Oscillator Strengths and Predissociation Widths for Rydberg Transitions in CO between 930 and 935 Å S.R. Federman, Y. Sheffer (Univ. of Toledo) M. Eidelsberg, J.L. Lemaire, F. Rostas (Obs. de Paris, Meudon and Univ. de Cergy-Pontoisse) J.H. Fillion (Univ. UMPC, Paris VI) This research was supported by NASA and the CNRS-PCMI program

Introduction Background CO observed in many astronomical environments –Diffuse and dark, molecular interstellar clouds –Circumstellar shells of asymptotic giant branch stars and planetary nebulae –Circumstellar disks around newly formed stars –Comets and planetary atmospheres

Introduction Processes affecting mix of isotopologues Isotope Charge Exchange – favors 13 C 16 O –It has lower zero-point energy – 13 C C 16 O → 12 C C 16 O – ΔE (ΔE/k ≈ 35 K) Selective Isotopic Photodissociation – favors more abundant isotopic variant –Dissociation occurs through line absorption at far UV wavelengths –More abundant variant has lines that are more optically thick, shielding itself from further dissociation

Introduction Hubble Space Telescope results on diffuse interstellar clouds IS Ratios: 12 C/ 13 C = 70±7; 16 O/ 18 O = 560±25; 16 O/ 17 O = 1900±200 RatioX Per  Oph A χ Oph  Oph N( 12 C 16 O)/N( 13 C 16 O)73±12125±23117±35167±15 N( 12 C 16 O)/N( 12 C 18 O)3000± ±500…1550±440 N( 12 C 16 O)/N( 12 C 17 O)8700±3600……≥ 5900

Introduction Problems Detailed models can reproduce either the isotopologic ratios or the total column density, but not both with the same model Models for diffuse molecular clouds produce too little CO Solution? Part of the problem may lie in adopted oscillator strengths (f-values), which now seem too small for many important transitions –Small f-values lessen amount of self shielding, but need more self shielding

Our Previous Measurements on CO Federman et al. (2001, ApJS, 134, 133) Used the Synchrotron Radiation Center of the Univ. of Wisconsin-Madison Derived f-values for the B – X (0-0), B – X (1-0), C – X (0-0), C – X (1-0), and E – X (0-0) bands (above 1075 Å) –Our results agree with other determinations based on electron energy loss and laser absorption

Our Previous Measurements on CO Far Ultraviolet Spectroscopic Explorer Observations HD A (Sheffer et al. 2003, ApJ, 597, L29)

Our Previous Measurements on CO Eidelsberg et al. (2004, A&A, 424, 355) Used the SU5 beam line at the SuperACO Synchrotron in Orsay Derived f-values for the K – X (0-0), L′ – X (1-0), L – X (0-0) bands for 12 C 16 O, 13 C 16 O, and 13 C 18 O (967 – 972 Å) –There is significant mixing among bands, but sum of f-values independent of isotopologue –First measurements on 13 C 18 O

Our Previous Measurements on CO Eidelsberg et al. (2006, ApJ, 647, 1543) Published additional data acquired on SU5 beam line –Focus on the W – X (v′-0; v′=0-3) bands as well as E – X (1-0) and B – X (6-0) bands [B – X (6-0) formerly called F – X (0-0) band] –Studied f-values and predissociation widths for 12 C 16 O, 13 C 16 O, and 13 C 18 O –Analysis based on profile syntheses that adjusted the band oscillator strength and line width (instrumental, thermal, and predissociation) in a non-linear least-squares fashion –Allowed for J-dependent predissociation widths

Oscillator Strengths for CO Comparison of Results for W – X Bands (f-value × 10 3 ) Italics: measurements at 20 K Reference(0-0)(1-0)(2-0)(3-0) Eidelsberg et al ( 12 C 16 O)16.6± ± ± ±1.4 Sheffer et al ( 12 C 16 O)…15.8±2.023±519.8±2.4 Eidelsberg et al ( 12 C 16 O)12.1± ± ± ±1.6 Stark et al. 1992, 1993, 1994 ( 12 C 16 O)12.9± ± ± ±1.5 Yoshino et al ( 12 C 16 O)13.6± ± ± ±2.6 Eidelsberg et al ( 13 C 16 O)15.1± ± ± ±1.4 Eidelsberg et al ( 13 C 16 O)13.2± ± ± ±1.9 Eidelsberg et al ( 13 C 18 O)13.8±2.0perturbed29.7± ±2.4 Eidelsberg et al ( 13 C 18 O)13.2± ± ± ±1.9

Measurements at the SOLEIL Synchrotron Used the DESIRS beamline with a VUV FTS

Measurements at the SOLEIL Synchrotron The FTS (de Oliveira et al. 2009, Rev. Sci. Instru., 80, ) Resolving power as high as 750,000 Based on wave front division instead of amplitude division Relies on modified bimirror configuration requiring only flat mirrors Path difference scanning through translation of one reflector

Measurements at the SOLEIL Synchrotron Preliminary results Calibration band and line profile –Used the B – X (0,0) and (1,0) bands for calibration [perturbations affect the E – X (0,0) band and W – X bands too strong] –Used an Airy function for the line shape

Measurements at the SOLEIL Synchrotron Preliminary results Initial studies of series of bands between 930 and 935 Å in 12 C 16 O, 13 C 16 O, 13 C 18 O, and 12 C 17 O (first measurements on 12 C 17 O) Significant mixing is present –In 12 C 16 O have interactions among 4pπ(2), II 1 Π, 4pσ(2), 5pπ(0), 5pσ(0), and I 1 Π

Measurements at the SOLEIL Synchrotron Preliminary results

Measurements at the SOLEIL Synchrotron Preliminary results

Measurements at the SOLEIL Synchrotron Preliminary results § integrated limits a this value represents only the f-value of the R branch of 5p b this is sum of II 1 Π, 4pσ(2), and 5pπ(0) c this is sum of 5pσ(0) and I 1 Π Band λ (Ǻ) f-values (upper level) limits ( × ) PresentE91 S91 Y95 4p  (2) (0.7)6.1(0.9) II 1  § - 4p σ (2) (2.2) 5p  (0) Σ = b § 5p  (0) (0.8) a § - I1I1 (1.6) Σ = c §  (5.4)

Future Work Complete analysis on these bands, including a set of predissociation widths With the improved spectral resolution, refine results for the W – X bands Perform measurements with a cooled free jet (≈ 30K) A special focus on transitions in 12 C 17 O Study many of the bands between 885 and 972 Å, especially those thought to be important for photodissociation in interstellar space