Formation Mechanisms of
Cyanopolyynes and Chemical Evolution
in the High-Mass Star-Forming Regions	 HC2n+1N (n = 1,2,3,..)	
 Kotomi Taniguchi (SOKENDAI/Nobeyama Radio Observatory)
Main Supervisor; Prof. Masao Saito (NAOJ/SOKENDAI)
Tomoya Hirota (NAOJ), Hiroyuki Ozeki (Toho Univ.),
Fumitaka Nakamura (NAOJ), Yusuke Miyamoto, Tetsuhiro Minamidani,
Hiroyuki Kaneko (NRO), T. K. Sridharan (CfA),
Kazuhito Dobashi, Tomomi Shimoikura (Tokyo Gakugei Univ.)

Self Introduction	
 B.S. Department of Environmental Science, Faculty of Science, Toho University(Supervisor; Hiroyuki Ozeki)

2013 Mar“Laboratory spectroscopy, Spectroscopic identification of CH2IBr”
M.S. Department of Environmental Science, Faculty of Science, Toho University/Nobeyama Radio Observatory2015 Mar“Observations of the 13C isotopologues of HC5N”
2015 Apr. – present SOKENDAI/Nobeyama Radio Observatory(Supervisors; Masao Saito, Tomoya Hirota)
2017 Apr. - JSPS Fellowship (DC2)	
 Research Interest : Astrochemistry, Star/Planet Formation	 2018/02/02

2

Contents	 1. Introduction² Massive Star Formation Process² Astrochemistry& Carbon-Chain Chemistry in Low-Mass Star-Forming Regions² Chemistry in High-Mass Star-Forming Regions

2. Motivation of This Dissertation
3. Observations, Results & Discussions² Long Cyanopolyynes around MYSOs² Formation Mechanism of Cyanopolyynes in G28.28-0.36² Chemical Evolution in the High-Mass Star-Forming Regions

4. Summary
2018/02/02

3

Publications Related to Dissertation	 1. K. Taniguchi, H. Ozeki, M. Saito et al., ApJ, 817, 147 (2016)
2. K. Taniguchi, M. Saito, & H. Ozeki, ApJ, 830, 106 (2016)
3. K. Taniguchi, M. Saito, T. Hirota, et al., ApJ, 844, 68 (2017)
4. K. Taniguchi, H. Ozeki, & M. Saito, ApJ, 846, 46 (2017)
5. K. Taniguchi & M. Saito, PASJ, 69, L7 (2017)
6. K. Taniguchi, M. Saito, T. K. Sridharan, & T. Minamidani,
accepted by ApJ
2 papers are under preparation.	
 2018/02/02

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Contents	 1. Introduction² Massive Star Formation Process² Astrochemistry& Carbon-Chain Chemistry in Low-Mass Star-Forming Regions² Chemistry in High-Mass Star-Forming Regions

2. Motivation of This Dissertation
3. Observations, Results & Discussions² Long Cyanopolyynes around MYSOs² Formation Mechanism of Cyanopolyynes in G28.28-0.36² Chemical Evolution in the High-Mass Star-Forming Regions

4. Summary
2018/02/02

5

Massive Star Formation Process	
 overlapped	 High-Mass
High-Mass
Starless Core Protostellar Object(HMSC)	
 (HMPO)	
 n ~ 104-105 cm-3,
T ~ 15 K	 n ~ 106 cm-3,
T ~ 50 K	 Without 8.3 µm With 8.3 µm emission,
HMPO
HMSC
emission,
With
Without 3.6
cm emission	 1.2 mm emission	 ~ 104 yr
~ 6 × 104 yr

Hot Core	 Ultracompact
HII region(UCHII)	
 n > 107 cm-3,
T > 100 K,0.1 pc	
 n ~ 104 cm-3,
T ~100 - 200 K	
 6.7 GHz CH3OH
Hot Core
maser	 With cm emission	 Ultracompact
HII region~ 4 × 104 yr~ 104 yrGerner et al. (2014)	
 DestroyedbyFormed by the gas
Formed in warm Formed in warm
phase
processes
dense gas
Stillpoorlyunderstooddense
duecoreto observationaldifficultiesUV radiation(far, small sample, born in cluster)

Evaporation of CH4 & C2H2

2018/02/02

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Astrochemistry & Carbon-Chain Molecules	 Chemical composition : a good diagnostic tool forphysical conditions & evolutionary stages	 Carbon : Contained in ~75% molecules detected in the Universe
Carbon-chain molecules :ü ~ 40% of 200 interstellar moleculesü Provide useful information about starformation process from the foremost stage(e.g., chemical evolution)

Carbon-chain molecules= Important for star formation 	 http://dbnst.nii.ac.jp/view_image/763/1893?height=785&width=605	
 Confirmed only in low-mass star-forming regions	 2018/02/02

7

The Carbon-Chain Chemistry in
Low-Mass Star-Forming Regions (SFRs)	
 1. Chemical Evolutional IndicatorØ Abundant in young starless cores

N[CCS] (1012 cm-2)	
 (e.g., Suzuki et al., 1992, Hirota et al., 2009) 	
 

100	
 

Taurus	 Low-mass
SFRs	
 

10	
 

Ø Deficient in evolved star-forming cores	 They are formed by the gas-phase ionmolecule reactions containing C and C+	 2. Warm Carbon Chain Chemistry(e.g., L1527; Sakai et al., 2008) 	
 Methane(CH4)	
 
dust	
 

1	
 

0.1	
 
1	
 

10	
  100	
  1000	
 10000	
 N[NH3]/N[CCS]	
 T. Hirota et al. (2009)	
 Gas-phase reactions	 Carbon-chain
Evaporation	  CH4 + C+	 molecules	 T ~ 25 K	 (Yamamoto et al., 1983)	
 2018/02/02

8

Chemistry in High-Mass SFRs	 overlapped	 High-Mass
High-Mass
Starless Core Protostellar Object(HMSC)	
 (HMPO)	
 n ~ 104-105 cm-3,
T ~ 15 K	 n ~ 106 cm-3,
T ~ 50 K	 Without 8.3 µm
With 8.3 µm emission,
HMPO
HMSC
emission,
With
Without 3.6
cm emission	 1.2 mm emission	 ~ 104 yr
~ 6 × 104 yr

Formed by the gas?	
 phase processes

Hot Core	 Ultracompact
HII region(UCHII)	
 n > 107 cm-3,
T > 100 K, 0.1 pc	
 n ~ 104 cm-3,
T ~100 - 200 K	
 6.7 GHz CH3OH
Hot Core
maser	 With cm emission	 Ultracompact
HII region~ 4 × 104 yr~ 104 yrComplex
Organic
Formed in warm
Formedin warm
Molecules
dense coredense gas(e.g., CH3OH, CH3CN)	
 Evaporation of CH4 & C2H2

Gerner et al. (2014)	
 Destroyedby
UV radiation
2018/02/02

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Chemical Evolutionin High-Mass Star-Forming Regions	 Low-Mass Star-Forming Regions	 N[CCS] (1012 cm-2)	
 

100	
 

Taurus	 Low-mass
SFRs	
 How about High-Mass Star-Forming
Regions?	
 Expectation; Similar to that in
low-mass star-forming regions	
 

10	
 

N[carbon chains]	
 1	
 Destruction by
UV radiation	
 

HMSC	
 
0.1	
 
1	
 

10	
  100	
  1000	
 10000	
 N[NH3]/N[CCS]	
 T. Hirota et al. (2009)	
 

HMPO	
 
N[N-bearing species]/N[carbon chains]	
 2018/02/02

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Previous Researches on
Cyanopolyynes in Hot Cores	 Survey observation of HC5N (J = 12-11; Eu = 10.0 K)
toward hot cores associated with 6.7 GHz CH3OH maser	 	 (Green et al., 2014)	
 Detection Rate = 44% (35/79)(may be ambient cold gas component)

Beam size	 Beam size = 0.95’ (0.7 pc at d = 3 kpc) 	
 c.f. Typical hot core size ~ 0.1 pc	
 Their observations are not enough to
confirm that HC5N exists in hot cores	 2018/02/02

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Contents	 1. Introduction² Massive Star Formation Process² Astrochemistry& Carbon-Chain Chemistry in Low-Mass Star-Forming Regions² Chemistry in High-Mass Star-Forming Regions

2. Motivation of This Dissertation
3. Observations, Results & Discussions² Long Cyanopolyynes around MYSOs² Formation Mechanism of Cyanopolyynes in G28.28-0.36² Chemical Evolution in the High-Mass Star-Forming Regions

4. Summary
2018/02/02

12

Motivation & Goal of This Dissertation	
 Goal : Understand chemical properties of carbon-chain moleculesin the high-mass star-forming regions with evolution	 1. Are carbon-chain molecules associated with and/or formed
around massive young stellar objects (MYSOs)?
If they are formed, how are they formed?	
 Yes: Cyanopolyynes are formed from CH4/C2H2	
 2. Do carbon-chain molecules have relationship with evolutionof massive stars?
Probably Yes: (N(N2H+)/N(HC3N))	
 Focus on cyanopolyyne series (HC2n+1N; n=1,2,3,…)	
 Survive in the hot gas (T ~ 80 K) (Hassel et al., 2011)	
 2018/02/02

13

Contents	 1. Introduction² Massive Star Formation Process² Astrochemistry& Carbon-Chain Chemistry in Low-Mass Star-Forming Regions² Chemistry in High-Mass Star-Forming Regions

2. Motivation of This Dissertation
3. Observations, Results & Discussions² Long Cyanopolyynes around MYSOs² Formation Mechanism of Cyanopolyynes in G28.28-0.36² Chemical Evolution in the High-Mass Star-Forming Regions

4. Summary
2018/02/02

14

Long Cyanopolyynes
around Massive Young Stellar Objects	 Clear whether long cyanopolyynes exist in the warm gas
Ultracompact
aroundHot Core
HMSCMYSOs HMPOHII region

HMSC~ 104 yrHMPO
~ 6 × 104 yr

Hot~ 4 ×Core104 yrFormed by the gas
Formed in warm Formed in warmüConfirm
warm component
N gas
phase
processes
dense core of HC5dense

UCHII	
 ~ 104 yrDestroyed by
UV radiation

ü Detection of HC7N

Evaporation of CH4 & C2H2

ü A possibility of the chemical differentiation among MYSOs	
 WCCCChapman’s
mechanism
2018/02/02

15

Observational Details	
 G10.30-0.15(6.6 × 104 Lsun)	
 G12.89+0.49(3.4 × 104 Lsun)	
 Source Selection
Selected from HC5N-detectedsource list by Green et al. (2014)
applying the following criteria:
Spitzer	 Spitzer	 1. Decl. > -21°
G16.86-2.16
G28.28-0.36(4 × 103 Lsun)	
 (5.2 × 104 Lsun)	
 2. D < 3 kpc
3. CH3CN (hot core tracer) was
detected (Purcell et al., 2006)
WISE	
 Spitzer	 In order to detect HC7N, observations in the 27-29 GHz is suitable	
 GBT	
 In order to derive Trot of HC5N accurately, we need data with awide frequency range	
 
NRO	
 

2018/02/02	  16	
 Spectra Obtained with the GBT	 First detection of HC7N in 3 sources,
except G10.30-0.15	
 Rich inlong cyanopolyynes	 2018/02/02	  17	
 Spectra Obtained with the GBT	 First detection of HC7N in 3 sources	
 

HC7N	
 

HC7N	
 

2018/02/02	  18	
 Spectra Obtained with the GBT	 First detection of HC7N in 3 sources	 2018/02/02	  19	
 Spectra of HC5N with the Nobeyama	 G12.89+0.49	
 G16.86-2.16	
 G28.28-0.36	
 Trot > 15 K (17 ± 2 K)

Trot > 12 K
(13.8 ± 1.5 K)

J=38-37 (Eu = 94.7 K)	
 J=39-38 (Eu = 99.7 K)	
 Trot > 16 K (18 ± 2 K)

c.f. Typical Trot
Dark cloud; 5-8 K (Suzuki et al., 1992)
WCCC; 12-15 K (Sakai et al., 2008)	
 Warm component of HC5N	 2018/02/02	
  20	
 

15.5

70

15.0

60
X(HC5N) [×10-10]log[N(HC5N)/W(CH3OH)]

Chemical Differentiation among
High-Mass Star-Forming Cores	
 

14.5
14.0
13.5
13.0
12.5

G10.30-0.15 G12.89+0.49 G16.86-2.16 G28.28-0.36

Chemical differentiation
among four target MYSOs	
 

50
40
30

L1527 (WCCC)	
 

20
10
0

G10.30-0.15 G12.89+0.49 G16.86-2.16 G28.28-0.36

Carbon-chain molecules
are efficiently formed
around MYSOs	
 2018/02/02	
  21	
 Summary of This Subsection	
 Ultracompact

HMSC

HMPO

Hot Core

HMSC~ 104 yrHMPO
~ 6 × 104 yr

Hot~ 4 ×Core104 yrFormed by the gas
phase processes

HII regionUCHII	
 ~ 104 yrDestroyed by
Formed in warm Formed in warm
HCcorethe
5N exists in
UV radiation
dense
dense
gaswarm gas

around MYSOs abundantly	 Evaporation of CH4 & C2H2
WCCCChapman’s
Are carbon-chain moleculesmechanism

formed at the hot core position?	
 2018/02/02

22

Formation Mechanism of Cyanopolyynesin G28.28-0.36	
 Investigate possible triggers of cyanopolyyne formation
Ultracompact
Hot Core
inHMSCthis hot core	  HMPOHII region
HMSC~ 104 yrHMPO
~ 6 × 104 yr

Hot~ 4 ×Core104 yr

UCHII	
 ~ 104 yrDestroyed by
Formed by the gas
Formed in warm Formed in warmü Determinationof mainmechanismof
UV radiation
phase
processes
dense
core formation
dense
gas

HC3N from its 13C isotopic fractionation
Evaporation of CH4 & C2H2

ü Spatial distributions of cyanopolyynes

WCCCChapman’s
mechanism
2018/02/02

23

Spectra of 13C Isotopologues of HC3N
with the Nobeyama	 J = 9-8 in the 82 GHz band	 (Eu = 19.6 K)	
 J = 10-9 in the 91 GHz band
(Eu = 24.0 K)	
 Integrated Intensity Ratios(J = 9-8 transition)	
 H13CCCN	  HC13CCN	  HCC13CN	
 
1.0 (±0.2)	
 

1.00	
 

1.47 (±0.17)	
 2018/02/02	
  24	
 Possible Formation Pathways of HC3N 	
 
CCH

C2H2
C2H2+

+ HNC, - H+ CN, - H

+ HCNH+,- H2+ HCN,-H

HC3N+ e-, -H

HC3NH+
C3Hn+(n = 3-5)+ N,- H /- H2

Observational results	 H13CCCN	  HC13CCN	  HCC13CN	
 
1.0 (±0.2)	
 

1.00	
 

1.47 (±0.17)	
 (Based on UMIST 2012)	
 Expected fractionation patternsof each formation pathway	 The main formation pathway of HC3N
in G28.28-0.36 is “C2H2 + CN”	 Pathway 1 CCH + HNC[H13CCCN]:[HC13CCN]:[HCC13CN] = x : 1 : y	
 x > 1	 Pathway 2 C2H2 + CN
[H13CCCN]:[HC13CCN]:[HCC13CN] = 1 : 1 : z	 Pathway 3 HC3NH+ + e[H13CCCN]:[HC13CCN]:[HCC13CN] ~ 1 : 1 : 1	
 2018/02/02	  25	
 Comparisons with 450 µm
Warm Dust Emission	 Long cyanopolyynes exist
at the hot core region	 I’m sorry that I cannot upload figures in this slide,because the paper is under preparation.	
 2018/02/02

26

Possible Formation Mechanisms in
the G28.28-0.36 Hot Core I	 Warm Carbon Chain Chemistry (CH4-origin chemistry)
Methane(CH4)	
 dust	
 Gas-phase reactions	 Carbon-chain
Evaporation	  CH4 + C+	 molecules	 T ~ 25 K	 (Yamamoto et al., 1983)	
 X(HC5N)
G28.28-0.36 >> L1527 (× 20)	 

WCCC mechanism is not enoughto reproduce the observed X(HC5N)
in G28.28-0.36	
 2018/02/02

27

Possible Formation Mechanisms in
the G28.28-0.36 Hot Core II	
 Chapman’s Mechanism (C2H2-origin chemistry) (Chapman et al. 2009)	
 Acetylene(C2H2)	
 dust	
 Evaporation	
  C2H2 + CN → HC3N etc.	
 Tdust ≥ 50 K (Yamamoto et al., 1983)	
 Previous observations support this modelü C2H2 abundances in the gas phase in hot cores are highü C2H2 is thought to be evaporated from grain mantles	
 (Lahuis & van Dishoeck, 2000)	
 2018/02/02

28

Summary of This Subsection	
 Ultracompact

HMSC

HMPO

Hot Core

HMSC~ 104 yrHMPO
~ 6 × 104 yr

Hot~ 4 ×Core104 yrFormed by the gas
phase processes

HII regionUCHII	
 ~ 104 yrFormed in HC
warmN exists
Formedin warm
warm gas Destroyed byin the5
UV radiation
dense coredenseabundantly	 gasaround MYSOs
Evaporation of CH4 & C2H2

dust	
 

Evaporation	
 Cyanopolyynes are
WCCCChapman’sformedin the warm gas 	 mechanism

2018/02/02

29

Chemical Evolution
in the High-Mass Star-Forming Regions	 Investigate more common characteristics of HC3N in the early
Ultracompact
HMPO
high-mass
regions	  Hot Core
HMSC star-forming
HII region

HMSC~ 104 yrHMPO
~ 6 × 104 yr

Formed by the gas
Formed in warmü N(HC
ratio
phase
processes
dense
core
3N) vs. L/M

Hot~ 4 ×Core104 yr

UCHII	
 ~ 104 yrFormed in warm
dense gas

Destroyed by
UV radiation

ü Chemical evolutional indicator, N(N2H+)/N(HC3N) ratio
Evaporation of CH4 & C2H2

WCCCChapman’s
mechanism
2018/02/02

30

Observational Details	
 Source Selection	 Selected from HMSC list (Sridharan et al., 2005) & HMPO list
(Sridharan et al., 2002) applying the following criteria:
1. Decl. > -6° for HMSCs & +6° for HMPOs
2. NH3 has been detected
3. HMPOs located in the same region as the observed HMSCs
Species & Line Selection	
 HC3N : High detection rate & surely excited even in HMSCs
N2H+ : Tex and N can be derived from its hyperfine splitting &D isotopologues	 2018/02/02

31

Correlation between N(HC3N) and N(H2)	
 
1014

N(HC3N) [cm-2]

1e+0141013
1e+0131012

1e+012●: HMSC (Present work)〇: HMPO (Present work)▲: HMSC (Sakai et al., 2008)△: HMPO (Sakai et al., 2008)

1e+011
1e+0231022

1e+024

1023
Ngas [cm-2]

1e+0251024

10-90.0000000010

Kendall’s tau correlation coefficient (τ)
HMSC : +0.16 (p = 38.4 %) → Independent
HMPO : +0.63 (p = 5 ×10-4%) → Positive
10-10
correlation	
 HC3N exists indense gas in HMPOs	
 )0.0000000001

2018/02/02	  32	
 Relationship between Physics &Chemistry in HMPOs	
 Luminosity-to-mass ratio (L/M) : physical evolutional indicator 	
 (Sridharan et al., 2002)	
 τ = -0.34 (p = 31 %)→ Weak negative correlation
Physical evolution	
 HC3N is destroyed by stellar activities (e.g., UV radiation)	
 2018/02/02	  33	
 Chemical Evolutional Indicator	 N(HC3N) increases
N(N2H+) slightly decreases	 I’m sorry that I cannot upload the figure in this slide,because the paper is under preparation.	
 2018/02/02	  34	
 Interpretation of Chemical
Evolutional Indicator	 Increasing N(HC3N)	
 • WCCC (CH4-origin)mechanism• Chapman’s (C2H2-origin)mechanism

Decreasing N(N2H+)	
 • N2H+ + CO → N2 + HCO+	
 • Tsub(CO) = 20 K
(Yamamoto et al., 1983)	
 Tdust ~ 50 – 200 K (HMPOs)(Sridharan et al., 2002)• Tsub(CH4) = 25 K

CH4, C2H2, and CO can• Tsub(C2H2) = 50 K
evaporate into the gas phase	 (Yamamoto et al., 1983)	
 2018/02/02	  35	
 High-Mass SFR vs. Low-Mass SFR	 N[carbon chains]	
 The tendency in the high-mass SFR is
opposite to the low-mass SFR	 Temperature	
 N[N-bearing species]/N[carbon chains]	
 High-mass SFR	 I’m sorry that I cannot upload the figure,because the paper is under preparation.	
 N[CCS] (1012 cm-2)	
 

100	
 

Low-mass
Taurus	  SFR	
 Low-mass SFRs	
 

10	
 

1	
 

0.1	
 
1	
 

10	
  100	
  1000	
 10000	
 N[NH3]/N[CCS]	
 T. Hirota et al. (2009)	
 2018/02/02	
  36	
 Summary of This Subsection	
 Ultracompact

HMSC

HMPO

Hot Core

HMSC~ 104 yrHMPO
~ 6 × 104 yr

Hot~ 4 ×Core104 yrFormed by the gas
Formed in warm Formed in warm+
1. processes
N(N2H )/N(HCN) ratio dense gas
phase
dense3core

HII regionUCHII	
 ~ 104 yrDestroyed by
UV radiation

decreases from HMSCs to HMPOs	
 Evaporation of CH4 & C2H2

2. HC3N is formed in the warm
dense gas around YSOs	
  WCCCChapman’s
mechanism

2018/02/02

37

Contents	 1. Introduction² Massive Star Formation Process² Astrochemistry& Carbon-Chain Chemistry in Low-Mass Star-Forming Regions² Chemistry in High-Mass Star-Forming Regions

2. Motivation of This Dissertation
3. Observations, Results & Discussions² Long Cyanopolyynes around MYSOs² Formation Mechanism of Cyanopolyynes in G28.28-0.36² Chemical Evolution in the High-Mass Star-Forming Regions

4. Summary
2018/02/02

38

Summary of the Cyanopolyyne Chemistryin High-Mass Star-Forming Regions	
 
HMSC

HMPO

Hot Core

Ultracompact
HII region

~ 104 yr

~ 6 × 104 yr~ 4 × 104 yr~ 104 yrFormed by the gas
phase processes

Formed in warm
dense core

Formed in warm
dense gas

Destroyed by
UV radiation

May be more
evolved than lowmass starless cores	 Evaporation of CH4 & C2H2
WCCCChapman’s
mechanism

Gerner et al. (2014)	
 2018/02/02

39

Summary	 1. Are carbon-chain molecules associated with and/or formed
around massive young stellar objects (MYSOs)?
If they are formed, how are they formed?
Yes : Cyanopolyynes are formed from CH4 and/or C2H2
evaporated from grain mantles around MYSOs.	
 2. Do carbon-chain molecules have relationship withevolution of massive stars?
Probably Yes : The N(N2H+)/N(HC3N) ratio decreases from
HMSCs to HMPOs.	
 Observations of cyanopolyynes= a good tool for investigation ofmassive star formation process successively
Thank you very much for your attention

2018/02/02

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