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1864 first spectrum of a comet (Donati, comet Tempel C/1864 N1)1868 identification of carbon and Swan bands C2 (Huggins)1881 identification of Na, other emissions of CH, CN, C2, C3 (comet Cruls-Tebbutt 1881III)1911 indentification of CO+ by de la Baume Pluvinel and Baldet (comet Morehouse 1908III)1941 idendification of OH (comet Cunningham 1941I)
Hunt for molecules in comets(spectroscopy)
Visible and UV windows: essentially radicals and ions
exceptions : CO and S2
tentative detection of phenanthene and pyrene in 1P/Halley
IR 2-5 m window : fundamental bands of vibration
hot bands of water (e.g., 3-2)
emission process : fluorescence
radio window (cm to submm): privileged tool
cold atmospheres
UV cometary spectraHST spectra of C/1996 B2 (Hyakutake) FUSE spectrum of C/2001 A2 (LINEAR)
Weaver et al. (1998)
Feldman et al. (2002)
Possible idendification of phenanthrene C14H10
TKS/Vega@450 km1P/Halley
Q/Q(H2O) = 1.5x10-3
Moreels et al. A&A 282, 643
Possible identification of pyrene C16H10 : C16H10 / C14H10 = 0.04
(Clairemidi et al. PSS 52, 761, 2004)
PAHs, if present, are released from grains (Joblin et al. 1997 PSS 45)
Comparaison with laser-induced fluorescencespectra /jet-cooled conditions
Visible and UV windows: essentially radicals and ions
exceptions : CO and S2
tentative detection of phenanthene and pyrene in 1P/Halley
IR 2-5 m window : fundamental bands of vibration
hot bands of water (e.g., 3-2)
emission process : fluorescence
radio window (cm to submm): privileged tool
cold atmospheres
Hunt for molecules in comets(spectroscopy)
IR spectroscopy
Combes et al. (1986)
IKS/VEGA
Simple species : H2O, CO, CO2, H2CO, CH3OH3.3-3.5 m band : CH-bearing species in gas phase unidentified compounds at 3.42m 3.28 m band: PAHs ? PAHs bands at higher wavelengths not seen in Hale-Bopp ISO spectra
IR spectroscopy
C/1999 H1 (Lee) Keck/NIRSPEC Mumma et al. (2001)
High spectral resolutionro-vibrational lines ofCH4, C2H2, C2H6
CH3OH, HCN
Unidentified lines
need for detailed ro-vibrationalstructure and strength of CH3OH bands in 3 m region+ other organic species
Visible and UV windows: essentially radicals and ions
exceptions : CO and S2
tentative detection of phenanthene and pyrene in 1P/Halley
IR 2-5 m window : fundamental bands of vibration
hot bands of water (e.g., 3-2)
emission process : fluorescence
radio window (cm to submm): privileged tool
cold atmospheres
Hunt for molecules in comets(spectroscopy)
Radio spectroscopy
OH 18cm lines (1973, comet Kohoutek, Nançay)
HCN 89 GHz (1985, comet Halley, IRAM 30-m)
19 molecules (not including isotopes, radicals, ions) now detected
many first identifications in comets Hyakutake and Hale-Bopp
(in Hale Bopp: 10% of the 85-375 GHz window with IRAM 30m, PdBi and CSO)
Isotopes: HDO, DCN, H13CN, HC15N, C34S, H234S
Radicals and ions: NS, CS, SO, CN, H3O+ ,CO+
Historical radio spectra of comets
First OH 18 cm detection (Nançay)
Comet Kohoutek, Biraud et al. (1974) HCN J(1-0) detection (IRAM 30-m)
Comet Halley, Despois et al. (1986)
Bockelée-Morvan et al. A&A 353, 1101, 2000
Crovisier et al. 2004A&A 418, L35, 2004
Ethylene glycol HOCH2CH2OH11 lines identified in 2003 whenfrequencies available in Colognedatabase
230.578 GHz
New molecules in Hale-Bopp
Crovisier 2005
Evidence for chemicaldiversity Diversity among Oort cloudcomets
No systematic differencesbetween Oort cloud and
« Kuiper belt » comets
Molecular complexity
Crovisier et al. A&A 418, 1141,2004
abundances when complexity
C2H5OH/CH3OH <1/25
cyanopolyynes
but CH4 ~ C2H2 ~ C2H6
reduced alcohols wrt aldehydes
CH3OH > H2CO
OHCH2CH2OH > CH2OHCHO
Grain surface reactions ?
Deuterium in comets
In H2O: D/H = 3 10-4
In HCN: D/H = 2.3 10-3
Atomic D detected (HST)
In CH3OH, H2CO, NH3, CH4:upper limits of 10-2 to a few 10-2
Bockelée-Morvan et al. (1998)
Meier et al. (1998)
C/1996B2 HyakutakeCSO
JCMT
Recent resultsC/2001 Q4 (NEAT) methane Tspin = 33±3 K Kawakita et al. 2005, ApJ 623, L49
C/1999 S4 (LINEAR) water Tspin > 30 K Dello Russo et al. 2005, ApJ 621, 537
C/1999 H1 (Lee) water Tspin ≈ 30 K idem
C/2001 A2 (LINEAR) water Tspin = 23±4 K idem
Why are all these temperatures similar?What is their signification?
Table from Kawakita et al. 2004, ApJ 601, 1152
Ortho-para ratios
What new from Deep Impact ?
A’Hearn et al. 2005 Sciencexpress
9P/Tempel 1, 4 July 4 2005
4.9 x 7.6 km dark nucleus with low thermal inertia, low density, negligible strength
smooth and rough terrains, natural impact craters
DI impact: fine dust ejected, no dramatic increase in gas production (see Biver talk)
Deep Impact spectra : large increase in the amount of organics compared to water
Keller et al. 2005 Sciencexpress
Strong increase in silicate emission after impactNumerous bands reported : Al2O3, PAHs, smectite clay, carbonates ….
Deep Impact : les premiers resultats
Olivier Groussin
Observatoire de Meudon
Lundi 7 Novembre
11H
PUB
Open questions in comet chemistry
a lot of lines still unidentified
some radicals remain orphans : e.g. C3, NS
origin of HNC : coma or nucleus product
origin of CN ?
nature of distributed sources of H2CO and CO
nature of dust organics ?
How abundances in the coma are related to abundances in the nucleus ?
(chemical differenciation in the nucleus)
degree of compositional heterogeneity in comet nuclei
HNC@PdBi
What the composition tells us about the origin of comet material?
molecular composition present analogies with composition of star forming regions and interstellar ices
D/H ratios kept interstellar signatures unequilibrated ortho/para ratios
low-T formation (grain surface, ion-molecule processes)
highly processed material is present however (cristalline silicates) mixing with nebular products
Chemical diversity in comets : how to explain it ?
Future prospects
current instrumentation : bright comets needed studies are focussing on chemical diversity/spatial distribution
ALMA : factor 10 increase in sensitivity large uv-coverage, instantaneous maps
Herschel Observatory: water, D/H ratio, bending modes of PAHs ?
Space missions : Deep impact, Rosetta