Why Chemistry? Satoshi Yamamoto Nami Sakai, Yoshimasa Watanabe, Department of Physics, The Univ....
-
Upload
blaze-wilkerson -
Category
Documents
-
view
225 -
download
0
description
Transcript of Why Chemistry? Satoshi Yamamoto Nami Sakai, Yoshimasa Watanabe, Department of Physics, The Univ....
Why Chemistry?
Satoshi Yamamoto Nami Sakai, Yoshimasa Watanabe,
Department of Physics, The Univ. of Tokyo
初期宇宙における揺らぎ
銀河形成
星形成
惑星系形成
物質の進化
原子分子
原始太陽系の環境はどうやってできあがったの?
宇宙における構造形成
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+, C6H-
• HC3N, HC5N, HC7N, HC9N, HC11N• C2H, C3H, C4H, C5H, C6H, C8H, CCS, C3S• CH3OH, HCOOCH3, (CH3)2O, C2H5CN, CH3CHO, HCOOH, C2H5OH, ~ 160 Species
Tycho’s SNRHayato et al. 2010
Physical Condition T, n etc.
Observed Spectrum
シミュレーション
多くの場合
Physical Condition T(t), n(t) etc.
Observed Spectrum
複雑な構造、複雑な化学過程複雑な励起機構、非平衡
電波による化学組成研究
事実上無理
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 yrtd: 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 Cloudstdep: Time Scale for Depletion of Molecules
Observed Spectrum
Physical Condition T(t), n(t) etc.
Astrochemical Concept
分子の示す意味とその背景を明らかにする
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
Carbon Chains
HN2+, NH3
Deuterated SpeciesDCO+, H2D+
Complex Organic Molecules
C → CO Conversion CO Depletion Mantle Evaporation
Chemical Evolution of Molecular Clouds
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 C2H5CN HCOOCH3
Compact Distribution Hot Corino
Evaporation from Grain Mantles
See Poster 23 by Pineda et al.
IRAS 16293-2422 with ALMA SV Pineda et al. (2012)
Another NEWS:Detection of Glycolaldehyde HCOCH2OH Jorgensen et al. (2012 )
60”
L1527
(Tobin et al. 2008)
Existence of Various Carbon Chains
Eu = 21 KN=9-8, F2
C6H -C4H
C5H, C6H, C4H2, HC5N, HC7N, HC9N, C4H- etc.
Efficient Production of Various Carbon-Chain Molecules around the ProtostarTriggered by Evaporation of Methane from Grain Mantles (Warm Carbon Chain Chemistry)(Sakai et al. 2008; 2009; 2010)
Discovery of Carbon-Chain Rich Protostar Sakai et al. (2008, 2009)
e.g.) CH4 + C+ C2H3+ + H
C2H3+ + e C2H + H + H - - - -
Hot Corino(TIMASS: Caux et al. 2011)
WCCC sourceHC3N
C4H
CCH
CO
CO
CO CO
CO
COH
H
H
H
H
CH3OH CH3OH
CH3OH
CO
CH3OHC C
C
C
CO
H
C
H
HH H CH4
CH4CH4
depleted as CO
depleted as C
Slow contraction
Fast contraction( ~ free fall timescale)
Scenario
Abundant COMs(HCOOCH3, (CH3)2O, etc.)
Abundant Carbon-Chains
(ex. IRAS16293-2422 and NGC1333IRAS4A/4B)
(ex. L1527 and IRAS15398-3359)
CH4C
C
C
Hot Corino Chemistry
Warm Carbon Chain Chemistry
Sakai et al. (2009)
Tentative Detection of Deuterated Methane
2012Sakai et al. ApJL in press.
Line Survey of Low-mass Protostars with ASTE (Watanabe et al.)
Hot Corino
WCCC
Chemical Diversity
?
?
?
?
Chemical Evolution toward Protostellar Disks
Star Formation Process
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.