Ultraviolet Spectroscopy of HD 44179

Abstract

We have re-analyzed the ultraviolet spectrum of HD 44179, the central star(s) of the Red Rectangle nebula, providing improved estimates of the column density, rotational, and vibrational temperatures of the 4th Positive A-X system of CO in absorption. The flux shortward of 2200 A is a complex blend of CO features with no discernible stellar photosphere, making the identification of other molecular species difficult, and the direct derivation of the dust extinction curve impossible. We confirm that the spin-forbidden CO (a-X) Cameron bands are likely produced by either collisional excitation or a chemical reaction, not photoexcitation, but with a higher internal vibrational excitation than previously determined. We also detect the spin-forbidden CO a'-X, d-X, and e-X absorption features. The hot CO (A-X) bands exhibit a blue-shift of ~300 km/s, likely occurring close to the white dwarf star(s) suspected as the original source of the ultraviolet flux in the system, and forming the base of the outflow of material in the Red Rectangle. The OH "comet-band" system near 3000 A is also analyzed, and estimates of its rovibrational temperatures determined. The source of the molecules studied in this system is still unknown, but may be a combination of gaseous material associated with the star(s), or processed material from the surrounding dust torus.Comment: 40 pages, 14 figure

C2emission features in the Red Rectangle

“…A very broad Hα component as well as the fluorescent CO line emission in the UV reveal the presence of a hot (T 5500 K) fast molecular outflow ( 300 km s −1 ). There is also evidence for a rotationally cold (T 50 K) but vibrationally excited CO component (T 2000 K) which requires no velocity shift and has a width of some 20 km s −1 , comparable to the value derived from the C 2 lines (Sitko et al 2008). In contrast, the observed broadening of the C 2 bandhead is much larger than the width of the submillimeter, pure rotational, CO lines ( 5 km s −1 ).…”

“…This width is comparable to the narrow component, prominent in the Hα profile and the atomic (e.g., KI, CaII) and molecular lines (e.g., CH, CH + , and CN) lines (Hobbs et al 2004;Witt et al 2009). Some atomic lines show a more complex velocity profile with two components, at 13 and 25 km s −1 (Sitko et al 2008). Generally these components have comparable strength but not so for the Na D lines.…”

“…This accretion disk may have been (previously) fed by Roche lobe overflow from the post-AGB object, and part of the accretion disk material is accelerated outwards in a fast jet evident in the broad Hα and CO (UV) emission components (Sitko et al 2008;Witt et al 2009). The narrow Hα component has been attributed to a small HII region close to the binary stars, ionized by UV emission from the accretion disk (Jura et al 1997;Witt et al 2009).…”

Interstellar fullerene compounds and diffuse interstellar bands

“…Such conditions might be expected, but would need to be confirmed from models similar to that of Men'shchikov et al (2002), yielding a lack of ionizing far-UV photons resulting from the reddened F-type stellar spectrum and the absence of an additional ionizing source, together with a high gas density n > ∼ 10 4 cm −3 . But building such models would be difficult because of the complexity of the far-UV spectrum of the RR (Sitko et al 2008). …”

Excitation of thea 3Πstate of CO by electron impact

“…Since CO is a constituent of Earth's as well as Mars and Venus atmospheres, studies of electron impact excitation of CO are also of interest for planetary astrophysics [3]. Electron impact excitation is also recognized as an important mechanism for producing CO in the a 3 state, which has been detected via spin-forbidden Cameron bands in UV spectra of Mars and of other galactic objects beyond the Solar System [4].…”