Photoelectric Photometry of Diffuse Galactic Nebulae and Comet Arend-Roland
1960; Institute of Physics; Volume: 72; Linguagem: Inglês
10.1086/127467
ISSN1538-3873
Autores Tópico(s)Stellar, planetary, and galactic studies
ResumoThese have been made with a 12-inch Cassegrain telescope, equipped for photoelectric observations,1 in a new small observatory 18 miles from Iowa City during 1957-58. The following data for selected regions of a number of bright diffuse nebulae have been obtained : the surface brightness in F-mag./D, the B V and U B colors, the degree of polarization and the position angle of the plane of polarization, and a measure of the presence of Hs emission relative to the continuum in the surrounding B and V passbands. The data were taken much as for a star except that the field centers were defined by first centering the star of the nebula in a diaphragm, then moving it to the N, E, S, or W edge of the diaphragm. A smaller diaphragm was then inserted, it was checked that no star could be seen in the smaller diaphragm, and the centering was rechecked at the end of a run of filters. The same exposures were immediately made on a nearby area of sky supposedly free of nebulosity, and again repeated on the nebula. The telescope had to be moved the order of Io rather than Y as is customary for sky backgrounds in stellar photometry. One set of observations of a center plus sky background for magnitudes, etc., consisted of 39 exposures, usually of 20 seconds each. Nightly extinction observations were made of some of nine standard stars of spectral classes B0-G8 taken from a list published by Johnson and Harris.2 Reductions of the observed magnitudes to natural outside-atmosphere magnitudes, and of the latter to U, B, V magnitudes, followed Johnson and Morgan3 and Sharpless.4 No observations were started except in the clearestlooking sky, and they were made only without twilight, moonlight, or visible aurorae, excepting on the comet. Table I gives the
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