J/MNRAS/469/521 CO, C & O gas content of debris discs predictions (Kral+, 2017)
Predictions for the secondary CO, C and O gas content of debris discs from the
destruction of volatile-rich planetesimals.
Kral Q., Matra L., Wyatt M.C., Kennedy G.M.
<Mon. Not. R. Astron. Soc., 469, 521-550 (2017)>
=2017MNRAS.469..521K 2017MNRAS.469..521K (SIMBAD/NED BibCode)
ADC_Keywords: Models ; Stars, masses ; Carbon monoxide
Keywords: accretion, accretion discs - hydrodynamics - interplanetary medium -
planetary systems - planet-disc interactions - circumstellar matter
Abstract:
This paper uses observations of dusty debris discs, including a
growing number of gas detections in these systems, to test our
understanding of the origin and evolution of this gaseous component.
It is assumed that all debris discs with icy planetesimals create
second generation CO, C and O gas at some level, and the aim of this
paper is to predict that level and assess its observability. We
present a new semi-analytical equivalent of the numerical model of
Kral et al. (2016MNRAS.461.1614K 2016MNRAS.461.1614K) allowing application to large
numbers of systems. That model assumes CO is produced from
volatile-rich solid bodies at a rate that can be predicted from the
debris discs fractional luminosity. CO photodissociates rapidly into C
and O that then evolve by viscous spreading. This model provides a
good qualitative explanation of all current observations, with a few
exceptional systems that likely have primordial gas. The radial
location of the debris and stellar luminosity explain some
non-detections, e.g. close-in debris (like HD 172555) is too warm to
retain CO, while high stellar luminosities (like η Tel) result in
short CO lifetimes. We list the most promising targets for gas
detections, predicting >15 CO detections and >30 CI detections with
ALMA, and tens of CII and O I detections with future far-IR missions.
We find that CO, CI, CII and OI gas should be modelled in non-LTE for
most stars, and that CO, CI and OI lines will be optically thick for
the most gas-rich systems. Finally, we find that radiation pressure,
which can blow out CI around early-type stars, can be suppressed by
self-shielding.
Description:
We tested our new gas model developed for beta Pic in Kral et al.
(2016MNRAS.461..845K 2016MNRAS.461..845K) on all systems with gas detected to check
whether our model could explain all observations so far and then give
predictions concerning future observations. The model assumes that CO
gas observed around debris disc stars is secondary and is created from
the solid volatile-rich bodies residing in the parent belt of the
discs. Once CO gas is created, it photodissociates into carbon and
oxygen atoms, which viscously spread to form an atomic accretion disc
inside the parent belt and a decretion disc outside. The model
calculates the ionization fraction of carbon, the gas temperature and
population levels at different radial locations in the disc. It also
takes into account CO self-shielding against photodissociation and CI
self-shielding against photoionization. When computing the
detectability, we take into account NLTE effects and optical thickness
of lines.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablec1.dat 74 190 *Description of the 190 stars used in this study
tablec2.dat 83 188 Model predictions for the 188 stars used in
this study
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Note on tablec1.dat: HD 95418 and HD 139006 not in tablec2.dat.
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Byte-by-byte Description of file: tablec1.dat
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Bytes Format Units Label Explanations
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1- 12 A12 --- Name Star name
15- 20 F6.2 pc d Distance to Earth
22- 26 I5 K Teff Star effective temperature
29- 35 F7.4 Lsun L* Star luminosity
37- 43 E7.3 --- LIR/L* Dust fractional luminosity
45- 50 F6.2 AU R0 Location of the belt
52- 58 E7.3 Jy F60 Flux at 60um
60- 66 E7.3 Jy F160 Flux at 160um
68- 74 E7.3 Jy F610 Flux at 610um
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Byte-by-byte Description of file: tablec2.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- Name Star name
13- 19 E7.3 Msun MCO CO mass
21- 27 E7.3 W/m2 FCO1300 CO flux at 1.3mm
29- 35 E7.3 W/m2 FCO870 CO flux at 870um
37- 43 E7.3 Msun MCI CI mass
45- 51 E7.3 W/m2 FCI610 CI flux at 610um
53- 59 E7.3 Msun MCII CII mass
61- 67 E7.3 W/m2 FCII158 CII flux at 158um
69- 75 E7.3 Msun MOI OI mass (with extra water, see Section 6.2)
77- 83 E7.3 W/m2 FOI63 OI flux at 63um (with extra water)
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 30-Mar-2020