Changes in the Periods of RR Lyrae Stars in Omega Centauri.

Abstract

view Abstract Citations (1) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Changes in the Periods of RR Lyrae Stars in Omega Centauri. Belserene, Emilia Pisani Abstract This is the continuation of a study, begun by W. C. Martin (Ann. Sterrewacht Leiden 17, part 2, 1938), of period changes in the globular cluster Omega Centauri. There are, on this program, 32 of his 68 stars, all RR Lyrae variables of subclasses a and b, with regularly repeating light curves. For these 32 stars, as well as for the others, Martin had found increasing periods to predominate. The average rate of change was + 5 X 10-10 days per day, or about 0.2 days per million years. The new observations, in 1947-8 and in 1956-8, provide two new epochs for the determination of periods. For the 32 stars the mean period was od.6608544 from 1896 to 1933, 0.6608580 from 1931 to 1935, 0.6608584 from 1933 to 1947, 0.6608600 from 1947 to 1957. Thus the new observations confirm the trend detected by Martin. The average rate of change of period, over the whole time interval, is +4 X 10-10 days per day. Individual values range from -31 X 10-10 to +52x 10-10; the question arises as to the possibility that the trend is only apparent, resulting from the chance distribution of the extreme values. This does not appear to be the case, however. The rates of change show a frequency distribution with a reasonably narrow maximum at +3 X 10-10. It is not very likely that this distribution arose through chance selection of a sample from a population whose average period is constant. Unless some unsuspected systematic error is at work, then the periods of these regular RR Lyrae stars tend to increase with time. Publication: The Astronomical Journal Pub Date: March 1961 DOI: 10.1086/108522 Bibcode: 1961AJ.....66R..38B full text sources ADS |