ABSTRACT
Debris disks are tenuous, dusty belts surrounding main sequence stars generated by collisions between
planetesimals. HD 206893 is one of only two stars known to host a directly imaged brown dwarf orbiting
interior to its debris ring, in this case at a projected separation of 10.4 au. Here we resolve structure00
in the debris disk around HD 206893 at an angular resolution of 0. 6 (24 au) and wavelength of 1.3 mm
with the Atacama Large Millimeter/submillimeter Array (ALMA). We observe a broad disk extending+13
from a radius of < 51 au to 194 2 au. We model the disk with a continuous, gapped, and double
power-law model of the surface density profile, and find strong evidence for a local minimum in thesurface density distribution near a radius of 70 au, consistent with a gap in the disk with an inner+8+11radius of 63 16 au and width 31 7 au. Gapped structure has been observed in four other debris disks– essentially every other radially resolved debris disk observed with sufficient angular resolution andsensitivity with ALMA – and could be suggestive of the presence of an additional planetary-masscompanion.
1. INTRODUCTION

bris disks are a common outcome of the star and planet formation process, and serve as a signpost of mtary systems. Bright debris disks are observed around some 25-30% of main sequence stars (Trilling et al.
eau et al. 2014; Montesinos et al. 2016; Sibthorpe et al. 2018). The true incidence is likely to be higher, sintivity of current observations limits our ability to detect debris disks to those systems that are at least an or残骸円盤内を褐⾊矮星が公転している系(この系を含め, 2例のみ)；距離 40.8 pc; 中⼼星はF5V型
Hershell 70 μm画像 plus SED解析 ⇨ Rinner ≃ 50 AUは推定されていた; 褐⾊矮星伴星がL5-L9型, ~12 Mjup, age ~ 50 Myrsも推定されていた.
分光観測(Grandjean+2019)から第3の天体(惑星？BD?)の存在も⽰唆されていた.

Figure 1. (Left) Naturally weighted ALMA image of the 1.3 mm continuum emission from the HD 206893 system. (Right)
Same image with a visibility-domain taper of 200 k applied to bring out the large-scale structure of the source. In both panels,
contour levels are [-2,2,4,6]⇥ , where is the rms noise in the image: 5.5 µJy beam 1 for the naturally weighted image and1
6.0 µJy beam
for the image with the taper. The hatched ellipse in the lower left corner represents the size and orientationof the synthesized beam: 0.00 71⇥0.00 58 for the naturally weighted image and 0.00 9⇥1.00 0 for the tapered image. The star symbol
represents the pointing center of the observations, i.e., the expected position of the star including a proper motion correction,and the dot represents the position of the brown dwarf companion directly imaged by Milli et al. (2017).

021 , M. Bonavita11 , B. Lavie22, 12 , A. Zurlo10, 13 , J. Olofsson8, 14 , A. Boccaletti2 ,A. Vigan10 , R. Galicher2 , J.models
Hagelberg
中⼼星の諸元(Saumon & Marley 2008; Madhusudhan et al. 2011;
M0-M5
β/γ/VL-G dwarfs 1
8
1
15
25,
10
22
8
中⼼星と伴星の褐⾊矮星の諸元：先⾏研究からMorleyet al. 2014; Baudino et al.12015). The recent work by
F. Cantalloube , D. MouilletLiu ,et al.G.
Chauvin , F.-J. Hambsch Parameter, M. Langlois, S. Udry , 8T. M6-M9
Henning , J.-L. Beuzit ,(2016) focuses on a sample of substellar objects with
Value
Ref.
L0-L5
known ages and distances and has16
confirmed that low-gravity 24
obL6-L9 18
12
16
8,
17
22
18 ,
V (mag)6.69
Hipparcos
A&A 608, A79 (2017)
jects
populate
an area of NIR colour–magnitude
diagramthatisC.
Mordasini
,
P.
Lucas
,
F.
Marocco,B.
Biller,J.
Carson,A.
Cheetham,E.
Covino,V.
De
CaprioT0-T5
Astronomy
B V (mag)
0.439
Hipparcos
DOI: 10.1051/0004-6361/201731145
distinct from the area occupied by field brown&
dwarfs of the same
10
T6-T8
V I (mag)
0.51
Hipparcos
1
8
7
19
8
8
20
2
spectral type. This study also claims that low-masscompanions>T8
Astrophysics
J
(mag)
5.869
±
0.023
2MASS
A. Delboulbe , M.might
Feldt, J.distinct
Girard, isolated
N. Hubin, HA.-L.
Maire, A. Pavlov , C. Petit , D. Rouan ,have properties
from those of
low-mass(mag)
5.687 ± 0.034 2MASS
objects, while they should have similar gravity, hinting that other(mag)
5.593 ± 0.021222MASS
21 ,K and12parameters might also shape the NIR R.
SED ofRoelfsema
substellar objects.
F.
Wildi
Parallax (mas)24.59 ± 0.26
Gaia DR1
In this light the recent discovery of the very red close-in comTable 1. Stellar parameters of HD 206893.

SpeXprism lib.

c ESO 2017

UScoCTIO 108B
Best et al. 2015

A&A 608, A79 (2017)

CD-352722B

1RXS1609b1In-depth study of moderately young but extremely red, very dusty(Affiliations can be found after the references)
substellar companion HD 206893B

MJsµ↵ (mas yr )94.236 ± 0.044 Gaia DR1
panion HD 206893B (or HIP 107412 b) identified by Milli et al.
1µ (mas yr )0.164 ± 0.031 Gaia DR1(2017), o↵ers the opportunity to explore the physical proper1
RV (km s )–11.92 ± 0.32 this paper? substellar companion
ties of a relatively young mid-L dwarf
1
U (km s )–20.15 ± 0.23 this paper
and to try to understand its atypical properties. We carried out
V (km s 1 )–7.40 ± 0.15,
this paper
1,??
2
1
3
4,
26
2
3
5,
23
a
systematic
study
of
the
debrisdisc-bearing
host
star,
including
1
P. Delorme, T. Schmidt , M. Bonnefoy , S. Desidera , C. Ginski , B. Charnay , C. Lazzoni , V. Christiaens ,W (km s )–3.40 ± 0.26
this paper
new observations,to determine
its age and metallicity(Sect.
2).
6
3
7
8,
9
3
1
1
5,???
S. Messina , V. D’Orazi , J. Milli , J. E. Schlieder , ThroughR. Gratton, L. Rodet, A.-M.
Lagrange, O. Absil
T e↵ (K)6500 ± 100
this paper
the SpHere
INfraredsurveyfor Exoplanets(SHINE) ,22, 12 , A. Zurlo10, 13 , J. Olofsson8, 14 , A. Boccaletti2 ,log g4.45 ± 0.15
this paper
A. Vigan10 , R. Galicher2 , J. Hagelberg1 , M. Bonavita11 , GTO
B. Lavie
large programmewith SPHERE, we obtained additional[Fe/H]+0.04 ± 0.02
this paper
15 , M. observations
22 , T. under1,
resolvedof, thecompanion
very8 ,stable
obF. Cantalloube8 , D. Mouillet1 , G. Chauvin1 , F.-J. Hambsch
Langlois25, 10
S. Udry
Henning
J.-L. Beuzit
EW Li (mÅ)
28.5 ± 7.0
this paper
8, 17 , A. Cheetham
including 22
theC. Mordasini12 , P. Lucas16 , F. Marocco16 , B. Biller24 , J.serving
Carsonconditions,, E.low-resolution
Covino18 , V.spectroscopy
De Caprio18 ,A(Li)2.38 ± 0.10
this paperthat we present 8in Sect. 3. Theseobservations
confirm
that
1
8
7
19
8
20
2
A. Delboulbe , M. Feldt , J. Girard , N. Hubin HD, A.-L.
Maire, A.reddest
Pavlov, C. substellar
Petit , D.
Rouan
[Ba/Fe]0.20 ± 0.20
this paper
206893B
is theknown
object,even, red21
22
R. Roelfsema der, and
F. Wildi
v sin i (km s 1 )32 ± 2
this paperin NIR
than 2M1207 b (admittedly by a slight margin of aplog LX /Lbol–4.80 ±
this paper
proximately, Chauvin et al. 2004) or the recently discovered(Affiliations can be foundafter the1references)log RHK–4.77 ±
this paper
2MASS J223624+4751 (Bowler et al. 2017). Section 4 focusesProt (d)0.996 ± 0.003 this paper
the comparison
HD 206893B with known red L dwarfs.
Received 10 May 2017on/ Accepted
22 July of2017
Age (Myr)
250+450
this paper
Section 5 is dedicated to the characterisation of the atmospheric
これが主題の200
Mstar (M )1.32 ± 0.02
this paper
properties of this atypical young substellar companion, through
ABSTRACT
Rstar (R )1.26 ± 0.02
this paper
atmosphere and substellar evolution models. In Sect. 6 we detail
褐⾊矮星i (deg)30 ± 5this paper
theconstraints
be isderived
from
theH,observed
Fig. 3. Residual images of HD 206893B in
Y, orbital
J, H, and K
bands in linear thatscale. can
The scaleidentical in
Y, J, andbut is 4 timesKewider in K toContext. The substellar companion HD 206893b
hasrecently
been
discoveredbydirectimagingof
its
disc-bearing
host
star
with
the
Spectroaccommodate the brighter speckle residuals
and brightercompanionin theIRDIS K-bandand
image.
plerianmotionof thecompanion
determine that this detected
Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument.
companion cannot shape the colours
observeddisc alone.
Aims. We investigate the atypical properties3.0×10of the companion, which has the reddest near-infraredamong
all known substellar objects,presence of the brown dwarf companion would imply a maxiK1 and K2 filters after TLOCI-ADI reduction. No companion
either orbiting a star or isolated, and we provide a comprehensive characterisation of the host star-disc-companion
system.
was detected even though our detection limits reach respectively
mum
RV semi-amplitude only of the order of 0.15 km s 1 (from00
2.5×10
Methods. We conducted a follow-up of the companion with adaptive optics imaging and spectro-imaging
withof SPHERE,
and a multi-instrument
14.5 and 15.2 mag
contrast for separationsof 0.3 and 0.5
thefamily of orbits fitting the available astrometric data, see
2.
Host
star
properties(seeandFig. 5).
These detection
limits areat
computed
for a2.25
companfollow-up of its host star. We obtain a R = 30 spectrum from 0.95 to 1.64 µm of the companion
additional
photometry
2.11 andµm.
2.0×10Sect. 6.1), which is smaller than our current uncertainties on theion with a uniform contrast and are hence conservative because
We carried out extensive atmosphere model fitting for the companions The
and the
host
star
in
order
to
derive
their
age,
mass,
and
metallicity.
thedeep
absorption
bands
in
the
spectraofreal
substellarcomdetermination of the properties of the substellar object RV of the system and is hence neglected in the kinematic analyResults. We found no additional companion1.5×10
in the system in spite of exquisite observing conditions
resultinginthe
sensitivity
6 MJupdi↵erential(2 MJup )panionsslightly
improvesensitivity toofspectralaround the star depends
sensitivelyontheadoptedstellarpasis.
00
methods (seethe
e.g.possible
Rameau etKeplerianal. 2015). Foran ageof These spectroscopic data also show that HD 206893 is not a
at 0.5 for an age of 300 Myr (50 Myr). We detect orbital motion over more than one year imaging
and characterise
orbits.
We
rameters, and especiallystellarage. Unfortunately,
theage of limits
300on
Myr
(50
limits correspondto detectioninspectroscopic
binary.
1.0×10constrain the age of the system to a minimumof 50 Myr and a maximum of 700 Myr, and determine
thatMyr)thethese
host-star
metallicity
is nearly
solar.
mass, assuming
Bara↵e et al.
(2003) hot-startevolution models, The resulting space velocities of the system are U, V, W =mid-Fstars likeindicates
HD 206893
isdifficultto determine.
The comparisonand photometry to model
atmospheresthat
theparticularlycompanionisanextremely
dusty late L
00 of the companion spectrum5.0×10
ofrespectively
6
and
8
M
(2
and
3
M
).
Jup
Jup
On
the
one
hand,
their
evolutionisslow,
makingisochrone
fit20.15 ± 0.23, 7.40 ± 0.15, 3.40 ± 0.26 km s 1 . We used
dwarf, with an intermediate gravity (log g ⇠ 4.5–5.0) which is compatible with the independent age estimate of the system.
ting Mnot very
constraining
when
close
to is
thealsomain
sequence.with
Ona rangethese kinematics to investigate the possible membership ofConclusions. Though our best fit corresponds to0 a brown dwarf of 15–30
Myr,
our re-detection
analysiscompatible
Jup aged 100–3003.3.
No discin SHINE
data
thetoother
the
based
on rotation
and activity
are HDis 206893 to a young moving group using the BANYAN2
1.0
1.2object
1.4
1.6 indicatorsof masses and ages going from a 50 Myr 12 MJup planetary-mass
a 50hand,
MJup Hyades-age
brown
dwarf.
Even though
this companion
λ(µm)
We
initially
believedthat
ourK-bandIRDIS
SHINE
data showed
more
uncertain
for verycolderstars
due thatto thevery thinconveconline tool (Gagné et al. 2014b). Assuming that HD 206893 isextremely red, we note that it is more probable that it has an intermediate
gravityrather than
than thelowgravityisoften
associatedvery
a re-detection of the faint structure highlighted as witha probable
Fig.
4.
Extracted
spectrumofHD
206893B
through
TLOCI-ADI.
envelope.
et disc,al. (2017)
an
age
range
youngerthan 1 Gyr (see below), we obtain a 13.5% probabilred L dwarfs. We also find that the detected companion cannot shape thetive
observedouterMilli
debrishintingadopted
or extended
severaladditional
planetary
disc
detection
inthatthe oneH broad-band
IRDIS
imagesanalysedby+200
0.2–2.1
Gyr,while
Galicheretal.
(2016)
adopted200
Myrmass objects in the system might be necessary to explain the position of the disc inner edge. Milli et al. (2017). However, given the faintness
ity for membership in the Argus association and 86.5% for the
100 of this signal,
wecheckedwhethertheobserved
extendedstructurewas
indeedfrom X-ray and UV luminosity. Our approach is based on a young field.
the SHINE
Consortium– also
show that thebest
spectral resolution
an astrophysicalsignal or aninteractions
observational bias. Instead of deKey words. brown dwarfs – planets and withinsatellites:
atmospheres
techniques:highangular–severalplanet-disk
comprehensive
evaluationofage
indicators
to the actual paralfidelity, i.e. the ability to retrieve, within the error bars, the spec- rotating our sequence of images accordingfollowing
methods
described
in Desideraal. (2015).
Spectroscopic
trum of an injected fake companion isthebest whenusing only
ADI, lactic
angle of theetobservations,
we applieda de-rotation in the
Jupparameters2.2. Spectroscopic
while the best point-source sensitivityand
is achievedbycombining
opposite
direction,
whichshoulde↵ectively
kill any astrophysphotometric datasets were acquired to gather the required
ADI and SDI. When we probed the possible presence of addi- ical signal. Since the same fuzzy extended structure was still
information.
1. Introduction
the atmospheres
extrasolar
planets(Zurlo et al.
tional companions in the system we used
TLOCI
and PCA using ofvisible,it meant it giant
was causedby an observationalbias,2016;
probJup
Jupthe FEROS spectrograph on
The star was observed with

Young/Dusty/VL-G

14
HN Peg B

Received 10 May 2017 / Accepted 22 July 201716

Mace et al. 2013
2M1207b51 Eri b

これが主題の褐⾊矮星

18

ABSTRACTInterstellar (R=3.1)
0.5 µm forsterite

HIP 107412b

20-1
0 star 1with the
2 Spectro3
Context. The substellar companion HD 206893b has recently been discovered by direct imaging of its disc-bearing
host
J -K1

Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument.
Fig. 7. Placement of the IRDIS photometry of HD 206893B (HIP 107412
Aims. We investigate the atypical properties of the companion, which has the reddest near-infrared colours
among
all known
substellar
to thereddening vector
caused by forsterite
grains withobjects,
mean size 0.5 µm
parameter R = 3.1).
either orbiting a star or isolated, and we provide a comprehensive characterisation of the host star-disc-companion system.
Methods. We conducted a follow-up of the companion with adaptive optics imaging and spectro-imaging with50SPHERE,
and a multi-instrument
No correlated noise
follow-up of its host star. We obtain a R = 30 spectrum from 0.95 to 1.64 µm of the companion and additional photometry at 2.11 and 2.25 µm.
40
We carried out extensive atmosphere model fitting for the companions and the host star in order to derive their age,mass, and metallicity.
Results. We found no additional companion in the system in spite of exquisite observing conditions resulting in sensitivity to 6 MJup (2 MJup )30
at 0.5 for an age of 300 Myr (50 Myr). We detect orbital motion over more than one year and characterise the possible Keplerian orbits. We
constrain the age of the system to a minimum of 50 Myr and a maximum of 700 Myr, and determine that the host-starmetallicity is nearly solar.
20
The comparison of the companion spectrum and photometry to model atmospheres indicates that the companion is an extremely dusty late L
10dwarf, with an intermediate gravity (log g ⇠ 4.5–5.0) which is compatible with the independent age estimate of the system.
0 is also compatible with a range
Conclusions. Though our best fit corresponds to a brown dwarf of 15–30 M aged 100–300 Myr, our analysis
M5
L0
L5
T0
T5
Y0
of masses and ages going from a 50 Myr 12 M planetary-mass object to a 50 M Hyades-age brown dwarf. Even thoughthistypecompanion isSpectral
Bonnefoy et al. 2016; Vigan et al. 2016; De Rosa et al. 2016;2008 November 13 as part of the preparatory program for the
The discovery of young
giant planets
high- Chilcote
extremely
red,extrasolar
we notethatfound
it withis moreprobable
that
it
has
an
intermediate
thantheset-up
very
low gravity
that isof often
associated
with
very
et al.
2017).and young groups membership
SPHEREgravity
GTO survey. rather
Details on the
instrument
and reFig.
8.
Comparison
theNIR
spectrumandphotometryofHD
206893b to
2.1.
Kinematic
analysiscontrast imaging techniques (Chauvin et al. 2004; Marois et al.
ductionprocedure
are
given
in
Desideraetal.
(2015).
These previous
studies have shownthat while
young theexo- observed outer debris disc, hinting correlationnoiseorof theIFS spectrum;on the right, itplanetary
does.
red
dwarfs.
WeRameaualsoet al.findthecompanion
cannot
shape
that
one
severaladditional
2008; L
Lagrange
et al. 2010;2013;that
Delormeet al.detected
HDplanets
206893haveis included
in
Gaia
DR1
and
we
adoptedGaia
a spectral signature quite distinct from field brownAs done in our previous investigations (see e.g. Vigan et al.
2013; Bailey et al. 2014; Macintosh et al. 2015; Gauza et al.DR1 trigonometricparallax and proper motion (using a corre- 2016, for GJ 758 B) we derived spectroscopic parameters usdwarfsofequivalente↵ectivetemperature,theyhave many atmass
objectsinthesystemmight
benecessary
toexplainthepositionof the disc inner edge.
032015) o↵ers the opportunity to directly probe the proper-sponding distance of 40.6
pc; see Table 1),
unlikeMilli et al. ing
mospheric properties in common with isolated brown dwarfsthe code MOOG by Sneden (1973, 2014) and the Kurucz
s

−16

−16

−16

−16

−17

this combined “ASDI” approach with IFS data. Figure 3 shows
the resulting residuals maps in the Y, J, H, and K bands. The
Y, J, and H are a stack of the IFS channels after TLOCI-ASDI
reduction that have a wavelength corresponding to each photometric band, while the K-band image is a stack of the IRDIS
A79, page 6 of 25

ably the wind extending the coronagraphic halo along a privileged direction. As a sanity check, we also applied this procedure to the H-band data analysed by Milli et al. (2017), and weshow that as expected for an astrophysical disc signal, applying
an incorrect de-rotation angle destroys the signal in this case.
+0.5
0.4

G

Flux (Wm2µm−1)−16

PSO057+15

ULASJ2227-00

o↵set of the disk center from the star position (and indeed, the assumption is verified a posteriori by the lack of
2. Azimuthallyradial intensity
profileof thenaturally
weighted
image,
deprojectedalongcontours
2 elliptical1
residuals after Figure
the best-fit
model isaveraged
subtracted
from thedata).
We
assumeadust
opacityof
2.3
cmg(Beckwith
Nederlander
et andal. position angle of 60 . The blue shaded region
assuming a circular geometry and an inclination to the lineof sight of 45
et al. 1990), yielding
opticallythinerror
emissiontheall bin,of themodelswithindeviation
the parameter
space
byrepresents
the standardof the formean
fordusteach inradialwhere
the standard
is calculated
for explored
all pixels within
the MCMC chains.
densitytemperaturearethedegenerate
for opticallyemission,
we assume
that
these
the bin Since
and thendividedandby thesquare root of
number of beams
sampled. thin
The sizeof the synthesized
beam
is indicatedgray Gaussian
marked “Beam.”
The central
10.4 au projected
206893B (Milli
et al. 2017)
large grains arebyintheblackbody
equilibriumwith thestar andseparation
calculateof aHD
dust
grain
temperature
ofis marked with avertical dashed line.
✓
◆1/4
L⇤
Tdust =
(1)
1
2
The surface brightness of the central peak, 19.7
16⇡± 5.5
R µJy beam , is approximately consistent with the expected
flux density of 12.6 µJy for a star with a temperature of 6500 K and radius 1.26 R (Delorme et al. 2017), when
where L⇤ is thebolometric luminosity
the star, (in isthecase,Stefan-Boltzmann
constant,
andprovides
R is thethedistanceof theof
approximating
the star as aofblackbody
this
the systematic flux
uncertainty
largest source
dust grain fromerror
theincentral
star. We adopt
stellarluminosityof atL⇤millimeter= 2.83 L wavelengths
for HD 206893
et al. 2017).
the comparison).
Whilea thepropertiesof stars
are not(Delorme
well understood,
and can
We assumed several
possiblefunctional
for thedensityof the disk;
the functional
forms
for thedeviate di↵erent
significantly
from theexpectedforms
blackbodyfluxsurface
for a varietyof reasons
includingchromosphericemissionandsurface densityflaring
are summarized(Cranmer etinal.Table
2013; 4.
White et al. 2018, 2019, 2020), this estimate provides a ballpark figure to guide ourinterpretation of the emission morphology. As we demonstrate in Section 4 below, there is a statistically significant
Nederlander et al.

1 https://github.com/kevin-flaherty/disk model3

aged radial intensity profile of the naturally weighted image, deprojected along elliptical contours
y and an inclination to the line of sight of 45 and position angle of 60 . The blue shaded region
r of the mean for each radial bin, where the standard deviation is calculated for all pixels within
the square root of the number of beams sampled. The size of the synthesized beam is indicatedd “Beam.” The 10.4 au projected separation of HD 206893 B (Milli et al. 2017) is marked with aof the central peak, 19.7 ± 5.5 µJy beam 1 , is approximately consistent with the expectedor a star with a temperature of 6500 K and radius 1.26 R (Delorme et al. 2017), whena blackbody (in this case, the systematic flux uncertainty provides the largest source ofWhile the properties of stars at millimeter wavelengths are not well understood, and canthe expected blackbody flux for a variety of reasons including chromospheric emission and
13; White et al. 2018, 2019, 2020), this estimate provides a ballpark figure to guide oursion morphology. As we demonstrate in Section 4 below, there is a statistically significant
Figure 3. Elliptically averaged visibility profile comparing the data (blue points) with the best-fit flat disk (red line), double
power-law with a gap (green line) and triple power-law (orange line) models. The top panel shows the real part of the visibilities
while the bottom panel shows the imaginary part of the visibilities. The visibilities have been deprojected assuming an inclinationof 44 and a position angle of 60 , the best-fit values for the double power-law model.

5.
DISCUSSION
Nederlander et al.

5.1. Disk Structure Constraints
by Grandjean et al. (2019), as well as the 30 ± 5 inclination of the stellar po
The results of our MCMC fits demonstrate
残骸円盤の全体像 that the HD 206893 disk is wellInterestingly,
theversionoftheGrandjeanetal.
(2019)
dynamical
MCMC
ana
+13
内径
<
51
AU；外径
~194
AU
(表の
)⇨
褐⾊矮星まわりの残骸円盤
R+
ΔR•
distribution extending from radii of < 51 au to 194 2 in au (this constraint on. (Left) Naturally weighted ALMA image of the 1.3 mm continuum emission from the HD 206893 system, withaとして最⼤(と⾔ってもサンプル数⼩)
fromdistribution
radialvelocity,
astrometry,stellarpropermotion,anddirectimaging
resul
00 k applied to bring out the large-scale
structure of the source.
(CenterLeft)
Fullresolution
model
image
for
a
of
R
=
R
+
R,
which
is
not
shown
in
Figure
8),
with
a
ga
out
in
Resolved
DebrisDiskaround206893Right) Model image sampled at thehowing the structure of the disk
with a stellar
flux
equal
to zero.HD(Centersame+5• ⽅位⻆⽅向平均操作は妥当だった.
+11ofcompanionof
45±
3
engths and orientations asinclination
the ALMA data, showing
thethebest-fit model
without a gap in the
middleof thedust
disk.and a mass of 10 4 MJup , though they
anda width of 31 7 symbols
au.• mmサイズのダストが中⼼There are no ≲statisticallysignificant (> 3
Table from
3.exhibiting
MCMC
Fitting
Results
esidual image after subtracting the modelthe data
in thevisibility domain. Contour levels andare as37 AUに存在しないと輝度分布を説明できな
1.
data
is
six
times
higher
than
when
they
do
not
includethestellarpropermotio
い.
Parameter
Flat Disk
Double Power Law
withwell
Gap
Triple Power Law
observationsaredescribed
by an azimuthally symmetric and circular distribBest FitMedianBest FitMedianBest FitMedianmayratio
be someinconsistency
intheability
of
their
model
to
reproduce
both
the
R
of the data (the brightest parts
of
the
dust
disk
are
approximately
atthePlanetesimal belt (邦訳は微惑星帯？)
R (au)
9
< 44
21
< 51
35
29
perhaps
providing
additional
supportforthepresenceofanothercompanionin
残骸円盤円盤⾯とのなす⻆が⼤きい可能性を排除できない.
out
local
(or
point-to-point)
spatialvariations
in
flux
of
&
50%
on
spatial
scale
•
R(au)
155
151
176
166
159
164
Log(M ) (M )
-1.66
1.63
-1.61
1.63
-1.74
1.74
cannotrule
outmutualinclination
for the star and brown dwarf companion, copl
⇠30
au or
F (µJy)16
19
17 larger.
18
14
15
PA ( )
66
63
60
59
60
63
When wecompareourderiveddisk size to the sample of spatially resolved disk
i( )
47
47
45
44
43
47
x( )
0.11
0.14
0.16
0.11
0.11
0.09
we
that theof R0.06for HD 206893
accordingto thedefinition
laid out i
y( )
0.05
0.04 note 0.04
0.03 value0.05
5.2.
Gap
DetectionandImplications
R
(au)
67
63
115 au. 32Of theirsample of ten F stars, only one (HR 8799) has a larger radi
R
(au)
31
pp1
-2.0
1.1
-2.7
1.2 between the best-fit models provide strong evid
The AIC andBIC
comparisonギャップ
pp2
4.7 that> 0.23
unusual 2.8 Boo 3.0
spectrumis in some
ways
more
consistent
with
an
A
star
spec
• 図2-4の解析から, R~63 AUに幅30+/-10AUのギャップが 存在することは確実
pp3-3.7
3.0 of 80 au.
thesurfacedensityneararadius
This
marks
the
fourthdetection
of
a
ra
Rt1
97
102
71
is therefore
amongthe73 largest
known
debrisdisks around F stars, although co(⇦ 古屋疑問— Gapの幅、こんなに⼤きいのはBDまわりの残骸円盤だから？)
Rt2
113
115
HD
107146(Riccietal.
2015;
Marinoetal.
2018),HD
15115(MacGregoretal.
• ギャップの「今の姿」を説明するためには, 惑星による形成が⾃然で, ガスの運
Ln prob-10733015.1 (Sepulveda-10732991.8et al. 2019).
-10732995.1
動, 化学進化によるみかけ上のギャップ形成説や磁気流体不安定性による形成
Note— The inner radius2019).
is unresolved inWhile
the models without
a gap,
so the best-fit sizevalue of 9is
au ornot
21 au is large,
thesample
there
are
only
a
coupleofotherdebrismakes
not meaningful. The upper limit of 44Our
au or 51 aumodel
represents the 99.7th
percentileseveralof the posterior simplifying assumptions that may or may not be説を積極的に⽀持する証拠はない.
distribution.
05
belts that have been imaged with sufficient resolution and sensitivity at millimeter
Figure 4. (Left) Naturally weighted ALMA image of the 1.3 mm continuum emission from the HD 206893 system, with ataper of 200 k applied to bring out the large-scale structure of the source. (Center Left) Full resolution model image for aflat disk showing the structure of the disk with a stellar flux equal to zero. (Center Right) Model image sampled at the samebaseline lengths and orientations as the ALMA data, showing the best-fit model without a gap in the middle of the dust disk.
(Right) Residual image after subtracting the model from the data in the visibility domain. Contour levels and symbols are as
in Figure 1.

a

in

disk

⇤

00

00

in,Gap
Gap

+14
11
+0.03
0.03
+6
6
+3
3
+2
2
+0.07
0.07
+0.06
0.06

a

a

+20
16
+0.03
0.02
+5
5
+3
3
+3
3
+0.07
0.09
+0.05
0.05
+8
16
+11
7
+1.1
0.8
+1.0
0.9
+16
17

a

+7
20
+18
14
+0.07
0.07
+5
6
+3
3
+3
3
+0.08
0.09
+0.11
0.07

+0.8
1.1

+1.3
1.0
+9
33
+8
7

5.3. N-body Simulations of the Star, Brown Dwarf, and Putative Planeteory on which
baseWidth
our andestimateof Varying
planetBrown
massDwarf
is fundamentallya 3-body result, but adding
Tablewe
5. GapDepth withParameters
ce of the brown dwarf (e↵ectively treating the central star as a low-µ binary system) makes they a 4-body problem. We therefore conducted N-body simulations with and without the brown
erify that the gap depth and width were not significantly a↵ected by the presence of the brown
whether the orbital properties of the brown dwarf have a detectable impact on the width of thee gravitational interaction between the star, brown dwarf, putative planet, and dust particles
he N-body software REBOUND (Rein & Liu 2012) with hybrid integrator MERCURIUS (Rein et al.
from a fixed to variable timestep when any particle comes within a certain distance of a massive
to be three Hill radii. We chose the fixed timestep to be 4% of the brown dwarf’s initial period,of every dust particle’s period when the simulation begins. Dust particles are treated in the test

y randomly distributed with a uniform distribution of semimajor axes between 8 and 158 au, aof eccentricity from 0 to 0.02, and a uniform distribution of inclination from 0 to 10 . We
cles, adequate to sample the 150 au span of the disk and recover smooth images of the final disk
We assumed a stellar mass of 1.32 M and a stellar radius of 1.26 R (Delorme et al. 2017). The
d on a orbit with semimajor axis 10.4 au and assumed to have a radius of 1.3 RJup . We assumed
3
MJup and a bulk density of 1.3 g cm . We placed the planet on a circular orbit at 80 au. We

(a)いくつかの銀河では, ⾮対称的なガス分布(必然的に⾮対称性のある星形成率分布) ⇨ CMZ全域にわたって離⼼率の⼤きい
楕円軌道となり, ~10 Myrはつづく爆発的星形成(b)それ以外び銀河では, 滑らかなガス分布(同, 星形成率分布)07

Table 2. Physics & Numerics Explored in This Paper (and Papers II & III)
Physics/Numerics§

Effects in FIRE-2 Simulations

Guidelines / Default Choice

Resolution:
Mon. Not. R. Astron. Soc. 000, 000–000 (0000)

Printed 13 November 2018

(MN LATEX style file v2.2)

Mass Resolution

4.1

Collisionless (DM/Stellar)
Force Softening
Gas Force Softening

4.2

FIRE-2 Simulations: Physics versus Numerics in Galaxy Formation

arXiv:1702.06148v2 [astro-ph.GA] 11 Nov 2018

1,2,3

4

Philip F. Hopkins , Andrew Wetzel †, Dušan Kereš , Claude-André FaucherCriteria
Giguère5 , Eliot Quataert6 , Michael Boylan-Kolchin7 , Norman Murray8Timestep, Christopher
C. Hayward9 , Shea Garrison-Kimmel1 , Cameron Hummels1 , Robert Feldmann6,10 ,1Paul Torrey11 , Xiangcheng Ma1 , Daniel Anglés-Alcázar5 , Kung-Yi Su1 , Matthew
Hydro MethodOrr ,1 vs. SPH)
(MFM
Denise Schmitz1 , Ivanna Escala1 , Robyn Sanderson1 , Michael Y. Grudić
, Zachary
Artificial Pressure 4
Hafen5 , Ji-Hoon Kim12 , Alex Fitts7 , James S. Bullock13 , Coral Wheeler1 , “Floors”
T. K. Chan ,Magnetic Fields,
Oliver D. Elbert13 , Desika Narayanan14?1

1 TAPIR, Mailcode 350-17, California Institute of Technology, Pasadena, CA 91125, USA
2 Carnegie Observatories, Pasadena, CA 91101, USA

3 Department of Physics, University of California, Davis, CA 95616, USA

Conduction, Viscosity
Metal Diffusion(sub-resolution mixing)

4.2
4.3

5
6
F
7.2 & F

Molecular Chemistry/Cooling

7&B

8 Canadian Institute for Theoretical Astrophysics, 60 St. George Street, University of Toronto, ON M5S 3H8, Canada

Low-Temperature Cooling(T ⌧ 104 K)

7&B

7 Department of Astronomy, The University of Texas at Austin, 2515 Speedway, Stop C1400, Austin, TX 78712, USA

10 Institute for Computational Science, University of Zurich, Zurich CH-8057, Switzerland
11 Department of Physics, MIT, 77 Massachusetts Avenue, Cambridge, MA 02139, USA

12 Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics, Stanford University, Stanford, CA, USA
13 Department of Physics and Astronomy, University of California, Irvine, CA 92697, USA
14 Department of Astronomy, University of Florida, Gainesville, FL 32611, USA

Submitted to MNRAS, February 2017

ABSTRACTThe Feedback In Realistic Environments (FIRE) project explores feedback in cosmological galaxy formation simulations. Previous FIRE simulations used an identical source code (“FIRE-1”) for consistency. Motivated by the development of more accurate numerics – including hydrodynamic solvers, gravitational softening, and supernova couplingalgorithms – and exploration of new physics (e.g. magnetic fields), we introduce “FIRE-2”, an updated numerical implementation of FIRE physics for the GIZMO code. We run a suite of simulations and compare against FIRE-1: overall,
FIRE-2 improvements do not qualitatively change galaxy-scale properties. We pursue an extensive study of numerics
versus physics. Details of the star-formation algorithm, cooling physics, and chemistry have weak effects, provided that
we include metal-line cooling and star formation occurs at higher-than-mean densities. We present new resolution criteria
for high-resolution galaxy simulations. Most galaxy-scale properties are robust to numerics we test, provided: (1) Toomre
masses are resolved; (2) feedback coupling ensures conservation, and (3) individual supernovae are time-resolved. Stellar
masses and profiles are most robust to resolution, followed by metal abundances and morphologies, followed by properties of winds and circum-galactic media (CGM). Central (⇠kpc) mass concentrations in massive (> L⇤ ) galaxies are
sensitive to numerics (via trapping/recycling of winds in hot halos). Multiple feedback mechanisms play key roles: supernovae regulate stellar masses/winds; stellar mass-loss fuels late star formation; radiative feedback suppresses accretion
onto dwarfs and instantaneous star formation in disks. We provide all initial conditions and numerical algorithms used.
Key words: galaxies: formation — galaxies: evolution — galaxies: active — stars: formation — cosmology: theory —methods: numerical

Irrelevant for dwarfs. Important for massive galaxies with hot halos.
SPH may suppress cooling & artificially allows clumpy winds to vent
Unimportant unless set too large, then prevents real fragmentation.
Double-counts “sub-grid” treatment of fragmentation with SF model
Weak effects on sub-galactic scales (dense gas, morphology, turbulent ISM)
(Not studied here, but in Su et al. 2017; effects in CGM could be larger)
Small effects on galaxy properties & dynamics,
but potentially important for abundance distributions of stars

Newer methods recommended
Do not use with
self-gravity based SF models
See Su et al. (2017)
Best practice depends
on numerical hydro method

Cooling:

6 Department of Astronomy and Theoretical Astrophysics Center, University of California Berkeley, Berkeley, CA 94720

9 Center for Computational Astrophysics, Flatiron Institute, 162 Fifth Avenue, New York, NY 10010, USA

Resolution criteria in§ 4.1.3 (Eq. 5-7)
Optimal range of valuesin § 4.2.2
Fully-adaptive softenings(matching gas) should be used
Standard limiters + Stellar (Eq. 12)+ Adaptive softening (Eq. 13)(Magneto)-Hydrodynamics:

4 Department of Physics, Center for Astrophysics and Space Science, University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA
5 Department of Physics and Astronomy and CIERA, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, USA

Most results robust after resolving the Toomre scale, some (e.g.
massive galaxy morphology) depend on resolved winds/hot gas
Irrelevant unless extremely small or very large values used,adaptive collisionless softenings require additional timestep limiters
Forcing fixed softening generally has no effect, unless too large,
then fragmentation & SF are artificially suppressed
Provided that standard stability criteria are met, this has no effect.
Additional limiters needed for stellar evolution & adaptive softening

No effect on galaxy properties or star formation (just a tracer).
Not important star formation criterion if fragmentation is resolved
Details have no dynamical effects because tcool ⌧ tdyn in cold gas
to opacity limit

May be relevant at [Z/H] ⌧ 3, can beimportant for observational tracers
Some needed to form cold clouds,

proﬁles. Figure 3 compares directly against observed disper-

Next, we further demonstrate that Latte’s dwarf galaxies

考慮していない現象

時間分解能

空間分解能

ガス塊を星に置き換える条件考慮した現象10結果(a)いくつかの銀河では, ⾮対称的なガス分布(必然的に⾮対称性のある星形成率分布) ⇨ CMZ全域にわたって離⼼率の⼤きい楕円軌道となり, ~10 Myrはつづく爆発的星形成

星形成率の⾯密度
Msun yr-1 kpc-2

ガスの⾯密度Msun pc-2

天の川のCMZと⽐べるとき,
R<145 pc を⾒てください。
( | l | ≲ 1∘ at d of ~8.2 kpc)

星形成率の⾯密度
Msun yr-1 kpc-2

ガスの⾯密度Msun pc-2

どちらのタイプの渦巻銀河でも⻑寿命のリング構
造は確認されず(b)それ以外び銀河では, 滑らかなガス分布(同, 星形成率分布)

緑は上のタイプの銀河,
茶⾊は下のタイプの銀河
古屋納得しきれていない点「滑らか」と⾔われても緑と茶⾊の銀河での差は, ⽬でみた範囲ではわからない(定量化してほしい).
古屋理解しきれていない点
中段パネルの点線は明らかに灰⾊帯(天の川CMZ)より上にある. これが渦巻銀河中⼼部の通常の姿という主張か？
⼀時的に低減することは, 緑の破線からわかる. しかし, 本⽂でいうstarburstはここではみられない.

11

結果

天の川のCMZと⽐べるとき,
R<145 pc を⾒てください。
( | l | ≲ 1∘ at d of ~8.2 kpc)

ガスの枯渇時間 = ガスの平均⾯密度を星形成率⾯密度を10 Myrsにわたって積分したもので除した.
Myrs
灰⾊帯は天の川CMZ

古屋理解しきれていない点
緑の破線の振る舞い(⼿書きメモ箇所). ガスが枯渇したあともSFR密度があがったままの銀河あるのは, なぜ？

12

結果

最後にKS則と合っていることを⽰したいらしい
⽔⾊とピンクの帯は, 天の川銀河CMZ
少なくとも解析した7つの銀河の値は, 帯の交差部分付近にくる(⇦それってすでにFigs.1&2で⽰したことじゃないの？. さらにその時間変化の軌跡は, KS則と⼤きな⽭盾はない.
議論に付⾔されていたこと
バーエンドでの星形成率↑は, 定常的で⼤きく時間変化しない.

素⼈のツッコミ, 解釈
KS則と⽐較するためには, ガス⾯密度⽅向のダイナミックレンジが⼩さすぎる.
KS則との整合性の⽂脈でみるよりかは, むしろ, 帯の交差部分よりもシミュレーション点がひろがっていることや(緑の線に⾒られるように)KS則からずれた軌跡を描く中⼼領域が多いことは, KS則成⽴はあくまでも, いわゆる円盤部だけでは？ ⇨ むしろ星形成のモードの議論へのヒントになるのでは？
SMBHフィードバック、特にsuperwindなどを考慮しないでも, ある程度, 説明できるのですね.
銀河シュミレーションの結果という意味では, 私の知る限りでは, 特段新しい知⾒(物理の提案)はなかった. この論⽂がApJ Lettersに受理された⼤きな理由は, cosmologicalなシュミレーションから出発して, z = 0の銀河の中⼼領域の振る舞いをそれなりにそれなりの分解能で(Δt~2Myrs, 数100 pc = JCMTで数Mpcの銀河を観測する分解能)再現できたことではないか？

13

Gemini Northで2008年に取得した⾯分光データのトモグラフィ plus PCA再解析導出された, 科学的な結果はそれほど画期的ではないかもしれないが, ⼿法がユニークで”変数分離”に成功 ⇨ PC n成分ごとに何らかの天体構造の抽出に成功(n=5まで析している.)

14