A B S T R A C TWe have observed the Red Rectangle nebula with the Multi-Object Spectrograph on the WIYN telescope. Moderate-resolution spectra (Dl ¼ 0.4 Å ) in the region of 5800 Å were obtained in 3-arcsec apertures at over 50 positions in the nebula. Accurate and precise wavelength calibrations were obtained against a thorium-argon lamp and the sodium lines in the sky and nebula. The peak position and full width at half-maximum of the 5800-Å Red Rectangle band (RRB) were measured to beyond 15 arcsec from the star. The shortest wavelength of the band is found to be 5799.10^0.15 Å in the rest frame of the nebula. None of the emission bands has intensity coincident with the wavelength of the diffuse interstellar band (DIB) at 5797.11^0.05 Å . The 2-Å offset cannot be explained by an instrumental, spectroscopic or photophysical effect. The hypothesis that the same molecule may be the carrier of the RRB and the DIB is contradicted by these observations. As a further test of the hypothesis, absorption has been sought that would be due to a potential DIB carrier in the nebula. Tentative evidence for absorption is found in the RRB spectra taken within 9 arcsec of the star; but any absorption has a peak position essentially coincident in wavelength with the band maximum of the emission band.

No abstract

No abstract

A B S T R A C TWe have calculated synthetic spectra of perpendicular and parallel rovibronic bands of cumulene carbene molecules of the form C n H 2 . The perpendicular bands are consistent with a regularly spaced group of diffuse interstellar bands (DIBs) near 6850 A Ê . Parallel bands calculated for these molecular structures are consistent with the intrinsic profile of the associated 6614-A Ê DIB. Both types of bands are expected for an electronic transition that these species should have at those energies. We could not determine if the molecule was charged or if an atom other than carbon terminated the chain-end. Constraints due to molecular geometry and temperature place the chain length at 7±15 carbons to fit the 6850-A Ê group and 9±13 carbons to fit the 6614-A Ê DIB.

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

We have constructed a concentric-shell, one-dimensional kinetic model that examines the chemistry of hydrogen and oxygen species in detail. We have studied the effects of the reactions of the reactive OH, O(3 P), and O(1 D) species with themselves and with the abundant stable molecules in the inner coma of moderately and highly active comets. We find that the reactions (1) Oð 1 DÞ þ H 2 O ! 2OH and (2) Oð 3 PÞ þ OH ! O 2 þ H play important roles in the inner comae of active comets. Inclusion of reaction (2) predicts the formation of significant amounts of molecular oxygen. As the densities of O 2 may be as high as 1% those of water in some cases, the possibility of detection exists. We suggest the possibility that the ion O þ 2 may contribute to some previously unassigned features in the optical ion-tail spectra of comets. We also consider the role that reactions of the reactive species might play in the destruction of CO, NH 3 , and organic molecules in the inner coma of the active comet. We find that destruction of formaldehyde, for example, by reaction with OH has a small but essentially negligible effect on the predicted production rate of formaldehyde. Finally, we examine the significance of the reaction of OH with CO in the dense inner coma.

No abstract

No abstract