1. Resolved CO & H2 Abundance Structure in TW Hya
Kamber Schwarz, University of Michigan Edwin Bergin, University of Michigan L. Ilsedore Cleeves, Harvard-Smithsonian CfA Geoffrey Blake, California Institute of Technology Ke Zhang, University of Michigan Karin Öberg, Harvard-Smithsonian CfA Ewine van Dishoeck, Leiden University Chunhua Qi, Harvard-Smithsonian CfA
Half a Decade of ALMA: Cosmic Dawns Transformed
September 22, 2016

2. CO in Protoplanetary Disks
Resolvable snow line (Qi+ 2013)
Good tracer of dense ISM gas
Complicated in disks by
High density
Chemistry
Temperature Gradients
Under predicts mass (Bergin+ 2013, Miotello+ 2014, Reboussin+ 2015)
Solution: HD
Qi+ 2013

3. HD in Protoplanetary Disks
Flux
wavelength
Bergin+ 2013
Flux
wavelength
McClure+ 2016
TW Hya
DM Tau
GM Aur
Mdisk: M M M
X(CO): (0.1-3) × ≤ 2 ×
X(CO) ISM ~ 10-4

4. CO Abundance in TW Hya X(CO) = (0.1-3) × 10-5
Favre+ 2013
 Tex(C18O) = 20 K
 Tex(C18O) = Tex(HD)
X(CO)
temperature (K)
X(CO) = (0.1-3) × 10-5
Sensitive to thermal structure

5. ALMA Observations beam: 0”.5 × 0”.3 (27 AU × 16 AU) beam: 0”.4 × 0”.2

6. ALMA Observations thick thin beam: 0”.5 × 0”.3 (27 AU × 16 AU) thick

7. Temperature from CO 13CO 3-2 TK TK 13CO 6-5 C18O 3-2 C18O 6-5
thick
C18O 6-5
C18O 3-2
13CO 3-2
13CO 6-5 TK
Schwarz+ 2016

8. Temperature from CO 13CO 3-2 TK 13CO 6-5 C18O 3-2 ΣCO C18O 6-5
thin
ΣCO TK
thick
C18O 6-5
C18O 3-2
13CO 3-2
13CO 6-5
Schwarz+ 2016
Correct for fractional pop. in J = 6 & J = 3

9. Warm Mass from HD Derive HD emission profile
Σ(R) shape from Menu small grains
Scale to observed emission
NJ=1(HD) Σgas
HD/H2 = 3e-5
HD emission profile

10. Warm Mass from HD Excludes: Warm (>20 K) gas mass 5.6×10-3 M
Gas < 20 K
Midplane where τ112μm>1
Warm (>20 K) gas mass ×10-3 M
Total gas mass ~5×10-2 M
Consistent with Bergin upper limit
Schwarz+ 2016

11. CO Abundance Depleted everywhere Returns inside 30 AU
X(CO)ISM ~ 10-4
Returns inside 30 AU
To an extent
see also Nomura+ 2016
Schwarz+ 2016

12. Where’s the carbon? Self shielding raises 12CO/C18O (Miotello+ 2014)
Expected for 10-2 M
X(CO) = 3.2×10-6
Hydrocarbons?
Need to remove from chemistry
Schwarz+ 2016

13. Where’s the carbon? Icy pebbles? (e.g. Xu+ 2016)
Results in C/O > 1 (Bergin+ 2016)
Explains C2H & c-C3H2 rings CO
grain

14. Where’s the carbon? Icy pebbles? (e.g. Xu+ 2016)
Results in C/O > 1 (Bergin+ 2016)
Explains C2H & c-C3H2 rings CO
grain
Bergin+ 2016

15. ALMA Observations: Snow Line
N2H+ 4-3
Schwarz+ 2016
Surface CO snow line detected in 2 transitions

16. ALMA Observations: Snow Line
N2H+ 4-3
Schwarz+ 2016
Surface CO snow line detected in 2 transitions

17. ALMA Observations: Snow Line
ice
gas
J = 3
Schwarz+ 2016
J=3 & J=6 emit near the surface
Do not trace midplane

18. Tracing the Warm Molecular Layer
ice
gas
Schwarz+ 2016
Extended emission from the warm molecular layer
Tsub < 21 K
EB/k ~ 960 K
EB/k = 885 K for CO-CO ice (Oberg+ 2005)

19. Midplane Snow Line Solve for TK where freeze out = desorption:
Schwarz+ 2016
Compare with model TK (Cleeves+ 2015)
R = AU
We can test this prediction!

20. Summary 5.6×10-3 M warm (>20 K) disk X(CO) ~ 10-6
CO does not return to the gas inside the snow line
Grains coated in CO ice
Surface snow line ~30 AU
Midplane snow line 17 AU

21. ΣHD Assumption Difference < factor of 3 for R=1-40 AU Schwarz+ 2016
Menu+ 2014
Cleeves+ 2015
Andrews+ 2012
Schwarz+ 2016