Galactic Structure from Photoelectric Distances of Early-Type Stars.

Abstract

view Abstract Citations (1) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Galactic Structure from Photoelectric Distances of Early-Type Stars. Beer, Arthur Abstract An analysis is presented of 3080 direct observations of the integrated light of the Hw region in 435 stars of types O and B in the northern sky and brighter than 7'~5. Two independent and consistent series of measurements were obtained, in 1960 and 1961, with the narrow-band spectrometer attached to the 36-inch reflector (f/18 coude' focus) of the Observatories, Cambridge, England. Using the pulse-counting method and two photomultipliers fed by appropriate windows in the focal-plane diaphragm of the grating, simultaneous readings were recorded of the intensity A due to the light through the Hw window at AA4325- 4357, as well as of the total intensity B due to two comparison windows placed at AX4255~289 and ~x4399-4427. At least two successive one-minute counts S per star were made in each of its nights, followed after about every third star by counts L of a standard lamp. The quotients S (B ) /L (B) over S(A)YL(A) gave the final H~ ratios R. On the average, each star was covered by 7.1 observations; each of these took an over-all telescope time of 7.4 min, inclusive of the lamp measurements spaced in the mean by 22.8 min. The program included 130 standard stars whose known absolute magnitudes were adopted for the present calibration, as a result of discussions by R. W. Petrie, Victoria 1953, by I. M. Kopylov, Crimea 1958, and by U. Sinnerstad, Stockholm 1961. The error of the mean of all the R values per star is t0.65%, corresponding to ft0rn.1 ~i~ absolute magnitude; and this, together with the intrinsic scatter within the whole of the calibration stars, leads to an estimated total error in luminosity of the order of about -~0.3 mag. Using measured color excesses to allow for interstellar absorption, the calibrated R values provide some three hundred new B-star distances. Their map- ping with respect to the 21-cm H I pattern of the Milky Way amplifies the author's conclusions from his recent equivalent-width measurements on some 420 spectrograms of 137 southern stars (Beer, A. Monthly Notices Roy. Asfron. Soc. 123, 191, 1961). New evidence is discussed, based on a close relationship between R and the MK luminosity system, comparisons with the concept of equivalent width, and the spatial distribution of clusters, associations, and H ii regions. The over-all picture has been correlated with proposed features of galactic structure and Milky Way arms. There are clearly great potentialities in further developments of this rapid observational method, particularly in view of the suggested large-scale applications to faint stars (e.g., by extending the counting time to several minutes), and it might well replace methods of detailed equivalent-width measurements by its speed, accuracy, and scope. Publication: The Astronomical Journal Pub Date: March 1962 DOI: 10.1086/108814 Bibcode: 1962AJ.....67Q.268B full text sources ADS |