astrochemistry panel members: jacqueline keane hideko nomura ted bergin tatsuhiko hasegawa karin...
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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]
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