Astrochemistry Panel Members:

Jacqueline Keane Hideko Nomura

Ted Bergin Tatsuhiko Hasegawa

Karin Öberg Yi-Jehng Kuan

COMETS

Obama.blogspot

l A'Hearn et al. 2007 (Icarus xxx); 2011 (Science xxx) Deep Impact/ EPOXI l Meech et al. 2011 xxx l Mumma & Charnley 2011 ARAA l Ootsubo et al. 2012 (AKARI) & WISE mission ...... important volatiles

Constraints on Chemistry/Physics in Early Solar System, Natal Cloud ….. ?

…..... “Chemistry Works” ….....

…..... What Chemistry Works ? ….....

l  OPR … ortho-to-para ratios l  Spin temperatures, infer formation temperature .... model dependent ? l  H2O & NH3 molecules all cluster around 30 K

l  Hama et al. 2011; Tspin does not reflect temperature at which the ice condensed

l  D/H Ratios l  Finally ! Herschel, ALMA, painful gnd-based observations l  H/D exchange in ice ? Ratajczak et al. 2009

l  Abundances & Nitrogen & ….. l  Bulk compositions ? …ratios do not vary significantly over passage (?) l  Molecule relative to …what ? (A'Hearn et al 2012; comet forming

region) l  HDO/H2O approaching VSMOW (?) ...... but comets are N-poor

COMETS : some issues with chemistry

Chemical Structure of PPDs (e.g., Dutrey+ 1997; Markwick+2002, Aikawa+ 2002, Bergin+ 2007)

ESA

Halley

H2O, CO2, CH4, CH3OH, H2CO, NH3, etc.

・Depletion of CO: midplane of outer disk ・Relatively large molecules: middle layer ・Radicals: disk surface

Chemical Structure of PPDs (e.g., Dutrey+ 1997; Markwick+2002, Aikawa+ 2002, Bergin+ 2007)

ESA

Halley

H2O, CO2, CH4, CH3OH, H2CO, NH3, etc.

How can we trace physical processes in disks using molecular lines?

・Depletion of CO: midplane of outer disk ・Relatively large molecules: middle layer ・Radicals: disk surface

Chemical Structure of PPDs (e.g., Dutrey+ 1997; Markwick+2002, Aikawa+ 2002, Bergin+ 2007)

ESA

Halley

H2O, CO2, CH4, CH3OH, H2CO, NH3, etc.

PDRs

dense cores

How can we trace physical processes in disks using molecular lines?

・Depletion of CO: midplane of outer disk ・Relatively large molecules: middle layer ・Radicals: disk surface

FUV

(e.g., White & Sandell 1995, Fuente+ 1996, …)

FUV

13CO/C18O

CI/CO

Av

PDRs

Dust continuum

C17O

(e.g., Caselli+ 1999, Tafalla+ 2004)

L1498 by IRAM

center R

dense cores

Find useful tracer!

Basic properties have been studied in PDRs,

dense cores, etc…

CO depletion

Photochemistry

G. Mathews’ talk yesterday

Complexity vs Simplicity How predictive are chemical models?

A general procedure (there are others)

➡ Use dust SED (and sometimes submm imaging) to constrain dust physical structure assuming grain size distribution (variable) and composition

➡ perform UV/Xray radiation transfer within this framework alongside gas chemistry/thermal balance

➡ predict abundances/column densities and sometimes emission

➡  large number of chemical and physical assumptions (constrained as best we can)

CO Ladder workshop

BUT - not all species are CO!

Complexity vs Simplicity

What does this mean ➡ complex models can betray what species trace what

layers in the disk (think turbulence/ionization) -- can be confirmed with observations

➡ simple assumptions of abundance structure are reliable approach to directly match observations (ALMA surveys) - need information from models to make approximations

➡ complex models can betray what chemistry/physics is needed to even approach observational results

11/6/17

Whittet et al. (1985, MNRAS, 216, 45p) UKIRT

M band observations in the 1980’s

Lacy et al. (1984, ApJ, 276, 533) Palomar 5m

Mitchell et al. (1990, ApJ, 363, 554) CFHT + FTS

Interstellar gas and ice (OCN- band detection)

11/6/17

The OCN- 4.63 micron band in a YSO

ISO  spectrum  NGC  7538  IRS  1  

wavenumbers  (cm-­‐1)  

                       wavelength  

Nature vs Nurture •  How much of the final disk chemistry is inherited from previous interstellar phases? (Water destruction and reformation in disks? Aikawa’s talk)

•  Under which circumstances can such an inheritance be ignored when modeling? (ProDiMo, Chapillon’s, Bergin’s and Millar’s talks, etc)

•  Contradictory evidence from disk and Solar system observations? (H2CO in disks, comet compositions)

•  Is there any chemistry that is unique to the pre-disk stages?

How much is the chemistry reset during disk formation?

What Class 0/1 molecular observations would help?

Evidence from T Tauri stage

observations?

Evidence from comet abundances?

[Herbst & van Dishoeck 2009]