Common Warm Dust Temperatures Around Main Sequence Stars

NASA Technical Reports Server (NTRS)

Morales, Farisa; Rieke, George; Werner, Michael; Stapelfeldt, Karl; Bryden, Geoffrey; Su, Kate

2011-01-01

We compare the properties of warm dust emission from a sample of main-sequence A-type stars (B8-A7) to those of dust around solar-type stars (F5-KO) with similar Spitzer Space Telescope Infrared Spectrograph/MIPS data and similar ages. Both samples include stars with sources with infrared spectral energy distributions that show evidence of multiple components. Over the range of stellar types considered, we obtain nearly the same characteristic dust temperatures (∼ 190 K and ∼60 K for the inner and outer dust components, respectively)-slightly above the ice evaporation temperature for the inner belts. The warm inner dust temperature is readily explained if populations of small grains are being released by sublimation of ice from icy planetesimals. Evaporation of low-eccentricity icy bodies at ∼ 150 K can deposit particles into an inner/warm belt, where the small grains are heated to dust Temperatures of -190 K. Alternatively, enhanced collisional processing of an asteroid belt-like system of parent planetesimals just interior to the snow line may account for the observed uniformity in dust temperature. The similarity in temperature of the warmer dust across our B8-KO stellar sample strongly suggests that dust-producing planetesimals are not found at similar radial locations around all stars, but that dust production is favored at a characteristic temperature horizon.

The influence of grain growth in circumstellar dust envelopes on observed colors and polarization of some eruptive stars

NASA Technical Reports Server (NTRS)

Efimov, Yu. S.

1989-01-01

R CrB stars are classical examples of stars where dust envelope formation takes place. Dust envelope formation was detected around the Kuwano-Honda object (PU Vul) in 1980 to 1981 when the star's brightness fell to 8(sup m). Such envelopes are also formed at nova outbursts. The process of dust envelope formation leads to appreciable variations in optical characteristics, which are seen in specific color and polarization variations in the course of light fading and the appearance of IR radiation. It is shown that the model of a circumstellar dust envelope with aligned particles of changing size can be successfully applied to explain most phenomena observed at the time of light minima for a number of eruptive stars. The polarization may arise in a nonspherical dust envelope or be produced by alignment of nonspherical particles.

New Dust Features Observed with ISO

NASA Technical Reports Server (NTRS)

Tielens, Alexander G. G. M.; Young, Richard E. (Technical Monitor)

1997-01-01

This paper will review our current knowledge of circumstellar and interstellar dust with the emphasis on infrared spectroscopy with ISO. Objects embedded in or located behind molecular clouds show a wealth of absorption features due to simple molecules in an icy mantle. The SWS on ISO has provided us, for the first time, with complete 3-45 um spectra which allow an inventory of interstellar ice. Among the species identified are H2O, CH3OH, CH4, CO2, CO, and OCS. These species are formed through simple reactions among gas phase species accreted on grain surfaces, possibly modified by FUV photolysis and warm-up (ie., outgassing). The implications of the observations for our understanding of these processes will be reviewed. The IR spectra of many UV bright objects are dominated by strong emission features at 3.3, 6.2, 7.7, and 11.3 micrometers. These are generally attributed to Polycyclic Aromatic Hydrocarbons (PAHs) molecules. The observational evidence will be reviewed. The emphasis will be on recent data which show widespread spectral variations, particularly among protoplanetary and planetary nebulae, and their implications. One of the most exciting, recent discoveries on interstellar and circumstellar dust has been the detection of spectral structure due to crystalline olivine and enstatite in a variety of objects surrounded by circumstellar silicates. These spectra will be reviewed and circumstellar silicate mineralogy will be discussed.

Working Group on Circumstellar/Interstellar Relationships

NASA Technical Reports Server (NTRS)

Glassgold, A. E.

1986-01-01

Stars of various types are believed to be the main source of interstellar (IS) dust grans. The most important confirmed source is evolved giant and supergiant stars. Supernovae also contribute to the mass loss. The differences between circumstellar (CS) and IS dust were reviewed using the following topics: alteration of CS dust grains, size distribution, space observation of CS and IS dust, comparison of infrared spectra, isotopic signatures, Magellanic clouds and nearby galaxies, life cycles of dust grains, and physical and chemical data.

Rapid disappearance of a warm, dusty circumstellar disk.

PubMed

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

2012-07-04

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 typically is 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 amount of cooler dust. Such a phase of rapid ejecta evolution has not been previously predicted or observed, and no currently available physical model satisfactorily explains the observations.

Disentangling the Origin and Heating Mechanism of Supernova Dust: Late-Time Spitzer Spectroscopy of the Type IIn SN 2005ip

NASA Technical Reports Server (NTRS)

Fox, Ori D.; Chevalier, Roger A.; Dwek, Eli; Skrutskie, Michael F.; Sugerman, Ben E. K.; Leisenring, Jarron M.

2010-01-01

This paper presents late-time near-infrared and Spitzer mid-infrared photometric and spectroscopic observations of warm dust in the Type IIn SN 2005ip in NGC 2906. The spectra show evidence for two dust components with different temperatures. Spanning the peak of the thermal emission, these observations provide strong constraints on the dust mass, temperature, and luminosity, which serve as critical diagnostics for disentangling the origin and heating mechanism of each component. The results suggest the warmer dust has a mass of approx. 5 x 10(exp -4) Solar Mass and originates from newly formed dust in the ejecta, continuously heated by the circumstellar interaction. By contrast, the cooler component likely originates from a circumstellar shock echo that forms from the heating of a large, pre-existing dust shell approx. 0.01 - 0.05 Solar Mass by the late-time circumstellar interaction. The progenitor wind velocity derived from the blue edge of the He I 1.083 micro P Cygni profile indicates a progenitor eruption likely formed this dust shell approx.100 years prior to the supernova explosion, which is consistent with a Luminous Blue Variable (LBV) progenitor star. Subject

A Mid-Infrared Study of the Circumstellar Dust Composition and Phase Behavior of Oxygen-rich Mira Variables

NASA Astrophysics Data System (ADS)

Guth, Tina

2017-08-01

The elements essential as building blocks of life, such as carbon and oxygen, have long been considered to come from exploding stars, known as supernovae. However, in the last several years, observations obtained with improved telescopes and instruments have shown that these heavier elements, i.e. elements beyond helium, are readily found in mass-loss products of stars called Asymptotic Giant Branch (AGB) stars. The sub-category of AGB stars that have regular pulsation periods of 200 - 500 days, called Mira variables, are of particular interest. These regular pulsators are quite bright in both the optical and infrared wavelengths, and exhibit large changes in magnitude that are easily observable. Studying their circumstellar dust environment allows astronomers to determine the presence of compounds, such as silicates and oxides, which are indicative of common elements found on Earth - oxygen, carbon, and silicon. Mira variables are dynamic stars, which implies that the circumstellar dust composition should change as the star goes through its pulsation cycle. In order to study the dust behavior with pulsational phase, repeated infrared observations were obtained with the Spitzer Space Telescope. This infrared, space-based telescope was launched in 2003 and carries the Infrared Spectrograph (IRS) instrument, which produces brightness versus wavelength, i.e. a spectrum (Houck et al., 2004). Due to the pulsation period of these stars, they were observed approximately monthly during the campaign run in 2008-9. This work focuses on the high-resolution data over a wavelength range of 9.8 - 40 microns because it provides a high signal-to-noise ratio and examines the part of the spectrum where dust features are most apparent. The full dataset obtained with Spitzer consists of 25 stars and covers nearly 100 spectra spanning all three chemical subclasses, however the focus of this dissertation is on investigating the dusty environment of oxygen-rich Mira variables. First, an

High Spatial Resolution Mid-IR Imaging of V838 Monocerotis: Evidence of New Circumstellar Dust Creation

NASA Technical Reports Server (NTRS)

Wisniewski, John P.; Clampin, Mark; Bjorkman, Karen S.; Barry, Richard K.

2008-01-01

We report high spatial resolution 11.2 and 18.1 mm imaging of V838 Monocerotis obtained with Gemini Observatory's Michelle instrument in 2007 March. Strong emission is observed from the unresolved stellar core of V838 Mon in our Gemini imagery and is confirmed by Spitzer MIPS 24 micron imaging obtained in 2007 April. The 2007 flux density of the unresolved mid-infrared emission component is approx.2 times brighter than that observed in 2004. No clear change in the net amount of 24 mm extended emission is observed between the 2004 and 2007 epoch Spitzer imagery. We interpret these data as evidence that V838 Mon has experienced a new circumstellar dust creation event. We suggest that this newly created dust has condensed from the expanding ejecta produced from V838 Mon's 2002 outburst events and is most likely clumpy. We speculate that one (or more) of these clumps might have passed through the line of sight in late 2006, producing the brief multiwavelength photometric event reported by H. Bond in 2006 and U. Munari et al. in 2007b. We detect no evidence of extended emission above a level of approx.1 mJy at 11.2 microns and approx.7 mJy at 18.1 microns over radial distances of 1860-93,000 AU (0.3" - 15.0") from the central source. Using the simple assumption that ejecta material expands at a constant velocity of 300-500 km/s, this gap of thermal emission suggests that no significant prior circumstellar dust production events have occurred within the past approx.900-1500 yr.

High Resolution Spectroscopy of Vega-like Stars: Abundances and Circumstellar Gas

NASA Technical Reports Server (NTRS)

Dunkin, S. K.; Barlow, M. J.; Ryan, Sean G.

1996-01-01

Vega-like stars are main-sequence stars exhibiting excess infrared emission. In an effort to improve the information available on this class of star, 13 stars have been analyzed which have been classed as Vega-like, or have an infra-red excess attributable to dust in their circumstellar environment. In a separate paper stellar properties such as effective temperature and log g have been derived and in this poster we highlight the results of the photospheric abundance analysis also carried out during this work. King recently drew attention to the possible link between Vega-like stars and the photospheric metal-depleted class of A-stars, the Lambda Bootis stars. Since Vega-like stars are thought to have disks of dust, it might be expected that accretion of depleted gas onto the surface of these stars may cause this same phenomenon. In the 6 stars studied for depletions, none showed the extreme underabundance patterns observed in Lambda Bootis stars. However, depletions of silicon and magnesium were found in two of the sample, suggesting that these elements are in silicate dust grains in the circumstellar environment of these stars. Absorption lines attributed to circumstellar gas have been positively identified in three stars in our sample. Individual cases show evidence either of high-velocity outflowing gas, variability in the circumstellar lines observed, or evidence of circumstellar gas in excited lines of Fe II. No previous identification of circumstellar material has been made for two of the stars in question.

Constraining the Origin and Heating Mechanism of Dust in Type IIn Supernovae

NASA Astrophysics Data System (ADS)

Fox, Ori; Skrutskie, Michael; Filippenko, Alex

2012-12-01

More than any other supernova subclass, Type IIn supernovae tend to exhibit late-time (>1 year) infrared emission from warm dust. Identifying the origin and heating mechanism of the dust provides an important probe of the supernova explosion, circumstellar environment, and progenitor system. Yet mid-infrared observations, which span the peak of the thermal emission, are rare. Three years ago, we executed a warm Spitzer survey (P60122) that uncovered a unique sample of ten supernovae with unreported late-time infrared excesses, in some cases more than 5 years post-explosion. The data from this single epoch are most consistent with a pre-existing dust shell that is continuously heated by visible and/or X-ray emission generated by ongoing shock interaction. Furthermore, the lack of any detections beyond ~2000 days suggests the dust is destroyed once the forward shock overruns the pre-existing shell. The actual shell sizes remain unknown, however, since the derived blackbody radii offer only lower limits. Last year, we obtained second epoch observations of these ten re-discovered SNe IIn (plus the well-studied Type IIn SN 2010jl). The project aimed for non-detections to constrain the light-curve ``turn-off'' times and, thereby, the shell sizes and progenitor mass-loss models. Only two SNe (2005gn and 2008J), however, went undetected. The other nine SNe remain bright at mid-IR wavelengths, which means the dust shell radii are larger than expected. Here we propose continued monitoring of these nine SNe IIn to constrain the size of the circumstellar dust shell and characterize the supernova progenitor system. We can obtain all the necessary data in only 6.1 hours of observation.

Spread of the dust temperature distribution in circumstellar disks

NASA Astrophysics Data System (ADS)

Heese, S.; Wolf, S.; Dutrey, A.; Guilloteau, S.

2017-07-01

Context. Accurate temperature calculations for circumstellar disks are particularly important for their chemical evolution. Their temperature distribution is determined by the optical properties of the dust grains, which, among other parameters, depend on their radius. However, in most disk studies, only average optical properties and thus an average temperature is assumed to account for an ensemble of grains with different radii. Aims: We investigate the impact of subdividing the grain radius distribution into multiple sub-intervals on the resulting dust temperature distribution and spectral energy distribution (SED). Methods: The temperature distribution, the relative grain surface below a certain temperature, the freeze-out radius, and the SED were computed for two different scenarios: (1) Radius distribution represented by 16 logarithmically distributed radius intervals, and (2) radius distribution represented by a single grain species with averaged optical properties (reference). Results: Within the considered parameter range, I.e., of grain radii between 5 nm and 1 mm and an optically thin and thick disk with a parameterized density distribution, we obtain the following results: in optically thin disk regions, the temperature spread can be as large as 63% and the relative grain surface below a certain temperature is lower than in the reference disk. With increasing optical depth, the difference in the midplane temperature and the relative grain surface below a certain temperature decreases. Furthermore, below 20 K, this fraction is higher for the reference disk than for the case of multiple grain radii, while it shows the opposite behavior for temperatures above this threshold. The thermal emission in the case of multiple grain radii at short wavelengths is stronger than for the reference disk. The freeze-out radius (snowline) is a function of grain radius, spanning a radial range between the coldest and warmest grain species of 30 AU.

Does warm debris dust stem from asteroid belts?

NASA Astrophysics Data System (ADS)

Geiler, Fabian; Krivov, Alexander V.

2017-06-01

Many debris discs reveal a two-component structure, with a cold outer and a warm inner component. While the former are likely massive analogues of the Kuiper belt, the origin of the latter is still a matter of debate. In this work, we investigate whether the warm dust may be a signature of asteroid belt analogues. In the scenario tested here, the current two-belt architecture stems from an originally extended protoplanetary disc, in which planets have opened a gap separating it into the outer and inner discs which, after the gas dispersal, experience a steady-state collisional decay. This idea is explored with an analytic collisional evolution model for a sample of 225 debris discs from a Spitzer/IRS catalogue that are likely to possess a two-component structure. We find that the vast majority of systems (220 out of 225, or 98 per cent) are compatible with this scenario. For their progenitors, original protoplanetary discs, we find an average surface density slope of -0.93 ± 0.06 and an average initial mass of (3.3^{+0.4}_{-0.3})× 10^{-3} solar masses, both of which are in agreement with the values inferred from submillimetre surveys. However, dust production by short-period comets and - more rarely - inward transport from the outer belts may be viable, and not mutually excluding, alternatives to the asteroid belt scenario. The remaining five discs (2 per cent of the sample: HIP 11486, HIP 23497, HIP 57971, HIP 85790, HIP 89770) harbour inner components that appear inconsistent with dust production in an 'asteroid belt.' Warm dust in these systems must either be replenished from cometary sources or represent an aftermath of a recent rare event, such as a major collision or planetary system instability.

Constraining dust properties in circumstellar envelopes of C-stars in the Small Magellanic Cloud: optical constants and grain size of carbon dust

NASA Astrophysics Data System (ADS)

Nanni, Ambra; Marigo, Paola; Groenewegen, Martin A. T.; Aringer, Bernhard; Girardi, Léo; Pastorelli, Giada; Bressan, Alessandro; Bladh, Sara

2016-10-01

We present a new approach aimed at constraining the typical size and optical properties of carbon dust grains in circumstellar envelopes (CSEs) of carbon-rich stars (C-stars) in the Small Magellanic Cloud (SMC). To achieve this goal, we apply our recent dust growth description, coupled with a radiative transfer code to the CSEs of C-stars evolving along the thermally pulsing asymptotic giant branch, for which we compute spectra and colours. Then, we compare our modelled colours in the near- and mid-infrared (NIR and MIR) bands with the observed ones, testing different assumptions in our dust scheme and employing several data sets of optical constants for carbon dust available in the literature. Different assumptions adopted in our dust scheme change the typical size of the carbon grains produced. We constrain carbon dust properties by selecting the combination of grain size and optical constants which best reproduce several colours in the NIR and MIR at the same time. The different choices of optical properties and grain size lead to differences in the NIR and MIR colours greater than 2 mag in some cases. We conclude that the complete set of observed NIR and MIR colours are best reproduced by small grains, with sizes between ˜0.035 and ˜0.12 μm, rather than by large grains between ˜0.2 and 0.7 μm. The inability of large grains to reproduce NIR and MIR colours seems independent of the adopted optical data set. We also find a possible trend of the grain size with mass-loss and/or carbon excess in the CSEs of these stars.

Astrophysical dust grains in stars, the interstellar medium, and the solar system

NASA Technical Reports Server (NTRS)

Gehrz, Robert D.

1991-01-01

Studies of astrophysical dust grains in circumstellar shells, the interstellar medium, and the solar system may provide information about stellar evolution and about physical conditions in the primitive solar nebula. The following subject areas are covered: (1) the cycling of dust in stellar evolution and the formation of planetary systems; (2) astrophysical dust grains in circumstellar environments; (3) circumstellar grain formation and mass loss; (4) interstellar dust grains; (5) comet dust and the zodiacal cloud; (6) the survival of dust grains during stellar evolution; and (7) establishing connections between stardust and dust in the solar system.

Delayed Shock-induced Dust Formation in the Dense Circumstellar Shell Surrounding the Type IIn Supernova SN 2010jl

NASA Astrophysics Data System (ADS)

Sarangi, Arkaprabha; Dwek, Eli; Arendt, Richard G.

2018-05-01

The light curves of Type IIn supernovae are dominated by the radiative energy released through the interaction of the supernova shock waves with their dense circumstellar medium (CSM). The ultraluminous Type IIn supernova SN 2010jl exhibits an infrared emission component that is in excess of the extrapolated UV–optical spectrum as early as few weeks postexplosion. This emission has been considered by some as evidence for the rapid formation of dust in the cooling postshock CSM. We investigate the physical processes that may inhibit or facilitate the formation of dust in the CSM. When only radiative cooling is considered, the temperature of the dense shocked gas rapidly drops below the dust condensation temperature. However, by accounting for the heating of the postshock gas by the downstream radiation from the shock, we show that dust formation is inhibited until the radiation from the shock weakens as it propagates into the less dense outer regions of the CSM. In SN 2010jl, dust formation can therefore only commence after day ∼380. Only the IR emission since that epoch can be attributed to the newly formed CSM dust. Observations on day 460 and later show that the IR luminosity exceeds the UV–optical luminosity. The postshock dust cannot extinct the radiation emitted by the expanding SN shock. Therefore, its IR emission must be powered by an interior source, which we identify as the reverse shock propagating through the SN ejecta. IR emission before day 380 must therefore be an IR echo from preexisting CSM dust.

Measurement of the sizes of circumstellar dust shells around evolved stars with high mass loss rates

NASA Technical Reports Server (NTRS)

Phillips, T. G.; Knapp, G. R.

1992-01-01

The research supported by the NASA ADP contract NAG5-1153 has been completed. The attached paper, which will be submitted for publication in the Astrophysical Journal in January 1992, presents the results of this work. Here is a summary of the project and its results. A set of computer programs was developed to process the raw 60 micron and 100 micron IRAS survey data. The programs were designed to detect faint extended emission surrounding a bright unresolved source. Candidate objects were chosen from a list of red giant stars and young planetary nebulae which have been detected in millimeter/submillimeter lines of CO. Of the 279 stars examined, 55 were resolved at 60 microns. The principle results of the study are given. The average age for the shells surrounding the 9 Mira-type stars which are extended is 6 x 10(exp 4) yr. This suggests that the period during which these stars lose mass lasts for approx 10(exp 5) yr. The oldest shell found surrounds U Ori, and the youngest surrounds Mira itself. Some shells appear to be detached from the central star. This phenomenon is more common among older stars, suggesting that the mass loss becomes more episodic as the star sheds its envelope. Although all 8 stars less distant than 200 pc are resolved in the IRAS 60 micron data, 29 stars within 500 pc were not. These stars probably have younger circumstellar shells than those which were resolved. Almost all the carbon stars with distances of 500 pc or less have resolved shells, while only 1/2 of the oxygen-rich stars do. The resolved carbon star shells also are older on average than the oxygen-rich ones. These facts imply that carbon stars have been losing mass for a longer period, on average, than oxygen-rich red giants. Large circumstellar shells tend to be found at large distances from the galactic plane, confirming that the ISM density limits the size to which a dust shell can grow. Surprisingly, even very large shells seem to be nearly spherical, and do not appear to

Constraining Dust Properties in Circumstellar Envelopes of C-Stars in the Small Magellanic Cloud: Optical Constants And Grain Size Of Carbon Dust

NASA Astrophysics Data System (ADS)

Nanni, Ambra; Marigo, Paola; Groenewegen, Martin A. T.; Aringer, Berhard; Girardi, Léo; Pastorelli, Giada; Bressan, Alessandro; Bladh, Sara

2016-07-01

We present our recent investigation aimed at constraining the typical size and optical properties of carbon dust grains in Circumstellar envelopes (CSEs) of carbon-rich stars (C-stars) in the Small Magellanic Cloud (SMC).We applied our recent dust growth model, coupled with a radiative transfer code, to the dusty CSEs of C-stars along the TP-AGB phase, for which we computed spectra and colors. We then compared our modeled colors in the Near and Mid Infrared (NIR and MIR) bands with the observed ones, testing different assumptions in our dust scheme and employing different optical constants data sets for carbon dust. We constrained the optical properties of carbon dust by identifying the combinations of typical grain size and optical constants data set which simultaneously reproduce several colors in the NIR and MIR wavelengths. In particular, the different choices of optical properties and grain size lead to differences in the NIR and MIR colors greater than two magnitudes in some cases. We concluded that the complete set of selected NIR and MIR colors are best reproduced by small grains, with sizes between 0.06 and 0.1 mum, rather than by large grains of 0.2-0.4 mum. The inability of large grains to reproduce NIR and MIR colors is found to be independent of the adopted optical data set and the deviations between models and observations tend to increase for increasing grain sizes. We also find a possible trend of the typical grain size with mss-loss and/or carbon-excess in the CSEs of these stars.The work presented is preparatory to future studies aimed at calibrating the TP-AGB phase through resolved stellar populations in the framework of the STARKEY project.

ALMA observations of anisotropic dust mass loss in the inner circumstellar environment of the red supergiant VY Canis Majoris

NASA Astrophysics Data System (ADS)

O'Gorman, E.; Vlemmings, W.; Richards, A. M. S.; Baudry, A.; De Beck, E.; Decin, L.; Harper, G. M.; Humphreys, E. M.; Kervella, P.; Khouri, T.; Muller, S.

2015-01-01

The processes leading to dust formation and the subsequent role it plays in driving mass loss in cool evolved stars is an area of intense study. Here we present high resolution ALMA Science Verification data of the continuum emission around the highly evolved oxygen-rich red supergiant VY CMa. These data enable us to study the dust in its inner circumstellar environment at a spatial resolution of 129 mas at 321 GHz and 59 mas at 658 GHz, thus allowing us to trace dust on spatial scales down to 11 R⋆ (71 AU). Two prominent dust components are detected and resolved. The brightest dust component, C, is located 334 mas (61 R⋆) southeast of the star and has a dust mass of at least 2.5 × 10-4 M⊙. It has a dust emissivity spectral index of β = -0.1 at its peak, implying that it is optically thick at these frequencies with a cool core of Td ≲ 100 K. Interestingly, not a single molecule in the ALMA data has emission close to the peak of this massive dust clump. The other main dust component, VY, is located at the position of the star and contains a total dust mass of 4.0 × 10-5 M⊙. It also contains a weaker dust feature extending over 60 R⋆ to the north with the total component having a typical dust emissivity spectral index of β = 0.7. We find that at least 17% of the dust mass around VY CMa is located in clumps ejected within a more quiescent roughly spherical stellar wind, with a quiescent dust mass loss rate of 5 × 10-6 M⊙yr-1. The anisotropic morphology of the dust indicates a continuous, directed mass loss over a few decades, suggesting that this mass loss cannot be driven by large convection cells alone. Appendices are available in electronic form at http://www.aanda.org

A METHOD FOR COUPLING DYNAMICAL AND COLLISIONAL EVOLUTION OF DUST IN CIRCUMSTELLAR DISKS: THE EFFECT OF A DEAD ZONE

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

Charnoz, Sebastien; Taillifet, Esther, E-mail: charnoz@cea.fr

Dust is a major component of protoplanetary and debris disks as it is the main observable signature of planetary formation. However, since dust dynamics are size-dependent (because of gas drag or radiation pressure) any attempt to understand the full dynamical evolution of circumstellar dusty disks that neglect the coupling of collisional evolution with dynamical evolution is thwarted because of the feedback between these two processes. Here, a new hybrid Lagrangian/Eulerian code is presented that overcomes some of these difficulties. The particles representing 'dust clouds' are tracked individually in a Lagrangian way. This system is then mapped on an Eulerian spatialmore » grid, inside the cells of which the local collisional evolutions are computed. Finally, the system is remapped back in a collection of discrete Lagrangian particles, keeping their number constant. An application example of dust growth in a turbulent protoplanetary disk at 1 AU is presented. First, the growth of dust is considered in the absence of a dead zone and the vertical distribution of dust is self-consistently computed. It is found that the mass is rapidly dominated by particles about a fraction of a millimeter in size. Then the same case with an embedded dead zone is investigated and it is found that coagulation is much more efficient and produces, in a short timescale, 1-10 cm dust pebbles that dominate the mass. These pebbles may then be accumulated into embryo-sized objects inside large-scale turbulent structures as shown recently.« less

Dust disks around Vega-type stars

NASA Astrophysics Data System (ADS)

Chini, R.; Kruegel, E.; Kreysa, E.; Shustov, B.; Tutukov, A.

1991-12-01

This study presents 1300-micron observations of the circumstellar dust around Vega-type stars. A comparison of the new data (24-arcsec HPBW) for Alpha PsA, Tau-1 Eri and Epsilon Eri with previous measurements made at an angular resolution of 11-arcsec shows that the dust emission is extended. From measurements at different positions it is concluded that the circumstellar dust around Beta Pic does not exceed the size of the optical disk of 500 AU. A model for Beta Pic that fits optical as well as IR data is discussed. Finally, a scenario for the evolution of circumstellar grains is suggested where, on one side, the Poynting-Robertson effect removes the small particles and, on the other side, collisions lead to the formation of larger bodies. Time-dependent IR spectra in reasonable agreement with observations are presented.

Warm Debris Disk Candidates from WISE

NASA Technical Reports Server (NTRS)

Padgett, Deborah; Stapelfeldt, Karl; Liu, Wilson; Leisawitz, David

2011-01-01

The Wide Field Infrared Survey Explorer (WISE) has just completed a sensitive all-sky survey in photometric bands at 3.4, 4.6, 12, and 22 microns. We report on a preliminary investigation of main sequence Hipparcos and Tycho catalog stars with 22 micron emission in excess of photospheric levels. This warm excess emission traces material in the circumstellar region likely to host terrestrial planets and is preferentially found in young systems with ages < 1 Gyr. Nearly a hundred new warm debris disk candidates are detected among FGK stars and 150 A stars within 120 pc. We are in the process of obtaining spectra to determine spectral types and activity level of these stars and are using HST, Herschel and Keck to characterize the dust, multiplicity, and substellar companions of these systems. In this contribution, we will discuss source selection methods and individual examples from among the WISE debris disk candidates.

Warm Debris Disks from WISE

NASA Technical Reports Server (NTRS)

Padgett, Deborah L.

2011-01-01

"The Wide Field Infrared Survey Explorer (WISE) has just completed a sensitive all-sky survey in photometric bands at 3.4, 4.6, 12, and 22 microns. We report on a preliminary investigation of main sequence Hipparcos and Tycho catalog stars with 22 micron emission in excess of photospheric levels. This warm excess emission traces material in the circumstellar region likely to host terrestrial planets and is preferentially found in young systems with ages < 1 Gyr. Nearly a hundred new warm debris disk candidates are detected among FGK stars and a similar number of A stars within 120 pc. We are in the process of obtaining spectra to determine spectral types and activity level of these stars and are using HST, Herschel and Keck to characterize the dust, multiplicity, and substellar companions of these systems. In this contribution, we will discuss source selection methods and individual examples from among the WISE debris disk candidates. "

THE S{sup 4}G PERSPECTIVE ON CIRCUMSTELLAR DUST EXTINCTION OF ASYMPTOTIC GIANT BRANCH STARS IN M100

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

Meidt, Sharon E.; Schinnerer, Eva; Munoz-Mateos, Juan-Carlos

2012-04-01

We examine the effect of circumstellar dust extinction on the near-IR (NIR) contribution of asymptotic giant branch (AGB) stars in intermediate-age clusters throughout the disk of M100. For our sample of 17 AGB-dominated clusters we extract optical-to-mid-IR spectral energy distributions (SEDs) and find that NIR brightness is coupled to the mid-IR dust emission in such a way that a significant reduction of AGB light, of up to 1 mag in the K band, follows from extinction by the dust shell formed during this stage. Since the dust optical depth varies with AGB chemistry (C-rich or O-rich), our results suggest thatmore » the contribution of AGB stars to the flux from their host clusters will be closely linked to the metallicity and the progenitor mass of the AGB star, to which dust chemistry and mass-loss rate are sensitive. Our sample of clusters-each the analogue of a {approx}1 Gyr old post-starburst galaxy-has implications within the context of mass and age estimation via SED modeling at high-z: we find that the average {approx}0.5 mag extinction estimated here may be sufficient to reduce the AGB contribution in the (rest-frame) K band from {approx}70%, as predicted in the latest generation of synthesis models, to {approx}35%. Our technique for selecting AGB-dominated clusters in nearby galaxies promises to be effective for discriminating the uncertainties associated with AGB stars in intermediate-age populations that plague age and mass estimation in high-z galaxies.« less

Mapping Circumstellar Matter with Polarized Light: The Case of Supernova 2014J in M82

NASA Astrophysics Data System (ADS)

Yang, Yi; Wang, Lifan; Baade, Dietrich; Brown, Peter. J.; Cikota, Aleksandar; Cracraft, Misty; Höflich, Peter A.; Maund, Justyn R.; Patat, Ferdinando; Sparks, William B.; Spyromilio, Jason; Stevance, Heloise F.; Wang, Xiaofeng; Wheeler, J. Craig

2018-02-01

Optical polarimetry is an effective way of probing the environment of a supernova for dust. We acquired linear HST ACS/WFC polarimetry in bands F475W, F606W, and F775W of the supernova (SN) 2014J in M82 at six epochs from ∼277 days to ∼1181 days after the B-band maximum. The polarization measured at day 277 shows conspicuous deviations from other epochs. These differences can be attributed to at least ∼{10}-6 {M}ȯ of circumstellar dust located at a distance of ∼ 5× {10}17 {cm} from the SN. The scattering dust grains revealed by these observations seem to be aligned with the dust in the interstellar medium that is responsible for the large reddening toward the supernova. The presence of this circumstellar dust sets strong constraints on the progenitor system that led to the explosion of SN 2014J; however, it cannot discriminate between single- and double-degenerate models.

The chromosphere of VV cephei and the distribution of circumstellar dust around red giants and supergiants

NASA Technical Reports Server (NTRS)

Bauer, Wendy Hagen

1992-01-01

The work on this project has followed two separate paths of inquiry. The first project was entitled 'the Chromosphere of VV Cephei.' The examination of the archival spectra revealed significant changes in the spectra. Therefore, we obtained additional observing time with IUE to monitor the system during the summer of 1991. Short-term changes continue to be seen in both the overall spectrum and individual line profiles. Work continues on this object. The second project was entitled 'the Distribution of Circumstellar Dust around Red Giants and Supergiants.' A number of cool evolved stars are surrounded by dust shells of sufficient angular size as to appear extended in the IRAS survey data. The aim of this project has been to convolve the predictions of the flux distribution from model dust shells with the IRAS beam profiles in order to reproduce the observed IRAS scans. At the time of the last status report, the cross-scan profiles of the IRAS detectors had just been added to the modeling procedure. For scans in which the star passed near the detector center, there was no significant variation in predicted scan profile for different detectors. Scans in which the detector did not pass over the bright central star had been anticipated to be particularly useful in determining the dust distribution; however, significant differences in the predicted scan profiles were seen for different detector profiles. For this reason, and due to the cross-talk effects discussed in the previous status report, further work on the scans not including a central star has been postponed in favor of further analysis of scans passing over the central star.

Rapid formation of large dust grains in the luminous supernova 2010jl.

PubMed

Gall, Christa; Hjorth, Jens; Watson, Darach; Dwek, Eli; Maund, Justyn R; Fox, Ori; Leloudas, Giorgos; Malesani, Daniele; Day-Jones, Avril C

2014-07-17

The origin of dust in galaxies is still a mystery. The majority of the refractory elements are produced in supernova explosions, but it is unclear how and where dust grains condense and grow, and how they avoid destruction in the harsh environments of star-forming galaxies. The recent detection of 0.1 to 0.5 solar masses of dust in nearby supernova remnants suggests in situ dust formation, while other observations reveal very little dust in supernovae in the first few years after explosion. Observations of the spectral evolution of the bright SN 2010jl have been interpreted as pre-existing dust, dust formation or no dust at all. Here we report the rapid (40 to 240 days) formation of dust in its dense circumstellar medium. The wavelength-dependent extinction of this dust reveals the presence of very large (exceeding one micrometre) grains, which resist destruction. At later times (500 to 900 days), the near-infrared thermal emission shows an accelerated growth in dust mass, marking the transition of the dust source from the circumstellar medium to the ejecta. This provides the link between the early and late dust mass evolution in supernovae with dense circumstellar media.

An Infrared Study of the Circumstellar Material Associated with the Carbon Star R Sculptoris

NASA Astrophysics Data System (ADS)

Hankins, M. J.; Herter, T. L.; Maercker, M.; Lau, R. M.; Sloan, G. C.

2018-01-01

The asymptotic giant branch (AGB) star R Sculptoris (R Scl) is one of the most extensively studied stars on the AGB. R Scl is a carbon star with a massive circumstellar shell (M shell ∼ 7.3 × 10‑3 M ⊙) that is thought to have been produced during a thermal pulse event ∼2200 years ago. To study the thermal dust emission associated with its circumstellar material, observations were taken with the Faint Object InfraRed CAMera for the SOFIA Telescope (FORCAST) at 19.7, 25.2, 31.5, 34.8, and 37.1 μm. Maps of the infrared emission at these wavelengths were used to study the morphology and temperature structure of the spatially extended dust emission. Using the radiative-transfer code DUSTY, and fitting the spatial profile of the emission, we find that a geometrically thin dust shell cannot reproduce the observed spatially resolved emission. Instead, a second dust component in addition to the shell is needed to reproduce the observed emission. This component, which lies interior to the dust shell, traces the circumstellar envelope of R Scl. It is best fit by a density profile with n ∝ r α , where α ={0.75}-0.25+0.45 and a dust mass of {M}d={9.0}-4.1+2.3× {10}-6 {M}ȯ . The strong departure from an r ‑2 law indicates that the mass-loss rate of R Scl has not been constant. This result is consistent with a slow decline in the post-pulse mass loss that has been inferred from observations of the molecular gas.

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

NASA Astrophysics Data System (ADS)

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

A mid-IR study of the circumstellar environment of Herbig Be stars

NASA Astrophysics Data System (ADS)

Verhoeff, A. P.; Waters, L. B. F. M.; van den Ancker, M. E.; Min, M.; Stap, F. A.; Pantin, E.; van Boekel, R.; Acke, B.; Tielens, A. G. G. M.; de Koter, A.

2012-02-01

Context. The study of the formation of massive stars is complicated because of the short times scales, large distances, and obscuring natal clouds. There are observational and theoretical indications that the circumstellar environment of Herbig Be (HBe) stars is substantially different from that of their lower mass counterparts, the T Tauri and Herbig Ae stars. Aims: We map the spatial distribution and mineralogy of the warm circumstellar dust of a sample of HBe stars. We compare our results to a sample of less massive Herbig Ae stars. Methods: We used literature photometry to obtain optical extinctions and stellar parameters of the targets. We obtained N-band imaging and long-slit spectroscopic data with the VISIR instrument at the VLT and we analyzed these data. We performed photometry of the images and extracted spatial information. We corrected the spectra for extinction and performed mineralogical fits. We fitted Gaussian profiles to characterize the spatial extent of the spectra along the VISIR slit. Results: We find that the mid-infrared (IR) emission of the HBe stars is typically characterized by a circumstellar disk that efficiently reprocesses a substantial portion of the stellar flux. The mid-IR flux levels, the spatial compactness, and the dust composition are quite similar to those of the Herbig Ae stars. We find upper limits to the full-width-at-half-maximum (FWHM) size of the mid-IR emission of ~500 AU. The main differences with the lower mass stars are the lower overall IR excess with a greater variety in shapes, the weaker PAH reprocessing power, and the lack of a silica-forsterite relation. The discrepancies between VISIR and IRAS photometry, the far-IR contributions and the large PAH sizes of HBe stars are attributed to natal clouds. Conclusions: Our results suggest that the Herbig Be disks are flatter than those around lower mass stars and they are likely truncated from the outside by photoevaporation. Based on observations collected at the

Luminous and Variable Stars in M31 and M33. IV. Luminous Blue Variables, Candidate LBVs, B[e] Supergiants, and the Warm Hypergiants: How to Tell Them Apart

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

Humphreys, Roberta M.; Gordon, Michael S.; Hahn, David

In this series of papers we have presented the results of a spectroscopic survey of luminous stars in the nearby spirals M31 and M33. Here, we present spectroscopy of 132 additional stars. Most have emission-line spectra, including luminous blue variables (LBVs) and candidate LBVs, Fe ii emission line stars, the B[e] supergiants, and the warm hypergiants. Many of these objects are spectroscopically similar and are often confused with each other. We examine their similarities and differences and propose the following guidelines that can be used to help distinguish these stars in future work. (1) The B[e] supergiants have emission linesmore » of [O i] and [Fe ii] in their spectra. Most of the spectroscopically confirmed sgB[e] stars also have warm circumstellar dust in their spectral energy distributions (SEDs). (2) Confirmed LBVs do not have the [O i] emission lines in their spectra. Some LBVs have [Fe ii] emission lines, but not all. Their SEDs show free–free emission in the near-infrared but no evidence for warm dust . Their most important and defining characteristic is the S Dor-type variability. (3) The warm hypergiants spectroscopically resemble the LBVs in their dense wind state and the B[e] supergiants. However, they are very dusty. Some have [Fe ii] and [O i] emission in their spectra like the sgB[e] stars, but are distinguished by their A- and F-type absorption-line spectra. In contrast, the B[e] supergiant spectra have strong continua and few if any apparent absorption lines. Candidate LBVs should share the spectral characteristics of the confirmed LBVs with low outflow velocities and the lack of warm circumstellar dust.« less

The circumstellar environment of the B[e] star GG Car: an interferometric modeling

NASA Astrophysics Data System (ADS)

Domiciano de Souza, A.; Borges Fernandes, M.; Carciofi, A. C.; Chesneau, O.

2015-01-01

The research of stars with the B[e] phenomenon is still in its infancy, with several unanswered questions. Physically realistic models that treat the formation and evolution of their complex circumstellar environments are rare. The code HDUST (developed by A. C. Carciofi and J. Bjorkman) is one of the few existing codes that provides a self-consistent treatment of the radiative transfer in a gaseous and dusty circumstellar environment seen around B[e] supergiant stars. In this work we used the HDUST code to study the circumstellar medium of the binary system GG Car, where the primary component is probably an evolved B[e] supergiant. This system also presents a disk (probably circumbinary), which is responsible for the molecular and dusty signatures seen in GG Car spectra. We obtained VLTI/MIDI data on GG~Car at eight baselines, which allowed to spatially resolve the gaseous and dusty circumstellar environment. From the interferometric visibilities and SED modeling with HDUST, we confirm the presence of a compact ring, where the hot dust lies. We also show that large grains can reproduce the lack of structure in the SED and visibilities across the silicate band. We conclude the dust condensation site is much closer to the star than previously thought. This result provides stringent constraints on future theories of grain formation and growth around hot stars.

Integrated approach towards understanding interactions of mineral dust aerosol with warm clouds

NASA Astrophysics Data System (ADS)

Kumar, Prashant

2011-12-01

Mineral dust is ubiquitous in the atmosphere and represents a dominant type of particulate matter by mass. Dust particles can serve as cloud condensation nuclei (CCN), giant CCN (GCCN), or ice nuclei (IN), thereby, affecting cloud microphysics, albedo, and lifetime. Despite its well-recognized importance, assessments of dust impacts on clouds and climate remain highly uncertain. This thesis addresses the role of dust as CCN and GCCN with the goal of improving our understanding of dust-warm cloud interactions and their representation in climate models. Most studies to date focus on the soluble fraction of aerosol particles when describing cloud droplet nucleation, and overlook the interactions of the hydrophilic insoluble fraction with water vapor. A new approach to include such interactions (expressed by the process of water vapor adsorption) is explored, by combining multilayer Frenkel-Halsey-Hill (FHH) physical adsorption isotherm and curvature (Kelvin) effects. The importance of adsorption activation theory (FHH-AT) is corroborated by measurements of CCN activity of mineral aerosols generated from clays, calcite, quartz, and desert soil samples from Northern Africa, East Asia/China, and Northern America. A new aerosol generation setup for CCN measurements was developed based on a dry generation technique capable of reproducing natural dust aerosol emission. Based on the dependence of critical supersaturation with particle dry diameter, it is found that the FHH-AT is a better framework for describing fresh (and unprocessed) dust CCN activity than the classical Kohler theory (KT). Ion Chromatography (IC) measurements performed on fresh regional dust samples indicate negligible soluble fraction, and support that water vapor adsorption is the prime source of CCN activity in the dust. CCN measurements with the commonly used wet generated mineral aerosol (from atomization of a dust aqueous suspension) are also carried out. Results indicate that the method is subject

Dust Spectroscopy and the Nature of Grains

NASA Technical Reports Server (NTRS)

Tielens, A. G. G. M.

2006-01-01

Ground-based, air-borne and space-based, infrared spectra of a wide variety of objects have revealed prominent absorption and emission features due to large molecules and small dust grains. Analysis of this data reveals a highly diverse interstellar and circumstellar grain inventory, including both amorphous materials and highly crystalline compounds (silicates and carbon). This diversity points towards a wide range of physical and chemical birthsites as well as a complex processing of these grains in the interstellar medium. In this talk, I will review the dust inventory contrasting and comparing both the interstellar and circumstellar reservoirs. The focus will be on the processes that play a role in the lifecycle of dust in the interstellar medium.

Dust-forming molecules in VY Canis Majoris (and Betelgeuse)

NASA Astrophysics Data System (ADS)

Kamiński, T.; Gottlieb, C. A.; Schmidt, M. R.; Patel, N. A.; Young, K. H.; Menten, K. M.; Brünken, S.; Müller, H. S. P.; Winters, J. M.; McCarthy, M. C.

2013-05-01

The formation of inorganic dust in circumstellar environments of evolved stars is poorly understood. Spectra of molecules thought to be most important for the nucleation, i.e. AlO, TiO, and TiO2, have been recently detected in the red supergiant VY CMa. These molecules are effectively formed in VY CMa and the observations suggest that non-equilibrium chemistry must be involved in their formation and nucleation into dust. In addition to exploring the recent observations of VY CMa, we briefly discuss the possibility of detecting these molecules in the "dust-poor" circumstellar environment of Betelgeuse.

Infrared circumstellar shells - Origins, and clues to the evolution of massive stars

NASA Technical Reports Server (NTRS)

Stencel, Robert E.; Pesce, Joseph E.; Bauer, Wendy Hagen

1989-01-01

The infrared fluxes, spatial and spectral characteristics for a sample of 111 supergiant stars of spectral types F0 through M5 are tabulated, and correlations examined with respect to the nature of their circumstellar envelopes. One-fourth of these objects were spatialy resolved by IRAS at 60 microns and possess extended circumstellar shell material, with implied expansion ages of about 10 to the 5th yr. Inferences about the production of dust, mass loss, and the relation of these characteristics of the evolution of massive stars, are discussed.

Circumstellar Material on and off the Main Sequence

NASA Astrophysics Data System (ADS)

Steele, Amy; Debes, John H.; Deming, Drake

2017-06-01

There is evidence of circumstellar material around main sequence, giant, and white dwarf stars that originates from the small-body population of planetary systems. These bodies tell us something about the chemistry and evolution of protoplanetary disks and the planetary systems they form. What happens to this material as its host star evolves off the main sequence, and how does that inform our understanding of the typical chemistry of rocky bodies in planetary systems? In this talk, I will discuss the composition(s) of circumstellar material on and off the main sequence to begin to answer the question, “Is Earth normal?” In particular, I look at three types of debris disks to understand the typical chemistry of planetary systems—young debris disks, debris disks around giant stars, and dust around white dwarfs. I will review the current understanding on how to infer dust composition for each class of disk, and present new work on constraining dust composition from infrared excesses around main sequence and giant stars. Finally, dusty and polluted white dwarfs hold a unique key to our understanding of the composition of rocky bodies around other stars. In particular, I will discuss WD1145+017, which has a transiting, disintegrating planetesimal. I will review what we know about this system through high speed photometry and spectroscopy and present new work on understanding the complex interplay of physics that creates white dwarf pollution from the disintegration of rocky bodies.

KP Equation in a Three-Dimensional Unmagnetized Warm Dusty Plasma with Variable Dust Charge

NASA Astrophysics Data System (ADS)

El-Shorbagy, Kh. H.; Mahassen, Hania; El-Bendary, Atef Ahmed

2017-12-01

In this work, we investigate the propagation of three-dimensional nonlinear dust-acoustic and dust-Coulomb waves in an unmagnetized warm dusty plasma consisting of electrons, ions, and charged dust particles. The grain charge fluctuation is incorporated through the current balance equation. Using the perturbation method, a Kadomtsev-Petviashvili (KP) equation is obtained. It has been shown that the charge fluctuation would modify the wave structures, and the waves in such systems are unstable due to high-order long wave perturbations.

Exozodiacal clouds: hot and warm dust around main sequence stars

NASA Astrophysics Data System (ADS)

Kral, Quentin; Krivov, Alexander V.; Defrère, Denis; van Lieshout, Rik; Bonsor, Amy; Augereau, Jean-Charles; Thébault, Philippe; Ertel, Steve; Lebreton, Jérémy; Absil, Olivier

2017-04-01

A warm/hot dust component (at temperature $>$ 300K) has been detected around $\\sim$ 20% of stars. This component is called "exozodiacal dust" as it presents similarities with the zodiacal dust detected in our Solar System, even though its physical properties and spatial distribution can be significantly different. Understanding the origin and evolution of this dust is of crucial importance, not only because its presence could hamper future detections of Earth-like planets in their habitable zones, but also because it can provide invaluable information about the inner regions of planetary systems. In this review, we present a detailed overview of the observational techniques used in the detection and characterisation of exozodiacal dust clouds ("exozodis") and the results they have yielded so far, in particular regarding the incidence rate of exozodis as a function of crucial parameters such as stellar type and age, or the presence of an outer cold debris disc. We also present the important constraints that have been obtained, on dust size distribution and spatial location, by using state-of-the-art radiation transfer models on some of these systems. Finally, we investigate the crucial issue of how to explain the presence of exozodiacal dust around so many stars (regardless of their ages) despite the fact that such dust so close to its host star should disappear rapidly due to the coupled effect of collisions and stellar radiation pressure. Several potential mechanisms have been proposed to solve this paradox and are reviewed in detail in this paper. The review finishes by presenting the future of this growing field.

INVESTIGATING PLANET FORMATION IN CIRCUMSTELLAR DISKS: CARMA OBSERVATIONS OF RY Tau AND DG Tau

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

Isella, Andrea; Carpenter, John M.; Sargent, Anneila I., E-mail: isella@astro.caltech.ed

2010-05-10

We present CARMA observations of the thermal dust emission from the circumstellar disks around the young stars RY Tau and DG Tau at wavelengths of 1.3 mm and 2.8 mm. The angular resolution of the maps is as high as 0.''15, or 20 AU at the distance of the Taurus cloud, which is a factor of 2 higher than has been achieved to date at these wavelengths. The unprecedented detail of the resulting disk images enables us to address three important questions related to the formation of planets. (1) What is the radial distribution of the circumstellar dust? (2) Doesmore » the dust emission show any indication of gaps that might signify the presence of (proto-)planets? (3) Do the dust properties depend on the orbital radius? We find that modeling the disk surface density in terms of either a classical power law or the similarity solution for viscous disk evolution reproduces the observations well. Both models constrain the surface density between 15 and 50 AU to within 30% for a given dust opacity. Outside this range, the densities inferred from the two models differ by almost an order of magnitude. The 1.3 mm image from RY Tau shows two peaks separated by 0.''2 with a decline in the dust emission toward the stellar position, which is significant at about 2{sigma}-4{sigma}. For both RY Tau and DG Tau, the dust emission at radii larger than 15 AU displays no significant deviation from an unperturbed viscous disk model. In particular, no radial gaps in the dust distribution are detected. Under reasonable assumptions, we exclude the presence of planets more massive than 5 M{sub J} orbiting either star at distances between about 10 and 60 AU, unless such a planet is so young that there has been insufficient time to open a gap in the disk surface density. The radial variation of the dust opacity slope, {beta}, was investigated by comparing the 1.3 mm and 2.8 mm observations. We find mean values of {beta} of 0.5 and 0.7 for DG Tau and RY Tau, respectively. Variations in {beta

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

NASA Technical Reports Server (NTRS)

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

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

NASA Astrophysics Data System (ADS)

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

2013-07-01

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

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

NASA Astrophysics Data System (ADS)

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

2016-02-01

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 as the 2010-2011 event. 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 the tidally disrupted circumstellar material. Recent hydrodynamical simulations of the eccentric fly-by of RW Aur B suggest the occulting body to be a bridge of material connecting RW Aur A and B. These simulations also suggest the possibility of additional occultations which are supported by the observations presented in this work. The color evolution of the dimmings suggest that the tidally stripped disk material includes dust grains ranging in size from small grains at the leading edge, typical of star-forming regions, to large grains, ices or pebbles producing gray or nearly gray extinction deeper within the occulting material. It is not known whether this material represents arrested planet building prior to the tidal disruption event, or perhaps accelerated planet building as a result of the disruption event, but in any case the evidence suggests the presence of advanced planet building material in the space between the two stars of the RW Aur system.

Some Coolness on Martian Global Warming and Reflections on the Role of Surface Dust

NASA Astrophysics Data System (ADS)

Richardson, M. I.; Vasavada, A. R.

2007-12-01

Recent comparisons of global snap-shots of Mars' surface taken by the Viking and Mars Global Surveyor (MGS) cameras have been used to suggest that Mars has darkened, and hence has warmed, between the 1970's and 1990's. While this conclusion is not supported by more quantitative analysis of albedo data, the idea of Martian darkening and warming has found its way into the terrestrial climate change debate. Through blogs and other opinion pieces it has been used, both amusingly and disturbingly, to argue that Mars' apparent natural warming should alleviate our concerns about anthropomorphic climate change on Earth. Relating planetary research results to terrestrial analogs is instructive and promotes public understanding, but this example provides a cautionary tale of misinterpretation in this age of politicized science. The dust cycle is the dominant short-term component of the Martian climate. The atmosphere is strongly forced via dust's modification of atmospheric radiative heating rates, while dust loading displays dramatic interannual variability, from background opacity to aperiodic global dust storms. Until recently, the atmospheric component of the dust cycle was better documented than the surface component (which on Mars can be gauged via albedo). But now thanks to the combination of regional imaging, spot thermal infrared spectra, and spot short-wavelength photometry sampled at synoptic time and length scales by MGS, a rich new view of the relationship between specific meteorological phenomena and the patterns of surface dust is emerging. Seasonal cap winds, local, regional, and global dust storms, and monsoonal circulations all redistribute surface dust on large spatial scales, while dust devils are surprisingly shown to be insignificant. Rapid and widespread albedo modification is accomplished by storms that darken relatively bright regions through dust removal, and deposit dust upon largely dust free areas, brightening them. (It is not possible with

Measuring the structure and composition of circumstellar debris disks

NASA Astrophysics Data System (ADS)

Ballering, Nicholas Paul

In this dissertation, I measure the structure and composition of circumstellar debris disks to probe the underlying planetary systems. In Chapter 1, I provide an introduction to the field of debris disks. I highlight our current observational and theoretical understanding of the field, rather than providing a detailed history. This is intended to give the reader context and motivation for the subsequent chapters. I also describe important developments in debris disk science that are not the focus of this dissertation, but are nevertheless vital for a complete overview. In Chapter 2, I describe my analysis of a large sample of cold (<130 K) debris disks seen in Spitzer/IRS data. Previous work had suggested a common temperature for these disk components, regardless of spectral type. I find that there is trend with spectral type and argue that the locations of cold disks are not set by snow lines, but more likely by the formation/evolution of planets. This work was published in Ballering et al. (2013). In Chapter 3, I turn my focus to the warm (˜190 K) debris components identified in Chapter 2--specifically those exhibiting silicate emission features. I show that these features arise from exozodiacal dust in the habitable zones around these stars. This was published in Ballering et al. (2014). In Chapter 4, I examine the remainder of the warm disks to investigate what mechanism sets their location. I find that for many systems, the locations trace the water snow line in the primordial protoplanetary disk, rather than the current snow line. This favors the interpretation that warm debris components arise from asteroid belts in these systems. This study will be published soon. In Chapter 5, I analyze images of the debris disk around beta Pictoris at five different wavelengths, including in thermal emission and scattered light. I find that matching the disk brightness at all wavelengths constrains the composition of the dust, with a mixture of astronomical silicates and

Guilt by Association: The 13 Micron Dust Emission Feature and Its Correlation to Other Gas and Dust Features

NASA Astrophysics Data System (ADS)

Sloan, G. C.; Kraemer, Kathleen E.; Goebel, J. H.; Price, Stephan D.

2003-09-01

A study of all full-scan spectra of optically thin oxygen-rich circumstellar dust shells in the database produced by the Short Wavelength Spectrometer on ISO reveals that the strength of several infrared spectral features correlates with the strength of the 13 μm dust feature. These correlated features include dust features at 19.8 and 28.1 μm and the bands produced by warm carbon dioxide molecules (the strongest of which are at 13.9, 15.0, and 16.2 μm). The database does not provide any evidence for a correlation of the 13 μm feature with a dust feature at 32 μm, and it is more likely that a weak emission feature at 16.8 μm arises from carbon dioxide gas rather than dust. The correlated dust features at 13, 20, and 28 μm tend to be stronger with respect to the total dust emission in semiregular and irregular variables associated with the asymptotic giant branch than in Mira variables or supergiants. This family of dust features also tends to be stronger in systems with lower infrared excesses and thus lower mass-loss rates. We hypothesize that the dust features arise from crystalline forms of alumina (13 μm) and silicates (20 and 28 μm). Based on observations with the ISO, a European Space Agency (ESA) project with instruments funded by ESA member states (especially the Principal Investigator countries: France, Germany, the Netherlands, and the United Kingdom) and with the participation of the Institute of Space and Astronautical Science (ISAS) and the National Aeronautics and Space Administration (NASA).

Low-temperature crystallization of silicate dust in circumstellar disks.

PubMed

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

1999-10-07

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

Signatures of Exo-Solar Planets in Dust Debris Disks

NASA Technical Reports Server (NTRS)

Ozernoy, Leonid M.; Gorkavyi, Nick N.; Mather, John C.; Taidakova, Tanya A.

1999-01-01

We have developed a new numerical approach to the dynamics of minor bodies and dust particles, which enables us to increase, without using a supercomputer, the number of employed particle positions in each model up to 10(exp 10) - 10(exp 11), a factor of 10(exp 6) - 10(exp 7) higher than existing numerical simulations. We apply this powerful approach to the high-resolution modeling of the structure and emission of circumstellar dust disks, incorporating all relevant physical processes. In this Letter, we examine the resonant structure of a dusty disk induced by the presence of one planet of mass in the range of (5 x 10(exp -5) - 5 x 10(exp -3))M. It is shown that the planet, via resonances and gravitational scattering, produces (i) a central cavity void of dust; (ii) a trailing (sometimes leading) off-center cavity; and (iii) an asymmetric resonant dust belt with one, two, or more clumps. These features can serve as indicators of planet(s) embedded in the circumstellar dust disk and, moreover, can be used to determine the mass of the planet and even some of its orbital parameters. The results of our study reveal a remarkable similarity with various types of highly asymmetric circumstellar disks observed with the JCMT around Epsilon Eridani and Vega.

Probing Protoplanetary Disk Upper Atmospheres for Heating and Dust Settling Using Synthetic CO Spectra

NASA Astrophysics Data System (ADS)

Lewis, Josiah; Brittain, S. D.

2010-01-01

CO emission is a useful probe of the warm gas distribution in the planet forming regions of disks around Herbig Ae/Be stars. We model UV fluoresced and thermally excited CO in the circumstellar disks of several HAeBes. We find indications of dust settling in the upper atmospheres of HD 141569 and HD 7048 and a correlation between PAH luminosity and gas heating in these two systems. This project was funded by a partnership between the National Science Foundation (NSF AST-0552798), Research Experiences for Undergraduates (REU), and the Department of Defense (DoD) ASSURE (Awards to Stimulate and Support Undergraduate Research Experiences) programs.

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

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

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

2013-07-01

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

[Petrological Analysis of Astrophysical Dust Analog Evolution

NASA Technical Reports Server (NTRS)

Rietmeijer, Frans J. M.

1997-01-01

This project "Petrological analysis of astrophysical dust analog evolution" was initiated to try to understand the vapor phase condensation, and the nature of the reaction products, in circumstellar environments, such as the solar nebula 4,500 Myrs ago, and in the interstellar medium. Telescope-based infrared [IR] spectroscopy offers a broad-scale inventory of the various types of dust in these environments but no details on small-scale variations in terms of chemistry and morphology and petrological phase relationships. Vapor phase condensation in these environments is almost certainly a non-equilibrium process. The main challenge to this research was to document the nature of this process that, based on astrophysical observations, seems to yield compositionally consistent materials. This observation may suggest a predictable character during non-equilibrium condensation. These astrophysical environments include two chemically distinct, that is, oxygen-rich and carbon-rich environments. The former is characterized by silicates the latter by carbon-bearing solids. According to cosmological models of stellar evolution circumstellar dust accreted into protoplanets wherein thermal and/or aqueous processes will alter the dust under initially, non-equilibrium conditions.

Carbon stars with oxygen-rich circumstellar material

NASA Technical Reports Server (NTRS)

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.

Rapid variation in the circumstellar 10 micron emission of Alpha Orionis

NASA Technical Reports Server (NTRS)

Bloemhof, E. E.; Danchi, W. C.; Townes, C. H.

1985-01-01

The spatial distribution of 10 micron continuum flux around the supergiant star Alpha Orionis was measured on two occasions separated by an interval of 1 yr. A significant change in the infrared radiation pattern on the subarcsecond scale was observed. This change cannot be explained plausibly by macroscopic motion but may be due to a change in the physical properties of the circumstellar dust.

Dust Around Herbig Ae Stars: Additional Constraints from their Photometric and Polarimetric Variability

NASA Technical Reports Server (NTRS)

Krivova, N. A.; Ilin, V. B.; Fischer, O.

1996-01-01

For the Herbig Ae stars with Algol-like minima (UX Ori, WW Vul, etc), the effects of circumstellar dust include: excess infrared emission, anomalous ultraviolet extinction, the 'blueing' of the stars in minima accompanying by an increase of intrinsic polarization. Using a Monte-Carlo code for polarized radiation transfer we have simulated these effects and compared the results obtained for different models with the observational data available. We found that the photometric and polarimetric behavior of the stars provided essential additional constraints on the circumstellar dust models. The models with spheroidal shell geometry and compact (non-fluffy) dust grains do not appear to be able to explain all the data.

Interrelationships among Circumstellar, Interstellar and Interplanetary Dust

NASA Technical Reports Server (NTRS)

Nuth, J. A., III (Editor); Stencel, R. E. (Editor)

1986-01-01

Proceedings of a workshop held from February 27 to March 1, l985. The workshop was attended by 50 astronomers, astrophysicists, planetary scientists and meteoriticists; and emphasized the interdisciplinary nature of studies of cosmic dust.

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

NASA Technical Reports Server (NTRS)

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

2012-01-01

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

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

NASA Astrophysics Data System (ADS)

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

2012-12-01

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

DIRT: Dust InfraRed Toolbox

NASA Astrophysics Data System (ADS)

Pound, Marc W.; Wolfire, Mark G.; Mundy, Lee G.; Teuben, Peter; Lord, Steve

2011-02-01

DIRT is a Java applet for modelling astrophysical processes in circumstellar dust shells around young and evolved stars. With DIRT, you can: select and display over 500,000 pre-run model spectral energy distributions (SEDs) find the best-fit model to your data set account for beam size in model fitting manipulate data and models with an interactive viewer display gas and dust density and temperature profiles display model intensity profiles at various wavelengths

The Abundance of C2H4 in the Circumstellar Envelope of IRC+10216.

PubMed

Fonfría, J P; Hinkle, K H; Cernicharo, J; Richter, M J; Agúndez, M; Wallace, L

2017-02-01

High spectral resolution mid-IR observations of ethylene (C 2 H 4 ) towards the AGB star IRC+10216 were obtained using the Texas Echelon Cross Echelle Spectrograph (TEXES) at the NASA Infrared Telescope Facility (IRTF). Eighty ro-vibrational lines from the 10.5 µ m vibrational mode ν 7 with J ≲ 30 were detected in absorption. The observed lines are divided into two groups with rotational temperatures of 105 and 400 K (warm and hot lines). The warm lines peak at ≃ -14 km s -1 with respect to the systemic velocity, suggesting that they are mostly formed outwards from ≃ 20 R ⋆ . The hot lines are centered at -10 km s -1 indicating that they come from a shell between 10 and 20 R ⋆ . 35% of the observed lines are unblended and can be fitted with a code developed to model the emission of a spherically symmetric circumstellar envelope. The analysis of several scenarios reveal that the C 2 H 4 abundance relative to H 2 in the range 5 - 20 R ⋆ is 6.9 × 10 -8 in average and it could be as high as 1.1 × 10 -7 . Beyond 20 R ⋆ , it is 8.2 × 10 -8 . The total column density is (6.5 ± 3.0) × 10 15 cm -2 . C 2 H 4 is found to be rotationally under local thermodynamical equilibrium (LTE) and vibrationally out of LTE. One of the scenarios that best reproduce the observations suggests that up to 25% of the C 2 H 4 molecules at 20 R ⋆ could condense onto dust grains. This possible depletion would not influence significantly the gas acceleration although it could play a role in the surface chemistry on the dust grains.

The Abundance of C2H4 in the Circumstellar Envelope of IRC+10216

PubMed Central

Fonfría, J. P.; Hinkle, K. H.; Cernicharo, J.; Richter, M. J.; Agúndez, M.

2017-01-01

High spectral resolution mid-IR observations of ethylene (C2H4) towards the AGB star IRC+10216 were obtained using the Texas Echelon Cross Echelle Spectrograph (TEXES) at the NASA Infrared Telescope Facility (IRTF). Eighty ro-vibrational lines from the 10.5 µm vibrational mode ν7 with J ≲ 30 were detected in absorption. The observed lines are divided into two groups with rotational temperatures of 105 and 400 K (warm and hot lines). The warm lines peak at ≃ −14 km s−1 with respect to the systemic velocity, suggesting that they are mostly formed outwards from ≃ 20R⋆. The hot lines are centered at −10 km s−1 indicating that they come from a shell between 10 and 20R⋆. 35% of the observed lines are unblended and can be fitted with a code developed to model the emission of a spherically symmetric circumstellar envelope. The analysis of several scenarios reveal that the C2H4 abundance relative to H2 in the range 5 − 20R⋆ is 6.9 × 10−8 in average and it could be as high as 1.1 × 10−7. Beyond 20R⋆, it is 8.2 × 10−8. The total column density is (6.5 ± 3.0) × 1015 cm−2. C2H4 is found to be rotationally under local thermodynamical equilibrium (LTE) and vibrationally out of LTE. One of the scenarios that best reproduce the observations suggests that up to 25% of the C2H4 molecules at 20R⋆ could condense onto dust grains. This possible depletion would not influence significantly the gas acceleration although it could play a role in the surface chemistry on the dust grains. PMID:28184097

SMA Continuum Survey of Circumstellar Disks in Serpens

NASA Astrophysics Data System (ADS)

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

2017-06-01

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

Creating Compositionally-Driven Debris Disk Dust Models

NASA Astrophysics Data System (ADS)

Zimmerman, Mara; Jang-Condell, Hannah; Schneider, Glenn; Chen, Christine; Stark, Chris

2018-06-01

Debris disks play a key role in exoplanet research; planetary formation and composition can be inferred from the nature of the circumstellar disk. In order to characterize the properties of the circumstellar dust, we create models of debris disks in order to find the composition. We apply Mie theory to calculate the dust absorption and emission within debris disks. We have data on nine targets from Spitzer and Hubble Space Telescope. The Spitzer data includes mid-IR spectroscopy and photometry. We have spatially-resolved optical and near-IR images of the disks from HST. Our goal is to compare this data to the model. By using a model that fits for photometric and mid-IR datasimultaneously, we gain a deeper understanding of the structure and composition of the debris disk systems.

Dust Coagulation in Protoplanetary Accretion Disks

NASA Technical Reports Server (NTRS)

Schmitt, W.; Henning, Th.; Mucha, R.

1996-01-01

The time evolution of dust particles in circumstellar disk-like structures around protostars and young stellar objects is discussed. In particular, we consider the coagulation of grains due to collisional aggregation. The coagulation of the particles is calculated by solving numerically the non-linear Smoluchowski equation. The different physical processes leading to relative velocities between the grains are investigated. The relative velocities may be induced by Brownian motion, turbulence and drift motion. Starting from different regimes which can be identified during the grain growth we also discuss the evolution of dust opacities. These opacities are important for both the derivation of the circumstellar dust mass from submillimeter/millimeter continuum observations and the dynamical behavior of the disks. We present results of our numerical studies of the coagulation of dust grains in a turbulent protoplanetary accretion disk described by a time-dependent one-dimensional (radial) alpha-model. For several periods and disk radii, mass distributions of coagulated grains have been calculated. From these mass spectra, we determined the corresponding Rosseland mean dust opacities. The influence of grain opacity changes due to dust coagulation on the dynamical evolution of a protostellar disk is considered. Significant changes in the thermal structure of the protoplanetary nebula are observed. A 'gap' in the accretion disk forms at the very frontier of the coagulation, i.e., behind the sublimation boundary in the region between 1 and 5 AU.

Correlated nanoscale characterization of a unique complex oxygen-rich stardust grain: Implications for circumstellar dust formation

NASA Astrophysics Data System (ADS)

Leitner, J.; Hoppe, P.; Floss, C.; Hillion, F.; Henkel, T.

2018-01-01

We report the light to intermediate-mass element abundances as well as the oxygen, magnesium, silicon, and titanium isotope compositions of a unique and unusually large (0.8 μm × 3.75 μm) presolar O-rich grain from the Krymka LL3.2 chondrite. The O-, Al-, and Ti-isotopic compositions are largely compatible with an origin from an asymptotic giant branch (AGB) star of 1.5 solar masses with a metallicity that is 15% higher than the solar metallicity. The grain has an elevated 17O/16O ratio (8.40 ± 0.16 × 10-4) compared to solar, and slightly sub-solar 18O/16O ratio (1.83 ± 0.03 × 10-3). It shows evidence for the presence of initial 26Al, suggesting formation after the first dredge-up, during one of the early third dredge-up (TDU) episodes. Titanium isotopic data indicate condensation of the grain before significant amounts of material from the He-burning shell were admixed to the stellar surface with progressive TDUs. We observed a small excess in 30Si (δ30Si = 41 ± 5‰), which most likely is inherited from the parent star's initial Si-isotopic composition. For such stars stellar models predict a C/O-ratio < 1 even after the onset of TDU, thus allowing the condensation of O-rich dust. The grain is an unusual complex presolar grain, consisting of an Al-Ca-Ti-oxide core, surrounded by an Mg-Ca-silicate mantle, and resembles the condensation sequence for a cooling gas of solar composition at pressures and dust/gas ratios typically observed for circumstellar envelopes around evolved stars. We also report the first observation of phosphorus in a presolar grain, although the origin of the P-bearing phase remains ambiguous.

A search for circumstellar material around pulsars

NASA Astrophysics Data System (ADS)

Phillips, J. A.; Chandler, C. J.

1994-01-01

We have searched for thermal dust emission from circumstellar disks around five neutron stars using the Owens Valley millimeter array at 99 GHz and the James Clerk Maxwell Telescope at 380 GHz. Two of the neutron stars (PSR 0950+08 and 1133+16) are nearby isolated pulsars with characteristic ages 106 to 107 yr. The remaining three (PSR 1257+12, 1534+12, and 1937+21) are old millisecond pulsars with ages in the range 108 to 109 yr. None of the pulsars was detected above the noise, giving 2 sigma limits on the mass of disk material of approximately 10-2 solar mass if their disks are similar to those around pre-main-sequence stars. We discuss mechanisms for clearing dust grains from circumpulsar disks. We show that dust particles orbiting a neutron star lose angular momentum due to the ram pressure of the interstellar medium, which is approximately 104 times stronger for pulsars than for normal stars because of their high space velocity. For a pulsar moving at 100 km/s through an ambient medium with number density n approximately 1/cu cm, dust grains 0.1 micrometer(s) in size spiral into the star in approximately 106 years. This mechanism is more effective at clearing grains than the Poynting-Robertson effect and may limit the detectability of disks around old neutron stars.

Dust and gas around young stars

NASA Astrophysics Data System (ADS)

Chen, Christine Hsiao-Ching

To understand how asteroids, planets, and comets form in circumstellar disks of gas and dust, we have carried out a high resolution mid-infrared imaging study and a high resolution ultra violet spectroscopic study of the dust and gas around nearby pre-main sequence Herbig Ae stars and dusty main sequence stars. We have used the Keck I telescope to image at 11.7 μm and 17.9 μm the dust emission around ζ Lep, a main sequence A-type star with an infrared excess, 21.5 pc from the Sun. The excess is at most marginally resolved at 17.9 μm. The dust distance from the star is probably ≤6 AU, although some dust may extend to 9 AU. The mass of observed dust is ˜10 22 g. Since the lifetime of dust particles is about 104 yr because of the Poynting- Robertson effect, we robustly estimate at least 4 × 1026 g must reside in parent bodies which may be asteroids if the system is in a steady state and has an age of ˜300 Myr. This mass is approximately 200 times that contained within the main asteroid belt in our solar system. We have obtained FUSE spectra of σ 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 Å, N II* at 1085 Å, and N II** at 1086 Å 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. Since σ Her has a high luminosity, we suggest that there is a radiatively driven wind, arising from the circumstellar matter, rather than accretion as occurs around β Pic. 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⊙ yr-1. This wind depletes the minimum mass of parent bodies in less than

Infrared Study of Supernova Ejecta and Dust

NASA Astrophysics Data System (ADS)

Meikle, W. Peter; Farrah, Duncan; Fesen, Robert; Fransson, Claes; Gerardy, Christopher; Hoeflich, Peter; Kotak, Rubina; Kozma, Cecilia; Lucy, Leon; Lundqvist, Peter; Mattila, Seppo; Pozzo, Monica; Sollerman, Jesper; van Dyk, Schuyler; Wheeler, Craig

2004-09-01

We propose to use IRAC and IRS to gain powerful new insights on the nature of supernova (SN) explosions and test the hypothesis that SNe are major sources of cosmic dust. One of our two aims is to carry out robust tests of SN explosion models through the measurement of fine-structure (FS) lines and, where possible, their evolution. The important molecule, SiO, will also be measured. By comparison with our spectral synthesis models, we shall test the explosion model-sensitive predictions of abundances and their distribution. Most of the FS lines arise from ground state transitions and so, in comparison with optical or near-IR spectra, are much less sensitive to temperature and density uncertainties. However, the FS lines are only accessible in the MIR and the most useful abundance measurements can only be achieved at late times when the ejecta are optically thin. Consequently, ground-based MIR observations at the necessary late epochs are difficult if not impossible for nearly all SNe. Observation with the Spitzer Space Telescope is therefore essential. Our second goal is to test the proposal that core-collapse SNe (CCSNe) are, or have been, the major source of dust in the universe. Direct evidence in support of this is still very sparse. Warm dust emits most strongly in the MIR region, and so is the ideal wavelength range for following the condensation of dust within the ejecta or, in the case of Type IIn SNe, in a cool, dense shell formed at the ejecta/progenitor wind interface. Alternatively, such radiation may arise from IR light echo emission from dust in the progenitor wind. Discrimination between condensing dust and pre-existing circumstellar dust can be achieved by measurement of its MIR spectral energy distribution and evolution. Such measurements can also provide dust mass estimates and give clues about the nature of the grain material. To achieve our two goals, we propose to use IRAC and IRS to observe up to 17 SNe at epochs ranging from about 100 days to

Integrative Analysis of Desert Dust Size and Abundance Suggests Less Dust Climate Cooling

NASA Technical Reports Server (NTRS)

Kok, Jasper F.; Ridley, David A.; Zhou, Qing; Miller, Ron L.; Zhao, Chun; Heald, Colette L.; Ward, Daniel S.; Albani, Samuel; Haustein, Karsten

2017-01-01

Desert dust aerosols affect Earths global energy balance through interactions with radiation, clouds, and ecosystems. But the magnitudes of these effects are so uncertain that it remains unclear whether atmospheric dust has a net warming or cooling effect on global climate. Consequently, it is still uncertain whether large changes in atmospheric dust loading over the past century have slowed or accelerated anthropogenic climate change, and the climate impact of possible future alterations in dust loading is similarly disputed. Here we use an integrative analysis of dust aerosol sizes and abundance to constrain the climatic impact of dust through direct interactions with radiation. Using a combination of observational, experimental, and model data, we find that atmospheric dust is substantially coarser than represented in current climate models. Since coarse dust warms global climate, the dust direct radiative effect (DRE) is likely less cooling than the 0.4 W m superscript 2 estimated by models in a current ensemble. We constrain the dust DRE to -0.20 (-0.48 to +0.20) W m superscript 2, which suggests that the dust DRE produces only about half the cooling that current models estimate, and raises the possibility that dust DRE is actually net warming the planet.

Mid-Infrared Signatures from Type Ia Supernovae Strongly Interacting with a Circumstellar Medium

NASA Astrophysics Data System (ADS)

Fox, Ori

2015-10-01

Type Ia supernovae (SNe Ia) are well-known for their use as precise cosmological distance indicators due to a standardizable peak luminosity resulting from a thermonuclear explosion. A growing subset of SNe Ia, however, show evidence for interaction with a dense circumstellar medium during the first year post-explosion, and sometimes longer (SNe Ia-CSM). The origin of this dense CSM is unknown and suggests either a) the less typical single-degenerate progenitor scenario must be considered or b) the exploding star was not a thermonuclear explosion of a white dwarf at all (i.e., core-collapse). Mid-infrared (IR) observations, in particular, are critical for tracing the density profile of dust (and hence gas) in the surrounding CSM. Yet no Spitzer light curve exists for this subclass within the first year post-expolosion. Here we propose a 'low-impact' (>8 weeks) ToO to obtain 3 epochs of Spitzer imaging of a SN Ia-CSM within 100 Mpc over 1 year post-explosion. The strength of this program is that it will be in conjunction with pre-approved multi-wavelength programs on HST/STIS/UV (GO 13649), Chandra/ASIS-S (Num: 17500672), the Keck/LRIS optical spectrograph (Num: U037LA), and the RATIR visible/infrared robotic imager. Requiring only 2.1 hours of observation total, this program will not only distinguish between the SN explosion mechanisms, but also trace CSM interaction, constrain the progenitor mass loss history, and identify late-time heating mechanisms of warm dust.

The infrared spectrum of M8 E - Evidence for circumstellar CO

NASA Technical Reports Server (NTRS)

Larson, H. P.; Fink, U.; Hofmann, R.

1986-01-01

High-resolution spectroscopic observations of the compact infrared source M8 E are reported in the region from 3 to 5 microns. Very prominent CO absorption lines are observed in the v = 1-0 band at 4.7 microns. The velocity width and rotational temperature suggest that this CO absorption occurs in a highly excited region. The high background continuum flux level and the prominent appearance of the CO features suggest that the CO line-forming region must be in front of the dust emission region. A blister model for M8 E, which places most of the dust continuum emission behind the source, satisfies this requirement. According to this picture, the observed circumstellar CO spectrum shows a high rotational temperature and a large velocity dispersion because of the combined effects of the strong stellar wind and possible shock heating near the dust zone as the wind encounters the ambient molecular cloud.

Modelling the Dust Around Vega-Like Stars

NASA Technical Reports Server (NTRS)

Sylvester, Roger J.; Skinner, C. J.; Barlow, M. J.

1996-01-01

Models are presented of four Vega-like stars: main-sequence stars with infrared emission from circumstellar dust. The dusty environments of the four stars are rather diverse, as shown by their spectral energy distributions. Good fits to the observations were obtained for all four stars.

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

NASA Astrophysics Data System (ADS)

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

2017-12-01

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

The Circumstellar Disk HD 169142: Gas, Dust, and Planets Acting in Concert?

NASA Astrophysics Data System (ADS)

Pohl, A.; Benisty, M.; Pinilla, P.; Ginski, C.; de Boer, J.; Avenhaus, H.; Henning, Th.; Zurlo, A.; Boccaletti, A.; Augereau, J.-C.; Birnstiel, T.; Dominik, C.; Facchini, S.; Fedele, D.; Janson, M.; Keppler, M.; Kral, Q.; Langlois, M.; Ligi, R.; Maire, A.-L.; Ménard, F.; Meyer, M.; Pinte, C.; Quanz, S. P.; Sauvage, J.-F.; Sezestre, É.; Stolker, T.; Szulágyi, J.; van Boekel, R.; van der Plas, G.; Villenave, M.; Baruffolo, A.; Baudoz, P.; Le Mignant, D.; Maurel, D.; Ramos, J.; Weber, L.

2017-11-01

HD 169142 is an excellent target for investigating signs of planet-disk interaction due to previous evidence of gap structures. We perform J-band (˜1.2 μm) polarized intensity imaging of HD 169142 with VLT/SPHERE. We observe polarized scattered light down to 0.″16 (˜19 au) and find an inner gap with a significantly reduced scattered-light flux. We confirm the previously detected double-ring structure peaking at 0.″18 (˜21 au) and 0.″56 (˜66 au) and marginally detect a faint third gap at 0.″70-0.″73 (˜82-85 au). We explore dust evolution models in a disk perturbed by two giant planets, as well as models with a parameterized dust size distribution. The dust evolution model is able to reproduce the ring locations and gap widths in polarized intensity but fails to reproduce their depths. However, it gives a good match with the ALMA dust continuum image at 1.3 mm. Models with a parameterized dust size distribution better reproduce the gap depth in scattered light, suggesting that dust filtration at the outer edges of the gaps is less effective. The pileup of millimeter grains in a dust trap and the continuous distribution of small grains throughout the gap likely require more efficient dust fragmentation and dust diffusion in the dust trap. Alternatively, turbulence or charging effects might lead to a reservoir of small grains at the surface layer that is not affected by the dust growth and fragmentation cycle dominating the dense disk midplane. The exploration of models shows that extracting planet properties such as mass from observed gap profiles is highly degenerate. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO program 095.C-0273.

Searching for Dust around Hyper Metal Poor Stars

NASA Astrophysics Data System (ADS)

Venn, Kim A.; Puzia, Thomas H.; Divell, Mike; Côté, Stephanie; Lambert, David L.; Starkenburg, Else

2014-08-01

We examine the mid-infrared fluxes and spectral energy distributions for stars with iron abundances [Fe/H] <-5, and other metal-poor stars, to eliminate the possibility that their low metallicities are related to the depletion of elements onto dust grains in the formation of a debris disk. Six out of seven stars examined here show no mid-IR excesses. These non-detections rule out many types of circumstellar disks, e.g., a warm debris disk (T <= 290 K), or debris disks with inner radii <=1 AU, such as those associated with the chemically peculiar post-asymptotic giant branch spectroscopic binaries and RV Tau variables. However, we cannot rule out cooler debris disks, nor those with lower flux ratios to their host stars due to, e.g., a smaller disk mass, a larger inner disk radius, an absence of small grains, or even a multicomponent structure, as often found with the chemically peculiar Lambda Bootis stars. The only exception is HE0107-5240, for which a small mid-IR excess near 10 μm is detected at the 2σ level; if the excess is real and associated with this star, it may indicate the presence of (recent) dust-gas winnowing or a binary system.

A Model of Silicate Grain Nucleation and Growth in Circumstellar Outflows

NASA Technical Reports Server (NTRS)

Paquette, John A.; Ferguson, Frank T.; Nuth, Joseph A., III

2011-01-01

Based on its abundance, high bond energy, and recent measurements of its vapor pressure SiO is a natural candidate for dust nucleation in circumstellar outflows around asymptotic giant branch stars. In this paper, we describe a model of the nucleation and growth of silicate dust in such outflows. The sensitivity of the model to varying choices of poorly constrained chemical parameters is explored, and the merits of using scaled rather than classical nucleation theory are briefly considered, An elaboration of the model that includes magnesium and iron as growth species is then presented and discussed. The composition of the bulk of the grains derived from the model is consistent with olivines and pyroxenes, but somewhat metal-rich grains and very small, nearly pure SiO grains are also produced,

OISTER optical and near-infrared observations of the super-Chandrasekhar supernova candidate SN 2012dn: Dust emission from the circumstellar shell

NASA Astrophysics Data System (ADS)

Yamanaka, Masayuki; Maeda, Keiichi; Tanaka, Masaomi; Tominaga, Nozomu; Kawabata, Koji S.; Takaki, Katsutoshi; Kawabata, Miho; Nakaoka, Tatsuya; Ueno, Issei; Akitaya, Hiroshi; Nagayama, Takahiro; Takahashi, Jun; Honda, Satoshi; Omodaka, Toshihiro; Miyanoshita, Ryo; Nagao, Takashi; Watanabe, Makoto; Isogai, Mizuki; Arai, Akira; Itoh, Ryosuke; Ui, Takahiro; Uemura, Makoto; Yoshida, Michitoshi; Hanayama, Hidekazu; Kuroda, Daisuke; Ukita, Nobuharu; Yanagisawa, Kenshi; Izumiura, Hideyuki; Saito, Yoshihiko; Masumoto, Kazunari; Ono, Rikako; Noguchi, Ryo; Matsumoto, Katsura; Nogami, Daisaku; Morokuma, Tomoki; Oasa, Yumiko; Sekiguchi, Kazuhiro

2016-10-01

We present extensively dense observations of the super-Chandrasekhar supernova (SC SN) candidate SN 2012dn from -11 to +140 d after the date of its B-band maximum in the optical and near-infrared (NIR) wavelengths conducted through the OISTER ToO (Optical and Infrared Synergetic Telescopes for Education and Research Target of Opportunity) program. The NIR light curves and color evolutions up to 35 days after the B-band maximum provided an excellent match with those of another SC SN 2009dc, providing further support to the nature of SN 2012dn as an SC SN. We found that SN 2012dn exhibited strong excesses in the NIR wavelengths from 30 d after the B-band maximum. The H- and Ks-band light curves exhibited much later maximum dates at 40 and 70 d after the B-band maximum, respectively, compared with those of normal SNe Ia. The H- and Ks-band light curves subtracted by those of SN 2009dc displayed plateaued evolutions, indicating an NIR echo from the surrounding dust. The distance to the inner boundary of the dust shell is limited to 4.8-6.4 × 10-2 pc. No emission lines were found in its early phase spectra, suggesting that the ejecta-circumstellar material interaction could not occur. On the other hand, we found no signature that strongly supports the scenario of dust formation. The mass-loss rate of the pre-explosion system is estimated to be 10-6-10-5 M⊙ yr-1, assuming that the wind velocity of the system is 10-100 km s-1, which suggests that the progenitor of SN 2012dn could be a recurrent nova system. We conclude that the progenitor of this SC SN could be explained by the single-degenerate scenario.

Observational constraints for the circumstellar disk of the B[e] star CPD-52 9243

NASA Astrophysics Data System (ADS)

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

2012-12-01

Context. The formation and evolution of gas and dust environments around B[e] supergiants are still open issues. Aims: We intend to study the geometry, kinematics and physical structure of the circumstellar environment (CE) of the B[e] supergiant CPD-52 9243 to provide further insights into the underlying mechanism causing the B[e] phenomenon. Methods: The influence of the different physical mechanisms acting on the CE (radiation pressure, rotation, bi-stability or tidal forces) is somehow reflected in the shape and kinematic properties of the gas and dust regions (flaring, Keplerian, accretion or outflowing disks). To investigate these processes we mainly used quasi-simultaneous observations taken with high spatial resolution optical long-baseline interferometry (VLTI/MIDI), near-IR spectroscopy of CO bandhead features (Gemini/Phoenix and VLT/CRIRES) and optical spectra (CASLEO/REOSC). Results: High angular resolution interferometric measurements obtained with VLTI/MIDI provide strong support for the presence of a dusty disk(ring)-like structure around CPD-52 9243, with an upper limit for its inner edge of ~8 mas (~27.5 AU, considering a distance of 3.44 kpc to the star). The disk has an inclination angle with respect to the line of sight of 46 ± 7°. The study of CO first overtone bandhead evidences a disk structure in Keplerian rotation. The optical spectrum indicates a rapid outflow in the polar direction. Conclusions: The IR emission (CO and warm dust) indicates Keplerian rotation in a circumstellar disk while the optical line transitions of various species are consistent with a polar wind. Both structures appear simultaneously and provide further evidence for the proposed paradigms of the mass-loss in supergiant B[e] stars. The presence of a detached cold CO ring around CPD-52 9243 could be due to a truncation of the inner disk caused by a companion, located possibly interior to the disk rim, clearing the center of the system. More spectroscopic and

A Nonlocal Calculation of Circumstellar OH Masers

NASA Astrophysics Data System (ADS)

Collison, A. J.; Nedoluha, G. E.

1993-12-01

We present calculations for circumstellar OH masers which explicitly account for the nonlocal interaction throughout the masing region. Excitation temperatures and observed emission are calculated for all four ground state maser lines. All other transitions are treated using a modified Sobolev approximation. Calculations are performed within the context of a simplified dust/outflow model which provides the pumping conditions and their variation with radius. Total velocity relaxation is implicitly assumed in the calculations. We find general agreement with the qualitative results of earlier work (Collison & Nedoluha, ApJ, 10 Feb 94 issue) and agree with the conclusions of Alcock & Ross (1986, ApJ, 305, 837) who showed that observed profiles can not be produced by a smooth, spherically symmetric wind model of the outflow.

COSMIC DUST AGGREGATION WITH STOCHASTIC CHARGING

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

Matthews, Lorin S.; Hyde, Truell W.; Shotorban, Babak, E-mail: Lorin_Matthews@baylor.edu

2013-10-20

The coagulation of cosmic dust grains is a fundamental process which takes place in astrophysical environments, such as presolar nebulae and circumstellar and protoplanetary disks. Cosmic dust grains can become charged through interaction with their plasma environment or other processes, and the resultant electrostatic force between dust grains can strongly affect their coagulation rate. Since ions and electrons are collected on the surface of the dust grain at random time intervals, the electrical charge of a dust grain experiences stochastic fluctuations. In this study, a set of stochastic differential equations is developed to model these fluctuations over the surface ofmore » an irregularly shaped aggregate. Then, employing the data produced, the influence of the charge fluctuations on the coagulation process and the physical characteristics of the aggregates formed is examined. It is shown that dust with small charges (due to the small size of the dust grains or a tenuous plasma environment) is affected most strongly.« less

Dust Acoustic Wave Excitation in a Plasma with Warm Dust

NASA Astrophysics Data System (ADS)

Rosenberg, M.; Thomas, E., Jr.; Marcus, L.; Fisher, R.; Williams, J. D.; Merlino, R. L.

2008-11-01

Measurements of the dust acoustic wave dispersion relation in dusty plasmas formed in glow discharges at the University of Iowa [1] and Auburn University [2] have shown the importance of finite dust temperature effects. The effect of dust grains with large thermal speeds was taken into account using kinetic theory of the ion-dust streaming instability [3]. The results of analytic and numerical calculations of the dispersion relation based on the kinetic theory will be presented and compared with the experimental results. [1] E. Thomas, Jr., R. Fisher, and R. L. Merlino, Phys. Plasmas 14, 123701 (2007). [2] J. D. Williams, E. Thomas Jr., and L. Marcus, Phys. Plasmas 15, 043704 (2008). [3] M. Rosenberg, E. Thomas Jr., and R. L. Merlino, Phys. Plasmas 15, 073701 (2008).

Propierties of dust in circumstellar gas around Wolf-Rayet stars

NASA Astrophysics Data System (ADS)

Jiménez-Hernández, P.; Arthur, S. J.; Toalá, J. A.

2017-11-01

Using archive photometric observations from Herschel (70μm, 100μm, 160μm and 250μm), Spitzer (24μm) and WISE (22μm and 12μm) we obtained infrared SED's of nebulae around the Wolf-Rayet stars WR 124, WR 16 and WR 7. We used the photoionization code Cloudy to construct models of the nebulae, taking into account the spectrum of the central star and varying the density and distance of the photoionized shell as well as the size distribution and chemical composition of the dust grains mixed with the gas, and we compared the resulting SEDs with the observations in order to study the properties of the dust in these objects. We discuss whether the dust properties depend on the spectral type of the central star and the age of the nebulae.

From stars to dust: looking into a circumstellar disk through chondritic meteorites.

PubMed

Connolly, Harold C

2005-01-07

One of the most fundamental questions in planetary science is, How did the solar system form? In this special issue, astronomical observations and theories constraining circumstellar disks, their lifetimes, and the formation of planetary to subplanetary objects are reviewed. At present, it is difficult to observe what is happening within disks and to determine if another disk environment is comparable to the early solar system disk environment (called the protoplanetary disk). Fortunately, we have chondritic meteorites, which provide a record of the processes that operated and materials present within the protoplanetary disk.

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

NASA Technical Reports Server (NTRS)

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.

Radio Interferometric Detection of TiO and TiO_2 in VY Canis Majoris: "seeds" of Inorganic Dust Formation

NASA Astrophysics Data System (ADS)

Brunken, S.; Muller, H. S. P.; Kaminski, T.; Menten, K. M.; Gott-Lieb, C. A.; Patel, N. A.; Young, K. H.; McCarthy, M. C.; Winters, J. M.; Decin, L.

2013-06-01

Circumstellar envelopes around late-type stars harbour a rich variety of molecular gas and copious amounts of dust, originating from the mass-loss of the central star during the asymptotic giant branch (AGB) or the red supergiant phase. The formation of dust in these objects, in particular the first nucleation stages out of gas phase molecules, is still poorly understood. Here we report the first detection of pure rotational transitions of the two simplest titanium oxides, TiO and TiO_2, towards the oxygen-rich red supergiant VY Canis Majoris (VY CMa). This actually represents the first secure identification of TiO_2 in space. Observations of several rotational emission lines of both species with the Submillimeter Array (SMA) in the 345 GHz-band and with the IRAM Plateau de Bure Interferometer (PdBI) around 220 GHz confirm the presence of these refractory species in the cool (<1000 K) circumstellar envelope in a region several times the size of the dust formation zone. The role of Ti oxides as "seeds" of inorganic dust formation in oxygen-rich circumstellar envelopes will be discussed in view of the present observations.

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

NASA Astrophysics Data System (ADS)

Hony, S.; Tielens, A. G. G. M.; Waters, L. B. F. M.; de Koter, A.

2003-04-01

We present a detailed study of the circumstellar envelope of the post-asymptotic giant branch ``21 mu m 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'' radius around the central star. This shell originates from a short period during which the mass-loss rate exceeded 10-4 Msun/yr. We find that the strength of the ``21'' mu m 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 strength of the feature. Other nano-crystalline metal carbides should be considered as well. We find that hydrogenated amorphous carbon in radiative equilibrium with the local radiation field does not reach a high enough temperature to explain the strength of the 3.3-3.4 and 6-9 mu m hydrocarbon features relative to the 11-17 mu m hydrocarbon features. We propose that the carriers of these hydrocarbon features are not in radiative equilibrium but are transiently heated to high temperature. We find that 2 per cent of the dust mass is required to explain the strength of the ``30'' mu m feature, which fits well within the measured atmospheric abundance of Mg and S. This further strengthens the MgS identification of the ``30'' mu m feature. Based on observations taken at the European Southern Observatory, La Silla, Chile and observation obtained with ISO, an ESA project with instruments funded by ESA Member states (especially the PI countries: France, Germany, The Netherlands and

Studies of Young, Star-forming Circumstellar Disks

NASA Astrophysics Data System (ADS)

Bae, Jaehan

2017-08-01

Disks of gas and dust around forming stars - circumstellar disks - last only a few million years. This is a very small fraction of the entire lifetime of Sun-like stars, several billion years. Nevertheless, by the time circumstellar disks dissipate stars complete building up their masses, giant planets finish accreting gas, and terrestrial bodies are nearly fully grown and ready for their final assembly to become planets. Understanding the evolution of circumstellar disks are thus crucial in many contexts. Using numerical simulations as the primary tool, my thesis has focused on the studies of various physical processes that can occur throughout the lifetime of circumstellar disks, from their formation to dispersal. Chapters 2, 3, and 4 emphasize the importance of early evolution, during which time a forming star-disk system obtains mass from its natal cloud: the infall phase. In Chapter 2 and 3, I have modeled episodic outbursts of accretion in protostellar systems resulting from disk instabilities - gravitational instability and magnetorotational instability. I showed that outbursts occur preferentially during the infall phase, because the mass addition provides more favorable conditions for gravitational instability to initiate the outburst cycle, and that forming stars build up a significant fraction of their masses through repeated short-lived, episodic outbursts. The infall phase can also be important for the formation of planets. Recent ALMA observations revealed sets of bright and dark rings in circumstellar disks of young, forming stars, potentially indicating early formation of planets. In Chapter 4, I showed that infall streams can create radial pressure bumps near the outer edge of the mass landing on the disk, from which vortices can form, collecting solid particles very efficiently to make initial seeds of planets. The next three chapters highlight the role of planets in setting the observational appearance and the evolution of circumstellar disks

Investigations of the Formation of Carbon Grains in Circumstellar Outflows

NASA Technical Reports Server (NTRS)

Contreras, Cesar; Salama, Farid

2013-01-01

The study of formation and destruction processes of cosmic dust is essential to understand and to quantify the budget of extraterrestrial organic molecules. Although dust with all its components plays an important role in the evolution of interstellar chemistry and in the formation of organic molecules, little is known on the formation and destruction processes of carbonaceous dust. PAHs are important chemical building blocks of interstellar dust. They are detected in interplanetary dust particles and in meteoritic samples. Additionally, observational, laboratory, and theoretical studies have shown that PAHs, in their neutral and ionized forms, are an important, ubiquitous component of the interstellar medium. Also, the formation of PAHs from smaller molecules has not been extensively studied. Therefore, it is imperative that laboratory experiments be conducted to study the dynamic processes of carbon grain formation from PAH precursors. Studies of interstellar 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 under conditions that simulate interstellar and circumstellar environments. The species formed in the pulsed discharge nozzle (PDN) plasma source are detected and characterized with a high-sensitivity cavity ringdown spectrometer (CRDS) coupled to a Reflectron time-of-flight mass spectrometer (ReTOF-MS), thus providing both spectroscopic and ion mass information in-situ. We report the first set of measurements obtained in these experiments and identify the species present in the experiments and the ions that are formed in the plasma process. From these unique measurements, we derive information on the size and the structure of interstellar dust grain particles, the growth and the destruction processes of interstellar dust and the resulting budget of extraterrestrial organic molecules.

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

NASA Astrophysics Data System (ADS)

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

2013-03-01

Context. Warm debris disks are a sub-sample of the large population of debris disks, and display excess emission in the mid-infrared. Around solar-type stars, very few objects (~2% of all debris disks) show emission features in mid-IR spectroscopic observations that are attributed to small, warm silicate dust grains. The origin of this warm dust could be explained either by a recent catastrophic collision between several bodies or by transport from an outer belt similar to the Kuiper belt in the solar system. Aims: We present and analyze new far-IR Herschel/PACS photometric observations, supplemented by new and archival ground-based data in the mid-IR (VLTI/MIDI and VLT/VISIR), for one of these rare systems: the 10-16 Myr old debris disk around HD 113766 A. We improve an existing model to account for these new observations. Methods: We implemented the contribution of an outer planetesimal belt in the Debra code, and successfully used it to model the spectral energy distribution (SED) as well as complementary observations, notably MIDI data. We better constrain the spatial distribution of the dust and its composition. Results: We underline the limitations of SED modeling and the need for spatially resolved observations. We improve existing models and increase our understanding of the disk around HD 113766 A. We find that the system is best described by an inner disk located within the first AU, well constrained by the MIDI data, and an outer disk located between 9-13 AU. In the inner dust belt, our previous finding of Fe-rich crystalline olivine grains still holds. We do not observe time variability of the emission features over at least an eight-year time span in an environment subjected to strong radiation pressure. Conclusions: The time stability of the emission features indicates that μm-sized dust grains are constantly replenished from the same reservoir, with a possible depletion of sub- μm-sized grains. We suggest that the emission features may arise from

Dust in a Type Ia Supernova Progenitor: Spitzer Spectroscopy of Kepler's Supernova Remnant

NASA Technical Reports Server (NTRS)

Williams, Brian J.; Borkowski, Kazimierz; Reynolds, Stephen P.; Ghavamian, Parviz; Blair, William P.; Long, Knox S.; Sankrit, Ravi

2012-01-01

Characterization of the relatively poorly-understood progenitor systems of Type Ia supernovae is of great importance in astrophysics, particularly given the important cosmological role that these supernovae play. Kepler's Supernova Remnant, the result of a Type Ia supernova, shows evidence for an interaction with a dense circumstellar medium (CSM), suggesting a single-degenerate progenitor system. We present 7.5-38 micron IR spectra of the remnant, obtained with the Spitzer Space Telescope, dominated by emission from warm dust. Broad spectral features at 10 and 18 micron, consistent with various silicate particles, are seen throughout. These silicates were likely formed in the stellar outflow from the progenitor system during the AGB stage of evolution, and imply an oxygen-rich chemistry. In addition to silicate dust, a second component, possibly carbonaceous dust, is necessary to account for the short-wavelength IRS and IRAC data. This could imply a mixed chemistry in the atmosphere of the progenitor system. However, non-spherical metallic iron inclusions within silicate grains provide an alternative solution. Models of collisionally-heated dust emission from fast shocks (> 1000 km/s) propagating into the CSM can reproduce the majority of the emission associated with non-radiative filaments, where dust temperatures are approx 80-100 K, but fail to account for the highest temperatures detected, in excess of 150 K. We find that slower shocks (a few hundred km/s) into moderate density material (n(sub o) approx 50-100 / cubic cm) are the only viable source of heating for this hottest dust. We confirm the finding of an overall density gradient, with densities in the north being an order of magnitude greater than those in the south.

HIRAS images of fossil dust shells around AGB stars

NASA Technical Reports Server (NTRS)

Waters, L. B. F. M.; Kester, Do J. M.; Bontekoe, Tj. Romke; Loup, C.

1994-01-01

We present high resolution HIRAS 60 and 100 micron images of AGB stars surrounded by fossil dust shells. Resolving the extended emission of the circumstellar dust allows a determination of the mass loss history of the star. We show that the geometry of the 60 micron emission surrounding HR 3126 agrees well with that of the optical reflection nebula. The emission around the carbon star U Hya is resolved into a central point source and a ring of dust, and the mass loss rate in the detached shell is 70 times higher than the current mass loss rate.

Dust devils on Mars

NASA Technical Reports Server (NTRS)

Thomas, P. G.; Gierasch, P.

1985-01-01

Large columns of dust have been discovered rising above plains on Mars. The storms are probably analogous to terrestrial dust devils, but their size indicates that they are more similar to tornadoes in intensity. They occur at locations where the soil has been strongly warmed by the Sun, and there the surface is smooth and fine grained. These are the same conditions that favor dust devils on Earth. Warm gas from the lowest atmospheric layer converges and rises in a thin column, with intense swirl developing at the edge of the column. In one area a mosaic of Viking images shows 97 vortices in a three day period. This represents a density of vortices of about one in each 900 square kilometers. Thus, these dust devils may be important in moving dust or starting over dust storms.

Interstellar and Ejecta Dust in the Cas A Supernova Remnant

NASA Technical Reports Server (NTRS)

Arendt, Richard G.; Dwek, Eli; Kober, Gladys; Rho, Jonghee; Hwang, Una

2013-01-01

The ejecta of the Cas A supernova remnant has a complex morphology, consisting of dense fast-moving line emitting knots and diffuse X-ray emitting regions that have encountered the reverse shock, as well as more slowly expanding, unshocked regions of the ejecta. Using the Spitzer 5-35 micron IRS data cube, and Herschel 70, 100, and 160 micron PACS data, we decompose the infrared emission from the remnant into distinct spectral components associated with the different regions of the ejecta. Such decomposition allows the association of different dust species with ejecta layers that underwent distinct nuclear burning histories, and determination of the dust heating mechanisms. Our decomposition identified three characteristic dust spectra. The first, most luminous one, exhibits strong emission features at approx. 9 and 21 micron, and a weaker 12 micron feature, and is closely associated with the ejecta knots that have strong [Ar II] 6.99 micron and [Ar III] 8.99 micron emission lines. The dust features can be reproduced by magnesium silicate grains with relatively low MgO-to-SiO2 ratios. A second, very different dust spectrum that has no indication of any silicate features, is best fit by Al2O3 dust and is found in association with ejecta having strong [Ne II] 12.8 micron and [Ne III] 15.6 micron emission lines. A third characteristic dust spectrum shows features that best matched by magnesium silicates with relatively high MgO-to-SiO2 ratio. This dust is primarily associated with the X-ray emitting shocked ejecta and the shocked interstellar/circumstellar material. All three spectral components include an additional featureless cold dust component of unknown composition. Colder dust of indeterminate composition is associated with [Si II] 34.8 micron emission from the interior of the SNR, where the reverse shock has not yet swept up and heated the ejecta. The dust mass giving rise to the warm dust component is about approx. 0.1solar M. However, most of the dust mass

A search for ultraviolet circumstellar gas absorption features in alpha Piscis Austrinus (Fomalhaut), a possible Beta Pictoris-like system

NASA Technical Reports Server (NTRS)

Cheng, K.-P.; Bruhweiler, Fred C.; Kondo, Yoji

1994-01-01

Archival high-dispersion International Ultraviolet Explorer (IUE) spectra have been used to search for circumstellar gas absorption features in alpha PsA (A3 V), a nearby (6.7 pc) proto-planetary system candidate. Recent sub-millimeter mapping observations around the region of alpha PsA indicate a spatially resolved dust disk like the one seen around Beta Pic. To determine how closely this putative disk resembles that of Beta Pic, we have searched for signatures of circumstellar gaseous absorption in all the available IUE high-dispersion data of alpha PsA. Examination of co-added IUE spectra shows weak circumstellar absorptions from excited levels in the resonance multiplet of Fe II near 2600 A. We also conclude that the sharp C I feature near 1657 A, previously identified as interstellar absorption toward alpha PsA, likely has a circumstellar origin. However, because the weakness of these absorption features, we will consider the presence of circumstellar gas as tentative and should be verified by using the Goddard High-Resolution Spectrograph aboard the Hubble Space Telescope. No corresponding circumstellar absorption is detected in higher ionization Fe III and Al III. Since the collisionally ionized nonphotospheric Al III resonance absorption seen in Beta Pic is likely formed close to the stellar surface, its absence in the UV spectra of alpha PsA could imply that, in contrast with Beta Pic, there is no active gaseous disk infall onto the central star. In the alpha PsA gaseous disk, if we assume a solar abundance for iron and all the iron is in the form of Fe II, plus a disk temperature of 5000 K, the Fe II UV1 absorption at 2611.8743 A infers a total hydrogen column density along the line of sight through the circumstellar disk of N(H) approximately equals 3.8 x 10(exp 17)/cm.

Mid-Infrared Imaging of a Circumstellar Disk around HR 4796: Mapping the Debris of Planetary Formation

NASA Astrophysics Data System (ADS)

Koerner, D. W.; Ressler, M. E.; Werner, M. W.; Backman, D. E.

1998-08-01

We report the discovery of a circumstellar disk around the young A0 star HR 4796 in thermal infrared imaging carried out at the W. M. Keck Observatory. By fitting a model of the emission from a flat dusty disk to an image at λ=20.8 μm, we derive a disk inclination, i=72deg+6deg-9deg from face-on, with the long axis of emission at P.A. 28deg+/-6deg. The intensity of emission does not decrease with radius, as expected for circumstellar disks, but increases outward from the star, peaking near both ends of the elongated structure. We simulate this appearance by varying the inner radius in our model and find an inner hole in the disk with radius Rin=55+/-15 AU. This value corresponds to the radial distance of our own Kuiper belt and may suggest a source of dust in the collision of cometesimals. By contrast with the appearance at 20.8 μm, excess emission at λ=12.5 μm is faint and concentrated at the stellar position. Similar emission is also detected at 20.8 μm in residual subtraction of the best-fit model from the image. The intensity and ratio of flux densities at the two wavelengths could be accounted for by a tenuous dust component that is confined within a few AU of the star with mean temperature of a few hundred degrees K, similar to that of zodiacal dust in our own solar system. The morphology of dust emission from HR 4796 (age 10 Myr) suggests that its disk is in a transitional planet-forming stage, between that of massive gaseous protostellar disks and more tenuous debris disks such as the one detected around Vega.

What Sets the Radial Locations of Warm Debris Disks?

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

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

The architectures of debris disks encode the history of planet formation in these systems. Studies of debris disks via their spectral energy distributions (SEDs) have found infrared excesses arising from cold dust, warm dust, or a combination of the two. The cold outer belts of many systems have been imaged, facilitating their study in great detail. Far less is known about the warm components, including the origin of the dust. The regularity of the disk temperatures indicates an underlying structure that may be linked to the water snow line. If the dust is generated from collisions in an exo-asteroid belt,more » the dust will likely trace the location of the water snow line in the primordial protoplanetary disk where planetesimal growth was enhanced. If instead the warm dust arises from the inward transport from a reservoir of icy material farther out in the system, the dust location is expected to be set by the current snow line. We analyze the SEDs of a large sample of debris disks with warm components. We find that warm components in single-component systems (those without detectable cold components) follow the primordial snow line rather than the current snow line, so they likely arise from exo-asteroid belts. While the locations of many warm components in two-component systems are also consistent with the primordial snow line, there is more diversity among these systems, suggesting additional effects play a role.« less

Dust discs around low-mass main-sequence stars

NASA Technical Reports Server (NTRS)

Wolstencroft, R. D.; Walker, Helen J.

1988-01-01

The current understanding of the formation of circumstellar disks as a natural accompaniment to the process of low-mass star formation is examined. Models of the thermal emission from the dust disks around the prototype stars Alpha Lyr, Alpha PsA, Beta Pic, and Epsilon Eri are discussed, which indicate that the central regions of three of these disks are almost devoid of dust within radii ranging between 17 and 26 AU, with the temperature of the hottest zone lying between about 115 and 210 K. One possible explanation of the dust-free zones is the presence of a planet at the inner boundary of each cloud which sweeps up grains crossing its orbit.

ALMA Maps of Dust and Warm Dense Gas Emission in the Starburst Galaxy IC 5179

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

Zhao Yinghe; Lu, Nanyao; Xu, C. Kevin

We present our high-resolution (0.″15 × 0.″13, ∼34 pc) observations of the CO (6−5) line emission, which probes the warm and dense molecular gas, and the 434 μ m dust continuum emission in the nuclear region of the starburst galaxy IC 5179, conducted with the Atacama Large Millimeter Array (ALMA). The CO (6−5) emission is spatially distributed in filamentary structures with many dense cores and shows a velocity field that is characteristic of a circumnuclear rotating gas disk, with 90% of the rotation speed arising within a radius of ≲150 pc. At the scale of our spatial resolution, the COmore » (6−5) and dust emission peaks do not always coincide, with their surface brightness ratio varying by a factor of ∼10. This result suggests that their excitation mechanisms are likely different, as further evidenced by the southwest to northeast spatial gradient of both CO-to-dust continuum ratio and Pa- α equivalent width. Within the nuclear region (radius ∼ 300 pc) and with a resolution of ∼34 pc, the CO line flux (dust flux density) detected in our ALMA observations is 180 ± 18 Jy km s{sup −1} (71 ± 7 mJy), which accounts for 22% (2.4%) of the total value measured by Herschel .« less

IRAS observations of a large circumstellar dust shell around W Hydrae

NASA Technical Reports Server (NTRS)

Hawkins, G. W.

1990-01-01

IRAS observations at 60 and 100 microns reveal a large 30-40-arcmin (about 1-pc) diameter dust shell centered on the oxygen-rich red giant W Hya. Except for SNRs, this is the largest mass-loss envelope, in apparent diameter, known around any evolved star, including PN. W Hya's radiation field, stronger than the interstellar radiation field in the outer envelope, is sufficient to heat dust grains with IR emissivity proportional to lambda exp -1.2 to temperatures of about 40 K implied by the ratio of intensities at 60 and 100 microns.

Warm water vapour in the sooty outflow from a luminous carbon star.

PubMed

Decin, L; Agúndez, M; Barlow, M J; Daniel, F; Cernicharo, J; Lombaert, R; De Beck, E; Royer, P; Vandenbussche, B; Wesson, R; Polehampton, E T; Blommaert, J A D L; De Meester, W; Exter, K; Feuchtgruber, H; Gear, W K; Gomez, H L; Groenewegen, M A T; Guélin, M; Hargrave, P C; Huygen, R; Imhof, P; Ivison, R J; Jean, C; Kahane, C; Kerschbaum, F; Leeks, S J; Lim, T; Matsuura, M; Olofsson, G; Posch, T; Regibo, S; Savini, G; Sibthorpe, B; Swinyard, B M; Yates, J A; Waelkens, C

2010-09-02

The detection of circumstellar water vapour around the ageing carbon star IRC +10216 challenged the current understanding of chemistry in old stars, because water was predicted to be almost absent in carbon-rich stars. Several explanations for the water were postulated, including the vaporization of icy bodies (comets or dwarf planets) in orbit around the star, grain surface reactions, and photochemistry in the outer circumstellar envelope. With a single water line detected so far from this one carbon-rich evolved star, it is difficult to discriminate between the different mechanisms proposed. Here we report the detection of dozens of water vapour lines in the far-infrared and sub-millimetre spectrum of IRC +10216 using the Herschel satellite. This includes some high-excitation lines with energies corresponding to approximately 1,000 K, which can be explained only if water is present in the warm inner sooty region of the envelope. A plausible explanation for the warm water appears to be the penetration of ultraviolet photons deep into a clumpy circumstellar envelope. This mechanism also triggers the formation of other molecules, such as ammonia, whose observed abundances are much higher than hitherto predicted.

Carriers of the mid-IR emission bands in PNe reanalysed. Evidence of a link between circumstellar and interstellar aromatic dust

NASA Astrophysics Data System (ADS)

Joblin, C.; Szczerba, R.; Berné, O.; Szyszka, C.

2008-10-01

Context: It has been shown that the diversity of the aromatic emission features can be rationalized into different classes of objects, in which differences between circumstellar and interstellar matter are emphasised. Aims: We probe the links between the mid-IR emitters observed in planetary nebulae (PNe) and their counterparts in the interstellar medium in order to probe a scenario in which the latter have been formed in the circumstellar environment of evolved stars. Methods: The mid-IR (6-14 μm) emission spectra of PNe and compact H II regions were analysed on the basis of previous work on photodissociation regions (PDRs). Galactic, Large Magellanic Cloud (LMC), and Small Magellanic Cloud (SMC) objects were considered in our sample. Results: We show that the mid-IR emission of PNe can be decomposed as the sum of six components. Some components made of polycyclic aromatic hydrocarbon (PAH) and very small grain (VSG) populations are similar to those observed in PDRs. Others are fitted in an evolutionary scenario involving the destruction of the aliphatic component observed in the post-AGB stage, as well as strong processing of PAHs in the extreme conditions of PNe that leads to a population of very large ionized PAHs. This species called PAHx are proposed as the carriers of a characteristic band at 7.90 μm. This band can be used as part of diagnostics that identify PNe in nearby galaxies and is also observed in galactic compact H II regions. Conclusions: These results support the formation of the aromatic very small dust particles in the envelopes of evolved stars, in the Milky Way, as well as in the LMC and SMC, and their subsequent survival in the interstellar medium. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the

Imaging the asymmetric dust shell around CI Cam with long baseline optical interferometry

NASA Astrophysics Data System (ADS)

Thureau, N. D.; Monnier, J. D.; Traub, W. A.; Millan-Gabet, R.; Pedretti, E.; Berger, J.-P.; Garcia, M. R.; Schloerb, F. P.; Tannirkulam, A.-K.

2009-09-01

We present the first high angular resolution observation of the B[e] star/X-ray transient object CI Cam, performed with the two-telescope Infrared Optical Telescope Array (IOTA), its upgraded three-telescope version (IOTA3T) and the Palomar Testbed Interferometer (PTI). Visibilities and closure phases were obtained using the IONIC-3 integrated optics beam combiner. CI Cam was observed in the near-infrared H and K spectral bands, wavelengths well suited to measure the size and study the geometry of the hot dust surrounding CI Cam. The analysis of the visibility data over an 8yr period from soon after the 1998 outburst to 2006 shows that the dust visibility has not changed over the years. The visibility data show that CI Cam is elongated which confirms the disc-shape of the circumstellar environment and totally rules out the hypothesis of a spherical dust shell. Closure phase measurements show direct evidence of asymmetries in the circumstellar environment of CI Cam and we conclude that the dust surrounding CI Cam lies in an inhomogeneous disc seen at an angle. The near-infrared dust emission appears as an elliptical skewed Gaussian ring with a major axis a = 7.58 +/- 0.24mas, an axis ratio r = 0.39 +/- 0.03 and a position angle θ = 35° +/- 2°.

COMPUTING THE DUST DISTRIBUTION IN THE BOW SHOCK OF A FAST-MOVING, EVOLVED STAR

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

Van Marle, A. J.; Meliani, Z.; Keppens, R.

2011-06-20

We study the hydrodynamical behavior occurring in the turbulent interaction zone of a fast-moving red supergiant star, where the circumstellar and interstellar material collide. In this wind-interstellar-medium collision, the familiar bow shock, contact discontinuity, and wind termination shock morphology form, with localized instability development. Our model includes a detailed treatment of dust grains in the stellar wind and takes into account the drag forces between dust and gas. The dust is treated as pressureless gas components binned per grain size, for which we use 10 representative grain size bins. Our simulations allow us to deduce how dust grains of varyingmore » sizes become distributed throughout the circumstellar medium. We show that smaller dust grains (radius <0.045 {mu}m) tend to be strongly bound to the gas and therefore follow the gas density distribution closely, with intricate fine structure due to essentially hydrodynamical instabilities at the wind-related contact discontinuity. Larger grains which are more resistant to drag forces are shown to have their own unique dust distribution, with progressive deviations from the gas morphology. Specifically, small dust grains stay entirely within the zone bound by shocked wind material. The large grains are capable of leaving the shocked wind layer and can penetrate into the shocked or even unshocked interstellar medium. Depending on how the number of dust grains varies with grain size, this should leave a clear imprint in infrared observations of bow shocks of red supergiants and other evolved stars.« less

Dust grains from the heart of supernovae

NASA Astrophysics Data System (ADS)

Bocchio, M.; Marassi, S.; Schneider, R.; Bianchi, S.; Limongi, M.; Chieffi, A.

2016-03-01

Dust grains are classically thought to form in the winds of asymptotic giant branch (AGB) stars. However, there is increasing evidence today for dust formation in supernovae (SNe). To establish the relative importance of these two classes of stellar sources of dust, it is important to know the fraction of freshly formed dust in SN ejecta that is able to survive the passage of the reverse shock and be injected in the interstellar medium. With this aim, we have developed a new code, GRASH_Rev, that allows following the dynamics of dust grains in the shocked SN ejecta and computing the time evolution of the mass, composition, and size distribution of the grains. We considered four well-studied SNe in the Milky Way and Large Magellanic Cloud: SN 1987A, CasA, the Crab nebula, and N49. These sources have been observed with both Spitzer and Herschel, and the multiwavelength data allow a better assessment the mass of warm and cold dust associated with the ejecta. For each SN, we first identified the best explosion model, using the mass and metallicity of the progenitor star, the mass of 56Ni, the explosion energy, and the circumstellar medium density inferred from the data. We then ran a recently developed dust formation model to compute the properties of freshly formed dust. Starting from these input models, GRASH_Rev self-consistently follows the dynamics of the grains, considering the effects of the forward and reverse shock, and allows predicting the time evolution of the dust mass, composition, and size distribution in the shocked and unshocked regions of the ejecta. All the simulated models aagree well with observations. Our study suggests that SN 1987A is too young for the reverse shock to have affected the dust mass. Hence the observed dust mass of 0.7-0.9 M⊙ in this source can be safely considered as indicative of the mass of freshly formed dust in SN ejecta. Conversely, in the other three SNe, the reverse shock has already destroyed between 10-40% of the

The IRS 1 circumstellar disk, and the origin of the jet and CO outflow in B5

NASA Technical Reports Server (NTRS)

Langer, W. D.; Velusamy, T.; Xie, T.; Levin, S. M. (Principal Investigator)

1996-01-01

We report the discovery of the inner edge of the high velocity CO outflow associated with the bipolar jet originating from IRS 1 in Barnard 5 and the first ever resolution of its circumstellar disk in the 2.6 mm dust continuum and C18O. From high spatial resolution observations made with the Owens Valley Millimeter Array we are able to locate the origin of the outflow to within approximately 500 AU on either side of IRS 1 and apparently at the edge of, or possibly within, its circumstellar disk. The orientation of the continuum disk is perpendicular to the highly collimated jet outflow recently seen in optical emission at much farther distances. The disk has been detected in C18O giving a disk mass approximately 0.16 M (solar). Our HCO+ and HCN maps indicate significant chemical differentiation in the circumstellar region on small scales with HCO+ tracing an extended disk of material. The 12CO interferometer maps of the outflow show two conelike features originating at IRS 1, the blue one fanning open to the northeast and the red one to the southwest. The vertices of the cones are on either side of the circumstellar disk and have a projected opening angle of about 90 degrees. The intrinsic opening angle is in the range of 60 degrees-90 degrees which leads to significant interaction between outflow and infall.

Eolian Dust and the Origin of Sedimentary Chert

USGS Publications Warehouse

Cecil, C. Blaine

2004-01-01

This paper proposes an alternative model for the primary source of silica contained in bedded sedimentary chert. The proposed model is derived from three principal observations as follows: (1) eolian processes in warm-arid climates produce copious amounts of highly reactive fine-grained quartz particles (dust), (2) eolian processes in warm-arid climates export enormous quantities of quartzose dust to marine environments, and (3) bedded sedimentary cherts generally occur in marine strata that were deposited in warm-arid paleoclimates where dust was a potential source of silica. An empirical integration of these observations suggests that eolian dust best explains both the primary and predominant source of silica for most bedded sedimentary cherts.

The WIRED Survey. IV. New Dust Disks from the McCook & Sion White Dwarf Catalog

NASA Technical Reports Server (NTRS)

Hoard, D.W.; Debes, John H.; Wachter, Stefanie; Leisawitz, David T.; Cohen, Martin

2013-01-01

We have compiled photometric data from the Wide-field Infrared Survey Explorer All Sky Survey and other archival sources for the more than 2200 objects in the original McCook & Sion Catalog of Spectroscopically Identified White Dwarfs. We applied color-selection criteria to identify 28 targets whose infrared spectral energy distributions depart from the expectation for the white dwarf photosphere alone. Seven of these are previously known white dwarfs with circumstellar dust disks, five are known central stars of planetary nebulae, and six were excluded for being known binaries or having possible contamination of their infrared photometry. We fit white dwarf models to the spectral energy distributions of the remaining ten targets, and find seven new candidates with infrared excess suggesting the presence of a circumstellar dust disk. We compare the model dust disk properties for these new candidates with a comprehensive compilation of previously published parameters for known white dwarfs with dust disks. It is possible that the current census of white dwarfs with dust disks that produce an excess detectable at K-band and shorter wavelengths is close to complete for the entire sample of known WDs to the detection limits of existing near-IR all-sky surveys. The white dwarf dust disk candidates now being found using longer wavelength infrared data are drawn from a previously underrepresented region of parameter space, in which the dust disks are overall cooler, narrower in radial extent, and/or contain fewer emitting grains.

Magnetically aligned dust and SiO maser polarisation in the envelope of the red supergiant VY Canis Majoris

NASA Astrophysics Data System (ADS)

Vlemmings, W. H. T.; Khouri, T.; Martí-Vidal, I.; Tafoya, D.; Baudry, A.; Etoka, S.; Humphreys, E. M. L.; Jones, T. J.; Kemball, A.; O'Gorman, E.; Pérez-Sánchez, A. F.; Richards, A. M. S.

2017-07-01

Aims: Polarisation observations of circumstellar dust and molecular (thermal and maser) lines provide unique information about dust properties and magnetic fields in circumstellar envelopes of evolved stars. Methods: We use Atacama Large Millimeter/submillimeter Array (ALMA) Band 5 science verification observations of the red supergiant VY CMa to study the polarisation of SiO thermal/maser lines and dust continuum at 1.7 mm wavelength. We analyse both linear and circular polarisation and derive the magnetic field strength and structure, assuming the polarisation of the lines originates from the Zeeman effect, and that of the dust originates from aligned dust grains. We also discuss other effects that could give rise to the observed polarisation. Results: We detect, for the first time, significant polarisation ( 3%) of the circumstellar dust emission at millimeter wavelengths. The polarisation is uniform with an electric vector position angle of 8°. Varying levels of linear polarisation are detected for the J = 4 - 328SiO v = 0, 1, 2, and 29SiO v = 0, 1 lines, with the strongest polarisation fraction of 30% found for the 29SiO v = 1 maser. The linear polarisation vectors rotate with velocity, consistent with earlier observations. We also find significant (up to 1%) circular polarisation in several lines, consistent with previous measurements. We conclude that the detection is robust against calibration and regular instrumental errors, although we cannot yet fully rule out non-standard instrumental effects. Conclusions: Emission from magnetically aligned grains is the most likely origin of the observed continuum polarisation. This implies that the dust is embedded in a magnetic field >13 mG. The maser line polarisation traces the magnetic field structure. The magnetic field in the gas and dust is consistent with an approximately toroidal field configuration, but only higher angular resolution observations will be able to reveal more detailed field structure. If the

Coronagraphic imaging of circumstellar material around evolved massive stars

NASA Astrophysics Data System (ADS)

Lomax, Jamie R.; Levesque, Emily; Wisniewski, John

2018-01-01

While many astronomical subfields (e.g. the solar, exoplanet, and disk communities) have been using coronagraphy to combat contrast ratio problems for years, the use of coronagraphic imaging techniques to probe the circumstellar environments of massive stars has been surprisingly underutilized. While current extreme adaptive optics coronagraphic imaging systems (e.g. GPI on Gemini South, SPHERE at the VLT, and SCExAO at Subaru) were built for the sole purpose of detecting exoplanets, their ability to provide large contrast ratios and small inner working angles means they can detect gas, dust, and companions that are closer to the central star than ever before. In this poster we present pilot studies of evolved massive stars using several coronagraphic imaging systems and summarize potential science gains this technique might provide.

ALMA Maps of Dust and Warm Dense Gas Emission in the Starburst Galaxy IC 5179

NASA Astrophysics Data System (ADS)

Zhao, Yinghe; Lu, Nanyao; Díaz-Santos, Tanio; Xu, C. Kevin; Gao, Yu; Charmandaris, Vassilis; van der Werf, Paul; Zhang, Zhi-Yu; Cao, Chen

2017-08-01

We present our high-resolution (0.″15 × 0.″13, ˜34 pc) observations of the CO (6-5) line emission, which probes the warm and dense molecular gas, and the 434 μm dust continuum emission in the nuclear region of the starburst galaxy IC 5179, conducted with the Atacama Large Millimeter Array (ALMA). The CO (6-5) emission is spatially distributed in filamentary structures with many dense cores and shows a velocity field that is characteristic of a circumnuclear rotating gas disk, with 90% of the rotation speed arising within a radius of ≲150 pc. At the scale of our spatial resolution, the CO (6-5) and dust emission peaks do not always coincide, with their surface brightness ratio varying by a factor of ˜10. This result suggests that their excitation mechanisms are likely different, as further evidenced by the southwest to northeast spatial gradient of both CO-to-dust continuum ratio and Pa-α equivalent width. Within the nuclear region (radius ˜ 300 pc) and with a resolution of ˜34 pc, the CO line flux (dust flux density) detected in our ALMA observations is 180 ± 18 Jy km s-1 (71 ± 7 mJy), which accounts for 22% (2.4%) of the total value measured by Herschel. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

Dust grains from the heart of supernovae

NASA Astrophysics Data System (ADS)

Bocchio, Marco; Marassi, Stefania; Schneider, Raffaella; Bianchi, Simone; Limongi, Marco; Chieffi, A.

2016-06-01

Dust grains are classically thought to form in the winds of asymptotic giant branch (AGB) stars. However, there is increasing evidence today for dust formation in supernovae (SNe). To establish the relative importance of these two classes of stellar sources of dust, it is important to know the fraction of freshly formed dust in SN ejecta that is able to survive the passage of the reverse shock and be injected in the interstellar medium. We have developed a new code (GRASH_Rev) which follows the newly-formed dust evolution throughout the supernova explosion until the merging of the forward shock with the circumstellar ISM. We have considered four well studied SNe in the Milky Way and Large Magellanic Cloud: SN1987A, CasA, the Crab Nebula, and N49. For all the simulated models, we find good agreement with observations and estimate that between 1 and 8% of the observed mass will survive, leading to a SN dust production rate of (3.9± 3.7)×10^(-4) MM_{⊙})/yr in the Milky Way. This value is one order of magnitude larger than the dust production rate by AGB stars but insufficient to counterbalance the dust destruction by SNe, therefore requiring dust accretion in the gas phase.

Submillimeter Imaging of Dust Around Main Sequence Stars

NASA Technical Reports Server (NTRS)

Jewitt, David

1998-01-01

This grant was to image circumstellar dust disks surrounding main-sequence stars. The delivery of the SCUBA detector we had planned to use for this work was delayed repeatedly, leading us to undertake a majority of the observations with the UKT14 submillimeter detector at the JCMT (James Clerk Maxwell Telescope) and optical imagers and a coronagraph at the University of Hawaii 2.2-m telescope. Major findings under this grant include: (1) We discovered 5 asymmetries in the beta Pictoris regenerated dust disk. The discovery of these asymmetries was a surprise, since smearing due to Keplerian shear should eliminate most such features on timescales of a few thousand years. One exception is the "wing tilt" asymmetry, which we interpret as due to the scattering phase function of dust disk particles. From the wing tilt and a model of the phase function, we find a disk plane inclination to the line of sight of < 5 degrees. Other asymmetries (e.g. the butterfly asymmetry) suggest a disk that has been recently disturbed. We searched for possible nearby perturbers but found no clear candidates. Low mass stars (M dwarfs) and brown dwarfs would have fallen beneath the sensitivity threshhold of our survey, however. (2) We calculated a set of disk models to assess the detectability of dust disks around stars as a function of (a) distance, (b) disk, inclination (c) dust optical depth/mass, and (d) imaging resolution. These models guided our observational strategy on Mauna Kea. (3) We performed a coronagraphic survey of approx. 100 main-sequence stars in search of additional examples of circumstellar disks. The best new candidate disk, around the 5 M(sun) star BD+31deg.643, is distinguished by its large extent (few x 10( exp 3) AU). This disk, if real, cannot be rotationally supported. We suggest that the dust particles are ejected from a smaller, unseen disk (Kuiper Belt?) by strong radiation pressure forces due to the high luminosity central star. (4) SCUBA images of

Circumstellar Light Echo as a Possible Origin of the Polarization of Type IIP Supernovae

NASA Astrophysics Data System (ADS)

Nagao, Takashi; Maeda, Keiichi; Tanaka, Masaomi

2017-10-01

Type IIP supernovae (SNe IIP) are the most common class of core-collapse SNe. They often show a rapid increase of polarization degree in the late phase. This time evolution is generally believed to originate from the emergence of an inner aspherical core, while the effect of polarized-scattered echoes by circumstellar (CS) dust around the SN may also substantially contribute to this polarization feature. In this study, we examine the effects of the scattered echoes on the SN polarization through radiative transfer simulations for various geometries and amounts of CS dust. It is found that asymmetrically distributed CS dust, which is generally inferred for red supergiants, can reproduce the observed polarization features. We have applied our results to SNe 2004dj and 2006ov, deriving the geometry and amount of CS dust to explain their observed polarization features in this scenario. For both SNe, the blob-like or bipolar distribution of CS dust rather than the disk-like distribution is favored. The derived dust masses {M}{dust} in the blob model (the bipolar CS dust model) for SNe 2004dj and 2006ov are ˜ 7.5× {10}-4 {M}⊙ (˜ 8.5× {10}-4 {M}⊙ ) and ˜ 5.2× {10}-4 {M}⊙ (˜ 1.3× {10}-3 {M}⊙ ), respectively. Even in the case where this process would not play a dominant role in the observed polarization signals, this effect should in principle contribute to it, the strength of which depends on the nature of the CS dust. Therefore, this effect must be taken into account in discussing the multi-dimensional structure of an SN explosion through polarimetric observations.

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

NASA Technical Reports Server (NTRS)

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

1994-01-01

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

Dust and molecules in extra-galactic planetary nebulae

NASA Astrophysics Data System (ADS)

Garcia-Hernandez, Domingo Aníbal

2015-08-01

Extra-galactic planetary nebulae (PNe) permit the study of dust and molecules in metallicity environments other than the Galaxy. Their known distances lower the number of free parameters in the observations vs. models comparison, providing strong constraints on the gas-phase and solid-state astrochemistry models. Observations of PNe in the Galaxy and other Local Group galaxies such as the Magellanic Clouds (MC) provide evidence that metallicity affects the production of dust as well as the formation of complex organic molecules and inorganic solid-state compounds in their circumstellar envelopes. In particular, the lower metallicity MC environments seem to be less favorable to dust production and the frequency of carbonaceous dust features and complex fullerene molecules is generally higher with decreasing metallicity. Here, I present an observational review of the dust and molecular content in extra-galactic PNe as compared to their higher metallicity Galactic counterparts. A special attention is given to the level of dust processing and the formation of complex organic molecules (e.g., polycyclic aromatic hydrocarbons, fullerenes, and graphene precursors) depending on metallicity.

Characterizing the Evolution of Circumstellar Systems with the Hubble Space Telescope and the Gemini Planet Imager

NASA Astrophysics Data System (ADS)

Wolff, Schuyler; Schuyler G. Wolff

2018-01-01

The study of circumstellar disks at a variety of evolutionary stages is essential to understand the physical processes leading to planet formation. The recent development of high contrast instruments designed to directly image the structures surrounding nearby stars, such as the Gemini Planet Imager (GPI) and coronagraphic data from the Hubble Space Telescope (HST) have made detailed studies of circumstellar systems possible. In my thesis work I detail the observation and characterization of three systems. GPI polarization data for the transition disk, PDS 66 shows a double ring and gap structure with a temporally variable azimuthal asymmetry. This evolved morphology could indicate shadowing from some feature in the innermost regions of the disk, a gap-clearing planet, or a localized change in the dust properties of the disk. Millimeter continuum data of the DH Tau system places limits on the dust mass that is contributing to the strong accretion signature on the wide-separation planetary mass companion, DH Tau b. The lower than expected dust mass constrains the possible formation mechanism, with core accretion followed by dynamical scattering being the most likely. Finally, I present HST scattered light observations of the flared, edge-on protoplanetary disk ESO H$\\alpha$ 569. I combine these data with a spectral energy distribution to model the key structural parameters such as the geometry (disk outer radius, vertical scale height, radial flaring profile), total mass, and dust grain properties in the disk using the radiative transfer code MCFOST. In order to conduct this work, I developed a new tool set to optimize the fitting of disk parameters using the MCMC code \\texttt{emcee} to efficiently explore the high dimensional parameter space. This approach allows us 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

Early dust formation and a massive progenitor for SN 2011ja?

NASA Astrophysics Data System (ADS)

Andrews, J. E.; Krafton, Kelsie M.; Clayton, Geoffrey C.; Montiel, E.; Wesson, R.; Sugerman, Ben E. K.; Barlow, M. J.; Matsuura, M.; Drass, H.

2016-04-01

SN 2011ja was a bright (I = -18.3) Type II supernova occurring in the nearby edge on spiral galaxy NGC 4945. Flat-topped and multipeaked H α and H β spectral emission lines appear between 64 and 84 d post-explosion, indicating interaction with a disc-like circumstellar medium inclined ˜45° from edge-on. After day 84, an increase in the H- and K-band flux along with heavy attenuation of the red wing of the emission lines are strong indications of early dust formation, likely located in the cool dense shell created between the forward shock of the SN ejecta and the reverse shock created as the ejecta plows into the existing circumstellar material. Radiative transfer modelling reveals both ≈1 × 10-5 M⊙ of pre-existing dust located ˜1016.7 cm away and up to ≈6 × 10-4 M⊙ of newly formed dust. Spectral observations after 1.5 yr reveal the possibility that the fading SN is located within a young (3-6 Myr) massive stellar cluster, which when combined with tentative 56Ni mass estimates of 0.2 M⊙ may indicate a massive (≥25 M⊙) progenitor for SN 2011ja.

Fossil dust shells around luminous supergiants

NASA Technical Reports Server (NTRS)

Stothers, R.

1975-01-01

The observed frequency with which infrared excesses appear in F, G, and K supergiants of luminosity class Ia supports the idea that these excesses arise in a 'fossil' circumstellar dust shell that was formed during a prior M-super-giant phase of evolution. The required leftward evolution of the star on the H-R diagram would then imply that the Ledoux, rather than the Schwarzschild, criterion for convective mixing is the correct criterion to use in stellar evolution calculations.

The effects of circumstellar gas on terrestrial planet formation: Theory and observation

NASA Astrophysics Data System (ADS)

Mandell, Avram M.

Our understanding of the evolution of circumstellar material from dust and gas to fully-formed planets has taken dramatic steps forward in the last decade, driven by rapid improvements in our ability to study gas- and dust-rich disks around young stars and the discovery of more than 200 extra-solar planetary systems around other stars. In addition, our ability to model the formation of both terrestrial and giant planets has improved significantly due to new computing techniques and the continued exponential increase in computing power. In this dissertation I expand on existing theories of terrestrial planet formation to include systems similar to those currently being detected around nearby stars, and I develop new observational techniques to probe the chemistry of gas-rich circumstellar disks where such planetary systems may be forming. One of the most significant characteristics of observed extrasolar planetary systems is the presence of giant planets located much closer to their parent star than was thought to be possible. The presence of "Hot Jupiters", Jovian-mass planets with very short orbital periods detected around nearby main sequence stars, has been proposed to be primarily due to the inward migration of planets formed in orbits initially much further from the parent star. Close-in giant planets are thought to have formed in the cold outer regions of planetary systems and migrated inward, passing through the orbital parameter space occupied by the terrestrial planets in our own Solar System; the migration of these planets would have profound effects on the evolution of inner terrestrial planets in these systems. I first explore this scenario with numerical simulations showing that a significant fraction of terrestrial planets could survive the migration process; damping forces could then eventually re-circularize the orbits at distances relatively close to their original positions. Calculations suggest that the final orbits of a significant fraction of

Estimating dust production rate of carbon-rich stars in the Small Magellanic Cloud

NASA Astrophysics Data System (ADS)

Nanni, A.; Marigo, P.; Groenewegen, M. A. T.; Aringer, B.; Pastorelli, G.; Rubele, S.; Girardi, L.; Bressan, A.; Bladh, S.

We compute a grid of spectra describing dusty Circumstellar Envelopes of Thermally Pulsing Asymptotic Giant Branch carbon-rich stars by employing a physically grounded description for dust growth. The optical constants for carbon dust have been selected in order to reproduce simultaneously the most important color-color diagrams in the Near and Mid Infrared bands. We fit the Spectral Energy Distribution of ≈2000 carbon-rich in the Small Magellanic Cloud and we compute their total dust production rate. We compare our results with the ones in the literature. Different choices of the dust-to-gas ratio and outflow expansion velocity adopted in different works, yield, in some cases, a total dust budget about three times lower than the one derived from our scheme, with the same optical data set for carbon dust.

On the properties of dust and gas in the environs of V838 Monocerotis

NASA Astrophysics Data System (ADS)

Exter, K. M.; Cox, N. L. J.; Swinyard, B. M.; Matsuura, M.; Mayer, A.; De Beck, E.; Decin, L.

2016-12-01

Aims: We aim to probe the close and distant circumstellar environments of the stellar outburst object V838 Mon. Methods: Herschel far-infrared imaging and spectroscopy were taken at several epochs to probe the central point source and the extended environment of V838 Mon. PACS and SPIRE maps were used to obtain photometry of the dust immediately around V838 Mon, and in the surrounding infrared-bright region. These maps were fitted in 1d and 2d to measure the temperature, mass, and β of the two dust sources. PACS and SPIRE spectra were used to detect emission lines from the extended atmosphere of the star, which were then modelled to study the physical conditions in the emitting material. HIFI spectra were taken to measure the kinematics of the extended atmosphere but unfortunately yielded no detections. Results: Fitting of the far-infrared imaging of V838 Mon reveals 0.5-0.6 M⊙ of ≈19 K dust in the environs (≈2.7 pc) surrounding V838 Mon. The surface-integrated infrared flux (signifying the thermal light echo), and derived dust properties do not vary significantly between the different epochs. We measured the photometry of the point source. As the peak of the SED (Spectral Energy Distribution) lies outside the Herschel spectral range, it is only by incorporating data from other observatories and previous epochs that we can usefully fit the SED; with this we explicitly assume no evolution of the point source between the epochs. We find that warm dust with a temperature 300 K distributed over a radius of 150-200 AU. We fit the far-infrared lines of CO arising from the point source, from an extended environment around V838 Mon. Assuming a model of a spherical shell for this gas, we find that the CO appears to arise from two temperature zones: a cold zone (Tkin ≈ 18 K) that could be associated with the ISM or possibly with a cold layer in the outermost part of the shell, and a warm (Tkin ≈ 400 K) zone that is associated with the extended environment of V838

Infrared Spectroscopy of the Dust in Comets and Relationships to Interstellar Dust

NASA Technical Reports Server (NTRS)

Hanner, Martha S.

2003-01-01

Infrared spectroscopy of the dust in comets reveals a complex mix of silicate materials, including both crystalline and non-crystalline components of both olivine (forsterite) and pyroxene composition. These various components do not necessarily share a common origin. Since comets formed in cold regions of the solar nebula, pre-solar grains in the nebula could have been accreted into comets with little alteration. Some of the cometary silicates may be of circumstellar (formed in circumstellar outflows of evolved stars) or interstellar (formed in dense region of the interstellar medium) origin. Spectral similarities to both circumstellar and interstellar silicates are seen in comet spectra. the short-period Kuiper Belt comets) show weak or no spectral features. The lack of features is generally explained as a particle size effect: the small silicate grains are embedded in larger, optically thick particles. However, compositional differences cannot be ruled out. For example, no unambiguous signature of forsterite has yet been seen in the spectrum of a short-period comet. Thus, the Stardust sample from short-period comet P/Wild 2 will be extremely valuable. Not only grain by grain composition and isotopic ratios but also grain morphology, irradiation history, and evidence of organic refractory mantles are important for understanding their origin. The relative abundance and distinguishing characteristics of the various crystalline and non-crystalline silicate components needs to be established. While some comets, such as Hale-Bopp, display a rich infrared spectrum, others (particularly

Guilt by Association: The 13 micron Dust Feature in Circumstellar Shells and Related Spectral Features

NASA Astrophysics Data System (ADS)

Sloan, G. C.; Kraemer, K. E.; Goebel, J. H.; Price, S. D.

A study of spectra from the SWS on ISO of optically thin oxygen-rich dust shells shows that the strength of the 13 micron dust emission feature is correlated with the CO2 bands (13--17 microns) and dust emission features at 19.8 and 28.1 microns. SRb variables tend to show stronger 13 micron features than Mira variables, suggesting that the presence of the 13 micron and related features depends on pulsation mode and mass-loss rate. The absence of any correlation to dust emission features at 16.8 and 32 microns makes spinel an unlikely carrier. The most plausible carrier of the 13 micron feature remains crystalline alumina, and we suggest that the related dust features may be crystalline silicates. When dust forms in regions of low density, it may condense into crystalline grain structures.

A SOFIA FORCAST Grism Study of the Mineralogy of Dust in the Winds of Proto-planetary Nebulae: RV Tauri Stars and SRd Variables

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

Arneson, R. A.; Gehrz, R. D.; Woodward, C. E.

We present a SOFIA FORCAST grism spectroscopic survey to examine the mineralogy of the circumstellar dust in a sample of post-asymptotic giant branch (post-AGB) yellow supergiants that are believed to be the precursors of planetary nebulae. Our mineralogical model of each star indicates the presence of both carbon-rich and oxygen-rich dust species—contrary to simple dredge-up models—with a majority of the dust in the form of amorphous carbon and graphite. The oxygen-rich dust is primarily in the form of amorphous silicates. The spectra do not exhibit any prominent crystalline silicate emission features. For most of the systems, our analysis suggests thatmore » the grains are relatively large and have undergone significant processing, supporting the hypothesis that the dust is confined to a Keplerian disk and that we are viewing the heavily processed, central regions of the disk from a nearly face-on orientation. These results help to determine the physical properties of the post-AGB circumstellar environment and to constrain models of post-AGB mass loss and planetary nebula formation.« less

Resolving the dusty circumstellar environment of the A[e] supergiant HD 62623 with the VLTI/MIDI

NASA Astrophysics Data System (ADS)

Meilland, A.; Kanaan, S.; Borges Fernandes, M.; Chesneau, O.; Millour, F.; Stee, Ph.; Lopez, B.

2010-03-01

Context. B[e] stars are hot stars surrounded by circumstellar gas and dust which is responsible for the presence of emission lines and IR-excess in their spectra. How dust can be formed in this highly illuminated and diluted environment remains an open issue. Aims: HD 62623 is one of the very few A-type supergiants showing the B[e] phenomenon. We studied the geometry of its circumstellar envelope in the mid-infrared using long-baseline interferometry, which is the only observing technique able to spatially resolve objects smaller than a few tens of milliarcseconds. Methods: We obtained nine calibrated visibility measurements between October 2006 and January 2008 using the VLTI/MIDI instrument in SCI-PHOT mode and PRISM spectral dispersion mode with projected baselines ranging from 13 to 71 m and with various position angles (PA). We used geometrical models and physical modeling with a radiative transfer code to analyze these data. Results: The dusty circumstellar environment of HD 62623 is partially resolved by the VLTI/MIDI, even with the shortest baselines. The environment is flattened (a/b~1.3±0.1) and can be separated into two components: a compact one whose extension grows from 17 mas at 8 μm to 30 mas at 9.6 μm and stays almost constant up to 13 μm, and a more extended one that is over-resolved even with the shortest baselines. Using the radiative transfer code MC3D, we managed to model HD 62623's circumstellar environment as a dusty disk with an inner radius of 3.85±0.6 AU, an inclination angle of 60±10°, and a mass of 2 × 10-7 M_⊙. Conclusions: It is the first time that the dusty disk inner rim of a supergiant star exhibiting the B[e] phenomenon is significantly constrained. The inner gaseous envelope likely contributes up to 20% to the total N band flux and acts like a reprocessing disk. Finally, the hypothesis of a stellar wind deceleration by the companion's gravitational effects remains the most probable case since the bi-stability mechanism

ASPHERICITY, INTERACTION, AND DUST IN THE TYPE II-P/II-L SUPERNOVA 2013EJ IN MESSIER 74

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

Mauerhan, Jon C.; Graham, Melissa L.; Filippenko, Alexei V.

2017-01-10

SN 2013ej is a well-studied core-collapse supernova (SN) that stemmed from a directly identified red supergiant (RSG) progenitor in galaxy M74. The source exhibits signs of substantial geometric asphericity, X-rays from persistent interaction with circumstellar material (CSM), thermal emission from warm dust, and a light curve that appears intermediate between supernovae of Types II-P and II-L. The proximity of this source motivates a close inspection of these physical characteristics and their potential interconnection. We present multiepoch spectropolarimetry of SN 2013ej during the first 107 days and deep optical spectroscopy and ultraviolet through infrared photometry past ∼800 days. SN 2013ej exhibitsmore » the strongest and most persistent continuum and line polarization ever observed for a SN of its class during the recombination phase. Modeling indicates that the data are consistent with an oblate ellipsoidal photosphere, viewed nearly edge-on and probably augmented by optical scattering from circumstellar dust. We suggest that interaction with an equatorial distribution of CSM, perhaps the result of binary evolution, is responsible for generating the photospheric asphericity. Relatedly, our late-time optical imaging and spectroscopy show that asymmetric CSM interaction is ongoing, and the morphology of broad H α emission from shock-excited ejecta provides additional evidence that the geometry of the interaction region is ellipsoidal. Alternatively, a prolate ellipsoidal geometry from an intrinsically bipolar explosion is also a plausible interpretation of the data but would probably require a ballistic jet of radioactive material capable of penetrating the hydrogen envelope early in the recombination phase. Finally, our latest space-based optical imaging confirms that the late interaction-powered light curve dropped below the stellar progenitor level, confirming the RSG star’s association with the explosion.« less

Infrared Luminosities and Dust Properties of z ≈ 2 Dust-obscured Galaxies

NASA Astrophysics Data System (ADS)

Bussmann, R. S.; Dey, Arjun; Borys, C.; Desai, V.; Jannuzi, B. T.; Le Floc'h, E.; Melbourne, J.; Sheth, K.; Soifer, B. T.

2009-11-01

We present SHARC-II 350 μm imaging of twelve 24 μm bright (F 24 μm > 0.8 mJy) Dust-Obscured Galaxies (DOGs) and Combined Array for Research in Millimeter-wave Astronomy (CARMA) 1 mm imaging of a subset of two DOGs. These objects are selected from the Boötes field of the NOAO Deep Wide-Field Survey. Detections of four DOGs at 350 μm imply infrared (IR) luminosities which are consistent to within a factor of 2 of expectations based on a warm-dust spectral energy distribution (SED) scaled to the observed 24 μm flux density. The 350 μm upper limits for the 8 non-detected DOGs are consistent with both Mrk 231 and M82 (warm-dust SEDs), but exclude cold dust (Arp 220) SEDs. The two DOGs targeted at 1 mm were not detected in our CARMA observations, placing strong constraints on the dust temperature: T dust > 35-60 K. Assuming these dust properties apply to the entire sample, we find dust masses of ≈3 × 108 M sun. In comparison to other dusty z ~ 2 galaxy populations such as submillimeter galaxies (SMGs) and other Spitzer-selected high-redshift sources, this sample of DOGs has higher IR luminosities (2 × 1013 L sun versus 6 × 1012 L sun for the other galaxy populations) that are driven by warmer dust temperatures (>35-60 K versus ~30 K) and lower inferred dust masses (3 × 108 M sun versus 3 × 109 M sun). Wide-field Herschel and Submillimeter Common-User Bolometer Array-2 surveys should be able to detect hundreds of these power-law-dominated DOGs. We use the existing Hubble Space Telescope and Spitzer/InfraRed Array Camera data to estimate stellar masses of these sources and find that the stellar to gas mass ratio may be higher in our 24 μm bright sample of DOGs than in SMGs and other Spitzer-selected sources. Although much larger sample sizes are needed to provide a definitive conclusion, the data are consistent with an evolutionary trend in which the formation of massive galaxies at z ~ 2 involves a submillimeter bright, cold-dust, and star

INFRARED LUMINOSITIES AND DUST PROPERTIES OF z approx 2 DUST-OBSCURED GALAXIES

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

Bussmann, R. S.; Dey, Arjun; Jannuzi, B. T.

We present SHARC-II 350 mum imaging of twelve 24 mum bright (F{sub 24m}u{sub m} > 0.8 mJy) Dust-Obscured Galaxies (DOGs) and Combined Array for Research in Millimeter-wave Astronomy (CARMA) 1 mm imaging of a subset of two DOGs. These objects are selected from the Booetes field of the NOAO Deep Wide-Field Survey. Detections of four DOGs at 350 mum imply infrared (IR) luminosities which are consistent to within a factor of 2 of expectations based on a warm-dust spectral energy distribution (SED) scaled to the observed 24 mum flux density. The 350 mum upper limits for the 8 non-detected DOGsmore » are consistent with both Mrk 231 and M82 (warm-dust SEDs), but exclude cold dust (Arp 220) SEDs. The two DOGs targeted at 1 mm were not detected in our CARMA observations, placing strong constraints on the dust temperature: T{sub dust} > 35-60 K. Assuming these dust properties apply to the entire sample, we find dust masses of approx3 x 10{sup 8} M{sub sun}. In comparison to other dusty z approx 2 galaxy populations such as submillimeter galaxies (SMGs) and other Spitzer-selected high-redshift sources, this sample of DOGs has higher IR luminosities (2 x 10{sup 13} L{sub sun} versus 6 x 10{sup 12} L{sub sun} for the other galaxy populations) that are driven by warmer dust temperatures (>35-60 K versus approx30 K) and lower inferred dust masses (3 x 10{sup 8} M{sub sun} versus 3 x 10{sup 9} M{sub sun}). Wide-field Herschel and Submillimeter Common-User Bolometer Array-2 surveys should be able to detect hundreds of these power-law-dominated DOGs. We use the existing Hubble Space Telescope and Spitzer/InfraRed Array Camera data to estimate stellar masses of these sources and find that the stellar to gas mass ratio may be higher in our 24 mum bright sample of DOGs than in SMGs and other Spitzer-selected sources. Although much larger sample sizes are needed to provide a definitive conclusion, the data are consistent with an evolutionary trend in which the formation of massive

On the source of the dust extinction in type Ia supernovae and the discovery of anomalously strong Na I absorption

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

Phillips, M. M.; Morrell, Nidia; Hsiao, E. Y.

High-dispersion observations of the Na I D λλ5890, 5896 and K I λλ7665, 7699 interstellar lines, and the diffuse interstellar band at 5780 Å in the spectra of 32 Type Ia supernovae are used as an independent means of probing dust extinction. We show that the dust extinction of the objects where the diffuse interstellar band at 5780 Å is detected is consistent with the visual extinction derived from the supernova colors. This strongly suggests that the dust producing the extinction is predominantly located in the interstellar medium of the host galaxies and not in circumstellar material associated with themore » progenitor system. One quarter of the supernovae display anomalously large Na I column densities in comparison to the amount of dust extinction derived from their colors. Remarkably, all of the cases of unusually strong Na I D absorption correspond to 'Blueshifted' profiles in the classification scheme of Sternberg et al. This coincidence suggests that outflowing circumstellar gas is responsible for at least some of the cases of anomalously large Na I column densities. Two supernovae with unusually strong Na I D absorption showed essentially normal K I column densities for the dust extinction implied by their colors, but this does not appear to be a universal characteristic. Overall, we find the most accurate predictor of individual supernova extinction to be the equivalent width of the diffuse interstellar band at 5780 Å, and provide an empirical relation for its use. Finally, we identify ways of producing significant enhancements of the Na abundance of circumstellar material in both the single-degenerate and double-degenerate scenarios for the progenitor system.« less

Peculiarities of the circumstellar envelopes of some Herbig Ae/Be stars

NASA Astrophysics Data System (ADS)

Pogodin, M. A.

1985-10-01

The results of a spectral and photometric investigation of nine Herbig Ae/Be stars in the visible region of the spectrum in the period from 1978 to 1982 are presented. Certain physical and kinematic parameters of the circumstellar envelopes of the investigated objects are determined on the basis of the observational material obtained and Sobolev's (1947) probabilistic method for moving envelopes. It is shown that the observed spectral characteristics of the envelopes of Herbig Ae/Be stars and their variability can be explained by using models of extended isothermal envelopes with varying structural-kinematic parameters. The existence of a correlation between the amount of dust IR excess and the presence of signs of H2O absorption in the spectra of the investigated objects is noted.

Hot Dust! Late-Time Infrared Emission From Supernovae

NASA Astrophysics Data System (ADS)

Fox, Ori; Skrutskie, M. F.; Chevalier, R. A.

2010-01-01

Supernovae light curves typically peak and fade in the course of several months. Some supernovae , however, exhibit late-time infrared emission that in some cases can last for several years. These supernovae tend to be of the Type IIn subclass, which is defined by narrow hydrogen and helium emission lines arising from a dense, pre-existing circumstellar medium excited by the supernova radiation. Such a late-time ``IR excess'' with respect to the optical blackbody counterpart typically indicates the presence of warm dust. The origin and heating mechanism of the dust is not, however, always well constrained. In this talk, I will explore several scenarios that explain the observed late-time emission. In particular, I will discuss the case of the Type IIn SN 2005ip, which has displayed an ``IR excess'' for over 3 years. The results allow us to interpret the progenitor system and better understand the late stages of stellar evolution. Much of the data used for this analysis were obtained with TripleSpec, a medium-resolution near-infrared spectrograph located at Apache Point Observatory, NM, and FanCam, a JHK imager located at Fan Mountain Observatory, just outside of Charlottesville, VA. These two instruments were designed, fabricated, built, and commissioned by our instrumentation group at the University of Virginia. I will also spend some time discussing these instruments. I would like to thank the following for financial support of this work throughout my graduate career: NASA GSRP, NSF AAG-0607737, Spitzer PID 50256, Achievement Reward for College Scientists (ARCS), and the Virginia Space Grant Consortium.

DUST AROUND R CORONAE BOREALIS STARS. I. SPITZER/INFRARED SPECTROGRAPH OBSERVATIONS

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

Anibal Garcia-Hernandez, D.; Kameswara Rao, N.; Lambert, David L., E-mail: agarcia@iac.es, E-mail: nkrao@iiap.res.in, E-mail: dll@astro.as.utexas.edu

2011-09-20

Spitzer/infrared spectrograph (IRS) spectra from 5 to 37 {mu}m for a complete sample of 31 R Coronae Borealis stars (RCBs) are presented. These spectra are combined with optical and near-infrared photometry of each RCB at maximum light to compile a spectral energy distribution (SED). The SEDs are fitted with blackbody flux distributions and estimates are made of the ratio of the infrared flux from circumstellar dust to the flux emitted by the star. Comparisons for 29 of the 31 stars are made with the Infrared Astronomical Satellite (IRAS) fluxes from three decades earlier: Spitzer and IRAS fluxes at 12 {mu}mmore » and 25 {mu}m are essentially equal for all but a minority of the sample. For this minority, the IRAS to Spitzer flux ratio exceeds a factor of three. The outliers are suggested to be stars where formation of a dust cloud or dust puff is a rare event. A single puff ejected prior to the IRAS observations may have been reobserved by Spitzer as a cooler puff at a greater distance from the RCB. RCBs which experience more frequent optical declines have, in general, a circumstellar environment containing puffs subtending a larger solid angle at the star and a quasi-constant infrared flux. Yet, the estimated subtended solid angles and the blackbody temperatures of the dust show a systematic evolution to lower solid angles and cooler temperatures in the interval between IRAS and Spitzer. Dust emission by these RCBs and those in the LMC is similar in terms of total 24 {mu}m luminosity and [8.0]-[24.0] color index.« less

Spectral Evidence for an Inner Carbon-rich Circumstellar Belt in the Young HD 36546 A-star System

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

Lisse, C. M.; Sitko, M. L.; Russell, R. W.

Using the NASA/IRTF SpeX and BASS spectrometers we have obtained 0.7–13 μ m observations of the newly imaged 3–10 Myr old HD 36546 disk system. The SpeX spectrum is most consistent with the photospheric emission expected from an L {sub *} ∼ 20 L {sub ⊙}, solar abundance A1.5V star with little to no extinction, and excess emission from circumstellar dust detectable beyond 4.5 μ m. Non-detections of CO emission lines and accretion signatures point to the gas-poor circumstellar environment of a very old transition disk. Combining the SpeX + BASS spectra with archival WISE / AKARI / IRAS /more » Herschel photometry, we find an outer cold dust belt at ∼135 K and 20–40 au from the primary, likely coincident with the disk imaged by Subaru, and a new second inner belt with a temperature ∼570 K and an unusual, broad SED maximum in the 6–9 μ m region, tracing dust at 1.1–2.2 au. An SED maximum at 6–9 μ m has been reported in just two other A-star systems, HD 131488 and HD 121191, both of ∼10 Myr age. From Spitzer , we have also identified the ∼12 Myr old A7V HD 148657 system as having similar 5–35 μ m excess spectral features. The Spitzer data allows us to rule out water emission and rule in carbonaceous materials—organics, carbonates, SiC—as the source of the 6–9 μ m excess. Assuming a common origin for the four young A-star systems’ disks, we suggest they are experiencing an early era of carbon-rich planetesimal processing.« less

The circumstellar environments of B[e] Supergiants

NASA Astrophysics Data System (ADS)

Maravelias, G.; Kraus, M.; Cidale, L.; Arias, M. L.; Aret, A.; Borges Fernandes, M.

2017-11-01

The evolution of massive stars encompasses short-lived transition phases in which mass-loss is more enhanced and usually eruptive. A complex environment, combining atomic, molecular and dust regions, is formed around these stars. In particular, the circumstellar environment of B[e] Supergiants is not well understood. To address that, we have initiated a campaign to investigate their environments for a sample of Galactic and Magellanic Cloud sources. Using high-resolution optical and near-infrared spectra (MPG-ESO/FEROS, GEMINI/Phoenix and VLT/CRIRES, respectively), we examine a set of emission features ([OI], [CaII], CO bandheads) to trace the physical conditions and kinematics in their formation regions. We find that the B[e] Supergiants are surrounded by a series of rings of different temperatures and densities, a probable result of previous mass-loss events. In many cases the CO forms very close to the star, while we notice also an alternate mixing of densities and temperatures (which give rise to the different emission features) along the equatorial plane.

SWIFT ULTRAVIOLET OBSERVATIONS OF SUPERNOVA 2014J IN M82: LARGE EXTINCTION FROM INTERSTELLAR DUST

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

Brown, Peter J.; Smitka, Michael T.; Wang, Lifan

We present optical and ultraviolet (UV) photometry and spectra of the very nearby and highly reddened supernova (SN) 2014J in M82 obtained with the Swift Ultra-Violet/Optical Telescope (UVOT). Comparison of the UVOT grism spectra of SN 2014J with Hubble Space Telescope observations of SN2011fe or UVOT grism spectra of SN 2012fr are consistent with an extinction law with a low value of R{sub V} ∼1.4. The high reddening causes the detected photon distribution in the broadband UV filters to have a much longer effective wavelength than for an unreddened SN. The light curve evolution is consistent with this shift andmore » does not show a flattening due to photons being scattered back into the line of sight (LOS). The light curve shapes and color evolution are inconsistent with a contribution scattered into the LOS by circumstellar dust. We conclude that most or all of the high reddening must come from interstellar dust. We show that even for a single dust composition, there is not a unique reddening law caused by circumstellar scattering. Rather, when considering scattering from a time-variable source, we confirm earlier studies that the reddening law is a function of the dust geometry, column density, and epoch. We also show how an assumed geometry of dust as a foreground sheet in mixed stellar/dust systems will lead to a higher inferred R{sub V}. Rather than assuming the dust around SNe is peculiar, SNe may be useful probes of the interstellar reddening laws in other galaxies.« less

Circumstellar Disks Around Rapidly Rotating Be-type Stars

NASA Astrophysics Data System (ADS)

Touhami, Yamina

2012-01-01

Be stars are rapidly rotating B-type stars that eject large amounts of gaseous material into a circumstellar equatorial disk. The existence of this disk has been confirmed through the presence of several observational signatures such as the strong hydrogen emission lines, the IR flux excess, and the linear polarization detected from these systems. Here we report simultaneous near-IR interferometric and spectroscopic observations of circumstellar disks around Be stars obtained with the CHARA Array long baseline interferometer and the Mimir spectrograph at Lowell observatory. The goal of this project was to measure precise angular sizes and to characterize the fundamental geometrical and physical properties of the circumstellar disks. We were able to determine spatial extensions, inclinations, and position angles, as well as the gas density profile of the circumstellar disks using an elliptical Gaussian model and a physical thick disk model, and we show that the K-band interferometric angular sizes of the circumstellar disks are correlated with the H-alpha angular sizes. By combining the projected rotational velocity of the Be star with the disk inclination derived from interferometry, we provide estimates of the equatorial rotational velocities of these rapidly rotating Be stars.

EXTINCTION LAWS TOWARD STELLAR SOURCES WITHIN A DUSTY CIRCUMSTELLAR MEDIUM AND IMPLICATIONS FOR TYPE IA SUPERNOVAE

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

Nagao, Takashi; Maeda, Keiichi; Nozawa, Takaya, E-mail: nagao@kusastro.kyoto-u.ac.jp

Many astronomical objects are surrounded by dusty environments. In such dusty objects, multiple scattering processes of photons by circumstellar (CS) dust grains can effectively alter extinction properties. In this paper, we systematically investigate the effects of multiple scattering on extinction laws for steady-emission sources surrounded by the dusty CS medium using a radiation transfer simulation based on the Monte Carlo technique. In particular, we focus on whether and how the extinction properties are affected by properties of CS dust grains by adopting various dust grain models. We confirm that behaviors of the (effective) extinction laws are highly dependent on themore » properties of CS grains, especially the total-to-selective extinction ratio R{sub V}, which characterizes the extinction law and can be either increased or decreased and compared with the case without multiple scattering. We find that the criterion for this behavior is given by a ratio of albedos in the B and V bands. We also find that either small silicate grains or polycyclic aromatic hydrocarbons are necessary for realizing a low value of R{sub V} as often measured toward SNe Ia if the multiple scattering by CS dust is responsible for their non-standard extinction laws. Using the derived relations between the properties of dust grains and the resulting effective extinction laws, we propose that the extinction laws toward dusty objects could be used to constrain the properties of dust grains in CS environments.« less

R associations. VI - The reddening law in dust clouds and the nature of early-type emission stars in nebulosity from a study of five associations

NASA Technical Reports Server (NTRS)

Herbst, W.; Warner, J. W.; Miller, D. P.; Herzog, A.

1982-01-01

Positions, identification charts, UBVRIKLMN photometry and spectral types are given for stars, illuminating reflection nebulae that are visible on the POSS prints, which have been identified in five associations. With a ratio of total to selective extinction of 4.2, the reddening law applicable to the dust clouds in which the stars are embedded is steeper than normal. The five associations exhibit 18 early-type stars with circumstellar shells, of which those with spectral types earlier than B5 characteristically have weak IR excesses, in contrast to the strong excesses indicative of circumstellar dust, of later-type stars. Color-magnitude charts show a distribution lying above the ZAMS by up to about 2 mag for both the circumstellar shell stars and those classified as rapid rotators. It is suggested that (1) rapid rotation accounts for the scatter in the color-magnitude diagram, and (2) many of the nebulous early-type emission-line stars are rapid rotators rather than pre-main sequence objects.

Dust in Supernovae and Supernova Remnants II: Processing and Survival

NASA Astrophysics Data System (ADS)

Micelotta, E. R.; Matsuura, M.; Sarangi, A.

2018-03-01

Observations have recently shown that supernovae are efficient dust factories, as predicted for a long time by theoretical models. The rapid evolution of their stellar progenitors combined with their efficiency in precipitating refractory elements from the gas phase into dust grains make supernovae the major potential suppliers of dust in the early Universe, where more conventional sources like Asymptotic Giant Branch (AGB) stars did not have time to evolve. However, dust yields inferred from observations of young supernovae or derived from models do not reflect the net amount of supernova-condensed dust able to be expelled from the remnants and reach the interstellar medium. The cavity where the dust is formed and initially resides is crossed by the high velocity reverse shock which is generated by the pressure of the circumstellar material shocked by the expanding supernova blast wave. Depending on grain composition and initial size, processing by the reverse shock may lead to substantial dust erosion and even complete destruction. The goal of this review is to present the state of the art about processing and survival of dust inside supernova remnants, in terms of theoretical modelling and comparison to observations.

Modeling Spectral Variations of Dusty Circumstellar Envelopes During Microlensing Events

NASA Astrophysics Data System (ADS)

Bunker, Christina; Ignace, R.; Bjorkman, J. E.

2007-12-01

Microlensing surveys have proven to be tremendously fruitful in providing valuable data products for many fields of astrophysics, from eclipse lightcurves for substellar candidates to limb darkening in stellar atmospheres. We report on a program of modeling observables from microlensing of circumstellar envelopes, particularly those of red giant stars that are the most likely to show finite source effects. Recent modeling results for the time dependent spectral energy distributions from microlensing of dusty winds are presented. In effect, wavelength-dependent continuum variations that occur as the lens-star separation changes can provide information about the emissivity distribution of dust in the wind. This project was funded by a partnership between the National Science Foundation (NSF AST-0552798), Research Experiences for Undergraduates (REU), and the Department of Defense (DoD) ASSURE (Awards to Stimulate and Support Undergraduate Research Experiences) programs.

The Molecular and Dust Envelope of HD 56126

NASA Astrophysics Data System (ADS)

Meixner, M.; Zalucha, A.; Ueta, T.; Fong, D.; Justtanont, K.

2004-10-01

We present millimeter interferometry images of the CO J=1-0 line emission arising in the circumstellar envelope of HD 56126 (=IRAS 07134+1005), which is one of the best-studied 21 μm proto-planetary nebulae (PPNs). The CO emission extends from 1.2" to 7" in radius from the central star and appears consistent with a simple expanding envelope, as expected for a post-AGB star. The CO envelope is very clumpy with no apparent fast wind to explain these microstructures that must have arisen during the AGB mass loss. We quantitatively model the molecular envelope using a radiative transfer code that we have modified for detached shells. Our best-fit model reveals that two sequential winds created the circumstellar envelope of HD 56126: an AGB wind that lasted 6500 yr with a mass-loss rate of 5.1×10-6 Msolar yr-1 and a more intense superwind that lasted 840 yr with a mass-loss rate of 3×10-5 Msolar yr-1 and that ended the star's life on the AGB 1240 yr ago. The total mass of this envelope is 0.059 Msolar, which indicates a lower limit progenitor mass for the system of 0.66 Msolar, quite reasonable for this low-metallicity star that probably resides in the thick disk of the Galaxy. Comparison with images of the dust emission reveals a structure similar to that of the gas in the inner regions. Using 2-D UST, we model the dust emission of this source so that the model is consistent with the CO emission model and find a total dust mass of 7.8×10-4 Msolar, a superwind-dust mass-loss rate of 1.9×10-7 Msolar yr-1 and an AGB-dust mass-loss rate of 9.6×10-8 Msolar yr-1. We derive an average gas-to-dust mass ratio of 75, which is consistent with ISM values but low for what most consider for carbon stars. Our results indicate that TiC nanocrystals are probably not the carrier of the 21 μm feature.

Cooked GEMS - Insights into the Hot Origins of Crystalline Silicates in Circumstellar Disks and the Cold Origins of GEMS

NASA Technical Reports Server (NTRS)

Brownlee, D. E.; Joswiak, D. J.; Bradley, J. P.; Matrajt, G.; Wooden, D. H.

2005-01-01

The comparison of interstellar, circumstellar and primitive solar nebula silicates has led to a significant conundrum in the understanding of the nature of solid materials that begin the planet forming processes. Crystalline silicates are found in circumstellar regions around young stars and also evolved stars ejecting particles into the interstellar medium (ISM) but they are not seen in the interstellar medium itself, the source material for star and planet formation. Crystalline silicates are minor to major components of all known early solar system materials that have been examined as meteorites or interplanetary dust samples. The strong presence of Mg-rich crystalline silicates in Oort cloud comets and their minor presence in some Kuiper belt comets is also indicated by 11.2 m peak in approx. 10 microns "silicate" infrared feature. This evidence strongly indicates that Mg-rich crystalline silicates were abundant components of the solar nebula disk out to at least 10 AU, and present out to 30 AU.

THE COVERING FACTOR OF WARM DUST IN WEAK EMISSION-LINE ACTIVE GALACTIC NUCLEI

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

Zhang, Xudong; Liu, Yuan, E-mail: zhangxd@ihep.ac.cn, E-mail: liuyuan@ihep.ac.cn

2016-10-20

Weak emission-line active galactic nuclei (WLAGNs) are radio-quiet active galactic nuclei (AGNs) that have nearly featureless optical spectra. We investigate the ultraviolet to mid-infrared spectral energy distributions of 73 WLAGNs (0.4 < z < 3) and find that most of them are similar to normal AGNs. We also calculate the covering factor of warm dust of these 73 WLAGNs. No significant difference is indicated by a KS test between the covering factor of WLAGNs and normal AGNs in the common range of bolometric luminosity. The implication for several models of WLAGNs is discussed. The super-Eddington accretion is unlikely to bemore » the dominant reason for the featureless spectrum of a WLAGN. The present results are still consistent with the evolution scenario, i.e., WLAGNs are in a special stage of AGNs.« less

Gas and dust in the TW Hydrae association as seen by the Herschel Space Observatory

NASA Astrophysics Data System (ADS)

Riviere-Marichalar, P.; Pinte, C.; Barrado, D.; Thi, W. F.; Eiroa, C.; Kamp, I.; Montesinos, B.; Donaldson, J.; Augereau, J. C.; Huélamo, N.; Roberge, A.; Ardila, D.; Sandell, G.; Williams, J. P.; Dent, W. R. F.; Menard, F.; Lillo-Box, J.; Duchêne, G.

2013-07-01

Context. Circumstellar discs are the places where planets form, therefore knowledge of their evolution is crucial for our understanding of planet formation. The Herschel Space Observatory is providing valuable data for studying disc systems, thanks to its sensitivity and wavelength coverage. This paper is one of several devoted to analysing and modelling Herschel-PACS observations of various young stellar associations from the GASPS open time key programme. Aims: The aim of this paper is to elucidate the gas and dust properties of circumstellar discs in the ~10 Myr TW Hya association (TWA) using new far-infrared (IR) imaging and spectroscopy from Herschel-PACS. Methods: We obtained far-IR photometric data at 70, 100, and 160 μm of 14 TWA members; spectroscopic observations centred on the [OI] line at 63.18 μm were also obtained for 9 of the 14. The new photometry for each star was incorporated into its full spectral energy distribution. Results: We detected excess IR emission that is characteristic of circumstellar discs from five TWA members, and computed upper limits for another nine. Two TWA members (TWA 01 and TWA 04B) also show [OI] emission at 63.18 μm. Discs in the TWA association display a variety of properties, with a wide range of dust masses and inner radii, based on modified blackbody modelling. Both transitional and debris discs are found in the sample. Models for sources with a detected IR excess give dust masses in the range from ~0.15 M⊕ to ~63 M⊕. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

Modeling of the Dust and Gas Outflows from OH 26.5+0.6: The Superwind

NASA Technical Reports Server (NTRS)

Justtanont, K.; Skinner, C. J.; Tielens, A. G. G. M.; Meixner, M.; Baas, F.

1996-01-01

We have observed the extreme OH/IR star, OH 26.5+0.6, in the infrared dust continuum and in the sub- millimeter rotational lines of CO. Mid-infrared images reveal the compact nature of the circumstellar shell (less than 0.5 sec). A deep 9.7 microns absorption feature and an absorption at 18 microns show that the dust mass-loss rate is very high. However, the low antenna temperatures of CO J = 1-0 and 2-1 lines suggest that the outer part of the circumstellar shell is much more tenuous. In order to resolve this discrepancy, we have observed the J = 3-2 and 4-3 CO rotational transitions. We have developed a model for the circumstellar shell for OH 26.5 + 0.6 which is consistent with the infrared and submillimeter observations. The dust and gas data are well fitted by a two-shell model, consisting of a dense shell surrounded by a more tenuous shell. The former we identify with the superwind (M = 5.5 x 10(exp -4) solar mass/ yr), and the latter we identify with mass loss on the asymptotic giant branch (AGB) (M = 10(exp -6) solar mass/ yr). The transition between the two mass-loss phases is shown to be rather abrupt ((Delta)t less than 150 yr). Depending on the mass of the progenitor, this superwind phase may be the last thermal pulse (for M(sub *) less than 1.5 solar mass), or the first of a series of the superwind phases (for up to 8 solar mass), punctuated by a period of low mass-loss rates, before the star evolves off the AGB.

A tunnel and a traffic jam: How transition disks maintain a detectable warm dust component despite the presence of a large planet-carved gap

NASA Astrophysics Data System (ADS)

Pinilla, P.; Klarmann, L.; Birnstiel, T.; Benisty, M.; Dominik, C.; Dullemond, C. P.

2016-01-01

Context. Transition disks are circumstellar disks that show evidence of a dust cavity, which may be related to dynamical clearing by embedded planet(s). Most of these objects show signs of significant accretion, indicating that the inner disks are not truly empty, but that gas is still streaming through to the star. A subset of transition disks, sometimes called pre-transition disks, also shows a strong near-infrared excess, interpreted as an optically thick dusty belt located close to the dust sublimation radius within the first astronomical unit. Aims: We study the conditions for the survival and maintenance of such an inner disk in the case where a massive planet opens a gap in the disk. In this scenario, the planet filters out large dust grains that are trapped at the outer edge of the gap, while the inner regions of the disk may or may not be replenished with small grains. Methods: We combined hydrodynamical simulations of planet-disk interactions with dust evolution models that include coagulation and fragmentation of dust grains over a large range of radii and derived observational properties using radiative transfer calculations. We studied the role of the snow line in the survival of the inner disk of transition disks. Results: Inside the snow line, the lack of ice mantles in dust particles decreases the sticking efficiency between grains. As a consequence, particles fragment at lower collision velocities than in regions beyond the snow line. This effect allows small particles to be maintained for up to a few Myr within the first astronomical unit. These particles are closely coupled to the gas and do not drift significantly with respect to the gas. For lower mass planets (1 MJup), the pre-transition appearance can be maintained even longer because dust still trickles through the gap created by the planet, moves invisibly and quickly in the form of relatively large grains through the gap, and becomes visible again as it fragments and gets slowed down

The Cold Dust Content of the Oxygen-rich Supernova Remnant G292.0+1.8

NASA Astrophysics Data System (ADS)

Ghavamian, Parviz; Williams, Brian J.

2016-11-01

We present far-infrared images of the Galactic oxygen-rich supernova remnant (SNR) G292.0+1.8, acquired with the PACS and SPIRE instruments of the Herschel Space Observatory. We find that the SNR shell is detected in the PACS blue (100 μm) band, but not in the red (160 μm) band, broadly consistent with results from AKARI observations. There is no discernible emission from G292.0+1.8 in SPIRE imagery at 250, 350 and 500 μm. Comparing the 100 μm emission to that observed with Spitzer at 24 and 70 μm, we find a very similar appearance for G292.0+1.8 at all three wavelengths. The infrared emission is dominated by dust from non-radiative circumstellar shocks. In addition, the radiatively shocked O-rich clump known as the “Spur” on the eastern side of G292.0+1.8 is clearly detected in the PACS blue images, with marginal detection in the red. Fitting the existing 14-40 μm IRS spectra of the Spur together with photometric measurements from 70 μm MIPS and 100 μm PACS photometry, we place an upper limit of ≲ 0.04 M ⊙ of ejecta dust mass in the Spur, under the most conservative assumption that the ejecta dust has a temperature of 15 K. Modeling the dust continuum in the IRS spectra at four positions around the rim, we estimate post-shock densities ranging from {n}p=3.5 cm-3 to 11 cm-3. The integrated spectrum of the entire SNR, dominated by swept-up circumstellar dust, can be fitted with a two-component dust model with a silicate component at 62 K and graphite component at 40 K for a total dust mass of 0.023 M ⊙.

Aliphatic Hydrocarbon Content of Interstellar Dust

NASA Astrophysics Data System (ADS)

Günay, B.; Schmidt, T. W.; Burton, M. G.; Afşar, M.; Krechkivska, O.; Nauta, K.; Kable, S. H.; Rawal, A.

2018-06-01

There is considerable uncertainty as to the amount of carbon incorporated in interstellar dust. The aliphatic component of the carbonaceous dust is of particular interest because it produces a significant 3.4 μm absorption feature when viewed against a background radiation source. The optical depth of the 3.4 μm absorption feature is related to the number of aliphatic carbon C-H bonds along the line of sight. It is possible to estimate the column density of carbon locked up in the aliphatic hydrocarbon component of interstellar dust from quantitative analysis of the 3.4 μm interstellar absorption feature providing that the absorption coefficient of aliphatic hydrocarbons incorporated in the interstellar dust is known. We report laboratory analogues of interstellar dust by experimentally mimicking interstellar/circumstellar conditions. The resultant spectra of these dust analogues closely match those from astronomical observations. Measurements of the absorption coefficient of aliphatic hydrocarbons incorporated in the analogues were carried out by a procedure combining FTIR and 13C NMR spectroscopies. The absorption coefficients obtained for both interstellar analogues were found to be in close agreement (4.76(8) × 10-18 cm group-1 and 4.69(14) × 10-18 cm group-1), less than half those obtained in studies using small aliphatic molecules. The results thus obtained permit direct calibration of the astronomical observations, providing rigorous estimates of the amount of aliphatic carbon in the interstellar medium.

The Circumstellar Environment of VY CMa

NASA Astrophysics Data System (ADS)

Smith, N.; Humphreys, R. M.; Krautter, J.; Gehrz, R. D.; Davidson, K.; Jones, T. J.; Hubrig, S.

1999-05-01

VY Canis Majoris is one of the most luminous known M supergiants. It is near the upper liminosity limit for cool stars on the HR Diagram. The optical star is partially obscured by its own circumstellar material. We present preliminary results of recent HST/WFPC2 optical imaging, and ground-based near-IR and mid-IR imaging of VY CMa and its circumstellar environment. We compare these results with previously obtained images of the related, but more evolved object IRC+10420 and discuss implications for their possible evolutionary and mass loss histories.

Dissipation of circumstellar disks of Be stars

NASA Astrophysics Data System (ADS)

Sabogal, B. E.; Ubaque, K. Y.; García-Varela, A.; álvarez, M.; Salas, L.

2017-07-01

Studies of L-band spectra of Be stars are useful to set constraints to the models of formation and evolution mechanisms of the circumstellar disks around these stars. Because few such studies have been performed, more of them are needed to confirm the characteristics reported about the optical depth and evolution of these disks. In this work, we studied new L-band spectra of 7 bright galactic Be stars that were obtained by using CID-InSb spectrograph at the 2.1-m telescope at OAN/UNAM San Pedro Martir Observatory, Baja California, Mexico. We used these data to locate these stars, and the Be stars previously studied in the IR, on a flux ratio diagram (log Hu14/Pfγ vs log Hu14/Brα). We found that 28 Cyg has moved significantly along this diagram implying strong changes of its disk from optically thick to an optically thin one between 2001 and 2014. On the base of the absence of emission lines in the spectra, the circumstellar disks of θ CrB and 66 Oph have been almost totally dissipated. These three stars have decaying circumstellar disks. The other stars: γ Cas, φ Per, 28 Tau and o Her have optically thin disks, that have been almost stable in time. It will be important monitoring these and other Be stars in the L-band to observe the changes on their circumstellar disks, and to observe also in this band, the building-up stars, i.e. stars that create a new disk, or that change it from a very tenuous one to an optically thick circumstellar disk. Our spectra contribute to enlarge the infrared spectroscopic database of Be stars.

Molecules and dust in the Large Magellanic Cloud: new colour classifications for post-Main-Sequence stars

NASA Astrophysics Data System (ADS)

Markwick-Kemper, Ciska; Leisenring, Jarron; Meixner, Margaret; van Dyk, Schuyler; Szczerba, Ryszard

In the Large Magellanic Cloud (LMC), as in the Milky Way, dust formation predominantly occurs in the circumstellar environments of evolved stars. The process of dust condensation is not fully understood, and investigating the dust condensation sequence in the low metallicity environment of the LMC (about half of the solar metallicity), may yield additional insights in the dust condensation process. Topics to be studied include the final condensation products, the correlation of the condensation sequence with evolutionary status of the star, degree of crystallinity of the silicates and ratio of carbon-rich dust producing stars. The composition and properties of dust are most easily studied using infrared spectroscopy, and using the high sensitivity of the Infrared Spectrograph (IRS) on board of Spitzer, we were able to observe the thermal emission from circumstellar dust of these stars individually. A sample of 63 post-Main-Sequence stars were selected, using their 2MASS/MSX colours (Egan et al. 2001). We aimed to cover all post-Main-Sequence evolutionary stages, to make an inventory of the dust condensation products, while we placed a certain emphasis on oxygen-rich AGB stars with a intermediate mass-loss rate, to study the existence of a threshold mass-loss rate above which crystalline silicates are observed (Kemper et al. 2001). Here we will present the observed spectra, along with their spectral classification. We find that a large fraction of the stars we observed exhibit spectral features of carbon-rich dust and molecules, such as SiC, C2H2 and MgS. In fact we find that many of these stars are previously classified as oxygen-rich AGB stars, or as OH/IR stars based on their NIR/MIR colours (Egan et al. 2001). These colours are determined for Galactic samples, while in the LMC sample, stars with a carbon-rich chemistry in their outflows occupy a much larger region of the various colour-colour diagrams. In addition, a large fraction of the sample show amorphous

Astronomy in Denver: Spatial distributions of dust properties via far-IR broadband map with HerPlaNS

NASA Astrophysics Data System (ADS)

Asano, Kentaro; Ueta, Toshiya; Ladjal, Djazia; Exter, Katrina; Otsuka, Masaaki; HerPlaNS Consortium

2018-06-01

We present the results of our analyses on dust properties in all of Galactic planetary nebulae based on 5-band broadband images in the far-IR taken with the Herschel Space Observatory.By fitting surface brightness distributions of dust thermal emission at 70, 160, 250, 350 and 500 microns with a single-temperature modified black body function, we derive spatially resolved maps of the dust emissivity power-law index (beta) and dust temperature (Td), as well as the column density.We find that circumstellar dust grains in PNe occupy a specific region in the beta-Td space, which is distinct from that occupied by dust grains in the Interstellar Matter (ISM) and star forming regions (SFRs). Unlike those in the ISM and SFRs, dust grains in PNe exhibit little variation in beta while a large spread in Td, suggesting rather homogeneous dust properties.This work is part of the Herschel Planetary Nebula Survey Plus (HerPlaNS+) supported by the NASA Astrophysics Data Analysis Program.

A Submillimeter Continuum Survey of Local Dust-obscured Galaxies

NASA Astrophysics Data System (ADS)

Lee, Jong Chul; Hwang, Ho Seong; Lee, Gwang-Ho

2016-12-01

We conduct a 350 μm dust continuum emission survey of 17 dust-obscured galaxies (DOGs) at z = 0.05-0.08 with the Caltech Submillimeter Observatory (CSO). We detect 14 DOGs with S 350 μm = 114-650 mJy and signal-to-noise > 3. By including two additional DOGs with submillimeter data in the literature, we are able to study dust content for a sample of 16 local DOGs, which consist of 12 bump and four power-law types. We determine their physical parameters with a two-component modified blackbody function model. The derived dust temperatures are in the range 57-122 K and 22-35 K for the warm and cold dust components, respectively. The total dust mass and the mass fraction of the warm dust component are 3-34 × 107 M ⊙ and 0.03%-2.52%, respectively. We compare these results with those of other submillimeter-detected infrared luminous galaxies. The bump DOGs, the majority of the DOG sample, show similar distributions of dust temperatures and total dust mass to the comparison sample. The power-law DOGs show a hint of smaller dust masses than other samples, but need to be tested with a larger sample. These findings support that the reason DOGs show heavy dust obscuration is not an overall amount of dust content, but probably the spatial distribution of dust therein.

Circumstellar disks revealed by H/K flux variation gradients

NASA Astrophysics Data System (ADS)

Pozo Nuñez, F.; Haas, M.; Chini, R.; Ramolla, M.; Westhues, C.; Hodapp, K.-W.

2015-06-01

The variability of young stellar objects (YSO) changes their brightness and color preventing a proper classification in traditional color-color and color magnitude diagrams. We have explored the feasibility of the flux variation gradient (FVG) method for YSOs, using H and K band monitoring data of the star forming region RCW 38 obtained at the University Observatory Bochum in Chile. Simultaneous multi-epoch flux measurements follow a linear relation FH = α + β·FK for almost all YSOs with large variability amplitude. The slope β gives the mean HK color temperature Tvar of the varying component. Because Tvar is hotter than the dust sublimation temperature, we have tentatively assigned it to stellar variations. If the gradient does not meet the origin of the flux-flux diagram, an additional non- or less-varying component may be required. If the variability amplitude is larger at the shorter wavelength, e.g. α< 0, this component is cooler than the star (e.g. a circumstellar disk); vice versa, if α> 0, the component is hotter like a scattering halo or even a companion star. We here present examples of two YSOs, where the HK FVG implies the presence of a circumstellar disk; this finding is consistent with additional data at J and L. One YSO shows a clear K-band excess in the JHK color-color diagram, while the significance of a K-excess in the other YSO depends on the measurement epoch. Disentangling the contributions of star and disk it turns out that the two YSOs have huge variability amplitudes (~3-5 mag). The HK FVG analysis is a powerful complementary tool to analyze the varying components of YSOs and worth further exploration of monitoring data at other wavelengths.

TW HYA ASSOCIATION MEMBERSHIP AND NEW WISE-DETECTED CIRCUMSTELLAR DISKS

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

Schneider, Adam; Song, Inseok; Melis, Carl, E-mail: aschneid@physast.uga.edu, E-mail: song@physast.uga.edu, E-mail: cmelis@ucsd.edu

2012-07-20

We assess the current membership of the nearby, young TW Hydrae association and examine newly proposed members with the Wide-field Infrared Survey Explorer (WISE) to search for infrared excess indicative of circumstellar disks. Newly proposed members TWA 30A, TWA 30B, TWA 31, and TWA 32 all show excess emission at 12 and 22 {mu}m providing clear evidence for substantial dusty circumstellar disks around these low-mass, {approx}8 Myr old stars that were previously shown to likely be accreting circumstellar material. TWA 30B shows large amounts of self-extinction, likely due to an edge-on disk geometry. We also confirm previously reported circumstellar disksmore » with WISE and determine a 22 {mu}m excess fraction of 42{sup +10}{sub -{sub 9}}% based on our results.« less

Multiwavelength interferometric observations and modeling of circumstellar disks

NASA Astrophysics Data System (ADS)

Schegerer, A. A.; Ratzka, T.; Schuller, P. A.; Wolf, S.; Mosoni, L.; Leinert, Ch.

2013-07-01

Aims: We investigate the structure of the innermost region of three circumstellar disks around pre-main sequence stars HD 142666, AS 205 N, and AS 205 S. We determine the inner radii of the dust disks and, in particular, search for transition objects where dust has been depleted and inner disk gaps have formed at radii of a few tenths of AU up to several AU. Methods: We performed interferometric observations with IOTA, AMBER, and MIDI in the infrared wavelength ranges 1.6-2.5 μm and 8-13 μm with projected baseline lengths between 25 m and 102 m. The data analysis was based on radiative transfer simulations in 3D models of young stellar objects (YSOs) to reproduce the spectral energy distribution and the interferometric visibilities simultaneously. Accretion effects and disk gaps could be considered in the modeling approach. Results from previous studies restricted the parameter space. Results: The objects of this study were spatially resolved in the infrared wavelength range using the interferometers. Based on these observations, a disk gap could be found for the source HD 142666 that classifies it as transition object. There is a disk hole up to a radius of Rin = 0.30 AU and a (dust-free) ring between 0.35 AU and 0.80 AU in the disk of HD 142666. The classification of AS 205 as a system of classical T Tauri stars could be confirmed using the canonical model approach, i.e., there are no hints of disk gaps in our observations. Based on observations made with telescopes of the European Organisation for Astronomical Research in the southern Hemisphere (ESO) at the Paranal Observatory, Chile, under the programs 073.A-9014, 075.C-0014, 075.C-0064, 075.C-0253, 077.C-0750, 079.C-0101, and 079.C-0595.Appendix A is available in electronic form at http://www.aanda.org

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

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

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

2014-12-10

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

Dust Properties of Local Dust-obscured Galaxies with the Submillimeter Array

NASA Astrophysics Data System (ADS)

Hwang, Ho Seong; Andrews, Sean M.; Geller, Margaret J.

2013-11-01

We report Submillimeter Array observations of the 880 μm dust continuum emission for four dust-obscured galaxies (DOGs) in the local universe. Two DOGs are clearly detected with S ν(880 μm) =10-13 mJy and S/N > 5, but the other two are not detected with 3σ upper limits of S ν(880 μm) =5-9 mJy. Including an additional two local DOGs with submillimeter data from the literature, we determine the dust masses and temperatures for six local DOGs. The infrared luminosities and dust masses for these DOGs are in the ranges of 1.2-4.9 × 1011(L ⊙) and 4-14 × 107(M ⊙), respectively. The dust temperatures derived from a two-component modified blackbody function are 23-26 K and 60-124 K for the cold and warm dust components, respectively. Comparison of local DOGs with other infrared luminous galaxies with submillimeter detections shows that the dust temperatures and masses do not differ significantly among these objects. Thus, as argued previously, local DOGs are not a distinctive population among dusty galaxies, but simply represent the high-end tail of the dust obscuration distribution.

A Mid-Summer's Dust Devil

NASA Technical Reports Server (NTRS)

2001-01-01

One objective for the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) in the Extended Mission is to continue looking for changes and dynamic events taking place on the red planet. The feature shown here elicited gasps of excitement among the MOC Operations Staff when it was received in early April 2001.

The feature is a dust devil. Dust devils are spinning, columnar vortices of wind that move across the landscape, pick up dust, and look somewhat like miniature tornadoes. Dust devils are a common occurrence in dry and desert landscapes on Earth as well as Mars. When this dust devil was spied in Amazonis Planitia on April 10th, the MOC was looking straight down. Usually when the camera is looking down the dust devil will appear as a circular, fuzzy patch with a straight shadow indicating its columnar shape. In this case, however, the dust devil is somewhat curved and kinked--its shape is best seen in the shadow it casts to the right. A thin, light-toned track has been left by the dust devil as it moved eastward across the landscape. Usually, such tracks are darker than the surroundings, in this case the light tone might indicate that the dust being removed by the passing dust devil is darker than the surface underneath the thin veneer of dust.

Dust devils most typically form when the ground heats up during the day, warming the air immediately above the surface. As the warmed air nearest the surface begins to rise, it spins. The spinning column begins to move across the surface and picks up loose dust (if any is present). The dust makes the vortex visible and gives it the 'dust devil' or tornado-like appearance. This dust devil occurred at an optimal time for dust devils whether on Earth or Mars--around 2 p.m. local time in the middle of Northern Hemisphere Summer. North is up, sunlight illuminates the scene from the left (west), and 500 meters is about 547 yards. The shadow cast by the dust devil goes off the edge of the image, but the length shown

Multiwavelength studies of the gas and dust disc of IRAS 04158+2805

NASA Astrophysics Data System (ADS)

Glauser, A. M.; Ménard, F.; Pinte, C.; Duchêne, G.; Güdel, M.; Monin, J.-L.; Padgett, D. L.

2008-07-01

We present a study of the circumstellar environment of IRAS 04158+2805 based on multi-wavelength observations and models. Images in the optical and near-infrared, a polarisation map in the optical, and mid-infrared spectra were obtained with VLT-FORS1, CFHT-IR, and Spitzer-IRS. Additionally we used an X-ray spectrum observed with Chandra. We interpret the observations in terms of a central star surrounded by an axisymmetric circumstellar disc, but without an envelope, to test the validity of this simple geometry. We estimate the structural properties of the disc and its gas and dust content. We modelled the dust disc with a 3D continuum radiative transfer code, MCFOST, based on a Monte-Carlo method that provides synthetic scattered light images and polarisation maps, as well as spectral energy distributions. We find that the disc images and spectral energy distribution narrowly constrain many of the disc model parameters, such as a total dust mass of 1.0-1.75×10-4 M_⊙ and an inclination of 62°-63°. The maximum grain size required to fit all available data is of the order of 1.6-2.8 μm although the upper end of this range is loosely constrained. The observed optical polarisation map is reproduced well by the same disc model, suggesting that the geometry we find is adequate and the optical properties are representative of the visible dust content. We compare the inferred dust column density to the gas column density derived from the X-ray spectrum and find a gas-to-dust ratio along the line of sight that is consistent with the ISM value. To our knowledge, this measurement is the first to directly compare dust and gas column densities in a protoplanetary disc. Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii. Based also on data collected

Polarimetry with the Gemini Planet Imager. Methods, performance at first light, and the circumstellar ring around HR 4796A

DOE PAGES

Perrin, Marshall D.; Duchene, Gaspard; Millar-Blanchaer, Max; ...

2015-01-28

We report he 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 (PSF) 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 evenmore » 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. Based on a synthesis of the total and polarized intensities, we now believe that the west side is closer to us, contrary to most prior interpretations. Forward scattering by relatively large silicate dust particles leads to the strong polarized intensity on the west side, and the ring must be slightly optically thick in order to explain the lower brightness in total intensity there. In conclusion, these findings suggest that the ring is geometrically narrow and dynamically cold, perhaps shepherded by larger bodies in the same manner as Saturn’s F ring.« less

Polarimetry with the Gemini Planet Imager: methods, performance at first light, and the circumstellar ring around HR 4796A

DOE PAGES

Perrin, Marshall D.; Duchene, Gaspard; Millar-Blanchaer, Max; ...

2015-01-28

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 di erential 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 clearlymore » 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. Based on a synthesis of the total and polarized intensities, we now believe that the west side is closer to us, contrary to most prior interpretations. Forward scattering by relatively large silicate dust particles leads to the strong polarized intensity on the west side, and the ring must be slightly optically thick in order to explain the lower brightness in total intensity there. These findings suggest that the ring is geometrically narrow and dynamically cold, perhaps shepherded by larger bodies in the same manner as Saturn's F ring.« less

From Nuclei to Dust Grains: How the AGB Machinery Works

NASA Astrophysics Data System (ADS)

Gobrecht, D.; Cristallo, S.; Piersanti, L.

2015-12-01

With their circumstellar envelopes AGB stars are marvelous laboratories to test our knowledge of microphysics (opacities, equation of state), macrophysics (convection, rotation, stellar pulsations, magnetic fields) and nucleosynthesis (nuclear burnings, slow neutron capture processes, molecules and dust formation). Due to the completely different environments those processes occur, the interplay between stellar interiors (dominated by mixing events like convection and dredge-up episodes) and stellar winds (characterized by dust formation and wind acceleration) is often ignored. We intend to develop a new approach involving a transition region, taking into consideration hydrodynamic processes which may drive AGB mass-loss. Our aim is to describe the process triggering the mass-loss in AGB stars with different masses, metallicities and chemical enrichments, possibly deriving a velocity field of the outflowing matter. Moreover, we intend to construct an homogeneous theoretical database containing detailed abundances of atomic and molecular species produced by these objects. As a long term goal, we will derive dust production rates for silicates, alumina and silicon carbides, in order to explain laboratory measurements of isotopic ratios in AGB dust grains.

IONIZATION AND DUST CHARGING IN PROTOPLANETARY DISKS

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

Ivlev, A. V.; Caselli, P.; Akimkin, V. V., E-mail: ivlev@mpe.mpg.de

2016-12-10

Ionization–recombination balance in dense interstellar and circumstellar environments is a key factor for a variety of important physical processes, such as chemical reactions, dust charging and coagulation, coupling of the gas with magnetic field, and development of instabilities in protoplanetary disks. We determine a critical gas density above which the recombination of electrons and ions on the grain surface dominates over the gas-phase recombination. For this regime, we present a self-consistent analytical model, which allows us to calculate exactly the abundances of charged species in dusty gas, without making assumptions on the grain charge distribution. To demonstrate the importance ofmore » the proposed approach, we check whether the conventional approximation of low grain charges is valid for typical protoplanetary disks, and discuss the implications for dust coagulation and development of the “dead zone” in the disk. The presented model is applicable for arbitrary grain-size distributions and, for given dust properties and conditions of the disk, has only one free parameter—the effective mass of the ions, shown to have a small effect on the results. The model can be easily included in numerical simulations following the dust evolution in dense molecular clouds and protoplanetary disks.« less

Dust grains and gas in the circumstellar envelopes around luminous red giant stars

NASA Technical Reports Server (NTRS)

Zuckerman, B.; Dyck, H. M.

1986-01-01

Far-infrared color-color diagrams have been constructed for over 100 of the brightest evolved stars in the IRAS Point Source Catalog. The diagrams are used to deduce average values of the dust grain emissivity index (p) between 12 and 100 microns. Grains in C-rich and O-rich environments have similar values of p between 12 and 25 microns and between 60 and 100 microns, but between 25 and 60 microns p is larger by approximately 0.4 for the O-rich stars. Dust grains in envelopes around S-type stars seem to have 25 to 60 micron emissivities more nearly like grains in O-rich rather than C-rich environments. CO and HCN emissions from various stars are used to reclassify several stars as oxygen or carbon rich.

Dust Storm Covers Opportunity

NASA Image and Video Library

2018-06-10

This global map of Mars shows a growing dust storm as of June 6, 2018. The map was produced by the Mars Color Imager (MARCI) camera on NASA's Mars Reconnaissance Orbiter spacecraft. The blue dot shows the approximate location of Opportunity. The storm was first detected on June 1. The MARCI camera has been used to monitor the storm ever since. Full dust storms like this one are not surprising, but are infrequent. They can crop up suddenly but last weeks, even months. During southern summer, sunlight warms dust particles, lifting them higher into the atmosphere and creating more wind. That wind kicks up yet more dust, creating a feedback loop that NASA scientists still seek to understand. https://photojournal.jpl.nasa.gov/catalog/PIA22329

Dust Devils Seen by Spirit

NASA Technical Reports Server (NTRS)

2005-01-01

[figure removed for brevity, see original site] Figure 1 Annotated

At the Gusev site recently, skies have been very dusty, and on its 421st sol (March 10, 2005) NASA's Mars Exploration Rover Spirit spied two dust devils in action. This pair of images is from the rover's rear hazard-avoidance camera. Views of the Gusev landing region from orbit show many dark streaks across the landscape -- tracks where dust devils have removed surface dust to show relatively darker soil below -- but this is the first time Spirit has photographed an active dust devil.

Scientists are considering several causes of these small phenomena. Dust devils often occur when the Sun heats the surface of Mars. Warmed soil and rocks heat the layer of atmosphere closest to the surface, and the warm air rises in a whirling motion, stirring dust up from the surface like a miniature tornado. Another possibility is that a flow structure might develop over craters as wind speeds increase. As winds pick up, turbulence eddies and rotating columns of air form. As these columns grow in diameter they become taller and gain rotational speed. Eventually they become self-sustaining and the wind blows them down range.

One sol before this image was taken, power output from Spirit's solar panels went up by about 50 percent when the amount of dust on the panels decreased. Was this a coincidence, or did a helpful dust devil pass over Spirit and lift off some of the dust?

By comparing the separate images from the rover's different cameras, team members estimate that the dust devils moved about 500 meters (1,640 feet) in the 155 seconds between the navigation camera and hazard-avoidance camera frames; that equates to about 3 meters per second (7 miles per hour). The dust devils appear to be about 1,100 meters (almost three-quarters of a mile) from the rover.

Crystallographically Anisotropic Shape of Forsterite: New Probe for Evaluating Dust Formation History from Infrared Spectroscopy

NASA Astrophysics Data System (ADS)

Takigawa, Aki; Tachibana, Shogo

2012-05-01

Crystalline dust has been observed by infrared spectroscopy around dust-enshrouded asymptotic giant branch stars, in protoplanetary disks, and from some comets. Crystalline materials often have a specific shape related to a specific crystallographic orientation (crystallographically anisotropic shape), which reflects the anisotropic nature of crystals, and their infrared spectral features depend on crystallographically anisotropic shapes. The crystallographically anisotropic shape is thus a potentially powerful probe to evaluate circumstellar dust-forming conditions quantitatively. In order to assess the possibility to determine the crystallographically anisotropic shape from infrared spectra, we calculated mass absorption coefficients for ellipsoidal forsterite particles, the most abundant circumstellar crystalline silicate, elongated and flattened along the crystallographic a-, b-, and c-axes with various aspect ratios in the wavelength range of 9-70 μm. It was found that differences in infrared features caused by various crystallographicaly anisotropic shapes are distinguishable from each other irrespective of the effects of temperature, size, chemical composition, and grain edges of forsterite in the range of 9-12 μm and 15-20 μm. We thus concluded that the crystallographically anisotropic shape of forsterite can be deduced from peak features in infrared spectra. We also showed that the crystallographically anisotropic shapes formed by evaporation and condensation of forsterite can be distinguished from each other and the temperature condition for evaporation can be evaluated from the peak features. We applied the present results to the infrared spectrum of a protoplanetary disk HD100546 and found that a certain fraction (~25%) of forsterite dust may have experienced high-temperature evaporation (>1600 K).

A SUBMILLIMETER CONTINUUM SURVEY OF LOCAL DUST-OBSCURED GALAXIES

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

Lee, Jong Chul; Hwang, Ho Seong; Lee, Gwang-Ho, E-mail: jclee@kasi.re.kr

We conduct a 350 μ m dust continuum emission survey of 17 dust-obscured galaxies (DOGs) at z = 0.05–0.08 with the Caltech Submillimeter Observatory (CSO). We detect 14 DOGs with S{sub 350μm} = 114–650 mJy and signal-to-noise > 3. By including two additional DOGs with submillimeter data in the literature, we are able to study dust content for a sample of 16 local DOGs, which consist of 12 bump and four power-law types. We determine their physical parameters with a two-component modified blackbody function model. The derived dust temperatures are in the range 57–122 K and 22–35 K for themore » warm and cold dust components, respectively. The total dust mass and the mass fraction of the warm dust component are 3–34 × 10{sup 7} M {sub ⊙} and 0.03%–2.52%, respectively. We compare these results with those of other submillimeter-detected infrared luminous galaxies. The bump DOGs, the majority of the DOG sample, show similar distributions of dust temperatures and total dust mass to the comparison sample. The power-law DOGs show a hint of smaller dust masses than other samples, but need to be tested with a larger sample. These findings support that the reason DOGs show heavy dust obscuration is not an overall amount of dust content, but probably the spatial distribution of dust therein.« less

Dust around the Cool Component of D-Type Symbiotic Binaries

NASA Astrophysics Data System (ADS)

Jurkic, Tomislav; Kotnik-Karuza, Dubravka

2018-04-01

D type symbiotic binaries are an excellent astrophysical laboratory for investigation of the dust properties and dust formation under the influence of theMira stellar wind and nova activity and of the mass loss and mass transfer between components in such a widely separated system. We present a study of the properties of circumstellar dust in symbiotic Miras by use of long-term near-IR photometry and colour indices. The published JHKL magnitudes of o Ceti, RX Pup, KM Vel, V366 Car, V835 Cen, RR Tel, HM Sge and R Aqr have been collected, analyzed and corrected for short-term variations caused by Mira pulsations. Assuming spherical temperature distribution of the dust in the close neighbourhood of the Mira, the DUSTY code was used to solve the radiative transfer in order to determine the dust temperature and its properties in each particular case. Common dust properties of the symbiotic Miras have been found, suggesting similar conditions in the condensation region of the studied symbiotic Miras. Silicate dust with the inner dust shell radius determined by the dust condensation and with the dust temperature of 900-1200 K can fully explain the observed colour indices. R Aqr is an exception and showed lower dust temperature of 650 K. Obscuration events visible in light curves can be explained by variable dust optical depth with minimal variations of other dust properties. More active symbioticMiras that underwent recent nova outbursts showed higher dust optical depths and larger maximum grain sizes of the order of μm, which means that the post-nova activity could stimulate the dust formation and the grain growth. Optically thicker dust shells and higher dust condensation temperatures have been found in symbiotic Miras compared to their single counterparts, suggesting different conditions for dust production.

CSM interaction and dust formation in SN 2010jl .

NASA Astrophysics Data System (ADS)

Krafton, K.; Clayton, G. C.

The origin of dust in galaxies >1 Gyr old has remained an unsolved mystery for over a decade. One proposed solution is dust produced by core collapse supernovae (CCSNe). Theorists have shown that 0.1-1 M⊙ of dust must be produced per supernova for this to work as an explanation for the dust in young galaxies. SN 1987A has produced ˜1 M⊙ of dust since its detonation. However, most supernovae have been found to only produce 10-4 - 10-2 M⊙ of dust. The energetic type IIn SN 2010jl is located in UGC 5189, in a dense shell of CSM. As dust condenses in the SN ejecta, we see, (1) a sudden decrease in continuum brightness in the visible due to increased dust extinction, (2) the development of an infrared excess in the SN light curve arising from dust grains absorbing high-energy photons and re-emitting them in the infrared, and (3) the development of asymmetric, blue-shifted emission-line profiles, caused by dust forming in the ejecta, and preferentially extinguishing redshifted emission. A dense circumstellar material (CSM) may increase the dust production by supernovae. We observe signs of strong interaction between the SN ejecta and a dense CSM in SN 2010jl. SN 2010jl has been a source of much debate in the CCSN community, particularly over when and how much dust it formed. The light curve shows strong signs of dust formation after 260 days. Arguments over these subjects have been based on the evolution of the light curve and spectra. We present new optical and IR photometry, as well as optical spectroscopy, of SN 2010jl over 2000 days. We estimate dust masses using the DAMOCLES and MOCASSIN radiative transfer codes.

Circumstellar Structure Properties of Young Stellar Objects: Envelopes, Bipolar Outflows, and Disks

NASA Astrophysics Data System (ADS)

Kwon, Woojin

2009-12-01

Physical properties of the three main structures in young stellar objects (YSOs), envelopes, bipolar outflows, and circumstellar disks, have been studied using radio interferometers: the Berkeley-Illinois-Maryland Association (BIMA) array and the Combined Array for Research in Millimeter-wave Astronomy (CARMA). (1) Envelopes. Three Class 0 YSOs (L1448 IRS 2, L1448 IRS 3, and L1157) have been observed by CARMA at λ = 1.3 mm and 2.7 mm continuum. Through visibility modeling to fit the two wavelength continuum data simultaneously, we found that the dust opacity spectral index (β) of Class 0 YSOs is around unity, which implies that dust grains have significantly grown already at the earliest stage. In addition, we discussed the radial dependence of β detected in L1448 IRS 3B and also estimated the density distribution of the three targets. (2) Bipolar outflows. Polarimetric observations in the λ = 1.3 mm continuum and CO, as well as spectral line observations in 13CO and C18O have been carried out toward L1448 IRS 3, which has three Class 0 YSOs, using BIMA. We clearly identified two interacting bipolar outflows from the "binary system" of IRS 3A and 3B and estimated the velocity, inclination, and opening angle of the 3B bipolar outflow, using Bayesian inference. Also, we showed that the "binary system" can be bound gravitationally and we estimated the specific angular momentum, which is between those of binary stars and molecular cloud cores. In addition, we marginally detected linear polarizations at the center of IRS 3B (implying a toroidal magnetic field) in continuum and at the bipolar outflow region in CO. (3) Circumstellar disks. We present the results of 6 objects (CI Tau, DL Tau, DO Tau, FT Tau, Haro 6-13, and HL Tau) in our T Tauri disk survey using CARMA. The data consist of λ = 1.3 mm and 2.7 mm continuum with an angular resolution up to 0.13". Through visibility modeling of two disk models (power-law disk with a Gaussian edge and viscous accretion

DUST PROPERTIES OF LOCAL DUST-OBSCURED GALAXIES WITH THE SUBMILLIMETER ARRAY

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

Hwang, Ho Seong; Andrews, Sean M.; Geller, Margaret J., E-mail: hhwang@cfa.harvard.edu, E-mail: sandrews@cfa.harvard.edu, E-mail: mgeller@cfa.harvard.edu

We report Submillimeter Array observations of the 880 μm dust continuum emission for four dust-obscured galaxies (DOGs) in the local universe. Two DOGs are clearly detected with S{sub ν}(880 μm) =10-13 mJy and S/N > 5, but the other two are not detected with 3σ upper limits of S{sub ν}(880 μm) =5-9 mJy. Including an additional two local DOGs with submillimeter data from the literature, we determine the dust masses and temperatures for six local DOGs. The infrared luminosities and dust masses for these DOGs are in the ranges of 1.2-4.9 × 10{sup 11}(L{sub ☉}) and 4-14 × 10{sup 7}(M{submore » ☉}), respectively. The dust temperatures derived from a two-component modified blackbody function are 23-26 K and 60-124 K for the cold and warm dust components, respectively. Comparison of local DOGs with other infrared luminous galaxies with submillimeter detections shows that the dust temperatures and masses do not differ significantly among these objects. Thus, as argued previously, local DOGs are not a distinctive population among dusty galaxies, but simply represent the high-end tail of the dust obscuration distribution.« less

Modelling of mid-infrared interferometric signature of hot exozodiacal dust emission

NASA Astrophysics Data System (ADS)

Kirchschlager, Florian; Wolf, Sebastian; Brunngräber, Robert; Matter, Alexis; Krivov, Alexander V.; Labdon, Aaron

2018-01-01

Hot exozodiacal dust emission was detected in recent surveys around two dozen main-sequence stars at distances of less than 1 au using the H- and K-band interferometry. Due to the high contrast as well as the small angular distance between the circumstellar dust and the star, direct observation of this dust component is challenging. An alternative way to explore the hot exozodiacal dust is provided by mid-infrared interferometry. We analyse the L, M and N bands interferometric signature of this emission in order to find stronger constraints for the properties and the origin of the hot exozodiacal dust. Considering the parameters of nine debris disc systems derived previously, we model the discs in each of these bands. We find that the M band possesses the best conditions to detect hot dust emission, closely followed by L and N bands. The hot dust in three systems - HD 22484 (10 Tau), HD 102647 (β Leo) and HD 177724 (ζ Aql) - shows a strong signal in the visibility functions, which may even allow one to constrain the dust location. In particular, observations in the mid-infrared could help to determine whether the dust piles up at the sublimation radius or is located at radii up to 1 au. In addition, we explore observations of the hot exozodiacal dust with the upcoming mid-infrared interferometer Multi AperTure mid-Infrared SpectroScopic Experiment (MATISSE) at the Very Large Telescope Interferometer.

ADONIS Discovers Dust Disk around a Star with a Planet

NASA Astrophysics Data System (ADS)

2000-10-01

Zodiacal Light in the iota Horologii Extrasolar Planetary System Retraction (August 2001) The presumed detection of a dust disk around iota Horologii, presented in this Press Release, has been found to be due to an instrumental artefact and is therefore not real. This is the conclusion reached by the astronomers working with the ADONIS Adaptive Optics instrument, following a series of extremely careful tests. In September 2000, iota Horologii - a star which was found earlier by radial velocity measurements to be orbited by a planetary companion - was observed by ADONIS, the adaptive optics system at the ESO 3.6-m telescope. These observations showed an elliptically shaped excess emission around this star when comparing with two reference stars. Such an excess, if real, can only be explained by the presence of a dust disk around this star. A series of new observations - again with the ADONIS system - have not confirmed the previous results. The search for dust disks around stars is a very difficult observational task, because the star is much brighter than the faint extended emission of a dust disk, It is therefore necessary to block the light of the star by means of a so-called coronographic mask. But even this is not sufficient - it is also necessary to subtract the remaining "light-wings" from the star (i.e., the pattern that results from the stray light in the telescope and camera). For this purpose, a "reference" star assumed to be without excess emission is always observed before and after each observation of the "target" star. The light pattern observed for the "reference" star (the standard Point-Spread-Function) is then used to remove numerically the pattern of the "target" star, thereby isolating any additional light that may come from a circumstellar disk. For this analysis, it is crucial that the Point-Spread-Function remains unchanged during the observation of the reference and target stars. In fact, for each observation of the target star, at least two

The Lack of Chemical Equilibrium does not Preclude the Use of the Classical Nucleation Theory in Circumstellar Outflows

NASA Technical Reports Server (NTRS)

Paquette, John A.; Nuth, Joseph A., III

2011-01-01

Classical nucleation theory has been used in models of dust nucleation in circumstellar outflows around oxygen-rich asymptotic giant branch stars. One objection to the application of classical nucleation theory (CNT) to astrophysical systems of this sort is that an equilibrium distribution of clusters (assumed by CNT) is unlikely to exist in such conditions due to a low collision rate of condensable species. A model of silicate grain nucleation and growth was modified to evaluate the effect of a nucleation flux orders of magnitUde below the equilibrium value. The results show that a lack of chemical equilibrium has only a small effect on the ultimate grain distribution.

Onset of frequent dust storms in northern China at ~AD 1100.

PubMed

He, Yuxin; Zhao, Cheng; Song, Mu; Liu, Weiguo; Chen, Fahu; Zhang, Dian; Liu, Zhonghui

2015-11-26

Dust storms in northern China strongly affect the living and health of people there and the dusts could travel a full circle of the globe in a short time. Historically, more frequent dust storms occurred during cool periods, particularly the Little Ice Age (LIA), generally attributed to the strengthened Siberian High. However, limited by chronological uncertainties in proxy records, this mechanism may not fully reveal the causes of dust storm frequency changes. Here we present a late Holocene dust record from the Qaidam Basin, where hydrological changes were previously reconstructed, and examine dust records from northern China, including the ones from historical documents. The records, being broadly consistent, indicate the onset of frequent dust storms at ~AD 1100. Further, peaked dust storm events occurred at episodes of high total solar irradiance or warm-dry conditions in source regions, superimposed on the high background of frequent dust storms within the cool LIA period. We thus suggest that besides strong wind activities, the centennial-scale dust storm events over the last 1000 years appear to be linked to the increased availability of dust source. With the anticipated global warming and deteriorating vegetation coverage, frequent occurrence of dust storms in northern China would be expected to persist.

Eclipses and dust formation by WC9 type Wolf-Rayet stars

NASA Astrophysics Data System (ADS)

Williams, P. M.

2014-12-01

Visual photometry of 16 WC8-9 dust-making Wolf-Rayet (WR) stars during 2001-2009 was extracted from the All-Sky Automated Survey All Star Catalogue (ASAS-3) to search for eclipses attributable to extinction by dust formed in clumps in our line of sight. Data for a comparable number of dust-free WC6-9 stars were also examined to help characterize the data set. Frequent eclipses were observed from WR 104, and several from WR 106, extending the 1994-2001 studies by Kato et al., but not supporting their phasing the variations in WR 104 with its `pinwheel' rotation period. Only four other stars showed eclipses, WR 50 (one of the dust-free stars), WR 69, WR 95 and WR 117, and there may have been an eclipse by WR 121, which had shown two eclipses in the past. No dust eclipses were shown by the `historic' eclipsers WR 103 and WR 113. The atmospheric eclipses of the latter were observed but the suggestion by David-Uraz et al. that dust may be partly responsible for these is not supported. Despite its frequent eclipses, there is no evidence in the infrared images of WR 104 for dust made in its eclipses, demonstrating that any dust formed in this process is not a significant contributor to its circumstellar dust cloud and suggesting that the same applies to the other stars showing fewer eclipses.

Grand-design Spiral Arms in a Young Forming Circumstellar Disk

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

Tomida, Kengo; Lin, Chia Hui; Machida, Masahiro N.

We study formation and long-term evolution of a circumstellar disk in a collapsing molecular cloud core using a resistive magnetohydrodynamic simulation. While the formed circumstellar disk is initially small, it grows as accretion continues, and its radius becomes as large as 200 au toward the end of the Class-I phase. A pair of grand-design spiral arms form due to gravitational instability in the disk, and they transfer angular momentum in the highly resistive disk. Although the spiral arms disappear in a few rotations as expected in a classical theory, new spiral arms form recurrently as the disk, soon becoming unstablemore » again by gas accretion. Such recurrent spiral arms persist throughout the Class-0 and I phases. We then perform synthetic observations and compare our model with a recent high-resolution observation of a young stellar object Elias 2–27, whose circumstellar disk has grand-design spiral arms. We find good agreement between our theoretical model and the observation. Our model suggests that the grand-design spiral arms around Elias 2–27 are consistent with material arms formed by gravitational instability. If such spiral arms commonly exist in young circumstellar disks, it implies that young circumstellar disks are considerably massive and gravitational instability is the key process of angular momentum transport.« less

Multiple Stellar Flybys Sculpting the Circumstellar Architecture in RW Aurigae

NASA Astrophysics Data System (ADS)

Rodriguez, Joseph E.; Loomis, Ryan; Cabrit, Sylvie; Haworth, Thomas J.; Facchini, Stefano; Dougados, Catherine; Booth, Richard A.; Jensen, Eric L. N.; Clarke, Cathie J.; Stassun, Keivan G.; Dent, William R. F.; Pety, Jérôme

2018-06-01

We present high-resolution ALMA Band 6 and 7 observations of the tidally disrupted protoplanetary disks of the RW Aurigae binary. Our observations reveal tidal streams in addition to the previously observed tidal arm around RW Aur A. The observed configuration of tidal streams surrounding RW Aur A and B is incompatible with a single star–disk tidal encounter, suggesting that the RW Aurigae system has undergone multiple flyby interactions. We also resolve the circumstellar disks around RW Aur A and B, with CO radii of 58 au and 38 au consistent with tidal truncation, and 2.5 times smaller dust emission radii. The disks appear misaligned by 12° or 57°. Using new photometric observations from the American Association of Variable Star Observers (AAVSO) and the All Sky Automated Survey for SuperNovae (ASAS-SN) archives, we have also identified an additional dimming event of the primary that began in late 2017 and is currently ongoing. With over a century of photometric observations, we are beginning to explore the same spatial scales as ALMA.

Martian Arctic Dust Devil, Phoenix Sol 104

NASA Technical Reports Server (NTRS)

2008-01-01

The Surface Stereo Imager on NASA's Phoenix Mars Lander caught this dust devil in action west-southwest of the lander at 11:16 a.m. local Mars time on Sol 104, or the 104th Martian day of the mission, Sept. 9, 2008.

Dust devils have not been detected in any Phoenix images from earlier in the mission, but at least six were observed in a dozen images taken on Sol 104.

Dust devils are whirlwinds that often occur when the Sun heats the surface of Mars, or some areas on Earth. The warmed surface heats the layer of atmosphere closest to it, and the warm air rises in a whirling motion, stirring dust up from the surface like a miniature tornado.

The dust devil visible in the center of this image just below the horizon is estimated to be about 400 meters (about 1,300 feet) from Phoenix, and 4 meters (13 feet) in diameter. It is much smaller than dust devils that have been observed by NASA's Mars Exploration Rover Spirit much closer to the equator. It is closer in size to dust devils seen from orbit in the Phoenix landing region, though still smaller than those.

The image has been enhanced to make the dust devil easier to see.

The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.

Far-Ultraviolet Observations of the Circumstellar Gas in the 2 Andromedae System

NASA Astrophysics Data System (ADS)

Cheng, K.-P.; Neff, James E.

2003-02-01

The A5 star β Pictoris is a possible young planetary system and has the best-studied circumstellar disk. Our visible and ultraviolet observations of 2 Andromedae indicated that this A3 star has β Pictoris-like gas infall. We present the far-ultraviolet spectrum (905-1195 Å) of 2 And we obtained with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer (FUSE). Unlike β Pic, 2 And's FUSE spectrum does not show strong chromospheric emission lines from C III and O VI. However, 2 And's FUSE spectrum contains many nonphotospheric lines that allow us to probe the circumstellar gas. For example, between 1120 and 1140 Å, we detected several Fe III absorption lines arising from hyperfine levels of ground state, which cannot be formed in the interstellar medium. These lines are good diagnostics of the circumstellar gas. We also detected circumstellar Fe II, Cr III, Mn III, and O I (1D) lines. The simultaneous presence of these species suggests that the circumstellar environment of 2 And could include regions with different temperatures and densities.

The heating of dust in starburst galaxies: The contribution of the nonionizing radiation

NASA Technical Reports Server (NTRS)

Calzetti, D.; Bohlin, R. C.; Kinney, Anne L.; Storchi-Bergmann, T.; Heckman, Timothy M.

1995-01-01

The IUE UV and optical spectra and the far-infrared (FIR) IRAS flux densities of a sample of starburst and blue compact galaxies are used to investigate the relationship between dust obscuration and dust emission. The amount of dust obscuration at UV wavelengths correlates with the FIR-to-blue ratio; and an analysis of the correlation indicates that not only the ionizing but also the nonionizing radiation contribute to the FIR emission. The amount of UV and optical energy lost to dust obscuration accounts for most of the cool dust FIUR emission and for about 70% of the warm dust FIR emission. The remaining 30% of the warm dust FIR flux is probably due to dust emission from regions of star formation which are embedded in opaque giant molecular clouds and do not contribute to the integrated UV and optical spectrum. The use of the FIR emission as an indicator of high-mass star formation rate in star-forming galaxies can be problematic, since the contribution to the FIR flux from cool dust emission heated by relatively old stars is nonnegligible.

Infrared and X-Ray Spectroscopy of the Kes 75 Supernova Shell Characterizing the Dust and Gas Properties

NASA Technical Reports Server (NTRS)

Temim, Tea; Arendt, Richard G.; Dwek, Eli; Slane, Patrick

2012-01-01

We present deep Chandra observations and Spitzer Space Telescope infrared (IR) spectroscopy of the shell in the composite supernova remnant (SNR) Kes 75 (G29.7-0.3). The remnant is composed of a central pulsar wind nebula and a bright partial shell in the south that is visible at radio, IR, and X-ray wavelengths. The X-ray emission can be modeled by either a single thermal component with a temperature of approx 1.5 keV, or with two thermal components with temperatures of 1.5 and 0.2 keY. Previous studies suggest that the hot component may originate from reverse-shocked SN ejecta. However, our new analysis shows no definitive evidence for enhanced abundances of Si, S, Ar, Mg, and Fe, as expected from supernova (SN) ejecta, or for the IR spectral signatures characteristic of confirmed SN condensed dust, thus favoring a circumstellar or interstellar origin for the X-ray and IR emission. The X-ray and IR emission in the shell are spatially correlated, suggesting that the dust particles are collisionally heated by the X-ray emitting gas. The IR spectrum of the shell is dominated by continuum emission from dust with little, or no line emission. Modeling the IR spectrum shows that the dust is heated to a temperature of approx 140 K by a relatively dense, hot plasma, that also gives rise to the hot X-ray emission component. The density inferred from the IR emission is significantly higher than the density inferred from the X-ray models, suggesting a low filling factor for this X-ray emitting gas. The total mass of the warm dust component is at least 1.3 x 10(exp -2) Solar Mass, assuming no significant dust destruction has occurred in the shell. The IR data also reveal the presence of an additional plasma component with a cooler temperature, consistent with the 0.2 keV gas component. Our IR analysis therefore provides an independent verification of the cooler component of the X-ray emission. The complementary analyses of the X-ray and IR emission provide quantitative

The HOSTS Survey—Exozodiacal Dust Measurements for 30 Stars

NASA Astrophysics Data System (ADS)

Ertel, S.; Defrère, D.; Hinz, P.; Mennesson, B.; Kennedy, G. M.; Danchi, W. C.; Gelino, C.; Hill, J. M.; Hoffmann, W. F.; Rieke, G.; Shannon, A.; Spalding, E.; Stone, J. M.; Vaz, A.; Weinberger, A. J.; Willems, P.; Absil, O.; Arbo, P.; Bailey, V. P.; Beichman, C.; Bryden, G.; Downey, E. C.; Durney, O.; Esposito, S.; Gaspar, A.; Grenz, P.; Haniff, C. A.; Leisenring, J. M.; Marion, L.; McMahon, T. J.; Millan-Gabet, R.; Montoya, M.; Morzinski, K. M.; Pinna, E.; Power, J.; Puglisi, A.; Roberge, A.; Serabyn, E.; Skemer, A. J.; Stapelfeldt, K.; Su, K. Y. L.; Vaitheeswaran, V.; Wyatt, M. C.

2018-05-01

The Hunt for Observable Signatures of Terrestrial Systems survey searches for dust near the habitable zones (HZs) around nearby, bright main-sequence stars. We use nulling interferometry in the N band to suppress the bright stellar light and to probe for low levels of HZ dust around the 30 stars observed so far. Our overall detection rate is 18%, including four new detections, among which are the first three around Sun-like stars and the first two around stars without any previously known circumstellar dust. The inferred occurrence rates are comparable for early-type and Sun-like stars, but decrease from {60}-21+16% for stars with previously detected cold dust to {8}-3+10% for stars without such excess, confirming earlier results at higher sensitivity. For completed observations on individual stars, our sensitivity is five to ten times better than previous results. Assuming a lognormal excess luminosity function, we put upper limits on the median HZ dust level of 13 zodis (95% confidence) for a sample of stars without cold dust and of 26 zodis when focusing on Sun-like stars without cold dust. However, our data suggest that a more complex luminosity function may be more appropriate. For stars without detectable Large Binocular Telescope Interferometer (LBTI) excess, our upper limits are almost reduced by a factor of two, demonstrating the strength of LBTI target vetting for future exo-Earth imaging missions. Our statistics are limited so far, and extending the survey is critical to informing the design of future exo-Earth imaging surveys.

A SCUBA-2 850-micron Survey of Circumstellar Disks in the λ Orionis Cluster

NASA Astrophysics Data System (ADS)

Ansdell, Megan; Williams, Jonathan P.; Cieza, Lucas A.

2015-06-01

We present results from an 850 μm survey of the ˜5 Myr old λ Orionis star-forming region. We used the SCUBA-2 camera on the James Clerk Maxwell Telescope to survey a ˜0.°5-diameter circular region containing 36 (out of 59) cluster members with infrared excesses indicative of circumstellar disks. We detected only one object at \\gt 3σ significance, the Herbig Ae star HD 245185, with a flux density of ˜74 mJy beam-1 corresponding to a dust mass of ˜150 {M}\\oplus . Stacking the individually undetected sources did not produce a significant mean signal but gives an upper limit on the average dust mass for λ Orionis disks of ˜3 {M}\\oplus . Our follow-up observations of HD 245185 with the Submillimeter Array found weak CO 2-1 line emission with an integrated flux of ˜170 mJy km s-1 but no 13CO or C18O isotopologue emission at 30 mJy km s-1 sensitivity, suggesting a gas mass of ≲ 1 M{}{Jup}. The implied gas-to-dust ratio is thus ≳ 50 times lower than the canonical interstellar medium value, setting HD 245185 apart from other Herbig Ae disks of similar age, which have been found to be gas rich; as HD 245185 also shows signs of accretion, we may be catching it in the final phases of disk clearing. Our study of the λ Orionis cluster places quantitative constraints on planet formation timescales, indicating that at ˜5 Myr the average disk no longer has sufficient dust and gas to form giant planets and perhaps even super-Earths; the bulk material has been mostly dispersed or is locked in pebbles/planetesimals larger than a few mm in size.

The spectra of WC9 stars: evolution and dust formation

NASA Astrophysics Data System (ADS)

Williams, P. M.; Crowther, P. A.; van der Hucht, K. A.

2015-05-01

We present analyses of new optical spectra of three WC9 stars, WR 88, WR 92 and WR 103 to test the suggestion that they exemplify an evolutionary sequence amongst the WC9 stars. The spectrum of WR 88 shows conspicuous lines of N III and N IV, leading to classification as a transitional WN8o/WC9 star. The three stars show a sequence of increasing O II and O III line strengths, confirming and extending earlier studies. The spectra were analysed using CMFGEN models, finding greater abundances of oxygen and carbon in WR 103 than in WR 92 and, especially, in WR 88. Of the three stars, only WR 103 makes circumstellar dust. We suggest that oxygen itself does not enhance this process but that it is its higher carbon abundance that allows WR 103 to make dust.

Circumstellar chlorine chemistry and a search for AlCl

NASA Astrophysics Data System (ADS)

Clegg, R. E. S.; Wootten, H. A.

1980-09-01

The J = 7-6 transition of AlCl has been sought in carbon-rich circumstellar shells, Orion A, and Sgr B-2. The upper limit for IRC + 10216 is 20 times less than the predicted value for fully associated AlCl. It is suggested that either the initial density in the circumstellar gas flow (not greater than 10 to the 10th per cu cm) or the gaseous Al and Cl are depleted by grains in this object.

IUE observations of circumstellar emission from the late type variable R Aquarii /M7 + pec/

NASA Technical Reports Server (NTRS)

Michalitsianos, A. G.; Hobbs, R. W.; Kafatos, M.

1980-01-01

IUE observations of R Aquarii (M7 + pec) have been obtained in low dispersion in order to study its circumstellar emission. Strong permitted, semiforbidden, and forbidden emission lines are identified that are superposed on a bright ultraviolet continuum. From the analysis it is deduced that the strong emission-line spectrum that involves semiforbidden C III, C IV, semiforbidden Si III, forbidden O II, and forbidden O III probably arises from a dense compact nebula the size of which is comparable to the binary system of which R Aqr is the primary star. Low-excitation emission lines of Fe II, Mg II, O I, and Si II suggest the presence of a warm chromosphere (T less than about 10,000 K) in the primary M7 late type giant. The secondary is identified as a white dwarf, comparable to or somewhat brighter than the sun, since such a star can produce enough ionizing photons to excite the continuum and emission-line spectrum and yet be sufficiently faint to escape detection by direct observation. The UV continuum observed is attributed to Balmer recombination and not to blackbody emission from the hot companion. The general spectral properties of R Aqr between 1200 A and 3200 A are discussed in the context of the model for the circumstellar nebula, the companion, and the mass-loss rate of the primary star.

Infrared and X-Ray Spectroscopy of the KES 75 Supernova Remnant Shell: Characterizing the Dust and Gas Properties

NASA Technical Reports Server (NTRS)

Temim, Tea; Dwek, Eli; Slane, Patrick; Arendt, Richard G.

2009-01-01

We present deep Chandra observations and Spitzer Space Telescope infrared (IR) spectroscopy of the shell in the composite supernova remnant (SNR) Kes 75 (G29.7-0.3). The remnant is composed of a central pulsar wind nebula and a bright partial shell in the south that is visible at radio, IR, and X-ray wavelengths. The X-ray emission can be modeled by either a single thermal component with a temperature of 1.5 keV, or with two thermal components with temperatures of 1.5 and 0.2 keV. Previous studies suggest that the hot component may originate from reverse-shocked SN ejecta. However, our new analysis shows no definitive evidence for enhanced abundances of Si, S, Ar, Mg, and Fe, as expected from supernova (SN) ejecta, or for the IR spectral signatures characteristic of confirmed SN condensed dust, thus favoring a circumstellar or interstellar origin for the X-ray and IR emission. The X-ray and ill emission in the shell are spatially correlated, suggesting that the dust particles are collisionally heated by the X-ray emitting gas. The IR spectrum of the shell is dominated by continuum emission from dust with little, or no line emission. Modeling the IR spectrum shows that the dust is heated to a temperature of 140 K by a relatively dense, hot plasma, that also gives rise to the hot X-ray emission component. The density inferred from the IR emission is significantly higher than the density inferred from the X-ray models, suggesting a low filling factor for this X-ray emitting gas. The total mass of the warm dust component is at least 1.3 x 10(exp -2) solar mass, assuming no significant dust destruction has occurred in the shell. The IR data also reveal the presence of an additional plasma component with a cooler temperature, consistent with the 0.2 keV gas component. Our IR analysis therefore provides an independent verification of the cooler component of the X-ray emission. The complementary analyses of the X-ray and IR emission provide quantitative estimates of

Infrared and X-Ray Spectroscopy of the Kes 75 Supernova Remnant Shell: Characterizing the Dust and Gas Properties

NASA Technical Reports Server (NTRS)

Temim, Tea; Slane, Patrick; Arendt, Richard G.; Dwek, Eli

2011-01-01

We present deep Chandra observations and Spitzer Space Telescope infrared (IR) spectroscopy of the shell in the composite supernova remnant (SNR) Kes 75 (G29.7-0.3). The remnant is composed of a central pulsar wind nebula and a bright partial shell in the south that is visible at radio, IR, and X-ray wavelengths. The X-ray emission can be modeled by either a single thermal component with a temperature of approximately 1.5 keY, or with two thermal components with temperatures of 1.5 and 0.2 keY. Previous studies suggest that the hot component may originate from reverse-shocked supernova (SN) ejecta. However, our new analysis shows no definitive evidence for enhanced abundances of Si, S, Ar, Mg, and Fe, as expected from SN ejecta, or for the IR spectral signatures characteristic of confirmed SN condensed dust, thus favoring a circumstellar or interstellar origin for the X-ray and IR emission. The X-ray and IR emission in the shell are spatially correlated, suggesting that the dust particles are collisionally heated by the X-ray emitting gas. The IR spectrum of the shell is dominated by continuum emission from dust with little, or no line emission. Modeling the IR spectrum shows that the dust is heated to a temperature of approximately 140 K by a relatively dense, hot plasma that also gives rise to the hot X-my emission component. The density inferred from the IR emission is significantly higher than the density inferred from the X-ray models, suggesting a low filling factor for this X-my emitting gas. The total mass of the warm dust component is at least 1.3 x 10(exp -2) x solar mass, assuming no significant dust destruction has occurred in the shell. The IR data also reveal the presence of an additional plasma component with a cooler temperature, consistent with the 0.2 keV gas component. Our IR analysis therefore provides an independent verification of the cooler component of the X-ray emission. The complementary analyses of the X-ray and IR emission provide

Infrared and X-Ray Spectroscopy of the Kes 75 Supernova Remnant Shell: Characterizing the Dust and Gas Properties

NASA Astrophysics Data System (ADS)

Temim, Tea; Slane, Patrick; Arendt, Richard G.; Dwek, Eli

2012-01-01

We present deep Chandra observations and Spitzer Space Telescope infrared (IR) spectroscopy of the shell in the composite supernova remnant (SNR) Kes 75 (G29.7-0.3). The remnant is composed of a central pulsar wind nebula and a bright partial shell in the south that is visible at radio, IR, and X-ray wavelengths. The X-ray emission can be modeled by either a single thermal component with a temperature of ~1.5 keV, or with two thermal components with temperatures of 1.5 and 0.2 keV. Previous studies suggest that the hot component may originate from reverse-shocked supernova (SN) ejecta. However, our new analysis shows no definitive evidence for enhanced abundances of Si, S, Ar, Mg, and Fe, as expected from SN ejecta, or for the IR spectral signatures characteristic of confirmed SN condensed dust, thus favoring a circumstellar or interstellar origin for the X-ray and IR emission. The X-ray and IR emission in the shell are spatially correlated, suggesting that the dust particles are collisionally heated by the X-ray emitting gas. The IR spectrum of the shell is dominated by continuum emission from dust with little, or no line emission. Modeling the IR spectrum shows that the dust is heated to a temperature of ~140 K by a relatively dense, hot plasma that also gives rise to the hot X-ray emission component. The density inferred from the IR emission is significantly higher than the density inferred from the X-ray models, suggesting a low filling factor for this X-ray emitting gas. The total mass of the warm dust component is at least 1.3 × 10-2 M ⊙, assuming no significant dust destruction has occurred in the shell. The IR data also reveal the presence of an additional plasma component with a cooler temperature, consistent with the 0.2 keV gas component. Our IR analysis therefore provides an independent verification of the cooler component of the X-ray emission. The complementary analyses of the X-ray and IR emission provide quantitative estimates of density and

Detecting Exoplanets with the New Worlds Observer: The Problem of Exozodiacal Dust

NASA Technical Reports Server (NTRS)

Roberge, A.; Noecker, M. C.; Glassman, T. M.; Oakley, P.; Turnbull, M. C.

2009-01-01

Dust coming from asteroids and comets will strongly affect direct imaging and characterization of terrestrial planets in the Habitable Zones of nearby stars. Such dust in the Solar System is called the zodiacal dust (or 'zodi' for short). Higher levels of similar dust are seen around many nearby stars, confined in disks called debris disks. Future high-contrast images of an Earth-like exoplanet will very likely be background-limited by light scattered of both the local Solar System zodi and the circumstellar dust in the extrasolar system (the exozodiacal dust). Clumps in the exozodiacal dust, which are expected in planet-hosting systems, may also be a source of confusion. Here we discuss the problems associated with imaging an Earth-like planet in the presence of unknown levels of exozodiacal dust. Basic formulae for the exoplanet imaging exposure time as function of star, exoplanet, zodi, exozodi, and telescope parameters will be presented. To examine the behavior of these formulae, we apply them to the New Worlds Observer (NWO) mission. NWO is a proposed 4-meter UV/optical/near-IR telescope, with a free flying starshade to suppress the light from a nearby star and achieve the high contrast needed for detection and characterization of a terrestrial planet in the star's Habitable Zone. We find that NWO can accomplish its science goals even if exozodiacal dust levels are typically much higher than the Solar System zodi level. Finally, we highlight a few additional problems relating to exozodiacal dust that have yet to be solved.

Constraints on cosmic silicates

NASA Astrophysics Data System (ADS)

Ossenkopf, V.; Henning, Th.; Mathis, J. S.

1992-08-01

Observational determinations of opacities of circumstellar silicates, relative to the peak value near 10 microns, are used to estimate the optical constants n and k, the real and imaginary parts of the index of refraction. Circumstellar dust is modified by processing within the interstellar medium. This leads to higher band strengths and a somewhat larger ratio of the opacities at the 18 and 10-micron peaks, compared with circumstellar silicates. By using an effective-medium theory, we calculate the effects of small spherical inclusions of various materials (various oxides, sulfides, carbides, amorphous carbon, and metallic iron) upon silicate opacities. Some of these can increase the absorption coefficient k in the 2-8 micron region appreciably, as is needed to reconcile laboratory silicate opacities with observations of both the interstellar medium and envelopes around late-type stars. We give tables of two sets of optical constants for warm oxygen-deficient and cool oxygen-rich silicates, representative for circumstellar and interstellar silicates. The required opacity in the 2-8 micron region is provided by iron and magnetite.

The Circumstellar Disk and Asymmetric Outflow of the EX Lup Outburst System

NASA Astrophysics Data System (ADS)

Hales, A. S.; Pérez, S.; Saito, M.; Pinte, C.; Knee, L. B. G.; de Gregorio-Monsalvo, I.; Dent, B.; López, C.; Plunkett, A.; Cortés, P.; Corder, S.; Cieza, L.

2018-06-01

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations at 0.″3 resolution of EX Lup, the prototype of the EXor class of outbursting pre-main-sequence stars. The circumstellar disk of EX Lup is resolved for the first time in 1.3 mm continuum emission and in the J = 2–1 spectral line of three isotopologues of CO. At the spatial resolution and sensitivity achieved, the compact dust continuum disk shows no indications of clumps, fragments, or asymmetries above the 5σ level. Radiative transfer modeling constrains the characteristic radius of the dust disk to 23 au and the total dust mass to 1.0 × 10‑4 M ⊙ (33 M ⊕), similar to other EXor sources. The 13CO and C18O line emissions trace the disk rotation and are used to constrain the disk geometry, kinematics, and a total gas disk mass of 5.1 × 10‑4 M ⊙. The 12CO emission extends out to a radius of 200 au and is asymmetric, with one side deviating from Keplerian rotation. We detect blueshifted, 12CO arc-like emission located 0.″8 to the northwest and spatially disconnected from the disk emission. We interpret this extended structure as the brightened walls of a cavity excavated by an outflow, which are more commonly seen in FUor sources. Such outflows have also been seen in the borderline FU/EXor object V1647 Ori, but not toward EXor objects. Our detection provides evidence that the outflow phenomenon persists into the EXor phase, suggesting that FUor and EXor objects are a continuous population in which outflow activity declines with age, with transitional objects such as EX Lup and V1647 Ori.

Radiative Cooling of Warm Molecular Gas

NASA Technical Reports Server (NTRS)

Neufeld, David A.; Kaufman, Michael J.

1993-01-01

We consider the radiative cooling of warm (T >= 100 K), fully molecular astrophysical gas by rotational and vibrational transitions of the molecules H2O, CO, and H2. Using an escape probability method to solve for the molecular level populations, we have obtained the cooling rate for each molecule as a function of temperature, density, and an optical depth parameter. A four-parameter expression proves useful in fitting the run of cooling rate with density for any fixed values of the temperature and optical depth parameter. We identify the various cooling mechanisms which are dominant in different regions of the astrophysically relevant parameter space. Given the assumption that water is very abundant in warm regions of the interstellar medium, H2O rotational transitions are found to dominate the cooling of warm interstellar gas over a wide portion of the parameter space considered. While chemical models for the interstellar medium make the strong prediction that water will be produced copiously at temperatures above a few hundred degrees, our assumption of a high water abundance has yet to be tested observationally. The Infrared Space Observatory and the Submillimeter Wave Astronomy Satellite will prove ideal instruments for testing whether water is indeed an important coolant of interstellar and circumstellar gas.

Dynamics of dust in astrophysical plasma and implications

NASA Astrophysics Data System (ADS)

Hoang, Thiem

2012-06-01

Dust is a ubiquitous constituent of the interstellar medium, molecular clouds, and circumstellar and protoplanetary disks. Dust emission interferes with observations of cosmic microwave background (CMB) temperature anisotropy and its polarized emission dominates the CMB B-mode polarization that prevents us from getting insight into the inflation epoch of the early universe. In my PhD thesis, I have studied fundamental physical processes of dust dynamics in astrophysical plasma and explored their implications for observations of the CMB, studies of magnetic fields, and formation of planets. I have investigated the spinning dust emission from very small grains (e.g., polycyclic aromatic hydrocarbons) of non-spherical shapes (including spheroid and triaxial ellipsoid shapes) that have grain axes fluctuating around grain angular momentum due to internal thermal fluctuations within the grain. I have proposed an approach based on Fourier transform to find power spectrum of spinning dust emission from grains of arbitrary grain shape. In particular, I have devised a method to find exact grain angular momentum distribution using the Langevin equation. I have explored the effects of transient spin-up by single-ion collisions, transient heating by single UV photons, and compressible turbulence on spinning dust emission. This improved model of spinning dust emission well reproduces observation data by Wilkinson Microwave Anisotropy Probe and allows a reliable separation of Galactic contamination from the CMB. I have identified grain helicity as the major driver for grain alignment via radiative torques (RATs) and suggested an analytical model of RATs based on this concept. Dust polarization predicted by the model has been confirmed by numerous observations, and can be used as a frequency template for the CMB B-mode searches. I have proposed a new type of dust acceleration due to magnetohydrodynamic turbulence through transit time damping for large grains, and quantified a

Dust Storms and Mortality in the United States, 1995-2005

EPA Science Inventory

Extreme weather events, such as dust storms, are predicted to become more frequent as the global climate warms through the 21st century. The impact of dust storms on human health has been studied extensively in the context of Asian, Saharan, Arabian, and Australian storms, but t...

Estimating the dust production rate of carbon stars in the Small Magellanic Cloud

NASA Astrophysics Data System (ADS)

Nanni, Ambra; Marigo, Paola; Girardi, Léo; Rubele, Stefano; Bressan, Alessandro; Groenewegen, Martin A. T.; Pastorelli, Giada; Aringer, Bernhard

2018-02-01

We employ newly computed grids of spectra reprocessed by dust for estimating the total dust production rate (DPR) of carbon stars in the Small Magellanic Cloud (SMC). For the first time, the grids of spectra are computed as a function of the main stellar parameters, i.e. mass-loss rate, luminosity, effective temperature, current stellar mass and element abundances at the photosphere, following a consistent, physically grounded scheme of dust growth coupled with stationary wind outflow. The model accounts for the dust growth of various dust species formed in the circumstellar envelopes of carbon stars, such as carbon dust, silicon carbide and metallic iron. In particular, we employ some selected combinations of optical constants and grain sizes for carbon dust that have been shown to reproduce simultaneously the most relevant colour-colour diagrams in the SMC. By employing our grids of models, we fit the spectral energy distributions of ≈3100 carbon stars in the SMC, consistently deriving some important dust and stellar properties, i.e. luminosities, mass-loss rates, gas-to-dust ratios, expansion velocities and dust chemistry. We discuss these properties and we compare some of them with observations in the Galaxy and Large Magellanic Cloud. We compute the DPR of carbon stars in the SMC, finding that the estimates provided by our method can be significantly different, between a factor of ≈2-5, than the ones available in the literature. Our grids of models, including the spectra and other relevant dust and stellar quantities, are publicly available at http://starkey.astro.unipd.it/web/guest/dustymodels.

Resolving the circumstellar environment of the B[e] star V921 Scorpii in the near-infrared with VLTI/AMBER

NASA Astrophysics Data System (ADS)

Kreplin, A.; Kraus, S.; Hofmann, K.-H.; Schertl, D.; Weigelt, G.; Driebe, T.

2012-01-01

Aims: We study the AU-scale circumstellar environment of the unclassified B[e] star V921 Sco in the near-infrared. For interpreting the observations, we employ temperature-gradient disk models. Methods: Using the near-infrared beam combiner instrument AMBER, we recorded spectrally dispersed (spectral resolution R = 35) interferograms in the H and K bands. To obtain an improved calibration of the visibilities, we developed a method that is able to equalize the histograms of the optical path difference of target and calibrator. We fit temperature-gradient disk models to the visibilities and spectral energy distribution (SED) to analyze the circumstellar dust geometry. Results: We derived a geometric ring-fit radius of 2.10 ± 0.16 mas in the K band. If we adopt the distance of 1150 ± 150 pc reported elsewhere, we obtain a ring-fit radius of 2.4 AU, which is slightly smaller than the 3.5 AU dust sublimation radius predicted by the size-luminosity relation. The fitted H-band radius of 1.61 ± 0.23 mas (1.85 AU) is found to be more compact than the K-band radius. The best-fit temperature-gradient disk model has an inner disk radius of ~1.45 AU, an inner-edge disk temperature T0 = 1533 K, and a temperature-gradient exponent q = 0.46 suggesting a flared disk geometry. Conclusions: The distance and luminosity of V921 Sco are not well known. If we assume a distance of 1150 ± 150 pc, we derive a ring-fit radius of ~2.4 AU, which is approximately consistent with the computed temperature-gradient disk model with inner and outer ring radii of 1.45 and 8.5 AU, respectively. If the inner radius of V921 Sco is more compact than the sublimation radius, this compact observed size can be explained by emitting material (e.g., a gaseous disk) inside the dust sublimation radius, as suggested for several other B[e] stars. Based on observations made with ESO telescopes at Paranal Observatory under program ID (MPG-VISA GTO): 079.C-0212(A).

Hubble imaging of V1331 Cygni: proper motion study of its circumstellar structures

NASA Astrophysics Data System (ADS)

Choudhary, A.; Stecklum, B.; Linz, Hendrik

2016-05-01

Aims: The young star V1331 Cyg received previous attention because it is surrounded by an optical, arc-like reflection nebula. V1331 Cyg is commonly considered to be a candidate for an object that has undergone an FU-Ori (FUOR) outbreak in the past. This in turn could lead to a time-varying appearance of the dusty arcs that may be revealed by multi-epoch imaging. In particular, a radial colour analysis of the dust arcs can then be attempted to check whether the radial grain size distribution was modified by a previous FUOR wind. Methods: Second-epoch imaging of V1331 Cyg was obtained by us in 2009 using the Hubble Space Telescope (HST). By comparing this to archival HST data from 2000, we studied the time evolution of the circumstellar nebulae. After a point spread function subtraction using model point spread functions, we used customised routines to perform a proper motion analysis. The nebula expansion was derived by deconvolving and correlating the two-epoch radial brightness profiles. Additional data from other facilities - TLS, UKIDSS, Spitzer, and Herschel - were also incorporated to improve our understanding of the star in terms of environment, viewing angle, bipolar outflow length, and the FUOR phenomenon. Results: The outer dust arc is found to be expanding at ≈14.8 ± 3.6 km s-1 on average. The expansion velocity for the inner ring is less consistent, between 0.8 km s-1 and 3.0 km s-1. The derived radial colour profiles do not indicate a spatial separation of the dust grain sizes. The Herschel 160 μm images show for the first time thermal emission from dust probably residing in the outer arc. By viewing V1331 Cyg almost pole-on, the length of the bipolar outflow exceeds previous estimates by far. Conclusions: The outer arc expansion timescale is consistent with the implantation time of the CO torus, which supports the hypothesis of an outburst that occurred a few thousand years ago. The azimuthal colour variation of the outer arc is probably due to

A Coupled Ice-Atmosphere-Dust Model for a Neoproterozoic "Mudball Earth"

NASA Astrophysics Data System (ADS)

Goodman, J. C.; Strom, D.

2010-12-01

The Neoproterozoic "Snowball Earth" glaciations remain a subject of intense debate. While many have used field data to argue for either a totally or partially ice-covered Earth, fewer efforts have been made to establish the basic physical climate state and internal dynamics of these alternatives. Description of feedbacks is especially important: how does a globally ice-covered Earth reinforce itself as a stable climate system, and/or sow the seeds for its own destruction? In previous work, we investigated the flow properties of thick floating global ice sheets, and found that flow from pole to equator tends to eliminate regions of thin ice in the tropics. We briefly mentioned that ice flow and sublimation could lead to a "lag deposit" of dust on top of the tropical ice. The consequences of this were explored in detail by Dorian Abbott and others, who found that the accumulation of dust atop tropical ice causes a strong warming effect, which strongly promotes deglaciation of a Snowball climate. However, Abbott et al specified a dust layer ab initio in their GCM simulations, leaving aside the processes which produce it. Here, we present the results of our efforts to add dust processes to an earlier coupled atmosphere/ocean/ice model originally developed by David Pollard and Jim Kasting. Their model includes energy balance equations for the atmosphere and an ice mechanics model for glacial flow. To this we have added variables tracking the fraction of dust incorporated into snow and ice; the transport and accumulation of this dust through ice flow; the effects of dust on albedo and penetration of sunlight into the ice; restriction of evaporation from dust-covered surfaces; and density and buoyancy effects of dusty ice. Dust is added to the surface globally at a fixed rate, and is removed by meltwater runoff. We find that ice in tropical regions of net evaporation quickly develops a surface dust layer which drastically lowers its albedo. This dust layer develops

Circumstellar disc lifetimes in numerous galactic young stellar clusters

NASA Astrophysics Data System (ADS)

Richert, A. J. W.; Getman, K. V.; Feigelson, E. D.; Kuhn, M. A.; Broos, P. S.; Povich, M. S.; Bate, M. R.; Garmire, G. P.

2018-07-01

Photometric detections of dust circumstellar discs around pre-main sequence (PMS) stars, coupled with estimates of stellar ages, provide constraints on the time available for planet formation. Most previous studies on disc longevity, starting with Haisch, Lada & Lada, use star samples from PMS clusters but do not consider data sets with homogeneous photometric sensitivities and/or ages placed on a uniform time-scale. Here we conduct the largest study to date of the longevity of inner dust discs using X-ray and 1-8 µm infrared photometry from the MYStIX and SFiNCs projects for 69 young clusters in 32 nearby star-forming regions with ages t ≤ 5 Myr. Cluster ages are derived by combining the empirical AgeJX method with PMS evolutionary models, which treat dynamo-generated magnetic fields in different ways. Leveraging X-ray data to identify disc-free objects, we impose similar stellar mass sensitivity limits for disc-bearing and disc-free young stellar objects while extending the analysis to stellar masses as low as M ˜ 0.1 M⊙. We find that the disc longevity estimates are strongly affected by the choice of PMS evolutionary model. Assuming a disc fraction of 100 per cent at zero age, the inferred disc half-life changes significantly, from t1/2 ˜ 1.3-2 Myr to t1/2 ˜ 3.5 Myr when switching from non-magnetic to magnetic PMS models. In addition, we find no statistically significant evidence that disc fraction varies with stellar mass within the first few Myr of life for stars with masses <2 M⊙, but our samples may not be complete for more massive stars. The effects of initial disc fraction and star-forming environment are also explored.

Circumstellar Disk Lifetimes In Numerous Galactic Young Stellar Clusters

NASA Astrophysics Data System (ADS)

Richert, A. J. W.; Getman, K. V.; Feigelson, E. D.; Kuhn, M. A.; Broos, P. S.; Povich, M. S.; Bate, M. R.; Garmire, G. P.

2018-04-01

Photometric detections of dust circumstellar disks around pre-main sequence (PMS) stars, coupled with estimates of stellar ages, provide constraints on the time available for planet formation. Most previous studies on disk longevity, starting with Haisch, Lada & Lada (2001), use star samples from PMS clusters but do not consider datasets with homogeneous photometric sensitivities and/or ages placed on a uniform timescale. Here we conduct the largest study to date of the longevity of inner dust disks using X-ray and 1-8 {μ m} infrared photometry from the MYStIX and SFiNCs projects for 69 young clusters in 32 nearby star-forming regions with ages t ≤ 5 Myr. Cluster ages are derived by combining the empirical AgeJX method with PMS evolutionary models, which treat dynamo-generated magnetic fields in different ways. Leveraging X-ray data to identify disk-free objects, we impose similar stellar mass sensitivity limits for disk-bearing and disk-free YSOs while extending the analysis to stellar masses as low as M ˜ 0.1 M⊙. We find that the disk longevity estimates are strongly affected by the choice of PMS evolutionary model. Assuming a disk fraction of 100% at zero age, the inferred disk half-life changes significantly, from t1/2 ˜ 1.3 - 2 Myr to t1/2 ˜ 3.5 Myr when switching from non-magnetic to magnetic PMS models. In addition, we find no statistically significant evidence that disk fraction varies with stellar mass within the first few Myr of life for stars with masses <2 M⊙, but our samples may not be complete for more massive stars. The effects of initial disk fraction and star-forming environment are also explored.

Millimeter wave studies of circumstellar chemistry

NASA Astrophysics Data System (ADS)

Tenenbaum, Emily Dale

2010-06-01

Millimeter wave studies of molecules in circumstellar envelopes and a planetary nebula have been conducted. Using the Submillimeter Telescope (SMT) of the Arizona Radio Observatory (ARO) on Mt. Graham, a comparative spectral survey from 215-285 GHz was carried out of the carbon-rich asymptotic giant branch star IRC +10216 and the oxygen-rich supergiant VY Canis Majoris. A total of 858 emission lines were observed in both objects, arising from 40 different molecules. In VY Canis Majoris, AlO, AlOH, and PO were detected for the first time in interstellar space. In IRC +10216, PH3 was detected for the first time beyond the solar system, and C3O, and CH2NH were found for the first time in a circumstellar envelope. Additionally, in the evolved planetary nebula, the Helix, H2CO, C2H, and cyclic-C3H2 were observed using the SMT and the Kitt Peak 12 m telescopes. The presence of these three molecules in the Helix suggests that relatively complex chemistry occurs in planetary nebulae, despite the harsh ultraviolet field. Overall, the research on molecules in circumstellar and planetary nebulae furthers our understanding of the nature of the material that is fed back into the interstellar medium from evolved stars. Besides telescope work, laboratory research was also conducted -- the rotational spectrum of ZnCl was measured and its bond length and rotational constants were determined. Lastly, in partial fulfillment of a graduate certificate in entrepreneurial chemistry, the commercial applications of terahertz spectroscopy were explored through literature research.

Warm H2O and OH Disk Emission in V1331 Cyg

NASA Astrophysics Data System (ADS)

Doppmann, Greg W.; Najita, Joan R.; Carr, John S.; Graham, James R.

2011-09-01

We present high-resolution (R = 24, 000) L-band spectra of the young intermediate-mass star V1331 Cyg obtained with NIRSPEC on the Keck II telescope. The spectra show strong, rich emission from water and OH that likely arises from the warm surface region of the circumstellar disk. We explore the use of the new BT2 water line list in fitting the spectra, and we find that it does a much better job than the well-known HITRAN water line list in the observed wavelength range and for the warm temperatures probed by our data. By comparing the observed spectra with synthetic disk emission models, we find that the water and OH emission lines have similar widths (FWHM ~= 18 km s-1). If the line widths are set by disk rotation, the OH and water emission lines probe a similar range of disk radii in this source. The water and OH emission are consistent with thermal emission for both components at a temperature ~1500 K. The column densities of the emitting water and OH are large, ~1021 cm-2 and ~1020 cm-2, respectively. Such a high column density of water is more than adequate to shield the disk midplane from external UV irradiation in the event of complete dust settling out of the disk atmosphere, enabling chemical synthesis to continue in the midplane despite a harsh external UV environment. The large OH-to-water ratio is similar to expectations for UV irradiated disks, although the large OH column density is less easily accounted for. Data presented herein were obtained at the W. M. Keck Observatory from telescope time allocated to the National Aeronautics and Space Administration through the agency's scientific partnership with the California Institute of Technology and the University of California. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

Binary energy source of the HH 250 outflow and its circumstellar environment

NASA Astrophysics Data System (ADS)

Comerón, Fernando; Reipurth, Bo; Yen, Hsi-Wei; Connelley, Michael S.

2018-04-01

Aims: Herbig-Haro flows are signposts of recent major accretion and outflow episodes. We aim to determine the nature and properties of the little-known outflow source HH 250-IRS, which is embedded in the Aquila clouds. Methods: We have obtained adaptive optics-assisted L-band images with the NACO instrument on the Very Large Telescope (VLT), together with N- and Q-band imaging with VISIR also on the VLT. Using the SINFONI instrument on the VLT we carried out H- and K-band integral field spectroscopy of HH 250-IRS, complemented with spectra obtained with the SpeX instrument at the InfraRed Telescope Facility (IRTF) in the JHKL bands. Finally, the SubMillimeter Array (SMA) interferometer was used to study the circumstellar environment of HH 250-IRS at 225 and 351 GHz with CO (2-1) and CO (3-2) maps and 0.9 mm and 1.3 mm continuum images. Results: The HH 250-IRS source is resolved into a binary with 0.''53 separation, corresponding to 120 AU at the adopted distance of 225 pc. The individual components show heavily veiled spectra with weak CO absorption indicative of late-type stars. Both are Class I sources, but their spectral energy distributions between 1.5 μm and 19 μm differ markedly and suggest the existence of a large cavity around one of the components. The millimeter interferometric observations indicate that the gas mainly traces a circumbinary envelope or disk, while the dust emission is dominated by one of the circumstellar envelopes. Conclusions: HH 250-IRS is a new addition to the handful of multiple systems where the individual stellar components, the circumstellar disks and a circumbinary disk can be studied in detail, and a rare case among those systems in which a Herbig-Haro flow is present. Based on observations obtained with the VLT (Cerro Paranal, Chile) in programs 089.C-0196(A), 095.C-0488(A), and 095.C-0488(B), as well as with IRTF (Mauna Kea, Hawaii), SMA (Mauna Kea, Hawaii), and the Nordic Optical Telescope (La Palma, Canary Islands, Spain

SN 2013fs and SN 2013fr: exploring the circumstellar-material diversity in Type II supernovae

NASA Astrophysics Data System (ADS)

Bullivant, Christopher; Smith, Nathan; Williams, G. Grant; Mauerhan, Jon C.; Andrews, Jennifer E.; Fong, Wen-Fai; Bilinski, Christopher; Kilpatrick, Charles D.; Milne, Peter A.; Fox, Ori D.; Cenko, S. Bradley; Filippenko, Alexei V.; Zheng, WeiKang; Kelly, Patrick L.; Clubb, Kelsey I.

2018-05-01

We present photometry and spectroscopy of SN 2013fs and SN 2013fr in the first ˜100 d post-explosion. Both objects showed transient, relatively narrow H α emission lines characteristic of SNe IIn, but later resembled normal SNe II-P or SNe II-L, indicative of fleeting interaction with circumstellar material (CSM). SN 2013fs was discovered within 8 h of explosion; one of the earliest SNe discovered thus far. Its light curve exhibits a plateau, with spectra revealing strong CSM interaction at early times. It is a less luminous version of the transitional SN IIn PTF11iqb, further demonstrating a continuum of CSM interaction intensity between SNe II-P and SNe IIn. It requires dense CSM within 6.5 × 1014 cm of the progenitor, from a phase of advanced pre-SN mass loss beginning shortly before explosion. Spectropolarimetry of SN 2013fs shows little continuum polarization (˜0.5 per cent, consistent with zero), but noticeable line polarization during the plateau phase. SN 2013fr morphed from an SN IIn at early times to an SN II-L. After the first epoch, its narrow lines probably arose from host-galaxy emission, but the bright, narrow H α emission at early times may be intrinsic to the SN. As for SN 2013fs, this would point to a short-lived phase of strong CSM interaction if proven to be intrinsic, suggesting a continuum between SNe IIn and SNe II-L. It is a low-velocity SN II-L like SN 2009kr, but more luminous. SN 2013fr also developed an infrared excess at later times, due to warm CSM dust that requires a more sustained phase of strong pre-SN mass loss.

Spitzer-IRS Spectroscopic Studies of Oxygen-Rich Asymptotic Giant Branch Star and Red Supergiant Star Dust Properties

NASA Astrophysics Data System (ADS)

Sargent, Benjamin A.; Srinivasan, Sundar; Speck, Angela; Volk, Kevin; Kemper, Ciska; Reach, William T.; Lagadec, Eric; Bernard, Jean-Philippe; McDonald, Iain; Meixner, Margaret

2015-01-01

We analyze the dust emission features seen in Spitzer Space Telescope Infrared Spectrograph (IRS) spectra of Oxygen-rich (O-rich) asymptotic giant branch (AGB) and red supergiant (RSG) stars. The spectra come from the Spitzer Legacy program SAGE-Spectroscopy (PI: F. Kemper) and other archival Spitzer-IRS programs. The broad 10 and 20 micron emission features attributed to amorphous dust of silicate composition seen in the spectra show evidence for systematic differences in the centroid of both emission features between O-rich AGB and RSG populations. Radiative transfer modeling using the GRAMS grid of models of AGB and RSG stars suggests that the centroid differences are due to differences in dust properties. We present an update of our investigation of differences in dust composition, size, shape, etc that might be responsible for these spectral differences. We explore how these differences may arise from the different circumstellar environments around RSG and O-rich AGB stars. BAS acknowledges funding from NASA ADAP grant NNX13AD54G.

Supernova Remnants As Laboratories For Determining The Properties Of Ejecta Dust And The Processing Of Dust Grains In Shocks

NASA Astrophysics Data System (ADS)

Dwek, Eli; Temim, Tea

Recent infrared satellites, such as the Spitzer, Herschel, and WISE, have obtained a wealth of spectral and broadband data on the infrared (IR) emission from dust in supernova remnants (SNRs). Supernovae (SNe) are important producers of newly condensed dust during the early free-expansion phase of their evolution, and the dominant destroyers of dust during the subsequent remnant phase of their evolution. The infrared observations hold the key for determining their role in the origin and evolution of dust in the universe. We propose to model the composition, abundance, and size distribution of the dust in select Galactic and Magellanic Cloud remnants. As explained in detail below, the remnants were selected for the availability of IR and X-ray observations. All selected remnants have Spitzer IRS spectral data in the 5-35 μm regions which allow us to determine the effect of grain processing in the shock. Some have spectral maps that allow the distinction between the IR emission from SN-condensed and swept up circumstellar and interstellar dust. All remnants have also been covered by Spitzer, Herschel, and WISE imaging, and have existing X-ray Chandra and/or XMM observations. The dust in some remnants is radiatively-heated by a pulsar wind nebula, and in others collisionally- heated by shocked X-ray or line emitting gas. We will use physical models to calculate the radiative and collisional heating of SNR dust, the equilibrium or fluctuating dust temperatures, and the resulting IR emission for various dust compositions and size distributions. Specific examples of Cas A, SN1987A, the Crab Nebula, and Puppis A, are discussed in detail to illustrate our modeling approach. Our study will be the first comprehensive and physical analysis of a large sample of SNRs in different evolutionary states and different astrophysical environments. They will cover a wide range of interactions between the dust grains and their surroundings, including the radioactively- powered and

Spirit Captures Two Dust Devils On the Move

NASA Technical Reports Server (NTRS)

2005-01-01

[figure removed for brevity, see original site] Figure 1 Annotated

At the Gusev site recently, skies have been very dusty, and on its 421st sol (March 10, 2005) NASA's Mars Exploration Rover Spirit spied two dust devils in action. This is an image from the rover's navigation camera.

Views of the Gusev landing region from orbit show many dark streaks across the landscape -- tracks where dust devils have removed surface dust to show relatively darker soil below -- but this is the first time Spirit has photographed an active dust devil.

Scientists are considering several causes of these small phenomena. Dust devils often occur when the Sun heats the surface of Mars. Warmed soil and rocks heat the layer of atmosphere closest to the surface, and the warm air rises in a whirling motion, stirring dust up from the surface like a miniature tornado. Another possibility is that a flow structure might develop over craters as wind speeds increase. As winds pick up, turbulence eddies and rotating columns of air form. As these columns grow in diameter they become taller and gain rotational speed. Eventually they become self-sustaining and the wind blows them down range.

One sol before this image was taken, power output from Spirit's solar panels went up by about 50 percent when the amount of dust on the panels decreased. Was this a coincidence, or did a helpful dust devil pass over Spirit and lift off some of the dust?

By comparing the separate images from the rover's different cameras, team members estimate that the dust devils moved about 500 meters (1,640 feet) in the 155 seconds between the navigation camera and hazard-avoidance camera frames; that equates to about 3 meters per second (7 miles per hour). The dust devils appear to be about 1,100 meters (almost three-quarters of a mile) from the rover.

HD 172555: Detection of 63 micrometers [OI] Emission in a Debris Disc

NASA Technical Reports Server (NTRS)

Riviere-Marichalar, P.; Barrado, D.; Augereau, J. -C.; Thi, W. F.; Roberge, A.; Eiroa, C.; Montesinos, B.; Meeus, G.; Howard, C.; Sandell, G.;

On circumstellar molecules in the Pleiades.

NASA Technical Reports Server (NTRS)

Hobbs, L. M.

1972-01-01

Consideration of both old and new observations of the interstellar 4232-A line of CH(+) for the brightest members of the Pleiades. These observations suggest that the molecules are circumstellar in some sense, perhaps resembling in this respect the micron-sized grains inferred to be present in this region.

Estimating dust distances to Type Ia supernovae from colour excess time evolution

NASA Astrophysics Data System (ADS)

Bulla, M.; Goobar, A.; Amanullah, R.; Feindt, U.; Ferretti, R.

2018-01-01

We present a new technique to infer dust locations towards reddened Type Ia supernovae and to help discriminate between an interstellar and a circumstellar origin for the observed extinction. Using Monte Carlo simulations, we show that the time evolution of the light-curve shape and especially of the colour excess E(B - V) places strong constraints on the distance between dust and the supernova. We apply our approach to two highly reddened Type Ia supernovae for which dust distance estimates are available in the literature: SN 2006X and SN 2014J. For the former, we obtain a time-variable E(B - V) and from this derive a distance of 27.5^{+9.0}_{-4.9} or 22.1^{+6.0}_{-3.8} pc depending on whether dust properties typical of the Large Magellanic Cloud (LMC) or the Milky Way (MW) are used. For the latter, instead, we obtain a constant E(B - V) consistent with dust at distances larger than ∼50 and 38 pc for LMC- and MW-type dust, respectively. Values thus extracted are in excellent agreement with previous estimates for the two supernovae. Our findings suggest that dust responsible for the extinction towards these supernovae is likely to be located within interstellar clouds. We also discuss how other properties of reddened Type Ia supernovae - such as their peculiar extinction and polarization behaviour and the detection of variable, blue-shifted sodium features in some of these events - might be compatible with dust and gas at interstellar-scale distances.

A circumstellar molecular gas structure associated with the massive young star Cepheus A-HW 2

NASA Technical Reports Server (NTRS)

Torrelles, Jose M.; Rodriguez, Luis F.; Canto, Jorge; Ho, Paul T. P.

1993-01-01

We report the detection via VLA-D observations of ammonia of a circumstellar high-density molecular gas structure toward the massive young star related to the object Cepheus A-HW 2, a firm candidate for the powering source of the high-velocity molecular outflow in the region. We suggest that the circumstellar molecular gas structure could be related to the circumstellar disk previously suggested from infrared, H2O, and OH maser observations. We consider as a plausible scenario that the double radio continuum source of HW 2 could represent the ionized inner part of the circumstellar disk, in the same way as proposed to explain the double radio source in L1551. The observed motions in the circumstellar molecular gas can be produced by bound motions (e.g., infall or rotation) around a central mass of about 10-20 solar masses (B0.5 V star or earlier).

Evolution of thermally pulsing asymptotic giant branch stars - II. Dust production at varying metallicity

NASA Astrophysics Data System (ADS)

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

2013-09-01

We present the dust ejecta of the new stellar models for the thermally pulsing asymptotic giant branch (TP-AGB) phase computed with the COLIBRI code. We use a formalism of dust growth coupled with a stationary wind for both M- and C-stars. In the original version of this formalism, the most efficient destruction process of silicate dust in M-giants is chemisputtering by H2 molecules. For these stars, we find that dust grains can only form at relatively large radial distances (r ˜ 5R*), where they cannot be efficiently accelerated, in agreement with other investigations. In the light of recent laboratory results, we also consider the alternative case that the condensation temperature of silicates is determined only by the competition between growth and free evaporation processes (i.e. no chemisputtering). With this latter approach we obtain dust condensation temperatures that are significantly higher (up to Tcond ˜ 1400 K) than those found when chemisputtering is included (Tcond ˜ 900 K), and in better agreement with condensation experiments. As a consequence, silicate grains can remain stable in inner regions of the circumstellar envelopes (r ˜ 2 R*), where they can rapidly grow and can be efficiently accelerated. With this modification, our models nicely reproduce the observed trend between terminal velocities and mass-loss rates of Galactic M-giants. For C-stars the formalism is based on the homogeneous growth scheme where the key role is played by the carbon over oxygen excess. The models reproduce fairly well the terminal velocities of Galactic stars and there is no need to invoke changes in the standard assumptions. At decreasing metallicity the carbon excess becomes more pronounced and the efficiency of dust formation increases. This trend could be in tension with recent observational evidence in favour of a decreasing efficiency, at decreasing metallicity. If confirmed by more observational data, it would indicate that either the amount of the carbon

Discovery of a Circumstellar Disk in the Lagoon Nebula

NASA Astrophysics Data System (ADS)

1997-04-01

Circumstellar disks of gas and dust play a crucial role in the formation of stars and planets. Until now, high-resolution images of such disks around young stars within the Orion Nebula obtained with the Hubble Space Telescope (HST) constituted the most direct proof of their existence. Now, another circumstellar disk has been detected around a star in the Lagoon Nebula - also known as Messier 8 (M8) , a giant complex of interstellar gas and dust with many young stars in the southern constellation of Sagittarius and four times more distant than the Orion Nebula. The observations were carried out by an international team of scientists led by Bringfried Stecklum (Thüringer Landessternwarte, Tautenburg, Germany) [1] who used telescopes located at the ESO La Silla observatory and also observations from the HST archive. These new results are paving the road towards exciting research programmes on star formation which will become possible with the ESO Very Large Telescope. The harsh environment of circumstellar disks The existence of circumstellar disks has been inferred from indirect measurements of young stellar objects, such as the spectral energy distribution, the analysis of the profiles of individual spectral lines and measurements of the polarisation of the emitted light [2]. Impressive images of such disks in the Orion Nebula, known as proplyds (PROto-PLanetarY DiskS), have been obtained by the HST during the recent years. They have confirmed the interpretation of previous ground-based emission-line observations and mapping by radio telescopes. Moreover, they demonstrated that those disks which are located close to hot and massive stars are subject to heating caused by the intense radiation from these stars. Subsequently, the disks evaporate releasing neutral gas which streams off. During this process, shock fronts (regions with increased density) with tails of ionised gas result at a certain distance between the disk and the hot star. These objects appear on

Dust Storms in the United States are Associated with Increased Cardiovascular Mortality

EPA Science Inventory

Background: Extreme weather events such as dust storms are predicted to become more frequent as the global climate warms through the 21st century. Studies of Asian, Saharan, Arabian, and Australian dust storms have found associations with cardiovascular and total non-accidental...

Biological consequences of earlier snowmelt from desert dust deposition in alpine landscapes.

PubMed

Steltzer, Heidi; Landry, Chris; Painter, Thomas H; Anderson, Justin; Ayres, Edward

2009-07-14

Dust deposition to mountain snow cover, which has increased since the late 19(th) century, accelerates the rate of snowmelt by increasing the solar radiation absorbed by the snowpack. Snowmelt occurs earlier, but is decoupled from seasonal warming. Climate warming advances the timing of snowmelt and early season phenological events (e.g., the onset of greening and flowering); however, earlier snowmelt without warmer temperatures may have a different effect on phenology. Here, we report the results of a set of snowmelt manipulations in which radiation-absorbing fabric and the addition and removal of dust from the surface of the snowpack advanced or delayed snowmelt in the alpine tundra. These changes in the timing of snowmelt were superimposed on a system where the timing of snowmelt varies with topography and has been affected by increased dust loading. At the community level, phenology exhibited a threshold response to the timing of snowmelt. Greening and flowering were delayed before seasonal warming, after which there was a linear relationship between the date of snowmelt and the timing of phenological events. Consequently, the effects of earlier snowmelt on phenology differed in relation to topography, which resulted in increasing synchronicity in phenology across the alpine landscape with increasingly earlier snowmelt. The consequences of earlier snowmelt from increased dust deposition differ from climate warming and include delayed phenology, leading to synchronized growth and flowering across the landscape and the opportunity for altered species interactions, landscape-scale gene flow via pollination, and nutrient cycling.

OT2_dardila_2: PACS Photometry of Transiting-Planet Systems with Warm Debris Disks

NASA Astrophysics Data System (ADS)

Ardila, D.

2011-09-01

Dust in debris disks is produced by colliding or evaporating planetesimals, the remnant of the planet formation process. Warm dust disks, known by their emission at =<24 mic, are rare (4% of FGK main-sequence stars), and specially interesting because they trace material in the region likely to host terrestrial planets, where the dust has very short dynamical lifetimes. Dust in this region comes from very recent asteroidal collisions, migrating Kuiper Belt planetesimals, or migrating dust. NASA's Kepler mission has just released a list of 1235 candidate transiting planets, and in parallel, the Wide-Field Infrared Survey Explorer (WISE) has just completed a sensitive all-sky mapping in the 3.4, 4.6, 12, and 22 micron bands. By cross-identifying the WISE sources with Kepler candidates as well as with other transiting planetary systems we have identified 21 transiting planet hosts with previously unknown warm debris disks. We propose Herschel/PACS 100 and 160 micron photometry of this sample, to determine whether the warm dust in these systems represents stochastic outbursts of local dust production, or simply the Wien side of emission from a cold outer dust belt. These data will allow us to put constraints in the dust temperature and infrared luminosity of these systems, allowing them to be understood in the context of other debris disks and disk evolution theory. This program represents a unique opportunity to exploit the synergy between three great space facilities: Herschel, Kepler, and WISE. The transiting planet sample hosts will remain among the most studied group of stars for the years to come, and our knowledge of their planetary architecture will remain incomplete if we do not understand the characteristics of their debris disks.

Synchrotron FTIR Examination of Interplanetary Dust Particles: An Effort to Determine the Compounds and Minerals in Interstellar and Circumstellar Dust

NASA Technical Reports Server (NTRS)

Flynn, G. J.; Keller, L. P.

2002-01-01

Some interplanetary dust particles (IDPs), collected by NASA from the Earth's stratosphere, are the most primitive extraterrestrial material available for laboratory analysis. Many exhibit isotopic anomalies in H, N, and O, suggesting they contain preserved interstellar matter. We report the preliminary results of a comparison of the infrared absorption spectra of subunits of the IDPs with astronomical spectra of interstellar grains.

Stellar and Circumstellar Properties of the Pre-Main-Sequence Binary GV Tau from Infrared Spectroscopy

NASA Astrophysics Data System (ADS)

Doppmann, Greg W.; Najita, Joan R.; Carr, John S.

2008-09-01

We report spatially resolved spectroscopy of both components of the low-mass pre-main-sequence binary GV Tau. High-resolution spectroscopy in the K and L bands is used to characterize the stellar properties of the binary and to explore the nature of the circumstellar environment. We find that the southern component, GV Tau S, is a radial velocity variable, possibly as a result of an unseen low-mass companion. The strong warm gaseous HCN absorption reported previously by Gibb and coworkers toward GV Tau S was not present during the epoch of our observations. Instead, we detect warm (~500 K) molecular absorption with similar properties toward the northern infrared companion, GV Tau N. At the epoch of our observations, the absorbing gas toward GV Tau N was approximately at the radial velocity of the GV Tau molecular envelope, but it was redshifted with respect to the star by ~13 km s-1. One interpretation of our results is that GV Tau N is also a binary and that most of the warm molecular absorption arises in a circumbinary disk viewed close to edge-on. Data presented herein were obtained at the W. M. Keck Observatory from telescope time allocated to the National Aeronautics and Space Administration through the agency's scientific partnership with the California Institute of Technology and the University of California. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

Late-time Dust Emission from the Type IIn Supernova 1995N

NASA Astrophysics Data System (ADS)

Van Dyk, Schuyler D.

2013-05-01

Type IIn supernovae (SNe IIn) have been found to be associated with significant amounts of dust. These core-collapse events are generally expected to be the final stage in the evolution of highly massive stars, either while in an extreme red supergiant phase or during a luminous blue variable phase. Both evolutionary scenarios involve substantial pre-supernova mass loss. I have analyzed the SN IIn 1995N in MCG -02-38-017 (Arp 261), for which mid-infrared archival data obtained with the Spitzer Space Telescope in 2009 (~14.7 yr after explosion) and with the Wide-field Infrared Survey Explorer in 2010 (~15.6-16.0 yr after explosion) reveal a luminous (~2 × 107 L ⊙) source detected from 3.4 to 24 μm. These observations probe the circumstellar material, set up by pre-SN mass loss, around the progenitor star and indicate the presence of ~0.05-0.12 M ⊙ of pre-existing, cool dust at ~240 K. This is at least a factor ~10 lower than the dust mass required to be produced from SNe at high redshift, but the case of SN 1995N lends further evidence that highly massive stars could themselves be important sources of dust.

Martian Arctic Dust Devil and Phoenix Meteorology Mast

NASA Technical Reports Server (NTRS)

2008-01-01

The Surface Stereo Imager on NASA's Phoenix Mars Lander caught this dust devil in action west-southwest of the lander at 11:16 a.m. local Mars time on Sol 104, or the 104th Martian day of the mission, Sept. 9, 2008.

Dust devils have not been detected in any Phoenix images from earlier in the mission, but at least six were observed in a dozen images taken on Sol 104.

Dust devils are whirlwinds that often occur when the Sun heats the surface of Mars, or some areas on Earth. The warmed surface heats the layer of atmosphere closest to it, and the warm air rises in a whirling motion, stirring dust up from the surface like a miniature tornado.

The vertical post near the left edge of this image is the mast of the Meteorological Station on Phoenix. The dust devil visible at the horizon just to the right of the mast is estimated to be 600 to 700 meters (about 2,000 to 2,300 feet) from Phoenix, and 4 to 5 meters (10 to 13 feet) in diameter. It is much smaller than dust devils that have been observed by NASA's Mars Exploration Rover Spirit much closer to the equator. It is closer in size to dust devils seen from orbit in the Phoenix landing region, though still smaller than those.

The image has been enhanced to make the dust devil easier to see.

The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.

Laboratory Studies of Optical Characteristics and Condensation Processes of Cosmic Dust Particles

NASA Technical Reports Server (NTRS)

Spann, J. F., Jr.; Abbas, M. M.; Venturini, C. C.

2000-01-01

Information about the optical characteristics and physical processes involving cosmic dust particles is vital for interpretation of astronomical observations and an understanding of the formation and processing of dust in the evolutionary cycle of matter in the interstellar medium. Cosmic dust particles are formed in a variety of astrophysical environments such as in cool stellar outflows and circumstellar envelopes. Definitive knowledge of the nature, composition, and physical processes of cosmic dust grains, however, can only be inferred from astronomical observations through laboratory experiments on the analogs of hypothesized dust particles and with modeling calculations. Laboratory investigations of the nature, composition, and optical characteristics of cosmic dust particles are being, carried out at many institutions with a variety of experimental techniques. Despite a wealth of available data, however, many basic issues remain unresolved. An experimental facility based on suspension of dust particles in electrodynamic balance in a pressure/temperature controlled environment in a cavity has been operational at the NASA Marshall Space Flight Center, and is currently being employed for studies of dust particle charging mechanisms using electron beams and with UV radiation. In this paper, we discuss two general classes of experiments under planning stages that may be simultaneously carried out on this facility for cosmic dust investigations (i) Infrared optical characteristics (extinction coefficients and scattering phase functions) of the analogs of hypothesized of cosmic dust particles, such as natural and synthetic amorphous silicates with varying compositions, amorphous carbon grains, polycyclic aromatic hydrocarbons (PAHs), and icy core-mantle particles etc. The initial spectral range under consideration is 1-25 micrometers, to be extended to the far infrared region in the future (ii) Condensation of volatile gases on nucleus dust particles to be

The Physics and Chemistry of Oxygen-Rich Circumstellar Envelopes as Traced by Simple Molecules

NASA Astrophysics Data System (ADS)

Wong, Ka Tat

2018-04-01

multiple radio inversion lines of NH3. Furthermore, mid-infrared absorption of NH3 has been observed by the NASA Infrared Telescope Facility (IRTF) for IK Tau and VY CMa. Full radiative transfer modelling including mid-infrared pumping to the first vibrationally excited state (v2=1) has been carried out to reproduce the observed emission and absorption spectra and to retrieve the NH3 abundances in the targets. It is found that the NH3 emission in the CSEs of the targets arises from localised spatial-kinematic structures in which the gas density may be higher than in the surrounding gas. Circumstellar shocks may contribute to, but cannot fully account for, the formation of the molecule. Besides circumstellar chemistry, our understanding of the dust formation and wind-driving mechanisms of oxygen-rich evolved stars is still incomplete. One of the obstacles in the past was the difficulty in imaging the dust condensation and wind acceleration zones due to the lack of high-angular resolution instruments. Thanks to the Atacama Large Millimeter/submillimeter Array (ALMA), which has the longest baseline of about 15 km, we are now able to produce high-fidelity images at unprecedented angular resolutions of tens of milliarcseconds (mas) in the (sub)millimetre regime. Such angular resolutions, which are comparable to the stellar radii of nearby objects, are necessary to understand the gas dynamics and chemical evolution in the pulsating atmosphere and dust formation zone of nearby AGB stars. The eponymous Mira-type long-period variable, o Cet, was observed as a Science Verification target during the first ALMA Long Baseline Campaign that took place in 2014. The observations produced images of the stellar radio photosphere and the molecular transitions of SiO and H2O at an angular resolution of about 30 mas near 220 GHz (1.3 mm). The millimetre stellar disc of o Cet was resolved and modelled. More importantly, this is the first time that molecular line absorption against the

Interferometric view of the circumstellar envelopes of northern FU Orionis-type stars

NASA Astrophysics Data System (ADS)

Fehér, O.; Kóspál, Á.; Ábrahám, P.; Hogerheijde, M. R.; Brinch, C.

2017-11-01

Context. FU Orionis-type objects are pre-main sequence, low-mass stars with large outbursts in visible light that last for several years or decades. They are thought to represent an evolutionary phase during the life of every young star when accretion from the circumstellar disk is enhanced during recurring time periods. These outbursts are able to rapidly build up the star while affecting the physical conditions inside the circumstellar disk and thus the ongoing or future planet formation. In many models, infall from a circumstellar envelope seems to be necessary to trigger the outbursts. Aims: We characterise the morphology and the physical parameters of the circumstellar material around FU Orionis-type stars using the emission of millimetre-wavelength molecular tracers. The high-spatial-resolution study provides insight into the evolutionary state of the objects, the distribution of parameters in the envelopes and the physical processes forming the environment of these stars. Methods: We observed the J = 1-0 rotational transition of 13CO and C18O towards eight northern FU Orionis-type stars (V1057 Cyg, V1515 Cyg, V2492 Cyg, V2493 Cyg, V1735 Cyg, V733 Cep, RNO 1B and RNO 1C) and determine the spatial and velocity structure of the circumstellar gas on a scale of a few thousand AU. We derive temperatures and envelope masses and discuss the kinematics of the circumstellar material. Results: We detected extended CO emission associated with all our targets. Smaller-scale CO clumps were found to be associated with five objects with radii of 2000-5000 AU and masses of 0.02-0.5 M⊙; these are clearly heated by the central stars. Three of these envelopes are also strongly detected in the 2.7 mm continuum. No central CO clumps were detected around V733 Cep and V710 Cas which can be interpreted as envelopes but there are many other clumps in their environments. Traces of outflow activity were observed towards V1735 Cyg, V733 Cep and V710 Cas. Conclusions: The diversity of

Martian Dust Devil Movie, Phoenix Sol 104

NASA Technical Reports Server (NTRS)

2008-01-01

The Surface Stereo Imager on NASA's Phoenix Mars Lander caught this dust devil in action west of the lander in four frames shot about 50 seconds apart from each other between 11:53 a.m. and 11:56 a.m. local Mars time on Sol 104, or the 104th Martian day of the mission, Sept. 9, 2008.

Dust devils have not been detected in any Phoenix images from earlier in the mission, but at least six were observed in a dozen images taken on Sol 104.

Dust devils are whirlwinds that often occur when the Sun heats the surface of Mars, or some areas on Earth. The warmed surface heats the layer of atmosphere closest to it, and the warm air rises in a whirling motion, stirring dust up from the surface like a miniature tornado.

The dust devil visible in this sequence was about 1,000 meters (about 3,300 feet) from the lander when the first frame was taken, and had moved to about 1,700 meters (about 5,600 feet) away by the time the last frame was taken about two and a half minutes later. The dust devil was moving westward at an estimated speed of 5 meters per second (11 miles per hour), which is similar to typical late-morning wind speed and direction indicated by the telltale wind gauge on Phoenix.

This dust devil is about 5 meters (16 feet) in diameter. This is much smaller than dust devils that have been observed by NASA's Mars Exploration Rover Spirit much closer to the equator. It is closer in size to dust devils seen from orbit in the Phoenix landing region, though still smaller than those..

The image has been enhanced to make the dust devil easier to see. Some of the frame-to-frame differences in the appearance of foreground rocks is because each frame was taken through a different color filter.

The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.

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

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

Kuchner, Marc J.; McElwain, Michael; Padgett, Deborah L.

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

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

NASA Astrophysics Data System (ADS)

Kuchner, Marc J.; Silverberg, Steven M.; Bans, Alissa S.; Bhattacharjee, Shambo; Kenyon, Scott J.; Debes, John H.; Currie, Thayne; García, Luciano; Jung, Dawoon; Lintott, Chris; McElwain, Michael; Padgett, Deborah L.; Rebull, Luisa M.; Wisniewski, John P.; Nesvold, Erika; Schawinski, Kevin; Thaller, Michelle L.; Grady, Carol A.; Biggs, Joseph; Bosch, Milton; Černohous, Tadeáš; Durantini Luca, Hugo A.; Hyogo, Michiharu; Wah, Lily Lau Wan; Piipuu, Art; Piñeiro, Fernanda; Disk Detective Collaboration

2016-10-01

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

Spitzer c2d Legacy, Circumstellar Disks around wTT Stars

NASA Astrophysics Data System (ADS)

Wahhaj, Zahed; c2d Legacy Team

2007-05-01

The Spitzer Legacy Project From "Molecular Cores to Planet-forming Disks" conducted a 3.6 to 70um photometric survey of roughly 160 weak- line TTauri Stars (wTTs) and 20 classical TTauri stars (cTTs) in the nearby star-forming regions Chamaeleon, Lupus, Ophiuchus and Taurus. WTTs are so named because they possess weaker H-alpha emission lines signifying weaker disk accretion on to the star than cTTs. The evolution of dust disks around these young stars (Age 10 Myrs) is key to understanding planet formation. From the observed infrared excesses, we infer the presence of circumstellar disks around 12% of wTTs and 75% of cTTs. However, when considering on-cloud sources only, the wTTs disk fraction is 22%, while it is only 6% for off- cloud sources, suggesting an older age for the latter. WTTs, while not discernibly younger than cTTs in age diagnostics, in general have disks which exhibit lower fractional luminosities and larger inner clearings. However, quite a few wTTs systems have fractional disk luminosities as high as cTTs systems. In light of these findings, wTTs seem to be transitional objects between cTTs and debris disks.

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

NASA Technical Reports Server (NTRS)

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

A SYMMETRIC INNER CAVITY IN THE HD 141569A CIRCUMSTELLAR DISK

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

Mazoyer, J.; Choquet, É.; Perrin, M. D.

2016-02-20

Some circumstellar disks, called transitional or hybrid disks, present characteristics of both protoplanetary disks (significant amount of gas) and debris disks (evolved structures around young main-sequence stars, composed of second generation dust, from collisions between planetesimals). Therefore, they are ideal astrophysical laboratories to witness the last stages of planet formation. The circumstellar disk around HD 141569A was intensively observed and resolved in the past from space, but also from the ground. However, the recent implementation of high contrast imaging systems has opened up new opportunities to re-analyze this object. We analyzed Gemini archival data from the Near-infrared Coronagraphic Imager obtained inmore » 2011 in the H band, using several angular differential imaging techniques (classical ADI, LOCI, KLIP). These images reveal the complex structures of this disk with an unprecedented resolution. We also include archival Hubble Space Telescope images as an independent data set to confirm these findings. Using an analysis of the inner edge of the disk, we show that the inner disk is almost axisymmetrical. The measurement of an offset toward the east observed by previous authors is likely due to the fact that the eastern part of this disk is wider and more complex in substructure. Our precise reanalysis of the eastern side shows several structures, including a splitting of the disk and a small finger detached from the inner edge to the southeast. Finally, we find that the arc at 250 AU is unlikely to be a spiral, at least not at the inclination derived from the first ring, but instead could be interpreted as a third belt at a different inclination. If the very symmetrical inner disk edge is carved by a companion, the data presented here put additional constraints on its position. The observed very complex structures will be confirmed by the new generation of coronagraphic instrument (GPI, SPHERE). However, a full understanding of this

Spitzer-IRS Spectroscopic Studies of the Properties of Dust from Oxygen-Rich Asymptotic Giant Branch and Red Supergiant Stars

NASA Astrophysics Data System (ADS)

Sargent, Benjamin A.; Speck, A.; Volk, K.; Kemper, C.; Reach, W. T.; Lagadec, E.; Bernard, J.; McDonald, I.; Meixner, M.; Srinivasan, S.

2014-01-01

We analyze the dust emission features seen in Spitzer Space Telescope Infrared Spectrograph (IRS) spectra of Oxygen-rich (O-rich) asymptotic giant branch (AGB) and red supergiant (RSG) stars. The spectra come from the Spitzer Legacy program SAGE-Spectroscopy (PI: F. Kemper) and other archival Spitzer-IRS programs. The broad 10 and 20 micron emission features attributed to amorphous dust of silicate composition seen in the spectra show evidence for systematic differences in the centroid of both emission features between O-rich AGB and RSG populations. Radiative transfer modeling using the GRAMS grid of models of AGB and RSG stars suggests that the centroid differences are due to differences in dust properties. We investigate differences in dust composition, size, shape, etc that might be responsible for these spectral differences. We explore how these differences may arise from the different circumstellar environments around RSG and O-rich AGB stars. BAS acknowledges funding from NASA ADAP grant NNX13AD54G.

Identifying sources of aeolian mineral dust: Present and past

USGS Publications Warehouse

Muhs, Daniel R; Prospero, Joseph M; Baddock, Matthew C; Gill, Thomas E

2014-01-01

glacial periods are likely due to greater production of glaciogenic dust particles from expanded ice sheets and mountain glaciers, but could also include dust inputs from exposed continental and insular shelves now submerged. Future dust sources are difficult to assess, but will likely differ from those of the present because of global warming. Global warming could bring about shifts in dust sources by changes in degree or type of vegetation cover, changes in wind strength, and increases or decreases in the size of water bodies. A major uncertainty in assessing dust sources of the future is related to changes inhuman land use, which could affect land surface cover, particularly due to increased agricultural endeavors and water usage.

Very Large Telescope Interferometer observations of the dust geometry around R Coronae Borealis stars

NASA Astrophysics Data System (ADS)

Bright, S. N.; Chesneau, O.; Clayton, G. C.; De Marco, O.; Leão, I. C.; Nordhaus, J.; Gallagher, J. S.

2011-06-01

We are investigating the formation and evolution of dust around the hydrogen-deficient supergiants known as R Coronae Borealis (RCB) stars. We aim to determine the connection between the probable merger past of these stars and their current dust-production activities. We carried out high angular resolution interferometric observations of three RCB stars, namely RY Sgr, V CrA and V854 Cen, with the mid-infrared interferometer (MIDI) on the Very Large Telescope Interferometer (VLTI), using two telescope pairs. The baselines ranged from 30 to 60 m, allowing us to probe the dusty environment at very small spatial scales (˜50 mas or 400R★). The observations of the RCB star dust environments were interpreted using both geometrical models and one-dimensional radiative transfer codes. From our analysis, we find that asymmetric circumstellar material is apparent in RY Sgr, may also exist in V CrA and is possible for V854 Cen. Overall, we find that our observations are consistent with dust forming in clumps ejected randomly around the RCB star so that over time they create a spherically symmetric distribution of dust. However, we conclude that the determination of whether there is a preferred plane of dust ejection must wait until a time series of observations are obtained. Based on observations made with the Very Large Telescope Interferometer at Paranal Observatory under programme 079.D-0415.

Herschel/PACS photometry of transiting-planet host stars with candidate warm debris disks

NASA Astrophysics Data System (ADS)

Ardila, David R.; Merin, Bruno; Ribas, Alvaro; Bouy, Herve; Bryden, Geoffrey; Stapelfeldt, Karl R.; Padgett, Deborah

2015-01-01

Dust in debris disks is produced by colliding or evaporating planetesimals, which are remnants of the planet formation process. Warm dust disks, known by their emission at ≤24 μm, are rare (4% of FGK main sequence stars) and especially interesting because they trace material in the region likely to host terrestrial planets, where the dust has a very short dynamical lifetime. Statistical analyses of the source counts of excesses as found with the mid-IR Wide Field Infrared Survey Explorer (WISE) suggest that warm-dust candidates found for the Kepler transiting-planet host-star candidates can be explained by extragalactic or galactic background emission aligned by chance with the target stars. These statistical analyses do not exclude the possibility that a given WISE excess could be due to a transient dust population associated with the target. Here we report Herschel/PACS 100 and 160 micron follow-up observations of a sample of Kepler and non-Kepler transiting-planet candidates' host stars, with candidate WISE warm debris disks, aimed at detecting a possible cold debris disk in any one of them. No clear detections were found in any one of the objects at either wavelength. Our upper limits confirm that most objects in the sample do not have a massive debris disk like that in beta Pic. We also show that the planet-hosting star WASP-33 does not have a debris disk comparable to the one around eta Crv. Although the data cannot be used to rule out rare warm disks around the Kepler planet-hosting candidates, the lack of detections and the characteristics of neighboring emission found at far-IR wavelengths support an earlier result suggesting that most of the WISE-selected IR excesses around Kepler candidate host stars are likely due to either chance alignment with background IR-bright galaxies and/or to interstellar emission.

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

NASA Technical Reports Server (NTRS)

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;

Cooling of the North Atlantic by Saharan Dust

NASA Technical Reports Server (NTRS)

Lau, K. M.; Kim, K. M.

2007-01-01

Using aerosol optical depth, sea surface temperature, top-of-the-atmosphere solar radiation flux, and oceanic mixed-layer depth from diverse data sources that include NASA satellites, NCEP reanalysis, in situ observations, as well as long-term dust records from Barbados, we examine the possible relationships between Saharan dust and Atlantic sea surface temperature. Results show that the estimated anomalous cooling pattern of the Atlantic during June 2006 relative to June 2005 due to attenuation of surface solar radiation by Saharan dust remarkably resemble observations, accounting for approximately 30-40% of the observed change in sea surface temperature. Historical data analysis show that there is a robust negative correlation between atmospheric dust loading and Atlantic SST consistent with the notion that increased (decreased) Saharan dust is associated with cooling (warming) of the Atlantic during the early hurricane season (July- August-September).

Emission Lines in the Near-infrared Spectra of the Infrared Quintuplet Stars in the Galactic Center

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

Najarro, F.; Geballe, T. R.; Figer, D. F.

We report the detection of a number of emission lines in the 1.0–2.4 μ m spectra of four of the five bright-infrared dust-embedded stars at the center of the Galactic center’s (GC) Quintuplet Cluster. Spectroscopy of the central stars of these objects is hampered not only by the large interstellar extinction that obscures all of the objects in the GC, but also by the large amounts of warm circumstellar dust surrounding each of the five stars. The pinwheel morphologies of the dust observed previously around two of them are indicative of Wolf–Rayet colliding wind binaries; however, infrared spectra of eachmore » of the five have until now revealed only dust continua steeply rising to long wavelengths and absorption lines and bands from interstellar gas and dust. The emission lines detected, from ionized carbon and from helium, are broad and confirm that the objects are dusty late-type carbon Wolf–Rayet stars.« less

Marching Dust Devils

NASA Image and Video Library

2015-11-05

On an early fall afternoon in Ganges Chasma Valles Marineris, NASA Mars Reconnaissance Orbiter spacecraft managed to capture a cluster of eight dust devils, five of them in the enhanced color strip. They're together on a dark sandy surface that tilts slightly to the north, towards the Sun. Both of these factors help warm the surface and generate convection in the air above. The surface is streaked with the faint tracks of earlier dust devils. A pair of dust devils appears together at top right, spaced only 250 meters apart. These two have quite different morphologies. The bigger one (on the right) is about 100 meters in diameter and is shaped like a doughnut with a hole in the middle. Its smaller companion is more compact and plume-like, but it too has a small hole in the center, where the air pressure is lowest. It may be that the smaller dust devil is younger than the larger one. A row of four dust devils are in the middle of the color strip, separated by about 900 meters from one another. This image might answer some interesting questions about the behavior of dust devils. Dust devils are theoretically expected to migrate uphill on a sloping surface, or migrate downwind when there is a breeze. Where they are found close together in pairs, they are expected to rotate in opposite directions. HiRISE color observations can be used to determine the direction of rotation and-for fast moving dust devils-the direction of their travel. This is because the different color observations (infrared, red, and blue) are taken at slightly different times. The differences between the earliest color observation and the last tell us about the changes that took place during that time interval. All this requires careful analysis, but if these dust devils are moving fast enough, and spaced closely enough, these here might display some interesting "social dynamics," possibly marching together and rotating in alternating directions. http://photojournal.jpl.nasa.gov/catalog/PIA20045

Exozodiacal Dust Workshop

NASA Technical Reports Server (NTRS)

Backman, D. E. (Editor); Caroff, L. J. (Editor); Sandford, S. A. (Editor); Wooden, D. H. (Editor)

1998-01-01

The purpose of the workshop was to understand what effect circumstellar dust clouds will have on NASA's proposed Terrestrial Planet Finder (TPF) mission's ability to search for terrestrial-sized planets orbiting stars in the solar neighborhood. The workshop participants reviewed the properties of TPF, summarized what is known about the local zodiacal cloud and about exozodiacal clouds, and determined what additional knowledge must be obtained to help design TPF for maximum effectiveness within its cost constraint. Recommendations were made for ways to obtain that additional knowledge, at minimum cost. The workshop brought together approximately 70 scientists, from four different countries. The active participants included astronomers involved in the study of the local zodiacal cloud, in the formation of stars and planetary systems, and in the technologies and techniques of ground- and space-based infrared interferometry. During the course of the meeting, 15 invited talks and 20 contributed poster papers were presented, and there were four working sessions. This is a collection of the invited talks, contributed poster papers, and summaries of the working sessions.

The 0.4-Msun eclipsing binary CU Cancri. Absolute dimensions, comparison with evolutionary models and possible evidence for a circumstellar dust disk

NASA Astrophysics Data System (ADS)

Ribas, I.

2003-01-01

Photometric observations in the R and I bands of the detached M-type double-lined eclipsing binary CU Cnc have been acquired and analysed. The photometric elements obtained from the analysis of the light curves have been combined with an existing spectroscopic solution to yield high-precision (errors la 2%) absolute dimensions: MA=0.4333+/-0.0017 Msun, MB= 0.3980+/-0.0014 Msun, RA=0.4317+/-0.0052 Rsun, and RB=0.3908+/-0.0094 Rsun. The mean effective temperature of the system has been estimated to be Teff= 3140+/-150 K by comparing multi-band photometry (optical and infrared) with synthetic colors computed from state-of-the-art model atmospheres. Additionally, we have been able to obtain an estimate for the age ( ~ 320 Myr) and chemical composition ([Fe/H]~ 0.0) of the binary system through its membership of the Castor moving group. With all these observational constraints, we have carried out a critical test of recent stellar models for low-mass stars. The comparison reveals that most evolutionary models underestimate the radius of the stars by as much as 10%, thus confirming the trend observed by Torres & Ribas (\\cite{TR02}) for YY Gem and V818 Tau. In the mass-absolute magnitude diagram, CU Cnc is observed to be dimmer than other stars of the same mass and this makes the comparison with stellar models not so compelling. After ruling out a number of different scenarios, the apparent faintness of CU Cnc can be explained if its components are some 10% cooler than similar-mass stars or if there is some source of circumstellar dust absorption. The latter could be a tantalizing indirect evidence for a coplanar (Vega-like) dusty disk around this relatively young M-type binary. Tables 1 and 2 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/398/239}

H i and CO in the circumstellar environment of the S-type star RS Cancri

NASA Astrophysics Data System (ADS)

Libert, Y.; Winters, J. M.; Le Bertre, T.; Gérard, E.; Matthews, L. D.

2010-06-01

Context. The history of mass loss during the AGB phase is key to understanding the stellar evolution and the gas and dust replenishment of the interstellar medium. The mass-loss phenomenon presents fluctuations with a wide variety of timescales and spatial scales and requires combining data from multiple tracers. Aims: We study the respective contributions of the central source and of the external medium to the complex geometry of circumstellar ejecta. Methods: This paper presents Plateau de Bure Interferometer and IRAM 30-m telescope CO rotational line observations, along with H i data obtained with the Nançay Radio Telescope for the oxygen-rich semi-regular variable RS Cnc, in order to probe its circumstellar environment on different scales. Results: We detect both the CO(1-0) and the CO(2-1) rotational lines from RS Cnc. The line profiles are composite, comprising two components of half-width ~2 km s-1 and ~8 km s-1, respectively. Whereas the narrow velocity component seems to originate in an equatorial disk in the central part of the CO envelope, the broad component reveals a bipolar structure, with a north-south velocity gradient. In addition, we obtain new H i data on the source and around it in a field of almost 1 square degree. The H i line is centered on vLSR = 7 km s-1 in agreement with CO observations. A new reduction process reveals a complex extended structure in the northwest direction, of estimated size ~18', with a position angle (~310°) opposite the direction of the stellar proper motion (~140°). We derive an H i mass of ~3 × 10-2 M_⊙ for this structure. Based on a non spherical simulation, we find that this structure is consistent with arising from the interaction of the star undergoing mass loss at an average rate of ~10-7 M⊙ yr-1 over ~2-3 × 105 years with the interstellar medium. Conclusions: Using CO and H i lines, we show that the circumstellar environment around RS Cnc includes two related but well separated regions. With CO, we

Dust Devils in Gusev Crater, Sol 463

NASA Technical Reports Server (NTRS)

2005-01-01

This movie clip shows a several dust devils -- whirlwinds that loft dust into the air -- moving across a plain below the hillside vantage point of NASA's Mars Exploration Rover Spirit. Several of the dust devils are visible at once in some of the frames in this sequence. The local solar time was about 2 p.m., when the ground temperature was high enough to cause turbulence that kicks up dust devils as the wind blows across the plain. The number of seconds elapsed since the first frame is indicated at lower left of the images, typically 20 seconds between frames. Spirit's navigation camera took these images on the rover's 463rd martian day, or sol (April 22, 2005.) Contrast has been enhanced for anything in the images that changes from frame to frame, that is, for the dust devil.

Scientists expected dust devils since before Spirit landed. The landing area inside Gusev Crater is filled with dark streaks left behind when dust devils pick dust up from an area. It is also filled with bright 'hollows,' which are dust-filled miniature craters. Dust covers most of the terrain. Winds flow into and out of Gusev crater every day. The Sun heats the surface so that the surface is warm to the touch even though the atmosphere at 2 meters (6 feet) above the surface would be chilly. That temperature contrast causes convection. Mixing the dust, winds, and convection can trigger dust devils.

Heliotropic dust rings for Earth climate engineering

NASA Astrophysics Data System (ADS)

Bewick, R.; Lücking, C.; Colombo, C.; Sanchez, J. P.; McInnes, C. R.

2013-04-01

This paper examines the concept of a Sun-pointing elliptical Earth ring comprised of dust grains to offset global warming. A new family of non-Keplerian periodic orbits, under the effects of solar radiation pressure and the Earth's J2 oblateness perturbation, is used to increase the lifetime of the passive cloud of particles and, thus, increase the efficiency of this geoengineering strategy. An analytical model is used to predict the orbit evolution of the dust ring due to solar-radiation pressure and the J2 effect. The attenuation of the solar radiation can then be calculated from the ring model. In comparison to circular orbits, eccentric orbits yield a more stable environment for small grain sizes and therefore achieve higher efficiencies when the orbit decay of the material is considered. Moreover, the novel orbital dynamics experienced by high area-to-mass ratio objects, influenced by solar radiation pressure and the J2 effect, ensure the ring will maintain a permanent heliotropic shape, with dust spending the largest portion of time on the Sun facing side of the orbit. It is envisaged that small dust grains can be released from a circular generator orbit with an initial impulse to enter an eccentric orbit with Sun-facing apogee. Finally, a lowest estimate of 1 × 1012 kg of material is computed as the total mass required to offset the effects of global warming.

HIGH-RESOLUTION MID-INFRARED IMAGING OF THE CIRCUMSTELLAR DISKS OF HERBIG Ae/Be STARS

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

Marinas, N.; Telesco, C. M.; Packham, C.

2011-08-20

We have imaged the circumstellar environments of 17 Herbig Ae/Be stars at 12 and 18 {mu}m using MICHELLE on Gemini North and T-ReCS on Gemini South. Our sample contained eight Group I sources, those having large rising near- to far-infrared (IR) fluxes, and nine Group II sources, those having more modest mid-IR fluxes relative to their near-IR flux (in the classification of Meeus et al.). We have resolved extended emission from all Group I sources in our target list. The majority of these sources have radially symmetric mid-IR emission extending from a radius of 10 AU to hundreds of AU.more » Only one of the nine Group II sources is resolved at the FWHM level, with another two Group II sources resolved at fainter levels. Models by Dullemond et al. explain the observed spectral energy distribution of Group II sources using self-shadowed cold disks. If this is the case for all the Group II sources, we do not expect to detect extended emission with this study, since the IR emission measured should arise from a region only a few AU in size, which is smaller than our resolution. The fact that we do resolve some of the Group II sources implies that their disks are not completely flat, and might represent an intermediate stage. We also find that none of the more massive (>3 M{sub sun}) Herbig Ae/Be stars in our sample belongs to Group I, which may point to a relationship between stellar mass and circumstellar dust evolution. Disks around more massive stars might evolve faster so that stars are surrounded by a more evolved flat disk by the time they become optically visible, or they might follow a different evolutionary path altogether.« less

The Effect of Dust on the Martian Polar Vortices

NASA Technical Reports Server (NTRS)

Guzewich, Scott D.; Toigo, A. D.; Waugh, D. W.

2016-01-01

The influence of atmospheric dust on the dynamics and stability of the martian polar vortices is examined, through analysis of Mars Climate Sounder observations and MarsWRF general circulation model simulations. We show that regional and global dust storms produce transient vortex warming events that partially or fully disrupt the northern winter polar vortex for brief periods. Increased atmospheric dust heating alters the Hadley circulation and shifts the downwelling branch of the circulation poleward, leading to a disruption of the polar vortex for a period of days to weeks. Through our simulations, we find this effect is dependent on the atmospheric heating rate, which can be changed by increasing the amount of dust in the atmosphere or by altering the dust optical properties (e.g., single scattering albedo). Despite this, our simulations show that some level of atmospheric dust is necessary to produce a distinct northern hemisphere winter polar vortex.

The effect of dust on the martian polar vortices

NASA Astrophysics Data System (ADS)

Guzewich, Scott D.; Toigo, A. D.; Waugh, D. W.

2016-11-01

The influence of atmospheric dust on the dynamics and stability of the martian polar vortices is examined, through analysis of Mars Climate Sounder observations and MarsWRF general circulation model simulations. We show that regional and global dust storms produce ;transient vortex warming; events that partially or fully disrupt the northern winter polar vortex for brief periods. Increased atmospheric dust heating alters the Hadley circulation and shifts the downwelling branch of the circulation poleward, leading to a disruption of the polar vortex for a period of days to weeks. Through our simulations, we find this effect is dependent on the atmospheric heating rate, which can be changed by increasing the amount of dust in the atmosphere or by altering the dust optical properties (e.g., single scattering albedo). Despite this, our simulations show that some level of atmospheric dust is necessary to produce a distinct northern hemisphere winter polar vortex.

Shedding light on the Type Ia supernova extinction puzzle: dust location found

NASA Astrophysics Data System (ADS)

Bulla, M.; Goobar, A.; Dhawan, S.

2018-06-01

The colour evolution of reddened Type Ia supernovae can place strong constraints on the location of dust and help address the question of whether the observed extinction stems from the interstellar medium or from circumstellar material surrounding the progenitor. Here we analyse BV photometry of 48 reddened Type Ia supernovae from the literature and estimate the dust location from their B - V colour evolution. We find a time-variable colour excess E(B - V) for 15 supernovae in our sample and constrain dust to distances between 0.013 and 45 pc (4 × 1016 - 1020 cm). For the remaining supernovae, we obtain a constant E(B - V) evolution and place lower limits on the dust distance from the explosion. In all the 48 supernovae, the inferred dust location is compatible with an interstellar origin for the extinction. This is corroborated by the observation that supernovae with relatively nearby dust (≲ 1 pc) are located close to the center of their host galaxy, in high-density dusty regions where interactions between the supernova radiation and interstellar clouds close by are likely to occur. For supernovae showing time-variable E(B - V), we identify a potential preference for low RV values, unusually strong sodium absorption and blue-shifted and time-variable absorption features. Within the interstellar framework, this brings evidence to a proposed scenario where cloud-cloud collisions induced by the supernova radiation pressure can shift the grain size distribution to smaller values and enhance the abundance of sodium in the gaseous phase.

Langmuir wave phase-mixing in warm electron-positron-dusty plasmas

NASA Astrophysics Data System (ADS)

Pramanik, Sourav; Maity, Chandan

2018-04-01

An analytical study on nonlinear evolution of Langmuir waves in warm electron-positron-dusty plasmas is presented. The massive dust grains of either positively or negatively charged are assumed to form a fixed charge neutralizing background. A perturbative analysis of the fluid-Maxwell's equations confirms that the excited Langmuir waves phase-mix and eventually break, even at arbitrarily low amplitudes. It is shown that the nature of the dust-charge as well as the amount of dust grains can significantly influence the Langmuir wave phase-mixing process. The phase-mixing time is also found to increase with the temperature.

Spectroscopy and nonthermal processes

NASA Technical Reports Server (NTRS)

Querci, Monique

1987-01-01

Stellar spectra are analyzed to determine nonthermal processes for cool stars. A shock wave crossing model is supported by a study of the behavior of absorption and emission spectra. The shock waves are attributed to atmospheric kinetics. Circumstellar spectral lines are studied for information about gaseous circumstellar layers. The description of stellar envelopes is carried on through circumstellar dust. Characteristic properties of polarization in the dust are described in the case of specific stars, emphasizing narrowband observations in Mira, semiregular, and supergiant stars. Finally, the direct approach to measuring the angular diameters of stars and mapping the distribution of circumstellar dust and gas by lunar occultation or interferometry is discussed, using two prototype stars, an M supergiant and a dusty carbon star.

Response of the Water Cycle of West Africa and Atlantic to Radiative Forcing by Saharan Dust

NASA Technical Reports Server (NTRS)

Lau, K. M.; Kim, Kyu-Myong; Sud, Yogesh C.; Walker, Gregory L.

2010-01-01

The responses of the atmospheric water cycle and climate of West Africa and the Atlantic to radiative forcing of Saharan dust are studied using the NASA finite volume general circulation model (fvGCM), coupled to a mixed layer ocean. We find evidence in support of the "elevated heat pump" (EHP) mechanism that underlines the responses of the atmospheric water cycle to dust forcing as follow. During the boreal summer, as a result of large-scale atmospheric feed back triggered by absorbing dust aerosols, rainfall and cloudiness are enhanced over the West Africa/Easter Atlantic ITCZ, and suppressed over the West Atlantic and Caribbean. region. Shortwave radiation absorption by dust warms the atmosphere and cools the surface, while long wave has the opposite response. The elevated dust layer warms the air over Nest Africa and the eastern Atlantic. The condensation heating associated with the induced deep convection drives and maintains an anomalous large-scale east-west overturning circulation with rising motion over West Africa/eastern Atlantic, and sinking motion over the Caribbean region. The response also includes a strengthening of the West African monsoon, manifested in northward shift of the West Africa precipitation over land, increased low-level westerlies flow over West Africa at the southern edge of the dust layer, and a near surface energy fluxes, resulting in cooling of the Nest African land and the eastern Atlantic, and a warming in the West Atlantic and Caribbean. The EHP effect is most effective for moderate to highly absorbing dusts, and becomes minimized for reflecting dust with single scattering albedo at 0.95 or higher.

The abundance of HCN in circumstellar envelopes of AGB stars of different chemical type

NASA Astrophysics Data System (ADS)

Schöier, F. L.; Ramstedt, S.; Olofsson, H.; Lindqvist, M.; Bieging, J. H.; Marvel, K. B.

2013-02-01

Aims: A multi-transition survey of HCN (sub-) millimeter line emission from a large sample of asymptotic giant branch (AGB) stars of different chemical type is presented. The data are analysed and circumstellar HCN abundances are estimated. The sample stars span a large range of properties such as mass-loss rate and photospheric C/O-ratio. The analysis of the new data allows for more accurate estimates of the circumstellar HCN abundances and puts new constraints on chemical models. Methods: In order to constrain the circumstellar HCN abundance distribution a detailed non-local thermodynamic equilibrium (LTE) excitation analysis, based on the Monte Carlo method, is performed. Effects of line overlaps and radiative excitation from dust grains are included. Results: The median values for the derived abundances of HCN (with respect to H2) are 3 × 10-5, 7 × 10-7 and 10-7 for carbon stars (25 stars), S-type AGB stars (19 stars) and M-type AGB stars (25 stars), respectively. The estimated sizes of the HCN envelopes are similar to those obtained in the case of SiO for the same sample of sources and agree well with previous results from interferometric observations, when these are available. Conclusions: We find that there is a clear dependence of the derived circumstellar HCN abundance on the C/O-ratio of the star, in that carbon stars have about two orders of magnitude higher abundances than M-type AGB stars, on average. The derived HCN abundances of the S-type AGB stars have a larger spread and typically fall in between those of the two other types, however, slightly closer to the values for the M-type AGB stars. For the M-type stars, the estimated abundances are much higher than what would be expected if HCN is formed in thermal equilibrium. However, the results are also in contrast to predictions from recent non-LTE chemical models, where very little difference is expected in the HCN abundances between the various types of AGB stars. This publication is based on data

Interannual similarity in the Martian atmosphere during the dust storm season

NASA Astrophysics Data System (ADS)

Kass, D. M.; Kleinböhl, A.; McCleese, D. J.; Schofield, J. T.; Smith, M. D.

2016-06-01

We find that during the dusty season on Mars (southern spring and summer) of years without a global dust storm there are three large regional-scale dust storms. The storms are labeled A, B, and C in seasonal order. This classification is based on examining the zonal mean 50 Pa (˜25 km) daytime temperature retrievals from TES/MGS and MCS/MRO over 6 Mars Years. Regional-scale storms are defined as events where the temperature exceeds 200 K. Examining the MCS dust field at 50 Pa indicates that warming in the Southern Hemisphere is dominated by direct heating, while northern high latitude warming is a dynamical response. A storms are springtime planet encircling Southern Hemisphere events. B storms are southern polar events that begin near perihelion and last through the solstice. C storms are southern summertime events starting well after the end of the B storm. C storms show the most interannual variability.

Interannual Similarity in the Martian Atmosphere During the Dust Storm Season

NASA Technical Reports Server (NTRS)

Kass, D. M.; Kleinboehl, A.; McCleese, D. J.; Schofield, J. T.; Smith, M. D.

2016-01-01

We find that during the dusty season on Mars (southern spring and summer) of years without a global dust storm there are three large regional-scale dust storms. The storms are labeled A, B, and C in seasonal order. This classification is based on examining the zonal mean 50 Pa (approximately 25 km) daytime temperature retrievals from TES/MGS and MCS/MRO over 6 Mars Years. Regional-scale storms are defined as events where the temperature exceeds 200 K. Examining the MCS dust field at 50 Pa indicates that warming in the Southern Hemisphere is dominated by direct heating, while northern high latitude warming is a dynamical response. A storms are springtime planet encircling Southern Hemisphere events. B storms are southern polar events that begin near perihelion and last through the solstice. C storms are southern summertime events starting well after the end of the B storm. C storms show the most interannual variability.

High Spatial Resolution Mid-IR Imaging of V838 Monocerotis: Evidence of New Circumstellar Dust Creation

NASA Technical Reports Server (NTRS)

Winsiewski, John P.; Clampin, Mark; Bjorkman, Karen S.; Barry, Richard K.

2008-01-01

The eruptive variable V838 Monocerotis experienced three dramatic outbursts in early 2002. Its unexpectedly erratic photometric behavior wes matched by strong spectroscopic variability, in which the srar transitioned through the F, K, G spectral type s in 2002 February, reseabled a M5 supergiant by 2002 Aprll, and had a L-type super qiant spectram in 2002 October. The star is also infamous for producisg e spectacu lar light echo whose evolction has beer traced by HST/ACS. We report high sFatial resolution 11.2 and 18.1 micron imagicq of V838 Nonoceroris obrained with Genini Ob servatory's Klchelle in 2007 March. The 2007 flux density of the unresclved stellar core of is rouqhly 2 tixes brighter than zhaz observed in 2C04. We interpret tkese aata as evidecce t-at V838 Mon has experienced a new circumsellar dust creatioc evezt. We suggest that this newly c reated dust is Likely clumpy, and speculate that one (or ore) of Ekese clumps migh t have passed through the line-cf-sight in late 2036, prodccing the brief rnalti-wav elength pkotonetric event reported by Bond (2006) and Yunari ez a1 (2007). A gap o f spatially exzended therrrzl (18 micron) emission is present over radial distances of 1860 - 93000 AU from che central source. Assuming ejecta material expands at a constant velocity of 300-500 km/s, this gap suggests that no prior significanz circ unstellar dust production events have occurred withiin the past approx. 900-1500 years.

SOFIA Observations of SN 2010jl: Another Non-Detection of the 9.7 Micrometer Silicate Dust Feature

NASA Technical Reports Server (NTRS)

Williams, Brian J.; Fox, Ori D.

2015-01-01

We present photometric observations from the Stratospheric Observatory for Infrared Astronomy (SOFIA) at 11.1 micrometers of the Type IIn supernova (SN IIn) 2010jl. The SN is undetected by SOFIA, but the upper limits obtained, combined with new and archival detections from Spitzer at 3.6 and 4.5 micrometers, allow us to characterize the composition of the dust present. Dust in other SN IIn has been shown in previous works to reside in a circumstellar shell of material ejected by the progenitor system in the few millennia prior to explosion. Our model fits show that the dust in the system shows no evidence for the strong, ubiquitous 9.7 micrometer feature from silicate dust, suggesting the presence of carbonaceous grains. The observations are best fit with 0.01-0.05 solar mass of carbonaceous dust radiating at a temperature of approximately 550-620 degrees Kelvin. The dust composition may reveal clues concerning the nature of the progenitor system, which remains ambiguous for this subclass. Most of the single star progenitor systems proposed for SNe IIn, such as luminous blue variables, red supergiants, yellow hypergiants, and B[e] stars, all clearly show silicate dust in their pre-SN outflows. However, this post-SN result is consistent with the small sample of SNe IIn with mid-infrared observations, none of which show signs of emission from silicate dust in their infrared spectra.

Characterizing the Disk of a Recent Massive Collisional Event

NASA Astrophysics Data System (ADS)

Song, Inseok

2015-10-01

Debris disks play a key role in the formation and evolution of planetary systems. On rare occasions, circumstellar material appears as strictly warm infrared excess in regions of expected terrestrial planet formation and so present an interesting opportunity for the study of terrestrial planetary regions. There are only a few known cases of extreme, warm, dusty disks which lack any colder outer component including BD+20 307, HD 172555, EF Cha, and HD 23514. We have recently found a new system TYC 8830-410-1 belonging to this rare group. Warm dust grains are extremely short-lived, and the extraordinary amount of warm dust near these stars can only be plausibly explainable by a recent (or on-going) massive transient event such as the Late Heavy Bombardment (LHB) or plantary collisions. LHB-like events are seen generally in a system with a dominant cold disk, however, warm dust only systems show no hint of a massive cold disk. Planetary collisions leave a telltale sign of strange mid-IR spectral feature such as silica and we want to fully characterize the spectral shape of the newly found system with SOFIA/FORCAST. With SOFIA/FORCAST, we propose to obtain two narrow band photometric measurements between 6 and 9 microns. These FORCAST photometric measurements will constrain the amount and temperature of the warm disk in the system. There are less than a handful systems with a strong hint of recent planetary collisions. With the firmly constrained warm disk around TYC 8830-410-1, we will publish the discovery in a leading astronomical journal accompanied with a potential press release through SOFIA.

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

Tinyanont, Samaporn; Kasliwal, Mansi M.; Lau, Ryan

We present a systematic study of mid-infrared emission from 141 nearby supernovae (SNe) observed with Spitzer /IRAC as part of the ongoing SPIRITS survey. We detect 8 Type Ia and 36 core-collapse SNe. All Type Ia/Ibc SNe become undetectable within three years of explosion, whereas 22 ± 11% of Type II SNe continue to be detected. Five Type II SNe are detected even two decades after discovery (SN 1974E, 1979C, 1980K, 1986J, and 1993J). Warm dust luminosity, temperature, and a lower limit on mass are obtained by fitting the two IRAC bands, assuming an optically thin dust shell. We derive warm dust masses between 10{sup −6} and 10{sup −2}more » M {sub ⊙} and dust color temperatures between 200 and 1280 K. This observed warm dust could be pre-existing or newly created, but in either case represents a lower limit to the dust mass because cooler dust may be present. We present three case studies of extreme SNe. SN 2011ja (II-P) was over-luminous ([4.5] = −15.6 mag) at 900 days post explosion with increasing hot dust mass, suggesting either an episode of dust formation or intensifying circumstellar material (CSM) interactions heating up pre-existing dust. SN 2014bi (II-P) showed a factor of 10 decrease in dust mass over one month, suggesting either dust destruction or reduced dust heating. The IR luminosity of SN 2014C (Ib) stayed constant over 800 days, possibly due to strong CSM interaction with an H-rich shell, which is rare among stripped-envelope SNe. The observations suggest that this CSM shell originated from an LBV-like eruption roughly 100 years pre-explosion. The observed diversity demonstrates the power of mid-IR observations of a large sample of SNe.« less

Herschel/PACS photometry of transiting-planet host stars with candidate warm debris disks

NASA Astrophysics Data System (ADS)

Merín, Bruno; Ardila, David R.; Ribas, Álvaro; Bouy, Hervé; Bryden, Geoffrey; Stapelfeldt, Karl; Padgett, Deborah

2014-09-01

Dust in debris disks is produced by colliding or evaporating planetesimals, which are remnants of the planet formation process. Warm dust disks, known by their emission at ≤24 μm, are rare (4% of FGK main sequence stars) and especially interesting because they trace material in the region likely to host terrestrial planets, where the dust has a very short dynamical lifetime. Statistical analyses of the source counts of excesses as found with the mid-IR Wide Field Infrared Survey Explorer (WISE) suggest that warm-dust candidates found for the Kepler transiting-planet host-star candidates can be explained by extragalactic or galactic background emission aligned by chance with the target stars. These statistical analyses do not exclude the possibility that a given WISE excess could be due to a transient dust population associated with the target. Here we report Herschel/PACS 100 and 160 micron follow-up observations of a sample of Kepler and non-Kepler transiting-planet candidates' host stars, with candidate WISE warm debris disks, aimed at detecting a possible cold debris disk in any one of them. No clear detections were found in any one of the objects at either wavelength. Our upper limits confirm that most objects in the sample do not have a massive debris disk like that in β Pic. We also show that the planet-hosting star WASP-33 does not have a debris disk comparable to the one around η Crv. Although the data cannot be used to rule out rare warm disks around the Kepler planet-hosting candidates, the lack of detections and the characteristics of neighboring emission found at far-IR wavelengths support an earlier result suggesting that most of the WISE-selected IR excesses around Kepler candidate host stars are likely due to either chance alignment with background IR-bright galaxies and/or to interstellar emission. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important

Vulnerability Assessment of Dust Storms in the United States under a Changing Climate Scenario

EPA Science Inventory

Severe weather events, such as flooding, drought, forest fires, and dust storms can have a serious impact on human health. Dust storm events are not well predicted in the United States, however they are expected to become more frequent as global climate warms through the 21st cen...

The Copernicus observations - Interstellar or circumstellar material. [UV spectra of early stars

NASA Technical Reports Server (NTRS)

Steigman, G.; Strittmatter, P. A.; Williams, R. E.

1975-01-01

It is suggested that the sharp absorption lines observed in the ultraviolet spectra of early-type stars by the Copernicus satellite may be entirely accounted for by the circumstellar material in the H II regions and associated transition zones around the observed stars. If this interpretation is correct, the Copernicus results yield little information on the state of any interstellar (as opposed to circumstellar) gas and, in particular, shed little light on the degree of element depletion in interstellar space.

Increasing aeolian dust deposition to snowpacks in the Rocky Mountains inferred from snowpack, wet deposition, and aerosol chemistry

USGS Publications Warehouse

Clow, David W.; Williams, Mark W.; Schuster, Paul F.

2016-01-01

Mountain snowpacks are a vital natural resource for ∼1.5 billion people in the northern Hemisphere, helping to meet human and ecological demand for water in excess of that provided by summer rain. Springtime warming and aeolian dust deposition accelerate snowmelt, increasing the risk of water shortages during late summer, when demand is greatest. While climate networks provide data that can be used to evaluate the effect of warming on snowpack resources, there are no established regional networks for monitoring aeolian dust deposition to snow. In this study, we test the hypothesis that chemistry of snow, wet deposition, and aerosols can be used as a surrogate for dust deposition to snow. We then analyze spatial patterns and temporal trends in inferred springtime dust deposition to snow across the Rocky Mountains, USA, for 1993–2014. Geochemical evidence, including strong correlations (r2 ≥ 0.94) between Ca2+, alkalinity, and dust concentrations in snow deposited during dust events, indicate that carbonate minerals in dust impart a strong chemical signature that can be used to track dust deposition to snow. Spatial patterns in chemistry of snow, wet deposition, and aerosols indicate that dust deposition increases from north to south in the Rocky Mountains, and temporal trends indicate that winter/spring dust deposition increased by 81% in the southern Rockies during 1993–2014. Using a multivariate modeling approach, we determined that increases in dust deposition and decreases in springtime snowfall combined to accelerate snowmelt timing in the southern Rockies by approximately 7–18 days between 1993 and 2014. Previous studies have shown that aeolian dust emissions may have doubled globally during the 20th century, possibly due to drought and land-use change. Climate projections for increased aridity in the southwestern U.S., northern Africa, and other mid-latitude regions of the northern Hemisphere suggest that aeolian dust emissions may continue to

Several Dust Devils in Gusev Crater, Sol 461

NASA Technical Reports Server (NTRS)

2005-01-01

This movie clip shows a several dust devils -- whirlwinds that loft dust into the air -- moving across a plain below the hillside vantage point of NASA's Mars Exploration Rover Spirit. Several of the dust devils are visible at once in some of the 21 frames in this sequence. The local solar time was about 2 p.m., when the ground temperature was high enough to cause turbulence that kicks up dust devils as the wind blows across the plain. The number of seconds elapsed since the first frame is indicated at lower left of the images, typically 20 seconds between frames. Spirit's navigation camera took these images on the rover's 461st martian day, or sol (April 20, 2005.) Contrast has been enhanced for anything in the images that changes from frame to frame, that is, for the dust devil.

Scientists expected dust devils since before Spirit landed. The landing area inside Gusev Crater is filled with dark streaks left behind when dust devils pick dust up from an area. It is also filled with bright 'hollows,' which are dust-filled miniature craters. Dust covers most of the terrain. Winds flow into and out of Gusev crater every day. The Sun heats the surface so that the surface is warm to the touch even though the atmosphere at 2 meters (6 feet) above the surface would be chilly. That temperature contrast causes convection. Mixing the dust, winds, and convection can trigger dust devils.

Weather and Large-Scale Dust Activity during Martian Northern Spring and Summer

NASA Astrophysics Data System (ADS)

Kass, David M.; Kleinboehl, Armin; McCleese, Daniel J.; Schofield, John Tim; Smith, Michael D.; Heavens, Nicholas

2016-10-01

Observations from MCS, TES and THEMIS now span the northern spring and summer seasons (Ls 0° to 180°) of 10 consecutive Mars Years (MY 24 through MY 33). These observations show very similar behavior each year. However, there are also noticeable differences and clear signs of inter-annual variability. To best study the three datasets, we examine zonal mean observations of the lower atmosphere (50 Pa, or ~25 km). This region was selected to provide the best quality from all three instruments. We separate the daytime (afternoon) and nighttime (early morning) data in the analysis.The climate at these seasons is dominated by the aphelion cloud belt, and 50 Pa is often close to the peak opacities in the clouds. There is also a strong diurnal thermal tide signature throughout the season at this altitude. The overall behavior is a rapid cooling at the start of the year (as the dust from the dusty season sediments out of the atmosphere) over the the first ~30° of Ls. The coldest temperatures then last until about the solstice and are followed by a slow warming trend through most of the rest of the season. The last ~30° prior to the fall equinox show a more rapid warming trend and significant inter-annual variability. In about half of the years, there is a warming event of the 50 Pa temperatures in the second half of northern summer. The warming is the signature of dust being lofted above the boundary layer, into the lower atmosphere. Due to the relatively clear atmosphere overall, even modest amounts of dust will create noticeable temperature changes. The temperature signature of the dust is more pronounced in the northern hemisphere.

Detection of circumstellar material in a normal type Ia supernova.

PubMed

Patat, F; Chandra, P; Chevalier, R; Justham, S; Podsiadlowski, Ph; Wolf, C; Gal-Yam, A; Pasquini, L; Crawford, I A; Mazzali, P A; Pauldrach, A W A; Nomoto, K; Benetti, S; Cappellaro, E; Elias-Rosa, N; Hillebrandt, W; Leonard, D C; Pastorello, A; Renzini, A; Sabbadin, F; Simon, J D; Turatto, M

2007-08-17

Type Ia supernovae are important cosmological distance indicators. Each of these bright supernovae supposedly results from the thermonuclear explosion of a white dwarf star that, after accreting material from a companion star, exceeds some mass limit, but the true nature of the progenitor star system remains controversial. Here we report the spectroscopic detection of circumstellar material in a normal type Ia supernova explosion. The expansion velocities, densities, and dimensions of the circumstellar envelope indicate that this material was ejected from the progenitor system. In particular, the relatively low expansion velocities suggest that the white dwarf was accreting material from a companion star that was in the red-giant phase at the time of the explosion.

Hot exozodiacal dust resolved around Vega with IOTA/IONIC

NASA Astrophysics Data System (ADS)

Defrère, D.; Absil, O.; Augereau, J.-C.; di Folco, E.; Berger, J.-P.; Coudé du Foresto, V.; Kervella, P.; Le Bouquin, J.-B.; Lebreton, J.; Millan-Gabet, R.; Monnier, J. D.; Olofsson, J.; Traub, W.

2011-10-01

Context. Although debris discs have been detected around a significant number of main-sequence stars, only a few of them are known to harbour hot dust in their inner part where terrestrial planets may have formed. Thanks to infrared interferometric observations, it is possible to obtain a direct measurement of these regions, which are of prime importance for preparing future exo-Earth characterisation missions. Aims: We resolve the exozodiacal dust disc around Vega with the help of infrared stellar interferometry and estimate the integrated H-band flux originating from the first few AUs of the debris disc. Methods: Precise H-band interferometric measurements were obtained on Vega with the 3-telescope IOTA/IONIC interferometer (Mount Hopkins, Arizona). Thorough modelling of both interferometric data (squared visibility and closure phase) and spectral energy distribution was performed to constrain the nature of the near-infrared excess emission. Results: Resolved circumstellar emission within ~6 AU from Vega is identified at the 3-σ level. The most straightforward scenario consists in a compact dust disc producing a thermal emission that is largely dominated by small grains located between 0.1 and 0.3 AU from Vega and accounting for 1.23 ± 0.45% of the near-infrared stellar flux for our best-fit model. This flux ratio is shown to vary slightly with the geometry of the model used to fit our interferometric data (variations within ± 0.19%). Conclusions: The presence of hot exozodiacal dust in the vicinity of Vega, initially revealed by K-band CHARA/FLUOR observations, is confirmed by our H-band IOTA/IONIC measurements. Whereas the origin of the dust is still uncertain, its presence and the possible connection with the outer disc suggest that the Vega system is currently undergoing major dynamical perturbations.

GAS in Protoplanetary Systems (GASPS). I. First results

NASA Astrophysics Data System (ADS)

Mathews, G. S.; Dent, W. R. F.; Williams, J. P.; Howard, C. D.; Meeus, G.; Riaz, B.; Roberge, A.; Sandell, G.; Vandenbussche, B.; Duchêne, G.; Kamp, I.; Ménard, F.; Montesinos, B.; Pinte, C.; Thi, W. F.; Woitke, P.; Alacid, J. M.; Andrews, S. M.; Ardila, D. R.; Aresu, G.; Augereau, J. C.; Barrado, D.; Brittain, S.; Ciardi, D. R.; Danchi, W.; Eiroa, C.; Fedele, D.; Grady, C. A.; de Gregorio-Monsalvo, I.; Heras, A.; Huelamo, N.; Krivov, A.; Lebreton, J.; Liseau, R.; Martin-Zaidi, C.; Mendigutía, I.; Mora, A.; Morales-Calderon, M.; Nomura, H.; Pantin, E.; Pascucci, I.; Phillips, N.; Podio, L.; Poelman, D. R.; Ramsay, S.; Rice, K.; Riviere-Marichalar, P.; Solano, E.; Tilling, I.; Walker, H.; White, G. J.; Wright, G.

2010-07-01

Context. Circumstellar discs are ubiquitous around young stars, but rapidly dissipate their gas and dust on timescales of a few Myr. The Herschel Space Observatory allows for the study of the warm disc atmosphere, using far-infrared spectroscopy to measure gas content and excitation conditions, and far-IR photometry to constrain the dust distribution. Aims: We aim to detect and characterize the gas content of circumstellar discs in four targets as part of the Herschel science demonstration phase. Methods: We carried out sensitive medium resolution spectroscopy and high sensitivity photometry at λ ~ 60-190 μm using the Photodetector Array Camera and Spectrometer instrument on the Herschel Space Observatory. Results: We detect [OI] 63 μm emission from the young stars HD 169142, TW Hydrae, and RECX 15, but not HD 181327. No other lines, including [CII] 158 and [OI] 145, are significantly detected. All four stars are detected in photometry at 70 and 160 μm. Extensive models are presented in associated papers. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

The wind speeds, dust content, and mass-loss rates of evolved AGB and RSG stars at varying metallicity

NASA Astrophysics Data System (ADS)

Goldman, Steven R.; van Loon, Jacco Th.; Zijlstra, Albert A.; Green, James A.; Wood, Peter R.; Nanni, Ambra; Imai, Hiroshi; Whitelock, Patricia A.; Matsuura, Mikako; Groenewegen, Martin A. T.; Gómez, José F.

2017-02-01

We present the results of our survey of 1612-MHz circumstellar OH maser emission from asymptotic giant branch (AGB) stars and red supergiants (RSGs) in the Large Magellanic Cloud (LMC). We have discovered four new circumstellar maser sources in the LMC, and increased the number of reliable wind speeds from infrared (IR) stars in the LMC from 5 to 13. Using our new wind speeds, as well as those from Galactic sources, we have derived an updated relation for dust-driven winds: vexp ∝ ZL0.4. We compare the subsolar metallicity LMC OH/IR stars with carefully selected samples of more metal-rich OH/IR stars, also at known distances, in the Galactic Centre and Galactic bulge. We derive pulsation periods for eight of the bulge stars for the first time by using near-IR photometry from the Vista Variables in the Via Lactea survey. We have modelled our LMC OH/IR stars and developed an empirical method of deriving gas-to-dust ratios and mass-loss rates by scaling the models to the results from maser profiles. We have done this also for samples in the Galactic Centre and bulge and derived a new mass-loss prescription which includes luminosity, pulsation period, and gas-to-dust ratio dot{M} = 1.06^{+3.5}_{-0.8} × }10^{-5 (L/10^4 L_{⊙})^{0.9± 0.1}(P/500 {d})^{0.75± 0.3} (r_gd/200)^{-0.03± 0.07} M⊙ yr-1. The tightest correlation is found between mass-loss rate and luminosity. We find that the gas-to-dust ratio has little effect on the mass-loss of oxygen-rich AGB stars and RSGs within the Galaxy and the LMC. This suggests that the mass-loss of oxygen-rich AGB stars and RSGs is (nearly) independent of metallicity between a half and twice solar.

Polycyclic aromatic hydrocarbons and molecular hydrogen in oxygen-rich planetary nebulae: the case of NGC 6720

PubMed Central

Cox, N. L. J.; Pilleri, P.; Berné, O.; Cernicharo, J.; Joblin, C.

2015-01-01

Evolved stars are primary sources for the formation of polycyclic aromatic hydrocarbons (PAHs) and dust grains. Their circumstellar chemistry is usually designated as either oxygen-rich or carbon-rich, although dual-dust chemistry objects, whose infrared spectra reveal both silicate- and carbon-dust features, are also known. The exact origin and nature of this dual-dust chemistry is not yet understood. Spitzer-IRS mid-infrared spectroscopic imaging of the nearby, oxygen-rich planetary nebula NGC 6720 reveals the presence of the 11.3 μm aromatic (PAH) emission band. It is attributed to emission from neutral PAHs, since no band is observed in the 7–8 μm range. The spatial distribution of PAHs is found to closely follow that of the warm clumpy molecular hydrogen emission. Emission from both neutral PAHs and warm H2 is likely to arise from photo-dissociation regions associated with dense knots that are located within the main ring. The presence of PAHs together with the previously derived high abundance of free carbon (relative to CO) suggest that the local conditions in an oxygen-rich environment can also become conducive to in-situ formation of large carbonaceous molecules, such as PAHs, via a bottom-up chemical pathway. In this scenario, the same stellar source can enrich the interstellar medium with both oxygen-rich dust and large carbonaceous molecules. PMID:26924856

The global transport of dust: An intercontinental river of dust, microorganisms and toxic chemicals flows through the Earth's atmosphere

USGS Publications Warehouse

Griffin, Dale; Kellogg, Christina; Garrison, Virginia; Shinn, Eugene

2002-01-01

The coral reefs in the Caribbean have been deteriorating since the 1970s, and no one is quite sure why. Such environmental devastation is usually blamed on Homo sapiens, but that doesn’t seem to be what’s going on here. Recently, some scientists at the USGS think they’ve solved the puzzle: Bacteria and fungi have been hitching trans-Atlantic rides on dust from the Sahara desert and settling into the warm waters of the Caribbean. Microbiologist Dale Griffin and his colleagues make the case for this hypothesis and explore the dangers of dust and microbe transport across the globe.

A GCM Study of Responses of the Atmospheric Water Cycle of West Africa and the Atlantic to Saharan Dust Radiative Forcing

NASA Technical Reports Server (NTRS)

Lau, K. M.; Kim, K. M.; Sud, Y. C.; Walker, G. K.

2009-01-01

The responses of the atmospheric water cycle and climate of West Africa and the Atlantic to radiative forcing of Saharan dust are studied using the NASA finite volume general circulation model (fvGCM), coupled to a mixed layer ocean. We find evidence of an "elevated heat pump" (EHP) mechanism that underlines the responses of the atmospheric water cycle to dust forcing as follow. During the boreal summerr, as a result of large-scale atmospheric feedback triggered by absorbing dust aerosols, rainfall and cloudiness are ehanIed over the West Africa/Eastern Atlantic ITCZ, and suppressed over the West Atlantic and Caribbean region. Shortwave radiation absorption by dust warms the atmosphere and cools the surface, while longwave has the opposite response. The elevated dust layer warms the air over West Africa and the eastern Atlantic. As the warm air rises, it spawns a large-scale onshore flow carrying the moist air from the eastern Atlantic and the Gulf of Guinea. The onshore flow in turn enhances the deep convection over West Africa land, and the eastern Atlantic. The condensation heating associated with the ensuing deep convection drives and maintains an anomalous large-scale east-west overturning circulation with rising motion over West Africa/eastern Atlantic, and sinking motion over the Caribbean region. The response also includes a strengthening of the West African monsoon, manifested in a northward shift of the West Africa precipitation over land, increased low-level westerlies flow over West Africa at the southern edge of the dust layer, and a near surface westerly jet underneath the dust layer overr the Sahara. The dust radiative forcing also leads to significant changes in surface energy fluxes, resulting in cooling of the West African land and the eastern Atlantic, and warming in the West Atlantic and Caribbean. The EHP effect is most effective for moderate to highly absorbing dusts, and becomes minimized for reflecting dust with single scattering albedo at0

WISE Detections of Dust in the Habitable Zones of Planet-Bearing Stars

NASA Technical Reports Server (NTRS)

Morales, Farisa Y.; Padgett, Deborah L.; Bryden, Geoffrey; Werner, M. W.; Furlan, E.

2012-01-01

We use data from the Wide-field Infrared Survey Explorer (WISE) all-sky release to explore the incidence of warm dust in the habitable zones around exoplanet-host stars. Dust emission at 12 and/or 22 microns (T(sub dust) approx.300 and/or approx.150 K) traces events in the terrestrial planet zones; its existence implies replenishment by evaporation of comets or collisions of asteroids, possibly stirred by larger planets. Of the 591 planetary systems (728 extrasolar planets) in the Exoplanet Encyclopedia as of 2012 January 31, 350 are robustly detected by WISE at > or = 5(sigma) level. We perform detailed photosphere subtraction using tools developed for Spitzer data and visually inspect all the WISE images to confirm bona fide point sources. We find nine planet-bearing stars show dust excess emission at 12 and/or 22 microns at > or = 3(sigma) level around young, main-sequence, or evolved giant stars. Overall, our results yield an excess incidence of approx.2.6% for stars of all evolutionary stages, but approx.1% for planetary debris disks around main-sequence stars. Besides recovering previously known warm systems, we identify one new excess candidate around the young star UScoCTIO 108.

The brightest high-latitude 12-micron IRAS sources

NASA Technical Reports Server (NTRS)

Hacking, P.; Beichman, C.; Chester, T.; Neugebauer, G.; Emerson, J.

1985-01-01

The Infrared Astronomical Satellite (IRAS) Point Source catalog was searched for sources brighter than 28 Jy (0 mag) at 12 microns with absolute galactic latitude greater than 30 deg excluding the Large Magellanic Cloud. The search resulted in 269 sources, two of which are the galaxies NGC 1068 and M82. The remaining 267 sources are identified with, or have infrared color indices consistent with late-type stars some of which show evidence of circumstellar dust shells. Seven sources are previously uncataloged stars. K and M stars without circumstellar dust shells, M stars with circumstellar dust shells, and carbon stars occupy well-defined regions of infrared color-color diagrams.

Earlier vegetation green-up has reduced spring dust storms

PubMed Central

Fan, Bihang; Guo, Li; Li, Ning; Chen, Jin; Lin, Henry; Zhang, Xiaoyang; Shen, Miaogen; Rao, Yuhan; Wang, Cong; Ma, Lei

2014-01-01

The observed decline of spring dust storms in Northeast Asia since the 1950s has been attributed to surface wind stilling. However, spring vegetation growth could also restrain dust storms through accumulating aboveground biomass and increasing surface roughness. To investigate the impacts of vegetation spring growth on dust storms, we examine the relationships between recorded spring dust storm outbreaks and satellite-derived vegetation green-up date in Inner Mongolia, Northern China from 1982 to 2008. We find a significant dampening effect of advanced vegetation growth on spring dust storms (r = 0.49, p = 0.01), with a one-day earlier green-up date corresponding to a decrease in annual spring dust storm outbreaks by 3%. Moreover, the higher correlation (r = 0.55, p < 0.01) between green-up date and dust storm outbreak ratio (the ratio of dust storm outbreaks to times of strong wind events) indicates that such effect is independent of changes in surface wind. Spatially, a negative correlation is detected between areas with advanced green-up dates and regional annual spring dust storms (r = −0.49, p = 0.01). This new insight is valuable for understanding dust storms dynamics under the changing climate. Our findings suggest that dust storms in Inner Mongolia will be further mitigated by the projected earlier vegetation green-up in the warming world. PMID:25343265

Earlier vegetation green-up has reduced spring dust storms.

PubMed

Fan, Bihang; Guo, Li; Li, Ning; Chen, Jin; Lin, Henry; Zhang, Xiaoyang; Shen, Miaogen; Rao, Yuhan; Wang, Cong; Ma, Lei

2014-10-24

The observed decline of spring dust storms in Northeast Asia since the 1950s has been attributed to surface wind stilling. However, spring vegetation growth could also restrain dust storms through accumulating aboveground biomass and increasing surface roughness. To investigate the impacts of vegetation spring growth on dust storms, we examine the relationships between recorded spring dust storm outbreaks and satellite-derived vegetation green-up date in Inner Mongolia, Northern China from 1982 to 2008. We find a significant dampening effect of advanced vegetation growth on spring dust storms (r = 0.49, p = 0.01), with a one-day earlier green-up date corresponding to a decrease in annual spring dust storm outbreaks by 3%. Moreover, the higher correlation (r = 0.55, p < 0.01) between green-up date and dust storm outbreak ratio (the ratio of dust storm outbreaks to times of strong wind events) indicates that such effect is independent of changes in surface wind. Spatially, a negative correlation is detected between areas with advanced green-up dates and regional annual spring dust storms (r = -0.49, p = 0.01). This new insight is valuable for understanding dust storms dynamics under the changing climate. Our findings suggest that dust storms in Inner Mongolia will be further mitigated by the projected earlier vegetation green-up in the warming world.

Planetesimal Formation in the Warm, Inner Disk: Experiments with Tempered Dust

NASA Astrophysics Data System (ADS)

de Beule, Caroline; Landers, Joachim; Salamon, Soma; Wende, Heiko; Wurm, Gerhard

2017-03-01

It is an open question how elevated temperatures in the inner parts of protoplanetary disks influence the formation of planetesimals. We approach this problem here by studying the tensile strength of granular beds with dust samples tempered at different temperatures. We find via laboratory experiments that tempering at increasing temperatures is correlated with an increase in cohesive forces. We studied dust samples of palagonite (JSC Mars-1a) which were tempered for up to 200 hr at temperatures between 600 and 1200 K, and measured the relative tensile strengths of highly porous dust layers once the samples cooled to room temperature. Tempering increases the tensile strength from 800 K upwards. This change is accompanied by mineral transformations, the formation of iron oxide crystallites as analyzed by Mössbauer spectroscopy, changes in the number size distribution, and the morphology of the surface visible as cracks in larger grains. These results suggest a difference in the collisional evolution toward larger bodies with increasing temperature as collisional growth is fundamentally based on cohesion. While high temperatures might also increase sticking (not studied here), compositional evolution will already enhance the cohesion and the possibility of growing larger aggregates on the way toward planetesimals. This might lead to a preferred in situ formation of inner planets and explain the observed presence of dense inner planetary systems.

Planetesimal Formation in the Warm, Inner Disk: Experiments with Tempered Dust

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

De Beule, Caroline; Landers, Joachim; Salamon, Soma

2017-03-01

It is an open question how elevated temperatures in the inner parts of protoplanetary disks influence the formation of planetesimals. We approach this problem here by studying the tensile strength of granular beds with dust samples tempered at different temperatures. We find via laboratory experiments that tempering at increasing temperatures is correlated with an increase in cohesive forces. We studied dust samples of palagonite (JSC Mars-1a) which were tempered for up to 200 hr at temperatures between 600 and 1200 K, and measured the relative tensile strengths of highly porous dust layers once the samples cooled to room temperature. Temperingmore » increases the tensile strength from 800 K upwards. This change is accompanied by mineral transformations, the formation of iron oxide crystallites as analyzed by Mössbauer spectroscopy, changes in the number size distribution, and the morphology of the surface visible as cracks in larger grains. These results suggest a difference in the collisional evolution toward larger bodies with increasing temperature as collisional growth is fundamentally based on cohesion. While high temperatures might also increase sticking (not studied here), compositional evolution will already enhance the cohesion and the possibility of growing larger aggregates on the way toward planetesimals. This might lead to a preferred in situ formation of inner planets and explain the observed presence of dense inner planetary systems.« less

Climatic controls of the interannual to decadal variability in Saudi Arabian dust activity: Towards the development of a seasonal prediction tool

NASA Astrophysics Data System (ADS)

Yu, Y.; Notaro, M.; Liu, Z.; Alkolibi, F.; Fadda, E.; Bakhrjy, F.

2013-12-01

Atmospheric dust significantly influences the climate system, as well as human life in Saudi Arabia. Skillful seasonal prediction of dust activity with climatic variables will help prevent some negative social impacts of dust storms. Yet, the climatic regulators on Saudi Arabian dust activity remain largely unaddressed. Remote sensing and station observations show consistent seasonal cycles in Saudi Arabian dust activity, which peaks in spring and summer. The climatic controls on springtime and summertime Saudi Arabian dust activity during 1975-2010 are studied using observational and reanalysis data. Empirical Orthogonal Function (EOF) of the observed Saudi Arabian dust storm frequency shows a dominant homogeneous pattern across the country, which has distinct interannual and decadal variations, as revealed by the power spectrum. Regression and correlation analyses reveal that Saudi Arabian dust activity is largely tied to precipitation on the Arabian Peninsula in spring and northwesterly (Shamal) wind in summer. On the seasonal-interannual time scale, warm El Niño-Southern Oscillation (ENSO) phase (El Niño) in winter-to-spring inhibits spring dust activity by increasing the precipitation over the Rub'al Khali Desert, a major dust source region on the southern Arabian Peninsula; warm ENSO and warm Indian Ocean Basin Mode (IOBM) in winter-to-spring favor less summer dust activity by producing anomalously low sea-level pressure over eastern north Africa and Arabian Peninsula, which leads to the reduced Shamal wind speed. The decadal variation in dust activity is likely associated with the Atlantic Multidecadal Oscillation (AMO), which impacts Sahel rainfall and North African dust, and likely dust transport to Saudi Arabia. The Pacific Decadal Oscillation (PDO) and tropical Indian Ocean SST also have influence on the decadal variation in Saudi Arabian dust activity, by altering precipitation over the Arabian Peninsula and summer Shamal wind speed. Using eastern

Coordinated Stem and NanoSIMS Analysis of Enstatite Whiskers in Interplanetary Dust Particles

NASA Technical Reports Server (NTRS)

Nakamura-Messenger, K.; Messenger, Scott; Keller, L. P.

2009-01-01

Enstatite whiskers (less than 10 micrometer length, less than 200 nanometer width) occur in chondritic-porous interplanetary dust particles (CP IDPs), an Antarctic micrometeorite and a comet 81P/Wild-2 sample. The whiskers are typically elongated along the [100] axis and contain axial screw dislocations, while those in terrestrial rocks and meteorites are elongated along [001]. The unique crystal morphologies and microstructures are consistent with the enstatite whiskers condensing above approximately 1300 K in a low-pressure nebular or circumstellar gas. To constrain the site of enstatite whisker formation, we carried out coordinated mineralogical, chemical and oxygen isotope measurements on enstatite whiskers in a CP IDP.

SPITZER SEARCH FOR DUST DISKS AROUND CENTRAL STARS OF PLANETARY NEBULAE

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

Bilikova, Jana; Chu Youhua; Gruendl, Robert A.

2012-05-01

Two types of dust disks have been discovered around white dwarfs (WDs): small dust disks within the Roche limits of their WDs and large dust disks around hot WDs extending to radial distances of 10-10{sup 2} AU. The majority of the latter WDs are central stars of planetary nebulae (CSPNs). We have therefore used archival Spitzer Infrared Array Camera (IRAC) and Multiband Imaging Photometer for Spitzer (MIPS) observations of PNs to search for CSPNs with IR excesses and to make a comparative investigation of dust disks around stars at different evolutionary stages. We have examined available images of 72 resolvedmore » PNs in the Spitzer archive and found 56 of them large enough for the CSPN to be resolved from the PN. Among these, only 42 CSPNs are visible in IRAC and/or MIPS images and selected for photometric measurements. From the spectral energy distributions (SEDs) of these CSPNs, we find 19 cases with clear IR excess. Of these, seven are [WC]-type stars, two have apparent visual companions that account for the observed excess emission, two are symbiotic CSPNs, and in eight cases the IR excess originates from an extended emitter, likely a dust disk. For some of these CSPNs, we have acquired follow-up Spitzer MIPS images, Infrared Spectrograph spectra, and Gemini NIRI and Michelle spectroscopic observations. The SEDs and spectra show a great diversity in the emission characteristics of the IR excesses, which may imply different mechanisms responsible for the excess emission. For CSPNs whose IR excesses originate from dust continuum, the most likely dust production mechanisms are (1) breakup of bodies in planetesimal belts through collisions and (2) formation of circumstellar dust disks through binary interactions. A better understanding of post-asymptotic giant branch binary evolution as well as debris disk evolution along with its parent star is needed to distinguish between these different origins. Future observations to better establish the physical

SO and SO2 in mass-loss envelopes of red giants - Probes of nonequilibrium circumstellar chemistry and mass-loss rates

NASA Technical Reports Server (NTRS)

Sahai, Raghvendra; Wannier, Peter G.

1992-01-01

SO emission was searched for in one or more of four transitions toward 23 oxygen-rich red giant or supergiant stars and one S star, selected primarily on the basis of their nonmaser SiO emission. SO was detected in a total of 14 circumstellar envelopes, 13 of which are new detections. The circumstellar abundance of SO (and SO2) is significantly enhanced over the equilibrium value achieved in the photospheres of these stars. In general, the SO abundances are significantly larger than predicted by nonequilibrium circumstellar chemistry models. Sulfur cannot be significantly depleted onto circumstellar grains, and probably exists as H2S (and/or SH) in the inner regions of the envelopes. The SO rotational-level population in most circumstellar envelopes observed is characterized by excitation temperatures less than or approximately equal to 50 K. The circumstellar abundance of SO2 is comparable to, or larger than, that of SO, ruling out the 'large' value adopted for the unshielded photodissociation rate for SO2 in recent models.

Constraining the Post-Thermal Pulse Mass-Loss History of R Scl with SOFIA/FORCAST

NASA Astrophysics Data System (ADS)

Hankins, Matthew; Herter, Terry; maercker, matthias; Lau, Ryan M.; Sloan, Greg

2018-06-01

R Sculptoris (R Scl) is a nearby (~370 pc) carbon star with a massive circumstellar shell (Mshell∼7×10‑3 M⊙) which is thought to have been produced by a thermal pulse event ∼2200 years ago. We observed R Scl with the Faint Object InfraRed CAMera for the SOFIA Telescope (FORCAST) at 19.7, 25.2, 31.5, 34.8, and 37.1 μm to study its circumstellar dust emission. Maps of the infrared emission were used to examine the morphology and temperature structure of the spatially extended dust emission. We used the radiative transfer code DUSTY to fit the radial density profile of the circumstellar material, and find that a geometrically thin dust shell cannot reproduce the observed emission. Instead, a second dust component is needed to model the emission. This component, which lies interior to the dust shell, traces the post-thermal pulse mass loss of R Scl and is indicative of a slow decline in the star’s mass loss over thousands of years. This result is at odds with 'classical' thermal pulse models but is consistent with earlier observations of molecular gas in R Scl’s circumstellar environment.

Long-term variability of dust events in Iceland (1949-2011)

NASA Astrophysics Data System (ADS)

Dagsson-Waldhauserova, P.; Arnalds, O.; Olafsson, H.

2014-06-01

Long-term frequency of atmospheric dust observations was investigated for the southern part of Iceland and merged with results obtained from the Northeast Iceland (Dagsson-Waldhauserova et al., 2013). In total, over 34 dust days per year on average occurred in Iceland based on conventionally used synoptic codes for dust. Including codes 04-06 into the criteria for dust observations, the frequency was 135 dust days annually. The Sea Level Pressure (SLP) oscillation controlled whether dust events occurred in NE (16.4 dust days annually) or in southern part of Iceland (about 18 dust days annually). The most dust-frequent decade in S Iceland was the 1960s while the most frequent decade in NE Iceland was the 2000s. A total of 32 severe dust storms (visibility < 500 m) was observed in Iceland with the highest frequency during the 2000s in S Iceland. The Arctic dust events (NE Iceland) were typically warm and during summer/autumn (May-September) while the Sub-Arctic dust events (S Iceland) were mainly cold and during winter/spring (March-May). About half of dust events in S Iceland occurred in winter or at sub-zero temperatures. A good correlation was found between PM10 concentrations and visibility during dust observations at the stations Vik and Storhofdi. This study shows that Iceland is among the dustiest areas of the world and dust is emitted the year-round.

Heterogeneous chemistry of atmospheric mineral dust particles and their resulting cloud-nucleation properties

NASA Astrophysics Data System (ADS)

Sullivan, Ryan Christopher

Mineral dust particles are a major component of tropospheric aerosol mass and affect regional and global atmospheric chemistry and climate. Dust particles experience heterogeneous reactions with atmospheric gases that alter the gas and particle-phase chemistry. These in turn influence the warm and cold cloud nucleation ability and optical properties of the dust particles. This dissertation investigates the atmospheric chemistry of mineral dust particles and their role in warm cloud nucleation through a combination of synergistic field measurements, laboratory experiments, and theoretical modeling. In-situ measurements made with a single-particle mass spectrometer during the ACE-Asia field campaign in 2001 provide the motivation for this work. The observed mixing state of the individual ambient particles with secondary organic and inorganic components is described in Chapter 2. A large Asian dust storm occurred during the campaign and produced dramatic changes in the aerosol's composition and mixing state. The effect of particle size and mineralogy on the atmospheric processing of individual dust particles is explored in Chapters 3 & 4. Sulfate was found to accumulate preferentially in submicron iron and aluminosilicate-rich dust particles, while nitrate and chloride were enriched in supermicron calcite-rich dust. The mineral dust (and sea salt particles) were also enriched in oxalic acid, the dominant component of water soluble organic carbon. Chapter 5 explores the roles of gas-phase photochemistry and partitioning of the diacids to the alkaline particles in producing this unique behavior. The effect of the dust's mixing state with secondary organic and inorganic components on the dust particles' solubility, hygroscopicity, and thus warm cloud nucleation properties is explored experimentally and theoretically in Chapter 6. Cloud condensation nucleation (CCN) activation curves revealed that while calcium nitrate and calcium chloride particles were very hygroscopic

Probing Cosmic Infrared Sources: A Computer Modeling Approach

DTIC Science & Technology

1992-06-01

developed to study various physical phenomena involving dust grains, e.g., molecule formation on grains, grain formation in expanding circumstellar...EVALUATION OF METHODS OF ANALYSIS IN INFRARED ASTR9?NOMY 16 4.0 THEORETICAL STUDIES INVOLVING DUST GRAINS., 16 4.1 Theory of Molecule Formation on Dust Grains...17 4.2 Modeling Grain Formation in Stellar Outflows 7 18 4.3 Infrared Emission from Fractal Grains * 19 4.4 Photochemistry in Circumstellar Envelopes

Infrared heterodyne spectroscopy of circumstellar molecules

NASA Technical Reports Server (NTRS)

Betz, A. L.; Mclaren, R. A.

1980-01-01

Ammonia has been detected in the circumstellar envelopes of IRC+10216, VY CMa, VX Sgr, and IRC+10420. A number of absorption lines of (N-14)H3 in the nu sub 2 vibration-rotation band around 28 THz (950 per cm) have been observed at a velocity resolution of 0.2 km/s. Typical linewidths are 1 to 4 km/s, and the details of the line profiles provide additional insights on the process of mass loss in these stars.

Comparative Studies of the Dust around Red Supergiant and Oxygen-Rich Asymptotic Giant Branch Stars in the Local Universe

NASA Astrophysics Data System (ADS)

Sargent, Benjamin; Srinivasan, Sundar; Speck, Angela K.; Volk, Kevin; Kemper, Ciska; Reach, William; Lagadec, Eric; Bernard, Jean-Philippe; McDonald, Iain; Meixner, Margaret; Sloan, Greg; Jones, Olivia

2015-08-01

We analyze the dust emission features seen in Spitzer Space Telescope Infrared Spectrograph (IRS) spectra of red supergiant (RSG) and oxygen-rich asymptotic giant branch (AGB) stars in the Large Magellanic Cloud and Small Magellanic Cloud galaxies and in various Milky Way globular clusters. The spectra come from the Spitzer Legacy program SAGE-Spectroscopy (PI: F. Kemper), the Spitzer program SMC-Spec (PI: G. Sloan), and other archival Spitzer-IRS programs. The broad 10 and 20 μm emission features attributed to amorphous dust of silicate composition seen in the spectra show evidence for systematic differences in the centroid of both emission features between O-rich AGB and RSG populations. Radiative transfer modeling using the GRAMS grid of models of AGB and RSG stars suggests that the centroid differences are due to differences in dust properties. We investigate differences in dust composition, size, shape, etc that might be responsible for these spectral differences. We explore how these differences may arise from the different circumstellar environments around RSG and O-rich AGB stars and assess effects of varying metallicity (LMC versus SMC versus Milky Way globular cluster) and other properties (mass-loss rate, luminosity, etc.) on the dust originating from these stars. BAS acknowledges funding from NASA ADAP grant NNX13AD54G.

Comparative Studies of the Dust around Red Supergiant and Oxygen-Rich Asymptotic Giant Branch Stars in the Local Universe

NASA Astrophysics Data System (ADS)

Sargent, B. A.; Srinivasan, S.; Speck, A.; Volk, K.; Kemper, F.; Reach, W.; Lagadec, E.; Bernard, J.-P.; McDonald, I.; Meixner, M.; Sloan, G. C.; Jones, O.

We analyze the dust emission features seen in Spitzer Space Telescope Infrared Spectrograph (IRS) spectra of red supergiant (RSG) and oxygen-rich asymptotic giant branch (AGB) stars in the Large Magellanic Cloud and Small Magellanic Cloud galaxies and in various Milky Way globular clusters. The spectra come from the Spitzer Legacy program SAGE-Spectroscopy (PI: F. Kemper), the Spitzer program SMC-Spec (PI: G. Sloan), and other archival Spitzer-IRS programs. The broad 10 and 20 micron emission features attributed to amorphous dust of silicate composition seen in the spectra show evidence for systematic differences in the centroid of both emission features between O-rich AGB and RSG populations. Radiative transfer modeling using the GRAMS grid of models of AGB and RSG stars suggests that the centroid differences are due to differences in dust properties. We investigate differences in dust composition, size, shape, etc that might be responsible for these spectral differences. We explore how these differences may arise from the different circumstellar environments around RSG and O-rich AGB stars and assess effects of varying metallicity (LMC versus SMC versus Milky Way globular cluster) and other properties (mass-loss rate, luminosity, etc.) on the dust originating from these stars. BAS acknowledges funding from NASA ADAP grant NNX13AD54G.

On large-scale transport of dust storms and anthropogenic dust-falls over east Asia observed in central Korea in 2009

NASA Astrophysics Data System (ADS)

Chung, Y. S.; Kim, Hak-Sung; Chun, Youngsin

2014-05-01

Dust air pollution has been routinely monitored in central Korea for the last two decades. In 2009, there were eight typical episodes of significant dust loadings in the air: four were caused by dust storms from deserts in Mongolia and Northern China, while the remaining were typical cases of anthropogenic air pollution masses arriving from the Yellow Sea and East China. These natural dust loadings occurred with cool northwesterly airflows in the forward side of an intense anticyclone coming from Mongolia and Siberia. The mean concentrations of the four natural dustfall cases for TSP, PM10 and PM2.5 were 632, 480 and 100 μg m-3, respectively. In contrast, the anthropogenic dust-pollution episodes occurred with the warm westerly and southwesterly airflows in the rear side of an anticyclone. This produced a favorable atmospheric and chemical condition for the build-up of anthropogenic dust air pollution in the Yellow Sea. The mean concentrations of the four anthropogenic dust loadings for TSP, PM10 and PM2.5 were 224, 187 and 137 μg m-3, respectively. The contents of fine dust loadings of PM2.5 were comparatively high in the cases of anthropogenic air pollution. High atmospheric concentrations of fine particles in the atmosphere cause poor visibility and constitute a health hazard. Satellite observations clearly showed the movement of dust-pollution masses from Mongolia and Northern China and from the Yellow Sea and East China that caused these dust pollution episodes in Korea.

Probing the pre-PN Mass Loss Histories in the PPN Dust Shells

NASA Astrophysics Data System (ADS)

Ueta, T.

2001-12-01

Proto-planetary nebulae (PPNs) are immediate progenitors of planetary nebulae (PNs) rapidly evolving over a relatively short time scale. Unlike the full-fledged PNs, the circumstellar dust shells of PPNs have neither been photo-ionized nor been swept up by fast winds. Since the PPN shells retain pristine fossil records of mass loss histories of these stars during the pre-PN phases, these dust shells provide ideal astronomical laboratories in which to investigate the origin of complex PN structures that we observe. We have conducted imaging surveys of the PPN shells in mid-infrared and optical wavelengths, probing the dust distribution directly via mid-infrared thermal dust emission arising from the shells and indirectly via dust-scattered stellar optical emission passing through the shells. From these surveys, we have found that (1) the PPN shells are intrinsically axisymmetric due to equatorially-enhanced superwind mass loss that occurred immediately before the beginning of the PPN phase, and (2) the variable degree of equatorial enhancement in the shells, which is probably related to the progenitor mass, has resulted in different optical depths and morphologies. To characterize the PPN shell geometries, we have developed and employed a 2.5 dimensional radiative transfer code that treats dust absorption, reemission, and an/isotropic scattering in any axisymmetric system illuminated by a central energy source. In the code, the dust optical properties are derived from the laboratory-measured refractive index using Mie theory allowing a distribution of sizes for each species in each composition layer in the shell. Our numerical analysis would be able to de-project and recover 3-D geometrical quantities, such as the pole-to-equator density ratio, from the observational data. These model calculations would provide constraining parameters for hydrodynamical models intended to generate equatorial enhancements during dust mass loss as well as initial parameters for

Silicate Dust in Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Xie, Yanxia; Li, Aigen; Hao, Lei

2017-01-01

The unification theory of active galactic nuclei (AGNs) hypothesizes that all AGNs are surrounded by an anisotropic dust torus and are essentially the same objects but viewed from different angles. However, little is known about the dust that plays a central role in the unification theory. There are suggestions that the AGN dust extinction law appreciably differs from that of the Galaxy. Also, the silicate emission features observed in type 1 AGNs appear anomalous (I.e., their peak wavelengths and widths differ considerably from that of the Galaxy). In this work, we explore the dust properties of 147 AGNs of various types at redshifts z≲ 0.5, with special attention paid to 93 AGNs that exhibit the 9.7 and 18 μm silicate emission features. We model their silicate emission spectra obtained with the Infrared Spectrograph aboard the Spitzer Space Telescope. We find that 60/93 of the observed spectra can be well explained with “astronomical silicate,” while the remaining sources favor amorphous olivine or pyroxene. Most notably, all sources require the dust to be micron-sized (with a typical size of ˜1.5 ± 0.1 μm), much larger than submicron-sized Galactic interstellar grains, implying a flat or “gray” extinction law for AGNs. We also find that, while the 9.7 μm emission feature arises predominantly from warm silicate dust of temperature T ˜ 270 K, the ˜5-8 μm continuum emission is mostly from carbon dust of T ˜ 640 K. Finally, the correlations between the dust properties (e.g., mass, temperature) and the AGN properties (e.g., luminosity, black hole mass) have also been investigated.

AN INVESTIGATION OF THE DUST CONTENT IN THE GALAXY PAIR NGC 1512/1510 FROM NEAR-INFRARED TO MILLIMETER WAVELENGTHS

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

Liu Guilin; Calzetti, Daniela; Yun, Min S.

2010-03-15

We combine new ASTE/AzTEC 1.1 mm maps of the galaxy pair NGC 1512/1510 with archival Spitzer IRAC and MIPS images covering the wavelength range 3.6-160 {mu}m from the SINGS project. The availability of the 1.1 mm map enables us to measure the long-wavelength tail of the dust emission in each galaxy, and in sub-galactic regions in NGC 1512, and to derive accurate dust masses. The two galaxies form a pair consisting of a large, high-metallicity spiral (NGC 1512) and a low-metallicity, blue compact dwarf (NGC 1510), which we use to compare similarities and contrast differences. Using the models of Drainemore » and Li, the derived total dust masses are (2.4 {+-} 0.6) x 10{sup 7} M {sub sun} and (1.7 {+-} 3.6) x 10{sup 5} M {sub sun} for NGC 1512 and NGC 1510, respectively. The derived ratio of dust mass to H I gas mass for the galaxy pair, M{sub d}/M{sub H{sub 1}}{approx}0.0034, is much lower (by at least a factor of 3) than expected, as previously found by Draine et al. In contrast, regions within NGC 1512, specifically the central region and the arms, do not show such unusually low M{sub d}/M{sub H{sub 1}} ratios; furthermore, the dust-to-gas ratio is within expectations for NGC 1510. These results suggest that a fraction of the H I included in the determination of the M{sub d}/M{sub H{sub 1}} ratio of the NGC 1512/NGC 1510 pair is not associated with the star-forming disks/regions of either galaxy. Using the dust masses derived from the models of Draine and Li as references, we perform simple two-temperature modified blackbody fits to the far-infrared/millimeter data of the two galaxies and the sub-regions of NGC 1512, in order to derive and compare the dust masses associated with warm and cool dust temperature components. As generally expected, the warm dust temperature of the low-metallicity, low-mass NGC 1510 (T{sub w} {approx} 36 K) is substantially higher than the corresponding warm temperature of the high-metallicity spiral NGC 1512 (T{sub w} {approx} 24 K

The Dust Content and Opacity of Actively Star-Forming Galaxies

NASA Technical Reports Server (NTRS)

Calzetti, Daniela; Armus, Lee; Bohlin, Ralph C.; Kinney, Anne L.; Koornneef, Jan; Storchi-Bergmann, Thaisa

2000-01-01

We present far-infrared (FIR) photometry at 150 and 205 micron(s) of eight low-redshift starburst galaxies obtained with the Infrared Space Observatory (ISO) ISOPHOT. Five of the eight galaxies are detected in both wave bands, and these data are used, in conjunction with IRAS archival photometry, to model the dust emission at lambda approximately greater than 40 microns. The FIR spectral energy distributions (SEDs) are best fitted by a combination of two modified Planck functions, with T approx. 40 - 55 K (warm dust) and T approx. 20-23 K (cool dust) and with a dust emissivity index epsilon = 2. The cool dust can be a major contributor to the FIR emission of starburst galaxies, representing up to 60% of the total flux. This component is heated not only by the general interstellar radiation field, but also by the starburst itself. The cool dust mass is up to approx. 150 times larger than the warm dust mass, bringing the gas-to-dust ratios of the starbursts in our sample close to Milky Way values, once resealed for the appropriate metallicity. The ratio between the total dust FIR emission in the range 1-1000 microns and the IRAS FIR emission in the range 40 - 120 microns is approx. 1.75, with small variations from galaxy to galaxy. This ratio is about 40% larger than previously inferred from data at millimeter wavelengths. Although the galaxies in our sample are generally classified as "UV bright," for four of them the UV energy emerging shortward of 0.2 microns is less than 15% of the FIR energy. On average, about 30% of the bolometric flux is coming out in the UV-to-near-IR wavelength range; the rest is emitted in the FIR. Energy balance calculations show that the FIR emission predicted by the dust reddening of the UV-to-near-IR stellar emission is within a factor of approx. 2 of the observed value in individual galaxies and within 20% when averaged over a large sample. If our sample of local starbursts is representative of high-redshift (z approx. greater than 1

Circumstellar Disks and Outflows in Turbulent Molecular Cloud Cores: Possible Formation Mechanism for Misaligned Systems

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

Matsumoto, Tomoaki; Machida, Masahiro N.; Inutsuka, Shu-ichiro, E-mail: matsu@hosei.ac.jp

2017-04-10

We investigate the formation of circumstellar disks and outflows subsequent to the collapse of molecular cloud cores with the magnetic field and turbulence. Numerical simulations are performed by using an adaptive mesh refinement to follow the evolution up to ∼1000 years after the formation of a protostar. In the simulations, circumstellar disks are formed around the protostars; those in magnetized models are considerably smaller than those in nonmagnetized models, but their size increases with time. The models with stronger magnetic fields tend to produce smaller disks. During evolution in the magnetized models, the mass ratios of a disk to amore » protostar is approximately constant at ∼1%–10%. The circumstellar disks are aligned according to their angular momentum, and the outflows accelerate along the magnetic field on the 10–100 au scale; this produces a disk that is misaligned with the outflow. The outflows are classified into two types: a magnetocentrifugal wind and a spiral flow. In the latter, because of the geometry, the axis of rotation is misaligned with the magnetic field. The magnetic field has an internal structure in the cloud cores, which also causes misalignment between the outflows and the magnetic field on the scale of the cloud core. The distribution of the angular momentum vectors in a core also has a non-monotonic internal structure. This should create a time-dependent accretion of angular momenta onto the circumstellar disk. Therefore, the circumstellar disks are expected to change their orientation as well as their sizes in the long-term evolutions.« less

Mars' Annular Polar Vortices and their Response to Atmospheric Dust Opacity

NASA Astrophysics Data System (ADS)

Guzewich, S.; Waugh, D.; Toigo, A. D.

2016-12-01

The potential vorticity structure of the martian polar vortices is distinct from Earth's stratospheric or tropospheric vortices. Rather than exhibiting monotonically increasing potential vorticity toward the geographic pole, as on Earth, the martian fall and winter polar vortices are annular with the potential vorticity maximum situated off the pole and a local minimum in potential vorticity at the pole. Using the MarsWRF general circulation model (GCM), we perform a series of simulations to examine the source of this annular structure. We find that latent heat exchange from the formation of CO2 ice aerosols within the vortex, in a region very near the geographic pole, destroys potential vorticity and creates the annular structure. Furthermore, we describe Mars Climate Sounder and Thermal Emission Spectrometer observations of "transient vortex warming" events, where the air inside the northern hemisphere winter polar vortex is briefly warmed. During the Mars Year 28 (2007) global dust storm, the temperature inside the vortex increased by 70 K and dust directly entered the vortex. Using additional GCM simulations, we diagnose the dynamical changes associated with these transient vortex warming events and find that poleward expansion of the descending branch of the meridional overturning circulation during periods of increased dust opacity disrupts the northern hemisphere winter polar vortex. These increased temperatures also suppress CO2 condensation at the pole, creating a more Earth-like polar vortex where potential vorticity is maximized near the geographic pole.

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

NASA Astrophysics Data System (ADS)

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

2009-07-01

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

Tracing ram-pressure stripping with warm molecular hydrogen emission

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

Sivanandam, Suresh; Rieke, Marcia J.; Rieke, George H., E-mail: sivanandam@dunlap.utoronto.ca

We use the Spitzer Infrared Spectrograph to study four infalling cluster galaxies with signatures of ongoing ram-pressure stripping. H{sub 2} emission is detected in all four, and two show extraplanar H{sub 2} emission. The emission usually has a warm (T ∼ 115-160 K) and a hot (T ∼ 400-600 K) component that is approximately two orders of magnitude less massive than the warm one. The warm component column densities are typically 10{sup 19} to 10{sup 20} cm{sup –2} with masses of 10{sup 6} to 10{sup 8} M {sub ☉}. The warm H{sub 2} is anomalously bright compared with normal star-formingmore » galaxies and therefore may be excited by ram-pressure. In the case of CGCG 97-073, the H{sub 2} is offset from the majority of star formation along the direction of the galaxy's motion in the cluster, suggesting that it is forming in the ram-pressure wake of the galaxy. Another galaxy, NGC 4522, exhibits a warm H{sub 2} tail approximately 4 kpc in length. These results support the hypothesis that H{sub 2} within these galaxies is shock-heated from the interaction with the intracluster medium. Stripping of dust is also a common feature of the galaxies. For NGC 4522, where the distribution of dust at 8 μm is well resolved, knots and ripples demonstrate the turbulent nature of the stripping process. The Hα and 24 μm luminosities show that most of the galaxies have star-formation rates comparable to similar mass counterparts in the field. Finally, we suggest a possible evolutionary sequence primarily related to the strength of ram-pressure that a galaxy experiences to explain the varied results observed in our sample.« less

Climate Effects and Efficacy of Dust and Soot in Snow

NASA Astrophysics Data System (ADS)

Zender, C. S.; Flanner, M. G.; Randerson, J. T.; Mahowald, N. M.; Rasch, P. J.; Yoshioka, M.; Painter, T.

2006-12-01

Dust and industrial and biomass burning emissions from low and mid-latitudes dominate the absorbing impurities trapped in snow at mid- and high-latitudes. We study the effects of dust and smoke on global and regional climate using a general circulation model driven by observed and predicted aerosol emissions determined from satellite and in situ observations. The model has sophisticated treatments of aerosol and snowpack radiative and thermodynamic processes that compare well with observations of snow albedo evolution and impurity concentration. This presentation focuses on the individual and combined contributions of present day dust and soot to snow-albedo forcing and on the global temperature and snowpack responses. Results are emphasized near India and East Asia, where the anthropogenic aerosol forcing of surface albedo and hydrology is greatest. We find that dust and black carbon (BC) aerosols have climate change efficacies (surface temperature change per unit forcing) about 3--4 times greater than CO2, making them the most efficacious forcing agents known. We estimate present day dust and soot snowpack-forcing of ~ 0.050 W m-2 warms global climate by ~ 0.16 °K. Anthropogenic soot from fossil fuel sources causes more than 50% of this warming, and biomass burning can account for up to 30% in strong tropical or boreal burn years. The greatest forcings occur in the Tarim/Mongol region (due to dust), northeastern China (due to soot), and the Tibetan Plateau (both). Dirty springtime snow in these regions can darken albedo by more than 0.1 and increase surface absorption by more than 20 W m-2. These results have implications for the strength of the Asian Monsoon, which is negatively correlated with antecedent snow cover in non-ENSO years. Dust and soot have such strong efficacies because they increase spring melt rates thus reduce summer snow cover. In some regions and seasons, dirty snow reduces snowpack depth and cover by 50%, triggering strong snow and sea

Interstellar and Cometary Dust

NASA Technical Reports Server (NTRS)

Mathis, John S.

1997-01-01

/carbonaceous matrix, without organic refractory mantles, in between the ices. Unfortunately, they may be significantly processed by chemical processes accompanying the warming (over the 10 K of the dark cloud cores) which occurs in the outer solar system. Evidence of this processing is the chemical anomalies present in interplanetary dust particles collected in the stratosphere, which may be the most primitive materials we have obtained to date. The comet return mission would greatly clarify the situation, and probably provide samples of genuine interstellar grains.

Infrared Spectroscopy of Anhydrous Interplanetary Dust Particles

NASA Technical Reports Server (NTRS)

Keller, L. P.; Flynn, G. J.

2003-01-01

Infrared (IR) spectroscopy is the primary means of mineralogical analysis of materials outside our solar system. The identity and properties of circumstellar grains are inferred from spectral comparisons between astronomical observations and laboratory data from natural and synthetic materials. These comparisons have been facilitated by the Infrared Space Observatory (ISO), which obtained IR spectra from numerous astrophysical objects over a wide spectral range (out to 50/cm) where crystalline silicates and other phases have distinct features. The anhydrous interplanetary dust particles (IDPs) are particularly important comparison materials because some IDPs contain carbonaceous material with non-solar D/H and N-15/N-14 ratios and amorphous and crystalline silicates with non-solar 0- isotopic ratios, demonstrating that these IDPs contain preserved interstellar material. Here, we report on micro- Fourier transform (FT) IR spectrometry of IDPs, focusing on the inorganic components of primitive IDPs (FTIR spectra from the organic/carbonacecous materials in IDPs are described elsewhere).

Circumstellar X-ray Emission from SN1978K

NASA Astrophysics Data System (ADS)

Schlegel, Eric M.; Colbert, E.; Petre, R.

1995-02-01

We present the X-ray light curve in the 0.2 2.4 keV band based on fiveROSAT observations of SN1978K in NGC 1313. The X-ray emission is believed to arise from the interaction of the reverse shock and the expanding debris from the supernova. The reverse shock becomes established after the outgoing shock runs into circumstellar matter.

Kinematic Dynamo In Turbulent Circumstellar Disks

NASA Technical Reports Server (NTRS)

Stepinski, T.

1993-01-01

Many circumstellar disks associated with objects ranging from protoplanetary nebulae, to accretion disks around compact stars allow for the generation of magnetic fields by an (alpha)omega dynamo. We have applied kinematic dynamo formalism to geometrically thin accretion disks. We calculate, in the framework of an adiabatic approximation, the normal mode solutions for dynamos operating in disks around compact stars. We then describe the criteria for a viable dynamo in protoplanetary nebulae, and discuss the particular features that make accretion disk dynamos different from planetary, stellar, and galactic dynamos.

Potential climate effect of mineral aerosols over West Africa: Part II—contribution of dust and land cover to future climate change

NASA Astrophysics Data System (ADS)

Ji, Zhenming; Wang, Guiling; Yu, Miao; Pal, Jeremy S.

2018-04-01

Mineral dust aerosols are an essential component of climate over West Africa, however, little work has been performed to investigate their contributions to potential climate change. A set of regional climate model experiments with and without mineral dust processes and land cover changes is performed to evaluate their climatic effects under the Representative Concentration Pathway 8.5 for two global climate models. Results suggest surface warming to be in the range of 4-8 °C by the end of the century (2081-2100) over West Africa with respect to the present day (1981-2000). The presence of mineral dusts dampens the warming by 0.1-1 °C in all seasons. Accounting for changes in land cover enhances the warming over the north of Sahel and dampens it to the south in spring and summer; however, the magnitudes are smaller than those resulting from dusts. Overall dust loadings are projected to increase, with the greatest increase occurring over the Sahara and Sahel in summer. Accounting for land cover changes tends to reduce dust loadings over the southern Sahel. Future precipitation is projected to decrease by 5-40 % in the western Sahara and Sahel and increase by 10-150 % over the eastern Sahel and Guinea Coast in JJA. A dipole pattern of future precipitation changes is attributed to dust effects, with decrease in the north by 5-20 % and increase by 5-20 % in the south. Future changes in land cover result in a noisy non-significant response with a tendency for slight wetting in MAM, JJA, and SON and drying in DJF.

The enigmatic nature of the circumstellar envelope and bow shock surrounding Betelgeuse as revealed by Herschel. I. Evidence of clumps, multiple arcs, and a linear bar-like structure

NASA Astrophysics Data System (ADS)

Decin, L.; Cox, N. L. J.; Royer, P.; Van Marle, A. J.; Vandenbussche, B.; Ladjal, D.; Kerschbaum, F.; Ottensamer, R.; Barlow, M. J.; Blommaert, J. A. D. L.; Gomez, H. L.; Groenewegen, M. A. T.; Lim, T.; Swinyard, B. M.; Waelkens, C.; Tielens, A. G. G. M.

2012-12-01

Context. The interaction between stellar winds and the interstellar medium (ISM) can create complex bow shocks. The photometers on board the Herschel Space Observatory are ideally suited to studying the morphologies of these bow shocks. Aims: We aim to study the circumstellar environment and wind-ISM interaction of the nearest red supergiant, Betelgeuse. Methods.Herschel PACS images at 70, 100, and 160 μm and SPIRE images at 250, 350, and 500 μm were obtained by scanning the region around Betelgeuse. These data were complemented with ultraviolet GALEX data, near-infrared WISE data, and radio 21 cm GALFA-HI data. The observational properties of the bow shock structure were deduced from the data and compared with hydrodynamical simulations. Results: The infrared Herschel images of the environment around Betelgeuse are spectacular, showing the occurrence of multiple arcs at ~6-7' from the central target and the presence of a linear bar at ~9'. Remarkably, no large-scale instabilities are seen in the outer arcs and linear bar. The dust temperature in the outer arcs varies between 40 and 140 K, with the linear bar having the same colour temperature as the arcs. The inner envelope shows clear evidence of a non-homogeneous clumpy structure (beyond 15''), probably related to the giant convection cells of the outer atmosphere. The non-homogeneous distribution of the material even persists until the collision with the ISM. A strong variation in brightness of the inner clumps at a radius of ~2' suggests a drastic change in mean gas and dust density ~32 000 yr ago. Using hydrodynamical simulations, we try to explain the observed morphology of the bow shock around Betelgeuse. Conclusions: Different hypotheses, based on observational and theoretical constraints, are formulated to explain the origin of the multiple arcs and the linear bar and the fact that no large-scale instabilities are visible in the bow shock region. We infer that the two main ingredients for explaining

20th-Century doubling in dust archived in an Antarctic Peninsula ice core parallels climate change and desertification in South America

PubMed Central

McConnell, Joseph R.; Aristarain, Alberto J.; Banta, J. Ryan; Edwards, P. Ross; Simões, Jefferson C.

2007-01-01

Crustal dust in the atmosphere impacts Earth's radiative forcing directly by modifying the radiation budget and affecting cloud nucleation and optical properties, and indirectly through ocean fertilization, which alters carbon sequestration. Increased dust in the atmosphere has been linked to decreased global air temperature in past ice core studies of glacial to interglacial transitions. We present a continuous ice core record of aluminum deposition during recent centuries in the northern Antarctic Peninsula, the most rapidly warming region of the Southern Hemisphere; such a record has not been reported previously. This record shows that aluminosilicate dust deposition more than doubled during the 20th century, coincident with the ≈1°C Southern Hemisphere warming: a pattern in parallel with increasing air temperatures, decreasing relative humidity, and widespread desertification in Patagonia and northern Argentina. These results have far-reaching implications for understanding the forces driving dust generation and impacts of changing dust levels on climate both in the recent past and future. PMID:17389397

Long-term variability of dust events in Iceland (1949-2011)

NASA Astrophysics Data System (ADS)

Dagsson-Waldhauserova, P.; Arnalds, O.; Olafsson, H.

2014-12-01

The long-term frequency of atmospheric dust observations was investigated for the southern part of Iceland and interpreted together with earlier results obtained from northeastern (NE) Iceland (Dagsson-Waldhauserova et al., 2013). In total, over 34 dust days per year on average occurred in Iceland based on conventionally used synoptic codes for dust observations. However, frequent volcanic eruptions, with the re-suspension of volcanic materials and dust haze, increased the number of dust events fourfold (135 dust days annually). The position of the Icelandic Low determined whether dust events occurred in the NE (16.4 dust days annually) or in the southern (S) part of Iceland (about 18 dust days annually). The decade with the most frequent dust days in S Iceland was the 1960s, but the 2000s in NE Iceland. A total of 32 severe dust storms (visibility < 500 m) were observed in Iceland with the highest frequency of events during the 2000s in S Iceland. The Arctic dust events (NE Iceland) were typically warm, occurring during summer/autumn (May-September) and during mild southwesterly winds, while the subarctic dust events (S Iceland) were mainly cold, occurring during winter/spring (March-May) and during strong northeasterly winds. About half of the dust events in S Iceland occurred in winter or at sub-zero temperatures. A good correlation was found between particulate matter (PM10) concentrations and visibility during dust observations at the stations Vík and Stórhöfði. This study shows that Iceland is among the dustiest areas of the world and that dust is emitted year-round.

Advancing spaceborne tools for the characterization of planetary ionospheres and circumstellar environments

NASA Astrophysics Data System (ADS)

Douglas, Ewan Streets

. Laboratory operations of the PICTURE coronagraph achieved the high-contrast imaging sensitivity necessary to test for the predicted warm circumstellar belt around Epsilon Eridani. Interferometric wavefront measurements of calibration target Beta Orionis recorded during the second test flight in November 2015 demonstrate the first active wavefront sensing with a piezoelectric mirror stage and activation of a micromachine deformable mirror in space. These two studies advance our "close-to-home'' knowledge of atmospheres and move exoplanetary studies closer to detailed measurements of atmospheres outside our solar system.

Impacts of interactive dust and its direct radiative forcing on interannual variations of temperature and precipitation in winter over East Asia: Impacts of Dust on IAVs of Temperature

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

Lou, Sijia; Russell, Lynn M.; Yang, Yang

We used 150-year pre-industrial simulations of the Community Earth System Model (CESM) to quantify the impacts of interactively-modeled dust emissions on the interannual variations of temperature and precipitation over East Asia during the East Asian Winter Monsoon (EAWM) season. The simulated December-January-February dust column burden and dust optical depth are lower over northern China in the strongest EAWM years than those of the weakest years, with regional mean values lower by 38.3% and 37.2%, respectively. The decrease in dust over the dust source regions (the Taklamakan and Gobi Deserts) and the downwind region (such as the North China Plain) leadsmore » to an increase in direct radiative forcing (RF) both at the surface and top of atmosphere by up to 1.5 and 0.75 W m-2, respectively. The effects of EAWM-related variations in surface winds, precipitation and their effects on dust emissions and wet removal contribute about 67% to the total dust-induced variations of direct RF at the surface and partly offset the cooling that occurs with the EAWM strengthening by heating the surface. The variations of surface air temperature induced by the changes in wind and dust emissions increase by 0.4-0.6 K over eastern coastal China, northeastern China, and Japan, which weakens the impact of EAWM on surface air temperature by 3–18% in these regions. The warming results from the combined effects of changes in direct RF and easterly wind anomalies that bring warm air from the ocean to these regions. Moreover, the feedback of the changes in wind on dust emissions weakens the variations of the sea level pressure gradient on the Siberian High while enhancing the Maritime Continent Low. Therefore, cold air is prevented from being transported from Siberia, Kazakhstan, western and central China to the western Pacific Ocean and decreases surface air temperature by 0.6 K and 2 K over central China and the Tibetan Plateau, respectively. Over eastern coastal China, the

Variable Circumstellar Disks of “Classical” Be Stars

NASA Astrophysics Data System (ADS)

Gerhartz, Cody; Bjorkman, K. S.; Wisniewski, J. P.

2013-06-01

Circumstellar disks are common among many stars, all spectral types, and at different stages of their lifetimes. Among the near-main sequence “Classical” Be stars, there is growing evidence that these disks can form, dissipate, and reform, on timescales that are differ from case to case. We present data for a subset of cases where observations have been obtained throughout the different phases of the disk cycle. Using data obtained with the SpeX instrument at the NASA IRTF, we examine the IR spectral line variability of these stars to better understand the timescales and the physical mechanisms involved. The primary focus in this study are the V/R variations that are observed in the sample. The second stage of our project is to examine a sample of star clusters known to contain Be stars, with the goal to develop a more statistically significant sample of variable circumstellar disk systems. With a robust multi-epoch study we can determine whether these Be stars exhibit disk-loss or disk-renewal phases. The larger sample will enable a better understanding of the prevalence of these disk events.

Exploring the multifaceted circumstellar environment of the luminous blue variable HR Carinae

NASA Astrophysics Data System (ADS)

Buemi, C. S.; Trigilio, C.; Leto, P.; Umana, G.; Ingallinera, A.; Cavallaro, F.; Cerrigone, L.; Agliozzo, C.; Bufano, F.; Riggi, S.; Molinari, S.; Schillirò, F.

2017-03-01

We present a multiwavelength study of the Galactic luminous blue variable HR Carinae, based on new high-resolution mid-infrared (IR) and radio images obtained with the Very Large Telescope (VLT) and the Australia Telescope Compact Array (ATCA), which have been complemented by far-infrared Herschel-Photodetector Array Camera and Spectrometer (PACS) observations and ATCA archive data. The Herschel images reveal the large-scale distribution of the dusty emitting nebula, which extends mainly to the north-east direction, up to 70 arcsec from the central star, and is oriented along the direction of the space motion of the star. In the mid-infrared images, the brightness distribution is characterized by two arc-shaped structures, tracing an inner envelope surrounding the central star more closely. At radio wavelengths, the ionized gas emission lies on the opposite side of the cold dust with respect to the position of the star, as if the ionized front were confined by the surrounding medium in the north-south direction. Comparison with previous data indicates significant changes in the radio nebula morphology and in the mass-loss rate from the central star, which has increased from 6.1 × 10-6 M⊙ yr-1 in 1994-1995 to 1.17 × 10-5 M⊙ yr-1 in 2014. We investigate possible scenarios that could have generated the complex circumstellar environment revealed by our multiwavelength data.

Possible influence of dust on hurricane genesis

NASA Astrophysics Data System (ADS)

Bretl, Sebastian; Reutter, Philipp; Raible, Christoph C.; Ferrachat, Sylvaine; Lohmann, Ulrike

2014-05-01

Tropical Cyclones (TCs) belong to the most extreme events in nature. In the past decade, the possible impact of dust on Atlantic hurricanes receives growing interest. As mineral dust is able to absorb incoming solar radiation and therefore warm the surrounding air, the presence of dust can lead to a reduction of sea surface temperature (SST) and an increase in atmospheric stability. Furthermore, resulting baroclinic effects and the dry Saharan easterly jet lead to an enhanced vertical shear of the horizontal winds. SST, stability, moisture and vertical wind shear are known to potentially impact hurricane activity. But how Saharan dust influences these prerequisites for hurricane formation is not yet clear. Some dynamical mechanisms induced by the SAL might even strengthen hurricanes. An adequate framework for investigating the possible impact of dust on hurricanes is comparing high resolution simulations (~0.5°x0.5°, 31 vertical levels) with and without radiatively active dust aerosols. To accomplish this task, we are using the general circulation model ECHAM6 coupled to a modified version of the aerosol model HAM, ECHAM6-HAM-Dust. Instead of the five aerosol species HAM normally contains, the modified version takes only insoluble dust into account, but modifies the scavenging parameters in order to have a similar lifetime of dust as in the full ECHAM6-HAM. All remaining aerosols are prescribed. To evaluate the effects of dust on hurricanes, a TC detection and tracking method is applied on the results. ECHAM6-HAM-Dust was used in two configurations, one with radiatively active dust aerosols and one with dust being not radiatively active. For both set-ups, 10 Monte-Carlo simulations of the year 2005 were performed. A statistical method which identifies controlling parameters of hurricane genesis was applied on North Atlantic developing and non-developing disturbances in all simulations, comparing storms in the two sets of simulations. Hereby, dust can be assigned

Circumstellar Matter Studied by Spectrally-Resolved Interferometry

NASA Astrophysics Data System (ADS)

Millour, F.

2012-12-01

This paper describes some generalities about spectro-interferometry and the role it has played in the last decade for the better understanding of circumstellar matter. I provide a small history of the technique and its origins, and recall the basics of differential phase and its central role for the recent discoveries. I finally provide a small set of simple interpretations of differential phases for specific astrophysical cases, and intend to provide a "cookbook" for the other cases.

A systematic investigation of the mass loss mechanism in dust forming long-period variable stars

NASA Astrophysics Data System (ADS)

Winters, J. M.; Le Bertre, T.; Jeong, K. S.; Helling, Ch.; Sedlmayr, E.

2000-09-01

In order to investigate the relations between the mass loss from pulsating red giants and quantities which can be obtained from observations, we have explored the behavior of theoretical models which treat the time-dependent hydrodynamics of circumstellar outflows, including a detailed treatment of the dust formation process. This approach, while ignoring effects such as a possible non-sphericity of the stellar atmospheres which are difficult to assess, accounts correctly for factors such as the grain formation and destruction which are crucial to the mass-loss mechanism. We built a grid of ~ 150 models covering a wide range of physical situations. This grid allows us to characterize the effects of different parameters, such as the stellar luminosity and temperature, the period and the amplitude of the pulsation, and the C/O element abundance ratio, on the behavior of AGB winds and on the rates of mass loss. We find two regimes for the stellar outflows. The first one (A) is characterized by stable winds with a layered structure of the circumstellar dust shell, outflow velocities in excess of 5 km s-1, and a large rate of mass loss. These outflows are dominated by radiation pressure on dust. For these models we find good correlations between near-infrared colors and the mass loss rates. In the second regime (B), the winds are slow and do not present a layered structure. The outflows displaying the second behavior come, e.g., from red giants with low luminosity, high temperature, or short period. For them there is no correlation between color and mass loss rate. The mass loss rates are low and never exceed 3 10-7 Msunyr-1. Radiation pressure on dust plays only a minor role in this regime. We have explored the effect of different parameters on the behavior of the stellar winds. We find that, in general, all other parameters been kept identical, there is a narrow range of values for each parameter within which the models abruptly change from B to A, and that once a

Infrared Spectroscopy of HR 4796A's Bright Outer Cometary Ring + Tenuous Inner Hot Dust Cloud

NASA Astrophysics Data System (ADS)

Lisse, C. M.; Sitko, M. L.; Marengo, M.; Vervack, R. J., Jr.; Fernandez, Y. R.; Mittal, T.; Chen, C. H.

2017-11-01

We have obtained new NASA/IRTF SpeX spectra of the HR 4796A debris ring system. We find a unique red excess flux that extends out to ˜9 μm in Spitzer IRS spectra, where thermal emission from cold, ˜100 K dust from the system’s ring at ˜75 au takes over. Matching imaging ring photometry, we find the excess consists of NIR reflectance from the ring, which is as red as that of old, processed comet nuclei, plus a tenuous thermal emission component from close-in, T ˜ 850 K circumstellar material evincing an organic/silicate emission feature complex at 7-13 μm. Unusual, emission-like features due to atomic Si, S, Ca, and Sr were found at 0.96-1.07 μm, likely sourced by rocky dust evaporating in the 850 K component. An empirical cometary dust phase function can reproduce the scattered light excess and 1:5 balance of scattered versus thermal energy for the ring with optical depth < τ > ≥slant 0.10 in an 8 au wide belt of 4 au vertical height and M dust > 0.1-0.7 M Mars. Our results are consistent with HR 4796A, consisting of a narrow shepherded ring of devolatilized cometary material associated with multiple rocky planetesimal subcores and a small steady stream of dust inflowing from this belt to a rock sublimation zone at ˜1 au from the primary. These subcores were built from comets that have been actively emitting large, reddish dust for >0.4 Myr at ˜100 K, the temperature at which cometary activity onset is seen in our solar system.

The close circumstellar environment of the semi-regular S-type star π 1 Gruis

NASA Astrophysics Data System (ADS)

Sacuto, S.; Jorissen, A.; Cruzalèbes, P.; Chesneau, O.; Ohnaka, K.; Quirrenbach, A.; Lopez, B.

2008-05-01

Aims: We study the close circumstellar environment of the nearby S-type star π1 Gruis using high spatial-resolution, mid-infrared observations from the ESO/VLTI. Methods: Spectra and visibilities were obtained with the MIDI interferometer on the VLT Auxiliary Telescopes. The cool M5III giant β Gruis was used as bright primary calibrator, and a dedicated spectro-interferometric study was undertaken to determine its angular diameter accurately. The MIDI measurements were fitted with the 1D numerical radiative transfer code DUSTY to determine the dust shell parameters of π1 Gruis. Taking into account the low spatial extension of the model in the 8-9 μm spectral band for the smallest projected baselines, we consider the possibility of a supplementary molecular shell. Results: The MIDI visibility and phase data are mostly dominated by the spherical 21 mas (694 R_⊙) central star, while the extended dusty environment is over-resolved even with the shortest baselines. No obvious departure from spherical symmetry is found on the milliarcsecond scale. The spectro-interferometric observations are well-fitted by an optically thin (τ_dust<0.01 in the N band) dust shell that is located at about 14 stellar radii with a typical temperature of 700 K and composed of 70% silicate and 30% of amorphous alumina grains. An optically thin (τ_mol<0.1 in the N band) H{2}O + SiO molecular shell extending from the photosphere of the star up to 4.4 stellar radii with a typical temperature of 1000 K is added to the model to improve the fit in the 8-9 μm spectral band. We discuss the probable binary origin of asymmetries as revealed by millimetric observations. Based on observations made with the Very Large Telescope Interferometer at Paranal Observatory under programs 077.D-0294(D/E/F). Reduced visibilities and differential phases are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/482/561

DUST AROUND R CORONAE BOREALIS STARS. II. INFRARED EMISSION FEATURES IN AN H-POOR ENVIRONMENT

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

Garcia-Hernandez, D. A.; Rao, N. Kameswara; Lambert, D. L., E-mail: agarcia@iac.es, E-mail: nkrao@iiap.res.in, E-mail: dll@astro.as.utexas.edu

2013-08-20

Residual Spitzer/Infrared Spectrograph spectra for a sample of 31 R Coronae Borealis (RCB) stars are presented and discussed in terms of narrow emission features superimposed on the quasi-blackbody continuous infrared emission. A broad {approx}6-10 {mu}m dust emission complex is seen in the RCBs showing an extreme H-deficiency. A secondary and much weaker {approx}11.5-15 {mu}m broad emission feature is detected in a few RCBs with the strongest {approx}6-10 {mu}m dust complex. The Spitzer infrared spectra reveal for the first time the structure within the {approx}6-10 {mu}m dust complex, showing the presence of strong C-C stretching modes at {approx}6.3 and 8.1 {mu}mmore » as well as of other dust features at {approx}5.9, 6.9, and 7.3 {mu}m, which are attributable to amorphous carbonaceous solids with little or no hydrogen. The few RCBs with only moderate H-deficiencies display the classical ''unidentified infrared bands (UIRs)'' and mid-infrared features from fullerene-related molecules. In general, the characteristics of the RCB infrared emission features are not correlated with the stellar and circumstellar properties, suggesting that the RCB dust features may not be dependent on the present physical conditions around RCB stars. The only exception seems to be the central wavelength of the 6.3 {mu}m feature, which is blueshifted in those RCBs showing also the UIRs, i.e., the RCBs with the smallest H deficiency.« less

A SELF-CONSISTENT MODEL OF THE CIRCUMSTELLAR DEBRIS CREATED BY A GIANT HYPERVELOCITY IMPACT IN THE HD 172555 SYSTEM

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

Johnson, B. C.; Melosh, H. J.; Lisse, C. M.

2012-12-10

Spectral modeling of the large infrared excess in the Spitzer IRS spectra of HD 172555 suggests that there is more than 10{sup 19} kg of submicron dust in the system. Using physical arguments and constraints from observations, we rule out the possibility of the infrared excess being created by a magma ocean planet or a circumplanetary disk or torus. We show that the infrared excess is consistent with a circumstellar debris disk or torus, located at {approx}6 AU, that was created by a planetary scale hypervelocity impact. We find that radiation pressure should remove submicron dust from the debris diskmore » in less than one year. However, the system's mid-infrared photometric flux, dominated by submicron grains, has been stable within 4% over the last 27 years, from the Infrared Astronomical Satellite (1983) to WISE (2010). Our new spectral modeling work and calculations of the radiation pressure on fine dust in HD 172555 provide a self-consistent explanation for this apparent contradiction. We also explore the unconfirmed claim that {approx}10{sup 47} molecules of SiO vapor are needed to explain an emission feature at {approx}8 {mu}m in the Spitzer IRS spectrum of HD 172555. We find that unless there are {approx}10{sup 48} atoms or 0.05 M{sub Circled-Plus} of atomic Si and O vapor in the system, SiO vapor should be destroyed by photo-dissociation in less than 0.2 years. We argue that a second plausible explanation for the {approx}8 {mu}m feature can be emission from solid SiO, which naturally occurs in submicron silicate ''smokes'' created by quickly condensing vaporized silicate.« less

Variable Circumstellar Disks of Classical Be Stars in Clusters

NASA Astrophysics Data System (ADS)

Gerhartz, C.; Bjorkman, K. S.; Bjorkman, J. E.; Wisniewski, J. P.

2016-11-01

Circumstellar disks are common among many stars, at most spectral types, and at different stages of their lifetimes. Among the near-main-sequence classical Be stars, there is growing evidence that these disks form, dissipate, and reform on timescales that differ from star to star. Using data obtained with the Large Monolithic Imager (LMI) at the Lowell Observatory Discovery Channel Telescope (DCT), along with additional complementary data obtained at the University of Toledo Ritter Observatory (RO), we have begun a long-term monitoring project of a well-studied set of galactic star clusters that are known to contain Be stars. Our goal is to develop a statistically significant sample of variable circumstellar disk systems over multiple timescales. With a robust multi-epoch study we can determine the relative fraction of Be stars that exhibit disk-loss or disk-renewal phases, and investigate the range of timescales over which these events occur. A larger sample will improve our understanding of the prevalence and nature of the disk variability, and may provide insight about underlying physical mechanisms.

New directions: Mineral dust and ozone - Heterogeneous chemistry

NASA Astrophysics Data System (ADS)

Ramachandran, S.

2015-04-01

Aerosols, the tiny solid or liquid particles suspended in air and produced from natural sources and anthropogenic activities, continue to contribute the largest uncertainty to radiative forcing (IPCC, 2013). Aerosol particles give rise to radiative forcing directly through scattering and absorption of solar and infrared radiation in the atmosphere. Aerosols also give rise to indirect radiative forcing by modifying the cloud optical properties and lifetimes. Among the aerosol species mineral dust and black carbon cause a warming (positive forcing) while sulphate and sea salt cause a cooling (negative forcing) of the Earth-atmosphere system. In tropics and sub-tropics mineral dust is a major contributor to aerosol loading and optical thickness. The global source strength of dust aerosol varies significantly on spatial and temporal scales. The source regions of dust are mainly deserts, dry lake beds, and semi-arid regions, in addition to drier regions where vegetation has been reduced or soil surfaces that are disturbed by man made activities. Anthropogenic activities mainly related to agriculture such as harvesting, ploughing, overgrazing, and cement production and transport also produce mineral dust. An estimated 2500 terragram (Tg, 1012 g) of mineral dust is emitted into the atmosphere per year, and dominates the aerosol mass over continental regions in south Asia and China accounting for ∼35% of the total aerosol mass (IPCC, 2013). In India, dust is prevalent throughout the north and western India during the year and peaks during premonsoon season.

Ubiquitous Instabilities of Dust Moving in Magnetized Gas

NASA Astrophysics Data System (ADS)

Hopkins, Philip F.; Squire, Jonathan

2018-06-01

Squire & Hopkins (2017) showed that coupled dust-gas mixtures are generically subject to "resonant drag instabilities" (RDIs), which drive violently-growing fluctuations in both. But the role of magnetic fields and charged dust has not yet been studied. We therefore explore the RDI in gas which obeys ideal MHD and is coupled to dust via both Lorentz forces and drag, with an external acceleration (e.g., gravity, radiation) driving dust drift through gas. We show this is always unstable, at all wavelengths and non-zero values of dust-to-gas ratio, drift velocity, dust charge, "stopping time" or drag coefficient (for any drag law), or field strength; moreover growth rates depend only weakly (sub-linearly) on these parameters. Dust charge and magnetic fields do not suppress instabilities, but give rise to a large number of new instability "families," each with distinct behavior. The "MHD-wave" (magnetosonic or Alfvén) RDIs exhibit maximal growth along "resonant" angles where the modes have a phase velocity matching the corresponding MHD wave, and growth rates increase without limit with wavenumber. The "gyro" RDIs are driven by resonances between drift and Larmor frequencies, giving growth rates sharply peaked at specific wavelengths. Other instabilities include "acoustic" and "pressure-free" modes (previously studied), and a family akin to cosmic ray instabilities which appear when Lorentz forces are strong and dust streams super-Alfvénically along field lines. We discuss astrophysical applications in the warm ISM, CGM/IGM, HII regions, SNe ejecta/remnants, Solar corona, cool-star winds, GMCs, and AGN.

THE DUST PROPERTIES OF TWO HOT R CORONAE BOREALIS STARS AND A WOLF-RAYET CENTRAL STAR OF A PLANETARY NEBULA: IN SEARCH OF A POSSIBLE LINK

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

Clayton, Geoffrey C.; Gallagher, J. S.; Freeman, W. R.

2011-08-15

circumstellar dust around these stars. HV 2671 and CPD -56{sup 0} 8032 require both a flared inner disk with warm dust and an extended diffuse envelope with cold dust to fit their SEDs. The SED of V348 Sgr can be fit with a much smaller disk and envelope. The cold dust in the extended diffuse envelopes inferred around HV 2671 and CPD -56{sup 0} 8032 may consist of interstellar medium swept up during mass-loss episodes.« less

Oxygen-rich Mass Loss with a Pinch of Salt: NaCl in the Circumstellar Gas of IK Tauri and VY Canis Majoris

NASA Astrophysics Data System (ADS)

Milam, S. N.; Apponi, A. J.; Woolf, N. J.; Ziurys, L. M.

2007-10-01

The NaCl molecule has been observed in the circumstellar envelopes of VY Canis Majoris (VY CMa) and IK Tauri (IK Tau)-the first identifications of a metal refractory in oxygen-rich shells of evolved stars. Five rotational transitions of NaCl at 1 and 2 mm were detected toward VY CMa and three 1 mm lines were observed toward IK Tau, using the telescopes of the Arizona Radio Observatory. In both objects, the line widths of the NaCl profiles were extremely narrow relative to those of other molecules, indicating that sodium chloride has not reached the terminal outflow velocity in either star, likely a result of early condensation onto grains. Modeling the observed spectra suggests abundances, relative to H2, of f~5×10-9 in VY CMa and f~4×10-9 in IK Tau, with source sizes of 0.5" and 0.3", respectively. The extent of these sources is consistent with the size of the dust acceleration zones in both stars. NaCl therefore appears to be at least as abundant in O-rich shells as compared to C-rich envelopes, where f~(0.2-2)×10-9, although it appears to condense out earlier in the O-rich case. Chemical equilibrium calculations indicate that NaCl is the major carrier of sodium at T~1100 K for oxygen-rich stars, with predicted fractional abundances in good agreement with the observations. These measurements suggest that crystalline salt may be an important condensate for sodium in both C- and O-rich circumstellar shells.

Swirling Dust in Gale Crater, Mars, Sol 1613

NASA Image and Video Library

2017-02-27

This frame from a sequence of images shows a dust-carrying whirlwind, called a dust devil, on lower Mount Sharp inside Gale Crater, as viewed by NASA's Curiosity Mars Rover during the summer afternoon of the rover's 1,613rd Martian day, or sol (Feb. 18, 2017). Set within a broader southward view from the rover's Navigation Camera, the rectangular area outlined in black was imaged multiple times over a span of several minutes to check for dust devils. Images from the period with most activity are shown in the inset area. The images are in pairs that were taken about 12 seconds apart, with an interval of about 90 seconds between pairs. Timing is accelerated and not fully proportional in this animation. Contrast has been modified to make frame-to-frame changes easier to see. A black frame provides a marker between repeats of the sequence. On Mars as on Earth, dust devils result from sunshine warming the ground, prompting convective rising of air that has gained heat from the ground. Observations of dust devils provide information about wind directions and interaction between the surface and the atmosphere. An animation is available at http://photojournal.jpl.nasa.gov/catalog/PIA21483

A dust and water disk in AFGL 2591

NASA Astrophysics Data System (ADS)

van der Tak, Floris; Walmsley, Malcolm; Herpin, Fabrice; Ceccarelli, Cecilia

High-mass stars may form by disk accretion like low-mass stars, but observational evidence for massive circumstellar disks remains sparse even after intense searches. We present Plateau de Bure observations of dust continuum and H218O line emission at 1.3 mm wavelength which show a rotating disk around the nearby (d=1 kpc) high-mass (L = 2 × 104 Lsol) protostar AFGL 2591. The 205 GHz map shows three sources. Comparison with OVRO 86 GHz images in- dicates that the strongest source is due to dust, while the other two are dominated by ionized gas. The dust source is compact (? ≍ 800 AU) and somewhat elongated (axis ratio ≍ 0.8). Its flux density indicates a mass of ≍ 0.8 Msol which is ≍ 5% of the mass of the central star. The dust opacity index β ≍ 1, suggesting grain growth. These observations suggest a disk at an inclination of ≍ 32◦ (almost face-on), but spectral line data are needed to test this idea. H218O line emission is only detected toward the dust source. The size and shape of the emission are very similar to that of the continuum. All of the single-dish line flux is recovered, so that there is probably little extended flux missing. Radiative transfer models indicate a H2O abundance of ~10-4, similar to the H2O ice abundance measured in the mid-infrared. The origin of the H2O thus seems to be evaporation of grain mantles. The position of the H218O emission peak shows a systematic shift with velocity. Such a gradient could arise in a bipolar outflow, but the high column densities (N(H2O) ~ 3 × 1019 cm-2; N(H2) ~ 2 × 1024 cm-2) argue against this. Moreover, the velocity gradient is not oriented East-West like the large-scale outflow from AFGL 2591. Thus the H218O velocity gradient probably traces a rotating disk. The magnitude of the velocity gradient is consistent with Keplerian rotation around the central star. In the near future, we plan to use more extended array configurations to resolve the velocity field.

The turbulent life of dust grains in the supernova-driven, multiphase interstellar medium

NASA Astrophysics Data System (ADS)

Peters, Thomas; Zhukovska, Svitlana; Naab, Thorsten; Girichidis, Philipp; Walch, Stefanie; Glover, Simon C. O.; Klessen, Ralf S.; Clark, Paul C.; Seifried, Daniel

2017-06-01

Dust grains are an important component of the interstellar medium (ISM) of galaxies. We present the first direct measurement of the residence times of interstellar dust in the different ISM phases, and of the transition rates between these phases, in realistic hydrodynamical simulations of the multiphase ISM. Our simulations include a time-dependent chemical network that follows the abundances of H+, H, H2, C+ and CO and take into account self-shielding by gas and dust using a tree-based radiation transfer method. Supernova explosions are injected either at random locations, at density peaks, or as a mixture of the two. For each simulation, we investigate how matter circulates between the ISM phases and find more sizeable transitions than considered in simple mass exchange schemes in the literature. The derived residence times in the ISM phases are characterized by broad distributions, in particular for the molecular, warm and hot medium. The most realistic simulations with random and mixed driving have median residence times in the molecular, cold, warm and hot phase around 17, 7, 44 and 1 Myr, respectively. The transition rates measured in the random driving run are in good agreement with observations of Ti gas-phase depletion in the warm and cold phases in a simple depletion model. ISM phase definitions based on chemical abundance rather than temperature cuts are physically more meaningful, but lead to significantly different transition rates and residence times because there is no direct correspondence between the two definitions.

Gusev Dust Devil Movie, Sol 459 (Enhanced)

NASA Technical Reports Server (NTRS)

2005-01-01

This movie clip shows a dust devil scooting across a plain inside Gusev Crater on Mars as seen from the NASA rover Spirit's hillside vantage point during the rover's 459th martian day, or sol (April 18, 2005). The individual images were taken about 20 seconds apart by Spirit's navigation camera, and the contrast has been enhanced for anything in the images that changes from frame to frame, that is, for the dust devil.

The movie results from a new way of watching for dust devils, which are whirlwinds that hoist dust from the surface into the air. Spirit began seeing dust devils in isolated images in March 2005. At first, the rover team relied on luck. It might catch a dust devil in an image or it might miss by a few minutes. Using the new detection strategy, the rover takes a series of 21 images. Spirit sends a few of them to Earth, as well as little thumbnail images of all of them. Team members use the 3 big images and all the small images to decide whether the additional big images have dust devils. For this movie, they specifically told Spirit to send back frames that they knew had dust devils.

The images were processed in three steps. All images were calibrated to remove known camera artifacts. The images were then processed to remove stationary objects. The result is a gray scene showing only features that change with time. The final step combined the original image with the image that shows only moving features, showing the martian scene and the enhanced dust devils.

Scientists expected dust devils since before Spirit landed. The landing area inside Gusev Crater is filled with dark streaks left behind when dust devils pick dust up from an area. It is also filled with bright 'hollows,' which are dust-filled miniature craters. Dust covers most of the terrain. Winds flow into and out of Gusev crater every day. The Sun heats the surface so that the surface is warm to the touch even though the atmosphere at 2 meters (6 feet) above the surface

Gusev Dust Devil Movie, Sol 456 (Enhanced)

NASA Technical Reports Server (NTRS)

2005-01-01

This movie clip shows a dust devil scooting across a plain inside Gusev Crater on Mars as seen from the NASA rover Spirit's hillside vantage point during the rover's 456th martian day, or sol (April 15, 2005). The individual images were taken about 20 seconds apart by Spirit's navigation camera, and the contrast has been enhanced for anything in the images that changes from frame to frame, that is, for the dust devil.

The movie results from a new way of watching for dust devils, which are whirlwinds that hoist dust from the surface into the air. Spirit began seeing dust devils in isolated images in March 2005. At first, the rover team relied on luck. It might catch a dust devil in an image or it might miss by a few minutes. Using the new detection strategy, the rover takes a series of 21 images. Spirit sends a few of them to Earth, as well as little thumbnail images of all of them. Team members use the 3 big images and all the small images to decide whether the additional big images have dust devils. For this movie, they specifically told Spirit to send back frames that they knew had dust devils.

The images were processed in three steps. All images were calibrated to remove known camera artifacts. The images were then processed to remove stationary objects. The result is a gray scene showing only features that change with time. The final step combined the original image with the image that shows only moving features, showing the martian scene and the enhanced dust devils.

Scientists expected dust devils since before Spirit landed. The landing area inside Gusev Crater is filled with dark streaks left behind when dust devils pick dust up from an area. It is also filled with bright 'hollows,' which are dust-filled miniature craters. Dust covers most of the terrain. Winds flow into and out of Gusev crater every day. The Sun heats the surface so that the surface is warm to the touch even though the atmosphere at 2 meters (6 feet) above the surface

Gas and dust in the star-forming region ρ Oph A. The dust opacity exponent β and the gas-to-dust mass ratio g2d

NASA Astrophysics Data System (ADS)

Liseau, R.; Larsson, B.; Lunttila, T.; Olberg, M.; Rydbeck, G.; Bergman, P.; Justtanont, K.; Olofsson, G.; de Vries, B. L.

2015-06-01

Aims: We aim at determining the spatial distribution of the gas and dust in star-forming regions and address their relative abundances in quantitative terms. We also examine the dust opacity exponent β for spatial and/or temporal variations. Methods: Using mapping observations of the very dense ρ Oph A core, we examined standard 1D and non-standard 3D methods to analyse data of far-infrared and submillimetre (submm) continuum radiation. The resulting dust surface density distribution can be compared to that of the gas. The latter was derived from the analysis of accompanying molecular line emission, observed with Herschel from space and with APEX from the ground. As a gas tracer we used N2H+, which is believed to be much less sensitive to freeze-out than CO and its isotopologues. Radiative transfer modelling of the N2H+ (J = 3-2) and (J = 6-5) lines with their hyperfine structure explicitly taken into account provides solutions for the spatial distribution of the column density N(H2), hence the surface density distribution of the gas. Results: The gas-to-dust mass ratio is varying across the map, with very low values in the central regions around the core SM 1. The global average, = 88, is not far from the canonical value of 100, however. In ρ Oph A, the exponent β of the power-law description for the dust opacity exhibits a clear dependence on time, with high values of 2 for the envelope-dominated emission in starless Class -1 sources to low values close to 0 for the disk-dominated emission in Class III objects. β assumes intermediate values for evolutionary classes in between. Conclusions: Since β is primarily controlled by grain size, grain growth mostly occurs in circumstellar disks. The spatial segregation of gas and dust, seen in projection toward the core centre, probably implies that, like C18O, also N2H+ is frozen onto the grains. Based on observations with APEX, which is a 12 m diameter submillimetre telescope at 5100 m altitude on Llano Chajnantor

Simulating southwestern U.S. desert dust influences on supercell thunderstorms

NASA Astrophysics Data System (ADS)

Lerach, David G.; Cotton, William R.

2018-05-01

Three-dimensional numerical simulations were performed to evaluate potential southwestern U.S. dust indirect microphysical and direct radiative impacts on a real severe storms outbreak. Increased solar absorption within the dust plume led to modest increases in pre-storm atmospheric stability at low levels, resulting in weaker convective updrafts and less widespread precipitation. Dust microphysical impacts on convection were minor in comparison, due in part to the lofted dust concentrations being relatively few in number when compared to the background (non-dust) aerosol population. While dust preferentially serving as cloud condensation nuclei (CCN) versus giant CCN had opposing effects on warm rain production, both scenarios resulted in ample supercooled water and subsequent glaciation aloft, yielding larger graupel and hail. Associated latent heating from condensation and freezing contributed little to overall updraft invigoration. With reduced rain production overall, the simulations that included dust effects experienced slightly reduced grid-cumulative precipitation and notably warmer and spatially smaller cold pools. Dust serving as ice nucleating particles did not appear to play a significant role. The presence of dust ultimately reduced the number of supercells produced but allowed for supercell evolution characterized by consistently higher values of relative vertical vorticity within simulated mesocyclones. Dust radiative and microphysical effects were relatively small in magnitude when compared to those from altering the background convective available potential energy and vertical wind shear. It is difficult to generalize such findings from a single event, however, due to a number of case-specific environmental factors. These include the nature of the low-level moisture advection and characteristics of the background aerosol distribution.

Magnetically regulated collapse in the B335 protostar? I. ALMA observations of the polarized dust emission

NASA Astrophysics Data System (ADS)

Maury, A. J.; Girart, J. M.; Zhang, Q.; Hennebelle, P.; Keto, E.; Rao, R.; Lai, S.-P.; Ohashi, N.; Galametz, M.

2018-06-01

The role of the magnetic field during protostellar collapse is poorly constrained from an observational point of view, although it could be significant if we believe state-of-the-art models of protostellar formation. We present polarimetric observations of the 233 GHz thermal dust continuum emission obtained with ALMA in the B335 Class 0 protostar. Linearly polarized dust emission arising from the circumstellar material in the envelope of B335 is detected at all scales probed by our observations (50 to 1000 au). The magnetic field structure producing the dust polarization has a very ordered topology in the inner envelope, with a transition from a large-scale poloidal magnetic field, in the outflow direction, to strongly pinched in the equatorial direction. This is probably due to magnetic field lines being dragged along the dominating infall direction since B335 does not exhibit prominent rotation. Our data and their qualitative comparison to a family of magnetized protostellar collapse models show that, during the magnetized collapse in B335, the magnetic field is maintaining a high level of organization from scales 1000 au to 50 au: this suggests the field is dynamically relevant and capable of influencing the typical outcome of protostellar collapse, such as regulating the disc size in B335.

Constraints on the Progenitor of SN 2010jl and Pre-existing Hot Dust in its Surrounding Medium

NASA Technical Reports Server (NTRS)

Dwek, Eli; Arendt, Richard G.; Fox, Ori D.; Kelly, Patrick L.; Smith, Nathan; Van Dyk, Schuyler D.; Filippenko, Alexei, V.; Andrews, Jennifer; Shivvers, Isaac

2017-01-01

A search for the progenitor of SN 2010jl, an unusually luminous core-collapse supernova of Type IIn, using pre-explosion Hubble/WFPC2 and Spitzer/IRAC images of the region, yielded upper limits on the UV and near infrared (IR) fluxes from any candidate star. These upper limits constrain the luminosity and effective temperature of the progenitor, the mass of any pre-existing dust in its surrounding circumstellar medium (CSM), and dust proximity to the star. A lower limit on the CSM dust mass is required to hide a luminous progenitor from detection by Hubble. Upper limits on the CSM dust mass and constraints on its proximity to the star are set by requiring that the absorbed and reradiated IR emission not exceed the IRAC upper limits. Using the combined extinction-IR emission constraints, we present viable M(sub d)-R(sub 1) combinations, where M(sub d) and R(sub 1) are the CSM dust mass and its inner radius. These depend on the CSM outer radius, dust composition and grain size, and the properties of the progenitor. The results constrain the pre-supernova evolution of the progenitor, and the nature and origin of the observed post-explosion IR emission from SN 2010jl. In particular, an eta Car-type progenitor will require at least 4 mag of visual extinction to avoid detection by Hubble. This can be achieved with dust masses greater than approximately equal to 10(exp -3) solar mass (less than the estimated 0.2-0.5 solar mass around eta Car), which must be located at distances of greater than approximately equal to 10(exp 16) cm from the star to avoid detection by Spitzer.

Martian Dust Devil Action in Gale Crater, Sol 1597

NASA Image and Video Library

2017-02-27

This frame from a sequence of images shows a dust-carrying whirlwind, called a dust devil, scooting across the ground inside Gale Crater, as observed on the local summer afternoon of NASA's Curiosity Mars Rover's 1,597th Martian day, or sol (Feb. 1, 2017). Set within a broader southward view from the rover's Navigation Camera, the rectangular area outlined in black was imaged multiple times over a span of several minutes to check for dust devils. Images from the period with most activity are shown in the inset area. The images are in pairs that were taken about 12 seconds apart, with an interval of about 90 seconds between pairs. Timing is accelerated and not fully proportional in this animation. A dust devil is most evident in the 10th, 11th and 12th frames. In the first and fifth frames, dust blowing across the ground appears as pale horizontal streak. Contrast has been modified to make frame-to-frame changes easier to see. A black frame is added between repeats of the sequence. On Mars as on Earth, dust devils are whirlwinds that result from sunshine warming the ground, prompting convective rising of air that has gained heat from the ground. Observations of Martian dust devils provide information about wind directions and interaction between the surface and the atmosphere. An animation is available at http://photojournal.jpl.nasa.gov/catalog/PIA21270

The LBTI Hunt for Observable Signatures of Terrestrial Systems (HOSTS) Survey: a Key NASA Science Program on the Road to Exoplanet Imaging Missions (SPIE Proceedings 2)

NASA Technical Reports Server (NTRS)

Danchi, William C.; Bailey, V.; Defrere, D.; Haniff, C.; Hinz, P.; Kennedy, G.; Mennesson, B.; Millan-Gabet, R.; Rieke, G.; Roberge, Aki;

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

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

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

We present ∼0.″4 resolution images of CO(3–2) and associated continuum emission from the gas-bearing debris disk around the nearby A star 49 Ceti, observed with the Atacama Large Millimeter/Submillimeter Array (ALMA). We analyze the ALMA visibilities in tandem with the broadband spectral energy distribution to measure the radial surface density profiles of dust and gas emission from the system. The dust surface density decreases with radius between ∼100 and 310 au, with a marginally significant enhancement of surface density at a radius of ∼110 au. The SED requires an inner disk of small grains in addition to the outer diskmore » of larger grains resolved by ALMA. The gas disk exhibits a surface density profile that increases with radius, contrary to most previous spatially resolved observations of circumstellar gas disks. While ∼80% of the CO flux is well described by an axisymmetric power-law disk in Keplerian rotation about the central star, residuals at ∼20% of the peak flux exhibit a departure from axisymmetry suggestive of spiral arms or a warp in the gas disk. The radial extent of the gas disk (∼220 au) is smaller than that of the dust disk (∼300 au), consistent with recent observations of other gas-bearing debris disks. While there are so far only three broad debris disks with well characterized radial dust profiles at millimeter wavelengths, 49 Ceti’s disk shows a markedly different structure from two radially resolved gas-poor debris disks, implying that the physical processes generating and sculpting the gas and dust are fundamentally different.« less

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

NASA Technical Reports Server (NTRS)

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

The past, present and future of African dust.

PubMed

Evan, Amato T; Flamant, Cyrille; Gaetani, Marco; Guichard, Françoise

2016-03-24

African dust emission and transport exhibits variability on diurnal to decadal timescales and is known to influence processes such as Amazon productivity, Atlantic climate modes, regional atmospheric composition and radiative balance and precipitation in the Sahel. To elucidate the role of African dust in the climate system, it is necessary to understand the factors governing its emission and transport. However, African dust is correlated with seemingly disparate atmospheric phenomena, including the El Niño/Southern Oscillation, the North Atlantic Oscillation, the meridional position of the intertropical convergence zone, Sahelian rainfall and surface temperatures over the Sahara Desert, all of which obfuscate the connection between dust and climate. Here we show that the surface wind field responsible for most of the variability in North African dust emission reflects the topography of the Sahara, owing to orographic acceleration of the surface flow. As such, the correlations between dust and various climate phenomena probably arise from the projection of the winds associated with these phenomena onto an orographically controlled pattern of wind variability. A 161-year time series of dust from 1851 to 2011, created by projecting this wind field pattern onto surface winds from a historical reanalysis, suggests that the highest concentrations of dust occurred from the 1910s to the 1940s and the 1970s to the 1980s, and that there have been three periods of persistent anomalously low dust concentrations--in the 1860s, 1950s and 2000s. Projections of the wind pattern onto climate models give a statistically significant downward trend in African dust emission and transport as greenhouse gas concentrations increase over the twenty-first century, potentially associated with a slow-down of the tropical circulation. Such a dust feedback, which is not represented in climate models, may be of benefit to human and ecosystem health in West Africa via improved air quality and

Observations of Circumstellar Thermochemical Equilibrium: The Case of Phosphorus

NASA Technical Reports Server (NTRS)

Milam, Stefanie N.; Charnley, Steven B.

2011-01-01

We will present observations of phosphorus-bearing species in circumstellar envelopes, including carbon- and oxygen-rich shells 1. New models of thermochemical equilibrium chemistry have been developed to interpret, and constrained by these data. These calculations will also be presented and compared to the numerous P-bearing species already observed in evolved stars. Predictions for other viable species will be made for observations with Herschel and ALMA.

Meteorological Situations Favouring the Development of Dust Plumes over Iceland

NASA Astrophysics Data System (ADS)

Schepanski, K.; Szodry, K.

2017-12-01

The knowledge on mineral dust emitted at high latitudes is limited, but its impact on the polar environments is divers. Within a warming climate, dust emitted from regions in cold climates is expected to increase due to the retreat of the ice sheet and increasing melting rates. Therefore, and for its extensive impacts on different aspects of the climate system, a better understanding of the atmospheric dust life-cycle at high latitudes/cold climates in general, and the spatio-temporal distribution of dust sources in particular, are essential. At high-latitudes, glacio-fluvial sediments as found on river flood plains e.g. supplied by glaciers are prone to wind erosion when dry and bare. In case of the occurrence of strong winds, sediments are blown out and dust plumes develop. As dust uplift is controlled by soil surface characteristics, the availability of suitable sediments, and atmospheric conditions, an interannual variability in dust source activity is expected. We investigated atmospheric circulation patterns that favour the development of dust plumes over Iceland, which presents a well-known dust source at high latitudes. Using the atmosphere model COSMO (COnsortium for Small-scale MOdeling), we analysed the wind speed distribution over the Iceland region for identified and documented dust cases. As one outcome of the study, the position of the Icelandic low, the anticyclones located over Northern Europe, and the resulting pressure gradients are of particular relevance. The interaction of the synoptic-scale winds with the Icelandic orography may locally enhance the wind speeds and thus foster local dust emission. Results from this study suggest that the atmospheric circulation determined by the pressure pattern is of particular relevance for the formation of dust plumes entering the North Atlantic.

The role of atmospheric nuclear explosions on the stagnation of global warming in the mid 20th century

NASA Astrophysics Data System (ADS)

Fujii, Yoshiaki

2011-04-01

This study suggests that the cause of the stagnation in global warming in the mid 20th century was the atmospheric nuclear explosions detonated between 1945 and 1980. The estimated GST drop due to fine dust from the actual atmospheric nuclear explosions based on the published simulation results by other researchers (a single column model and Atmosphere-Ocean General Circulation Model) has served to explain the stagnation in global warming. Atmospheric nuclear explosions can be regarded as full-scale in situ tests for nuclear winter. The non-negligible amount of GST drop from the actual atmospheric explosions suggests that nuclear winter is not just a theory but has actually occurred, albeit on a small scale. The accuracy of the simulations of GST by IPCC would also be improved significantly by introducing the influence of fine dust from the actual atmospheric nuclear explosions into their climate models; thus, global warming behavior could be more accurately predicted.

Dust Devils Seen Streaking Across Mars: PART II--They're the Work of the Devil!

NASA Technical Reports Server (NTRS)

2000-01-01

[figure removed for brevity, see original site]

[figure removed for brevity, see original site]

In December 1999, the MOC team finally had an answer! A dust devil, shown in the above left figure, was caught in the act of creating a swirly, dark streak! An eerie sensation washed over the first team members who saw this picture--here was an event on Mars 'caught in the act' just hours before the picture was played back to Earth. A 'smoking gun.'

The first dust devil seen making a streak--located in Promethei Terra (above, left)--was traveling from right (east) to left (west). A columnar shadow was cast by sunlight coming from the upper left. This shadow indicates the true shape of the dust devil. The bright dust devil itself does not look like a column because the picture was taken from a camera looking straight down on it. The dust devil is less than 100 meters (less than 100 yards) wide and the picture covers an area approximately 1.5 by 1.7 kilometers (about 1 by 1 mile).

Dust devils are spinning, columnar vortices of wind that move across the landscape, pick up dust, and look somewhat like miniature tornadoes. Dust devils are a common occurrence in dry and desert landscapes on Earth as well as Mars. They form when the ground heats up during the day, warming the air immediately above the surface. As the warmed air nearest the surface begins to rise, it spins. The spinning column begins to move across the surface and picks up loose dust (if any is present). The dust makes the vortex visible and gives it the 'dust devil' or tornado-like appearance. On Earth, dust devils typically last for only a few minutes.

The fourth picture (above, right) shows a surface in southwestern Terra Sirenum near 63oS, 168oW, that has seen the activity of so many dust devils that it looks like a plate of dark gray spaghetti. This image, taken in early summer during February 2000, covers an area 3 km wide and 30 km long (1.9 by 19 miles). In fact, a dust devil

Nucleation Studies under the Conditions of Carbon-rich AGB Star Envelopes: TiC

NASA Astrophysics Data System (ADS)

Patzer, A. B. C.; Wendt, M.; Chang, C.; Sülzle, D.

2011-09-01

Many studies of dust nucleation in winds of carbon-rich AGB stars consider primarily carbon as the dust forming material. But dust grains formed in such circumstellar envelopes are rather a mixture of several chemical elements such as titanium or silicon in addition to carbon, as verified by many investigations of pre-solar grains enclosed in meteorites, for example. In this contribution we focus on the study of the nucleation of titanium carbide particles from the gas phase. The necessary properties of molecular titanium carbide clusters have been estimated by the density functional approach, and the first implications for the homogeneous nucleation of TiC are studied for conditions representative of circumstellar dust shells around carbon-rich AGB stars.

The Role of Grain Surface Reactions in the Chemistry of Star Forming Regions

NASA Technical Reports Server (NTRS)

Kress, M. E.; Tielens, A. G. G. M.; Roberge, W. G.

1998-01-01

The importance of reactions at the surfaces of dust grains has long been recognized to be one of the two main chemical processes that form molecules in cold, dark interstellar clouds where simple, saturated (fully-hydrogenated) molecules such as H2 water, methanol, H2CO, H2S, ammonia and CH4 are present in quantities far too high to be consistent with their extremely low gas phase formation rates. In cold dark regions of interstellar space, dust grains provide a substrate onto which gas-phase species can accrete and react. Grains provide a "third body" or a sink for the energy released in the exothermic reactions that form chemical bonds. In essence, the surfaces of dust grains open up alternative reaction pathways to form observed molecules whose abundances cannot be explained with gas-phase chemistry alone. This concept is taken one step further in this work: instead of merely acting as a substrate onto which radicals and molecules may physically adsorb, some grains may actively participate in the reaction itself, forming chemical bonds with the accreting species. Until recently, surface chemical reactions had not been thought to be important in warm circumstellar media because adspecies rapidly desorb from grains at very low temperatures; thus, the residence times of molecules and radicals on the surface of grains at all but the lowest temperatures are far too short to allow these reactions to occur. However, if the adspecies could adsorb more strongly, via a true chemical bond with surfaces of some dust grains, then grain surface reactions will play an important role in warm circumstellar regions as well. In this work, the surface-catalyzed reaction CO + 3 H2 yields CH4 + H2O is studied in the context that it may be very effective at converting the inorganic molecule CO into the simplest organic compound, methane. H2 and CO are the most abundant molecules in space, and the reaction converting them to methane, while kinetically inhibited in the gas phase under

The Role of African Easterly Wave on Dust Transport and the Interaction Between Saharan Dust Layer and Atlantic ITCZ During Boreal Summer

NASA Technical Reports Server (NTRS)

Lau, William K. M.; Kim, Kyu-Myong

2012-01-01

In this paper, we investigate the relationships among Saharan dust outbreak and transport, African easterly waves (AEW), African easterly jet (AEJ) and associated convective activities of Atlantic Intertropical Convergence Zone (ITCZ) using Cloudsat-Calipso, MODIS and MERRA data. We find that a major Saharan dust outbreak is associated with the formation of a westward propagating strong cyclone around 15-25N over the western part northern Saharan. The strong cyclonic flow mobilizes and lifts the dust from the desert surface to a high elevation. As the cyclone propagate westward, it transports a thick elevated dust layer between 900 -500 hPa from the African continent to the eastern Atlantic. Cloudiness is reduced within the warm, dry dusty layer, but enhanced underneath it, possibly due to the presence of a shallow inversion layer over the marine boundary layer. The dust outbreak is linked to enhanced deep convection in the northern part of Atlantic ITCZ, abutting the southern flank of the dust layer, and a strengthening of the northward flank of the AEJ. As the dust layer spreads westward, it loses elevation and becomes increasing diffused as it reaches the central and western Atlantic. Using band pass filtered EOF analysis of MERRA winds, we find that AEWs propagating westward along two principal tracks, centered at 15-25N and 5-10N respectively. The easterly waves in the northern track are highly correlated with major dust outbreak over North Africa and associated with slower moving systems, with a quasi-periodicity of 6-9 day. On the other hand, easterly waves along the southern track are faster, with quasi-periodicity of 3-5 days. These faster easterly waves are closely tied to rainfall/cloud variations along the Atlantic ITCZ. Dust transport along the southern track by the faster waves generally leads rainfall/cloud anomalies in the same region by one or two days, suggesting the southern tracks of dust outbreak are regions of strong interaction between

Herschel observations of the circumstellar environments of the Herbig Be stars R Mon and PDS 27

NASA Astrophysics Data System (ADS)

Jiménez-Donaire, M. J.; Meeus, G.; Karska, A.; Montesinos, B.; Bouwman, J.; Eiroa, C.; Henning, T.

2017-09-01

Context. The circumstellar environments of Herbig Be stars in the far-infrared are poorly characterised, mainly because they are often embedded and rather distant. The analysis of far-infrared spectroscopy allows us to make a major step forward by covering multiple rotational lines of molecules, e.g. CO, that are useful probes of the physical conditions of the gas. Aims: We characterise the gas and dust in the discs and environments of Herbig Be stars, and we compare the results with those of their lower-mass counterparts, the Herbig Ae stars. Methods: We report and analyse far-infrared observations of two Herbig Be stars, R Mon and PDS 27, obtained with the Herschel instruments PACS and SPIRE. We construct spectral energy distributions and derive the infrared excess. We extract line fluxes from the PACS and SPIRE spectra and construct rotational diagrams in order to estimate the excitation temperature of the gas. We derive CO, [O I] and [C I] luminosities to determine the physical conditions of the gas, and the dominant cooling mechanism. Results: We confirm that the Herbig Be stars are surrounded by remnants from their parental clouds, with an IR excess that mainly originates in a disc. In R Mon we detect [O I], [C I], [C II], CO (26 transitions), water and OH, while in PDS 27 we only detect [C I] and CO (8 transitions). We attribute the absence of OH and water in PDS 27 to UV photo-dissociation and photo-evaporation. From the rotational diagrams, we find several components for CO; we derive Trot949 ± 90 K, 358 ± 20 K and 77 ± 12 K for R Mon; 96 ± 12 K and 31 ± 4 K for PDS 27; and 25 ± 8 K and 27 ± 6 K for their respective compact neighbours. The forsterite feature at 69 μm was not detected in either of the sources, probably due to the lack of (warm) crystalline dust in a flat disc. We find that cooling by molecules is dominant in the Herbig Be stars, while this is not the case in Herbig Ae stars where cooling by [O I] dominates. Moreover, we show that in

Combined impacts of current and future dust deposition and regional warming on Colorado River Basin snow dynamics and hydrology

USGS Publications Warehouse

Deems, Jeffrey S.; Painter, Thomas H.; Barsugli, Joseph J.; Belnap, Jayne; Udall, Bradley

2013-01-01

The Colorado River provides water to 40 million people in seven western states and two countries and to 5.5 million irrigated acres. The river has long been overallocated. Climate models project runoff losses of 5–20% from the basin by mid-21st century due to human-induced climate change. Recent work has shown that decreased snow albedo from anthropogenic dust loading to the CO mountains shortens the duration of snow cover by several weeks relative to conditions prior to western expansion of the US in the mid-1800s, and advances peak runoff at Lees Ferry, Arizona, by an average of 3 weeks. Increases in evapotranspiration from earlier exposure of soils and germination of plants have been estimated to decrease annual runoff by more than 1.0 billion cubic meters, or ~5% of the annual average. This prior work was based on observed dust loadings during 2005–2008; however, 2009 and 2010 saw unprecedented levels of dust loading on snowpacks in the Upper Colorado River Basin (UCRB), being on the order of 5 times the 2005–2008 loading. Building on our prior work, we developed a new snow albedo decay parameterization based on observations in 2009/10 to mimic the radiative forcing of extreme dust deposition. We convolve low, moderate, and extreme dust/snow albedos with both historic climate forcing and two future climate scenarios via a delta method perturbation of historic records. Compared to moderate dust, extreme dust absorbs 2× to 4× the solar radiation, and shifts peak snowmelt an additional 3 weeks earlier to a total of 6 weeks earlier than pre-disturbance. The extreme dust scenario reduces annual flow volume an additional 1% (6% compared to pre-disturbance), a smaller difference than from low to moderate dust scenarios due to melt season shifting into a season of lower evaporative demand. The sensitivity of flow timing to dust radiative forcing of snow albedo is maintained under future climate scenarios, but the sensitivity of flow volume reductions decreases

Warming ancient Mars with water clouds

NASA Astrophysics Data System (ADS)

Hartwick, V.; Toon, B.

2017-12-01

High clouds in the present day Mars atmosphere nucleate on interplanetary dust particles (IDPs) that burn up on entry into the Mars atmosphere. Clouds form when superstaturated water vapor condenses on suspended aerosols. Radiatively active water ice clouds may play a crucial role in warming the early Mars climate. Urata and Toon (2011) simulate a stable warm paleo-climate for Mars if clouds form high in the atmosphere and if particles are sufficiently large (r > 10 μm). The annual fluence of micrometeoroids at Mars was larger early on in the evolution of our solar system. Additionally, the water vapor budget throughout the middle and high atmosphere was likely heightened . Both factors should contribute to enhanced nucleation and growth of water ice cloud particles at high altitudes. Here, we use the MarsCAM-CARMA general circulation model (GCM) to examine the radiative impact of high altitude water ice clouds on the early Mars climate and as a possible solution to the faint young sun problem for Mars.

Grain Formation Processes in Oxygen-Rich Circumstellar Outflows: Testing the Metastable Eutectic Condensation Hypothesis and Measuring Atom-Grain & Grain-Grain Sticking Coefficients (A Sub-orbital Investigation)

NASA Astrophysics Data System (ADS)

Nuth, Joseph

hypothesis would be a major step in establishing a simple, chemical kinetic model for the nucleation, growth and annealing of circumstellar oxide dust. Since strong convective flows in the terrestrial laboratory make it almost impossible to measure the growth and aggregation of freshly condensed, refractory grains, we will conduct experiments in microgravity to eliminate these flows. We propose to measure the efficiency of grain growth from simple SiO, AlO and FeO vapors and the sticking coefficients for dust coagulation via analyses of the grain morphology and size distribution of condensates collected and returned to earth during each rocket experiment. We will discuss the unique experimental systems used to produce our analog samples and the general nature of these materials. We note that these experimental systems were not designed to produce samples at equilibrium like typical petrologic systems. Indeed, they were designed to make samples that will help us to understand the properties of materials produced under highly dynamic conditions, quite far from equilibrium, that are often found in nature wherever steep temperature, pressure and/or compositional gradients result in highly unequilibrated solid systems. This design is an advantage as it presents the chance to compare and contrast samples produced at equilibrium with unequilibrated samples in order to identify distinctive traits that could be used to identify conditions under which natural samples have been formed. We will describe both the laboratory system and the rocket payload. We will present data from previous experiments in these systems and discuss why recovery of the flight payload and analyses of the particles produced is essential to build a rigorous, laboratory-based model of grain formation in astrophysical environments.

Decadal-scale progression of Dansgaard-Oeschger warming events - Are warmings at the end of Heinrich-Stadials different from others?

NASA Astrophysics Data System (ADS)

Erhardt, T.; Capron, E.; Rasmussen, S.; Schuepbach, S.; Bigler, M.; Fischer, H.

2017-12-01

During the last glacial period proxy records throughout the Northern Hemisphere document a succession of rapid millennial-scale warming events, called Dansgaard Oeschger (DO) events. Marine proxy records from the Atlantic also reveal, that some of the warming events where preceded by large ice rafting events, referred to as Heinrich events. Different mechanisms have been proposed, that can produce DO-like warming in model experiments, however the progression and plausible trigger of the events and their possible interplay with the Heinrich events is still unknown. Because of their fast nature, the progression is challenging to reconstruct from paleoclimate data due to the temporal resolution achievable in many archives and cross-dating uncertainties between records. We use new high-resolution multi-proxy records of sea-salt and terrestrial aerosol concentrations over the period 10-60 ka from two Greenland deep ice cores in conjunction with local precipitation and temperature proxy records from one of the cores to investigate the progression of environmental changes at the onset of the individual warming events. The timing differences are then used to explore whether the DO warming events that terminate Heinrich-Stadials progressed differently in comparison to those after Non-Heinrich-Stadials. Our analysis indicates no difference in the progression of the warming terminating Heinrich-Stadials and Non-Heinrich-Stadials. Combining the evidence from all warming events in the period, our analysis shows a consistent lead of the changes in both local precipitation and terrestrial dust aerosol concentrations over the change in sea-salt aerosol concentrations and local temperature by approximately one decade. This implies that both the moisture transport to Greenland and the intensity of the Asian winter monsoon changed before the sea-ice cover in the North Atlantic was reduced, rendering a collapse of the sea-ice cover as a trigger for the DO events unlikely.

Gusev Dust Devil Movie, Sol 456 (Plain and Isolated)

NASA Technical Reports Server (NTRS)

2005-01-01

This movie clip shows a dust devil scooting across a plain inside Gusev Crater on Mars as seen from the NASA rover Spirit's hillside vantage point during the rover's 456th martian day, or sol (April 15, 2005). The individual images were taken about 20 seconds apart by Spirit's navigation camera. Each frame in this movie has the raw image on the top half and a processed version in the lower half that enhances contrast and removes stationary objects, producing an image that is uniformly gray except for features that change from frame to frame.

The movie results from a new way of watching for dust devils, which are whirlwinds that hoist dust from the surface into the air. Spirit began seeing dust devils in isolated images in March 2005. At first, the rover team relied on luck. It might catch a dust devil in an image or it might miss by a few minutes. Using the new detection strategy, the rover takes a series of 21 images. Spirit sends a few of them to Earth, as well as little thumbnail images of all of them. Team members use the 3 big images and all the small images to decide whether the additional big images have dust devils. For this movie, they specifically told Spirit to send back frames that they knew had dust devils.

Scientists expected dust devils since before Spirit landed. The landing area inside Gusev Crater is filled with dark streaks left behind when dust devils pick dust up from an area. It is also filled with bright 'hollows,' which are dust-filled miniature craters. Dust covers most of the terrain. Winds flow into and out of Gusev crater every day. The Sun heats the surface so that the surface is warm to the touch even though the atmosphere at 2 meters (6 feet) above the surface would be chilly. That temperature contrast causes convection. Mixing the dust, winds, and convection should trigger dust devils.

Scientists will use the images to study several things. Tracking the dust devils tells which way the wind blows at different times

Gusev Dust Devil Movie, Sol 459 (Plain and Isolated)

NASA Technical Reports Server (NTRS)

2005-01-01

This movie clip shows a dust devil scooting across a plain inside Gusev Crater on Mars as seen from the NASA rover Spirit's hillside vantage point during the rover's 459th martian day, or sol (April 18, 2005). The individual images were taken about 20 seconds apart by Spirit's navigation camera. Each frame in this movie has the raw image on the top half and a processed version in the lower half that enhances contrast and removes stationary objects, producing an image that is uniformly gray except for features that change from frame to frame.

The movie results from a new way of watching for dust devils, which are whirlwinds that hoist dust from the surface into the air. Spirit began seeing dust devils in isolated images in March 2005. At first, the rover team relied on luck. It might catch a dust devil in an image or it might miss by a few minutes. Using the new detection strategy, the rover takes a series of 21 images. Spirit sends a few of them to Earth, as well as little thumbnail images of all of them. Team members use the 3 big images and all the small images to decide whether the additional big images have dust devils. For this movie, they specifically told Spirit to send back frames that they knew had dust devils.

Scientists expected dust devils since before Spirit landed. The landing area inside Gusev Crater is filled with dark streaks left behind when dust devils pick dust up from an area. It is also filled with bright 'hollows,' which are dust-filled miniature craters. Dust covers most of the terrain. Winds flow into and out of Gusev crater every day. The Sun heats the surface so that the surface is warm to the touch even though the atmosphere at 2 meters (6 feet) above the surface would be chilly. That temperature contrast causes convection. Mixing the dust, winds, and convection should trigger dust devils.

Scientists will use the images to study several things. Tracking the dust devils tells which way the wind blows at different times

Resolving the clumpy circumstellar environment of the B[e] supergiant LHA 120-S 35

NASA Astrophysics Data System (ADS)

Torres, A. F.; Cidale, L. S.; Kraus, M.; Arias, M. L.; Barbá, R. H.; Maravelias, G.; Borges Fernandes, M.

2018-05-01

Context. B[e] supergiants are massive post-main-sequence stars, surrounded by a complex circumstellar environment where molecules and dust can survive. The shape in which the material is distributed around these objects and its dynamics as well as the mechanisms that give rise to these structures are not well understood. Aims: The aim is to deepen our knowledge of the structure and kinematics of the circumstellar disc of the B[e] supergiant LHA 120-S 35. Methods: High-resolution optical spectra were obtained in three different years. Forbidden emission lines, that contribute to trace the disc at different distances from the star, are modelled in order to determine the kinematical properties of their line-forming regions, assuming Keplerian rotation. In addition, we used low-resolution near-infrared spectra to explore the variability of molecular emission. Results: LHA 120-S 35 displays an evident spectral variability in both optical and infrared regions. The P-Cygni line profiles of H I, as well as those of Fe II and O I, suggest the presence of a strong bipolar clumped wind. We distinguish density enhancements in the P-Cygni absorption component of the first Balmer lines, which show variations in both velocity and strength. The P-Cygni profile emission component is double-peaked, indicating the presence of a rotating circumstellar disc surrounding the star. We also observe line-profile variations in the permitted and forbidden features of Fe II and O I. In the infrared, we detect variations in the intensity of the H I emission lines as well as in the emission of the CO band-heads. Moreover, we find that the profiles of each [Ca II] and [O I] emission lines contain contributions from spatially different (complete or partial) rings. Globally, we find evidence of detached multi-ring structures, revealing density variations along the disc. We identify an inner ring, with sharp edge, where [Ca II] and [O I] lines share their forming region with the CO molecular bands

Gas Modelling in the Disc of HD 163296

NASA Technical Reports Server (NTRS)

Tilling, I.; Woitke, P.; Meeus, G.; Mora, A.; Montesinos, B.; Riviere-Marichalar, P.; Eiroa, C.; Thi, W. -F.; Isella, A.; Roberge, A.;

Modelling the carbon AGB star R Sculptoris. Constraining the dust properties in the detached shell based on far-infrared and sub-millimeter observations

NASA Astrophysics Data System (ADS)

Brunner, M.; Maercker, M.; Mecina, M.; Khouri, T.; Kerschbaum, F.

2018-06-01

Context. On the asymptotic giant branch (AGB), Sun-like stars lose a large portion of their mass in an intensive wind and enrich the surrounding interstellar medium with nuclear processed stellar material in the form of molecular gas and dust. For a number of carbon-rich AGB stars, thin detached shells of gas and dust have been observed. These shells are formed during brief periods of increased mass loss and expansion velocity during a thermal pulse, and open up the possibility to study the mass-loss history of thermally pulsing AGB stars. Aims: We study the properties of dust grains in the detached shell around the carbon AGB star R Scl and aim to quantify the influence of the dust grain properties on the shape of the spectral energy distribution (SED) and the derived dust shell mass. Methods: We modelled the SED of the circumstellar dust emission and compared the models to observations, including new observations of Herschel/PACS and SPIRE (infrared) and APEX/LABOCA (sub-millimeter). We derived present-day mass-loss rates and detached shell masses for a variation of dust grain properties (opacities, chemical composition, grain size, and grain geometry) to quantify the influence of changing dust properties to the derived shell mass. Results: The best-fitting mass-loss parameters are a present-day dust mass-loss rate of 2 × 10-10 M⊙ yr-1 and a detached shell dust mass of (2.9 ± 0.3) × 10-5 M⊙. Compared to similar studies, the uncertainty on the dust mass is reduced by a factor of 4. We find that the size of the grains dominates the shape of the SED, while the estimated dust shell mass is most strongly affected by the geometry of the dust grains. Additionally, we find a significant sub-millimeter excess that cannot be reproduced by any of the models, but is most likely not of thermal origin. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

Water isotopologues in the circumstellar envelopes of M-type AGB stars

NASA Astrophysics Data System (ADS)

Danilovich, T.; Lombaert, R.; Decin, L.; Karakas, A.; Maercker, M.; Olofsson, H.

2017-06-01

Aims: In this study we intend to examine rotational emission lines of two isotopologues of water: H217O and H218O. By determining the abundances of these molecules, we aim to use the derived isotopologue - and hence oxygen isotope - ratios to put constraints on the masses of a sample of M-type AGB stars that have not been classified as OH/IR stars. Methods: We have used detailed radiative transfer analysis based on the accelerated lambda iteration method to model the circumstellar molecular line emission of H217O and H218O for IK Tau, R Dor, W Hya, and R Cas. The emission lines used to constrain our models came from Herschel/HIFI and Herschel/PACS observations and are all optically thick, meaning that full radiative transfer analysis is the only viable method of estimating molecular abundance ratios. Results: We find generally low values of the 17O/18O ratio for our sample, ranging from 0.15 to 0.69. This correlates with relatively low initial masses, in the range 1.0 to 1.5 M⊙ for each source, based on stellar evolutionary models. We also find ortho-to-para ratios close to 3, which are expected from warm formation predictions. Conclusions: The 17O/18O ratios found for this sample are at the lower end of the range predicted by stellar evolutionary models, indicating that the sample chosen had relatively low initial masses. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

The circumstellar envelope around the S-type AGB star W Aql. Effects of an eccentric binary orbit

PubMed Central

Ramstedt, S.; Mohamed, S.; Vlemmings, W. H. T.; Danilovich, T.; Brunner, M.; De Beck, E.; Humphreys, E. M. L.; Lindqvist, M.; Maercker, M.; Olofsson, H.; Kerschbaum, F.; Quintana-Lacaci, G.

2017-01-01

arc patterns with different separations. The larger pattern is predicted by the binary interaction model with separations of ~10″ and therefore likely due to the known companion. It is consistent with a binary orbit with low eccentricity. The smaller separation pattern is asymmetric and coincides with the dust distribution, but the separation timescale (200 yrs) is not consistent with any known process of the system. The separation of the known companions of the system is large enough to not have a very strong effect on the circumstellar morphology. The density contrast across the envelope of a binary with an even larger separation will not be easily detectable, even with ALMA, unless the orbit is strongly asymmetric or the AGB star has a much larger mass-loss rate. PMID:29142327

The circumstellar envelope around the S-type AGB star W Aql. Effects of an eccentric binary orbit.

PubMed

Ramstedt, S; Mohamed, S; Vlemmings, W H T; Danilovich, T; Brunner, M; De Beck, E; Humphreys, E M L; Lindqvist, M; Maercker, M; Olofsson, H; Kerschbaum, F; Quintana-Lacaci, G

2017-09-21

. The larger pattern is predicted by the binary interaction model with separations of ~10″ and therefore likely due to the known companion. It is consistent with a binary orbit with low eccentricity. The smaller separation pattern is asymmetric and coincides with the dust distribution, but the separation timescale (200 yrs) is not consistent with any known process of the system. The separation of the known companions of the system is large enough to not have a very strong effect on the circumstellar morphology. The density contrast across the envelope of a binary with an even larger separation will not be easily detectable, even with ALMA, unless the orbit is strongly asymmetric or the AGB star has a much larger mass-loss rate.

Climatology of atmospheric circulation patterns of Arabian dust in western Iran.

PubMed

Najafi, Mohammad Saeed; Sarraf, B S; Zarrin, A; Rasouli, A A

2017-08-28

Being in vicinity of vast deserts, the west and southwest of Iran are characterized by high levels of dust events, which have adverse consequences on human health, ecosystems, and environment. Using ground based dataset of dust events in western Iran and NCEP/NCAR reanalysis data, the atmospheric circulation patterns of dust events in the Arabian region and west of Iran are identified. The atmospheric circulation patterns which lead to dust events in the Arabian region and western Iran were classified into two main categories: the Shamal dust events that occurs in warm period of year and the frontal dust events as cold period pattern. In frontal dust events, the western trough or blocking pattern at mid-level leads to frontogenesis, instability, and air uplift at lower levels of troposphere in the southwest of Asia. Non-frontal is other pattern of dust event in the cold period and dust generation are due to the regional circulation systems at the lower level of troposphere. In Shamal wind pattern, the Saudi Arabian anticyclone, Turkmenistan anticyclone, and Zagros thermal low play the key roles in formation of this pattern. Summer and transitional patterns are two sub-categories of summer Shamal wind pattern. In summer trough pattern, the mid-tropospheric trough leads to intensify the surface thermal systems in the Middle East and causes instability and rising of wind speed in the region. In synthetic pattern of Shamal wind and summer trough, dust is created by the impact of a trough in mid-levels of troposphere as well as existing the mentioned regional systems which are contributed in formation of summer Shamal wind pattern.

The Effect of Asian Dust Aerosols on Cloud Properties and Radiative Forcing from MODIS and CERES

NASA Technical Reports Server (NTRS)

Huang, Jianping; Minnis, Patrick; Lin, Bing; Wang, Tianhe; Yi, Yuhong; Hu, Yongxiang; Sun-Mack, Sunny; Ayers, Kirk

2005-01-01

The effects of dust storms on cloud properties and radiative forcing are analyzed over northwestern China from April 2001 to June 2004 using data collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) and Clouds and the Earth's Radiant Energy System (CERES) instruments on the Aqua and Terra satellites. On average, ice cloud effective particle diameter, optical depth and ice water path of the cirrus clouds under dust polluted conditions are 11%, 32.8%, and 42% less, respectively, than those derived from ice clouds in dust-free atmospheric environments. The humidity differences are larger in the dusty region than in the dust-free region, and may be caused by removal of moisture by wet dust precipitation. Due to changes in cloud microphysics, the instantaneous net radiative forcing is reduced from -71.2 W/m2 for dust contaminated clouds to -182.7 W/m2 for dust-free clouds. The reduced cooling effects of dusts may lead to a net warming of 1 W/m2, which, if confirmed, would be the strongest aerosol forcing during later winter and early spring dust storm seasons over the studied region.

Lidar network observation of dust layer evolution over the Gobi Desert in MAY 2013

NASA Astrophysics Data System (ADS)

Kawai, Kei; Kai, Kenji; Jin, Yoshitaka; Sugimoto, Nobuo; Batdorj, Dashdondog

2018-04-01

A lidar network captured the evolution of a dust layer in the Gobi Desert on 22-23 May 2013. The lidar network consists of a ceilometer and two AD-Net lidars in Mongolia. The dust layer was generated by a strong wind due to a cold front and elevated over the surface of the cold front by an updraft of the warm air in the cold-front system. It was evolving from the atmospheric boundary layer to the free troposphere while moving 600 km through the desert with the cold front.

Influence of the Latitudinal Temperature Gradient on Soil Dust Concentration and Deposition in Greenland

NASA Technical Reports Server (NTRS)

Tegen, Ina; Rind, David

2000-01-01

To investigate the effects of changes in the latitudinal temperature gradient and the global mean temperature on dust concentration in the Northern Hemisphere, experiments with the Goddard Institute for Space Studies General Circulation Model (GISS GCM) are performed. The dust concentration over Greenland is calculated from sources in central and eastern Asia, which are integrated on-line in the model. The results show that an increase in the latitudinal temperature gradient increases both the Asian dust source strength and the concentration over Greenland. The source increase is the result of increased surface winds, and to a minor extent, the increase in Greenland dust is also associated with increased northward transport. Cooling the climate in addition to this increased gradient leads to a decrease in precipitation scavenging, which helps produce a further (slight) increase in Greenland dust in this experiment. Reducing the latitudinal gradient reduces the surface wind and hence the dust source, with a subsequent reduction in Greenland dust concentrations. Warming the climate in addition to this reduced gradient leads to a further reduction in Greenland dust due to enhanced precipitation scavenging. These results can be used to evaluate the relationship of Greenland ice core temperature changes to changes in the latitudinal and global temperatures.

Positive low cloud and dust feedbacks amplify tropical North Atlantic Multidecadal Oscillation

DOE PAGES

Yuan, Tianle; Oreopoulos, Lazaros; Zelinka, Mark; ...

2016-02-04

The Atlantic Multidecadal Oscillation (AMO) is characterized by a horseshoe pattern of sea surface temperature (SST) anomalies and has a wide range of climatic impacts. While the tropical arm of AMO is responsible for many of these impacts, it is either too weak or completely absent in many climate model simulations. Here we show, using both observational and model evidence, that the radiative effect of positive low cloud and dust feedbacks is strong enough to generate the tropical arm of AMO, with the low cloud feedback more dominant. The feedbacks can be understood in a consistent dynamical framework: weakened tropicalmore » trade wind speed in response to a warm middle latitude SST anomaly reduces dust loading and low cloud fraction over the tropical Atlantic, which warms the tropical North Atlantic SST. Together they contribute to the appearance of the tropical arm of AMO. Most current climate models miss both the critical wind speed response and two positive feedbacks though realistic simulations of them may be essential for many climatic studies related to the AMO.« less

Positive Low Cloud and Dust Feedbacks Amplify Tropical North Atlantic Multidecadal Variability

NASA Technical Reports Server (NTRS)

Yuan, Tianle; Oraiopoulos, Lazaros; Zelinka, Mark; Yu, Hongbin; Norris, Joel R.; Chin, Mian; Platnick, Steven; Meyer, Kerry

2016-01-01

The Atlantic Multidecadal Oscillation (AMO) is characterized by a horseshoe pattern of sea surface temperature (SST) anomalies and has a wide range of climatic impacts. While the tropical arm of AMO is responsible for many of these impacts, it is either too weak or completely absent in many climate model simulations. Here we show, using both observational and model evidence, that the radiative effect of positive low cloud and dust feedbacks is strong enough to generate the tropical arm of AMO, with the low cloud feedback more dominant. The feedbacks can be understood in a consistent dynamical framework: weakened tropical trade wind speed in response to a warm middle latitude SST anomaly reduces dust loading and low cloud fraction over the tropical Atlantic, which warms the tropical North Atlantic SST. Together they contribute to appearance of the tropical arm of AMO. Most current climate models miss both the critical wind speed response and two positive feedbacks though realistic simulations of them may be essential for many climatic studies related to the AMO.

The potential influence of Asian and African mineral dust on ice, mixed-phase and liquid water clouds

NASA Astrophysics Data System (ADS)

Wiacek, A.; Peter, T.; Lohmann, U.

2010-02-01

This modelling study explores the availability of mineral dust particles as ice nuclei for interactions with ice, mixed-phase and liquid water clouds, also tracking the particles' history of cloud-processing. We performed 61 320 one-week forward trajectory calculations originating near the surface of major dust emitting regions in Africa and Asia using high-resolution meteorological analysis fields for the year 2007. Without explicitly modelling dust emission and deposition processes, dust-bearing trajectories were assumed to be those coinciding with known dust emission seasons. We found that dust emissions from Asian deserts lead to a higher potential for interactions with high clouds, despite being the climatologically much smaller dust emission source. This is due to Asian regions experiencing significantly more ascent than African regions, with strongest ascent in the Asian Taklimakan desert at ~25%, ~40% and 10% of trajectories ascending to 300 hPa in spring, summer and fall, respectively. The specific humidity at each trajectory's starting point was transported in a Lagrangian manner and relative humidities with respect to water and ice were calculated in 6-h steps downstream, allowing us to estimate the formation of liquid, mixed-phase and ice clouds. Practically none of the simulated air parcels reached regions where homogeneous ice nucleation can take place (T≲-40 °C) along trajectories that have not experienced water saturation first. By far the largest fraction of cloud forming trajectories entered conditions of mixed-phase clouds, where mineral dust will potentially exert the biggest influence. The majority of trajectories also passed through regions supersaturated with respect to ice but subsaturated with respect to water, where "warm" (T≳-40 °C) ice clouds may form prior to supercooled water or mixed-phase clouds. The importance of "warm" ice clouds and the general influence of dust in the mixed-phase cloud region are highly uncertain due to

IDENTIFYING NEARBY, YOUNG, LATE-TYPE STARS BY MEANS OF THEIR CIRCUMSTELLAR DISKS

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

Schneider, Adam; Song, Inseok; Melis, Carl

2012-10-01

It has recently been shown that a significant fraction of late-type members of nearby, very young associations (age {approx}<10 Myr) display excess emission at mid-IR wavelengths indicative of dusty circumstellar disks. We demonstrate that the detection of mid-IR excess emission can be utilized to identify new nearby, young, late-type stars including two definite new members ('TWA 33' and 'TWA 34') of the TW Hydrae Association (TWA). Both new TWA members display mid-IR excess emission in the Wide-field Infrared Survey Explorer catalog and they show proper motion and youthful spectroscopic characteristics-namely, H{alpha} emission, strong lithium absorption, and low surface gravity featuresmore » consistent with known TWA members. We also detect mid-IR excess-the first unambiguous evidence of a dusty circumstellar disk-around a previously identified UV-bright, young, accreting star (2M1337) that is a likely member of the Lower-Centaurus Crux region of the Scorpius-Centaurus Complex.« less

A Northward Shift of the North Atlantic Ocean Intertropical Convergence Zone in Response to Summertime Saharan Dust Outbreaks

NASA Technical Reports Server (NTRS)

Wilcox, Eric M.; Lau, K. M.; Kim, Kyu-Myong

2010-01-01

The influence on the summertime North Atlantic Ocean inter-tropical convergence zone (ITCZ) of Saharan dust outbreaks is explored using nine years of continuous satellite observations and atmospheric reanalysis products. During dust outbreak events rainfall along the ITCZ shifts northward by 1 to 4 degrees latitude. Dust outbreaks coincide with warmer lower-tropospheric temperatures compared to low dust conditions, which is attributable to advection of the warm Saharan Air Layer, enhanced subtropical subsidence, and radiative heating of dust. The enhanced positive meridional temperature gradient coincident with dust outbreaks is accompanied by an acceleration of the easterly winds on the n011h side of the African Easterly Jet (AEJ). The center of the positive vorticity region south of the AEJ moves north drawing the center of low-level convergence and ITCZ rainfall northward with it. The enhanced precipitation on the north side of the ITCZ occurs in spite of widespread sea surface temperature cooling north of the ITCZ owing to reduced surface solar insolation by dust scattering.

When Bad Masks Turn Good

NASA Astrophysics Data System (ADS)

Abraham, Roberto G.

In keeping with the spirit of a meeting on ‘masks,' this talk presents two short stories on the theme of dust. In the first, dust plays the familiar role of the evil obscurer, the enemy to bedefeated by the cunning observer in order to allow a key future technology (adaptive optics) to be exploited fully by heroic astronomers. In the second story, dust itself emerges as the improbable hero, in the form of a circumstellar debris disks. I will present evidence of a puzzling near-infrared excess in the continuum of high-redshift galaxies and will argue that the seemingly improbable origin of this IR excess is a population of young circumstellar disks formed around high-mass stars in distant galaxies. Assuming circumstellar disks extend down to lower masses,as they do in our own Galaxy, the excess emission presents us with an exciting opportunity to measure the formation rate of planetary systems in distant galaxies at cosmic epochs before our own solar system formed.

Parameterizing the Dust Around Herbig Ae/Be Stars: Multiwavelength Imaging, Radiative Transfer Modeling, and Near-Infrared Instrumentation

NASA Astrophysics Data System (ADS)

Doering, Ryan L.

2009-01-01

Determining Herbig Ae/Be star dust parameters provides constraints for planet formation theory, and yields information about the matter around intermediate-mass stars as they approach the main sequence. In this dissertation talk, I present the results of a multiwavelength imaging and radiative transfer modeling study of Herbig Ae/Be stars, and a near-infrared instrumentation project, with the aim of parameterizing the dust in these systems. The Hubble Space Telescope was used to search for optical light scattered by dust in a sample of young stars. This survey provided the first scattered-light image of the circumstellar environment around the Herbig Ae/Be star HD 97048. Structure is observed in the dust distribution similar to that seen in other Herbig Ae/Be systems. A ground-based near-infrared imaging study of Herbig Ae/Be candidates was also carried out. Photometry was collected for spectral energy distribution construction, and binary candidates were resolved. Detailed dust modeling of HD 97048 and HD 100546 was carried out with a two-component geometry consisting of a flared disk and an extended envelope. The models achieve a reasonable global fit to the spectral energy distributions, and produce images with the desired geometry. The disk midplane densities are found to go as r-0.5 and r-1.8, giving disk dust masses of 3.0 x 10-4 and 5.9 x 10-5 Msun for HD 97048 and HD 100546, respectively. A gas-to-dust mass ratio lower limit of 3.2 was calculated for HD 97048. Furthermore, I have participated in the development of the WIYN High Resolution Infrared Camera. The instrument operates in the near-infrared ( 0.8 - 2.5 microns), includes 13 filters, and has a pixel size of 0.1 arcsec, resulting in a field of view of 3 arcmin x 3 arcmin. An angular resolution of 0.25 arcsec is anticipated. I provide an overview of the instrument and report performance results.

Detection of Dermatophagoides farinae in the dust of air conditioning filters.

PubMed

Liu, Zhigang; Bai, Yu; Ji, Kunmei; Liu, Xiaoyu; Cai, Chengyu; Yu, Haiqiong; Li, Meng; Bao, Ying; Lian, Yuyin; Gao, Bo

2007-01-01

The allergenic dust mite species Dermatophagoides pteronyssinus and Dermatophagoides farinae generally inhabit warm moist environments. This study tested the hypothesis that these allergenic species may thrive in air conditioner filters. A year-long investigation of the dust mite population densities and species identities living in air conditioner filters in Shenzhen City in Southern China was performed. Additional data describing the levels of major dust mite allergen proteins from samples collected in July and August 2004 were analyzed. Genetic polymorphism analysis of Der f 1 and Der f 2 genes in the collected animals was also conducted. Our investigation revealed that larval dust mites started to grow in March, from which time their populations proceeded to steadily increase until reaching their population zenith in July and August. The dust mite populations decreased sharply in October and live dust mites were no longer observed in the winter. Among the mites collected in July and August, 30.1 and 25.8% were of the species D. farinae. The concentration of Der f 1 was 3.04 +/- 1.75 and 3.21 +/- 1.84 microg/g dust in July and August, respectively, and that of Der f 2 was 2.15 +/- 0.82 and 2.04 +/- 1.15 microg/g dust. Four types of Der f 1 and 5 types of Der f 2 cDNA sequences were cloned from collected Der f mites. Their sequences were highly homologous with those previously published in GenBank (No. AB034946.1 and No. AB195580.1). This research demonstrated that Der f allergens exist in the dust of air conditioner filters in this area.

Properties and Alignment of Interstellar Dust Grains toward Type Ia Supernovae with Anomalous Polarization Curves

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

Hoang, Thiem, E-mail: thiemhoang@kasi.re.kr; Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, ON M5S 3H8; Institute of Theoretical Physics, Goethe Universität Frankfurt, D-60438 Frankfurt am Main

Recent photometric and polarimetric observations of Type Ia supernovae (SNe Ia) show unusually low total-to-selective extinction ratios ( R {sub V} < 2) and wavelengths of maximum polarization ( λ{sub max} < 0.4 μ m) for several SNe Ia, which indicates peculiar properties of interstellar (IS) dust in the SN-hosted galaxies and/or the presence of circumstellar (CS) dust. In this paper, we use an inversion technique to infer the best-fit grain size distribution and the alignment function of interstellar grains along the lines of sight toward four SNe Ia with anomalous extinction and polarization data (SN 1986G, SN 2006X, SNmore » 2008fp, and SN 2014J). We find that to reproduce low values of R{sub V}, a significant enhancement in the mass of small grains of radius a < 0.1 μ m is required. For SN 2014J, a simultaneous fit to its observed extinction and polarization is unsuccessful if all the data are attributed to IS dust (model 1), but a good fit is obtained when accounting for the contribution of CS dust (model 2). For SN 2008fp, our best-fit results for model 1 show that in order to reproduce an extreme value of λ{sub max} ∼ 0.15 μ m, small silicate grains must be aligned as efficiently as big grains. For this case, we suggest that strong radiation from the SN can induce efficient alignment of small grains in a nearby intervening molecular cloud via the radiative torque (RAT) mechanism. The resulting time dependence polarization from this RAT alignment model can be tested by observing at ultraviolet wavelengths.« less

Testing the sensitivity of past climates to the indirect effects of dust

NASA Astrophysics Data System (ADS)

Sagoo, Navjit; Storelvmo, Trude

2017-06-01

Mineral dust particles are important ice nuclei (IN) and as such indirectly impact Earth's radiative balance via the properties of cold clouds. Using the Community Earth System Model version 1.0.6, and Community Atmosphere Model version 5.1, and a new empirical parameterization for ice nucleation on dust particles, we investigate the radiative forcing induced by dust IN for different dust loadings. Dust emissions are representative of global conditions for the Last Glacial Maximum and the mid-Pliocene Warm Period. Increased dust leads to smaller and more numerous ice crystals in mixed phase clouds, impacting cloud opacity, lifetime, and precipitation. This increases the shortwave cloud radiative forcing, resulting in significant surface temperature cooling and polar amplification—which is underestimated in existing studies relative to paleoclimate archives. Large hydrological changes occur and are linked to an enhanced dynamical response. We conclude that dust indirect effects could potentially have a significant impact on the model-data mismatch that exists for paleoclimates.