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 Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

Carbonates have repeatedly been discussed as possible carriers of stardustemission bands. However, the band assignments proposed so far were mainly basedon room temperature powder transmission spectra of the respective minerals.Since very cold calcite grains have been claimed to be present in protostarsand in Planetary Nebulae such as NGC 6302, the changes of their dielectricfunctions at low temperatures are relevant from an astronomical point of view.We have derived the IR optical constants of calcite and dolomite fromreflectance spectra - measured at 300, 200, 100 and 10K - and calculated smallparticle spectra for different grain shapes, with the following results: i) Theabsorption efficiency factors both of calcite and dolomite are extremelydependent on the particle shapes. This is due to the high peak values of theoptical constants of CaCO3 and CaMg[CO3]2. ii) The far infrared properties ofcalcite and dolomite depend also very significantly on the temperature. Below200K, a pronounced sharpening and increase in the band strengths of the FIRresonances occurs. iii) In view of the intrinsic strength and sharpening of the44 mum band of calcite at 200-100K, the absence of this band -- inferred fromInfrared Space Observatory data -- in PNe requires dust temperatures below 45K.iv) Calcite grains at such low temperatures can account for the '92' mum band,while our data rule out dolomite as the carrier of the 60-65 mum band. Theoptical constants here presented are publicly available in the electronicdatabase http://www.astro.uni-jena.de/Laboratory/OCDB

Carbonates in space - The challenge of low temperature data