Chemistry

Why Chemistry?
Satoshi Yamamoto
Nami Sakai, Yoshimasa Watanabe,
Department of Physics, The Univ. of Tokyo
宇宙における構造形成
初期宇宙における揺らぎ
物質の進化
銀河形成
原子
星形成
分子
原始太陽系の
環境はどうやって
できあがったの？
惑星系形成
Line Survey of TMC-1 with NRO 45 m
Kaifu et al. (2004)
HC3N
HC5N
HC7N
CCS, CCCS, c-C3H,
CCO, CCCO, C4H2, etc
Interstellar Molecules
•
•
•
•
•
•
•
H2
CO
HCN, HNC, H2CO, NH3, CS, SiO, CN, SO, SO2
H3+, HCO+, HN2+, HCS+, C6HHC3N, HC5N, HC7N, HC9N, HC11N
C2H, C3H, C4H, C5H, C6H, C8H, CCS, C3S
CH3OH, HCOOCH3, (CH3)2O, C2H5CN,
CH3CHO, HCOOH, C2H5OH,
～160 Species
Tycho’s SNR
Hayato et al. 2010
多くの場合
Observed Spectrum
シミュレーション
Physical Condition
T, n etc.
電波による化学組成研究
Observed Spectrum
事実上無理
Physical Condition
T(t), n(t) etc.
複雑な構造、複雑な化学過程
複雑な励起機構、非平衡
Time Scale for Chemical Equilibrium
1/τ＝1/tf + 1/td
tf: Time Scale for Formation of Molecules
H3+ + X → HX+ + H2
a few 105 yr
td: Time Scale for Destruction of Molecules
Av > 5 Ionic Destruction slow > 106 yr
c.f. Reactions with He+, H+, etc.
Av < 3 Photodissociation fast
102 yr
In Actual Cloud Cores
τ～tdyn ～ tdep
tdyn: Dynamical Time Scale for Molecular Clouds
tdep: Time Scale for Depletion of Molecules
Observed Spectrum
分子の示す意味と
その背景を明らかにする
Astrochemical
Concept
Physical Condition
T(t), n(t) etc.
Basic Physics &
Chemistry
昔むかし。。。
用いるスペクトル線による見え方の違い
Zhou et al. 1989
分子ごとの分布の違いを目の前にして。。。
• ひとつの意見
- いったい何を信じればいいのか？
- ＣＯ以外は信用できない。
- 質量（柱密度）を最もよく表すものは何か？
- 化学組成は役に立たない。研究の障害！
• もう一つの意見
- 分布の違いの原因は何だろう？
- 原因究明から新しいことがわかるのでは？
化学組成の違いの探求 CCS vs NH3
CCS
NH3
CCS
NH3
Suzuki et al. 1992
Chemical Evolution of Molecular Clouds
C → CO Conversion
CO Depletion
Carbon Chains
HN2+, NH3
Deuterated Species
DCO+, H2D+
Complex Organic Molecules
Mantle Evaporation
Detection of Complex Organic Molecules
in the low-mass protostar IRAS 16293-2422
Cazaux et al. 2003；Bottinelli et al. 2004; Kuan et al. 2004
HCOOCH3
HCOOCH3
C2H5CN
See Poster 23 by
Pineda et al.
Compact Distribution
Hot Corino
Evaporation from Grain Mantles
IRAS 16293-2422 with ALMA SV
Pineda et al. (2012)
Another NEWS:
Detection of Glycolaldehyde
HCOCH2OH
Jorgensen et al. (2012）
Discovery of Carbon-Chain Rich Protostar
Sakai et al. (2008, 2009)
Efficient Production of Various Carbon-Chain Molecules around the Protostar
Triggered by Evaporation of Methane from Grain Mantles
(Warm Carbon Chain Chemistry)(Sakai et al. 2008; 2009; 2010)
e.g.) CH4 + C+  C2H3+ + H
C2H3+ + e C2H + H + H  - - - Existence of Various Carbon Chains
C4H
C6H－
L1527
N=9-8, F2
Eu = 21 K
60”
C5H, C6H, C4H2, HC5N, HC7N, HC9N, C4H- etc.
(Tobin et al. 2008)
Hot Corino
(TIMASS: Caux et al. 2011)
WCCC source
CCH
HC3N
C4H
Scenario
CO
Hot Corino Chemistry
CO
H
Slow contraction
H
C depleted as CO
CO
H
CO
CO
CO
C
Abundant COMs
(HCOOCH3, (CH3)2O, etc.)
CH3OH
H
CH4
H
CH3OH
CH3OH
(ex. IRAS16293-2422 and NGC1333IRAS4A/4B)
C
Warm Carbon Chain Chemistry
Abundant Carbon-Chains
Fast contraction
C
（~ free fall timescale）
CO
H
H
C
H C
C
depleted as C
CO
H
H
C
CH4
CH4
CH4 CH3OH
(ex. L1527 and IRAS15398-3359)
Sakai et al.
(2009)
Tentative Detection of Deuterated Methane
2012
Sakai et al. ApJL in press.
Line Survey of Low-mass Protostars with ASTE
(Watanabe et al.)
Chemical Evolution toward Protostellar Disks
Hot Corino
Star Formation
Process
WCCC
？
？
？
？
Chemical Diversity
Requirements for Unbiased Spectral Line
Survey toward Many Sources
(1) High Sensitivity  Large Aperture
(2) Wide Frequency Coverage
 Mm to Submm (THz), Good Atmospheric Transmision
(3) Large Instantaneous Bandwidth
 Large Correlator System & Multi-Band Obs.
(4) Reliable Observations
 Stable Pointing, Good Calibration Accuracy
Observing Frequency
(1) 70 – 400 GHz: Basic Band
Various Organic Molecules (COMs, CCs, etc. )
Full Aperture (50 m)
(2) 400 – 900 GHz: High Band
High Excitation Lines of Fundamental Molecules
Medium Aperture (30 m)
(3) 900 – 1500 GHz: THz Band
Fundamental Species (H2D+, HD2+, NH, NH2 etc.)
Small Aperture (15 m)
Example of Observing Mode
(1) 80-88 GHz
140-148 GHz
230-238 GHz
340-348 GHz
Total 32 GHz (dual pol.)
5-6 sets are necessary to cover the whole band.
(2) 92-100 GHz
108-116 GHz
230-238 GHz
246-254 GHz
Total 32 GHz (dual pol.)
2-3 sets are necessary to cover the two bands.
Roles of Large Single Dish
• Finding ‘New’ Sources rather than Ordinary Sources
•
• Obtaining Large/Complete Statistical Data
• Studying Large Scale Phenomena
Unbiased Survey both in Spatial and Frequency Domains
Frequency Domain Survey → Chemical Diagnosis
• Complimentary to ALMA
→ Detailed Characterization of Each Source
Why Chemistry?
Because it is crucial to understand evolution of
matter in space.
It also provides us with novel views on physical
processes of star and planet formation.

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