Open AccessThe period–luminosity relation for type II Cepheids in globular clusters
Author(s) -
Matsunaga Noriyuki,
Fukushi Hinako,
Nakada Yoshikazu,
Tanabé Toshihiko,
Feast Michael W.,
Menzies John W.,
Ita Yoshifusa,
Nishiyama Shogo,
Baba Daisuke,
Naoi Takahiro,
Nakaya Hidehiko,
Kawadu Takahiro,
Ishihara Akika,
Kato Daisuke
Publication year - 2006
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2006.10620.x
Subject(s) - physics , cepheid variable , globular cluster , astrophysics , metallicity , luminosity , stars , astronomy , star cluster , rr lyrae variable , horizontal branch , variable star , galaxy
We report the result of our near‐infrared observations ( JHK s ) for type II Cepheids (including possible RV Tau stars) in galactic globular clusters. We detected variations of 46 variables in 26 clusters (10 new discoveries in seven clusters) and present their light curves. Their periods range from 1.2 d to over 80 d. They show a well‐defined period–luminosity relation at each wavelength. Two type II Cepheids in NGC 6441 also obey the relation if we assume the horizontal branch stars in NGC 6441 are as bright as those in metal‐poor globular clusters in spite of the high metallicity of the cluster. This result supports the high luminosity which has been suggested for the RR Lyr variables in this cluster. The period–luminosity relation can be reproduced using the pulsation equation assuming that all the stars have the same mass. Cluster RR Lyr variables were found to lie on an extrapolation of the period–luminosity relation. These results provide important constraints on the parameters of the variable stars. Using Two Micron All‐Sky Survey (2MASS) data, we show that the type II Cepheids in the Large Magellanic Cloud (LMC) fit our period–luminosity relation within the expected scatter at the shorter periods. However, at long periods ( P > 40 d, i.e. in the RV Tau star range) the LMC field variables are brighter by about one magnitude than those of similar periods in galactic globular clusters. The long‐period cluster stars also differ from both these LMC stars and galactic field RV Tau stars in a colour–colour diagram. The reasons for these differences are discussed.