Identity of the Carrier of 5797 Diffuse Interstellar

Identity of the Carrier of λ 5797 Diffuse Interstellar Band λ 5800 Red-Rectangle Emission Band Keir Adams and Takeshi Oka 73 rd International Symposium on Molecular Spectroscopy June 18 -22, 2018 University of Illinois at Urbana-Champaign

The Diffuse Interstellar Bands: Matching Absorption Bands with Carriers What are the DIBs? • Series of ~500 broad absorption bands observed in the spectra of stars • Originate from gas-phase molecules throughout the interstellar medium • Since their discovery in 1919, only 2 DIBs have been matched with carriers Carbon Chains Fullerenes Polycyclic Aromatic Hydrocarbons (PAHs)

The Red-Rectangle Nebula: DIBs in Emission? ESA/NASA, Hubble

λ 5800 RRB and λ 6615 RRB λ 6613 DIB λ 5800 RRB λ 5797 DIB Van Winckel, H. , Cohen, M. , & Gull, T. R. 2002, A&A, 390, 147

λ 5797 DIB in the Red Rectangle λ 5800 RRB λ 5797 DIB University of Chicago DIB Database

Challenge to DIB-RRB Hypothesis: Non-Convergence of λ 5800 RRB to 5797 Å 6. 6” 2. 5” 10. 0” 14. 7” ESA/NASA, Hubble Sharp, R. G. , Reilly, N. J. , Kable, S. H. , Schmidt, T. W. : 2006, Ap. J, 639, 194

Hypothesis: Foreground-Absorption Red-Shifts the λ 5797 DIB Emission Peaks Objectives: I. To simulate the 5797 DIB emission spectrum, utilizing a polar carbon chain model II. To model the saturation of the blueward 5797 DIB emission by DIB absorbers within the Red Rectangle

Simulating λ 5797 DIB Emission Spectrum λ 5797 DIB Parameters (Huang & Oka, 2015)

Simulating the Extended Tail Toward Red (ETR)

Peak Wavelength Evolution of Simulated Emission 14. 7” 11. 8” 8. 5” 4. 8” 2. 5” ESA/NASA, Hubble

λ 5797 DIB Foreground Absorption

Combining λ 5797 Emission with Foreground Absorption Parameters Transition Dipole: 3 Debye DIB Column Density: Offset 2. 5” 1400 K 300 K 6. 6” 400 K 22 K 14. 3” 70 K 20 K

Conclusions I. λ 5797 DIB and λ 5800 RRB are caused by identical molecular carriers II. λ 5800 RRB’s broadened tail results from HD 44179 radiatively pumping high rotational states (the ETR effect) III. λ 5800 RRB’s non-convergence to 5797 Å is a consequence of self-absorption within the nebula that saturates the lower-wavelength emission

References 1. Huang, J. & Oka, T. 2015, Mol. Phys. 113, 15 2. Oka, T. , Welty, D. E. , Johnson, S. , York, D. G. , Dahlstrom, J. , & Hobbs, L. M. 2013, Ap. J, 773: 42 3. Van Winckel, H. , Cohen, M. , & Gull, T. R. 2002, A&A, 390, 147 4. Sharp, R. G. , Reilly, N. J. , Kable, S. H. , & Schmidt, T. W. 2006, Ap. J, 639: 194 5. Schmidt, G. D. , & Witt, A. N. 1991, Ap. J, 383: 698 6. Witt, A. N. , Vijh, U. P. , Hobbs, L. M. , Aufdenberg, J. P. , Thorburn, J. A. , & York, D. G. 2009, 693: 1946