Jan/2005Interstellar Ices-I1 Interstellar Ices-2 Ice Inventory Protostellar Environments Energetic...

Jan/2005 Interstellar Ices-I 1

Interstellar Ices-2Ice Inventory Protostellar Environments

Energetic Processing?

Laboratory Simulations

New Spitzer Satellite Results

Adwin BoogertCalifornia Inst. of Technology


Contents

–what else is present in interstellar ices, besides H2O and CO?–basic chemistry: Are new molecules formed through energetic processes?–complexity in the 5-10 m region–Ice inventory. Where is NH3?–energetic processing diffuse/dense ISM?–Ions in the ices?–Complex CH3OH/CO2/CO/H2O mixtures


A Grain in Space

More realistic:

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Laboratory Simulations

●Chemical processes occurring

in space can be simulated in

laboratory at low T (>=10 K)

and low pressure. ●Thin films of ice condensed on a

surface and absorption or reflection

spectrum taken.●Temperature and irradiation by UV

light or energetic particles of

ice sample can be controlled.●Astrophysical laboratories: Leiden,

Catania, NASA Ames/Goddard,

ParisGerakines et al. A&A 357, 793 (2000)

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Spitzer Spectroscopy of Ices toward Protostars

/SVS 4-5

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Ice Inventory6


Ice Inventory

[H2O and silicate subtracted!]

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[H2O and silicate subtracted!]

Ice Inventory6


NH3/CH3OH=4

NH3/CH3OH<0.5

(SVS 4-5)

Ice Inventory6


'Typical' abundances w.r.t. H2O ice

Factors of 2 abundance variations between sight-lines are common!

Note uncertain NH3

abundance. Will Spitzer spectra finally establish

presence of NH3 in

interstellar ices?

Ice Inventory

CO few-50%

CO2 15-35%

CH4 2-4%

CH3OH <8, 30%

HCOOH 3-8%

[NH3] <10, 40% (?)

H2CO <2, 7%

[HCOO-] 0.3%OCS <0.05, 0.2%

[SO2] <=3%

[NH4+] 3-12%

[OCN-] <0.2, 7%

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Evidence for Energetic Processing?

●UV/CR processing simple ices in laboratory produces organic residues ('yellow' stuff). ●Problem: no such complex stuff observed in icy sightlines. Much explained by grain surface chemistry and thermal processing of simple ices.●Selection effect?●Low infrared sensitivity?●Better observe sublimated species (more sensitive)-see lecture Cecilia.Greenberg et al. ApJ 455, L177 (1995): launched

processed ice sample in earth orbit exposing directly to solar radiation (EUREKA experiment). Yellow stuff turned brown: highly carbonaceous residue, also including PAH.

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Evidence for Energetic Processing?

3.4 um absorption feature observed in diffuse ISM (e.g. Galactic Center). Triple peaks due to hydrocarbons (-CH,

-CH2, -CH3). Little evidence production by UV/CR bombardment of ices: *formed in evolved star envelopes, and injected in ISM *band not polarized as opposed to silicates/ices: not in processed mantle but separate grains *3.4 um band observed in dense clouds, but not triple

peaked.NH3/H2O complex

(hydrate)?

Pendleton et al. 1994, Adamson et al. 1998, Chiar et al. 1998, Chiar et al. 2000

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Protostellar luminosity unimportant factor in ice formation and processing

Low Mass versus High Mass Protostar

Noriega-Crespo et al. ApJS 154, 352 (2004)

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Major solid state band not firmly identified yet. Observational constraint: band shifts to red for warmer lines of sight

Condition fulfilled by NH4+

[Schutte & Khanna A&A 398, 1049, 2003]. Corresponding 3.25 and 3.47 m bands

NH4+ would require NH3 as well as

thermal- or photo-processing to be continued...

Identification: the 6.85 m band7


Ions in Ices

–NH4+ roughly has spectral

characteristics that fit interstellar 6.85 m band.

–NH4+ easily produced by warming

acid/base mixture NH3+HNCO

–also produces OCN-, which has observed feature at 4.62 m and might account for charge balance; further study needed.

–In fact, 4.62 um band attributed to CN-bearing species ('XCN') last 15 years and always considered strongest evidence energetic UV/CR processing. Now less likely.

H2O:CO2:NH3:O2 at different T and mixing ratios

H2O:N2:CH4 after irradiation:

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Complex CO2/CH3OH/H2O/CO Ice Mixtures

H2O:CO2:CH3OH at different CH3OH

concentrations. Note CO2:CH3OH

complexes.

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Weak wing in 2 Spitzer sources consistent with low CH3OH abundance derived from other features

Overall width due to H2O:CO2

Bottom of profile indicates apolar

CO/CO2 component

[Boogert et al. ApJS 154, 359 (2004)]

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H2O:CO2:CH3OH=1:1:1 heated. Double peak characteristic for

pure CO2 appears after H2O crystallization.

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Evolution of Ices as Function of Protostellar Stage

No obvious evolution of ice abundances [other than evaporation of volatiles]Effects of heating commonly observed: CO ice band, 6.8 m band, CO2 ice band

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Evidence envelope heating:

• CO2 crystallization (Boogert et al. 2000;

Gerakines et al. 1999)

• H2O crystallization (Smith et al. 1989)

• gas/solid ratio increases (van Dishoeck et al. 1997)

• Detailed modelling gas phase mm-wave observations (van der Tak et al. 2000)

Solid 13CO2:

Ice Processing Massive YSOs8


Solid 13CO2:

Ice Processing Massive YSOs

Evidence envelope heating:

• CO2 crystallization (Boogert et al. 2000;

Gerakines et al. 1999)

• H2O crystallization (Smith et al. 1989)

• gas/solid ratio increases (van Dishoeck et al. 1997)

• Detailed modelling gas phase mm-wave observations (van der Tak et al. 2000)

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Evolution of Ices: Conclusions

Ice composition evolution with protostellar phase?

No (tentatively), but evaporation of volatiles occurs. What causes composition variations between lines of sight?

Ice temperature evolution in low mass protostars?

Yes. Profiles 6.8 um and 15 um CO2 band, apolar CO evaporation, H2O crystallization. Also in disks.

Ice composition influenced by protostellar mass/luminosity?

No observational evidence, except possibly CO2:

new CO/CO2 ice phase

larger CO2 ice abundance

NH3: surprisingly large variations between sightlines (tentative)

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ISO/SWS+LWS 2-200 m spectrum Elias 29 ( Oph)with flared face-on disk model (Boogert et al. 2002, ApJ 570, 708).


• Ices abundant toward Elias 29: most luminous (30 Lsun) low mass (1-2 Msun) protostar in Oph cloud

• [Before drawing conclusions on ice processing, one needs to locate ices along line of sight]

Ices in Low Mass YSOs

Jan/2005Interstellar Ices-I1 Interstellar Ices-2 Ice Inventory Protostellar Environments Energetic...

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