Chunhua Qi HarvardSmithsonian CfA Qi et al 2008 Qi et al in prep Image credit Bill Saxton NRAO Star Formation Stages Sketch of the physical and chemical structure of a 15 Myr old protoplanetary disk around a Sunlike star ID: 635888
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Slide1
Probing CO freeze-out and desorption in protoplanetary disks
Chunhua QiHarvard-Smithsonian CfA
[Qi et al. 2008]
[Qi et al. in prep]Slide2
Image credit: Bill Saxton (NRAO)
Star Formation StagesSlide3
Sketch of the physical and chemical structure of a ∼1–5 Myr old protoplanetary disk around a Sun-like star.
Protoplanetary disk structure
CO freeze-out/desorption probe ?
CO snow line location ?
[Henning & Semenov 2013]
[
Öberg
, Murray-Clay & Bergin 2011]Slide4
1. CO freeze-out/desorption probe ?Slide5
CO disks are “huge”
Classical T Tauri star
8-12 Myr oldInclination 7o
Herbig Ae star3-5 Myr oldInclination 44o
TW HyaHD 163296Slide6
Temperature Contour
Disk temperature decreases radially away from the star
and
vertically toward disk midplane
20 KSlide7
Optically thick CO lines on the surface hide
the CO freezeout information at midplane
,
12C17OSlide8
Chemical imaging of CO freeze-out:Ring structures
[Qi et al. 2013]Slide9
Chemical imaging of the CO snow line:N2H
+ ring structure
DCO+
N2H+ is destroyed by the gas CO and enhanced by the freeze-out of gas CO
Inner Edge
[Qi et al. 2013]
TW
Hya
N
2
H
+
+ CO
HCO
+ + N2Slide10
Chemical imaging – DCO+ ring structure
DCO+
DCO
+ abundance is balanced by CO freeze-out and temperature-dependent D enhancement
Outer Edge
H
2
D+ + CO DCO
+
+ H
2
[Mathews et al. 2013]Slide11
Probing CO
photodesorption[Öberg et al. 2015]
IM LupSlide12
ALMA images of N
2H+ and DCO+ toward TW Hya
[Qi et al. in prep]N2
H+DCO+Slide13
ALMA images of N
2H+ and DCO
+ toward TW Hya[Qi et al. in prep]
N2H+DCO+Slide14
ALMA images of N
2H+ and DCO+ toward TW Hya
[Qi et al. in prep]DCO+
N2H+ and
DCO+Slide15
Slide credit: T.
BirnstielSlide16
Impact of radial drift on the global
dust temperature structure
Drift of the mm grains allow the reprocessed radiation from the upper layer penetrating deeper.The outer disk midplane directly heated by the upper layer
[Cleeves 2016]Slide17
Imaging the CO desorption
C
18O
[Nomura et al. 2016]
[Qi et al. in prep]
N
2
H+ and DCO+Slide18
2. The CO snow line location ?Slide19
How to locate the CO snow line …
R [AU]
CO abundance
R
CO
CO abundance drop
Chemical imagingSlide20
CO (radial and) vertical structure
,
12C17O
HD 163296 CO multi-transition multi-isotope studies with SMA [Qi et al. 2011]Slide21
Resolving protoplanetary disks spatially and spectrally
Figure+Movie
credit:Ian CzekalaSlide22
Locating CO snow line based on SMA 13
CO 2-1 emission
HD 163296
[Qi et al. 2011]
R
CO
= 155 AUSlide23
[Qi et al. submitted]
R
CO=155 AU [Qi11]
Locating CO snow line based on ALMA C
18O 2-1 emission Slide24
CO snow line is at
90 AU in HD 163296 disk
[Qi et al. 2015]
R
CO=155 AU [Qi+11]RCO
=90 AU
Locating CO snow line based on ALMA C
18
O 2-1 emission
Have to consider the optical depth problem.
Hard to distinguish from radial profile.
Slide25
[Qi et al. 2015]
The inner edge of N2H+ ring in HD 163296 disk is around 90
AU, consistent with C18O analysis HD 163296 Slide26
[Qi et al. 2013]
TW
Hya
However, the new 13C18O observation of TW Hya indicates the CO snow line around 21 AU, smaller than 30 AU found with N2H+ emission
[Zhang et al. 2017]Slide27
[Van ‘t Hoff et al. 2016]
Model FD: considering only freeze-out and desorptionModel
CH: considering simple chemical network for N2H+Chemical model indicates the N2H+
emission can peak much further out beyond the CO snow line, and a rather smooth fall-off inward. Slide28
However,
the inner edge of N2H+ emission toward TW Hya
found to be very sharp[Qi in prep]Slide29
Summary
N2H+ is sensitive to the CO freeze-out but whether it can serve as a robust probe of the CO snow line is still under debate. DCO+
can be used as a probe of the CO desorption, although more works are needed to disentangle the nature of desorption. Optically thin CO isotopologue emission
can be used locate the CO snow line directly but very tricky due to optical depth and sensitivity issue.Slide30
[Qi et al. in prep]
[Qi et al. 2013]
[Qi et al. 2008]Slide31
Collaborators:
K. Öberg, D.
Wilner, S. Andrews, L.I. Cleeves (CfA);
E. Bergin, N. Calvet (U. Michigan); A.M. Hughes (Wesleyan U.) ;
C. Espaillat (Boston U.); Michiel Hogerheijde (Leiden U.)Slide32
ENDSlide33
I
mpact of radial drift on the global dust temperature structure
[Andrews 2015]
[Cleeves 2016]