English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We have analyzed the 8 13:5 mU KIRT CGS3 spectra of 142 M-type stars including 80 oxygen- rich AGB stars and 62 red supergiants, with a view to understanding the dierences and similarities between the dust features of these stars. We have classied the spectra into groups according to the observed appearance of the infrared features. In each case the normalized continuum- subtracted spectrum has been compared to those of the other stars to nd similarities and form groups. The dust features of the AGB stars are classied into six groups: broad AGB, where the feature extends from 8 mt o about 12.5 m with little structure; broad+sil AGB, which con- sists of a broad feature with an emerging 9.7 m silicate bump; and four silicate AGB groups in which a \clas- sic" 9.7 m silicate feature gets progressively narrower. Likewise, the supergiant spectra have also been classied 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 ex- tends from about 9 mt o about 13m; and four silicate Super groups, which again show a progression towards the narrowest \classic" 9.7 m silicate feature. We compare the mean spectrum for each group, which yields two main results. Firstly, while the \classic" silicate feature is essen- tially identical for both AGB stars and red supergiants, the broad features observed for these two stellar types are quite dierent. We suggest that the dust in these two en- vironments follows dierent evolutionary paths, with the dust around Mira stars, whose broad feature spectra can be t by a combination of alumina (Al2O3) and magne- sium silicate, progressing from this composition to dust dominated by magnesium silicate only, while the dust around supergiants, whose broad feature can be t by a combination of Ca-Al-rich silicate and Al2O3, progresses from this initial composition to one eventually also dom- inated by magnesium silicate. The reason for the dier- ence in the respective broad features is not clear as yet, but could be influenced by lower C/O ratios and chro- mospheric UV radiation elds in supergiant outflow envi- ronments. The second result concerns the 12.5 13.0 m feature discovered in IRAS LRS spectra and widely at- tributed to Al2O3. 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 Al2O3 or, as has more recently been suggested, spinel (MgAl2O4), but could be associated with silicon dioxide or highly poly- merized silicates (not pyroxenes or olivines).

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