astrochemistry panel members: jacqueline keane · pdf fileastrochemistry panel members:...
TRANSCRIPT
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]