M. Araki1, S. Takano2, N. Sakai3, S. Yamamoto4, T. Oyama1, N. Kuze5, and K. Tsukiyama1

1 Tokyo University of Science, 2 Nihon University, 3 RIKEN, 4 The University of Tokyo, 5 Sophia University

International Symposium on Molecular Spectroscopy2016/06/22

The precise observationsof the 13C isotopic abundance ratios of carbon chain molecule HC3N in the low-mass star forming region L1527 by radio observations

Introduction

• Carbon-chain molecules constitute 40%

of the observed interstellar molecules.

• Formation Scheme

• Trace of formation scheme of carbon

chain.

→ Observation of 13C isotopic species

• Trace of formation scheme of carbon chain.

→ Observation of 13C isotopic species

C : 13C = 1 : 60

• Abundant molecule• If number of carbon is larger than

three, 13C observation is difficult.

HC3N

Introduction

Previous Research of HC3N

Takano et al., A&A. 329, 1156, 1998

[H13CCCN]:[HC13CCN]:[HCC13CN] = 1.0:1.0:1.4

Column Density (cm-2)

Relative ratio[Normal]/[13C]

H13CCCN (2.0 ± 0.2) × 1012 79 ±11

HC13CCN (2.1 ± 0.2) × 1012 75 ±10

HCC13CN (2.9 ± 0.3) × 1012 55 ±7

Dark Cloud TMC-1

equivalent

Thermal Isotopic Exchange Reaction

If thermal isotopic exchange reaction is working,

H13CCCN

HC13CCN

0 K

-48.9 K

-56.8 K

-63.8 KHCC13CN

HCCCN

Zero

-Poi

nt E

nerg

y

H13CCCN < HC13CCN < HCC13CN

H13CCCN = HC13CCN = HCC13CN

Previous Research of HC3N

Takano et al., A&A. 329, 1156, 1998

[H13CCCN]:[HC13CCN]:[HCC13CN] = 1.0:1.0:1.4

XCCX + YCNZ → HCCCN + ….

Dark Cloud TMC-1

Formation scheme from equivalent two carbons

⇒ Dicarbide Chemistry

C2H2 + CN → HC3N + H

C2H + HNC → HC3N + H

C2H2+ + HCN → HC3NH+ + H

C2H2 + HCNH+ → HC3NH+ + H2

Dicarbide Chemistry of HC3N in TMC-1 *

*Takano et al., A&A., 329, 1156, 1998

[13CCH] < [C13CH] in TMC-1Sakai et al., A&A. 512, A31, 2010

Formation scheme from equivalent two carbons

• Universality of the dicarbide chemistryfor evolutional phases ?

Dark cloud10 K

Star forming region25 K

CloudEvolution

Protostar

L1527 (class 0)Warm Carbon Chain

Chemistry region

Dicarbide Chemistry of HC3N

TMC-1

How about HC3N in star forming region ?

C2H2 + CN → HC3N + H

C2H + HNC → HC3N + H

C2H2+ + HCN → HC3NH+ + H

C2H2 + HCNH+ → HC3NH+ + H2

XCCX + YCNZ → HCCCN + …

*Takano et al, A&A, 329, 1156, 1998

Expected Dicarbide Chemistry of HC3N in L1527

[13CCH] < [C13CH] in L1527Sakai et al., A&A. 512, A31, 2010

[H13CCCN]:[HC13CCN] = 1 : 1 ?

L1527 4h 39m 53.89s 26d 03' 11".0 (J2000)

Outdoor sky map 2000

Galactic Plane

The equinoctial

Orion

Taurus

L1527: Low-mass star-forming region

Galactic Longitude [degree]

Gal

acti

c Lat

itud

e [

degr

ee]

Tokyo Gakugei University, http://darkclouds.u-gakugei.ac.jp/

TMC-1

L1527

Light Extinction

L1527: Low-mass star-forming region

Taurus Dark-Clouds Region

• Low-mass star-forming region L1527

• Green Bank 100 m telescope

• March-October 2015（on site and remote）

• HC3N, J = 5‒4, 42.5-45.5 GHｚ

• 43 hours of Observation Time

• S/N = 35‒44 for 13C species

• Excitation Temperature

J = 9-8 & 10-9 (NRO 45 m)

Observationon site remote

Results and Discussion

GBT

NRO

NRO

Excitation Temp. 12.1 KColumn Density (Isotopic Ratio)

GBT

NRO

NRO

Column Density of HCCCNOptically thick

τ = 0.44

Hyper Fine StructureHyper Fine Structure

Optically thinOptically thin

L1527 TMC-1*

H13CCCN 2.91 × 1011 (2.0 ± 0.2) × 1012

HC13CCN 2.95 × 1011 (2.1 ± 0.2) × 1012

HCC13CN (3.93 ± 0.17) × 1011 (2.9 ± 0.3) × 1012

HCCCN 2.52 × 1013 (1.6 ± 0.1) × 1014

Excitation Temp. 12.1 K-fix 7.1K-fix

Column Density

*Takano et al, A&A, 329, 1156, 1998

smallerby one order

(cm-2)

[H13CCCN] : [HC13CCN] : [HCC13CN] : [HCCCN]

1 : 1 : 1.4 : 79

1 : 1.01±0.03 : 1.35±0.04 : 86.4±2.2L1527

TMC-1

Precise Isotopic Abundance Ratios

C2H2 + CN → HC3N + H

C2H2+ + HCN → HC3NH+ + H

C2H2 + HCNH+ → HC3NH+ + H2

XCCX + YCNZ → HCCCN + …

• Dicarbide Chemistry in L1527

• Universality of the dicarbide chemistry of

HC3N for evolutional phases for dark cloud

(TMC-1) to Warm Carbon Chain Chemistry

Region (L1527).

Formation Scheme of HC3N in L1527

[H13CCCN] : [HC13CCN] : [HCC13CN] : [HCCCN]

1 : 1 : 1.4 : 79

1 : 1.01±0.03 : 1.35±0.04 : 86.4±2.2L1527

TMC-1

13C+ + CN C+ + 13CN + DE

13C+ + HCNH+ C + H13CNH+ + DE

kf

kb kf

kb

kb/kf DE L152725 K

TMC-110 K

CN 52.8 K 0.12 0.01

HCNH+ 32.4 K 0.27 0.04concentration × ✔

B3LYP/cc-pVTZ by Gaussian 09W

In case the 13C concentration scheme is thermally regulated, …

[H13CCCN] : [HC13CCN] : [HCC13CN] : [HCCCN]

1 : 1 : 1.4 : 79

1 : 1.01±0.03 : 1.35±0.04 : 86.4±2.2L1527

TMC-1

The 13C concentration scheme is not thermally regulated in L1527.

D and 15N species

GBT

GBT

[HCCCN]/[HCCC15N] = 338 ± 15

[DCCCN]/[HCCCN] = 0.0370 ± 0.0010

VLSR [Km/s]

• By using Green Bank 100 m telescope,

the 13C isotopic abundance ratios of HC3N were precisely observed.

• HC3N is formed by Dicarbide Chemistry with C2H2 and C2H2

+.

• Universality of the formation scheme of HC3N was found in evolutional phases from a dark cloud (TMC-1) to a warm carbon-chain chemistry region (L1527).

Summary