J/A+A/704/A28 Disc Instability Population SYnthesis (DIPSY) II. (Schib+, 2025)
DIPSY: A new Disc Instability Population SYnthesis.
II. The populations of companions formed through disc instability.
Schib O., Mordasini C., Emsenhuber A., Helled R.
<Astron. Astrophys. 704, A28 (2025)>
=2025A&A...704A..28S 2025A&A...704A..28S (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Exoplanets ; Models
Keywords: planets and satellites: dynamical evolution and stability -
planets and satellites: formation -
planets and satellites: gaseous planets - protoplanetary disks -
planet-disk interactions
Abstract:
Disc instability (DI) might provide an explanation for the formation
of some observed exoplanets. At the same time, our understanding of
this top-down formation mechanism remains limited. Existing studies
have made strong simplifications, and the predicted population is
poorly known.
We aim at overcoming several limitations and produce a more advanced
synthetic population of companions formed via DI that can be used for
quantitative statistical comparisons with observations, and to make
predictions for future surveys.
We applied the global end-to-end model described in Paper I of this
series to perform a population synthesis of companions formed via DI.
By using initial conditions compatible with both observations and
hydrodynamical simulations, and by studying a large range of primary
masses (0.05M☉ to 5M☉), we can provide quantitative
predictions of the outcome of DI.
In the baseline population, we find that ∼10% of the discs fragment,
and about half of these end up with a surviving companion after
100Myr. Based on their mass, 75% of the companions are in the brown
dwarf regime, 15% are low-mass stars, and 10% planets. At distances
larger than ∼100AU, DI produces planetary-mass companions on a low
percent level. Inside of 100AU, however, planetary-mass companions
are very rare (low per mill level). The average companion mass is
∼30MJup scaling weakly with stellar mass. Very few companions of all
masses reside inside of 10AU; outside this distance, the distribution
is approximately flat in log-space. Eccentricities and inclinations
are significant, with averages of 0.4 and 40°. In systems with
surviving companions, there is either one (80%) or two (20%)
companions. The fraction of surviving synthetic brown dwarfs is
consistent with observations, while that of planets is lower than
observed. Most of the initial fragments do not survive on a Myr
timescale; they either collide with other fragments or are ejected,
resulting in a population of free-floating objects (about 1-2 per
star). We also quantify several variant populations to critically
assess some of our assumptions used in the baseline population.
DI appears to be a key mechanism in the formation of distant
companions with masses ranging from low-mass stars down to the
planetary regime, contributing, however, only marginally to planetary
mass objects inside of 100AU. Our results are sensitive to a number
of physical processes, which are not completely understood. Two of
them, gas accretion and clump-clump collisions, are particularly
important and need to be investigated further. Magnetic fields and
heavy-element accretion have not been considered in our study,
although they are also expected to affect the inferred population. We
suggest acknowledging the importance of the gravito-turbulent phase,
which most protoplanetary discs experience. Exploring hybrid DI-core
accretion scenarios, and quantitative comparisons of theory and
observations will improve our understanding of star and planet
formation.
Description:
We performed a large-scale population synthesis study of companion
formation in the DI paradigm, applying the model described in Paper I
(Schib et al., 2025A&A...704A..27S 2025A&A...704A..27S). By combining descriptions of
physical processes in star and disc formation and evolution (e.g.
infall, disc structure, and stellar evolution), disc GI and
fragmentation, multiple clump formation, evolution through gas
accretion, interior structure evolution with second collapse, clump
orbital migration, clump thermal and tidal destruction, as well as
N-body interactions with collisions and many other effects, we were
able to globally follow companion formation by DI and quantitatively
predicted occurrence rates and physical properties of companions
around stars from 0.05M☉ to 5M☉.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
list.dat 55 11 List of numerical data for the baseline
population DIPSY-0 for different times files
files/* . 11 Individual numerical data for the baseline
population DIPSY-0 for different times files
--------------------------------------------------------------------------------
Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 A19 --- FileName Name of the table in subdirectory files
21- 48 A28 --- Title Title of the table
49- 55 E7.2 yr Time Time
--------------------------------------------------------------------------------
Byte-by-byte Description of file: files/*
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 I5 --- Id System id
9- 18 E10.5 Msun Mp Primary mass
25- 34 E10.5 Mjup Mc Companion mass
41- 50 E10.5 au sma Semi-major axis
57- 66 E10.5 --- ecc Eccentricity
73- 82 E10.5 deg Incl Inclination
90- 92 I3 --- Comp Companion id
97- 98 I2 --- Ncomp Number of active companions in system
105-114 E10.5 --- rweight Relative weight of bin according to
xi(log(m)) (1)
--------------------------------------------------------------------------------
Note (1): Chabrier-2005-IMF, see Sect.5.2.2 of the paper.
--------------------------------------------------------------------------------
Acknowledgements:
Oliver Schib, oliver.schib(at)unibe.ch
(End) Patricia Vannier [CDS] 03-Oct-2025