Extinction (astronomy)

Last updated July 18, 2024

In astronomy, extinction is the absorption and scattering of electromagnetic radiation by dust and gas between an emitting astronomical object and the observer. Interstellar extinction was first documented as such in 1930 by Robert Julius Trumpler.^[1]^[2] However, its effects had been noted in 1847 by Friedrich Georg Wilhelm von Struve,^[3] and its effect on the colors of stars had been observed by a number of individuals who did not connect it with the general presence of galactic dust. For stars lying near the plane of the Milky Way which are within a few thousand parsecs of the Earth, extinction in the visual band of frequencies (photometric system) is roughly 1.8 magnitudes per kiloparsec.^[4]

For Earth-bound observers, extinction arises both from the interstellar medium and the Earth's atmosphere; it may also arise from circumstellar dust around an observed object. Strong extinction in Earth's atmosphere of some wavelength regions (such as X-ray, ultraviolet, and infrared) is overcome by the use of space-based observatories. Since blue light is much more strongly attenuated than red light, extinction causes objects to appear redder than expected; this phenomenon is called interstellar reddening.^[5]

Interstellar reddening

Interstellar reddening is a phenomenon associated with interstellar extinction where the spectrum of electromagnetic radiation from a radiation source changes characteristics from that which the object originally emitted. Reddening occurs due to the light scattering off dust and other matter in the interstellar medium. Interstellar reddening is a different phenomenon from redshift, which is the proportional frequency shifts of spectra without distortion. Reddening preferentially removes shorter wavelength photons from a radiated spectrum while leaving behind the longer wavelength photons, leaving the spectroscopic lines unchanged.

In most photometric systems, filters (passbands) are used from which readings of magnitude of light may take account of latitude and humidity among terrestrial factors. Interstellar reddening equates to the "color excess", defined as the difference between an object's observed color index and its intrinsic color index (sometimes referred to as its normal color index). The latter is the theoretical value which it would have if unaffected by extinction. In the first system, the UBV photometric system devised in the 1950s and its most closely related successors, the object's color excess $E_{B-V}$ is related to the object's B−V color (calibrated blue minus calibrated visible) by:

$E_{B-V}=(B-V)_{\textrm {observed}}-(B-V)_{\textrm {intrinsic}}\,$

For an A0-type main sequence star (these have median wavelength and heat among the main sequence) the color indices are calibrated at 0 based on an intrinsic reading of such a star (± exactly 0.02 depending on which spectral point, i.e. precise passband within the abbreviated color name is in question, see color index). At least two and up to five measured passbands in magnitude are then compared by subtraction: U, B, V, I, or R during which the color excess from extinction is calculated and deducted. The name of the four sub-indices (R minus I etc.) and order of the subtraction of recalibrated magnitudes is from right to immediate left within this sequence.

General characteristics

Interstellar reddening occurs because interstellar dust absorbs and scatters blue light waves more than red light waves, making stars appear redder than they are. This is similar to the effect seen when dust particles in the atmosphere of Earth contribute to red sunsets.^[6]

Broadly speaking, interstellar extinction is strongest at short wavelengths, generally observed by using techniques from spectroscopy. Extinction results in a change in the shape of an observed spectrum. Superimposed on this general shape are absorption features (wavelength bands where the intensity is lowered) that have a variety of origins and can give clues as to the chemical composition of the interstellar material, e.g. dust grains. Known absorption features include the 2175 Å bump, the diffuse interstellar bands, the 3.1 μm water ice feature, and the 10 and 18 μm silicate features.

In the solar neighborhood, the rate of interstellar extinction in the Johnson–Cousins V-band (visual filter) averaged at a wavelength of 540 nm is usually taken to be 0.7–1.0 mag/kpc−simply an average due to the clumpiness of interstellar dust.^[7]^[8]^[9] In general, however, this means that a star will have its brightness reduced by about a factor of 2 in the V-band viewed from a good night sky vantage point on earth for every kiloparsec (3,260 light years) it is farther away from us.

The amount of extinction can be significantly higher than this in specific directions. For example, some regions of the Galactic Center are awash with obvious intervening dark dust from our spiral arm (and perhaps others) and themselves in a bulge of dense matter, causing as much as more than 30 magnitudes of extinction in the optical, meaning that less than 1 optical photon in 10¹² passes through.^[10] This results in the zone of avoidance, where our view of the extra-galactic sky is severely hampered, and background galaxies, such as Dwingeloo 1, were only discovered recently through observations in radio and infrared.

The general shape of the ultraviolet through near-infrared (0.125 to 3.5 μm) extinction curve (plotting extinction in magnitude against wavelength, often inverted) looking from our vantage point at other objects in the Milky Way, is fairly well characterized by the stand-alone parameter of relative visibility (of such visible light) R(V) (which is different along different lines of sight),^[11]^[12] but there are known deviations from this characterization.^[13] Extending the extinction law into the mid-infrared wavelength range is difficult due to the lack of suitable targets and various contributions by absorption features.^[14]

R(V) compares aggregate and particular extinctions. It is $A(V)/E(B-V)$ . Restated, it is the total extinction, A(V) divided by the selective total extinction (A(B)−A(V)) of those two wavelengths (bands). A(B) and A(V) are the total extinction at the B and V filter bands. Another measure used in the literature is the absolute extinction A(λ)/A(V) at wavelength λ, comparing the total extinction at that wavelength to that at the V band.

R(V) is known to be correlated with the average size of the dust grains causing the extinction. For the Milky Way Galaxy, the typical value for R(V) is 3.1,^[15] but is found to vary considerably across different lines of sight.^[16] As a result, when computing cosmic distances it can be advantageous to move to star data from the near-infrared (of which the filter or passband Ks is quite standard) where the variations and amount of extinction are significantly less, and similar ratios as to R(Ks):^[17] 0.49±0.02 and 0.528±0.015 were found respectively by independent groups.^[16]^[18] Those two more modern findings differ substantially relative to the commonly referenced historical value ≈0.7.^[11]

The relationship between the total extinction, A(V) (measured in magnitudes), and the column density of neutral hydrogen atoms column, N_H (usually measured in cm⁻²), shows how the gas and dust in the interstellar medium are related. From studies using ultraviolet spectroscopy of reddened stars and X-ray scattering halos in the Milky Way, Predehl and Schmitt^[19] found the relationship between N_H and A(V) to be approximately:

{\frac {N_{H}}{A(V)}}\approx 1.8\times 10^{21}~{\mbox{atoms}}~{\mbox{cm}}^{-2}~{\mbox{mag}}^{-1}

(see also:^[20]^[21]^[22]).

Astronomers have determined the three-dimensional distribution of extinction in the "solar circle" (our region of our galaxy), using visible and near-infrared stellar observations and a model of distribution of stars.^[23]^[24] The dust causing extinction mainly lies along the spiral arms, as observed in other spiral galaxies.

Measuring extinction towards an object

To measure the extinction curve for a star, the star's spectrum is compared to the observed spectrum of a similar star known not to be affected by extinction (unreddened).^[25] It is also possible to use a theoretical spectrum instead of the observed spectrum for the comparison, but this is less common. In the case of emission nebulae, it is common to look at the ratio of two emission lines which should not be affected by the temperature and density in the nebula. For example, the ratio of hydrogen-alpha to hydrogen-beta emission is always around 2.85 under a wide range of conditions prevailing in nebulae. A ratio other than 2.85 must therefore be due to extinction, and the amount of extinction can thus be calculated.

The 2175-angstrom feature

One prominent feature in measured extinction curves of many objects within the Milky Way is a broad 'bump' at about 2175 Å, well into the ultraviolet region of the electromagnetic spectrum. This feature was first observed in the 1960s,^[26]^[27] but its origin is still not well understood. Several models have been presented to account for this bump which include graphitic grains with a mixture of PAH molecules. Investigations of interstellar grains embedded in interplanetary dust particles (IDP) observed this feature and identified the carrier with organic carbon and amorphous silicates present in the grains.^[28]

Extinction curves of other galaxies

The form of the standard extinction curve depends on the composition of the ISM, which varies from galaxy to galaxy. In the Local Group, the best-determined extinction curves are those of the Milky Way, the Small Magellanic Cloud (SMC) and the Large Magellanic Cloud (LMC).

In the LMC, there is significant variation in the characteristics of the ultraviolet extinction with a weaker 2175 Å bump and stronger far-UV extinction in the region associated with the LMC2 supershell (near the 30 Doradus starbursting region) than seen elsewhere in the LMC and in the Milky Way.^[30]^[31] In the SMC, more extreme variation is seen with no 2175 Å bump and very strong far-UV extinction in the star forming Bar and fairly normal ultraviolet extinction seen in the more quiescent Wing.^[32]^[33]^[34]

This gives clues as to the composition of the ISM in the various galaxies. Previously, the different average extinction curves in the Milky Way, LMC, and SMC were thought to be the result of the different metallicities of the three galaxies: the LMC's metallicity is about 40% of that of the Milky Way, while the SMC's is about 10%. Finding extinction curves in both the LMC and SMC which are similar to those found in the Milky Way^[29] and finding extinction curves in the Milky Way that look more like those found in the LMC2 supershell of the LMC^[35] and in the SMC Bar^[36] has given rise to a new interpretation. The variations in the curves seen in the Magellanic Clouds and Milky Way may instead be caused by processing of the dust grains by nearby star formation. This interpretation is supported by work in starburst galaxies (which are undergoing intense star formation episodes) which shows that their dust lacks the 2175 Å bump.^[37]^[38]

Atmospheric extinction

Atmospheric extinction gives the rising or setting Sun an orange hue and varies with location and altitude. Astronomical observatories generally are able to characterise the local extinction curve very accurately, to allow observations to be corrected for the effect. Nevertheless, the atmosphere is completely opaque to many wavelengths requiring the use of satellites to make observations.

This extinction has three main components: Rayleigh scattering by air molecules, scattering by particulates, and molecular absorption. Molecular absorption is often referred to as telluric absorption, as it is caused by the Earth (telluric is a synonym for terrestrial). The most important sources of telluric absorption are molecular oxygen and ozone, which strongly absorb radiation near ultraviolet, and water, which strongly absorbs infrared.

The amount of such extinction is lowest at the observer's zenith and highest near the horizon. A given star, preferably at solar opposition, reaches its greatest celestial altitude and optimal time for observation when the star is near the local meridian around solar midnight and if the star has a favorable declination (i.e., similar to the observer's latitude); thus, the seasonal time due to axial tilt is key. Extinction is approximated by multiplying the standard atmospheric extinction curve (plotted against each wavelength) by the mean air mass calculated over the duration of the observation. A dry atmosphere reduces infrared extinction significantly.

Related Research Articles

A galaxy is a system of stars, stellar remnants, interstellar gas, dust, and dark matter bound together by gravity. The word is derived from the Greek galaxias (γαλαξίας), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. Galaxies, averaging an estimated 100 million stars, range in size from dwarfs with less than a thousand stars, to the largest galaxies known – supergiants with one hundred trillion stars, each orbiting its galaxy's center of mass. Most of the mass in a typical galaxy is in the form of dark matter, with only a few percent of that mass visible in the form of stars and nebulae. Supermassive black holes are a common feature at the centres of galaxies.

A molecular cloud, sometimes called a stellar nursery (if star formation is occurring within), is a type of interstellar cloud, the density and size of which permit absorption nebulae, the formation of molecules (most commonly molecular hydrogen, H₂), and the formation of H II regions. This is in contrast to other areas of the interstellar medium that contain predominantly ionized gas.

<span class="mw-page-title-main">Large Magellanic Cloud</span> Satellite galaxy of the Milky Way

The Large Magellanic Cloud (LMC) is a dwarf galaxy and satellite galaxy of the Milky Way. At a distance of around 50 kiloparsecs (163,000 light-years), the LMC is the second- or third-closest galaxy to the Milky Way, after the Sagittarius Dwarf Spheroidal (c. 16 kiloparsecs (52,000 light-years) away) and the possible dwarf irregular galaxy called the Canis Major Overdensity. Based on the D₂₅ isophote at the B-band (445 nm wavelength of light), the Large Magellanic Cloud is about 9.86 kiloparsecs (32,200 light-years) across. It is roughly one-hundredth the mass of the Milky Way and is the fourth-largest galaxy in the Local Group, after the Andromeda Galaxy (M31), the Milky Way, and the Triangulum Galaxy (M33).

<span class="mw-page-title-main">Star formation</span> Process by which dense regions of molecular clouds in interstellar space collapse to form stars

Star formation is the process by which dense regions within molecular clouds in interstellar space, sometimes referred to as "stellar nurseries" or "star-forming regions", collapse and form stars. As a branch of astronomy, star formation includes the study of the interstellar medium (ISM) and giant molecular clouds (GMC) as precursors to the star formation process, and the study of protostars and young stellar objects as its immediate products. It is closely related to planet formation, another branch of astronomy. Star formation theory, as well as accounting for the formation of a single star, must also account for the statistics of binary stars and the initial mass function. Most stars do not form in isolation but as part of a group of stars referred as star clusters or stellar associations.

The interstellar medium (ISM) is the matter and radiation that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as dust and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space. The energy that occupies the same volume, in the form of electromagnetic radiation, is the interstellar radiation field. Although the density of atoms in the ISM is usually far below that in the best laboratory vacuums, the mean free path between collisions is short compared to typical interstellar lengths, so on these scales the ISM behaves as a gas, responding to pressure forces, and not as a collection of non-interacting particles.

The Andromeda Galaxy is a barred spiral galaxy and is the nearest major galaxy to the Milky Way. It was originally named the Andromeda Nebula and is cataloged as Messier 31, M31, and NGC 224. Andromeda has a D₂₅ isophotal diameter of about 46.56 kiloparsecs (152,000 light-years) and is approximately 765 kpc (2.5 million light-years) from Earth. The galaxy's name stems from the area of Earth's sky in which it appears, the constellation of Andromeda, which itself is named after the princess who was the wife of Perseus in Greek mythology.

The Galactic Center is the barycenter of the Milky Way and a corresponding point on the rotational axis of the galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a compact radio source which is almost exactly at the galactic rotational center. The Galactic Center is approximately 8 kiloparsecs (26,000 ly) away from Earth in the direction of the constellations Sagittarius, Ophiuchus, and Scorpius, where the Milky Way appears brightest, visually close to the Butterfly Cluster (M6) or the star Shaula, south to the Pipe Nebula.

The Zone of Avoidance, or Zone of Galactic Obscuration (ZGO), is the area of the sky that is obscured by the Milky Way.

The Sombrero Galaxy is a peculiar galaxy of unclear classification in the constellation borders of Virgo and Corvus, being about 9.55 megaparsecs from the Milky Way galaxy. It is a member of the Virgo II Groups, a series of galaxies and galaxy clusters strung out from the southern edge of the Virgo Supercluster. It has an isophotal diameter of approximately 29.09 to 32.32 kiloparsecs, making it slightly bigger in size than the Milky Way.

In astronomy a superbubble or supershell is a cavity which is hundreds of light years across and is populated with hot (10⁶ K) gas atoms, less dense than the surrounding interstellar medium, blown against that medium and carved out by multiple supernovae and stellar winds. The winds, passage and gravity of newly born stars strip superbubbles of any other dust or gas. The Solar System lies near the center of an old superbubble, known as the Local Bubble, whose boundaries can be traced by a sudden rise in dust extinction of exterior stars at distances greater than a few hundred light years.

<span class="mw-page-title-main">Milky Way</span> Galaxy containing the Solar System

The Milky Way is the galaxy that includes the Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye.

A megamaser is a type of astrophysical maser, which is a naturally occurring source of stimulated spectral line emission. Megamasers are distinguished from other astrophysical masers by their large isotropic luminosity. Megamasers have typical luminosities of 10³ solar luminosities (L_☉), which is 100 million times brighter than masers in the Milky Way, hence the prefix mega. Likewise, the term kilomaser is used to describe masers outside the Milky Way that have luminosities of order L_☉, or thousands of times stronger than the average maser in the Milky Way, gigamaser is used to describe masers billions of times stronger than the average maser in the Milky Way, and extragalactic maser encompasses all masers found outside the Milky Way. Most known extragalactic masers are megamasers, and the majority of megamasers are hydroxyl (OH) megamasers, meaning the spectral line being amplified is one due to a transition in the hydroxyl molecule. There are known megamasers for three other molecules: water (H₂O), formaldehyde (H₂CO), and methine (CH).

<span class="mw-page-title-main">Eyes Galaxies</span> Pair of galaxies in the constellation Virgo

The Eyes Galaxies are a pair of galaxies about 52 million light-years away in the constellation Virgo. The pair are members of the string of galaxies known as Markarian's Chain.

Baade's Window is an area of the sky with relatively low amounts of interstellar dust along the line of sight from Earth. This area is considered an observational "window" as the normally obscured Galactic Center of the Milky Way is visible in this direction. This makes the apparent Large Sagittarius Star Cloud visible.

<span class="mw-page-title-main">W Cephei</span> Variable star in the constellation Cepheus

W Cephei is a spectroscopic binary and variable star located in the constellation Cepheus. It is thought to be a member of the Cep OB1 stellar association at about 8,000 light years. The supergiant primary star is one of the largest known stars and as well as one of the most luminous red supergiants.

A color–color diagram is a means of comparing the colors of an astronomical object at different wavelengths. Astronomers typically observe at narrow bands around certain wavelengths, and objects observed will have different brightnesses in each band. The difference in brightness between two bands is referred to as color. On color–color diagrams, the color defined by two wavelength bands is plotted on the horizontal axis, and the color defined by another brightness difference will be plotted on the vertical axis.

<span class="mw-page-title-main">Ionization cone</span> Astronomical phenomenon

Ionization cones are cones of ionized material extending from active galactic nuclei, predominantly observed in type II Seyfert galaxies. They are detected through their emission of electromagnetic radiation in the visible and infrared parts of the spectrum. The main method of observation is through spectroscopy, using spectral line analysis to measure the shape of the ionized region and the condition of the material such as temperature, density, composition, and degree of ionization.

WOH G64 is an unusual red supergiant (RSG) star in the Large Magellanic Cloud (LMC) satellite galaxy in the southern constellation of Dorado. It is one of the largest known stars, being described as possibly being the largest star known. It is also one of the most luminous and massive red supergiants, with a radius calculated to be around 1,540 times that of the Sun (R_☉) and a luminosity around 282,000 times the solar luminosity (L_☉).

The Serpens–Aquila Rift (also known as the Aquila Rift) is a region of the sky in the constellations Aquila, Serpens Cauda, and eastern Ophiuchus containing dark interstellar clouds. The region forms part of the Great Rift, the nearby dark cloud of cosmic dust that obscures the middle of the galactic plane of the Milky Way, looking inwards and towards its other radial sectors. The clouds that form this structure are called "molecular clouds", constituting a phase of the interstellar medium which is cold and dense enough for molecules to form, particularly molecular hydrogen (H₂). These clouds are opaque to light in the optical part of the spectrum due to the presence of interstellar dust grains mixed with the gaseous component of the clouds. Therefore, the clouds in the Serpens-Aquila Rift block light from background stars in the disk of the Galaxy, forming the dark rift. The complex is located in a direction towards the inner Galaxy, where molecular clouds are common, so it is possible that not all components of the rift are at the same distance and physically associated with each other.

References

↑ Trumpler, R. J. (1930). "Preliminary results on the distances, dimensions and space distribution of open star clusters". Lick Observatory Bulletin. 14 (420): 154–188. Bibcode:1930LicOB..14..154T. doi: 10.5479/ADS/bib/1930LicOB.14.154T .
↑ Karttunen, Hannu (2003). Fundamental astronomy. Springer. p. 289. ISBN 978-3-540-00179-9.{{cite book}}: |work= ignored (help)
↑ Struve, F. G. W. 1847, St. Petersburg: Tip. Acad. Imper., 1847; IV, 165 p.; in 8.; DCCC.4.211
↑ Whittet, Douglas C. B. (2003). Dust in the Galactic Environment. Series in Astronomy and Astrophysics (2nd ed.). CRC Press. p. 10. ISBN 978-0750306249.
↑ See Binney and Merrifeld, Section 3.7 (1998, ISBN 978-0-691-02565-0), Carroll and Ostlie, Section 12.1 (2007, ISBN 978-0-8053-0402-2), and Kutner (2003, ISBN 978-0-521-52927-3) for applications in astronomy.
↑ "Interstellar Reddening, Extinction, and Red Sunsets". Astro.virginia.edu. 2002-04-22. Archived from the original on 2017-11-22. Retrieved 2017-07-14.
↑ Gottlieb, D. M.; Upson, W.L. (1969). "Local Interstellar Reddening". Astrophysical Journal. 157: 611. Bibcode:1969ApJ...157..611G. doi: 10.1086/150101 .
↑ Milne, D. K.; Aller, L.H. (1980). "An average model for the galactic absorption". Astrophysical Journal. 85: 17–21. Bibcode:1980AJ.....85...17M. doi: 10.1086/112628 .
↑ Lynga, G. (1982). "Open clusters in our Galaxy". Astronomy & Astrophysics. 109: 213–222. Bibcode:1982A&A...109..213L.
↑ Schlegel, David J.; Finkbeiner, Douglas P; Davis, Marc (1998). "Maps of Dust Infrared Emission for Use in Estimation of Reddening and Cosmic Microwave Background Radiation Foregrounds". Astrophysical Journal. 500 (2): 525–553. arXiv: astro-ph/9710327 . Bibcode:1998ApJ...500..525S. doi:10.1086/305772. S2CID 59512299.
1 2 Cardelli, Jason A.; Clayton, Geoffrey C.; Mathis, John S. (1989). "The relationship between infrared, optical, and ultraviolet extinction". Astrophysical Journal. 345: 245–256. Bibcode:1989ApJ...345..245C. doi:10.1086/167900.
↑ Valencic, Lynne A.; Clayton, Geoffrey C.; Gordon, Karl D. (2004). "Ultraviolet Extinction Properties in the Milky Way". Astrophysical Journal. 616 (2): 912–924. arXiv: astro-ph/0408409 . Bibcode:2004ApJ...616..912V. doi:10.1086/424922. S2CID 119330502.
↑ Mathis, John S.; Cardelli, Jason A. (1992). "Deviations of interstellar extinctions from the mean R-dependent extinction law". Astrophysical Journal. 398: 610–620. Bibcode:1992ApJ...398..610M. doi:10.1086/171886.
↑ T. K. Fritz; S. Gillessen; K. Dodds-Eden; D. Lutz; R. Genzel; W. Raab; T. Ott; O. Pfuhl; F. Eisenhauer; F. Yusuf-Zadeh (2011). "Line Derived Infrared Extinction toward the Galactic Center". The Astrophysical Journal. 737 (2): 73. arXiv: 1105.2822 . Bibcode:2011ApJ...737...73F. doi:10.1088/0004-637X/737/2/73. S2CID 118919927.
↑ Schultz, G. V.; Wiemer, W. (1975). "Interstellar reddening and IR-excess of O and B stars". Astronomy and Astrophysics. 43: 133–139. Bibcode:1975A&A....43..133S.
1 2 Majaess, Daniel; David Turner; Istvan Dekany; Dante Minniti; Wolfgang Gieren (2016). "Constraining dust extinction properties via the VVV survey". Astronomy and Astrophysics. 593: A124. arXiv: 1607.08623 . Bibcode:2016A&A...593A.124M. doi:10.1051/0004-6361/201628763. S2CID 54218060.
↑ R(Ks) is, mathematically likewise, A(Ks)/E(J−Ks)
↑ Nishyiama, Shogo; Motohide Tamura; Hirofumi Hatano; Daisuke Kato; Toshihiko Tanabe; Koji Sugitani; Tetsuya Nagata (2009). "Interstellar Extinction Law Toward the Galactic Center III: J, H, KS Bands in the 2MASS and the MKO Systems, and 3.6, 4.5, 5.8, 8.0 μm in the Spitzer/IRAC System". The Astrophysical Journal. 696 (2): 1407–1417. arXiv: 0902.3095 . Bibcode:2009ApJ...696.1407N. doi:10.1088/0004-637X/696/2/1407. S2CID 119205751.
↑ Predehl, P.; Schmitt, J. H. M. M. (1995). "X-raying the interstellar medium: ROSAT observations of dust scattering halos". Astronomy and Astrophysics. 293: 889–905. Bibcode:1995A&A...293..889P.
↑ Bohlin, Ralph C.; Blair D. Savage; J. F. Drake (1978). "A survey of interstellar H I from L-alpha absorption measurements. II". Astrophysical Journal. 224: 132–142. Bibcode:1978ApJ...224..132B. doi:10.1086/156357.
↑ Diplas, Athanassios; Blair D. Savage (1994). "An IUE survey of interstellar H I LY alpha absorption. 2: Interpretations". Astrophysical Journal. 427: 274–287. Bibcode:1994ApJ...427..274D. doi: 10.1086/174139 .
↑ Güver, Tolga; Özel, Feryal (2009). "The relation between optical extinction and hydrogen column density in the Galaxy". Monthly Notices of the Royal Astronomical Society . 400 (4): 2050–2053. arXiv: 0903.2057 . Bibcode:2009MNRAS.400.2050G. doi: 10.1111/j.1365-2966.2009.15598.x .
↑ Marshall, Douglas J.; Robin, A.C.; Reylé, C.; Schultheis, M.; Picaud, S. (Jul 2006). "Modelling the Galactic interstellar extinction distribution in three dimensions". Astronomy and Astrophysics. 453 (2): 635–651. arXiv: astro-ph/0604427 . Bibcode:2006A&A...453..635M. doi:10.1051/0004-6361:20053842. S2CID 16845046.
↑ Robin, Annie C.; Reylé, C.; Derrière, S.; Picaud, S. (Oct 2003). "A synthetic view on structure and evolution of the Milky Way". Astronomy and Astrophysics. 409 (2): 523–540. arXiv: astro-ph/0401052 . Bibcode:2003A&A...409..523R. doi:10.1051/0004-6361:20031117.
↑ Cardelli, Jason A.; Sembach, Kenneth R.; Mathis, John S. (1992). "The quantitative assessment of UV extinction derived from IUE data of giants and supergiants". Astronomical Journal. 104 (5): 1916–1929. Bibcode:1992AJ....104.1916C. doi:10.1086/116367. ISSN 0004-6256.
↑ Stecher, Theodore P. (1965). "Interstellar Extinction in the Ultraviolet". Astrophysical Journal. 142: 1683. Bibcode:1965ApJ...142.1683S. doi:10.1086/148462.
↑ Stecher, Theodore P. (1969). "Interstellar Extinction in the Ultraviolet. II". Astrophysical Journal. 157: L125. Bibcode:1969ApJ...157L.125S. doi: 10.1086/180400 .
↑ Bradley, John; Dai, ZR; et al. (2005). "An Astronomical 2175 Å Feature in Interplanetary Dust Particles". Science. 307 (5707): 244–247. Bibcode:2005Sci...307..244B. doi:10.1126/science.1106717. PMID 15653501. S2CID 96858465.
1 2 Gordon, Karl D.; Geoffrey C. Clayton; Karl A. Misselt; Arlo U. Landolt; Michael J. Wolff (2003). "A Quantitative Comparison of the Small Magellanic Cloud, Large Magellanic Cloud, and Milky Way Ultraviolet to Near-Infrared Extinction Curves". Astrophysical Journal. 594 (1): 279–293. arXiv: astro-ph/0305257 . Bibcode:2003ApJ...594..279G. doi:10.1086/376774. S2CID 117180437.
↑ Fitzpatrick, Edward L. (1986). "An average interstellar extinction curve for the Large Magellanic Cloud". Astronomical Journal. 92: 1068–1073. Bibcode:1986AJ.....92.1068F. doi: 10.1086/114237 .
↑ Misselt, Karl A.; Geoffrey C. Clayton; Karl D. Gordon (1999). "A Reanalysis of the Ultraviolet Extinction from Interstellar Dust in the Large Magellanic Cloud". Astrophysical Journal. 515 (1): 128–139. arXiv: astro-ph/9811036 . Bibcode:1999ApJ...515..128M. doi:10.1086/307010. S2CID 14175478.
↑ Lequeux, J.; Maurice, E.; Prevot-Burnichon, M. L.; Prevot, L.; Rocca-Volmerange, B. (1982). "SK 143 - an SMC star with a galactic-type ultraviolet interstellar extinction". Astronomy and Astrophysics. 113: L15–L17. Bibcode:1982A&A...113L..15L.
↑ Prevot, M. L.; Lequeux, J.; Prevot, L.; Maurice, E.; Rocca-Volmerange, B. (1984). "The typical interstellar extinction in the Small Magellanic Cloud". Astronomy and Astrophysics. 132: 389–392. Bibcode:1984A&A...132..389P.
↑ Gordon, Karl D.; Geoffrey C. Clayton (1998). "Starburst-like Dust Extinction in the Small Magellanic Cloud". Astrophysical Journal. 500 (2): 816–824. arXiv: astro-ph/9802003 . Bibcode:1998ApJ...500..816G. doi:10.1086/305774. S2CID 18090417.
↑ Clayton, Geoffrey C.; Karl D. Gordon; Michael J. Wolff (2000). "Magellanic Cloud-Type Interstellar Dust along Low-Density Sight Lines in the Galaxy". Astrophysical Journal Supplement Series. 129 (1): 147–157. arXiv: astro-ph/0003285 . Bibcode:2000ApJS..129..147C. doi:10.1086/313419. S2CID 11205416.
↑ Valencic, Lynne A.; Geoffrey C. Clayton; Karl D. Gordon; Tracy L. Smith (2003). "Small Magellanic Cloud-Type Interstellar Dust in the Milky Way". Astrophysical Journal. 598 (1): 369–374. arXiv: astro-ph/0308060 . Bibcode:2003ApJ...598..369V. doi:10.1086/378802. S2CID 123435053.
↑ Calzetti, Daniela; Anne L. Kinney; Thaisa Storchi-Bergmann (1994). "Dust extinction of the stellar continua in starburst galaxies: The ultraviolet and optical extinction law". Astrophysical Journal. 429: 582–601. Bibcode:1994ApJ...429..582C. doi:10.1086/174346. hdl: 10183/108843 .
↑ Gordon, Karl D.; Daniela Calzetti; Adolf N. Witt (1997). "Dust in Starburst Galaxies". Astrophysical Journal. 487 (2): 625–635. arXiv: astro-ph/9705043 . Bibcode:1997ApJ...487..625G. doi:10.1086/304654. S2CID 2055629.