12 research outputs found
CCD time-series photometry of the globular cluster NGC 5053: RR Lyrae, Blue Stragglers and SX Phoenicis stars revisited
We report the results of CCD , and time-series photometry of the
globular cluster NGC 5053. New times of maximum light are given for the eight
known RR Lyrae stars in the field of our images and their periods are revised.
Their light curves were Fourier decomposed to estimate their physical
parameters. A discussion on the accuracy of the Fourier-based iron abundances,
temperatures, masses and radii is given. New periods are found for the 5 known
SX Phe stars and a critical discussion of their secular period changes is
offered. The mean iron abundance for the RR Lyrae stars is found to be [Fe/H]
and lower values are not supported by the present
analysis. The absolute magnitude calibrations of the RR Lyrae stars yield an
average true distance modulus of or a distance of kpc. Comparison of the observational CMD with theoretical isochrones
indicates an age of Gyrs for the cluster. A careful
identification of all reported Blue Stragglers (BS) and their magnitudes
leads to the conclusion that BS12, BS22, BS23 and BS24 are not BS. On the other
hand, three new BS are reported. Variability was found in seven BS, very likely
of the SX Phe type in five of them, and in one red giant star. The new SX Phe
stars follow established relationships and indicate a distance in
agreement with the distance from the RR Lyrae stars.Comment: 21 pages, 16 figures, 11 tables. Accepted for publication in MNRA
First Cool-Down Performance of the LHD
The first cool-down test of the Large Helical Device (LHD) and the performance of the LHD cryogenic system during the first cycle operation are described. The first cool-down started on Feb. 23, 1998 and finished on Mar. 22. After the cool-down, the excitation tests of the SC coils up to 1.5 T and the first cycle operations for plasma physics experiments were conducted until May 18. The first cycle operation was successfully completed after the warm-up process to room temperature from May 19 to Jun. 15. The cooling characteristics of the LHD, such as temperature distribution during cool-down, heat loads under steady state condition, reliability during long-term operation, are reporte