Dust Arcs Research Articles

Erratum: Infrared dust arcs around the stars: I. effect of the radiation pressure

Erratum: Infrared dust arcs around the stars: I. effect of the radiation pressure

Infrared dust arcs around stars – I. Effect of the radiation pressure

In this paper we consider the distribution of the interstellar dust in the vicinity of the star under an influence of the stellar gravitation and radiation pressure. This study is applicable to the stars with relatively weak stellar wind and strong radiation, when the stellar radiation swept out the interstellar dust much further from the star than the position of the bow shock created by an interaction of the stellar and interstellar plasma flows. In this case the number density of dust for a certain dust grains radius can be calculated analytically based on the classical `cold model'. The dust density distribution for the mixture of dust grains with different radii is calculated. We also calculated intensity maps of the thermal infrared emission at 24~$\mu$m from dust due to heating by the stellar radiation. It is shown that the obtained maps of the infrared emission extremely depends on the model parameters: material of dust grains, dust size distribution assumed in the interstellar medium, the approach used to calculate the dust temperature. The bright distinct arc at the intensity maps is seen for graphite dust grains and almost disappears for silicates. Absolute values of intensity in the case of graphite are several order of magnitudes larger than for silicates due to more intensive heating of graphite. Possible application of the presented theory is proposed as an algorithm for analysis of the observational images of the infrared arc around the star.

Comparison of the orbital properties of Jupiter Trojan asteroids and Trojan dust

In a previous paper we simulated the orbital evolution of dust particles from the Jupiter Trojan asteroids ejected by the impacts of interplanetary particles, and evaluated their overall configuration in the form of dust arcs. Here we compare the orbital properties of these Trojan dust particles and the Trojan asteroids. Both Trojan asteroids and most of the dust particles are trapped in the Jupiter 1:1 resonance. However, for dust particles, this resonance is modified because of the presence of solar radiation pressure, which reduces the peak value of the semi-major axis distribution. We find also that some particles can be trapped in the Saturn 1:1 resonance and higher order resonances with Jupiter. The distributions of the eccentricity, the longitude of pericenter, and the inclination for Trojans and the dust are compared. For the Trojan asteroids, the peak in the longitude of pericenter distribution is about 60 degrees larger than the longitude of pericenter of Jupiter; in contrast, for Trojan dust this difference is smaller than 60 degrees, and it decreases with decreasing grain size. For the Trojan asteroids and most of the Trojan dust, the Tisserand parameter is distributed in the range of two to three.

Dust arcs in the region of Jupiter’s Trojan asteroids

Aims. The surfaces of the Trojan asteroids are steadily bombarded by interplanetary micrometeoroids, which releases ejecta of small dust particles. These particles form the faint dust arcs that are associated with asteroid clouds. Here we analyze the particle dynamics and structure of the arc in the region of the L4 Trojan asteroids. Methods. We calculate the total cross section of the L4 Trojan asteroids and the production rate of dust particles. The motion of the particles is perturbed by a variety of forces. We simulate the dynamical evolution of the dust particles, and explore the overall features of the Trojan dust arc. Results. The simulations show that the arc is mainly composed of grains in the size range 4−10 microns. Compared to the L4 Trojan asteroids, the dust arc is distributed more widely in the azimuthal direction, extending to a range of [30, 120] degrees relative to Jupiter. The peak number density does not develop at L4. There exist two peaks that are azimuthally displaced from L4.

The JCMT Gould Belt Survey: evidence for radiative heating and contamination in the W40 complex

We present SCUBA-2 450{\mu}m and 850{\mu}m observations of the W40 complex in the Serpens-Aquila region as part of the James Clerk Maxwell Telescope (JCMT) Gould Belt Survey (GBS) of nearby star-forming regions. We investigate radiative heating by constructing temperature maps from the ratio of SCUBA-2 fluxes using a fixed dust opacity spectral index, {\beta} = 1.8, and a beam convolution kernel to achieve a common 14.8" resolution. We identify 82 clumps ranging between 10 and 36K with a mean temperature of 20{\pm}3K. Clump temperature is strongly correlated with proximity to the external OB association and there is no evidence that the embedded protostars significantly heat the dust. We identify 31 clumps that have cores with densities greater than 105cm{^{-3}}. Thirteen of these cores contain embedded Class 0/I protostars. Many cores are associated with bright-rimmed clouds seen in Herschel 70 {\mu}m images. From JCMT HARP observations of the 12CO 3-2 line, we find contamination of the 850{\mu}m band of up to 20 per cent. We investigate the free-free contribution to SCUBA-2 bands from large-scale and ultracompact H ii regions using archival VLA data and find the contribution is limited to individual stars, accounting for 9 per cent of flux per beam at 450 {\mu}m or 12 per cent at 850 {\mu}m in these cases. We conclude that radiative heating has potentially influenced the formation of stars in the Dust Arc sub-region, favouring Jeans stable clouds in the warm east and fragmentation in the cool west.

Hubbleimaging of V1331 Cygni: proper motion study of its circumstellar structures

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) the 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 radial grain size distribution was modified by a previous FUOR wind. 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 first 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. The derived radial colour profiles do not indicate a spatial separation of the dust grain sizes. The HERSCHEL 160 micron images show for the 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. 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 changes of the scattering angle, imposed by a tilt or helical geometry of the dust configuration.

Dense molecular globulettes and the dust arc toward the runaway O star AE Aurigae (HD 34078)

Some runaway stars are known to display IR arc-like structures around them, resulting from their interaction with surrounding interstellar material. The properties of these features as well as the processes involved in their formation are still poorly understood. We aim at understanding the physical mechanisms that shapes the dust arc observed near the runaway O star AEAur (HD34078). We obtained and analyzed a high spatial resolution map of the CO(1-0) emission that is centered on HD34078, and that combines data from both the IRAM interferometer and 30m single-dish antenna. The line of sight towards HD34078 intersects the outer part of one of the detected globulettes, which accounts for both the properties of diffuse UV light observed in the field and the numerous molecular absorption lines detected in HD34078's spectra, including those from highly excited H2 . Their modeled distance from the star is compatible with the fact that they lie on the 3D paraboloid which fits the arc detected in the 24 {\mu}m Spitzer image. Four other compact CO globulettes are detected in the mapped area. These globulettes have a high density and linewidth, and are strongly pressure-confined or transient. The good spatial correlation between the CO globulettes and the IR arc suggests that they result from the interaction of the radiation and wind emitted by HD 34078 with the ambient gas. However, the details of this interaction remain unclear. A wind mass loss rate significantly larger than the value inferred from UV lines is favored by the large IR arc size, but does not easily explain the low velocity of the CO globulettes. The effect of radiation pressure on dust grains also meets several issues in explaining the observations. Further observational and theoretical work is needed to fully elucidate the processes shaping the gas and dust in bow shocks around runaway O stars. (Abridged)

Dust-driven Winds Beyond Spherical Symmetry

AbstractNew 2D dynamical models for the winds of AGB stars are presented which include hydrodynamics with radiation pressure on dust, equilibrium chemistry, time-dependent dust formation theory, and coupled frequency-dependent Monte Carlo radiative transfer. The simulations reveal a much more complicated picture of the dust formation and wind acceleration as compared to 1D spherical wind models. Triggered by non-spherical pulsations or large-scale convective motions, dust forms event-like in the cooler regions above the stellar surface which are temporarily less illuminated, followed by the radial ejection of dust arcs and clumps. These simulations can possibly explain recent high angular resolution interferometric IR observations of red giants, which show an often non-symmetric and highly time-variable innermost dust formation and wind acceleration zone. The dependence of the mass-loss rates on stellar parameters is less threshold-like as used from 1D models, and therefore, it seems quite possible that the phenomenon of dust-driven winds may occur also in less evolved red giants.

Monte Carlo Radiative Transfer in Multi-D Dynamical Models of Dust-Driven Winds

New 2D dynamical models for carbon-rich and oxygen-rich AGB stars, and red supergiants are presented which include hydrodynamics with gravity and radiation pressure on dust, equilibrium chemistry, time-dependent dust formation, and coupled frequency-dependent Monte Carlo radiative transfer. The simulations reveal a much more complicated picture of the dust formation and wind acceleration of red giants as compared to 1D spherical models. Triggered by non-spherical pulsations or large-scale convective motions, dust forms event-like in the cooler regions above the stellar surface which temporarily receive less radiation from the star, followed by the radial ejection of dust arcs and clumps. These simulations can possible explain recent high angular resolution interferometric IR observations of red giants, which show an often non-symmetric and highly time-variable innermost dust formation and wind acceleration zone. The new wind models are intended to harvest the results of future interferometric mission like Chara, AMBER on the Vlti, and Alma, aiming to provide the physical answers of the scientific questions arising from these new instruments.

Molecular Shells in IRC+10216: Evidence for Nonisotropic and Episodic Mass‐Loss Enhancement

We report high angular resolution VLA observations of cyanopolyyne molecules HC3N and HC5N from the carbon rich circumstellar envelope of IRC+10216. The observed low-lying rotational transitions trace a much more extended emitting region than seen in previous observations at higher frequency transitions. We resolve the hollow quasi-spherical distribution of the molecular emissions into a number of clumpy shells. These molecular shells coincide spatially with dust arcs seen in deep optical images of the IRC+10216 envelope, allowing us to study for the first time the kinematics of these features. We find that the molecular and dust shells represent the same density enhancements in the envelope separated in time by ~120 to ~360 yr. From the angular size and velocity spread of the shells, we estimate that each shell typically covers about 10% of the stellar surface at the time of ejection. The distribution of the shells seems to be random in space. The good spatial correspondence between HC3N and HC5N emissions is in qualitative agreement with a recent chemical model that takes into account the presence of density-enhanced shells. The broad spatial distribution of the cyanopolyyne molecules, however, would necessitate further study on their formation.

Ionized and neutral gas in the peculiar star/cluster complex in NGC 6946

The characteristics of ionized and H I gas in the peculiar star/cluster complex in NGC 6946, obtained with the 6-m telescope (BTA) Special Astrophysical Observatory Russian Academy of Sciences (RAS), the Gemini North telescope, and the Westerbork Synthesis Radio Telescope, are presented. The complex is unusual as hosting a super star cluster, the most massive known in an apparently non-interacting giant galaxy. It contains a number of smaller clusters and is bordered by a sharp C-shaped rim. We found that the complex is additionally unusual in having peculiar gas kinematics. The velocity field of the ionized gas reveals a deep oval minimum, similar to 300 pc in size, centred 7 arcsec east of the supercluster. The V-r of the ionized gas in the dip centre is 100 km s(-1) lower than in its surroundings, and emission lines within the dip appear to be shock-excited. This dip is near the centre of an H I hole and a semi-ring of H II regions. The H I (and less certainly, H II) velocity fields reveal expansion, with the velocity reaching similar to 30 km s(-1) at a distance about 300 pc from the centre of expansion, which is near the deep minimum position. The superstar cluster is at the western rim of the minimum. The sharp western rim of the whole complex is plausibly a manifestation of a regular dust arc along the complex edge. Different hypotheses about the complex and the V-r depression's origins are discussed, including a high-velocity H I cloud/dark minihalo impact, a blue compact dwarf galaxy merging, and a gas outflow due to release of energy from the supercluster stars.

2D models for dust-driven AGB star winds

New axisymmetric (2D) models for dust-driven winds of C-stars are presented which include hydrodynamics with radiation pressure on dust, equilibrium chemistry and time-dependent dust formation with coupled grey Monte Carlo radiative transfer. Considering the simplest case without stellar pulsation (hydrostatic inner boundary condition) these models reveal a more complex picture of the dust formation and wind acceleration than earlier published spherically symmetric (1D) models. The so-called exterior κ-mechanism causes radial oscillations with short phases of active dust formation between longer phases without appreciable dust formation, just like in the 1D models. However, in 2D geometry, the oscillations can be out-of-phase at different places above the stellar atmosphere which results in the formation of dust arcs or smaller caps that only occupy a certain fraction of the total solid angle. These dust structures are accelerated outward by radiation pressure, expanding radially and tangentially like mushroom clouds, while dust-poor matter is falling back towards the star at other places. A highly dynamical and turbulent dust formation zone is created in this way, which again leads to inhomogeneous dust production. Further away from the star, flow instabilities (e.g. Rayleigh-Taylor) have time to fragment the outward moving arcs and shells to produce numerous small-scale cloud-like sub-structures.

Thermal Dust Emission from Proplyds, Unresolved Disks, and Shocks in the Orion Nebula

We present a new 11.7 micron mosaic image of the Orion nebula obtained with T-ReCS on Gemini South. The map includes the BN/KL region, the Trapezium, and OMC-1 South. Excluding BN/KL, we detect 91 point sources, with 27 known proplyds and over 30 ``naked'' stars showing no extended structure in HST images. Within the region we surveyed, 80 percent of known proplyds show detectable emission, almost 40 percent of naked stars are detected at 11.7 micron, and the fraction of all visible sources with IR excess emission is roughly 50 percent. Thermal dust emission from stars with no extended structure in HST images means that they have dust disks comparable to the size of our solar system. Proplyds and stars with IR excess show a clear anti-correlation in their spatial distribution, with proplyds clustered close to theta1C, and other infrared sources found farther away. We suspect that the clustered proplyds trace the youngest 0.5 Myr age group associated with the Trapezium, while the more uniformly-distributed sources trace the older 1-2 Myr population of the ONC. This suggests that small disks persist for a few Myr in irradiated environments, and hints that hierarchical sub-clustering has been important. Within 30 arcsec of theta1C, all proplyds are detected at 11.7 micron. The star theta1D is associated with the most prominent mid-IR dust arc in the nebula. We propose that this arc is the consequence of theta1D being the closest member of the Trapezium to the background cloud. Finally, we detect dust emission from HH jets in Orion, including HH202, HH529, HH513, and HH514. This is the first detection of mid-IR continuum emission from dust in the body of a collimated HH jet or bow shock.

Mid‐Infrared Imaging of NGC 6334 I

We present high-resolution (<05) mid-infrared Keck II images of individual sources in the central region of NGC 6334 I. We compare these images to images at a variety of other wavelengths from the near-infrared to centimeter radio continuum and speculate on the nature of the NGC 6334 I sources. We assert that the cometary shape of the ultracompact H II (UCHII) region here, NGC 6334F, is due to a champagne-like flow from a source on the edge of a molecular clump and not due to a bow shock caused by the supersonic motion of the UCHII region through the interstellar medium. The mid-infrared emission is concentrated into an arc of dust that defines the boundary between the UCHII region and the molecular clump. This dust arc contains a majority of the masers in the region. We discuss the nature of the four near-infrared sources associated with IRS I1 and suggest that one of the sources, IRS 1E, is responsible for the heating and ionizing of the UCHII region and the mid-infrared dust arc. Infrared source IRS I2, which has been thought to be a circumstellar disk associated with a linear distribution of methanol masers, is found not to be directly coincident with the masers and elongated at a much different position angle. IRS I3 is found to be a extended source of mid-infrared emission coming from a cluster of young dusty sources seen in the near-infrared.

Gas dynamics in the barred Seyfert galaxy NGC 4151 -- II. High-resolution HI study

We present sensitive, high angular resolution (6 ′′ × 5 ′′ ) λ21-cm observations of the neutral hydrogen in the nearby barred Seyfert galaxy, NGC4151. These HI observations, obtained using the VLA in B-configuration, are the highest resolution to date of this galaxy, and reveal hitherto unprecedented detail in the distribution and kinematics of the HI on sub-kiloparsec scales. A complete analysis and discussion of the HI data are presented and the global properties of the galaxy are related to the bar dynamics presented in Paper I. HI absorption, consistent with previous studies, is detected against the radio continuum nucleus and shows two components – a deep absorption component, centred at 987 ± 1 km s −1 and width 87 ± 3 km s −1 , and a weaker component, redshifted to 1096 ± 6 km s −1 with a width of 35 ± 15 km s −1 . An alternative fit is also presented. In addition to the absorption, a high velocity cloud is detected in emission, coincident with the nucleus. This cloud is red-shifted by 260 km s −1 from systemic, has an HI mass of 2.3 × 10 7 M⊙, and corresponds to outflow on the far side of the nucleus. Contrary to previous studies, no HI bridge is detected reaching from the shocks directly across the nucleus. Instead, the gas streams from the shocks onto smaller orbits and forms fingers of HI which wind around the nucleus, consistent with predictions from general numerical simulations of bars. These fingers correspond closely with dust arcs seen in optical studies and resemble nuclear features seen by others in weak barred galaxies such as M100. A new rotation curve is presented, extending to within 8 ′′ of the nucleus and showing a turnover at a radius of �35 ′′ , which was previously undetected in lower resolution studies. The corresponding resonance curve and the properties of the shocks (Paper I) yield a bar pattern speed of 24.5 ± 3.7 km s −1 and one Inner Lindblad Resonance (ILR) at a radius of 2.8 ±0.6 kpc. Our observations, however, do not rule out the possibility of an Inner ILR.

North Polar Dust Storms in Early Spring on Mars

Observations of Mars during 1996–1997 by the Hubble Space Telescope covered the entire spring season in the northern hemisphere of Mars, which was favorably positioned for viewing the north polar region. This paper reports observations of dust activity during this period. Local dust activity occurred near the edge of the subliming north polar cap during early spring; this included local dust clouds, similar to those seen by Viking near the edge of the south polar cap, and unusual, arc-shaped dust features that seem to represent a new type of dust phenomenon. These dust arcs may explain the Rima Tenuis rift, which has been occasionally seen by groundbased observers of Mars. Analysis of numerical simulations from a Mars general circulation model for the early northern spring season have provided insights into the plausible meteorological background at high latitudes in the vicinity of the retreating north polar cap. These Hubble observations extend the geographic and seasonal ranges during which local dust activity seems to be common on Mars. The combination of image analysis and model calculations support the hypothesis that these dust storms are the result of winds associated with fronts moving across the seasonal cap that lift dust exposed on the cap during CO2sublimation.

Inner coma imaging of Comet Levy (1990c) with the Hubble space telescope

Comet Levy (1990c) was observed with the Hubble Space Telescope (HST) on UT 27 September 1990 when both the heliocentric and geocentric distances were ∼1 AU. Two sets of images of the comet were taken 6.5 hr apart with the Wide-Field Camera (WFC) through a broadband red filter that was selected to isolate continuum emission peaking sharply at the nucleus. A single WFC pixel projected to a distance of ∼78 km at the comet, and deconvolution techniques were used to recover virtually the full spatial resolution capability of the HST. The images show a highly asymmetrical coma in which the sunward- facing hemisphere is more than a factor of 2 brighter than the tailward hemisphere, consistent with volatile sublimation occurring primarily on the dayside of the nucleus. The azimuthal dependence of the spatial brightness distribution on the sunward side is roughly Gaussian with FWHM ∼ 135° and an axis of symmetry that is nearly coincident with the projected Sun-comet line. While the azimuthal profile is clearly not consistent with isotropic emission of dust into the sunward hemisphere, the profile width is significantly larger than the widths of dust jets observed by the Halley Multicolor Camera on the Giotto spacecraft (H.J. Reitsema et al. 1989, Icarus 81, 31–40). Radial brightness profiles perpendicular to the Sun-comet line are very symmetric about the nucleus and follow approximately a ϱ −1 law (where ϱ is the projected distance to the nucleus). For the time-averaged radial brightness profile, the relative I-band luminosity increases linearly with aperture size over the entire range 0″.1 ≤ ϱ ≤ 10″. However, the coma of Comet Levy is definitely not in steady state. Detailed analysis of the images appears to show a hemispherical arc of dust propagating through the coma with an average projected velocity of ∼0.16 km sec −1. Periodic occurrences of similar dust arcs could be responsible for the temporal variability in the continuum photometry observed from the International Ultraviolet Explorer (P.D. Feldman et al. Icarus 95, 65–72.) and from the ground (D.G. Schleicher et al. 1991, Icarus 94, 511–523).

An Observational Search for the Schuerman Dust Arcs

AbstractLarge-scale interplanetary dust arcs were predicted by Schuerman (1980) to be associated with the planets. An arc, if one exists, would produce asymmetries on opposite sides of the Gegenschein during the Earth’s two passages through the arc each year. A brief description is given of Gegenschein/arc observing constraints, of future viewing opportunities, and of the results of a test program conducted from Mt. Haleakala, Hawaii, in Jan/Feb 1984 when the Earth encountered the arc associated with Saturn.