Studies of interstellar extinction at high galactic latitudes.

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view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Studies of interstellar extinction at high galactic latitudes. Poveda, Arcadio Abstract Investigations of the spatial distribution of galaxies by Neyman, Scott and Shane are based on the simplifying assumption that the regions in the sky covered by their work are free from irregular galactic absorption. This point may be investigated by comparing Shane's and Wirtanen's counts of images of galaxies with the counts of faint stars. If the region studied contains irregular interstellar clouds then these clouds will affect the apparent magnitudes of some stars and of all the galaxies and thus create a positive component in the covariance between the two counts. Empirical material for the study is composed of Shane's and Wirtanen S counts in 10' X 10' squares and of the author's counts of faint stars, of apparent magnitude roughly between 14.5 and 18.7, made in 4' >c 4' squares concentric with the 10' >( 10' cells used for counts of galaxies. Unfortunately, in addition to the possible presence of interstellar clouds, there are several other possible sources of positive correlation between counts of galaxies and of faint stars. These include (I) errors in counting, for sometimes when counting stars we misidentify a nebula and call it a star, and vice versa; (2) plate effect, or irregularities of emulsion sensitivity and developing process; (3) telescopic effect, for at the center of a plate the counts are higher than at the edges. In order to check the importance of (I) an experiment was performed with 16 standard nebulae supplied by Dr. Sandage with 17.6 < mpg < 19.2. The result gave us the probability, when counting stars, of classifying a nebula as a star approximately equal to 0.02, for counts on the 2o-inch survey plates. This type of error is not considered important. In order to eliminate (2) and (3) eleven fields were selected for study for which there are available duplicate plates taken at the Lick Observatory either by Dr. C. D. Shane or by Mr. Wirtanen; for all of these plates there are available duplicate counts of stars, and for some of them duplicate counts of nebulae. Let Xf, i, 5, k denote the number of stars obtained at the jth count (j = 1, 2) in the kth square (k = 1, 2, ..; K = 1296) of the ith plate (i = 1, 2) taken over the fth field (f = 1, 2, F = I i), and a dot the average over the index it replaces. With this notation, the estimate of the covariance component between the counts of galaxies and the counts of stars due to irregular galactic absorption is given by either of the ex- pressions (a) or (b): (a) IKXy F K Kfl kfI k F - I k=l F K + F(7- i) i= b LKXy F K Kfi kfi k F - I k=l F K + F(F1- i) j=i kZ=iX! ~ki$f ~ k where Y , , , k is a similarly defined quantity for the number of nebulae. Preliminary results indicate these covariances are very small or zero. Leuschner Observatory, University of Calsfornia, Berkeley, Ca 1sf. Publication: The Astronomical Journal Pub Date: February 1957 DOI: 10.1086/107447 Bibcode: 1957AJ.....62...30P full text sources ADS |