Balmer line photometry of the 30 doradus nebula

Abstract

The 30 Doradus nebula was scanned at 29 strips of constant declination with a square diaphragm of 30" x 30" using Hα and Hβ interference filters. The absolute flux calibration was obtained from observations of six planetary nebulae. Maps, integrated fluxes, and peak brightness values are given. The ratio between the Hα and Hβ intensities is compared with the theoretical value obtained from recombination theory, to calculate the amount of interstellar reddening. The visual absorption fluctuates rapidly from point to point, but there is a systematic increase from about 0ṃ7 to more than 2m in the NW to SE direction. Comparing optical with radio data, the mean visual absorption is 1ṃ2.