Rejection of the C7- diffuse interstellar band hypothesis

Using the new high-resolution (similar to8 km s(-1)) echelle spectrograph on the 3.5 in telescope at the Apache Point Observatory, we have begun a high-sensitivity survey of the diffuse interstellar bands (DIBs) in a large sample of reddened stars. Now that we are 2 years into this long-term survey, our sample includes over 20 reddened stars that show at least one of the DIBs that had been suggested to be caused by C-7(-), based on the gas-phase measurement of the C-7(-) spectrum by J. P. Maier's group. The high-quality astronomical data from this larger sample of stars, along with the spectroscopic constants from the new laboratory work recently reported by Maier's group, have enabled us to examine more carefully the agreement between C-7(-) and the DIBs. We find that none of the C-7(-) bands match the DIBs in wavelength or expected profile. One of the DIBs (lambda 5748) attributed to C-7(-) is actually a stellar line. The two strongest DIBs attributed to C-7(-) (lambda 6270 and lambda 4964) are not correlated in strength, so they cannot share the same carrier. On the whole, we find no evidence supporting the hypothesis that C-7(-) is a carrier of the DIBs.