Scanner Observations of λ 4430

Abstract

The interstellar band at X 4430 has been observed using the Lick Observatory scanning spectrophotometer. Although in some instances, particularly with early B supergiants, the feature is badly blended with stellar lines, in general the central depth of X 4430 has been determined to an accuracy exceeding 0.5 per cent of the stellar continuum. The feature has been found to have a fairly symmetrical profile although there may be changes in the profile from star to star. The extended wings reported by other observers were not detected and also no change in polarization due to the feature was found. The correlation between X 4430 and color excess is not one-to-one. Even field stars lying in the galactic plane show much intrinsic scatter in the ratio of X 4430 to color excess. For some clusters the slope of the correlation between X 4430 and color excess differs from that found for field stars; this can be interpreted as local variations in the ratio of X 4430 absorption to interstellar dust. Destruction of X 4430 in the vicinity of hot stars cannot account for all of these variations. The band at X 4430 is found to be weakened in dust clouds that lie outside the galactic plane. The scatter in the relationship between X 4430 and color excess as well as the probable detection of X 4430 in p Leonis is evidence that X 4430 may be produced by an agent of the interstellar medium other than that which causes the extinction.