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THE RR LYRAE STARS IN THE LARGE MAGELLANIC CLOUD

J. A. GRAHAM
Publications of the Astronomical Society of the Pacific
Vol. 89, No. 530 (August 1977), pp. 425-465
Stable URL: http://www.jstor.org/stable/40677045
Page Count: 41
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Abstract

A field covering an area 1º × 1.ͦ3 in the Large Magellanic Cloud (LMC) has been searched for variable stars. Sixty-eight variable stars with periods less than a day and amplitudes of several tenths of a magnitude are identified as being of the RR Lyrae type. Sixty are of Bailey class ab and eight of Bailey class c. Multiple discovery statistics show that the search for ab-type stars is about 90% complete but that the discovery of the c-type variables is very incomplete possibly being as small as 16% of the total number actually present. No large amplitude ab-type variables with periods shorter than 0ḍ45 are found in the LMC. The mean periods of the ab- and c-type variables are 0ḍ564 and 0ḍ328, respectively. The arithmetic mean blue magnitudes, peak between 19ṃ5 and 19ṃ7. In contrast to the sample studied in the Small Magellanic Cloud, there is no small group of variables with mean magnitude about 1ṃ5 brighter than the majority. For all stars with periods, $\langle \bar B\rangle$ is found to be 19ṃ60 Measurements of two yellow plates give a similar mean visual magnitude $\langle \bar V\rangle$ of 19ṃ2. All magnitudes are determined on the basis of the standard photometric sequence established in this field by Gascoigne. Adopting a true distance modulus of 18ṃ5 for the LMC, a mean absolute visual magnitude of +0ṃ7 ± 0ṃ25 is proposed for the RR Lyrae stars in the Large Magellanic Cloud.

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