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Future Challenges Related to Star and Planet Formation
Edwin Bergin University of Michigan
Molecules and Star/Planet Formation
• We - as a field - need to connect to exoplanets as the largest growth area in astrophysics.
• Two ways to accomplish this
➡Composition of giant planet atmospheres
➡Bulk/surface composition of terrestrial planets
• All relate to formation…..
• New capabilities: Space based submm/far-IR, expand VLA, enhance ALMA
!"#$%&'$()*+%#",-*).
Caveat: assuming some O in silicates but does not include organics (C-rich + O) and additional unidentified oxygen component
water snow line
CO2 snow line
CO snow line
Oberg, Murray-Clay, & Bergin 2011
Beyond our solar system: C/O Ratio
!"#$%&'$()*+%#",-*).
Inside water snow-line: volatiles in gas. C/O = (C/O)⊙ ~ 0.5
CO, CO2 in gas, water in ice Gas: C/O ~ 2/3
Ice: C/O << (C/O)⊙
C/O Ratio CO in gas, water, CO2 in ice Gas: C/O ~ 1
Ice: C/O < (C/O)⊙
water, CO, CO2 in ice Ice: C/O = (C/O)⊙
Oberg, Murray-Clay, & Bergin 2011
Need to isolate snow-lines of major condensibles:
water, ammonia, carbon monoxide, carbon dioxide, molecular nitrogen
Carbon
10-4
10-3
10-2
10-1
100
101
(N/S
i) A
tom
ic R
atio
810-5
2
4
Venu
s (B
S)
(Low
er L
imit)
ISM
Gas
Ear
th S
urfa
ce R
eser
voir
ISM
Dus
t(lo
wer
lim
it)
Terrestrial Planet/Asteroid Forming Zone
Comet Forming Zone ISM
10-5
10-4
10-3
10-2
10-1
100
101
(C/S
i) A
tom
ic R
atio
ISM
Gas
ISM
Dus
t(lo
wer
lim
it)
Ear
th
(BSE
)
Sun
enst
atit
e ch
ond
rite
s
ordinary chondrites
carb
ona
ceo
us
cho
ndri
tes
comets
sun-grazing
Halley
dus
t
dus
t+g
as ISM
dus
t
gas
carb
ona
ceo
us
cho
ndri
tes
ord
inar
y ch
ond
rite
s
enst
atit
e ch
ond
rite
s
Ear
th
(BSE
)
Sun
comets
sun-grazing
Halley
dus
t
dus
t+g
as ISMd
ust
gas
10-4
10-3
10-2
10-1
100
101
(N/S
i) A
tom
ic R
atio
810-5
2
4
Venu
s (B
S)
(Low
er L
imit)
ISM
Gas
Ear
th S
urfa
ce R
eser
voir
ISM
Dus
t(lo
wer
lim
it)
Terrestrial Planet/Asteroid Forming Zone
Comet Forming Zone ISM
10-5
10-4
10-3
10-2
10-1
100
101
(C/S
i) A
tom
ic R
atio
ISM
Gas
ISM
Dus
t(lo
wer
lim
it)
Ear
th
(BSE
)
Sun
enst
atit
e ch
ond
rite
s
ordinary chondrites
carb
ona
ceo
us
cho
ndri
tes
comets
sun-grazing
Halley
dus
t
dus
t+g
as ISM
dus
t
gas
carb
ona
ceo
us
cho
ndri
tes
ord
inar
y ch
ond
rite
s
enst
atit
e ch
ond
rite
s
Ear
th
(BSE
)
Sun
comets
sun-grazing
Halley
dus
t
dus
t+g
as ISM
dus
t
gas
Ber
gin
et a
l. 20
15
Carbon
10-4
10-3
10-2
10-1
100
101
(N/S
i) A
tom
ic R
atio
810-5
2
4
Venu
s (B
S)
(Low
er L
imit)
ISM
Gas
Ear
th S
urfa
ce R
eser
voir
ISM
Dus
t(lo
wer
lim
it)
Terrestrial Planet/Asteroid Forming Zone
Comet Forming Zone ISM
10-5
10-4
10-3
10-2
10-1
100
101
(C/S
i) A
tom
ic R
atio
ISM
Gas
ISM
Dus
t(lo
wer
lim
it)
Ear
th
(BSE
)
Sun
enst
atit
e ch
ond
rite
s
ordinary chondrites
carb
ona
ceo
us
cho
ndri
tes
comets
sun-grazing
Halley
dus
t
dus
t+g
as ISM
dus
t
gas
carb
ona
ceo
us
cho
ndri
tes
ord
inar
y ch
ond
rite
s
enst
atit
e ch
ond
rite
s
Ear
th
(BSE
)
Sun
comets
sun-grazing
Halley
dus
t
dus
t+g
as ISMd
ust
gas
10-4
10-3
10-2
10-1
100
101
(N/S
i) A
tom
ic R
atio
810-5
2
4
Venu
s (B
S)
(Low
er L
imit)
ISM
Gas
Ear
th S
urfa
ce R
eser
voir
ISM
Dus
t(lo
wer
lim
it)
Terrestrial Planet/Asteroid Forming Zone
Comet Forming Zone ISM
10-5
10-4
10-3
10-2
10-1
100
101
(C/S
i) A
tom
ic R
atio
ISM
Gas
ISM
Dus
t(lo
wer
lim
it)
Ear
th
(BSE
)
Sun
enst
atit
e ch
ond
rite
s
ordinary chondrites
carb
ona
ceo
us
cho
ndri
tes
comets
sun-grazing
Halley
dus
t
dus
t+g
as ISM
dus
t
gas
carb
ona
ceo
us
cho
ndri
tes
ord
inar
y ch
ond
rite
s
enst
atit
e ch
ond
rite
s
Ear
th
(BSE
)
Sun
comets
sun-grazing
Halley
dus
t
dus
t+g
as ISM
dus
t
gas
something happensto interstellar
carbonaceous grains
something happensduring planet formation
Ber
gin
et a
l. 20
15
Nitrogen
10-4
10-3
10-2
10-1
100
101
(N/S
i) A
tom
ic R
atio
810-5
2
4Ve
nus
(BS
)(L
ower
Lim
it)
ISM
Gas
Ear
th S
urfa
ce R
eser
voir
ISM
Dus
t(lo
wer
lim
it)
Terrestrial Planet/Asteroid Forming Zone
Comet Forming Zone ISM
10-5
10-4
10-3
10-2
10-1
100
101
(C/S
i) A
tom
ic R
atio
ISM
Gas
ISM
Dus
t(lo
wer
lim
it)
Ear
th
(BSE
)
Sun
enst
atit
e ch
ond
rite
s
ordinary chondrites
carb
ona
ceo
us
cho
ndri
tes
comets
sun-grazing
Halley
dus
t
dus
t+g
as ISM
dus
t
gas
carb
ona
ceo
us
cho
ndri
tes
ord
inar
y ch
ond
rite
s
enst
atit
e ch
ond
rite
s
Ear
th
(BSE
)
Sun
comets
sun-grazing
Halley
dus
t
dus
t+g
as ISM
dus
t
gas
On the way to making the Earth there is a tale of successive depletion
of major elements - need to track origins and abundances of major carriers
Ber
gin
et a
l. 20
15
Locating Snow-Lines• Methods:
➡ Infer temperature profile and assume ice/vapor transition at sublimation temperature
HL Tau
➡ Indirect inference from unresolved data spanning a range of molecular excitation states
Spitzer (hot water) + Herschel (cold water)
➡Direct imaging
SMA, NOEMA, ALMA
Water and CO Snow-line
• H2O snow-line (Tdust ~150 - 200 K)
➡ close to the star (~1-3 AU)
➡ strongest transitions need space-based observation (e.g. Spitzer/Herschel)
➡ see Zhang+ 2013; Du+ 2015; Blevins+ 2015, in. prep.)
Oxygen in TW HyaDebes et al. 2013
Zhang et al. 2013
hot water
warm water
Zhang et al. 2013Hogerheijde et al. 2011
cold water
Water and CO Snow-line• H2O snow-line (Tdust ~150 - 200 K)
➡ close to the star (~1-3 AU)
➡ JWST cannot do this alone!! need access to cold transitions from space
➡OR!!!! could add dishes to ALMA to increase sensitivity —- ALMA 2.0 — resolve the most important chemical transition!
Water and CO Snow-line
• CO snow-line (Tdust ~ 20 - 40 K)
➡greater distances from star (tens of AU)
➡ can be resolved with ground-based telescopes
➡ numerous stable C and O isotopes to reduce optical depth (12C16O, 13C16O, 12C18O, 12C17O, 13C18O, 13C17O)
TW Hya CO Snow-line
-2-1012
-2
-1
0
1
2
Δα (″)
Δδ
(″)
N2H+ J = 4-3
-2-1012-2
-1
0
1
2
Δα (″)
Δδ
(″)
C18O J =3-2
N2H+ + CO ⇒ N2 + HCO+
50 AU
Qi+ 2013Schwarz+ 2015, in prep.
TW Hya CO Snow-line
-2-1012-2
-1
0
1
2
Δα (″)
Δδ
(″)
C18O J =3-2
13CO 6-5, 3-2, C18O 6-5, 3-2 & abundance analysis CO surface snow-line = 25 - 30 AU; midplane ~20 -25 AU
Schwarz+ 2015, in prep.
Protoplanetary Disk Gas Mass
• Linchpin for determination of chemical abundances
• Cannot trace H2 directly - need to use proxies
➡ thermal emission from dust grains at mm/sub-mm
➡ thermo-chemical modeling of CO gas emission
important question: If we measure abundance in emissive layers (excluding freeze out zone) - is it low gas mass or low abundance?
• Low CO/dust & CI/dust
(Chapillon+ 2008; Dutrey+ 2003; Tsukagoshi+2015; Kama+ 2015)
• Cold water emission survey - no detections beyond TW Hya and HD100546 (Hogerheijde+ 2011; Du et al., in prep.)
• C+ detected in 27% of 47 T Tauri stars (Dent et al. 2013)
• O I less emissive compared to continuum in 21 disks (Keane et al. 2014)
Missing C,O or H2?
Herschel Detection of HD towards TW Hya
➡HD is a million times more emissive than H2 at T ~ 20 K.
➡Atomic D/H ratio inside the local bubble is well characterized (~1.5 x 10-5)
➡More direct measurement of disk gas mass (~0.05 M⨀)
➡Caveat: strong T dependency
3.8
3.7
3.6
3.5
Flux
(Jy)
114113112Wavelength (µm)
HD J = 1-0
CO J = 23-22
4.2
4.0
3.8
3.6
3.4
Flux
(Jy)
57.056.556.0Wavelength (µm)
HD J = 2-1
OH 2Π1/2 9/2-7/2
Bergin et al. 2013
Surface CO Snow-line
freeze-out
snowline
warm mol. layer
TW Hya
13CO 6-5
13CO 3-2average
Schwarz et al. 2015, in prep.
Mass DistributionMenu small grainsMenu large grainsCleevesAndrews pCAndrews sC13CO 6-5 profile
0 10 20 30 40 50 60R (AU)
0
5
10
15
20
Σ w
arm
gas
(g c
m-2
)
Schwarz et al. 2015, in prep.
HD and C18O in TW Hya• Favre et al. 2013
➡Emission ratio FJ=2-1(C18O)/FJ=1-0(HD) is proportional to the CO abundance
➡ Excitation
-HD will not emit if Tgas < 20 K
-CO freezes onto grains if Tgr < 20 K
➡ CO Abundance < 10-5 (+ confirmed by ALMA observations - Schwarz et al. 2015, in prep.)
➡ Same result for water (Du et al. 2015).
Where is the O and C
0 100 200 300
50
100
150
Z(A
U)
a)
−24.0
−21.0
−18.0
−15.0
−12.0
ρ gas[g
cm−3]
0 100 200 300
50
100
150
b)
−24.0
−21.5
−19.0
−16.5
−14.0
ρ dust[g
cm−3]
0 100 200 300
50
100
150
c)
0.8
1.1
1.4
1.7
2.0
Tdust[K
]
0 100 200 300
R(AU)
50
100
150
Z(A
U)
d)
0.8
1.1
1.4
1.7
2.0
Tga
s[K
]
0 100 200 300
R(AU)
50
100
150
e)
101.0
102.5
104.0
105.5
107.0
FXR[phot/s/cm
2]
0 100 200 300
R(AU)
50
100
150
f)
103.0
105.0
107.0
109.0
1011.0
FUV(con
t)[phot/s/cm
2]
evaporation
(thermal/photo)
0 100 200 300
50
100
150
Z(A
U)
a)
−24.0
−21.0
−18.0
−15.0
−12.0
ρ gas[g
cm−3]
0 100 200 300
50
100
150
b)
−24.0
−21.5
−19.0
−16.5
−14.0ρ d
ust[g
cm−3]
0 100 200 300
50
100
150
c)
0.8
1.1
1.4
1.7
2.0
Tdust[K
]
0 100 200 300
R(AU)
50
100
150
Z(A
U)
d)
0.8
1.1
1.4
1.7
2.0
Tga
s[K
]
0 100 200 300
R(AU)
50
100
150
e)
101.0
102.5
104.0
105.5
107.0
FXR[phot/s/cm
2]
0 100 200 300
R(AU)
50
100
150
f)
103.0
105.0
107.0
109.0
1011.0
FUV(con
t)[phot/s/cm
2]
Possible Mechanism• radial + vertical
pressure gradients
• dust settling + growth + radial drift
• sequesters volatiles in midplane (more water than CO)
• particles must be large enough to frustrate feedback Du+ 2015; but see Chapillon+ 2008
Evidence for Radial DriftCO 3-2
Andrews 2015Consequences:
1.Dust mass and surface density concentrated vertically and radially
2. Ices must follow 3. What about larger grains - expanded VLA!
We are tracking the implantation of ices that seed terrestrial worlds!
What about Nitrogen?
• Trace N2 via N2H+ - cannot measure inside CO snow-line!
•Cannot get NH3 - we will NOT know what is going on with N
• emission is very weak — need expanded VLA
Salinas et al. 2015, in prep.
Summary• Far-IR/Space:
➡ Survey of HD emission in disks using a sensitive Far-IR telescope is central to science case for a future instrument
➡ Could survey hundreds of systems and obtain real statistics.
• Expanded VLA:
➡ ONLY way to set any constraints on nitrogen - the 5th most abundant element, a key biogenic element, major constituent of our atmosphere
➡ needed to probe dust evolution
• ALMA 2.0
➡ Could resolve water snowline - most important chemical/physical transition in the disk
