57 research outputs found
The Impact of Contaminated RR Lyrae/Globular Cluster Photometry on the Distance Scale
RR Lyrae variables and the stellar constituents of globular clusters are
employed to establish the cosmic distance scale and age of the universe.
However, photometry for RR Lyrae variables in the globular clusters M3, M15,
M54, M92, NGC2419, and NGC6441 exhibit a dependence on the clustercentric
distance. For example, variables and stars positioned near the crowded
high-surface brightness cores of the clusters may suffer from photometric
contamination, which invariably affects a suite of inferred parameters (e.g.,
distance, color excess, absolute magnitude, etc.). The impetus for this study
is to mitigate the propagation of systematic uncertainties by increasing
awareness of the pernicious impact of contaminated and radial-dependent
photometry.Comment: To appear in ApJ
A collection of various research projects in astronomy
121 leaves : ill. ; 29 cm.Includes abstracts.Includes bibliographical references.We consider the possibility of cluster membership for 13 planetary nebulae that are located in close proximity to open clusters lying in their lines of sight. The short lifetimes and low sample size of intermediate-mass planetary nebulae with respect to nearby open clusters conspire to reduce the probability of observing a true association. Not surprisingly, line of sight coincidences almost certainly exist for 7 of the 13 cases considered. Additional studies are advocated, however, for 6 planetary nebula/open cluster coincidences in which a physical association is not excluded by the available evidence, namely M 1-80/Berkeley 57, NGC 2438/NGC 2437, NGC 2452/NGC 2453, VBRC 2 & NGC 2899/IC 2488, and HeFa 1/NGC 6067. A number of additional potential associations between planetary nebulae and open clusters is tabulated for reference purposes. It is noteworthy that the strongest cases involve planetary nebulae lying in cluster coronae, a feature also found for short-period cluster Cepheids, which are themselves potential progenitors of planetary nebulae
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