# COMMUNICATIONS / MITTEILUNGEN

## S.M. Kung

## The Zero Point of the Period-Luminosity Relation of Cepheids
and the Absolute Magnitude of the RR Lyrae Variables

No. 47
Budapest, 1960

## Abstract

33 results including 3 results of this paper in connection with the zero
point of the period-luminosity relation since Wilson's result of 1939 are tabulated. They
are collected in 6 tables according both the nature of the results and the methods used.
A comment for each result is made. 11 results are rejected for various reasons stated in
section II. The absolute magnitude of cepheids fainter more than 1m in Wilson's result,
according which the original zero point of Shapley's P-L relation was fixed is fully
explained. The expression for the correction due to the spread both of the apparent and
absolute magnitudes of the stars is derived in section III. With the correction thus
derived the correct formula for the product of the mean distance and the mean parallax,
r*pi, is obtained. Finally, in section IV all the useful results are collected separately
to get 3 weighted means, one for the difference between the observed magnitude and the
calculated magnitude, based on the assumed absolute magnitude of the RR Lyrae
variables and the Shapley's P-L relation, one for the correction to the zero point of the
P-L relation, and one for the absolute magnitude of the RR Lyrae variables. With
the double weight for the first one, we obtain from all the 3 kinds of data taken
together the correction to the zero point of the Shapley's P-L relation to be -1.28m and
the absolute magnitude of the RR Lyrae variables to lie +0.34m.
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