Talk for Heidelberg - IPAG Workshop

1. Richard Teague, Dmitry Semenov, Stephane Guilloteau,
Thomas Henning, Anne Dutrey & the CID Collaboration
Disk Diagnostics
with Deuteration

2. DSS Consor)um, SDSS, NASA/ESA, Akira Fujii
DCO+
in DM Tau

3. Hydrosta)c equilibrium leads to a strongly stra)fied structure.
Molecular line emission will probe the intermediate layer.
Henning & Semenov (2013)

4. RD is the ra)o of a deuterated isotopologue
to the non-­‐deuterated isotopologue.
In protoplanetary disks HCO+ is a readily observable molecule.
It allows for comparisons with other epochs in the evolu)on of molecular gas.

5. We imaged with the Plateau de Bure Interferometer
HCO+ J=(3-­‐2), (1-­‐0) and DCO+ J=(3-­‐2) emission in DM Tau.
a hRp://www.iram.fr/IRAMFR/GILDAS/
Obtained a ~1.5’’ spaCal and ~0.2 km s-­‐1 velocity resoluCon.
Data was reduced with the standard MAPPINGa soXware.

6. Column densi)es of HCO+ and DCO+ were extracted using DISKFITa.
Describes physical properCes of the disk with power laws.
Assumes LTE and fits the visibili)es in the uv-­‐plane.

7. Column DensiCes RD = N(DCO+) / N(HCO+)
RD varies between 0.1 and 0.2.
!
Computa)onal model used similar physical structure of D’Alessio et al. (1999).
Chemical model run with ALCHEMICa which includes an
extended deuterium networkb and ortho/para chemistryc.
!
a Semenov et al. (2010), b Albertsson et al. (2013), c Albertsson et al. (2014a)

8. Column densi)es were found to agree well with observaConally derived values.
RD clearly evolves with Cme, and also fits qualita)vely well with observa)ons…
Column DensiCes RD = N(DCO+) / N(HCO+)

9. H2 H2
H2D+
H2
HCO+
DCO+
H3
+
H2
+
H2
CO
HD
H2
H2
ice
ice
CO
What controls the abundances of HCO+ and DCO+?
An incredibly simplified chemical network for the molecular layer…

10. H2 H2
H2D+
H2
HCO+
DCO+
H3
+
H2
+
H2
CO
HD
H2
H2
ice
ice
CO
Cold region chemistry driven by ion -­‐ neutral reac)ons.
Requires ini)al ionizaCon of H2 to kick start chemistry.

11. H2 H2
H2D+
H2
HCO+
DCO+
H3
+
H2
+
H2
CO
HD
H2
H2
ice
ice
CO
…deuterium fracConaCon will occur in cold environments…
(here we neglect the doubly and triply deuterated isotopologues.)

12. H2 H2
H2D+
H2
HCO+
DCO+
H3
+
H2
+
H2
CO
HD
H2
H2
ice
ice
CO
…due to the energy barrier which deters backwards reac)ons.

13. H2 H2
H2D+
H2
HCO+
DCO+
H3
+
H2
+
H2
CO
HD
H2
H2
ice
ice
CO
Assuming CO is present in the gas phase and has not frozen out…
(or other forms of deple)on)

14. H2 H2
H2D+
H2
HCO+
DCO+
H3
+
H2
+
H2
CO
HD
H2
H2
ice
ice
CO
…fast ion-­‐neutral reac)ons with CO transfer this
deuterium ra)o to HCO+ and DCO+.

15. H2 H2
H2D+
H2
HCO+
DCO+
H3
+
H2
+
H2
CO
HD
H2
H2
ice
ice
CO
Ioniza)on, frac)ona)on efficiency and CO deple)on all
affect the measured RD values.

16. 100
R, AU
11.5
12.0
12.5
13.0
13.5
14.0
14.5
Log10[N(X),cm-2
]
HCO+
DCO+
Best-fit
LX=1031
erg/s
100
R, AU
11.5
12.0
12.5
13.0
13.5
14.0
14.5
Log10[N(X),cm-2
]
HCO+
DCO+
Best-fit
LX=3x1028
erg/s
Reduced X-­‐RaysIncreased X-­‐Rays
LX = 3x1028 erg s-­‐1LX = 1031 erg s-­‐1
Solid lines are the HCO+ column densi)es and the dashed DCO+
Comparisons between the best fit model
and a model with an altered physical parameter.
X-­‐rays are the dominant ionizaCon source where HCO+ is present.
High ioniza)on can suppress frac)ona)on by increasing ortho-­‐H2 abundances.

17. Solid lines are the HCO+ column densi)es and the dashed DCO+
100
R, AU
11.5
12.0
12.5
13.0
13.5
14.0
14.5
Log10[N(X),cm-2
]
HCO+
DCO+
Best-fit
no IS UV
100
R, AU
11.5
12.0
12.5
13.0
13.5
14.0
14.5
Log10[N(X),cm-2
]
HCO+
DCO+
Best-fit
agr=1um
No Interstellar UV Increased Grain Sizes
a = 1 um
Comparisons between the best fit model
and a model with an altered physical parameter.
CO deple)on is sensi)ve to UV driven photodesorpCon of heavy ices
and efficiency of CO freeze out onto grains.

18. Conclusions
• In DM Tau RD ~ 0.1 -­‐ 0.2 between 50 and 550 au.
Consistent with con)nued gaseous processing and values found in other
disks.
!
• X-­‐rays are the dominant ionizaCon source in the molecular layer.
Different depths of HCO+ and DCO+ layers result in the two being affected
by changes in X-­‐ray luminosity differently .
!
• DepleCon of CO strongly affects the local RD.
CO deple)on is sensi)ve to the freeze out efficiency and the level of UV
driven photodesorp)on.