The Detection of Cold Dust in Cas A: Evidence for the Formation of Metallic Needles in the Ejecta

Recently, Dunne et al. (2003) obtained 450 and 850 micron SCUBA images of CasA, and reported the detection of 2-4 M_sun of cold, 18K, dust in the remnant. Here we show that their interpretation of the observations faces serious difficulties. Their inferred dust mass is larger than the mass of refractory material in the ejecta of a 10 to 30 M_sun star. The cold dust model faces even more difficulties if the 170 micron observations of the remnant are included in the analysis, decreasing the cold dust temperature to ~ 8K, and increasing its mass to > 20 M_sun. We offer here a more plausible interpretation of their observation, in which the cold dust emission is generated by conducting needles with properties that are completely determined by the combined submillimeter and X-ray observations of the remnant. The needles consist of metallic whiskers with <1% of embedded impurities that may have condensed out of blobs of material that were expelled at high velocities from the inner metal-rich layers of the star in an asymmetric explosion. The needles are collisionally heated by the shocked gas to a temperature of 8K. Taking the destruction of needles into account, a dust mass of only 1E-4 to 1E-3M_sun is needed to account for the observed SCUBA emission. Aligned in the magnetic field, needles may give rise to observable polarized emission. The detection of submillimeter polarization will therefore offer definitive proof for a needle origin for the cold dust emission. Supernovae may still be proven to be important sources of interstellar dust, but the evidence is still inconclusive.Comment: 18 pages including 4 figures. Accepted for publication in the ApJ. Missing reference adde

Novel room temperature ionic liquids of hexaalkyl substituted guanidinium salts for dye-sensitized solar cells

A novel family of room temperature ionic liquids, N,N-diethyl-N′,N′-dipropyl-N′′-hexyl-N′′-methylguanidinium iodide (SGI) and N,N,N′,N′-tetramethyl-N′′,N′′-dipentylguanidinium tricyanomethanide (SGTM) were designed and synthesized. Due to the strong charge delocalization on the tricyanomethanide anion and, thus, weaker ion-pairing, SGTM has a lower viscosity than SGI salt that has iodide as an anion. SGI was successfully used as an iodide resource for dye-sensitized nanocrystalline solar cells. The device with a solvent-free, SGI-based electrolyte achieved a 5.9% power conversion efficiency under an air mass 1.5 incident light of 9.47mW/cm

Episodic and long-lasting Paleozoic felsic magmatism in the pre-Alpine basement of the Suretta nappe (eastern Swiss Alps)

The Suretta nappe of eastern Switzerland contains a series of meta-igneous rocks, with the Rofna Porphyry Complex (RPC) being the most prominent member. We present LA-ICP-MS U-Pb zircon data from 12 samples representing a broad spectrum of meta-igneous rocks within the Suretta nappe, in order to unravel the pre-Alpine magmatic history of this basement unit. Fine-grained porphyries and coarse-grained augengneisses from the RPC give crystallization ages between 284 and 271Ma, which either represent distinct magma pulses or long-lasting magmatic activity in a complex magma chamber. There is also evidence for an earlier Variscan magmatic event at ~320-310Ma. Mylonites at the base of the Suretta nappe are probably derived from either the RPC augengneisses or another unknown Carboniferous-Permian magmatic protolith with a crystallization age between 320 and 290Ma. Two polymetamorphic orthogneisses from the southern Suretta nappe yield crystallization ages of ~490Ma. Inherited zircon cores are mainly of late Neoproterozoic age, with minor Neo- to Paleoproterozoic sources. We interpret the Suretta nappe as mainly representing a Gondwana-derived crustal unit, which was subsequently intruded by minor Cambrian-Ordovician and major Carboniferous-Permian magmatic rocks. Finally, the Suretta nappe was thrust into its present position during the Alpine orogeny, which hardly affected the U-Pb system in zirco

Decomposing Dusty Galaxies. I. Multi-Component Spectral Energy Distribution Fitting

We present a new multi-component spectral energy distribution (SED) decomposition method and use it to analyze the ultraviolet to millimeter wavelength SEDs of a sample of dusty infrared-luminous galaxies. SEDs are constructed from spectroscopic and photometric data obtained with the Spitzer Space Telescope, in conjunction with photometry from the literature. Each SED is decomposed into emission from populations of stars, an AGN accretion disk, PAHs, atomic and molecular lines, and distributions of graphite and silicate grains. Decompositions of the SEDs of the template starburst galaxies NGC7714 and NGC2623 and the template AGNs PG0804+761 and Mrk463 provide baseline properties to aid in quantifying the strength of star-formation and accretion in the composite systems NGC6240 and Mrk1014. We find that obscured radiation from stars is capable of powering the total dust emission from NGC6240, although we cannot rule out a contribution from a deeply embedded AGN visible only in X-rays. The decomposition of Mrk1014 is consistent with ~65% of its power emerging from an AGN and ~35% from star-formation. We suggest that many of the variations in our template starburst SEDs may be explained in terms of the different mean optical depths through the clouds of dust surrounding the young stars within each galaxy. Prompted by the divergent far-IR properties of our template AGNs, we suggest that variations in the relative orientation of their AGN accretion disks with respect to the disks of the galaxies hosting them may result in different amounts of AGN-heated cold dust emission emerging from their host galaxies. We estimate that 30-50% of the far-IR and PAH emission from Mrk1014 may originate from such AGN-heated material in its host galaxy disk.Comment: 27 pages, 12 figures. Accepted for publication in the Ap

An Investigation of Diffuse Interstellar Gas toward a Large, Low Extinction Window into the Inner Galaxy

Halpha and Hbeta spectroscopy with the Wisconsin H-Alpha Mapper (WHAM) reveals a strong concentration of high velocity emission in a ~ 5 by 5 deg area centered near (l.b) = (27,-3), known as the Scutum Cloud. The high velocities imply that we are detecting optical emission from near the plane of the Galaxy out to the tangent point at heliocentric distances of D \gtrsim 6 kpc, assuming the gas participates in circular Galactic rotation. The ratio of the Halpha to Hbeta emission as a function of velocity suggests that dust along these lines of sight produces a total visual extinction of A_v ~ 3 at D ~ 6 kpc. This makes it possible to use optical emission lines to explore the physical conditions of ionized gas in the inner Galaxy. At a Galactocentric distance R_G ~ 4 kpc, for example, we find that the H^+ has an rms midplane density of ~ 1 cm^-3 with a vertical scale height of ~ 300 pc. We also find evidence for an increase in the flux of Lyman continuum photons and an increase in the ratio of ionized to neutral hydrogen toward the inner Galaxy. We have extended the measurements of E(B-V) in this direction to distances far beyond what has been accessible through stellar photometry and find E(B-V)/N_H to be near the local mean of 1.7 x 10^-22 cm^2 mag, with evidence for an increase in this ratio at R_G ~ 4 kpc. Finally, our observations of [NII] 6583, [SII] 6716, and [OIII] 5007 toward the window reveal that in the inner Galaxy the temperature of the gas and the ionization state of oxygen increase with increasing height from the midplane.Comment: ApJ, accepted. 28 pages, 13 figures, 1 tabl

Hydration dynamics at fluorinated protein surfaces

Water-protein interactions dictate many processes crucial to protein function including folding, dynamics, interactions with other biomolecules, and enzymatic catalysis. Here we examine the effect of surface fluorination on water-protein interactions. Modification of designed coiled-coil proteins by incorporation of 5,5,5-trifluoroleucine or (4S)-2-amino-4-methylhexanoic acid enables systematic examination of the effects of side-chain volume and fluorination on solvation dynamics. Using ultrafast fluorescence spectroscopy, we find that fluorinated side chains exert electrostatic drag on neighboring water molecules, slowing water motion at the protein surface

Polarization of absorption lines as a diagnostics of circumstellar, interstellar and intergalactic magnetic fields: Fine structure atoms

The relative population of the fine structure sublevels of an atom's ground state is affected by radiative transitions induced by an anisotropic radiation flux. This causes the alignment of atomic angular momentum. In terms of observational consequences for the interstellar and intergalactic medium, this results in the polarization of the absorption lines. In the paper we consider the conditions necessary for this effect and provide calculations of polarization from a few astrophysically important atoms and ions with multiple upper and lower levels for an arbitrary orientation of magnetic fields to the a) source of optical pumping, b) direction of observation, c) absorbed source. We also consider an astrophysically important ``degenerate'' case when the source of optical pumping coincides with the source of the absorbed radiation. We present analytical expressions that relate the degree of linear polarization and the intensity of absorption to the 3D orientation of the magnetic field with respect to the pumping source, the source of the absorbed radiation, and the direction of observations. We discuss how all these parameters can be determined via simultaneous observations of several absorption lines and suggest graphical means that are helpful in practical data interpretation. We prove that studies of absorption line polarization provide a unique tool to study 3D magnetic field topology in various astrophysical conditions.Comment: 22 pages, 10 figures, ApJ, in pres

Discovery of Large-Scale Gravitational Infall in a Massive Protostellar Cluster

We report Mopra (ATNF), Anglo-Australian Telescope, and Atacama Submillimeter Telescope Experiment observations of a molecular clump in Carina, BYF73 = G286.21+0.17, which give evidence of large-scale gravitational infall in the dense gas. From the millimetre and far-infrared data, the clump has mass ~ 2 x 10^4 Msun, luminosity ~ 2-3 x 10^4 Lsun, and diameter ~ 0.9 pc. From radiative transfer modelling, we derive a mass infall rate ~ 3.4 x 10^-2 Msun yr-1. If confirmed, this rate for gravitational infall in a molecular core or clump may be the highest yet seen. The near-infrared K-band imaging shows an adjacent compact HII region and IR cluster surrounded by a shell-like photodissociation region showing H2 emission. At the molecular infall peak, the K imaging also reveals a deeply embedded group of stars with associated H2 emission. The combination of these features is very unusual and we suggest they indicate the ongoing formation of a massive star cluster. We discuss the implications of these data for competing theories of massive star formation.Comment: v1: 23 pages single-column, 6 figures (some multipart) at end v2: 14 pages 2-column, 6 figures interspersed v3: edited to referee's comments with new sections and new figures; accepted to MNRAS, 20 pages 2-column, 8 figures (some multipart) intersperse

Herschel observations of interstellar chloronium

Using the Herschel Space Observatory's Heterodyne Instrument for the Far-Infrared (HIFI), we have observed para-chloronium (H2Cl+) toward six sources in the Galaxy. We detected interstellar chloronium absorption in foreground molecular clouds along the sight-lines to the bright submillimeter continuum sources Sgr A (+50 km/s cloud) and W31C. Both the para-H2-35Cl+ and para-H2-37Cl+ isotopologues were detected, through observations of their 1(11)-0(00) transitions at rest frequencies of 485.42 and 484.23 GHz, respectively. For an assumed ortho-to-para ratio of 3, the observed optical depths imply that chloronium accounts for ~ 4 - 12% of chlorine nuclei in the gas phase. We detected interstellar chloronium emission from two sources in the Orion Molecular Cloud 1: the Orion Bar photodissociation region and the Orion South condensation. For an assumed ortho-to-para ratio of 3 for chloronium, the observed emission line fluxes imply total beam-averaged column densities of ~ 2.0E+13 cm-2 and ~ 1.2E+13 cm-2, respectively, for chloronium in these two sources. We obtained upper limits on the para-H2-35Cl+ line strengths toward H2 Peak 1 in the Orion Molecular cloud and toward the massive young star AFGL 2591. The chloronium abundances inferred in this study are typically at least a factor ~10 larger than the predictions of steady-state theoretical models for the chemistry of interstellar molecules containing chlorine. Several explanations for this discrepancy were investigated, but none has proven satisfactory, and thus the large observed abundances of chloronium remain puzzling.Comment: Accepted for publication in the Astrophysical Journa

Stellar Evolutionary Effects on the Abundances of PAH and SN-Condensed Dust in Galaxies

Spectral and photometric observations of nearby galaxies show a correlation between the strength of their mid-IR aromatic features, attributed to PAH molecules, and their metal abundance, leading to a deficiency of these features in low-metallicity galaxies. In this paper, we suggest that the observed correlation represents a trend of PAH abundance with galactic age, reflecting the delayed injection of carbon dust into the ISM by AGB stars in the final post-AGB phase of their evolution. AGB stars are the primary sources of PAHs and carbon dust in galaxies, and recycle their ejecta back to the interstellar medium only after a few hundred million years of evolution on the main sequence. In contrast, more massive stars that explode as Type II supernovae inject their metals and dust almost instantaneously after their formation. We first determined the PAH abundance in galaxies by constructing detailed models of UV-to-radio SED of galaxies that estimate the contribution of dust in PAH-free HII regions, and PAHs and dust from photodissociation regions, to the IR emission. All model components: the galaxies' stellar content, properties of their HII regions, and their ionizing and non-ionizing radiation fields and dust abundances, are constrained by their observed multiwavelength spectrum. After determining the PAH and dust abundances in 35 nearby galaxies using our SED model, we use a chemical evolution model to show that the delayed injection of carbon dust by AGB stars provides a natural explanation to the dependence of the PAH content in galaxies with metallicity. We also show that larger dust particles giving rise to the far-IR emission follow a distinct evolutionary trend closely related to the injection of dust by massive stars into the ISM.Comment: ApJ, 69 pages, 46 figures, Accepte