. Early-time signatures of {\\gamma}-ray emission from supernovae in dense circumstellar media

    Kantzas, Dimitrios; Mastichiadis, Apostolos

    2016-01-01

    We present our results on the {\\gamma}-ray emission from interaction-powered supernovae (SNe), a recently discovered SN type that is suggested to be surrounded by a circumstellar medium (CSM) with densities 10^7-10^12~ cm^-3. Such high densities favor inelastic collisions between relativistic protons accelerated in the SN blast wave and CSM protons and the production of {\\gamma}-ray photons through neutral pion decays. Using a numerical code that includes synchrotron radiation, adiabatic losses due to the expansion of the source, photon-photon interactions, proton-proton collisions and proton-photon interactions, we calculate the multi-wavelength non-thermal photon emission soon after the shock breakout and follow its temporal evolution until 100-1000 days. Focusing on the {\\gamma}-ray emission at >100 MeV, we show that this could be detectable by the Fermi-LAT telescope for nearby (10^11 cm^-3).

  5. A HOT MOLECULAR CIRCUMSTELLAR DISK AROUND THE MASSIVE PROTOSTAR ORION SOURCE I

    Hirota, Tomoya; Honma, Mareki [National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Kim, Mi Kyoung [Korea Astronomy and Space Science Institute, Hwaam-dong 61-1, Yuseong-gu, Daejeon, 305-348 (Korea, Republic of); Kurono, Yasutaka, E-mail: tomoya.hirota@nao.ac.jp [Chile Observatory, National Astronomical Observatory of Japan, Osawa 2-21-1, Mitaka, Tokyo 181-8588 (Japan)

    2014-02-20

    We report new Atacama Large Millimeter/Submillimeter Array (ALMA) observations of a circumstellar disk around Source I in Orion KL, an archetype of massive protostar candidates. We detected two ortho-H{sub 2}O lines at 321 GHz (10{sub 2,} {sub 9}-9{sub 3,} {sub 6}) and 336 GHz (ν{sub 2} = 1, 5{sub 2,} {sub 3}-6{sub 1,} {sub 6}) for the first time in Source I. The latter one is in a vibrationally excited state at the lower state energy of 2939 K, suggesting evidence of hot molecular gas close to Source I. The integrated intensity map of the 321 GHz line is elongated along the bipolar outflow while the 336 GHz line map is unresolved with a beam size of 0.''4. Both of these maps show velocity gradients perpendicular to the bipolar outflow. The velocity centroid map of the 321 GHz line implies a spatial and velocity structure similar to that of vibrationally excited SiO masers tracing the root of the outflow emanating from the disk surface. In contrast, the 336 GHz line is most likely emitting from the disk midplane with a diameter of 0.''2 (84 AU) as traced by radio continuum emission and a dark lane devoid of the vibrationally excited SiO maser emission. The observed velocity gradient and the spectral profile of the 336 GHz H{sub 2}O line can be reconciled with a model of an edge-on ring-like structure with an enclosed mass of >7 M{sub ☉} and an excitation temperature of >3000 K. The present results provide further evidence of a hot and neutral circumstellar disk rotating around Source I with a diameter of ∼100 AU scale.

  6. A HOT MOLECULAR CIRCUMSTELLAR DISK AROUND THE MASSIVE PROTOSTAR ORION SOURCE I

    We report new Atacama Large Millimeter/Submillimeter Array (ALMA) observations of a circumstellar disk around Source I in Orion KL, an archetype of massive protostar candidates. We detected two ortho-H2O lines at 321 GHz (102, 9-93, 6) and 336 GHz (ν2 = 1, 52, 3-61, 6) for the first time in Source I. The latter one is in a vibrationally excited state at the lower state energy of 2939 K, suggesting evidence of hot molecular gas close to Source I. The integrated intensity map of the 321 GHz line is elongated along the bipolar outflow while the 336 GHz line map is unresolved with a beam size of 0.''4. Both of these maps show velocity gradients perpendicular to the bipolar outflow. The velocity centroid map of the 321 GHz line implies a spatial and velocity structure similar to that of vibrationally excited SiO masers tracing the root of the outflow emanating from the disk surface. In contrast, the 336 GHz line is most likely emitting from the disk midplane with a diameter of 0.''2 (84 AU) as traced by radio continuum emission and a dark lane devoid of the vibrationally excited SiO maser emission. The observed velocity gradient and the spectral profile of the 336 GHz H2O line can be reconciled with a model of an edge-on ring-like structure with an enclosed mass of >7 M☉ and an excitation temperature of >3000 K. The present results provide further evidence of a hot and neutral circumstellar disk rotating around Source I with a diameter of ∼100 AU scale

  7. The warm circumstellar envelope and wind of the G9 IIb star HR 6902

    Kirsch, T.; Baade, R.; Reimers, D.

    2001-12-01

    IUE observations of the eclipsing binary system HR 6902 obtained at various epochs spread over four years indicate the presence of warm circumstellar material enveloping the G9 IIb primary. The spectra show Si Iv and C Iv absorption up to a distance of 3.3 giant radii (Rg). Line ratio diagnostics yields an electron temperature of ~ 78 000 K which appears to be constant over the observed height range. Applying a least square fit absorption line analysis we derive column densities as a function of height. We find that the inner envelope (improved agreement with observations over the whole height regime including the emission line region is obtained with an outflow model. We demonstrate that the common β power-law as well as a P ∝ ρ wind yield appropriate fit models. Adopting a continuous mass outflow we obtain a mass-loss rate of M⊙=0.8 - 3.4 × 10-11 Msolar yr-1 depending on the particular wind model. The emission lines observed during total eclipse are attributed mostly to resonance scattering of B star photons in the extended envelope of the giant. By means of a multi-dimensional line formation study we show that the global envelope properties are consistent with the wind models derived from the absorption line analysis. We argue that future high resolution UV spectroscopy will resolve the large-scale velocity structure of the circumstellar shell. As an illustration we present theoretical Si Iv and C Iv emission profiles showing model-dependent line shifts and asymmetries.

  8. A Rotating Circumstellar Disk Around a High-Mass Protostar in IRAS 18162-2048

    Fernández-López, M.; Girart, J. M.; Curiel, S.; Patel, N.; Gómez, Y.; Ho, P. T. P.

    2011-10-01

    Searching for molecular tracers of disks in massive star-formation regions is a complex task. There are molecules that show emission from the envelope and the disk simultaneously. Other molecules show optically thick emission, thus complicating the kinematic study of disks. On the other hand, S-bearing species (such as H2S, SO, SO2, CS, and OCS) could be intimately linked with the evaporation process of the disk surface becoming good tracers of the dynamics of the innermost parts of the high-mass protostars. Recently, several papers have been published on the detection of S-bearing species in disks and other warm gas structures of massive star-forming regions. In particular, SO2 transitions, ubiquitous within the (sub)millimeter range, show a very compact nature, suggesting their close association with circumstellar structures. We have carried out sub-arcsecond SMA observations towards the central region of the HH 80-81 system. The mm continuum emission shows two main sources, one of them located at the center of the extremely large (5.3 pc long) bipolar radio continuum jet observed in this region. The dust emission appears compact and coincides with a radio continuum source. Between the spectral lines detected (H2CO and SO), the SO2 line transitions show compact emission toward this source. These molecular lines clearly show a velocity gradient perpendicular to the radio jet axis. Both, the dust continuum and the molecular line emission suggest the existence of a rotating circumstellar disk around a massive protostar.

  9. Double radio source associated with L1551 IRS 5: Binary system or ionized circumstellar torus

    Using the VLA at 2 cm, we mapped the core of L1551 with an angular resolution of approx.0.''15. We find that the two unresolved sources detected by Bieging and Cohen and reported in 1985 are centered in a region of extended (approx.2'' x 1'') emission. This suggests that the two compact sources may be the ionized inner part of a confining torus with radius of approx.25 AU seen in projection, and not two stars as was previously surmised. We propose that the energy source of the system is a star located between the two radio peaks and as yet undetected in the radio. The observed ionization can be explained if a small fraction of a predominantly neutral stellar wind from the central object shocks against the confining torus. This extended emission was not present in the map of Bieging and Cohen and may be time variable. Using pressure equilibrium arguments we estimate the density of the gaseous torus to be approx.1010 cm-3. This density is similar to that expected in photoplanetary clouds at positions tens of AU from the forming star. If our interpretation is correct, we have detected the inner, ionized walls of the dense circumstellar structure first hypothesized by Snell, Loren, and Plambeck in 1980. The axis of the bipolar CO outflow is different from that expected if this 0''.3 torus were the only collimating agent. Thus, there is evidence in L1551 of focusing and collimation processes acting on size scales from tens of AU (circumstellar dimensions) to tenths of parsecs (interstellar dimensions)

  10. Modelling the circumstellar medium in RS Ophiuchi and its link to Type Ia supernovae

    Booth, R. A.; Mohamed, S.; Podsiadlowski, Ph.

    2016-03-01

    Recent interpretations of narrow, variable absorption lines detected in some Type Ia supernovae suggest that their progenitors are surrounded by dense, circumstellar material. Similar variations detected in the symbiotic recurrent nova system RS Oph, which undergoes thermonuclear outbursts every 20 years, making it an ideal candidate to investigate the origin of these lines. To this end, we present simulations of multiple mass transfer-nova cycles in RS Oph. We find that the quiescent mass transfer produces a dense, equatorial outflow, i.e. concentrated towards the binary orbital plane, and an accretion disc forms around the white dwarf. The interaction of a spherical nova outburst with these aspherical circumstellar structures produces a bipolar outflow, similar to that seen in Hubble Space Telescope imaging of the 2006 outburst. In order to produce an ionization structure that is consistent with observations, a mass-loss rate of 5 × 10-7 M⊙ yr-1 from the red giant is required. The simulations also produce a polar accretion flow, which may explain the broad wings of the quiescent H line and hard X-rays. By comparing simulated absorption line profiles to observations of the 2006 outburst, we are able to determine which components arise in the wind and which are due to the novae. We explore the possible behaviour of absorption line profiles as they may appear should a supernova occur in a system like RS Oph. Our models show similarities to supernovae like SN 2006X, but require a high mass-loss rate, dot{M} ˜ 10^{-6}-10-5 M⊙ yr-1, to explain the variability in SN 2006X.

  11. Silica Aerogel: Synthesis and Applications

    Silica aerogels have drawn a lot of interest both in science and technology because of their low bulk density (up to 95% of their volume is air), hydrophobicity, low thermal conductivity, high surface area, and optical transparency. Aerogels are synthesized from molecular precursors by sol-gel processing. Special drying techniques must be applied to replace the pore liquid with air while maintaining the solid network. Supercritical drying is most common; however, recently developed methods allow removal of the liquid at atmospheric pressure after chemical modification of the inner surface of the gels, leaving only a porous silica network filled with air. Therefore, by considering the surprising properties of aerogels, the present review addresses synthesis of silica aerogels by the sol-gel method, as well as drying techniques and applications in current industrial development and scientific research.

  12. Silica Aerogel: Synthesis and Applications

    Jyoti L. Gurav

    2010-01-01

    Full Text Available Silica aerogels have drawn a lot of interest both in science and technology because of their low bulk density (up to 95% of their volume is air, hydrophobicity, low thermal conductivity, high surface area, and optical transparency. Aerogels are synthesized from molecular precursors by sol-gel processing. Special drying techniques must be applied to replace the pore liquid with air while maintaining the solid network. Supercritical drying is most common; however, recently developed methods allow removal of the liquid at atmospheric pressure after chemical modification of the inner surface of the gels, leaving only a porous silica network filled with air. Therefore, by considering the surprising properties of aerogels, the present review addresses synthesis of silica aerogels by the sol-gel method, as well as drying techniques and applications in current industrial development and scientific research.

  13. Physisorbed Water on Silica at Mars Temperatures

    Sutter, B.; Sriwatanapongse, W.; Quinn, R.; Klug, C.; Zent, A.

    2002-01-01

    The usefulness of nuclear magnetic resonance spectroscopy in probing water interactions on silica at Mars temperatures is discussed. Results indicate that two types of water occur with silica at Mars temperatures. Additional information is contained in the original extended abstract.

  14. Synthesis and Characterization of Bimodal Mesoporous Silica

    ZHANG Xiaofang; GUO Cuili; WANG Xiaoli; WU Yuanyuan

    2012-01-01

    Mesoporous silica with controllable bimodal pore size distribution was synthesized with cetyltrimethylammonium bromide (CTAB) as chemical template for small mesopores and silica gel as physical template for large mesopores.The structure of synthesized samples were characterized by Fourier transform infrared (FT-IR) spectroscopy,X-ray diffraction (XRD),scanning electron microscopy (SEM),transmission electron microscopy (TEM) and N2 adsorption-desorption measurements.The experimental results show that bimodal mesoporous silica consists of small mesopores of about 3 nm and large mesopores of about 45 nm.The small mesopores which were formed on the external surface and pore walls of the silica gel had similar characters with those of MCM-41,while large mesopores were inherited from parent silica gel material.The pore size distribution of the synthesized silica can be adjusted by changing the relative content of TEOS and silica gel or the feeding sequence of silica gel and NH4OH.

  15. Polyurethane reinforced by silica and silica filled with polyurethane

    Serkis, Magdalena; Špírková, Milena; Poreba, Rafal

    Prague : Institute of Macromolecular Chemistry AS CR, 2015. L9. ISBN 978-80-85009-83-5. [Workshop "Career in Polymers" /7./. 03.07.2015, Prague] R&D Projects: GA ČR(CZ) GA13-06700S Institutional support: RVO:61389013 Keywords : polyurethane water dispersion * polycarbonate macrodiol * colloidal silica Subject RIV: CD - Macromolecular Chemistry

  16. A study on the consecutive preparation of silica powders and active carbon from rice husk ash

    Rice husk ash (RHA) is an abundant agricultural by-product. The present research work deals with the production of silica powders and active carbon from RHA with a consecutive method. The RHA is firstly treated with acid leaching to remove mineral composition, and then is boiled with base to leach silica. The filtrate is used to synthesize silica powders with CO2 precipitator and solid residue is used to prepare active carbon. The optimum conditions of preparing silica powders are as follows: the concentration of Na2CO3 is 25 wt.%, the base-leached time is 4 h, and the impregnation ratio of Na2CO3 solution to RHA is 6:1. The yield of silica leached from RHA is 84.57 wt.%. The synthesized silica powders are hydrated with amorphous structure, moreover, with a relative smooth surface and high purity. The residue is activated with potassium hydroxide (KOH) after base-leached. The activated carbons are found to be a mixture of micropore and mesopore pore structures. The maximum pore volume, BET surface area and iodine adsorption capacity of as-prepared active carbon can reach 1.22 cm3/g, 1936.62 m2/g and 1259.06 mg/g, respectively. Field emission scanning electron microscopy (SEM) is used to characterize the morphological features of the ash after step by step treatment.

  17. Nearby Supernova Factory Observations of SN 2005gj: Another Type Ia Supernova in a Massive Circumstellar Envelope

    We report the independent discovery and follow-up observations of supernova 2005gj by the Nearby Supernova Factory. This is the second confirmed case of a ''hybrid'' Type Ia/IIn supernova, which like the prototype SN 2002ic, we interpret as the explosion of a white dwarf interacting with a circumstellar medium. Our early-phase photometry of SN 2005gj shows that the strength of the interaction between the supernova ejecta and circumstellar material is much stronger than for SN 2002ic. Our .rst spectrum shows a hot continuum with broad and narrow Hα emission. Later spectra, spanning over 4 months from outburst, show clear Type Ia features combined with broad and narrow Hγ, Hβ,Hα and He I λλ5876,7065 in emission. At higher resolution, P Cygni profiles are apparent. Surprisingly, we also observe an inverted P Cygni profile for [O III] λ5007. We find that the lightcurve and measured velocity of the unshocked circumstellar material imply mass loss as recently as 8 years ago. This is in contrast to SN 2002ic, for which an inner cavity in the circumstellar material was inferred. Within the context of the thin-shell approximation, the early lightcurve is well-described by a flat radial density profile for the circumstellar material. However, our decomposition of the spectra into Type Ia and shock emission components allows for little obscuration of the supernova, suggesting an aspherical or clumpy distribution for the circumstellar material. We suggest that the emission line velocity profiles arise from electron scattering rather than the kinematics of the shock. This is supported by the inferred high densities, and the lack of evidence for evolution in the line widths. Ground- and space-based photometry, and Keck spectroscopy, of the host galaxy are used to ascertain that the host galaxy has low metallicity (Z/Z#circledot# < 0.3; 95% confidence) and that this galaxy is undergoing a significant star formation event that began roughly 200 ± 70 Myr ago. We discuss the

  18. Poling of Planar Silica Waveguides

    Arentoft, Jesper; Kristensen, Martin; Jensen, Jesper Bo

    1999-01-01

    UV-written planar silica waveguides are poled using two different poling techniques, thermal poling and UV-poling. Thermal poling induces an electro-optic coefficient of 0.067 pm/V. We also demonstrate simultaneous UV-writing and UV-poling. The induced electro-optic effect shows a linear dependence...

  19. Solar System Abundances of the Elements

    Lodders, Katharina

    2010-01-01

    Representative abundances of the chemical elements for use as a solar abundance standard in astronomical and planetary studies are summarized. Updated abundance tables for solar system abundances based on meteorites and photospheric measurements are presented.

  20. Silica-Coated Liposomes for Insulin Delivery

    Neelam Dwivedi

    2010-01-01

    Full Text Available Liposomes coated with silica were explored as protein delivery vehicles for their enhanced stability and improved encapsulation efficiency. Insulin was encapsulated within the fluidic phosphatidylcholine lipid vesicles by thin film hydration at pH 2.5, and layer of silica was formed above lipid bilayer by acid catalysis. The presence of silica coating and encapsulated insulin was identified using confocal and electron microscopy. The native state of insulin present in the formulation was evident from Confocal Micro-Raman spectroscopy. Silica coat enhances the stability of insulin-loaded delivery vehicles. In vivo study shows that these silica coated formulations were biologically active in reducing glucose levels.

  1. Silica Pigments for Glossy Ink Jet Media

    Sun Qi; Michael R. Sestrick; Yoshi Sugimoto; William A. Welsh

    2004-01-01

    Silica is a versatile pigment for ink jet media. Micronized silica gel is the worldwide standard for high performance matte ink jet media. For glossy ink jet media, several different forms of silica are widely used. Submicron silica gel dispersions, with either anionic or cationic surfaces, can be employed in either absorptive basecoat layers or in the glossy ink receptive top layer. Colloidal silica, with a variety of particle sizes and surface modifications, is utilized extensively in glossy top layers. It will show how various silica pigments can be utilized in glossy ink receptive coatings, both in cast based glossy media and RC based glossy media. Several novel silica pigments will be examined by relating the physical properties of the pigments and the formula variables to the print quality of the ink jet media.

  2. Polarimetry with the Gemini Planet Imager: Methods, Performance at First Light, and the Circumstellar Ring around HR 4796A

    Perrin, Marshall D; Millar-Blanchaer, Max; Fitzgerald, Michael P; Graham, James R; Wiktorowicz, Sloane J; Kalas, Paul G; Macintosh, Bruce; Bauman, Brian; Cardwell, Andrew; Chilcote, Jeffrey; De Rosa, Robert J; Dillon, Daren; Doyon, René; Dunn, Jennifer; Gavel, Donald; Goodsell, Stephen; Hartung, Markus; Hibon, Pascale; Ingraham, Patrick; Kerley, Daniel; Konapacky, Quinn; Larkin, James E; Maire, Jérôme; Marchis, Franck; Marois, Christian; Mittal, Tushar; Morzinski, Katie M; Oppenheimer, B R; Palmer, David W; Patience, Jennifer; Poyneer, Lisa; Pueyo, Laurent; Rantakyrö, Fredrik T; Sadakuni, Naru; Saddlemyer, Leslie; Savransky, Dmitry; Soummer, Rémi; Sivaramakrishnan, Anand; Song, Inseok; Thomas, Sandrine; Wallace, J Kent; Wang, Jason J; Wolff, Schuyler G

    2014-01-01

    We present the first results from the polarimetry mode of the Gemini Planet Imager (GPI), which uses a new integral field polarimetry architecture to provide high contrast linear polarimetry with minimal systematic biases between the orthogonal polarizations. We describe the design, data reduction methods, and performance of polarimetry with GPI. Point spread function subtraction via differential polarimetry suppresses unpolarized starlight by a factor of over 100, and provides sensitivity to circumstellar dust reaching the photon noise limit for these observations. In the case of the circumstellar disk around HR 4796A, GPI's advanced adaptive optics system reveals the disk clearly even prior to PSF subtraction. In polarized light, the disk is seen all the way in to its semi-minor axis for the first time. The disk exhibits surprisingly strong asymmetry in polarized intensity, with the west side >9 times brighter than the east side despite the fact that the east side is slightly brighter in total intensity. Ba...

  3. Lines of Circumstellar C2, CN, and CH$^+$ in the Optical Spectra of Post-Agb Stars

    Bakker, E J; Van Dishoeck, E F; Bakker, Eric J.; Lambert, David L.; Dishoeck, Ewine F. van

    1996-01-01

    Recent optical spectra of post-AGB stars show the presence of C2, CN, and CH+ originating in the circumstellar shell. We present here new, higher resolution spectra which provide constraints on the physical parameters and information on the line profiles. An empirical curve of growth for the C2 Phillips and CN Red system lines in the spectrum of HD 56126 yields b = 0.50 (+0.59, -0.23) km/s. CH+ (0,0) emission lines in the spectrum of the Red Rectangle have been resolved with a FWHM approx 8.5 pm 0.8 km/s. The circumstellar CN lines of IRAS 08005--2356 are resolved into two separate components with a velocity separation of Delta v = 5.7 pm 2.0 km/s. The line profiles of CN of HD 235858 have not been resolved.

  4. Tracing planet-induced structures in circumstellar disks using molecular lines

    Ober, F.; Wolf, S.; Uribe, A. L.; Klahr, H. H.

    2015-07-01

    Context. Circumstellar disks are considered to be the birthplace of planets. Specific structures like spiral arms, gaps, and cavities are characteristic indicators of planet-disk interaction. Investigating these structures can provide insights into the growth of protoplanets and the physical properties of the disk. Aims: We investigate the feasibility of using molecular lines to trace planet-induced structures in circumstellar disks. Methods: Based on 3D hydrodynamic simulations of planet-disk interactions obtained with the PLUTO code, we perform self-consistent temperature calculations and produce N-LTE molecular line velocity-channel maps and spectra of these disks using our new N-LTE line radiative transfer code Mol3D. Subsequently, we simulate ALMA observations using the CASA simulator. We consider two nearly face-on inclinations, five disk masses, seven disk radii, and two different typical pre-main-sequence host stars (T Tauri, Herbig Ae) at a distance of 140 pc. We calculate up to 141 individual velocity-channel maps for five molecules/isotopoloques (12C16O, 12C18O, HCO+, HCN, and CS) in a total of 32 rotational transitions to investigate the frequency dependence of the structures indicated above. Results: We find that the majority of protoplanetary disks in our parameter space could be detected in the molecular lines considered. However, unlike the continuum case, gap detection is not straightforward in lines. For example, gaps are not seen in symmetric rings but are masked by the pattern caused by the global (Keplerian) velocity field. By comparison with simulated observations of undisturbed disks we identify specific regions in the velocity-channel maps that are characteristic of planet-induced structures. Conclusions: Simulations of high angular resolution molecular line observations demonstrate the potential of ALMA to provide complementary information about the planet-disk interaction as compared to continuum observations. In particular, the detection

  5. Radiation curing of silica for silica-rubber composites

    The functional modification of silica samples based on the reaction of '' grafting '' of polybutadiene oligomers carried out by gamma-irradiation in the presence of air at room temperature has been investigated. The yield of grafted PB reaches a maximum at doses of about 30 kGy, then decreases as a consequence of the oxidative degradation. The reaction is accompanied by the build up of carbonyls and peroxides up to 0.1 moles/kg and it leads to a rapid consumption of the double bonds concentration as determined by both FTIR and Raman spectroscopy. The results of the EPR analysis are diagnostic of a mechanism of immobilization of the oligomer based on cross-linking of polybutadiene which is initiated by the SiO2 radiolytic species. Depending on the nature of the SiO2 species, the mechanism of initiation leads to immobilized PB either really grafted to the silica surface or simply physically absorbed. (authors)

  6. Simulating the circum-stellar environment of supernova and GRB progenitors by combining stellar evolution models and hydrodynamical code

    Georgy, Cyril; Walder, Rolf; Folini, Doris

    2011-01-01

    The medium around massive stars is strongly shaped by the stellar winds. Those winds depend on various stellar parameters (effective temperature, luminosity, chemical composition, rotation, ...), which are varying as a function of the time. Using the wind properties obtained by classical stellar evolution code allows for the multi- D hydrodynamical simulation of the circum-stellar medium accounting for the time variations of the wind. We present here the preliminary results of the simulation ...

  7. Environmentally-Friendly Geopolymeric Binders Made with Silica

    Erdogan, S. T.

    2013-12-01

    Portland cement (PC) is the ubiquitous binding material for constructions works. It is a big contributor to global warming and climate change since its production is responsible for 5-10 % of all anthropogenic CO2 emissions. Half of this emission arises from the calcination of calcareous raw materials and half from kiln fuel burning and cement clinker grinding. Recently there have been efforts to develop alternative binders with lower greenhouse gas emissions. One such class of binders is geopolymers, formed by activating natural or waste materials with suitable alkaline or acidic solutions. These binders use natural or industrial waste raw materials with a very low CO2 footprint from grinding of the starting materials, and some from the production of the activating chemicals. The total CO2 emissions from carefully formulated mixtures can be as low as 1/10th - 1/5th of those of PC concrete mixtures with comparable properties. While use of industrial wastes as raw materials is environmentally preferable, the variability of their chemical compositions over time renders their use difficult. Use of natural materials depletes resources but can have more consistent properties and can be more easily accepted. Silica sand is a natural material containing very high amounts of quartz. Silica fume is a very fine waste from silicon metal production that is mostly non-crystalline silica. This study describes the use of sodium hydroxide and sodium silicate solutions to yield mortars with mechanical properties comparable to those of portland cement mortars and with better chemical and thermal durability. Strength gain is slower than with PC mixtures at room temperature but adequate ultimate strength can be achieved with curing at slightly elevated temperatures in less than 24 h. The consistency of the chemical compositions of these materials and their abundance in several large, developing countries makes silica attractive for producing sustainable concretes with reduced carbon

  8. Spectroscopic Evolution of Disintegrating Planetesimals: Minutes to Months Variability in the Circumstellar Gas Associated with WD 1145+017

    Redfield, Seth; Cauley, P Wilson; Parsons, Steven G; Gaensicke, Boris T; Duvvuri, Girish

    2016-01-01

    With the recent discovery of transiting planetary material around WD 1145+017, a critical target has been identified that links the evolution of planetary systems with debris disks and their accretion onto the star. We present a series of observations, five epochs over a year, taken with Keck and the VLT, which for the first time show variability of circumstellar absorption in the gas disk surrounding WD 1145+017 on timescales of minutes to months. Circumstellar absorption is measured in more than 250 lines of 14 ions among ten different elements associated with planetary composition, e.g., O, Mg, Ca, Ti, Cr, Mn, Fe, Ni. Broad circumstellar gas absorption with a velocity spread of 225 km/s is detected, but over the course of a year blue shifted absorption disappears while redshifted absorption systematically increases. A correlation of equivalent width and oscillator strength indicates that the gas is not highly optically thick (median tau approximately 2). We discuss simple models of an eccentric disk couple...

  9. Investigations of the Circumstellar Disk Fraction as a Function of Mass in Young Embedded Clusters in Orion B

    De Furio, Matthew; Lada, Elizabeth A.; Marinas, Naibi

    2016-01-01

    In the current paradigm of star formation, all stars form with circumstellar disks. However, recent studies of the young NGC 2264 clusters (age ~ 2Myr, Marinas et al 2013; 2015) have unexpectedly revealed that stars with masses less than 0.3 solar masses exhibit a lower circumstellar disk fraction than more massive stars in the clusters. Is it possible that a significant number of very low mass stars form without a disk? To answer this, we are studying three very young embedded clusters (ageOrion B Molecular Cloud. For these clusters, we are determining the disk fraction as a function of spectral type and inferred mass. Since the clusters are very young, the disk fractions should represent the initial frequency distribution of disks in these clusters. We are using FLAMINGOS NIR spectroscopy (Levine PhD UF 2006) and photometry to estimate the masses of the stars and FLAMINGOS JHK and Spitzer photometry to estimate the disk frequency of our spectroscopic sample. Our work should provide valuable insights toward understanding the formation and early evolution of circumstellar disks around low mass stars in embedded clusters.

  10. Super-luminous X-ray Emission from the Interaction of Supernova Ejecta with Dense Circumstellar Shells

    Pan, Tony; Loeb, Abraham

    2013-01-01

    For supernova powered by the conversion of kinetic energy into radiation due to the interactions of the ejecta with a dense circumstellar shell, we show that there could be X-ray analogues of optically super-luminous SNe with comparable luminosities and energetics. We consider X-ray emission from the forward shock of SNe ejecta colliding into an optically-thin CSM shell, derive simple expressions for the X-ray luminosity as a function of the circumstellar shell characteristics, and discuss the different regimes in which the shock will be radiative or adiabatic, and whether the emission will be dominated by free-free radiation or line-cooling. We find that even with normal supernova explosion energies of 10^51 erg, there exists CSM shell configurations that can liberate a large fraction of the explosion energy in X-rays, producing unabsorbed X-ray luminosities approaching 10^44 erg/s events lasting a few months, or even 10^45 erg/s flashes lasting days. Although the large column density of the circumstellar sh...