SIMBAD references

1998ApJ...508..387B - Astrophys. J., 508, 387-396 (1998/November-3)

The circumstellar shell of the post-asymptotic giant branch star HD 56126: 12C12C/12C13C isotope ratio and 12C16O column density.

BAKKER E.J. and LAMBERT D.L.

Abstract (from CDS):

We have made the first detection of circumstellar absorption lines of the 12C13C A{thinsp}1Πu-X{thinsp}1Σ+g (Phillips) system 1-0 band and the 12C16O X{thinsp}1Σ+ first-overtone 2-0 band in the spectrum of the post-AGB star HD 56126 (IRAS 07134+1005). All current detections of circumstellar molecular absorption lines toward HD 56126 (12C2, 12C13C, 12C14N, 13C14N, and 12C16O) yield the same heliocentric velocity of VCSE = 77.6 ± 0.4 km.s–1. The 12C2, 12C13C, and 12C16O lines give rotational temperatures and integrated column densities of Trot = 328±37 K, log Nint = 15.34±0.10 cm–2, Trot = 256±30 K, log Nint = 13.79±0.12 cm–2, and Trot = 51±37 K, log Nint = 18.12±0.13 cm–2, respectively. The rotational temperatures are lower for molecules with a higher permanent dipole moment. Derived relative column densities ratios are 12C2/12C13C = 36±13 and 12C16O/(12C2 + 12C13C) = 606±230. Combined with data from a previous paper, we find relative column densities of 12C16O/(12C14N + 13C14N) = 475 ± 175 and 12C14N/13C14N = 38±2. Under chemical equilibrium conditions, 12C13C is formed twice as easily as 12C2. The isotopic exchange reaction for 12C2 is too slow to significantly alter the 12C2/12C13C ratio, and the 12C2 to 12C13C ratio is a good measure of half the carbon isotope ratio: 12C/13C = 2x12C2/12C13C = 72±26. This is in agreement with our prediction that the isotopic exchange reaction for 12C14N is efficient and our observation in Paper III of 12C14N/13C14N = 38±2. A fit of the C2 excitation model of van Dishoeck & Black to the relative population distribution of C2 yields nc{thinsp}σ/I = 3.3±1.0x10–14. At r ≃ 1016 cm, this translates into nc = 1.7x107 cm–3 and M{dot}≃2.5x10–4 M.yr–1.

Abstract Copyright:

Journal keyword(s): Stars: Circumstellar Matter - Line: Identification - Molecular Data - Molecular Processes - Stars: AGB and Post-AGB - Stars: Individual: Henry Draper Number: HD 561265 (read: HD 56126)

Simbad objects: 6

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