Abstract
CENTRAL STAR OF RING NEBULA IN LYRA.—M. W. Stratonoff, of the Tashkent Observatory, has been engaged in measuring the brightness of the central star of the annular nebula in Lyra, and has communicated his. results to the Astronomische Nachrichten, Bd. 151, No. 3607. A considerable number of photographs of the nebula have been obtained with the large telescope of 0.83m. aperture, extending over the period September 8, 1895, to September 15, 1899, the exposures varying from 30 to 90 minutes. From his measures of the brightness of the central star as compared with the magnitudes of 30 neighbouring comparison stars, M. Stratonoff shows that the magnitude varies from 13.1 to 9.5. A special series of photographs taken with extra long exposures, however, renders the question of variability, as measured from photographic impressions, somewhat doubtful. On a plate exposed for anything between 22m. and ih. 23m. the mean magnitude of the star was 11.6. On a plate exposed for 10 hours, the magnitude was 10.1; while on exposing for 20 hours, the measured magnitude was 3.6. The author suggests, as explanation of this, that the star may really be simply a condensation of part of the whole nebulous matter, and the effect of long exposure will be to lessen the contrast between the condensed centre and the outlying fainter matter.
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