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Imaging [CI] around HD 131835: reinterpreting young debris discs with protoplanetary disc levels of CO gas as shielded secondary discs
- Source :
- Scopus-Elsevier, Monthly Notices of the Royal Astronomical Society, Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP): Policy P-Oxford Open Option A, 2018, ⟨10.1093/mnras/sty2923⟩
- Publication Year :
- 2018
- Publisher :
- Oxford University Press (OUP), 2018.
-
Abstract
- Despite being $>10$Myr, there are $\sim$10 debris discs with as much CO gas as in protoplanetary discs. Such discs have been assumed to be "hybrid", i.e., with secondary dust but primordial gas. Here we show that both the dust and gas in such systems could instead be secondary, with the high CO content caused by accumulation of neutral carbon (C$^0$) that shields CO from photodissociating; i.e., these could be "shielded secondary discs". New ALMA observations are presented of HD131835 that detect $\sim 3 \times 10^{-3}$ M$_\oplus$ of C$^0$, the majority 40-200au from the star, in sufficient quantity to shield the previously detected CO. A simple semi-analytic model for the evolution of CO, C and O originating in a volatile-rich planetesimal belt shows how CO shielding becomes important when the viscous evolution is slow (low $\alpha$ parameter) and/or the CO production rate is high. Shielding by C$^0$ may also cause the CO content to reach levels at which CO self-shields, and the gas disc may become massive enough to affect the dust evolution. Application to the HD 131835 observations shows these can be explained if $\alpha \sim 10^{-3}$; an inner cavity in C$^0$ and CO may also mean the system has yet to reach steady state. Application to other debris discs with high CO content finds general agreement for $\alpha=10^{-3}$ to $0.1$. The shielded secondary nature of these gas discs can be tested by searching for C$^0$, as well as CN, N$_2$ and CH$^{+}$, which are also expected to be shielded by C$^0$.<br />Comment: accepted to MNRAS
- Subjects :
- Planetesimal
FOS: Physical sciences
Shields
chemistry.chemical_element
Astrophysics
circumstellar matter
01 natural sciences
law.invention
law
0103 physical sciences
Shielded cable
planetary systems
010303 astronomy & astrophysics
ComputingMilieux_MISCELLANEOUS
[PHYS]Physics [physics]
Earth and Planetary Astrophysics (astro-ph.EP)
Physics
Accretion (meteorology)
010308 nuclear & particles physics
Astronomy and Astrophysics
Planetary system
chemistry
13. Climate action
Space and Planetary Science
Electromagnetic shielding
Content (measure theory)
accretion, accretion discs
[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Carbon
Astrophysics - Earth and Planetary Astrophysics
Subjects
Details
- ISSN :
- 13652966 and 00358711
- Database :
- OpenAIRE
- Journal :
- Monthly Notices of the Royal Astronomical Society
- Accession number :
- edsair.doi.dedup.....4a93280203d85ad369df10c363985678