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Photometry and classification of stars around the reflection nebula NGC 7023 in Cepheus. II. Interstellar extinction and cloud distances  [PDF]
K. Zdanavicius,J. Zdanavicius,V. Straizys,M. Maskoliunas
Physics , 2009,
Abstract: Interstellar extinction is investigated in a 1.5 square degree area in the direction of the reflection nebula NGC 7023 at l = 104.1 deg, b = +14.2 deg. The study is based on photometric classification and the determination of interstellar extinctions and distances of 480 stars down to V = 16.5 mag from photometry in the Vilnius seven-color system published in Paper I (2008). The investigated area is divided into five smaller subareas with slightly different dependence of the extinction on distance. The distribution of reddened stars is in accordance with the presence of two dust clouds at 282 pc and 715 pc, however in some directions the dust distribution can be continuous or more clouds can be present.
Correcting for the Effects of Interstellar Extinction  [PDF]
Edward L. Fitzpatrick
Physics , 1998, DOI: 10.1086/316293
Abstract: This paper addresses the issue of how best to correct astronomical data for the wavelength-dependent effects of Galactic interstellar extinction. The main general features of extinction from the IR through the UV are reviewed, along with the nature of observed spatial variations. The enormous range of extinction properties found in the Galaxy, particularly in the UV spectral region, is illustrated. Fortunately, there are some tight constraints on the wavelength dependence of extinction and some general correlations between extinction curve shape and interstellar environment. These relationships provide some guidance for correcting data for the effects of extinction. Several strategies for dereddening are discussed along with estimates of the uncertainties inherent in each method. In the Appendix, a new derivation of the wavelength dependence of an average Galactic extinction curve from the IR through the UV is presented, along with a new estimate of how this extinction law varies with the parameter R = A(V)/E(B-V). These curves represent the true monochromatic wavelength dependence of extinction and, as such, are suitable for dereddening IR--UV spectrophotometric data of any resolution, and can be used to derive extinction relations for any photometry system.
A revised HRD for individual components of binary systems from BaSeL BVRI synthetic photometry. Influence of interstellar extinction and stellar rotation  [PDF]
E. Lastennet,J. Fernandes,Th. Lejeune
Physics , 2002, DOI: 10.1051/0004-6361:20020439
Abstract: Johnson BVRI photometric data for individual components of binary systems have been provided by ten Brummelaar et al. (2000). This is essential because such binaries could play a critical role in calibrating the single-star stellar evolution theory. While they derived the effective temperature from their estimated spectral type, we infer metallicity-dependent Teffs from a minimizing method fitting the B-V, V-R and V-I colours. For this purpose, a grid of 621,600 flux distributions were computed from the Basel Stellar Library (BaSeL 2.2) of model-atmosphere spectra, and their theoretical colours compared with the observed photometry. As a matter of fact, the BaSeL colours show a very good agreement with the BVRI metallicity-dependent empirical calibrations of Alonso et al. (1996), temperatures being different by 3+-3 % in the range 4000-8000 K for dwarf stars. Before deriving the metallicity-dependent Teff from the BaSeL models, we paid particular attention to the influence of reddening and stellar rotation. A comparison between the MExcess code and neutral hydrogen column density data shows a good agreement for the sample but we point out a few directions where the MExcess model overestimates the E(B-V) colour excess. Influence of stellar rotation on the BVRI colours can be neglected except for 5 stars with large vsini, the maximum effect on temperature being less than 5%. Our final results are in good agreement with previous spectroscopic determinations available for a few primary components, and with ten Brummelaar et al. below ~10,000 K. Nevertheless, we obtain an increasing disagreement with their Teffs beyond 10,000 K. Finally, we provide a revised Hertzsprung-Russell diagram for the systems with the more accurately determined temperatures. (Abridged)
The Gaia-ESO Survey: Tracing interstellar extinction  [PDF]
M. Schultheis,G. Kordopatis,A. Recio-Blanco,P. de Laverny,V. Hill,G. Gilmore,E. J. Alfaro,M. T. Costado,T. Bensby,F. Damiani,S. Feltzing,E. Flaccomio,C. Lardo,P. Jofre,L. Prisinzano,S. Zaggia,F. Jimenez-Esteban,L. Morbidelli,A. C. Lanzafame,A. Hourihane,C. Worley,P. Francois
Physics , 2015, DOI: 10.1051/0004-6361/201425333
Abstract: 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. 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. 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. 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 JHKs bands. Therefore, extinction maps using mean colour-excesses and assuming a constant extinction coefficient can be used without introducing any systematic errors.
Interstellar extinction and interstellar polarization: old and new models  [PDF]
N. V. Voshchinnikov
Physics , 2012, DOI: 10.1016/j.jqsrt.2012.06.013
Abstract: The review contains an analysis of the observed and model curves of the interstellar extinction and polarization. The observations mainly give information on dust in diffuse and translucent interstellar clouds. The features of various dust grain models including spherical/non-spherical, homogeneous/inhomogeneous particles are discussed. A special attention is devoted to the analysis of the grain size distributions, alignment mechanisms and magnetic field structure in interstellar clouds. It is concluded that the interpretation of interstellar extinction and polarization is not yet complete.
Modeling the Infrared Interstellar Extinction  [PDF]
Shu Wang,Aigen Li,B. W. Jiang
Physics , 2014, DOI: 10.1016/j.pss.2014.03.018
Abstract: How dust scatters and absorbs starlight in the interstellar medium (ISM) contains important clues about the size and composition of interstellar dust. While the ultraviolet (UV) and visible interstellar extinction is well studied and can be closely fitted in terms of various dust mixtures (e.g., the silicategraphite mixture), the infrared (IR) extinction is not well understood, particularly, the mid-IR extinction in the 3-8 micron wavelength range is rather flat (or "gray") and is inconsistent with the standard Mathis, Rumpl, & Nordsieck (MRN) silicate-graphite dust model. We attempt to reproduce the flat IR extinction by exploring various dust sizes and species, including amorphous silicate, graphite, amorphous carbon and iron. We find that the flat IR extinction is best explained in terms of micrometer-sized amorphous carbon dust which consumes ~ 60 carbon atoms per million hydrogen atoms (i.e., C/H ~ 60 ppm). To account for the observed UV/visible and near-IR extinction, the silicate-graphite model requires Si/H ~ 34 ppm and C/H ~ 292 ppm. We conclude that the extinction from the UV to the mid-IR could be closely reproduced by a mixture of submicrometer-sized amorphous silicate dust, submicrometer-sized graphitic dust, and micrometer-sized amorphous carbon dust, at the expense of excess C available in the ISM (i.e., this model requires a solid-phase C abundance of C/H ~ 352 ppm, considerably exceeding what could be available in the ISM).
Interstellar Grains: Effect of Inclusions on Extinction  [PDF]
Nisha Katyal,Ranjan Gupta,D. B. Vaidya
Physics , 2011, DOI: 10.5047/eps.2011.06.031
Abstract: A composite dust grain model which simultaneously explains the observed interstellar extinction, polarization, IR emission and the abundance constraints, is required. We present a composite grain model, which is made up of a host silicate oblate spheroid and graphite inclusions. The interstellar extinction curve is evaluated in the spectral region 3.4-0.1$\mu m$ using the extinction efficiencies of the composite spheroidal grains for three axial ratios. Extinction curves are computed using the discrete dipole approximation (DDA). The model curves are subsequently compared with the average observed interstellar extinction curve and with an extinction curve derived from the IUE catalogue data.
The Interaction of Supernova Remnant G357.7+0.3 with the Interstellar Medium  [PDF]
J. P. Phillips,R. A. Marquez-Lugo
Physics , 2010, DOI: 10.1111/j.1365-2966.2010.17340.x
Abstract: The supernova remnant (SNR) G357.7+0.3 appears to have caused considerable shredding of the local interstellar medium (ISM), leading to the formation of multiple cloud fragments having bright rims and cometary structures. We investigate five of these regions using mid-infrared (MIR) imaging and photometry deriving from the Spitzer Space Telescope (SST), as well as photometry deriving from the 2MASS near-infrared all sky survey, the Mid-Course Science Experiment (MSX), and the Multiband Imaging Photometer for Spitzer (MIPSGAL) survey of the Galactic plane. It is noted that two of the rims show evidence for emission by shock excited H2 transitions, whilst the centres of the clouds also show evidence for dark extinction cores, observed in silhouette against the bright emission rims. Levels of extinction for these cores are determined to be of order AV ~ 17-26 mag, whilst densities n(HI) are of order ~ 10^4 cm^(-3), and masses in the region of ~40-100 Msun. It is shown that the wavelength dependence of extinction is probably similar to that of Cardelli et al. and Martin & Whittet, but differs from the MIR extinction trends of Indebetouw et al. The distributions of Class I young stellar objects (YSOs) implies that many of them are physically associated with the clouds, and were likely formed as a result of interaction between the clouds and SN winds. A determination of the spectral energy distributions (SEDs) of these stars, together with 2-D radiative transfer modelling of their continua is used to place constraints upon their properties.
Silicon nanoparticles and interstellar extinction  [PDF]
Victor G. Zubko,Tracy L. Smith,Adolf N. Witt
Physics , 1998, DOI: 10.1086/311831
Abstract: To examine a recently proposed hypothesis that silicon nanoparticles are the source of extended red emission (ERE) in the interstellar medium, we performed a detailed modeling of the mean Galactic extinction in the presence of silicon nanoparticles. For this goal we used the appropriate optical constants of nanosized Si, essentially different from those of bulk Si due to quantum confinement. It was found that a dust mixture of silicon nanoparticles, bare graphite grains, silicate core-organic refractory mantle grains and three-layer silicate-water ice-organic refractory grains works well in explaining the extinction and, in addition, results in the acceptable fractions of UV/visible photons absorbed by silicon nanoparticles: 0.071-0.081. Since these fractions barely agree with the fraction of UV/visible photons needed to excite the observed ERE, we conclude that the intrinsic photon conversion efficiency of the photoluminescence by silicon nanoparticles must be near 100%, if they are the source of the ERE.
Interstellar extinction and polarization with homogeneous and composite grains  [cached]
N. V. Voshchinnikov
Atti della Accademia Peloritana dei Pericolanti : Classe di Scienze Fisiche, Matematiche e Naturali , 2011, DOI: 10.1478/c1v89s1p011
Abstract: We discuss possible ways to solve problems arising due to non-unique interpretation of interstellar extinction and linear polarization.
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