ROBERT J. HARGREAVE

Srha rg rea@odu .edu

KENNETH

HINKLEh ink le@noao.edu

PETER F. BERNATH

pberna th@odu .edu

SMALL CARBON CHAINS IN CIRCUMSTELLAR SHELLS

MONDAY 16 T H JUNE 2014

I m a g e : L e ã o e t a l . 2 0 0 6 ( V LT )

AGB STELLAR EVOLUTION

Star forming region

(Orion Nebula)

Small star(Sun)

Red Giant(Aldebaran)

Planetarynebula

White dwarf

Massive star (Rigel)

Red supergiant(Betelgeuse)

Neutron star

Supernova

Black HoleAdapted from Essayweb 2014

Matter returns to form new stars

CIRCUMSTELLARENVELOPE

CIRCUMSTELLAR ENVELOPES

Thermal equilibrium stellar core

Dust Shell Acceleration Zone (shocks, pulsations)

Circumstellar envelope (3-30 km/s)

Outer envelope

r (cm)T (K)

~1013 (R*)~3000

~1014 (10R*)~1000

~1015 (100R*)~100

C/O < 1 H2O, TiO, VO, SiO, H2, CO…

OH → O + HH2O → OH +H

C/O > 1H2, CO, CN, C2,

C2H2, HCN…HCN → CN + H

CN → C + N

hν

hν

hν

hν

ISMPulsation Expanding Shell

IRC +10216 best studied example Over 80 molecules

Small carbon chains (C2, C3, C5) Long carbon containing chains are prominent species

HCn (n=1-8) H2Cn (n=2-4) HC2nN (n=1-5)

Small carbon chains expected to be building blocks Cyanopolyynes Polycyclic aromati c hydrocarbons (PAHs) Fullerenes (C60, C70 in planetary nebulae - Cami et al. 2010) Further complex molecules (amino acids?)

Circumstellar shells Obscures bright central star Ideal for observati ons in IR

CARBON-RICH SHELLS

Linear chains No permanent dipole moment Pure rotati onal lines forbidden Possess strongest vib-rot band in similar region Even numbered chains (excluding C 2) are less abundant

This study considered the following chains C3

ν3 mode at 2040.02 cm -1

Hinkle et al. (1988) in IRC +10216 C5

ν3 mode at 2169.44 cm -1

Bernath et al. (1989) in IRC +10216 C7

ν4 mode at 2138.31 cm -1

Yet to be identi fi ed in an astrophysical environment

SMALL CARBON CHAINS

6 obscured carbon stars observed GS-2010A-Q-74a

Similar AGB Mira variables Each has a circumstellar envelope Also bright reference stars

Phoenix spectrograph on Gemini South 8.1 m mirror Queue scheduled (GS-2010A-Q-74) R = λ/Δλ = 70,000

Reference observati ons are poor Noise was 5 % in some cases Bad for removing telluric features

OBSERVATIONS

Object 2045 cm-1

C3

2168 cm-1

C5

2138 cm-1

C7

CRL 865 24 Feb 21 Feb 23 Feb

IRC +10216 03 Mar 25 Feb 23 Feb

CRL 1922 12 Jun 01 Mar 26 Apr

CRL 2023 12 Jun 04 Mar 22 May

CRL 2178 - 23 May 27 Jun

CRL 3099 - 27 Jun -

Developed by Anu Dudhia (Oxford) www.atm.ox.ac.uk/RFM/

Line-by-l ine radiati ve transfer model Based on model by D. P. Edwards (1992) Typically used for MIPAS reference spectra

Instrument on the ENVISAT satellite in 2002 Limb scans of Earth’s atmosphere

Benefi ts Good for astronomical observati ons due to geometric

possibiliti es Cell transmitt ance Atmospheric transmitt ance Flux calculati ons Limb Radiance

Easy to use! HITRAN line list input

REFERENCE FORWARD MODEL (RFM)

No measured atmospheric profi le available for Gemini

Adjusted the ngt.atm profi le Used NCEP forcast model for lower

atmosphere profi le Matched to Gemini temperature

Molecular concentrati ons left unadjusted except: CO2 level updated to 2010 H2O scaled to match observation

SYNTHETIC REFERENCE SPECTRUM

170.00 220.00 270.00 320.00 370.001.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

1.0E+01

1.0E+02

1.0E+03

Synthetic

ngt.atm

NCEP

Gemini Telescope

Temperature [K]

Pre

ssu

re [m

b]

Spectra calibrated using l ines from HITRAN (Rothman et al. 2013) Reducti ons employed the IRAF routi nes to remove telluric l ines

Yields circumstellar shell transmission spectra

SYNTHETIC REFERENCE SPECTRUM

From Beer-Lambert:

Integrati ng over lineshape:

COLUMN DENSITIES

𝐼=𝐼 0 exp [−𝑆′𝑔 (𝜈−𝜈0 )𝑁𝑙 ]

𝑁 𝑙=1

𝑺′ ∫ 𝐥𝐧 (𝑰𝟎/ 𝑰 )𝒅𝝂

𝑺′=2𝜋 2𝜈𝑺 𝑱 ′ 𝑱 ′ ′

3𝜀0 h𝑐𝑄𝑇

exp (− 𝐸′ ′

𝑘𝑻 )[1− exp(−h𝜈𝑘𝑻 ) ]

Area of absorption peak

Absolute line strength

𝑺 𝑱 ′ 𝑱 ′ ′=|𝑀𝜈′𝜈′ ′|2∙ ( 𝐽 ′+1 )

Fit of observed peak intensities𝐼 ∝ ( 𝐽 ′+ 𝐽 ′ ′+1 )𝑒−𝐵′ ′ ( 𝐽 ′ ′ +1) h𝑐 /𝑘𝑇

PGOPHER Developed by C. Western

(pgopher.chm.bris.ac.uk) Simulates spectra based

on vib/rot constants Allows S’ to be calculated

Band strengths from ab initi o calculati on C3 – Jensen et al. 1992 C5 – Botschwina & Sebald

1989 C7 – Kranze et al. 1996

COLUMN DENSITIES

M =

M =

M =

C3

C3 R(2) C3 R(4) C3 R(8)

IRC +10216

ORIGIN used to fi t the C 3 l ines

Gaussian profi le All lines averaged

Esti mated 20% error

C3 COLUMN DENSITIES

Average ~7.3 x 1014 molecules/cm2C3 R(8)

C5

≤≤≤≤≤

IRC +10216

Only possible using syntheti c reference spectrum

Upper limit = 4.7 x 10 1 2 molecules/cm2

C7

IRC +10216

C3 agrees well with previous value Absorpti on depth ~20% Average ~7.3 x 1014 molecules/cm2

For IRC +10216 = 8.8 x 1014 molecules/cm2

Hinkle et al. (1988) =1.0(±0.15) x 10 15 molecules/cm2

C5 less than previous observati on 1.3 x 1013 molecules/cm2 with absorpti on depth ~1% Bernath et al. (1989), FTS observe ~3% depth

9.0(±2.5) x 1013 molecules/cm2

New value is 15% Within 25% of Botschwina & Sebald (1989) = 5 x 10 13 molecules/cm2

C7 upper limit Hinkle & Bernath (1993) = 2 x 10 13 molecules/cm2

New value lowers this limit to ≤ 4.7 x 1012 molecules/cm2

IRC +10216 COMPARISONS

Circumstellar model Millar et al. (2000) Nl for carbon chains Neutral carbon from Keene et al.

(1993)

Empirical column densiti es suggest a exponenti al decrease

Small carbon chain abundance Over esti mated by many orders

of magnitude C5 is 10,000 ti mes less abundant

than the model predicts

MODEL COMPARISONS

IRC +10216 carbon chain column densities

Linear carbon chain growth over esti mated in models C2 + CnH → Cn+2 + H

Cn + Cm → Cn+m + hν ( Cn+m + hν → Cn+m + e )

Complex processing leads to PAHs Cyanopolyynes Fullerenes

Loison et al. (2014) consider a revised model Interstellar clouds Include break down reaction for longer chains

e.g. C + C7 → C3 + C5

Limits abundance of longer chains

CONCLUSIONS

Demonstrated the power of syntheti c spectra Telescope ti me valuable Potenti al to replace reference observati ons

IRC +10216 Prototypical example Small carbon chain column densiti es compared

Suggest chemical models need refi ning

Provided C3 column densiti es for 3 additi onal circumstellar shells Included C5 upper limit for 5 circumstellar shells

Higher resoluti on observati ons are needed to detect C 7

Our results have reduced the upper limit column density

SUMMARY

THANKS FOR LISTENING

This work has been supported by NASA.

Thanks to the Daniel J. Frohman for advising upon the transiti on dipole moment strengths.

a T h i s w o r k wa s b a s e d o n o b s e r va ti o n s o b ta i n e d a t t h e G e m i n i O b s e r va t o r y ( G S - 2 0 1 0 A - Q - 7 4 ) , w h i c h i s o p e ra te d b y t h e A s s o c i a ti o n o f U n i ve rs i ti e s fo r R e s e a rc h i n A s t ro n o my, I n c . , u n d e r a co o p e ra ti ve a g r e e m e n t w i t h t h e N S F o n b e h a l f o f t h e G e m i n i p a r t n e rs h i p : t h e N a ti o n a l S c i e n c e F o u n d a ti o n ( U n i te d S ta te s ) , t h e N a ti o n a l Re s e a rc h C o u n c i l ( C a n a d a ) , CO N I C Y T ( C h i l e ) , t h e A u s t ra l i a n Re s e a rc h C o u n c i l ( A u s t ra l i a ) , M i n i s té r i o d a C i ê n c i a , Te c n o l o g i a e I n o va çã o ( B ra z i l ) a n d M i n i s te r i o d e C i e n c i a , Te c n o l o g í a e I n n o va c i ó n P ro d u c ti v a ( A rg e n ti n a ) .

Possible to determine shell speed IRAF can determine local standard of rest from velocity

contributi ons in directi on of observati on from date:

The shell can then be obtained as:

CIRCUMSTELLAR SHELL

𝑣 h𝑠 𝑒𝑙𝑙=𝑣 𝑙𝑠𝑟 −𝑣𝑜𝑏𝑗

𝑣 𝑙𝑠𝑟=𝑣𝑑𝑖𝑢𝑟𝑛𝑎𝑙+𝑣𝑎𝑛𝑛𝑢𝑎𝑙+𝑣 𝑙𝑢𝑛𝑎𝑟+𝑣𝑠𝑜𝑙𝑎𝑟

𝑣 h𝑠 𝑒𝑙𝑙𝑣 𝑙𝑠𝑟

𝑣𝑜𝑏𝑗