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Title

A λ 3 mm and 1 mm line survey toward the yellow hypergiant IRC +10420: N-rich chemistry and IR flux variations

AuthorsQuintana Rodríguez, Carmen ; Agúndez, Marcelino ; Cernicharo, José ; Bujarrabal, V.; Sánchez Contreras, C.; Castro-Carrizo, A.; Alcolea, J.
KeywordsStars: individual: IRC +10420
Molecular processes
Circumstellar matter
Radio lines: stars
Issue Date22-Jul-2016
PublisherEDP Sciences
CitationAstronomy and Astrophysics 592: A51 (2016)
Abstract[Aims] Our knowledge of the chemical properties of the circumstellar ejecta of the most massive evolved stars is particularly poor. We aim to study the chemical characteristics of the prototypical yellow hypergiant star, IRC +10420. For this purpose, we obtained full line surveys at 1 and 3 mm atmospheric windows.
[Methods] We have identified 106 molecular emission lines from 22 molecular species. Approximately half of the molecules detected are N-bearing species, in particular HCN, HNC, CN, NO, NS, PN, and NH. We used rotational diagrams to derive the density and rotational temperature of the different molecular species detected. We introduced an iterative method that allows us to take moderate line opacities into account.
[Results] We have found that IRC +10420 presents high abundances of the N-bearing molecules compared with O-rich evolved stars. This result supports the presence of a N-rich chemistry, expected for massive stars. Our analysis also suggests a decrease of the C/C ratio from ≳ 7 to ∼3.7 in the last 3800 yr, which can be directly related to the nitrogen enrichment observed. In addition, we found that SiO emission presents a significant intensity decrease for high-J lines when compared with older observations. Radiative transfer modeling shows that this variation can be explained by a decrease in the infrared (IR) flux of the dust. The origin of this decrease might be an expansion of the dust shell or a lower stellar temperature due to the pulsation of the star.
Publisher version (URL)https://doi.org/10.1051/0004-6361/201527688
URIhttp://hdl.handle.net/10261/185935
Identifiersdoi: 10.1051/0004-6361/201527688
e-issn: 1432-0746
issn: 0004-6361
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