Ultraviolet Extinction Curve Research Articles

Expanded Sample of Small Magellanic Cloud Ultraviolet Dust Extinction Curves: Correlations between the 2175 Å Bump, q PAH, Ultraviolet Extinction Shape, and N(H i)/A(V)

The Small Magellanic Cloud (SMC) shows a large variation in ultraviolet (UV) dust extinction curves, ranging from Milky Way (MW) like to significantly steeper curves with no detectable 2175 Å bump. This result is based on a sample of only nine sight lines. From Hubble Space Telescope Space Telescope Imaging Spectrograph and IUE spectra of OB stars, we have measured UV extinction curves along 32 SMC sight lines where eight of these curves were published previously. We find 16 sight lines with steep extinction with no detectable 2175 Å bump, four sight lines with MW-like extinction with a detectable 2175 Å bump, two sight lines with fairly flat UV extinction and weak/absent 2175 Å bumps, and 10 sight lines with unreliable curves due to low SMC dust columns. Our expanded sample shows that the sight lines with and without the 2175 Å bump are located throughout the SMC and not limited to specific regions. The average extinction curve of the 16 bump-less sight lines is very similar to the previous average based on four sight lines. We find no correlation between dust column and the strength of the 2175 Å bump. We test the hypothesis that the 2175 Å bump is due to the same dust grains that are responsible for the mid-infrared carbonaceous (polycyclic aromatic hydrocarbon) emission features and find they are correlated, confirming recent work in the MW. Overall, the slope of the UV extinction increases as the amplitudes of the 2175 Å bump and far-ultraviolet curvature decrease. Finally, the UV slope is correlated with N(H i)/A(V) and the 2175 Å bump and nonlinear far-ultraviolet rise amplitudes are anticorrelated with N(H i)/A(V).

The 2175 Å interstellar extinction bump: is the wavelength variable?

ABSTRACT The most striking characteristics of the mysterious 2175$\mathring{\rm A}$ extinction bump, the strongest spectroscopic absorption feature seen on the interstellar extinction curve, are the invariant central wavelength and variable bandwidth: its peak position at 2175$\mathring{\rm A}$ is remarkably constant, while its bandwidth varies from one line of sight to another. However, recent studies of the lines of sight towards a number of Herbig Ae/Be stars have revealed that the extinction bump exhibits substantial shifts from the canonical wavelength of 2175$\mathring{\rm A}$. In this work, we revisit these lines of sight and take a physical approach to determine the ultraviolet (UV) extinction curve for each line of sight. It is found that the wavelengths of the derived UV extinction bumps are around 2200$\mathring{\rm A}$ and the scatters are considerably smaller than those of the previous study based on the same set of Herbig Ae/Be stars, consistent with the conventional wisdom of a stable bump position. Nevertheless, the scatters are still appreciably larger than those associated with the nominal bump position of 2175$\mathring{\rm A}$. This is discussed in the context that Herbig Ae/Be stars are not well suited for interstellar extinction studies.

Effects of dust sources on dust attenuation properties in IllustrisTNG galaxies at z ∼ 7

ABSTRACT Dust emission from high-redshift galaxies gives us a clue to the origin and evolution of dust in the early Universe. Previous studies have shown that different sources of dust (stellar dust production and dust growth in dense clouds) predict different ultraviolet (UV) extinction curves for galaxies at z ∼ 7 but that the observed attenuation curves depend strongly on the geometry of dust and star distributions. Thus, we perform radiative transfer calculations under the dust–star geometries computed by a cosmological hydrodynamic simulation (IllustrisTNG). This serves to investigate the dust attenuation curves predicted from ‘realistic’ geometries. We choose objects with stellar mass and star formation rate appropriate for Lyman break galaxies at z ∼ 7. We find that the attenuation curves are very different from the original extinction curves in most of the galaxies. This makes it difficult to constrain the dominant dust sources from the observed attenuation curves. We further include infrared dust emission in the analysis and plot the infrared excess (IRX)–UV spectral slope (β) diagram. We find that different sources of dust cause different IRX–β relations for the simulated galaxies. In particular, if dust growth is the main source of dust, a variation of dust-to-metal ratio causes a more extended sequence with smaller IRX in the IRX–β diagram. Thus, the comprehensive analysis of the abundance of dust and metals, the UV slope, and the dust emission could provide a clue to the dominant dust sources in the Universe.

Relations between Mid-infrared Dust Emission and UV Extinction

Abstract We analyze low-resolution Spitzer infrared (IR) 5−14 μm spectra of the diffuse emission toward a carefully selected sample of stars. The sample is composed of sight lines toward stars that have well-determined ultraviolet (UV) extinction curves and that are shown to lie beyond effectively all of the extinguishing and emitting dust along their lines of sight. Our sample includes sight lines whose UV curve extinction curves exhibit a wide range of curve morphology and that sample a variety of interstellar environments. As a result, this unique sample enabled us to study the connection between the extinction and emission properties of the same grains, and to examine their response to different physical environments. We quantify the emission features in terms of the polycyclic aromatic hydrocarbon (PAH) model given by Draine & Li and a set on additional features not known to be related to PAH emission. We compare the intensities of the different features in the Spitzer mid-infrared spectra with the Fitzpatrick & Massa parameters that describe the shapes of UV to near-infrared extinction curves. Our primary result is that there is a strong correlation between the area of the 2175 Å UV bump in the extinction curves of the program stars and the strengths of the major PAH emission features in the mid-infrared spectra for the same lines of sight.

Milky Way Mid-Infrared Spitzer Spectroscopic Extinction Curves: Continuum and Silicate Features

Abstract We measured the mid-infrared (MIR) extinction using Spitzer photometry and spectroscopy (3.6–37 μm) for a sample of Milky Way sight lines (mostly) having measured ultraviolet extinction curves. We used the pair method to determine the MIR extinction that we then fit with a power law for the continuum and modified Drude profiles for the silicate features. We derived 16 extinction curves having a range of A(V) (1.8–5.5) and R(V) values (2.4–4.3). Our sample includes two dense sight lines that have 3 μm ice feature detections and weak 2175 Å bumps. The average A(λ)/A(V) diffuse sight-line extinction curve we calculate is lower than most previous literature measurements. This agrees better with literature diffuse dust grain models, though it is somewhat higher. The 10 μm silicate feature does not correlate with the 2175 Å bump, for the first time providing direct observational confirmation that these two features arise from different grain populations. The strength of the 10 μm silicate feature varies by ∼2.5 and is not correlated with A(V) or R(V). It is well fit by a modified Drude profile with strong correlations seen between the central wavelength, width, and asymmetry. We do not detect other features with limits in A(λ)/A(V) units of 0.0026 (5–10 μm), 0.004 (10–20 μm), and 0.008 (20–40 μm). We find that the standard prescription of estimating R(V) from C × E(K s − V)/E(B − V) has C = −1.14 and a scatter of ∼7%. Using the IRAC 5.6 μm band instead of K s gives C = −1.03 and the least scatter of ∼3%.

Towards understanding physical origin of 2175 Å extinction bump in interstellar medium

ABSTRACT The 2175 Å ultraviolet (UV) extinction bump in interstellar medium (ISM) of the Milky Way was discovered in 1965. After intensive exploration of more than a half century, however, its exact origin still remains a big conundrum that is being debated. Here, we propose a mixture model by which the extinction bump in ISM is argued possibly relevant to the clusters of hydrogenated T-carbon (HTC) molecules (C40H16) that have intrinsically a sharp absorption peak at the wavelength 2175 Å. By linearly combining the calculated absorption spectra of HTC mixtures, graphite, MgSiO3, and Fe2SiO4, we show that the UV extinction curves of optional six stars can be nicely fitted. This work poses an alternative explanation towards understanding the physical origin of the 2175 Å extinction bump in ISM of the Milky Way.

On the Number of Independent Parameters of Interstellar Extinction Curves

Abstract The number of independent parameters that ultraviolet interstellar extinction curves depend on has never been decisively clarified, yet the issue is critical for the comprehension and modeling of interstellar extinction observations. Cardelli, Clayton, & Mathis (CCM89) concluded that normalized extinction curves rely on only one parameter, but E. Fitzpatrick and others consider this finding at most a first-order approximation favored by uncertainties in measurement. However, the multiparameter fits successively introduced by Fitzpatrick & Massa were intended to give the best possible analytical representation of extinction curves, not to investigate their degrees of freedom. A deeper examination of these fits and of the CCM89 conclusion shows that they do not necessarily conflict. Fitzpatrick & Massa’s parameterization of extinction curves and the large database (nearly 600 directions) published by Krelowski & Strobel are used in this paper to show that, within the precision allowed by the data, E(λ − V) correlates tightly with E(B − V) for all λ within the near-infrared to far-ultraviolet spectrum. This correlation confirms the relationships that led to the CCM89 fit and calls into question the reliability of today’s interstellar dust models, which all need at least seven parameters (reddening included) to fit observed ultraviolet extinction curves.

DIFFUSE INTERSTELLAR BANDS AND THE ULTRAVIOLET EXTINCTION CURVES: THE MISSING LINK REVISITED

A large number of interstellar absorption features at ~ 4000\AA\ -- 1.8 {\mu}m, known as the "diffuse interstellar bands" (DIBs), remains unidentified. Most recent works relate them to large polycyclic aromatic hydrocarbon (PAH) molecules or ultrasmall carbonaceous grains which are also thought to be responsible for the 2175 \AA\ extinction bump and/or the far ultraviolet (UV) extinction rise at $\lambda^{-1} > 5.9\ {\mu}m^{-1}$. Therefore, one might expect some relation between the UV extinction and DIBs. Such a relationship, if established, could put important constraints on the carrier of DIBs. Over the past four decades, whether DIBs are related to the shape of the UV extinction curves has been extensively investigated. However, the results are often inconsistent, partly due to the inconsistencies in characterizing the UV extinction. Here we re-examine the connection between the UV extinction curve and DIBs. We compile the extinction curves and the equivalent widths of 40 DIBs along 97 slightlines. We decompose the extinction curve into three Drude-like functions composed of the visible/near-infrared component, the 2175 \AA\ bump, and the far-UV extinction at $\lambda^{-1} > 5.9\ {\mu}m^{-1}$. We argue that the wavelength-integrated far-UV extinction derived from this decomposition technique best measures the strength of the far-UV extinction. No correlation is found between the far-UV extinction and most (~90\%) of the DIBs. We have also shown that the color excess E(1300-1700), the extinction difference at 1300 \AA\ and 1700 \AA\ often used to measure the strength of the far-UV extinction, does not correlate with DIBs. Finally, we confirm the earlier findings of no correlation between the 2175 \AA\ bump and DIBs or between the 2175 \AA\ bump and the far-UV extinction.

Ultraviolet Extinction Properties in the Milky Way

We have assembled a homogeneous database of 417 ultraviolet (UV) extinction curves for reddened sightlines having International Ultraviolet Explorer (IUE) spectra. We have combined these with optical and 2MASS photometry allowing estimates of the ratio of total-to-selective extinction, R(V), for the entire sample. Fitzpatrick-Massa (FM) parameters have also been found for the entire sample. This is the largest study of parameterized UV extinction curves yet published and it covers a wide range of environments, from dense molecular clouds to the diffuse interstellar medium (ISM), with extinctions A(V) ranging from 0.50 to 4.80. It is the first to extend far beyond the solar neighborhood and into the Galaxy at large, with 30 sightlines having distances > 5 kpc. Previously, the longest sightlines with FM parameters and R(V) extended ~ 1 kpc. We find that (1.) the CCM extinction law applies for 93% of the sightlines, implying that dust processing in the Galaxy is efficient and systematic; (2.) the central wavelength of the 2175 A bump is constant; (3.) the 2175 A bump width is dependent on environment. Only four sightlines show systematic deviations from CCM, HD 29647, 62542, 204827, and 210121. These sightlines all sample dense, molecule-rich clouds. The new extinction curves and values of R(V) allow us to revise the CCM law.

Chemical abundances of planetary nebulae from optical recombination lines - I. Observations and plasma diagnostics

We have obtained deep optical spectra of medium resolution for a sample of 12 Galactic planetary nebulae (PNe). Optical recombination lines (ORLs) from carbon, nitrogen and oxygen have been detected in 11 of them and neon ORLs in nine of them. All spectra were obtained by scanning a long slit across the nebular surface, yielding relative line intensities for the entire nebula that are suitable for comparison with integrated line fluxes measured in other wavelength regions using space-borne facilities, such as the Infrared Space Observatory (ISO) and the International Ultraviolet Explorer (IUE). For 11 PNe, ISO infrared spectra between 2.4 and 197 µm are available, most of them taken by ourselves, plus a Kuiper Airborne Observatory (KAO) infrared spectrum of NGC 6210. IUE ultraviolet (UV) spectra are available for all nebulae except one in our sample. The UV, optical and infrared spectra have been combined to study nebular thermal and density structures and to determine elemental abundances. We have determined UV to optical extinction curves towards these PNe by examining observed fluxes of H I and He II recombination lines, radio free‐free continuum flux density, and UV to optical nebular continua. For 11 PNe in our sample, the derived optical reddening curves are found to be consistent with the standard Galactic extinction law for a total-toselective extinction ratio, R ≡ A(V)/EB‐V = 3.1. However, the optical extinction curve towards Hu 1‐2 yields R = 2.0. The UV extinction towards Hu 1‐2 and NGC 6572 is also found to be much steeper than the standard Galactic reddening law. In contrast, the UV extinction curve along the sight lines towards NGC 6210 is found to be much shallower, although in the latter case the uncertainties involved are quite large. Electron temperatures and densities have been derived using a variety of diagnostic ratios of collisionally excited lines (CELs) in the UV, optical and infrared. The results show clear stratifications, both in temperature and density. Lines emitted by ions formed in regions of higher ionization degree yield higher temperatures than lines arising from regions of lower ionization degree, while densities deduced from ratios of infrared diagnostic CELs of low critical densities, such as the [O III] 88-µm/52-µm ratio, are systematically lower than those derived from UV and optical diagnostic lines, which in general have much higher critical densities than the infrared fine-structure lines. Electron temperatures have also been derived from the ratio of the nebular continuum Balmer discontinuity to H 11 for 11 PNe. For four of these, the Balmer jump temperatures are more than 1000 K lower than values derived from the [O III] optical collisionally excited diagnostic line ratio. With a difference of 3580 K, NGC 40 has the lowest Balmer jump temperature relative to the [O III] optical forbidden-line temperature. High-order Balmer line decrements

The Ultraviolet Extinction Curve of Intraclump Dust in Taurus (TMC‐1): Constraints on the 2175 A Bump Absorber

Ultraviolet extinction curves for three early-type stars that sample dust in the Taurus dark cloud in the vicinity of TMC-1 are analyzed to examine the contribution of internal (intraclump) dust to the total line-of-sight extinction. One of our selected targets samples only dust in the "diffuse-screen" component of the cloud, where the dust grains lack ice mantles and have optical properties similar to average "diffuse-ISM" dust. Comparison with data for more heavily reddened stars that also sample dust within TMC-1 (where grains are mantled) allows us to determine the intraclump extinction. Our principal result is that the 2175 Å "extinction bump" is extremely weak or absent inside the clump. The feature present in the observed extinction curves appears to arise almost entirely in the diffuse screen. This dramatic reduction in bump amplitude in the high-density environment is consistent with the prediction of the graphite model that the feature is suppressed by hydrogenation. Amplitude reduction is accompanied by a more subtle change in the profile of the bump, specifically, an increase in width. Comparison of Taurus and other clouds strongly suggests that the increase in width results from accumulation of surface coatings on the carrier grains rather than from particle clustering.

The Extinction Law in High‐Redshift Galaxies

We estimate the dust extinction laws in two intermediate redshift galaxies. The dust in the lens galaxy of LBQS1009-0252, which has an estimated lens redshift of zl~0.88, appears to be similar to that of the SMC with no significant feature at 2175 A. Only if the lens galaxy is at a redshift of zl~0.3, completely inconsistent with the galaxy colors, luminosity or location on the fundamental plane, can the data be fit with a normal Galactic extinction curve. The dust in the zl=0.68 lens galaxy for B0218+357, whose reddened image lies behind a molecular cloud, requires a very flat ultraviolet extinction curve with (formally) R(V)=12 +- 2. Both lens systems seem to have unusual extinction curves by Galactic standards.

The Role of Polycyclic Aromatic Hydrocarbons in Ultraviolet Extinction. I. Probing Small Molecular Polycyclic Aromatic Hydrocarbons

We have obtained new Hubble Space Telescope/Space Telescope Imaging Spectrograph spectra to search for structure in the ultraviolet interstellar extinction curve, with particular emphasis on a search for absorption features produced by polycyclic aromatic hydrocarbons (PAHs). The presence of these molecules in the interstellar medium has been postulated to explain the infrared emission features seen in the 3-13 μm spectra of numerous sources. Ultraviolet (UV) spectra are uniquely capable of identifying specific PAH molecules. We obtained high signal-to-noise ratio UV spectra of stars that are significantly more reddened than those observed in previous studies. These data put limits on the role of small (30-50 carbon atoms) PAHs in UV extinction and call for further observations to probe the role of larger PAHs. PAHs are of importance because of their ubiquity and high abundance inferred from the infrared data, and also because they may link the molecular and dust phases of the interstellar medium. A presence or absence of UV absorption bands due to PAHs could be a definitive test of this hypothesis. We should be able to detect a 20 Å wide feature down to a 3 σ limit of ~0.02 AV. No such absorption features are seen other than the well-known 2175 Å bump.

On Ultrasmall Silicate Grains in the Diffuse Interstellar Medium

The abundance of both amorphous and crystalline silicates in very small grains is limited by the fact that the 10 micron silicate emission feature is not detected in the diffuse ISM. On the basis of the observed IR emission spectrum for the diffuse ISM, the observed ultraviolet extinction curve, and the 10 micron silicate absorption profile, we obtain upper limits on the abundances of ultrasmall (a < 15 Angstrom) amorphous and crystalline silicate grains. Contrary to previous work, as much as ~20% of interstellar Si could be in a < 15 Angstrom silicate grains without violating observational constraints. Not more than ~5% of the Si can be in crystalline silicates (of any size).

On the Correlation between CO Absorption and Far‐Ultraviolet Nonlinear Extinction toward Galactic OB Stars

A sample of 59 sight lines to reddened Galactic OB stars was examined for correlations of the strength of the CO Fourth Positive (A 1 � − X 1 � + ) absorption band system with the ultraviolet interstellar extinction curve parameters. We used archival high-dispersion NEWSIPS IUE spectra to measure the CO absorption for comparison to parametric fits of the extinction curves from the literature. A strong correlation with the non-linear far-UV curvature term was found with greater absorption, normalized to E(B − V ), being associated with more curvature. A weaker trend with the linear extinction term was also found. Mechanisms for enhancing CO in dust environments exhibiting high non-linear curvature are discussed. Subject headings: Dust, extinction — ISM: abundances — ISM: molecules — ultraviolet: ISM

The Ultraviolet Extinction Curve for Circumstellar Dust Formed in the Hydrogen‐poor Environment of V348 Sagittarii

New International Ultraviolet Explorer (IUE) spectra with high signal-to-noise ratios have been obtained during the recovery of the hot R Coronae Borealis star, V348 Sgr, from its 1992 minimum. These spectra have been combined with spectra from the IUE archives to obtain a definitive extinction curve for dust recently ejected from this star, and make available for the first time an extinction curve of high accuracy in the far-UV for circumstellar dust formed in a hydrogen-poor environment. We find that a Drude profile with a central wavelength of 2425 A and a full width at half-maximum of 1.342 μm-1 is able to satisfactorily represent the circumstellar dust ejected from V348 Sgr, not just during one ejection episode, but in general. We calculated theoretical extinction curves for comparison with the observed data using 400 A graphite grains and 300 A amorphous carbon grains. It is clear that scattering is very important at short wavelengths. Neither type of grain works very well when scattering is not included. The amorphous carbon fits are somewhat better than the graphite fits. The data seem to be more consistent with a cloud covering the entire star, and not just lying in our line of sight. This contradicts other empirical evidence that points toward the formation of patchy clouds around R Coronae Borealis stars.

The Translucent Molecular Clouds toward HD 154368. I. Extinction, Abundances, and Depletions

We report the results of a comprehensive analysis of a line of sight observed using the Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope (HST), toward HD 154368, an 09.5 Iab star located about 800 pc away. The line of sight intersects translucent interstellar cloud material, having a color excess E(B - V) = 0.82 and known high molecular abundances from ground-based data. The HST observations consist of high-resolution spectra obtained with grating ECH-B at wavelengths longward of 1800 Angstrom, and moderate-resolution spectra from grating G160M at shorter wavelengths. We observed some 19 wavelength settings, covering the positions of numerous atomic and molecular transitions. We also incorporate IUE and ground-based data in the study, the latter coming from several observatories at visible and millimeter wavelengths. In this paper we report on the general goals and results of the study, with emphasis on the atomic abundances and depletions. We find that the column densities of most species are slightly higher, relative to the adopted total gas column density, than in some thinner clouds in which most of the absorption arises in a single dense component. Consequently the depletions of elements from the gas phase onto the dust are less than in ''typical'' diffuse clouds such as the one toward zeta Oph. Most of the gas toward HD 154368 resides in two main clouds, centered near -3.26 and -20.95 km s(-1) (heliocentric). Our profile analyses show that the depletions in these two clouds are similar. We discuss the possible relationship of this result to the ultraviolet extinction curve toward HD 154368, derived from IUE spectra.

On the System of Diffuse Interstellar Bands at 5844 and 5850 Angstrom

view Abstract Citations (7) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the System of Diffuse Interstellar Bands at 5844 and 5850 Angstrom Krelowski, J. ; Snow, Theodore P. ; Papaj, J. ; Seab, C. G. ; Wszolek, B. Abstract Two neighboring diffuse interstellar bands (DIBs) at 5844 and 5850 Å are shown to be of different origin. The presence or absence of the 5844 DIB is related to the ratio of the two prominent DIBs at 5780 and 5797 Å as well as to the nature of the ultraviolet extinction curve. The 5844 Å DIB is very sensitive to the extinction, being completely absent in cases where the far-UV extinction is low. This suggests that the carrier is destroyed by photons having energies above 11 or 12 eV. The 5850 Å DIB correlates very well with the well-studied DIB at 5797 Å, suggesting that these two features belong to the same family of DIBs and may be produced by the same carrier. Publication: The Astrophysical Journal Pub Date: December 1993 DOI: 10.1086/173519 Bibcode: 1993ApJ...419..692K Keywords: ISM: MOLECULES; LINE: IDENTIFICATION full text sources ADS | data products SIMBAD (8)

Neutral and ionized polycyclic aromatic hydrocarbons, diffuse interstellar bands and the ultraviolet extinction curve

Download options Please wait... Article information DOI https://doi.org/10.1039/FT9938902277 Article type Paper Download Citation J. Chem. Soc., Faraday Trans., 1993,89, 2277-2284 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Neutral and ionized polycyclic aromatic hydrocarbons, diffuse interstellar bands and the ultraviolet extinction curve F. Salama and L. J. Allamandola, J. Chem. Soc., Faraday Trans., 1993, 89, 2277 DOI: 10.1039/FT9938902277 To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author Farid Salama Louis John Allamandola

On graphite and the variations in the ultraviolet extinction curve

A silicate-graphite model of interstellar extinction has been compared with recent observational information about the ultraviolet part of the extinction curve. The model has large (>0.01 μm) and small (0.005 μm) grains of each composition, and the number densities of the four components are assumed to vary independently and randomly within certain limits. A total of 50 extinction curves have been generated and subjected to analysis similar to that for the ultraviolet observations