Dark Dust and single-cloud sightlines in the ISM

Abstract

The precise characteristics of clouds and the nature of dust in the diffuse interstellar medium can only be extracted by inspecting the rare cases of single-cloud sightlines. In our nomenclature such objects are identified by interstellar lines, such as K I, that show at a resolving power of $\lambda /\Delta \lambda \sim 75,000$ one dominating Doppler component that accounts for more than half of the observed column density. We searched for such sightlines using high-resolution spectroscopy towards reddened OB stars for which far-UV extinction curves are known. We compiled a sample of 186 spectra, 100 of which were obtained specifically for this project with UVES. In our sample we identified 65 single-cloud sightlines, about half of which were previously unknown. We used the CH/CH${}^{+}$ line ratio of our targets to establish whether the sightlines are dominated by warm or cold clouds. We found that CN is detected in all cold (CH/CH${}^{+}>1$) clouds, but is frequently absent in warm clouds. We inspected the WISE ($3-22\mu$m) observed emission morphology around our sightlines and excluded a circumstellar nature for the observed dust extinction. We found that most sightlines are dominated by cold clouds that are located far away from the heating source. For 132 stars, we derived the spectral type and the associated spectral type-luminosity distance. We also applied the interstellar Ca II distance scale, and compared these two distance estimates with GAIA parallaxes. These distance estimates scatter by 40%. By comparing spectral type-luminosity distances with those of GAIA, we detected a hidden dust component that amounts to a few mag of extinction for eight sightlines. This Dark Dust is populated by $\ge 1\mu$m large grains and predominately appears in the field of the cold interstellar medium.

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References in corpus (29)

• The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance
• Estimating distances from parallaxes IV: Distances to 1.33 billion stars in Gaia Data Release 2
• An Analysis of the Shapes of Interstellar Extinction Curves. V. The IR-Through-UV Curve Morphology
• 2018 Census of Interstellar, Circumstellar, Extragalactic, Protoplanetary Disk, and Exoplanetary Molecules
• The ELODIE archive
• An Analysis of the Shapes of Interstellar Extinction Curves. VII. Milky Way Spectrophotometric Optical-through-Ultraviolet Extinction and Its R-Dependence
• VLT/UVES Abundances in Four Nearby Dwarf Spheroidal Galaxies: II. Implications for Understanding Galaxy Evolution
• Ultraviolet Extinction Properties in the Milky Way
• FUSE Measurements of Far-Ultraviolet Extinction. III. The Dependence on R(V) and Discrete Feature Limits from 75 Galactic Sightlines
• A Fractal Origin for the Mass Spectrum of Interstellar Clouds: II. Cloud Models and Power Law Slopes
• The BOES spectropolarimeter for Zeeman measurements of stellar magnetic fields
• The Apache Point Observatory Catalog of Optical Diffuse Interstellar Bands
• High-Resolution Observations of Interstellar Ca I Absorption -- Implications for Depletions and Electron Densities in Diffuse Clouds
• Cloud Structure and Physical Conditions in Star-Forming Regions from Optical Observations. II. Analysis
• Instabilities of Spiral Shocks -- II. A quasi-steady State in the multi-phase inhomogeneous ISM
• The ESO Diffuse Interstellar Bands Large Exploration Survey: EDIBLES I. Project description, survey sample and quality assessment
• Large dust grains in the wind of VY Canis Majoris
• Early-type stars observed in the ESO UVES Paranal Observatory Project: I -- Interstellar Na I UV, Ti II and Ca II K observations
• The importance of non-photon noise in stellar spectropolarimetry. The spurious detection of a non-existing magnetic field in the A0 supergiant HD 92207
• Large Interstellar Polarisation Survey. LIPS I: FORS2 spectropolarimetry in the Southern Hemisphere
• A Principal component analysis of the diffuse interstellar bands
• Large Circumbinary Dust Grains Around Evolved Giants?
• Variable Interstellar Absorption toward the Halo Star HD 219188 - Implications for Small-Scale Interstellar Structure
• Herschel/HIFI Spectral Mapping of C${}^{+}$, CH${}^{+}$, and CH in Orion BN/KL: The Prevailing Role of Ultraviolet Irradiation in CH${}^{+}$ Formation
• Extinction and dust properties in a clumpy medium
• HD 62542: Probing the Bare, Dense Core of a Translucent Interstellar Cloud
• Large Interstellar Polarisation Survey II. UV/optical study of cloud-to-cloud variations of dust in the diffuse ISM
• Observational analysis of the well--correlated diffuse bands: 6196 and 6614 Å
• Interstellar H2 toward HD 37903

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• Towards a complete picture of the Sco-Cen outflow
• Broadened profiles of Diffuse Interstellar Bands
• Dark Dust III: The high-quality single-cloud reddening curve sample. Scrutinizing extinction curves in the Milky Way
• A Tale of Three Dust Populations: Variable $R_{\mathrm{V}}$ and Extreme Polarization Along Sightlines Toward $\zeta$ Ophiuchi
• Polarization position angle standard stars: a reassessment of $\theta$ and its variability for seventeen stars based on a decade of observations
• On the intrinsic rest wavelengths of diffuse interstellar bands
• Extreme Starlight Polarization Efficiency Toward $\zeta$ Ophiuchi: A Case for Line-of-Sight Foreground Subtraction
• Large Interstellar Polarisation Survey. III. Observational constraints on the structure of grains
• The PRIMA promise of deciphering interstellar dust evolution with observations of the nearby Universe