uu.seUppsala University Publications
Change search
ReferencesLink to record
Permanent link

Direct link
ALMA observations of the variable (CO)-C-12/(CO)-C-13 ratio around the asymptotic giant branch star R Sculptoris
Show others and affiliations
2013 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 556, L1- p.Article in journal (Refereed) Published
Abstract [en]

The (CO)-C-12/(CO)-C-13 ratio is often used as a measure of the C-12/C-13 ratio in the circumstellar environment, carrying important information about the stellar nucleosynthesis. External processes can change the (CO)-C-12 and (CO)-C-13 abundances, and spatially resolved studies of the (CO)-C-12/(CO)-C-13 ratio are needed to quantify the effect of these processes on the globally determined values. Additionally, such studies provide important information on the conditions in the circumstellar environment. The detached-shell source R Scl, displaying CO emission from recent mass loss, in a binary-induced spiral structure as well as in a clumpy shell produced during a thermal pulse, provides a unique laboratory for studying the differences in CO isotope abundances throughout its recent evolution. We observed both the (CO)-C-12(J = 3 -> 2) and the (CO)-C-13(J = 3 -> 2) line using ALMA. We find significant variations in the (CO)-C-12/(CO)-C-13 intensity ratios and consequently in the abundance ratios. The average CO isotope abundance ratio is at least a factor three lower in the shell (similar to 19) than that in the present-day (less than or similar to 300 years) mass loss (>60). Additionally, variations in the ratio of more than an order of magnitude are found in the shell itself. We attribute these variations to the competition between selective dissociation and isotope fractionation in the shell, of which large parts cannot be warmer than similar to 35 K. However, we also find that the (CO)-C-12/(CO)-C-13 ratio in the present-day mass loss is significantly higher than the C-12/C-13 ratio determined in the stellar photosphere from molecular tracers (similar to 19). The origin of this discrepancy is still unclear, but we speculate that it is due to an embedded source of UV-radiation that is primarily photo-dissociating (CO)-C-13. This radiation source could be the hitherto hidden companion. Alternatively, the UV-radiation could originate from an active chromosphere of R Scl itself. Our results indicate that caution should be taken when directly relating the (CO)-C-12/(CO)-C-13 intensity and C-12/C-13 abundance ratios for specific asymptotic giant branch stars, in particular binaries or stars that display signs of chromospheric stellar activity.

Place, publisher, year, edition, pages
2013. Vol. 556, L1- p.
Keyword [en]
stars: abundances, stars: AGB and post-AGB, stars: carbon, circumstellar matter
National Category
Natural Sciences
URN: urn:nbn:se:uu:diva-208664DOI: 10.1051/0004-6361/201321821ISI: 000323893500158OAI: oai:DiVA.org:uu-208664DiVA: diva2:653979
Available from: 2013-10-07 Created: 2013-10-07 Last updated: 2013-10-07Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full text

Search in DiVA

By author/editor
Ramstedt, Sofia
By organisation
Theoretical Astrophysics
In the same journal
Astronomy and Astrophysics
Natural Sciences

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Altmetric score

Total: 461 hits
ReferencesLink to record
Permanent link

Direct link