Optical and near-infrared photometry of old galactic clusters

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dc.contributor.author Rosvick, Joanne Marie
dc.date.accessioned 2018-07-18T21:58:51Z
dc.date.available 2018-07-18T21:58:51Z
dc.date.copyright 1996 en_US
dc.date.issued 2018-07-18
dc.identifier.uri https://dspace.library.uvic.ca//handle/1828/9718
dc.description.abstract The open clusters NGC 2141, NGC 6791, NGC 6819 and NGC 7142, all suspected of having ages greater than 2 billion years (Gyr), were observed at optical and near-infrared wavelengths. The images were reduced using standard IRAF routines, and magnitudes for the stars were determined using DAOPHOT (Stetson, 1987). These data were used to construct colour-magnitude diagrams (CMDs) for each cluster, as well as two-colour diagrams (J - K, V - K), (J - H, H - K) of the giants. Colour excesses were redetermined by comparing the optical CMD main sequences to semi-empirical ZAMS calibrations (VandenBerg and Poll, 1989; this work) and are as follows: E{B - V) = 0.32 ± 0.04, 0.23 ± 0.03, 0.11 ± 0.03 and 0.29 ± 0.04, for NGC 2141, NGC 6791, NGC 6819 and NGC 7142, respectively. Apparent distance moduli for the clusters listed above were found to be (m - M ) v = 13.93 ± 0.13, 13.52 ± 0.13, 12.10 ± 0.13 and 12.96 ± 0.16. The optical CMDs were compared to sets of theoretical isochrones to ascertain ages and test whether canonical or convective overshooting models best represent the data. It was found that isochrones which allowed for convective overshooting provided the best fits, resulting in ages of 2.5 Gyr, 10 Gyr, 2.5 Gyr and 2.5 Gyr for NGC 2141, NGC 6791, NGC 6819 and NGC 7142, respectively. Two sets of overshooting isochrones (Bertelli et al., 1994; Dowler and VandenBerg, 1996) yielded ages within 0.5 Gyr. The MAR method (Anthony-Twarog and Twarog, 1985) placed the three younger clusters at an approximate age of 3 Gyr. In theory, the two-colour diagrams may be used to distinguish between cluster giants and field stars. However, in practice this is not an easy task since the infrared observations are not always accurate enough to separate the cluster members and field stars. This was the case for these data, since a problem with the H magnitudes resulted in colours offset from what was expected. The infrared (V,V - K and K, V - K) CMDs were useful in defining the giant branch locus based on the position of cluster members. {V - K)o colours were computed for each giant suspected of being a member. These were used to determine effective temperatures and bolometric luminosities which in turn were used to produce an HR diagram for each cluster. These were compared to HR diagrams of other open and globular clusters (Houdashelt et al., 1992; Frogel et al., 1983), as well as evolutionary tracks (Bertelli et al., 1994). The giant branch loci of the near-solar abundance and metal-poor clusters were found to lie between those defined by the clusters M67 and 47 Tuc. The comparison between the cluster HR diagrams and evolutionary tracks indicated that the theoretical temperatures may be too hot. The new cluster results were plotted on the age-metallicity relation defined by Houdashelt et al.’s (1992) and Friel and Janes’ (1993) sample of open clusters, and confirmed the lack of correlation between these two quantities. The galactocentic distances (calculated from the distances given above) for the clusters studied here were determined and used with the cluster metallicities to support the presence of a metallicity gradient (~ -0.09 dex kpc-1) in the galaxy. en_US
dc.language English eng
dc.language.iso en en_US
dc.rights Available to the World Wide Web en_US
dc.subject Stars en_US
dc.subject Open clusters en_US
dc.subject Astronomical photometry en_US
dc.title Optical and near-infrared photometry of old galactic clusters en_US
dc.type Thesis en_US
dc.contributor.supervisor Scarfe, C. D.
dc.contributor.supervisor Davidge, T. J.
dc.degree.department Department of Physics and Astronomy en_US
dc.degree.level Doctor of Philosophy Ph.D. en_US
dc.description.scholarlevel Graduate en_US

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