Silicate Dust Emission Research Articles

Multi isotope systematics of precipitation to trace the sources of air pollutants in Seoul, Korea

Multiple sulfur (δ34Ssulfate, Δ33Ssulfate, & Δ36Ssulfate), nitrogen and oxygen (δ15Nnitrate & δ18Onitrate) and strontium (87Sr/86Sr) isotope compositions of precipitation collected from Seoul, South Korea were analyzed to study the sources, transportation and deposition of air pollutants in East Asia. The δ34Ssulfate values (from 1.9 to 14.6‰ with a median of 4.7‰) and the δ15Nnitrate values (from −2.0 to 13.3‰ with a median of 1.0‰) suggest that fossil fuel use (emission from coal combustion and vehicle exhaust) is a predominant source for sulfur and nitrogen, but other natural sources including biogenic contributions of DMS also add to their total budget. The seasonal variations are observed in δ34Ssulfate and δ15Nnitrate values (both higher in winter season), which is likely to result from the increase of coal use for domestic heating in China. The δ18Onitrate values also varied seasonally depending on the NOx oxidation pathway, being about 20‰ higher in winter than in summer season. The Δ33Ssulfate and Δ36Ssulfate values are not anomalous, showing the absence of MIF signals in precipitation of Seoul. The 87Sr/86Sr ratio of the precipitation samples range from 0.70988 to 0.71487 with a median of 0.71073, indicating the influence of at least three end-member (silicate dust, carbonate dust and anthropogenic emission). Ionic ratios such as (K++NH4+)/(Ca2++Mg2+) and Cl−/Na+ suggest the overwhelming effect of anthropogenic input rather than carbonate dust on the end-member with lower 87Sr/86Sr ratios.

SOFIA/FORCAST Observations of R Aqr: Monitoring the Dust Emission

Abstract We present mid-infrared spectra of the symbiotic Mira, R Aqr obtained with the Faint Object infraRed CAmera instrument on the Stratospheric Observatory for Infrared Astronomy in 2016 and 2017. These data, supplemented with Infrared Space Observatory observations from 20 yr earlier, allow us to study the variation of the silicate dust emission over short and long timescales. Radiative transfer models for the dust emission from the circumstellar shell indicate that changes that occur within a pulsation period are driven mainly by the variation properties of the asymptotic giant branch star, and do not require any change in the grain composition. The models show that the longer-term changes are due to variations in the dust density, probably modulated by the orbital separation of the binary companion stars. The models also suggest the presence of micron-size dust grains at all epochs.

Are SiO molecules the seed of silicate dust around evolved stars?

AbstractSilicate is the most popular dust species in the circumstellar envelope of evolved oxygen-rich stars, yet its seed particles have not been well identified. Among the candidates, corundum and SiO attract intense attention and study. SiO was suggested to be the seed particles in early 1980s and has received various supports as well as oppositions. In this work we investigate the relation of SiO maser and silicate dust emission powers. With both our own observation by using the PMO/Delingha 13.7-m telescope and the archival data, a sample is assembled of 21 SiO v=1, J=2-1 sources and 28 SiO v=1, J=1-0 sources that exhibit silicate emission features in the ISO/SWS spectrum. The analysis of their SiO maser and silicate emission power shows a moderate correlation, which agrees with the idea that SiO molecules are the seed nuclei of silicate dust.

Optical Properties of Non-stoichiometric Amorphous Silicates with Application to Circumstellar Dust Extinction

Abstract We determine the optical constants of non-stoichiometric amorphous magnesium-iron silicates and demonstrate that they can well reproduce the observed mid-infrared emission spectra of evolved stars. Stoichiometric and non-stoichiometric amorphous magnesium-iron silicate films are fabricated by pulsed laser deposition. Transmittance and ellipsometry measurements are performed in the wavelength range between 2 and 200 μm and 1.7 and 33 μm, respectively. Optical constants are derived from transmittance and ellipsometric Ψ and Δ spectra by means of oscillator models. These newly obtained optical constants are applied in radiative transfer models for examining reproducibility of the observed spectral features of circumstellar dust shells around supergiants. The spectra of four selected supergiants are dominated by amorphous silicate dust emission in the wavelength range between 9 and . To obtain a good fit to the observed spectra, we take into account amorphous corundum and metallic iron particles as additional dust components to the model calculations to rationalize the dust emission at . For each of the objects, a set of model parameters (dust mass and condensation temperature) is derived by an automated optimization procedure that reproduces the observation well. Consequently, our model spectra using new optical data reveal that the silicate bands at ∼10 and depend on the magnesium and iron ratio in the silicate system, and that a good fit requires a significant iron content of the amorphous silicate dust component to reproduce the observed peak positions and shape of the silicate bands.

On the Relation of Silicates and SiO Maser in Evolved Stars

Abstract The SiO molecule is one of the candidates for the seed of silicate dust in the circumstellar envelope of evolved stars, but this opinion is challenged. In this work we investigate the relation of the SiO maser emission power and the silicate dust emission power. With both our own observation by using the PMO/Delingha 13.7 m telescope and archive data, a sample is assembled of 21 SiO v = 1, J = 2 − 1 sources and 28 SiO v = 1, J = 1 − 0 sources that exhibit silicate emission features in the ISO/SWS spectrum as well. The analysis of their SiO maser and silicate emission power indicates a clear correlation, which is not against the hypothesis that the SiO molecules are the seed nuclei of silicate dust. On the other hand, no correlation is found between SiO maser and silicate crystallinity, which may imply that silicate crystallinity does not correlate with mass-loss rate.

The progenitor mass of the Type IIP supernova SN 2004et from late-time spectral modeling

SN 2004et is one of the nearest and best-observed Type IIP supernovae, with a progenitor detection as well as good photometric and spectroscopic observational coverage well into the nebular phase. Based on nucleosynthesis from stellar evolution/explosion models we apply spectral modeling to analyze its 140-700 day evolution from ultraviolet to mid-infrared. We find a M_ZAMS= 15 Msun progenitor star (with an oxygen mass of 0.8 Msun) to satisfactorily reproduce [O I] 6300, 6364 {\AA} and other emission lines of carbon, sodium, magnesium, and silicon, while 12 Msun and 19 Msun models under- and overproduce most of these lines, respectively. This result is in fair agreement with the mass derived from the progenitor detection, but in disagreement with hydrodynamical modeling of the early-time light curve. From modeling of the mid-infrared iron-group emission lines, we determine the density of the "Ni-bubble" to rho(t) = 7E-14*(t/100d)^-3 g cm^-3, corresponding to a filling factor of f = 0.15 in the metal core region (V = 1800 km/s). We also confirm that silicate dust, CO, and SiO emission are all present in the spectra.

THE NATURE OF LoBAL QSOs. I. SEDs AND MID-INFRARED SPECTRAL PROPERTIES

We have obtained Spitzer IRS spectra and MIPS 24, 70, and 160 micron photometry for a volume-limited sample of 22 SDSS-selected Low-ionization Broad Absorption Line QSOs (LoBALs) at 0.5 < z < 0.6. By comparing their mid-IR spectral properties and far-IR SEDs with those of a control sample of 35 non-LoBALs matched in M_i, we investigate the differences between the two populations in terms of their infrared emission and star formation activity. Twenty five percent of the LoBALs show PAH features and 45% have weak 9.7 micron silicate dust emission. We model the SEDs and decouple the AGN and starburst contributions to the far-infrared luminosity in LoBALs and in non-LoBALs. Their median total, starburst, and AGN infrared luminosities are comparable. Twenty percent (but no more than 60%) of the LoBALs and 26% of the non-LoBALs are ultra-luminous infrared galaxies (ULIRGs; L_IR>10^12*L_sun). We estimate star formation rates (SFRs) corrected for the AGN contribution to the FIR flux and find that LoBALs have comparable levels of star formation activity to non-LoBALs when considering the entire samples. However, the SFRs of the IR-luminous LoBALs are 80% higher than those of their counterparts in the control sample. The median contribution of star formation to the total far-infrared flux in LoBALs and in non-LoBALs is estimated to be 40-50%, in agreement with previous results for PG QSOs. Overall, our results show that there is no strong evidence from the mid- and far-IR properties that LoBALs are drawn from a different parent population than non-LoBALs.

Carbonaceous molecules in the oxygen-rich circumstellar environment of binary post-AGB stars

Context. The circumstellar environment of evolved stars is generally rich in molecular gas and dust. Typically, the entire environment is either oxygen-rich or carbon-rich, depending on the evolution of the central star. Aims. In this paper we discuss three evolved disc sources with evidence of atypical emission lines in their infrared spectra. The stars were taken from a larger sample of post-AGB binaries for which we have Spitzer infrared spectra, characterised by the presence of a stable oxygen-rich circumbinary disc. Our previous studies have shown that the infrared spectra of post-AGB disc sources are dominated by silicate dust emission, often with an extremely high crystallinity fraction. However, the three sources described here are selected because they show a peculiar molecular chemistry. Methods. Using Spitzer infrared spectroscopy, we study in detail the peculiar mineralogy of the three sample stars. Using the observed emission features, we identify the different observed dust, molecular and gas species. Results. The infrared spectra show emission features due to various oxygen-rich dust components, as well as CO2 gas. All three sources show the strong infrared bands generally ascribed to polycyclic aromatic hydrocarbons. Furthermore, two sample sources show C60 fullerene bands. Conclusions. Even though the majority of post-AGB disc sources are dominated by silicate dust in their circumstellar environment, we do find evidence that, for some sources at least, additional processing must occur to explain the presence of large carbonaceous molecules. There is evidence that some of these sources are still oxygen-rich, which makes the detection of these molecules even more surprising.

Extended Silicate Dust Emission in Palomar‐Green QSOs

This paper addresses the origin of the silicate emission observed in PG QSOs, based on observations with the Spitzer Space Telescope. Scenarios based on the unified model suggest that silicate emission in AGNs arises mainly from the illuminated faces of the clouds in the torus at temperatures near sublimation. However, detections of silicate emission in type 2 QSOs, and the estimated cool dust temperatures, argue for a more extended emission region. To investigate this issue we present the mid-infrared spectra of 23 QSOs. These spectra, and especially the silicate emission features at ~10 and ~18 μm, can be fitted using dusty narrow-line region (NLR) models and a combination of blackbodies. The bolometric luminosities of the QSOs allow us to derive the radial distances and covering factors for the silicate-emitting dust. The inferred radii are 100-200 times larger than the dust sublimation radius, much larger than the expected dimensions of the inner torus. Our QSO mid-IR spectra are consistent with the bulk of the silicate dust emission arising from the dust in the innermost parts of the NLR.

A warped m= 2 water maser disc in V778 Cyg?

The silicate carbon star V778 Cyg is a source of 22 GHz water maser emission which was recently resolved by MERLIN. Observations revealed an elongated S-like structure along which the velocities of the maser features show a linear dependence on the impact parameter. This is consistent with a doubly-warped m=2 disc observed edge-on. Water masers and silicate dust emission (detected by IRAS and ISO) have a common origin in O-rich material and are likely to be co-located in the disc. We propose a detailed self-consistent model of a masing gas-dust disc around a companion to the carbon star in a binary system, which allows us to estimate the companion mass of 1.7 +- 0.1 M_sun, the disc radius of 40 +-3 AU and the distance between companions of about 80 AU. Using a dust-gas coupling model for water masing, we calculate the maser power self-consistently, accounting for both the gas and the dust energy balances. Comparing the simulation results with the observational data, we deduce the main physical parameters of the masing disc, such as the gas and dust temperatures and their densities. We also present an analysis of the stability of the disc.

Dust emission in early-type galaxies: The mid-infrared view

We present mid-infrared (MIR) maps for a sample of 18 early-type galaxies observed at 4.5, 6.7 and 15 µm with the ISOCAM instrument on board the ISO satellite with a 6 �� spatial resolution. We model the Spectral Energy Distribution (SED) of these galaxies using the stellar evolutionary synthesis model P ´ EGASE and we derive the MIR excess over the stellar component. We then explore the nature of this excess in terms of dust and Polycyclic Aromatic Hydrocarbon molecules (PAHs). We find that out of 18 galaxies, 10 show excess at 6.7 µm (due to the presence of PAH features) and 14 show excess at 15 µm (due to the presence of warm dust). In two galaxies, where a more complete wavelength coverage exists, an excess around 9.7 µm is seen (presumably due to silicate dust emission), while two other galaxies are totally devoid of dust. We also examine the morphology of the galaxies in these wavelengths by plotting the azimuthally averaged radial profiles as well as the MIR color profiles. We find that for the majority of the galaxies the 4.5 µm emission is well described by a de Vaucouleurs profile. The 6.7 µm and 15 µm emission is smoothly distributed throughout the galaxy while only a few galaxies show MIR emission which is more concentrated close to the center. Two dwarf galaxies in our sample show patchy distributions of the MIR emission while two other galaxies show edge-on disks. With color-color diagrams we delineate the regions occupied by late-type and early-type galaxies. Finally we show that the MIR excess found in strong radio galaxies like NGC 4486 (M87) can be explained by synchrotron emission.

Spatially Resolved STIS Spectroscopy of Betelgeuse's Outer Atmosphere

We present spatially resolved spectra observed with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope of the upper chromosphere and dust envelope of Betelgeuse (α Orionis, M2 Iab). In the fall of 2002 a set of five high-resolution near-UV spectra was obtained by scanning at intensity peak-up position and four off-limb target positions up to one arcsecond, using a small aperture (200 by 63 mas), to investigate the thermal conditions and flow dynamics in the outer atmosphere of this important nearby cool supergiant star.Based on Mg ii h &amp; k, Fe ii λ2716, C ii λ2327, and Al ii] λ2669 emission lines we provide the first evidence for the presence of warm chromospheric plasma at least 1 arcsecond away from the star at ∼40 R* (1 R*≃700 R⊙). The STIS spectra reveal that Betelgeuse's upper chromosphere extends far beyond the circumstellar Hα envelope of ∼5 R*, determined from previous ground-based imaging (Hebden et al. 1987).The flux in the broad and self-absorbed resonance lines of Mg ii decreases by a factor of ∼700 compared to the flux at chromospheric disk center. We observe strong asymmetry changes in the Mg ii h and Si i resonance line profiles when scanning off-limb, signaling the outward acceleration of gas outflow in the upper chromosphere.From the radial intensity distributions of Fe i and Fe ii emission lines we determine the radial non-LTE iron ionization balance. We compute that the local kinetic gas temperatures of the warm chromospheric gas component in the outer atmosphere exceed 2600 K, when assuming local gas densities of the cool gas component we determine from radiative transfer models that fit the 9.7 μm silicate dust emission feature. The spatially resolved STIS spectra directly demonstrate that warm chromospheric plasma co-exisists with cool gas in Betelgeuse's circumstellar dust envelope.

Classification of 2.4–45.2 Micron Spectra from the Infrared Space Observatory Short Wavelength Spectrometer

The Infrared Space Observatory observed over 900 objects with the Short Wavelength Spectrometer in full-grating scan mode (2.4-45.2 μm). We have developed a comprehensive system of spectral classification using these data. Sources are assigned to groups based on the overall shape of the spectral energy distribution (SED). The groups include naked stars, dusty stars, warm dust shells, cool dust shells, very red sources, and sources with emission lines but no detected continuum. These groups are further divided into subgroups based on spectral features that shape the SED such as silicate or carbon-rich dust emission, silicate absorption, ice absorption, and fine-structure or recombination lines. Caveats regarding the data and data reduction, as well as biases intrinsic to the database, are discussed. We also examine how the subgroups relate to the evolution of sources to and from the main sequence and how this classification scheme relates to previous systems.

Hydrodynamic Simulations of Proplyd Bow Shocks

We present two-dimensional hydrodynamic simulations of the interaction between an ionized photoevaporation flow from a proplyd and a stellar wind from a hot star. We consider both the case of a fully supersonic wind and the case of a wind that passes through a global shock to become subsonic before reaching the proplyd. We compare the results of our simulations with the observed properties of the standoff bow shocks in the Orion proplyds, finding good agreement with the supersonic case for the closer-in proplyds. This allows the momentum flux, V, of the stellar wind of θ1 Ori C to be constrained. More distant proplyds do not fit this model but may be explained by the subsonic case, offering the prospect of using the proplyds to probe the position of the inner shock in the wind from θ1 Ori C. Comparison of predicted silicate dust emission with published mid-infrared imaging provides evidence that submicron-sized grains are underabundant in the proplyd flows by an order of magnitude.

Modelling near-IR spectra and mid-IR dust emission of Mira variables at different phases

We model the spectral changes of late oxygen-rich Miras observed in different pulsation phases. From a combination of variable near-IR spectra and UKIRT spectro-photometry of the 9.7-μm silicate dust emission feature in different phases we study the influence of the changing atmospheric circumstances on the conditions in the circumstellar dust shell. From a detailed modelling of TiO and VO bands in the near-IR spectra, we determine changes of the effective temperature and the effective atmospheric acceleration of the central star. The corresponding model spectral energy distribution is redistributed through the dust shell by means of radiative transfer calculations in order to perform a detailed modelling of shape changes observed in the silicate feature. We show that the latter are mainly caused by changes in the flux distribution of the incident radiation field with stellar pulsation, whereas intensity changes of the dust emission result from stellar luminosity changes as they are enshrouded by very optically thin dust shells. In the case of the Mira o Cet we compute that the effective temperature increases from Teff=2400 K in the minimum phase to 3000 K (±100 K) around the maximum phase. The amplified momentum transfer around maximum light enhances the acceleration of the dust outflow near the dust condensation radius of ∼6 R∗. This produces variations of the terminal dust outflow velocity with phase (Δv∞≃5 km s−1) at larger distance from the star. The corresponding small changes in flux mean opacity and gas mass-loss rates (from 2.8 to 3.2×10−7 M⊙ yr−1) are sufficient to model the shape changes observed in the dust emission feature. A comparison with the modelling results for another long period Mira, U Ori, is also provided.

ISOPHOT Observations of Dust Disks around Main Sequence (Vega-Like) Stars

The photometer (ISOPHOT) on the Infrared Space Observatory (ISO) has proved to be invaluable for investigating the dust around main sequence stars (both prototypes and candidate Vega-like stars). The long wavelength camera (at 60 and 90 μm) has been used to map the area around the stars to establish whether the dust disk is extended. Low-resolution spectra between 5.8 and 11.6 μm show whether the dust is composed of silicate grains, and whether molecular features are present. The four prototype Vega-like stars (Vega, β Pic, Fomalhaut, ϵ Eri) are studied, as well as eight other stars, which are main sequence stars with cool dust associated with them. We find that the spectra of β Pic, 49 Cet, HD98800, and HD135344 show excess emission from the cool dust around the star, HD144432 and HD139614 show silicate dust emission, HD169142 and HD34700 show emission features from carbon-rich molecules (possibly PAHs, polycyclic aromatic hydrocarbon molecules), and HD142666 shows emission features from both carbon-rich molecules and silicate dust. Up to 11.6 μm, the emission from Vega, Fomalhaut, and ϵ Eri is dominated by the stellar photosphere. At 60 and 90 μm, the extended dust emission is mapped, and the disk resolved in eight cases. The dust mass in the disks is found to range from around 10 −9 to 10 −4 M ⊙. Since several of the stars are younger than the Sun, and the disks have sufficient material of the type found in the Solar System, these disks could be in the early stages of planet formation.

Do S stars show strong silicate dust emission?

S stars are generally regarded as intermediate between M and carbon stars in their properties, including the composition of their circumstellar material, as befits stars having an intermediate level of C/O enhancement. The existence of several stars with optical S classification but very strong silicate dust emission at 10 μ m presents an anomaly. One suggestion was that these stars are intermediate between M stars and the 13C-rich carbon stars with silicate dust emission from circumstellar material. However, new optical spectra show that these stars are either M stars or marginal MS stars, so that silicate dust emission declines along the M MS S sequence and is not present in C stars, with the exception of a few J-type silicate-carbon stars.

10 micron spectroscopy of younger stars in the rho Ophiuchi cloud

view Abstract Citations (63) References (41) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS 10 Micron Spectroscopy of Young Stars in the rho Ophiuchi Cloud Hanner, M. S. ; Brooke, T. Y. ; Tokunaga, A. T. Abstract Spectra in the 10 micrometer region were obtained of 14 young stars associated with the central core of the rho Oph dark cloud complex. Silicate dust emission and absorption features can be fairly well reproduced with simple models using the emissivity of the silicates in the Orion Trapezium region, believed to be typical of molecular cloud dust. A spectrum of the Trapezium star theta1 Ori D was obtained to define the emissivity more precisely. The emissivity of silicate dust around the late-type giant Mu Cep does not improve the fits to the absorption features and provides a poorer match to the emission features. None of the sources display a strong 11.2 micrometer peak like that seen in comet Halley and attributed to crystalline olivine. A broad weak feature near 11.2 micrometer, possibly related to the comet feature, may be present in the emission spectrum of the Herbig Ae star HD 150193. Absorption features toward two of the objects are narrower than would be expected from Trapezium-like silicates, suggesting differences in the composition of the silicates. The relation between the silicate extinction band depth and H2O ice band depths is determined for the deeply embedded objects. One late-type object, Elias 14, clearly shows the 11.25 micrometer aromatic hydrocarbon emission feature, possibly excited by the nearby B star, HD 147889, though the latter does not exhibit the feature. Publication: The Astrophysical Journal Pub Date: January 1995 DOI: 10.1086/175069 Bibcode: 1995ApJ...438..250H Keywords: Absorption Spectra; Emission Spectra; Infrared Astronomy; Infrared Spectra; Ophiuchi Clouds; Pre-Main Sequence Stars; Astronomical Spectroscopy; Silicates; Stellar Envelopes; Astronomy; INFRARED: STARS; ISM: INDIVIDUAL NAME: RHO OPHIUCHI; STARS: CIRCUMSTELLAR MATTER; STARS: PRE--MAIN-SEQUENCE full text sources ADS | data products SIMBAD (17)