Stellar Spectra from 2.8 to 14 Microns

Gillett, F. C.; Low, F. J.; Stein, W. A.

doi:10.1086/149789

Cited by 92 publications

(36 citation statements)

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“…A similar feature (covering the same wavelength range) is found in the IR spectra of many O-rich evolved stars (e.g. Gillett et al 1968;Little-Marenin & Little 1990;Kraemer et al 2002), which it is usually attributed to a combination of silicates and aluminiumoxide with the possible addition of spinel at 13 μm (e.g. Woolf & Ney 1969;Hackwell 1972;Posch et al 1999;Cami 2002).…”

Section: The Broad Feature In the Sws Spectra Of S Starssupporting

confidence: 54%

An ISO/SWS study of the dust composition around S stars

Hony

Heras

Molster

et al. 2009

A&A

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Aims. We investigate the composition of the solid-state materials in the winds around S-type AGB stars. The S stars produce dust in their wind that bears a resemblance to the dust produced in some O-rich AGB stars. However, the reported resemblance is mostly based on IRAS/LRS spectra with limited spectral resolution, sensitivity, and wavelength coverage. Methods. We investigate the dust composition around S stars using ISO/SWS data that surpass the previous studies in terms of spectral resolution and wavelength coverage. We selected the dust producing S stars in the ISO/SWS archive with enough signal to perform a detailed dust analysis, and then compare the dust spectra from the 9 sources with the O-rich AGB spectra and a subset of M super-giants. We constructed average dust emission spectra of the different categories. Results. We report the discovery of several previously unreported dust emission features in the S star spectra. The long wavelength spectra of W Aql and π 1 Gru exhibit the "30" μm feature attributed to MgS. Two sources exhibit a series of emission bands between 20 and 40 μm that we tentatively ascribe to Diopside. We show that the 10−20 μm spectra of the S stars are significantly different from the O-rich AGB stars. The O-rich stars exhibit a structured emission feature that is believed to arise from amorphous silicate and aluminium-oxide. The S stars lack the substructure found in the O-rich stars. Instead they show a smooth peak with a varying peakposition from source to source. We suggest that this feature is caused by a family of related materials, whose exact composition determines the peak position. The observed trend mimics the laboratory trend of non-stoichiometric silicates. In this scenario the degree of non-stoichiometry is related to the Mg to SiO 4 ratio, in other words, to the amount of free O available during the dust grain growth.

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Section: The Broad Feature In the Sws Spectra Of S Starssupporting

confidence: 54%

An ISO/SWS study of the dust composition around S stars

Hony

Heras

Molster

et al. 2009

A&A

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“…In some objects, the dust optical depth is so high that most of the stellar energy are emitted at wavelengths longer than 2 µm. Gillett et al (1968) and Woolf and Ney (1969) attributed an emission band around 10 µm to small silicate particles, and Gehrz and Woolf (1971) estimated circumstellar dust masses and mass-loss rates of M giants. Similar results were found for carbon stars (Woolf and Ney 1969).…”

Section: Early Indications Of Mass Lossmentioning

confidence: 99%

Mass loss of stars on the asymptotic giant branch

Höfner

Olofsson

2018

Astron Astrophys Rev

469

376

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As low-and intermediate-mass stars reach the asymptotic giant branch (AGB), they have developed into intriguing and complex objects that are major players in the cosmic gas/dust cycle. At this stage, their appearance and evolution are strongly affected by a range of dynamical processes. Large-scale convective flows bring newlyformed chemical elements to the stellar surface and, together with pulsations, they trigger shock waves in the extended stellar atmosphere. There, massive outflows of gas and dust have their origin, which enrich the interstellar medium and, eventually, lead to a transformation of the cool luminous giants into white dwarfs. Dust grains forming in the upper atmospheric layers play a critical role in the wind acceleration process, by scattering and absorbing stellar photons and transferring their outward-directed momentum to the surrounding gas through collisions. Recent progress in high-angularresolution instrumentation, from the visual to the radio regime, is leading to valuable new insights into the complex dynamical atmospheres of AGB stars and their windforming regions. Observations are revealing asymmetries and inhomogeneities in the photospheric and dust-forming layers which vary on time-scales of months, as well as more long-lived large-scale structures in the circumstellar envelopes. High-angularresolution observations indicate at what distances from the stars dust condensation occurs, and they give information on the chemical composition and sizes of dust grains in the close vicinity of cool giants. These are essential constraints for building B Susanne Höfner

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“…In the late sixties, while investigating deviations of stellar energy distributions from blackbodies, Gillett et al (1968) discovered a peak near 10 µm in the spectra of four late-type, evolved, variable stars. Woolf & Ney (1969) attributed this emission peak to circumstellar silicate grains around these stars.…”

Section: Previous Observation Of Dust Around O-rich Starsmentioning

confidence: 99%

Dust features in the 10-μm infrared spectra of oxygen-rich evolved stars

Speck¹,

Barlow

Sylvester

et al. 2000

Astron. Astrophys. Suppl. Ser.

181

226

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Abstract.We have analyzed the 8 − 13.5 µm UKIRT CGS3 spectra of 142 M-type stars including 80 oxygenrich AGB stars and 62 red supergiants, with a view to understanding the differences and similarities between the dust features of these stars. We have classified the spectra into groups according to the observed appearance of the infrared features. In each case the normalized continuumsubtracted spectrum has been compared to those of the other stars to find similarities and form groups. The dust features of the AGB stars are classified into six groups: broad AGB, where the feature extends from 8 µm to about 12.5 µm with little structure; broad+sil AGB, which consists of a broad feature with an emerging 9.7 µm silicate bump; and four silicate AGB groups in which a "classic" 9.7 µm silicate feature gets progressively narrower. Likewise, the supergiant spectra have also been classified into groups, however these do not all coincide with the AGB star groups. In the supergiant case we again have six groups: featureless, where there is little or no emission above the continuum; broad Super, where the feature extends from about 9 µm to about 13 µm; and four silicate Super groups, which again show a progression towards the narrowest "classic" 9.7 µm silicate feature. We compare the mean spectrum for each group, which yields two main results. Firstly, while the "classic" silicate feature is essentially identical for both AGB stars and red supergiants, the broad features observed for these two stellar types are quite different. We suggest that the dust in these two environments follows different evolutionary paths, with the dust around Mira stars, whose broad feature spectra can be fit by a combination of alumina (Al 2 O 3 ) and magnesium silicate, progressing from this composition to dust dominated by magnesium silicate only, while the dust around supergiants, whose broad feature can be fit by a combination of Ca-Al-rich silicate and Al 2 O 3 , progresses Send offprint requests to: A.K. Speck from this initial composition to one eventually also dominated by magnesium silicate. The reason for the difference in the respective broad features is not clear as yet, but could be influenced by lower C/O ratios and chromospheric UV radiation fields in supergiant outflow environments. The second result concerns the 12.5 − 13.0 µm feature discovered in IRAS LRS spectra and widely attributed to Al 2 O 3 . This feature is seen predominantly in the spectra of semiregular variables, sometime in Miras and only once (so far) in supergiant spectra. We argue that it is unlikely that this feature is due to Al 2 O 3 or, as has more recently been suggested, spinel (MgAl 2 O 4 ), but could be associated with silicon dioxide or highly polymerized silicates (not pyroxenes or olivines).

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Stellar Spectra from 2.8 to 14 Microns

Cited by 92 publications

References 0 publications

An ISO/SWS study of the dust composition around S stars

An ISO/SWS study of the dust composition around S stars

Mass loss of stars on the asymptotic giant branch

Dust features in the 10-μm infrared spectra of oxygen-rich evolved stars

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