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Testing new ideas regarding the nature of interstellar extinction
Canadian Journal of Physics, 2014
The nature of Galactic interstellar extinction is tested using reddening line parameters for several fields in conjunction with equivalent widths W(λ4430) for the diffuse interstellar band at 4430 Å. The Cardelli et al. relations (Astrophys. J. 345, 245 (1989). doi:10.1086/167900) at infrared, optical, and ultraviolet wavelengths are inconsistent with the newly-derived quadratic variation of RV(observed) on reddening slope X. A minimum of RV = 2.82 ± 0.06 exists for X = 0.83 ± 0.01, and is argued to represent true Galactic extinction described by A(λ) ∝ λ–1.375. It matches expectations for a new description of extinction in the infrared, optical, and ultraviolet by Zagury (Astron. Nachr. 334, 1107 (2013)). Additional consequences, reddened stars with no 2175 Å feature and a correlation of normalized λ4430 absorption with X, are not predicted by the Cardelli et al. relation (Astrophys. J. 345, 245 (1989). doi:10.1086/167900 ). Known variations in X from 0.62 to 0.83, and correspondin...
Dust in the Small Magellanic Cloud: Interstellar Polarization and Extinction
The Astrophysical Journal, 1997
The typical extinction curve for the Small Magellanic Cloud (SMC), in contrast to that for the Galaxy, has no bump at 2175Å and has a steeper rise into the far ultraviolet. For the Galaxy the interpretation of the extinction and, therefore, the dust content of the interstellar medium has been greatly assisted by measurements of the wavelength dependence of the polarization. To the present no such measurements existed for the SMC.
Modelling the Galactic interstellar extinction distribution in three dimensions
Astronomy and Astrophysics, 2006
Aims. The Two Micron All Sky Survey, along with the Stellar Population Synthesis Model of the Galaxy, developed in Besançon, is used to calculate the extinction distribution along different lines of sight. By combining many lines of sight, the large scale distribution of interstellar material can be deduced.
Mid-Infrared Extinction and Its Variation With Galactic Longitude
The Astrophysical Journal, 2009
Based on the data obtained from the Spitzer /GLIPMSE Legacy Program and the 2MASS project, we derive the extinction in the four IRAC bands, [3.6], [4.5], [5.8] and [8.0] µm, relative to the 2MASS K s band (at 2.16 µm) for 131 GLIPMSE fields along the Galactic plane within |l| ≤ 65 o , using red giants and red clump giants as tracers. As a whole, the mean extinction in the IRAC bands (normalized to the 2MASS K s band),
FUSE Measurements of Extragalactic Interstellar Extinction
2006
Observations of interstellar extinction provide a fundamental experimental basis for understanding the characteristics of dust, a primary constituent of the ISM. Interactions between dust grains and light depend in part upon the grain size relative to the wavelength of light extinguished; in particular, far-ultraviolet observations are useful for investigating the properties of small dust grains. We have acquired a sample of extragalactic sight lines that, in addition to possessing infrared, optical, and ultraviolet data, have also been observed by FUSE. Using extinction curves constructed from this sample we characterise the properties of Magellanic Cloud dust grains with special emphasis on how data at shorter wavelengths affect our current understanding of the differences and similarities between Galactic and Magellanic Cloud dust, particularly with respect to composition and size.
The Astrophysical Journal, 1999
We determine 37 differential extinctions in 23 gravitational lens galaxies over the range 0 < ∼ z l < ∼ 1. Only 7 of the 23 systems have spectral differences consistent with no differential extinction. The median differential extinction for the optically-selected (radio-selected) subsample is ∆E(B − V ) = 0.04 (0.06) mag. The extinction is patchy and shows no correlation with impact parameter. The median total extinction of the bluest images is E(B − V ) = 0.08 mag, although the total extinction distribution is dominated by the uncertainties in the intrinsic colors of quasars. The directly measured extinction distributions are consistent with the mean extinction estimated by comparing the statistics of quasar and radio lens surveys, thereby confirming the need for extinction corrections when using the statistics of lensed quasars to estimate the cosmological model. A disjoint subsample of two face-on, radio-selected spiral lenses shows both high differential and total extinctions, but standard dust-to-gas ratios combined with the observed molecular gas column densities overpredict the amount of extinction by factors of 2-5. For several systems we can estimate the extinction law, ranging from R V = 1.5 ± 0.2 for a z l = 0.96 elliptical, to R V = 7.2 ± 0.1 for a z l = 0.68 spiral. For the four radio lenses where we can construct non-parametric extinction curves we find no evidence for gray dust over the IR-UV wavelength range. The dust can be used to estimate lens redshifts with reasonable accuracy, although we sometimes find two degenerate redshift solutions.
Interstellar Dust Grains: Ultraviolet and Mid-IR Extinction Curves
arXiv: Astrophysics of Galaxies, 2019
Interstellar dust plays a central role in shaping the detailed structure of the interstellar medium, thus strongly influencing star formation and galaxy evolution. Dust extinction provides one of the main pillars of our understanding of interstellar dust while also often being one of the limiting factors when interpreting observations of distant objects, including resolved and unresolved galaxies. The ultraviolet (UV) and mid-infrared (MIR) wavelength regimes exhibit features of the main components of dust, carbonaceous and silicate materials, and therefore provide the most fruitful avenue for detailed extinction curve studies. Our current picture of extinction curves is strongly biased to nearby regions in the Milky Way. The small number of UV extinction curves measured in the Local Group (mainly Magellanic Clouds) clearly indicates that the range of dust properties is significantly broader than those inferred from the UV extinction characteristics of local regions of the Milky Way...
Interstellar extinction from photometric surveys: application to four high-latitude areas
Open Astronomy, 2018
Information on interstellar extinction and dust properties may be obtained from modern large photometric surveys data. Virtual Observatory facilities allow users to make a fast and correct cross-identification of objects from various surveys. It yields a multicolor photometry data on detected objects and makes it possible to estimate stellar parameters and calculate interstellar extinction. A 3D extinction map then can be constructed. The method was applied to 2MASS, SDSS, GALEX and UKIDSS surveys. Results for several high-latitude areas are obtained, compared with independent sources and discussed here.
Ultraviolet extinction toward a quiescent molecular cloud in the Small Magellanic Cloud
Astronomy & Astrophysics, 2012
Context. The mean UV extinction law for the Small Magellanic Cloud (SMC) is usually taken as a template for low-metallicity galaxies. However, its current derivation is based on only five stars, which renders its universality questionable. More targets with measured extinction laws in the SMC are necessary to determine its possible dependence on parameters such as metallicity and starforming activity. Aims. We aim to measure the UV extinction law for several stars in the quiescent molecular cloud SMC B1-1. Methods. We obtained HST/STIS slitless UV spectroscopy of a 25 × 25 field of view and combined it with ground-based NIR and visible photometry of the stars in the field. The results were processed using the Bayesian photometric package CHORIZOS to derive the visible-NIR extinction values for each star. The unextinguished spectral energy distributions (SEDs) obtained in this way were then used to derive the UV extinction law for the four most extinguished stars. We also recalculated the visible-NIR extinction for the five SMC stars with preexisting UV extinction laws. Results. The UV extinction law for four SMC B1-1 stars that are situated within several pc of each other differs significantly from star to star. The 2175 Å bump is moderately strong in one, weak in two, and absent in the fourth.
The Gaia -ESO Survey: Tracing interstellar extinction
Astronomy & Astrophysics, 2015
Context. Large spectroscopic surveys have enabled in the recent years the computation of three-dimensional interstellar extinction maps thanks to accurate stellar atmospheric parameters and line-of-sight distances. Such maps are complementary to 3D maps extracted from photometry, allowing a more thorough study of the dust properties. Aims. Our goal is to use the high-resolution spectroscopic survey Gaia-ESO in order to obtain with a good distance resolution the interstellar extinction and its dependency as a function of the environment and the Galactocentric position. Methods. We use the stellar atmospheric parameters of more than 5000 stars, obtained from the Gaia-ESO survey second internal data release, and combine them with optical (SDSS) and near-infrared (VISTA) photometry as well as different sets of theoretical stellar isochrones, in order to calculate line-of-sight extinction and distances. The extinction coefficients are then compared with the literature to discuss their dependancy on the stellar parameters and position in the Galaxy. Results. Within the errors of our method, our work does not show that there is any dependence of the interstellar extinction coefficient on the atmospheric parameters of the stars. We do not find any evidence of the variation of E(J − H)/E(J − K) with the angle from the Galactic centre nor with Galactocentric distance. This suggests that we are dealing with a uniform extinction law in the SDSS ugriz bands and the near-IR JHK s bands. Therefore, extinction maps using mean colour-excesses and assuming a constant extinction coefficient can be used without introducing any systematic errors.