ROBERT J. HARGREAVES KENNETH HINKLE PETER F. BERNATH SMALL CARBON CHAINS IN CIRCUMSTELLAR SHELLS MONDAY 16 TH JUNE 2014 Image: Leão et al (VLT)

AGB STELLAR EVOLUTION Star forming region (Orion Nebula) Small star (Sun) Red Giant (Aldebaran) Planetary nebula White dwarf Massive star (Rigel) Red supergiant (Betelgeuse) Neutron star Supernova Black Hole Adapted from Essayweb 2014 Matter returns to form new stars CIRCUMSTELLAR ENVELOPE

CIRCUMSTELLAR ENVELOPES Thermal equilibrium stellar core Dust Shell Acceleration Zone (shocks, pulsations) Circumstellar envelope (3-30 km/s) Outer envelope r (cm) T (K) ~ (R * ) ~ 3000 ~ (10R * ) ~1 000 ~ (100R * ) ~1 00 C/O < 1 H 2 O, TiO, VO, SiO, H 2, CO… OH → O + H H 2 O → OH +H C/O > 1 H 2, CO, CN, C 2, C 2 H 2, HCN… HCN → CN + H CN → C + N hνhν hνhν hνhν hνhν ISMPulsation Expanding Shell

 IRC best studied example  Over 80 molecules  Small carbon chains (C 2, C 3, C 5 )  Long carbon containing chains are prominent species  HC n (n=1-8)  H 2 C n (n=2-4)  HC 2n N (n=1-5)  Small carbon chains expected to be building blocks  Cyanopolyynes  Polycyclic aromatic hydrocarbons (PAHs)  Fullerenes (C 60, C 70 in planetary nebulae - Cami et al. 2010)  Further complex molecules (amino acids?)  Circumstellar shells  Obscures bright central star  Ideal for observations in IR CARBON-RICH SHELLS

 Linear chains  No permanent dipole moment  Pure rotational 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  C 3  ν 3 mode at cm -1  Hinkle et al. (1988) in IRC  C 5  ν 3 mode at cm -1  Bernath et al. (1989) in IRC  C 7  ν 4 mode at cm -1  Yet to be identified in an astrophysical environment SMALL CARBON CHAINS

 6 obscured carbon stars observed  GS-2010A-Q-74 a  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 observations are poor  Noise was 5 % in some cases  Bad for removing telluric features OBSERVATIONS Object 2045 cm -1 C cm -1 C cm -1 C 7 CRL Feb21 Feb23 Feb IRC Mar25 Feb23 Feb CRL Jun01 Mar26 Apr CRL Jun04 Mar22 May CRL May27 Jun CRL Jun-

 Developed by Anu Dudhia (Oxford)   Line-by-line radiative 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  Benefits  Good for astronomical observations due to geometric possibilities  Cell transmittance  Atmospheric transmittance  Flux calculations  Limb Radiance  Easy to use!  HITRAN line list input REFERENCE FORWARD MODEL (RFM)

 No measured atmospheric profile available for Gemini  Adjusted the ngt.atm profile  Used NCEP forcast model for lower atmosphere profile  Matched to Gemini temperature  Molecular concentrations left unadjusted except:  CO 2 level updated to 2010  H 2 O scaled to match observation SYNTHETIC REFERENCE SPECTRUM

 Spectra calibrated using lines from HITRAN (Rothman et al. 2013)  Reductions employed the IRAF routines to remove telluric lines  Yields circumstellar shell transmission spectra SYNTHETIC REFERENCE SPECTRUM

 From Beer-Lambert:  Integrating over lineshape: COLUMN DENSITIES Area of absorption peak Absolute line strength Fit of observed peak intensities

 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 initio calculation  C 3 – Jensen et al  C 5 – Botschwina & Sebald 1989  C 7 – Kranze et al COLUMN DENSITIES M =

C3C3 C 3 R(2) C 3 R(4) C 3 R(8) IRC

ORIGIN used to fit the C 3 lines  Gaussian profile  All lines averaged Estimated 20% error C 3 COLUMN DENSITIES Average ~ 7.3 x molecules/cm 2 C 3 R(8)

C5C5 ≤ ≤≤≤≤≤≤≤≤≤≤ IRC  Only possible using synthetic reference spectrum

 Upper limit = 4.7 x molecules/cm 2 C7C7 IRC

 C 3 agrees well with previous value  Absorption depth ~ 20%  Average ~ 7.3 x molecules/cm 2  For IRC = 8.8 x molecules/cm 2  Hinkle et al. (1988) =1.0(±0.15) x molecules/cm 2  C 5 less than previous observation  1.3 x molecules/cm 2 with absorption depth ~ 1%  Bernath et al. (1989), FTS observe ~ 3% depth  9.0(±2.5) x molecules/cm 2  New value is 15%  Within 25% of Botschwina & Sebald (1989) = 5 x molecules/cm 2  C 7 upper limit  Hinkle & Bernath (1993) = 2 x molecules/cm 2  New value lowers this limit to ≤ 4.7 x molecules/cm 2 IRC COMPARISONS

 Circumstellar model  Millar et al. (2000)  Nl for carbon chains  Neutral carbon from Keene et al. (1993)  Empirical column densities suggest a exponential decrease  Small carbon chain abundance  Over estimated by many orders of magnitude  C 5 is 10,000 times less abundant than the model predicts MODEL COMPARISONS IRC carbon chain column densities

 Linear carbon chain growth over estimated in models  C 2 + C n H → C n+2 + H  C n + C m → C n+m + hν ( C n+m + hν → C n+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 + C 7 → C 3 + C 5  Limits abundance of longer chains CONCLUSIONS

 Demonstrated the power of synthetic spectra  Telescope time valuable  Potential to replace reference observations  IRC  Prototypical example  Small carbon chain column densities compared  Suggest chemical models need refining  Provided C 3 column densities for 3 additional circumstellar shells  Included C 5 upper limit for 5 circumstellar shells  Higher resolution observations 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 transition dipole moment strengths. a This work was based on observations obtained at the Gemini Observatory (GS-2010A-Q-74), which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência, Tecnologia e Inovação (Brazil) and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina).

 Possible to determine shell speed  IRAF can determine local standard of rest from velocity contributions in direction of observation from date:  The shell can then be obtained as: CIRCUMSTELLAR SHELL