On the Red Rectangle optical emission bands

Abstract

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.

The offset dependent behavior of narrow optical emission features in the Red Rectangle proto-planetary nebula

“…Scarrott et al (1992) and Sarre et al (1995) argued that the carriers of certain (generally stronger) emission features in the Red Rectangle can be linked to carriers of specific DIBs and that the shifting wavelengths of the bands observed in the nebula would converge onto DIB wavelengths if measured to sufficiently large offsets from the central star of the Red Rectangle. This idea was challenged by Glinski & Anderson (2002). The present study also does not confirm this link between the Red Rectangle emission bands and the diffuse interstellar absorption bands (DIBs).…”

“…-The stronger emission bands in Fig. 3 (panels b, e and f), located at around ∼5800, 5825, 5852, 6380 and 6615 Å, have been reported previously to shift towards the blue and to narrow with distance from the central star (Schmidt & Witt 1991;Scarrott et al 1992;Sarre et al 1995;Van Winckel et al 2002;Sharp et al 2006) or at least to vary with distance (Glinski & Anderson 2002). These trends are confirmed here: particularly when the bands already appear for an offset of 3 , the bandshift becomes very obvious.…”

“…Superimposed on the ERE a chaotic pattern of narrow emission features has been found. The emission complex around 5800 Å with mainly stronger narrow emission features has been described by Schmidt & Witt (1991), Scarrott et al (1992), Sarre et al (1995), Van Winckel et al (2002), Glinski & Anderson (2002), and Sharp et al (2006). Recently, two of the weaker narrow emission bands have been attributed to C 2 emission features starting from rovibronically excited energy levels (Glinski et al 2009;Wehres et al 2010).…”

“…Some of these narrow emission features have been proposed as the emission equivalent of some A&A 533, A28 (2011) of the well known diffuse interstellar absorption bands (DIBs) (Scarrott et al 1992;Sarre et al 1995;Van Winckel et al 2002). For an opposing view see also Glinski & Anderson (2002).…”

An optical absorption study of the Helix planetary nebula

“…The initial findings of Scarrott et al (1992) and Sarre et al (1995) connecting the optical emission bands in the Red Rectangle (RR) with a subset of well-known DIBs have been qualified recently by Van Winckel et al (2002) and Glinski & Anderson (2002) on the basis of e.g. a 2 Å wavelength mismatch between the λ5797 DIB in the ISM and the nearby ∼5800 Å RR emission band.…”