Photographs of two great southern galaxies.

Abstract

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Photographs of two great southern galaxies. Duncan, John C. Abstract The extragalactic nebulae NGC ~ and NGC 253, in the constellation Sculptor, were among the objects photographed by the author with the 100-inch telescope at Mount Wilson in the summer of 1945. Lantern slides, made from negatives obtained on September 2, 1945, illustrate the paper. Slides from early drawings by the Herschels are also presented. NGC 55, in galactic latitude 770, is 3' wide and 29' long at its greatest extent. Though it has been classified as a spiral, it here appears as an irregular galaxy. Considerable obscuration is noticeable, especially in the brighter, preceding part. NGC 253, two degrees from the south galactic pole, has been assigned magnitude 7.0 by Shapley and Miss Ames, indicating that it is the second-brightest spiral nebula in the sky. It is a beautiful right-handed spiral 5' X 24' in dimensions. On the new photographs, obscuration is conspicuous, especially on the north-preceding side; there is a faint general veil of amorphous nebulosity suggesting the effect of multitudes of faint stars; numerous bright stars are so arranged as evidently to belong to the nebula; and there are several almost star-like objects that have a nebulous appearance. One of these, exhibited in an enlarged slide, is 10" in diameter and is crossed by a central bright bar. (In the accompanying Plate it appears as a star, 6~ mm from the right- hand edge and 40 mm from the bottom.) In the field surrounding the great nebula are numerous apparently small, undoubtedly more distant, extragalactic nebulae. The author is indebted to Dr. Harlow Shaple~ for determining the magnitudes of some of the stars in and around NGC 253 by comparing the plate of September 2 with a negative of the same region made with the Bruce telescope at Bloemfontein. Dr. Shapley finds that the 100-inch plate (which had 50 minutes' exposure) shows stars to approximate magnitude 19.5 on the Harvard scale, and that the brightest stars that can be confidently attributed to the nebula are of magnitude 17.5. The corresponding distance-modulus is 23.8 magnitudes, giving a distance of the nebula of 1,875,000 light-years, a diameter of about 13,000 ligbt-~~ears, and an absolute magni- tude - i6.8. Whitin Observatory, Wellesley, Mass. Publication: The Astronomical Journal Pub Date: July 1946 DOI: 10.1086/105898 Bibcode: 1946AJ.....52...42D full text sources ADS |