donghui quan eric herbst the ohio state university
DESCRIPTION
CHNO Isomers in the Universe HNCO TMC-1: ~ 5 × (Marcelino et al. 2009a) Sgr B2: ~ × (Churchwell et al. 1986; Liu & Snyder 1999; Brünken et al. 2009a,b) HOCN Sgr B2(OH): ~ 0.4% of [HNCO] (Brünken et al. 2009b; Turner 1991) Sgr B2 (M) : ~ 1.5% of [HNCO] (Brünken et al. 2009a,b; Marcelino et al. 2009b) TMC-1 : ~ 1% of [HNCO] (Brünken et al. 2009a,b ) Cold Cores: ~ 2% of [HNCO] (Marcelino et al. 2009b) HCNO TMC-1 : < 0.3% of [HNCO] (Marcelino et al. 2009a) Cold Cores : ~ 2% of [HNCO] (Marcelino et al. 2009a) L1527 : ~ 3% of [HNCO] (Marcelino et al. 2009a)TRANSCRIPT
Donghui Quan& Eric Herbst
The Ohio State University
OutlineObservational ResultsModeling MethodEssential ReactionsResults and DiscussionConclusion
CHNO Isomers in the UniverseHNCOTMC-1: ~ 5 × 10-10 (Marcelino et al.
2009a)Sgr B2: ~ 0.5-5× 10-9 (Churchwell et al. 1986; Liu & Snyder
1999; Brünken et al. 2009a,b)
HOCNSgr B2(OH): ~ 0.4% of [HNCO] (Brünken et al. 2009b; Turner
1991)Sgr B2 (M) : ~ 1.5% of [HNCO](Brünken et al. 2009a,b; Marcelino et al. 2009b)
TMC-1 : ~ 1% of [HNCO] (Brünken et al. 2009a,b )
Cold Cores: ~ 2% of [HNCO] (Marcelino et al. 2009b)
HCNOTMC-1 : < 0.3% of [HNCO] (Marcelino et al.
2009a)Cold Cores : ~ 2% of [HNCO] (Marcelino et al. 2009a)L1527 : ~ 3% of [HNCO] (Marcelino et al.
2009a)
Why different?
Modeling Method – Gas-grain Modeling
Four models: hot core, warm envelope, lukewarm, cold core.
Gas-grain network: ~700 species, >6000 reactions.
3-phase warm-up: T starts at low constant value, increases to and stays at higher value after certain time-point.
Non-thermal desorption: driven by energies from exothermic surface reactions.
Modeling Method – Physical Conditions and Initial Abundances
Essential Formation ReactionsGas phase: NCO+ + H2 -> HNCO+ + H, HNCO+ + H2 -> HNCOH+/H2NCO+ + H, HNCOH+ + e- -> HNCO/HOCN + H, H2NCO+ + e- -> HNCO + H. HCNO & HONC can be produced similarly, plus: CH2 + NO -> HCNO + H.
Grain surface (J): N + HCO -> NCO + H, JH + JNCO -> JHNCO/JHOCN. JC + JNO -> JCNO, JH + JCNO -> JHCNO/JHONC.
Essential Destruction ReactionsHNCO: cations, cosmic ray indirect destruction, photon dissociation etc.
HOCN: cations, cosmic ray indirect destruction, photon dissociation etc, C + HOCN -> CO + HCN, HCO + CN, H + OCNC, and OH +
CNC, O + HOCN -> OH + NCO.
HCNO: cations, cosmic ray indirect destruction, photon dissociation etc, C + HCNO -> C2H + NO.
HONC: cations, cosmic ray indirect destruction, photon dissociation etc, O + HONC -> O2H + CN.
Modeling results – Hot Core Model
• Peaks occur after warm-up;
• HNCO & HOCN: two time periods of best agreement;
• HCNO & HONC: abundances low.
Modeling resultsMODEL HNCO HOCN HCNO HONC Obs.
Source
Hot Core
Peak ~ 3× 105 yr
Sgr B2(M)
Evaporation after warm-up
Surface species show strong depletion into the gas-phase.
Comp. to Obs. HNCO & HOCN: best fit @1.2 - 1.5 × 105 yr & 1.1 - 1.6 × 106 yr.HCNO & HONC: abundance low during these time intervals.
Warm Env
Peak ~ 3× 105 yr , Smaller
~ 3× 105 yr , Smaller
No No Env. Sgr B2 (M) &
(N), Sgr
B2(OH)
Evaporation after warm-up
Surface species show fair depletion into the gas-phase.
Comp. to Obs. HNCO & HOCN: best fit @1.8-2.0 ×105 yr & 6.6-19×105 yr;HCNO: X ~ 10−12- 10 -11; HONC: abundance low.
Lukewarm
Peak No apparent peaks.
L1527Evaporation
after warm-up Insignificant.
Comp. to Obs. HNCO & HCNO: good agreement after t > 100 yr;HOCN: X > 10-11 when t > 2× 105 yr; HONC: abundance low.
Cold Core
Peak weak peak~ 2× 105 yr No No No
TMC-1 &
other Cold Cores
Comp. to Obs.
Good fit after 104 yr
HOCN to HNCO ratio
fits obs. @105 - 5× 106 yr
~ 1/10 -1/500 of HNCO
May be detectable.
An analogous system – CHNS Isomers
ConclusionsCHNO isomers are produced by a combination
of surface and gas-phase chemistry.
In general, our models are able to reproduce both the abundance of the dominant isomer HNCO and the minor isomer, HCNO or HOCN.
CHNS isomers present another interesting case of how astronomical environments lead to the production and destruction of differing isomers.
AcknowledgementDr. Yoshihiro Osamura
Dr. David Woon
Dr. Sandra Brünken
NSF funding
Thank you all!