Astrochemistry Panel Members:

Jacqueline KeaneHideko Nomura

Ted BerginTatsuhiko Hasegawa

Karin ÖbergYi-Jehng Kuan

COMETS

Obama.blogspot

A'Hearn et al. 2007 (Icarus xxx); 2011 (Science xxx) Deep Impact/ EPOXIMeech et al. 2011 xxxMumma & Charnley 2011 ARAAOotsubo et al. 2012 (AKARI) & WISE mission ...... important volatiles

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

…..... “Chemistry Works” ….....

…..... What Chemistry Works ? ….....

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

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

D/H RatiosFinally ! Herschel, ALMA, painful gnd-based observationsH/D exchange in ice ? Ratajczak et al. 2009

Abundances & Nitrogen & …..Bulk compositions ? …ratios do not vary significantly over passage

(?)Molecule relative to …what ? (A'Hearn et al 2012; comet forming

region)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 SimplicityHow 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]